Highly efficient white-LED-light-driven photocatalytic hydrogen production using highly crystalline ZnFe2O4/MoS2 nanocomposites

Designing efficient photocatalytic systems for hydrogen evolution is extremely important from the viewpoint of the energy crisis. Highly crystalline heterostructure catalysts have been established, considering their interface electric field effect and structural features, which can help improve their photocatalytic hydrogen-production activity. In this study, we fabricated a highly crystalline heterojunction consisting of ZnFe₂O₄ nanobricks anchored onto 2D molybdenum disulfide (MoS₂) nanosheets (i.e., ZnFe₂O₄/MoS₂) via a hydrothermal approach. The optimized ZnFe₂O₄/MoS₂ photocatalyst, with a ZnFe₂O₄ content of 7.5 wt%, exhibited a high hydrogen-production rate of 142.1 μmol h⁻¹ g⁻¹, which was 10.3 times greater than that for the pristine ZnFe₂O₄ under identical conditions. The photoelectrochemical results revealed that the ZnFe₂O₄/MoS₂ heterojunction considerably diminished the recombination of electrons and holes and promoted efficient charge transfer. Subsequently, the plausible Z-scheme mechanism for photocatalytic hydrogen production under white-LED light irradiation was discussed. Additionally, the influence of cocatalysts on the photocatalytic hydrogen evolution for the ZnFe₂O₄/MoS₂ heterostructure was investigated. This work has demonstrated a simplified coupling of one-dimensional or zero-dimensional structures with 2D nanosheets for improving the photocatalytic hydrogen production activity as well as confirmed that MoS₂ is a viable substitute for precious metal-free photocatalysis.     

Ultrathin MoS2 nanosheets in situ grown on rich defective Ni0.96S as heterojunction bifunctional electrocatalysts for alkaline water electrolysis

Developing earth-abundant and highly active bifunctional electrocatalysts are critical to advance sustainable hydrogen production via alkaline water electrolysis but still challenging. Herein, heterojunction hybrid of ultrathin molybdenum disulfide (MoS₂) nanosheets and non-stoichiometric nickel sulfide (Ni_0.96S) is in situ prepared via a facile one-step hydrothermal strategy, followed by annealing at 400 °C for 1 h. Microstructural analysis shows that the hybrid is composed of intimate heterojunction interfaces between Ni_0.96S and MoS₂ with exposed active edges provided by ultrathin MoS₂ nanosheets and rich defects provided by non-stoichiometric Ni_0.96S nanocrystals. As expected, it is evaluated as bifunctional electrocatalysts to produce both hydrogen and oxygen via water electrolysis with a hydrogen evolution reaction (HER) overpotential of 104 mV at 10 mA cm⁻² and an oxygen evolution reaction (OER) overpotential of 266 mV at 20 mA cm⁻² under alkaline conditions, outperforming most current noble-metal-free electrocatalysts. This work provides a simple strategy toward the rational design of novel heterojunction electrocatalysts which would be a promising candidate for electrochemical overall water splitting.     

Facile synthesis of three-dimensional spherical Ni(OH)2/NiCo2O4 heterojunctions as efficient bifunctional electrocatalysts for water splitting

Synthesis of highly efficient, non-noble and bi-functional electrocatalysts is exceedingly challenging and necessary for water splitting devices. In this work, three-dimensional spherical Ni(OH)₂/NiCo₂O₄ heterojunctions are prepared by a one-step hydrothermal method and the hybrids are explored as efficient electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte via tuning different Ni/Co atomic ratios of heterojunctions. The optimized Ni(OH)₂/NiCo₂O₄ (S (1:1)) exhibits high electrocatalytic activity with an ultralow over-potential of 189 mV at 10 mA cm⁻² for the HER. With regard to the OER, the over-potential of the as-synthesized S (1:1) heterojunction is only 224 mV at the current density of 10 mA cm⁻². The improved catalytic performance of the Ni(OH)₂/NiCo₂O₄ heterojunctions is attributed to the chemical synergic combining of Ni(OH)₂ and NiCo₂O₄, large specific surface area for exposing more accessible active sites, and heterointerface for activating the intermediates that facilitates electron/electrolyte transport. The prepared catalyst exhibits good durability and stability in HER and OER catalyzing conditions. This study provides a feasible approach for the building of highly efficient bifunctional water splitting electrocatalysts and stimulates the development of renewable energy conversion and storage devices.     

Visible-light-driven HSr2Nb3O10/CdS heterojunctions for high hydrogen evolution activity

In this study, layered perovskite HSr₂Nb₃O₁₀ ultrathin nanosheets (HSNO-ns) was successfully exfoliated within 2 h by a facile microwave-assisted method. Then, HSNO-ns/CdS heterojunction was fabricated through a facile hydrothermal route for deposition of CdS nanoparticles on HSNO-ns. The photocatalytic performances of composites were systematically investigated and discussed by varying the CdS content. The results illustrated that the photocatalytic hydrogen production rate of HSNO-ns were significantly increased by coupled CdS nanoparticles on the HSNO-ns. The optimized HSNO-ns/CdS3 composites without noble metal showed highest photocatalytic activity, which was about 8.38 times and 330 times higher than that of pristine CdS and HSNO-ns, respectively, under the visible light irradiation (≥420 nm) using triethanolamine as sacrificial agent. The enhanced photocatalytic H₂ production activity was predominantly attributed to the strong optical absorption capacity, high specific surface area and improved charge carrier separation efficiency. Our present work provides a new pathway into the design of two-dimension nanosheets-based photocatalysts and promotes their practical application in various environmental and energy issues.     

