Abstract
The novel heterojunction photocatalysts also known as carbon quantum dots-decorated BiOCOOH/ultrathin g-C3N4 nanosheets (CQDs/BiOCOOH/uCN) were designed, where carbon quantum dots (CQDs) acted as mediators to shuttle electrons between BiOCOOH and ultrathin g-C3N4 nanosheets (uCN). The physicochemical properties of as-obtained composites were systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The 4-CQDs/BiOCOOH/uCN consisting of 50 wt% ultrathin g-C3N4 nanosheets (uCN) and 4 mL CQDs solution manifested the optimal photoactivity. After 90 min of LED lamp irradiation, the STZ degradation efficiency by 4-CQDs/BiOCOOH/uCN reached 99.28% ± 1.04, and the corresponding degree of mineralization was 49.58% ± 1.36. The enhanced photocatalytic performance of 4-CQDs/BiOCOOH/uCN was owing to the fast photogenerated charges transfer and separation revealed by photoluminescence (PL), transient photocurrent responses and electrochemical impedance spectra (EIS) measurements. By means of the radicals quenching experiments and electron spin resonance spectroscopy (ESR) analysis, it was demonstrated that •O2– and •OH were the dominant reactive species of STZ degradation. Besides, the effects of catalyst dosage (0.2–1.2 g/L), pH value (3.0–11.0), natural organic matter and different anions (Cl−, SO42−, NO3−) on the photocatalytic activity of 4-CQDs/BiOCOOH/uCN composite were systematically explored. 17 main intermediates were found based on high-resolution mass spectrometry (HRMS) detection. Eventually, the 4-CQDs/BiOCOOH/uCN composite showed favorable reusability in recycling experiments, and displayed satisfactory degradation abilities for STZ in deionized water (99.28% ± 1.04), tap water (97.15% ± 1.16), river water (96.44% ± 0.76), and wastewater treatment plant effluent (96.19% ± 1.20).
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