First-order Reaction Model Research Articles

Reaction kinetics of an Mg/CO2 power system for Mars exploration

This study investigates the heterogeneous and homogeneous reaction characteristics of the Mg/CO2 and coexisting Mg/CO systems using thermal analysis kinetics and quantum chemical calculation methods, respectively. The corresponding kinetic parameters are subsequently obtained using detailed theoretical calculations. The Mg/CO2 power system is a very promising propulsion mode for future Mars exploration due to the abundant carbon dioxide resources in the atmosphere of Mars. At present, much of the research on Mg combustion in CO2 has focused on the ignition and combustion characteristics at the macro level and few databases exist for microreaction characteristics. Three sets of thermal analysis experiments at different temperature rise rates are carried out in CO2 and CO atmospheres to extract the kinetic parameters. The results show that the heterogeneous reactions between Mg and CO2/CO are controlled by the first-order reaction model (F1), that is, by linear kinetics. There are two intermediate transition states in the homogeneous reaction between Mg and CO2. However, a suitable transition state structure is not observed in the homogeneous reaction between Mg and CO. The total energy barrier of this reaction is significantly higher than that of the Mg/CO2 reaction system. In addition, the rate constant of the Mg/CO2 homogeneous reaction is 10–17 orders of magnitude higher than that of the Mg/CO homogeneous reaction in the temperature range between the boiling point of Mg and 2000 K. The conclusions of this study are valuable for the combustion models of Mg/CO2 systems, which are expected to contribute to the structural design and optimisation of Mg/CO2 rocket engines or burners for Mars exploration.

Reaction Kinetics of Levulinic Acid Synthesis from Glucose Using Bronsted Acid Catalyst

Glucose is one of the primary derivative products from lignocellulosic biomass, which is abundantly available. Glucose has excellent potential to be converted into valuable compounds such as ethanol, sorbitol, gluconic acid, and levulinic acid (LA). Levulinic acid is an exceptionally promising green platform chemical. It comprises two functional groups, ketone and carboxylate, acting as highly reactive electrophiles for a nucleophilic attack. Therefore, it has extensive applications, including fuel additives, raw materials for the pharmaceutical industry, and cosmetics. This study reports the reaction kinetics of LA synthesis from glucose catalyzed by hydrochloric acid (HCl), a Bronsted acid, that was carried out under a wide range of operating conditions; i.e. the temperature of 140–180 °C, catalyst concentration of 0.5–1.5 M, and initial glucose concentration of 0.1–0.5 M. The highest LA yield of 48.34 % was able to be obtained from an initial glucose concentration of 0.1 M and by using 1 M HCl at 180 °C. The experimental results show that the Bronsted acid-catalyzed reaction pathway consists of glucose decomposition to levoglucosan (LG), conversion of LG to 5-hydroxymethylfurfural (HMF), and rehydration of HMF to LA. The experimental data yields a good fitting by assuming a first-order reaction model. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Kinetic Analysis of Pyrolysis and Thermo-Oxidative Decomposition of Tennis String Nylon Wastes.

Thermal degradation of nylon-6 tennis string nylon wastes in inert nitrogen and air atmospheres was investigated by means of multiple heating-rate thermogravimetric analyses. The results obtained under the heating rates of 5–20 K/min are compared in terms of degradation feature and specific temperature for two atmospheres. Using nonisothermal data, kinetic analysis was thoroughly conducted using various isoconversional model-free methods, including Starink, Madhusudanan–Krishnan–Ninan, Tang, Coats–Redfern, and Flynn–Wall–Ozawa methods. With these kinetic analysis methods, the activation energy over the entire degradation process was successfully calculated. By means of the model-fitting master-plots method, the first-order chemical reaction model was determined to be the most appropriate mechanism function for describing pyrolysis and oxidative thermal degradation of nylon-6 waste. Using kinetic parameters, satisfactory matching against experimental data resulted using the Coats–Redfern method for both cases. Furthermore, thermodynamic parameters such as changes in entropy, enthalpy, and Gibbs free energy during thermal degradation processes were evaluated.

