Efficiency And Mechanisms Of Activation Of Sulfite By Nanoscale Zerovalent Iron-based Materials For The Removal Of Sulfamethazine In Aqueous Solution

Nano-zero-valent iron(NZVI)is a new type of environmental nanomaterial with high reactivity and large specific surface area,which has attracted more and more attention in the field of environmental pollution remediation.However,due to the chemical characteristics of NZVI,such as easy adsorption and agglomeration,passivation and deactivation,and strong dependence on environmental p H,the practical application of NZVI technology has been greatly limited.In this study,bare NZVI particles were modified by different modification methods to study the degradation efficiency and removal mechanism of organic pollutants in water by the advanced oxidation system of modified NZVI materials catalyzed activation of sulfites.The research contents of this experiment mainly include the following two parts:Part one: The catalytic performance of unmodified NZVI,sulfide modified nanozero valent iron(S/NZVI),bimetallic modified Fe-Ni composite bimetallic(Ni/NZVI),and activated carbon loading nano-zero valent iron(C/NZVI)on sulfite activation was compared and analyzed.By comparing the removal efficiency of sulfamethazine(SMT)in aqueous system,the improvement of NZVI activated sulfite properties by different modification methods was evaluated.In this experiment,the effects of dissolved oxygen concentration,material dosage,initial p H values and simulated groundwater environment on the removal process were investigated.The results show that the concentration of dissolved oxygen is a crucial factor affecting the generation of active radicals in the advanced sulfite oxidation system,and in the appropriate modification proportion range,excessive iron based activator and sulfite will directly consume the activated free radicals,resulting in the reduction of the removal efficiency of pollutants.In acidic and neutral reaction conditions,different iron-based activators all show good activation performance,but in alkaline environment,nano zero-valent iron is prone to surface passivation,and the oxidation products generated by the reaction are deposited on the surface of the material,which blocks the removal reaction,and Ni/NZVI particles can still maintain a relatively high removal efficiency of SMT due to the catalytic action of nickel.Co-existing ions in simulated groundwater environment also react with free radicals,thus inhibiting SMT removal.The results of XRD and SEM analysis show that the aging materials can still be used for the activation of sulfites,because the structure and substance on the surface of the materials are only partially oxidized.Part two: In this experiment,nanosized zero-valent Fe-Mn bimetallic composite material was synthesized to activate sulfite to remove SMT from water.The study found that in acidic conditions,unmodified bare zero-valent iron and manganese iron composite material has good capability of sulfite activation,and bare nano zero-valent manganese hardly has any removal effect,in neutral and alkaline conditions,different proportion of iron and manganese compound showed higher than bare NZVI materials on SMT removal efficiency,the equilibrium rate of the reaction is also increased greatly.From ESR detection and free radical quenching experiment results,it was found that HO? radical was the main reactive radical in the advanced oxidation system of SMT removal.According to the results of LC-MS identification of SMT degradation products,the degradation path of SMT in the activated sulfite system can be inferred.