FexOy

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Formaldehyde Controlling Synthesis of Multishelled SiO2/FexOy Hollow Porous Spheres Yunfei Chang, Yuze Li, Jingchuan Song, Miao Zhao, Jing Guo, Qingda An, Yumei Gong, and Qipeng Guo Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b00607 • Publication Date (Web): 26 Jun 2018 Downloaded from http://pubs.acs.org on June 26, 2018

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Formaldehyde Controlling Synthesis of Multishelled SiO2/FexOy Hollow Porous Spheres Yunfei Changa, Yuze Lib, Jingchuan Songc, Miao Zhaoa, Jing Guoa, Qingda And, Yumei Gonga,e*, and Qipeng Guoe* a

. School of Textile and Material Engineering, Dalian Polytechnic University, Dalian, 116034, China. b c

. School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300350, China.

. Changyuan Group Co., Ltd. Shenzhen, Guangdong, 518057, China.

d

. School of Light Industry and Chemical Engineering, Dalian Polytechnic University, Dalian, 116034, China. e

. Institute for Frontier Materials, Deakin University, Locked Bag 20000, Geelong, Victoria 3220, Australia. Corresponding Author [email protected]; [email protected]

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ABSTRACT. A concise and facile sol-gel method to prepare multiple magnetic SiO2/FexOy hollow porous spheres was developed. A series of SiO2/FexOy hollow porous spheres consisting of single shell, yolk-shell, double shells and triple shells could be obtained by simply adjusting formaldehyde amount, as Fe(acac)3 was used as the shell forming promoter. Only as the formaldehyde amount increases, the morphology of the as prepared hollow spheres changed from single-shelled, yolk-shelled, double-shelled, to triple-shelled, and then turn back. The spheres possess large specific surface area (∼ 966 m2/g), uniform mesoporous (∼ 4.5 nm), and large pore volume (1.37 cm3/g). Moreover, the yolk-shelled spheres have been successfully used in in-situ adsorbing and reducing heavy metal ions in aqueous solution, the results suggested that it was an efficient adsorbent and convenient to concentrate from water. Keywords. multishelled hollow spheres; nanoreactor; adsorbent


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1. Introduction Nanosized multishelled hollow mesoporous spheres have attracted much attention due to their potential applications in adsorption,1-3 catalysis,4-9 reactors,10-11 etc,12-20 depending on their size and complex hierarchical morphology. The preparation of multishelled hollow nanostructured materials is mainly carried out by using various template-assisted methods, such as hard-21-26 and soft-template.27-33 The hard-template methods are concise and straightforward, prefered adopted in some attempts to prepare multishelled hollow structures. Huang et al.25 and Wong et al.26 synthesized triple-shelled hollow SiO2 and Au@SiO2 nanospheres respectively through this approach. However, this strategy needs to be improved since the complicated and time consuming process and the hard template surface uniformity of precursor coating. Compared with hard-template, the soft-template method requires more serious experimental conditions such as pH, temperature, solvent, ionic strength, concentration of organic templates, and inorganic additives.27 Zhao et al.28 synthesized monodisperse multi-shelled periodic mesoporous organosilica hollow spheres via a facile and effecient multi-interface transformation approach involved in cetyltrimethyl ammonium bromide (CTAB) surfactant-directed sol−gel processes and a one-step hydrothermal treatment. Xu et al.29 synthesized adjustable multi-shelled hollow Cu2O spheres by using self-assemblied multi-vesicles of CTAB, which depends strongly on the concentration. Also, Liu et al.30 and Gu et al.31 prepared multi-shelled mesoporous hollow SiO2 nanospheres and mesoporous hollow carbon nanospheres respectively with tunable shell number by a similar process. However, the self-assemblied surfactant vesicle templates are usually unstable and the morphology is difficult to control exactly. Therefore, it is still a great challenge to develop concise process to synthesize well-defined tunable microstructures in these intriguing hollow nanospheres by controlling simple parameters.