Catalytic co-pyrolysis of wet-torrefied bamboo sawdust and plastic over the zeolite HY: Synergism and kinetics

In this study, the catalytic co-pyrolysis (CCP) of wet-torrefied bamboo sawdust (TB) and linear low-density polyethylene (LLDPE) over zeolites was carried out using the thermogravimetric analyzer. The analysis was carried out at four different heating rates (5–40 °C min−1) and under an inert (Ar) atmosphere. Four degradation stages were observed in the CCP of TB and LLDPE blends, the first stage being moisture removal. The peak decomposition temperature of catalytic pyrolysis (CP) of LLDPE over FAU was reduced by 251 °C as compared to that over HZSM-5 and the enhancement can be attributed to the topology of HY. The activation energies were calculated using isoconversional models: Kissinger–Akahira–Sunose model (KAS), Ozawa–Flynn–Wall model (OFW), and Friedman model (FM). The average activation energies (Eα) of the blends TBL3:1, TBL1:1, and TBL1:3 (TBL: Blend of torrefied biomass and LLDPE) were 171, 128, and 117 kJ mol−1, respectively, using the KAS model. The Eα of the blends was much lower as compared to that of TB, indicating a clear synergism. A multistep mechanism was observed in both CP of individual samples and CCP of blends, as analyzed by Criado's master plot. For example, the CCP of TBL1:3 followed geometric (volume) contraction (R3) and first-order reaction models at low and high conversions, respectively.

Rice husk and rice straw torrefaction: Properties and pyrolysis kinetics of raw and torrefied biomass

Torrefaction is an effective pretreatment process of biomass to enhance energy density and reduce moisture and oxygen contents. The kinetics analysis is important to estimate the torrefaction efficiency and understand the thermal degradation characteristics of torrefied biomass. In this study, the pyrolysis kinetics (Flynn–Wall–Ozawa method, Kissinger–Akahira–Sunose​ method, and Starink’s method) of rice husk (RH), rice straw (RS), and their torrefied solid products were investigated under different heating rates. The results demonstrated that the increase of torrefaction temperature decreased the content of hemicellulose and cellulose. TG-FTIR and TG/DTG curves of RH and RS showed a right shift trend after torrefaction. The average activation energy calculated was 149.79 and 161.76 kJ mol −1 for RH and RS pyrolysis. The activation energy of torrefied RH and RS showed an increasing trend with torrefaction temperature. According to the change of activation energy, the pyrolysis model of RH and RS was predicted by Z ( α ) master plots and compensation effect, respectively. Torrefaction could convert the First-order reaction model (F1) to nucleation and growth model (An) gradually for RH, and raise the reaction order of the pyrolysis reaction for RS. • Rice straw was more sensitive to torrefaction temperature than rice husk. • The average E a were 150 and 162 kJ mol -1 for rice husk and rice straw pyrolysis. • The activation energy of torrefied biomass was higher than that of raw biomass. • Torrefaction raised the pyrolysis reaction order of rice straw. • Pyrolysis of torrefied rice husk was dominated by nucleation and growth model.

Time-dependent phase quantification and local structure analysis of hydroxide-activated slag via X-ray total scattering and molecular modeling

Here, an approach to quantify the amorphous-to-disordered/crystalline transformation occurring in NaOH-activated ground granulated blast-furnace slag (GGBS) is outlined that combines atomistic modeling with in situ pair distribution function (PDF) analysis. Firstly, by using force-field molecular dynamics (MD) simulations, a detailed structural representation is generated for the amorphous GGBS that is in agreement with experimental X-ray scattering data. Use of this structural representation along with literature-derived structures for the reaction products allows for real space X-ray PDF refinement of the alkaline activation of GGBS, resulting in the quantification of all phases and the degree of reaction (DOR) as a function of reaction time. All phases and the DOR are seen to approximately follow a logarithmic-type time-dependent behavior up to 5 months, while at the early age (up to 11 h), the DOR is accurately captured by a modified pseudo-single step first-order reaction model. Lastly, the evolution of DOR is found to agree with several other complementary in situ data containing quantitative reaction information, including isothermal conduction calorimetry, Fourier transform infrared spectroscopy, and quasi-elastic neutron scattering.

Sustained A1 Adenosine Receptor Antagonist Drug Release from Nanoparticles Functionalized by a Neural Tracing Protein.

