Browsing by Author "Ashwani Kumar Singh"

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An effective approach to study the biocompatibility of Fe3O4 nanoparticles, graphene and their nanohybrid composite
(Springer Nature, 2018) Ashwani Kumar Singh; Pallavi Singh; Rajiv Kumar Verma; Suresh Yadav; Kedar Singh; Amit Srivastava
The present manuscript describes a simple, facile and effective solvothermal route to synthesize Fe3O4 nanoparticles (Fe3O4 NPs), reduced graphene oxide nanosheets (rGO NSs) and Fe3O4/reduced graphene oxide nanohybrid composite (Fe3O4/rGO nanohybrid composite) and subsequently examines their comparative biocompatibilities. The as-obtained Fe3O4 NPs, rGO NSs and Fe3O4/rGO nanohybrid composite have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The XRD studies and scanning electron microscope confirmed the proper phase formation and the surface morphology of the as-synthesized products, respectively. The Raman spectra of Fe3O4 NPs show the strongest peak at 673 cm−1 which can be assigned to A1g peak of bare Fe3O4 NPs and it complements the XRD studies. Furthermore, the increment in the ID/IG ratio in the Fe3O4/rGO nanohybrid composite suggests the creation of defects in graphene sheets due to strain caused by Fe3O4 NPs. The biocompatibility of these samples has been tested using Lung cancer cell line H1299 through MTT assay. The MTT assay reveals that the nanohybrid composite endows more biocompatible and effectiveness than rGO NSs and Fe3O4 NPs individually, as anti-proliferative agent for cancer treatment. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Biosynthesis of gold and silver nanoparticles by natural precursor clove and their functionalization with amine group
(2010) Ashwani Kumar Singh; Mahe Talat; D.P. Singh; O.N. Srivastava
We report a simple and cost effective way for synthesis of metallic nanoparticles (Au and Ag) using natural precursor clove. Au and Ag nanoparticles have been synthesized by reducing the aqueous solution of AuCl4 and AgNO3 with clove extract. One interesting aspect here is that reduction time is quite small (few minutes instead of hours as compared to other natural precursors). We synthesized gold and silver nanoparticles of different shape and size by varying the ratio of AuCl4 and AgNO3 with respect to clove extract, where the dominant component is eugenol. The evolution of Au and Ag nanoparticles from the reduction of different ratios of AuCl4 and AgNO3 with optimised concentration of the clove extract has been evaluated through monitoring of surface plasmon behaviour as a function of time. The reduction of AuCl4 and AgNO3 by eugenol is because of the inductive effect of methoxy and allyl groups which are present at ortho and para positions of proton releasing -OH group as two electrons are released from one molecule of eugenol. This is followed by the formation of resonating structure of the anionic form of eugenol. The presence of methoxy and allyl groups has been confirmed by FTIR. To the best of our knowledge, use of clove as reducing agent, the consequent very short time (minutes instead of hours and without any scavenger) and the elucidation of mechanism of reduction based on FTIR analysis has not been attempted earlier.
Enhanced antilipopolysaccharide (LPS) induced changes in macrophage functions by Rubia cordifolia (RC) embedded with Au nanoparticles
(2013) Ashwani Kumar Singh; Yamini B. Tripathi; Nidhi Pandey; D.P. Singh; Deepshikha Tripathi; O.N. Srivastava
In this paper, we have shown that gold nanoparticles (Au (NPs)) embedded in Rubia cordifolia (RC) matrix (RC-Au (NPs)) exhibit a high therapeutic value relating to its anti-inflammatory characteristics. It was prepared by utilizing the reducing properties of RC to convert HAuCl4 into Au (NPs). In order to compare its effectiveness, with respect to Au (NPs), the latter was synthesized separately by reducing HAuCl4 with lemon extract. These Au (NPs) along with RC-Au (NPs) were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), and UV-visible spectroscopy. The enhancement in anti-inflammatory characteristics was assessed as its inhibitory potential for lipopolysaccharide (LPS)-induced nitric oxide (NO) release, by rat peritoneal macrophages. The RC-Au (NPs) significantly enhanced its potential to inhibit NO release, which was reported in terms of inhibitory concentration for 50% inhibition (IC50=11.98 ng/ml), as compared to either RC extract (IC50=47 × 103 ng/ml) or to Au (NPs) (IC 50=587.50 ng/ml). © 2013 Elsevier Inc.
