Comparative Study On Catalytic Degradation Of Acid Blue 9 By Different Iron Oxides

In recent years,Advanced Oxidation Technology(AOP)has attracted much attention as a promising organic wastewater treatment method.The heterophasic Fenton reaction systems composed of various iron oxides and H2O2 have been widely applied because iron oxides can catalyze and decompose H2O2 in-situ to generate hydroxyl radical ·OH with strong oxidation capacity to degrade organic contaminants.However,there are many kinds of iron oxides and their catalytic activities might be affected by various factors such as crystallinity,morphology,particle size,composition and structure.Therefore,it is of great theoretical significance to elucidate the influence of various factors on its catalytic properties.And the influences of crystallinity,morphology and particle size on the catalytic properties of materials have been reported.Based on this,we selected three iron oxides γ-Fe2O3,α-Fe2O3 andγ-FeOOH with the same morphology and good crystallinity as the research objects,which were used to construct the research systems with visible light/H2O2(or visible light/Na2S2O8),respectively.The same target pollutant Acid Blue 9(AB 9)was degraded in the systems to explore the structure-activity relationship between the structures of iron oxides and macroscopic catalytic behaviors.The main contents and conclusions are as follows:(1)The acicular γ-FeOOH was prepared by Fe(Ⅱ)air oxidation and calcined to obtain γ-Fe2O3 and α-Fe2O3 samples.The three samples were characterized by XRD,SEM,XPS,FTIR and BET.AB 9 was selected as the target pollutant and the adsorption performances of AB 9 on the three samples were investigated.The results indicated that the samples were acicular particles with slightly different particle sizes.The specific surface areas of γ-Fe2O3,α-Fe2O3 and γ-FeOOH were 128.796,38.768 and 101.155 m2/g,respectively.The zero-points were 6.4,8.1 and 6.8,respectively.The adsorption capacities of AB 9 were 11.25,4.35 and 9.67 mg/g,respectively.(2)AB 9 was degraded in the Fenton-like system composed of γ-Fe2O3 and visible light/H2O2(or visible light/Na2S2O8).The degradation mechanisms of AB 9 in two systems by UV-VIS,HPLC and ESI-(+)MS were investigated.And the reusability of γ-Fe2O3 was determined.The results showed that the degradation rate of AB 9 was 80.28%when γ-Fe2O3 and H2O2 existed in the system.The degradation rate reached 100%after adding visible light irradiation.The most of AB 9 was mineralized into CO2 and H2O under the action of ·OH in the system,and a small part of AB 9 was transformed into six kinds of small organic species through 4 pathways.Inγ-Fe2O3/visible light/Na2S2O8 system,the most of AB 9 was degraded into CO2 and H2O under the action of ·SO4-and ·OH,and a small portion of AB 9 was converted into seven kinds of small molecules through six pathways.The degradation rate of AB 9 retained over 97%after 5 cycles.(3)The degradation processes of AB 9 in the Fenton-like system composed ofα-Fe2O3 and visible light/H2O2(or visible light/Na2S2O8)were investigated to obtain degradation mechanisms and the reusability of α-Fe2O3 was evaluated.The results showed that the degradation rate of AB 9 was 25.44%when α-Fe2O3 and H2O2 existed in the system,and the degradation rate increased to almost 100%after adding visible light irradiation.The majority of AB 9 was degradated into CO2 and H2O under the action of ·OH,and a small portion was converted into six kinds of small organics through three paths.In α-Fe2O3/visible light/Na2S2O8 system,the most of AB 9 was mineralized into CO2 and H2O under the action of ·SO4-and ·OH,and a small part of AB 9 was decomposed into ten kinds of small molecules via six paths.After 5 cycles,the recycling rate of α-Fe2O3 reached over 95%.(4)The degradation processes of AB 9 by γ-FeOOH/H2O2(or Na2S2O8)were investigated under the visible light irradiation to reveal the degradation mechanisms of AB 9.The results revealed that the degradation rate of AB 9 was 97.51%whenγ-FeOOH and H2O2 existed in the system.And the degradation rate increased to almost 100%after adding visible light irradiation.The majority of AB 9 was decomposed into CO2 and H2O under the action of ·OH in the γ-FeOOH/visible light/H2O2 system,and a small part was destroyed into six kinds of small organic molecules through four pathways.In γ-FeOOH/visible light/Na2S2O8 system,most of AB 9 was mineralized into CO2 and H2O under the action of ·SO4-and ·OH,and a small part of AB 9 was degraded into seven kinds of small organics via three pathways.(5)By comparing the adsorption and degradation properties of AB 9 in three iron oxides/visible light/H2O2 systems,it was seen that the degradation rates and degradation pathways of AB 9 in three systems were different.The results indicated that the composition and phase structure of iron oxides have important influences on their catalytic activities.