From a Novel Energetic Coordination Polymer Precursor to Diverse

Article pubs.acs.org/crystal

From a Novel Energetic Coordination Polymer Precursor to Diverse Mn2O3 Nanostructures: Control of Pyrolysis Products Morphology Achieved by Changing the Calcination Atmosphere Dong Jing,†,‡,# Dong Chen,†,# Guijuan Fan,† Qi Zhang,*,† Jinjiang Xu,† Shaohua Gou,‡ Hongzhen Li,† and Fude Nie*,† †

Institute of Chemical Materials, China Academy of Engineering Physics, Sichuan, Manyang 621900, China College of Chemistry and Chemical Engineering, Southwest Petroleum University, Sichuan, Chengdu 610500, China

‡

S Supporting Information *

ABSTRACT: A novel strategy to fabricate diverse α-Mn2O3 nanostructures from the nitrogen-rich energetic coordination polymer (ECP) [Mn(BTO)(H2O)2]n (BTO = 1H,1′H-[5,5′-bitetrazole]-1,1′-bis(olate)) has been developed by changing the pyrolysis atmosphere. The results show that the energetic constituent and calcination environment are vital factors to get quite different morphologies of pyrolysis products. When the calcination reaction occurs under N2 or O2, rod-shaped mesoporous αMn2O3 with a large specific surface of 50.2 m2·g−1 and monodispersed α-Mn2O3 with a size of 10−20 nm can be obtained, respectively, which provides a new platform to prepare specific shapes and sizes of manganese oxides. Inspired by the transformation of 1 under O2 atmosphere, we applied an in situ generated ultrafine α-Mn2O3 catalyst in the decomposition of ammonium perchlorate (AP) using ECP 1 as a precursor. The catalytic process of AP shows a remarkable decreased decomposition temperature (271 °C) and a narrower decomposition interval (from 253 to 275 °C). To our best knowledge, with such a low metal loading (0.65 wt %), the catalytic performance of in situ generated monodispersed ultrafine α-Mn2O3 is by far the best, which suggests that this ultraefficient catalyst has great potential in AP-based propellants.

■

context of the above-mentioned purposes.23−27 Therefore, a synthetic method for nano- or microsized manganese oxide particles with a specific morphology is still essential and significant. The recent advent of coordination polymers (CPs), which are crystalline solids composed of single or multinuclear metal cationic moieties as building units with tunable organic linker as the two key components, has attracted much attention of chemists due to their unique properties and the resulting useful applications such as gas storage,28−36 catalysis,37,38 and optics.39−41 Recently, solid-state pyrolysis of CPs has emerged as one particularly appealing approach for fabricating TMOs structures, because the advantages of CPs over other precursors

INTRODUCTION In recent years, the synthesis and characterization of metal oxides materials with controlled morphologies have received a great deal of attention as a result of their functional physical and chemical properties and potential applications.1−10 Moreover, with the development of nanotechnique transition-metal oxides (TMOs) nanoparticles that have a diameter of less than 100 nm behave significantly different from their bulk form and exhibit some peculiar performance. Among those TMOs, manganese oxides with different oxidation states of manganese are of extraordinary importance owing to their application in many different fields such as catalysts, lithium ion batteries, molecular sieves, and water treatment.11−22 However, compared with the investigation of other TMOs, only a few hydrothermal methodologies starting from different manganese salts have been developed for the preparation of manganese oxides with different morphologies and dimensions in the © XXXX American Chemical Society

Received: June 28, 2016 Revised: September 28, 2016 Published: October 21, 2016 A

DOI: 10.1021/acs.cgd.6b00975 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

obtained, which is proven to be an effective strategy to prepare monodispersed TMOs nanoparticles for the first time. On the basis of the pyrolysis behavior of 1 in an oxygen-rich condition, a new approach to the ultraefficient ammonium perchlorate (AP) decomposition catalyst is accomplished, where the catalytic ultrafine Mn2O3 nanoparticles with high accessible surface area are in situ generated and uniformly dispersed by the decomposition gas liberated from 1H,1′H-[5,5′-bitetrazole]-1,1′-bis(olate) (BTO2−) ligand. The study of thermogravimetric analysis−differential scanning calorimetry (TGA− DSC) and closed vessel experiments show that with such a low metal loading of the precursor (0.65 wt %), the catalytic performance of in situ generated monodispersed ultrafine αMn2O3 is by far the best. Considering the ECP precursor is made through a facile method, the in situ generated monodispersed ultrafine α-Mn2O3 has a promising application in catalytic decomposition of AP-based propellants.

for solid state synthesis are the tunability of the organic ligands and the long-range ordering that offer a unique opportunity to synthesize unusual TMOs morphologies. Nevertheless, most of the CPs based precursors are still limited to carbon skeleton ligands, such as carboxylate and low nitrogen-containing compounds,42−50 and there is no precedent of calcining high nitrogen CPs to prepare TMOs with diverse morphologies. In addition, the accomplished contributes in this field lack systematic investigation of the impact of organic constituents as a templating effect, as well as the judicious choice of calcination atmosphere to control the size and shape of TMOs. As a new flexible and general approach, nitrogen-rich transition-metal complexes containing nitrogen-rich energetic ligands are proven superior precursors for pyrolysis to form ultralow-density nanostructured metal foams by the Tappan group.51 In this example, the energetic nitrogen-rich ligands play an vital role for producing a nanoporous three-dimensional (3D) network, which acts as a blowing agent liberating decomposition gases on a molecular level and provides enough heat to make the pyrolysis reaction go smoothly. Inspired by this, we want to introduce the nitrogen-rich energetic coordination polymers (ECPs) on the calcination synthesis of metal oxide materials, because ECPs have inherent advantages.52−58 As is known, energetic materials are sensitive to the oxygen balance in which zero or positive oxygen balance will lead to an efficient redox reaction.59−61 We assume that by modulating the combustion atmosphere from inert gas to O2, the oxygen balance of the ECPs could be changed from negative to positive; as the result, the pyrolysis behavior of nitrogen-rich energetic organic linkers become more violent and even turn into explosions. Meanwhile, the intense decomposition process will prevent the aggregation of nanoparticles and provide a good opportunity to obtain uniformly ultrafine and well-dispersed TMOs nanoparticles. In this contribution, we report an original pyrolysis approach to prepare manganese oxides, where ECPs is utilized as calcination precursors. Herein, we propose a facile and green route for the large-scale synthesis of a novel manganese ionbased energetic coordination polymer [Mn(BTO)(H2O)2]n (compound 1) using 1H,1′H-[5,5′-bitetrazole]-1,1′-diol (H2BTO) as a chelating agent. Pyrolysis of this compound in different atmospheres results in the formation of two types of α-Mn2O3 with totally different morphologies (Scheme 1). When compound 1 was calcinated in N2, rod-shaped aggregations of Mn2O3 primary particles with an average particle size of about 25 nm are fabricated. Otherwise, when pyrolysis reaction of 1 is carried out in an O2 environment, monodispersed and ultrafine Mn 2 O 3 nanoparticles are

