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Organic–inorganic hybrid hierarchical aluminum phenylphosphonate microspheres
Journal of Colloid and Interface Science xxx (2014) xxx–xxx
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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
Organic–inorganic hybrid hierarchical aluminum phenylphosphonate microspheres Liqiu Zhang a, Xin Shi a,⇑, Shaomin Liu b, Vishnu K. Pareek b, Jian Liu b,⇑ a b
Institute of Chemistry for Functionalized Materials, School of Chemistry and Chemical Engineering, Liaoning Normal University, 850 Huanghe Road, Dalian 116029, China Department of Chemical Engineering, Curtin University, Perth, WA 6845, Australia
a r t i c l e
i n f o
Article history: Received 27 January 2014 Accepted 2 April 2014 Available online xxxx Keywords: Organic–inorganic hybrid composites Mesoporous materials Self-assembly Hydrothermal synthesis Crystal growth
a b s t r a c t Organic–inorganic hybrid phenylphosphonates with hierarchical morphologies have attracted much attention due to their structural versatility for various applications including catalysis, adsorption, and biomedicals, however, so far there have been no reports of the synthesis and application of aluminum phenylphosphonate microspheres. Here, we report a hydrothermal method for the synthesis of the flower-like porous aluminum phenylphosphonate microspheres by using phenylphosphinic acid and aluminum nitrate as the precursors. The nano-flakes formed in the initial growing stage are believed to play a key role in the formation of aluminum phenylphosphonate micro-flowers. The self-assembly of the flower-like microspheres has been identified to involve a two-stage growth process: a synergistic Ostwald ripening and oriented nanosheets attachment. The resultant aluminum phenylphosphonate micro-flowers can be easily converted to mesoporous amorphous aluminum phosphates by high temperature treatment without causing any morphology deterioration. The hierarchical aluminum phenylphosphonate microspheres have been applied to enrich peptide. This versatile synthesis method would enable to synthesize other metal phosphonates/phosphates spheres with interesting architecture for the potential application in catalysis, energy storage and nanomedicine. Ó 2014 Elsevier Inc. All rights reserved.
1. Introduction Construction of organic–inorganic hybrid materials is a rapidly expanding field of materials chemistry for the design of advanced materials with specific structure and functionality [1–3]. Metal phosphonate/diphosphonates as one such group of hybrid materials have attracted widespread interest because of their versatile applications in the areas of sorption, ion-exchange, catalysis, charge storage, and sensors [3–7]. In this connection, metal phenylphosphonates represent a particularly versatile field for investigation [8]. To date, the synthesis and application of various metal phenylphosphonates such as zirconium phenylphosphonate (Zr(O3PC6H5)2) [9], titanium phenylphosphonate (Ti(O3PC6H5)2) [10] and tin phenylphosphonate (Sn(O3PC6H5)2) [11] have been reported. One of the prototype metal phenylphosphonates is aluminum phenylphosphonate, Al2(O3PC6H5)3, which is a layered compound with an interlayer spacing of 11.7 Å [12]. Impressive studies have been conducted on the synthesis of aluminum phenylphosphonate and aluminum phosphates due to their wide applications [12–15]. However, to the best of our knowledge, there ⇑ Corresponding authors. E-mail addresses: [email protected] (X. Shi), [email protected] (J. Liu).
has been no report on the synthesis of hierarchical spheres selfassembled by layered Al2(O3PC6H5)3, which can provide the additional pores for accommodation of large bulk guest molecules without diffusion limitation to apply in adsorption, separation, catalysis and biomedicine. Metal phosphate/phosphonate spheres and their porous structure have attracted increasing attention due to their unique properties, morphology and great potential applications [16–24]. For example, Li and his colleagues demonstrated the synthesis of transition-metal (Mn, Fe, Co, Ni, and Cu) phosphate colloidal spheres by low-temperature solution-phase reactions [16]. Protein-incorporated Cu3(PO4)23H2O microspheres and nanoflowers were prepared by using copper (II) ions as the inorganic component and various proteins as the organic component [17]. Besides, Clearfield and co-workers developed a hydrothermal method to synthesize Sn(O3PC6H5)2 with aggregated spherical shape [11]. Attempts have also been made to synthesize mesoporous spherical zirconium phosphonate and titanium phosphonate [18,20]. By contrast, no hierarchical aluminum phenylphosphonate spheres have been reported. The crystalline microporous aluminophosphate with zeolite properties has been known for their immense significance in the field of heterogeneous catalysis [25–30], in which aluminum adopted 4-, 5- and 6-coordination
http://dx.doi.org/10.1016/j.jcis.2014.04.008 0021-9797/Ó 2014 Elsevier Inc. All rights reserved.
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mode to form different active acid sites for catalytic reactions. Additionally, aluminophosphate molecular sieves can be easily doped with other metal ions to improve the framework properties. So, it is desirable to develop a reliable method to synthesize the hierarchically porous aluminum phenylphosphonate spheres and aluminum phosphates spheres. Their hierarchical structure will provide void space for entrapment and transport of biomolecules, and unsaturatedly coordinated aluminum will act as active sites for capture of biomolecules, also the doped heteroatom ions will improve the framework properties and provide additional metal ion affinity for biomolecules. Here, we reported the synthesis of flower-like porous aluminum phenylphosphonate microspheres by using phenylphosphinic acid and aluminum nitrate as the precursors under acidic condition. As a result, new types of porous organicinorganic hybrids consisting of aluminum phenylphosphonate layered structures and spherical morphology have been obtained for the first time. The size and morphology of the resultant aluminum phenylphosphonates could be modulated by varying the reaction time. Moreover, the mechanism of the self-assembly process to form the flower-like microspheres is discussed in detail. By calcinations of these porous aluminum phenylphosphonate microspheres, mesoporous amorphous aluminum phosphate micro-flowers with uniform pore size of 5.5 nm can be prepared. For an application demonstration, the hierarchical aluminum phenylphosphonate microspheres have been assessed as a candidate material for peptide enrichment.
