Hydrogen atom H (≡ proton + electron) transfer (HAT), is the most common reaction that involves the transfer of two elementary particles, a proton and an electron. Antioxidant, proton-coupled electron transfer (PCET) reactions involve also the transfer of two elementary particles, a proton and an electron. These constitute the fundamental step in a wide range of processes, chemical energy technologies, which rely on e–/H+ transfer from combustion and aerobic oxidations, to enzymatic catalysis and the destructive effects of reactive oxygen species in vivo. Here we describe a novel phenomenon, plasmonically-enhanced PCET, using nanothin silica-coated plasmonic Ag nanoparticles, functionalized with gallic acid, a natural antioxidant molecule, that is able to perform PCET. These nanoparticles can transfer rapidly electrons and protons to stable radicals. The kinetics and yield of these PCET reactions can be enhanced by plasmonic resonance modes excited by low-power, near-Infrared (785nm) laser irradiation. The demonstration that these plasmonic nanoparticles can enhance the HAT rates for both electrons and protons expands the traditional view of interfacial PCET. The occurrence of interfacial plasmon-enhancement of PCET brings together so far unrelated domains of nanoplasmonics, electron/proton translocation with significant impact on a variety of applications and most notably in theranostics.

The fast dissolution of certain calcium-containing compounds makes them attractive carriers for trace minerals in nutritional applications, e.g., iron and zinc to alleviate mineral deficiencies in affected people. Here, CaO-based nanostructured mixed oxides containing nutritionally relevant amounts of Fe, Zn, Cu, and Mn were produced by one-step flame spray pyrolysis. The compounds were characterized by nitrogen adsorption, x-ray diffraction, (scanning) transmission electron microscopy, and thermogravimetric analysis. Dissolution in dilute acid (i.d.a.) was measured as an indicator of their in vivo bioavailability. High contents of calcium resulted in matrix encapsulation of iron and zinc preventing formation of poorly soluble oxides. For 3.6 ≤ Ca:Fe ≤ 10.8, Ca2Fe2O5 coexisted with CaO. For Ca/Zn compounds, no mixed oxides were obtained, indicating that the Ca/Zn composition can be tuned without affecting their solubility i.d.a. Aging under ambient conditions up to 225 days transformed CaO to CaCO3 without affecting iron solubility i.d.a. Furthermore, Cu and Mn could be readily incorporated in the nanostructured CaO matrix. All such compounds dissolved rapidly and completely i.d.a., suggesting good in vivo bioavailability.

Silver (Ag) nanoparticles dispersed in an amorphous silica (SiO2) matrix or coated by a SiO2 layer were synthesized by flame spray pyrolysis (FSP). The coated nanoparticles were produced by using a modified enclosed FSP setup, in which the SiO2 precursor was injected through a ring above the FSP nozzle at various burner-ring-distances (BRDs), after the core Ag nanoparticles had been formed. The produced nanoparticles were characterized by XRD, BET, TEM and UV/vis analysis. The Ag particle size was possible to be controlled by tuning the FSP parameters. For the SiO2 coated nanoparticles, larger Ag core sizes were obtained for higher BRDs. All the produced nanoparticles exhibited the characteristic plasmon resonance frequency of Ag nanoparticles.

The antibacterial activity of nanosilver against Gram negative Escherichia coli bacteria is investigated by immobilizing nanosilver on nanostructured silica particles and closely controlling Ag content and size. These Ag/SiO2 nanoparticles were characterized by S/TEM, EDX spectroscopy, X-ray diffraction. The antibacterical activity of these composite samples was investigated for a constant composite particle concentration. The highest activity was observed for the higher silver content particles.

Silver (Ag) nanoparticles dispersed in an amorphous silica (SiO2) matrix or coated by a SiO2 layer were synthesized by flame spray pyrolysis (FSP). The coated nanoparticles were produced by using a modified enclosed FSP setup, in which the SiO2 precursor was injected through a ring above the FSP nozzle at various burner-ring-distances (BRDs), after the core Ag nanoparticles had been formed. The produced nanoparticles were characterized by XRD, BET, TEM and UV/vis analysis. The Ag particle size was possible to be controlled by tuning the FSP parameters. For the SiO2 coated nanoparticles, larger Ag core sizes were obtained for higher BRDs. All the produced nanoparticles exhibited the characteristic plasmon resonance frequency of Ag nanoparticles.

Iron deficiency affects approximately 2 billion people worldwide, especially young women and children. Food fortification with iron is a sustainable approach to alleviate iron deficiency but remains a challenge. Water-soluble compounds with high bioavailability (e.g. the “gold standard” FeSO4) usually cause unacceptable sensory changes in foods, while compounds that are less reactive in food matrices are often less bioavailable. Solubility (and therefore bioavailability) can be improved by increasing the specific surface area (SSA) of the compound, i.e. decreasing its particle size to the nm range. Here, iron oxide-based nanostructured compounds with Mg or Ca are made using scalable flame aerosol technology. Addition of either element increased iron solubility to a level comparable to iron phosphate. Furthermore, these additions lightened the powder color and sensory changes in fruit yoghurt were less prominent than for FeSO4.

