宽带隙p区金属氧化物/氢氧化物对苯的光催化降解(英文)

苯具有高毒性和致病性,是空气中常见的一种挥发性有机污染物,对健康和环境危害大.以TiO2为代表的半导体光催化氧化技术是一种理想的环境治理技术,已广泛应用于一般室内挥发性有机物(VOCs)的去除.然而在处理苯等难降解有机污染物时,由于在催化剂表面生成难被降解的聚合物中间产物,往往导致TiO2光催化剂的失活.开发可在常温下使用的降解苯系污染物的高效光催化剂对于推广光催化技术在苯污染治理中的应用具有重大的意义.最近我们研究所开发出一系列宽带隙p区金属氧化物/氢氧化物光催化剂,它们对苯系污染物的光催化降解显示出很好的活性和稳定性,是一类极具应用前景的降解苯系污染物的新型光催化剂.在这篇文章中,我们总结这类宽带隙p区金属氧化物/氢氧化物光催化剂的制备及其光催化降解苯的活性,对其不同于TiO2的光催化机理,及其结构和光催化性能之间的关系进行初步的探讨.     

TiO2/BixTiyOz气相光催化降解苯的动力学模型及反应机理

在密闭不锈钢反应器内考察了TiO2/BixTjyOz催化剂气相光催化降解苯的性能.结果表明,TiO2负载于Bi12TiO20,Bi2Ti2O7和Bi4Ti3O12上制成的催化剂,光催化活性得到很人的提高,TiO2最佳负载量为2.0%;其中,TiO2/Bi12TiO20的光催化活性最高,苯最高转化率是纯TiO2的2倍,催化剂使用寿命也延长了1倍.在本文实验条件下,TiO2/Bi12TiO20上苯气相光催化降解符合Lang-muir-Hinshelwood动力学模型,光催化反应速率常数k和Langmuir吸附常数K分别为0.006 4mg/(L·min)和9.670 2L/mg.采用红外光谱对失活的催化剂进行表征,结果表明催化剂表面出现了羰基与羟基等的振动峰,同时检测到主要的中间产物是2,6-二叔丁基-4-甲基苯酚,它吸附在催化剂表面活性化上而导致催化剂失活.最后推测了苯在催化剂表面气相光催化降解的反应机理.     

气相苯在TiO2光催化剂上吸附常数和光催化反应常数测定

采用溶胶-凝胶法制备TiO2光催化剂以及掺杂Fe3 和Ce3 的TiO2光催化剂,进行间歇式光催化降解气相苯动力学实验,基于光催化Langmuir-Hinshelwood反应动力学模型(L-H模型),测定气相苯在3种光催化剂上的降解动力学常数和吸附平衡常数.根据光催化降解气相苯实验动力学曲线和L-H模型,估算出TiO2、Fe3 /TiO2和Ce3 /TiO2光催化剂光催化降解苯的反应速率常数k和Langmuir吸附常数K分别为0.5247g/m3·min、1.523g/m3·min、1.010g/m3·min和8.605×10-2m3/g、2.390×10-2m3/g、3.928×10-2m3/g.掺杂Fe3 和Ce3 可明显提高光催化剂光催化降解苯的反应速率常数k,其中Fe3 /TiO2,的反应速率常数k最大.     

TiO2/AC复合光催化剂对苯和丁醛的气相光催化降解机理

 利用溶胶-凝胶并水热处理法制备了TiO2光催化剂和TiO2/AC复合光催化剂,在静态光催化反应器中研究了苯和丁醛的气相吸附和光催化降解,利气相色谱分析确定了生成的中间体. 结果表明, TiO2/AC复合光催化剂比TiO2光催化剂具有较强的吸附能力和较高的光催化活性; 在TiO2和TiO2/AC上,苯(或丁醛)光催化降解产生相同的中间体,表明在两种催化剂上发生的光催化反应遵循相同的机理,进而讨论了其可能的光催化氧化途径.     

