Graphene Oxide Aerogels: From Synthesis Pathways to Mechanical Performance and Applications

Abstract

Graphene oxide (GO) aerogels were discovered as lightweight, highly porous materials with exceptional mechanical, electrical, and thermal properties. These properties make them suitable for a wide range of advanced applications. This paper discusses GO aerogel synthesis processes, characterization, mechanical properties, applications, and future directions. The synthesis methods discussed include hydrothermal reduction, chemical reduction, crosslinking methods, and 3D printing, with major emphasis on their effects on the aerogel’s structural and functional attributes. A detailed analysis of mechanical characterization techniques is elaborated upon, along with highlighting the effects of parameters such as porosity, crosslinking, and graphene concentration on mechanical strength, elasticity, and stability. Research has been carried out to find GO aerogel applications in various sectors, such as energy storage, environmental remediation, sensors, and thermal management, showcasing their versatility and potential. Additionally, the combination of nanoparticles and doping strategies to improve specific properties is addressed. The review concludes by identifying current challenges in scalability, brittleness, and property optimization and proposes future directions for synthesis innovations. This work will be helpful for researchers and engineers exploring new possibilities for GO aerogels in both academic and industrial areas.

1. Introduction

Graphene was discovered in 2004, and since then it has gained significant attention due to its remarkable electrical, thermal, and mechanical properties. It exhibits high strength, large strain-to-failure, and an extensive specific surface area [1,2]. These factors make graphene an important material for applications in various fields, including, but not limited to, composites [3], nanoelectronics [4], energy storage [5], sensors [6], catalysis [7], and biomedicine [8]. However, if graphene is added to polymeric matrices, then it often falls short in theoretical performance due to poor dispersion and agglomeration caused by π–π stacking interactions [9]. To fully explore graphene’s potential, researchers have focused on transforming its two-dimensional (2D) form into three-dimensional (3D) structures like aerogels [10], hydrogels [11], and macroporous films [12].

Graphene aerogels are lightweight, porous nanomaterials with high surface areas, tunable porosity, and large pore volumes [13]. These aerogels, typically prepared from GO through sol–gel methods followed by freeze- or supercritical drying, exhibit remarkable properties, such as high porosity (90–99%), low density, low thermal conductivity, and high mechanical strength [14]. GO serves as an ideal precursor for graphene oxide aerogels (GOAs) due to its excellent dispersibility in aqueous media and the abundance of oxygen-containing functional groups, which enable covalent interactions with various crosslinking agents and functional moieties. The self-assembly of GO sheets into three-dimensional porous networks is primarily driven by π–π stacking and hydrophobic interactions that occur upon partial reduction. However, the resulting aerogels often exhibit inherent brittleness, necessitating further structural optimization to improve their mechanical robustness [15].

GO aerogels are a distinct class of three-dimensional (3D) porous materials created by assembling GO nanosheets into lightweight, interconnected networks. They combine the unique two-dimensional structure and abundant surface functionalities of GO with a highly porous architecture, resulting in materials that are markedly different from both conventional aerogels and bulk GO powders. Compared to silica or polymer-based aerogels, which often exhibit brittleness and limited chemical tunability, GO aerogels offer superior elasticity, robust compressive resilience, and extensive opportunities for functionalization due to oxygenated groups on GO sheets [6,7,9,12]. This facilitates the incorporation of nanoparticles, polymers, or biomolecules, enabling multifunctional applications that traditional aerogels typically cannot achieve [13,14].

Unlike typical GO powders or films, which tend to restack and lose accessible surface area, GO aerogels maintain an open, interconnected pore network that supports rapid mass and ion transport [6,7,9,12,13,14]. This makes them particularly attractive for adsorption, catalysis, and energy-related applications. Moreover, their synthesis is highly versatile, encompassing hydrothermal self-assembly, chemical or polymeric crosslinking, and even 3D printing, allowing tailored macro- and microstructures for specific performance needs [7,12,13,14]. These features position GO aerogels as a promising platform for next-generation multifunctional materials, bridging the gap between exceptional nanoscale GO properties and practical macroscopic architecture.

Their unique combination of properties makes GO aerogels suitable for diverse applications, including energy storage as electrodes in lithium-ion batteries and supercapacitors [16] gas sensing [17], air purification [18], and photocatalysis [19]. Additionally, the incorporation of nanoparticles or doping with elements like nitrogen further enhances their functionality, such as improving their mechanical properties, lithium-ion storage, and thermal management. Despite challenges in scalability and brittleness, graphene aerogels (GAs) represent a promising class of materials for cutting-edge technologies, driving ongoing research into innovative synthetic strategies, characterization techniques, and application-specific optimization. This review aims to provide a comprehensive overview of GO aerogel synthesis, characterization, and applications, offering insights that are valuable to both academic and industrial audiences.

Table 1. Graphene oxide and its composite aerogel properties and applications.

Composite Material	Properties	Applications	Refs.
Graphene oxide/Polymer aerogel	High porosity, lightweight, improved mechanical strength	Thermal insulation, energy storage	[20]
Graphene oxide/SnO2	Superior anode performance, high specific capacity	Lithium-ion batteries	[21]
Reduced graphene oxide/Fe2O3	Enhanced supercapacitive performance, high porosity	Supercapacitors	[22]
Copper nanowires/Graphene aerogel	Improved thermal conductivity, EMI shielding	Electromagnetic interference shielding	[23]
MoSe2-Cu1.82Se@GA	High capacity, excellent cycle stability	Sodium-ion batteries	[24]
Graphene oxide/Polymer composite	High mechanical strength, flexibility, low density	Adsorption, separation, sensors	[25]

gives an overview of GO aerogels for different applications after manufacturing.

2. Synthesis Methods of GO Aerogels

2.1. Hydrothermal Reduction of GO Aerogels

The hydrothermal reduction method is the most common approach for producing graphene hydrogels, followed by drying (either through freeze-drying or supercritical drying) to obtain graphene aerogels [16]. This method consists of the self-assembly of graphene sheets by reduction of GO, which promotes the stacking and alignment of graphene nanosheets, in the end forming monoliths and 3D graphene structures [26]. This process requires high temperatures (120–200 °C) and high pressure. In this process, GO solution is sealed in an autoclave cylinder and heated for a required time and temperature [27,28]. These conditions help to control the gelation rate and maintain the structural integrity of the gel.

