Monodentate Complexes Research Articles

Synthesis and Coordination Behavior of a New Hybrid Bidentate Ligand with Phosphine and Silylene Donors.

This work describes the synthesis and coordination behavior of a new mixed‐donor ligand PhC(NtBu)2SiC6H4PPh2 (1) containing both silylene and phosphine donor sites. Ligand 1 was synthesized from a reaction of ortho‐lithiated diphenylphosphinobenzene (LiC6H4PPh2) with chlorosilylene (PhC(NtBu)2SiCl). Treatment of 1 with Se and GeCl2 resulted in SiIV compounds 2 and 3 by selective oxidation of the silylene donor. This strong σ‐donor ligand induces dissociation of CuCl and PhBCl2 leading to formation of ionic complexes 4 and 5 respectively. The reaction of 1 with ZnCl2 and AlCl3 resulted in the formation of chelate complexes 5 and 7, respectively, while treatment with EtAlCl2 and GaCl3 forms monodentate complexes 8 and 9. X‐ray analysis of 4 showed that the copper is in the spiro center of the two five‐membered rings. Moreover, the copper(I)chloride has not been oxidized but dissociates to Cu+ and [CuCl2]−. All the compounds are well characterized by mass spectrometry, elemental analysis, NMR spectroscopy, and single‐crystal X‐ray diffraction studies.

Adsorption of Mg2+ and K+ on the kaolinite (0 0 1) surface in aqueous system: A combined DFT and AIMD study with an experimental verification

Microscopic adsorption mechanism of Mg2+ and K+ on kaolinite (001) surface in aqueous system was investigated by density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations. A verification experiment has also been done to compare the adsorption capacity of kaolinite to the two ions. The structure for both hydrated complexes and mono-/bi-dentate adsorption complexes of Mg2+ and K+ in aqueous environment was examined, with radial distribution function and binding energies calculated. [Mg(H2O)6]2+ and [K(H2O)6]+ are the dominant complexes of hydrated Mg2+ and K+, respectively. Bidentate complexes of Mg2+ and monodentate complexes of K+ are their respective dominant complexes, and the binding energies of all the adsorption complexes of Mg2+ are higher than those of K+. Partial density of states projections combining with Mulliken bond charge and populations show the strong ionic characters and weak bonding and anti-bonding states filling of Mg − Os and K − Os in the adsorption complexes. The adsorption experiment verified that Mg2+ is easier to adsorb on kaolinite surface than K+.

An Atomic-Scale Understanding of the Solution Chemistry of Antimony(V): Insights from First-Principles Molecular Dynamics Simulation.

In this study, the structure, hydrolysis, and complexation of Sb(V) in aqueous solution has been elucidated by using first-principles molecular dynamics (FPMD) simulations. The results show that both antimonic acid and its deprotonated form have an octahedral configuration, with average Sb-OH2 and Sb-OH distances of 2.25 and 2.05 Å, respectively. The computed pKa of [Sb(OH)5(OH2)] is 1.8, while [Sb(OH)6]- has an extremely high pKa. Consequently, [Sb(OH)6]- is the most dominant species of Sb(V) under common environmental conditions. A stable aqueous complex can form between [Sb(OH)6]- and common cations, and an Sb-Al bidentate complex has the largest dissociation free energy, followed by a Sb-Mg bidentate complex, indicating that they have significantly higher stabilities. For Na+ and Ca2+, their respective monodentate and bidentate complexes have similar dissociation free energies, indicating very close possibilities. These findings provide a comprehensive understanding of the solution chemistry of Sb(V) from a quantitative and microscopic perspective.

