Nanoscale Zero-Valent Iron Size Regulation Improves The Performance Of P-Nitrophenol Degradation By Catalyzing Sodium Borohydride

Zero-valent iron(ZVI)adsorption and catalysis technologies were widely used in the remediation of environment pollutants.The particle size of zero-valent iron particles significantly affects its environmental remediation performance.The smaller ZVI particle size owns the higher reactivity.The activity of 3 nm ZVI was 1000 times higher reactivity than that of 1000 nm ZVI.However,the decrease of ZVI particle size hinders the trend of agglomeration,oxidation and deactivation during practical application.In this paper,metal-organic framework material or surfactant was used to control the size of nanoscale zero-valent iron(nZVI)and enhance surface activity,and they were used to activate sodium borohydride(NaBH₄)to reduce p-nitrophenol.The main research contents and results are as follows:(1)Zirconium-based metal-organic framework(UiO-66)was chosen as a supporter to enhance the reaction activity and stability of nanoscale zero-valent iron(nZVI)through controlled growth and morphology.The nZVI impregnated UiO-66(nZVI@UiO-66)was successfully synthesized via a one-step liquid-phase reduction method and used to reduce 4-Nitrophenol(4-NP)in water through catalyzing sodium borohydride(NaBH₄).The reduction kinetics(0.33 min^-1)of 4-NP in 5%nZVI@UiO-66 catalyzing sodium borohydride system was 100 times faster than that of pristine nZVI(?52 nm)due to the uniform immobilization of much smaller nZVI(?23 nm)on the surface of UiO-66.Water chemistry factors(nZVI loading ratios,4-NP concentration,catalyst content,initial p H and real water matrix)that influence the 4-NP reduction in nZVI@UiO-66 catalyzing sodium borohydride system were also investigated.The sole reduction product of 4-aminophenol(4-AP)was produced by the reduction of 4-NP through newly formed hydrogen during the nZVI catalyzing sodium borohydride process.Aging of nZVI@UiO-66 up to 4 months still remained87%removal efficiency of 4-NP comparing with 6%of pristine nZVI.The removal efficiency of 4-NP by nZVI@UiO-66 can still maintain 100%in various practical water bodies.(2)Surfactants can improve the performance of zero-valent iron in the reduction of p-nitrophenol(4-NP)by controling the size of zero-valent iron.Ultra-small size nanoscale zero-valent iron(S-nZVI)was rapidly synthesized by liquid-phase reduction method through using cationic surfactant cetrimonium bromide(CTAB)as dispersant,its physicochemical structure was characterized with XRD,FTIR and SEM,and the performance in the reduction of p-nitrophenol(4-NP)was also investigated.The results showed that the addition of CTAB effectively prevented the oxidation and agglomeration of nZVI,and the catalytic reduction kinetic rate constant(1.20 min^-1)of S-nZVI(?3 nm)catalyzing sodium borohydride system was 300 times faster than that of large nanoscale zero-valent iron(L-nZVI)(?55 nm),the only product of the reduction is also p-aminophenol.After four cycles reaction of S-nZVI,the removal efficiency of 4-NP remained above 90%.In actual printing and dyeing wastewater treatment,S-nZVI still maintained the same reactivity as distilled water.In this study,two methods were used to control and decrease the size of nZVI,which significantly increased the activity and stability of modified nZVI.The results provided a theoretical basis for promoting the application of nZVI in environmental remediation,which has potential application value for the removal of pollutants.