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Synthesis of SBA-15 assembled with silicon nanoparticles with different morphologies for oxygen sensing
Microporous and Mesoporous Materials 296 (2020) 110001
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Synthesis of SBA-15 assembled with silicon nanoparticles with different morphologies for oxygen sensing Ting Gong, Yanjuan Li, Haonan Zhang, Jianxian Zhou, Gening Xie, Bingfu Lei *, Jianle Zhuang, Yingliang Liu, Haoran Zhang ** Guangdong Provincial Engineering Technology Research Center for Optical Agriculture, Guangdong Laboratory of Lingnan Mordern Agriculture, College of Materials and Energy, South China Agricultural University, Guangzhou 510642, P. R. China
A R T I C L E I N F O
A B S T R A C T
Keywords: Spherical mesoporous SBA-15 Long rod-like mesoporous SBA-15 Hexagonal prism-like mesoporous SBA-15 Silicon nanoparticles Oxygen sensing
In this paper, our effort is focused on preparation and oxygen sensing of fluorescent silicon nanoparticles (Si NPs) assembled in three kinds of mesoporous SBA-15 with different morphologies, including spherical mesoporous SBA-15 (SPSBA-15), long rod-like mesoporous SBA-15 (LRSBA-15) and hexagonal prism-like mesoporous SBA-15 (HPSBA-15). The relationship of structure and sensing properties in mesoporous materials is studied. Small angle powder X-ray diffraction (SAXRD), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET), Discrete-Fourier-Transform (DFT) analyses and X-ray photoelectron spectroscopy (XPS) are used to characterize their structural properties. The obtained mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 possess abundant Si–O–Si bands of the inorganic framework and high surface-volume ratios. Particularly, mesoporous HPSBA-15 materials exhibit the largest surface areas than other two mesoporous materials. Accordingly, the adding volume of Si NPs was 8 ml in mesoporous HPSBA-15. At the same time, the hybrid materials show the shortest response time of 2.2 s and recovery time of 11.2 s. This result can be attributed to the uniform and nearly parallel porous structure of the HPSBA-15 materials supporting with large surface areas and narrow pore size distributions. Therefore, the properties in oxygen sensing can be improved by using mesoporous SBA-15 mate rials with larger BET surface area.
1. Introduction Oxygen sensors play an important role in our daily life such as me dicinal, environmental and food packaging. Traditionally, the oxygen concentration is determined by using a Clark-type amperometric elec trode, which is based on the principle that a current is supervised during electroreduction on a polarized cathode [1]. However, the Clark elec trode sensors require the consumption of oxygen during sensing test. Therefore, efforts have been devoted to design new optical oxygen sensors with high sensitivity and long-term stability. The optical oxygen sensors are based on the principle of lumines cence quenching under the presence of oxygen, because oxygen is a powerful quenching agent in the electron excited state of dye molecules [2]. In past years, the tremendous efforts have been devoted to focus on the fluorescent molecular [3–5]. The ruthenium (II) complex used as luminescent molecules show a strong signal for oxygen [6], while their
expensive cost and complicated synthesis process limit the application in oxygen sensing. Semiconductor QDs are also applied in oxygen sensing, but they are toxic and harmful for environment [7]. Therefore, it is very important and impending to develop the fluorescent molecular with simple synthesis, nontoxic and environmentally friendly. Until 1990, luminescent silicon nanoparticles (Si NPs) came out [8]. It shows ul trahigh stability and small size less than 5 nm [9]. Because of superior characteristics including excellent photostability, low toxicity and high quantum efficiency, Si NPs are widely used in long-term imaging, light-emitting diodes and sensing [10–12]. In oxygen sensor systems, effective diffusion of oxygen depends on the large surface-to-volume ratios of solid matrix, which can greatly improve the performance of oxygen sensing [2]. Mesoporous silica materials have high thermal stability and large surface-to-volume ratios. Thus, they facilitate the efficient diffusion of oxygen molecules in their channels. Recent studies have shown that the performance of oxygen
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (B. Lei), [email protected] (H. Zhang). https://doi.org/10.1016/j.micromeso.2020.110001 Received 19 September 2019; Received in revised form 25 November 2019; Accepted 6 January 2020 Available online 8 January 2020 1387-1811/© 2020 Published by Elsevier Inc.
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sensing can be greatly improved by assembling luminescent molecules into the pores of mesoporous silica materials [13]. Mesoporous silica materials are mainly formed by hydrolysis and polycondensation of organosilane and can be prepared into different shapes according to different performance requirements [14–16]. In recent years, they are widely used in catalysis and sensing [17,18]. In our previous work, Si NPs-doped hybrid materials based on fluorescent Si NPs and mesoporous SBA-15 materials were reported [5]. Although the hybrid materials exhibit large surface areas, narrow pore sizes distribution and fluores cent stability, they are not sensitive enough to oxygen. Therefore, there is still more effort to develop mesoporous silica materials with large surface-to-volume ratios so as to assemble more Si NPs. In this work, we report three kinds of Si NPs-based hybrid materials and regulate their oxygen sensing performance. Firstly, we synthesize spherical SPSBA-15, long rod-like LRSBA-15 and hexagonal prism-like HPSBA-15 by a simple hydrothermal method. They all exhibit high thermal stability, large surface areas and narrow pore sizes. Then the Si NPs-based hybrid materials are prepared by assembling Si NPs into the channel of SPSA-15, LRSBA-15 and HPSBA-15 through hydrogen band interactions, respectively. In oxygen sensing, the Si NPs-based hybrid materials show an extremely short response time of 2–4 s and recovery time of 11–13 s. Compared with SP and LR hybrid materials, the HP hybrid materials reveal the highest sensitivity due to the largest BET surface area. These results reveal that the properties in oxygen sensing can be improved by using mesoporous silica materials with higher surface-volume ratios.
2.4. Synthesis of long rod-like mesoporous SBA-15 (LRSBA-15) In a typical synthesis [21], 2 g P123 was dissolved in 65 g HCl (2 M) at 55 � C. Then, 4.28 g TEOs was added to this mixture and stirred with a magnetic stirrer at 400 rpm for 3 min. The reaction solution was sub sequently kept under static conditions for 24 h. After that, the solution was transferred into a Teflon bottle and heated under 100 � C for 24 h. Solid precipitate were filtrated and washed repeatedly with deionized water. After drying under 60 � C for 2 d, the products were calcined at 550 � C for 6 h in air. 2.5. Synthesis of hexagonal prism-like mesoporous SBA-15 (HPSBA-15) HPSBA-15 was synthesized by using P123 as a template [22]. The reaction compositions were 4 g P123:30 g H2O:120 g HCl (2 M):8.5 g TEOS. Then the solution was transferred into a Teflon bottle and heated under 100 � C for 24 h. After cooling to room temperature, the white precipitate was obtained by combination of filtration and calcining at 550 � C for 6 h to remove surface active agent. 2.6. Loading of Si NPs into SPSBA-15, LRSBA-15 and HPSBA-15 Scheme 1 exhibits the preparation process of SP, LR and HP hybrid materials. 0.4 g mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 were dispersed in the mixture of Si NPs and deionized water respectively. The total volume of the mixture solution was set at 30 ml. For mesoporous SPSBA-15 and LRSBA-15, the mass percent were 2, 4, 6 and 8 ml. While the mass percent were 2, 4, 6, 8, 10, 12 and 14 ml in mesoporous HPSBA15. After stirring for 10 h, the yellow precipitate was filtered by Buchner funnel, and dried at 60 � C in an oven. Their samples were named as SP (SP2, SP4, SP6 and SP8), LR (LR2, LR4, LR6 and LR8) and HP (HP2, HP4, HP6, HP8, HP10, HP12 and HP14) hybrid materials, respectively.
2. Experimental 2.1. Materials and reagents Triblock copolymer poly (ethylene glycol)-block-poly (propylene glycol)-block-poly-(ethylene glycol) (Pluronic P123; EO20PO70EO20; m. w. ¼ 5800) was purchased from Aldrich. Tetraethyl orthosilicate (TEOS) was supplied from Tianjin Chemicals Co. Ltd. Sodium citrate dehydrate (99%, AR; C6H5Na3O7⋅2H2O), N-[3-(Trimethoxysilyl) propyl] ethyl enediamine (DAMO; 95%, AR; C8H22N2Si) and hexadecyl trimethyl ammonium bromide (CTAB) were purchased from Macklin. Hydro chloric acid (AR; HCl) was purchased from Guangzhou chemical reagent factory. Deionized water was used throughout this work.
