Molecular structure of the phosphate mineral koninckite - a vibrational spectroscopic study

We have undertaken a study of the mineral koninckite from Litosice (Czech Republic), a hydrated ferric phosphate, using a combination of scanning electron microscopy with electron probe micro-analyzer (wavelength-dispersive spectroscopy) and vibrational spectroscopy. Chemical analysis shows that studied koninckite is a pure phase with an empirical formula Fe3+ (0.99)(PO4)(1.00) center dot 2.75 H2O, with minor enrichment in Al, Ca, Ti, Si, Zn, and K (averages 0.00X apfu). Raman bands and shoulders at 3495, 3312, 3120, and 2966 cm(-1) and infrared bands and shoulders at 3729, 3493, 3356, 3250, 3088, 2907, and 2706 cm(-1) are assigned to the nu OH stretching of structurally distinct differently hydrogen bonded water molecules, A Raman band at 1602 cm(-1) and shoulders at 1679, 1659, 1634, and 1617 cm(-1) and infrared bands at 1650 and 1598 cm(-1) are assigned to the nu(2)(delta) H2O bending vibrations of structurally distinct differently hydrogen bonded water molecules. Raman shoulders at 1576, 1554, 1541, 1532, and 1520 cm(-1) and infrared shoulders at 1541 and 1454 cm(-1) may be probably connected with zeolitically bonded water molecules located in the channels. Raman bands and shoulders at 1148, 1132, 1108, 1063, 1048, and 1015 cm(-1) and an infrared band and shoulders at 1131, 1097, 1049, and 1017 cm(-1) are assigned to the nu(3) PO43- triply degenerate antisymmetric stretching vibrations. A Raman band and a shoulder at 994 and 970 cm(-1), respectively, and an infrared band and a shoulder at 978 and 949 cm(-1), respectively, are assigned to the nu(1) PO43- symmetric stretching vibrations. Infrared shoulders at 873, 833, and 748 cm(-1) are assigned to libration modes of water molecules. Raman bands and shoulders at 670, 648, 631, 614, 600, 572, and 546 cm(-1) and infrared bands at 592 and 534 cm(-1) are assigned to the nu(4) (delta) PO(4)(3-)triply degenerate out-of-plane bending vibrations; weak band at 570 cm(-1) may coincide with the delta Fe-O bending vibration. Raman bands and shoulders at 453, 443, 419, and 400 cm(-1) are assigned to the nu(2) (delta) PO43- doubly degenerate in-plane bending vibrations. Raman bands at 385, 346, 324, 309, 275, 252, and 227 cm(-1) are assigned to the nu Fe-O stretching vibrations in FeO6 octahedra. Raman bands at 188, 158, 140, 112, 89, and 73 cm(-1) are assigned to lattice vibrations

Quick and efficient co-treatment of Zn2+/Ni2+ and CN- via the formation of Ni(CN)4 2- intercalated larger ZnAl-LDH crystals

The wide use of metal electroplating involving CN- necessitates the cost-effective treatment of both CN and metals (Zn, Cu, Ni etc.). In this research, we developed a novel strategy - Ni2+-assisted layered double hydroxide (LDH) precipitation - to simultaneously remove aqueous CN and Zn/Ni metals. The strategy is to convert CN-/Zn(CN)(4)(2-) to Ni(CN)(4)(2-) first, and then to quickly precipitate Ni(CN)(4)(2-)/CN- into LDH crystals. The conversion has been clearly evidenced by the change of CN characteristic FTIR bands of Zn-CN solution before and after adding Ni(NO3)(2). The intercalation and efficient removal of CN have also been confirmed through the formation of LDH crystals XRD and SEM. In particular, a set of optimized experimental factors has been obtained by investigating their effects on CN removal efficiency in the simulated tests. Remarkably, over 95% CN were removed with high removal efficiencies of metals. Our results thus suggest that the current strategy is a quick, efficient and promising way to simultaneously treat both Ni and metals/CN rich electroplating wastewaters. (C) 2014 Elsevier B.V. All rights reserved

Effective adsorption of sodium dodecylsulfate (SDS) by hydrocalumite (CaAl-LDH-Cl) induced by self-dissolution and re-precipitation mechanism

