Activation Energy Ea Research Articles

Defects engineering of nickel tellurium electrocatalyst to boost urea oxidation reaction: Electrodeposition mechanism and performance

The urea oxidation reaction (UOR) offers an attractive strategy to replace the oxygen evolution reaction (OER) for energy-saving hydrogen production due to its favorable thermodynamic property, but its development is hindered by the lack of efficient and cost-effective electrocatalysts. In this study, nickel-tellurium (Ni-Te) grown on 3D nickel foam was successfully synthesized using a simple and facile electrodeposition method. The electrodeposition process of Ni-Te follows the three-dimensional instantaneous nucleation/growth mechanism controlled by diffusion. The apparent activation energy (Ea) of Ni-Te in the electrodeposition process is as low as 36.5 kJ∙mol-1. Lattice distortion structure obtained by electrodeposition modifies the intrinsic electronic structure and optimizes the adsorption energy of intermediates. Thanks to the synergistic effects of fast electron transport, superhydrophilic surface and nanoflake structure, the prepared Ni-Te electrocatalyst shows excellent activity toward UOR with a low potential of 1.503 V vs. RHE at 100 mA·cm-2 and a small Tafel slope (63.6 mV·dec-1) in 1.0 M KOH containing 0.33 M urea solution.

Ferroelectric and antiferroelectric chiral multilactate liquid crystalline materials with negative dielectric anisotropy

In this work, the mesomorphic, electro-optic and dielectric properties have been discussed in the light of molecular structure-property correlations of two chiral multilactate liquid crystalline materials possessing the orthogonal paraelectric Smectic A* phase, tilted ferroelectric Smectic C* phase and the tilted antiferroelectric Smectic CA* phase, over a substantially broad temperature range. Interestingly, a reasonably rare re-entrant Smectic C* phase (SmCre*) has also been identified in one of the investigated materials. These materials differ in their linkage groups (keto or ether) and an additional chiral unit in the terminal chain. The phase transition temperatures and transition enthalpies were determined from Polarizing Optical Microscopy and Differential Scanning Calorimetry (DSC) measurements. The compounds exhibit negative dielectric anisotropy (Δε) throughout the mesomorphic range (maximum −18 and −4 in SmA* for both the compounds) and moderately high values of spontaneous polarization (∼153 nC/cm2 in SmCre* phase). The temperature dependence of the response time (τ), bulk viscosity (η) and the activation energies (Ea) throughout the mesomorphic phase have been determined from the spontaneous polarization measurements. To emphasize the structure-property correlations in more detail, dielectric spectroscopy measurement has also been performed to measure the dielectric strength, dielectric loss, frequency dependent permittivities, relaxation time and relaxation frequencies. The clear evidence of the relatively rare SmCre* phase has also been confirmed from the temperature and frequency dependence of the dielectric permittivity. These results shed important light on the emergence of these materials as a smart alternative for their application in multicomponent mixtures targeted for advanced electro-optic and photonic devices.

Facile synthesis of Ni-phyllosilicate assisted by polyacrylamide at room temperature for CO2 hydrogenation to methane

To elucidate the effect of solution viscosity on the synthesis of Ni-phyllosilicate, polyacrylamide was incorporated to create a viscous aqueous medium containing of sodium metasilicate, nickel nitrate and NH4F. The enhanced viscosity promotes the dispersion of the initial formed crystal seeds and the growth of Ni-phyllosilicate, culminating in a Ni-rich NiPs-RT-6 of a high Ni content of up to 55.2 wt%. Residual polyacrylamide elimination was accomplished via calcination, concurrently enhancing metal-support interaction. The as-synthesized samples display a nanoflower morphology with nanospheres overlaid with numerous thin nanosheets. The relatively small Ni particles around 5.7 nm were obtained after reduction even at a very high Ni loading, owing to its strong metal-support interaction. NiPs-RT-6 achieves a CO2 conversion of 75.9% at 450 °C, 0.1 MPa, 60 L g−1·h−1, which closely approximates thermodynamic equilibrium. The turn over frequency for CO2 (TOFCO2) was substantial, calculated at 3.7 × 10−3 s−1, accompanied by activation energy (Ea) of 80.6 kJ·mol–1. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) further disclosed that m-HCOO– serves as a crucial intermediate following a formate reaction pathway. With its high Ni content, finely distributed Ni particles, and strong metal-support interaction, NiPs-RT-6 demonstrates promising catalytic activity in CO2 methanation.

