Rejoint of Carbon Nitride Fragments into Multi-Interfacial Order-Disorder Homojunction for Robust Photo-Driven Generation of H2 O2.

Photocatalytic technology based on carbon nitride (C3 N4 ) offers a sustainable and clean approach for hydrogen peroxide (H2 O2 ) production, but the yield is severely limited by the sluggish hot carriers due to the weak internal electric field. In this study, a novel approach is devised by fragmenting bulk C3 N4  into smaller pieces (CN-NH4 ) and then subjecting it to a directed healing process to create multiple order-disorder interfaces (CN-NH4 -NaK). The resulting junctions in CN-NH4 -NaK significantly boost charge dynamics and facilitate more spatially and orderly separated redox centers. As a result, CN-NH4 -NaK demonstrates outstanding photosynthesis of H2 O2 via both two-step single-electron and one-step double-electron oxygen reduction pathways, achieving a remarkable yield of 16675 µmol h-1  g-1 , excellent selectivity (> 91%), and a prominent solar-to-chemical conversion efficiency exceeding 2.3%. These remarkable results surpass pristine C3 N4 by 158 times and outperform previously reported C3 N4 -based photocatalysts. This work represents a significant advancement in catalyst design and modification technology, inspiring the development of more efficient metal-free photocatalysts for the synthesis of highly valued fuels.

Controlling the Cooling Rate of Hydrothermal Synthesis to Enhance the Supercapacitive Properties of ß-Nickel Hydroxide Electrode Materials.

The demand for power storage devices with good quality, fast charging and high energy density is becoming more and more urgent in today's electronic technology. For batteries and traditional capacitors, it is an insurmountable challenge to combine fast charging and discharging, large capacitance and long-life properties. The characteristics of supercapacitors can meet all the above requirements at the same time. In this study, a simple one-step hydrothermal method was successfully used to grow ß-nickel hydroxide nanocone particles directly on the 3D foamed nickel substrate as a working electrode material for supercapacitors. After growing ß-nickel hydroxide crystals on 3D foamed nickel substrate, by controlling the cooling rate, a well-crystalized ß-nickel hydroxide with good capacitance characteristics can be obtained. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) were used to analyze the capacitance characteristics of the ß-nickel hydroxide electrode. The research results show that the specific capacitance value of the ß-Ni(OH)2/3D nickel foam electrode material prepared at the cooling rate of 10 °C/h can reach 539 F/g with the charge-discharge test at a current density of 3 A/g. After 1000 continuous charge and discharge cycles, the material still retains 94.1% of the specific capacitance value.

Preparation of Electrodes with ß-Nickel Hydroxide/CVD-Graphene/3D-Nickel Foam Composite Structures to Enhance the Capacitance Characteristics of Supercapacitors.

Supercapacitors have the characteristics of high power density, long cycle life, and fast charge and discharge rates, making them promising alternatives to traditional capacitors and batteries. The use of transition-metal compounds as electrode materials for supercapacitors has been a compelling research topic in recent years because their use can effectively enhance the electrical performance of supercapacitors. The current research on capacitor electrode materials can mainly be divided into the following three categories: carbon-based materials, metal oxides, and conductive polymers. Nickel hydroxide (Ni(OH)2) is a potential electrode material for use in supercapacitors. Depending on the preparation conditions, two crystal phases of nickel hydroxide, α and ß, can be produced. When compared to α-NiOH, the structure of ß-Ni(OH)2 does not experience ion intercalation. As a result, the carrier transmission rate of α-Ni(OH)2 is slower, and its specific capacitance value is smaller. Its carrier transport rate can be improved by adding conductive materials, such as graphene. ß-Ni(OH)2 was chosen as an electrode material for a supercapacitor in this study. Homemade low-pressure chemical vapor deposition graphene (LPCVD-Graphene) conductive material was introduced to modify ß-Ni(OH)2 in order to increase its carrier transport rate. The LPCVD method was used to grow high-quality graphene films on three-dimensional (3D) nickel foam substrates. Then, a hydrothermal synthesis method was used to grow ß-Ni(OH)2 nanostructures on the 3D graphene/nickel foam substrate. In order to improve the electrical properties of the composite structure, a high-quality graphene layer was incorporated between the nickel hydroxide and the 3D nickel foam substrate. The effect of the conductive graphene layer on the growth of ß-Ni(OH)2, as well as its electrical properties and electrochemical performance, was studied. When this ß-Ni(OH)2/CVD-Graphene/3D-NF (nickel foam) material was used as the working electrodes of the supercapacitor under a current density of 1 A/g and 3 A/g, they exhibited a specific capacitance of 2015 F/g and 1218.9 F/g, respectively. This capacitance value is 2.62 times higher than that of the structure without modification with a graphene layer. The capacitance value remains at 99.2% even after 1000 consecutive charge and discharge cycles at a current density of 20 A/g. This value also improved compared to the structure without graphene layer modification (94.7%).