Analysis of technetium immobilization and its molecular retention mechanisms by Fe(II)-Al(III)-Cl layered double hydroxide

Layered double hydroxides (LDH) play a decisive role in regulating the mobility of contaminants in natural and engineered environments. In this work, the retention of an Fe(II)-Al(III)-Cl LDH towards pertechnetate (TcO4–), which is the most stable and highly mobile form of Tc under aerobic conditions, is investigated comprehensively as a function of pH, Tc concentration and ionic strength. For a technetium initial concentration of 5 µM, its retention yield is higher than 80% from pH 3.5 to pH 10.5, especially at NaCl concentration below 0.1 M. A combination of vibrational and X-ray absorption spectroscopy provides structural information on the retention mechanism on a molecular scale. X-ray absorption near edge spectroscopy (XANES) confirms that most of the Tc uptake is due to an initial Tc(VII) reduction to Tc(IV), and consecutive Tc(IV) interaction with the solid. The analysis of the extended X-ray absorption fine structure (EXAFS) reveals two different mechanisms of Tc(IV) interaction with hematite (sub-product of the LDH oxidation and confirmed by Raman microscopy). At low pH, sorption of Tc(IV) dimers via inner-sphere monodentate complexation on hematite dominates. In contrast, under alkaline conditions, Tc(IV) is incorporated into the structure of hematite. Additionally, in situ attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR) evidences a small contribution of the total uptake corresponding to Tc(VII) anion exchange.The derived molecular structures increase confidence in predictive modelling of Tc migration patterns in subsurface environments, e.g. in the vicinity of a radioactive waste repository and treatment sites or in polluted areas due to other anthropogenic Tc sources.

Activation of MnFe2O4 by sulfite for fast and efficient removal of arsenic(III) at circumneutral pH: Involvement of Mn(III)

As(III) oxidation to As(V) is deemed necessary for better arsenic removal, and separation is still the optimal approach for water remediation from As(III). Herein, sulfite (SIV) was adopted to activate MnFe2O4 for simultaneous oxidation and adsorption of As(III) in neutral water. The As(III) removal was more efficient than a peroxidation of As(III) followed by adsorption. The adsorption capacity of MnFe2O4/S(IV) for As(III) (26.257 mg g−1) was much higher than those of MnFe2O4 alone for As(III) (9.491 mg g−1) and As(V) (9.142 mg g−1). The mechanistic study corroborated that intermediate Mn(III) was the dominant oxidant responsible for rapid oxidation of As(III), and the dual roles of S(IV) as a complexing ligand and a precursor of oxysulfur radicals accelerated the redox cycle of Mn(II)/Mn(III). Moreover, S(IV) enhanced arsenic adsorption by driving more production of monodentate complexes. As(III) can be effectively removed over a wide range of temperatures (283.15–313.15 K) and pH (3–10) with the optimal pH of 7. The effect of coexisting ions and reusability of MnFe2O4 were also investigated. Especially, the superior performance of MnFe2O4/S(IV) for As(III) removal in various water matrixes may help develop new removal technologies based on active Mn(III) for the water decontamination from As(III).

Phosphorus binding to soil organic matter via ternary complexes with calcium

Soil organic matter (SOM) is known to exert a major control on the mobility and bioavailability of cationic nutrients. However, the role of SOM in the fate of anionic nutrients, especially phosphorus (P), is less well characterized. The objectives of this study were to (1) compare the formation of binary complexes of calcium (Ca) with humic acids (HA) extracted from two contrasting soils, and (2) determine if binary HA-Ca complexes could incorporate P by forming ternary HA-Ca-P complexes. The Ca binding capacities of the HA extracted from an agricultural organic soil (AOS) and a pristine riparian soil (RS) were measured via potentiometric titrations; the formation of ternary complexes was analyzed by size fractionation using MWCO tubes. Proton and Ca binding capacities of RS-HA were higher than AOS-HA, and pH had a weaker effect on Ca binding to RS-HA. These differences are consistent with lower proportions of aromatic groups, and a higher proportion of alkyl groups derived from 13C NMR spectroscopy. Together, the NMR, titration and MWCO data indicate that Ca binds to RS-HA through monodentate complexes and electrostatic attraction that are capable of binding P producing ternary complexes. In contrast, at pH 8.5 Ca forms bidentate complexes with AOS-HA, which do not provide bridging positions to incorporate P. Overall, our results imply that the formation of HA-Ca and HA-Ca-P complexes depend on the structure of the HA, and that complexation to HA may play an important role in the fate of P in terrestrial and aquatic environments.

