Integrating Ru-modulated CoP nanosheets binary co-catalyst with 2D g-C3N4 nanosheets for enhanced photocatalytic hydrogen evolution activity

Harnessing the Power of Light: The Synergistic Effects of Crystalline Carbon Nitride and Ti3C2Tx MXene in Photocatalytic Hydrogen Production

Photocatalytic hydrogen evolution is an environmentally friendly means of energy generation. Although g-C3N4 possesses fascinating features, its inherent shortcomings limit its photocatalytic applications. Therefore, modifying the intrinsic properties of g-C3N4 and introducing cocatalysts are essential to ameliorate the photocatalytic efficiency. To achieve this, metal-like Ti3C2Tx is integrated with crystalline g-C3N4 via a combined salt-assisted and freeze-drying approach to form crystalline g-C3N4/Ti3C2Tx (CCN/TCT) hybrids with different Ti3C2Tx loading amounts (0, 0.2, 0.3, 0.4, 0.5, 1, 5, 10 wt.%). Benefiting from the crystallization of CN, as evidenced by the XRD graph, and the marvelous conductivity of Ti3C2Tx supported by EIS plots, CCN/TCT/Pt loaded with 0.5 wt.% Ti3C2Tx displays an elevated H2 (2) should be subscripted evolution rate of 2651.93 µmol g-1 h-1 and a high apparent quantum efficiency of 7.26% (420 nm), outperforming CN/Pt, CCN/Pt, and other CCN/TCT/Pt hybrids. The enhanced performance is attributed to the synergistic effect of the highly crystalline structure of CCN that enables fleet charge transport and the efficient dual cocatalysts, Ti3C2Tx and Pt, that foster charge separation and provide plentiful active sites. This work demonstrates the potential of CCN/TCT as a promising material for hydrogen production, suggesting a significant advancement in the design of CCN heterostructures for effective photocatalytic systems.

Investigation of Hydrogen and Oxygen Evolution on Cobalt-Nanoparticles-Supported Graphitic Carbon Nitride

This study focuses on fabricating cobalt particles deposited on graphitic carbon nitride (Co/gCN) using annealing, microwave-assisted and hydrothermal syntheses, and their employment in hydrogen and oxygen evolution (HER and OER) reactions. Composition, surface morphology, and structure were examined using inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The performance of Co-modified gCN composites for the HER and OER were investigated in an alkaline media (1 M KOH). Compared to the metal-free gCN, the modification of gCN with Co enhances the electrocatalytic activity towards the HER and OER. Additionally, thermal annealing of both Co(NO3)2 and melamine at 520 °C for 4 h results in the preparation of an effective bifunctional Co3O4/gCN catalyst for the HER with the lower Eonset of -0.24 V, a small overpotential of -294.1 mV at 10 mA cm-2, and a low Tafel slope of -29.6 mV dec-1 in a 1.0 M KOH solution and for the OER with the onset overpotential of 286.2 mV and overpotential of 422.3 mV to achieve a current density of 10 mA cm-2 with the Tafel slope of 72.8 mV dec-1.

Noble metal-free ternary cobalt-nickel phosphides for enhanced photocatalytic dye-sensitized hydrogen evolution and catalytic mechanism investigation

Transition metal phosphides have emerged as compelling alternatives to noble metal catalysts for photocatalytic hydrogen evolution, owing to their high efficiency, stability, ease of preparation, and low-cost-effectiveness. This study investigates a series of binary and ternary phosphides predominantly composed of cobalt and nickel employed for photocatalytic dye-sensitized hydrogen evolution. Under the optimal dye-to-catalyst mass ratio, CoNiP exhibited the highest hydrogen evolution activity (12.96 mmol g-1 h-1), demonstrating more significant and satisfactory performance than a variety of other reported materials. This can be attributed to the high conductivity and low hydrogen evolution overpotential of phosphides, which result from their metallic characteristics and the presence of free electrons, which promote efficient electron transfer between the catalyst and sensitizer. Density functional theory calculations revealed that the cobalt incorporation into the binary phosphides causes a negative shift in the average d-band center for CoNiP, weakening the adsorption affinity of the catalyst towards H2 molecules, thus effectively improving the hydrogen evolution rate compared to the pure binary phosphides. This work provides valuable insights for the development of low-cost and high-performance ternary phosphide photocatalysts.

