Preparation Of Graphene-Based Mesoporous Composites And Their Application In The Adsorption Of Methylene Blue

Due to the severe situations of dying pollution, it is particularly urgent to carry out the treatments of dyes. With its good adsorption property, easy operation and wide application, adsorption method was widely used in the pollution treatments. The huge theory specific surface area (～2600m2·g-1) and the abundant of organic groups on the surface make graphene have large adsorption capacity and high adsorption efficiency, showing great potential value in the field of adsorption. However, the agglomerate phenomena occurred between the graphene sheets and its difficulty separated from the aqueous solution for graphene oxide that greatly limit the application of graphene as an adsorbent in dye pollution treatment.Preparation of graphene-based mesoporous composites is regarded as an effective way to solve the two problems as above-mentioned. In this paper, soft-templated method is used to synthesize nano-mesoporous silica/graphene composites. The introduction of nano-mesoporous silica hampers the agglomeration between graphene layers, which greatly improves the graphene’s adsorption rate of methylene blue. With the formation of amide, we adopted the chemical method in producing SBA-15/graphene oxide composites and the hydrophobicity of SBA-15solves the problem that graphene oxide is difficult to separate from the aqueous solution. The main contents of this paper consist of two parts as follows:(1) Preparation of nano-mesoporous silica/graphene composites. By using cetyltrimethylammonium bromide as the template and adjusting the pH value of the synthesis system, nano-sized mesoporous silica can be formed on the surface of graphene. As is seen from the images of SEM and TEM, the uniform-sized mesoporous silica is evenly distributed on the surface of graphene. In this article, the composites were applied to the study on the adsorption of methylene blue. The effects of different pH, adsorption time, temperature and concentration on the adsorption properties of the composites were investigated. Both thermodynamic and kinetic study are applied in studying the adsorption system, and the experimental data are found to be well fitted by the pseudo-second-order kinetic model and Langmuir isotherm model. The thermodynamic analysis indicated that the adsorption of methylene blue onto the composites is an endothermic process. Compared with graphene, the composites show a higher rate in the adsorption of methylene blue.(2) Preparation of SBA-15/graphene oxide composites. Graphene oxide and SBA-15were functionalized with acid chloride groups and amino groups, respectively, and SBA-15was successfully immobilized onto graphene oxide with the help of the formed acyl chloride. Graphene oxide loaded with SBA-15could be separated from the solution by centrifugation, thus it solves the problem of graphene oxide used in dye pollution treatments. The composites were also applied in studying the adsorption of methylene blue. The impacts of adsorbent dosage, concentration and contact time on the adsorption properties of composites were investigated. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were used for the kinetic study in the adsorption system, and it turned out that the latter could better fit the experimental data. In addition, Langmuir isotherm model is better than Freundlich isotherm model to describe the adsorption behavior of composites, namely the monolayer adsorption of methylene blue occurred on the composites.