Chemical reduction and gelation or crosslinking occur simultaneously during the assembly of GO. This a phenomenon observed not only in hydrothermal methods but also in sol–gel [29] and other synthesis techniques [30,31]. This dual action makes hydrothermal reduction an efficient and widely adopted technique, as it is a simple process, but there are challenges such as limited control over pore size and uniformity. This may require further processing for specific applications [32]. However, the method remains a turning point in the development of high-performance GO-based aerogels [33]. Figure 1 shows a schematic of the hydrothermal process.

The hydrothermal approach drives the self-assembly of GO sheets through a combination of thermal reduction and enhanced molecular motion under elevated temperature and pressure. During this process (typically 120–200 °C in a sealed autoclave), partial deoxygenation restores the sp² domains on GO, increasing π–π stacking interactions between sheets [7,28]. Concurrently, the confined conditions accelerate collisions and facilitate sheet interlinking into a continuous 3D network. The concentration of GO is a crucial factor: too low may fail to reach the percolation threshold for gelation, while too high may lead to dense aggregates with reduced porosity [13]. The reaction time controls the extent of reduction and crosslinking, directly influencing pore wall thickness and the microstructure. This method often yields an isotropic, random, porous architecture with moderate pore sizes.

2.2. Chemical Reduction

The chemical reduction method is a versatile and widely used approach to produce graphene-based aerogels. This method involves the use of mild reducing agents, such as hydrazine, vitamin C, sodium ascorbate, or acids and bases to restore the sp² carbon network in GO [35,36,37,38]. Unlike thermal reduction, which requires high temperatures [28] and inert or reducing environments, chemical reduction offers a milder and more environmentally friendly route. It is also considered superior to hydrothermal reduction in some aspects, as it avoids the need for high pressure, high temperatures, and additional chemical crosslinkers. Figure 2 illustrates the chemical reduction process used for synthesizing GO aerogels. In this method, a suitable reducing agent—such as L-ascorbic acid, hydrazine, or sodium ascorbate—is added to a GO dispersion to restore the sp² carbon network. This initiates the self-assembly of GO sheets into a three-dimensional porous gel structure. The resulting hydrogel is then freeze-dried to preserve its architecture and obtain the final lightweight GO aerogel. This schematic highlights the simplicity and versatility of chemical reduction approaches in fabricating aerogels with tunable properties.

During the reduction process, GO sheets self-assemble into a 3D network structure. For example, Zhang et al. [7] demonstrated the use of oxalic acid and sodium iodide as a reaction system to create low-density, highly porous 3D graphene assemblies [39]. Additionally, mercaptoacetic acid and mercaptoethanol have been employed as reducing agents to facilitate in situ self-assembly of rGO [40]. While this method is effective, the π–π interactions between graphene layers during the reduction process often leads to restacking, which can reduce the surface area of the resulting aerogels. GO contains abundant oxygen-containing functional groups, which improve its dispersibility in water and facilitate chemical modification. By contrast, rGO has fewer functional groups and a more graphitic structure, leading to higher electrical conductivity but reduced hydrophilicity.

An alternative to chemical reduction is electrochemical reduction, which is often used to produce high-quality graphene-based materials. In this approach, graphene sheets act as substrates for supporting functional materials such as metal oxides [41]. For instance, Chen et al. [40] developed a one-step in situ electrochemical method to synthesize graphene/CeO₂ aerogels. This process involved electrochemical exfoliation of graphite and simultaneous deposition of CeO₂ nanoparticles on graphene sheets. The aerogels were subsequently obtained through freeze-drying. The inclusion of functional materials like transition metal oxides enhances the properties and potential applications of the aerogels, making this a promising route for advanced material synthesis.

In chemical reduction, self-assembly is triggered by adding mild reducing agents (like ascorbic acid, hydrazine, or sodium borohydride) to a GO dispersion. As oxygen-containing groups are removed, GO sheets become more hydrophobic, increasing van der Waals attractions and π–π interactions [37,38]. This destabilizes the colloidal stability of GO, promoting flocculation and 3D network formation. The choice and concentration of the reducing agent, solution pH (often maintained acidic to stabilize GO before reduction), and reaction temperature are critical. Faster reduction can produce smaller, more uniform pores by rapidly locking sheets into place, whereas slower reduction may allow more extended sheet reorganization, sometimes leading to larger, less uniform pores.

Overall, chemical reduction is a flexible and efficient method for producing GO aerogels, offering tunable properties and adaptability for various applications. However, challenges like restacking and reduced surface area may require optimization depending on the intended use [42].

2.3. Crosslinking Method

Crosslinking methods are one of the important procedures for the fabrication of robust and functional GO aerogels. This affects aerogel properties by enhancing the bonding between GO sheets and stabilizing the 3D network structure. Crosslinkers such as hydrogen bonds [43], multivalent metal ions [44], or chemical agents [13] promote gelation by increasing the bonding forces between GO sheets. As a result, aerogels became mechanically stable and tunable.

Hydrogen bonding plays a important role in the gelation of GO [45]. GO is a hydrophilic compound and forms a stable solution in water under neutral pH conditions. However, reducing the pH of the solution weakens electrostatic repulsion and strengthens hydrogen bonding due to the protonation of carboxyl groups on GO [46]. Hydrogen bonding promotes gelation and stabilizes the GO network. Crosslinkers with hydroxyl [47], oxygen-containing [48], or nitrogen functional groups [49] increase the bonding forces and contribute to the formation of stable GO aerogels.

Another effective crosslinking approach involves the use of multivalent metal ions, such as Ca²⁺, Mg²⁺, Pb²⁺, and Cr³⁺ [49,50]. These metal ions interact with GO sheets through strong bonding forces, facilitating self-assembly and gelation. The concentration of GO significantly affects the resulting pore density and size, enabling control over the aerogel’s structural properties [51].

