Internal Diffusion Mechanism Research Articles

Insights into pyrolysis of ginger via TG-FTIR and Py-GC/MS analyses: Thermochemical behaviors, kinetics, evolved gas, and products

One of the key leverages for lessening the heavy reliance on fossil fuels is the conversion of non-food biomass into bioenergy and high value-added products. This study aimed to quantify the bioenergetic, emission, and biochar performances of ginger (Zb) pyrolysis. The main pyrolysis stage of Zb occurred in the range of 127–540 °C, releasing gaseous products, primarily CO2, in significant quantities between 200–600 °C. The dominant pyrolysis products were CO functional groups, accounting for 52.18–62.68% of the total. As the temperature rose, the primary pyrolysis products transitioned from ketones to benzene and its derivatives. Through the application of three model-free and three model-fitting methods, the most suitable mechanism identified for the main pyrolysis stage (0.2 < conversion degree < 0.7) was the three-dimensional diffusion (spherically symmetric) function, serving as an internal diffusion mechanism. Results of this study provide impactful and actionable insights into control over the generation of bioenergy potential, gas emissions, and value-added products via the Zb pyrolysis.

Phosphate Removal by Ca-Modified Magnetic Sludge Biochar Prepared by a One-Step Hydrothermal Method

The problem of phosphorus pollution and its resource utilization has been a source of general concern. The preparation of green, renewable, and non-secondary pollution adsorbents has become a research direction. In this paper, a one-step hydrothermal preparation method of Ca-modified magnetic sludge biochar (Ca-MSBC) is used for enhancing phosphate removal. The results show that the adsorption rate of phosphate by Ca-MSBC is mainly controlled by chemisorption but is also related to physical adsorption and an internal diffusion mechanism. The maximum phosphorus adsorption capacity of Ca-MSBC was 89.25 mg g−1 at 343 K (initial phosphate concentration 500 mg L−1). After nine cycles of adsorption experiments, the adsorption capacity of 70.16 mg g−1 was still high. In addition, coexisting ions Cl−, NO3−, SO42−, and CO32− have no significant effect on the adsorption properties of phosphate. XRD, FT-IR, VSM, XPS, and N2 adsorption/desorption isotherms showed that the mechanism of phosphate removal from water by Ca-MSBC was mainly the chemical precipitation reaction of phosphate and calcium. The results of this study indicate that Ca-MSBC has potential application and environmental value as a solid waste recycling material for environmental remediation.

Influence of composition on the internal diffusion mechanism of pectin–starch gel beads

AbstractPectin is a hydrocolloid commonly used as a wall material for encapsulation, meantime using a filler such as starch can improve the retention in the matrix and control the release in specific places. Formulations of pectin and starch were evaluated for bead production by ionic gelation technique using dripping and jet cutter methods. In addition, beads were dried in a fluidized bed and rotating drum at 50°C. The mean diameter, mechanical strength, yield, moisture content, the morphology of wet and dry beads, and rehydration behavior were evaluated. Furthermore, the pomegranate extract (PE) encapsulation efficiency and release in water were measured. The beads with 2.85% solids content of which 70% are pectin and 30%, waxy corn starch proved to be technologically viable and were satisfactorily dried in a fluidized bed, while on a rotating drum, drying was not efficient. Compared with pure pectin, the pectin–starch beads showed a spherical shape, smoother and more homogeneous with greater mechanical strength and greater water absorption capacity after drying in a fluidized bed. The conventional encapsulation of PE added to biopolymer solutions showed low efficiency (4.7%–43.7%) and the release velocity was higher for drip beads (~70%).

