Removal of Heavy Metal Ions from Water and Wastewaters by Sulfur-Containing Precipitation Agents

Restrictive requirements for maximum concentrations of metals introduced into the environment lead to search for effective methods of their removal. Chemical precipitation using hydroxides or sulfides is one of the most commonly used methods for removing metals from water and wastewater. The process is simple and inexpensive. However, during metal hydroxide precipitation, large amounts of solids are formed. As a result, metal hydroxide is getting amphoteric and it can go back into the solution. On the other hand, use of sulfides is characterized by lower solubility compared with that of metal hydroxides, so a higher degree of metal reduction can be achieved in a shorter time. Disadvantages of that process are very low solubility of metal sulfides, highly sensitive process to the dosing of the precipitation agent, and the risks of emission of toxic hydrogen sulfide. All these restrictions forced to search for new and effective precipitants. Potassium/sodium thiocarbonate (STC) and 2,4,6-trimercaptotiazine (TMT) are widely used. Dithiocarbamate (DTC) compounds are also used, e.g., sodium dimethyldithiocarbamate (SDTC), and ligands for permanent metal binding, e.g., 1,3-benzenediamidoethanethiol (BDETH2), 2,6-pyridinediamidoethanethiol (PyDET), a pyridine-based thiol ligand (DTPY) or ligands with open chains containing many sulfur atoms, using of a tetrahedral bonding arrangement around a central metal atom. The possibility of improving the efficiency of metal precipitation is obtained by using a higher dose of precipitating agent. However, toxic byproducts are often produced. It is required that the precipitation agents not only effectively remove metal ions from the solution but also effectively bind with dyes or metal complexes.

A one-dimensional zinc(II) coordination polymer incorporating [1,1′-biphenyl]-4,4′-dicarboxylate andN,N′-bis(pyridin-3-ylmethyl)-[1,1′-biphenyl]-4,4′-dicarboxamide ligands

In the title compound,catena-poly[[[N,N′-bis(pyridin-3-ylmethyl)-[1,1′-biphenyl]-4,4′-dicarboxamide]chloridozinc(II)]-μ-[1,1′-biphenyl]-4,4′-dicarboxylato-[[N,N′-bis(pyridin-3-ylmethyl)-[1,1′-biphenyl]-4,4′-dicarboxamide]chloridozinc(II)]-μ-[N,N′-bis(pyridin-3-ylmethyl)-[1,1′-biphenyl]-4,4′-dicarboxamide]], [Zn2(C14H8O4)Cl2(C26H22N4O2)3]n, the ZnIIcentre is four-coordinate and approximately tetrahedral, bonding to one carboxylate O atom from a bidentate bridging dianionic [1,1′-biphenyl]-4,4′-dicarboxylate ligand, to two pyridine N atoms from twoN,N′-bis(pyridin-3-ylmethyl)-[1,1′-biphenyl]-4,4′-dicarboxamide ligands and to one chloride ligand. The pyridyl ligands exhibit bidentate bridging and monodentate terminal coordination modes. The bidentate bridging pyridyl ligand and the bridging [1,1′-biphenyl]-4,4′-dicarboxylate ligand both lie on special positions, with inversion centres at the mid-points of their central C—C bonds. These bridging groups link the ZnIIcentres into a one-dimensional tape structure that propagates along the crystallographicbdirection. The tapes are interlinked into a two-dimensional layer in theabplane through N—H...O hydrogen bonds between the monodentate ligands. In addition, the thermal stability and solid-state photoluminescence properties of the title compound are reported.

RAMAN SCATTERING STUDIES ON THE STRUCTURAL PROPERTIES OF PULSED LASER DEPOSITED AMORPHOUS CARBON NITRIDE THIN FILMS

Raman scattering analysis revealed that the structure of carbon films prepared by pulsed laser deposition (PLD) at room temperature is predominantly amorphous and the structure of amorphous carbon nitride ( a-CN x) thin films can be changed with varying substrate temperatures (ST) from 20°C to 500°C. The deposited a-CN x films are composed of C – N , C ≡ N and C – O bonded materials and the C – N and C ≡ N bonds are increased with ST. We have found that no other obvious peaks can be distinguished in the range 900–2300 cm-1 in which several peaks always appear in a-CN x films. The spectra were deconvoluted into Raman D and G peaks and the structural parameters are determined. The upward shifts of the Raman G peak towards 1592 cm-1 shows the evidence of a progressive formation of crystallites in a-CN x films upon increase of ST. While the upward shifts of the Raman D peak towards 1397 cm-1 have been related to the decrease of bond-angle disorder and sp3 tetrahedral bonding in its structure. Raman FWHM and I D /I G also indicate that N incorporation with increase of ST caused an increase in the number and/or size of graphitic domains in the a-CN x films.

RAMAN SCATTERING STUDIES ON THE STRUCTURAL PROPERTIES OF PULSED LASER DEPOSITED AMORPHOUS CARBON NITRIDE THIN FILMS

Raman scattering analysis revealed that the structure of carbon (C) films prepared by pulsed laser deposition at room temperature is predominantly amorphous and the structure of amorphous C nitride ( a-CN x) films can be changed with varying substrate temperatures (ST) from 20 to 500°C. The deposited a-CN x films are composed of C–N , C≡N and C–O bonded materials and the C–N and C≡N bonds are increased with ST. We have found no other obvious peaks that can be distinguished in the range of 900 to 2300 cm-1 in which several peaks always appear in a-CN x films. The spectra were deconvoluted into Raman D and G peaks and the structural parameters were determined. The upward shifts of Raman G peak towards 1592 cm-1 show evidence of a progressive formation of crystallites in a-CN x films upon increase of ST, while the upward shifts of Raman D peak towards 1397 cm-1 have been related to the decrease of bond-angle disorder and sp 3 tetrahedral bonding in its structure. Raman FWHM and I D /I G also indicate that N incorporation with increase of ST caused an increase in the number and/or size of graphitic domains in the a-CN x films.

Compositional and structural studies of amorphous GaN grown by ion-assisted deposition

Amorphous GaN films have been deposited onto various substrates by ion-assisted deposition. The films were deposited at room temperature using nitrogen ion energies in the range 40-900 eV. Rutherford backscattering spectroscopy and nuclear reaction analysis show that the Ga:N atomic ratio is approximately one for films grown with ion energy near 500 eV; these films have the highest transparency. Films grown with ion energies below 300 eV are Ga rich, and show reduced transparency across the visible. Raman spectroscopy, x-ray diffraction, and transmission electron microscopy confirm the amorphous nature of the films. Annealing studies on a-GaN establish that the films begin to crystallise at a temperature of about 700 C. To investigate the local bonding environment of the Ga or N atoms, we have measured the extended x-ray absorption fine structure (EXAFS) of the transparent GaN films. The EXAFS results indicate that the films are dominated by heteropolar tetrahedral bonding, with a low density of homopolar bonds.

Enumeration of four-connected three-dimensional nets. III. Conversion of edges of three-connected two-dimensional nets into saw chains

A three-repeat saw (s) chain has each vertical edge separated by a tooth composed of two tilted edges zig and zag. Some horizontal (h) edges from a parallel stack of three-connected two-dimensional (2D) nets can be converted into an s chain. Each resulting four-connected vertex in the three-dimensional (3D) net may be part of either one, two or three s chains. The first type of (h,s)* 3D net is related by a sigma-type mirror plane to a (h,z)* net listed in paper II [Han & Smith (1998). Acta Cryst. A55, 342–359]. The second type does not have an (h,z)* relative. Using the same three-connected 2D nets as in paper II, 174 four-connected 3D nets were selected from the first two types, including six in known structures: `nepheline hydrate' (International Zeolite Association Structure Commission code JBW), AlPO4-12-TAMU (ATT), offretite (OFF), Linde Type L (LTL), SUZ-4 (SZF) and ZSM-10 (ZST). The third type with three back-to-back s chains is represented by edingtonite (EDI), and systematic enumeration is in progress. The geometrical and topological properties of the 3D nets are given. Idealized unit-cell data and atomic coordinates for tetrahedral bonding were obtained for 40 selected 3D nets by distance-least-squares (DLS) refinement.