Thermal decomposition of SO4 2?-intercalated Mg–Al layered double hydroxide

The thermal properties of SO₄ ^2?-intercalated Mg?CAl layered double hydroxide (SO₄·Mg?CAl LDH) were investigated using simultaneous thermogravimetry?Cmass spectrometry (TG?CMS), and the elimination behavior of sulfur oxides from this double hydroxide was examined. The TG?CMS results showed that SO₄·Mg?CAl LDH decomposed in five stages. The first stage involved evaporation of surface-adsorbed water and interlayer water in SO₄·Mg?CAl LDH. In the second, third, and fourth stages, dehydroxylation of the brucite-like octahedral layers in SO₄·Mg?CAl LDH occurred. The fifth stage corresponded to the elimination of SO₄ ^2? intercalated in the interlayer of Mg?CAl LDH, producing SO₂ and SO₃. The thermal decomposition of SO₄·Mg?CAl LDH resulted in the formation of SO₂ and SO₃ at 900?C1000?°C, which then reacted with H₂O to form H₂SO₃ and H₂SO₄. The elimination of sulfur oxides increased with the decomposition time and temperature. Almost all of the intercalated SO₄ ^2? was desulfurized from SO₄·Mg?CAl LDH at 1000?°C; however, Mg?CAl oxide was not formed due to the production of MgO and MgAl₂O₄.     

Removal of sulfate from wastewater via synthetic Mg–Al layered double hydroxide: An adsorption,kinetics, and thermodynamic study

Sulfate-contaminated water is a major environmental problem that alters the taste of water, disturbs the digestive systems of animals and humans, and erodes both soil and metals. In this study, the layered double hydroxide LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ were prepared using a co-precipitation technique, and applied in the adsorption of SO₄^2- from an aqueous solution. The reaction is well described by the Langmuir adsorption model. LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ afforded maximum SO₄^2- adsorption values of 135.14 and 92.59 ​mg/g, respectively. The reaction is best explained by a pseudo-second-order mechanism, which suggests that chemisorption is the rate-determining step. The activation energies of LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ indicate that the adsorption of SO₄^2- on synthetic LDHs predominantly follows an anion-exchange mechanism, wherein SO₄^2- ions in the aqueous medium replaces intercalated NO₃^- ions in the synthetic LDHs. The thermodynamic parameters (ΔH̊, ΔS̊, and ΔG̊) were also calculated. The reaction was endothermic, and the synthetic LDHs afforded feasible and spontaneous adsorption of SO₄^2-.     

Confined rapid thermolysis/FTIR/ToF studies of imidazolium-based ionic liquids

Rapid scan FTIR spectroscopy and time-of-flight (ToF) mass spectrometry were utilized to study thermal decomposition of three imidazolium-based ionic liquids, with 1-ethyl-3-methyl-imidazolium (emim) as the cation, and NO₃⁻, Cl⁻, and Br⁻ as the anions. The thermal decomposition involved heating rates of 2000 K/s and temperatures to 435 °C in an ambient inert gas at 1 atm. Using sub-milligram quantities of each compound, examinations of the evolution of gas-phase species revealed that the most probable sites for proton transfer and subsequent secondary reactions were primarily the methyl group and secondarily the ethyl group. The ring appeared to remain intact, as there was no evidence of the formation of HCN, imines or related products. The most reactive compound is [emim]NO₃, since the nitrate group served as a strong oxidizer and reacted strongly with the methyl/ethyl groups at the elevated temperatures to produce common final products from combustion.     

A field-desorption study of thermal stability in potassium pentacyanocobaltates(III)

Field desorption has been applied to research the thermal stability of the compounds K_n[Co(CN)₅X], where X=SO₃ ^2–, CN^–, NO₂ ^–, NO^–, Cl^–, Br^–, I^–, and H₂O. A likely mechanism is proposed for the thermal decomposition. There is a correlation between the tetragonal-distortion parameters and the temperature of onset of destruction for the [Co(CN)₅X]^n– anion.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 111–115, January–February, 1985.     

