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Photothermal CO2 reduction is an efficient and sustainable catalytic path for CO2 treatment. Here, we successfully fabricated a novel series of Ni-based catalysts (Ni-x) via H2 reduction of NiAl-layered double hydroxide nanosheets at temperatures (x) ranging from 300 to 600 °C. With the increase of the reduction temperature, the methane generation rate of the Ni-x catalyst for photothermal CO2 hydrogenation gradually increased under ultraviolet-visible-infrared (UV-vis-IR) irradiation in a flow-type system. The Ni-600 catalyst showed a CO2 conversion of 78.4%, offering a CH4 production rate of 278.8 mmol·g−1h−1, with near 100% selectivity and 100 h long-term stability. Detailed characterization analyses showed metallic Ni nanoparticles supported on amorphous alumina are the catalytically active phase for CO2 methanation. This study provides a possibility for large-scale conversion and utilization of CO2 from a sustainable perspective.

Developing low-energy input route for conversion of methane (CH4) to value-added methanol (CH3OH) at room temperature is important in environment and industry. Bonding in electron donor-acceptor hybrid can potentially promote charge transfer and photocatalytic efficiency of CH4 conversion. Herein, bonding in electron donor rhodamine B (RhB)-acceptor (TiO2) hybrid (RhB/TiO2) significantly promotes the selectivity of photocatalytic oxidation of CH4 to CH3OH and utilization of visible light (low-energy photons) at ambient condition. Even under green light irradiation (λ = 550 nm), the noble-metal-free RhB/TiO2 hybrid synthesized presents enhanced oxidation of CH4 to CH3OH with a generation rate of 143 µmol·g−1·h−1 and selectivity of 94%. This work demonstrates the possibility and feasibility of noble-metal-free catalysts for activating CH4 under visible light at room temperature.

Designing bifunctional catalysts capable of driving the electrochemical hydrogen evolution reaction (HER) and also H2 evolution via the hydrolysis of hydrogen storage materials such as ammonia borane (AB) is of considerable practical importance for future hydrogen economies. Herein, we systematically examined the effect of tensile lattice strain in CoRu nanoalloys supported on carbon quantum dots (CoRu/CQDs) on hydrogen generation by HER and AB hydrolysis. By varying the Ru content, the lattice parameters and Ru-induced lattice strain in the CoRu nanoalloys could be tuned. The CoRu0.5 /CQDs catalyst with an ultra-low Ru content (1.33 wt.%) exhibited excellent catalytic activity for HER (η=18 mV at 10 mA cm-2 in 1 M KOH) and extraordinary activity for the hydrolysis of AB with a turnover frequency of 3255.4 mol ( H 2 ) mol-1 (Ru) min-1 or 814.7 mol ( H 2 ) mol-1 (cat) min-1 at 298 K, respectively, representing one of the best activities yet reported for AB hydrolysis over a ruthenium alloy catalyst. Moreover, the CoRu0.5 /CQDs catalyst displayed excellent stability during each reaction, including seven alternating cycles of HER and AB hydrolysis. Theoretical calculations revealed that the remarkable catalytic performance of CoRu0.5 /CQDs resulted from the optimal alloy electronic structure realized by incorporating small amounts of Ru, which enabled fast interfacial electron transfer to intermediates, thus benefitting H2 evolution kinetics. Results support the development of new and improved catalysts HER and AB hydrolysis.

Cu2 O, a low-cost, visible light responsive semiconductor photocatalyst represents an ideal candidate for visible light driven photocatalytic reduction of N2 to NH3 from the viewpoint of thermodynamics, but it remains unexplored. Reported here is the successful synthesis of uniformly sized and ultrafine Cu2 O platelets, with a lateral size of Cu 2 O -1 h-1 at λ>400 nm), with the origin of the high activity being long-lived photoexcited electrons in trap states, an abundance of exposed active sites, and the underlying support structure. This work guides the future design of ultrafine catalysts for NH3 synthesis and other applications.

Photothermal Fischer-Tropsch synthesis(FTS) has been extensively studied, but few reports were focused on systematically exploring the influence of support on catalytic performance. Herein, a series of Fe5C2-based catalysts with different supports was fabricated via a one-step wet-chemical method for photothermal conversion of syngas to lower olefins. Under light irradiation, the optimized Fe5C2/α-Al2O3 catalyst demonstrated remarkable photothermal FTS activity, delivering selectivity to lower olefins of 50.3% with a CO conversion rate of 52.5%. Characterization studies using X-ray diffraction and Mossbauer spectroscopy analysis revealed that the active catalyst mainly contained Fe5C2 nanoparticles on α-Al2O3 support. It was found that the weak interaction between active phase and α-Al2O3 could promote the formation of Fe5C2, which contributed to the high selectivity to lower olefins.

The pyrolysis of zeolitic imidazolate frameworks (ZIFs) is becoming a popular approach for the synthesis of catalysts comprising porphyrin-like metal single atom catalysts (SACs) on N-doped carbons (M-N-C). Understanding the structural evolution of M-N-C as a function of ZIF pyrolysis temperature is important for realizing high performance catalysts. Herein, we report a detailed investigation of the evolution of Zn single atom catalyst sites during the pyrolysis of ZIF-8 at temperatures ranging from 500 to 900 °C. Results from Zn L-edge and Zn K-edge X-ray absorption spectroscopy studies reveal that tetrahedral ZnN4 centers in ZIF-8 transform to porphyrin-like ZnN4 centers supported on N-doped carbon at temperatures as low as 600 °C. As the pyrolysis temperature increased in the range 600–900 °C, the Zn atoms moved closer to the N4 coordination plane. This subtle geometry change in the ZnN4 sites alters the electron density on the Zn atoms (formally Zn2+), strongly impacting the catalytic performance for the peroxidase-like decomposition of H2O2. The catalyst obtained at 800 °C (Zn-N-C-800) offered the best performance for H2O2 decomposition. This work provides valuable new insights about the evolution of porphyrin-like single metal sites on N-doped carbons from ZIF precursors and the factors influencing SAC activity.

