LED-driven controlled deposition of Ni onto TiO2 for visible-light expanded conversion of carbon dioxide into C1-C2 alkanes.

Photocatalytic gas-phase hydrogenation of CO2 into alkanes was achieved over TiO2-supported Ni nanoparticles under LED irradiation at 365 nm, 460 nm and white light. The photocatalysts were prepared using photo-assisted deposition of Ni salts under LED irradiation at 365 nm onto TiO2 P25 nanoparticles in methanol as a hole scavenger. This procedure yielded 2 nm Ni particles decorating the surface of TiO2 with a nickel mass content of about 2%. Before the photocatalytic runs, Ni/TiO2 was submitted to thermal reduction at 400 °C in a 10% H2 atmosphere which induced O-defective TiO2-x substrates. The formation of oxygen vacancies, Ti3+ centers and metallic Ni sites upon photocatalytic CO2 hydrogenation was confirmed by operando EPR analysis. In situ XPS under reaction conditions suggested a strong metal-support interaction and the co-existence of zero and divalent Ni states. These photoactive species enhanced the photo-assisted reduction of CO2 below 300 °C to yield CO, CH4 and C2H6 as final products.

Fast and simple assessment of surface contamination in operations involving nanomaterials.

The deposition of airborne nanosized matter onto surfaces could pose a potential risk in occupational and environmental scenarios. The incorporation of fluorescent labels, namely fluorescein isotiocyanate (FITC) or tris-1,3-phenanthroline ruthenium (II) chloride (Ru(phen)3Cl2), into spherical 80-nm silica nanoparticles allowed the detection after the illumination with LED light of suitable wavelength (365 or 405 nm respectively). Monodisperse nanoparticle aerosols from fluorescently labeled nanoparticles were produced under safe conditions using powder generators and the deposition was tested into different surfaces and filtering media. The contamination of gloves and work surfaces that was demonstrated by sampling and SEM analysis becomes immediately clear under laser or LED illumination. Furthermore, nanoparticle aerosols of about 105 nanoparticles/cm3 were alternatively fed through a glass pipe and personal protective masks to identify the presence of trapped nanoparticles under 405 nm or 365 nm LED light. This testing procedure allowed a fast and reliable estimation of the contamination of surfaces with nanosized matter, with a limit of detection based on the fluorescence emission of the accumulated solid nanoparticles of 40 ng of Ru(phen)3@SiO2 of silica per mg of non-fluorescent matter.

A versatile generator of nanoparticle aerosols. A novel tool in environmental and occupational exposure assessment.

The increasing presence of nanotechnology on the market entails a growing probability of finding ENMs in the environment. Nanoparticles aerosols are a yet unknown risk for human and environmental exposure that may normally occur at any point during the nanomaterial lifecycle. There is a research gap in standardized methods to assess the exposure to airborne nanoparticles in different environments. The controllable generation of nanoparticle aerosols has long been a challenging objective for researchers and industries dealing with airborne nanoparticles. In this work, a versatile system to generate nanoparticulate aerosols has been designed. The system allows the production of both i) instantaneous nanoparticle clouds and ii) continuous nanoparticle streams with quasi-stable values of particle concentration and size distribution. This novel device uses a compressed-air pressure pulse to disperse the target material into either the testing environment (instantaneous cloud formation) or a secondary chamber, from which a continuous aerosol stream can be drawn, with a tunable nanoparticle concentration. The system is robust, highly versatile and easy to operate, enabling reproducible generation of aerosols from a variety of sources. The system has been verified with four dry nanomaterials: TiO2, ZnO, CuO and CNT bundles.

Versatile hollow fluorescent metal-silica nanohybrids through a modified microemulsion synthesis route.

Silica-metal nanohybrids are common materials for applications in biomedicine, catalysis or sensing. Also, hollow structures are of interest as they provide additional useful features. However, in these materials the control of the size and accessibility to the inner regions of the structure usually requires complex synthesis procedures. Here we report a simple colloidal procedure for synthesizing hollow silica-metal nanohybrids, driven by the diffusion of metal precursors through the porous silica shell and subsequent reduction in aqueous solutions. The formation of hollow nanoparticles is controlled by the colloidal conditions during synthesis, which affect the ripening of hollow nanoparticles in presence of organosilanes. The modification of the conditions during synthesis affected the growth of silica precursors in presence of fluorescein isothiocyanate (FITC). The limited access to water molecules during the hydrolysis of silica precursors is attributed to the hydrophobicity of organic fluorescent molecules linked to the condensing silica clusters at the initial stages of nanoparticle formation and to the limitation of water content in the microemulsion method used. Finally, the growth of metal nanoseeds at the core of hollow nanoparticles can be easily achieved though a simple method in aqueous environment. The pH and thermal conditions during the reduction process affect the formation of metal-silica nanohybrids and their structural features.

Development of a self-cleaning dispersion and exposure chamber: application to the monitoring of simulated accidents involving the generation of airborne nanoparticles.

