@article{khare_martin_hesterberg_2007, title={Phosphate bonding configuration on ferrihydrite based on molecular orbital calculations and XANES fingerprinting}, volume={71}, ISSN={["0016-7037"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34548540954&partnerID=MN8TOARS}, DOI={10.1016/j.gca.2007.07.008}, abstractNote={Sorption of phosphate by Fe(III)- and Al(III)-(hydr)oxide minerals regulates the mobility of this potential water pollutant in the environment. The objective of this research was to determine the molecular configuration of phosphate bound on ferrihydrite at pH 6 by interpreting P K-edge XANES spectra in terms of bonding mode. XANES and UV–visible absorption spectra for aqueous Fe(III)–PO4 solutions (Fe/P molar ratio = 0–2.0) provided experimental trends for energies of P(3p)–O(2p) and Fe(3d)–O(2p) antibonding molecular orbitals. Molecular orbitals for Fe(III)–PO4 or Al(III)–PO4 complexes in idealized monodentate or bidentate bonding mode were generated by conceptual bonding arguments, and Extended-Hückel molecular orbital computations were used to understand and assign XANES spectral features to bound electronic states. The strong white line at the absorption edge in P K-edge XANES spectra for Fe–PO4 or Al–PO4 systems is attributable to an electronic transition from a P 1s atomic orbital into P(3p)–O(2p) or P(3p)–O(2p)–Al(3p) antibonding molecular orbitals, respectively. For Fe–PO4 systems, a XANES peak at 2–5 eV below the edge was assigned to a P 1s electron transition into Fe(4p)–O(2p) antibonding molecular orbitals. Similarly, a shoulder on the low-energy side of the white line for variscite corresponds to a transition into Al(3p)–O(2p) orbitals. In monodentate-bonded phosphate, Fe–O bonding is optimized and P–O bonding is weakened, and the converse is true of bidentate-bonded phosphate. These differences explained an inverse correlation between energies of P(3p)–O(2p) and Fe(3d)–O(2p) antibonding molecular orbitals consistent with a monodentate-to-bidentate transition in aqueous Fe(III)–PO4 solutions. The intensity of the XANES pre-edge feature in Fe(III)-bonded systems increased with increasing number of Fe(III)–O–P bonds. Based on the similarity of intensity and splitting of the pre-edge feature for phosphate sorbed on ferrihydrite at 750 mmol/kg at pH 6 and aqueous Fe–PO4 solutions containing predominantly bidentate complexes, XANES results indicated that phosphate adsorbed on ferrihydrite was predominantly a bidentate–binuclear surface complex.}, number={18}, journal={GEOCHIMICA ET COSMOCHIMICA ACTA}, author={Khare, Nidhi and Martin, James D. and Hesterberg, Dean}, year={2007}, month={Sep}, pages={4405–4415} }
 @article{khare_hesterberg_martin_2005, title={XANES investigation of phosphate sorption in single and binary systems of iron and aluminum oxide minerals}, volume={39}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-16844386656&partnerID=MN8TOARS}, DOI={10.1021/es049237b}, abstractNote={Phosphate sorption on Fe- and Al-oxide minerals helps regulate the solubility and mobility of P in the environment. The objective of this study was to characterize phosphate adsorption and precipitation in single and binary systems of Fe- and Al-oxide minerals. Varying concentrations of phosphate were reacted for 42 h in aqueous suspensions containing goethite, ferrihydrite, boehmite, or noncrystalline (non-xl) Al-hydroxide, and in 1:1 (by mass) mixed-mineral suspensions of goethite/boehmite and ferrihydrite/ non-xl Al-hydroxide at pH 6 and 22 degrees C. X-ray absorption near edge structure (XANES) spectroscopy was used to detect precipitated phosphate and distinguish PO4 associated with Fe(III) versus Al(III) in mixed-mineral systems. Changes in the full width at half-maximum height (fwhm) in the white-line peak in P K-XANES spectra provided evidence for precipitation in Al-oxide single-mineral systems, but not in goethite or ferrihydrite systems. Similarly, adsorption isotherms and XANES data showed evidence for precipitation in goethite/boehmite mixtures, suggesting that mineral interactive effects on PO4 sorption were minimal. However, sorption in ferrihydrite/non-xl Al-hydroxide systems and a lack of XANES evidence for precipitation indicated that mineral interactions inhibited precipitation in these binary mixtures.}, number={7}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Khare, N and Hesterberg, D and Martin, JD}, year={2005}, month={Apr}, pages={2152–2160} }
 @article{khare_hesterberg_beauchemin_wang_2004, title={XANES determination of adsorbed phosphate distribution between ferrihydrite and boehmite in mixtures}, volume={68}, DOI={10.2136/sssaj2004.4600}, abstractNote={Iron- and Al-(hydr)oxide minerals are important sorbents for retaining PO 4 in soils. Our objective was to determine the distribution of adsorbed PO, between ferrihydrite and boehmite in aqueous mixtures of these minerals. Phosphate was adsorbed in aqueous suspensions up to maximum concentrations of 1860, 850, and 1420 mmol kg -1 for ferrihydrite, boehmite, and 1:1 (by mass) mixtures of these minerals at pH 6. The solids were analyzed as moist pastes using P K-XANES (X-ray absorption near edge structure) spectroscopy. The adsorption isotherm for the mixed-mineral suspensions could essentially be described as a linear combination of Freundlich isotherm models for each single-mineral system, indicating negligible mineral interactive effects on PO 4 adsorption in the mixtures. X-ray absorption near edge structure spectra for PO 4 adsorbed on ferrihydrite or in ferrihydrite/ boehmite mixtures showed a pre-edge feature at approximately 2146 eV that was absent in boehmite systems. Linear combination fitting of the pre-edge region of XANES spectra for mixtures with average spectra for PO4 adsorbed on boehmite or ferrihydrite alone, indicated that 59 to 97% of the PO 4 was adsorbed on ferrihydrite in the mixtures. With increasing concentration of adsorbed PO 4 in the mineral mixtures, the concentration adsorbed on the ferrihydrite component increased linearly. Phosphate distribution trends in the mixtures suggested an affinity preference for ferrihydrite at the lowest adsorbed PO 4 concentration (100 mmol kg -1 minerals), no affinity preference for either mineral at intermediate concentrations (200 to 600 mmol PO 4 kg -1 ), and the possibility of a surface precipitate involving Al at the highest concentration (1300 mmol PO 4 kg -1 ).}, number={2}, journal={Soil Science Society of America Journal}, author={Khare, N. and Hesterberg, Dean and Beauchemin, S. and Wang, S. L.}, year={2004}, pages={460–469} }
 @article{khare_classen_pilkington_1997, title={Kinetics of whole hog fermentation}, number={974047}, journal={Paper (American Society of Agricultural Engineers)}, author={Khare, N. and Classen, J. J. and Pilkington, D.}, year={1997}, pages={11} }