Developing boron carbon nitride/boron carbon nitride-citric acid quantum dot metal-free photocatalyst and evaluating the degradation performance difference of photo-induced species for tetracycline via theoretical and experimental study

For opening a way to synthesize novel metal-free catalysts and clarifying the photodegradation performance difference of photoactive species (such as ·O2−, h+), a series of metal-free photocatalysts have been synthesized by using different existing forms of the same materials (boron carbon nitride (BCN) and boron carbon nitride-citric acid quantum dot (BCQD)) as precursors via calcinating their mixture at 350 °C. BCQD has good fluorescence and up-conversion fluorescence performance. BCN/BCQD-350 has the highest removal efficiency (90%, including adsorption 60% and photodegradation 30%) for tetracycline (TC) among all samples under visible light irradiation. TC adsorption by BCN/BCQD-350 conforms to pseudo-second-order kinetic and Langmuir isotherm models. TC photodegradation by BCN/BCQD-350 conforms to type II heterojunction mechanism. Photoactive species capture experiments suggest that·O2− makes a higher contribution for TC photodegradation, followed by h+, ·OH, 1O2 and e−. From LC-MS results, TC photodegradation is initiated by the dehydration step. TC dehydration activated by ·O2− has the lowest barrier (43.4 kcal/mol) than that (50.1 kcal/mol) activated by h+, that (64.8 kcal/mol) without the activation by photoactive species. TC removal rate of BCN/BCQD-350 (0.01563 min−1) is higher than that of g-C3N4, P25 (TiO2), BNPA, BCNPA, etc. Furthermore, BCN/BCQD-350 can also photodegrade TC under infrared light irradiation (λ > 800 nm).