Solving energy and environmental problems through solar‐driven photocatalysis is an attractive and challenging topic. Hence, various types of photocatalysts have been developed successively to ...address the demands of photocatalysis. Graphene‐based materials have elicited considerable attention since the discovery of graphene. As a derivative of graphene, nitrogen‐doped graphene (NG) particularly stands out. Nitrogen atoms can break the undifferentiated structure of graphene and open the bandgap while endowing graphene with an uneven electron density distribution. Therefore, NG retains nearly all the advantages of original graphene and is equipped with several novel properties, ensuring infinite possibilities for NG‐based photocatalysis. This review introduces the atomic and band structures of NG, summarizes in situ and ex situ synthesis methods, highlights the mechanism and advantages of NG in photocatalysis, and outlines its applications in different photocatalysis directions (primarily hydrogen production, CO2 reduction, pollutant degradation, and as photoactive ingredient). Lastly, the central challenges and possible improvements of NG‐based photocatalysis in the future are presented. This study is expected to learn from the past and achieve progress toward the future for NG‐based photocatalysis.
Nitrogen‐doped graphene plays a significant role in photocatalysis. Rational design, preparation, and understanding the mechanism of N‐doped graphene‐based photocatalysts provides a new opportunity to further enhance the photocatalytic performance. The research progress, atomic and band structures, photocatalytic mechanism, synthesis strategy, unique advantages, and wide application of N‐doped graphene in photocatalysis are highlighted.
Metal‐oxide photocatalysts have demonstrated great potential in photocatalytic H2O2 production. This review focuses on metal‐oxide‐based photocatalytic materials for H2O2 production and ...systematically discusses their pros and cons, modification strategies for enhanced performance, and prospects on future research directions. This review also summarizes the quantification methods for H2O2 and associated intermediates to provide guidance for future research in this area.
Hydrogen peroxide (H2O2) is a mild but versatile oxidizing agent with extensive applications in bleaching, wastewater purification, medical treatment, and chemical synthesis. The state‐of‐art H2O2 production via anthraquinone oxidation is hardly considered a cost‐efficient and environment‐friendly process because it requires high energy input and generates hazardous organic wastes. Photocatalytic H2O2 production is a green, sustainable, and inexpensive process which only needs water and gaseous dioxygen as the raw materials and sunlight as the power source. Inorganic metal oxide semiconductors are good candidates for photocatalytic H2O2 production due to their abundance in nature, biocompatibility, exceptional stability, and low cost. Progress has been made to enhance the photocatalytic activity toward H2O2 production, however, H2O2 photosynthesis is still in the laboratory research phase since the productivity is far from satisfaction. To inspire innovative ideas for boosting the H2O2 yield in photocatalysis, the most well‐studied metal oxide photocatalysts are selected and the modification strategies to improve their activity are listed. The mechanisms for H2O2 production over modified photocatalysts are discussed to highlight the facilitating role of the modification methods. Besides, methods for the quantification of H2O2 and associated radical intermediates are provided to guide future studies in this field.
CdS is one of the most well-known and important visible-light photocatalytic materials for water splitting to produce hydrogen energy. Owing to its serious photocorrosion property (poor photoinduced ...stability), however, CdS photocatalyst can unavoidably be oxidized to form S0 by its photogenerated holes, causing an obviously decreased photocatalytic performance. In this study, to improve the photoinduced stability of CdS photocatalyst, amorphous TiO2 (referred to as Ti(IV)) as a hole cocatalyst was successfully loaded on the CdS surface to prepare Ti(IV)/CdS photocatalysts. It was found that the resultant Ti(IV)/CdS photocatalyst exhibited an obviously enhanced photocatalytic stability, namely, its deactivation rate clearly decreased from 37.9% to 13.5% after five cycles of photocatalytic reactions. However, its corresponding photocatalytic activity only showed a very limited increase (ca. 37.4%) compared with the naked CdS. To further improve its photocatalytic performance, the amorphous Ni(II) as an electron cocatalyst was subsequently modified on the Ti(IV)/CdS surface to prepare the dual amorphous-cocatalyst modified Ti(IV)–Ni(II)/CdS photocatalyst. In this case, the resultant Ti(IV)–Ni(II)/CdS photocatalyst not only exhibited a significantly improved photocatalytic activity and stability, but also could maintain the excellent photoinduced stability of CdS surface structure. Based on the experimental results, a synergistic effect of dual amorphous Ti(IV)–Ni(II) cocatalysts is proposed, namely, the amorphous Ti(IV) works as a hole-cocatalyst to rapidly capture the photogenerated holes from CdS surface, causing the less oxidation of surface lattice S2– ions in CdS, while the amorphous Ni(II) functions as an electron-cocatalyst to rapidly transfer the photogenerated electrons and then promote their following interfacial H2-evolution reaction. Compared with the traditional noble metal cocatalysts (such as Pt and RuO2), the present amorphous Ti(IV) and Ni(II) cocatalysts are apparently low-cost, nontoxic, and earth-abundant, which can widely be applied in the design and development of highly efficient photocatalytic materials.
A stable catalyst: Ag2O is unstable under visible‐light irradiation and decomposes into metallic Ag during the photocatalytic decomposition of organic substances. However, after partial in situ ...formation of Ag on the surface of Ag2O, the Ag2OAg composite can work as a stable and efficient visible‐light photocatalyst (see figure; CB= conduction band, VB=valence band, e−=electrons, h= holes).
