MXene Templated Assembly of Hierarchical Al/CuO/V2C Nanothermite with Excellent Energy Release Efficiency and Highly Tunable Performance

doi:10.21203/rs.3.rs-5038378/v1

Download PDF

Article

MXene Templated Assembly of Hierarchical Al/CuO/V₂C Nanothermite with Excellent Energy Release Efficiency and Highly Tunable Performance

https://doi.org/10.21203/rs.3.rs-5038378/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Nanothermite garners significant interest due to its higher energy release rate and reactivity. However, the agglomeration of nanoparticles has become the major hindrance to the energy release efficiency of nanothermite. Here, we proposed a bottom-up strategy and a facile preparation method to build a hierarchical Al/CuO/V₂C nanocomposite triggered by ordered self-assembly of Al and CuO nanoparticles in ethanol suspension, using V₂C MXene as a template. The unique structure is formed by the competition between the electrostatic force of Al and the covalent Cu-O-V bond to the V₂C surface. The established structure as well as the high reactivity of V₂C result in a complete oxidation of Al, and the heat of the reaction reaches 3156.2 J/g with a 10 wt% addition of V₂C in air atmosphere, being sevenfold of the Al/CuO control group. The evolving concentration-dependent structure provides highly tunable energetic performance, which varies from a shortened 3-ms deflagration to a prolonged 16-ms combustion. The lower gas release improves the safety of Al/CuO/V₂C while paving the way for promising application in microinitiators.

Physical sciences/Materials science/Nanoscale materials/Nanoparticles

Physical sciences/Nanoscience and technology/Nanoscale materials/Structural properties

MXene

Self-assembly

Nanocomposite

Nanothermite

Energy release efficiency

Nanothermite is a new class of energetic materials that emerged from the blooming of nanotechnology, which has been widely used in igniters, thrusters, and ammunition ^1–3. As a combination of thermite and nanotechnology, nanothermite utilizes nanoparticles to replace traditional micro or larger-sized ones in both oxidizers and aluminum. The largest benefit of doing so is the significant improvement in the energy release rate of the thermite reaction due to the increment of the surface-to-volume ratio that facilitates the reactivity ^4–6. However, the large surface area of nano-sized Al and oxidizer also brings additional surface energy, leading to the spontaneous agglomeration of nanoparticles to minimize energy, which in turn severely damages the energy release efficiency of nanothermite ^7,8.

Large efforts have been made to alleviate the agglomeration of nano Al and oxidizer particles so that a more even mixing between Al and oxidizer can be achieved, which can be classified into two types according to whether additives are used. For those additive-free ones, a top-down micromachining method is generally adopted in the fabricating process, such as magnetic sputtering ^9,10, E-beam evaporation ^11,12, electrospray ¹³, and electrospinning ¹⁴. These methods achieved homogeneity through a multilayer or core-shell structure and are compatible with integrated circuits (IC) and micro electromechanical systems (MEMS) manufacturing, which can be potentially integrated into chips. However, these methods tend to introduce more alumina passivation layers at Al/oxidizer interfaces in the air atmosphere that impede reaction while being energy and time-consuming ¹⁵. For those including additives, a bottom-up strategy is preferable in which the additive serves as a binder between Al and oxidizer to build desired structures of nanothermite through self-assembly ¹⁶, such as core-shell ⁵ and nanocomposite ¹⁷ structures. These additives have successfully reduced the agglomeration of nanoparticles from the adhesion, allowing more contact between Al and the oxidizer. Nevertheless, the additives usually contribute little to the thermite reaction while hindering the oxygen diffusion aside from the initial alumina passivation layer, and the structural advantage is counteracted.

As summarized above, although many efforts have been made, both top-down and bottom-up approaches struggle to alleviate the agglomeration without harming the energy release efficiency of the thermite reaction. To tackle this challenge, here we introduced a strategy of fabricating hierarchical nanothermite through ordered self-assembly of Al and oxidizer nanoparticles using the single layer MXene as a template. MXenes have received a lot of attention owing to their rich surface chemistry, adjustable structures, and abundant surface terminations ¹⁸. While the negatively charged surface terminations provide chances for the self-assembly of positively charged Al and oxidizer nanoparticles through long-range electrostatic force ¹⁹, the highly reactive surface of MXene also opens the gate for the short-range interfacial covalent bonding with oxidizer particles ²⁰. The different types of bonding would result in the hierarchical structure during the self-assembly process when both Al, oxidizer, and MXene are present in the suspension, where oxidizer particles occupy the inner layer and Al particles take up the outer layer simultaneously. Leveraging the high oxidation tendency of MXene^21,22, such a layered Al/oxidizer/MXene structure can absorb oxygen from air to MXene and supply the oxidizer layer in the thermite reaction, thus facilitating energy release efficiency remarkably.

