An infinite chain, {[Ni(tn)2]3[Fe(CN)4(μ-CN)2]2}n,a new catalyst for electrochemical-driven water splitting and photochemical-driven hydrogen evolution from water under blue light

A new catalyst for both water reduction and oxidation, based on an infinite chain, {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n, is formed by the reaction of NiCl₂, 1,3-propanediamine (tn) and K₃ [Fe(CN)₆]. {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n can electro-catalyze hydrogen evolution from a neutral aqueous buffer (pH 7.0) with a turnover frequency (TOF) of 1561 mol of hydrogen per mole of catalyst per hour (H₂/mol catalyst/h) at an overpotential (OP) of 837 mV {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n also can electro-catalyze O₂ production from water with a TOF of ～45 mol O₂ (mol cat)^?1s^?1 at an OP of 591 mV. Under blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H₂A) as a sacrificial electron donor, {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n can photo-catalyze hydrogen generation from an aqueous buffer (pH 4.0) with a turnover number (TON) of 11,450 mol H₂ per mole of catalyst (mol of H₂ (mol of cat)^?1) during 10 h irradiation. The average of apparent quantum yield (AQY) is as high as 40.96% during 10 h irradiation. Studies indicate that {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n exists in two forms: a cyano-bridged chain ({[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n) in solid, and a salt ([Ni(tn)₂]₃ [Fe(CN)₆]₂) in aqueous media; Catalytic reaction occurs on the nickel center of [Ni(tn)₂]²⁺, and the introduction of [Fe(CN)₆]^3- can improve the catalytic efficiency of [Ni(tn)₂]²⁺ for H₂ or O₂ generation. We hope these findings can afford a new method for the design of catalysts for both water reduction and oxidation.     

Designing of a novel Mn0.2Cd0.8S@ZnO heterostructure with Type-II charge transfer path for efficient photocatalytic hydrogen evolution reaction

The development of photocatalysts with efficient hydrogen evolution activity has been the goal for sustainable hydrogen production. In this work, heterojunction composite photocatalyst is formed by hydrothermal coupling of ZnO and Mn_0.2Cd_0.8S. Compared with pure ZnO and Mn_0.2Cd_0.8S, the composite photocatalyst has the ability to provide more abundant active sites and better photogenerated carriers separation efficiency. The optimized composite photocatalyst shows a 9.36-fold increase in hydrogen evolution activity (4297.99 μmol g^?1 h^?1) compared to Mn_0.2Cd_0.8S (459.31 μmol g^?1 h^?1) and exhibits excellent cycling stability. Density functional theory calculations identifies Type-II charge transfer path in the composite photocatalyst, achieving effective separation in space of photogenerated electrons from holes and suppressing recombination within the semiconductor. The results show that the construction of Type-II heterojunction in this work achieves a significant enhancement of the hydrogen evolution activity of the photocatalyst by constructing carrier transport channels at the contact interface of the heterojunction.     

Integration of ReS2 on ZnIn2S4 for boosting the hydrogen evolution coupled with selective oxidation of biomass intermediate under visible light

Challenge remains to develop a high activity of photocatalyst for large-scale industrial application in photocatalytic selective conversion of biomass alcohols into the value-added chemicals accompany with H₂ evolution in aqueous solution. Herein, ReS₂ as high efficiency co-catalyst is utilized to modify the flower-like ZnIn₂S₄ (ZIS) microspheres to obtain heterojunction composite, result in dramatically enhancements in photocatalytic oxidation of furfural alcohols cooperative with H₂ evolution. Further studies show that the optimal catalyst containing 4.08 wt% ReS₂ (RZIS-3) realize remarkably generation rates of H₂ and furfural at 3092.9 and 2981.1 μmol g^?1 h^?1, respectively, nearly 12 times faster than that of blank ZnIn₂S₄. Mechanism studies verify that the migration of the photogenerated carriers from ZnIn₂S₄ to ReS₂ leading to the remarkably photoactivity of the composite. Moreover, the typical photocatalysis not rely on a single model substrate, and high performance of the composite has been identified for the oxidation of other alcohols biomass intermediate to value-added aldehydes/ketones, providing a new insight for design and fabrication of the novel photocatalytic hydrogen evolution systems.     

