Mechanism of Photocatalytic Reduction of CO₂ by Ag₃PO₄(111)/g-C₃N₄ Nanocomposite: A First-Principles Study

Abstract

Density functional Theory (DFT) calculations have been performed to investigate the electronic structure and photocatalytic activity of a hybrid Ag3PO4(111)/g-C3N4 structure. Due to Ag(d) and O(p) states forming the upper part of the valence band and C(p), N(p) and Ag(s) the lower part of the conduction band, the band gap of the hybrid material is reduced from 2.75 eV for Ag3PO4(111) and 3.13 eV for monolayer of g-C3N4 to about 2.52 eV, enhancing the photocatalytic activity of the Ag3PO4(111) surface and g-C3N4 sheet in the visible region. We have also investigated possible reaction pathways for photocatalytic CO2 reduction on the Ag3PO4(111)/g-C3N4 nanocomposite to determine the most favored adsorption geometries of reaction intermediates and the related reaction energies. For CO2 reduction, our findings demonstrate that the Ag3PO4(111)/g-C3N4 heterostructure thermodynamically exhibits a higher selectivity towards CH4 production than that of CH3OH. The CO2 reduction process takes place through either HCOOH * or HOCOH * as an intermediate species, where the highest exothermic reaction energy of-2.826 eV belongs to the hydrogenation of t-COOH * to HCOOH * and the lowest reaction energy of-0.182 eV for hydrogenations of CH2O * to CH2OH * and HCO * to c-HCOH *. Our results from charge density difference calculations of the Ag3PO4(111)/Ag/g-C3N4 revealed that the charge transfer between the Ag3PO4(111) slab and g-C3N4 monolayer occurs through mediation of atomic Ag, thus proposing a Z-scheme mechanism. Moreover, a smaller band gap energy of 0.73 eV is calculated for this ternary nanocomposite due to the mid-gap states of the atomic Ag at the interface. These results provide in depth understanding of the reaction mechanism in the reduction and conversion of CO 2 to useful chemicals via an Ag 3 PO 4 and g-C 3 N 4-based nanocomposite photocatalyst under visible light.

A First‐Principles Study of CO2 Hydrogenation on a Niobium‐Terminated NbC (111) Surface

“…In recent years, the amount of carbon dioxide (CO 2 ) in the atmosphere has increased due to the industrial revolution, in addition to the use of fossil fuels, as one of the major sources of energy in human life [1] . Carbon dioxide plays an important role in air pollution, global warming, and climate change, which causes many environmental problems such as moisturizing the air, damaging plants, etc.…”

“…In recent years, the amount of carbon dioxide (CO 2 ) in the atmosphere has increased due to the industrial revolution, in addition to the use of fossil fuels, as one of the major sources of energy in human life. [1] Carbon dioxide plays an important role in air pollution, global warming, and climate change, which causes many environmental problems such as moisturizing the air, damaging plants, etc.. [2] Therefore, the adsorption, activation, storage, and conversion of CO 2 into valuable products for environmental reasons has attracted the attention of many researchers. [3] Extensive researches have dealt with the conversion of CO 2 into alternative suitable hydrocarbon fuels such as methanol (CH 3 OH), methane (CH 4 ), formic acid (HCOOH), and formaldehyde (CH 2 O).…”

Challenges and prospects in the selective photoreduction of CO2 to C1 and C2 products with nanostructured materials: a review

“…In another case, Tafreshi et al reported a Z-scheme Ag 3 PO 4 (111)/g-C 3 N 4 composite in the CO 2 photoreduction and illustrated the mechanism with the help of DFT studies and experiments. 121 The authors demonstrated the higher selectivity of CH 4 over CH 3 OH due to the thermodynamically favourable exothermic reaction (energy released: 2.43 eV for CH 4 and 1.18 eV for CH 3 OH). All the possible intermediates and corresponding products using multiple electron reduction processes and water oxidation are summarized in the mechanism in Fig.…”

Inside‐and‐Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

“…Also, different products can be obtained by controlling surface structures, such as acid–base sites [ 76–78 ] and organic groups. [ 79,80 ] Since 2009, several new photocatalytic systems have been proposed gradually, including g‐C 3 N 4 , [ 81–90 ] CdS, [ 90–99 ] BiOCl, [ 100–102 ] and BiOIO 3 . [ 103 ] Synthetic strategies for various nano‐/microstructure were also developed, such as quantum dots (QDs), [ 104–106 ] nanowires (NWs), [ 107–109 ] nanosheets, [ 110–112 ] and heterostructures.…”