Arsenate zeolite analogues with 11 topological types

Crystal structure of Zn2(HTeO3)(AsO4)

Single crystals of Zn2(HTeO3)(AsO4), dizinc(II) hydroxidodioxidotellurate(IV) oxidoarsenate(V), were obtained as one of the by-products in a hydro-thermal reaction between Zn(NO3)2·6H2O, TeO2, H3AsO4 and NH3 in molar ratios of 2:1:2:10 at 483 K for seven days. The asymmetric unit of Zn2(HTeO3)(AsO4) contains one Te (site symmetry m), one As (m), one Zn (1), five O (three m, two 1) and one H (m) site. The ZnII atom exhibits a coordination number of 5 and is coordinated by four oxygen atoms and a hydroxide group, forming a distorted trigonal bipyramid. The hydroxide ion is positioned at a significantly larger distance on one of the axial positions of the bipyramid. The [ZnO4OH] polyhedra are connected to each other by corner-sharing to form ∞ 2[ZnO3/2(OH)1/2O1/1] layers extending parallel to (001). The TeIV atom is coordinated by three oxygen atoms and a hydroxide group in a one-sided manner in the shape of a bis-phenoid, revealing stereochemical activity of its 5s 2 electron lone pair. The AsV atom is coordinated by four oxygen atoms to form the tetra-hedral oxidoarsenate(V) anion. By corner-sharing, [TeO3OH] and [AsO4] groups link adjacent ∞ 2[ZnO3/2(OH)1/2O1/1] layers along [001] into a three-dimensional framework structure.

Enhanced Arsenate Removal Performance in Aqueous Solution by Yttrium-Based Adsorbents

Arsenic contamination in drinking water has become an increasingly important issue due to its high toxicity to humans. The present study focuses on the development of the yttrium-based adsorbents, with basic yttrium carbonate (BYC), Ti-loaded basic yttrium carbonate (Ti-loaded BYC) and yttrium hydroxide prepared using a co-precipitation method. The Langmuir isotherm results confirmed the maximum adsorption capacity of Ti-loaded BYC (348.5 mg/g) was 25% higher than either BYC (289.6 mg/g) or yttrium hydroxide (206.5 mg/g) due to its increased specific surface area (82 m²/g) and surface charge (PZC: 8.4). Pseudo first- and second-order kinetic models further confirmed that the arsenate removal rate of Ti-loaded BYC was faster than for BYC and yttrium hydroxide. It was subsequently posited that the dominant removal mechanism of BYC and Ti-loaded BYC was the carbonate-arsenate ion exchange process, whereas yttrium hydroxide was regarded to be a co-precipitation process. The Ti-loaded BYC also displayed the highest adsorption affinity for a wide pH range (3-11) and in the presence of coexisting anionic species such as phosphate, silicate, and bicarbonate. Therefore, it is expected that Ti-loaded BYC can be used as an effective and practical adsorbent for arsenate remediation in drinking water.

Gallium fluoroarsenates

Six new phases in the gallium-fluoride-arsenate system have been synthesised hydrofluorothermally using a fluoride-rich medium and "HAsF6" (HF : AsF5) as a reactant. RbGaF3(H2AsO4), KGaF(H2AsO4) and [piperazine-H2]2[Ga2F8(HAsO4)]·H2O have one dimensional structures, [DABCO-H2]2[Ga4F7O2H(AsO4)2]·4H2O consists of two dimensionally connected polyhedral layers, while GaF(AsO3[OH,F])2 and (NH4)3Ga4F9(AsO4)2 both have three-dimensionally connected polyhedral frameworks.

A weak-base fibrous anion exchanger effective for rapid phosphate removal from water

