Ultrahigh adsorption capacities for anionic and cationic dyes from wastewater using only chitosan

The removal of anionic dyes from dye wastewater with chitosan (CS) in various solid forms has been widely studied for environmental friendliness. In this work, a facile and green removing process of anionic and cationic dyes from wastewater with ultrahigh adsorption capacity only using CS was investigated. CS solution was added into anionic dye Congo red (CR) solution to remove CR and simultaneously CS-CR particles were formed without adding other additives. The obtained CS-CR particles with negative charges were reused to remove cationic dyes (methylene blue (MB) and rhodamine B (RhB)). The effects of the amount of adsorbent, adsorption time and initial dye concentration on dye removal were explored. The results suggested that the process of dye removal was fast and efficient. The removal rate of CR was up to 99.9% with an adsorption capacity of 14971.7 mg g−1 within 1 min under 30 mL dye solution of 500 mg L−1 and 0.1 g 1% CS solution. Ultrahigh adsorption capacity reached 44956.2 mg g−1 when the initial concentration was 2000 mg L−1, which is much higher than other values reported to date. The CS-CR particles, as a new adsorbent, exhibited a removal rate of 99.7% for MB with 1.5 mg CS-CR particles, and 86.9% for RhB with 3.0 mg CS-CR particles, when the dye amount was fixed at 30 mL 50 mg L−1 dye solution. Equilibrium adsorption capacities of 1457.1 mg g−1 for MB and 990.0 mg g−1 for RhB were achieved, which are superior to other CS-based adsorbents reported. Thus, a green and economical route using low-cost CS to remove anionic and cationic dyes was achieved.