Charu Dwivedi’s research while affiliated with Doon University and other places

Two‐dimensional (2D) tungsten disulphide (WS2) based heterostructures with modified interfaces have huge potential for photocatalytic applications. Integrating WS2 with one‐dimensional (1D) titanium dioxide (TiO2) and 2D molybdenum disulphide (MoS2) structures to form heterostructures, enhances its photocatalytic activity. The enrichment in photocatalytic activity of heterostructures may get affected by the electronic interaction at the interface as well as morphology and dimensionality also affect the catalytic activity. In this context, the present work focuses on the enrichment of photocatalytic activity by different tungsten disulphide (WS2) based heterostructures, which may get influenced by the interfacial interaction. In the present work, two different heterostructures 2D‐1D WS2/TiO2 and 2D‐2D MoS2/WS2 are formed using the hydrothermal method. Scanning electron microscopy (SEM) confirmed the morphology of prepared heterostructures. X‐ray photoelectron spectroscopy (XPS) analysis further revealed that the integration of 1D and 2D nanostructures with WS2 has been found effective to alter the interface by the development of the Ohmic and Schottky barrier. Moreover, Fourier transformation infra‐red (FTIR) spectroscopy confirms the presence of W−S, S−S, Mo−S, and Ti−O bonds in the prepared heterostructures. Furthermore, current‐voltage (I–V) data graphically illustrated the conductivity of catalysts. I–V curves confirm the presence of Schottky and ohmic barriers and the higher electrical conductivity of 2D‐2D MoS2/WS2 heterostructures, which facilitates the charge carrier's transportation. 2D‐1D WS2/TiO2 and 2D‐2D MoS2/WS2 heterostructures are further explored for photocatalytic activity by the methylene blue dye degradation. The overall catalytic activity of 2D‐2D MoS2/WS2 is better than 2D‐1D WS2/TiO2 and WS2, respectively. This result was accounted as 2D‐2D MoS2/WS2 had the highest conductivity and better charge separation at the interface in comparison to the other two synthesised catalysts.

In the quest to create effective sensors that operate at room temperature, consume less power and maintain their stability over time for detecting toxic gases in the environment, molybdenum disulfide (MoS2) and MoS2-based hybrids have emerged as potent materials. In this context, the current work describes the fabrication of Au-MoS2 hybrid gas sensor fabricated on gold interdigitated electrodes (GIEs) for sensing harmful CO and NH3 gases at room temperature. The GIEs-based Au-MoS2 hybrid sensors are fabricated by decorating MoS2 nanoflowers (MNF) with varying size of Au nanoparticles using an inert gas evaporation technique. It is observed that by varying the size of Au nanoparticles, the crystallinity gets modified, as confirmed by X-ray diffraction (XRD) and Micro-Raman spectroscopy (μRS). The gas sensing measurements revealed that the best sensing response is found from the Au-MoS2 hybrid (with an average particle size of 10 nm). This particular hybrid shows a 79% response to CO exposure and a 69% response to NH3 exposure. The measurements are about 3.5 and 5 times higher than the bare MoS2 when exposed to CO and NH3 at room temperature, respectively. This enhancement in sensing response is attributed to the modified interfacial interaction between the Au nanoparticles and MNF gets improved, which leads to the formation of a Schottky barrier, as confirmed using X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoelectron spectroscopy (UPS) analysis. This enables the development of efficient gas sensors that respond quickly to changes in the gas around them.

The present study describes the synthesis of CdSe-incorporated TiO2 nanotubes (CdSe@TNT) via a modified hydrothermal method from CdSe-incorporated spherical TiO2 (CdSe@sTiO2). The structural and photocatalytic activities of both composites are then compared with spherical TiO2 (sTiO2). Quantum dots of CdSe are synthesized by varying Cd:Se precursor ratios and were incorporated into the TiO2 nanotubes (CdSe@TNT) hydrothermally. It is observed that the ratio of Cd:Se used for forming CdSe quantum dots is directly related to the band gap of CdSe@TNT. Reduction in the band gap of TiO2 was confirmed using UV–Vis DRS spectroscopy, and the band gap energy was evaluated to be 3.02 eV, 2.94 eV and 2.89 eV for sTiO2, CdSe@sTiO2 and CdSe@TNT, respectively. XPS peaks reveal elemental peaks of Cd and Se in the TiO2 nanostructure, confirming the formation of the composite. The micro Raman spectroscopy and XRD analysis revealed that structure of TiO2 becomes strained due to incorporation of CdSe in TiO2. The average crystalline sizes of sTiO2, CdSe@sTiO2 and CdSe@TNT are 5.28 nm, 4.36 nm and 2.43 nm, respectively. The morphology of the CdSe@TNT was investigated by HR-TEM. The redesigned interface of heterostructures is further investigated by carrying out the electrochemical properties, and it was observed that the CdSe@TNT heterostructures had a better electrical conductivity. Photocurrent response (I-t) curves for sTiO2, CdSe@sTiO2 and CdSe@TNT reveal that after five cycles, a maximum photocurrent value of 0.0363, 0.0970 and 0.1144 mA cm⁻² for sTiO2, CdSe@sTiO2 and CdSe@TNT, respectively, was observed. The photocatalytic efficiency of the synthesized nanomaterial was further investigated using methylene blue dye as a model compound. Graphical Abstract

