Highly dispersed Pd nanoparticles hybridizing with 3D hollow-sphere g-C3N4 to construct 0D/3D composites for efficient photocatalytic hydrogen evolution

Strategies for improving photocatalytic performance of g-C3N4 by modulating charge separation and current research status

Graphitic carbon nitride (g-C3N4) has been extensively investigated over the past decade for its potential utilizations in photocatalytic energy generation and pollutant degradation. To better meeting the requirements for practical utilizations, it is crucial to address the issue of poor charge separation properties in g-C3N4, which origin from the strong interactions in photogenerated electron-hole pairs. In this review, we summarized the pertinent studies on developing strategies to promote the charge separation properties of g-C3N4. The strategies can be categorized into two categories of promoting the surface migration of charge carriers and prolonging the lifetime of surface charge. Finally, we present potential challenges in promoting charge separation and offer feasible suggestions to face these challenges.

Unlocking enhanced photocatalytic power: Donor-acceptor synergy in non-metallic g-C3N4 hollow nanospheres

Selecting safe, non-toxic, and non-metallic semiconductor materials that facilitate the degradation of pollutants in water stands out as an optimal approach to combat environmental pollution. Herein, graphitic carbon nitride (g-C3N4)-based hollow nanospheres nonmetallic photocatalyst modified with covalent organic framework materials named TpMA, based on 1, 3, 5-trimethylchloroglucuronide (Tp) and melamine (MA), was successfully synthesized (abbreviated as CNTP). The ordered electron donor-acceptor structure inherent in TpMA contributed to enhancing the transport efficiency of photogenerated carriers in CNTP. The CNTP photocatalysts exhibited excellent performance in degrading rhodamine B and tetracycline in visible light, with optimal degradation rates reached more than 90% in 60 and 80 min, respectively, which were 5.3 and 3.0 times higher than those of pure CNNS. The increased photocatalytic efficiency observed in CNTP composites could be traced back to the covalently connection between the two molecules, forming a π-conjugated system that facilitated the separative efficiency of photogenerated electron-hole pairs and intensified the utilization of visible light. This study provided a new means to design and fabricate highly efficient and environmentally friendly non-metallic photocatalytic materials.

Unveiling the Synergistic Role of Frustrated Lewis Pairs in Carbon-Encapsulated Ni/NiOx Photothermal Cocatalyst for Enhanced Photocatalytic Hydrogen Production

The development of high-density and closely spaced frustrated Lewis pairs (FLPs) is crucial for enhancing catalyst activity and accelerating reaction rates. However, constructing efficient FLPs by breaking classical Lewis bonds poses a significant challenge. Here, this work has made a pivotal discovery regarding the Jahn-Teller effect during the formation of grain boundaries in carbon-encapsulated Ni/NiOx (Ni/NiOx@C). This effect facilitates the formation of high-density O (VO) and Ni (VNi) vacancy sites with different charge polarities, specifically FLP-VO-C basic sites and FLP-VNi-C acidic sites. The synergistic interaction between FLP-VO-C and FLP-VNi-C sites not only reduces energy barriers for water adsorption and splitting, but also induces a strong photothermal effect. This mutually reinforcing effect contributes to the exceptional performance of Ni/NiOx@C as a cocatalyst in photothermal-assisted photocatalytic hydrogen production. Notably, the Ni/NiOx@C/g-C3N4 (NOCC) composite photocatalyst exhibits remarkable hydrogen production activity with a rate of 10.7 mmol g-1 h-1, surpassing that of the Pt cocatalyst by 1.76 times. Moreover, the NOCC achieves an impressive apparent quantum yield of 40.78% at a wavelength of 380 nm. This work paves the way for designing novel defect-state multiphase cocatalysts with high-density and adjacent FLP sites, which hold promise for enhancing various catalytic reactions.

Encapsulating lithium at the microscale: selective deposition in carbon-doped graphitic carbon nitride spheres

For stable lithium deposition without dendrites, three-dimensional (3D) porous structure has been intensively investigated. Here, we report the use of carbon-doped graphitic carbon nitride (C-doped g-C3N4) microspheres as a 3D host for lithium to suppress dendrite formation, which is crucial for stable lithium deposition. The C-doped g-C3N4microspheres have a high surface area and porosity, allowing for efficient lithium accommodation with high accessibility. The carbon-doping of the g-C3N4microspheres confers lithiophilic properties, which facilitate the regulation of Li+flux and dense filling of cavities with nucleated lithium, thereby preventing volume expansion and promoting dendrite-free Li deposition. The electrochemical performance was improved with cyclic stability and high Coulombic efficiency over 260 cycles at 1.0 mA cm-2for 1.0 mAh cm-2, and even over 70 cycles at 5.0 mA cm-2for 3.0 mAh cm-2. The use of C-doped g-C3N4microspheres as a 3D Li host shows promising results for stable lithium deposition without dendrite formation.

