Sweta Mohan

Photo-induced biosynthesis of silver nanoparticles using aqueous extract of Erigeron bonariensis and its catalytic activity against Acridine Orange.

The green synthesis of silver nanoparticles (AgNPs) has reduced the pollution load in the environment to a greater extent by avoiding the use of hazardous chemicals. In the present work we have developed an ecofriendly and zero cost approach for the green synthesis of more stable and spherical AgNPs using aqueous extract of Erigeron bonariensis (AEE) which act as both reducing and stabilizing agent. The reaction of AEE and AgNO3 was carried out in direct sunlight for the instant biosynthesis of AgNPs within minutes. The biosynthesis was monitored by UV-vis spectroscopy which exhibited a sharp SPR band at 442 nm and 435 nm after 5 and 35 min of sunlight exposure. The optimum conditions for biosynthesis of AgNPs were found to be 2.5mM AgNO3 concentration, 1.5% (v/v) of AEE inoculum dose and 35 min of sunlight exposure. Presence of spherical AgNPs with average size 13 nm was confirmed by SEM and TEM analysis. The XRD and SAED analysis confirmed the crystalline nature of the AgNPs where the Braggs diffraction pattern at (111), (200), (220) and (311) corresponded to face centered cubic crystal lattice of metallic silver. The average roughness of the synthesized AgNPs was 3.21 nm which was confirmed by AFM analysis. FTIR analysis was recorded between 4000 and 400 cm(-1) which confirmed the involvement of various functional groups in the synthesis of AgNPs. The AgNPs thus obtained showed catalytic activity towards degradation of Acridine Orange (AO) without involvement of any hazardous reducing agent. The concentration dependent catalytic activity of the synthesized AgNPs was also monitored using 1, 2 and 3 mL of silver colloids and was found that the degradation of AO followed pseudo first-order kinetics.

Photo-mediated optimized synthesis of silver nanoparticles for the selective detection of Iron(III), antibacterial and antioxidant activity

The AgNPs synthesized by green method have shown great potential in several applications such as biosensing, biomedical, catalysis, electronic etc. The present study deals with the selective colorimetric detection of Fe3+ using photoinduced green synthesized AgNPs. For the synthesis purpose, an aqueous extract of Croton bonplandianum (AEC) was used as a reducing and stabilizing agent. The biosynthesis was confirmed by UV-visible spectroscopy where an SPR band at λmax 436nm after 40s and 428nm after 30min corresponded to the existence of AgNPs. The optimum conditions for biosynthesis of AgNPs were 30min sunlight exposure time, 5.0% (v/v) AEC inoculum dose and 4mM AgNO3 concentration. The stability of synthesized AgNPs was monitored up to 9months. The size and shape of AgNPs with average size 19.4nm were determined by Field Emission Scanning Electron Microscope (FE-SEM) and High-Resolution Transmission Electron Microscope (HR-TEM). The crystallinity was determined by High-Resolution X-ray Diffractometer (HR-XRD) and Selected Area Electron Diffraction (SAED) pattern. The chemical and elemental compositions were determined by Fourier Transformed Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray Spectroscopy (EDX) respectively. The Atomic Force Microscopy (AFM) images represented the lateral and 3D topological characteristics of AgNPs. The XPS analysis confirmed the presence of two individual peaks which attributed to the Ag 3d3/2 and Ag 3d5/2 binding energies corresponding to the presence of metallic silver. The biosynthesized AgNPs showed potent antibacterial activity against both gram-positive and gram-negative bacterial strains as well as antioxidant activity. On the basis of results and facts, a probable mechanism was also proposed to explore the possible route of AgNPs synthesis, colorimetric detection of Fe3+, antibacterial and antioxidant activity.

Kinetic, isotherm and thermodynamic studies of adsorption behaviour of CNT/CuO nanocomposite for the removal of As(III) and As(V) from water

A CNT/CuO nanocomposite prepared by precipitation method was characterized through FT-IR, XRD, SEM, TGA, BET and Raman spectroscopy and utilized as a nanoadsorbent for the adsorption of As(III)/As(V) from water where maximum uptake capacities of 2267 μg g−1 for As(III) and 2395 μg g−1 for As(V) were achieved. This CNT/CuO nanocomposite is a better alternative to known conventional adsorbents because it has a high surface area (480 m2 g−1) and maximum uptake capacities were achieved at ambient temperature (30 °C) and near neutral pH (pH 7 for As(III) and 5 for As(V)). Kinetic studies indicated that a pseudo-second-order kinetic model described the kinetic data. The mass transfer and intraparticle diffusion studies suggested that both external mass transfer and intraparticle diffusion steps contributed to the rate controlling step. The Boyd model suggested that intraparticle diffusion was the main rate controlling step. Isotherm studies were conducted and it was found that the equilibrium data followed the Langmuir isotherm which indicated that the adsorption was a monolayer and all the binding sites were energetically equivalent. The D–R isotherm revealed that the adsorption was chemisorption. The thermodynamic studies revealed that the adsorption was spontaneous because ΔG0 was negative and the reaction was endothermic due to the positive value of ΔH0. XPS analysis revealed that CNT/CuO not only adsorbed As(III)/As(V) but also oxidized highly toxic As(III) to less toxic As(V) which is an added advantage of CNT/CuO as an adsorbent.