Enhanced Magnetotransport Properties of Ag-doped La0.7Ca0.3-xAg xMnO3 Polycrystalline Ceramics
(Springer, 2023) Pankaj Srivastava; Ashwani Kumar Singh; Udai Prakash Tyagi; Jai Singh; Amit Srivastava
The present report focuses on the successful synthesis of La0.7Ca0.3−xAg xMnO3 (x = 0, 0.10, 0.15, 0.20, and 0.30) polycrystalline manganite samples through a soft chemical polymeric precursor route and subsequent impact of Ag doping and grain size on their magnetotransport features. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses reveal that Ag doping leads to a phase transformation from the orthorhombic phase to the rhombohedral phase (for x ≥ 15%). Furthermore, it shows that the insulator–metal transition temperature (TIM) and paramagnetic–ferromagnetic (PM-FM) transition temperature (T C) increase with Ag doping concentration and also with the sintering temperature. The prime factors leading to the enhancement with Ag doping are the well-known oxygenation effect by metallic Ag, which helps to improve the transport properties of La1−xCa xMnO3 (LCMO) manganite, and the increase in the tolerance factor (τ), which in turn leads to the Mn-O-Mn bond angle and the structural disorder near the grain boundaries that weaken the double exchange. The room temperature magnetoresistance values are found to be higher for Ag-doped LCMO samples than for the pristine LCMO. The enhanced ferromagnetic ordering temperature along with low-field magnetoresistance (LFMR) of the as-synthesized Ag-doped LCMO polycrystalline ceramic indicate its potential for device fabrication. © 2023, The Minerals, Metals & Materials Society.
Excellent supercapacitive performance of graphene quantum dots derived from a bio-waste marigold flower (Tagetes erecta)
(Elsevier Ltd, 2021) Gopal Krishna Gupta; Pinky Sagar; Monika Srivastava; Ashwani Kumar Singh; Jai Singh; S.K. Srivastava; Amit Srivastava
Marigold flower (MG; Tagetes erecta) derived Graphene quantum dots (GQDs) have been successfully reported for the fabrication of supercapacitor electrodes in charge storage devices. The GQDs have been synthesized through a hydrothermal route using biomass viz. Waste material (MG) without adding any hazardous chemicals. The successful formation of GQDs as elaborated has been confirmed by various analytical characterization techniques. The as-synthesized GQDs have been electrodeposited on the Ni foil (working electrode) with the help of PVDF (binder) and subsequently, cyclic voltammetry (CV) has been conducted to access specific capacitance, energy density, and other parameters. Moreover, the galvanometric charge/discharge (GCD) technique has been employed due to its accuracy and reliability. Maximum areal specific capacitance has been found as 1.6008 F/cm2 with the current density of 2.0 A/g even after loading a little amount of material on the electrode. The high magnitude of columbic efficiency (160.08), energy density (17.78 Wh/kg), and specific capacitance of 200 F/g at current density 2.0 A/g within a voltage range of −0.55 V to +0.25 V in 2 M KOH electrolyte solution indicate a good electrocapacitive performance of the as-synthesized material. Moreover, the as-synthesized GQDs have shown excellent capacitive retention after 1000th cycles which clearly embarks its sustainable electrocapacitive nature and henceforth offers outstanding potential for the applications in energy storage devices like supercapacitors. © 2021
Hydrothermally synthesized nickel ferrite nanoparticles integrated reduced graphene oxide nanosheets as an electrode material for supercapacitors
(Springer, 2024) Gopal Krishna Gupta; Pinky Sagar; Monika Srivastava; Ashwani Kumar Singh; Jai Singh; S.K. Srivastava; Amit Srivastava
In the present study, we have employed an integrative strategy to synthesize a three-dimensional hierarchical electrode material consisting of NiFe2O4/r-GO nanostructures using a simple hydrothermal process and subsequently explored its electrocapacitive performance. The structural and morphological characteristics of the as-synthesized NiFe2O4/r-GO nanostructure have been accessed through X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), and X-ray photospectrometer (XPS). The electrocapacitive performances of the as-synthesized sample have been evaluated by galvanostatic charge–discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) using a three-electrode