Antibacterial activity of zinc oxide nanoparticles (ZnO-NPs) has received significant interest worldwide particularly by the implementation of nanotechnology to synthesize particles in the nanometer region. Many microorganisms exist in the range from hundreds of nanometers to tens of micrometers. ZnO-NPs exhibit attractive antibacterial properties due to increased specific surface area as the reduced particle size leading to enhanced particle surface reactivity. ZnO is a bio-safe material that possesses photo-oxidizing and photocatalysis impacts on chemical and biological species. This review covered ZnO-NPs antibacterial activity including testing methods, impact of UV illumination, ZnO particle properties (size, concentration, morphology, and defects), particle surface modification, and minimum inhibitory concentration. Particular emphasize was given to bactericidal and bacteriostatic mechanisms with focus on generation of reactive oxygen species (ROS) including hydrogen peroxide (H2O2), OH− (hydroxyl radicals), and O2 −2 (peroxide). ROS has been a major factor for several mechanisms including cell wall damage due to ZnO-localized interaction, enhanced membrane permeability, internalization of NPs due to loss of proton motive force and uptake of toxic dissolved zinc ions. These have led to mitochondria weakness, intracellular outflow, and release in gene expression of oxidative stress which caused eventual cell growth inhibition and cell death. In some cases, enhanced antibacterial activity can be attributed to surface defects on ZnO abrasive surface texture. One functional application of the ZnO antibacterial bioactivity was discussed in food packaging industry where ZnO-NPs are used as an antibacterial agent toward foodborne diseases. Proper incorporation of ZnO-NPs into packaging materials can cause interaction with foodborne pathogens, thereby releasing NPs onto food surface where they come in contact with bad bacteria and cause the bacterial death and/or inhibition.

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Review on Zinc Oxide Nanoparticles: Antibacterial Activity and Toxicity Mechanism.

The surface and materials science of tin oxide

We report a novel wet-chemical approach at 180 °C for the synthesis of monodispersed ZnO nanorods with high single-crystallinity. The method has successfully brought the ZnO nanorod diameter from a reported 150 nm down to the 50 nm regime in this work. The aspect ratio of the synthesized nanorods achieved is exceptionally high (in the range of 30−40). This simple low-cost approach should promise us a future large-scale synthesis of ZnO nanostructures for many important applications in nanotechnology in a controlled manner.

Hydrothermal synthesis of ZnO nanorods in the diameter regime of 50 nm.

Single-crystalline and uniform nanopolyhedra, nanorods, and nanocubes of cubic CeO2 were selectively prepared by a hydrothermal method at temperatures in the range of 100-180 degrees C under different NaOH concentrations, using Ce(NO3)3 as the cerium source. According to high-resolution transmission electron microscopy, they have different exposed crystal planes: {111} and {100} for polyhedra, {110} and {100} for rods, and {100} for cubes. During the synthesis, the formation of hexagonal Ce(OH)3 intermediate species and their transformation into CeO2 at elevated temperature, together with the base concentration, have been demonstrated as the key factors responsible for the shape evolution. Oxygen storage capacity (OSC) measurements at 400 degrees C revealed that the oxygen storage takes place both at the surface and in the bulk for the as-obtained CeO2 nanorods and nanocubes, but is restricted at the surface for the nanopolyhedra just like the bulk one, because the {100}/{110}-dominated surface structures are more reactive for CO oxidation than the {111}-dominated one. This result suggests that high OSC materials might be designed and obtained by shape-selective synthetic strategy.

Shape-selective synthesis and oxygen storage behavior of ceria nanopolyhedra, nanorods, and nanocubes.

One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

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One-dimensional ZnO nanostructures: Solution growth and functional properties

By decomposing Zn(OH)42- or Zn(NH3)42+ precursor in various solvents at suitable reaction conditions, zinc oxide with a diversity of well-defined morphologies was synthesized. Flowerlike ZnO built ...

Control of ZnO Morphology via a Simple Solution Route

Low‐Temperature Fabrication of Highly Crystalline SnO2 Nanorods

Pure hexagonal-phased Y1 - x BO3:Eu x (x = 0−0.30) nanocrystals with different particle sizes were prepared by a facile sol−gel pyrolysis process, and their photoluminescence spectra evidently showed a size-dependent characteristic because the ratio of the red emission transition (5D0 → 7F2) to the orange emission transition (5D0 → 7F1) (R/O) was much higher in the smaller particles. Both XRD patterns and IR spectra demonstrated that the lattices of YBO3:Eu nanocrystals were distorted and that as the particle size became smaller, the lattices became more distorted. Studies on the charge transfer (CT) bands indicated that Eu3+ ions can be excited preferentially by different excitation sources in both the bulk and the nanocrystals, suggesting that at least two different types of intrinsic luminescent sites, site 1 and site 2, coexist in YBO3:Eu. Site-selective excitation spectra also revealed that a particular site, site 3, existed concurrently in the nanocrystals. Site 2, the site with relatively inferior ...

Size-Dependent Chromaticity in YBO3:Eu Nanocrystals: Correlation with Microstructure and Site Symmetry

The rectangular cross-sectional ZnO nanowires were synthesized in a solution method. An attachment-driven growth mechanism was proposed for the morphology evolvement of ZnO nanocrystals from nanoparticles to nanoplates and eventually to nanowires. Due to the pileup attachment of the nanoplates to recrystallize into nanowires, unique one-dimensional (1D) ZnO nanowires with the rectangular cross section were obtained, which is different from those nanowires in the previous reports. It is the first time the evidence that "oriented attachment" can occur not only for nanoparticles but also for nanoplates was obtained, suggesting that "oriented attachment" is an intrinsic behavior for nanosized materials. According to the growth model proposed based on the direct TEM observations, ZnO nanocrystals can be easily controlled as nanoparticles, nanoplates, or nanowires by tuning the synthetic parameters.

Jia-Lu Yin

Papers

Control of ZnO Morphology via a Simple Solution Route

Low‐Temperature Fabrication of Highly Crystalline SnO2 Nanorods

Size-Dependent Chromaticity in YBO3:Eu Nanocrystals: Correlation with Microstructure and Site Symmetry

Attachment-Driven Morphology Evolvement of Rectangular ZnO Nanowires