ABSTRACT:In this study the poly(acrylamide-co-maleic acid) hydrogels containing small amounts of maleic acid have been synthesized, and the effect of pH, ionic strength, and nature of counterions on the equilibrium water uptake has been investigated. The incorporation of small amount of maleic acid results in the transition of swelling mechanism from Fickian to non-Fickian. The equilibrium mass swelling has been found to increase with pH of the swelling medium while increase in ionic strength causes a decrease in the swelling. The amount of maleic acid present in the hydrogel affects the swelling behavior in rather an unusual way. With lower acid contents, the equilibrium mass swelling increases while higher concentrations of maleic acid cause a decrease in the degree of swelling. The hydrogels have been found to undergo a number of swelling-deswelling cycles when pH of the swelling medium changes from 8.0 to 2.0. Hydrogels require more time to deswell compared to the time required for swelling, which has been explained on the basis of the fact that gels follow different mechanisms for the two processes. Various swelling parameters such as equilibrium mass swelling, diffusion coefficient, intrinsic diffusion coefficient, swelling exponent, etc., have been evaluated.

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ABSTRACT:The key objective of developing novel materials for hygienic living conditions is to lower the risk of transmitting diseases and biofouling. To this end, a number of silver-hydrogel nanocomposite systems are under development. In this study, we attempted a unique strategy to prepare silver-nanoparticle-loaded poly(acrylamide-co-N-vinyl-2-pyrolidone) hydrogel composites. To load nanosilver particles into such a nonionic hydrogel, a novel breathing-in/breathing-out (BI-BO) approach was employed. As the number of BI-BO cycles increased, the amount of the silver nanoparticles loaded into these hydrogels also increased. This behavior was obvious and was confirmed by ultraviolet-visible spectroscopy and thermal analysis. Furthermore, the hydrogel-silver-nanoparticle composites were confirmed with Fourier transform infrared spectroscopy and transmission electron microscopy studies. Antibacterial studies of these hydrogel-silver nanocomposites showed excellent results against Escherichia coli. The antibacterial activity increased with the number of BI-BO cycles, and samples that underwent three BI-BO cycles showed optimal bactericidal activity. The degree of crosslinking and the silver content had a great influence on the antibacterial efficacy.

This work involves chemical modification of cotton fabrics by natural, biocompatible, and biodegradable polysaccharide — chitosan — followed by incorporating silver nanoparticles in the fabrics. The excellent chelating property of chitosan binds the silver metal ions that are later on reduced to nanoparticles giving rise to chitosan-attached nanosilver-loaded fabrics. The silver nanoparticles-loaded chitosan-attached fabric has been characterized by surface plasmon resonance, transmission electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction analysis. These chitosan-attached nanosilver-loaded fabrics exhibit excellent antibacterial action against model bacteria E. coli.

The milk protein casein (Cas) has been employed as carbon resource material to synthesize nitrogen-doped carbon dots (N-CDs) via microwave exposure. The dots, when exposed to UV light, produced blue fluorescence. The N-CDs were characterized by ultra violet (UV) spectroscopy, Fourier transformation infrared spectroscopy, X-ray diffraction (XRD), dynamic light scattering analysis, fluorescent microscopy (FM), and transmission electron microscopy (TEM). The XRD analysis revealed a broad peak at 2θ = 20°, thus indicating the turbostratic carbon phase. TEM analysis and particle size distribution curve revealed that nearly, 85% of the particles had diameter below 10 nm and the particles had spherical geometry. The HRTEM analysis revealed that carbon dots exhibited lattice fringes with a d-spacing of 0.21 nm, corresponding to the (100) plane lattice of graphite. The fluorescence spectral studies indicated a red shift in the emission peak from 420 to 450 nm as the excitation wavelength increased from 300 to 340 nm. The zeta potential of particles was found to be -11.3 mV. Finally, impregnation of N-CDs was studied in Spinacia oleracea leaf. It was observed that as the concentration of N-CDs' solution increased, percent insertion (PI) also increased, but the time required for maximal insertion decreased with increasing concentrations of N-CDs in the feed solutions. In the carbon dots' solution with a concentration of 200 ppm, maximum percent insertion (MPI) was obtained after 80 min. However, with the increasing concentration of N-CDs in the feed solutions, time of getting MPI reduced, i.e., in 600 ppm, it was 30 min, and in 800 ppm, it was 10 min.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.