Study On Preparation Of Porous Hydrogel Adsorbents And Their Adsorption Behaviors For Heavy Metal Ions

Heavy metals have become a great environmental concern due to their significant toxic effects on human beings and other living organisms,even at low concentrations.Therefore,the development of simple,efficient and economical processing technology is imperative.Adsorption method is one of the most preferred techniques for the remediation of heavy metal ions from aquatic systems due to its simplicity of operation,rapidness,high efficiency and minimal sludge production.However,conventional adsorbents are relatively expensive,too slow and very diffic ult to regenerate,which limit their wide application.Hydrogel is a type of hydrophilic,water-swellable and insoluble polymer network,providing a fast channel for foreign molecules accessible to interior.Due to peculiar properties of hydrogels such as easy operation,easy modification,high efficiency,and recyclability,which provide a new way to solve heavy metal water pollution.In this paper,we aim to seeking for excellent adsorbents,the main research contents and results are as follows:?1?A polyvinyl alcohol enhanced?PVA/PAMPS?gel was prepared by radical polymerization.The gel was characterized by various methods including scanning electron microscope,FTIR spectroscopy,thermogravimetric analysis,vibrating sample magnetometer,and X-ray photoelectron spectroscopy.The effects of several parameters that affect the adsorption of Cd²⁺and Pb²⁺including pH,temperature,contact time,interfering ions and initial concentration were examined.In addition,the adsorption mechanism was also investigated.The results show that the gel shows a three-dimensional interconnected network structure with high chemical stability.The optimal pH of PVA/PAMPS gel for Pb²⁺and Cd²⁺were 5.0 and 6.0,respectively.The adsorption equilibrium reached within 1.0 h for Pb²⁺and 1.5 h for Cd²⁺on PVA/PAMPS gel.The adsorption process followed a pseudo-second-order rate equation and better fitted Langmuir monolayer adsorption.The existence of Na⁺,K⁺and humic acids had no significant effect on the adsorption of Pb²⁺and Cd²⁺.At the same time,the adsorbent had good selectivity for Pb²⁺and Cd²⁺.According to the Langmuir equation,the maximum adsorption capacities were 340.0 mg×g^-1 for Pb²⁺and 155.1 mg×g^-1 for Cd²⁺.The adsorption mechanism on PVA/PAMPS gel was attributed to ion exchange and complexation.After five adsorption-desorption cycles,the removal efficiency of Pb²⁺and Cd²⁺decreased by approximately 5%.?2?Jute/SA hydrogel sorbents were prepared using low cost jute and sodium alginate.The physical and chemical properties of the gels were characterized by SEM,FT-IR,TG and XPS.The adsorption behavior of Pb²⁺and Cd²⁺on Jute/SA hydrogel was studied in batches.In addition,the effects of pH,temperature,initial metal ion concentration and contact time on the adsorption performance of the Jute/SA gel were also investigated,as well as adsorption isotherm,kinetics,thermodynamics and other related mechanisms.The Jute/SA hydrogel show good adsorption properties in the initial pH range of 3.0⁶.0.The adsorption equilibrium was reached within 45.0minutes,and the adsorption of Jute/SA hydrogel for Pb²⁺and Cd²⁺was up to 291.3mg×g^-1 and 149.9 mg×g^-1,respectively.This adsorbent can selectively adsorb Pb²⁺and Cd²⁺from wastewater.Moreover,the adsorbent showed a good reusability,and the removal efficiencies maintained 96.3%for Pb²⁺and 95.7%for Cd²⁺in the fifth cycle.