least 6 h. The Brunauer–Emmett–Teller (BET) specific surface areas were calculated using adsorption data at the relative pressure range of P/P0 = 0.05–0.25. Pore size distributions were calculated from adsorption branch using the Barrett–Joyner–Halenda (BJH) method. The total pore volumes were estimated from the amounts adsorbed at a relative pressure (P/P0) of 0.99. High resolution scanning electron microscopy (HRSEM), field-emission scanning electron microscopy (FESEM) and scanning electron microscopy (SEM) were undertaken on a HITACHI S-5500, HITACHI SU 8010 and JSM 6360 LV microscope operating at an accelerating voltage of 1–30 kV, respectively. Transmission electron microscopy (TEM) was performed using a JEOL JEM-2010 at an acceleration voltage of 120 kV. FT-IR spectra were collected with a TENSOR 27 IR spectrometer in the range of 4000–400 cm1 using KBr pellet. 13 C (100.5 MHz) cross-polarization magic angle spinning (CPMAS), 31P (161.8 MHz) and 27Al (79.4 MHz) MAS solid-state NMR experiments were recorded on a BRUKER DRX 400 spectrometer equipped with a magic-angle spin probe in a 4-mm ZrO2 rotor. 13 C signals were referenced to tetramethylsilane, 31P NMR signal was referenced to H3PO4 (85 wt%). The experimental parameters were 6-kHz spin rate, 2-s pulse delay, 6-min contact time, for 13C CP-MAS NMR experiments; 8-kHz spin rate, 3-s pulse delay, 10-min contact time for 31P MAS NMR experiments. Thermal analysis (TGA and DTA) was carried out in air on a Perkin–Elmer Pyris Diamond TG-DTA 6300 at a heating rate of 5 °C min1 from room temperature to 800 °C. 2.4. Enrichment tests
2. Experimental section 2.1. Chemicals and reagents All materials were of analytical grade and used as received without any further purification. phenylphosphinic acid (PPA, C6H7O3P, 99%), aluminum nitrate nonahydrate, (Al(NO3)39H2O, P98%), a-cyano-4-hydroxycinnamic acid (CHCA, P99%, matrix use only), trifluoroacetic acid (TFA, P99%), acetonitrile (ACN, P99%) and proteins/peptides were purchased from Sigma–Aldrich. Other reagents were purchased from ShangHai Chemical Reagent. Inc. of Chinese Medicine Group. 2.2. Synthetic procedure Flower-like porous aluminum phenylphosphonate microspheres were synthesized by using C6H7O3P and Al(NO3)39H2O as the precursors under acidic condition. In a typical synthesis, 7.5 mL of 0.04 M C6H7O3P was added into a HNO3 solution (0.035 M) containing 7.5 mL of 0.04 M Al(NO3)39H2O, then, 0.44 mL of 1.5 M sodium hydroxide (NaOH) solutions was added into the above solution to tune the pH value to 1.6. The mixture was stirred for 30 min until a homogeneous solution was formed, and the resulted solution was transferred into a Teflon-lined autoclave and heated for 19 h at 100 °C under static conditions. The solid products were collected by centrifugation and washed with distilled water, respectively. The aluminum phenylphosphonates were denoted as AlPP-n, where n (n = 0.75, 1, 1.25, 2, 5, 19, and 72) is the hydrothermal treatment time at 100 °C. 2.3. Characterization Powder X-ray diffraction (XRD) patterns were recorded on an Empyrean powder diffraction system using Cu Ka radiation of 0.15406 nm wavelength. The nitrogen sorption experiments were performed at 77 K on a Micromeritics ASAP 3000 system. Prior to the measurement, the samples were outgassed at 120 °C for at
Enrichment tests toward peptides and proteins were performed, where the low concentrated solutions were prepared through a step-wise dilution manner. The microspheres were dispersed in water at a concentration of 10 mg/mL and 10 lL of the slurry was directly added to the prepared solutions. Then the supernatant was removed by centrifugation after 10 min enrichment and the microspheres were collected. For matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS), the microspheres were incubated with 1 lL of matrix solution (10 mg/mL CHCA in TFA/ACN/water, 0.1%/49.9%/ 50%, v/v/v) and analyzed on the plain steel MALDI plate. The MS spectra were collected accumulating 500 laser shots at 10 different spots on Bruker Autoflex II Smartbeam system and no smooth spectra were used. 3. Results and discussion 3.1. Aluminum phenylphosphonate flower-like microspheres Self-assembling in the form of aluminum phenylphosphonate flower-like microspheres was prepared by the reaction of equimolar amounts of phenylphosphinic acid (PPA) and aluminum nitrate (in a 1:1 molar ratio); NaOH solutions were then added to tune the pH value to 1.6. The morphology of the resultant aluminum phenylphosphonates (AlPP-19) with hydrothermal treatment 19 h was characterized by scanning electron microscopy (SEM) and transaction electron microscopy (TEM) with the results shown in Fig. 1. As can be seen from Fig. 1a, uniform and well-dispersed flower-like aluminum phenylphosphonate microspheres with an average diameter of 8 lm are observed. A SEM image (the left in Fig. S1) with a large amount of visible microspheres was also obtained in order to measure the particle size of aluminum phenylphosphonate microspheres. The diameter of aluminum phenylphosphonate microspheres was observed in the range of 5–13 lm and the maximum distribution located at 8 lm as shown in the right of Fig. S1, which can further confirm that the size of microspheres is
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Fig. 1. Morphological and structural characterizations: (a) SEM images; (b) TEM image; (c) high resolution TEM images; and (d) powder XRD pattern of aluminum phenylphosphonates (AlPP-19).
controllable. The morphology of the flowerlike nanostructures at a higher magnification is displayed in the inset of Fig. 1a, which reveals that these flowerlike microspheres are consisted of a multitude of micro-petals with smooth surfaces. These micro-petals, of thickness 25–80 nm and width 1–1.5 lm, were connected through a central core to form 3D flower-like hierarchical structures. The micro-petals-assembled flower-like morphology is further confirmed by TEM image with a large number of nano-flakes or petals clearly observed in Fig. 1b. Based on the typical TEM image of the cross-sections, the thickness of the petal is 50 nm, consistent with the SEM results. The high resolution TEM image shown in Fig. 1c further confirms that the nano-flakes have a layered structure with the inter-spacing between two layers about 1.1 nm. The structure of the resultant aluminum phenylphosphonate was investigated by powder X-ray diffraction (PXRD). In general, the as-synthesized metal oxides or metal phosphates from hydrothermal method show a poor degree of crystallinity. As shown in Fig. 1d, the observed two strong peaks at 2h of 3.7° and 7.4° correspond to the 100 reflection (23.8 Å), and the 200 reflection (11.9 Å), respectively, featuring the layer structures. There are other peaks at 11.0°, 13.7°, 18.6°, 19.2°, 20.9° and 26.8°. On the basis of these peak positions, the d-values (in Å) are calculated to be 8.0, 6.5, 4.8, 4.6, 4.2 and 3.3, corresponding to 300, 40–1, 30–2, 51–1, 510 and 71–2 facets of Al2(O3PC6H5)3H2O, respectively (Fig. 1d) [12,13]. A layered structure was formed in which phenyl molecules were packed inside the interlayer spacing of 11.9 Å. Such a layered structure would offer many nano-channels favoring the transporting or diffusion of guest molecules. Al2(O3PC6H5)3H2O was further characterized by FT-IR and solid state NMR to verify their chemical compositions. The IR spectrum of Al(O3PC6H5)3H2O displays a band at 1040 cm1 characteristic Al–O–P framework vibrations, indicating that the material was constructed by the coordination of aluminum with phosphonate
groups (Fig. S2). The P–OH stretching vibration at 940–950 cm1 cannot be observed, which is in consistent with the formula of Al(O3PC6H5)3H2O. The 27Al MAS NMR spectrum clearly shows two peaks at 42.4 and 20.1 ppm, which correspond to aluminums with tetrahedral and octahedral oxygen environments, respectively. These 27Al MAS NMR results were also observed on Al2(O3PC6H5)3H2O [12,13], confirming the same coordination environment of the aluminum in both materials (Fig. 2a). Two resonances located at 2.1 ppm and 0.9 ppm present in the 31P MAS NMR spectrum (Fig. 2b) may be due to the different coordination modes of PO3. As expected, the 13C MAS NMR spectrum has the peak for the phenyl carbons centered at 131.5 ppm (Fig. 2c). Solid sate NMR results together with FT-IR result demonstrate the integrity of phenylphosphonate into Al(O3PC6H5)3H2O, provide a good fingerprint of the proposed formula, and confirm that the phenylphosphonate group is stable during the synthesis process. Further evidence of the porous structure of AlPP-19 was supported by N2 sorption analysis. The adsorption–desorption isotherm of AlPP-19 shows a type IV behavior with a H3-type in the relative pressure ranges of 0.5–0.9 (Fig. S3), echoing with SEM and TEM results that the presence of a non-uniform mesopore is consistent with the hierarchical structure. The corresponding Barrett–Joyner–Halenda (BJH) pore size distribution presents a broad peak in the range of 10 to 50 nm, mirroring the void space between the nano-flakes (Fig. S3) [31–33]. In addition, the Brunauer–Emmett–Teller (BET) specific surface area and total pore volume of AlPP-19 microspheres are calculated to be 15 m2 g1 and 0.10 cm3 g1, respectively. From element analysis, the content of C and H is 39.57% and 3.13%, respectively, a P/Al ratio of 1.5 was obtained from ICP which further confirm the formula Al2(O3PC6H5)3H2O. The aluminum phenylphosphonate micro-flowers of AlPP-19 show near neutral framework in water (f potential: 2.76 mV). Fe3+ doped AlPP-19 (Fe3+–AlPP-19) can also be
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Fig. 2. Chemical composition characterizations: (a) 27Al MAS NMR (b) 31P MAS NMR spectra and (c) 13C CP/MAS NMR of Al2(O3PC6H5)3H2O, AlPP-19. Refers to the side band.
