Semiconductor polymeric graphitic carbon nitride (g-C3N4) photocatalysts have attracted dramatically growing attention in the field of the visible-light-induced hydrogen evolution reaction (HER) because of their facile synthesis, easy functionalization, attractive electronic band structure, high physicochemical stability and photocatalytic activity. This review article presents a panorama of the latest advancements in the rational design and development of g-C3N4 and g-C3N4-based composite photocatalysts for HER application. Concretely, the review starts with the development history, synthetic strategy, electronic structure and physicochemical characteristics of g-C3N4 materials, followed by the rational design and engineering of various nanostructured g-C3N4 (e.g. thinner, highly crystalline, doped, and porous g-C3N4) photocatalysts for HER application. Then a series of highly efficient g-C3N4 (e.g., metal/g-C3N4, semiconductor/g-C3N4, metal organic framework/g-C3N4, carbon/g-C3N4, conducting polymer/g-C3N4, sensitizer/g-C3N4) composite photocatalysts are exemplified. Lastly, this review provides a comprehensive summary and outlook on the major challenges, opportunities, and inspiring perspectives for future research in this hot area on the basis of pioneering works. It is believed that the emerging g-C3N4-based photocatalysts will act as the “holy grail” for highly efficient photocatalytic HER under visible-light irradiation.

Semiconductor polymeric graphitic carbon nitride photocatalysts: the “holy grail” for the photocatalytic hydrogen evolution reaction under visible light

Although semiconductor photocatalysis has made great progresses as a promising solution to solve the problem of environmental pollution, the highly efficient decomposition of organic pollutants driven by sunlight is still a challenge. Herein, we successfully constructed a Z-scheme photocatalyst BiOCl-Au-CdS for the first time by stepwise deposition of Au and CdS. It was found that the Au nanoparticles (NPs) were selectively anchored on the {001} facets of BiOCl nanosheets in the process of photoreduction while CdS NPs were further in situ deposited on Au NPs via the strong S–Au interaction. Compared to BiOCl, BiOCl-Au, and BiOCl-CdS, the Z-scheme BiOCl-Au-CdS exhibited evidently higher sunlight-driven photocatalytic activity toward the degradations of anionic dye Methyl Orange, cationic dye Rhodamine B, colorless pollutant phenol, and antibiotic sulfadiazine. The radical trapping experiments indicated that ·OH, h+, and ·O2– are the main reactive species responsible for the degradations of organic pollutan...

Z-Scheme BiOCl-Au-CdS Heterostructure with Enhanced Sunlight-Driven Photocatalytic Activity in Degrading Water Dyes and Antibiotics

Heterojunction photocatalysts have attracted widespread interest in photocatalysis because of their high-efficiency interfacial charge-transfer characteristics of nanoarchitectures. In this study, ...

Ag-Bridged Z-Scheme 2D/2D Bi5FeTi3O15/g-C3N4 Heterojunction for Enhanced Photocatalysis: Mediator-Induced Interfacial Charge Transfer and Mechanism Insights.

Z-scheme 2D/3D g-C3N4@ZnO with enhanced photocatalytic activity for cephalexin oxidation under solar light

S-scheme heterojunction has attracted much attention due to its unique structure and interface interaction. Herein, AgBr/BiOBr heterojunction with surface oxygen vacancies (OVs) was in situ synthesized by a facile chemical method. It was found that the evolution rates of photoreduction of CO2 to CO and CH4 with 0.33AB are 212.6 and 5.7 μmol g−1 h−1 respectively, which are 9.2 and 5.2 times higher than those of pure BiOBr. It was demonstrated that the S-scheme band structure could improve the utilization of sunlight, increase the reduction power of photogenerated electrons, and enhance the separation and transfer of photogenerated charge carriers. Furthermore, the OVs on the surface of BiOBr for AgBr/BiOBr heterojunction are conductive to the adsorption and activation of CO2 molecules. The synergetic effect of S-scheme band structure and OVs on photocatalytic reduction of CO2 was discussed. The work provides a facile method for in situ construction of S-scheme heterojunction with defect for CO2 photoreduction.

