Decrease In Specific Surface Area Research Articles

Tuning the sound frequency in the audible region during the synthesis of the precursor TiO2: Evaluation of the sound effect on the structure and photoactivity relationship

Due to their low efficiency, photocatalytic processes do not meet the requirements of commercial applicability, requiring new approaches in adjusting structural and electronic properties. Studies have been conducted in the development of the sonocatalysis technique where materials with better activity and stronger structure are observed. Although TiO2 can be easily prepared by traditional and relatively simple methods, it tends to crystallize in temperatures ranging from 673 K to 873 K. In general, this methodology promotes high shrinkage or collapse of the mesostructure and is eventually followed by an increase in nanoparticle size and a decrease in specific surface area. To obtain a non-agglomerated TiO2 crystal sample with good photocatalytic properties, we studied the audible sound frequency during the synthesis of the TiO2 precursor. All the TiO2 samples were prepared using a coprecipitation method and sonocatalysis, with some samples of TiO2 being impregnated with 10% nickel. The catalysts were prepared by keeping important variables constant during all synthesis and tuning the sound frequency on audible frequency. All the samples were synthetized in a “Synthesis Chamber” used for coprecipitation method preparations. The samples were characterized by TGA, XRD, SEM, EDX, and PTR. The photocatalysts were tested in photodegradation of the methylene blue dye under the UV-VIS light region. The influence of the chemical composition and the audible sound frequency application during the synthesis of the TiO2 precursor was evaluated establishing a relationship between the structure and photoactivity. The results suggest that sound waves applied during sample preparation have provided a good degree of crystallinity to the material, which could influence the crystallite size and the photocatalytic activity of the samples. Therefore, the audible sound associated with the “Synthesis Chamber” should be used as a tool to prepare and adjust the structural and electronic properties of the photocatalysts to promote TiO2 photoactivity.

Temporal post-discharge reactions effect on the oxidative catalytic properties of plasma-synthesized α-MnO2 nanorods

The evolution of the morphology, crystalline structure, and textural properties of α-MnO2 nanorods, which were obtained after reduction of a KMnO4 solution via gliding arc plasma process, have been followed along their ageing under temporal post-discharge conditions. When aged at 25 °C a partial transformation of α-MnO2 (cryptomelane) to γ-MnO2 (nsutite) occurred with an increase of specific surface area from 98 to 141 m2/g. In parallel, the starting nanorods were converted to nanoneedles after 24 and 48 h, and into nanosheets after 72 h. These transformations are ascribed to the evolution of maturation process of crystallites, thanks to post-discharge species (H2O2, HOONO,…). At the opposite, ageing at 100 °C induced a remarkable transformation of α-MnO2 to γ-MnO2 with a decrease of specific surface area from 98 to 35 m2/g after 3 h, which was in line with the observed agglomeration of nanorods. Finally, whereas a longer ageing at 100 °C provoked an activity diminution of the material, an augmentation of activity of plasma-synthesized α-MnO2 was recorded when implementing ageing at 25 °C.

Ex-situ catalytic upgrading of corncob pyrolysis vapors into furans and phenols over Pt-Re/AC: Effect of Pt/Re ratio and process parameter

In order to improve the quality of bio-oils, catalytic fast pyrolysis of corncob over Pt/Re supported activated carbon (AC) catalysts was conducted to produce bio-furans and bio-phenols. The effect of Pt/Re ratio on the catalytic pyrolysis performance was evaluated. Pt and Re are uniformly dispersed on AC, but it results in the decrease of specific surface area. In addition, the amount of weak acidic sites increased and higher total weak acidity of Pt-Re/AC was contributed to the production of target products at low catalytic upgrading temperature. AC and Pt/AC inhibited the formation of phenols, and Re/AC and Pt-Re/AC promoted the formation of phenols. The relative peak area of furans over 1Pt-3Re/AC and Re/AC is 44.36 % and 41.98 %, respectively. Pt-Re/AC catalysts have a high selectivity for methylfurans (MFs) and phenol (P), remaining at 19 % ∼ 33 % and 17 % ∼ 21 %, respectively. Finally, 1Pt-3Re/AC showed good reuse performance.

Pore-scale study of capacitive charging and desalination process in porous electrodes and effects of porous structures

The capacitive deionization (CDI) involves processes of ion transport and storage within porous electrodes. A pore-scale model based on the lattice Boltzmann (LB) method is developed to study the dynamics of capacitive charging and desalination in CDI cells by considering microstructures of porous electrodes. The governing equations for mass transport and potential within the separator and pores of electrodes are derived for the case of thin electrical double layers. For the salt adsorption and charge transport between the solution and charged matrixes, the effective boundary conditions suitable for LB simulations are developed based on the Gouy-Chapman-Stern model. The transient processes of capacitive charging and desalination upon the application of a step cell voltage are revealed, and effects of potential, porosity, particle diameter and porous structure on the dynamic processes are investigated. Simulation results show that the salt removal of the separator is a diffusion limited and relatively slow process compared with the charging process of porous electrodes. The amount of equilibrium salt removal is proportional to the cell voltage and specific surface area of porous electrode. The salt removal rate is mainly affected by the effective diffusivity of porous electrode. Approaches of enhancing the effective diffusivity, such as increasing the porosity under the same particle size and enlarging the particle diameter under the same porosity, can improve the salt removal rate but reduce the salt adsorption capacity due to the decrease of specific surface area. Under the same specific surface area, the porous electrode with large pores introduced along the diffusion direction shows the highest salt removal rate without decreasing in salt adsorption capacity.

Dual functional N,O,P containing covalent organic frameworks for adsorping iodine and fluorescence sensing to p-nitrophenol and iodine

Abstract Covalent-organic-frameworks (COFs) are emerging porous organic materials with fascinating structural features and potential applications in the fields of iodine capture and spectroscopy. However, no dual-functional COFs with both iodine adsorption and fluorescence sensing have been reported. We herein report the construction of the three dual-functional COFs via Schiff base polycondensations with flexible building blocks cyclophosphazene-based aldehydes (NOP-6-CHO) and benzidine (BD) with different substituent groups (-OCH3 and –OH). The resulting COFs show high thermal stability and exhibit different crystallinity. The specific surface area, pore volume, and crystallinity decrease due to the introduction of the substituent group into the linker. Hydrogen bonding interaction makes the significant improvement of microscopic order degree as well as crystallinity of the COFs. Remarkably, the as-prepared COFs exhibit excellent adsorptive performance for iodine molecules via vapor trapping adsorption, and adsorption capacity reach as high as 4.41, 3.78, and 4.47 g g−1 for HBD, HDASD, and HDOBD, respectively. When suspended in polar organic solvents, the three COFs have high fluorescence under UV light. They can detect p-nitrophenol (p-NP) and iodine with high sensitivity and selectivity.

Effects of short-term high-temperature calcinations on the physico-chemical and mineralogical properties of Ca-bentonites from Ünye (Ordu, NE Turkey)

Three Ca-bentonite samples from Unye (NE Turkey) were calcined up to 1000 °C with 200 °C increments at 25 min. The physico-chemical and mineralogical effects of high-temperature loadings were evaluated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET) and loss on ignition (LOI) analysis. The results of the experiments show that the dehydration up to 400 °C does not alter the properties of Ca-bentonites significantly; however, the endothermic reactions due to dehydroxylation between 400 and 800 °C cause the deformation in the Ca-smectite crystal structure revealed by the collapse of the basal reflection from 1.4 to 1.0 nm and the gradual disappearance of OH stretching of structural hydroxyl groups and decrease in specific surface area and the closure of micropores. By calcination at 1000 °C, the specific surface area reaches the minima of 1.33–2.05 m2 g−1 for all the samples, and the structure of Ca-smectite is almost completely decomposed for CaB2 and CaB3, however, partially decomposed for CaB1 due to incomplete dehydroxylation stage. The crystallinity of opal-CT intensifies, and the formation of amorphous silica phases is promoted for all samples at 1000 °C; however, the formation of mullite is enhanced only for CaB2 and CaB3. The sintering effect is revealed as much larger aggregates with more rounded morphologies. It is also determined that the calcination up to 1000 °C does not affect the mesoporous characteristics of Ca-bentonite samples.

Effect of supercritical CO2 extraction on CO2/CH4 competitive adsorption in Yanchang shale

Competitive adsorption characteristics of CO2/CH4 on shales before and after supercritical CO2 (ScCO2) extraction are closely related to CO2 injection in shale reservoir for CO2 sequestration and enhanced shale gas recovery (CS-ESGR). Using a self-developed PCTPro-type automatic high-pressure gas adsorption instrument, the adsorption behaviors of CH4, CO2 and their mixtures with different ratios were investigated on raw and ScCO2-treated (10 day/16 MPa/40 °C) shale collected from the Ordos Basin. The influences of ScCO2 extraction, pressure and CO2/CH4 cratios on adsorption capacity and selective adsorption factor of CO2/CH4 (SCO2/CH4) of shale have been analyzed. To interpret the experimental data, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, low-pressure gases adsorption and mercury intrusion were performed to evaluate the variations of mineral compositions and pore structure of shale exposure to ScCO2. It is found that SCO2/CH4 and the adsorption capacity of CO2/CH4 with different ratios decreased after ScCO2 extraction and are mainly attributable to the decrease of TOC, carbonates, clay minerals and specific surface area in ScCO2-treated shale. The feasibility of CS-ESGR cannot be affected by ScCO2 due to the values of SCO2/CH4 are always greater than 2.5 after ScCO2 extraction. Additionally, SCO2/CH4 decreased initially and then tended to be stable with increasing pressure, and it decreased slightly with increasing CH4 concentration in gas mixtures, suggesting that the reservoir pressure should be lowered before the injection of CO2 into shale reservoir, and the efficiency and engineering cost of CS-ESGR should be considered comprehensively. This study provides a reference for future optimization design of CS-ESGR.

Preparation and Characterization of the Sulfur-Impregnated Natural Zeolite Clinoptilolite for Hg(II) Removal from Aqueous Solutions

Sulfur-impregnated zeolite has been obtained from the natural zeolite clinoptilolite by chemical modification with Na2S at 150 °C. The purpose of zeolite impregnation was to enhance the sorption of Hg(II) from aqueous solutions. Chemical analysis, acid and basic properties determined by Bohem’s method, chemical behavior at different pHo values, zeta potential, cation-exchange capacity (CEC), specific surface area, X-ray powder diffraction (XRPD), scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), as well as thermogravimetry with derivative thermogravimetry (TG-DTG) were used for detailed comparative mineralogical and physico-chemical characterization of natural and sulfur-impregnated zeolites. Results revealed that the surface of the natural zeolite was successfully impregnated with sulfur species in the form of FeS and CaS. Chemical modification caused an increase in basicity and the net negative surface charge due to an increase in oxygen-containing functional groups as well as a decrease in specific surface area and crystallinity due to the formation of sulfur-containing clusters at the zeolite surface. The sorption of Hg(II) species onto the sulfur-impregnated zeolite was affected by the pH, solid/liquid ratio, initial Hg(II) concentration, and contact time. The optimal sorption conditions were determined as pH 2, a solid/liquid ratio of 10 g/L, and a contact time of 800 min. The maximum obtained sorption capacity of the sulfur-impregnated zeolite toward Hg(II) was 1.02 mmol/g. The sorption mechanism of Hg(II) onto the sulfur-impregnated zeolite involves electrostatic attraction, ion exchange, and surface complexation, accompanied by co-precipitation of Hg(II) in the form of HgS. It was found that sulfur-impregnation enhanced the sorption of Hg(II) by 3.6 times compared to the natural zeolite. The leaching test indicated the retention of Hg(II) in the zeolite structure over a wide pH range, making this sulfur-impregnated sorbent a promising material for the remediation of a mercury-polluted environment.

Enhancement of conductivity, mechanical and biological properties of polyaniline-poly(N-vinylpyrrolidone) cryogels by phytic acid

Polyaniline-based cryogels were prepared by oxidative cryopolymerization in the presence of various concentrations of poly(N-vinylpyrrolidone) and phytic acid used as a polymer support and a dopant, respectively. Mechanical strength and handling stability of the resulting macroporous materials (pore size up to 70 μm) were significantly improved by the addition of poly(N-vinylpyrrolidone) into the polymerization system compared to the cryogels crosslinked only by phytic acid. Increase of poly(N-vinylpyrrolidone) concentration in the reaction medium above 5 wt%, while not noticeably changing mechanical properties, was found to lead to a decrease of conductivity and specific surface area. Introduction of optimal amount of phytic acid (0.2 M) as an additional codopant, in opposite, allowed enhancement of the material conductivity and specific surface area as well as increase of their tensile modulus. Polyaniline-poly(N-vinylpyrrolidone) cryogels containing phytic acid also showed better cytocompatibility due to lower cytotoxicity and improved cell adhesion and proliferation.

Influence of Aeration Microporous Aperture on Oxygen Mass Transfer Efficiency in Terms of Bubble Motion Flow Field

Microporous aeration has been widely used to restore eutrophic water bodies. The gas–liquid mass transfer in the aeration process has a significant influence on the improvement of water quality. Therefore, the influence mechanism of oxygen mass transfer is worth studying. However, the influence of bubble movement characteristics on oxygen mass transfer has not been systematically studied. Thus, the present study explored the influence mechanism of microporous apertures on oxygen mass transfer in terms of bubble motion characteristics by investigating the oxygen mass transfer process and the feature of bubble movement under different aeration microporous aperture sizes. The results showed that the mass transfer efficiency was reduced as the micropore aperture increased from 200 to 400 μm. and the reduction rate was 7.17% when the aperture increased from 200 to 300 μm, which was lower than that from 300 to 400 μm (19.17%). Furthermore, the micropore aperture showed a positive correlation with the time-averaged velocity field. With the increase in aperture, the bubble velocity gradient (from the center to both sides of the edge) increased from about 0.2 to 0.4 m/s, which increased the oxygen mass transfer effect. The increase of micropore aperture caused the increase of average Sauter bubble diameter and the decrease of specific surface area of bubbles. In addition, the negative effects of the reduction of specific surface area and the shortening of bubble residence time on oxygen mass transfer efficiency were greater than the positive effects of the increase of turbulent kinetic energy. When the aperture changes from 300 to 400 μm, the shortening of bubble residence time should have played a major role. This study provides some theoretical parameters for investigating the mechanism of oxygen mass transfer in microporous aeration.

Mechanochemical synthesis of adsorbents based on silicon oxycarbide composites

In the work, an attempt was made to mechanochemically synthesize silicon oxycarbide composites from activated carbon and silica. Structure of the composites was studied using powder X-ray diffraction and IR spectroscopy. Formation of silicon oxycarbides was confirmed by presence of Si-O-C bond. Influence of the raw materials ratio on structural and chemical properties of resulting composites was revealed. With an increase of silica share in the initial mixture, a decrease in specific surface area and pore volume was noted, as well as an increase of the concentration of surface functional groups. Samples of the composites were tested in processes of sorption of methyl orange and fluoride ions. It was established that adsorption capacity for methyl orange decreased, while that for fluoride ions significantly increased comparing to activated carbon.

Influence of surface mineralogy on the activity of Halanaerobium sp. during microbial enhanced oil recovery (MEOR)

Microbial enhanced oil recovery (MEOR) is an economically attractive tertiary recovery technique and fermentative bacteria are frequently suggested for MEOR, partly because microbially produced organic acids have the potential for rock matrix dissolution.In this study, the metabolic activity and the community shift of a diverse microbiome of a high-salinity oilfield upon supplying MEOR nutrients was investigated in dynamic sandpacks set-up with and without crude oil using pure quartz sand and two types of reservoir rock. Geochemical characterization of the porous media included specific surface area (SSA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). During the experiments, substrate and metabolites, incremental oil and differential pressure were monitored and the microbial community shift was investigated via Illumina sequencing.Fermentative Halanaerobiales outcompeted other microbes and led to an incremental oil recovery of 24.5 ± 9.6%OOIP in reservoir rock. Microbial-induced dissolution of surface minerals was indicated by a decrease in SSA and surface-bound ferrous iron and concluded to be an important MEOR mechanism. Fermentation of sucrose was primarily limited by an insufficient acid neutralization capacity (ANC), but a carbonate content of 12% sustainably buffered the pH in a favorable growth range. Even minor amounts of other non-inert minerals (1% pyrite and calcite) facilitated microbial growth significantly, resulting in six-fold higher acetate production rates compared to quartz sand. Besides emphasizing the relevance of accessory minerals in MEOR, our results imply that the ANC could serve as potential screening parameter for predicting the performance of fermentation-based MEOR in the field.

Facile Synthesis and Characterization of the Reduced Graphene Oxide/Co\(_3\)O\(_4\) Nanocomposite for Capacitive Application

Reduced graphene oxide/Co\(_3\)O\(_4\) (rGO/Co\(_3\)O\(_4\)) were prepared by simple ultrasonic method from graphene oxide (GO) and Co(CH\(_3\)COO)\(_2\) precursor. The synthesized rGO/CO3O4 was thoroughly characterized by SEM/EDX, XRD, FTIR and BET. The obtained results indicate the presence of well-crystalized Co\(_3\)O\(_4\) nanoparticles onto the rGO nanosheets in the lamellar structure of rGO/Co\(_3\)O\(_4\). Despite slight decrease in BET specific surface area (from 389.9 m\(^2\)/g of rGO to 218.7 m\(^2\)/g of rGO/Co\(_3\)O\(_4\)), cyclic voltammetry studies show that the rGO/Co3O4 electrode exhibited high specific capacitance (95.8 F/ g at 50 mV/ s) with redox properties. The synthesized composites are expected to be a potential electrode candidate in supercapacitor as well as in hybrid capacitive deionization (HCDI) system for the desalination purpose.

Growth of Titanium Oxide Nanostructures on γ-Аl2О3 by Atomic Layer Deposition

This paper presents results on control over the surface composition, surface structure, and pore texture of core/shell materials, as exemplified by the growth of conformal titanium oxide nanocoatings on γ‑Аl2О3 by atomic layer deposition via sequential and alternating exposure of the alumina to TiCl4 and H2O vapor. The alumina surface and growing titanium oxide layer are shown to influence the characteristics of the forming two-phase material. Increasing the amount of titanium via an increase in the number of deposition cycles leads to a systematic decrease in specific surface area, pore volume, and pore size, which points to conformal pore filling in the starting matrix by a titanium oxide layer. The composition and structure of the titanium oxide coating are influenced by its thickness and the nature of the starting matrix. The coordination state of the titanium oxide in monolayer structures is characteristic of the titanium oxide polyhedra in aluminum titanate. As the distance from the top monolayer to the surface of the matrix (coating thickness) increases, an X-ray amorphous layer is formed in which the oxygen coordination environment of the titanium is similar to that in an anatase-like phase of titanium dioxide.

Mesoporous silicate/alginate composites as a carrier for amitriptyline hydrochloride and in vitro release

The objective of this research is to prepare mesoporous silica (M41) based nanomaterials and encapsulate in the solid polymeric matrix for controlled drug release application. Amitriptyline (AT) -loaded M41/sodium alginate (AL) composite microparticles were prepared by the ion exchanged gelation techniques. Composite microparticles were characterized by FT-IR spectroscopy; surface area analysis and scanning electron microscopy. Here we propose mesoporous silica (M41) for loading of hydrophilic drug, amitriptyline (AT) and further constructed drug loaded M41 into a pH-responsive alginate microparticles. The resulting drug loaded composites microparticles was characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR), particle size and zeta potential analyzer. Drug loading was confirmed by the decrease of specific surface area and pore volume in the drug loaded composites as well microparticles. The morphology of drug loaded hybrid nanomaterials and composite micro spherical particles were evaluated by scanning and transmission electron microscopy (SEM and TEM, respectively) measurements. The AT release from microspheres composites was pH dependent, and the release rate was much lesser in gastric pH than that in intestinal pH media. Thus, the biocompatible composite spherical particles hold the substantial potential to be further developed as effective and safe drug-delivery carriers. Drug release kinetics ( in vitro in simulated gastric and intestinal fluids) showed that both of them were affected by the properties of materials. The release profile of AT from composites was best fitted in Higuchi kinetic model while the Korsmeyer–Peppas model suggested a non fickian diffusion release mechanism. Such formulations show potential as an efficient controlled drug delivery system.