synthesized by in-situ introducing Fe(NO3)39H2O as precursor and the Fe content is 0.8% from inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. After Fe doping, the resultant micro-flowers tend to be more aggregated (Fig. S4a) and BET surface area is increased to 54 m2 g1 (Fig. S4b). In a typical synthesis of aluminum phenylphosphonate microspheres, the acidity of the phenylphosphonate ions resulted in a pH value of the initial mixed solution of approximately 1.3. Subsequent addition of NaOH would increase the pH value with the gradual formation of aluminum phenylphosphonate precipitate [Eq. (1)]. 3þ
2Al
þ 3ðO3 PC6 H5 Þ2 þ H2 O ! Al2 ðO3 PC6 H5 Þ3 H2 O
ð1Þ
In order to understand the formation process of the flower-like hierarchical nanostructures, the morphology and the structure evolution of the as-prepared microspheres with different NaOH concentrations and aging times were investigated through SEM analysis. As shown in Fig. S5, highly aggregated microspheres were obtained without the addition of NaOH to tune the pH value. When the amount of NaOH addition was reached at 0.5 mL, highly dispersed micro-flowers can be synthesized. Further adding a larger amount of NaOH, the morphology is transforming to hierarchical structured micro-sheets. These results indicate the product morphology is significantly affected by the pH value in the synthesis solution. Micro-flowers are formed at pH regime of 1.6–1.7 and at lower pH value, and the microspheres would be aggregated; however, increasing the pH value to 1.8 would result in the formation of irregular micro-sheets. 3.2. Mesoporous hierarchical aluminum phosphate microspheres The thermal behavior of the product was characterized via the thermogravimetric analysis (TGA) under air atmosphere (Fig. S6). From room temperature to 150 °C, there is a weight loss up to about 3.9%, which can be attributed to the loss of one water molecule and a small amount of physical adsorbed water. The weight
loss between 400 and 650 °C accounting for about 36% is due to the decomposition of organic framework. After heat treatment at 550 °C for 2 h, the sample was decomposed as amorphous aluminum phosphate based on the result of PXRD (Fig. S7). The SEM image of the calcined AlPO4 as shown in Fig. 3a reveals no visible change in particle size and morphology after annealing at 550 °C. Uniform mesopores of 5 nm can be observed on the surface of the micro-petals (Fig. 3b) and typical IV isotherm can be observed with the surface area and pore volume increased to 103 m2 g1 and 0.24 cm3 g1, respectively (Fig. 3c). Noteworthy is that the presence of uniform mesopores with 5.5 nm (Fig. 3b and d) may be resulted from the decomposition of organic groups and the reconstruction of the frameworks during the calcination step. It provides a new synthetic method for mesoporous metal phosphates. 3.3. Formation mechanism Fig. 4a shows the SEM images of aluminum phenylphosphonate synthesized at different times during the hydrothermal treatment at 100 °C. No solid products can be obtained at 0.5 h reaction. In the early stage (0.75 h), irregular micro-sheets were formed; subsequently, these micro-sheets were grown and populated by other newly formed smaller nano-sheets or spheres (1 h). When the reaction time reached 1.25 h, SEM image indicates the small micro-flowers were becoming larger with corolla size of 2 lm which were assembled by emerging these loosely aggregated micro-petals. Larger micro-flowers with 7 lm size were obviously formed at 2 h and the thickness of the petals is identified at 30 nm. With further reaction time extension to 5 h, the microflower corolla grew to 8 lm and hundreds of micro-petals were presented in one single flower. When the reaction time was 19 h, the thickness of the micro-petals was continuously increased to average 50 nm but with no obvious change in the corolla size. After 19 h, the morphology and size of the flowers remained basically unchanged and were similar to 19 h, as shown in Fig. 4a with
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Fig. 3. (a and b) SEM images, (c) nitrogen adsorption–desorption isotherm and (d) pore size distribution of AlPP-19 after calcinations at 550 °C for 2 h.
Fig. 4. Formation of aluminum phenylphosphonate micro-flowers: (a) SEM images as a function of aging time and (b) a schematic illustration of the proposed formation mechanism of aluminum phenylphosphonate micro-flowers.
reaction time for 72 h, which may be due to the completion of the reactant supply. The PXRD patterns of the sample synthesized at 0.75 and 72 h (Fig. S8) indicate the Al2(O3PC6H5)3H2O was formed at the initial stage, and the phase was maintained during the entire hydrothermal process. Certainly the crystallinity was improved with the extension of the hydrothermal reaction as indicated from the intensity of the characteristic peaks in XRD and SEM results. To clarify the growth process, the morphology evolution diagram of the 3D hierarchical porous micro-flowers is illustrated in
Fig. 4b. SEM images as a function of aging time as shown in Fig. 4a suggest the following mechanism for micro-flowers selfassembly. At the initial stage, micro-sheets with small crystals of aluminum phenylphosphonate were formed (Fig. 4b). Subsequently, nucleation and growth of aluminum phenylphosphonate crystals originated at the surface of micro-sheets to form the separate micro-petals through Oswald ripening, which is the key step underlying the formation of the micro-flowers. In the last stage, a synergistic growing process of Ostwald ripening and oriented
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Fig. 5. Enrichment and detection tests based on the hierarchical porous aluminum phenylphosphonate micro-flowers toward a standard peptide alpha-conotoxin IMI: (a) Control; (b) AlPP-19; (c) Fe3+–AlPP-19.
attachment would result in the complete formation of a branched flower-like structure (Fig. 4b). The details of the self-assembly growth mechanism of the flower-like hierarchical nanostructures will be investigated later with advanced in-situ characterization techniques. 3.4. Peptide detection Considering abundant aluminum ions on the surface nanoflakes of microspheres, the hierarchical aluminum phenylphosphonate porous micro-flowers were employed as capture agent to enrich low concentrated bio-molecules for matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI TOF MS) detection [34–36]. Alpha-conotoxin IMI, a functional peptide (sequence GCCSDPRCAWRC) was first used as a model bio-molecule, which can selectively block alpha-delta site of the muscle acetylcholine receptor. At a concentration of 7.4 nM, a clear peptide signal (signal strength 2700) at the m/z range of 1352 can be observed in the MS spectrum after enrichment by the microspheres, while no peptides can be detected in control without any enrichment (Fig. 5). Similar results can be obtained using the microspheres for the enrichment and detection of proteins. As displayed in Fig. S9, using cytochrome c as an example, the protein is only detectable after enrichment at a concentration of 39 nM. Interestingly, we found that by introducing metal ions (e.g. Fe3+) in the synthetic process, the peptides enrichment performance of the materials can be highly enhanced with signal strength over 12,000 (Fig. 5c, compared to Fig. 5b) due to the enhanced metal ion affinity on the surface [35]. The above results indicate the strong potential of microspheres constructed from phenylphosphonates and metal ions as promising alternatives for general capture and detection of low abundance peptides/proteins.
