Freeze Casting Method Research Articles

Corrigendum to “Changing conventional blending photocatalytic membranes (BPMs): Focuson improving photocatalytic performance of Fe3O4/g-C3N4/PVDF membranes through magnetically induced freezing casting method” [Chem. Eng. J. 365 (2019) 405–414

Corrigendum to “Changing conventional blending photocatalytic membranes (BPMs): Focuson improving photocatalytic performance of Fe3O4/g-C3N4/PVDF membranes through magnetically induced freezing casting method” [Chem. Eng. J. 365 (2019) 405–414

3D printing carbon from aqueous all aromatic polyimides

All-aromatic polyimides serve as versatile precursors for carbon formation due to their high aromatic content and repeating unit planarity, which synergistically enables pyrolysis to ordered carbon. Recent publications disclosed facile synthetic methods for additive manufacturing (3D printing) of all-aromatic polyimides using a pendant salt approach for ultraviolet-assisted direct ink write (DIW) additive manufacturing. This manuscript describes the introduction of pendant sodium sulfonate functionality to the poly(amic acids), and water-soluble all-aromatic polyimide precursors displayed suitable rheological properties for DIW at room temperature and vat photopolymerization (VP) at 50 °C. These aqueous solutions enabled the formation of microporous polyimide structures with a direct freeze-casting method and dense structures with gradual heating under inert atmosphere to 200 °C and subsequent thermal post-processing to 400 °C. Furthermore, polyimide 3D structures function as efficient carbon precursors when pyrolyzed at 2000 °C under inert atmosphere. Raman spectroscopy revealed carbonized 3D structures with characteristic graphitic and disordered carbon bands, which was indicative of polycrystalline, disordered glassy carbon. Furthermore, electrical conductivity measurements suggest opportunities for the formation of 3D conductive structures.

A hierarchical Bilayered scaffold for periodontal complex structure regeneration.

The periodontal tissue comprises alveolar bone, cementum, and periodontal ligament (PDL), forming a highly hierarchical architecture. Although current therapies could regenerate the hard tissue well, the simultaneous reconstruction of hard and soft tissue remains a great clinical challenge with the major difficulty in highly orientated PDL regeneration. Using the unidirectional freeze-casting method and biomimetic mineralization technique, we construct a hierarchical bilayer scaffold with the aligned chitosan scaffold with ZIF-8 resembling PDL, and intrafibrillarly mineralized collagen resembling alveolar bone. The hierarchical bilayer scaffold exhibits different geomorphic clues and chemical microenvironments to realize a perfect simulation of the natural periodontal hierarchical architecture. The aligned scaffold with ZIF-8 could induce the fibrogenic differentiation of bone mesenchymal stromal cells (BMSCs), and the mineralized scaffold could induce osteogenic differentiation of BMSCs. The hierarchical bilayer scaffold could simulate periodontal complex tissue, exhibiting great promise for synchronized multi-tissue regeneration of periodontal tissue.

MXene grafted porous carbon cloth with alumina for high thermal conductivity and EMI shielding effect

Thermal interface material (TIM) has a great potential for efficient heat management and safety of electronic devices. However, achieving high performance polymer-based TIM is still challenging because of its intrinsic thermal conductivity and weak mechanical properties. In particular, electromagnetic interference shielding effect (EMI SE) of polymer-based composites has a great attraction according to electronic devices have become ubiquitous, playing integral roles in everyday life in our increasingly interconnected world. Herein, a porous carbon cloth (CC) for use as a continuous thermally and electrically conductive template is prepared via a freeze-casting method, after which mxene (MX) is chemically grafted onto the CC surface. Then, the as-prepared MX-CC is used along with alumina (AO) to fill a poly vinyl alcohol (PVA) matrix in order to fabricate a thermally conductive film with electromagnetic interference (EMI) shielding properties. The resultant composite demonstrates remarkable characteristics, including an excellent EMI shielding effect of 28 dB, substantial tensile strength of 19 MPa, and impressive out of plane thermal conductivity (3.98 W/mK). When applied to a light-emitting diode (LED), the PVA/MX-CC/AO composite effectively manages heat, thereby resulting in a 49 °C reduction in the operating temperature. Therefore, the composites developed herein hold great promise for improving thermal management in electronic devices.

