Fabrication And Adsorption Properties Of Sustainable Carboxylated Cellulose Fabrics

With the development of modern industries,a great deal of contaminated water had been discharged into the environment.This raises a critical environmental concern and must be addressed on a priority basis.Dyes,heavy metal ions,rare earth metal ions,and other organic toxins are major contaminants of wastewater and the treatment of wastewater containing those toxicants need to be carried out urgently.A variety of porous materials,such as activated carbon,nanoparticles and nanofibers,such as metal oxide nanoparticles,inorganic nanofibers,carbon nanotubes,modified electrospun nanofibers,and enzyme.In reality,however,these filters suffer weaknesses including leaching out of particles,inadequate mechanical properties of non-woven fibers,and cost-effectiveness.An adsorption filter with high adsorption capability,high durability(sustainability),and high robustness while being cost-effective is essential for wastewater treatment.In this work,we developed a new type of cotton fabrics-based adsorption materials with high mechanical properties and a high adsorption capability for metal ions and dyes.Carboxylated cellulose fabric filters were fabricated by 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)-mediated oxidation and employed to remove heavy metal ions and dyes efficiently by adsorption from wastewater.A series of characterizations including infrared,TGA,and SEM measurements were employed to investigate their structure and morphologies.The carboxylated cellulose fabrics exhibited excellent mechanical properties evidenced by tensile experiments and comparisons with other non-woven counterparts.Lead ion(Pb-?)and methylene blue(MB)were introduced to investigate the filtration performance of carboxylated cellulose filters;high flux,high rejection ratio,and low pressure drop were achieved due to the internal micro-nanoscaled structure of the cellulose fabrics as revealed by XPS and elemental mapping characterizations.The maximum adsorption capacities for Pb(?)and MB were 81.30 and 76.92 mg/g,respectively,while the pressure drop for dynamic adsorption was as low as 0.07 kPa,indicating that the filtration performance was drivable by gravity.A spiral wound cartridge of cellulose fabrics was fabricated and a long-term filtration performance against multicomponent wastewater containing 2.0 mg/L Pb(?)and 2.0 mg/L MB,simultaneously,was demonstrated.The wastewater treatment capacities of 3.6 g of the filter were up to 21.7 L and 36.1 L,respectively,which was 10-times higher than that of the original cellulose fabrics;and the rejection ratios against MB and Pb(?)were 98.7%and 98.2%,respectively,which met the environmental criteria for wastewater disposal.The recycling and reusability of the filters were also demonstrated,indicating that the carboxylated cellulose fabrics can be considered as sustainable filters for wastewater treatment.The carboxylated cellulose filters were further employed as sustainable filters for removal and recovery of lanthanum ions(La(?))with high adsorption capability.The surface chemistry of the carboxylated cellulose fibers before and after adsorption of La(?)was investigated systematically.The distribution of La(?)on carboxylated cellulose fibers were explored by EDS mapping approach,which revealed that the adsorption occurred on both the surface and the internal structure of the cellulose fibers.The kinetics and isotherms of the adsorption were conducted to understand the adsorption mechanism of the carboxylated cellulose filter and to learn the maximum adsorption capacity for La(?)which was as high as 33.7 mg/g.The adsorption selectivity of the carboxylated cellulose filter for La(?)was determined when interfering ions including mono-and di-covalent ions were involved.The carboxylated cellulose filter exhibited high adsorption capability and high permeation flux evidenced by the breakthrough curves of the dynamic adsorption of La(?)under an extremely low pressure of 0.07 kPa.A variety of desorption reagents were selected to recover lanthanum from the carboxylated cellulose filter,where the optimized conditions for recovery were explored.Meanwhile,a spiral wound cartridge of the carboxylated cellulose fibrous mat was fabricated and the removal and the recovery of La(?,2.5 mg/L)from massive lanthanum-containing water were demonstrated.It was very impressive that the high rejection ratio of 94.3%was achieved under the low pressure drop of 3.0 kPa remaining throughout the separation process,and the treated solution volume was high up to 21.4 L,which was about six-times higher than that of commercially available nanofibrous adsorption membranes,indicating that the carboxylated cellulose filter could be used as a highly efficient adsorption medium for industrial recovery of rare earth metals.