Soft Lewis Base Research Articles

Na/Zn/Sn/S (NaZTS): Quaternary metal sulfide nanosheets for efficient adsorption of radioactive strontium ions

Metal sulfides are promising materials because their ability to capture radioactive nuclides from wastewater is superior to many others. Herein, Na/Zn/Sn/S (NaZTS) quaternary metal sulfide nanosheets were fabricated using a one-pot hydrothermal method. A series of characterizations revealed that these nanosheets had a structure identical to Na5Zn3.5Sn3.5S13·6H2O, consisting of [Zn3.5Sn3.5S13]5− frameworks and Na+ ions located at the center and corner of the open channels. Because of the S2− ligands in its structure, NaZTS was a soft Lewis base and showed high affinity toward Sr2+ ions. NaZTS was employed to remove Sr2+ from aqueous solutions and exhibited ultrafast kinetics (an equilibrium time of 5 min), a broad active pH range (a removal rate of >98.4% at pH 3–12), and a very low Sr2+ desorption rate of <0.04%. Its maximum adsorption capacity according to the Langmuir model was 40.4 mg g−1 at 318 K. The effects of adsorbent dosage and coexisting ions on Sr2+ adsorption were also discussed. Macroscopic adsorption experiments and microscopic X-ray photoelectron spectroscopy were used to study the adsorption mechanism, and the outstanding ability of NaZTS to capture Sr2+ ions could be attributed to ion exchange and strong Sr⋯S bonding. This work highlights the excellent adsorption of Sr2+ by NaZTS, which makes it a promising material for removing radioactive Sr2+ in cleanups of radioactive pollution.

Efficient capture of iodine by a polysulfide-inserted inorganic NiTi-layered double hydroxides

Effective capture of radioactive iodine is highly desirable but still remains a significant challenge. We reported here a polysulfide (Sx2−) intercalated inorganic cationic Ni-Ti layered double hydroxide, NiTi-Sx-LDH, which was prepared by coprecipitation method and ion exchange method for efficient capture of iodine. Due to the strong chemical attraction between the soft Lewis base Sx2− and the soft Lewis acid I2, and the reducing property of Sx2−, NiTi-Sx-LDH exhibits highly efficient iodine capture. During the adsorption process, I2 is reduced to I3− by the intercalated Sx2−. In combination with chemical adsorption and physical adsorption, the adsorption capacity of NiTi-Sx-LDH to iodine vapor reaches 52% (wt%). In addition, the adsorption properties of NiTi-Sx-LDH on elemental iodine in organic solvent cyclohexane were also studied, and the maximum adsorption capacity of NiTi-Sx-LDH for iodine reaches up to 527.4 mg/g. Compared with various sorbents for iodine, it is cost-effective, capable of achieving scale-up preparation, and the good performance for the iodine adsorption suggests that NiTi-Sx-LDH may be considered as a promising sorbent for efficient removal of radioactive iodine from reprocessing plant off-gas streams.

Rational Design of a Catalyst for the Selective Monoborylation of Methane

Combined computational and experimental studies elucidate the mechanism and suggest rational design and optimization strategies of a bis(phosphine)-supported iridium-catalyst for methane monoborylation. The activation of the C–H bond in methane via oxidative addition using tris(boryl) iridium(III) complexes bearing bis-chelating supporting ligands is modeled computationally. This model shows that the use of the soft Lewis base ligand such as 1,2-bis(dimethylphosphino)ethane (dmpe) lowers the activation barrier of the rate-determining step as it facilitates polarization of the metal-center, lowering the barrier of the oxidative addition to afford a seven-coordinate iridium(V) intermediate. The experimental optimization of this reaction using high-throughput methods shows that up to 170 turnovers can be achieved at 150 °C (500 psi) within 16 h using bis(pinacolato)diboron, a well-defined homogeneous and monomeric catalyst (dmpe)Ir(COD)Cl that is readily available from commercial precursors, with selectivity...