Compositing thermal conductivity behavior to enhance thermoelectric properties of honeycomb-like porous Ca3Co4O9 ceramics

Microstructures and thermoelectric properties of porous Ca3Co4O9 ceramics were investigated, which were prepared by tert-butanol alcohol (TBA)-based freeze casting method. The honeycomb-like porous Ca3Co4O9 ceramic presented an average pore diameter of 2.5 μm and the porosity of 65 %. The excellent low total thermal conductivity of 0.354 W (m K)−1 was obtained along the parallel channel direction, which was attributed to the oriented pores and isolated pores dispersed in ceramics matrix. The compositing thermal conductivity behavior of porous Ca3Co4O9 ceramics was jointly regulated by the parallel and Maxwell-Eucken (ME-1) models. The ZT value reached 0.37 at 1073 K. This work provides an effective strategy to improve thermoelectric properties of oxides thermoelectric ceramics, which can complete the decoupling of electrical and thermal properties.

Anisotropic cellulose-based phase change aerogels for acoustic-thermal energy conversion and management

Porous materials are usually used as sound-absorbing materials to alleviate noise pollution problems. However, the heat energy conversed from the acoustic energy is wasteful. Herein, anisotropic cellulose-based phase change aerogels (MXene/CNF-C/PEG aerogels) are fabricated by facile directional freeze casting method with anisotropic porous structure, efficient sound wave absorption, acoustic-thermal conversion and thermal management capability. MXene/CNF-C/PEG aerogels with shape stability are formed by hydrogen bonding forces between carboxylated cellulose nanofibers (CNF-C) and PEG without chemical crosslinking. The addition of MXene not only increases thermal conductive performance to 150 % but also enhances acoustic-thermal conversion ability effectively. Moreover, the directional porous MXene/CNF-C/PEG aerogels (DMCPs) possess high energy storage density (143.0 J/g) and acoustic-thermal conversion performance, which open up broad application prospect in the field of acoustic to heat energy conversion and storage.

Preparation of Fibrous Three-Dimensional Porous Materials and Their Research Progress in the Field of Stealth Protection.

Intelligent and diversified development of modern detection technology greatly affects the battlefield survivability of military targets, especially infrared, acoustic wave, and radar detection expose targets by capturing their unavoidable infrared radiation, acoustic wave, and electromagnetic wave information, greatly affecting their battlefield survival and penetration capabilities. Therefore, there is an urgent need to develop stealth-protective materials that can suppress infrared radiation, reduce acoustic characteristics, and weaken electromagnetic signals. Fibrous three-dimensional porous materials, with their high porosity, excellent structural adjustability, and superior mechanical properties, possess strong potential for development in the field of stealth protection. This article introduced and reviewed the characteristics and development process of fibrous three-dimensional porous materials at both the micrometer and nanometer scales. Then, the process and characteristics of preparing fibrous three-dimensional porous materials through vacuum forming, gel solidification, freeze-casting, and impregnation stacking methods were analyzed and discussed. Meanwhile, their current application status in infrared, acoustic wave, and radar stealth fields was summarized and their existing problems and development trends in these areas from the perspectives of preparation processes and applicability were analyzed. Finally, several prospects for the current challenges faced by fibrous three-dimensional porous materials were proposed as follows: functionally modifying fibers to enhance their applicability through self-cross-linking; establishing theoretical models for the transmission of thermal energy, acoustic waves, and electromagnetic waves within fibrous porous materials; constructing fibrous porous materials resistant to impact, shear, and fracture to meet the needs of practical applications; developing multifunctional stealth fibrous porous materials to confer full-spectrum broadband stealth capability; and exploring the relationship between material size and mechanical properties as a basis for preparing large-scale samples that meet the application's requirement. This review is very timely and aims to focus researchers' attention on the importance and research progress of fibrous porous materials in the field of stealth protection, so as to solve the problems and challenges of fibrous porous materials in the field of stealth protection and to promote the further innovation of fibrous porous materials in terms of structure and function.

