Single-Atom Engineering of Covalent Organic Framework for Photocatalytic H2 Production Coupled with Benzylamine Oxidation.

In photocatalysis, reducing the exciton binding energy and boosting the conversion of excitons into free charge carriers are vital to enhance photocatalytic activity. This work presents a facile strategy of engineering Pt single atoms on a 2D hydrazone-based covalent organic framework (TCOF) to promote H2 production coupled with selective oxidation of benzylamine. The optimised TCOF-Pt SA photocatalyst with 3 wt% Pt single atom exhibited superior performance to TCOF and TCOF-supported Pt nanoparticle catalysts. The production rates of H2 and N-benzylidenebenzylamine over TCOF-Pt SA3 are 12.6 and 10.9 times higher than those over TCOF, respectively. Empirical characterisation and theoretical simulation showed that the atomically dispersed Pt is stabilised on the TCOF support through the coordinated N1 -Pt-C2 sites, thereby induing the local polarization and improving the dielectric constant to reach the low exciton binding energy. These phenomena led to the promotion of exciton dissociation into electrons and holes and the acceleration of the separation and transport of photoexcited charge carriers from bulk to the surface. This work provides new insights into the regulation of exciton effect for the design of advanced polymer photocatalysts.

Metal-Organic Frameworks for NOx Adsorption and Their Applications in Separation, Sensing, Catalysis, and Biology.

Nitrogen oxide (NOx ) is a family of poisonous and highly reactive gases formed when fuel is burned at high temperatures during anthropogenic behavior. It is a strong oxidizing agent that significantly contributes to the ozone and smog in the atmosphere. Thus, NOx removal is important for the ecological environment upon which the civilization depends. In recent decades, metal-organic frameworks (MOFs) have been regarded as ideal candidates to address these issues because they form a reticular structure between proper inorganic and organic constituents with ultrahigh porosity and high internal surface area. These characteristics render them chemically adaptable for NOx adsorption, separation, sensing, and catalysis. In additional, MOFs enable potential nitric oxide (NO) delivery for the signaling of molecular NO in the human body. Herein, the different advantages of MOFs for coping with current environmental burdens and improving the habitable environment of humans on the basis of NOx adsorption are reviewed.

FabricatingZ-scheme C-doped TiO2/rGO nanocomposites for enhanced photocatalytic NO removal.

It is attractive to explore practical approaches to optimize the photodegraded NO property of TiO2. Herein, a typicalZ-shaped heterojunction C-TiO2/rGO composed of carbon-doped TiO2and reductive graphene oxide (rGO) was constructed to optimize the NO removal efficiency through anin situone-pot hydrothermal process with glucose as reductant and dopant. The C-TiO2/rGO (0.11%) composite displays a remarkable NO removal performance of 40.6% under visible light illumination. It was found that the C-TiO2nanoparticles were tightly attached to the rGO sheets and had strong interactions with rGO, which induced a positive impact on not only the light absorption and photo-generated charge separation but also the NO adsorption and reactive oxygen species formation, resulting in boosted photodegrade NO activity. As to the photodegrade NO process over the C-TiO2/rGO, the HO•and O2•-were the dominant radicals, of which the O2•-radical originated from the interactions between C-TiO2and rGO. We proposed aZ-scheme mechanism to illuminate the advanced photocatalytic activity of C-TiO2/rGO. This work affords an approach to developing effective photocatalysts in the NO purification field.

Highly Selective Photocatalytic CO2 Methanation with Water Vapor on Single-Atom Platinum-Decorated Defective Carbon Nitride.

Solar-driven CO2 methanation with water is an important route to simultaneously address carbon neutrality and produce fuels. It is challenging to achieve high selectivity in CO2 methanation due to competing reactions. Nonetheless, aspects of the catalyst design can be controlled with meaningful effects on the catalytic outcomes. We report highly selective CO2 methanation with water vapor using a photocatalyst that integrates polymeric carbon nitride (CN) with single Pt atoms. As revealed by experimental characterization and theoretical simulations, the widely explored Pt-CN catalyst is adapted for selective CO2 methanation with our rationally designed synthetic method. The synthesis creates defects in CN along with formation of hydroxyl groups proximal to the coordinated Pt atoms. The photocatalyst exhibits high activity and carbon selectivity (99 %) for CH4 production in photocatalytic CO2 reduction with pure water. This work provides atomic scale insight into the design of photocatalysts for selective CO2 methanation.