Photocatalytic hydrogen generation by WO3 in synergism with hematite-anatase heterojunction

The present study reports about exploration of a multi-component photocatalytic system comprising of WO₃, TiO₂ and Fe₂O₃ with tandem n-n heterojunctions. The ternary WO₃/TiO₂/Fe₂O₃ nanocomposite with WO₃ nanoparticles over the interfaces of Fe₂O₃ and TiO₂ is synthesized by wet precipitation followed by thermal decomposition. The WO₃/TiO₂/Fe₂O₃ nanocomposite has an enhanced photocatalytic performance towards hydrogen generation by water splitting reaction under visible light irradiation, when compared to the Fe₂O₃/TiO₂ system. A band gap of 2.10 eV, favouring visible light absorption was achieved with the distribution of WO₃ nanopartcles over the interfaces of Fe₂O₃ and TiO_2. The as prepared WTF heterojunction exhibited a maximum hydrogen production rate of 10.2 mL h⁻¹ for a catalyst loading of 0.025 g mL⁻¹. The enhanced photocatalytic performance is tested in presence of various sacrificial agents and proton source. In both cases, the higher photocatalytic efficiency is attributed to the more visible light harnessing ability and pronounced charge separation owing to the tandem n-n heterojunctions generated between TiO₂ with WO₃ and TiO₂ with Fe₂O₃ semiconductors and enhancing the lifetime of the photogenerated electron-hole pairs.     

In situ growing Cu2(OH)2CO3 on oxidized carbon nitride with enhanced photocatalytic hydrogen evolution and pollutant degradation

A novel composite has been successfully synthesized in situ via a coprecipitation method about the coupling of Cu₂(OH)₂CO₃ with oxidized carbon nitride (O-g-C₃N₄) forming Cu₂(OH)₂CO₃/O-g-C₃N₄ (CuCN) heterojunction structure. The as-prepared composites were characterized by diverse means. The CuCN composite with 3:5 mass ratio of Cu₂(OH)₂CO₃ to O-g-C₃N₄ (60CuCN) presented an extremely excellent photocatalytic activity. The photocatalytic H₂ evolution of 60CuCN was around 23.26 and 44.62 times higher than that of g-C₃N₄ and Cu₂(OH)₂CO₃, respectively. The photocatalytic degradation malachite green (MG) rate of 60CuCN was up to 91%, which was around 2.2 and 4.8 times as much as that of g-C₃N₄ and Cu₂(OH)₂CO₃, respectively. These results are mainly attributed to the structure property of O-g-C₃N₄ and the heterojunction structure of the composite, which could effectively accelerate the separation and transfer rate of photogenerated electrons and holes. The holes (h⁺) and superoxide radicals (·O₂⁻) played a dominant role in photocatalytic degradation MG reaction.     

A one-pot sealed ammonia self-etching strategy to synthesis of N-defective g-C3N4 for enhanced visible-light photocatalytic hydrogen

Photocatalytic hydrogen (H₂) evolution from water is considered as a prospective approach, which can convert inexhaustible solar energy into chemical energy to alleviate energy crisis and environmental problems. Herein, the N-defective g-C₃N₄ with porous structure was firstly synthesized in a sealed crucible by one-step thermal polymerization method. The experimental data showed that the yield of the catalyst was obviously increased under sealing condition. Moreover, the N-defective g-C₃N₄ prepared from urea precursor under sealed condition reached an optimum photocatalytic H₂ production rate of 597.4 μmol/h and an apparent quantum efficiency of 15.6% at wavelength of 420 nm. This enhanced photocatalytic H₂ production performance is mainly ascribed to the introduction of N-defects, which not only extended of the visible light absorption, but also acted as the electron trap centers to suppress the recombination of the photogenerated electron and hole pairs. This work offers one-step facile strategy for the introduction of N-defects to prepare N-defective g-C₃N₄ with superior photocatalytic activity, which is also a great substitute for the high-energy consuming and complicated synthetic routes.     