Biomimetic Leaf-Vein Aerogel for Electromagnetic Wave Absorption and Thermal Superinsulation.

Electromagnetic protection in extreme environments requires materials with excellent thermal insulation capability and mechanical property to withstand severe temperature fluctuations and complex external stresses. Achieving strong electromagnetic wave absorption (EMA) while sustaining these exceptional properties remains a significant challenge. Herein, a facile approach is demonstrated to fabricate a biomimetic leaf-vein MXene/CNTs/PI (MCP) aerogel with parallel venations through bidirectional freeze-casting method. Due to its multi-arch lamellar structure and parallel venations within the aerogel layers, the ultralight MCP aerogel (16.9 mg·cm-3) achieves a minimum reflection loss (RLmin) of -75.8dB and a maximum effective absorption bandwidth (EABmax) of 7.14GHz with an absorber content of only 2.4wt%, which also exhibits superelasticity and structural stability over a wide temperature range from -196 to 400°C. Moreover, this unique structure facilitates rapid heat dissipation within the layers, while significantly impeding heat transfer between adjacent layers, achieving an ultralow thermal conductivity of 15.3 mW·m-1·K-1 for thermal superinsulation. The combination of excellent EMA performance, robust structural stability, and thermal superinsulation provides a potential design scheme under extreme conditions, especially in aerospace applications.

Sponge-like porous polyvinyl alcohol/chitosan-based hydrogel with integrated cushioning, pH-indicating and antibacterial functions

Developing a packaging material with integrated cushioning, intelligent and active functions is highly desired but remains challenging in the food industry. Here we show that a sponge-like porous hydrogel with pH-indicating and antibacterial additives can meet this requirement. We use polyvinyl alcohol and chitosan as the primary polymers to construct a hydrogel with hierarchical structures through a freeze-casting method in combination with salting-out treatment. The synergy of aggregated polymer chains and the sponge-like porous structure makes the hydrogel resilient and efficient in energy absorption. It also enables rapid movement of molecules/particles and fast reaction due to the large specific surface area of the pore structures and the large amount of free water in it, leading to a sensitive pH-indicating function. The hydrogel shows an obvious color variation within a wide pH range in 3 min. The silver nanoparticles are fixed in the dense polymer networks, enabling a lasting release of silver ions. The porous structure makes the silver ion reach the protected item in a short time, achieving an antibacterial effect against S. aureus and E. coli with little cytotoxicity. This work paves the way for fabricating multifunctional hydrogels for diverse advanced packaging systems.

Control of microstructure to prepare compressible graphene aerogel via ice template

The microstructure of graphene aerogel (GA) plays a crucial role in determining its performance. However, challenges persist in simplifying and enhancing control over the microstructure of GA. In this study, we introduce a novel bidirectional freeze-casting method, allowing for the preparation of GAs with three different microstructures. Notably, the GA with concentric ring structure exhibits exceptional compressibility and fatigue resistance in both axial and radial directions, capable of undergoing 5000 compression-recovery cycles at 90 % strain and 70 % strain, respectively. In-situ SEM characterization provides insights into the energy dissipation mechanism during compression processes. GA with radial microstructure demonstrates an impressive absorption capacity ranging from 165.82 to 369.47 g/g. Moreover, the GA with concentric ring microstructure displays non-linear resistance changes with strain under both axial and radial compression. These GAs demonstrate significant potential applications in environmental remediation and flexible electronics.

(Ca0.25La0.5Dy0.25)CrO3 Ceramic Fiber@Biomass-Derived Carbon Aerogel with Enhanced Solute Transport Channels for Highly Efficient Solar Interface Evaporation.

