Thin Pore Walls Research Articles

Unveiling the impact of stabilization pretreatment on sodium storage performance in hard carbon

Stabilization pretreatment coupled with molecular cross-linking is commonly used to modify starch, aiming to obtain starch-based hard carbon materials with appropriate spherical particle sizes. Nevertheless, the impact of the intermediate stabilization process on its sodium storage performance remains unclear. Herein, a hard carbon material with no surface open pores, low specific surface area and abundant internal closed pores with thinner pore walls is successfully synthesized and exhibits significantly improved initial Coulombic efficiency and plateau capacity through a simple low-temperature pretreatment strategy, using renewable and cost-effective soluble starch as the raw material. Additionally, research indicates that an appropriate degree of disorder or defectiveness is conducive to forming a larger quantity of closed pores with thinner pore walls. Both excessively low and high defect levels are detrimental to the formation of closed pores. This work will encourage researchers to further focus on the impact of defectiveness on closed pores, which will promote the development of high-energy practical sodium-ion batteries.

A novel and promising thermal insulation material: Monazite-type porous LaPO4 ceramics possessing ultra-low thermal conductivity and enhanced strength

In this study, novel porous LaPO4 ceramics possessing closed spherical pores and thin pore walls have been firstly synthesized using the particle-stabilized foaming method. Affected by the calcination temperature together with solid loading, the obtained porous LaPO4 ceramics exhibit high porosity (81.69–94.21 %), very low thermal conductivity (κ) (0.124–0.398 W m−1 K−1) and relatively high compressive strength (0.886–9.30 MPa). When the calcination temperature and solid loading are 1500 °C and 35 wt%, optimized porous LaPO4 ceramics achieve a better balance between thermal conductivity (0.160 W m−1 K−1) and compressive strength (2.07 MPa). Based on this, the prediction model for the thermal conductivity is screened and the thermal insulating capability is further verified. This work suggests that porous LaPO4 ceramics have the potential to be applied as thermal insulation material in the future.

Optimizing the performance of iron coke by coal blending: Insights from the metallurgical properties and structural characteristics

Iron coke has gained widespread attention for its advantages in carbon reduction and efficient resource utilization. However, the structure and strength of iron coke have constrained its further advancement. This study systematically explores the impact of different coal blending structures on the three-dimensional structure and tensile strength of iron coke through three-dimensional reconstruction technology. It highlights the improvement mechanism of 1/3 coking coal addition on the microstructure and metallurgical properties of iron coke. The study shows that the tensile strength of iron coke increases with the addition of coking coal, while lean coal exhibits the opposite trend. The addition of an appropriate proportion of 1/3 coking coal (20–22 %) enhances the tensile strength and mechanical strength of iron coke, reaching the level of second-grade coke. However, an addition exceeding 22 % leads to increased porosity and reduced strength due to the high volatile content. Finite element analysis demonstrates that stress is primarily localized in regions with thinner pore walls and at the iron-carbon interface, and the aggregation effect of iron particles further causes stress concentration. Iron coke reactivity initially diminishes and subsequently rises with the addition of 1/3 coking coal, and it shows a linear negative correlation with the strength after reaction. Structural evolution reveals that the addition of 1/3 coking coal reduces the orderliness of carbon microcrystals, thereby increasing the active sites for gasification reactions. Meanwhile, the initial reduction followed by an increase in the specific surface area of iron coke can impact adsorption sites, thereby influencing reaction activity. These findings not only provide a new understanding of the structure-performance relationship of iron coke but also offer practical guidance for iron coke production.

Synthesis of MgO-Coated Canna Biochar and Its Application in the Treatment of Wastewater Containing Phosphorus

In order to treat phosphorus-containing wastewater and realize the resource utilization of wetland plant residues, biochar was prepared by the pyrolysis of canna aquatic plant waste at 700 °C, and the adsorption characteristics of phosphorus by MgO-modified biochar (MBC) were explored. The main results are as follows: the adsorption capacity of the MBC was eight times that of unmodified biochar (BC), and the adsorption capacity was up to 244 mg/g. The isothermal adsorption data were consistent with the Langmuir equation, which indicates monolayer adsorption. The functional groups changed little before and after the modification, but a new diffraction peak appeared after the modification. Compared with the standard card, it was suggested that there were MgO crystals with a higher purity. SEM images showed that the BC had a smooth surface, an obvious pore structure, and a thin pore wall, while the MBC had a rough surface and a layered structure, which can provide more adsorption sites for phosphate adsorption. In addition, an XPS analysis showed that Mg3(PO4)2 crystals appeared on the surface of the MBC after adsorption. The mechanism analysis showed that MgO is an important substance for MBC to adsorb phosphorus, and electrostatic adsorption and complex precipitation play key roles. In the test to verify the removal of actual phosphorus-containing wastewater by MBC, it was found that the removal rates for wastewater with 2.06 mg/L and 199.8 mg/L of phosphorus by MBC were as high as 93.4–93.9% and 99.2–99.3%, respectively. MBC can be used as an efficient adsorbent for phosphorus removal.