As a proof of concept, in this work, single-layer V₂C is selected as the MXene additive, and CuO is selected as the oxidizer, mainly due to the potential formation of Cu-O-V interfacial covalent bonds ^23,24. Al/CuO/V₂C is fabricated through a simple mixing in ethanol suspension with sonication. The structure of Al/CuO/V₂C evolves as the concentration of V₂C differs from the SEM and TEM observation, which in turn endow it with tunable energetic performance revealed later. The successful fabrication of Al/CuO/V₂C is confirmed by XPS and PXRD analysis, after which the superior thermal property is verified by DSC-TG analysis. The open burn result proves the catalytic effect of V₂C as well as the highly tunable performance along with the concentration of V₂C. Additionally, the closed-bomb test proves the improved safety and potential application for microinitiators. Finally, the electrostatic and covalent binding mechanism of Al/CuO/V₂C is further explored, accompanied by the discussion on the energy release efficiency improvement in terms of oxygen diffusion.

2.1 Morphological Analysis of Al/CuO/V₂C

The Al/CuO/V₂C samples prepared with different concentrations of V₂C MXene suspension result in diverse morphologies. As illustrated in Fig. 1a, although from the same procedures, the samples with lower concentrations (≤ 5 wt%) show a planar structure, while the ones with higher concentrations (> 5 wt%) tend to have a spherical structure. It turns out that the CuO and Al nanoparticles go through a self-assembly process with V₂C nanosheets in the suspension. However, in an ordered sequence rather than a random combination. When both CuO and Al particles are present, CuO has a higher tendency to bind on the V₂C surface. The spontaneous self-assembly procedures begin with the formation of CuO/V₂C precursor, and then the resulting Al/CuO/V₂C nanocomposite in both low and high concentration cases. This unique phenomenon suggests different types of bonding occur between Al, V₂C, and CuO, V₂C in terms of bonding strength and distance. Specifically, the bond strength between CuO and V₂C surface is higher than that of Al and V₂C, whereas the bond distance is shorter in the former case. From the SEM image of the low-concentration (1 wt%) Al/CuO/V₂C sample (Fig. 1b), the original morphology of the V₂C nanosheet is preserved after the assembly, with Al and CuO nanoparticles covering the surface. In the TEM image (Fig. 1c), following ultrasonic treatment of Al/CuO/V₂C, the CuO/V₂C precursor film reveals a dense attachment of plate-like CuO particles onto the V₂C surface. Through the EDS analysis on the HAADF-STEM images (Fig. 1d-g, Figure S1), both O, V, Al, and Cu are evenly distributed amongst the composite, in which the distribution of Cu, and O are almost identical, confirming the presence of CuO. Besides, although the Al element is also detected, from the low weight fraction (< 1 wt%) and similar distribution to the V element, it might be due to the residue Al inside V₂C due to incomplete etching of MAX phase. The high-resolution TEM image (Figure S2) evidences the adhesion of CuO on the V₂C surface. The interplanar spacing of CuO and V₂C is 0.24 nm for the (1–11) plane and 0.25 nm for the (0-110) plane respectively²⁵, and the contact line is marked with a red dashed line.

The general morphology of the Al/CuO/V₂C composite changes drastically as the concentration of V₂C increases. In Fig. 1h, microspheres comprised of nano-sized particles are observed. The TEM images (Fig. 1i-m) further unveil the internal structure. It appears that the V₂C nanosheet curls its surface, while the CuO and Al nanoparticles are present both in and out of the envelope. The mapping results prove the existence of both Al (Fig. 1l) and CuO (Fig. 1j, m, Figure S3) particles, indicating the successful incorporation. This also suggests the difference between the binding characteristics of Al and CuO. Compared with the V₂C distribution (Fig. 1k), CuO shows more overlapping area than Al and, therefore more affinity to the V₂C surface.

2.2 Compositional and Elemental Analysis of Al/CuO/V₂C

To further verify the composition of obtained samples, PXRD and XPS analyses have been carried out. From the PXRD result (Fig. 2a), the as-synthesized Al/CuO/V₂C contains Al, CuO, and V₂C, as it shows both characteristic diffraction peaks of the 3 components, each of which is marked with specific symbols. The peaks at 8° and 12° represent single²⁶ and multiple²⁷ layers of V₂C respectively. However, The V₂C diffraction peaks are hardly detectable in the sample, which is mainly due to low peak intensity, small quantity, and possible overlap with Al and CuO peaks. From the XPS survey scan (Fig. 2b), the major elements of Al/CuO/V₂C such as Al, Cu, O, V, C, and a small amount of F, are identified. The deconvoluted V 2p/O 1s region (Fig. 2c) shows peaks representing C = O, C-O, and Metal-O bonds, respectively²⁸. Where V⁵⁺ is present in V 2p orbital, indicating the surface oxidation of V₂C after the assembly. In the Cu 2p region (Fig. 2d), Cu²⁺ is presented with 2 satellite peaks, suggesting that CuO is not reduced throughout the preparation process.

2.3 Thermal Analysis of Al/CuO/V₂C

The thermal properties of energetic materials are central to their overall performance and safety. In this regard, a DSC-TG analysis has been conducted. Firstly, the effect of V₂C amount is discussed. In the air atmosphere, Al/CuO nanocomposite releases heat at 500–850 ℃ with 2 separated peaks (Fig. 3a). The addition of V₂C gradually postponed the onset temperature of the first peak from 510 ℃ (1 wt%) to 560 ℃ (5 wt%) and stabilized at higher concentrations. Meanwhile, the onset temperature of the second peak remains after the addition. The postponement is largely attributed to the high thermal conductivity of V₂C that effectively absorbs the heat from neighboring Al and CuO particles. Besides, the peak temperatures of Al/CuO/V₂C are also elevated from 580 ℃ (1 wt%) to 620 ℃ (5 wt%), which suggests the thermite reaction mechanism shifts from Al/CuO to Al/CuO/V₂O₅ as the concentration increases²⁹. The second peak is more complicated as the concentration increases, in which two exothermal peaks at 770 ℃ and 790 ℃ are predominant, each representing a thermite reaction of Al/CuO and Al/V₂O₅. According to the integral of DSC curves, the heat of the reaction (Fig. 3b) increases along with the concentration of V₂C from 1300 J/g (1 wt%) to 3156.2 J/g (10 wt%), then decreases to 1600 J/g (20 wt%). The addition of V₂C has a sevenfold improvement maximum on the heat release of Al/CuO thermite. Besides, the second exothermic peak contributes more to the total heat release, from 45% (1 wt%) to 70% (10 wt%). Although the heat from the oxidation of Al (10870.4 J/g, Figure S4) and V₂C (6471.3 J/g, Figure S5) by air contribute to the total heat of reaction, the actual heat release exceeds the sum of each component. This suggests the catalytic effect of V₂C. From the TG curves (Fig. 3c), the thermite reaction of Al/CuO/V₂C in air atmosphere is divided into 3 stages: in the first stage (200–500 ℃), the main reaction is the loss of the functional groups of V₂C, leading to a weight loss that is proportional to the amount of V₂C; in the second stage (500–700 ℃), the curves resemble the exothermic peaks in terms of onset temperature, and the weight gains due to the oxidation of Al and V₂C are associated with the heat release; in the final stage (700–850 ℃), the weight gain caused by Al and V₂C oxidation is also related strongly to the amount of heat release in the corresponding DSC curves.

The samples with different equivalent ratios behave distinctively. For the Al/CuO/V₂C samples with 5 wt% V₂C, the DSC curves (Fig. 3d) indicate that the heat release is maximum when Al is slightly excessive (Φ = 1.3), while the lack of fuel (Φ = 0.8, 1.0) appears to have more impact on the heat release of Al/CuO/V₂C compare with the lack of oxidant (Φ = 1.5, 1.8), which suggests that V₂C tend to behave as oxidant rather than fuel. Additionally, the reaction heat in the first exothermal peak (part 1) increases along with Φ, whereas that in the second peak (part 2) shows a maximum at Φ = 1.3 (Figure S6).

To better comprehend the role of V₂C in the reaction process, the reaction products (from 10 wt% V₂C samples) are taken after heating at different temperatures in the air atmosphere and then characterized using PXRD (Fig. 3e). The results show that at 350 ℃, after the release of surface terminations, a small amount of Cu₃V₅O₄ is detected due to the reaction between CuO and V₂C³⁰. At 700 ℃, the peak intensity of Al is sharply decreased, whereas that of CuO remains, also a small amount of Cu₂V₂O₇ is detected³¹. This indicates the oxidation of Al and V₂C as well as the reaction between CuO and V₂O₅. At 850 ℃, Al₂O₃ emerges as Al has completely been oxidized, where CuAl₂O₄ is detected due to a reaction between CuO and Al₂O₃ at high temperatures^32,33. Here the formation of copper vanadate is of particular interest. According to the morphology of the samples, CuO shows a high affinity to the V₂C surface with a large contact area, providing chances for the later formation of copper vanadate. Once the vanadate is formed at the interface, oxygen can readily diffuse from V₂O₅ to CuO through Cu-O-V bonds, changing the mechanism from Al/CuO to Al/CuO/V₂O₅. From the XPS analysis on the reaction product (Fig. 3f), the intensity of V⁵⁺ remains during the reaction process compared with those in the argon atmosphere in different concentrations of V₂C (Figure S7), indicating the high reactivity of V₂C surface to absorb oxygen from the air and prevent reduction during the reaction process.