■

RESULTS AND DISCUSSION Description of Structures. Single-crystal analysis demonstrates compound 1 crystallizes in the monoclinic space group P21/c, and the coordination environment of Mn atom is shown in Figure 1a. Mn(II) ion is hexa-coordinated by two nitrogen

Figure 1. (a) Coordination environment of the Mn atom in compound 1, with hydrogen atoms omitted for clarity. (b) Linear structure of compound 1.

Scheme 1. Illustration of the Porous and Monodispersed Ultrafine α-Mn2O3 Transformed from the Compound 1 Template under Different Calcinated Atmospheres

atoms and four oxygen atoms in a stretched octahedron, of which two nitrogen atoms and two oxygen atoms from two BTO2− are located in the axial position, and other oxygen atoms from coordinated water molecules are located in the equatorial plane. Each BTO2− adopts the tetradentate chelating modes to coordinate with two Mn2+ ions. Moreover, two kinds of unparallel chains were found in the spatial arrangement as shown in Figure S1, and the dihedral angle of tetrazole ring from adjacent unparallel chain is about 73.5°. The mononuclear structure as described is extended alongside a axis so as to form B



Article

The morphology of the resulted products transformed from compound 1 after heating to 500 °C with the heating rate of 10 °C·min−1 and maintaining the temperature at 500 °C for 1.5 h under N2 atmosphere was studied by field-emission scanning electron microscopy (FE-SEM). The SEM images of the resulted α-Mn2O3 (Figure 4a) display the similar morphology

the one-dimensional (1D) chain structure as shown in Figure 1b. The π−π stacking and hydrogen bonds further link those 1D linear structures to 3D networks (Figure S2). In contrast to the growth of single crystals, we developed a facile one-step preparation for the large-scale synthesis of compound 1 with a yield of 99%, which can be obtained by mixing water solutions of H2BTO and MnSO4 with the same mole ratio. Notably, such an environmentally friendly, low cost, and high yield route provides a good opportunity to further study and potential applications. The powder diffraction patterns of the as-prepared sample exhibit good agreement with the simulation results, as shown in Figure 2a, confirming

Figure 2. (a) Simulated and experimental XRD patterns of compound 1. (b) SEM image of compound 1.

the obtained sample is the pure compound 1. Meanwhile, the crystal morphology of compound 1 was observed by using a field-emission scanning electron microscopy (FE-SEM). Figure 2b illustrates that the rod-shaped compound 1 with a smooth face presents homogeneous crystals with a length of 10−20 μm. Structures and Morphologies of Pyrolysis Products αMn2O3. For systematically investigating the effect of the pyrolysis atmosphere on the morphology of the calcination products, the reaction of compound 1 under N2 and O2 was carried out in a conventional furnace, respectively. To identify the products of compound 1 after heating to 500 °C with the heating of 10 °C·min−1 and then heating for 1.5 h under N2 and O2 atmosphere, respectively, powder X-ray diffraction (PXRD) was performed on the obtained powder. As revealed in Figure 3, the PXRD patterns of these two as-obtained samples display

Figure 4. (a) SEM images of rod-shaped α-Mn2O3. (b) TEM image of rod-shaped α-Mn2O3. (c) HRTEM images of rod-shaped α-Mn2O3 (inset is the SAED pattern of rod-shaped α-Mn2O3). (d) EDS mapping images of rod-shaped α-Mn2O3.

as its precursor 1. Because of the decomposition of nitrogenrich ligand, the overall size of the rod-shaped α-Mn2O3 was reduced by about 45% from that of its parent crystal. To gain further insight into the morphology, a careful observation of the high-magnification SEM image demonstrates that the surfaces of the rod-shaped crystal are very rough with many cracks and are composed of numerous nanoparticles with a size of 20−30 nm. Subsequently, to carefully investigate the textural properties of the rod-shaped crystal, the transmission electron microscopy (TEM) images afford more comprehensive structural information on the rod-shaped α-Mn2O3. Figure 4b further confirms that the calcination products are the aggregation of 20−30 nm sized primary particles. Furthermore, high-resolution transmission electron microscopy (HRTEM) examination was carried out to determine its crystal orientation features, as shown in Figure 4c. The spacings were measured to be 0.22 nm, 0.25 nm, and 0.27 nm, corresponding to (411), (321), and (222) planes of α-Mn2O3. Additionally, the obtained selected area electron diffraction (SAED) patterns show multiple diffraction circles, implying that the prepared αMn2O3 sample exhibits polycrystalline features. Meanwhile, elemental mapping of the as-prepared sample by energydispersive X-ray spectroscopy (EDS) demonstrates the elements O and Mn are distributed throughout the whole rod-shaped crystal region (Figure 4d). Meanwhile, according to the above observations, the rodshaped α-Mn2O3 shows significant pore structure. BET surface area analysis also was performed on this porous material. The N2 adsorption−desorption isotherms of the resulted α-Mn2O3

Figure 3. PXRD patterns of the as-synthesized simples obtained under N2 and O2 atmosphere. Sticks are the reported values of the cubic phase of Mn2O3.

the same characteristics, and all of the observed peaks match exactly with the reported values of the cubic phase of crystalline α-Mn2O3 (JCPDS No. 41-1442), also indicating the products are of high purity. The α-Mn2O3 was fabricated under different atmospheres, which shows that the calcination atmosphere has little effect on the formation of manganese oxides from compound 1. C



