Preparation Of The PH-Sensitive Starch Hydrogel And Its Adsorption Performance Of Heavy Metal Ions

In this paper, hydroxyethyl starch (HES) was used as raw materials, whose hydroxy reacted with allyl glycidyl ether (AGE) by ring-opening reaction to prepare allyl starch, then the allyl starch reacted with mercaptoethylamine by "click reaction" to prepare 2-hydroxy-3-(3'-aminoethylthiopropoxy)propyl hydroxyethyl starch ether(HAEP-HES), finally a novel hydrogel based on HAEP-HES was synthesized by using glycol diglycidyl ether (EDGE) or epichlorohydrines (ECH) as crosslinking agent. We study the pH-sensitivity, swelling and deswelling behaviors and the influence of salt concentration on the hydrogel swelling performance, the pH-sensitivity of the hydrogel crosslinked by EDGE was better than ECH, as the pH was raised, the swelling ratio of the two hydrogels was reduced. Using the second order swelling kinetics of hydrogels to study the swelling kinetics, the result was that the maximum swelling ratio of the hydrogel (HAEP-HESEDGE) was 50.45, the other one was 34.25.The prepared hydrogels were characterized by FT-IR spectroscopy, Thermogravimetric Analysis(TGA) and Scanning Electron Microscopy (SEM).With respect to the environmental pollution caused by the heavy metal ions, such as mercury, lead, cadmium ions, the influencing factors such as the initial concentration of metal solution, contact time, the pH value of metal solution were investigated by adding about 0.1 g dry hydrogel as adsorbents into 50mL metal ions solution. The results were analyzed by Langmuir isotherm and the maximum adsorption capacities of HAEP-HESEDGE were 246.7 mg/g,149.2 mg/g,78.7 mg/g for mercury, lead, cadmium respectively, the other hydrogel were 260 mg/g,200.9 mg/g,86.6 mg/g for mercury, lead, cadmium respectively. The equilibrium adsorption time of the two hydrogels were 5 h,20 h,10 h for mercury, lead, cadmium respectively, and the adsorption was found to follow Pseudo-Second-Order kinetics, for the reason that correlation coefficient was higer than 0.99. In the acidic solution, it was unfavorable for the adsorption of heavy metal ions, the adsorption efficiency of lead and cadmium was close to zero when the pH was 2, which can be seen that the adsorption capacity increased with increasing pH from 2 to 6, but the adsorption efficiency was decreased when the solution was in basic solution, however, the adsorption efficiency of mercury was always above 30 percent for the reason that the sulfur had extremely high affinity for mercuric ion. In order to collect the metal ions, we study the influence of concentration of acid and desorption time, which indicated the maximum desorption efficiency for lead and cadmium existed in the 0.1 mol/L HCl solution, for mercury was in the 0.01 mol/L HNO3 solution. We chose the concentration of acid with the maximum desorption efficiency to study the influence of desorption time, the results showed that the maximum desorption efficiency of metal ions were obtained at two hours, the maximum values of lead and cadmium was as high as 95%, but the mercury was close to 50%.