Change In Coordination Environment Research Articles

Defect-controlled confined growth of nano-MOFs to prepare materials with hierarchical micro/mesoporous structures for efficient CO2 capture

In recent years, nanoporous materials with special structure have been widely used in various fields. In view of the poor stability of MOFs materials and the poor mass transfer ability, in this study, we developed a simple method to restrict the growth of UiO-66-NH2 crystals in hollow silica by “vacuum evaporation” strategy, different kinds of acid regulators were introduced, to obtain a composite material with hierarchical pore structure. By characterizing the physical chemistry and microstructure of the composite adsorbent, and calculating the structural defects under different acid regulation, the adsorption and desorption performance and stability of the adsorbent for CO2 were comprehensively investigated. The mechanism of action on CO2 was further analyzed by in-situ infrared and other techniques. The results show that the change of coordination environment and coordination rate caused by the competition of organic acids, which increases the defects and reduces the nucleation and aggregation effect of UiO-66-NH2, promotes the formation of hierarchical pore structure of the composites. Among them, benzoic acid is the best regulating monocarboxylic acid, which makes UiO-66-NH2 have good dispersion in the cavity and suitable crystal size. The specific surface area of the composite material is 717.96 m2·g-1. At the same time, due to its excellent CO2 adsorption capacity (3.35mmol·g-1) at 298K and 1.06bar, it is 48.07% higher than the original UiO-66-NH2. In order to accomplish the goal of effective CO2 adsorption performance of composites, this study offers a novel approach for the synthesis and modification of MOFs-based composites.

Strain-Driven Phase Transitions in Delafossite Cu1-xAxAlO2: A Key to Enhanced Photo(electro)catalytic Performance.

This study investigates the impact of intrinsic strain and phase transitions on the thermodynamic stability and electronic properties of Cu1-xAxAlO2 solid solutions, which are key to their photocatalytic performance. It is demonstrated that Cu1-xAxAlO2 with A = Ag, Au, Pt can form continuous isostructural solid solutions due to relatively small compressive strain, while a substantial increase strain restricts Cu1-xPdxAlO2 to forming only limited solutions. For A = Li, Na, the formation of heterostructural solid solutions is facilitated by structural motif alterations, accommodating significant differences in ionic radii and A-O bond characteristics. Specifically, Cu1-xLixAlO2 exhibits a phase transition at x ≈ 0.333, whereas Cu1-xNaxAlO2 undergoes three distinct phase transitions. Electronic structure analysis indicates that in Cu1-xAxAlO2 (A = Ag, Au), d10-d10 closed-shell interactions dominate, enabling tunable band gaps with varying solubility. Nevertheless, increased intrinsic strain in metal sublattices, as seen in A = Pd and Pt, shifts antibonding states to the Fermi level, inducing a semiconductor-to-metal transition. Experimental evidence confirms that Ag+ ions modulate the band gaps and carrier dynamics in Cu1-xAgxAlO2, with Cu0.75Ag0.25AlO2 exhibiting heightened photoelectrochemical activity and a 38.5-fold enhancement in H2 production rate over CuAlO2. Additionally, the coordination environment changes between alkali metals and O, induced by phase transitions, effectively tune the band edge positions and carrier dynamics of Cu1-xAxAlO2 (A = Li, Na) heterostructural solid solutions. Therefore, 3R-Cu0.97Li0.03AlO2 with asymmetric nonlinear dumbbell O-Cu-O demonstrates the highest photocatalytic H2 production activity, 72.9 times greater than CuAlO2. In contrast, α-Cu1-xAxAlO2 with a smaller CuO6 octahedral splitting energy exhibits increased band gaps, resulting in diminished photocatalytic activity. This research underscores that strain-driven phase transition provides an additional control factor and new mechanism for regulating the photo(electro)catalytic activity of Cu1-xAxAlO2 solid solutions.

