Preparation Of Bio-based Self-floating Adsorbents And Their Adsorption Properties

China is a major dye production country,and dye wastewater is one of the main hazardous industrial wastewater.The "Global Engineering Frontier 2020" issued by the Chinese Academy of Engineering pointed out that after the industrail wastewater is discharged,dyes can adsorb light to reduce water transparency,affect the growth of aquatic organisms and microorganisms,and are not conducive to water self-purification.Therefore,dye-based industrial water pollution is a global problem that needs to be solved urgently.Because of the cost-effectiveness of adsorption technology,it is widely used to treat dying wastewater.Adsorbent is the core and key of the adsorption process.Compared with adsorbents such as clay,zeolite,industrial by-products that are difficult to modify,and petroleum-based adsorbents that are prone to secondary pollution,chitosan and cyclodextrin are green,non-toxic and easily biodegradable.They contain a large number of amino groups or hydroxyl groups so they are easy to be modified by grafting,cross-linking and other methods.In addition,due to the low separation efficiency of traditional adsorbents and the instability of magnetic adsorbents in an acidic environment,this subject choose to add hollow glass microspheres of inert materials into the biosorbent,so that the adsorbent can float on the surface of water and the adsorption material can be quickly recovered.The subject synthesized the floating chitosan-based adsorbent and the floating cyclodextrin-based adsorbent,and studied the adsorption mechanism through the adsorption experiments of dyes,which has guiding significance for the treatment of dye wastewater in practical engineering.The alkali-treated hollow glass microspheres are coated by chitosan(CCFA),and then use KPS as initiator to copolymerize acrylamide and Methacryloxy ethyl dimethyl benzyl ammonium chloride(or methacryloxy ethyl trimethyl ammonium chloride)on the surface of the CCFA to synthesize the self-floating adsorbent BDSA(or MDSA).Through characterization and analysis,it is found that BDSA has rougher surface,better stability,and stronger cationic properties than MDSA.The adsorption experiment shows that BDSA has excellent adsorption performance for acid green 25,in the p H range of2～10,the removal efficiency of BDSA to AG25 remains above 90%,it maintains a higher removal efficiency for dyes after being recycled and reused for 5 times.By fitting the adsorption isotherm and the adsorption kinetic model,the surface adsorption process is coordinated by multiple mechanisms and the adsorption step is controlled by chemical adsorption,the theoretical maximum adsorption capacity of BDSA reaches 344.828mg/g.The adsorption mechanism is studied through Symmetry-adapted perturbation theory and independent gradient model.For the process of BDSA adsorb acid green 25,in addition to electrostatic effect,there is also π-π stacking between the benzyl group on the adsorbent and the aromatic rings on the dye,these two mechanisms play a key role in the effective and stable adsorption of AG25 molecules by BDSA.In view of the limited adsorption performance of chitosan-based adsorbents for cationic dyes,this subject also designed and synthesized cyclodextrin-based adsorbents.The alkali-treated hollow glass microspheres are contained in the adsorbent through cross-linking reaction between tetrafluoroterephthalonitrile and cyclodextrin to synthesize the self-floating biological adsorbent FTFCD,and then synthesis TFCD by the same cross-linking reaction with no hollow glass microspheres for comparison.After characterization and analysis,it can be seen that the thermal stability of FTFCD is better,and the addition of glass microspheres to the adsorbent does not significantly change the Zeta potential of the adsorbent.It can be known from the adsorption experiment that the adsorption performance of FTFCD is not worse than that of TFCD,in the range of p H1～10,the removal efficiency of malachite green in the solution is maintained above 95%by FTFCD,and it still maintains excellent adsorption efficiency after 5 times of recycling.By fitting the adsorption isotherm and the adsorption kinetic model,the surface adsorption process is a single-layer adsorption and the adsorption step is controlled by chemical adsorption,and the theoretical maximum adsorption capacity of FTFCD is 1449.478mg/g.Through FTIR analysis and XPS analysis,it can be known that the adsorption mechanism includes electrostatic interaction,inclusion of cyclodextrin hydrophobic cavity and hydrogen bond interaction in the process of dye adsorption.