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Song et al.34, 35 reported controllable synthesis of hollow mesoporous SiO2 particles through a facile one-pot sol–gel method in 2015 and 2017 by adjusting reagent amount such as the ratio of ethanol to water, TEOS, and total of 3-aminophenol and formaldehyde when the ratio of 3aminophenol to formaldehyde is 1:2, in preparing the sacrificial soft template. Here, considered the reaction activity of 3-aminophenol with formaldehyde and the size monodispersity of the resultant resin particles,36 3-aminophenol/formaldehyde resin is also chosen as the soft sacrificial template to prepare nanosized multishelled magnetic porous spheres (MSMPSs). This mainly involves a concise one-pot process and the number of shells (1 − 3) can be well controlled by simply adjusting the amount of one reagent formaldehyde. The MSMPSs possess a high surface area (∼ 966 m2/g), uniform mesoporous (∼ 4.5 nm), and large pore volume (1.37 cm3/g). Moreover, only as the formaldehyde amount increases, the morphology of MSMPSs changes from single-shelled, yolk-shelled, double-shelled, to triple-shelled, and then turn back. The MSMPSs are used as nanoreactors to synthesize MSMPSs-graft-polyacrylonitrile (MSMPSs-gPAN) followed by transforming the cyano groups to amidoxime groups to result in MSMPSs-gpolyamidoxime (MSMPSs-g-PAO), which is used as an adsorbent to in-situ adsorb and reduce heavy metal ions. It is verified effecient; the obtained particle is magnetic and expected to be suitable in targeted adsorption. 2. Experimental Section 2.1. Chemicals. Cetyltrimethyl ammonium bromide (CTAB) were purchased from Guangfu fine chemical research institute (Tianjin, China). 3-Aminophenol was purchased from Aladdin Industrial Corporation (Shanghai, China). Ammonia aqueous solution (25%), formaldehyde (37 wt%), tetraethylorthosilicate (TEOS) and ethanol were purchased from Kermel Reagent (Tianjin, China). Ferric acetylacetonate (Fe(acac)3) was purchased from Xiya Reagent (Chengdu, China).


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N,N-dimethylformamide (DMF) and ceric ammonium nitrate (CAN) were purchased from Sigma-Aldrich. Acrylonitrile (AN) was purchased from Tian-jin Fuchen Chemical Reagent Factory (China). K2Cr2O7, Na2CO3, and hydroxylamine hydrochloride (NH2OH·HCl) were purchased from Chengdu Kelong Chemical Reagent Co., Ltd. (China). All chemicals were used as received. 2.2. Multishelled Magnetic Porous Spheres (MSMPSs) Synthesis and their Application. 2.2.1 MSMPSs Synthesis. As displayed in Scheme 1, 0.21 mg CTAB was dissolved in a mixture of water (19 mL), ethanol (8 mL), and ammonia aqueous solution (80 µL) under stirring for 30 min at 30 ºC, the temperature and the stirring speed was maintained till the end. Then 0.20 g 3aminophenol was dissolved into the mixture for another 30 min. Subsequently, 0.72 mL TEOS was added dropwise into the system followed by quick injection of a controlled amount of formaldehyde (0.30 ~ 2.10 mL). After about 1 h, 20 mL Fe(acac)3 (0.22 g) in ethanol solution was added dropwise into the system for another 4 h. The reaction mixture was separated by centrifugation at 6000 rpm for 6 min and the deposition was collected. Then, the deposition was dried under 60 ºC for 24 h and calcined in air from room temperature to 550 ºC for 6 h at a heating rate of 1 ºC/min to obtain multishelled magnetic porous spheres (MSMPSs).


