A Single-Step Synthesis of Defective Graphitic Carbines from Melamine and Urea for Photocatalytic Applications

Abstract

Recently, there has been a growing interest in relying on photocatalytic technology for producing renewable fuels such as hydrogen and other environmental applications. The success of photocatalysis, however, requires developing visible light-responsive photocatalysts for the continuous production of H2 and other value-added chemicals. Graphitic carbon nitride (g-C3N4) is a promising material but has diminished photocatalytic ability. This work aims to design and develop visible light responsive g-C3N4 using a singlestep hydrothermal approach. The g-C3N4 was prepared through the thermal decomposition of melamine (named g-C3N4-M), urea (named g-C3N4-U), and a mixture of melamine-urea (named g-C3N4-MU). The samples were characterized using X-ray diffraction (XRD), UVvisible, and photoluminescence to assess the successful conversion to g-C3N4. XRD results revealed that urea was not successfully converted to g-C3N4; however, melamine was fully converted to g-C3N4. Interestingly, when melamine and urea were mixed as a fixed bed, the mix was successfully converted to defective g-C3N4. Visible light responsiveness was confirmed by the results of UV-visible analysis for all three materials. In the case of melamine, a higher visible light response was obtained (~482 nm), whereas g-C3N4-MU had slightly lower visible light absorption (~ 471 nm) due to the interaction of defects within the surface. These findings were further confirmed through photoluminescence analysis. The highest charge carrier recombination was obtained using g-C3N4-M, whereas charge separation was improved in the g-C3N4-U sample due to the presence of g-C3N4 composites and other intermediates. The highest charge separation ability was achieved for the g-C3N4-MU. This revealed that mixing melamine and urea is a promising approach for the singlestep synthesis of defective g-C3N4 with a higher ability for visible light absorption and photoinduced charge carrier separation. The findings of this work would be beneficial in different areas, such as solar energy conversion, greenhouse gas reduction, and wastewater degradation.