Visible light Cr(VI) reduction and organic chemical oxidation by TiO2 photocatalysis

Here we report the simultaneous Cr(VI) reduction and 4-chlorophenol (4-CP) oxidation in water under visible light (wavelength > 400 nm) using commercial Degussa P25 TiO2. This remarkable observation was attributed to a synergistic effect among TiO2, Cr(VI), and 4-CP. It is well known that TiO2 alone cannot remove either 4-CP or Cr(VI) efficiently under visible light. Moreover, the interaction between Cr(VI) and 4-CP is minimal if not negligible. However, we found that the combination of TiO2, Cr(VI), and 4-CP together can enable efficient Cr(VI) reduction and 4-CP oxidation under visible light. The specific roles of the three ingredients in the synergistic system were studied parametrically. It was found that optimal concentrations of Cr(VI) and TiO2 exist for the Cr(VI) reduction and 4-CP oxidation. Cr(VI) was compared experimentally with other metals such as Cu(ll), Fe(lll), Mn(IV), Ce(IV), and V(V). Among all these metal ions, only Cr(VI) promotes the photocatalytic oxidation of 4-CP. The amount of 4-CP removed was directly related to the initial concentration of Cr(VI). The system was also tested with four other chemicals (aniline, salicylic acid, formic acid, and diethyl phosphoramidate). We found that the same phenomenon occurred for organics containing acid and/or phenolic groups. Cr(VI) was reduced at the same time as the organic chemicals being oxidized during photoreaction under visible light. The synergistic effect was also found with pure anatase TiO2 and rutile TiO2. This study demonstrates a possible economical way for environmental cleanup under visible light.     

Photocatalytic oxidation of tabun simulant-diethyl cyanophosphate: FTIR in situ investigation

Gas phase photocatalytic oxidation of diethyl cyanophosphate vapor in a static reactor using TiO2 and modified TiO2 as the photocatalyst was studied with the FTIR in situ method. The transition metals Pt, Au, and Ag were used for TiO2 modification by the chemical and photochemical deposition methods as well as the mechanical mixture of TiO2 with manganese oxide to improve its adsorption and catalytic activity. Photocatalytic oxidation of diethyl cyanophosphate in a static reactor results in its complete mineralization with carbon dioxide, phosphoric and nitric acids, and water as the major final products. HCN was demonstrated to be the only toxic gaseous intermediate of diethyl cyanophosphate photocatalytic oxidation, formed as a result of diethyl cyanophosphate hydrolysis. Diethylphosphate and acetic and formic acids were registered as the surface intermediates. It was found that cyanhydric acid is oxidized slowly with the use of unmodified TiO2. The formation of surface cyanide complexes with Ag and Au ions could be responsible for the fast removal of HCN from the gas phase and its further photooxidation in the case of using TiO2 with deposited Au and Ag.     

Photocatalytic decomposition of bisphenol A in water using composite TiO2-zeolite sheets prepared by a papermaking technique

Titanium dioxide (TiO2) photocatalyst and zeolite adsorbent were made into a paper-like composite by a papermaking technique using pulp and ceramic fibers as sheet matrix. The photocatalytic performance for the degradation of bisphenol A (BPA) dissolved in water was investigated under UV irradiation. The TiO2 sheet prepared was easier to handle than the original TiO2 powders in aqueous media. The TiO2 sheet could decompose the BPA under UV irradiation, although at a lower degradation efficiency than the TiO2 suspension. The TiO2-free zeolite sheet could not remove the BPA from water completely because of its adsorption equilibrium. Furthermore, the composite TiO2-zeolite sheets exhibited a higher efficiency for BPA removal than the zeolite-free TiO2 sheets, the efficiency of the former being equivalent to that of the TiO2 suspension. The enhancement in removal efficiency was not attributed to the simple adsorption of BPA on zeolite but rather to the synergistic effect obtained through the combined use of TiO2 photocatalyst and zeolite adsorbent in the paper-like composite sheet, which is believed to accelerate the BPA photodegradation in water.     

