CoPtx‐loaded Zn0.5Cd0.5S nanocomposites for enhanced visible light photocatalytic H2 production

Zn_0.5Cd_0.5S solid solution, modified with bimetallic CoPt_x nanoparticles, has been prepared using a two‐step organic solution method. The photocatalytic H₂ production rate of CoPt_x–Zn_0.5Cd_0.5S nanocomposites with different composition and percentage of CoPt_x was investigated. The results showed that the 1 wt% CoPt₃–Zn_0.5Cd_0.5S sample had the best activity which was 4.7 times higher than that of pure Zn_0.5Cd_0.5S and 1.2 times higher than that of Pt–Zn_0.5Cd_0.5S for photocatalytic H₂ production. The transient photocurrent response of the Zn_0.5Cd_0.5S showed an obvious increase in the current density after CoPt_x loading. Electrochemical impedance spectra measurements showed that the CoPt_x–Zn_0.5Cd_0.5S nanocomposites with x = 2 and 3 had lower charge transfer resistance R_t than that of Pt–Zn_0.5Cd_0.5S. The enhanced catalytic properties of the CoPt_x–Zn_0.5Cd_0.5S nanocomposites are attributed to their better accumulation ability for photoexcited electrons and higher rate for charge separation and transportation. Copyright © 2016 John Wiley & Sons, Ltd.     

Facile synthesis of MoS2 QDs/TiO2 nanosheets via a self-assembly strategy for enhanced photocatalytic hydrogen production

The MoS₂ quantum dots (QDs) were interspersed on anatase TiO₂ nanosheets with exposed (001) facets by a facile self-assembly strategy. As expected, the MoS₂ QDs/TiO₂ nanosheets display an excellent photocatalytic performance for hydrogen production, and its hydrogen evolution rate is 139 μmol/h/g. More importantly, the hydrogen evolution rate of MoS₂ QDs/TiO₂ nanosheets is almost 4-fold in comparison to that of nude TiO₂ nanosheets. Based on the detailed characterizations, it can be obtained that the improved photocatalytic activity for hydrogen production can be ascribed to the particular characteristics of MoS₂ QDs, which can intensify the photo-absorption efficiency of TiO₂ nanosheets and enhance the separation and transfer efficiency of photo-excited charge carriers. It is anticipated that this work provides a novel paradigm to fabricate the highly-efficient photocatalysts for hydrogen evolution.     

1T-phase MoS2/holey ultrathin g-C3N4 nanosheets based 2D/2D heterostructure for enhanced photocatalytic hydrogen production

Although graphitic carbon nitride (g-C₃N₄) is widely used for photocatalytic hydrogen production, its practical application is restricted by the high recombination rate of photoinduced electron-hole pairs and limited active sites. In this work, holey ultrathin g-C₃N₄ nanosheets (HCN NSs) with rich active sites are prepared, followed by the growth of 1T-MoS₂ NSs on their surfaces to construct 2D/2D 1T-MoS₂/HCN heterostructure. Due to the high surface area and abundant hydrogen active sites of the hybrid, large and intimate 2D nanointerface between MoS₂ and HCN, hydrogen ion adsorption and charge separation/transport ability are greatly enhanced. As a result, 1T-MoS₂/HCN-4 with the optimal 1T-MoS₂ content of 8 wt% displays the highest H₂ production rate of 2724.2 μmol^?1 h^?1 g^?1 under simulated solar light illumination with apparent quantum efficiency of 8.1% (λ = 370 nm). Moreover, the 1T-MoS₂/HCN-4 hybrid manifests improved stability after a long-time test. This study opens the door to design highly-efficient g-C₃N₄ based 2D/2D heterostructures for photocatalytic H₂ production.     

