Fig 1

(a) Triazine and (b) tri-s-triazine structures of g-C3N4 32."

Fig 2

(a) The crystal structure of layered BP, (b) the front view of layered BP, (c) the vertical view of layered BP, and (d) the detailed lattice parameter of layered BP 37."

Fig 3

Band structures for n-layer BP calculated within the GW approach for n = 1–4 44. Zero energy corresponds to the center of the bandgap, blue circles show the band splitting near the gap. Color online."

Fig 4

Synthesis of graphene oxide by Hummers method 46."

Fig 5

Diagram of the synthesis process of ultra-thin porous Co3O4 nano sheet. Adapted from Applied Catalysis B: Environmental, Elsevier publisher 54."

Fig 6

The element composition of perovskite photocatalyst for the reduction of CO2 55 Dotted line box indicates layered perovskite."

Fig 7

Transition metals and sulfur group elements contained in about 40 kinds of TMDC displayed in color in the periodic table. Only part of Co, Rh, IR and Ni are shown in color, indicating that only part of these transition elements are layered. Adapted from Nature Chemistry, Springer publisher 68. Color online."

Fig 8

Reaction pathway of hydrogenation of CO2 at Ov in Ti2CO2 monolayer. I: CO2→ HCOO; II: HCOO → HCOOH; the blue lines represent desorption of formic acid; III: HCOOH → H2COOH; IV: H2COOH → HCHO + H2O 75. Color online."

Fig 9

Formation of coordination unsaturated ZnAl-LDH Nanosheets 22."

Fig 10

(a) UV-Vis diffuse reflectance spectra and (b) Tauc plots of gersiloxenes (x  =  0.1, 0.3, 0.5, 0.7, 0.9), GeH and Si6H3(OH)3; (c) schematic illustration of topotactic deintercalation of CaGe2−2xSi2x to gersiloxenes (GeH)1−x(SiOH)x (x  <   0.5) or (GeH)1−xSix(OH)0.5Hx−0.5(x ≥  0.5) 84. Ca, blue; Ge, green; H, white; O, red; Si, yellow. Color online."

Table 1

Preparation, modification methods, photocatalytic activity test conditions, and product yield of ultrathin layered catalyst for photocatalytic CO2 reduction"

Fig 11

Band structure of (a) BVO and (b) Co-doped BVO atomic layers; (c, d) density of states for O atoms of BVO atomic layers and for Co atoms of Co-doped BVO atomic layers 112."

Fig 12

ESR spectra of (A) ZnAl-1, (B) ZnAl-2, and (C) ZnAl-3; (D) UV-vis diffuse reflectance spectra of (a) ZnAl-1, (b) ZnAl-2, and (c) ZnAl-3 22. Each plot (A)–(C) contains spectra for (a) fresh catalyst, (b) catalyst after 20 min of visible light irradiation (λ > 400 nm), and (c) catalyst after 20 min of UV-Vis light irradiation. All ESR spectra were collected at room temperature under an Ar atmosphere. "

Fig 13

DFT calculations for calculated density of states of (A) V-defective o-BiVO4 single-unit-cell layer slab and (B) perfect o-BiVO4 single-·unit-cell layer slab along the [001] orientation; (C) positron lifetime spectrum of defects characterization for the Vv-rich and Vv-poor o-BiVO4 atomic layers; (D, E) schematic representation of trapped positrons 120."

Fig 14

(a) Photocatalytic CO2 → CO reduction activity of Cu/TiO2-2 for three consecutive runs, (b) high-resolution XPS spectra of the Cu 2p region of Cu/TiO2-2/24 h and Cu/TiO2-2, (c) UV-Vis absorption spectra of pristine TiO2, Cu/TiO2-2, Cu/TiO2-2/24 h, and Cu/TiO2/Air, (d) high-resolution XPS spectra of the O 1s region of Cu/TiO2-2/24 h and Cu/TiO2-2, (e) EDS mapping images of Cu/TiO2-2 125."

Fig 15

(a) PL spectra and (b) transient photocurrent responses of g-C3N4, NiAl-LDH, and g-C3N4/NiAl-LDH heterojunction photocatalysts; (c) Schematic illustration of the proposed mechanism for CO2 photoreduction in the g-C3N4/NiAl-LDH heterojunctions; (d) schematic illustration of the synthesis process of g-C3N4/NiAl-LDH hybrid heterojunctions 128."