Commercially available SiO2 nanoparticles (Aerosil, Degussa) with varying primary particle diameter, specific surface area (SSA), degree of aggregation and structure (fractal dimension) were compounded into PDMS-based nanocomposites. Thin sections of cured nanocomposites were analyzed with TEM and small and ultra-small angle X-ray scattering (U/SAXS) with respect to nanocomposite structure such as: filler primary particle, aggregate (chemically or sinter-bonded particles) and agglomerate (physically-bonded particles). Tensile tests (Young’s modulus) were used to determine the nanocomposite strength which increased with increasing filler volume fraction (up to 12 vol%) consistent with “bound rubber” theory.

Silver (Ag) nanoparticles dispersed in an amorphous silica (SiO2) matrix or coated by a SiO2 layer were synthesized by flame spray pyrolysis (FSP). The coated nanoparticles were produced by using a modified enclosed FSP setup, in which the SiO2 precursor was injected through a ring above the FSP nozzle at various burner-ring-distances (BRDs), after the core Ag nanoparticles had been formed. The produced nanoparticles were characterized by XRD, BET, TEM and UV/vis analysis. The Ag particle size was possible to be controlled by tuning the FSP parameters. For the SiO2 coated nanoparticles, larger Ag core sizes were obtained for higher BRDs. All the produced nanoparticles exhibited the characteristic plasmon resonance frequency of Ag nanoparticles.

Silver clusters (4-150 nm) anchored on nanostructured silica particles (300-400 m2/g) with closely controlled Ag content and size were made in one-step by scalable flame spray pyrolysis of Ag-nitrate and hexamethyldisiloxane containing solutions. Composite Ag/SiO2 nanoparticles were characterized by S/TEM, EDX spectroscopy, X-ray diffraction, N2 adsorption. The activity of such nanoparticles against the Gram negative bacterium Escherichia coli was investigated by monitoring the recombinantly synthesized green fluorescent protein. It is shown that higher Ag content particles exhibit a stronger antibacterial effect.

Rapid quenching during flame spray synthesis of Pt/TiO2 (0–10 wt% Pt) is demonstrated as a versatile method for independent control of support (TiO2) and noble metal (Pt) cluster characteristics. Titania grain size, morphology, crystal phase structure, and crystal size were analyzed by nitrogen adsorption, electron microscopy and x-ray diffraction, respectively, while Pt-dispersion and size were determined by CO-pulse chemisorption. The influence of quench cooling on the flame temperature was analyzed by Fourier transform infrared spectroscopy. Increasing the quench flow rate reduced the Pt diameter asymptotically. Optimal quenching with respect to maximum Pt-dispersion (∼60%) resulted in average Pt diameters of 1.7 to 2.3 nm for Pt-contents of 1–10 wt%, respectively.

Tin oxide nanoparticles for gas sensing application have been synthesized with an aerosol method. The particles were manufactured with the versatile Flame spray Pyrolysis (FSP) method producing highly crystalline powders with closely controlled a primary particle and crystallite size of 10 nm and 17 nm. The single crystalline particles were only slightly aggregated and directly used for thick film sensor deposition by drop coating and screen printing.The flame made SnO2 nanoparticles showed high and rapidresponse to reducing gases such as propanal and CO.

Concurrent synthesis of titania-carbon nanoparticles (up to 52 wt.% in C) was studied in a diffusion flame aerosol reactor by combustion of titanium tetraisopropoxide and acetylene. These graphitically layered carbon-coated titania particles were characterized by high-resolution transmission electron microscopy (HRTEM), with elemental mapping of C and Ti, x-ray diffraction (XRD), and nitrogen adsorption [Brunauer-Emmett-Teller (BET)]. The specific surface area of the powder was controlled by the acetylene flow rate from 29 to 62 m2/g as the rutile content decreased from 68 to 17 wt.%. Light blue titania suboxides formed at low acetylene flow rates. The average XRD crystal size of TiO2 decreased steadily with increasing carbon content of the composite powders, while the average BET primary particle size calculated from nitrogen adsorption decreased first and then approached a constant value. The latter is attributed to the formation of individual carbon particles next to carbon-coated titania particles as observed by HRTEM and electron spectroscopic imaging.

Optimum conditions for the synthesis of nonagglomerated BaTiO3 particles by salt-assisted spray pyrolysis (SASP) were investigated. The effect of particle residence time in the reactor and salt concentration on the crystallinity and surface morphology of BaTiO3 was examined by x-ray diffraction and scanning electron microscopy. Mixtures of a metal chloride or nitrate salt, dissolved in aqueous precursor solutions, were sprayed by an ultrasonic atomizer into a five-zone hot-wall reactor. By increasing the salt concentration or the particle residence time in the hot zone, the primary particle size was increased, and its surface texture was improved compared to BaTiO3 particles prepared by conventional spray pyrolysis. The SASP-prepared BaTiO3 crystal was transformed from cubic to tetragonal by simply increasing the salt concentration at constant temperature and residence time. Further thermal treatments such as calcination or annealing are not necessary to obtain nonagglomerated tetragonal BaTiO3 (200–500 nm) particles with a narrow size distribution. Increasing the carrier gas flow rate and decreasing the residence time in the hot zone resulted in cubic BaTiO3 particles about 20 nm in diameter.

