Enhanced sunlight-driven catalysis for hydrogen generation and dye remediation using synergistic p-Co3O4/n-TiO2 nanocomposites.

In this study, p-Co3O4/n-TiO2 nanocomposites were synthesized using different ratios of cobalt and titanium precursors through a hydrothermal method. These nanocomposites demonstrated notable potential in photocatalytic applications for hydrogen production and orange-red dye degradation under sunlight. Various techniques, including XRD, Raman spectroscopy, XPS, FESEM, TEM, and BET analysis, were used to comprehensively characterize their structural, morphological, and optical properties. The nanocomposites exhibited both cubic and tetragonal phases of Co3O4 and TiO2, and their combined effect resulted in a narrowed band gap. Additionally, the presence of Co3O4 induced surface plasmon resonance on the TiO2 surface, effectively impeding electron-hole recombination. The nanocomposites displayed an average particle size of ∼20 to 30 nm with substantial visible light absorption. High crystallinity and well-dispersed nanocomposites were confirmed by XRD and Raman, with BET surface areas ranging between 49 and 106 m2 g-1. Notably, the p-Co3O4/n-TiO2 nanocomposite showed superior photocatalytic activity, achieving a maximum hydrogen generation rate of 1120 µmol h-1 g-1 and an 83% degradation efficiency of the orange-red dye within 6 minutes under sunlight. This study emphasizes the enhanced performance of the p-Co3O4/n-TiO2 nanocomposite, indicating its potential in photocatalytic applications, conforming to a pseudo-first-order kinetics model.

Solution-based electrostatic self-assembly route for obtaining graphene-transition metal dichalcogenide heterostructures.

Heterostructures of 2D materials have provided splendid insights into fundamental phenomena and are also promising for numerous applications. However, the protocols for obtaining them remain highly specific and lack scalability. Herein, the demonstrated protocol employs surfactant-assisted exfoliation and centrifugation-based size-selection of nanosheets for synthesizing heterostructures through electrostatic self-assembly.

MoS2 nanobelts-carbon hybrid material for supercapacitor applications.

The MoS2 nanobelts/Carbon hybrid nanostructure was synthesized by the simple hydrothermal method. The MoS2 nanobelts were distributed in the interlayers of Lemon grass-derived carbon (LG-C), provides the active sites and avoid restacking of the sheets. The structural and morphological characterization of MoS2/LG-C and LG-C were performed by Raman spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical measurements were studied with cyclic voltammetry, the galvanostatic charge-discharge method, and electrochemical impedance spectroscopy. The specific capacitance of MoS2/LG-C and LG-C exhibits 77.5 F g-1 and 30.1 F g-1 at a current density of 0.5 A g-1. The MoS2/LG-C-based supercapacitor provided the maximum power density and energy density of 273.2 W kg-1 and 2.1 Wh kg-1, respectively. Furthermore, the cyclic stability of MoS2/LG-C was tested using charging-discharging up to 3,000 cycles, confirming only a 71.6% capacitance retention at a current density of 3 A g-1. The result showed that MoS2/LG-C is a superior low-cost electrode material that delivered a high electrochemical performance for the next generation of electrochemical energy storage.

Copper(ii) and cobalt(iii) Schiff base complexes with hydroxy anchors as sensitizers in dye-sensitized solar cells (DSSCs).

Two Schiff base complexes of copper(ii) and cobalt(iii) having the formulae [CuL2] (Cu-Sal) and [CoL3] (Co-Sal) (HL = 2-(((2-hydroxyethyl)imino)methyl)phenol) have been synthesized and characterized microanalytically, spectroscopically and in the case of Cu-Sal using single crystal X-ray diffraction technique. The single crystal X-ray analysis reveals a square planar geometry around Cu(ii) satisfied by phenoxide oxygen and imine nitrogen of the L- ligand to generate a six membered chelate ring. The solid state structure of Cu-Sal is satisfied by varied intermolecular non-covalent interactions. The nature of these interactions has been addressed with the aid of Hirshfeld surface analysis. Both compounds have been used as sensitizers in TiO2 based dye sensitized solar cells (DSSCs) and the DSSC experiments revealed that Co-Sal offers better photovoltaic performance in comparison to Cu-Sal. The Co-Sal exhibited a J sc of 9.75 mA cm-2 with a V oc of -0.648 V, incident photon to current conversion efficiency (IPCE) of 57% and η of 3.84%. The relatively better photovoltaic performance of Co-Sal could be attributed to better light absorption and dye loading than that of Cu-Sal.