Probing the critical point of MgSiO3 using deep potential simulation

The giant impact between proto-Earth and a Mars-sized planet called Theia resulted in the formation of the Earth–Moon system, and the silicate mantles of the initial bodies may have partly been vaporized. Here, we develop a machine learning potential for MgSiO3 based on the data from first-principles calculations to estimate its critical point. The variations in pressure along different isotherms yield the position of the critical point of MgSiO3 at 0.54 g cm−3 and 6750 ± 250 K, which agrees with the previous theoretical estimation. We also simulate the MgSiO3 melt under a spectrum of critical conditions to understand the changes in coordination environment with density and temperature. The fourfold Si–O coordination hardly changes with increasing density at 3000 K. However, with increasing temperature, the dominance of four-coordinated Si–O diminishes rapidly as density decreases. Regarding Mg–O coordination, the overall trend, which varies with temperature and density, remains largely consistent with Si–O but with a greater diversity in the types of coordination due to more bond breaking events. Our work opens a new avenue by employing machine learning methods to estimate the critical point of silicates.

Investigation of compound state of SiO2-TiO2 aerogel synthesized through controlled sol-gel reaction

In this work, a compound state of silica-titania aerogel was investigated through sol-gel reaction for hybridization of silica and titania with increasing reactivity by using high surface area and charge imbalances. By minimizing the sol-gel reaction rate difference and preparing a homogeneous and stable sol, a compound state of silica-titania aerogel could be obtained, without separation onto single metal oxide aerogel. The benefits of using the sol-gel synthesis method for synthesizing silica-titania compound aerogels are over a limit of substitution solubility and get binary metal oxide compound material. Diffraction and spectroscopic analyses showed that the heterogeneous linkage resulted from interaction among silicon, titanium, and oxygen ions. The coordination environment changes by the formation of an Si-O-Ti linkage following interaction among ions without phase separation on SiO2 and TiO2 aerogels. Thus, the atomically controlled sol-gel reaction can be used to design new metal-oxide-based compound aerogels and immiscible oxide materials.

Structural and electronic properties of novel BeN4/MgN4 nanoribbons

Nanostructures of novel materials are capable of altering the properties of materials quite drastically. Recently discovered Dirac monolayer BeN4 has drawn much attention since this Nitrogen-based material’s electronic structure is very similar to graphene. In this work, we have analyzed various possiblities of nanoribbons structures of MN4 (M=Be, Mg) monolayer materials. We have proposed several possible geometries of BeN4 and MgN4 nanoribbon structures. More specifically, we have proposed armchair nanoribbons with three possible edge configurations as well as zigzag nanoribbons based on edge geometry. Owing to the changes in coordination environment of nanoribbon edge atoms, the resulting bonding characteristics gets altered at the edges, leading to interesting electronic properties. The electronic structures of these nanoribbons are quite different from monolayer and reveal fascinating edge states that exclusively depend on the edge configuration. Though the armchair nanoribbons are found to be metallic, the electronic structure of zigzag nanoribbons exhibits band gap which lead to huge tunability potential of the investigated nanostructures. Therefore, these nanoribbons can function both, metallic as well as semiconducting as required in device applications which can be tuned by modulating the material geometry.

Unveiling the Potential of Sunlight‐Driven Multifunctional Blue Long Persistent Luminescent Materials via Cutting‐Edge Trap Modulation Strategies

AbstractNumerous challenges persist in the field of long persistent luminescence (LPL) materials, including the unclear mechanism of persistent luminescence, low efficiency of sunlight excitation, and limited availability of commercial materials. To address these issues, a LPL material, SrAl2Si2O8:x% Eu2+,y% Dy3+, is synthesized for excitation by UV lamps or sunlight. Dy3+ doping remarkably extends the afterglow duration from 2 to 7 h under UV lamp excitation, exhibiting a remarkable enhancement of 350%. Notably, SrAl2Si2O8:4.0% Eu2+, 3.0% Dy3+ shows 2 h afterglow duration when exposed to sunlight, surpassing other LPL materials and expanding potential applications. XPS and XANES measurements confirm Eu2+ as the luminescent and persistent luminescent centers, while Dy3+ increases trap diversity. Through meticulous analysis of the EPR and XPS data, it is elucidated that the material encompasses two distinct types of traps, namely oxygen vacancies and may be traps. This provides a basis for subsequent trap analysis in LPL materials. Microstructural analysis examined ion coordination environment changes due to Eu2+ and Dy3+ doping. The mechanical luminescent properties are characterized, and a plausible afterglow mechanism is proposed based on the experimental results, offering insights for further research into LPL materials.