Research Progress on Graphitic Carbon Nitride/Metal Oxide Composites: Synthesis and Photocatalytic Applications

Although graphitic carbon nitride (g-C3N4) has been reported for several decades, it is still an active material at the present time owing to its amazing properties exhibited in many applications, including photocatalysis. With the rapid development of characterization techniques, in-depth exploration has been conducted to reveal and utilize the natural properties of g-C3N4 through modifications. Among these, the assembly of g-C3N4 with metal oxides is an effective strategy which can not only improve electron-hole separation efficiency by forming a polymer-inorganic heterojunction, but also compensate for the redox capabilities of g-C3N4 owing to the varied oxidation states of metal ions, enhancing its photocatalytic performance. Herein, we summarized the research progress on the synthesis of g-C3N4 and its coupling with single- or multiple-metal oxides, and its photocatalytic applications in energy production and environmental protection, including the splitting of water to hydrogen, the reduction of CO2 to valuable fuels, the degradation of organic pollutants and the disinfection of bacteria. At the end, challenges and prospects in the synthesis and photocatalytic application of g-C3N4-based composites are proposed and an outlook is given.

EDTA-dominated hollow tube-like porous graphitic carbon nitride towards enhanced photocatalytic hydrogen evolution

Graphite carbon nitride (g-C₃N₄) as metal-free photocatalyst has been widely studied recently in photocatalytic water reduction, which is considered as one of the promising routes to realizing the hydrogen energy-based society in the future. The generally used preparation process based on thermal polymerization of precursors easily brought the formation of aggregated nanosheets morphology, severely limiting its photocatalytic activity. Herein, the hollow tube-like morphology with porous surface was elaborately obtained by ethylene diamine tetraacetic acid (EDTA)-involved hydrothermal treatment of melamine precursor. The hollow and porous features shortened the migration distance of photo-generated carriers, trapped the incident lights, and provided more photocatalytic reactive sites, then realizing the enhanced photocatalytic H₂-evolution activity up to 7.1 times that of pristine g-C₃N₄. The presence of EDTA acted as the pivotal role to control the recrystallization process of melamine and its derivative, cyanuric acid, and thus to determine the framework formation of the hollow tube-like microstructure. Moreover, complete thermal decomposition of cyanuric acid during the thermal polymerization of precursors was responsible for the hollow and porous features. This work extends the morphology regulation cognition of g-C₃N₄ based on hydrothermal treatment of precursors, and is expected to bring deep understanding and feasible strategies to design morphology-dominated highly-efficient g-C₃N₄ photocatalysts.

Highly hydrophilic covalent organic frameworks as efficient and reusable photocatalysts for oxidative coupling of amines in aqueous solution

Highly hydrophilic 2D-COFs, TFB-XX-DMTH, have been successfully constructed by a three-component in situ assembly strategy and exhibited superior photocatalytic performance in oxidative coupling reactions of benzylamines in aqueous solution.

Graphene quantum dot implanted supramolecular carbon nitrides with robust photocatalytic activity against recalcitrant contaminants

Graphene quantum dot implanted supramolecular carbon nitrides exhibit superior visible-light photocatalytic activity in the degradation of aqueous contaminants of emerging concern.

Conversion of methane to acetonitrile over GaN catalysts derived from gallium nitrate hydrate co-pyrolyzed with melamine, melem, or g-C3N4: the influence of nitrogen precursors

The GaN catalyst derived from co-pyrolyzing gallium nitrate hydrate and g-C3N4 is effective in the conversion of methane to acetonitrile because of its well dispersed GaN crystals and amorphous CN species.

