Zinc oxide nanoleaves: A scalable disperser-assisted sonochemical approach for synthesis and an antibacterial application

Sonochemical synthesis of bioinspired graphene oxide-zinc oxide hydrogel for antibacterial painting on biodegradable polylactide film

Graphene oxide nanosheet (GO) is a multifunctional platform for binding with nanoparticles and stacking with two dimensional substrates. In this study, GO nanosheets were sonochemically decorated with zinc oxide nanoparticles (ZnO) and self-assembled into a hydrogel of GO-ZnO nanocomposite. The GO-ZnO hydrogel structure is a bioinspired approach for preserving graphene-based nanosheets from van der Waals stacking. X-ray diffraction analysis (XRD) showed that the sonochemical synthesis led to the formation of ZnO crystals on GO platforms. High water content (97.2%) of GO-ZnO hydrogel provided good property of ultrasonic dispersibility in water. Ultraviolet-visible spectroscopic analysis (UV-vis) revealed that optical band gap energy of ZnO nanoparticles (∼3.2 eV) GO-ZnO nanosheets (∼2.83 eV). Agar well diffusion tests presented effective antibacterial activities of GO-ZnO hydrogel against gram-negative bacteria (E. coli) and gram-positive bacteria (S. aureus). Especially, GO-ZnO hydrogel was directly used for brush painting on biodegradable polylactide (PLA) thin films. Graphene-based nanosheets with large surface area are key to van der Waals stacking and adhesion of GO-ZnO coating to the PLA substrate. The GO-ZnO/PLA films were characterized using photography, light transmittance spectroscopy, coating stability, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopic mapping (EDS), antibacterial test and mechanical tensile measurement. Specifically, GO-ZnO coating on PLA substrate exhibited stability in aqueous food simulants for packaging application. GO-ZnO coating inhibited the infectious growth ofE. colibiofilm. GO-ZnO/PLA films had strong tensile strength and elastic modulus. As a result, the investigation of antibacterial GO-ZnO hydrogel and GO-ZnO coating on PLA film is fundamental for sustainable development of packaging and biomedical applications.

Recent Developments in Sonochemical Synthesis of Nanoporous Materials

Ultrasounds are commonly used in medical imaging, solution homogenization, navigation, and ranging, but they are also a great energy source for chemical reactions. Sonochemistry uses ultrasounds and thus realizes one of the basic concepts of green chemistry, i.e., energy savings. Moreover, reduced reaction time, mostly using water as a solvent, and better product yields are among the many factors that make ultrasound-induced reactions greener than those performed under conventional conditions. Sonochemistry has been successfully implemented for the preparation of various materials; this review covers sonochemically synthesized nanoporous materials. For instance, sonochemical-assisted methods afforded ordered mesoporous silicas, spherical mesoporous silicas, periodic mesoporous organosilicas, various metal oxides, biomass-derived activated carbons, carbon nanotubes, diverse metal-organic frameworks, and covalent organic frameworks. Among these materials, highly porous samples have also been prepared, such as garlic peel-derived activated carbon with an apparent specific surface area of 3887 m2/g and MOF-177 with an SSA of 4898 m2/g. Additionally, many of them have been examined for practical usage in gas adsorption, water treatment, catalysis, and energy storage-related applications, yielding satisfactory results.

Nanoparticles: From synthesis to applications and beyond

In modern-day research, nanoparticles (size < 100nm) are an indispensable tool for various applications, especially in the field of biomedicine. Although enormous efforts have been made to understand the properties and specificities of nanoparticles, many questions are still not answered and the new ones arise. In this review we summarize current trends in the nanoparticle synthesis and characterization and interpret the stability of nanoparticles in various media from aqueous solutions to biological milieu important for the in vitro and in vivo studies. To get more detailed insight into nanoparticle charging properties and interactions of nanoparticles with interfaces the theoretical models are presented. Finally, the overview of nanoparticle applications is given and the future prospects are discussed.

