Applied Catalysis B, Environmental (v.183, #C)
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Highly photocatalytic active thiomolybdate [Mo3S13]2− clusters/BiOBr nanocomposite with enhanced sulfur tolerance by Dongting Yue; Taiyang Zhang; Miao Kan; Xufang Qian; Yixin Zhao (1-7).
Display OmittedThe sulfur tolerant Mo3S13 2−/BiOBr nanocomposite photocatalysts were facilely fabricated by a hydrothermal method. The characterizations including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), UV–vis diffuse reflection spectroscopy (DRS) and photoluminescence (PL) investigate the structures, elemental composition, morphologies and photocatalytic activities of Mo3S13 2−/BiOBr nanocomposite. The 5.0 wt% Mo3S13 2−/BiOBr composite sample showed highest visible-light-driven photocatalytic activity for decolorization of organic dyes including Rhodamine B (RhB) and sulfure containing methylene blue (MB). The decolorization of RhB was dominated by the direct hole and the generated •O2 − radicals oxidation process. Our 5.0 wt% Mo3S13 2−/BiOBr nanocomposite exhibited comparable photocatalytic activity as the state of art 1 wt% BiOBr/Pt composite for photocatalytic decolorization of RhB. The 5.0 wt% Mo3S13 2−/BiOBr composite possessed better sulfur resistance than 1.0 wt% Pt/BiOBr composite.
Keywords: Photocatalyst; Mo3S13 2−/BiOBr; [Mo3S13]2− nanoclusters; Sulfur tolerant;
Cooperative In–Sn catalyst system for efficient methyl lactate synthesis from biomass-derived sugars by Koji Nemoto; Yoshiaki Hirano; Kei-ichi Hirata; Tsukasa Takahashi; Hideaki Tsuneki; Ken-ichi Tominaga; Kazuhiko Sato (8-17).
Display OmittedThe catalytic conversion of sugars to lactic acid esters holds great advantages over the conventional fermentation process; the reaction is faster and the product can be separated with a simple distillation process. As the conversion of the sugar to the lactic acid ester involves several elemental reactions, multi-component catalyst systems were expected to be effective for this reaction. This paper reports the use of a combination of indium chloride and tin chloride to synergistically catalyze the formation of methyl lactate (MeLac) from sugars in the presence of tetrafluoroborate salts, the maximum yield of which reaches 72%. A plausible reaction scheme is also proposed based on the electrospray ionization mass spectroscopy analyses of the reaction solutions and the effects of the indium species, tin species, and tetrafluoroborate salts on each elemental step from fructose to MeLac.
Keywords: Biomass; Lactate; Lewis acid; Synergistic effect; Indium; Tin;
Acetone and ethanol vapor oxidation via negative atmospheric corona discharge over titania-based catalysts by Mikhail N. Lyulyukin; Alexey S. Besov; Alexander V. Vorontsov (18-27).
Display OmittedThe paper is devoted to the oxidation of acetone and ethanol vapors by means of an optimized negative atmospheric corona discharge combined with TiO2-based catalysts located in a post-plasma position. A series of studied samples includes CuO-MnO2/TiO2, CuO/TiO2 and MnO2/TiO2 with 3 wt% of copper oxide and 6.8 wt% of manganese oxide. Experiments were performed at room temperature in a closed 404-L chamber with a ∼0.9-L active plasma region. It was shown that the use of the catalysts can provide a significant reduction in the concentrations of ozone and oxidation byproducts and a three-fold increased conversion of the reactants. It was unexpectedly found that copper oxide, as an active agent, did not significantly change the effect of post-plasma-located TiO2. The manganese-containing sample was found to be the best catalyst at the conditions considered. The presence of this catalyst in the post-plasma position inhibits the formation of unwanted products (O3 and CO) and promotes the deep oxidation of acetone and ethanol with increased selectivity toward CO2.
Keywords: NTP; Post-plasma catalysis; VOCs; Titanium dioxide; Copper oxide; Manganese oxide;
Visualizing the mobility of silver during catalytic soot oxidation by Diego Gardini; Jakob M. Christensen; Christian D. Damsgaard; Anker D. Jensen; Jakob B. Wagner (28-36).
Display OmittedThe catalytic activity and mobility of silver nanoparticles used as catalysts in temperature programmed oxidation of soot:silver (1:5 wt:wt) mixtures have been investigated by means of flow reactor experiments and in situ environmental transmission electron microscopy (ETEM). The carbon oxidation temperature was significantly lower compared to uncatalyzed soot oxidation with soot and silver loosely stirred together (loose contact) and lowered further with the two components crushed together (tight contact). The in situ TEM investigations revealed that the silver particles exhibited significant mobility during the soot oxidation, and this mobility, which increases the soot/catalyst contact, is expected to be an important factor for the lower oxidation temperature. In the intimate tight contact mixture the initial dispersion of the silver particles is greater, and the onset of mobility occurs at a lower temperature which is consistent with the lower oxidation temperature of the tight contact mixture.
Keywords: Silver mobility; Environmental TEM; Soot oxidation;
Effect of GO phase in Zn(OH)2/GO composite on the extent of photocatalytic reactive adsorption of mustard gas surrogate by Dimitrios A. Giannakoudakis; Javier A. Arcibar-Orozco; Teresa J. Bandosz (37-46).
Display OmittedComposites of zinc hydroxide with various contents of graphite oxide (GO) were synthesized with a controlled precipitation rate. They were used at ambient conditions as adsorbents of a mustard gas surrogate, 2-chloroethyl ethyl sulfide (CEES). The samples’ surface features were characterized by various physical and chemical methods. The materials acted as photocatalysts upon light irradiation, degrading CEES to less- or no-toxic compounds. Exposure to visible light and the presence of GO in the composites improved the performance. The results indicated a paramount role of terminal OH groups as well as the porosity in the reactive adsorption process. The enhanced performance is linked to an increase in the degree of chemical and structural heterogeneity upon addition of GO. The surface characteristics strongly depend on the amount of the carbonaceous phase and 10 wt% was found as an optimal content. The CEES degraded mainly to ethyl vinyl sulfide by dehydrohalogenation and to hydroxyethyl ethyl sulfide via a hydrolysis pathway. The irradiation under visible light led to further transformation to vinyl vinyl sulfide and methyl vinyl sulfide through radical's reaction. The presence of GO promotes the electrons transfer and oxygen activation.
Keywords: Zinc hydroxide; Graphite oxide composites; 2-Chloroethyl ethyl sulfide; Reactive adsorption; Mustard gas; Detoxification;
Self-assembly of CPO-27-Mg/TiO2 nanocomposite with enhanced performance for photocatalytic CO2 reduction by Mengtao Wang; Dengke Wang; Zhaohui Li (47-52).
Display OmittedCPO-27-Mg (also referred to as Mg2(DOBDC), DOBDC = 2,5-dioxido-1,4-benzenedicarboxylate), a Mg2+ based metal-organic framework which shows the highest CO2 uptake among the already reported MOF materials, was chosen to combine with TiO2 to form CPO-27-Mg/TiO2 nanocomposite via a hydrothermal self-assembly method. The as-obtained CPO-27-Mg/TiO2 nanocomposite is composed of TiO2 nanospheres on the spindle-shaped CPO-27-Mg microcrystal. Intimate contact between CPO-27-Mg and TiO2 nanospheres exists due to the coordination between the carboxylate groups in DOBDC and Ti4+ in TiO2. The as-obtained CPO-27-Mg/TiO2 nanocomposite exhibited enhanced performance for the photocatalytic CO2 reduction to form CO and CH4 due to its high adsorption capacity toward CO2 and the existence of open alkaline metal sites in CPO-27-Mg. By incorporating MOFs with open alkaline metal center into TiO2, the reduction of H2O to H2, a competitive reaction to photocatalytic CO2 reduction, was totally inhibited. This study highlights the promising prospect of incorporating MOFs with open alkaline metal sites into semiconductors for artificial CO2 photo-conversion.
Keywords: Photocatalysis; CO2 reduction; Metal-organic framework; Titanium dioxide;
Promotion of oxygen reduction and water oxidation at Pt-based electrocatalysts by titanium carbonitride by M. Roca-Ayats; E. Herreros; G. García; M.A. Peña; M.V. Martínez-Huerta (53-60).
Display OmittedThe oxygen electrode plays a crucial role in performance and lifetime of water electrolyzers and regenerative fuel cells due to its slow electrochemical processes under rigorously oxidizing or reducing environments. Herein, we report the use of titanium carbonitride as an efficient and stable support in acidic media. Pt3M (M = Ru, Ir, Ta) nanoparticles supported on titanium carbonitride were synthesized by the ethylene glycol method and characterized by transmission electron microscopy, X-ray diffraction and inductively coupled plasma optical emission spectrometry. The electrochemical activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as well as the stability of the catalysts, was tested employing a rotating ring-disk electrode. The activity of the three catalysts is similar for the ORR. However, for the OER, Pt3Ru/TiCN appears to be the best catalyst by far. Pt3Ru/TiCN was also compared with a commercial RuO2 catalyst, obtaining a better performance for the supported catalyst even though the low amount of Ru/RuO2 present in the supported sample. The high activity and stability of the Pt3Ru/TiCN catalyst for the ORR and OER is due to an interesting promotion effect of the titanium carbonitride support, so that this electrocatalyst has a great potential for the application in unitized regenerative fuel cells.
