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Applied Catalysis B, Environmental (v.98, #3-4)
Solvent free synthesis of organometallic catalysts for the copolymerisation of carbon dioxide and propylene oxide by Xia Zhong; Fariba Dehghani (pp. 101-111).
The aim of this study was to determine the potential of using high pressure CO2 as an alternative solvent for the synthesis of organometallic catalysts that can be used for the synthesis of biodegradable polymers. Zinc glutarate that is fabricated from reaction between zinc oxide and glutaric acid, is a solid heterogeneous catalyst with high efficiency for the synthesis of polymers such as aliphatic polycarbonate and polyglycidol. This catalyst is commonly prepared in a toxic organic solvent such as toluene. The yield of the reaction for the synthesis of zinc glutarate catalyst in high pressure carbon dioxide was 86%, which was comparable with the one fabricated in toluene. Processing by high pressure CO2 has negligible effects on the particle size, but significant effect on zince glutarate surface area (46% reduction) and crystallinity (12% enhancement) in crystallinity, compared with using toluene as a solvent. A catalyst with less porosity, hence lower surface area was formed in high pressure CO2. The activity of zinc glutarate catalyst produced in CO2 system was increased to 74.2gpolymer/g catalyst for the synthesis of poly(propylene carbonate) compared with 67.4gpolymer/g catalyst prepared with conventional method. This effect was attributed to the substantial enhancement in the degree of crystallinity and crystal perfectness of ZnGA catalysts in CO2 system. The results of FTIR and WXRD analysis demonstrate the feasibility of synthesizing other organometallic catalysts such as zinc adipate in high pressure CO2 with a high yield of 77.5%.
Keywords: High pressure CO; 2; Zinc glutarate; Copolymerisation
Reduction of NOx over a combined NSR and SCR system by Anna Lindholm; Hanna Sjövall; Louise Olsson (pp. 112-121).
Flow reactor experiments are performed over a model Pt/Ba/Al catalyst, an Fe-beta sample, and over a combined system where the Pt/Ba/Al catalyst is placed upstream the Fe-beta sample. The combined system show a superior NOx removal efficiency and a lower ammonia slip compared to the single Pt/Ba/Al catalyst at all temperatures examined. Ammonia, formed during the rich period over the Pt/Ba/Al, is stored in the SCR catalyst and consumed in the following lean period which results in a decrease of the NH3 slip and an increase of the NOx removal efficiency. The optimum temperature for NOx removal of the combined system is 300°C; at this temperature a remarkably high NOx removal efficiency of 99.5% is achieved. The SCR catalyst exhibit a high ammonia adsorption capacity at 200°C which results in a very low NH3 yield (3%) and a high N2 yield (85%) for the combined NSR and SCR system. There is a benefit when NO2 is present in the feed at low temperatures. The NOx removal efficiency of the combined system increases due to the increase in the amount of NOx stored over the Pt/Ba/Al sample. Furthermore, the amount of NOx removed over the combined system is influenced by the amount of hydrogen in the rich periods. A higher hydrogen concentration enhances the NOx removal efficiency at lower temperatures. At higher temperatures an optimum hydrogen concentration exists due to ammonia inhibition of the SCR reaction when an excessively high H2 concentration is used.
Keywords: Pt/Ba/Al catalyst; Fe-beta; Combined NSR; +; SCR system; NOx storage; NO; x; reduction; Ammonia; SCR
Photocatalytic degradation of boscalid in aqueous titanium dioxide suspension: Identification of intermediates and degradation pathways by Laura Lagunas-Allué; María-Teresa Martínez-Soria; Jesús Sanz-Asensio; Arnaud Salvador; Corinne Ferronato; Jean Marc Chovelon (pp. 122-131).
The photocatalytic degradation of boscalid in aqueous suspensions was investigated by using titanium dioxide (TiO2) as a photocatalyst. Accordingly, a complete degradation of fungicide was achieved by applying the optimal operational conditions of 2.5gL−1 of catalyst, natural pH of 6.0 and the temperature at 20±1°C after 90min irradiation. Photodegradation of boscalid exhibited pseudo-first-order reaction kinetics. The rate of photodecomposition of boscalid was measured using high performance liquid chromatography-diode array detector (HPLC-DAD) while its mineralization was followed using total organic carbon (TOC) analysis. The influence of physicochemical parameters such as photonic flux, presence of inorganic cations and anions, pH and oxygen concentration on the kinetic process was studied. The identification of reaction intermediate products was carried out using coupled techniques HPLC–MS/MS after a SPE pre-concentration step and a degradation pathway was proposed. By this technique, 17 degradation products were identified.