Room-temperature highly sensitive and selective NH3gas sensor using vertically aligned WS2nanosheets.

Here, we report the room temperature (35 °C) NH3gas sensor device made from WS2nanosheets obtained via a facile and low-cost probe sonication method. The gas-sensing properties of devices made from these nanosheets were examined for various analytes such as ammonia, ethanol, methanol, formaldehyde, acetone, chloroform, and benzene. The fabricated gas sensor is selective towards NH3and exhibits excellent sensitivity, faster response, and recovery time in comparison to previously reported values. The device can detect NH3down to 5 ppm, much below the maximum allowed workspace NH3level (20 ppm), and have a sensing response of the order of 112% with a response and recovery time of 54 s and 66 s, respectively. On the other hand, a sensor made from nanostructures has a bit longer recovery time than a device made from nanosheets. This was attributed to the fact that NH3molecules adsorbed on the surface site and those trapped in between WS2layers may have different adsorption energies . In the latter case, desorption becomes difficult and may give rise to slower recovery as noticed. Further, stiffened Raman modes upon exposure to NH3reveal strong electron-phonon interaction between NH3and the WS2channel. The present work highlights the potential use of scaled two-dimensional nanosheets in sensing devices and particularly when used with inter-digitized electrodes, may offer enhanced performance.

Enhanced energy storage performance and theoretical studies of 3D cuboidal manganese diselenides embedded with multiwalled carbon nanotubes.

The burst of energy produced from the sustainable energy sources need to be harnessed by energy storage systems. Development of novel and advanced energy storage devices such as supercapacitors discover an enormous future ahead. Recently, hybrid supercapacitors (electric double layer capacitor (EDLC) and pseudocapacitors) trend to be used as energy storage interfaces for their improved efficacy in energy density without altering the power density. In the ongoing workplan, transition metal selenides MnSe2 and its hybrid with multiwalled carbon nanotubes (MWCNTs) are synthesized by a simplistic hydrothermal protocol. Certainly, cubic phases of MnSe2-MWCNT(MS/CNT) manifested superior electrochemical performance in both symmetric and asymmetric full cell configurations in contrast to prestine MnSe2(MS). The asymmetric MS/CNT cell achieved an excellent charge storage capability with an high energy density of 39.45 Wh kg-1 at a power density of 2.25 kW kg-1 maintaining an energy density of 14.5 Wh kg-1 at a high power density of 4.5 kWh kg-1 and also revealed long term stability over 5000 consecutive charge/discharge cycles (capacitance retention of 95.2%). Furthermore, the preferable growth along (200) direction in the presence of MWCNTs favoured in enriching the supercapacitive property of MS. The quantum capacitance of MnSe2surfaces and MS/CNT heterostructure has been estimated using density functional theory simulation to confirm the experimental outcomes. Theoretical investigation simultaneously exposed the contribution of (200) plane of MnSe2 and MWCNTs cultured in enhanced DOS (density of states) near the Fermi level that remarkably promoted the energy storage efficiency of MS/CNT.

MoS2 and CdMoS4 nanostructure-based UV light photodetectors.

We have developed MoS2 nanosheets and CdMoS4 hierarchical nanostructures based on a UV light photodetector. The surface morphologies of the as-prepared samples were investigated via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The performance parameters for the present photodetectors are investigated under the illumination of UV light having a wavelength of ∼385 nm. Upon the illumination of UV light, the CdMoS4-based photodetector device showed a better response to UV light compared to the MoS2 device in terms of photoresponsivity, response time (∼72 s) and recovery time (∼94 s). Our results reveal that CdMoS4 hierarchical nanostructures are practical for enhancing the device performance.

Highly sensitive and flexible pressure sensor based on two-dimensional MoSe2 nanosheets for online wrist pulse monitoring.

The advancement of portable and flexible electronics that is integrated with multiple sensing functions has increasingly drawn considerable interest. The fabricated sensors would have the ability to sense multiple deformations like pressing, twisting and trivial vibrations such as pulses of wrist vibrations to mimic human skin. Presently, we implemented an easy, cost-effective and optimized fabrication technique for production of pressure sensors based on MoSe2 nanosheets coated on cellulose paper. The present sensor exhibits an incorporation of large pressure sensitivity of 18.42 kPa-1 in pressure range 0.001-0.5 kPa, 7.28 kPa-1 in pressure range 1-35 kPa and 2.63 kPa-1 in pressure range 40-100 kPa, working in broad pressure range (from 0.001 to 100 kPa) and long-term stability up to 200 deformation cycles at 2 kPa. The sensor showed excellent response towards the detection of vibrations of machines including cellular phone, compressor, etc. Besides, the sensor shows excellent environmental stability and exhibits immune piezo-resistive response to temperature variation.

