Preparation Of Carbon-based Composite Electrode And Its Electrosorption Performance For Heavy Metal Ions

In the era of rapid social development and continuous technological innovation,although people’s life has become rich and convenient,they are also suffering from the harm brought by modern industry.Among them,heavy metal pollution is the biggest threat to people’s life and health brought by modern industry.At present,heavy metal removal methods include chemical precipitation,membrane filtration,ion exchange,adsorption and electrochemical treatment.However,these traditional methods have certain limitations,so the development of a low energy consumption,low cost,simple operation and environmentally friendly water purification technology has become hot topic.In this thesis,a capacitive deionization（CDI）technique was introduced.Its basic principle is to remove heavy metal ions by electrostatic adsorption of charged ions.In CDI technology,the electrosorption performance to heavy metal largely depends on the properties of selected electrode materials,which is very important in the electrochemical process.Therefore,the selection of appropriate electrode materials is the key factor for its development,and different types of electrode materials will not only have excellent electrosorption performance for different charged ions,but even some electrode materials can selectively adsorb specific ions.Therefore,the research focus of this thesis is to explore the application of electrode materials based on CDI technology for selective electrosorption of heavy metal ions.Firstly,a nitrogen and sulfur co-doped FeS₂carbon composite（FeS₂@NSC）was developed as a new CDI anode material.The electrosorption performance of FeS₂@NSC for Cu²⁺ions at different concentrations was tested at 1 V voltage,and the adsorption capacity was as high as 508.5mg/g by Langmuir isotherm fitting.When the molar ratio of Cu²⁺/Na⁺was 1:10,the selectivity coefficient of FeS₂@NSC electrode for Cu²⁺ions reached the maximum of 71.6.Significantly,the FeS₂@NSC electrode had obvious Cu²⁺ion selective electrosorption behavior in mixed ions environment including Cu²⁺,Pb²⁺,Cd²⁺,Zn²⁺,Co²⁺and Mn²⁺ions.In order to elucidate the mechanism of selective electrosorption,we characterized the FeS₂@NSC electrode before and after electrosorption by XPS,and found that the highly selective electrosorption of Cu²⁺ion in FeS₂@NSC was dominated by the Faradic redox reaction of the Fe²⁺/Fe³⁺and Cu²⁺/Cu⁺couples.The selective electrosorption performance of FeS₂@NSC electrode was also confirmed by treatment of real copper-containing electroplating wastewater.Secondly,we utilized the melamine foam frame to prepare nitrogen-doped carbon nanotube encapsulated Fe₇S₈nanoparticles with three steps of hydrothermal,carbonization and sulfidation.Moreover,the exceptional removal capacity of Pb（Ⅱ）reached the maximum value of 203mg/g at 1.2V according to Langmuir model.The form of Pb S after pseudocapacitive coupling of Pb onto the surface of electrode was confirmed by ex-situ XRD and XPS.This work provides an idea for removeal of the heavy metal lead by CDI technology.Finally,a nitrogen-doped porous silk carbon（PSC）was prepared from silkworm cocoons.The material has a large specific surface area（959.1m²/g）and has two kinds of pore structures:microporous and mesoporous.In addition,nitrogen doping also enhances the Faraday effect and wettability of the material itself.Through CDI test,it showed an excellent electrosorption performance for Zn²⁺（33.1mg/g）and the PSC electrode has a good selectivity to Zn²⁺ions in the solution of Zn²⁺,Mg²⁺,Ca²⁺and Na⁺ion blends.Through electrochemical analysis,it was found that the cathode and anode of CV curve of PSC electrode in 1M ZnSO₄solution showed a peak,respectively,which was mainly due to the Faraday intercalation process of Zn²⁺ions,and this determined the selective adsorption of Zn²⁺ions by PSC.This study provides a direction for CDI to extract metal zinc of the strategic resource from wastewater in the future.