Improved Oxygen Activation over a Carbon/Co3O4 Nanocomposite for Efficient Catalytic Oxidation of Formaldehyde at Room Temperature.

Oxygen activation is a key step in the catalytic oxidation of formaldehyde (HCHO) at room temperature. In this study, we synthesized a carbon/Co3O4 nanocomposite (C-Co3O4) as a solution to the insufficient capability of pristine Co3O4 (P-Co3O4) to activate oxygen for the first time. Oxygen activation was improved via carbon preventing the agglomeration of Co3O4 nanoparticles, resulting in small particles (approximately 7.7 nm) and more exposed active sites (oxygen vacancies and Co3+). The removal efficiency of C-Co3O4 for 1 ppm of HCHO remained above 90%, whereas P-Co3O4 was rapidly deactivated. In static tests, the CO2 selectivity of C-Co3O4 was close to 100%, far exceeding that of P-Co3O4 (42%). Various microscopic analyses indicated the formation and interaction of a composite structure between the C and Co3O4 interface. The carbon composite caused a disorder on the surface lattice of Co3O4, constructing more oxygen vacancies than P-Co3O4. Consequently, the surface reducibility of C-Co3O4 was improved, as was its ability to continuously activate oxygen and H2O into reactive oxygen species (ROS). We speculate that accelerated production of ROS helped rapidly degrade intermediates such as dioxymethylene, formate, and carbonate into CO2. In contrast, carbonate accumulation on P-Co3O4 surfaces containing less ROS may have caused P-Co3O4 inactivation. Compared with noble nanoparticles, this study provides a transition metal-based nanocomposite for HCHO oxidation with high efficiency, high selectivity, and low cost, which is meaningful for indoor air purification.

Graphdiyne: A Brilliant Hole Accumulator for Stable and Efficient Planar Perovskite Solar Cells.

Traditional carbon materials have demonstrated immense potential in perovskite solar cells (PSCs) owing to their superior electrical properties and environmental stability. Graphdiyne (GDY), as an emerging carbon allotrope, features uniformly distributed pores, endless design flexibility, and unique electronic character compared with traditional carbon materials. Herein, graphdiyne is introduced into the upper part of the perovskite (CH3 NH3 PbI3 ) layer by utilizing a GDY-containing antisolvent during the one-step synthesis of perovskite. Intriguingly, GDY plays an essential role in hole accumulation and transportation because of its higher Fermi level than perovskite. As a result, the automatic separation of photogenerated carriers inside the perovskite film is achieved. Furthermore, the Schottky barrier formed on the interface between perovskite and GDY guarantees the unidirectional hole transport from perovskite to GDY, thereby benefiting further extraction to the hole transport layer. Consequently, GDY-modified perovskite-based planar PSCs exhibit a boosted Jsc of 24.21 mA cm-2 and up to 19.6% power conversion efficiency owing to the increased efficient light utilization and charge extraction. The device with GDY modification exhibits less than 10% shrinkage after a month in ambience. Overall, this work demonstrates an easy method for the utilization of GDY to boost the charge extraction and environmental stability in PSCs.

Active Complexes on Engineered Crystal Facets of MnOx-CeO2 and Scale-Up Demonstration on an Air Cleaner for Indoor Formaldehyde Removal.

Crystal facet-dominated surfaces determine the formation of surface-active complexes, and engineering specific facets is desirable for improving the catalytic activity of routine transition-metal oxides that often deactivate at low temperatures. Herein, MnOx-CeO2 was synthetically administered to tailor the exposure of three major facets, and their distinct surface-active complexes concerning the formation and quantitative effects of oxygen vacancies, catalytically active zones, and active-site behaviors were unraveled. Compared with two other low-index facets {110} and {001}, MnOx-CeO2 with exposed {111} facet showed higher activity for formaldehyde oxidation and CO2 selectivity. However, the {110} facet did not increase activity despite generating additional oxygen vacancies. Oxygen vacancies were highly stable on the {111} facet, and its bulk lattice oxygen at high migration rates could replenish the consumption of surface lattice oxygen, which was associated with activity and stability. High catalytically active regions were exposed at the {111}-dominated surfaces, wherein the predominated Lewis acid-base properties facilitated oxygen mobility and activation. The mineralization pathways of formaldehyde were examined by a combination of in situ X-ray photoemission spectroscopy and diffuse reflectance infrared Fourier transform spectrometry. The MnOx-CeO2-111 catalysts were subsequently scaled up to work as filter substrates in a household air cleaner. In in-field pilot tests, 8 h of exposure to an average concentration of formaldehyde after start-up of the air cleaner attained the Excellent Class of Indoor Air Quality Objectives in Hong Kong.