This work investigated that weak-base anion exchange fibers named FVA-c and FVA-f were selectively and rapidly taken up phosphate from water. The chemical structure of both FVA-c and FVA-f was the same; i.e., poly(vinylamine) chains grafted onto polyethylene coated polypropylene fibers. Batch study using FVA-c clarified that this preferred phosphate to chloride, nitrate and sulfate in neutral pH region and an equilibrium capacity of FVA-c for phosphate was from 2.45 to 6.87 mmol/g. Column study using FVA-f made it clear that breakthrough capacities of FVA-f were not strongly affected by flow rates from 150 to 2000 h(-1) as well as phosphate feed concentration from 0.072 to 1.6mM. Under these conditions, breakthrough capacities were from 0.84 to 1.43 mmol/g indicating high kinetic performances. Trace concentration of phosphate was also removed from feeds containing 0.021 and 0.035 mM of phosphate at high feed flow rate of 2500 h(-1), breakthrough capacities were 0.676 and 0.741 mmol/g, respectively. The column study also clarified that chloride and sulfate did not strongly interfere with phosphate uptake even in their presence of equimolar and fivefold molar levels. Adsorbed phosphate on FVA-f was quantitatively eluted with 1M HCl acid and regenerated into hydrochloride form simultaneously for next phosphate adsorption operation. Therefore, FVA-f is able to use long time even under rigorous chemical treatment of multiple regeneration/reuse cycles without any noticeable deterioration.

Removal of trace arsenic(V) and phosphate from water by a highly selective ligand exchange adsorbent

A highly selective ligand exchange type adsorbent was developed for the removal of trace arsenic(V) (As(V)) and phosphate from water. This adsorbent was prepared by loading zirconium(IV) on monophosphonic acid resin. This adsorbent was able to remove toxic anions efficiently at wide pH ranges. However, low pH was preferable for maximum breakthrough capacity in an adsorption operation. The effect of a large amount of competing anions such as chloride, bicarbonate, and sulfate on the adsorption systems of As(V) and phosphate anions was investigated. The experimental findings revealed that the As(V) and phosphate uptakes were not affected by these competing anions despite the enhancement of the breakthrough points and total adsorption. Phosphate anion was slightly preferable than As(V) in their competitive adsorption by the adsorbent. The adsorbed As(V) and phosphate on the Zr(IV)-loaded resin were quantitatively eluted with 0.1 mol/L sodium hydroxide solution, and the adsorbent was regenerated by 0.5 mol/L sulfuric acid. During several cycles of adsorption-elution-regeneration operations, no Zr(IV) was detected in the column effluents. Therefore, the Zr(IV)-loaded monophosphonic acid resin is an effective ligand exchange adsorbent for removing trace concentrations of As(V) and phosphate from water.

Formation of a 3D porous ferric arsenate containing novel cubane-like Fe4F4 building units

The purely inorganic microporous compound [H(3)O][Fe(4)F(4)(AsO(4))(3)] x 3 H(2)O (1), which contains novel cubane-like Fe(4)F(4) cages, exhibiting a 3D configuration with channels of dimensions 8 A x 8 A running along the [001], [010], and [100] directions, presents antiferromagnetic interactions.

Symmetry relationships of sodalite (SOD) – type crystal structures

The mineral sodalite with the ideal composition Na8[Al6Si6O24]Cl2is the prototype for numerous related crystal structures based on the same topology of the underlying net of strong bonds. This net has been assigned the code SOD by the Structure Commission of the International Zeolite Association. Minerals and synthetic compounds with a SOD-type framework represent the most comprehensive family of zeolite-type compounds with the highest number of published crystal structures. Among these are aluminosilicates (e.g., sodalite, haüyne, helvine, lazurite, nosean, tsaregorodtsevite), beryllosilicates (e.g., danalite, genthelvite, tugtupite), chlorides, sulfides (e.g., tetrahedrite, binnite, freibergite, galkhaite, goldfieldite, tennantite), borates (rhodizite), synthetic phosphates, aluminates, phosphides, nitrides and clathrate hydrates which have been shown by crystal structure analyses to adopt the SOD-type framework. More than 900 SOD-type crystal structures, which represent over 18% of the total number of published zeolite structures, are known. The complete symmetry relationships of SOD-type crystal structures comprising 27 space groups are listed in a Bärnighausen-tree together with the type and index of symmetry reduction. No other zeolite type displays such a rich harvest of symmetry as the sodalite-type. Seven additional space groups reported for SOD-types have not been considered here because they were not well supported by experimental evidence. Of the 26 low-symmetry derivatives six are due to an ordering of tetrahedrally coordinated framework cations. In two cases the lowering of symmetry is caused by some of the framework cations assuming 5- or 6-coordinations instead of the usual 4-coordination. This means that in 18 cases the lower space group symmetries are achieved by the influence of pore-filling matter.