TiO2晶须在深度净化饮用水过程中失活原因分析

研究了TiO₂晶须在光催化深度净化饮用水过程中失活的原因及相应的再生方法.对TiO₂薄膜失活前后的AFM、XRD表征,以及对失活前后TiO₂晶须酸洗液的ICP分析表明,TiO₂晶须失活的主要原因是难溶性碳酸钙在催化剂表面的沉积.由于自来水中钙离子的存在以及有机物光催化降解过程中产生的二氧化碳,生成的难溶性碳酸钙覆盖在催化剂的表面,影响了紫外光的透光率,限制了光生电子和光生空穴的生成,导致催化剂的光催化能力逐渐下降直至失活;失活的催化剂通过1 mol/L的盐酸酸洗4　h后,光催化活性可以恢复到95%左右;多次失活/再生的催化剂的光催化活性保持较好的稳定性.     

Fe-MnOx-CeO2/ZrO2低温催化还原NO性能研究

以纳米ZrO2为载体,用浸渍法制备出Fe-MnOx-CeO2/ZrO2催化剂,考察了活性组分配比和助剂负载量对催化剂低温NH3选择性催化还原NO活性的影响,并对催化剂进行了XRD、SEM、EDS和BET表征;探讨了温度、H2O和SO2对Fe-MnOx-CeO2/ZrO2催化剂低温下NH3选择性催化还原NO的影响,结果表明,无SO2和H2O条件下,8%Fe-10%MnOx-CeO2/ZrO2催化剂具有良好的催化活性和稳定性.120℃时,催化剂的脱硝效率为85.23%,当温度升至180℃时,脱硝效率可达到92.0%.SO2和H2O共存条件下,催化剂易失活,采用傅立叶变换红外光谱对各反应阶段的催化剂进行了表征,对其失活机制进行深入研究,结果表明,催化剂失活的主要原因是催化剂表面硫酸铵盐的沉积和催化剂本身活性成分的硫酸盐化.     

吸附相反应技术制备微弱光响应的多组分掺杂TiO2催化剂

利用弱光(紫外和可见)激发Ti O2光降解污染物是拓展多相光催化实际应用的关键之一.以吸附相反应技术为基础,利用N掺杂以及共掺杂两种方式制备多组分Ti O2光催化剂,并研究其在弱光下光降解甲基橙的过程.结合紫外可见漫反射光谱、X射线衍射、X射线电子能谱以及光致发光光谱等表征手段,探索焙烧温度、N掺杂量以及共掺杂对催化剂光吸收和可见光响应拓展的影响,进而研究弱光下催化剂活性的变化规律.结果发现,N掺杂可以显著增强催化剂的光吸收,从而显著提升其在弱紫外光下光降解甲基橙催化活性,所有N掺杂催化剂的活性均优于商用P25光催化剂.N掺杂对催化剂的可见光响应拓展作用不大,因而单一N掺杂后大部分催化剂在弱可见光下没有活性,仅5%N掺杂催化剂在900℃热处理后有微弱活性.N和Fe2O3二元耦合形成的共掺杂催化剂中,两者之间的协同作用既增强了复合光催化剂的光吸收,也显著拓展了催化剂的可见光响应,因而得到了在弱可见光下具有良好活性的复合光催化剂.     

TiO_2光催化氧化室内VOCs的失活再生研究进展

半导体TiO2纳米材料由于其无毒无害,化学性质稳定等优点,目前已经成为环境污染控制领域和材料学领域共同研究的热点。TiO2纳米材料对环境污染物光催化氧化效果显著,但是随着TiO2的反复使用,其催化效率会减低,最终失去光催化的活性;文章主要对TiO2在光催化降解环境污染物后的失活和再生情况进行了综述,讨论了TiO2光催化剂失活的机理以及其再生的途径。     

纳米TiO_2光催化技术及其在环境污染治理中的应用

光催化技术是一项新兴的环境污染物净化技术 ,系统介绍了 Ti O2 光催化净化的机理、纳米 Ti O2 光催化剂的制备技术和催化剂活性的影响因素、以及光催化净化技术在环境污染物治理中的应用。     

TiO2/PPY/Fe3O4的水热法制备及其光催化与磁回收性能

以化学氧化法制备的聚吡咯(PPY)包覆Fe3O4复合材料为磁核,用水热反应法(170℃, pH=7±0.2)在其表面负载了纳米Ti02,制成壳/壳/核结构的磁载二氧化钛光催化剂.并用X射线衍射仪(XRD)、透射电子显微镜(TEM)、傅里叶红外分光光度计(FT-IR)、振动样品磁强计(VSM)、Zeta电位仪对催化剂的物相组成、形貌、表面性质、磁学性质以及磁核的表面电位进行了表征分析.以初始浓度为25mg/L的苯酚溶液为模拟污染物, 对其进行光催化降解以考察其催化活性;并以自制的磁回收装置考察其磁回收率.结果表明,所制备的Ti02粒径在4~7nm,具有混晶结构,其中锐钛矿占95.2%,金红石占4.8%;PPY对Ti02在磁核表面的负载具有促进作用,TiO2在PPY/Fe3O4表面负载牢固;催化剂TPF(nTiO2:n PPY:nFe3O4 =30:2.1:1)具有良好的壳/壳/核结构,其磁感应强度为40emu/g,具有超顺磁性;所制备的催化剂光催化降解苯酚符合假一级反应动力学方程,其中纯TiO2、P25、TPF反应速率常数K值分别为0.0279、0.0264、0.0252,TPF循环使用5次后K值为0.020,催化活性略有降低,循环使用平均回收率可达到90.35%. 该法制备的磁载Ti02光催化剂具有优良的催化活性和磁回收性能,具有良好的应用前景.     

