科研之友
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摘要
The heteroatom-doped, carbon-activated peroxymonosulfate (PMS) system proceeding via the non-radical oxidation pathway involving singlet oxygen (O-1(2)) represents a promising advanced oxidation process (AOP) due to the resistance of O-1(2) to background anions in solution. However, the performance level of pollutant removal is not yet satisfied, and the mechanism of O-1(2) generation remains elusive. Herein, we report the development for the first time of a unique Si-engaged heteroatom (i.e., N)-doped carbon (Si/N-C) nanomaterial for PMS activation, which exhibits outstanding performance in the removal of various kinds of pollutants and an appreciably wide working pH range of 2.5 to 11. Taking rhodamine B (RhB) as an example, the Si/N-C@PMS system achieved a much higher reaction rate (0.64 min(-1)) than the Si-C (0.047 min(-1)), N-C (0.017 min(-1)), SiO2(0.021 min(-1)), and Co3O4 (0.026 min(-1); a standard catalyst) systems. In addition, the results of electron spin resonance (ESR) and scavenging experiments solidly support the conclusion that the mechanism of O-1(2) generation in this system is via the recombination of superoxide radicals O-2(center dot-), a pathway seldom reported for metal-free, catalyst-activated PMS systems. More importantly, we observed apparent inhibition effects of the anions (e.g., HCO3-, HPO42-, and PO43-) on the degradation performance, inconsistent with many previous reports suggesting that the O-1(2)-mediated oxidative system possesses a high selectivity toward pollutant degradation in the presence of these anions. Further studies with the anions, including Cl-, HCO3-, and HxPO4(3-x) (x = 0, 1, 2), suggest that the reaction between O-2(center dot-) and these anions is the main reason for the abnormal salt effect. This work will deepen the understanding of O-1(2) formation via the intermediate of O-2(center dot-) and provide a new insight into its salt resistance capacity.