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Scheme 1. Synthesis strategy of MSMPSs with different shell numbers tuned by formaldehyde. 2.2.2 MSMPS-g-PAO Preparation. 1 g yolk-shelled MSMPSs and 2 g CAN were dispersed in 100 mL distilled water under stirring at room temperature for 12 h. Then 3 mL acrylonitrile was added into the mixture dropwise to make it polymerized in vacuum desiccator at 0 ºC. Next, 40 mL distilled water was added into the reaction mixture followed by heating to 30 ºC under N2 for 60 min. The reaction mixture was separated by centrifugation at 6000 rpm for 15 min and the precipitate was washed in turn with DMF and water to remove homo-polyacrylonitrile, dried under 60 ºC for 24 h to result in MSMPSs-graft-polyacrylonitrile (MSMPSs-g-PAN). Subsequently, 3.47 g NH2OH·HCl was dispersed in 20 mL distilled water and the PH was adjusted to 7 by Na2CO3, the MSMPSs-g-PAN was added under stirring at 70 ºC for 4 h to result in MSMPS-g-polyamidoxime (MSMPS-g-PAO), which was collected by centrifugation and washed with water, dried under 60 ºC for 24 h. 2.2.3 Cr(VI) Adsorption on MSMPS-g-PAO. 50 mL of K2Cr2O7 in water with concentration (100 mg/L) in orange color was selected as the source of hexavalent chromium. 50 mg MSMPSg-PAO were dispersed into the solution under stirring at 25 ºC for 2 h. By using flame atomic


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absorption spectrophotometry the concentration of supernatant residue chromium ions were determined. The adsorption capacity was calculated according to our previous work.36 2.3 Characterization The morphology of the spheres was characterized by JEOL, JSM-6460LV scanning electron microscopy (SEM) and JEM-2000EX transmission electron microscopy (TEM). The X-ray diffraction pattern was obtained by using a Shimadzu XRD-7000 Maxima-D diffractometer with a rotating anode and Cu Kα radiation (λ = 0.154 nm). The N2-sorption measurement was performed by using Micromeritics Tristar3000 at 77 K, the specific surface area and the pore size distribution were estimated using the BET and BJH methods. To determine the adsorption capacity of the as perpared MSMPSs-g-PAO Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) was carried out on Optima 8000. The magnetization curves measured at room temperature by using physical property measurement system dynacool (PPMS), respectively. 3. Results and Discussion During the synthesis process, in the mixture of ethanol, water, ammonia aqueous solution, cetyltrimethyl ammonium bromide (CTAB), tetraethylorthosilicate (TEOS), 3-aminophenol, formaldehyde, and Fe(acac)3, the reaction mechanism is very complicated.37 Depending on the reagent adding sequence, 3-aminophenol is attacked at ortho- and para-positions of the phenol ring or the amino group by formaldehyde first due to its faster hydrolysis rate than TEOS and gel to generate phenolic resin microspheres (PRMSs) (Figure S1a) under the catalysis of ammonia. These PRMSs act as sacrificial templates for the deposition of SiO2 oligomers released from TEOS and assembled with CTAB (SiO2/CTAB) and the subsequent adsorption of the Fe(acac)3 to form composite spheres (Figure S1b) and prepare MSMPSs. During the process of Fe(acac)3


