ATR-FTIR spectroscopy reveals bond formation during bacterial adhesion to iron oxide

The contribution of various bacterial surface functional groups to adhesion at hematite and ZnSe surfaces was examined using attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. When live Shewanella oneidensis, Pseudomonas aeruginosa, and Bacillus subtilis cells were introduced to a horizontal hematite (alpha-Fe(2)O(3))-coated internal reflection element (IRE), FTIR peaks emerged corresponding to bacterial phosphate group binding. These IR peaks were not observed when bacteria were introduced to the uncoated ZnSe IRE. When cells were added to colloidal suspensions of alpha-Fe(2)O(3) at pH 7, spectra included peaks corresponding to P-OFe and nu(COOH), the latter being attributed to bridging of carboxylate at mineral surface OH groups. Selected model organic compounds with P-containing functionalities (phenylphosphonic acid [PPA], adenosine 5'-monophosphate [AMP], 2'-deoxyadenyl(3'-->5')-2'-deoxyadenosine [DADA], and deoxyribonucleic acid [DNA]) produce spectra with similar peaks corresponding to P-OFe when adsorbed to alpha-Fe(2)O(3). The data indicate that both terminal phosphate/phosphonate and phosphodiester groups, either exuded from the cell or present as surface biomolecules, are involved in bacterial adhesion to Fe-oxides through formation of innersphere Fe-phosphate/phosphonate complexes.     

Systematic control of size,shape, structure,and magnetic properties of uniform magnetite and maghemite particles

As an application of the gel-sol method especially developed for the synthesis of general monodisperse particles in large quantities, uniform hematite (alpha-Fe2O3), magnetite (Fe3O4), and maghemite (gamma-Fe2O3) particles, precisely controlled in size, aspect ratio, and internal structure, have been prepared. For the synthesis of uniform ellipsoidal single-crystal particles of alpha-Fe2O3, a highly condensed suspension of fine beta-FeOOH particles doped with a prescribed amount of PO4(3-) ion in their interiors was aged at 140 degrees C for 24 h with seed particles of alpha-Fe2O3 in an acidic medium containing optimum concentrations of HCl and NaNO3. Systematic control of the aspect ratio and mean size was achieved by regulating the concentration of PO4(3-) ion incorporated into the beta-FeOOH particles and the number of seeds added. The resulting hematite particles were converted into magnetite by reduction in a H2 stream at 330 degrees C for 6 h; the magnetite was then oxidized to maghemite in an air stream at 240 degrees C for 2 h. Magnetite and maghemite thus prepared retained the original shape of the hematite. On the other hand, polycrystalline hematite particles of different sizes and aspect ratios were also prepared by aging a condensed Fe(OH)3 gel in the presence of different concentrations of SO4(2-) ion and seeds. The polycrystalline hematite particles were similarly converted into magnetite and then maghemite. The magnetic properties of these magnetite and maghemite particles were analyzed as a function of their mean particle volume, aspect ratio, and internal structure.     

Surface complex characteristics of synthetic maghemite and hematite in aqueous suspensions

The acid-base properties of the maghemite (gamma-Fe2O3)/water and hematite (alpha-Fe2O3)/water interfaces have been studied by means of high precision potentiometric titrations and the experimental results are evaluated as surface complexation reactions. Synthetic maghemite and hematite were prepared and characterized using a combination of SEM, FT-IR and XRD. The specific surface area of the minerals was determined by the BET method. The titrations were performed at 25.0+/-0.2 degrees C within the range 2.8相似文献   

Heterogeneous uptake of ozone on reactive components of mineral dust aerosol: an environmental aerosol reaction chamber study

We have undertaken a kinetic study of heterogeneous ozone decomposition on alpha-Fe2O3 (hematite) and alpha-Al2O3 (corundum) aerosols under ambient conditions of temperature, pressure, and relative humidity in order to better understand the role of mineral dust aerosol in ozone loss mechanisms in the atmosphere. The kinetic measurements are made in an environmental aerosol reaction chamber by use of infrared and ultraviolet spectroscopic probes. The apparent heterogeneous uptake coefficient, gamma, for ozone reaction with alpha-Fe2O3 and alpha-Al2O3 surfaces is determined as a function of relative humidity (RH). The uptake of ozone by the iron oxide surface is approximately an order of magnitude larger than that by the aluminum oxide sample, under dry conditions. At the pressures used, alpha-Fe2O3 shows clear evidence for catalytic decomposition of ozone while alpha-Al2O3 appears to saturate at a finite ozone coverage. The measured uptake for both minerals decreases markedly as the RH is increased. Comparison with other literature reports and the atmospheric implications of these results are discussed.     

Rate coefficients for the gas-phase reaction of OH radicals with dimethyl sulfide: temperature and O2 partial pressure dependence

Rate coefficients for the gas-phase reaction of hydroxyl (OH) radicals with dimethyl sulfide (CH(3)SCH(3), DMS) have been determined using a relative rate technique. The experiments were performed under different conditions of temperature (250-299 K) and O(2) partial pressure (approximately 0 Torr O(2)-380 Torr O(2)), at a total pressure of 760 Torr bath gas (N(2) + O(2)), in a 336 l reaction chamber, using long path in situ Fourier transform (FTIR) absorption spectroscopy to monitor the disappearance rates of DMS and the reference compounds (ethene, propene and 2-methylpropene). OH was produced by the photolysis of H(2)O(2). The following Arrhenius expressions adequately describe the rate coefficients as a function of temperature (units are cm(3) molecule(-1) s(-1)): k = (1.56 +/- 0.20) x 10(-12) exp[(369 +/- 27)/T], for approximately 0 Torr O(2); (1.31 +/- 0.08) x 10(-14) exp[(1910 +/- 69)/T], for 155 Torr O(2); (5.18 +/- 0.71) x 10(-14) exp[(1587 +/- 24)/T], for 380 Torr O(2). The results are compared with previous investigations.     

Growth and magnetic properties of oriented alpha-Fe2O3 nanorods

alpha-Fe(2)O(3) nanorods have been deposited on Si substrates using the metal-organic chemical vapor deposition method. Structural analyses indicated that alpha-Fe(2)O(3) nanorods are preferentially oriented in the [104] direction on Si(100) substrates, and the nanorod possesses the single-crystalline structure. MFM image suggests that a spin domain is formed in the alpha-Fe(2)O(3) nanorod. Anisotropic magnetic property of the alpha-Fe(2)O(3) nanorods, i.e., the discrepancy of the saturation magnetization, is observed from SQUID measurements when the magnetic field are applied parallel and perpendicular to the substrate. A lower Morin temperature than that of the macroscopically crystalline hematite is observed when the magnetic field is applied parallel to the substrate.     

Adsorption of sulfur dioxide on hematite and goethite particle surfaces

The adsorption of sulfur dioxide (SO(2)) on iron oxide particle surfaces at 296 K has been investigated using X-ray photoelectron spectroscopy (XPS). A custom-designed XPS ultra-high vacuum chamber was coupled to an environmental reaction chamber so that the effects of adsorbed water and molecular oxygen on the reaction of SO(2) with iron oxide surfaces could be followed at atmospherically relevant pressures. In the absence of H(2)O and O(2), exposure of hematite (alpha-Fe(2)O(3)) and goethite (alpha-FeOOH) to SO(2) resulted predominantly in the formation of adsorbed sulfite (SO(3)(2-)), although evidence for adsorbed sulfate (SO(4)(2-)) was also found. At saturation, the coverage of adsorbed sulfur species was the same on both alpha-Fe(2)O(3) and alpha-FeOOH as determined from the S2p : Fe2p ratio. Equivalent saturation coverages and product ratios of sulfite to sulfate were observed on these oxide surfaces in the presence of water vapor at pressures between 6 and 18 Torr, corresponding to 28 to 85% relative humidity (RH), suggesting that water had no effect on the adsorption of SO(2). In contrast, molecular oxygen substantially influenced the interactions of SO(2) with iron oxide surfaces, albeit to a much larger extent on alpha-Fe(2)O(3) relative to alpha-FeOOH. For alpha-Fe(2)O(3), adsorption of SO(2) in the presence of molecular oxygen resulted in the quantitative formation of SO(4)(2-) with no detectable SO(3)(2-). Furthermore, molecular oxygen significantly enhanced the extent of SO(2) uptake on alpha-Fe(2)O(3), as indicated by the greater than two-fold increase in the S2p : Fe2p ratio. Although SO(2) uptake is still enhanced on alpha-Fe(2)O(3) in the presence of molecular oxygen and water, the enhancement factor decreases with increasing RH. In the case of alpha-FeOOH, there is an increase in the amount of SO(4)(2-) in the presence of molecular oxygen, however, the predominant surface species remained SO(3)(2-) and there is no enhancement in SO(2) uptake as measured by the S2p : Fe2p ratio. A mechanism involving molecular oxygen activation on oxygen vacancy sites is proposed as a possible explanation for the non-photochemical oxidation of sulfur dioxide on iron oxide surfaces. The concentration of these sites depends on the exact environmental conditions of RH.     

Nanostructured pure gamma-Fe2O3 via forced precipitation in an organic solvent

Pure maghemite, gamma-Fe(2)O(3), was prepared as ultra fine particles in the nanometer-sized range via the forced precipitation method in an organic solvent. The precipitation of iron(III) ions, from iron(III) chloride in 2-propanol led selectively to highly dispersed particles of ferrihydrite, which upon treatment with temperatures higher than 200 degrees C under dynamic vacuum resulted in high-surface-area particles of gamma-Fe(2)O(3). Precipitation in water also led to ferrihydrite, but the final product, after heating at 300 degrees C, contained a mixture of gamma-Fe(2)O(3) and alpha-Fe(2)O(3) (hematite). The precipitation from iron(III) nitrate in water resulted in goethite which was converted to hematite upon heating. On the other hand, the final product in 2-propanol was a mixture of maghemite and hematite. The products were characterized by FTIR, TGA, XRD, and gas sorption analysis. Nitrogen gas adsorption studies for the pure gamma-Fe(2)O(3) samples revealed mesoporous particles with high surface areas in the range of 70-120 m(2) g(-1) after heat treatment at 300 degrees C. The gamma-Fe(2)O(3) particles retained their gamma-phase as well as their mesoporous structure at relatively high temperatures, as high as 400 degrees C.     

Homogeneous Precipitation of Uniform alpha-Fe2O3 Particles from Iron Salts Solutions in the Presence of Urea

Uniform alpha-Fe2O3 particles within the nanometer range (100-300 nm) have been obtained by precipitation of iron (III) perchlorate in the presence of urea. Different morphology, from spheres to ellipsoidal particles with axial ratio up to approximately 10, was obtained by adding to the initial solution increasing amounts of phosphate anions up to 7 x 10(-3) M. The main targets of this work are the reduction in particle size and precipitation time and the increase of the particles axial ratio, keeping a narrow particle size distribution, in comparison to other methods previously developed to obtain homogenous alpha-Fe2O3 particles. A detailed analysis of the reaction products and a systematic study of the influence of the different precipitation conditions on the characteristics of the resulting particles have been carried out. Finally, some information on the formation mechanism of the ellipsoidal hematite particles in the iron (III) salt-urea-phosphate system is also given. Copyright 1999 Academic Press.     

Hydration number of glycine in aqueous solution: an experimental estimate

An experimental estimate of hydration number, N(H), of glycine in aqueous solution is given by using the calorimetric methodology developed by us earlier, which is briefly reviewed. We found NH to be 7+/-0.6 for glycine presumably in the zwitter ion form, 10+/-1 for sodium glycinate, and 5+/-0.4 for glycine hydrochloride. Both glycine and sodium glycinate seem to work purely as a hydration center without altering the nature of the bulk H2O away from the hydration shell. Glycine hydrochloride, in addition to the role of hydration center, seems also to act as a typical hydrophilic species such as polyols, urea, or polyethylene glycols. Hence, the effect of the latter on H2O is of a long range, like other hydrophilic species.     

Bicrystalline hematite nanowires

Bicrystalline nanowires of hematite (alpha-Fe(2)O(3)) have been successfully synthesized by the oxidation of pure iron. The product was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM in combination with focal series reconstruction, energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy. The bicrystalline nanowires have diameters of 20-80 nm and lengths up to 20 microm. All of the investigated materials are found to be alpha-Fe(2)O(3) with a rhombohedral crystal structure. Investigations indicate that most of the bicrystalline nanowires are nanotwins with ellipsoidal heads. The orientation relationship between the nanotwins can be described as (110)(M)//(110)(T), [110](M)//[0](T). An energy-filtered TEM investigation indicates that the ellipsoidal head is iron-rich. The growth mechanism of such unique nanostructures is considered to be a solid-phase growth via surface and internal diffusions of molecules from base to tip.     

Size-dependent structural transformations of hematite nanoparticles. 1. Phase transition

Using Fourier Transform InfraRed (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM), we characterize the structure and/or morphology of hematite (alpha-Fe(2)O(3)) particles with sizes of 7, 18, 39 and 120 nm. It is found that these nanoparticles possess maghemite (gamma-Fe(2)O(3))-like defects in the near surface regions, to which a vibrational mode at 690 cm(-1), active both in FTIR and Raman spectra, is assigned. The fraction of the maghemite-like defects and the net lattice disorder are inversely related to the particle size. However, the effect is opposite for nanoparticles grown by sintering of smaller hematite precursors under conditions when the formation of a uniform hematite-like structure throughout the aggregate is restricted by kinetic issues. This means that not only particle size but also the growth kinetics determines the structure of the nanoparticles. The observed structural changes are interpreted as size-induced alpha-Fe(2)O(3)<-->gamma-Fe(2)O(3) phase transitions. We develop a general model that considers spinel defects and absorbed/adsorbed species (in our case, hydroxyls) as dominant controls on structural changes with particle size in hematite nanoparticles, including solid-state phase transitions. These changes are represented by trajectories in a phase diagram built in three phase coordinates-concentrations of spinel defects, absorbed impurities, and adsorbed species. The critical size for the onset of the alpha-->gamma phase transition depends on the particle environment, and for the dry particles used in this study is about 40 nm. The model supports the existence of intermediate phases (protohematite and hydrohematite) during dehydration of goethite. We also demonstrate that the hematite structure is significantly less defective when the nanoparticles are immersed in water or KBr matrix, which is explained by the effects of the electrochemical double layer and increased rigidity of the particle environment. Finally, we revise the problem of applicability of IR spectroscopy to the lattice vibrations of hematite nanoparticles, demonstrating that structural comparison of different samples is much more reliable if it is based on the E(u) band at about 460 cm(-1) and the spinel band at 690 cm(-1), instead of the A(2u)/E(u) band at about 550 cm(-1) used in previous work. The new methodology is applied to analysis of the reported IR spectra of Martian hematite.     

The Raman spectrum of hematite: possible indicator for a compositional or firing distinction among Terra Sigillata wares

The Raman spectrum of hematite (alpha-Fe2O3) is here discussed as a distinctive feature for Terra Sigillata sample wares. The broadening of the Raman lines and the appearance and increasing of the disorder band at 660 cm(-1), while moving from the external slip to the inner body, are proposed as valuation parameters for the study of the mineralogical composition and firing process of pottery productions.     

Thermally stable hematite hollow nanowires

Thermally stable hematite (alpha-Fe(2)O(3)) hollow nanowires were synthesized by a vacuum-pyrolysis route from beta-FeOOH nanowires for the first time. The products can catalyze the oxidation of almost 100% carbon monoxide at 320 degrees C, exhibiting excellent catalytic performances despite their small BET surface area.     

Hematite spindles with optical functionalities: growth of gold nanoshells and assembly of gold nanorods

The layer-by-layer (LBL) assembly method, combined with the seeded growth technique, have been used to deposit gold shells on the surface of hematite (alpha-Fe(2)O(3)) spindles. While the LBL method yields dense coatings of preformed Au nanoparticles, when AuCl(-)(4) ions are further reduced by a mild reducing agent, thicker, rough nanostructured shells can be grown. The deposition process was monitored by TEM and UV-visible spectroscopy, demonstrating a gradual change in the optical features of the colloids as the surface is more densely covered. The particles so-prepared can find useful applications in cancer therapy and as SERS substrates. Additionally, we show that Au nanorods can be assembled on hematite spindles, providing a flexible way to tune the optical properties of the resulting composite colloids.     

Sorption of silicates on goethite, hematite, and magnetite: experiments and modelling

Sorption of H(4)SiO(4) (including experiments as a function of time, K(d) measurement with different m/v ratios and sorption edges) onto different iron (hydro)oxides as goethite (alpha-FeOOH), hematite (alpha-Fe(2)O(3)), and magnetite (Fe(3)O(4)) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namely FeH(3)SiO(4) and FeH(2)SiO(4)(-), are needed to describe properly the experimental observations.     