A new route for degradation of volatile organic compounds under visible light: using the bifunctional photocatalyst Pt/TiO2-xNx in H2-O2 atmosphere

The bifunctional photocatalyst Pt/TiO2-xNx has been successfully prepared by wet impregnation. The properties of Pt/ TiO2-xNx have been investigated by diffuse reflectance spectra, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, a photoluminescence technique with terephthalic acid, and electric field induced surface photovoltage spectra. The photocatalytic activity of the sample was evaluated by the decomposition of volatile organic pollutants (VOCs) in a H2-O2 atmosphere under visible light irradiation. The results demonstrated that nitrogen-doped and platinum-modified TiO2 in a H2-O2 atmosphere could enormously increase the quantum efficiency of the photocatalytic system with excellent photocatalytic activity and high catalytic stability. The increased quantum efficiency can be explained by enhanced separation efficiency of photogenerated electron-hole pairs, higher interface electron transfer rate, and an increased number of surface hydroxyl radicals in the photocatalytic process. A mechanism was proposed to elucidate the degradation of VOCs over PtTiO(2-x)Nx in a H2-O2 atmosphere under visible light irradiation.     

Size-tunable hydrothermal synthesis of SnS2 nanocrystals with high performance in visible light-driven photocatalytic reduction of aqueous Cr(VI)

SnS(2) nanocrystals with adjustable sizes were synthesized via a hydrothermal method from the aqueous solution of common and inexpensive SnCl(4)·5H(2)O, thioacetamide and citric acid, simply by varying the reaction temperature and reaction time. The structures, Brunauer-Emmett-Teller (BET) specific surface areas and optical properties of the resultant SnS(2) nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, N(2) adsorption/desorption isotherms, and UV-vis diffuse reflectance spectra. Besides, their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (λ > 420 nm) irradiation. It was found that the photocatalytic activities of SnS(2) nanocrystals in aqueous suspension depended on their synthesis conditions. The product synthesized under suitable hydrothermal conditions (for example, at 150 °C for 12 h) not only showed high visible light-driven photocatalytic activity in the reduction of aqueous Cr(VI), but also showed good photocatalytic stability. Our photocatalytic results suggested that SnS(2) nanocrystals are a promising photocatalyst in the efficient utilization of solar energy for the treatment of Cr(VI)-containing wastewater.     

Heterogeneous photocatalytic reduction of chromium(VI) over TiO2 particles in the presence of oxalate: involvement of Cr(V) species

Cr(VI) photocatalytic reduction experiments over TiO2 particles under near UV irradiation in the presence of excess oxalate were performed at acid pH (2 and 3) and under air and N2 bubbling. Initial photonic efficiencies for Cr(VI) reduction are nearly the same under aerobic and anaerobic conditions, but show a significant increase at the lowest pH. At pH 2, the addition of oxalate facilitates Cr(VI) reduction, hindering the electron-shuttle mechanism taking place in pure water. The oxalate synergistic effect at pH 2 is lower than that previously found for EDTA and negligible at pH 3. Chromium(V) oxalate concentration profiles were obtained by EPR spectroscopy in the presence of excess oxalate at pH 1.5. Coordinated Cr(V) complexes [Cr(V)(O)(Ox)2]-, [Cr(V)(OH2)(Ox)2]-, and [Cr(V)(O)(OH)2(Ox)]- were identified, on the basis of the comparison of their corresponding g values with recent literature data. The kinetic analysis of the temporal evolution of the paramagnetic Cr(V) species indicates also an effective photocatalytic degradation of chromium(V) oxalate complexes. This new evidence reinforces previous findings regarding sequential one-electron-transfer processes in Cr(VI) photocatalytic reduction, suggesting that this route may represent a general behavior for the Cr(VI) reduction over UV-irradiated TiO2 particles.     

微波改性Ce/TiO2光催化剂的制备及其降解活性艳红3BS的研究

利用溶胶-凝胶法合成了TiO2及Ce/TiO2光催化剂,并用微波进行处理.借助XRD对合成的纳米光催化剂微观结构及性能进行了研究.结果表明:TiO2经铈掺杂并经微波改性后的光催化降解效果优于单独铈掺杂改性的TiO2,铈单独掺杂改性的TiO2的光催化降解效果优于未掺杂改性的TiO2.     

