In vitro cytotoxicity evaluation of resveratrol-loaded nanoparticles: Focus on the challenges of in vitro methodologies

Assessment of toxic effects is mandatory before market placement of pharmaceutical and cosmetic products. Nanotoxicology is an emerging regulatory concern and still a challenging field. Topical application of resveratrol (RSV) has been extensively studied owing to its multi-mechanistic skin anti-aging effects. Nanoencapsulation has been suggested as a promising solution to overcome RSV stability issues. In this work RSV-loaded solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) were prepared using a homogenization/sonication technique. Cytotoxicity assays were conducted with an immortalized cell line of human keratinocytes (HaCaT). For a comprehensive cytotoxicity characterization MTT and Alamar Blue^® reduction assays (assessment of metabolic activity), Neutral red uptake (evaluation of lysosomal integrity), and Trypan blue (assessment of membrane integrity) were used. The results obtained with the different assays were not always concordant, as put in evidence by an adequate statistical analysis. Experimental parameters such as washing steps were found to be critical. The study is of interest because it draws attention to the importance of careful selected experimental conditions of in vitro nanotoxicological tests. Experimental protocols should be adapted taking into account nano-related features such as interference with the dyes and light dispersion/absorption properties.

Effect of cobalt loading on the solid state properties and ethyl acetate oxidation performance of cobalt-cerium mixed oxides

Cobalt-cerium mixed oxides were prepared by the wet impregnation method and evaluated for volatile organic compounds (VOCs) abatement, using ethyl acetate (EtAc) as model molecule. The impact of Co content on the physicochemical characteristics of catalysts and EtAc conversion was investigated. The materials were characterized by various techniques, including N₂ adsorption at -196°C, scanning electron microscopy (SEM), X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) to reveal the structure-activity relationship. The obtained results showed the superiority of mixed oxides compared to bare CeO₂ and Co₃O₄, demonstrating a synergistic effect. The optimum oxidation performance was achieved with the sample containing 20wt.% Co (Co/Ce atomic ratio of ca. 0.75), in which complete conversion of EtAc was attained at 260°C. In contrast, temperatures above 300°C were required to achieve 100% conversion over the single oxides. Notably, a strong relationship between both the: (i) relative population, and (ii) facile reduction of lattice oxygen with the ethyl acetate oxidation activity was found, highlighting the key role of loosely bound oxygen species on VOCs oxidation. A synergistic Co-Ce interaction can be accounted for the enhanced reducibility of mixed oxides, linked with the increased mobility of lattice oxygen.

Highly efficient and reusable CNT supported iron(ii) catalyst for microwave assisted alcohol oxidation

The highly efficient eco-friendly synthesis of ketones (yields over 99%) from secondary alcohols is achieved by combination of [FeCl2{η(3)-HC(pz)3}] (pz = pyrazol-1-yl) supported on functionalized multi-walled carbon nanotubes and microwave irradiation, in a solvent-free medium. The carbon homoscorpionate iron(ii) complex is the first one of this class to be used as catalyst for the oxidation of alcohols.

Molybdenum Carbide Nanoparticles on Carbon Nanotubes and Carbon Xerogel: Low-Cost Cathodes for Hydrogen Production by Alkaline Water Electrolysis

Low-cost molybdenum carbide (Mo2 C) nanoparticles supported on carbon nanotubes (CNTs) and on carbon xerogel (CXG) were prepared and their activity for the hydrogen evolution reaction (HER) was evaluated in 8 m KOH aqueous electrolyte at 25-85 °C. Measurements of the HER by linear scan voltammetry allowed us to determine Tafel slopes of 71 and 74 mV dec(-1) at 25 °C for Mo2 C/CNT and Mo2 C/CXG, respectively. Stability tests were also performed, which showed the steady performance of the two electrocatalysts. Moreover, the HER kinetics at Mo2 C/CNT was enhanced significantly after the long-term stability tests. The specific activity of both materials was high, and a higher stability was obtained for the activated Mo2 C/CNT (40 A g(-1) at -0.40 V vs. the reversible hydrogen electrode).

