Adsorption Behaviors Of Nitrogen Heterocyclic Compounds On Hyper-cross-linked Resins

The nitrogen heterocyclic compounds contained in industrial wastewater have extensive toxic,teratogenic,carcinogenic and mutagenic effects on natural organisms.Nitrogen heterocyclic compounds are quite recalcitrant to degradation by microbial metabolism and can easily accumulate in the environment,causing a potential threat to human health.In this study,concentrated sulfuric acid was used as the sulfonating agent to obtain four sulfonic acid functionalized resins from hyper-cross-linked resin NDA-150,such as 30-R,40-R,60-R,70-R.The sulfonic acid group contents of functionalized resins range from0.44-1.63 mmol/g.The surface area and pore size analyzer and Fourier-transform infrared spectroscopy(FT-IR)were used to characterize the resin before and after modification.The research focused specifically on the adsorption behavior and adsorption mechanism of sulfonic resin on pyridine,and the adsorption performance of sulfonic resin on pyrrole,imidazole,pyrazine,indole,quinoline,benzimidazole.The isotherm fitting results of the adsorption of pyridine by the sulfonic resin show monolayer adsorption mechanism at low concentration while multilayer adsorption mechanism at high concentration.The saturated adsorption capacity of pyridine on the sulfonic resin reached 2.65 mmol/g.The adsorption process of sulfonic resin for pyridine is a spontaneous endothermic reaction.Moreover,the adsorption process conforms to the pseudo-second-order kinetic model,and the adsorption equilibrium can be reached within 8hours,indicating that the adsorption process is dominated by chemical adsorption.The fitting result of the Weber-Morris model indicates that the intra-pore membrane diffusion and intra-particle diffusion during the adsorption process of pyridine are both rate-controlling steps.In addition,the adsorption mechanism experiments show that the adsorption forces between pyridine and sulfonic resin include ?-? EDA interaction,electrostatic interaction,and hydrophobic interaction.Among them,?-? EDA and electrostatic interaction play major roles in pyridine adsorption.To determine the desorption of pyridine from sulfonic resin,4 %HCl-ethanol(1:2)mixed solution was applied as a desorption agent.The desorption rates reached more than 87 %,and the absorption and desorption performance of the sulfonic resin was stable,indicating the resin can be reused.In this study,it is analyzed that the adsorption isotherms of seven nitrogen heterocyclic compounds(pyridine,pyrrole,imidazole,pyrazine,indole,quinoline,and benzimidazole)by sulfonic resin,revealing that the sulfonic acid functionalized resins have higher saturated adsorption capacities for all the compounds than unmodified resin.The saturated adsorption capacity of sulfonic resins for highly hydrophobic nitrogen heterocyclic compounds is affected by the content of sulfonic acid groups and the pore structure of the resin;while the saturated adsorption capacity of nitrogen heterocyclic compounds with weaker hydrophobicity is mainly affected by the content of sulfonic acid groups.Furthermore,sulfonic resin has a stronger adsorption affinity for nitrogen heterocyclic compounds that have higher electron density,are more hydrophobic,can be protonated.