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adsorption, the CTAB next to SiO2 deposited on PRMSs is washed by ethanol and replaced by Fe(acac)3.38 The formaldehyde improves the PRMS formation process and induces the number of PRMSs to increase; the adsorption thickness of SiO2/CTAB layer decreases. As a result, Fe(acac)3 passes through the SiO2/CTAB layer and adsorbs on the resin microspheres easily. As is calcined, all the organic components in the composite spheres are removed to obtain mesoand micro-pores, Fe(acac)3 forms FexOy to make the SiO2 shell reinforced in the MSMPSs. During this process, the adsorbed Fe(acac)3 and SiO2/CTAB simultaneously receive two forces of a cohesive force (σco) coming from the inner resin and an adhesive force (σad) from the outer SiO2/CTAB deposition shell.39 The σco makes the inner phenolic resin shrink inwards while the σad resists the inward shrinkage during removal of the organic phases through calcination, which manipulates the morphology of the MSMPSs.39 At the same time, the bulk and electron densities of these PRMSs, depending strongly on the substitution degree of the hydrogen at ortho- and para-positions on the phenol ring and the amino group with formaldehyde, will also influence the deposition amount of SiO2/CTAB and Fe(acac)3 on the composite spheres and accordingly play a role in the resultant MSMPSs morphology formation. The PRMS bulk and electron densities increase with the substitution degree of the hydrogen by electron donating hydroxymethyl group at the above positions in 3aminophenol.40 Hence, the adsorbed Fe(acac)3 on PRMSs increases with the substitution degree. In some cases, Fe(acac)3 may enter into the PRMSs. It increases the adhesive force (σad) during the heterogeneous calcination contraction process. This controllable σad is expected to be the key manipulation factor of the hollow spheres interior structure.39 Thus, tuning the adsorbed Fe(acac)3 amount should be an effective way to adjust the MSMPS morphology. It is notable that the substitution degree of the hydrogen at the above positions in 3-aminophenol molecules


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depends on the formaldehyde amount in the reaction system; the Fe(acac)3 can react with the free formaldehyde and influence the adsorbing ability by the PRMSs. The above analysis suggests that the formaldehyde amount in the reaction system will play a key role in the resultant MSMPSs morphology. Typical SEM and TEM images of the MSMPSs prepared at different formaldehyde amounts are shown in Figure 1 and Table S1. Figure 1 shows clearly that all of the MSMPSs are in a spherical morphology and have different interior structures. Figures 1a and 1b indicate that the spheres obtained at formaldehyde 0.3 mL have a typical hollow structure with an average outer diameter and shell thickness ~ 665 nm and ~ 148 nm, respectively. Moreover, as shown in the inserted SEM image in Figure 1a, the shell consists of two layers; the inner layer sized ~ 74 nm is loose, but the outer sized also ~ 74 nm is dense. When formaldehyde amounts to 0.6 mL, the resultant spheres have a yolk-shelled morphology, as shown in Figures 1c and 1d. The diameters of the outer hollow spheres and the inner solid core are ~ 477 and 129 nm, respectively, the shell thickness is ~ 38 nm. Figures 1e and 1f manifest that double-shelled spheres form under formaldehyde 0.9 mL. The diameter and shell thickness are ~ 381 and 30 nm for the outer shell, and ~ 150 and 9 nm for the inner one, respectively. When formaldehyde amounts further to 1.2 mL, more complicated triple-shelled hollow spheres are obtained, as shown in Figures 1g and 1h. The average diameters of the outer, the second outer, and the innermost hollow spheres are ~ 404, 120 and 42 nm, and the thickness of these shells are ~ 30, 12 and 6 nm, respectively. As formaldehyde amounts further, the shell number of the obtained MSMPSs amazingly decreases. The morphologies of the MSMPSs formed at formaldehyde 1.8 mL are double-shelled and those formed at formaldehyde 2.1 mL are yolk-shelled again (Figures S2a and S2b). These results


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clearly suggest that the amount of formaldehyde is a key factor in the complex MSMPSs morphologies formation. On the other hand, the effect of other factors such as Fe(acac)3 and the addition sequence of the TEOS and Fe(acac)3 is examined. Without Fe(acac)3, only solid SiO2 spheres sized ~ 110 nm are observed as formaldehyde amounts 0.6 mL (Figure S3a). It suggests that the hollow morphology forms here is very different from the hollow spherical morphology prepared in refs 34 and 35; Fe(acac)3 promotes the hollow structure formation here. Moreover, as another factor, the addition sequence of TEOS and Fe(acac)3, is interchanged, the shell structure can not be obtained neither (Figure S3b). In addition, the composition of the MSMPSs is analyzed by SEM EDS and the results show that all these MSMPSs consist of O, Si, and Fe elements. Typical images of the SEM and the element distribution in the MSMPSs formed at formaldehyde 1.2 mL are shown in Figure 2. Figures 2b, 2c, and 2d display the distribution of element O, Si, and Fe, respectively. They exhibit that all the three elements distribute uniformly in the nanospheres, the ratio of O:Si:Fe is ~ 74.44:23.13:2.43.


