ABSTRACT
A sago starch biopolymer with embedded silver nanoparticles has been studied as a material for the prevention of microbial growth. Approximately 8 nm in size, silver nanoparticles have been synthesized by reduction of the silver salt in aqueous solution in the presence of sago starch using sodium borohydride as a reducing agent. The obtained solutions were cast on glass plates to obtain thin supported silver-starch nanocomposite films. The morphology of the nanocomposites was investigated by scanning and transmission electron microscopy. UV-Vis absorption spectroscopy showed that during the film formation a part of the silver nanoparticles has been trapped in the water present in the sample, which enabled their partial oxidation into active Ag(+) species. The oxidation of the silver nanoparticles was confirmed by X-ray photoelectron spectroscopy. The antimicrobial activity tests have shown that the nanocomposite material can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.
Subject(s)
Anti-Bacterial Agents/pharmacology , Escherichia coli/drug effects , Nanocomposites , Silver/pharmacology , Staphylococcus aureus/drug effects , Starch/pharmacology , Anti-Bacterial Agents/chemistry , Borohydrides/chemistry , Candida albicans/drug effects , Candida albicans/physiology , Escherichia coli/physiology , Metal Nanoparticles/chemistry , Microscopy, Electron, Scanning , Microscopy, Electron, Transmission , Nanocomposites/chemistry , Photoelectron Spectroscopy , Silver/chemistry , Spectrum Analysis , Staphylococcus aureus/physiology , Starch/chemistry , Temperature , Water/chemistryABSTRACT
Adsorption of sulfide ions onto a surface of starch capped silver nanoparticles upon addition of thioacetamide was investigated. UV-vis absorption spectroscopy revealed that the adsorption of the sulfide ion on the surface of the silver nanoparticles induced damping as well as blue shift of the silver surface plasmon resonance band. Further increase in thioacetamide concentration led to shift of the resonance band toward higher wavelengths indicating the formation of the continuous Ag2S layer on the silver surface. Thus fabricated nanoparticles were investigated using electron microscopy techniques (TEM, HRTEM, and HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), which confirmed their core-shell structure.
Subject(s)
Biopolymers/chemistry , Nanoparticles/chemistry , Silver/chemistry , Starch/chemistry , Sulfur/chemistry , Adsorption , Microscopy, Electron, Transmission , Nanoparticles/ultrastructure , Spectrophotometry , Sulfides/chemistry , Surface Plasmon Resonance , Surface Properties , Thioacetamide/chemistry , X-Ray DiffractionABSTRACT
Ce-doped borosilicate (BSG), phosphosilicate (PSG), and borophosphosilicate (BPSG) glasses (B:P:Si molar ratios 8:0:92, 0:8:92, and 8:8:84; Ce:Si molar ratio 1 x 10(-)(4) to 1 x 10(-)(2)) were prepared by the sol-gel method. High-resolution transmission electron microscopy (HRTEM), (31)P, (29)Si, and (11)B magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), and UV-vis absorption investigations demonstrated that, in PSG and BPSG, Ce(3+) ions interact with phosphoryl, [O=PO(3/2)], metaphosphate, [O=PO(2/ 2)O](-), and pyrophosphate, [O=PO(1/2)O(2)](2)(-), groups, linked to a silica network. This inhibits both CeO(2) segregation and oxidation of isolated Ce(3+) ions to Ce(4+), up to Ce:Si = 5 x 10(-)(3). In BSG, neither trigonal [BO(3/2)] nor tetrahedral [BO(4/2)](-) boron units coordinate cerium; thus, Ce(3+) oxidation occurs even at Ce:Si = 1 x 10(-)(4), as in pure silica glass (SG). The homogeneous rare-earth dispersion in the host matrix and the stabilization of the Ce(3+) oxidation state enhanced the intensity of the photoluminescence emission in PSG and BPSG with respect to BSG and SG. The energy of the Ce(3+) emission band in PSG and BPSG matrixes agrees with the phosphate environment of the rare earth.
Subject(s)
Boron/chemistry , Cerium/chemistry , Glass/chemistry , Luminescent Agents/chemistry , Phosphorus/chemistry , Silicon Dioxide/chemistry , Absorption , Electron Spin Resonance Spectroscopy , Luminescent Measurements , Magnetic Resonance Spectroscopy , Microscopy, Electron, Transmission , Particle Size , Surface PropertiesABSTRACT
Low thermal expansion Li(2)O-Al(2)O(3)-SiO(2) (LAS) glass ceramic was examined as a host matrix for erbium ions. ZrO(2) was added to the glass since it serves as a nucleating agent and as a good environment for the luminescent ions. The study was carried out on amorphous powders of the Li(2)O-Al(2)O(3)-SiO(2)/ZrO(2)/Er(2)O(3) system prepared by the sol-gel method and successively crystallized at different temperatures. X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared (IR) spectroscopy were employed to study the evolution of the crystalline phases and the distribution of the erbium ions. The TEM micrographs confirmed that, after thermal treatment at 1000 degrees C, the crystallization of nanoparticles constituted by an Er(2)O(3)-ZrO(2) solid solution with narrow size distribution could be achieved. On the contrary, erbium silicate was detected in the samples without ZrO(2). The repartition constant of Er(2)O(3) between ZrO(2) and LAS matrix has been also evaluated.
