超薄g-C_(3)N_(4)吸附性能的研究

Comprehensive study of adsorption properties of ultrathin g-C_(3)N_(4)

吸附法具有操作简便、高效、吸附剂可再生等优点,被普遍认为是去除工业染料的最有效方法之一.以三聚氰胺为前驱体,采用热聚合法,制备了块体g-C_(3)N_(4),并使用热剥离法对其进行剥离,得到一次剥离g-C_(3)N_(4)和二次剥离g-C_(3)N_(4)产物.通过TEM、AFM、XRD、DRS、BET对其形貌、组成和结构进行了表征,同时探索了温度、pH、起始浓度、吸附时间对超薄g-C_(3)N_(4)的吸附性能的影响.结果表明:50 mg块体g-C_(3)N_(4)、一次剥离g-C_(3)N_(4)、二次剥离g-C_(3)N_(4)在1 h内对90 mg·L^(-1)有机染料罗丹明B(RhB)和100 mg·L^(-1)刚果红(CR)的最大吸附量分别为:7.270 mg·g^(-1)、5.207 mg·g^(-1);20.463 mg·g^(-1),20.909 mg·g^(-1);36.094 mg·g^(-1),50.375 mg·g^(-1).特别是在一次剥离g-C_(3)N_(4)的吸附体系中,证实了RhB和CR的吸附Freundlich等温线方程分别为ln q_(e)=-0.93+0.87ln c_(e)(R^(2)=0.90)、ln q_(e)=-0.09+0.73ln c_(e)(R^(2)=0.97);并且RhB的吸附为准一级动力学模型:ln(q_(e)-q_(t))=-0.04t+3.3(R^(2)=0.93),而CR的吸附为为准二级动力学模型:t/q_(t)=0.07t+0.14(R^(2)=0.99).第一性原理计算表明,超薄g-C_(3)N_(4)对RhB和CR的吸附动力学模型不同,主要是由于RhB和CR的分子结构不同、前线轨道不同、表面静电势不同,使其在超薄g-C_(3)N_(4)的表面上的吸附位点和吸附能不同等微观差异所导致的.这将为二维材料吸附、检测、降解环境污染物提供新的视野.

Adsorption has the advantages of easy operation,high efficiency and reproducible adsorbent,and is generally considered as one of the most effective methods for removing industrial dyes.In this paper,bulk g-C_(3)N_(4)was prepared from melamine by thermal polymerization,and ultrathin g-C_(3)N_(4)was fabricated by thermal exfoliation,thus obtaining primary exfoliated g-C_(3)N_(4)and secondary exfoliated g-C_(3)N_(4)samples.The morphology,composition and structure of the exfoliatied g-C_(3)N_(4)were characterized by TEM,AFM,XRD,DRS and BET.The effects of temperature,pH,initial concentration and adsorption time on the adsorption performance of ultrathin g-C_(3)N_(4)were also explored.The results showed that the maximum adsorption capacity of 50 mg bulk g-C_(3)N_(4),primary exfoliated g-C_(3)N_(4)and secondary exfoliated g-C_(3)N_(4)on 90 mg·L^(-1)organic dye Rhodamine B(RhB)and 100 mg·L^(-1)Congo red(CR)were 7.270 mg·g^(-1),5.207 mg·g^(-1);20.463 mg·g^(-1),20.909 mg·g^(-1);36.094 mg·g^(-1),50.375 mg·g^(-1),respectively.Especially in the primary exfoliated g-C_(3)N_(4)adsorption systems,the Freundlich isotherm equations for adsorption of RhB and CR are ln q_(e)=-0.93+0.87 ln c_(e)(R^(2)=0.90)and ln q_(e)=-0.09+0.73 ln c_(e)(R^(2)=0.97),respectively.Moreover,it was found that RhB adsorption is subject to the peseudo-first-order kinetic model:ln(q_(e)-q_(t))=-0.04t+3.3(R^(2)=0.93)and CR adsorption is subject to the peseudo-second-order kinetic model:t/q_(t)=0.07t+0.14(R^(2)=0.99).First-principles calculations indicated that the different adsorption kinetic models of ultrathin g-C_(3)N_(4)to RhB and CR are mainly caused many microscopic differences on the aspects of adsorption sites and adsorption energy on the surface of g-C_(3)N_(4),due to the different molecular structures,different front-line orbits,and different surface electrostatic potentials of RhB and CR.This work will provide new horizons for the adsorption,detection,and degradation of environmental pollutants by two-dimensional material.