Stable pyrazolate-based metal-organic frameworks for drug delivery

To explore materials stable in alkaline solution, a linear ligands 1,4-benzenedi(4′-pyrazolyl), in which the pyrazolate group was considered as a soft Lewis base, was used to reacted with two relative soft Lewis acid Ni(II) and Zn(II) metal ions, to constructed stable MOFs structure. Since the metal pyrazolate clusters resemble with metal carboxylate clusters performing the same connection mode during self-assembly, the obtained materials PFC-6 and PFC-7 exhibit same topologies with classic carboxylate-based MOFs UiO-66 and MIL-53, respectively. Due to the strong coordination bond between soft Lewis base and soft Lewis acid, PFC-6 and PFC-7 exhibit high porosity and excellent stability from pH = 2 to pH = 13. Inspired by these features, PFC-6 was used as a drug carrier and the DCF drug uptake/release behavior were investigated. This work presented here demonstrates that the pyrazolate-based ligands are capable of constructing MOFs structure possessing same topologies with carboxylate ligands but high stability in alkaline solution.

Efficient, stable and selective adsorption of heavy metals by thio-functionalized layered double hydroxide in diverse types of water

The designing of efficient, selective and stable adsorbents for heavy metals removal remained a challenging task, as most adsorbents did not exhibit consistent performance in diverse types of water. Unlike traditional adsorbents based on surface oxygen groups, thio-functionalized layered double hydroxide (LDH) as Mn-MoS4 was designed by inserting MoS42− anions into lamellar layers in LDH, and was applied as a highly stable, efficient and selective adsorbent for heavy metals removal. The record high distribution coefficient (Kd∼107–108mL/g), fast kinetics and enormous saturated uptake capacities (594, 564 & 357mg/g) for Hg2+, Ag+ and Pb2+ placed Mn-MoS4 as the most efficient adsorbent for the removal of such metals so far. Further, Mn-MoS4 can completely tolerate the impact of huge concentration of background electrolytes (Ca2+, Mg2+, Na+, Cl−, NO3− & SO42−), and effectively control the concentrations of Hg2+, Ag+ and Pb2+ ions from tap water, lake water or industrial wastewater far below the limitation in drinking water. Similarly, Mn-MoS4 is a potential filter due to its consistent performance over a broad pH range (from 2.0 to 11.0), changing ionic strength (up to 100mM) or in the presence of organic matters. These remarkable features originate from the dominant chemical adsorption mechanism through inner-sphere coordination between thio groups as soft Lewis acid and Hg2+, Ag+ and Pb2+ as soft Lewis bases. More interestingly, LDH layers offer protective space for intercalated MoS42− anions against oxidation, and facilitate Mn-MoS4 with the advantage of easy storage and application over other adsorbents.

Reversible and Efficient Sequestration of Cesium from Water by the Layered Metal Thiophosphate K0.48 Mn0.76 PS3 ⋅H2 O.

Water body contamination with radioactive species is an important issue due to significant developments in nuclear energy. Cesium (137 Cs) radioisotope is a non-actinide fission product of uranium and plutonium that is long-lived. Hence, selective removal/capture of cesium is essential for managing radioactive waste. Herein, a detailed Cs+ ion-exchange study on a potassium intercalated layered metal thiophosphate, K0.48 Mn0.76 PS3 ⋅H2 O (K-MPS-1), is reported. The sorption of Cs+ by K-MPS-1 follows the Langmuir model with a high capacity of 337.5 mg g-1 and high distribution coefficients in the order of about 104 mL g-1 . K-MPS-1 can sequester Cs+ efficiently, even from very low concentrations (ppb level). K-MPS-1 exhibits high cesium uptake over a broad pH range of 2-12 and the ion-exchange process reaches equilibrium within a short time (≈15 min), following pseudo-second-order kinetics. Moreover, K-MPS-1 demonstrates selectivity towards Cs+ capture in the presence of complex solutions containing excess Na+ , Ca2+ , and Mg2+ ions; this is due to favorable interactions between Cs (soft Lewis acid) and S (soft Lewis base). K-MPS-1 reversibly captures Cs+ and it can be regenerated by treating Cs-MPS-1 with a solution of KCl.

