Green Synthesis and Characterization of Silver/Chitosan/Polyethylene Glycol Nanocomposites without any Reducing Agent

This paper presents the green synthesis of silver nanoparticles (Ag NPs) in aqueous medium. This method was performed by reducing AgNO3 in different stirring times of reaction at a moderate temperature using green agents, chitosan (Cts) and polyethylene glycol (PEG). In this work, silver nitrate (AgNO3) was used as the silver precursor while Cts and PEG were used as the solid support and polymeric stabilizer. The properties of Ag/Cts/PEG nanocomposites (NCs) were studied under different stirring times of reaction. The developed Ag/Cts/PEG NCs were then characterized by the ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy

Calcium phosphate mineralizations beneath a polycationic monolayer at the air-water interface

The self-assembly of the amphiphilic block copolymer poly(n-butylmethacrylate)-block-poly[2-(dimethylamino)ethyl methacrylate] at the air-water interface was investigated at different pH values. Similar to Rehfeldt et al. (J. Phys. Chem. B 2006, 110, 9171), the subphase pH strongly affects the monolayer properties. Further experiments show that the formation of calcium phosphate beneath the monolayer can be tuned by adjusting the subphase pH and hence the monolayer charges and organization. After 12 h of mineralization at pH 5, the polymer monolayers are still transparent, but transmission electron microscopy (TEM) shows that very thin calcium phosphate fibers form, which aggregate into “cotton-balls” with diameters of ca. 20 nm. In contrast, after 12 hours of mineralization at pH 8, the polymer film is very slightly turbid and TEM shows dense aggregates with sizes between ca. 200 and 700 nm. The formation of calcium phosphate is further confirmed by IR, Raman, and energy dispersive X-ray spectroscopy (EDXS). The different calcium phosphate architectures can be assigned to effects of monolayer charge, which are different at different pH values. The study thus demonstrates that the effects of polycations should not be ignored if attempting to understand the colloid chemistry of biomimetic mineralization. It also shows that basic block copolymers are useful complementary systems to the much more commonly studied acidic block copolymer templates

Poly(ethylene oxide)-poly(ethylene imine) block copolymers as templates and catalysts for the in situ formation of monodisperse silica nanospheres

Block copolymers based on poly(ethylene oxide) (PEO) and poly(ethylene imine) (PEI) are efficient catalysts/templates for the formation of uniform silica nanoparticles. Addn. of tetraethylorthosilicate to a soln. of PEO-PEI or PEI-PEO-PEI block copolymers results in the formation of silica particles with a diam. of ca. 30 nm and narrow size distribution. The particles pptd. with the diblock copolymers can be redispersed in water after isolation as individual nanoparticles. Evidently, block copolymers based on PEO and PEI serve as excellent templates for the biomimetic and "soft" synthesis of silica nanoparticles. [on SciFinder(R)

Calcium phosphate growth beneath a polycationic monolayer at the air–water interface : effects of oscillating surface pressure on mineralization

The self-assembly of the amphiphilic block copolymer poly(butadiene)-block-poly[2- (dimethylamino)ethyl methacrylate] at the air–water interface and the mineralization of the monolayers with calcium phosphate was investigated at different pH values. As expected for polyelectrolytes, the subphase pH strongly affects the monolayer properties. The focus of the current study, however, is on the effect of an oscillating (instead of a static) polymer monolayer on calcium phosphate mineralization. Monitoring of the surface pressure vs. mineralization time shows that the monolayer is quite stable if the mineralization is performed at pH 8. In contrast, the monolayer at pH 5 shows a measurable decrease of the surface pressure already after ca. 2 h of mineralization. Transmission electron microscopy reveals that mineralization at low pH under constant oscillation leads to small particles, which are arranged in circular features and larger entities with holes of ca. 200 nm. The larger features with the holes disappear as the mineralization is continued in favor of the smaller particles. These grow with time and form necklace-like architectures of spherical particles with a uniform diameter. In contrast, mineralization at pH 8 leads to very uniform particle morphologies already after 2 h. The mineralization products consist of a circular feature with a dark dot in the center. The increasing contrast of the precipitates in the electron micrographs with mineralization time indicates an increasing degree of mineralization vs. reaction time. The study therefore shows that mechanical effects on mineralization at interfaces are quite complex

Characterization by SEM, TEM and Quantum-Chemical Simulations of the Spherical Carbon with Nitrogen (SCN) Active Carbon Produced by Thermal Decomposition of Poly(vinylpyridine-divinylbenzene) Copolymer

Amorphous Spherical Carbon with Nitrogen (SCN) active carbon has been prepared by carbonization of poly(vinylpyridine-divinylbenzene) (PVPDVB) copolymer. The PVPDVB dehydrogenation copolymer has been quantum chemically (QC) simulated using cluster and periodic models. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) studies of the resulting product have conformed the QC computation results. Great structural similarity is found both at the nano- and micro-levels between the N-doped SCN carbon and its pure carbonic SKS analog