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High acid resistant SiOC ceramic membranes for wastewater treatment
Author’s Accepted Manuscript High acid resistant SiOC ceramic membranes for wastewater treatment Fangwei Guo, Dong Su, Yang Liu, Jianming Wang, Xiao Yan, Jing Chen, Shunquan Chen www.elsevier.com/locate/ceri
PII: DOI: Reference:
S0272-8842(18)31020-4 https://doi.org/10.1016/j.ceramint.2018.04.149 CERI18066
To appear in: Ceramics International Received date: 12 April 2018 Revised date: 17 April 2018 Accepted date: 17 April 2018 Cite this article as: Fangwei Guo, Dong Su, Yang Liu, Jianming Wang, Xiao Yan, Jing Chen and Shunquan Chen, High acid resistant SiOC ceramic membranes for wastewater treatment, Ceramics International, https://doi.org/10.1016/j.ceramint.2018.04.149 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. 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.
High acid resistant SiOC ceramic membranes for wastewater treatment Fangwei Guo*a,b, Dong Su c,Yang Liub, Jianming Wangb,d, Xiao Yan*b, Jing Chenb, Shunquan Chenb a
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
b
Guangdong Key Laboratory of Membrane Materials and Membrane Separation, Guangzhou Institute
of Advanced Technology, Chinese Academy of Sciences, Guangzhou 511458, China. c
School of Materials Science and Engineering, Tianjin University, Tianjin, 300072, China.
d
Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China.
*Corresponding author. Fax: +86-20-22912525; Tel: +86-20-22912609; Email: [email protected] (X. Yan), [email protected] (F. Guo). Abstract Tailoring the pore structures of ceramic membranes is the essential challenge in its application for wastewater treatment. In this paper, silicon oxycarbide (SiOC) ceramic membranes with tunable pore structures are fabricated by coating polysiloxanes (PSO) onto YSZ hollow fiber membranes followed with subsequent pyrolysis. The SiOC ceramics, with a pore size in the range of 50 nm-2 μm and porosity of 35%-40%, have been obtained by varying the pore forming agents. Moreover, the SiOC layers endow the fiber membranes with high corrosion resistance regarding merely 0.07 wt.% weight loss in 20 wt.% H2SO4 solution, since that the unique silicon oxycarbide microlattice structures can provide remarkable chemical durability. Together with considerable mechanical strength and pure water permeate flux, such SiOC ceramic membranes should find applications in industrial wastewater treatment. Keywords: A. films; B. Porosity; C. Corrosion; D. Glass ceramics; E. Membranes. Introduction
1
Ceramic membranes possess combined advantages of high chemical inertness and high mechanical integrity, and are promising candidates for industrial wastewater treatment [1]. Conventional ceramic membranes are fabricated through multiple coating and sintering steps. Generally, a macroporous support is firstly fabricated and sintered at high temperature; then several functional layers are then coated in a specific order to achieve desired filtration precision [2], which is time-consuming and significantly increases the production cost. Recently, the phase inversion technique, a well-defined technique for constructing polymeric membranes with interconnected skeleton and multi-scale pore structures [3], has been proposed for fabricating ceramic membranes with asymmetric pore structures [4]. By combining multiple steps into one single step, the materials’ production time and cost can be wisely managed, making the membranes economically viable [5]. However, the high temperature heat treatment (> 1400 °C) is still required in this process, which often induces morphological changes and membrane performance deterioration [6]. Polymer-derived ceramics (PDCs) are novel Si-based advanced ceramics that can be fabricated from preceramic polymers at low temperatures (< 1000 °C) [7]. Structure and properties of the resulting ceramics can be precisely tuned by molecular modification of the polymeric precursors along with rationally designed processing techniques [8]. On this basis, ceramics with controllable microstructures and desired properties can be fabricated via a range of versatile and simple approaches, such as replica, sacrificial template, and direct foaming [9]. Recently, using this method, SiOC ceramics with complex shapes and cellular architectures have been obtained by 3D printing, indicating the great potential of this PDC procedure for scale-up manufacturing ceramic materials with delicate microstructures[10]. These features thus make PDC a very suitable strategy to fabricate SiOC hollow fiber membranes with tunable porosity for water treatment, yet there have been very few reports available by far. 2
