Photocatalytic Oxidation Process Research Articles

Adsorbent as an essential participant in photocatalytic processes of water and air purification: Computer simulation study

The influence of adsorbent on the kinetics of (photo)catalytic oxidation processes was studied using the simple single and double stage reaction mechanisms with the adsorption stages corresponding to Langmuir model. It was found that in the static reactor in all cases the usage of adsorbent leads to the prolongation of substrate ( A) removal and product ( P) accumulation kinetic curves but the substrate concentration becomes lower during almost all (photo)catalytic process. Fitting of experimental data points of acetone photocatalytic oxidation reaction demonstrated a good correlation with proposed reaction mechanism. Calculated adsorption constants values are close to those reported in literature. The using of adsorbent in flowing conditions leads to the decrease of maximum outlet substrate concentration in the case if the inlet substrate concentration is too high to be oxidized completely for one run. Kinetics simulation in the case of (photo)catalytic reaction with intermediate demonstrates that adsorbent could accumulate additional intermediate quantity thus keeping catalyst surface more active and contributing to faster substrate ( A) removal.

Liquid phase heterogeneous photocatalytic ozonation of phenol in liquid–solid fluidized bed: Simplified kinetic modeling

The isotherms of original AC (activated carbon) and photocatalysts (TiO 2-AC) calcined at 500 °C for phenol were measured. The results showed a reversible adsorption of phenol onto both kinds of particles at 25 °C, and could be fitted well to the Freundlich adsorption equation for the dilute solution. Five oxidation processes, namely O 3, O 3/UV, O 3/UV/AC, O 2/UV/TiO 2 and O 3/UV/TiO 2, for phenol degradation in fluidized bed were evaluated and compared, and the photocatalytic ozonation was found to give the highest phenol conversion because of the combined actions of homogenous ozonation in the liquid phase, heterogeneous ozonation on the surface of the catalyst support, i.e. activated carbon, and heterogeneous photocatalytic oxidation on the TiO 2 catalyst surface. With the simplified kinetic model, photolytic ozonation was confirmed to predominantly take place on the particle surface in comparison with the heterogeneous and homogeneous photolytic ozonation. Additionally, the heterogeneous photocatalytic oxidation constant was found to be enhanced by 3.73 times in photocatlaytic ozonation process with ozone as the scavenger compared to the photocatalytic oxidation process with oxygen as the scavenger.

A Study of the Photocatalytic Oxidation of Humic Acid on Anatase and Mixed-phase Anatase–Rutile TiO2 Nanoparticles

In this study, slurry photocatalytic oxidation process was investigated for natural organic matter removal from aqueous humic acid solutions by using different titanium dioxide (TiO2) under UV-A irradiation. Bench scale experimental studies were conducted at different humic acid concentration at the range of 10–50 mg/L and different pH. Anatase and mixed-phase anatase–rutile TiO2 nano particles used in the photocatalytic reactor. The results were evaluated in terms of the parameters that are specific to organic matter content such as dissolved organic carbon concentration, ultraviolet absorbance at 254 nm (UV254), specific ultaviolet absorbance at 254 nm, and color (VIS400). It was observed that increasing humic acid concentration decreases photocatalytic degradation efficiency. The reactivity of the mixed-phase anatase–rutile (Degussa P-25) TiO2 was greater than individual anatase particles and the highest efficiency was observed at pH 3 for anatase TiO2.