TiO2光催化降解苯和甲苯的动力学研究

利用溶胶-凝胶法制备了粒径约为13nm、晶型为锐钛矿相和金红石相混晶的TiO2光催化剂,并利用此催化剂对挥发性有机污染物苯和甲苯进行了光催化降解研究,对不同的催化剂用量、光源、污染物的初始浓度以及氧气对光催化反应速率的影响进行了研究。结果表明,光催化降解甲苯和苯的反应均符合假一级动力学方程,光强与光催化降解甲苯的反应的速率常数之间呈指数关系,光波长对光催化降解苯的影响也很显著;随着甲苯和苯初始浓度的增加,光催化反应速率常数降低;氧气加快了光催化降解甲苯和苯的速率;对于光催化降解初始浓度为37.6μmol/L的甲苯而言,催化剂的最佳使用量为0.30g,对于光催化降解初始浓度为9.0μmol/L的苯来说,催化剂的最佳用量为0.10g。     

甲基叔丁基醚光催化降解的反应历程

以自制的TiO2为催化剂,在间歇式光催化反应装置中考察了水中甲基叔丁基醚的光催化降解反应.结果表明,水中MTBE在TiO2催化剂、氧气和紫外光照射的条件下能被光催化转化成无毒产物并最终被矿化.MTBE光催化降解过程中产生的主要中间产物有甲酸叔丁酯、叔丁醇和丙酮,尽管降解速率不同,它们也都能被光催化降解.通过对反应物、中间物及产物的追踪分析,认为MTBE的光催化降解首先是通过羟基化过程来进行,进而提出MTBE光催化降解的可能反应历程.     

纳米TiO2掺杂改性与光催化性能研究

从TiO2的光催化降解机理入手,详细论述了纳米TiO2光催化性能,对近年来提高纳米TiO2光催化活性的多种方法进行了介绍。列举了纳米TiO2光催化降解处理染料废水、农药废水等应用,提出了环保领域中的应用研究现状、存在问题及其解决途径。     

载钛羟基磷灰石光催化降解内分泌干扰物双酚A（英文）

对载钛羟基磷灰石(TiHAP)进行了透射电镜、X射线衍射、紫外-可见光谱和Zeta电位表征,并应用液相色谱-质谱技术对比了TiHAP和P25 TiO2对环境内分泌干扰物双酚A(BPA)的吸附和光催化降解性能,探讨了富里酸和Fe3+对TiHAP薄膜光催化性能的影响.结果表明,TiHAP和TiO2粉体对BPA的吸附符合Langmuir吸附等温方程,且前者吸附性能更大.TiHAP薄膜光催化降解BPA的性能优于TiO2薄膜;富里酸和Fe3+对TiHAP和TiO2薄膜光催化性能的影响趋势不同,从能带结构、电子转移和吸光性等角度分析了性能不同的原因.本结果可以为应用TiHAP降解环境内分泌干扰物提供依据.     

MCM-41分子筛担载纳米TiO2复合材料光催化降解罗丹明B

采用溶胶.凝胶法将TiO2担载在介孔MCM-41分子筛上,制备了不同TiO2含量的系列TiO2/MCM-41复合材料,利用X射线衍射、N2吸附、紫外-可见光谱和透射电镜等方法对其进行表征.TiO2的晶型为锐钛矿相,复合材料的比表面积和孔体积随其中TiO2担载量(复合材料中TiO2与MCM-41的质量比)的增加而减小,TiO2的平均粒径随其担载量的增加而增大.以罗丹明B的光催化降解为探针反应,评价了TiO2/MCM-41复合材料的光催化降解活性.结果表明,在紫外光照射下,罗丹明B在该复合材料上的光催化降解反应遵循一级反应动力学,复合材料对罗丹明B的光催化降解活性明显高于商用TiO2(P-25),复合材料的光催化降解活性由复合材料的吸附能力和所含TiO2的光催化活性共同决定.     