Facile nanostructured zinc oxide coating technique for antibacterial and antifouling air filters with low pressure drop

Air filters effectively filtrate external contaminants including pathogenic bioaerosols; however, they also act as culture sites for the pathogenic bacteria captured in nutrient organic pollutants. Although many researchers have applied various antibacterial coatings to filters, the coating application inevitably increased the pressure drop, leading to the low efficiency and high energy consumption of the purification system. Herein, we report a simple nanostructured zinc oxide (ZnO) coating technique to confer a polypropylene nonwoven filter with superior antibacterial, antifouling and anti-biofilm properties without an additional pressure drop. For aerodynamic coating designs, filters were directly immersed into low concentration precursor solutions to enable the sedimentation of the ZnO sol-gel particles on the filter fibers according to fluid dynamic. The precursor concentration affected the surface topology and so properties of the as-fabricated coating. 0.07 M precursor solution produced a rose-like nanostructured coating exhibiting no pressure-drop increase. The large specific surface area and hydrophobic surface killed and then repelled the attached bacteria effectively. As a result, the bare filter promoted the growth and consequent biofilm formation of the surface bacteria in a favorable environment for the growth of microorganisms, while the coated filter successfully suppressed biofilm development.

Visible-light-driven photocatalytic inactivation of S. aureus in aqueous environment by hydrophilic zinc oxide (ZnO) nanoparticles based on the interfacial electron transfer in S. aureus/ZnO composites

Waterborne diseases caused by pathogenic microorganisms pose severe threats to human health. ZnO nanoparticles (NPs) hold great potentials as an effective, economical and eco-friendly method for water disinfection, but the exact antimicrobial mechanism of ZnO NPs under visible-light illumination is still not clear. Herein, we investigate the visible-light-driven photocatalytic inactivation mechanism of amino-functionalized hydrophilic ZnO (AH-ZnO) NPs against Staphylococcus aureus (S. aureus) in aqueous environment from the perspective of electron transfer theory. The results show that the antibacterial effects of AH-ZnO NPs are dependent on the AH-ZnO NPs concentration and treatment time. The bulk ORP value and released Zn²⁺ concentration in AH-ZnO NPs solutions increase with AH-ZnO NPs concentration. The SEM and intracellular protein leakage results indicate that AH-ZnO NPs can adhere to S. aureus surface without causing obvious cell membrane disruption. The photoluminescence (PL) intensity and fluorescence lifetime of AH-ZnO NPs are remarkedly decreased after adding S. aureus, which confirms the electron transfer from S. aureus to AH-ZnO NPs. Moreover, the ΔPL intensity is closely correlated with the inactivation efficiency, demonstrating that the interfacial electron transfer in S. aureus/AH-ZnO NPs composites contributes to the antibacterial activity, which is speculated to disrupt the normal respiratory electron transfer chain of S. aureus, thereby causing intracellular ROS generation, cell membrane depolarization and eventually apoptosis-like death.

Controlled dispersion of ZnO nanoparticles produced by basic precipitation in solvothermal processes

Zinc oxide nanoparticles were successfully synthesized under precipitation processes, using ZnSO4·7H2O as a Zn2+ precursor and K2CO3 used as a basic source, and hydrozincite was obtained as an intermediary, which was treated under two procedures; first procedure involved multiple stages to get final precipitated with NaOH, and in the second procedure the hydrozincite was straightforwardly dried at 220 °C. By both processes ZnO structures were obtained, which were turned into nanoparticles by a solvothermal treatment, for four hours in ethylene glycol at 200 °C. The final products for the first procedure was conglomerate of spherical nanoparticles with sizes ranged between 5-10 nm and dispersed ellipsoidal nanoparticles for the second procedure. Apart off the two procedures mentioned above, another synthesis was carried out with the same Zn2+ precursor but now using NaOH, and the solvothermal treatment produced ZnO mixed micro-structures which under ultrasonic cavitation disaggregated on mesoporous ZnO nanoplates of hexagonal shapes with nanopore sizes of approximately 0.35 nm. All ZnOs synthesized were structurally characterized with XRD, TEM and FT-IR techniques, and electronically with UV-Vis absorption and diffuse reflectance spectroscopies.

