The Removal Mechanism Of 1,2,4-trichlorobenzene By Modified Biochar Supported Fe/Pd Nanoparticles

As intermediates of industrial materials and pesticides,chlorobenzene pollutants have threaten the environment and human.Therefore,the technology about removal of chlorobenzene pollutants has become one of the research focuses.The use of nanoscale zero-valent iron(nZV1)to remove chlorobenzene pollutants has attracted researchers'attention.However,the nZV1 readily aggregate and was oxidized,the migration and reaction of nZVI would be limited in the environment.Therefore,the development of nZVI application method which is high-efficiency and green is of great significance.In this paper,biochar supported Fe/Pd nanoparticles were used to investigate.Through the characterization and analysis of nZVI and composite materials,the modification methods of biochar and influencing factors of 1,2,4-trichlorobenzene(1,2,4-TCB)removal were studied.The removal effects and reaction mechanism of 1,2,4-TCB were investigated.In this paper,biochar at pyrolysis temperatures of 300,500 and 700? were modified by HC1,NaOH,HF,H2O,HNO3 and KMnO4.The modified biochar supported Fe/Pd nanoparticles were prepared to remove 1,2,4-TCB,the 1,2,4-TCB removal efficiency by different modified composites was compared and the composites with better removal efficiency were selected.The effects of 1,2,4-TCB concentration and anion in the environment on the removal of 1,2,4-TCB were investigated,the intermediate products and pH in the reaction process were analyzed and the reaction mechanism was explored.In addition,in order to remove 1,2,4-TCB and its intermediate products completely,persulfate was added to the reaction system of modified biochar supported Fe/Pd nanoparticles and 1,2,4-TCB.The effects of persulfate concentration,1,2,4-TCB concentration and initial pH on the reaction were investigated,and the reaction mechanism was analyzed.The experimental results showed that the ash content of biochar after modification was decreased,the specific surface area and pore volume increased,and the specific surface area of FBC700 was up to 392.82 m2/g.The degradation of 1,2,4-TCB in the reaction was in accordance with pseudo-first-order reaction kinetics model.Compared with the removal efficiency of 1,2,4-TCB by unmodified composites,under the initial 1,2,4-TCB concentration of 10 mg L-1 and the solid-liquid ratio of 0.16 g L-1,the FBC700-nZVI-Pd and SBC300-nZVI-Pd demonstrated significantly enhanced removal efficiencies for 1,2,4-TCB achieving 98.8%and 94.7%after 48 h,respectively.When the pyrolysis temperature of biochar was 700?,the removal efficiency of 1,2,4-TCB was more favorable.The reaction rates of SBC700-nZVI-Pd and FBC700-nZVI-Pd reached 15.8 and 25.9(10-4·min-1),respectively.With the concentration of 1,2,4-TCB increased from 5 mg L-1 to 15 mg L-1,the removal efficiency of 1,2,4-TCB by modified composite was decreased.When the concentration of Cl-in solution was lower than 10 mM,the removal of 1,2,4-TCB could be promoted.The removal of 1,2,4-TCB would be inhibited due to the addition of CO32-,HCO3-,HNO3-and SO42-in the reaction.The intermediate products in the reaction process mainly include 1,2-DCB,1,3-DCB,1,4-DCB,CB,the final product was benzene.The mechanism of improving 1,2,4-TCB removal by modified composites was that the aromaticity,hydrophobicity and specific surface area of biochar was improved after HF and NaOH modification,and the loading and dispersion of Fe/Pd nanoparticles on biochar was promoted,therefore,the adsorption and reduction of 1,2,4-TCB by modified composites was improved.In the reaction system of sodium persulfate activated by biochar supported Fe/Pd nanoparticles,when the concentration of sodium persulfate was 1 mM and the initial concentration of 1,2,4-TCB was 5 mg L-1,the solid-liquid ratio of the composite was 0.16 g L-1,the removal efficiency of 1,2,4-TCB was the highest.When the pH of the reaction system was 4,it was conducive to the reaction.As the pH increased from 4 to 9,the removal efficiency of 1,2,4-TCB decreased.The removal mechanism of sodium persulfate activated by biochar supported Fe/Pd nanoparticles including activation of sodium persulfate by C-OH,C-OOH of biochar and Fe2+,SO4-was generated for the oxidative degradation of 1,2,4-TCB,so the degradation of 1,2,4-TCB was promoted.