Catalysis Today (v.101, #3-4)
Photocatalytic degradation of herbicide fluroxypyr in aqueous suspension of TiO2
by M.A. Aramendía; A. Marinas; J.M. Marinas; J.M. Moreno; F.J. Urbano (pp. 187-193).
The photocatalytic degradation of fluroxypyr (FLX) was studied using Degussa P-25 Titania as a catalyst. The disappearance of FLX was proved to follow a half-order kinetics. This implies that two active sites are involved in the adsorption of one molecule of fluroxypyr. In our conditions, complete mineralization of 40ppm of pure fluroxypyr occurred within ca. 240min of UV-radiation. Some reaction intermediates were identified by HPLCâ€“MS (ESI+) and a tentative degradation pathway was proposed. The presence of HCl (pH 2) seemed to have an inhibiting effect on the initial rate, whereas degradation of FLX was accelerated at basic pH values (pH 8 or 10, achieved with CaCO3 or NaOH, respectively). Photocatalysis proved to be an excellent new advanced oxidation technology (AOT) to eliminate fluroxypyr residues present in surface and ground waters.
Keywords: Fluroxypyr; Photocatalysis; Half-order kinetics; Photocatalytic degradation; Herbicide; Mineralization
Removal of selected persistent organic pollutants by heterogeneous photocatalysis in water
by Tusnelda E. Doll; Fritz H. Frimmel (pp. 195-202).
Environmentally relevant polar persistent organic pollutants (pharmaceuticals and diagnostic agents) were chosen according to human consumption and occurrence in the aquatic environment (sewage plant effluents, rivers and groundwater) to investigate their behavior during photocatalytic oxidation. From data compilation in the literature, the active metabolite clofibric acid of some lipid lowering agents, the anti-epileptic drug carbamazepine and the X-ray contrast media iomeprol were selected. The degradation of the persistent pollutant was monitored by HPLC/DAD/FLD. The study also focuses on the identification and quantification of possible degradation products by HPLC/DAD/FLD and HPLC/MS/MS. The degradation process was also monitored by determination of sum parameters and inorganic ions. Various aromatic and aliphatic degradation products have been identified and quantified. From analytical data, a possible degradation scheme for carbamazepine was proposed. Kinetic studies showed that the TiO2 photocatalyst P25 was more active in clofibric acid degradation than Hombikat UV100. For photocatalytic degradation of iomeprol Hombikat UV100 was more suitable than P25. In general the presence of NOM and carbamazepine retarded the photocatalysis of clofibric acid. Radiation attenuation, competition for active sites and surface deactivation of the catalyst by adsorption are the reason for that. The results of this work proof that photocatalysis is a promising technology to reduce persistent substances even if they are present in low concentrations or in a complex matrix.
Keywords: Persistent organic pollutant; Pharmaceuticals; X-ray contrast media; Degradation products; TiO; 2; 75% anatase and 25% rutile (P25); 100% anatase (Hombikat UV100); Aqueous suspensions; Water treatment; Competitive inhibition
Solar photocatalytic degradation and detoxification of EU priority substances
by M. Hincapié; M.I. Maldonado; I. Oller; W. Gernjak; J.A. Sánchez-Pérez; M.M. Ballesteros; S. Malato (pp. 203-210).
Several different pesticides (alachlor, atrazine, chlorfenvinphos, diuron, isoproturon and pentachlorophenol) considered PS (priority substances) by the European Commission and dissolved in water at 50mg/L (or at maximum water solubility) have been degraded at pilot-plant scale using photo-Fenton and TiO2 photocatalysis driven by solar energy. Two different iron concentrations (2 and 55mg/L) and TiO2 at 200mg/L have been tested and discussed, using mainly TOC mineralisation for comparison of treatment effectiveness. Vibrio fischeri (Microtox®) toxicity assays were also employed for evaluating the photocatalytic treatments, and comparison between these results and parent compound disappearance, TOC evolution and anion (or ammonia) release were discussed. Almost complete mineralisation and total detoxification were always attained. It has been demonstrated that evolution of chloride could be a key-parameter for predicting toxicity of chlorinated compounds.
Keywords: Advanced oxidation treatment; Pesticide degradation; Photocatalysis; Photo-Fenton; Toxicity evolution; Wastewater treatment
Photocatalytic degradation of imazapyr in water: Comparison of activities of different supported and unsupported TiO2-based catalysts
by P. Pizarro; C. Guillard; N. Perol; J.-M. Herrmann (pp. 211-218).
