Artigo Revisado por pares

Synthesis, characterisation, and evaluation of core–shell Fe 3 O 4 /SiO 2 /polypyrrole composite nanoparticles

2018; Institution of Engineering and Technology; Volume: 13; Issue: 7 Linguagem: Inglês

10.1049/mnl.2017.0907

ISSN

1750-0443

Autores

Bei Li, Yongsheng Qiao, Jinhui An, Lazhen Shen, Qi Ma, Yong Guo,

Tópico(s)

Electrochemical sensors and biosensors

Resumo

Micro & Nano LettersVolume 13, Issue 7 p. 902-906 ArticleFree Access Synthesis, characterisation, and evaluation of core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles Bei Li, Bei Li School of Chemistry and Materials Science, Shanxi Normal University, Linfen, 041004 People's Republic of China School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorYongsheng Qiao, Yongsheng Qiao Department of Chemistry, Xinzhou Teachers University, Xinzhou, 034000 People's Republic of ChinaSearch for more papers by this authorJinhui An, Jinhui An School of Chemistry and Materials Science, Shanxi Normal University, Linfen, 041004 People's Republic of China School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorLazhen Shen, Corresponding Author Lazhen Shen shenlazhen@163.com School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorQi Ma, Qi Ma School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorYong Guo, Yong Guo School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this author Bei Li, Bei Li School of Chemistry and Materials Science, Shanxi Normal University, Linfen, 041004 People's Republic of China School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorYongsheng Qiao, Yongsheng Qiao Department of Chemistry, Xinzhou Teachers University, Xinzhou, 034000 People's Republic of ChinaSearch for more papers by this authorJinhui An, Jinhui An School of Chemistry and Materials Science, Shanxi Normal University, Linfen, 041004 People's Republic of China School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorLazhen Shen, Corresponding Author Lazhen Shen shenlazhen@163.com School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorQi Ma, Qi Ma School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this authorYong Guo, Yong Guo School of Chemistry and Environmental Engineering, Institute of Applied Chemistry, Shanxi Datong University, Datong, 037009 People's Republic of ChinaSearch for more papers by this author First published: 01 July 2018 https://doi.org/10.1049/mnl.2017.0907Citations: 4AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract This work reported a facile synthetic approach to synthesise core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles with the superparamagnetic Fe3O4 nanoparticles as the inner core. The core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles were prepared through a three-step approach involving co-precipitation for the synthesis of Fe3O4 nanoparticles, Stöber method for SiO2 intermediate layer coating and solvothermal methods for polypyrrole shell. The as-prepared nanoparticles were characterised using transmission electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analyses and vibration sample magnetometer. The particle size of the inner core Fe3O4 nanoparticles was found to be 15 ± 3 nm, and the thicknesses of the SiO2 shell and polypyrrole shell were ∼2.5 and ∼5 nm, respectively. From Fe3O4 nanoparticles to Fe3O4/SiO2 and then to Fe3O4/SiO2/polypyrrole composite nanoparticles, the magnetic saturation gradually decreases from 67 to 34 emu/g, then dropped to 7 emu/g. The as-prepared Fe3O4/SiO2/polypyrrole composite nanoparticles showed potential applications in drug and gene delivery systems. 1 Introduction Fe3O4 nanoparticles as a magnetic nanomaterial have been extensively applied in many fields, especially for magnetic induced targeting drug and gene delivery, which are due to their specific magnetic properties, non-toxicity and easy to synthesis [[1]-[4]]. While bare Fe3O4 nanoparticles tend to aggregate that limit their applications. After the further modification of Fe3O4 nanoparticles, the new and original properties will be introduced by the subsequent coating, such as the photothermal conversion efficiency can be acquired through the coating of photothermal material layers [[5]], and the luminescent materials have the ability to endow the nanocomposites with the dual modality fluorescence and magnetic resonance imaging and real-time monitoring drug release process [[6], [7]]. Thus, the multimodal therapy systems will be gained after the functionalisation of Fe3O4 nanoparticles with diverse coatings. Functionalisation of Fe3O4 nanoparticles with SiO2 not only defend nanoparticles from aggregations also endow