光催化氧化苯甲酸时TiO2中毒机理及再生方法的研究

以苯甲酸作为模型污染物,采用强制中毒的方法研究了TiO2在悬浮光催化氧化体系中的中毒过程,并通过对中毒TiO2进行IR、SPS及XPS表征,分析了中毒后TiO2的表面性质,揭示了苯甲酸光催化降解过程中TiO2光催化剂的中毒机理.采用高温焙烧、UV光照射及超声波振荡等方法对中毒TiO2进行再生,并考察再生效果.研究表明,实验条件下,催化剂反复使用20次后将完全中毒.引起TiO2中毒的主要原因是苯甲酸及其降解中间产物,如羟基苯甲酸、顺丁烯二酸、反丁烯二酸等吸附、积累在TiO2表面,占据了TiO2的表面活性位置,使其光催化活性下降;TiO2在使用过程中出现的团聚现象也会导致其活性降低.比较了高温焙烧、UV光照及超声波清洗3种方法对中毒催化剂的再生效果的比较研究,结果表明,3种方法均能使中毒后TiO2的催化活性得到一定恢复,其中高温焙烧对中毒TiO2的再生效果较好.     

燃煤电厂商用SCR脱硝催化剂的失活机理及再生

对燃煤电站运行3年的失活脱硝催化剂进行失活机理分析和再生研究。失活机理研究表明:飞灰磨蚀和堵塞,以及碱金属K和Na中毒是该燃煤电站催化剂失活的主要原因;其次,少量硫酸盐在催化剂表面沉积降低其活性。分别采用水洗再生、硫酸酸洗再生和钒活性液浸渍再生工艺处理,结果表明:水洗再生脱硝活性可提升12%左右,酸洗再生可提升20%左右。采用多次浸渍法对预处理失活催化剂进行钒活性液浸渍再生,脱硝效率进一步提升,最高脱硝率达到99%。     

纳米TiO2对气相中甲醛光催化降解的研究

采用溶胶-凝胶法制备了掺杂金属离子的纳米TiO₂光催化剂,运用透射电镜和X射线衍射手段对催化剂的结构进行了表征,并将制备的光催化剂负载于不锈钢丝网、玻璃弹簧和泡沫镍板3种不同载体上,以室内空气典型污染物甲醛气体为模型反应物,研究了3种不同改性纳米TiO₂光催化剂对甲醛气体的光催化作用,3种光催化反应器的催化效率以及环境因素对光催化效率的影响,同时考察了催化剂的失活特征.结果表明:该负载型纳米TiO₂光催化剂具有较高的光催化活性,其中掺镧1.5%(质量分数)的TiO₂对甲醛的降解率最高,60 min达到91.5%,大于掺铁和掺银;泡沫镍板作为负载载体的光催化效率大于玻璃弹簧和不锈钢丝网;循环风量和不同波长紫外光对该光催化反应影响不大,反应中催化剂存在失活现象,但在清洁后能够恢复.      

核壳结构TiO_2/SiO_2/Fe_3O_4颗粒的制备及性能研究

针对纳米Ti O2光催化剂回收困难、成本较高等问题,采用溶胶-凝胶法在表面包覆了Si O2的磁基体Fe3O4上负载Ti O2,制备出一种具有光催化作用的核壳结构Ti O2/Si O2/Fe3O4功能纳米颗粒。通过TEM、XRD等对其包覆效果及结构进行表征,结果表明,Si O2、Ti O2包覆的醇∶酯∶水的比例分别为4.6∶12.3∶1和30.3∶12.5∶1时可以得到包覆均匀的Ti O2/Si O2/Fe3O4功能颗粒。在可见光和紫外光的照射下,Ti O2/Si O2/Fe3O4光催化剂降解亚甲基蓝溶液的脱色率分别为85.16%和78.86%,使用5次后颗粒的回收率仍能保持在75%以上,具有优异的光催化降解性能,并且可重复利用率高。     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day, Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury （HgT）, combinative mercury （Hgc） and gaseous mercury （HgG）, and content of total organic carbon （TOC）, but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average Hgv of profiles 1992, 1996, and 2000 was similar, but their average HgG was quite different. HgT was significantly correlated with Hgc in profile 1992 and 2000, and Hgv was significantly correlated with Hg6 in profile 1996. HgG/Hgv ratio in profile samples decreased in the order of （HgG,/HgT）1992〉（HgG/HgT）1996〉〉（HgG/HgT）2000. A simple outline of Hg release in landfill could be drawn： with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf〉root〉stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants （e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum） are capable of enriching more Hg than herbaceous plants.     