system with 3-M KOH electrolyte solution. As-prepared hierarchical electrode material exhibits specific capacity ∼ 362.46 F g−1 at a current density of 0.65 A g−1, suggesting good rate capability. Furthermore, NiFe2O4/r-GO-nanostructured electrode material displays a significant high energy ∼ 36.37 Wh/kg and power density as ∼ 276.22 W/kg. Moreover, the as-synthesized nanocomposite harvests a superior cycling stability over 5000 cycles without obvious capacitance attenuation. The NiFe2O4/r-GO provides rapid pathways for electron transfer and diminishes the ion diffusion routes due to NiFe2O4 over r-GO sheets, which ultimately results in exceptional electrochemical properties. Henceforth, NiFe2O4/r-GO nanocomposite which renders a new reasonable design to manifest more energy density and deliver maximum power may be enrooted as a promising/prospective electrode material due to its unique morphological properties, superior conductivity, and favorable cyclic stability in the field of energy storage applications. © 2024, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Lactose nano-probe optimized using response surface methodology
(2009) Alka Dwevedi; Ashwani Kumar Singh; Dinesh Pratap Singh; Onkar Nath Srivastava; Arvind M. Kayastha
A lactose nano-probe has been developed by immobilization of PsBGAL onto gold nanoparticles (AuNps). It is helpful for severe lactose intolerants for quality check of lactose hydrolyzed milk and estimation of hidden lactose present in variety of food products. Optimization of PsBGAL immobilization onto AuNps using spacer arm (cysteamine-glutaraldehyde) was carried out by response surface methodology (Box-Behnken design). The process has led to immobilization of enzyme onto AuNps with an efficiency of 140.81%. AuNp-PsBGAL was characterized using transmission electron microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. Immobilized enzyme showed broad temperature and pH optima and a significant enhancement in catalytic efficiency (Vmax/Km) with respect to soluble PsBGAL. AuNp-PsBGAL was stable under dried conditions than wet conditions for 6 months with loss of 10.2% and 87.53%, respectively. It has reusability of over five batchwise uses, with almost no loss in activity. Hill's coefficient was found to be 1.71 corresponding to lactose concentration ranging from 0.1% to 2.0%. © 2009 Elsevier B.V. All rights reserved.
Magnetic and Dielectric Properties of La and Ni Co-substituted BiFeO3 Nanoceramics
(Frontiers Media SA, 2020) Amit Srivastava; Ashwani Kumar Singh; O.N. Srivastava; H.S. Tewari; Khalid B. Masood; Jai Singh
The increasing plead for the realization of ultra-fast, miniaturized, compact, and ultra-low power consumption in electronic as well as spintronic devices has propelled the quest for novel multiferroic materials that efficiently enable voltage control of magnetism. The present work reports the phase stability, magnetic and dielectric responses of polycrystalline Bi1−xLaxFe1−yNiyO3 (0 ≤ x ≥ 0.2 and 0 ≤ y ≥ 0.2) multiferroic ceramics synthesized through a simplistic sol–gel approach. The maneuver substitutions of La at A− site of BiFeO3 multiferroic eliminate the secondary phases formed owing to impurities. Rietveld refined XRD analysis reveals the structural transformation of the orthorhombic (Pbnm) phase as La substitution increases. However, an additional lattice distortion is induced as a result of the substitutions of Ni atoms at B− site. A substantial enhancement in magnetic and dielectric responses has been found in the co-doped (Ni and La) sample at both A and B− sites as a result of the size confinement of nano-crystallites, the exchange interaction between Fe3+ and Ni2+ ions, and corresponding variation in Fe–O–Fe bond angles. The dielectric constant has increased substantially in the low-frequency region with simultaneous substitutions of La and Ni at the sites of Bi and Fe, respectively. A careful observation of temperature-dependent magnetization curves (FC and ZFC) indicates a spin glass response with entangled ferromagnetic components. The experimental findings infer that the co-substitutions of La and Ni at their respective sites in Bi1−xLaxFe1−yNiyO3 (0 ≤ x ≥ 0.2 and 0 ≤ y ≥ 0.2) may significantly improve the ferromagnetic and dielectric responses of the studied nanoceramics. © Copyright © 2020 Srivastava, Singh, Srivastava, Tewari, Masood and Singh.
