Browsing by Author "Rohit Ranjan Srivastava"

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2D SnS2 Nanostructure-Derived Photocatalytic Degradation of Organic Pollutants Under Visible Light
(Frontiers Media S.A., 2021) Rohit Ranjan Srivastava; Pramod Kumar Vishwakarma; Umakant Yadav; Suyash Rai; Sima Umrao; Rajiv Giri; Preeti Suman Saxena; Anchal Srivastava
Wastewater produced by the textile industry contains various dyes and organic compounds that directly or indirectly affect surface water or groundwater pollution. Visible-light-driven semiconductor photocatalysis is the leading pathway for the degradation of environmental pollutants. Herein we report the bottom-up hydrothermal growth of 2D tin disulfide nanostructures (SnS2 NSs) for the efficient photodegradation of organic pollutants such as Rhodamine B (Rh.B) and Methyl Violet (M.V) in an aqueous medium under visible light (λ > 400 nm) irradiation. The as-synthesized SnS2 NSs were characterized by various structural, morphological, and optical techniques such as XRD, RAMAN, TEM, UV–Vis, Brunauer–Emmett–Teller, etc. Furthermore, the low bandgap (∼1.6 eV), the high surface area (56 m2/g), and the anionic nature of SnS2 NSs attribute to it as an efficient photocatalyst for photocatalytic applications. The photocatalytic properties of SnS2 NSs showed good degradation efficiency of 94 and 99.6% for Rh. B and M.V, respectively, in 25 min. The kinetic rate constant of these dyes was estimated by using the Langmuir–Hinshelwood model. Here we also performed the recyclability test of the photocatalyst and discussed the plausible mechanism for the photocatalytic degradation of organic pollutants. The XPS spectra of SnS2 NSs were studied before and after the photodegradation of Rh.B and M.V, indicating the high stability of the photocatalyst. Moreover, in vitro cytotoxicity was also evaluated against human cervical cancer cell lines (HeLa cells) with different concentrations (0–1,000 μg/ml) of as-synthesized SnS2 NSs. This intended work provides a possible treatment for the degradation of organic pollutants under visible light to balance the aquatic ecosystems. Copyright © 2021 Srivastava, Kumar Vishwakarma, Yadav, Rai, Umrao, Giri, Saxena and Srivastava.
Characterizations of nanoscale two-dimensional materials and heterostructures
(Elsevier, 2020) Anchal Srivastava; Chandra Shekhar Pati Tripathi; Vijay Kumar Singh; Rohit Ranjan Srivastava; Sumit Kumar Pandey; Suyash Rai; Ravi Dutt; Amit Kumar Patel
In recent years, two-dimensional (2D) atomically thin crystals ranging from insulator to superconductor such as graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDs), etc. have attracted extensive attention due to their exceptional properties and many potential applications in various areas. In this chapter we focus on the experimental characterization of 2D materials and their heterostructures andcover brief introduction and detailed structural, optical, and chemical characterizations of some important 2D materials. © 2020 Elsevier Inc.
Eu:Y2O3 highly dispersed fluorescent PVA film as turn off luminescent probe for enzyme free detection of H2O2
(Elsevier B.V., 2017) Dhananjay Kumar; Sima Umrao; Himanshu Mishra; Rohit Ranjan Srivastava; Monika Srivastava; Anchal Srivastava; S.K. Srivastava
In this work, a novel sensing scaffold consisting highly dispersed Eu:Y2O3 fluorescent flexible film of poly vinyl alcohol (EYCP) was synthesized by simple mixing method and applied to facilitate non-enzymatic detection of hydrogen peroxide (H2O2) by turn off probe of fluorescence. The fluorescence spectra of EYCP consisting number of emission sharp transitions from excited, 5D0→7Fj (j = 0, 1, 2, 3, 4) energy levels of doped Eu3+ ion in Y2O3 host. In the presence of H2O2, the fluorescence intensity of the EYCP film was quenched due to the reduction of electron–hole pair recombination in Eu centers by electron transfer from Eu–O excited state to H2O2 energy level rather than 5D0 state of Eu3+, which reduces the number of electron in 5D0 state. The EYCP film shows excellent fluorescence quenching in presence of H2O2 by significantly increasing concentration of H2O2 and completely quenched at ∼150 μM. A linear relationship is observed between 0.0 and 60 μM with a correlation coefficient of 0.989. H2O2 sensing is also compared with the EYC nanoparticles. This study is expected to have a significant impact on further study of the Eu:Y2O3 fluorescent flexible film for wide range applications. © 2017 Elsevier B.V.
