Optimizing Antimicrobial Efficacy: Investigating the Impact of Zinc Oxide Nanoparticle Shape and Size.

Zinc oxide nanoparticles (ZnO NPs) have been investigated due to their distinct properties, variety of structures and sizes, and mainly for their antimicrobial activity. They have received a positive safety evaluation from the European Food Safety Authority (EFSA) for packaging applications as transparent ultraviolet (UV) light absorbers based on the absence of significant migration of zinc oxide in particulate form. ZnO NPs with different morphologies (spherical, flower, and sheet) have been synthesized via different sol-gel methods and extensively characterized by several solid-state techniques, namely vibrational spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), Fourier Transform Infrared Spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-VIS), electron paramagnetic resonance (EPR), and nitrogen adsorption-desorption isotherms. The ZnO NPs were assessed for their antibacterial activity against Escherichia coli (gram-negative bacteria) and Staphylococcus aureus (gram-positive bacteria) to study the influence of morphology and size on efficacy. ZnO NPs with different morphologies and sizes demonstrated antimicrobial activity against both bacteria. The highest microbial cell reduction rate (7-8 log CFU mL-1 for E. coli and 6-7 log CFU mL-1 for S. aureus) was obtained for the sheet- and spherical-shaped NPs as a result of the high specific surface area. In fact, the higher surface areas of the sheet- and spherical-shaped nanoparticles (18.5 and 13.4 m2 g-1, respectively), compared to the flower-shaped NPs (5.3 m2g-1), seem to promote more efficient bacterial cell reduction. The spherical-shaped particles were also smaller (31 nm) compared with the flower-shaped (233 × 249 nm) ones. The flower ZnO NP resulted in a 4-5 log CFU mL-1 reduction for E. coli and 3-4 log CFU mL-1 reduction for S. aureus. The lower apparent antibacterial activity of the flower-shaped could be associated with either the lack of defects on the particle core or the shape shielding effect. Compared to S. aureus, E. coli seems to be less resistant to ZnO NPs, which may be explained by the characteristics of its cell membrane. With simple synthesis techniques, which do not allow the size and shape of the nanoparticles to be controlled simultaneously, it is a challenge to elucidate the effect of each of these two parameters on antibacterial performance.

Tailoring of Mesoporous Silica-Based Materials for Enhanced Water Pollutants Removal.

The adsorptive performance of mesoporous silica-based materials towards inorganic (metal ions) and organic (dyes) water pollutants was investigated. Mesoporous silica materials with different particle size, surface area and pore volume were prepared and tailored with different functional groups. These materials were then characterised by solid-state techniques, namely vibrational spectroscopy, elemental analysis, scanning electron microscopy and nitrogen adsorption-desorption isotherms, allowing the successful preparation and structural modifications of the materials to be confirmed. The influence of the physicochemical properties of the adsorbents towards the removal of metal ions (Ni2+, Cu2+ and Fe3+) and organic dyes (methylene blue and methyl green) from aqueous solutions was also investigated. The results reveal that the exceptionally high surface area and suitable ζ-potential of the nanosized mesoporous silica nanoparticles (MSNPs) seem to favour the adsorptive capacity of the material for both types of water pollutants. Kinetic studies were performed for the adsorption of organic dyes by MSNPs and large-pore mesoporous silica (LPMS), suggesting that the process follows a pseudo-second-order model. The recyclability along consecutive adsorption cycles and the stability of the adsorbents after use were also investigated, showing that the material can be reused. Current results show the potentialities of novel silica-based material as a suitable adsorbent to remove pollutants from aquatic matrices with an applicability to reduce water pollution.

Iron(III) Arylhydrazone Complexes Immobilized on Amine-Functionalized Mesoporous Silica: Catalysts for the Valorization of Biomass-Derived Furfuryl Alcohol.