Ruthenium(II)-tris-bipyridine/titanium dioxide codoped zeolite Y photocatalyst: Performance optimization using 2,4-xylidine (1-amino-2,4-dimethyl-benzene)

The heterogeneous photocatalysts of the ruthenium(II)-tris-bipyridine/titanium dioxide/zeolite Y ([Ru(bpy) 3] 2+/TiO 2/zeolite Y) family perform in a manner very similar to a “Fenton-catalyst” in the oxidative degradation of the model pollutant 2,4-xylidine (1-amino-2,4-dimethyl-benzene). Upon photoexcitation using visible light, an electron-transfer reaction to hydrogen peroxide is observed. The oxidation rate of 2,4-xylidine follows a distinct percolation behavior, which is dependent on the amount of titanium dioxide incorporated as nanoparticles into the zeolite Y's framework. The maximum of the photocatalytic degradation of 2,4-xylidine at pH 3.0 was found to be at 34.5 ± 0.5% TiO 2 per weight. The optimization of the performance parameters of this particular [Ru(bpy) 3] 2+/TiO 2/zeolite Y photocatalyst was undertaken in a pilot reactor ( V = 3.25 L), equipped with a medium pressure mercury lamp (TQ 718). Important factors in the apparent photocatalytic efficiency have been determined: (a) the availability of dissolved oxygen, (b) the substrate concentration and (c) the concentration of the dispersed photocatalyst. At higher starting concentrations of 2,4-xylidine (>200 mg C L −1), the photocatalytic oxidation process is hampered by parasitic light absorption by an azo-dye formed and, especially, by competitive adsorption of hydrogen peroxide and 2,4-xylidine at the nanoscopic TiO 2-centers. It is noteworthy that 2,4-dimethylphenol and oxalic acid were the main reaction products, when 200 mg C L −1 of 2,4-xylidine were oxidatively degraded, whereas a multitude of reaction intermediates were detected when the starting concentration of 2,4-xylidine was 500 mg C L −1. Evidence is given that hydroxylamine is formed during the oxidation of 2,4-xylidine, which subsequently is either reduced to ammonium or generated from the disproportionation of hydroxylamine to ammonium and nitrogen. In the discussion section of this report, the observed reaction behavior is rationalized, based on the elementary chemical reactions occurring in the irradiated heterogeneous reaction mixture.

Granular-activated carbon adsorption followed by annular-type photocatalytic system for control of indoor aromatic compounds

An adsorbent coupled with other control devices may enhance the removal of various indoor pollutants, including indoor benzene, toluene, ethyl benzene, and xylene (BTEX). In addition, the regeneration of adsorbent is subsequently required for reusing and lowering disposal cost. Accordingly, this study investigated the technical feasibility of an activated carbon (AC)–photocatalytic oxidation (PCO) hybrid system connected in series for AC regenerations as well as for controls of indoor air levels of BTEX. The hybrid system presented higher removal efficiencies (close to 100%) compared to the AC unit alone. Unlike the AC unit alone, the relative humidity or inlet concentration dependence was insignificant for the hybrid system. The desorption efficiency of the AC unit was between 75 and 94% for the desorption temperature of 300 °C. PCO efficiencies of BTEX desorbed from the AC unit represented relatively high degradation efficiencies for low loadings ≤5000 ng (above 70%). An elevated CO concentration by PCO processes was a negligible addition to indoor CO levels. The hybrid system could enhance control efficiency of BTEX in indoor air levels compared with AC adsorption alone, without a significant CO generation. Under certain conditions, the PCO unit located downstream from the adsorbent unit could effectively be employed for AC regeneration.

Photocatalytic treatment of IGCC power station effluents in a UV-pilot plant

The aim of this work is to improve the quality of water effluents coming from an Integrated Gasification Combined Cycle (IGCC) power station to meet with future environmental legislation. This study has been made using an homogeneous photocatalytic oxidation process (UV/Fe(II)/H 2O 2) in a pilot plant. The efficiency of the process was determined from the analysis of the following parameters: cyanides, formates and TOC content. In the first stage, a factorial experimental design allowed to determine the influence of operation variables (initial concentration of H 2O 2 and Fe(II), pH and temperature) on the degradation kinetics. pH was always kept in a value >9.5 during cyanides destruction to avoid gaseous HCN formation and lowered later to enhance formates degradation. Experimental kinetic constants were fitted using neural networks (NNs). Under the optimum conditions ([H 2O 2] = 1700 ppm, [Fe(II)] = 2 ppm, pH 2 after cyanides destruction, and T = 30 °C), it is possible to degrade 100% of cyanides in 15 min and 76% of formates in 120 min. The use of an homogeneous process with UV light can offer an economical and practical alternative to heterogeneous photocatalysis for the destruction of environmental pollutants present in thermoelectric power stations effluents, since it can treat very high flowrates using a lower H 2O 2 concentration. Furthermore, it does not require additional operations to recover the solid catalyst and regenerate it due to deactivation as occurs in heterogeneous catalysis.