Insights to the strained thiocarbamate derivative complexes of platinum group metals induced by azide as a co-ligand: Characterization and biological studies

Halide bridged metal precursors of platinum group on reaction with thiocarbamate derivative ligands (L1 and L2) yielded a series of neutral mono-dentate complexes (1–6) formulated as [(arene)M(κ1(S)-L)Cl2] where, L = L1 and L2, M = Ru, Rh and Ir, arene = p-cymene, Cp∗. Structural studies revealed the ligands coordinated to the metal centers through the thione sulfur in a mono-dentate fashion. These neutral complexes (1–6) were further reacted with NaN3 in methanol which resulted in the formation of highly strained κ2(N,S) azido complexes (7–12). Further treatment of the azido complexes with diethyl acetylene dicarboxylate (DEAD) yielded in the case of rhodium and iridium triazolo complexes (13–16). All these complexes were characterized by various spectroscopic techniques. NMR analysis revealed the triazolo ring coordinated to the metal center via the central nitrogen. Besides the varied coordination of the complexes, these complexes as well as the ligands exhibited antibacterial activity against some bacterial strains under study as well as profound antioxidant potency.

Ab Initio Insight into Mechanisms of Ozone Interaction with a Surface of Dehydrated Nanocrystalline TiO2.

Density functional theory (DFT) study of ozone adsorption on dehydrated nanocrystalline TiO2 is presented. Singlet and triplet binding modes of ozone to the oxide's titanium cations are considered. In both the modes, monodentate and bidentate ozone complexes are formed. According to DFT, the triplet monodentates are the most stable species. The formation of monodentate ozone adsorption complexes is in-line with an earlier interpretation of infrared (IR) spectroscopic data on ozone adsorption on an anatase surface. However, the computed difference in the fundamental vibrational frequencies (ν1 - ν3) of ozone in the triplet monodentates is significantly larger than the corresponding IR value. This discrepancy is resolved by demonstrating that the triplet monodentates readily decompose, realizing molecular oxygen that is consistent with published experimental data. The predicted energy barrier of the dissociative adsorption is less than 2 kcal/mol. In contrast, the computed difference in the fundamental vibrational frequencies (ν1 - ν3) of adsorbed ozone in the singlet bidentates perfectly agrees with the experiment.

Synthesis, structures, and electrocatalytic properties of phosphine‐monodentate, −chelate, and ‐bridge diiron 2,2‐dimethylpropanedithiolate complexes related to [FeFe]‐hydrogenases

To further extend diiron subsite models of [FeFe]‐hydrogenases, the various substitutions of all‐carbonyl diiron complex Fe2(μ‐Me2pdt)(CO)6 (A, Me2pdt = (SCH2)2CMe2) with monophosphines or small bite‐angle diphosphines are studied as follows. Firstly, the monodentate complexes Fe2(μ‐Me2pdt)(CO)5{κ1‐P(C6H4R‐p)3} [R = Me (1a) and Cl (1b)] and Fe2(μ‐Me2pdt)(CO)5{κ1‐Ph2PX'} [X' = NHPh (2a) and CH2PPh2 (2b)] are readily afforded through the Me3NO‐assisted reactions of A with monophosphines P(C6H4R‐p)3 (R = Me, Cl) and diphosphines (Ph2P)2X (X = NPh, CH2 (dppm)) in MeCN at room temperature, respectively. Secondly, the chelate complexes Fe2(μ‐Me2pdt)(CO)4(κ2‐(Ph2P)2X) [X = NPh (3a) and NBun (3b)] can be efficiently prepared by the UV‐irradiated reactions of A with small bite‐angle diphosphines (Ph2P)2X (X = NPh, NBun) in toluene. Thirdly, the bridge complexes Fe2(μ‐Me2pdt)(CO)4(μ‐(Ph2P)2X) [X = NPh (4a) and CH2 (4b)] are well obtained from the refluxing solutions of A and diphosphines (Ph2P)2X (X = NPh, CH2) in xylene. Rarely, the diphosphine‐bridge complex 4b may be produced in low yield via the UV‐irradiated solutions of A and the dppm ligand in toluene emitting at 365 nm. Eight new complexes obtained above have been well characterized by using element analysis, FT‐IR, NMR (1H, 31P) spectroscopies, and particularly for 1a, 1b, 2a, 3b, 4a, 4b by X‐ray crystallography. Meanwhile, the electrochemical and electrocatalytic properties of three representative complexes 2a, 3a, and 4a with pendant N‐phenyl groups are investigated and compared by using cyclic voltammetry (CV) in the absence and presence of trifluoroacetic acid (TFA) as a proton source, indicating that they are all found to be active for electrocatalytic proton reduction to hydrogen (H2).

