Study On Preparation And Properties Of Polyethyleneimine-Lignin Based Adsorbents

With the rapid development of industry and agriculture in China, water pollution containing heavy metals and dyes become more and more serious. Therefore, dealing with heavy metals and dyes pollution in water has become an important facet of protecting environment. Lignin has been widely used in many fields for its abundant resources, low cost, renewability, and good environmental compatibility. Hence, an efficient way to get chelating adsorbent is to modify lignin’s structure, and the adsorbents produced have been testified that they can adsorb many kinds of heavy metals and dyes in aqueous medium, which has drawn more and more attention.Four types of novel lignin-based adsorbents were mildly prepared in aqueous solutions by crosslinking and electrostatic self-assembly, alkali lignin and lignin sulfonate as raw material. Magnetic lignin-based adsorbents were further synthesized by embedding magnetic particles. These synthesis conditions were optimized based on nitrogen content and adsorbing capacity of these products by single factor experiments. These prepared adsorbents were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). The adsorption of Cu2+ and Pb2+ ions on adsorbents from aqueous solutions were measured with inductively coupled plasma mass spectrophotometer (ICP-MS), and the removal of methyl orange and black ATT dyes from water were determined by UV spectrophotometer (UV). The influences of temperature, pH value, contact time, initial concentration of metal ions and dyes were studied. The adsorption kinetics and thermodynamics were also investigated. These studies provide basic data and technical support for the development and utilization of lignin resource. The research contents and results are as follows.A novel adsorbent based on alkali lignin (PEI-AL) was successfully prepared via modifying with polyethyleneimine (PEI) by cross-linking of glutaraldehyde in an aqueous medium. Fe3O4-PEI-AL was further synthesized by coating Fe3O4. The optimized conditions were obtained based nitrogen and adsorption capacity of PEI-AL toward methyl orange and Pb2+ by single factor experiments. When AL to PEI mass ratio is 1:1.5 and glutaraldehyde is in an amount of 20% for 2 h at 25 ℃, the nitrogen content of PEI-AL was 10.72%, the adsorption capacity of methyl orange and Pb2+ were 80.26 and 103.78 mg/g. respectively. The adsorption kinetics of PEI-AL and Fe3O4-PEI-AL are well described by pseudo-second-order model. The adsorption equilibrium data exhibited that Cu2+ and Pb2+ ions adsorption of PEI-AL and Fe3O4-PEI-AL followed Langmuir isotherm models well with monolayer adsorption. The adsorption processes are exothermic and spontaneous with reduced entropy. While the best interpretation for the equilibrium data of methyl orange and black ATT dyes were given by Freundlich isotherms with heterogeneous surface adsorption. They are endothermic and spontaneous with increased entropy.A polyethyleneimine-lignin trimethyl quaternary amine salt (PEI-QL) adsorbent was prepared from polyethyleneimine and lignin trimethyl quaternary amine salt using glutaraldehyde as cross-linking agent in an aqueous medium. On the basis of the nitrogen content of PEI-QL and the adsorption capacity for methyl orange and Pb2+ ion, the optimum conditions were studied by single factor experiments. When PEI to QL mass ratio is 1:1, glutaraldehyde is in an amount of 25% in 3h at 35℃, the nitrogen content of PEI-QL was 11.97%, the adsorption capacity for methyl orange and Pb2+ were 126.71mg·g-1 and 119.02mg·g-1, respectively. All of the adsorption kinetics for methyl orange, black ATT, Cu2+ and Pb2+ followed the mechanism of the pseudo-second order equation. Langmuir model is a good fit for Cu2+ and Pb2+ ions onto PEI-QL and Fe3O4-PEI-QL adsorbents, the adsorption process is exothermic and spontaneous with reduced entropy. However, their adsorption data for methyl orange and black ATT obeyed the Freundlich equation, and the adsorption are endothermic and spontaneous processes in which entropy were increased.A new composite, polyethyleneimine-lignosulfonate (PEI-SL), was prepared from water via a glutaraldehyde cross-linker in the presence of lignosulfonate and polyethyleneimine, and then was coated by Fe3O4 to obtain Fe3O4-PEI-SL. When the ratio of SL/PEI was 1:2.5 (m/m) with glutaraldehyde in an amount of 15% at 25 ℃ for 2 h, the higher nitrogen content (13.14%) of PEI-SL adsorbent was achieved through single factor experiments, adsorption of methyl orange and Pb2+ were 95.74mg·g-1 and 163.72mg·g-1, respectively. For methyl orange, black ATT, Cu2+ and Pb2+, the adsorption processes of PEI-SL and Fe3O4-PEI-SL were all well-described by the pseudo second-order model. Their adsorption data for Cu2+ and Pb2+ ions obeyed the Langmuir equation, and the calculated thermodynamic parameters of the adsorption showed that the adsorption of Cu2+ and Pb2+ on PEI-SL and FesO4-PEI-SL are exothermic and spontaneous. However, their adsorption data for methyl orange and black ATT obeyed the Freundlich equation, and the adsorption are endothermic and spontaneous processes with increase in entropy.Lignosulfonate-polyethyleneimine (SL-PEI) adsorbent was synthesized by electrostatic self assembly using lignosulfonate and polyethyleneimine under mild condition. Then Fe3O4-SL-PEI were further prepared in the same way. When the acceptable mass ratio of SL to PEI was 1:3 at 25 ℃ for 4 h in pH4, the nitrogen content of SL-PEI adsorbent reached 11% by single factor experiments, and the adsorption capacity of methyl orange and Pb2+ were 78.76mg·g-1 and 148.5mg·g-1, respectively. Kinetically, the pseudo-second-order equation governed the overall process for the adsorption of methyl orange, black ATT, Cu2+ and Pb2+ ions on SL-PEI and Fe3O4-SL-PEI. Regarding the equilibrium data, the Langmuir isotherms were fitted well for the adsorption of Cu2+ and Pb2+ ions on both the adsorbents, and the adsorption processes are exothermic and spontaneous with reduced entropy. Freundlich isotherms were found to be the best representative for methyl orange and black ATT adsorption on SL-PEI and Fe3O4-SL-PEI, and the thermodynamic parameters suggest that the adsorption are endothermic and spontaneous in nature.