Graphene Oxide Sheets Decorated with Octahedral Molybdenum Cluster Complexes for Enhanced Photoinactivation of Staphylococcus aureus.

The emergence of multidrug-resistant microbial pathogens poses a significant threat, severely limiting the options for effective antibiotic therapy. This challenge can be overcome through the photoinactivation of pathogenic bacteria using materials generating reactive oxygen species upon exposure to visible light. These species target vital components of living cells, significantly reducing the likelihood of resistance development by the targeted pathogens. In our research, we have developed a nanocomposite material consisting of an aqueous colloidal suspension of graphene oxide sheets adorned with nanoaggregates of octahedral molybdenum cluster complexes. The negative charge of the graphene oxide and the positive charge of the nanoaggregates promoted their electrostatic interaction in aqueous medium and close cohesion between the colloids. Upon illumination with blue light, the colloidal system exerted a potent antibacterial effect against planktonic cultures of Staphylococcus aureus largely surpassing the individual contributions of the components. The underlying mechanism behind this phenomenon lies in the photoinduced electron transfer from the nanoaggregates of the cluster complexes to the graphene oxide sheets, which triggers the generation of reactive oxygen species. Thus, leveraging the unique properties of graphene oxide and light-harvesting octahedral molybdenum cluster complexes can open more effective and resilient antibacterial strategies.

Electrospun PA6 Nanofibers Bearing the CeO2 Dephosphorylation Catalyst.

Two types of CeO2 nanoparticles (CeNPs) prepared by low-temperature (<100 °C) precipitation methods in water were successfully immobilized in a matrix of electrospun PA6 nanofibers. The colloidal solutions of CeNPs in AcOH were directly mixed with the polymer solution before the needle electrospinning process, thereby achieving their good dispersion in the nanofibers. CeNPs embedded in the structure and on the surface of nanofibers exposing their reactive surfaces showed robust dephosphorylation catalytic activity, as demonstrated by monitoring the hydrolytic cleavage of three phosphodiester molecules (p-NP-TMP, p-NPPC, BNPP) in water by the HPLC method. This procedure allowed us to study the kinetics and mechanism of the hydrolytic cleavage and the ability of immobilized CeNPs to cleave different types of P-O bonds. One of the main hydrolysis products, p-nitrophenol, was effectively adsorbed on PA6 nanofibers, which may allow the selective separation of the degradation products after hydrolysis.

Reusable and Antibacterial Polymer-Based Nanocomposites for the Adsorption of Dyes and the Visible-Light-Driven Photocatalytic Degradation of Antibiotics.

Adsorption and advanced oxidation processes, especially photocatalysis, are amongst the most common water treatment methodologies. Unfortunately, using each of these techniques independently does not fully eliminate the pollutants of diverse nature, which are present in wastewater. Here, an avenue for multifunctional materials for water treatment is opened by reporting for the first time the preparation, characterization, and study of the properties of a novel multifunctional nanocomposite with both adsorption and visible-light-driven photocatalysis abilities. These multifunctional nanocomposites, namely iron (II, III) oxide/poly(N-isopropylacrylamide-co-methacrylic acid)/silver-titanium dioxide (Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2), are prepared by combining magnetic polymeric microspheres (Fe3O4/P(NIPAM-co-MAA)) with silver-decorated titanium dioxide nanoparticles (Ag-TiO2 NPs). Cationic dyes, such as basic fuchsin (BF), can be adsorbed by the nanocomposites thanks to the carboxylic groups of Fe3O4/P(NIPAM-co-MAA) microspheres. Concomitantly, the presence of Ag-TiO2 NPs endows the system with the visible-light-driven photocatalytic degradation ability toward antibiotics such as ciprofloxacin (CIP) and norfloxacin (NFX). Furthermore, the proposed nanocomposites show antibacterial activity toward Escherichia coli (E. coli), thanks to the presence of silver nanoparticles (Ag NPs). Due to the superparamagnetic properties of iron (II, III) oxide nanoparticles (Fe3O4 NPs), the nanocomposites can be also recycled and reused, after the cleaning process, by using an external magnetic field.

Nickel-Decorated Mesoporous Iron-Cerium Mixed Oxides: Microstructure and Catalytic Activity in Methanol Decomposition.

Nickel-decorated mesoporous cerium-iron oxide composites were synthesized by a combination of incipient wetness impregnation and template-assisted hydrothermal techniques. The effects of the Fe/Ce ratio and the calcination temperature of cerium-iron oxides on the phase composition, texture, structure, and redox properties of the composites were studied by a combination of N2 physisorption, XRD, high-resolution transmission electron microscopy, SEM, Mössbauer, Raman, XPS, ultraviolet-visible and FTIR spectroscopies, H2-temperature-programmed reduction, and total oxidation of ethyl acetate as a catalytic test. The combined physicochemical characterization and in situ FTIR investigation of methanol decomposition was used for a proper understanding of the microstructure of the Ni/FeCe oxide composites and the mechanism of the reaction occurring on them. The complex role of the FeCe support in the stabilization of highly dispersed Ni particles, the generation of surface intermediates, and the impact of the support phase transformation under the reaction medium are discussed.

