Preparation And Application In Pollutant Treatment Of Dually Thermo-and Photo-responsive Adsorbent Containing β-cyclodextrin

With the overall improvement of global medical level,the net increase of world population remains high,and the supply of fresh water resources is facing great challenges.At the same time,the environmental pollution caused by the increase of population also promotes the strict protection of clean water sources.However,the development of many traditional and emerging industries has resulted in a large amount of p-nitrophenol(PNP)wastewater,especially in developing countries,where water pollution events occur frequently.Therefore,special treatment for PNP pollution is needed.The adsorption method is considered to be a promising solution in the mature water treatment system because of its simple process and low cost.In this paper,a smart adsorbent is prepared,which uses poly-N-isopropylacrylamide to build the thermo-sensitive network of the adsorbent;the cyclodextrin/azobenzene supramolecular complex is grafted onto the main chain as a photo-responsive adsorption unit.Among them,β-cyclodextrin has a unique structure of external hydrophilicity and internal hydrophobicity,and can form a photosensitive inclusion compound with azobenzene,and N-isopropylacrylamide has a special volume transition effect,which will be triggered when the temperature is near its lowest critical transition temperature.Therefore,it can not only be used as an adsorbent to remove PNP in the aqueous solution,but also can easily release the adsorbed pollutants according to external stimuli to achieve green regeneration.We modified β-cyclodextrin and p-aminoazobenzene to obtain two intermediate products,acryloyl-β-cyclodextrin with double bonds and acrylamide-azobenzene,and then polymerized with N-isopropylacrylamide to obtain adsorbent.Subsequently,the stimulus response properties of the prepared smart adsorbent,i.e.photo-sensitivity and thermo-sensitivity,were studied.Firstly,the photo-sensitivity of the smart adsorbent was verified by the changes of ultraviolet absorbance under different light conditions and electrochemical experiments.Similarly,the thermo-sensitivity of the smart adsorbent was verified by the change of swelling rate under different temperature conditions and electrochemical experiments.Then,the influence of cross-linking agent and NIPAM content on the swelling effect of the adsorbent was further studied.The results show that the smart adsorbent has good photo-and thermo-response.Finally,the adsorption performance of the prepared intelligent adsorbent was studied,and the influence of p H,initial concentration of PNP,temperature and other factors on the adsorption of PNP was discussed.According to the calculation of thermodynamic parameters,the double dynamic fitting analysis of PNP adsorption curve was carried out(based on the framework of thermodynamics and reaction kinetics),and the adsorption mechanism was discussed,the regeneration ability of the adsorbent was tested.Adsorption of PNP by adsorbents is mainly hydrophobic and hydrogen bonding.During the adsorption process,the adsorption of PNP conforms to the Pseudo-First-Order dynamic model and Langmuir model,and the maximum adsorption capacity of PNP is 87.8 mg/g at 298 K.After being heated and illuminated by visible light,the adsorbent can be regenerated directly in water,avoiding secondary pollution and promoting the practical application of the adsorbent.After 5cycles of experiments,the performance of the adsorbent has not significantly decreased.