Keywords: Boscalid degradation; Photocatalysis; TiO; 2; Intermediate products; HPLC–MS/MS
Effect of pore morphology of mesoporous carbons on the electrocatalytic activity of Pt nanoparticles for fuel cell reactions by Shuqin Song; Yeru Liang; Zhenghui Li; Yi Wang; Ruowen Fu; Dingcai Wu; Panagiotis Tsiakaras (pp. 132-137).
In the present investigation, the role of the pore morphology of mesoporous carbons in the electrocatalytic activity of Pt nanoparticles for fuel cell reactions has been successfully revealed by adopting ordered mesoporous carbon CMK-3 and disordered wormhole-like mesoporous carbon (WMC) as the support material, respectively. Both materials possess very similar pore characteristics (pore volume, BET surface area, mesopore size) except pore morphology. It has been found that CMK-3 can provide Pt nanoparticles with more electrochemically active Pt sites and higher electrochemical surface area, and thus, Pt/CMK-3 exhibits superior fuel cell reactions activity compared to Pt/WMC, especially in the case of liquid reactants (e.g. ethanol). This could be attributed to the much easier mass transportation through CMK-3 support profiting from both the high ordered degree and the very good 3D interconnection of the nano-spacings of their hexagonally arrayed carbon nanorods (i.e. mesopores), thus leading to more accessibility of Pt nanoparticles. The above results demonstrates that the pore morphology of carbon supports plays a decisive role in the electrocatalytic activity of their supported Pt nanoparticles, although other structure parameters like pore size are very similar.
Keywords: Pore morphology; Mesoporous carbon; Pt nanoparticles; PEM fuel cells; Ethanol electrooxidation; Oxygen reduction reaction
Controllable synthesis of Bi2MoO6 and effect of morphology and variation in local structure on photocatalytic activities by Liwu Zhang; Tongguang Xu; Xu Zhao; Yongfa Zhu (pp. 138-146).
Highly crystalline orthorhombic Bi2MoO6 particles with high visible-light photocatalytic activity have been controllably synthesized via a facile hydrothermal process without adding any surfactant. The morphologies of Bi2MoO6 with nanosheet and microrod can be selectively obtained by adjusting the pH value of the reactant. The formation mechanisms of nanosheet and microrod structures were then discussed based on the H+ cations adsorption abilities on different crystal faces. The Bi2MoO6 samples prepared at acidic condition showed 12 times higher photocatalytic activity than that prepared at basic condition under visible-light irradiation. The reason for the big difference in the photocatalytic activities for the Bi2MoO6 samples obtained at different pH values were systematically studied based on their shape, size and the variation of local structure.
Keywords: Photocatalysis; Visible-light; Bi; 2; MoO; 6; Local structure; Nanosheet
Catalytic activity for methane combustion of the perovskite-type La1− xSr xCoO3− δ oxide prepared by the urea decomposition method by Zhiming Gao; Ruiyan Wang (pp. 147-153).
Four methods were adopted to prepare perovskite-type oxide with molar ratio of La/Sr/Co=0.9/0.1/1.0. The oxide prepared by the urea decomposition method showed the highest catalytic activity for methane combustion and a good durability at 600°C for 90h. Surface structure features of this oxide were discussed by use of XPS data. This method was further applied to prepare other perovskite oxides with nominal degree of substitution x=0.0, 0.2 and 0.3. Relation of catalytic activity with degree of substitution was discussed in view of cooperation of surface lattice oxygen vacancy with surrounding cobalt ions at lower oxidation states.
Keywords: Perovskite; Catalytic combustion; Oxygen non-stoichiometry; Methane; XPS
A novel thin-layer photoelectrocatalytic (PEC) reactor with double-faced titania nanotube arrays electrode for effective degradation of tetracycline by Jing Bai; Yanbiao Liu; Jinhua Li; Baoxue Zhou; Qing Zheng; Weimin Cai (pp. 154-160).
