Dipole field as charge-transfer bridge between Cu atomic clusters/PtCu alloy nanocubes and nitrogen-rich C3N5 for superior photocatalytic hydrogen evolution.

Utilizing spontaneous polarization field to harness charge transfer kinetics is a promising strategy to boost photocatalytic performance. Herein, a novel Cu atom clusters/PtCu alloy nanocubes coloaded on nitrogen-rich triazole-based C3N5 (PtCu-C3N5) with dipole field was constructed through facile photo-deposition and impregnation method. The dipole field-drive spontaneous polarization in C3N5 acts as a charge-transfer bridge to promote directional electron migration from C3N5 to Cu atom clusters/PtCu alloy. Through the synergistic effects between Cu atom clusters, PtCu alloy and dipole field in C3N5, the optimized Pt2Cu3-C3N5 achieved a record-high performance with H2 formation rate of 4090.4 µmol g-1 h-1 under visible light, about 154.4-fold increase compared with pristine C3N5 (26.5 µmol g-1 h-1). Moreover, the apparent quantum efficiency was up to 25.33 % at 320 nm, which is greatly superior than most previous related-works. The directional charge transfer mechanism was analyzed in detail through various characterizations and DFT calculations. This work offers a novel pathway to construct high-efficiency multi-metal photocatalysts for solar energy conversion.

Size-dependent Copper Nanoparticles Supported on Carbon Nanotubes with Balanced Cu+ and Cu0 Dual Sites for the Selective Hydrogenation of Ethylene Carbonate.

Cyclic carbonate hydrogenation offers an alternative for the efficient indirect CO2 utilization. In this study, a series of carbon nanotubes (CNTs) supported xCu/CNTs catalysts with different Cu loadings were fabricated using a convenient impregnation method, and exhibited excellent catalytic activity for the hydrogenation of ethylene carbonate to methanol and ethylene glycol. The structural and physicochemical properties revealed that acid treatment of CNTs resulted in plentiful oxygen-containing functional groups, providing sufficient anchoring sites for copper species. The calcination process conducted under an inert atmosphere resulted in the formation of ternary CuO, Cu2O, and Cu composites, enhancing the metal-support interaction and facilitating the formation of balanced Cu0 and Cu+ dual sites as well as high active surface area after reduction. Contributed to the synergetic effect of balanced Cu+ and Cu0 species proved by density functional theory calculation and the electron-rich CNTs surface, the 40Cu/CNTs catalyst achieved strengthened catalytic performance with methanol yield of 83%, ethylene glycol yield of 99% at ethylene carbonate conversion of >99%, and 150 h of long-term running stability. Consequently, CNTs supported Cu serve as efficient non-silica based catalyst for ester hydrogenation.

Rational design of covalent organic frameworks/NaTaO3 S-scheme heterostructure for enhanced photocatalytic hydrogen evolution.

As a typical perovskite material, NaTaO3 has been regarded as a potential catalyst for photocatalytic hydrogen evolution (PHE) process, due to its excellent photoelectric property and superior chemical stability. However, the photocatalytic activity of pure NaTaO3 was largely restricted by its poor visible-light absorption ability and rapid recombination of photogenerated charge carriers. Therefore, a covalently bonded TpBpy covalent organic framework (COF)/NaTaO3 (TpBpy/NaTaO3) heterostructure was designed and synthesized by the post modification strategy with (3-aminopropyl) triethoxysilane (APTES) and the in situ solvothermal process. Benefiting from the enhanced built-in electric field by the interfacial covalent bonds and the formation of S-scheme heterostructure between TpBpy and NaTaO3, which were proved by the Ar+-cluster depth profile and X-ray photoelectron spectroscopy (XPS), as well as density functional theory (DFT) calculation results, both the charge transfer efficiency and the PHE performance of the TpBpy/NaTaO3 composites were significantly improved. Additionally, the composites exhibited an excellent absorption performance in the visible region, which was also beneficial for the photocatalytic process. As expected, the optimal TpBpy/20%NaTaO3 composite achieved a remarkable hydrogen evolution rate of 17.3 mmol·g-1·h-1 (10 mg of catalyst) under simulated sunlight irradiation, which was about 173 and 2.4 times higher than that of pure NaTaO3 and TpBpy, respectively. This work provided a novel strategy for constructing highly effective and stable semiconductor/COFs heterostructures with strong interfacial interaction for photocatalytic hydrogen evolution.