Flux-assisted synthesis of bismuth nanoparticle decorated carbon nitride for efficient photocatalytic degradation of endocrine disrupting compound.

Traditional approaches to synthesizing bismuth nanoparticle decorated carbon nitride (C3N4) materials suffer from the complex synthesis process and the addition of a surfactant, which is not conducive to environmental protection. To address these problems, we adopted a simple and green flux-assisted approach for the first time to fabricate metallic bismuth nanoparticle decorated C3N4 (BiCCN). Electron microscopy results suggested that bismuth vanadate was converted into small bismuth nanoparticles via the flux-assisted approach. Highly dispersed Bi nanoparticles dramatically intensify light absorption, facilitate spatial charge separation as electron acceptors, shorten the charge diffusion length, and reserve more active sites for generating reactive species via surface photo-redox reactions. Consequently, the derived optimized photocatalyst BiCCN-15 rendered around 26 times higher photocatalytic degradation efficiency toward an endocrine disrupting compound (bisphenol A) than C3N4. This work provides a novel approach for developing non-precious metal decorated photocatalytic materials for sustainable water decontamination.

Fabrication of Graphene/Zinc Oxide Nano-Heterostructure for Hydrogen Sensing.

In this study, hydrogen (H2) and methane (CH4) were used as reactive gases, and chemical vapor deposition (CVD) was used to grow single-layer graphene on a copper foil substrate. The single-layer graphene obtained was transferred to a single-crystal silicon substrate by PMMA transfer technology for the subsequent growth of nano zinc oxide. The characteristics of CVD-deposited graphene were analyzed by a Raman spectrometer, an optical microscope, a four-point probe, and an ultraviolet/visible spectrometer. The sol-gel method was applied to prepare the zinc oxide seed layer film with the spin-coating method, with methanol, zinc acetate, and sodium hydroxide as the precursors for growing ZnO nanostructures. On top of the ZnO seed layer, a one-dimensional zinc oxide nanostructure was grown by a hydrothermal method at 95 °C, using a zinc nitrate and hexamethylenetetramine mixture solution. The characteristics of the nano zinc oxide were analyzed by scanning electron microscope(SEM),x-ray diffractometer(XRD), and Raman spectrometer. The obtained graphene/zinc oxide nano-heterostructure sensor has a sensitivity of 1.06 at a sensing temperature of 205 °C and a concentration of hydrogen as low as 5 ppm, with excellent sensing repeatability. The main reason for this is that the zinc oxide nanostructure has a large specific surface area, and many oxygen vacancy defects exist on its surface. In addition, the P-N heterojunction formed between the n-type zinc oxide and the p-type graphene also contributes to hydrogen sensing.

Effect of different temperatures to remove reduction gas on the photoluminescence properties of Eu-doped Li2 (Ba1-x Srx )SiO4 phosphors.

In this study, Eu-doped Li2 (Ba1-x Srx )SiO4 powders (x = 0, 0.2, 0.4, and 0.6) were synthesized at 850°C in a reduction atmosphere (5% H2 + 95% N2 ) for a duration of 1 h using a solid-state reaction method. The reduction atmosphere was infused as the synthesis temperature reached 850°C, and was removed as the temperature dropped to 800-500°C. Li2 (Ba1-x Srx )SiO4 (or Li2 BaSiO4 ), (Ba,Sr)2 SiO4 (or BaSiO4 ), and Li4 SiO4 phases co-existed in the synthesized Eu-doped Li2 (Ba1-x Srx )SiO4 powders. A new finding was that the reduction atmosphere removing (RAR) temperature of the Li2 (Ba1-x Srx )SiO4 phosphors had a large effect on their photoluminescence excitation (PLE) and PL properties. Except for the 800°C-RAR-treated Li2 BaSiO4 phosphor, PLE spectra of all other Li2 (Ba1-x Srx )SiO4 phosphors had one broad emission band with two emission peaks centred at ~242 and ~283 nm; these PL spectra had one broad emission band with one emission peak centred at 502-514 nm. We showed that the 800°C-RAR-treated Li2 BaSiO4 phosphor emitted a red light and all other Li2 (Ba1-x Srx )SiO4 phosphors emitted a green light. Reasons for these results are discussed thoroughly.

Programmable Digital Liquid Metal Droplets in Reconfigurable Magnetic Fields.

