The Application Of Modified Cellulose And Its Thermo-Responsive Composite Hydrogel In Water Pollutant Treatment

With the rapid development of industrialization and urbanization,excessive pollutants are discharged into the environment,which will damage the ecological environment and even threaten human health.In recent years,the removal of water pollutants have caused widespread concern.Due to the advantages of simple technology,easy operation,no sludge,strong regeneration ability and good cost-effectiveness,adsorption methodology has attracted much attention.Hydrogel can be used as a new type of adsorbent material with rapid reaction and good adsorption capacity for removing pollutants in aqueous solution.In order to satisfied the requirements of ecological civilization construction,the development of environmental friendly hydrogel adsorbent is a hot spot in water pollution treatment.In addition,how to realize the reuse of hydrogel adsorbent more quickly and easily is also a question needed to be considered.Cellulose is the most abundant polymer in nature,has abundant surface active groups?hydroxyl groups?and high specific surface area,which can be introduced into hydrogels to improve the specific surface area and mechanical properties of hydrogels,as well as to enrich the active functional groups of hydrogels.As a result,the adsorption performance of environmental friendly hydrogels would be improved.However,the reactive group on the surface of the cellulose is limited to the hydroxyl group.By modifying the surface of the cellulose,it can be converted into the cellulose derivative having different functional groups,so as to endow hydrogels with special functions and construct intelligent composite hydrogel with good adsorption performance.In this paper,cellulose is used as raw material to prepare thermo-responsive hydrogel by in-situ polymerization based on dopamine with catechol structure and isopropylacrylamide?NIPAM?with good temperature sensitivity.The obtained hydrogel can be used to treat the water pollutant through the coordination effect of the abundant functional groups.Also,the characteristics of shrinkage and water loss of the hydrogel near the phase transition temperature?about 32°C?played an important role in the improvement of the adsorption capacity.Traditional adsorbent activated carbon has the advantages of abundant surface area,good pore size distribution and strong adsorption capacity,while the disadvantages of being difficult to recover restricted the application of activated carbon.In this paper,the activated carbon is loaded into the thermo-responsive hydrogel to both have good adsorption performance and good recovery performance.The adsorption properties of composite hydrogel on heavy metal ions and dyes were studied respectively.The optimal adsorption parameters of hydrogel were determined by optimizing different adsorption conditions.The specific research work of this paper is as follows:?1?Utilizing the most abundant natural polymers-cellulose and dopamine as raw materials,a physically modified dopamine coated nanocellulose?PDA@CNC?was prepared.The chemical structure,thermal stability and morphology of PDA@CNC were analyzed by FTIR,TGA,XRD and TEM.The results showed that dopamine was self-polymerized on the surface of the rod-shaped CNC to form a thin layer of polydopamine in an alkaline solution of pH=8.5.?2?Thermo-responsive PDA@CNC/PNIPAM hydrogel was prepared by in-situ polymerization based on PDA@CNC and NIPAM.The analysis showed that the addition of PDA@CNC not only improved the mechanical strength of the hydrogels,but also introduced the catechol group with strong ability to coordinate with metal ions,resulting in the improvement of adsorption performance of the hydrogels on metal ions.The effects of initial pH,time and solution concentration on the adsorption performance were investigated.The results showed that the maximum adsorption capacity of PDA@CNC/PNIPAM hydrogel for Pb²⁺and Cr³⁺ions was53.2mg/g and 39.4mg/g respectively.The adsorption process followed well to the Langmuir isotherm model and the pseudo-second-order kinetic model.?3?Activated carbon,PDA@CNC and NIPAM was used to prepare the thermo-responsive composite hydrogel as a new adsorbent material.The combination of activated carbon and hydrogel can overcome the disadvantages of the fact that activated carbon was not easily recovered.The thermal stability,microscopic appearance and adsorption properties of the composite hydrogel were investigated.The maximum adsorption capacity of the thermo-responsive composite hydrogel on the malachite green was found to be 534.4mg/g when the adsorption time was 3h and the pH was 7.0.The adsorption process is consistent with the Freundlich isotherm model and the pseudo second-order kinetic model.Combiningtheexcellentperformanceoftheabove PDA@CNC/PNIPAM and PDA@CNC/PNIPAM/C composite hydrogel and the effective treatment of water pollutants,it has a very promising application prospect as a new type of water pollutant treatment adsorption material.