ZnO@Ni foam photoelectrode modified with heteroatom doped graphitic carbon for enhanced photoelectrochemical water splitting under solar light

In this study, an electrocatalyticaly inactive ZnO@Ni foam photoelectrode was modified with heteroatom doped graphitic carbon to achieve enhanced photoelectrochemical (PEC) water splitting performance. The O, S and N doped graphitic carbon was simultaneously deposited with ZnO on Ni foam substrate under hydrothermal deposition. One dimensional ZnO nanorods with flower-like graphitic carbon on their surface were obtained on the Ni foam substrate, which was directly used as photoelectrode to derive photoelectrochemical water splitting under solar light irradiation. The pristine ZnO@NF exhibit unattractive PEC performance evidenced by the high overpotential required for the oxygen evolution reaction (OER) couple of water splitting reaction (398 mV vs. RHE). The carbon modified ZnO–C@NF photoelectrode lowers the overpotential required to 317 mV. This enhancement was attributed to the carbon modification which serves as both active site and photoelectron reservoir; facilitating the sluggish kinetics of OER couple reaction and promoting separation of photogenerated charge carriers.     

Role of thermodynamic miscibility gaps in phase selection in sol-gel synthesis of yttrium silicates

Yttrium monosilicate and disilicate are important materials for environmental barrier coatings. The two silicates were synthesized by sol-gel route and their phase selection upon calcination and thermal exposure was studied. First products of crystallization were the monosilicate and yttria. Amorphous silica precipitated out at 1300 °C as apatite phase. During prolonged high temperature treatment, up to 100 h at 1400 °C, the apatite disappeared and the disilicate appeared, only to disappear itself as the system approached equilibrium. Thermodynamic calculations performed using Thermo-Calc software show the presence of a metastable miscibility gaps in the amorphous (liquid) phase field. As a consequence, phase separation in the amorphous phase prior to crystallization is responsible for the formation of yttria-rich and silica-rich phases during crystallization. Multiple phase formation during both, yttrium monosilicate and disilicate synthesis is consistent with the presence of the amorphous phase miscibility gaps around the silicate compositions.     

Effect of low energy proton beam irradiation on structural and electrical properties of ZnO:Al thin films

In this study, we report the structural modification and change in electrical behaviour of aluminium doped zinc oxide by low energy (100 keV) proton irradiation. Aluminium doped zinc oxide films were deposited using DC magnetron sputtering and then annealed for a short duration at 600 °C before irradiation. Structural and defect studies of the films carried out using XRD and Raman spectroscopy. It suggests that the crystalline ordering increases at higher fluences due to annealing of defects in the film. The increase in crystallinity at higher fluences decreases the grain boundary scattering and causes low resistivity. There is no significant change in carrier concentration after the irradiation, however the mobility and resistivity of the Al doped ZnO films change with proton irradiated fluences. The development of defect due to irradiation has been confirmed through Raman spectroscopic studies. The increase in activation energy of particles has been suggested by low energy proton irradiations at higher fluences in the annealed Al doped ZnO thin films. The uniform particle distribution increases with fluences of the irradiation that may be helpful for spintronics and sensor device technology.     

Nitrogen‐doped self‐shrinking porous 3D graphene capacitor deionization electrode

Traditional three‐dimensional (3D) graphene has a large pore structure, which makes the graphene structure not well interact with the anion and cation during the desalination process, thereby restricting the capacitive deionization (CDI) ability of the 3D graphene. In this work, we prepared a nitrogen‐doped self‐shrinking porous 3D graphene electrode by adding a pyrrole monomer to a graphene oxide solution, which was then applied to a CDI electrode. The results show that the electrochemical performance of the as‐prepared nitrogen‐doped self‐shrinking porous 3D graphene (NSPG) is significantly improved. Compared with traditional 3D graphene, NSPG has a denser pore structure with a larger specific surface area, thus exhibiting a good CDI performance: The NSPG electrode has an electroadsorption capacity of 13.16 mg/g.     

Morphology‐dependent electrochemical performance of nitrogen‐doped carbon dots@polyaniline hybrids for supercapacitors

In this work, the binary N‐CDs@PANI hybrids were fabricated by introducing zero‐dimensional nitrogen‐doped carbon dots (N‐CDs) into reticulated PANI. Firstly, N‐CDs were prepared by one‐pot microwave method, and then, the N‐CDs were introduced into in situ oxidative polymerization of aniline (ANI) monomer. The N‐CDs with abundant functional groups and high electronic cloud density played a significant role in guiding the polyaniline‐ordered growth into intriguing morphologies. Moreover, morphology‐dependent electrochemical performances of N‐CDs@PANI hybrids were investigated and N‐CDs improve static interaction and enhance the special capacitances in the N‐CDs@PANI hybrids. Especially, the specific capacitance of PC4 hybrid can reach 785 F g^?1, which exceed that of pure PANI (274 F g^?1) at current density of 0.5 A g^?1 according to three‐electrode measurement. And the capacitance retention of the PC4 hybrid still keeps 70% after 2000 cycles of charge and discharge. The N‐CDs@PANI hybrids can have potential applications in electrode materials, supercapacitors, nonlinear optics, and microwave absorption.     

