室内空气中三氯乙烯在TiO2/AC上的光催化氧化反应动力学

采用具有多层结构的蜂窝状整体式光催化净化块为催化材料，设计了室内空气净化光催化反应器，以三氯乙烯（TCE）为模拟污染物，在25℃、常压下，进行水、TCE的吸附等温线的测试和TCE的光催化降解反应动力学研究。水与TCE的平衡吸附采用Langmrir吸附等温线表示；TCE在TiO2表面的光催化反应采用简单的L-H速率方程来表征，并进行了模型值与实验值的比较，结果令人满意。     

气固相光催化氧化反应动力学分析

对气固相光催化氧化基元反应进行了动力学分析 ,建立了简单适用的动力学模型 .理论分析表明 ,在较低的紫外光强度下 ,光催化反应速率与光强成正比 ;在较高的光强度下 ,速率与光强的平方根成正比 ;在极高光强度下 ,速率与光强无关 .因此将光催化反应简单分解为 3个速率步骤 ,即光子传递步骤、表面作用步骤、扩散步骤 .设计了新颖的气固相光催化反应器 ,采用三氯乙烯 (TCE)为模拟污染物 ,实验结果验证了气固相光催化反应存在光子传递和表面作用控制步骤     

光催化降解炼化反渗透浓水的动力学特性和影响因素

以难生化处理的炼厂反渗透(RO)浓水为降解对象,考察反应时间、pH、催化剂投加量等对悬浮体系纳米TiO_2(P25)光催化降解RO浓水的影响,并对光催化降解RO浓水的动力学模型和吸附模型进行研究。结果表明,在低压汞灯光照8 h,光催化剂投加量为1 g/L,pH为4.5时,CODCr最高去除率达到47.51%;在不同pH下催化剂的吸附过程符合准二级动力学方程,平衡吸附量随pH增大而减小;光催化降解过程随反应时间遵循Langmuir-Hinshelwood动力学模型,反应符合准一级反应动力学方程。经光催化处理后,RO浓水B/C值从0.01提高到0.22,可生化性显著提高,为后续生化处理创造条件,也为光催化技术应用于难降解工业污水提供借鉴和参考。     

光催化降解炼化反渗透浓水的动力学特性和影响因素

以难生化处理的炼厂反渗透(RO)浓水为降解对象,考察反应时间、pH、催化剂投加量等对悬浮体系纳米TiO_2(P25)光催化降解RO浓水的影响,并对光催化降解RO浓水的动力学模型和吸附模型进行研究。结果表明,在低压汞灯光照8 h,光催化剂投加量为1 g/L,pH为4.5时,CODCr最高去除率达到47.51%;在不同pH下催化剂的吸附过程符合准二级动力学方程,平衡吸附量随pH增大而减小;光催化降解过程随反应时间遵循Langmuir-Hinshelwood动力学模型,反应符合准一级反应动力学方程。经光催化处理后,RO浓水B/C值从0.01提高到0.22,可生化性显著提高,为后续生化处理创造条件,也为光催化技术应用于难降解工业污水提供借鉴和参考。     

介孔氧化钛晶须气相光催化降解三氯乙烯

以水合氧化钛和K2CO3为原料合成了介孔TiO2晶须,表征结果显示,其为锐钛矿型,具有微米级形貌和较高的比表面积和均匀的孔径. 在波长为365 nm的紫外光下光催化降解三氯乙烯(TCE),介孔TiO2晶须对TCE的降解率达到95%,高于Degussa P-25 TiO2粉末对TCE的降解率(87%),具有更高的光催化氧化活性,降解速率随TCE初始浓度升高而加快,当空气流速为1.64 cm/s时转化速率最高,其中氧气加快了光催化反应,光催化反应符合Langmuir-Hinshelwood动力学方程.     