A novel thin-layer photoelectrocatalytic (PEC) reactor has been developed and successfully applied to the degradation of tetracycline, a typical pharmaceutical and personal care products (PPCPs), in bulk wastewater treatment. The reactor is designed with double thin-layer in order to increase the A/V ratio (ratio of electrode area and solution volume) and improve the mass transfer as well as the photonic efficiency of the system. The efficiency of organic degradation by the new reactor is much higher in comparison with conventional PEC process under similar treatment conditions. Using 20–120mgL−1 model tetracycline wastewater as the target organics, the PEC removal rate of tetracycline in the reactor reached 96.4–54.8% with a single-side illumination, much higher than that of conventional PEC reactor (about 80.4–14.6%) within 1h. When the reactor was illuminated from double sides, the treatment efficiency of thin-layer reactor was doubled without increasing new electrodes. This novel reactor always keeps high quantum efficiency regardless of the different concentration levels of the organic compounds, especially superior for the treatment of high concentration solutions. Repeated experiments in the treatment of 400mgL−1 tetracycline solution demonstrated excellent stability and reliability of the TNAs electrode.
Keywords: Thin-layer PEC reactor; Titania nanotube arrays; Tetracycline
Preferential oxidation of CO catalyzed by supported polymer-protected palladium-based nanoparticles by Izaskun Miguel-García; Ángel Berenguer-Murcia; Diego Cazorla-Amorós (pp. 161-170).
Palladium nanoparticles protected by polyvinylpyrrolidone (PVP) have been synthesized by the reduction-by-solvent method and deposited on alumina by impregnation. The prepared catalysts have been tested in the preferential oxidation of carbon monoxide (PrOx) in H2-rich gaseous streams and the results have been compared with catalysts prepared by conventional impregnation. Pd-nanoparticles protected by PVP have good activity and outstanding selectivity towards CO oxidation (above 50% in some cases). On the contrary, the impregnated catalyst has very low selectivity (about 10%). The influence of crucial parameters such as the capping agent-to-metal ratio or the synthesis temperature of the nanoparticles on the catalytic performance of the prepared materials has been analyzed. Our results show that within the 2.5–3.5nm region, particle size of supported nanoparticles does not seem to exert a significant influence on the studied reaction. However, the amount of capping agent seems to be crucial to prepare efficient, stable catalysts. The samples prepared show 100% CO removal at 180°C when tested in the presence of CO2 and water vapour.
Keywords: Preferential oxidation of CO (PrOx); Noble metal nanoparticles; Alumina; Hydrogen purification
Degradation kinetics of hydroxy and hydroxynitro derivatives of benzoic acid by fenton-like and photo-fenton techniques: A comparative study by Daniela Nichela; Ménana Haddou; Florence Benoit-Marquié; Marie-Thérèse Maurette; Esther Oliveros; Fernando S. García Einschlag (pp. 171-179).
The oxidative degradation of a series of hydroxy and hydroxynitro derivatives of benzoic acid by Fenton-like and photo-Fenton processes was compared under identical conditions (initial concentrations, pH and temperature). In spite of closely related chemical structures, (2-hydroxybenzoic (2H-BA), 2,4-dihydroxybenzoic (24DH-BA), 2-hydroxy-5-nitrobenzoic (2H5N-BA), 4-hydroxy-3-nitrobenzoic (4H3N-BA) and 2-hydroxy-4-nitrobenzoic (2H4N-BA) acids), the degradation timescales were remarkably different. A common feature was, however, that autocatalytic decay profiles were displayed by the substrates and H2O2. A simple equation, which may be used as a valuable tool for a semiquantitative analysis of the main kinetic features of the inverted “S” profiles, is presented. In addition, a method for the estimation of the relative contribution of photoinduced pathways in photo-Fenton systems (photoenhancement factors) is proposed.In order to assess the key processes governing the kinetic profiles observed, complementary studies were performed to evaluate the formation of ferric complexes, the reactivity towards HO and Fe(II) production efficiencies. Except for 4H3N-BA, the model substrates form highly stable complexes with Fe(III). Competition experiments showed that the reactivities of both the substrates and the ferric complexes with hydroxyl radicals cannot explain the large timescale differences observed in Fenton-like and photo-Fenton systems. The comparison of Fe(II) production under irradiation in the absence of H2O2 with the decay profiles observed in both Fenton-like and photo-Fenton systems confirms that the main factor controlling the autocatalytic behavior is the formation of organic intermediates that are capable of reducing Fe(III) species. An additional factor in the photo-Fenton process may be the efficiency of photoinduced Fe(II) production, which is affected by complex formation since the studied complexes exhibit a lower efficiency of Fe(III) photoreduction than the Fe(III)–aquo complex.