In Situ Intermediates Determination and Cytotoxicological Assessment in Catalytic Oxidation of Formaldehyde: Implications for Catalyst Design and Selectivity Enhancement under Ambient Conditions.

Formation and decay of formaldehyde oxides (CH2OO) affect the complete oxidation of formaldehyde. However, the speciation and reactivity of CH2OO are poorly understood because of its extremely fast kinetics and indirect measurements. Herein, three isomers of CH2OO (i.e., main formic acid, small dioxirane, and minor CH2OO Criegee) were in situ determined and confirmed as primary intermediates of the room-temperature catalytic oxidation of formaldehyde with two reference catalysts, that is, TiO2/MnO x-CeO2 and Pt/MnO x-CeO2. CH2OO Criegee is quite reactive, whereas formic acid and dioxirane have longer lifetimes. The production, stabilization, and removal of the three intermediates are preferentially performed at high humidity, matching well with the decay rate of CH2OO at approximately 6.6 × 103 s-1 in humid feed gas faster than 4.0 × 103 s-1 in dry feed. By contrast, given that a thinner water/TiO2 interface was well-defined in TiO2/MnO x-CeO2, fewer reductions in the active sites and catalytic activity were found when humidity was decreased. Furthermore, lethal intermediates mostly captured at the TiO2/MnO x-CeO2 surface suppressed the toxic off-gas emissions. This study provides practical insights into the rational design and selectivity enhancement of a reliable catalytic process for indoor air purification under unfavorable ambient conditions.

Two-dimensional polyimide heterojunctions for the efficient removal of environmental pollutants under visible-light irradiation.

Two-dimensional (2D) heteromaterials with large interface contact and intimate interfacial charge transition have been considered to be an ideal model for constructing highly efficient photocatalysts. However, few studies have reported on these 2D heterojunctions. Herein, we report a series of new 2D heterojunctions comprising polyimide (PI) and perylene-3,4,9,10-tetracarboxylic dianhydride (TD). These heterojunctions, denoted as PI-TDx (where x represents the amount of TD added, i.e., x = 0.13, 0.18, 0.27, 0.54, and 1.08 g), were prepared by the solid thermal copolymerization of melamine (MA), pyromellitic dianhydride (PD), and different amounts of TD. FT-IR spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses were used to verify the 2D heterojunction structure. Photocatalytic experiments reveal that PI-TDx exhibit excellent and stable photocatalytic performance for the degradation of the organic dyes rhodamine B (RhB) and methyl violet (MV), as well as for the photoreduction of Cr(vi), under visible-light irradiation. Among the samples, PI-TD0.18 exhibits the best photocatalytic performance. Its activity is about 2.7 times and 7.5 times higher than that of individual PIMP (formed by MA and PD) and PIMT (formed by MA and TD) for RhB degradation, respectively. Notably, PI-TD0.18 retains a certain photocatalytic activity under light irradiation at 600 nm. The photocatalytic-mechanism study demonstrates that PI-TD0.18 has a classic type-II heterojunction. Its 2D heterojunction greatly enhances the visible-light absorption of the composites and effectively suppresses the radiation recombination of photogenerated carriers, thereby improving its charge transfer and separation abilities and providing excellent photocatalytic performance. This work may serve as an important reference for the design and construction of new highly efficient 2D organic conjugated-polymer photocatalysts.

Organophosphate flame retardants and bisphenol A in children's urine in Hong Kong: has the burden been underestimated?

