Thermal decomposition of hydronium jarosite (H3O)Fe3(SO4)2(OH)6

Thermogravimetry combined with mass spectrometry has been used to study the thermal decomposition of a synthetic hydronium jarosite. Five mass loss steps are observed at 262, 294, 385, 557 and 619°C. The mass loss step at 557°C is sharp and marks a sharp loss of sulphate as SO₃ from the hydronium jarosite. Mass spectrometry through evolved gases confirms the first three mass loss steps to dehydroxylation, the fourth to a mass loss of the hydrated proton and a sulphate and the final step to the loss of the remaining sulphate. Changes in the molecular structure of the hydronium jarosite were followed by infrared emission spectroscopy. This technique allows the infrared spectrum at the elevated temperatures to be obtained. Infrared emission spectroscopy confirms the dehydroxylation has taken place by 400 and the sulphate loss by 650°C. Jarosites are a group of minerals formed in evaporite deposits and form a component of the efflorescence. The minerals can function as cation and heavy metal collectors. Hydronium jarosite has the potential to act as a cation collector by the replacement of the proton with a heavy metal cation.     

Thermal decomposition of the synthetic hydrotalcite iowaite

The thermal stability and thermal decomposition pathways for synthetic iowaite have been determined using thermogravimetry in conjunction with evolved gas mass spectrometry. Chemical analysis showed the formula of the synthesised iowaite to be Mg_6.27Fe_1.73(Cl)_1.07(OH)₁₆(CO₃)_0.336.1H₂O and X-ray diffraction confirms the layered structure. Dehydration of the iowaite occurred at 35 and 79°C. Dehydroxylation occurred at 254 and 291°C. Both steps were associated with the loss of CO₂. Hydrogen chloride gas was evolved in two steps at 368 and 434°C. The products of the thermal decomposition were MgO and a spinel MgFe₂O₄. Experimentally it was found to be difficult to eliminate CO₂ from inclusion in the interlayer during the synthesis of the iowaite compound and in this way the synthesised iowaite resembled the natural mineral.     

Thermal decomposition of ammonium jarosite (NH4)Fe3(SO4)2(OH)6

Thermogravimetry combined with mass spectrometry has been used to study the thermal decomposition of a synthetic ammonium jarosite. Five mass loss steps are observed at 120, 260, 389, 510 and 541°C. Mass spectrometry through evolved gases confirms these steps as loss of water, dehydroxylation, loss of ammonia and loss of sulphate in two steps. Changes in the molecular structure of the ammonium jarosite were followed by infrared emission spectroscopy (IES). This technique allows the infrared spectrum at the elevated temperatures to be obtained. IES confirms the dehydroxylation to have taken place by 300°C and the ammonia loss by 450°C. Loss of the sulphate is observed by changes in band position and intensity after 500°C.     

Thermal decomposition of synthetic hydrotalcites reevesite and pyroaurite

A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of synthetic hydrotalcites reevesite (Ni₆Fe₂(CO₃)(OH)₁₆·4H₂O) and pyroaurite (Mg₆Fe₂(SO₄,CO₃)(OH)₁₆·4H₂O) and the cationic mixtures of the two minerals. XRD patterns show the hydrotalcites are layered structures with interspacing distances of around 8.0. Å. A linear relationship is observed for the d(001) spacing as Ni is replaced by Mg in the progression from reevesite to pyroaurite. The significance of this result means the interlayer spacing in these hydrotalcites is cation dependent. High resolution thermal analysis shows the decomposition takes place in 3 steps. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and carbon dioxide.     

Synthesis of the mixed oxide catalysts based upon the nickel-copper hydrotalcites of the type Ni<Subscript>x</Subscript>Cu<Subscript>6-x</Subscript>Cr<Subscript>2</Subscript>(OH)<Subscript>16</Subscript>(CO<Subscript>3</Subscript>)×4H<Subscript>2</Subscript>O

Summary High resolution TG coupled to a gas evolution mass spectrometer has been used to study the thermal properties of a chromium based series of Ni/Cu hydrotalcites of formulae Ni_xCu_6-xCr₂(OH)₁₆(CO₃)×4H₂O where x varied from 6 to 0. The effect of increased Cu composition results in the increase of the endotherms and mass loss steps to higher temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps and that the interlayer carbonate anion is lost simultaneously with hydroxyl units. Differential scanning calorimetry was used to determine the heat flow steps for the thermal decomposition of the synthetic hydrotalcites. Hydrotalcites in which M²⁺ consist of Cu, Ni or Co form important precursors for mixed metal-oxide catalysts. The application of these mixed metal oxides is in the wet catalytic oxidation of low concentrations of retractable organics in water. Therefore, the thermal behaviour of synthetic hydrotalcites, Ni_xCu_6-xCr₂(OH)₁₆CO₃×nH₂O was studied by thermal analysis techniques in order to determine the correct temperatures for the synthesis of the mixed metal oxides.     

Thermal stability of flexible polyurethane foams containing modified layered double hydroxides and zinc borate

Abstract

Flexible polyurethane foams (FPUFs) have been modified to contain layered double hydroxides (LDHs) by dihydrogen phosphate (H₂PO₄ ^?). The thermal stability of the prepared foams has been characterized using thermogravimetric analysis (TGA) at 5, 10, 20, 30, and 40?°C/min heating rates. The experimental data indicate that the temperature range for the two pyrolysis stages of FPUF is about 212–350?°C and 350–565?°C, respectively. Integral programmed decomposition temperature (IPDT) has been calculated according to the measured data, which was found that the IPDT of the modified FPUF was increased to 526?°C. Additionally, the thermal stability of FPUF composite has been also evaluated by the activation energy (E) on the basis of the pyrolysis kinetics of FPUF composites during thermal decomposition using Coats–Redfern integral method. These results manifest that the presence of intercalated LDHs enhances the thermal stability of FPUF.     

CuO/Cu2(OH)2CO3梭型中空颗粒的制备及其气敏性能

以Cu₂(OH)₃NO₃为前驱体,采用无模板溶剂热法成功合成了大小为1~2 μm的CuO/Cu₂(OH)₂CO₃中空梭型微粒.高倍电镜显示其外壳层由高度弥散的CuO和Cu₂(OH)₂CO₃纳米颗粒组成.通过控制反应时间证明了该中空梭型粒子的形成过程是由自组装和奥斯特瓦尔德熟化过程控制.该纳米材料的特殊结构使其对乙醇、丙酮等有机气体有良好的气敏性能.     

CuO/Cu2(OH)2CO3梭型中空颗粒的制备及其气敏性能

以Cu₂(OH)₃NO₃为前驱体,采用无模板溶剂热法成功合成了大小为1~2μm的CuO/Cu₂(OH)₂CO₃中空梭型微粒。高倍电镜显示其外壳层由高度弥散的CuO和Cu₂(OH)₂CO₃纳米颗粒组成。通过控制反应时间证明了该中空梭型粒子的形成过程是由自组装和奥斯特瓦尔德熟化过程控制。该纳米材料的特殊结构使其对乙醇、丙酮等有机气体有良好的气敏性能。     

Thermal analysis of β-Co2(OH)3Cl and Zn5(OH)5Cl2 · H2O

Samples of β-Co₂(OH)₃Cl and Zn₅(OH)₈Cl₂ · H₂O have been prepared and their thermal decomposition studied in air and N₂ by DTA and TG up to 1000°C. X-Ray diffraction analysis of the thermal treatment products in air at various temperatures from 100 to 100°C was also carried out. The results obtained made it possible to establish the steps through which the pyrolysis of both compounds proceeds.     

Thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O: II. Identification of the gaseous products

The main goal of the presented work was to verify the previously assumed decomposition stages of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O (HACOT) [Thermochim. Acta 354 (2000) 45] under different atmospheres (inert, oxidising and reducing). The gaseous products of the decomposition were qualitatively and quantitatively analysed by mass spectrometry (MS) and Fourier-transformed infrared spectroscopy (FT-IR). It was confirmed that the gaseous products of HACOT decomposition under studied atmospheres there were H₂O (stage I) and NH₃, CO₂ (stage II). The main gaseous products in the third stage in argon and hydrogen (20 vol.% H₂/Ar) were CO and CO₂, whereas in air (20 vol.% O₂/Ar) only CO₂ was identified. Under the oxidising as well as reducing atmospheres the influence of secondary reactions on the composition of both, solid and gaseous products was found particularly strong during the third stage of the process. The studies of the multistage decomposition of HACOT, additionally complicated by many secondary reactions, required application of the hyphenated TA-MS or TA-FT-IR techniques combined with the pulse thermal analysis PTA^® allowing quantification of the spectroscopic signals and investigation of gas-solid and gas-gas reactions in situ.     

配合物[Mn(bipy)3](ClO4)2的晶体结构和热分析研究

The complex [Mn(bipy)₃]·(ClO₄)₂ was synthesied and characterized by X-ray diffraction. X-ray diffraction result for the single crystal showed that the crystal belongs to triclinic, space group P1, a=0.8123(2),b=1.1024(2), c=1.8646(4)nm,α=102.30(3)°,β=91.00(3)°,γ=99.69(3)°,V=1.6056(6)nm³,Z=2,D_c=1.494g·cm^-3. The thermal decomposition of [Mn(bipy)₃](ClO₄)₂ occurred in a three steps pattern. The reaction mechanism of the first step decomposition was deduced as n(1-α)[-ln(1-α)](n-1)/n with the activation energy of 130kJ·mol^-1.     

Luminescence properties of CdTe QDs embedded in Zn5(CO3)2(OH)6 matrix

CdTe@Zn₅(CO₃)₂(OH)₆ composites were synthesized by a hydrothermal method. CdTe@Zn₅(CO₃)₂(OH)₆ composite nanospheres were characterized via X-ray diffraction, scanning electron microscopy, energydispersive X-ray spectroscopy, and photoluminescence (PL). The hydrothermal reaction time and the mole ratios of Zn/Te played important roles in the growth and fluorescence intensity of CdTe@Zn₅(CO₃)₂(OH)₆ composites. The composite powders showed peak PL at 578 nm at 1.6 times the intensity of powdered CdTe QDs. CdTe@Zn₅(CO₃)₂(OH)₆ exhibited a strong yellow fluorescence emission, and its preparation method was easy and economical. Therefore, CdTe@Zn₅(CO₃)₂(OH)₆ offers potential applications in biological markers and light-emitting diodes.     

The photo-decomposition and self-restructuring dynamic equilibrium mechanism of Cu2(OH)2CO3 for stable photocatalytic CO2 reduction

Developing suitable photocatalysts and understanding their intrinsic catalytic mechanism remain key challenges in the pursuit of highly active, good selective, and long-term stable photocatalytic CO₂ reduction(PCO₂R) systems. Herein, monoclinic Cu₂(OH)₂CO₃ is firstly proven to be a new class of photocatalyst,which has excellent catalytic stability and selectivity for PCO₂R in the absence of any sacrificial agent and cocatalysts. B...     

Crystal structure of Mg2(OH)2CO3, deduced from the topotactic thermal decomposition of artinite

By means of single-crystal X-ray diffraction of nondecomposed, partly, and fully decomposed artinite (Mg₂(OH)₂CO₃·3H₂O), it has been shown that the intermediate product of decomposition, Mg₂(OH)₂CO₃, is not amorphous. Its unit cell has been determined and a model of its structure has been deduced, which can account for both the lattice parameters and the relative orientations of the unit cells of artinite, intermediate product, and magnesium oxide found experimentally. The decomposition reaction can be described as a topotactic process with conservation of chains in both and additional conservation of layers in the second step.     

CdCu3(OH)6Cl2: A new layered hydroxide chloride

A new transition metal hydroxide chloride containing kagomé layers of magnetic ions, CdCu₃(OH)₆Cl₂, has been synthesized and structurally characterized. The actual low symmetry P2₁/n structure can be derived from the ideal trigonal one with a change in cation distribution and coherent distortions of the anion framework. The result is a fundamentally different Cu²⁺ kagomé framework than found in the related Herbertsmithite and Kapellasite minerals. Magnetization measurements show no transition to long range magnetic order above T=2 K, despite strong antiferromagnetic interactions with a Weiss temperature of θ_w=−150 K. Furthermore, we show that the structure of CdCu₃(OH)₆Cl₂ and related hydroxide chlorides can be rationalized on the basis of [(OH)₃Cl]⁴⁻ pseudopolyatomic anions that pack and rotate, in much the same way as do traditional polyatomic anions. This opens the door to rational design of new and useful hydroxide chloride materials.     

由M0.02Cu0.4Mg5.6Al1.98(OH)16CO3 (M=Ru,Re)水滑石为前驱体制备的双金属固体碱催化甘油氢解

采用共沉淀法合成了M_0.02Cu_0.4Mg_5.6Al_1.98(OH)₁₆CO₃ (M = Ru,Re)水滑石前驱体,然后经焙烧和还原制备了铜分散度较高的双功能M-Cu/固体碱催化剂.这些双功能催化剂在粗甘油氢解制备丙二醇反应中表现出了很好的催化活性.表征结果证明,M的加入增强了催化剂表面氢的吸附和活化,进而促进了甘油的转化.     