MCM-41分子筛担载纳米TiO2复合材料光催化降解罗丹明B

采用溶胶-凝胶法将TiO2担载在介孔MCM-41分子筛上, 制备了不同TiO2含量的系列TiO2/MCM-41复合材料, 利用X射线衍射、N2吸附、紫外-可见光谱和透射电镜等方法对其进行表征. TiO2的晶型为锐钛矿相, 复合材料的比表面积和孔体积随其中TiO2担载量(复合材料中TiO2与MCM-41的质量比)的增加而减小, TiO2的平均粒径随其担载量的增加而增大. 以罗丹明B的光催化降解为探针反应, 评价了TiO2/MCM-41复合材料的光催化降解活性. 结果表明, 在紫外光照射下, 罗丹明B在该复合材料上的光催化降解反应遵循一级反应动力学, 复合材料对罗丹明B的光催化降解活性明显高于商用TiO2 (P-25), 复合材料的光催化降解活性由复合材料的吸附能力和所含TiO2的光催化活性共同决定.     

Photocatalytic decomposition of tetrachloroethylene in the gas phase with titanium dioxide as catalyst

The gas phase photocatalytic destruction of tetrachloroethylene (PCE) was investigated by using an in situ photocatalytic reactor with FT-IR analysis in batch mode. The main products of PCE degradation are CO₂ and COCl₂, with trichloroacetylchloride as an intermediate. It was found that the rate of PCE degradation and the appearance of products in the gas phase are highly dependent on their adsorption properties on the surface of the catalyst, besides other reaction conditions, such as the intensity of irradiation and the composition of the reaction mixture.     

LED照射光催化剂用于苯、甲苯、乙苯和二甲苯分解(英文)

Studies on the use of gas phase applications of light emitting diodes(LEDs) in photocatalysis are scarce although their photocatalytic decomposition kinetics of environmental pollutants are likely different from those in aqueous solutions.The present study evaluated the use of chips of visible light LEDs to irradiate nitrogen doped titania(N-TiO2) prepared by hydrolysis to decompose gaseous benzene,toluene,ethyl benzene,m-xylene,p-xylene,and o-xylene.Photocatalysts calcined at different temperatures were characterized by various analytical instruments.The degradation efficiency of benzene was close to zero for all conditions.For the other compounds,a conventional 8 W daylight lamp/N-TiO2 unit gave a higher photocatalytic degradation efficiency as compared with that of visible-LED/N-TiO2 units.However,the ratios of degradation efficiency to electric power consumption were higher for the photocatalytic units that used two types of visible-LED lamps(blue and white LEDs).The highest degradation efficiency was observed with the use of a calcination temperature of 350 oC.The average degradation efficiencies for toluene,ethyl benzene,m-xylene,p-xylene,and o-xylene were 35%,68%,94%,and 93%,respectively.The use of blue-and white-LEDs,high light intensity,and low initial concentrations gave high photocatalytic activities for the photocatalytic units using visible-LEDs.The morphological and optical properties of the photocatalysts were correlated to explain the dependence of photocatalytic activity on calcination temperature.The results suggest that visible-LEDs are energy efficient light source for photocatalytic gas phase applications,but the activity depends on the operational conditions.     

Working principle and application of photocatalytic optical fibers for the degradation and conversion of gaseous pollutants

Photocatalytic optical fibers are promising for the degradation of gaseous and volatile pollutants in air due to their high specific surface area, high light utilization efficiency, easy regeneration, and sustainability. In particular, photocatalytic optical fibers have proven highly useful for the removal and conversion of different kinds of air pollutants in air. However, these fibers suffer from low photocatalytic degradation efficiencies. In this review, we have focused on introducing photocatalytic quartz optical fibers and photocatalytic plastic optical fibers for the degradation and transformation of gas-phase air pollutants. The principle of photocatalytic optical fibers and main methods for improving their photocatalytic and light utilization efficiencies based on semiconductor photocatalytic coatings are summarized. Moreover, the Langmuir-Hinshelwood kinetic rate equation was summarized to analyze the photocatalytic reduction of gaseous pollutants. Finally, an outlook on the future of photocatalytic optical fibers toward the removal and conversion of gaseous air pollutants is discussed.     

