Advertisement

Chemistry Africa

, Volume 2, Issue 2, pp 267–276 | Cite as

Silica, Mesoporous Silica and Its Thiol Functionalized Silica Coated MgO and Mg(OH)2 Materials

  • Issa M. El-Nahhal
  • Fawzi S. KodehEmail author
  • Jamil K. Salem
  • Talaat Hammad
  • Sylvia Kuhn
  • Rolf Hempelmann
  • Sara Al Bhaisi
Original Article
  • 187 Downloads

Abstract

Silica (SiO2) and mesoporous silica (mSiO2) coated magnesium oxide composites were prepared based on hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) in presence of magnesium oxide nanoparticles (MgO-NPs) and cetyltrimethylammonium bromide (CTAB). Functionalization with thiolorganofunctional silane precursor was conducted onto the surface of mesosilica (Scheme 1). Silica coated MgO composites and its thiol functionalized material have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope, Fourier transform spectroscopy (FTIR), ultra violet–visible spectra and thermal analysis (TGA). TEM analysis showed that the MgO nanoparticles were encapsulated into the SiO2 or mSiO2 precursors. XRD analysis reveals that magnesium oxide are exist into both forms, cubic MgO-structure and hexagonal Mg(OH)2-structure, which is converted into cubic structure upon silica coating. The mean crystallite size of MgO-NPs remains almost unchanged after coating with silica precursors. TGA and FTIR results indicated that the coated mesosilica layer around magnesium oxide nanoparticles has been successfully grafted by thiolorganofunctional silane groups.
Scheme 1

Descriptive of formation SiO2 or mSiO2 coated MgO-NPs and its thiol functionalized material

Keywords

MgO nanostructure Silica coated MgO-NPs composites Thiol functional mesoporous silica Nanocomposites 

1 Introduction

Metal oxides with high surface area and porosity have attracted considerable interest for scientific research due to their potential application such as functional components for nanoelectronics, optoelectronics and sensing devices [1]. In particular, magnesium oxide (MgO) as a versatile oxide material with assorted properties finds extensive applications in catalysis, ceramics, toxic waste remediation, or as an additive in refractory, paint and superconductor products [2, 3]. Also, owing to its very large band gap, excellent thermodynamical stability, low dielectric constant and refractive index, it has been used as a transition layer for growing various thin film materials [4, 5]. In the previous years, the specific surface area, dispersion stability and morphological characteristic of the magnesia particles have been intensively identified and examined as important parameters that influence high-performance for such applications [6, 7]. Therefore, many approaches to control these properties of magnesia particles have been investigated [8, 9, 10, 11]. Silica-based coatings are of particular interest because it has good environmental stability with different materials [12, 13, 14, 15, 16], their low refractive index, water-compatibility, lower toxicity and ease of surface functionalization [17]. Another reason for coating nanoparticles is to reduce the potential for photocatalysis and formation of free radicals [17]. There were some reported articles in which dispersant agents were used as coupling agents for the fabrication of silica coated metal oxides nanoparticles [17, 18]. The synthesis of silica coated metal oxide nanomaterials were recently reported using two main strategies: the first strategy is to incorporated silane precursors during the growth of metal oxides as coating agent [19, 20, 21, 22, 23, 24, 25, 26], the second strategy is to use sol–gel process for coating of previously prepared metal oxide nanoparticles [27, 28, 29, 30, 31]. Most metal oxides that have been coated with silica are ZnO [27, 28], CuO [29], NiO [30], TiO [31]. Very little research has been devoted to the fabrication of silica coated magnesium oxide [32, 33, 34, 35]. Recently different methods were used for preparations of MgO@SiO2 core–shell or Mg-SiO2 composites using the sol–gel process [35, 36]. The coated MgO@SiO2 materials have been used in different applications. In this research, five new different composites using modified Stöber method [37]: MgO@SiO2, MgO@mSiO2, MgO free@mSiO2, MgO@mSiO2SH and MgOfree@mSiO2SH were prepared. The MgO/Mg(OH)2 nanoparticles were first prepared by the co-precipitation method, then the MgO/Mg(OH)2 nanoparticles were ultrasonicated to disperse them into aqueous ethanolic solution in presence of base, prior to the sol–gel coating process with TEOS. The Free MgO silica coated and mesosilica materials are also obtained by etching the MgO from the mesosilica and thiol functionalized mesosilica using HCl. Silica coating by sol–gel process is used to protect the MgO-NPs from the outside environment, since MgO material is very reactive. mesosilica layer is used to protect the MgO-NPs core and is used for the thiol functionalization.

