Investigating the Nucleation Kinetics of Calcium Carbonate Using a Zero-Water-Loss Microfluidic Chip

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 toward 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 midgap states of the atomic Ag at the interface. These results provide in depth understanding of the reaction mechanism in the reduction and conversion of CO2 to useful chemicals via an Ag3PO4 and g-C3N4-based nanocomposite photocatalyst under visible light.