Parma Nand Bajaj

Silver nanoparticle-loaded PVA/gum acacia hydrogel: synthesis, characterization and antibacterial study.

A simple one-pot method for in situ synthesis of silver nanoparticles (AgNPs), within polyvinyl alcohol/gum acacia (PVA-GA) hydrogel matrix, by gamma radiation-induced cross-linking is reported here. The synthesized hydrogels were characterized by FT-IR, thermogravimetry, dynamic light scattering and inductively coupled mass spectrometry method. The thermal stability was found to be more for the hydrogel loaded with silver nanoparticles and also the percentage silver loading was found to increase with increase in cross-linking density. The influence of gum acacia (GA) concentration on the equilibrium degree of swelling of the synthesized hydrogels, and also on the silver release from hydrogel matrix, was investigated. The size of the silver nanoparticles formed in the hydrogel matrix was in the range of 10-40 nm. The rheological gel point was found to be at 25.34 kGy of radiation dose, for a typical hydrogel synthesized, using 5% GA, 3% PVA and 1mM AgNO3. The antibacterial studies of the synthesized nanosilver-containing hydrogels showed good antibacterial activity against gram-negative bacterium, Escherichia coli.

Resorcinol-formaldehyde coated XAD resin beads for removal of cesium ions from radioactive waste: synthesis, sorption and kinetic studies

A novel synthetic method was developed to synthesize resorcinol-formaldehyde (RF) resin in spherical form, of required mesh size, using XAD-4 as template beads. The synthesized RF-coated XAD (RF-XAD) beads were characterized, using different techniques. Suitable size and mechanical stability, along with their spherical shape, make these beads most appropriate for column operation. The efficiency of these beads was evaluated for removal of cesium from alkaline medium, in batch conditions, using a radioanalytical technique. The effect of sodium ion concentration, the initial cesium ion concentration and the contact time were also investigated. It was observed that the Kd value for Cs+ ions decreases with increase in Na+ ion concentration. The equilibrium data were fitted into different isotherm models, and were found to be represented well by the Langmuir isotherm equation, with a monolayer sorption capacity of 287 mg g−1. Kinetic modeling analysis, using pseudo first-order, pseudo second-order and intraparticle diffusion equations, shows that the pseudo second-order equation is the most appropriate model for the description of the sorption of cesium ions onto the RF-XAD beads. The rate constants were determined at different initial concentrations. The process mechanism was found to be complex, consisting of both surface sorption and pore diffusion.

An Organic Acid-induced Synthesis and Characterization of Selenium Nanoparticles

A simple wet chemical method has been developed to synthesize selenium nanoparticles (size 40–100 nm), by the reaction of sodium selenosulphate precursor with different organic acids in aqueous medium, under ambient conditions. Polyvinyl alcohol has been used to stabilize the selenium nanoparticles. The synthesized nanoparticles can be separated from its sol by using a high-speed centrifuge and can be redispersed in aqueous medium with a sonicator. UV-visible optical absorption spectroscopy, X-ray diffraction, energy dispersive X-rays, differential scanning calorimetry, atomic force microscopy, and transmission electron microscopy techniques have been employed to characterize the synthesized selenium nanoparticles.

Potassium cobalthexacyanoferrate–gel beads for cesium removal: kinetics and sorption studies

The hydrogel–sorbent composite beads of potassium cobalthexacyanoferrate (KCoHCF) were synthesized for separation of cesium from waste generated in the nuclear industry. Cross-linked sodium alginate, containing PVA, was used as a binding matrix for the synthesis of spherical beads of 2 mm diameter. The characterization of these beads was carried out, using TGA, SEM and BET surface area analysis techniques, which indicated the highly porous and hydrophilic nature of the beads. The sorption of cesium ions onto these synthesized beads was studied, using a radiotracer technique. To determine equilibrium sorption and kinetic parameters for different initial cesium ion concentrations, all the studies were conducted by a batch method. The experimental data were analyzed, using the different sorption isotherms, and found to be described the best by a Langmuir sorption isotherm. The monolayer capacity of KCoHCF–gel beads is found to be 15 mg g−1 of the dry beads. Sorption kinetics data were analysed, using different kinetic models. The results show that the sorption follows pseudo second-order reaction kinetics. The initial sorption rate and the rate constants for the pseudo first-order, pseudo second-order and intraparticle diffusion were evaluated, and discussed for different initial concentrations in the range 1–20 mg L−1. The mechanism of the sorption of cesium ions onto the synthesized beads was also investigated and film diffusion was found to be the rate determining step.

