Multi-step Decomposition Process Research Articles

Ionic liquid based NCPBE membranes for electrochemical capacitor applications: Structural, thermal and electrical transport properties

The current study focuses on the preparation and characterisation of imidazolium ionic liquid based plasticized nano-composite polymer blend electrolytes (NCPBEs). Semi-crystalline nature of the synthesized samples was observed using XRD analysis. ATR-FTIR results demonstrate the interaction among the carbonyl (CO) and hydroxyl (O–H) groups of polymers with ionic liquid (IL) and salt, NaI. Furthermore, thermo-gravimetric analysis (TGA) indicates multi-step decomposition process. Ion transport mechanism has been analysed using temperature dependent conductivity analysis, ac conductivity analysis and dielectric properties study. The sample containing 25 wt% IL i.e. NCPBE-25 has the ionic conductivity ∼9.30 × 10−4 Scm−1 with the optimum vale of charge carrier density, mobility, and ion diffusivity at 30oC. Ions are principal charge carriers in the present electrolytes. The sample NCPBE-25 has the electro-chemical stability window −3.6 to 1.5 V at room temperature. The fabricated electro-chemical capacitor has the specific capacitance, energy density and power density 363.27 Fg-1, 50.45 Whkg−1 and 18.16 kW/kg, respectively at the scan rate 5 mV/s.

Electrospun (K,Na)NbO3 Piezoceramic Fibers for Self‐Powered Tactile Sensing Application

This study investigates the electrical properties of electrospun ceramic fiber mats based on potassium sodium niobate ((K,Na)NbO3;KNN) for potential applications in soft‐robotic tactile sensors. The rheological studies of electrospinning solutions exhibit shear thinning behavior, with a viscosity plateau between shear rates of 1–100 s−1. The thermal decomposition behavior of the KNN samples is analyzed using thermogravimetric analysis; the samples show multistep decomposition processes leading into a phase pure perovskite structure. For the electrospun KNN fiber mats, the electrical characterization reveals ferroelectric hysteresis loops with a high leakage current of ≈270 nA at 20 kV cm−1 and switching current behavior. The ferroelectric results indicate that a full polarization of KNN‐fiber mats is not possible due to their electrical breakdown at high electrical fields. The integration of KNN short fibers into a soft‐bending actuator demonstrates successful tactile sensing capabilities. The experimental findings reported here highlight the potential of electrospun KNN fiber mats for flexible and autonomous device applications in soft robotics.

Pyrolysis of low-value waste miscanthus grass: Physicochemical characterization, pyrolysis kinetics, and characterization of pyrolytic end products

The current study explored the bioenergy potential of waste miscanthus grass (WMG). The kinetic study of WMG was evaluated via two model-free methods, in a thermogravimetric analyzer (TGA), at dynamic heating rates under an inert ambiance. The pyrolysis was performed in a semi-batch fixed bed reactor at 500 oC, 80 oC min heating rate, and 1 mm particle size. The evolution of hot vapours during pyrolysis was explored using a TGA-FTIR analyzer. Finally, the bio-oil and biochar were characterized by their physicochemical properties. The kinetic results established that WMG followed a multi-step decomposition process, and the average activation energy gained from KAS and ST was found to be 197.66 and 179.64 kJ mol-1, respectively. TGA-FTIR study revealed the foremost release of carbon dioxide (28.22%), followed by a carbonyl (25.40%), and ether (19.12%). Further, the pyrolysis of WMG yielded 29.32 wt% of bio-oil at the optimized condition whereas, physicochemical results of bio-oil established; 65.16% carbon content, 26.16 MJ kg-1 HHV, 34.15 cP viscosity, and 812 kg m-3 density. GC-MS study of bio-oil confirmed the maximal release of hydrocarbons and phenols. Finally, characterization results of miscanthus grass biochar (MGB) demonstrated an excellent feedstock for industrial and domestic applications.

