Unraveling the Role of 2D Ti3C2Tx MXene Nanosheets in Cu-Based Double Perovskite Active Layer for Enhanced Photovoltaic Performance.

Although the atmospheric stability of lead-free inorganic double perovskite (DP) solar cells (PSCs) looks promising, their further development is hampered by inadequate film quality and non-radiative carrier recombination at the interfaces. Herein, the incorporation of a newly developed intriguing class of 2D material Ti3C2Tx MXene nanosheets with the photo-absorbing Cu2AgBiI6 (CABI) active layer of a fully inorganic solar cell is reported. The highly conductive Ti3C2Tx nanosheets work as a multi-functional additive by tuning the band gap, reducing the non-radiative carrier recombination, and inhibiting carrier accumulation. In addition, the presence of Ti3C2Tx MXene increases the surface free energy of the perovskite film, which elevates the energy barrier for nucleation and realizes a highly crystalline CABI perovskite film. Primarily, the MXene modification accelerates the charge extraction and transport at the interfaces of the active layer, utilizing energy level alignment with the charge transport layers. Consequently, the photo-conversion efficiency (PCE) of the device with MXene is substantially enhanced to 1.50%. Moreover, the 2D Ti3C2Tx nanosheets increased the long-term stability of the devices by retaining 70% of the initial PCE after 1680 h. With regard to relieving the severe carrier recombination at the interfaces, this work sets a new paradigm toward imminent solar energy conversion.

Acidic and Alkaline pH Controlled Oxygen Reduction Reaction Pathway over Co-N4C Catalyst.

Enhanced oxygen reduction reaction (ORR) kinetics and selectivity are crucial to advance energy technologies like fuel cells and metal-air batteries. Single-atom catalysts (SACs) with M-N4/C structure have been recognized to be highly effective for ORR. However, the lack of a comprehensive understanding of the mechanistic differences in the activity under acidic and alkaline environments is limiting the full potential of the energy devices. Here, a porous SAC is synthesized where a cobalt atom is coordinated with doped nitrogen in a graphene framework (pCo-N4C). The resulting pCo-N4C catalyst demonstrates a direct 4e- ORR process and exhibits kinetics comparable to the state-of-the-art (Pt/C) catalyst. Its higher activity in an acidic electrolyte is attributed to the tuned porosity-induced hydrophobicity. However, the pCo-N4C catalyst displays a difference in ORR activity in 0.1 m HClO4 and 0.1 m KOH, with onset potentials of 0.82 V and 0.91 V versus RHE, respectively. This notable activity difference in acidic and alkaline media is due to the protonation of coordinated nitrogen, restricted proton coupled electron transfer (PCET) at the electrode/electrolyte interface. The effect of pH over the catalytic activity is further verified by Ab-initio molecular dynamics (AIMD) simulations using density functional theory (DFT) calculations.

Influence of Indium as a Promoter on the Stability and Selectivity of the Nanocrystalline Cu/CeO2 Catalyst for CO2 Hydrogenation to Methanol.

Stable catalyst development for CO2 hydrogenation to methanol is a challenge in catalysis. In this study, indium (In)-promoted Cu nanoparticles supported on nanocrystalline CeO2 catalysts were prepared and explored for methanol production from CO2. In-promoted Cu catalysts with ∼1 wt % In loading showed a methanol production rate of 0.016 mol gCu-1 h-1 with 95% methanol selectivity and no loss of activity for 100 h. It is found that the addition of indium remarkably increases Cu dispersion and decreases Cu particle size. In addition led to an increased metal-support interaction, which stabilizes Cu particles against sintering during the reaction, leading to high stability and activity. In addition, density functional theory calculations suggested that the reaction is proceeding via reverse water gas shift (RWGS) mechanism where the presence of In stabilized intermediate species and lowered CO2 activation energy barriers.

Morphologically controlled cobalt oxide nanoparticles for efficient oxygen evolution reaction.

