The enhancement of photodegradation efficiency using Pt–TiO2 catalyst

This study investigates the mechanism of photosensitization and the recombination of excited electron–hole pairs affected by depositing platinum (Pt) on the surface of titanium dioxide (TiO₂). A new catalyst of Pt–TiO₂ was prepared by a photoreduction process. Being model reactions, the photocatalytic oxidation of methylene blue (MB) and methyl orange (MO) in aqueous solutions using the Pt–TiO₂ catalyst was carried out under either UV or visible light irradiation. The experimental results indicate that an optimal content of 0.75%Pt–TiO₂ achieves the best photocatalytic performance of MB and MO degradation and that the Pt–TiO₂ catalyst can be sensitized by visible light. The interaction of Pt and TiO₂ was investigated by means of UV–Vis absorption spectra, photoluminescence emission spectra, and X-ray photoelectron emission spectroscopy. The Pt⁰, Pt²⁺ and Pt⁴⁺ species existing on the surface of Pt–TiO₂, and the Ti³⁺ species existing in its lattice may form a defect energy level. The Pt impurities, including Pt, Pt(OH)₂, and PtO₂, and the defect energy level absorb visible light more efficiently in comparison with the pure TiO₂ and hinder the recombination rate of excited electron–hole pairs.     

纳米TiO2改性可见光催化降解有机物研究进展

光催化降解水中有机污染物是一项颇有发展前途的废水处理技术.目前主要的研究工作由紫外光逐步向可见光催化方向发展,使这项技术向实用性又迈进了一步.系统介绍了纳米TiO2的光催化降解有机污染物的原理,光催化处理水的现状,并从离子掺杂、表面光敏化和分子筛负载几个方面综述了可见光化的研究现状和发展方向.     

Photochemical degradation and mineralization of 4-chlorophenol

INTENTION, GOAL, SCOPE, BACKGROUND: Since the intermediate products of some compounds can be more toxic and/or refractory than the original compund itself, the development of innovative oxidation technologies which are capable of transforming such compounds into harmless end products, is gaining more importance every day. Advanced oxidation processes are one of these technologies. However, it is necessary to optimize the reaction conditions for these technologies in order to be cost-effective. OBJECTIVE: The main objectives of this study were to see if complete mineralization of 4-chlorophenol with AOPs was possible using low pressure mercury vapour lamps, to make a comparison of different AOPs, to observe the effect of the existence of other ions on degradation efficiency and to optimize reaction conditions. METHODS: In this study, photochemical advanced oxidation processes (AOPs) utilizing the combinations of UV, UV/H2O2 and UV/H2O2/Fe2+ (photo-Fenton process) were investigated in labscale experiments for the degradation and mineralization of 4-chlorophenol. Evaluations were based on the reduction of 4-chlorophenol and total organic carbon. The major parameters investigated were the initial 4-chlorophenol concentration, pH, hydrogen peroxide and iron doses and the effect of the presence of radical scavengers. RESULTS AND DISCUSSION: It was observed that the 4-chlorophenol degradation efficiency decreased with increasing concentration and was independent of the initial solution pH in the UV process. 4-chlorophenol oxidation efficiency for an initial concentration of 100 mgl(-1) was around 89% after 300 min of irradiation in the UV process and no mineralization was achieved. The efficiency increased to > 99% with the UV/H2O2 process in 60 min of irradiation, although mineralization efficiency was still around 75% after 300 min of reaction time. Although the H2O2/4-CP molar ratio was kept constant, increasing initial 4-chlorophenol concentration decreased the treatment efficiency. It was observed that basic pHs were favourable in the UV/H2O2 process. The results showed that the photo-Fenton process was the most effective treatment process under acidic conditions. Complete disappearance of 100 mgl(-1) of 4-chlorophenol was achieved in 2.5 min and almost complete mineralization (96%) was also possible after only 45 min of irradiation. The efficiency was negatively affected from H2O2 in the UV/H2O2 process and Fe2+ in the photo-Fenton process over a certain concentration. The highest negative effect was observed with solutions containing PO4 triple ions. Required reaction times for complete disappearance of 100 mgl(-1) 4-chlorophenol increased from 2.5 min for an ion-free solution to 30 min for solutions containing 100 mgl(-1) PO4 triple ion and from 45 min to more than 240 min for complete mineralization. The photodegradation of 4-chlorophenol was found to follow the first-order law. CONCLUSION: The results of this study showed that UV irradiation alone can degrade 4-CP, although at very slow rates, but cannot mineralize the compound. The addition of hydrogen peroxide to the system, the so-called UV/H2O2 process, significantly enhances the 4-CP degradation rate, but still requires relatively long reaction periods for complete mineralization. The photo-Fenton process, the combination of homogeneous systems of UV/H2O2/Fe2+ compounds, produces the highest photochemical elimination rate of 4-CP and complete mineralization is possible to achieve in quite shorter reaction periods when compared with the UV/H2O2 process. RECOMMENDATIONS AND OUTLOOK: It is more cost effective to use these processes for only purposes such as toxicity reduction, enhancement of biodegradability, decolorization and micropollutant removal. However the most important point is the optimization of the reaction conditions for the process of concern. In such a case, AOPs can be used in combination with a biological treatment systems as a pre- or post treatment unit providing the cheapest treatment option. The AOP applied, for instance, can be used for toxicity reduction and the biological unit for chemical oxygen demand (COD) removal.     