XANES Studies of Zinc Tin Oxide Films Deposited by Atomic Layer Deposition: Revealing Process-Structure Relationships for Amorphous Oxide Semiconductors

Amorphous oxide semiconductors have grown in technological relevance in displays, information technology, energy, and catalysis. Recent research efforts have converged on the need to develop design principles for the electronic structure of these materials. Here, we systematically vary the cation composition and annealing temperatures of zinc tin oxide films using atomic layer deposition (ALD) and study their process-structure relationships with synchrotron X-ray absorption near-edge spectroscopy (XANES). Measurements of the O K-edge, Sn M-edge, and Zn L-edge are analyzed with ab initio and nonlinear statistical modeling to understand the changes in geometric and electronic structure of the films. A key finding from this approach is the ability to measure the changes in the relative contribution of the Zn and Sn s orbitals to the density of states near the conduction band minimum. Furthermore, we identify and delineate critical process-structure design principles when working with amorphous oxide semiconductor (AOS) material systems: (1) use of complementary diffraction and absorption spectroscopy techniques to characterize the as-deposited coordination environment; (2) accounting for gradual and abrupt changes in coordination environment as a function of processing parameters (stoichiometry, annealing, etc.); (3) revealing and exploiting the relevant knowledge and interdependence of coordination environments, orbital hybridizations, the density of states, and band structures. In the future, this multimodal X-ray analysis and modeling framework can be applied to understand the process-structure relationships needed to optimize AOS performance in devices.

In situ identification of surface sites in Cu-Pt bimetallic catalysts: Gas-induced metal segregation.

The effect of gases on the surface composition of Cu-Pt bimetallic catalysts has been tested by in situ infrared (IR) and x-ray absorption spectroscopies. Diffusion of Pt atoms within the Cu-Pt nanoparticles was observed both in vacuum and under gaseous atmospheres. Vacuum IR spectra of CO adsorbed on CuPtx/SBA-15 catalysts (x = 0-∞) at 125K showed no bonding on Pt regardless of Pt content, but reversible Pt segregation to the surface was seen with the high-Pt-content (x ≥ 0.2) samples upon heating to 225K. In situ IR spectra in CO atmospheres also highlighted the reversible segregation of Pt to the surface and its diffusion back into the bulk when cycling the temperature from 295 to 495K and back, most evidently for diluted single-atom alloy catalysts (x ≤ 0.01). Similar behavior was possibly observed under H2 using small amounts of CO as a probe molecule. In situ x-ray absorption near-edge structure data obtained for CuPt0.2/SBA-15 under both CO and He pointed to the metallic nature of the Pt atoms irrespective of gas or temperature, but analysis of the extended x-ray absorption fine structure identified a change in coordination environment around the Pt atoms, from a (Pt-Cu):(Pt-Pt) coordination number ratio of ∼6:6 at or below 445K to 8:4 at 495K. The main conclusion is that Cu-Pt bimetallic catalysts are dynamic, with the composition of their surfaces being dependent on temperature in gaseous environments.

Mind the Interface Gap: Exposing Hidden Interface Defects at the Epitaxial Heterostructure between CuO and Cu2O.

Well designed and optimized epitaxial heterostructures lie at the foundation of materials development for photovoltaic, photocatalytic, and photoelectrochemistry applications. Heterostructure materials offer tunable control over charge separation and transport at the same time preventing recombination of photogenerated excitations at the interface. Thus, it is of paramount importance that a detailed understanding is developed as the basis for further optimization strategies and design. Oxides of copper are nontoxic, low cost, abundant materials with a straightforward and stable manufacturing process. However, in individual applications, they suffer from inefficient charge transport of photogenerated carriers. Hence, in this work, we investigate the role of the interface between epitaxially aligned CuO and Cu2O to explore the potential benefits of such an architecture for more efficient electron and hole transfer. The CuO/Cu2O heterojunction nature, stability, bonding mechanism, interface dipole, electronic structure, and band bending were rationalized using hybrid density functional theory calculations. New electronic states are identified at the interface itself, which are originating neither from lattice mismatch nor strained Cu-O bonds. They form as a result of a change in coordination environment of CuO surface Cu2+ cations and an electron transfer across the interface Cu1+-O bond. The first process creates occupied defect-like electronic states above the valence band, while the second leaves hole states below the conduction band. These are constitutional to the interface and are highly likely to contribute to recombination effects competing with the improved charged separation from the suitable band bending and alignment and thus would limit the expected output photocurrent and photovoltage. Finally, a favorable effect of interstitial oxygen defects has been shown to allow for band gap tunability at the interface but only to the point of the integral geometrical contact limit of the heterostructure itself.