Electrochemical water oxidation is one of the thrust areas of research today in solving energy and environmental issues. The morphological control in the synthesis of nanomaterials plays a crucial role in designing efficient electrocatalyst. In general, various synthetic parameters can direct the morphology of nanomaterials and often this is the main driving force for the electrocatalyst in tuning the rate of the oxygen evolution reaction (OER) for the electrochemical water-splitting. Here, a facile and cost-effective synthesis of spinel cobalt oxides (Co3O4) via a one-pot hydrothermal pathway with tunable morphology has been demonstrated. Different kinds of morphologies have been obtained by systematically varying the reaction time i.e. nanospheres, hexagon and nanocubes. Their catalytic activity has been explored towards OER in 1.0 M alkaline KOH solution. The catalyst Co3O4-24 h nanoparticles synthesized in 24 h reaction time shows the lowest overpotential (η) value of 296 mV at 10 mA cm-2 current density, in comparison to that of other as-prepared catalysts i.e. Co3O4-pH9 (311 mV), Co3O4-12 h (337 mV), and Co3O4-6 h (342 mV) with reference to commercially available IrO2 (415 mV). Moreover, Co3O4-24 h sample shows the outstanding electrochemical stability up to 25 h time.

Facile Synthesis of Spinel CoFe2O4 Nanoparticle and Its Application as Magnetic Recoverable Photocatalyst for Degradation of Metronidazole and Some Selected Organic Dyes.

A novel and facile approach for one-pot synthesis of spinel cobalt ferrites (CoFe2O4) nanoparticle (NPs) and is photocatalytic activity for degradation of pharmaceuticals waste and organic dye. The synthesis involves homogeneous chemical precipitation followed by hydrothermal heating, using of hexamine as a hydroxylating agent. As-synthesized CoFe2O4 photocatalyst was characterised by XRD, SEM, SEM Mapping, TEM, XPS, and BET-surface area analysis. The TEM image reveals cubic shapes with an average size of 10-20 nm. The surface area of the CoFe2O4 NPs was found to be 16.42 m² g-1. The photocatalytic activity of CoFe2O4 has proved to be an excellent photocatalyt for degradation of metronidazole and organic dyes such as methylene blue (MB) and rhodamine B (RhB). The rate of the reaction was found to be 0.102, 0.198 and 0.213 min-1 for metronidazole, MB and RhB respectively. The catalyst also proved to be noteworthy as it does not loss in its catalytic activity even after five cycles of reuse.

Highly efficient conversion of the nitroarenes to amines at the interface of a ternary hybrid containing silver nanoparticles doped reduced graphene oxide/ graphitic carbon nitride under visible light.

In this report, a ternary Ag-rGO/g-C3N4 hybrid was synthesized by a simple hydrothermal approach for the photocatalytic reduction of nitroarene compounds into their corresponding amines under visible light. Importantly, the present method did not require reducing agents, like hydrazine hydrate; instead methanol has been used as a source of electrons and protons for the photoreduction process. After grafting of Ag NPs, a significant enhancement in the efficiency of the rGO/g-C3N4 for the reduction of nitrobenzenes was observed. Under optimized experimental conditions, the conversion of nitrobenzene and yield of aniline were determined to be 99% and 98%, respectively under visible light illumination for 4 h. The nitrobenzene compounds bearing both electron donating and withdrawing groups were selectively converted into their corresponding aniline products without altering the functionality. The enhanced performance of the developed photocatalyst attributed to the effective separation of photoexcited electrons on the photocatalyst surface and their subsequent transfer for the reduction of nitrobenzene molecules.

Induced Vacancy-Assisted Filamentary Resistive Switching Device Based on RbPbI3-xClx Perovskite for RRAM Application.