Keywords: Titanium carbonitride; Oxygen reduction reaction; Oxygen evolution reaction; Bifunctional electrocatalyst; Platinum;
Degradation and debromination of bromophenols using a free-base porphyrin and metalloporphyrins as photosensitizers under conditions of visible light irradiation in the absence and presence of humic substances by Qianqian Zhu; Mami Igarashi; Masahide Sasaki; Takafumi Miyamoto; Ritsu Kodama; Masami Fukushima (61-68).
Display OmittedThe photodegradation and debromination of 2,4,6-tribromophenol (TrBP) and tetrabromobisphenol A (TBBPA) were investigated in the presence of a free-base porphyrin and metalloporphyrins as photosensitizers under conditions of visible light irradiation. Among the photosensitizers, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (H2TMPyP) and Zn(II)-tetrakis(N-methylpyridinium-4-yl)porphyrin (ZnTMPyP) were effective in the photodegradation of bromophenols. In particular, 96% of the debromination was achieved in the case of the ZnTMPyP photosensitization system for TBBPA after 24 h of irradiation. ESR spectra with a spin-trapping reagent indicated that singlet oxygen (1O2) was the major photo-induced reactive oxygen species. The presence of humic substances and natural organic matter, which are common components in landfill leachates, inhibited the photodegradation of TrBP via competitive oxidation by 1O2 when ZnTMPyP was used as a photosensitizer. The presence of humic acids, which contained higher levels of electron-rich moieties like aromatic carbons, strongly inhibited the photodegradation of TrBP. TrBP and TBBPA were ultimately decomposed to organic acids, such as maleic and fumaric acids, as evidenced by LC/TOF-MS analysis. Thus, the photoirradiation of H2TMPyP and ZnTMPyP can induce 1O2 generation, which is effective in the photodegradation and debromination of TrBP and TBBPA.
Keywords: Photosensitizer; Singlet oxygen; Metalloporphyrin; Bromophenols; Humic substances;
Pd–MgNi x nanospheres/black-TiO2 porous films with highly efficient hydrogen production by near-complete suppression of surface recombination by Jianyun Zheng; Shanhu Bao; Xiaoli Zhang; Haibo Wu; Rongxiang Chen; Ping Jin (69-74).
Display OmittedHydrogen generated from solar-driven photocatalytic water splitting has the potential to be a clean, sustainable and abundant energy source. Herein, we demonstrate that Pd–MgNi x nanospheres/black-TiO2 porous films serve as a highly efficient and convenient catalyst for photogeneration of hydrogen from water. Near-complete suppression of surface recombination ensures the excellent photocatalytic activity of Pd–MgNi x nanospheres/black-TiO2 porous films, corresponding to high hydrogen production rates (34.93 mmol h−1 g−1). The result is promising for overall solar water splitting in a simple system, and is encouraging for application of this surface modification strategy to other candidate semiconductors.
Keywords: Pd–MgNi x nanospheres; Black-TiO2 porous films; Efficient hydrogen production; Suppression of surface recombination;
Photoelectrocatalytic oxidation of bisphenol A over mesh of TiO2/graphene/Cu2O by Lixia Yang; Zhongyan Li; Huimin Jiang; Wenjing Jiang; Rongkui Su; Shenglian Luo; Yan Luo (75-85).
Display OmittedMesh of TiO2/graphene/Cu2O was fabricated by chemical vapor deposition of graphene following electrochemical deposition of Cu2O on anodized Ti soft wire bearing TiO2 nanotubes. The mesh of TiO2/graphene/Cu2O was applied in photoelectrocatalytic oxidation of bisphenol A (BPA). The as-prepared TiO2/graphene/Cu2O mesh was used as both catalyst and electrode. Under visible light irradiation, BPA was effectively oxidized through photoelectrocatalysis over the TiO2/graphene/Cu2O mesh. Three main intermediates were evidenced during photoelectrocatalytic degradation of BPA, and no toxic products were determined. A detailed pathway of BPA degradation by TiO2/G/Cu2O is proposed based on the identified intermediates.
Keywords: TiO2/graphene/Cu2O mesh; Photocatalyst; Photoelectrocatalytic degradation; Bisphenol A;
Disinfection capability of Ag/g-C3N4 composite photocatalysts under UV and visible light illumination by Mario J. Muñoz-Batista; Olga Fontelles-Carceller; Manuel Ferrer; Marcos Fernández-García; Anna Kubacka (86-95).
Display OmittedThe biocidal capability of Ag/g-C3N4 composite photocatalysts against Escherichia coli was evaluated as a function of the Ag content of the material upon UV and visible light excitation. The Ag/g-C3N4 composite system shows significant biocidal activity, presenting a behavior with a strong dependence on the silver content as well as on the excitation wavelength. The physico-chemical characterization of the samples together with a Langmuir–Hinshelwood-type kinetic modelling of biocidal experiments and the (photoluminescence and electron paramagnetic resonance) analysis of charge handling properties of the solids were used to interpret the photocatalytic response of the composite materials. The overall analysis shows that the wavelength dependence observed for all Ag/g-C3N4 composite photocatalysts is strongly correlated with the semiconductor—metal heterojunction effect on charge separation, handling and recombination, indicating the key role of the cooperative action between the two components of the system. Such cooperative effect is studied along the sample series and discussed to be related to the efficient use of both hole and electron related species in the disinfection action.
Keywords: Photo-catalysis; Carbon nitride; Silver; Sunlight; Biocide; Germicide;
Photocatalytic transformation of the antipsychotic drug risperidone in aqueous media on reduced graphene oxide—TiO2 composites by P. Calza; C. Hadjicostas; V.A. Sakkas; M. Sarro; C. Minero; C. Medana; T.A. Albanis (96-106).
Display OmittedIn the present study reduced graphene oxide—TiO2 composites were synthesized at two different ratios (1:10 and 1:5) through a hydrothermal method using graphene oxide and commercial P25 as starting materials. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET surface area and ultraviolet–visible (UV–vis) absorption spectroscopy were employed to investigate the morphology and properties of the produced composites. The photocatalytic performance of TiO2–rGO catalysts was evaluated under artificial solar light and visible light in distilled water, as well as, different surface waters (at natural pH) with respect to risperidone (antipsychotic drug) degradation. Irrespectively of the irradiated aqueous matrix, the photocatalytic efficiency of the tested composite materials under simulated solar light and visible light irradiation was higher compared to bare TiO2–P25 (reference catalyst).The identification of intermediate compounds, the assessment of mineralization and the evaluation of toxicity were performed as well. LC/HRMS was brought to bear in assessing the temporal course of the photocatalyzed process. Along with risperidone decomposition, the formation of twenty intermediate compounds (TPs) occurred in the presence of TiO2. Irradiation of risperidone in the presence of the hybrid material resulted in the identification of thirty-four TPs. The transformation of risperidone progressed through the formation of compounds more harmful than the drug itself, as assessed by the measurement of acute toxicity, evaluated using the Vibrio fischeri bacteria test. When employing TiO2–rGO, all the identified transformation products were quicker degraded compared to TiO2–P25. At the same time both the reduction of toxicity and mineralization were faster achieved than with bare TiO2–P25.
Keywords: Reduced graphene oxide; Photocatalysis; Risperidone;
Mild ultrasound-assisted synthesis of TiO2 supported on magnetic nanocomposites for selective photo-oxidation of benzyl alcohol by Juan C. Colmenares; Weiyi Ouyang; Manuel Ojeda; Ewelina Kuna; Olga Chernyayeva; Dmytro Lisovytskiy; Sudipta De; Rafael Luque; Alina M. Balu (107-112).
Display OmittedA simple and effective ultrasound-assisted wet impregnation method was developed for the preparation of magnetically separable TiO2/maghemite-silica photo-active nanocomposites. The resulting nanomaterials were characterized by several techniques and subsequently tested for their photocatalytic activities in the liquid phase selective oxidation of benzyl alcohol. An unprecedented selectivity in organic media (90% in acetonitrile) towards benzaldehyde was achieved at a benzyl alcohol conversion of ca. 50%, being remarkably superior in terms of activity to any other supported transition metal catalysts reported to date as well as commercial titania Evonik P-25 photocatalyst.
Keywords: Selective photo-oxidation; Ultrasound-assisted impregnation; TiO2; Aromatic alcohols; Magnetic photocatalysts;
Construction of SnNb2O6 nanosheet/g-C3N4 nanosheet two-dimensional heterostructures with improved photocatalytic activity: Synergistic effect and mechanism insight by Zhengyuan Zhang; Deli Jiang; Di Li; Minqiang He; Min Chen (113-123).