2-methyl imidazole electrolyte additive enabling ultra-stable Zn anode

Although aqueous zinc ion batteries are considered to be a promising next-generation energy storage battery, their commercialization is limited by the stability and safety issues of zinc anode. Herein, 2-methyl imidazole (Hmim) is introduced as electrolyte additive to in-situ construct a robust inorganic–organic zinc-rich (Zn4SO4(OH)6/Zn(Hmim)) solid electrolyte interface film for realizing high-stable dendrite-free Zn anode. On one hand, the zincophilic properties of Hmim and its chelation with Zn2+ result in more active sites for initial nucleation, leading to the uniform zinc deposition, and the change of coordination environment makes the diffusivity of ions decrease and the nucleation overpotential increase, which result in smaller grains in the initial zinc deposition stage. On the other hand, the formed inorganic–organic solid electrolyte interface film with good chemical and thermal stability can protect Zn anode well, and thus the side reactions and zinc dendrites can be effectively inhibited. Consequently, the Hmim-based electrolyte promotes dendrite-free Zn plating/striping with high Coulombic efficiency (97.32 %) and highly stability (cycling up to 2000 h). When applied in full cell, the Zn-V2O5 cell also demonstrates outstanding electrochemical performances. This work provides a simple and effective method for the implementation of high performance and high safety zinc-ion batteries.

Solvent Effects on the Electrochemistry of Nickel (II) Diethyldithiocarbamate

Multielectron molecular redox couples have been used both as anolytes and catholytes in redox flow batteries (RFBs). The energy stored in an RFB is proportional to the number of electrons transferred per molecule. Thus, increasing the number of electrons transferred per molecule can enhance the amount of stored energy. Previous works in this field mostly looked for molecules containing multiple 1e- redox couples. The advantage of a single 2e- redox couple over multiple 1e- redox couples is that both electrons are stored and released at the same potential. Nickel (II) diethyldithiocarbamate, NiII(Et2dtc)2 undergoes 2e- oxidation at a single potential to form [NiIV(Et2dtc)3]+.1 In different nonaqueous solvents NiII(Et2dtc)2 can offer divergent redox behavior based on their coordination properties.2 This divergent redox behavior means significant changes on the electrochemistry of the complex during oxidation and reduction. Pyridine, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetonitrile (MeCN), methanol (MeOH), acetone, and dichloromethane (DCM) have been studied in this work as they have dissimilar donor numbers with different coordination abilities towards the Ni center. Both cyclic voltammetry and spectroscopic data in the above-mentioned solvents show distinct behavior which is expected as solvent coordination ability varies. Due to its highest coordination ability among the solvents used in this study, pyridine hinders the Ni (II) to Ni (IV) oxidation by coordinating strongly to the Ni (III) center to form [NiIII(Et2dtc)2(Py)2]+. On the contrary, noncoordinating DCM allows oxidation to Ni (IV) albeit through two distinguishable 1e- oxidation processes. MeCN and acetone allow Ni (II)→(IV) oxidation at a single potential. DMSO, DMF, and MeOH show intermediate redox behavior between 1e- and 2e- transfer reactions. These studies point to the ability of solvent to aid or hinder multielectron redox strategies which use Ligand Coupled Electron Transfer where changes in coordination environment are necessary.3 Mazumder, M. M.; Burton, A.; Richburg, C.; Saha, S.; Cronin, B.; Duin, E.; Farnum, B., Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate. Inorganic Chemistry 2021.Islam, R.; Mazumder, M. M. R.; Farnum, B. H., Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage, ECS Meeting s, IOP Publishing: 2021; p 54. Saha, S.; Sahil, S. T.; Mazumder, M. M. R.; Stephens, A. M.; Cronin, B.; Duin, E. C.; Jurss, J. W.; Farnum, B. H., Synthesis, characterization, and electrocatalytic activity of bis (pyridylimino) isoindoline Cu (II) and Ni (II) complexes. J Dalton Transactions 2021, 50 (3), 926-935. Figure 1