Constructing Ru@C3 N4 /Cu Tandem Electrocatalyst with Dual-Active Sites for Enhanced Nitrate Electroreduction to Ammonia

Electroreduction of nitrate to ammonia reaction (NO₃ ^- RR) is considered as a promising carbon-free energy technique, which can eliminate nitrate from waste-water also produce value-added ammonia. However, it remains a challenge for achieving satisfied ammonia selectivity and Faraday efficiency (FE) due to the complex multiple-electron reduction process. Herein, a novel Tandem electrocatalyst that Ru dispersed on the porous graphitized C₃ N₄ (g-C₃ N₄ ) encapsulated with self-supported Cu nanowires (denoted as Ru@C₃ N₄ /Cu) for NO₃ ^- RR is presented. As expected, a high ammonia yield of 0.249 mmol h^-1  cm^-2 at -0.9 V and high FE_NH3 of 91.3% at -0.8 V versus RHE can be obtained, while achieving excellent nitrate conversion (96.1%) and ammonia selectivity (91.4%) in neutral solution. In addition, density functional theory (DFT) calculations further demonstrate that the superior NO₃ ^- RR performance is mainly resulted from the synergistic effect between the Ru and Cu dual-active sites, which can significantly enhance the adsorption of NO₃ ^- and facilitate hydrogenation, as well as suppress the hydrogen evolution reaction, thus lead to highly improved NO₃ ^- RR performances. This novel design strategy would pave a feasible avenue for the development of advanced NO₃ ^- RR electrocatalysts.

Size effect of ruthenium nanoparticles on water cracking properties with different crystal planes for boosting electrocatalytic hydrogen evolution

Small size ruthenium (Ru) nanoparticles have shown remarkable potential for electrocatalytic hydrogen evolution reaction (HER). Nevertheless, the complicated preparation and relatively low activity of small size Ru nanoparticles are two key challenges. In this work, carbon nanotubes supported Ru nanoparticles catalysts (cnts@NC-Ru t °C) with different sizes were prepared via using the combination of L-3,4-dihydroxyphenylalanine (l-dopa) self-polymerization oxidation reaction and different high temperature annealing to study the variation of particle activity with size. Electrochemical test results showed that the optimized cnts@NC-Ru 700 °C catalyst exhibited a very low overpotential at 10 mA/cm² (21 mV) and tafel slope of 34.93 mV/dec when the mass loading of precious metal per unit area was merely 12.11 μg/cm² that surpassed most recently reported high-performance Ru based catalyst. The results of density functional theory (DFT) calculation showed that small Ru nanoparticles had abundant active sites, and the H₂O dissociation on small Ru nanoparticles (110) surface is quite easy than other surfaces, while (111) surface of small Ru nanoparticles is beneficial for Tafel step of HER. The synergy between (110) and (111) surfaces on the Ru cluster contributes to its outstanding HER performance. This study provides a novel design idea in promoting the preparation method and uncovering the reason of high activity of small size Ru nanoparticles.

Transition Metal Phosphide Nanoarchitectonics for Versatile Organic Catalysis

Transition metal phosphides (TMP) posses unique physiochemical, geometrical, and electronic properties, which can be exploited for different catalytic applications, such as photocatalysis, electrocatalysis, organic catalysis, etc. Among others, the use of TMP for organic catalysis is less explored and still facing many complex challenges, which necessitate the development of sustainable catalytic reaction protocols demonstrating high selectivity and yield of the desired molecules of high significance. In this regard, the controlled synthesis of TMP-based catalysts and thorough investigations of underlying reaction mechanisms can provide deeper insights toward practical achievement of desired applications. This review aims at providing a comprehensive analysis on the recent advancements in the synthetic strategies for the tailored and tunable engineering of structural, geometrical, and electronic properties of TMP. In addition, their unprecedented catalytic potential toward different organic transformation reactions is succinctly summarized and critically analyzed. Finally, a rational perspective on future opportunities and challenges in the emerging field of organic catalysis is provided. On the account of the recent achievements accomplished in organic synthesis using TMP, it is highly anticipated that the use of TMP combined with advanced innovative technologies and methodologies can pave the way toward large scale realization of organic catalysis.

