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Toxic arsenic occurs in drinking water from natural and/or anthropogenic sources. It causes health problems worldwide. Among the existing arsenic removal techniques adsorption is the commonly used one. [gamma]-[Fe.sub.2][O.sub.3] nanoparticles were found recently to be a good adsorbent for arsenate because of its relatively high adsorption capacity and simple separation of the particles from the treated water. The aim of the study was to investigate the arsenate adsorption mechanism on the crystal [gamma]- [Fe.sub.2][O.sub.3] nanoparticles. Adsorption experiments were carried out with three different kinds of maghemite nanoparticles: (i) homemade one with mechanochemical method; (ii) homemade one with sol-gel process; and (iii) a commercially available one. The adsorption process was monitored by characterizing with Fourier transform infrared, x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron microscopy, and zeta potential analyzer. No crystal and amorphous precipitation were found on the iron oxide surfaces. The inner-sphere complex formation was found to be the predominant mechanism of adsorption. DOI: 10.1061/(ASCE)EE.1943-7870.0000233 CE Database subject headings: Adsorption; Particles; Nanotechnology; Arsenic; Drinking water: Water pollution. Author keywords: Adsorption mechanism; Arsenate; Inner-sphere complex; Maghemite: Nanoparticle.

Thermochemical cycles are a type of heat engine that utilize high-temperature heat to produce chemical work. Like their mechanical work producing counterparts, their efficiency depends on the operating temperature and on the irreversibility of their internal processes. With this in mind, we have invented innovative design concepts for two-step solar-driven thermochemical heat engines based on iron oxide and iron oxide mixed with other metal oxide (ferrites) working materials. The design concepts utilize two sets of moving beds of ferrite reactant materials in close proximity and moving in opposite directions to overcome a major impediment to achieving high efficiency--thermal recuperation between solids in efficient countercurrent arrangements. They also provide an inherent separation of the product hydrogen and oxygen and are an excellent match with a high-concentration solar flux. However, they also impose unique requirements on the ferrite reactants and materials of construction as well as an understanding of the chemical and cycle thermodynamics. In this paper, the counter-rotating-ring receiver/reactor/ recuperator solar thermochemical heat engine concept is introduced, and its basic operating principles are described. Preliminary thermal efficiency estimates are presented and discussed. Our results and development approach are also outlined. Keywords: solar, thermochemical, hydrogen, metal oxide, ferrite, redox, heat engine

The structure and reactivity of Fe/iron oxide core-shell nanoparticles (Fe-Ox) that are coated with dopamine are reported. The results have shown that the reactivity between [Fe.sup.3+] and dopamine quickly facilitates the degradation of the nanoparticles.

Several studies are conducted to understand the reducing reaction of the [Fe.sub.3][O.sub.4] nanowires in various nanoscopic reactors of amorphous C:H nanotubes (a-CNTs), which are then used to analyze the chemical reaction mechanism in such reactors. The results show that the carbon in the a-CNT shell exhibit better reducing properties than hydrogen, which is not the case with a macroscopic system.

We describe a family of calcium indicators for magnetic resonance imaging (MRI), formed by combining a powerful iron oxide nanoparticle-based contrast mechanism with the versatile calcium-sensing protein calmodulin and its targets. Calcium-dependent protein--protein interactions drive particle clustering and produce up to 5-fold changes in T2 relaxivity, an indication of the sensors' potency. A variant based on conjugates of wild-type calmodulin and the peptide M13 reports concentration changes near 1 [micro]M [Ca.sup.2+], suitable for detection of elevated intracellular calcium levels. The midpoint and cooperativity of the response can be tuned by mutating the protein domains that actuate the sensor. Robust MRI signal changes are achieved even at nanomolar particle concentrations ( magnetic resonance | T2 relaxation | signal transduction | molecular imaging | neuroimaging

The effective Knudsen diffusion coefficients for characteristic oxide powder beds used in heterogeneous uptake experiments were measured using countercurrent diffusion and transient pressure drop technique. The value of careful uptake measurements in both the low and high sample mass is reinforced, as this allows uptake corrections independent of explicitly measured or estimated diffusion coefficient values.