Halide perovskite (HP) materials are actively researched for resistive switching (RS) memory devices due to their current-voltage hysteresis along with low-temperature processability, superior charge mobility, and simple fabrication. In this study, all-inorganic RbPbI3 perovskite has been doped with Cl in the halide site and incorporated as a switching media in the Ag/RbPbI3-xClx/ITO structure, since pure RbPbI3 is nonswitchable. Five compositions of the RbPbI3-xClx (x = 0, 0.3, 0.6, 0.9, and 1.2) films are fabricated, and the conductivity was found to be increasing upon increase in Cl concentration, as revealed by dielectric and I-V measurements. The device with a 20% chloride-substituted film exhibits a higher on/off ratio, extended endurance, long retention, and high-density storage ability. Finally, a plausible explanation of the switching mechanism from iodine vacancy-mediated growth of conducting filaments (CFs) is provided using conductive atomic force microscopy (c-AFM). The c-AFM measurements reveal that pure RbPbI3 is insulating in nature, whereas Cl-doped films demonstrate resistive switching behavior.

Facile Solvothermal Synthesis of CuCo2S4 Yolk-Shells and Their Visible-Light-Driven Photocatalytic Properties.

In this present work, we synthesized a yolk-shell shaped CuCo2S4 by a simple anion exchange method. The morphological and structural properties of the as-synthesized sample were characterized using X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (UV-vis DRS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SEM and TEM results confirmed that the uniform yolk-shell structure was formed during the solvothermal process. The band gap was about 1.41 eV, which have been confirmed by UV⁻vis DRS analysis. The photocatalytic property was evaluated by the photocatalytic degradation of methylene blue (MB) dye as a target pollutant under the visible-light irradiation. The experimental results confirmed the potential application of yolk-shell shape CuCo2S4 in visible-light photocatalytic applications.

Waste snail shell derived heterogeneous catalyst for biodiesel production by the transesterification of soybean oil.

A waste snail shell (Pila spp.) derived catalyst was used to produce biodiesel from soybean oil at room temperature for the first time. The snail shell was calcined at different temperatures of 400-1000 °C. The synthesized catalysts underwent XRD, SEM, TEM, EDS, FTIR, XRF, TG/DTA and N2 adsorption-desorption isotherm (BET) analysis. The major component CaO was determined at a calcination temperature of 900 °C as depicted in the XRD results. 100% conversion of soybean oil to methyl ester biodiesel was obtained, as confirmed by 1H NMR. A biodiesel yield of 98% was achieved under optimized reaction conditions such as a calcination temperature of 900 °C, a catalyst loading of 3 wt%, a reaction time of 7 h and a methanol to oil ratio of 6 : 1, and biodiesel conversion was confirmed by FT-NMR and IR spectroscopies. A total of 9 fatty acid methyl esters (FAMEs) were identified in the synthesized biodiesel by the retention time and fragmentation pattern data of GC-MS analysis. The catalyst was recycled 8 times without appreciable loss in its catalytic activity. A high biodiesel yield of 98% was obtained under these optimised conditions. The catalyst has the advantage of being a waste material, therefore it is easily prepared, cost free, highly efficient, biogenic, labor effective and environmentally friendly, making it a potential candidate as a green catalyst for low cost production of biodiesel at an industrial scale.

Paederia foetida Linn. promoted biogenic gold and silver nanoparticles: Synthesis, characterization, photocatalytic and in vitro efficacy against clinically isolated pathogens.

Development of newer improved therapeutic agents with efficient antimicrobial activities continues to draw attention of researchers till date. Moreover, abatement of polluting dyes released from industry with enhanced efficiency is currently being considered as challenging task for people working on material sciences. In the present study, we report a facile biogenic synthesis of gold and silver nanoparticles (NPs) in which aqueous extracts of Paederia foetida Linn. was used as reducing as well as stabilizing agent. The biosynthesized Au and Ag NPs were characterized by UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The photocatalytic activity of these nanoparticles were tested against Rhodamine B (RhB). The antimicrobial activity of these biosynthesized NPs were investigated against four human pathogens viz. B. cereus, E. coli, S. aureus and A. niger. Biogenic silver nanoparticles presented a strong antimicrobial activity against B. cereus (26.13) followed by E. coli (26.02), S. aureus (25.43) and A. niger (22.69). Ag NPs owing to their small size (5-25nm) could have easily penetrate into the cell membrane, disturb the metabolism, cause irretrievable damage finally leading to the microbial cell death. Interestingly biogenic gold nanoparticles didn't show any antimicrobial activity.