Display OmittedIn this study, novel SnNb2O6/g-C3N 2D/2D nanosheet heterostructures with strong interfacial interaction were successfully constructed by a facile two-step wet chemistry method. The SnNb2O6/g-C3N4 2D/2D heterostructures exhibit distinctly enhanced visible light photocatalytic performance toward the degradation of methylene blue (MB) as compared to pristine g-C3N4 and SnNb2O6, which can be attributed to the synergistic effect of 2D/2D heterostructures with strong interfacial interaction and abundant 2D coupling interfaces, facilitating efficient charge separation. The optimum photocatalytic activity of 30% SnNb2O6/g-C3N4 heterostructure for the degradation of MB was about 3.9 and 3.2 times higher than those of g-C3N4 and SnNb2O6. It was demonstrated that the photogenerated holes and superoxide radicals are the two main photoactive species toward photocatalytic degradation of MB over the SNO/CN heterostructures. This work may provide some inspiration for the fabrication of 2D/2D nanosheet heterostructures with efficient photocatalytic performance.
Keywords: g-C3N4; SnNb2O6; 2D/2D heterostructures; Synergistic effect; Photocatalysis;
Post-plasma catalytic removal of methanol over Mn–Ce catalysts in an atmospheric dielectric barrier discharge by Xinbo Zhu; Shiyun Liu; Yuxiang Cai; Xiang Gao; Jinsong Zhou; Chenghang Zheng; Xin Tu (124-132).
Display OmittedA post-plasma catalysis system has been developed for the removal of methanol over Mn–Ce oxide catalysts with different Mn/Ce molar ratios at low temperatures. The Mn50Ce50 oxide catalyst (Mn/Ce = 1:1) shows the best performance in terms of methanol removal efficiency and energy efficiency of the plasma-catalytic process. The maximum methanol removal efficiency of 95.4% can be achieved at a discharge power of 15 W and a gas flow rate of 1 L/min, while the highest energy efficiency of the plasma-catalytic process is 47.5 g/kW h at 1.9 W. The combination of plasma and Mn–Ce catalysts significantly reduces the formation of major by-products (methane, formaldehyde and formic acid) based on the Fourier transform infrared spectra. Possible reaction mechanisms and pathways of the post-plasma catalytic removal of methanol are also proposed. A three-layer back propagation artificial neural network (ANN) model has been developed to get a better understanding of the roles of different process parameters on methanol removal efficiency and energy efficiency in the post-plasma catalytic process. The predicted data from the ANN model show a good agreement with the experimental results. Catalyst composition (i.e. Mn/Ce ratio) is found to be the most important factor affecting methanol removal efficiency with a relative importance of 31.53%, while the discharge power is the most influential parameter for energy efficiency with a relative weight of 30.40%. These results indicate that the well-trained ANN model provides an alternative approach for accurate and fast prediction of the plasma-catalytic chemical reactions.
Keywords: Plasma-catalysis; Dielectric barrier discharge; Methanol removal; Artificial neural network; Environmental clean-up;
A stable Ag3PO4@g-C3N4 hybrid core@shell composite with enhanced visible light photocatalytic degradation by Li Liu; Yuehong Qi; Jinrong Lu; Shuanglong Lin; Weijia An; Yinghua Liang; Wenquan Cui (133-141).
Display OmittedAg3PO4@g-C3N4 core@shell composites were prepared via an ultrasonication/chemisorption method. The degradation of methylene blue (MB) over Ag3PO4@g-C3N4 composites was investigated to evaluate their photocatalytic performance. The Ag3PO4@g-C3N4 sample presented the best photocatalytic activity, degrading 97% MB after irradiation for 30 min. Superior stability was also observed in the cyclic runs. The composite has excellent photocatalytic activity and photo-stability and the optimal content of g-C3N4 in the composites is 7.0 wt.%. The efficient photo-generated charge separation originated from a strong interaction in the intimately contact interface, which was confirmed by the results of photocurrent and EIS measurements. Based on the experimental results, a photocatalytic mechanism for organics degradation over Ag3PO4@g-C3N4 photocatalysts was proposed.
Keywords: Photocatalysis; Ag3PO4@g-C3N4; Core@shell; Degradation; Stability;
Cs x WO3 nanorods: Realization of full-spectrum-responsive photocatalytic activities from UV, visible to near-infrared region by Guilian Li; Chongshen Guo; Mei Yan; Shaoqin Liu (142-148).
Display OmittedEffective utilization of solar energy in photocatalytic materials is one of most essential issues what the photochemists are very concerned all along. In this work, full-spectrum-response photocatalytic activities covering UV, visible and near infrared regions on degradation of methylene blue have been realized firstly on single matter of the mixed valence Cs0.32WO3 nanorod. As revealed by optical absorption results, advantages of Cs0.32WO3 nanorod used in this purpose originated from its high optical absorption in the whole solar spectrum of 300–2500 nm. Benefitting from this unique photo-absorption property, the photocatalytic property of Cs x WO3 nanorod displayed a significant advance in fully utilization of all solar energy, especially for NIR part, which holds considerable percentage of sunlight but seldom is utilized up to now. The removal rates of MB on Cs x WO3 nanorod were determined to be 72, 70 and 37% under 185 mw/cm2 UV, 166 mw/cm2 visible and 42.7 mW/cm2 NIR irradiation within the test duration, respectively. In addition, a plausible mechanism toward understanding the near-infrared driven photocatalytic activity on Cs0.32WO3 nanorod has been proposed on the basis of ESR results and polaron absorption theory.
Keywords: Tungsten bronze; Full-spectrum-response photocatalysis; Cs x WO3; Near infrared;
Glass fiber-supported TiO2 photocatalyst: Efficient mineralization and removal of toxicity/estrogenicity of bisphenol A and its analogs by Boštjan Erjavec; Petra Hudoklin; Katja Perc; Tatjana Tišler; Marija Sollner Dolenc; Albin Pintar (149-158).
Display OmittedBisphenol A (BPA) and its analogs (BPF and BPAF) are a class of industrial chemicals that are proven to elicit endocrine disrupting effects, thus it is important to reduce their concentrations in effluent streams as much as possible. In this study, a simple and highly active glass fiber-supported TiO2 photocatalyst was synthesized and applied in a UV-irradiated three-phase batch and continuous stirred-tank reactor (CSTR) for removal of toxicity and estrogenicity of water dissolved bisphenols. Bioassays of photocatalytically treated aqueous samples showed no estrogenic activity and complete removal of toxicity after 4 h of illumination, which was in accordance with high mineralization extent of bisphenols and their reaction derivatives. The photocatalytic examination of bisphenolic compounds revealed considerably higher stability of BPAF under UV light irradiation, due to two CF3 groups attached to the central C atom. Moreover, these fluorinated groups were responsible for markedly higher toxicity of BPAF to crustaceans Daphnia magna in comparison to non-halogenated BPA and BPF, which manifested daphnids as excellent aquatic species for sensing fluorinated (halogenated) bisphenolic compounds. In addition, photocatalytic oxidation of bisphenol analogs in CSTR demonstrated feasibility of using the immobilized TiO2 photocatalyst in continuous-flow light-assisted water purification systems. Detailed characterization of fresh and used photocatalysts confirmed substantial changes in active material structure. However, the corresponding impact on photocatalyst stability was found insignificant.
Keywords: Immobilized TiO2; Bisphenol analogs; Photocatalysis; Toxicity; Estrogenicity;
Visible light photocatalytic activity for hydrogen production from water–methanol mixtures of open-framework V-doped mixed-valence titanium phosphate by Marco Serra; Herme G. Baldovi; Ferran Albarracin; Hermenegildo Garcia (159-167).
Mixed valence framework titanium phosphate behaves as semiconductor and generates hydrogen from water–methanol mixtures upon irradiation with visible light.Display OmittedTitanium dioxide is the most widely used photocatalyst for hydrogen production from water. Its main limitation consists in the lack of photocatalytic activity under visible light irradiation. One strategy to overcome this problem consists in using as photocatalyst Ti3+-self-doped TiO2 that presents an absorption in the visible range. In this context, we report the synthesis, characterization as semiconductor and photocatalytic activity under visible light or solar light irradiation of open-framework V-doped, mixed-valence titanium phosphate. These materials are characterized by an intense absorption spanning all the visible wavelength range caused by the presence of Ti3+ centers in equimolar ratio respect Ti4+. This long wavelength absorption band allows the photocatalytic production of hydrogen under visible light irradiation. Suitable V-doping provides an additional charge separation level in the intra band-gap space that results in an enhancement of initial hydrogen production rate of a factor 5, reaching values of 47 μmol/H2 h−1gTi −1, in the absence of any noble metal as co-catalyst. Transient electron absorption spectroscopy has allowed to detect the state of charge separation in this phosphate that behave differently upon excitation in the UV or in the visible regions and whose intensity increases upon V-doping, reaching a maximum response at 0.5 wt.% in V. The flat band potential of the conduction band, measured by photocurrent as a function of the bias voltage, was estimated to be −0.10 V vs. NHE and the charge carrier density determined by impedance spectroscopy was 2 × 1020 carriers/cm3.
Keywords: Water splitting; Hydrogen production; Framework phosphate; Visible light photocatalytic activity; Mixed valence Ti3+/Ti4+ titanium phosphate;
Characteristics and catalytic properties of Ni/CaAlO x catalyst for hydrogen-enriched syngas production from pyrolysis-steam reforming of biomass sawdust by Fangyuan Chen; Chunfei Wu; Lisha Dong; Anthony Vassallo; Paul T. Williams; Jun Huang (168-175).