Several methods and techniques were used for structural characterization of these new materials. These methods include: X-ray diffraction (XRD), transition electron microscopy with energy dispersive X-Ray Spectrometer (TEM–EDX), Fourier transform spectroscopy (FTIR), Ultra violet–visible spectra (UV/VIS), and thermalgravimetric analysis (TGA).

2 Materials and Methods

2.1 Materials

All chemicals given bellow were purchased and used as received. Tetraethylorthosilicate (TEOS), cetyltrimethylammonium bromide (CTAB) and alkyl hydroxyethyl dimethyl ammonium chloride (HY, R = 12–14) were purchased from Merck. An organoalkoxy silane selected for the functionalization process was 3-thiolpropyltrimethoxysilane (TPTS, 99%), this reagent was purchased from Aldrich Company. Toluene and ethanol (spectroscopic grade) were purchased from Aldrich. Magnesium sulfate heptahydrate and ammonium hydroxide solutions (28%) were obtained from Merck.

2.2 Synthesis

2.2.1 Synthesis of MgO/Mg (OH)2-NPs

In typical synthesis of MgO-NPs [39], 20 mmol of magnesium sulfate heptahydrate MgSO4·7H2O was dissolved into 25 mL of deionized water. 20 mmol of oxalic acid was dissolved in an equal volume of deionized water and dropwise added to magnesium sulfate solution under magnetic stirring for 60 min, white precipitate of magnesium oxalate was isolated, washed with water several times and dried at 100 °C for 24 h. The dried material was grounded using mortar and pestle to produce fine powder precursor. Subsequently, the precursor, magnesium oxalate was annealed in muffle furnace under air at 500 °C for 4 h to form MgO nanostructure (Scheme 2, Table 1).
Scheme 2

Formation of MgO/Mg(OH)2-NPs

Table 1

Experimental data

Material

Synthesis description

Notes

MgO-NPs

MgSO4 + H2C2O4 → MgC2O4\(\xrightarrow{\text{calcination}}\)(500 °C for 4 h → MgO-NPs + H2O → Mg(OH)2 (scheme 2)

Two species of MgO, Mg(OH)2 can be observed with an agglomerated species in rode like shape of 30 nm length and 3.0 nm width is clearly seen

MgO/Mg(OH)2@SiO2

MgO + TEOS + NH4OH \(\xrightarrow{\text{sonication}}\) for 1 h, annealed at 500 °C for 4 h(scheme 3)

MgO/Mg(OH)2@SiO2 coated by silica layer, where high content of Mg are detected

MgO@mSiO2

MgO + TEOS + NH4OH + CTAB + sonication for 1 h, annealed at 500 °C for 4 h (scheme 4)

MgO@mSiO2 + 2 M HCl → MgO free@mSiO2 (scheme 4)

Wormlike mSiO2 material is obtained, MgO-NPs of 5.3 nm particle size are well dispersed into the mesopores. Empty mSiO2 is obtained with very low MgO content

MgO@mSiO2-SH

MgO@mSiO2 + thiolsilane, reflux in dry toluene at 110 °C overnight → MgO@mSiO2-SH(scheme 5)

Thiol functionalization of mesoporous silica layer, high content of MgO NPs are detected

MgO free@mSiO2-SH

MgO@mSiO2-SH + 2 M HCl → MgO free@mSiO2-SH (scheme 6)

Great reduction of MgO NPs and low density material is formed

2.2.2 Synthesis of MgO/Mg(OH)2 @SiO2 composite

The coated silica magnesium oxide composite labeled as MgO@SiO2 was prepared in a similar reported method [26, 27, 28] through a simple sol–gel process using Stöber modified method [37]. Briefly, 0.10 g of MgO/Mg(OH)2-NPs were dispersed in a mixture of ethanol (40 mL), deionized water (10 mL), and concentrated ammonia solution (28 wt%, 1.2 mL) by ultrasonication for 1 h. To the solution, 0.43 mL of tetraethylorthosilicate (TEOS) was added drop wise. After stirring for 6 h, the product was collected and washed with ethanol and deionized water. The product was dried under vacuum at 60 °C for 8 h (Scheme 3, Table 1).
Scheme 3

