| Fe~0-based nanocatalysis has been one of the most intensively studied environmental purification processes in the past 20 years due to its high reducibility and strong adsorption capacity.Freshly prepared zero-valent Fe-based nanoparticles(n ZVI)have been shown to treat a wide range of organic and inorganic pollutants in water and soil due to their highly reactive properties with many active sites on their surfaces.In the past,most research has focused on broadening the Fe base of nanometer catalytic technology application scope(e.g.,processing new pollutants),and by using various support(stabilizer or surface modifier)for improving the preparation of Fe base nanoparticles classic boron hydride reduction method,to enhance its dispersion and implement application ability can be transmitted over a long distance.However,the low electron transfer efficiency caused by the passivation layer and the selection of suitable supports to enhance its stability and take into account the electron transfer efficiency are still two challenges to be faced.Researchers have adopted a variety of n ZVI activity regulation strategies,among which M/Fe bimetallic nanoparticles prepared by adding transition metals and coupled support to inhibit particle aggregation are excellent representatives.However,it is still necessary to systematically compare the reactivity differences of different transition metal catalysts,expand the indicators to describe the catalytic activity,and establish the dechlorination path in a quantitative way,as well as the structure-activity relationship between the support characteristics and the reactivity.More importantly,the identification and clarity of micro reaction mechanism can provide theoretical support for the design of efficient reaction process,selection of application scenarios and even cross-application of other environmental governance technologies.In this study,the catalytic activities of Fe-based bimetallic nanoparticles formed by different transition metals were compared to screen out more efficient catalysts.On this basis,the following research and experiment are designed for the bottleneck problems of n ZVI technology.It focuses on the mechanism and performance expansion of catalytic reaction,taking the rate of electron transfer through Fe~0 corrosion as the core point of entry,mainly including the following three parts:In the first part(Chapter 2 and 3),the removal activity of the typical pollutants(4-CP and Cr(Ⅵ))coexisting in wastewater by using n ZVI and the bimetallic nanoccatalysts(M/Fe)formed by n ZVI loaded with transition metals was evaluated,and the interaction between the two pollutants and the catalytic mechanism were further explored.The results show that loading the second transition metal on n ZVI can significantly improve the catalytic performance of removing 4-CP and Cr(Ⅵ).The catalytic activity trend of M/Fe NPs was Pd/Fe>Ni/Fe>Cu/Fe>Pt/Fe>Ag/Fe>Au/Fe.The catalytic hydrodechlorination activity of bimetals can be well described by volcanic curves and explained by hydrogen adsorption energy on transition metal surfaces.The presence of Cr(Ⅵ)can inhibit the catalytic hydrodechlorination activity of Pd/Fe,resulting in a serious loss of dechlorination capacity,and the inhibition effect is affected by the initial Concentration of Cr(Ⅵ).The initial concentration of 4-CP affects the catalytic dechlorination activity of Pd/Fe NPs,but has little effect on the removal of Cr(Ⅵ)and total Cr.Subsequently,the influence of electrolyte composition,corrosion electrochemical characteristics and long-term corrosion performance under different catalyst systems were discussed by combining electrochemical characterization methods,which provided theoretical support for subsequent coupling support experiments.The second part(Chapter 4 and Chapter 5)is based on the first part of the study,aiming at the characteristics of Fe based nanoparticles are easy to agglomeration and sedimentation,taking the specific surface area and electrochemical performance of the support as the descriptor,to evaluate the changes of the morphology,particle size and catalytic performance of Pd/Fe nanoparticles with the highest catalytic activity dispersed on the common support.To explore the mechanism of support materials in enhancing the catalytic activity of Pd/Fe nanoparticles.The results show that the stable dispersion of Pd/Fe nanoparticles by the support is not the main reason to change the reactivity of the nanoparticles in the dechlorination process.The dechlorination activity of Pd/Fe nanoparticles is highly dependent on the electrochemical properties of the support.On this basis,a series of conductive polymers(CPs)were used as the support to load Pd/Fe nanoparticles(Pd/Fe@CPs),in order to realize particle dispersion and enhance the interface electron transfer rate.At the same time,by means of electrochemical characterization test,the structural activity relationship between dechlorination path and catalytic performance was established by quantitative method.The contribution of dechlorination pathway to dechlorination is also discussed.It was found that the reaction rate constant of Pd/Fe@CPs to 4-CP was 1.5～6.2 times higher than that of Pd/Fe.In addition,cyclic voltammetry can be used as a powerful tool to distinguish and identify the dehalogenation mechanism of chlorinated environmental pollutants on Fe-based bimetallic particles.Both direct and indirect electron transfer mechanisms have a good correlation with the dehalogenation performance on the surface of Fe-based bimetal particles.The correlation between the indirect electron transfer path mediated by H*and the dehalogenation performance is slightly higher than that of the direct electron transfer path.The third part(Chapter 6)is based on the first part and inspired by the research of the second part.Aiming at the bottleneck problem of electron and hydrogen supply in the Fe~0 corrosion process,the external electron and hydrogen source is introduced to design the 3D electro-driven Pd/Fe NPs catalytic system and verify its removal performance and reaction mechanism.The results show that Cr(Ⅵ)and 4-CP can be efficiently and synchronously removed by the catalytic system.Compared with electrochemical catalysis and chemical catalysis alone,the removal rate and dechlorination rate of 4-CP in the synergistic catalytic system coupled with the two catalysts have been greatly improved.Pd particles are an important factor driving the reduction cracking of C-Cl bond.Adding Pd/Fe NPs after chemical catalytic reaction into the electrocatalytic system can still achieve a removal rate of 72.8%～94.8%for 4-CP,indicating that the system has the advantage of waste resource recovery and can become the preferred choice in practical water purification. |
PDF Full Text Request