A comparative study between thermal etching and liquid exfoliation of bulk graphitic carbon nitride to nanosheets for the photocatalytic degradation of a model environmental pollutant, Rhodamine B

Abstract

Graphitic carbon nitride (g-C3N4) is a metal-free photoactive material which has gained significant interest in the advancement of electronic and optical devices because of its attractive optoelectronic properties, such as tuneable band gap, and suitable chemical and thermal stability. This material has been utilized in a range of applications including photocatalysis, biosensing and photovoltaics. Bulk g-C3N4 (B-g-C3N4) has been shown to exhibit low photo-efficiency due to its low specific surface area and high rate of recombination of photo-generated charges; thus, there is a need for its exfoliation. Also, the type of exfoliation method utilized is crucial. In this work, two exfoliation methods of g-C3N4, namely, liquid and thermal etching exfoliation, were investigated. Both methods successfully produced g-C3N4 nanosheets, but those synthesized by liquid exfoliation (CNNS-LE) had a much larger specific surface area of 41.68 m2 g−1 than those prepared by thermal exfoliation (CNNS-TE) (14.76 m2 g−1) or the parent B-g-C3N4 (3.22 m2 g−1). The band gap energies of B-g-C3N4, CNNS-LE and CNNS-TE were found to be 2.71, 2.59 and 1.89 eV, respectively. Graphitic carbon nitride nanosheets prepared by thermal exfoliation (CNNS-TE) were found to be 2.5 times more effective in the photo-degradation of Rhodamine B than B-g-C3N4 and CNNS-LE. This is attributed to the positive effect of their porous structure, which gives rise to effective separation of charges, and their extended light absorption properties. Thus, thermal treatment introduces structural defects and electronic modifications that result in an enhanced photocatalytic performance. Consequently, thermal etching is effective in exfoliation of B-g-C3N4 to form a material suitable for photo-driven applications.