CoP decorated 2D/2D red phosphorus/B doped g-C3N4 type II heterojunction for boosted pure water splitting activity via the two-electron pathway

CoP decorated 2D/2D red phosphorus/B doped g-C3N4 heterojunction enabled photocatalytic pure water splitting to produce H2 with a two-electron process.

Carbon vacancy-mediated exciton dissociation in Ti3C2Tx/g-C3N4 Schottky junctions for efficient photoreduction of CO2

Earth-abundant g-C₃N₄ is a promising photocatalyst for CO₂ reduction, but its practical application is severely limited by the excitonic effect of g-C₃N₄ derived from strong binding energy and lack of electron-enriched active sites. Herein, we design a novel 2D/2D Schottky junction photocatalysts comprising of Ti₃C₂T_x-modified defective g-C₃N₄ nanosheets with carbon vacancy (denoted as Ti₃C₂T_x/V_c-CN) by a self-assembly method. The carbon vacancies in g-C₃N₄ promote exciton dissociation into free charge, while the formed Schottky junctions between Ti₃C₂T_x and V_c-CN further enables a directional charge transfer, thus providing an electron-rich catalytic surface for the CO₂ reduction. Thanks to the synergy of promoted exciton dissociation and directional electron transfer, the optimal 20% Ti₃C₂T_x/V_c-CN display a high CO evolution rate of 20.54 µmol·g^-1·h^-1 under visible light irradiation, which is 7.4 times higher than that of bare CN. This work highlights the synergy of the promoted exciton dissociation and directional electron transfer in the activity enhancement of photocatalytic CO₂ reduction.

Hierarchical NiCo2S4/ZnIn2S4 heterostructured prisms: High-efficient photocatalysts for hydrogen production under visible-light

Exploring low-cost co-catalyst to ameliorate the photocatalytic activity of semiconductors sets a clear direction for solving energy crisis and achieving efficient solar-chemical energy conversion. In this work, a unique hierarchical hollow heterojunction was constructed by in-situ growing ZnIn₂S₄ nanosheets on the porous NiCo₂S₄ hollow prisms through a low temperature solvothermal method, in which NiCo₂S₄ with semi-metal property acted as non-noble metal co-catalyst. NiCo₂S₄ co-catalyst was innovatively encapsulated in ZnIn₂S₄, which not only relieved the light shielding effect caused by the large loading amount of co-catalyst, but also supplied abundant active sites for H₂ evolution. The hierarchical hollow heterostructure of NiCo₂S₄/ZnIn₂S₄ provided a highly efficient channel for charge transfer. Combining these advantages, NiCo₂S₄/ZnIn₂S₄ composite demonstrated excellent photocatalytic activity. In the absence of sacrificial agent, the NiCo₂S₄/ZnIn₂S₄ photocatalyst achieved a remarkable improved H₂ yield of 0.77 mmol g^-1h^-1 under visible light irradiation (λ > 400 nm), which is 6.6 times greater than that of ZnIn₂S₄. Besides, NiCo₂S₄ even exhibited better performance on the H₂ evolution improvement of ZnIn₂S₄ than precious metal Pt. This work will offer novel insights into the reasonable design of non-noble metal photocatalysts with respectable activity for water splitting.

Synergetic Photo-Thermo Catalytic Hydrogen Production by Carbon Materials

Photo-thermo catalytic hydrogen production represents one of the most promising routes for channeling solar energy but typically suffers from high reaction temperatures. In this work, we develop photo-thermo catalytic hydrogen production at low temperatures by cost-effective, nonplasmonic, and metal-free nitrogen-doped carbon materials (CNO_1-x). We demonstrate that due to the photothermal conversion of CNO_1-x, carrier generation is improved and electron migration is enhanced to suppress the recombination of electron-hole pairs, both of which promote hydrogen production by photocatalysis, while generated hydrogen radicals facilitate the regeneration of active sites for hydrogen production by thermocatalysis. Such synergy greatly promotes photo-thermo catalytic hydrogen production at low temperatures. These results demonstrate the great promise of photo-thermo catalytic hydrogen production over carbon materials at low temperatures.