Display OmittedThe production of hydrogen-enriched syngas from the thermo-chemical conversion of biomass was studied using Ni/CaAlO x catalysts prepared by co-precipitation method. The effect of Ca addition with different molar ratios of Ca:Al (1:3, 1:2, 1:1, 2:1, 3:1) on the properties and catalytic behavior in relation to syngas production and the coke formation on the surface of the catalysts were investigated. Catalysts were characterized by BET, XRD, TPR, SEM, and TEM. The SEM and TEM results showed that rod-shaped nano-particles were highly dispersed on the surface of the catalyst. The particle size of NiO was slightly affected with the increase of Ca content in the catalyst. It appeared that the selectivity of CO was increased and the selectivity of CO2 was reduced with the increase of Ca addition to the catalyst. For example, CO2 concentration was reduced from 20 to 12 vol.%, when the molar ratio of Ca/Al was increased from 1:3 to 3:1 for the Ni/CaAlO x catalyst; it is suggested that the water gas shift reaction was inhibited and CO2 reforming reactions were promoted in the presence of the catalyst with higher Ca content. The CO/H2 molar ratio could be manipulated by changing the Ca content in the catalyst, while the H2 concentration remained almost constant (around 45 vol.%). Thus, using the Ni/CaAlO x catalyst developed in this work could provide a promising route to control the syngas composition, which is an important factor for syngas applications.
Keywords: Biomass; Pyrolysis; Co-precipitation; Calcium: Ni-catalyst;
A new oxynitride-based solid state Z-scheme photocatalytic system for efficient Cr(VI) reduction and water oxidation by Yansong Zhou; Gang Chen; Yaoguang Yu; Lichen Zhao; Jingxue Sun; Fang He; Hongjun Dong (176-184).
Display OmittedAchieving ideal photocatalytic systems by mimicking Z-scheme mechanism in natural photosynthesis results in highly efficient artificial photosynthesis. A new oxynitride-based solid state Z-scheme photocatalytic system containing (GaxZn1-x )(NxO1-x ) and Nb3.49N4.56O0.44 was constructed. Nb3.49N4.56O0.44/(GaxZn1-x )(NxO1-x )(6.0) exhibits the highest rate for complete reduction of Cr(VI) within 30 min under simulated sunlight irradiation as well as extremely high apparent quantum efficiency of 68% at 350 nm 24.4% at 420 nm for photocatalytic water oxidation. A similar solid state Z-scheme photocatalytic system was also obtained when compositing Nb3.49N4.56O0.44 with TaON. It’s expected that Nb3.49N4.56O0.44 can also be composed with other oxynitride semiconductor to construct more oxynitride-based solid state Z-scheme photocatalytic systems.
Keywords: Oxynitride semiconductors; Photocatalysis; Solid-state; Z-scheme; Energy conversion;
Repercussion of the carbon matrix for the activity and stability of Fe/N/C electrocatalysts for the oxygen reduction reaction by Carlota Domínguez; Francisco José Pérez-Alonso; Mohamed Abdel Salam; Shaeel A. Al-Thabaiti; Miguel Antonio Peña; F. Javier García-García; Laura Barrio; Sergio Rojas (185-196).
Display OmittedGraphene-like (G), multiwalled carbon nanotubes (CNTs) and active carbon (AC) have been used as carbon matrix for the synthesis of Fe/N/C catalysts for the oxygen reduction reaction. A thorough physicochemical characterization of the electrocatalysts, including X-ray photoelectronic and X-ray absorption spectroscopies, reveal that the formation of Fe/Nx ensembles is favored when the graphene-like or the CNTs are used as the carbon matrix. As a result, the catalyst prepared with the graphene matrix (Fe/N/G) records the highest activity for the ORR in the series of 3.1 A g−1 at 0.9 V. This very high ORR activity positions these catalysts as a realistic alternative to replace Pt/C cathodes in alkaline fuel cells. Moreover, using graphene as the carbon matrix endows the catalyst with very high stability during the ORR showing stable catalytic performance for the ORR even after being subjected to severe treatments of 3000 cycles up to 1.4 V. In situ IRRA spectra demonstrate that such a high stability for the ORR relates to the excellent resistance against corrosion of the graphene-based catalyst.
Keywords: Fuel cells; Oxygen reduction reaction; Graphene; Iron; Durability;
Novel photocatalysts Pt/Cd1−x Zn x S/ZnO/Zn(OH)2: Activation during hydrogen evolution from aqueous solutions of ethanol under visible light by Ekaterina A. Kozlova; Svetlana V. Cherepanova; Dina V. Markovskaya; Andrey A. Saraev; Evgeny Yu. Gerasimov; Valentin N. Parmon (197-205).
Display OmittedThe transformations of single-phase Pt/Cd1−x Zn x S and multiphase Pt/Cd1−x Zn x S/ZnO/Zn(OH)2 and Pt/Cd1−x Zn x S/Zn(OH)2 during photocatalytic hydrogen evolution from aqueous solutions of ethanol under visible light (λ = 450 nm) were investigated. Cyclic tests including long-term experiments were conducted for all photocatalysts. The photocatalysts were investigated before and after the photocatalytic reaction by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy techniques. Activation during photocatalytic hydrogen evolution was observed for all multiphase photocatalysts, whereas single phase Pt/Cd1−x Zn x S was shown to exhibit a strong deactivation. The activation is likely caused by the formation of the ϵ-Zn(OH)2 phase in a basic medium. The highest exhibited rate of hydrogen evolution on the composite photocatalyst was 3400 μmol g−1 h −1, and stability during ten 5-hour photocatalytic runs was observed.
Keywords: Photocatalytic hydrogen production; Visible light; Ethanol; Pt/Cd1−x Zn x S;
Insight into the function of alkaline earth metal oxides as electron promoters for Au/TiO2 catalysts used in CO oxidation by Kai Yang; Yongfan Zhang; Yi Li; Pan Huang; Xun Chen; Wenxin Dai; Xianzhi Fu (206-215).
The addition of AEMO can raise the Fermi level of TiO2 from E F to E F*. Consequently, the more electrons of TiO2–AEMO will transfer through the Au/supports interface to Au sites, resulting in the promoted activation of CO adsorbed at Au surfaces. Moreover, the electron-donating ability of TiO2–AEMO enhances with the increase of its Fermi level in the following order: TiO2–BaO > TiO2–SrO > TiO2–CaO > TiO2–MgO.Display OmittedIntroduction of alkaline earth metal oxide (AEMO) into TiO2 was found to promote CO oxidation (in the order BaO > SrO > CaO > MgO) over Au nanoparticles supported on TiO2. From experimental (electron-transfer reaction, CO electrochemical oxidation, CO adsorption and Mott–Schottky plots) and theoretical (density functional theory) calculations, it is proposed that AEMO may act as an electron promoter for CO oxidation, but not as an exclusive structural promoter as widely regarded. Introduction of AEMO raises the Fermi level of the TiO2 support, resulting in an enhanced electron transfer from the support to the Au sites and promoting activation of CO adsorbed at Au sites. Moreover, the enhanced catalytic activities induced by AEMO depend on the increase in the Fermi level of the support in the order: TiO2–BaO > TiO2–SrO > TiO2–CaO > TiO2–MgO. This investigation provides a new insight to understand the role of the electron promoters in the thermocatalytic reactions.
Keywords: Alkaline earth metal oxide; Au/TiO2; Electron promoters; Fermi level; DFT calculations;
Stöber-like method to synthesize ultradispersed Fe3O4 nanoparticles on graphene with excellent Photo-Fenton reaction and high-performance lithium storage by Bocheng Qiu; Qiaoying Li; Bin Shen; Mingyang Xing; Jinlong Zhang (216-223).
A simple and facile Stöber-like method is used to prepare the ultradispersed Fe3O4 nanoparticles (3–8 nm) on the reduced graphene oxide (RGO) sheet. The prepared Fe3O4/RGO composites not only possess ultrathin graphene (≤4 layers) and a high surface area of ∼199.8 m2 g−1, but also exhibit superior and stable Photo-Fenton activity, and very excellent reversible lithium storage capacity.Display OmittedIn this paper, we report a facile Stöber-like method to prepare the ultra-dispersed Fe3O4 nanoparticles (3–8 nm) on the reduced graphene oxide (RGO) sheet by using Iron (III) acetylacetonate (Fe(acac)3) as the iron precursor. This strategy provides a facile and environmentally friendly method for the large-scale synthesis of Fe3O4/RGO without any additional reductants and organic surfactants. The prepared hybrid materials are used as the Photo-Fenton catalyst to display a high and stable performance for the recyclable degradation of methyl orange pollutant, owing to the high conversion efficiency of Fe3+/Fe2+ and the magnetic property of Fe3O4. Furthermore, the hybrids also show superior lithium storage performance with large reversible capacity, excellent cyclic performance (624 mAh g−1 for up to 50 charge/discharge cycles at a current density of 0.1 A g−1), and good rate capability (624 and 415 mAh g−1 at 0.1 and 2.4 A g−1, respectively) as an anode material, owing to its superior electrical conductivity, high surface area, excellent electrode homogeneity and dispersity. We believe that the involved Stöber-like pre-treatment method can be further extended to prepare various metal oxides/graphene composites with promising applications across a broad range of catalysis, sensors, supercapacitors, and batteries.