A Zwitterionic Gold(I) Diphenylphosphane Oxide Complex Stabilized by a Hard Pulling Lewis Acid and a Soft Pushing Lewis Base

The reaction of Ph2P(O)H with B(C6F5)3 provided the Lewis pair complex Ph2(H)POB(C6F5)3 (5) containing a bipolar +P–O–B– linkage. The reaction of 5 with [(tht)AuCl] (tht = tetrahydrothiophene) proceeded with elimination of HCl and formation of [{(C6F5)3BOPPh2}Au(tht)] (6), which can be regarded as push–pull complex between a zwitterionic OPPh2Au unit and a hard Lewis acid, B(C6F5)3, coordinating at the oxygen atom, and a soft Lewis base, tht, coordinating at the gold atom.

Effect of loading on the nature of the REE–humate complexes as determined by Yb3+ and Sm3+ LIII-edge EXAFS analysis

Humic substances are major natural complexing agents that strongly influence the cycling of metal cations in the environment. The metal to humic acid (HA) concentration ratio (metal loading) can significantly impact the overall HA complexation properties in natural soils and waters. At low metal loading, cations bind to strong multi-carboxylate or -phenolate sites of HA. In addition, these strong sites might contain soft Lewis bases such as N or S, the contribution of which is still a matter of debate. Based on the possible ability of Rare Earth Elements (REE) to trace HA binding properties, the present study aimed at evaluating the influence of REE-loading on the HA binding mechanisms of two hard Lewis acids, Sm3+ and Yb3+. Extended X-ray Absorption Fine Structure (EXAFS) at the Sm and Yb LIII edge was used to analyze the local coordination of these intermediate and heavy REE ions, respectively, in a low and a high REE-loading HA sample. Data were interpreted by comparison with EXAFS data for a series of aqueous REE complexes with iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and a carboxylic-grafted resin. In all these samples, both a Yb–O (~2.31Å) and a Yb–N (~2.50Å) backscattering path could be identified in the first coordination shell of Yb. At low REE loading, the first coordination shell around the Yb bond to HA is described by a single Yb–O backscattering path, i.e. the presence of N could not be evidenced. By contrast, the carboxylic-grafted resin exhibits both a short (2.31Å) and a long Yb–O average distance (2.44Å), suggesting the coordination of carboxylate is bidentate. The Fourier transform of the high loading HA samples exhibits a broad first shell peak possibly described by two Yb–O distances (2.29 and 2.43Å) suggesting two coordination modes of the carboxylic groups. Different Yb–HA complex structures can therefore be observed at different metal loadings. Unfortunately, the Sm EXAFS spectra could only be recorded up to k=10Å−1. There was no evidence of either a clear difference between the metal loadings or with Yb–HA complex structures. A comparison between the EXAFS results, PHREEQC-Model VI simulations, and the pattern of the REE complexation constants with simple organic ligands (REE:ligand 1:1 and 1:2 complexes) provides evidence that, at high loading, REE are bound to HA through bi-ligand complexes without any chelation effect in which REE may potentially act as a cation bridge between two organic molecules. At low loading, the fact that N could not be detected in the Yb first shell suggests that, at low loading, Yb binds to O-containing groups of HA rather than N-containing groups. This may call into question the definition of HA strong sites for REE binding such as soft Lewis base-containing sites.

The selectivity of diglycolamide (TODGA) and bis-triazine-bipyridine (BTBP) ligands in actinide/lanthanide complexation and solvent extraction separation - a theoretical approach.

