Core-Shell Semiconductor-Graphene Nanoarchitectures for Efficient Photocatalysis: State of the Art and Perspectives

Semiconductor photocatalysis holds great promise for renewable energy generation and environment remediation, but generally suffers from the serious drawbacks on light absorption, charge generation and transport, and structural stability that limit the performance. The core-shell semiconductor-graphene (CSSG) nanoarchitectures may address these issues due to their unique structures with exceptional physical and chemical properties. This review explores recent advances of the CSSG nanoarchitectures in the photocatalytic performance. It starts with the classification of the CSSG nanoarchitectures by the dimensionality. Then, the construction methods under internal and external driving forces were introduced and compared with each other. Afterward, the physicochemical properties and photocatalytic applications of these nanoarchitectures were discussed, with a focus on their role in photocatalysis. It ends with a summary and some perspectives on future development of the CSSG nanoarchitectures toward highly efficient photocatalysts with extensive application. By harnessing the synergistic capabilities of the CSSG architectures, we aim to address pressing environmental and energy challenges and drive scientific progress in these fields.

Solar-activated and hydrothermally synthesized effective rGO/Ag2S composites for the destruction of naphthol green B dye and antibacterial applications

Graphene-based nanocomposites are developing as a new class of materials with several uses. The varied weight percentages of rGO on Ag2S catalysts were synthesized using a simple hydrothermal process and employed for the decomposition of anionic dye naphthol green B (NGB) under solar light. The reduced graphene oxide-based silver sulfide (rGO/Ag2S) nanoparticles were then examined using XRD, SEM, EDS, HR-TEM, XPS, UV-DRS, and PL analysis. Using solar light, the photocatalytic activity of the produced catalyst was examined for the degradation of naphthol green B (NGB) in an aqueous solution. At pH 9, rGO/Ag2S is discovered to be more effective than the other catalysts for the NGB dye mineralization. Analyses have been conducted on the influence of operational parameters on the photo-mineralization of NGB, including the initial pH, initial dye concentration, and catalyst dosage. The dye concentration increased; the efficiency of photocatalytic degradation tended to decrease. Chemical oxygen demand (COD) studies have verified the NGB dye mineralization. Active species trapping revealed that holes, hydroxyl radicals, and superoxide radicals all played major roles in the photocatalytic deterioration of NGB processes. Additionally, a potential mechanism of NGB dye degradation by rGO/Ag2S catalyst is presented. The synthesized compound was further evaluated for antibacterial activity, and the results indicated that rGO/Ag2S were potentially effective antibacterial agents.

Synergistic Effect of Redox Dual PdO x /MnO x Cocatalysts on the Enhanced H2 Production Potential of a SnS/α-Fe2O3 Heterojunction via Ethanol Photoreforming

In the quest for optimal H₂ evolution (HE) through ethanol photoreforming, a dual cocatalyst-modified heterocatalyst strategy is utilized. Tin(II) sulfide (SnS) was hybridized with α-Fe₂O₃ to form the heterocatalyst FeOSnS with a p-n heterojunction structure as confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffusive reflectance spectroscopy (UV-vis DRS), and Brunauer-Emmett-Teller (BET) techniques. PdO _x and PdO _x /MnO _x cocatalysts were loaded onto the FeOSnS heterocatalyst through the impregnation method, as verified by high-resolution transform electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and elemental mapping. Photocatalytic ethanol photoreforming resulted in the production of H₂ as the main product with a selectivity of 99% and some trace amounts of CH₄. The FeOSnS2-PdO _x 2%/MnO _x 1% photocatalyst achieved the highest HE rate of 1654 μmol/g, attributed to the synergistic redox contribution of the PdO _x and MnO _x species.

Construction of α-Fe2O3/Sulfur-Doped Polyimide Direct Z-Scheme Photocatalyst with Enhanced Solar Light Photocatalytic Activity

A novel two-dimensional α-Fe₂O₃/sulfur-doped polyimide (FO/SPI) direct Z-scheme photocatalyst was successfully constructed by a facile thermal treatment method. The effects of α-Fe₂O₃ nanosheets on the morphology, chemical structure, and photoelectronic properties of FO/SPI composites were systematically characterized by different spectroscopic means. These methods include X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, transient fluorescence spectra, and so forth. It was confirmed that the small amounts of α-Fe₂O₃ can availably facilitate exfoliation of bulk SPI, resulting in a transformation of SPI from bulk to 2D layered composite that illustrates tight interface through the coordination Fe-N bond and an all-solid-state direct Z-scheme junction. Thus, the transfer and separation efficiency of photogenerated electron/hole pairs were significantly enhanced, which greatly promoted improvement of the photocatalytic activity of the FO/SPI composite for methyl orange degradation under solar light. This work provides a new approach to constructing efficient inorganic-organic Z-scheme photocatalyst based on strong interface interaction.

