Yi Yuan,Wen-Long Wang,Zhi-Wei Wang,Jin Wang,Qian-Yuan Wu
Carbon nitride has been extensively used as a visible-light photocatalyst, but it has the disadvantages of a low specific surface area, rapid electron–hole recombination, and relatively low light absorbance. In this study, single-atom Ag was successfully anchored on ultrathin carbon nitride (UTCN) via thermal polymerization, the catalyst obtained is called AgUTCN. The Ag hardly changed the carbon nitride's layered and porous physical structure. AgUTCN exhibited efficient visible-light photocatalytic performances in the degradation of various recalcitrant pollutants, eliminations of 85% were achieved by visible-light irradiation for 1 hr. Doping with Ag improved the photocatalytic performance of UTCN by narrowing the forbidden band gap from 2.49 to 2.36 eV and suppressing electron–hole pair recombination. In addition, Ag doping facilitated O 2 adsorption on UTCN by decreasing the adsorption energy from −0.2 to −2.22 eV and favored the formation of O 2 ·− . Electron spin resonance and radical-quenching experiments showed that O 2 ·− was the major reactive species in the degradation of Acetaminophen (paracetamol, APAP).
Ag-based catalysts have been extensively investigated in HCHO oxidation on account of the low price of the Ag precursor and their considerable low-temperature activity. It is known that H2 pretreatment has a remarkable promotion effect on Pt- and Pd- catalysts for HCHO oxidation, whereas the effect of H2 reduction on Ag-based catalysts has been rarely reported, probably due to the coexistence of multiple states of Ag species resulting from the high Ag loading. Herein, we prepared a 1% Ag/Al2O3 (Ag/Al-fresh) catalyst with Ag species in a uniform state and then reduced Ag/Al-fresh with H2 at 600 °C to obtain the Ag/Al-600H2 catalyst. We observed that H2 reduction had a significant influence on the performance of Ag/Al2O3 nanocatalysts in HCHO oxidation. In a dry reaction atmosphere, Ag/Al-fresh and Ag/Al-600H2 exhibited comparable HCHO conversion levels, but Ag/Al-600H2 showed much higher CO2 selectivity than Ag/Al-fresh. The presence of water vapor severely suppressed the HCHO conversion of the Ag/Al-fresh catalyst, while Ag/Al-600H2 showed high water resistance, maintaining high HCHO conversion and CO2 selectivity at 35% RH. Characterization results showed that the Ag species on Ag/Al-fresh and Ag/Al-600H2 were single-atom cationic Ag and metallic Ag nanoparticles, respectively. It was revealed that the Ag0 nanoparticles were more conducive than single-atom Ag+ to formate decomposition, as well as O2 and H2O activation, thus accelerating the conversion of HCOO– and CO intermediates to CO2 and contributing to the higher activity and water resistance of the Ag/Al-600H2 catalyst.
Photocatalytic technique has been widely accepted as a promising and effective candidate for eliminating antibiotic and pathogen pollutants in aquatic environment. Herein, a novel O, K co-doped g-C 3 N 4 photocatalyst embedded with single-atom Ag (denoted as Ag/OKCN) was successfully constructed to achieve the enhanced photocatalytic degradation and disinfection efficiency under visible light irradiation. The optimal Ag/OKCN-6 could eliminate 80.4 % of tetracycline (TC) within 60 min with a rate constant of 0.0259 min −1 , which was 4.98 times of pristine g-C 3 N 4 . Meanwhile, Ag/OKCN-6 could also completely inactivate>7-log CFU·mL −1 of Escherichia coli ( E. coli ) by efficient disruption of cell membranes. The synergistic effect of O, K co-doping and single-atom Ag embedding contributed to an extended light response, preeminent separation and transfer of photoexcited charges, prolonged carrier lifetime as well as ameliorative hydrophilicity, which was conducive to the excellent photocatalytic performance. Radical trapping and electron spin resonance (ESR) experiments validated that superoxide radicals ( • O 2 − ) were crucially responsible for the superior photocatalytic activity. This work provides a facile route to construct multi-strategy modified g-C 3 N 4 -related photocatalysts for efficiently eliminating aquatic environmental pollutants.
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