Photocatalytic H2 Production by Visible Light on Cd0.5Zn0.5S Photocatalysts Modified with Ni(OH)2 by Impregnation Method

Nowadays, the study of environmentally friendly ways of producing hydrogen as a green energy source is an increasingly important challenge. One of these potential processes is the heterogeneous photocatalytic splitting of water or other hydrogen sources such as H₂S or its alkaline solution. The most common catalysts used for H₂ production from Na₂S solution are the CdS-ZnS type catalysts, whose efficiency can be further enhanced by Ni-modification. In this work, the surface of Cd_0.5Zn_0.5S composite was modified with Ni(II) compound for photocatalytic H₂ generation. Besides two conventional methods, impregnation was also applied, which is a simple but unconventional modification technique for the CdS-type catalysts. Among the catalysts modified with 1% Ni(II), the impregnation method resulted in the highest activity, for which a quantum efficiency of 15.8% was achieved by using a 415 nm LED and Na₂S-Na₂SO₃ sacrificial solution. This corresponded to an outstanding rate of 170 mmol H₂/h/g under the given experimental conditions. The catalysts were characterized by DRS, XRD, TEM, STEM-EDS, and XPS analyses, which confirmed that Ni(II) is mainly present as Ni(OH)₂ on the surface of the CdS-ZnS composite. The observations from the illumination experiments indicated that Ni(OH)₂ was oxidized during the reaction, and that it therefore played a hole-trapping role.

Amine-Functionalized Silane-Assisted Preparation of AgNP-Deposited α-Ni(OH)2 Composite Materials and Their Application in Hg2+ Ion Sensing

A facile synthetic methodology for the deposition of different concentrations of Ag nanoparticles (AgNPs) on α-Ni(OH)₂ sheets (α-Ni₁(OH)₂-Ag_0.5, α-Ni₁(OH)₂-Ag₁, α-Ni₁(OH)₂-Ag₂, and α-Ni₁(OH)₂-Ag₃) is reported using N-[3-(trimethoxysilyl)propyl]diethylenetriamine (TPDT) silane. The TPDT aminosilane facilitates the formation of α-Ni(OH)₂ sheets and reduces the Ag⁺ precursor to AgNPs, leading to the deposition of AgNPs on α-Ni(OH)₂ sheets. UV-vis absorption spectroscopy, transmission microscopy analyses, X-ray photoelectron spectroscopy, X-ray diffraction, and attenuated total reflectance-Fourier transform infrared spectroscopy techniques were used to characterize the prepared α-Ni₁(OH)₂-Ag_0.5-3 composite materials. High-angle annular dark-field scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy mapping images and scanning electron microscopy-energy-dispersive X-ray spectroscopy mapping images were recorded to understand the α-Ni₁(OH)₂-Ag composite sheet materials. The optical sensing property of α-Ni₁(OH)₂-Ag_0.5-3 composite materials toward toxic Hg²⁺ ions were investigated using a UV-vis absorption spectroscopy technique. The α-Ni₁(OH)₂-Ag₂ composite material showed selective sensing behavior.

Engineering of Ni(OH)2 Modified Two-Dimensional ZnIn2S4 Heterostructure for Boosting Hydrogen Evolution under Visible Light Illumination

Developing efficient catalysts to produce clean fuel by using solar energy has long been the goal to mitigate the issue of traditional fossil fuel scarcity. In this work, we design a heterostructure photocatalyst by employing two green components, Ni(OH)2 and ZnIn2S4, for efficient photocatalytic H2 evolution under the illumination of visible light. After optimization, the obtained photocatalyst exhibits an H2 evolution rate at 0.52 mL h-1 (5 mg) (i.e., 4640 μmol h-1 g-1) under visible light illumination. Further investigations reveal that such superior activity is originated from the efficient charge separation due to the two-dimensional (2D) structure of ZnIn2S4 and existing high-quality heterojunction.

Construction of CoS2 /Zn0.5 Cd0.5 S S-Scheme Heterojunction for Enhancing H2 Evolution Activity Under Visible Light

In the field of photocatalysis, building a heterojunction is an effective way to promote electron transfer and enhance the reducibility of electrons. Herein, the S-scheme heterojunction photocatalyst (CoS₂ /Zn_0.5 Cd_0.5 S) of CoS₂ nanospheres modified Zn_0.5 Cd_0.5 S solid solution was synthesized and studied. The H₂ evolution rate of the composite catalyst reached 25.15 mmol g^-1  h^-1 , which was 3.26 times that of single Zn_0.5 Cd_0.5 S, whereas pure CoS₂ showed almost no hydrogen production activity. Moreover, CoS₂ /Zn_0.5 Cd_0.5 S had excellent stability and the hydrogen production rate after six cycles of experiments only dropped by 6.19 %. In addition, photoluminescence spectroscopy and photoelectrochemical experiments had effectively proved that the photogenerated carrier transfer rate of CoS₂ /Zn_0.5 Cd_0.5 S was better than CoS₂ or Zn_0.5 Cd_0.5 S single catalyst. In this study, the synthesized CoS₂ and Zn_0.5 Cd_0.5 S were both n-type semiconductors. After close contact, they followed an S-scheme heterojunction electron transfer mechanism, which not only promoted the separation of their respective holes and electrons, but also retained a stronger reduction potential, thus promoting the reduction of H⁺ protons in photocatalytic experiments. In short, this work provided a new basis for the construction of S-scheme heterojunction in addition to being used for photocatalytic hydrogen production.

