Antibacterial and Photocatalytic Activity of ZnO/Au and ZnO/Ag Nanocomposites.

The use of a combination of nanoparticles as antimicrobial agents can be one strategy to overcome the tendency of microbes to become resistant to antibiotic action. Also, the optimization of nano-photocatalysts to efficiently remove persistent pollutants from wastewater is a hot topic. In this study, two composites ZnO/Au (1% wt.) and ZnO/Ag (1% wt.) were synthesized by simple aqueous solution methods. The structure and morphology of the r nanocomposites were analyzed by structural and optical characterization methods. The formation of AuNPs and AgNPs in these experiments was also discussed. The antimicrobial properties of ZnO, ZnO/Au, and ZnO/Ag nanomaterials were investigated against Gram-negative bacteria (Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus). The results showed an increase of 80% in the antimicrobial activity of ZnO/Au against Pseudomonas aeruginosa compared with 30% in the case of ZnO/Ag. Similarly, in the case of the S. aureus strain tests, ZnO/Au increased the antimicrobial activity by 55% and ZnO/Ag by 33%. The photocatalytic tests indicated an improvement in the photocatalytic degradation of methylene blue (MB) under UV irradiation using ZnO/Au and ZnO/Ag nanocomposites compared to bare ZnO. The photocatalytic degradation efficiency of ZnO after 60 min of UV irradiation was ∼83%, while the addition of AuNPs enhanced the degradation rate to ∼95% (ZP2), and AgNP presence enhanced the efficiency to ∼98%. The introduction of noble metallic nanoparticles into the ZnO matrix proved to be an effective strategy to increase their antimicrobial activity against P. aeruginosa and S. aureus, and their photocatalytic activity was evaluated through the degradation of MB dye. Comparing the enhancing effects of Au and Ag, it was found that ZnO/Au was a better antimicrobial agent while ZnO/Ag was a more effective photocatalyst under UV irradiation.

Ag-Decorated Iron Oxides-Silica Magnetic Nanocomposites with Antimicrobial and Photocatalytic Activity.

Nanotechnology offers unlimited possibilities for creating effective hybrid materials, which combine functional performance in environment depollution and antimicrobial defense with a lack of toxicity, biocompatibility, biodegradability, and natural availability. This paper presents the silver effect on photocatalytic and antibacterial activities of double-coated iron oxide nanoparticles (NPs), Fe3O4@SiO2/ZnO-Ag. The structural, morphological, and textural information of the, core-shell iron oxides-based superparamagnetic nanoparticles (IOMNPs) decorated with 5% Ag by ultrasound-assisted synthesis were evaluated by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDX), X-ray diffraction, Raman spectroscopy, and Brunauer-Emmett-Teller physisorption measurements. Although two synthesis temperatures of 95 and 80 °C were used for the co-precipitated iron oxide cores, the XRD patterns revealed the formation of a single magnetite, Fe3O4, phase. The sorption-photocatalytic activities under dark and UV irradiation encountered a maximum removal efficiency of the MB (90.47%) for the Fe3O4@SiO2/ZnO-Ag sample with iron oxide core obtained at 80 °C. The rate constant for the second-order kinetics was 0.0711 min-1 for 2 h, and the correlation coefficient R2 closed to unity. Two samples with Ag-decorated hybrid SiO2/ZnO shell and hierarchically interconnected porous structure with large surface area (328.8 and 342.5 m2g-1) exhibited the best disk diffusion antimicrobial activity against four microorganisms, especially gram-positive Staphylococcus aureus.

Magnetic Core-Shell Iron Oxides-Based Nanophotocatalysts and Nanoadsorbents for Multifunctional Thin Films.

In recent years, iron oxides-based nanostructured composite materials are of particular interest for the preparation of multifunctional thin films and membranes to be used in sustainable magnetic field adsorption and photocatalysis processes, intelligent coatings, and packing or bio-medical applications. In this paper, superparamagnetic iron oxide (core)-silica (shell) nanoparticles suitable for thin films and membrane functionalization were obtained by co-precipitation and ultrasonic-assisted sol-gel methods. The comparative/combined effect of the magnetic core co-precipitation temperature (80 and 95 °C) and ZnO-doping of the silica shell on the photocatalytic and nano-sorption properties of the resulted composite nanoparticles were investigated by ultraviolet-visible (UV-VIS) spectroscopy monitoring the discoloration of methylene blue (MB) solution under ultraviolet (UV) irradiation and darkness, respectively. The morphology, structure, textural, and magnetic parameters of the investigated powders were evidenced by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) measurements, and saturation magnetization (vibrating sample magnetometry, VSM). The intraparticle diffusion model controlled the MB adsorption. The pseudo- and second-order kinetics described the MB photodegradation. When using SiO2-shell functionalized nanoparticles, the adsorption and photodegradation constant rates are three-four times higher than for using starting core iron oxide nanoparticles. The obtained magnetic nanoparticles (MNPs) were tested for films deposition.