The urine levels of organophosphate flame retardants (PFRs) and bisphenol A (BPA) in kindergarten children (n = 31, 4-6 years old, sampling performed in 2016) in Hong Kong were measured. The detection frequency of the target PFRs, tri(2-chloroethyl)phosphate (TCEP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(chloroisopropyl)phosphate (TCIPP), triphenyl phosphate (TPHP) and 2-ethylhexyl diphenyl phosphate (EHDPP) ranged from 52% to 84%. The 95th percentile urinary concentrations of TPHP, TDCIPP, TCIPP, EHDPP and TCEP were 1.70, 0.24, 0.03, 0.05, 0.68 and 0.03 ng/mL, respectively. The median urine level of BPA was 1.69 ng/mL, with a detection frequency of 77%. Due to the lack of metabolism information, two scenarios were used to calculate the estimated daily intake (EDI) of these compounds. Back-calculated EDIs of PFRs using the urinary excretion rates from in vivo animal data (scenario 2) were up to 2.97 µg/kg/d (TDCIPP), which was only a little less than that observed in a sample of American infants, and the reference dose (RfD), meaning that the potential health risk of TDCIPP cannot be ignored. Dust ingestion was suggested to be the major pathway of exposure to PFRs, but when the levels in dust and air particles in kindergartens in Hong Kong were used to predict EDIs, these values were nearly half as much as those predicted from urinary TDCIPP in this study. This suggested that children's PFRs burden may be underestimated when considering only PFR levels in dust or air. There is thus a need for further studies with large-scale surveys and investigation of exposure routes.

Environment-Friendly Carbon Quantum Dots/ZnFe2O4 Photocatalysts: Characterization, Biocompatibility, and Mechanisms for NO Removal.

A highly efficient and environmentally-friendly oxidation process is always desirable for air purification. This study reported a novel carbon quantum dots (CQDs)/ZnFe2O4 composite photocatalyst for the first time through a facile hydrothermal process. The CQDs/ZnFe2O4 (15 vol %) composite demonstrates stronger transient photocurrent response, approximately 8 times higher than that of ZnFe2O4, indicating superior transfer efficiency of photogenerated electrons and separation efficiency of photogenerated electron-hole pairs. Compared with pristine ZnFe2O4 nanoparticles, CQDs/ZnFe2O4 displayed enhanced photocatalytic activities on gaseous NOx removal and high selectivity for nitrate formation under visible light (λ > 420 nm) irradiation. Electron spin resonance analysis and a series of radical-trapping experiments showed that the reactive species contributing to NO elimination were ·O2- and ·OH radicals. The possible mechanisms were proposed regarding how CQDs improve the photocatalytic performance of ZnFe2O4. The CQDs are believed to act as an electron reservoir and transporter as well as a powerful energy-transfer component during the photocatalysis processes over CQDs/ZnFe2O4 samples. Furthermore, the toxicity assessment authenticated good biocompatibility and low cytotoxity of CQDs/ZnFe2O4. The results of this study indicate that CQDs/ZnFe2O4 is a promising photocatalyst for air purification.

A Hierarchical Z-Scheme CdS-WO3 Photocatalyst with Enhanced CO2 Reduction Activity.

The development of an artificial photosynthetic system is a promising strategy to convert solar energy into chemical fuels. Here, a direct Z-scheme CdS-WO(3) photocatalyst without an electron mediator is fabricated by imitating natural photosynthesis of green plants. Photocatalytic activities of as-prepared samples are evaluated on the basis of photocatalytic CO(2) reduction to form CH(4) under visible light irradiation. These Z-scheme-heterostructured samples show a higher photocatalytic CO(2) reduction than single-phase photocatalysts. An optimized CdS-WO(3) heterostructure sample exhibits the highest CH(4) production rate of 1.02 µmol h(-1) g(-1) with 5 mol% CdS content, which exceeds the rates observed in single-phase WO(3) and CdS samples for approximately 100 and ten times under the same reaction condition, respectively. The enhanced photocatalytic activity could be attributed to the formation of a hierarchical direct Z-scheme CdS-WO(3) photocatalyst, resulting in an efficient spatial separation of photo-induced electron-hole pairs. Reduction and oxidation catalytic centers are maintained in two different regions to minimize undesirable back reactions of the photocatalytic products. The introduction of CdS can enhance CO(2) molecule adsorption, thereby accelerating photocatalytic CO(2) reduction to CH(4). This study provides novel insights into the design and fabrication of high-performance artificial Z-scheme photocatalysts to perform photocatalytic CO(2) reduction.