One-Step Green Synthesis of Gold Nanoparticles Using Black Cardamom and Effect of pH on Its Synthesis
(Springer New York LLC, 2015) Ashwani Kumar Singh; O.N. Srivastava
In the present article, an effective, one-step, and environmentally benign protocol for the synthesis of gold nanoparticles has been discussed. The black cardamom extract is used as a reducing agent for HAuCl4.3H2O. In order to synthesize gold nanoparticles, an aqueous solution of HAuCl4.3H2O was mixed with an optimized concentration of black cardamom extract where 1,8-cineole is the dominant component. Choosing black cardamom extract as a reducing agent can be justified under the light of the fact that it has a very fast reducing ability. Gold nanoparticles with different shapes and sizes were synthesized by varying the ratio of AuCl4 ions to black cardamom extract. Kinetics of reactions has been evaluated through monitoring of surface plasmon behavior of gold nanoparticles as a function of time. Based on Fourier transform infrared spectroscopy (FTIR) studies, a tentative mechanism of reduction of Au nanoparticles has also been proposed which includes oxidation of 1,8-cineole to 2-oxo-1,8-cineole. Further, a comprehensive study to investigate the effect of pH on the synthesis of Au nanoparticles has been carried out. © 2015, Singh and Srivastava.
Optimization of process variables by central composite design for the immobilization of urease enzyme on functionalized gold nanoparticles for various applications
(2011) Mahe Talat; Ashwani Kumar Singh; O.N. Srivastava
In the present study, enzyme urease has been immobilized on amine-functionalized gold nanoparticles (AuNPs). AuNPs were synthesized using natural precursor, i.e., clove extract and amine functionalized through 0.004 M l-cysteine. Enzyme (urease) was extracted and purified from the vegetable waste, i.e., seeds of pumpkin to apparent homogeneity (sp. activity 353 U/mg protein). FTIR spectroscopy and transmission electron microscopy was used to characterize the immobilized enzyme. The immobilized enzyme exhibited enhanced activity as compared with the enzyme in the solution, especially, at lower enzyme concentration. Based on the evaluation of activity assay of the immobilized enzyme, it was found that the immobilized enzyme was quite stable for about a month and could successfully be used even after eight cycles having enzyme activity of about 47%. In addition to this central composite design (CCD) with the help of MINITAB ® version 15 Software was utilized to optimize the process variables viz., pH and temperature affecting the enzyme activity upon immobilization on AuNPs. The results predicted by the design were found in good agreement (R 2 = 96.38%) with the experimental results indicating the applicability of proposed model. The multiple regression analysis and ANOVA showed the individual and cumulative effect of pH and temperature on enzyme activity indicating that the activity increased with the increase of pH up to 7.5 and temperature 75 °C. The effects of each variables represented by main effect plot, 3D surface plot, isoresponse contour plot and optimized plot were helpful in predicting results by performing a limited set of experiments. © 2011 Springer-Verlag.