The effect of atmosphere is also discussed. The DSC curves from the Al/CuO/V₂C samples in the argon atmosphere show two types of thermite reaction from 300 to 800 ℃ as separated by the dashed line (Figure S8). The curves for concentrations lower than 5 wt% have similar behavior to the ones in the air atmosphere, while curves for higher concentrations suggest more subtle reactions with separated exothermic peaks. The onset temperature is also advanced to 400 ℃ at most (10 wt%). The TG curves in the argon atmosphere (Figure S9) also suggest the detachment of surface terminations of V₂C before 350 ℃ (stage 1). However, the subsequent weight gain in the stage 2, and 3 is less in correlation with the DSC curves, especially for the higher concentration samples, which is probably due to the continuous participation of oxygen in air. For the 10 wt% samples in the argon atmosphere (Figure S10), the reduction of CuO began as early as 400 ℃ by the presence of Cu₂O. Vanadium is detected at 500 ℃ as a sign of the thermal decomposition of V₂C. At 600 ℃, the Cu₂O is further reduced to Cu. The presence of Al₂O₃ peaks and disappearance of Al peaks at 700 and 800 ℃ indicate that the Al/CuO thermite reaction has completed.

2.4 Energetic Performance of Al/CuO/V₂C

An open burn experiment is carried out to assess the energetic performance of Al/CuO/V₂C (Video S1-4). The Al/CuO sample without the addition of V₂C burned for 6 ms total, and the flame reached a maximum of 1 ms (Fig. 4a). After adding 1 wt% V₂C, the total burning time is reduced by half (3 ms), and the flame is maximum at 0.4 ms with a great enhancement in terms of covering area (Fig. 4b). For the sample with 5 wt% V₂C, the burning performance is similar to that of the 1 wt% sample, with a short postpone of burning, and the maximum covering area occurs at 0.5 ms (Fig. 4c). The property of flame changes as the concentration of V₂C further increases. In the 10 wt% sample case, instead of an explosion in former samples, it steadily burns until the reaction is complete, creating a flame that lasts for 16 ms (Fig. 4d). The drastic change in the burning property of samples is mainly induced by the evolution in morphology (Fig. 4e). For low concentrations, Al/CuO/V₂C forms a planar structure, where Al and CuO nanoparticles attach to the V₂C surface successively. In this manner, the agglomeration of nanoparticles is alleviated, bringing more contact area between Al and CuO particles, thus enhancing the average diffusion rate of oxygen, which results in shorter burning time and higher energy release rate. However, for high concentrations, Al/CuO/V₂C forms a quasi-spherical structure where V₂C is the shell and Al, CuO particles are located both inside and outside of it, resisting the particles inside to explode freely, which reduces the reaction rate significantly from explosion to combustion while largely increase the energy release efficiency and duration.

Lowering the pressure is essential for nanothermite in both safety and microinitiator applications ¹. Therefore, the closed-bomb test is conducted to test the combustion property in a confined space as well as the generating ability of Al/CuO/V₂C samples. The dynamic pressure of Al/CuO/V₂C samples is lower than that of Al/CuO, reaching a maximum of 0.1 s (Fig. 4f). The lowered pressure is mainly due to the introduction of gasless V₂C, and partly because of the insufficient oxygen that slightly alters the reaction mechanism. The trend of pressurization rate is identical to the peak pressure for Al/CuO/V₂C samples (Fig. 4g). Generally, the peak pressure and pressurization rate decrease as the concentration of V₂C increases, whereas it shows dependency on the structure of Al/CuO/V₂C (grey region). The general trend is mainly caused by the decrease in gas generation since the decomposition of V₂C contributes little to the gaseous product. However, the peak pressure and pressurization rate of Al/CuO/V₂C with 5 wt% and 7.5 wt% is similar to those of the 1 wt% sample, indicating the role of structural difference. The peak pressure and pressurization rate of Al/CuO/V₂C were reduced by 55.4% and 57.5% respectively (from the comparison of 0 and 10 wt% samples), which means V₂C can greatly improve the safety of Al/CuO and is feasible for microinitiator application.

2.5 Binding Mechanism Analysis of Al/CuO/V₂C

As the highly tunable performance of Al/CuO/V₂C is driven by the unique structures deeply rooted in the ordered self-assembly of the components, the mechanism behind the assembly is worth further exploration. Al/V₂C and CuO/V₂C samples are fabricated and characterized by PXRD (Figure S11). The possible covalent interaction at the CuO/V₂C interface is examined by Raman spectroscopy (Fig. 5a). A characteristic peak at 895 cm^− 1 representing the vibration of the Cu-O-V bond is found in the CuO/V₂C sample while being absent in other samples, which is direct evidence of the covalent bond at the CuO/V₂C interface ²³. The absence in the Al/CuO/V₂C spectrum is probably because the CuO/V₂C interface is more densely covered. From FT-IR spectroscopy (Fig. 5b), the -CH₂-CH₂- vibration is identified with multiple characteristic peaks in both Al/CuO/V₂C and CuO/V₂C samples while being absent in other samples. As -CH₂-CH₂- vibration is commonly present in graphene samples ³⁴, one reasonable deduction is that V atoms at the interface form Cu-O-V bonds by breaking V-C bonds, leaving a small fraction of carbon nanosheet, which indirectly supported the existence of Cu-O-V bonds. From the XPS analysis result (Fig. 5c), both Cu²⁺ 2p_3/2 and Cu²⁺ 2p_1/2 orbits shift slightly to higher binding energy, which also suggests the appearance of the Cu-O-V bond ³⁵. Al nanoparticles exhibit a more randomized distribution around CuO/V₂C and a weaker binding strength compared with the covalent bonding between CuO and V₂C, therefore the assembly mechanism is presumably the electrostatic attraction. From the zeta potential analysis (Fig. 5d), the mean zeta potential of Al and CuO particles is positive, while that of the V₂C suspension is negative. After mixing with a low concentration (1, 5 wt%) of V₂C, the zeta potential of the system is more positive than each component, mainly because V₂C reduces the agglomeration of the nanoparticles while influencing little to the overall zeta potential. As the concentration increases (10, 20 wt%), zeta potential drops sharply until reaching that of pure V₂C, suggesting that the charge is neutralized by V₂C.