Modification of twin crystal Cd0.5Zn0.5S photocatalyst with up-conversion nanoparticles for efficient photocatalytic H2-production

The photocatalytic H₂-production by solar light has been considered a promising technology to converse solar energy into carbon-free hydrogen. The development of efficient and stable catalysts is the most urgent problem in this technology. Up to now, twin crystal Cd_0.5Zn_0.5S solid solution has been regarded as the best efficient pristine sulphide catalysts for visible-light-driven hydrogen production. Its catalytic activity can be remarkably improved further by loading suitable co-catalyst, such as PdP_~0.33S_~1.67, noble metal Pt, and NiS_x. However, these twin crystal Cd_0.5Zn_0.5S-based nanocomposites can only response to partial (wavelength less than 520 nm) visible light irradiation. Large amount of visible light and near infrared light (NIR) in solar spectrum can not be absorbed by Cd_0.5Zn_0.5S and, therefore, do not contribute to the H₂ production. In this work, β-NaYF₄:Yb³⁺,Tm³⁺,Er³⁺ up-conversion nanoparticles (UPNs) are prepared by a hydrothermal process and the corresponding nanocomposite photocatalyst (twin crystal Cd_0.5Zn_0.5S/β-NaYF₄:Yb³⁺,Tm³⁺,Er³⁺ (T-CZS/UPNs)) based on this kind of up-conversion nanoparticles and twin crystal Cd_0.5Zn_0.5S nanocrystal is successfully prepared for the first time. The compositions, morphologies, and optical properties of the T-CZS/UPNs are investigated using XRD, SEM, HRTEM, UV–vis–NIR absorption spectra and photoluminescence (PL) spectrum. The photocatalytic hydrogen evolution experiments are performed under the irradiation of visible light, NIR light or simulated solar light, respectively. The H₂ production rate over T-CZS/UPNs-15 nanocomposite under the irradiation of simulated solar light in the presence of Na₂S/Na₂SO₃ as sacrificial agent is measured to be 159.3 mmol/h/g, which is 3.4 times higher than that of pristine T-CZS nanocrystals. In particular, this nanocomposite exhibits also significant photocatalytic hydrogen production rate (0.497 mmol/g/h) under NIR light irradiation (λ > 800 nm), reveals the contribution of NIR light to H₂ production via an photon-up-conversion process. This work gives an innovative vision in constructing efficient photocatalysts to make the efficient use of NIR solar light.     

Hollow In2O3 nanotubes decorated with Cd0.67Mo0.33Se QDs for enhanced photocatalytic hydrogen production performance

Novel Cd_0.67Mo_0.33Se/In₂O₃ hollow nanotubes were prepared for photocatalytic hydrogen production application. Under visible light irradiation, Cd_0.67Mo_0.33Se/In₂O₃ hollow nanotubes showed enhanced photocatalytic performance. And the apparent quantum efficiency of 34.86% was obtained when irradiated with 420 nm monochromatic light. The modification of Cd_0.67Mo_0.33Se QDs on the surface of In₂O₃ hollow nanotubes effectively improved the utilization rate of light absorption, increased the separation and migration rate of electrons, inhibited the recombination of photo-generated electron and hole pairs, thus enhancing the photocatalytic activity of water splitting to produce hydrogen. It would be an efficient photocatalyst for hydrogen production application in future.     

Noble metal-free bimetallic NiCo decorated Zn0.5Cd0.5S solid solution for enhanced photocatalytic H2 evolution under visible light

As we know, noble metal (Pt, Pd and Au) with appropriate adsorption free energy of H atoms and higher work function as cocatalyst has been considered to be an effective tactic to enhance photocatalytic activity. However, they are limited severely by scarcity and high-cost. Herein, Zn_0.5Cd_0.5S solid-solution photocatalyst decorated with noble metal-free NiCo cocatalyst has been successfully obtained through one-step photochemical route. It is found that the lifespan of charge carriers of Zn_0.5Cd_0.5S@NiCo can be prolonged dramatically after modification, and the photocatalytic H₂ rate reach to 34.7  mmol g⁻¹·h⁻¹ is nearly 9 times higher than the bare Zn_0.5Cd_0.5S (λ ≥ 420 nm). The superior photocatalytic activity for ZCS@NiCo could be mainly ascribed to higher separation and transfer efficiency of photogenerated carriers by introduced bimetallic NiCo cocatalysts possessing the superior electron transfer property and reducing the onset over-potential of water reduction, which was proved by experiment. This study can provide a potential strategy to design a more efficient noble metal-free cocatalyst over photocatalyst.     