In this paper, SiOC ceramic membranes with tailorable pore structures were fabricated using the PDC method with the assistance of sacrificial fillers. A thin SiOC layer with desired pore structure was then coated onto the YSZ substrate without significantly affecting its water permeability. Effect of filler types and filler ratio on the microstructures was also evaluated along with the corrosion resistance properties of the obtained membranes. Experimental Polyhydromethylsiloxane (PHMS, average Mn: ~3500, viscosity: 100 mPa s, J&K scientific, Beijing, China) and tetramethyltetravinylcycletetra siloxane (D4Vi, Kewei, Tianjin, China) were selected as PSO precursors. Linear methy-terminated polymethylsiloxane (PDMS, Average Mn: ~17000, viscosity: 200 mPa s, Kewei, Tianjin, China) and silicone S184 (viscosity: 300 mPa s, Aladdin, Shanghai, China) were used as sacrificial fillers. Precursor gels were prepared following the process in the literature [11] and then coated onto YSZ hollow fiber membranes. Mixtures of PDMS and S184 with various weight ratios (1:2, 2:2, 3:2) were set as 30 wt.%, 40 wt.%, and 50 wt.% to PSO precursors, respectively. Pyrolysis was carried out in an argon flow at 800 °C for 1 h at a ramp rate of 5 °C min-1 to form porous SiOC ceramic membranes. The microstructure of the materials was characterized by scanning electronic microscopy (SEM, S4800, Hitachi, Japan). Bulk densities and porosities of the SiOC ceramics were measured by Archimedes method using water as the medium and further confirmed by mercury porosimetry (AutoPore IV9500 V1.07, Micromeritics, US). The SiOC membranes were characterized by a contact angle test (Dropmetre A-300, Maist, China) and pure water permeate flux measurement as described in Reference [12]. The fiber membranes were assembled into single fiber modules and the pure water permeate flux was measured at 0.1 MPa. The flux for each specimen was calculated by averaging the testing values of 3
5 measurements. Corrosion resistance was measured by weighing the samples before and after the treatment in boiling 20 wt.% H2SO4 for 8 hours. Results and Discussion The schematic routes to synthesize the SiOC ceramics from liquid polymeric precursors is illustrated in Figure 1. Generally, the pore structures stem from the phase separation process in the crosslinking stage: PDMS and S184 forms continuous pore directing phases and the active groups in the PSO components, Si-H and CH2=CH, react with each other to form a network. The obtained SiOC ceramics are amorphous and hydrophilic, with a contact angle of 70°, similar to that of YSZ membranes. Linear PDMS and S184 function as sacrificial fillers to direct the pore forming process, and their ratio has a significant impact on the pore structure of the obtained materials. Structural characteristics of the SiOC obtained with various filler ratio are listed in Table 1. Generally, as the filler ratio is increased, the linear shrinkage and porosity of the ceramic increase while the yields of the ceramics decreases. This can be attributed to the decomposition of the precursors and the release of the sacrificial fillers.
Figure 1. Polymer derived approach to SiOC ceramics 4
Table 1. Structural characteristic of SiOC ceramics with various filler ratio.
Filler ratio
Linear shrinkage
Ceramic yields
Density
Porosity*
(wt. %)
(%)
(wt%)
(g/cm3)
(%)
PDMS
30
32.0
71.2
1.45
34.1
+S184
40
37.0
62.8
1.36
38.2
(1:1)
50
46.0
54.2
1.29
41.4
* The porosity is calculated according to the density of full dense SiOC of 2.23 g/cm3[13]. The pore structures of the polymer derived SiOC ceramics can be tuned by selecting different filler agents and adjusting their ratio in the precursor. The microstructures of the typical SiOC ceramics with the PDMS and the S184 fillers (30 wt.%) are presented in Figure 2, respectively. The SiOC ceramics using PDMS filler have large interconnected pore structures, with pore size in the range of 1 to 2 μm (Figure 2a, b); while PDMS and S184 mixtures can induce nanometer-sized pores in the range of 50-800 nm (Figure 2c, d). This is attributed to the fact that the vinyl terminated S184 can react with the active groups of the PSO precursor (Si-H and CH=CH2) in the crosslinking stage and result in denser ceramics with higher yields[14]. Moreover, the pore structure of the SiOC ceramics can also be tuned by simply varying the filler ratio. Figure 2e compares the pore size distribution of SiOC ceramics with the mixture filler ratios of 30 wt.% and 50 wt.%. SiOC with 30 wt. % fillers presents a predominant peak at 226 nm, which shifts to 350 nm when the fillers are increased to 50 wt.%, while the two smaller peaks at 60 nm and 350 nm shift to 150 nm and 677 nm, respectively.