Development of New Two‐Dimensional Small Molecules Based on Benzodifuran for Efficient Organic Solar Cells

A new organic small molecule, DCA3TBDF, with a 2D benzo[1,2‐b:4,5‐b′]difuran (BDF) moiety as the central core and octyl cyanoacetate units as the end‐capped blocks, was designed and synthesized for solution‐processed bulk heterojunction solar cells. DCA3TBDF possesses good solubility in common organic solvents such as toluene, CH₂Cl₂, chlorobenzene, and CHCl₃ and good thermal stability with an onset decomposition temperature with 5 % weight‐loss occurring at 361 °C. The DCA3TBDF thin film showed a broad absorption at λ=320–700 nm and high crystallinity. Small‐molecule organic solar cells based on DCA3TBDF and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester demonstrated promising power conversion efficiency with a high fill factor under the illumination of AM 1.5G (100 mW cm^?2).     

Reaction of the PtIII complex, [Pt2(μ-NHCOMe)4Cl2], with 1,10-phenanthroline and solid-state thermolysis of 1,10-phenanthroline-containing platinum blues

Platinum blues with the composition Pt(phen)(NHCOMe)₂X (phen is 1,10-phenanthroline, X = NO₃ ^?, CF₃SO₃ ^?, or Cl^?), were synthesized starting from the complex [Pt₂(NHCOMe)₄Cl₂]. The resulting compounds apparently have a polymeric structure with metal centers in different valence states. The reaction of the complex Pt(phen)(NHCOMe)₂NO₃ with H₂O affords crystalline binuclear acetamidate [Pt^III ₂(phen)₂(??-NHCOMe)₂(NHCOMe)₂](NO₃)₂, whose structure was determined by X-ray diffraction. The reaction of the complex Pt(phen)(NHCOMe)₂NO₃ with HCF₃SO₃ leads to the decomposition of the starting compound, the reduction of the Pt atoms, and the formation of the complex [Pt^II ₂(phen)₄](CF₃SO₃)₄. The thermal decomposition of the resulting complexes, as well as the complexes [(phen)Pt-(??-NHCOMe)₂Pt(phen)]₂(NO₃)₄ and [Pt(phen)Cl₂], under an inert atmosphere was studied by DSC and TGA. Metallic platinum nanopowders are thermal decomposition products of the complexes under study.     

Synthesis and UV absorption properties of 5, 5′-thiodisalicylic acid intercalated Zn−Al layered double hydroxides

5, 5′-Thiodisalicylic acid (TDSA) has been intercalated into a ZnAl-NO₃ layered double hydroxide (LDH) by an ion-exchange reaction. After intercalation of TDSA, the basal spacing in the LDH increased from 0.89 to 1.53 nm, suggesting that the TDSA anions were arranged in the interlayer galleries of ZnAl-TDSA-LDH as a tilted monolayer arrangement of dianions. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TGA-DTA), and UV-Visible spectroscopy (UV-Vis). The results show that the NO₃⁻ anions in the precursor have been completely replaced by TDSA anions to give ZnAl-TDSA-LDH having crystalline-layered structure. Detailed studies reveal the presence of a complex system of supramolecular interactions between LDH layers and TDSA anions. TGA-DTA curves suggest that the thermostability of TDSA was markedly enhanced by intercalation in the LDH host. Photostability tests show that the film of ZnAl-TDSA-LDH/PP possessed higher stability to UV radiation than either the film of TDSA/PP or pristine PP.     

Thermal energy rate constants for the reactions NO2 + Cl2 → Cl2 + NO2, Cl2 + NO2 → Cl + NO2Cl,SH + NO2 → NO2 + SH,SH + Cl2 → Cl2 + SH,and S + NO2 → NO2 + S

It is found that charge-transfer on NO⁻₂ with Cl₂ is fast at thermal energy. The Cl⁻₂ ion reacts with NO₂ to produce Cl⁻ and NO₂Cl, and SH⁻ charge-transfers rapidly with both Cl₂ and NO₂. From the exothermicities implied it is deduced that EA (SH)<EA (NO₂)< EA (Cl₂) or EA (NO₂) = 2.38 ± 0.06 eV and EA (Cl₂ = 2.46 ± 0.14 eV.     

Temporal characterisation of river waters in urban and semi-urban areas using physico-chemical parameters and chemometric methods

Three sampling campaigns were carried out in rivers located at two hydrographic basins affected by urban and semi-urban areas around the Metropolitan area of A Coruña (ca. 500,000 inhabitants, NW-Spain) to study local and temporal variations of 21 physicochemical parameters (pH, conductivity, Cl⁻, SO₄²⁻, SiO₂, Ca²⁺, Mg²⁺, Na⁺, K⁺, hardness, NO₃⁻, NO₂⁻, NH₄⁺, COD, PO₄³⁻, Zn²⁺, Cu²⁺, Mn²⁺, Pb²⁺, alkalinity and acidity) in 23 sampling points. The temporal evolution of the water quality was assessed by matrix augmentation principal components analysis (MA-PCA) and parallel factor analysis (PARAFAC). Moreover, classical principal components analysis (PCA) (one per sampling campaign) was applied with exploratory and comparison purposes. The first factor of the different studies comprised variables associated to the mineral content and it differentiated the samples according to their hydrographic basins. The second factor was mainly associated to organic matter, from domestic wastes and decomposition of natural debris. The temporal evolution of the water quality was mostly related to seasonal increments of the physicochemical parameters defining the decomposition of the organic matter.The three models applied (PCA, MA-PCA and PARAFAC) led to similar conclusions, nonetheless, MA-PCA excelled, since the refolding of scores provided more straightforward and convenient overview of sample time and geographical variations than individual PCA and it is more flexible and adaptable to environmental studies than PARAFAC.     

Thermal analysis of corrosion products formed on carbon steel in ammonium chloride solution

The influence of different ions NO₃ ^? and SO₄ ^2? on the carbon steel corrosion in ammonium chloride was investigated using mass loss measurements and potentiodynamic polarization. Corrosion products were analyzed using X-ray photoelectron spectroscopy (XPS) and simultaneous thermal and differential scanning calorimetry (TG/DSC). XPS analysis shows that the main product of corrosion is a non-stoichiometric Fe³⁺ oxyhydroxide, consisting of a mixture of FeO(OH) and FeO(OH) containing inclusions of these anions, species such as Fe³⁺O(OH,Cl^?); Fe³⁺O(OH,SO₄ ^2?); and Fe³⁺O(OH,NO₃ ^?). TG/DSC confirms the decomposition of the rusty products formed by chemical corrosion, compounds like Fe³⁺ oxyhydroxides, with β-FeOOH as the major phase, crystal structure of which may contain Cl^?, NO₃ ^?, and SO₄ ^2?—e.g., akaganeite [Fe³⁺O(OH,A)].     

2, 2′-Dihydroxyazobenzene-based fluorescent system for the colorimetric ‘turn-on’ sensing of cyanide

2, 2′-Dihydroxyazobenzene (DHAB) demonstrated high sensitivity and low selectivity toward three anions: CN⁻, CO₃²⁻, and HCO₃⁻. In the presence of Cu(II), complex DHAB-Cu(II) could give rise to enhanced fluorescence intensity by about 45-fold at 590 nm and visible red-to-reddish orange color change upon the addition of cyanide by utilizing an indirect method, while no changes were observed in the presence of other anions, including F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, CH₃COO⁻, NO₃⁻, CO₃²⁻ and HCO₃⁻, and SO₄²⁻, making the DHAB-Cu(II) complex a selective and sensitive cyanide chemosensor.     

Zirconium(IV)-porphyrins as novel ionophores for fluoride-selective polymeric membrane electrodes