光催化反应器中光降解重金属Cr(Ⅵ)的研究

在光催化反应器中进行不同酸性条件下Cr(Ⅵ)吸附转化试验。结果表明TiO2对Cr(Ⅵ)吸附在pH值为1.5～2.5时最大,在此期间光照3h后,Cr(Ⅵ)降解转化率可大于95%。在pH值为1.5时,酸性反应阻抑作用可按磷酸>硫酸>盐酸>硝酸依次减弱,因为TiO2表面不同酸根离子对Cr(Ⅵ)离子的竞争吸附能力有差异。在pH值为4.0时,以甲醛、甲酸作为空穴消除剂,二氧化钛吸附性能及反应速率都明显提高,但在同一条件下,甲酸协同作用效果优于甲醛。在磷酸存在时,甲酸、甲醛对反应促进作用不明显。     

纳米TiO2光催化氧化愈创木酚的降解机理

以木质素的模型物愈创木酚(G-M)为研究对象,采用自制的纳米TiO2作光催化剂,在一定的降解条件下对G-M光催化降解的动力学和机理进行了研究.实验表明G-M的光催化降解过程包括吸附和降解两部分,通过对G-M在TiO2表面吸附性能的测定,得到其吸附平衡常数,在此基础上运用L-H方程对G-M光催化降解的动力学方程进行讨论,得到降解反应动力学方程1/r=1.744/C 0.103 4.采用有机物特征功能团的显色法,对G-M光催化降解反应过程的中间产物进行了分析,推断在G-M降解反应过程中出现了开环、脱羧,最终完全分解矿化生成二氧化碳和水.     

光催化与吸附联合技术的应用初探

从室内空气的分类出发,介绍了其来源、污染现状以及其对人体的危害,并在此基础上具体地介绍了目前净化室内空气的基本方法,比如吸收技术、光催化、膜分离技术、植物净化技术等。同时探讨了光催化技术和吸附技术在净化室内空气上的应用。从而提出了光催化与吸附技术在联合应用上急需解决的问题以及发展趋势。     

三氯乙酸光催化降解过程中pH值变化影响因素的研究

研究了三氯乙酸在TiO2薄膜为催化剂的光催化反应体系中发生光催化降解反应时pH值的变化与影响因素。结果表明在反应过程中pH值不断变化呈现逐渐降低的趋势,pH值条件对三氯乙酸的光催化降解反应有一定的影响,低pH值有利于反应的进行。     

pH值对SnO2/ZnO形貌及光催化性能的影响

为考察酸度对SnO_2/ZnO样品的形貌及光催化活性的影响,以氯化锌和四氯化锡为原料,采用水热反应法在不同酸度条件下制备系列SnO_2/ZnO,并以亚甲基蓝作为目标降解物测试SnO_2/ZnO的光催化活性。采用Fourier红外光谱仪、X射线衍射仪、扫描电子显微镜、紫外可见漫反射光谱仪、X光电子能谱仪、荧光发射光谱及N_2吸附–脱附技术对SnO_2/Zn O进行表征。结果表明:通过调节反应溶液酸度可得到粒状、立方体和球状等不同形貌的SnO_2/ZnO复合材料。光催化实验表明:SnO_2/ZnO系列样品的光催化活性均高于ZnO和SnO_2,在pH值为9的条件下制备的具有立方体结构的样品(Zn-9)光催化效果最好,光照70 min对10 mg/L亚甲基蓝溶液的降解率达97.5%,循环使用5次后依然保持较高的光催化活性。     

Photocatalytic degradation of gaseous trichloroethene using immobilized ZnO/SnO2 coupled oxide in a flow‐through photocatalytic reactor

The photocatalytic degradation of gaseous trichloroethene (TCE) was investigated on immobilized ZnO/SnO₂ coupled oxide in a flow‐through photocatalytic reactor. It was found that gaseous photocatalysis is an efficient method for volatile organic compounds' abatement and air purification. Degradation of ～100% was found for TCE at the concentrations examined, up to 400 ppmv, in a flow‐through dry synthetic gas stream. In our tested conditions, the flow rate had little influence on the photocatalytic degradation efficiencies of TCE, while the relative humidity had a significant influence on the photocatalytic degradation of TCE. The photocatalytic degradation efficiencies of TCE increased slowly below 20% relative humidity and then decreased as the relative humidity increased further. The deactivation of used immobilized photocatalyst was not observed within the 200 h testing period in the present experiment, although the surface of the photocatalyst changed greatly during the use of the photocatalyst. Copyright © 2004 Society of Chemical Industry     

PHOTOCATALYTIC DEGRADATION OF GASEOUS AMMONIA AND TRICHLOROETHYLENE OVER TiO 2 ULTRAFINE POWDERS DEPOSITED ON ACTIVATED CARBON PARTICLES

Two kinds of activated carbon (AC) particles, which possess large adsorption capacity for gaseous ammonia and trichloroethylene (TCE), were selected as the carrier of TiO 2 ultrafine powders. Commercially available TiO 2 sol solutions were used as the source of TiO 2 powders. For the sake of comparison, porous glass (PG) particles and alumina (AL) particles were also selected as the carrier. The photocatalytic activity of TiO 2 /AC, TiO 2 /PG, and TiO 2 /AL was examined using a circulation reaction method. The photocatalytic degradation of gaseous ammonia and TCE was found apparently to obey the first-order reaction with respect to ammonia or TCE. The first-order reaction rate constant over TiO 2 /AC was shown apparently to be higher than those over TiO 2 /PG and TiO 2 /AL. The observed relationship between the apparent first-order rate constant and the TiO 2 catalyst loading could be interpreted satisfactorily in terms of a reaction model based on the premise that the degradation rate constant is proportional to the illumination intensity, whose decay obeys the Lambert-Beer law; this is an extension of the reaction model in a three-phase fluidized-bed reactor under illumination proposed in our preceding paper.     

Kinetic study for photocatalytic degradation of volatile organic compounds in air using thin film TiO2 photocatalyst

The present paper examined the kinetics of photocatalytic degradation of volatile organic compounds (VOCs) including gaseous trichloroethylene (TCE), acetone, methanol and toluene. Variable parameters were initial concentration of VOCs, water vapor content and photon flux of ultra-violet (UV) light. A batch photo-reactor was specifically designed for this work. The photocatalytic degradation rate increased with increasing the initial concentration of VOCs, but maintained almost constant beyond a certain concentration. It matched well with the Langmuir–Hinshelwood (L–H) kinetic model. For the influence of water vapor in a gas phase photocatalytic degradation rate, there was an optimum concentration of water vapor in the degradation of TCE and methanol. And, water vapor enhanced the photocatalytic degradation rate of toluene, whereas it inhibited that of acetone. As for the effect of photon flux, it was found that photocatalytic degradation occurs in two regimes with respect to photon flux.     

Cr3+掺杂TiO2粉末的水热制备及光催化活性

以钛酸四丁酯为钛源,采用水热法制备了铬离子掺杂的TiO2纳米粉末光催化剂。通过X射线衍射(XRD),扫描电子显微镜(SEM)、透射电子显微镜(TEM),高分辨透射电子显微镜(HRTEM)和比表面积(BET)等方法对新制备的二氧化钛粉末进行表征。新制二氧化钛的光催化活性通过在紫外光照射下光催化降解室温下空气中的丙酮来表征。研究并探讨了Cr3+掺杂浓度对二氧化钛粉末的微结构和光催化活性的影响。实验结果表明,制备的掺杂浓度0.5%的Cr3+-TiO2纳米粉末具有最好的光催化活性。     

新颖填充床光催化反应器的辐射能分布模拟

采用以玻璃弹簧为载体的新颖负载型光催化剂 ,设计实验测试该催化剂的辐射能分布状况 ,通过实验测量修正双通量模型的参数 ,并使用修正双通量模型进行计算 ,上述实验值与理论计算值吻合较好 ,说明修正双通量模型可准确模拟多相光催化反应器的辐射能传递行为 .最后 ,采用该模型描述了由此负载型催化剂构成的平板式填充床光催化反应器内的辐射能分布和吸收状况     

Kinetic behaviour of the adsorption and photocatalytic degradation of salicylic acid in aqueous TiO2 microsphere suspension