Reduction of CO2 to solar fuels by artificial photosynthesis technology has attracted considerable attention. However, insufficient separation of charge carriers and weak CO2 adsorption hamper the photocatalytic CO2 reduction activity. Herein, we tackle these challenges by introducing oxygen vacancies (OVs) on the two-dimensional Bi4Ti3O12 ultrathin nanosheets via a combined hydrothermal and post-reduction process. Selective photodeposition experiment of Pt over Bi4Ti3O12 discloses that the ultrathin structure shortens the migration distance of photo-induced electrons from bulk to the surface, benefiting the fast participation in the CO2 reduction reaction. The introduction of OVs on ultrathin Bi4Ti3O12 nanosheets leads to enormous amelioration on surface state and electronic structure, thereby resulting in enhanced CO2 adsorption, photoabsorption and charge separation efficiency. The photocatalytic experiments uncover that ultrathin Bi4Ti3O12 nanosheets with OVs reveal a largely enhanced CO2 photoreduction activity for producing CO with a rate of 11.7 μmol g−1 h−1 in the gas–solid system, ~3.2 times higher than that of bulk Bi4Ti3O12. This work not only yields efficient ultrathin photocatalysts with OVs, but also furthers our understanding on enhancing CO2 reduction via cooperative tactics.

The electrochemical CO2 reduction reaction (CO2RR) represents a very promising future strategy for synthesizing carbon-containing chemicals in a more sustainable way. In spite of great progress in electrocatalyst design over the last decade, the critical role of wettability-controlled interfacial structures for CO2RR remains largely unexplored. Here, we systematically modify the structure of gas-liquid-solid interfaces over a typical Au/C gas diffusion electrode through wettability modification to reveal its contribution to interfacial CO2 transportation and electroreduction. Based on confocal laser scanning microscopy measurements, the Cassie-Wenzel coexistence state is demonstrated to be the ideal three phase structure for continuous CO2 supply from gas phase to Au active sites at high current densities. The pivotal role of interfacial structure for the stabilization of the interfacial CO2 concentration during CO2RR is quantitatively analysed through a newly-developed in-situ fluorescence electrochemical spectroscopic method, pinpointing the necessary CO2 mass transfer conditions for CO2RR operation at high current densities., Great advances have been made in CO2 electroreduction, however, the role of wettability-controlled interfacial structures remains poorly understood. Here, the authors apply confocal laser scanning microscopy to gain deeper understanding of these phenomena in gas diffusion electrodes.

Photocatalytic CO2 reduction holds promise as a future technology for the manufacture of fuels and commodity chemicals. However, factors controlling product selectivity remain poorly understood. Herein, we compared the performance of a homologous series of Zn-based layered double hydroxide (ZnM-LDH) photocatalysts for CO2 reduction. By varying the trivalent or tetravalent metal cations in the ZnM-LDH photocatalysts (M = Ti4+, Fe3+, Co3+, Ga3+, Al3+), the product selectivity of the reaction could be precisely controlled. ZnTi-LDH afforded CH4 as the main reduction product; ZnFe-LDH and ZnCo-LDH yielded H2 exclusively from water splitting; whilst ZnGa-LDH and ZnAl-LDH generated CO. In-situ diffuse reflectance infrared measurements, valence band XPS and density function theory calculations were applied to rationalize the CO2 reduction selectivities of the different ZnM-LDH photocatalysts. The analyses revealed that the d-band center (ed) position of the M3+ or M4+ cations controlled the adsorption strength of CO2 and thus the selectivity to carbon-containing products or H2. Cations with d-band centers relatively close to the Fermi level (Ti4+, Ga3+ and Al3+) adsorbed CO2 strongly yielding CH4 or CO, whereas metal cations with d-band centers further from the Fermi level (Fe3+ and Co3+) adsorbed CO2 poorly, thereby yielding H2 only (from water splitting). Our findings clarify the role of trivalent and tetravalent metal cations in LDH photocatalysts for the selective CO2 reduction, paving new ways for the development of improved LDH photocatalyst with high selectivities to specific products.

Carbon-supported NiII single-atom catalysts with a tetradentate Ni-N2 O2 coordination formed by a Schiff base ligand-mediated pyrolysis strategy are presented. A NiII complex of the Schiff base ligand (R,R)-(-)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine was adsorbed onto a carbon black support, followed by pyrolysis of the modified carbon material at 300 °C in Ar. The Ni-N2 O2 /C catalyst showed excellent performance for the electrocatalytic reduction of O2 to H2 O2 through a two-electron transfer process in alkaline conditions, with a H2 O2 selectivity of 96 %. At a current density of 70 mA cm-2 , a H2 O2 production rate of 5.9 mol gcat. -1 h-1 was achieved using a three-phase flow cell, with good catalyst stability maintained over 8 h of testing. The Ni-N2 O2 /C catalyst could electrocatalytically reduce O2 in air to H2 O2 at a high current density, still affording a high H2 O2 selectivity (>90 %). A precise Ni-N2 O2 coordination was key to the performance.

In recent years, two-dimensional (2D) semiconductor photocatalysts have been widely applied in water splitting, CO2 reduction, N2 fixation, as well as many other important photoreactions. Photocatalysts in the form of 2D nanosheet possess many inherent advantages over traditional 3D nanopowder photocatalysts, including improved light absorption characteristics, shorter electron and hole migration paths to the photocatalysts’ surface (thus minimizing undesirable electron-hole pair recombination), and abundant surface defects which allow band gap modulation and facilitate charge transfer from the semiconductor to adsorbates. When synergistically exploited and optimized, these advantages can impart 2D photocatalysts with remarkable activities relative to their 3D counterparts. Accordingly, a wide range of experimental approaches is now being explored for the synthesis of 2D photocatalysts, with computational methods increasingly being used for identification of promising new 2D photocatalytic materials. Herein, we critically review recent literatures related to 2D photocatalyst development and design. Particular emphasis is placed on 2D photocatalyst synthesis and the importance of computational studies for the fundamental understanding of 2D photocatalyst electronic structure, band gap structure, charge carrier mobility and reaction pathways. We also explore the practical challenges of using 2D photocatalysts, such as their difficulty to synthesize in large quantity and also their characterization. The overarching aim of this review is to provide a snapshot of recent work targeting high-performance 2D photocatalysts for efficient solar energy conversion, thus laying a firm base for future advancements in this rapidly expanding area of photocatalysis research.

The development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the large-scale production of fuel cells. Platinum (Pt) nanoparticle catalysts show excellent performance for ORR, though the high cost of Pt is a limiting factor that directly impacts fuel cell production costs. Alloying Pt with other transition metals is an effective strategy to reduce Pt utilization whilst maintaining good ORR performance. In this work, novel hollow PtFe alloy catalysts were successfully synthesized by high-temperature pyrolysis of SiO2 -coated Pt-Fe3 O4 nanoparticle dimers supported on carbon at 900 °C, followed by SiO2 shell removal and partial dealloying of the PtFe nanoparticles formed using HF. The obtained hollow PtFe nanoparticle catalysts (denoted herein as PtFe-900) showed a 2.3-fold enhancement in ORR mass activity compared to PtFe nanoparticles synthesized without SiO2 protection, and a remarkable 7.8-fold enhancement relative to a commercial Pt/C catalyst. Further, after 10 000 potential cycles, the ORR mass activity of PtFe-900 remained very high (90.9 % of the initial mass activity). The outstanding ORR performance of PtFe-900 can be attributed to the modification of Pt lattice and electronic structure by alloying with Fe at high temperature under the protection of the SiO2 coating. This work guides the development of improved, highly dispersed Pt-based alloy nanoparticle catalysts for ORR and fuel cell applications.