Photocatalytic oxidation in aqueous phase of imazapyr, a systemic herbicide characterized by its high persistence and mobility in soils, has been investigated using two different titania photocatalysts: commercial Degussa P-25 and industrial Millennium PC-500. Despite potentially better textural and crystalline properties of PC-500, its photocatalytic activity is smaller than that of P-25 for that reaction. A less efficiency of PC-500 powders absorbing the irradiated photons, as well as a low substrate adsorption capacity, has been attributed as the main responsible for such behaviour. Variables such as concentration of imazapyr, amount of catalyst and the physical state of TiO2 (as a powder or deposited on an Ahlstrom paper) have been studied to elucidate their influence on the efficiency of the photocatalyzed degradation of imazapyr. It has been determined that both adsorption capacities of the catalyst and the reaction rates are strongly affected by the above mentioned parameters. They are even able to modify both the mechanism and kinetic order of the process, by affecting the interfacial substrateâ€“TiO2 interactions.
Keywords: TiO; 2; Kinetic; Mechanism; Imazapyr
Decomposition of diclofenac by solar driven photocatalysis at pilot plant scale
by L.A. Pérez-Estrada; M.I. Maldonado; W. Gernjak; A. Agüera; A.R. Fernández-Alba; M.M. Ballesteros; S. Malato (pp. 219-226).
Pilot plant experiments applying solar titanium dioxide photocatalysis and solar photo-Fenton treatment at different pH and iron concentrations with an initial diclofenac concentration of 50mgLâˆ’1 are described.In preliminary experiments absence of hydrolysis and slow photolysis under solar irradiation of diclofenac solutions were observed. Solar photo-Fenton treatment with freshly precipitated iron at pH around 7 showed first order kinetics, the reaction taking place on the surface of the iron precipitate. Simultaneous oxidation, precipitation and re-dissolution processes of diclofenac governed photo-Fenton decomposition kinetics at pH 2.8. The use of different iron concentrations (0.03â€“0.75mM) showed no influence on the reaction rate in a neutral medium due to reactor geometry. Similar behaviour (no influence of iron concentration) was observed at pH 2.8, due to precipitation problems. A pH of around 4, close to the p Ka of diclofenac, showed promising results, partly overcoming both iron and diclofenac precipitation. Solar titanium dioxide photocatalysis with Degussa P-25 followed first order kinetics and no precipitation or adsorption occurred.Decomposition of diclofenac took around 100min under all photo-Fenton treatment conditions employed. Decomposition by titanium dioxide photocatalysis took about 200min. In photo-Fenton treatment, hydrogen peroxide consumption to diclofenac decomposition was about 80â€“110mM at pH 2.8 and 40mM in the other two treatments (neutral pH and pH=4).
Keywords: Diclofenac; Non-steroidal anti-inflammatory drugs; Solar photocatalysis; Photo-Fenton; Advanced oxidation process; Wastewater treatment
Photocatalytic degradation of 2,4-dichlorophenol by TiO2/UV: Kinetics, actinometries and models
by B. Bayarri; J. Giménez; D. Curcó; S. Esplugas (pp. 227-236).
Heterogeneous photocatalysis has proved to be a useful tool for the degradation of water pollutants as it can be observed by the high number of references appeared the last 30 years. Despite this strong research, some points, as more satisfactory and accurate kinetic models, still have to be more developed. In this work, as reaction model, the photocatalytic treatment of 2,4-dichlorophenol has been studied by using TiO2 in suspension as catalyst. The influence of different variables (TiO2 concentration, pH effect, radiation) on the reaction rate has been tested. Afterwards, two new kinetic models are proposed. The first one takes into account the effect of intermediates in the degradation rate of the parent pollutant, which allows a better agreement for long time reactions. The second one attempts to include the radiation effect into the kinetic expression by means of a new term which refers to the absorbed light by the photocatalyst. Both models fit quite well with the experimental data and seem to be interesting future tools for the comparison and scaling-up of different photocatalytic systems.
Keywords: Photocatalysis; Radiation models; Reactor modelling; Pollutants treatment; Kinetic models
Microscopic characterization of the photocatalytic oxidation of oxalic acid adsorbed onto TiO2 by FTIR-ATR
by Cecilia B. Mendive; Detlef W. Bahnemann; Miguel A. Blesa (pp. 237-244).
Sequential FTIR-ATR spectra of an illuminated Degussa P-25 film deposited onto the ATR crystal were recorded to follow the photocatalytic oxidation of oxalic acid in acidic media. The results show that illumination ensues in the depletion of adsorbed oxalate from its equilibrium condition. The equilibrium spectral and thermodynamic data obtained previously from measurements in the dark were used to derive the time evolution, upon illumination, of the surface coverage of each of the three known surface complexes formed by oxalic acid adsorbed onto TiO2. The results demonstrate that the most stable species is also the most photo-labile one, and that the surface speciation is determined by a fast surface redistribution among the three species, without equilibration with the bulk solution. Thus, zero-order kinetics are observed at high degrees of coverage during the disappearance of the least stable species. At low concentrations, the disappearance of the most stable species is characterised by first-order kinetics.