Alumina Incorporation in Self-Supported Poly(ethylenimine) Sorbents for Direct Air Capture.

Self-supported branched poly(ethylenimine) scaffolds with ordered macropores are synthesized with and without Al2O3 powder additive by cross-linking poly(ethylenimine) (PEI) with poly(ethylene glycol) diglycidyl ether (PEGDGE) at -196 °C. The scaffolds' CO2 uptake performance is compared with a conventional sorbent, i.e., PEI impregnated on an Al2O3 support. PEI scaffolds with Al2O3 additive show narrow pore size distribution and thinner pore walls than alumina-free materials, facilitating higher CO2 uptake at conditions relevant to direct air capture. The PEI scaffold containing 6.5 wt % Al2O3 had the highest CO2 uptake of 1.23 mmol/g of sorbent under 50% RH 400 ppm of CO2 conditions. In situ DRIFT spectroscopy and temperature-programmed desorption experiments show a significant CO2 uptake contribution via physisorption as well as carbamic acid formation, with lower CO2 binding energies in PEI scaffolds relative to conventional PEI sorbents, likely a result of a lower population of primary amines due to the amine cross-linking reactions during scaffold synthesis. The PEI scaffold containing 6.5 wt % Al2O3 is estimated to have the lowest desorption energy penalty under humid conditions, 4.6 GJ/tCO2, among the sorbents studied.

Elucidating the Bulk Morphology of Cellulose‐Based Conducting Aerogels with X‐Ray Microtomography

AbstractConducting cellulose composites are promising sustainable functional materials that have found application in energy devices, sensing and water purification. Herein, conducting aerogels are fabricated based on nanofibrillated cellulose and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate, using the ice templating technique, and their bulk morphology is characterized with X‐ray microtomography. The freezing method (−20 °C in a freezer vs liquid nitrogen) does not impact the mean porosity of the aerogels but the liquid‐N2 aerogels have smaller pores. The integration of carbon fibers as addressing electrodes prior to freezing results in increased mean porosity and pore size in the liquid‐N2 aerogels signifying that the carbon fibers alter the morphology of the aerogels when the freezing is fast. Spatially resolved porosity and pore size distributions also reveal that the liquid‐N2 aerogels are more inhomogeneous. Independent of the freezing method, the aerogels have similar electrochemical properties. For aerogels without carbon fibers, freezer‐aerogels have higher compression modulus and are less stable under cycling compression fatigue test. This can be explained by higher porosity with larger pores in the center of liquid‐N2 aerogels and thinner pore walls. This work demonstrates that micro‐CT is a powerful tool for characterizing the morphology of aerogels in a non‐destructive and spatially resolved manner.

Influence of alkaline activator and precursor on the foam characterization and alkali-activated foamed concrete properties

This study proposes a solution by adding recycled brick powder in the alkali-activated foamed concrete to improve the fresh stability and thermal insulation. The roles of activator modulus and Na2O concentration on the fresh and hardened properties of alkali-activated foamed concrete with slag-fly ash based and slag-recycled brick powder based were investigated. The presence of alkaline activator was detrimental to the foamability and foam stability, and these characteristics were deteriorated with an increase in activator modulus and Na2O concentration. This primarily caused an inferior stability of fresh foamed concrete but achieved short initial setting time and high fluidity loss, owing to the synergistic effect of foam stability and alkali-activated cements slurry. Microstructure results shown that with the increasing of activator modulus and Na2O concentration, a growth tendency on the amount of pores with larger size and irregular shape led to increase the mean pore diameter and mean roundness. Overall, incorporation of recycled brick powder in the low alkalinity was unfavourable to the water absorption and compressive strength of foamed concrete, but it performed better in enhancing stability, water resistance, thermal insulation and strength development under higher alkaline environment and achieved spherical shape, thin pore wall and better pore refinement.

