Preparation Of Renewable Chitosan Materials With High Adsorption Capacity And Its Performance And Mechanism To Capture Hg From Wastewater

The complex composition of industrial wastewater containing mercury varied accompany by the changing processing parameters,which need to meet the strict national discharge standard.As such,how to explore a method to capture and recover mercury from industrial wastewater is a headache problem.,adsorption treatment technology was attractive for the advantages of high efficiency,environmental protection,energy-saving,and ease of operation compared with other sewage treatment methods,which is a research hotspot in industrial wastewater treatment.The natural organic polymer is favored in adsorbents because of its merits of low cost,environmental friendliness,high selectivity,and regeneration.Chitosan is a kind of natural polymer owning the feature of abundant reserves and biodegradable material.At the same time,the molecular chain contains abundant amino and hydroxyl functional groups,which is beneficial for easy functionalization to improve the adsorption performance to achieving as an ideal adsorbent.In this research,two kinds of new modified chitosan adsorbents were prepared via amidation reaction with different modifiers.The microstructure and surface properties of the resulting materials were characterized by infrared spectra analysis（FT-IR）,photoelectron spectroscopy（XPS）,elemental analysis（EDS）,thermogravimetric analysis（TGA）,scanning electron microscopy（SEM）,density functional analysis（DFT）.And then the adsorption behavior of the adsorbent to Hg（II）was studied;the influence of p H,initial concentration,and competing ions was investigated in sequence.Finally,the mechanism of action between adsorbent and Hg（II）was analyzed.The specific research work and its results are listed as follows:（1）The porous gel bead was prepared through an amidation reaction with bis（carboxymethyl）trithiocarbonate（BCTTC）as the modifier combined with the freeze-drying to produce a porous structure.The reason for severe polycondensation of gel beads during drying was investigated,and porous chitosan gel beads（PBCSB）with high affinity to mercury were successfully synthesized.The as-prepared gel beads could almost completely remove Hg（II）at an initial concentration of 500 mg L^-1,showing outstanding adsorption capacity,which also showed excellent selectivity to Hg（Ⅱ）.In addition,PBCSB can be regenerated via a simple one-step pickling process,and its adsorption performance remained high after 5 adsorption-desorption cycles.The binding of PBCSB and Hg（II）accorded with the quasi-second-order kinetic model and Langmuir isothermal model,suggesting that monolayer chemisorption is dominant,and the maximum adsorption capacity was estimated to be 1139.82 mg g^-1.The systematical characterization methods were used to further identify the adsorption mechanism,which implied chemical chelation ascribing to the N/S group and electrostatic attraction originating from the carboxyl group were the dominant contributors.（2）A novel chitosan/polyethylene imine composite（CDP）sponge was successfully prepared by grafting polyethylene imine（PEI）through crosslinked with dimercaptosuccinic acid.The CDP was unique for rapid solid-liquid separation,easy to regenerate,excellent acid resistance,and mechanical stability.More importantly,CDP possessed a large number of interconnecting mass transfer channels at about 100μm,wealthy active groups（—SH,—NH₂）to achieve a distinct adsorption capacity(1220mg g^-1),high-speed kinetics（10 min,Re>98%）,applicable at a wide p H range（1-7）as well as high selectivity.In addition,the results of the dynamic column experiment indicated that the column height,initial concentration,and flow rate produced significant effects on the efficiency.The adsorption saturation capacity of the system is about 1030.3 mg g^-1,which can realize in situ regeneration and recycling.Based on the aforementioned data,the efficiency prediction model mercury was established and verified by using machine learning,realizing the prediction of the adsorption capacity of sponge material as a packed column and the concentration of mercury in the effluent（R²=0.9752）,which is beneficial to acquiring the process conditions to meet the discharge requirement of the national standard.In the proposed study,the as-prepared PBCSB and CDP sponge were implemented rapidly and efficiently to capture the Hg（II）from the complicated aquatic environment,respectively,and endowing numerous merits,for example,low preparation cost,simple regeneration technology,remarkable selectivity,and adsorption capacity.These properties prompted them to be a promising candidate and presented broad application prospects in the field of industrial wastewater containing high contents of Hg（Ⅱ）.The finding could provide a reference for the preparation,application,and removal efficiency prediction of the congeneric material.