Theoretical calculations (density functional theory with the scalar relativistic ZORA Hamiltonian) have been performed to obtain the energy and Gibbs free energy of formation of cationic 1 : 3 complexes of americium(iii) and europium(iii) with a tri-O-dentate diglycolamide ligand TEDGA (a model of TODGA extractant), as well as the free energy of their partition between water and an organic diluent. The distribution of electron density over the atoms, bonds, and molecular orbitals was analyzed by means of Mulliken population analysis, the localization procedure of natural bond orbitals, and the Quantum Theory of Atoms-in-Molecules. The stabilities of both [M(TEDGA)(3)](3+) complexes are similar to each other. On the other hand, our recent data for a similar pair of cationic Am/Eu complexes with a softer (HSAB) tetra-N-dentate ligand C2-BTBP show that the [Am(C2-BTBP)(2)](3+) complex is significantly more stable in aqueous solution than its Eu counterpart. The decisive factor stabilizing the Am(3+) complexes over their Eu(3+) analogues is the charge transfer from the ligands, somewhat greater on the 6d(Am(III)) than on 5d(Eu(III)) orbitals. The covalency of M-N bonds in the [M(C2-BTBP)(2)](3+) complexes is greater than that of M-O bonds in [M(TEDGA)(3)](3+), but the latter is not negligible, in particular in the bonds with the oxygen atoms of the amide groups in TEDGA. The analysis of charge distribution over the whole molecules of the complexes shows that the TEDGA molecule is not hard as expected, but a relatively soft Lewis base, only slightly harder than BTBP. This conclusion has been confirmed by the calculation of the chemical hardness of the ligands. Moreover, the comparison of the results of bonding analysis with the calculated energies of complex formation in water and in the gas phase allows us to conclude that the population analysis, QTAIM topological parameters, and SOPT stabilization energy, as well as Wiberg and overlap-weighted NAO indices are the tools for analyzing the covalency rather than the total bond strength.

Sulfone-Based Electrolyte Solutions for Rechargeable Magnesium Batteries Using 2,5-Dimethoxy-1,4-Benzoquinone Positive Electrode

Rechargeable magnesium batteries may be an option for replacing the rechargeable lithium batteries because magnesium is much more abundant in the earth’s crust and is more widely distributed than lithium. To achieve rechargeable magnesium batteries, it is important to consider the combination of the electrolyte and the positive electrode with the Mg negative electrode. We previously reported that an organic molecule, 2,5-dimethoxy-1,4-benzoquinone (DMBQ), acts as a positive electrode material in a Mg electrolyte solution, Mg(ClO4)2/GBL, in a half-cell setup1, in which reversible Mg deposition/dissolution does not occur on the negative electrode.In the present study, we investigated three sulfones (RR´SO2) for use as a solvent to dissolve the Mg solute in rechargeable magnesium batteries; viz., sulfolane (SL), ethyl-i-propyl sulfone (EiPS) and di-n-propyl sulfone (DnPS). As the Mg electrolyte, we used magnesium bis(trifluoromethanesulfonyl)amide (Mg(TFSA)2) because it can tolerate a high potential and the large TFSA anion, a soft Lewis base, should facilitate its dissociation from the Mg2+cation.The thermal stability of the electrolyte solutions examined by DSC indicated that these solutions remain stable as electrolytes over a wide temperature range < 250˚C. The specific conductivity of these solutions was 1~2 mS cm- 1 at 30˚C, which is about an order of magnitude lower than that of the electrolyte solutions used in conventional rechargeable lithium batteries, ~10 mS cm- 1. The potential window of the electrolyte solutions examined by LSV indicated that all three solutions remained stable between 0 and 2.0 V vs. Mg reference electrode (Mgquasi). From the viewpoint of the width of the potential window as well as both the thermal stability and specific conductivity, Mg(TFSA)2/SL was the best electrolyte solution among the three tested in this study.The charge-discharge properties of the DMBQ electrode were investigated in the three-electrode cell between 0 and 2.0 V vs. Mgquasi. The first discharge curves showed two potential plateaus that were often observed for quinone-based electrodes in Li, Na and Mg systems. The DMBQ electrode was successfully oxidized in the subsequent charge process. From EDX measurement and XRD analysis, it was found that DMBQ crystal reversibly accommodates and releases Mg2+in the sulfone electrolyte solutions during cycles.The electrochemical properties of the metallic Mg electrode in the sulfone electrolyte solutions were investigated by cyclic voltammetry at room temperature in the three-electrode cell. The reduction-oxidation current of the metallic Mg electrode was observed. SEM observations and XRD analysis suggest that Mg2+in the electrolyte solution is indeed reduced to Mg(0) and deposited on the electrode during a cathodic sweep.The properties of a two-electrode cell consisting of Mg|Mg(TFSA)2/SL|DMBQ were examined as a rechargeable Mg battery at 30˚C. The cycle trend of the cell is shown in Figure 1. The discharge capacity increases in the initial seven cycles to reach ca. 100 mAh g(DMBQ)- 1. Although the capacity substantially decreases upon cycling, it retains 20% of the maximum capacity after 50 cycles.1. H. Sano, H. Senoh, M. Yao, H. Sakaebe, and T. Kiyobayashi, Chem. Lett., 41, 1594-1596 (2012)