TiO2 Photocatalysis of Natural Organic Matter in Surface Water: Impact on Trihalomethane and Haloacetic Acid Formation Potential

In this study, changes in the physical and structural properties of natural organic matter (NOM) during titanium dioxide photocatalytic oxidation process were investigated using several complementary analytical techniques. Potential of the treated water to form trihalomethanes (THMs) and haloacetic acids (HAAs) was also studied. High-performance size exclusion chromatography analysis showed that NOM with apparent molecular weights of 1-4 kDa were preferentially degraded, leading to the formation of lower molecular weight organic compounds. Resin fractionation of the treated water demonstrated that the photocatalytic oxidation changed the affinity of the bulk organic character from predominantly hydrophobic to more hydrophilic. Short chain aldehydes and ketones were identified by mass spectroscopy as one of the key degradation products. The addition of hydrogen peroxide to photocatalysis was found to increase the degradation kinetics but did not affect the reaction pathway, thus producing similar degradation end products. The amount of THMs normalized per dissolved organic carbon (specific THM) formed upon chlorination of NOM treated with photocatalytic oxidation was reduced from 56 to 10 microg/mg. In contrast, the specific HAAs formation potential of the treated water remained relatively unchanged from the initial value of 38 microg/mg, which could be due to the presence of hydrophilic precursor compounds that were formed as a result of the photocatalytic oxidation process.

Influence of Metals and Reduced Oxygen Species on the Photooxidation of 2‐Propanol with a Cesium Peroxidotitanate Complex

AbstractThe mechanism of the photocatalytic degradation of 2‐propanol under anaerobic condition was investigated in the presence of the novel cesium peroxoidotitanate complex Cs2(NH4)6[Ti4(O2)4(Hcit)2(cit)2]Cl2·8H2O (1) (cit = citrate). This complex contains two different kinds of peroxido units. Two peroxido groups bind to the titanium atom in a side‐on η2‐fashion, the other peroxido units are directly bonded to the titanium and cesium atoms. These bridging peroxido groups are responsible for the inhibited activity in the photooxidation in contrast to what was found in previous studies about unbridged peroxidotitanate complexes. The decelerated oxidation of the alcohol is useful for the determination of the mechanism during the photocatalytic oxidation process. Therefore, ESI mass spectrometry and 13C NMR spectroscopy were applied to obtain a deeper insight into the mechanism in the alcohol oxidation. Furthermore, an influence of the metal salt (Cs vs. Li) with respect of the photocatalysis was detected. The cesium peroxido complex 1 shows significant results in the photochemical oxidation of 2‐propanol to acetone. More than 50 % acetone was obtained without detection of any side products. The conversion yield from 2‐propanol to acetone was monitored by 1H and 13C NMR spectroscopy and by Raman spectroscopy. The catalytic activity is not limited to 2‐propanol; 1‐phenylethanol could also be oxidized by 1. An intermediate of the photooxidation could be isolated and was characterized. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