Ultrasound-assisted synthesis of ZnO photocatalysts for gas phase pollutant remediation: Role of the synthetic parameters and of promotion with WO3

The synthesis of ZnO photocatalysts by ultrasound-assisted technique was here investigated. Several experimental parameters including the zinc precursor (acetate, chloride, nitrate), sonication conditions (amplitude, pulse) and post-synthetic thermal treatment (up to 500 °C) were studied. Crystalline ZnO samples were obtained without thermal treatments due to the adopted reactant ratios and synthesis temperature. Sonication plays a major role on the morphological oxide features in terms of particle size and surface area, the latter showing a 20-fold increase with respect to conventional synthesis. Interestingly, 1 and 3 s sonication pulses led to morphological properties similar to continuous sonication. A thermal treatment at moderate temperatures (400-450 °C) promoted the loss of surface hydroxylation and the formation of lattice defects, while higher temperatures were detrimental for the sample morphology. The prepared ZnO was decorated with WO₃ particles comparing an ultrasound-assisted technique using 1 s pulses with a conventional approach, giving rise to composites with promoted visible light absorption. Samples were tested towards the photocatalytic degradation of nitrogen oxides (500-1000 ppb) in humidified air under both UV and visible light. By carefully controlling the synthetic procedure, better performance were observed with respect to the commercial benchmark. Samples from ultrasound-assisted syntheses, also in the case of pulsed sonication, showed consistently better results than conventional references, in particular for ZnO-WO₃ composites. The composite by ultrasound-assisted synthesis showed > 95% degradation in 180 min and doubled NO_x degradation under visible light with respect to the conventional composite.

Zinc oxide nanoparticles decorated fluorescent and antibacterial glass fiber pre-filter paper

Zinc oxide nanoparticles (ZnO–NPs) were synthesized and decorated simultaneously onto the glass fiber pre-filter paper (GF paper) by the sonochemical method without using any additional reagents (a ‘Green’ synthesis approach). ZnO–NPs decorated GF paper was characterized by electron, confocal laser scanning and atomic force microscopy, fourier transform infrared and atomic emission spectroscopy, X-ray diffraction, and thermogravimetric analysis etc. Due to the massive void volume space, exceptional dimensional stability, large thickness (790 μm) of the GF paper (unlike other paper materials) and ultrasonic irradiation effects, ZnO–NPs were decorated in the enormous amount (96 mg per paper) without causing any adverse effects on the GF paper. Such a huge amount decoration onto GF paper makes it multifunctional, fluorescencet (orange-pink color, 535–624 nm) under ultra-violet light (360 nm) and antibacterial. The antibacterial activity of the ZnO–NPs decorated GF paper was examined against Gram-positive bacteria Bacillus subtilis 168 and Staphylococcus aureus (MCC 2043, pathogenic). The outcomes from the antibacterial experiments revealed ∼99% (2 log) reduction in the survival of the filtered bacteria (B. subtilis) on the ZnO–NPs decorated GF paper due to the toxicity of ZnO–NPs on bacterial cells like cell shrinkage, cytoplasmic leakage, cell burst, etc. Multifunctional, ZnO–NPs decorated GF paper could be used for fluorescencet and antibacterial paper-based applications.

Heat Treatment of Pine Wood: Possible Effect of Impregnation with Silver Nanosuspension

The scope of the present work was to study the effects of heat treatment (at different mild temperatures) on the physicomechanical properties of pine wood, and to find out if impregnation with nanosilver may have any potential influence on the impact of heat treatment. Impregnation of wood with a 400-ppm silver nanosuspension was carried out under an initial vacuum pressure of 0.07 MPa, followed by a pressure of 0.25 MPa for thirty minutes, before heat treatment. Heat treatment was carried out under hot air at three relatively mild temperatures, 145, 165, and 185 °C. Results showed improvement of some properties in heat-treated wood at 145 °C. This was indicative of the improving impact caused by hornification and irreversible hydrogen bonding in the course of water movements due to heat treatment; significant fluctuations in the intensities of FTIR spectra bands at 1750–1500 cm−1 were corroborating evidence of chemical alterations in hemicellulose polymer. The high mass loss at temperature 185 °C, and the extreme thermal degradation thereof, overcame the improving effects of hornification and formation of irreversible hydrogen bonds, consequently mechanical properties decreased significantly. Interaction of different elements involved made it hard to predict properties in specimens modified at 165 °C. Impregnation of specimens with nanosilver suspension resulted in significant increase of mass loss in specimens heat-treated at 185 °C, and significant fluctuations in properties of specimens heat-treated at 145 °C.