Sorption of arsenic by composts and biochars derived from the organic fraction of municipal solid wastes: Kinetic, isotherm and oral bioaccessibility study

The historic contamination of water and soils by arsenic (As) is an extremely alarming environmental and public health issue worldwide. This study investigated the relationship between As sorption and physicochemical properties of composts and biochars derived from the organic fraction of municipal solid wastes (OFMSW) towards the development of promising sorbents with value-added solid wastes management solutions. The sorbents were characterized and their effectiveness on the As sorption was tested. Several isothermal and kinetic sorption models were used for the prediction of sorption. Composts did not show promising sorption capacities, and in some cases, the As immobilization was practically null. In contrast, biochars achieved higher sorption performance, and the experimental data fitted well on Dubinin-Rabushkevich and Langmuir models, with higher R2 values. The maximum sorption capacities of BC700 estimated by such models were 6.495 and 170.252 mg g−1, respectively, whereas those of BC500 estimated by D-R and Langmuir models were only 0.066 and 0.070 mg g−1, respectively. In sorption kinetics, As was retained onto biochars at a faster first stage, reaching equilibrium after approximately 1 h and 2 h for initial concentrations of 10 and 100 mg L−1. The pseudo-second-order, Ritchie's second-order, Ritchie's, and Elovich models more adequately described the sorption kinetics of As onto biochars with high R2 values. Overall, the complexation and precipitation were predominant mechanisms for As sorption by OFMSW-derived biochars. Furthermore, the mathematical models indicated contributions arise from physisorption and external and internal diffusion mechanisms. Although BC700 can immobilize large As amounts, the gastric phase of the oral bioaccessibility test revealed more than 80% of the sorbed As could be released under conditions similar to a human stomach (pH~1.2). Such conclusions have given important insights about the refining of effective and eco-friendly remediation technologies for the management and rehabilitation of As-contaminated soil and water, particularly in developing countries.

Obtaining food dyes of the anthocyanin class from grape pomace: the mechanism of the extraction process

In order to determine the mechanism and factors of optimization of the process of extraction of anthocyanin dyes from crushed grape pomace, the kinetics of the process at the temperatures of 14 and 800C was studied using aqueous and aqueous-ethanolic solutions under conditions of intensive mixing. For the theoretical description of the kinetic data, a model of the extraction process from a porous solid body was used under conditions of relatively small values of constrained diffusion coefficients. It was established that the experimental data are well described by the equation for the internal diffusion mechanism of the extraction process. It was shown that the experimental data are also well described by the Yander equation proposed for modeling diffusion-controlled heterogeneous processes with constant parameters of the diffusion. It was concluded that both equations are similar to each other and differ only in the coefficients at the degrees of transformation, which is due to the assumptions that were made in their derivation. The conclusion about the nature of the limiting stage of the process of extraction of anthocyanin dyes was confirmed by calculations of the apparent activation energy, the value of which was 14.0 kJ mol–1. The obtained data allowed determining the factors of optimization of anthocyanin extraction process from grape pomace: particle size of raw materials, anthocyanin concentration in solution, temperature, ethanol content in solution, solution acidity, degree of plant cell destruction and ultrasonic treatment.

Empirical models of kinetic rate for river treatment analysis of cellulosic materials

The utilisation of cellulosic fibre in removing organic and nutrients pollutants in polluted river is becoming an increasingly popular alternative cost-effective and sustainable option. However, the related empirical models are yet to be fully comprehensive to study the adsorption mechanisms of natural adsorbents. This paper discusses developed empirical model used to estimate the mass transfer of organic pollutants into two natural fibres – coconut fibres and oil palm fibres to filter pollutant molecules in water. An empirical model was developed to estimate the mass transfer of organic pollutants in water onto the fibres in a fabricated physical model. The mass transfer relations were derived based on the substrates loading rates and the predicted accumulation rates of substrates in fibres along with the percentage of outflows. Matching empirical results with experimental results showed that the modified model was able to accurately predict the mass transfer rate. The higher adsorption rate of CF (91.02% COD) depicted greater global mass transfer rate (1.3696 d−1) than OPF (82.35% COD) which only had 1.2768 d−1 of global mass transfer rate in 3% of COD outflow. The contribution of internal diffusion mechanism was significant due to the physical (porosity) and chemical (lignin and cellulosic content) characteristics of both CF and OPF. The study concluded that the performance of biological adsorption using CF and OPF is promising.