운전조건에 따른 O3/UV, TiO2/UV 및 O3/TiO2/UV 시스템의 BTEX 증기처리에 관한 비교 연구

A multilayer tower-type photoreactor, in which <TEX>$TiO_2$</TEX>-coated glass-tubes were installed, was used to measure the vapor-phase BTEX removal efficiencies by ozone oxidation (<TEX>$O_3$</TEX>/UV), photocatalytic oxidation (<TEX>$TiO_2$</TEX>/UV) and the combination of ozone and photocatalytic oxidation (<TEX>$O_3/TiO_2$</TEX>/UV) process, respectively. The experiments were conducted under various relative humidities, temperatures, ozone concentrations, gas flow rates and BTEX concentrations. As a result, the BTEX removal efficiency and the oxidation rate by <TEX>$O_3/TiO_2$</TEX>/UV system were highest, compared to <TEX>$O_3$</TEX>/UV and <TEX>$TiO_2$</TEX>/UV system. The <TEX>$O_3/TiO_2$</TEX>/UV system accelerated the low oxidation rate of low-concentration organic compounds and removed organic compounds to a large extent in a fixed volume of reactor in a short time. Therefore, <TEX>$O_3/TiO_2$</TEX>/UV system as a superimposed oxidation technology was developed to efficiently and economically treat refractory VOCs. Also, this study demonstrated feasibility of a technology to scale up a photoreactor from lab-scale to pilot-scale, which uses (i) a separated light-source chamber and a light distribution system, (ii) catalyst fixing to glass-tube media, and (iii) unit connection in series and/or parallel. The experimental results from <TEX>$O_3/TiO_2$</TEX>/UV system showed that (i) the highest BTEX removal efficiencies were obtained under relative humidity ranging from 50 to 55% and temperature ranging from 40 to <TEX>$50^{\circ}C$</TEX>, and (ii) the removal efficiencies linearly increased with ozone dosage and decreased with gas flow rate. When applying Langmuir-Hinshelwood model to <TEX>$TiO_2$</TEX>/UV and <TEX>$O_3/TiO_2$</TEX>/UV system, reaction rate constant for <TEX>$O_3/TiO_2$</TEX>/UV system was larger than that for <TEX>$TiO_2$</TEX>/UV system, however, it was found that adsorption constant for <TEX>$O_3/TiO_2$</TEX>/UV system was smaller than that for <TEX>$TiO_2$</TEX>/UV system due to competitive adsorption between organics and ozone.

A review on UV/TiO2 photocatalytic oxidation process (Journal Review)

Advanced oxidation processes (AOPs) with UV irradiation and photocatalyst titanium dioxide (TiO2) are gaining growing acceptance as an effective wastewater treatment method. A comprehensive review of the UV-TiO2 photocatalytic oxidation process was conducted with an insight into the mechanism involved, catalyst TiO2, irradiation sources, types of reactors, comparison between effective modes of TiO2 application as immobilized on surface or as suspension, and photocatalytic hybrid membrane system. Photocatalytic degradation technique with titanium dioxide is generally applied for treating wastewater containing organic contaminants due to its ability to achieve complete mineralization of the organic contaminants under mild conditions such as ambient temperature and ambient pressure. Recently, photocatalysis studies using TiO2 have been gaining attention for the degradation of persistent organic pollutants and other organic chemicals which are known to be endocrine disruptors. Treatment of wastewater in a titanium dioxide-suspended slurry reactor has been widely utilized due to its simplicity and enhanced degradation efficiency. However, this system requires separation of TiO2 from water after the photocatalytic process. The final section of the manuscript focuses on the removal of TiO2 using a membrane hybrid system. A two-stage coagulation and sedimentation process coupled with microfiltration hollow-fibre membrane process was found to achieve complete removal of TiO2, and the recovered TiO2 can be reused for a photocatalytic process after regeneration.

Influence of relative humidity on the photocatalytic oxidation (PCO) of toluene by TiO2 loaded on activated carbon fibers: PCO rate and intermediates accumulation

