Efficient adsorption of xylenol orange by reusable carbon quantum dots/cross-linked chitosan composites

In this work, a series of carbon quantum dots/cross-linked chitosan composites (CQDs/CCS) with different ratios were obtained from citric acid and chitosan by hydrothermal treatment and freeze-drying. The morphology, structure and composition of the composites (CQDs/CCS) were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The effects of the material ratio, adsorption time, pH, and solution concentration on the adsorption performance of xylenol orange were explored. The results revealed that the best material adsorption performance of the composite was obtained when the CQDs : CS mass ratio was 1 : 100. Under these conditions, the composite exhibited a remarkable adsorption capacity, with the highest adsorption amount of xylenol orange reaching 468.3 mg g^-1 at a pH of 4. It was experimentally verified that the material was in good agreement with both the pseudo-first-order model and the pseudo-second-order model and complied with the Langmuir isotherm. In addition, the CQDs/CCS-2 material showed good adsorption and desorption effects after four adsorption-desorption cycles, which indicated that the composite material had excellent regeneration properties.