Response surface analysis of nano-ureases from canavalia ensiformis and cajanus cajan
(Elsevier B.V., 2011) Alka Dwevedi; Satya Brata Routh; Amit Singh Yadav; Ashwani Kumar Singh; Onkar Nath Srivastava; Arvind M. Kayastha
Ureases isolated from leguminous sources, Canavalia ensiformis and Cajanus cajan were immobilized onto gold nanoparticles (nano-ureases). Optimization of the urease immobilization was carried using response surface methodology based on Central Composite Design. Immobilization efficiency of nano-urease from C. ensiformis and C. cajan were found to be 215.10% and 255.92%, respectively. The methodology adopted has deviation of 2.56% and 3.01% with respect to experimental values in case of C. ensiformis and C. cajan, respectively. Nano-urease from C. cajan has broad physico-chemical parameters with pH optimum from 7.1 to 7.3 and temperature optimum from 50 to 70 °C. Nano-urease from C. ensiformis has sharp pH and temperature optima at 7.3 and 70 °C, respectively. Fourier transform infra-red spectroscopy has revealed involvement of groups viz. amino, glycosyl moiety, etc. in urease immobilization onto gold nano-particles. Transmission and scanning electron micrographs revealed that arrangement of urease onto gold nano-particles from C. ensiformis was uniform while it was localized in case of C. cajan. Nano-urease from C. ensiformis has higher specificity and catalysis toward urea as compared to nano-urease from C. cajan. Nano-ureases from both sources are equally stable for 6 months under dried conditions and can be used for 10 washes. © 2011 Elsevier B.V.
Shape and Size-Dependent Magnetic Properties of Fe3O4 Nanoparticles Synthesized Using Piperidine
(Springer New York LLC, 2017) Ashwani Kumar Singh; O.N. Srivastava; Kedar Singh
In this article, we proposed a facile one-step synthesis of Fe3O4 nanoparticles of different shapes and sizes by co-precipitation of FeCl2 with piperidine. A careful investigation of TEM micrographs shows that the shape and size of nanoparticles can be tuned by varying the molarity of piperidine. XRD patterns match the standard phase of the spinal structure of Fe3O4 which confirms the formation of Fe3O4 nanoparticles. Transmission electron microscopy reveals that molar concentration of FeCl2 solution plays a significant role in determining the shape and size of Fe3O4 nanoparticles. Changes in the shape and sizes of Fe3O4 nanoparticles which are influenced by the molar concentration of FeCl2 can easily be explained with the help of surface free energy minimization principle. Further, to study the magnetic behavior of synthesized Fe3O4 nanoparticles, magnetization vs. magnetic field (M-H) and magnetization vs. temperature (M-T) measurements were carried out by using Physical Property Measurement System (PPMS). These results show systematic changes in various magnetic parameters like remanent magnetization (Mr), saturation magnetization (Ms), coercivity (Hc), and blocking temperature (TB) with shapes and sizes of Fe3O4. These variations of magnetic properties of different shaped Fe3O4 nanoparticles can be explained with surface effect and finite size effect. © 2017, The Author(s).
Silver Nanoparticles/Gelatin Composite: A New Class of Antibacterial Material
(Wiley-Blackwell, 2017) Ashwani Kumar Singh; Manish Tripathi; Onkar Nath Srivastava; Rajiv Kumar Verma
A simple and fast, one-step, cost effective protocol for silver nanoparticle (AgNP) synthesis has been reported. AgNO3 is reduced using black cardamom (B.C.) extract to produce nanoparticles. Variable size nanoparticles were obtained by choosing the different composition of a reaction mixture comprised of AgNO3 solution and B.C. extract. Nanoparticle formation was monitored by the color change of reaction mixture as well as by UV-Visible spectroscopy. AgNPs has been characterized thoroughly by XRD and TEM analysis for shape and size. A plausible mechanism for reduction of Ag+ has been proposed based on oxidation products of 1,8-cineole, which is one of the major components of B.C. extract. A very important application of these AgNPs has also been shown by preparing AgNP-gelatin composite to check its activity against different strains of bacteria. The results suggest excellent antibacterial activities of the above-mentioned composite films, which can be further developed as antibacterial films for different purposes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim