The Synthesis Of Magnetic Carbon Microsphere And Its Applied Basic Research In The Removal Of Se(?)and Cr(?)wastewater

In recent years,the researches about the composite materials of carbon microspheres?CMSs?as a carrier in wastewater treatment are more and more popular.Abundant organic groups,such as carboxyl and hydroxy,existed on the surface of CMSs and the organic groups can react with the metal ions,which is possible for the removal of heavy metals.Moreover,CMSs have been regarded as ideal candidates due to their excellent properties,including high specific surface area,high structural,and chemical stability.However,CMSs are difficult to be separated in water because their density is similar to water's,and they are in small scale,which limits the application of CMSs in water treatments.In terms of heavy matal removal,iron oxides play an important role.Many researches proved that iron oxides can effectively remove heavy metals from water.Compared with other iron oxides,Fe₃O₄ possesses unique properties such as superparamagnetism and reducibility.So Fe₃O₄ can be easily separated from the reaction medium with an external magnetic field,and it is possible to reduce metallic ions to more insoluble zero vaule metals.Nevertheless,the aggregation of Fe₃O₄ will easily happen during the reaction,especially for nanoscale Fe₃O₄.Immobilizing Fe₃O₄ on CMSs can not only solve the aggregation of Fe₃O₄,but also make the CMSs be separated from water more easily.In the present work,the CMSs were synthesized via a green method of hydrothermal carbonization,and Fe₃O₄ nanoscale particles?NPs?were introduced to the surface of CMSs to form magnetic carbon microspheres?MCMSs?by coprecipitation.Then,the CMSs and MCMSs were used to investigate the ability in removing Se???and Cr???from aqueous solutions.This research applied single factor analytic approach to study the removal efficiency of Se???,Cr???,and Se???-Cr???coexisting system.The characterizations of CMSs and MCMSs before and after reaction were carried out by scanning electron microscopy with energy dispersive spectroscopy?SEM-EDS?,transmission electron microscopy?TEM?,Fourier transform infrared?FTIR?,X–ray diffraction?XRD?,Brunauer-Emmett-Teller method?BET?,vibrating sample magnetometry?VSM?,and X–ray photoelectron spectroscopy?XPS?,aiming to elucidate the reaction mechanism for removal of Se???and Cr???by CMSs and MCMSs.The main achievements of this study are as follows:?1?CMSs synthesized via hydrothermal method were uniformly spherical with the diameter of ²00 nm.Fe₃O₄ NPs were dispersedly immobilized on the surface of CMSs by coprecipitation method.There were lots of oxygen containing groups generated on the surface of CMSs and MCMSs,which including –OH,C=O,C=C,C-H,C-OH and COOH.The N2 adsorption/desorption isotherm of MCMSs became a typical ? isotherm with an obvious hysteresis loop,which indicating the mesoporous structure appeared in MCMSs.Calculated by the BJH model,the average pore diameter for CMSs and MCMSs were distributed from 1.3 nm to 12.6 nm and from 1.5 nm to 12.9 nm,respectively.?2?In initial pH range from 3.0 to 11.0,MCMSs showed the regular pattern where the lower pH value,the lower residual Se???concentration.At initial pH 3.0,the removal of Se???was slightly influenced in the presence of sulfate,nitrate,chloride,carbonate,and silicate,but greatly influenced in the presence of phosphate.?3?The Se???removal by MCMSs occurred due to two aspects.First,the Se???in the solution formed inner–sphere complexes with Fe₃O₄ on MCMSs so that the Se???in the solution transferred to MCMSs.Second,Se???was reduced to insoluble Se0 by the Fe?II?in MCMSs,and the Se0 was immobilized on the surface of MCMSs.?4?CMSs and MCMSs can effectively remove Cr???in water and reduce Cr???to Cr?III?.The removal of Cr???by CMSs can be explained by the hydrogen bonding between Cr???and carboxylate groups,and the generation of Cr?III?can be attributed to the reduction of Cr???by the C-O on the surface of CMSs.In MCMSs,besides CMSs can remove Cr???,the Fe₃O₄ nanoscale particles on the surface of CMSs can form outer-sphere complexes with Cr???and reduce Cr???to Cr?III?by Fe?II?.?5?In Se???-Cr???coexisting water,Cr???in the solution obviously improved the removal efficiency of Se???by CMSs.The Cr?III?reduced by C-O functional groups can gather on the surface of CMSs The Cr?III?-enriched surface may be favorable to improve the removal efficiency of Se???in coexisting system by forming Cr?III?-Se???conplexes,so the Se???in the water can be transferred to CMSs.Consequently,Cr???in the solution obviously improved the removal efficiency of Se???by CMSs in MCMSs.Meanwhile,the Fe₃O₄ on MCMSs can form inner-sphere comlpexes with Se???.The Se???bonding with Fe₃O₄ can be reduced to Se0 by Fe?II?.