Facile construction of a robust CuS@NaNbO3 nanorod composite: A unique p-n heterojunction structure with superior performance in photocatalytic hydrogen evolution.

The construction of heterojunctions is commonly regarded as an efficient way to promote the production of hydrogen via photocatalytic water splitting through the enhancement of interfacial interactions. The p-n heterojunction is an important kind of heterojunction with an inner electric field based on the different properties of semiconductors. In this work, we reported the synthesis of a novel CuS/NaNbO3 p-n heterojunction by depositing CuS nanoparticles on the external surface of NaNbO3 nanorods, using a facile calcination and hydrothermal method. Through the screening of different ratios, the optimum hydrogen production activity reached 1603 µmol·g-1·h-1, which is much higher than that of NaNbO3 (3.6 times) and CuS (2.7 times). Subsequent characterizations proved semiconductor properties and the existence of p-n heterojunction interactions between the two materials, which inhibited the recombination of photogenerated carriers and improved the efficiency of electron transfer. This work provides a meaningful strategy to utilize the p-n heterojunction structure for the promotion of photocatalytic hydrogen production.

Copper phyllosilicate-derived ultrafine copper nanoparticles with plenty of Cu0and Cu+ for the enhanced catalytic performance of ethylene carbonate hydrogenation to methanol.

The hydrogenation of CO2-derived carbonates to methanol is an alternative route for the indirect utilization of abundant C1 sources. Various Cu/SiO2catalysts with different copper loading content prepared by using an ammonia evaporation hydrothermal method are implemented to evaluate the catalytic performance of ethylene carbonate (EC) hydrogenation to methanol and ethylene glycol (EG). The Cu loading content was identified to significantly affect the Cu nanoparticles (NPs) size and metal-support interaction. Highly dispersed Cu NPs restricted and embedded in copper phyllosilicate presented a smaller average particle size than the impregnated Cu/SiO2-IM catalyst. ThexCu/SiO2catalyst with ultrafine Cu NPs showed abundant Cu-O-Si interfaces, acidic sites, and coherent Cu0and Cu+species. The 5Cu/SiO2catalyst achieved methanol yield of 76% and EG yield of 98% at EC conversion of 99%, and no obvious deactivation was observed after long-term operation. The superior catalytic performance of the 5Cu/SiO2catalyst is attributed to the synergetic effect between the appropriate Cu0surface area which provides sufficient active hydrogen, and the atomic ratio of Cu+for the polarization and activation of carbon-oxygen bonds.

Robust S-scheme hierarchical Au-ZnIn2S4/NaTaO3: Facile synthesis, superior photocatalytic H2 production and its charge transfer mechanism.

Designing Step-scheme (S-scheme) heterojunction with the directional charge transfer pathway has been considered as a promising strategy for realizing effective spatial separation of photo-generated carriers in a photocatalytic system by utilizing broadband solar energy. Herein, the novel and ternary S-scheme heterojunction photocatalysts were fabricated by embedding Au nanoparticles (NPs) on the surface of ZnIn2S4/NaTaO3 composites through a facile two-step hydrothermal method for the first time. As expected, it showed an enhanced hydrogen evolution rate of 11404 µmol g-1 h-1, which was approximately 58 and 10 times higher than that of the pristine NaTaO3 nanocubes (197 µmol g-1 h-1) and ZnIn2S4 microspheres (1180 µmol g-1 h-1) under simulated sunlight irradiation, respectively. An intimate heterojunction interface as well as Au nanoparticles as electron reservoir and reactive sites, which enhanced light absorption capacity and accelerated charge carrier separation, was answerable to the huge promotion in the photocatalytic performance. Most notably, XPS, EPR analysis and density functional theory (DFT) calculation results, revealed that the presence of strong interfacial electric fields promoted superior separation efficiency in the Au-ZnIn2S4/NaTaO3 S-scheme heterojunction. This innovative work may shed light on a more appealing and meaningful approach to modify sodium tantalate for the promising application in photocatalytic hydrogen generation.

