One-step synthesis of nitrogen and sulfur co-doped mesoporous graphite-like carbon nanosheets as a bifunctional material for tetracycline removal via adsorption and catalytic degradation processes: Performance and mechanism

In this study, nitrogen and sulfur co-doped mesoporous graphite-like carbon nanosheets (NS-MGCNS) were synthesized via a facile pyrolysis method. The as-prepared sample at a calcined temperature of 800 °C (NS-MGCNS-800) exhibited remarkably outstanding removal capacity for tetracycline (TC). About 94.5% of TC (20 mg/L) was removed within 60 min via the synergistic effect of adsorption and catalytic degradation processes. Pseudo-second-order adsorption plot and Langmuir models fitted well with the adsorption process. The maximum adsorption capacity of NS-MGCNS-800 was 91.57 mg/g through π-π interactions. Besides, NS-MGCNS-800 could activate persulfate (PS) for TC degradation with the pseudo-first-order degradation reaction rate constant of 0.144 min−1, which was 51.4, 24.0, and 1.3-fold as high as that over graphitic carbon nitride (CN), pure carbon (C), and nitrogen doped carbon nanosheets (N-CNS), respectively. Meanwhile, NS-MGCNS-800 possessed superior reusability for removing TC with the removal efficiency of over 87% after 5 cycles. Quenching tests, electron spin resonance spectroscopy (ESR), and electrochemical measurement revealed that radical and non-radical pathways were involved in the NS-MGCNS-800/PS/TC system. More importantly, by means of experimental methods and density functional theory (DFT) calculations, the introduction of sulfur could significantly adjust the electron density of the carbon lattice though the synergistic effect of nitrogen doped carbon nanosheests, promoting the TC adsorption and PS activation of NS-MGCNS-800. Finally, TC intermediates were detected and six possible degradation pathways of TC were proposed. Consequently, this study not only developed a high-performance bifunctional graphite-like carbon nanomaterial, but also provided a new direction for removing the trace antibiotics in environmental remediation.