Keywords: Surface phenomena; TiO; 2; Oxalic acid; Photocatalytic degradation
Enhanced photocatalytic degradation of maleic acid by Fe(III) adsorption onto the TiO2 surface
by Maria Isabel Franch; José A. Ayllón; José Peral; Xavier Domènech (pp. 245-252).
The role of Fe(III) on the TiO2-assisted photocatalytic degradation of maleic acid has been investigated. The study on the kinetics of the removal of organic matter, as well as the identification of all the stable mineralization intermediates, demonstrates that the presence of Fe(III), adsorbed onto the TiO2 surface, renders a more efficient process through a cleaner mineralization pathway compared to bare TiO2. Furthermore, the behaviour of the system does not depend on the iron source. On the other hand, the study of the Fe(III) influence on the interaction of maleic acid with TiO2 in the solid phase, by means of ATRâ€“FT-IR technique, has been performed. From all the reported results, it is concluded that the Fe(III) effects are mainly due to surface phenomena. The enhanced photocatalytic activity is interpreted under different perspectives, including adsorbed Feâ€“maleic complexes, enhanced adsorption of oxygen and lower geminate recombination yields.
Keywords: Photocatalysis; Maleic acid; Surface modification; Fe(III)
Oxalic acid destruction at high concentrations by combined heterogeneous photocatalysis and photo-Fenton processes
by Natalia Quici; María E. Morgada; Gabriela Piperata; Paola Babay; Raquel T. Gettar; Marta I. Litter (pp. 253-260).
Heterogeneous photocatalysis (HP) using UV/TiO2, photo-Fenton (PF) reaction using UV/Fe/H2O2 and the combination UV/TiO2/Fe/H2O2 (HPâ€“PF) were tested as processes to degrade oxalic acid (Ox) at relatively high concentrations (0.032M). PF reactions were generally more efficient than HP including the reaction in the absence of H2O2. Oppositely to previous results (e.g., with EDTA), HPâ€“PF combinations did not result, in the case of oxalate, better techniques for degradation than systems in the absence of TiO2. The kinetic behavior was not unique and two parameters were taken to evaluate the efficiency of each system: initial rates ( R0) and time to 95% of total mineralization (TOC95). Addition of hydrogen peroxide improves the initial HP reaction rate and reduces TOC95. Addition of Fe3+ also affects the reaction parameters but the effect of H2O2 seems to be higher, at least under the present conditions. When both H2O2 and iron were added simultaneously, the efficiency was higher. The optimal H2O2:Ox:Fe molar ratio was established and the results indicated that, at a fixed iron concentration, H2O2 increased R0 until a limit beyond which it did not cause any effect. No intermediates were formed in the reaction, oxalate being degraded directly to CO2. Analogies and differences with the EDTA system are presented.
Keywords: Oxalic acid; Heterogeneous photocatalysis; Advanced oxidation technologies
Role of Cu in the Cu-TiO2 photocatalytic degradation of dihydroxybenzenes
by J. Araña; C. Fernández Rodríguez; O. González Díaz; J.A. Herrera Melián; J. Pérez Peña (pp. 261-266).
The photocatalytic degradation of three dihydroxybenzenes (hydroquinone, catechol and resorcinol) by TiO2 and Cu-TiO2 has been studied. Degradation rates depend on the molecule catalyst surface interaction type. FTIR studies have shown that Cu presence modifies the organics interactions with the catalysts surface. Therefore, catalysts have shown different types of behaviour with each compound.Resorcinol interaction with Cu-TiO2 may produce a hydroxyphenolate thus reducing the number of activating centres in the aromatic ring. However, catechol interaction provides a catecholate bidentate which virtually deactivates the aromatic ring, hence reducing its degradation byOH radicals attacks. Hydroquinone interaction with Cu-TiO2 occurs by means of a hydrogen bond, while with TiO2 this interaction is established through the formation of a hydroxyphenolate monodentate. This justifies the improved catalytic behaviour of Cu-TiO2.Studies in presence of H2O2 have shown the existence of similar degradation mechanisms, but degradation rates have been notably higher.
Keywords: Photocatalysis; Cu-TiO; 2; Dihydroxybenzenes; TiO; 2
Evaluation of humic acid photocatalytic degradation by UVâ€“vis and fluorescence spectroscopy
by Ceyda Senem Uyguner; Miray Bekbolet (pp. 267-274).
Photodegradation of humic substances causes drastic changes in the UVâ€“vis absorption and fluorescence properties of humic acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of humic acids during photocatalytic oxidation processes and elucidate the effects observed on the molecular size distribution of humic acid focusing on their analysis by UVâ€“vis and fluorescence spectroscopy.As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of humic acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10kDa, UV254 absorbing moieties in treated humic acid samples become higher than that of raw humic acid designating the generation of new species during photocatalysis. UVâ€“vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated humic acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time.