Emerging Cocatalysts on g-C3 N4 for Photocatalytic Hydrogen Evolution

Over the past few decades, graphitic carbon nitride (g-C₃ N₄ ) has arisen much attention as a promising candidate for photocatalytic hydrogen evolution reaction (HER) owing to its low cost and visible light response ability. However, the unsatisfied HER performance originated from the strong charge recombination of g-C₃ N₄ severely inhibits the further large-scale application of g-C₃ N₄ . In this case, the utilization of cocatalysts is a novel frontline in the g-C₃ N₄ -based photocatalytic systems due to the positive effects of cocatalysts on supressing charge carrier recombination, reducing the HER overpotential, and improving photocatalytic activity. This review summarizes some recent advances about the high-performance cocatalysts based on g-C₃ N₄ toward HER. Specifically, the functions, design principle, classification, modification strategies of cocatalysts, as well as their intrinsic mechanism for the enhanced photocatalytic HER activity are discussed here. Finally, the pivotal challenges and future developments of cocatalysts in the field of HER are further proposed.

Photo-promoted in situ reduction and stabilization of Pd nanoparticles by H2 at photo-insensitive Sm2O3 nanorods

Controlled synthesis of noble metal nanoparticles with well-defined size and good dispersion on supports has been a long-standing challenge in heterogeneous catalysis. Here we report a facile photo-assisted H₂in situ reduction process to synthesize monodispersed Pd nanoparticles with 2-4 nm size on photo-insensitive Sm₂O₃ rare-earth metal oxide with nanorod morphology. Thanks to the contribution of UV irradiation, the photoelectrons generation in the Sm₂O₃ support accelerates the H₂ reduction of Pd²⁺ ions into Pd⁰ and stabilize the growth of very small Pd nanoparticles homogeneously dispersed on the support. The homogeneous distribution of the Pd NPs on the surface of Sm₂O₃ is most likely attributed to the profuse nucleation sites created by the UV irradiation and the abundance of hydroxyl groups on the support. The hydrogenation of styrene to ethylbenzene was studied as a model reaction. As a result, the UV radiated sample shows an excellent TOF value of 7419 h^-1, which is quadruple of the sample without UV irradiation, under the condition of 0.1 MPa H₂ at a content of 1.0 wt% Pd. Besides, UV radiated sample shows a negligible performance degradation during the repeated cycling process. This photo-promoted H₂ reduction process provides a convenient and straightforward route for assembling materials with novel structures and functions for nanotechnology applications.

Hollow ZIF-67 derived porous cobalt sulfide as an efficient bifunctional electrocatalyst for overall water splitting

A hollow ZIF-67 templating approach was used to fabricate a hollow cobalt sulfide superstructure with enhanced activity for overall water splitting.

Atomic-level localization of π-electrons in defect engineered tri-s-triazine units for increased photocatalytic hydrogen generation of polymeric carbon nitride

N defects in tri-s-triazine units can localize π electrons to reduce charge recombination and act as active sites, thus improving the efficiency of photocatalytic hydrogen production.

Tale of Two Layered Semiconductor Catalysts toward Artificial Photosynthesis

The ever-increasing reliance on nonrenewable fossil fuels due to massive urbanization and industrialization created problems such as depletion of the primary feedstock and raised the atmospheric CO₂ levels causing global warming. A smart and promising approach is artificial photosynthesis that photocatalytically valorizes CO₂ into high-value chemicals. The inexpensive layered semiconductors like g-C₃N₄ and rGO or GO have the potential to make the process practically feasible for real applications. The suitable band positions with respect to the reduction potentials coupled with the typical surface properties of these layered semiconductors play a beneficial role in photoreduction of CO₂. Additionally, the creation of heterojunction interfaces to achieve the Z-scheme by anchoring g-C₃N₄ and rGO with another semiconductor with proper band alignment and dispersing plasmonic nano metals to obtain Schottky barriers on the layered surfaces also help retarding the electron-hole recombination and boost up the catalytic efficacy. Extensive exploration happened in recent years toward artificial photosynthesis over these materials, which needs a critical compendium. Surprisingly, in spite of the recent explosion of studies on photocatalytic reduction of CO₂ over metal-free semiconductors, there is not a single review on comparing the mechanistic aspects of photoreduction of CO₂ over the layered semiconductors g-C₃N₄ and rGO. This review stands out as a unique documentation, where the mechanism of photocatalytic reduction of CO₂ over this set of materials is critically examined in the context of band and surface modifications. An overall conclusion and outlook at the end indicates the need to develop prototypes for artificial photosynthesis with these well-studied semiconducting layered materials to yield solar fuels.