2.7. Characterizations The fluorescent spectra were analyzed by a Hitachi F-7000 fluores cence spectrophotometer equipped with a monochromator (resolution: 0.2 nm) and a 150-W Xenon lamp as the excitation source. The UV–vis absorption spectrum was acquired using a Shimadzu UV-3600 spectro photometer (Tokyo, Japan). The particle morphologies were obtained by a scanning electron microscope (SEM, XL-30; Philips, North Billerica, MA) and a transmission electron microscope (TEM, TECNAI12, Holland). The element types and contents in microregions were ob tained by Energy Dispersive Spectrometer (EDS, Oxford). The crystal structures of the mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 were tested by small angle powder X-ray diffraction (SAXRD, Rigaku) with Cu Kα radiation (λ ¼ 1.5418 Å). The data were collected in a 2θ range from 0.5� to 4� with a scanning step of 0.02� and a scanning rate of 0.2� /min. The Infrared spectra were recorded on Fourier transform infrared spectrometer (FT-IR) equipped with an integrating sphere, using KBr as reference. Surface functional groups were analyzed by X-ray photo electron spectroscopy (XPS, Thermo Fisher Scientific) with an Al Ka Xray monochromator and pass energy of 30 eV. Surface areas and pore sizes were calculated by the Brunauer-Emmett-Teller (BET) method and Discrete-Fourier-Transform (DFT) method, respectively. In testing oxygen sensing properties, 0.2 g samples were first pressed into a groove with a diameter of 10 mm and a thickness of 1 mm. The oxygen and nitrogen were mixed at different concentrations by Best equipment gas mixing system and the fluorescent spectra were collected by Hitachi F-7000 fluorescence spectrophotometer.
2.2. Synthesis of fluorescent Si NPs The preparation of Si NPs was referenced to our previous study [19]. In a 500 ml triangle flask, 5.58 g trisodium citrate dehydrate was dis solved in 120 ml water and bubbled with nitrogen gas for about 10 min to remove dissolved oxygen. Then 30 ml DAMO was added into the above solution under vigorous stirring. The stirring was continued for about 25 min under nitrogen protection to form the Si NPs precursors. Then the resultant precursor solution was transferred into Teflon-lined autoclave and started hydrothermal reaction under 200 � C for 12 h. After cooling to room temperature, the excess products were removed by dialysis (1 kDa). Finally, the Si NPs solution was freeze-dried and configured into a concentration of 17 mg/ml for later use. 2.3. Synthesis of spherical mesoporous SBA-15 (SPSBA-15) Typically [20], 2 g P123 and 0.33 g CTAB were stirred in the mixed solution of 40 ml HCl (2 M), 10 ml H2O and 20 ml ethanol for 1 h. Then 6.6 ml TEOS was added and stirred under 40 � C for 2 h. After hydro thermal treatment under 80 � C for 24 h, the white products were ob tained by filtration and drying. The calcination was carried out at 550 � C for 6 h.
3. Results and discussion 3.1. Preparation of the SP, LR and HP hybrid materials SP, LR and HP hybrid materials were obtained by a facile physical 2
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Scheme 1. Schematic illustration of the preparation process of SP, LR and HP hybrid materials.
stirring. The preparation process was shown in Scheme 1. Due to hydrogen band interactions, fluorescent Si NPs were assembled into the pores of mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 [23].
the atomic percentages of the elements present of three kinds of SBA-15 with different morphologies, SP4, LR4 and HP8 hybrid materials by EDS spectra. As show in Table S1, the percentage of silicon atomic have significant difference. The increase of silicon atomic percentage in hybrid materials have attributed to the addition of Si NPs. This com parison with the atomic percentages in SBA-15 and hybrid materials further confirm that Si NPs are assembled in the channel of SBA-15.
3.2. Synthesis and characterization of Si NPs As demonstrated in Fig. 1a, fluorescent Si NPs can be facilely syn thesized with DAMO as the silicon source and sodium citrate dehydrate as the reductant. After hydrothermal reaction, the solution has turned from colorless to yellow under daylight and shows an intensive blue emission under UV light of 365 nm (inset of Fig. 1b). The typical ab sorption features of the as-purified Si NPs are observed at 300–400 nm. The fluorescence spectra of the Si NPs show maximum emission wave length around 445 nm and excitation wavelength around 369 nm (Fig. 1b). Fig. 1c shows a representative TEM image of Si NPs displaying the well monodisperse. As shown in the inset of Fig. 1c, a high-resolution TEM (HRTEM) image of an individual particle display a lattice plane of 0.21 nm, which suggests that Si NPs possess crystalline Si–Si domains in their structures [24]. The size distribution shows that the mean diameter of the as-purified Si NPs is 5.36 nm through TEM images of 100 indi vidual particles.
3.4. Surface structure properties The SAXRD patterns provide an efficient evidence for an ordered mesostructure (Fig. 3a). SPSBA-15, LRSBA-15 and HPSBA-15 all show three obvious diffraction peaks approximately centered at 0.9, 1.5 and 1.8, respectively. The three diffraction peaks are attributed to (100), (110) and (210), which confirms an ordered mesoporous structure with p6mm hexagonal symmetry of SPSBA-15, LRSBA-15 and HPSBA-15 [25]. In addition, the FT-IR spectra are used to characterize the surface functional groups and chemical bond interactions (Fig. 3 (b and c)). The fluorescent Si NPs show the characteristic peak of Si–O–Si stretching vibration at 1000-1200 cm 1, affirming the existence of silicon atoms [26,27]. Meanwhile, it is demonstrated that the Si NPs have several other functional groups such as the N–H (bending vibration around 1600 cm 1, stretching vibration at 3300 cm 1), C–H (stretching vibra tion between 2850 and 2950 cm 1), and O–H (stretching vibrations at 3400 cm 1) on the surface [28]. The FT-IR spectra of the mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 display abundant Si–O–Si bands of the inorganic framework and plentiful O–H on the surface (Fig. 3b). It is observed that there is no peak at 2940 cm 1 assigned to C–H stretching vibration, indicating the template agent has been removed [29]. When Si NPs are assembled into the pore of SPSBA-15, LRSBA-15 and HPSBA-15, the peak at 2940 cm 1 in the FT-IR spectra of SP4, LR4 and HP8 hybrid materials is observed (Fig. 3c). The result further verifies the fact that Si NPs are successfully assembled into the channel of SPSBA-15,
3.3. Microscopic morphologies The microscopic morphologies of the SPSBA-15, LRSBA-15, HPSBA15, SP4, LR4 and HP8 hybrid materials are studied with the SEM and TEM as shown in Fig. 2 and Fig. S1. As seen from Fig. 2, the spherical mesoporous SPSBA-15, long rod-like mesoporous LRSBA-15 and hex agonal prism-like mesoporous HPSBA-15 are successfully obtained. After assembling fluorescent Si NPs, the SP4, LR4 and HP8 hybrid ma terials present the same morphologies as SPSBA-15, LRSBA-15 and HPSBA-15, respectively (Fig. S1 (a, b and c)). Fig. S1 (d, e and f) demonstrate the SP4, LR4 and HP8 hybrid materials process a uniform worm-like pores with p6mm hexagonal symmetry. We have analyzed
Fig. 1. (a) Schematic representation of the preparation of fluorescent Si NPs using DAMO and sodium citrate dehydrate. (b) Absorption (black), fluorescence excitation (red), and emission (blue) spectra of the Si NPs in aqueous solution. Inset shows the corresponding photographs under daylight (left) and UV of 365 nm (right), respectively. (c) Typical TEM image of the as-prepared Si NPs. Insets show the HRTEM image and size distribution histogram. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 3
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Fig. 2. (a, b and c) The SEM images of SPSBA-15 (a), LRSBA-15 (b) and HPSBA-15 (c), respectively.
Fig. 3. (a) The SAXRD patterns of SPSBA-15, LRSBA-15 and HPSBA-15. (b and c) The FT-IR spectra of Si NPs, SBA-15 with different morphologies (SPSBA-15, LRSBA-15 and HPSBA-15) (b) and Si NPs/SBA-15 hybrid materials (SP4, LR4 and HP8) (c), respectively.