Keywords: Photocatalytic degradation; Humic acid; Molecular size distribution; Fluorescence spectroscopy
Efficient photocatalysts by hydrothermal treatment of TiO2
by A.I. Kontos; I.M. Arabatzis; D.S. Tsoukleris; A.G. Kontos; M.C. Bernard; D.E. Petrakis; P. Falaras (pp. 275-281).
Mixed phase nanocrystalline TiO2 powders (anataseâ€“rutile) (Degussa P25) were prepared by hydrothermal modification. The preparation procedure took place at 200Â°C for 1â€“10 days in an autoclave system with water as the solvent. Thus, different degrees of modification were achieved. TiO2 water modified nanocrystalline thin films were immobilized on glass substrates by applying a doctor-blade's deposition technique. A variety of spectroscopic [UVâ€“vis reflectance, infra-red (IR), Raman, structural X-ray diffraction (XRD), N2 absorption (BET)] and microscopic [atomic force microscopy (AFM), scanning electron microscopy (SEM)] techniques were applied to characterize the modified films. A model textile industry pollutant (methyl orange) was used in order to evaluate the photocatalytic efficiency of the modified material. Our results show that the photocatalytic activity of the modified films is improved by a factor of 2 when we extend the hydrothermal treatment up from 1 to about 4 days in the autoclave system. Scratch tests revealed favorable interconnection of the titania nanoparticles as well as significantly higher adhesion to the glass substrate for the modified films, in comparison to the original P25 material.
Keywords: TiO; 2; nanocrystalline thin films; Hydrothermal treatment; AFM; Photocatalyst activity; Methyl orange; Adherence; Pollutant degradation
Synthesis of TiO2 particles by reverse microemulsion method using nonionic surfactants with different hydrophilic and hydrophobic group and their photocatalytic activity
by Man Sig Lee; Seong Soo Park; Gun-Dae Lee; Chang-Sik Ju; Seong-Soo Hong (pp. 283-290).
TiO2 nanoparticles were prepared using hydrolysis of titanium tetraisopropoxide in W/O microemulsions consisting of water, nonionic Brij series surfactants with different hydrophilic and Tween series surfactants with different hydrophobic group, and cyclohexane. The properties of these particles were characterized by TEM, XRD, FT-IR, TGA and DTA. The photocatalytic degradation of p-nitrophenol has been studied in order to compare the photocatalytic activity of prepared nanosized titania. TiO2 particles calcined at 500°C have a stable anatase phase which has no organic surfactants and the product completely transforms into the anatase phase above 300°C and the rutile phase begins to appear at 600°C regardless of surfactants. The particles are shown to have a spherical shape and have an uniform size distribution but the shape becomes distorted with a decrease of hydrophilic group chain length according to rapid hydrolysis of water and titanium alkoxide. In addition, the crystallite size and crystallinity increase with a decrease of hydrophilic and hydrophobic group chain length and an increase of calcination temperature. The photocatalytic activity increases with an increase of hydrophilic and hydrophobic group length and the titania calcined at 500°C shows the highest activity on the photocatalytic degradation of p-nitrophenol regardless of surfactants.
Keywords: Nanosized titania; Brij surfactant; Tween surfactant; Reverse micelle; Photocatalytic degradation of; p; -nitrophenol
Photocatalytic conversion of benzene to phenol using modified TiO2 and polyoxometalates
by Hyunwoong Park; Wonyong Choi (pp. 291-297).
The application of photocatalytic reactions to organic synthesis has attracted interests in view of the development of environmentally benign synthetic processes. This study investigated the effects of various parameters (electron acceptor, surface modification, and the combination of photocatalysts) on the direct synthesis of phenol from benzene using photocatalytic oxidation processes. The OH radicals generated on UV-illuminated TiO2 photocatalyst directly hydroxylate benzene to produce phenol, hydroquinone, and catechol. The addition of Fe3+, H2O2, or Fe3++H2O2 highly enhanced the phenol production yield and selectivity in TiO2 suspension. Surface modifications of TiO2 had significant influence on the phenol synthetic reaction. Depositing Pt nanoparticles on TiO2 (Pt/TiO2) markedly enhanced the yield and selectivity. Surface fluorination of TiO2 (F-TiO2) increased the phenol yield two-fold because of the enhanced production of mobile (free) OH radicals on F-TiO2. Polyoxometalate (POM) in phenol synthesis played the dual role both as a homogeneous photocatalyst and as a reversible electron acceptor in TiO2 suspension. POM alone was as efficient as TiO2 alone in the phenol production. In particular, the addition of POM to the TiO2 suspension increased the phenol yield from 2.6% to 11% (the highest yield obtained in this study). Reaction mechanisms for each photocatalytic system were discussed in relation to the phenol synthesis.
Keywords: Photocatalysis; Phenol synthesis; TiO; 2; Polyoxometalate; Environmentally benign reaction
Photocatalytic decomposition of 4-nitrophenol on Ti-containing MCM-41
by Yoon-Jeong Do; Jin-Ho Kim; Jin-Hwan Park; Seong-Soo Park; Seong-Soo Hong; Cha-Soo Suh; Gun-Dae Lee (pp. 299-305).
