Noble metal-free bimetallic phosphide-decorated Zn0.5Cd0.5S with efficient photocatalytic H2 evolution

The rapid recombination of charge carriers in semiconductor-based photocatalysts results in a low photocatalytic activity. Co-catalysis is considered a promising strategy to improve the photocatalytic performance of semiconductors. In this study, a bimetallic phosphide was grown by a facile in situ growth method. Loading the cocatalyst (7 wt% NiCoP) leads to activity enhancement by a factor of approximately 27 times in the visible-light-driven hydrogen evolution relative to the pristine Zn0.5Cd0.5S. The photocatalysis shows a high hydrogen evolution rate of 19.5 mmol g-1 h-1, which is much higher than that of the single metal phosphide (Ni2P: 7.0 mmol g-1 h-1; CoxP: 8.1 mmol g-1 h-1) and 7 wt% Pt modified Zn0.5Cd0.5S (0.3 mmol g-1 h-1). Its apparent quantum efficiency reaches 41.6% at 420 nm. Moreover, the photocatalyst exhibits a remarkable photostability for five consecutive cycles of photocatalytic activity measurements with a total reaction time of 15 hours. The excellent photocatalytic activity of the photocatalyst was attributed to the in situ-formed NiCoP cocatalyst, which not only acts as a reactive site but also accelerates the separation of charge carriers.

Plasmon Au/K-doped defective graphitic carbon nitride for enhanced hydrogen production

Knowledge of the photocatalytic H₂-evolution mechanism is of critical importance for water splitting, and for designing active catalysts for a sustainable energy supply. In this study, we prepared plasmon Au-modified K-doped defective graphitic carbon nitride (Au/KCNx) and then applied it in photocatalytic hydrogen-production tests. The hydrogen-production rate of the Au/KCNx photocatalyst (8.85 mmol g^-1 h^-1) was found to be almost 104 times higher than that of Au/g-C₃N₄ (0.085 mmol g^-1 h^-1), together with an apparent quantum efficiency of 12.8% at 420 nm. It could significantly improve the photocatalytic activities of the Au/KCNx sample, which was attributed to the synergistic effects of the plasmon effect, potassium doping, and nitrogen vacancy. In addition, the Au/KCNx photocatalyst had a large surface area, which was beneficial for photogenerated carrier separation and transfer. The novel strategy proposed here is a potential new method for the development of graphitic carbon nitride photocatalysts with obviously enhanced activities.

Heterojunctions on Ta2O5@MWCNT for Ultrasensitive Ethanol Sensing at Room Temperature

Heterojunctions of Ta₂O₅ and multiwalled carbon nanotubes (MWCNTs) have been successfully synthesized by a facile and cost-effective hydrothermal method, with a super thin and uniform Ta₂O₅ shell wrapped around the MWCNT. The combination of Ta₂O₅ and MWCNTs at the interface not only modifies the morphology but also forms the p-n heterojunction, which contributes to the reconstruction of band structure, as well as the low resistance of matrix and highly chemisorbed oxygen content. The Ta₂O₅@MWCNT p-n heterojunction exhibits ultrasensitive performance to ethanol at room temperature, with a response of 3.15 toward 0.8 ppm ethanol and a detection limit of 0.173 ppm. The sensor has a high reproducibility at various concentrations of ethanol, superior selectivity to other gases, and long-term stability. The strategy of hybriding metal oxide semiconductors with MWCNT promises to provide a feasible and further developable pathway for high-performance room-temperature gas sensors.

Ultrafast charge separation in a WC@C/CdS heterojunction enables efficient visible-light-driven hydrogen generation

The rapid recombination of photogenerated carriers and strong photocorrosion have considerably limited the practical application of CdS in the field of photocatalysis. Loading a cocatalyst has been widely utilized to largely enhance photocatalytic activity. In the present work, a WC@C cocatalyst was prepared by a novel molten salt method and explored as an efficient noble-metal-free cocatalyst to significantly enhance the photocatalytic hydrogen evolution rate of CdS nanorods. The WC@C/CdS composite photocatalyst with a 7 wt% content of WC@C showed the highest photocatalytic hydrogen evolution rate of 8.84 mmol g^-1 h^-1, which was about 21 and 31 times higher than those of CdS and 7 wt% Pt/CdS under visible light irradiation. A high apparent quantum efficiency (AQY) of 55.28% could be achieved under 420 nm monochromatic light. Furthermore, the photocatalytic activity of the 7 wt% WC@C/CdS photocatalyst exhibited good stability for 12 consecutive cycles of the photocatalytic experiment with a total reaction time of 42 h. The excellent photocatalytic performance of the photocatalyst was attributed to the formation of a Schottky junction and the loading cocatalyst, which not only accelerated the separation of the photogenerated carrier but also provided a reactive site for hydrogen evolution. This work revealed that WC@C could act as an excellent cocatalyst for enhancing the photocatalytic activity of CdS nanorods.

