Swapan K. Dolui

Synthesis and evaluation of antioxidant and antibacterial behavior of CuO nanoparticles

CuO nanoparticles were synthesized by thermal decomposition methods and characterized by UV-visible spectroscopy, XRD and TEM analysis. The resultant particles are nearly spherical and particle size is in the range of 15-30 nm. The antioxidant behavior of synthesized CuO nanoparticles was evaluated by scavenging free radicals of 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH). The free radical scavenging activity of CuO nanoparticles was monitored by UV-visible spectrophotometry. The antibacterial activity of CuO nanoparticles was tested against different bacterial strains. CuO nanoparticles showed efficient antioxidant activity and bactericidal effect against Eschericia coli and Pseudomonas aeruginosa.

Synthesis of ZnO nanoparticles and evaluation of antioxidant and cytotoxic activity.

ZnO nanoparticles were synthesized by thermal decomposition method and were characterized by UV-vis spectroscopy, XRD, SEM, EDX and TEM analysis. The resultant nanoparticles are nearly spherical and size is in the range of 40-50 nm. The antioxidant behavior of ZnO nanoparticles was assessed by scavenging free radicals of 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) with varying nanoparticle concentration and time interval individually. The DPPH scavenging activity was monitored by UV-vis spectrophotometer. ZnO nanoparticles were also showing cytotoxic activity which was studied by hemolytic potentiality test.

Biocompatible carboxymethylcellulose-g-poly(acrylic acid)/OMMT nanocomposite hydrogel for in vitro release of vitamin B12

The present work describes the preparation of a biocompatible nanocomposite hydrogel based on CMC-g-PAA and organo-MMT nanoclay by using methylene bis-acrylamide (MBA) as a cross-linker and potassium persulfate (KPS) as an initiator through radical graft polymerization. The nanocomposite hydrogels were characterized by using techniques such as FTIR, SEM and XRD analysis. The effects of various parameters on the swelling behaviour of the hydrogels were studied. The mechanical strength of the nanocomposite hydrogels was determined by dynamic mechanical analysis (DMA) and all the samples showed an increase in the storage modulus (G′) with an increase in cross-linker amount. The in vitro biocompatibility of the nanocomposite hydrogels showed that the presence of nanoclay in the nanocomposite hydrogel enhanced the in vitro blood compatibility. The vitamin B12 release mechanism has been studied during different time periods using a UV-visible spectrophotometer. The drug release kinetics revealed that release of vitamin B12 follows a non-Fickian diffusion mechanism.

Synthesis of copper oxide/reduced graphene oxide nanocomposite and its enhanced catalytic activity towards reduction of 4-nitrophenol

Graphene oxide (GO) and its derivatives have attracted extensive interest in many fields, including catalytic chemistry, organic synthesis, and electrochemistry. Integrating nanoparticles into GO enhances the properties and functionality of the nanocomposites due to the synergetic effects between GO nanosheets and the nanoparticles. A facile and novel hydrothermal method of preparing copper oxide–reduced graphene oxide (CuO–rGO) nanocomposites has been developed. The nanocomposites were prepared from a mixture of GO and cuprous chloride (CuCl). In this method simultaneous formation of CuO and reduction of GO takes place without using any foreign materials. The synthesized composites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. 4-Nitrophenol (4-NP) was used as a probe to assess the catalytic activities of the prepared CuO–rGO nanocomposites. The nanocomposites exhibited excellent and stable catalytic activity towards reduction of 4-NP to 4-aminophenol (4-AP) in the presence of NaBH4. The catalytic activities of the nanocomposites were also studied by changing the ratio of GO and Cu. The reaction kinetics followed a pseudo-first-order rate law and the maximum value of the rate constant is 13.951 min−1, which is superior to all other reported works. The catalyst can be easily regenerated and reused with good recyclability even for up to five catalytic cycles.

Preparation of core‐shell latex from co‐polymer of styrene‐butyl acrylate‐methyl methacrylate and their paint properties

Purpose – The purpose of this paper is to study the effect of monomer composition in core‐shell latex prepared from co‐polymer of styrene‐butylacrylate (BA)‐methyl methacrylate (MMA) and their paint properties.Design/methodology/approach – The core‐shell latex was prepared by a stepwise semi‐batch emulsion polymerisation. A set of dispersion was made with the different core‐shell compositions. The core phase consists of a copolymer of styrene‐BA‐acrylic acid (AA) and the shell phase consists of a copolymer of MMA‐AA. The properties of latex were determined by solid content, viscosity, pH and particle size. Subsequently, emulsion paint (PVC‐37 per cent and NVM‐53 per cent) was prepared using core‐shell latex. The paint properties were determined by block resistance, gloss, elongation at break, etc. The particle morphology was characterised with transmission electron microscope (TEM).Findings – Core‐shell structure of latex was confirmed by TEM. The performance of core‐shell latex has been optimised and the...

