Removal Of Organic Pollutants Using Reduced Graphene Oxide-supported Nanoscale Zerovalent Iron

Graphene has caught lots of attention with its unique structure and performance since it was discovered in 2004,and quickly became a focus of research at the forefront of disciplines.Graphene has a unique two-dimensional plane structure and huge specific surface area,which makes it an ideal supporting material for inorganic nanoparticles.At present,the combination of graphene and functional particles have been reported in a broad range of studies to form composite materials.In addition,zero-valent iron nanoparticles(nZVI)shows its extremely obvious advantages in the environmental remediation,but there are still some problems in practical applications,because bare iron nanoparticles tend to rapidly agglomerate and be oxidized.All of those limit the removal efficiency of the environment pollutants for nZVI.The reduced graphene oxide-supported nanoscale zerovalent iron(nZVI/rGO)composites can prevent the agglomerate of nZVI nanoparticles and improves its efficiency,which extend the potential applications of graphene in environmental remediation.The major objective of the present study is to investigate the feasibility of using nZVI/rGO for the removal of the organic pollutants Rhodamine B(Rh B)and polybrominated diphenyl ethers(PBDEs),which can provide useful information for practical applications.The main research contents are as follows:The zero-valent iron nanoparticles were prepared by using liquid phase reduction method.Graphene oxide(GO)was synthesized from graphite using the modified Hummer's method,and utilize sodium borohydride as the reducing agent to prepare the nZVI/rGO composites.Then the characterization of the synthesized nZVI/rGO was performed with X-ray diffraction(XRD),scanning electron microscopy(SEM),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS)and N2-sorption.The RSM and ANN-GA models were developed to determine the optimum process conditions for the removal efficiency of Rh B.Both models provide a good quality prediction for the adsorption behavior.Obviously,based on the experimental data with the optimum conditions,the ANN-GA model was found to be more accurate in predicting the removal efficiency of Rh B than the RSM model(absolute error of 3.57% and 7.86% for ANN-GA and RSM,respectively).It is noted that the most important individual process variable was initial concentration via ANOVA analysis for the RSM model.The Freundlich model and the pseudo-second order kinetic model was more suited for describing the process of Rh B removal by nZVI/rGO.The degradation effect of BDE-47,BDE-100 and BDE-154 was compared by using both the nZVI and nZVI/rGO composit materials.The nZVI and nZVI/rGO can rapidly degrade PBDEs at the initial stage.With the adsorption and reduction capacity decreased,the degradation rate is slowed gradually.Compared with BDE-47 and BDE-100,BDE-154 was degraded more rapidly due to the more substituted bromines.The pseudo-first order kinetic model and pseudo-second order kinetic model were used for describing the process of PBDEs removal by the nZVI and nZVI/rGO.Based on the actual situation,we performed a theoretical study on PBDEs.The density functional theory(DFT)methods of B3PW91/6-311+G(d,p)and PBE/TZ2P/ZORA were used to optimize the structures of BDE-28,BDE-30,BDE-32,BDE-51,BDE-116 and BDE-166.And the calculational results of C-Br and the C-O bond lengths were compared with their experimental values.Meanwhile the QST2 method was used to study the BDE-7 and BDE-12 configuration transition state and the conversion relationship between the anionic states.The dehalogenation pathway of BDE-47,BDE-17,BDE-15,BDE-8,BDE-7 and BDE-4 were also studied in solution.Finally,the debromination rate constants for the selected BDE congeners were predicted by establishing the quantitative structure-activity relationship models.