Homoleptic Mononuclear Tris‐Chelate Complexes of FeII, CoII, NiII, and ZnII Based on a Redox‐Active Imidazolyl‐2‐thione Ligand: Structural and Electrochemical Correlation

Five mononuclear tris‐chelate complexes of FeII, CoII, NiII and ZnII, containing the bidentate ligand 3‐methyl‐1‐(2‐pyridyl)imidazolyl‐2‐thione (L), have been synthesised and characterised, namely [MII(L)3](BF4)2, where M = Fe (1), Co (2), Ni (3) and Zn (4), and [FeII(L)3](PF6)2 {1‐(PF6)2}. The complexes have been characterised by standard methods and single‐crystal X‐ray diffraction, showing that all the complexes are isostructural and isomorphs, crystallising in the P1 space group, except for 1‐(PF6)2, which crystallises in the P21/c, as expected due to the different size and symmetry of the anion. The metal centre is found in a distorted meridional‐N3S3 octahedral geometry. In all the complexes, two ligand strands within the same complex cation unit interact via an almost perfect face‐to‐face π–π stacking. The double intramolecular interaction occurs between a pyridyl ring of one ligand strand and an imidazolyl ring of a second ligand strand and vice versa. The FeII and CoII complexes, 1 and 2, are stabilised in the high spin state, based on the bond lengths and angles obtained by SC‐XRD and by VT‐magnetic studies in the solid state and NMR Evans method in CD3CN solution. The cyclic voltammetry behaviour for compounds 1–4 showed an EC mechanism for the oxidation process, in which two ligand strands are electrochemically oxidised, instead of the metal centre, followed by a chemical process (de‐coordination and dimerisation). Whereas, the reduction process involved metal electrodeposition for the FeII, NiII and ZnII complexes. In the case of the CoII complex, the voltammetric response suggested a multistep decomposition process during the electrochemical reduction. Finally, a linear correlation between the oxidation potential of the ligand and the average M–N bond length has been found, permitting the modification of the oxidation potential by selection of the metal centre.

Physico-chemical study of steroids from different matureness corn silk material

This study shows an ultrasonic assisted extraction procedure of steroids from corn silk (CS). The total steroids contents were positively correlated with the ultrasonic assisted extraction time. The extracted steroids contents varied according to the different maturity stages of CS. There were three tested CS maturity stages: silking stage (CS-S), milky stage (CS-M) and mature stage (CS-MS). The β - sitosterol standardization method with 530 nm wavelength colorimetric measurements were applied to determine the content of extracted steroids. Measured steroids concentrations range were from 38.3 × 10-3 mg.mL-1 to 368.9 × 10-3 mg.mL-1 in different extraction time and CS maturity stages. The highest concentration of steroids, 368.9 × 10-3 mg.mL-1 was found in CS-MS sample with the 75 minutes ultrasonic extraction time. The fluorescence mapping techniques were used to confirm the existence of steroids. The thermal analysis illustrated a typical multistep decomposition process for the CS-S, CS-M and CS-MS samples. Two endothermic peaks were found: The first one was 54.3 °C for CS-S and CS-MS, 60.2 °C for CS-M, the second one, 397 °C (CS-MS), 415.1 °C (CS-M) and 419.7 °C (CS-S) attributed to the total thermal decomposition. The observed exotheric process found at 524 °C corresponded to CS-MS sample decomposition. The optimal ultrasonic-assisted extraction time for all samples under study CS-S, CS-M and CS-MS was about 75 minutes and the optimal steroids extraction contents obtained were 92.8 × 10-3 mg.mL-1 (CS-S), 124.2 × 10-3 mg.mL-1 (CS-M) and 368.9 × 10-3 mg.mL-1 (CS-MS) respectively.

Tetranuclear yttrium and gadolinium 2-acetylcyclopentanoate clusters: Synthesis and their use as spin-coating precursors for metal oxide film formation for field-effect transistor fabrication

Lanthanide clusters [Ln4(μ3-OH)2(η2-accp)4((μ-O)-η2-accp)6] (Ln = Y (4), Gd (5); accp = 2-acetylcyclopentanoate) are accessible by treatment of [M(NO3)3·6H2O] (M = Y (1), Gd (2)) with 3 equiv. of Haccp (3) in presence of NaOH. The molecular structures of 4 and 5 in the solid-state are discussed. The thermal behavior of 4 and 5 was studied by TG under Ar and O2, showing multistep decomposition processes. Additionally, DSC studies were carried out under an atmosphere of O2. PXRD measurements of the TG residues confirm the formation of Ln2O3. Spin-coating experiments were carried out with 4 and 5 for Ln2O3 film deposition on silicon substrates. The layers are smooth, close and are of thicknesses of 18.87 ± 1.13 nm and 25.59 ± 4.55 nm for Ln = Y and Gd, which was evidenced by SEM and EDX studies. Field-effect transistors were successfully fabricated by deposition of carbon nanotubes on top of the Y2O3 films and formation of palladium contacts by a lift-off procedure. An on/off ratio of more than 4 orders of magnitude is achieved without considerable leakage currents. These results demonstrate the potential use of spin-coated Y2O3 as a gate dielectric in electronic devices.

