Intermediate Decomposition Products Research Articles

Development of the detailed mechanism of pyrolysis and combustion of triphenyl phosphate: New quantum chemistry calculations and experimental data on structure of the H2/O2/Ar flame doped with TPP

A possible method for a flammability reduction of the polymeric materials is the introduction of flame retardants into their composition. An effective search for optimal flame retardants and an understanding of their inhibition mechanisms requires the extensive information on the chemistry of their transformation in flames. A new data on chemical flame structure of a premixed H2/O2/Ar flame doped with 1000 ppm of triphenyl phosphate (TPP) at a pressure of 1 atm was obtained with a molecular-beam mass-spectrometry technique. Among intermediate products of the TPP decomposition were identified: several large phosphorus containing compounds, small phosphorus containing species (PO, PO2, HOPO, HOPO2), cyclic hydrocarbons (benzene, toluene, phenol), phenyl and phenoxy radicals. The detailed kinetic mechanism proposed earlier for the thermal degradation of TPP was updated with several new reactions including reactions with common flame radicals H/OH/CH3. Reaction rate constants were calculated using the Rice-Ramsberger-Kassel-Marcus theory and potential energy surfaces obtained by the DLPNO-CCSD(T)/cc-pVQZ//ωb97xd/6-31G(d) method. A comparison between experimental data and simulation results with the new model has shown a satisfactory qualitative and quantitative agreement, which confirmed that, the TPP decomposition occurs in flame according to the proposed scheme.

Peracetic acid pretreatment improves biogas production from anaerobic digestion of sewage sludge by promoting organic matter release, conversion and affecting microbial community

Peracetic acid (PAA) pretreatment is considered as a novel and effective chemical pretreatment method for sludge. However, there is little information available on potential mechanisms of how PAA pretreatment affects sludge anaerobic digestion (AD). To fill the knowledge gap, this study investigated the effects and potential mechanisms of PAA pretreatment on sludge AD systems from physicochemical and microbiological perspectives. Batch experiments resulted that biogas production was enhanced by PAA pretreatment and the highest cumulative biogas yield (297.94 mL/g VS (volatile solid)) was obtained with 2 mM/g VS of PAA pretreatment. Kinetic model analysis illustrated that the PAA pretreatment improved the biogas potential (Pt) of sludge AD, but prolonged the lag phase (λ) of AD. Mechanistic studies revealed that reactive oxygen species (ROS) (HO•, O2−•, 1O2 and CH3C(O)OO•) were the major intermediate products of PAA decomposition. These ROS effectively promoted the decomposition and solubilization of sludge, and provided more biodegradable organic matter for the following AD reactions. 16S rRNA amplicon sequencing showed that some functional microorganisms associated with hydrolysis, acidogenesis, acetogenesis as well as methanogenesis, such as Hydrogenispora, Romboutsia, Longivirga, Methanosarcina and Methanosaet, were significantly enriched in reactors pretreated with PAA. Redundancy analysis and variation partitioning analysis indicated that functional microorganisms were significantly correlated with intermediate metabolites (soluble carbohydrate, soluble protein, soluble chemical oxygen demand and volatile fatty acids) and cumulative biogas production. This study provides a fresh understanding of the effects and mechanisms of PAA pretreatment on sludge AD, updates the insights into the response of functional microorganisms to PAA pretreatment, and the findings obtained might provide a fundamental basis for chemical pretreatment of sludge AD using oxidants.

FT-IR Spectroscopic Study of the Radiation-Chemical Decomposition of n-Hexane on Nano-ZrO2

The radiation-chemical decomposition of n-hexane in the nano-ZrO2 +n-hexane system under the action of gamma radiation at room temperature is studied by the method of Fourier-IR spectroscopy. The molecular and dissociative form of adsorption of n-hexane in zirconium nanodioxide was revealed. The intermediate products of the radiation-heterogeneous decomposition of n-hexane were analyzed.