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are utilized extensively in energy conversion and storage devices including polymer electrolyte membrane fuel cells (PEMFCs), rechargeable metal–air batteries and water electrolysers. Herein, we review recent breakthroughs in the design of metal alloy-based nanostructures for oxygen electrocatalysis, placing particular emphasis on how alloy structure and complex architecture influence electrochemical performance. Emerging design principles for alloy-based catalysts include composition regulation, size optimization, morphology control, structure engineering, and interface engineering. By employing one or more of these five design principles, a wide range of alloy systems have been successfully developed in recent years that offer superior ORR and OER activity and stability relative to the benchmark Pt/C and IrO2 or RuO2 electrocatalysts traditionally used in these reactions. Further, many of these well-engineered alloy catalysts offer outstanding electrochemical performance as cathode catalysts in PEMFCs or air electrode catalysts in rechargeable metal–air batteries (e.g., Zn–air and Li–air batteries), thus enabling lower cost fabrication of these devices.

A challenging but pressing task to design and synthesize novel, efficient, and robust pH‐universal hydrogen evolution reaction (HER) electrocatalysts for scalable and sustainable hydrogen production through electrochemical water splitting. Herein, we report a facile method to prepare an efficient and robust Ru‐M (M=Ni, Mn, Cu) bimetal nanoparticle and carbon quantum dot hybrid (RuM/CQDs) for pH‐universal HER. The RuNi/CQDs catalysts exhibit outstanding HER performance at all pH levels. The unexpected low overpotentials of 13, 58, and 18 mV shown by RuNi/CQDs allow a current density of 10 mA cm−2 in 1 m KOH, 0.5 m H2SO4, and 1 m PBS, respectively, for Ru loading at 5.93 μgRu cm−2. This performance is among the best catalytic activities reported for any platinum‐free electrocatalyst. Theoretical studies reveal that Ni doping results in a moderate weakening of the hydrogen bonding energy of nearby surface Ru atoms, which plays a critical role in improving the HER activity.

Approximately 2% of the energy consumed by humans each year is used to make nitrogen-based fertilizers, with ammonia (NH3) production being the most significant contributor to this energy demand. C...

For many two-dimensional (2D) materials, low coordination edges and corner sites offer greatly enhanced catalytic performance compared to basal sites, motivating the search for new synthetic approaches towards ultrathin and ultrafine 2D nanomaterials with high specific surface areas. To date, the synthesis of catalysts that are both ultrathin (monolayer) and ultrafine (lateral size

The photothermal conversion of syngas (CO and H2) offers a relatively straightforward method for the production of solar fuels with high solar-to-fuel conversion efficiencies. Herein, we report the successful synthesis of a series of novel Co-based catalysts via hydrogen reduction of CoAl layered-double-hydroxide (LDH) nanosheets at temperatures(x) in the range 300–700 °C. With increasing reduction temperature, the selectivity of the Co-x catalysts for photothermal CO hydrogenation under UV-vis irradiation shifted progressively from CH4 to high-value hydrocarbons, with the Co-700 catalyst affording a remarkable C2+ selectivity of 65% (∼36.3% C2-4 vs ∼28.7% C5+) at a CO conversion of 35.4%. High-resolution transmission electron microscopy, X-ray diffraction and Co K-edge extended X-ray absorption fine structure analyses revealed the Co-700 catalyst contained metallic Co nanoparticles supported by amorphous alumina, whilst density functional theory calculations revealed that metallic Co nanoparticle formation improved the C-C coupling ability of the LDH-derived catalysts, thus enhancing the selectivity to higher hydrocarbons. This study further highlights the great promise of photothermal catalytic systems for CO conversion to fuels and other valuable chemicals feedstocks.

Herein, this work constructs a three-dimensional porous graphitic carbon nitride assembled by highly crystalline and ultrathin nanosheets (3D g-C3N4 NS). 3D g-C3N4 NS could directly split pure water into H2 and O2 with high evolution rate up to 101.4 and 49.1 μmol g−1 h−1 under visible light, respectively, approximately 11.8 and 5.1 times higher than bulk g-C3N4 and g-C3N4 NS. Besides, it achieves a notable apparent quantum yield of 1.4% at 420 nm, significantly superior to previously reported Pt/g-C3N4. The efficient activity of 3D g-C3N4 NS is mainly attributed to its 3D interconnected open-framework, assembled by highly crystalline ultrathin nanosheet unit, provides a pathway for faster charge carrier transport. Moreover, benefitting from its 3D structure for preventing agglomeration of nanosheets, 3D g-C3N4 NS is stable for more than 100 h of overall water splitting reaction.

A simple one-step thermal polymerization method was developed for synthesis of holey graphitic carbon nitride nanotubes, involving direct heating of mixtures of melamine and urea or melamine and cyanuric acid in specific mass ratios. Supramolecular structures formed between the precursor molecules guided nanotube formation. The porous and nanotubular structure of the nanotubes facilitated efficient charge carrier migration and separation, thereby enhancing photocatalytic H2 production in 20 vol.% lactic acid under visible light irradiation. Nanotubes synthesized using melamine and urea in a 1:10 mass ratio (denoted herein as CN-MU nanotubes) exhibited a photocatalytic hydrogen production rate of 1,073.6 μmol·h−1·g−1 with Pt as the cocatalyst, a rate of 4.7 and 3.1 times higher than traditional Pt/g-C3N4 photocatalysts prepared from graphitic carbon nitride (g-C3N4) obtained by direct thermal polymerization of melamine or urea, respectively. On the basis of their outstanding performance for photocatalytic H2 production, it is envisaged that the holey g-C3N4 nanotubes will find widespread uptake in other areas, including photocatalytic CO2 reduction, dye-sensitized solar cells and photoelectrochemical sensors.