Silica coated MgO/Mg(OH)2 composite

2.2.3 Synthesis of MgO@mSiO2 composite

Coated mesoporous magnesium oxide material labeled as MgO@mSiO2 composite was prepared in a similar reported method [26, 27, 28, 34] by dispersed 0.10 g of MgO-NPs in 60 mL ethanol and 1.2 mL concentrated ammonia solution (28 wt%), then ultrasonicated for 1 h. An ethanolic solution of 0.30 g CTAB was added to the magnesium oxide nanoparticles mixture under constant stirring at room temperature. 0.43 mL of TEOS was added drop wise to the mixture under constant stirring for further 6 h. The product was separated by centrifuge of 4000 rpm and washed with dionized water. Finally the product was dried at 100 °C for 12 h and calcinated at 500 °C for 3 h. Free MgO@mSiO2 composite was obtained by treatment of the MgO@mSiO2 composite with 2 M HCl (Scheme 4, Table 1).
Scheme 4

Mesoporos silica coated MgO composite

2.2.4 Synthesis of thiol-functionalized MgO@mSiO2-SH composite

Thiol-functionalized of MgO@mSiO2 materials was prepared as previously described [26, 27, 28] by disperse 1.0 g of MgO@mSiO2 nanomaterial with excess amount of 3-thiolpropyltrimethoxy silane (0.37 g, 0.002 mol) in 20 ml of dry toluene. The mixture was refluxed for 24 h at 110 °C. The thiol functionalized materials labeled as MgO@mSiO2-SH was filtered off washed with ethanol and dried in vacuum at 80 °C (Scheme 5, Table 1).
Scheme 5

Thiol-functionalized MgO@mSiO2-SH

2.2.5 Synthesis of magnesium oxide free mesosilica materials

Magnesium oxide free thiol mesoporous silica MgO free @mSiO2-SH material was obtained by treating 0.5 g MgO@mSiO2-SH material with 20 mL of 2 M hydrochloric acid with continuous stirring (Scheme 6, Table 1) [26, 27]. The magnesium oxide free thiol functionalized silica material was separated and washed with distilled water. The product was then dried in vacuum at 60 °C for 8 h.
Scheme 6

Removal of MgO-NPs

3 Results and Discussion

3.1 Synthesis

MgO-NPs were obtained by thermal decomposition of magnesium oxalate, which were agglomerated as porous material with rode like shape (Scheme 2, Table 1) [39]. Both species the cubic MgO and hexagonal Mg(OH)2 structures are obtained (confirmation was evident from XRD and TEM). The silica coated magnesium oxide material labeled as MgO/Mg(OH)2@SiO2 was prepared as previously reported [26, 27, 28] using modified Stöber method [37] through a simple sol–gel process, briefly, by ultrasonicated of MgO-NPsin aqueous ethanol in presence of ammonium hydroxide and tetraethylorthosilicate (TEOS). The ultrasonication of nanoparticles prior the coating process in aqueous ethanol was used to obtain well homogeneous dispersion of the nanoparticles and to prevent self agglomerization of MgO nanoparticles [25], no dispersant agent was used. In this sol–gel process, TEOS acts as a silica coating precursor and NH4OH acts as the catalyst. When TEOS was added to the solvated-nanoparticle mixture, the silane material began to undergo hydrolysis and co-condensation process to establish MgO/Mg(OH)2–SiO2 linkages on the particle surface [25, 40]. The interaction between MgO/Mg(OH)2 species with mesoporous silica (mSiO2), form MgO-mSiO2 linkages after calcinations at 500 °C. This is probably due to transformation of Mg(OH)2 to MgO. This was clearly evident from the XRD analysis, where the diffraction peaks of Mg(OH)2 have disappeared after coating with mSiO2. Upon coating MgO/Mg(OH)2 particles with silica SiO2 precursor MgO/Mg(OH)2-SiO2 linkages are probably formed. This was confirmed from XRD analysis, where the diffraction peaks corresponding due to Mg(OH)2 and MgO are appeared after sol–gel encapsulation process. The silica coating reaction has occurred when TEOS silane precursor is added to MgO/Mg(OH)2. Therefore both species of magnesium oxide and magnesium hydroxide nanoparticles are formed. Further discussion is given in TEM section and XRD and FTIR.