Versatile Synthesis of Hollow-structured Mesoporous Carbons by Enhanced Surface Interaction for High-performance Lithium-ion Batteries.

Nanoporous carbons are very attractive for various applications including energy storage. Templating methods with assembled amphiphilic molecules or porous inorganic templates are typically used for the synthesis. Amongst the different members of this family, CMK-5-like structures that are constructed to consist of sub-10nm amorphous carbon nanotubes and ultrahigh specific surface area due to their thin pore walls, have the best properties in various respects. However, the fabrication of such hollow-structured mesoporous carbons entails elaborately tailoring the surface properties of template pore walls and selecting specific carbon precursors. Thus, very limited cases are successful. Herein, wereport a versatile and general silanol-assisted surface-casting method to create hollow-structured mesoporous carbons and heteroatom-doped derivatives with numerous organic molecules (e.g., furfuryl alcohol, resol, 2-thiophene methanol, dopamine, tyrosine) and different structural templates. These carbon materials exhibit ultrahigh surface area (2400 m2 g-1 ), large pore volume (4.0 cm3 g-1 ), as well as satisfactory lithium-storage capacity (1460 mAh g-1 at 0.1 A g-1 ), excellent rate capability (320 mAh g-1 at 5 A g-1 ), and very outstanding cycling performance (2000 cycles at 5 A g-1 ). This article is protected by copyright. All rights reserved.

The fracture characteristics and enhancement mechanism of crushing strength for the coke with hot pressing

High-strength coke is essential to the ironmaking and steelmaking industries. The crushing strength of coke could be improved effectively when the hot pressing technique is carried out with proper parameters. The fracture characteristics and enhancement mechanism of crushing strength for the coke with hot pressing were investigated by experiment and finite element method with the brittle cracking model. Results show that the crushing strength of coke is improved greatly when the hot pressing is conducted at 420 ℃∼440 ℃ for the 1/3 coking coal. Coke's crushing strength is mainly affected by porosity and pores' spatial distribution. For the high porosity, the coke has thin pore walls and the cracks could easily penetrate the entire coke. Therefore, the high porosity contributes to the decrease of crushing strength. If the pore distribution is uneven, the cracks expand rapidly in the pores aggregation region and the coke has lower crushing strength. In the initial and middle thermoplastic stages, conducting the hot pressing technique with low stress could enhance the crushing strength of coke. The coke porosity is high when the coal is pressed with high stress at the early thermoplastic stage. The high pressing stress may result in uneven pores distribution if the hot pressing technique is conducted at the middle thermoplastic stage. Therefore, the high pressing stress would impede the enhancement of crushing strength when the coal is pressed at the early and middle thermoplastic stages. When the hot pressing technique is conducted with high stress at the later thermoplastic stage, the coke would have low porosity, even pore distribution, low reactivity and high crushing strength.

Regulating closed pore structure enables significantly improved sodium storage for hard carbon pyrolyzing at relatively low temperature

AbstractThe closed pore has been considered as the key structure for Na ion storage in hard carbon. However, the traditional view is that closed pores can only be formed by the curling of graphite‐like crystallites in the case of high temperature carbonization. Ingenious designing of closed pore structures at lower temperature is still blank. Herein, for the first time, engineering the wall thickness and number of closed pores in waste rosewood‐derived hard carbon was successfully achieved at a low temperature of 1100°C by removing the lignin and hemicellulose components in wood precursor. When applied as an anode material, the optimum sample exhibits a high capacity of 326 mAh/g at 20 mA/g and a remarkable rate capability of 230 mAh/g at 5000 mA/g, significantly higher than those of the untreated sample (only 33 mAh/g at 5000 mA/g). The significantly improved Na storage performance should be attributed to abundant closed pores that provide sufficient spaces for Na storage and thin pore wall structure that is beneficial to the diffusion of Na+ in the bulk phase. This work provides a new idea for the future application of biomass‐based hard carbon for advanced Na ion batteries.