Figure 3 illustrates the synthesis strategy of a typical GO-chitosan (GO-CS) aerogel, adapted from Pinelli et al. [52]. In this approach, a GO suspension is vigorously mixed with an aqueous chitosan solution, followed by the addition of ammonium persulfate (APS) as an oxidizing agent to induce crosslinking of the polymeric network. The resulting hydrogel is then subjected to freeze-drying to obtain the final porous GO-CS aerogel. Such schematics help to highlight the versatility of crosslinking strategies in fabricating mechanically stable, multifunctional GO-based aerogels.

In addition to physical and ionic interactions, chemical crosslinking methods such as the sol–gel [31] process offer stronger bonding. In this method, covalent bonds form between GO sheets through polymerization. This reaction produces graphene/carbon aerogels, which, after pyrolysis, exhibit exceptional properties, including high specific capacitance (122 F g⁻¹ at 50 mA g⁻¹), large surface area (361–763 m² g⁻¹), low density (0.11–0.19 g cm⁻³), and high electrical conductivity (528 S m⁻¹). These materials are valuable for most of applications, like supercapacitors [53] and energy storage devices [54].

Crosslinking strategies stabilize GO networks by introducing polymers (like chitosan and polyvinyl alcohol) or multivalent ions (e.g., Ca²⁺ and Fe³⁺) that bind to GO sheets via hydrogen bonding, ionic interactions, or even covalent bonding [54]. This chemically or physically bridges the GO sheets, forcing them into a stable 3D gel structure even at relatively low GO concentrations. The crosslinker concentration, solution pH (which affects ionization and availability of binding sites), and mixing protocol are critical in determining gelation time and the resulting network density. Crosslinking often leads to more robust but slightly denser pore walls, yielding microstructures that are well suited for mechanical reinforcement. Crosslinking methods provide flexibility for changing the mechanical, electrical, and structural properties of GO aerogels. Researchers can design aerogels by selecting appropriate crosslinkers and processes for a wide range of advanced applications.

2.4. 3D Printing

3D printing combined with freeze-drying has emerged as a versatile and efficient method for fabricating GO aerogels with complex shapes and tunable properties. This approach allows precise control over the structure and porosity of the aerogel while enabling the creation of intricate geometries for advanced applications [55]. A notable technique is the freeze gelation method, which involves the use of organic solvents with high boiling points and vapor pressures to replace water as the freezing medium [56]. This process enables solidification at room temperature (RT) without the need for a container, unlike aqueous freeze gelation methods.

In this method, graphene-based materials such as pristine graphene or rGO are dispersed in a solvent above its boiling point (typically 50–120 °C) through sonication. The mixture is then cooled, forming a solid material at RT. Subsequent rapid solvent sublimation at ambient conditions results in a nanostructured, porous graphene aerogel. The advantages of using organic solvents include flexibility in processing, as materials can be molded, extruded, or 3D-printed before solidification. This eliminates the need for surfactants or functionalization agents to disperse the materials.

Three-dimensional printing further enhances the utility of GO aerogels by enabling the deposition of GO solutions in precise patterns [57]. Typically, aqueous GO solutions mixed with polymers are printed and then gelated through water removal via freeze-drying or supercritical drying [58]. Following gelation, the aerogels are reduced at elevated temperatures to achieve rGO aerogels with improved mechanical and electrical properties [55].

The RTFG method also supports the incorporation of additional materials, such as multiwalled carbon nanotubes (MWCNTs) and polymers, to improve the aerogel’s mechanical strength [56]. For instance, adding poly(vinyl alcohol) (PVA) to a graphene/phenol solution significantly increases the Young’s modulus and yield strength of the resulting aerogel [59]. The final microstructure of these aerogels depends on factors such as the graphene concentration, solvent type, polymer content, and cooling rate [60]. Solvent rejection during solidification creates a microporous network with graphene-rich regions, forming nanoporosity within the microporous walls [61].

In extrusion-based 3D printing, GO or GO/polymer inks are deposited layer by layer. The shear force during extrusion aligns GO sheets along the printing direction [58]. Upon subsequent freeze-drying or thermal reduction, this alignment is partially preserved, creating anisotropic microstructures. Critical factors include ink rheology (viscosity adjusted by GO concentration or added polymers), extrusion speed, and nozzle diameter, all of which determine strand uniformity and interlayer adhesion. This method enables the design of macro-architectured aerogels with controlled orientation and gradient porosity, distinct from random isotropic networks formed by conventional self-assembly. Overall, 3D printing combined with freeze-drying or RTFG provides a powerful platform for producing high-performance GO aerogels with customizable properties for a range of applications.

Beyond these primary approaches, additional techniques such as freeze-casting and layer-by-layer (LbL) assembly have also been explored to fabricate GO aerogels with distinct microstructural features. In freeze-casting, a GO dispersion is directionally frozen so that growing ice crystals expel the GO sheets into concentrated interstitial regions. Upon freeze-drying, this results in a highly aligned lamellar or columnar pore structure, with the freezing rate and imposed temperature gradient critically determining pore size and orientation [2,7,13]. This method is particularly advantageous for engineering aerogels with anisotropic mechanical strength and directional mass transport pathways. Meanwhile, LbL assembly constructs 3D architectures by alternately depositing GO nanosheets and oppositely charged polyelectrolytes or differently functionalized GO layers, building up the structure through successive electrostatic adsorption steps. This process allows precise control over layer thickness, composition, and interfacial chemistry, enabling the creation of stratified porous networks with tailored surface functionalities. Although slower than bulk gelation techniques, LbL offers exceptional tunability, making it suitable for applications requiring carefully engineered pore connectivity or chemical selectivity [20]. Incorporating these additional strategies broadens the design space for GO aerogels, providing diverse routes to tune microstructure in line with specific functional requirements.

In summary, the microstructure of GO aerogels varies significantly depending on the synthesis method employed. Figure 4 provides representative images of aerogel microstructure produced by various methods of fabrication. Hydrothermal reduction typically yields a sponge-like, three-dimensional porous network with interconnected, wrinkled graphene walls and large meso- to macropores formed due to gas evolution during thermal reduction. By contrast, chemical reduction using agents such as ascorbic acid or hydrazine produces aerogels with a more lamellar or stacked morphology, often displaying less uniform porosity and a tendency toward partial restacking of sheets. Crosslinking methods introduce covalent or non-covalent bonds between GO sheets, leading to a more stable and uniformly distributed pore structure with enhanced mechanical strength and reduced collapse under stress. Finally, 3D printing allows for precise architectural control, generating aerogels with highly ordered, anisotropic pore channels and designed geometries, although sometimes at the expense of nanoscale porosity. Overall, hydrothermal and crosslinking methods offer superior internal connectivity and flexibility, while 3D printing provides structural customization ideal for engineered applications.