Elucidation of Operating Mechanism of BiFeO3 As a Negative Electrode for Na-Ion Batteries Using in Operando XAS Investigation

Sodium-ion batteries (SIBs) are gaining much attention in the global market of rechargeable batteries especially in the field of large-scale electrical energy storage systems. Considering the increasing demand for the efficient energy storage systems, it is necessary to design new electrode materials, which are capable to deliver higher reversible capacity. A wide spectra of positive electrode materials were employed in sodium ion batteries, whereas more development is required in the field of negative electrodes. Anode materials of sodium-ion batteries were mainly classified under insertion, conversion and alloying type materials1. Among the conversion type materials, Perovskite materials have gained significant attention as conversion type anode materials in sodium-ion batteries, owing to the high theoretical capacity possessed by these materials2,3.BiFeO3 is one such perovskite which possess the potential to deliver higher reversible capacity through conversion and alloying reactions4.In the present work, BiFeO3 was synthesized using a sol-gel method. Structural and morphological characterizations were done with X-ray diffraction and Field emission scanning electron microscopy techniques. Further, electrochemical studies were carried out in a sodium half-cell in the voltage range 0.01-3.00 V vs. Na+/Na. In the cyclic voltammogram, pronounced difference is observed between the first and subsequent cycles and to understand the reason behind this, elucidation of operating mechanism is required. In situ/ex situ XRD techniques are usually not sufficient to get information regarding the operating mechanism of conversion type electrode materials as these converts into metallic nanoclusters (without a long-range order) distributed in Na2O matrix during the insertion of Na+ ions. Hence, in this work, element specific X-ray absorption spectroscopic (XAS) technique was applied to elucidate the oxidation state and coordination environment changes of BiFeO3 during cycling in a sodium half-cell. Evidences for the electrochemical activity of Bi through conversion reaction (Bi3+ - Bi0) and alloying reaction (with metallic Na) during first discharge was obtained from XAS results. Further, involvement of Fe in the charge storage mechanism through conversion of its oxidized (Fe3+) form to metallic Fe was also observed, which is absent in previous literature reports. In the subsequent charging, reversible dealloying and subsequent oxidation of Bi and oxidation of Fe were noted. The Bi LIII edge and Fe K edge XAS results during second discharge reveals that similar conversion and alloying reactions occur as in the case of first discharge by reduction of Bi and Fe oxides. However, Fe and Bi oxides exists in different oxidation states at the end of first charge than in pristine BiFeO3.In addition to the elucidation of operating mechanism, the electrochemical performance of BiFeO3 was optimized by varying binder and electrolyte compositions. The best electrochemical performance was obtained when Fluoroethylene carbonate was used as an electrolyte additive. Acknowledgement A. Bhaskar gratefully acknowledge financial support from “DST-IISc Energy Storage Platform on Supercapacitors and Power Dense Devices” through the MECSP-2K17 program under grant no. DST/TMD/MECSP/2K17/20”. D. Dixon acknowledges the financial support from funding agency, Science and Engineering Board (SERB), New Delhi, India through Ramanujan Fellowship, under the grant number SB/S2/ RJN-162/2017. A. Surendran is grateful to UGC New Delhi (Ref. no.:63/CSIR-UGC NET DEC. 2017) for the UGC SRF grant and Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India. A.T acknowledges the Council of Scientific and Industrial Research (CSIR) for a senior research fellowship and Innovative Research (AcSIR), Ghaziabad- 201002. DESY, Hamburg, Germany is acknowledged for the beamtime allocation at the P65 beamline at PETRA III and we acknowledge the beamline scientist Dr. Edmund Welter for the support. The CIF, CSIR-CECRI is acknowledged for technical support with material characterization. Reference [1] Wu, C., Dou, S. X. & Yu, Y. The State and Challenges of Anode Materials Based on Conversion Reactions for Sodium Storage. Small 14, 1–20 (2018).[2] M. Nakayama, H. Ikuta, Y. Uchimoto, M. Wakihara, Changes in local structure during electrochemical Li insertion into A-site deficient perovskite oxides, La1/3NbO3, J. Phys. Chem. B,107(2003)10715-10721[3] M. Kong, K. Liu, J. Ning, J. Zhou, H. Songa, Perovskite framework NH4FeF3/carbon composite nanosheets as a potential anode material for Li and Na ions storage, J. Mater. Chem. A, 5(2017)19280-19288[4] X. Dinga, Y.Liub, Hollow bismuth ferrite combined graphene as advanced anode material for sodium-ion batteries, 30(2020)153-159

