Divesh N. Srivastava

Enhanced photocatalytic performance of morphologically tuned Bi2S3 NPs in the degradation of organic pollutants under visible light irradiation

Here in, morphologically tuned Bi2S3 NPs were successfully synthesized from a single-source precursor complex [Bi(ACDA)3] [HACDA=2-aminocyclopentene-1-dithiocarboxylic acid] by decomposing in various solvents using a simple solvothermal method. The as-obtained products were characterized by XRD, TEM, UV-vis spectroscopy and BET surface area measurements. Structural analyses revealed that the as-prepared Bi2S3 NPs can be tuned to different morphologies by varying various solvents and surfactants. The interplay of factors that influenced the size and morphology of the nanomaterials has been studied. Moreover, mastery over the morphology of nanoparticles enables control of their properties and enhancement of their usefulness for a given application. These materials emerged as a highly active visible light-driven photocatalyst towards degradation of methylene blue dye and the efficiencies are dependent on size and surface area of the NPs. In addition, photocatalytic degradation of highly toxic dichlorodiphenyltrichloroethane was studied using synthesized Bi2S3 NPs as catalyst and the rate of degradation has been found to be much better compared to that exhibited by commercial WO3. We believe that this new synthesis approach can be extended to the synthesis of other metal sulfide nanostructures and open new opportunities for device applications.

Enhanced photocatalytic activity of Eu-doped Bi2S3 nanoflowers for degradation of organic pollutants under visible light illumination

Europium (Eu)-doped Bi2S3 nanoparticles (NPs) with different Eu contents were successfully synthesized by solvothermal decomposition of the precursor complexes Bi(ACDA)3 and [Eu(ACDA)3·H2O] [ACDA = 2-aminocyclopentene-1-dithiocarboxylic acid] in ethylenediamine (EN). The precursors were characterized by usual techniques such as UV-vis and FT-IR spectroscopy, and CHN and TGA analyses. The prepared nanomaterials were characterized by XRD, EDX, SEM and TEM analyses. The XRD results demonstrate that the particles were highly crystallized. The TEM images ascertain the NPs to be of flower-like structure consisting of ultrathin nanoplates with an average diameter of 9–10 nm. Photocatalytic efficiency of the Eu-doped Bi2S3 NPs was evaluated by monitoring the degradation of methylene blue (MB) in aqueous solution under visible light. It was observed that the rate of photocatalytic degradation of MB increases with an increase in the amount of the dopant ion. In addition, the photocatalytic degradation of various toxic organic pollutants such as phenol, p-cresol, 4-chlorophenol, 4-tert-butylphenol, 2,5-dimethylphenol and 2,6-di-tert-butyl-p-cresol was carried out with doped NPs in visible light. Under identical conditions, the degradation rate of 4-chlorophenol is higher than the corresponding phenol, p-cresol and 4-tert-butylphenol. Finally, the mechanism of the degradation pathway for phenol and the substituted phenols is discussed.

Colorimetric detection of Cu2+ and Pb2+ ions using calix[4]arene functionalized gold nanoparticles

Abstract.Calixarene functionalized gold nanoparticles (CFAuNPs) have been prepared and characterized by spectroscopic and microscopic (TEM) techniques. To use this material as potential colorimetric sensor, the binding property of this new material has been investigated with a large number of metal ions. It exhibited sharp colour change from dark brown to green and blue, detectable by naked-eye, in the presence of Cu2+ and Pb2+ ions, respectively. It has also triggered substantial change in surface plasmon resonance (SPR) band of the functionalized gold nanoparticles, which in case of Pb(II) is due to the inter particle plasmon coupling arising from the metal-induced aggregation of the nanoparticles and for Cu(II), it is because of the formation of AuCu alloy due to anti-galvanic exchange. The size and aggregation of the nanoparticles are confirmed from HRTEM images, elemental analysis and the line profiling for both the metal ions have been done by STEM-EDX analysis. Graphical AbstractCalixarene functionalized gold nanoparticles have been prepared, which detect Cu2+ and Pb2+ ions with visible colour change. For Pb(II), the colour change is due to metal-induced aggregation of the nanoparticles and for Cu(II), it is due to formation of Au–Cu alloy.