3. Factors Affecting Mechanical Properties

3.1. Density and Porosity

The density and porosity of GO aerogels are important parameters that heavily influence their mechanical properties. These mainly depend on the initial concentration of GO in the precursor solution and the synthesis process [28,53,66]. Low-density aerogels are characterized by high compressibility and lightweight structures. These low-density aerogels are perfect for applications like thermal insulation and lightweight components [67]. However, these aerogels mostly lack the mechanical strength required for load-bearing applications [68]. On the other hand, high-density aerogels have greater rigidity and strength, which makes them suitable for structural uses [69]. The porosity, containing micropores, mesopores, and macropores, of GO aerogels affects their energy absorption and load distribution capabilities [70]. Required pore size and distribution is produced by fine control over parameters such as freezing rates [71], crosslinking agents [45], and drying techniques [72]. For example, rapid freezing produces smaller pores, while slower freezing allows for larger, more uniform pore structures. This ability to modify their density and porosity makes GO aerogels highly versatile. This enables their optimization for use in various applications that require specific mechanical and functional properties.

Generally, higher porosity results in reduced mechanical strength due to a larger volume of voids, which diminishes the load-bearing capacity of the aerogel structure [53,70]. Conversely, aerogels with lower porosity (higher density) possess a greater solid framework, leading to enhanced compressive strength and stiffness but often at the expense of flexibility and energy absorption capacity [28,53,66]. Thus, optimizing porosity is essential to balance mechanical robustness with lightweight and functional requirements for specific applications.

The porosity of GO aerogels is typically measured using techniques such as nitrogen adsorption–desorption isotherms (BET analysis) to determine the specific surface area and pore size distribution [53], mercury intrusion porosimetry for quantifying total porosity and pore throat sizes [70], and micro-computed tomography (micro-CT) to visualize and quantify the three-dimensional pore architecture [71]. These characterization methods provide insights into how synthesis parameters (e.g., GO concentration, freezing rates, and crosslinkers) influence the hierarchical pore structure, thereby directly affecting the aerogel’s mechanical properties [53].

3.2. Crosslinking Agents

Crosslinking agents play an important role in improving mechanical strength and structural integrity. The main purpose of these agents is to create bonds between graphene sheets to form a robust three-dimensional network [73]. Commonly used crosslinking agents are poly vinyl alcohol [59], resorcinol-formaldehyde [74], and multivalent metal ions like Ca²⁺ or Mg²⁺. The type and concentration of the crosslinking agent has a direct effect on gelation, which ultimately influences the mechanical properties of the aerogel. In one study, resorcinol-formaldehyde was used as the crosslinking agent to form a strong covalent bond. After synthesis, the results were analyzed, revealing an aerogel with high strength and rigidity because the multivalent ions enhanced self-assembly through ionic bonding [75]. In another study, scientists used hydrogen as a natural crosslinking mechanism for low-pH environments. This promoted gelation without the need for additional chemicals [76]. Crosslinking not only improves the mechanical properties but also provides stability against external forces. These two properties make GO aerogels suitable for applications like energy storage. Therefore, careful selection of crosslinking agent is important to improve mechanical performance to meet specific requirements.

3.3. Freezing and Drying Methods

To prepare aerogels, freeze-drying is used to remove water molecules from the hydrogel. It influences the properties of the aerogel. The method selected impacts the aerogel microstructure and consequently its mechanical properties. The freezing rate decides the aerogel’s structure and size of pores [72,77]. Unidirectional freezing creates anisotropic structures [78] with lamellar or aligned pores. This aligned structure provides higher strength and specific orientations [79]. On the other hand, non-directional freezing creates isotropic structures with uniform mechanical properties [80]. One study showed the difference between the effects of freeze-drying and supercritical drying on the aerogel’s structural integrity [81]. Freeze-drying removes the solvent by sublimation, which keeps the porous network as is with minimal shrinkage [82]. In supercritical drying, the surface tension effects are removed, resulting in aerogels with higher mechanical strength and lower density [83]. These methods not only influence the mechanical properties but also determine the aerogel’s thermal and electrical conductivity. Therefore, selection of the freeze-drying technique is important based on the requirements and application. Figure 5 shows the difference in the structure of the aerogel if it is dried using the freeze-drying (FD) method or the supercritical drying method (ScD).

In freeze-drying, the water present in the hydrogel is first frozen and then sublimated under low pressure. This minimizes capillary forces that could otherwise collapse the delicate porous network. As a result, freeze-dried GO aerogels retain their highly porous architecture, typically with porosities exceeding 90% and low bulk densities (~5–20 mg/cm³) [72,82].

By contrast, conventional air drying causes substantial shrinkage and collapse of the pore walls due to strong capillary stresses during solvent evaporation, leading to denser, less porous, and mechanically weaker materials. For example, Ye et al. [72] demonstrated that freeze-dried GO-epoxy aerogels maintained an elastic porous network, whereas air-dried samples suffered structural collapse, drastically reducing their surface area and mechanical resilience.

Freeze-drying also allows control over pore size via tuning the freezing rate. Rapid freezing results in smaller pores, whereas slower freezing creates larger pore architectures [71]. Moreover, studies by Xie et al. [81] comparing freeze-drying (FD) and supercritical drying (ScD) showed that while ScD can yield slightly higher mechanical strength due to reduced surface tension effects, FD better preserves hierarchical porosity and is more practical for large-scale synthesis. Thus, freeze-drying offers an effective, scalable method to fabricate GO aerogels with tailored microstructures, balancing mechanical integrity with high porosity.

During freeze-drying, the ice crystal growth velocity determines the size and distribution of the pores formed upon sublimation. Rapid freezing leads to the formation of numerous small ice crystals, resulting in aerogels with smaller, more uniform pores and thicker walls, which generally translates into higher compressive strength and stiffness [71]. This is due to a more homogeneous and denser skeletal network that better resists mechanical deformation. However, overly rapid freezing may trap stresses and lead to micro-cracks upon thawing or drying.