many bonding sites for therapeutic molecules and further coatings [[8]-[12]]. Various methods have been applied for the preparation of Fe3O4/SiO2 nanocomposites, such as Stöber method, reverse microemulsion approach, one-pot polyol process and sonochemical method [[11], [13], [14]]. In the most previous studies, the Fe3O4 nanoparticles were dispersed in the mixture solution of ethanol, distilled water and ammonium hydroxide before the addition of silicon source tetraethyl orthosilicate (TEOS) to obtain few defined core–shell Fe3O4/SiO2 nanocomposites [[8], [10]]. Polypyrrole nanoparticles display high electrically conducting, stability and biocompatibility, also supply amino groups on their backbone for therapeutic agents linking, and potentially provide a new photothermal therapy agent for cancer treatment [[15], [16]]. Unfortunately, there is a bottleneck in the direct coating of polypyrrole on Fe3O4 nanoparticles, thus a surfactant or intermediate layer or combination of them is indispensable [[17]-[19]]. Usually, the modification of surfactant requires a tediously long stirring process, and the surfactant could not link uniformly on the Fe3O4 nanoparticles, which directly affect the coating of polypyrrole [[16], [18]]. In the study of Yao et al. [[18]], they used SiO2 coating as an intermediate layer, and for the linking of polypyrrole shell, the poly(N-vinylpyrrolidone) (PVP) was firstly absorbed on the surface of Fe3O4/SiO2 nanoparticles under a lengthy stirring of more than 24 h, and another 10 h stirring was also essential for the formation of polypyrrole. Herein, to prevent these problems, the core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles were prepared through a three-step approach involving co-precipitation for the synthesis of Fe3O4 nanoparticles, Stöber method for SiO2 intermediate layer coating and solvothermal methods for polypyrrole modification in this Letter. The second step of the coating of SiO2 directly determines the success coating of polypyrrole. The key to the second step of this experiment is to hydrolyse TEOS first, and then add Fe3O4 nanoparticles to the TEOS mixture at a suitable time to form a complete silica shell, instead of adding Fe3O4 nanoparticles before TEOS hydrolysis. Furthermore, we applied a simple and practicable hydrothermal approach in the absence of surfactants to fabricate the polypyrrole shell, the SiO2 coating was employed as an intermediate layer. For the formation of polypyrrole shell, the pyrrole monomers were firstly absorbed on the surface of the SiO2 intermediate layer via electrostatic interaction with only 1 h of stirring, and then the polypyrrole layer was obtained through in situ polymerisation without adding any surfactants under 8 h of hydrothermal reaction at 140°C. In this method, the time-consuming stirring processes of surfactant modification and polypyrrole generation could be best avoided, and the polypyrrole layers were more uniformly dispersing on the surface of Fe3O4/SiO2 nanoparticles. The as-prepared Fe3O4/SiO2/polypyrrole composite nanoparticles with superparamagnetic and photothermal stability polypyrrole shells will serve as a drug/gene carriers for cancer therapy. 2 Experimental section 2.1 Preparation of Fe3O4 nanoparticles Fe3O4 nanoparticles were prepared by co-precipitation method. In the typical synthesis, 3.6 g of anhydrous Fe2 (SO4)3 and 3.3 g of FeSO4 ·7H2 O were dissolved in 100 ml distilled water to be a homogeneous dark orange solution with magnetic stirring. An aqueous NaOH solution (5.1 g NaOH dissolved in 50 ml distilled water) was then injected into the above solution under vigorous stirring. The reaction was allowed to proceed with stirring for 5 h at room temperature. Finally, the products were filtered out and washed several times with ethanol and distilled water in turn, and dispersed in distilled water by the ultrasonic treatment of 3 min for the next step. 2.2 Preparation of core–shell Fe3O4/SiO2 composite nanoparticles Core–shell Fe3O4/SiO2 nanoparticles were synthesised by the Stöber method according to the previous study [[19]]. Generally, 50 ml of ethanol, 1 ml of deionised water, 2 ml of ammonium hydroxide (25%) and 300 μl TEOS were mixed under mechanical stirring in a 40°C water bath for hydrolysing and condensing of TEOS [[19], [20]]. After 10 min, 3 ml of a Fe3O4 solution containing about 100 mg Fe3O4 nanoparticles was added to this mixed solution. After the reaction was allowed to proceed for 12 h at room temperature, the products were collected by magnetic separation, followed by washing with distilled water and ethanol for several times, respectively, and finally dispersed