Preparation And Adsorption Performance Of Graphene-based Nanocomposites

In this paper,graphene oxide?GO?suspension was prepared by modified Hummers method.Three GO-based composite adsorbents including corn stalk core/GO?CSC-GO?,TiO₂-modified corn stalk pith/GO?CSP-GO-TiO₂?and magnetic chitosan/GO?MC-GO?were prepared by freeze-drying process.In addition,a magnetic chitosan/corn stalk core?MCS-CSC?biomass adsorbent was prepared for adsorption of dyes in water.The corn stalk core was taken out,pulverized,pretreated to remove impurities such as pectin,mixed with the GO suspension according to a certain ratio,and freeze-dried to obtain a CSC-GO,which had three-dimensional structure and ability to adsorb methylene blue?MB?in water.The adsorption test showed that the adsorbent could achieve a higher adsorption amount when the content of GO was 5 wt.%?CSC-5GO?.The factors including the amount of adsorbent,pH of the solution,adsorption time and temperature could affect the adsorption capacity of CSC-GO.Pseudo-second-order kinetic model and Temkin isotherm model could describe the adsorption process well.The maximum adsorption capacity of CSC-5GO to MB calculated by Pseudo-second-order kinetic model was 322.58 mg g^-1.The removal efficiency of CSC-5GO to MB was 90.62%after five cyclic adsorption tests.TiO₂ nanoparticles were introduced into CSC-GO to prepare CSP-GO-TiO₂ adsorbent with photocatalytic function.CSP-GO-TiO₂ could adsorb and degrade MB,Rhodamine B?Rb?and Malachite Green?MG?in water.The results of the adsorption and degradation tests showed that the adsorbent had the best comprehensive performance when the content of GO and TiO₂ were 5 wt.%and 20 wt.%?CSP-2GO-20TiO₂?.The Pseudo-second-order kinetic model and the Langmuir isotherm model can describe the adsorption process well.The adsorption capacities of CSP-2GO-20TiO₂ for MB,Rb and MG calculated by isotherm model were 215.05 mg g^-1,213.68 mg g^-1 and 242.13 mg g^-1,respectively.CSP-2GO-20TiO₂adsorbing dyes could degrade dyes under UV light.After five adsorption-degradation cycle,the removal efficiency of the CSP-2GO-20TiO₂ on MG,MB and Rb decreased by 3.77%,23.89%and 32.01%,respectively.The magnetic nanoparticle CoFe₂O₄ was prepared by hydrothermal method,and the magnetic chitosan was prepared by cross-linking CoFe₂O₄ with chitosan in the emulsion.Then the crosslinked magnetic chitosan was compound with GO to form MC-GO that could be separated by an applied magnetic field.The adsorption test showed that the comprehensive performance of the adsorbent was best when the content of GO was 20 wt.%?MC-20GO?.Pseudo-second-order kinetic model and Freundlich isotherm model could describe the adsorption process well.The maximum adsorption capacity of MC-20GO to MB was 352 mg g^-1 calculated by Pseudo-second-order kinetic model.After five cycle adsorption tests,the removal efficiency was 83.22%.In the process of preparing magnetic chitosan,the treated CSC powder was added,and MCS-CSC adsorbent was prepared,which had magnetic propertie that could be separated by adding an applied magnetic field.The adsorption test was carried out and the results showed that the optimal addition amount of CSC powder was 75 wt.%.Pseudo-second-order kinetic model and Langmuir isotherm model could describe the adsorption process well.The maximum adsorption capacity of the adsorbent to MB was calculated to be 123.9 mg g^-1 by Pseudo-second-order.After five cycle adsorption tests,the removal efficiency of the adsorbent to MB was 80.6%.