A series of Ti-containing MCM-41 samples, such as Ti-MCM-41 with variable Si/Ti ratios and Crâ€“Ti-substituted TiO2-loaded MCM-41 having different TiO2 loading, were prepared and studied for the photocatalytic decomposition of 4-nitrophenol in UV and visible light. The samples were characterized using surface area measurement, XRD, FT-IR, and UVâ€“vis DRS techniques. In the case of the Ti-MCM-41 samples with Si/Ti ratios higher than 20 which were found to have typical mesoporous structure, the framework incorporation of Ti into MCM-41 increased with decreasing Si/Ti ratio. On the contrary, the Ti-MCM-41 with lower Si/Ti ratio (Si/Ti=10) shows low structural integrity and the formation of Ti-oxide species, leading to a considerable decrease in surface area. In the case of Crâ€“Ti-substituted TiO2-loaded MCM-41 samples, significant absorption occurs in visible light and the absorption in both UV and visible region increases with increasing TiO2 loading. However, when the amount of TiO2 loaded on Crâ€“Ti-MCM-41 increased above 33wt.%, the absorption in visible light increased slightly. Thus, it seems that, at higher TiO2 loading, some TiO2 particles are not closely bound to the wall of Crâ€“Ti-MCM-41. The photocatalytic activities of Ti-containing MCM-41 samples were strongly influenced by the amount of Ti. Under UV illumination, the highest photocatalytic activity for photocatalytic decomposition of 4-NP was observed for the Ti-MCM-41 having Si/Ti ratio of 20. Among various Ti-containing MCM-41 materials prepared in this work, only Crâ€“Ti-substituted TiO2-loaded MCM-41 catalysts exhibited discernable photocatalytic activities in visible light, and their photocatalytic activities increased considerably with increasing TiO2 loading up to 33wt.%. Further increase in TiO2 loading enhanced photocatalytic activity slightly.
Keywords: Ti-containing MCM-41; Photocatalytic decomposition; 4-Nitrophenol; UV and visible light
Role of the support on the activity of silica-supported TiO2 photocatalysts: Structure of the TiO2/SBA-15 photocatalysts
by María-José López-Muñoz; Rafael van Grieken; José Aguado; Javier Marugán (pp. 307-314).
Immobilization of TiO2 on silica materials has been commonly proposed in order to make easier the separation of the catalyst after the photocatalytic reactions in aqueous systems. The main drawback of the supported photocatalysts is that they usually show lower activities in comparison with powdered TiO2 materials. The aim of this work is to elucidate the structure of some silica-supported TiO2 photocatalysts recently developed as well as to evaluate the role that the porous structure of the support can play in the observed photocatalytic activities. In comparison with the use of an amorphous silica support, the use of the mesostructured silica SBA-15 produces an ordered structure in which TiO2 crystals of similar sizes, independently of titania loading, are located inside the mesoporous channels of the support. The photocatalytic treatment of several cyanide-containing compounds is analyzed and the results are explained in terms of the structure of every catalyst. Depending on the model compound, the characteristic structure of the TiO2/SBA-15 materials allows increasing up to eight times the activity achieved by the Degussa P25 TiO2. The main conclusion of this work is the strong influence of the textural properties of the support on the catalytic activity of immobilized TiO2 photocatalysts.
Keywords: Photocatalysis; Silica-supported TiO; 2; Cyanides
Photocatalytic activity of Cu2O/TiO2, Bi2O3/TiO2 and ZnMn2O4/TiO2 heterojunctions
by Y. Bessekhouad; D. Robert; J.-V. Weber (pp. 315-321).
Cu2O/TiO2, Bi2O3/TiO2 and ZnMn2O4/TiO2 heterojunctions were studied for potential applications in water decontamination technology and their capacity to induce an oxidation process under VIS light. UVâ€“vis spectroscopy analysis showed that the junctions-based Cu2O, Bi2O3 and ZnMn2O4 are able to absorb a large part of visible light (respectively, up to 650, 460 and 1000nm). This fact was confirmed in the case of Cu2O/TiO2 and Bi2O3/TiO2 by photocatalytic experiments performed under visible light. A part of the charge recombination that can take place when both semiconductors are excited was observed when a photocatalytic experiment was performed under UVâ€“vis illumination. Orange II, 4-hydroxybenzoic and benzamide were used as pollutants in the experiment. Photoactivity of the junctions was found to be strongly dependent on the substrate. The different phenomena that were observed in each case are discussed.
Keywords: Titanium dioxide; Cu; 2; O; Bi; 2; O; 3; ZnMn; 2; O; 4; Heterojunction; Photocatalysis
Macroscopic carbon nanofibers for use as photocatalyst support
by Nicolas Keller; Guillaume Rebmann; Elodie Barraud; Orfan Zahraa; Valérie Keller (pp. 323-329).