Design of a photocatalyst for bromate decomposition: surface modification of TiO2 by pseudo-boehmite

The rate of BrO3- reduction by a commercial TiO2 photocatalyst under UV illumination in an aqueous solution was increased by lowering the pH from 7 to 5. The effect is attributable to an enhancement of the electrical interaction between BrO3- and the positively charged surfaces of the TiO2 photocatalyst. The surface charge can be controlled by a surface modification of the TiO2 photocatalyst without controlling the pH of the water. In fact, the isoelectric point of surface-modified TiO2 was higher than that of the unloaded TiO2 photocatalyst, resulting in an increase in the rate of the photocatalytic reduction of BrO3- at a neutral pH. This increase is explained by an increase in the amount of adsorbed BrO3- on the photocatalyst surface.     

掺磷纳米TiO2的制备及其在染料降解中的应用

采用溶胶-凝胶法合成了纳米TiO<,2>光催化剂,以钛酸丁酯为前驱物,无水乙醇为溶剂,冰醋酸为抑制剂,探讨了不同反应条件(温度、pH、助剂用量等)对其凝胶时间的影响,在此基础上制备了掺磷纳米TiO<,2>.利用XRD、UV-vis等测试技术研究了纳米TiO<,2>的形态结构,并利用制备的粉体进行了甲基橙紫外光光催化试验.结果显示:制备透明稳定凝胶的最佳条件是将去离子水滴加到混合了钛酸丁酯的乙醇溶液中,并控制温度在40℃,pH为2.5,n(钛酸丁酯):n(无水乙醇):n(水):n(冰醋酸)=1:25:5:1.5,得到的凝胶透明度好;掺磷量为4%时,制备的粉体紫外光光催化活性最好.     

Development of an E-H2O2/TiO2 photoelectrocatalytic oxidation system for water and wastewater treatment

In this study, an innovative E-H2O2/TiO2 (E-H2O2 = electrogenerated hydrogen peroxide) photoelectrocatalytic (PEC) oxidation system was successfully developed for water and wastewater treatment. A TiO2/Ti mesh electrode was applied in this photoreactor as the anode to conduct PEC oxidation, and a reticulated vitreous carbon (RVC) electrode was used as the cathode to electrogenerate hydrogen peroxide simultaneously. The TiO2/Ti mesh electrode was prepared with a modified anodic oxidation process in a quadrielectrolyte (H2SO4-H3PO4-H2O2-HF) solution. The crystal structure, surface morphology, and film thickness of the TiO2/Ti mesh electrode were characterized by X-ray diffraction and scanning electron microscopy. The analytical results showed that a honeycomb-type anatase film with a thickness of 5 microm was formed. Photocatalytic oxidation (PC) and PEC oxidation of 2,4,6-trichlorophenol (TCP) in an aqueous solution were performed under various experimental conditions. Experimental results showed that the TiO2/Ti electrode, anodized in the H2SO4-H3PO4-H2O2-HF solution, had higher photocatalytic activity than the TiO2/Ti electrode anodized in the H2SO4 solution. It was found that the maximum applied potential would be around 2.5 V, corresponding to an optimum applied current density of 50 microA cm(-2) under UV-A illumination. The experiments confirmed that the E-H2O2 on the RVC electrode can significantly enhance the PEC oxidation of TCP in aqueous solution. The rate of TCP degradation in such an E-H2O2-assisted TiO2 PEC reaction was 5.0 times that of the TiO2 PC reaction and 2.3 times that of the TiO2 PEC reaction. The variation of pH during the E-H2O2-assisted TiO2 PEC reaction, affected by individual reactions, was also investigated. It was found that pH was well maintained during the TCP degradation in such an E-H2O2/TiO2 reaction system. This is beneficial to TCP degradation in an aqueous solution.     

改性聚丙烯腈纤维负载MoSx/TiO2光催化材料制备及其降解染料性能

为提升MoS_x/TiO₂异质结的光催化性能,使用偕胺肟改性的聚丙烯腈(PAN)纤维作为载体,先通过静电结合及原位转化负载MoS_x,再通过配位作用结合TiO₂合成了复合光催化剂。分析了该催化剂的表面形貌、化学结构和光吸收性能,并考察了其在可见光下对印染废水的处理效果。结果表明:MoS_x和TiO₂可均匀分布于PAN纤维表面,且MoS_x的引入大幅提升了催化剂的光吸收性能,并能够在波长大于500 nm的可见光下快速氧化降解染料废水,其反应速率常数达到单独负载TiO₂纤维催化剂的4.7倍;该催化剂具有优异的重复使用性能,其高活性主要来源于MoS_x对污染物的强吸附能力及其在可见光下对TiO₂的敏化作用。     