The discovery of improved chemical processes for CO and CO2 hydrogenation to valuable hydrocarbon fuels and alcohols is of paramount importance for the chemical industry. Such technologies have the potential to reduce anthropogenic CO2 emissions by adding value to a waste stream, whilst also reducing our consumption of fossil fuels. Current thermal catalytic technologies available for CO and CO2 hydrogenation are demanding in terms of energy input. Various alternative technologies are now being developed for COx hydrogenation, with solar-driven processes over two-dimensional (2D) and 2D-related composite materials being particularly attractive due to the abundance of solar energy on Earth and also the high selectivity of defect-engineered 2D materials towards specific valuable products under very mild reaction conditions. This review showcases recent advances in the solar-driven COx reduction to hydrocarbons over 2D-based materials. Optimization of 2D catalyst performance demands interdisciplinary research that embraces catalyst electronic structure manipulation and morphology control, surface/interface engineering, reactor engineering and density functional theory modelling studies. Through improved understanding of the structure–performance relationships in 2D-related catalysts which is achievable through the application of modern in situ characterization techniques, practical photo/photothermal/photoelectrochemical technologies for CO and CO2 reduction to high-valuable products such as olefins could be realized in the not-too-distant future.

The exploration of photocatalysts used in converting CO2 into applicable organic products is of significant importance for addressing the universal problems of both global warming and energy shortage. In this work, the sensitizer Cu(II) tetra(4-carboxylphenyl)porphyrin (CuTCPP) was successfully combined with hydroxylated commercial P25 (TiO2) by hydrothermal treatment (denoted as P25m). The as-prepared composite CuTCPP/P25m shows photocatalytic activity for CO2 reduction to give methane under UV-vis irradiation. The characterizations entailed in our work not only confirm the effective combination of the composite, but exhibit a stronger light absorption capability than P25m. During the photocatalytic evaluation, the photocatalytic system employing 0.5% CuTCPP/P25m (CuTCPP account for 0.5% in the total amount) engendered approximately 46 times higher methane than generated by P25m alone. This impressive amelioration can be attributed to a strengthened capability of CuTCPP/P25m in light absorption and enhanced separation efficiency of photo-induce electrons and holes.

Monoclinic Nb2O5 nanorod superstructures were first synthesized by a facile yet effective hydrothermal route using Sn2Nb2O7 nanoparticles as the precursor. These unique Nb2O5 nanorod superstructures assembled by small nanorods facilitate the spatial separation of photogenerated charge carriers, thus leading to improved photocatalytic H2 production activity in methanol aqueous solution under ultraviolet light irradiation, which is about 151 times higher than that of commercial Nb2O5 powders.

The construction of natural photosynthesis-inspired Z-scheme tandem system has been considered as a promising strategy to fulfill efficient electron-hole separation and charge transportation in composite photocatalysts, providing a unique opportunity to achieve improved solar-driven photocatalytic water splitting performance superior to conventional heterojunctions. The presence of an ideal electron mediator is critical to promote effective electron transfer in Z-scheme semiconductor photocatalytic systems. Herein, for the first time, we report the fabrication of CeVO4/three-dimensional (3D) reduced graphene oxide (RGO) aerogel/BiVO4 ternary composites and their use as photocatalysts for visible-light-driven water oxidation and tetracycline (TC) degradation. As-prepared hybrid materials exhibit well-organized heterostructures where two vanadates with different dimensional features are surrounded by 3D aerogel networks. Under visible light irradiation, the optimal composite material revealed highly improved photocatalytic activity both in oxygen evolution from water splitting and TC degradation. The enhancement in photocatalytic efficiency is assumed to come from illuminated Z-scheme CeVO4/3D RGO/BiVO4 configuration, in which conductive 3D RGO aerogel functions as an effective electron mediator and builds the bridge between two vanadates, offering a tandem channel for more efficient charge transfer in two semiconductors. This work may provide a new clue for the design of all-solid-state Z-scheme composite photocatalytic materials in energy and environmental applications.

Polymeric carbon nitride as an intriguing earth-abundant visible light photocatalyst for H2 evolution has projected huge potentials. A high-performance polymeric carbon nitride photocatalyst system always requires fabrication of nanostructure or assistance of other semiconductors for ample reactive sites or rapid carrier migration/charge separation. Here, we disclose that hydroxylation as an efficient surface polarization decoration tactic without involving nanostructure or other semiconductors can substantially promote local spatial charge separation and proton activation of polymeric carbon nitride, thus achieving high photocatalytic H2 evolution. The post-hydrothermal treatment allows polymeric carbon nitride surface controllable grafting of abundant hydroxyls (-OH) on the -C≡N sites, which not only extends the 2D conjugate electron system of polymeric carbon nitride to 3D space to realize local spatial charge separation, but also polarizes the neighboring N atoms (C-N=C) to promote the proton adsorption and activation on them, further contributing to the high H2 evolution performance. The deep hydroxylation offered by introduction of basic ammonium salts discloses a pH-dependent hydroxylation-level mechanism and renders a ~ 11-fold enhancement in H2 generation rate with an AQY of 9.1% at 420 ± 15 nm. The finding may bring a new opportunity for developing highly-efficient HER materials base on surface polarization of functional groups.

Crystal defects of semiconductor materials exert huge impact on their physical and chemical properties. Herein, we report the development of oxygen vacancy (OV) concentration-tunable Bi2O2CO3 (BOC) via a facile and scalable precipitation approach with assistance of glyoxal as reductant at atmospheric environment. Introduction of OV takes a triple-functional role in regulating the band structure and charge movement behaviors of BOC. It not only renders appearance of defect band level in the forbidden band, allowing BOC drastically extended photoabsorption from 360 to 520 nm, but also tremendously promotes the charge carrier density, bulk charge separation, surface charge separation and interfacial charge transfer. In contrast to pristine BOC, OV-BOC demonstrates highly promoted photocatalytic performance for water splitting into H2 evolution, NO removal from the gas phase and degradation of a typical antibiotic tetracycline hydrochloride, where the H2 production is first reported for BOC. Additionally, the OV concentration of BOC can be continuously modulated only by regulating the concentration of glyoxal, thereby achieving the adjustable photoabsorption and band structure. Our work enables smart design on oxygen vacancy-activated photocatalytic materials for solar-energy-conversion applications through a readily achievable tactic.