Graphene oxide based ultrafiltration membranes for photocatalytic degradation of organic pollutants in salty water

Flat sheet ultrafiltration (UF) membranes with photocatalytic properties were prepared with lab-made TiO2 and graphene oxide-TiO2 (GOT), and also with a reference TiO2 photocatalyst from Evonik (P25). These membranes were tested in continuous operation mode for the degradation and mineralization of a pharmaceutical compound, diphenhydramine (DP), and an organic dye, methyl orange (MO), under both near-UV/Vis and visible light irradiation. The effect of NaCl was investigated considering simulated brackish water (NaCl 0.5 g L(-1)) and simulated seawater (NaCl 35 g L(-1)). The results indicated that the membranes prepared with the GOT composite (M-GOT) exhibited the highest photocatalytic activity, outperforming those prepared with bare TiO2 (M-TiO2) and P25 (M-P25), both inactive under visible light illumination. The best performance of M-GOT may be due to the lower band-gap energy (2.9 eV) of GOT. In general, the permeate flux was also higher for M-GOT probably due to a combined effect of its highest photocatalytic activity, highest hydrophilicity (contact angles of 11°, 17° and 18° for M-GOT, M-TiO2 and M-P25, respectively) and higher porosity (71%). The presence of NaCl had a detrimental effect on the efficiency of the membranes, since chloride anions can act as hole and hydroxyl radical scavengers, but it did not affect the catalytic stability of these membranes. A hierarchically ordered membrane was also prepared by intercalating a freestanding GO membrane in the structure of the M-GOT membrane (M-GO/GOT). The results showed considerably higher pollutant removal in darkness and good photocatalytic activity under near-UV/Vis and visible light irradiation in continuous mode experiments.

Modification of the surface chemistry of single- and multi-walled carbon nanotubes by HNO3 and H2SO4 hydrothermal oxidation for application in direct contact membrane distillation

A specific methodology based on nitric acid hydrothermal oxidation was used to control the surface chemistry of multi-walled (MWCNTs) and single-walled (SWCNTs) carbon nanotubes (CNTs) with different lengths, and this methodology was adapted to the use of sulphuric acid containing ammonium persulfate as an oxidizing agent. The amount of oxygen-containing surface groups depends on the number and length of the graphene layers of the CNTs, thicker and shorter CNTs having more reactive sites for surface functionalization. In particular, the oxidation of MWCNTs was more pronounced than that of short SWCNTs and less surface groups were introduced into long SWCNTs, regardless of the acid used at any fixed concentration. It was also possible to tailor the surface chemistry of both SWCNTs and MWCNTs by using the adopted methodologies, and the amount of both oxygen- and sulphur-containing functional groups was correlated with the concentration of each oxidizing agent used. Mathematical functions that allow precise control of the amount and type of the surface groups introduced into carbon nanotubes were obtained. Buckypapers were also prepared over a polytetrafluoroethylene commercial membrane. These membranes were tested in direct contact membrane distillation and, under salinity conditions, the membrane prepared using oxidized MWCNTs (instead of SWCNTs) was the most efficient, the permeate flux of the commercial membrane significantly increasing in the presence of these CNTs, while completely rejecting chloride ions. In addition, the permeate flux was precisely correlated with the amount of oxygenated functional surface groups (as well as with the pH of point of zero charge) of the oxidized MWCNTs.

Redox properties and VOC oxidation activity of Cu catalysts supported on Ce₁-xSmxOδ mixed oxides

A series of Cu catalysts supported on Ce1-xSmxOδ mixed oxides with different molar contents (x=0, 0.25, 0.5, 0.75 and 1), was prepared by wet impregnation and evaluated for volatile organic compounds (VOC) abatement, employing ethyl acetate as model molecule. An extensive characterization study was undertaken in order to correlate the morphological, structural and surface properties of catalysts with their oxidation activity. The optimum performance was obtained with Cu/CeO2 catalyst, which offers complete conversion of ethyl acetate into CO2 at temperatures as low as 260°C. The catalytic performance of Cu/Ce1-xSmxOδ was interpreted on the basis of characterization studies, showing that incorporation of samarium in ceria has a detrimental effect on the textural characteristics and reducibility of catalysts. Moreover, high Sm/Ce atomic ratios (from 1 to 3) resulted in a more reduced copper species, compared to CeO2-rich supports, suggesting the inability of these species to take part in the redox mechanism of VOC abatement. Sm/Ce surface atomic ratios are always much higher than the nominal ratios indicating an impoverishment of catalyst surface in cerium oxide, which is detrimental for VOC activity.

Design of graphene-based TiO2 photocatalysts--a review

There is a recent increase in the interest of designing high-performance photocatalysts using graphene-based materials. This review gathers some important aspects of graphene-TiO(2), graphene oxide-TiO(2), and reduced graphene oxide-TiO(2) composites, which are of especial relevance as next generation photocatalysts. The methods used for the preparation of these materials, the associated mechanistic fundamentals, and the application of graphene-based composites on the photocatalytic degradation of pollutants are reviewed. Some structural, textural, and chemical properties of these materials and other photo-assisted applications, such as hydrogen production from water splitting and dye-sensitized solar cells, are also briefly included.