An infinite square lattice of super-supertetrahedral T6-like tin oxyselenide clusters

A new super-supertetrahedral cluster, resembling a coreless supertetrahedral T6 cluster, was made as a tin oxyselenide by integrating hard and soft Lewis bases (O(2-) and Se(2-)) into the tetravalent system. Its hierarchical architecture, built from supertetrahedral T3-[Sn10O4Se20] and Sn2Se6 clusters, represents a new level of complexity in the cluster-based construction. Compared to pure tin selenides, the new tin oxyselenide material in this work shows much enhanced stability and size-dependent band energy level.

2-ACYLTHIOAMIDES IN THE BIGINELLI REACTION

It was shown for the first time that 2-acylthioamides enter the Biginelli reaction with aromatic aldehydes and ureas/thioureas producing N ‑Ar 1 ‑4-Ar 2 -6-R 1 -1-R 2 -2-oxo(thioxo)-1,2,3,4-tetrahydropyrimidine-5‑carbothioamides. The regioselectivity of the process is in agreement with the hard and soft Lewis acid and base theory. It was established that under action of nitrous acid or other oxidants on the obtained products N ‑Ar 1 -4‑Ar 2 -6‑R 1 -1-R 2 -2-oxo(thioxo)-1,2,3,4-tetrahydropyrimidine-5‑carboxamides are formed, but not the expected 4‑Ar 2 -6-R 1 -1-R 2 -5‑(1,3‑benzothiazol-2-yl)-1,2,3,4‑tetrahydropyrimidin-2-оnes(thiones). How to Cite Kurmach, M. N.; Ryabitskiy, A. B.; Britsun, V. N. Chem. Heterocycl. Compd. 2014 , 49 , 1770. [ Khim. Geterotsikl. Soedin. 2013 , 1910.] For this article in the English edition see DOI 10.1007/s10593-014-1429-z

Synthesis and Characterization of Thiolated Chitosan Beads for Removal of Cu(II) and Cd(II) from Wastewater

Removal of Cu(II) and Cd(II) from wastewater using porous chitosan beads is likely to be enhanced by the introduction of thiol groups (−SH). This is because, in accordance with the Hard Soft Acid Base concept, the soft Lewis base of –SH forms a strong bond with soft Lewis acid of Cd(II) or with borderline Lewis acids such as Cu(II). Possible formation of thiourea and disulfide crosslinks (−S–S–) may also confer increased bead stability in acidic solution. Thiolated chitosan beads (ETB) prepared and investigated in this study had a total sulfur content of 7.9 %. The thiolation process slightly increased the Brunauer-Emmett-Teller surface area of the chitosan beads from 39.5 to 46.3 m2/g. This ETB was categorised as a microporous material (pore aperture: 1.8 nm) with multiple and uniform porous layers. Analysis by X-ray photoelectron spectroscopy indicated the presence of three sulfur species, S(−I), S(−II) and S(V) attributed to –S–S–, –SH and sulfonate (−SO3 −) groups. The Langmuir sorption capacity, q max, for Cd(II) was improved by 18 times by thiolation of chitosan. However, the q max for Cu(II) by ETB was seven times lower than that of pristine chitosan beads, possibly due to exhaustion of amine groups (−NH2). The batch sorption data was generally fitted well by a linearised Freundlich isotherm model and a Ho’s pseudo-second-order kinetic model, indicating metal interaction with the heterogeneous surface of ETB and chemical adsorption as the possible rate-limiting step, respectively. The metal uptake has resulted in the oxidation of –SH to –SO3 − group in ETB, thereby decreasing the stability of metal-sulfide bonds as well as their metal uptake.