Keywords: Autocatalysis; Photoenhancement; Fe(III) photoreduction
Catalytic combustion of VOCs over a series of manganese oxide catalysts by Sang Chai Kim; Wang Geun Shim (pp. 180-185).
Catalytic combustion of volatile organic compounds (VOCs: benzene and toluene) was studied over manganese oxide catalysts (Mn3O4, Mn2O3 and MnO2) and over the promoted manganese oxide catalysts with alkaline metal and alkaline earth metal. Their properties and performance were characterized by using the Brunauer Emmett Teller (BET), temperature programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The sequence of catalytic activity was as follows: Mn3O4>Mn2O3>MnO2, which was correlated with the oxygen mobility on the catalyst. Each addition of potassium (K), calcium (Ca) and magnesium (Mg) to Mn3O4 catalyst enhanced the catalytic activity of Mn3O4 catalyst. Accordingly, K, Ca and Mg seemed to act as promoters, and the promoting effect might be ascribed to the defect-oxide or a hydroxyl-like group. A mutual inhibitory effect was observed between benzene and toluene in the binary mixture. In addition, the order of catalytic activity with respect to VOC molecules for single compound is benzene>toluene, and the binary mixture showed the opposite order of toluene>benzene.
Keywords: Catalytic combustion; Manganese oxide; Alkaline metal; Alkaline earth metal; Promoter
Nanoparticle molybdenum dioxide: A highly active catalyst for partial oxidation of aviation fuels by Oscar Marin-Flores; Timothy Turba; Caleb Ellefson; Kang Wang; Joe Breit; Jeongmin Ahn; M. Grant Norton; Su Ha (pp. 186-192).
The More Electric Airplane (MEA) concept may be the most innovative development in aviation since the Wright “Flyer” and certainly represents the most transformative change in commercial aviation since the first use of jet engines in 1952. One of the key requirements for enabling the MEA is fuel-flexible solid oxide fuel cell systems that operate directly on logistics fuels such as Jet-A. Of the many fuel cell systems, a solid oxide fuel cell with an internal reforming is most interesting technology for commercial aviation due to its simplicity. In this paper, we show that nanoparticle molybdenum dioxide (MoO2) synthesized directly from a reducing ethylene glycol/water solution can catalyze the partial oxidation of dodecane (a C-12 hydrocarbon surrogate for Jet-A fuel) at weight-hourly-space-velocities up to 10h−1. Even at these very high flow rates the MoO2 nanoparticle catalyst shows a remarkably high fuel conversion of>90% with a hydrogen yield of>70% and an exceptional coking resistance. Under similar environments, conventional Ni-based catalysts and commercial low surface-area MoO2 quickly deactivate due to coking. Our results demonstrate that in its nanoparticle form MoO2 represents a very promising alternative to expensive noble metals for the internal reforming anode of direct Jet-A solid oxide fuel cell and is an important step towards realization of the MEA.
Keywords: Molybdenum dioxide nanoparticles; Hydrogen production; Partial oxidation; Jet fuels
New approaches to preferential CO oxidation over noble metals by Mikhail Kipnis; Elvira Volnina (pp. 193-203).
