Preparation Of Cellulose Nanocrystals Composite Silica Aerogel And Its Adsorption Properties For Water Pollutants

With the steady development of China’s industrialized economy,all issues related to water environment management have become one of the hot topics for people to study at present.In particular,the rational disposal of organic dyes and antibiotic pollutants in industrial wastewater is the key task to maintain the drinking water environment in China.On this thesis,we focus on the preparation of nano-crystalline cellulose（CNCs）composite silicon dioxide aerogels by using microcrystalline cellulose（MCC）and cheap water glass as raw materials.The unique tetrahedral structure of the silicon dioxide is fully grown in the CNCs suspension,and the self-assembly behavior of the CNCs is stimulated to bond more closely with the silicon dioxide.Through a comprehensive study of the adsorption of methylene blue（MB）and ciprofloxacin（CIP）at different initial concentrations and temperatures,the experimental data and thermodynamic parameters were analyzed and fitted well.Pseudo-first-order and pseudo-second-order adsorption kinetic models were used to explain the removal of composite aerogels.The adsorption mechanism of pollutants in water provides a reference for subsequent simulation calculations and industrial equipment design.The aerogels with large specific surface area,low density,high porosity,large amount of pollutants adsorbed,enhanced mechanical properties and more stable structure are prepared.The specific content of the study is as follows:（1）The MCC was treated by orthogonal design of experiments and inorganic acid hydrolysis in the early stage,with the final yield of CNCs as the hard standard,combined with the shape（such as color,viscosity）of the material in each stage of the preparation process,the samples were analyzed.The effects of hydrolysis temperature,acid concentration,hydrolysis time and solid-liquid ratio on the final yield of CNCs were considered,and the results were effectively used directly to optimize the preparation conditions of CNCs.At the same time,the traditional process for preparing Si O2 sol is fully improved.（2）An excellent pore structure(the maximum specific surface area can reach440.715 mg·g^-1)of CNCs/Si O₂ aerogel that with good self-assembly behavior,which will be used in the study of MB adsorption.The results of adsorption experiments show that.The adsorption process of MB is spontaneous and endothermic,while maximum adsorption capacity is 190.85 mg·g^-1.And the whole adsorption process satisfies pseudo-second-order kinetic equation and nonlinear Langmuir isothermal model well,indicating that the adsorption is mainly chemically homogeneous adsorption to the material.The stable porous structure of the composite aerogel mainly adsorbs MB by hydrogen bonding,electrostatic interaction and partial Johannes Diderik van der Waals force.The removal rate of the aerogel remained around 60%after 5 cycles of adsorption and desorption.（3）The addition of polyvinyl alcohol（PVA）was selected to assist in the construction of the composite aerogel,which further enhanced the mechanical properties of the aerogel,and successfully explored the feasibility of its adsorption of CIP（a pollutant in water）.The following analysis results were obtained:Although the specific surface area of PVA-assisted composite aerogel decreased(127.559 mg·g^-1)in the process,compared with the CNCs/Si O₂ aerogel,the maximum load（3790 N,11.32MPa）exhibited higher compressive values at fracture.As the concentration of adsorbate is higher as 150 mg·L^-1,the maximum adsorption capacity is 272.74 mg·g^-1.While the fitting parameter（R²）in the pseudo-second order kinetics and Langmuir isothermal model is more than 0.97,that means it’s a good fitting.In addition,the spontaneous and endothermic adsorption process assisted to explain that the adsorption mechanism of the composite aerogel to CIP mainly depends on electrostatic interaction force,hydrogen bond andπ-πinteraction.