Functional Monochalcogenides: Raman Evidence Linking Properties, Structure, and Metavalent Bonding.

Pressure- and temperature-dependent Raman scattering in GeSe, SnSe, and GeTe for pressures beyond 50 GPa and for temperatures ranging from 78 to 800 K allow us to identify structural and electronic phase transitions, similarities between GeSe and SnSe, and differences with GeTe. Calculations help to deduce the propensity of GeTe for defect formation and the doping that results from it, which gives rise to strong Raman damping beyond anomalous anharmonicity. These properties are related to the underlying chemical bonding and consistent with a recent classification of bonding in several chalcogenide materials that puts GeTe in a separate class of "incipient" metals.

Enhanced Antifungal Activity of WS2/ZnO Nanohybrid against Candida albicans.

Candida albicans forms persistent infections through the formation of biofilms that confer resistance to existing antifungal drugs. Biofilm targeting is therefore a promising strategy to combat Candida albicans infections. The WS2/ZnO nanohybrids exhibits considerably improved antibiofilm activity and inhibited the biofilm formation by 91%, which is quite better than that for pristine WS2, which is only 74%. The physical blend prepared by mixing WS2 nanosheets and WS2/ZnO in the ratio of 70:30 showed an antibiofilm activity of 58%, which was intermediate to that observed for pristine materials. The as-synthesized nanohybrid also demonstrates dose-dependent antifungal activity as calculated using the disc diffusion test. WS2/ZnO nanohybrid shows 1.5 times higher activity compared to pristine WS2 nanosheets suggesting that the nanohybrid materials are more effective as novel antifungal materials.

TiO2 nanoflowers based humidity sensor and cytotoxic activity.

We have systematically investigated the humidity sensing performance and cytotoxic activity of TiO2 nanoflowers synthesized by hydrothermal method. Our result reveals that TiO2 nanoflower based sensor devices show good performance at room temperature with a maximum sensitivity of ∼815% along with a response time of ∼143 s and a recovery time of ∼33 s. Our findings also evaluate the cytotoxic effect of TiO2 nanoflowers on human HepG2 cell lines. The cells are cultured in DMEM medium with varying concentrations of TiO2 nanoflowers for 24, 48 and 72 hours respectively. The results indicate that TiO2 nanoflower doses time dependently suppress the proliferation of HepG2 cell lines.

Phase transformation in tungsten oxide nanoplates as a function of post-annealing temperature and its electrochemical influence on energy storage.

The morphology and crystal structure of electrode materials have an enormous impact on their electrochemical properties for employment in supercapacitors for various applications. In this study, the transformations of the crystal structure of WO3·H2O nanoplates were conducted by post-annealing at 200 °C and 400 °C. The morphological and structural evolution of the electrodes was studied via FEG-SEM, HRTEM, FTIR, XRD, and Raman spectroscopy. The phase transition and enhanced degree of crystallinity were observed with increasing temperature. The orthorhombic structures of the hydrate WO3·H2O (W80), the mixed-phase with mesoporous structure (W200), and finally the monoclinic phase of WO3 structures (W400) were achieved at annealing temperatures of 80 °C, 200 °C, and 400 °C respectively. The electrochemical performance of electrode W200 showed the highest specific capacitance of 606 F g-1 as compared to electrode W80 (361 F g-1), and was two-fold greater than electrode W400 (302 F g-1) at a current density of 1 A g-1. Moreover, electrode W200 exhibited excellent cyclic stability of 89% at an ultrahigh scan rate of 100 mV s-1 after 4000 cycles. The results highlight that the mixed-phase WO3 nanoplates would make a suitable electrode material for supercapacitors with desired electrochemical features.

Synthesis of a 3D free standing crystalline NiSex matrix for electrochemical energy storage applications.

