Insight into the role of charge carrier mediation zone for singlet oxygen production over rod-shape graphitic carbon nitride: Batch and continuous-flow reactor

Abstract

As a new approach of creating the photo-exited electron (e(-)) and hole (h(+)) mediation zone for highly selective singlet oxygen (O-1(2)) production, the rod-type graphitic carbon nitride (NCN) has been synthesized from the nitric acid-modified melamine followed by the calcination. The NCN exhibited a higher surface area and surface oxygen adsorption ability than bulk graphitic carbon nitride (BCN). The increment of C=O and NHx groups on NCN corresponded to e(-) and h(+) mediation groups, respectively, resulting in higher production of O-1(2) than BCN. Moreover, those mediation groups on NCN result in higher recombination efficiency and longer e(-) decay time. As a result, the optimized NCN-0.5 (derived from 0.5 M of nitric acid-modified melamine) displayed 5.8 times higher kinetic rate constant of atrazine (ATZ) removal under UVA-LED irradiation compared to BCN. This study also evaluated the ATZ degradation pathways and toxicity effect of by-products. In addition, continuous flow experiments using NCN-0.5 showed superior ATZ removal performance with a hybrid concept between a slurry photocatalysis and a continuous stirred tank reactor system using actual effluent obtained from a wastewater treatment plant. Thus, this work provides an insight into the strategy for highly selective O-1(2) production and the potential for water purification application.