A new photocatalyst, named TiO₂ microspheres, prepared by a sol‐spraying‐calcination method, can freely suspend with air bubbling in its aqueous suspension and easily settle down from a water phase under gravity. The experimental results demonstrated that TiO₂ microspheres had better adsorption capacity than conventional TiO₂ powders, due to large surface area, large pore volume, and also a porous structure. The photocatalytic activity of TiO₂ microspheres in aqueous suspension was evaluated using salicylic acid (SA) as a model substrate. It was found that the Langmuir–Hinshelwood model in its integral form described the kinetics of SA photocatalytic degradation in the TiO₂ microsphere suspensions better than its simplified form as a first‐order reaction model, since the significant substrate adsorption on the catalysts was not negligible. The kinetics of SA photocatalytic degradation with different initial concentrations and pH was further investigated. The experiments demonstrated that the change of pH could significantly affect the adsorption of SA in the TiO₂ microsphere suspensions. The effects of substrate adsorption rate and photoreaction rate on the overall performance of photocatalytic degradation is also discussed on the basis of experimental data. Copyright © 2004 Society of Chemical Industry     

Investigation into Photocatalytic Degradation of Gaseous Benzene in a Circulated Photocatalytic Reactor (CPCR)

Due to the fact that suspended TiO₂ powder enjoys free contact with gaseous pollutant molecules in photocatalytic reactors, it can generally achieve better efficiency than immobilized TiO₂ catalysts. However, difficulties with the separation of this catalyst powder from treated pollutants and its re‐use often limit its application. Therefore, a circulated photocatalytic reactor (CPCR) was designed to enhance the performance of the photocatalytic degradation of gaseous benzene. TiO₂ film photocatalysts were prepared by the sol‐gel method at low temperatures and coated onto the inner wall of this reactor by a bonding agent composed of poly‐(2, 2‐dimethyl)‐acrylic ethylene ester emulsion in which TiO₂ powder was characterized by FTIR, TEM and SEM. In particular, the influences of initial concentration and gas flow rate of benzene on the degradation conversion, D_p, apparent reaction rate constants, k_r, initial degradation rate, r, and the deactivation and regeneration of catalyst in the CPCR, were investigated. The results indicated that the degradation conversion, apparent reaction rate constants and initial degradation rate were closely correlated to the initial concentration of benzene. To elucidate the factors governing the observations, the adsorption characteristics and kinetics of the photocatalytic degradation of benzene were analyzed using the Langmuir adsorption isotherm and Langmuir‐Hinshelwood kinetic model. It was found that the reaction kinetics were best described by a fixed pseudo‐first‐order kinetic equation of photocatalytic degradation of gaseous benzene in the CPCR.     

Synthesis of Reduced Graphene Oxide/Copper Tin Sulfide (Cu2SnS3) Composite for the Photocatalytic Degradation of Tetracycline

Reduced graphene oxide (rGO)-copper tin sulfide (Cu₂SnS₃), (rGO-CTS), composites were successfully synthesized through a facile ex-situ process and the obtained composites were utilized as photocatalysts for the degradation of tetracycline (TCE) under a UV-LED irradiation. Physicochemical and morphological characterization of the composites confirmed the incorporation of CTS unto rGO. The optical study of the composites, using absorption spectroscopy, showed a red shift to lower energy with increase in the percentage of rGO in the composites. This reduction in band gap suggests a possible enhancement in photocatalytic potency due to enhanced charge carrier generation. The photocatalytic degradation study showed an increase in TCE degradation with increase in rGO content of the composite. This enhanced photocatalytic activity could be ascribed to: (i) enhanced adsorption properties due to the increased presence of oxygenated functional groups on rGO, and (ii) increased charge carrier generation and separation due to modification of the band edge potentials of the composites by the incorporation of rGO. Radical scavenging studies of the degradation process showed that photogenerated holes played the most significant role in the degradation process. A plausible mechanism was proposed for the degradation process based on the radical scavenging experiment and charge carrier characteristics of the catalyst.

     

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.     

Effect of humidity on the photocatalytic degradation of trichloroethylene in gas Phase over TiO2 thin films treated by different conditions

The effect of humidity on the photocatalytic degradation reaction of trichloroethylene (TCE) in gas phase was investigated by using pretreated TiO₂ sol-gel films. It was observed that the photocatalytic activity of the TiO₂ films depended more greatly on the pretreatment conditions, for example, UV pre-illumination, than on the moisture content. When the relative humidity was over 50%, the reaction rates decreased regardless of treatment conditions of the photocatalyst. The photocatalytic decomposition rate of TCE increased with the increase of light intensity. However, the influence of humidity on the reaction rate was less significant under the increased light intensity. The intermediates and byproducts of the reaction were not changed in different humidity conditions.