Facile synthesis of highly fluorescent water-soluble SnS2 QDs for effective detection of Fe3+ and unveiling its fluorescence quenching mechanism
(Elsevier B.V., 2020) Rohit Ranjan Srivastava; Vijay K. Singh; Anchal Srivastava
In recent years, inorganic semiconductor quantum dots (QDs) have garnered significant attention of scientific diaspora owing to their unique photophysical properties. In this series, SnS2-QDs are predicted as one of the promising inorganic quantum dots. However, investigation on the photoluminescence property of SnS2 QDs and its biosensing applications is limited. Therefore, it needs serious exploration. In this work, we report the synthesis of in-situ functionalized fluorescent tin disulfide quantum dots (f-SnS2 QDs) using one-step bottom-up hydrothermal technique. The obtained f-SnS2 QDs are monodispersed in nature and exhibits strong blue fluorescence under UV exposure with a high quantum yield (QY ~8.7%) in aqueous medium. Interestingly, it is observed that fluorescence of f-SnS2 QDs significantly quenched in the presence of Fe3+ ions. The developed optical sensor shows linear response for Fe3+ ions in the concentration range of 0 μM–68 μM (~0.84 μM detection limit). Further, to understand the quenching kinetics, the PL and TRPL studies are conducted which reveal that the quenching phenomenon is both static as well as dynamic in nature. The underneath detailed mechanism is also discussed in the paper. © 2020 Elsevier B.V.
Mechanistic insights on Bi-potentiodynamic control towards atomistic synthesis of electrocatalysts for hydrogen evolution reaction
(Nature Research, 2023) Rohit Ranjan Srivastava; Divyansh Gautam; Rajib Sahu; P.K. Shukla; Bratindranath Mukherjee; Anchal Srivastava
Herein, electrochemically assisted dissolution-deposition (EADD) is utilized over a three-electrode assembly to prepare an electrocatalyst for hydrogen evolution reaction (HER). Cyclic voltammetry is performed to yield atomistic loading of platinum (Pt) over SnS2 nanostructures via Pt dissolution from the counter electrode (CE). Astonishingly, the working electrode (WE) swept at 50 mV/s is found to compel Pt CE to experience 1000–3000 mV/s. The effect of different potential scan rates at the WE have provided insight into the change in Pt dissolution and its deposition behaviour over SnS2 in three electrode assembly. However, uncontrolled overpotentials at CE in a three-electrode assembly made Pt dissolution-deposition behavior complex. Here, for the first time, we have demonstrated bi-potentiodynamic control for dissolution deposition of Pt in four-electrode assembly over Nickel (Ni) foam. The dual cyclic voltammetry is applied to achieve better control and efficiency of the EADD process, engendering it as a pragmatically versatile and scalable synthesis technique. © 2023, Springer Nature Limited.
Nanoparticles decorated carbon nanotubes as novel matrix: A comparative study of influences of immobilization on the catalytic properties of Lens culinaris β-galactosidase (Lcβ-gal)
(Elsevier B.V., 2020) Anjali Yadav; Dinesh Chand Agrawal; Rohit Ranjan Srivastava; Anchal Srivastava; Arvind M. Kayastha
In the present study, Multiwalled carbon nanotubes (MWCNT) decorated with two different nanoparticles namely tungsten disulfide (WS2) and tin oxide (SnO2), nanocomposites (NCs) were synthesized via hydrothermal method. Spectroscopic studies showed that both synthesized NCs possess nearly same functional groups but MWCNT-SnO2 NCs are rich in O-functional group. Microscopic studies revealed that both NCs have different morphological microstructure. Lens culinaris β-galactosidase (Lcβ-gal) was immobilized using glutaraldehyde cross-linker resulted in immobilization efficiency of 91.5% and 88% with MWCNT-WS2 and MWCNT-SnO2 NCs, respectively. Remarkable increase in rate of hydrolysis of whey lactose has been observed with both NCs i.e. Lcβ-gal immobilized MWCNT-WS2 hydrolyzes the 97% whey lactose in 1.5 h while MWCNT-SnO2 showed maximum 92% of whey hydrolysis in 2 h at optimum conditions. Both nanobiocatalyst could serve as a promising candidates for dairy industries and would offer a potential platform for enzyme based biosensor fabrication. © 2019 Elsevier B.V.