Attenuated total reflectance–Fourier transform infrared study of the effects of citrate on the adsorption of phosphate at the hematite surface

AbstractCarboxylic acids affect the retention and solubility of phosphate in soils and rhizospheres, but spectroscopic studies addressing the mechanisms involved are scarce. Here, we used in situ attenuated total reflectance Fourier transform infrared spectroscopy to study the mechanisms of adsorption of orthophosphate and citric acid onto hematite in binary and ternary systems at pH 4.5, 5.5, and 6.5. In binary systems, phosphate adsorbed as a mixture of two inner‐sphere species assigned as monodentate and bridging complexes, with the fraction of bridging species increasing with decreasing pH. Citrate coordinated to the hematite surface through the carboxylate groups, which consisted of a mixture of inner‐sphere complexes and either noncoordinated or outer‐sphere complexes, with inner‐sphere complexation becoming more important at lower pH. Introduction of citrate into pre‐equilibrated phosphate–hematite systems induced desorption of both the monodentate and bridging phosphate species, with competitive effects increasing with decreasing pH. At pH 5.5 and 6.5, the bridging complexes were mobilized to a larger extent than initially present on the surface, indicating preferential desorption. Similarly, pre‐equilibration of hematite with citrate preferentially inhibited the formation of the bridging phosphate surface complexes. Their relatively strong susceptibility to interference by citrate suggests that the bridging phosphate species are protonated monodentate complexes engaged in hydrogen bonding to adjacent surface sites. The results of this study refine our understanding of the mechanisms of phosphate retention at Fe‐oxide mineral surfaces and demonstrate that carboxylic acids may affect not only phosphate solubility but also the speciation of phosphate associated with Fe‐oxides in soil and rhizosphere environments.

Effect of Synthesis Medium on the Structure and Physicochemical Properties of Biomineral Composites Based on Hydroxyapatite and Hyaluronic Acid

Dispersions based on sodium hyaluronate and hydroxyapatite, which is synthesized both by the classical method in an aqueous medium to obtain submicron particles and in a bioactive hyaluronan medium with the formation of nanosized particles, are obtained. The synthesized hydroxyapatite nanoparticles have a complex structure based on a monodentate complex hyaluronan–Ca2+ which remains in the dispersion both when adding a hyaluronan solution and when diluted with water. Physicochemical methods show that there is a significant difference between the energy characteristics of the surfaces of biocomposites obtained from dispersions. The rheology of dispersions of hydroxyapatite micro- and nanoparticles is investigated, the effect of dispersed phase concentration on it is revealed, and the viscoplastic behavior of dispersions of microparticles is demonstrated. This behavior disappears upon addition of the hyaluronan solution, which, however, leads to the loss of stability by the system. The introduction of hydroxyapatite nanoparticle additives into hyaluronan solutions has a weak effect on the rheology; no flocculation of nanoparticles occurs. The resulting composites consisting of hydroxyapatite and sodium hyaluronate can be considered a basis of a drug for the rehabilitation treatment of periodontitis.