The adsorption and infectivity of one occluded and two nonoccluded viruses, Helicoverpa armigera single nucleopolyhedrovirus (HaSNVP) (Baculoviridae), Cricket paralysis virus (CrPV) (Dicistroviridae) and Invertebrate iridescent virus 6 (IIV-6) (Iridoviridae) respectively in mixtures with a choice of soil-forming minerals are compared. Results reveal that the interactions between soil-forming minerals and insect viruses appear to be most important in nucleopolyhedroviruses, followed by invertebrate iridescent viruses and least important in CrPV which might reflect the ecology of these pathogens.

A new approach toward development of advanced immunosensors based on chemically functionalized core-shell [Fe.sub.3][O.sub.4] at the rate of Ag magnetic nanoparticles is described with the preparation, characterization, and measurement of relevant properties of the immunosensor useful for the detection of carcinoembryonic antigen (CEA) in clinical immunoassay. The immobilized anti-CEA molecules show an excellent electrochemical response selective to the CEA and the core-shell nanostructure presents good magnetic properties to facilitate and modulate the way it was integrated into a carbon paste.

The adsorption of carbon dioxide on hydroxylated metal oxide surfaces like [Fe.sub.2][O.sub.3] and [Al.sub.2][O.sub.3] was investigated by FTIR spectroscopy combined with isotope labeling experiments and quantum chemical calculations. Reactions of C[O.sub.2] with these surfaces results in the formation of adsorbed bicarbonate and carbonate and the proton transfer mechanism occurs through an intermolecular process involving either coadsorbed hydroxyl groups or carbonate.

A sonochemical method for the preparation of a colloidal solution of iron oxide in decalin by the use of oleic acid as a long-chain stabilizer is described. Replacing long-chain PVA by SDS resulted in the disappearance of dendrite fractal structures which is due to the extensive magnetic interactions between the particles.

The density functional theory (DFT) calculations are used to gauge the oxidative reactivity of the ferric-hydrogen peroxide complex of cytochrome P450 compared with the high-valent oxo-iron species Compound I (Cpd I) and the ferric hydroperoxide Compound 0 (Cpd 0). The results of the hydroxylation of a radical probe and the kinetic isotope effect (KIE) for substrate oxidation are presented.

Phosphate deficiency often limits crop production in acid tropical soils because of the strong bonding of phosphate by Fe and Al oxides. Organic-acid exudation from roots is one reported plant adaptation to P deficiency. The objective of this study was to predict the efficacy of this P-deficiency stress response in different soil types by investigating the mechanism of organic-acid-induced P mobilization from different oxide minerals. Greater proportions of Fe and initially adsorbed P were released from ferrihydrite when compared with goethite. More P was released and Fe dissolved at pH 4.0 than pH 5.5 or 7.0 from both oxides. For ferrihydrite, the order of effectiveness of the organic ligands for P release at pH 4 was citrate (19% of the total initially adsorbed P) > malate (14%) > tartrate (5%) >> oxalate = malonate = succinate (0.3-1.2%). For Fe release at pH 4, the order was oxalate (18% of total oxide suspension Fe dissolved) [approximately equal to] citrate (17%) malonate (13%) > malate (8%) > tartrate (5%) >> succinate (0.02%). Faster phosphate readsorption in the case of oxalate than citrate probably accounted for the low apparent release of P by oxalate in spite of its greater Fe dissolution. At the smaller adsorbed-P concentration (1/4 of the adsorption maximum), the predominant mechanism of organic-acid induced P release was ligand-enhanced dissolution of the Fe oxide rather than ligand exchange. At 3/4 of the adsorption maximum, ligand exchange contributed to a greater extent to P release. Under low P-fertility conditions, organic-acid exudation would be more effective at increasing P availability in soils dominated by poorly crystalline than well-crystalline Fe oxides.