The aquasoluble FeIII complexes [Fe(H2 O)3 (L1 )] ⋅ 4H2 O (Fe1) and [Fe(H2 O)3 (L2 )] ⋅ 3H2 O (Fe2), bearing the basic forms of 5-chloro-3-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)-2-hydroxy-benzenesulfonic acid (H3 L1 ) and 3-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonic acid (H3 L2 ), were incorporated for the first time into amine-functionalized SBA-15 support via an impregnation method. The successful preparation of the composites was confirmed by Fourier-Transform Infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), scanning electron microscope (SEM/EDS), transmission electron microscopy (TEM), elemental analysis, and nitrogen adsorption-desorption isotherms. The resulting Fe1@aptesSBA-15 and Fe2@aptesSBA-15 composites were tested as the first SBA-15-based heterogeneous catalysts for the conversion of furfuryl alcohol under mild reaction conditions (80 to 100 °C) and with an environmentally friendly oxidant (TBHP, 70 % aq. sol. with 1 : 1 oxidant/substrate molar ratio). The influence of various factors, such as reaction time, amounts of oxidant and catalyst, was investigated. The reaction time can be fairly reduced by adopting a microwave-assisted method allowing it to reach complete conversion after 0.25 h, in the absence of any added solvent or additive. Under these conditions, a vigorous furfuryl alcohol polymerization process occurred, with furfural as a by-product. Recycling studies were carried out for Fe2@aptesSBA-15 and after four consecutive runs, the overall conversion of furfuryl alcohol remained high (≥99 %), without an appreciable change in the obtained yield.

Lindqvist@Nanoporous MOF-Based Catalyst for Effective Desulfurization of Fuels.

An effective and sustainable oxidative desulfurization process for treating a multicomponent model fuel was successfully developed using as a heterogeneous catalyst a composite material containing as an active center the europium Lindqvist [Eu(W5O18)2]9- (abbreviated as EuW10) encapsulated into the nanoporous ZIF-8 (zeolitic imidazolate framework) support. The EuW10@ZIF-8 composite was obtained through an impregnation procedure, and its successful preparation was confirmed by various characterization techniques (FT-IR, XRD, SEM/EDS, ICP-OES). The catalytic activity of the composite and the isolated EuW10 was evaluated in the desulfurization of a multicomponent model fuel containing dibenzothiophene derivatives (DBT, 4-MDBT and 4,6-DMDBT) with a total sulfur concentration of 1500 ppm. Oxidative desulfurization was performed using an ionic liquid as extraction solvent and aqueous hydrogen peroxide as oxidant. The catalytic results showed a remarkable desulfurization performance, with 99.5 and 94.7% sulfur removal in the first 180 min, for the homogeneous active center EuW10 and the heterogeneous EuW10@ZIF-8 catalysts, respectively. Furthermore, the stability of the nanocomposite catalyst was investigated by reusing and recycling processes. A superior retention of catalyst activity in consecutive desulfurization cycles was observed in the recycling studies when compared with the reusing experiments. Nevertheless, the nanostructure of ZIF-8 incorporating the active POM (polyoxometalate) was shown to be highly suitable for guaranteeing the absence of POM leaching, although structural modification was found for ZIF-8 after catalytic use that did not influenced catalytic performance.

Mesoporous Silica vs. Organosilica Composites to Desulfurize Diesel.

The monolacunary Keggin-type [PW11O39]7- (PW11) heteropolyanion was immobilized on porous framework of mesoporous silicas, namely SBA-15 and an ethylene-bridged periodic mesoporous organosilica (PMOE). The supports were functionalized with a cationic group (N-trimethoxysilypropyl-N, N, N-trimethylammonium, TMA) for the successful anchoring of the anionic polyoxometalate. The PW11@TMA-SBA-15 and PW11@TMA-PMOE composites were evaluated as heterogeneous catalysts in the oxidative desulfurization of a model diesel. The PW11@TMA-SBA-15 catalyst showed a remarkable desulfurization performance by reaching ultra-low sulfur levels (<10 ppm) after only 60 min using either a biphasic extractive and catalytic oxidative desulfurization (ECODS) system (1:1 MeCN/diesel) or a solvent-free catalytic oxidative desulfurization (CODS) system. Furthermore, the mesoporous silica composite was able to be recycled for six consecutive cycles without any apparent loss of activity. The promising results have led to the application of the catalyst in the desulfurization of an untreated real diesel supplied by CEPSA (1,335 ppm S) using the biphasic system. The system has proved to be a highly efficient process by reaching desulfurization values higher than 90% for real diesel during three consecutive cycles.

Multifunctionality in Two Families of Dinuclear Lanthanide(III) Complexes with a Tridentate Schiff-Base Ligand.

The employment of N-(2-carboxyphenyl)salicylideneimine in 4f metal chemistry has led to two families of dinuclear complexes depending on the lanthanide(III) used. Representative members exhibit interesting magnetic, optical, and catalytic properties.

Improving the Catalytic Performance of Keggin [PW12O40]3- for Oxidative Desulfurization: Ionic Liquids versus SBA-15 Composite.