Fluorinating solid electrolyte interphase by regulating polymer–solvent interaction in lithium metal batteries

The cycling stability of high-energy-density lithium (Li) metal batteries is severely hindered by uneven Li deposition, which is caused by the heterogeneous transport of Li ions in solid electrolyte interphase (SEI) on the surface of Li metal anodes. LiF-rich SEI emerges as a promising solution to improve homogeneous transport of Li ions. Herein, constructing LiF-rich SEI by regulating the interaction between the polymer coating on Li metal anode and fluoroethylene carbonate (FEC) in electrolytes was demonstrated. The polymer coating with uniformly distributed polar functional groups can interact with intermediate decomposition products of FEC, promoting the formation of LiF. LiF-rich SEI ensures improved uniformity of Li deposition, which promises stable operation of Li metal batteries under practical conditions for 143 cycles in comparison with 89 cycles of control group. Moreover, a prototype pouch cell of 1.0 Ah maintains a capacity retention of 90% after 180 cycles. This work provides a fresh attempt to construct LiF-rich SEI by regulating the interaction between solvent and polymer for long-cycling Li metal batteries.

Antimicrobial properties of oxygen-active disinfectants

Oxygen-active disinfectants are widely used for the nonspecific prevention of infectious diseases: hydrogen peroxide, chlorine dioxide, potassium fluoride peroxyhydrate, perborates, persulfates, perphosphates, and percarbonates. These compounds have a broad spectrum of antimicrobial activity against bacteria (including Mycobacterium tuberculosis), viruses, fungi, and spores of bacilli.
 The primary exposure targets exposure for oxygen-containing disinfectants are proteins and lipids in the cytoplasmic membranes of bacterial cells and the spore membranes of bacterial spores. When a bacterial cell is exposed to hydrogen peroxide at the stage of contact with the cytoplasmic membrane, hydrogen peroxide decomposes into highly reactive hydroxyl radicals, which have a destructive effect on the membranes. Hydroxyl radicals are powerful oxidizing agents, have a short existence and interact with lipids, proteins, and nucleic acids. Lipid oxidation, mainly unsaturated fatty acids, leads to increased membrane permeability. During the membrane protein oxidation consisting of amino acids with disulfide bonds, the latter are converted into SH-radicals, forming cross-links at amino groups and resulting in protein-lipid complexes. The proteins are oxidized and denatured, leading to cell death. Hydroxyl radicals and other intermediate decomposition products of hydrogen peroxide, such as hydronium cation (Н3О+) and perhydroxylanion (НО2-), have damaging effects.
 This article analyzes scientific papers on the mechanism of action of oxygen-active disinfectants on vegetative cells and bacterial spores.

Water trophy assessment of the cooling system of the “Dolna Odra” power plant on the basis of algae indicator organisms

The paper presents the results of water trophy assessment from various stations of the cooling system of the “Dolna Odra” (Poland) power plant. The assessment was made based on the indicator phytoplankton species collected four times at four sites located in different parts of the hydrological system cooling the technical infrastructure of the power plant. The sites were characterised by water with a natural temperature for individual seasons, as well as by thermals changed as a result of the discharge of cooling waters. For each site, the saprobic index was calculated based on indicator species.
 The analysis showed that the changes in trophic conditions, both in waters with changed thermals and in waters not subject to the influence of after-cool waters, are not subject to significant changes. The waters of all studied sites in the analysed periods of the year should be classified according to Sladeček and Sládečková (1996) to the waters of the β–mesosaprobic zone, with a saprobic index value ranging from 1.51 to 2.50 (average S = 2.0). This zone is characterised by the course of biochemical processes under aerobic conditions, as a result of which complete oxidation of the intermediate products of decomposition of organic compounds takes place.