MoS2-mesoporous LaFeO3 hybrid photocatalyst: Highly efficient visible-light driven photocatalyst

Perovskite type materials have high potential photocatalytic application towards both hydrogen energy generation and organic dye degradation due to their high stability and good reusability. Here, it is the first analysis of photocatalytic degradation of RhB and hydrogen energy evolution under visible light over MoS₂/LaFeO₃ nanocomposite. The physicochemical properties of the materials were characterized using a range of techniques such as XRD, TEM, XPS, FTIR, PL, photocurrent, etc. The optical properties of the nanocomposite show good absorption in UV-Vis spectra as compared to the bare LaFeO₃. In this study, MoS₂/LaFeO₃ nanocomposite was synthesized through single step in situ hydrothermal processes with a narrow bandgap, enhanced photocatalytic application under visible light. This novel MoS₂/LaFeO₃ nanocomposite is an efficient and promising photocatalyst for both hydrogen energy evolution and organic dye degradation.     

Photocatalytic hydrogen production over CuO and TiO2 nanoparticles mixture

Cheap and efficient photocatalysts were fabricated by simply mixing TiO₂ nanoparticles (NPs) and CuO NPs. The two NPs combined with each other to form TiO₂/CuO mixture in an aqueous solution due to the opposite surface charge. The TiO₂/CuO mixture exhibited photocatalytic hydrogen production rate of up to 8.23 mmol h⁻¹ g⁻¹ under Xe lamp irradiation when the weight ratio of P25 to CuO was optimized to 10. Although the conduction band edge position of CuO NPs is more positive than normal hydrogen electrode, the TiO₂/CuO mixture exhibited good photocatalytic hydrogen production performance because of the inter-particle charge transfer between the two NPs. The detailed mechanism of the photocatalytic hydrogen production is discussed. This mixing method does not require a complicated chemical process and allows mass production of the photocatalysts.     

Photo-electrochemistry of metallic titanium/mixed phase titanium oxide

In this study, the effect of potassium hydroxide concentration in anodization bath, anodization time, and calcination temperature on the photo-electrochemical behavior of metallic titanium/mixed phase titanium oxide is investigated. Further, the phase structure of a titanium oxide photocatalyst prepared on a titanium electrode through a high-voltage anodization method is examined. The study exploits photo-electrochemical, Fourier transform infrared spectroscopy attenuated total reflectance (FTIR–ATR), X-ray diffraction, and Raman spectroscopic methods to obtain better insights into the mechanism of mixed-phase titanium oxide formation. In this regard, the photo-electrochemical properties of the photocatalysts prepared in single excitation energy, violet light (410 nm), were investigated. The anodization time and the potassium hydroxide concentration in the anodization bath have significant effects on the photo-electrochemical properties of the photocatalysts. The experiments show that the effect of potassium hydroxide concentration is a function of the anodization potential applied, demonstrating different patterns as the anodization potential changes. Furthermore, FTIR-ATR, X-ray diffraction, and Raman spectroscopic studies reveal that the extended anodization times decrease the population of OH-containing groups, leading to lower photo-electrochemical performance. On the other hand, the formation of anatase phases becomes more favorable only in the extended anodization times before application of the calcination process. Additionally, the calcination temperature has a significant impact on the anatase to rutile ratio. Finally, increasing potassium hydroxide concentration leads to the formation of an amorphous titanium oxide layer. It can be concluded that the obtained information might have a significant impact on the preparation of titanium oxide and other metal oxide photocatalysts through the high voltage anodization process.     

A facile synthesis of nano-layer structured g-C3N4 with efficient organic degradation and hydrogen evolution using a MDN energetic material as the starting precursor

The construction of a high-performance g-C₃N₄ photocatalyst through a facile and green synthesis method remains a great challenge for H₂ production and organic pollutants degradation. In this work, we developed a nano-layer structured g-C₃N₄ (NL-CN) photocatalyst with a 230 m²/g surface area via the thermal polymerization method using melaminium dinitrate (MDN), which is one of the more energetic materials, as the precursor. The energy coming from the drastic decomposition of nitrate anions in MDN caused the thick layers of bulk CN to be exfoliated to produce many much-thinner nano-layers when at 500 °C for 2 h, which obviously elevated the surface area of the g-C₃N₄. The resultant NL-CN displays a superior visible-light H₂-generation and rhodamine B (RhB) photodegradation efficiency (λ > 420 nm) compared to those of bulk g-C₃N₄ (CN) prepared through heating melamine because of the nano-layered structures, which lead to higher specific surface areas, a rapid charge transfer efficiency and a higher redox potential. These results demonstrate that the utilization of MDN as a starting material provides a new opportunity for the facile and green synthesis of high-efficiency nanostructured g-C₃N₄ photocatalysts with lower energy consumption and environmental pollution levels.