An efficient quasi solid state dye sensitized solar cell based on polyethylene glycol/graphene nanosheet gel electrolytes

A poly(ethylene glycol)/graphene nanosheet quasi solid gel electrolyte was synthesized using an in situ polymerization technique for dye-sensitized solar cells (DSSCs). Fabrication of the DSSCs was carried out by sandwiching the poly(ethylene glycol)/graphene nanosheet (PEG/graphene nanosheet) gel electrolyte in between the dye sensitized TiO2 nanoflower photoanode and platinum based counter electrode using a spacer of thickness 25 μm. However, the graphene nanosheets form a network with PEG matrix channels in the gel electrolyte which enhances charge transportation. The PEG/graphene nanosheet gel electrolyte was characterized using Fourier transform infrared spectroscopy, cyclic voltammetry, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, atomic force microscopy and electrochemical impedance spectroscopy. Electrochemical impedance spectroscopy results demonstrate the reduction of charge transfer resistance (Rct) with the incorporation of graphene nanosheets which promotes charge transportation through the gel electrolyte. The reduction of (Rct) enhances the device efficiency which was observed in the current density vs. voltage (J–V) measurements and thereby the incident photon to converted electron (IPCE) curves. The maximum photovoltaic conversion efficiency of 5.16% was achieved.

Structural and physico-chemical characterization of a dirhamnolipid biosurfactant purified from Pseudomonas aeruginosa: application of crude biosurfactant in enhanced oil recovery

The present study describes the structural characterization and biotechnological application of a dirhamnolipid biosurfactant produced by Pseudomonas aeruginosa strain NBTU-01 isolated from a petroleum oil-contaminated soil sample. Characterization of partially purified biosurfactant by LC-MS/MS analysis indicated predominant production (78%) of dirhamnolipids Rha-Rha-C10-C10 and Rha-Rha-C12-C10 with a minor production of monorhamnolipids (22%). NMR analysis of the purified major biosurfactant produced by P. aeruginosa strain NBTU-01 identified it as dirhamnolipid and its deduced structure was L-rhamnosyl-L-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate. The LC-MS/MS analysis of intracellular proteins of P. aeruginosa strain NBTU-01 identified key enzymes and other proteins associated with regulation and biosynthesis of rhamnolipids. Critical micelle concentration of purified dirhamnolipid biosurfactant was determined at 72 ​± 2.25 mg l−1 and it reduced the surface tension of water from 72.2 to 29.5 mN m−1. The crude rhamnolipid biosurfactant effectively emulsified crude petroleum-oil, diesel, kerosene and coconut oil, and removed 70 ± 3.5% crude petroleum oil from a saturated sand pack column. Heating the crude rhamnolipid biosurfactant at 100 °C for 5 h did not affect oil recovery from the sand pack column. Moreover, rhamnolipid biosurfactant showed stability at pH values between 6.0 and 10.0. The crystallization and melting temperature of purified dirhamnolipid biosurfactant was found to be 99 and 134 °C, respectively, suggesting it can withstand thermal denaturation and is suitable for application in high temperature wells for tertiary oil recovery.

A graphene oxide incorporated TiO2 photoanode for high efficiency quasi solid state dye sensitized solar cells based on a poly-vinyl alcohol gel electrolyte

An effective self assembly method was used to synthesize hybrid nanocomposites of TiO2 nanoparticles on graphene oxide (GO) sheets for application in Dye Sensitized Solar Cells (DSSCs). The successful incorporation of TiO2 on the GO sheets was confirmed by X-ray diffraction (XRD), Energy Dispersive X-ray (EDX), Raman and UV-visible spectroscopy. The morphology and size of the TiO2 nanoparticles on the GO sheets were analyzed by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. This study is concerned with the effects of different GO contents of the photoanode on the energy conversion efficiency of the PVA gel electrolyte based DSSCs. DSSCs based on the GO@TiO2 nanocomposite photoanode with an optimum GO content of 2.5 wt% showed a short circuit current density (Jsc) of 7.67 mA cm−2, an open circuit voltage (Voc) of 0.76 V and photoconversion efficiency of 3.97% which is much higher than that of the pure TiO2 nanoparticles.

Synthesis of Powdered Polymeric Microparticles by Using Supercritical Carbon Dioxide as the Polymerizing Medium

Polystyrene microparticles were synthesized by emulsion polymerization in supercritical carbon dioxide (sc-CO2) using (polydimethylsiloxane) (PDMS) as a surfactant/stabilizer and azobisisobutyronitrile (AIBN) as initiator. The emulsion polymerization was carried out by varying pressures within the range 13.79–17.93 MPa. At the end of polymerization, powdered polymeric micoparticles were collected by depressurizing CO2. The powdered polymeric microparticles were characterized by SEM, GPC, DSC and TGA. The influence of pressure on conversion, molecular weight, particle size and polydispersity index was studied. The molecular weight (Mn) of the polymer is in the range of 35,542 to 45,078 g/mol. Polydispersity index is in the range of 1.45–1.86 and particle size in the range of 3.25 µm–6.3 µm.

Synthesis, Characterization, and Study of Electrochemical Behavior of N-alkyl Substituted Polycarbazole Derivatives

Poly(9-dodecylcarbazole) (PDDC) and poly[(9-dodecylcarbazole)-co-thiophene] (PDDCT) were synthesized via oxidative coupling method using FeCl3 and the polymers exhibited good solubility in polar aprotic solvents. The synthesized polymers were characterized using UV-visible, FTIR, 1H-NMR spectroscopic techniques. The polymers exhibited thermal stability up to 300°C. The absorption spectra showed the maximum absorption peak at 414 and 443 nm (λmax), respectively, for PDDC and PDDCT. The electrochemical analysis revealed that the band gaps calculated for PDDC and PDDCT are 2.21 eV and 1.91 eV, respectively. The study of anodic peak current against scan rate showed that the electrochemical process is diffusion-limited.