By contrast, slower freezing rates allow the growth of larger ice crystals, yielding aerogels with larger pores and thinner walls. These structures typically exhibit lower compressive strength but demonstrate improved deformability, energy absorption, and resilience under cyclic loading due to their open architecture [77]. Moreover, directional or unidirectional freezing not only controls the rate but also orients the ice growth in a specific direction, producing anisotropic lamellar structures. These aerogels display significantly enhanced mechanical strength and modulus along the aligned direction while maintaining flexibility perpendicular to it [78,79]. This anisotropy is particularly beneficial for applications that demand directional load bearing or shock absorption.

3.4. GO Concentration

The concentration of the GO solution has a direct impact on the final density, porosity, and mechanical properties of graphene aerogels. High GO concentrations result in aerogels with tightly packed graphene sheets, leading to higher density and improved mechanical strength [84]. These aerogels are better suited for applications requiring rigidity and durability. On the other hand, low GO concentrations produce ultralight aerogels, resulting in low strength, higher flexibility, and compressibility. Ultralight aerogels are suitable for thermal insulation and cushioning. Concentration affects the gelation process and the distribution of pores within the aerogel [42]. According to a study conducted to analyze the effect of higher concentrations, the results showed that it promotes smaller and more uniform pores, which enhances structural stability [85]. As the concentration of the GO solution increases, the time required for the gelation process also increases. Overall, by adjusting the GO concentration, researchers can fine-tune the balance between strength, flexibility, and weight to meet application requirements [86]. Additionally, Figure 6 indicates the effect of GO concentration on various aerogel properties. It shows that the gelation time decreases with increasing GO content up to 1.0 wt% due to enhanced sheet interactions. Beyond 1.0 wt%, the gelation time rises slightly, likely due to increased viscosity and aggregation, indicating an optimal GO loading for efficient gelation. Figure 6 demonstrates that both Mode I fracture toughness (K_IC) and fracture surface roughness (Ra) increase with graphene contents of up to ~0.8 wt%, indicating improved crack resistance due to better load transfer and interfacial bonding. However, at higher contents, performance plateaus or slightly drops, likely due to graphene agglomeration. Comparison with other carbon-based fillers (c) shows that GA/EP composites outperform others, particularly when aligned parallel to the loading direction, emphasizing the role of filler orientation and dispersion quality

Higher GO concentrations facilitate the formation of a tightly interconnected graphene network with reduced voids, thereby significantly increasing the compressive strength and Young’s modulus [85]. For instance, studies have shown that increasing the GO content up to ~0.8 wt% improves fracture toughness (K_IC) and surface roughness due to better load transfer and enhanced interfacial bonding [85]. Beyond this threshold, however, excessive GO may induce aggregation, leading to localized defects that slightly compromise mechanical performance and reduce porosity, affecting functionalities like adsorption and mass transport.

Lower GO concentrations yield ultra-lightweight aerogels with very high porosity and large interconnected voids, which enhances flexibility and specific surface area but generally results in diminished mechanical robustness [84]. Additionally, lower concentrations can prolong gelation time due to insufficient sheet interactions [86]. Therefore, careful optimization of the GO concentration is critical to balance between achieving desirable mechanical strength and maintaining the high porosity essential for many functional applications, such as adsorption, catalysis, and sensor platforms.

3.5. Additives and Reinforcements

The incorporation of additives and reinforcements significantly enhances the mechanical properties of GO aerogels by reinforcing the aerogel matrix and providing additional load-bearing pathways. The most-used additives include carbon nanotubes (CNTs), polymers such as poly vinyl alcohol (PVA), and metal oxides. Taking CNTs as an example [87], they improve the tensile strength and elasticity of GO aerogels by fulfilling gaps between graphene sheets and distributing stress more evenly. Polymers like PVA increase the Young’s modulus and yield strength by introducing elastic and covalent bonds within the aerogel structure [88,89,90]. Metal oxides can add functionality, such as improved thermal or electrical conductivity, while simultaneously enhancing mechanical performance [91]. The selection and concentration of additives must be carefully optimized to avoid compromising the aerogel’s lightweight and porous nature. These reinforcements enable the development of GO aerogels with superior mechanical properties, making them suitable for advanced applications, including aerospace, energy storage, and flexible electronics.

3.6. Temperature and Pressure During Synthesis

The temperature and pressure conditions during the synthesis of graphene aerogels greatly influence their mechanical properties. High-temperature and high-pressure processes, such as hydrothermal reduction, promote the alignment and bonding of graphene sheets, resulting in aerogels with enhanced strength and stiffness [92]. These conditions also facilitate the reduction of GO to rGO [93], restoring the sp2 carbon network and improving mechanical and electrical properties [94]. However, milder synthesis conditions, such as those used in chemical reduction, produce aerogels with different mechanical profiles. The ability to control the temperature and pressure provides a versatile tool for tailoring the mechanical properties of GO aerogels to meet specific application needs.

3.7. Structural Anisotropy

The anisotropy of the internal structure of graphene aerogels significantly affects their mechanical behavior. Aerogels with directional microstructures, such as those produced by unidirectional freezing, exhibit higher strength along specific orientations due to the alignment of graphene sheets and pores [79]. This anisotropy can be advantageous for applications requiring directional load-bearing capabilities. By contrast, isotropic aerogels, formed through non-directional freezing methods, offer uniform strength and flexibility in all directions [95]. The degree of anisotropy can be controlled during synthesis by adjusting the freezing rate [96], solvent [97], and additives [98]. Understanding and leveraging structural anisotropy allows for the design of GO aerogels with tailored mechanical properties for specialized applications, such as lightweight structural components and energy-absorbing materials.