Mechanistic Study of Radium Adsorption onto Goethite

Radium (Ra2+) is a radioactive element with a long half-life. It is used in industry and is often found in shallow aquifers due to natural or anthropogenic leakage or spill of brine from deep subsurface. A major factor influencing the transport and fate of Ra2+ in water is the adsorption/desorption process onto soil particles. Goethite, a ubiquitous natural mineral generally present as a coating of soil particles, contributes significantly to the adsorption of Ra2+ in the subsurface. However, the chemical reactions of adsorption of Ra2+ onto goethite are not well-established, yet. Previous studies reported that Ra2+ creates either tetradentate or monodentate complexes on goethite and no distinction between outer-sphere and inner-sphere types of complexes were made. Knowledge of the type and structure of Ra–goethite surface complexes is important to predict the behavior and the fate of Ra2+ in the subsurface, e.g., upon a spill and during the remediation of a contaminated site. Here, the adsorption of Ra2+ onto goethite is investigated by density functional theory (DFT) calculations. By using a combination of geometric structure, adsorption energy, and electronic state (i.e., density of states and magnetic moment) analyses, the outer-sphere adsorption was found to dominate Ra2+ complexation on goethite, suggesting a significant effect of salinity on Ra2+ transport in the subsurface. Inner-sphere adsorption configuration was not observed to be thermodynamically favorable, resulting from ionic rather than covalent interaction between Ra2+ and goethite. Based on these results, a surface complexation model was developed and validated successfully with literature data. This study provides insights into the mechanism of Ra2+ adsorption on soils containing goethite and provides chemical reactions of Ra–goethite surface interaction that can be coupled with a transport model to predict Ra2+ migration in the subsurface.

Influence of CO<sub>2</sub> Molecules Adsorption on the Electronic Properties of Zigzag and Armchair ZnO Nanotubes

Here, the adsorption behavior of the CO2 molecules on electronic properties of zigzag and armchair ZnO nanotubes (ZnONTs) has been studied at M06-2X/6-31G(d) level of theory. It is found that CO2 molecules can be physically adsorbed on the nanotubes. Two minima structures A (monodentate) and B (bidentate) were found on the potential energy surface. Inspection of the results shows that in zigzag and armchair nanotubes, the monodentate complex is more stable than bidentate complex. Also, the stability of complexes increases by increasing the number of CO2 molecules. Comparison of adsorption energies shows that adsorption of CO2 molecules over zigzag (6, 0) model is stronger than armchair (4,4) model. In this work, the various parameters such as electronic chemical potential (m), hardness (ƞ), softness (S), the maximum amount of electronic charge (DNmax), electrophilicity index (ω), dipole moment and work function were investigated to evaluate the reactivity of structures. It is predicted that the conductivity and reactivity of nanotubes increase upon complexation. Based on the natural bond orbital (NBO) analysis, in all complexes charge transfer occurs from CO2 molecules to the nanotube. Theory of atoms in molecules (AIM) was also applied to characterize OCO2… Zn interaction in nanotubes. In addition, the interaction strength is studied through the reduced density gradient (RDG) function. It is predicted that the ZnONTs can be introduced as a favorable candidate in the design and construction of sensors for detecting CO2 molecules.

Multidentate Pyridyl‐Aminophosphinite and Pyridyl‐Phosphoramidite Ruthenium(II) Complexes: Synthesis, Structure and Application as Levulinic Acid Hydrogenation Pre‐Catalysts

Novel multidentate pyridyl‐aminophosphinite (L1) and pyridyl‐phosphoramidite (L2) ligands of N^P^P^N‐donor system have been synthesized via a series of simple steps. The ligands are symmetrical and as a result, their reactions with [Ru(p‐cymene)Cl2]2 and [Ru(benzene)Cl2]2 lead to the formation of four monodentate bimetallic complexes (1–4) that retain the symmetry of the ligands. Meso and racemic mixtures (rac) of bidentate bimetallic complexes 5–8 were formed from the monodentate complexes through coordination of the pyridine nitrogen atoms to the two metal centers. The isomerism occurs at each metal center, which was evidenced by 31P{1H}, 1H NMR spectroscopy and single‐crystal X‐ray diffraction. The complexes were active towards hydrogenation of levulinic acid (LA) to γ‐valerolactone (GVL) using formic acid as the hydrogen source. The complexes are active at relatively low temperatures and are able to perform the hydrogenation in the absence of any additional solvent apart from the reagents to give high TON of 3 600. The catalysts are recyclable up to the fourth cycle, following which 20 % loss of activity is seen.

