Photocatalytic production of 1O2 and *OH mediated by silver oxidation during the photoinactivation of Escherichia coli with TiO2

Development of environmentally friendly catalyst Ag-ZnO@cellulose acetate derived from discarded cigarette butts for reduction of organic dyes and its antibacterial applications

The release of harmful organic dyes from different industries besides its degradation products is a major contributor to environmental contamination. The catalytic reduction of these organic pollutants using nanocomposites based on polymeric material presents potential advantages for the environment. In this study, novel nanocomposite based on cellulose acetate (CA)-derived from discharged cigarette butts and zinc oxide nanoparticles (ZnO NPs) was prepared utilizing a very simple and low-cost solution blending method and used as support for silver nanoparticles (Ag NPs). A simple reduction method was used to anchor different percentages of Ag NPs on the ZnO@CA nanocomposite surface via utilizing sodium borohydride as a reducing agent. The Ag-ZnO@CA nanocomposite was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The TEM analysis showed spherical Ag NPs, with an average diameter of ∼17.6 nm, were uniformly anchored on the ZnO@CA nanocomposite surface. The prepared nanocomposites were evaluated as catalysts for the reduction of organic dyes in water. It was found that 10 % Ag-ZnO@CA nanocomposite showed a remarkable reduction of Rhodamine B (RhB), Rhodamine 6G (Rh6G), Methylene Blue (MB), and Sunset Yellow (SY) dyes in short time. In the presence of this nanocomposite, the rate constant, kapp values for RhB, Rh6G, MB, and SY were 0.3498 min-1, 1.51 min-1, 0.2292 min-1, and 0.733 min-1, respectively. This nanocomposite was recovered and reused in five successive cycles, with a negligible loss of its activity. Furthermore, the nanocomposites demonstrated moderate antibacterial activity toward Staphylococcus aureus and Escherichia coli. Thus, this study directed attention on recycling of waste material to a valuable nanocomposite and its applications in environmental protection.

Synthesis and Catalytic Study of NiAg Bimetallic Core-Shell Nanoparticles

This publication presents the synthesis of core-shell nanoparticles, where the core was Ni, and the shell was a Ag-Ni nano alloy. The synthesis was based on the reduction of Ni and Ag ions with sodium borohydride in the presence of trisodium citrate as a stabilizer. In order to determine the phase composition of the obtained nanoparticles, an XRD study was performed, and in order to identify the oxidation states of the nanoparticle components, an XPS spectroscopic study was performed. The composition and shape of the particles were determined using the HR-TEM EDS test. The obtained nanoparticles had a size of 11 nm. The research on catalytic properties was carried out in the model methylene blue reduction system. The investigation of the catalytic activity of colloids was carried out with the use of UV-Vis spectrophotometry. The Ag-Ni alloy was about ten times more active than were pure silver nanoparticles of a similar size.

An approach to the photocatalytic mechanism in the TiO2-nanomaterials microorganism interface for the control of infectious processes

The approach of this timely review considers the current literature that is focused on the interface nanostructure/cell-wall microorganism to understand the annihilation mechanism. Morphological studies use optical and electronic microscopes to determine the physical damage on the cell-wall and the possible cell lysis that confirms the viability and microorganism death. The key parameters of the tailoring the surface of the photoactive nanostructures such as the metal functionalization with bacteriostatic properties, hydrophilicity, textural porosity, morphology and the formation of heterojunction systems, can achieve the effective eradication of the microorganisms under natural conditions, ranging from practical to applications in environment, agriculture, and so on. However, to our knowledge, a comprehensive review of the microorganism/nanomaterial interface approach has rarely been conducted. The final remarks point the ideal photocatalytic way for the effective prevention/eradication of microorganisms, considering the resistance that the microorganism could develop without the appropriate regulatory aspects for human and ecosystem safety.

