Boosting the activation of molecular oxygen and the degradation of tetracycline over high loading Ag single atomic catalyst

•A single atomic Ag-g-C3N4 (SAACN) with 10 wt% loading of Ag catalyst is designed.•When using SAACN, 17.24% of dissolved O2 is converted to reactive oxygen species.•The rate constants (k) for degrading the tetracycline are 0.0409 min-1 over SAACN.•Abundant ROS generate over SAACN due to O2 adsorption and electron transfer.•A potential method for converting O2 into ROS and degraded pollutants is provided. Photocatalytic activation of molecular oxygen (O2) is a promising way in oxidative degradation of organic pollutants. However, it suffers from low efficiency mainly due to the limited active sites for O2 activation over traditional photocatalysts. Therefore, we established a single atomic Ag-g-C3N4 (SAACN) catalyst with 10 wt% loading of Ag single sites for boosting the O2 activation during the degradation of tetracycline (TC), and 10 wt% loading of nanoparticle Ag-g-C3N4 (NPACN) was studied as a comparison. When using SAACN, the accumulative concentration of superoxide (•O2−), hydroxyl radical (•OH), singlet oxygen (1O2) reached up to 0.66, 0.19, 0.33 mmol L−1h−1, respectively, within 120 min, 11.7, 5.7 and 4.9 times compared with those using NPACN, representing 17.24% of dissolved O2 was converted to reactive oxygen species (ROS). When additionally feeding air or O2, the accumulative concentrations of •O2−, •OH, 1O2 were even higher (air: 4.21, 0.97, 2.02 mmol L−1 h−1; O2: 17.13, 1.32, 9.00 mmol L−1 h−1). The rate constants (k) for degrading the TC were 0.0409 min−1 over SAACN and 0.00880 min−1 over NPACN, respectively (mineralization rate: 95.7% vs. 59.9% after 3 h of degradation). Moreover, the degradation ability of SAACN did not decrease in a wide range of pH value (4–10) or under low temperature (10 °C). Besides the high exposure of Ag single sites, other advances of SAACN were: 1(O2 was more energetic favorable to adsorb on single atomic Ag sites; 2) Positive Ag single sites were easier to obtain the electrons from the surrounding N atoms, and facilitated electron transfer towards adsorbed O2. [Display omitted]