Kinetics of Gas-Phase Reaction of OH with Morpholine: An Experimental and Theoretical Study

Kinetics of reaction of OH radical with morpholine, a heterocyclic molecule with both oxygen and nitrogen atoms, has been investigated using laser photolysis-laser-induced fluorescence technique, in the temperature range of 298-363 K. The rate constant at room temperature (k(298)) is (8.0 +/- 0.1) x 10(-11) molecule(-1) cm(3) s(-1). The rate constant decreases with temperature in the range studied, with the approximate dependence given by k(T) = (1.1 +/- 0.1) x 10(-11) exp[(590 +/- 20)/T] cm(3) molecule(-1) s(-1). The rate constants are high compared with those of similar heterocyclic molecules with oxygen atom but comparable to those reported for aliphatic amines. Ab initio molecular orbital calculations show that prereactive complexes, 5-7 kcal mol(-1) lower in energy as compared with the reactants, are formed because of hydrogen bond interaction between OH and the N/O atom of morpholine. The stability of the complex involving the nitrogen atom is found to be more than that involving the oxygen atom. The optimized transition-state structures and energies for the different pathways of hydrogen abstraction from these prereactive complexes explain the observation of negative activation energy.

Precursor concentration and temperature controlled formation of polyvinyl alcohol-capped CdSe-quantum dots

Summary Polyvinyl alcohol-capped CdSe quantum dots, with a size within their quantum confinement limit, were prepared in aqueous solution at room temperature, by a simple and environmentally friendly chemical method. The size of the CdSe quantum dots was found to be dependent on the concentrations of the precursors of cadmium and selenium ions, as well as on the aging time and the reaction temperature; all of which could be used conveniently for tuning the size of the particles, as well as their optical properties. The synthesized quantum dots were characterized by optical absorption spectroscopy, fluorescence spectroscopy, X-ray diffraction, atomic force microscopy and transmission electron microscopy. The samples were fluorescent at room temperature; the green fluorescence was assigned to band edge emission, and the near-infrared fluorescence peaks at about 665 and 865 nm were assigned to shallow and deep trap states emissions, respectively. The quantum dots were fairly stable up to several days.

Photodissociation dynamics of 3-bromo-1,1,1-trifluoro-2-propanol and 2-(bromomethyl) hexafluoro-2-propanol at 234 nm: Resonance-enhanced multiphoton ionization detection of Br (2Pj)

The photodissociation dynamics of 3-bromo-1,1,1-trifluoro-2-propanol (BTFP) and 2-(bromomethyl) hexafluoro-2-propanol (BMHFP) have been studied at 234 nm, and the C-Br bond dissociation investigated using resonance-enhanced multiphoton ionization coupled with time-of-flight mass spectrometer (REMPI-TOFMS). Br formation is a primary process and occurs on a repulsive surface involving the C-Br bond of BTFP and BMHFP. Polarization dependent time-of-flight profiles were measured, and the translational energy distributions and recoil anisotropy parameters extracted using forward convolution fits. A strong polarization dependence of time-of-flight profiles suggest anisotropic distributions of the Br((2)P(3/2)) and Br((2)P(1/2)) fragments with anisotropy parameter, β, of respectively 0.5 ± 0.2 and 1.2 ± 0.2 for BTFP, and 0.4 ± 0.1 and 1.0 ± 0.3 for BMHFP. The measured velocity distributions consist of a single velocity component. The average translational energies for the Br((2)P(3/2)) and Br((2)P(1/2)) channels are 9.2 ± 1.0 and 7.4 ± 0.9 kcal/mol for BTFP, and 15.4 ± 1.8 and 15.1 ± 2.0 kcal/mol for BMHFP. The relative quantum yields of Br((2)P(3/2)) and Br((2)P(1/2)), which are 0.70 ± 0.14 and 0.30 ± 0.06 in BTFP and 0.81 ± 0.16 and 0.19 ± 0.04 in BMHFP, indicate that the yield of the former is predominant. The measured anisotropy parameters for the Br((2)P(3/2)) and Br((2)P(1/2)) channels suggest that the former channel has almost equal contributions from both the parallel and the perpendicular transitions, whereas the latter channel has a significant contribution from a parallel transition. Non-adiabatic curve crossing plays an important role in the C-Br bond dissociation of both BTFP and BMHFP. The estimated curve crossing probabilities suggest a greater value in BTFP, which explains a greater observed value of the relative quantum yield of Br((2)P(1/2)) in this case.

