Browsing by Author "Shobhit Pandey"

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A possible mechanism for the emergence of an additional band gap due to a Ti-O-C bond in the TiO2-graphene hybrid system for enhanced photodegradation of methylene blue under visible light
(Royal Society of Chemistry, 2014) Sima Umrao; Shiju Abraham; Frank Theil; Shobhit Pandey; Valerian Ciobota; P.K. Shukla; Caroline J. Rupp; Sudip Chakraborty; Rajeev Ahuja; Jürgen Popp; Benjamin Dietzek; Anchal Srivastava
Here we report the experimental and theoretical study of two TiO2-graphene oxide (TG) and TiO2-reduced graphene oxide (TR) composites synthesized by a facile and ecological route, for enhanced visible light (∼470 nm) photocatalytic degradation of Methylene Blue (MB) (99% efficiency), with high rate constant values (1800% over bare TiO2). TG couples TiO2 nanopowder with Graphene Oxide (GO) while TR couples it with reduced graphene oxide (RGO). The present study, unlike previous reports, discusses never-before-reported double absorption edges obtained for both TG (3.51 eV and 2.51 eV) and TR (3.42 eV and 2.39 eV) composites, which represents the reason behind feasible visible light (2.56 eV) induced photocatalysis. TiO2 domains in the composites dominate the higher band edge, while GO/RGO domains explain the lower band edge. Formation of Ti-O-C bonds in both TG and TR drives the shifting upwards of the valence band edge and reduction in band gap. Further, these bonds provide a conductive pathway for charge carriers from TiO2 nanopowder to the degraded species via the GO/RGO matrix, resulting in decreased charge carrier recombination in TiO2 and enhanced efficiency. To attest that the developed theory is correct, density function theory (DFT) calculations were performed. DFT obtained energetics and electronic structures support experimental findings by demonstrating the role of the Ti-O-C bond, which results in double band edge phenomenon in composites. Finally, the mechanism behind MB degradation is discussed comprehensively and the effect of the weight percent of GO/RGO in the composite on the rate constant and photodegradation efficiency has been studied experimentally and explained by developing analytical equations. © The Royal Society of Chemistry 2014.
Different shades of cholesterol: Gold nanoparticles supported on MoS2 nanoribbons for enhanced colorimetric sensing of free cholesterol
(Elsevier Ltd, 2015) Narsingh R. Nirala; Shobhit Pandey; Anushka Bansal; Vijay K. Singh; Bratindranath Mukherjee; Preeti S. Saxena; Anchal Srivastava
In the present study, we manifest that traditionally used gold nanoparticles when supported on molybdenum disulfide nanoribbons matrix (MoS2 NRs-Au NPs) show synergistically enhanced intrinsic peroxidase like catalytic activity and can catalyze the oxidation of 3,3',5,5' tetramethyl benzidine by H2O2 to produce a highly sensitive blue shade product depending on level of free cholesterol, when tested on complex system of human serum. Further the system attests appreciable kinetics, owing to Km value as low as 0.015mM and better loading capacity (Vmax=6.7×10-6Ms-1). Additionally, the proposed system is stable for weeks with ability to perform appreciably in wide pH (3-6) and temperature range (25-60°C). Utilizing this potential, the present work proposes a cholesterol detection color wheel which is used along with cost effective cholesterol detection strips fabricated out of proposed MoS2 NRs-Au NPs system for quick and reliable detection of free cholesterol using unaided eye. © 2015 Elsevier B.V.
Enhanced electrochemical biosensing efficiency of silica particles supported on partially reduced graphene oxide for sensitive detection of cholesterol
(Elsevier B.V., 2015) Shiju Abraham; Saurabh Srivastava; Vinod Kumar; Shobhit Pandey; Pankaj Kumar Rastogi; Narsingh R. Nirala; Sunayana Kashyap; Sunil K. Srivastava; Vidya Nand Singh; Vellaichamy Ganesan; Preeti S. Saxena; Anchal Srivastava
The present work introduces partially reduced graphene oxide (pRGO)-silica (SiO2) particles hybrid system (pRGOSHs) for sensitive and cost effective free cholesterol detection. Fabricated out of thin layers of pRGOSHs, these proposed ChOx/pRGOSHs/ITO based biosensors have a detection range of 2.6-15.5 mM with an appreciable detection limit of 1.3 mM and sensitivity of 11.1 μA/mM/cm2. Low Michaelis-Menten constant (Km) (4.9 × 10- 4 mM) and high diffusivity constant (D) (3.2 × 10- 10 cm2/s) values clearly indicate enhanced immobilization of enzyme over the substrate. Additionally, electrochemical impedance studies indicate that the synergistic combination of SiO2 and pRGO also results in much lower impedance values (40% and 18% decrease in comparison to SiO2 and pRGO respectively) for an overall enhanced sensing performance. These results are further corroborated by the density functional theory based theoretical simulations indicating enhanced electron density (theoretically) in case of the proposed hybrid system. Finally, the present work also highlights the importance of Si-OH bonds formation in the proposed pRGOSHs composite system for attaining such enhanced biosensing ability. © 2015 Elsevier B.V.
Functional graphene-gold nanoparticle hybrid system for enhanced electrochemical biosensing of free cholesterol
(Royal Society of Chemistry, 2015) Shiju Abraham; Narsingh R. Nirala; Shobhit Pandey; Monika Srivastava; Sunil Srivastava; Bernd Walkenfort; Anchal Srivastava
Realizing the unavailability of fast and reliable diagnostic techniques, especially for cholesterol measurement, the present work reports the development of cost effective bioelectrodes based on a reduced graphene oxide-functionalized gold nanoparticle (∼25 nm) hybrid system (RGO-Fn Au NPs). The electrodes fabricated by the electrophoretic deposition technique attest a synergistically enhanced electrochemical sensing ability of 193.4 μA mM-1 cm-2 for free cholesterol detection, which is much higher than that of the traditional RGO system. The electrochemical impedance studies (EIS) show low charge transfer resistance, RCT, for the hybrid system which is 57% and 60% lower than those of RGO and Au NPs respectively. Also higher loading capacity and enhanced kinetics have been realized for the hybrid system, owing to lower Km value (0.005 mM) and enhanced rate constant (3.8 × 10-4 cm s-1) in comparison with RGO and Au NPs. Moreover, the RGO-Fn Au NP platform promises a wider range of cholesterol detection (0.65-12.93 mM), while simultaneously being capable of detecting as low as 0.34 mM of free cholesterol. Apart from better sensitivity, loading capacity, kinetics and detection range, the system also has appreciable selectivity and stability. This supports its potential to be brought on field in the near future for cost effective and reliable detection from the complex system of human serum. This journal is © The Royal Society of Chemistry 2015.