Macrofabrication Of Cellulose Nanocrystal-Based Hybrid Porous Microspheres And Their Application In Water Treatment

In recent years,the development of various dyestuff-related industries has generated a large amount of industrial dye wastewater,and the high toxicity and carcinogenicity of chemical dyestuffs have further aggravated environmental pollution.In order to protect the ecological environment,it is necessary to purify or recover the pollutants in such wastewater.For new adsorbent materials,effective recovery and utilization are the top priorities for development.However,traditional wastewater treatment materials,such as activated carbon,are difficult to handle after failure and can cause secondary breakage of the ring,while the production process is accompanied by a large carbon footprint.Therefore,there is an urgent need to develop a new recyclable and efficient adsorbent material to treat dye wastewater.Cellulose nanocrystal（CNC）is a green and environmentally friendly material derived from cellulose,which has good adsorbent properties such as very large specific surface area,strong mechanical tolerance,high functionality and high biocompatibility of the surface,and has promising applications in wastewater treatment.In recent years,there are also many studies proving the application of CNC in water treatment process.However,the nature of CNC itself leads to the difficulty of reuse after removal of pollutants and the difficulty of release of occupied active sites.Therefore,it is necessary to effectively address the regeneration and utilization of CNC-based water treatment materials.Metal oxides are currently the most widely used photocatalysts,which can be excited by light energy to generate hole-electron pairs and thus degrade surrounding organic molecules.Therefore,cellulose nanocrystal（CNC）/transition metal oxide hybrid porous microspheres usually have high adsorption properties,excellent chemical stability,and the ability to rapidly degrade pollutants,which are of high value in dye wastewater treatment.For example,titanium dioxide（TiO₂）,the most used photocatalyst,has a high band gap energy（3.2 e V）,which causes it to be excited only by higher energy UV light and cannot make full use of natural light,while manganese dioxide（MnO₂）,which has a lower band gap energy（1-2 e V）,can be excited by visible light or even IR light,but After excitation,it is easy to recombine due to its low band gap.Therefore,effective improvement of the bandgap effect of photocatalysts can greatly improve their photodegradation performance.Interestingly,TiO₂ and MnO₂hybridization,after being excited by light,electron transfer occurs between the two,forming a synergistic effect that can increase the wavelength range of light that can be absorbed and utilized by the hybridizable materials,while also more effectively blocking the recombination of electron-hole pairs generated by photoexcitation,thus greatly improving the performance of rapid degradation using photocatalysis.In the present work,bubble templates were used.In this work,CNC/MnO₂/TiO₂porous microspheres were prepared by a combination of bubble template and ionic cross-linking.The synergistic catalytic effect of TiO₂and MnO₂hybridization within the porous microspheres enabled the porous microspheres to rapidly degrade the internal dye by light after removing the dye molecules from the dye wastewater,and to achieve simple and efficient recycling.In addition,the porous microspheres use gel as the carrier of nanomaterials,which solves the problems of difficult recovery of nanoparticles from the environment,high cost of recovery,and easy to cause secondary damage to the environment.We systematically investigated their performance on the removal of organic dye pollutants,and the main research contents are as follows:The first part is the preparation and characterization of CNC/MnO₂/TiO₂porous microspheres.Anatase TiO₂was prepared by sol-gel method.The CNC/MnO₂prepared by oxidation with potassium permanganate was doped with a small amount of sodium alginate（SA）,the emulsion was formed after high speed stirring and foaming,and the gel microspheres were prepared by the chelation of SA and Ca²⁺.Finally,the CNC/MnO₂/TiO₂porous microspheres were prepared by freeze drying technology The results showed that the porous microspheres presented a honeycomb structure with a pore size of 100-200μm.The surface of the microspheres was loaded with metal oxide nanoparticles and formed a rough inner wall structure,which increased the active sites that could be adsorbed and degraded.In the second part,the removal efficiency and degradation efficiency of methylene blue dye by CNC/MnO₂/TiO₂porous microspheres were studied.The removal efficiency of dye molecules in dye solution by CNC/MnO₂/TiO₂porous microspheres was usually composed of adsorption and degradation.The test results showed that the maximum removal capacity of porous microspheres was as high as 310.2 mg/g within 5 min Desorption experiment was used to test the proportion of degraded dyes in the microspheres.After 30 min illumination,the proportion of degraded dyes in the porous microspheres reached more than 98%,all of which benefited from the adsorption of CNC inside the microspheres and the synergistic catalytic degradation of metal nanoparticles.In the third part,the synergistic mechanism and regeneration performance of metal oxides in CNC/MnO₂/TiO₂porous microspheres were studied When TiO₂and MnO₂were doped,a synergistic effect would occur,and the electrons produced by MnO₂were captured by TiO₂,thus inhibiting the electron-hole recombination and enhancing its photocatalytic performance At the same time,the addition of MnO₂makes up for the disadvantage that TiO₂can only use UV light due to its large band gap,forming a collaborative catalytic system that can fully utilize visible light and inhibit electron-hole recombination The synergistic catalysis enables the microspheres to rapidly degrade the internal dyes under 30 min light and release the active sites occupied by the dye molecules.The results show that the repeated removal efficiency and degradation rate of the regenerated microspheres are above 97%,which shows a good application prospect in the field of wastewater treatment.