Observation of rapid decay and optical properties of micro-pyramidically grown molybdenum diselenide MoSe2 crystal
(Elsevier B.V., 2024) Ravi Dutt; Rohit Ranjan Srivastava; Himanshu Mishra; Anchal Srivastava
In two-dimensional transition metal dichalcogenides (2D-TMDs), the existence of excitons and trions promises their fascinating optical properties for applications in nanophotonic. The more exotic the nanostructure geometry, the less explored its optical responses. The chemical vapor deposition (CVD) technique enables the synthesis of nanostructures with different geometries ranging from monolayers to pyramids driven by a screw-dislocation mechanism. Here we report the CVD synthesis of micro-pyramids with a curious optical response exotic geometry like pyramid. The photoluminescence of as-grown micro-pyramids is significantly diminished compared to their flat-layered structures. In contrast, nanostructured micro-pyramids exhibit a large number of higher-order phononic resonances when excited resonantly by the Raman signal, allowing a more detailed exploration of exciton dynamics. The spectral peak position, intensity, and ratio of the spectral peak reveal local variations in the atomic arrangement of the center and sides of the micro-pyramid. We have investigated the optical response of MoSe2 micro-pyramids and correlated them with their growth-induced nano geometry. In this study, we have taken into account the first step towards producing tunable nanophotonic devices with applications ranging from optoelectronics to nonlinear optics. © 2024
pH dependent luminescence switching of tin disulfide quantum dots
(Elsevier B.V., 2019) Rohit Ranjan Srivastava; Himanshu Mishra; Vijay K. Singh; K. Vikram; Rajesh Kumar Srivastava; S.K. Srivastava; Anchal Srivastava
Designing a molecule with pH, temperature and ion concentration sensitive luminescence properties is always fascinating. Tin disulfide (SnS2), a member of layered metal dichalcogenides (LMDs)family, is explored much for their commendable applications, however, its fluorescence property is still less explored. Present study reports a facile and eco-friendly bottom up synthesis route for tin disulfide quantum dots (SnS2-QDs). Transmission electron microscopic (TEM), and Atomic force microscopic (AFM)analysis revealed an average particle size of ∼3.6 nm. Our reported synthesis method provide the in-situ functionalization of quantum dots (QDs)making it highly sensitive to its environment. SnS2-QDs are found to be pH sensitive and hence a detailed pH dependent luminescence study has been performed. Interestingly it was found that SnS2-QDs possess ∼16 fold enhanced luminescence intensity in acidic condition (pH ∼ 1, QY = 5.32%)rather its basic condition (pH ∼ 12, QY = 1.17%). To explain this pH dependent behavior of SnS2-QDs, a mechanism has been proposed where this luminescence switching is mainly supposed due to protonation and deprotonation between –NH2 and –COOH groups. We believe present study may provide an insight for the development of pH sensor using SnS2-QDs for practical applications. © 2019 Elsevier B.V.
SERS based rapid and ultrasensitive detection of Japanese Encephalitis Virus
(Elsevier B.V., 2022) Manish Nath Tripathi; Kirti Singh; Umakant Yadav; Rohit Ranjan Srivastava; Mayank Gangwar; Gopal Nath; Preeti S. Saxena; Anchal Srivastava
Japanese encephalitis (JE) is a mosquito-borne flavivirus infection named Japanese Encephalitis Virus (JEV), prevalent in Asia-pacific countries, requires an accurate and rapid diagnosis to contain the outbreak of the disease. In cases of low viral load in early-stage infections, this task becomes difficult. Therefore, we have developed a surface-enhanced Raman spectroscopy (SERS) based biosensor for rapid, sensitive, and early-stage detection of JE antigen. In this work, silver nanoparticles were deposited over a glass coverslip and used as a substrate for designing the sensing platform. Silver Nanoparticles have good metallic properties and plasmon activity. Therefore, it amplifies the Raman signals and provides a suitable surface for the SERS substrate. The developed platform has been used for the detection of the Japanese encephalitis virus (JEV). The fabricated sensor shows a linear response from 5 ng/mL to 80 ng/mL with a limit of detection (LoD) of ∼7.6 ng/mL. Therefore, this method could be a significant addition to the diagnostic modalities for early, sensitive, and specific diagnoses of JE antigen even at the nanogram level. © 2022 Elsevier B.V.
Study of morphological evolution and growth mechanism of CVD grown 2D tin disulfide
(Elsevier B.V., 2023) Rohit Ranjan Srivastava; Subhankar Sarkar; Anchal Srivastava
Fractal patterns formed during non-equilibrium growth processes and are abundant in nature. However, the mechanism of their formation remains unknown. Several growth factors such as relaxation rate, cooling rate, diffusion anisotropy and growth time were identified for regulating the fractal growth. Nevertheless, most articles focused on regular shaped (such as triangles and hexagons) 2D layered metal dichalcogenides (LMDs), whereas fractals have received less attention. Therefore, understanding the controlled synthesis of LMDs materials with unique edge structures is highly desired for various potential applications. Here, we report large fractal growth of tin disulfide (SnS2) by atmospheric pressure chemical vapor deposition technique. The edge length of the atomically thin SnS2 fractals range from 5 to 100 µm. Our study shows the morphological evolution from fractal to triangular-like structure during the CVD growth process. To understand this phenomenon, we anticipated that the early phase of the growth mostly occurs via kinetic regulated pathway resulting fractal like structure. As the domains go through numerous relaxation phases throughout the edge diffusion process, the morphology gets more compact or regular, indicating increased thermodynamic control over the growth process. We have also provided a physical model for the growth mechanism of CVD grown SnS2. © 2023