Cerium-Bismuth Oxides/Oxynitrates with Low Toxicity for the Removal and Degradation of Organophosphates and Bisphenols.

Nanoscale cerium-bismuth oxides/oxynitrates were prepared by a scalable low-temperature method at ambient pressure using water as the sole solvent. Solid solutions were formed up to a 1:1 Ce/Bi molar ratio, while at higher doping levels, bismuth oxynitrate photocatalysts with a pronounced layered structure were formed. Bismuth caused significant changes in the structure and surface properties of nanoceria, such as the formation of defects, oxygen-containing surface groups, and Lewis and Brønsted acid sites. The prepared bifunctional adsorbents/photocatalysts were efficient in the removal of toxic organophosphate (methyl paraoxon) from water by reactive adsorption followed by photocatalytic decomposition of the parent compound and its degradation product (p-nitrophenol). Bi-doped ceria also effectively adsorbed and photodegraded the endocrine disruptors bisphenols A and S and outperformed pure ceria and the P25 photocatalyst in terms of efficiency, durability, and long-term stability. The very low toxicity of Bi-nanoceria to mammalian cells, aquatic organisms, and bacteria has been demonstrated by comprehensive in vivo/in vitro testing, which, in addition to its simple "green" synthesis, high activity, and durability, makes Bi-doped ceria promising for safe use in abatement of toxic chemicals.

Enhanced visible-light photodegradation of fluoroquinolone-based antibiotics and E. coli growth inhibition using Ag-TiO2 nanoparticles.

Antibiotics in wastewater represent a growing and worrying menace for environmental and human health fostering the spread of antimicrobial resistance. Titanium dioxide (TiO2) is a well-studied and well-performing photocatalyst for wastewater treatment. However, it presents drawbacks linked with the high energy needed for its activation and the fast electron-hole pair recombination. In this work, TiO2 nanoparticles were decorated with Ag nanoparticles by a facile photochemical reduction method to obtain an increased photocatalytic response under visible light. Although similar materials have been reported, we advanced this field by performing a study of the photocatalytic mechanism for Ag-TiO2 nanoparticles (Ag-TiO2 NPs) under visible light taking in consideration also the rutile phase of the TiO2 nanoparticles. Moreover, we examined the Ag-TiO2 NPs photocatalytic performance against two antibiotics from the same family. The obtained Ag-TiO2 NPs were fully characterised. The results showed that Ag NPs (average size: 23.9 ± 18.3 nm) were homogeneously dispersed on the TiO2 surface and the photo-response of the Ag-TiO2 NPs was greatly enhanced in the visible light region when compared to TiO2 P25. Hence, the obtained Ag-TiO2 NPs showed excellent photocatalytic degradation efficiency towards the two fluoroquinolone-based antibiotics ciprofloxacin (92%) and norfloxacin (94%) after 240 min of visible light irradiation, demonstrating a possible application of these particles in wastewater treatment. In addition, it was also proved that, after five Ag-TiO2 NPs re-utilisations in consecutive ciprofloxacin photodegradation reactions, only a photocatalytic efficiency drop of 8% was observed. Scavengers experiments demonstrated that the photocatalytic mechanism of ciprofloxacin degradation in the presence of Ag-TiO2 NPs is mainly driven by holes and ˙OH radicals, and that the rutile phase in the system plays a crucial role. Finally, Ag-TiO2 NPs showed also antibacterial activity towards Escherichia coli (E. coli) opening the avenue for a possible use of this material in hospital wastewater treatment.

Laser-Induced Modification of Hydrogenated Detonation Nanodiamonds in Ethanol.

Apart from the frequently used high-temperature annealing of detonation nanodiamonds (DNDs) in an inert environment, laser irradiation of DNDs in a liquid can be effectively used for onion-like carbon (OLC) formation. Here, we used fully de-aggregated hydrogenated DNDs (H-DNDs) dispersed in ethanol, which were irradiated for up to 60 min using a 532 nm NdYAG laser with an energy of 150 mJ in a pulse (5 J/cm2) at a pulse duration of 10 ns and a repetition rate of 10 Hz. We investigated the DND surface chemistry, zeta potential, and structure as a function of laser irradiation time. Infrared spectroscopy revealed a monotonical decrease in the C-Hx band intensities and an increase of the C-O and C=O features. Transmission electron microscopy (TEM) revealed the formation of OLC, as well as a gradual loss of nanoparticle character, with increasing irradiation time. Surprisingly, for samples irradiated up to 40 min, the typical and unchanged DND Raman spectrum was recovered after their annealing in air at 450 °C for 300 min. This finding indicates the inhomogeneous sp3 to sp2 carbon transformation during laser irradiation, as well as the insensitivity of DND Raman spectra to surface chemistry, size, and transient structural changes.