Innovative Wood Surface Treatments Based on Nanotechnology

This work reviewed innovative wood surface treatments based on nanotechnology. It is well documented in the literature that the cell walls of wood present significant porosity; this porosity is on a molecular scale. The main reason for the use of nanotechnology in wood science and technology is the unique characteristic of nano-based materials to effectively penetrate deeply into wood substrates, which, in turns, results in the alteration of their surface chemistry. This subsequently causes an improvement in wood properties. Any potential change in the wood properties due to treatment with nanomaterials is based on the higher interfacial area which is developed due to the treatment. This occurs because the number of particles is significantly reduced to the nanoscale. The nanomaterials improve the properties of wood as a raw material and alter its original features to a limited extent. However, their potential impact on both health and the environment should be addressed by applying tools such as life-cycle assessments. This will avoid mistakes being made in which new technologies are released on the market prior to an impact assessment having been carried out.

Zinc Oxide for Functional Textile Coatings: Recent Advances

The use of ZnO for the functionalization of textile substrates is growing rapidly, since it can provide unique multifunctional properties, such as photocatalytic self-cleaning, antimicrobial activity, UV protection, flame retardancy, thermal insulation and moisture management, hydrophobicity, and electrical conductivity. This paper aims to review the recent progress in the fabrication of ZnO-functionalized textiles, with an emphasis on understanding the specificity and mechanisms of ZnO action that impart individual properties to the textile fibers. The most common synthesis and application processes of ZnO to textile substrates are summarized. The influence of ZnO concentration, particle size and shape on ZnO functionality is presented. The importance of doping and coupling procedures to enhance ZnO performance is highlighted. The need to use binding and seeding agents to increase the durability of ZnO coatings is expressed. In addition to functional properties, the cytotoxicity of ZnO coatings is also discussed. Future directions in the use of ZnO for textile functionalization are identified as well.

Nanomaterials and Chemical Modifications for Enhanced Key Wood Properties: A Review

This work briefly reviews the research milestones in the area of wood chemical modification, focusing on acetylated and furfurylated wood which have been scaled up, and exploits the solutions that nanotechnology can offer to wood protection as an alternative green innovative approach in improving key wood properties, namely the dimensional stability when subjected to a fluctuating moisture content and a susceptibility to biodegradability by microorganisms. Recently, nanomaterials were found to be able applicable in wood science. The target is to improve some special physicochemical characteristics of wood in order to resist extreme conditions (climate, bacteria, etc.), giving an enhanced potentiality. It is well-established that the wood cell wall shows a porosity of molecular scale dimensions; this is caused by the partial filling of spaces between the microfibrils of the cellulose mainly by polyoses and lignin. The small-sized nanoparticles can deeply and effectively penetrate into the wood, altering its surface chemistry, improving its properties, and therefore, resulting in a hyper-performance product.

Mini submersible pump assisted sonochemical reactors: Large-scale synthesis of zinc oxide nanoparticles and nanoleaves for antibacterial and anti-counterfeiting applications

