Photocatalytic H2 Evolution, CO2 Reduction, and NOx Oxidation by Highly Exfoliated g-C3N4

Abstract

g-C3N4, with specific surface area up to 513 m2/g, was prepared via three successive thermal treatments at 550 °C in air with gradual precursor mass decrease. The obtained bulk and exfoliated (1ex, 2ex, and 3ex) g-C3N4 were characterized and tested as photocatalysts for H2 production, CO2 reduction, and NOx oxidation. The exfoliated samples demonstrated graphene-like morphology with detached (2ex) and sponge-like framework (3ex) of layers. The surface area increased drastically from 20 m2/g (bulk) to 513 m2/g (3ex). The band gap (Eg) increased gradually from 2.70 to 3.04 eV. Superoxide radicals (·O2−) were mainly formed under UV and visible light. In comparison to the bulk, the exfoliated g-C3N4 demonstrated significant increase in H2 evolution (~6 times), CO2 reduction (~3 times), and NOx oxidation (~4 times) under UV light. Despite the Eg widening, the photocatalytic performance of the exfoliated g-C3N4 under visible light was improved too. The results were related to the large surface area and low e−-h+ recombination. The highly exfoliated g-C3N4 demonstrated selectivity towards H2 evolution reactions.

Pilot-Scale Studies of WO3/S-Doped g-C3N4 Heterojunction toward Photocatalytic NOx Removal

“…Graphitic carbon nitride has unique physicochemical properties such as a suitable bandgap energy (~2.7 eV), corresponding to visible-light absorption [7]. Therefore, g-C 3 N 4 can be applied as a visible-light-driven photocatalyst toward NO x removal in the gas phase, which was confirmed in the previous studies [8,9]. From the technological point of view, the synthesis of g-C 3 N 4 is simple (typical calcination of N-containing organic precursor, e.g., urea, melamine) and low-price.…”

Photocatalytic hydrogen generation from a methanol–water mixture in the presence of g-C3N4 and graphene/g-C3N4

“…The weak peak at around 2 θ = 13° 2 θ , which corresponds to the reflection (100) is attributed to the repeated tri- s -thiazine units, and the stronger one at around 2 θ = 27.5° 2 θ , which corresponds to the reflection (002), is related to the interlayer graphitic like structure. 45,46 A slight shift to lower 2 θ values of the (002) peaks from bulk to the exfoliated g-C 3 N 4 with melamine was noticed from 27.41° 2 θ to 27.28° 2 θ , resulting in a slight increase in the interlayer distance. From d = 0.3253 nm to d = 0.3266 nm, the distance was calculated using Bragg's law (Table 1), where the shift is attributed to the less dense stacking caused by the chemical treatment.…”

“…4a. The band gap ( E g ) of the samples were determined using the Tauc plot according to indirect and direct interband transition models, 45,50 and the differential reflectance method. 37,51 The results are listed in Table 2.…”

High surface area, spongy graphitic carbon nitride derived by selective etching by Pt and Ru nanoparticles in hydrogen

“…Apart from chemical methods of exfoliation, thermal exfoliation is also applied. It allows for an increase in SSA of g-C 3 N 4 to 150 m 2 g -1 [13] and sometimes even (repeating exfoliation three times) to 513 m 2 g -1 [12]. However, it should be pointed out that the final product yield did not exceed 6% in the latter case.…”

“…In a number of potential applications such as photo-, electro-, heterogeneous-catalysis, and gas storage, a high SSA is essential. Hence, attempts were made to synthesize the high-surface area of g-C 3 N 4 by using hard or soft template methods [7][8][9][10], by exfoliation into nanosheets [11][12][13][14] or by heteroatom doping [15,16]. The most commonly used method is the hard template method based on the use of high-surface area inorganic material, which acts as the matrix on which g-C 3 N 4 is synthesized.…”