The electrochemical performance for energy storage of three-dimensional (3D) self-supported heterogeneous NiSex cubic-orthorhombic nanocrystals grown by a facile one-step chemical vapour deposition (CVD) approach on Ni foam substrates has been explored. NiSex shows a high specific capacitance of 1333 F g-1 with ultra-high energy (105 W h kg-1) and power (54 kW kg-1) densities. Furthermore, by integrating the as-grown NiSex as the anode and reduced graphene oxide as the cathode, a hybrid supercapacitor (HSC) prototype with a coin cell configuration has been fabricated. The device shows better capacitance (40 F g-1) with high energy (22 W h kg-1) and power (5.8 kW kg-1) densities and robust cycling durability (∼88% capacitance retention after 10 000 repeated cycles). For practical reliability of the as-fabricated HSC, a red LED has been illuminated by connecting it with two charged coin cells. These outstanding performances of the HSC prove to be promising for applications in high energy storage systems.

Pressure-Induced Phase Transitions in Germanium Telluride: Raman Signatures of Anharmonicity and Oxidation.

Pressure-induced phase transitions in GeTe, a prototype phase change material, have been studied to date with diffraction which is not sensitive to anharmonicity-induced dynamical effects. GeTe is also prone to surface oxidation which may compromise surface sensitive measurements. These factors could be responsible for the lack of clarity about the phases and transitions intervening in the phase diagram of GeTe. We have used high-pressure Raman scattering and ab initio pseudopotential density functional calculations to unambiguously establish the high-pressure phase diagram and identify three phases up to 57 GPa, a low-pressure rhombohedral phase, an intermediate pressure cubic phase, and a high-pressure orthorhombic phase. We detect substantial broadening and softening of Raman modes at low pressure and identify the transition regions and possible intermediate phases.

Freestanding Borophene and Its Hybrids.

Borophene, an elemental metallic Dirac material is predicted to have unprecedented mechanical and electronic character. Need of substrate and ultrahigh vacuum conditions for deposition of borophene restricts its large-scale applications and significantly hampers the advancement of research on borophene. Herein, a facile and large-scale synthesis of freestanding atomic sheets of borophene through a novel liquid-phase exfoliation and the reduction of borophene oxide is demonstrated. Electron microscopy confirms the presence of ß12 , X3 , and their intermediate phases of borophene; X-ray photoelectron spectroscopy, and scanning tunneling microscopy, corroborated with density functional theory band structure calculations, validate the phase purity and the metallic nature. Borophene with excellent anchoring capabilities is used for sensing of light, gas, molecules, and strain. Hybrids of borophene as well as that of reduced borophene oxide with other 2D materials are synthesized, and the predicted superior performance in energy storage is explored. The specific capacity of borophene oxide is observed to be ≈4941 mAh g-1 , which significantly exceeds that of existing 2D materials and their hybrids. These freestanding borophene materials and their hybrids will create a huge breakthrough in the field of 2D materials and could help to develop future generations of devices and emerging applications.

Temperature-dependent Raman spectroscopy and sensor applications of PtSe2 nanosheets synthesized by wet chemistry.

We report on a wet chemistry method used to grow PtSe2 nanosheets followed by thermal annealing. The SEM and TEM analysis confirms the formation of PtSe2 nanosheets. Furthermore, XRD, Raman, XPS and SAED patterns were used to analyze the crystal structure and to confirm the formation of the PtSe2 phase. The temperature-dependent Raman spectroscopy investigations were carried out on PtSe2 nanosheets deposited on Si substrates in the temperature range 100-506 K. The shifts in Raman active Eg and A1g modes as a function of temperature were monitored. The temperature coefficient for both modes was calculated and was found to match well with the reported 2D transition metal dichalcogenides. A PtSe2 nanosheet-based sensor device was tested for its applicability as a humidity sensor and photodetector. The humidity sensor based on PtSe2 nanosheets showed an excellent recovery time of ≈5 s, indicating the great potential of PtSe2 for future sensor devices.

Development of pristine and Au-decorated Bi2O3/Bi2WO6 nanocomposites for supercapacitor electrodes.