Properties of ceria nanoparticles with surface modified by acidic groups

The effect of the precursor and surface modification by sulfate and phosphate groups on the properties of cerium oxide was studied. The obtained materials were characterized by infrared (IR) and Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM), thermogravimetric analysis (TGA) with the gas phase composition analysis, Brunauer–Emmett–Teller (BET) method, and impedance spectroscopy. The significant fraction of Се3+ ions at the surface of cerium oxide particles obtained from Ce(NO3)3 promotes the formation of double sodium cerium sulfate and cerium phosphate upon treatment with solutions of sodium hydrogen sulfate and sodium dihydrogen phosphate, respectively. The modification of ceria surface by sulfate groups leads to a decrease in specific surface area and water content of the obtained materials, as well as to a significant decrease in their proton conductivity. CeO2 samples prepared from cerium ammonium nitrate have a significantly smaller particle size and higher conductivity. Its value for cerium oxide modified with phosphate groups increases up to 3.5 × 10−4 S/cm at 65 °C. The effect of hydration degree as well as Ce3+ content on the cerium oxides properties is discussed.

Modification of a phase-inhomogeneous alumina support of a palladium catalyst. Part I: effect of the amorphous phase on the textural and acidic characteristics of alumina and methods for controlling its phase homogeneity

The contribution of the amorphous phase in aluminum hydroxide and alumina to their properties was investigated in this work. It was shown that the amorphous phase in aluminum hydroxide is stabilized by alumoxanes, and it is a source of a finely porous component and capable of increasing the surface area by ~78%. In γ-Al2O3, amorphous alumina raises the surface area and the acidity. It was established that the method of chemical modification does not change the phase inhomogeneity but allows adjusting the acid properties while maintaining the high specific surface area. It was shown that the amorphous phase is more reactive when processing phase-inhomogeneous aluminum hydroxide with acetic acid. Crystallization of amorphous alumina as a result of high-temperature treatment of phase-inhomogeneous aluminum hydroxide is accompanied by significant decrease in specific surface area and acidity.

How do specific surface area and particle size distribution change when granular media dissolve?

The measured dissolution rate of a granular medium depends on its surface area and how the surface area changes during the course of the measurement. Moreover, the assumption that the specific surface area either remains constant or initially increases during dissolution is not always valid. This paper demonstrates that when the particle size distribution has sufficient variance, the instantaneous change in surface area during dissolution can be negative, even before the smallest particles dissolve away. The concept is explained using spherical particles, extended for use with prismatic particles, and demonstrated experimentally with gypsum powder. For the commercial gypsum powder used, the specific surface area decreases by about 50% during the first 10% of mass loss in water, so this effect may have practical importance and have a significant impact on the uncertainty in reported dissolution rates measured with batch reactors.

The Effect of the Stabilization and Carbonization Temperatures on the Properties of Microporous Carbon Nanofiber Cathodes for Fuel Cells on Polybenzimidazole Membrane

Materials based on pyrolyzed electrospun nanofiber polyacrylonitrile were studied by the method of standard contact porosimetry. An influence of oxidation and pyrolysis temperatures on specific surface area. It was shown that an increase of oxidation temperature from 300 to 350°C and of pyrolysis temperature from 900 to 1000°C leads to a decrease of pore specific surface area and to a decrease of a part of micropore specific surface area. Platinated samples showed sufficient values of electrochemically active platinum surface area (12‒35 m2 g $$_{{{\text{Pt}}}}^{{ - 1}}$$ ) and were tested as cathodes for high temperature polymer electrolyte membrane fuel cell. An increase in power density was found when a part of electrode micropore specific surface area was decreasing.

Reaction kinetics and internal diffusion of Zhundong char gasification with CO2

Mass transfer usually affects the rate of chemical reactions in coal. The effect of internal diffusion on char gasification with CO2 in the temperature range from 1123 K to 1273 K was investigated via thermogravimetric analysis and assessment of char morphology features. The results revealed that the effect of internal diffusion on the initial reaction rate was more significant with an increase of particle size, due to the concentration gradient of the gasification agent within the solid particles. In the early stage of gasification, the generation of new micropores and the opening of closed pores led to an increase in specific surface area. As the reaction proceeded, the openings were gradually expanded and the specific surface area continued to increase. However, with further reaction, disappearance of edge pores, melting and collapse of the pore structure led to a decrease in specific surface area. The intrinsic activation energy and reaction order based on the nth-order model were 157.67 kJ·mol−1 and 0.36, respectively. Thus, temperature zones corresponding to chemical reaction and diffusion control were identified. Moreover, the calculated effectiveness factor provided a quantitative estimation of internal diffusion in the initial stage.