Analysis of volatile organic chemicals in aqueous samples by purge/GC with selective water removal

A gas chromatographic method for volatile organic chemicals in which an aqueous sample is purged directly to a cryogenically cooled, fused silica column uses a Nafion tube drier between the purge vessel and GC column. The Nafion strips water from the gas stream during the purge step while allowing volatile halocarbons and aromatics to continue to the GC column. Examples of this technique are presented on 0.53 mm and 0.25 mm fused silica columns coated with a variety of stationary phases.     

Cholesteryl acetate as a stationary phase for the gas chromatography of some volatile oil constituents

Cholesteryl acetate provides a useful low-polarity stationary phase in packed columns for the gas chromatography of some volatile oil constituents like terpene hydrocarbons, certain terpenoids and some aromatics. With a high mobile phase flow-rate, it is best used above its melting point as a normal liquid (115°C and more) although it has a narrow mesomeric temperature range below this as a chiral nematic liquid crystal. It can be used to resolve racemic linalol, but not carvone.     

Synthesis of nanoscale titania embedded in MIL‐101 for the adsorption and degradation of volatile pollutants with thermal desorption gas chromatography and mass spectrometry detection

Nanoscale anatase titania was embedded within the porous chromium terephthalate MIL‐101 under low‐temperature hydrothermal treatment. The metal–organic framework shell acting as host matrix can effectively prevent the titania nanoparticles from aggregating and enable a good dispersion of these nanoparticles. The X‐ray diffraction spectra, transmission electron micrography and X‐ray photoelectron spectra clearly showed successful impregnation of the nano‐sized anatase titania within the body of MIL‐101. The resulting TiO₂/MIL‐101 nanocomposite was considered as bifunctional material with abundant adsorptive domains and catalytic domains, and was packed in a quartz tube as a convenient trapping and photocatalytic reactor for hazardous volatile pollutants. The composite showed great potential for adsorptive and photocatalytic degradation of these volatile pollutants, such as formaldehyde and o‐xylene, which were online monitored by thermal desorption gas chromatography with mass spectrometric detection.     

Photocatalytic degradation intrinsic kinetics of gaseous cyclohexane in a fluidized bed photocatalytic reactor

The special photocatalytic degradation intrinsic kinetics of gaseous cyclohexane were investigated in a designed fluidized bed photocatalytic reactor (FBPR). A series of photocatalytic kinetic reaction equations were developed to explore the relationship of degradation efficiency and operating variables based on photocatalytic mechanism and particle fluidization hydrodynamic characteristics. The corresponding results indicated that the initial concentration has influenced the photocatalytic degradation reaction conversion, and having a concentration inflexion point which theoretically divided the photocatalysis into a first-order apparent kinetic rate equation at low concentrations and a zero-order kinetic rate equation at high concentrations. Furthermore, these results were validated theoretically by the intrinsic kinetic models of photocatalytic degradation conversion developed according to variation of cyclohexane concentration and gas velocity. Based on the experimental results, the optimal operating gas velocity range was determined. The multi-factors synergy effect resulting from gas velocity on photocatalytic degradation efficiency was explored and proved by mass transfer, illumination transmission and adsorption models. Finally, the degradation pathways of the cyclohexane and deactivation mechanism of the photocatalyst were studied according to the intermediates degraded on TiO₂ surface, and a feasible method presented for catalyst regeneration.     

室内空气中微量甲醛光催化降解研究进展

综述了甲醛的室内空气污染的研究现状及其对人体健康的影响,阐述了光催化降解的基本原理,分析了液相和气相条件下甲醛降解的途径和影响因素,以及光催化降解甲醛的催化剂的发展情况,讨论了甲醛光催化降解进一步研究的方向和应用前景.     

Novel one step hydrothermal synthesis of TiO2/WO3 nanocomposites with enhanced photocatalytic activity

A novel and simple one step hydrothermal process is used to prepare TiO(2)/WO(3) nanocomposites, in which WO(3) and TiO(2) are present in hexagonal and anatase crystalline forms, respectively, and have enhanced photocatalytic activity towards trichloroethylene degradation in the gas phase.     

Condensed phase aromatization during degradation of poly(vinyl chloride)

Proton NMR results for partially degraded PVC show that aromatization accompanies dehydrochlorination in the condensed phase; subsequent fragmentation leads to loss of volatile aromatics.