Physico-chemical study of flavonoids from different matureness corn silk material

There was tested a simple extraction procedure of flavonoids separation from the original corn silk (CS) material. It was found, that the total flavonoids content differs with the extraction time and extraction temperature. There were found different flavonoids contents in extracts prepared from different maturity stages of the original corn silk material (silking stage (CS-S), milky stage (CS-M)). Extracted flavonoids content was quantified by the lutin standardization method by means of colorimetry at 510 nm wavelength. Obsreved flavonoids concentration was ranging from 2×10-3 mg.mL-1 to 7 ×10-3 mg.mL-1 dependent on the extraction time period and extraction temperature. The highest flavonoids concentration of 7.5×10-3 mg.mL-1 was found for CS-M after 20 minutes extraction time and 80 °C extraction temperature. There was confirmed the presence of flavonoids by fluorescence mapping experiments. There was found a typical multistep decomposition process for both CS-S and CS-M materials by TG analysis. There was found a melting temperature of flavonoids of 54.3 °C for corn silk silking stage material exhibiting 58.9 J.g-1 heat of fusion and 60.2 °C for corn silk milky stage material with 112.9 J.g-1 heat of fusion. The optimal conditions of corn silk flavonoids extraction were 40 ℃, 50 minutes for CS-S, the optimal flavonoids extraction content was (6.8 ±2.1)×10-3 mg.mL-1, 80℃, 20 minutes for CS-M and the optimal extraction content was (7.2 ±0.3)×10-3 mg.mL-1.

Investigation of Methylammonium Tin Strontium Bromide Perovskite Systems

The properties of methylammonium-tin-strontium bromide systems (CH3NH3Sn1-xSrxBr3, 0.0 ≤ x ≤ 0.1) were investigated. The X-ray diffraction analysis (XRD) revealed the presence of the untilted cubic Pm-3m perovskite and orthorhombic SnBr2 as major crystalline phases. The morphological analysis confirmed the XRD data by detecting the formation of polyhedral shaped crystallites attributed to MASnBr3 perovskite and elongated crystallites related to SnBr2 phase. Derivative differential thermal analysis (DDTA) and derivative thermogravimetric analysis (DTG) revealed a thermal stability of MASnBr3 phase till T = 250°C and showed the presence of more thermal events related to a multistep decomposition process. The addition of Sr-ions retained the cubic crystalline structure of the perovskite and enhanced its thermal stability at T = 150°C by reducing the weight loss rates. The optical spectra displayed values of absorption edges between 624 nm and 636 nm. The Tauc plots revealed a direct semiconducting behavior with band energy gaps at ∼2.02–2.03 eV. The emission photoluminescence (PL) spectra, measured at room temperature and excitation wavelength λexc = 380 nm as well as the excitation photoluminescence (PL) spectra, measured at room temperature and emission wavelength λem = 520 nm showed a dramatic increase of the intensity by adding the Sr-ions reaching a maximum for x = 0.025.

First-Principles Study on the Mechanism of Photoselective Catalytic Reduction of NO by NH3 on Anatase TiO2(101) Surface

A promising method for NO abatement is photoselective reduction with a proper semiconductor, such as TiO2. Here we report a systematic theoretical study on NO abatement through an adsorbed NH3 molecule on the anatase TiO2(101) surface. The reaction mechanism proposed by experiments has been verified. The key process, namely, the oxidation of the adsorbed NH3 molecule by photogenerated hole, has been investigated by two different methods: one is to use the triplet state to mimic the real excited state and the other is to inject a hole to the slab by the adsorption of ·OH radical. Both methods give almost the same result, and the oxidation of the NH3 molecule is found to be a concerted proton coupled charge transfer process. The ·NH2 radical, resulting from the oxidation of NH3, can be attacked by a NO molecule from the gas phase to form a NH2NO complex spontaneously. The decomposition of this complex to N2 and H2O is the rate limiting step of the overall reaction. This multistep decomposition process consi...

The stability of inclusion compounds under heating

The thermal decomposition of three inclusion compounds: [Zn 2 (camph) 2 dabco]·DMF·H 2 O, [Zn 2 (camph) 2 bipy]·3DMF·H 2 O and [Zn 2 (camph) 2 bpe]·5DMF·H 2 O was studied in the inert atmosphere. TG and DTG curves confirm multi-step decomposition process, the dehydration being the first step. Thermogravimetric data (obtained at different rates of linear heating) were processed with computer program (with 'Model-free' approach). Kinetic parameters of decomposition were calculated for the DMF multi-step removal, the processes are described by Avrami-Erofeev equations. The connection between the kinetic parameters and structural features of the host frameworks (ligand linker lengths and porous-free volumes) are discussed.