LRSBA-15 and HPSBA-15. As seen from Fig. 3 (b and c), hydrogen bonds linking is the reason, resulting in Si NPs assembling into the pore of SPSBA-15, LRSBA-15 and HPSBA-15 [30]. XPS measurements were performed to determine the chemical bond of the fabricated the hybrid samples. C1s, N1s, O1s, Si2p and Si2s signals in the XPS full survey spectra confirm the existence of C, O, N and Si elements (shown in Fig. S2). The high resolution XPS peaks of C1s, N1s, O1s and Si2p of SP4, LR4 and HP8 hybrid materials are shown in Fig. S3. The typical hybrid materials have the same chemical bonds. The C1s XPS spectra exhibit – C), minor three peaks, i.e., the dominant graphitic sp2 carbons (C–C/C– – O) and sp3 carbons (C–O/C–N). The O1s and N1s carbonyl carbons (C– – C, O–C, N–H and N-(C)3 XPS spectra confirm the existence of O–Si, O– chemical bonds. The high-resolution Si2p spectra show the presence of Si–O–H and Si–O–Si chemical bonds.
isotherms exhibit typical type-IV curves with H1-shaped hysteresis loops, indicating their mesostructured silica (Fig. 4b) [31]. Their cor responding textural data (BET surface area, pore volume and pore size) are list in Table 1. By analyzing these data, the mesoporous HPSBA-15 materials possess the highest BET surface area of 841.11 m2 g-1 and a wide pore volume of 0.96 cm3 g-1. The mesoporous SPSBA-15 materials exhibit a larger BET surface area of 798.46 m2 g-1 and the widest pore volume of 1.05 cm3 g-1. As the adding volume of Si NPs increases, the pore-size distribution curves and nitrogen adsorption-desorption isotherms of SP, LR and HP hybrid materials can be seen from Fig. 5. These hybrid materials retain the type-IV curves with H1-shaped hysteresis loops. And the pore-size distributions are maintained in a range of mesoporous pore sizes. Table 1 Textural data of SPSBA-15, LRSBA-15 and HPSBA-15, respectively.
3.5. Pore structure properties The pore-size distribution curves and nitrogen adsorption-desorption isotherms are used to evaluate the BET surface area, pore volume and pore size. As seen from Fig. 4 (a), the mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 show a narrowed pore size with 2–10 nm. Their
Samples
SBET (m2g 1)
V (cm3g
SPSBA-15 LRSBA-15 HPSBA-15
798.46 665.11 841.11
1.05 0.93 0.96
1
)
D (nm) 2.33 3.27 2.76
Fig. 4. (a and b) The pore-size distribution curves (a) and nitrogen absorption-desorption isotherms (b) of SPSBA-15, LRSBA-15 and HPSBA-15, respectively. 4
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Fig. 5. The pore-size distribution curves and nitrogen adsorption-desorption isotherms of (a, b) SP, (c, d) LR and (d, e) HP hybrid materials, respectively.
Table S2 summarizes the BET surface areas, pore volumes and pore sizes of hybrid materials with different adding volumes of Si NPs. As Si NPs are assembled into the pores of SPSBA-15, LRSBA-15 and HPSBA-15, the BET surface areas, pore sizes and pore volumes of hybrid materials all decrease.
adding volumes of Si NPs are measured in pure nitrogen atmosphere under the excitation of 360 nm (Fig. 6). As Fig. 6 shows, the SP4, LR4 and HP8 hybrid materials show the characteristic emission peak centered at ~440 nm. As the adding volumes of Si NPs increase, the fluorescent intensity of hybrid materials increase at first and then descend. The most optimal volumes of Si NPs are 4, 4 and 8 ml in mesoporous SPSBA-15, LRSBA-15 and HPSBA-15, respectively. Meso porous SPSBA-15 and LRSBA-15 have the same optimal doping volume. However, according to pore structural data, the BET surface area and
3.6. Fluorescent properties The fluorescent spectra of SP, LR, HP hybrid materials with different
Fig. 6. (a, b and c) The fluorescent spectra of SP (a), LR (b), HP (c) hybrid materials with different adding volumes of Si NPs under the excitation of 360 nm in pure nitrogen atmosphere. 5
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pore volume of mesoporous SRSBA-15 materials are larger than LRSBA15. Therefore, it can be seen that the fluorescent intensity of SP4 is higher than that of LR4. The HP8 hybrid materials have the highest fluorescent intensity corresponding to the optimal adding volume of Si NPs. It is observed that mesoporous HPSBA-15 materials are well suited as a solid matrix with largest BET surface area that can accommodate more Si NPs.
Fig. 8 (b) presents the typical intensity-based Stern-Volmer plots and the fitted curve using Demas two-site model equation. The Stern-Volmer equation reveals the fluorescent ratio (I0/I) under different oxygen volumes in homogeneous media. It can be described as [34]: I0 = I ¼ 1 þ KSV PO2
(1)
where I is the fluorescent intensity of the hybrid materials, the subscript 0 denotes the absence of oxygen, I0/I denotes the fluorescence intensity ratio, KSV is the Stern-Volmer constant, KSV is the quenching constant, and PO2 denotes the oxygen volume fraction at normal atmospheric pressure. An ideal Stern-Volmer curve is supposed to be a linear one. As shown in Fig. 8 (b), the Stern-Volmer oxygen-quenching plots of SP4, LR4 and HP8 hybrid materials appear more nearly linear at low O2 concentra tions. However, it is obvious that the curves of the experimental data gradually show a tendency of downward bending. It is attributed to nonuniform distribution of Si NPs and different degrees of difficulty in quenching oxygen accordingly. Therefore, the Demas two-site model equation is proposed to fit the experimental data [35].
3.7. Oxygen sensing properties The selectivity of oxygen in SP4, LR4 and HP8 hybrid materials are evaluated by their emission response at oxygen or carbon dioxide at mosphere. As seen from Fig. 7 (d, e and f), the fluorescent intensity of SP4, LR4 and HP8 hybrid materials almost unchanged at different car bon dioxide volume fractions. But as the oxygen volume tuned from 0 to 100%, the fluorescent intensity of SP4, LR4 and HP8 hybrid materials rapidly decrease (Fig. 7 (a, b and c)). This result indicates the hybrid materials have high selectivity to oxygen. To compare the oxygen sensing properties of SP4, LR4 and HP8 hybrid materials, the typical dynamic response are measured on expo sure the different ratios of pure N2 and O2 atmospheres (Fig. 8a). By analyzing the time-dependent spectra, the 95% response (t↓) and 95% recovery (t↑) times can be calculated. The 95% response (t↓) and 95% recovery (t↑) times are defined as the time needed of fluorescence in tensity attained 95% of its initial intensity when the gas is converted from pure nitrogen to pure oxygen and from pure oxygen to pure ni trogen, respectively. These values are summarized in Table 2. From Fig. 8 (a), it is observed that SP4, LR4 and HP8 hybrid materials all exhibit a fully reversible response and their response to oxygen is stable and very rapid. As summarized in Table 2, SP4 hybrid materials show a shorter response time of 2.6 s and recovery time of 11.6 s than LR4 hybrid materials. The most possible reason for the higher oxygen sensing performance of SP4 hybrid materials can be attributed to the larger BET surface area and the higher fluorescent intensity compared with LR4 hybrid materials. In addition, HP8 hybrid materials exhibit a shortest response time of 2.2 s and recovery time of 11.2 s, which is shorter than response and recovery time mentioned in previous studies [5,32,33]. This confirms that Si NPs-doped hybrid materials based on Si NPs and the mesoporous HPSBA-15 with large surface-to-volume ratios have the higher potential in oxygen sensing.
I0 1 ¼ I 1þKf 01 P þ 1þKf 02 P SV1 O2 SV2 O2
(2)
where f01 and f02 values are the fraction of each of the two sites contributing to the unquenched intensity, KSV1 and KSV2 values are the quenching constants for the two sites, and PO2 is the partial pressure of oxygen at 1 atm pressure. The solid lines are fitted by Demas two-site model equation to calculate the KSVi and f01 values, which are summarized in Table 2. The KSVi and f01 values reveal the oxygen sensing performance. The higher values of KSV and the lower values of f01 are more beneficial to a higher oxygen quenching response. The highest KSV values of HP8 hybrid ma terials compared to those of SP4 and LR4 hybrid materials indicate that the fluorescent Si NPs in HP8 hybrid materials are more easily quenched by oxygen. In addition, the sensitivity to oxygen can also be expressed as I0/I. When the oxygen volumes reach to 100%, I0/I of HP8 hybrid ma terials exhibit a highest value of 9.74 than other hybrid materials. This result can be attributed to the uniform and nearly parallel porous structure of the mesoporous HPSBA-15 materials support with large surface areas and narrow pore size distributions.
Fig. 7. (a, b and c) Emission spectra of SP4 (a), LR4 (b) and HP8 (c) hybrid materials excited by 360 nm under different oxygen volume fractions, respectively. (d, e and f) Emission spectra of SP4 (d), LR4 (e) and HP8 (f) hybrid materials excited by 360 nm under different carbon dioxide volume fractions, respectively. 6
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Fig. 8. (a) Response and recovery time and relative intensity of SP4, LR4 and HP8 hybrid materials when switching between 100% nitrogen and 100% oxygen. (b) A typical Stern-Volmer point diagram based luminescence intensity of SP4, LR4 and HP8 hybrid materials under different oxygen volume fractions. The solid lines are fitted by Demas two-site model equation. Table 2 Values of response (I0/I100), Stern-Volmer model and Demas model oxygen-quenching fitting parameters of SP4, LR4 and HP8 hybrid materials, respectively. Samples
I0/I100
t↓ (s)
t↑ (s)
1
SP4 LR4 HP8 a b
6.49 4.10 9.74
3.4 2.6 2.2
12.2 11.6 11.2
Demas Two-site modela
Stern-Volmer model 2
KSV (O2% )
r
0.0632 � 0.0028 0.0356 � 0.0015 0.0939 � 0.0020
0.9072 0.9243 0.9817
KSV1(O2%
1
)
0.1169 � 0.0076 0.0625 � 0.0058 0.1217 � 0.0070
KSV2(O2% 1) 0.0017 � 0.0012 0.0023 � 0.0016 0.0021 � 0.0028
f01b
r2
0.9328 � 0.0131 0.9091 � 0.0278 0.9775 � 0.0105
0.9983 0.9972 0.9987
Terms are from Eq. (2). f01þf02 ¼ 1.