Respiratory dysfunction is a major cause of death in people with spinal cord injury (SCI). A remaining unsolved problem in treating SCI is the intolerable side effects of the drugs to patients. In a significant departure from conventional targeted nanotherapeutics to overcome the blood-brain barrier (BBB), this work pursues a drug-delivery approach that uses neural tracing retrograde transport proteins to bypass the BBB and deliver an adenosine A1 receptor antagonist drug, 1,3-dipropyl-8-cyclopentyl xanthine, exclusively to the respiratory motoneurons in the spinal cord and the brainstem. A single intradiaphragmatic injection at one thousandth of the native drug dosage induces prolonged respiratory recovery in a hemisection animal model. To translate the discovery into new treatments for respiratory dysfunction, we carry out this study to characterize the purity and quality of synthesis, stability, and drug-release properties of the neural tracing protein (wheat germ agglutinin chemically conjugated to horseradish peroxidase)-coupled nanoconjugate. We show that the batch-to-batch particle size and drug dosage variations are less than 10%. We evaluate the nanoconjugate size against the spatial constraints imposed by transsynaptic transport from pre to postsynaptic neurons. We determine that the nanoconjugate formulation is capable of sustained drug release lasting for days at physiologic pH, a prerequisite for long-distance transport of the drug from the diaphragm muscle to the brainstem. We model the drug-release profiles using a first-order reaction model and the Noyes-Whitney diffusion model. We confirm via biological electron microscopy that the nanoconjugate particles do not accumulate in the tissues at the injection site. We define the nanoconjugate storage conditions after monitoring the solution dispersion stability under various conditions for 4 months. This study supports further development of neural tracing protein-enabled nanotherapeutics for treating respiratory problems associated with SCI.

Degradation kinetic modeling of bioactive compounds and enzyme activity in wheat germ during stabilization

The stability of α-tocopherol (α-toco), total phenolic content (TPC), antioxidant capacity (DPPH and ABTS•+ radical scavenging capacity assays), activity of lipase (LA) and lipoxygenase (LOX) were investigated during stabilization of raw wheat germ with an industrial convection oven at different temperatures (120, 130, 140, 150 and 160 °C) and times (0, 5, 10, 15, and 20 min). Degradation kinetics were best fitted by first-order reaction models for all measured parameters with high R2 and low root mean square (RMSE) values, except ABTSassay which was modeled accurately with the second-order model. The temperature dependence of rate constants for all degradation kinetic parameters were calculated according to the Arrhenius, Eyring-Polanyi, and Ball models. Following the Arrhenius and Eyring models, activation energy (Ea) ranged from 20.69 to 55.04 kJ mol−1, activation enthalpy (ΔH*) ranged from 20.44 to 51.61 kJ mol−1 whereas the activation entropy (ΔS*) varied between −179.313 and −213.447 J mol−1K−1 for the stabilized germ, respectively. It can be concluded that heat treatment at 120 °C for 20 min was the best processing conditions to stabilize the raw germ to preserve its valuable bioactive compounds, antioxidant activity and the models can be useful to design different heat treatment conditions.

Flash Pyrolysis Kinetics of Extracted Lignocellulosic Biomass Components

Biomass is a complex material mainly composed of the three lignocellulosic components: cellulose, hemicellulose and lignin. The different molecular structures of the individual components result in various decomposition mechanisms during the pyrolysis process. To understand the underlying reactions in more detail, the individual components can be extracted from the biomass and can then be investigated separately. In this work, the pyrolysis kinetics of extracted and purified cellulose, hemicellulose and lignin are examined experimentally in a small-scale fluidized bed reactor (FBR) under N2 pyrolysis conditions. The FBR provides high particle heating rates (approx. 104 K/s) at medium temperatures (573–973 K) with unlimited reaction time and thus complements typically used thermogravimetric analyzers (TGA, low heating rate) and drop tube reactors (high temperature and heating rate). Based on the time-dependent gas concentrations of 22 species, the release rates of these species as well as the overall rate of volatiles released are calculated. A single first-order (SFOR) reaction model and a 2-step model combined with Arrhenius kinetics are calibrated for all three components individually. Considering FBR and additional TGA experiments, different reaction regimes with different activation energies could be identified. By using dimensionless pyrolysis numbers, limits due to reaction kinetics and heat transfer could be determined. The evaluation of the overall model performance revealed model predictions within the ±2σ standard deviation band for cellulose and hemicellulose. For lignin, only the 2-step model gave satisfying results. Modifications to the SFOR model (yield restriction to primary pyrolysis peak or the assumption of distributed reactivity) were found to be promising approaches for the description of flash pyrolysis behavior, which will be further investigated in the future.