Mechanochemical characteristics and influence mechanisms of a biomass hydrogel artificial muscle based on different parameters of the sodium alginate adjustment

Biomass hydrogel artificial muscle (BHAM) is a kind of ionic electroactive polymers, such as ionic polymer gels of good biocompatibility and stimulus responsiveness under electric field, which is largely used in the fields of soft robots and electric actuators. In this paper, based on the freeze-drying process, effect and influence mechanisms of sodium alginate (SA) parameters adjustment on the BHAM mechanochemical characteristics were researched extensively, which was verified by a set of perfect characteristic evaluation and experimental test methods, such as the porosity P (v%), water retention rate W r (w%), mechanochemical property testing and scanning electron microscope shots. The results showed that when the concentration of SA was 20 g l−1, the actuating film of BHAM had suitable thickness and stomata in macroscopic appearance, and its micro pore distribution and size were uniform with the thin pore wall, which resulted in the highest porosity (i.e. ion channel) of 73.5 v%, the largest water retention rate of 76.2 w% and the optimum tensile strength of 0.38 MPa. Furthermore, calcium chloride (CaCl2) was adopted as a cross-linking agent to react with the SA to form calcium alginate (CA) by different CaCl2 cross-linking ratios, that was to modify the three-dimensional microstructure of the BHAM to improve its mechanical properties with the best deflection displacement of 23.9 mm and bending strain of 3.45% under the ideal CaCl2 cross-linking ratio of 1%. Besides, the diffraction of x-rays analysis and thermal decomposition experiments of the BHAM were performed, which was demonstrated that the thermal stability of the CA-based BHAM was higher than that of the SA-based BHAM.

Anomalous elasticity and damping in covalently cross-linked graphene aerogels

Elasticity in materials is a phenomenon that provides a basis for widespread practical applications in engineering, medicine, and electronics. Most of the conventional materials can withstand only small deformations within the elastic limit, typically below 5% of their original size. Here, we report a graphene aerogel made of covalently cross-linked graphene sheets that exhibits anomalous superelastic behavior up to 92% of compressive and 68% tensile strain. We show that the graphene aerogel has a nonlinear stress-strain characteristic with the compressive and tensile yield strength of 4.5 GPa and 0.6 MPa, respectively. By considering the elastic bending of graphene sheets and buckle folding of pore walls, we develop a quantitative origami model that describes the stress-strain behavior of the aerogel. In addition, we analyze the mechanical oscillations of the graphene aerogel, observing superfast vibration damping within a time scale of 50–250 ns. Our study demonstrates the unusual coexistence of superelasticity and superfast damping within a cellular material with atomically thin pore walls, a phenomenon that does not occur in bulk elastic materials described by Hook’s law.

Energy level regulation to optimize hydrogen sensing performance of porous bimetallic gallium-indium oxide with ultrathin pore walls

Although hydrogen sensors with high-response have been extensively studied and developed, it is still a great challenge to achieve ultra-fast response and recovery, high sensitivity and excellent selectivity towards hydrogen (H2) for a gas sensor. Herein, porous Ga-In bimetallic oxide with atomically thin pore wall was synthesized by electrospinning and followed calcination. The sensor based on this sensing material (Ga1.2In0.8O3) showed ultra-short response and recovery time (≈1 s and 3 s), high response (Ra/Rg≈15–500 ppm H2), good reproducibility, remarkable stability, low detection limit (2 ppm) and excellent selectivity (without cross-response to carbon monoxide). The enhanced hydrogen gas sensing performance of this material can be attributed to its novel atomically thin wall, optimal Fermi level and abundant chemisorbed oxygen.

Preparation of Freeze-Dried Porous Chitosan Microspheres for the Removal of Hexavalent Chromium

Novel porous chitosan microspheres were successfully produced by a freezing–lyophilization drying method in this study and were then used as adsorbents to remove a toxic iron metal, hexavalent chromium (Cr(VI)). The effects of the concentration of the chitosan solution, syringe diameter, and freezing time on the morphologies of porous chitosan microspheres were characterized. The metal ion adsorption for Cr(VI) was also studied. Results showed that freezing chitosan hydrogel beads at a temperature of −20 °C and subsequently lyophilizing the frozen structure allowed to easily obtain the porous chitosan microspheres with rough surfaces and large pores, which were more suitable for adsorption materials to remove metal ions. A chitosan solution concentration of 3% (w/v) and a syringe diameter of 500 μm allowed the porous microspheres to have a good sphericity, thinner pore walls, and small pore sizes. The adsorption capacity of porous chitosan microspheres for Cr(VI) increased with the increase in freezing time. The pH of the initial adsorption solution ranged from 3.0 to 5.0 and was beneficial to the maximum adsorption efficiency for Cr(VI). The porous chitosan microspheres prepared with 3% (w/v) chitosan solution at −20 °C for a freezing time of 72 h had a higher adsorption capacity of 945.2 mg/g for Cr(VI) than the those at 24-h and 48-h freezing times. Kinetic study showed that the adsorption process could be described by a pseudo-second order (PSO) kinetic model. The equilibrium adsorption rate constant and the adsorption amount at equilibrium for the porous chitosan microspheres increased with an increase in the freezing time, and those for the porous microspheres prepared with 3% chitosan solution at −20 °C for a 72-h freezing time were 1.83 × 10−5 g mg−1 min−1 and 1070.5 mg g−1, respectively. The porous chitosan microspheres have good potential to facilitate the separation and recycling of expensive and toxic Cr(VI) from wastewater.