Ultrasensitive electrochemical immunoassay for surface array protein, a Bacillus anthracis biomarker using Au–Pd nanocrystals loaded on boron-nitride nanosheets as catalytic labels

Bacillus anthracis, the causative agent of anthrax, is a well known bioterrorism agent. The determination of surface array protein (Sap), a unique biomarker for B. anthracis can offer an opportunity for specific detection of B. anthracis in culture broth. In this study, we designed a new catalytic bionanolabel and fabricated a novel electrochemical immunosensor for ultrasensitive detection of B. anthracis Sap antigen. Bimetallic gold-palladium nanoparticles were in-situ grown on poly (diallyldimethylammonium chloride) functionalized boron nitride nanosheets (Au-Pd NPs@BNNSs) and conjugated with the mouse anti-B. anthracis Sap antibodies (Ab2); named Au-Pd NPs@BNNSs/Ab2. The resulting Au-Pd NPs@BNNSs/Ab2 bionanolabel demonstrated high catalytic activity towards reduction of 4-nitrophenol. The sensitivity of the electrochemical immunosensor along with redox cycling of 4-aminophenol to 4-quinoneimine was improved to a great extent. Under optimal conditions, the proposed immunosensor exhibited a wide working range from 5 pg/mL to 100 ng/mL with a minimum detection limit of 1 pg/mL B. anthracis Sap antigen. The practical applicability of the immunosensor was demonstrated by specific detection of Sap secreted by the B. anthracis in culture broth just after 1h of growth. These labels open a new direction for the ultrasensitive detection of different biological warfare agents and their markers in different matrices.

Co3O4 microcubes with exceptionally high conductivity using a CoAl layered double hydroxide precursor via soft chemically synthesized cobalt carbonate

Cubic microparticles of Co3O4 spinel were synthesized by calcination of CoCO3 obtained using CoAl layered double hydroxide (LDH) as a unitary precursor through soft-chemical decomposition. The obtained cobalt spinel showed an exceptionally high electrical conductivity at room temperature. This is attributed to high concentrations of charge carriers (Co4+), unique morphology, high reduction temperature and low activation barrier.

Synthesis and self-assembly properties of well-defined four-arm star poly( ε -caprolactone)- b -poly( N -vinylpyrrolidone) amphiphilic block copolymers

Abstract Well-defined amphiphilic four-arm star diblock copolymers of poly(ε-caprolactone) (PCL) and poly(N-vinylpyrrolidone) (PNVP) have successfully been synthesized by combining the ring-opening polymerization (ROP) of ε-caprolactone (CL) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP). The resulting block copolymer shows the formation of spherical micelles in water as revealed by transmission electron microscopy (TEM) and supported by light-scattering study. The critical micellar concentration (cmc) value of the micelle increases with the increase in the PNVP block length. Hydrodynamic diameter distribution of the micelles decreases with the increase in the PNVP block length. The effective hydrodynamic ratio (Rh) remains almost constant over the angles of scattering measurements above the corresponding cmc value. The usefulness of the synthesized star amphiphilic block copolymers was checked by the successful synthesis of silver nanoparticles.Graphical abstract Well-defined four-arm star poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) amphiphilic block copolymers are prepared by the combination of ring opening polymerization and xanthate-mediated reversible addition-fragmentation chain transfer polymerization and their self-assembly properties are studied using 1H NMR, fluorescence spectroscopy, dynamic light scattering, and TEM.

A fluorescent probe for bisulfite ions: its application to two-photon tissue imaging

A benzoxazinone based fluorescent probe for the specific and efficient detection of bisulfite ions in aqueous medium is described. The probe formed a bisulfite/sulphite adduct with an associated turn-on fluorescence response in the red wavelength region. No interference was observed in the detection process from all possible competing anions and molecules, including cyanide ion, cysteine, homocysteine and glutathione. In addition, the probe showed a fast response time, low detection limit, and cell membrane permeability. Furthermore, the probe was two-photon excitable, enabling imaging of endogenous bisulfite ions in HeLa cells as well as in deep tissues from different organs of mouse.

