Research Of γ-PGA Composites Preparation And The Metal Ions Adsorption Capability

γ-PGA is a polyamino acid formed by the amide bond linkage between the amino group of one glutamic acid and the carboxyl group of the next glutamic acid. It has been successfully utilized in bioglue, mecicine, agriculture, cosmetic, food, wastewater treatment, et al. It has many carboxyl groups that make it a polyanionic biopolymer. In the thesis,γ-PGA crosslinking with gelatin and chitosan and the adsorption with metal ions were studied as following:1)γ-PGA was crosslinked with gelatin and chitosan respectively, when crosslinking with gelatin, the best temperature, pH, glycerol drops and glutaric dialdehyde volume were studied. The best temperature was 5℃, pH 6.5, 3 drops glycerol, 2mL 1% glutaric dialdehyde. When crosslinking with chitosan, the optimal temperature was 10℃, 2mL 1% HAc volume.2) The adsorption pH ofγ-PGA composites with Cu²⁺, Cr³⁺, Pb²⁺ were studied, three concentrations of 50, 100 and 200mg/L Cu²⁺, Cr³⁺, Pb²⁺ solutions were each prepared using Cu²⁺, Cr³⁺, Pb²⁺ nitrate salts, adjusted to different pH values with nitrate acid and dipped in the solution with PGA composites for 2 h to ensure the optimal pH with EDS. The optimal pH were 6, 4, 3 for Cu²⁺, Cr³⁺ and Pb²⁺.3) At the optimal pH, 0.6g/mLγ-PGA composites soked into 20,30,40,50,60,80,100,120,140,160 and 200mg/L Cu²⁺, Cr³⁺, Pb²⁺ nitrate salts solution at 288K, 298K, 308K, 318K for 2h to study the isotherm models, the Freundlich, Langmuir and Redlich-Peterson models were studied respectively and Redlich-Peterson had higher r2 and lowerχ2.γ-PGA/gelatin had more adsorption thanγ-PGA/chitosan, and the activity of metal ions ordeer was:Cu²⁺>Cr³⁺>Pb²⁺。4) The equilibrium constant (b) values derived from the Langmuir modeling of isotherms at different temperatures were used to determine thermodynamic parameters enthalpy changes (ΔH°), and then determined entropy (ΔS°) and free energy (ΔG°). The negativeΔH°,ΔS°andΔG°affirmed that the sorption ofγ-PGA composites was more favored at lower temperatures and reacted spontaneously.5) Adsorption kinetics was conducted at 100 and 200mg/L at optimal pH with 1.0g/L ofγ-PGA composites to different time intervals, tested with EDS, and then simulated with pseudo first and second order model, which showed that a more precise fit of kinetic data was shown by pseudo second order model than by pseudo first order model. 6) Distilled waters adjusted to different pH with nitric acid were tested as desorbing agents. The metal-adsorbedγ-PGA composites were taken out, washed with distilled water and agitated with desorbing agent for 1h and then the amount of metal ions inγ-PGA composites were determined with EDS. During five successive cycles of operation, only a minor loss in adsorption efficiency ofγ-PGA composites was shown.It was shown thatγ-PGA composites had good adsorption capability with metallic ions, and can be used more than three times with little loss. It was non-toxic, biodegradable and edible, which can be produced industrializedly.