The release of hazardous nanoparticulate matter in accidental situations was simulated in a specially designed 13-m(3) stainless steel airtight chamber, which allowed the dispersion analysis of airborne matter in a practically particle-free environment (less than 2 #/cm(3)) and in presence of background atmospheric aerosols. A fast recovering of the initial situation was achieved by means of a tandem HEPA-filtered air and deionized water system. Both unintended spilling of silica-based nanoparticulate powders and continuous emission of 100-nm SiO2 nanoparticles were used as aerosol generation events. The emission of airborne nanoparticles was analyzed in terms of particle number concentrations (PNC), size distributions and source strengths. The emission of nanoparticulate aerosols reached peak PNC for particles in the range from 5 nm to 1 µm with source strengths about 10(8) #/h in a background-filled environment and 10(10) #/h in a practically particle-free atmosphere. No agglomeration was noticed for the released nanoparticles, suggesting that PNC was low enough to prevent coagulation and that particle diameters were over 80 nm. Results indicate that emitted matter was within the range of the most penetrating particle sizes and with source strengths similar to accidental scenarios.

Unintended emission of nanoparticle aerosols during common laboratory handling operations.

Common laboratory operations such as pouring, mashing in an agate mortar, transferring with a spatula, have been assessed as potential sources for emission of engineered nanoparticles in simulated occupational environments. Also, the accidental spilling from an elevated location has been considered. For workplace operations, masses of 1500 or 500mg of three dry-state engineered nanoparticles (SiO2, TiO2 and Ce-TiO2) with all dimensions under 30nm, and one fibrous nanomaterial (MWCNT) with diameter under 10nm and length about 1.5µm were used. The measured number emission factors (NEF) for every operation and material in this work were in the range of 10(5) #s(-1). The traceability of emitted nanoparticles has been improved using Ce-doping on TiO2 nanoparticles. With this traceable material it was possible to show that generated aerosol nanoparticles are rapidly associated with background particles to form large-sized aerosol agglomerates.

Intense generation of respirable metal nanoparticles from a low-power soldering unit.

Evidence of intense nanoparticle generation from a low power (45W) flux soldering unit is presented. This is a familiar device often used in daily life, including home repairs and school electronic laboratories. We demonstrate that metal-containing nanoparticles may reach high concentrations (ca. 10(6) particles/cm(3)) within the breathing range of the operator, with initial size distributions centered at 35-60nm The morphological and chemical analysis of nanoparticle agglomerates collected on TEM grids and filters confirms their multiparticle structure and the presence of metals.

Al-promoted increase of surface area and adsorption capacity in ordered mesoporous silica materials with a cubic structure.

The structure of ordered mesoporous materials presenting a cubic structure undergoes a strong modification after adding aluminium alkoxides to the synthesis gel. As a result, an outstanding increase in the surface area and pore volume is observed, together with changes in the mesopore ordering. Hydrated aluminium species influence the chemical environment of the micelles during synthesis, which seems to induce the accumulation of stacking faults in the mesopore framework, and give rise to closer structural packing. The adsorption and release of ibuprofen as a test molecule correlates well with the textural changes observed.

Surface electrochemistry of mesoporous silicas as a key factor in the design of tailored delivery devices.

The fundamental mechanisms of biologically active molecule adsorption and release from ordered mesoporous silica are discussed in terms of the variation of surface electrochemistry after functionalization. Specifically, ordered mesoporous SBA-15 has been grafted with aminopropyl, etilenediamine, phosphatoethyl, propyl methacrylate, and carboxylic acid groups at different degrees of functionalization. To test the molecular adsorption and release features, three molecules of clinical interest have been selected, namely, antiresorptive zoledronic acid, amino acid L-tryptophan, and protein bovine serum albumin. Molecular loading and delivery aspects have been studied by emphasizing the host-guest interactions, which determine the adsorption and release behavior. It has been found that careful control of surface electrochemistry by functionalization determines the bioactive molecule adsorption whereas the release can be mainly thought of as a diffusion matter dependent on the surface area and molecule size. This enhanced approach opens up new ways to optimize molecule loading for specific clinical needs.

Biomimetic apatite deposition on polymeric microspheres treated with a calcium silicate solution.

Bioactive polymeric microspheres can be prepared by means of coating them with a calcium silicate solution and subsequently soaking in a simulated body fluid (SBF). Such combination should allow for the development of bioactive microspheres for several applications in the medical field including tissue engineering carriers. Four types of polymeric microspheres, with different sizes, were used in this work: (i) ethylene-vinyl alcohol copolymer (20-30 mum), (ii) polyamide 12 with 10% magnetite (100 mum), (iii) polyamide 12 (10-30 mum) and (iv) polyamide 12 (300 mum). These microspheres were soaked in a calcium silicate solution at 36.5 degrees C for various periods of time under different conditions. Afterwards, they were dried in air at 60 and 100 degrees C for 24 hr. Then, the samples were soaked in SBF for 1, 3, and 7 days. Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that after the calcium silicate treatment and the subsequent soaking in SBF, the microspheres successfully formed an apatite layer on their surfaces in SBF within 7 days due to the formation of silanol groups, which are effective for apatite formation.

Flexible porous metal-organic frameworks for a controlled drug delivery.

Flexible nanoporous chromium or iron terephtalates (BDC) MIL-53(Cr, Fe) or M(OH)[BDC] have been used as matrices for the adsorption and in vitro drug delivery of Ibuprofen (or alpha- p-isobutylphenylpropionic acid). Both MIL-53(Cr) and MIL-53(Fe) solids adsorb around 20 wt % of Ibuprofen (Ibuprofen/dehydrated MIL-53 molar ratio = 0.22(1)), indicating that the amount of inserted drug does not depend on the metal (Cr, Fe) constitutive of the hybrid framework. Structural and spectroscopic characterizations are provided for the solid filled with Ibuprofen. In each case, the very slow and complete delivery of Ibuprofen was achieved under physiological conditions after 3 weeks with a predictable zero-order kinetics, which highlights the unique properties of flexible hybrid solids for adapting their pore opening to optimize the drug-matrix interactions.

L-Trp adsorption into silica mesoporous materials to promote bone formation.

The properties of ordered mesoporous silicas as bioactive materials, able to induce bone-tissue regeneration, have been combined with their abilities to host and release specific biomolecules in a controlled fashion. The possibility of locally deliver peptides and proteins is of great scientific importance because it opens new paths for the design of implantable biomaterials than can promote bone formation where needed. These biomaterials can host such biofactors, and their adsorption can be enhanced by chemically modifying the silica surface, with the aim of encouraging host-guest interaction and, thereby, increasing the loading capacity of the biomaterial matrix. L-Tryptophan (L-Trp) is a hydrophobic amino acid present in the three-dimensional structure of numerous proteins, and it is used here as model system to predict peptide delivery systems. Unmodified, silanol-rich, bioactive SBA-15 ordered mesoporous silica has been found to be incapable of confining L-Trp in its mesopores due to the hydrophobic character of this molecule. Organically modifying SBA-15 with quaternary amines results in approximately two-thirds of the silica surface being functionalized, increases the surface hydrophobicity allowing an increased L-Trp loading, and also induces different release kinetics. The control of the L-Trp release is the first step in controlled and localized protein delivery technologies, and opens novel perspectives for designing bioactive silica-based devices suitable for bone-healing applications.

Silica materials for medical applications.

The two main applications of silica-based materials in medicine and biotechnology, i.e. for bone-repairing devices and for drug delivery systems, are presented and discussed. The influence of the structure and chemical composition in the final characteristics and properties of every silica-based material is also shown as a function of the both applications presented. The adequate combination of the synthesis techniques, template systems and additives leads to the development of materials that merge the bioactive behavior with the drug carrier ability. These systems could be excellent candidates as materials for the development of devices for tissue engineering.

Mesoporous materials for drug delivery.

Research on mesoporous materials for biomedical purposes has experienced an outstanding increase during recent years. Since 2001, when MCM-41 was first proposed as drug-delivery system, silica-based materials, such as SBA-15 or MCM-48, and some metal-organic frameworks have been discussed as drug carriers and controlled-release systems. Mesoporous materials are intended for both systemic-delivery systems and implantable local-delivery devices. The latter application provides very promising possibilities in the field of bone-tissue repair because of the excellent behavior of these materials as bioceramics. This Minireview deals with the advances in this field by the control of the textural parameters, surface functionalization, and the synthesis of sophisticated stimuli-response systems.

Drug confinement and delivery in ceramic implants.

Ordered silica-based mesoporous materials could be specially designed and chemically modified for the adsorption of drugs that would be locally released. The drug adsorption and release kinetics are controlled by several factors such as pore size, volume, architecture and chemistry of the silica walls.

Confinement and controlled release of bisphosphonates on ordered mesoporous silica-based materials.

Bisphosphonates have been confined in siliceous ordered mesoporous materials, and the drug release rate of these systems has been investigated. The bisphosphonate adsorption rate has been increased from 1% in oral administration to around 40% locally delivered. Drug dosage can be modulated through amine modification of the material surface, leading to a bisphosphonate adsorption in the ordered mesoporous matrices 3 times larger than that for unmodified materials. The use of these drug delivery systems opens new fields with new possibilities for tissue engineering.

Formation of bone-like apatite on organic polymers treated with a silane-coupling agent and a titania solution.

Polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH) and Nylon 6 in plate form were treated with silane-coupling agents, a titanium alkoxide-alcohol solution and a hot HCl solution to form a thin crystalline titanium oxide layer. When placed in a simulated body fluid with ion concentrations nearly equal to those of the human blood plasma, nanosized bone-like apatite formed uniformly on the surfaces of these treated polymers: within 2 days for PET and Nylon 6, and 7 days for EVOH. This indicates that such titania-modified polymers might form bone-like apatite in the living body, and bond to living bone through this apatite layer. Three-dimensional fabrics of these polymer fibers, with open spaces in various sizes, are expected to be useful as bone substitutes, as they will be integrated with the natural bone.