Gallium-based liquid metals exhibit excellent locomotion and deformation capabilities under external stimuli and has potential in developing intelligent robots. Programing the locomotion and morphology of the Liquid metal (LM) to endow it with functionalities and intelligence as robots is charming but remains challenging. In this study, we develop a programmable digital LM (PDLM) control platform that can realize versatile locomotion and morphological manipulation of magnetic LM (MLM) droplets using arrays of electromagnets. We demonstrate on-demand transportation, deformation, breakup, and merging of multiple MLM droplets simultaneously and precisely. We find that the intriguing behaviors of MLM under a magnetic field are due to the interplay of surface tension and magnetic forces. Furthermore, we present a functional cooperative droplet robot by equipping the MLM droplets with three-dimensionally printed microtool modules. We show that both the position and orientation of a rod-shaped object can be precisely manipulated by the cooperation of the MLM droplet robots. More interestingly, we explore the capability of the MLM droplet robots for cooperatively handling a copper wire to connect and disconnect electronic circuits. Finally, we demonstrate that the PDLM control platform is capable of programing a group of MLM droplets to accomplish a digital display task. We believe that the PDLM control system presents a promising potential in developing LM-based reconfigurable circuits, digital display systems, and biomimetic soft robotic systems with high controllability, multifunctionalities, and intelligence.

Particle-Based Porous Materials for the Rapid and Spontaneous Diffusion of Liquid Metals.

Gallium-based room-temperature liquid metals have enormous potential for realizing various applications in electronic devices, heat flow management, and soft actuators. Filling narrow spaces with a liquid metal is of great importance in rapid prototyping and circuit printing. However, it is relatively difficult to stretch or spread liquid metals into desired patterns because of their large surface tension. Here, we propose a method to fabricate a particle-based porous material which can enable the rapid and spontaneous diffusion of liquid metals within the material under a capillary force. Remarkably, such a method can allow liquid metal to diffuse along complex structures and even overcome the effect of gravity despite their large densities. We further demonstrate that the developed method can be utilized for prototyping complex three-dimensional (3D) structures via direct casting and connecting individual parts or by 3D printing. As such, we believe that the presented technique holds great promise for the development of additive manufacturing, rapid prototyping, and soft electronics using liquid metals.

The Role of ALD-ZnO Seed Layers in the Growth of ZnO Nanorods for Hydrogen Sensing.

Hydrogen is one of the most important clean energy sources of the future. Because of its flammability, explosiveness, and flammability, it is important to develop a highly sensitive hydrogen sensor. Among many gas sensing materials, zinc oxide has excellent sensing properties and is therefore attracting attention. Effectively reducing the resistance of sensing materials and increasing the surface area of materials is an important issue to increase the sensitivity of gas sensing. Zinc oxide seed layers were prepared by atomic layer deposition (ALD) to facilitate the subsequent hydrothermal growth of ZnO nanorods. The nanorods are used as highly sensitive materials for sensing hydrogen due to their inherent properties as oxide semiconductors and their very high surface areas. The low resistance value of ALD-ZnO helps to transport electrons when sensing hydrogen gas and improves the sensitivity of hydrogen sensors. The large surface area of ZnO nanorods also provides lots of sites of gas adsorption which also increases the sensitivity of the hydrogen sensor. Our experimental results show that perfect crystallinity helped to reduce the electrical resistance of ALD-ZnO films. High areal nucleation density and sufficient inter-rod space were determining factors for efficient hydrogen sensing. The sensitivity increased with increasing hydrogen temperature, from 1.03 at 225 °C, to 1.32 at 380 °C after sensing 100 s in 10,000 ppm of hydrogen. We discuss in detail the properties of electrical conductivity, point defects, and crystal quality of ALD-ZnO films and their probable effects on the sensitivity of hydrogen sensing.

Local geometric and electronic structures of gasochromic VO(x) films.

VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target at room temperature. Local atomic and electronic structures of the films were then modified by thermal annealing. The oxidation state and structural and gasochromic properties of the films were elucidated by X-ray absorption spectroscopy. Analytical results indicate that the as-deposited VOx films were amorphous with mixed V(4+) and V(5+) valences. The amorphous VOx had a disordered and expanded lamellar structure resembling that of polymer-intercalated V2O5 gels. VOx films were crystallized into orthorhombic V2O5 at 300 °C, and the lamellar structure was eliminated at 400 °C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V(5+) and V(3+). Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V2O5 crystalline phase irreversibly into an H1.43V2O5 phase. Based on the results of this study, amorphous VOx with a lamellar structure is recommended for use in H2 gas sensors.