Human frataxin can enhance the availability of Fe(II) in monomeric and assembled form. However, the monomer is unable to prevent iron-catalyzed radical reactions and the formation of insoluble ferric iron oxides.

A series of molecules including of CH4, CH3Cl, CH2Cl2, CHCl3, and CCl4 are used as probes to test the chemical reactivity of the FeO(111) surface. The temperature-programmed desorption spectra show no evidence of dissociative adsorption or chemical reaction between the substrate and the adsorbates.

An electrochemical technique for growing Fe3O4 nanostructures is presented. Hydrazine and iron compounds in an aqueous solution undergo chemical reactions with hydroxides and form magnetite at the surface of the working electrode of an electrochemical cell.

The high-power ultrasonic irradiation of preformed magnetite ([Fe.sub.3][O.sub.4]) nanoparticles in the presence of monoelectronic Ce-containing ceric ammonium nitrate [[Ce.sup.IV][(N[H.sub.4]).sub.2][(N[O.sub.3]).sub.6]] oxidant in MeCOMe was performed to yield hydrophilic 50 nm-sized colloidal, highly stable maghemite ([gamma]-[Fe.sub.2][O.sub.3]) nanoparticles. The observed nanoparticle antiaggregation phenomenon could be decreased by an 'inorganic' Ce atom doping of the NP surface.

The article presents a new methodology that can be employed for the facile synthesis of superparamagnetic and fluorescent [Fe.sub.3][O.sub.4]/ZnS hallow nanospheres. These nanospheres are shown to be nontoxic and porous and hence can exhibit extremely high magnetic resonance and fluorescence.

A new approach to cisplatin storage and release using porous hollow nanoparticles (PHNPs) of [Fe.sub.3][O.sub.4] is reported. The model experimental results indicated that the low pH-responsive PHNPs of [Fe.sub.3][O.sub.4] could be exploited as a cisplatin delivery vehicle for target-specific therapeutic applications.

The time-resolved Faraday rotation measurements are applied to study the role of surface spins in the relaxation of magnetization in optically excited [Fe.sub.3][O.sub.4] nanocrystals. The [Fe.sub.3][O.sub.4] nanocrystals are found to be passivated with oleic acid and the surface of the nc is found to be three times more efficient in spin-lattice relaxation than the interior.

Dumbbell-like Au-[Fe.sub.3][O.sub.4] nanoparticles (NPs) are made and coupled with Herceptin and a platin complex. The studies have shown that the dumbbell-like Au-[Fe.sub.3][O.sub.4] NPs are promising nanocarriers for highly sensitive diagnostic and therapeutic applications.

Binary superlattices (BSLs) of stereically stabilized, hydrophobic, large [Fe.sub.2][O.sub.3] and small Au nanocrystals are assembled by slow evaporation of colloidal dispersions on titled substrates and are analyzed by using transmission and scanning electron microscopy (TEM and SEM) and grazing incidence small-angle X-ray scattering (GISAXS). Nearly periodic superlattice dislocations consisting of inserted half-planes of gold nanocrystals are seen by SEM in some BSLs.

The systematic studies of the heme dynamics and induced protein conformational relaxations in two redox states of ferric and ferrous cytochrome c upon femtosecond excitation are described. The dynamics have occurred at the local site, which has included ultrafast internal conversion in hundreds of femtoseconds, vibrational cooling on the similar picosecond time scale.

The abundances of hyperthermophilic heterotrophs, methanogens and autotrophic reducers of amorphous Fe(III) oxide are measured in the samples of deep-sea hydrothermal vent sulfide chimneys of the Endeavour Segment. The results have shown that conditions have favored the growth of iron reducers toward the interiors of these deposits and that of heterotrophs toward the outer surfaces near high-temperature polychaete worms.