5
(a)
(e)
0.25
30 wt% 50 wt%
specfic pore volume(ml/g)
0.20
0.15
0.10
0.05
0.00 0
200
400
600
800
pore diameter(nm)
Figure 2. Pore structures of the SiOC ceramics with various fillers and filler ratio. (a) and (b) PDMS as fillers, (c) and (d) PDMS+S184 as fillers, (e) pore size distribution at 30 wt.% and 50 wt.% of mixture filler ratio. SiOC films were coated onto YSZ hollow fiber substrates by dip-coating PSO solutions following with crosslink and pyrolysis. The SiOC films are ~15 μm thick, homogeneously and intactly coated on the YSZ (Figure 3a and 3b), forming a gradient in the cross-section which favors for separation and filtration applications. SEM observation under high magnifications reveals that the SiOC layers consist of particle aggregates with nanometer-sized voids (Figure 3c). The voids function could serve as water transfer channels. Thus, the SiOC membranes have merely negligible decrease in water permeate flux (1549 L m-2 h-1) compared with the pure YSZ membranes (1645 L m-2 h-1). Conventional ceramic membranes often suffer from lattice misfit between substrates and coating films, which can induce internal stress and lead to materials failure. This is not the case for SiOC membranes, since the SiOC ceramics are amorphous at the low firing temperature of 800 °C (Figure 3d). 6
(a)
(b)
(c)
(d)
10
20
30
40
50
60
70
80
2 (degree)
Figure 3 SEM images of SiOC ceramic membrane. (a) Cross section of the membrane; (b) Enlarged SiOC coating area; (c) Surface of the membrane; (d) XRD patteren of SiOC. The corrosion resistance properties are essential to the ceramic membranes since they are usually used in extreme environments during the waste water treatment. Figure 4 presents the weight losses of the SiOC ceramic membranes prepared with different amounts of mixture fillers, after being treated in boiling 20 wt.% H2SO4 for 8 h, respectively. It can be seen that weight losses of the SiOC membranes are generally lower despite of the increased filler ratio. Our previous study on Fe2O3-YSZ membranes have exhibit weight loss of no more than 0.6 wt.%, much lower compared to that of alumina hollow fibers (1.25 wt.%) [15] and cordierite membranes (17.0 wt.%) [16]. Also Fe2O3-YSZ membranes can retain a bending strength of ~130±10 MPa. This is much more favorable than the cordierite-based membranes which show ~55% loss in strength after being treated with 20 wt% H2SO4 solution [17]. 7
Literature reports have suggested that sulfuric acid can initiate the corrosion at zirconia grain boundaries and cause complete transformation from tetragonal to monoclinic phase [18], which is often responsible for the degradation of YSZ and can result in cracking and materials failure [19]. The very low weight loss of 0.07 wt.% of the SiOC membranes after acid treatment indicates an excellent resistance against chemical corrosion, which can be attributed to the unique nanodomains of silicon-oxygen tetrahedral, which are further encased in a network of graphene in the SiOC ceramics [20].