Termination effects of single-atom decorated v-Mo2CTx MXene for the electrochemical nitrogen reduction reaction

The lack of the green, economical and high-efficient catalysts restrict the development of electrochemical nitrogen reduction reaction (NRR). By means of density functional theory (DFT) calculations, we have systematically investigated the NRR catalytic performance of single atoms decorated v-Mo2CT2 (T = O, F, OH, Cl, and Li) MXene (TM@v-Mo2CT2). Our calculation results reveal the introduction of single atom can significantly improve the NRR activity and selectivity on v-Mo2CO2, and Ir@v-Mo2CO2 system possesses the lowest limiting potential of only −0.33 V among all studied systems. The termination effects of TM@v-Mo2CT2 are further discussed and a descriptor of the adsorption energy of *NNH species (ΔE(*NNH)) is proposed to establish the relationship with NRR limiting potential (UL(NRR)), in which a moderate (ΔE(*NNH)) is required for high NRR activity. Moreover, a good linear relationship between the ΔE(*NNH) and the excess electrons on Ir atom shows that different ΔE(*NNH) originates from the difference of valence state of Ir atom, which is due to the change of coordination environment. Importantly, the synergistic effects of Ir atom and the surface O-terminations during the first hydrogenation step lead to a promoted NRR performance. Our study might provide new possibilities for rational design of cost-effective MXene-based NRR electrocatalysts.

Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage

In the field of electrochemical energy storage, multielectron molecular redox couples play significant roles. These redox couples have been used both as anolytes and catholytes in redox flow batteries (RFBs). The energy stored in an RFB is proportional to the number of electrons transferred per molecule. Thus, increasing the number of electrons transferred per molecule can enhance the amount of stored energy. Previous works in this field mostly looked for molecules containing multiple 1e- redox couples. The advantage of a single 2e- redox couple over multiple 1e- redox couples is that both electrons are stored and released at the same potential. In the case of multiple 1e- redox couples, two redox potentials are usually separated by more than 0.3 V. This can cause significant shifts in battery voltage and power during charging and discharging of an RFB. Nickel (II) diethyldithiocarbamate, NiII(Et2dtc)2 undergoes 2e- oxidation at a single potential to form [NiIV(Et2dtc)3]+. In different nonaqueous solvents NiII(Et2dtc)2 can offer divergent redox behavior based on their coordination properties. This divergent redox behavior means significant changes on the electrochemistry of the complex during oxidation and reduction. Pyridine, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetonitrile (MeCN), methanol (MeOH), acetone, and dichloromethane (DCM) have been studied in this work as they have dissimilar donor numbers with different coordination abilities towards the Ni center. Both cyclic voltammetry and spectroscopic data in the above-mentioned solvents show distinct behavior which is expected as solvent coordination ability varies. Due to its highest coordination ability among the solvents used in this study, pyridine hinders the Ni (II) to Ni (IV) oxidation by coordinating strongly to the Ni (III) center to form [NiIII(Et2dtc)2(Py)2]+. On the contrary, noncoordinating DCM allows oxidation to Ni (IV) albeit through two distinguishable 1e- oxidation processes. MeCN and acetone allow Ni (II)→(IV) oxidation at a single potential. DMSO, DMF, and MeOH show intermediate redox behavior between 1e- and 2e- transfer reactions. The presence of Ni (III) in the case of highly coordinating solvents was confirmed by low temperature EPR and UV-vis absorbance spectroscopy with the use of a chemical oxidant. These studies point to the ability of solvent to aid or hinder multielectron redox strategies which use Ligand Coupled Electron Transfer where changes in coordination environment are necessary.