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Figure 1. The SEM (left column) and TEM (right column) images of the MSMPSs obtained at formaldehyde 0.3 mL (a and b), 0.6 mL (c and d), 0.9 mL (e and f), and 1.2 mL (g and h), all scale bars are 100 nm.


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Figure 2. The SEM image (a) and elemental mapping of O (b), Si (c), and Fe (d) of the MSMPSs synthesized at formaldehyde 1.2 mL. The above results suggest that the complex MSMPSs morphology formation with formaldehyde amount is as follows. As far as the synthesis process of phenolic resin in this system, a molar ratio of 3-aminophenol to formaldehyde is 1:1.2 ~ 5.0;37, 40 the polymerization rate increases with the formaldehyde amount. When formaldehyde amounts to 0.3 mL, corresponding to the molar ratio of 3-aminophenol to formaldehyde 1:2, the formaldehyde amount is little, the number of PRMSs is few, the PRMSs display a low bulk density and weak attraction of Fe(acac)3, which makes plenty of the deposited SiO2/CTAB adsorbed on the PRMSs and forms a thick layer; Fe(acac)3 lacks ability to be adsorbed on the phenolic resin surface through passing across the whole as-deposited SiO2/CTAB layer. Hence, one kind of composite sphere consisting of phenol resin core covered by a layer of SiO2/CTAB and outer layer of SiO2/CTAB/Fe(acac)3 forms. After calcining in air to remove all the organic components, a


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hollow sphere with a double-layered shell consisting of loose SiO2 inner layer and SiO2/FexOy outer layer is obtained, as shown in Figures 1a and 1b. As the formaldehyde amounts to 0.6 mL, the molar ratio of 3-aminophenol to formaldehyde is 1:4. In this case, the PRMSs generation rate is elevated and the resin displays a strong attraction to Fe(acac)3 due to the higher substitution degree of the hydrogen by electron donating hydroxymethyl group at ortho- and para-positions on the phenol ring. And accordingly the Fe(acac)3 can enter deeper to the layer of SiO2/CTAB to form resin@Fe(acac)3/SiO2/CTAB composite spheres. When calcined in air the competition between σco and σad may cause the SiO2/FexOy to aggregate and form a solid sphere as a yolk located within the SiO2/FexOy shell,39 as shown in Figures 1c and 1d.Moreover, these two forces rely on the property of the phenolic resin and then also the substitution degree. When the formaldehyde increases further to 0.9 mL, the molar ratio of 3-aminophenol to formaldehyde is 1:6. The formaldehyde is excess, a thinner SiO2/CTAB layer is formed and the hydrogen on the 3-aminophenol is substituted further by hydroxymethyl group and hence the phenolic resin shows a stronger attraction to Fe(acac)3. The adsorbed Fe(acac)3 amount on PRMSs increases and σad increases,39 thereby the double-shelled hollow spheres are observed as shown in Figures 1e and 1f. With a further formaldehyde increase (1.2 mL) to the molar ratio 1:8 of 3-aminophenol to formaldehyde, the Fe(acac)3 adsorbed on the phenolic resin continuously increases and the σad increases further, which results in the triple-shelled hollow spheres formation as shown in Figures 1g and 1h. With the formaldehyde increasing further, the free formaldehyde can react with Fe(acac)3 and decrease its attraction by the phenolic resin, the Fe(acac)3 content in the composite spheres decreases; the σad thus decreases, double-shelled