3.8. Functionalization and Reduction

The functionalization and degree of reduction of GO to rGO play crucial roles in determining the mechanical properties of graphene aerogels. Functional groups on GO sheets, such as hydroxyl, carboxyl, and epoxy groups, facilitate crosslinking and enhance gelation [53]. However, excessive reduction can lead to restacking of graphene sheets due to strong π–π interactions, reducing porosity and surface area [99]. Controlled reduction processes, such as chemical or electrochemical methods [100], balance the restoration of the sp2 carbon network with preservation of the aerogel’s porous structure. Functionalization with polymers, metal ions [101], or other additives [86] further enhances the mechanical performance by strengthening the aerogel matrix. By carefully managing functionalization and reduction, researchers can optimize the mechanical properties and functionality of graphene aerogels for diverse applications.

Table 2. Graphene oxide synthesis processes and its results.

Process Sequence	Description	Porosity	Mechanical Properties	Advantages	Challenges	Refs.
1. GO Dispersion → Hydrothermal Treatment → Freeze-Drying	GO is dispersed in water, heated in an autoclave to induce gelation, then freeze-dried to form an aerogel.	High porosity (80–99%)	Moderate compressive strength, ~0.2–0.8 MPa	Simple method, preserves 3D structure	Long processing time, high energy requirement	[102]
2. GO Dispersion → Chemical Reduction → Freeze-Drying	GO dispersion is chemically reduced (e.g., with hydrazine), then freeze-dried to form an aerogel.	High porosity (80–98%)	Improved strength, ~1–5 MPa	Good reduction of GO, lightweight aerogel	Toxic reductants (e.g., hydrazine), requires freeze-drying	[103]
3. GO Dispersion → Self-Assembly → Supercritical Drying	GO forms a gel via self-assembly, which is then supercritically dried to form an aerogel.	Very high porosity (>95%)	Moderate mechanical strength, ~0.1–0.5 MPa	Preserves high porosity and surface area	Requires expensive supercritical drying equipment	[104]
4. GO Dispersion → Freeze-Casting → Freeze-Drying	GO solution is directionally frozen, followed by sublimation and reduction to form an anisotropic aerogel.	Anisotropic porosity (~99%)	Low compressive strength (up to ~0.02 MPa)	Tailored anisotropic pore structure, Low mechanical properties	Requires control over freezing conditions	[105]
7. GO Dispersion → Electrostatic Layer-by-Layer Assembly → Drying	GO is assembled layer-by-layer using electrostatic interactions, then dried to form an aerogel.	High porosity (~90–95%)	Tunable mechanical properties (~0.2–0.4 MPa)	Controlled structure, layer thickness	Time-consuming, not highly scalable	[106]
8. GO Dispersion → Crosslinking (Polymer) → Freeze-Drying	GO is crosslinked using a polymer, followed by freeze-drying to form an aerogel.	Moderate porosity (~75–90%)	Enhanced mechanical properties (~0.02–0.2 MPa)	Tailored mechanical properties	Requires additional crosslinking agent	[72]
9. GO Dispersion → 3D Printing → Drying (Freeze/Supercritical)	Direct ink writing or extrusion of GO/polymer inks into designed lattices, followed by drying and reduction.	Customizable; ~75–95%	High flexibility, fatigue-resistant, shape recovery >80%	Precise architecture, scalable, multifunctional	Requires rheological tuning, limited resolution	[57,58]

illustrates the process sequences for the preparation of GO aerogels and their impacts on aerogel properties.

4. Characterization of Mechanical Properties

The mechanical characterization of GO aerogels is critical to understanding their potential applications in structural, energy storage, thermal insulation, and tribological systems. Due to the hierarchical and porous architecture of GO aerogels, their mechanical behavior significantly varies with synthesis method, structural parameters (porosity, density, pore orientation), chemical functionalization, and reinforcement strategy. The primary mechanical properties relevant to GO aerogels include compressive strength, elastic modulus, toughness, flexibility, recoverability, and fatigue resistance.

Compressive strength represents the maximum stress a GO aerogel can withstand under compression before structural failure occurs. For example, hydrothermally reduced GO aerogels, known for their interconnected porous networks, typically demonstrate compressive strengths ranging between 0.5 and 1 MPa at densities of around 10–20 mg/cm³ [107,108,109]. This high strength-to-weight ratio is particularly favorable for lightweight structural applications.

The elastic modulus (Young’s modulus) quantifies the stiffness of GO aerogels, indicating their resistance to deformation under mechanical stress. Chemically crosslinked GO aerogels often prepared using covalent or ionic crosslinkers (e.g., borate ions and polyvinyl alcohol) exhibit elastic moduli between 10 and 100 kPa, highlighting their capability to retain structural integrity under repeated mechanical loads [72,110,111,112].

Toughness, defined as the total energy absorbed by the aerogel before fracture, is crucial for applications involving energy dissipation, such as vibration damping and protective packaging. GO aerogels reinforced with polymers, carbon nanotubes (CNTs), or biomolecules often exhibit significantly enhanced toughness (approximately 50–200 J/m³) due to effective energy dissipation mechanisms facilitated by their composite nature [113,114,115].

Flexibility and recoverability are particularly critical for aerogel materials subjected to cyclic mechanical stresses. Aerogels prepared via freeze-casting or directional freezing typically possess aligned pore structures, which endow them with high flexibility and shape recoverability. These structures can recover over 80% of their original dimensions after significant compressive deformation, highlighting their suitability for cyclic mechanical applications [116,117,118,119].

Fatigue resistance measures an aerogel’s capability to withstand repeated mechanical loading cycles without structural degradation. Aerogels produced via additive manufacturing (3D printing) often display superior fatigue resistance due to their precise architectural design and controlled pore orientation. For instance, 3D-printed GO aerogels with engineered lattices exhibit negligible structural changes even after thousands of compressive loading cycles, thus demonstrating their robustness for long-term use [120,121,122,123].

The mechanical properties of GO aerogels synthesized using various techniques are summarized in

Table 3. Mechanical properties and typical ranges according to previous studies.

Mechanical Property	Example (Aerogel Type)	Typical Range/Value	References
Compressive Strength	Hydrothermally reduced GO aerogel	0.5–1 MPa	[107,108,109]
Elastic Modulus	Chemically crosslinked GO aerogel	10–100 kPa	[72,110,111,112]
Toughness	Polymer-GO composite aerogel	50–200 J/m3	[113,114,115]
Flexibility and Recoverability	Freeze-casted/directionally frozen GO aerogel	>80% shape recovery	[116,117,118,119]
Fatigue Resistance	3D-printed GO aerogel	>1000 cycles with minimal degradation	[120,121,122,123]

.