The structures of ferric, deoxy and carbon monoxide-bound C-terminal PAS domain (bjFixLH) in a new space group (P1) and at higher resolutions are described. The studies have quantified quaternary structural changes induced by carbon monoxide binding to a bjFixLH dimer, in which monomers have rotated by up to 2 [degree] relative to each other.

A convenient and high yield procedure to obtain the [F.sub.10] family of single-strand 'ferric wheels' involving the methanolysis under basic conditions of [[[Fe.sub.3]O[([O.sub.2]CR).sub.6][([H.sub.2]O).sub.3].sup.+] salts in MeOH is developed. The carboxylate substitution on preformed [Fe.sub.10] wheels, phenolysis, and reaction with the N-based chelate ethylenediamine could be used to yield [Fe.sub.2] and two [Fe.sub.8] products with 'Christmas star' like topology.

The article discusses a new approach for the fabrication and modulation of the magnetically supramolecular hydrogels, the aqueous colloidal dispersion of magnetic iron oxide nanoparticles. The block copolymer and the incorporated iron oxide nanoparticles are shown to highly affect the formation kinetics of the hydrogels.

The experimental and computational studies are carried out to obtain more direct vibrational signatures for protonation of the monooxygen ligand. The results establish the high sensitivity of the Fe-O stretching frequency and FeO tilting which would provide vibrational signatures for the protonation state in structural studies of ferryl heme protein intermediates.

The article presents the synthesis of uniform iron oxide hydroxide (goethite) nanotubes having a parallelogram cross section. The current approach is found to be extremely simple and highly reproducible.

The polynuclear iron clusters with tridentate ligands are analyzed for the structural diversity. All the complexes possess a unique core topology of an iron oxide ring.

The synthesis of novel 'tadpole' -like [Fe.sub.3][O.sub.4]/multiwalled carbon nanotube (MWCNT) heterojunctions were carried out by the position-selectively attaching [Fe.sub.3][O.sub.4] sphere on the tips of (MWCNTs) through a straightforward and effective polyol-medium solvothermal method. The tadpolelike nanocomposites were able to orient and self-assemble into one-dimensional structure under external magnetic field, thus displaying great potential in precise manipulation and organization of carbon nanotube-based structures into integrated functional system.

The morphology, magnetic properties, crystallization mechanism and applications of the nanoparticles of amorphous Iron oxide are studied. The size of these amorphous particles predetermines the structure of the initial crystalline polymorph.

An iron oxide (magnetite) nanoparticle is synthesized within the interior cavity of a genetically engineered human H-chain ferritin (HFn). Both magnetite-containing and fluorescently labeled RGD4C-Fn cages bound C32 melanoma cells in vitro and jointly these results show the capability of a genetically modified protein cage architecture to serve as a multifunctional nanoscale container for simultaneous iron oxide loading and cell-specific targeting.

A study reports the growth of oriented alpha-[Fe.sub.2][O.sub.3] nanorods on Si substrates using metal-organic chemical vapor deposition (MOCVD). Structural analyses reveal that alpha-[Fe.sub.2][O.sub.3] nanorods are preferentially oriented in the [104] direction on Si(100) substrates, and the nanorod possesses the single-crystalline structure.

The synthesis and characterization of silica-encapsulated iron oxide magnetic nanoparticles of controlled dimension as an enzyme carrier is reported. The results have suggested that the optimum pH and thermal stability of the attached enzyme are greatly influenced by the local environment of the silica and it is shown that the immobilized enzyme can be recovered and reused upon repeated application of magnetic separation.

The three novel clusters [Mn6O4(OMe)2(OAc)4(Mesalim)4], [Mn8O2(OH)2(OMe)12(OAc)2(Mesalim)4] and [Fe10O4(OMe)12Cl2(Mesalim)6] are synthesized from a simple bidentate ligand HMesalim. Although the bridging coordination mode is commonly observed for ligands containing phenoxo donors, including HEtsalim, (super 19,55-57) the HMesalim ligand occupies terminal positions in these clusters.