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•Ultrasonic fabrication of MgO nanosheets by an one-step ultrasonic method.•Both Se(IV) and Se(VI) adsorption by MgO nanosheets from aqueous solutions.•High adsorption Qmax for Se(IV) ...(103.52mgg−1) and Se(VI) (10.28mgg−1).•Inner-sphere surface complexes formation (SeO32−/SeO42−) on the surface of MgO nanosheets.
MgO nanosheets with thickness ranges of 3–10 molecule layers and high specific area (166.44m2g−1) were successfully fabricated by an ultrasound-assisted exfoliation method and used as adsorbent for the removal of both selenite (Se(IV)) and selenate (Se(VI)) from aqueous solutions. The resulting MgO nanosheets displayed high maximum adsorption capacities of 103.52 and 10.28mgg−1 for Se(IV) and Se(VI), respectively. ATR-FTIR and XPS spectroscopic results suggested that both Se(IV) and Se(VI) formed inner-sphere surface complexes on MgO nanosheets under the present experimental conditions. Furthermore, high adsorption capacity for Se(IV/VI) in the presence of coexistent anions (SO42−, PO43−, Cl−, and F−) and efficient regeneratability of adsorbent by NaOH solution were observed in the competitive adsorption and regeneration steps. The simple one-step synthesis process of MgO nanosheets and high adsorption capacities offer a promising method for Se(IV/VI) removal in water treatment.
A systematic study has been carried out on the 3d divalent metal formate 3D magnetic frameworks templated by protonated amines, and the achievements have revealed that metal formate frameworks are ...very malleable, and their structures depend on the size, shape, charge, and hydrogen bonding geometries of the templating cations. Six kinds of metal formate frameworks have been created. They are chiral frameworks with a (49 · 66) topology, perovskite ones with a (412 · 63) topology, bi‐nodal frameworks of (412 · 63)(49 · 66)n (n = 1, 2, 3) topologies, and porous diamond frameworks with 66 topology. These materials display promising and abundant magnetic, dielectric, porous, and optical properties and the possible combination of them. Therefore, they are of great interest for the study of molecule‐based materials. It has been demonstrated that formate, being the smallest and simplest carboxylate, cheap and with low toxicity, thus more biocompatible and environmentally friendly, and having been more or less ignored, will find an important role in the construction of molecule‐based materials and provide new materials with interesting properties.
A study of the 3d divalent metal formates, templated by protonated amines, has created chiral (49 · 66), perovskite (412 · 63), bi‐nodal (412 · 63)(49 · 66)n (n = 1 to 3), and diamond 66 metal formate frameworks, depending on the templates used. These materials display various magnetic, dielectric, porous, and optical properties, and combinations thereof. It is expected that the more or less ignored formate will play an important role in the study of molecule‐based materials.
Hematite nanoparticles are abundant in the photic zone of aquatic environments, where they play a prominent role in photocatalytic transformations of bound organics. Here, we examine the ...photocatalytic degradation of rhodamine B by visible light using two different structurally well-defined hematite nanoparticle morphologies. In addition to detailed solid characterization and aqueous kinetics measurements, we also exploit species-selective scavengers in electron paramagnetic resonance spectroscopy to sequester specific reaction channels and thereby assess their impact. The photodegradation rates for nanoplates dominated by {001} facets and nanocubes dominated by {012} facets were 0.13 and 0.7 h–1, respectively, and the turnover frequencies for the active sites on {001} and {012} were 7.89 × 10–3 and 3.07× 10–3 s–1, yielding apparent activation energies of 17.13 and 24.94 kcal/mol within the energetic span model, respectively. Facet-specific differences appear to be directly not linked with the simple aerial cation site density but instead with their extent of undercoordination. By establishing this linkage, the findings lay a foundation for predicting the photocatalytic degradation efficiency for the myriad of possible hematite nanoparticle morphologies and more broadly help unveil key reactions at the interface that may govern photocatalytic organic transformations in natural and engineered aquatic environments.
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Water vapor binding to metal oxide surfaces produces thin water films with properties controlled by interactions with surface hydroxo sites. Hydrogen bonding populations vary across ...films and induce different molecular orientations than at the surface of liquid water. Identifying these differences can open possibilities for tailoring film-mediated catalytic reactions by choice of the supporting metal oxide substrate.
The (0001) face of a single sapphire (α-Al2O3) sample exposed to water vapor and the surface of liquid water were probed by polarization dependent Sum Frequency Generation-Vibration Spectroscopy (SFG-VS). Molecular dynamics (MD) provided insight into the hydrogen bond populations and molecular orientations across films and liquid water.
SFG-VS revealed a submonolayer film on sapphire exposed to 43% relative humidity (R.H.), and a multilayer film at 78% R.H. Polarization dependent SFG-VS spectra showed that median tilt angles of free OH bonds on the top of films are at ∼43° from the normal of the (0001) face but at 38° on neat liquid water. These values align with MD simulations, which also show that up to 36% of all OH bonds on films are free. This offers new means for understanding how interfacial reactions on sapphire-supported water films could contrast with those involving liquid water.
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•Synthesis of iron doped lithium ion-sieves H2FexTi1−xO3 (x≤0.15) by conventional doping technology.•Occurrence of grain shrinkage with doping Fe into Li2TiO3.•Required saturated ...magnetization values and enhanced BET surface area of Fe/Ti-0.15(H).•Excellent large-scale and continuously magnetic efficiency (96%) and superior lithium adsorption capacity (53mg/g).