Formation of Catalytic Active Sites in Hydrothermally Obtained Binary Ceria-Iron Oxides: Composition and Preparation Effects.

A series of mesoporous cerium-iron binary oxides was prepared by a hydrothermal technique using CTAB as a template. The influence of the Fe/Ce ratio and the variations in the preparation techniques such as the type of solvent and the precipitation agent, the approach of the template release, and the temperature of calcination on the phase composition, textural, structural, surface, and redox properties of the obtained materials was studied in details by XRD, nitrogen physisorption, TPR, FTIR, UV-vis, XPS, Raman, and Moessbauer spectroscopies. The materials were tested as catalysts in methanol decomposition and total oxidation of ethyl acetate. It was assumed that the binary materials represented a complex mixture of differently substituted ceria- and hematite-like phases. Critical assessment of their formation on the base of a common mechanism scheme was proposed. This scheme declares the key role of the formation of shared Ce-O-Fe structures by insertion of Fe3+ in the ceria lattice and further competitive compensation of the lattice charge balance by the existing in the system ions, which could be controlled by the Fe/Ce ratio and the hydrothermal synthesis procedure used. This mechanism provides proper understanding and regulation of the catalytic behavior of cerium-iron oxide composites in methanol decomposition with a potential for hydrogen production and total oxidation of ethyl acetate as a model of VOCs.

Crucial cytotoxic and antimicrobial activity changes driven by amount of doped silver in biocompatible carbon nitride nanosheets.

The use of Ag-modified nanomaterials continues to attract attention in biological contamination control, their potential cytotoxicity is often overlooked. Herein, biocompatible carbon nitride is modified with 1 and 5 wt.% Ag and effects of different nanomaterial dose and Ag content on antimicrobial activity and cytotoxicity is studied. Pure Ag nanoparticles and AgNO3 is tested for comparison, together with ten bacterial strains including pan-resistant Pseudomonas aeruginosa. Cytotoxicity is then investigated in three adherent and two suspension human cell lines, and results confirm that cancer adherent cell lines are the most immune lines and human cervical adenocarcinoma cells (HeLa) are more resilient than human lung adenocarcinoma cells (A549). The HeLa remains over 90 % viable even after 24 -h treatment with the highest concentration of 5%Ag/g-C3N4 (300 mg L-1) while A549 sustained viability only up to 100 mg L-1. Higher concentrations then induce cytotoxicity and A549 cell viability decreases. Our results show the importance of complementary testing of cytotoxicity by LIVE/DEAD assay using flow cytometry with more different human cell lines, which might be less immune to tested nanomaterials than HeLa and A549. Combined controls of new antibacterial agent activity tests then provide increased knowledge of their biocompatibility.

Salt-washed graphene oxide and its cytotoxicity.

The carbon nanomaterials and congeners, e.g., graphene or graphene oxide (GO), dispose of numerous unique properties, which are not necessarily intrinsic but might be related to a content of impurities. The oxidation step of GO synthesis introduces a considerable amount of metallic species. Therefore, large-scale purification is an actual scientific challenge. Here we describe new purification technique (salt­washing), which is based on three consecutive steps: (a) aggregation of GO sheets with NaCl (b) washing of the aggregates and (c) removing of the salt to afford purified GO (swGO). The considerably improved purity of swGO was demonstrated by ICP and EPR spectroscopy. The microscopic methods (TEM with SEAD, AFM) proved that the salt-washing does not affect the morphology or concentration of defects, showing the aggregation of GO with NaCl is fully reversible. The eligibility of swGO for biomedical applications was tested using fibroblastic cell cultures. The determined IC50 values clearly show a strong correlation between the purity of samples and cytotoxicity. Although the purification decreases cytotoxicity of GO, the IC50 values are still low proving that cytotoxic effect is not only impurities-related but also an intrinsic property. These findings may represent a serious limitation for usage of GO in biomedical applications.

Room-temperature synthesis of nanoceria for degradation of organophosphate pesticides and its regeneration and reuse.

A simple low-temperature water-based and one-pot synthesis was developed for the preparation of nanocrystalline CeO2 that was used for degradation of the toxic organophosphate pesticide parathion methyl. By changing the reaction temperature in the range from 5 °C to 95 °C, several properties (i.e., crystallinity, grain size and surface area) of nanoceria can be easily controlled. The catalytic decomposition of parathion methyl to its degradation product 4-nitrophenol was highly dependent on the CeO2 preparation temperature. It was demonstrated that at low temperature (i.e. 5 °C), CeO2 with very small crystallites (<2 nm) and high surface area can be obtained. For practical use, it was demonstrated that highly crystalline CeO2 can be prepared at room-temperature (30 °C) in at least 100 g batches. It was shown that precipitated nanoceria had high thermal stability and its post-synthesis annealing up to 400 °C did not significantly alter the material properties and hence the catalytic activity. Furthermore, as shown by the reusability tests, the sorbent can be reactivated by simply washing with water which demonstrated its durability.