Based on the binding properties, it is clearer how the layered structure of Al/CuO/V₂C from ordered self-assembly facilitates the thermite reaction in terms of oxygen diffusion. As depicted in Fig. 5e, for Al/CuO nanocomposite upon ignition, the oxygen atoms begin to diffuse from CuO to the neighboring Al particles through the Al/CuO interface. However, the random assembly of particles and agglomeration tend to result in incomplete thermite reaction due to poor contact area between Al and CuO. In the Al/CuO/V₂C case (Fig. 5f), once ignited, oxygen atoms can not only migrate easily from CuO to nearby Al particles, which benefits from the larger interface area brought by the layered structure but also be replenished from V₂C through Cu-O-V bond in air atmosphere, leading to the complete oxidation of Al into Al₂O₃. To better show the difference between the ordered self-assembly and as-reported electrostatic self-assembly method, the Al/CuO/V/GO control group is fabricated with the same elemental composition to the Al/CuO/V₂C sample. From the comparison of DSC curves from Al/CuO/V₂C and Al/CuO/V/GO control group (Figure S12), the exothermal peaks of Al/CuO/V/GO are separated into Al/V₂O₅ (622 ℃) and Al/CuO (567 ℃) peaks. The result indicates that the connection between the components of Al/CuO/V/GO is poor, and part of Al only reacts with CuO while the other part only reacts with V₂O₅. This finally leads to a lower heat release due to incomplete thermite reaction and agglomeration. Unlike previously published additives, V₂C improves both the structure and reactivity of Al/CuO. Besides, the highly tunable energetic performance from its structural evolution enlightens more possibilities for future application.

In summary, Al/CuO/V₂C nanocomposite has been prepared with unique structures from ordered self-assembly of Al and CuO nanoparticles, which evolves from planar to quasi-spherical as the concentration of V₂C increases from 1 to 10 wt%. During the self-assembly, CuO shows a higher affinity to the V₂C surface than Al, resulting in a layered organization. Owing to the synergetic effect of the 2D structure and high reactivity of V₂C, the onset temperature of the exothermic reaction is postponed for 60 ℃, and heat release of Al/CuO/V₂C (3156.2 J/g) increases sevenfold than the Al/CuO (454.4 J/g) in air atmosphere. The reaction mechanism changes from Al/CuO to Al/CuO/V₂O₅. The burning property of Al/CuO/V₂C alters along with the concentration of V₂C drastically from a facilitated explosion within 3 ms to a sustained combustion for 16 ms due to the structural evolution, and the peak pressure has reduced by 44.6% than Al/CuO. It turns out that the origin of the ordered self-assembly of Al/CuO/V₂C is the different types of bonding of Al, V₂C, and CuO, V₂C, in which the former is electrostatic force, and the latter is a covalent bond. Such a structure takes advantage in terms of higher efficiency of oxygen transportation and complete oxidation of Al.

Materials

the nano aluminum powder is purchased from Zhonghangzhongmai Metal Material Inc. with a diameter range from 80 − 200 nm (Figure S13), and an active content of 80%. The nano copper oxide powder is self-made using the thermal pyrolysis method at 300 ℃ for 90 min from Cu(OH)₂, with a diameter range from 80 − 100 nm (Figure S14). The V₂C MXene single-layer suspension is purchased from Shandong Xiyan Material Inc. with a concentration of 10 mg/mL, dispersed in DMF. The absolute alcohol is purchased from Standard Chemical Inc. (ACS grade). Vanadium powder is purchased from Aladdin Inc., 99.5% metals basis, ≥ 325 mesh. Graphene oxide powder is purchased from Aladdin Inc., > 99%. All chemicals are used without further purification.

Preparation of Al/CuO/V ₂ C

The composition of all samples is listed in Table S1. For the typical preparation procedures of Al/CuO/V₂C with 10 wt% V₂C, in the Φ = 1.3 case, firstly, 20.4 mg Al powder is added into 5mL absolute ethanol as suspension A, 69.6 mg CuO powder is added into 5mL absolute ethanol as suspension B, 1 mL V₂C suspension is added into 10 mL absolute ethanol as suspension C. Then, A, B, and C are sonicated for 1 h. Next, both A and B are added into C, and C is sonicated for another 1 h. After that, C is placed in the vacuum oven and dried overnight at 60 ℃. Finally, C is collected as the sample.