Article

and the pore size distribution of the rod-shaped α-Mn2O3 are shown in Figures S3 and S4, respectively. Detailed textural properties of the rod-shaped α-Mn2O3 superstructure are quantitatively shown as follows: the mesopore size distribution curve shows a size distribution centered at 2.2 nm, and the BET specific surface area is up to 50.2 m2·g−1. The value of surface area is higher than that of the commercially available Mn2O3 and in-lab prepared α-Mn2O3 nanocrystals, which have a specific surface area of 4.0 m2·g−1 and 19m2·g−1, respectively.62,63 Moreover, this surface area obtained by pyrolysis of nonporous compound 1 is similar to that of Mn 2 O 3 transformed from a porous MOF template,42 which indicates the calcination templates constructed from nitrogen-rich organic ligand BTO2− are superior to MOF templates at producing the porosity. Moreover, the synthesis of porous templates is more complicated than that of nonporous coordination polymer 1 in a facile route. In addition, this novel way to prepare pure crystallized mesoporous Mn2O3 overcomes the shortcomings of the existence of various stable oxidation states and different thermodynamically stable polymorphs.64−66 On the basis of the literature reports, mesoporous Mn2O3 has been proven as having potential applications in many fields.67−74 Therefore, the obtained mesoporous α-Mn2O3 also could be the ideal candidate for catalyst, rechargeable batteries, magnetic sensors, and super capacitors. Additionally, to evaluate the influence of the heating rate on the morphologies and structure of the products, the morphologies of the obtained products transformed from compound 1 under N2 calcinated atmosphere with the heating rate of 5 °C·min−1, 15 °C·min−1, and 20 °C·min−1 were studied by FE-SEM, respectively. From the SEM images (Figures S5, S6, and S7), when the heating rate is 5 °C·min−1, the morphology of the products is also similar to their parents’ morphology; the deformation of the products becomes overt when the heating rate is 15 °C·min−1, while the precursor’s morphology is still faintly visible on the pyrolysis products. However, the morphology of the products obtained at the heating rate of 20 °C·min−1 is completely different from the precursor. And as a replacement the smaller blocks are observed. Evidently, with the increase of the heating rate, the morphology of the resulting products changed distinctly, and the parent’s structure is no longer maintained when the heating rate is higher than 15 °C·min−1. It is obvious that the increment of the heating rate will cause a more intense decomposition process, which makes the morphology of the products change entirely. Characterizations of the products transformed from compound 1 under O2 atmosphere were also studied in the same process as in the N2 environment, which was heated to 500 at 10 °C·min−1 and then held at 500 °C for 1.5 h. The morphology of the calcinated product was examined by SEM and TEM. To obtain carefully the original morphology of the products, in situ observation with SEM was carried out on the silicon wafer where the calcination occurs. As revealed in Figure 5a, the typical SEM image of the sample displays a totally different morphology. In contrast to what is obtained under N2, the morphologies of these precursors disappear completely and are replaced by the monodispersed nanoparticles with a size of 10−20 nm. On the basis of the above experimental results, it is concluded that the α-Mn2O3 with different morphologies can be fabricated by changing the calcination atmosphere. The enhancement of the oxygen balance leads to intense gas burst-

Figure 5. (a) SEM image of monodispersed α-Mn2O3. (b) TEM image of obtained α-Mn2O3. (c) HRTEM image of obtained α-Mn2O3 (inset is the SAED pattern of obtained α-Mn2O3). (d) EDS mapping images of obtained α-Mn2O3.

out which will destroy the initial precursor and provide monodispersed ultrafine α-Mn2O3. In this decomposition process, the nitrogen-rich energetic organic ligand acts as the blowing agent on the molecular level, so under the existence of O2 compound 1 can instantaneously liberate gas to effectively prevent the aggregation of nanoparticles and disperse α-Mn2O3 evenly. It needs to be mentioned that it is difficult to obtain the monodispersed nanoparticles through conventional MOFs template of the carboxylic acid ligand, which is a low or no nitrogen containing ligand. As far as we know, this is the first report that mentioned the monodispersed ultrafine Mn2O3 fabricated by calcining the Mn-based ECP, which means that a new application of the ECPs has been explored. Since the agglomeration is an inherent property of nanoparticles, it occurs in the process of sample preparation of the TEM analysis when ethanol was used to transfer the nanoparticles from the silicon wafer to the copper grids, so the TEM image of as-synthesized sample (Figure 5b) shows an aggregation of the nanoparticles. The HRTEM image as shown in Figure 5c demonstrates that the size of single nanoparticle is 10−20 nm, which matches well with the size observed by SEM. The agglomeration is composed of different orientation nanosized crystals further confirmed by the SAED pattern. As revealed by EDS, only O and Mn elements were observed in the elements mapping images (Figure 5d), which shows that the resulting αMn2O3 is not doped by other elements. To determine the specific surface area of monodispersed α-Mn2O3. The N2 adsorption−desorption isotherms and the pore size distribution of the monodispersed α-Mn2O3 are shown in Figures S8 and S9. The mesopore size distribution curve shows a size distribution centered at 6.6 nm, and the BET specific surface area is 206.6 m2·g−1. Compared to the specific surface area and structure pore width of rod-shape α-Mn2O3, the monodispersed fine powder results in a higher specific surface area and a larger piled pore diameter. D



Article

energetic coordination can fully disperse the nanoparticles and the monodispersed ultrafine α-Mn2O3 is obtained. Catalytic Decomposition of Ammonium Perchlorate (AP). Ammonium perchlorate (AP) as the most common oxidizer in composite propellants, and modified double-base propellants plays an important role in the development of aerospace and missile technology. The thermal decomposition characteristics of AP directly affect the combustion performance of propellants owing to its additive ratio for more than 60%, and the thermal decomposition characteristics of AP are remarkably sensitive to certain additives. Manganese dioxide is one of the first active catalysts reported for AP decomposition,75,76 perceived as a burning rate enhancer for AP-based composite propellants. It is important to note that the AP catalyzed reaction belongs to a typical solid−solid heterogeneous catalytic reaction, and the catalytic effect depends largely on the dispersion and surface area of the catalyst. However, physical methods for dispersing the catalyst are still inadequate. Furthermore, limited by the particle size and the aggregation behavior of nanomaterials, a well dispersed and high specific surface area catalytic system can hardly be obtained. Therefore, the demand for the preparation of monodispersed ultrafine catalyst is very high. Inspired by the transformation of ECPs under O2 atmosphere in this work, we assume the violent decomposition of compound 1 can also occur and precisely disperse catalytic active species throughout the combustion system when oxygen is replaced by AP; in return, the in situ generated ultrafine α-Mn2O3 could act as an ultraefficiently catalyst for the decomposition of AP. In order to evaluate the catalytic performance of in situ resulting Mn2O3 for the decomposition of AP, TGA−DSC was carried out with a heating rate of 5 °C·min−1 at a flow rate of 40 mL·min−1 under the N2 atmosphere. The TG−DSC curve of pure AP is shown in Figure S15, where three peaks are observed at 247.7, 307, and 437 °C, associated with the phase transition temperature of orthorhombic AP to cubic AP, low temperature decomposition (LTD) of AP, and high temperature decomposition (HTD) of AP. When 1%, 2%, 3%, and 5% (wt/wt) of compound 1 were added into AP, as shown in DSC curves Figure 6a, the endothermic peak had no significant change, which revealed that the compound 1 hardly impacts the phase transition. However, with four different loadings of the precursor 1, the in situ calcinations monodispersed ultrafine αMn2O3 remarkably decrease the decomposition temperature, which corresponds to 297 °C, 291 °C, 271 °C, 271 °C, respectively. Compared to pure AP, the HTD temperature is decreased by 140−166 °C. Simultaneously, in the Figure 6b TG curves illustrate a wider decomposition interval of pure AP is substituted by a narrower one. When compound 1 content is 3 wt %, the total decomposition temperature range is merely 22 °C (from 253 to 275 °C), while the decomposition interval of pure AP is about 160 °C. Evidently, in situ obtained α-Mn2O3 can not only drop the thermal decomposition temperature, but also accelerate the decomposition rate of AP, which well satisfies the requirement of the shorter ignition delay time and higher burning rate of AP-based propellants. It should be noted that under the optimal conditions, the metal ions content is only 0.65 wt %. Compared to the literature,77−85 with such a small amount of metal content, a much lower decomposition temperature and narrower decomposition interval of AP are accomplished. To the best of our knowledge, the catalytic performance of this in situ obtained α-Mn2O3 is by far the best. Then, a series of control tests also were carried out to

Moreover, the effect of the heating rate on the products’ morphology under O2 calcination atmosphere was also investigated. The SEM images of different products obtained under a heating rate of 5 °C·min−1, 15 °C·min−1, and 20 °C· min−1 are shown in Figure S10, Figure S11, and Figure S12, respectively. The particle size of these three obtained products are approximately about 10−20 nm, which can further infer that the heating rate rarely impacts the size of particles. It is interesting to note, in the decomposition process of this compound under O2 calcination atmosphere, with the increment of the heating rate, gas release of the decomposed compound becomes exceedingly intense, which is accord with the behavior observed from the N2 calcinated atmosphere. Admittedly, a more violent gas releasing will blow the generated particle further afield. Therefore, with the increase of the heating rate, the nanoparticles become more scattered. Moreover, to investigate the decomposition course of compound 1 under different gas atmosphere, TGA was carried out with a linear heating rate of 5 °C·min−1 under N2 and O2 atmosphere with Al2O3 as the reference material. The TG curve of compound 1 under N2 atmosphere is shown in Figure S13, which illustrates there are one endothermic peak and one obvious exothermic peak in the range of 188−388 °C, corresponding to the loss of coordination water and the decomposition of the ligand, respectively. The curve also shows that the decomposition process of the organic ligand generally occurs from 275 to 388 °C. Additionally, in the TG experiment under N2 atmosphere the sample size was 0.98 mg, and complete curve was obtained in this condition. However, under O2 atmosphere even the amount of compound 1 using in the TG experiment reduced to one-third of that in N2 (0.34 mg), and it still failed to obtain the complete TG curve, since the decomposition process of compound 1 evolved into an explosion process and made the crucible fall from the stage of the TG sensor. Compared to the slow decomposition, an intense decomposition process of compound 1 should be easily inferred from the fragmentary TG curve of compound 1 under O2 atmosphere, as revealed in Figure S14. On the basis of the diverse thermal decomposition features of compound 1 under a different calcinated atmosphere, it can be deduced that a moderate decomposition course tends to maintain the original morphology of the calcinated precursor. In contrast, when adequate O2 is supplied, the gas products release rapidly during an intense decomposition or an explosion process of the highnitrogen energetic ligand, which results in the generation of monodispersed nanoparticles. From all the experiments above, with the presence of the nitrogen-rich energetic organic linkers, the porous rod-shaped α-Mn2O3 and monodispersed ultrafine α-Mn2O3 can be synthesized by changing the calcination atmosphere. Actually, changing the calcination atmosphere can effectively tune the decomposition intensity of the nitrogen-rich energetic precursor. Meanwhile, systematic research shows that decomposition intensity impacts the morphologies of the products directly: under inert gas N2 atmosphere, the gas produced by moderate decomposition of ECP 1 is insufficient to make nanoparticles separate from each other but is helpful to generate a porous structure. Therefore, the structure of its parent precursor is retained and the rod-shaped mesoporous αMn2O3 is obtained; when calcination occurs in combustionsupporting gas O2 atmosphere, due to the presence of energetic high nitrogen ligand, the decomposition process becomes extraordinarily intense, and gas produced by decomposition of E



Article

decomposition temperature of AP decreased to 311 °C and 293 °C, respectively, which demonstrates both the rod-shaped α-Mn2O3 and monodispersed α-Mn2O3 are able to effectively drop the decomposition temperature of AP. Moreover, the performance of the monodispersed α-Mn2O3 is better than that of rod-shaped α-Mn2O3 which should be attributed to the higher specific surface area of former. Furthermore, compared with the decomposition of AP catalyzed by in situ α-Mn2O3, these two catalysts show less effective performance owing to the reduction of the specific surface caused by the agglomeration and the nonuniform dispersion, which illustrates that the catalytic performance of α-Mn2O3 is tightly related to the dispersion extent and the specific surface area of the catalyst. In contrast, in the system of in situ generated catalyst, because the existence of AP compound 1 can rapidly burn and decompose into catalytic nanoparticles, then the particles are dispersed uniformly by the large amounts of decomposition gas liberated from the energetic organic linker of compound 1, which makes the dispersion extent of the catalyst in this process far better than that in mechanical mixing due to the assistance of the decomposition gas. So the catalytic performance of in situ synthesized catalytic species is more efficienct than as-prepared α-Mn2O3. In addition, it is obvious that this in situ catalyst can dramatically improve the decomposition efficiency of AP and satisfy the requirements of high energy generation at low burning temperature. In order to assess the practical value of this catalytic system, the burning rate, which is an important performance parameter of AP-based propellants, is introduced. For a gas generating reaction, the pressure rate is the per unit time gas production, which can directly reflect the burning rate. The decomposition of AP as a typical gas production reaction, the pressure-time relation is utilized to assess the burning rate. In order to detect the thermal decomposition acceleration effect of compound 1 for AP, the pressure−time relation was measured in a closed vessel. For comparison, the pressure−time relation of pure AP also was measured in the same way. As shown in Figure 6d, The pressure rate of compound 1/AP and pure AP rapidly increases during the reaction propagation. Evident combustion acceleration was observed when 3 wt % compound 1 is added into AP. It is noteworthy that the highest pressure release rate of compound 1/AP is 630 MPa·s−1, which is more than twice as high as the highest pressure release rate of pure AP. As far as we know, compared to the exogenous catalyst, with such low metal loading, the performance of the burning rate increase is unprecedented, which is attributed to better dispersion hardly achieved by the physical mixing and higher specific surface area made by the violent gas liberation of the nitrogen-rich ligand. It is obvious that the higher rate of gas generation can meet the requirements of high burning rate propellant formulations used in volume-limited or high-thrust propulsion systems. In order to explore the true catalytic species, some characterization experiments were carried out. As revealed in Figure S16, the PXRD patterns of the decomposition solid residual are in agreement with the α-Mn2O3 (JCPDS Card No. 41-1442), indicating the catalytic active species is α-Mn2O3. To confirm the morphology of the decomposition solid residual, SEM and TEM images were examined through the obtained residual. The monodispersed ultrafine nanoparticles with a size of about 20−30 nm were verified by SEM as shown in Figure S17 and Figure S18a, which is similar to the calcination product of compound 1 under O2 atmosphere. This result supports the initial hypothesis that AP as an oxidant makes compound 1

Figure 6. (a) DSC curves of AP+1%, 2%, 3%, and 5% (wt/wt) compound 1. (b) TG curves of AP+1%, 2%, 3% and 5% (wt/wt) compound 1. (c) DSC curves of AP+0.915 wt % rod-shaped α-Mn2O3, AP+0.915 wt % monidispersed α-Mn2O3, AP+1.97 wt % H2BTO and AP+1.76 wt % MnSO4. (d) Pressure release rate of compound 1/AP and pure AP.

understand the catalytic mechanism, such as the catalytic performance of the same mole ratio of MnSO4, H2BTO, rodshaped and monodispersed α-Mn2O3. The DSC curves of different mixed systems are shown in Figure 6c, it can be seen that the MnSO4 and H2BTO have little effect on the thermal decomposition of AP. When using as-prepared rod-shaped αMn2O3 or monodispersed α-Mn2O3 as the catalyst, the F



Article

decompose more violently and produce ultraefficiency αMn2O3 catalytic nanoparticles. Because of the high accessible surface of the in situ generated monodispersed ultrafine αMn2O3, the catalytic performance becomes unsurpassed. The size of nanoparticles is confirmed by the TEM analysis as shown in Figure S18b. SAED patterns (Figure S18c) also prove the solid residual is α-Mn2O3 As revealed in the mapping image, Figure S18d illustrates elements O and Mn evenly distributed throughout the region.

Field emission scanning electron microscopy (FESEM, Sigma-HD, Zeiss), X-ray diffraction (XRD, D8 advance, Bruker), transmission electron microscopy (TEM JEM-2100F, JEOL), selected area electron diffraction (SAED), and energy dispersive spectrometer (EDS, Oxford 832) were applied to identify the structure and morphology. The BET surface area analysis was performed by using a Micromeritics 3Flex surface characterization analyzer. The pore size and size distributions of the products were calculated by the Barrett−Joyner−Halenda (BJH) method. Thermogravimetric and differential scanning calorimetry (TGA−DSC 2, Mettler Toledo) were used to evaluate the thermal decomposition characteristics. Synthesis of Compound 1. A: H2BTO (10.2 mg, 0.06 mmol) was added to 4 mL of warm water with constant stirring until the mixture was clarified; B:MnSO4 (10.01 mg, 0.06 mmol) was dissolved in 1 mL of water then 3 mL of anhydrous ethanol was added to the solution; C: 2 mL of water and anhydrous ethanol mixture with the same-size ratio. Solution A was shifted in the bottom of a clean centimeter diameter glass tube, and then B and C was added onto the surface of the previous solution slowly in order to form a diffusion system. Colorless crystals were obtained in the diffused part after several days. Large-scale Synthesis of Compound 1. 0.1 mol of H2BTO was dissolved in 4 L of hot water and 0.1 mol of MnSO4 was dissolved in 50 mL of water. Then MnSO4 solution was poured into H2BTO solution with string constantly for 20 min. The crude product obtained by suction filtration was dried with a vacuum pump at 60 °C for 6 h. X-ray Crystallography and Data Collection. Suitable crystals were chosen and placed in a Rigaku supernova single X-ray diffractometer area detector using graphite monochromated Mo kα radiation (λ = 0.71073 Å) at 298(2) K. Its structures were solved by direct methods and successive Fourier difference syntheses using the SHELXTL software suite. Hydrogen atoms attached to oxygen were placed from difference Fourier maps and were refined using riding model. Other details of crystal data are given in Table S1, and data collection parameters and refinement statistics are given in Table S2. Synthesis of Different Morphologies α-Mn2O3. For the synthesis of α-Mn2O3, the as-presented compound 1 crystals loaded in a ceramic crucible was placed in a tube furnace and heated under N2 or O2 gas flow at 500 °C for 1.5 h at certain heating rate, respectively. Two kinds of powders were obtained after a calcinations treatment in relevant gas atmosphere. Preparations for Catalytic Thermal Decomposition Systems. AP, compound 1, MnSO4, H2BTO, and the decomposition product residual of compound 1 were ground into a fine powder in an agate mortar, respectively. Then, the AP and other components were mixed at a certain mass ratio. These mixtures were stored in an airtight bottle. Measurement of Combustion in a Closed Vessel. The pressure−time relation of the pure AP and compound 1/AP mixture were determined by measuring the generated pressure during combustion as a function of time in a closed vessel. For each test, loose powders with the same amount of pure AP or compound 1/AP mixture (2.20 g) were loaded into a closed vessel with a volume of 100 cm3. The pressure of the closed vessel was measured using a piezoelectric sensor with a pressure limit of 60 MPa, a response frequency of 400 kHz, and a rise time of 2 ls. The time-pressure curve was generated through data processing based on an amplifier and an oscilloscope.