Adsorption, desorption, and dissociation of benzene onTiO2(110)andPd∕TiO2(110): Experimental characterization and first-principles calculations

Adsorption and reaction of benzene molecules on clean ${\mathrm{TiO}}_{2}(110)$ and on ${\mathrm{TiO}}_{2}(110)$ with deposited Pd nanoparticles are investigated using a combination of scanning tunneling microscopy (STM), temperature-programmed desorption, and first-principles calculations. Above $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the one-dimensional motion of benzene between bridging oxygen rows is shown to be too fast for STM imaging. At $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ benzene molecules form chains on top of titanium rows, with calculations indicating every other benzene is rotated $30\ifmmode^\circ\else\textdegree\fi{}$. Both experimental and theoretical studies find no dissociative reactivity of benzene on the clean ${\mathrm{TiO}}_{2}(110)$ surface, due to little hybridization between ${\mathrm{TiO}}_{2}$ and benzene electronic states. After deposition of Pd nanoparticles, molecular benzene is observed with STM both on the substrate and adjacent to metallic particles. Upon heating to $800\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, benzene fully breaks down into its atomic constituents in a multistep decomposition process.

Semi-interpenetrating polymer networks of polyurethane and poly(vinyl chloride)

A series of semi-interpenetrating polymer networks (semi-IPN) of polyurethane (PU) and poly(vinyl chloride) (PVC) has been obtained by prepolymer method and characterised by FTIR; morphological features were examined by SEM-EDS. It has been found that PVC spherical aggregates are dispersed in the PU matrix, but Cl atoms location indicates partial miscibility of both polymers at the interphase which is probably due to hydrogen bonding and/or dipole-dipole interactions. The PVC component influences the phase behaviour of PU’s hard segments, as evidenced by DSC results. Thermogravimetric analysis (TG) reveals a complex, multi-step decomposition process with the main mass loss at 503-693 K, while the DTG maxima are located between 540 and 602 K.

Mechanism of mass spectral fragmentation of dinuclear copper(ii) complexes with heterocyclic dithiocarbamates and octaazamacrocyclic ligand

The mass spectral fragmentation of five dinuclear Cu(II) complexes of the general formula [Cu2(Rdtc)tpmc] (ClO4)3, where tpmc and Rdtc refer to N, N′, N″, N‴-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc), or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, has been investigated. The results were shown to be of mechanistic significance, clarifying the major products of their fragmentation. A possible mechanism entails a multi-step decomposition process that can be separated into individual steps depending on their molecular structures. Every step is determined to some extent by the nature of the intermediates.

Spectral assignments and molecular modeling of dinuclear cobalt(II) complexes with a bridged bidentate β-diketone and a cyclic octaamine ligand

Four new cobalt(II) complexes of the general formula [Co 2(Rac)tpmc](ClO 4) 3, where tpmc and Rac refer to N, N′, N″, N‴-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane and β-diketonato ligands i.e. 2,4-pentanedionato (acac), 1,3-diphenyl-1,3-propanedionato (dibzac), 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato (hfac) or 2,2,6,6-tetramethyl-3,5-heptanedionato (tmhd) ions, respectively, have been prepared. Elemental analyses, conductometric measurements, UV/VIS, IR, EPR and mass spectroscopy were used for the complex characterization. Each cobalt(II) ion is coordinated with four nitrogen atoms in an exo arrangement of tpmc groups while the additional β-diketone bridges metal-ion centers through the both enolate oxygens. The presence of different R-groups on the diketone influence the ν( C ▪ O) and ν( C ▪ C) vibrations in the IR spectra. These frequencies decrease in the order of the complexes with coordinated hfac>dibzac>acac>tmhd ligands. The mechanism of the mass spectral fragmentation of the complexes entails a multi-step decomposition process. The g eff-factors estimated from EPR spectra suggest a similar molecular character of the complexes. Molecular modeling calculations were used to characterize the complex species.