Preparation of Al/CuO/V/GO

In the Φ = 1.3, 10 wt% V/GO case, suspension C is comprised of the mixture of 9 mg V powder and 1 mg GO powder dispersed in 10 mL absolute ethanol. Other materials and procedures are identical to those of Al/CuO/V₂C.

Preparation of Al/V ₂ C and CuO/V ₂ C

For a better comparison, Al/V₂C and CuO/V₂C samples are prepared using the same materials and methods for Al/CuO/V₂C without the addition of CuO or Al. For example, 20.4 mg Al powder and 10 mg V₂C are mixed for Al/V₂C, 69.6 mg CuO and 10 mg V₂C are mixed for CuO/V₂C as the control group of Al/CuO/V₂C with 10 wt% content and Φ = 1.3.

Characterization of Al/CuO/V ₂ C

Scanning electron microscopy (SEM) pictures are taken with Quanta FEI 450. Transmission electron microscopy (TEM) and high-resolution scanning transmission electron microscopy high-angle annular dark-field (STEM-HAADF) images are gathered by with FEI Talos F200x, samples are dispersed in ethanol and sonicate for 1 min before testing. X-ray photoelectron spectroscopy (XPS) is performed with Thermo Scientific K-Alpha. Powder X-ray diffraction (PXRD) is performed with Rigaku SmartLab from 5–80° at 30 kV using Cu Kα radiation (λ = 0.15418 nm). The thermogravimetry (TG) and differential scanning calorimetry (DSC) results are acquired by METTLER TGA/DSC 3 + which records the weight and heat flow of one sample simultaneously. For each test, around 2 mg samples are put into a 50 µL alumina crucible, and then heated at a heating rate of 10 ℃/min under high-purity air or argon flow (20 mL/min). To obtain comparable data, all DSC curves are divided by the sample weight at 60℃. Raman analysis was done with a confocal Raman microscope (CRM) (Alpha300R, WITec GmbH, Germany) equipped with a TEM single-frequency laser (λ = 532nm, laser power = 40 mW, WITec GmbH, Germany). The laser light was focused through a 100x oil immersion objective (numerical aperture = 0.9) (Carl Zeiss, Germany) onto the sample and the backscattered Raman signal directed through an optic multifibre (50 µm diameter) to a spectrometer (UHTS 300 WITec, Germany) (300 g∙mm^− 1 grating) and detected by the CCD camera (Andor DU401 BV, Belfast, North Ireland). On the selected areas (e.g., 30 um x 20 um) on the sample every 0.5 µm a full wavenumber range (50–4000 cm^− 1) Raman spectrum was acquired with an integration time of 1s. The Control Five (WITec GmbH, Germany) acquisition software was used for the Raman measurements set up, and Project Five (WITec GmbH, Germany) to reconstruct Raman images based on the integral band of the ester group at 1734 cm^− 1 and the hydroxyl groups at 3400 cm^− 1. Fourier-transform infrared spectroscopy (FT-IR) is conducted with Thermo Fisher Scientific Nicolet iS5 in the range of 400–4000 cm^− 1, in which all samples are dried at 65 ℃ for 1 h to remove water before testing. Zeta potentials are acquired by Malvern Zetasizer Nano ZS90, samples are dispersed in ethanol to form a 1–2 mg/mL suspension and sonicate for 30 min before testing.

Open burn test of Al/CuO/V ₂ C

All samples are grounded and dried at 60℃ before testing. A PTFE cylinder mold is made with a height of 10 mm and a diameter of 50 mm, and a cylinder hole at the center with a height of 5 mm and a diameter of 6 mm (Figure S15). For each test, an alumina crucible with a height of 5 mm and diameter of 5 mm is filled with 6 mg of the sample and then placed in the hole of the PTFE mold. Next, a nichrome wire with a diameter of 0.2 mm is connected to the power source set with a current of 2.7 A and is buried in the crucible to make full contact with the sample. Once the power source is opened, the sample is ignited, and the process is captured by the high-speed camera (Phantom, VEO 710) with 10000 FPS and an exposure time of 20 µs.

Closed-bomb test of Al/CuO/V ₂ C

All samples are grounded and dried at 60℃ before testing. Typically, a 20 mg sample is gathered in the confined cell made of stainless steel with a fixed volume of 8 mL and subsequently ignited by a nichrome wire (0.2 mm in diameter) under a 2.8 A current. The dynamic pressure during the reaction process is measured by a piezoelectric pressure sensor (PCB Piezotronics, Model 112B05) attached to the cell, and the pressure signal is transformed into a voltage signal through a signal conditioner (PCB Piezotronics, Model 482C54), and then recorded by the oscilloscope (Tek, DPO3032).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author Contributions

M.T., K.Z. devised and developed the research. M.T., K.M. and Y.L. conducted the experiments. M.T., K.M., Y.L. and I.H. performed material characterizations and analyzed the data. M.T. and K.M. wrote the manuscript. All authors contributed to general discussions and edited and reviewed the manuscript.