Low cost, environmentally friendly and industrial-scale approaches for the synthesis of anti-counterfeiting and antibacterial materials are a challenging task. The current research reports novel and inexpensive approaches for the synthesis of zinc oxide nanostructures (ZnO-NSs) using Mini Submersible Pump (MSP) assisted sonochemical reactors. Zinc oxide nanoleaves (ZnO-NLs) were synthesized using MSP assisted sonochemical mixing reactor at gram-scale (4 g). Zinc oxide nanoparticles (ZnO-NPs) were synthesized using MSP assisted sonochemical flow loop reactor at gram-scale (11.5 g). Synthesized ZnO-NSs were characterized by UV-visible spectroscopy, fluorescence spectroscopy, XRD, FTIR, TGA, BET, FEG-SEM, and FEG-TEM. Bare ZnO-NPs and ZnO-NPs coated cotton fabric showed high antibacterial activity against diseases causing Gram-positive bacteria Staphylococcus aureus. Based on the UV fluorescence property of the ZnO-NLs, invisible security ink was developed for anti-counterfeiting applications. The invisible security ink was tested as a rubber stamp and fountain pen inks which were found to be stable on the various kinds of microporous papers. As compared to our previously reported method, disperser assisted sonochemical approach for ZnO-NLs synthesis; the current approach reduces the cost of equipment used from ∼1700 to 4 USD. Both reactors are designed simply (less complicated), based on an environmentally friendly approach, highly scalable, increases the effectiveness of the sonochemical technique and suitable for industrial applications.

Zinc phosphate-based nanoparticles as a novel antibacterial agent: in vivo study on rats after dietary exposure

Background

Development of new nanomaterials that inhibit or kill bacteria is an important and timely research topic. For example, financial losses due to infectious diseases, such as diarrhea, are a major concern in livestock productions around the world. Antimicrobial nanoparticles (NPs) represent a promising alternative to antibiotics and may lower antibiotic use and consequently spread of antibiotic resistance traits among bacteria, including pathogens.

Results

Four formulations of zinc nanoparticles (ZnA, ZnB, ZnC, and ZnD) based on phosphates with spherical (ZnA, ZnB) or irregular (ZnC, ZnD) morphology were prepared. The highest in vitro inhibitory effect of our NPs was observed against Staphylococcus aureus (inhibitory concentration values, IC₅₀, ranged from 0.5 to 1.6 mmol/L), followed by Escherichia coli (IC₅₀ 0.8-1.5 mmol/L). In contrast, methicillin resistant S. aureus (IC₅₀ 1.2-4.7 mmol/L) was least affected and this was similar to inhibitory patterns of commercial ZnO-based NPs and ZnO. After the successful in vitro testing, the in vivo study with rats based on dietary supplementation with zinc NPs was conducted. Four groups of rats were treated by 2,000 mg Zn/kg diet of ZnA, ZnB, ZnC, and ZnD, for comparison two groups were supplemented by 2,000 mg Zn/kg diet of ZnO-N and ZnO, and one group (control) was fed only by basal diet. The significantly higher (P < 0.05) Zn level in liver and kidney of all treated groups was found, nevertheless Zn NPs did not greatly influence antioxidant status of rats. However, the total aerobic and coliform bacterial population in rat feces significantly decreased (P < 0.05) in all zinc groups after 30 d of the treatment. Furthermore, when compared to the ZnO group, ZnA and ZnC nanoparticles reduced coliforms significantly more (P < 0.05).

Conclusions

Our results demonstrate that phosphate-based zinc nanoparticles have the potential to act as antibiotic agents.

Visible light responsive flower-like ZnO in photocatalytic antibacterial mechanism towards Enterococcus faecalis and Micrococcus luteus

Flower-like ZnO micro/nanostructures were successfully fabricated via a surfactant-free co-precipitation method. The as-synthesized product was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL) analyses. In the presence of visible light irradiation, the as-synthesized flower-like ZnO showed higher antibacterial activities against Enterococcus faecalis (E. faecalis) and Micrococcus luteus (M. luteus) than that of commercial ZnO. The excellent antibacterial performance of synthesized flower-like ZnO was also observed via the bacterial morphological change, K⁺ ions leakage and protein leakage in extracellular suspension. In addition, the FTIR investigation on both treated bacteria further confirmed the bacterial membrane damage via cellular substance alteration. The enhancement of the antibacterial activity of synthesized ZnO can be attributed to the unique flower-like morphology which can increase the surface OH^- groups and the quantity of photogenerated electron-hole pair available to participate in the photocatalytic reaction. The reactive oxidizing species (ROS) scavengers experiments showed that H₂O₂ played a main role in the photocatalytic antibacterial process. Our study showed that the synthesized flower-like ZnO micro/nanostructures can act as efficient antibacterial agents in the photocatalytic antibacterial process under visible light irradiation.