Zeolitic Imidazolate Framework-67-Derived P-Doped Hollow Porous Co3O4 as a Photocatalyst for Hydrogen Production from Water

As a part of photocatalytic water splitting, the design of low-cost, high-activity catalysts plays an essential role in the development of photocatalytic water splitting. Metal oxides have the advantages of a wide range of sources, many varieties, and easy preparation. Doping engineering on their surface can construct new active sites and adjust their catalytic activity. In this work, a new strategy was developed through anion hybridization to regulate electron delocalization. Using one of the cobalt-based zeolitic imidazole skeletons (ZIF-67) as a precursor material, a two-step calcination method was used to prepare a P-doped Co₃O₄ mixed anion composite photocatalyst. The hydrogen production rate of P@Co₃O₄ is 39 times that of ZIF-67 and 6.8 times that of Co₃O₄. Through density functional theory (DFT) calculations, the electron delocalization state of the sample surface is predicted and the reaction energy barrier is reduced to promote the process of the hydrogen evolution reaction (HER). The special O(δ-)-Co(δ+)-P(δ-) surface bonding state promotes the bridging of isolated electronic states and provides active sites for the adsorption and activation of reaction substrates. The improved electron transport pathway and the synergy between the catalytic sites under the high electron transport rate are the main reasons for the enhanced photocatalytic hydrogen evolution activity. This strategy, including changing the surface bond state and optimizing the structure and composition of the catalyst not only provides a new method for preparing other MOF-derived nanomaterials with porous structures but also inspires the reasonable development of other MOF-based advanced photocatalysts.

Bimetallic zeolite-imidazole framework-based heterostructure with enhanced photocatalytic hydrogen production activity

Bimetallic zeolite-imidazole frameworks with controllable flat band position, band gap and hydrogen evolution reaction characteristics were adopted as a photocatalytic hydrogen production catalyst. Furthermore, the g-C3N4-MoS2 2D-2D surface heterostructure was introduced to the ZnM-ZIF to facilitate the separation as well as utilization efficiency of the photo-exited charge carriers in the ZnM-ZIFs. On the other hand, the ZnM-ZIFs not only inhibited the aggregation of the g-C3N4-MoS2 heterostructure, but also improved the separation and transport efficiency of charge carriers in g-C3N4-MoS2. Consequently, the optimal g-C3N4-MoS2-ZnNi-ZIF exhibited an extraordinary photocatalytic hydrogen evolution activity 214.4, 37.5, and 3.7 times larger than that of the pristine g-C3N4, g-C3N4-ZnNi-ZIF and g-C3N4-MoS2, respectively, and exhibited a H2-evolution performance of 77.8 μmol h-1 g-1 under UV-Vis light irradiation coupled with oxidation of H2O into H2O2. This work will furnish a new MOF candidate for photocatalysis and provide insight into better utilization of porous MOF-based heterostructures for hydrogen production from pure water.

Metal/semiconductor interfaces in nanoscale objects: synthesis, emerging properties and applications of hybrid nanostructures

Hybrid nanostructures, composed of multi-component crystals of various shapes, sizes and compositions are much sought-after functional materials. Pairing the ability to tune each material separately and controllably combine two (or more) domains with defined spatial orientation results in new properties. In this review, we discuss the various synthetic mechanisms for the formation of hybrid nanostructures of various complexities containing at least one metal/semiconductor interface, with a focus on colloidal chemistry. Different synthetic approaches, alongside the underlying kinetic and thermodynamic principles are discussed, and future advancement prospects are evaluated. Furthermore, the proved unique properties are reviewed with emphasis on the connection between the synthetic method and the resulting physical, chemical and optical properties with applications in fields such as photocatalysis.

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.

0D/2D spatial structure of CdxZn1−xS/Ni-MOF-74 for efficient photocatalytic hydrogen evolution

A novel zero-dimensional/two-dimensional Cd_xZn_1−xS/Ni-MOF-74 (CZS/NMF) heterojunction was rationally constructed via a simple hydrothermal and physical mixing method.

An amorphous nickel boride-modified ZnxCd1−xS solid solution for enhanced photocatalytic hydrogen evolution

In this work, the rational design of amorphous Ni_xB as a co-catalyst for the modification of Zn_xCd_1−xS was achieved.

Hydroxides Ni(OH)2&Ce(OH)3 as a novel hole storage layer for enhanced photocatalytic hydrogen evolution

In this work, a novel photocatalyst Ni(OH)₂&Ce(OH)₃@P-CdS was synthesized successfully by phosphorization of CdS and in situ loading of Ni(OH)₂&Ce(OH)₃ on the surface of P-CdS.