■

CONCLUSION In summary, an efficient calcination approach to the synthesis of pure α-Mn2O3 with different morphologies using a novel energetic coordination polymer 1 as a pyrolysis template, which is composed of manganese ion and nitrogen-rich organic ligand BTO2− prepared via a facile route in large scale, is described. With the presence of nitrogen-rich energetic linker, the size and shape of calcination product greatly depend on the calcination atmosphere. When calcination occurs under inert gas N2, the original morphology of the precursor compound 1 is maintained on the resulting mesoporous α-Mn2O3, and the surface area is up to 50.2 m2·g−1, which is larger than the commercially available Mn2O3 and in-lab prepared the αMn2O3 nanocrystals. In combustion-supporting gas O2, an intense decomposition process occurs and makes the template collapse completely, and the monodispersed α-Mn2O3 with a size of 10−20 nm is provided. As far as we know, this is the first report that monodispersed ultrafine Mn2O3 is fabricated with Mn-based ECP by th ecalcination method. It is worth mentioning that this novel way to provide pure crystallized Mn2O3 overcomes the shortcoming of the existence of various stable oxidation states of manganese and different thermodynamically stable polymorphs, which also suggests that a new application of the Mn-based ECPs has been exploited and can be extended to other kinds of ECPs precursors to provide multimorphologies TMOs nanoparticles. Inspired by the transformation of ECP 1 under O2 atmosphere, we developed a in situ generated high-efficiency ultrafine α-Mn2O3 catalyst for decomposition of solid oxidant AP. The decomposition feature of AP on TGA shows a remarkably lower decomposition temperature (271 °C) and narrower decomposition interval (from 253 to 275 °C). Moreover, the acceleration of the catalyst assessed by a closed vessel experiment of the combustion indicates that the in situ generated α-Mn2O3 nanoparticles can obviously enhance the burning rate of AP (twice as much as pure AP). Compared to the exogenous catalyst, the in situ generated monodispersed ultrafine α-Mn2O3 has better dispersion and higher specific surface area because of the violent gas liberation brought by pyrolysis of the highnitrogen ligand BTO2−, which is hardly achieved by the physical mixing owing. For all we know, with such low metal loading (0.65 wt %), the catalytic performance of in situ generated monodispersed ultrafine α-Mn2O3 is by far the best. Considering the facile approach to produce large scale ECPs precursor 1 and the excellent catalytic performance, this in situ generated monodispersed ultrafine α-Mn2O3 has a promising application in catalytic decomposition of AP-based propellants.

■

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b00975. Description of crystal structures, additional figures and tables described herein (PDF)

EXPERIMENTAL SECTION

Accession Codes

Materials and Instruments. All reagents used for this experiment were purchased from commercial sources and used without further purification. The deionized water was used throughout the experiments.

CCDC 1477885 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ G



Article

(18) Robinson, D. M.; Go, Y. B.; Mui, M.; Gardner, G.; Zhang, Z.; Mastrogiovanni, D.; Garfunkel, E.; Li, J.; Greenblatt, M.; Dismukes, G. C. J. Am. Chem. Soc. 2013, 135, 3494−3501. (19) Mattioli, G.; Zaharieva, I.; Dau, H.; Guidoni, L. J. Am. Chem. Soc. 2015, 137, 10254−10267. (20) Lei, K.; Han, X.; Hu, Y.; Liu, X.; Cong, L.; Cheng, F.; Chen, J. Chem. Commun. 2015, 51, 11599−11602. (21) Burda, C.; Chen, X.; Narayanan, R.; El-Sayed, M. A. Chem. Rev. 2005, 105, 1025−1102. (22) Yue, W.; Zhou, W. Prog. Nat. Sci. 2008, 18, 1329−1338. (23) Ding, Y. S.; Shen, X. F.; Gomez, S.; Luo, H.; Aindow, M.; Suib, S. L. Adv. Funct. Mater. 2006, 16, 549−555. (24) Feng, Q.; Horiuchi, T.; Liu, L.; Yanagisawa, K.; Mitsushio, T. Chem. Lett. 2000, 29, 284−285. (25) Tian, Z.; Feng, Q.; Sumida, N.; Makita, Y.; Ooi, K. Chem. Lett. 2004, 33, 952−953. (26) Wang, X.; Li, Y. Chem. - Eur. J. 2003, 9, 300−306. (27) Cheng, F.; Zhao, J.; Song, W.; Li, C.; Ma, H.; Chen, J.; Shen, P. Inorg. Chem. 2006, 45, 2038−2044. (28) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi, E.; Yazaydin, A. Ö .; Snurr, R. Q.; O’Keeffe, M.; Kim, J.; Yaghi, O. M. Science 2010, 329, 424−428. (29) Lee, J. E.; Lee, N.; Kim, H.; Kim, J.; Choi, S. H.; Kim, J. H.; Kim, T.; Song, I. C.; Park, S. P.; Moon, W. K.; Hyeon, T. J. Am. Chem. Soc. 2010, 132, 552−557. (30) Farha, O. K.; Yazaydin, A. Ö .; Eryazici, I.; Malliakas, C. D.; Hauser, B. G.; Kanatzidis, M. G.; Nguyen, S. T.; Snurr, R. Q.; Hupp, J. T. Nat. Chem. 2010, 2, 944−948. (31) Zhao, D.; Timmons, D. J.; Yuan, D.; Zhou, H. C. Acc. Chem. Res. 2011, 44, 123−133. (32) Burrows, A. D.; Fisher, L. C.; Richardson, C.; Rigby, S. P. Chem. Commun. 2011, 47, 3380−3382. (33) Wang, Z.; Cohen, S. M. Chem. Soc. Rev. 2009, 38, 1315−1329. (34) Perry, J. J., IV; Perman, J. A.; Zaworotko, M. J. Chem. Soc. Rev. 2009, 38, 1400−1417. (35) Murray, L. J.; Dincă, M.; Long, J. R. Chem. Soc. Rev. 2009, 38, 1294−1314. (36) Maji, T. K.; Matsuda, R.; Kitagawa, S. Nat. Mater. 2007, 6, 142− 148. (37) Tonigold, M.; Lu, Y.; Bredenkötter, B.; Rieger, B.; Bahnmüller, S.; Hitzbleck, J.; Langstein, G.; Volkmer, D. Angew. Chem., Int. Ed. 2009, 48, 7546−7550. (38) Dang, D.; Wu, P.; He, C.; Xie, Z.; Duan, C. J. Am. Chem. Soc. 2010, 132, 14321−14323. (39) Fantacci, S.; De Angelis, F.; Wang, J.; Bernhard, S.; Selloni, A. J. Am. Chem. Soc. 2004, 126, 9715−9723. (40) Lee, C. Y.; Farha, O. K.; Hong, B. J.; Sarjeant, A. A.; Nguyen, S. T.; Hupp, J. T. J. Am. Chem. Soc. 2011, 133, 15858−15861. (41) Wang, C.; Lin, W. J. Am. Chem. Soc. 2011, 133, 4232−4235. (42) Nayak, S.; Malik, S.; Indris, S.; Reedijk, J.; Powell, A. K. Chem. Eur. J. 2010, 16, 1158−1162. (43) Peng, L.; Zhang, J.; Xue, Z.; Han, B.; Li, J.; Yang, G. Chem. Commun. 2013, 49, 11695−11697. (44) Cho, W.; Lee, Y. H.; Lee, H. J.; Oh, M. Chem. Commun. 2009, 4756−4758. (45) Li, C.; Yin, X.; Chen, L.; Li, Q.; Wang, T. Chem. - Eur. J. 2010, 16, 5215−5221. (46) Cho, W.; Lee, Y. H.; Lee, H. J.; Oh, M. Adv. Mater. 2011, 23, 1720−1723. (47) Kundu, T.; Sahoo, S. C.; Banerjee, R. Cryst. Growth Des. 2012, 12, 2572−2578. (48) Kimitsuka, Y.; Hosono, E.; Ueno, S.; Zhou, H.; Fujihara, S. Inorg. Chem. 2013, 52, 14028−14033. (49) Lee, H. J.; Park, J. U.; Choi, S.; Son, J.; Oh, M. Small 2013, 9, 561−569. (50) Lee, K. J.; Kim, T. H.; Kim, T. K.; Lee, J. H.; Song, H. K.; Moon, H. R. J. Mater. Chem. A 2014, 2, 14393−14400.

[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

AUTHOR INFORMATION

Corresponding Authors

*(Q.Z.) E-mail: [email protected]; jackzhang531@gmail. com. *(F.N.) E-mail: [email protected]. Author Contributions #

D.J. and D.C. contributed equally.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank Prof. Dr. Tao Yang (College of Chemistry and Chemical Engineering, Chongqing University, China) for measuring the crystal structure and Dr. Wenfang Zheng (School of Chemical engineering, Nanjing University Of Science And Technology, China) for assistance in combusition experiment. This work was supported by the National Natural Science Foundation of China (no.21302176, no.11302200 and no.21502179) and the Development Foundation of CAEP (no.2013B0302038).

■

ABBREVIATIONS ECPs, energetic coordination polymers; BTO, 1H,1′H-[5,5′bitetrazole]-1,1′-bis(olate); TMOs, transition-metal oxides; AP, ammonium perchlorate

■

REFERENCES

(1) Lee, I. S.; Lee, N.; Park, J.; Kim, B. H.; Yi, Y. W.; Kim, T.; Kim, T. K.; Lee, I. H.; Paik, S. R.; Hyeon, T. J. Am. Chem. Soc. 2006, 128, 10658−10659. (2) Nam, K. T.; Kim, D. W.; Yoo, P. J.; Chiang, C. Y.; Meethong, N.; Hammond, P. T.; Chiang, Y. M.; Belcher, A. M. Science 2006, 312, 885−888. (3) Xiong, H. M.; Xu, Y.; Ren, Q. G.; Xia, Y. Y. J. Am. Chem. Soc. 2008, 130, 7522−7523. (4) Xie, X.; Li, Y.; Liu, Z. Q.; Haruta, M.; Shen, W. Nature 2009, 458, 746−749. (5) Yu, X.; Marks, T. J.; Facchetti, A. Nat. Mater. 2016, 15, 383−396. (6) Lee, J. H.; Huh, Y. M.; Jun, Y. W.; Seo, J. W.; Jang, J. T.; Song, H. T.; Kim, S.; Cho, E. J.; Yoon, H. G.; Suh, J. S.; Cheon, J. Nat. Med. 2007, 13, 95−99. (7) Daniel, M. C.; Astruc, D. Chem. Rev. 2004, 104, 293−346. (8) Reddy, M. V.; Subba Rao, G. V.; Chowdari, B. V. R. Chem. Rev. 2013, 113, 5364−5457. (9) Ren, Y.; Ma, Z.; Bruce, P. G. Chem. Soc. Rev. 2012, 41, 4909− 4927. (10) Yuan, C.; Wu, H. B.; Xie, Y.; Lou, X. W. D. Angew. Chem., Int. Ed. 2014, 53, 1488−1504. (11) Espinal, L.; Suib, S. L.; Rusling, J. F. J. Am. Chem. Soc. 2004, 126, 7676−7682. (12) Cao, H.; Suib, S. L. J. Am. Chem. Soc. 1994, 116, 5334−5342. (13) Yang, Z.; Zhang, Y.; Zhang, W.; Wang, X.; Qian, Y.; Wen, X.; Yang, S. J. Solid State Chem. 2006, 179, 679−684. (14) Jiao, F.; Bruce, P. G. Adv. Mater. 2007, 19, 657−660. (15) Bruce, P. G.; Scrosati, B.; Tarascon, J. M. Angew. Chem. 2008, 120, 2972−2989. (16) Débart, A.; Paterson, A. J.; Bao, J.; Bruce, P. G. Angew. Chem., Int. Ed. 2008, 47, 4521−4524. (17) Wiechen, M.; Zaharieva, I.; Dau, H.; Kurz, P. Chem. Sci. 2012, 3, 2330−2339. H



Article

(51) Tappan, B. C.; Huynh, M. H.; Hiskey, M. A.; Chavez, D. E.; Luther, E. P.; Mang, J. T.; Son, S. F. J. Am. Chem. Soc. 2006, 128, 6589−6594. (52) Yan, Z.; Li, M.; Gao, H. L.; Huang, X. C.; Li, D. Chem. Commun. 2012, 48, 3960−3962. (53) Yang, C.; Kaipa, U.; Mather, Q. Z.; Wang, X.; Nesterov, V.; Venero, A. F.; Omary, M. A. J. Am. Chem. Soc. 2011, 133, 18094− 18097. (54) Szafranowska, B.; Beck, J. Eur. J. Inorg. Chem. 2013, 2013, 3167−3177. (55) Joas, M.; Klapötke, T. M.; Stierstorfer, J.; Szimhardt, N. Chem. Eur. J. 2013, 19, 9995−10003. (56) Garcia, Y.; Kahn, O.; Rabardel, L.; Chansou, B.; Salmon, L.; Tuchagues, J. P. Inorg. Chem. 1999, 38, 4663−4670. (57) Bushuyev, O. S.; Brown, P.; Maiti, A.; Gee, R. H.; Peterson, G. R.; Weeks, B. L.; Hope-Weeks, L. J. J. Am. Chem. Soc. 2012, 134, 1422−1425. (58) Li, S.; Wang, Y.; Qi, C.; Zhao, X.; Zhang, J.; Zhang, S.; Pang, S. Angew. Chem., Int. Ed. 2013, 52, 14031−14035. (59) Lothrop, W. C.; Handrick, G. R. Chem. Rev. 1949, 44, 419−445. (60) Martin, A. R.; Yallop, H. J. Trans. Faraday Soc. 1958, 54, 257− 263. (61) Wu, Q.; Zhu, W.; Xiao, H. J. Mater. Chem. A 2014, 2, 13006− 13015. (62) Han, Y. F.; Chen, F.; Zhong, Z. Y.; Ramesh, K.; Widjaja, E.; Chen, L. W. Catal. Commun. 2006, 7, 739−744. (63) Han, Y. F.; Ramesh, K.; Chen, L.; Widjaja, E.; Chilukoti, S.; Chen, F. J. Phys. Chem. C 2007, 111, 2830−2833. (64) Tian, Z. R.; Tong, W.; Wang, J. Y.; Duan, N. G.; Krishnan, V. V.; Suib, S. L. Science 1997, 276, 926−930. (65) Poyraz, A. S.; Kuo, C. H.; Biswas, S.; King’ondu, C. K.; Suib, S. L. Nat. Commun. 2013, 4, 94−105. (66) Biswas, S.; Dutta, B.; Mullick, K.; Kuo, C. H.; Poyraz, A. S.; Suib, S. L. ACS Catal. 2015, 5, 4394−4403. (67) Ding, Y.; Hou, C.; Li, B.; Lei, Y. Electroanalysis 2011, 23, 1245− 1251. (68) Zhang, Y.; Yan, Y.; Wang, X.; Li, G.; Deng, D.; Jiang, L.; Shu, C.; Wang, C. Chem. - Eur. J. 2014, 20, 6126−6130. (69) Liu, R.; Zhao, S.; Zhang, M.; Feng, F.; Shen, Q. Chem. Commun. 2015, 51, 5728−5731. (70) Bai, Z.; Zhang, Y.; Zhang, Y.; Guo, C.; Tang, B.; Sun, D. J. Mater. Chem. A 2015, 3, 5266−5269. (71) An, H. B.; Kim, J. M.; Jurng, J.; Bae, G. N.; Jeon, J. K.; Park, S. H.; Park, Y. K. J. Nanosci. Nanotechnol. 2013, 13, 7472−7476. (72) Qiu, Y.; Xu, G. L.; Yan, K.; Sun, H.; Xiao, J.; Yang, S.; Sun, S. G.; Jin, L.; Deng, H. J. Mater. Chem. 2011, 21, 6346−6353. (73) Subramanian, V.; Zhu, H.; Wei, B. Chem. Phys. Lett. 2008, 453, 242−249. (74) Maiti, S.; Pramanik, A.; Mahanty, S. CrystEngComm 2016, 18, 450−461. (75) Bircumshaw, L. L.; Newman, B. H. Proc. R. Soc. London, Ser. A 1954, 227, 115−132. (76) Galwey, A. K.; Jacobs, P. W. M. Trans. Faraday Soc. 1959, 55, 1165−1172. (77) Hong, F.; Ni, Y.; Zhong, Y.; Wu, H. J. Alloys Compd. 2016, 659, 112−121. (78) Fu, T.; Liu, F.; Liu, L.; Guo, L.; Li, F. Catal. Commun. 2008, 10, 108−112. (79) Chandru, R. A.; Patra, S.; Oommen, C.; Munichandraiah, N.; Raghunandan, B. N. J. Mater. Chem. 2012, 22, 6536−6538. (80) Zhao, H.; Guo, L.; Chen, S.; Bian, Z. RSC Adv. 2013, 3, 19929− 19932. (81) Li, N.; Geng, Z.; Cao, M.; Ren, L.; Zhao, X.; Liu, B.; Tian, Y.; Hu, C. Carbon 2013, 54, 124−132. (82) Wang, J.; Qiao, Z.; Zhang, L.; Shen, J.; Li, R.; Yang, G.; Nie, F. CrystEngComm 2014, 16, 8673−8677. (83) Chen, L.; Zhu, D. Ceram. Int. 2015, 41, 7054−7058. (84) Tian, S.; Li, N.; Zeng, D.; Li, H.; Tang, G.; Pang, A.; Xie, C.; Zhao, X. CrystEngComm 2015, 17, 8689−8696.

(85) Sharma, J. K.; Srivastava, P.; Ameen, S.; Akhtar, M. S.; Singh, G.; Yadava, S. J. Colloid Interface Sci. 2016, 472, 220−228.

I


From a Novel Energetic Coordination Polymer Precursor to Diverse

Recommend Documents