Catalytic Degradation Of Orange Ⅱ Wastewater And The Mechanism Investigations By Iron Oxide-based Composite Materials

Azo dyes not only have high stability and chromaticity,but also have poor biodegradability in aerobic conditions,which makes them difficult to eliminate from the environment.The Fenton-like advanced oxidation technology(AOPs)degrades the organic matter that is difficult to degrade in dye wastewater by completely oxidizing and mineralizing harmful organic compounds.In this paper,three kinds of iron oxide matrix composites were prepared and their morphology,structure and composition were analyzed.The catalytic degradation of Orange Ⅱ dye wastewater assisted by NaHSO3 and Na2S2O8 was successively studied and the degradation mechanism was proposed.Research achievements were as follows:(1)Chemical degradation of Orange Ⅱ by Ce-Fe-X/NaHSO3 systemThe Ce-Fe-X nanocomposites with Ce:Fe molar ratios of 5:2,1:1,2:5 were prepared by water bath heating method.The nanocomposite with a mole ratio of Ce to Fe of 5:2(designated as Ce-Fe-1)was the best for degradation of Orange Ⅱ in the presence of NaHSO3.The catalytic activity of Ce-Fe-1/NaHSO3 was significantly higher than that of the Fe2O3 or CeO2 with NaHSO3 in the system.After 120 min degradation of Orange Ⅱ,the degradation efficiencies of Ce-Fe-1/NaHSO3,CeO2/NaHSO3 and Fe2O3/NaHSO3 were 98.2%,18.0%and 50.4%,respectively.The results of X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS)and Brunauer-Emmett-Teller(BET)showed that Fe2O3 was successfully deposited on the CeO2.The degradation efficiency of Ce-Fe-1 nanocomposite for Orange Ⅱ was as high as 90.9%after three cycles.(2)Activation of Na2S2O8 by α-Fe2O3/CuS composite oxides for the degradation of Orange Ⅱ under visible light irradiationThe α-Fe2O3/CuS catalyst was synthesized and was applied to activate PS for the first time.The PS was activated by α-Fe2O3/CuS to degrade OII(50 mg/L)reached 97.8%within 25 min,which was ascribed to the synergy of Fe3+ and Cu2+ on the surface of it.At the same time,exploring that theα-Fe2O3/CuS/PS/visible light system can operate in a wider pH range(pH=3-9).In addtion,the removal of MB and MG was also present more marked activity with 93.4%and 94.2%,respectively.For structurally and chemically stable OG,the degradation rate can also reach 46.9%.The results of XRD,SEM,XPS showed that CuS was successfully deposited on the α-Fe2O3.The ESR spectral analysis and radical quenching experiment revealed that ·SO4-,·OH and ·O2-radicals were responsible for the rapid degradation of OII.The α-Fe2O3/CuS also showed high stability,and its efficiency did not decrease significantly after four recycling runs.(3)Persulfate activated by α-Fe2O3/CdS composites for efficient degradation of Orange ⅡNanocomposites of α-Fe2O3/CdS-X catalysts were synthesized using various iron to cadmium ratios and were then applied to activate persulfate.The α-Fe2O3/CdS-C nanocomposites were characterized by XRD,SEM,TEM.The results revealed that α-Fe2O3/CdS-C(Fe:Cd ratio of 1:1)exhibited excellent performance in the degradation of Orange Ⅱ(50 mg/L)leading to 98.3%in 20 min.The α-Fe2O3/CdS-C nanocomposite with Fe:Cd ratio of 1:1 generated more active species(·SO4-,·OH and·O2-)than other composites of different Fe:Cd ratios which can confirm this by quenching experiments and ESR.Moreover,the catalyst of the degradation efficiency can still reach 91.9%after five successive degradation cycles.In addition,we also found that lower pH was beneficial to the removal of Orange II because a lot of active species(·SO4-,·OH)were produced under acidic conditions.