Keywords: Stöber-like method; Fe3O4; Graphene; Lithium ion battery; Photo-Fenton reaction;
A highly efficient BiVO4/WO3/W heterojunction photoanode for visible-light responsive dual photoelectrode photocatalytic fuel cell by Ligang Xia; Jing Bai; Jinhua Li; Qingyi Zeng; Xuejin Li; Baoxue Zhou (224-230).
A visible-light responsive dual photoelectrode photocatalytic fuel cell based on a highly efficient BiVO4/WO3/W heterojunction photoanode and Pt modified buried junction silicon photocathode was constructed for efficient organics degradation and simultaneously electricity generation in this paper.Display OmittedA highly efficient BiVO4/WO3/W heterojunction photoanode was fabricated based on the nanoporous WO3 film, which was prepared on the tungsten plate by anodic oxidation, in order to facilitate the electrons transfer from BiVO4 to WO3 by providing a natural connection between WO3 film and W substrate. Then, a visible-light responsive dual photoelectrode photocatalytic fuel cell (PFC) consisted of BiVO4/WO3/W photoanode and Pt modified commercial buried junction silicon (Pt/BJS) photocathode was constructed. The results showed that the optimized BiVO4/WO3/W photoanode obtained a photocurrent of 2.01 mA/cm2 at 0.6 V (vs Ag/AgCl) in 0.1 M KH2PO4 (pH 7) electrolyte under simulated AM1.5 solar light, which was 180% and 205% higher than that of bare WO3 film and bare BiVO4 film, respectively. The established dual photoelectrode PFC showed high converting performance of organics into electricity. For example, a short-circuit current density of 0.26 mA cm−2, which is higher than most of the reported visible-light responsive dual photoelectrode PFC systems, was obtained with the open-circuit voltage of 0.78 V and maximum power output of 2.0 × 10−4 W cm−2 in 20 mg L−1 tetracycline hydrochloride. Furthermore, a removal ratio of 78% after 4 h was achieved with a stable output photocurrent in the degradation process.
Keywords: BiVO4/WO3 heterojunction; Tungsten substrate; Photocatalytic fuel cell (PFC); Organic compounds degradation; Electricity generation;
Constructing a novel ternary Fe(III)/graphene/g-C3N4 composite photocatalyst with enhanced visible-light driven photocatalytic activity via interfacial charge transfer effect by Qiong Liu; Yarong Guo; Zhihong Chen; Zhengguo Zhang; Xiaoming Fang (231-241).
Schematic illustration of hole–electron separation and transfer process for the 25%-Fe/GE/CN photocatalysts under visible light irradiation (>420 nm).Display OmittedInterfacial charge transfer effect (IFCT) was introduced into g-C3N4 by grafting Fe(III) species on its surface via a simple impregnation method. It has been shown that the obtained Fe(III)-grafted g-C3N4 photocatalyst exhibited enhanced visible-light absorption, reduced charge recombination and improved photocatalytic activity as compared with those of g-C3N4, due to the interfacial charge transfer between the Fe(III) species and g-C3N4. Furthermore, a novel ternary Fe(III)/graphene/g-C3N4 photocatalyst was successfully constructed by integrating graphene into the binary Fe(III)/g-C3N4 composite as the electron mediator. It has been found that the introduction of graphene made the Fe species show well distribution, smaller size and relatively high content in the ternary photocatalyst as compared with those in the binary one, revealing a synergistic effect between the Fe(III) species and graphene existed in the ternary photocatalyst. Consequently, the photocatalytic activity of the ternary Fe(III)/graphene/g-C3N4 photocatalyst was superior to that of the binary one, originating from its stronger visible-light absorption and more reduced charge combination. The ternary composite that consists of transition metal, graphene and g-C3N4 represents a new kind of high-efficiency visible-light-driven photocatalysts for water disinfection.
Keywords: Photocatalysis; Visible-light driven photocatalyst; g-C3N4; Interfacial charge transfer;
Efficient Co-B-codoped TiO2 photocatalyst for degradation of organic water pollutant under visible light by R. Jaiswal; N. Patel; Alpa Dashora; R. Fernandes; M. Yadav; R. Edla; R.S. Varma; D.C. Kothari; B.L. Ahuja; A. Miotello (242-253).
Display OmittedLattice location of B in TiO2 is tuned to determine its effect on the photocatalytic activity of Co-B codoped TiO2. Sol–gel method was used to synthesize the samples. The concentrations of Co and B were first optimized by maximizing the photocatalytic activity for the monodoped (Co or B)-TiO2. In addition to the DFT calculations for discovering new energetic levels introduced in TiO2 by codoping, various characterization techniques were used to determine the dopant lattice sites in TiO2 and interactions between them; and also determining their consequences on electronic, morphological, structural, and optical properties. At low concentration of B-doping (1 at.%), B occupies the interstitial site (Bint), but as the concentration increases (2 at.% and 3 at.%) B also occupies substitutional O position (Bsub) in addition to Bint to form TiO2 containing Bint+sub. Both these B-doped TiO2 showed improved photocatalytic activity attributed to effective charge separation obtained for TiO2–Bint due to the formation of shallow energy level while higher visible light absorption is achieved with TiO2–Bint+sub owing to the presence of two deep energy levels in the band gap as confirmed by DFT calculations. In the case of Co doping, the band gap of TiO2 is reduced but the recombination rates are always high and are caused by the formation of Co states in the band gap. For Co monodoped TiO2, the photocatalytic activity is low for all the concentrations considered, except for very low concentration of Co (0.1 at.%). Two opposite effects were observed when small amount of Co (0.1 at.%) was codoped with Bint or Bint+sub. In particular, the photocatalytic degradation rate of organic aqueous pollutants (p-nitrophenol and rhodamine B dye) reduces for TiO2–Co–Bint whereas it is enhanced remarkably for TiO2–Co–Bint+sub as compared to (Co or B) monodoped (∼2.1 times) and undoped (∼7.8 times) TiO2. Higher photocatalytic activity observed in Co-doped TiO2–Bint+sub is discussed in terms of the interactions of Co with B at two different lattice positions in TiO2 and the synergistic effect created by higher visible light absorption and the improved charge separation.
Keywords: Codoped TiO2; Photocatalytic activity; Visible light absorption; Sol–gel method; Organic pollutant degradation;
Advanced photocatalytic performance of graphene-like BN modified BiOBr flower-like materials for the removal of pollutants and mechanism insight by Jun Di; Jiexiang Xia; Mengxia Ji; Bin Wang; Sheng Yin; Qi Zhang; Zhigang Chen; Huaming Li (254-262).
Novel graphene-like BN modified BiOBr materials have been synthesized via an ionic liquid assisted solvothermal process. The enhanced light harvesting ability and higher separation efficiency of photogenerated electron–hole pairs by the modification of graphene-like BN contributed to the higher photocatalytic activity.Display OmittedNovel graphene-like BN modified BiOBr materials have been synthesized via an ionic liquid assisted solvothermal process. The structure, morphology, optical and electronic properties were explored by the XRD, XPS, FT-IR, SEM, TEM, DRS, PL, EIS and photocurrent. The photocatalytic performance of the graphene-like BN/BiOBr materials was evaluated by the degradation of colorless antibiotic agent ciprofloxacin (CIP), tetracycline hydrochloride (TC) and rhodamine B (RhB) under visible light irradiation. When the mass fraction of graphene-like BN is 1%, the graphene-like BN/BiOBr materials exhibited the highest activity. The enhanced light harvesting ability and higher separation efficiency of photogenerated electron–hole pairs by the modification of graphene-like BN contributed to the higher photocatalytic activity. The photo-degradation is dominant by the O2 • − and hole oxidation process. This exploration of graphene-like BN modified BiOBr open a window for the use of other graphene-like BN based composites in photocatalysis field.
Keywords: Graphene-like BN; BiOBr; Photocatalytic; Visible light;
Photodegradation of phenol via C3N4-agar hybrid hydrogel 3D photocatalysts with free separation by Mo Zhang; Wenjun Jiang; Di Liu; Jun Wang; Yanfang Liu; Yanyan Zhu; Yongfa Zhu (263-268).
Display OmittedThe agar-C3N4 hybrid hydrogel photocatalysts with 3 dimension (3D) network structure have been prepared via thermoreversible phase transition of agar. The hybrid hydrogels show high efficient pollutants removal ability by synergistic effect of adsorption and photocatalytic degradation. The removal ability of phenol and methylene blue (MB) by hybrid hydrogel is about 1.3 and 4.5 times of pure g-C3N4 respectively. The pollution can be degraded continuously via agar-C3N4 hybrid hydrogels photocatalysts without separation.
Keywords: g-C3N4; Agar; Hybrid hydrogel; Photocatalysis;
Promotional effects of zirconium doped CeVO4 for the low-temperature selective catalytic reduction of NO x with NH3 by Xin Zhao; Lei Huang; Hongrui Li; Hang Hu; Xiaonan Hu; Liyi Shi; Dengsong Zhang (269-281).