Bimodally porous titania powders with controlled phase composition and porosity were made by hydrolysis of titanium tetraisopropoxide (TTIP) and calcination. The extent of calcination was followed by thermogravimetric differential thermal analysis and Fourier transform infrared spectroscopy. The specific surface area (SSA) of the powders ranged from 10 to 500 m2/g as determined by nitrogen adsorption. The SSA increased by decreasing either the water concentration during hydrolysis or the calcination temperature. The pore size distribution was bimodal with fine intraparticle pore diameters at 1–6 nm and larger interparticle pore diameters at 30–120 nm as determined by nitrogen adsorption isotherms. The particle phase composition as determined by x-ray diffraction ranged from amorphous to crystalline anatase and rutile largely proportional to the calcination temperature and to a lesser extent on the initial H2O/TTIP molar ratio.

Nano-sized porous silica powders are synthesized by a room temperature aerosol process. Reactant mixing configuration, reactant temperature, and drying temperature effects on the physical and morphological features of these powders are studied by nitrogen adsorption and small angle xray scattering techniques. These silica powders have high specific surface areas up to 600 m2/g, and show narrowly confined mesoporous characteristics. The powders display some structural change with temperature. The morphological features are modeled as mass fractals by small angle x-ray scattering. Measured fractal dimensions are around 2.8, indicating diffusion limited growth processes.

Nanophase particles with precisely controlled characteristics are made by oxidation of their halide vapors in electrically assisted hydrocarbon flames using needle-shaped or plate electrodes. The particle size and crystallinity decrease with increasing field strength across the flame. The field generated by the electrodes across the flame decreases the particle residence time in the high temperature region of the flame. Furthermore, it charges the newly formed particles, resulting in electrostatic repulsion and dispersion that decreases particle growth by coagulation. Electric fields reduced the primary particle size of TiO2, the agglomerate size of SnO2, and both the agglomerate and primary size of SiO2.

Aluminum nitride (AlN) powders were produced in an aerosol flow reactor by direct nitridation of aluminum vapor with ammonia and nitrogen in flowing argon. In the presence of excess NH3, pure AlN powders were obtained from 1400 to 1873 K. These powders had higher specific surface areas than commercially available AlN powders. The effects of reactor temperature and gas flow rate on AlN purity, yield, and grain and crystallite size were investigated. The BET grain diameter of AlN increased as the process temperature increased, indicating sintering controlled particle formation and growth. Both the crystallite size and the BET grain size of pure AlN powders slightly decreased as ammonia flow rate was increased. Increasing temperature and flow rate increased the AlN yield.

The role of aluminum as dopant in gas phase synthesis of titania powders was experimentally investigated in an aerosol flow reactor between 1300 and 1700 K. Titania was produced by vapor phase oxidation of titanium tetrachloride in the presence of dopant aluminum trichloride vapor. The presence of aluminum altered the particle morphology from polyhedral to irregular crystals. Energy dispersive analysis and transmission electron microscopy indicated that the powders were mixtures of crystalline titania and amorphous alumina. Analysis by XPS indicated significant enrichment of aluminum on the particle surface. Some aluminum titanate (up to 17% by volume) was formed at 1700 K when a high concentration of AlCl3 was used (AlCl3/TiCl4 ≥ 0.07). Measurements of lattice parameters by x-ray diffraction indicated that aluminum formed a solid solution in titania. While titania synthesized in the absence of aluminum was about 90% anatase, the introduction of aluminum resulted in pure rutile at AlCl3/TiCl4 = 0.07. The effects of aluminum on titania phase composition and morphology are explained by the creation of oxygen vacancies in the titania crystallites and by the enhancement of the sintring rate of titania grains.

The flocculation of polystyrene particles with aluminum sulfate or alum (Al2 (SO4)3) by turbulent shear was studied as a function of the applied shear rates (63–129 s−1) and flocculant concentrations (11 and 32 mg/L) in a stirred tank. Increasing the shear rate increased the floc growth rate but decreased the maximum attainable floc size. Increasing the concentration of alum increased the floc growth rate and the maximum floc size. A steady state between floc growth and breakage was attained after which the floc size distribution no longer changed. The normalized steady state size distributions allowed evaluation of the relative contributions of shear rate and flocculant concentration to the performance of the process.

Ultrafine silica fibers were coated with nanosized particles by an aerosol process. The fibers were introduced in a diffusion flame reactor where silica particle formation took place by oxidation of SiCl4. Coagulation of particles with fibers resulted in fractal-like structures on the latter, enhancing the specific surface area of the product fibers. Ferrocene used as an additive at a mole fraction of 6.6 × 10−5 in the flame promoted the surface area enhancement. A sol-gel coating technique was also used to produce particle coated fibers.