Pentane Depletion by a Surface DBD and Catalysis Processing

We study pentane depletion using a hybrid plasma system based on a surface dielectric barrier discharge (SDBD), with and without a catalyst, and as a function of plasma power and alkane concentration. We evaluate pentane decomposition efficiency based on plasma power and quantify the role of the catalyst in the resulting depletion of intermediate products. Analyses of the temporal evolution of pentane and the intermediate decomposition products allow us to estimate the corresponding decomposition rates according to the plasma parameters. We find that depletion efficiency increases as a function of pentane concentration. Furthermore, it is shown that the catalytic processes are responsible for a significant increase in the depletion rates of the intermediate reaction products, thus contributing to the total abatement process of pentane.

Cooperative microbial interactions mediate community biogeochemical responses to saltwater intrusion in wetland soils.

In freshwater wetlands, competitive and cooperative interactions between respiratory, fermentative and methanogenic microbes mediate the decomposition of organic matter. These interactions may be disrupted by saltwater intrusion disturbances that enhance the activity of sulfate-reducing bacteria (SRB), intensifying their competition with syntrophic bacteria and methanogens for electron donors. We simulated saltwater intrusion into wetland soil microcosms and examined biogeochemical and microbial responses, employing metabolic inhibitors to isolate the activity of various microbial functional groups. Sulfate additions increased total carbon dioxide production but decreased methane production. Butyrate degradation assays showed continued (but lower) levels of syntrophic metabolism despite strong demand by SRB for this key intermediate decomposition product and a shift in the methanogen community toward acetoclastic members. One month after removing SRB competition, total methane production recovered by only ∼50%. Similarly, butyrate assays showed an altered accumulation of products (including less methane), although overall rates of syntrophic butyrate breakdown largely recovered. These effects illustrate that changes in carbon mineralization following saltwater intrusion are driven by more than the oft-cited competition between SRB and methanogens for shared electron donors. Thus, the impacts of disturbances on wetland biogeochemistry are likely to persist until cooperative and competitive microbial metabolic interactions can recover fully.

Строение кристаллогидратов петафторидоциркониевой кислоты по данным колебательной спектроскопии

Crystalline hydrates of pentafluoridozirconic acid HZrF5∙3H2O, HZrF5∙2H2O and intermediate product of the thermal decomposition of acids ZrF4∙H2O were studied by vibrational spectroscopy and thermogravimetry. It is shown that the crystalline hydrates HZrF5∙nH2O (n=2, 3) are salts with complex H5O2+ and H7O3+ cations. Based on the results of quantum chemical calculations, the bands in the IR and Raman spectra were assigned.

Study on the inhibitory property and mechanism of inert powder on dust explosion flame of oil shale

In order to study the inhibitory property and mechanism of inert powder on dust explosion flame in oil shale, five common inert powder and two types of oil shale were selected for the explosion flame inhibition experiment by using the dust explosion flame propagation test system. First, a high-speed camera was used to record the flame image during the inhibition of oil shale dust explosion by inert powder, and the differences in explosion flame length, minimum inerting ratio and flame morphology and structure were analyzed in detail. Then, the thermal decomposition and endothermic characteristics of the inert powder were tested by Thermogravimetric-Differential Scanning Calorimetry (TG-DSC), and the TG-DTG-DSC thermal characteristic curve of the inert powder was analyzed. Combined with the analysis of the inhibition effect of the inert powder in the preheating zone and the combustion flame zone, the inhibitory property and the mechanism of the inert powder on the oil shale dust explosion flame were systematically studied. The research results show that the inhibitory performance of inert powder to the explosion flame of two kinds of oil shale dust is ranked as: ABC dry powder ＞Al(OH)3＞Mg(OH)2＞NaHCO3＞rock powder, and their explosion inhibition performance against Huadian oil shale (HDOS) is better than that of Longkou oil shale (LKOS). In this paper, the physical model of the inhibition mechanism of inert powder on the explosion flame of oil shale dust is established and the inhibition mechanism is analyzed. Through the mechanism analysis, it is shown that the high-efficiency explosive inhibition powder should have good thermal stability (decomposition temperature around 200−400 ℃), high heat absorption, and the decomposition of intermediate products can combine with the combustion reactive radical to play a chemical inhibition effect. The research results can provide theoretical basis and basis for the design of explosion inhibition of oil shale dust and the development of explosive inhibition powder.

Understanding the KOH activation mechanism of zeolitic imidazolate framework-derived porous carbon and their corresponding furfural/acetic acid adsorption separation performance

Efficient separation of furfural from an acid-containing aqueous solution is a critical step in the furfural production process. Zeolitic imidazolate framework (ZIF)-derived porous carbons with acid resistance and tunable surface chemistry/pore structure are promising adsorbents for the separation of organic compounds from acid-containing aqueous solutions. However, little attention has been given to establish the trend of distribution of micropores and mesopores in the chemical activation of ZIF-derived porous carbon, which directly affects the adsorption performance. Herein, we investigated the relationship between the distribution of micropores and mesopores and the N species content/type in the chemical activation of the N-doped ZIF-8-derived porous carbon, and the KOH activation mechanism was proposed. The intermediates K2CO3/K2O reacted with the C species of NCZIF-81000C with a low N content, the CO was formed, and the structural deformation was not substantial, which is beneficial for the construction of abundant and larger micropores (10–20 Å), and a few mesopores (20–30 Å). While the reaction of the intermediate K2CO3/K2O with the higher-reactivity C–N species (pyridine and pyrrolic) of NCZIF-8800C with a high N content resulted in the formation of the intermediate product KOCN and decomposition product CO and NO, and the structural deformation was substantial, which led to the formation of abundant and larger mesopores (30–60 Å). Furthermore, the furfural (5.0 wt.%) static adsorption on the designed NCZIF-81000C-700A with the abundant micropores is 1189.8 mg g−1, and the selectivity of furfural/acetic acid mixture (5.0/2.0 wt.%) is 91.5, which exceeds that of traditional adsorbents.

Effect of glycerol on the thermal decomposition behavior of nickel propionate-based precursor

In this work a detailed analysis of the decomposition behavior of nickel acetylacetonato-propionate with and without additive addition was investigated through thermogravimetry (TG) coupled with differential thermal analyses (DTA) and mass spectrometry (MS), while chemical characterization has been carried out with Fourier transform infrared spectrometry (FTIR), X-ray diffraction analyses (XRD). Electron Spin Resonance and UV–vis measurements were performed to confirm whether the complexation of the precursor with additive occurs. The glycerol addition has effect on decomposition behavior of the precursor powder by shifting the main decomposition temperature with more than 100 °C to lower values. Regarding the intermediate decomposition products, they are similar at lower temperatures, while at final decomposition temperatures high exchanges occurs Ni metallic it is fully oxidized in the case of thermal decomposition of the nickel acetylacetonato-propionate precursor, while in the case of the precursor with glycerol addition, metallic nickel is still observed concomitant with NiO phase. The thermal decomposition mechanism of the precursors has been proposed.

Thermal hazards of benzaldehyde oxime: Based on decomposition products and kinetics analysis by adiabatic calorimeter

As a self-reactive substance, benzaldehyde oxime (BO) is prone to a highly exothermic runaway reaction and thermal hazard analysis and the reaction kinetics calculation of BO have great significance. In this work, the decomposition products of BO in nitrogen atmosphere were identified by GC–MS and HPLC techniques. The impact of the decomposition products on the decomposition behaviors of BO were analyzed by comparison of the ARC test results of pure BO and mixture of BO and decomposition products. It was found that N-benzylidene benzylamine was the intermediate decomposition product and benzoic acid, benzamide, N-benzyl benzamide, and 2,4,5-triphenylimidazole were the final products of BO. A two-step continuous autocatalytic reaction model was established to depict the decomposition process of BO. The kinetic parameters of the model were calculated by applying the nonlinear optimization method. Finally, thermal behaviors under different process temperature were predicted based on the kinetic model, and the time to maximum rate (TMRad) was predicted as 112.04 °C under 24 h, and 122.19 °C of 8 h, which offer crucial safety information to optimize the safety conditions of BO during usage, storage and transportation, which minimizes the industrial disasters.

Thermal decomposition of tris(O-ethyldithiocarbonato)-antimony(III)\u2014a single-source precursor for antimony sulfide thin films

Thermal decomposition of tris(O-ethyldithiocarbonato)-antimony(III) (1), a precursor for Sb2S3 thin films synthesized from an acidified aqueous solution of SbCl3 and KS2COCH2CH3, was monitored by simultaneous thermogravimetry, differential thermal analysis and evolved gas analysis via mass spectroscopy (TG/DTA-EGA-MS) measurements in dynamic Ar, and synthetic air atmospheres. 1 was identified by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) measurements, and quantified by NMR and elemental analysis. Solid intermediates and final decomposition products of 1 prepared in both atmospheres were determined by X-ray diffraction (XRD), Raman spectroscopy, and FTIR. 1 is a complex compound, where Sb is coordinated by three ethyldithiocarbonate ligands via the S atoms. The thermal degradation of 1 in Ar consists of three mass loss steps, and four mass loss steps in synthetic air. The total mass losses are 100% at 800 °C in Ar, and 66.8% at 600 °C in synthetic air, where the final product is Sb2O4. 1 melts at 85 °C, and decomposes at 90–170 °C into mainly Sb2S3, as confirmed by Raman, and an impurity phase consisting mostly of CSO22− ligands. The solid-phase mineralizes fully at ≈240 °C, which permits Sb2S3 to crystallize at around 250 °C in both atmospheres. The gaseous species evolved include CS2, C2H5OH, CO, CO2, COS, H2O, SO2, and minor quantities of C2H5SH, (C2H5)2S, (C2H5)2O, and (S2COCH2CH3)2. The thermal decomposition mechanism of 1 is described with chemical reactions based on EGA-MS and solid intermediate decomposition product analysis.

Rhizosphere Bacterium Rhodococcus sp. P1Y Metabolizes Abscisic Acid to Form Dehydrovomifoliol.

The phytohormone abscisic acid (ABA) plays an important role in plant growth and in response to abiotic stress factors. At the same time, its accumulation in soil can negatively affect seed germination, inhibit root growth and increase plant sensitivity to pathogens. ABA is an inert compound resistant to spontaneous hydrolysis and its biological transformation is scarcely understood. Recently, the strain Rhodococcus sp. P1Y was described as a rhizosphere bacterium assimilating ABA as a sole carbon source in batch culture and affecting ABA concentrations in plant roots. In this work, the intermediate product of ABA decomposition by this bacterium was isolated and purified by preparative HPLC techniques. Proof that this compound belongs to ABA derivatives was carried out by measuring the molar radioactivity of the conversion products of this phytohormone labeled with tritium. The chemical structure of this compound was determined by instrumental techniques including high-resolution mass spectrometry, NMR spectrometry, FTIR and UV spectroscopies. As a result, the metabolite was identified as (4RS)-4-hydroxy-3,5,5-trimethyl-4-[(E)-3-oxobut-1-enyl]cyclohex-2-en-1-one (dehydrovomifoliol). Based on the data obtained, it was concluded that the pathway of bacterial degradation and assimilation of ABA begins with a gradual shortening of the acyl part of the molecule.

Catalytic ozonation of ethyl acetate over mesoporous manganese oxides synthesized by a sonochemical method

AbstractEthyl acetate is one of typical volatile organic compounds (VOCs) emitting from solvent use, and removing ethyl acetate from exhaust air is vital to VOCs abatement. The mesoporous manganese oxide (MnOx) samples were sonochemically synthesized by the reduction of KMnO4 using Mn(NO3)2. The characterization shows that γ‐MnO2, β‐MnO2, and bixbyite‐like Mn2O3 were obtained by calcining the MnOx samples from 200°C to 500°C. The results show that γ‐MnO2 and β‐MnO2 possess more Mn4+ than bixbyite‐like Mn2O3. β‐MnO2 has the highest contents of surface oxygen species (Oads) and average oxidation state (AOS) among the MnOx catalysts. Based on a 7‐day test, β‐MnO2 performed the highest activity for the catalytic ozonation of ethyl acetate compared with the other MnOx catalysts. The results show that ethyl acetate is easy to be destroyed but difficult to be completely mineralized by catalytic ozonation. Lower gas hourly space velocity (GHSV) leads to higher CO2 selectivity and more intermediate products form in the catalytic ozonation of ethyl acetate under higher GHSV. A further study indicates that β‐MnO2 has a long‐term stability for catalytic ozonation of ethyl acetate because the accumulation and the decomposition of intermediate products are in a dynamic equilibrium during the catalytic ozonation.

Investigation of structural and optical properties of zirconia dioxide nanoparticles by radiation and thermal methods

The X-ray diffraction (XRD) spectrum of the nano-ZrO2 compound was drawn, the crystal structure was determined at room temperature and under normal conditions. Radiation-thermal decomposition of water on nanosized ZrO2 in the temperature range of [Formula: see text]–673 K has been studied by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. It has been shown that nanosized zirconium dioxide adsorbs water via the molecular and dissociative mechanisms. Intermediate products of the radiation-induced heterogeneous decomposition of water, namely, the molecular oxygen and hydrogen peroxide radical ions, zirconium hydride, and hydroxyl radicals have been detected. A comparative analysis of changes in the absorption bands (ABs) of molecular water and surface hydroxyl groups with temperature has been conducted, and the stimulating role of radiation in the radiation-thermal process of water decomposition has been revealed. With the participation of nano-ZrO2 during the radiation-heterogeneous decomposition of water to reveal the role of unbalanced cargo carriers that play the role of energy carriers under the influence of gamma-quantities in nano-ZrO2 and nano-[Formula: see text] systems paramagnetic centers, their origin and acquisition kinetics learned by the EPR method.

Soil organic carbon accumulation modes between pioneer and old‐growth forest ecosystems

Abstract Increasing evidence suggests that high biomass and litterfall do not necessarily bring about soil organic carbon (SOC) sinks, contrary to the assumption that higher litterfall implies higher SOC when designing carbon models. The underlying mechanism is related to the quality of litter. We conducted 15 years (2000–2015) of consecutive field measurements of δ13C values in SOC and plants in a pioneer forest (Pinus massoniana forest, PF) and an old‐growth forest (monsoon evergreen broadleaved forest, BF), using an isotope mixing model based on mass balance to quantify the effects of vegetation on SOC stock and soil characteristics. The carbon to nitrogen (C/N) ratio of litter in BF was lower than that in PF. The proportion of organic carbon yield input to the soil (Cinput) to the total litter carbon loss during decomposition was 38.7 ± 3.3% and 28.0 ± 2.1% in BF and PF respectively. New carbon input was higher in BF (148.7 ± 8.8 g C m−2 year−1) than PF (99.7 ± 4.5 g C m−2 year−1), though there was a non‐significant difference in annual litterfall between the two forests. Moreover, the Cinput was concentrated in the topsoil layer in PF but distributed in a more dispersed state across the whole soil profile in BF. Consequently, only the δ13C values of SOC decreased in the topsoil layer of PF, whereas these decreased at both soil depths in BF from 2000 to 2015. Compared with PF, BF exhibited higher carbon input and a more favourable soil environment for carbon storage. It was the amount of intermediate product (i.e. Cinput) of litter decomposition, not the amount of litterfall itself, that drove the contrasting differences in SOC status. Synthesis and applications. Litter quality controls soil organic carbon (SOC) accumulation by regulating the fate of decomposing litter, which may explain why old‐growth forests can sustainably accumulate carbon in soil. This finding questions the carbon models that predict the dependence of SOC accumulation on biomass and litter yield and suggests that litter quality should be valued in future carbon cycling models.