In situ construction of S-scheme AgBr/BiOBr heterojunction with surface oxygen vacancy for boosting photocatalytic CO2 reduction with H2O

The mismatches of lattices and energy bands in heterojunction are the dominant factors restricting the generation efficiency of reactive oxygen species (ROS) that are powerful tools for water purification and anti-bacteria. In this paper, the mediated lattice matching role of amorphous Al 2 O 3 is presented for constructing the ternary g-C 3 N 4 /Al 2 O 3 /ZnO heterojunctions, which exhibit higher molecular oxygen activation performance than binary g-C 3 N 4 /ZnO and g-C 3 N 4 /Al 2 O 3 heterojunctions. The oxygen activation ability and the ROS generation were testified by the electron paramagnetic resonance (EPR) measurement, transformation of nitroblue tetrazolium (NBT) and degradation of methylene blue (MB). The ROS include superoxide anion radical ( O 2 − ) and consequent product of hydroxyl radical ( OH). The superior oxygen activation performance of the ternary heterojunctions can be attributed to the lattices matching of the mediated amorphous Al 2 O 3 and the resultant efficient cascade electron transfer.

Fabrication of ternary g-C3N4/Al2O3/ZnO heterojunctions based on cascade electron transfer toward molecular oxygen activation

Heterostructured Bi3O4Br/α-Bi2O3 nanocomposites are prepared via in situ one-step self-combustion of ionic liquids. Tetrabutylammonium bromide (TBAB) is employed to be fuel, complexing agent for ionic liquids, as well as the reactant supplying Br for the objective material. The ratio of Bi3O4Br/α-Bi2O3 can be easily adjusted by controlling the amount of TBAB. The heterojunctions show higher photocatalytic ability towards both azo dye methyl orange (MO) and colorless pollutant phenol. The electron spin resonance (ESR) test and p-nitro blue tetrazolium chloride (NBT) degradation result indicate that generation amounts of superoxide anion radicals ( O2−) over heterojunctions are less than that over pure Bi3O4Br. Photoelectrochemical measurements show that separation efficiencies of photo-generated electrons and holes are decreased after the combination of Bi3O4Br and α-Bi2O3. Work function test and scavenger experiments display that holes play key role for pollutant degradation and the position of holes on α-Bi2O3 is lowered via hybridization. Thus, the enhanced photocatalytic activity over composites can be attributed to the position decline of α-Bi2O3 valence band, thus improving the reactivity of holes in direct oxidation of pollutants. In this case, valence band position is confirmed to be more important than separation efficiency of charge carriers in affecting photocatalytic performance.

Comparison of importance between separation efficiency and valence band position: The case of heterostructured Bi 3 O 4 Br/α-Bi 2 O 3 photocatalysts

Fabrication of core-shell BiVO4@Fe2O3 heterojunctions for realizing photocatalytic hydrogen evolution via conduction band elevation

One-step construction of {001} facet-exposed BiOCl hybridized with Al2O3 for enhanced molecular oxygen activation

The main process of carbon dioxide (CO2) photoreduction is that excited electrons are transported to surface active sites to reduce adsorbed CO2 molecules. Obviously, electron transfer to the active site is one of the key steps in this process. However, current catalysts for CO2 adsorption, activation, and electron reduction occur in different locations, which greatly reduce the efficiency of photocatalysis. Herein, through a spontaneous chemical redox approach, the plasmonic photocatalysts of Au-BiOCl-OV with enhanced interfacial interaction were fabricated for visible light CO2 reduction through the simultaneous adsorption, activation and in situ reduction of CO2 without a sacrificial agent. By loading gold (Au) on the oxygen vacancy (OV), Au and BiOCl-OV formed a direct and tight interface contact, whose fine structure was confirmed by SEM, TEM, EPR and XPS, which not only effectively boosts the light utilization efficiency and the light carrier separation ability, but also can simultaneously adsorb, activate and in situ reduce carbon dioxide for highly efficient visible light photocatalysis. Thanks to the synergistic influence of Au and OV, Au-BiOCl-OV exhibits excellent photocatalytic performance without sacrificial agent and outstanding stability with a high CO and CH4 production yield, reaching 4.85 μmol g-1 h-1, which were 2.8 times higher than C-Au-BiOCl-OV (obtained by traditional NaBH4 reduction). This study proposes a new strategy for the production of high-performance collaborative catalysis in photocatalytic CO2 reduction.

Yi-lei Li

Papers

Fabrication of ternary g-C3N4/Al2O3/ZnO heterojunctions based on cascade electron transfer toward molecular oxygen activation

Comparison of importance between separation efficiency and valence band position: The case of heterostructured Bi 3 O 4 Br/α-Bi 2 O 3 photocatalysts

Fabrication of core-shell BiVO4@Fe2O3 heterojunctions for realizing photocatalytic hydrogen evolution via conduction band elevation

One-step construction of {001} facet-exposed BiOCl hybridized with Al2O3 for enhanced molecular oxygen activation

The simultaneous adsorption, activation and in situ reduction of carbon dioxide over Au-loading BiOCl with rich oxygen vacancies.