The use of solar interface evaporation for seawater desalination or sewage treatment is an environmentally friendly and sustainable approach; however, achieving efficient solar energy utilization and ensuring the long-term stability of the evaporation devices are two major challenges for practical application. To address these issues, we developed a novel ceramic fiber@bioderived carbon composite aerogel with a continuous through-hole structure via electrospinning and freeze-casting methods. Specifically, an aerogel was prepared by incorporating perovskite oxide (Ca0.25La0.5Dy0.25)CrO3 ceramic fibers (CCFs) and amylopectin-derived carbon (ADC). The CCFs exhibited remarkable photothermal conversion efficiencies, and the ADC served as a connecting agent and imparted hydrophilicity to the aerogel due to its abundant oxygen-containing functional groups. After optimizing the composition and microstructure, the (Ca0.25La0.5Dy0.25)CrO3 ceramic fiber@biomass-derived carbon aerogel demonstrated remarkable properties, including efficient light absorption and rapid transport of water and solutes. Under 1 kW m-2 light intensity irradiation, this novel material exhibited a high temperature (48.3 °C), high evaporation rate (1.68 kg m-2 h-1), and impressive solar vapor conversion efficiency (91.6%). Moreover, it exhibited long-term stability in water evaporation even with highly concentrated salt solutions (25 wt%). Therefore, the (Ca0.25La0.5Dy0.25)CrO3 ceramic fiber@biomass-derived carbon aerogel holds great promise for various applications of solar interface evaporation.

Synthesis of micro/nano multi-scale polyimide aerogels via confinement-controlled freeze-casting

The freeze-casting is widely utilized as a tool for regulating micro-scale pore structures in the fabrication of flexible polyimide (PI) aerogels for applications in adsorption, filtration, and fire-retardant. Herein, a confinement-controlled freeze-casting method is developed to fabricate PI aerogels with excellent thermal insulation properties by designing multi-scale structural adaptability. In a confinement-controlled system, the enhanced solid/solid and solid/liquid interface interactions in the solution dispersion system induce dendritic evolution of ice crystals. Under the directional freezing, grown dendritic ice crystals squeeze the loaded particles to form polyamic acid salt (PAAs) cryogels. Followed by template removal and thermal imidization, PI aerogels with a micro/nano-scale slit-like porous structure were obtained. The PI aerogels are characterized by ultra-low density (as low as 9.82 mg/cm3) and exceptional thermal insulation performance (25.0 mW/(m·K) at 25 °C).

Freeze-cast porous Al2O3/MgO ceramics as potential acoustic sound absorption

In acoustic engineering and architecture, materials called acoustic absorbers are widely used. There are currently numerous options for such materials, and many more are being researched. This study is conducted on porous ceramics produced via the freeze-casting process to propose new solutions with unique properties, like resistance to harsh environments. The freeze-casting method allows for the controlled creation of open-connected porous structures for different class materials through the cryogenic freezing of the suspension. The material samples are produced with Al2O3 (alumina)/MgO (magnesium oxide) material using camphene as solvent. The specimen samples are prepared using three different concentrations of the two solid components (60/40, 72/28, and 90/10 in weight). Each sample concentration achieves different morphology phase compositions and porous structures. Hence, we explore in the paper how those concentration parameters could interfere with acoustic absorption. Further, the samples were characterised using numerical and experimental methods related to sound absorption and microstructure. The 60/40 and 90/10 samples achieve sound absorption coefficient values upwards of 0.7 around the 2000-3000 Hz frequency range. The microstructure characteristics show the porosity gradually changing along its thickness, interfering with their sound absorption properties. Our findings highlight the complexities of characterising porous ceramics and emphasise the significance of understanding some material composition factors affecting sound absorption. Hence, this study provides valuable insights into the intricate nature of porous ceramic freeze-cast materials and their acoustic properties, substantially contributing to the ongoing exploration in this domain.