Mechanism of NO Photocatalytic Oxidation on g-C3-N4 Was Changed by Pd-QDs Modification. [Corrected].

Quantum dot (QD) sensitization can increase the light absorption and electronic transmission of photocatalysts. However, limited studies have been conducted on the photocatalytic activity of photocatalysts after modification by noble metal QDs. In this study, we developed a simple method for fabricating Pd-QD-modified g-C3N4. Results showed that the modification of Pd-QDs can improve the NO photocatalytic oxidation activity of g-C3N4. Moreover, Pd-QD modification changed the NO oxidation mechanism from the synergistic action of h⁺ and O2(-) to the single action of ·OH. We found that the main reason for the mechanism change was that Pd-QD modification changed the molecular oxygen activation pathway from single-electron reduction to two-electron reduction. This study can not only develop a novel strategy for modifying Pd-QDs on the surface of photocatalysts, but also provides insight into the relationship between Pd-QD modification and the NO photocatalytic oxidation activity of semiconductor photocatalysts.

Immobilization of polymeric g-C3N4 on structured ceramic foam for efficient visible light photocatalytic air purification with real indoor illumination.

The immobilization of a photocatalyst on a proper support is pivotal for practical environmental applications. In this work, graphitic carbon nitride (g-C3N4) as a rising visible light photocatalyst was first immobilized on structured Al2O3 ceramic foam by a novel in situ approach. Immobilized g-C3N4 was applied for photocatalytic removal of 600 ppb level NO in air under real indoor illumination of an energy-saving lamp. The photocatalytic activity of immobilized g-C3N4 was gradually improved as the pyrolysis temperature was increased from 450 to 600 °C. The optimized conditions for g-C3N4 immobilization on Al2O3 supports can be achieved at 600 °C for 2 h. The NO removal ratio could reach up to 77.1%, exceeding that of other types of well-known immobilized photocatalysts. Immobilized g-C3N4 was stable in activity and can be used repeatedly without deactivation. The immobilization of g-C3N4 on Al2O3 ceramic foam was found to be firm enough to overwhelm the continuous air flowing, which can be ascribed to the special chemical interaction between g-C3N4 and Al2O3. On the basis of the 5,5'-dimethyl-1-pirroline-N-oxide electron spin resonance (DMPO ESR) spin trapping and reaction intermediate monitoring, the active species produced from g-C3N4 under illumination were confirmed and the reaction mechanism of photocatalytic NO oxidation by g-C3N4 was revealed. The present work could provide new perspectives for promoting large-scale environmental applications of supported photocatalysts.

Novel in situ N-doped (BiO)2CO3 hierarchical microspheres self-assembled by nanosheets as efficient and durable visible light driven photocatalyst.

Novel N-doped (BiO)(2)CO(3) hierarchical microspheres (N-BOC) were fabricated by a facile one-pot template free method on the basis of hydrothermal treatment of bismuth citrate and urea in water for the first time. The N-BOC sample was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, N(2) adsorption-desorption isotherms, and Fourier transform-infrared spectroscopy. The N-BOC was constructed by the self-assembly of single-crystalline nanosheets. The aggregation of nanosheets led to the formation of hierarchical framework with mesopores, which is favorable for efficient transport of reaction molecules and harvesting of photoenergy. Due to the in situ doped nitrogen substituting for oxygen in the lattice of (BiO)(2)CO(3), the band gap of N-BOC was reduced from 3.4 to 2.5 eV, making N-BOC visible light active. The N-BOC exhibited not only excellent visible light photocatalytic activity, but also high photochemical stability and durability during repeated and long-term photocatalytic removal of NO in air due to the special hierarchical structure. This work demonstrates that the facile fabrication method for N-BOC combined with the associated outstanding visible light photocatalytic performance could provide new insights into the morphology-controlled fabrication of nanostructured photocatalytic materials for environmental pollution control.

Construction and Activity of an All-Organic Heterojunction Photocatalyst Based on Melem and Pyromellitic Dianhydride.

