Carbon Containing Materials Loaded With Sulfidated Nanoscale Zero-Valent Iron For The Removal Of U(Ⅵ) And Their Microbial Toxicity

Nanoscale zero-valent iron(nZVI)has been widely used for the removal of environmental pollutants,but its application is limited by the disadvantages such as easy oxidation and agglomeration.Sulfidated nanoscale zero-valent iron(S-nZVI)is a method of modifying the surface of nanoscale zero-valent iron through sulfidation reaction.Sulfidation can improve the removal performance of nanoscale zero-valent iron for pollutants,but S-nZVI still has disadvantages such as easy agglomeration.Therefore,this study proposes to load S-nZVI on carbon-containing materials.The study selected reduced graphene oxide and graphitic carbon nitride,successfully prepared reduced graphene oxide loaded sulfidated nanoscale iron(rGOS-nZVI)and carbon nitride loaded sulfidated nanoscale iron(g-C3N4-S-nZVI),and applied it to the removal of U(Ⅵ)pollution.The experiment first studied the removal effect and mechanism of U(Ⅵ)by rGO-S-nZVI and g-C3N4-S-nZVI.The results show that:(1)rGO-S-nZVI and g-C3N4-S-nZVI have good removal effects on U(Ⅵ),and the removal process conforms to the pseudo-second-order kinetics.The two materials show an upward trend with the increase of reaction pH,and then a downward trend.The best pH is 7;at a concentration of 50 mg/L,a dosage of 0.2 g/L,and a reaction time of 120 min,the removal rate of U(Ⅵ)can reach over 95%.(2)The solid materials after the reaction were further characterized by transmission electron microscopy,X-ray diffraction and X-ray photoelectron spectroscopy.The results show that both materials contain FeS on the surface before the reaction,while the products after the reaction are mainly Fe2O3 and Fe2(SO4)3;U is removed by both materials in the form of U(Ⅵ).The study further explored the impact of graphene,carbon nitride,S-nZVI,rGO-S-nZVI and g-C3N4-S-nZVI on microbial growth.A fungus was isolated and purified from sediment and identified as Arthrographis arxii.The results showed that graphene and carbon nitride alone have no significant effect on the growth of Arthrographis arxii,while the other three materials have strong killing effects on Arthrographis arxii.The bactericidal strength is g-C3N4-SnZVI>S-nZVI>rGO-S-nZVI.In order to clarify the bactericidal mechanism,the study explored from three aspects:direct contact,Fe2+concentration and oxidative stress.The toxic mechanisms of rGO-S-nZVI and gC3N4-S-nZVI to Arthrographis arxii were determined.The main toxic mechanism of rGO-SnZVI to Arthrographis arxii is Fe2+and oxidative stress;while the main toxic mechanism of gC3N4-S-nZVI to Arthrographis arxii is direct contact,Fe2+ and oxidative stress.The study further analyzed the impact of S-nZVI,rGO-S-nZVI and g-C3N4-S-nZVI on bacterial communities and fungal communities in sediment through high-throughput sequencing methods from the aspects such as sequence processing,species composition,Alpha diversity index and Venn diagram.From a macro perspective,it compared the toxicity of three materials and provided theoretical guidance for their practical application.The results show that all three materials reduce the diversity of bacterial community structure,with S-nZVI having the most obvious reduction.g-C3N4-S-nZVI has the greatest impact on fungal community diversity.