Hydrocalumite (CaAl-LDH-Cl) were synthesized through a rehydration method involving a freshly prepared tricalcium aluminate (C3A) with CaCl2 solution. To understand the intercalation behaviour of sodium dodecylsulfate (SDS) with CaAl-LDH-Cl, X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectrometer (ICP) and elemental analysis have been undertaken. The sorption isotherms with SDS reveal that the maximum sorption amount of SDS by CaAl-LDH-Cl could reach 3.67 mmol•g-1. The results revealed that CaAl-LDH-Cl holds a self-dissolution property, about 20-30% of which is dissolved. And the dissolved Ca2+, Al3+ ions are combined with SDS to form CaAl-SDS or Ca-SDS precipitation. It has been highlighted that the composition of resulting products is strongly dependent upon the SDS concentration. With increasing SDS concentrations, the main resulting product changes from CaAl-SDS to Ca-SDS, and the value of interlayer spacing increased to 3.27 nm

Mechanism of interaction of hydrocalumites (Ca/Al-LDH) with methyl orange and acidic scarlet GR

The development of new materials for water purification is of universal importance. Among these types of materials are layered double hydroxides (LDHs). Non-ionic materials pose a significant problem as pollutants. The interaction of methyl orange (MO) and acidic scarlet GR (GR) adsorption on hydrocalumite (Ca/Al-LDH-Cl) were studied by X-ray diffraction (XRD), infrared spectroscopy (MIR), scanning electron microscope (SEM) and near-infrared spectroscopy (NIR). The XRD results revealed that the basal spacing of Ca/Al-LDH-MO was expanded to 2.45 nm, and the MO molecules were intercalated with a inter-penetrating bilayer model in the gallery of LDH, with 49o tilting angle. Yet Ca/Al-LDH-GR was kept the same d-value as Ca/Al-LDH-Cl. The NIR spectrum for Ca/Al-LDH-MO showed a prominent band around 5994 cm-1, assigned to the combination result of the N-H stretching vibrations, which was considered as a mark to assess MO- ion intercalation into Ca/Al-LDH-Cl interlayers. From SEM images, the particle morphology of Ca/Al-LDH-MO mainly changed to irregular platelets, with a “honey-comb” like structure. Yet the Ca/Al-LDH-GR maintained regular hexagons platelets, which was similar to that of Ca/Al-LDH-Cl. All results indicated that MO- ion was intercalated into Ca/Al-LDH-Cl interlayers, and acidic scarlet GR was only adsorped upon Ca/Al-LDH-Cl surfaces

Abatement of aqueous anionic contaminants by thermo-responsive nanocomposites: (Poly(N-isopropylacrylamide))-co-silylanized Magnesium/Aluminun layered double hydroxides

A series of novel thermo-responsive composite sorbents, were prepared by free-radical co-polymerization of N-isopropylacrylamide (NIPAm) and the silylanized Mg/Al layered double hydroxides (SiLDHs), named as PNIPAm-co-SiLDHs. For keeping the high affinity of Mg/Al layered double hydroxides towards anions, the layered structure of LDHs was assumed to be reserved in PNIPAm-co-SiLDHs by the silanization of the wet LDH plates as evidenced by the X-ray powder diffraction. The sorption capacity of PNIPAm-co-SiLDH (13.5 mg/g) for Orange-II from water was found to be seven times higher than that of PNIPAm (2.0 mg/g), and the sorption capacities of arsenate onto PNIPAm-co-SiLDH are also greater than that onto PNIPAm, for both As(III) and As(V). These sorption results suggest that reserved LDH structure played a significant role in enhancing the sorption capacities. NO3− intercalated LDHs composite showed the stronger sorption capacity for Orange-II than that of CO32−. After sorption, the PNIPAm-co-SiLDH may be removed from water because of its gel-like nature, and may be easily regenerated contributing to the accelerated desorption of anionic contaminants from PNIPAm-co-SiLDHs by the unique phase-transfer feature through slightly heating (to 40 °C). These recyclable and regeneratable properties of thermo-responsive nanocomposites facilitate its potential application in the in-situ remediation of organic and inorganic anions from contaminated water