Validity of Egyptian Na‐montmorillonite for adsorption of Pb2+, Cd2+ and Ni2+ under acidic conditions: characterization, isotherm, kinetics, thermodynamics and application study

AbstractThis study investigated the applicability of natural Egyptian Na‐montmorillonite (Na‐MMT) to remove Pb2+, Cd2+ and Ni2+ under acidic conditions that mimic industrial wastewater acidity. Cation exchange capacity of Na‐MMT was found 91 meq/100 g and the specific surface area 42 m2 g−1. The adsorbent was characterized using X‐ray fluorescence, scanning electron micrograph that showed significant morphological changes after adsorption and Fourier transform infrared spectroscopy, which confirmed that the adsorption occurred mainly in the lattice region. Removal efficiency was evaluated as a function of pH, contact time, initial concentration, and adsorbent mass. Acidic pH value was chosen for the following experiments. Langmuir and Freundlich isotherm models were applied. Freundlich model showed better fitting suggesting heterogeneous adsorption scenario. Freundlich capacity values decreased in the order of Pb2+ (3.71 mg g−1) &gt; Cd2+ (2.45 mg g−1) &gt; Ni2+ (1.76 mg g−1). Kinetic data were accurately fitted to pseudo‐second‐order, indicating the adsorption occurrence in the interior surface of Na‐MMT and the contribution of internal diffusion mechanism was significant. Intraparticle diffusion model gave multi‐linear curves so more than one‐step controlled the adsorption process. Under temperature range 290–328 K, thermodynamic parameters revealed that adsorption of Pb2+ and Cd2+ was spontaneous but Ni2+ non‐spontaneous. Adsorption was exothermic for Pb2+ and Ni2+ but endothermic for Cd2+. Arrhenius activation energy values were 5.78, 8.51 and 11.45 kJ mol−1 for Pb2+, Cd2+ and Ni2+ respectively stating the physical adsorption. Na‐MMT reusability was confirmed by regeneration experiments. Application study showed excellent efficiency of Na‐MMT within range (23.4–81.2%) removal for Pb2+, Cd2+ and Ni2+ from textile dyeing and tannery wastewater. Copyright © 2017 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Thermodynamics of Multivalent Carbohydrate−Lectin Cross-Linking Interactions: Importance of Entropy in the Bind and Jump Mechanism

The high affinity (K(d) = 0.2 nM) of the soybean agglutinin (SBA), a tetrameric GalNAc specific lectin, for a modified form of porcine submaxillary mucin, a linear glycoprotein, with a molecular mass of approximately 10(6) Da and approximately 2300 GalNAcalpha1-O-Ser/Thr residues (Tn-PSM) has been ascribed to an internal diffusion mechanism that involves binding and jumping of the lectin from GalNAc to GalNAc residue of the mucin [Dam, T. K., et al. (2007) J. Biol. Chem. 282, 28256-28263]. Hill plot analysis of the raw ITC data shows increasing negative cooperativity, which correlates with an increasing number of lectin-mucin cross-linking interactions and decreasing favorable binding entropies. However, the affinity of bound SBA for other Tn-PSM molecules during cross-linking is much higher than that of free SBA for GalNAcalpha1-O-Ser, a monovalent analogue. The high affinity of bound SBA for GalNAc residues on other Tn-PSM molecules appears to be due to the favorable entropy of binding associated with the internal diffusion mechanism. Furthermore, the increasing negative cooperativity of SBA binding to Tn-PSM correlates with a decreasing level of internal diffusion of the lectin on the mucin as cross-linking occurs. These findings indicate the importance of the internal diffusion mechanism in generating large, favorable entropies of binding that drive lectin-mucin cross-linking interactions. The results are important for understanding the energetics of lectin-mucin cross-linking interactions that are associated with biological signaling on the surface of cells and the role of the internal diffusion mechanism in ligand-biopolymer interactions in general.