A template-free hydrothermal-assisted thermal polymerization method has been developed for the large-scale synthesis of one-dimensional (1D) graphitic carbonnitride (g-C3N4) microtubes. The g-C3N4 microtubes were obtained by simple thermal polymerization of melamine-cyanuric acid complex microrods under N2 atmosphere, which were synthesized by hydrothermal treatment of melamine solution at 180 °C for 24 h. The as-obtained g-C3N4microtubes exhibited a large surface area and a unique one-dimensional tubular structure, which provided abundant active sites for proton reduction and also facilitated the electron transfer processes. As such, the g-C3N4 microtubes showed enhanced photocatalytic H2 productionactivity in lactic acid aqueous solutions under visible light irradiation (λ ≥ 420 nm), which was ∼ 3.1 times higher than that of bulk g-C3N4 prepared by direct thermal polymerization of the melamine precursor under the same calcination conditions.

The development of low cost, metal free semiconductor photocatalysts for CO2 reduction to fuels and valuable chemical feedstocks is a practically imperative for reducing anthropogenic CO2 emissions. In this work, black phosphorus quantum dots (BPQDs) were successfully dispersed on a graphitic carbon nitride (g-C3N4) support via a simple electrostatic attraction approach, and the activities of BP@g-C3N4 composites were evaluated for photocatalytic CO2 reduction. The BP@g-C3N4 composites displayed improved carrier separation efficiency and higher activities for photocatalytic CO2 reduction to CO (6.54 µmol g−1 h−1 at the optimum BPQDs loading of 1 wt%) compared with pure g-C3N4 (2.65 µmol g−1 h−1) . This work thus identifies a novel approach towards metal free photocatalysts for CO2 photoreduction.

We use a two-step hydrothermal method to successfully synthesize Sn2Nb2O7 nanocrystals with an average size of approximately 20 nm. The as-obtained samples are characterized by powder X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, Brunauer-Emmett-Teller analysis, scanning electron microscopy, and transmission electron microscopy. The photocatalytic activity of the Sn2Nb2O7 nanocrystals is evaluated by photocatalytic water splitting under visible light irradiation. The Sn2Nb2O7 nanocrystals with a large surface area of 52.2 m2/g show an enhanced visible-light-driven photocatalytic H2 production activity, approximately 5.5 times higher than that of bulk Sn2Nb2O7 powder. The higher photocatalytic activity of Sn2Nb2O7 nanocrystals is mainly attributed to its relatively high dispersity of nanosized particles and larger specific surface area when compared with the bulk powder.

The electrochemical conversion of greenhouse gases (mainly CO2 and CH4) into ethylene has attracted worldwide attention. Compared with thermal cracking and dehydrogenation ethylene production processes, electrochemical ethylene production is an energy-saving and environmentally friendly process with high atom and energy economies. Great efforts have been made in enhancing the performance of electrochemical COx reduction and alkane dehydrogenation reactions in recent years. The complicated interactions between gas reactants, electrolytes, and catalysts force the three-phase interface mass transfer process an important issue in determining the electrochemical activity and product selectivity. Herein, we summarize the recent progresses on electrochemical ethylene production. Special attention has been paid to the principles for the design of gas–liquid–solid and gas–solid–solid three-phase interfaces and their influence on the electrochemical COx reduction and alkane dehydrogenation reactions. The comprehensive understanding of those different ethylene production reactions together from the perspective of the three-phase interface-related mass transfer process would provide new insights into the design of advanced electrochemical cells for green ethylene production.

Four cyanostyryl-substituted carbazole derivatives (CN-ODEC1, CN-ODEC2, CN-DDEC1, and CN-DDEC) were synthesized and their self-assembly properties have been studied. It was found that they could form organogels especially in aromatic solvents. Scanning electron microscopy and light microscopy images show that the xerogels formed from monosubstituted derivatives (CN-O/DDEC1) gave well-organized tapes, and those from disubstituted derivatives (CN-O/DDEC2) exhibited heavy entangled three-dimensional structures. The UV–vis absorption and fluorescence emission spectra, as well as X-ray diffraction patterns, suggest that carbazole derivatives underwent J-type π-stacking. Meanwhile, we suggested that strong H-bonding and moderate π–π interactions were the key driving force for the gelation of the monosubstituted derivatives, and head-to-tail “ladder-type” J-aggregates were formed in the gel state. On the other hand, strong π–π interaction might be considered as the main driving force for the gelation of disubstituted derivatives, and J-aggregates with no well-organized packing mode of molecules were obtained in the gel phase. It should be noticed that aggregation-induced emission was observed during the gelation processes.

Fabrication of a Z-scheme photocatalytic system for hydrogen production and overall water splitting has huge potential in confronting the increasing worldwide energy crisis. But it is highly challenging to realize due to the harsh requirement for band edge levels and interfacial contact. Herein, we report the preparation of a high-efficiency and stable Z-scheme catalyst Cd0.5Zn0.5S–BiVO4 with a core–satellite structure through the charge-induced assembly process in a mild water bath. A Cd0.5Zn0.5S–BiVO4 Z-scheme junction shows an enormously enhanced photocatalytic activity for H2 evolution under visible light illumination. The optimal photocatalytic H2 evolution rate reaches 2.35 mmol g−1 h−1, which is 7.13 times higher than that of Cd0.5Zn0.5S, and an appreciable apparent quantum efficiency of 24.1% at λ = 420 nm was achieved. In particular, without any sacrificial donor, the Cd0.5Zn0.5S–BiVO4 Z-scheme junction can overall split water into H2 and O2. The efficient photocatalytic activity of Cd0.5Zn0.5S–BiVO4 is attributed to the formation of an intimate core–satellite structure and a Z-scheme photocatalytic mechanism, which not only greatly benefit the charge separation, but also prompt the photoinduced holes from Cd0.5Zn0.5S to rapidly recombine with the electrons of BiVO4, hence reserving the most favorable reductive and oxidative reaction sites. Meanwhile, it inhibits the photocorrosion of Cd0.5Zn0.5S, guaranteeing the high photochemical stability (no activity decay after half a year). This work provides a new reference for the fabrication of a high-performance Z-schematic photocatalyst for water splitting.

Single-layer catalysis sparks huge interests and gains widespread attention owing to its high activity. Simultaneously, three-dimensional (3D) hierarchical structure can afford large surface area and abundant reactive sites, contributing to high efficiency. Herein, we report an absorbing single-unit-cell layer established Bi2WO6 3D hierarchical architecture fabricated by a sodium dodecyl benzene sulfonate (SDBS)-assisted assembled strategy. The DBS− long chains can adsorb on the (Bi2O2)2+ layers and hence impede stacking of the layers, resulting in the single-unit-cell layer. We also uncovered that SDS with a shorter chain is less effective than SDBS. Due to the sufficient exposure of surface O atoms, single-unit-cell layer 3D Bi2WO6 shows strong selectivity for adsorption on multiform organic dyes with different charges. Remarkably, the single-unit-cell layer 3D Bi2WO6 casts profoundly enhanced photodegradation activity and especially a superior photocatalytic H2 evolution rate, which is 14-fold increase in contrast to the bulk Bi2WO6. Systematic photoelectrochemical characterizations disclose that the substantially elevated carrier density and charge separation efficiency take responsibility for the strengthened photocatalytic performance. Additionally, the possibility of single-unit-cell layer 3D Bi2WO6 as dye-sensitized solar cells (DSSC) has also been attempted and it was manifested to be a promising dye-sensitized photoanode for oxygen evolution reaction (ORR). Our work not only furnish an insight into designing single-layer assembled 3D hierarchical architecture, but also offer a multi-functional material for environmental and energy applications.