A mesoporous silica shell has introduced to encapsulate MgO nanoparticles into the mesopores by using tetraethylorthosilicate (TEOS), cetyltrimethyl ammonium bromide(CTAB) as cationic surfactant in ethanol with presence of ammonium hydroxide similar to previously reported methods [26, 27, 28, 38] (Scheme 4, Table 1). After removal of CTAB by calcinations at 500 °C, only the cubic MgO species were present and the Mg(OH)2 species were disappeared. They are probably involved in condensation with silanol groups during the sol–gel coating process. The MgO-NPs are probably dispersed into the mesopores of mesoporous region. This was confirmed by TEM results discussed later. Free MgO@mSiO2 material was obtained easily by treatment of mesoporous coated magnesium oxide composites with hydrochloric acid as shown in Scheme 4, Table 1. The morphology of the silica precursor is maintained after the removal of metal oxide particles, which is reflected from the TEM analysis.

Thiol functionalized composite (MgO@mSiO2-SH) was prepared by treatment of MgO@mSiO2 with 3-thiolpropyltrimethoxysilane (TPTS) in dry toluene [26, 27, 28] as shown in Scheme 5, Table 1. FreeMgO@mSiO2-SH materials was obtained easily by treatment of MgO@mSiO2-SH composite with hydrochloric acid (Scheme 6, Table 1).

3.2 Infrared spectra

The FT-IR spectra of MgO-NPs, MgO@SiO2, MgO@mSiO2, freeMgO@mSiO2 and MgO@mSiO2-SH materials are shown in Fig. 1a–e, respectively. Three regions of absorption at 3300–3650 cm−1, 1400–1700 cm−1 and 500–1100 cm−1 are observed due to ν(O–H), δ(O–H) and ν(Si–O–Si) vibrations, respectively. The two peaks at 3710 cm−1 and 3500 cm−1 (broad) (Fig. 1a, b) are associated with free ν(O–H) and hydrogen bonding ν(O–H) of MgO-NPs crystallizing water molecules, respectively. The absorption peak at 1650 cm−1 and at 1438 cm−1 are probably associated with δ(O–H) vibrations [26, 27, 28, 29, 30, 41]. The presence of strong a new peaks at 1076 cm−1 and 808 cm−1 are associated with Si–O–Si asymmetric and symmetric stretching vibrations, the band at 461 cm−1 is correspond to the Si–O–Si bending vibration. The presence of Si–O–Si peaks at 1076–461 cm−1 and the decreasing in the intensity of (O–H) peaks at 3710 and 1438 cm−1 upon coating with silica is provide strong evidence for the incorporated of silica onto the surface of MgO-NPs and formation of Si–O–Mg linkages [26, 27, 28, 29, 30]. This also provides evidence for the conversion from the Mg(OH)2 to MgO upon silica coating. The presence of a shoulder ca 530 cm−1 and a band at 461 cm−1 for the silica coated MgO material (Fig. 1b–d) which are reduced to small peak at 461 cm−1 for MgO-NPs free silica coated material(Fig. 1 e) provide strong evidence that the shoulder at ca 530 cm−1 is corresponding to Mg-O stretching vibration. FT-IR spectrum of MgO@mSiO2-SH after functionalization with TPTS was evident from the presence of absorption bands at 2932 cm−1 ν(C–H) and 1485 cm−1 δ(C–H) vibrations [40].
Fig. 1

FTIR spectra of (a) MgO pure, (b) MgO/Mg(OH)2@SiO2, (c) MgO@mSiO2, (d) MgOfree@mSiO2 (e) MgO@mSiO2-SH

3.3 Thermal Analysis

Thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTA) for MgO@mSiO2 and its thiol functionalized MgO@mSiO2-SH nanoparticles were examined under nitrogen atmosphere at 20–600 °C of rate 10 °C/min (Fig. 2a, b). The thermogram of the MgO@mSiO2 nanomaterial (Fig. 2a) shows two peaks, the main preak occurs at ~ 75 °C due to loss of 9.9% of its initial weight. This attributed to loss of physisorbed water and alcohol from the system pores [26, 27, 41]. The second peak is very broad centered at ~ 390 °C due to loss of 3.6%, which is probably due to dehydroxylation and loss of water or alcohol from silica and mesosilica precursors [26, 27, 39, 41, 42]. The total loss of weight was 13.5%. Figure 2b shows the thermogram of the MgO@mSiO2-SH nanomaterial. Three peaks were observed, the first preak occurs at ~ 75 °C due to loss of 7.2% of its initial weight. This attributed to loss of physisorbed water and alcohol from the system pores [26, 27, 37, 42]. The second peak and third peaks are observed at 350 °C and at 450, respectively. They are due to loss of the thiol organofunctional groups from the system and dehydroxylation and loss of water or alcohol from silica of 17.6% [26, 27, 41, 42]. The total loss of weight was 24.8%. The difference between the total loss of the two materials (11.3%) is probably due to the thiol organofunctional group.
Fig. 2

