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We devised a quantum chemical simulation protocol that can rapidly and accurately predict ground and excited state reduction potentials (E0 and E*, respectively) of acridinium photoredox catalysts (PCs). To bypass time‐consuming excited state geometry optimizations, we used ground state equilibrium geometries to compute the electronic energy of excited states, which provides reasonable E0 and E* estimates. The contribution of Hartree‐Fock exchange (HFX) in density functionals was systematically varied to estimate E0 and E*. In addition to reproducing experimental results, physically sensible models, such as correct descriptions of exciton behavior, are highly necessary. Based on the exciton correlation values, the appropriate amount of HFX in the B3LYP functional was determined to be 30 % to yield physically sensible bound electron‐hole pairs for small organic molecules. We also investigated the impact of basis sets on the predictability of E0 and E*. Geometry optimizations with B3LYP‐D2(HFX 20 %)/6‐31G and single point energy refinement with (TD‐)B3LYP‐D2(HFX 30%)/6‐311++G(d,p) yielded the best results. The transferability of the suggested protocol was confirmed with a test set consisting of eight acridinium derivatives. This study can provide reasonably accurate results with relatively small amounts of computational resources, and it is therefore expected to greatly contribute to the development of new acridinium PCs. [ABSTRACT FROM AUTHOR]

Incorporating electrocatalytic active sites into the reticular framework allows for the design of novel catalytic structures promoting desired catalytic reactions with efficient mass transfer. However, to fully exploit the advantages of such a framework, it is crucial to ensure the electrochemical stability of the material. In this context, alkaline‐stable bimetallic MxNi2‐xCl2BTDD (M = Fe, Co) metal–organic frameworks (MOFs) are employed as electrocatalysts for alkaline water oxidation reaction (WOR) to understand the correlation between secondary metal incorporation and catalytic activity changes. For a specific Fe ratio within the MOF, the optimal catalytic activity is achieved at an overpotential of 315 mV at a WOR current density of 10 mA cm−2geo. Based on its well‐defined crystal structure and uniformly arranged metal nodes, which are not limited to specific facets, the cooperative electrocatalytic mechanism during the faradaic WOR process is investigated through operando Raman spectroscopy and density functional theory calculations. These results enable the interpretation of the electrochemical WOR mechanism based on MOF, providing a further fundamental understanding of electrocatalytic activity in bimetallic systems. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene has been increasingly utilized in a variety of energy-related applications, serving as a catalyst or support material for fuel cells, and as an anode material for lithium-ion batteries, among others. The thermal reduction of graphene oxide (GO) in nitrogenous sources to incorporate nitrogen, producing nitrogen-doped reduced graphene oxide (NRGO), is the most favored method. Controlling atomic configurations of nitrogen-doped sites is the key factor for tailoring the physico-chemical properties of NRGO, but major challenges remain in identifying detailed atomic arrangements at nitrogen binding sites on highly defective and chemically functionalized GO surfaces. In this paper, we present atomistic-scale modeling of the nitrogen doping process of GO with different types of vacancy defects. Molecular dynamics simulations using a reactive force field indicate that the edge carbon atoms on defect sites are the dominant initiation location for nitrogen doping. Further, first-principles calculations using density functional theory present energetically favorable chemical transition pathways for nitrogen doping. The significance of this work lies in providing important chemical insights for the effective control of the desired properties of NRGO by suggesting a detailed mechanism of the nitrogen doping process of GO. [ABSTRACT FROM AUTHOR]

Due to their optimal bandgap size and large defect tolerance, nitrides are becoming pivotal materials in several optoelectronic devices, photovoltaics, and photocatalysts. A computational method that can accurately predict their electronic structures is indispensable for exploring new nitride materials. However, the relatively small bandgap of nitrides, which stems from the subtle balance between ionic and covalent bond characteristics, makes conventional density functional theory challenging to achieve satisfactory accuracy. Here, we employed a self-consistent hybrid functional where the Hartree–Fock mixing parameter is self-consistently determined and thus the empiricism of the hybrid functional is effectively removed to calculate the bandgaps of various nitride compounds. By comparing the bandgaps from the self-consistent hybrid functional calculations with the available experimental and high-level GW calculation results, we found that the self-consistent hybrid functional can provide a computationally efficient approach for quantitative predictions of nitride electronic structures with an accuracy level comparable to the GW method. Additionally, we aligned the band edge positions of various nitride compounds using self-consistent hybrid functional calculations, providing material design principles for heterostructures of nitride-based optoelectronic devices. We anticipate the wide use of the self-consistent hybrid functional for accelerating explorations and predictions of new nitride-based functional materials in various photoactive applications. [ABSTRACT FROM AUTHOR]