Synthesis and characterization of poly(divinylbenzene)-coated magnetic iron oxide nanoparticles as precursor for the formation of air-stable carbon-coated iron crystalline nanoparticles

Maghemite (gamma-Fe2O3) nanoparticles of 15 +/- 3 nm diameter were prepared by nucleation of gelatin/iron oxide followed by growth of gamma-Fe2O3 films onto these nuclei. The gamma-Fe2O3 nanoparticles were coated with polydivinylbenzene (PDVB) by emulsion polymerization of divinylbenzene (DVB) in an aqueous continuous phase containing the gamma-Fe2O3 nanoparticles. The PDVB-coated gamma-Fe2O3 nanoparticles, dispersed in water, were separated from homo-PDVB nanoparticles using the high gradient magnetic field (HGMF) technique. The influence of DVB concentration on the amount of PDVB coating, on the size and size distribution of the coated gamma-Fe2O3 nanoparticles and on their magnetic properties, has been investigated. Air-stable carbon-coated iron (alpha-Fe/C) crystalline nanoparticles of 41 +/- 12 nm diameter have been prepared by annealing the PDVB-coated gamma-Fe2O3 nanoparticles at 1050 degrees C in an inert atmosphere. These nanoparticles exhibit high saturation magnetization value (83 emu g(-1)) and excellent resistance to oxidation. Characterization of the PDVB-coated gamma-Fe2O3 and of the alpha-Fe/C nanoparticles has been accomplished by TEM, HRTEM, DLS, FTIR, XRD, thermal analysis, zeta-potential, and magnetic measurements.     

Understanding of the finite size effects on lattice vibrations and electronic transitions of nano alpha-Fe2O3

Alpha-Fe(2)O(3) nanocrystals with controlled diameters ranging from 10 to 63 nm were successfully prepared. The finite size effects in alpha-Fe(2)O(3) nanocrystals were probed by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, UV-visible spectrum, and magnetization measurements. With a size reduction, alpha-Fe(2)O(3) nanocrystals showed a lattice expansion and an enlarged axial ratio of c/a that is in apparent contradiction to the previous conjecture of high lattice symmetry for alpha-Fe(2)O(3) nanocrystals at small sizes. The surface terminations of alpha-Fe(2)O(3) nanocrystals were found to be highly hydrated with a size dependence that surprisingly follows the surface hydration chemistry of anatase TiO2 nanocrystals reported recently by us. The lattice vibrations, electronic transitions, and magnetic properties of alpha-Fe(2)O(3) nanocrystals were significantly modified by surface hydration and lattice expansion. The finite size effects that occurred in alpha-Fe(2)O(3) nanocrystals at small sizes were first found to give a red shift in frequencies of perpendicular mode at 540 cm(-1), a blue shift in the electronic transition of double exciton process in visible region, and a significant decrease in the coercive force.     

Adsorption of organic matter at mineral/water interfaces: 7. ATR-FTIR and quantum chemical study of lactate interactions with hematite nanoparticles

The interaction of the l-lactate ion ( l-CH3CH(OH)COO(-), lact(-1)) with hematite (alpha-Fe2O3) nanoparticles (average diameter 11 nm) in the presence of bulk water at pH 5 and 25 degrees C was examined using a combination of (1) macroscopic uptake measurements, (2) in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and (3) density functional theory modeling at the B3LYP/6-31+G* level. Uptake measurements indicate that increasing [ lact(-1)]aq results in an increase in lact(-1) uptake and a concomitant increase in Fe(III) release as a result of the dissolution of the hematite nanoparticles. The ATR-FTIR spectra of aqueous lact(-1) and lact(-1) adsorbed onto hematite nanoparticles at coverages ranging from 0.52 to 5.21 micromol/m2 showed significant differences in peak positions and shapes of carboxyl group stretches. On the basis of Gaussian fits of the spectra, we conclude that lact(-1) is present as both outer-sphere and inner-sphere complexes on the hematite nanoparticles. No significant dependence of the extent of lact(-1) adsorption on background electrolyte concentration was found, suggesting that the dominant adsorption mode for lact(-1) is inner sphere under these conditions. On the basis of quantum chemical modeling, we suggest that inner-sphere complexes of lact(-1) adsorbed on hematite nanoparticles occur dominantly as monodentate, mononuclear complexes with the hydroxyl functional group pointing away from the Fe(III) center.     

Facile fabrication of long alpha-Fe(2)O(3), alpha-Fe and gamma-Fe(2)O(3) hollow fibers using sol-gel combined co-electrospinning technology

Long alpha-Fe(2)O(3) hollow fibers have been prepared through a facile sol-gel combined co-electrospinning technique using ferric citrate as precursor, and alpha-Fe and gamma-Fe(2)O(3) hollow fibers have been obtained by reduction and reoxidation at different conditions. The outer diameter of the as-prepared hollow fibers is 0.5-5 microm with wall thickness of 200-800 nm. The obtained tubular fibers were characterized by thermal gravimetric (TG), FT-IR spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman techniques. In addition, magnetic properties of alpha-Fe and gamma-Fe(2)O(3) hollow fibers have also been investigated.