Embedding indium nitride at the interface of indium-oxide/indium-zinc-sulfide heterostructure with enhanced interfacial charge transfer for high photocatalytic hydrogen evolution.

Enhancing the interfacial charge carriers transfer efficiency is important for designing photocatalysts with excellent hydrogen evolution performance. In this work, we have successfully constructed a In2O3@InN/ZnIn2S4 ternary heterostructure by embedding InN at the interface of thin-layered ZnIn2S4 and tubular In2O3 derived from metal-organic frameworks (MOFs) nanorods for the first time. The InN can not only adjust the energy band structure of In2O3, but also boost the photogenerated charge carriers transfer at the interface of In2O3 and ZnIn2S4. The optimum photocatalytic hydrogen evolution rate of In2O3@InN/ZnIn2S4 composite reaches 275 µmol/h (50 mg of catalyst) under simulated sunlight irradiation, which is obviously higher than pure In2O3 (12.5 times), ZnIn2S4 (2.5 times) and binary In2O3/ZnIn2S4 (1.8 times) photocatalysts. This work can offer a meaningful strategy to promote the interfacial charge separation in the heterostructure for excellent photocatalytic hydrogen evolution activity.

Which Is More Efficient in Promoting the Photocatalytic H2 Evolution Performance of g-C3N4: Monometallic Nanocrystal, Heterostructural Nanocrystal, or Bimetallic Nanocrystal?

Generally, an excellent cocatalyst could promote the photocatalytic hydrogen (H2) evolution performance of g-C3N4 significantly. Herein, a superior cocatalyst of gold-platinum (AuPt) nanocrystal with an ultralow content of Pt was successfully decorated on carbon self-doping g-C3N4 nanosheets (AuPt/CCN) via a facile photodeposition route. The corresponding Pt/CCN, Au/CCN, Au/Pt/CCN, and Pt/Au/CCN were also prepared for comparison. It is found that AuPt/CCN exhibits much superior photocatalytic H2 evolution performance (1135 µmol/h) when irradiated with a 300 W Xe lamp, up to 20, 12, 5, 2, and 1.5 times that of the pristine CCN, Pt/CCN, Au/CCN, Au/Pt/CCN, and Pt/Au/CCN, respectively. The quantum efficiency (QE) of AuPt/CCN at 420 nm reaches 12.5%. The experimental and density functional theory calculation results suggested that the improved AuPt performance can be mainly ascribed to the non-plasmon-related synergistic effect of Au and Pt atoms in AuPt nanocrystal: (1) the proximity and the electronegativity difference of Au and Pt atoms in AuPt accelerate the transfer and separation of charge carriers and (2) the synergistic interaction between Pt and Au atoms optimizes the Gibbs free energy (ΔGH*) of H* (atom) adsorption on AuPt, promoting the H2 generation kinetics of AuPt/CCN.

Hierarchical fabrication of hollow Co2P nanocages coated with ZnIn2S4 thin layer: Highly efficient noble-metal-free photocatalyst for hydrogen evolution.