Photocatalytic oxidation (PCO) tests were carried out for toluene adsorbed on the activated carbon fibers (ACFs)-supported TiO2 photocatalyst in an environmental condition controlled chamber. TiO2/ACF catalyst was made and characterized by N2 adsorption isotherm for pore structure and scanning electron microscopy (SEM) for morphology, respectively. Through exploring the remnant of toluene and the accumulation of intermediates on the TiO2/ACF catalyst including species, amount and their change processes under different relative humidity (RH), this study aimed to explore the influence of RH on the PCO of toluene and the roles of water vapor in the PCO process: PCO reaction paths and the accumulation of intermediates on the TiO2/ACF catalyst. Results showed that (1) with the increase of RH in the chamber (15%, 30%, 45% and 60%) the PCO conversion rate of toluene was positive correlated and no catalyst deactivation was observed under all RH levels; (2) during the gas–solid PCO process of toluene, byproducts of aromatic ring oxidation including 2-methyl, p-benzoquinone and o(m, p)-cresol were observed on the TiO2/ACF catalyst which had not been reported, together with the intermediates of side chain oxidation including benzyl alcohol, benzaldehyde and benzoic acid which had been reported; (3) although benzaldehyde was the primary intermediate under all RH level, amounts of the byproducts of aromatic ring oxidation were increased with the increase of RH; and (4) elevated RH increased the accumulation of benzyl alcohol but assuredly decreased the accumulation of benzaldehyde. These results suggested that (1) RH affects both the PCO rate and the PCO reaction path of toluene; (2) although methyl group oxidation is the major path, aromatic ring oxidation, which is not the expected path for the PCO of toluene, is enhanced when the RH increases; (3) apart from the role of hydroxyl radical (OH) produced from water by TiO2, water molecule also directly takes part in the PCO process. A hypothesis has been suggested: transition species comprised of benzaldehyde, hydroxyl and water molecule exists in the PCO conversion process from benzaldehyde to benzoic acid, though the hypothesis has not been confirmed.

Sonochemical and sonophotocatalytic degradation of malachite green: The effect of carbon tetrachloride on reaction rates

A comparative study between the sonolytic, photocatalytic and sonophotocatalytic oxidation processes of aqueous solutions of malachite green was carried out in the presence of carbon tetrachloride, under a low power ultrasonic field (<15W) and using titanium dioxide as a photocatalyst. The effect of a number of parameters such as ultrasonic intensity, TiO2 crystalline structure and the presence of CCl4 were studied using an inexpensive reactor. Enhanced rates of sonolytic degradation of malachite green in the presence of CCl4 were demonstrated. On the other hand, the simultaneous use of sonolysis and photocatalysis in the presence of CCl4 does not improve the degradation rate of malachite green in comparison with the one obtained using only sonolysis, but it makes possible a faster oxidative degradation of some reaction intermediaries. Finally, in air saturated solutions both processes, the sonolytic and the photocatalytic one, follow a first-order rate law.

Comparison study of dyestuff wastewater treatment by the coupled photocatalytic oxidation and biofilm process

Abstract Degradation of Rhodamine B (RhB) and COD by means of the coupled photocatalytic oxidation (PCO) and biofilm systems has been studied. The coupled PCO-biofilm systems were divided into two operation systems. The one (R1) consisted of a pre-PCO and a post-biofilm reactor system and the other (R2) was a pre-biofilm and a post-PCO reactor system. In a batch experiment, the order of initial decolorization rate was photocatalytic oxidation > adsorption > photolysis. The color removal rate of RhB was decreased with an increase of the initial COD concentration. In a continuous experimental study, almost all color was removed in the PCO reactor. During 180 days, the color and COD removal efficiencies in the R2 (pre-biofilm + post-PCO) system were higher than those in the R1 (pre-PCO + post-biofilm) system. In our experimental ranges, the PCO process was superior to Fenton oxidation in the color and COD removal.

Development and evaluation of an alternative method for municipal wastewater treatment using homogeneous photocatalysis and constructed wetlands

Wastewater collection and treatment is an important parameter of sustainable development. In Mediterranean region especially, the design and operation of competitive wastewater treatment systems for small communities and touristic facilities is a challenge to wastewater engineers. Within this context an alternative method of wastewater treatment has been developed that is based on solar photocatalytic oxidation and natural processes. The system combines the synergetic action of the homogeneous photocatalytic oxidation with the surface flow constructed wetlands in order to utilize the high solar irradiation and the ability of the constructed wetlands to improve water quality through natural processes. Aim of this work is to present the design, development, and experimental evaluation of the combined system. Experiments were conducted at laboratory scale using artificial as well as solar irradiation, for the treatment of both synthetic and cesspool wastewater. The data evaluation revealed that the combined system may effectively reduce the organic load and nutrients of wastewater, even in cases of great inflow variability, in terms of hydraulic and organic load, and thus may be proven a promising, competitive and environmental friendly solution for wastewater treatment in the near future.