TG/DTA analysis of a MgO@mSiO2, b MgO@mSiO2-SH

3.4 XRD Analysis

The XRD analysis for MgO-NPs and its silica coated composites are given in Fig. 3.
Fig. 3

XRD patterns of (a) standard MgO pure, (b) MgO pure, (c) MgO@SiO2, (d) MgO@mSiO2, (e) MgOfree@mSiO2 (f) MgO@mSiO2-SH

The XRD pattern of standard MgO-NPs (Fig. 3a) showed a diffraction pattern matches with face centered cubic structure of MgO nanoparticles (JCPDS No. 87-0653). The major peaks at 2θ values of 36.8°, 42.9°, 62.2°, 74.6°, and 78.6° can be indexed to the lattice planes of (111), (200), (220), (311) and (222), respectively [42, 43, 44]. The XRD diffraction peaks showed the presence of both forms, pure cubic structure(*) of MgO and hexagonal structure($) of Mg(OH)2 [39, 45]. The XRD pattern of our (MgO-NPs) material prepared from thermal decomposition of magnesium oxalate (Fig. 3b) showed the presence of a mixture of two forms, the cubic structure MgO and hexagonal structure Mg(OH)2 with higher contribution of the hexagonal species. After the sol–gel silica coating, there was a significant decrease of intensity of peaks correspond to hexagonal Mg(OH)2 species and an increase of intensity of the peaks correspond to cubic MgO species. This is probably due to partial silica coating of the MgO-NPs has occurred (both forms are present). After coating with mesoporous silica layer, the peaks correspond to the cubic form of MgO are appeared and no peaks of correspond to Mg(OH)2 are detected Fig. 3d, f. This implies that all Mg(OH)2 species are converted into cubic MgO upon silica coating.

The magnesium oxide free coated silica materials (Fig. 3e) showed no XRD peaks correspond to MgO-NPs, this may confirm that a complete removal of magnesium oxide nanoparticles form mesoporous silica coated magnesium oxide microspheres. The XRD assignments were based on reported XRD data of similar systems [26, 27]. The XRD pattern for MgO@mSiO2 and that of its thiol functionalized ligand systems MgO@mSiO2-SH (Fig. 3d, f) showed diffraction patterns correspond to cubic MgO structure and no peaks correspond of Mg(OH)2 species are presents. A complete conversion from hexagonal Mg(OH)2 to cubic MgO species occurred upon silica coating. This is probably due to the condensation of hydroxyl groups of silica silanols and magnesium hydroxide forming MgO-SiO2 linkages.

The mean crystallite size is determined using Scherrer’s formula, d = 0.9 λ/β cos θ, where d is the crystallite size, λ is wavelength of X-ray radiation, β is full width at half maximum and θ is the diffraction angle. The obtained particle size of the different materials is summarized in Table 2. The average sizes were found in the range (6–8.7 nm), which means that the particle size was almost remain unchanged after silica coating. There was no obvious change in the line width which confirms that the coating process does not alter the crystallite size of the particles Fig. 3b, c, d, f.
Table 2

Mean crystallite size of materials

Material

Particles size (nm)

MgO/Mg(OH)2

6.4

MgO/Mg(OH)2@SiO2

6.9

MgO@mSiO2

8.7

MgO@mSiO2-SH

6.4

3.5 Ultraviolet–Visible (UV–vis) Spectroscopy

The UV/vis spectra for pure MgO and silica coated magnesium oxide nanomaterials are shown in Fig. 4. The spectrum of MgO nanoparticles exhibits one well-defined band in HY at 300 nm (Fig. 4a). HY was used as coupling agent to incorporate and stabilize MgO nanoparticles. Upon coating with silica layer, There was a decrease in peak intensity (Fig. 4b), The high intensity of peak for MgO@mSiO2 (Fig. 4c) in comparison with other silica coated samples is probably due to the presence of meso silica shell and high content of MgO-NPs. The spectra for FreeMgO@mSiO2 (Fig. 4d) shows no peaks which is probably due to the absence of MgO-NPs [26, 27]. In literature, MgO is reported to exhibit absorptions in the UV region in between 160 and 200 nm [45].
Fig. 4

UV-Vis absorption spectra of (a) MgO/Mg(OH)2 pure, (b) MgO/Mg(OH)2@SiO2,(c) MgO@mSiO2,(d) MgO free @m-SiO2