Development of multi-responsive catalytic materials is a highly meaningful and challenging subject for forwarding the understanding on catalysis mechanism. In this work, we for the first time disclose the piezoelectric-catalytic performance and morphology-dependent photocatalytic activity of Bi 4 Ti 3 O 12 . Via introducing and manipulating the mineralizer sodium hydroxide, we developed a series of Bi 4 Ti 3 O 12 catalysts with diverse morphologies, including nanorods, slice-assembled microspheres, nest-like hollow microspheres, and cube assembly. The photocatalytic activity of these hydrothermally-yielded Bi 4 Ti 3 O 12 as well as sol-gel derived Bi 4 Ti 3 O 12 is investigated by degradation of phenol, and the photocatalytic mechanism is explored. The Bi 4 Ti 3 O 12 microsphere exhibits the most efficient degradation activity, and also presents universal photoreactivity for removing multiform contaminants and antibiotics, like bisphenol A, rhodamine B, chlorotetracycline and tetracycline hydrochloride, boding for its promising practical applications. Significantly, Bi 4 Ti 3 O 12 demonstrates a high piezoelectric-catalytic performance for ultrasonic-assisted decomposition of methyl orange, bisphenol A and tetracycline hydrochloride. It is uncovered that both powerful superoxide ( O 2 − ) and hydroxyl ( OH) radicals are generated with production rates of 6.4 and 2.4 μmol g −1 h −1 , respectively, which take crucial roles in the piezoelectric-catalytic process. The corresponding mechanism is tentatively speculated. This work may push forward to the development of multi-responsive catalytic materials, and provide insights into piezoelectric-catalysis for environmental applications.

Metal-free graphitic carbon nitride (g-C3N4) has triggered huge interests for converting solar energy into fuels. However, direct-calcination derived bulk g-C3N4 always suffers from low surface area and high recombination of charge carriers, prompting attempts to foster g-C3N4 nano/microstructures to achieve high performance. Conventional routes, like templating method, always yields g-C3N4 with tedious morphology and requires post-treatment. Here we release the first report on development of horn-like hollow mesoporous ultrathin (HHMU) g-C3N4 tubes via first forming a horn-like Br-containing intermediate followed by further decomposition transformation under co-pyrolysis of melamine and substantial NH4Br. The multiple-superiorities achieved here (hollow/mesoporous/ultrathin/horn-like) allows g-C3N4 high surface area, drastically boosted bulk charge separation, carrier density and surface charge transfer efficiency. This advanced g-C3N4 thus casts outstanding photocatalytic performance for H2 evolution with an apparent quantum efficiency (AQE) of 14.3% at 420 ± 15 nm, far exceeding most of reported g-C3N4. HHMU g-C3N4 also delivers a strengthened photocatalytic CO2 reduction activity into CO and CH4. Selective photo-deposition results provide an in-depth insight into charge movement behavior and high photo-reactivity that the photo-generated electrons migrate to the outer shell and holes prefer to transfer onto the inner shell of HHMU g-C3N4 tubes, thus achieving efficient spatial anisotropic charge separation. The current study may furnish a reference towards developing efficient tactics for integrally advancing g-C3N4 for renewable energy generation, and disclose a new perspective into promoting charge separation via microstructure design.

Rechargeable zinc-air batteries are attracting enormous attention owing to their extremely high specific energy densities. However, their large scale deployment hinges on the discovery of cheap and efficient electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Herein, the successful synthesis of a bifunctional hybrid electrocatalyst capable of driving both OER and ORR is reported, comprising Co,N-codoped carbon nanoframes (Co,N-CNF) decorated with 14 nm Ni3FeN particles, in which the Co,N-codoped carbon nanoframe (Co,N-CNF) with ORR activity was introduced as a scaffold to disperse the precursors and mitigate their further aggregation. The Ni3FeN/Co,N-CNF hybrid afforded remarkable OER activity (overpotential of 0.27 V, superior to IrO2) and excellent ORR performance (half-wave potential of 0.81 V vs RHE, superior to Pt/C), the origins of which can be traced to the inherent activities of the metallic Ni3FeN nanoparticles and Co,N-CNF support, respectively. Cathodes made from the Ni3FeN/Co,N-CNF electrocatalyst demonstrated superior efficiency and durability to state-of-the-art Pt/C+IrO2 electrocatalysts in both primary and rechargeable zinc-air batteries, showcasing the versatility of the newly developed Ni3FeN/Co,N-CNF electrocatalyst system.

Efficient photo- and piezoelectric-induced molecular oxygen activation are both achieved by macroscopic polarization enhancement on a noncentrosymmetric piezoelectric semiconductor BiOIO3 . The replacement of V5+ ions for I5+ in IO3 polyhedra gives rise to strengthened macroscopic polarization of BiOIO3 , which facilitates the charge separation in the photocatalytic and piezoelectric catalytic process, and renders largely promoted photo- and piezoelectric induced reactive oxygen species (ROS) evolution, such as superoxide radicals (. O2- ) and hydroxyl radicals (. OH). This work advances piezoelectricity as a new route to efficient ROS generation, and also discloses macroscopic polarization engineering on improvement of multi-responsive catalysis.

Photocatalytic CO2 reduction into solar fuels illustrates huge charm for simultaneously settling energy and environmental issues. The photo-reduction ability of a semiconductor is closely correlated to its conduction band (CB) position. Homogeneous-phase solid-solution with same crystal system always has monotonously changed CB position, and the high CB level has to be sacrificed to achieve a benign photoabsorption. Herein, we report the fabrication of heterogeneous-phase solid-solution ZnXCa1-XIn2S4 between trigonal ZnIn2S4 and cubic CaIn2S4. The ZnXCa1-XIn2S4 solid solutions with orderly tuned photoresponsive range from 540 nm to 640 nm all presents more negative CB level and highly enhanced charge separation efficiency. Profiting from these merits, all the ZnXCa1-XIn2S4 solid solutions exhibit remarkably strengthened photocatalytic CO2 reduction performance under visible light (λ > 420 nm) irradiation. Zn0.4Ca0.6In2S4 bearing the most negative CB position and highest charge separation efficiency casts ...