ZIF-67 derived Co@NC/g-C3N4 as a photocatalyst for enhanced water splitting H2 evolution

Graphitic carbon nitride (g-C₃N₄), as the one of the most promising photocatalysts, usually relies on noble metal co-catalysts in the photocatalytic water splitting H₂ evolution process, which greatly increases the use cost. Here, a zeolite imidazole framework (ZIF-67) derived Co@NC/g-C₃N₄ composite was constructed through facile thermal condensation of ZIF-67 and melamine. The obtained Co@NC/g-C₃N₄ composites can drive water splitting H₂ evolution without any noble metal co-catalyst under simulated sunlight. The optimal sample exhibits the highest H₂ evolution rate of 161 μmol g^-1·h^-1, which is 6 times of pure g-C₃N₄. The N doped carbon in carbonized ZIF-67 can not only quickly capture separated electrons from g-C₃N_4, but also serve as the co-catalyst. The well dispersed cobalt intermediate on carbonized ZIF-67 also play a role in promoting electron conversion. The formation of junction between carbonized ZIF-67 and g-C₃N₄ could promote quick charge carrier separation and transfer. This work provides a new idea for photocatalytic H₂ evolution without noble metal co-catalysis.

Optically and Electrocatalytically Decoupled Si Photocathodes with a Porous Carbon Nitride Catalyst for Nitrogen Reduction with Over 61.8% Faradaic Efficiency

The photoelectrochemical (PEC) approach is attractive as a promising route for the nitrogen reduction reaction (NRR) toward ammonia (NH₃ ) synthesis. However, the challenges in synergistic management of optical, electrical, and catalytic properties have limited the efficiency of PEC NRR devices. Herein, to enhance light-harvesting, carrier separation/transport, and the catalytic reactions, a concept of decoupling light-harvesting and electrocatalysis by employing a cascade n⁺ np⁺ -Si photocathode is implemented. Such a decoupling design not only abolishes the parasitic light blocking but also concurrently improves the optical and electrical properties of the n⁺ np⁺ -Si photocathode without compromising the efficiency. Experimental and density functional theory studies reveal that the porous architecture and N-vacancies promote N₂ adsorption of the Au/porous carbon nitride (PCN) catalyst. Impressively, an n⁺ np⁺ -Si photocathode integrating the Au/PCN catalyst exhibits an outstanding PEC NRR performance with maximum Faradaic efficiency (FE) of 61.8% and NH₃ production yield of 13.8 µg h^-1 cm^-2 at -0.10 V versus reversible hydrogen electrode (RHE), which is the highest FE at low applied potential ever reported for the PEC NRR.

Ultrasonication-assisted liquid-phase exfoliation enhances photoelectrochemical performance in α-Fe2O3/MoS2 photoanode

This study successfully manufactured a p-n heterojunction hematite (α-Fe₂O₃) structure with molybdenum disulfide (MoS₂) to address the electron-hole transfer problems of conventional hematite to enhance photoelectrochemical (PEC) performance. The two-dimensional MoS₂ nanosheets were prepared through ultrasonication-assisted liquid-phase exfoliation, after which the concentration, number of layers, and thickness parameters of the MoS₂ nanosheets were respectively estimated by UV-vis, HRTEM and AFM analysis to be 0.37 mg/ml, 10-12 layers and around 6 nm. The effect of heterojunction α-Fe₂O₃/MoS₂ and the role of the ultrasonication process were investigated by the optimized concentration of MoS₂ in the forms of bulk and nanosheet on the surface of the α-Fe₂O₃ electrode while measuring the PEC performance. The best photocurrent density of the α-Fe₂O₃/MoS₂ photoanode was obtained at 1.52 and 0.86 mA.cm^-2 with good stability at 0.6 V vs. Ag/AgCl under 100 mW/cm² (AM 1.5) illumination from the back- and front-sides of α-Fe₂O₃/MoS₂; these values are 13.82 and 7.85-times higher than those of pure α-Fe₂O₃, respectively. The results of electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis showed increased donor concentration (2.6-fold) and decreased flat band potential (by 20%). Moreover, the results of IPCE, ABPE, and OCP analyses also supported the enhanced PEC performance of α-Fe₂O₃/MoS₂ through the formation of a p-n heterojunction, leading to a facile electron-hole transfer.