3.6 Transmission Electron Microscopy (TEM), EDAX

TEM images along EDX of MgO/Mg(OH)2-NPs, its silica/mesoporous silica coated MgO and the thiol functionalized materials are given in Figs. 5, 6, 7, 8 and 9. TEM image of MgO-NPs shows a mixture of two forms, probably the cubic MgO structure and the hexagonal Mg(OH)2 structures, one type is agglomeration of MgO-NPs as rode like shape of ca 30 nm length and 3.0 nm clearly observed (Fig. 5a, Table 1). TEM–EDX of MgO-NPs shows the presence of only Mg and O atoms and with absence of Si atoms (Fig. 5b). The presence of very small peak corresponding to Si atoms is probably due to some contaminations or impurities.
Fig. 5

Structural characterization of MgO/Mg(OH)2 nanoparticles: a TEM image and b EDAX spectra

Fig. 6

Structural characterization of MgO/Mg(OH)2@SiO2: a TEM image and b EDAX spectra

Fig. 7

Structural characterization of MgO@mSiO2: a TEM image and b EDAX spectra

Fig. 8

Structural characterization of MgO free@mSiO2: a TEM image and b EDAX spectra

Fig. 9

Structural characterization of MgO@mSiO2-SH: a TEM image and b EDAX spectra

Figure 6a shows the TEM image of MgO/Mg(OH)2@SiO2 in which MgO/Mg(OH)2-NPs seem to be partially coated by sol–gel silica. The reason for this behavior is probably due to the self-agglomeration of magnesium oxide particles which leads to weak interaction and formation of MgO/Mg(OH)2-SiO2 linkages. Therefore TEM–EDX Fig. 6b for MgO/Mg(OH)2@SiO2 shows the presence of high content of Mg atoms and low contents of Si atoms. The presence of C atoms is probably due to presence of some unhydrolyzed alkoxy groups.

TEM image of MgO@mSiO2 is given in Fig. 7a where MgO-NPs of average crystallite size 5.3 nm are fully dispersed into mesopores of the mesoporous silica material which are seen in dark and the coated silica are in grey colour. The reason for this behavior is that in the case of mesoporous silica, there were a higher surface area and lot of silanol groups available to cooperate with the surface of Mg(OH)2-NPs in comparison with silica [46]. Therefore TEM–EDX Fig. 7b for MgO@mSiO2 shows peaks correspond to low content of Mg atoms and high content of O and Si atoms. The TEM image Fig. 8a of free MgO@mSiO2 material shows absence MgO-NPs, which confirmed the removal of MgO NPs from the mesopores of the mesoporous silica network. The TEM/EDX Fig. 8b shows peaks correspond to very low content of Mg and high content of Si and C atoms are observed. The morphology of the mesoporous silica network is maintain and empty microspheres of mSiO2 after removal of metal oxide are clearly seen image 8a. An internal void appeared in the mSiO2 shell as the MgO was removed, indicating that the meso-SiO2 is well coated on the surface of the MgO core. The SiO2 shell has wormlike mesoporous (Fig. 8a).

The TEM image Fig. 9a of thiol-mesoporous silica coated magnesium oxide (MgO@mSiO2-SH) material shows that MgO nanoparticles are homogeneously dispersed into the mesopores of the functionalized mesoporous silica network. High content of Mg atoms and low content of Si atoms are detected in the TEM/EDX Fig. 9b.

4 Conclusion

Silica, mesporous silica coated MgO-NPs and its thiol functionalized materials were by modified Stöber method. MgO-NPs are encapsulated into silica and mesoporous silica pores as confirmed from TEM analysis. Functionalized of the mesoporous silica with thiolsilane coupling agent are successfully grafted at the surface of mesoporous silica shell as confirmed by FTIR and TGA analysis. TGA and FTIR revealed that thiolorganofunctional groups are covalently attached to the mesoporous silica layer. XRD results confirmed the formation of cubic MgO structure and hexagonal Mg(OH)2 structure nanoparticles, where the Mg(OH)2 species are disappeared after the sol–gel coating process. The mean average particle size of MgO NPs remains unchanged before and after the silica coating with mean average crystallite size of 6.4–8.7 nm. Magnesium oxide free mesoporous silica materials have low density mesoporous silica spheres showed no XRD peaks due to complete etching of MgO core. These materials could be tested for extraction and removal of toxic heavy metal ions as Hg2+ [47]. and also for extraction and removal of dyes [39].