Invited for this month's cover is the group of Wingkei Ho at The Education University of Hong Kong. The Cover shows the effect of the number of heterojunction knots in an all-organic photocatalyst on the separation of photogenerated carriers. The heterojunction knots could improve the migration efficiency of carriers between Melem and the formed pyromellitic diimide. The oxygen adsorbed on the surface of the material can be reduced by electrons to the reactive oxygen species superoxide anion (⋅O2 - ), thereby achieving the purpose of removing pollutants. The Research Article itself is available at 10.1002/cssc.202200477.

Construction and Activity of an All-Organic Heterojunction Photocatalyst Based on Melem and Pyromellitic Dianhydride.

The separation efficiency of photogenerated carriers in the g-C3 N4 system could be improved by the construction of all-organic heterojunctions. However, g-C3 N4 has a large π-π conjugated plane that induces a low number of amino groups (-NH2 ), which are the sites of the heterojunction reaction with organic molecules. In this case, few heterojunction knots can be constructed, and the enhancement effect of the heterojunction cannot be fully displayed. In this study, an all-organic heterojunction with PMDA is constructed with melem instead of g-C3 N4 . Although the photocatalytic activity of melem is far below that of g-C3 N4 , the photocatalytic activity of PI (the all-organic heterojunction constructed with melem) is considerably higher than that of CP (the all-organic heterojunction constructed with g-C3 N4 ). This result is attributed to melem that has more -NH2 groups to form more heterojunction knots, which can enable the effective transfer and separation of electron-hole pairs. These new findings may shed light on the design of all-organic heterojunction photocatalysts.

Exploring the photocatalytic conversion mechanism of gaseous formaldehyde degradation on TiO2-x-OV surface.

To understand the conversion mechanism of photocatalytic gaseous formaldehyde (HCHO) degradation, strontium (Sr)-doped TiO2-x-OV catalysts was designed and synthesized in this study, with comparable HCHO removal performance. Our results proved that foreign-element doping reduced Ti4+ to the lower oxidation state Ti(4- x)+, and that the internal charge kinetics was largely facilitated by the unbalanced electron distribution. Oxygen vacancies (OVs) were developed spontaneously to realize an electron-localized phenomenon in TiO2-x-OV, thereby boosting O2 adsorption and activation for the enhanced generation of reactive oxygen species (ROS). At the chemisorption stage, in-situ DRIFTS spectra and density functional theory calculation results revealed that surface adsorbed O2 (Oads) and lattice O (Olat) engaged in the isomerisation of HCHO to dioxymethylene (DOM) on TiO2-x-OV and TiO2, respectively. Time-resolved DRIFTS spectra under light irradiation revealed that the DOM was then converted to formate and thoroughly oxidized to CO2 and H2O in TiO2-x-OV. While bicarbonate byproducts were detected from DOM hydroxylation or possible side conversion of CO2 in TiO2, owing to insufficient consumption of surface hydroxyl. Our study enhances the understanding on the photocatalytic oxidation of HCHO, thereby promoting the practical application in indoor air purification.

Review on nickel-based adsorption materials for Congo red.

Excessive synthetic dyestuffs in the aquatic environment pose various ecological and health issues that are detrimental to sustainable development. Adsorption is considered a feasible technique of eliminating dye pollutants from the water environment because of its advantages of high efficiency, low cost, easy operation, and absence of secondary pollution. Among the many dyes, Congo red (CR) is a widely used azo dye. Nickel-based materials, including nickel hydroxide, nickel oxide, nickel-containing layered double hydroxides, nickel-based spinel and metal-organic frameworks, metallic nickel, nickel-based sulfide, and nickel composites, have been extensively studied for CR adsorption due to their morphological diversity, large specific surface area, and strong affinity toward CR. However, fabricating nickel-based adsorbents with high efficiency and stability and excellent recyclability for practical application remains a challenge. This review outlines the research progress of nickel-based materials in CR adsorption. The interaction between CR molecules and nickel-based adsorbents is systematically presented, and the possible adsorption mechanisms are summarized. Finally, the challenges and future development directions of the practical application of nickel-based adsorbent materials are proposed.

Design, Fabrication, and Mechanism of Nitrogen-Doped Graphene-Based Photocatalyst.

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.