Contact Ion Pair Formation between Hard Acids and Soft Bases in Aqueous Solutions Observed with 2DIR Spectroscopy

The interaction of charged species in aqueous solution has important implications for chemical, biological, and environmental processes. We have used 2DIR spectroscopy to study the equilibrium dynamics of thiocyanate chemical exchange between free ion (NCS(-)) and contact ion pair configurations (MNCS(+)), where M(2+) = Mg(2+) or Ca(2+). Detailed studies of the influence of anion concentration and anion speciation show that the chemical exchange observed with the 2DIR measurements results from NCS(-) exchanging with other anion species in the first solvation shell surrounding Mg(2+) or Ca(2+). The presence of chemical exchange in the 2DIR spectra provides an indirect, but robust, determinant of contact ion pair formation. We observe preferential contact ion pair formation between soft Lewis base anions and hard Lewis acid cations. This observation cannot be easily reconciled with Pearson's acid-base concept or Collins' Law of Matching Water Affinities. The anions that form contact ion pairs also correspond to the ions with an affinity for water and protein surfaces, so similar physical and chemical properties may control these distinct phenomena.

Mild C–H activation of activated aromatics with [8,8′-μ-I-3,3′-Co(1,2-C2B9H10)2]: Just mix them

Reactions of the iodonium derivative of cobalt bis(dicarbollide) anion [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] with activated aromatics were studied. The reactions with ortho- and meta-xylenes result in mild arene C–H activation under ambient conditions, whereas the reaction with para-xylene requires the presence of PPh3 as soft Lewis base. The obtained aryl derivatives [8-Ar-8′-I-3,3′-Co(1,2-C2B9H10)2]− were found to have the transoid conformation both in the solid state and in solution due to intramolecular hydrogen CHcarb⋯IB bonds and aromatic CHcarb⋯π interactions between the dicarbollide ligands. The Lewis acidity of the quasi-borinium cation formed on the breakage of the iodonium bridge was estimated using Beckett–Gutmann method. According to the Gutmann acceptor number AN = 112 (in CD2Cl2), this quasi-borinium cation belongs to the most strong boron Lewis acids and can be considered as Lewis superacid.

Adsorption of Some Typical Fission Products onto a Novel Macroporous Silica-based Dialkyl Derivative of Pyridine Impregnated Material

A macroporous silica-based multidentate soft-ligand 2,6-bis(5,6-di(iso-hexyl)-1,2,4-triazine-3-yl)pyridine (BDIHTP) material, BDIHTP/SiO2-P, was synthesized by impregnating and immobilizating BDIHTP into the pores of the SiO2-P particles. The adsorption behavior of some typical fission products Mo(VI), Zr(IV), Ru(III), Pd(II), Rh(III), and a part of rare earths La(III), Ce(III), Nd(III), Eu(III), Gd(III), Dy(III), Er(III), Yb(III), and Y(III) contained in highly active liquid waste (HLW) onto BDIHTP/SiO2-P was investigated. The effects of contact time and the concentration of HNO3 in the range of 0.3 M to 5.0 M were examined. The BDIHTP/SiO2-P materials showed excellent adsorption ability and high selectivity for Pd(II) greater than all of the tested metals. It was contributed to the effective complexation of Pd(II), a soft-Lewis acid and an electron-pair acceptor, with BDIHTP, a soft-Lewis base and an electron-pair donor. The chromatographic partitioning of the tested metals from 1.0 M HNO3 by BDIHTP/SiO2-P packed column was performed. Pd(II) was effectively eluted with 0.2 M thiourea-0.1 M HNO3 and then separated from the others. The results are beneficial to partitioning of the long-lived minor actinides and Pd(II) together from HLW by the BDIHTP/SiO2-P materials.

