Controllable Preparation And Adsorption Of Carboxylated Porous Cellulose Beads

The deep treatment of textile industrial wastewater and the high quality utilization of waste fiber resources are important topics for the green and low carbon cycle development of textile industry.In the context of today’s green and low-carbon development,green and efficient adsorbent materials are prepared by using textile waste resources and applied to textile wastewater treatment to achieve green and low-carbon cycle development.Based on this,the paper uses waste cotton fibers as raw materials to prepare carboxylated porous cellulose beads with both surface hierarchical pore structure and a large number of active groups by drop-in phase separation method and citric acid esterification modification through molecular design and structural property modulation.The paper systematically investigated the effects of cellulose bead preparation process and carboxylation modification parameters on the size morphology,microscopic morphology,porous structure,chemical structure,surface properties and mechanical properties of cellulose beads,explored the key factors influencing the controllable preparation of carboxylated porous cellulose beads,and established the technical principles and methods for the simultaneous regulation of hierarchical pore structure and surface carboxylation;used cationic dyes as a contaminant model to study the static properties of carboxylated cellulose beads.The static adsorption behavior and adsorption mechanism of hierarchical pore cellulose beads were studied,and the laws between the surface properties and microstructure of cellulose beads and the efficient separation of target pollutants were established,and an efficient wastewater treatment device based on the cellulose beads was constructed.Potential The specific research contents and results of the paper are as follows.（1）Porous cellulose beads with tunable preparation and structural control:The porous cellulose beads with shell-core structure were successfully prepared by drop-in phase separation method using textile waste cotton fibers as raw materials,and the influence of nozzle diameter,solidification bath conditions,cellulose concentration and other process factors on the size,microstructure and mechanical properties of cellulose beads was investigated.The experimental results showed that diameter of the cellulose beads were obtained by adjusting the diameter of the nozzle,which of range is 1.27-3.35 mm.The best overall performance of the cellulose beads was obtained when the solidification bath was 1.5 M H₂SO₄and 80 g/L Na₂SO₄,the solidification bath temperature was 30 ^oC,and the concentration of cellulose solution was 4 wt%,with uniform size,interconnected porous structure,95.85%porosity,97.34 m²/g specific surface area,and 470.11 k Pa compressive strength.The adsorption performance of the porous cellulose beads for methylene blue（MB）was found to reach the adsorption equilibrium at 2 h with a maximum adsorption capacity of 47.05 mg/g.（2）Carboxylation modification of porous cellulose beads and design of hierarchical pore structure:To further improve the adsorption efficiency of porous cellulose beads,carboxylated porous cellulose beads were prepared by citric acid esterification modification method,and the effects of different citric acid dosage,reaction temperature and reaction time on the microstructure,surface properties and mechanical properties of cellulose beads were investigated.The amount of 4 g citric acid,reaction temperature of 120 ^oC and reaction time of 6 h were determined as the most suitable modification process conditions（the sample was named as CCB120-6）.By regulating the carboxylation process,the hierarchical pore structure of the cellulose beads was controlled while the surface was carboxylated.The surface of the cellulose beads showed micron-level open pore structure and internal bimodal mesoporous structure,and the surface carboxyl content was as high as 4.925 mmol/g,and the specific surface area was as high as 156.85 m²/g,which was 1.6 times higher than that of the original cellulose beads.The carboxylation modification,while giving the cellulose beads a multistage pore structure,high specific surface area and high active surface,substantially increased their compressive strength from 470.11 to 3300 k Pa due to the synergistic effect of esterification cross-linking of citric acid and densification of the cellulose bead skeleton structure.In addition,the adsorption kinetics and adsorption isotherms of MB showed that,relative to the porous cellulose beads,the multistage pore structure synergistically with the high carboxyl content,the maximum adsorption capacity of carboxylated porous cellulose beads for MB was enhanced by 19.5 times.（3）Adsorption behavior and mechanism of carboxylated hierarchical pore cellulose beads:CCB120-6 was selected as the adsorbent,and the effects of adsorption time,initial concentration of dyestuff,solution p H,adsorption temperature,and coexistence of additives on the adsorption performance of cationic dyestuffs such as methylene blue,malachite green and basic-red-46were systematically investigated,and the adsorption mechanism and cyclic regeneration capacity were discussed.The experimental results showed that CCB120-6 had excellent adsorption performance on cationic dyes,and its saturation adsorption amounts of methylene blue,malachite green and basic-red-46 reached 918.23 mg/g,841.57 mg/g and 472.86 mg/g,respectively.The adsorption process was analyzed by isothermal adsorption model,adsorption kinetic model and thermodynamic study,and its adsorption process was a spontaneous monolayer chemisorption process.The effects of solution p H,adsorption temperature and additive coexistence on the adsorption performance were also investigated.It was found that CCB120-6 maintained excellent adsorption performance in a wide range of p H（5-10）and temperature（20-50 ^oC）use interval,and urea and Na Cl additive coexistence environment,showing good environmental adaptability and anti-disturbance ability.The regeneration and cycling experiments revealed that the efficient desorption and regeneration of the carboxylated porous cellulose beads could be achieved by the segmental elution method of HCl and ethanol,and the desorption rate remained at 94%after 10 regeneration cycles,and the adsorption amount of MB was 88%of the initial adsorption,and no significant changes were found in the pore structure,showing a stable and recyclable regeneration performance.（4）Construction and dynamic adsorption performance of carboxylated hierarchical pore cellulose beads wastewater treatment device:Based on the excellent adsorption capacity,mechanical properties and cycling stability of carboxylated hierarchical pore cellulose beads,a cellulose beads wastewater treatment device was constructed using them as fillers.The effect of packing height,inlet flow rate,inlet concentration and packing size on the penetration curve was investigated,and it was found that the operating time and effluent quality of the wastewater treatment plant could be improved by increasing the packing height,decreasing the inlet speed and concentration,and using small size of packing.By further designing the packing structure,an efficient wastewater device with mixed ball structure was constructed,which prolonged its effective operation time and improved the treatment capacity and dye removal rate of the wastewater.A wastewater treatment device filled with 1.2 g carboxylated hierarchical pore cellulose balls could treat 14 L of dye wastewater,and the dye removal rate reached 78.36%.In addition,the dynamic adsorption mechanism of MB by the wastewater treatment unit was analyzed using Thomas,Yoon-Nelson and Adams-Bohart models,and the dynamic adsorption behavior of MB was found to be in good accordance with the Thomas and Yoon-Nelson model,which is a uniform monolayer adsorption on the surface.