4. Conclusions In summary, organic–inorganic hierarchical porous aluminum phenylphosphonate micro-flowers have been successfully synthesized through a hydrothermal synthesis method. Various aluminum phenylphosphonates with different sizes and morphologies can be obtained by tailoring the synthesis parameters such as, the pH value of the reaction solution, or aging time during the hydrothermal reaction. On the basis of experimental results of morphology evolution with reaction time, the self-assembly of the flower-like hierarchical nanostructures was proposed to involve a two-stage growth process, namely Ostwald ripening and oriented attachment. Mesoporous aluminum phosphate microflowers with uniform 5.5 nm pores were synthesized by the direct calcination of the aluminum phenylphosphonate micro-flowers. Preliminary studies have demonstrated that the as-prepared
flower-like hierarchical nanostructures show a promising enrichment property toward alpha-conotoxin IMI and cytochrome c. The stable aluminum phenylphosphonate and aluminum phosphates with these special morphology and porous structure would be of great interest for the potential applications in many other fields such as catalysis, ion exchange, adsorption and bio-medicals. Based on this work, the synthesis of a series of novel organic–inorganic hybrid phenylphosphonate materials with advanced functions can be envisaged by simply adjusting the chemical precursors in the demonstrated synthesis protocol. Author contributions L.Q.Z performed the experiments with technical support from the coauthors and obtained data representation. S.X. and J.L. supervised the whole work. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Acknowledgments This work was supported by the National Natural Science Foundation of China (21173108) and the Opening Foundation of State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences (N-12-11). This work was also partially supported by the Australian Research Council (ARC) Discovery Project program (DP1094070). Appendix A. Supplementary materials Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcis.2014.04.008. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
F. Hoffmann, M. Froba, Chem. Soc. Rev. 40 (2011) 608–620. Q.H. Yang, J. Liu, L. Zhang, C. Li, J. Mater. Chem. 19 (2009) 1945–1955. K.J. Gagnon, H.P. Perry, A. Clearfield, Chem. Rev. 112 (2012) 1034–1054. B. Shpeizer, D.M. Poojary, K. Ahn, C.E. Runyan, A. Clearfield, Science 266 (1994) 1357–1359. S.R.J. Oliver, Chem. Soc. Rev. 38 (2009) 1868–1881. H.E. Katz, G. Scheller, T.M. Putvinski, M.L. Schilling, W.L. Wilson, C.E.D. Chidsey, Science 254 (1991) 1485–1487. G.K.H. Shimizu, R. Vaidhyanathan, J.M. Taylor, Chem. Soc. Rev. 38 (2009) 1430– 1449. L. Raki, C. Detellier, Chem. Commun. (1996) 2475–2476. P. Varhadi, M. Kotwal, D. Srinivas, Appl. Catal. A: Gen. 462–463 (2013) 129– 136. A.A. Anilloa, M.A. Villa-Garcíaa, R. Llavonaa, M. Suáreza, J. Rodrígueza, Mater. Res. Bull. 34 (1999) 627–640. J. Huang, A. Subbiah, D. Pyle, A. Rowland, B. Smith, A. Clearfield, Chem. Mater. 18 (2006) 5213–5222. A. Cabeza, M.A.G. Aranda, S. Bruque, D.M. Poojary, A. Clearfield, J. Sanz, Inorg. Chem. 37 (1998) 4168–4178.
Please cite this article in press as: L. Zhang et al., J. Colloid Interface Sci. (2014), http://dx.doi.org/10.1016/j.jcis.2014.04.008
L. Zhang et al. / Journal of Colloid and Interface Science xxx (2014) xxx–xxx [13] G. Chaplais, J. Le Bideau, D. Leclercq, H. Mutin, A. Vioux, J. Mater. Chem. 10 (2000) 1593–1601. [14] G. Guerrero, P.H. Mutin, A. Vioux, J. Mater. Chem. 11 (2001) 3161–3165. [15] N. Zakowsky, G.B. Hix, R.E. Morris, J. Mater. Chem. 10 (2000) 2375–2380. [16] C. Chen, W. Chen, J. Lu, D.R. Chu, Z.Y. Huo, Q. Peng, Y.D. Li, Angew. Chem.-Int. Ed. 48 (2009) 4816–4819. [17] J. Ge, J.D. Lei, R.N. Zare, Nat. Nanotech. 7 (2012) 428–432. [18] T.Y. Ma, Z.Y. Yuan, ChemSusChem 4 (2011) 1407–1419. [19] T.Y. Ma, H. Li, A.N. Tang, Z.Y. Yuan, Small 7 (2011) 1827–1837. [20] Y.J. Jia, Y.J. Zhang, R.W. Wang, J.J. Yi, X. Feng, Q.H. Xu, Ind. Eng. Chem. Res. 51 (2012) 12266–12273. [21] X. Shi, J.P. Li, Y. Tang, Q.H. Yang, J. Mater. Chem. 20 (2010) 6495–6504. [22] X. Shi, J. Liu, C.M. Li, Q.H. Yang, Inorg. Chem. 46 (2007) 7944–7952. [23] A. Subbiah, D. Pyle, A. Rowland, J. Huang, R.A. Narayanan, P. Thiyagarajan, J. Zon, A. Clearfield, J. Am. Chem. Soc. 127 (2005) 10826–10827. [24] Z.K. Wang, J.M. Heising, A. Clearfield, J. Am. Chem. Soc. 125 (2003) 10375– 10383. [25] C. Serre, J.A. Groves, P. Lightfoot, A.M.Z. Slawin, P.A. Wright, N. Stock, T. Bein, M. Haouas, F. Taulelle, G. Ferey, Chem. Mater. 18 (2006) 1451–1457.
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[26] H.G. Harvey, J. Hu, M.P. Attfield, Chem. Mater. 15 (2003) 179–188. [27] K. Maeda, Y. Kiyozumi, F. Mizukami, Angew. Chem.-Int. Ed. 33 (1994) 2335– 2337. [28] S. Cabrera, J. El Haskouri, C. Guillem, A. Beltran-Porter, D. Beltran-Porter, S. Mendioroz, M.D. Marcos, P. Amoros, Chem. Commun. (1999) 333–334. [29] S. Oliver, A. Kuperman, G.A. Ozin, Angew. Chem.-Int. Ed. 37 (1998) 47–62. [30] M. Tiemann, M. Froba, Chem. Mater. 13 (2001) 3211–3217. [31] X.F. Yang, C.J. Jin, C.L. Liang, D.H. Chen, M.M. Wu, J.C. Yu, Chem. Commun. 47 (2011) 1184–1186. [32] J. Liu, S.Z. Qiao, H. Liu, J. Chen, A. Orpe, D.Y. Zhao, G.Q. Max Lu, Angew. Chem.Int. Ed. 50 (2011) 5947–5951. [33] J. Liu, H.Q. Yang, F. Kleitz, Z.G. Chen, T.Y. Yang, E. Strounina, G.Q. Max Lu, S.Z. Qiao, Adv. Funct. Mater. 22 (2012) 591–599. [34] K. Zhang, D. Zheng, L.L. Hao, J.I. Cutler, E. Auyeung, C.A. Mirkin, Angew. Chem.Int. Ed. 51 (2012) 1169–1172. [35] H.Q. Qin, P. Gao, F.J. Wang, L. Zhao, J. Zhu, A.Q. Wang, T. Zhang, R. Wu, H.F. Zou, Angew. Chem.-Int. Ed. 50 (2011) 12218–12221. [36] K. Qian, W. Gu, P. Yuan, F. Liu, Y. Wang, M. Monteiro, C. Yu, Small 8 (2012) 231–236.