Synthesis and characterization of rGO/ZrO2 nanocomposite for enhanced removal of fluoride from water: kinetics, isotherm, and thermodynamic modeling and its adsorption mechanism

A nanocomposite of rGO/ZrO2 prepared by a simple hydrothermal method using GO and ZrOCl2·8H2O has been successfully utilized for the removal of fluoride from aqueous solutions by adsorption. The synthesized nanocomposite was characterized by various techniques, such as FT-IR, XRD, SEM, EDX, TGA, XPS, Raman spectroscopy and BET surface area measurement. Various process parameters viz. rGO/ZrO2 dose, initial fluoride concentration, temperature and pH, which influence the removal of fluoride, were studied and it was found that the maximum uptake capacity of the nanocomposite was 46 mg g−1 at 30 °C, pH 7, rGO/ZrO2 dose of 0.5 g L−1 and initial fluoride concentration of 25 mg L−1. The rGO/ZrO2 possesses a high surface area (632 cm2 g−1) and maximum adsorption occurs at neutral pH and ambient temperature. Therefore, rGO/ZrO2 can be used for the adsorption of fluoride without much alteration in the quality of drinking water. The experimental data was applied to various kinetics, isotherm and thermodynamic studies. The monolayer adsorption of fluoride followed a pseudo-second order kinetic model, which was found to be spontaneous and endothermic in nature. The results obtained from the current adsorption system might be helpful for designing a continuous column system for the treatment of fluoride contaminated water.

Green synthesis of silver nanoparticle for the selective and sensitive colorimetric detection of mercury (II) ion

An ecofriendly and zero cost approach has been developed for the photoinduced synthesis of more stable AgNPs using an aqueous extract of Murraya koenigii (AEM) as a reducing and stabilizing agent. The exposed reaction mixture of AEM and AgNO3 to sunlight turned dark brown which primarily confirmed the biosynthesis of AgNPs. The biosynthesis was monitored by UV-vis spectroscopy which exhibited a sharp SPR band at 430nm after 30min of sunlight exposure. The optimum conditions for biosynthesis of AgNPs were 30min of sunlight exposure, 2.0% (v/v) of AEM inoculuam dose and 4.0mM AgNO3 concentration. TEM analysis confirmed the presence of spherical AgNPs with average size 8.6nm. The crystalline nature of the AgNPs was confirmed by XRD analysis where the Braggs diffraction pattern at (111), (200), (220) and (311) corresponded to face centered cubic crystal lattice of metallic silver. The surface texture was analyzed by AFM analysis where the average roughness of the synthesized AgNPs was found 1.8nm. FTIR analysis was recorded between 4000 and 400cm-1 which confirmed the involvement of various functional groups in the synthesis of AgNPs. On the basis of the linear relationship between SPR band intensity and different concentration of Hg2+, the synthesized AgNPs can be used for colorimetric detection of Hg2+ with a linear range from 50nm to 500μM. Based on experimental findings, an oxidation-reduction mechanism between AgNPs and Hg2+ was also proposed.

Enhanced electron transfer mediated detection of hydrogen peroxide using a silver nanoparticle–reduced graphene oxide–polyaniline fabricated electrochemical sensor

The current study aims at the development of an electrochemical sensor based on a silver nanoparticle–reduced graphene oxide–polyaniline (AgNPs–rGO–PANI) nanocomposite for the sensitive and selective detection of hydrogen peroxide (H2O2). The nanocomposite was fabricated by simple in situ synthesis of PANI at the surface of rGO sheet which was followed by stirring with AEC biosynthesized AgNPs to form a nanocomposite. The AgNPs, GO, rGO, PANI, rGO–PANI, and AgNPs–rGO–PANI nanocomposite and their interaction were studied by UV-vis, FTIR, XRD, SEM, EDX and XPS analysis. AgNPs–rGO–PANI nanocomposite was loaded (0.5 mg cm−2) on a glassy carbon electrode (GCE) where the active surface area was maintained at 0.2 cm2 for investigation of the electrochemical properties. It was found that AgNPs–rGO–PANI–GCE had high sensitivity towards the reduction of H2O2 than AgNPs–rGO which occurred at −0.4 V vs. SCE due to the presence of PANI (AgNPs have direct electronic interaction with N atom of the PANI backbone) which enhanced the rate of transfer of electron during the electrochemical reduction of H2O2. The calibration plots of H2O2 electrochemical detection was established in the range of 0.01 μM to 1000 μM (R2 = 0.99) with a detection limit of 50 nM, the response time of about 5 s at a signal-to-noise ratio (S/N = 3). The sensitivity was calculated as 14.7 μA mM−1 cm−2 which indicated a significant potential as a non-enzymatic H2O2 sensor.