Graphitic carbon nitride (g-C 3 N 4 ) has attracted enormous research attention as a promising low cost, visible-light driven semiconductor photocatalyst. However, low photoabsorption efficiencies and unsatisfactory charge separation limit the potential of g-C 3 N 4 in many applications, motivating attempts to manipulate the structure and electronic properties of g-C 3 N 4 to achieve improved performance. Here we describe a novel precursor-reforming strategy that ultimately affords 3D mesoporous ultrathin g-C 3 N 4 with superior photocatalytic performance compared to conventional calcination-derived g-C 3 N 4 . We demonstrate that during hydrothermal treatment of melamine and urea, melamine undergoes an irreversible monoclinic to orthorhombic phase transformation, and the additive urea (excess typically 3-fold) serves as an additional N source and porogen. Calcination of the orthorhombic melamine yields mesoporous g-C 3 N 4 with enhanced photoabsorption properties and an outstanding photoactivity. A 23-fold increased hydrogen evolution rate of 3579 μmol h −1 g −1 (λ > 420 nm) was achieved with an apparent quantum efficiency (AQE) of 27.8% at 420 ± 15 nm, a level of performance far beyond any AQE previously reported for ultrathin/porous/doped g-C 3 N 4 photocatalyst. Our work conclusively demonstrates a new synthetic strategy towards high performance g-C 3 N 4 -based photocatalytic materials for energy applications.

Carbon quantum dots (CQDs) have attracted widespread interest for photocatalytic applications, owing to their low cost and excellent electron donor/acceptor properties. However, their advancement as visible-light photosensitizers in CQDs/semiconductor nanocomposites is currently impaired by their poor quantum yields (QYs). Herein, we describe the successful fabrication of a series of nitrogen-doped CQDs (NCDs) with N/C atomic ratios ranging from 0.14-0.30. NCDs with the highest N-doping level afforded a remarkable external QY of 66.8 % at 360 nm, and outstanding electron transfer properties and photosensitization efficiencies when physically adsorbed on P25 TiO2 . A NCDs/P25-TiO2 hybrid demonstrated excellent performance for hydrogen evolution in aqueous methanol under both UV and visible-light illumination relative to pristine P25 TiO2 . Controlled nitrogen doping of CQDs therefore represents a very effective strategy for optimizing the performance of CQDs/semiconductor hybrid photocatalysts.

Photocatalysis currently remains a series of key challenges, such as difficult recovery of powder, low efficiency, etc, which grievously impede the practical application of powdery photocatalysts in environmental remediation and renewable energy generation. In this work, we integrate a flexible and porous organic matrix polyurethane foam (PUF) with nanosheet-array-like bismuth oxyhalides (BiOX) as efficient and stable photocatalysts via a facile dipping-hydrolysis means. The BiOX/PUF foam photocatalysts uncover profoundly promoted photocatalytic performance for treating multiform organic contaminants ranging from azo dye, phenol to antibiotic, in comparison with the powdery counterparts. These foam photocatalysts also display enhanced photocatalytic activity toward water splitting into H 2 evolution. Significantly, they show absorbing performance in many aspects, including high stability, easy recovery, good recycling and excellent controllability and adaptability, strongly boding for their promising practical prospect. The study may not only advance a series of practical photocatalysts for environmental control and renewable energy generation, but also have the potential to be extended to development of other high-performance photocatalytic materials.

Design of three-dimensional (3D) hierarchical architectures and nano-phase-junctions are of huge significance for semiconductor photocatalysis. Herein, we report the fabrication of a series of 3D hierarchical bismuth oxyiodides via in situ phase transformation and phase-junction construction utilizing BiOI microspheres as self-sacrificed template through a facile calcination strategy. The multiform bismuth oxyiodides obtained at different temperatures include hierarchical BiOI, Bi4O5I2, Bi4O5I2-Bi5O7I phase-junction and Bi5O7I. These bismuth oxyiodides exhibit very distinct microstructure and band structure, and their photoabsorption was orderly tuned from 700 to 400 nm, rendering the adjustable oxidation and reduction ability of band energy levels. The photocatalytic activity of the bismuth oxyiodide series is systematically assessed by degradation of diverse antibiotic and contaminants, such as tetracycline hydrochloride, bisphenol A (BPA) and azo dye Rhodamine B (RhB). It disclosed that they present discrepant photocatalytic performance with activity order of Bi4O5I2-Bi5O7I > Bi4O5I2 > Bi5O7I > BiOI, which is closely associated with the charge separation efficiency, band structure and surface area. Additionally, the photocatalytic mechanism and degradation pathway are also surveyed. The study may furnish new insights into development of novel 3D hierarchical architectures and nano-phase-junctions for heterogeneous photocatalysis.

Metal-free graphitic carbon nitride (g-C3N4) shows tremendous potentials in energy and environmental domains. Nonetheless, amelioration on the crystal configuration, electronic structure and microstructure of g-C3N4 for high-performing visible-light photocatalysis is still challenging and anticipated. Here we report the development of chlorine (Cl) intercalated g-C3N4 via co-pyrolysis of melamine and excessive ammonium chloride (excessive is very pivotal). This protocol renders not only Cl intercalation in the interlayer of g-C3N4, but also a homogeneous porous structure, thereby endowing g-C3N4 with multiple superiority effects, including significantly promoted charge migration by establishing interlayer pathway, up-shifted conduction-band level, narrowed band gap as well as enhanced surface area. The as-prepared Cl intercalated mesoporous g-C3N4 parades outstanding photocatalytic performance for water splitting into H2, CO2 reduction, liquid and air contaminants removal. The most enhanced photocatalytic performance was obtained at Cl-C3N4-3 for H2 evolution activity, which shows a 19.2-fold increase in contrast to pristine g-C3N4, accompanying with a high apparent quantum efficiency of 11.9% at 420 ± 15 nm. Experimental and DFT calculations results co-disclose that the aforementioned advantageous factors account for the profoundly boosted photooxidation and photoreduction capabilities of g-C3N4 under visible light. The present work may furnish a bottom-up tactic for integrally advancing g-C3N4, and also hold huge promise to be extended to other layered materials for photochemical or photoelectrochemical applications.

Band gap opening and engineering make up one of the primary goals of developing novel materials for photocatalytic hydrogen generation. We report here a facile synthesis of graphene decorated with in-plane boron nitride domains via control of both the doping sequence of heteroatoms and the oxygen content of the graphene precursor, showing significant differences in the doping pattern compared with B and/or N singly doped or co-doped graphene. We uncover that the formation of BN domains in graphene is critical for engineering the band gap and delivering an improved activity for photocatalytic hydrogen generation in the absence of any photosensitizer. This work paves the way for the rational design and construction of graphene-based photocatalysts for efficient photocatalysis.

With the ambition of solving the challenges of the shortage of fossil fuels and their associated environmental pollution, visible-light-driven splitting of water into hydrogen and oxygen using semiconductor photocatalysts has emerged as a promising technology to provide environmentally friendly energy vectors. Among the current library of developed photocatalysts, organic conjugated polymers present unique advantages of sufficient light-absorption efficiency, excellent stability, tunable electronic properties, and economic applicability. As a class of rising photocatalysts, organic conjugated polymers offer high flexibility in tuning the framework of the backbone and porosity to fulfill the requirements for photocatalytic applications. In the past decade, significant progress has been made in visible-light-driven water splitting employing organic conjugated polymers. The recent development of the structural design principles of organic conjugated polymers (including linear, crosslinked, and supramolecular self-assembled polymers) toward efficient photocatalytic hydrogen evolution, oxygen evolution, and overall water splitting is described, thus providing a comprehensive reference for the field. Finally, current challenges and perspectives are also discussed.

There is interest in metal single atom catalysts due to their remarkable activity and stability. However, the synthesis of metal single atom catalysts remains somewhat ad hoc, with no universal strategy yet reported that allows their generic synthesis. Herein, we report a universal synthetic strategy that allows the synthesis of transition metal single atom catalysts containing Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Pt or combinations thereof. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy confirm that the transition metal atoms are uniformly dispersed over a carbon black support. The introduced synthetic method allows the production of carbon-supported metal single atom catalysts in large quantities (>1 kg scale) with high metal loadings. A Ni single atom catalyst exhibits outstanding activity for electrochemical reduction of carbon dioxide to carbon monoxide, achieving a 98.9% Faradaic efficiency at −1.2 V., Single-atom catalysts are a promising class of catalytic materials, but general synthetic methods are limited. Here, the authors develop a ligand-mediated strategy that allows the large-scale synthesis of diverse transition metal single atom catalysts supported on carbon.

Nanozymes have attracted extensive interest owing to their high stability, low cost and easy preparation, especially in the field of cancer therapy. However, the relatively low catalytic activity of nanozymes in the tumor microenvironment (TME) has limited their applications. Herein, we report a novel nanozyme (PtFe@Fe3 O4 ) with dual enzyme-like activities for highly efficient tumor catalytic therapy. PtFe@Fe3 O4 shows the intrinsic photothermal effect as well as photo-enhanced peroxidase-like and catalase-like activities in the acidic TME, thereby effectively killing tumor cells and overcoming the tumor hypoxia. Importantly, a possible photo-enhanced synergistic catalytic mechanism of PtFe@Fe3 O4 was first disclosed. We believe that this work will advance the development of nanozymes in tumor catalytic therapy.

Synthesizing nanomaterials with anisotropic architectures, especially two-dimensional (2D) nanosheets (NSs), is a key focus of materials science research. Metal sulfide nanosheets (MSNSs) are typically obtained involving exfoliation of bulk metal sulfides with layered structures. The synthesis of NSs of intrinsically non-layered metal sulfides has received relatively less attention. Metal alkanethiolates with lamellar structures are now shown to serve as effective scaffolds for constructing NSs. A novel photochemical step was employed to transform 2D metal thiolates into MSNSs. By this strategy the 2D nature of metal thiolate precursors was preserved in the final products, resulting in the successful synthesis of NSs of binary PbS, CdS, and Cu9 S5 , as well as ternary wurtzite CuInS2 , Cu2 SnS3 . Results encourage the wider utilization of photochemical strategies in the synthesis of anisotropic MSNSs.

Fe single-atom catalysts (Fe SACs) with atomic FeNx active sites are very promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR). The pyrolysis of metal-organic frameworks (MOFs) is a common approach for preparing Fe SACs, though most MOF-derived catalysts reported to date are microporous and thus suffer from poor mass transfer and a high proportion of catalytically inaccessible FeNx active sites. Herein, NH2 -MIL-101(Al), a MOF possessing a mesoporous cage architecture, is used as the precursor to prepare a series of N-doped carbon supports (denoted herein as NC-MIL101-T) with a well-defined mesoporous structure at different pyrolysis temperatures. The NC-MIL101-T supports are then impregnated with a Fe(II)-phenanthroline complex, and heated again to yield Fe SAC-MIL101-T catalysts rich in accessible FeNx single atom sites. The best performing Fe SAC-MIL101-1000 catalyst offers outstanding ORR activity in alkaline media, evidenced by an ORR half-wave potential of 0.94 V (vs RHE) in 0.1 m KOH, as well as excellent performance in both aqueous primary zinc-air batteries (a near maximum theoretical energy density of 984.2 Wh kgZn -1 ) and solid-state zinc-air batteries (a peak power density of 50.6 mW cm-2 and a specific capacity of 724.0 mAh kgZn -1 ).

Recently, heterogeneous photocatalysts have achieved much interest on account of their great potential applications in resolving many tough energy and environmental troubles around the world through an ecologically sustainable way. Heterogeneous nanocomposites composed of graphitic carbon nitride (g-C3 N4 ) and carbon dots (CDs) possess broad spectrum absorption, appropriate electronic band structures, rapid carrier mobility, abundant reserves, excellent chemical stability, and facile synthesis methods, which make them promising composite photocatalysts for suitable applications such as photocatalytic solar fuels production and contaminant decomposition. With the rapid development in photocatalysis by hybridization of g-C3 N4 and CDs, a systematic summary and prospection of performance improvement are urgent and meaningful. This review first focuses on various kinds of effectively synthetic methods of composites. Following, the strategies available for enhanced performance, including morphology optimization, spectral absorption improvement, ternary or quaternary composition hybrid, lateral or vertical heterostructures construction, heteroatom doping, and so forth, are fully discussed. Then, the applications mainly in efficient photocatalytic hydrogen generation, photocatalytic carbon dioxide reduction, and organic pollutants degradation are systematically demonstrated. Finally, the remaining issues and prospect of further development are proposed as some kind of guidance for powerful combination of g-C3 N4 and CDs with high efficiency to photocatalysis.