Integrated adsorption and photodegradation of tetracycline by bismuth oxycarbonate/biochar nanocomposites

Adsorption and photodegradation are two widely studied wastewater treatment technologies. In this work, we have firstly prepared the bismuth oxycarbonate (Bi2O2CO3) and biochar nanocomposites for synergistic adsorption-photodegradation of tetracycline (TC). It was found that Bi2O2CO3 and biochar composites exhibited stronger adsorption capacity and photocatalytic activity compared to Bi2O2CO3. Among them, Bi2O2CO3/2.5 wt % biochar possessed the highest adsorption capacity for TC (173.0 mg/L) and the best combined removal rate of TC (84.7 %) in 60 min by adsorption and photodegradation, which were 1.9 times and 1.5 times that of Bi2O2CO3, respectively. The biochar in the composite increased the specific surface area, promoted the adsorption of TC, facilitated charge transfer capability, thereby enhanced the photocatalytic activity of com-posites. The effects of experimental parameters (temperature, co-existing ions, and initial pH) on TC degradation were examined. Electron spin resonance (ESR) and trapping experiments of free radical confirmed that O-1(2), O-center dot(2)- and h(+) were the main species in photocatalytic degradation. The potential degradation pathways were proposed based on liquid chromatograph mass spectrometer (LC-MS) test of the intermediates of TC degradation. It is hoped that this work not only represents the significantly importance of biochar in photocatalytic wastewater treatment, but also promotes further interests in design synergistic adsorption-photodegradation materials.