改进Fenton体系处理蒽醌染料的研究

以活性艳蓝KN-R作为研究对象,用UV/Fenton和solar/Fenton/草酸(H2C O4)体系对其进行处理,对反应体系的影响因素作综合的评价.得到处理蒽醌染料废水的最佳条件:dye(活性艳蓝KN-R):Fe2 :H2O2:H2C2O4为5:1:15:1.5,pH为3.0,反应时间为40 min.在最佳条件下,solar/Fenton/H2C2O4体系脱色率达到100%,COD和TOC去除率分别达到87%和66%以上.改进的Fenton方法能使难降解有机染料迅速脱色,矿化程度较高.并对此体系处理活性艳蓝KN-R废水的脱色过程进行动力学模拟,得到此反应为拟一级反应.     

含碳纳米C-TiO_2薄膜光催化降解气相甲苯研究

对以工业丙烷为燃料、空气为氧化剂、TiCl4为先驱物的火焰CVD法制备的含碳纳米C-TiO2光催化剂,用沉降法在石英玻璃管内壁制备C-TiO2纳米薄膜,以管式反应器为光催化氧化装置,实验研究了含碳纳米C-TiO2的纳米薄膜对甲苯气体的光催化降解规律。探讨了甲苯初始浓度和相对湿度等因素对降解率的影响。实验结果表明,相对湿度约为60%时,对甲苯有最佳的光催化降解效果。在催化剂负载量约为4.9mg、主波长为254nm和365nm的8W紫外灯各一盏、甲苯初始浓度约为60mg/m3、气体流量为400mL/min(甲苯在光催化器中停留时间约为3.45s)的条件下,甲苯的降解率可达45%。     

可光－生降解聚乙烯薄膜的降解性能试验

用自然光照法、模拟光照法和堆肥法进行了可光一生降解聚乙烯薄顺和普通聚乙烯薄膜的光降解和微生物降解对比试验。结果表明，前者的光降解和微生物降解性能都明显优于后者。     

纳米TiO2光催化降解直接耐晒蓝的研究

利用溶胶-凝胶法以钛酸四丁酯制备TiO2纳米粉末，考察不同温度焙烧的TiO2催化剂对直接耐晒蓝的光催化降解性能，并用XRD和TEM对催化剂进行了表征．结果表明，400-550℃焙烧的TiO2使直接耐晒蓝溶液的颜色逐渐褪去。最后将苯环结构分解。6h时染料溶液CODcr降解率为88％．降解产物中除含极微量有机酸外，其余均为无机物．当TiO2的焙烧温度为475℃时(颗粒大小为10-20nm)，反应速率最大，为0．0186min^-1，分别比焙烧温度为400℃和550℃时的反应速率大6．8和7．1倍．当体系起始pH值为4．50-7．52时，反应速率随pH值的降低而增大。     

Absence of status signalling by structurally based ultraviolet plumage in wintering blue tits (<Emphasis Type="Italic">Cyanistes caeruleus</Emphasis>)

Structurally based ultraviolet (UV)-reflective plumage parts can be important cues in mate choice. However, it remains largely unknown if UV plumage variation can also function as a signal of social status during competitive interactions. In blue tits (Cyanistes caeruleus), the UV-reflective crown plumage functions as a female mate choice cue that probably indicates male quality, as males with higher UV reflectance have been shown to have better chances of over-winter survival. Possibly, the UV crown plumage acts as a status signal in the competition over scarce food sources during winter. To test this idea, we related dominance of individuals at an artificial food source during adverse winter conditions to spectrophotometric measurements of their crown plumage. However, while controlling for the confounding effects of sex, age, and distance from territory, we found no significant effect of crown UV reflectance on dominance. Consistent with this result, we also found no relation between crown UV reflectance and over-winter survival. We conclude that the structurally based UV reflectance of the blue tit crown feathers plays little role in competition between individuals during winter despite its importance as a cue in mate choice.     

青霉菌对活性艳蓝 KN-R的吸附作用

研究了青霉菌(Penicillium X5)对活性艳蓝KN—R的吸附作用．通过对培养液的波谱分析和宏观现象的观察，结果表明，在72h内，脱色是由吸附引起的．当染料的浓度为100mg/L时，活菌体对染料的吸附率可达88．66％．本实验还研究了对实际应用和吸附过程有影响的几个因素，包括葡萄糖、NaCl、温度和pH.结果表明：葡萄糖浓度在0-20g／L时，随着葡萄糖浓度的增加，菌体的干重相应增加，说明对活性艳蓝KN—R的吸附具有促进作用，但浓度在10-20g／L时，吸附作用不显著；而随着NaCl浓度(0-2％)的增加，吸附率却显著降低．最佳脱色温度为25℃，pH为4．0．活菌体与死菌体的生物吸附均符合Langmuir方程，活菌体比死菌体具有更好的吸附性能．吸附在菌丝体上的染料可以用甲酵进行洗脱，菌丝球在下次使用前用蒸馏水冲洗至pH中性，此菌丝球可重复使用3次．固8表2参11     

Treatment of methylene blue-containing wastewater using microorganisms supported on granular activated carbon under packed column operation

We studied the feasibility of using biological granular activated carbon-packed column in treating methylene blue-containing wastewater. The granular activated carbon with immobilized microbes was packed into a column and fed with 3 liter methylene blue-containing wastewater daily. With initial 1350 mg/l of methylene blue and 1550 mg/l of chemical oxygen demand, it was observed that the colour and chemical oxygen demand removal efficiencies were 99 and 78%, respectively. The high treatment performance of the system could be due to the simultaneous adsorption and biodegradation processes and advantages of immobilized microbes compare to suspended cell system.