Sodium Doping Controlled Synthesis of Monodisperse Lanthanide Oxysulfide Ultrathin Nanoplates Guided by Density Functional Calculations

Doping of nanocrystals is an intriguing field, since the intentional introduction of impurities has long been regarded as a major way of tailoring the properties of materials. Furthermore, it was recently found that the use of dopants in the synthesis of inorganic colloidal nanocrystals can not only introduce novel properties but also influence shape and size evolution during nanocrystal nucleation and growth. For example, Liu and co-workers showed that NaYF4-based nanocrystals can be precisely tuned in size, phase, and upconversion emission through Gd doping. Wang and co-workers reported that lanthanide doping of alkaline earth metal fluoride nanocrystals can lead to a significant increase in monodispersity. On the other hand, the special 4f electron configurations of lanthanides endow their compounds with promising functionalities, such as luminescence, catalytic activity, and permanent magnetism. This has therefore stimulated recent efforts to synthesize colloidal lanthanide-based nanocrystals (Ln-based NCs) with tunable morphologies and unique material properties. For example, both the small size and excellent luminescence properties make Ln-based NCs a potential new type of fluorescent probes. Specifically, lanthanide oxysulfides (Ln2O2S; Ln=La, Gd, Y) can serve as one of the most effective hosts for fluorescence applications, and research on Ln2O2S NCs is therefore highly intriguing. [4] However, the synthesis of monodisperse Ln2O2S NCs remains a challenge, since the theory of hard and soft acids and bases (HSAB) predicts a lack of affinity between the hard Lewis acid Ln and the soft Lewis base S . Previously, Gao and coworkers presented pioneering work in the synthesis of monodisperse lanthanide oxysulfide nanocrystals, yet due to the difficulty in preparing the corresponding single-source precursors, this method was limited to only a few lanthanides (i.e., Sm, Eu, Gd). On the basis of both experimental characterization and DFT calculations, we now demonstrate that introduction of monovalent Na ions as dopants in trivalent Ln host lattices can significantly facilitate the formation of Ln2O2S NCs in oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE) mixed solvent by creating oxygen vacancies in the host lattice during sulfurization reactions. In a typical synthesis, monodisperse and single-crystalline Na-doped La2O2S nanoplates were formed with a diameter of (22.3 2.0) nm (Figure 1a and b). High-resolution transmission electron microscopy (HRTEM) revealed that the morphology of the as-synthesized nanoplates was mainly hexagons with six {100} facets as their side planes (Figure 1b). When the dispersion of nanoplates in cyclohexane was highly

Selectivity of some basic solutes on a poly(methyltetradecylsiloxane)‐silica stationary phase

Complex analyses of polar compounds, especially basic ones, require more selective stationary phases. The present paper describes a stationary phase prepared by thermal immobilization of poly(methyltetradecylsiloxane) onto chromatographic silica (PMTDS-SiO(2)). This stationary phase presents hydrophobic and ion-exchange interactions that confer both high retention and unique selectivities for basic solutes. The influence of ion-exchange interactions is confirmed by the increase in retention factors of basic solutes when the mobile-phase pH changes from acidic to neutral and by the decrease in retention factors when the mobile-phase pH changes from neutral to alkaline. The ion-exchange properties of the stationary phase are enriched in neutral mobile phase (pH 7-7.5) using soft Lewis bases such as tricine and tris as buffers but are suppressed in both acidic (pH 2.5-6) and highly alkaline mobile phases (pH≤10). Increasing both temperature and flow rate permits more rapid separations while maintaining the selectivity. The stability of the stationary phase is evaluated with acid, neutral and alkaline mobile phases.