Winter nocturnal warming affects the freeze-thaw frequency, soil aggregate distribution, and the contents and decomposability of C and N in paddy fields

Climate warming is expected to cause greater increases in nocturnal temperatures than daytime temperatures, thereby altering freeze-thaw cycles. Although the importance of freeze-thaw cycles in regulating soil aggregate stability and nutrient availability has attracted increasing attention, little is known about how winter nocturnal warming modulates freeze-thaw frequency, soil aggregate distribution, or the contents and mineralization of soil organic carbon (SOC) and total nitrogen (TN) in paddy fields. The nocturnal soil temperature in the upper 0–2 cm layer in a paddy field was elevated by approximately 2 °C using a passive nocturnal warming method during winter. An anaerobic experiment with a first-order reaction model was conducted to measure the C decomposition (C0) and N mineralization (N0) potentials in bulk soil and four soil aggregate fractions. Winter nocturnal warming significantly decreased freeze-thaw frequency and affected soil aggregate distribution and SOC and TN contents in <0.25 mm aggregate. Both SOC and TN fractions were significantly increased in the 0.25–1 mm aggregate but decreased in the >2 mm aggregate due to winter nocturnal warming. Winter nocturnal warming did not affect C0, N0, C0/SOC, and N0/TN in bulk soil. However, it decreased C0 and C0/SOC in all aggregates except the 0.25–1 mm aggregate, and increased N0 and N0/TN in all aggregates except the >2 mm aggregate. In the nocturnal warming treatment, the highest C0 and N0 values were found in the <0.25 mm aggregate, but only the N0 in the <0.25 mm aggregate was significantly larger than that in the other three soil aggregates. Our study indicated that winter nocturnal warming would reduce the freeze-thaw frequency and change C and N distributions in soil aggregates, resulting in increased soil N availability in the subsequent rice growth season.

Study of selective hydrogenation of biodiesel in a DBD plasma reactor

In order to achieve the selective hydrogenation of biodiesel at room temperature and under normal pressure, we researched the upgrading of soybean biodiesel using a dielectric-barrier discharge (DBD) reaction system. Using Raney-Ni as the hydrogenation catalyst, the effects of the operating parameters on the hydrogenation depth and the selectivity of biodiesel were systematically analyzed. The results show that the polyunsaturated components in soybean methyl ester were reduced by 57.04%, and that the polyunsaturated components were hydrogenated to monounsaturated components with a selectivity of 77.75%. Based on the gas chromatography and mass spectrometry (GC-MS) test results, we established a kinetic model for biodiesel hydrogenation. A comparison of the calculated and experimental results shows that the hydrogenation of the biodiesel can be described by a quasi first-order reaction model. The calculated reaction rate constants indicate that under DBD plasma reaction conditions, the hydrogenation of biodiesel has high selectivity for the formation of monounsaturated components.

A new biodiesel production by water addition to supercritical tert-butyl methyl ether using a plug flow reactor

The water addition to supercritical tert-butyl methyl ether for continuous biodiesel production from rapeseed oil has been carried out to promote an essential enhancement of biodiesel yield. We developed a new biodiesel production by supercritical tert-butyl methyl ether with water and evaluated process variables influence using response surface methodology to obtain an optimum condition. We found that the optimum condition was at water addition of 25 wt%, temperature of 300 °C, and pressure of 20 MPa at space time of 30 min to achieve 77.39 wt% of biodiesel yield. In addition, the reaction rate constants were determined by first-order reaction model. We suggested that water addition to the supercritical tert-butyl methyl ether accelerates reaction rate and diminishes activation energy since the water acts as a catalyst for the reaction. The thermodynamic parameters were calculated using Eyring-Polanyi equation based on the transition state theory. We found that the supercritical reaction was endothermic, endergonic, and non-spontaneous.

Kinetics modeling, thermodynamics and thermal performance assessments of pyrolytic decomposition of Moringa oleifera husk and Delonix regia pod

A non-isothermal decomposition of Moringa oleifera husk and Delonix regia seed pod was carried out in an N2 pyrolytic condition with the primary objective of undertaking the kinetics modeling, thermodynamics and thermal performance analyses of the identified samples. Three different isoconversional models, namely, differential Friedman, Flynn–Wall–Ozawa, and Starink techniques were utilized for the deduction of the kinetics data. The thermodynamic parameters were deduced from the kinetic data based on a first-order chemical reaction model. In the kinetics study, a strong correlation (R2 > 0.9) was observed throughout the conversion range for all the kinetic models. The activation energy profiles showed two distinctive regions. In the first region, the average activation energy values were relatively higher—a typical example is in the Flynn–Wall–Ozawa technique—MH (199 kJ/mol) and RP (194 kJ/mol), while in the second region, MH (292 kJ/mol) and RP (234 kJ/mol). It was also demonstrated that the thermal process for the samples experienced endothermic reactions thought the conversion range. In summary, both the kinetic and thermodynamic parameters vary significantly with conversion—underscoring the complexity associated with the thermal conversion of lignocellulosic biomass samples.

