Construction Of Carbon-iron-copper Ternary Micro-electrolysis System For The Treatment Of P-chloronitrobenzene Wastewater

p-Chloronitrobenzene wastewater comes from the manufacturing industries such as dyes,pesticides,medicines,and corrosion inhibitors,and has the characteristics of high biological toxicity,high oxidation resistance and recalcitrance,thus posing a critical threat to human health and ecosystems.Generally,traditional binary micro-electrolysis system like iron-carbon and iron-copper could increase the removal of p-chloronitrobenzene from water,but the problems of low reducing power,metal agglomeration and copper leaching limited their practical application.Thus,in this study,a GAC-Fe-Cu ternary micro-electrolysis system composed of a granular activated carbon（GAC）supported nanoscale zero valent iron（n ZVI）and nanoscale zero valent copper（n ZVC）nanocomposite was synthesized for the removal of p-chloronitrobenzene.Studies of the optimization of preparation procedures,the influences of different factors and the possible mechanism of the ternary system have been fully investigated under anoxic and oxic conditions,respectively.The objectives of the present work are to（i）clarify the degradation process of p-chloronitrobenzene in the GAC-Fe-Cu ternary micro-electrolysis system through laboratory research;（ii）elucidate the mechanism and differences of enhanced degradation of p-chloronitrobenzene under anoxic and oxic conditions;and（iii）deeply understand the high reactivity of the GAC-Fe-Cu ternary micro-electrolysis system from the perspective of electron transfer.The main conclusions are as follows:（1）The optimization of preparation precedures was conducted and the physicochemical properties of the optimal samples were analysed under anoxic and oxic conditions,respectively.The results showed that the optimal preparation parameters of GAC-Fe-Cu were Fe-Cu loading content of 20.00 wt%and Fe/Cu mass ratio of 9:1 and the obtained sample was named as GAC₂₀-Fe₉-Cu.The BET surface area of GAC₂₀-Fe₉-Cu was 1412.6 m²/g with abundant micropores and mesopores as well as oxygen functional groups.The highly dispersed and crystallized n ZVI and n ZVC nanoparticles with particle size of 5-20 nm were stably anchored on GAC surface.Under oxic conditions,the optimal preparation parameters of GAC-Fe-Cu were Fe-Cu loading content of 25.00 wt%and Fe/Cu mass ratio of 9:1 and the obtained sample was named as GAC₂₅-Fe₉-Cu.The BET surface area of GAC₂₀-Fe₉-Cu was 704.6 m²/g with abundant micropores and mesopores.The highly dispersed Fe and Cu nanoparticles with particle size of 10-40 nm were stably anchored on GAC surface.（2）Under anoxic conditions,a single factor experiment was used to investigate the effects of different factors on the treatment of chloronitrobenzene by GAC₂₀-Fe₉-Cu ternary internal electrolysis system.SEM/EDS and XPS analyses were used to comparatively analyze the physicochemical properties of GAC₂₀-Fe₉-Cu before and after the reaction,the distribution of p-chloronitrobenzene and the formation of reduction products during the reaction process were studied to reveal the electron transfer paths and the degradation mechanism of pollutants.The results showed that 95.3%of p-chloronitrobenzene could be removed by GAC₂₀-Fe₉-Cu ternary micro-electrolysis system at the initial solution p H of 3.0,GAC₂₀-Fe₉-Cu dosage of 0.20 g/L,initial p-chloronitrobenzene concentration of 40 mg/L and electrolyte concentration of 10 mmol/L.The GAC₂₀-Fe₉-Cu ternary micro-electrolysis system possessed higher removal efficiency for p-chloronitrobenzene and TOC than other binary systems,and showed high stability and reusability.Furthermore,the iron corrosion reaction in the system played an important role in the removal of p-chloronitrobenzene,and the specific reaction mechanism and degradation pathways were as follows:（i）The conductive GAC cathode pre-accepted the released electrons from the n ZVI anode,and transferred them to the n ZVC cathode,then the electron-rich n ZVC cathode could intensively release electrons with strong reducing power to dramatically enhance the hydrodechlorination of the organic pollutants.（ii）Some of the electrons participated in the stepwise reduction from Cu⁺and Cu²⁺to n ZVC,which was beneficial to improve the stability and activity of the GAC₂₀-Fe₉-Cu ternary micro-electrolysis system.（iii）p-Chloronitrobenzene could be rapidly adsorbed onto the surface of GAC₂₀-Fe₉-Cu for in-situ reduction,and be converted into p-chloroaniline,aniline and Cl^–,then the reduction intermediates were detached from the surface,leaving the majority of adsorption sites and catalytic sites available on the GAC-Fe-Cu surface for another adsorption and reduction.（3）Under oxic conditions,a single factor experiment was used to investigate the effects of different factors on the treatment of p-chloronitrobenzene by GAC₂₅-Fe₉-Cu ternary internal electrolysis system.Particularly,the removal pathways of p-chloronitrobenzene by the GAC₂₅-Fe₉-Cu system were explored at different initial p Hs.Furthermore,XPS analyses were used to comparatively analyze the physicochemical properties of GAC₂₅-Fe₉-Cu before and after the reaction,and the generation of degradation products were analysed by GC-MS to clarify the potential mechanism of p-chloronitrobenzene removal by GAC₂₅-Fe₉-Cu system.The results showed that 97.0%of the p-chloronitrobenzene could be removed by GAC₂₅-Fe₉-Cu ternary micro-electrolysis system at aeration rate of 500 m L/min and the initial solution p H of 7.2 with aeration throughout the reaction,and GAC₂₅-Fe₉-Cu ternary micro-electrolysis system was stable and reusable.p-Chloronitrobenzene could be removed by degradation,co-precipitation and adsorption,and degradation was the prime removal pathway under acidic and neutral conditions,while co-precipitation dominated the removal of p-chloronitrobenzene under alkaline conditions.And the effect of p-chloronitrobenzene removing through various pathways was closely related to the distribution of iron content in the system.Furthermore,the synergistic effect of reduction and oxidation played an important role in the removal of p-chloronitrobenzene,and the specific reaction mechanism and degradation pathways were as follows:（i）carbon-copper dual cathode enhanced the electron transfer and release,which was conducive to improving the reactivity of the system.（ii）The adsorption of GAC₂₅-Fe₉-Cu and its surface functional groups could enhance the electronic selectivity of the system toward organic pollutants,and further increasing the in-situ reduction efficiency to form p-chloronitrosobenzene,p-chlorophenylhydroxylamine and p-chloroaniline.（iii）Dissolved oxygen could accept electrons to generate a variety of reactive oxygen species such as H₂O₂,^·OH and^·O₂^-for oxidative degradation and mineralization of reduction products,forming a series of low molecular weight organic matters,and eventually converting into CO₂ and H₂O.