Antibacterial Films of Silver Nanoparticles Embedded into Carboxymethylcellulose/Chitosan Multilayers on Nanoporous Silicon: A Layer-by-Layer Assembly Approach Comparing Dip and Spin Coating.

The design and engineering of antibacterial materials are key for preventing bacterial adherence and proliferation in biomedical and household instruments. Silver nanoparticles (AgNPs) and chitosan (CHI) are broad-spectrum antibacterial materials with different properties whose combined application is currently under optimization. This study proposes the formation of antibacterial films with AgNPs embedded in carboxymethylcellulose/chitosan multilayers by the layer-by-layer (LbL) method. The films were deposited onto nanoporous silicon (nPSi), an ideal platform for bioengineering applications due to its biocompatibility, biodegradability, and bioresorbability. We focused on two alternative multilayer deposition processes: cyclic dip coating (CDC) and cyclic spin coating (CSC). The physicochemical properties of the films were the subject of microscopic, microstructural, and surface-interface analyses. The antibacterial activity of each film was investigated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria strains as model microorganisms. According to the findings, the CDC technique produced multilayer films with higher antibacterial activity for both bacteria compared to the CSC method. Bacteria adhesion inhibition was observed from only three cycles. The developed AgNPs-multilayer composite film offers advantageous antibacterial properties for biomedical applications.

Phonon Structure, Infra-Red and Raman Spectra of Li2MnO3 by First-Principles Calculations.

The layer-structured monoclinic Li2MnO3 is a key material, mainly due to its role in Li-ion batteries and as a precursor for adsorbent used in lithium recovery from aqueous solutions. In the present work, we used first-principles calculations based on density functional theory (DFT) to study the crystal structure, optical phonon frequencies, infra-red (IR), and Raman active modes and compared the results with experimental data. First, Li2MnO3 powder was synthesized by the hydrothermal method and successively characterized by XRD, TEM, FTIR, and Raman spectroscopy. Secondly, by using Local Density Approximation (LDA), we carried out a DFT study of the crystal structure and electronic properties of Li2MnO3. Finally, we calculated the vibrational properties using Density Functional Perturbation Theory (DFPT). Our results show that simulated IR and Raman spectra agree well with the observed phonon structure. Additionally, the IR and Raman theoretical spectra show similar features compared to the experimental ones. This research is useful in investigations involving the physicochemical characterization of Li2MnO3 material.

Hydrothermal control of the lithium-rich Li2MnO3 phase in lithium manganese oxide nanocomposites and their application as precursors for lithium adsorbents.

Lithium manganese oxides (LMOs) are key materials due to their role in Li-ion batteries and lithium recovery from aqueous lithium resources. In the present work, we investigated the effect of the crystallization temperature on the formation by hydrothermal synthesis of LMO nanocomposites with high Li/Mn ratios. It is demonstrated that LMOs with a high Li/Mn ratio can be formed by systematically favoring the lithium-rich layered monoclinic phase (Li2MnO3) in a mixture of monoclinic and spinel crystalline phases. LMO nanocomposites have been characterized in terms of morphology, size, crystallinity, chemical composition and surface properties. Moreover, lithium adsorption experiments were conducted using acid-treated LMOs (HMOs) to evaluate the functionality of the nanocomposites as lithium adsorbent materials in a LiCl buffer solution. This study spotlights the structural, compositional, and functional properties of different LMO nanocomposites obtained by the hydrothermal method using the same Li and Mn precursor compounds at slightly different crystallization temperatures. According to our knowledge, this is the first report of the successful application of the lithium-rich Li2MnO3 phase in lithium manganese oxide nanocomposites as lithium adsorbent materials. Therefore, specific LMO nanocomposites with controlled amounts of the layered phase can be engineered to optimize lithium recovery from aqueous lithium resources.

Fabrication and characterization of nanostructured porous silicon-silver composite layers by cyclic deposition: dip-coating vs spin-coating.

Composites of nanostructured porous silicon and silver (nPSi-Ag) have attracted great attention due to the wide spectrum of applications in fields such as microelectronics, photonics, photocatalysis and bioengineering, Among the different methods for the fabrication of nanostructured composite materials, dip and spin-coating are simple, versatile, and cost-effective bottom-up technologies to provide functional coatings. In that sense, we aimed at fabricating nPSi-Ag composite layers. Using nPSi layers with pore diameter of 30 nm, two types of thin-film techniques were systematically compared: cyclic dip-coating (CDC) and cyclic spin-coating (CSC). CDC technique formed a mix of granular and flake-like structures of metallic Ag, and CSC method favored the synthesis of flake-like structures with Ag and Ag2O phases. Flakes obtained by CDC and CSC presented a width of 110 nm and 70 nm, respectively. Particles also showed a nanostructure surface with features around 25 nm. According to the results of EDX and RBS, integration of Ag into nPSi was better achieved using the CDC technique. SERS peaks related to chitosan adsorbed on Ag nanostructures were enhanced, especially in the nPSi-Ag composite layers fabricated by CSC compared to CDC, which was confirmed by FTDT simulations. These results show that CDC and CSC produce different nPSi-Ag composite layers for potential applications in bioengineering and photonics.