Ferrate(VI) enhanced photocatalytic oxidation of pollutants in aqueous TiO2 suspensions
Ferrate(VI) enhanced photocatalytic oxidation of pollutants in aqueous TiO2 suspensions
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DOI：
10.1007/s11356-009-0170-0
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发表时间：
2010-02
影响因子：
5.8
通讯作者：
V. Sharma;N. Graham;Xiang-zhong Li;Baoling Yuan
中科院分区：
文献类型：
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作者：
V. Sharma;N. Graham;Xiang-zhong Li;Baoling Yuan
背景、目的和范围利用紫外光照射的TiO 2光催化氧化已被广泛研究，并具有许多潜在的工业应用，包括降解水和废水中的柠檬酸类污染物。氧化过程中的一个限制因素是导带电子（e−cb）与辐照过的TiO 2表面上的电子空穴（hvb+）的复合;因此，在水性条件下，有效的电子清除剂的存在将有利于氧化过程的效率。高铁酸盐（FeO 42 −）作为水处理化学品最近受到了广泛关注，因为它同时作为氧化剂和混凝剂。高铁酸盐[Fe（VI）]与UV/TiO 2 O3的组合提供了由Fe（VI）清除e− c产生的氧化协同作用，以及由Fe（VI）还原产生的Fe（V）的相应有益形成。本文回顾了最近的研究有关的光催化氧化有问题的污染物和没有ferrate.Materials和methodsThe文件回顾了实验室实验的结果，旨在遵循选定的污染物的光催化降解的环境意义和实验条件的影响（例如pH值，反应物浓度和溶解氧）。具体化合物如下：氨、氰酸盐、甲酸、双酚A、邻苯二甲酸二甲酯和微囊藻毒素LR。在这些研究中的主要重点是反应的速率，而不是反应途径和products.ResultsThe的存在下，UV/TiO 2加速的化学还原的高铁酸盐，还原速率随pH值下降，由于高铁酸盐离子的去质子化。对于所有选定的污染物，在高铁酸盐的存在下，光催化氧化速率更大，这被认为是协同作用，而不是添加剂。溶液中溶解氧的存在降低了高铁酸盐/高氯酸盐体系中邻苯二甲酸二甲酯的降解速率。在微囊藻毒素-LR的研究中，很明显，存在一个最佳的高铁酸盐浓度，从而更高的Fe（VI）浓度高于最佳导致减少微囊藻毒素-LR降解。此外，微囊藻毒素-LR的降解速率强烈依赖于pH值，在pH 6时降解速率最大。在溶解氧的存在下，速率下降可能是由于氧和高铁酸盐之间的竞争作为电子清除剂和非生产性的自由基物种的相互作用。高铁酸盐（VI）和微囊藻毒素-LR之间的反应在pH值为6.0-10.0的范围内最有可能由质子化的Fe（VI）物种HFeO 4 −控制。这是由于高铁酸盐在抑制TiO 2表面上hvb+-e−cbpair复合以及相应的高氧化性Fe（V）物种的产生中的作用。高铁酸盐/过氧化氢体系的性能受反应条件的强烈影响，特别是pH值和溶解氧浓度。
Background, aim and scopePhotocatalytic oxidation using UV irradiation of TiO2has been studied extensively and has many potential industrial applications, including the degradation of recalcitrant contaminants in water and wastewater treatment. A limiting factor in the oxidation process is the recombination of conduction band electrons (e−cb) with electron holes (hvb+) on the irradiated TiO2surface; thus, in aqueous conditions, the presence of an effective electron scavenger will be beneficial to the efficiency of the oxidation process. Ferrate (FeO42−) has received much recent attention as a water treatment chemical since it behaves simultaneously as an oxidant and coagulant. The combination of ferrate [Fe(VI)] with UV/TiO2photocatalysis offers an oxidation synergism arising from the Fe(VI) scavenging of e−cband the corresponding beneficial formation of Fe(V) from the Fe(VI) reduction. This paper reviews recent studies concerning the photocatalytic oxidation of problematic pollutants with and without ferrate.Materials and methodsThe paper reviews the published results of laboratory experiments designed to follow the photocatalytic degradation of selected contaminants of environmental significance and the influence of the experimental conditions (e.g. pH, reactant concentrations and dissolved oxygen). The specific compounds are as follows: ammonia, cyanate, formic acid, bisphenol-A, dibutyl- and dimethyl-phthalate and microcystin-LR. The principal focus in these studies has been on the rates of reaction rather than on reaction pathways and products.ResultsThe presence of UV/TiO2accelerates the chemical reduction of ferrate, and the reduction rate decreases with pH owing to deprotonation of ferrate ion. For all the selected contaminant substances, the photocatalytic oxidation rate was greater in the presence of ferrate, and this was believed to be synergistic rather than additive. The presence of dissolved oxygen in solution reduced the degradation rate of dimethyl phthalate in the ferrate/photocatalysis system. In the study of microcystin-LR, it was evident that an optimal ferrate concentration exists, whereby higher Fe(VI) concentrations above the optimum leads to a reduction in microcystin-LR degradation. In addition, the rate of microcystin-LR degradation was found to be strongly dependent on pH and was greatest at pH 6.DiscussionThe initial rate of photocatalytic reduction under different conditions was analysed using a Langmuirian form. Decrease in rates in the presence of dissolved oxygen may be due to competition between oxygen and ferrate as electron scavengers and to non-productive radical species interactions. The reaction between ferrate(VI) and microcystins-LR in the pH range of 6.0–10.0 is most likely controlled by the protonated Fe(VI) species, HFeO4−.ConclusionsThe photocatalytic oxidation of selected, recalcitrant contaminants was found to be significantly greater in the presence of ferrate, arising from the role of ferrate in inhibiting the hvb+–e−cbpair recombination on TiO2surfaces and the corresponding generation of highly oxidative Fe(V) species. The performance of the ferrate/photocatalysis system is strongly influenced by the reaction conditions, particularly the pH and dissolved oxygen concentration …