Preparation of coal-based C-Dots/TiO2 and its visible-light photocatalytic characteristics for degradation of pulping black liquor

Coal-based carbon-dots (C-Dots) with a graphene-like structure is prepared from the coal mined of Xinjiang Wucaiwan by an acid/ultrasonic mixed oxidation technique. Subsequently, the C-Dots is combined with the in-situ synthesized TiO2 particles, yielding C-Dots/TiO2 nanoparticles. These were characterized by TEM, XRD, TG, Raman, BET, XPS, EDS, UV-vis DRS and PL, respectively. It was found that the C-Dots/TiO2 are subsphaeroidal particles formed by the deposition of C-Dots on the surface of TiO2. Those particles are linked to various functional groups such as CC, COH/COC, CO, TiO, and are 30-50 nm in diameter and evenly distributed without agglomeration. After combination with C-Dots, the band gap of C-Dots/TiO2 decreases from 3.2 eV in the case of pure TiO2 to 2.9 eV, the PL intensity of C-Dots/TiO2 centered at 400 nm dropped significantly, indicates stronger visible light photocatalytic activity. The photocatalytic activities of the nanocomposites are evaluated by the photocatalytic degradation of cotton pulp cooking black liquor in the presence of visible light irradiation. The composite catalysts exhibited higher photocatalytic activity for the degradation of organic pollutants than pure TiO2 and coal-based C-dots, which is due to the synergistic effect of C-Dots.