Yeast-assisted Preparation Of Iron Carbon Micro-electrolysis Material And Its Performance For Removal Of Cr(Ⅵ) From Aqueous Solutions

Hexavalent chromium[Cr（VI）]pollution is growing seriously due to industrial growth.As a common method for treatment of Cr（VI）-containing wastewater,iron-carbon micro-electrolysis technique is characterized by high removal efficiency and low cost.Among many iron-carbon micro-electrolysis materials,the iron carbon micro-electrolysis from biochar loaded nano zero valent iron（n ZVI）is not only environmentally friendly but also has high reactivity,which can effectively achieve the removal of Cr（VI）from water.The main starting point of this paper is to improve performance and safety of biochar loaded n ZVI micro-electrolysis composites.Firstly,this paper optimized the green synthesis condition for the preparation of n ZVI with good dispersibility and strong antioxidant capacity.Then nitrogen doped porous yeast carbon loaded nano zero valent iron（YC/Z@n ZVI）was prepared by selecting yeast as a carbon source due to its rich protein content.Finally,calcium alginate embedded YC/Z@n ZVI microelectrolysis composite（CA_F-（YC/Z@n ZVI））was further prepared using YC/Z@n ZVI as a raw material.The experiments investigated the performance of different yeast based ion carbon microelectrolysis materials for the removal of Cr（VI）from water and discussed the important roles of endogenous nitrogen doping in improving the effect of micro electrolysis system.Finally,the safety and environmental friendliness of yeast based iron carbon micro electrolysis materials were analyzed based on the iron ion overflow from the system.The main research contents and conclusions of this paper are as follows:（1）Green synthesized nanoscale zero-valent iron（n ZVI）was prepared using pomegranate peel extract as reducing agent and stabilizer.The physicochemical properties of n ZVI were characterized by SEM,XRD,FTIR and TGA.The effects of synthesis conditions such as reaction time,iron salt concentration and polyphenol concentration on particle size and yield were discussed and the possible synthesis patterns was also studied.Results showed that n ZVI synthesized from pomegranate peel extract have an amorphous structure and the mean particle size is 200 nm,while polyphenols in the extract could not only participated in the Fe²⁺reduction,but also acted as stabilizers to coat the n ZVI surface.Besides the results proved that120 min reaction time,0.05 mol/L Fe²⁺and 15mg/m L polyphenol was the best preparation condition of n ZVI with the highest yield and smallest particle size.（2）Nitrogen-doped porous yeast carbon-loaded nano-zero-valent iron microelectrolytic materials（YC/Z@n ZVI）were prepared via Zn Cl₂ activation method using protein-rich yeast as carbon source and pomegranate peel polyphenol extract as a reducing agent.The morphology,structure and properties were characterized by SEM,XRD,BET,XPS and EIS.The experiment not only investigated the Cr（VI）removal performance of YC/Z@n ZVI in water but also explored the effect of nitrogen doped of yeast carbon to enhance the Cr（VI）removal performance of the material and the possible mechanism of Cr（VI）removal by YC/Z@n ZVI in water.Results show that the yeast carbon（YC/Z）activated by Zn Cl₂ were ellipsoidal structure with a size of 2.70μm,average pore diameter of 3.37 nm,and specific surface area of 3.32m²/g,which have excellent adsorption as well as electrochemical performance.Besides experiments have shown that the removal efficiency of Cr（VI）by YC/Z@n ZVI was significantly higher than YC@n ZVI,the removal efficiency of Cr（VI）are93%and 71%at a reaction time of 60 min respectively.Mechanistic analysis suggests that the YC/Z@n ZVI system achieves Cr（VI）removal from water by giving electrons and releasing Fe（II）to n ZVI for Cr（VI）reduction,while the nitrogen-doped YC/Z not only provide a large number of active sites for Cr（VI）adsorption and enrichment but also facilitate the transfer and release of electrons by its efficient electron transport properties,both n ZVI and YC/Z participate in the removal process of Cr（VI）.（3）Calcium alginate-yeast carbon based microelectrolytic composites（CA_F-（YC/Z@n ZVI））were prepared using calcium alginate gel（CA）as a carrier for embedding YC/Z@n ZVI.The morphology,structure and properties were characterized by SEM and FTIR.The effectiveness and environmental friendliness of CA_F-（YC/Z@n ZVI）for Cr（VI）were investigated,and the mechanism of the structure and adsorption characteristics of calcium alginate composite gel was given.The result showed that CA_F-（YC/Z@n ZVI）prepared by freeze-drying method retain the internal structure of the gel effectively,which is conducive to obtaining sufficient reaction contact space.The removal efficiency of CA_F-（YC/Z@n ZVI）for Cr（VI）is higher than YC/Z@n ZVI,while the concentrations of total iron and total chromium in CA_F-（YC/Z@n ZVI）systems after reaction is lower than YC/Z@n ZVI.Mechanism analysis experiments concluded that the reduction and removal of Cr（VI）from water by CA_F-（YC/Z@n ZVI）could be divided into two parts:firstly,the Cr（VI）through external migration and pore diffusion enters the gel,and then continues to be removed by YC/Z@n ZVI micro-electrolysis.Additionally,adsorption and ion exchange are the main reasons for the decrease of total iron and chromium release.