Preparation Of Graphene Oxide/Silica Composites And Study On Their Adsorption Properties

Although heavy metal ions and dyes have good applications in industrial industries such as leather,textiles and special chemicals,once they are discharged into the natural world,they will seriously endanger the health of microorganisms and even humans,and the presence of multiple pollutants will undoubtedly make the wastewater treatment difficult.Adsorption is one of effective methods for treating water pollution for its low material cost,strong operability and high efficiency.Mesoporous silica with high specific surface area,adjustable pore size and abundant silanol groups on the surface that various functional modifications can be achieved and graphene oxide with abundant oxygen-containing functional groups and huge specific surface area,they all good adsorbent selection.Aiming at the hot issue of removing multiple pollutants in water and overcoming the shortcomings of low adsorption capacity of traditional adsorption materials,this study intends to combine the advantages of graphene oxide and silica to prepare the graphene oxide/silica by different methods.The composite materials was functionalized and applied to adsorb hexavalent chromium and Congo red.Firstly,the prepared materials were characterized and analyzed.Then various factors affecting adsorption are explored to obtain the optimal adsorption conditions and the adsorption theories were used to explore the principle of the adsorption process.Finally,the selectivity and renewable properties of the materials were all explored.The main research contents are as follows:(1)The silicon source hydrolyzed and grown on graphene oxide by co-condensation method to prepare the graphene oxide/silica materials using graphene oxide as the base material and different surfactants(cationic surfactants and non-ionic surfactants).This composites was subsequently modified with the hyperbranched polymer HBP.Scanning and transmission electron microscopy showed that the prepared material was a sheet-like structure with clear channels.The nitrogen adsorption and desorption curves showed that the pore channel is multi-mesoporous andthe pore size distribution was between 1.87-3.83 nm.(2)The mesoporous silica sphere was firstly prepared by sol-gel method,and the bifunctional modification was carried out to load them into graphene oxide by covalent bond.Scanning and transmission electron microscopy showed that there were uniformly distributed mesoporous silica spheres that with clear channels on the graphene oxide flakes,but the pore size distribution was wide.And the zero potential of the modified materials was 7.8.(3)The two prepared materials were used to adsorb hexavalent chromium ions respectively.It studied various factors that affecting adsorption such as the amount of adsorbent added(m),the adsorption time(t),the initial solution concentration and p H.The appropriate adsorption conditions were m=20 mg,t=1 h,p H=2.The adsorption kinetic curves of hexavalent chromium ions were more suitable for the description of quasi-second-order kinetics,indicating that chemical adsorption plays a major role in the whole process.The fitted isotherm adsorption curves were more in line with Langmuir,and the maximum adsorption quantity based on this were92.2510 mg/g(co-condensation method)and 93.7286 mg/g(post-grafting method).The thermodynamic analysis showed that it was spontaneous and endothermic to adsorb hexavalent chromium ions,and the disorder of the solid-liquid interface increases.The removal rate of hexavalent chromium is more than 90% in the solutions where chromium with copper,zinc,and nickel ions coexist,which is much higher than other heavy metal ions.After three cycles,the removal rate of hexavalent chromium can still reach more than 90%.(4)The two prepared materials were used to adsorb Congo red dye respectively.It studied various factors that affecting adsorption such as the amount of adsorbent added(m),the adsorption time(t),the initial solution concentration and p H.The appropriate adsorption conditions were m=10 mg,t=4 h and 8 h,p H=5-9.The adsorption kinetic curves of Congo red were more suitable for the description of quasi-second-order kinetics,indicating that chemical adsorption plays a major role in the whole process.The fitted isotherm adsorption curves were more in line with Langmuir,and the maximum adsorption quantity based on this were 416.6667mg/g(co-condensation method)and 257.6944 mg/g(post-grafting method).The thermodynamic analysis showed that it was spontaneous and endothermic to adsorb Congo red,and the disorder of the solid-liquid interface increases.In the solution of Congo Red,Methylene Blue and Xylenol Orange coexist,Congo Red is almost completely removed while the other two dyes remain.At theregeneration experiments,the Congo red removal rate decreased significantly after the second cycle.