Plasmonic Photocatalysts for Microbiological Applications

Wide-bandgap semiconductors modified with nanostructures of noble metals for photocatalytic activity under vis irradiation due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively investigated over the last decade. Most literature reports discuss the properties and activities of plasmonic photocatalysts for the decomposition of organic compounds and solar energy conversion. Although noble metals, especially silver and copper, have been known since ancient times as excellent antimicrobial agents, there are only limited studies on plasmonic photocatalysts for the inactivation of microorganisms (considering vis-excitation). Accordingly, this review has discussed the available literature reports on microbiological applications of plasmonic photocatalysis, including antibacterial, antiviral and antifungal properties, and also a novel study on other microbiological purposes, such as cancer treatment and drug delivery. Although some reports indicate high antimicrobial properties of these photocatalysts and their potential for medical/pharmaceutical applications, there is still a lack of comprehensive studies on the mechanism of their interactions with microbiological samples. Moreover, contradictory data have also been published, and thus more study is necessary for the final conclusions on the key-factor properties and the mechanisms of inactivation of microorganisms and the treatment of cancer cells.

Evaluating Weathering of Food Packaging Polyethylene-Nano-clay Composites: Release of Nanoparticles and their Impacts

Nano-fillers are increasingly incorporated into polymeric materials to improve the mechanical, barrier or other matrix properties of nanocomposites used for consumer and industrial applications. However, over the life cycle, these nanocomposites could degrade due to exposure to environmental conditions, resulting in the release of embedded nanomaterials from the polymer matrix into the environment. This paper presents a rigorous study on the degradation and the release of nanomaterials from food packaging composites. Films of nano-clay-loaded low-density polyethylene (LDPE) composite for food packaging applications were prepared with the spherilene technology and exposed to accelerated weathering of ultraviolet (UV) irradiation or low concentration of ozone at 40 °C. The changes in the structural, surface morphology, chemical and physical properties of the films during accelerated weathering were investigated. Qualitative and quantitative changes in properties of pristine and aged materials and the release of nano-clay proceeded slowly until 130 hr irradiation and then accelerated afterward resulting complete degradation. Although nano-clay increased the stability of LDPE and improved thermal and barrier properties, they accelerated the UV oxidation of LDPE. With increasing exposure to UV, the surface roughness, chemiluminescence index, and carbonyl index of the samples increased while decreasing the intensity of the wide-angle X-ray diffraction pattern. Nano-clay particles with sizes ranging from 2-8 nm were released from UV and ozone weathered composite. The concentrations of released nanoparticles increased with an increase in aging time. Various toxicity tests, including reactive oxygen species generation and cell activity/viability were also performed on the released nano-clay and clay polymer. The released nano-clays basically did not show toxicity. Our combined results demonstrated the degradation properties of nano-clay particle-embedded LDPE composites toxicity of released nano-clay particles to A594 adenocarcinomic human alveolar basal epithelial cells was observed, which will help with future risk based-formulations of exposure.

Electrospinning Cu–TiO2nanofibers used for photocatalytic disinfection of bacteriophage f2: preparation, optimization and characterization

Cu-Doped TiO₂nanofibers were prepared using the electrospinning method and applied for the disinfection of bacteriophage f2.

Synergistic photocatalytic inactivation mechanisms of bacteria by graphene sheets grafted plasmonic AgAgX (X = Cl, Br, I) composite photocatalyst under visible light irradiation

By coupling graphene sheet and plasmonic photocatalysis technologies, a series of AgAgX/RGOs (X = Cl, Br, I; RGO = reduced graphene oxide) composites were prepared and found to be efficient antimicrobial agents for water disinfection upon visible light. Attributed to the efficient charge transfer by RGO sheets, the optimum AgAgBr/0.5% RGO could completely inactivate 2 × 10(7) cfu mL(-1) of Escherichia coli within 8 min, much faster than bare AgAgBr within 35 min. The synergistic antimicrobial mechanism of AgAgBr/0.5% RGO was studied by Ag(+) ions release evaluation, radical scavengers study, and radical determination. The enhanced photocatalytic activity of irradiated AgAgBr/0.5% RGO originated from the synergistic activities of its three components including Ag, AgBr and RGO, and the proposed mechanisms contained enhanced attraction by RGO followed by two pathways: primary oxidative stress caused by plasma induced reactive species like H2O2 and bactericidal effect of released Ag(+) ions. Furthermore, characterization of E. coli cells using SEM, fluorescent microscopy, and cytoplasmic substance leakage illustrated that VL irradiated AgAgBr/0.5% RGO could not only cause metabolic dysfunction but also destroy the cell envelope and biomolecular, while irradiated Ag(+) ions play a differential bactericidal action with a limited metabolic injury and no cell-membrane damage. The present work provides an efficient water disinfection technology and also opens a new idea in studying the antimicrobial mechanism of plasmonic photocatalyst.