The feasibility of using Zr(IV)-porphyrins as novel ionophores for preparing anion-selective polymeric membrane electrodes is examined. Electrodes constructed using o-nitrophenyl octyl ether plasticized poly(vinyl chloride) membranes containing Zr(IV)-octaethylporphyrin (OEP) dichloride (Zr(IV)[OEP]Cl₂) or Zr(IV)-tetraphenylporphyrin (TPP) dichloride (Zr(IV)[TPP]Cl₂) were found to exhibit enhanced potentiometric selectivity toward fluoride compared to electrodes based on a typical anion-exchanger (e.g. tridodecylmethylammonium chloride). At pH 5.5, the electrodes displayed the following selectivity sequences: ClO₄⁻ > SCN⁻ > I⁻ > F⁻ > NO₃⁻ > Br⁻ > NO₂⁻ > Cl⁻ and F⁻ > ClO₄⁻ > SCN⁻ > I⁻ > NO₂⁻ > NO₃⁻ > Br⁻ > Cl⁻ for membranes doped with Zr(IV)[OEP]Cl₂) and Zr(IV)[TPP]Cl₂, respectively. Both ionophores are shown to operate via a charged carrier mechanism, with 10 mol% of lipophilic tetraphenylborate derivative in the membrane phase required to achieve optimal selectivity. Electrodes prepared with both metalloporphyrin species display super-Nernstian response toward fluoride with slopes typically greater than −100 mV per decade. It is shown, via UV-VIS spectroscopy of the membrane phase, that this behavior occurs due to spontaneous formation of hydroxide ion bridged porphyrin dimers in the membrane in the presence of the lipophilic anionic additive. The dimers are easily converted to monomeric species upon increasing the concentration of fluoride in the sample solution. Decreasing the pH of sample buffer background solution (from pH 5.5 to pH 3) decreases the lower detection limit (DL) of the electrode response toward fluoride (by two-order of magnitude) and improves the electrodes’ selectivity.     

Single-run ion chromatographic separation of inorganic and low-molecular-mass organic anions under isocratic elution: Application to environmental samples

For the isocratic ion chromatography (IC) separation of low-molecular-mass organic acids and inorganic anions three different anion-exchange columns were studied: IonPac AS14 (9 μm particle size), Allsep A-2 (7 μm particle size), and IC SI-50 4E (5 μm particle size). A complete baseline separation for all analyzed anions (i.e., F⁻, acetate, formate, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, HPO₄²⁻ and SO₄²⁻) in one analytical cycle of shorter than 17 min was achieved on the IC SI-50 4E column, using an eluent mixture of 3.2 mM Na₂CO₃ and 1.0 mM NaHCO₃ with a flow rate of 1.0 mL min⁻¹. On the IonPac AS14 column, it was possible to separate acetate from inorganic anions in one run (i.e., less than 9 min), but not formate, under the following conditions: 3.5 mM Na₂CO₃ plus 1.0 mM NaHCO₃ with a flow rate of 1.2 mL min⁻¹. Therefore, it was necessary to adapt a second run with a 2.0 mM Na₂B₄O₇ solution as an eluent under a flow rate of 0.8 mL min⁻¹ for the separation of organic ions, which considerably enlarged the analysis time. For the Allsep A-2 column, using an eluent mixture of 1.2 mM Na₂CO₃ plus 1.5 mM NaHCO₃ with a flow rate of 1.6 mL min⁻¹, it was possible to separate almost all anions in one run within 25 min, except the fluoride-acetate critical pair. A Certified Multianion Standard Solution PRIMUS for IC was used for the validation of the analytical methods. The lowest RSDs (less than 1%) and the best LODs (0.02, 0.2, 0.16, 0.11, 0.06, 0.05, 0.04, 0.14 and 0.09 mg L⁻¹ for F⁻, Ac⁻, For⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, HPO₄²⁻ and SO₄²⁻, respectively) were achieved using the IC SI-50 4E column. This column was applied for the separation of concerned ions in environmental precipitation samples such as snow, hail and rainwater.     

Evidences for decarbonation and exfoliation of layered double hydroxide in N,N-dimethylformamide-ethanol solvent mixture

The behavior of a Hydrotalcite-like material (carbonate-containing Mg,Al-layered double hydroxide) in N,N-dimethylformamide (DMF)-ethanol mixture, at ambient temperature, has been investigated. The releasing of CO₂ and production of a formate-containing material occurred mainly for 1:1 (v/v) solvent mixture. Decarbonation of Hydrotalcite is promoted by DMF hydrolysis followed by neutralization of brucite-like layers through HCOO⁻ intercalation. Translucent colloidal dispersion of LDH nanoparticles from the formate-containing phase was characterized by transmission electron (TEM) and atomic force (AFM) microscopies. The absence of (00?) reflection at X-ray diffraction (XRD) pattern for dried colloidal dispersion indicated delamination of Hydrotalcite. The restacked sample exhibited broad reflections and typical hydroxide ordered layers non-basal (110) diffraction peaks. A LDH-HCOO⁻ material was also prepared and characterized by FTIR and FT-Raman spectroscopies. Decarbonation and exfoliation of Hydrotalcite in N,N-dimethylformamide-ethanol mixed solvent provide an interesting method for preparation of new intercalated LDH materials.     

Preparation of NdCrO3 nanoparticles and their catalytic activity in the thermal decomposition of ammonium perchlorate by DSC/TG-MS

Orthorhombic structural perovskite NdCrO₃ nanocrystals with size of 60 nm were prepared by microemulsion method, and characterized by XRD, TEM, HRTEM, SEM, EDS and BET. The catalytic effect of the NdCrO₃ for thermal decomposition of ammonium perchlorate (AP) was investigated by DSC and TG-MS. The results revealed that the NdCrO₃ nanoparticles had effective catalysis on the thermal decomposition of AP. Adding 2% of NdCrO₃ nanoparticles to AP decreased the temperature of thermal decomposition by 87° and increased the heat of decomposition from 590 to 1073 J g⁻¹. Gaseous products of thermal decomposition of AP were NH₃, H₂O, O₂, HCl, N₂O, NO, NO₂ and Cl₂. The mechanism of catalytic action was based on the presence of superoxide ion O₂ ⁻ on the surface of NdCrO₃, and the difference of thermal decomposition of AP with 2% of NdCrO₃ and pure AP was mainly caused by the different extent of oxidation of ammonium.     

Nickel-aluminum layered double hydroxide as a nanosorbent for selective solid-phase extraction and spectrofluorometric determination of salicylic acid in pharmaceutical and biological samples

The nickel-aluminum layered double hydroxide (Ni-Al LDH) was synthesized by a simple co-precipitation method and used as a solid-phase extraction (SPE) sorbent for separation and pre-concentration of trace levels of salicylic acid (SA) from aqueous solutions. Extraction of analyte is based on the adsorption of salicylate ions on the Ni-Al (NO₃⁻) LDH and/or their exchanging with LDH interlayer NO₃⁻ ions. The retained analyte on the LDH was stripped by 3 mol L⁻¹ NaOH solution and its concentration was subsequently determined spectrofluorometrically at λ_em = 400 nm with excitation at λ_ex = 270 nm. Various parameters affecting the extraction efficiency of SA on the Ni-Al (NO₃⁻) LDH, such as pH, amount of nano-sorbent, sample loading flow rate, elution conditions, sample volume and matrix effects were investigated. In the optimum experimental conditions, the limit of detection (3 s) and enrichment factor were 0.12 μg L⁻¹ and 40, respectively. The relative standard deviation (RSD) for six replicate determinations of 10 μg L⁻¹ SA was 2.3%. The calibration graph using the pre-concentration system was linear in the range of 0.3-45 μg L⁻¹ with a correlation coefficient of 0.9985. The optimized method was successfully applied to the determination of SA in blood serum, willow leaf and aspirin tablet.     

Chemical analysis of sulfur species in geothermal waters

Analytical methods have been developed to determine sulfur species concentrations in natural geothermal waters using Reagent-Free™ Ion Chromatography (RF™-IC), titrations and spectrophotometry. The sulfur species include SO₄²⁻, S₂O₃²⁻, and ∑S²⁻ with additional determination of SO₃²⁻ and S_xO₆²⁻ that remains somewhat semiquantitative. The observed workable limits of detections were ≤0.5 μM depending on sample matrix and the analytical detection limits were 0.1 μM. Due to changes in sulfur species concentrations upon storage, on-site analyses of natural water samples were preferred. Alternatively, the samples may be stabilized on resin for later elution and analysis in the laboratory. The analytical method further allowed simultaneous determination of other anions including F⁻, Cl⁻, dissolved inorganic carbon (DIC) and NO₃⁻ without sample preservation or stabilization. The power of the newly developed methods relies in routine analysis of sulfur speciation of importance in natural waters using techniques and facilities available in most laboratories doing water sample analysis. The new methods were successfully applied for the determination of sulfur species concentrations in samples of natural and synthetic waters.     