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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
Organic–inorganic hybrid hierarchical aluminum phenylphosphonate microspheres Liqiu Zhang a, Xin Shi a,⇑, Shaomin Liu b, Vishnu K. Pareek b, Jian Liu b,⇑ a b
Institute of Chemistry for Functionalized Materials, School of Chemistry and Chemical Engineering, Liaoning Normal University, 850 Huanghe Road, Dalian 116029, China Department of Chemical Engineering, Curtin University, Perth, WA 6845, Australia
a r t i c l e
i n f o
Article history: Received 27 January 2014 Accepted 2 April 2014 Available online xxxx Keywords: Organic–inorganic hybrid composites Mesoporous materials Self-assembly Hydrothermal synthesis Crystal growth
a b s t r a c t Organic–inorganic hybrid phenylphosphonates with hierarchical morphologies have attracted much attention due to their structural versatility for various applications including catalysis, adsorption, and biomedicals, however, so far there have been no reports of the synthesis and application of aluminum phenylphosphonate microspheres. Here, we report a hydrothermal method for the synthesis of the flower-like porous aluminum phenylphosphonate microspheres by using phenylphosphinic acid and aluminum nitrate as the precursors. The nano-flakes formed in the initial growing stage are believed to play a key role in the formation of aluminum phenylphosphonate micro-flowers. The self-assembly of the flower-like microspheres has been identified to involve a two-stage growth process: a synergistic Ostwald ripening and oriented nanosheets attachment. The resultant aluminum phenylphosphonate micro-flowers can be easily converted to mesoporous amorphous aluminum phosphates by high temperature treatment without causing any morphology deterioration. The hierarchical aluminum phenylphosphonate microspheres have been applied to enrich peptide. This versatile synthesis method would enable to synthesize other metal phosphonates/phosphates spheres with interesting architecture for the potential application in catalysis, energy storage and nanomedicine. Ó 2014 Elsevier Inc. All rights reserved.
1. Introduction Construction of organic–inorganic hybrid materials is a rapidly expanding field of materials chemistry for the design of advanced materials with specific structure and functionality [1–3]. Metal phosphonate/diphosphonates as one such group of hybrid materials have attracted widespread interest because of their versatile applications in the areas of sorption, ion-exchange, catalysis, charge storage, and sensors [3–7]. In this connection, metal phenylphosphonates represent a particularly versatile field for investigation [8]. To date, the synthesis and application of various metal phenylphosphonates such as zirconium phenylphosphonate (Zr(O3PC6H5)2) [9], titanium phenylphosphonate (Ti(O3PC6H5)2) [10] and tin phenylphosphonate (Sn(O3PC6H5)2) [11] have been reported. One of the prototype metal phenylphosphonates is aluminum phenylphosphonate, Al2(O3PC6H5)3, which is a layered compound with an interlayer spacing of 11.7 Å [12]. Impressive studies have been conducted on the synthesis of aluminum phenylphosphonate and aluminum phosphates due to their wide applications [12–15]. However, to the best of our knowledge, there ⇑ Corresponding authors. E-mail addresses: [email protected] (X. Shi), [email protected] (J. Liu).
has been no report on the synthesis of hierarchical spheres selfassembled by layered Al2(O3PC6H5)3, which can provide the additional pores for accommodation of large bulk guest molecules without diffusion limitation to apply in adsorption, separation, catalysis and biomedicine. Metal phosphate/phosphonate spheres and their porous structure have attracted increasing attention due to their unique properties, morphology and great potential applications [16–24]. For example, Li and his colleagues demonstrated the synthesis of transition-metal (Mn, Fe, Co, Ni, and Cu) phosphate colloidal spheres by low-temperature solution-phase reactions [16]. Protein-incorporated Cu3(PO4)23H2O microspheres and nanoflowers were prepared by using copper (II) ions as the inorganic component and various proteins as the organic component [17]. Besides, Clearfield and co-workers developed a hydrothermal method to synthesize Sn(O3PC6H5)2 with aggregated spherical shape [11]. Attempts have also been made to synthesize mesoporous spherical zirconium phosphonate and titanium phosphonate [18,20]. By contrast, no hierarchical aluminum phenylphosphonate spheres have been reported. The crystalline microporous aluminophosphate with zeolite properties has been known for their immense significance in the field of heterogeneous catalysis [25–30], in which aluminum adopted 4-, 5- and 6-coordination
http://dx.doi.org/10.1016/j.jcis.2014.04.008 0021-9797/Ó 2014 Elsevier Inc. All rights reserved.
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mode to form different active acid sites for catalytic reactions. Additionally, aluminophosphate molecular sieves can be easily doped with other metal ions to improve the framework properties. So, it is desirable to develop a reliable method to synthesize the hierarchically porous aluminum phenylphosphonate spheres and aluminum phosphates spheres. Their hierarchical structure will provide void space for entrapment and transport of biomolecules, and unsaturatedly coordinated aluminum will act as active sites for capture of biomolecules, also the doped heteroatom ions will improve the framework properties and provide additional metal ion affinity for biomolecules. Here, we reported the synthesis of flower-like porous aluminum phenylphosphonate microspheres by using phenylphosphinic acid and aluminum nitrate as the precursors under acidic condition. As a result, new types of porous organicinorganic hybrids consisting of aluminum phenylphosphonate layered structures and spherical morphology have been obtained for the first time. The size and morphology of the resultant aluminum phenylphosphonates could be modulated by varying the reaction time. Moreover, the mechanism of the self-assembly process to form the flower-like microspheres is discussed in detail. By calcinations of these porous aluminum phenylphosphonate microspheres, mesoporous amorphous aluminum phosphate micro-flowers with uniform pore size of 5.5 nm can be prepared. For an application demonstration, the hierarchical aluminum phenylphosphonate microspheres have been assessed as a candidate material for peptide enrichment.