Selective photocatalytic oxidation of NH3 to N2 on platinized TiO2 in water

Selective photocatalytic oxidation of NH3 to N2 is proposed as a new treatment method for controlling the levels of ammonia in water. The photocatalytic oxidation of ammonia on naked and metallized TiO2 in water saturated with air, nitrogen, or NO2 gas was investigated. While the slow photocatalytic oxidation of NH3 to NO2-/NO3- is the only pathway for decomposition of NH3 on naked TiO2 and Au/TiO2, a new pathway, that of selective oxidation of ammonia to dinitrogen, opens up on Pt/TiO2. The formation of dinitrogen from the oxidation of 15NH3 was confirmed by mass spectrometric detection of 15N2. The photocatalytic conversion of NH3 to N2 greatly increases when the Pt/TiO2 suspension is saturated with NO2 gas, whereas NO2 itself shows little reactivity with naked TiO2 and Au/TiO2. Over 80% of the total nitrogen available in ammonia (0.1 mM) is converted into N2 within 40 min illumination of the N2O-saturated Pt/TiO2 suspension. The ability of N2O to accept the conduction band electrons of Pt/TiO2 was verified by photoelectrochemical measurements. NO2 reductively decomposes to generate OH radicals on Pt/TiO2; the rate of ammonia degradation in the NO2-saturated Pt/TiO2 suspension significantly decreases in the presence of excess tert-butyl alcohol, an OH radical scavenger. The presence of Pt deposits on the TiO2 particles changes the photocatalytic pathway of ammonia conversion by both enhancing OH radical production from NO2 and stabilizing intermediate NHx (x=0, 1, 2) species to facilitate their recombination into N2.     

光接枝丙烯酸棉纤维素基TiO2/C光催化剂的制备与光催化性

针对回收利用废弃棉织物的功能和附加值低的问题,采用光接枝丙烯酸的废弃棉纤维素为模板,钛酸四丁酯为前驱体,无水乙醇为溶剂,经磷酸二氢铵处理后,通过表面溶胶凝胶法和火焰燃烧的方法制备具有纤维形貌的锐钛矿型二氧化钛和炭（TiO2/C） 的复合光催化材料。分别研究了丙烯酸接枝改性、磷酸二氢铵处理对TiO2/C光催化性能的影响。采用扫描电子显微镜、X射线衍射和热重分析对TiO2/C光催化材料的表面形貌和晶体结构以及质量损失率进行分析。结果表明,质量分数为30%的丙烯酸光接枝改性棉织物,经质量分数为15%的磷酸二氢铵溶液浸渍处理,用钛酸丁酯溶液抽滤沉积10次,在空气中燃烧2h制得的TiO2/C光催化剂具有较为优异的光催化性能。此时的光催化剂中锐钛矿型二氧的粒度相对较小,分布较均匀,更有利于光催化降解。     

银/二氧化钛可见光催化自清洁织物的制备及其性能

为制备基于可见光光催化降解机制的自清洁织物,吡咯(Py)为单体,以硝酸银为银源,通过化学氧化聚合在商业化的纳米二氧化钛(TiO2 )表面形成聚吡咯掺杂银包覆层(PPy-Ag/ TiO2 ),然后高温焙烧去除PPy,获得可见光响应催化剂银/ 二氧化钛(Ag/ TiO2 )。通过共分散溶液用浸渍涂覆法将其涂覆到聚丙烯腈(PAN)纤维上,经加捻、合股织制成织物。借助扫描电子显微镜、红外光谱分析仪、热重分析仪、紫外可见分光光度计等测试织物的结构和性能。结果表明：Ag/ TiO2 粒子较均匀地负载到PAN 纤维表面,其负载率约为3. 17%;涂覆Ag/ TiO2 的织物对亚甲基蓝、罗丹明B 和红酒在可见光下具有良好的降解作用,表现出良好的自清洁效果;经多次洗涤后,该织物仍保持良好的光催化效果,具有良好的耐洗牢度。     

Simultaneous and synergistic conversion of dyes and heavy metal ions in aqueous TiO2 suspensions under visible-light illumination