4. Conclusions
Appendix A. Supplementary data
In summary, we have demonstrated that mesoporous HPSBA-15 materials are the most suitable solid matrix for an optical oxygen sensor compared to mesoporous SPSBA-15 and LRSBA-15 materials. Mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 materials doped with Si NPs (SP, LR and HP hybrid materials) are a potential material in the field of oxygen sensing due to their nontoxic, environment friendly and excellent optical properties. Especially, due to the highest surface to volume ratio of the mesoporous HPSBA-15 materials, more Si NPs can be assembled into the channel. The optimal adding volume of Si NPs is 8 ml. HP8 hybrid materials exhibit the shortest response time of 2.2 s and recovery time of 11.2 s compared with SP4 and LR4 hybrid materials. In addition, the lower values of f01 and the higher values of KSV and I0/I100 further prove that HP8 hybrid materials possess the superior perfor mance of oxygen sensing. This feature can be attributed to the uniform and nearly parallel porous structure of the mesoporous HPSBA-15 ma terials support with large surface areas and narrow pore size distributions.
Supplementary data to this article can be found online at https://doi. org/10.1016/j.micromeso.2020.110001.
Declaration of competing interest
[1] L.C. Clark Jr., Trans. Am. Soc. Artif. Intern. Organs 2 (1956) 41–48. [2] B. Lei, B. Li, H. Zhang, S. Lu, Z. Zheng, W. Li, Y. Wang, Adv. Funct. Mater. 16 (2006) 1883–1891. [3] F. Lin, F. Li, Z. Lai, Z. Cai, Y. Wang, O.S. Wolfbeis, X. Chen, ACS Appl. Mater. Interfaces 10 (2018) 23335–23343. [4] Y. He, J. He, L. Wang, Z. Yu, H. Zhang, Y. Liu, B. Lei, Sens. Actuators B Chem. 251 (2017) 918–926. [5] T. Gong, Y. Li, B. Lei, J. Zhuang, Y. Liu, H. Zhang, Mater. Res. Bull. 111 (2019) 1–6. [6] Z. Jiang, X. Yu, S. Zhai, Y. Hao, Ratiometric dissolved oxygen sensors based on ruthenium complex doped with silver nanoparticles, Sensors 17 (2017) 548. [7] X. Tong, Y. Zhou, L. Jin, K. Basu, R. Adhikari, G.S. Selopala, X. Tong, H. Zhao, S. Sun, A. Vomiero, Z.M. Wang, F. Rosei, Nano Energy 31 (2017) 441–449. [8] L.T. Canham, Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers, Appl. Phys. Lett. 57 (1990) 1046–1048. [9] Y. Han, Y. Chen, J. Feng, J. Liu, S. Ma, X. Chen, Anal. Chem. 89 (2017) 3001–3008. [10] Y.-K. Dou, Y. Chen, X.-W. He, W.-Y. Li, Y.-H. Li, Y.-K. Zhang, Anal. Chem. 89 (2017) 11286–11292. [11] C.M. Gonzalez, M. Iqbal, M. Dasog, D.G. Piercey, R. Lockwood, T.M. Klapotke, J.G. C. Veinot, Nanoscale 6 (2014) 2608–2612. [12] W. Gu, X. Liu, X. Pi, X. Dai, S. Zhao, L. Yao, D. Li, Y. Jin, M. Xu, D. Yang, IEEE Photonics J. 9 (2017) 1–10. [13] L. Wang, H. Zhang, X. Zhou, Y. Liu, B. Lei, J. Colloid Interface Sci. 478 (2016) 256–262. [14] H. Yang, N. Coombs, G.A. Ozin, Nature 386 (1997) 692–695.
Author Contribution Statement Ting Gong: Methodology, Investigation, Writing - Original Draft. Yanjuan Li: Data Curation, Writing - Review & Editing. Haonan Zhang: Software. Jianxian Zhou: Validation. Gening Xie: Formal analysis. Bingfu Lei: Conceptualization, Methodology, Writing - Review & Editing. Jianle Zhuang: Supervision. Yingliang Liu: Resources. Haoran Zhang: Resources, Writing - Review & Editing. References
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. Acknowledgments The present work was supported by the National Natural Science Foundations of China (Grant No. 21671070), the Project supported by GDUPS (2018) for Prof. Bingfu LEI, the Project for Construction of Highlevel University in Guangdong Province of China, the Guangzhou Sci ence & Technology Project, China (No. 201707010033) and the Special Funds for the Cultivation of Guangdong College Students’ Scientific and Technological Innovation (No. 201910564035).
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T. Gong et al.
Microporous and Mesoporous Materials 296 (2020) 110001 [25] G.L. Li, J. Lan, J.Y. Liu, G.B. Jiang, J. Colloid Interface Sci. 405 (2013) 164–170. [26] X. Chen, X. Zhang, L.-Y. Xia, H.-Y. Wang, Z. Chen, F.-G. Wu, Nano Lett. 2 (2018) 1159–1167. [27] W. Jeong, S. Jo, J. Park, B. Kwon, Y. Choi, A. Chae, S.Y. Park, I. In, Int. J. Mater. Sci. 53 (2018) 2443–2452. [28] J. Sun, T. Hu, C. Chen, D. Zhao, F. Yang, X. Yang, Anal. Chem. 88 (2016) 9789–9795. [29] B. Lei, L. Wang, H. Zhang, Y. Liu, H. Dong, M. Zheng, X. Zhou, Sens. Actuators B Chem. 230 (2016) 101–108. [30] Y. He, J. He, H. Zhang, Y. Liu, B. Lei, Opt. Mater. Express 7 (2017) 945. [31] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024–6036. [32] X. Wang, Y. Yang, B. He, Sens. Actuators B Chem. 241 (2017) 957–966. [33] J. Luo, T. Dziubla, R. Eitel, Sens. Actuators B Chem. 240 (2017) 392–397. [34] Z.C. Bao, Z.G. Feng, W. Wong, Sens. Actuators B Chem. 234 (2016) 167–175. [35] S. Banerjee, O.V. Arzhakova, A.A. Dolgova, D.B. Papkovsky, Sens. Actuators B Chem. 230 (2016) 434–441.
[15] L. Du, H. Song, S. Liao, Appl. Surf. Sci. 255 (2009) 9365–9370. [16] J. Chen, Y. Sheng, Y. Song, M. Chang, X. Zhang, L. Cui, D. Meng, H. Zhu, Z. Shi, H. Zou, ACS Sustain. Chem. Eng. 6 (2018) 3533–3545. [17] M. Cheng, H. Zhao, J. Yang, J. Zhao, L. Yan, H. Song, L. Chou, Microporous Mesoporous Mater. 266 (2018) 117–125. [18] A.L. Lee, C.T. Gee, B.P. Weegman, S.A. Einstein, A.R. Juelfs, H.L. Ring, K.R. Hurley, S.M. Egger, G. Swindlehurst, M. Garwood, W.C.K. Pomerantz, C.L. Haynes, ACS Nano 11 (2017) 5623–5632. [19] T. Gong, Y. Li, B. Lei, X. Zhang, Y. Liu, H. Zhang, J. Mater. Chem. C 7 (2019) 5962–5969. [20] M. Vinoba, M. Bhagiyalakshmi, S.K. Jeong, Y. II Yoona, S.C. Nama, Colloids Surfaces B Biointerfaces 90 (2012) 91–96. [21] D. Gao, A. Duan, X. Zhang, Z. Zhao, H. E, J. Li, H. Wang, Appl. Catal. B Environ. 165 (2015) 269–284. [22] A. Sayari, B.-H. Han, Y. Yang, J. Am. Chem. Soc. 126 (2004) 14348–14349. [23] C. Cheng, D.L. Lu, B. Shen, Y.D. Liu, J.Y. Lei, L.Z. Wang, J.L. Zhang, M. Matsuoka, Microporous Mesoporous Mater. 226 (2016) 79–87. [24] Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S.T. Lee, Y. He, J. Am. Chem. Soc. 135 (2013) 8350–8356.