A controllable foaming approach for the fabrication of “rattan-like” graphene-based composite aerogel with desirable microwave absorption capacity

As a common environmental pollutant, microwave can cause great harms to human health. The development of high-performance microwave absorber with lightweight is indeed necessary. Herein, “rattan-like” graphene-based composite aerogels, having macroscopic pores surrounded by plenty of small pores, were designed and fabricated via an in-situ foaming then carbonized approach. Firstly, graphene oxide (GO), nanocellulose and ferrous ions were integrated into an aerogel with uniform large pores via a freeze-casting method. Then, the aerogel was immersed into a H2O2 solution, during which bubble clusters generated in situ. These bubbles were driven into the stacked GO sheets and formed small pores. With the increase of the H2O2 concentration from 0.5 to 10 wt%, the count percentage of the small pores in the aerogel increased from 81.5 to 95.2%. After the final carbonization, the graphene sheets were dually interconnected with magnetic nanoparticles and carbonized nanocellulose. The unique porous structure and dual-connected networks endowed the aerogel with enhanced conductive loss and optimized impedance matching capacity, and thus an excellent microwave absorption performance, whose maximum reflection loss achieves −68.5 dB. Further, the aerogel also exhibited superior sound absorption performance (noise reduction coefficient up to 0.91 in 1000–6300 Hz), and good mechanical stability.

Microstructural evolution of lamellar freeze-cast Fe-Cu-Ni foams during oxidation/reduction cycling

A novel iron-based alloy, Fe-15Cu-10Ni (wt%), has been introduced as a candidate for storage energy of iron air batteries. Cyclical experiments involving steam oxidation and hydrogen reduction were conducted on the Fe-15Cu-10Ni (wt%), lamellar foams fabricated by freeze-casting method, and were compared with the Fe-25Cu and Fe-25Ni alloys with the same foam structure. The experiments were carried out at a high temperature of 800 °C, which is relevant to the energy storage in iron-air batteries. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques are employed to analyze the microstructure and chemical evolution of the cycled foams. Upon oxidation, Fe-15Cu-10Ni lamellae form a core rich in Ni and Cu (since Cu and Ni do not oxidize under steam), surrounded by an Fe3O4 shell. This reduces fractures and slows down the growth of Kirkendall pores, thereby delaying the sintering and densification of the foam structure. Upon reducing Fe3O4, the Fe-rich shells and the Cu-rich and Ni-rich cores homogenize, creating a reversible microstructure after a complete redox cycle. The Fe-15Cu-10Ni composition presents notable advantages compared to Fe-25Ni, exhibiting a higher oxidation rate, increased energy density, and lower cost. As a result, Fe-15Cu-10Ni emerges as the optimal composition within the scope of this study, showcasing superior properties.

Enhanced electromagnetic absorption properties of the double-layer Ti3C2Tx MXene absorber with orthogonal microstructures

A double-layer MXene absorber with orthogonal microstructures was designed unidirectional freeze-casting method, which yielded favorable electromagnetic wave absorption properties by tuning the thickness ratio of the parallel ends when the parallel sample was used as an impedance matching layer.

Biobased Tannic Acid-Chitosan Composite Membranes as Reusable Adsorbents for Effective Enrichment of Phosphopeptides.

High-performance reusable materials from renewable resources are rare and urgently required in bioseparation. Herein, a series of tannic acid-chitosan composite membranes for the enrichment of phosphopeptides were fabricated by the freeze casting method. First, a tannic acid-chitosan composite membrane was acquired via the multiple hydrogen bonds between tannic acid and chitosan, which had a long-range aligned three-dimensional microstructure. Second, a covalent-hydrogen bond hybrid composite was also fabricated, with stable and aligned honeycomb-like microstructures that formed by the synergy of covalence and hydrogen bonding. Besides, a ternary composite membrane was "one-pot" synthesized by the copolymerization of tannic acid, chitosan, and Ti4+ ions, indicating the feasibility of involving metal ions in the composition of the polymer skeleton in place of additional modification steps. The as-prepared chitosan composite membranes exhibited excellent performance in the enrichment of phosphopeptides from β-casein tryptic digest and human serum. Benefitting from the long-range aligned honeycomb-like structure coordinated by hydrogen bonds and covalent bonds, and a large number of pyrogallol functional groups provided by tannic acid, the covalent-hydrogen bond hybrid membrane showed excellent reusability and could be reused up to 16 times in phosphopeptide enrichment, as far as we know, which is the best reported result to date.

