Sankararao Chappa

Change in the Affinity of Ethylene Glycol Methacrylate Phosphate Monomer and Its Polymer Anchored on a Graphene Oxide Platform toward Uranium(VI) and Plutonium(IV) Ions.

The complexation behavior of the carbonyl and phosphoryl ligating groups bearing ethylene glycol methacrylate phosphate (EGMP) monomer and its polymer fixed on a graphene oxide (GO) platform was studied to understand the coordination ability of segregated EGMP units and polymer chains toward UO2(2+) and Pu(4+) ions. The cross-linked poly(EGMP) gel and EGMP dissolved in solution have a similar affinity toward these ions. UV-initiator induced polymerization was used to graft poly(EGMP) on the GO platform utilizing a double bond of EGMP covalently fixed on it. X-ray photoelectron spectroscopy (XPS) of the GO and GO-EGMP was done to confirm covalent attachment of the EGMP via a -C-O-P- link between GO and EGMP. The extent of poly(EGMP) grafting on GO by thermal analyses was found to be 5.88 wt %. The EGMP units fixed on the graphene oxide platform exhibited a remarkable selectivity toward Pu(4+) ions at high HNO3 conc. where coordination is a dominant mode involved in the sorption of ions. The ratio of distribution coefficients of Pu(IV) to U(VI) (DPu(IV)/DU(VI)) followed a trend as cross-linked poly(EGMP) (0.95) < EGMP in solvent methyl isobutyl ketone (1.3) < GO-poly(EGMP) (25) < GO-EGMP (181); the DPu(IV)/DU(VI) values are given in parentheses. The density functional theory computations have been performed for the complexation of UO2(2+) and Pu(4+) ions with the EGMP molecule anchored on GO in the presence of nitrate ions. This computational modeling suggested that Pu(4+) ion formed a strong coordination complex with phosphoryl and carbonyl ligating groups of the GO-EGMP as compared to UO2(2+) ions. Thus, the nonselective EGMP becomes highly selective to Pu(IV) ions when it interacts as a single unit fixed on a GO platform.

Self-reducing asymmetric polymer membrane for in situ formation and containment of noble metal nanocatalysts

A polymer membrane having an asymmetric physical structure, dense at the surfaces with a fibrous interior, is developed to host the Ag, Au, Pd, Rh and Ru nanocatalysts that are formed by in situ reductions of the precursor ions with functional groups covalently attached to the membrane matrix. This membrane mimics an eggshell membrane in terms of the reduction and stabilization of the nanocatalysts without involving external reagents. The nanocatalysts in this membrane exhibit high catalytic activity in both inorganic and organic reductions.

Palladium Nanoparticles Hosted on Hydrazine-Grafted Magnetite and Silica Particles to Catalyze the Reduction of Oxymetal Ions with Formic Acid

A new synthetic route has been developed to anchor a large amount of Pd nanoparticles (NPs) on the surface of hydrazine‐grafted and (3‐glycidyloxypropyl)trimethoxysilane‐coated inorganic host particles such as Fe3O4 and SiO2. The hydrazine‐grafted inorganic particles reduce Pd2+ ions spontaneously under ambient conditions. This results in the production of Pd0 seeds and their nucleation, which leads to the growth of Pd NPs on the surface of the host particle itself. These anchored Pd NPs on Fe3O4 and SiO2 have been characterized by elemental analysis, microscopy, and elemental mapping. Spherical Pd NPs of ≈0.3 and 1 nm are formed uniformly on Fe3O4 (25 nm) and SiO2 (100 nm) particles, respectively. Their concentration on the host particles was 12 mg g−1 for Fe3O4 and 20 mg g−1 for SiO2. These host particles loaded with Pd NPs have been investigated for their catalytic activity in the reduction of representative oxymetal ions such as UO22+ and Cr2O72− ions with formic acid. NP‐loaded SiO2 exhibited a good catalytic activity in both these reductions, whereas Pd NPs on Fe3O4 could reduce Cr2O72− ions only.

Phosphate-bearing polymer grafted glass for plutonium(IV) ion-selective alpha spectrometry

A phosphate-bearing polymer thin film was covalently anchored on a glass substrate for alpha spectrometric determination of Pu4+ ions in aqueous samples. This method combined matrix elimination, preconcentration and source preparation into one-step sample manipulation. The thin polymer film was formed by first coupling 3-(trimethoxysilyl)propyl acrylate (TMSPA) on a hydrolyzed glass substrate by a sol–gel process, and simultaneously utilizing the double bonds of TMSPA for the UV-initiator-induced graft polymerization of bis[2-(methacryloyloxy)ethyl] phosphate monomers. The thin phosphate ligand bearing the thus formed poly(bis[2-(methacryloyloxy)ethyl] phosphate) (poly(BMEP)) film was characterized for homogeneity, physical morphology, and its affinity toward representative actinide ions such as UO22+, Am3+, Th4+ and Pu4+ in a HNO3 medium. Alpha track radiography and elemental mapping of the C and P atoms indicated uniform formation of the poly(BMEP) film on the glass substrate. Atomic force microscopy indicated a 10–15 nm thickness of the film, and the alpha spectrum of Pu4+-loaded glass@poly(BMEP) exhibited well defined alpha energy peaks without any significant loss of energy in the host matrix. The glass@poly(BMEP) film was found to sorb Pu4+ ions preferentially in 3 mol L−1 HNO3 in the presence of competing UO22+ and Th4+ ions. Am3+ ions did not sorb to a significant extent under similar conditions, even in the absence of Pu4+ ions. The Pu4+ ions loaded on the glass@poly(BMEP) substrate were quantified by isotope-dilution alpha spectrometry. This glass@poly(BMEP)-based alpha spectrometric method was applied successfully to quantify Pu in aqueous samples. The concentrations of Pu measured by this technique were reproducible within ±6% and required a minimum preconcentration of 2.95 Bq Pu activity in the glass@poly(BMEP) film. The measured Pu concentrations showed good agreement with those obtained by standard thermal ionization mass spectrometry.

Poly(ethylenimine) functionalized magnetic nanoparticles for sorption of Pb, Cu, and Ni: potential application in catalysis

ABSTRACT The poly(ethylenimine) functionalized magnetite particles were studied for their preconcentration efficiencies toward Cu2+, Pb2+, and Ni2+ ions. The loading capacities were found to be 26 mg g−1, 46 mg g−1, and 13 mg g−1 of Cu2+, Pb2+, and Ni2+ ions, respectively. Cu2+ ions loaded on the magnetically retrievable nanoparticles were used for Henry reaction as a representative example of a heterogeneous catalyst. These particles were characterized for their chemical, physical, thermal and magnetic properties. The Henry reaction involved reaction between m-nitro benzaldehyde and nitromethane to afford the nitroaldol adducts 1-(3-nitrophenyl)-2-nitrosoethanol with 80% yield in ethanol at room temperature.

Functionalized glass fiber membrane for extraction of iodine species

ABSTRACT Poly(vinylpyrrolidone) (PVP) has been anchored on the glass fiber membrane for capturing radioiodine in gaseous state and dissolved in water. First, precursor alkoxy silane monomer was anchored by sol-gel method on the glass fiber membrane and its polymerizing double bond was used subsequently for the anchoring of PVP by UV graft-polymerization. Thus formed PVP-membrane was characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy with EDS and thermo-gravimetric analysis. The sorption efficiency and loading capacity of the membrane toward I2, and stability of I2 complexed in the membrane were studied by UV-Vis spectrophotometry and 131I radiotracer method.

Phosphate functionalized radiation grafted Teflon for capturing and quantifications of U(VI) and Pu(IV) ions at ultra-trace concentration in aqueous samples

A phosphate groups bearing thin polymer film has been anchored on Teflon by radiation induced grafting and subsequent chemical modification. Thus formed phosphate-g-Teflon (Ph-g-T) sheet has been characterized appropriately and studied for its selectivity towards Pu(IV) and U(VI) ions at different acidities. Depending upon acidity dependent selectivity of Ph-g-T toward actinides ions, the solid state nuclear track detector based methods was developed to quantify Pu(IV) and U(VI) at ultra-trace concentration in a variety of aqueous samples.