This study reports synergistic effects in the simultaneous conversion of dyes and heavy metal ions in aqueous TiO2/dye/metal ion systems (ternary components) under visible light (lambda > 420 nm). TiO2/Cr(VI)/Acid Orange 7 (AO7), TiO2/Cr(VI)/Rhodamine B (RhB), TiO2/Ag+/AO7, and TiO2/Ag+/RhB were chosen as test systems. Although dyes can be degraded in TiO2 suspensions under visible light, their removal rates were markedly enhanced in the presence of metal ions. Similarly, the reduction rates of metal ions in visible-light-illuminated TiO2 suspensions were negligible, but they were highly accelerated with dyes present. In particular, the synergistic effect in the ternary system of TiO2/Cr(VI)/AO7 was outstanding. The presence of dissolved oxygen increased the photoreduction rate of Cr(VI) despite the fact that Cr(VI) and O2 are competing electron acceptors. This is ascribed to in-situ photogenerated H2O2 from O2, which acts as a reductant of Cr(VI). RhB and Ag+ ions could be also converted simultaneously under visible light both in the presence and absence of TiO2. The visible-light-induced reduction of Ag+ did not occur at all in TiO2/Ag+ system, but it was enabled in both TiO2/Ag+/ RhB and TiO2/Ag+/AO7 to generate Ag particles. On the other hand, the binary systems of Cr(VI)/AO7, Ag+/AO7, and Ag+/RhB show significant visible-light activities for the conversion of both dye and metal ion. In this case, metal ions and dyes seem to form complexes that induce intracomplex electron transfers upon visible-light absorption. The Cr(VI)/RhB system, however, exhibited insignificant visible-light reactivity.     

Use of synchrotron XANES and Cr-doped coal to further confirm the vaporization of organically bound Cr and the formation of chromium(VI) during coal oxy-fuel combustion

Through the use of synchrotron XANES and Cr-doped brown coal, extensive efforts have been made to clarify the volatility of organically bound Cr during oxy-fuel combustion and the mode of occurrence and leachability of Cr in resulting fly ashes. As the continuation of our previous study using raw coal, the Cr-doped coal has been tested in this study to improve the signal-to-noise ratio for Cr K-edge XANES spectra, and hence the accuracy for Cr(VI) quantification. As has been confirmed, the abundant CO(2) as a balance gas for oxy-firing has the potential to inhibit the decomposition of organically bound Cr, thereby favoring its retention in solid ash. It also has the potential to promote the oxidation of Cr(III) to Cr(VI) to a minor extent. Increasing the oxygen partial pressure, particularly in the coexistence of HCl in flue gas, favored the oxidation of Cr(III) into gaseous Cr(VI)-bearing species such as CrO(2)Cl(2). Regarding the solid impurities including Na(2)SO(4) and CaO, Na(2)SO(4) has proven to preferentially capture the Cr(III)-bearing species at a low furnace temperature such as 600 °C. Its promoting effect on the oxidation of Cr(III) to Cr(VI), although thermodynamically available at the temperatures examined here, is negligible in a lab-scale drop tube furnace (DTF), where the particle residence time is extremely short. In contrast, CaO has proven facilitating the capture of Cr(VI)-bearing species particularly oxychloride vapors at 1000 °C, forming Ca chromate with the formulas of CaCrO(4) and Ca(3)(CrO(4))(2) via a direction stabilization of Cr(VI) oxychloride vapor by CaO particle or an indirect oxidation of Cr(III) via the initial formation of Ca chromite. The fly ash collected from the combustion of Cr-doped coal alone has a lower water solubility (i.e., 58.7%) for its Cr(VI) species, due to the formation of Ba/Pb chromate and/or the incorporation of Cr(VI) vapor into a slagging phase which is water-insoluble. Adding CaO to coal increased the water-solubility of both Cr(VI) and Cr(III) by forming Ca chromite and chromate, respectively.     