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Synthesis of SBA-15 assembled with silicon nanoparticles with different morphologies for oxygen sensing Ting Gong, Yanjuan Li, Haonan Zhang, Jianxian Zhou, Gening Xie, Bingfu Lei *, Jianle Zhuang, Yingliang Liu, Haoran Zhang ** Guangdong Provincial Engineering Technology Research Center for Optical Agriculture, Guangdong Laboratory of Lingnan Mordern Agriculture, College of Materials and Energy, South China Agricultural University, Guangzhou 510642, P. R. China
A R T I C L E I N F O
A B S T R A C T
Keywords: Spherical mesoporous SBA-15 Long rod-like mesoporous SBA-15 Hexagonal prism-like mesoporous SBA-15 Silicon nanoparticles Oxygen sensing
In this paper, our effort is focused on preparation and oxygen sensing of fluorescent silicon nanoparticles (Si NPs) assembled in three kinds of mesoporous SBA-15 with different morphologies, including spherical mesoporous SBA-15 (SPSBA-15), long rod-like mesoporous SBA-15 (LRSBA-15) and hexagonal prism-like mesoporous SBA-15 (HPSBA-15). The relationship of structure and sensing properties in mesoporous materials is studied. Small angle powder X-ray diffraction (SAXRD), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET), Discrete-Fourier-Transform (DFT) analyses and X-ray photoelectron spectroscopy (XPS) are used to characterize their structural properties. The obtained mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 possess abundant Si–O–Si bands of the inorganic framework and high surface-volume ratios. Particularly, mesoporous HPSBA-15 materials exhibit the largest surface areas than other two mesoporous materials. Accordingly, the adding volume of Si NPs was 8 ml in mesoporous HPSBA-15. At the same time, the hybrid materials show the shortest response time of 2.2 s and recovery time of 11.2 s. This result can be attributed to the uniform and nearly parallel porous structure of the HPSBA-15 materials supporting with large surface areas and narrow pore size distributions. Therefore, the properties in oxygen sensing can be improved by using mesoporous SBA-15 mate rials with larger BET surface area.
1. Introduction Oxygen sensors play an important role in our daily life such as me dicinal, environmental and food packaging. Traditionally, the oxygen concentration is determined by using a Clark-type amperometric elec trode, which is based on the principle that a current is supervised during electroreduction on a polarized cathode [1]. However, the Clark elec trode sensors require the consumption of oxygen during sensing test. Therefore, efforts have been devoted to design new optical oxygen sensors with high sensitivity and long-term stability. The optical oxygen sensors are based on the principle of lumines cence quenching under the presence of oxygen, because oxygen is a powerful quenching agent in the electron excited state of dye molecules [2]. In past years, the tremendous efforts have been devoted to focus on the fluorescent molecular [3–5]. The ruthenium (II) complex used as luminescent molecules show a strong signal for oxygen [6], while their
expensive cost and complicated synthesis process limit the application in oxygen sensing. Semiconductor QDs are also applied in oxygen sensing, but they are toxic and harmful for environment [7]. Therefore, it is very important and impending to develop the fluorescent molecular with simple synthesis, nontoxic and environmentally friendly. Until 1990, luminescent silicon nanoparticles (Si NPs) came out [8]. It shows ul trahigh stability and small size less than 5 nm [9]. Because of superior characteristics including excellent photostability, low toxicity and high quantum efficiency, Si NPs are widely used in long-term imaging, light-emitting diodes and sensing [10–12]. In oxygen sensor systems, effective diffusion of oxygen depends on the large surface-to-volume ratios of solid matrix, which can greatly improve the performance of oxygen sensing [2]. Mesoporous silica materials have high thermal stability and large surface-to-volume ratios. Thus, they facilitate the efficient diffusion of oxygen molecules in their channels. Recent studies have shown that the performance of oxygen
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (B. Lei), [email protected] (H. Zhang). https://doi.org/10.1016/j.micromeso.2020.110001 Received 19 September 2019; Received in revised form 25 November 2019; Accepted 6 January 2020 Available online 8 January 2020 1387-1811/© 2020 Published by Elsevier Inc.
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sensing can be greatly improved by assembling luminescent molecules into the pores of mesoporous silica materials [13]. Mesoporous silica materials are mainly formed by hydrolysis and polycondensation of organosilane and can be prepared into different shapes according to different performance requirements [14–16]. In recent years, they are widely used in catalysis and sensing [17,18]. In our previous work, Si NPs-doped hybrid materials based on fluorescent Si NPs and mesoporous SBA-15 materials were reported [5]. Although the hybrid materials exhibit large surface areas, narrow pore sizes distribution and fluores cent stability, they are not sensitive enough to oxygen. Therefore, there is still more effort to develop mesoporous silica materials with large surface-to-volume ratios so as to assemble more Si NPs. In this work, we report three kinds of Si NPs-based hybrid materials and regulate their oxygen sensing performance. Firstly, we synthesize spherical SPSBA-15, long rod-like LRSBA-15 and hexagonal prism-like HPSBA-15 by a simple hydrothermal method. They all exhibit high thermal stability, large surface areas and narrow pore sizes. Then the Si NPs-based hybrid materials are prepared by assembling Si NPs into the channel of SPSA-15, LRSBA-15 and HPSBA-15 through hydrogen band interactions, respectively. In oxygen sensing, the Si NPs-based hybrid materials show an extremely short response time of 2–4 s and recovery time of 11–13 s. Compared with SP and LR hybrid materials, the HP hybrid materials reveal the highest sensitivity due to the largest BET surface area. These results reveal that the properties in oxygen sensing can be improved by using mesoporous silica materials with higher surface-volume ratios.
2.4. Synthesis of long rod-like mesoporous SBA-15 (LRSBA-15) In a typical synthesis [21], 2 g P123 was dissolved in 65 g HCl (2 M) at 55 � C. Then, 4.28 g TEOs was added to this mixture and stirred with a magnetic stirrer at 400 rpm for 3 min. The reaction solution was sub sequently kept under static conditions for 24 h. After that, the solution was transferred into a Teflon bottle and heated under 100 � C for 24 h. Solid precipitate were filtrated and washed repeatedly with deionized water. After drying under 60 � C for 2 d, the products were calcined at 550 � C for 6 h in air. 2.5. Synthesis of hexagonal prism-like mesoporous SBA-15 (HPSBA-15) HPSBA-15 was synthesized by using P123 as a template [22]. The reaction compositions were 4 g P123:30 g H2O:120 g HCl (2 M):8.5 g TEOS. Then the solution was transferred into a Teflon bottle and heated under 100 � C for 24 h. After cooling to room temperature, the white precipitate was obtained by combination of filtration and calcining at 550 � C for 6 h to remove surface active agent. 2.6. Loading of Si NPs into SPSBA-15, LRSBA-15 and HPSBA-15 Scheme 1 exhibits the preparation process of SP, LR and HP hybrid materials. 0.4 g mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 were dispersed in the mixture of Si NPs and deionized water respectively. The total volume of the mixture solution was set at 30 ml. For mesoporous SPSBA-15 and LRSBA-15, the mass percent were 2, 4, 6 and 8 ml. While the mass percent were 2, 4, 6, 8, 10, 12 and 14 ml in mesoporous HPSBA15. After stirring for 10 h, the yellow precipitate was filtered by Buchner funnel, and dried at 60 � C in an oven. Their samples were named as SP (SP2, SP4, SP6 and SP8), LR (LR2, LR4, LR6 and LR8) and HP (HP2, HP4, HP6, HP8, HP10, HP12 and HP14) hybrid materials, respectively.
2. Experimental 2.1. Materials and reagents Triblock copolymer poly (ethylene glycol)-block-poly (propylene glycol)-block-poly-(ethylene glycol) (Pluronic P123; EO20PO70EO20; m. w. ¼ 5800) was purchased from Aldrich. Tetraethyl orthosilicate (TEOS) was supplied from Tianjin Chemicals Co. Ltd. Sodium citrate dehydrate (99%, AR; C6H5Na3O7⋅2H2O), N-[3-(Trimethoxysilyl) propyl] ethyl enediamine (DAMO; 95%, AR; C8H22N2Si) and hexadecyl trimethyl ammonium bromide (CTAB) were purchased from Macklin. Hydro chloric acid (AR; HCl) was purchased from Guangzhou chemical reagent factory. Deionized water was used throughout this work.