Phosphorus doped and defect modified graphitic carbon nitride for boosting photocatalytic hydrogen production

The enhancement of photogenerated carrier separation efficiency is a significant factor in the improvement of photocatalyst performance in photocatalytic hydrogen evolution. Heteroatom doping and defect construction have been considered valid methods to boost the photocatalytic activity of graphitic carbon nitride. Herein, we report graphitic carbon nitride modified with P doping and N defects (PCN_x), and the effects of doping and defects were investigated in photocatalytic H₂ evolution. Its hydrogen evolution rate can reach up to about 59.1 μmol h^-1, which is more than 123.1 times higher than pristine graphitic carbon nitride under visible light irradiation. Importantly, the apparent quantum efficiency reaches 8.73% at 420 nm. The excellent performance of the PCN_x photocatalyst was attributed to the following aspects: (I) the large BET surface area of PCN_x affords more active sites for H₂ production and (II) the introduction of P and N defects can accelerate the charge carrier separation and transfer efficiency, leading to more efficient photocatalytic hydrogen production. The photocatalyst showed obviously enhanced activities.

Interlayer Charge Transfer Over Graphitized Carbon Nitride Enabling Highly-Efficient Photocatalytic Nitrogen Fixation

Exploiting cost-effective, high-efficiency, and contamination-free semiconductors for photocatalytic nitrogen reduction reaction (N₂ RR) is still a great challenge, especially in sacrificial-free system. On basis of the electron "acceptance-donation" concept, a boron-doped and carbon-deficient g-C₃ N₄ (B_x CvN) is herein developed through precise dopant and defect engineering. The optimized B₁₅ CvN exhibisted an NH₃ production rate of 135.3 µmol h^-1  g^-1 in pure water with nine-fold enhancement to the pristine graphitic carbon nitride (g-C₃ N₄ ), on account of the markedly elevated visible-light harvesting, N₂ activation, and multi-directional photoinduced carriers transfer. The decorated B atoms with coexistent occupied and empty sp³ hybridized orbitals are theoretically proved to be in charge of the increase of N₂ adsorption energy from -0.08 to -0.26 eV and the change in N₂ adsorption model from one-way to two-way end-on pattern. Noticeably, the elaborate coordination of doped B atoms and carbon vacancies greatly facilitated the interlayer interaction and vertical charge migration of B_x CvN, which is distinctly revealed through the charge density difference calculations. The current study provides an alternative groundbreaking perspective for advancing photocatalytic N₂ RR through the targeted configuration of the defect and dopant sites.

Surveying the Synthesis, Optical Properties and Photocatalytic Activity of Cu3N Nanomaterials

This review addresses the most recent advances in the synthesis approaches, fundamental properties and photocatalytic activity of Cu₃N nanostructures. Herein, the effect of synthesis conditions, such as solvent, temperature, time and precursor on the precipitation of Cu₃N and the formation of secondary phases of Cu and Cu₂O are surveyed, with emphasis on shape and size control. Furthermore, Cu₃N nanostructures possess excellent optical properties, including a narrow bandgap in the range of 0.2 eV–2 eV for visible light absorption. In that regard, understanding the effect of the electronic structure on the bandgap and on the optical properties of Cu₃N is therefore of interest. In fact, the density of states in the d-band of Cu has an influence on the band gap of Cu₃N. Moreover, the potential of Cu₃N nanomaterials for photocatalytic dye-degradation originates from the presence of active sites, i.e., Cu and N vacancies on the surface of the nanoparticles. Plasmonic nanoparticles tend to enhance the efficiency of photocatalytic dye degradation of Cu₃N. Nevertheless, combining them with other potent photocatalysts, such as TiO₂ and MoS_2, augments the efficiency to 99%. Finally, the review concludes with perspectives and future research opportunities for Cu₃N-based nanostructures.