Charge transfer (CT) in donor–acceptor complexes can occur in two directions: from donor to acceptor (forward CT, CTF) and from acceptor to donor (backward CT, CTB). For an ethylene and tetrafluoroethylene model system, coupled cluster calculations predict that CTF is more stable than CTB. Meanwhile, density functional theory (DFT) and time‐dependent DFT (TDDFT) employing B3LYP functional show a different CT state order depending on the Hartree–Fock exchange (HFX) contribution. The impact of basis sets as a possible cause to induce such unreasonable CT state reverse along with the increase of HFX was investigated. The physical origin of CT state reversal is examined in terms of molecular orbital energy. We analyzed two additional molecular pairs that feature CT state reversal along with the amount of HFX in B3LYP functional. Despite the reduced gap, we suggest constrained DFT using M06‐HF functional as an effective approach to estimate two CT state energies on equal footing. [ABSTRACT FROM AUTHOR]

The π–π interaction is a major driving force that stabilizes protein assemblies during protein folding. Recent studies have additionally demonstrated its involvement in the liquid–liquid phase separation (LLPS) of intrinsically disordered proteins (IDPs). As the participating residues in IDPs are exposed to water, π–π interactions for LLPS must be modeled in water, as opposed to the interactions that are often established at the hydrophobic domains of folded proteins. Thus, we investigated the association of free energies of benzene and phenol dimers in water by integrating van der Waals (vdW)-corrected density functional theory (DFT) and DFT in classical explicit solvents (DFT-CES). By comparing the vdW-corrected DFT and DFT-CES results with high-level wavefunction calculations and experimental solvation free energies, respectively, we established the quantitative credibility of these approaches, enabling a reliable prediction of the benzene and phenol dimer association free energies in water. We discovered that solvation influences dimer association free energies, but not significantly when no direct hydrogen-bond-type interaction exists between two monomeric units, which can be explained by the enthalpy–entropy compensation. Our comprehensive computational study of the solvation effect on π–π interactions in water could help us understand the molecular-level driving mechanism underlying the IDP phase behaviors. [ABSTRACT FROM AUTHOR]

Solid–liquid interfaces are ubiquitous in scientifically and technologically important systems, and they govern complex chemophysical processes such as those in electrochemistry and heterogeneous catalysis. Atomic‐level elucidation of interfacial structures has been extensively pursued; however, related research is still limited. A major obstacle lies in the intrinsic character of interfaces: they are located between two bulk phases that make the application of spectroscopic or surface‐science techniques be difficult. Although this suggests the possibility of employing computational approaches to explore interfacial structures, modern molecular simulation methods suffer from an inability to simulate large interfacial systems in a sufficient time scale at the all‐atom resolution. To develop a method capable of simulating solid–liquid interfaces, we have been developing a mean‐field quantum mechanics/molecular mechanics (QM/MM) method. This Review briefly summarizes the theoretical background of mean‐field QM/MM, as well as recent efforts to advance it. Furthermore, we summarize several studies performed based on this method. [ABSTRACT FROM AUTHOR]

The hybridization of conductive nanospecies has garnered significant research interest because of its high efficacy in improving the diverse functionalities of nanostructured materials. In this study, a novel synthetic strategy is developed to optimize the defect structure, structural ordering, and energy‐related functionality of nanostructured‐materials by employing a multilayer multicomponent two‐dimenstional (2D) graphene/metal oxide/graphene nanosheet (NS) as a versatile hybridization matrix. The hybridization of the robust trilayer, polydiallyldiammonium (PDDA)‐anchored reduced‐graphene oxide (prGO)/metal oxide/prGO NS effectively enhance the structural ordering and porosity of the hybridized MoS2/MnO2 NS through suppression of defect formation and tight stacking. In comparison with monolayer rGO/RuO2 NS‐based homologs, the 2D superlattice trilayer prGO/RuO2/prGO NS hybrids deliver better functionalities as a hydrogen evolution electrocatalyst and as a supercapacitor electrode, demonstrating the merits of hybridization with multilayer NSs. The advantages of using multilayer multicomponent conductive NSs as hybridization matrices arise from the enhancement of charge and mass transport through the layer flattening or defect suppression of the hybridized NSs and the increase in porosity, as evidenced by density functional theory calculations. Finally, the universal utility of multilayer NSs is confirmed by investigating the strong effect of the stacking order on the electrocatalytic functionality of MoS2/rGO/RuO2 films fabricated through layer‐by‐layer deposition. [ABSTRACT FROM AUTHOR]