Nitrogen-doped graphene-supported zinc sulfide nanorods as efficient Pt-free for visible-light photocatalytic hydrogen production

Nitrogen-doped graphene-ZnS composite (NG-ZnS) was synthesized by thermal treatment of graphene-ZnS composite (G-ZnS) in NH₃ medium. In the second step, the as-synthesized samples were deposited on indium tin oxide glass (ITO) by electrophoretic deposition for photocatalytic hydrogen evolution reaction. The as-prepared NG-ZnS-modified ITO electrode displayed excellent photocatalytic activity, rapid transient photocurrent response, superior stability and high recyclability compared to the pure ZnS and G-ZnS-modified ITO electrode due to the synergy between the photocatalytic activity of ZnS nanorods and the large surface area and high conductivity of N-graphene.     

Structural/texture evolution of CaO/MCM‐41 nanocatalyst by doping various amounts of cerium for active and stable catalyst: Biodiesel production from waste vegetable cooking oil

In present work, the aim of producing biodiesel from waste cooking oil was pursued by doping the cerium element into the MCM‐41 framework as catalyst with various Si/Ce molar ratio (5, 10, 25, 50, and Ce = 0). The catalytic performance and stability improved by employing the ultrasound irradiation in active phase loading step of catalyst preparation. The physicochemical characteristics of synthesized samples were investigated using various techniques as follows: Brunauer‐Emmett‐Teller (BET), X‐ray powder diffraction (XRD), Fourier transfer infrared (FTIR), energy‐dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), and field emission scanning electron microscope (FESEM). The XRD patterns along with the results of FTIR and BET analysis revealed the MCM‐41 framework destruction while increasing the Ce content. The FESEM images of the nanocatalysts illustrated a well distribution and uniform morphology for the Ca/CeM (Si/Ce = 25). The particle size and size distribution of the Ca/CeM (Si/Ce = 25) were subsequently determined by TEM and FESEM images. The activity of fabricated nanocatalysts was evaluated by measuring the free acid methyl ester (FAME) content of produced biodiesel. The tests were carried out at constant operational conditions: T = 60°C, catalyst loading = 5 wt%, methanol/oil molar ratio = 9, and 6‐hour reaction time. A superior activity was observed for Ca/CeM (Si/Ce = 25) among other nanocatalysts with 96.8% conversion of triglycerides to biodiesel. The mentioned sample was utilized in five reaction cycles, and at the end of the fifth cycle, the conversion reached to 91.5% which demonstrated its significant stability.     

Visible-light-responsive γ-Fe2O3/PMMA/S-TiO2 core/shell nanocomposite: Preparation,characterization and photocatalytic activity

Organic-inorganic composite materials have demonstrated many potential applications in environmental field. This paper presented a facile preparation method for γ-Fe₂O₃/PMMA/S-TiO₂ nanocomposite with core-shell structure and its application in degradation of phenanthrene under visible light irradiation. Firstly, γ-Fe₂O₃/PMMA nanoparticles were synthesized by the modified-suspension-polymerization method. Then γ-Fe₂O₃/PMMA/S-TiO₂ core-shell nanocomposites were prepared by adding as-synthesized γ-Fe₂O₃/PMMA nanoparticles into the sol solution formed by sol-gel method using tetrabutyltitanate as Ti source and thiourea as sulfur source. The characterization result of the obtained products by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicated that the layer of sulfur doped titania was successfully coated onto the surface of γ-Fe₂O₃/PMMA nanoparticles. Thermogravimetry (TG) analysis presented that the layer of sulfur doped TiO₂ could efficiently reduce the decomposition of polymethylmethacrylate (PMMA) even at higher temperature up to 500 °C. UV–vis diffuse reflectance spectroscopy showed that γ-Fe₂O₃/PMMA/S-TiO₂ nanocomposite clearly exhibits the red-shift of the absorption edge compared with γ-Fe₂O₃/PMMA/TiO_2. The photocatalytic activity evaluation showed that the γ-Fe₂O₃/PMMA/S-TiO₂ nanocomposite exhibited the best photocatalytic activity for degradation of phenanthrene under the conditions of 0.8 mol% of sulfur doping, calcination temperature at 300 °C and the addition concentration of 1.0 g/L. Moreover, the nanocomposites have good recovery ability by the recovery experiment.