Preparation Of Graphene - Based Composites And Their Adsorption Properties For Dyes

With the rapid development of printing and dyeing industry, more and more wastewater containing dyes are discharged into the water environment. As a kind of simple and promising technique, adsorption is widely used in water purification treatment due to its low cost and simple operation, particularly, suitable for treatment of wastewater with more complex composition. The key of adsorption is adsorbent. So inexpensive and more efficient adsorbents made by simple process are always the goal of researchers trying to seek or prepare.As a new member of carbon-based materials, graphene has the structure features of high specific surface area, which endow it good adsorption. Some papers have reported materials based graphene are used as adsorbents in wastewater treatment. In this paper, Hummers method was changed to prepare graphene oxide(GO). Then hydrogen, hydrothermal method, hydrazine hydrate and hydrobromic were used to reduce graphene oxide to prepare graphene by a reduction treatment. We researched the adsorption properties of graphene oxide and graphene made by four kinds of styles to four different dyes. The results showed that graphene oxide and graphene reduced by hydrogen and hydrobromic had the best adsorption capacities, and the solution pH could affect the adsorption.The construction of macroscopic graphene composites is the most effective way to promote their practical application. Because the good adsorption properties and the simpler preparing process than graphene, we used graphene oxide and polyvinyl alcohol(PVA) with good biocompatibility to prepare PVA/GO composite hydrogel materials. The adsorption properties of these materials to methylene blue were studied. In PVA/GO composite hydrogel, graphene oxide was anchored in the PVA matrix to form a gel with three-dimensional network structure, which leaded the adsorbent could be easily removed by precipitating and filtering after finishing adsorption, and avoided the secondary pollution caused by tiny pure graphene oxide. The maximum adsorption capacity of PVA/GO composite hydrogel to adsorb methylene blue was 476.2 mg/g, which showed it was a good adsorbent to methylene blue.Three kinds of isotherm models were used to fit the adsorption of methylene blue by PVA/GO composite hydrogel. The results showed that Freundlich and Dubinin-Radushkevich model fitted the dates well. We investigated the influence of different external factors on the adsorption process, such as initial concentration, the content of graphene oxide, the amount of adsorbent, initial pH, temperature, time and so on. Kinetic studies showed that the adsorption process could be well described by the pseudo-second-order kinetic model and the intra-particle diffusion model, which demonstrated that the adsorption involved two processes of surface adsorption and intra-particle diffusion. Thermodynamic studies also proved the process of adsorbing methylene blue by PVA/GO composite hydrogel were spontaneous feasible, endothermic and physical adsorption process.Using graphene oxide and anionic polyacrylamide(APAM) with odorless, nontoxic and good water-soluble property, we prepared directly the APAM/GO composite hydrogels. Then hydrogels were dried by vacuum freeze-drying machine to prepare APAM/GO composite aerogels. These aerogels had light, loose, porous structure characteristics, and their adsorption properties to basic fuchsin were studied. In APAM/GO composite aerogels, graphene oxide was fixed in the APAM matrix, which leaded the adsorbents could be easily removed by precipitating and filtering after the completion of adsorption. The maximum adsorption capacity of APAM/GO composite aerogels to basic fuchsin was 1034.3 mg/g, which indicated their superior adsorption capacity to high concentration basic fuchsin with positive charge. This was the result of rich porous structure and polyfunctional interaction. Adsorption mechanism lies in the interaction between dye molecules and the adsorbents, not only including van der Waals forces, hydrogen bonding, ionic bonding, electrostatic interactions and π-π bonding interactions, but also including crosslinking bridge, charge neutralization and other flocculation mechanisms.Three kinds of isotherm models were used to fit the adsorption of basic fuchsin by APAM/GO composite aerogels. The results showed that Langmuir and Dubinin-Radushkevich model fitted the dates well. We investigated the influence of different external factors on the adsorption process, such as initial concentration, the amount of adsorbent, initial pH, temperature, time and so on. Kinetic studies showed that the adsorption process could be well described by the pseudo-second-order kinetic model.