Features of preferential CO oxidation (CO-PROX) over alumina-supported Pt-, Rh-, Ru-, Au-catalysts are investigated. As found in experiments (flow reactor of quartz, hydrogen-containing gas with admixtures of CO, O2∼1vol.%, high gas flow rate), the nature of CO-PROX is found to be governed by a combination of two main decisive factors: high exothermicity of reactions (CO, H2 oxidation), and peculiarities of interaction of reaction mixture components with metal. Due to high exothermicity, CO-PROX can be realized in a special macrokinetic mode, catalyst surface ignition (CSI), which is an external mass transfer control regime on O2 as the key component.The reaction can be transferred into CSI mode either by heating up to the critical temperature of ignition or by feeding the reaction gas to the catalyst at temperatures above the critical value. In heating, the transition into CSI mode starts with an overheat of the catalyst downstream, after which “hot spot” of the reaction drifts upstream. Variations of temperature allow to observe both ignition and extinction of catalyst surface.Experiments performed with gas mixtures of different composition showed that in CO absence from the reaction gas, H2 is easily oxidized over Pt and Rh at rather low temperatures close to a room one; reaction proceeds in CSI mode with the “hot spot” at the top of the catalyst bed. In CO-PROX over Pt, Rh, there is a deactivating effect of strong CO adsorption, while for Ru it is strong O2 adsorption. As in the case of Ru-catalysts, hydrogen makes substantial positive effect on CO oxidation over Au-catalysts.Effects of temperature, O2 content in gas, Rh content in catalysts are investigated. It is found that a decrease in residual CO content in CSI mode is favored by higher O2 content, lower temperature and lower metal content (for example, down from 1 to 0.2wt.%).
Keywords: Preferential CO oxidation; Surface ignition; Platinum-group metals; Gold; Strong adsorption
Preferential oxidation of CO in H2-rich stream over CuO/Ce1− xTi xO2 catalysts by Zhiwei Wu; Huaqing Zhu; Zhangfeng Qin; Hui Wang; Lichun Huang; Jianguo Wang (pp. 204-212).
CuO/Ce1− xTi xO2 prepared by sol–gel impregnation was used as catalysts for the preferential oxidation (PROX) of CO in H2-rich stream. The effects of support composition, catalyst calcination temperature as well as the presence of H2O and CO2 in the reaction stream on the catalytic performance of CuO/Ce1− xTi xO2 were investigated. The results indicated that the catalyst CuO/Ce0.8Ti0.2O2 exhibits the highest activity and the optimal temperature for the catalyst calcination is 500°C. The presence of H2O and CO2 in the reaction stream has a negative effect on the catalytic activity and stability of CuO/Ce0.8Ti0.2O2. The negative effect of CO2 on the catalyst stability is stronger than that of H2O, suggesting that the accumulation of carbonate species may be the main reason for catalyst deactivation. The characterization by means of XRD, HRTEM, and H2-TPR indicated that the doping of TiO2 in CeO2 enhances the surface area of the composite oxide support, decreases its particle size, and promotes the dispersion of active copper species. The strong interaction between TiO2 and CeO2 in the support as well as the interfacial interaction between CuO and the support may also contribute to the high catalytic activity of CuO/Ce0.8Ti0.2O2.
Keywords: CO preferential oxidation (PROX); CuO catalyst; CeO; 2; TiO; 2; Sol–gel method
Hydrodeoxygenation of 2-ethylphenol as a model compound of bio-crude over sulfided Mo-based catalysts: Promoting effect and reaction mechanism by Y. Romero; F. Richard; S. Brunet (pp. 213-223).
The hydrodeoxygenation of 2-ethylphenol was carried out under 7MPa of total pressure and at 340°C in a fixed-bed reactor over unpromoted Mo/Al2O3 catalyst and over two promoted catalysts (CoMo/Al2O3 and NiMo/Al2O3). For all experiments, dimethyldisulfide was added to the feed to maintain the sulfidation state of the catalysts. On these sulfided catalysts, the transformation of 2-ethylphenol is considered to proceed by three pathways: (1) prehydrogenation of the aromatic ring followed by a dehydration reaction leading to a mixture of alkenes (1-ethylcyclohexene and 3-ethylcyclohexene) and after hydrogenation leading to ethylcyclohexane (HYD pathway); (2) direct cleavage of the Csp2–O bond leading to ethylbenzene (DDO pathway); (3) disproportionation and isomerization reactions leading to oxygenated products (phenol, isomers of 2-ethylphenol and diethylphenols) and their deoxygenated products (ACI pathway). The production of those oxygenated compounds mainly involved the support acidity. The presence of nickel and cobalt allowed an increase of the deoxygenation rate. Nickel only promoted the HYD pathway whereas cobalt promoted both the HYD and DDO pathways. Consequently, the DDO/HYD selectivity was very dependent on the catalyst used. The highest DDO/HYD selectivity was obtained for CoMo/Al2O3. Sulfur vacancies are proposed as active sites for both deoxygenation pathways of 2-ethylphenol, although other active sites (e.g. brim sites) could be involved to explain that the HYD pathway was always predominant. For both deoxygenation pathways, two probable mechanisms are described. The adsorption mode of the molecule most likely determines the deoxygenation route.
