Himani Sharma’s research while affiliated with Doon University and other places

Hydrogen, essential for clean and sustainable energy solutions, encounters significant challenges in electrochemical water splitting. This study introduces a Z-Scheme WS2/TiO2 heterostructure synthesized via a hydrothermal method, aimed at enhancing hydrogen evolution reaction (HER) performance through interface engineering. Comprehensive interfacial investigations were conducted by using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and UV–vis spectroscopy. XPS analysis revealed peak shifts in the heterostructure, indicative of electronic modifications at the interface. These shifts enhance active site availability, and charge transfer kinetics also corroborated its UPS and UV–vis studies. The establishment of an intimate interface fostering a Z-scheme charge transfer mechanism has been reported. A lower work function of 4.2 eV suggests improved charge transfer at the interface. Furthermore, the development of an internal electric field to achieve Fermi level equilibrium also led to improved HER performance of the Z-scheme-based heterostructure. The prepared heterostructure demonstrated enhanced HER with a lower onset potential (−0.04 V in light and −0.05 V in dark) as compared to pristine WS2 and a lower charge transfer resistance (36.4 Ω in light and 51.2 Ω in dark), highlighting a promising approach for constructing efficient photoelectrochemical device. The study’s insights into strain-induced effects further underscore the potential of the WS2/TiO2 heterostructure for sustainable energy applications. This result paves the way for constructing the facile and efficient method for generating a photoelectrochemical device with solar-to-hydrogen (STH) efficiency equal to 1.16% determined using the water displacement method.

Titanium dioxide (TiO2) is gaining popularity as a potential contender for photocatalytic carbon dioxide (CO2) reduction to transform industrial CO2 gas into fuels. It is also associated with the storage of inconsistent and sustainable energy of solar in the form of chemical bonds to close the carbon cycle. Nevertheless, pure TiO2 has a high band gap (3.2 eV), quick electron and hole recombination, and limited selectivity for photocatalysis. Much progress has recently been achieved in enhancing the efficiency of TiO2 photocatalysts to minimize greenhouse gas emissions. In this chapter, we first address the foundations and problems of photocatalysis for greenhouse gas reduction using TiO2-based catalysts. After that, the newly developing advancements and improvements in TiO2 nanostructures by making hybrid nanostructures and heterostructures for conquering the aforementioned barriers to obtain good photocatalytic activity, as well as the capacity to prevent electron–hole pair recombination, are explored.

Hydrogen as a clean fuel is increasingly sought after for its potential to replace non-renewable energy sources, with the hydrogen evolution reaction (HER) presenting a sustainable method for its production. This study focuses on enhancing HER efficiency through the fabrication of a Z-scheme based tungsten di sulfide/titanium di oxide (WS2/TiO2) heterostructure via hydrothermal synthesis. Transition metal dichalcogenides like WS2, known for their unique properties, are integrated with TiO2 nanorods to create a robust photocatalytic system. Characterization techniques such as X-ray diffraction (XRD), Raman spectroscopy, Field-emission scanning electron microscopy (FE-SEM) and Brunauer-Emmett-Teller (BET) were performed. X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoelectron spectroscopy (UPS) provided comprehensive insights into the electronic interactions and charge transfer kinetics. A shift in peak positions in XPS spectra indicate the enhancement in catalytic active sites which is in corroboration with the UPS studies. An altered energy environment causing the Z-scheme charge transfer in heterostructure was proved, enhancing the hydrogen production. From the UPS studies, a lower work function for heterostructure i.e. 5.47 eV as compared to 5.5 eV for pristine WS2 indicates improvement in charge transfer. Electrochemical measurements including linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) confirmed the improved HER performance of heterostructure with lower value of onset potential (0.031 V) and charge transfer resistance (3.5 k Ω) as compared to pristine samples. Thus, proving WS2/TiO2 heterostructure to be a potential candidate for sustainable hydrogen production.

Dual functional heterostructure of Bismuth vanadate and Tungsten trioxide (BiVO 4 /WO 3) was developed and its use in the generation of hydrogen and the degradation of dyes was shown. BiVO 4 was synthesized by the sol gel method, and its heterostructure with WO 3 was created by the solvothermal method. To study the morphological, structural, and optical characteristics of BiVO 4 and BiVO 4 /WO 3, X-Ray diffraction (XRD), Field emission scanning electron microscope (FESEM), UV-visible spectroscopy (UV Vis), Raman spectroscopy and X-Ray photoelectron spectroscopy (XPS) was performed. Using Electrochemical Impedance Spectroscopy (EIS) and Linear Sweep Voltammetry (LSV), the electrochemical characteristics were ascertained. When exposed to visible light, BiVO 4 alone demonstrated a 73.4% degradation efficiency for methylene blue; however, the hybrid system yielded an 87.2% degradation efficiency. In the presence of 1M KOH solution an increase in current density and a lower value of onset potential (0.388 V vs RHE) was observed for the BiVO 4 /WO 3. Similarly, EIS indicated a decrease in charge transfer resistance (83.92K) in the case of hybrid. Better performance from the hybrid system in HER further presented its capacity to both clean up the environment and produce energy from renewable sources.

Using hybrids and photon illumination together is an important step toward making high-performance gas sensors. Hybrid materials have their own properties that can improve the way gas sensors work, and photon illumination can make the sensor more sensitive. There is currently a lack of understanding regarding the impact of photoassisted gas sensing properties of hybrid materials, making it imperative that the connection between light photons and heterostructures for gas sensing materials be clarified. In this article, we design and develop a photoassisted molybdenum disulfide (MoS2) based hybrid gas sensor with a low detection limit (10 ppm). Also, the mentioned sensor has robust antihumidity interference by incorporating the localized surface plasmon resonance (LSPR) effect using metal nanoparticles of Ag and Pd decorated over the MoS2 nanoflowers. It has been discovered that the performance of sensing is enhanced when MoS2 is modified with Ag and Pd nanoparticles of nearly 5 nm in diameter in conjunction with green light (533 nm). The AgMoS2 displays a higher response value (76%) to 10 ppm of NH3 at room temperature compared to the PdMoS2 (43.7%) and bare MoS2 (19.5%). This improvement in sensing response is a result of LSPR in AgMoS2 hybrids and of the formation of a Schottky barrier in PdMoS2 hybrids, as confirmed by UV−vis, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) measurements. These findings open up a route for creating real-time gas detection sensors that can operate at lower temperatures. KEYWORDS: transition metal dichalcogenides, 2D materials, light-assisted gas sensors, hybrid gas sensors, localized surface plasmon resonance (LSPR)

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.