Dopant and Defect Doubly Modified CeO₂/g-C₃N₄ Nanosheets as 0D/2D Z-Scheme Heterojunctions for Photocatalytic Hydrogen Evolution: Experimental and Density Functional Theory Studies

Abstract

Exploring novel 2D heterojunction photocatalysts with a wide spectral response and high active site exposure has been a huge challenge. A small-sized catalyst with high dispersibility has been considered an ideal model for maximizing active sites and increasing atomic efficiency. Herein, the 0D/2D Z-scheme heterojunction was designed by in situ solvothermal and subsequent calcination in air by integrating dopant and defect doubly modified CeO2 nanodots and g-C3N4 nanosheets (CNNS). Ultrafine cobalt-doped CeO2 nanodots (≈4 to 5 nm) with enriched oxygen vacancies (Co-CeO2–OVs) were uniformly and tightly anchored on the surface of CNNS to form a heterojunction. The density functional theory (DFT) calculations confirmed that cobalt dopants and oxygen vacancies form impurity energy states at the top of a valence band, thus narrowing the band gap. The optimized 0D/2D heterojunction showed a remarkable hydrogen production rate of ∼203.6 μmol/h, which was approximately 4.9- and 30.8-fold higher than that of CNNS (∼41.2 μmol/h) and CeO2 (∼6.6 μmol/h), respectively. Moreover, a large quantum yield of ∼8.94% was achieved at 420 nm. The 0D/2D heterojunction with a larger intimate area provided abundant reactive active sites and strong electron interactions to excite photogenerated carrier dynamics, and the doping and defect engineering could expand the light response range by regulating the electronic band structure. Strong evidence provided by experimental results and DFT calculations proved the Z-scheme charge transfer pathway. This work not only provided a novel approach to integrate 0D nanodots and 2D nanosheets for the formation of intimate Z-scheme heterointerfaces but also deepened the understanding of the dopant–defect synergistic modification to optimize the band structure and electronic structures for high-efficient solar energy capture and conversion.

Generation of singlet oxygen over CeO2/K,Na-codoped g-C3N4 for tetracycline hydrochloride degradation over a wide pH range

“…The peaks at μ′ and ν′ are ascribed to Ce 3+ , and the other peaks belong to Ce 4+ , suggesting the existence of Ce 3+ and oxygen vacancies in CeO 2 /CN. 35,52,67,68 Compared with CeO 2 , all the peaks of Ce 3d for CeO 2 /CN present a negative shift (see Table S1†), indicating the existence of strong interaction between CeO 2 and CN. The high-resolution XPS spectra of O 1s (Fig.…”

“…The peaks at μ′ and ν′ are ascribed to Ce 3+ , and the other peaks belong to Ce 4+ , suggesting the existence of Ce 3+ and oxygen vacancies in CeO 2 /CN. 35,52,67,68 Compared with CeO 2 , all the peaks of Ce 3d for CeO 2 /CN present a negative shift (see…”

“…32,34,43,45,46–48 For example, the doping of Na in g-C 3 N 4 leads to the electron transfer from Na to the complex N 2C of g-C 3 N 4 . 34 The g-C 3 N 4 /CeO 2 heterojunctions have been extensively investigated for photocatalytic/photo-Fenton pollutant degradation, 46,49–51 H 2 production, 52 CO 2 reduction, 29 and antibacterial applications 35 owing to the enhanced adsorption of visible lights and charge separation efficiency. In a 0D/2D S-scheme CeO 2 QDs/PCN heterojunction, 35 it was found that the electrons could migrate from g-C 3 N 4 to CeO 2 of CeO 2 /g-C 3 N 4 in darkness, but reverse electron transfer process was observed under illumination by in situ XPS studies and theoretical calculations.…”

Point‐to‐face contact heterojunctions: Interfacial design of 0D nanomaterials on 2D g‐C3N4 towards photocatalytic energy applications

“…In addition to the “veteran” TiO 2 , other 0D metal oxide NPs, like CeO 2 , 164 Co 3 O 4 , 165 CoO, 166 and Fe 2 O 3 , 167 have also been used to promote the photocatalytic efficiency of g‐C 3 N 4 . Zhang et al 168 modified CeO 2 /g‐C 3 N 4 nanosheet photocatalysts using a two‐step approach involving solvothermal and calcination processes (Figure 10A,B). The uniqueness of the study was the double modification of the CeO 2 NPs by doping with Co and introduction of OV defects.…”

“…(A) TEM and (B) HRTEM images of Co‐CeO 2 –OVs/g‐C 3 N 4 . Reproduced with permission: Copyright 2021, American Chemical Society 168 . (C) Schematic diagram including (D) the zeta potential value, and HRTEM images (E) before and (F) after calcination for the fabrication of Fe 2 O 3 /g‐C 3 N 4 using a two‐step approach.…”