Optimized photodegradation of Reactive Blue 19 on TiO2 and ZnO suspensions

The photocatalytic discoloration of Reactive Blue 19 (RB-19), a textile anthraquinone dye, were investigated in aqueous suspensions containing TiO₂ or ZnO as catalysts. The reactions can be mathematically described as a function of parameters pH, amount of catalyst and dye concentration being modeled by the use of response surfaces methodology. Optimized values for the concentration of the catalyst and the pH for each reaction systems were determined. ZnO showed greater degradation activity than TiO₂ when the reaction was carried out in a 4 l circulating reactor under optimized conditions. The figure-of-merit electric energy per order (EE/O) allows to determine that the electrical energy cost of reducing the color by one order of magnitude was three times higher for TiO₂. In both reaction systems, the acute toxicity evolved from zero to around 50 toxicity units in the initial stages of irradiation, depleting to minimal values after 30 min of reaction.     

Preparation and photocatalytic properties of a nanometer ZnO–SnO2 coupled oxide

A nanometer coupled oxide ZnO–SnO₂ was prepared using the co-precipitation method employing NH₃·H₂O as the precipitant. The oxide was characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and UV diffuse reflectance spectrum (DRS). The photocatalytic activity of nanometer coupled oxides was studied using methyl orange as a mode organic pollutant. The relationship between the photocatalytic activity and the microstructure of nanometer coupled oxides was also discussed in the paper. Experimental results showed that the nanometer coupled oxides mainly consist of nanometer ZnO and SnO₂, and they have the same excellent photocatalytic activity as Degussa P25 TiO₂ for the degradation of methyl orange (MO). Moreover, the photocatalytic activity of the coupled oxides increases gently at first, then decreases rapidly with the increase of the calcination temperature. But a small amount of nanometer Zn₂SnO₄ was formed in the mixture of coupled oxides when the calcination temperature was higher than 700 °C.     

Enhancement of photoinduced hydrogen production from irradiated Pt/TiO2 suspensions with simultaneous degradation of azo-dyes

The production of hydrogen from aqueous Pt/TiO₂ suspensions illuminated with UV–vis light has been examined in the absence and in presence of azo-dyes in solution. The effects of operational variables, including dye concentration, solution pH and temperature, on the rate of hydrogen production were investigated. It has been found that deposition of Pt (0.5 wt.%) on the semiconductor surface results in an increase of the H₂ production rate, which goes through a maximum with time of irradiation and then drops to steady-state values comparable to those obtained over bare TiO₂. Both, maximum and steady-state rates obtained over Pt/TiO₂ suspensions were found to increase with increasing solution pH and temperature. Addition of small quantities of azo-dyes in solution results in significantly enhanced rates of H₂ production for a period which depends on dye concentration, solution pH and, to a lesser extent, solution temperature. It is proposed that the dye acts as a scavenger of photogenerated oxidizing species while it is degraded toward CO₂ and inorganic ions. When complete mineralization is achieved, oxygen can no longer be removed from the photocatalyst surface and the rate drops to steady-state values, comparable to those obtained in the absence of azo-dye in solution. The amount of additional H₂ produced is directly proportional to the amount of dye added in the solution. The rate increases with increasing solution pH, where dye degradation is faster, indicating that the process is limited by the rate of consumption of photogenerated oxygen. It is concluded that, under certain experimental conditions, it is possible to obtain significantly enhanced rates of photoinduced hydrogen production from Pt/TiO₂ suspensions with simultaneous mineralization of azo-dyes. The process could be used for combined production of fuel H₂ and degradation of organic pollutants present in water.     

钒掺杂二氧化钛光催化活性研究

二氧化钛凭借优异的光催化性能,越来越受到人们的广泛关注和重视。以钛酸四丁酯为原料,利用水解-水热-干燥/煅烧工艺制备得到未掺杂TiO₂光催化剂和掺钒TiO₂光催化剂,利用其对甲基橙溶液的降解率做了比较分析。结果表明,以钛酸四丁酯为原料,采用溶胶-凝胶法制备钒掺杂TiO₂光催化剂是可行的。制备V/TiO₂产品的最佳工艺条件：钒钛质量比为6∶100、水热温度为160 ℃、水热时间为12 h,120 ℃下干燥14 h。紫外光照射条件下,甲基橙光催化降解效率达到99.10%,降解时间小于45 min。     

Photocatalytic degradation of short-chain organic diacids

The heterogeneous photocatalytic oxidation of fumaric, maleic and oxalic acids over TiO₂ has been investigated. For aqueous suspensions at pH lower than the point of zero charge (pzc) of TiO₂, the photocatalytic degradation of the three studied diacids follows the Langmuir–Hinshelwood kinetic model, with the rate constant of the process decreasing in the order oxalic acid>maleic acidfumaric acid. At these low pH media, the adsorption of the organic diacids onto TiO₂ particles is a key feature for their degradation, which is initiated by a photo-Kolbe process. For fumaric and maleic acids, a cis–trans isomerisation induced by the interaction between adsorbed molecule and semiconductor surface occurs. At pH’s higher than the pzc of TiO₂ the rate of oxalic acid oxidation decreases noticeably, while fumaric and maleic acids are both efficiently degraded in homogeneous phase by reacting with OH√ radicals photochemically generated on the TiO₂ surface, giving rise to a significant increment of both isomers degradation rate with increasing pH. At these pH’s higher than the pzc of the TiO₂, the three studied diacids show a very low degree of adsorption onto the semiconductor surface and no evidence of cis–trans isomerisation for both maleic and fumaric acids is detected. In accordance with the observed pH effects on degradation rate and over detected intermediates, a different mineralisation pathway is proposed as function of initial pH.     

Preparation of Au/TiO2 catalysts from Au(I)–thiosulfate complex and study of their photocatalytic activity for the degradation of methyl orange

Gold loaded on TiO₂ (Au/TiO₂) catalysts were prepared using Au(I)–thiosulfate complex (Au(S₂O₃)₂³⁻) as the gold precursor for the first time. The samples were characterized by UV–vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS) methods. Using Au(S₂O₃)₂³⁻ as gold precursor, ultra-fine gold nanoparticles with a highly disperse state can be successfully formed on the surface of TiO₂. The diameter of Au nanoparticles increases from 1.8 to 3.0 nm with increasing the nominal Au loading from 1% to 8%. The photocatalytic activity of Au/TiO₂ catalysts was evaluated from the analysis of the photodegradation of methyl orange (MO). With the similar Au loading, the catalysts prepared with Au(S₂O₃)₂³⁻ precursor exhibit higher photocatalytic activity for methyl orange degradation when compared with the Au/TiO₂ catalysts prepared with the methods of deposition–precipitation (DP) and impregnation (IMP). The preparation method has decisive influences on the morphology, size and number of Au nanoparticles loaded on the surface of TiO₂ and further affects the photocatalytic activity of the obtained catalysts.     

Structural peculiarities of TiO2 and Pt/TiO2 catalysts for the photocatalytic oxidation of aqueous solution of Acid Orange 7 Dye upon ultraviolet light

TiO₂ (anatase) with different microstructure was synthesized by thermal hydrolysis of the titanyl sulfate and studied by X-ray powder diffraction, high resolution transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The effect of titanium dioxide structure, regular or distorted, on the photocatalytic degradation of Acid Orange 7 Dye (AO7) in water upon ultraviolet light was studied. It was found that synthesized TiO₂ possesses a relatively high reactivity when illuminated but also show different adsorption in the dark. The relationship between these behaviors depends on the real structure of the catalysts. Catalysts with a perfect structural ordering formed after heating at temperature higher than 500 °C show better photocatalytic performance. Small amount of Pt added into the TiO₂ structure was found to improve further the catalyst reactivity. Pt-modified titania catalysts oxidize AO7 more efficiently than P-25 Degussa TiO₂. Doping effect of Pt on the structural and photocatalytic properties of the samples is discussed.     

Sonophotocatalytic/H2O2 degradation of phenolic compounds in agro-industrial effluents

The treatment of a model solution containing 13 compounds typically found in olive mill wastewaters (OMW), at a concentration of 50 mg/L each, by means of sonophotocatalysis over 0.75 g/L Degussa TiO₂ suspensions was studied. Experiments were conducted at an ultrasound frequency and intensity of 80 kHz and 120 W, respectively, ultraviolet power of 9, 250 and 400 W with or without the addition of 0.118 mol/L H₂O₂. Treatment efficiency was assessed following changes in total phenols (TPh) concentration, individual species concentration, chemical oxygen demand (COD), total organic carbon (TOC) and ecotoxicity. In general, photocatalytic degradation increased with increasing UVA power, while sonolysis alone failed to cause any degradation. Process coupling and addition of extra oxidant resulted in substantial levels of degradation. For instance, sonophotocatalytic treatment at 400 W UVA power with H₂O₂ for 120 min resulted in complete mineralization followed by significant toxicity reduction. TiO₂ characterization before and after use showed that the catalyst suffered no composition or morphology changes during treatment. However, a substantial surface area increase was noted and this was attributed to the ultrasound de-aggregating catalyst particles. Preliminary tests with an actual OMW showed that the sonophotocatalytic/H₂O₂ treatment is a promising technology for this type of effluents.     

TiO2-photocatalysis as a tertiary treatment of naturally treated wastewater

Solar TiO₂-photocatalysis was applied to waters from a natural wastewater treatment plant located in the Universidad de Las Palmas de Gran Canaria. Degussa P-25 TiO₂ and its mixture with activated carbon (AC–TiO₂) were used as catalysts. The presence of ozone and certain ions such as phosphates on the photocatalytic degradation of organic matter was also studied.

Disinfection experiments have provided interesting results, particularly when using the catalyst AC–TiO₂ and ozone, since total disinfection was achieved in less than 60 min. No bacterial reappearance at 24 or 48 h was observed. Additionally, this catalyst gave important TOC and some ions concentrations reductions.

Studies in catalyst reuse revealed that the catalyst AC–TiO₂ showed almost no deactivation.     

稀土元素Ce掺杂TiO_2光催化剂制备及微波强化光催化活性

在[Bmim]PF6离子液体介质中微波辅助制备稀土元素Ce掺杂改性的TiO_2光催化剂TiO_2-Ce,以甲基橙溶液和苯酚溶液为模拟污染物,在紫外光照和微波辐射-紫外光照降解条件下考察TiO_2-Ce催化剂的光催化活性。利用荧光技术以对苯二甲酸作为荧光探针检测TiO_2-Ce催化剂表面产生的羟基自由基,并对光催化降解反应进行动力学分析,以了解光催化降解反应机理。结果表明,通过优化反应条件制得的TiO_2-Ce催化剂具有较高光催化降解活性和热稳定性,在紫外光照和微波辐射-紫外光照条件下降解60 min后,甲基橙降解率分别为98.6%和99.3%,苯酚降解率分别为96.6%和97.2%。荧光光谱分析表明,TiO_2-Ce在微波辐射-紫外光照条件下产生的羟基自由基比紫外光照多,因而微波辐射-紫外光照具有强化TiO_2-Ce降解模拟污染物作用的效果。反应动力学数据表明,TiO_2-Ce光催化降解甲基橙溶液反应呈一级反应动力学规律,其表观速率常数k最大值为0.056 2 min-1。     

金属氧化物掺杂高岭土纳米 二氧化钛光催化复合材料研究

以高岭石为载体,以钛酸四丁酯为前驱体,采用溶胶-凝胶法制备金属氧化物掺杂高岭土纳米二氧化钛光催化复合材料。采用X射线衍射（XRD）、红外光谱（FT-IR）和拉曼光谱（Raman）对复合材料进行表征,并通过在紫外光下降解云母珠光工业废水来考察其光催化性能。研究了不同金属氧化物掺杂浓度对复合材料光催化活性的影响。实验结果表明：金属氧化物三氧化二铁、氧化锌掺杂使锐钛矿二氧化钛晶相特征衍射峰宽化,掺杂生成钛铁矿、红锌矿新相,影响锐钛矿二氧化钛结晶度。在紫外光下降解6 h,掺杂质量分数为0.5%的三氧化二铁对废水降解率为98.8%,掺杂质量分数为1.5%的氧化锌对其降解率为91.4%。     

Structure and photocatalytic performance of TiO2/clay nanocomposites for the degradation of dimethachlor

In the present study TiO₂/clay composites were synthesized by dispersion of TiO₂ on the surfaces of a natural montmorillonite and a synthetic hectorite in order to increase the sorption ability of TiO₂ and therefore its photocatalytic action. Six materials with different loading in TiO₂ (15, 30 and 55 wt%) were prepared and characterized by several analytical techniques including XRD, BET and SEM analysis. The synthetic procedure allows the development of delaminated layers for hectorite–TiO₂ samples, while in the case of montmorillonite–TiO₂ composites we have the formation of a more lamellar-like aggregation. It was found that, the greater the percentage of TiO₂, the greater the pore volume and the specific surface area of the montmorillonite–TiO₂ samples. On the contrary, in the case of hectorite–TiO₂ samples, as the content of TiO₂ increases, the surface area and pore volume decreases. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (dimethachlor) in water as model compound. The primary degradation of dimethachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. All supported catalysts exhibit good photodegradation efficiency and their overall removal efficiency per mass of TiO₂ was better than that of bare TiO₂ produced by the sol–gel method. In conclusion, together with their good sedimentation ability the composite materials could be considered as a promising alternative for the removal of organic water contaminants.     

微米级TiO2/AC催化剂在光催化-膜分离耦合反应装置中降解酸性红B废水

采用X射线衍射分析、扫描电镜分析和傅里叶红外光谱分析对溶胶-凝胶法制得的负载型微米级TiO₂/活性炭（AC）催化剂性能进行了表征,并对其在光催化-膜分离耦合反应装置中光催化降解酸性红B废水时的性能和膜通量的影响进行了研究。结果表明：在最佳煅烧温度400℃时负载的TiO₂以锐钛矿为主,与载体活性炭之间以Ti-O-C键结合,且分布较为均匀;微米级TiO₂/AC催化剂的光催化降解性能随其煅烧温度的升高和粒径的减小而均呈现为先增加、后降低的趋势,TiO₂/AC对膜通量的影响则随煅烧温度的升高和粒径的减小而呈先降低、后增加的趋势,且TiO₂/AC粒径以10.272μm为宜。椰壳活性炭为载体的TiO₂/AC催化剂的光催的化降解性能高于褐煤活性炭为载体的,且前者对膜通量的影响更小。微米级TiO₂/AC催化剂的光催化降解性能高于商业TiO₂的,且对膜通量的影响比商业TiO₂的低。     

色氨酸辅助合成光催化活性增强的球形纳米TiO2

以L-色氨酸（L-Trp）为生物模板,采用简单水解及煅烧后制备了球形结构TiO₂纳米光催化剂。通过X射线衍射、扫描电子显微镜、红外光谱、紫外-可见漫反射光谱、光致发光光谱和N₂吸附-解吸等方法对制得的TiO₂纳米材料进行表征。在催化剂合成过程中,L-Trp作为生物模板发挥至关重要的作用,能够指导球形结构纳米TiO₂的形成。考察了不同煅烧温度下制备的TiO₂样品光催化活性,结果表明550℃时制备的TiO₂样品具有优异的光催化活性,紫外光照射30min对甲基橙溶液的降解率达到95%左右,主要是由于较大比表面积和球形结构的协同效应。光催化剂稳定性实验表明,所制备的TiO₂纳米材料可作为一种实用有效的光催化剂用于紫外光照射下降解有机染料。同时,对L-Trp辅助下球形结构TiO₂纳米颗粒的可能生长机理进行讨论。     

Iodosulfuron degradation by TiO2 photocatalysis: Kinetic and reactional pathway investigations

The photocatalytic degradation of a sulfonylurea herbicide, iodosulfuron methyl ester (IOME), has been studied in TiO₂ aqueous suspensions under UV irradiation. The influence of various parameters such as initial concentration, TiO₂ concentration and light intensity on the kinetic process was investigated. Disappearance rate of iodosulfuron followed pseudo-first order kinetics. A special attention was devoted to the identification of intermediates, using a new analytical approach which consists of coupling HPLC–DAD (UV), HPLC–ESI-MS and HPLC–¹H NMR techniques after a SPE pre-concentration step. By combining UV, MS and NMR data, up to 20 degradation products were unambiguously identified. Furthermore, ¹H NMR data allowed the differentiation of several positional isomers, in particular those of hydroxylation resulting from the attack of OH radicals on the benzene ring of IOME. Kinetic evolution profiles of main intermediates, end products (NO₃⁻, NH₄⁺, SO₄²⁻) and total organic carbon (TOC) were also examined in detail. From obtained kinetic and analytical results, the presence of privileged sites for the attack of OH radicals was shown and a detailed degradation pathway was proposed.     

Study of the synergic effect of sulphate pre-treatment and platinisation on the highly improved photocatalytic activity of TiO2

An important improvement of the photocatalytic activity of sol–gel prepared TiO₂ has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples.

The presence of sulphuric acid clearly stabilised TiO₂ surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5 wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO₂ surface was studied.

Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO₂. Simultaneously sulphated and platinised TiO₂ samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO₂ Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples.

A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported.     

Comparison of photocatalytic efficiencies of TiO2 in suspended and immobilised form for the photocatalytic degradation of nitrobenzenesulfonic acids

The photocatalytic efficiency of TiO₂ immobilised on various supports (glass, cement, red brick and inorganic fibres), using different techniques (sputtering, sol–gel dip-coating, patented method for inorganic fibres), are compared with the photocatalytic efficiency of TiO₂ Degussa P25 in suspension 2 g l⁻¹, for the degradation of 3-nitrobenzenesulfonic acid (3-NBSA) and 4-nitrotoluenesulfonic acid (4-NTSA). In all cases, the fixation of TiO₂ on solid supports appreciably reduces the photocatalytic efficiency. The best results were obtained with TiO₂ on inorganic fibres.     

Effects of hydrothermal temperature and time on the photocatalytic activity and microstructures of bimodal mesoporous TiO2 powders

Bimodal nanocrystalline mesoporous TiO₂ powders with high photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate (TiO(C₄H₉)₄, TBOT) as precursor. The as-prepared TiO₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption–desorption measurements. The photocatalytic activity of the as-prepared TiO₂ powders was evaluated by the photocatalytic degradation of acetone (CH₃COCH₃) under UV-light irradiation at room temperature in air. The effects of hydrothermal temperature and time on the microstructures and photocatalytic activity of the TiO₂ powders were investigated and discussed. It was found that hydrothermal treatment enhanced the phase transformation of the TiO₂ powders from amorphous to anatase and crystallization of anatase. All TiO₂ powders after hydrothermal treatment showed bimodal pore-size distributions in the mesoporous region: one was intra-aggregated pores with maximum pore diameters of ca. 4–8 nm and the other with inter-aggregated pores with maximum pore diameters of ca. 45–50 nm. With increasing hydrothermal temperature and time, the average crystallite size and average pore size increased, in contrast, the Brunauer-Emmett-Teller (BET) specific surface areas, pore volumes and porosity steadily decreased. An optimal hydrothermal condition (180 °C for 10 h) was determined. The photocatalytic activity of the prepared TiO₂ powders under optimal hydrothermal conditions was more than three times higher than that of Degussa P25.     

钇沉积的二氧化钛-SBA-15纳米催化剂制备及其应用

近年来,二氧化钛被广泛应用于污水处理领域。为合理改善二氧化钛在光催化应用中的缺陷,提高二氧化钛的使用范围,首先采用水热法制备了介孔型分子筛SBA-15,将二氧化钛沉积到介孔型分子筛上,再通过硝酸钇的浸渍将不同质量的钇沉积到分子筛上,制备出新型光催化剂钇-二氧化钛-SBA-15（Y-TiO₂-SBA-15）。采用X射线衍射仪（XRD）、透射电镜（TEM）、元素分析仪（EDS）、傅里叶红外光谱仪（FT-IR）和氮气吸附-脱附等对催化剂进行分析,并以甲基橙溶液为目标降解物考察了催化剂在不同条件下对甲基橙的的光降解能力。结果表明:在溶液pH=4且采用300 W氙灯照射140 min条件下,甲基橙脱色效果明显,降解率为93.1%。     

Optimisation of degradation conditions of 1,8-diazabicyclo[5.4.0]undec-7-ene in water and reaction kinetics analysis using a cocurrent downflow contactor photocatalytic reactor

The photocatalytic degradation of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, a non-biodegradable nitrogenous organic compound) in water was optimised under UV radiation using titanium dioxide photocatalyst. The reactor used was a pilot scale cocurrent downflow contactor photocatalytic reactor (CDCPR), a system offering very high mass transfer efficiency. The effect of photocatalyst loading, initial substrate concentration, temperature, pH, and different combinations of UV, O₂, H₂O₂ and TiO₂ on the photocatalytic oxidation of DBU was investigated. The TiO₂ photocatalyst used was Degussa VP Aeroperl P25/20, a granulated form of Degussa P-25, recently developed to ameliorate downstream catalyst separation problems. The CDCPR was fitted with an internally and vertically mounted 1.0 kW UV lamp. The reactions were carried out at 40–60 °C and 1 barg, with the reactor being operated in closed loop recycle mode and suspended photocatalyst being re-circulated. Optimisation of reaction conditions using a combination of TiO₂, UV radiation and O₂ gave the most rapid degradation and mineralisation of the DBU in comparison with other processes. Under optimised conditions, 100% degradation of DBU was achieved in 45 min, with a quantum yield of 7.39, using a 1 kW lamp, 0.5 g/dm³ TiO₂, 100 mg/dm³ DBU, 1 barg, 50 °C and pH of 3.17. Investigating the reaction pathway and its modelling showed a first order dependency, incorporating the effect of first intermediates of degradation. The activation energy was found to be 54.68 kJ mol⁻¹ showing a significant influence of temperature on the photocatalytic degradation of DBU.