Study On The Preparation And Performance Of A New Type Of Adsorbent

With the development of industry,the pollution of mercury and lead metal ions has become an important threat to human health and environment and it is necessary to develop new technologies to remove them.In this work,three kinds of selective adsorbents were prepared by grafting ion recognition functional groups onto nano-silica and agricultural by-product?corn bract?and characterized.Simultaneously,the factors of solution pH,contact time,initial ion concentration,reaction temperature,selectivity and reusability were investigated.And the adsorption mechanism was studied in terms of adsorption kinetics,isotherms,thermodynamics and the changes of surface functional groups.This work provided new methods for the removal of Hg²⁺and Pb²⁺.In the second chapter,the three adsorbents were prepared and characterized.Three coupling agents were linked on the surface of backing material to create conditions for the modification of diethanolamine,phosphinic acid and trithiocyanuric acid.The synthesis process was analysised by FT-IR,EDS and XPS and physicochemical properties of the adsorbents were determined by SEM,TGA and BET.In the third chapter,the adsorption kinetics and thermodynamics were analyzed.The adsorption equilibrium time of PA-SNPs,TCA-CCB and DPM-SNPs was 60 min,400 min and 60 min,respectively.The adsorption processes fitted well with the Pseudo-second-order kinetic model,which showed that the adsorptions were chemical adsorption.Simultaneously,the Boyd model showed that the rate determining step of Hg²⁺and Pb²⁺adsorption was film diffusion.Besides,thermodynamic results showed that the process of Hg²⁺adsorption by PA-SNPs and TCA-CCB was spontaneous and endothermic and Pb²⁺adsorption via DPM-SNPs was spontaneous and exothermic.In the fourth chapter,the adsorption isotherms were studied and the three materials were compared with other reported adsorbents.The adsorption capacity of PA-SNPs,TCA-CCB and DPM-SNPs were 274.32 mg/g,390 mg/g and 154.38 mg/g,respectively.The process of Hg²⁺adsorption by PA-SNPs and Pb²⁺adsorption by DPM-SNPs can be described well by Langmuir model,suggesting that the adsorptions were monolayer adsorption on the homogeneous surface;Hill model can well describe the process of Hg²⁺adsorption by TCA-CCB,indicating the average number of Hg²⁺adsorbed by single site is 1.6875.The calculated results of free energy?E?and Langmuir-based K_R values showed that the three adsorption processes were feasible and irreversible chemical adsorption.Compared with the reported adsorbents,the three adsorbents presented good applications for the removal of Hg²⁺and Pb²⁺.In the fifth chapter,the selectivity,repeatability,adsorption-desorption and adsorption mechanism were systematically studied.The results showed that PA-SNPs,TCA-CCB and DPM-SNPs have high selectivity and good reusability for Pb²⁺and Hg²⁺.The adsorption mechanisms were proved to be chelation,ion exchange and electrostatic interaction.