Low-Temperature and UV Irradiation Effect on Transformation of Zirconia -MPS nBBs-Based Gels into Hybrid Transparent Dielectric Thin Films.

Bottom-up approaches in solutions enable the low-temperature preparation of hybrid thin films suitable for printable transparent and flexible electronic devices. We report the obtainment of new transparent PMMA/ZrO2 nanostructured -building blocks (nBBs) hybrid thin films (61-75 nm) by a modified sol-gel method using zirconium ethoxide, Zr(OEt)4, and 3-methacryloxypropyl trimethoxysilane (MPS) as a coupling agent and methylmethacrylate monomer (MMA). The effect of low-temperature and UV irradiation on the nBBs gel films is discussed. The thermal behaviors of the hybrid sols and as-deposed gel films were investigated by modulated thermogravimetric (mTG) and differential scanning calorimetry (DSC) analysis. The chemical structure of the resulted films was elucidated by X-ray photoelectron (XPS), infrared (IR) and Raman spectroscopies. Their morphology and crystalline structure were observed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and grazing incidence X-ray diffraction. The cured films show zirconia nanocrystallites of 2-4 nm in the hybrid matrix and different self-assembled structures for 160 °C or UV treatment; excellent dielectric behavior, with dielectric constant values within 6.7-17.9, depending on the Zr(OEt)4:MMA molar ratio, were obtained.

A Chitosan-Agarose Polysaccharide-Based Hydrogel for Biomimetic Remineralization of Dental Enamel.

Developing multifunctional systems for the biomimetic remineralization of human enamel is a challenging task, since hydroxyapatite (HAP) rod structures of tooth enamel are difficult to replicate artificially. The paper presents the first report on the simultaneous use of chitosan (CS) and agarose (A) in a biopolymer-based hydrogel for the biomimetic remineralization of an acid-etched native enamel surface during 4-10-day immersion in artificial saliva with or without (control group) fluoride. Scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, Fourier transform infrared and Raman spectroscopies, X-ray diffraction, and microhardness tests were applied to investigate the properties of the acid-etched and remineralized dental enamel layers under A and CS-A hydrogels. The results show that all biomimetic epitaxial reconstructed layers consist mostly of a similar hierarchical HAP structure to the native enamel from nano- to microscale. An analogous Ca/P ratio (1.64) to natural tooth enamel and microhardness recovery of 77.4% of the enamel-like layer are obtained by a 7-day remineralization process in artificial saliva under CS-A hydrogels. The CS component reduced carbonation and moderated the formation of HAP nanorods in addition to providing an extracellular matrix to support growing enamel-like structures. Such activity lacked in samples exposed to A-hydrogel only. These data suggest the potential of the CS-A hydrogel in guiding the formation of hard tissues as dental enamel.

Uniform arrays of ZnO 1D nanostructures grown on Al:ZnO seeds layers by hydrothermal method.

In obtaining uniform array of ZnO 1D nanostructures, especially using solution based methods, the thickness and the morphology of the epitaxial seeds layer are very important. The paper presents the effect of the thickness and the morphology of the Al:ZnO seeds layer on the morphology and properties of ZnO nanowires array grown by hydrothermal method. Compact and vertically aligned ZnO 1D nanostructures were obtained. Concentration of 0.02 M of zinc nitrate was found to be optimal for growing nanowires with diameters up to 50 nm and lengths between 1.5 and 2.5 microns. Using 0.04 M solution, nanorods with diameter between 50 and 100 nm were obtained. The correlation between the crystal structure and optical properties of ZnO nanowires is discussed. From electrical measurements on single nanowire, resistivity value of 9 x 10(-2) omega cm was obtained. The I-V curves of single ZnO NWs show quasi diode characteristic when an e-beam is irradiating the NWs, and a typical semiconductive behaviour when the e-beam is turned off.