Keywords: Hydrodeoxygenation; NiMo; CoMo; 2-Ethylphenol; Promoting effect
Catalytic abatment of styrene traces in polystyrene: A model study of styrene reaction with excess cumene by Aziz Fihri; Robert Durand; Francesco di Renzo; François Fajula; Bernard Coq; Thomas-Maurice Roussel; Bruno Vuillemin (pp. 224-228).
The conversion of styrene in the presence of cumene has been studied on a family of aluminosilicate acid catalysts. This study was part of a project aimed at the removal of styrene monomer traces in polystyrene (PS). The catalytic experiments were performed at 200°C in a closed stirred tank reactor with 1.92mmol styrene, 49.8mmol cumene and 60mL n-dodecane as solvent. The evaluated catalytic materials were faujasite and beta zeolites, and amorphous silica-aluminas with disordered or ordered mesoporosity. Four reaction paths are involved in the styrene conversion. A free-radical chain polymerization in the homogeneous phase is mostly sensitive in the presence of catalysts of low activity. The three other transformation routes are catalyzed by the acid sites of the materials: (1) hydrogen transfer between styrene and cumene to ethylbenzene and α-methylstyrene; (2) ring oligomerization of styrene to dimers and trimers; (3) alkylation of cumene by styrene into primary and secondary alkylates. The presence of acid sites is a prerequisite for the styrene transformation to occur on the materials. However, the key factor for the catalytic activity is the presence of a large mesoporous volume favoring the molecular traffic within the solid. Mesoporous silica-aluminas behave most favorably in this sense. As regards the distribution of products, a strong acid strength as well as the increase of the cumene/styrene molar ratio favor the alkylation pathway. There is a dark coloration of the reaction medium when carbocations are trapped within the micropores of zeolites. Among the catalysts investigated, the most attractive materials as regards activity, selectivity and a coloration of the solution are mesoporous silica-aluminas and, more preferably, those featuring an ordered porosity of the MCM-41 type.
Keywords: Styrene; Heterogeneous catalysis; Zeolites; Mesoporous silica-alumina; Polystyrene
Silver–TiO2 nanocomposites: Synthesis and harmful algae bloom UV-photoelimination by V. Rodríguez-González; S. Obregón Alfaro; L.M. Torres-Martínez; Sung-Hun Cho; Soo-Wohn Lee (pp. 229-234).
The photocatalytic effects of the silver TiO2 nanocomposites on the killing of marine algae were examined by using either Amphidinium carterae (red tide) or noxious Tetraselmis suecica (green tide) as a probe. After 1h under UV irradiation, both harmful algae were inactivated by the silver nanocomposites. The fatal damages to the green tide induced by the TiO2–Ag sol–gel semiconductor occurred faster than those promoted by the photodeposited Ag/P25 and TiO2 sol–gel isolated supports.Silver TiO2 nanocomposites were synthesized by two methods: silver UV photodeposition (Ag/P25) and a sol–gel process incorporating silver nitrate during the titanium alkoxide gelling step (TiO2-Ag). The obtained nanocomposites were characterized by means of XRD, N2 adsorption, XPS, and DRS. All the silver-TiO2 semiconductors have anatase as the principal crystalline TiO2 phase and the average band gap was found in the edge of the visible–ultraviolet region (3.26eV). According to XPS and HAADF-STEM studies, highly dispersed silver nanoparticles were found on the titania surface as Ag°. The photocatalytic effects of the silver TiO2 nanocomposites on the killing of marine algae were examined by using either Amphidinium carterae (red tide) or noxious Tetraselmis suecica (green tide) as a probe. After 1h under UV irradiation, both harmful algae were inactivated by the silver nanocomposites. The fatal damages to these microorganisms induced by the TiO2-Ag sol–gel semiconductor occurred faster than those promoted by the Ag/P25 and TiO2 sol–gel isolated supports. In addition to the biocide properties of silver in aqueous medium, the silver nanoparticles acted as electron traps, retarding electron–hole recombination, which enhanced the photocatalytic activity.
Keywords: TiO; 2; sol–gel; Silver nanoparticles; Harmful algae bloom; Silver photodeposition