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hollow spheres obtained at the molar ratio of 3-aminophenol to formaldehyde 1:12 (Figure S2a) and yolk-shelled spheres obtained at the ratio of 1:14 (Figure S2b). The XRD profiles shown in Figure 3 display all four MSMPSs exhibiting perfect peaks at 2θ = 33.2o, 35.7o, 49.5o, 54.1o, and 64.0o, corresponding to the (104), (110), (024), (116), and (300) planes respectively of α-Fe2O3 phase (PDF#87-1165), and the peaks at 2θ = 30.4o, 35.7o, 53.9o and 63.2o, corresponding to the (220), (311), (422)and (440) planes respectively of Fe3O441 (PDF#75-0449). Together with the HRTEM image of the MSMPSs obtained at formaldehyde 1.2 mL as shown in Figure 4 which also shows two lattice parameters of Fe2O3 (0.18 nm, corresponding to 024 plane, as shown in the inserted TEM image a) and Fe3O4 (0.29 nm, corresponding to 220 plane, as shown in the inserted TEM image b), the iron oxide can then be defined as FexOy. Furthermore, the XRD profile also shows that there is a broad peak between 2θ = 15 ~ 30o, corresponding to the amorphous SiO2. Therefore, this one-pot process to synthesize MSMPSs route indeed provides a feasible way to design and synthesize magnetic hollow particles with desired morphologies and properties.

Figure 3. XRD profiles of all four MSMPSs obtained from different formaldehyde amounts, (a) 0.3 mL, (b) 0.6 mL, (c) 0.9 mL (d) 1.2 mL.


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Figure 4. The HRTEM image of the MSMPSs obtained at formaldehyde 1.2 mL. Based on the above analysis of the morphology and structure, the magnetization curves measured at room temperature of the MSMPSs are presented in Figure 5. It shows a perfect hysteresis loop. The saturated magnetization of hollow spheres, yolk-shelled spheres, doubleshelled spheres, and triple-shelled spheres is 4.2, 4.8, 5.4, and 5.7 emu·g-1 respectively. The hollow spheres have the smallest saturation magnetization moment due to the content of FexOy is very low. While the saturation magnetization of the other three spheres is higher since the content of FexOy increases due to the strong phenol resin adsorption of Fe(acac)3 with the increase amount of formaldehyde. The data also present 0.37 × 10-4, 2.0 × 10-4, 2.0 × 10-4, and 1.6 × 10-4 emu·g-1 remanences and 0.16, 3.44, 6.7, and 16.0 Oe coercivities for hollow spheres, yolk-shelled spheres, double-shelled spheres, and triple-shelled spheres respectively. When the yolk-shelled MSMPSs are put near a magnet they are aggregated at once, as shown in the inserted image in Figure 5.


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Figure 5. Magnetization curve for MSMPSs prepared at formaldehyde 0.3 mL, 0.6 mL, 0.9 mL, 1.2 mL respectively. The inserted shows yolk-shelled spheres aggregated in ethanol solution by an external magnet. For the four MSMPSs, the specific surface area (SSA) and the pore volume (PV) are measured through the adsorption and desorption of N2 and the adsorption-desorption isotherms are shown in Figure 6. Obviously, all four MSMPSs exhibit perfect type-IV isotherms, indicative of the presence of mesopores. The SSA and the PV of the hollow spheres, yolk-shelled spheres, double-shelled and triple-shelled spheres are 966, 954, 737, and 580 m2·g-1, and 1.37, 0.96, 0.67, and 1.09 cm3·g-1 respectively, with a relatively uniform pore size ~ 4.5 nm. On the other hand, combined with the morphology as shown in Figure 1, the hollow spheres have the highest SSA and PV may be due to the inner loose layer of the shell. The triple-shelled spheres have the lowest SSA but a relatively high PV because there are two kinds of pores sized 2 nm and 4.5 nm, respectively.


