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.
Highlights
The increasing energy demand and the environmental pollution are two major problems that need to be resolved by the modern society
The XRD patterns of the synthesized and exfoliated (1ex, 2ex and 3ex) samples presented in Figure 1 are typical for g-C3 N4
The (002) diffraction peak reflects the graphite-like stacking of g-C3 N4 layers that consist of conjugated aromatic units
Summary
The increasing energy demand and the environmental pollution are two major problems that need to be resolved by the modern society. The photocatalytic technology is regarded as a potential solution because both hydrogen (H2 ) production and air depollution (CO2 reduction and oxidation of NOx , VOCs, SOx , etc.) can be achieved using abundant solar light [1]. For the photocatalytic H2 production, water and various organic compounds have been used as sources. H2 and O2 have been produced by water splitting, while H2 , CO2 , and H2 O have been obtained by reforming of organic compounds under UV or visible light irradiation [2]. Modified TiO2 and CdS are widely used as photocatalysts. G-C3 N4 is intensively investigated as photocatalyst for H2 evolution due to its visible light activation (band gap ~2.7 eV), suitable band gap potentials, stability, and low cost [4,5]
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