Sustainable production of value-added chemicals and fuels by using a citric acid-modified carbon nitride optical semiconductor

• Published in: Applied catalysis. A, General General, 2021-01, Vol.609, p.117912, Article 117912
• Main Authors: Fernandes, Raquel A., Sampaio, Maria J., Da Silva, Eliana S., Boumeriame, Hanane, Lopes, Tânia, Andrade, Luísa, Mendes, Adélio, Faria, Joaquim L., Silva, Cláudia G.
• Format: Article
• Language: English
• Subjects: Carbon; Carbon nitride; Catalysts; Chemical synthesis; Citric acid; Copolymerization; Electromagnetic absorption; Electron transitions; Ethylenediaminetetraacetic acids; Hydrogen production; Nanoparticles; p-Anisaldehyde; Photocatalysis; Platinum; Porosity; Selectivity; Water splitting
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2020.117912

[Display omitted] •Copolymerization of dicyandiamide and citric acid resulted in a defective carbon nitride catalyst.•The presence of nitrogen vacancies in copolymerized materials indicate a higher amount of active sites.•GCN-20CA proved to be highly efficient both in the synthesis of p-anisaldehyde and hydrogen.•Reusability tests evidenced the high stability of the copolymerized catalyst. Citric acid-modified graphite-like carbon nitride materials (GCN-zCA) were synthetized by thermal co-polymerization of dicyandiamide with different amounts of citric acid (z = between 5 and 25 mg). The resulting materials presented surface porosity, defective polymeric structure, and enhanced visible light absorption in the 450−700 nm range, attributed to the existence of mid-gap states and n-π* electronic transitions. All the modified catalysts presented high selectivity (>99 %) towards the conversion of p-anisyl alcohol into p-anisaldehyde under visible-LED irradiation, the best performing photocatalyst (GCN-20CA) reaching 63 % yield (contrasting with 22 % obtained with bulk GCN) after 240 min reaction. GCN-20CA was also applied for hydrogen generation from water splitting. The modified material practically duplicated the hydrogen production when compared to bulk GCN (75 and 44 μmol H2 evolved in three hours, respectively), by using platinum nanoparticles as co-catalyst and EDTA as sacrificial electron donor. Moreover, p-anisyl alcohol was successfully used as sacrificial agent for water splitting, with simultaneous production of p-anisaldehyde and H2. Reusability tests showed that GCN-20CA remained stable in a series of consecutive runs both for p-anisaldehyde synthesis and hydrogen production.