Creating triazine units to bridge carbon nitride with titania for enhanced hydrogen evolution performance

In this work, a wealth of triazine units was created in carbon nitride through a facile molten salt method to bridge titania and carbon nitride for accelerating charge transportation and enhancing hydrogen production performance. The doping of triazine ring into C₃N₄ framework results in more exposure of - CN - and - CN bond and forms a homojunction (MCN), which favors photocatalysis by acting as photoresponse and active centers, respectively. Moreover, the triazine units can bridge the hybridized C₃N₄ and TiO₂, forming a stable MCN/TiO₂ homo-heterojunction. Attributed to the matched band energy structure of MCN and TiO₂ and the structural characteristics of triazine/heptazine heterocyclic, the light response, charge separation and transfer as well as the lifetime of carriers on MCN/TiO₂ hybrid are improved significantly. As a result, the MCN/TiO₂ homo-heterojunction exhibits excellent activity and stability for photocatalytic hydrogen production performance, up to 2594 μmol∙g^-1∙h^-1 under simulated solar irradiation, which is 5.5 times higher than that of the bare g-C₃N₄.

Well-designed oxidized Sb/g-C3N4 2D/2D nanosheets heterojunction with enhanced visible-light photocatalytic disinfection activity

2D/2D heterojunction photocatalysts with excellent photocatalytic activity highlight considerable potential in water disinfection. Here, an oxidized Sb/g-C₃N₄ 2D/2D nanosheets heterojunction (Sb-SbO_x/CNS) was constructed based on a facile one-step liquid-phase exfoliation method using concentrated sulfuric acid. By doing so, bulk Sb and g-C₃N₄ were exfoliated simultaneously and then, intercalated each other. Compared with CNS and Sb-SbO_x, the obtained Sb-SbO_x/CNS demonstrated better photocatalytic disinfection activity towards Escherichia coli K-12 (E. coli K-12) under visible light irradiation. The 5% oxidized Sb/g-C₃N₄ 2D/2D nanosheets heterojunction (5.0% Sb-SbO_x/CNS) exhibited the best photocatalytic performance and admirable cycling stability, which was ascribed to the unique structure where the interfacial charge separation was strengthened by the strong coupling effect between Sb-SbO_x and CNS. Meanwhile, the fundamental mechanism of photocatalytic disinfection was also proposed. The photogenerated ROS (reactive oxygen species) violently attacked the E. coli K-12 membrane, creating massive and irreparable holes on the cell membrane. The leakage of cations (K⁺, Na⁺, Ca²⁺ and Mg²⁺), adenosine triphosphate, total soluble sugar and protein accelerated the destruction of E. coli K-12. Trapping experiments suggested that the photocatalytic disinfection process against E. coli K-12 was dominated by h⁺ generated on 5.0% Sb-SbO_x/CNS. This work offers a new promising way to modify the 2D/2D heterojunction featuring efficient photocatalytic disinfection performance.

Modification of the surface of Mn0.25Cd0.75S polyhedra with NiB: reducing the surface work function and promoting electron migration for enhanced photocatalytic hydrogen production

NiB is compounded on the surface of Mn0.25Cd0.75S to bring them into close contact. The photocatalytic hydrogen production rate of 10% NiB/Mn0.25Cd0.75S is 13.06 mmol g−1 h−1, which is 3.7 times higher than that of pure Mn0.25Cd0.75S.

Transition metal phosphide of nickel and cobalt-modified Zn0.5Cd0.5S for efficient photocatalytic hydrogen evolution with visible light irradiation

Three transition metal phosphating compounds (NiCoP, Ni2P and Co2P) were loaded on Zn0.5Cd0.5S respectively. Among them, the Zn0.5Cd0.5S/NiCoP composite photocatalyst has the best hydrogen evolution activity.

Carbon nitride based Schottky junction with a Ni–Mo synergistic interaction for highly efficient photocatalytic hydrogen production

A CN/3NiMoP2 Schottky junction with a Ni–Mo synergistic interaction demonstrates a comparable photocatalytic HER performance to CN/3 wt% Pt and satisfactory stability.