Weight loss (%)
0.08
0.06
0.04
0.02
0.00
30
40
50
Filler ratio (%)
Figure 4 Weight loss of SiOC ceramic membranes as a function of filler ratios. Conclusions SiOC ceramic membranes with tunable microstructures and low fabrication cost are demonstrated with polymer derived ceramics approach using PDMS and S184 as sacrificial fillers at low pyrolysis temperature. Their pore structures can be varied by adjusting the filler types and filler ratios, indicating the high flexibility of such fabrication process. The SiOC films can provide fine pore structures as well as remarkable corrosion resistance for membrane applications due to the chemical inertness of SiOC ceramics. Such SiOC fiber membranes can be applied for separating and recycling the valuable resources from high acidic industrial waste water. Acknowledgements 8
This work was supported by the National Natural Science Foundation of China (grant numbers 51502045), the Guangzhou Science and Technology Program (grant number 2014Y2-00173 and 201604010070), the Shenzhen Basic Research Program (grant number JCYJ20150521094519490) and the Nansha Science and Technology Program (grant number 2017CX012). References [1] M.M. Pendergast, E.M.V. Hoek, A review of water treatment membrane nanotechnologies, Energy & Environmental Science 4(6) (2011) 1946-1971. [2] K. Li, X. Tan, Y. Liu, Single-step fabrication of ceramic hollow fibers for oxygen permeation, Journal of Membrane Science 272(1) (2006) 1-5. [3] X. Yang, Y. Chen, M. Wang, H. Zhang, X. Li, H. Zhang, Phase Inversion: A Universal Method to Create High-Performance Porous Electrodes for Nanoparticle-Based Energy Storage Devices, Advanced Functional Materials 26(46) (2016) 8427-8434. [4] J. Malzbender, Mechanical aspects of ceramic membrane materials, Ceramics International 42(7) (2016) 7899-7911. [5] H. Chen, X. Jia, M. Wei, Y. Wang, Ceramic tubular nanofiltration membranes with tunable performances by atomic layer deposition and calcination, Journal of Membrane Science 528(Supplement C) (2017) 95-102. [6] K. Guan, W. Qin, Y. Liu, X. Yin, C. Peng, M. Lv, Q. Sun, J. Wu, Evolution of porosity, pore size and permeate flux of ceramic membranes during sintering process, Journal of Membrane Science 520(Supplement C) (2016) 166-175. [7] P. Colombo, C. Vakifahmetoglu, S. Costacurta, Fabrication of ceramic components with hierarchical porosity, Journal of Materials Science 45(20) (2010) 5425-5455. [8] P. Colombo, G. Mera, R. Riedel, G.D. Sorarù, Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics, Journal of the American Ceramic Society 93(7) (2010) 1805-1837. [9] A.R. Studart, U.T. Gonzenbach, E. Tervoort, L.J. Gauckler, Processing Routes to Macroporous Ceramics: A Review, Journal of the American Ceramic Society 89(6) (2006) 1771-1789. [10] Z.C. Eckel, C. Zhou, J.H. Martin, A.J. Jacobsen, W.B. Carter, T.A. Schaedler, Additive manufacturing of polymer-derived ceramics, Science 351(6268) (2016) 58-62. [11] X. Yan, D. Su, S. Han, Phase separation induced macroporous SiOC ceramics derived from polysiloxane, Journal of the European Ceramic Society 35(2) (2015) 443-450. [12] X. Liu, S. Wang, J. Miao, Y. Liu, X. Yan, S. Chen, Enhanced performance of Fe2O3 doped yttria stabilized zirconia hollow fiber membranes for water treatment, Ceramics International 42(14) (2016) 15618-15622. [13] C. Moysan, R. Riedel, R. Harshe, T. Rouxel, F. Augereau, Mechanical characterization of a polysiloxane-derived SiOC glass, Journal of the European Ceramic Society 27(1) (2007) 397-403. [14] D. Su, Y. Li, F. Hou, X. Yan, Synthesis and Characterization of Ethylene-Bridged Copolycarbosilazane as Precursors for Silicon Carbonitride Ceramics, Journal of the American Ceramic Society 97(4) (2014) 1311-1316. [15] Y. Dong, B. Lin, J.-e. Zhou, X. Zhang, Y. Ling, X. Liu, G. Meng, S. Hampshire, Corrosion 9
resistance characterization of porous alumina membrane supports, Materials Characterization 62(4) (2011) 409-418. [16] Y. Dong, X. Feng, D. Dong, S. Wang, J. Yang, J. Gao, X. Liu, G. Meng, Elaboration and chemical corrosion resistance of tubular macro-porous cordierite ceramic membrane supports, Journal of Membrane Science 304(1) (2007) 65-75. [17] Y. Dong, X. Feng, D. Dong, S. Wang, J. Yang, J. Gao, X. Liu, G. Meng, Elaboration and chemical corrosion resistance of tubular macro-porous cordierite ceramic membrane supports, Journal of Membrane Science 304(1–2) (2007) 65-75. [18] P. Kritzer, Corrosion in high-temperature and supercritical water and aqueous solutions: a review, The Journal of Supercritical Fluids 29(1) (2004) 1-29. [19] M. Schacht, N. Boukis, E. Dinjus, K. Ebert, R. Janssen, F. Meschke, N. Claussen, Corrosion of zirconia ceramics in acidic solutions at high pressures and temperatures, Journal of the European Ceramic Society 18(16) (1998) 2373-2376. [20] A. Saha, R. Raj, D.L. Williamson, A Model for the Nanodomains in Polymer-Derived SiCO, Journal of the American Ceramic Society 89(7) (2006) 2188-2195.
10
PII: DOI: Reference:
S0272-8842(18)31020-4 https://doi.org/10.1016/j.ceramint.2018.04.149 CERI18066
To appear in: Ceramics International Received date: 12 April 2018 Revised date: 17 April 2018 Accepted date: 17 April 2018 Cite this article as: Fangwei Guo, Dong Su, Yang Liu, Jianming Wang, Xiao Yan, Jing Chen and Shunquan Chen, High acid resistant SiOC ceramic membranes for wastewater treatment, Ceramics International, https://doi.org/10.1016/j.ceramint.2018.04.149 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. 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.
High acid resistant SiOC ceramic membranes for wastewater treatment Fangwei Guo*a,b, Dong Su c,Yang Liub, Jianming Wangb,d, Xiao Yan*b, Jing Chenb, Shunquan Chenb a
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
b
Guangdong Key Laboratory of Membrane Materials and Membrane Separation, Guangzhou Institute
of Advanced Technology, Chinese Academy of Sciences, Guangzhou 511458, China. c
School of Materials Science and Engineering, Tianjin University, Tianjin, 300072, China.
d
Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China.
*Corresponding author. Fax: +86-20-22912525; Tel: +86-20-22912609; Email: [email protected] (X. Yan), [email protected] (F. Guo). Abstract Tailoring the pore structures of ceramic membranes is the essential challenge in its application for wastewater treatment. In this paper, silicon oxycarbide (SiOC) ceramic membranes with tunable pore structures are fabricated by coating polysiloxanes (PSO) onto YSZ hollow fiber membranes followed with subsequent pyrolysis. The SiOC ceramics, with a pore size in the range of 50 nm-2 μm and porosity of 35%-40%, have been obtained by varying the pore forming agents. Moreover, the SiOC layers endow the fiber membranes with high corrosion resistance regarding merely 0.07 wt.% weight loss in 20 wt.% H2SO4 solution, since that the unique silicon oxycarbide microlattice structures can provide remarkable chemical durability. Together with considerable mechanical strength and pure water permeate flux, such SiOC ceramic membranes should find applications in industrial wastewater treatment. Keywords: A. films; B. Porosity; C. Corrosion; D. Glass ceramics; E. Membranes. Introduction
1
Ceramic membranes possess combined advantages of high chemical inertness and high mechanical integrity, and are promising candidates for industrial wastewater treatment [1]. Conventional ceramic membranes are fabricated through multiple coating and sintering steps. Generally, a macroporous support is firstly fabricated and sintered at high temperature; then several functional layers are then coated in a specific order to achieve desired filtration precision [2], which is time-consuming and significantly increases the production cost. Recently, the phase inversion technique, a well-defined technique for constructing polymeric membranes with interconnected skeleton and multi-scale pore structures [3], has been proposed for fabricating ceramic membranes with asymmetric pore structures [4]. By combining multiple steps into one single step, the materials’ production time and cost can be wisely managed, making the membranes economically viable [5]. However, the high temperature heat treatment (> 1400 °C) is still required in this process, which often induces morphological changes and membrane performance deterioration [6]. Polymer-derived ceramics (PDCs) are novel Si-based advanced ceramics that can be fabricated from preceramic polymers at low temperatures (< 1000 °C) [7]. Structure and properties of the resulting ceramics can be precisely tuned by molecular modification of the polymeric precursors along with rationally designed processing techniques [8]. On this basis, ceramics with controllable microstructures and desired properties can be fabricated via a range of versatile and simple approaches, such as replica, sacrificial template, and direct foaming [9]. Recently, using this method, SiOC ceramics with complex shapes and cellular architectures have been obtained by 3D printing, indicating the great potential of this PDC procedure for scale-up manufacturing ceramic materials with delicate microstructures[10]. These features thus make PDC a very suitable strategy to fabricate SiOC hollow fiber membranes with tunable porosity for water treatment, yet there have been very few reports available by far. 2
In this paper, SiOC ceramic membranes with tailorable pore structures were fabricated using the PDC method with the assistance of sacrificial fillers. A thin SiOC layer with desired pore structure was then coated onto the YSZ substrate without significantly affecting its water permeability. Effect of filler types and filler ratio on the microstructures was also evaluated along with the corrosion resistance properties of the obtained membranes. Experimental Polyhydromethylsiloxane (PHMS, average Mn: ~3500, viscosity: 100 mPa s, J&K scientific, Beijing, China) and tetramethyltetravinylcycletetra siloxane (D4Vi, Kewei, Tianjin, China) were selected as PSO precursors. Linear methy-terminated polymethylsiloxane (PDMS, Average Mn: ~17000, viscosity: 200 mPa s, Kewei, Tianjin, China) and silicone S184 (viscosity: 300 mPa s, Aladdin, Shanghai, China) were used as sacrificial fillers. Precursor gels were prepared following the process in the literature [11] and then coated onto YSZ hollow fiber membranes. Mixtures of PDMS and S184 with various weight ratios (1:2, 2:2, 3:2) were set as 30 wt.%, 40 wt.%, and 50 wt.% to PSO precursors, respectively. Pyrolysis was carried out in an argon flow at 800 °C for 1 h at a ramp rate of 5 °C min-1 to form porous SiOC ceramic membranes. The microstructure of the materials was characterized by scanning electronic microscopy (SEM, S4800, Hitachi, Japan). Bulk densities and porosities of the SiOC ceramics were measured by Archimedes method using water as the medium and further confirmed by mercury porosimetry (AutoPore IV9500 V1.07, Micromeritics, US). The SiOC membranes were characterized by a contact angle test (Dropmetre A-300, Maist, China) and pure water permeate flux measurement as described in Reference [12]. The fiber membranes were assembled into single fiber modules and the pure water permeate flux was measured at 0.1 MPa. The flux for each specimen was calculated by averaging the testing values of 3
5 measurements. Corrosion resistance was measured by weighing the samples before and after the treatment in boiling 20 wt.% H2SO4 for 8 hours. Results and Discussion The schematic routes to synthesize the SiOC ceramics from liquid polymeric precursors is illustrated in Figure 1. Generally, the pore structures stem from the phase separation process in the crosslinking stage: PDMS and S184 forms continuous pore directing phases and the active groups in the PSO components, Si-H and CH2=CH, react with each other to form a network. The obtained SiOC ceramics are amorphous and hydrophilic, with a contact angle of 70°, similar to that of YSZ membranes. Linear PDMS and S184 function as sacrificial fillers to direct the pore forming process, and their ratio has a significant impact on the pore structure of the obtained materials. Structural characteristics of the SiOC obtained with various filler ratio are listed in Table 1. Generally, as the filler ratio is increased, the linear shrinkage and porosity of the ceramic increase while the yields of the ceramics decreases. This can be attributed to the decomposition of the precursors and the release of the sacrificial fillers.
Figure 1. Polymer derived approach to SiOC ceramics 4
Table 1. Structural characteristic of SiOC ceramics with various filler ratio.
