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Resorcinol based reduction and capping of ultra-small colloidal silver nanoparticles (Ag NPs) optimally formed hydrogen bond driven clusters within the water-based solution. Large-area self-assembled fractal structures of Ag NPs aggregates were fabricated by solvent evaporation technique on silicon substrate. The final dried surface structures were found to be pH dependent which was adjusted to particular values after the optimal reduction of silver salt, capping of Ag NPs, followed by cluster formation at an optimum pH in the solution phase. These self-assembled surface structures show controlled enhancement of various surface optical phenomena such as Raman spectra of a model dye and luminescence of Ag NPs as a function of pH dependent fractal dimension of the resulting structures. The structure, morphology and various relevant optical properties of self-assembled fractals of Ag NPs were further established by combined use of X-Ray diffractometry (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), UV-Visible, photoluminescence and Raman spectroscopy analysis. Image 1 • Ag NPs were synthesized using resorcinol as reducing and capping agent and was found to be luminescent. • SPR show peaks at 353 and ~500 nm and their PL emission was observed at 411 nm and 544 nm respectively. • Fractal dimension (F D) was calculated to be 1.89 which decreases to ~1.6 with pH variation in acidic and basic. • R6G was used as probe molecules for SERS measurements which verified that the substrate has high sensitivity to SERS response. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ag@Ag 2 S core shell nanoparticles were synthesized by soft chemical route. • SPR of Ag NPs blue shifts from 408 to 378 nm with increasing sulfur ion concentration. • Ag@Ag 2 S CSNPs exhibit tunable (1.43–1.50 eV) NIR luminescence with increasing sulfur ion concentration. Abstract Ag-Ag 2 S core-shell nano-structured particles, prepared by soft chemical route, were found to be luminescent in the near-infrared (NIR) range. The silver nanoparticles were pre-synthesized with size control by poly-vinyl-pyrrolidone (PVP) polymer capping from silver nitrate solution, by reduction using sodium borohydride in solution, which were further subjected to reaction with sulfur ions in the later stage by mixing controlled amount of Na 2 S in the solution. With increasing concentration of sulfur ions, the plasmonic peak of Ag showed progressive blue shift and damping, leading to final diminishment. Enhanced NIR luminescence obtained from Ag@Ag 2 S core-shell nanoparticles were found to be asymmetric and blue shifting with reduced intensity and increasing sulfur ion concentration. The mechanism behind such a behavior is predicted due to formation of composite layer of Ag 2 S-Ag both at the surface and the volume, with Ag core at the center, diminishing in size with increasing sulfur concentration. The structure, chemical composition, morphology and final core-shell structure formation were further established by combination of X-ray diffractometry (XRD), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) analysis. [ABSTRACT FROM AUTHOR]

Hybrid nano-structure consisting of silver nanoparticles (Ag NPs) on two dimensional (2D) MoS 2 nanosheets (NS), prepared by liquid exfoliation method and ultrasonic mixing, showed solar energy driven enhanced photocatalytic capability on a model organic dye methylene blue (MB), having possible consequence in water purification. The Schottky junction between the Ag NP and MoS 2 NS interface induces shift of Fermi level to more negative potential, thereby increasing the life time of the charge carriers even more which leads to formation of sink for photo-excited electrons, and the Ag NPs and ultra-small (US) Ag NPs based Ag-MoS 2 samples show quick photocatalytic degradation of MB dye within 30 min (87%) and 8 min (93%), monitored by UV-Vis spectroscopy, with rate constants 64.1 × 10−3 min−1 and 88.6 × 10−3 min−1 respectively. With decreasing size of Ag NPs a wide surface area was covered and quantum confinement occurred which enhanced the electron transfer at the interface. These electrons are relocated to the constitutively existing molecular oxygen to produce numbers of influential oxidative radicals which results in effective degradation of MB. The corresponding photoluminescence spectra show blue shift and quenching with decreasing Ag NP size and lower MoS 2 number of layers, determined by Raman spectroscopy with respect to that of original MoS 2 nanosheet structures. The corresponding microstructures were determined by transmission electron microscopy (TEM), while the chemical composition was found using X-ray photoelectron spectroscopy (XPS). [Display omitted] • Ag/USAg-MoS 2 hybrid structures were prepared by liquid exfoliation method. • Ag/USAg-MoS 2 blue shift indicates increase in band gap due to quantum confinement. • Raman shows Δω was 19.76 cm−1, which confirms that, USAg-MoS 2 consist of bilayers. • Ag/USAg-MoS 2 exhibits enhanced photocatalytic activity towards MB degradation within 8 min. [ABSTRACT FROM AUTHOR]