三维氧化石墨烯气凝胶高效吸附与可见光光催化去除六价铬

High efficient adsorption and photocatalytic removal of hexavalent chromium over three-dimensional graphene oxide aerogel under visible light

三维气凝胶材料由于具有大比表面积和优异的光学、电学等性能,近年来引起研究者的关注.本研究以氧化石墨烯(graphene oxide,GO)为前驱体,结合交联法与超临界CO_(2)萃取法制备了三维多孔和易于回收的氧化石墨烯气凝胶(graphene oxide aerosol,GOA).采用扫描电子显微镜、X-射线衍射仪、拉曼光谱和氮气吸附法对其理化性质进行了表征,考察了其对于六价铬(Cr(Ⅵ))的吸附和可见光下的光催化还原性能.GOA制备过程中GO被水热还原且基面产生了较多缺陷,三聚氰胺与三聚氰酸作为交联剂增大层间距的同时使GOA拥有大比表面积和丰富的多孔结构.GO、三聚氰胺、三聚氰酸质量比为3:3:3且GO浓度为6 mg L^(-1)时,获得的样品GOA_(333-6)的比表面积和缺陷密度最大,且展现出对Cr(Ⅵ)最优的吸附能力和可见光光催化效率.GOA对Cr(Ⅵ)的吸附行为符合拟二阶动力学模型和Langmuir吸附等温模型,说明该吸附过程为单层的化学吸附,其中初始吸附阶段颗粒内扩散是限速步骤.本研究结合了吸附和光催化技术,制备出的GOA样品对于提高污染物去除效率和GO样品的开发利用都具有参考意义.

Heavy metal ions such as hexavalent chromium (Cr(Ⅵ)) existed in wastewater have caused serious pollution problems.Cr(Ⅵ) is teratogenic and carcinogenic,while trivalent chromium (Cr(Ⅲ)) is an essential nutrient for humans and animals.Adsorption method can transfer Cr(Ⅵ) from liquid phase to absorbent surface,but it needs follow-up treatment to remove Cr(Ⅵ).Photocatalysis technique can reduce Cr(Ⅵ) to Cr(Ⅲ),so as to decrease its toxicity,but the adsorption capacity towards Cr(Ⅵ) is always small due to poor surface area of some traditional semiconductor oxide photocatalysts.Therefore,a new material with both good adsorption capacity and photocatalytic activity is needed for Cr(Ⅵ) removal.As an emerging kind of carbon materials,graphene oxide (GO) has attracted particular attention in the catalysis field.Graphene oxide aerogel (GOA),a three dimensional nanomaterial,possesses numerous adsorption sites and superior ability to accept and transport photogenerated electrons,would thus present good adsorption capacity and high photocatalytic performance simultaneously.So far,most studies on GO-base material are towards investigating its co-catalyst role (adsorption enhancement or electron shuttle) in improving efficiency of metal or semiconductor photocatalysts.Only a few studies have applied GO-base material as a sole photocatalyst.In this study,combined with the cross-linking method and the supercritical CO;fluid extraction method,three-dimensional porous and recyclable GOA with large specific surface area and defect sites was prepared by using GO as the precursor.The physicochemical properties were characterized by SEM,XRD,Raman spectroscopy and nitrogen adsorption methods.The adsorption behavior and photocatalytic reduction performance of GOA towards Cr(Ⅵ) under visible light were investigated.GO was hydrothermally reduced during the preparation process,and many defects were generated on GO sheets.Melamine and cyanuric acid were used as crosslinking agents to increase the interlayer spacing,and at the same time providing GOA a large specific surface area and a rich porous structure.When the mass ratio of GO,melamine,and cyanuric acid was 3:3:3 and the GO concentration was 6 mg L;,GOA exhibited the largest specific surface area and defect density.This kind of GOA,i.e.,GOA;presented the best adsorption capacity and photocatalytic efficiency of Cr(Ⅵ).The adsorption behavior of GOA on Cr(Ⅵ) fits to the quasi-second-order kinetic model and the Langmuir adsorption isotherm model,indicating that the adsorption process was a single-layer chemical adsorption,in which the intra-particle diffusion in the initial adsorption stage was the rate-limiting step.The three-dimensional graphene oxide aerogel GOA obtained in this study exhibited large adsorption capacity,high photocatalytic removal efficiency for high concentration Cr(Ⅵ) under visible light,and good repeatability.Single GOA material has potential application in removing heavy metal ions from polluted wastewater.