Modification Of Bismuth Sulfide Nanomaterials And Its Application In Cr(?) Wastewater Treatment

Hexavalent chromium(Cr(?))in wastewater is seriously harmful to the environment due to its strong oxidation ability and carcinogenicity.Adsorption and catalytic reduction methods are commonly used in Cr(?)removal.Recently,bismuth sulfide(Bi₂S₃)with mi-cro-/nano structure have been widely used in Cr(?)treatment due to its special structure and ideal photocatalytic performance.It was found that the Cr(?)removal performance of Bi₂S₃ was closely related to its morphology and structure.Moreover,the variation of p H value and different kinds of ions in the actual Cr(?)-containing wastewater have a great influence on the Cr(?)removal ability of Bi₂S₃.In addition,the powder Bi₂S₃ difficult to be recycle from actual Cr(?)-containing wastewater,it limited the practical application of Bi₂S₃.Based on this,in this thesis,the work focused on the modification of Bi₂S₃ and its application in actural Cr(?)containing wastewater treatment.The main works are summa-rized as follows:1.Double sulfur precursors Bi₂S₃ micro-/nanostructure materials were prepared via hydrothermal method in ethylene glycol by using any two kinds of sulfur precursors among thioacetamide,thiourea,L-cysteine and ammonium sulfide.The products were character-ized by powder X-ray diffraction,scanning electron microscope and physical adsorption apparatus.It was found that the morphologies of Bi₂S₃ obtained from different sulfur pre-cursors were different.The double sulfur precursor Bi₂S₃ possessed larger BET surface area and smaller particle size than that of the single sulfur precursor Bi₂S₃.The Cr(?)adsorption and photocatalytic reduction performance upon visible light irradiation over single sulfur precursor Bi₂S₃and double sulfur precursors Bi₂S₃were investigated,indicating that the Cr(?)removal performance of double sulfur precursors Bi₂S₃ was better than that of single sulfur precursor Bi₂S₃.The Cr(?)removal performance of Bi₂S₃ prepared by different dou-ble sulfur precursors were quite different.The double sulfur precursors Bi₂S₃ prepared from L-cysteine and ammonium sulfide(BS9)displayed the best adsorption ability and photo-catalytic reduction performance for Cr(?)in water.The effect of the p H value on the Cr(?)adsorption and photocatalytic reduction performance of double sulfur precursors Bi₂S₃(BS9)were also investigated.It showed that BS9 exhibited the best adsorption performance of Cr(?)with the maximum Cr(?)adsorption capacity of 132.48 mg/g when the p H value was 2.When the p H value was 5,85%Cr(?)could be reduced by BS9 after 120 minutes visible light irradition.Moreover,BS9 possessed good stability,which could maintain more than 90%of the Cr(?)removal rate after 5 cycles of Cr(?)adsorption and photocatalytic reduction.2.The double sulfur precursors Bi₂S₃(BS9)synthesized from L-cysteine and ammo-nium sulfide was selected to investigate its Cr(?)removal performance in two different batches of actual electroplating wastewater.The results showed that BS9 possessed better Cr(?)adsorption performance in these two batches of actual electroplating wastewater compared with the prepared Cr(?)solution(p H=2).The maximum adsorption capacity of Cr(?)of BS9 in two batches of actual electroplating wastewater were 202.10 and 157.61mg/g,respectively.The main components in the actual electroplating wastewater were ana-lyzed,and the influence of p H value and ions in the actual electroplating wastewater on the Cr(?)removal over Bi₂S₃ were discussed.The results indicated that SO₄^2-and Cl^-anions could promote the Cr(?)removal,while other ions had no significant effect.However,when the pH value was higher than 2,the anions had little effect on the adsorption of Cr(?)by Bi₂S₃.The products after Cr(?)adsorption in the solutions containing different ions were characterized by X-ray photoelectron spectroscopy.It was found that SO₄^2-and Cl^-could promote the adsorption and reduction of Cr(?)by Bi₂S₃,while inhibited the adsorp-tion of Cr(III).This work provided reliable data for the application of Bi₂S₃ in actual elec-troplating wastewater.3.In order to improve the photoreduction and recovery performance of powder Bi₂S₃,magnetic Fe₃S₄/Bi₂S₃ composite was obtained by combining Bi₂S₃ sample synthesized from thioacetamide(BS1)with magnetic material ferric tetrasulfide(Fe₃S₄).Powder X-ray dif-fraction(XRD)and physical adsorption measurement were used for the characterization of the products.It showed that when the ratio of Bi³⁺/Fe³⁺in the Fe₃S₄/Bi₂S₃sample was 2:1,Fe₃S₄/Bi₂S₃ exhibited the largest BET surface area and the best photoreduction performance of Cr(?).Fe₃S₄/Bi₂S₃ also displayed strong adsorption and photoreduction properties of Cr(?)when it was applied to actual electroplating wastewater.However,the stability of Fe₃S₄/Bi₂S₃ was still worthy to be improved.It provided a clue for the problem that Bi₂S₃was difficult to apply in practical wastewater treatment.