Molybdenum disulfide (MoS2) is one of the most potent transition metal dichalcogenide (TMDc) material for gas sensing applications due to its various advantageous properties. It exhibits modest electron mobilities, reduced dimensionality, and favorable mechanical properties. The deposition of metal nanoparticles on nanostructured MoS2 leads to the modification in their sensing properties. By keeping in view, present work reports the fabrication of stable MoS2 nanoflowers (MNF) and their hybrids (Au-MoS2 nanoflowers). The hydrothermal approach was used to synthesize MNF nanostructures and in order to form the hybrid Au-MoS2 nanoflower (AuMNF) Au nanoparticle were deposited over MNF by an inert gas evaporation method. X-ray Diffraction and micro–Raman spectroscopy were used to study MNF and AuMNF hybrid structures. XRD found MoS2 1 T-2H mixed-phase. The peak shift and broadening in E1g, J3, and E3g modes for AuMNF hybrids was observed compared to MNF. The flower-like morphology of the pristine and hybrid nanostructures was confirmed via the Scanning electron microscopy (SEM) technique and transmission electron microscopy (TEM). Furthermore, the fabricated samples MNF and AuMNF hybrids were investigated for environmental gas sensing. According to the results of the gas sensing tests, the AuMNF hybrid provides the best sensing response. The gas sensing measurements revealed that the best sensing response is found from the AuMNF hybrid. This hybrid shows a response of 21.2 % in the presence of CO, which is 5.5 times higher than the response of pure MoS2. These findings contribute to a better interpretation of how the resistance of MoS2 nanostructures reacts towards CO gas exposure. These findings contribute to a better interpretation of how the resistance of MoS2 nanostructures reacts towards CO gas exposure.

Zinc imidazolate framework (ZIF-8) and titanium dioxide (TiO2) have been extensively studied as photocatalysts and have shown remarkable potential. In this study, we report the synthesis of a type II heterojunction photocatalyst based on carbon-doped TiO2 (C-TiO2) and ZIF-8 as a potentially improved material for solar light-harvested methylene blue (MB) degradation. Pure ZIF-8 has a wide band gap of 4.9 eV, due to which the application of this material to visible light-assisted photocatalytic performance is a challenging task. Therefore, C-TiO2 has been chosen as a composite material with ZIF-8 owing to its narrow band gap compared to TiO2. This enables the free radical–initiated photocatalytic reaction to shift into the visible region instead of the ultraviolet region. To construct the C-TiO2/ZIF-8 heterostructure, the zinc-based ZIF matrix has been built upon the exterior of C-TiO2 nanoparticles. UV–Vis diffuse reflectance spectroscopy (UV–Vis-DRS) corroborated the decrease in the band gap of ZIF-8 after the fabrication of C-TiO2/ZIF-8, while X-ray diffraction (XRD) analysis demonstrated a decrease in average d-spacing and average crystallite size of the synthesized photocatalyst. Raman spectra and X-ray photoelectron spectroscopy (XPS) analysis of the synthesized samples were also performed to further understand their chemical structure and elemental content. Ultraviolet photoelectron spectroscopy (UPS) and high-resolution transmission electron microscopy (HRTEM) analyses were performed to understand the valence band (VB) states and the morphology of C-TiO2/ZIF-8. The comparison between pure ZIF-8 and C-TiO2/ZIF-8 in the photocatalytic degradation of MB under visible light has also been drawn. A possible charge-transfer mechanism for the same has also been proposed. It is concluded that the synergistic effect of C-TiO2 and ZIF-8 in C-TiO2/ZIF-8 produces an effective material for photocatalytic dye degradation.