Photolysis and photooxidation of typical gaseous VOCs by UV Irradiation: Removal performance and mechanisms

UV photodegradation of 27 typical VOCs was systematically investigated. Contribution of photolysis and photooxidation to VOCs removal was identified. Gaseous VOC could be partially converted to particles by 185/254 nm UV irradiation. The mineralization and conversion of 27 VOCs by UV irradiation were reported. Photodegradation by ultraviolet irradiation (UV) is increasingly applied in volatile organic compound (VOC) and odor gas treatments. In this study, 27 typical VOCs, including 11 hydrocarbons and 16 hydrocarbon derivatives, at 150–200 ppm in air and nitrogen gas were treated by a laboratory-scale UV reactor with 185/254 nm irradiation to systematically investigate their removal and conversion by UV irradiation. For the tested 27 VOCs, the VOC removal efficiencies in air were within the range of 13%–97% (with an average of 80%) at a retention time of 53 s, which showed a moderate positive correlation with the molecular weight of the VOCs (R = 0.53). The respective contributions of photolysis and photooxidation to VOC removal were identified for each VOC. According to the CO₂ results, the mineralization rate of the tested VOCs was within the range of 9%–90%, with an average of 41% and were negatively correlated to the molecular weight (R = -0.63). Many of the tested VOCs exhibited high concentration particulate matters in the off-gases with a 3–283 mg/m³ PM₁₀ range and a 2–40 mg/m³ PM_2.5 range. The carbon balance of each VOC during UV irradiation was analyzed based on the VOC, CO₂ and PM₁₀ concentrations. Certain organic intermediates and 23–218 ppm ozone were also identified in the off-gases. Although the UV technique exhibited a high VOC removal efficiency, its drawbacks, specifically low mineralization, particulate matters production, and ozone emission, must be considered prior to its application in VOC gas treatments.     

儿茶素、表儿茶素没食子酸酯对百菌清的光敏化降解

为研究百菌清的光化学降解,研究了两种外源物质（天然提取物儿茶素和表儿茶素没食子酸酯）在不同条件下对百菌清的光化学降解作用效应和降解途径.结果表明：百菌清（1.88 μmol）水溶液中分别加入10物质的量比的儿茶素和表儿茶素没食子酸酯,在太阳光、紫外灯、高压汞灯照射下百菌清的光降解半衰期分别为12.4、15.4 min,10.7、12.8 min和6.2、2.3 min,儿茶素和表儿茶素没食子酸酯作用下的百菌清降解速率分别提高10.8~37.6和10.0~18.6倍.在稻田水、池塘水和田沟水3种自然水中,百菌清在3种光源下的降解半衰期分别为22.4~86.6、21.7~99.0和14.8~86.6 min;当添加10当量儿茶素时,百菌清的光降解速率分别提高3.0~5.9、1.5~3.0和1.8~2.9倍;当添加10当量表儿茶素没食子酸酯时,百菌清的光降解速率分别提高1.4~4.8、1.6~5.0和2.0~4.3倍.百菌清在儿茶素、表儿茶素没食子酸酯作用下主要降解产物为5-氯-1,3-二氰苯,避免了高毒降解产物4-羟基百菌清的产生;作用机理表现为发生光还原脱氯反应.研究结果可为百菌清使用过程中产生的水体污染修复提供技术参考.     

亚甲基蓝光敏氧化处理造纸废水研究

以造纸废水为例,工业上对高浓度有机废水多采用H2O2及相关组合强化氧化法处理,成本高;尝试利用亚甲基蓝光敏氧化法处理高浓度造纸黄液,探讨其相关条件及处理潜力。实验发现,光解过程复合(太阳)光比利用紫外光效果好;在光敏剂的加入量仅为9．0mg/L,溶解氧含量高于2．0．mg／L,光照水力停留4h时,造纸废水的CODcr的去除率可达到26．8％,达到了H2O2质量浓度为1250．mg／L的Fenton试剂的处理效果。     

表面活性剂光催化降解动力学研究

为了研究光催化法对不同电荷类型表面活性剂的降解性能,在紫外光照射下,用TiO2光催化剂对阴离子表面活性剂十二烷基磺酸钠(SDS)、阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)和两性表面活性剂十八烷基甜菜碱(BS18)进行降解试验.同时,探讨了TiO2光催化剂加入量、表面活性剂初始质量浓度及初始pH对光降解的影响及其动力学过程.结果表明,3种表面活性剂的降解行为符合准一级动力学规律,3种表面活性剂降解速率快慢顺序为:BS18CTABSDS.SDS和BS18的最佳TiO2催化剂用量为1 g.L-1,而CTAB的最优用量为2g.L-1;CTAB和BS18的光降解速率随着活性剂初始质量浓度的增大而线性减小,SDS的降解速率则随活性剂初始质量浓度的增加而缓慢增大;CTAB和BS18在偏碱性条件下降解最快,而SDS在弱酸条件下具有最大的动力学降解速率.     

双氯酚在蒙脱石悬浮水溶液中的光降解

利用金属卤化物灯(钠铊铟灯系列,250W,λ≥365nm)为光源,研究了蒙脱石KSF对悬浮水溶液中双氯酚的光降解及其影响因素。结果表明双氯酚能够在KSF存在下被有效的光降解。在pH3.2,KSF4g/L条件下,5mg/L双氯酚经过100min光照降解去除率达到82.7%;在pH3.0~9.0范围内,双氯酚的去除率在pH值为3时达到最高;在改姓蒙脱石KSF投放量在0~4g/L时,双氯酚的去除率随着投放量的增大而增大;同时,在反应体系中加入羧酸盐可使双氯酚的去除率有一定程度的提高。     

天然日光辐照下河口区CDOM的光化学降解

2005年5月初和5月末,对经0.2μm滤膜过滤的九龙江口低盐度水样进行了2次每天6h、为期1周的天然日光辐照实验,研究有色溶解有机物(CDOM)的荧光与吸收性质的光化学降解特征.结果表明, CDOM的类腐殖质荧光(λEx/λEm = 350/450nm)、类色氨酸荧光(λEx/λEm = 225/350nm)以及吸收系数在初夏短期日光辐照下均发生明显的光化学降解,其降解过程符合一级动力学方程,相应计算出类腐殖质和类色氨酸荧光以及吸收系数a(280)的半衰期分别为3.5～5.1 d、3.0～4.5 d及6.3 d.吸收损失光谱研究表明,对CDOM光降解起主要作用的是太阳辐射的紫外波段.照射42h后,类腐殖质荧光的损失(70%)远高于吸收系数a(280)的损失(约40%),表明CDOM荧光团比发色团更易被光漂白,但两者之间仍保持良好的正相关性.与对照组相比, CDOM经日光辐照后其A250/A350比值增大,表明光化学降解可使其平均分子粒径变小.结果表明, CDOM在入海后可通过光降解作用在近海海域发生转化及清除,光降解是陆源 CDOM 入海后的一个重要归宿.     

碳纳米管负载TiO2对1,2,4-三氯苯的光降解研究

碳纳米管负载TiO2复合光催化剂与纳米TiO2光催化剂对1,2,4-三氯苯的光催化降解效果,及降解动力学的研究结果表明,复合光催化剂比纳米TiO2有更好的光催化降解效果,经254 nm紫外光辐照60 min后,使用复合光催化剂的1,2,4-三氯苯降解了70%,而使用纳米TiO2为催化剂的1,2,4-三氯苯仅降解了51%...     

A new photon kinetic-measure based on the kinetics of electron-hole pairs in photodegradation of textile wastewater using the UV-H2O2FS-TiO2 process

Actual textile wastewater and synthesized wastewater containing various textile dyes were photocatalytic degraded by the UVH2O2Fs-TiO2 process in an aimular-flow photocatalytic reactor. In this process, a photon kinetic-measure was adopted to obtain constant rates of dyes decomposition. It was theorized that, by illumination at different UV frequencies, the electrons within the semiconductor were excited from the valence band to the conduction band, yielding the formation of electron-hole pairs which are the pre-requisites for photocatalysis. CPT （critical photonic time） exposure required to cause 90% of vibrations between the double and single bonds along the molecular chain of the dyes to be oxidized, was taken to measure the photocatalytic activities. The CPTs varied with the frequencies of the UV spectral areas. The derivatization of CPT from the first-order kinetic law was presented.     

阿替洛尔在模拟太阳光照射下的光解

以1000W氙灯为光源,研究了阿替洛尔在模拟太阳光照射下的光降解行为,采用HPLC和SPE-LC-MS技术鉴定了阿替洛尔在250～600nm波长照射下的主要光解产物并提出了可能的光解途径.探讨了溶液pH值、硝酸根离子浓度、腐殖质和碳酸氢根离子等因素对阿替洛尔在模拟太阳光照射下光解的影响.结果表明,阿替洛尔在模拟太阳光下的直接光解很难发生,且改变溶液pH值不能促进直接光解.而在250～600nm波长照射下,阿替洛尔4h光解率达42%,光解途径主要有母体羟基化和支链的断裂反应.在模拟太阳光照下,NO3-对阿替洛尔光解有显著的光敏化作用,而富里酸(SRFA)光敏化作用微弱.HCO3-抑制了模拟太阳光照下阿替洛尔在NO3-溶液中的光解,腐殖质则通过自由基淬灭和内滤机制抑制了阿替洛尔在NO3-溶液中的光解.     

Photolysis of chlortetracycline in aqueous solution: Kinetics, toxicity and products

The aqueous photodegradation of the widely used antibiotic chlortetracycline (CTC) was investigated under simulated sunlight. The quantum yield of photodegradation increased from 3.3 × 10^-4 to 8.5 × 10^-3 within the pH range of 6.0 to 9.0. The presence of Ca²⁺, Fe³⁺, and NO₃^- enhanced the photodegradation of CTC, whereas Mg²⁺, Mn²⁺, and Zn²⁺ inhibited the degradation with the order Mn²⁺ > Zn²⁺ > Mg²⁺ at pH 7.3. The monovalent cations (Na⁺ and K⁺) had negligible effect on the photolysis of CTC. Fulvic acid (FA) decreased the photodegradation of CTC due to light screening effect. Hydrogen peroxide (H₂O₂) was formed concurrently with direct photodegradation of CTC. The generation rate of H₂O₂ increased from 0.027 to 0.086 μupmol/(L.min) when the pH ranged from 6.0 to 9.0. The CTC solution was about three-fold more toxic to the Photobacterium phosphoreum bacteria after irradiation, suggesting that the photoproducts and H₂O₂ formed in the CTC solution exhibited high risk on the bacteria. By LC-ESI(+)-MS, the photoproducts of CTC were identified. The direct photodegradation of CTC was involved in hydroxylation and N-demethyl/dedismethyl processes. The main photoproducts included the iso-CTC analog containing hydroxyl groups (m/z 511.4 and 495.4), and the N-demethyl/dedismethyl products of the photoproduct m/z 495.4 (m/z 481.3 and 467.4). In addition, the photochemical dechlorination of CTC led to tetracycline (m/z 445.5).