Removal Of Roxarsone From Water By Photocatalytic System Based On Novel Resorcinol-formaldehyde Resin

Roxarsone is one of organic contaminants containing arsenic,and its degradation products seriously threaten the safety of ecological environment and human health.Roxarsone has been widely used as a feed additive worldwide to help prevent disease in poultry,improve feed efficiency and promote the growth of livestock.Roxarsone has strong migration in water,and can form arsenic-containing organic and inorganic compounds through biotransformation and photolysis in natural environment.Studies have found that inorganic arsenic is a low-dose,long-term exposure carcinogen,associated with cancer,cardiovascular disease and other serious threats to the natural environment and human health.At present,the removal methods of organic arsenic include biological methods,adsorption methods,photolysis methods and advanced oxidation methods.However,most of the methods have low efficiency to remove organic arsenic and cannot deal with the highly toxic degradation intermediates,which makes the removal of organic arsenic more difficult.In recent years,advanced oxidation technology has become a key research direction for removing organic pollutants in water due to its strong oxidation ability,which can decompose organic matter efficiently and thoroughly.The combination of advanced oxidation technology and inorganic arsenic adsorption can perfectly remove arsenic pollution in water.Roxarsone decomposes rapidly under the attack of active oxygen species,and the generated inorganic arsenic can be removed by in-situ adsorption.As a new type of non-metallic photocatalytic material,resorcinol-formaldehyde resin has strong photocatalytic performance and can produce hydrogen peroxide(H2O2)efficiently under sunlight irradiation.H2O2 is an important oxidant in advanced oxidation technology and can produce active oxygen species with strong oxidizing ability activated by transition metal.Moreover,iron-based materials are widely used in the activation of oxidants such as H2O2 and persulfate because of their low toxicity,low cost and easy preparation.At the same time,ironbased materials are good materials as inorganic arsenic adsorbents because of their high affinity for inorganic arsenic and large adsorption capacity.Therefore,in this paper,resorcinolformaldehyde resin was combined with different iron-based materials to construct a system for efficient degradation of organic arsenic in water and in-situ adsorption of inorganic arsenic under simulated sunlight irradiation.Specific research contents and results are as follows:(1)Resorcinol-formaldehyde resin(RFs)was firstly synthesized by an extended Stober method.Then resorcinol-formaldehyde resin loaded with ferric oxide(RFs-Fe2O3)was synthesized by secondary hydrothermal method.Among them,RFs-Fe2O3-10 with a theoretical load of 10%Fe2O3 showed the best effect in activating peroxomonosulphate(PMS)to degrade Roxarsone(ROX)under simulated sunlight irradiation.The RFs-Fe2O3-10/PMS system maintained a good removal rate at a wide pH range(2.47-8.21)and a low dose of PMS(4 mM)and 60%inorganic arsenic was adsorbed by catalyst.In addition,in the ion influence experiment,a variety of ions had little influence on the system,and more than 85%ROX was decomposed by oxidation.Fe(Ⅲ)was reduced to Fe(Ⅱ)by the electrons produced by phenolic resin after light irradiation,and the redox cycle of Fe(Ⅲ)/Fe(Ⅱ)was accelerated.(2)Resorcinol-formaldehyde resin(RFs-FeQDs)loaded with FeOOH quantum dots(FeOOH QDs)was synthesized by a typical synthesis method at room temperature.FeOOH QDs not only reacted with H2O2 to produce reactive species,but also acted as an adsorbent for arsenic compounds.RFs-FeQDs-20 could adsorb more than 60%of ROX and 99%of inorganic arsenic.Under simulated sunlight irradiation,H2O2 produced by RFs reacted with FeOOH QDs to produce singlet oxygen(1O2),which degraded ROX adsorbed on the surface of the catalyst.In addition,the catalyst scooped electrons from the pollutant through electron transfer pathway,leading to the self-decomposition of part of the ROX.RFs-FeQDs-20 had good stability in a wide pH range and a variety of ions coexistence,and kept the same removal rate after washing with 0.1 M NaOH in 5 cycles.(3)Using graphene oxide(GO)as a carrier,FeOOH QDs was loaded firstly and then resorcinol-formaldehyde resin was combined to form a composite material RFs-GO-FeQDs for the removal of arsenic pollution.Using graphene oxide as a support carrier,provided more loading sites for FeOOH QDs,enhancing the adsorption of ROX and decomposition of H2O2,and as a platform for electron transport,facilitated charge separation in the composite.The experimental results showed that RFs-GO-FeQDs could remove more than 98%of ROX within 60 min,in which singlet oxygen(1O2)and electron transfer were the main degradation pathways of ROX.The As(Ⅲ)and As(Ⅴ)generated from the degradation of ROX were in-situ adsorbed by catalysts.RFs-GO-FeQDs showed high removal effect on ROX in pH influence experiments and ion influence experiments,and still maintained high removal rate after multiple cycles.