least 6 h. The Brunauer–Emmett–Teller (BET) specific surface areas were calculated using adsorption data at the relative pressure range of P/P0 = 0.05–0.25. Pore size distributions were calculated from adsorption branch using the Barrett–Joyner–Halenda (BJH) method. The total pore volumes were estimated from the amounts adsorbed at a relative pressure (P/P0) of 0.99. High resolution scanning electron microscopy (HRSEM), field-emission scanning electron microscopy (FESEM) and scanning electron microscopy (SEM) were undertaken on a HITACHI S-5500, HITACHI SU 8010 and JSM 6360 LV microscope operating at an accelerating voltage of 1–30 kV, respectively. Transmission electron microscopy (TEM) was performed using a JEOL JEM-2010 at an acceleration voltage of 120 kV. FT-IR spectra were collected with a TENSOR 27 IR spectrometer in the range of 4000–400 cm1 using KBr pellet. 13 C (100.5 MHz) cross-polarization magic angle spinning (CPMAS), 31P (161.8 MHz) and 27Al (79.4 MHz) MAS solid-state NMR experiments were recorded on a BRUKER DRX 400 spectrometer equipped with a magic-angle spin probe in a 4-mm ZrO2 rotor. 13 C signals were referenced to tetramethylsilane, 31P NMR signal was referenced to H3PO4 (85 wt%). The experimental parameters were 6-kHz spin rate, 2-s pulse delay, 6-min contact time, for 13C CP-MAS NMR experiments; 8-kHz spin rate, 3-s pulse delay, 10-min contact time for 31P MAS NMR experiments. Thermal analysis (TGA and DTA) was carried out in air on a Perkin–Elmer Pyris Diamond TG-DTA 6300 at a heating rate of 5 °C min1 from room temperature to 800 °C. 2.4. Enrichment tests
2. Experimental section 2.1. Chemicals and reagents All materials were of analytical grade and used as received without any further purification. phenylphosphinic acid (PPA, C6H7O3P, 99%), aluminum nitrate nonahydrate, (Al(NO3)39H2O, P98%), a-cyano-4-hydroxycinnamic acid (CHCA, P99%, matrix use only), trifluoroacetic acid (TFA, P99%), acetonitrile (ACN, P99%) and proteins/peptides were purchased from Sigma–Aldrich. Other reagents were purchased from ShangHai Chemical Reagent. Inc. of Chinese Medicine Group. 2.2. Synthetic procedure Flower-like porous aluminum phenylphosphonate microspheres were synthesized by using C6H7O3P and Al(NO3)39H2O as the precursors under acidic condition. In a typical synthesis, 7.5 mL of 0.04 M C6H7O3P was added into a HNO3 solution (0.035 M) containing 7.5 mL of 0.04 M Al(NO3)39H2O, then, 0.44 mL of 1.5 M sodium hydroxide (NaOH) solutions was added into the above solution to tune the pH value to 1.6. The mixture was stirred for 30 min until a homogeneous solution was formed, and the resulted solution was transferred into a Teflon-lined autoclave and heated for 19 h at 100 °C under static conditions. The solid products were collected by centrifugation and washed with distilled water, respectively. The aluminum phenylphosphonates were denoted as AlPP-n, where n (n = 0.75, 1, 1.25, 2, 5, 19, and 72) is the hydrothermal treatment time at 100 °C. 2.3. Characterization Powder X-ray diffraction (XRD) patterns were recorded on an Empyrean powder diffraction system using Cu Ka radiation of 0.15406 nm wavelength. The nitrogen sorption experiments were performed at 77 K on a Micromeritics ASAP 3000 system. Prior to the measurement, the samples were outgassed at 120 °C for at
Enrichment tests toward peptides and proteins were performed, where the low concentrated solutions were prepared through a step-wise dilution manner. The microspheres were dispersed in water at a concentration of 10 mg/mL and 10 lL of the slurry was directly added to the prepared solutions. Then the supernatant was removed by centrifugation after 10 min enrichment and the microspheres were collected. For matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS), the microspheres were incubated with 1 lL of matrix solution (10 mg/mL CHCA in TFA/ACN/water, 0.1%/49.9%/ 50%, v/v/v) and analyzed on the plain steel MALDI plate. The MS spectra were collected accumulating 500 laser shots at 10 different spots on Bruker Autoflex II Smartbeam system and no smooth spectra were used. 3. Results and discussion 3.1. Aluminum phenylphosphonate flower-like microspheres Self-assembling in the form of aluminum phenylphosphonate flower-like microspheres was prepared by the reaction of equimolar amounts of phenylphosphinic acid (PPA) and aluminum nitrate (in a 1:1 molar ratio); NaOH solutions were then added to tune the pH value to 1.6. The morphology of the resultant aluminum phenylphosphonates (AlPP-19) with hydrothermal treatment 19 h was characterized by scanning electron microscopy (SEM) and transaction electron microscopy (TEM) with the results shown in Fig. 1. As can be seen from Fig. 1a, uniform and well-dispersed flower-like aluminum phenylphosphonate microspheres with an average diameter of 8 lm are observed. A SEM image (the left in Fig. S1) with a large amount of visible microspheres was also obtained in order to measure the particle size of aluminum phenylphosphonate microspheres. The diameter of aluminum phenylphosphonate microspheres was observed in the range of 5–13 lm and the maximum distribution located at 8 lm as shown in the right of Fig. S1, which can further confirm that the size of microspheres is
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Fig. 1. Morphological and structural characterizations: (a) SEM images; (b) TEM image; (c) high resolution TEM images; and (d) powder XRD pattern of aluminum phenylphosphonates (AlPP-19).
controllable. The morphology of the flowerlike nanostructures at a higher magnification is displayed in the inset of Fig. 1a, which reveals that these flowerlike microspheres are consisted of a multitude of micro-petals with smooth surfaces. These micro-petals, of thickness 25–80 nm and width 1–1.5 lm, were connected through a central core to form 3D flower-like hierarchical structures. The micro-petals-assembled flower-like morphology is further confirmed by TEM image with a large number of nano-flakes or petals clearly observed in Fig. 1b. Based on the typical TEM image of the cross-sections, the thickness of the petal is 50 nm, consistent with the SEM results. The high resolution TEM image shown in Fig. 1c further confirms that the nano-flakes have a layered structure with the inter-spacing between two layers about 1.1 nm. The structure of the resultant aluminum phenylphosphonate was investigated by powder X-ray diffraction (PXRD). In general, the as-synthesized metal oxides or metal phosphates from hydrothermal method show a poor degree of crystallinity. As shown in Fig. 1d, the observed two strong peaks at 2h of 3.7° and 7.4° correspond to the 100 reflection (23.8 Å), and the 200 reflection (11.9 Å), respectively, featuring the layer structures. There are other peaks at 11.0°, 13.7°, 18.6°, 19.2°, 20.9° and 26.8°. On the basis of these peak positions, the d-values (in Å) are calculated to be 8.0, 6.5, 4.8, 4.6, 4.2 and 3.3, corresponding to 300, 40–1, 30–2, 51–1, 510 and 71–2 facets of Al2(O3PC6H5)3H2O, respectively (Fig. 1d) [12,13]. A layered structure was formed in which phenyl molecules were packed inside the interlayer spacing of 11.9 Å. Such a layered structure would offer many nano-channels favoring the transporting or diffusion of guest molecules. Al2(O3PC6H5)3H2O was further characterized by FT-IR and solid state NMR to verify their chemical compositions. The IR spectrum of Al(O3PC6H5)3H2O displays a band at 1040 cm1 characteristic Al–O–P framework vibrations, indicating that the material was constructed by the coordination of aluminum with phosphonate
groups (Fig. S2). The P–OH stretching vibration at 940–950 cm1 cannot be observed, which is in consistent with the formula of Al(O3PC6H5)3H2O. The 27Al MAS NMR spectrum clearly shows two peaks at 42.4 and 20.1 ppm, which correspond to aluminums with tetrahedral and octahedral oxygen environments, respectively. These 27Al MAS NMR results were also observed on Al2(O3PC6H5)3H2O [12,13], confirming the same coordination environment of the aluminum in both materials (Fig. 2a). Two resonances located at 2.1 ppm and 0.9 ppm present in the 31P MAS NMR spectrum (Fig. 2b) may be due to the different coordination modes of PO3. As expected, the 13C MAS NMR spectrum has the peak for the phenyl carbons centered at 131.5 ppm (Fig. 2c). Solid sate NMR results together with FT-IR result demonstrate the integrity of phenylphosphonate into Al(O3PC6H5)3H2O, provide a good fingerprint of the proposed formula, and confirm that the phenylphosphonate group is stable during the synthesis process. Further evidence of the porous structure of AlPP-19 was supported by N2 sorption analysis. The adsorption–desorption isotherm of AlPP-19 shows a type IV behavior with a H3-type in the relative pressure ranges of 0.5–0.9 (Fig. S3), echoing with SEM and TEM results that the presence of a non-uniform mesopore is consistent with the hierarchical structure. The corresponding Barrett–Joyner–Halenda (BJH) pore size distribution presents a broad peak in the range of 10 to 50 nm, mirroring the void space between the nano-flakes (Fig. S3) [31–33]. In addition, the Brunauer–Emmett–Teller (BET) specific surface area and total pore volume of AlPP-19 microspheres are calculated to be 15 m2 g1 and 0.10 cm3 g1, respectively. From element analysis, the content of C and H is 39.57% and 3.13%, respectively, a P/Al ratio of 1.5 was obtained from ICP which further confirm the formula Al2(O3PC6H5)3H2O. The aluminum phenylphosphonate micro-flowers of AlPP-19 show near neutral framework in water (f potential: 2.76 mV). Fe3+ doped AlPP-19 (Fe3+–AlPP-19) can also be
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Fig. 2. Chemical composition characterizations: (a) 27Al MAS NMR (b) 31P MAS NMR spectra and (c) 13C CP/MAS NMR of Al2(O3PC6H5)3H2O, AlPP-19. Refers to the side band.