Effective degradation of tetracycline in aqueous solution by an electro-Fenton process using chemically modified carbon/α-FeOOH as catalyst.

This study applied an electro-Fenton process using chemically modified activated carbon derived from rubber seed shells loaded with α-FeOOH (RSCF) as catalyst to remove tetracycline residues from aquatic environment. Catalyst characteristics were evaluated using SEM, EDS, XRD, and XPS, showing successful insertion of iron onto the activated carbon. The effects of the parameters were investigated, and the highest treatment efficiency was achieved at pH of 3, Fe: H2O2 ratio (w/w) of 500:1, catalyst dose of 1g/L, initial TCH concentration of 100mg/L, and electric current of 150mA, with more than 90% of TCH being eliminated within 30min. Furthermore, even after five cycles of use, the treatment efficiency remains above 90%. The rate constant is calculated to be 0.218min-1, with high regression coefficients (R 2 = 0.93). The activation energy (Ea) was found to be 32.2kJ/mol, indicating that the degradation of TCH was a simple reaction with a low activation energy. These findings showed that the RSCF is a highly efficient and cost-effective catalyst for TCH degradation. Moreover, the use of e-Fenton process has the advantage of high efficiency, low cost thanks to the recyclability of the catalyst, and environmental friendliness thanks to less use of H2O2.

ZnIn2S4-based multi-interface coupled photocatalyst for efficient photothermal synergistic catalytic hydrogen evolution

Photothermal synergistic catalysis is a novel technology that converts energy. In this study, ZnIn2S4 with S-vacancy (ZIS-Vs) is combined with Nickel, Nickle Oxide and Carbon Nanofiber aggregates (Ni-NiO@CNFs) to create a multi-interface coupled photocatalyst with double Schottky barrier, double channel and mixed photothermal conversion effect. Theoretical calculation confirms that the Gibbs free energy (ΔG*H) of the S-scheme heterojunction in the composite material is −0.07 eV, which is close to 0. This promotes the adsorption of H* and accelerates the formation of H2. Internal photothermal catalysis is achieved by visible-near infrared (Vis-NIR, RT) irradiation. The internal photothermal catalytic hydrogen production rate of the best sample (0.9Ni-NiO@CNFs/ZIS-Vs) is as high as 17.24 mmol·g−1·h−1, and its photothermal conversion efficiency (η) is as high as 61.42 %. Its hydrogen production efficiency is 20.52 times that of ZIS-Vs (0.84 mmol·g−1·h−1) under visible light (Vis, RT) conditions. When the Vis-NIR light source is combined with external heating (75 ℃), the hydrogen production efficiency is further improved, and the hydrogen production efficiency (29.16 mmol·g−1·h−1) is 26.75 times that of ZIS-Vs (1.09 mmol·g−1·h−1, Vis-NIR, RT). Further analysis shows that the increase in hydrogen production resulted from the apparent activation energy (Ea) of the catalyst decreasing from 16.7 kJ·mol−1 to 9.28 kJ·mol−1. This study provides a valuable prototype for the design of an efficient photothermal synergistic catalytic system.

Combustion Characteristics, Kinetics and Thermodynamics of Peanut Shell for Its Bioenergy Valorization

To realize the utilization of peanut shell, this study investigates the combustion behavior, chemical kinetics and thermodynamic parameters of peanut shell using TGA under atmospheric air at the heating rates of 10, 20, and 30 K/min. Results indicate that increasing the heating rate leads to higher ignition, burnout, and peak temperatures, as observed in the TG/DTG curves shifting to the right. Analysis of combustion performance parameters suggest that higher heating rates can enhance combustion performances. Kinetic analysis using two model-free methods, KAS and FWO, shows that the activation energy (Eα) ranges from 93.30 to 109.65 kJ/mol for FWO and 89.72 to 103.88 kJ/mol for KAS. The data fit well with coefficient of determination values (R2) close to 1 and the mean squared error values (MSE) less than 0.006. Pre-exponential factors using FWO range from 2.19 × 106 to 8.08 × 107 s–1, and for KAS range from 9.72 × 105 to 2.25 × 107 s–1. Thermodynamic analysis indicates a low-energy barrier (≤±6 kJ/mol) between activation energy and enthalpy changes, suggesting easy reaction initiation. Furthermore, variations in enthalpy (ΔH), Gibbs free energy (ΔG), and entropy (ΔS) upon conversion (α) suggest that peanut shell combustion is endothermic and non-spontaneous, with the generation of more homogeneous or well-ordered products as combustion progresses. These findings offer a theoretical basis and data support for the further utilization of agricultural biomass.