Display OmittedIn this work, we developed a novel zirconium doped CeVO4 to form Ce1−x Zr x VO4 (x = 0.05, 0.10, 0.15, 0.20, 0.30, 0.50, 0.70, 0.80) solid solution as a low-temperature catalyst for the selective catalytic reduction (SCR) of NO x with NH3. The optimized catalysts showed excellent performance at low temperature. The light-off temperature (the temperature at which the conversion of NO reaches 50%) was down to about 125 °C, while the temperature window (the NO conversion is above 80%) ranged from 150 to 375 °C. The selectivity was kept close to 100% during the whole temperature range. Furthermore, the catalysts also exhibited good H2O/SO2 durability and fascinating performance at high gas hourly space velocity of 400,000 h−1. Hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, ammonia and nitrogen oxides temperature-programmed desorption and in-situ diffuse reflectance infrared Fourier transform experiments were performed to study the influence of Zr doping on the SCR performance. It was found that the introduction of Zr in CeVO4 with a proper amount could significantly increase the surface area, oxidative ability, active oxygen species and especially surface acid sites of the catalysts, which were beneficial to the promotion of SCR performance.
Keywords: Selective catalytic reduction; Zr doped; CeVO4; Vanadates; deNO x ;
Promoted V2O5/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperatures by Siva Sankar Reddy Putluru; Leonhard Schill; Anita Godiksen; Raju Poreddy; Susanne Mossin; Anker Degn Jensen; Rasmus Fehrmann (282-290).
Display OmittedThe influence of varying the V2O5 content (3–6 wt.%) was studied for the selective catalytic reduction (SCR) of nitrogen oxides by ammonia on heteropoly acid (HPA)- and tungsten oxide (WO3)-promoted V2O5/TiO2 catalysts. The SCR activity and alkali deactivation resistance of HPA-promoted V2O5/TiO2 catalysts was found to be much higher than for WO3- promoted catalysts. By increasing the vanadium content from 3 to 5 wt.% the catalysts displayed a two fold increase in activity at 225 °C and retained their initial activity after alkali doping at a molar K/V ratio of 0.181. Furthermore, the catalysts were characterized by N2 physisorption, XRPD, NH3-TPD, H2-TPR, Raman, FTIR and EPR spectroscopy to investigate the properties of the catalysts. XRPD, Raman and FTIR showed that promotion with 15 wt.% HPA does not cause V2O5 to be present in crystalline form, also at a loading of 5 wt.% V2O5. Hence, use of HPAs does not cause increased N2O formation or unselective oxidation of NH3. NH3-TPD showed that promotion by HPA instead of WO3 causes the catalysts to possess a higher number of acid sites, both in fresh and alkali poisoned form, which might explain their higher potassium tolerance. Ex-situ EPR spectroscopy revealed that HPA-promoted catalysts have higher V4+/Vtotal ratios than their WO3-promoted counterparts. H2-TPR suggests that HPAs do not have a beneficial effect on the V5+-V3+ redox system, relative to WO3.
Keywords: SCR of NO with NH3; V2O5; Potassium poisoning; Heteropoly acids;
Enhanced generation of reactive oxygen species for efficient pollutant elimination catalyzed by hemin based on persistent free radicals by Bin Jiang; Yuyuan Yao; Renjie Xie; Dejun Dai; Wangyang Lu; Wenxing Chen; Li Zhang (291-297).
Display OmittedPorphyrin has received increasing interest in the catalysis field due to their excellent catalytic performance, nevertheless, the development of highly efficient porphyrin catalysts is still a significant challenge. In this work, a representative of persistent free radicals (PFRs), multiwalled carbon nanotubes (MWCNTs), was innovatively employed to construct an outstanding catalytic system, hemin-MWCNTs/H2O2. The introduction of MWCNTs greatly enhanced the catalytic activity of hemin, representing about 61 times higher reaction rate constant with the dye of methylene blue (MB) as probe compound, which was attributed to more reactive oxygen species (ROS) (•OH and hemin (FeIV ＝O)) generation. When MWCNTs were introduced to hemin/H2O2 system, the decrease of PFRs concentration in MWCNTs were observed with larger number of trapped electrons, indicating that PFRs might transfer electrons to hemin, thus speeding up the reaction rate-determining step of hemin (FeIII) to hemin (FeII), resulting in enhanced production of •OH and hemin (FeIV ＝O). This study initiates an up-to-date research domain of PFRs-enhanced catalysis, paving the avenue toward developing robust processes for the efficient generation of ROS for applications in catalysis field.
Keywords: Persistent free radicals; Multiwalled carbon nanotubes; Hemin; Reactive oxygen species;
Chemical looping tar reforming using La/Sr/Fe-containing mixed oxides supported on ZrO2 by Martin Keller; Henrik Leion; Tobias Mattisson (298-307).
Display OmittedBiomass gasification gas contains condensable hydrocarbons usually referred to as “tars”. The use of chemical-looping reforming (CLR) has been proposed as a downstream technology for tar removal from the hot raw gasification gas. In this work two different ZrO2 support materials impregnated with La, Sr, Fe and mixtures thereof have been investigated as bed material for this proposed CLR process, with benzene and ethylene as tar surrogates. It was found that only combinations of La and Fe yielded significant catalytic activity for benzene conversion that could be further improved by adding Sr. Over this material, the benzene conversion reaction was found to be of first order with respect to benzene, and a simple kinetic model indicates that a high degree of benzene conversion can be obtained at reasonable residence times when the reactor temperature is sufficiently high (T = 850 °C). It was also observed that this material exhibited some activity for selective catalytic oxidation of benzene, which could further increase the tar conversion when either the bed material provided oxygen to the gas or a small stream of molecular O2 was added to the gasification gas feed. XRD analysis of the used bed materials revealed that a pyrochlore phase and SrZrO3 perovskite were formed during the experiment.
Keywords: Tar reforming; Chemical-looping reforming; Gasification; Dual fluidized bed; Zirconia;
A modular calcination method to prepare modified N-doped TiO2 nanoparticle with high photocatalytic activity by Lei Zeng; Zhao Lu; Minghui Li; Jin Yang; Wulin Song; Dawen Zeng; Changsheng Xie (308-316).
Display OmittedIn this paper, a highly active modified N-doped TiO2 nanoparticle is prepared by a novel modular calcination method. The combination among ammonia, hydrogen, air and vacuum module is investigated comprehensively. Moreover, the effect of calcination order on photocatalytic activity is also studied. The photocatalytic property of sample annealed in ammonia firstly is better than that of the sample annealed in ammonia last. NV-TiO2 sample which is prepared by combination between ammonia and vacuum module possesses the highest photocatalytic activity towards benzene. The photodegradation result shows that 300 ppm benzene can be decomposed completely during four hour visible light illumination. The excellent photocatalytic performance is attributed to the improvement of light harvesting, charge separation and increased surface electron scavenger, simultaneously. Besides, the photocatalytic degradation reaction path of benzene demonstrates that phenol is an important intermediate product. The faster decomposition of phenol is corresponded to higher photocatalytic reaction rate. In fact, the effect of calcination order on the photocatalytic activity is embodied in differences of the amount of oxygen vacancy and surface cleanliness. These findings aid us to prepare highly efficient visible light active photocatalyst by using a simple method and deepen the understanding on the mechanism of decomposing benzene.
Keywords: Modular calcination; N-doped TiO2; Benzene; Visible light; Superoxide anion radical;
Deep HDS of FCC gasoline over alumina supported CoMoS catalyst: Inhibiting effects of carbon monoxide and water by Florian Pelardy; Antoine Daudin; Elodie Devers; Céline Dupont; Pascal Raybaud; Sylvette Brunet (317-327).
Display OmittedThe selective hydrodesulfurization (HDS) of FCC gasoline is a key catalytic process for reducing sulfur content in gasoline. In the present work, we focus on the effect of H2O amount alone or in mixture with CO on the transformation of a model FCC gasoline composed of 2-methylthiophene (2MT) and 2,3-dimethylbut-2-ene (23DMB2N) molecules, over an alumina supported CoMoS catalyst. A negative impact of water and CO on the conversion of 2MT and 23DMB2N is found. However the effect in the presence of CO is much stronger. The comparison of Density Functional Theory (DFT) calculations of CO and water adsorption on the S- and M-edge sites of the CoMoS slabs shows a significantly stronger CO adsorption energy than water adsorption energy. When CO and water were introduced simultaneously, the negative impact observed in the transformation of the model feed is mainly due only to the presence of CO. However whatever the oxygenated molecules used and their amount, no impact in the selectivity measured by the ratio between the activity in hydrodesulfurization and in hydrogenation is observed.
Keywords: Hydrodesulfurization; Olefin hydrogenation; FCC gasoline; Carbon monoxide; CoMoS/Al2O3; Edge sites; Density functional theory;
Rapid synthesis of photoactive hydrogenated TiO2 nanoplumes by Viviana Scuderi; Giuliana Impellizzeri; Massimo Zimbone; Ruy Sanz; Alessandro Di Mauro; Maria Antonietta Buccheri; Maria Miritello; Antonio Terrasi; Giancarlo Rappazzo; Giuseppe Nicotra; Vittorio Privitera (328-334).