A Novel N-Doped Nanoporous Bio-Graphene Synthesized from Pistacia lentiscus Gum and Its Nanocomposite with WO3 Nanoparticles: Visible-Light-Driven Photocatalytic Activity

This paper reports the synthesis of a new nitrogen-doped porous bio-graphene (NPBG) with a specific biomorphic structure, using Pistacia lentiscus as a natural carbon source containing nitrogen that also acts as a bio-template. The obtained NPBG demonstrated the unique feature of doped nitrogen with a 3D nanoporous structure. Next, a WO₃/N-doped porous bio-graphene nanocomposite (WO₃/NPBG-NC) was synthesized, and the products were characterized using XPS, SEM, TEM, FT-IR, EDX, XRD, and Raman analyses. The presence of nitrogen doped in the structure of the bio-graphene (BG) was confirmed to be pyridinic-N and pyrrolic-N with N1 peaks at 398.3 eV and 400.5 eV, respectively. The photocatalytic degradation of the anionic azo dyes and drugs was investigated, and the results indicated that the obtained NPBG with a high surface area (151.98 m²/g), unique electronic properties, and modified surface improved the adsorption and photocatalytic properties in combination with WO₃ nanoparticles (WO₃-NPs) as an effective visible-light-driven photocatalyst. The synthesized WO₃/NPBG-NC with a surface area of 226.92 m²/g displayed lower bandgap and higher electron transfer compared with blank WO₃-NPs, leading to an increase in the photocatalytic performance through the enhancement of the separation of charge and a reduction in the recombination rate. At the optimum conditions of 0.015 g of the nanocomposite, a contact time of 15 min, and 100 mg/L of dyes, the removal percentages were 100%, 99.8%, and 98% for methyl red (MR), Congo red (CR), and methyl orange (MO), respectively. In the case of the drugs, 99% and 87% of tetracycline and acetaminophen, respectively, at a concentration of 10 mg/L, were removed after 20 min.

The synergy of photodeposited CoNi co-catalysts for the photocatalytic performance of C3N4/CdS nanosheets: optimized Gibbs free energy and Co–S bridging bonds

The photocatalytic performance of C₃N₄/CdS is enhanced by the photodeposited CoNi alloyed NPs: the synergy of the optimized Gibbs free energy of the CoNi co-catalysts and the formed Co–S bridging bonds between CoNi and CdS.

Redox Dual-Cocatalyst-Modified CdS Double-Heterojunction Photocatalysts for Efficient Hydrogen Production

Cadmium sulfide (CdS) as one of the most common visible-light-responsive photocatalysts has been widely investigated for hydrogen generation. However, its low solar-hydrogen conversion efficiency caused by fast carrier recombination and poor catalytic activity hinders its practical applications. To address this issue, we develop a novel and highly efficient nickel-cobalt phosphide and phosphate cocatalyst-modified CdS (NiCoP/CdS/NiCoPi) photocatalyst for hydrogen evolution. The dual-cocatalysts were simultaneously deposited on CdS during one phosphating step by using sodium hypophosphate as the phosphorus source. After the loading of the dual-cocatalysts, the photocurrent of CdS significantly increased, while its electrical impedance and photoluminescence emission dramatically decreased, which indicates the enhancement of charge carrier separation. It was proposed that the NiCoP cocatalyst accepts electrons and promotes hydrogen evolution, while the NiCoPi cocatalyst donates electrons and accelerates the oxidation of sacrificial agents (e.g., lactic acid). Consequently, the visible-light-driven hydrogen evolution of this composite photocatalyst greatly improved. The dual-cocatalyst-modified CdS with a loading content of 5 mol % showed a high hydrogen evolution rate of 80.8 mmol·g^-1·h^-1, which was 202 times higher than that of bare CdS (0.4 mmol·g^-1·h^-1). This is the highest enhancement factor for metal phosphide-modified CdS photocatalysts. It also exhibited remarkable stability in a continuous photocatalytic test with a total reaction time of 24 h.

Noble metal-free 0D-1D NiCoP/Mn0.3Cd0.7S nanocomposites for highly efficient photocatalytic H2 evolution under visible-light irradiation

Efficient and noble metal-free co-catalyst loading is an effective solution for separating and transferring photo-generated carriers and lowering the overpotential in photocatalytic H₂ evolution activity. In this work, we designed and prepared a series of novel NiCoP/Mn_0.3Cd_0.7S (NCP/MCS) composites by modifying MCS nanorods with the co-catalyst NCP using a simple calcination method. Notably, the 10-NCP/MCS composite displays the optimum photocatalytic H₂ evolution rate of 118.5 mmol g^-1 h^-1 under visible-light irradiation. This is approximately 3.39 times higher than that of pure MCS. The corresponding apparent quantum efficiency is 10.2% at 420 nm. The superior photocatalytic activity of the NCP/MCS composites can be attributed to the efficient separation of photogenerated carriers caused by the intimate heterojunction interface between NCP and MCS, smaller transfer resistance, and lower overpotential of NCP. Moreover, the NCP/MCS composites exhibit remarkable photostability. A plausible mechanism is proposed.