Different methodologies were used to increase the oxidative desulfurization efficiency of the Keggin phosphotungstate [PW12O40]3- (PW12). One possibility was to replace the acid proton by three different ionic liquid cations, forming the novel hybrid polyoxometalates: [BMIM]3PW12 (BMIM as 1-butyl-3-methylimidazolium), [BPy]3PW12 (BPy as 1-butylpyridinium) and [HDPy]3PW12 (HDPy as hexadecylpyridinium. These hybrid Keggin compounds showed high oxidative desulfurization efficiency in the presence of [BMIM]PF6 solvent, achieving complete desulfurization of multicomponent model diesel (2000 ppm of S) after only 1 h, using a low excess of oxidant (H2O2/S = 8) at 70 °C. However, their stability and activity showed some weakness in continuous reused oxidative desulfurization cycles. An improvement of stability in continuous reused cycles was reached by the immobilization of the Keggin polyanion in a strategic positively-charged functionalized-SBA-15 support. The PW12@TM⁻SBA-15 composite (TM is the trimethylammonium functional group) presented similar oxidative desulfurization efficiency to the homogeneous IL⁻PW12 compounds, having the advantage of a high recycling capability in continuous cycles, increasing its activity from the first to the consecutive cycles. Therefore, the oxidative desulfurization system catalyzed by the Keggin-type composite has high performance under sustainable operational conditions, avoids waste production during recycling and allows catalyst recovery.

Production of ultra-deep sulfur-free diesels using a sustainable catalytic system based on UiO-66(Zr).

The porous metal-organic framework UiO-66(Zr) obtained via non modulated synthesis, has revealed to be a notable heterogeneous catalyst, enabling extremely fast and very efficient desulfurization of a multicomponent model diesel and also a real diesel fuel.

Novel polyoxometalate silica nano-sized spheres: efficient catalysts for olefin oxidation and the deep desulfurization process.

A novel method to prepare silica nano-sized particles incorporating polyoxometalates was developed leading to a new efficient heterogeneous oxidative catalyst. Zinc-substituted polyoxotungstate [PW11Zn(H2O)O39](5-) (PW11Zn) was encapsulated into silica nanoparticles using a cross-linked organic-inorganic core, performed through successive spontaneous reactions in water. The potassium salt of PW11Zn and the composite formed, PW11Zn-APTES@SiO2, were characterized by a myriad of solid-state methods such as FT-IR, FT-Raman, (31)P and (13)C CP/MAS solid-state NMR, elemental analysis and SEM-EDS, confirming the integrity of the PW11Zn structure immobilized in the silica nanoparticles. The new composite has shown to be a versatile catalyst for the oxidation of olefins and also to catalyze the desulfurization of a model oil using H2O2 as the oxidant and acetonitrile as the solvent. The novel composite material was capable of being recycled without significant loss of activity and maintaining its structural stability for consecutive desulfurization and olefin oxidative cycles.

Dinuclear lanthanide(III) complexes by metal-ion-assisted hydration of di-2-pyridyl ketone azine.

The initial employment of di-2-pyridyl ketone azine in 4f metal chemistry has led to a unique ligand transformation; the resulting anionic ligand is able to bridge two Ln(III) ions, affording neutral and cationic dinuclear complexes with interesting properties.

FT-IR, FT-Raman, SERS and computational study of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole.

FT-IR, FT-Raman and surface-enhanced Raman scattering spectra of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian09 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution calculations. The presence of CH(2), SO(2) and CH(3) modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface which affects the orientation and metal molecule interaction. The synthesis, NMR spectra and antibacterial properties are reported. The title compound shows more inhibitory effect against Pseudomonas aeruginosa than ampicillin and found to be more potent against Klebsiella pneumoniae and drug-resistant Bacillus subtilis than the other microorganisms. A computation of the first hyperpolarizability indicates that the compound may be a good candidate as a NLO material. The RMS errors of the observed Raman and IR bands are found to be 30.93, 29.77 for HF and 9.57, 6.75 for DFT methods, respectively.

IR, Raman and SERS spectra of 2-phenoxymethylbenzothiazole.

The FT-IR and FT-Raman spectra of 2-phenoxymethylbenzothiazole were recorded and analyzed. The surface enhanced Raman scattering (SERS) spectrum was recorded in a silver colloid. The vibrational wavenumbers of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values. The appearance of the Ag-O stretching mode at 237cm(-1) in the SERS spectrum along with theoretically calculated atomic charge density, leads us to suggest that the molecule is adsorbed through the oxygen atom with the molecular plane tilted on the colloidal silver surface. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory.