Studies On Roxarsone Degradation-adsorption Through Persulfate Or Hydrogen Peroxide Catalyzed By Fe-based Nanocomposites

Aromatic organoarsenics such as roxarsone?3-nitro-4-hydroxy benzene arsenic acid,ROX?are widely used in animal husbandry as feed additives to improve meat yield,control parasites and improve animals'appearance.However,the assimilation of organoarsenic in livestock appears to be extremely low.Most of it is excreted chemically unchanged and finally enters the environment through poultry litter.In the environment,organoarsenic can be converted into more toxic inorganic arsenic compounds including arsenates?As?V??and arsenites?As?III??through biotic and abiotic transformation under anaerobic conditionsand,which can do great damage to the environment.However,when ROX was ecomposed by traditional advanced oxidation technology,the inorganic arsenic products formed remain in the solution or in the arsenic-bearing precipitate,which can not completely remove total arsenic and bring serious secondary pollution.In this paper,persulfate and hydrogen peroxide systems activated by catalytic-adsorptive bifunctional iron-based nanocomposites to oxidate ROX and in-situ adsorbe inorganic As compounds were proposed.Then,the recovered inorganic arsenic is used as a potential photocatalyst.The specific research contents and conclusions are as follows:?1?A composite of reduced graphene oxide and carbon nanotubes was impregnated with goethite designated as?-FeOOH@GCA and tested as an integrated catalyst and adsorbent for ROX decontamination.Nearly 100%of the ROX was transformed in?-FeOOH@GCA activating persulfate?PS?under UV₃₆₅ irradiation system at relatively low dosage of the?-FeOOH@GCA catalyst(250?mg?L^-1)in120?min.The As?V?released in the ROX oxidation was simultaneously adsorbed onto the surface of the?-FeOOH@GCA.Finally,the As?V?adsorbed on catalyst was recovered and used to form an efficient Ag₃AsO₄ photocatalyst.Compared with traditional adsorption technology,this work further extends the oxidation-adsorption technology in solving organoarsenical contamination without producing secondary pollution.?2?Iron-based metal-organic framework MIL-101?Fe?was synthesized by hydrothermal method as a bifunctional catalyst for catalysis and adsorption of ROX.The results show that under the irradiation of ultraviolet-visible light,the removal rate of ROX is about 95%within 120 minutes in the MIL-101?Fe?(250 mg L^-1)activating H₂O₂?1.00 mM?system,and the inorganic arsenic compounds produced during the reaction will be adsorbed on the material surface of MIL-101?Fe?at the same time.The total arsenic removal rate is nearly 85%from the solution.·OH and O₂^·–free radicals play a major role in ROX degradation.ROX degradation is initiated by·OH and O₂^·–free radicals attacking As–C bond to produce As?V?and nitrophenol.Actual water in the system has a positive effect on ROX removal.The technology of combining organic arsenic oxidation,inorganic arsenic adsorption and recovery was proposed in this paper,which provide a new idea for the removal of organic arsenic and a new direction for the final green disposal of arsenic.It has certain theoretical value and practical significance.