To reduce the drawbacks related to the use of powders or immobilized catalysts in gas- and liquid-phase applications, a new material for the use as photocatalyst support was obtained by chemical vapor decomposition at 700Â°C of an ethaneâ€“hydrogen mixture over a woven glass microfiber supported nickel catalyst, consequently leading to carbon nanofibers with macroscopic shaping, consisting in woven glass microfibers supporting a dense network of entangled 40nm diameter carbon nanofibers. This material could be directly used after synthesis without any subsequent purification treatment due to the high yield and totally selective carbon nanofiber production. This shape memory design results in the direct use of the carbon nanofiberâ€“woven glass microfiber composite as support without any post-synthesis shaping. The presence of hydrophilic oxygenated groups located at the outer surface of the carbon nanofibers allowed the solâ€“gel preparation of a woven glass microfiberâ€“carbon nanofiber supported TiO2 (20wt.%) catalyst, using tetraisopropoxide as precursor. This new photocatalyst was totally stable under UV irradiation.
Keywords: Photocatalysis; Catalyst support; Carbon nanofiber; Morphology; Microstructure
Use of coaxial photocatalytic reactor (CAPHORE) in the TiO2 photo-assisted treatment of mixed E. coli and Bacillus sp. and bacterial community present in wastewater
by Angela-Guiovana Rincón; Cesar Pulgarin (pp. 331-344).
This paper reports the photocatalytic disinfection of water contaminated by a mixture of Escherichia coli and Bacillus sp. as well as that of wastewater containing a larger microbial community. The photocatalytic reactions were carried out in a coaxial photocatalytic reactor called CAPHORE, using TiO2 P-25 of Degussa. E. coli is more sensitive than Bacillus sp. to photocatalytic treatment. Bacterial inactivation was dependent on organic matter and dissolved oxygen (DO) concentration.Of the bacterial community present in partially treated wastewater, E. coli appears to be more sensitive to the treatment than Enterococcus sp., coliforms (other than E. coli), and Gram-negative (other than coliforms). After photocatalytic treatment, no bacterial recovery of previous groups was observed for 24h in the dark. However a very low bacterial inactivation rate was observed for the whole bacterial population present in wastewater and detected by non-selective media. The effective disinfection time (EDT), the time necessary for total inactivation of bacteria without re-growth in a subsequent dark period referenced at 24h (or 48h), was reached only for Enterococcus sp., and coliform groups. EDT24 was not reached for the whole population.
Keywords: Water disinfection; TiO; 2; Photocatalysis; Solar disinfection; UV-irradiation; E. coli; Bacillus; sp.; Entreococcos; sp.; Total coliform; EDT
Water disinfection by solar photocatalysis using compound parabolic collectors
by P. Fernández; J. Blanco; C. Sichel; S. Malato (pp. 345-352).
TiO2 solar photocatalysis has been proven to be a degradation process for aqueous organic contaminant leading to total mineralisation of a large number of compounds. Furthermore, the interest in using this technique for water disinfection has grown in the last decade. Recent publications have reported photokilling of bacteria and viruses by TiO2 photocatalysis. Therefore, solar photocatalysis disinfection seems to be a very promising process, which could help to improve public health in rural areas of developing countries.The objective of this work was to assess the feasibility of using TiO2 solar photocatalysis to disinfect water supplies for future applications in developing countries. This article reviews the viability of solar photocatalysis for disinfection in low cost compound parabolic collectors, using sunlight and titanium dioxide semiconductor, both applied as slurry and supported. We report on the bactericidal action of TiO2 on a pure culture of Escherichia coli with a low cost photoreactor based on compound parabolic collectors. The influence of different experimental set-ups and parameters are also analysed.The results and potential application of the solar photocatalysis technology to water disinfection are studied within the frame of two research EU projects whose objective consist on the development of a fully autonomous solar reactor system to purify drinking water in remote locations of developing countries.
Keywords: Compound parabolic collector (CPC); Solar photocatalysis; Disinfection; Titanium dioxide
The dependence on temperature of gas-phase photocatalytic oxidation of methyl tert-butyl ether and tert-butyl alcohol
by Sergei Preis; Anna Kachina; Nuria Capdet Santiago; Juha Kallas (pp. 353-358).
The influence of temperature on the mechanism and kinetics of gas-phase photocatalytic oxidation (PCO) and thermal oxidation (TO) of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA) over TiO2 was studied in a continuous flow annular reactor. The reaction products of PCO of both substances included acetone, water, carbon dioxide and carbon monoxide. Volatile TO products of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Thermal oxidation of MTBE became noticeable at 388K, TBA started to decompose thermally at 393K. Both PCO and TO fit well to the Langmuirâ€“Hinshelwood (Lâ€“H) model for monomolecular reactions. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation. The TiO2 catalyst showed no deactivation at temperatures above 373K but gradually lost its activity below 373K.