References

  1. 1.
    Jintakosol T, Singjai P (2009) Effect of annealing treatment on luminescence property of MgO nanowires. Curr Appl Phys 9:1288–1292CrossRefGoogle Scholar
  2. 2.
    Duan G, Yang X, Chen J, Huang G, Lu L, Wang X (2007) The catalytic effect of nanosized MgO on the decomposition of ammonium perchlorate. Powder Technol 172:27–29CrossRefGoogle Scholar
  3. 3.
    Niu H, Yang Q, Tang K, Xie Y (2006) Self-assembly of porous MgO nanoparticles into coral-like microcrystals. Scr Mater 54:1791–1796CrossRefGoogle Scholar
  4. 4.
    Shah MA, Qurashi A (2009) Novel surfactant-free synthesis of MgO nanoflakes. J Alloys Compd 482:548–551CrossRefGoogle Scholar
  5. 5.
    Qiu T, Wu XL, Jin FY, Huang AP, Chu PK (2007) Self-assembled growth of MgO nanosheet arrays via a micro-arc oxidation technique. Appl Surf Sci 253:3987–3990CrossRefGoogle Scholar
  6. 6.
    Muraoka T, Kashimura T, Iizuka S (2009) Spherical MgO microparticle deposition by RF impulse discharge with small coaxial electrodes. Thin Solid Films 518:1012–1015CrossRefGoogle Scholar
  7. 7.
    Xia Y, Yang P, Sun Y, Wu Y, Mayers B, Gates B, Yin Y, Kim F, Yan H (2003) One-dimentional nanostructures; synthesis, characterization and applications. Adv Mater 15:353–389CrossRefGoogle Scholar
  8. 8.
    Aramendia MA, Borau V, Jimenez C, Marinas JM, Ruiz JR, Urbano FJ (2003) Influence of the preparation method on the structural and surface properties of various magnesium oxides and their catalytic activity in the Meerwein–Pondorf–Verley reaction. Appl Catal A Gen 244:207–215CrossRefGoogle Scholar
  9. 9.
    Jost H, Braun M, Carius C (1997) The role of reactivity in syntheses and the properties of magnesium oxide. Solid State Ion 101:221–228CrossRefGoogle Scholar
  10. 10.
    Liu H, Yi J (2009) Polystyrene/magnesium hydroxide nanocomposite particles prepared by surface-initiated in situ polymerization. Appl Surf Sci 255:5714–5720CrossRefGoogle Scholar
  11. 11.
    Wei Z, Qi H, Ma P, Bao J (2002) A new route to prepare magnesium oxide whisker. Inorg Chem Commun 5:147–149CrossRefGoogle Scholar
  12. 12.
    Wang JF, Tsuzuki T, Sun L, Wang XG (2009) Reducing the photocatalytic activity of zinc oxide quantum dots by surface modification. J Am Ceram Soc 92:2083–2088CrossRefGoogle Scholar
  13. 13.
    Yi DK (2011) A study of optothermal and cytotoxic properties of silica coated Au nanorods. Mater Lett 65:2319–2321CrossRefGoogle Scholar
  14. 14.
    Nakade M, Ogawa M (2007) Synthesis and characterization of zinc oxide fine particle coated with titania/PDMS hybrid. J Mater Sci Technol 42:4254–4259Google Scholar
  15. 15.
    Gerhard R, Werner H, Holger P, Heinrich S, Seidlitz HK, Hohn B (2000) Elevated UV-B radiation reduces genome stability in plants. Nature 406:98–101CrossRefGoogle Scholar
  16. 16.
    Fernandez L, Garro N, Haskouri EJ, Perez-Cabero M, Alvarez- Rodriguez J, Latorre J, Guillem C, Beltran A, Beltran D, Amoros P (2008) Mesosynthesis of ZnO–SiO2 porous nano-composites with low-defect ZnO nanometric domains. Nanotechnology 19:10Google Scholar
  17. 17.
    Wang J, Tsuzuk T, Tang B, Cizek P, Sun L, Wang X (2010) Synthesis of silica-coated ZnO nanocomposite: the resonance structure of polyvinyl pyrrolidone (PVP) as a coupling agent. Colloid Polym Sci 288:1705–1711CrossRefGoogle Scholar
  18. 18.
    Graf C, Vossen DLJ, Imhof A, Blaaderen AV (2003) A general method to coat colloidal particles with silica. Langmuir 19:6693–6700CrossRefGoogle Scholar