Magnetic Fe3O4/attapulgite hybrids for Cd(II) adsorption: Performance, mechanism and recovery

Herein, a Fe3O4 decorated attapulgite adsorbent (FA) is fabricated for the removal of Cd(II) from wastewater, and subsequently a feasible strategy for converting the saturated waste adsorbent to CdS/FA photocatalyst is reported. Owing to the in situ growth of Fe3O4 on the attapulgite (ATP), the FA adsorbents exhibit enlarged surface area and increased adsorption sites. More importantly, the strong interaction between Fe3O4 and ATP leads to changes of coordination environment around the O‒Fe‒O bond with the ATP. Based on the results of density functional theory calculations, the electrons are more readily transferred from Fe to O, and the hanging O atoms with more electronegativity act as the efficient adsorption sites for Cd(II), efficiently improving the adsorption performance of the Fe3O4 phases. Furthermore, the waste FA adsorbent could be conveniently separated from the treated water by magnets and converted to CdS/FA photocatalyst, which exhibits satisfying degradation efficiency for tetracycline with low concentration. This work provides a potential strategy to optimize the ATP-based materials for heavy ions adsorption and reutilize the waste adsorbents.

Solution structure of a europium-nicotianamine complex supports that phytosiderophores bind lanthanides.

We report the solution structure of a europium-nicotianamine complex predicted from ab initio molecular dynamics simulations with density functional theory. Emission and excitation spectroscopy show that the Eu3+ coordination environment changes in the presence of nicotianamine, suggesting complex formation, such as what is seen for the Eu3+-nicotianamine complex structure predicted from computation. We modeled Eu3+-ligand complexes with explicit water molecules in periodic boxes, effectively simulating the solution phase. Our simulations consider possible chemical events (e.g. coordination bond formation, protonation state changes, charge transfers), as well as ligand flexibility and solvent rearrangements. Our computational approach correctly predicts the solution structure of a Eu3+-ethylenediaminetetraacetic acid complex within 0.05 Å of experimentally measured values, backing the fidelity of the predicted solution structure of the Eu3+-nicotianamine complex. Emission and excitation spectroscopy measurements were also performed on the well-known Eu3+-ethylenediaminetetraacetic acid complex to validate our experimental methods. The electronic structure of the Eu3+-nicotianamine complex is analyzed to describe the complexes in greater detail. Nicotianamine is a metabolic precursor of, and structurally very similar to, phytosiderophores, which are responsible for the uptake of metals in plants. Although knowledge that nicotianamine binds europium does not determine how plants uptake rare earths from the environment, it strongly supports that phytosiderophores bind lanthanides.

Comparison of Arsenate Adsorption from Neutral pH Aqueous Solutions Using Two Different Iron-Trimesate Porous Solids: Kinetics, Equilibrium Isotherms, and Synchrotron X-Ray Absorption Experiments

We have explored the use of two different iron-based porous materials for arsenic uptake from neutral pH aqueous solutions. Both materials are reminiscent of a material known as MIL-100(Fe), a Metal Organic Framework (MOF) built upon the coordination of Fe(III) ions with trimesate organic linkers (benzene tricarboxylic acid). Aside from the proverbial high surface area with extended microporosity/mesoporosity, the presence of Fe(III) centers offers the possibility of specific strong interactions with arsenic, therefore making it appealing for its use in detection and purification technologies. Our approach tackles the characterization of the system from both physical and chemical perspectives. We report equilibrium isotherms and time dependent arsenic uptake for the determination of adsorption capacity and kinetics; and also, by means of synchrotron-based X-ray absorption techniques, we probe possible changes in coordination environments and oxidation states of Fe and As in the porous network occurring upon adsorption at high and low loadings. The results presented bring further insight on the nature and diversity of adsorption sites present and confirm the suitability of the proposed adsorbents for the intended use.