Preparation of a Macroporous Silica-Based Pyridine Impregnated Material and Its Adsorption for Palladium

A macroporous silica-based 2,6-bis(5,6-di(iso-hexyl)-1,2,4-triazine-3-yl)pyridine (BDIHTP) multinitrogen molecular recognition material, BDIHTP/SiO2-P, was prepared. It was performed through impregnation and immobilization of BDIHTP into the pores of the macroporous SiO2-P particle support with a mean diameter of 50 μm. The adsorption of some typical alkali metal and alkaline earths Cs(I), Na(I), K(I), Rb(I), Sr(II), and Ba(II), as well as Pd(II), a representative of precious metals, contained in highly active liquid waste (HLW), onto the BDIHTP/SiO2-P material was investigated at 298 K. It was carried out by examining the effects of contact time and the HNO3 concentration in the range 0.3–5.0 M. BDIHTP/SiO2-P showed excellent adsorption ability and high selectivity for Pd(II) over all the tested metals, which had weak or almost no adsorption. It was attributed to the strong chemical complexation of Pd(II), a soft Lewis acid and an electron-pair acceptor, with nitrogen inside BDIHTP, a soft Lewis base and...

Adsorption of Pb (II) and Cd (II) from aqueous solutions onto sodium tetraborate-modified Kaolinite clay: Equilibrium and thermodynamic studies

Kaolinite clay sample obtained from Ubulu-Ukwu in Delta State of Nigeria was modified with sodium tetraborate to obtain NTB-modified kaolinite clay. XRD measurements of NTB-modified kaolinite adsorbent showed no observable change in the d-spacing of its crystal lattice. Also, the data of XRD confirmed that this kaolinite clay sample is a mixture of kaolinite and Illite clay minerals. The SEM of modified and unmodified samples showed irregular crystal structures. FTIR results proved the surface modification of the kaolinite at –Al–O and –Si–O centers. The NTB-modified adsorbent presented with broader peaks of inner –OH. Modification of kaolinite clay sample with sodium tetraborate decreased its PZC from pH 4.40 to 3.70 while its Specific Surface Area (SSA) was increased from 10.56 m 2 g − 1 to 15.84 m 2 g − 1 . Modification with sodium tetraborate reagent increased the adsorption capacity of kaolinite clay from 16.16 mg/g to 42.92 mg/g for Pb (II) and 10.75 mg/g to 44.05 mg/g for Cd (II) at 298 K. Increasing temperature was found to increase the adsorption of both metals onto both adsorbents suggesting an endothermic adsorption reaction. The simultaneous presence of electrolyte in aqueous solution with Pb and Cd (II) was found to decrease the adsorption capacity of NTB-modified adsorbent for Pb and Cd (II). Using the Pearson's Hard and Soft Lewis Acid and Base (HSAB) theory the higher selectivity of unmodified kaolinite clay adsorbent for Pb and NTB-modified kaolinite clay for Cd (II) was justified. The thermodynamic calculations for the modified kaolinite clay sample indicated an endothermic nature of adsorption ( ΔH mean + 4.35 kJ mol − 1 for Pb(II) and + 3.79 kJ mol − 1 for Cd (II)) and an increase in entropy as a result of adsorption of Pb (II) and Cd (II) ( ΔS mean − 21.73 J mol − 1 K for Pb (II) and − 18.30J mol − 1 K for Cd (II)). The small positive values of free energy change ( ΔG mean) indicated that the adsorption of Pb (II) and Cd (II) onto the modified adsorbent may require some small amount of energy to make it more feasible. Modeling equilibrium adsorption data obtained suggested that NTB-modified adsorbent sample has homogeneous adsorption sites and fit very well with Langmuir adsorption model. Regeneration studies suggest that ≈ 85% of the metals were desorbed from both adsorbents. On reuse of the adsorbents only ≈ 80% of metals were adsorbed. NTB-modified kaolinite clay sample show some very good potentials as a low-cost adsorbent for the adsorption of Pb (II) and Cd (II) from aqueous solutions.