Thermochemical Conversion Behavior of Turkish Lignite/Poppy Capsule Pulp Blends in N2 and CO2 Atmospheres

In this study, Thermogravimetric Analyzer coupled with Fourier Transform Infrared Spectroscopy (TGA-FTIR) was used for the determination of the thermochemical conversion reactivity of two different types of Turkish lignite coal (Tunçbilek and Orhaneli-Gümüşpınar) and poppy capsule pulp (PCP) mixtures under pyrolysis conditions at nitrogen (N2) and carbon dioxide (CO2) atmospheres. Activation energies (Ea) and pre-exponential factors (A) were determined according to Coats-Redfern method and first-order reaction model. In CO2 atmosphere, all samples exhibited an extra weight loss around 800 - 850 ° C, different from the N2 atmosphere, due to the reactive nature of CO2 during thermal decomposition. FTIR analysis confirmed this finding, at high temperatures CO formation were observed in the CO2 atmosphere. In all mixtures, the third zone experimental decomposition temperature is lower than that obtained theoretically in N2 atmosphere, showing that there might a synergistic interaction between the PCP and the lignite samples. The Ea of PCP/Tunçbilek lignite mixtures are smaller than the Ea of their parent components indicating synergy in N2 and CO2 atmospheres. However, initial and maximum decomposition temperatures for the parent components remain unchanged for these mixtures. Moreover, especially at temperatures higher than 600 °C, the Ea for biomass/lignite mixtures found lower than the theoretical values, due to the possible synergistic interactions between PCP and coal samples. According to FTIR analysis, CO, CH4, CHn and ether/amine components were detected. Gaseous pyrolysis product compositions were highly dependent on temperature, and gas species formation was consistent with the weight loss of samples.

Agar-stabilized sulfidated microscale zero-valent iron: Its stability and performance in chromate reduction

Sulfidated microscale zero-valent iron (SmZVI) attracts much attention recently in remediation of contaminated groundwater, but whether polymer coating on SmZVI would impact on its reactivity and capacity is yet to be understood. In this work, SmZVI was prepared by milling mZVI with elemental sulfur, and its stability in agar solution was evaluated. The impact of polymer coating on SmZVI grains’ capacity and reactivity for chromate reduction was then examined. Experimental results indicated that SmZVI having the best overall performance was attained by grinding mZVI with elemental sulfur at 0.05 S/Fe molar ratio for 10 h. SmZVI’s stability can be substantially improved if dispersed in 2.0 g/L agar solution. Existence of agar films on the SmZVI grain (A-SmZVI) lowered the material’s capacity for chromate reduction by 56%, and the associated reaction kinetics by 70.4%, as estimated by pseudo first-order reaction model using the early-stage experimental data. Analysis of XPS spectra of A-SmZVI post reaction with chromate indicated that multiple reductive species including Fe0, Fe(II), FeS, and S(-II) may have jointly participated in the redox reaction taking place on the A-SmZVI-water interface. Fitting of XPS data supported that S(-II) was oxidized to SO42-, S2O32-, and S0, in order of decreasing surface concentration.

Kinetics of propane cracking and position-specific isotope fractionation: Insights into the origins of natural gases

Position-specific isotope analysis (PSIA) of propane can provide novel and valuable information to constrain the origin and history of natural gases. We conducted a systematic experimental study to determine the kinetics of propane pyrolysis, including bulk and position-specific carbon and hydrogen isotope fractionation of propane at 415 – 465 °C. As the dominant gaseous products, the yields of CH4 and C2H6 increased with increasing C3H8 consumption. A significant amount of aromatic residues (C/H: ∼1) was generated, which was comparable to the yields of CH4 and C2H6. Position-specific δ13C values of propane increased by up to 8.3 and 8.8‰ at the center and terminal positions respectively, while δ2Hcenter and δ2Hterminal increased by 110 and 131‰. An activation energy (Ea) of 69.9 (±29.1) kcal/mol and frequency factor (A) of 3.1 × 1015 (±7.9 × 108) s−1 were obtained based on a first-order reaction model. Using the average kinetic parameters from this study and previous studies on wet-gas cracking, propane cracking starts above 215 (±10.5) oC at a geological heating rate of 5 °C/m.y., corresponding to Easy Ro of 2.31%. An Arrhenius plot of kinetic isotope fractionation indicates both central C and H of propane show larger isotope fractionations compared with those at the terminal position in natural reservoirs. Position-specific (PS) isotopic fractionation factors (k*/k) at 215 °C were estimated as 0.983 and 0.987 for δ13Ccenter and δ13Cterminal, and 0.815 and 0.838 for δ2Hcenter and δ2Hterminal, respectively. PS isotopic compositions of natural propane in the ΔCc-t - ΔHc-t diagram may serve as a diagnostic indicator for the origins (kerogen vs. oil) and degradation (thermal cracking vs. biodegradation) of natural gases in sedimentary basins.