synthesized by in-situ introducing Fe(NO3)39H2O as precursor and the Fe content is 0.8% from inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. After Fe doping, the resultant micro-flowers tend to be more aggregated (Fig. S4a) and BET surface area is increased to 54 m2 g1 (Fig. S4b). In a typical synthesis of aluminum phenylphosphonate microspheres, the acidity of the phenylphosphonate ions resulted in a pH value of the initial mixed solution of approximately 1.3. Subsequent addition of NaOH would increase the pH value with the gradual formation of aluminum phenylphosphonate precipitate [Eq. (1)]. 3þ
2Al
þ 3ðO3 PC6 H5 Þ2 þ H2 O ! Al2 ðO3 PC6 H5 Þ3 H2 O
ð1Þ
In order to understand the formation process of the flower-like hierarchical nanostructures, the morphology and the structure evolution of the as-prepared microspheres with different NaOH concentrations and aging times were investigated through SEM analysis. As shown in Fig. S5, highly aggregated microspheres were obtained without the addition of NaOH to tune the pH value. When the amount of NaOH addition was reached at 0.5 mL, highly dispersed micro-flowers can be synthesized. Further adding a larger amount of NaOH, the morphology is transforming to hierarchical structured micro-sheets. These results indicate the product morphology is significantly affected by the pH value in the synthesis solution. Micro-flowers are formed at pH regime of 1.6–1.7 and at lower pH value, and the microspheres would be aggregated; however, increasing the pH value to 1.8 would result in the formation of irregular micro-sheets. 3.2. Mesoporous hierarchical aluminum phosphate microspheres The thermal behavior of the product was characterized via the thermogravimetric analysis (TGA) under air atmosphere (Fig. S6). From room temperature to 150 °C, there is a weight loss up to about 3.9%, which can be attributed to the loss of one water molecule and a small amount of physical adsorbed water. The weight
loss between 400 and 650 °C accounting for about 36% is due to the decomposition of organic framework. After heat treatment at 550 °C for 2 h, the sample was decomposed as amorphous aluminum phosphate based on the result of PXRD (Fig. S7). The SEM image of the calcined AlPO4 as shown in Fig. 3a reveals no visible change in particle size and morphology after annealing at 550 °C. Uniform mesopores of 5 nm can be observed on the surface of the micro-petals (Fig. 3b) and typical IV isotherm can be observed with the surface area and pore volume increased to 103 m2 g1 and 0.24 cm3 g1, respectively (Fig. 3c). Noteworthy is that the presence of uniform mesopores with 5.5 nm (Fig. 3b and d) may be resulted from the decomposition of organic groups and the reconstruction of the frameworks during the calcination step. It provides a new synthetic method for mesoporous metal phosphates. 3.3. Formation mechanism Fig. 4a shows the SEM images of aluminum phenylphosphonate synthesized at different times during the hydrothermal treatment at 100 °C. No solid products can be obtained at 0.5 h reaction. In the early stage (0.75 h), irregular micro-sheets were formed; subsequently, these micro-sheets were grown and populated by other newly formed smaller nano-sheets or spheres (1 h). When the reaction time reached 1.25 h, SEM image indicates the small micro-flowers were becoming larger with corolla size of 2 lm which were assembled by emerging these loosely aggregated micro-petals. Larger micro-flowers with 7 lm size were obviously formed at 2 h and the thickness of the petals is identified at 30 nm. With further reaction time extension to 5 h, the microflower corolla grew to 8 lm and hundreds of micro-petals were presented in one single flower. When the reaction time was 19 h, the thickness of the micro-petals was continuously increased to average 50 nm but with no obvious change in the corolla size. After 19 h, the morphology and size of the flowers remained basically unchanged and were similar to 19 h, as shown in Fig. 4a with
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Fig. 3. (a and b) SEM images, (c) nitrogen adsorption–desorption isotherm and (d) pore size distribution of AlPP-19 after calcinations at 550 °C for 2 h.
Fig. 4. Formation of aluminum phenylphosphonate micro-flowers: (a) SEM images as a function of aging time and (b) a schematic illustration of the proposed formation mechanism of aluminum phenylphosphonate micro-flowers.
reaction time for 72 h, which may be due to the completion of the reactant supply. The PXRD patterns of the sample synthesized at 0.75 and 72 h (Fig. S8) indicate the Al2(O3PC6H5)3H2O was formed at the initial stage, and the phase was maintained during the entire hydrothermal process. Certainly the crystallinity was improved with the extension of the hydrothermal reaction as indicated from the intensity of the characteristic peaks in XRD and SEM results. To clarify the growth process, the morphology evolution diagram of the 3D hierarchical porous micro-flowers is illustrated in
Fig. 4b. SEM images as a function of aging time as shown in Fig. 4a suggest the following mechanism for micro-flowers selfassembly. At the initial stage, micro-sheets with small crystals of aluminum phenylphosphonate were formed (Fig. 4b). Subsequently, nucleation and growth of aluminum phenylphosphonate crystals originated at the surface of micro-sheets to form the separate micro-petals through Oswald ripening, which is the key step underlying the formation of the micro-flowers. In the last stage, a synergistic growing process of Ostwald ripening and oriented
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Fig. 5. Enrichment and detection tests based on the hierarchical porous aluminum phenylphosphonate micro-flowers toward a standard peptide alpha-conotoxin IMI: (a) Control; (b) AlPP-19; (c) Fe3+–AlPP-19.
attachment would result in the complete formation of a branched flower-like structure (Fig. 4b). The details of the self-assembly growth mechanism of the flower-like hierarchical nanostructures will be investigated later with advanced in-situ characterization techniques. 3.4. Peptide detection Considering abundant aluminum ions on the surface nanoflakes of microspheres, the hierarchical aluminum phenylphosphonate porous micro-flowers were employed as capture agent to enrich low concentrated bio-molecules for matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI TOF MS) detection [34–36]. Alpha-conotoxin IMI, a functional peptide (sequence GCCSDPRCAWRC) was first used as a model bio-molecule, which can selectively block alpha-delta site of the muscle acetylcholine receptor. At a concentration of 7.4 nM, a clear peptide signal (signal strength 2700) at the m/z range of 1352 can be observed in the MS spectrum after enrichment by the microspheres, while no peptides can be detected in control without any enrichment (Fig. 5). Similar results can be obtained using the microspheres for the enrichment and detection of proteins. As displayed in Fig. S9, using cytochrome c as an example, the protein is only detectable after enrichment at a concentration of 39 nM. Interestingly, we found that by introducing metal ions (e.g. Fe3+) in the synthetic process, the peptides enrichment performance of the materials can be highly enhanced with signal strength over 12,000 (Fig. 5c, compared to Fig. 5b) due to the enhanced metal ion affinity on the surface [35]. The above results indicate the strong potential of microspheres constructed from phenylphosphonates and metal ions as promising alternatives for general capture and detection of low abundance peptides/proteins.
