Exceptional performance of Fe@carbon-rich nanoparticles prepared via hydrothermal carbonization of oil mill wastes for H2S removal.

Carbon-encapsulated iron oxide nanoparticles (CE-nFe) have been obtained from an industrial waste (oil mill wastewater-OMW, as a carbonaceous source), and using iron sulfate as metallic precursor. In an initial step, the hydrochar obtained has been thermally activated under an inert atmosphere at three different temperatures (600 °C, 800 °C and 1000 °C). The thermal treatment promotes the development of core-shell nanoparticles, with an inner core of α-Fe/Fe3O4, surrounded by a well-defined graphite shell. Temperatures above 800 °C are needed to promote the graphitization of the carbonaceous species, a process promoted by iron nanoparticles through the dissolution, diffusion and growth of the carbon nanostructures on the outer shell. Breakthrough column tests show that CE-nFe exhibit an exceptional performance for H2S removal with a breakthrough capacity larger than 0.5-0.6 g H2S/gcatalyst after 3 days experiment. Experimental results anticipate the crucial role of humidity and oxygen in the adsorption/catalytic performance. Compared to some commercial samples, these results constitute a three-fold increase in the catalytic performance under similar experimental conditions.

Improved photocatalytic performance of TiO2/carbon photocatalysts: Role of carbon additive.

A series of TiO2 - based photocatalysts have been prepared by the incorporation of 10 wt% of various carbon-based nanomaterials as modifying agents to titania. More specifically, commercial TiO2 P25 was modified through a wet impregnation approach with methanol with four different carbon nanostructures: single-walled carbon nanotubes (SWCNTs), partially reduced graphene oxide (prGO), graphite (GI), and graphitic carbon nitride (gCN). Characterization results (XPS and Raman) anticipate the occurrence of important interfacial phenomena, preferentially for samples TiO2/SWCNT and TiO2/prGO, with a binding energy displacement in the Ti 2p contribution of 1.35 eV and 1.54 eV, respectively. These findings could be associated with an improved electron-hole mobility at the carbon/oxide interface. Importantly, these two samples constitute the most promising photocatalysts for Rhodamine B (RhB) photodegradation, with nearly 100% conversion in less than 2 h. These promising results must be associated with intrinsic physicochemical changes at the formed heterojunction structure and the potential dual-role of the composites able to adsorb and degrade RhB simultaneously. Cyclability tests confirm the improved performance of the composites (e.g., TiO2/SWCNT, 100% degradation in 1 h) due to the combined adsorption/degradation ability, although the regeneration after several cycles is not complete due to partial blocking of the inner cavities in the carbon nanotubes by non-reacted RhB. Under these reaction conditions, Rhodamine-B xanthene dye degrades via the de-ethylation route.

Controlling the Adsorption and Release of Ocular Drugs in Metal-Organic Frameworks: Effect of Polar Functional Groups.

A series of UiO-66 materials with different functional groups (-H, -NH2, and -NO2) have been evaluated for the adsorption and release of a common ocular drug such as brimonidine tartrate. UiO-66 samples were synthesized under solvothermal conditions and activated by solvent exchange with ethanol. Experimental results suggest that the incorporation of surface functionalities gives rise to the development of structural defects (missing linker defects) but without altering the basic topology of the UiO-66 framework. These defects improve the adsorption performance of the parent metal-organic framework (MOF), while the bulkier functionalities infer slower release kinetics, with the associated benefits for prolonged delivery of brimonidine. Among the evaluated MOFs, defective UiO-66-NO2 can be proposed as the most promising candidate due to the combination of a larger brimonidine volumetric uptake (680 mg/cm3), a prolonged delivery (period of up to 25 days), a small particle size, and a larger instability. Contrariwise, at high concentrations UiO-66-NO2 has higher toxicity toward human retinal pigment epithelium cells (ARPE-19) compared to the pure and NH2-functionalized UiO-66.

MOF-Based Polymeric Nanocomposite Films as Potential Materials for Drug Delivery Devices in Ocular Therapeutics.

Novel MOF-based polymer nanocomposite films were successfully prepared using Zr-based UiO-67 as a metal-organic framework (MOF) and polyurethane (PU) as a polymeric matrix. Synchrotron X-ray powder diffraction (SXRPD) analysis confirms the improved stability of the UiO-67 embedded nanocrystals, and scanning electron microscopy images confirm their homogeneous distribution (average crystal size ∼100-200 nm) within the 50 µm thick film. Accessibility to the inner porous structure of the embedded MOFs was completely suppressed for N2 at cryogenic temperatures. However, ethylene adsorption measurements at 25 °C confirm that at least 45% of the MOF crystals are fully accessible for gas-phase adsorption of nonpolar molecules. Although this partial blockage limits the adsorption performance of the embedded MOFs for ocular drugs (e.g., brimonidine tartrate) compared to the pure MOF, an almost 60-fold improvement in the adsorption capacity was observed for the PU matrix after incorporation of the UiO-67 nanocrystals. The UiO-67@PU nanocomposite exhibits a prolonged release of brimonidine (up to 14 days were quantified). Finally, the combined use of SXRPD, thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) analyses confirmed the presence of the drug in the nanocomposite film, the stability of the MOF framework and the drug upon loading, and the presence of brimonidine in an amorphous phase once adsorbed. These results open the gate toward the application of these polymeric nanocomposite films for drug delivery in ocular therapeutics, either as a component of a contact lens, in the composition of lacrimal stoppers (e.g., punctal plugs), or in subtenon inserts.