Refinement of the gradient method for the estimation of natural source zone depletion at petroleum contaminated sites

Rates of natural source zone depletion (NSZD) are increasingly being used to aid remedial decision making and light non-aqueous phase liquid (LNAPL) longevity estimates at petroleum release sites. Current NSZD estimate methods, based on analyses of carbon dioxide (CO2) and oxygen (O2) soil-gas concentration gradients (“gradient method”) assume linear concentration profiles with depth. This assumption can underestimate the concentration gradients especially above LNAPL sources that are typically characterized by curvilinear or semi-curvilinear O2 and CO2 concentration profiles. In this work, we proposed a new method that relies on calculating the O2 and CO2 concentration gradient using a first-order reaction model. The method requires an estimate of the diffusive reaction length that can be easily derived from soil-gas concentration data. A simple step-by-step guide for applying the new method is provided. Nomographs were also developed to facilitate method application. Application of the nomographs using field data from published literature showed that NSZD rates could be underestimated by nearly an order of magnitude if reactivity in the vadose zone is not accounted for. The new method helps refine NSZD rates estimation and improve risk-based decision making at certain petroleum contaminated sites.

The Degradation Kinetics Model of Apricot during HA Drying

The browning index and carotenoid studies were carried out durning HA drying process. The effect s different HA drying temperature(40 °C, 50 °C, 60 °C, 40 °C (10 h)→60 °C(end), 50 °C(10 h)→60 °C(end), 40 °C(10 h)→50 °C(10 h)→60 °C(end)) and air velocities(2 m/s, 3 m/s, 4 m/s) on colour and carotenoid of apricot were studied. Meanwhile a HA drying degradation model was established. The test showed that the BI value increased and carotenoid content reduced with the passing of the processing time during the drying process. The browning action durning the HA drying process was fit according to the zero and first-order reaction model. Furthermore, the activation energy was obtained by the Arrhenius equation, which was 17.59 kJ/mol. This research provided the theoretical basis for the quality control of dried apricot slice.

Synthesis, characterization and optical properties of Co2+ doped PbS nanocrystals

We present theoretical and experimental results in PbS nanocrystalline thin films systematically doped with Co2+ ions utilizing the green Chemical Bath Deposition technique at ∼90 °C. All growth parameters are kept constant by systematically adding different solution's volume containing the Co2+ ions. We apply the first-order chemical kinetic reaction model to investigate some physicochemical parameters. The crystalline phase is investigated by X-ray Diffraction, identifying the cubic phase in all samples. After dopping the PbS sample (PbSCo2+), the grain size decreases from ∼29.7 nm to ∼15.7 nm and dislocation density increases from ∼3.4 lines m−2 to ∼6.4 lines m−2. The absorbance and bandgap studies conducted in the Vis-UV region show the typical 1Se→1Sh and 1Se→1Ph electronic transitions and the excitonic bands located at ∼1.5 eV and ∼1.8 eV due to higher energy transitions from 1Dh→1De, and 1Fh→1Fe respectively in nanocrystals. Finally, we apply three theoretical models to elucidate the correlation associated with the crystal radius and the bandgap energy (Eg).

Drying characteristics and bioactivity evolution of Platycodon grandiflorum as affected by different microwave combined drying methods

Abstract This study was to investigate the effect of different drying methods on the drying kinetics, physical properties, and bioactivity of Platycodon grandiflorum (PG). Four drying methods were employed to conduct the dehydrated process, namely, hot air drying (AD), vacuum drying (VD), microwave hot airflow rolling-bed drying (MHARD), and pulse-spouted microwave vacuum drying (PSMVD). PSMVD showed the highest drying rate among four drying methods based on the result of fitting first-order reaction model. And PSMVD-dried product showed higher rehydration ratio and better mechanical properties, suggesting a better rehydration characteristic. In addition, considering the content of Platycodin D, PSMVD is a promising drying technology for the dehydration of PG.