Highly efficient and sustainable carboxylated cellulose filters for removal of cationic dyes/heavy metals ions

Treatment of textile wastewater containing highly toxic dyes and heavy metal ions raises serious health concerns that need to be addressed urgently. 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 simulated wastewater. A series of characterizations including ATR, 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 (II)) 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 (II) 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 longterm filtration performance against multicomponent wastewater containing 2.0 mg/L Pb (II) 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 (II) were 98.7% and 98.2%, respectively, which ma 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.