Search

The double perovskites (DPs) are outstanding materials for renewable energy and other optoelectronic applications. Here in this paper, the thermoelectric and optical behavior of X2HfI6 (X = Ga, In, Tl) have been explained systematically by DFT. The structural stability has been certified using ionic radii in terms of tolerance factor, and dynamic stability has been confirmed by positive phonon dispersion frequencies in acoustic modes. The band structure findings show the direct band gaps for (Ga, In, Tl) based DPs. The optical properties have been investigated by dispersion, absorption, refection, and related other optical characteristics. The absorption bands are existing in ultraviolet region and shifted to higher energy (blue shift). The reflection and optical loss of light are noted less than 0.3 which increases their potential for optoelectronic devices. The high Seebeck coefficient and electrical conductivity along with ultralow lattice thermal conductivity confirm the high figure of merit at and below the room temperature.

Zinc oxide (ZnO) nanocrystallites with different weight ratios are incorporated into carbon nanotubes (ZnO/CNTs) or graphene oxide (ZnO/GO) nanohybrids using ultrasonication/hydrothermal approach. The produced nanohybrids were tested in heterogeneous photocatalytic degradation of methylene blue dye (MB) under visible light illumination and in-situ ultrasonication. The zinc oxide incorporated carbon nanotubes nanohybrid having about 70 wt% of ZnO (ZnO(70)/CNT) showed marked visible light photocatalytic activity enhancement for MB degradation (99%, 0.5 g/L catalyst, 0.015 min−1) compared to the rest of the nanohybrids. The performance of MB degradation using ZnO(70)/CNT nanohybrid was even enhanced during employing the dual sonophotocatalysis approach achieving a rate constant of 0.019 min−1. This arises from the structural advantages at the ZnO(70)/CNT interface by which an improvement in electronic conductivity, facile electron transfer, charge carriers separation and increased oxygen vacancies were thoroughly achieved. This was highly ascertained via the catalysts characterization performed via many physiochemical techniques including XRD, TEM-SAED, FTIR, UV–Vis diffuse reflectance, and electrical conductivity, IPCE, PL and EIS. The scavenger studies of the photocatalytic and sonophotocatalytic processes of the MB degradation using ZnO(70)/CNT illustrate the importance of OH (followed by an electron) and holes (followed by OH), respectively proposing the importance of direct and indirect production of OH; as a strong oxidizing moiety.

Herein, we report the Cu(0)-based nanoparticles film generated by in situ electrochemical reductions of Cu(II) ions modified silica exhibits a high activity and durable HER catalyst in acid solution. Copper ions were attached to silica surface using chemical modification with propyl ethylene diamine (PEDA) linker followed by treating with copper sulfate solution to form Cu(II)-PEDA/silica complex. Copper nanoparticles then were obtained by electrochemical reduction of the silica immobilized Cu(II) ions in sulfuric acid solution. The physicochemical properties of the resulted from copper nanoparticles incorporated silica were investigated and analyzed by Energy Dispersive x-ray Spectroscopy (EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction XRD, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM). The electrochemical characterizations confirm that the Cu(0) nanoparticles supported on silica substrate combining both high activity and stability for hydrogen evolution reaction with overpotential(η), of 200 mV and Tafel slope of 67 mV/dec could serve as Cu-based electrocatalysts in practical applications for hydrogen production in 0.5 M of H2SO4 solution. The catalyst exhibited respectable stability and steadily produced hydrogen at several potentials. The catalyst has the perspective to expressively lower the cost of manufacturing hydrogen fuel, thus helping to spread the use of hydrogen fuel which does not harm the environment.

Nanocomposites of hexagonal ZnO nanorods incorporated into carbon nanotube-graphene (ZnO/CNT-GO) were prepared using a simple hydrothermal approach. The structure, light absorption, surface texturing, and morphology characterizations have established the strong interaction between ZnO, carbon nanotubes, and graphene oxide components because of the presence of well-dispersed ZnO nanorods with an aspect ratio of 3.4 (L × D = 75 × 22 nm). The assembled dye-sensitized solar cell of a ZnO/CNT-GO photoanode exhibited a superior performance, with a power conversion efficiency of 7.73%, surpassing those of its ZnO/CNT (5.07%) and ZnO/GO (3.96%) counterparts. Although CNT-GO exhibited a higher incident photon-to-current conversion efficiency (IPCE) and lower photoluminescence (PL) intensity than those of the ZnO/CNT-GO composite, it presented a lower conversion efficiency of 5.60%. This can be attributed to the presence of structural defects at the CNT/GO interface, which resulted in lower electronic conductivity (0.25 × 10−3 Ω−1 cm−1 vs. 0.8 × 10−3 Ω−1 cm−1 for ZnO/CNT-GO) and optical performance. The ZnO/CNT-GO composite showed a superior Isc value of 17.6 mA/cm2 but a lower Voc value of 0.63 V in comparison to those of its ZnO/GO analog (3.9 mA/cm2, 0.8 V); it also showed a manifested increase in surface area and pore radius values (227.5 m2/g, 58.9 A) toward the dye absorption. The electrochemical capacitance performance obtained via using charge-discharge and impedance spectroscopy revealed an excellent specific capacitance in the order of ZnO/CNT-G (290 F/g) > CNT-G (275 F/g) > ZnO/G (230 F/g) > ZnO/CNT (183 F/g) at 1.0 A g−1. This is attributed to the synergistic effect of ZnO within the CNT/GO nanocomposite and affirms its charge collection efficiency toward the improvement of dye-sensitized solar cells. The formation of a p/n junction between CNT/G and ZnO nanorods, as evidenced by the Mott-Schottky analysis, played a vital role in the improvement of solar cell devices based on the narrowing of the band gap (Eg = 2.64 eV), ease of electronic transfer, transient photocurrent density, as well as framework mesoporosity.