Transesterification reaction for biodiesel production from soybean oil using Ni0.5Zn0.5Fe2O4 nanomagnetic catalyst: Kinetic study

Biodiesel was successfully produced by transesterification process of soybean oil and methanol using Ni_0.5Zn_0.5Fe₂O₄ nanomagnetic catalyst. The Ni_0.5Zn_0.5Fe₂O₄ catalyst was synthesized by the combustion method and its properties were investigated using X-ray diffraction, N₂ physisorption at 77 K, Fourier transform infrared analysis, thermogravimetric analysis, scanning electron microscopy, and a transmission electron microscopy. The performance of catalyst was investigated during transesterification reaction for fatty acid methyl esters (FAMEs) production. FAMEs were studied by gas chromatography technique. The effect of reaction conditions such as molar ratio of methanol/soybean oil, catalyst amount, reaction temperature, and reaction time on FAMEs yield was also evaluated. The biodiesel yield of 92.1% was obtained under the following reaction conditions: 9:1 of methanol/soybean oil molar ratio and, 2% of catalyst loading at 180°C in 3 hours. Furthermore, the energy of activation (E_a) was 67.4 kJ.mo1⁻¹ and the pre-exponential factor (k_o) was 8.35 × 10⁴ L mol⁻¹ min⁻¹ determined using Arrhenius equation.     

NiSe2/Cd0.5Zn0.5S as a type-II heterojunction photocatalyst for enhanced photocatalytic hydrogen evolution

A designed type-II heterojunction photocatalyst, NiSe₂/Cd_0.5Zn_0.5S (NiSe₂/CZS), was successfully synthesized and it exhibits outstanding photocatalytic hydrogen evolution performance. The optimal loading amount of NiSe₂ on Cd_0.5Zn_0.5S is 13 wt %, and the corresponding hydrogen production rate is approximately 121.01 mmol g^?1 h^?1 under visible light. The heterojunction structure between Cd_0.5Zn_0.5S and NiSe₂ promoted the separation of photogenerated electron-hole pairs, effectively suppressed the photogenerated carrier recombination and endowed the material with excellent interfacial charge transfer properties, thus improving the photocatalytic performance.     

Crown-like Zn0.5Cd0.5S/M-TiO2 composites derived from metal-organic frameworks for photocatalytic hydrogen production

Photocatalytic hydrogen production has been recognized as one of the most desirable approaches to overcome the worldwide energy and environmental issues. Here, novel sea urchin-like Zn_0.5Cd_0.5S and mesoporous TiO₂ (M-TiO₂) are designed, and a series of crown-like Zn_0.5Cd_0.5S/M-TiO₂ composites with different contents of M-TiO₂ are synthesized by hydrothermal method. The optimum hydrogen production rate of composites reaches 180.4 mmolh^?1g^?1 with the AQE up to 48.9% at 420 nm, which is 3.5 and 216 times that of pure Zn_0.5Cd_0.5S and the M-TiO₂, respectively. The outstanding performance of optimized Zn_0.5Cd_0.5S/M-TiO₂ composite prepared in this work exceeds most reported Cd-S-based catalysts. The improvement on the photocatalytic performance of composites is mainly due to the enlarged specific surface area, the exposure of more active sites, and the enhancement of the electron-hole separation efficiency.     

(Zn,Cd)S porous layers for dye-sensitized solar cell application

Porous (Zn,Cd)S structures were formed by screen printing of CdS, ZnS, ZnCl₂ and CdCl₂ powders in different configurations and sintering in air at high temperature. The XRD (X-ray diffraction) analysis of these layers sintered at different temperatures revealed that the CdO and ZnO formation in the (Zn,CdS) matrix is by the phase transformation of (Zn,Cd)S. The structure, composition and photosensitivity of this composite structure depends on the sintering temperature, sintering atmosphere and the flux to semiconductor (F/S) ratio. The results indicate that the screen printed (Zn,Cd)S structure may be used as a photoconductor in solid state devices and as a photoelectrode in photo-electro-chemical energy conversion systems.     