Effects of Clustered Epitopes in Multivalent Ligand−Receptor Interactions

Many biological ligands are composed of clustered binding epitopes. However, the effects of clustered epitopes on the affinity of ligand-receptor interactions in many cases are not well understood. Clustered carbohydrate epitopes are present in naturally occurring multivalent carbohydrates and glycoproteins, which are receptors on the surface of cells. Recent studies have provided evidence that the enhanced affinities of lectins, which are carbohydrate binding proteins, for multivalent carbohydrates and glycoproteins are due to internal diffusion of lectin molecules from epitope to epitope in these multivalent ligands before dissociation. Indeed, binding of lectins to mucins, which are large linear glycoproteins, appears to be similar to the internal diffusion mechanism(s) of protein ligands binding to DNA, which have been termed the "bind and slide" or "bind and hop" mechanisms. The observed increasing negative cooperativity and gradient of decreasing microaffinity constants of a lectin binding to multivalent carbohydrates and glycoproteins result in an initial fraction of lectin molecules that bind with very high affinity and dynamic motion. These findings have important implications for the mechanisms of binding of lectins to mucins, and for other ligand-biopolymer interactions and clustered ligand-receptor systems in general.

Removal of Cd(II), Zn(II) and Pb(II) from aqueous solutions by brown marine macro algae: Kinetic modelling

Specific marine macro algae species abundant at the Portuguese coast ( Laminaria hyperborea, Bifurcaria bifurcata, Sargassum muticum and Fucus spiralis) were shown to be effective for removing toxic metals (Cd(II), Zn(II) and Pb(II)) from aqueous solutions. The initial metal concentrations in solution were about 75–100 mg L −1. The observed biosorption capacities for cadmium, zinc and lead ions were in the ranges of 23.9–39.5, 18.6–32.0 and 32.3–50.4 mg g −1, respectively. Kinetic studies revealed that the metal uptake rate was rather fast, with 75% of the total amount occurring in the first 10 min for all algal species. Experimental data were well fitted by a pseudo-second order rate equation. The contribution of internal diffusion mechanism was significant only to the initial biosorption stage. Results indicate that all the studied macro algae species can provide an efficient and cost-effective technology for eliminating heavy metals from industrial effluents.

The fate of smectite in KOH solutions

The aim of the present study was to investigate the detailed evolution of the SAz-1 smectite in 1 M KOH at 80 °C at a solid/liquid ratio of 1/80. AFM observations indicated no change in crystal size or shape. XRD measurements at 40% relative humidity revealed changes in expandability of the smectite. The (001) reflection profile of smectite was modeled using a trial-and-error approach. The results indicate that with increasing run time, the number of non-expandable layers with zero or one water layer increases and that the coherent scattering domain size of the smectite decreases. IR spectroscopy of the reacted smectite suggests that there is no change from the initial clay products. The dehydroxylation temperature showed a slight decrease from 619 to 605 °C. STA measurements demonstrated that the cis-vacant character of the octahedral sheet remained nearly unchanged throughout the experiment. Determination of the average layer charge showed a continuous increase from 0.32 to 0.42 eq/(Si/Al)4O10, whereas the layer charge distribution indicated the appearance of high charged smectite layers with a charge of ~ 0.6 eq/(Si/Al)4O10 and the disappearance of the low charged layers. XPS and SEM measurements indicate an increase of Al in the smectite samples. Isotope data support the theory of an internal diffusion mechanism by gradual changes in δ18O values.

