Metal–organic framework-derived nanocomposite metal-oxides with enhanced catalytic performance in thermal decomposition of ammonium perchlorate

Highlights

• CuO@NiO nanocomposites were prepared using Ni-MOF at two different calcinations temperature.

• CuO@NiO-400(2:1) showed enhanced catalytic performance in AP thermal decomposition.

• CuO@NiO-400(2:1) increased the evolved heat from 400 J g⁻¹ to 1505 J g⁻¹ and reduced the HTD temperature from 420 to 310 °C.

Abstract

In this work, CuO@NiO nanocomposites have been prepared using a 3D metal-organic framework, [Ni(μ₃-tp) (μ₂-pyz)]_n as precursor, where H₂tp and pyz corresponds to 1,4-benzenedicarboxylic acid and pyrazine, respectively. Calcinations of the precursor at two different temperatures (400 and 500 °C) following precipitating copper nitrate by NaOH (Cu:Ni molar ratio of 1:2) resulted in metal oxide nanocomposites with different characteristics (CuO@NiO-400 (2:1) and CuO@NiO-500 (2:1), respectively). Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) coupled with EDS mapping, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and dynamic light scattering (DLS) analyses have been used to obtain compositional and morphological features of the prepared samples. The effect of calcination temperature on textural characteristics of the nanocomposites have been examined by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. It was found that higher calcination temperature destroyed the porous structure of the nanoparticles due to agglomeration. Catalytic performance of the nanocomposites was investigated toward thermal decomposition of ammonium perchlorate (AP) by means of differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results showed that the composite metal oxides (CuO@NiO) had more catalytic activity compared with CuO and NiO nanoparticles. CuO@NiO-400 (1:2) nanocomposites with larger surface area and smaller particle size exhibited significant catalytic activity compared with CuO@NiO-500 (1:2). The decomposition temperature was notably decreased from 420 to 310 °C. The released heat from AP decomposition was increased from 450 J g⁻¹ to 1535 J g⁻¹ over CuO@NiO-400 (1:2) nanocomposites. Also, the effect of different molar ratios (1:1 and 2:1) of CuO and NiO was investigated on AP thermal decomposition. The obtained nanocomposites are promising enough for further catalytic studies on the thermal decomposition of AP.

Introduction

Metal-organic frameworks attracted a great deal of attention since they can be used as templates in order to obtain the desired nano-materials. MOFs offer distinct advantages because of the high-ordered crystalline structure which provide a unique opportunity to develop a new class of highly tailorable nanomaterials with promising applications. Nano-materials with different morphologies and characteristics can be obtained from different MOF precursors [[1], [2], [3], [4]]. Despite the great progress achieved so far, the research on synthesis of inorganic functional materials derived from MOFs is still in its early stage. Preparation of different metal-oxide nanoparticles from MOFs are reported previously [[5], [6], [7]]. CuO/Cu₂O hollow polyhedra which were synthesized by thermal decomposition of Cu–MOF have been stated by Hu et al. [8]. Porous NiO architecture has been prepared by han et al. through calcining a Ni-MOF in air [5]. Nano-strand mesoporous NiO was obtained through calcination of a Ni coordination polymer, [Ni₃(BTC)₂·12H₂O], in which NiO arrays keep the morphology of the precursor [9]. Also, application of In–MOFs as templates for the preparation of In₂O₃ hollow structures have been reported [2].

Ammonium perchlorate (AP) is an important constituent of modern composite propellants [10]. Composite propellant have been reported as supercapacitors in energy storage field [[11], [12], [13], [14], [15], [16]]. The thermal decomposition behavior of AP is frequently applied to evaluate the combustion behavior of the composite propellant. Therefore, reducing the high-temperature thermal decomposition (HTD) will decrease the ignition delay time and improves the rate of composite propellants burning [17,18]. It was established that thermal decomposition of AP is very susceptible respect to additives [19,20]. Several literatures have intensively studied various types of the additives which influence the AP thermal decomposition behavior. Among the reported additives, transition metal oxides including Fe₂O₃, CuO, MnO₂, NiO, Cr₂O₃ and Co₂O₃, Co₃O₄ and ZnO with a variety of morphologies and structures are mostly reported as effective and promising catalysts to accelerate the AP thermal decomposition [10,[21], [22], [23], [24], [25], [26]]. CuO nanoparticles as effective and inexpensive catalyst [27] with high surface area and lots of dislocations was selected as suitable catalyst for thermal decomposition of AP due to p-type semi-conductivity characteristics [28]. Nickel oxide (NiO) is an important inorganic material since it is widely used in catalysis, electrochemistry, p-type transparent conducting films and water treatment [29,30]. There are many different methods reported for the synthesis of nanometer-sized nickel oxide [31,32], in which the size and morphology of the particles influenced the catalytic behavior. However, compared to the single metal oxides, the complex oxides with two or more phases with spinel structure have concerned much attention in materials research because of the enhanced catalytic performance made by the synergistic interactions between two different oxides [[33], [34], [35]].

CuO and NiO nanoparticles separately showed outstanding performance in catalyzing AP thermal decomposition [36,37]. Though, tendency of pure CuO nanoparticles to aggregation led to formation of less active sites and consequently decreases the catalytic activity. Therefore, employing a second component or phase for anchoring CuO nanoparticles might be conceivable to inhibit aggregation and retain their high specific surface area [38] and catalytic capacity [39]. On the other hand, the NiO nanostructure either have structural defects such as having large size and irregular margins, or requiring organic solvents for preparation. Although surfactants are always necessary in many wet chemical synthesis procedures, they adsorb onto the surface of the particles and are difficult to eliminate, which may finally deteriorate the properties and limit the applications of the final products. Therefore, the exploration of simple and surfactant-free methods for the preparation of uniform metal oxide particles with high purity is still in demand [40].

Following the advantages reported for both CuO and NiO nanoparticles in thermal decomposition of AP, in the present study CuO@NiO nanocomposites with molar ratio of 1:2 have been prepared to investigate their performance in the AP thermal decomposition. The nanocomposites were characterized by FT-IR, XRD, BET-BJH, SEM/EDS, XPS, TEM and DLS analyses. The effects of calcination temperature on the phase, morphology, textural properties and catalytic properties of the nanocomposites were studied. Also, the molar ratios were changed (1:1 and 2:1) during preparation of CuO@NiO-400 to compare the catalytic performance of CuO and NiO separately. The catalytic performance of the prepared nanocomposites were compared with Ni-MOF precursor and NiO nanoparticles. The catalytic activity was assessed through DSC and TGA measurements.