Photocatalytic O₂ activation by metal-free carbon nitride nanotube for rapid reactive species generation and organic contaminants degradation

Advanced oxidation processes (AOPs) using oxygen (O-2) as an oxidant represent a low-cost and sustainable wastewater treatment process. Herein, a metal-free nanotubular carbon nitride photocatalyst (CN NT) was prepared to activate O-2 to degrade organic contaminants. The nanotube structure allowed for sufficient O-2 adsorption, while the optical and photoelectrochemical properties enabled photogenerated charge to be efficiently transferred to the adsorbed O-2 to trigger the activation process. The developed CN NT/Vis-O-2 system based on O-2 aeration degraded various organic contaminants and mineralized 40.7% of chloroquine phosphate within 100 min. In addition, the toxicity and environmental risk of treated contaminants were reduced. Mechanistic studies suggested that the enhanced O-2 adsorption capacity and fast charge transfer behavior on CN NT surface led to reactive center dot O-2(-), O-1(2) and h(+) generation, each of which played a distinct role in contaminants degradation. Importantly, the proposed process could overcome the interference from water matrices and outdoor sunlight, and the energy and chemical reagent savings reduced the operating cost to about 1.63 US$center dot m(-3). Altogether, this work provides insights into the potential application of metal-free photocatalysts and green O-2 activation for wastewater treatment.