【作者】 张黎；

【导师】 杨莉；

【作者基本信息】 长安大学 ， 环境科学与工程， 2022， 硕士

【摘要】 随着工业化的发展,水体中Cr（VI）污染问题日益严重。铁碳微电解法具有去除效率高和成本低廉等特点,是处理含Cr（VI）废水的常用方法。在众多的铁碳微电解材料中,生物碳负载纳米零价铁（n ZVI）所形成的铁碳微电解材料不仅环境友好,而且具有较高的反应活性,可实现水体中Cr（VI）的有效去除。本文以提升生物碳负载纳米零价铁微电解复合材料性能及安全性为主要入手点,首先对绿色合成法制备n ZVI的实验条件进行优化,在获得分散性好、抗氧化能力强的n ZVI的基础上,选择蛋白质含量丰富的酵母为碳源制备了氮掺杂多孔酵母碳负载纳米零价铁（YC/Z@n ZVI）,并进一步构建了海藻酸钙包埋YC/Z@n ZVI的微电解复合材料（CA_F-（YC/Z@n ZVI））。实验考察了基于酵母的铁碳微电解材料去除水中Cr（VI）的性能,探讨了酵母碳的内源氮掺杂对微电解体系去除Cr（VI）性能提升的作用,并从体系铁离子溢出的角度分析了酵母基铁碳微电解材料的绿色安全性。本文的主要研究内容及结论如下:（1）以石榴皮提取物为还原剂和分散剂,使用绿色合成法制备了n ZVI。通过SEM、XRD、FTIR、TGA等分析手段对n ZVI的物理化学性质进行表征,讨论了反应时间、铁盐浓度、提取物多酚浓度等合成条件对n ZVI粒径和产率的影响,并对其可能的合成规律进行了探究。实验结果表明:石榴皮提取物合成的n ZVI呈无定型结构,尺寸为200nm左右;来自于石榴皮提取物的多酚类物质不仅参与了Fe²⁺还原,还可作为分散剂包覆在n ZVI表面。当反应时间为120 min,Fe²⁺浓度为0.05 mol/L,多酚浓度为15 mg/m L时合成产物n ZVI的粒径及产率为最优。（2）以蛋白质含量丰富的酵母为碳源,石榴皮多酚提取物为还原剂,采用Zn Cl₂活化法制备了氮掺杂多孔酵母碳负载纳米零价铁微电解材料（YC/Z@n ZVI）。利用SEM、XRD、BET、电化学阻抗、XPS等手段对样品的形貌、结构以及性能进行表征,考察了YC/Z@n ZVI对水中Cr（VI）的去除性能,探究了酵母碳的氮掺杂提升材料的Cr（VI）去除性能的作用以及YC/Z@n ZVI去除水中Cr（VI）的可能机理。结果表明:Zn Cl₂活化后的酵母碳（YC/Z）呈椭球形结构,尺寸2.70μm左右,平均孔径为3.37nm,比表面积3.32m²/g,具有优异的Cr（VI）吸附以及电化学性能。实验表明YC/Z@n ZVI对水中Cr（VI）去除效果显著优于YC@n ZVI,反应时间为60min时,二者对Cr（VI）去除率分别为93%和71%。机理分析认为,YC/Z@n ZVI在去除水中Cr（VI）过程中,n ZVI主要通过释放的电子以及产生的Fe（II）作用实现Cr（VI）的还原,而氮掺杂的YC/Z则在为Cr（VI）吸附和富集提供大量活性位点的同时,还利用其高效的电子传输性能促进了电子的传递和释放,二者共同参与了体系Cr（VI）的去除。（3）利用海藻酸钙凝胶（CA）对YC/Z@n ZVI进行包埋处理,制备了海藻酸钙-酵母碳基微电解复合材料（CA_F-（YC/Z@n ZVI））。通过SEM、FTIR等表征手段对样品的形貌、结构及物理化学性质进行表征,考察了CA_F-（YC/Z@n ZVI）去除水中Cr（VI）的性能及体系铁离子溢出情况,并结合CA_F-（YC/Z@n ZVI）的结构及吸附性能给出了可能的机理解释。实验结果表明:冷冻干燥制备的CA_F-（YC/Z@n ZVI）能较好的保留凝胶内部结构,有利于获得充足的反应接触空间,该样品去除水中Cr（VI）的性能优于未包埋样品YC/Z@n ZVI,而且反应后CA_F-（YC/Z@n ZVI）体系中总铁和总铬的浓度均明显小于YC/Z@n ZVI体系。机理分析实验认为,CA_F-（YC/Z@n ZVI）对水中Cr（VI）的还原去除作用分为两个过程:Cr（VI）首先经迁移及孔道扩散进入凝胶结构,进而在YC/Z@n ZVI的铁碳微电解作用下去除;吸附作用与离子交换作用是总铁及总铬释放量减少的主要原因。更多还原

【Abstract】 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.更多还原