Investigation of the catalytic activity of Ag(0) nanoparticles supported into anionic hydrogel networks for hydrogen production process

In the presented study, the hydrogen production from the hydrolysis of the morpholine-borane (MB) with hydrogel supported Ag(0) nanoparticle catalyst system was reported. For this purpose, nanosized p(sulfopropyl acrylate potassium salt-co-itaconic acid)@Ag composite material, (p-SIH@Ag), was prepared and used as catalyst. In this study, the effects of base, catalyst amount, MB substrate concentration and temperature were investigated for the MB hydrolysis reaction. p-SIH@Ag catalyzed MB hydrolysis reaction at 30 °C, the activation energy (Ea) was determined as 24.3 kjmol−1 and the turn over frequency (TOF) as 37.52 mol H2(mol Ag(0).h)−1. In reusability studies, the catalyst preserved 72% of its activity even after the 5th catalytic cycle despite the sensitivity of Ag metal to oxidation. Our study is the first in the literature to use hydrogel supported Ag metal catalyst system in hydrogen production via MB hydrolysis.

Oil produced from Ghana Shea Nut crop for prospective industrial applications

Though little research has been done, shea nut oil (Shea Butter), is a promising shea product with great potential for use in industrial shea product manufacture. To assess the oil obtained from the shea nuts for personal, commercial, and industrial use, this study focuses on the extraction process, the optimal solvent for extraction, thermodynamics and kinetic studies, and characterization of the oil. Using different solvents as well as extraction temperatures and times, the oil was extracted using the solvent extraction method. Moreover, models of thermodynamics and kinetics were used in examining the Shea nut oil extraction at different durations and temperatures. At the highest temperature of 333 K (at 130min), the highest oil yields of 70.2 % and 59.9 % for n-hexane and petroleum ether, respectively, were obtained, following first order kinetics. For both petroleum ether and n-hexane, the regression coefficient (R2) was 1. For the extraction with n-hexane and petroleum ether, the mass transfer coefficient (Km), activation energy (Ea), entropy change (ΔS), enthalpy change (ΔH), and Gibb's free energy (ΔG) were, respectively, (0.0098 ± 0.0061 and 0.0123 ± 0.0084) min−1, 74.59 kJ mol−1 and 88.65 kJ mol−1, (−236.15 ± 0.16 and −235.63 ± 0.17) J/mol K, (71.88 ± 0.06 and 85.94 ± 0.06) kJ/mol, and (148.75 ± 1.52 and 162.46 ± 1.52) kJ/mol. These values favor an irreversible, forward, endothermic, and spontaneous process. Gas chromatography analysis was used to identify the principal fatty acids in the oil, which include stearic acid (52 %), oleic acid (30 %), and linoleic acid (3 %), as well as various minor fatty acids. The oil's potential bonds and functional groups were identified using Fourier Transform Infrared analysis, and the physicochemical parameters such as the iodine value, peroxide value, acid and free fatty acid values were found to be within acceptable ranges for use in domestic, commercial, and industrial settings.

Efficient production of biodiesel from palm fatty acid distillate using a novel hydrochar-based solid acid catalyst derived from palm leaf waste

To combat fuel shortages, pollution, and the exhaustion of natural oil resources, an environmentally friendly alternative to fossil fuels, such as biodiesel, is essential for meeting global transportation demands. A novel heterogeneous acid catalyst for production of biodiesel from low-cost, high free fatty acid feedstocks was synthesized in this study by activating and impregnating hydrochar from palm leaf (PL) waste with H3PO4 and H2SO4. Subsequently, the sulfonated catalyst was utilized for the esterification of palm fatty acid distillate (PFAD). FT-IR, XRD, FESEM, EDX, BET, TGA, and surface acidity methods were employed to characterize the acid catalyst. Using the one-variable-at-a-time (OVAT) technique, the optimized reaction conditions for esterification of PFAD using the hydrochar-based catalyst were 4 wt% catalyst loading, 353.15 K reaction temperature, 4 h reaction time, and 18:1 methanol: PFAD molar ratio. At these conditions, a maximum biodiesel yield of 93.56% was achieved. The catalyst exhibited excellent reusability and stability throughout five reaction cycles, maintaining biodiesel yields above 80% after each cycle. Analysis of the fuel properties revealed that the biodiesel derived from PFAD met the physiochemical criteria outlined in ASTM D6751, the American biodiesel standard. The kinetic study revealed that the esterification reaction followed pseudo-first-order kinetics with an activation energy (Ea) of 23.70 kJ/mol. Furthermore, the thermodynamic enthalpy (∆H*) and Gibbs' free energy (∆G*) of esterification were 20.9 and 33.41 kJ/mol, respectively, indicating that the reaction was an endothermic and non-spontaneous process.