Novel noble-metal free S/Ni12P5/Cd0.5Zn0.5S composite with enhanced H2 evolution activity under visible light

Constructing composite photocatalyst is an efficient way to realize the application of photocatalysis owing to the fast separation of photocarriers. In this report, we constructed a novel ternary noble-metal free S/Ni₁₂P₅/Cd_0.5Zn_0.5S (S/Ni₁₂P₅/CZS) composite which displayed much higher activity than binary Ni₁₂P₅/CZS, S/CZS and especially CZS solid solution for H₂ generation under visible light illumination (λ ≥ 420 nm). 15% S/Ni₁₂P₅/CZS showed the highest activity of H₂ production (525.5 μmol h⁻¹) among all the samples due to the optimal separating efficiency of photocarriers, and its apparent quantum efficiency is 4.37% at 420 nm. In the photocatalytic process, the photogenerated electrons of CZS solid solution quickly moved to elemental S through Ni₁₂P₅ as solid electron transfer mediator, resulting in high separation efficiency of photocarriers and outstanding activity of H₂ production over S/Ni₁₂P₅/CZS. Moreover, S/Ni₁₂P₅/CZS presented excellent stability after 10 runs recycling experiment. The significant finding of this paper provides new strategy to rationally design composite photocatalyst for efficiently splitting water to generate clean energy H₂.     

The TiO2/Mn0.2Cd0.8S hollow heterojunction with Mn/Cd bimetallic synergy towards photocatalytic hydrogen production enhancement

The TiO₂/Mn_0.2Cd_0.8S hollow heterojunction with Mn/Cd bimetallic synergy is prepared via a continuous chemical-hydrothermal-etching method. There, the TiO₂ shell and Mn_0.2Cd_0.8S nanoparticles were deposited by continuous chemical-hydrothermal method on the surface of SiO₂ template, and subsequently the SiO₂ template was etched via a chemical method. Evaluated by HER, the as-prepared TiO₂/Mn_0.2Cd_0.8S hollow heterojunction exhibits an obvious photocatalytic enhancement to about ~5822.94 μmol/g∙h(~40 folds of TiO₂, ~7 folds of Mn_0.2Cd_0.8S), which can be mainly ascribed to that, the narrow band gap of Mn_0.2Cd_0.8S can increase the visible light energy utilization, the TiO₂/Mn_0.2Cd_0.8S heterojunction and Mn/Cd bimetallic synergy can separate/transfer the photo-generated charge carriers efficiently, and the sufficient specific surface areas and actives from 3D hollow structure can promote the charge carrier diffusing into water quickly for achieving H₂ generation. Additionally, the hollow 3D structure can provide a decent physical-chemical stability to improve the photocatalytic stability.     

Non-noble metal ultrathin MoS2 nanosheets modified Mn0.2Cd0.8S heterostructures for efficient photocatalytic H2 evolution with visible light irradiation

A series of non-noble metal ultrathin MoS₂ nanosheets modified Mn_0.2Cd_0.8S heterostructured composites were prepared by an ultrasonic assisted hydrothermal synthesis process. Comparing with the pristine Mn_0.2Cd_0.8S composite, the obtained ultrathin MoS₂/Mn_0.2Cd_0.8S composites exhibited a significantly improved photocatalytic activity for hydrogen evolution from water with visible light response. The optimized photocatalytic activity toward MoS₂/Mn_0.2Cd_0.8S composite is around 8 times of the pristine Mn_0.2Cd_0.8S composite. Moreover, the ultrathin MoS₂/Mn_0.2Cd_0.8S composites displayed good photocatalytic stability in the course of photochemical reaction. The excellent photocatalytic activity of the ultrathin MoS₂/Mn_0.2Cd_0.8S composites might be attributed to the formed heterojunctions in composites itself and the sufficient active edge sites in MoS₂ phase. A possible photocatalytic mechanism was tentatively proposed. Considering its excellent photocatalytic activity and good photochemical stability, the obtained ultrathin MoS₂/Mn_0.2Cd_0.8S composite has potential application in photocatalytic hydrogen evolution from water by using solar energy.     