Perovskite titanates at the nanoscale: Tunable luminescence by energy transfer and enhanced emission with Li+ co-doping

Three series of highly luminescent Ca1-xTiO3:xDy3+, Ca0.98-yDy0.02TiO3:yEu3+ and Ca0.91-zDy0.02Eu0.07TiO3:zLi+ nanophosphors have been synthesized by solution combustion method. X-ray diffraction analysis and Rietveld refinements of these phosphors confirms the pnma (62) structure and the occupancy of substituent ions in the matrix. Increase in intensity of the Raman modes viz., O–Ti–O bending mode (249 ​cm−1) and local vibrational mode (800 ​cm−1) signifies the occupancy of rare earth ions in the lattice. XPS analysis verifies the change in coordination environment around the RE3+ ions due to the variation in electron density by the observed shift in binding energy corresponding to the chemical states of Dy 3d and Eu 3d when Li+ ions are codoped. Ca1-xTiO3:xDy3+ exhibits a luminescence close to standard white and tuning of correlated color temperature is achieved by varying the excitation wavelength. In Ca0.98-yDy0.02TiO3:yEu3+ phosphors, co-doping of Eu3+ enables red component in white emission and at higher concentration of Eu3+, emission changes from orange red to purplish red, when wavelength of excitation is altered from 366 to 388 ​nm by virtue of energy transfer mechanism. An enhancement of luminescence intensity by 2.1 times has been observed due to Li+ substitution at optimum concentration in Ca0.91-zDy0.02Eu0.07TiO3:zLi+. This evidences the role of Li+ ions in modifying the crystal field interaction in perovskite luminescent materials.

SYNTHESIS AND SPECTRAL CHARACTERISTICS OF PERSPECTIVE NANOSIZED CARBON QUANTUM DOTS FOR ADSORPTION AND CATALYTIC PROCESSES

Processes of interaction between carbon quantum dots (CQDs) and solutions of rhodium, ruthenium and palladium chlorides in the surface layer have been investigated by electron and IR spectroscopy. When rhodium chloride is added to a solution of CQDS, a bathochromic shift of the β- and p-absorption bands (ABs) at 48725 and 41711 cm-1 as well as hypsochromic shift of the α-AB at 28935 cm-1 indicate that rhodium adsorption occurs on the surface of CQDs. The bathochromic shift of the absorption bands at 22400 сm1 together with the hypsochromic shift of ABs corresponding to d-d electron transitions in the metal ions indicates the formation of rhodium with CQDs. When ruthenium and palladium chlorides are added to an aqueous solution of CQDs, the intensive of ABs characterizing the complex anions [RuCl6]3-, [RuCl6]2- or [PdCl4]2- are absent in the UV-Vis spectra. This indicates the passage of adsorption processes of metals on the surface of CQDs. The present of ABs (at 27055 and 25125 сm-1) indicate the trivalent state of ruthenium ion; the p-ABs bathochromic shift as well as α-ABs hypsochromic shift indicates the probable complex formation of CQDs with Ru3+ ions. The change in the position of the absorption bands of d-d electron transitions (at 25448 сm1) together with the bathochromic shift of p-ABs and hypsochromic shift of α-ABs indicates a change in coordination environment in the palladium ion with the possible formation of Pd → N bond. The IR-spectra data of CQDs showed the presence of a number of characteristic ABs for functionalized CQDs: ν(N–H) at 3260 сm1, (C=O) at 1830, 1840 and 1850 сm1, –С=O(NH) at 1770 сm1, ν(C=N) at 1680 and δ(N–H) at 1640 сm1, which confirms the coordination of metals on the surface of CQDs.

Experimental determination of Ni isotope fractionation during Ni adsorption from an aqueous fluid onto calcite surfaces

The fractionation of Ni isotopes during Ni adsorption from aqueous fluids onto calcite surfaces was measured at 25 °C and as a function of pH from 7.7 to 8.9. Experiments showed that the percent Ni adsorbed and the degree of Ni isotope fractionation attained constant values in less than 30 hours after the calcite was exposed to the Ni bearing, calcite saturated aqueous solution. The percentage of Ni adsorbed from the fluid onto the calcite surfaces increased from 9 to 67% as the pH increased over this range. Calcite preferentially adsorbs light Ni isotopes during adsorption, resulting in a fractionation between adsorbed and aqueous, Δ60Nicalcite-fluid, of −0.52 ± 0.16‰. This value is pH independent, within uncertainty, over the experimental pH range. The preferential adsorption of light Ni isotopes into calcite likely results from the change in coordination environment between adsorbed and aqueous nickel; the NiO length in the NiCO3 bond formed at the calcite surface is greater than that in the Ni2+ aquo ion.