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

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.

Automated summary

By synthesizing rod-type graphitic carbon nitride (NCN), a highly selective production of singlet oxygen can be achieved compared to bulk graphitic carbon nitride (BCN). NCN exhibits higher surface area and surface oxygen adsorption ability, resulting in increased production of O-1(2) under photo-excitation, along with higher recombination efficiency and longer e(-) decay time, showing superior performance in ATZ removal.