The directional synthesis of transition metal phosphides was considered to be an effective strategy to solve the overdependence of noble metals on photocatalytic hydrogen evolution (PHE) reactions. Inspiringly, this work reported a facile method for constructing hollow Co2P nanocages (Co2P NCGs) that derived from ZIF-67 by calcining and phosphiding procedure in nitrogen atmosphere to act as non-noble metal cocatalysts. Followed with further coating thin-layered ZnIn2S4 (ZIS) on the surface of Co2P NCGs through a hydrothermal reaction, the hierarchical robust Co2P/ZnIn2S4 nanocages (Co2P/ZIS NCGs) were then delicately fabricated as efficient photocatalysts for PHE reactions. The uniquely hollow structure of Co2P NCGs largely diffused the photogenerated chargers that induced from ZIS and the closely interfacial contact significantly promoted the separation and transfer of electrons from ZIS to Co2P according to density functional theory (DFT) calculation, synergistically resulting in an efficient hydrogen generation performance. PHE results showed that an efficient H2 evolution rate of 7.93 mmol/g/h over 10% Co2P/ZIS NCGs was achieved, about 10 times higher than that of pristine ZnIn2S4. More importantly, the hierarchically hollow Co2P/ZIS NCGs exhibited ascendant PHE activity in comparison with that of 1% noble metal (Pt, Au, Ag) loaded ZnIn2S4 with superior sustainability, all indicating the efficient and stable photocatalysts of Co2P/ZIS NCGs for PHE reactions.

Superior sponge-like carbon self-doping graphitic carbon nitride nanosheets derived from supramolecular pre-assembly of a melamine-cyanuric acid complex for photocatalytic H2 evolution.

The photocatalytic evolution of hydrogen (H2) from water splitting is considered a promising route to overcome the energy crisis, and the key lies in the preparation of efficient photocatalysts. Herein, superior ordered sponge-like carbon self-doped graphitic carbon nitride (g-C3N4) nanosheets (SCCNS) were prepared via a combined strategy of melamine-cyanuric acid complex supramolecular pre-assembly and solvothermal pre-treatment using ethylene glycol (EG) aqueous solutions (EG:water = 50:50 vol.%) as a solvent and carbon doping source. The following pyrolysis converts the naturally arranged melamine-EG-cyanuric acid supramolecular intermediates to highly crystalline SCCNS with large specific surface areas. The optimal SCCNS-180 exhibits superior photocatalytic H2 evolution activities (∼4393 and 11 320 µmol h-1 g-1) when irradiated with visible light and simulated sunlight; these values are up to ∼17- and ∼18-fold higher than that of bulk g-C3N4. The quantum efficiency of SCCNS-180 at λ = 420 nm can reach 6.0%. The excellent photocatalytic performance of SCCNS-180 derives from its distinct ordered sponge-like nanosheet structure with highly crystallinity and the carbon doping, leading to its improved optical absorption, accelerated photoinduced electron-hole pair transfer and separation rate and enlarged specific surface area (134.4 m2 g-1).

Facile one-step hydrothermal synthesis of single-crystalline SnNb2O6 nanosheets with greatly extended visible-light response for enhanced photocatalytic performance and mechanism insight.

The conventional preparation of SnNb2O6 invariably involves complex and laborious steps, which unavoidably introduces defect into the host lattice and also increases the reaction period and costs, resulting in undesired recombination of photo-generated electron-hole pairs. For the first time in this work, we manage to synthesize single-crystalline two-dimensional (2D) SnNb2O6 nanosheets with ultrathin structure through a facile one-step hydrothermal method. Comparative studies were explored to analyze the structure and phase evolution during the preparation course. The synthesized 2D structure demonstrated a narrower band gap of 2.09 eV and specific surface area of 76.1 m2 g-1, which exhibited significantly extended visible-light-responsive range and larger surface area by contrast with the state-of-the-art reports, resulting in excellent visible-light-driven photoactivity towards H2 production and water purification as well. Additionally, further enhanced photocatalytic performance was achieved by the incorporation of Pt as co-catalyst to indirectly indicate the advantage of the SnNb2O6 nanosheets in this method over other reported counterparts. It was found that, a very small amount of Pt loaded on the surface of SnNb2O6 nanosheets would contribute to remarkably higher activity than pure SnNb2O6 nanosheets and exhibit superior stability as well. Moreover, a deep insight into the underlying photocatalytic mechanism was proposed. This work sheds light on a new facile way to fabricate high-performance photocatalytic materials and provided new opportunities for solar-energy conversion.