Display OmittedIn this study we employed hydrogen peroxide etching of Ti films as a straightforward method to synthesize hydrogenated TiO2 nanoplumes. The material was extensively characterized, showing, among other special features, the inclusion of OH groups. These groups together with the generated structural defects and the nanostructuration are crucial for the high photocatalytic properties under ultraviolet (UV) and visible (VIS) light irradiation. In particular, nanoplumes show a reaction rate about 5 times the rate of TiO2 flat films. Furthermore, nanoplumes display a significant antibacterial activity under VIS light irradiation, compared with TiO2 films.
Keywords: TiO2; Photocatalysis; Nanostructures; UV–VIS light;
Removal of pollutants by the new Fenton-like highly active catalysts containing an imidazolium salt and a Schiff base by M. Neamțu; F. Macaev; V. Boldescu; V.-D. Hodoroaba; C. Nădejde; R.J. Schneider; A. Paul; G. Ababei; U. Panne (335-342).
Display OmittedTwo iron-based molten salts comprising an imidazolium and Schiff base were evaluated as catalysts for removal of carbamazepine (CBZ) from water. The catalysts were fully characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), nuclear magnetic resonance spectroscopy (NMR), electrospray ionisation–mass spectrometry (ESI–MS), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption–desorption isotherms (BET). Additionally, the formation of photo-sensitized oxygen was investigated by spin-trapping using electron spin resonance (ESR). The catalytic activity in heterogeneous oxidation of the micropollutant (CBZ) was also evaluated. The effects of catalyst loading, pH, H2O2 dosage and UV light on the oxidation of the selected compound were investigated. After 15 min of UVA irradiation in the presence of 200 μM H2O2, CBZ was completely removed over both catalysts.
Keywords: Fe-based highly active ionic liquids; Characterization of catalysts; Removal of carbamazepine; Singlet oxygen;
Pd model catalysts: Effect of aging environment and lean redispersion by Jason A. Lupescu; Johannes W. Schwank; Kevin A. Dahlberg; Chang Yup Seo; Galen B. Fisher; Sabrina L. Peczonczyk; Kevin Rhodes; Mark J. Jagner; Larry P. Haack (343-360).
Display OmittedThe performance of automotive three-way catalysts (TWC) deteriorates with time, temperature and aging environment. Engine control methods are needed to minimize the extent of catalyst deactivation and provide an environment capable of partially redispersing noble metal catalyst particles. In this study, palladium-based model powder catalysts on ceria-zirconia or alumina supports were exposed to three different exhaust compositions, lean-only, rich-only and redox, each at 700 °C for 16 h. Catalyst activity was determined by CO oxidation with the water gas shift (WGS) reaction and oxygen storage capacity (OSC) measurements to probe the contact between the noble metal and support at a given state of catalyst deterioration. Lean catalyst treatments at 550 °C and 700 °C were applied to determine the effect on measured Pd size and catalyst activity. The lean-only gas environment was above the PdO decomposition condition, yet showed slightly deteriorated catalyst activity from the fresh state. The rich-only and redox gas environments significantly deteriorated catalytic activity through a combination of metal oxidation state effects and support/additive interactions, both with various degrees of reversibility depending on lean treatment time and temperature. The insight gained from this work could be used to develop engine control and after treatment design strategies to track (or infer) the aging process on the vehicle, avoid severe aging modes and actively intervene at various points to regenerate the catalyst.
Keywords: Palladium; Redispersion; TWC; Regeneration;
Synthesis and photocatalytic performance of yttrium-doped CeO2 with a porous broom-like hierarchical structure by Bin Xu; Qitao Zhang; Saisai Yuan; Ming Zhang; Teruhisa Ohno (361-370).
Display OmittedIn this study, yttrium-doped CeO2 with a broom-like porous hierarchical structure was successfully prepared by a simple template-free hydrothermal method with cerium nitrate hexahydrate and yttrium nitrate hexahydrate as original materials. Through systematic experiments, the different effects of doping concentrations on characteristics of the ceria were examined in detail and the optimal doping ratio was determined simultaneously. The morphology and element distribution of the as-prepared samples were characterized by field emission scanning electron microscopy and high-resolution transmission electron microscopy. Structure information with Rietveld refined data were obtained by using an X-ray diffractometer. Extinctive oxygen vacancy and doping oxygen vacancy were analyzed from Raman spectra. Analyses of elements and chemical valence analysis were carried out by X-ray photoelectron spectroscopy, and changes in reactive oxygen species were determined by calculation. Based on structural information, element valence states, results of hydrogen temperature-programmed reduction and oxygen temperature-programmed decomposition analysis and the results of photocatalytic decomposition of acetaldehyde, we can draw the conclusion that a certain amount of Y-doped CeO2 with a broom-like porous hierarchical structure has high catalytic activity, attributed to more oxygen vacancies and surface active oxygen species generated after yttrium doping.
Keywords: CeO2 nanoparticles; Yttrium-doped; Hierarchical structure; Porous; Oxygen vacancy;
Enhanced self-catalytic degradation of CuEDTA in the presence of H2O2/UV: Evidence and importance of Cu-peroxide as a photo-active intermediate by Shenyu Lan; Ya Xiong; Shuanghong Tian; Jinxi Feng; Tianyao Xie (371-376).
Display OmittedA new insight into the degradation of CuEDTA with UV/H2O2 was performed. It was found that the degradation was an UV-enhanced self-catalytic process with two main stages. The first was the induction stage in which cupric ions were produced in CuEDTA degradation with UV photolysis or/and H2O2 oxidation. The second was the photo-catalytic degradation stage in which CuEDTA was oxidized by UV-enhanced cupric ion-based Fenton process. The degradation efficiency reached as high as 82.2% during 18 min, being 37.4 times higher than the efficiency sum of single H2O2 oxidation and single UV photolysis. The enhancement effect can be contributed to the synergetic interaction between H2O2, cupric ion and UV, specially, to the excellent photo-activity of copper-peroxide intermediates. One of them was identified to be CuO2 by analysis of its CE-C4D electropherograms, UV–vis adsorption spectra, FT-IR spectra, Raman spectra, especially XPS spectra. The enhancement mechanism was experimentally confirmed to be due to the acceleration of Cu(II)-to-Cu(I) transform by the photolysis of copper-peroxide intermediates, leading to the increasing CuEDTA degradation.
Keywords: CuEDTA; Self-catalysis; CuO2; Photo-active intermediate;
Multivariate analysis of the effect of biodiesel-derived contaminants on V2O5‑WO3/TiO2 SCR catalysts by Sandra Dahlin; Marita Nilsson; Daniel Bäckström; Susanna Liljegren Bergman; Emelie Bengtsson; Steven L. Bernasek; Lars J. Pettersson (377-385).
Display OmittedThis study investigates the effect of biodiesel-derived contaminants on vanadia-based NH3-SCR catalysts in heavy-duty exhaust aftertreatment. The aim was to study, not only the effect of single contaminants on the catalyst performance, but also of possible interaction effects between poisons.The effect of six potential catalyst poisons (Na, K, Mg, P, S and Zn) was evaluated using an experimental design and multivariate data analysis. Monolithic V2O5-WO3/TiO2 catalysts were subjected to accelerated laboratory-scale aging, where the six contaminants were fed simultaneously using a wet impregnation method. In addition to NO x conversion tests, the catalysts were characterized by means of ICP-OES, SEM-EDX, XPS, N2 physisorption and NH3-TPD. The lab-aged samples were compared to fresh and vehicle-aged catalysts.The accelerated aging method showed good reproducibility and gave rise to surface compounds similar to those found in vehicle-aged catalysts. Despite plausible differences regarding penetration depth of the contaminants into the walls of the catalyst, the aging method appears to be an efficient way to point out significant chemical poisons.The model obtained from the experimental design was found to correlate well with the experimental data and can therefore be used to predict effects of the various poisons and poison interactions. Significant effects on the NO x conversion were found for P, S, Na, Mg and K as well as for the interactions P × Na, P × K and S × Na. A poisoning effect was found for Mg, Na, K, P × K, and P × Na, where Na and K exhibited the strongest poisoning effect. The deactivating effect of alkali was lowered in the presence of phosphorus and sulfur, which is explained by the formation of phosphates and sulfates, preventing the interaction of the alkali metals with the vanadia active sites.
Keywords: NH3-SCR; V2O5-WO3/TiO2; Chemical deactivation; Design of experiments (DoE);
Direct electrochemical oxidation of ethanol on SOFCs: Improved carbon tolerance of Ni anode by alloying by Brittany Farrell; Suljo Linic (386-393).
Display OmittedSolid oxide fuel cells (SOFCs) are electrochemical devices that convert chemical energy in fuels into electrical energy through an electrochemical oxidation process. This technology is attractive since SOFCs can in principle utilize a range of combustible fuels including hydrogen, carbon monoxide, and hydrocarbons offering higher efficiencies than conventional electricity generators with limited emission of a number of common air pollutants such as NO x and SO x . The environmental efficiency of SOFC devices can further be improved by utilizing fuels that are more carbon-neutral (e.g., biofuels such as ethanol) than conventional fossil fuels. One of the problems with employing oxygenated liquid biofuels is that conventional Ni anode electro-catalysts deactivate due to carbon deposition on the surface of the anode during the process of electocatalytic fuel oxidation. We show that the stability of Ni SOFC anode electrocatalysts during electrochemical oxidation of ethanol is significantly improved when a small amount of Sn is introduced in the electrocatalyst design. The improvement in the stability is manifested in a more stable operation and higher kinetic currents of Sn/Ni compared to Ni electrodes under identical conditions with ethanol fuel. We discuss the underlying molecular mechanisms responsible for the enhanced stability of the anodes and propose a number of guiding principles for the design of carbon-tolerant anodes for oxidation of oxygenated hydrocarbons.