One-pot hydrothermal synthesis of nano-sheet assembled NiO/ZnO microspheres for efficient sulfur dioxide detection

The nano-sheet assembled NiO/ZnO microspheres with a diameter of ca. 2 μm have been synthesized via facile hydrothermal method followed by a thermal treatment process. The gas-sensing measurement results show that the sensor using nano-sheet assembled NiO/ZnO microspheres exhibits improved response to sulfur dioxide gas compared with the pure ZnO microspheres sensor. In particular, the sensor with a Ni/Zn molar ratio of 0.5 (0.5 mol% NiO/ZnO) shows high response value (S = 107) and superior selectivity to 10 ppm sulfur dioxide at a low operating temperature of 160 °C and the detection limit of the NiO/ZnO sensor toward sulfur dioxide is down to 1 ppm (S = 6). The enhanced sensing performance is attributed to the formation of p-n heterojunctions on the interface, the catalytic function of NiO and the three-dimensional microspheres composed of the lamellar structure with a large specific surface area. The three-dimensional microspheres provide more active sites for gas adsorption, and the interlayer gap facilitates the diffusion of gas in three-dimensional structure, resulting in high sensitivity and superior selectivity. This work provides a simple method for the synthesis of NiO/ZnO heterojunction microspheres with superior gas-sensing performance, which can be used as a potential material for sulfur dioxide detection.     

Construction of Au/TiO2 Heterojunction with high photocatalytic performances under UVA illumination

Anatase TiO₂ nanoparticles (NPs) were successfully prepared through a hydrothermal approach, and Au NPs at various Au (0.1–2 wt%) contents were photodeposited onto the TiO₂ NPs surface. The photocatalytic efficiency for the Au/TiO₂ NPs for resorcinol photodegradation throughout UVA illumination was assessed. The TEM images and XPS findings indicated that the Au NPs are highly distributed onto TiO₂ surface in the metallic state. The 0.1%Au/TiO₂ NPs exhibited the highest photocatalytic efficiency of about 95.34%; however, 72.36% is given by pure TiO₂ NPs. It was found that the photodegradation rate of 0.1% Au/TiO₂ NPs exhibited 1.5 times of magnitude higher than pure TiO₂ NPs. 0.1%Au/TiO₂ NPs was considered to be the outstanding photoactive due to the ultimate efficient charge-carriers separation through charge transfer between Au and TiO₂ NPs. The Au NPs sizes, its dispersity on TiO₂ surface and surface plasmon resonance (SPR) were believed the critical factors for the higher photocatalytic performance of 0.1% Au/TiO₂ NPs. The prepared photocatalysts are found to be the promising materials for toxic organic compounds remediation and solar conversion.     

12 GHz GaAs/InGaAs异质结双栅功率场效应晶体管

报道了GaAs／InGaAs异质结双杨功率场效应晶体管的设计考虑、器件结构和制作，讨论了所采用的一些关键工艺，给出了器件性能。在12GHz下，最大输出功率≥130mW，增益≥12dB，功率附加效率≥30％。     

适合器件设计和电路模拟的SiGe基区HBT物理模型

提出了一个模拟ＳｉＧｅ基区ＨＢＴ器件特性的物理模型。在基区部分考虑了发射结处的价带不连续、大注入效应、Ｇｅ组份变化及重掺杂效应引起的能带变化的影响；在集电区分析时考虑了基区推出效应、载流子速度饱和效应、电流引起的空间电荷区效应以及准饱和效应。在此基础上给出了ＳｉＧｅ基区ＨＢＴ器件的电流和电荷公式。同时开发了ＳｉＧｅ基区ＨＢＴ的直流瞬态模型和小信号模型。利用修改的ＳＰＩＣＥ程序模拟了实际ＳｉＧｅ基区     

High-speed InP/lnGaAs heterojunction bipolar transistor utilizing nonalloyed contacts on n+-InP contacting layers

We have demonstrated a high-speed InP/lnGaAs heterojunction bipolar transistor with nonalloyed TiPtAu contacts on n⁺-InP emitter and collector contacting layers. The use of SiBr₄ as a silicon doping source enabled the formation of low resistance (p_c <2 × 10⁻⁶Ω. cm²), nonalloyed TiPtAu contacts to the heavily doped (n = 2 × 10¹⁹ cm⁻³) InP contacting layers. A device with a 3 × 10 Μm² emitter contact exhibited excellent dc characteristics and had ƒ_T = ƒ_max = 107 GHz. Emitter and collector resistances are compared to a device with InGaAs contacting layers.     

非晶硅集成型色敏元件及其传感器

研究了一种新型的非晶硅ＰＩＮ异质结集成型色敏元件及其传感器的制备工艺和结构，详细讨论了色敏元件的优化设计以及响应特性、暗电流等性能。