Pristine and Au-decorated Bi2O3/Bi2WO6 nanocomposites were synthesized via a facile hydrothermal method. Characterization techniques such as XRD, FESEM, HRTEM and XPS were used to explore the structural, morphological and electronic properties. Furthermore, electrochemical characterizations including cyclic voltammetry (CV), the galvanostatic charge-discharge (GCD) method, and electrochemical impedance spectroscopy (EIS) were performed to investigate the supercapacitance behaviour of the synthesized materials. Interestingly, the Au-decorated Bi2O3/Bi2WO6 nanocomposite showed a higher capacitance of 495.05 F g-1 (1 M aqueous KOH electrolyte) with improved cycling stability (99.26%) over 2000 cycles, measured at a current density of 1 A g-1, when compared to the pristine Bi2O3/Bi2WO6 composite (capacitance of 148.81 F g-1 and good cycling stability (95.99%) over 2000 cycles at a current density of 1 A g-1). The results clearly reveal that the decoration of the Bi2O3/Bi2WO6 composite with Au nanoparticles enhances its supercapacitance behaviour, which can be attributed to an increase in electrical conductivity, good electrical contact between the electrode and electrolyte, and an increase in effective area. The Au-decorated Bi2O3/Bi2WO6 nanocomposite can be considered as an electrode material for supercapacitor application.

2D-MoS2 nanosheets as effective hole transport materials for colloidal PbS quantum dot solar cells.

Herein, we demonstrate for the first time matrix-free deposition of two dimensional (2D) MoS2 nanosheets as an efficient hole transport layer (HTL) for colloidal lead sulfide (PbS) quantum dot (QD) solar cells. We have developed all-solution-processed n-p-p+ architecture solar cells where ZnO nanoparticles were used as an n-type window layer, a PbS QD layer acted as a light absorbing p-type layer and 2D-MoS2 nanosheets acted as a p+-type hole transport layer. The MoS2 nanosheets allow better interface with the PbS QD layers. The incorporation of the MoS2 hole transport layer leads to superior fill factor, higher open circuit voltage and better performance in colloidal PbS QD solar cells. These results show that one layer of MoS2 nanosheets improves the power conversion efficiency of the device from 0.92% for a hole transport material free device to 2.48%. The present work reveals the development of 2D-MoS2 nanosheets as a new hole transport layer for the fabrication of cost-effective, durable and efficient colloidal PbS quantum dot solar cells.

Improved Nonenzymatic Glucose Sensing Properties of Pd/MnO2 Nanosheets: Synthesis by Facile Microwave-Assisted Route and Theoretical Insight from Quantum Simulations.

The electrocatalytic properties of manganese oxide (MnO2) can be improved significantly by making hybrids/composites with noble metals (Au, Pd). Here, efforts have been made to synthesize the MnO2/Au and MnO2/Pd nanocomposites by a facile, rapid microwave irradiation method. The products characterized by X-ray diffraction and transmission electron microscopy exhibited their tetragonal phase and nanosheet morphology. The efficiency of the prepared composite materials as glucose sensor was tested by cyclic voltammetry and chronoamperometry measurements, and the results are discussed. The study revealed that successful modification of MnO2 by Pd led to excellent sensing performance by the reduction of size and the synergistic effect between MnO2 and PdO, which expedites the electron transfer. Besides, the wide detection range, good selectivity, and stability demonstrate its robustness in the design of electrochemical sensor platform. To get theoretical insight into the excellent sensing performance of MnO2/Pd, we have performed detailed density functional theory simulations to explore the charge transfer and bonding mechanism of glucose on MnO2 and Pd/Au-doped MnO2 surface. Pd is bonded strongly on MnO2 and makes MnO2/Pd more conducting due to the enhancement of density of states near Fermi level. The higher binding energy of glucose and enhanced charge transfer from glucose to Pd-doped MnO2 compared to bare MnO2 infer that Pd-doped MnO2 possess superior charge-transfer kinetics, resulting in higher glucose sensing performance, which supports our experimental observations.

Humidity Sensing and Photodetection Behavior of Electrochemically Exfoliated Atomically Thin-Layered Black Phosphorus Nanosheets.

Recent investigations on two-dimensional black phosphorus material mainly highlight work on few atomic layers and multilayers. It is still unknown if the black phosphorus atomically thin sheet is an ideal structure for the enhanced gas-solid interactions due to its large surface area. To further investigate this concern, we have synthesized few atomic layer thick nanosheets of black phosphorus using an electrochemical exfoliation method. The surface morphology and thickness of the nanosheet were identified using AFM, TEM, and Raman spectroscopy. The black phosphorus nanosheet thick film device was used for the gas sensing application with exposure to different humidites. Further, the few layer black phosphorus nanosheet based transistor shows good mobility and on/off ratio. The UV light irradiation on the black phosphorus nanosheet shows good response time. The overall results show that the few layer thick film of black phosphorus nanosheets sample exhibits creditable sensitivity and better recovery time to be used in humidity sensor and photodetector applications.