Rapid synthesis of carbon nanoparticles with an optimized combination of specific surface area and crystallinity by a plasma-assisted single-step process

This paper reports controlled synthesis of carbon nanoparticles by an expanded thermal plasma jet assisted technique through a single-step, high-throughput process. The plasma discharge zone in the experimental reactor remained isolated from the particle nucleation/growth chamber through a supersonic nozzle, which allowed using the sample collection chamber pressure as an efficient control parameter to synthesize carbon nanostructures with tailored combination of some important properties. Low chamber pressure conditions produced samples with both good specific surface area and crystallinity, which may be ideal for use as an efficient catalyst support material as well as in batteries and super capacitors. This dominantly mesoporous sample was also found to have good hydrogen absorption properties. Another significant observation was that the average number of carbon nano-sheets stacked together inside the crumpled paper like layers increased with pressure in the sample collection chamber. Optical emission spectroscopic techniques were used to measure the effective cooling rates responsible for the particle nucleation process under different experimental conditions, which also indicated that C2 dimer molecules are the basic precursors behind the formation of these carbon nanostructures.

Solvent assisted and solvent free orientation of growth of nanoscaled lanthanide sulfides: tuning of morphology and manifestation of photocatalytic behavior

A new class of precursor complexes Ln(acda)3(phen), (where Ln = Nd, Sm, Eu, Tb and Yb, acda− is the anion of 2-aminocyclopentene-1-dithiocarboxylic acid and phen stands for 1,10-phenanthroline) have been used to obtain phase pure lanthanide sulfide nanoparticles by solution-based as well as solution-free thermal treatments at inert conditions. During solution-phase thermolysis, long chain alkyl-amine solvents have been used to promote the reaction at much lower temperature (280 °C) than the solid-phase reaction (650 °C). A contrasting growth feature is observed for nano sulfides and consequently the shape of the material is varied from isotropic cube-like morphology to anisotropic short nanofibers according to the variation of surfactants. The study confirmed that the introduction of 1-dodecanethiol as a structure-modifying capping agent along with reacting amine significantly facilitates the anisotropic growth in a preferred direction. These have been characterized by XRD, TEM, FESEM, UV-vis spectroscopy and BET surface area measurements. The optical absorption data indicated a narrow band gap energy ranging from 1.71–1.97 eV for different EuS. The material emerged as a highly active visible light-driven photocatalyst among the lanthanide sulfides towards the degradation of organic dyes. A comparative catalytic study with morphologically different EuS revealed that the degradation rate changes with varying morphology and for all the dyes it strictly follows the decreasing order of sphere-like particles > cube-like particles > nanofibers.

Controllable gold nanoparticle deposition on carbon nanotubes and their application in immunosensing

A CNT–AuNPs hybrid nanocomposite platform was prepared from nanodisperse AuNPs in N-[3-(trimethoxysilyl)propyl]ethylenediamine (EDAS) sol–gel matrices with purified MWCNT. EDAS, an amine group-containing sol–gel solution, was utilized for its ability to stabilize the nanoparticles in solution. The developed model system was based on immobilized rabbit anti-mouse IgG-HRP (horseradish peroxidase) for reagentless detection of mouse IgG. The immunosensing platform was prepared by using Nafion for the immobilization of rabbit anti-mouse IgG-HRP and CNT–AuNPs hybrid nanocomposite on a glassy carbon electrode used for the detection of mouse IgG which provides a biocompatible microenvironment. The resulting CNT–AuNPs nanocomposite brings new capabilities for electrochemical devices by using the synergistic action of its electrocatalytic activity. The CNT–AuNPs were characterized using SEM, TEM, EIS, and AFM, and the analytical performance was monitored by differential pulse voltammetry. The detection limit of mouse IgG is 0.5 ng mL−1 (S/N ratio = 3). In addition, the immunosensor efficiently allowed a specific electrochemical analysis of mouse IgG and easy discrimination of goat IgG, chicken IgG, and rabbit IgG.