Anchoring N and Co species on the aluminum-graphite surface to enhance oxygen activation for the degradation of tetracycline at neutral conditions

Abstract

Molecular oxygen (O2) activation for reactive species (RSs) production has recently received increasing interest. Reported herein is a novel O2 activator (Al-Gr-N/Co), synthesized by anchoring N and Co species on the aluminum-graphite (Al-Gr) surface, that could achieve efficient degradation of tetracycline (TC) by activating O2 in air purging water. RSs, including HO•, O2•− and 1O2, could be generated in the Al-Gr-N/Co/Air process, achieving 97.8 % of TC degradation at pH 7. This degraded TC can be attributed to the oxidation by 1O2 and HO•; direct adsorption by Al-Gr-N/Co also contributed to the TC degradation. The N species promoted the H2O2 production during O2 activation by Al-Gr-N/Co; these produced H2O2 could be further converted to RSs by Co and N species. Demethylation, hydroxylation and dehydration reactions were proposed as the oxidation pathways of TC by Al-Gr-N/Co/Air. TOC result suggests that TC and the oxidized intermediates could be adsorbed by Al-Gr-N/Co or converted to inorganic compounds. Negligible amount of the dissolved metal ions (<0.44 mg/L) was observed after reaction. Highly efficient removal of TC (>82.2 %) in lake water, tap water and MBR secondary effluents suggested that the Al-Gr-N/Co/Air process could be potentially applied in real water systems.