Mpact of pasteurisationand storage conditions on the physicochemical properties of acerola jelly

Acerola, a fruit rich in bioactive compounds such as polyphenols and vitamin C, is highly susceptible to degradation under temperature influences. This study aimed to evaluate the impact of pasteurisationand storage conditions on the stability of these compounds in acerola jelly. Analytical findings revealed that thermal treatment at 80°C for 5 minutes effectively eradicated total aerobic bacteria and mould yeast content. Furthermore, this treatment preserved the vitamin C and phenolic content, as well as the sensory quality of the jelly, better than other samples. The study also discovered that during storage, the degradation of vitamin C and polyphenols in acerola jelly adhered to the first-order model and the Arrhenius model. In contrast, attributes such as total soluble solids (TSS), pH, and titratable acidity (TA) remained constant during pasteurisationand storage. Kinetic parameters, including D-value, k-value, z-value, and activation energy (Ea), indicated high stability of the product when stored at a low temperature of 4-6oC. These findings suggest that acerola jelly has considerable potential for commercial production.

Improved hydrogen generation via NaBH4 hydrolysis: Synergistic role of sulfur and C4+-Doping unveils (440) high-index facets and modulates Co2+/Co3+ ratios in the Co3O4 lattice

Sodium borohydride (NaBH4) is crucial for eco-friendly “green” hydrogen (H2) storage, employing controlled release through catalyzed NaBH4 hydrolysis, mitigating its inherent sluggish self-hydrolysis. Precious metal catalysts enhance this process, but face scarcity and cost issues hindering widespread use, prompting interest in Co3O4, specifically with (311) orientation for abundant Co2+ sites. However, excess Co2+ on dominant (311) facets limits catalytic efficacy. This study presents a nuanced synthesis of sulfur (S)- and carbon (C4+)-doped Co3O4 that expose high-index (440) facets and optimize Co2+/Co3+ distribution. The catalytic performance of CoSC-0.1-700 on (440) facets demonstrates remarkable hydrogen generation rate of 4.1 L g−1. min−1 within 10.5 min, 1.81×, 2.42×, and 3.83× higher than control samples, and undoped Co3O4 with (311) dominance, and 1.24× higher than (220). An estimated activation energy (Ea) of 33.63 kJ mol−1, comparable to noble metals, indicates high performance and stability over ten (10) cycles. This approach promises sustainable future in "green" H2 production.

Drying kinetic, thermodynamic and quality analyses of infrared drying of truffle slices.

Kinetic and thermodynamic parameters are the most important part for making a suitable tool for drying agricultural products. Moreover, calculation of the energy required for the drying of product, the properties of the rehydration ratio, the food appearance changes, and the evaluation of the microstructure of food are crucial. Since the thermodynamic properties of truffle slices have not yet been reported, this study aims to establish a mathematical model to describe drying process of agriculture product, evaluate the effective moisture diffusion coefficient (Deff), determining the activation energy (Ea) to elucidate the thermodynamic characteristics, measure color characteristics, and rehydration ratio (RR) during the drying process of truffle slices. Truffle slices were dried in an infrared (IR) dryer at four temperatures of 50-80°C and two thicknesses of 0.5 and 1cm. The best model to describe the drying process of truffle slices was Midilli etal.'s model. The value of Deff, SEC, and RR were in the range of 3.06 × 10-8 to 2.48 × 10-7 m2/s, 79.68-191.271kWh/kg, and 5.99-7.49, respectively. The Deff of truffle slices increased with the above-mentioned parameters of the samples. The Ea obtained was 26.62-27.43kJ/mol. The results indicated that enthalpy and entropy decreased with increasing drying temperature, while Gibbs free energy improved. The enthalpy, entropy, and Gibbs free energy values changed between 24.48-25.28kJ/mol, -130.47 to -122.63 J/mol °K, and 63.97-70.17kJ/mol, respectively. In addition, the results of color attributes decreased with increasing temperature, while chroma oppositely increased.