in 20 ml distilled water by the ultrasonic treatment for 3 min for the pyrrole coating step. 2.3 Preparation of core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles A typical preparation of core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles was carried out according to the method reported previously [[21]]. Briefly, 300 μl of pyrrole monomer was dropped into the above Fe3O4/SiO2 nanoparticles solution under stirring. After stirring for 1 h, the mixture was transferred to a Teflon autoclave, and then (NH4)2S2O8 (APS) solution (0.1 g APS dissolved in 10 ml distilled water) was dropped slowly into the mixture, followed by reacting at 140°C for 8 h in Teflon autoclave. Then the autoclave was naturally cooled down to room temperature to harvest the precipitates using a magnet. After washed with distilled water and ethanol for several times, the final products were then dried at room temperature in air for several hours. 2.4 Characterisations A BDX-3300 model JEOL 100CX-II transmission electron microscope (TEM) was used to carry out the TEM measurements to investigate the morphology and the size of samples. X-ray powder diffraction (XRD) data was collected on a Bruker D8 Focus diffractometer. Fourier-transform infrared (FTIR) spectra of the samples were recorded on an FTIR-650 spectrometer. The magnetic measurement of the products was carried out in an MPMS SQUID vibrating sample magnetometer (VSM). Thermogravimetric analyses (TGA) were performed using TG 209 F3 Tarsus instrument under an air atmosphere with a heating rate of 10°C/min from room temperature up to 1000°C. 3 Results and discussions 3.1 Synthesis mechanism of core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles In this work, the core–shell Fe3O4/SiO2/polypyrrole composites nanoparticles were synthesised successfully. Fig. 1 illustrates the formation process and mechanism of core–shell Fe3O4/SiO2 nanocomposites and Fe3O4/SiO2/polypyrrole composites nanoparticles. As shown in the produce, the finally obtained nanocomposites consists of three parts, Fe3O4 magnetic core could endow the nanocomposites with the ability of magnetic-guided targeting drug/gene delivery and MRI, the SiO2 intermediate layer could not only prevent the magnetic nanoparticles from aggregations but exhibit the capability of connecting polypyrrole outer shell, and the photothermal therapy effect would be provided by the polypyrrole shell. First, the Fe3O4 magnetic core is fabricated via traditional co-precipitation method, which is easily accessibe and only needs simple reaction condition under room temperature. During the preparation of core–shell Fe3O4/SiO2 nanoparticles, we injected TEOS in the mixture of ethanol, distilled water and ammonium hydroxide and water bath at 40°C for the hydrolysis and condensation of TEOS. In the beginning, two or three TEOS were condensed into each other to form the chains to aggregate the primary silica particles. In 10 min or so, these primary silica particles are colloidally unstable and are ready to aggregate into large particles with surface charge large enough to prevent the irreversible Brownian aggregation [[22]]. At this time Fe3O4 nanoparticles were added and could aggregate with the primary SiO2 nanoparticles each other. Under stirring condition at room temperature, the produced primary SiO2 particles can aggregate around the magnetic nanoparticles due to the chemical affinity, when the amount of aggregated primary SiO2 particles up to the appropriate value, they can further grow to form SiO2 layers, and the clearly defined core–shell structure Fe3O4/SiO2 nanocomposites were harvested. Especially, the adding time of magnetic nanoparticles was also a decisive factor in this procedure, which was due to the formed primary SiO2 particles turned into single SiO2 nanoparticles instead of the layer structure after more than 20 min. Therefore, we should add the magnetic nanoparticles at the accurate time point, which was during a period of most primary SiO2 particles have been formed while there are no alone SiO2 nanoparticles are created. This is the essential difference between our adopted fabricating procedure and other similar methods. This Stöber method we applied will yield excellent effect for the harvest of nanocomposites containing magnetic core and SiO2 shell and the produced Fe3O4/SiO2 nanoparticles display outstanding thermal stability. Third, unlike another fabricating process, we employ a distinctive hydrothermal way without any surfactant to link the polypyrrole layer. The pyrrole monomers can fully adsorb on the surface of the obtained Fe3O4/SiO2 nanocomposites through electrostatic interactions under the action of stirring, and then polypyrrole layers subsequently result via in-situ polymerisation with no surfactant assisted under hydrothermal condition. At last the core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles are synthesised. Fig. 1Open in figure viewerPowerPoint Illustration of the preparation procedure of the core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles 3.2 TEM results The morphologies of bare Fe3O4, core–shell Fe3O4/SiO2 nanocomposites and core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles are presented in Fig. 2. As expected, the Fe3O4 nanoparticles as shown in Fig. 2a are well monodisperse and nearly uniform in dimension with particle size of 15 ± 3 nm. Compared with Fig. 2a, it is found that a visible silica layer with a thickness of about 2.5 nm deposits on the Fe3O4 nanoparticles inner core (Fig. 2b) and the magnetic core in the Fe3O4/SiO2 composite nanoparticles exist in the form of a single nucleus basically. Fig. 2c shows that the Fe3O4/SiO2 surrounded by polypyrrole shell can be clearly observed and the good uniformity core–shell Fe3O4/SiO2/polypyrrole nanoparticles were achieved. TEM image in Fig. 2c confirms the Fe3O4/SiO2/polypyrrole composites process a well-defined core/shell structure as the polypyrrole shell uniformly covers on the surface of Fe3O4/SiO2 composite nanoparticles. The average diameter of the composite nanoparticles is about 30 nm and the polypyrrole shell thickness is about 5 nm. However, when the Fe3O4 nanoparticles were added to the TEOS solution after mixing for 20 min, the silica will not be coated on the surface of the Fe3O4 nanoparticles to form free SiO2 nanoparticles rather than core–shell Fe3O4/SiO2 nanoparticles in the resulting product as shown in Fig. 2d. Fig. 2Open in figure viewerPowerPoint TEM images of a Bare Fe3O4 b Core–shell Fe3O4/SiO2 nanocomposites c Core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles d Free Fe3O4 and SiO2 nanoparticles 3.3 XRD results Fig. 3 shows the XRD patterns of bare Fe3O4, core–shell Fe3O4/SiO2 nanocomposites and core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles. The XRD pattern of Fig. 3a shows five characteristic peaks at 2θ = 30.54°, 35.60°, 43.34°, 57.32°, 63.00° related to their corresponding indices (220), (311), (400), (511) and (440), respectively. All diffraction peaks can be matched with the standard Fe3O4 reflections (JCPDS Card No. 89-0688), suggesting that the obtained samples are pure Fe3O4 with spinel structure [[2], [8]]. From Figs. 3b and c, it can be found that the same diffraction peaks appeared on the XRD patterns of the Fe3O4/SiO2 and Fe3O4/SiO2/polypyrrole nanoparticles, and the patterns can be easily indexed to Fe3O4 according to the reflection peak positions and relative intensities. A weak broad peak can be found around 2θ = 24° (Fig. 3b), indicating that the existence of the small mass fraction of amorphous SiO2 relative to Fe3O4 based on the thin thickness of silica shell [[9], [10]]. After being coated by polypyrrole, the diffraction intensity of the wide peak between 18° and 25° of 2θ increases obviously as shown in Fig. 3c due to a marked increase in thickness of polypyrrole shell [[17], [23]], indicating that amorphous polypyrrole exists in the sample. Fig. 3Open in figure viewerPowerPoint XRD patterns of a Bare Fe3O4 b Core–shell Fe3O4/SiO2 nanocomposites c Core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles 3.4 FTIR results The structural information and chemical component of the products are further identified by the FTIR spectroscopy. For comparison, the FTIR spectra for core–shell Fe3O4/SiO2 nanocomposites and Fe3O4/SiO2/polypyrrole composite nanoparticles, as well as pure Fe3O4 nanoparticles are recorded and shown in Fig. 4. It can be seen from Fig. 4, the bare Fe3O4, Fe3O4/SiO2 and Fe3O4/SiO2/polypyrrole nanoparticles all show the characteristic peaks, related to the Fe–O stretching vibration near 570 cm−1 [[3], [4]]. Compared to the bare Fe3O4 nanoparticles (Fig. 4a), three new absorption peaks around 467, 780 and 1100 cm−1 in Figs. 4b and c were observed, which are associated with the stretching vibration of Si–O, Si–O–Si and Si–OH bonds, respectively [[24], [25]]. Those bands are indicative of the existence of SiO2 in the Fe3O4/SiO2 nanoparticles. The band at 784 cm−1 as displayed in Fig. 4c changes from 780 cm−1 (Fig. 4b) due to the contribution of C–H ring out-of-plane bending of polypyrrole around 790 cm−1. The bands at 854, 928 and 1180 cm−1 in Fig. 4c are originated from the C–H out-plane and in-plane deformation of polypyrrole [[26]]. The peaks of =C–H in-plane vibration and C–N stretching