Thermal insulating and mechanical properties of high entropy pyrochlore oxide ceramic with hierarchical porous structures

High entropy pyrochlore oxide ceramics with hierarchical porous structures were prepared by coprecipitation, freeze-casting, and press-less sintering methods. In the fabrication process, a Ca2+-crosslinked alginate network was utilized to control the growth of ice crystals, resulting in uniformly dispersed micro-scale circular pores. The submicron pores were formed in the high entropy oxide ceramic during the press-less sintering method. The XRD was employed to explore the phase of the high entropy pyrochlore oxide ceramic. The porous structures of high-entropy ceramic were analyzed through the discussion of microstructure and pore size distribution. The tests show that the prepared series of ceramics with high porosity have optional compressive strength and thermal insulation properties. The high entropy oxide ceramic (La0.2Y0.2Gd0.2Sm0.2Nd0.2)2Zr2O7 with hierarchical porous structures possess moderate density (0.4 g/cm3) and low thermal conductivity (0.04 W m−1 K−1). The excellent comprehensive performance makes the porous high entropy oxide ceramic could be applied as a thermal insulating material.

Porous mullite fiber-based ceramics inspired by biomimetic natural pine wood

How to further improve the strength of fiber porous ceramics has always been the focus of researchers. Herein, inspired by the unique microstructure of natural woods which exhibit excellent mechanical and thermal insulation properties, a high strength mullite fiber-based porous ceramic with wood-like microstructure was successfully designed and fabricated. The wood-like porous ceramics were mainly composed of two kinds of layered structures that are perpendicular to each other. The horizontally oriented lamellar structure was constructed by assembling the fiber membranes layer by layer, and the vertically oriented lamellar structure perpendicular to the fiber layer was constructed by the directional freeze casting method. The results indicated that as to the mullite fiber-based porous ceramics with the similar density (∼0.36 g/cm3), the compressive strength along the X-axis direction of porous ceramics with wood-like microstructure prepared by the directional freeze casting method (3.4 MPa) was much higher than that of porous ceramics prepared by the non-directional freeze casting method (1.04 MPa), owing to the formation of silica lamellar structure perpendicular to the fiber layers. In addition, the wood-like mullite fiber-based porous ceramics also exhibited excellent thermal insulation performance along the X direction due to existence of a large number of pores in the fiber layers. This study provides a new strategy for the preparation of a high-strength thermal insulating fiber-based porous ceramic.

Fabrication and characterization of glycerin-plasticized soy protein amyloid fibril scaffolds by unidirectional freeze casting method

Soy protein amyloid fibrils (SAFs) plasticized with glycerin were prepared into aligned porous scaffolds through the unidirectional freeze casting method. The impact of the amount of glycerin on the structural and functional properties of the SAFs-Gly scaffolds was investigated. Scanning electron microscopy confirmed that the aligned pore size and distribution of the scaffolds, with diameters ranging of 10–50 μm, could be adjusted by varying the amount of glycerin. Increasing the glycerin content decreased the median pore size of the scaffolds and increased the strain at the yield point by up to 40%. Additionally, the water resistance of the scaffolds significantly increased without any obvious changes in morphology. Differential scanning calorimetry analysis revealed two glass transitions in the SAFs/glycerin systems, corresponding to the glycerin-rich and protein-rich domains, respectively. FTIR spectroscopy indicated the formation of hydroxyl interactions and intermolecular hydrogen bonding between SAFs and glycerin. X-ray diffraction and small-angle X-ray scattering suggested that glycerin can induce SAFs crystallization, structural separation, and exfoliation of β-sheets to some extent. These results demonstrate the prospective application of this approach in the preparation of food-based polymer scaffolds and its usefulness in the food industry.