The role and synergistic effect of the light irradiation and H2O2 in photocatalytic inactivation of Escherichia coli

Inactivation of Escherichia coli K-12 was conducted by applying a continuous supplying of commercial H2O2 to mimic the H2O2 production in a photocatalytic system, and the contribution of H2O2 in photocatalytic inactivation was investigated using a modified "partition system" and five E. coli mutants. The concentration of exogenous H2O2 required for complete inactivation of bacterial cells was much higher than that produced in-situ in common photocatalytic system, indicating that H2O2 alone plays a minor role in photocatalytic inactivation. However, the concentration of exogenously produced H2O2 required for effective inactivation of E. coli K-12 was much lower when the light irradiation was applied. To further investigate the possible physiological changes, inactivation of E. coli BW25113 (the parental strain), and its corresponding isogenic single-gene deletion mutants with light pretreatment was compared. The results indicate that light irradiation increases the bacterial intracellular Fe(2+) level and favors hydroxyl radical (OH) production via the catalytic reaction of Fe(2+), leading to increase in DNA damage. Moreover, the results indicate that the properties of light source, such as intensity and major emission wavelength, may alter the physiology of bacterial cells and affect the susceptibility to in-situ resultant H2O2 in the photocatalytic inactivation processes, leading to significant influence on the photocatalytic inactivation efficiencies of E. coli K-12.

Controllable Synthesis and Tunable Photocatalytic Properties of Ti(3+)-doped TiO2

Photocatalysts show great potential in environmental remediation and water splitting using either artificial or natural light. Titanium dioxide (TiO2)-based photocatalysts are studied most frequently because they are stable, non-toxic, readily available, and highly efficient. However, the relatively wide band gap of TiO2 significantly limits its use under visible light or solar light. We herein report a facile route for controllable synthesis of Ti(3+)-doped TiO2 with tunable photocatalytic properties using a hydrothermal method with varying amounts of reductant, i.e., sodium borohydride (NaBH4). The resulting TiO2 showed color changes from light yellow, light grey, to dark grey with the increasing amount of NaBH4. The present method can controllably and effectively reduce Ti(4+) on the surface of TiO2 and induce partial transformation of anatase TiO2 to rutile TiO2, with the evolution of nanoparticles into hierarchical structures attributable to a high pressure and strong alkali environment in the synthesis atmosphere; in this way, the photocatalytic activity of Ti(3+)-doped TiO2 under visible-light can be tuned. The as-developed strategy may open up a new avenue for designing and functionalizing TiO2 materials for enhancing visible light absorption, narrowing band gap, and improving photocatalytic activity.

Enhanced visible-light-driven photocatalytic inactivation of Escherichia coli by Bi2O2CO3/Bi3NbO7 composites

The Bi2O2CO3/Bi3NbO7 (BiCO/BiNbO) composite was successfully fabricated by a simple hydrothermal method and found to be an effective visible-light-driven photocatalyst for inactivation of Escherichia coli (E. coli). The BiCO/BiNbO composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectrum (UV-vis DRS), and Fourier transform infrared (FT-IR) spectroscopy. The BiCO/BiNbO composite exhibited largely enhanced photocatalytic inactivation of E. coli as compared to the pure Bi3NbO7 under visible light irradiation. The enhanced photocatalytic performance can be attributed to the improved separation efficiency of the photogenerated holes and electrons. In addition, the possible bactericidal mechanism of the BiCO/BiNbO composite under visible light irradiation was discussed.