Photocatalytic oxidation and decomposition of acetic acid on titanium silicalite

Transient reaction of adsorbed monolayers of acetic acid was used to characterize the photocatalytic properties of titanium silicalite zeolites (TS-1). The TS-1 zeolites having Si/Ti ratios of 5, 12.5, and 50 are effective catalysts at room temperature for both photocatalytic oxidation (PCO) and decomposition (PCD) of acetic acid. The rates of PCO are higher than the rates of PCD for each catalyst. Acetic acid oxidized photocatalytically in 0.2% O2 to form gas-phase CO2 and CH4 and adsorbed H2O on the TS-1 catalysts, whereas no CH4 formed on Degussa P25 TiO2. Isotope labeling showed that, on both TiO2 and TS-1 catalysts, the alpha-carbon formed CO2 whereas the beta-carbon formed CH4 and CO2. The rates of oxidation of the two carbons have different dependencies on UV intensity. The catalysts with higher Si/Ti ratios adsorbed significantly more acetic acid, and the PCO rates per gram of titanium are highest on the TS-1 catalyst with the lowest Ti content, apparently because a larger fraction of the Ti atoms are surface atoms on this catalyst. During PCD in an inert atmosphere, CO2, CH4, and C2H6 formed on TiO2 and on the catalyst with a Si/Ti ratio of 5, but C2H6 was not detected on the other catalysts. The CO2/CH4 selectivity during PCD increased with increasing Si/Ti ratio. The first step in PCO and PCD on TS-1 catalysts appears to be similar and involves formation of a CH3 radical.     

Some critical structure factors of titanium oxide nanotube array in its photocatalytic activity

A highly ordered TiO2 nanotube array on Ti substrate was fabricated by using an electrochemical anodic oxidation method. The morphology, crystalline phase, and photoelectrochemical property of the nanotube array were characterized. The photocatalytic activity of the nanotube array was evaluated by the decolorization of methyl orange in aqueous solution using the different light sources. The effects of structure and morphology of the nanotube array on its photocatalytic activity were investigated. It was found that the photoabsorption behavior of the TiO2 nanotube film depended on the structures of the nanotube array. The nanotube array films exhibited a drastically enhanced photocurrent, and a higher photocatalytic activity compared with the TiO2 nanoparticle film prepared by the regular sol-gel method. The experimental results indicated that the film thickness markedly influenced the photocatalytic activity of nanotube array film, and the 2.5 microm-thick TiO2 nanotube array film appeared a maximum photodegradation efficiency to methyl orange. However, for a given nanotube length, the tube diameter was only very slightly affected the photocatalytic efficiency in this work. The explanation for some critical structure factors of TiO2 nanotube array in the photocatalytic activity was discussed as well.     

Preparation of a novel TiO2-based p-n junction nanotube photocatalyst

TiO2 nanotube semiconductors contain free spaces in their interior that can be filled with active materials such as chemical compounds, enzymes, and noble metals, giving them a fundamental advantage over colloids. Although the unique shape of semiconductor nanotubes makes them promising for a range of potential applications, significant developmental research is required. In this research, a novel TiO2 nanotube photocatalyst was prepared that has a p-n junction. The photocatalyst particle surface is physically divided into reduction and oxidation surfaces, which poses a potential driving force for the transport of photogenerated charge carriers. The structure of this nanotube catalyst was characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The catalyst activity was evaluated by coating the catalyst on HEPA filters and determining the destruction rate of toluene in air. The p-n junction nanotube catalyst was shown to have a much higher photocatalytic destruction rate than that of commercially available, nonnanotube structured material, and a higher destruction rate for nanotube catalysts that did not contain a p-n junction.     

Photocatalytic activity for degradation of nitrogen oxides over visible light responsive titania-based photocatalysts

This study investigates photocatalytic degradation of nitrogen oxides overtitania-based photocatalysts illuminated by ultraviolet and visible light. The TiO2 photocatalyst was synthesized in a sol-gel process using titanium butoxide as the precursor. After calcination between 150 and 300 degrees C, the synthesized TiO2 responded strongly to visible light photocatalytically degrading NO(x), probably because of the existence of carbonaceous species that act as sensitizers. The optimum calcination temperature was found to be around 200 degrees C. Additionally, platinum ion-doped TiO2 was prepared by impregnation using Pt(NH3)4(NO3)2 as a dopant, which improved the photocatalytic activity that degraded NO(x) in the visible light region. The Pt ion was doped in oxide form at the surface of TiO2 and was expected to be responsible for sensitization. At an optimum calcination temperature of around 200 degrees C, the Pt ion-doped TiO2 exhibited higher activity in the further oxidation of NO2 to NO3- clearly reducing NO2 selectivity. The TiO2 catalysts chemically prepared by either the sol-gel process or impregnation exhibited stronger activity than conventional TiO2 when illuminated under a fluorescent lamp. Rinsing with water was responsible for the restored reactivity of prepared TiO2 catalysts for NO(x) degradation.