Hydrothermal Fabrication of Spindle-Shaped ZnO/Palygorskite Nanocomposites Using Nonionic Surfactant for Enhancement of Antibacterial Activity

Effect of ZnCl2 assisted chemical bath deposition on preferred orientations and optical properties of ZnO films

Using zinc chloride as an additive assisted with conventional solutions of zinc acetate dihydrate and hexamethylenetetramine, the synthesis of ZnO films by chemical bath deposition was investigated and characterized by x-ray diffraction, field emission scanning electron microscopy, atomic force microscope, photoluminescence (PL) and UV-Vis spectrophotometry. ZnO films with (0002), (101̄2), (112̄2), (112̄0), and (101̄0) preferential growth orientation were prepared by changing the concentration of the introduced zinc chloride. The results of UV-Vis spectrophotometry show that the ZnO films with different preferential growth orientations have optical transmittance of more than 80% in the visible light region. Results from PL show that compared to the typical polar (0002) preferential growth orientation of ZnO, other films with different preferential growth orientations have different visible emissions. It was also confirmed that the concentration of Cl- can affect the defects and preferred orientations of ZnO films. This work enriches the fabrication of ZnO films with different preferential growth orientations and also provides new ideas for the fabrication of ZnO-based transparent nanodevices.

Preparation and Application of High-Efficiency, Antibacterial, and Antiviral PET-PTHP Fibers

Transmission through the respiratory tract is one of the most important ways for bacteria and viruses to infect the human body; the use of high-performance antibacterial and antiviral protective equipment is the most effective way to prevent the spread of respiratory diseases. However, at present, most personal protective equipment lacks the ability to kill pathogens. In this paper, a kind of polytetrahydropyrimidine-polyethylene terephthalate functional fiber (PET-PTHP fibers) with highly sustained antibacterial and antiviral properties was prepared. The inactivation rate of the fibers against Staphylococcus aureus and Escherichia coli was as high as 99.99%, and the antibacterial time was more than 72 h. The fibers have an obvious destructive effect on lentiviruses and can reduce the infection rate of lentiviruses in BxPC-3 cells from 25.4 to 9.7%. The cytotoxicity test, cell live/dead staining test, and cell proliferation test all confirmed that PET-PTHP fibers have no obvious cytotoxicity and good cytocompatibility. By applying the functional fibers to the inner layer of the masks, a new type of mask with adsorption, filtration, and killing properties against pathogens was prepared. The filtration efficiency of the new masks was 99.3%, and the pressure drop was 104 Pa. The new masks have excellent air permeability and filtration effect, meet the practical application conditions, and are of grade A; therefore, these masks provide medical protection as well as kill pathogens at the same time, further reducing the risk of human infection.

Fibrous Clays in Dermopharmaceutical and Cosmetic Applications: Traditional and Emerging Perspectives

Functionalization of natural clay minerals for high value-added pharmaceutical and cosmetic applications receives significant research attention worldwide attributable to a rising demand and ongoing search for green, efficient, economically sustainable and ecofriendly geomaterials. Fibrous clays, i.e. palygorskite and sepiolite, are naturally-occurring hydrated magnesium aluminum silicate clay minerals with 2:1 layer-chain microstructure and one-dimensional nanofibrous morphology. Due to their unique structural, textural and compatibility features, over the past decade, fibrous clays and their organic modified derivatives are increasingly used in the dermopharmaceutical and cosmetic fields as excipients, active agents or nanocarriers to develop novel skin delivery systems or to modify drug release profile for enhanced health effects. This comprehensive review presents the up-to-date information on fibrous clays used in topically-applied products for therapeutic and cosmetic purposes with the focus on their performance-related structural characteristics and the underlying mechanisms. The recent advancement of fibrous clay-based skin delivery systems was summarized in wide range of applications including pelotherapy, wound healing, antimicrobial action, coloration and UV protection. An overview of the commonly used topically-applied dosage forms (powders, hydrogels, films, peloids and Pickering emulsion) as well as the toxicological aspects was also included, which might provide guidance to the design and development of fibrous clay-based skin delivery systems.

Palygorskite-Based Organic-Inorganic Hybrid Nanocomposite for Enhanced Antibacterial Activities

A synergistic antibacterial strategy is effective in enhancing the antibacterial efficacy of a single antibacterial material. Plant essential oils (PEOs) are safe antibacterial agents. However, some of their characteristics such as intense aroma, volatility, and poor thermal stability limit their antibacterial activity and applications. In this paper, five kinds of PEOs were incorporated onto ZnO/palygorskite (ZnO/PAL) nanoparticles by a simple adsorption process to form organic-inorganic nanocomposites (PEOs/ZnO/PAL) with excellent antibacterial properties. TEM and SEM analyses demonstrated that ZnO nanoparticles uniformly anchored onto the surface of rod-like PAL, and that the structure of ZnO/PAL maintained after the incorporation of ZnO nanoparticles and PEOs. It was found that carvacrol/ZnO/palygorskite (CAR/ZnO/PAL) exhibited higher antibacterial activities than other PEOs/ZnO/PAL nanocomposites, with minimum inhibitory concentration (MIC) values of 0.5 mg/mL and 1.5 mg/mL against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively. Moreover, the antibacterial efficiency of CAR/ZnO/PAL nanocomposites was superior to that of ZnO/PAL and pure CAR, demonstrating the synergistic effect that occurs in the combined system. PAL serving as a carrier for the combination of organic PEOs and ZnO nanoparticles is an effective strategy for enhanced, clay-based, organic-inorganic hybrid antibacterial nanocomposites.