Oxalic Acid Adsorption on Rutile: Molecular Dynamics and ab Initio Calculations.

Detailed analysis of the adsorption of oxalic acid ions, that is, oxalate and hydrogenoxalate, on the rutile (110) surface was carried out using molecular dynamics augmented by free energy calculations and supported by ab initio calculations. The predicted adsorption on perfect nonhydroxylated and hydroxylated surfaces with surface charge density from neutral to +0.208 C/m2 corresponding to pH values of about 6 and 3.7, respectively, agrees with experimental adsorption data and charge-distribution multisite ion complexation model predictions obtained using the most favorable surface complexes identified in our simulations. We found that outer-sphere complexes are the most favorable, owing to strong hydrogen binding of oxalic acid ions with surface hydroxyls and physisorbed water. The monodentate complex, the most stable among inner-sphere complexes, was about 15 kJ/mol higher in energy, but separated by a large energy barrier. Other inner-sphere complexes, including some previously suggested in the literature as likely adsorption structures such as bidentate and chelate complexes, were found to be unstable both by classical and by ab initio modeling. Both the surfaces and (hydrogen)oxalate ions were modeled using charges scaled to 75% of the nominal values in accord with the electronic continuum theory and our earlier parameterization of (hydrogen)oxalate ions, which showed that nominal charges exaggerate ion-water interactions.

Reactions of Fe2(μ‐odt)(CO)6 (odt = 1, 3‐oxadithiolate) with small bite‐angle diphosphines to afford the monodentate, chelate, and bridge diiron complexes: Selective substitution, structures, protonation, and electrocatalytic proton reduction

Selective substitutions of Fe2(μ‐odt)(CO)6 (odt = 1,3‐oxadithiolate, A) and small bite‐angle diphosphines (Ph2P)2X [X = CH2 (dppm) or N (CH2CHMe2) (dppa)] have been well investigated in this study. With Me3NO·2H2O in MeCN at room temperature, the reaction of A and dppm produced the monodentate complex [Fe2(μ‐odt)(CO)5(κ1‐dppm)] (1), whereas the similar reaction with dppa afforded the chelate complex [Fe2(μ‐odt)(CO)4(κ2‐dppa)] (2). Using UV irradiation in toluene emitting at 365 nm, the treatment of A and dppm rarely resulted in the formation of the bridge complex [Fe2(μ‐odt)(CO)4(μ‐dppm)] (3), whereas the similar treatment with dppa formed the chelate complex 2. Under thermolysis condition, refluxing solution of A with dppm or dppa gave the bridge complex 3 and [Fe2(μ‐odt)(CO)4(μ‐dppa)] (4), respectively, in which the former was formed in toluene (110 °C) but the latter was produced in xylene (138 °C). All the new complexes 1–4 obtained above were characterized by element analysis, FT‐IR, NMR (1H, 31P) spectroscopies, and particularly for 1–3 by X‐ray crystallography. Furthermore, the in situ protonations of 2 with a weak acid HOAc (acetic acid) and a strong acid TFA (trifluoroacetic acid) are explored by means of FT‐IR and NMR (1H, 31P) spectra. In addition, the electrochemical behaviors of 2–4 are studied and compared through cyclic voltammetry (CV) in the absence and presence of a strong acid (TFA) as a proton source, indicating that they all are active for electrocatalytic proton reduction to hydrogen (H2).