Multi-step decomposition processes for some antibiotics: A kinetic study

In the present study, a kinetic analysis on decomposition processes of some oxacillin salts (oxacillin, cloxacillin and dicloxacillin) was carried out to identify their kinetic parameters. As expected by their complex structures, several steps with different activation energies occurred in the decomposition processes. The application of the model-fitting kinetic method to multi-step decomposition process results to be unsuitable for the non-isothermal data. As far as isothermal data are concerned this method gives rises to more reliable results which, however, are likely to conceal the kinetic complexity. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gives different dependencies of the activation energies as a function of the extent of conversion and allows detecting multi-step processes over a wide temperature range.

Kinetic Analysis of Single or Multi-Step Decomposition Processes; Limits introduced by statistical analysis

A kinetic study on decomposition processes of some penicillin and some commercial drugs was carried out. As expected by the complex structures of penicillins, several steps with different activation energies occurred in their decomposition processes. Model-fitting and model-free kinetic approach were applied to non-isothermal and isothermal data. In the model-fitting methods the kinetic triplets (f(α), A and E a) that defines a single reaction step resulted in being at variance with the multi-step nature of penicillins decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. The complex nature of the multi-step process of the studied compounds was more easily revealed using a broader temperature range in non-isothermal isoconversional method. The failure in the model fitting method did not allow calculating storage times. Model-fitting and model-free methods, both isothermal and non-isothermal, showed that F1 mechanism is able to describe decomposition processes for drugs (having Phosphomycin salts as active component) for which a single decomposition process occurs. Statistical analysis allowed us to select reliable kinetic parameters related to the decomposition processes for these last compounds. This procedure showed that the values obtained by extrapolation, outside the temperature range where the processes occurred must be used with caution. Indeed half-life and shelf-life values, commonly extrapoled at room temperature, seemed to be unrealistic.

Study of CoGa deposition from the single source precursor (CO) 4CoGaCl 2 (THF)

Depositions of thin films of CoGa from the single-source precursor (CO) 4CoGaCl 2(THF) ( 1) have been carried out in an epitaxial organometallic chemical vapor deposition reactor. Prior to deposition, mass spectrometric (MS) and thermogravimetric (TGA) analyses of 1 were undertaken. Electron impact MS reveals a tendency for 1 partially to disproportionate (after loss of THF) into ClGa[(CoCO) 4] 2 and GaCl 3 at probe temperature (120°C). The parent molecular ion for 1 appears with only low relative intensity (1%) indicating easy loss of THF as the first step. The principal features of the spectrum can be assigned to step-wise CO-loss series of peaks derived from three parent ions [(CO) 4CoGaCl 2] + (a), [(CO) 4CoGaCl] + (b), and [(CO) 4Co] + (c). The relatively high intensity of the peaks derived from parent ions (a) and (b) indicate a relatively good stability of the CoGa bond through to the species [CoGa] + (rel. int. 15%). TGA of 1 under Ar shows decomposition in a single step in the range 100 to 230°C; residual weight of 44% is higher than expected for CoGa alone. Under H 2 however, a multistep decomposition process is observed culminating at 400–450°C; residual weight is 33%, close to that expected for CoGA. In the (cold wall) CVD reactor, optimum deposition occurs under reduced pressure (0.9–6 torr) and laminar flow conditions using H 2 as carrier gas for (100)GaAs, (100)Si, and Al 2O 3 as substrates; growth rates are about 1.8 μm/h. Polycrystalline films are obtained under all conditions; annealing under H 2 for 2 h at 500°C gives relatively sharp XRD patterns for β-CoGa. For depositions in the range 250 to 350°C the Co/Ga ratio in the films is close to 1/1 showing control of stoichiometry by the precursor. These films however still contain some Cl. In the range 350 to 400°C the Cl content is lowered, however, the films become Co rich indicating loss of Cl is accompanied by loss of Ga. The stoichiometric control achieved in the present work indicates that single source precursors of ratio CoGa 2 could give Ga rich (64 at.% Ga) β-cubic CoGa for lattice matching to (100)GaAs.

Direct observation of multistep decomposition processes of metastable ions

The operation of a metastable ion selector is described, which by variation of the electric sector voltage of a double focusing mass spectrometer allows a more detailed observation of metastable transitions. By proper adjustment of the sector voltage one can tune in a fragment ion formed in a metastable transition in the region between accelerating field and electric sector and then by scanning the main magnetic field one can observe products of further fragmentation of these ions in the region between electric sector and main magnet. They appear in the spectrum like ordinary metastable peaks in normal spectra and can be evaluated in the same manner. Two- and three-step degradation sequences and effects related to rate constants have been observed. Some aspects and potential applications of this mode of instrument operation are discussed.