Cd0.5Zn0.5S/Ni2P noble-metal-free photocatalyst for high-efficient photocatalytic hydrogen production: Ni2P boosting separation of photocarriers

Establishing efficient co-catalytic loaded semiconductors for efficient charge separation is a hopeful way for enhance photocatalytic water splitting hydrogen evolution. Herein, we successfully constructed the Cd_0.5Zn_0.5S/Ni₂P (CZS/Ni₂P) nanocomposites via two-step hydrothermal method. The CZS/Ni₂P composites show much improved activity than the origin CZS for photocatalytic H₂ generation. When the content of Ni₂P loaded on the Cd_0.5Zn_0.5S (CZS) is 0.3 mol%, the photocatalyst achieves the highest photocatalytic hydrogen generation rate of 41.26 mmol g⁻¹ h⁻¹ under visible light. The Ni–S bonds on the close contact interface between CZS and Ni₂P can be act as electron-bridge to provide a channel for electron transfer. During the photocatalysis processing, Ni₂P can be used as electron traps to attract electrons from CZS, resulting in the improvement of the photocatalytic performance.     

In situ photodeposition of metalloid Ni2P co-catalyst on Mn0.5Cd0.5S for enhanced photocatalytic H2 evolution with visible light

Developing a suitable and low-cost co-catalyst is highly desired for promoting photocatalytic water splitting of H₂ production. Herein, we adopted a simple in situ photodeposition strategy by coupling Mn_0.5Cd_0.5S with non-noble co-catalyst Ni₂P to construct Ni₂P/Mn_0.5Cd_0.5S composites and achieved obviously improved H₂ amount (31.83 mmol/h/g) in visible-light region, which is nearly 2.8 times than that of pure Mn_0.5Cd_0.5S. Such photocatalytic performance is in a relatively superior position among Mn_xCd_1?xS-based photocatalysts. The apparent quantum efficiency of Ni₂P/Mn_0.5Cd_0.5S-7 composites reaches 32% at 420 nm. Through optical and photoelectrochemical measurements, a possible mechanism was proposed, it was found that the interface between metalloid Ni₂P and Mn_0.5Cd_0.5S contacts closely, which facilitates transfer and separation of charge carriers, thus promotes the reduction of H⁺ to H₂. This study provides a new design of cut-price, high-efficiency photocatalyst for H₂ evolution.     

Fabrication of direct Z-scheme heterojunction between Zn0.5Cd0.5S and N-rich graphite carbon nitride for boosted H2 production

In this work, a novel direct Z-scheme g-C₃N₅/Zn_0.5Cd_0.5S (CN/ZCS) heterojunction was successfully synthesized. Furthermore, its photocatalytic activity for hydrogen production was also investigated, whose photoluminescence spectrum revealed the charge transfer procedure of g-C₃N₅ and ZCS. Moreover, the optimized hydrogen production rate of ZCS with 15 wt% of g-C₃N₅ (15% CN/ZCS) was about 142.8 mmol/h/g and quantum efficiency (Q.E.) was circa 33.7% under 420 nm monochromatic light. Compared with the pure ZCS and ZCS with 2 wt% of Pt, the 15% CN/ZCS composite exhibited considerable improved hydrogen production rate, which was about 20 times and 7 times, respectively. The formation of CN/ZCS composite resulted in faster separation of the photogenerated electron-hole pairs. Our work may supply valuable data for the application of g-C₃N₅ on photocatalysis.     

Mn2+‐doped Zn2GeO4 for photocatalysis hydrogen generation

Zn₂GeO₄ and Zn₂GeO₄:Mn²⁺ were synthesized by a hydrothermal method. The phase, microstructure, and optical and photoelectrochemical properties were investigated. The photocatalytic activities were evaluated by the photocatalytic hydrogen generation. The X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer‐Emmett‐Teller (BET) results indicate the Mn²⁺ doping has no obvious influence on the phase and microstructure of Zn₂GeO₄. But the Mn²⁺ doping influences the optical and photoelectrochemical properties obviously. The Mn²⁺ doping leads to the red shift of band gap edge and the light absorption in visible region. The Zn₂GeO₄:Mn²⁺ has the greater light absorption efficiency, more efficient e^?‐h⁺ pair separation and promoting charge transfer across the electrode/electrolyte interface. These characteristics of Zn₂GeO₄:Mn²⁺ suggest that it has higher activity than that of Zn₂GeO₄ and this is confirmed by the highly efficient hydrogen generation.     