Efficient Visible Light Degradation of Rhodamine B by a Photo-Electrochemical Process Based on a Bi2WO6 Nanoplate Film Electrode

In this paper, a Bi2WO6 nanoplate film electrode was prepared by a hydrothermal method, combined with a spin coating technique. A photoelectrochemical (PEC) oxidation system based on this electrode was then constructed to degrade rhodamine B (RhB) in aqueous solution under visible light (λ > 420 nm). The PEC system based on Bi2WO6 nanoplate film electrode could degrade 87.2% of RhB with concentration of 5 mg/L in 120 min, operated at low voltage and under visible light irradiation, whereas only 36.8% and 39.5% degradation of RhB were observed for electro-oxidation process (EC) and photocatalytic oxidation process (PC), respectively, operated under the same condition. These results revealed a significant synergetic effect on degrading RhB via electro-oxidation and photocatalysis under visible light irradiation. A possible mechanism for this synergetic degradation of RhB was proposed on the basis of characterization results. Meanwhile, the degradation pathway of RhB during PEC under visible light irradiatio...

Decomposition of gas-phase toluene by the combination of ozone and photocatalytic oxidation process (TiO2/UV, TiO2/UV/O3, and UV/O3)

The gas-phase toluene removal efficiencies by photocatalytic oxidation (TiO2/UV), the combination of ozone and photocatalytic oxidation (TiO2/UV/O3), and the UV/O3 reaction were tested using a quartz tube photoreactor. The experiments were conducted under various ozone concentrations (3.3–15ppm), toluene concentrations (1–9ppm), relative humidity (5–80%), and gas flow rates (200–1200mL/min). The toluene oxidation rates (TORs) of TiO2/UV/O3, and UV/O3 reactions were proportional to the ozone concentrations. The TORs of TiO2/UV, TiO2/UV/O3, and UV/O3 reactions increased with toluene concentration. However, there were negative correlations between the toluene removal efficiencies of these three kinds of reactions and the toluene concentrations. The order of the TORs and the CO2 yield rates of these three reactions were TiO2/UV/O3>TiO2/UV>UV/O3. The kinetics of TiO2/UV, and TiO2/UV/O3 reactions fit the Langmuir–Hinshelwood rate form. The rate constants (k) and Langmuir adsorption constants (K) are as follows: TiO2/UV: k=0.0102ppmm/s, K=0.146ppm−1; TiO2/UV/O3: k=0.0268ppmm/s, K=0.0796ppm−1. The reciprocal of UV/O3 reaction rate showed a positive linear relationship with the reciprocals of humidity and of toluene concentration. Ozone, also an air pollutant, was removed in the TiO2/UV/O3, and UV/O3 reactions. The ozone removal efficiency of TiO2/UV/O3 reaction in the presence and absence of toluene ranged from 61.1 to 99.5% and 38.1 to 95.1%, respectively.

Treatment of wastewater containing Cu(II)-EDTA using immobilized TiO2/solar light