Constructing g-C3N4/Cd1−xZnxS-Based Heterostructures for Efficient Hydrogen Production under Visible Light

Two types of photocatalysts, 1%Pt/Cd1−xZnxS/g-C3N4 (x = 0.2–0.3) and Cd1−xZnxS/1%Pt/g-C3N4 (x = 0.2–0.3), were synthesized by varying the deposition order of platinum, and a solid solution of cadmium and zinc sulfides onto the surface of g-C3N4. The characterization of photocatalysts showed that, for 1%Pt/Cd1−xZnxS/g-C3N4, small platinum particles were deposited onto a solid solution of cadmium and zinc sulfides; in the case of Cd1−xZnxS/1%Pt/g-C3N4, enlarged platinum clusters were located on the surface of graphitic carbon nitride. Based on the structure of the photocatalysts, we assumed that, in the first case, type II heterojunctions and, in the latter case, S-scheme heterojunctions were realized. The activity of the synthesized samples was tested in hydrogen evolution from triethanolamine (TEOA) basic solution under visible light (λ = 450 nm). A remarkable increase in hydrogen evolution rate compared to single-phase platinized 1%Pt/Cd1−xZnxS photocatalysts was observed only in the case of ternary photocatalysts with platinum located on the g-C3N4 surface, Cd1−xZnxS/1%Pt/g-C3N4. Thus, we proved using kinetic experiments and characterization techniques that, for composite photocatalysts based on Cd1−xZnxS and g-C3N4, the formation of the S-scheme mechanism is more favorable than that for type II heterojunction. The highest activity, 2.5 mmol H2 g−1 h−1, with an apparent quantum efficiency equal to 6.0% at a wavelength of 450 nm was achieved by sample 20% Cd0.8Zn0.2S/1% Pt/g-C3N4.

Supercritically exfoliated Bi2Se3 nanosheets for enhanced photocatalytic hydrogen production by topological surface states over TiO2

Owing to the unique electronic properties of layered materials, topological insulators have interestingly grabbed much attention in the field of photocatalytic water splitting. Nowadays, 2D layered materials were composited with semiconductor photocatalysts, encourage much as it provides enormous active sites and also significantly prevent photogenerated charge recombination. Especially, Bi₂Se₃ possesses exceptional properties like topologically preserved conducting surface states with bulk insulating behavior and high surface area, which provides unconventional electron dynamics, resulting in facile electron transport and effective charge separation to photocatalyst. So far, several methods have been attempted to synthesize few-layered Bi₂Se₃ nanosheets from its bulk crystals. Here, a unique attempt is made and succeeded to exfoliate bulk Bi₂Se₃ to few layered nanosheets via surfactant free supercritical fluid processing using N-Methyl-2-pyrrolidone (NMP) as an exfoliating agent, with a short reaction time of 15 min. The exfoliation of Bi₂Se₃ crystal was confirmed by several characterization techniques, such as XRD, SEM, Raman, and HR-TEM. Furthermore, different weight percentages of exfoliated Bi₂Se₃ sheets/anatase TiO₂ nanoparticles were prepared and examined the photocatalytic activity using glycerol as a hole scavenger. Among them, 15 wt.% Bi₂Se₃ coupled TiO₂ nanocomposite showed enormous hydrogen evolution rate of 84.9 mmol h^-1g^-1_cat, which is 80 times higher than that of TiO₂ nanoparticles. In addition, the photostability of the nanocomposite was also verified, where it retains 94% of activity even after 4 cycles of continuous experiments. The improved rate of H₂ production was understood by theoretical calculations that topologically preserved conducting surface states of co-catalyst, Bi₂Se₃ nanosheets is supported to high mobile and scatter free electrons. It mediates the transport of electrons with TiO₂ nanoparticles that helped the effective charge separation. Thus, it proves a promising candidate for photocatalytic hydrogen production.

0D ultrafine ruthenium quantum dot decorated 3D porous graphitic carbon nitride with efficient charge separation and appropriate hydrogen adsorption capacity for superior photocatalytic hydrogen evolution

Ultrafine Ru quantum dot decorated 3D porous g-C₃N₄ (U-Ru/3DpCN) photocatalysts were prepared. The optimal photocatalyst U-1Ru/3DpCN achieves an excellent H₂ evolution of 2945.47 μmol g⁻¹ h⁻¹ under visible light with a high AQE of 9.5% at 420 nm.