Activation of Kagome lattice-structured Cu3V2O7(OH)2·2H2O volborthite via hydrothermal crystallization for boosting visible light-driven water oxidation.

We report a feasible strategy via hydrothermal crystallization to activate Kagome lattice-structured Cu3V2O7(OH)2·2H2O volborthite mineral as a stable visible-light-driven photocatalyst. It was demonstrated to play a crucial role in stimulating absorption ability and photodegradation performance for the removal of methylene blue present in high concentration. In contrast, direct calcination was almost ineffective, whereas post-calcination was significantly detrimental. Moreover, the photocatalytic water oxidation activity of hydrothermally crystallizated volborthite was comparable to that of BiVO4, and it was clearly higher than those of WO3 and g-C3N4 from aqueous NaIO3 solution. By further in situ decoration with an optimum amount of CoOx cocatalysts (i.e., 2 wt%), the oxygen evolution rate of volborthite was greatly enhanced, and it was 1.6-fold, 1.8-fold and 2.9-fold higher than those of BiVO4, WO3 and g-C3N4, respectively. The importance of hydrothermal crystallization can be elucidated in terms of water-Kagome lattice structure interactions involving built-in intrinsic electric field and formation of single hydrogen bonds.

Continuous synthesis of methanol: heterogeneous hydrogenation of ethylene carbonate over Cu/HMS catalysts in a fixed bed reactor system.

Continuous fixed-bed catalytic hydrogenation of ethylene carbonate (EC) to methanol and ethylene glycol (EG), an emerging synthetic process of methanol via indirect conversion of CO2, was successfully performed over Cu/HMS catalysts prepared by the ammonia evaporation (AE) method. The catalysts possessed superb performance with a conversion of 100% and a selectivity to methanol of 74%.

Ag3PO4 nanoparticles loaded on 3D flower-like spherical MoS2: a highly efficient hierarchical heterojunction photocatalyst.

Novel 3D hierarchical Ag3PO4/MoS2 composites were successfully prepared through a facile and reproducible hydrothermal-in situ precipitation method. The 3D flower-like spherical MoS2 nanoarchitectures acted as an excellent supporting matrix for the in situ growth of Ag3PO4 nanoparticles. The photocatalytic performance of the composites and the effect of the amount of MoS2 were investigated. The obtained hierarchical Ag3PO4/MoS2 composites exhibited significantly enhanced performance for photocatalytic oxidation of Rhodamine B (RhB) compared with pure Ag3PO4 under visible light irradiation. Ag3PO4/MoS2 composites with 15 wt% of MoS2 showed the optimal photoactivity for the degradation of RhB, which was approximately 4.8 times as high as that of pure Ag3PO4. What's more, the optimal Ag3PO4/MoS2 composite also showed better photodegradation efficiency for methyl orange (MO) and p-chlorophenol (4-CP) than pure Ag3PO4. More attractively, the stability of Ag3PO4 was improved after the in situ deposition of Ag3PO4 particles on the surface of MoS2 nanoflakes due to the conductivity of MoS2 itself as electron acceptors. The enhanced performance of the hierarchical Ag3PO4/MoS2 composites under visible light was caused by a synergistic effect including the improved separation of photogenerated charge carriers, boosted light harvesting, a relatively high surface area and matching energy band structures between the two components. Interestingly, the heterostructured Ag3PO4/MoS2 composite reduced the use of the noble metal silver, thereby effectively reducing the cost of the Ag3PO4 based photocatalyst. Ultimately, a MoS2 involved photocatalytic mechanism for the hierarchical Ag3PO4/MoS2 composites was also proposed.

CeO2 nanorod/g-C3N4/N-rGO composite: enhanced visible-light-driven photocatalytic performance and the role of N-rGO as electronic transfer media.