An effective methodology to stabilize highly dispersed metal nanoparticles is developed by employing the exfoliated 2D metal oxide nanosheets with variable surface structures as substrates. The selection of appropriate crystal structure of titanate nanosheet is very crucial in stabilizing atomically dispersed Pt nanoparticles through the tuning of chemical interaction between Pt and titanate substrate. A theoretical study using density functional theory calculations confirms the significant influence of the crystal structure of layered titanate nanosheet on the crystal growth behavior of immobilized metal nanoparticle. As a consequence of the good dispersion of Pt nanoparticles, the Pt-trititanate nanohybrids with stronger interaction show much higher content of atomically dispersed Pt and better catalyst performances than do the Pt-lepidocrocite titanate ones. The applicability of the present method for other metal species is evidenced by the successful tuning of the crystal size and functionality of Au nanoparticles via immobilization on layered titanate nanosheets. The functionality of Au for surface-enhanced Raman spectroscopy becomes improved by the anchoring on the lepidocrocite-type titanate nanosheet. The present study underscores that the use of the metal oxide 2D nanosheets with appropriate surface structure as substrates is effective in tailoring the crystal growth and the functionalities of immobilized metal nanoparticles. [ABSTRACT FROM AUTHOR]

Lithium Lanthanum Titanate (LLTO) is a Li-ion conducting perovskite-type oxide ceramic which has attracted significant attention as a prospective solid electrolyte for use in all-solid-state Li-ion batteries. However, recent investigations have shown that the material exhibits electronic conductivity under certain conditions. Notably, the amorphous phase of the material does not seem to suffer from this deficiency. In this work density functional theory calculations are used to elucidate the exact nature of electronic conductivity in LLTO, and comparisons are drawn between the crystalline and amorphous cases. Results show that Li interstitial defects form spontaneously within LLTO, and that even slight variations in the Li content of the material will introduce electronically conductive states. This behavior is the same in the crystalline and amorphous phases. However, in the amorphous phase the band edge states are highly localized, so electronic conduction does not occur in the material. For this reason, amorphous LLTO may serve as a viable solid electrolyte for all-solid-state batteries despite the known problems with the crystalline phase. [Display omitted] • Minor changes in the Li content of LLTO introduce electronically conductive states • In amorphous LLTO, Anderson localization prevents electron transport • Crystalline LLTO is a mixed ionic electronic conductor (MIEC) • Amorphous LLTO is an ionic conductor only [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) interactions are important in numerous physical, chemical, and biological systems. However, traditional density functional theory (DFT) within local or semi-local approximations can hardly treat this interaction. Among various attempts to handle vdW interactions in DFT, semi-empirical correction methods are known to present the advantages of low additional computational costs and easy implementation in conventional DFT codes. In this review, we summarize the state-of-the-art semi-empirical vdW correction methods based on pairwise summations within the atoms-in-molecules scaling framework, such as the Grimme's D3 methods and variants of the Tkatchenko-Scheffler method. In addition, we compare the performance of these methods for systems ranging from molecules to solids, which have dispersive to ionic interactions: 128 molecular pairs, 23 molecular crystals, 4 noble gas crystals, 27 two-dimensional layered materials, and 9 ionic crystals. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Seven methods, including three van der Waals density functionals (vdW-DFs) and four different variants of the Tkatchenko-Scheffler (TS) methods, are tested on the A24, L7, and Taylor et al.’s “blind” test sets. It is found that for these systems, the vdW-DFs perform better that the TS methods. In particular, the vdW-DF-cx functional gives binding energies that are the closest to the reference values, while the many-body correction of TS does not always lead to an improvement in the description of molecular systems. In light of these results, several directions for further improvements to describe van der Waals interactions are discussed. [ABSTRACT FROM AUTHOR]