Keywords: Photocatalytic oxidation; Thermal oxidation; Methyl; tert; -butyl ether; tert; -Butyl alcohol; Titanium dioxide
Supported photosensitizers as new efficient materials for gas-phase photo-oxidation
by V. Latour; T. Pigot; P. Mocho; S. Blanc; S. Lacombe (pp. 359-367).
The photosensitised oxidation of dimethylsulfide in the gas phase was carried out for the first time on original silica materials in a flow reactor and under visible light irradiation. The photocatalysts were prepared either by physisorption of two different photosensitizers, 9,10-dicyanoanthracene or 9,10-anthraquinone on commercial silica beads, or by incorporation of 9,10-dicyanoanthracene in solâ€“gel monoliths. Oxidation products are mainly sulfoxide, sulfone and disulfide, and it is assumed that singlet oxygen is the most probable reactive oxygen species.These materials display several advantages as they are activated by visible light, and they act as very efficient traps for partially oxidized products. Accordingly, the gas-flow at the outlet of the photocatalytic device is free of any toxic or nauseous product for several days. As soon as products appear in the gas flow, the catalyst is deactivated, but the silica beads can be easily regenerated by mild thermal treatment under controlled conditions.With regard to the photo-oxidative efficiency, our results point out the influence of the properties of the silica support itself, such as transparency, homogeneity and specific surface area. The adsorption capacity of the material is a crucial parameter, as the most DMS adsorbing material is also the most efficient.
Keywords: Alkylsulfide; Photo-oxidation; Photosensitization; Gasâ€“solid reactions; Supported photocatalysts
Iron(II)-catalyzed enhancement of ultrasonic-induced degradation of diethylstilbestrol (DES)
by N. Ben Abderrazik; A. Azmani; C. Râ€™kiek; Weihua Song; Kevin E. O'Shea (pp. 369-373).
The oxidation of the endocrine disruptor, diethylstilbestrol (DES) in aqueous media by ultrasound is significantly enhanced by Fe(II) catalyst. The observed enhancement is likely the result of increased levels of hydroxyl radicals from the iron-promoted reduction of the hydrogen peroxide produced during ultrasonic irradiation. The degradation is effective over a range of concentrations and is consistent with pseudo first-order kinetics. Relatively high concentrations of hydrogen peroxide, âˆ¼450mM, are present in solution under our experimental conditions after 1h of ultrasonic irradiation (665kHz). The concentration of H2O2 in solution decreased with the addition of Fe(II) along with an increase in the degradation of DES. Hydrogen peroxide alone does not appreciably degrade DES. Our results demonstrate ultrasonic-induced degradation of DES can be accelerated with the addition of Fe(II). The combination of ultrasonic irradiation and Fe(II)-promoted conversion of H2O2 to hydroxyl radical may provide a valuable strategy for the treatment of organic pollutants.
Keywords: Diethylstilbestrol; Ultrasound; Advanced oxidation; Catalysis; Hydroxyl radicals
Supported Fe/C and Fe/Nafion/C catalysts for the photo-Fenton degradation of Orange II under solar irradiation
by Damien Gumy; Pilar Fernández-Ibáñez; Sixto Malato; Cesar Pulgarin; Octav Enea; John Kiwi (pp. 375-382).
The physicochemical properties and photocatalytic behavior of Fe/C and Fe/Nafion/C fabrics have been investigated under laboratory conditions (small vial, artificial light) and in large-scale photo-reactors under sunlight to achieve low-cost decontamination of textile and agro-chemical industry effluent wastewater. Fe-ions deposited onto chemically treated C fabrics or encapsulated in Nafion thin films cast directly onto the carbon fabrics are efficient in decomposing H2O2 used as an oxidant in the photo-assisted abatement of non-biodegradable azo-dyes used in textiles. The Orange II taken as a model pollutant quickly fades under solar irradiation even at an initial pH 6. This range of pH is not possible with the homogeneous photo-Fenton process. In contrast, the use of supported catalysts on C fabrics allows the costly pH adjustment to be avoided. This makes catalyst recovery and economical decontamination of wastewater containing non-biodegradable pollutants possible.
Keywords: Photo-Fenton; Solar photo-reactor; Compound parabolic collector (CPC); Flat-type reactor; Orange II
Synthesis, loading control and preliminary tests of 2,4,6-triphenylpyrylium supported onto Y-zeolite as solar photocatalyst
by Ana M. Amat; Antonio Arques; Stefan H. Bossmann; André M. Braun; Miguel A. Miranda; Rosa F. Vercher (pp. 383-388).