There are a few characterization technique used in day-to-day life for analyzing other various aspects of materials, such as X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy [40]. More than that, advanced techniques for the characterization of the mechanical properties of GO aerogels can be innovatively performed by integrating multi-modal analysis [124] and real-time performance monitoring [125] under specific conditions. Conventional methods that mainly focus on bulk properties, such as compressive strength or elasticity, can be incorporated along with advanced imaging techniques like X-ray computed tomography (XCT) or 3D electron microscopy. This provides more clarity for researchers to visualize the internal microstructure under stress. This offers deeper insights into failure mechanisms, crack propagation, and structural anisotropy.

Hybrid mechanical testing setups, such as combining dynamic mechanical analysis (DMA) [69] with acoustic emission sensors, can capture subtle mechanical responses like micro-fractures or viscoelastic damping that are often missed in traditional setups [126]. According to recent trends, incorporating machine learning models to analyze test data in real time can help to predict GO aerogels’ mechanical behavior. This information can be utilized to decide the range of operating conditions and provide predictive insights into long-term durability [127].

One step ahead of traditional characterization, researchers have integrated environmental chambers for simultaneous testing under required conditions, including high humidity, temperature gradients, or oxidative environments, mimicking real-world applications [128]. Ahmedi et al. [129] used a novel approach that involved multiscale mechanical testing, where nanoindentation results were correlated with macroscopic compression or tensile testing data to fill the gap between local and global material properties.

Finally, combining traditional mechanical tests with functional property measurements, such as electrical conductivity or thermal insulation under deformation, provides a broader perspective of how mechanical strain influences multifunctionality [130]. These innovations provide clearer analyses of GO aerogels’ properties as well as directions for design optimization for next-generation applications. These directions are useful for creating adaptive materials, energy-absorbing devices, and multifunctional composites.

5. Applications

While numerous studies have explored the potential applications of GO aerogels, it is equally important to understand the current technological limitations in each field and how GO aerogels offer unique solutions. This section discusses not only representative applications but also the state-of-the-art, critical challenges, and innovative ways GO aerogels can help to advance these domains.

There are diverse applications of GO aerogels because of their exceptional mechanical properties, such as compressive strength and elasticity [128]. For energy storage devices, their lightweight yet strong structures ensure durability under cyclic loads [88]. However, the thermal insulation capabilities of GO aerogels make them suitable for aerospace [131] and cryogenic applications [132]. The porous property of aerogels supports environmental uses like water purification and oil spill cleanup [133], as well as biomedical applications such as tissue scaffolds and drug delivery systems [134]. Their shock absorption and energy dissipation properties make aerogels suitable for protective gear, impact-resistant packaging, and acoustic insulation. This wide property range of GO aerogels makes them multifunctional materials in cutting-edge technologies. Table 4 discusses the applications of GO aerogels and desired properties in special case examples.

The circular schematic shown in Figure 7 provides a comprehensive overview of graphene-based composite aerogels, emphasizing their composition, structure, and diverse applications. It highlights how different material combinations, such as polymers, 2D nanosheets, metal nanoparticles, and ionic materials, affect their structural performance and enhance functionalities like porosity, thermal insulation, and electrochemical behavior. The outermost layer connects these features to real-world applications, including water purification, biomedical usage, sensors, energy storage, and flame-retardant materials, showcasing the multifunctional nature of GO aerogels and their significance in advanced material science.

Figure 7. Overview of graphene-based composite aerogels, illustrating their composition, structure, properties, and wide range of applications [135].

Figure 7. Overview of graphene-based composite aerogels, illustrating their composition, structure, properties, and wide range of applications [135].

Table 4. Graphene oxide aerogel applications and related properties.

Application	Relevance to Mechanical Properties	Key Features Utilized	Examples/Use Cases	Refs.
Energy Storage Devices	High porosity, lightweight structure, and mechanical stability ensure long-term performance under cyclic loads.	High surface area, low density, excellent compressive strength.	Supercapacitors, lithium-ion batteries, fuel cells.	[54]
Thermal Insulation	Low thermal conductivity with adequate compressive strength to maintain structural integrity.	Low density, resilience under thermal expansion.	Heat shields, cryogenic insulators in space technology.	[136]
Environmental Applications	Good mechanical stability supports repeated use in adsorption and filtration processes.	Compressive strength, chemical resilience.	Oil spill cleanup, heavy metal adsorption, water purification filters.	[137]
Biomedical Scaffolds	Biocompatibility combined with structural support for tissue engineering and drug delivery.	Elasticity, porosity, and compressive strength suitable for cellular growth.	Bone tissue scaffolds, slow-release drug carriers.	[138]
Lightweight Structural Materials	High compressive modulus and toughness ensure performance under load without significant deformation.	Superior strength-to-weight ratio.	Aerospace components, lightweight automobile parts.	[139]
Shock Absorption	Energy dissipation is under impact due to elastic deformation of the aerogel matrix.	Viscoelastic behavior, reversible compressive deformation.	Impact-resistant packaging, vibration dampers in machinery.	[140]
Catalysis Support	Strong, stable structures maintain integrity during catalytic reactions under extreme conditions.	Mechanical durability under high temperature and pressure.	Catalyst carriers in chemical reactors, photocatalysis applications.	[7]
Flexible Electronics	Elastic properties and flexibility enable integration into wearable devices and stretchable sensors.	High elasticity, durability under repetitive deformation.	Wearable health monitors, pressure sensors, strain gauges.	[141]

Table 4. Graphene oxide aerogel applications and related properties.