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils.Bidens maximowicziana is a new Pb hyperaccumulator,which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb.The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues.The Pb distribution order in the B. maximowicziana was:leaf>stem>root.The effect of amendments on phytoremediation was also studied.The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application.Compared with CK(control check),EDTA application promoted translocation of Pb to overground parts of the plant.The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg.This research demonstrated that B.maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil,especially,combination with EDTA.     

Potential of plant polyphenol oxidases in the decolorization and removal of textile and non-textile dyes

In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.     

Decomposition of alachlor by ozonation and its mechanism

Decomposition and corresponding mechanism of alachlor, an endocrine disruptor in water by ozonation were investigated. Results showed that alachlor could not be completely mineralized by ozone alone. Many intermediates and final products were formed during the process, including aromatic compounds, aliphatic carboxylic acids, and inorganic ions. In evoluting these products, some of them with weak polarity were qualitatively identified by GC-MS. The information of inorganic ions suggested that the dechlorination was the first and the fastest step in the ozonation of alachlor.     

Enzymatic oxidation of aqueous pentachlorophenol

The influence of the nonionic surfactant Tween 80 on pentachlorophenol （PCP） oxidation catalyzed by horseradish peroxidase was studied. The surfactant was tested at concentrations below and above its critical micelle concentration （CMC）. Enhancement of PCP removal was observed at sub-CMCs. The presence of Tween 80 in the reaction mixture reduced enzyme inactivation which occurred through a combination of free radical attack and sorption by precipitated products. A simple first-order model was able to simulate time profiles for enzyme inactivation in the presence or absence of Tween 80. At supra-CMCs, the surfactant caused noticeable reductions in PCP removal, presumably through micelle partitioning of PCP which precluded the hydrophobic PCP molecule from interacting with the enzyme.     

Removal of heavy metals from sewage sludge by low costing chemical method and recycling in agriculture

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Organochlorine pesticides in soils under different land usage in the Taihu Lake region, China

A field study was conducted in the Taihu Lake region, China in 2004 to reveal the organochlorine pesticide concentrations in soils after the ban of these substances in the year 1983. Thirteen organochlorine pesticides (OCPs) were analyzed in soils from paddy field, tree land and fallow land. Total organochlorine pesticide residues were higher in agricultural soils than in uncultivated fallow land soils. Among all the pesticides, ΣDDX (DDD, DDE and DDT) had the highest concentration for all the soil samples, ranging from 3.10 ng/g to 166.55 ng/g with a mean value of 57.04 ng/g and followed by ΣHCH, ranging from 0.73 ng/g to 60.97 ng/g with a mean value of 24.06 ng/g. Dieldrin, endrin, HCB and α-endosulfan were also found in soils with less than 15 ng/g. Ratios of p,p'-(DDD DDE)/DDT in soils under three land usages were: paddy field ＞ tree land ＞ fallow land, indicating that land usage inlfuenced the degradation of DDT in soils. Ratios of p,p'-(DDD DDE)/DDT ＞1, showing aged residues of DDTs in soils of the Taihu Lake region. The results were discussed with data from a former study that showed very low actual concentrations of HCH and DDT in soils in the Taihu Lake region, but according to the chemical half-lives and their concentrations in soils in 1980s, the concentration of DDT in soils seemed to be underestimated. In any case our data show that the ban on the use of HCH and DDT resulted in a tremendous reduction of these pesticide residues in soils, but there are still high amounts of pesticide residues in soils, which need more remediation processes.     

Single and joint effects of pesticides and mercury on soil urease

The influence of two pesticides including chlorimuron-ethyl and furadan and mercury （Hg） on urease activity in 4 soils （meadow burozem and phaeozem） was investigated. The soils were exposed to various concentrations of the two pesticides and Hg individually and simultaneously. Results showed that there was a close relationship between urease activity and organic matter content in soil. Chlorimuron-ethyl and furadan could both activate urease in the 4 soils. The maximum increment of urease activity by chlorimuronethyl was up to 14%-18%. There was almost an equal increase （up to 13%-21%） in the urease activity by furadan. On the contrary, Hg markedly inhibited soil urease activity. A logarithmic equation was used to describe the relationship （P〈0.05） between the concentration of Hg and the activity of soil urease in the 4 tested soils. Semi-effect dose （ED50） values by the stress of Hg based on the inhibition of soil urease in the 4 soils were 88, 5.5, 24 and 20 mg/kg, respectively, according to the calculation of the corresponding equations. The interactive effect of chlorimuron-ethyl or furadan with metal Hg on soil urease was mainly synergic at the highest tested concentrations.