2.7. Characterizations The fluorescent spectra were analyzed by a Hitachi F-7000 fluores cence spectrophotometer equipped with a monochromator (resolution: 0.2 nm) and a 150-W Xenon lamp as the excitation source. The UV–vis absorption spectrum was acquired using a Shimadzu UV-3600 spectro photometer (Tokyo, Japan). The particle morphologies were obtained by a scanning electron microscope (SEM, XL-30; Philips, North Billerica, MA) and a transmission electron microscope (TEM, TECNAI12, Holland). The element types and contents in microregions were ob tained by Energy Dispersive Spectrometer (EDS, Oxford). The crystal structures of the mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 were tested by small angle powder X-ray diffraction (SAXRD, Rigaku) with Cu Kα radiation (λ ¼ 1.5418 Å). The data were collected in a 2θ range from 0.5� to 4� with a scanning step of 0.02� and a scanning rate of 0.2� /min. The Infrared spectra were recorded on Fourier transform infrared spectrometer (FT-IR) equipped with an integrating sphere, using KBr as reference. Surface functional groups were analyzed by X-ray photo electron spectroscopy (XPS, Thermo Fisher Scientific) with an Al Ka Xray monochromator and pass energy of 30 eV. Surface areas and pore sizes were calculated by the Brunauer-Emmett-Teller (BET) method and Discrete-Fourier-Transform (DFT) method, respectively. In testing oxygen sensing properties, 0.2 g samples were first pressed into a groove with a diameter of 10 mm and a thickness of 1 mm. The oxygen and nitrogen were mixed at different concentrations by Best equipment gas mixing system and the fluorescent spectra were collected by Hitachi F-7000 fluorescence spectrophotometer.
2.2. Synthesis of fluorescent Si NPs The preparation of Si NPs was referenced to our previous study [19]. In a 500 ml triangle flask, 5.58 g trisodium citrate dehydrate was dis solved in 120 ml water and bubbled with nitrogen gas for about 10 min to remove dissolved oxygen. Then 30 ml DAMO was added into the above solution under vigorous stirring. The stirring was continued for about 25 min under nitrogen protection to form the Si NPs precursors. Then the resultant precursor solution was transferred into Teflon-lined autoclave and started hydrothermal reaction under 200 � C for 12 h. After cooling to room temperature, the excess products were removed by dialysis (1 kDa). Finally, the Si NPs solution was freeze-dried and configured into a concentration of 17 mg/ml for later use. 2.3. Synthesis of spherical mesoporous SBA-15 (SPSBA-15) Typically [20], 2 g P123 and 0.33 g CTAB were stirred in the mixed solution of 40 ml HCl (2 M), 10 ml H2O and 20 ml ethanol for 1 h. Then 6.6 ml TEOS was added and stirred under 40 � C for 2 h. After hydro thermal treatment under 80 � C for 24 h, the white products were ob tained by filtration and drying. The calcination was carried out at 550 � C for 6 h.
3. Results and discussion 3.1. Preparation of the SP, LR and HP hybrid materials SP, LR and HP hybrid materials were obtained by a facile physical 2
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Scheme 1. Schematic illustration of the preparation process of SP, LR and HP hybrid materials.
stirring. The preparation process was shown in Scheme 1. Due to hydrogen band interactions, fluorescent Si NPs were assembled into the pores of mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 [23].
the atomic percentages of the elements present of three kinds of SBA-15 with different morphologies, SP4, LR4 and HP8 hybrid materials by EDS spectra. As show in Table S1, the percentage of silicon atomic have significant difference. The increase of silicon atomic percentage in hybrid materials have attributed to the addition of Si NPs. This com parison with the atomic percentages in SBA-15 and hybrid materials further confirm that Si NPs are assembled in the channel of SBA-15.
3.2. Synthesis and characterization of Si NPs As demonstrated in Fig. 1a, fluorescent Si NPs can be facilely syn thesized with DAMO as the silicon source and sodium citrate dehydrate as the reductant. After hydrothermal reaction, the solution has turned from colorless to yellow under daylight and shows an intensive blue emission under UV light of 365 nm (inset of Fig. 1b). The typical ab sorption features of the as-purified Si NPs are observed at 300–400 nm. The fluorescence spectra of the Si NPs show maximum emission wave length around 445 nm and excitation wavelength around 369 nm (Fig. 1b). Fig. 1c shows a representative TEM image of Si NPs displaying the well monodisperse. As shown in the inset of Fig. 1c, a high-resolution TEM (HRTEM) image of an individual particle display a lattice plane of 0.21 nm, which suggests that Si NPs possess crystalline Si–Si domains in their structures [24]. The size distribution shows that the mean diameter of the as-purified Si NPs is 5.36 nm through TEM images of 100 indi vidual particles.
3.4. Surface structure properties The SAXRD patterns provide an efficient evidence for an ordered mesostructure (Fig. 3a). SPSBA-15, LRSBA-15 and HPSBA-15 all show three obvious diffraction peaks approximately centered at 0.9, 1.5 and 1.8, respectively. The three diffraction peaks are attributed to (100), (110) and (210), which confirms an ordered mesoporous structure with p6mm hexagonal symmetry of SPSBA-15, LRSBA-15 and HPSBA-15 [25]. In addition, the FT-IR spectra are used to characterize the surface functional groups and chemical bond interactions (Fig. 3 (b and c)). The fluorescent Si NPs show the characteristic peak of Si–O–Si stretching vibration at 1000-1200 cm 1, affirming the existence of silicon atoms [26,27]. Meanwhile, it is demonstrated that the Si NPs have several other functional groups such as the N–H (bending vibration around 1600 cm 1, stretching vibration at 3300 cm 1), C–H (stretching vibra tion between 2850 and 2950 cm 1), and O–H (stretching vibrations at 3400 cm 1) on the surface [28]. The FT-IR spectra of the mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 display abundant Si–O–Si bands of the inorganic framework and plentiful O–H on the surface (Fig. 3b). It is observed that there is no peak at 2940 cm 1 assigned to C–H stretching vibration, indicating the template agent has been removed [29]. When Si NPs are assembled into the pore of SPSBA-15, LRSBA-15 and HPSBA-15, the peak at 2940 cm 1 in the FT-IR spectra of SP4, LR4 and HP8 hybrid materials is observed (Fig. 3c). The result further verifies the fact that Si NPs are successfully assembled into the channel of SPSBA-15,
3.3. Microscopic morphologies The microscopic morphologies of the SPSBA-15, LRSBA-15, HPSBA15, SP4, LR4 and HP8 hybrid materials are studied with the SEM and TEM as shown in Fig. 2 and Fig. S1. As seen from Fig. 2, the spherical mesoporous SPSBA-15, long rod-like mesoporous LRSBA-15 and hex agonal prism-like mesoporous HPSBA-15 are successfully obtained. After assembling fluorescent Si NPs, the SP4, LR4 and HP8 hybrid ma terials present the same morphologies as SPSBA-15, LRSBA-15 and HPSBA-15, respectively (Fig. S1 (a, b and c)). Fig. S1 (d, e and f) demonstrate the SP4, LR4 and HP8 hybrid materials process a uniform worm-like pores with p6mm hexagonal symmetry. We have analyzed
Fig. 1. (a) Schematic representation of the preparation of fluorescent Si NPs using DAMO and sodium citrate dehydrate. (b) Absorption (black), fluorescence excitation (red), and emission (blue) spectra of the Si NPs in aqueous solution. Inset shows the corresponding photographs under daylight (left) and UV of 365 nm (right), respectively. (c) Typical TEM image of the as-prepared Si NPs. Insets show the HRTEM image and size distribution histogram. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 3
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Fig. 2. (a, b and c) The SEM images of SPSBA-15 (a), LRSBA-15 (b) and HPSBA-15 (c), respectively.
Fig. 3. (a) The SAXRD patterns of SPSBA-15, LRSBA-15 and HPSBA-15. (b and c) The FT-IR spectra of Si NPs, SBA-15 with different morphologies (SPSBA-15, LRSBA-15 and HPSBA-15) (b) and Si NPs/SBA-15 hybrid materials (SP4, LR4 and HP8) (c), respectively.
LRSBA-15 and HPSBA-15. As seen from Fig. 3 (b and c), hydrogen bonds linking is the reason, resulting in Si NPs assembling into the pore of SPSBA-15, LRSBA-15 and HPSBA-15 [30]. XPS measurements were performed to determine the chemical bond of the fabricated the hybrid samples. C1s, N1s, O1s, Si2p and Si2s signals in the XPS full survey spectra confirm the existence of C, O, N and Si elements (shown in Fig. S2). The high resolution XPS peaks of C1s, N1s, O1s and Si2p of SP4, LR4 and HP8 hybrid materials are shown in Fig. S3. The typical hybrid materials have the same chemical bonds. The C1s XPS spectra exhibit – C), minor three peaks, i.e., the dominant graphitic sp2 carbons (C–C/C– – O) and sp3 carbons (C–O/C–N). The O1s and N1s carbonyl carbons (C– – C, O–C, N–H and N-(C)3 XPS spectra confirm the existence of O–Si, O– chemical bonds. The high-resolution Si2p spectra show the presence of Si–O–H and Si–O–Si chemical bonds.
isotherms exhibit typical type-IV curves with H1-shaped hysteresis loops, indicating their mesostructured silica (Fig. 4b) [31]. Their cor responding textural data (BET surface area, pore volume and pore size) are list in Table 1. By analyzing these data, the mesoporous HPSBA-15 materials possess the highest BET surface area of 841.11 m2 g-1 and a wide pore volume of 0.96 cm3 g-1. The mesoporous SPSBA-15 materials exhibit a larger BET surface area of 798.46 m2 g-1 and the widest pore volume of 1.05 cm3 g-1. As the adding volume of Si NPs increases, the pore-size distribution curves and nitrogen adsorption-desorption isotherms of SP, LR and HP hybrid materials can be seen from Fig. 5. These hybrid materials retain the type-IV curves with H1-shaped hysteresis loops. And the pore-size distributions are maintained in a range of mesoporous pore sizes. Table 1 Textural data of SPSBA-15, LRSBA-15 and HPSBA-15, respectively.