Characterizing Preferential Adsorption of Phosphate on Binary Sorbents of Goethite and Maghaemite using in situ ATR-FTIR and 2D Correlation Spectroscopy

Recent developments in analytics using infrared spectroscopy have enabled us to identify the adsorption mechanism at interfaces, but such methods are applicable only for simple systems. In this study, the preferential adsorption of phosphate on binary goethite and maghaemite was investigated. As a result, monodentate and bidentate complexes were the major complexes on goethite and maghaemite, respectively. A shrinking effect in goethite and a swelling effect in maghaemite were identified, and environmental perturbations caused a significant decrease in the integrated absorbance of phosphate complexes on maghaemite, while no effect was observed on goethite, which implies that different adsorption mechanisms were involved. Based on the results, a bridging complex was proposed, and the swelling effect is explained by the negatively charged maghaemite surface resulting from the bidentate complex. The isolation of phosphate by the shrinking effect explains the low phosphate bioavailability in the soil environment, while the colloidal properties of the bidentate complex on maghaemite are the reason for colloidal mobilization. To the best of our knowledge, this study not only addresses the shrinking and swelling properties of iron (hydr)oxide nanoparticles but also demonstrates preferential adsorption on binary sorbents using in situ ATR-FTIR for the first time.

Cr(VI) adsorption performance and mechanism of an effective activated carbon prepared from bagasse with a one-step pyrolysis and ZnCl2 activation method

The utilization of bagasse as a raw material to prepare activated carbon adsorbents is an effective way to solve the water pollution problem, while achieving the goal of treating waste simultaneously. An effective activated carbon-based adsorbent was prepared from sugar cane bagasse with a one-step method of pyrolysis and ZnCl2 activation for efficient Cr(VI) removal from water. Morphology, physicochemical properties and structure of the adsorbent samples were studied by Scanning Electron Microscope, Energy Dispersive Spectroscopy, X-ray Diffraction, N2 adsorption and desorption, Fourier Transform infrared spectroscopy and X-ray Photoelectron Spectroscopy. The batch and fixed bed adsorption experiments were adopted to confirm the one-step preparation of pyrolysis and ZnCl2 during the activation process and to investigate the adsorption mechanism of Cr(VI). The maximum adsorption capacity was 80.880 mg g−1, while the adsorption behavior fitted better with Freundlich equation and pseudo-second-order kinetics. These results confirmed that chemical adsorption is the strongest adsorption interaction during the adsorbing process of Cr(VI), and the adsorbents could effectively capture Cr(VI) to form monodentate and bidentate complexes.

A Computational Study of Carbene Ligand Stabilization of Biomimetic Models of the Rotated Hred State of [FeFe]‐Hydrogenase

Stabilization of fully rotated conformation at one of the iron center has been achieved for the reduced Fe(I)Fe(I) state in chelated cyclic alkyl amino carbene (CAAC) substituted biomimetic hydrogenase model complex. This study indicates that the spatial orientation of the chelated NHCs at one of the iron center plays a major role in determining the geometry at the other iron center. We also made an attempt at explaining the electronic origin behind the favorability of rotated vs. unrotated structure in asymmetrically substituted chelated vs. monodentate NHC complexes.

Phosphate adsorption on hydrous ferric oxide (HFO) at different salinities and pHs

Phosphate adsorption on suspended sediments is largely influenced by the variations in salinity and pH such as is the case in estuaries where freshwater mixes with seawater, exhibiting strong physico-chemical gradients. In this research, the influence of salinity and pH on the adsorption of phosphate on hydrous ferric oxides (HFO) was investigated in NaCl solutions. The adsorption isotherm data at different salinities can be well fitted with the Langmuir-Freundlich model. At pH 8.5 the maximum adsorption capacity increases with increasing salinity, from 22.7 mg PO4/g at salinity 0–78.5 mg PO4/g at salinity 35 PSU (Practical Salinity Unit) with the largest increase occurring in the low salinity range (76.8 mg PO4/g at salinity 5 PSU). Phosphate adsorption is also highly pH dependent and the adsorption capacity decreases with increasing pH. The dependence of phosphate adsorption on salinity could be attributed to the inner-sphere complexation. The presence of Na+ modifies the phosphate speciation, which can also facilitate phosphate adsorption. Fourier-transform infrared spectroscopy (FTIR) results show that both bidentate (≡Fe2PO4) and monodentate (≡FePO4) complexes are formed during phosphate adsorption on HFO surface. Quantitative relationships between phosphate adsorption and salinity are proposed for the different pHs investigated in this study, which is important for the understanding of the phosphate adsorption dynamics during estuarine mixing.