Tuning porosity in macroscopic monolithic metal-organic frameworks for exceptional natural gas storage.

Widespread access to greener energy is required in order to mitigate the effects of climate change. A significant barrier to cleaner natural gas usage lies in the safety/efficiency limitations of storage technology. Despite highly porous metal-organic frameworks (MOFs) demonstrating record-breaking gas-storage capacities, their conventionally powdered morphology renders them non-viable. Traditional powder shaping utilising high pressure or chemical binders collapses porosity or creates low-density structures with reduced volumetric adsorption capacity. Here, we report the engineering of one of the most stable MOFs, Zr-UiO-66, without applying pressure or binders. The process yields centimetre-sized monoliths, displaying high microporosity and bulk density. We report the inclusion of variable, narrow mesopore volumes to the monoliths' macrostructure and use this to optimise the pore-size distribution for gas uptake. The optimised mixed meso/microporous monoliths demonstrate Type II adsorption isotherms to achieve benchmark volumetric working capacities for methane and carbon dioxide. This represents a critical advance in the design of air-stable, conformed MOFs for commercial gas storage.

Gate-opening effect in ZIF-8: the first experimental proof using inelastic neutron scattering.

The gate-opening phenomenon in ZIFs is of paramount importance to understand their behavior in industrial molecular separations. Here we show for the first time using in situ inelastic neutron scattering (INS) the swinging of the -CH3 groups and the imidazolate linkers in the prototypical ZIF-8 and ZIF-8@AC hybrid materials upon exposure to mild N2 pressure.

Improved mechanical stability of HKUST-1 in confined nanospace.

One of the main concerns in the technological application of several metal-organic frameworks (MOFs) relates to their structural instability under pressure (after a conforming step). Here we report for the first time that mechanical instability can be highly improved via nucleation and growth of MOF nanocrystals in the confined nanospace of activated carbons.

Use of eutectic mixtures for preparation of monolithic carbons with CO2-adsorption and gas-separation capabilities.

With global warming becoming one of the main problems our society is facing nowadays, there is an urgent demand to develop materials suitable for CO2 storage as well as for gas separation. Within this context, hierarchical porous structures are of great interest for in-flow applications because of the desirable combination of an extensive internal reactive surface along narrow nanopores with facile molecular transport through broad "highways" leading to and from these pores. Deep eutectic solvents (DESs) have been recently used in the synthesis of carbon monoliths exhibiting a bicontinuous porous structure composed of continuous macroporous channels and a continuous carbon network that contains a certain microporosity and provides considerable surface area. In this work, we have prepared two DESs for the preparation of two hierarchical carbon monoliths with different compositions (e.g., either nitrogen-doped or not) and structure. It is worth noting that DESs played a capital role in the synthesis of hierarchical carbon monoliths not only promoting the spinodal decomposition that governs the formation of the bicontinuous porous structure but also providing the precursors required to tailor the composition and the molecular sieve structure of the resulting carbons. We have studied the performance of these two carbons for CO2, N2, and CH4 adsorption in both monolithic and powdered form. We have also studied the selective adsorption of CO2 versus CH4 in equilibrium and dynamic conditions. We found that these materials combined a high CO2-sorption capacity besides an excellent CO2/N2 and CO2/CH4 selectivity and, interestingly, this performance was preserved when processed in both monolithic and powdered form.

Catalytic nanomedicine: a new field in antitumor treatment using supported platinum nanoparticles. In vitro DNA degradation and in vivo tests with C6 animal model on Wistar rats.

Novel nanostructured TiO2 and SiO2 based biocatalysts, with 3-4 wt. % of Pt have been developed. The obtained materials exhibit a high surface area together with a broad pore size distribution. The method of synthesis allowed obtaining high dispersed platinum metal nanoparticles. In vitro DNA reactivity test of the biocatalysts were carried out by electrophoresis and formation of DNA adducts was observed. The most active biocatalyst was H2PtCl6/SiO2. These biocatalysts were also tested in an experimental model of C6 brain tumours in Wistar rats. Administration of the material was made by stereotactic brain surgery to place it directly in the malignant tissue. A significant decrease in tumour size and weight as well as morphologic changes in cancer cells were observed.