Fabrication of flexible ceramic membranes derived from hard Si3N4 and soft MnO2 nanowires

Journal Pre-proof Fabrication of flexible ceramic membranes derived from hard Si3N4 and soft MnO2 nanowires Xuejie Yue, Tao Zhang, Dongya Yang, Fengxian Qiu PII:

S0272-8842(19)33419-4

DOI:

https://doi.org/10.1016/j.ceramint.2019.11.226

Reference:

CERI 23595

To appear in:

Ceramics International

Received Date: 24 September 2019 Revised Date:

31 October 2019

Accepted Date: 26 November 2019

Please cite this article as: X. Yue, T. Zhang, D. Yang, F. Qiu, Fabrication of flexible ceramic membranes derived from hard Si3N4 and soft MnO2 nanowires, Ceramics International (2019), doi: https:// doi.org/10.1016/j.ceramint.2019.11.226. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Fabrication of flexible ceramic membranes derived from hard Si3N4 and soft MnO2 nanowires Xuejie Yue a, Tao Zhang a, b*, Dongya Yang a, Fengxian Qiu a* a

School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, Jiangsu Province, China. b

Institute of Green Chemistry and Chemical Technology, Jiangsu University, Zhenjiang 212013, Jiangsu Province, China.

*Corresponding authors: Tel./fax: +86 511 88791800. E-mail: [email protected] (T. zhang); [email protected] (F. Qiu) 1

Abstract: Flexible ceramic material, as a fundamental component of a toolset for the design of multifunctional materials, is very desirable, but a simple and effective preparation strategy is still missing. Herein, a flexible Si3N4/MnO2 ceramic membrane was fabricated by facile vacuum filtration progress using hard Si3N4 particles and soft ultralong MnO2 nanowires as building blocks. The Si3N4 particles were uniformly anchored into the porous flexible membrane, depending on the mechanical entanglement from ultralong MnO2 nanowires, resulting in the excellent interface stability between them. Thanks to the flexibility of MnO2 nanowires and interface stability, the as-prepared flexible membrane achieves superior flexibility including bending, folding, and twining. The flexible ceramic membrane can broaden the application range beyond the traditional ceramic use as hard structural materials. Moreover, the design strategies developed herein is applicable to other hard ceramic with similar issues. Keywords: MnO2 nanowires, Si3N4, flexibility, ceramic membrane

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1. Introduction Ceramic materials are usually identified as the composite materials that are compound of non-metal, metal, or metalloid atoms primarily held in ionic and covalent bonds [1, 2]. Among various ceramic materials, silicon nitride (Si3N4) has received widespread attention in recent years, because of the excellent balance on toughness and mechanical properties, as well as the outstanding integration of superior biocompatibility, thermal stability, remarkable wear and creep resistance, and extreme corrosion resistance [3-5]. Considering the key role of Si3N4 ceramics as functional materials, various Si3N4 ceramic matrix composites with different structures are extremely expected for the applications. Unfortunately, compared with more interesting on the crystal phase conversion and formation mechanism, few works that were simply focused on the flexile Si3N4 ceramic materials, were reported, due to the fragility caused from high-pressure/high-temperature sintering and the challenge to thickness reduction [6, 7]. Flexible Si3N4 ceramic membrane, one of the promising materials, has been an increasingly keen and wide interest for researchers, due to the unique properties including superior bendability and adhesion to irregular shaped subtracts [8-10]. Moreover, the outstanding integration of these special properties from the flexibility and the excellent physical and chemical nature of Si3N4 renders the flexible Si3N4 ceramic membrane the potential applications in emerging fields. For example, Kim et al. [11] fabricated a superlattice crystals–mimic ceramic membrane with excellent flexibility

for

high-performance

battery 3

separators

via

a

simultaneous

electrospraying/electrospinning electrospraying/electrospinning

process. technology is

However,

the

typically tailored

simultaneous for

specific

ceramic-driven material, due to the requirement of appropriate precursor ceramic sol, complicated manipulation processes and special equipment, resulting in the inconvenient and limited applications. Other technologies utilize the polymer materials as binders to obtain ceramic-polymer composites, which integrated the flexible from polymer and chemical and thermal stability from ceramic particles [12, 13]. The dispersion of ceramic powder in the polymer and the interface compatibility between polymer and ceramic powder cannot be ignored, due to the huge differences in physical properties between them. For these reasons, no meaningful results have been achieved, and a versatile strategy to endow the hard-ceramic materials with flexibility remains a significant challenge. Ultralong MnO2 nanowires, characterized by outstanding electrochemical properties, natural abundance and environmental benignity, are attracting much interest because they are expected to play an important role in catalytic and electrochemical [14]. Moreover, the ideal flexibility, ultrahigh aspect ratio, and excellent dispersion in water suggest the potential to enhance the flexibility of Si3N4 ceramic [15]. Herein, a new class of flexible ceramic membrane via vacuum filtration progress using ultralong MnO2 nanowires and Si3N4 powder as building blocks. The ultralong MnO2 nanowires can work as the reinforcing skeleton to entangle the compactly packed Si3N4 ceramic powder, thereby contributing to mechanical flexibility without the aid of polymer. Moreover, these composite fibers preserved 4

excellent mechanical stability under the static soaking test and high thermal conductivity. In addition, this proposed approach can be extended to conventional hard ceramic materials to fabricate flexible ceramic membranes.

2. Experimental section 2.1. Materials Si3N4 powder was purchased from Aladdin Chemical Co., Ltd., Shanghai, China. Ethyl alcohol (C2H5OH), potassium sulphate (K2SO4), potassium persulphate (K2S2O8), and manganese sulphate monohydrate (MnSO4·H2O) were provided by Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Deionized water was used for the preparation of all solutions and all agents were used without any further refinement. 2.2. Preparing ultralong MnO2 nanowires dispersion Ultralong MnO2 nanowires were fabricated with the aid of high temperature hydrothermal technique. Typically, the stoichiometric mixtures of K2SO4 (30 mmol), K2S2O8 (60 mmol), and MnSO4·H2O (30 mmol) were added into 150 mL of deionized water. After being allowed to react at 250 oC for 5 days in a Teflon-lined autoclave, the obtained mud-like ultralong MnO2 nanowires were thoroughly washed by deionized water and then dried under a vacuum. Lastly, 0.1 g of ultralong MnO2 nanowires were dispersed into 100 mL of deionized water with strong stirring for 24 h, forming wool-like ultralong MnO2 nanowires suspension. 2.3. Preparation of flexible Si3N4/MnO2 nanowires hybrid membrane

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The flexible Si3N4/MnO2 nanowires hybrid membrane was obtained via a vacuum filtration technology. In a typical procedure, 30 mL of ultralong MnO2 nanowires suspension and 30 mg of Si3N4 powder were mixed under stirring for 3 h. The obtained mixture suspension was then filtered using a vacuum filtration device equipped with a filter membrane to prepare a flexible Si3N4/MnO2 membrane. Finally, the obtained membrane was peeled from the filter membrane carefully and then incubated for 5 h under 10 kPa pressure. 2.4. Characterization The surface morphologies of samples were observed by a field emission scanning electron microscope (FE-SEM, JEOL, JSM-7800F). X-ray diffraction (XRD, Shimadzu XRD-6100 instrument) analysis was used to evaluate the crystal structure of different samples. The water contact angle (WCA) was measured using a commercial CAM200 optical system. Thermal conductivity meter (WZ-HC-074-200) was used to evaluate the thermal conductivity of samples.

3. Results and discussion 3.1. Structure and morphology The structural morphology of functional materials plays a key role in physical and chemical properties, since such surface morphology can affect multiple performance parameters including surface area and wettability. The micrographs of Si3N4 powder and ultralong MnO2 nanowires are shown in Figure 1. In Figure 1A, numerous Si3N4 particles with irregular sizes and shapes randomly stack together, forming various gaps. These gaps indicate the weak connection between the particles 6

and week membrane forming property. Moreover, Si3N4 particles show a rough surface in Figure 1B. Usually, high-temperature sintering of Si3N4 particles is a common strategy to fabricate porous ceramic membranes. But they tend to be fragile and fail to withstand structural integrity. To fabricate flexible ceramic materials, ultralong MnO2 nanowires are used to enhance the membrane forming property, and the general morphology information is shown in Figure 1C. Abundant randomly oriented ultralong MnO2 nanowires and nanowire bundles with length up to 50 µm are entangled with one another at large scale, forming open network structure. Importantly, ultralong MnO2 nanowires were bended and entangled with each other, indicating

the

extreme

flexibility

and

membrane-forming

property.

The

high-magnification SEM image in Figure 1D reveals nanowire bundles composed by ultralong MnO2 nanowires, which have typical diameters of ~ 50 nm, indicating the ultrahigh aspect ratios up to about 103. Such flexibility and ultrahigh aspect ratio indicate the high quality and are also expected to enhance the flexibility of the ceramic membrane.

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Figure 1. SEM images of pristine Si3N4 powder (A-B) and ultralong MnO2 nanowires (c-d) at different magnification. The flexible ceramic membrane was directly obtained via facile vacuum filtration technology and the surface morphologies of flexible ceramic membrane are shown in Figure 2. In Figure 2A, a ceramic membrane with rough surface is composed of Si3N4 particles and ultralong MnO2 nanowires. Abundant Si3N4 particles with different shapes and sizes are homogeneously anchored with the aid of ultralong MnO2 nanowires. No gaps and collapse are observed, implying the excellent compatibility between Si3N4 particles and ultralong MnO2 nanowires. Figure 2B reveals

the self-entanglement

of ultralong

MnO2

nanowires,

forming an

interpenetrating porous network. More importantly, Si3N4 particles are tightly anchored in the flexible membrane by the winding of ultralong MnO2 nanowires. Apart from large Si3N4 particles, small Si3N4 particles can also be anchored in a 8

mechanical winding, as shown in Figure 2C. It can be seen from element mappings in Figure 2D that Si, K, Mn, and O distribute uniformly and overlap each other, indicating that Si3N4 particles are uniformly dispersed in the interconnected ultralong MnO2 nanowires network. The uniform distribution, superior compatibility, and interpenetrating porous network suggest the flexibility of the ceramic membrane.

Figure 2. (A-C) SEM images of flexible ceramic membrane at different magnification. (D) mapping images of flexible ceramic membrane. XRD analysis was used to investigate the phase purity of samples, and the XRD pattern was shown in Figure 3A. All the reflections peaks of ultralong MnO2 nanowires are consistent with the pattern reported for typical tetragonal phase of α-MnO2 (JCPDS card no. 44-0141). There is no other crystalline phase existing, suggesting the high purity. In general, α-MnO2 is composed of a well-defined tunnel structure with a size of 4.6 Å × 4.6 Å, which are constructed from edge-shared double [MnO6] octahedral chains. There are several inorganic cations with appropriate sizes and small amounts of water are present in the tunnels to balance and stabilize the structure. In this work, K2SO4 and K2S2O8 were used to fabricate ultralong MnO2 9

nanowires, and K+ partially occupies the tunnel, which is proved by the mapping image in Figure 2D. Moreover, the K+ not only can be ion-exchanged with other inorganic cations, but can also be active sites for selective catalysis. The diffraction pattern of Si3N4 particles shows a number of well-defined reflections and weak background, implying a high degree of long-range order. In detail, Si3N4 particles show oriented peaks, which are well indexed as β-Si3N4 (JCPDS card no. 33-1160). No α-Si3N4 phase or other crystalline phases were shown, indicating the high purity of the Si3N4 particles. Figure 3B shows the XRD patterns of flexible ceramic membranes with different Si3N4 content. All the XRD patterns show the typical diffraction peaks of β-Si3N4 and α-MnO2. As the filling amount of Si3N4 particles increases, strong intensity of the typical (2 0 0), (1 0 1), and (2 1 0) peaks of Si3N4 become stronger, indicating the integration of them in one flexible ceramic membrane. Moreover, the controlled load can endow the flexible ceramic membrane with controllable performances for potential applications (e.g. thermal conduction and microwave absorbing).

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Figure 3. (A) XRD patterns of the pristine ultralong MnO2 nanowires and Si3N4 particles. (B) XRD patterns of hybrid flexible ceramic membrane prepared by different contents of Si3N4 ceramic particles. 3.2. Flexibility of hybrid membrane For a practical application, a static soaking test was used to evaluate the stability of the flexible ceramic membrane. The tailored flexible ceramic membranes (1cm × 4 cm) were soaked in the water with different temperatures. Flexible ceramic membrane can be thoroughly wetted, as shown in Figure 4A, due to its superhydrophilicity (Figure S1). After soaking for 48 h, the water in the bottle is transparent, and no detachment is observed. In addition, the stability of the membrane is further evaluated in the hot water soaking, and a similar result is obtained as excepted. The excellent compatibility can be explained by the hydrogen bonding between Si3N4 particles and ultralong MnO2 nanowires and the immobilizing in a mechanical winding. More importantly, as shown in Figure 2B, the hybrid ceramic membrane can be bended, folded without cracking, and even twining the tiny glass rod, suggesting the superior flexibility of the hybrid membrane, which is mainly caused by its interface stability and the flexibility of ultralong MnO2 nanowires. Its flexibility can provide convenience for the development of functional flexible ceramic materials.

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Figure 4. (A) The digital photos of flexible ceramic membrane before and after soaking in water with different temperatures. (B) The flexibility of the ceramic membrane. In general, surface roughness plays an important role in understanding the nature of membrane surfaces. The surface roughness of pure ultralong MnO2 nanowires membrane and flexible ceramic membrane were evaluated by a non-contact optical profiler, as shown in Figure 5. In Figure 5A, the surface of pristine ultralong MnO2 nanowires membrane displays a relatively uniform color distribution, implying a relatively flat surface. Due to the flexibility and ultrahigh aspect ratio, ultralong MnO2 nanowires have the superior membrane-forming property. As excepted, the pristine ultralong MnO2 nanowires membrane has shown a low Ra value of 1.364 µm. Moreover, the profiles along the X axis and Y axis of the membrane are shown in Figure 5B and C, suggesting the low rough surface with small ∆Z (-3.924 µm for X axis and 1.346 µm for Y axis). Compared to the pristine ultralong MnO2 nanowires, 12

flexible ceramic membrane shows an irregular surface with a slightly increased Ra value of 2.38 µm, indicating a rough surface. The enhanced roughness is caused by the anchored Si3N4 particles on the ceramic membrane surface. In addition, the X and Y profiles of flexible ceramic membrane prove the huge range of surface topography with high ∆Z (-6.5866 µm for X axis and -5.6439 µm for Y axis).

Figure 5. Optical profilometry image(A) and X and Y profiles (B and C) of ultralong MnO2 nanowires membrane. Optical profilometry image (D) and X and Y profiles (E and F) of flexible ceramic membrane.

4. Conclusions In conclusion, a novel self-standing and flexible ceramic membrane was fabricated by simple vacuum filtration technology. Based on the advantages in hydrogen bonding interactions and immobilizing in a mechanical winding, the 13

dispersed Si3N4 micro-particles can be efficiently anchored into the self-assembly and porous ultralong MnO2 nanowires networks, forming Si3N4/MnO2 hybrid membrane. The simple preparation strategy can not only avoid the complicated manipulation processes, like calcination with the aid of solders, but can also endow the ceramic membrane with superior flexibility. The as-prepared flexible membrane shows satisfied interface stability proved by the static soaking test and optical profilometry image. The outstanding preparties including superior flexibility, simple fabrication progress, excellent interface stability, and porosity promise their potential application in wearable materials, microwave absorbing materials, chemically active separators, etc. Moreover, this simple fabrication strategy is quite versatile and thus is immediately applicable to other hard ceramic with similar issues.

Acknowledgments This work was financially supported by the National Natural Science Foundation of China (21706100 and 21878132).

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Declaration of interests ☒ 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. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: