SO2的气相光催化氧化及催化剂的失活和再生研究

在模拟大气环境中,紫外光照射以及纳米TiO2光催化剂的作用下,气相无机污染物SO2被完全氧化为SO3或H2SO4。本文提出了SO2的非均相光催化氧化机理,并得出光催化反应速率符合一级动力学过程;经过连续使用之后,TiO2的光催化活性降低,最后活性消失;经过水洗之后,失活的TiO2可以得到再生。失活的TiO2和新鲜的TiO2的IR和XPS光谱差异表明,失活的TiO2表面存在H2SO4,其被认为是使催化剂失活的成分。     

SO2的气相光催化氧化及催化剂的失活和再生研究

在模拟大气环境中,紫外光照射以及纳米TiO2光催化剂的作用下,气相无机污染物SO2被完全氧化为SO3或H2SO4.本文提出了SO2的非均相光催化氧化机理,并得出光催化反应速率符合一级动力学过程;经过连续使用之后,TiO2的光催化活性降低,最后活性消失;经过水洗之后,失活的TiO2可以得到再生.失活的TiO2和新鲜的TiO2的IR和XPS光谱差异表明,失活的TiO2表面存在H2SO4,其被认为是使催化剂失活的成分.     

SO2的气相光催化氧化及催化剂的失活和再生研究

在模拟大气环境中，紫外光照射以及纳米TiO2光催化剂的作用下，气相无机污染物SO2被完全氧化为SO2或H2SO4。本文提出了SO2的非均相光催化氧化机理，并得出光催化反应速率符合一级动力学过程；经过连续使用之后，TiO2的光催化活性降低，最后活性消失；经过水洗之后，失活的TiO2可以得到再生。失活的TiO2和新鲜的TiO2的IR和XPS光谱差异表明，失活的TiO2表面存在H2SO4，其被认为是使催化剂失活的成分。     

TiO2膜降解水中污染物的稳定性考察与再生方法研究

针对实际水处理中对催化剂性能的要求,以光催化降解苯酚溶液作为探针反应,考察了玻璃纤维网上负载的TiO2膜催化剂长期使用条件下的稳定性,研究了催化剂在自来水中使用失活后的再生方法.结果表明,经过50次使用之后,膜催化剂120 min反应对苯酚的降解率从100%下降至83%,总体上看,所制催化剂还是具有相当好的稳定性;在反应器中用蒸馏水浸泡配合光催化反应对TiO2膜催化剂进行原位再生是一种可行的再生途径.     

TiO2膜降解水中污染物的稳定性考察与再生方法研究

针对实际水处理中对催化剂性能的要求，以光催化降解苯酚溶液作为探针反应，考察了玻璃纤维网上负载的TiO₂膜催化剂长期使用条件下的稳定性，研究了催化剂在自来水中使用失活后的再生方法。结果表明，经过50次使用之后，膜催化剂120 min反应对苯酚的降解率从100%下降至83%，总体上看，所制催化剂还是具有相当好的稳定性；在反应器中用蒸馏水浸泡配合光催化反应对TiO₂膜催化剂进行原位再生是一种可行的再生途径。     

双氧水催化氧化中Cu/γ-Al_2O_3催化剂的稳定性研究

针对废水湿式双氧水催化氧化,采用浸渍法制备Cu催化剂,研究非均相Cu催化剂在常温常压湿式双氧水催化氧化中的稳定性与失活问题。研究表明,催化剂制备条件及催化氧化反应条件对催化剂中Cu2＋溶出均有影响。研究同时表明,催化剂失活与活性组分流失和活性组分被有机中间产物覆盖有关,高温焙烧可对催化剂再生。     

双氧水催化氧化中Cu/γ-Al_2O_3催化剂的稳定性研究

针对废水湿式双氧水催化氧化,采用浸渍法制备Cu催化剂,研究非均相Cu催化剂在常温常压湿式双氧水催化氧化中的稳定性与失活问题。研究表明,催化剂制备条件及催化氧化反应条件对催化剂中Cu2＋溶出均有影响。研究同时表明,催化剂失活与活性组分流失和活性组分被有机中间产物覆盖有关,高温焙烧可对催化剂再生。     

一种光催化体系光催化降解苯胺的研究

以钛酸丁酯为原料．以膨润土为载体,用酸性溶胶法合成TiO2纳米复合物,并利用该复合物作催化剂,在H2O2存在下进行光催化降解苯胺溶液。结果表明,该催化剂在UV／H2O2系统中对苯胺溶液有很好的光催化降解效果,其效果优于纯TiO2;H2O2的存在提高了苯胺光催化降解速率,在本实验条件下其最佳摩尔浓度是5mmol／L;溶液pH是影响反应速率的重要因素．pH在中性范围内具有更强的光催化活性;该体系中苯胺能够有效地被降解,其光催化反应遵循一级反应动力学规律。     

反应条件对Cu/Ni/Fe类水滑石去除CS2的影响

采用共沉淀法合成Cu/Ni/Fe三元类水滑石衍生氧化物作为催化剂,从反应温度、空速、进口浓度、氧含量和相对湿度等方面考察了该催化剂对二硫化碳（CS2）催化水解性能的影响以及不同反应条件对催化剂硫容的影响。实验结果表明：当反应温度为60~70℃、反应空速为2 000~4 000 h-1、进口浓度为100~340 mg·m-3、相对湿度为0.47%~0.67%时,该催化剂具有较高的脱硫效果和工作硫容;O2含量的增加促进了水解产物H2S氧化为硫酸盐,进而堵塞催化剂的碱性位,加快了催化剂中毒失活;H2O和CS2之间存在竞争吸附,一定含量的水蒸气有利于CS2的水解反应,而过高含量的水会阻碍水解反应的进行,导致催化剂失活。     

微米级负载型TiO2催化剂在光催化-膜分离反应器中的应用

基于光催化．膜分离三相流化床反应器的结构特点及膜分离特性,以微米级MCM-41分子筛为载体,采用原位生成法制备微米级负载型TiO2催化剂。针对微米级负载型TiO2催化剂在光催化一膜分离反应器中的分布特性、悬浮特性、分离特性及膜污染特性进行研究。结果表明,曝气量一定的情况下,微米级负载型TiO2催化剂在光催化一膜分离反应器中具有良好的悬浮特性,且优于纳米TiO2。随着催化剂投加量的增加,悬浮浓度也随之增加。光催化反应器底部曝气0．3m。／h、催化剂投加量为1g／L时为宜。膜分离器中催化剂悬浮浓度明显低于光催化反应器;该微米级催化剂与纳米TiO2相比具有不粘附、不堵塞膜孔等优良特性,能够有效降低膜污染,延长分离膜使用寿命。膜底曝气为0．1m3／h时,反应器连续运行5h（未加反冲洗）后,微米级负载型TiO2催化剂和纳米TiO2对膜组件的污染程度分别为膜通量衰减率4．3％和37．4％。反应器连续运行72h,膜组件依然具有很好的分离特性。     

Photocatalytic oxidation of gaseous DMF using thin film TiO2 photocatalyst

The heterogeneous photocatalytic oxidation of gaseous N,N'-dimethylformamide (DMF) widely used in the manufacture of synthetic leather and synthetic textile was investigated. The experiments were carried out in a plug flow annular photoreactor coated with Degussa P-25 TiO2. The oxidation rate was dependent on DMF concentration, reaction temperature, water vapor, and oxygen content. Photocatalytic deactivation was observed in these reactions. The Levenspiel deactivation kinetic model was used to describe the decay of catalyst activity. Fourier transform infrared (FTIR) was used to characterize the surface and the deactivation mechanism of the photocatalyst. Results revealed that carbonylic acids, aldehydes, amines, carbonate and nitrate were adsorbed on the TiO2 surface during the photocatalytic reaction. The ions, NH4+ and NO3-, causing the deactivation of catalysts were detected on the TiO2 surface. Several treatment processes were applied to find a suitable procedure for the regeneration of catalytic activity. Among these procedures, the best one was found to be the H2O2/UV process.     

Photocatalytic oxidation of gaseous chlorinated organics over titanium dioxide

The photocatalytic oxidation of high levels of volatile chlorinated organic compounds in gas phase has been studied using a specially designed photoreactor. The influence of light intensity, initial water vapour concentration, temperature, inlet contaminant concentration and flow rate on destruction efficiency has been investigated. The performance of the titanium catalyst was strongly affected by the presence of water in the air stream. Experiments have been most successfully conducted at room temperature, low initial contaminant concentrations, low flow rates and high light intensities. Several by-products have been detected performing photocatalytic degradation of trichloroethylene (TCE) and tetrachloroethylene (PCE). No catalyst deactivation was observed.     

Deactivation of titanium dioxide photocatalyst by oxidation of polydimethylsiloxane and silicon sealant off-gas in a recirculating batch reactor

We have studied deactivation of titanium dioxide (TiO2) photocatalyst by oxidation of polydimethylsiloxane and silicone sealant off-gas in a recirculating batch reactor. Polydimethylsiloxane vapor is a model indoor air pollutant. It does not adsorb strongly on TiO2 in the dark, but undergoes oxidation when the ultraviolet (UV) photons are also present. Commercial silicone (room-temperature vulcanizing) sealant off-gas is an actual indoor air pollutant subject to short-term spikes in concentration. It does adsorb on the TiO2 surface in the dark, but UV photons also catalyze its oxidation. The oxidation of the Si-containing vapors was monitored using a Fourier transform infrared spectroscope equipped with a gas cell. Subsequent to each incremental exposure, a hexane oxidation reaction was performed to track the titania catalyst's activity. The exposures were repeated until substantial deactivation was achieved. We have also documented the regenerative effect of washing the catalyst surface with water. Surface science techniques were used to view the topography of the catalyst and to identify the elements causing the deactivation. Procedural observations of interest in the context of our recirculating batch reactor include the following: the rate of oxidation of hexane was used to assess the activity of a photocatalyst sample; hexane is an appropriate choice of a probe molecule because it does not adsorb in the dark and it undergoes photocatalytic oxidation (PCO) completely, forming CO2; and hexane does not deactivate the photocatalyst surface.     

Photocatalytic oxidation of nitrogen oxides using TiO2 loading on woven glass fabric

TiO2 loading on woven glass fabric is applied to treat nitrogen oxides (NOx) by photocatalytic oxidation (PCO). In this paper, the PCO behavior of NO at high concentrations was studied by PCO of NOx at source levels (20-168 ppm). The PCO efficiency reached 27% in this experiment, while the inlet NOx concentration was 168 ppm (147 ppm NO). The dependency of the reaction rate on several key influencing factors (relative humidity, space time, inlet concentration, oxygen percentage) was also studied. The results illustrate that the resulting hydroxyl radical and active oxide play an important role in the oxidation of NOx. The reactions are limited by the thermodynamic equilibrium after ca. 15s space time. A possible explanation for the catalyst deactivation is the accumulation of nitric acid and nitrous acid on the TiO2 surface during the PCO of NOx. However, the photocatalytic activity can be recovered with a simple heat treatment. The results from the study of the effect of the inlet concentration were described with the Langmuir-Hinshelwood model.     

Photochemical and photocatalytic degradation of gaseous toluene using short-wavelength UV irradiation with TiO2 catalyst: comparison of three UV sources

The feasibility of the use of short-wavelength UV (254+185 nm) irradiation and TiO2 catalyst for photodegradation of gaseous toluene was evaluated. It was clear that the use of TiO2 under 254+185 nm light irradiation significantly enhanced the photodegradation of toluene relative to UV alone, owed to the combined effect of photochemical oxidation in the gas phase and photocatalytic oxidation on TiO2. The photodegradation with 254+185 nm light irradiation was compared with other UV wavelengths (365 nm (black light blue lamp) and 254 nm (germicidal UV lamp)). The highest conversion and mineralization were obtained with the 254+185 nm light. Moreover, high conversions were achieved even at high initial concentrations of toluene. Catalyst deactivation was also prevented with the 254+185 nm light. Regeneration experiments with the deactivated catalyst under different conditions revealed that reactive oxygen species played an important role in preventing catalyst deactivation by decomposing effectively the less reactive carbon deposits on the TiO2 catalyst. Simultaneous elimination of photogenerated excess ozone and residual organic compounds was accomplished by using a MnO2 ozone-decomposition catalyst to form reactive species for destruction of the organic compounds.     

臭氧-二氧化钛光催化技术脱除硫化氢

在连续性反应器内以臭氧-光催化技术氧化硫化氢,证实了臭氧对光催化脱除硫化氢有促进作用,探讨了可能存在的主要基元反应和二氧化钛失活的原因,考察了反应温度、臭氧含量、硫化氢初始体积分数等因素对臭氧-光催化技术脱除硫化氢的影响。结果表明,臭氧在光催化作用下快速分解为活性氧离子或自由基,硫化氢在臭氧和光催化联合作用下快速氧化为二氧化硫,最终转化为硫酸;硫酸在二氧化钛表面的沉积使其催化活性降低,导致硫化氢和二氧化硫的转化率逐渐下降。研究还发现,当硫化氢的初始体积分数为100×10-6时,臭氧和硫化氢的最佳摩尔比约为2:1;臭氧-光催化脱除硫化氢的最佳温度为70℃左右;降低硫化氢的初始体积分数可大幅度降低二氧化硫的选择性。     

Effects of dissolved oxygen, pH, and anions on the 2,3-dichlorophenol degradation by photocatalytic reaction with anodic TiO(2) nanotube films

In this study, the highly-ordered TiO(2) nanotube (TNT) arrays on titanium sheets were prepared by an anodic oxidation method. Under UV illumination, the TNT films demonstrated the higher photocatalytic activity in terms of 2,3-dichlorophenol (2,3-DCP) degradation in aqueous solution than the conventional TiO(2) thin films prepared by a sol-gel method. The effects of dissolved oxygen (DO) and pH on the photocatalytic degradation of 2,3-DCP were investigated. The results showed that the role of DO in the 2,3-DCP degradation with the TNT film was significant. It was found that 2,3-DCP in alkaline solution was degraded and dechlorinated faster than that in acidic solution whereas dissolved organic carbon removal presented an opposite order in dependence of pH. In the meantime, some main intermediate products from 2,3-DCP degradation were identified by a (1)H NMR technique to explore a possible degradation pathway. A major intermediate, 2-chlororesorcinol, was identified from the 2,3-DCP decomposition as a new species compared to the findings in previous reports. Photocatalytic deactivation was also evaluated in the presence of individual anions (NO(3)(-), Cl(-), SO(4)(2-), and H(2)PO(4)(-)). The inhibition degree of photocatalytic degradation of 2,3-DCP caused by these anions can be ranked from high to low as SO(4)(2-)>Cl(-)>H(2)PO(4)(-)>NO(3)(-). The observed inhibition effect can be attributed to the competitive adsorption and the formation of less reactive radicals during the photocatalytic reaction.     

Competitive removal of pharmaceuticals from environmental waters by adsorption and photocatalytic degradation

This work explores the competitive removal of pharmaceuticals from synthetic and environmental waters by combined adsorption-photolysis treatment. Five drugs usually present in waterways have been used as target compounds, some are pseudo-persistent pollutants (carbamazepine, clofibric acid, and sulfamethoxazole) and others are largely consumed (diclofenac and ibuprofen). The effect of the light source on adsorption of drugs onto activated carbons followed by photolysis with TiO₂ was assessed, being UV-C light the most effective for drug removal in both deionized water and river water. Different composites prepared from titania nanoparticles and powdered activated carbons were tested in several combined adsorption-photocatalysis assays. The composites prepared by calcination at 400 °C exhibited much better performance than those synthesized at 500 °C, being the C400 composite the most effective one. Furthermore, some synthetic waters containing dissolved species and environmental waters were used to investigate the effect of the aqueous matrix on each drug removal. In general, photocatalyst deactivation was found in synthetic and environmental waters. This was particularly evident in the experiments performed with bicarbonate ions as well as with wastewater effluent. In contrast, tests conducted in seawater showed adsorption and photocatalytic degradation yields comparable to those obtained in deionized water. Considering the peculiarities of substrate competition in each aqueous matrix, the combined adsorption-photolysis treatment generally increased the overall elimination of drugs in water.     

Study on the photocatalytic reduction of dichromate and photocatalytic oxidation of dichlorvos

In this paper, dichromate and dichlorvos are selected as the deputies of inorganic and organic pollutants, respectively, and TiO2/beads is used as a photocatalyst. The effects of various parameters, such as the amount of the photocatalyst, H2O2 concentration, metal ions, anions, pH value, and organic compounds on the photocatalytic reduction of dichromate and photocatalytic oxidation of dichlorvos are studied. From the studies, the differences of the parameters effect on the photocatalytic degradation of organic and inorganic pollutants are obtained. The results show that the optimum amount of the photocatalyst used is 6.0 g cm(-3) for the photocatalytic reactions. With the addition of a small amount of H2O2, the photocatalytic reduction of dichromate is inhibited while the photocatalytic oxidation of dichlorvos is accelerated. With the addition of trace amounts of Fe3+ or Cu2+, both the reactions are accelerated, and with the addition of Zn2+ and Na+, no obvious effects on the reactions are observed. Acidic solution is favorable for the photocatalytic reduction of dichromate; and acidic and alkaline solutions are favorable for the photocatalytic oxidation of dichlorvos. Adding SO4(2-), the photocatalytic oxidation is accelerated and adding Cl- the reaction is inhibited; and with the addition of trace amounts of SO4(2-), Cl- and NO3-, no obvious effects on the photocatalytic reduction of dichromate are observed. With the addition of methanol and toluene, the photocatalytic reduction of dichromate is accelerated, and the photocatalytic oxidation of dichlorvos is inhibited. The possible roles of the additives on the reactions are also discussed.