A novel CeO2 nanorod/g-C3N4/N-rGO ternary composite was synthesized using a simple ultrasonic-heat treatment method for application in the photocatalytic degradation of organic pollutants under the irradiation of visible light. This material shows superior photocatalytic activity compared with pure g-C3N4 and CeO2 nanorods, and the photodegradation rate of RhB is up to 2.1-fold higher than that of the g-C3N4/N-rGO (at the optimum content of 0.25 wt% N-rGO) catalyst when the content of CeO2 nanorods was 2 wt%. The enhancement of photocatalytic activity could be attributed to the synergistic effect among CeO2, g-C3N4 and N-rGO (serves as a conductive network), which was found to lead to more efficient separation of photogenerated electron-hole pairs, resulting in the effective photodegradation of organic pollutants. In addition, superoxide radical anions (˙O2(-)) and holes (h(+)) were considered as the main reactive species during the photodegradation process, and the ternary composite also exhibited preferable stability for the decomposition of RhB. This work provides an in-depth perspective for understanding the N-doped graphene-involved photocatalytic mechanism.

Solvent feedstock effect: the insights into the deactivation mechanism of Cu/SiO2 catalysts for hydrogenation of dimethyl oxalate to ethylene glycol.

The variation of the supports on the Cu/SiO2 catalyst plays an important role in the catalytic performance for hydrogenation of dimethyl oxalate. The loss of silica in the form of tetramethoxysilane from the support under the reaction conditions is responsible for the deactivation of the Cu/SiO2 catalyst.

Highly stable and efficient Ag/AgCl@TiO2 photocatalyst: preparation, characterization, and application in the treatment of aqueous hazardous pollutants.

A new plasmonic photocatalyst of Ag-AgCl@TiO(2) was prepared by deposition-precipitation and photoreduction. This photocatalyst exhibited efficient photocatalytic activity for the degradation of 4-chlorophenol and photoreduction of Cr(VI) ion under visible light irradiation. Its high photocatalytic activity can be attributed to the surface plasmon resonance effect of Ag nanoparticles, which were highly dispersed on the surface of Ag-AgCl@TiO(2). N(2) adsorption and desorption isotherm spectra, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to determine the correlation between the micro-structure and the catalytic properties of the as-prepared photocatalysts.

Synthesis of ZnO nanoflowers and their wettabilities and photocatalytic properties.

By combing laser direct writing and hydrothermal growth, we demonstrate the growth of three-dimensional flowerlike ZnO nanostructures from aqueous solution. Our approach offers synthetic flexibility in controlling film architecture, coating texture and crystallite size. The wettability is studied by measurement of time-dependent contact angles in the as-grown samples. In addition, superior photocatalytic activity of the flowerlike ZnO nanostructures in the degradation of Rhodamine B is investigated as well. The influence factors and formation mechanism of the flowerlike ZnO nanostructures are also analyzed and discussed.

High activity and selectivity of Ag/SiO2 catalyst for hydrogenation of dimethyl oxalate.

Ag/SiO(2) prepared by a sol-gel process is highly effective for selective gas-phase hydrogenation of dimethyl oxalate to corresponding alcohols. The catalysts are of great potential as industrially viable and novel catalysts for the production of methyl glycolate and ethylene glycol.

X-ray photoelectron spectroscopic and Raman analysis of silk fibroin-Cu(II) films.

There is evidence to suggest that Cu(II) is involved in the natural spinning process of a silkworm helping to convert the concentrated silk fibroin (SF) solution (or dope) into tough insoluble threads. To investigate the interaction between SF and Cu(II), a series of regenerated SF (RSF) films with different mass ratios of Cu(II) to SF were prepared. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical interaction between Cu(II) and SF in these Cu(II)-RSF films. A significant change in the binding energy of Cu 2p(3/2) demonstrated that the chemical state of Cu(II) in the Cu(II)-RSF films was affected by the interaction between Cu(II) and SF. Moreover, chemical shifts of N 1s and O 1s of SF were also detected, implying that Cu(II) may coordinate with both N and O atoms in the SF. In addition, Raman spectra of the same series of Cu(II)-RSF films recorded the conformation transition of SF that may occur by the coordination of Cu(II) and SF macromolecular chains.