Deciphering the impacts of symmetric and asymmetric structures in heptazine units over g-C3N4 on piezo-photocatalysis for H2O2 production from pure water

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2025-01, Vol.504, p.158657, Article 158657
• Main Authors: Phuong Ly, Pho, Nguyen, Duc-Viet, Anh Luu, Tuyen, Chien Nguyen, Minh, Duc Minh Phan, Pham, Phuoc Toan, Huynh, Van Nguyen, Tiep, Pham, Minh-Thuan, Dieu Thi Ung, Thuy, Danh Bich, Do, Thi Pham, Hue, Thi Ngoc Nguyen, Hue, Jong Yu, Woo, Hyun Hur, Seung, Quang Hung, Nguyen, Vuong, Hoai-Thanh
• Format: Article
• Language: English
• Subjects: Cluster vacancies; g-C3N4; H2O2 production; Monovacancies; Piezo-photocatalysis
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2024.158657

[Display omitted] •The asymmetric and symmetric structures in heptazine units over g-C3N4 were determined.•The asymmetric structures would favor piezo-photocatalysis by overcoming charge compensation effects.•The symmetric structures would suffer the loss of piezo potential under piezo-photocatalytic conditions.•The thorough mechanistic studies for producing H2O2 via oxygen reduction were investigated. The vacancy-engineering approach is showing promise in modulating graphitic carbon nitride (g-C3N4) structures to accelerate catalytic yield. Nonetheless, current studies mainly focus on the catalytic influences of carbon or nitrogen monovacancies in the materials’ structures, resulting in the elusive roles of cluster vacancies, where the co-presence of nitrogen and carbon vacancies can create asymmetric or symmetric structures in the heptazine units of g-C3N4, influencing the total catalytic outcomes under light or/and ultrasound irradiation. In this work, taking the piezo-photocatalytic production of H2O2 from pure water as a model reaction and utilizing positron annihilation techniques, we realize the hiding roles of cluster vacancies in g-C3N4. The results show that asymmetric structures can help overcome adverse charge compensation effects. The disorders will act as trapping states to store excited electrons and avoid charge neutralization processes between photo- and piezo-induced processes. In contrast, the symmetry in a local heptazine unit will enhance the piezocatalytic activity but degrade the piezo-photocatalytic outcomes under light irradiation. Therefore, this study unveils the roles of symmetric and asymmetric structures in response to visible light, UV light, and ultrasound over g-C3N4−based catalysts, which would be necessary for material designs and developments at a molecular level.