Filler ratio
Linear shrinkage
Ceramic yields
Density
Porosity*
(wt. %)
(%)
(wt%)
(g/cm3)
(%)
PDMS
30
32.0
71.2
1.45
34.1
+S184
40
37.0
62.8
1.36
38.2
(1:1)
50
46.0
54.2
1.29
41.4
* The porosity is calculated according to the density of full dense SiOC of 2.23 g/cm3[13]. The pore structures of the polymer derived SiOC ceramics can be tuned by selecting different filler agents and adjusting their ratio in the precursor. The microstructures of the typical SiOC ceramics with the PDMS and the S184 fillers (30 wt.%) are presented in Figure 2, respectively. The SiOC ceramics using PDMS filler have large interconnected pore structures, with pore size in the range of 1 to 2 μm (Figure 2a, b); while PDMS and S184 mixtures can induce nanometer-sized pores in the range of 50-800 nm (Figure 2c, d). This is attributed to the fact that the vinyl terminated S184 can react with the active groups of the PSO precursor (Si-H and CH=CH2) in the crosslinking stage and result in denser ceramics with higher yields[14]. Moreover, the pore structure of the SiOC ceramics can also be tuned by simply varying the filler ratio. Figure 2e compares the pore size distribution of SiOC ceramics with the mixture filler ratios of 30 wt.% and 50 wt.%. SiOC with 30 wt. % fillers presents a predominant peak at 226 nm, which shifts to 350 nm when the fillers are increased to 50 wt.%, while the two smaller peaks at 60 nm and 350 nm shift to 150 nm and 677 nm, respectively.
5
(a)
(e)
0.25
30 wt% 50 wt%
specfic pore volume(ml/g)
0.20
0.15
0.10
0.05
0.00 0
200
400
600
800
pore diameter(nm)
Figure 2. Pore structures of the SiOC ceramics with various fillers and filler ratio. (a) and (b) PDMS as fillers, (c) and (d) PDMS+S184 as fillers, (e) pore size distribution at 30 wt.% and 50 wt.% of mixture filler ratio. SiOC films were coated onto YSZ hollow fiber substrates by dip-coating PSO solutions following with crosslink and pyrolysis. The SiOC films are ~15 μm thick, homogeneously and intactly coated on the YSZ (Figure 3a and 3b), forming a gradient in the cross-section which favors for separation and filtration applications. SEM observation under high magnifications reveals that the SiOC layers consist of particle aggregates with nanometer-sized voids (Figure 3c). The voids function could serve as water transfer channels. Thus, the SiOC membranes have merely negligible decrease in water permeate flux (1549 L m-2 h-1) compared with the pure YSZ membranes (1645 L m-2 h-1). Conventional ceramic membranes often suffer from lattice misfit between substrates and coating films, which can induce internal stress and lead to materials failure. This is not the case for SiOC membranes, since the SiOC ceramics are amorphous at the low firing temperature of 800 °C (Figure 3d). 6
(a)
(b)
(c)
(d)
10
20
30
40
50
60
70
80
2 (degree)
Figure 3 SEM images of SiOC ceramic membrane. (a) Cross section of the membrane; (b) Enlarged SiOC coating area; (c) Surface of the membrane; (d) XRD patteren of SiOC. The corrosion resistance properties are essential to the ceramic membranes since they are usually used in extreme environments during the waste water treatment. Figure 4 presents the weight losses of the SiOC ceramic membranes prepared with different amounts of mixture fillers, after being treated in boiling 20 wt.% H2SO4 for 8 h, respectively. It can be seen that weight losses of the SiOC membranes are generally lower despite of the increased filler ratio. Our previous study on Fe2O3-YSZ membranes have exhibit weight loss of no more than 0.6 wt.%, much lower compared to that of alumina hollow fibers (1.25 wt.%) [15] and cordierite membranes (17.0 wt.%) [16]. Also Fe2O3-YSZ membranes can retain a bending strength of ~130±10 MPa. This is much more favorable than the cordierite-based membranes which show ~55% loss in strength after being treated with 20 wt% H2SO4 solution [17]. 7
Literature reports have suggested that sulfuric acid can initiate the corrosion at zirconia grain boundaries and cause complete transformation from tetragonal to monoclinic phase [18], which is often responsible for the degradation of YSZ and can result in cracking and materials failure [19]. The very low weight loss of 0.07 wt.% of the SiOC membranes after acid treatment indicates an excellent resistance against chemical corrosion, which can be attributed to the unique nanodomains of silicon-oxygen tetrahedral, which are further encased in a network of graphene in the SiOC ceramics [20].