Enhanced antimicrobial activity and physicochemical stability of rapid pyro-fabricated silver-kaolinite nanocomposite

The present research aims to enhance the antimicrobial activity of kaolinite surfaces by a one-step cost-effective and energy-efficient dry thermal reaction, producing an antibacterial and antifungal silver-kaolinite (Ag-Kao) nanocomposite agent. Pharmaceutical grade kaolin powder samples, with variable kaolinite structural order-disorder degree, were homogeneously mixed with silver nitrate in a proportion 1:4 AgNO₃:kaolin (w/w) and sintered at 400 °C for 30 min. The composition, microstructure, microtexture and surface characteristics of the pyro-fabricated nanocomposites were characterized by XRD/XRF diffractometry, differential scanning calorimetry DSC, FT-IR spectroscopy, TEM/EDX, zeta potential (mV) measured within the 2-12 pH range, and BET method. Physicochemical stability was evaluated by silver dissociation testing under close-neutral and acidic conditions with Ag content assay using ICP-OES. The resulting Ag-Kao nanocomposites exhibited bulk silver contents ranging from 9.29% to 13.32% with high physicochemical stability in both neutral and acidic mediums (Ag dissociation rate <0.5% in 5 days). Ag nanocrystals exhibited particle sizes ranging from 5 to 30 nm, which were embedded and reinforced within the kaolinite matrix. The sizes of the Ag nanocrystals and their distribution patterns on the edges and faces of kaolinite platelets were controlled by the structural order-disorder degree. Highly ordered kaolinites (Hinckley Index, HI > 1) produced platelet edge-clustered silver nanocrystals due to the abundance of the dangling hydroxyls on platelet edges, while the highly disordered kaolinite (HI < 1) provided homogeneous platelet basal-doped silver nanocrystals due to the presence of some residual charges by exposed basal hydroxyl groups with interplatelet silver diffusivity. At pH 2, the magnitude of the positive surface charge was influenced by the silver nanocrystal size. Nanocomposites with the smallest silver nanocrystals (10-5 nm) exhibited the highest positive zeta potential (+15.2 mV to +17.0 mV), while those with larger silver nanocrystals (up to 30 nm) indicated lower positive zeta potential values (+9.5 mV to +3.6 mV). Under the same testing conditions using the Mueller-Hinton broth microdilution method, the raw kaolin samples did not show any significant antimicrobial activity, while all the pyro-fabricated Ag-Kao nanocomposite samples showed potent antibacterial and antifungal activity at low doses (MIC range 0.1-0.0125 mg/mL). Therefore, modulation of the effective electrostatic surface charge of the kaolinite platelets, via thermal doping of silver within their basal planes and edges, was found to be strongly dependent on the pH as well as the size and microtexture of the silver nanocrystals (mainly controlled by the order-disorder degree HI). The resulting modified nanostructure, with physicochemical stability and the efficient surface properties of the designed pyro-fabricated nanocomposite, led to an enhanced synergistic biophysical antimicrobial activity.

Incorporation of quaternary ammonium chitooligosaccharides on ZnO/palygorskite nanocomposites for enhancing antibacterial activities

Quaternary ammonium chitooligosaccharides (QACOS) was incorporated onto the ZnO/palygorskite (ZnO/PAL) nanocomposite by a simple electrostatic self-assembly process to produce a new organic-inorganic nanocomposite (QACOS/ZnO/PAL) with excellent antibacterial activity. After loading QACOS, the Zeta potential of ZnO/PAL was changed from -26.7 to +30.3 mV, which facilitates to improve the targeting behavior of ZnO/PAL towards bacteria and its contact with bacteria, resulting in a significant improvement of antibacterial capability. The MIC values of QACOS/ZnO/PAL for inhibiting bacteria (0.5 mg/mL for E. coli and 1 mg/L for S. aureus) were superior to ZnO/PAL and QACOS, demonstrated an expected synergistic antibacterial effect between QACOS and ZnO/PAL. The improved contact and interface interaction between QACOS/ZnO/PAL and bacteria makes it easier to destroy the structural integrity of bacteria. As a whole, the incorporation of polysaccharide as regulators of surface charge opens up a new way to further enhance the antibacterial activity of inorganic antibacterial materials.