An electrocatalyst of potassium nickel aluminium hexafluoride (KNiAlF6) nanosheets has been prepared using solid-phase synthesis at 900 °C. X-ray diffraction, scanning electron microscopy, and conductivity studies confirmed the formation of KNiAlF6 nanosheets having a cubic defect pyrochlore structure with an average thickness of 60–70 nm and conductivity of 1.297 × 103 S m−1. The electrochemical catalytic activity of the KNiAlF6 nanosheets was investigated for urea oxidation in alkaline solution. The results show that the KNiAlF6 nanosheets exhibit a mass activity of ∼395 mA cm−2 mg−1 at 1.65 V vs. HRE, a reaction activation energy of 4.02 kJ mol−1, Tafel slope of 22 mV dec−1 and an oxidation onset potential of ∼1.35 V vs. HRE which is a significant enhancement for urea oxidation when compared with both bulk Ni(OH)2 and nickel hydroxide-based catalysts published in the literature. Chronoamperometry and impedance analysis of the KNiAlF6 nanosheets reveal lower charge transfer resistance and long-term stability during the prolonged urea electro-oxidation process, particularly at 60 °C. After an extended urea electrolysis process, the structure and morphology of the KNiAlF6 nanosheets were significantly changed due to partial transformation to Ni(OH)2 but the electrochemical activity was sustained. The enhanced electrochemical surface area and the replacement of nickel in the lattice by aluminium make KNiAlF6 nanosheets highly active electrocatalysts for urea oxidation in alkaline solution.

B-site doping in potassium sodium niobate (KNN) with Mn2+ (M⁢nNb″′) and Ti4+ (T⁢iNb′) dopants were soluble but prevented KNN from achieving a high relative density, while Sn4+ (S⁢nNb′) was not soluble in the structure as evidenced by second phase peaks in X-ray diffraction (XRD) traces. However, SnO2 was an effective sintering aid in KNN-50/50. A-site doping with Sr2+ (S⁢r(Na,K)⋅) up to 1 mol% initially improved dielectric properties but higher sintering temperatures were required for compositions with >1 mol% Sr. Samples with 5% and 7% of Sr-doping completely shifted the transition of TO–T to below RT and broadened the TC peaks as the relaxor. All Ti-doped and Sr-doped compositions showed an increase in conductivity, manifested as high values of dielectric loss (tanδ). More than 1% of acceptor and donor dopants showed the ionic-type conduction mechanism, while 1% displayed the electronic mechanism as attributed from the strongly frequency-dependent tanδ. In conclusion, these samples have the potential to open up new applications in the field of electroceramics.

In the present work, ZnO and Ag@ZnO nanoparticles based photocatalyst were synthesized via green route by using the leaves extract of pecan nuts (Carya illinoinensis) for the first time. The phytochemicals present in leaf of extract pecan nuts (Carya illinoinensis) such as methyl gallate and kaempferol act as capping and reducing agents. The obtained photocatalyst were analyzed via various techniques such as XRD (X-ray diffraction), TEM (transmission electron microscopy), SEM (scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), PL (Photoluminescence spectroscopy), XPS (X-ray photoelectron spectroscopy) and UV (UV-visible spectroscopy). The activity of biogenic photocatalyst were investigated against RhB (Rhodamine B) dye and the results demonstrated that the catalytic properties become enhanced significantly after Ag doping as compared to bare ZnO. The effect of various parameters were also investigated such as pH, catalyst dose, initial concentration of dye. The obtained results showed highest efficacy of catalyst at pH 10, further the photo-degradation of Rhodamine B (RhB) dye followed pseudo first order kinetic model. The reusability test of biogenic photocatalyst revealed that the catalyst was an excellent option for practical use with high stability even after 5 cycles. The mechanism for, ZnO and Ag@ZnO synthesis and degradation pathway of RhB dye was proposed.

Electrooxidation of urea plays a substantial role in the elimination of urea-containing wastewater and industrial urea. Here, we report the electrodeposition of nickel hydroxide catalyst on commercial carbon paper (CP) electrodes from dimethyl sulphoxide solvent (Ni(OH)2-DMSO/CP) for urea electrooxidation under alkaline conditions. The physicochemical features of Ni(OH)2-DMSO/CP catalysts using scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the Ni(OH)2-DMSO/CP catalyst shows nanoparticle features, with loading of &lt, 1 wt%. The cyclic voltammetry and electrochemical impedance spectroscopy revealed that the Ni(OH)2-DMSO/CP electrode has a urea oxidation onset potential of 0.33 V vs. Ag/AgCl and superior electrocatalytic performance, which is a more than 2-fold higher activity in comparison with the counterpart Ni(OH)2 catalyst prepared from the aqueous electrolyte. As expected, the enhancement in electrocatalytic activity towards urea was associated with the superficial enrichment in the electrochemically active surface area of the Ni(OH)2-DMSO/CP electrodes. The results might be a promising way to activate commercial carbon paper with efficient transition metal electrocatalysts, for urea electrooxidation uses in sustainable energy systems, and for relieving water contamination.