Preparation and characterization of potassium nickel hexacyanoferrate-loaded hydrogel beads for the removal of cesium ions

A novel synthetic approach has been used to prepare sorbent hydrogel composite beads of potassium nickel hexacyanoferrate (KNiHCF), using PVA and cross-linked alginate as the binding matrix. The characterization study indicates the high hydrophilicity and high surface area of the synthesized beads. The application potential of these beads for removal of cesium ions from low level liquid nuclear waste has been studied in batch mode using a 137Cs radiotracer. The equilibrium sorption and kinetic data are obtained at different initial cesium ion concentrations. These data are analysed using various sorption isotherm and kinetic models. It is observed that the sorption process can be best described by the Langmuir isotherm model, and the monolayer capacity of the beads is determined to be 7 mg per g of the swollen beads, which corresponds to ~64 mg per g of the dry beads. The sorption of cesium ions onto the sorbent beads is found to follow pseudo second-order kinetics over the entire studied concentration range. The ion-exchange mechanism involves the exchange of cesium ions with potassium ions. The mechanism of the sorption process is also investigated using the intraparticle diffusion model and Boyds plot, and the results indicate that the sorption of cesium ions onto the beads is a complex process, involving both intraparticle diffusion and film diffusion.

PC-88A – impregnated polymeric beads: Preparation, characterization and application for extraction of Pu(IV) from nitric acid medium

Abstract The extractant-impregnated polymeric beads (EIPBs), containing polyethersulfone as base polymer and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) as an extractant, were prepared by phase inversion method. These EIPBs were characterized by FTIR, TGA and SEM techniques. The beads were found to have excellent acid stability, since these did not exhibit any structural deformation or loss of the extractant into aqueous nitric acid solution (6 M), for a period of 15 d. The feasibility of Pu(IV) extraction, using these beads, from nitric acid solution was tested by batch equilibration method. Parametric dependence of Pu(IV) extraction on experimental variables, like strength of nitric acid, equilibration time, Pu(IV) concentration, etc., was investigated. The present study also addressed the important practical issues, like maximum loading capacity and the reusability of these beads. Under optimized conditions, equilibrium capacity and maximum loading capacity for Pu(IV) were found to be 2.03 and 7.50 mg per gram of the swollen beads, respectively. The reusability of the beads was also ascertained by repetitive extraction-stripping of Pu(IV) up to 7 cycles of operation, without significant change in their extraction performance. The extraction of Pu(IV) by the blank polymeric beads was observed to be almost negligible, under the similar experimental conditions.

Study of Extraction of Co(II) Ions using the Synthesized Polyacrylonitrile-Manganese Dioxide Composite Beads

Extraction of cobalt ions from aqueous medium has been studied, using macroporous polyacrylonitrile-manganese dioxide composite beads. Polyacrylonitrile, synthesized by γ-radiation induced polymerization of saturated aqueous solution of acrylonitrile monomer, has been employed, to produce polyacrylonitrile-manganese dioxide composite beads. Results of the extraction study indicate efficient adsorption of cobalt ions from neutral, or slightly acidic, aqueous solutions. The cobalt ions, adsorbed on the composite beads, can be leached out with 0.1 M HNO3 solution. The effect of various experimental parameters, such as concentration of cobalt ions, pH of the aqueous solution, etc., on the adsorption process and its kinetics has been studied. Further, adsorption capacity of the beads for cobalt ion, as well as their reusability for multiple adsorption-desorption of the cobalt ions, have also been evaluated. SEM and BET techniques have been used to determine the porous nature of the beads. IR spectroscopy has been used to understand the interaction of the polyacrylonitrile-manganese dioxide composite beads with cobalt ions.