Synergistic flame retardancy of aluminum diethylphosphinate and piperazine pyrophosphate/β‐cyclodextrin in polylactic acid

AbstractPolylactic acid has good biodegradability and processability, but its flammability and serious droplet characteristics limit its development and application. Therefore, developing safer flame‐retardant PLA materials is crucial. This research develops a novel flame‐retardant polylactic acid (PLA) material blend, utilizing aluminum diethylphosphinate (AlPi), piperazine pyrophosphate (PAPP), and β‐cyclodextrin. Optimal synergy occurs at a 5:1 PAPP/β‐CD mass ratio with 4 wt.% AlPi. This combination significantly reduces the heat release peak from 294.89 to 144.21 kW·m−2 and generates non‐combustible residues. The sample forms a stable, uniform carbon layer during combustion due to hydrogen bond crosslinking and Lewis acid–base reactions. The activation energy (Eα) is raised from 264.99 to 281.08 kJ·mol−1 between 312 and 402°C. Thus, an AlPi‐PAPP‐β‐CD based P‐C‐N composite flame retardant is investigated, offering a promising research direction for developing fire‐safe polylactic acid materials. This research may yield valuable insights for diverse applications.

Growth of L asparagine monohydrate doped potassium dihydrogen phosphate semiorganic crystals and its structural, thermal and optical properties

A novel semiorganic crystal is harvested by doping organic amino acid L asparagine monohydrate (LAM) with inorganic compound Potassium dihydrogen phosphate (KDP) by adopting slow evaporation method. Rietveld refinement of the XRD data was performed and the structural study exhibits single phase nature of the LAM doped KDP (LAM-KDP) crystals with a slight decrease in c-axis of the unit cell parameters. Other crystallographic parameters such as crystallite size and strain were also evaluated. The interaction of LAM with KDP was studied from FT-IR analysis by detecting functional groups. The constituting elements of the crystal were identified by energy dispersive X-ray (EDX) analysis. Etching study has been employed to study surface morphology of these crystals. From UV–vis transmittance data, optical band gap and different optical constants like Urbach energy, dielectric constants, electrical and optical conductivities were evaluated. Optical transparency of the LAM-KDP crystals is observed to increase. The third order nonlinear susceptibility χ(3) and nonlinear refractive index n2 of the grown crystals have been predicted using empirical Miller's rule. The value of χ(3) has increased from 1.87 × 10−13 esu to 4.29 × 10−13 esu due to LAM doping. Change in enthalpy (ΔH), change in Gibb's free energy (ΔG) and activation energy Ea during chemical reaction were calculated by thermogravimetric analysis (TGA). Thermal decomposition characteristics of the crystals were analyzed by differential scanning calorimetry (DSC). The high transparency of LAM-KDP crystals in the entire visible spectrum and larger values of nonlinear susceptibility χ(3) and nonlinear refractive index n2 make the synthesized crystal applicable for NLO and optoelectronic devices applications.

Enhanced dielectric and relaxation properties in Sm3+ doped KNNT ceramics

The effect of Sm3+ doping on KNNT ceramic were comprehensively investigated, specifically focusing on the phase, microstructure, and dielectric properties of (1-x)K0.5Na0.5Nb0.7Ta0.3O3·xSm2O3(x = 0–1.6 %) (denoted KNNT–xSm) ceramics. All ceramics have the perovskite structure, and doping with Sm3+ refined the ceramic grains, resulting in an increase in the room-temperature dielectric permittivity from 998 to 1568 at 100 kHz. In addition, the dielectric loss (tanδ) reduced from 0.026 to 0.019, relaxation diffusion coefficient(γ) increased from 1.35 to 1.88, and the activation energy (Ea) was 0.9–1.08eV. Thus, the dielectric and relaxation properties of KNNT ceramic can be significantly improved by Sm3+ doping.

