Thermo-responsive selective recovery of protonated dyes by carbon-doped boron nitride-(N-isopropylacrylamide) composite gel

Abstract

Approximately 280,000 tons of textile dyes are discharged into water bodies annually worldwide, which have the potential to be transformed into resources through selective recovering them from the effluents. Herein, a series of thermo-responsive carbon-doped boron nitride composite gels (TBCN) have been successfully synthesized, with optimum mass ratio BCN:NIPAM = 0.2:1 and pH 7. SEM-EDX, FTIR, XPS and theoretical calculation support that carbon-doped boron nitride (BCN) was uniformly dispersed inside the N-isopropylacrylamide (NIPAM) matrix through van der Waals interaction and hydrogen bonding. TBCN samples selectively recover protonated dyes from binary dyes solution through adjusting temperature instead of pH, which reduce the secondary pollution of acidic wastewater and are easier to recycle than powder adsorption materials. The removal rates of neutral red (NR)and malachite green (MG)by TBCN-2 reach 98.80 % and 98.40 %, which are obviously higher than methyl orange (MO: 42.48 %) and methylene blue (MB: 44.27 %). Through rising the temperature to 40 ℃, the adsorbed NR and MG are released, and the recovery rates are 78.50 % and 77.32 %, whereas those of MO and MB are only 26.05 % and 24.53 %. Furthermore, NR (or MG) can be selectively recovered from the mixed solution of NR-MB and NR-MO (or MG-MB and MG-MO) by TBCN-2, with the maximum removal rate of 93.51 %. For cycle stability, TBCN-2 can be used repeatedly at least four times with recovery rate＞58.80 %. TBCN-2 is an eco-friendly material and has good application prospect in dye resource utilization.