Preparation of Ordered Nanoporous Indium Tin Oxides with Large Crystallites and Individual Control over Their Thermal and Electrical Conductivities.

Metal oxides are considered suitable candidates for thermoelectric materials owing to their high chemical stabilities. The formation of ordered nanopores within these materials, which decreases thermal conductivity (κ), has attracted significant interest. However, the electrical conductivity (σ) of reported nanoporous metal oxides is low, owing to electron scattering at the thin pore walls and many grain boundaries formed by small crystallites. Therefore, a novel synthesis method that can control pore walls while forming relatively large crystallites to reduce κ and retain σ is required. In this study, we used indium tin oxide (ITO), which is a typical example among metal oxides with high σ. Nanoporous ITOs with large crystallite sizes of several hundred nanometers and larger were successfully prepared using indium chloride as a source of indium. The pore sizes were varied using colloidal silica nanoparticles with different particle sizes as templates. The crystal phase and nanoporous structure of ITO were preserved after spark plasma sintering at 723 K and 80 MPa. The κ was significantly lower than that reported for bulk ITO due to the phonon scattering caused by the nanoporous structure and thin pore walls. There was a limited decrease in σ even with high porosity. These findings show that κ and σ are independently controllable through the precise control of the structure. The control of the thickness of the pore walls at tens of nanometers was effective for the selective scattering of phonons, while almost retaining electron mobility. The remarkable preservation of σ was attributed to the large crystallites that maintained paths for electron conduction and decreased electron scattering at the grain boundaries.

Effect of anodizing temperature and organic acid addition on the structure and corrosion resistance of anodic aluminum oxide films

Anodic aluminum oxide films, industrially produced by anodizing aluminum alloys under the galvanostatic mode at a relatively low temperature of 20°C (electrolyte bath temperature), present the reliable anticorrosive effect for numerous applications. For fabricating anodic aluminum oxide films with the promising corrosion resistance as well as high growth rate in a wide temperature range, the effect of anodizing temperatures on the structure and growth mechanism of anodic aluminum oxide films was investigated. As the temperature increases up to 30°C, the stress-driven breakdown of porous-type anodic aluminum oxide layers induced by their thinner pore walls was estimated. This phenomenon is interpreted by an increase of electronic current and thus a strong scour effect of O2 bubbles on the porous-type anodic aluminum oxide layers. Moreover, with the addition of composite organic acid into the sulfuric acid-based electrolyte solution, the anions (C6H5O73−,C4H4O62−) that incorporated into the anodic oxide contribute to lowering the electronic current and thus suppressing the formation of oxygen bubbles, resulting in a thicker barrier-type anodic aluminum oxide layer. This is assumed to be responsible for the enhanced corrosion resistance of anodic aluminum oxide films prepared at 30°C with 50 g/L organic acid addition.

Fast and efficient oil-water separation under harsh conditions of the flexible polyimide aerogel containing benzimidazole structure

Fast and efficient oil-water separation materials under harsh conditions become urgent requirement for eliminating destruction of environment from offshore oil spill, oily wastewater produced in industry and life. Here, we designed and prepared polyimide (PI) aerogel with strong hydrogen bond by introducing benzimidazole structure. The hydrogen bond increases the intermolecular interactions to overcome the expansion force and capillary force during ice crystal growth and sublimation. The obtained PI aerogel has a mutually interleaved sheet three-dimensional network structure of thin pore walls (about 85 nm), interconnected pores and tortuous channels with a low shrinkage (about 7.8%). Moreover, due to the high hydrophobicity and morphological characteristics, the PI aerogel can be used for oil-water separation continuously under different harsh conditions, such as high viscosity oil (above 570 mPa·s), oil in cold/hot water (0 °C/120 °C), corrosive solution and emulsion. The separation efficiency and maximum oil flux can reach 99. 9% and 14320 L·m−2 h-1, respectively. Because of their fast and efficient oil-water separation performance in harsh environments, this PI aerogel shows great potential in the field of petroleum, municipal and industrial wastewater treatment.