The reduction potentials of a tris(2,2′-bipyridinyl)iron (III/II) and iron(III/II) couples complexed with 2,2′-bipyridinyl derivatives in acetonitrile are predicted using density functional theory. The calculation protocol proposed by Kim et al. (Kim, J. Park, Y. S. Lee, J. Comput. Chem. 2013, 34, 2233) showing reliable performance for the reduction potential is used. The four kinds of the functional groups, a methoxy group, a methyl group, a chlorine atom, and a cyanide group, are substituted at the ligands to examine the electronic effect on the reduction potential. Electron donating/withdrawing effect is analyzed by comparing the reduction potential having different substituents at the same position. The influence of the geometrical strain on the reduction potential is investigated. The good correlation between the experimental results and the calculated results is obtained. Not only the general trend, but also the detailed phenomena are correctly reproduced. The maximum deviation from the experimental value is 0.083 V for the methyl substitution at the position 4. The mean absolute error for the seven couples is 0.047 V. The difference of the reduction potential between the chlorine atom substituted at the positions 4 and 5, 0.1 V, is well described. The difference between the CN and the Cl substitution of 0.318 and 0.228 V for the position 4 and 5 is correctly obtained as 0.325 and 0.213 V, respectively. The simple linear relation between the lowest unoccupied molecular orbital (LUMO) energy of the Fe(III) complexes in solution and the calculated reduction potentials is obtained with the R2 of 0.977. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Density functional theory calculation has been performed to calculate the redox potential and the correct ground spin state of iron complexes in acetonitrile. Widely used B3LYP functional is applied with the spin state corrected basis sets. The newly developed protocol for the set of 21 iron complexes is to optimize the structure at the level of the B3LYP/6-31G* and to calculate the single point electronic energy with the same functional and the modified basis sets s6-31G* for the iron atom and 6-31+G* for other ligand atoms. The solvation energy is considered through the polarized continuum model and the cavity creation energy is included for the accurate spin state description. Modifying the cavity size by employing the different scaling factor according to the mean absolute value of the natural population analysis charge (MA-NPA) is introduced. The molecule with the large MA-NPA requires the cavity size smaller than the less polar one. This protocol gives only 1 wrong ground spin state among the 18 iron complexes for which experimental data are known. For the open circuit voltage (OCV) calculation, our protocol performs well yielding the mean absolute error of 0.112 V for the test set. The close correlation between the calculated and the experimental OCV are obtained. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The reduction of p-nitrophenol (p-NP) to p -aminophenol (p-AP) by nanoscale zero-valent iron (NZVI)/NaBH 4 system in an oxygen environment was studied by means of liquid chromatography, spectroscopy (vibration and X-ray photoelectron), solid analyses (transmission electron microscopy and X-ray diffraction) and density functional theory (DFT) calculations. Addition of NaBH 4 into NZVI suspension showed the disintegration of NZVI (60–100 nm), resulting in the formation of much smaller particles (15–40 nm) due to the chemical etching of outermost surfaces (i.e., magnetite). Interestingly, complete reduction of p-NP and high conversion efficiency of p-AP (>98%) were observed in NZVI/NaBH 4 system even after four recycling which is quite comparable with widely used noble metallic catalysts. Surface analysis confirmed that NaBH 4 can prevent the oxidation of NZVI surface, leading to the continuous reduction of p-NP in oxygen environments. Experimental results and DFT calculations suggested that not only the formation of smaller NZVI but also thermodynamic preferences for reduction of p-NP on outermost surfaces of NZVI (i.e., magnetite) may significantly affect the reduction process of p-NP in NZVI/NaBH 4 system. These novel findings can promote the development of new NZVI technologies which can be used for wastewater reductive treatment in oxygen environments. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • PEALD grown polycrystalline WS 2 using W(CO) 6 precursor and H 2 S plasma as a reactant. • H 2 S plasma to facilitate ALD reaction elucidated from DFT calculation. • Excellent uniformity and conformality of PEALD-WS 2 on 3 dimensional Ni-foam. • Applications as a binder and carbon-free anode in SIBs and catalyst for HER. Abstract Tungsten disulfide (WS 2) thin films are grown on several types of substrates by plasma-enhanced atomic layer deposition (PEALD) technique using tungsten hexacarbonyl [W(CO) 6 ] and H 2 S plasma at a relatively low temperature of 350 °C. The method delivers polycrystalline WS 2 film with (0 0 2) preferential growth and the high quality films could be successfully grown with as low as 30 ALD cycles (corresponding to ∼3 nm of thickness). Density functional theory (DFT) calculation results reveal that both adsorption of W(CO) 6 and removal of CO ligand would be facilitated by usage of H 2 S plasma by generating the different defect sites on the basal plane. The typical self-limiting film growth (growth rate of ∼0.1 nm/cycle), characteristic of ideal ALD, is clearly observed with both the precursor and reactant pulsing time. X-ray diffractometry (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS) are performed in details to study the as-grown WS 2 film on Si/SiO 2 substrate. The analysis results confirm the formation of polycrystalline film, with high purity and well-defined stoichiometry. The as-deposited WS 2 films are then explored as an electrode in the field of energy generation as well as energy storage. The films are uniformly and conformally grown on high surface-area 3 dimensional Ni-foam that show excellent activity towards hydrogen evolution reaction (HER). Significantly low overpotential of ∼280 mV is observed at a high operational current density of 100 mA cm−2 during HER in acid electrolyte. In addition, the as-grown films on stainless steel substrate also reveal the stable electrochemical performances in Na-ion battery as an anode with reasonably high areal capacity of ∼44.5 μAh cm−2 at the end of 50 charge-discharge cycles. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) is a method to fabricate uniform and conformal thin films based on surface chemistry. Al 2 O 3 (alumina) is the most widely and thoroughly studied material in the field of oxide ALD. Most previous mechanistic studies on ALD of Al 2 O 3 have been focused on the surface reaction step of Al-containing precursor: for the popular trimethylaluminum, it is known that the surface becomes terminated with Al-CH 3 groups. However, reaction mechanisms for oxygen sources other than H 2 O has been largely unexplored. In this study, the surface reaction mechanisms for the CH 3 -terminated alumina surface with H 2 O, H 2 O 2 , and O 3 oxidants were investigated at molecular level. Density functional theory (DFT) calculations were used to obtain the energy change along reaction coordinates. It is confirmed that all three oxidants considered in this study would show facile oxidation of surface CH 3 into OH under ALD conditions. Still, the exact mechanisms and number of oxidant molecules required for a full reaction to generate hydroxyl-terminated surface vary. The molecular reactivity toward ALD of Al 2 O 3 at low deposition temperatures for the three oxidizing agents are expected to be H 2 O < H 2 O 2  < O 3 . [ABSTRACT FROM AUTHOR]