The photocatalytic oxidation (PCO) of Cu(II)-ethylene diamine tetra-acetic acid (EDTA), employing immobilized TiO2, under natural sunlight rather than artificial UV light conditions, was investigated at a latitude 38°. The immobilized TiO2 film was prepared using a sol gel process, the crystalline structure of which was identified, by X-ray diffraction analysis, as a mixture of the rutile and anatase forms. The PCO of Cu(II)-EDTA was examined in a circulating reactor with 20 L of 10− 4 M Cu(II)-EDTA and synthetic and real wastewaters at pH 4 and 6.5, respectively. The removals of both Cu(II) and DOC were initially relatively rapid, but slowed as the reaction proceeded and generally followed first-order kinetics. The rate constants for the removal of Cu(II) and DOC were 1.1 × 10− 3 and 1.6 × 10− 3 min− 1, respectively. The efficiency of the PCO in the decomplexation of Cu(II)-EDTA increased with increasing H2O2 dose using both the synthetic and real wastewaters. Therefore, we suggest the PCO process using the solar/immobilized TiO2 system, with addition of H2O2 as well as filtration for the removal of suspended solids, can be effectively applied to the treatment of Cu(II)-EDTA containing real wastewater.

Sonophotocatalytic degradation of congo red and methyl orange in the presence of TiO2 as a catalyst

A comparative study between the photocatalytic and sonophotocatalytic oxidation process of congo red was carried out using titanium dioxide as a catalyst. The effect of a number of parameters, such as the initial concentration of dye, the presence of oxygen and ultrasound, the TiO2 crystalline structure and the amount of TiO2, was studied using an inexpensive reactor. In the second part of this document, the oxidation and reduction processes of methyl orange was studied using the same reactor, but by changing the chemical environment in order to drive either the oxidation or the reduction reaction. The results showed, for all the cases studied, a sinergistic effect between sonolysis and photocatalysis when an ultrasonic bath of 80W was used as a source of ultrasound. On the other hand, the electrochemical experiments showed that the current densities for the oxidation process of the azodyes were higher when a conducting glass electrode covered with a thin film of TiO2 was used as a working electrode instead of a platinum electrode, showing that the TiO2 electrode is not passivated by the oxidation reaction.

Photocatalytic degradation of pollutants from Elcogas IGCC power station effluents

The aim of this work is to improve the quality of water effluents coming from Elcogas IGCC power station (Puertollano, Spain) with the purpose of fulfilling future more demanding normative, using heterogeneous photocatalytic oxidation processes (UV/H 2O 2/TiO 2 or ZnO). The efficiency of photocatalytic degradation for the different catalysts (TiO 2 and ZnO) was determined from the analysis of the following parameters: cyanides, formates and ammonia content. In a first stage, the influence of two parameters (initial concentration of H 2O 2 and amount of catalyst) on the degradation kinetics of cyanides and formates was studied based on a factorial experimental design. pH was always kept in a value >9.5 to avoid gaseous HCN formation. The degradation of cyanides and formates was found to follow pseudo-first order kinetics. Experimental kinetic constants were fitted using neural networks (NNs). The mathematical model reproduces experimental data within 90% of confidence and allows the simulation of the process for any value of parameters in the experimental range studied. Moreover, a measure of the saliency of the input variables was made based upon the connection weights of the neural networks, allowing the analysis of the relative relevance of each variable with respect to the others. Results showed that the photocatalytic process was effective, being the degradation rate of cyanides about five times higher when compared to removal of formates. Finally, the effect of lowering pH on the degradation of formates was evaluated after complete cyanides destruction was reached (10 min of reaction). Under the optimum conditions (pH 5.2, [H 2O 2] = 40 g/l; [TiO 2] = 2 g/l), 100% of cyanides and 92% of initial NH 3 concentration are degraded after 10 min, whereas 35 min are needed to degrade 98% of formates.

Direct Observation of Reactive Trapped Holes in TiO2 Undergoing Photocatalytic Oxidation of Adsorbed Alcohols: Evaluation of the Reaction Rates and Yields

To investigate the primary process of photocatalytic oxidation of TiO2, interfacial charge-transfer reaction of trapped holes formed in nanocrystalline TiO2 films by UV irradiation was directly measured by highly sensitive femtosecond and nanosecond transient absorption spectroscopy under low intensity excitation condition to avoid fast electron-hole recombination. Accordingly, the rates and yields of photocatalytic oxidation of several alcohols adsorbed on TiO2 were evaluated successfully.