vibration of polypyrrole are found at 1047 and 1319 cm−1, respectively [[27]]. The peaks near 1602 and 3430 cm−1 might be attributed to the stretching vibrations of –OH, which is assigned to OH− absorbed by the samples [[8]]. And Fe3O4/SiO2/polypyrrole nanoparticles exhibit more sharp peaks than that of Fe3O4 and Fe3O4/SiO2 at about 1602 and 3430 cm−1 due to the C=C stretching mode and N–H stretching vibration absorption band of polypyrrole, respectively [[18]]. These results confirm the presence of polypyrrole in the composite nanoparticles. Fig. 4Open in figure viewerPowerPoint FTIR spectra of a Bare Fe3O4 b Core–shell Fe3O4/SiO2 nanocomposites c Core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles In brief summary, both the XRD and FTIR results support the presence of Fe3O4 phase, as well as Si–O–Si vibrations in the obtained Fe3O4/SiO2, and –NH vibrations in the prepared Fe3O4/SiO2/polypyrrole composite nanoparticles. 3.5 Magnetic properties The diagram of the magnetisation versus magnetic field at room temperature for bare Fe3O4, core–shell Fe3O4/SiO2 nanocomposites and core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles are depicted in Fig. 5. All the samples have magnetic and there are no coercivity and residual magnetism in bare Fe3O4 and Fe3O4/SiO2/polypyrrole nanoparticles that endow them with superparamagnetism [[28]], which are the prerequisite for targeted drug and gene delivery systems. The bare Fe3O4 nanoparticles exhibit a saturation magnetisation of 67 emu/g as shown in Fig. 5a. The saturation magnetisation of the core–shell Fe3O4/SiO2 nanoparticles decreased to 34 emu/g after being coated with a layer of nonporous silica (Fig. 5b), then saturation magnetisation of the core–shell Fe3O4/SiO2/polypyrrole nanoparticles further decreased to 7 emu/g (Fig. 5c), the change of saturation magnetisation is similar to previous researches [[29], [30]]. The decrease in saturation magnetisation is attributed to the introduction of non-magnetic SiO2 and polypyrrole layers outside the Fe3O4 core, which again shows the successful coating of double shells of SiO2 and polypyrrole. Though the saturation magnetisation is reduced, the targeted releasing still can be triggered by the act of magnetic field. Fig. 5Open in figure viewerPowerPoint Room temperature magnetisation curves of a Bare Fe3O4 b Core–shell Fe3O4/SiO2 nanocomposites c Core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles 3.6 TGA results The TGA curves of bare Fe3O4, Fe3O4/SiO2 and Fe3O4/SiO2/polypyrrole nanoparticles are displayed in Fig. 6. For the bare Fe3O4 (Fig. 6a), from room temperature to 120°C, the residual water was evaporated with about 5% mass loss. Then, the crystalline water and adhered hydroxyl were decomposed that causing the weight loss during 200–600°C. The maximum weight loss at around 700°C could be ascribed to the phase transformation of Fe3O4 nanoparticles [[31]], the residual water was evaporated with about 5% mass loss. From Fig. 6b, there are three-stage mass losses in Fe3O4/SiO2 nanocomposites, the remnant traces water and alcohol were decomposed below 110°C during the first stage. The second stage during 200–400°C was associated with the decomposition of unreacted TEOS and absorbed hydroxyl [[32]], and the mass loss at about 800°C might owe to the phase transformation of little Fe3O4 nanoparticles. For Fe3O4/SiO2/polypyrrole nanoparticles (Fig. 6c), only 0.5% of weight loss was due to the evaporation of residual water and decomposition of pyrrole monomer, and then the ploypyrrole chains were degraded during 300–500°C. Then the carbonisations of polypyrrole were appeared above 600°C, accompanied with the phase transformation of little Fe3O4 nanoparticles, which causes more weight loss (8%) than Fe3O4/SiO2 nanocomposites (4%) between 600 and 800°C and further proved the realisation of polypyrrole layers. The extremely high weight percent of the final obtained nanocomposites showed that the as-prepared nanocomposites exhibited superior thermal stability in compared with other methods. Fig. 6Open in figure viewerPowerPoint TGA curves of a Bare Fe3O4 b Core–shell Fe3O4/SiO2 nanocomposites c Core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles 4 Conclusion In conclusion, a facile Stöber and hydrothermal methods without using any surfactants were utilised to prepare the core–shell Fe3O4/SiO2/polypyrrole composite nanoparticles. The hydrothermal method for the synthesis of ploypyrrole would supply a new thought for the preparation of other similar core–shell nanocomposite in the absence of tedious surface modification process. 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