Facile hydrothermal synthesis of 3D flower‐like La‐MoS2 nanostructure for photocatalytic hydrogen energy production

Three‐dimensional (3D) flower‐like MoS₂ nanostructures were prepared via facile and cost‐effective hydrothermal method by varying hydrothermal temperature (180°C, 200°C, and 220°C) and reaction time (6, 12, 24, and 36 hours). The results demonstrated that the sample prepared at 200°C for 24 hours have 3D flower‐like MoS₂ nanostructure (SEM) with hexagonal phase structure (XRD). Moreover, this novel photocatalyst was also modified by lanthanum element (La³⁺) with varying La³⁺ atomic ratio (0.5%, 1%, 2%, 3%, and 4%). Interestingly, the La³⁺ incorporation into MoS₂ has good effect on the specific surface area and optical properties of MoS₂ photocatalyst. Furthermore, the flower‐like 3%LaMoS₂ nanostructure photocatalyst exhibited 5.2‐times higher efficiency for H₂ evolution via water splitting as compared with pure MoS₂ under the same conditions. This superior efficiency of the photocatalyst for H₂ production arises from the positive synergistic effect between MoS₂ and lanthanum in the composite photocatalyst due to higher surface area, enhanced light absorption, and inhibited electron‐holes pair recombination. This study presents an expensive photocatalyst for energy production via water spitting.     

A thin clothe coated architecture of ZnIn2S4/H2Ta2O6 for enhanced photocatalytic hydrogen production

Focused on energy and environment issues, in present investigation, an economical and eco-friendly photocatalyst for hydrogen evolution in water splitting reaction has been designed and fabricated. The characteristics by XRD, TEM, XPS and AFM confirmed that an octahedral H₂Ta₂O₆ is uniformly capsuled by ZnIn₂S₄ thin clothes to form a package ZnIn₂S₄/H₂Ta₂O₆ heterojunction. The assembled ZnIn₂S₄/H₂Ta₂O₆ exhibits superior hydrogen generated performance with a value of 3217.31 μmol g⁻¹•h⁻¹ under simulated sunlight irradiation, without obvious deactivation in five consecutive cycles. The enhanced activity and reusability are mainly attributed to ultrathin clothe-like shell, the well-matched band structure and a large tight contact interface in the package type construction, which can promote redox ability, extend light harvesting range and boost charge separation efficiency. The present study proposes a new design idea to assemble a highly efficient and durable photocatalyst for solar hydrogen generation by splitting water.     

Carbon nitride quantum dots (CNQDs)/TiO2 nanoparticle heterojunction photocatalysts for enhanced ultraviolet-visible-light-driven bisphenol a degradation and H2 production

The extension of the absorption band of solar energy is an efficient strategy to dramatically enhance the application value of TiO₂. Based on this, we have prepared carbon nitride quantum dots (CNQDs)/TiO₂ nanoparticle heterojunctions by mixing TiO₂ and the as-prepared CNQDs by the simple mechanical stirring method. The synthesized CNQDs-x/TiO₂ composites were systematically characterized in term of their physicochemical properties, the performance of photocatalytic degradation of Bisphenol A, and their photocatalytic hydrogen evolution performance under stimulated sunlight. The CNQDs/TiO₂ nanoparticle exhibited a lattice spacing of 0.352 nm, assigning to the (101) crystal plane of anatase phase TiO_2. Intriguingly, the modification of TiO₂ nanoparticle with CNQDs can indeed get a narrower optical band gap of 3.02 eV, with a wider absorption range extending to visible light region and could enhance their overall photocatalytic performance over the commercially TiO₂ nanoparticles. In Addition, it was demonstrated that the ratios of CNQDs to TiO₂ exhibited obvious influence on the photocatalytic performance of the obtained composite catalysts.By contrast to the pure TiO₂, all the CNQDs-x/TiO₂ composites displayed higher photocatalytic activities, and the CNQDs-2/TiO₂ possessed the highest photocatalytic degradation capacity towards bisphenol A with a reaction rate constant 0.30 (0.17 for pure TiO₂). Meanwhile, the H₂ production rate of CNQDs-2/TiO₂ sample is about 30 μmol g⁻¹ h⁻¹ higher than that of the pure TiO₂ nanoparticles. Moreover, the photocurrent intensity of CNQDs-2/TiO₂ was about 25 times higher compared to that of pure TiO₂ nanoparticles. Therefore, our research results can provide valuable guidance for exploring high-performance photocatalytic materials.