Fine cutting edge shaped Bi2O3rods/reduced graphene oxide (RGO) composite for supercapacitor and visible-light photocatalytic applications.

Bi2O3 rods/RGO composite has been synthesized by a simple precipitation and calcination method. The crystallnity, structural, and morphological features were studied by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and high resolution transmission electron microscopy (HR-TEM) techniques. The supercapacitor behavior was studied using cyclic voltammetry, galvanostatic charge discharge and impedance analysis, respectively. The Bi2O3 rods/RGO nanocomposite exhibits a maximum specific capacitance of 1041Fg-1 at a current density of 2Ag-1. The photocatalytic activity of Bi2O3 rods/RGO composite was evaluated by photocatalytic degradation of methylene blue (MB) dye under visible-light irradiation. The enhancement of photocatalytic properties of Bi2O3 rods/RGO composite attributed to the synergistic effect between Bi2O3 rods and graphene sheets which effectively prevents recombination of the photogenerated electron-hole pairs in Bi2O3 rods. The present study provides a new approach in improving the performance of Bi2O3 rods/RGO composite in energy and environmental applications.

Photocatalytic and antibacterial activities of gold and silver nanoparticles synthesized using biomass of Parkia roxburghii leaf.

The present study reports a green approach for synthesis of gold (Au) and silver (Ag) nanoparticles (NPs) using dried biomass of Parkia roxburghii leaf. The biomass of the leaf acts as both reductant as well as stabilizer. The as-synthesized nanoparticles were characterized by time-dependent UV-visible, Fourier transform infrared (FT-IR), powder X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The UV-visible spectra of synthesized Au and Ag NPs showed surface plasmon resonance (SPR) at 555 and 440 nm after 12h. Powder XRD studies revealed formation of face-centered cubic structure for both Au and Ag NPs with average crystallite size of 8.4 and 14.74 nm, respectively. The TEM image showed the Au NPs to be monodispersed, spherical in shape with sizes in the range of 5-25 nm. On the other hand, Ag NPs were polydispersed, quasi-spherical in shape with sizes in the range of 5-25 nm. Investigation of photocatalytic activities of Au and Ag NPs under solar light illumination reveals that both these particles have pronounced effect on degradation of dyes viz., methylene blue (MB) and rhodamine b (RhB). Antibacterial activity of the synthesized NPs was studied on Gram positive bacteria Staphylococcus aureus and Gram negative bacteria Escherichia coli. Both Au and Ag NPs showed slightly higher activity on S. aureus than on E. coli.

Facile synthesis of novel CaFe2O4/g-C3N4 nanocomposites for degradation of methylene blue under visible-light irradiation.

Hybrid organic/inorganic nanocomposites comprised of calcium ferrite (CaFe2O4) and graphitic carbon nitride (g-C3N4) were prepared via a simple two-step process. The hybridized CaFe2O4/g-C3N4 heterostructure was characterized by a variety of techniques, including X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy, electrochemical impedance spectroscopy (EIS), and photoelectrochemical studies. Photocatalytic activity of the prepared samples was evaluated against degradation of methylene blue (MB) under visible-light irradiation. The photocatalytic activity of CaFe2O4 30%/g-C3N4 nanocomposite, as optimum photocatalyst, for degradation of MB was superior to the pure CaFe2O4 and g-C3N4 samples. It was demonstrated that the photogenerated holes and superoxide ion radicals were the two main reactive species towards the photocatalytic degradation of MB over the nanocomposite. Based on the experimental results, a possible photocatalytic mechanism for the MB degradation over the nanocomposite was proposed. This work may provide some inspiration for the fabrication of spinel ferrites with efficient photocatalytic performance.