Enhancement of PMS activation in an UV/ozone process for cyanide degradation: a comprehensive study

PurposeThis paper aims to study peroxymonosulfate (PMS) activation in the ultraviolet (UV)/ozone process for toxic cyanide degradation from aqueous solution by a novel and simple method.Design/methodology/approachPhotocatalytic degradation of cyanide (CN-) was carried out using a bench-scale photoreactor. Optimization of the UV/ozone process for the highest removal of cyanide was obtained. The effect of parameters such as ozone concentration, PMS concentration, temperature, cations (Cu2+, Co2+ and Fe2+), cyanide concentration, anions (bicarbonate, carbonate, chloride, nitrite, nitrate and sulfate [SO42−]) and scavengers (ethanol [EtOH], humic acid, TBA and NaN3) was investigated for CN- degradation.FindingsComplete removal of 50 mg/L cyanide was obtained in 4 min in an ozone/UV/PMS process. The cyanide removal increased from 49.3% to 100% by adding the persulfate dosage up to 100 mg/L. The effect of various cations (II) on the cyanide degradation was enhanced in the order Cu2+ > Co2+ > Fe2+. Hydroxyl radical based on different radical quenchers such as salicylic acid proved as the main oxidizing radical for oxidation. The application of ozone/UV/PMS to treat wastewater containing cyanide shows high degradation efficiency.Research limitations/implicationsThe ozone/UV/PMS system could be a process for degradation and detoxification of cyanide.Practical implicationsThis study provided a simple and effective method for degradation of cyanide from aqueous solution. This method was applicable to protect environment from a huge amount of toxic cyanide wastewater produced by different industrial processes.Originality/valueThe PMS activation is done via a simple and effective method, which is carried out with the ozone/UV system. There are two main innovations. One is that the novel catalytic role of bimetallic ions in the ozone reaction with cyanide and the further decomposition of intermediate products is investigated. The other is that the optimized conditions were obtained for the removal of cyanide as a water contaminant. Furthermore, predominant oxidizing species by PMS activation are identified.

CaNa[Cr(OH)6] – A Layered Hydroxochromate(III) with Ordered Brucite Structure and its Thermal Decomposition

Green single‐crystals of the hydroxochromate(III) CaNa[Cr(OH)6] were grown under highly alkaline hydrothermal conditions at about 200 °C. The starting materials Ca(NO3)2·6H2O and Cr(NO3)3·9H2O were reacted in a mixture of water and sodium hydroxide with the molar ratio of 2.8:1. CaNa[Cr(OH)6] crystallizes in the non‐centrosymmetric trigonal space group R3 with the lattice parameters a = 583.86(2) pm and c = 1428.73(6) pm [T = 100(1) K]. Characteristically, the crystals are reverse‐obverse as well as inversion twins. The crystal structure is a stack of uncharged metal hydroxide layers, which can be regarded as a cation‐ordered rhombohedral variant of the Mg(OH)2 (brucite) structure type. The oxidation state of chromium(III) and its coordination by hydroxide groups was confirmed by UV/Vis and IR spectroscopy, respectively. Temperature‐dependent magnetic measurements revealed paramagnetic behavior with an effective moment of 3.82 μB per chromium atom. The thermal decomposition of CaNa[Cr(OH)6] takes place at about 225 °C, where the fast elimination of 1.5 equivalents of water is followed by the oxidation of chromium(III) to chromium(VI). Upon further heating to 1000 °C and 1200 °C, the intermediate decomposition products CaCrO4 and Na2CrO4 transform into the oxochromates(V) Ca5(CrO4)3O0.5 and Ca3(CrO4)2, respectively.