Hierarchical ternary titanium dioxide decorated with graphene quantum dot/ZIF-8 nanocomposite for the photocatalytic degradation of doxycycline and dye using visible light

Herein, the ternary nanostructure of titania (TiO2) decorated with graphene quantum dot (GQD)/zeolitic imidazolate framework-8 (ZIF-8) (T/G/Z: TiO2/GQD/ZIF-8) was synthesized by a hierarchical approach, and its photocatalytic activity was investigated for the degradation of the doxycycline (DOX) as a pharmaceutical and dyes under visible light irradiation. Increasing the doping content of the graphene quantum dot from 0.002 g to 0.02 g was accompanied by an increase in photocatalytic activity. A further increase to 0.2 g, the thickening or aggregation of the GQD layer on the TiO2 surface, or the thorough coverage of the TiO2 surface with the GQD occurred and effective light irradiation to TiO2 nanoparticles has not been done well. Thus the reduction of the catalytic activity happened. The photocatalytic degradation rate has increased outstandingly over this period of time for ternary composite in this concentration at intervals of the sampling period. The increase in pollutant concentration was associated with decreased photocatalytic degradation. Increasing the dose of photocatalysts improved the rate of pollutant degradation. The degradation efficiency of doxycycline in the presence of l-ascorbic acid scavenger had a notable decrease, while the presence of formic acid and isopropyl alcohol was less effective in the DOX degradation. It can be explained that the superoxide anion radical has the greatest effect on the degradation process of doxycycline. The DOX degradation kinetics followed the first-order kinetics with high correlation coefficients. This work has provided profound insight based on heterogeneous structures for efficient photocatalysts in the degradation of wastewater pollutants (pharmaceutical and dyes).