The Preparation And Application Of Double Network Hydrogel As Heavy Metal Adsorbent

Heavy metal pollution of water body has drawn increasing attentions throughout the world because of its serious biotoxicity, non-degradation and long-time hazard. In recent decades, many physical and chemistry strategies have been used in dealing with heavy metal pollution, for example precipitation, electrochemical treatment, ion exchange and adsorption. Among them, adsorption method is appreciated by industry for its simple operation and low cost. Traditional adsorbents suffer from low economical and adsorption efficiency as well as low reusability, so it's necessary to develop efficient and recyclable adsorbents for industrial sectors. Double network(DN) hydrogel processes water permeability, prefect mechanical property and expansibility, which are benefit to build reusable nubbly hydrogel adsorbent. Based on this condition, this study introduced a new kind of bulk hydrogel heavy metal adsorbent--PSA-GO gel, which was synthesized mainly by sodium acrylate(SA),graphene oxide(GO) and polyethylene polyamine(PEPA), utilizing the concept of DN gel. The adsorption behavior and mechanism of PSA-GO gel were deeply studied and its potential for practical application was also investigated. Main research contents and results of the thesis are as follows:(1) The preparation and characterization of PSA-GO gel. An ingenious separate-adding method was developed to synthesize the new DN hydrogel, which successfully avoided the instability of the synthesis system. The synthesis process was mild and replicable after optimizing the conditions, which brought PSA-GO bulk gel with satisfactory appearance morphology. The existence of various active groups was confirmed by several characterization methods such as FTIR and Raman spectra. The mechanical strength was assessed through uniaxial compression tests. The results showed that PSA-GO gel possesses much stronger mechanical strength than pure PSA hydrogel.(2) The adsorption behavior and mechanism of PSA-GO gel. Amounts of adsorption experiments, including environmental factors, contact time, temperature and initial concentration effect experiments, had been carried out to research the adsorption behavior. The results display that the PSA-GO gel can tolerate not only a relative wide p H range, but also the existence of Na Cl and fulvic acid. The adsorption of heavy metal onto the gel is a really fast process, which is well described bypseudo-second-order rate equation. The experimental data of isothermal adsorption is best fit to the Langmuir–Freundlich dual model, and the theoretical maximum uptake capacities for Cd2+and Mn2+are 238.27 mg/g and 165.48 mg/g(303K) according to Langmuir isotherm equation. The thermodynamic analysis indicates that the heavy metal sorption onto PSA-GO gel is a spontaneous endothermic process. The adsorption process is a complicated process with different sorption mechanisms including electrostatic interaction, ion exchange and complexation. Among them,complexation and coordination between amino groups and metal ions play a key role in the adsorption.(3) The potential for practical application of PSA-GO gel. Selective adsorption,recyclability test and practical industrial effluent test were used to investigate the application value of the new material. The results reveal that PSA-GO gel is a selective adsorbent of Cd2+ and Mn2+. It can be easily recovered by acid-base eluting after each adsorption cycle, and shows satisfactory reusability. PSA-GO gel is also proved effective in dealing with practical industrial effluent. In consideration of its relative low cost, PSA-GO gel processes potential utility value in waste water treatment.PSA-GO gel synthesized in this study exerts distinguished heavy metal adsorption effectivity and maintains the advantages of DN hydrogel. Its excellent adsorption ability and recyclability uncovers the potential of PSA-GO gel for practical application.