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

One dimensional nanostructures based hybrids have proven to be potent for photocatalytic applications. The hybrids having modified interface play a vigorous role in enrichment of photocatalytic activity by electronic interaction. Electronic interaction at interface occurs by the formation of electronic barriers (Ohmic/Schottky) that affects the transport of charge carriers and hence photocatalytic activity. The present work reports the switching of role play between Ohmic and Schottky barriers using different hybrids in order to have enhancement in photocatalytic activity. In order to form hybrids, MeNPs (Pd and Zn) and BiMeNPs (ZnPd) are chosen to study the modification of interface by XPS and UPS. The analysis revealed that Pd and ZnPd crafted TiO2 nanorods (TiO2 NR) shows the formation of Schottky barrier with upward band bending at interface. Similarly, Zn crafted TiO2 NR shows the Ohmic barrier with downward band bending at interface. The band bending in hybrids is accredited to interfacial electronic interaction and charge separation at interface. The modified hybrids are studied for electrochemical analysis using cyclic voltammetry. It is analyzed that higher electrical conductivity is present in ZnPd/TiO2 NR, facilitates the transport of charge carriers. The improved charge separation at interface of ZnPd/ TiO2 NR leads to enhanced photocatalytic activity in comparison to Pd/TiO2 NR and Zn/TiO2 NR.

Low energy ion-irradiated hybrid nanostructures with altered interfaces have sparked a lot of interest in the field of photocatalytic applications. In context to that, the present work on low energy ion (LEI) irradiation at different fluences is carried out to study the modification in TiO2hybrids and hence their photocatalytic studies. LEI is carried out using 50 keV of P ions for TiO2 nanorods (TiNRs)-based hybrids (Ag-TiNRs and Au-TiNRs) at different fluences to induce structural, morphological, and interfacial changes. It is found that these hybrid nanostructures get modified at low fluence (5X1014ions/cm2), whereas at higher fluence (5X1015ions/cm2), their morphologies are damaged. These changes are studied using Micro-Raman spectroscopy. The analysis revealed that the blue shift in the Eg mode of LEI hybrids is attributed to compressive strain, which introduces defects in the TiO2 nanostructures. The X-ray photoelectron spectroscopy analysis reveals the formation of the Schottky barrier with a shift towards the lower binding energy and this is credited to interfacial interaction and separation of charges at the interfaces. The effects of structural and interfacial modifications of LEI hybrids are further studied for electrochemical and photocatalytic analyses.

One-dimensional (1D) titanium dioxide (TiO2) nanostructures have enormous attention for next-generation renewal energy resources. In reference to that, present work reports the effect of different voltages (40 V and 60 V) on the structural and morphological properties of 1D-TiO2 nanotubes (TONTs) and their hybrids by grafting of bimetallic nanoparticles (BiMNPs) of AgAu. The growth at different voltages affects the morphology and diameters of TONTs as imaged using field emission scanning electron microscopy (FESEM). The variation in anodization voltage from 40 to 60 V increases the diameter of TONTs that offers a larger active surface area of TONTs. It is further revealed that the crystallinity and crystallite size of TONTs is increased after increasing the anodization voltage. Furthermore, TONTs are integrated with AgAu BiMNPs to form the hybrid structures. The AgAu-TONT hybrid forms a modified interface and induces less compressive strains that improve the charge separation at the interface and hence improve the electronic structure, as investigated by X-ray photoelectron spectroscopy (XPS) and X-ray Diffraction (XRD). On further exploring the 1D-TONTs and AgAu-TONTs for photocatalytic studies, it is observed that the photocatalytic activity of AgAu-TONTs is better than TONTs-40 V and TONTs-60 V. The improved photocatalytic activity in the AgAu-TONTs is due to the large surface area, charge carrier generation, and lesser compressive strain present at the interface.

One dimensional oxide-based hybrid nanostructures have immense potential for next generation energy applications. By considering that, the present work dwells into interfacial interaction in strain induced bimetallic nanoparticles-TiO2 nanohybrids for photo energy harvesting. The hybrid nanostructure system consists of bimetallic nanoparticles (Pd-Pt, Cu-Pd, Ag-Au)/TiO2 nanostructures (MNPs/TiNs). The different pathways are used to craft Cu-Pd and Pd-Pt on TiNs in comparison to Ag-Au. The crafting of MNPs on TiNs has been found effectual to modify the interface and hence electronic structure of MNPs/TiNs as evident by X-ray photoelectron spectroscopy (XPS). The detailed analysis in to the strains induced in the hybrid system is investigated using micro-Raman spectroscopy and is corroborated with X-ray diffraction (XRD) and XPS studies. The analysis revealed that the crafting of the bimetallic nanoparticles in the TiNs induce compressive strains that improve the charge separation at the interface. The strain induced hybrids are further explored for photocatalysis. It is observed that overall photocatalytic light harvesting of compressively strained Ag-Au/TiNs system is better than Cu-Pd/TiNs and Pd-Pt/TiNs owing to better charge separation at the interface. The time dependence of the photo-degradation using a model compound is also studied and the system is found to be following pseudo-first order kinetics.

Titanium dioxide (TiO2) is one of the most effective n-type semiconductors for photocatalytic applications. Compared with the bulk TiO2 nanostructures, the one-dimensional (1D) TiO2 nanostructures have elicited great interest due to its various advantageous properties such as high surface-volume ratio, high chemical stability, strong oxidizing power, nontoxicity and low cost. TiO2 exists mainly in two crystalline phases namely anatase and rutile. When different phases of TiO2 are combined, they have better charge transport and light absorption properties than pristine nanotubes and nanorods. In reference to that, mixed phases play an important role in the modification of the photocatalytic properties. In the present work, three different nanostructures (TiO2 nanotubes, nanorods and mixed phase nanohybrids) are fabricated by electrochemical anodization and hydrothermal processes, respectively. TiO2 nanotubes are synthesized by electrochemical anodization of highly pure titanium foil in a solution containing ethylene glycol, ammonium fluoride and distilled water, TiO2 nanorods are grown on fluorine-doped tin oxide (FTO) using a hydrothermal method and hybrid TiO2 nanostructures consisting of rutile TiO2 nanorods synthesized by hydrothermal method on anodized TiO2 nanotubes in a high temperature and high-pressure condition with titanium-n-butoxide as the reaction precursor. The three different morphologies of nanotubes, nanorods and nanohybrids are investigated using scanning electron microscopy (SEM). The crystallinity of the TiO2 nanotubes, nanorods and nanohybrids are studied using Raman spectroscopy and X-ray diffraction (XRD) techniques. TiO2 nanotubes, nanorods and nanohybrids are crystalized in anatase, rutile and mixed phase (anatase and rutile), respectively. The structural transformation of the formed TiO2 nanohybrid is compared with TiO2 nanorods and nanotubes that further be explored for photocatalysis by degradation of methylene blue (10 μM) under xenon lamp in the presence of catalysts. It is observed that overall photocatalytic activity of mixed phase TiO2 nanohybrids is better than TiO2 nanotubes and nanorods owing to better electron hole separation and transportation.