Fabrication and characterization of boron doped carbon dots@chitosan/polyvinyl alcohol hydrogels for methylene blue adsorption

Abstract In this study, a new boron doped carbon dots@chitosan/polyvinyl alcohol (B-CDs@CS/PVA) hydrogel was prepared for methylene blue (MB) removal from aqueous solution. The B-CDs were first synthesized using orange peel with the addition of boric acid by microwave heating process and then the B-CDs were embedded with chitosan and PVA. The structure and characterization of B-CDs and B-CDs@CS/PVA hydrogel were performed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TG), UV–Vis spectrophotometer and fluorescence spectrophotometer. The results showed that B-CDs solution with an abundance hydroxyl and carbonyl functional groups exhibited UV absorption and fluorescence properties. There is a strong interaction between B-CDs and CS/PVA, which improved the crystallinity and thermal stability of B-CDs@CS/PVA hydrogels. The adsorption performance of B-CDs@CS/PVA hydrogels for MB was studied through batch experiments. The maximum adsorption capacity of the B-CDs/PVA hydrogel for MB was 3.573 mg/g for 12 h. In addition, it was found that the adsorption behavior obeyed the pseudo-second-order kinetic and Freundlich models. The composite hydrogels are promising adsorbent for dye wastewater purification.