Cu[C5H3N(CCH3=N-C6H5)2]2(PF6)2配合物的合成、晶体结构和热分解反应动力学

The title complex Cu[C₅H₃N(CCH₃=N-C₆H₅)₂]₂(PF₆)₂ has been synthesized by reaction of Schiff base C₅H₃N(CCH₃=N-C₆H₅)₂ and cupric sulfate in toluene solution. The crystal structure was determined by X-ray diffraction method and the chemical formula weight of the complex is 1041.85. The crystal structure belongs to triclinic system with space group P1 and cell parameters: a=12.6470(10)?, b=14.123(2)?, c=15.613(2)?;α=66.150(10)°,β=79.470(10)°,γ=78.290(10)°, V=2481.6(5)?³, Z=2, D_c=1.394Mg·m^-3 and F(000)=1064. The final R[I >2σ(I)]:R₁=0.0668, wR₂=0.1927; R(all data): R₁=0.1133, wR₂=0.2357. The Cu(Ⅱ) was coordinated by six nitrogen, at the same time the Cu(Ⅱ) formed a distorted octahedron, besides the angles and planes of this compound were discussed . The result of kinetics of the thermal decomposition indicated that the first step of it is 2 series chemical reactions, the function of machanism is f(a)=(1-a)², and the activation energy is 144.64E/kJ. CCDC: 180872.     

The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

The steps associated with the thermal decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O and ZnOHNO₃·H₂O are re-examined. Previous reports have suggested that Zn₅(OH)₈(NO₃)₂·2H₂O decomposes to ZnO via two intermediates, Zn₅(OH)₈(NO₃)₂ and Zn₃(OH)₄(NO₃)₂ whereas ZnOHNO₃·H₂O has been reported to decompose to ZnO via a Zn₃(OH)₄(NO₃)₂ intermediate. In this study, we demonstrate using TG, mass spectral analysis of evolved gases and in situ variable temperature powder X-ray diffraction analysis that, in fact, in the decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O an anhydrous zinc nitrate intermediate is also involved. We, additionally, show that the decomposition of ZnOHNO₃·H₂O to ZnO also involves the formation of an anhydrous zinc nitrate intermediate. The anhydrous zinc nitrate formed in both cases is poorly crystallised and this observation may explain why this phase could not be observed by PXRD analysis in the previous studies.     

La(OH)3和 La2O2CO3纳 米 棒 的 合 成 及 其 催 化 Claisen-Schmidt缩合反应性能简

通过调节溶液的pH值,在水热条件下合成出长径比为2-45的La（OH）₃纳米棒. 对水热合成过程中间体的结构演变分析,发现高碱度有利于小尺寸晶核的形成,La（OH）₃晶体结构的各向异性导致这些晶种沿着C轴方向生长,进而形成纳米棒结构. 将La（OH）₃纳米棒前驱体于773 K焙烧可以得到长径比为2-20的La₂O₂CO₃纳米棒. 随着长径比的增加,La₂O₂CO₃纳米棒暴露的（110）晶面逐渐增加,La³⁺-O^2-碱性位的数目也从0.08增加到0.24 mmol/g. 因此,在Claisen-Schmidt缩合反应中,La₂O₂CO₃纳米棒催化剂上的反应速率随着长径比的增加而逐渐增大.     

Mg-Al-CO3与Zn-Al-CO3水滑石热稳定性差异的研究

层状双金属氢氧化物（Ｌayered double hydroxides,简称ＬＤＨs）是一种类近年来发展迅速的阴离了型粘土,又称水滑石,其组成通式为[M（II）1－xM(III)x(OH)2]x(OH)2]^x＋Ax/n^n-mH2O,其中M（II）是二介金属离子,M（III）是三价金属离子,A^n-是阴离子,这种材料是由相互平行的层板组成,层板带有永在电荷,层间具有可交换的阴离子以维持电荷平衡,通过离子交换可在层间嵌入不同的基团,制备许多功能材料,被广泛作催化剂、吸附剂及油田化学品等,已引起人们的关注^[1-4]。有关Mg-Al-CO3与Zn-Al-CO3水滑石的合成及性能研究国内外已有大量报道^[1,2],本文对两者热稳定性存在的差异进行了研究,这对深化此类材料的认识具有参考作用。