Removal Of Arsenic In Aqueous Solution Through Simultaneous Photocatalytic Oxidation And Adsorption By Fe₃O₄ Based Composites

With the rapid development of economy and the increase of the human production activities,arsenic contamination becomes more and more serious.The organic arsenic compounds with high solubility can’t be removed by conventional water treatment processes.The organic arsenic degradation of accompanied with the production of inorganic arsenic,leading to high-toxic inorganic arsenic residue.A variety of technologies,including chemical precipitation,ion exchange,membrane filtration,electric coagulation and adsorption,have been applied to remove arsenic from water.Due to its ease of control,high removal efficiency,low cost and renewability,adsorption is one of the most widely used technologies.However,most adsorbents are highly effective for the As（V）removal,but fail in the case of As（Ⅲ）.To achieve higher removal efficiency,an oxidation pretreatment is employed to convert As（Ⅲ）to As（V）prior to adsorption,leading to the treatment process complexity.In this study,As（Ⅲ）and p-ASA were selected as targeted pollutants.Fe₃O₄ based composites combined good photocatalytic properties and high adsorption capacities were fabricated and characterized.Due to the synergy of composites,As（Ⅲ）and p-ASA were translated into As（V）by photocatalytic and further efficiently removed through adsorption.Moreover,the effects of major factors on the arsenic removal were investigated,and the mechanism of the arsenic removal through photocatalytic oxidation and adsorption was also explore.To improve the removal efficiency of arsenic,ZrO₂-Fe₃O₄ and Ce O₂-Fe₃O₄were fabricated.Comparison of physicochemical properties,adsorption capacities,and arsenic removal efficiencies,Fe₃O₄ based composites UV photocatalytic oxidation and adsorption system were constructed and applied to remove As（Ⅲ）and p-ASA.The results showed the dosage of CeO₂-Fe₃O₄,initial As（Ⅲ）concentration were 200 mg/L and 10 mg/L,under neutral condition,As（Ⅲ）was completely oxidized to As（V）within 30 min.The removal effici ency of As（V）was98%until adsorption equilibrium.When the initial p-ASA concentration was 10mg-As/L,the degradation efficiency of p-ASA reached 100%within 28 min.The removal efficiency of the released inorganic arsenic reached above 99%.To save energy and use solar energy,comparison of visible light photocatalytic active components,Cu O-Fe₃O₄ visible light photocatalytic oxidation and adsorption system was constructed and applied to remove As（Ⅲ）and p-ASA.The dosage of Cu O-Fe₃O₄,initial As（Ⅲ）concentration were 200 mg/L and 10 mg/L,As（Ⅲ）was completely oxidized to As（V）within 40 min.The removal efficiency of As（V）was above 90%until adsorption equilibrium.When the p-ASA concentration was 10mg-As/L,the degradation efficiency of p-ASA reached 100%within 32 min.The removal efficiency of the released inorganic arsenic reached above 95%.The effects of major factors on arsenic removal during the photocatalytic oxidation and adsorption were investigated.As for the p-ASA photocatalytic oxidation degradation,the increase of dissolved oxygen and p H promoted the p-ASA degradation.The co-existing Cl^-、HCO₃^-and HA might inhibit the degradation efficiency by scavenging free radicals or other ways.As for the As（V）adsorption,the As（V）removal efficiency decreased with the As（Ⅲ）concentration increasing.The presence of Cl^-、NO₃^-and SO₄^2-did not have any influence on As（V）removal.Due to competing adsorption,the presence of CO₃^2-、Si O₃^2-and PO₄^3-decreased the As（V）removal efficiency.Based on the above analysis,the mechanism of the oxidation degradation of p-ASA and As（Ⅲ）and the adsorption of As（V）was explored.The results showed that·OH and·O₂^-were regarded as the main role of the p-ASA and As（Ⅲ）oxidation processes.The photocatalytic degradation of p-ASA accompanied with the production of As（Ⅲ）、As（V）、NH₄⁺and organic intermediate products.As（Ⅲ）was rapidly oxidized to As（V）,subsequently.Thus As（V）was identified as the eventual arsenic product for p-ASA degradation,which could be efficiently removed by adsorption onto Fe₃O₄ based composites via inner-sphere complexation.The adsorption processes of As（V）on the Fe₃O₄ based compounds were fitted the pseudo-second order model and Freundlich model well.The adsorption between As（V）and Fe₃O₄ based composites mainly belonged to chemisorption.In this study,the Fe₃O₄ based photocatalyst/adsorbent with good photocatalytic property and high adsorption capacity were fabricated.The UV/visible light photocatalytic oxidation and adsorption systems were constructed.As（Ⅲ）and p-ASA were translated into low toxicity As（V）through photocatalytic oxidation,which was further efficiently removed through adsorption.This study developed a new treatment technology for arsenic pollution,and gave a new way for the restoration of arsenic pollution in aquatic environment and drinking water security.