Acknowledgments

This work was supported by the Hong Kong Research Grants Council (CityU 11201522).

He W, Liu PJ, He GQ, Gozin M, Yan QL (2018) Highly Reactive Metastable Intermixed Composites (MICs): Preparation and Characterization. Adv Mater 30:e1706293. 10.1002/adma.201706293
Ma X et al (2020) Core-Shell Structured Nanoenergetic Materials: Preparation and Fundamental Properties. Adv Mater 32:e2001291. 10.1002/adma.202001291
Wang A, MacRobbie CJ, Baranovsky A, Hickey J-P, Wen JZ (2024) Microstructure and energetic characteristics of direct ink printed polymer-free rGO/nanothermite aerogel. Carbon 216. 10.1016/j.carbon.2023.118596
Wang H et al (2019) Direct Writing of a 90 wt% Particle Loading Nanothermite. Adv Mater 31:e1806575. 10.1002/adma.201806575
Shi K et al (2021) Alcohol-thermal synthesis of approximately core-shell structured Al@CuO nanothermite with improved heat-release and combustion characteristics. Combust Flame 228:331–339. 10.1016/j.combustflame.2021.02.008
Shi W et al (2024) Enhancing the energy release performance of nanothermites through metal oxides free oxygen and pores. Chem Eng J 481. 10.1016/j.cej.2023.148483
Ma X et al (2021) Additive-Free Energetic Film Based on Graphene Oxide and Nanoscale Energetic Coordination Polymer for Transient Microchip. Adv Funct Mater 31. 10.1002/adfm.202103199
Jiang Y et al (2022) Perfluoroalkyl-Functionalized Graphene Oxide as a Multifunctional Additive for Promoting the Energetic Performance of Aluminum. ACS Nano 16:14658–14665. 10.1021/acsnano.2c05271
Chen Y et al (2020) Reactivity adjustment from the contact extent between CuO and Al phases in nanothermites. Chem Eng J 402. 10.1016/j.cej.2020.126288
Singh V et al (2022) Influence of process parameters on energetic properties of sputter-deposited Al/CuO reactive multilayers. Nanotechnology 33. 10.1088/1361-6528/ac85c5
Li Y et al (2023) Synthesis of Co(OH)F@Al nanobelt array on various substrates for pyro-MEMS. Chem Eng J 466. 10.1016/j.cej.2023.143192
Zhu Y et al (2018) In situ preparation of explosive embedded CuO/Al/CL20 nanoenergetic composite with enhanced reactivity. Chem Eng J 354:885–895. 10.1016/j.cej.2018.08.063
Wang W et al (2022) Effects of oxidizer and architecture on the thermochemical reactivity, laser ignition and combustion properties of nanothermite. Fuel 314. 10.1016/j.fuel.2022.123141
Fahd A, Baranovsky A, Dubois C, Chaouki J, Wen JZ (2021) Superior performance of quaternary NC/GO/Al/KClO4 nanothermite for high speed impulse small-scale propulsion applications. Combust Flame 232. 10.1016/j.combustflame.2021.111527
Kwon J et al (2013) Interfacial chemistry in Al/CuO reactive nanomaterial and its role in exothermic reaction. ACS Appl Mater Interfaces 5:605–613. 10.1021/am3019405
Séverac F, Alphonse P, Estève A, Bancaud A, Rossi C (2011) High-Energy Al/CuO Nanocomposites Obtained by DNA‐Directed Assembly. Adv Funct Mater 22:323–329. 10.1002/adfm.201100763
Tang D-Y et al (2020) Metastable intermixed Core-shell Al@M(IO3)x nanocomposites with improved combustion efficiency by using tannic acid as a functional interfacial layer. Chem Eng J 384. 10.1016/j.cej.2019.123369
Wei Y, Zhang P, Soomro RA, Zhu Q, Xu B (2021) Advances in the Synthesis of 2D MXenes. Adv Mater 33:e2103148. 10.1002/adma.202103148
Cheng J et al (2023) Doping of Al/CuO with microwave absorbing Ti3C2 MXene for improved ignition and combustion performance. Chem Eng J 451. 10.1016/j.cej.2022.138375
Li Y et al (2021) Adhesion Between MXenes and Other 2D Materials. ACS Appl Mater Interfaces 13:4682–4691. 10.1021/acsami.0c18624
Cao F et al (2022) Recent Advances in Oxidation Stable Chemistry of 2D MXenes. Adv Mater 34:e2107554. 10.1002/adma.202107554
Hou P et al (2023) Unraveling the Oxidation Behaviors of MXenes in Aqueous Systems by Active-Learning-Potential Molecular-Dynamics Simulation. Angew Chem Int Ed Engl 62:e202304205. 10.1002/anie.202304205
Tian H et al (2024) Selective electrooxidation of methane to formic acid by atomically dispersed CuOx and its induced Lewis acid sites on V2O5 in a tubular electrode. Appl Catal B: Environ Energy 351. 10.1016/j.apcatb.2024.124001
Liu B, Yu L, Yu F, Ma J (2021) In-situ formation of uniform V2O5 nanocuboid from V2C MXene as electrodes for capacitive deionization with higher structural stability and ion diffusion ability. Desalination 500. 10.1016/j.desal.2020.114897
Huang D et al (2019) Demonstration of a White Laser with V(2) C MXene-Based Quantum Dots. Adv Mater 31:e1901117. 10.1002/adma.201901117
Liu F et al (2017) Preparation of High-Purity V2C MXene and Electrochemical Properties as Li-Ion Batteries. J Electrochem Soc 164:A709–A713. 10.1149/2.0641704jes
Liu Y et al (2020) In-Situ Electrochemically Activated Surface Vanadium Valence in V2C MXene to Achieve High Capacity and Superior Rate Performance for Zn‐Ion Batteries. Adv Funct Mater 31. 10.1002/adfm.202008033
Zada S et al (2020) Algae Extraction Controllable Delamination of Vanadium Carbide Nanosheets with Enhanced Near-Infrared Photothermal Performance. Angew Chem Int Ed Engl 59:6601–6606. 10.1002/anie.201916748
Streletskii AN et al (2022) Mechanochemical activation of Al/V2O5 composites: Thermal transformations. Mater Chem Phys 292. 10.1016/j.matchemphys.2022.126798
Shaheen WM, Maksod IHAE (2009) Thermal characterization of individual and mixed basic copper carbonate and ammonium metavanadate systems. J Alloys Compd 476:366–372. 10.1016/j.jallcom.2008.08.053
Guo W et al (2015) Synthesis and Characterization of CuV2O6 and Cu2V2O7: Two Photoanode Candidates for Photoelectrochemical Water Oxidation. J Phys Chem C 119:27220–27227. 10.1021/acs.jpcc.5b07219
Zhang T, Yuan B, Wang W, He J, Xiang X (2023) Tailoring *H Intermediate Coverage on the CuAl(2) O(4) /CuO Catalyst for Enhanced Electrocatalytic CO(2) Reduction to Ethanol. Angew Chem Int Ed Engl 62:e202302096. 10.1002/anie.202302096
Jacob KT, Alcock CB (2006) Thermodynamics of CuAlO2 and CuAl2O4 and Phase Equilibria in the System Cu2O-CuO‐Al2O3. J Am Ceram Soc 58:192–195. 10.1111/j.1151-2916.1975.tb11441.x
Tucureanu V, Matei A, Avram AM (2016) FTIR Spectroscopy for Carbon Family Study. Crit Rev Anal Chem 46:502–520. 10.1080/10408347.2016.1157013
Gopalakrishnan R, Chowdari B, Tan K, Radhakrishnan K (1995) Surface and electrical studies of CuO: V2O5 thin films. Thin Solid Films 260:161–167