Selective chemical vapor deposition (CVD) of Co on Cu interconnect lines is an advantageous method because it can simplify unit process and suppress side effects resulting from the metal etching process. Density functional theory calculations show that CoCp(CO) 2 has a relatively higher kinetic barrier (36.2 kcal/mol) on SiO 2 than that of Co 2 (CO) 8 (22.9 kcal/mol). This indicates that CoCp(CO) 2 could be a promising candidate as a Co precursor for selective CVD. Selective CVD of Co films is demonstrated experimentally by deposition on SiO 2 and Cu substrates at 200 and 300 °C. To reduce C contents in the deposited film, a NH 3 plasma process is adopted into conventional CVD in a cyclic CVD process. This process enables deposition of Co films with lower C content while maintaining selective deposition. [ABSTRACT FROM AUTHOR]

Chlorinatedorganics are the principal and most frequently foundcontaminants in soil and groundwater, generating significant environmentalproblems. Over the past several decades, Fe-containing minerals naturallyoccurring in aquatic and terrestrial environments have been used asnatural electron donors, which can effectively dechlorinate a varietyof chlorinated organics. However, a full understanding of the reactionmechanism of the dechlorination pathway cannot be obtained by experimentalinvestigations alone, due to the immeasurability of chemical speciesformed over a short reaction time. In this report, we describe experimentsand density functional theory (DFT) calculations carried out to investigatethe complex reduction pathway of carbon tetrachloride (CT) on a vivianite(FeII3(PO4)2·8H2O) surface. Our results indicate that chloroform (HCCl3) and formate are the primary transformation products. Theexperimental results reveal that the reduction kinetics of CCl4can be dramatically accelerated as the pH is increased from3 to 11. On the basis of the DFT calculations, we found that HCCl3can be formed by •CCl3and :CCl3–* on a deprotonated vivianite surface (anadsorbate on vivianite is denoted using an asterisk). In addition,:CCl3–* can be nonreductively dechlorinatedto form :CCl2* followed by sequential nucleophilic attackby OH–*, resulting in the formation of :CCl(OH)*and :C(OH)2*, which are responsible for production of COand formate, respectively. The results obtained from this study canfacilitate the modeling of systems of other halogenated species andminerals, which will provide fundamental insight into their correspondingreaction mechanisms. [ABSTRACT FROM AUTHOR]

The effects of the ligand of precursor on the growth characteristics and electrical properties of W films prepared by ALD were systematically investigated using two newly synthesized precursors, WCl 5 and HEtCpW(CO) 3. [Display omitted] • Newly synthesized precursors for atomic layer deposition (ALD) of tungsten thin films. • Comparison of WCl 5 and HEtCpW(CO) 3 with theoretical calculation and film properties. • Quantum chemical calculations of the precursor adsorption on the substrate surface. We compared the growth characteristics and film properties of tungsten (W) thin films prepared by atomic layer deposition (ALD) using two newly synthesized precursors, tungsten pentachloride (WCl 5) and ethylcyclopentadienyltungsten(V) tricarbonyl hydride (HEtCpW(CO) 3), with Ar/H 2 plasma as the reactant. The purpose of this study was to evaluate the suitability of these precursors for W thin films used in interconnect technology. The growth characteristics and film properties were significantly affected by the ligands of the precursors. The chemical compositional analysis results showed that high-purity thin films were obtained using the WCl 5 precursor, compared to the films obtained using the HEtCpW(CO) 3 precursor, which were relatively high in carbon content and oxygen impurities. The W thin films obtained from the WCl 5 precursor showed superior electrical properties compared to those of the HEtCpW(CO) 3 precursor, which were related to the crystallinity and film density in addition to the impurities. These results provide profitable information regarding the selection of a pertinent precursor for the device fabrication. [ABSTRACT FROM AUTHOR]

• Presence of Ca2+, Na+, HCO 3 − ions significantly inhibited removal of Cr(VI) by vivianite. • Geochemical modeling revealed formation of CaCrO 4(aq) and NaCrO 4 − by ions addition. • DFT showed that CaCrO 4(aq) and NaCrO 4 − are less favorable for adsorption on vivianite surface. • XAS revealed the reductive immobilization of Cr(VI) by vivianite via inner-sphere complexation. A systematic study was conducted to investigate the effect of major groundwater ions (i.e., Ca2+, Na+, and HCO 3 −) on removal of hexavalent chromium (Cr(VI)) by an Fe(II)-phosphate mineral (i.e., vivianite). The batch experiments revealed that the second-order rate constant for Cr(VI) removal by vivianite with Ca2+ + CO 3 2− (0.076–1.90 mM) and Na+ + HCO 3 − (0.26–6.50 mM) was 1.5–5.2 times lower than that without these ions. The removal kinetics of Cr(VI) by vivianite was abruptly slowed down with the increased ion concentration, which showed their inhibitory effect on the reaction. The results of the geochemical modeling and density functional theory calculations showed that the presence of Ca2+ + HCO 3 − and Na+ + HCO 3 − can form less favorable Cr(VI) species (i.e., CaCrO 4(aq) and NaCrO 4 −) on the Fe–B site of vivianite surface, leading to the inhibitory effect observed in this study. Finally, the X-ray absorption spectroscopy results showed that reductive immobilization of Cr(VI) to Cr(III) occurred by structural Fe(II) oxidation of vivianite to amorphous mixed-valence Fe-phosphate via an inner-sphere complexation. The results suggest that the presence of Ca2+, Na+, and HCO 3 − in phosphorous-enriched iron-reducing environments may lower the remedial efficiency of Cr(VI) removal. [ABSTRACT FROM AUTHOR]