|Alternative Title||Dynamic Monitoring and Control of Highly Toxic Intermediates during Photocatalytic Degradation of Pentachlorophenol 【作者】 马海艳 中国科学院生态环境研究中心|
|Place of Conferral||北京|
|Keyword||Tio2光催化,五氯酚,卤代醌,Ros,降解 Tio2 Photocatalysis, Pentachlorophenol, Halobenzoquinones, Ros, Degradation|
首先检测了TiO2/PCP体系所产生的中间产物。四氯-1,4-苯醌（TCBQ），四氯-1,4-氢醌（TCHQ），三氯一羟基-1,4-苯醌（OH-TrCBQ）和2,5-二氯-3,6-二羟基-1,4-苯醌（OH-DDBQ）被确定为主要中间产物。在这些主要中间产物中， TCBQ和OH-TrCBQ具有比PCP还高或者与PCP相当的毒性。由于TCBQ和OH-TrCBQ都能在H2O2存在下产生化学发光（CL），我们开发了一种连续流化学发光（CFCL）方法，用于动态监测光催化降解PCP中产生的两种有毒中间产物。我们将PCP/TiO2悬浮液在光催化反应池中照射使之发生降解反应，然后在降解过程中将PCP/TiO2悬浮液连续泵入化学发光检测池并与H2O2混合以产生化学发光信号。CFCL曲线在初始pH = 7的条件下显示出两次化学信号升高再降低的过程。我们利用高效液相色谱法（HPLC）测量中间产物的浓度变化确定它们分别对应的是OH-TrCBQ和TCBQ。我们从TCBQ能够迅速水解的角度考虑PCP的降解机理，提出PCP的降解过程既包括光催化的过程又包括水解的过程。此外，PCP/TiO2悬浮液的CFCL响应曲线显示出与降解过程中毒性变化非常相似的趋势。因此，CFCL法可作为简单、低成本的方法用于动态监测PCP降解过程中所生成的TCBQ和OH-TrCBQ。
The presence of pentachlorophenol (PCP) in water cause water quality problems owe to its past widespread application and stability, harmful to human health. Photocatalysis, which was a powerful technique for the decomposition of pollutants, mainly involved in the reactive oxygen species (ROS) reaction, has a large potential as a sustainable water treatment process. However, toxic intermediates might be generated which have become a great concern recently. Although contributions of ROS on PCP degradation have been reported, the roles of ROS in the whole degradation process including parent PCP and its highly toxic intermediates such as chloranil are not yet clearly defined. The main objectives of this work were to study the detailed photocatalytic degradation characteristics and pathways of PCP on the TiO2 suspension, define the roles of ROS involved in the degradation of the main toxic intermediate and elucidate the degradation mechanisms, and find a solution to effectively degrades PCP and the main intermediates. This work mainly includes three parts as follows:
Firstly, the intermediates produced by the TiO2/PCP system were examined. Tetrachloro-1,4-benzoquinone (TCBQ), tetrachloro-1,4-hydroquinone (TCHQ), trichlorohydroxy-1,4-benzoquinone (OH-TrCBQ) and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (OH-DDBQ) were identified as main intermediates. Among the main intermediates, TCBQ and OH-TrCBQ showed higher or similar toxicity to PCP. As both TCBQ and OH-TrCBQ can produce chemiluminescence (CL) in the presence of H2O2, a continuous flow chemiluminescence (CFCL) method was developed for dynamic monitoring of toxic intermediates generated in the photocatalytic degradation of PCP. A PCP/TiO2 suspension was irradiated in a photoreactor, then pumped continuously into a detection cell and mixed with H2O2 to produce CL signals. The time-dependent CL response displayed two distinctive peaks at initial pH 7, which were attributed to the generation of OH-TrCBQ and TCBQ respectively by comparing with their changes measured by High-Performance Liquid Chromatography (HPLC). We Proposed the degradation mechanism of PCP included both the photocatalytic process and the hydrolysis process. Furthermore, the CL response curve of PCP/TiO2 suspension showed a pattern very similar to their bacteria inhibition. Therefore, the CFCL could be used as a simple and low-cost method for online monitoring of TCBQ and OH-TrCBQ to ensure complete removal of not only PCP but also highly toxic degradation intermediates.
Secondly, the production of the ROS including hydroxyl radicals (?OH), superoxide anion (O2?-), and hydrogen peroxide (H2O2) was studied on three kinds of TiO2 (P25, Anatase, and Rutile). The roles of generated ROS were systematically explored during the photocatalytic degradation of PCP and its main intermediates by the TiO2/ultraviolet (UV) system using different radical quenchers to elucidate the oxidation mechanisms. The results showed that ?OH played the dominant role in the photocatalytic degradation of PCP. Interestingly, O2?? played a more contributing role in the photocatalytic degradation of TCBQ than ?OH. H2O2 exhibited major contribution for the degradation of OH-TrCBQ and OH-DDBQ. These results offered us an insight into the degradation mechanism of PCP involved with ?OH, O2?-, and H2O2. It can also serve as the basis for controlling and blocking the generation of highly toxic substances through regulating the ROS kinds during the PCP degradation.
Finally, we investigated the effect of H2O2 on the generation of reactive oxygen species (ROS) in TiO2 photocatalytic system which includes ?OH, O2?- and H2O2. The results showed that after the addition of H2O2, the amount of all three ROS produced by TiO2 (P25) solution increased and the degradation rate of PCP increased. The H2O2 caused TiO2 (anatase) solution produced less ?OH and more O2?-/H2O2 and decreased the degradation rate of PCP. The amount of all three ROS produced by TiO2 (rutile) solution increased after the addition of H2O2 and the degradation rate of PCP increased by 50 times. The intermediate products of PCP/TiO2/H2O2 system were identified by HPLC. The results showed that TCBQ and TCHQ were not produced during the degradation process. Luminescent bacteria inhibition test was used to detect the change of toxicity during the degradation process and the results showed that acute toxicity was significantly reduced after addition of H2O2.
|马海艳. 五氯酚光催化降解过程中高毒性中间产物的动态监测及其控制[D]. 北京. 中国科学院生态环境研究中心,2018.|
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