There is NO Competing Interest.

Download PDF

Version 1

posted

You are reading this latest preprint version

MXene Templated Assembly of Hierarchical Al/CuO/V₂C Nanothermite with Excellent Energy Release Efficiency and Highly Tunable Performance

Status:

Version 1

Abstract

Figures

1 Introduction

2 Results and Discussion

2.1 Morphological Analysis of Al/CuO/V₂C

2.2 Compositional and Elemental Analysis of Al/CuO/V₂C

2.3 Thermal Analysis of Al/CuO/V₂C

2.4 Energetic Performance of Al/CuO/V₂C

2.5 Binding Mechanism Analysis of Al/CuO/V₂C

3 Conclusions

4 Experimental Section

Declarations

Declaration of Competing Interest

Author Contributions

Acknowledgments

References

Additional Declarations

Supplementary Files

Status:

Version 1

MXene Templated Assembly of Hierarchical Al/CuO/V2C Nanothermite with Excellent Energy Release Efficiency and Highly Tunable Performance

Status:

Version 1

Abstract

Figures

1 Introduction

2 Results and Discussion

2.1 Morphological Analysis of Al/CuO/V2C

2.2 Compositional and Elemental Analysis of Al/CuO/V2C

2.3 Thermal Analysis of Al/CuO/V2C

2.4 Energetic Performance of Al/CuO/V2C

2.5 Binding Mechanism Analysis of Al/CuO/V2C

3 Conclusions

4 Experimental Section

Declarations

Declaration of Competing Interest

Author Contributions

Acknowledgments

References

Additional Declarations

Supplementary Files

Status:

Version 1

MXene Templated Assembly of Hierarchical Al/CuO/V₂C Nanothermite with Excellent Energy Release Efficiency and Highly Tunable Performance

2.1 Morphological Analysis of Al/CuO/V₂C

2.2 Compositional and Elemental Analysis of Al/CuO/V₂C

2.3 Thermal Analysis of Al/CuO/V₂C

2.4 Energetic Performance of Al/CuO/V₂C

2.5 Binding Mechanism Analysis of Al/CuO/V₂C