Application	Relevance to Mechanical Properties	Key Features Utilized	Examples/Use Cases	Refs.
Energy Storage Devices	High porosity, lightweight structure, and mechanical stability ensure long-term performance under cyclic loads.	High surface area, low density, excellent compressive strength.	Supercapacitors, lithium-ion batteries, fuel cells.	[54]
Thermal Insulation	Low thermal conductivity with adequate compressive strength to maintain structural integrity.	Low density, resilience under thermal expansion.	Heat shields, cryogenic insulators in space technology.	[136]
Environmental Applications	Good mechanical stability supports repeated use in adsorption and filtration processes.	Compressive strength, chemical resilience.	Oil spill cleanup, heavy metal adsorption, water purification filters.	[137]
Biomedical Scaffolds	Biocompatibility combined with structural support for tissue engineering and drug delivery.	Elasticity, porosity, and compressive strength suitable for cellular growth.	Bone tissue scaffolds, slow-release drug carriers.	[138]
Lightweight Structural Materials	High compressive modulus and toughness ensure performance under load without significant deformation.	Superior strength-to-weight ratio.	Aerospace components, lightweight automobile parts.	[139]
Shock Absorption	Energy dissipation is under impact due to elastic deformation of the aerogel matrix.	Viscoelastic behavior, reversible compressive deformation.	Impact-resistant packaging, vibration dampers in machinery.	[140]
Catalysis Support	Strong, stable structures maintain integrity during catalytic reactions under extreme conditions.	Mechanical durability under high temperature and pressure.	Catalyst carriers in chemical reactors, photocatalysis applications.	[7]
Flexible Electronics	Elastic properties and flexibility enable integration into wearable devices and stretchable sensors.	High elasticity, durability under repetitive deformation.	Wearable health monitors, pressure sensors, strain gauges.	[141]

Traditional adsorbents like activated carbon and silica aerogels, while effective for certain contaminants, often struggle with slow adsorption kinetics, limited regeneration cycles, and structural collapse after repeated use. Recent advances emphasize the need for materials that combine high surface area with robust recyclability and tunable surface chemistry to target diverse pollutants [133]. GO aerogels, with their interconnected porous networks and abundant oxygen-containing groups, have demonstrated superior adsorption efficiencies and faster kinetics, as reported by Ye et al. [72]. However, challenges remain in designing aerogels that can selectively adsorb contaminants in multi-component systems and in developing low-energy regeneration processes.

The current state-of-the-art in supercapacitor and battery electrodes relies heavily on activated carbons or carbon nanotube composites, which often face trade-offs between high surface area and sufficient electrical conductivity [54]. GO aerogels, particularly after partial reduction, bridge this gap by offering large accessible surface areas with continuous conductive networks. For instance, Korkmaz and Kariper [53] demonstrated that rGO aerogel-based electrodes delivered specific capacitances exceeding 200 F/g with stable cycling. Despite these advances, optimizing ion transport within hierarchically porous structures and scaling reproducible electrode architectures remain pressing challenges [142,143]. On the other hand, researchers have discovered that they can be used as insulators as well [144].

Conventional silica or polymer aerogels excel at minimizing thermal conductivity but often suffer from brittleness, restricting their application in dynamic or load-bearing environments. GO aerogels provide a compelling alternative by simultaneously offering low thermal conductivity (~0.03 W/mK) and exceptional mechanical resilience, maintaining over 90% height after repeated compressive cycles, as reported by Joshi et al. [77]. Nonetheless, further work is needed to engineer directional heat flow via anisotropic pore architectures, an area where freeze-casting and 3D printing are beginning to show promise.

In biomedical and sensing applications, the combination of high porosity, ease of functionalization, and mechanical flexibility makes GO aerogels attractive as scaffolds or responsive platforms [134,138]. However, ensuring biocompatibility over long implantation periods and integrating precise electrical or chemical responsiveness remain key areas for future research.

6. Future Directions

After the discovery of GO aerogels, tremendous work has been conducted; however, there are few areas that need to be explored. Upcoming research on the mechanical characterization of GO aerogels should focus on integrating advanced analytical techniques and expanding application-specific testing frameworks. One such advanced testing technique is the development of in situ systems that combine mechanical analysis with high-resolution imaging such as 4D X-ray computed tomography (XCT) or in situ electron microscopy. This testing would help to monitor real-time microstructural evolution under stress. Also, machine learning algorithms can be utilized to analyze large datasets from multiscale tests. This would provide output as predictive models for mechanical performance and failure mechanisms under diverse operating conditions.

Research on the relationship between mechanical properties and multifunctionality is a gray area. Studies need to be conducted on how mechanical strain affects other functional properties, like electrical conductivity, thermal insulation, or catalytic efficiency. This opens the door for the design of smart aerogels that adapt to external stimuli. Also, research on the changes in properties of GO aerogels under extreme environments, such as high radiation, cryogenic temperatures, or corrosive conditions, can improve their potential in aerospace, energy storage, and environmental remediation applications.

Another crucial point is the development of customized fabrication techniques to obtain microstructures for specific mechanical properties. Extensive studies need to be performed on composites of GO aerogels, including combining GO with other materials, such as carbon nanotubes, metallic nanoparticles, or polymers, to enhance strength, elasticity, and durability. Also, utilizing knowledge of bio-inspired designs and hierarchical structures will make aerogels mechanically robust and lightweight.

Finally, there is a need to conduct research on preparing standardized protocols for the characterization of GO aerogels to make it reproduceable and compatible across studies. This discussion points to enriching the understanding of GO aerogels’ mechanical behavior and broadening their applicability in next-generation materials for cutting-edge technologies.

7. Summary

GO aerogels represent a unique class of lightweight, highly porous materials with remarkable mechanical, thermal, and electrical properties. This review has comprehensively examined their synthesis strategies, including hydrothermal reduction, chemical reduction, crosslinking, and 3D printing, and their influence on the resulting aerogel’s microstructure and mechanical behavior. Each method offers distinct advantages in tailoring porosity, alignment, and network stability. The mechanical performance of GO aerogels, characterized by parameters such as compressive strength, elasticity, toughness, and fatigue resistance, is influenced by several factors, including density, pore morphology, crosslinking chemistry, GO concentration, and drying protocols. GO aerogels demonstrate immense potential across a broad spectrum of applications, ranging from energy storage and thermal insulation to environmental remediation, sensors, and biomedical scaffolds, owing to their multifunctionality and tunable architecture. However, challenges such as brittleness, scale-up limitations, and reproducibility in mechanical behavior remain critical barriers. Addressing these challenges through composite integration, smart structural design, and machine learning-guided optimization will be key to expanding the utility of GO aerogels in next-generation materials and engineering systems.