CHIRAL SWITCHING CONTROL OF PHARMACEUTICAL SUBSTANCES

Objective: The aim of this study was to demonstrate that chiral switching should be recognized as a widespread phenomenon that extends beyond the production of pure enantiomeric drugs. Methods: To investigate the optical activity of substances from various chemical classes, enantiomers of chiral compounds (Sigma-Aldrich, USA) were chosen: valine and its racemic form (D-valine, L-valine, and racemic valine with optical purity ≥ 99%), L-ascorbic acid (content ≥ 99%), carbohydrates (D-glucose, D-galactose, L-galactose, contents ≥ 99.5%). Solutions were prepared using deuterium-depleted water (DDW–"light" water, D/H=4 ppm), natural deionized high-ohmic water (BD, D/H=140 ppm), and heavy water (99.9% D2O; Sigma-Aldrich). Optical activity was measured using the Atago POL-1/2 polarimeter. Results: One of the components in the racemic medication mixture can act as an inert agent, exhibit toxicity, or undergo undesirable biotransformation mechanisms, resulting in the formation of products with unknown properties. It has been established that a change in the deuterium/protium (D/H) ratio in water leads to a change in the equilibrium and kinetic characteristics of optically active compounds across various chemical classes, such as amino acids, carboxylic acids, and carbohydrates. An inequality was observed in the absolute values of the optical rotation of the L-and D-isomers of valine and galactose, depending on the D/H isotope ratio. The impact of chiral water clusters on optical rotation accounts for the sudden shift in the specific rotation of dilute solutions (less than 0.5%) of L-ascorbic acid in water, based on the D/H ratio. The influence of the isotopic composition of water was confirmed by studying the temperature-dependent mutarotation kinetics of D-glucose and L-and D-galactose in Arrhenius coordinates. The mutarotation process in natural high-resistivity water is characterized by an activation energy (Ea) of 40.8±1.4 kJ mol-1, while in deuterium-depleted water, Ea = 63.6±3.5 kJ mol-1. This results in a kinetic isotope effect for deuterium (KIED) of 1.6. Conclusion: Methodological approaches have been developed to control chiral switching based on the isotopic composition of water in vivo and in vitro. The study of changes in the optical activity of hierarchical structures in the human body, the influence of solvent properties on the mechanisms of optical rotation, as well as the use of KIED values, can be utilized to monitor various chiral transitions in vitro and living organisms.

Magnetic exchange interactions and non-Debye relaxation in spin-3/2 frustrated Kagomé magnet Co3V2O8

We report the experimental determination of the magnetic exchange parameter ( J/kB = 2.88 ± 0.02 K) for the Spin-3/2 ferromagnetic (FM) Kagomé lattice system: Co3V2O8 using the temperature dependence of dc-magnetic susceptibility χ(T) data by employing the fundamental Heisenberg linear chain model. Our results are quite consistent with the theoretically reported nearest neighbor dominant FM exchange coupling strength Jex−NN∼ 2.45 K. Five different magnetic phase transitions (6.2–11.2 K) and spin-flip transitions (9.6–7.7 kOe) have been probed using the ∂ ( χT )/ ∂T vs. T, heat capacity (CP -T) and differential isothermal magnetization curves. Among such sequence of transitions, the prominent ones being incommensurate antiferromagnetic (AFM) state at 11.2 K, commensurate AFM state at 8.8 K, and commensurate FM state across 6.2 K. All the successive magnetic phase transitions have been mapped onto a single H-T plane through which one can easily distinguish the above-mentioned different phases. The magnetic contribution of the CP -T near TN (11.2 K) has been analyzed using the power-law expression CM = A|T — TN|−α resulting in the critical exponent α = 0.18 ± 0.01 (0.15 ± 0.003) for T < TN (T > TN ), respectively for the Co3V2O8. It is interesting to note that non-Debye type dipole relaxation is quite prominent in Co3V2O8 and was evident from the Kohlrausch–Williams–Watts analysis of complex modulus and impedance spectra (0 ⩽β⩽ 1). Mott’s variable-range hopping of charge carriers process is evident through the resistivity analysis ( ρac -T −1/4 ) in the temperature range 275 ∘C–350 ∘C. Moreover, the frequency-dependent analysis of σac (ω) follows Jonscher’s power law yielding two distinct activation energies ( Ea∼ 0.37 and 2.29 eV) between the temperature range 39 ∘C–99 ∘C and 240 ∘C–321 ∘C.

