Metal-organic framework MIL-68(In)-NH2-derived carbon-covered cobalt-doped bi-crystalline In2O3 tubular structures for efficient photocatalytic degradation of tetracycline hydrochloride

Tubular carbon-covered cobalt-doped bi-crystalline phase In2O3 (denoted as CoInO-x) was synthesized by one-step calcination of the metal-organic framework cobalt-doped MIL-68(In)-NH2 precursor. The photocatalytic activity of CoInO-x was investigated using tetracycline hydrochloride (TCH) degradation. The removal of TCH by CoInO-500 obtained by calcination at 500 degrees C under visible light irradiation was 90.1% after 70 min, which was significantly higher than that of In2O3. The reaction rate constant of CoInO-500 was 11.02 times higher than that of In2O3 and could maintain a better photocatalytic performance after four cycles. The effects of photocatalyst dosing, pH, and inorganic anions on photocatalytic degradation were studied. The mechanism of photocatalytic degradation was analyzed in detail by reactive radical trapping experiments, Mott-Schottky measurements, and electron paramagnetic resonance (EPR) signal characterization. Enhanced photocatalytic performance is mostly attributed to the cobalt doping creating impurity energy levels and narrowing the forbidden bandwidth of In2O3, enhancing the visible light utilization and the photogenerated charge separation efficiency. Carbon covering can serve as a bridge for charge transport, accelerating the rapid transport of photogenerated charges.