3.5. Pore structure properties The pore-size distribution curves and nitrogen adsorption-desorption isotherms are used to evaluate the BET surface area, pore volume and pore size. As seen from Fig. 4 (a), the mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 show a narrowed pore size with 2–10 nm. Their
Samples
SBET (m2g 1)
V (cm3g
SPSBA-15 LRSBA-15 HPSBA-15
798.46 665.11 841.11
1.05 0.93 0.96
1
)
D (nm) 2.33 3.27 2.76
Fig. 4. (a and b) The pore-size distribution curves (a) and nitrogen absorption-desorption isotherms (b) of SPSBA-15, LRSBA-15 and HPSBA-15, respectively. 4
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Fig. 5. The pore-size distribution curves and nitrogen adsorption-desorption isotherms of (a, b) SP, (c, d) LR and (d, e) HP hybrid materials, respectively.
Table S2 summarizes the BET surface areas, pore volumes and pore sizes of hybrid materials with different adding volumes of Si NPs. As Si NPs are assembled into the pores of SPSBA-15, LRSBA-15 and HPSBA-15, the BET surface areas, pore sizes and pore volumes of hybrid materials all decrease.
adding volumes of Si NPs are measured in pure nitrogen atmosphere under the excitation of 360 nm (Fig. 6). As Fig. 6 shows, the SP4, LR4 and HP8 hybrid materials show the characteristic emission peak centered at ~440 nm. As the adding volumes of Si NPs increase, the fluorescent intensity of hybrid materials increase at first and then descend. The most optimal volumes of Si NPs are 4, 4 and 8 ml in mesoporous SPSBA-15, LRSBA-15 and HPSBA-15, respectively. Meso porous SPSBA-15 and LRSBA-15 have the same optimal doping volume. However, according to pore structural data, the BET surface area and
3.6. Fluorescent properties The fluorescent spectra of SP, LR, HP hybrid materials with different
Fig. 6. (a, b and c) The fluorescent spectra of SP (a), LR (b), HP (c) hybrid materials with different adding volumes of Si NPs under the excitation of 360 nm in pure nitrogen atmosphere. 5
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pore volume of mesoporous SRSBA-15 materials are larger than LRSBA15. Therefore, it can be seen that the fluorescent intensity of SP4 is higher than that of LR4. The HP8 hybrid materials have the highest fluorescent intensity corresponding to the optimal adding volume of Si NPs. It is observed that mesoporous HPSBA-15 materials are well suited as a solid matrix with largest BET surface area that can accommodate more Si NPs.
Fig. 8 (b) presents the typical intensity-based Stern-Volmer plots and the fitted curve using Demas two-site model equation. The Stern-Volmer equation reveals the fluorescent ratio (I0/I) under different oxygen volumes in homogeneous media. It can be described as [34]: I0 = I ¼ 1 þ KSV PO2
(1)
where I is the fluorescent intensity of the hybrid materials, the subscript 0 denotes the absence of oxygen, I0/I denotes the fluorescence intensity ratio, KSV is the Stern-Volmer constant, KSV is the quenching constant, and PO2 denotes the oxygen volume fraction at normal atmospheric pressure. An ideal Stern-Volmer curve is supposed to be a linear one. As shown in Fig. 8 (b), the Stern-Volmer oxygen-quenching plots of SP4, LR4 and HP8 hybrid materials appear more nearly linear at low O2 concentra tions. However, it is obvious that the curves of the experimental data gradually show a tendency of downward bending. It is attributed to nonuniform distribution of Si NPs and different degrees of difficulty in quenching oxygen accordingly. Therefore, the Demas two-site model equation is proposed to fit the experimental data [35].
3.7. Oxygen sensing properties The selectivity of oxygen in SP4, LR4 and HP8 hybrid materials are evaluated by their emission response at oxygen or carbon dioxide at mosphere. As seen from Fig. 7 (d, e and f), the fluorescent intensity of SP4, LR4 and HP8 hybrid materials almost unchanged at different car bon dioxide volume fractions. But as the oxygen volume tuned from 0 to 100%, the fluorescent intensity of SP4, LR4 and HP8 hybrid materials rapidly decrease (Fig. 7 (a, b and c)). This result indicates the hybrid materials have high selectivity to oxygen. To compare the oxygen sensing properties of SP4, LR4 and HP8 hybrid materials, the typical dynamic response are measured on expo sure the different ratios of pure N2 and O2 atmospheres (Fig. 8a). By analyzing the time-dependent spectra, the 95% response (t↓) and 95% recovery (t↑) times can be calculated. The 95% response (t↓) and 95% recovery (t↑) times are defined as the time needed of fluorescence in tensity attained 95% of its initial intensity when the gas is converted from pure nitrogen to pure oxygen and from pure oxygen to pure ni trogen, respectively. These values are summarized in Table 2. From Fig. 8 (a), it is observed that SP4, LR4 and HP8 hybrid materials all exhibit a fully reversible response and their response to oxygen is stable and very rapid. As summarized in Table 2, SP4 hybrid materials show a shorter response time of 2.6 s and recovery time of 11.6 s than LR4 hybrid materials. The most possible reason for the higher oxygen sensing performance of SP4 hybrid materials can be attributed to the larger BET surface area and the higher fluorescent intensity compared with LR4 hybrid materials. In addition, HP8 hybrid materials exhibit a shortest response time of 2.2 s and recovery time of 11.2 s, which is shorter than response and recovery time mentioned in previous studies [5,32,33]. This confirms that Si NPs-doped hybrid materials based on Si NPs and the mesoporous HPSBA-15 with large surface-to-volume ratios have the higher potential in oxygen sensing.
I0 1 ¼ I 1þKf 01 P þ 1þKf 02 P SV1 O2 SV2 O2
(2)
where f01 and f02 values are the fraction of each of the two sites contributing to the unquenched intensity, KSV1 and KSV2 values are the quenching constants for the two sites, and PO2 is the partial pressure of oxygen at 1 atm pressure. The solid lines are fitted by Demas two-site model equation to calculate the KSVi and f01 values, which are summarized in Table 2. The KSVi and f01 values reveal the oxygen sensing performance. The higher values of KSV and the lower values of f01 are more beneficial to a higher oxygen quenching response. The highest KSV values of HP8 hybrid ma terials compared to those of SP4 and LR4 hybrid materials indicate that the fluorescent Si NPs in HP8 hybrid materials are more easily quenched by oxygen. In addition, the sensitivity to oxygen can also be expressed as I0/I. When the oxygen volumes reach to 100%, I0/I of HP8 hybrid ma terials exhibit a highest value of 9.74 than other hybrid materials. This result can be attributed to the uniform and nearly parallel porous structure of the mesoporous HPSBA-15 materials support with large surface areas and narrow pore size distributions.
Fig. 7. (a, b and c) Emission spectra of SP4 (a), LR4 (b) and HP8 (c) hybrid materials excited by 360 nm under different oxygen volume fractions, respectively. (d, e and f) Emission spectra of SP4 (d), LR4 (e) and HP8 (f) hybrid materials excited by 360 nm under different carbon dioxide volume fractions, respectively. 6
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Microporous and Mesoporous Materials 296 (2020) 110001
Fig. 8. (a) Response and recovery time and relative intensity of SP4, LR4 and HP8 hybrid materials when switching between 100% nitrogen and 100% oxygen. (b) A typical Stern-Volmer point diagram based luminescence intensity of SP4, LR4 and HP8 hybrid materials under different oxygen volume fractions. The solid lines are fitted by Demas two-site model equation. Table 2 Values of response (I0/I100), Stern-Volmer model and Demas model oxygen-quenching fitting parameters of SP4, LR4 and HP8 hybrid materials, respectively. Samples
I0/I100
t↓ (s)
t↑ (s)
1
SP4 LR4 HP8 a b
6.49 4.10 9.74
3.4 2.6 2.2
12.2 11.6 11.2
Demas Two-site modela
Stern-Volmer model 2
KSV (O2% )
r
0.0632 � 0.0028 0.0356 � 0.0015 0.0939 � 0.0020
0.9072 0.9243 0.9817
KSV1(O2%
1
)
0.1169 � 0.0076 0.0625 � 0.0058 0.1217 � 0.0070
KSV2(O2% 1) 0.0017 � 0.0012 0.0023 � 0.0016 0.0021 � 0.0028
f01b
r2
0.9328 � 0.0131 0.9091 � 0.0278 0.9775 � 0.0105
0.9983 0.9972 0.9987
Terms are from Eq. (2). f01þf02 ¼ 1.