Anion recognition by 2,2′-binaphthalene derivatives bearing urea and thiourea groups at 8- and 8′-positions by UV-vis and fluorescence spectroscopies

Synthesis and anion recognition properties of 2,2′-binaphthalene derivatives bearing two thiourea (1) and urea (2) groups at 8- and 8′-positions were studied. The structure of receptor 1 was determined by X-ray crystallography. UV-vis spectra of the receptors showed characteristic changes around 300-400 nm through isosbestic points upon the addition of biologically relevant anions such as acetate, dihydrogenphosphate, and chloride in MeCN and DMSO due to restriction of the rotation around the single bond connecting two naphthyl moieties by cooperative guest binding of two recognition sites. Job’s plots showed 1:1 complexation for guest anions. The fluorescence quantum yields of free form of 1 and 2 in MeCN were determined to be 0.021 and 0.57, respectively. The fluorescence intensities of the receptors diminished upon the addition of anions in MeCN. The association constants of receptors 1 and 2 were one or two orders of magnitude greater than the corresponding monothiourea and urea receptors 3 and 4 indicating cooperative hydrogen bonding with guest anions. The selectivity trends of association of anions were F⁻>AcO⁻>H₂PO₄⁻>Cl⁻>>HSO₄⁻≈NO₃⁻≈Br⁻≈I⁻ for 1, and F⁻>AcO⁻≈Cl⁻>H₂PO₄⁻>Br⁻>HSO₄⁻>I⁻≈NO₃⁻ for 2. Receptor 2 showed remarkable Cl⁻ selectivity presumably owing to suitable orientation for effective hydrogen bond formation with Cl⁻.     

Simultaneous determination of chloride, nitrate and sulphate in vegetable samples by single-column ion chromatography

A new ion chromatography method is described for the simultaneous determination of Cl⁻, NO₃⁻ and SO₄²⁻, using a selected eluent 1.3-mM sodium gluconate/1.3-mM borax (pH 8.5). The extraction methods of Cl⁻, NO₃⁻, SO₄²⁻ in vegetables are studied. The determination limits of Cl⁻, NO₃⁻, SO₄²⁻ are 0.17 μg/ml, 0.63 μg/ml and 0.81 μg/ml. The linear ranges are 060 μg/ml, 090 μg/ml and 090 μg/ml. The relative S.D. are <2.5%. The mean recoveries of Cl⁻, NO₃⁻, SO₄²⁻ in vegetables range from 97.0 to 104%.     

Simultaneous determination of three chloroacetic acids,three herbicides,and 12 anions in water by ion chromatography

An ion chromatography method was developed for the simultaneous detection of three soluble herbicides (glyphosate, bentazone and picloram), three chlorine disinfection byproducts (monochloroacetic acid, dichloroacetic acid and trichloroacetic acid) and 12 anions in water (Cl^–, Br^–, SO₄^2–, CO₃^2–, ClO₃^–, ClO₄^–, BrO₃^–, PO₄^3–, NO₂^–, NO₃^–, CH₃COO^– and COO^–). High linearity (r² > 0.996) was observed for all target analytes for each respective concentration range. The limit of detection and limit of quantitation were between 0.21–0.85 and 0.06–25.46 μg/L, respectively. However, the interference effect of Cl^–, NO₃^–, SO₄^2– and CO₃^2– on some target analytes must be considered during the analysis. Sample pre‐treatment by a hydrogen column (H‐column) required to reduce the negative effect of CO₃^2–. Additionally, sample pre‐treatment by a sliver–hydrogen column (Ag–H‐column) is required when Cl^– > 100 mg/L and SO₄^2– < 50 mg/L, and pre‐treatment by both a barium column (Ba‐column) and an H‐column is required when Cl^– > 100 mg/L and SO₄^2– > 50 mg/L. When Cl^– > 100 mg/L, SO₄^2– > 50 mg/L and CO₃^2– > 20 mg/L, the sample pre‐treatment by either an Ag–H–Ba‐column or an Ag–H‐column and Ba‐column is required to minimize interference.