The recent research on adsorption-based lithium recovery from lithium-containing solutions has been centred on adsorption capacity and separation of lithium ion-sieves powder from solutions. Herein, an effective iron-doped lithium titanium oxide (Fe-doped Li2TiO3) was synthesized by Fe-doping via solid state reactions followed by acid treatment to form iron-doped lithium ion-sieves (Fe/Ti-x(H)). The resulting solid powder displays both superior adsorption capacity of lithium and high separation efficiency of the adsorbent from the solutions. SEM imaging and BET surface area measurement results showed that at Fe doping levels x≤0.15, Fe-doping led to grain shrinkage as compared to Li2TiO3 and at the same time the BET surface area increased. The Fe/Ti-0.15(H) exhibited saturated magnetization values of 13.76emug−1, allowing effective separation of the material from solid suspensions through the use of a magnet. Consecutive magnetic separation results suggested that the Fe/Ti-0.15(H) powders could be applied at large-scale and continuously removed from LiOH solutions with separation efficiency of 96% or better. Lithium adsorption studies indicated that the equilibrium adsorption capacity of Fe/Ti-0.15(H) in LiOH solutions (1.8gL−1 Li, pH 12) reached 53.3mgg−1 within 24h, which was higher than that of pristine Li2TiO3 (50.5mgg−1) without Fe doping. Competitive adsorption and regeneration results indicated that the Fe/Ti-0.15(H) possessed a high selectivity for Li with facile regeneration. Therefore, it could be expected that the iron-doped lithium ion-sieves have practical applicability potential for large scale lithium extraction and recovery from lithium-bearing solutions.
We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal–organic perovskite ABX3, C(NH2)3MII(HCOO)3, in which A=C(NH2)3 is guanidinium, B=M is ...a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO−. The compounds could be synthesized by either diffusion or hydrothermal methods from water or water‐rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna21. In the perovskite structures, the octahedrally coordinated metal ions are connected by the anti–anti formate bridges, thus forming the anionic NaCl‐type M(HCOO)3− frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn–Teller effect of Cu2+ results in a distorted anionic Cu–formate framework that can be regarded as Cu–formate chains through short basal CuO bonds linked by the long axial CuO bonds. These materials show higher thermal stability than other metal–organic perovskite series of AmineHM(HCOO)3 templated by the organic monoammonium cations (AmineH+) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin‐canted antiferromagnetism, with a Néel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6 K (Cu). In addition to the general spin‐canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin‐flop and a spin‐flip to the paramagnetic phase) within 50 kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics.
Nice cubes: A family of metal–organic perovskite salts of C(NH2)3M(HCOO)3 for divalent Mn to Zn were synthesized from water or water‐rich solutions. They possess anionic NaCl‐type frameworks of M(HCOO)3 with guanidinium in the cubic cavities (see figure); the magnetic members show spin‐canted antiferromagnetism.
A porous molecular crystal with guest ethanol molecules, Mn3(HCOO)6(C2H5OH), was found to be a new type of multifunctional molecular system, which exhibits a ferroelectric transition at 165 K and a ...ferrimagnetic transition at 8.5 K. Mn3(HCOO)6(C2H5OH) will give a hint to design “multiferroic” molecular materials where ferroelectric and ferromagnetic orders coexist.
This work proposes a model predictive control (MPC) approach for a switching linear system where the switching signal is prescribed with unknown future values. The switching signal is known only at ...its current value, satisfies a minimal dwell-time restriction of τ steps between successive switchings and is otherwise arbitrary. Under such a setting, the MPC optimization problem has to allow for all admissible switching sequences within a given horizon length. Such a formulation necessitates several other features: the use of a modified returnable set as the terminal constraint; the introduction of consistency constraints on the predicted controls; a min-max optimization criterion as the cost function; the splitting of the horizon into two portions for recursive feasibility consideration and exponential stability of the closed-loop system. The proposed approach is demonstrated by a numerical example.
The aluminum oxyhydroxide boehmite is an important crystalline phase in nature and industry. We report development of a flexible additive-free hydrothermal synthesis method to prepare high quality ...boehmite nanoplates with sizes ranging from under 20 nm to 5 μm via using hydrated alumina gels and aluminum hydroxide amorphous powders as precursors. The size and morphology of the boehmite nanoplates was systematically varied between hexagonal and rhombic by adjusting precursor concentrations, pH, and the synthesis temperature, due to face-specific effects. The transformation mechanism is consistent with dissolution and reprecipitation, and involves transitory initial appearance of metastable gibbsite that is later consumed upon nucleation of boehmite. Detailed X-ray pair distribution characterization of the solids over time showed similarities in short-range order that suggest linkages in local chemistry and bonding topology between the precursors and product boehmite, yet also that precursor-specific differences in long-range order appear to manifest subtle changes in resulting boehmite characteristics, suggesting that the rate and extent of water release or differences in the resulting solubilized aluminate speciation lead to slightly different polymerization and condensation pathways. The findings suggest that, during dissolution of the precursor, precursor-specific dehydration or solution speciation could be important aspects of the transformation impacting the molecular-level details of boehmite nucleation and growth.
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