Two-Dimensional Materials and Composites as Potential Water Splitting Photocatalysts: A Review

Hydrogen production via water dissociation under exposure to sunlight has emanated as an environmentally friendly, highly productive and expedient process to overcome the energy production and consumption gap, while evading the challenges of fossil fuel depletion and ecological contamination. Various classes of materials are being explored as viable photocatalysts to achieve this purpose, among which, the two-dimensional materials have emerged as prominent candidates, having the intrinsic advantages of visible light sensitivity; structural and chemical tuneability; extensively exposed surface area; and flexibility to form composites and heterostructures. In an abridged manner, the common types of 2D photocatalysts, their position as potential contenders in photocatalytic processes, their derivatives and their modifications are described herein, as it all applies to achieving the coveted chemical and physical properties by fine-tuning the synthesis techniques, precursor ingredients and nano-structural alterations.

A size tunable bimetallic nickel-zinc nitride as a multi-functional co-catalyst on nitrogen doped titania boosts solar energy conversion

To enable high-efficiency solar energy conversion, rational design and preparation of low cost and stable semiconductor photocatalysts with associated co-catalysts are desirable. However preparation of efficient catalytic systems remains a challenge. Here, N-doped TiO2/ternary nickel-zinc nitride (N-TiO2-Ni3ZnN) nanocomposites have been shown to be a multi-functional catalyst for photocatalytic reactions. The particle size of Ni3ZnN can be readily tuned using N-TiO2 nanospheres as the active support. Due to its high conductivity and Pt-like properties, Ni3ZnN promotes charge separation and transfer, as well as reaction kinetics. The material shows co-catalytic performance relevant for multiple reactions, demonstrating its multifunctionality. Density functional theory (DFT) based calculations confirm the intrinsic metallic properties of Ni3ZnN. N-TiO2-Ni3ZnN exhibits evidently improved photocatalytic performances as compared to N-TiO2 under visible light irradiation.

New Versatile Synthetic Route for the Preparation of Metal Phosphate Decorated Hydrogen Evolution Photocatalysts

Photocatalytic hydrogen generation will benefit from the realization of more active but less expensive cocatalysts compared with noble metal counterparts. Herein we developed a universal vapor deposition method that selectively uses the thermal decomposition products of sodium hypophosphite as a phosphorus source for the fabrication of inexpensive and highly efficient metal phosphate (MPi) modified CdS nanorods. We find that the modification with a bimetal phosphate (i.e., 5 wt % NiCoPi) leads to an activity enhancement by a factor of approximately 52 in boosting visible-light-driven hydrogen evolution relative to the pristine CdS nanorods. The photocatalyst exhibits a high hydrogen generation rate of 13.44 mmol·g^-1·h^-1, which is much higher than that of its single metal counterparts (NiPi, 8.70 mmol·g^-1·h^-1; CoPi, 5.79 mmol·g^-1·h^-1) and 1 wt % Pt modified CdS (1.33 mmol·g^-1·h^-1). Its apparent quantum efficiency reaches 23.5% at 420 nm. Furthermore, it also shows remarkable photostability for eight consecutive cycles of photocatalytic activity tests with total reaction time of 24 h. The excellent photocatalytic performance of the photocatalyst is believed to be associated with the in situ formed Ni^ICoP and NiCo^IIIPi cocatalysts, which not only play an important role in photogenerated charge separation but also provide highly active catalytic reaction sites for the corresponding hydrogen evolution reaction and the sacrificial agent oxidation reaction.

Nickel-decorated g-C3N4 hollow spheres as an efficient photocatalyst for hydrogen evolution and oxidation of amines to imines

Photocatalysts composed of earth-abundant elements are highly desired for photocatalytic hydrogen evolution as well as oxidation of amines to imines without the requirement of precious metals.

Fabrication of a novel Ni3N/Ni4N heterojunction as a non-noble metal co-catalyst to boost the H2 evolution efficiency of Zn0.5Cd0.5S

Ni_xN/Zn_0.5Cd_0.5S composites displayed better photocatalytic hydrogen production from water in comparison with pristine Zn_0.5Cd_0.5S (ZCS), as well as Pt/ZCS and Ni₃N/ZCS.

Interfaces of graphitic carbon nitride-based composite photocatalysts

This review concentrates on the interface issues of g-C₃N₄-based photocatalysts, including methods for constructing interfaces, techniques for identifying interfaces, and the types and roles of the as-developed interfaces.

Prussian blue derived Fe2N for efficiently improving the photocatalytic hydrogen evolution activity of g-C3N4 nanosheets

Prussian blue derived Fe₂N nanoparticles to efficiently improve the photocatalytic H₂-generation rate over pure g-C₃N₄ nanosheets.