Keywords: Solid oxide fuel cell; Ethanol; Tin; Ni/YSZ; Carbon deposition;
A kinetic model for sulfur poisoning and regeneration of Cu/SSZ-13 used for NH3-SCR by Louise Olsson; Kurnia Wijayanti; Kirsten Leistner; Ashok Kumar; Saurabh Y. Joshi; Krishna Kamasamudram; Neal W. Currier; Aleksey Yezerets (394-406).
Display OmittedIn this study, we have developed a multi-site kinetic model that describes the sulfur poisoning and gradual sulfur removal over Cu/SSZ-13 used for NH3-SCR. Sulfur poisoning was conducted under SCR conditions and thereafter, repeated SCR experiments were conducted to examine the effect of such poisoning and the subsequent gradual removal of sulfur. In addition, the effect of sulfur poisoning was examined on NH3 TPD and ammonia oxidation experiments. The following sites were used in the kinetic model: copper in the six-membered rings as described by S1Cu, copper in the larger cages with S2 and S3 as a site where physisorbed ammonia can attach. Further, ammonia was also adsorbed on the Brönsted sites, represented by S1Brön in the model, but in order not to further complicate the model, small amounts of ammonia storage on Brönsted sites were also lumped into S2. In the model, SO2 was adsorbed on the sites containing copper, which are S1Cu and S2. It should be noted that S1Cu and S2 represents hydrated copper sites. Interestingly, we observed experimentally that ammonia storage was larger after sulfur poisoning compared to before, which is why we added ammonia storage and desorption to the S1Cu–SO2 and S2–SO2 sites. However, ammonia was already adsorbing on the copper site; thus, these steps did not result in increased storage. Consequently, reaction steps were added where additional ammonia was adsorbed to form S1Cu–SO2–(NH3)2 and S2–SO2–(NH3)2 species, which could be interpreted as precursors to ammonium sulfates. Another aspect that must be addressed in the model is the observation in the literature that SO2 is more easily desorbed in SO2 + NH3 + O2 TPD than SO2 + O2 TPD. Reversible reaction steps were therefore added whereby the S1Cu–SO2–NH3 and S2–SO2-NH3 species were decomposed to form SO2. A final reaction step was incorporated into the model to describe the SCR reaction with ammonia attached to the sulfur sites. The developed model could well describe the sulfur poisoning and gradual regeneration during repeated SCR experiments. In addition, the model well described the NH3 TPD and NH3 oxidation before and after sulfur poisoning.
Keywords: Kinetic model; Ammonia-SCR; Sulfur poisoning; Cu/SSZ-13; Cu-zeolites;
Decomposition of organic chemicals by zeolite-TiO2 nanocomposite supported onto low density polyethylene film under UV-LED powered by solar radiation by Mohammad Reza Eskandarian; Mostafa Fazli; Mohammad Hossein Rasoulifard; Hyeok Choi (407-416).
Display OmittedZeolite-TiO2 nanocomposite was synthesized to maximize its surface area for high reactivity and then immobilized onto a low density polyethylene film to enhance its mechanical stability and application practicality. Ultraviolet light emitting diode (UV-LED) was applied instead of traditional UV lamps to activate the TiO2 composite. Photovoltaics was also introduced to utilize solar radiation as an energy source of UV-LED. The reactivity of zeolite-TiO2 nanocomposite under UV-LED powered by solar radiation was evaluated in the presence of potassium persulfate (K2S2O8) as an oxidant to decompose reactive dyes and pharmaceuticals (reactive black 5, cefiximetrihydrate, and phenazopyridine). Reactivity of various chemical, photolytic, photochemical, and photocatalytic decomposition processes and routes was in order of UV-LED ≈ TiO2 ≈ zeolite ≈ zeolite-TiO2 ≈ UV-LED/zeolite ≈ UV-LED/TiO2 < K2S2O8 << TiO2/K2S2O8 < zeolite-K2S2O8 < UV-LED/K2S2O8 < UV-LED/zeolite-TiO2 < UV-LED/TiO2/K2S2O8 < UV-LED/zeolite/K2S2O8 << zeolite-TiO2/K2S2O8 < UV-LED/zeolite-TiO2/K2S2O8. Use of zeolite-TiO2 nanocomposite contributed to enhanced decomposition of target contaminants more significantly than any other factors such as addition of persulfate and introduction of UV-LED. Effect of persulfate concentration, absorbance spectral changes and discoloration, and reusability of zeolite-TiO2 nanocomposite were also discussed. Since all devices including UV-LED were powered by a photovoltaic module and organic decomposition was successful, the photovoltaics-powered UV-LED photoreactor was proposed as a sustainable, self-powered, and practical point-of-use decontamination system to decompose water contaminants under solar radiation.
Keywords: TiO2 photocatalysis; UV-LED; Photovoltaics; Persulfate; Zeolite;
Dramatic coupling of visible light with ozone on honeycomb-like porous g-C3N4 towards superior oxidation of water pollutants by Jiadong Xiao; Yongbing Xie; Faheem Nawaz; Yuxian Wang; Penghui Du; Hongbin Cao (417-425).
Display OmittedPorous g-C3N4 (PGCN) has attracted enormous attention due to its accessible nanoporous framework benefiting photocatalytic reactions. Here, we reported a one-pot template-free method to fabricate honeycomb-like PGCN by simply mixing ammonia chloride with the precursor of g-C3N4 before calcination. The resulting PGCN exhibited obviously improved photocatalytic activity for p-hydroxybenzoic acid (PHBA) degradation under visible light due to its high surface area and enlarged band gap, but PHBA can hardly be mineralized in this process. Hence, for the first time, Vis/PGCN was coupled with ozone in this paper and the results showed that PGCN could trigger a vigorous synergy between photocatalysis and ozonation. Vis/O3/PGCN led to almost complete mineralization of PHBA with an ozone dosage of 1.5 mg/min, and the process could be further accelerated by increasing the ozone dosage. Such a remarkable mineralization enhancement was mainly attributed to the systematically promoted generation of non-selective hydroxyl radicals (•OH). The high CB level of PGCN benefited electron capture by ozone molecules, thus significantly enhanced charge separation and the decay of ozone into abundant •OH. •OH could vigorously react with PHBA and its ozone-recalcitrant intermediates such as the identified carboxylic acids, finally leading to thorough mineralization. Electrospray ionization–mass spectrometry was adopted to detect the evolution of degradation intermediates in ozonation and Vis/O3/PGCN, and the mineralization procedure from the original PHBA to CO2 and H2O was comprehensively proposed. This study contributes to the integration of sunlight/PGCN with ozone as an efficient metal-free advanced oxidation process for water treatment.
Keywords: Porous g-C3N4; Photocatalytic ozonation; Intermediates; Mechanism; Water treatment;
Facile synthesis and enhanced visible-light photoactivity of DyVO4/g-C3N4I composite semiconductors by Huiquan Li; Yuxing Liu; Yumin Cui; Wenbao Zhang; Cong Fu; Xinchen Wang (426-432).
Display OmittedOnce DyVO4 and g-C3N4I are integrated together, the band alignment between the two semiconductors can drive the migration of photo-generated electrons (e−) from g-C3N4I to DyVO4 by the conduction band offset between g-C3N4I and DyVO4, whereas the photo-induced holes (h+) are transferred from DyVO4 to g-C3N4I by the valence band offset. The redistribution of electrons on one side of the junction (DyVO4) and holes on the opposite side (g-C3N4I) can greatly reduce the recombination of electrons and holes.DyVO4/iodine modified graphitic carbon nitride (DyVO4/g-C3N4I) composite semiconductors with different weight percents of DyVO4 were successfully synthesized by a facile heating method, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (UV–vis DRS), photoluminescence (PL) and electron paramagnetic resonance (EPR) spectra, N2 adsorption–desorption analysis and photo-electrochemical measurement. The resulting DyVO4/g-C3N4I semiconductor with a suitable weight percents of 6.3% DyVO4 showed the highest visible-light photoactivity, and its degradation ratio for methylene blue was more than 1.8 time higher than that of DyVO4, g-C3N4 and g-C3N4I. The H2 evolution rate of 6.3% DyVO4/g-C3N4I was 10.6, 4.7 and 1.7 times higher than that of DyVO4, g-C3N4 and g-C3N4I, respectively, while still having excellent reusability and stability. The obviously enhanced photoactivity of 6.3% DyVO4/g-C3N4I is mainly ascribed to the fact that the proper DyVO4 modified g-C3N4I increase its specific surface area, decrease band-gap energy, enhance absorption in the 400–700 nm region and promote efficient separation of photo-generated carriers. The mechanism on the improvement of visible-light photoactivity is discussed.
Keywords: DyVO4; g-C3N4I; Conjugated polymer; Visible-light photocatalysis;