A heterogeneous photocatalyst has been obtained by hosting the 2,4,6-triphenylpyrylium cation inside the supercages of Y-zeolite. Preparation of the new material has been achieved by means of a formal ion exchange in aqueous medium. Nevertheless, the mechanism is more complex, as bulky 2,4,6-triphenylpyrylium cation is unable to diffuse through the channels of Y-zeolite. The following steps are involved: (a) hydrolytic opening of the pyrylium ion to give a linear diketone; (b) diffusion of the diketone through the channels to reach the supercages; and (c) thermal recyclization under dehydrating conditions. Elemental analysis of the new material was consistent with the pyrylium cation located inside the zeolite. No sulfur was found in the loaded zeolite, indicating that hydrogensulfate is no longer the counter-ion of pyrylium. Accordingly, the stoichiometric amount of Na+ was found in the filtered waters recovered after the synthesis. Besides, the IR spectrum of the dry material was coincident with that of 2,4,6-triphenylpyrylium, while the spectrum of a less thoroughly dried sample showed, together with the absorption bands corresponding to pyrylium, other bands assignable to the diketone. Zeolite loading can be controlled in the range of 3â€“15% of organic carbon. The performance of the new material as a solar photocatalyst for oxidative pollutant degradation was checked using four cinnamic acid derivatives as target compounds. Aqueous solutions (250mL) of these model pollutants (0.001M) were irradiated by solar light in the presence of different amounts of solid photocatalyst. Oxidation was efficiently achieved as analysed by HPLC and followed in all cases a pseudo first order kinetics. The most satisfactory results were obtained using 1g/L of Y-zeolite containing 6% of 2,4,6-triphenylpyrylium cation.
Keywords: Pyrylium salts; Photocalysis; Phenolic pollutants; Heterogeneous catalysis; Zeolites; Synthetic methods; Solar irradiation
Vis and UV photocatalytic detoxification methods (using TiO2, TiO2/H2O2, TiO2/O3, TiO2/S2O82âˆ’, O3, H2O2, S2O82âˆ’, Fe3+/H2O2 and Fe3+/H2O2/C2O42âˆ’) for dyes treatment
by Joaquín R. Domínguez; Jesús Beltrán; Oscar Rodríguez (pp. 389-395).
The degradation of Acid Red 88 azo dye in water was investigated in laboratory-scale experiments using 21 oxidation processes. Colour, COD and TOC removals were evaluated for each oxidation system. The processes were studied in three groups: processes deriving from the heterogeneous photocatalysis (using TiO2), oxidation systems based on Fenton-type reactions (homogeneous photocatalysis) and processes based on the application of ozone (ozone catalysis). The results obtained showed that the decolourization rate was quite different for each oxidation process. After 15min reaction time the relative decolourization order established was: H2O2=vis2O2/Fe3+/vis2/H2O2/vis=TiO2/vis2O82âˆ’2O2/Fe3+/C2O42âˆ’/vis2O2/UV2O2/Fe3+/UV2/S2O82âˆ’/UV2/UV=TiO2/H2O2/UV33/H2O23/H2O2/UV3/UV=O3/vis3/H2O2/UV/Fe3+3/TiO2/vis3/TiO2. Nevertheless, taking into account the mineralization of the compound (measured as TOC and COD removal) at the end of the experiment, the order was slightly different. For example, the photo-Fenton-ozone process (O3/H2O2/UV/Fe3+) seems to be more appropriate than O3/TiO2. Also, in a kinetic study, the pseudo-first-order kinetic rate was determined for each oxidation system. This overall constant was split up into two components: direct oxidation by irradiation (photolysis) and oxidation by free radicals (mainly HO).
Keywords: Advanced oxidation processes; Titanium dioxide; Ozone; Azo dye; Acid Red 88; Photo-Fenton
Photo-electro-chemical properties of TiO2 mediated by the enzyme glucose oxidase
by Rossano Amadelli; Alessandra Molinari; Irene Vitali; Luca Samiolo; Giovanni Maria Mura; Andrea Maldotti (pp. 397-405).
Electrochemical measurements show that the enzyme glucose oxidase (GO) is adsorbed on the surface of TiO2 without apparently changing the flat band potential of the semiconductor, indicating that it does not cause a change of the energy of conduction band electrons. On the other hand, it is observed that GO markedly increases the efficiency of the two electron reduction of O2 to H2O2 which is accumulated in the solution phase.ESR spin trapping investigations indicate that GO favors the formation of OH radicals, due to either the inhibition of charge recombination processes or to H2O2 reduction by conduction band electrons. Accordingly, photo-oxidation of different alcohols to the corresponding radical species is also enhanced in the presence of GO.The photo-oxidation of 1,2-propandiol on TiO2/GO is regioselective in that (i) partial oxidation to hydroxyacetone is observed and (ii) no mineralization (full combustion to CO2) of the substrate occurs. These facts are of particular interest in the field of studies concerning the design of new photocatalytic systems with enhanced activity and controllable oxidative power.
Keywords: Radicals; TiO; 2; Glucose oxidase