In Situ Corrosion Fabrication of NaNbO3 /Nb3 O7 F Heterojunctions with Optimized Band Realignment for Enhanced Photocatalytic Hydrogen Evolution

Heterostructured photocatalysis is a significant issue owing to the unique band alignment, improved spectrum absorption, and enhanced photocatalytic activity. However, the construction of uniform, controllable, and effective heterojunctions is still a huge challenge. Herein, NaNbO₃ /Nb₃ O₇ F heterojunctions are fabricated through an in situ corrosion technique for the first time. The influence of phase transformation on the hydrogen evolution reaction (HER) activity is investigated systematically in terms of photocatalytic water splitting for H₂ production. Interestingly, the band realignment and good interfacial contact endow the NaNbO₃ /Nb₃ O₇ F heterojunctions with a high HER activity (43.3 mmol g^-1  h^-1 ), which is about 2.4 times that of pure Nb₃ O₇ F and 1.36 times that of pure NaNbO₃ . The results may provide some new insights into the corrosion technique and HER activity of novel heterostructured catalysts.

Enhanced stability and activity of Cu–BTC by trace Ru3+ substitution in water photolysis for hydrogen evolution

Constructing stable, efficient and cost-effective cocatalysts is of great significance for photocatalytic H2 evolution in a dye-sensitization system.

A review on g-C3N4/graphene nanocomposites: multifunctional roles of graphene in the nanohybrid photocatalyst toward photocatalytic applications

Schematic representation of the g-C3N4/graphene hybrid photocatalyst.

NH2-MIL-125(Ti) with transient metal centers via novel electron transfer routes for enhancing photocatalytic NO removal and H2 evolution

The transient YbII/III center coordinated with –NH2 of NH2-MIL-125(Ti) to form a ligand metal charge transfer (LLCMT) pathway, which promoted the rapid transfer of electrons, thereby enhancing photocatalytic NO removal and hydrogen production.

rGO supported self-assembly of 2D nano sheet of (g-C3N4) into rod-like nano structure and its application in sonophotocatalytic degradation of an antibiotic

Graphitic carbon nitride (g-C₃N₄) is an analog of graphite due to its unique electronic structure. g-C₃N₄ based materials have been used in photocatalytic applications. However, pure g-C₃N₄ suffers from major shortcomings which include poor disparity, low surface area and a high recombination rate of photo generated electron-hole pairs that significantly reduce its photocatalytic activity. In this work, self-assembly of g-C₃N₄ sheet into rod shaped g-C₃N₄ was developed via a simple polymerisation method. A composite made of g-C₃N₄ nanorods and rGO (rGO-RCN) was also prepared. The band gap g-C₃N₄ was shifted from 2.77 to 2.6 eV evidented by UV-DRS data. As a result, rGO-RCN showed a relatively high absorption in the visible region. Moreover, a fast electron transfer rate was observed with rGO-RCN composite as conformed from PL analysis and photocurrent measurement. The formation of nanorod and sheet morphologies was confirmed via TEM analysis. The photocatalytic activities of prepared sheet-g-C₃N₄ (SCN)_, Rod g-C₃N₄ (RCN), reduced graphene oxide supported sheet-g-C₃N₄ (rGO-SCN) and reduced graphene oxide supported Rod-g-C₃N₄ (rGO-RCN) were evaluated using a commonly used antibiotic (tetracycline). Among these catalysts, rGO-RCN nanocomposite showed sonophotocatalytic activity 3 times higher compared to pure g-C₃N₄. This superior sonophotocatalytic activity could be due to enhanced visible light absorption of the material, active sites generated by ultrasound, and the high electron transport property of rGO.

Surface-state-induced upward band bending in P doped g-C3N4 for the formation of an isotype heterojunction between bulk g-C3N4 and P doped g-C3N4: photocatalytic hydrogen production

The staggered type heterojunction with g-C₃N₄ based nanomaterials has received much attention owing to its change in chemical potential between two semiconductors.

Carbon nitride nested tubes with graphene as a dual electron mediator in Z-scheme photocatalytic deoxynivalenol degradation

Schematic illustration of the electronic energy level structure and mechanism in the photocatalytic reaction of Z-scheme CNTZG systems under light irradiation.

Dual role of a g-C3N4/carbon intra-Schottky junction in charge carrier generation and separation for efficient solar H2 production

Intra-Schottky junction facilitated charge carrier generation and separation in g-C₃N₄ for efficient solar H₂ production.