Experimental Investigations on the Electrical Conductivity and Complex Dielectric Permittivity of ZnxMn1−xFe2O4 (x = 0 and 0.4) Ferrites in a Low-Frequency Field

Two samples of ZnxMn1−xFe2O4 (x = 0, sample A; and x = 0.4, sample B) were synthesized by the hydrothermal method. From complex impedance measurements in the range 100 Hz–2 MHz and for temperatures T between 30 and 130 °C, the barrier energy between localized states ΔErelax was determined for the first time in these samples. For sample B, a single value of ΔErelax was highlighted (0.221 eV), whilst, for sample A, two values were obtained (0.012 eV and 0.283 eV, below 85 °C and above 85 °C, respectively), associated with two zones of different conductivities. Using the Mott’s VRH model and the CBH model, we determined for the first time both the bandgap energy barrier (Wm) and the hopping (crossover) frequency (ωh), at various temperatures. The results show that, for sample A, Wm has a maximum equal to 0.72 eV at a temperature between 70 and 80 °C, whilst, for sample B, Wm has a minimum equal to 0.28 eV at a temperature of 60 °C, the results being in good agreement with the temperature dependence of the static conductivity σDC(T) of the samples. By evaluating σDC and eliminating the conduction losses, we identified, using a novel approach, a dielectric relaxation phenomenon in the samples, characterized by the activation energy EA,rel. At various temperatures, we determined EA,rel, which ranged from 0.195 eV to 0.77 eV. These results are important, as understanding these electrical properties is crucial to various applications, especially in technologies where temperature variation is significant.

Plasma catalysis. A study of the influence of oxysulfur, SOx• species through the degradation of sulfonated dyes by non-thermal plasma

This work studied the degradation reaction of sulfonated dyes, indigo carmine, phenol red, and their mixtures by non-thermal plasma (NTP). Interestingly, the degradation rate constant showed a faster process and lower activation energy (Ea) for the dye mixtures than for the degradation reaction of the individual dyes. This unexpected result opened up new opportunities for understanding plasma chemistry and the interaction between reactive species formed by the plasma and the target molecule. As no catalyst or chemical additive was added to the reactor, the decrease in Ea came from a self-synergistic effect (SSE), through the dye molecules fragmentation, which resulted in plasma catalysis. The hypothesis proposed in this work is that oxysulfur (SOx) species are formed by the desulfonation reaction of dyes. The sulfonic groups (SO3) present in the chemical structures of dyes can function as precursors for forming several SOx•– species. Studies based on oxygenated sulfonated species such as SO3•–, SO4•– and SO5•– have been widely applied in advanced oxidative and reductive processes due to their satisfactory efficiency and low cost. Among them, SO4•– is the key reactive species with the best performance in the degradation of pollutants due to its high oxidation potential (E° = 2.60 V). In addition, it is an alternative source of HO• in aqueous media, improving the oxidation reaction. In order to elucidate the SSE, the kinetic process was followed by UV–Vis analysis, and the reactive species, such as alkyl, hydroxyl, and oxy-sulfur radicals were identified by Electron Paramagnetic Resonance. The by-products of the NTP degradation reaction were analyzed by ultrafast liquid chromatography coupled with a mass spectrometer, and a fragmentation route was proposed.

Conversion of ammonia to hydrogen in the microwave reactor system using Mo@Alumina catalysts with the promotion of rare-earth and alkaline earth elements

In this study, microwave assisted ammonia decomposition reaction to produce high purity hydrogen over γ-Al2O3 supported molybdenum based catalysts were investigated and the effects of various promoters, rare-earth (lanthanum, cerium) and alkaline-earth (calcium and barium) elements on the catalytic activity were studied. Ammonia conversions of over 94 % were obtained over the unpromoted catalysts above 350 °C at a flow rate of 60 ml/min of pure ammonia. The overall hydrogen production rate per gram of catalyst was found to be 72.86 mmol/min.gcat with for 30 wt% Mo loaded unpromoted catalyst at 350 °C. The apparent activation energy (Ea) values for these catalysts were found to be around 85 kJ/mol. Among the promoters, Ba and Ce gave better performance below 350 °C than Ca and La and the optimum loading was found to be 4 wt% for them. Neither molybdenum nitride nor molybdenum carbide were detected in the spent form of the catalysts.