Mesoporous Nitrogen-Doped Carbon-Nanosphere-Supported Isolated Single-Atom Pd Catalyst for Highly Efficient Semihydrogenation of Acetylene.

Semihydrogenation of acetylene in the ethylene feed is a vital step for the industrial production of polyethylene. Despite their favorable reaction activity and ethylene selectivity, the Pd-based intermetallic compound and single-atom alloy catalysts still suffer from the limitation of atomic utilization derived from the partial exposure of active Pd atoms. Herein, a hard-template Lewis acid doping strategy is reported that can overcome the inefficient utilization of Pd atoms. In this strategy, N-coordinated isolated single-atomic Pd sites are fully embedded on the inner walls of mesoporous nitrogen-doped carbon foam nanospheres (ISA-Pd/MPNC). This synthetic strategy has been proved to be applicable to prepare other ISA-M/MPNC (M = Pt and Cu) materials. This ISA-Pd/MPNC catalyst with both high specific surface area (633.8 m2 g-1 ) and remarkably thin pore wall (1-2 nm) exhibits higher activity than that of its nonmesoporous counterpart (ISA-Pd/non-MPNC) catalyst by a factor of 4. This work presents an efficient way to tailor and optimize the catalytic activity and selectivity by atomic-scale design and structural control.

Impact of membrane pore morphology on multi-cycle fouling and cleaning of hydrophobic and hydrophilic membranes during MBR operation

This study investigated the impact of membrane pore morphology on repeated fouling and physical cleaning behavior during > 1000 h operation of a membrane bioreactor process. Four microfiltration membranes with different backbone polymers (PVDF and PTFE) and varied hydrophobicity, operated in parallel, were compared. The PVDF membranes presented a porous particulate-packing morphology, while the PTFE/PVDF blend membranes (PTFE accounting for > 80% of monomer proportion) resembled a nonwoven network of thin fibrous material. These membranes had similar short-term apparent fouling rates in a single fouling-and-cleaning cycle, but different long-term fouling development due to their physical cleaning efficiencies differing in the order: hydrophobic PVDF << hydrophobic blend < hydrophilic (PVDF and blend) membranes, as revealed by statistical analyses. The physically irreversible fouling was likely attributed to hydrophobic adsorption onto the membranes, with the adsorbed polysaccharides and proteins detected using confocal laser scanning microscopy. The irreversibility of fouling on the blend membranes was much less sensitive to membrane hydrophobicity than that on the PVDF membranes, probably because the blend membranes had smaller adsorption propensity. For further evidence, the adsorption properties of the membranes were explored via batch tests of dynamic adsorption using model compounds, with the adsorption rate and equilibrium constants quantified using the Thomas model. The thin thread-like pore walls (which characterized the morphology of the blend membranes) may provide limited contact area for foulant adsorption, and/or weaken the interfacial membrane–foulant interaction via shape effect. Therefore, it is suggested that membranes with thin fibrous network-like pore morphology may perform more robustly and be less troubled by adsorptive irreversible fouling for long-term operation of MBR.

Physicochemical and microstructural characterisation of green gram and foxtail millet starch gels.

The starch and starch gels from green gram (GG) and foxtail millet (FM) were characterised for their physicochemical, thermal and microstructural characteristics; the features of shape and size were determined by image analysis. Both GG and FM formed well-set gels at 9% concentration of starch. The fracture strain of the gels was between 78 and 80% indicating non-brittle gels. The peak temperatures of the native flour of GG (74.9°C) and FM (75.7°C) were significantly higher than their corresponding starch samples (72.2 and 75.0°C). The conclusion temperatures of the FM native flour (81.2°C) and starch (79.4°C) samples were higher than the native GG flour (79.9°C) and GG starch (77.1°C) samples. Starches were nearly spherical as the roundness values were between 0.88 and 0.95. Green gram starch was pentagonal having an average diameter of 3.9-9.2µm while foxtail millet starch was spherical with a diameter of 4.9-10.1µm. The freeze-dried GG and FM starch gels showed cellular structure containing organised hexagonal pores, bound by thin pore walls; the GG starch gels deviated from the circular shape as they had the highest elongation value of 4.21. The thicker pore walls were observed for GG starch gels (0.88μm) compared to that of FM samples (0.57μm). The higher pore wall thickness in the case of GG gel showed the formation of junction zones.