The interaction between a co‐catalyst and photocatalyst usually induces spontaneous free‐electron transfer between them, but the effect and regulation of the transfer direction on the ...hydrogen‐adsorption energy of the active sites have not received attention. Herein, to steer the free‐electron transfer in a favorable direction for weakening S−Hads bonds of sulfur‐rich MoS2+x, an electron‐reversal strategy is proposed for the first time. The core–shell Au@MoS2+x cocatalyst was constructed on TiO2 to optimize the antibonding‐orbital occupancy. Research results reveal that the embedded Au can reverse the electron transfer to MoS2+x to generate electron‐rich S(2+δ)− active sites, thus increasing the antibonding‐orbital occupancy of S−Hads in the Au@MoS2+x cocatalyst. Consequently, the increase in the antibonding‐orbital occupancy effectively destabilizes the H 1s‐p antibonding orbital and weakens the S−Hads bond, realizing the expedited desorption of Hads to rapidly generate a lot of visible H2 bubbles. This work delves deep into the latent effect of the photocatalyst carrier on cocatalytic activity.
To create a beneficial transfer direction for cultivating moderate hydrogen‐atom adsorption/desorption on a co‐catalyst, an electron‐reversal strategy is proposed that optimizes the antibonding‐orbital occupancy. The embedded Au can reverse the free‐electron transfer to MoS2+x to form electron‐rich S(2+δ)−, which causes an increased antibonding‐orbital occupancy, thus weakening S−Hads bonds for photocatalytic H2 evolution.
Hexagonal molybdenum carbide (Mo
2
C) as an effective non-noble cocatalyst is intensively researched in the photocatalytic H
2
-evolution field owing to its Pt-like H
+
-adsorption ability and good ...conductivity. However, hexagonal Mo
2
C-modified photocatalysts possess a limited H
2
-evolution rate because of the weak H-desorption ability. To further improve the activity, cubic MoC was introduced into Mo
2
C to form the carbon-modified MoC-Mo
2
C nanoparticles (MoC-Mo
2
C@C) by a calcination method. The resultant MoC-Mo
2
C@C (ca. 5 nm) was eventually coupled with TiO
2
to acquire high-efficiency TiO
2
/MoC-Mo
2
C@C by electrostatic self-assembly. The highest H2-generation rate of TiO
2
/MoC-Mo
2
C@C reached of 918 μmol·h−1·g−1, which was 91.8, 2.7, and 1.5 times than that of the TiO
2
, TiO
2
/MoC@C, and TiO
2
/Mo
2
C@C, respectively. The enhanced rate of TiO
2
attributes to the carbon layer as cocatalyst to transmit electrons and the hetero-phase MoC-Mo
2
C as H
2
-generation active sites to boost H
2
-evolution reaction. This research offers a novel insight to design photocatalytic materials for energy applications.
The preferential adsorption of targeted contaminants on a photocatalyst surface is highly required to realize its photocatalytic selective decomposition in a complex system. To realize the tunable ...preferential adsorption, altering the surface charge or polarity property of photocatalysts has widely been reported. However, it is quite difficult for a modified photocatalyst to realize the simultaneously preferential adsorption for both cationic and anionic dyes. In this study, to realize the selective adsorption for both cationic and anionic dyes on a photocatalyst surface, the negative reduced graphene oxide (rGO) nanosheets and positive phenylamine (PhNH2) molecules are successfully loaded on the TiO2 surface (PhNH2/rGO-TiO2) with spatially separated adsorption sites, where the negative rGO and positive PhNH2 molecules work as the preferential adsorption sites for cationic and anionic dyes, respectively. It was interesting to find that although all the TiO2 samples (including the naked TiO2, PhNH2/TiO2, rGO-TiO2, and PhNH2/rGO-TiO2) clearly showed a better adsorption performance for cationic dyes than anionic dyes, only the PhNH2/rGO-TiO2 with spatially separated adsorption-active sites exhibited an opposite photocatalytic selectivity, namely, the naked TiO2, PhNH2/TiO2, and rGO-TiO2 showed a preferential decomposition for cationic dyes, while the resultant PhNH2/rGO-TiO2 exhibited an excellently selective decomposition for anionic dyes. In addition, the resultant PhNH2/rGO-TiO2 photocatalyst not only realizes the tunable photocatalytic selectivity but also can completely and sequentially decompose the opposite cationic and anionic dyes.
Bimodal mesoporous anatase-phase TiO
2 hollow microspheres are one-pot fabricated by hydrothermal treatment of acidic Ti(SO
4)
2 solution with NH
4F. Fluoride not only induces the outward hollowing ...of the spherical TiO
2 aggregates, but also promotes the crystallization of primary anatase TiO
2 nanocrystals, resulting in enlarged crystallite sizes and decreased specific surface areas. The hierarchical mesopores exhibit peak intra-aggregated mesopore sizes of 3–10 nm and peak interaggregated mesopore sizes of 30–50 nm, depending on the specific molar ratio of fluoride to titanium (
R
). The pore volume increases in parallel with the average pore size with increasing
R
until the collapse of interaggregated pores at
R
=
2
. The photocatalytic efficiency in decomposition of gaseous acetone by as-obtained hollow TiO
2 microspheres generally exceeds that by Degussa P25 when
R
is <2. The influence of fluoride on photoactivity are discussed in terms of phase structures and pore structures.
Through the use of a strategy that involves narrowing the TiO2 band gap by shifting its conduction band positively and utilizing the catalytic activity of photoproduced Cu(I) for oxygen reduction, a ...novel visible-light-sensitive TiO2 photocatalyst, Cu(II)-grafted Ti1−3x W x Ga2x O2, was designed and synthesized. The Cu(II)/Ti1−3x W x Ga2x O2 photocatalyst produced high activity under visible-light irradiation. In fact, it decomposed 2-propanol to CO2 via acetone under visible light (>400 nm) with a high quantum efficiency of 13%. The turnover number for this reaction exceeded 22, indicating that it functioned catalytically.