4. Conclusions
Appendix A. Supplementary data
In summary, we have demonstrated that mesoporous HPSBA-15 materials are the most suitable solid matrix for an optical oxygen sensor compared to mesoporous SPSBA-15 and LRSBA-15 materials. Mesoporous SPSBA-15, LRSBA-15 and HPSBA-15 materials doped with Si NPs (SP, LR and HP hybrid materials) are a potential material in the field of oxygen sensing due to their nontoxic, environment friendly and excellent optical properties. Especially, due to the highest surface to volume ratio of the mesoporous HPSBA-15 materials, more Si NPs can be assembled into the channel. The optimal adding volume of Si NPs is 8 ml. HP8 hybrid materials exhibit the shortest response time of 2.2 s and recovery time of 11.2 s compared with SP4 and LR4 hybrid materials. In addition, the lower values of f01 and the higher values of KSV and I0/I100 further prove that HP8 hybrid materials possess the superior perfor mance of oxygen sensing. This feature can be attributed to the uniform and nearly parallel porous structure of the mesoporous HPSBA-15 ma terials support with large surface areas and narrow pore size distributions.
Supplementary data to this article can be found online at https://doi. org/10.1016/j.micromeso.2020.110001.
Declaration of competing interest
[1] L.C. Clark Jr., Trans. Am. Soc. Artif. Intern. Organs 2 (1956) 41–48. [2] B. Lei, B. Li, H. Zhang, S. Lu, Z. Zheng, W. Li, Y. Wang, Adv. Funct. Mater. 16 (2006) 1883–1891. [3] F. Lin, F. Li, Z. Lai, Z. Cai, Y. Wang, O.S. Wolfbeis, X. Chen, ACS Appl. Mater. Interfaces 10 (2018) 23335–23343. [4] Y. He, J. He, L. Wang, Z. Yu, H. Zhang, Y. Liu, B. Lei, Sens. Actuators B Chem. 251 (2017) 918–926. [5] T. Gong, Y. Li, B. Lei, J. Zhuang, Y. Liu, H. Zhang, Mater. Res. Bull. 111 (2019) 1–6. [6] Z. Jiang, X. Yu, S. Zhai, Y. Hao, Ratiometric dissolved oxygen sensors based on ruthenium complex doped with silver nanoparticles, Sensors 17 (2017) 548. [7] X. Tong, Y. Zhou, L. Jin, K. Basu, R. Adhikari, G.S. Selopala, X. Tong, H. Zhao, S. Sun, A. Vomiero, Z.M. Wang, F. Rosei, Nano Energy 31 (2017) 441–449. [8] L.T. Canham, Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers, Appl. Phys. Lett. 57 (1990) 1046–1048. [9] Y. Han, Y. Chen, J. Feng, J. Liu, S. Ma, X. Chen, Anal. Chem. 89 (2017) 3001–3008. [10] Y.-K. Dou, Y. Chen, X.-W. He, W.-Y. Li, Y.-H. Li, Y.-K. Zhang, Anal. Chem. 89 (2017) 11286–11292. [11] C.M. Gonzalez, M. Iqbal, M. Dasog, D.G. Piercey, R. Lockwood, T.M. Klapotke, J.G. C. Veinot, Nanoscale 6 (2014) 2608–2612. [12] W. Gu, X. Liu, X. Pi, X. Dai, S. Zhao, L. Yao, D. Li, Y. Jin, M. Xu, D. Yang, IEEE Photonics J. 9 (2017) 1–10. [13] L. Wang, H. Zhang, X. Zhou, Y. Liu, B. Lei, J. Colloid Interface Sci. 478 (2016) 256–262. [14] H. Yang, N. Coombs, G.A. Ozin, Nature 386 (1997) 692–695.
Author Contribution Statement Ting Gong: Methodology, Investigation, Writing - Original Draft. Yanjuan Li: Data Curation, Writing - Review & Editing. Haonan Zhang: Software. Jianxian Zhou: Validation. Gening Xie: Formal analysis. Bingfu Lei: Conceptualization, Methodology, Writing - Review & Editing. Jianle Zhuang: Supervision. Yingliang Liu: Resources. Haoran Zhang: Resources, Writing - Review & Editing. References
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. Acknowledgments The present work was supported by the National Natural Science Foundations of China (Grant No. 21671070), the Project supported by GDUPS (2018) for Prof. Bingfu LEI, the Project for Construction of Highlevel University in Guangdong Province of China, the Guangzhou Sci ence & Technology Project, China (No. 201707010033) and the Special Funds for the Cultivation of Guangdong College Students’ Scientific and Technological Innovation (No. 201910564035).
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T. Gong et al.
Microporous and Mesoporous Materials 296 (2020) 110001 [25] G.L. Li, J. Lan, J.Y. Liu, G.B. Jiang, J. Colloid Interface Sci. 405 (2013) 164–170. [26] X. Chen, X. Zhang, L.-Y. Xia, H.-Y. Wang, Z. Chen, F.-G. Wu, Nano Lett. 2 (2018) 1159–1167. [27] W. Jeong, S. Jo, J. Park, B. Kwon, Y. Choi, A. Chae, S.Y. Park, I. In, Int. J. Mater. Sci. 53 (2018) 2443–2452. [28] J. Sun, T. Hu, C. Chen, D. Zhao, F. Yang, X. Yang, Anal. Chem. 88 (2016) 9789–9795. [29] B. Lei, L. Wang, H. Zhang, Y. Liu, H. Dong, M. Zheng, X. Zhou, Sens. Actuators B Chem. 230 (2016) 101–108. [30] Y. He, J. He, H. Zhang, Y. Liu, B. Lei, Opt. Mater. Express 7 (2017) 945. [31] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024–6036. [32] X. Wang, Y. Yang, B. He, Sens. Actuators B Chem. 241 (2017) 957–966. [33] J. Luo, T. Dziubla, R. Eitel, Sens. Actuators B Chem. 240 (2017) 392–397. [34] Z.C. Bao, Z.G. Feng, W. Wong, Sens. Actuators B Chem. 234 (2016) 167–175. [35] S. Banerjee, O.V. Arzhakova, A.A. Dolgova, D.B. Papkovsky, Sens. Actuators B Chem. 230 (2016) 434–441.
[15] L. Du, H. Song, S. Liao, Appl. Surf. Sci. 255 (2009) 9365–9370. [16] J. Chen, Y. Sheng, Y. Song, M. Chang, X. Zhang, L. Cui, D. Meng, H. Zhu, Z. Shi, H. Zou, ACS Sustain. Chem. Eng. 6 (2018) 3533–3545. [17] M. Cheng, H. Zhao, J. Yang, J. Zhao, L. Yan, H. Song, L. Chou, Microporous Mesoporous Mater. 266 (2018) 117–125. [18] A.L. Lee, C.T. Gee, B.P. Weegman, S.A. Einstein, A.R. Juelfs, H.L. Ring, K.R. Hurley, S.M. Egger, G. Swindlehurst, M. Garwood, W.C.K. Pomerantz, C.L. Haynes, ACS Nano 11 (2017) 5623–5632. [19] T. Gong, Y. Li, B. Lei, X. Zhang, Y. Liu, H. Zhang, J. Mater. Chem. C 7 (2019) 5962–5969. [20] M. Vinoba, M. Bhagiyalakshmi, S.K. Jeong, Y. II Yoona, S.C. Nama, Colloids Surfaces B Biointerfaces 90 (2012) 91–96. [21] D. Gao, A. Duan, X. Zhang, Z. Zhao, H. E, J. Li, H. Wang, Appl. Catal. B Environ. 165 (2015) 269–284. [22] A. Sayari, B.-H. Han, Y. Yang, J. Am. Chem. Soc. 126 (2004) 14348–14349. [23] C. Cheng, D.L. Lu, B. Shen, Y.D. Liu, J.Y. Lei, L.Z. Wang, J.L. Zhang, M. Matsuoka, Microporous Mesoporous Mater. 226 (2016) 79–87. [24] Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S.T. Lee, Y. He, J. Am. Chem. Soc. 135 (2013) 8350–8356.
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