环境纳米技术与健康效应重点实验室知识库

      化工、冶炼生产过程中通常会产生含多种重金属污染物的废水，如冶炼废水、电镀废水、酸性矿山废水，对环境产生严重威胁。这些多种重金属共存的废水处理难度大，常规技术往往难以实现一步有效去除。本研究以水中共存的Cr(VI)与As(III)的同步转化与去除为目标，通过引入碘离子、铁碳复合材料介导的光催化作用，实现同步氧化还原转化并去除Cr(VI)/As(III)复合污染；在此基础上将铁碳复合材料应用于去除有机污染物对氯苯酚（4-CP）。博士后期间取得了以下创新性成果：
      1) 在紫外光254 nm条件下，向溶液中引入碘离子，利用碘自催化的碘钟反应，同时将As(III) 和Cr(VI)快速氧化还原为As(V)和Cr(III)。机理研究表明，I-在紫外光作用下可生成衍生物，并可以通过的循环转化，实现Cr(VI)/ As(III)的同步氧化还原，同时将As(III)氧化为As(V)、Cr(VI)还原为Cr(III)，从而降低了重金属的毒性，有利于下一步的去除。此外，体系中As(III)和Cr(VI)的共存促进了彼此的氧化还原转化，而且在As(III)氧化为As(V)过程中起到了主要作用，同时生成的•OH对As(III)氧化的贡献完全可以忽略。
      2) 成功制备了水热碳包裹Fe3O4(HCS@Fe3O4)复合光催化材料，在模拟太阳光照射下，实现了同步氧化还原转化并快速去除Cr(VI)和As(III)复合污染。研究发现，HCS@Fe3O4在光催化作用下产生的Fe(II)离子，在直接还原Cr(VI) 和通过产生•OH自由基间接氧化As(III)的反应过程中起到了关键性作用。光照加速了Fe(III)/Fe(II)的循环速率，进而显著提高了As(III) 氧化和Cr(VI)还原的效率。同时溶解的Fe(III)不仅能够促进As(III)的氧化，也可以与As(V)反应生成沉淀而得以去除。
      3) 在上述工作基础上，进一步将铁碳复合材料应用于非均相光Fenton催化降解4-CP。在可见光照射下，Fe0/HTC复合材料可以有效地增加对4-CP的降解率和矿化率，分别达到100%和~73.9%。研究发现，pH为4.0时，HTC和光照可以通过强化Fe(III)/Fe(II)的循环转化，明显增加•OH的产生量，从而强化对4-CP 的降解和矿化效率。另外，Fe0颗粒被限域在HTC框架内，在类Fenton反应过程中可以抑制铁离子的溶出，并延长了材料的循环使用生命周期。

       The complex heavy metal pollutants in the smelting wastewater, electroplating wastewater, acidic mine drainage from chemical and smelting processes, have become widespread environmental problem throughout the world. It is difficult to treat wastewater containing many kinds of heavy metals, and it is often difficult to achieve one-step effective removal with conventional technology. In this study, the simultaneous redox conversion and removal of Cr(VI) and As(III) were studied by introducing and Fe/C composites as activators assisted by photocatalytic, on the base of which, Fe/C composite was used to removal 4-CP. New process and innovative results were achieved as follows:
      1) The synergistic redox conversion of Cr(VI) and As(III) was achieved by employing iodide() as the catalyst under UV light irradiation. A “clock reaction” mechanism based on the () cycling was proposed to elucidate the redox conversion in the Cr(VI)/KI/As(III) system. The coupling of Cr(VI) and As(III) in solution markedly enhanced their individual redox rate to each other. was proved to be the primary oxidizing species for the conversion of As(III) to As(V), while •OH has the negligible contribution to the redox.
      2) By employing iron oxide encapsulated in hydrothermal carbon sphere (HCS@Fe3O4), the synergistic photocatalytic reduction of Cr(VI) and oxidation of As(III) were markedly accelerated under simulated solar light irradiation. The transformed Cr(III) and As(V) were readily removed by forming Cr(OH)3 and FeAsO4 precipitates. The Fe(III)/Fe(II) cycle in the system, which was greatly reinforced by photocatalysis in the presence of HCS@Fe3O4, has been demonstrated to be critical in the redox of Cr(VI) and As(III). It can keep sufficient Fe(II) in solution to both directly reduce Cr(VI) and promote the generation of •OH for the oxidation of As(III).
      3) Heterogeneous Fenton-like catalyst, nano-Fe0 encapsulated in hydrothermal carbon (Fe0/HTC), was prepared via a green chemistry route, aiming at increasing the degradation efficiency of p-chlorophenol (4-CP) by controlling the stability of the catalyst and Fe(III)/Fe(II) cycling in the advanced oxidation process. Fe0/HTC composite markedly enhanced both the degradation (100%) and the mineralization efficiency (~73.9%) for 100 ppm 4-CP within 60 mins at pH 4.0. More importantly, the catalyst presented a high stability to resist the side oxidation even after 5 successive cycling experiments. Electron spin resonance confirmed that in the presence of both HTC and visible light irradiation greatly enhanced the production of •OH for the degradation and mineralization of 4-CP, which can be attributed to the enhancement of Fe(III)/Fe(II) cycling.