Sorption of Zn(II), Pb(II), and Co(II) using natural sorbents: Equilibrium and kinetic studies

Natural Jordanian sorbent (consisting of primary minerals, i.e., quartz and aluminosilicates and secondary minerals, i.e., calcite and dolomite) was shown to be effective for removing Zn(II), Pb(II) and Co(II) from aqueous solution. The major mineral constitutions of the sorbent are calcite and quartz. Dolomite was present as minor mineral and palygorskite was present as trace mineral. The sorbent has microporous structure with a modest surface area of 14.4 m 2 g −1. pH zpc (pH of zero point charge) of the sorbent was estimated by alkaline–titration methods and a value of 9.5 was obtained. The sorption capacities of the metals were: 2.860, 0.320, 0.076 mmol cation g −1 for Zn(II), Pb(II) and Co(II) at pH 6.5, 4.5 and 7.0, respectively. The shape of the experimental isotherm of Zn(II) was of a “L2” type, while that of Pb(II) and Co(II) was of a “L1” type according to Giles classification for isotherms. Sorption data of metals were described by Langmuir and Freundlich models over the entire concentration range. It was found that the mechanism of metal sorption was mainly due to precipitation of metal carbonate complexes. The overall sorption capacity decreased after acid treatment, as this decreased the extent of precipitation on calcite and dolomite. The effect of Zn(II) ions concentration on sorption kinetics was investigated. Kinetic data were accurately fitted to pseudo-first order and external diffusion models which indicated that sorption of Zn(II) occurred on the exterior surface of the sorbent and the contribution of internal diffusion mechanism was insignificant. Furthermore, the sorption rate of Zn(II) was found to be slow, where only 10–20% of the maximum capacity was utilized in the first 30 min of interaction.

Lead-acid battery model for the derivation of Peukert’s law

In this paper a survey is given of the pros and cons of the existing models for the lead-acid battery. Next, a diffusion model is proposed which explains inter alia the occurrence of sharp lead sulfate walls observed earlier by Haebler et al. The model also leads to an expression similar to Peukert’s law. Finally, in order to account for secondary effects in the lead sulfate distribution the model has been extended to include a second internal diffusion mechanism.

Therapeutic delivery of calcitonin to inhibit external inflammatory root resorption. I. Diffusion kinetics of calcitonin through the dental root.

Insertion of calcitonin into root canals of monkey teeth has been shown to inhibit external inflammatory root resorption and suppress inflammation. Regulation of this therapeutic event depends upon the rate of arrival (diffusion) of the hormone at sites of resorptive activity. In the present study, the diffusion characteristics of calcitonin through the dental root in an extracted human-tooth model are described, and the role of cementum in the diffusion process is also addressed. Root-canals were endodontically prepared to form a reservoir for [125I]-calcitonin, and macerated to remove organic material from dentinal tubules. In teeth with intact cementum, an initial period of delay (4-5 h) prior to the detection of calcitonin at the external tooth-root surface was followed by a rapid release of the calcitonin during the first 10.5 h (rate peaks at 6 h). Slower, sustained releases of calcitonin through intact cementum were measured for the following 9 days. Removal of cementum, to expose "smear-free" dentine, resulted in an earlier efflux of calcitonin (2 h) at external tooth surfaces and increased amounts of calcitonin release over 9 days. Biphasic delivery of calcitonin by such internal diffusion mechanisms suggests that loss of cementum will enhance therapeutic availability, while prolonged delivery to intact external dental-root surfaces following early intra-canal placement may also be useful for the therapeutic prevention of external inflammatory root resorption.

Ion-exchange kinetics in natural heulandite and clinoptilolite

The kinetics of sorption of Ca2+ ions from aqueous solution by K+-substituted forms of heulandite and clinoptilolite have been studied at 298 K. The K+-Ca2+ ion exchange in heulandite and clinoptilolite is described by an internal diffusion mechanism. Self-diffusion coefficients were determined for Ca2+ ions in these zeolites.

Selected Area Electron Diffraction Study of α ‐ Fe2 O 3 Platelet Growths Twinned on Twist Grain Boundaries

Broad, rounded draperylike platelet growths result from the oxidation of unannealed iron in dry oxygen at 400°C. Their skewed sandwich structure is a new type of twinning in which the composition plane is a twist grain boundary. This twin interface and the platelet faces are on the basal plane. A 13.174° twist angle is common; 21.787°, 26.66°, and 35.22° were also found. Such a rounded platelet would be expected to result from the proposed internal diffusion mechanism.