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Figure 6. N2 adsorption-desorption isotherm and the corresponding pore size distribution curves of the MSMPSs obtained at different formaldehyde. (a) 0.3 mL, (b) 0.6 mL, (c) 0.9 mL (d) 1.2 mL. The as-prepared MSMPSs is used as a support to graft polyacrylonitrile (PAN) followed by transforming the cyano groups (AN) in PAN into amidoxime groups (AO) and obtained MSMPSs-graft-poly(amidoximated acrylonitrile) (MSMPSs-g-PAO), which then is used as an adsorbent to in-situ adsorb and reduce heavy metal ions.36 When the yolk-shelled MSMPS-gPAO is applied in in-situ adsorbing and reducing Cr(VI) to Cr(III), the yellow K2Cr2O7 solution fades rapidly and the ruddish brown particles can be aggregated by a magnet (Figure S4). The adsorption chromium amount is 47 mg·g-1, indicative of an excellent adsorption ability to Cr(VI). 4. Conclusions In summary, we have demonstrated a simple and efficient strategy to synthesize MSMPSs with single-shelled, yolk-shelled, double-shelled, and triple-shelled morphology, respectively. The shell number can be easily controlled by simply varying formaldehyde amount. The


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MSMPSs are magnetic and possess a high surface area (∼ 966 m2/g), uniform mesoporous (∼ 4.5 nm), large pore volume (1.37 cm3/g) The MSMPSs should have great application in adsorption, ferrofluids, catalysts, etc. ACKNOWLEDGMENT This work is supported by Natural Science Foundation of Liaoning Province (201602048) and the Fund of China Scholarship Council (20163035). ASSOCIATED CONTENT Supporting Information Detailed information on the morphologies of the PRMs, Fe(acac)3/SiO2/CTAB composite spheres, nanoparticles prepared at formaldehyde 1.8 and 2.1 mL, no shell formation without Fe(acac)3 or interchange the addition order of Fe(acac)3 and TEOS, and application in in-situ adsorbing and reducing Cr(VI) to Cr(III). This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author Yumei Gong: [email protected]; Qipeng Guo: [email protected] Notes The authors declare no competing financial interests. REFERENCES


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for the Table of Contents (TOC) graphic Formaldehyde Controlling Synthesis of Multishelled SiO2/FexOy Hollow Porous Spheres

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Table of contents and all the graphics

A concise and facile one-pot method to prepare multiple SiO2/FexOy hollow mesoporous spheres by simply adjusting one reagent is developed.


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Scheme 1. Synthesis strategy of MSMPSs with different shell numbers tuned by formaldehyde.


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Figure 1. The SEM (left column) and TEM (right column) images of the MSMPSs obtained at formaldehyde 0.3 mL (a and b), 0.6 mL (c and d), 0.9 mL (e and f), and 1.2 mL (g and h), all scale bars are 100 nm.


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Figure 2. The SEM image (a) and elemental mapping of O (b), Si (c), and Fe (d) and the contain (e) of the MSMPSs synthesized at formaldehyde 1.2 mL.


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Figure 3. XRD profiles of all four MSMPSs obtained from different formaldehyde amounts, (a) 0.3 mL, (b) 0.6 mL, (c) 0.9 mL (d) 1.2 mL.


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Figure 4. The HRTEM image of the MSMPSs obtained at formaldehyde 1.2 mL.


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Figure 5. Magnetization curve for MSMPSs prepared at formaldehyde 0.3 mL, 0.6 mL, 0.9 mL, 1.2 mL respectively. The inserted shows yolk-shelled spheres aggregated in ethanol solution by an external magnet.


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Figure 6. N2 adsorption-desorption isotherm and the corresponding pore size distribution curves of the MSMPSs obtained at different formaldehyde. (a) 0.3 mL, (b) 0.6 mL, (c) 0.9 mL (d) 1.2 mL.


FexOy

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