4. Conclusions In summary, organic–inorganic hierarchical porous aluminum phenylphosphonate micro-flowers have been successfully synthesized through a hydrothermal synthesis method. Various aluminum phenylphosphonates with different sizes and morphologies can be obtained by tailoring the synthesis parameters such as, the pH value of the reaction solution, or aging time during the hydrothermal reaction. On the basis of experimental results of morphology evolution with reaction time, the self-assembly of the flower-like hierarchical nanostructures was proposed to involve a two-stage growth process, namely Ostwald ripening and oriented attachment. Mesoporous aluminum phosphate microflowers with uniform 5.5 nm pores were synthesized by the direct calcination of the aluminum phenylphosphonate micro-flowers. Preliminary studies have demonstrated that the as-prepared
flower-like hierarchical nanostructures show a promising enrichment property toward alpha-conotoxin IMI and cytochrome c. The stable aluminum phenylphosphonate and aluminum phosphates with these special morphology and porous structure would be of great interest for the potential applications in many other fields such as catalysis, ion exchange, adsorption and bio-medicals. Based on this work, the synthesis of a series of novel organic–inorganic hybrid phenylphosphonate materials with advanced functions can be envisaged by simply adjusting the chemical precursors in the demonstrated synthesis protocol. Author contributions L.Q.Z performed the experiments with technical support from the coauthors and obtained data representation. S.X. and J.L. supervised the whole work. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Acknowledgments This work was supported by the National Natural Science Foundation of China (21173108) and the Opening Foundation of State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences (N-12-11). This work was also partially supported by the Australian Research Council (ARC) Discovery Project program (DP1094070). Appendix A. Supplementary materials Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcis.2014.04.008. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
F. Hoffmann, M. Froba, Chem. Soc. Rev. 40 (2011) 608–620. Q.H. Yang, J. Liu, L. Zhang, C. Li, J. Mater. Chem. 19 (2009) 1945–1955. K.J. Gagnon, H.P. Perry, A. Clearfield, Chem. Rev. 112 (2012) 1034–1054. B. Shpeizer, D.M. Poojary, K. Ahn, C.E. Runyan, A. Clearfield, Science 266 (1994) 1357–1359. S.R.J. Oliver, Chem. Soc. Rev. 38 (2009) 1868–1881. H.E. Katz, G. Scheller, T.M. Putvinski, M.L. Schilling, W.L. Wilson, C.E.D. Chidsey, Science 254 (1991) 1485–1487. G.K.H. Shimizu, R. Vaidhyanathan, J.M. Taylor, Chem. Soc. Rev. 38 (2009) 1430– 1449. L. Raki, C. Detellier, Chem. Commun. (1996) 2475–2476. P. Varhadi, M. Kotwal, D. Srinivas, Appl. Catal. A: Gen. 462–463 (2013) 129– 136. A.A. Anilloa, M.A. Villa-Garcíaa, R. Llavonaa, M. Suáreza, J. Rodrígueza, Mater. Res. Bull. 34 (1999) 627–640. J. Huang, A. Subbiah, D. Pyle, A. Rowland, B. Smith, A. Clearfield, Chem. Mater. 18 (2006) 5213–5222. A. Cabeza, M.A.G. Aranda, S. Bruque, D.M. Poojary, A. Clearfield, J. Sanz, Inorg. Chem. 37 (1998) 4168–4178.
Please cite this article in press as: L. Zhang et al., J. Colloid Interface Sci. (2014), http://dx.doi.org/10.1016/j.jcis.2014.04.008
L. Zhang et al. / Journal of Colloid and Interface Science xxx (2014) xxx–xxx [13] G. Chaplais, J. Le Bideau, D. Leclercq, H. Mutin, A. Vioux, J. Mater. Chem. 10 (2000) 1593–1601. [14] G. Guerrero, P.H. Mutin, A. Vioux, J. Mater. Chem. 11 (2001) 3161–3165. [15] N. Zakowsky, G.B. Hix, R.E. Morris, J. Mater. Chem. 10 (2000) 2375–2380. [16] C. Chen, W. Chen, J. Lu, D.R. Chu, Z.Y. Huo, Q. Peng, Y.D. Li, Angew. Chem.-Int. Ed. 48 (2009) 4816–4819. [17] J. Ge, J.D. Lei, R.N. Zare, Nat. Nanotech. 7 (2012) 428–432. [18] T.Y. Ma, Z.Y. Yuan, ChemSusChem 4 (2011) 1407–1419. [19] T.Y. Ma, H. Li, A.N. Tang, Z.Y. Yuan, Small 7 (2011) 1827–1837. [20] Y.J. Jia, Y.J. Zhang, R.W. Wang, J.J. Yi, X. Feng, Q.H. Xu, Ind. Eng. Chem. Res. 51 (2012) 12266–12273. [21] X. Shi, J.P. Li, Y. Tang, Q.H. Yang, J. Mater. Chem. 20 (2010) 6495–6504. [22] X. Shi, J. Liu, C.M. Li, Q.H. Yang, Inorg. Chem. 46 (2007) 7944–7952. [23] A. Subbiah, D. Pyle, A. Rowland, J. Huang, R.A. Narayanan, P. Thiyagarajan, J. Zon, A. Clearfield, J. Am. Chem. Soc. 127 (2005) 10826–10827. [24] Z.K. Wang, J.M. Heising, A. Clearfield, J. Am. Chem. Soc. 125 (2003) 10375– 10383. [25] C. Serre, J.A. Groves, P. Lightfoot, A.M.Z. Slawin, P.A. Wright, N. Stock, T. Bein, M. Haouas, F. Taulelle, G. Ferey, Chem. Mater. 18 (2006) 1451–1457.
7
[26] H.G. Harvey, J. Hu, M.P. Attfield, Chem. Mater. 15 (2003) 179–188. [27] K. Maeda, Y. Kiyozumi, F. Mizukami, Angew. Chem.-Int. Ed. 33 (1994) 2335– 2337. [28] S. Cabrera, J. El Haskouri, C. Guillem, A. Beltran-Porter, D. Beltran-Porter, S. Mendioroz, M.D. Marcos, P. Amoros, Chem. Commun. (1999) 333–334. [29] S. Oliver, A. Kuperman, G.A. Ozin, Angew. Chem.-Int. Ed. 37 (1998) 47–62. [30] M. Tiemann, M. Froba, Chem. Mater. 13 (2001) 3211–3217. [31] X.F. Yang, C.J. Jin, C.L. Liang, D.H. Chen, M.M. Wu, J.C. Yu, Chem. Commun. 47 (2011) 1184–1186. [32] J. Liu, S.Z. Qiao, H. Liu, J. Chen, A. Orpe, D.Y. Zhao, G.Q. Max Lu, Angew. Chem.Int. Ed. 50 (2011) 5947–5951. [33] J. Liu, H.Q. Yang, F. Kleitz, Z.G. Chen, T.Y. Yang, E. Strounina, G.Q. Max Lu, S.Z. Qiao, Adv. Funct. Mater. 22 (2012) 591–599. [34] K. Zhang, D. Zheng, L.L. Hao, J.I. Cutler, E. Auyeung, C.A. Mirkin, Angew. Chem.Int. Ed. 51 (2012) 1169–1172. [35] H.Q. Qin, P. Gao, F.J. Wang, L. Zhao, J. Zhu, A.Q. Wang, T. Zhang, R. Wu, H.F. Zou, Angew. Chem.-Int. Ed. 50 (2011) 12218–12221. [36] K. Qian, W. Gu, P. Yuan, F. Liu, Y. Wang, M. Monteiro, C. Yu, Small 8 (2012) 231–236.
Please cite this article in press as: L. Zhang et al., J. Colloid Interface Sci. (2014), http://dx.doi.org/10.1016/j.jcis.2014.04.008