An Investigation into the Stability of Graphitic C₃N₄ as a Photocatalyst for CO₂ Reduction

Abstract

The increasing CO2 concentration in the atmosphere exerts a significant influence on global warming and climate change. The capture and utilization of CO2 by conversion to useful products is an area of active research. In this work, the photo-driven reduction of CO2 was investigated using graphitic carbon nitride (g-C3N4) as a potential photocatalyst. The photocatalytic reduction of CO2 was investigated with g-C3N4 powder immobilized on a glass support in a batch gas phase photoreactor. The experiments were carried out under UV-Vis irradiation at 70°C and an initial pressure of 2.5 bar. The only gas phase product detected during the irradiation of the g-C3N4 in the presence of CO2 was CO, and the rate of production was observed to decrease over time. Oxygen doped g-C3N4 was also tested for CO2 reduction but had lower efficiency that the parent g-C3N4. Repeated cycles of photocatalytic CO2 reduction showed a decline in the activity of the g-C3N4. In the absence of CO2 some CO generation was also observed. Characterization of used and unused materials, using FTIR and XPS, showed an increase in the oxygen functional groups following UV-Vis irradiation or thermal treatment. While others report the use of g-C3N4 as a photocatalyst, this work highlights the important need for replicates and control testing to determine material stability.

Catalytic conversion of CO2 to chemicals and fuels: the collective thermocatalytic/photocatalytic/electrocatalytic approach with graphitic carbon nitride

“…Moreover, the percentage of different N-types varies based on the geometry of their linkages as shown in Scheme 4 (inset table). 62 The stability of g-C 3 N 4 after catalysis can be estimated by the % of different types of N so that the breakage of linkages, chain fragmentation, and different structural changes can be predicted. CO 2 adsorption and its activation highly depend on the type of N-moieties present (pyridinic, pyrrolic/ pyridonic, and graphitic nitrogen).…”

“…But, a close look at the valence band edge potential and theoretical calculations confirm that only g-h-heptazine fulfills the thermodynamic requirements for water oxidation. 62 Notably, the g-h-heptazine based polymorphic g-C 3 N 4 material has been most widely investigated as a photocatalyst with a bandgap of 2.7 eV where the conduction band is situated at (À1.2 V vs. NHE) and the valence band is positioned at (+1.5 V vs. NHE) at pH = 7. The CB and VB indicate that it is capable of reducing the CO 2 molecule and also can oxidize H 2 O to produce O 2 and H + required for the production of hydrocarbons/ oxygenated hydrocarbons in CO 2 photoreduction.…”

“…189 For the first time ever, the stability aspect of g-C 3 N 4 in the CO 2 photoreduction reaction has been investigated in-depth by F. R. Poimilla et al, in which the authors provide insights about the stability of the melem framework before and after catalytic activity evaluation (Table 3, entry 25). 62 They have synthesized g-C 3 N 4 by following a two-step thermal polymerization of melamine. For comparison purposes, they have also synthesized O-doped g-C 3 N 4 by treating carbon nitride with H 2 O 2 .…”

Overview of Photocatalytic Membrane Reactors in Organic Synthesis, Energy Storage and Environmental Applications

“…An accumulation of carbon species (by total organic carbon analysis) and NO 3 − ions in water under photocatalytic reactions (sunlight/O 2 /nanostructured C 3 N 4 conditions) was found, suggesting chemical instability of g-C 3 N 4 in the aqueous phase. Pomilla et al [99] studied the changes in photocatalytic activity as a function of time and reuse cycle during the photocatalytic reduction of CO 2 in the gas phase by using water as the reducing agent and g-C 3 N 4 or an oxygen-doped g-C 3 N 4 as photocatalysts. The main detected product was CO.…”

Kinetic and Mechanistic Study of Rhodamine B Degradation by H2O2 and Cu/Al2O3/g-C3N4 Composite

“…With a suitable band gap (2.7 eV) and high response to visible light, g-C 3 N 4 has been intensively explored as a photocatalyst for energy and environmental applications [3,[32][33][34]. Apart from this, g-C 3 N 4 could also be applied as a Fenton-like catalyst in the absence of light irradiation through the combination with other materials [35,36].…”