Silver and gold nanoparticles have been grown on calcium alginate gel beads using a green photochemical approach. The gel served as both a reductant and a stabilizer. The nanoparticles were characterized using UV-visible spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), energy dispersive X-ray (EDS), and selected area electron diffraction (SAED) analyses. The particles are spherical, crystalline, and the size ranges for both Ag and Au nanoparticles are <10 nm. It is noticed from the sorption experiment that the loading of gold on calcium alginate beads is much more compared to that of Ag. The effectiveness of the as-prepared dried alginate-stabilized Ag and Au nanoparticles as a solid phase heterogeneous catalyst has been evaluated, for the first time, on the well-known 4-nitrophenol (4-NP) reduction to 4-aminophenol (4-AP) in the presence of excess borohydride. The reduction was very efficient and followed zero-order kinetics for both Ag and Au nanocomposites. The effects of borohydride, initial 4-NP concentration, and catalyst dose were evaluated. The catalyst efficiency was examined on the basis of turnover frequency (TOF) and recyclability. The catalytic efficiency of alginate-based Ag catalyst was much more compared to that of the Au catalyst. The as-prepared new solid-phase biopolymer-based catalysts are very efficient, stable, easy to prepare, eco-friendly, and cost-effective, and they have the potential for industrial applications.

Nanocrystalline HAp powder was synthesized using surfactant template systems. Composition of the microemulsion and synthesis parameters had significant effect on the formation of HAp nanopowder and their surface area and morphology. Powders were prepared with a surface area of 130 m2/g and particle size between 30 and 50 nm with needle shape and spherical morphology. Nanocrystalline hydroxyapatite (HAp) powder was synthesized using the reverse micelle-processing route. Cyclohexane was used as the oil phase, mixed poly(oxyethylene)5 nonylphenol ether (NP-5) and poly(oxyethylene)12 nonylphenol ether (NP-12) as the surfactant phase, and a solution of Ca(NO3)2 and H3PO4 was used as the aqueous phase. The powders were characterized by BET surface area analyzer, powder X-ray diffraction, and transmission electron microscopy. It was found that experimental conditions such as aqueous/organic phase volume ratio, pH, aging time, aging temperature, and metal ion concentration in the aqueous phase affected the crystalline phase, surface area, particle size, and morphology of HAp nanopowders. With the use of this technique, nanopowders were prepared with different morphology depending on the reaction parameters.

The present research describes synthesis of hydroxyapatite (HAp) nanopowders using a sol–gel route with calcium nitrate and ammonium hydrogen phosphate as calcium and phosphorous precursors, respectively. Sucrose is used as template material, and alumina is added as a dopant to study its effects on particle size and surface area. Synthesized powders are characterized using X‐ray diffractometry, BET surface‐area analysis, and transmission electron microscopy. Results show that alumina stabilizes the HAp crystalline phase. Average particle size of mesoporous HAp samples is between 30 and 50 nm with surface area of 51–60 m2/g.

Novel hierarchical flower-like nanostructures of Ag-doped MnO 2 have been obtained by facile wet chemical and photochemical routes. UV-visible absorption spectroscopy measurement reveals that doping of Ag nanoparticles in MnO 2 nanostructures leads to a red shift of the absorption edge and reduces the optical band gap energy from 2.68 to 2.51 eV while compared with undoped MnO 2 . Raman study reveals that the band broadens and shifts toward higher wavenumbers as the MnO 6 octahedron is contorted by Ag doping and thus the loss of translational symmetry activates otherwise Raman-forbidden oxygen vibrations. Finally, SERS activity upsurges from Ag-doped MnO 2 with Rhodamine 6G and 2-aminothiophenol as probe molecules.

Polysaccharide alginate gel beads have been used as a template for photochemical growth of monometallic and bimetallic Au and Ag manoclusters. The gel served both as a reductant under photoirradiation and as a stabilizer. Fourier transform infrared (FTIR) analysis indicated that the secondary hydroxyl function reduced the Au(III) and Ag(I) to their metallic state with the concomitant oxidation of the hydroxyl function to carbonyl group. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), energy-dispersive X-ray spectrometry (EDX) analyses were used to characterize nanoparticle structure, size, and morphology. The effectiveness of this alginate gel-stabilized nanoparticles as substrate toward surface-enhanced Raman scattering (SERS) detection was evaluated by use of two probes, 2-aminothiophenol and 1,10-phenanthroline. Intensity of SERS signals was a function of analyte adsorption as evidenced from UV−visible absorption spectroscopy. Among all the substrates, alginate-stabilized Au has been found to be the best for SERS detection. The enhancement factors are in the range of 104 and the detection limits are in the subpicogram level.