TiO2-photocatalyzed As(III) oxidation in aqueous suspensions:: Reaction kinetics and effects of adsorption
TiO2-photocatalyzed As(III) oxidation in aqueous suspensions:: Reaction kinetics and effects of adsorption
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DOI：
10.1021/es048795n
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发表时间：
2005-03-15
影响因子：
11.4
通讯作者：
Hering, JG
中科院分区：
文献类型：
--
作者：
Ferguson, MA;Hoffmann, MR;Hering, JG
许多水处理技术需要将亚砷酸盐 As(III) 氧化为砷酸盐 As(V)，以有效去除砷。二氧化钛 (TiO2) 上的 As(III) 光催化氧化为该单元操作提供了一种环境友好的方法。在这项研究中，我们探索了 TiO2 光催化 As(III) 氧化在中性 pH 值附近和接近水处理系统中通常遇到的 As(111) 浓度范围内的功效和机制。我们重点关注砷吸附对观察到的光氧化速率的影响。在 pH 6.3 下，在溶解砷浓度 [As](diss) 范围内（0.10-89 μM）和 0.2 或 0.05 g L-1 TiO2（对于 As (III) 和 As(V) 而言），分别检查了 As(III) 和 As(V) 在 Degussa P25 TiO2 上的吸附（在黑暗中）。吸附等温线通常遵循 Langmuir-Hinshelwood 模型，As(III) 的吸附最大值为 32 mu mol g(-1)。在所检查的实验条件下，As(V) 吸附并未达到稳定水平；观察到的最大吸附浓度为130 mu mol g(-1)。在动力学研究开始和结束时观察到的 As(111) 和 As(V) 吸附程度与吸附等温线中观察到的一致。在 pH 6.3、0.8-42 mu M As(111) 和 0.05 g L-1 TiO2 的间歇系统中进行动力学研究；在 365 nm 照射 10-60 分钟内观察到 As(III) 的完全氧化。观察到的 As(III) 浓度对反应动力学的影响与较高浓度下的表面饱和度一致。添加0.5-10μM的磷酸盐对As(III)吸附或其光氧化速率几乎没有影响，但确实抑制产物As(V)的吸附。选择性使用羟基自由基猝灭剂和超氧化物歧化酶证明超氧化物O-2(中心点-)在As(III)氧化成As(V)的过程中起主要作用。
Oxidation of arsenite, As(III), to arsenate, As(V), is required for the efficient removal of arsenic by many water treatment technologies. The photocatalyzed oxidation of As(III) on titanium dioxide, TiO2, offers an environmentally benign method for this unit operation. In this study, we explore the efficacy and mechanism of TiO2-photocatalyzed As(III) oxidation at circumneutral pH and over a range of As(111) concentrations approaching those typically encountered in water treatment systems. We focus on the effect of As adsorption on observed rates of photooxidation. Adsorption (in the dark) of both As(III) and As(V) on Degussa P25 TiO2 was examined at pH 6.3 over a range in dissolved arsenic concentrations, [As](diss), of 0.10-89 mu M and 0.2 or 0.05 g L-1 TiO2 for As (III) and As(V), respectively. Adsorption isotherms generally followed the Langmuir-Hinshelwood model with As(Ill) exhibiting an adsorption maxima of 32 mu mol g(-1). As(V) adsorption did not reach a plateau under the experimental conditions examined; the maximum adsorbed concentration observed was 130 mu mol g(-1). The extent of As(111) and As(V) adsorption observed at the beginning and end of the kinetic studies was consistent with that observed in the adsorption isotherms. Kinetic studies were performed in batch systems at pH 6.3 with 0.8-42 mu M As(111) and 0.05 g L-1 TiO2; complete oxidation of As(III) was observed within 10-60 min of irradiation at 365 nm. The observed effect of As(III) concentration on reaction kinetics was consistent with surface saturation at higher concentrations. Addition of phosphate at 0.5-10 mu M had little effect on either As(Ill) sorption or its photooxidation rate but did inhibit adsorption of the product As(V). The selective use of hydroxyl radical quenchers and superoxide dismutase demonstrated that superoxide, O-2(center dot-), plays a major role in the oxidation of As(III) to As(V).