Weight loss (%)
0.08
0.06
0.04
0.02
0.00
30
40
50
Filler ratio (%)
Figure 4 Weight loss of SiOC ceramic membranes as a function of filler ratios. Conclusions SiOC ceramic membranes with tunable microstructures and low fabrication cost are demonstrated with polymer derived ceramics approach using PDMS and S184 as sacrificial fillers at low pyrolysis temperature. Their pore structures can be varied by adjusting the filler types and filler ratios, indicating the high flexibility of such fabrication process. The SiOC films can provide fine pore structures as well as remarkable corrosion resistance for membrane applications due to the chemical inertness of SiOC ceramics. Such SiOC fiber membranes can be applied for separating and recycling the valuable resources from high acidic industrial waste water. Acknowledgements 8
This work was supported by the National Natural Science Foundation of China (grant numbers 51502045), the Guangzhou Science and Technology Program (grant number 2014Y2-00173 and 201604010070), the Shenzhen Basic Research Program (grant number JCYJ20150521094519490) and the Nansha Science and Technology Program (grant number 2017CX012). References [1] M.M. Pendergast, E.M.V. Hoek, A review of water treatment membrane nanotechnologies, Energy & Environmental Science 4(6) (2011) 1946-1971. [2] K. Li, X. Tan, Y. Liu, Single-step fabrication of ceramic hollow fibers for oxygen permeation, Journal of Membrane Science 272(1) (2006) 1-5. [3] X. Yang, Y. Chen, M. Wang, H. Zhang, X. Li, H. Zhang, Phase Inversion: A Universal Method to Create High-Performance Porous Electrodes for Nanoparticle-Based Energy Storage Devices, Advanced Functional Materials 26(46) (2016) 8427-8434. [4] J. Malzbender, Mechanical aspects of ceramic membrane materials, Ceramics International 42(7) (2016) 7899-7911. [5] H. Chen, X. Jia, M. Wei, Y. Wang, Ceramic tubular nanofiltration membranes with tunable performances by atomic layer deposition and calcination, Journal of Membrane Science 528(Supplement C) (2017) 95-102. [6] K. Guan, W. Qin, Y. Liu, X. Yin, C. Peng, M. Lv, Q. Sun, J. Wu, Evolution of porosity, pore size and permeate flux of ceramic membranes during sintering process, Journal of Membrane Science 520(Supplement C) (2016) 166-175. [7] P. Colombo, C. Vakifahmetoglu, S. Costacurta, Fabrication of ceramic components with hierarchical porosity, Journal of Materials Science 45(20) (2010) 5425-5455. [8] P. Colombo, G. Mera, R. Riedel, G.D. Sorarù, Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics, Journal of the American Ceramic Society 93(7) (2010) 1805-1837. [9] A.R. Studart, U.T. Gonzenbach, E. Tervoort, L.J. Gauckler, Processing Routes to Macroporous Ceramics: A Review, Journal of the American Ceramic Society 89(6) (2006) 1771-1789. [10] Z.C. Eckel, C. Zhou, J.H. Martin, A.J. Jacobsen, W.B. Carter, T.A. Schaedler, Additive manufacturing of polymer-derived ceramics, Science 351(6268) (2016) 58-62. [11] X. Yan, D. Su, S. Han, Phase separation induced macroporous SiOC ceramics derived from polysiloxane, Journal of the European Ceramic Society 35(2) (2015) 443-450. [12] X. Liu, S. Wang, J. Miao, Y. Liu, X. Yan, S. Chen, Enhanced performance of Fe2O3 doped yttria stabilized zirconia hollow fiber membranes for water treatment, Ceramics International 42(14) (2016) 15618-15622. [13] C. Moysan, R. Riedel, R. Harshe, T. Rouxel, F. Augereau, Mechanical characterization of a polysiloxane-derived SiOC glass, Journal of the European Ceramic Society 27(1) (2007) 397-403. [14] D. Su, Y. Li, F. Hou, X. Yan, Synthesis and Characterization of Ethylene-Bridged Copolycarbosilazane as Precursors for Silicon Carbonitride Ceramics, Journal of the American Ceramic Society 97(4) (2014) 1311-1316. [15] Y. Dong, B. Lin, J.-e. Zhou, X. Zhang, Y. Ling, X. Liu, G. Meng, S. Hampshire, Corrosion 9
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