  19. 19.
    Tang EJ, Dong SY (2009) Preparation of styrene polymer/ZnO nanocomposite latex via miniemulsion polymerization and its antibacterial property. Colloid Polym Sci 287:1025–1032CrossRefGoogle Scholar
  20. 20.
    Halliwell CM, Cass AEG (2001) A factorial analysis of silanization conditions for the immobilization of oligonucleotides on glass surfaces. Anal Chem 73:2476–2483CrossRefGoogle Scholar
  21. 21.
    Liu S, Luc L, Yang Z, Cool P, Vansant EF (2006) Further investigations on the modified Stöber method for spherical MCM-41. Mater Chem Phys 97:203–206CrossRefGoogle Scholar
  22. 22.
    Ibrahim IAM, Zikry A, Sharaf MA (2010) Preparation of spherical silica nanoparticles: Stober silica. J Am Sci 6:985–989Google Scholar
  23. 23.
    Kim KD, Kim HT (2002) Formation of silica nanoparticles by hydrolysis of TEOS using a mixed semi-batch/batch method. J Sol-Gel Sci Technol 25:183–189CrossRefGoogle Scholar
  24. 24.
    Japic D, Djerdj I, Marinek M, Orel ZC (2013) In situ and ex situ TEOS coating of ZnO nanoparticles and the preparation of composite ZnO/PMMA for UV–VIS absorbers. Acta Chim Slov 60:797–806Google Scholar
  25. 25.
    Ramasamy M, Kim YJ, Gao H, YiD K, An JH (2014) Synthesis of silica coated zinc oxide–poly(ethylene-co-acrylic acid) matrix and its UV shielding evaluation. Mater Res Bull 51:85–91CrossRefGoogle Scholar
  26. 26.
    Yuan Q, Li N, Chi Y, GengW Yan W, Zhao Y, Li X, Dong B (2013) Effect of large pore size of multifunctional mesoporous microsphere on removal of heavy metal ions. J Hazard Mater 254(255):157–165CrossRefGoogle Scholar
  27. 27.
    El Nahhal MI, Salem KJ, Sylvia Kuhn S, Hammad MT, Hempelmann R, Al-Bohisi S (2016) Synthesis & characterization of silica coated and functionalized silica coated zinc oxide nanomaterials. Powder Technol 287:439–446CrossRefGoogle Scholar
  28. 28.
    Wang J, Tsuzuki T, Sun L, Wang X (2009) Reducing the photocatalytic activity of zinc oxide quantum dots by surface modification. J Am Ceram Soc 92:2083–2088CrossRefGoogle Scholar
  29. 29.
    El Nahhal MI, Salem KJ, Sylvia Kuhn S, Hammad MT, Hempelmann R, Al-Bohisi S (2016) Synthesis and characterization of silica-, meso-silica- and their functionalized silica-coated copper oxide nanomaterials. J Sol-Gel Technology 79:573–583CrossRefGoogle Scholar
  30. 30.
    Hui W, Zhang JF, Bai YX, Wang W, Tan Y, Han Y (2016) NiO@SiO2 core-shell catalyst for low-temperature methanation of syngas in slurry reactor. J Fuel Chem Technol 44:548–556CrossRefGoogle Scholar
  31. 31.
    Sun J, Xu K, Shi C, Ma J, Li W, Shen X (2017) Influence of core/shell TiO2@SiO2 nanoparticles on cement hydration. Constr Build Mater 156:114–122CrossRefGoogle Scholar
  32. 32.
    Hoang HT, Sertsova AA, Marakulina SI, Subcheva EN, Zaitseva MP, Yurtova EV (2018) Manufacture of magnesium oxide nanoparticles coated with silica shells. Russ J Inorg Chem 63:1414–1418CrossRefGoogle Scholar
  33. 33.
    Alimunnisa J, Ravichandran K, Meena KS (2017) Synthesis and characterization of Ag@SiO2 core-shell nanoparticles for antibacterial and environmental applications. J Mol Liq 231:281–287CrossRefGoogle Scholar
  34. 34.
    Pei Yanyan, Wang Man, Tian Di, Xuefeng Xu, Yuan L (2015) Synthesis of core–shell SiO2@MgO with flower like morphology for removal of crystal violet in water. J Colloid Interface Sci 453:194–201CrossRefGoogle Scholar
  35. 35.
    Hu M, Yan X, Hu X, Zhang J, Feng R, Zhou M (2018) Ultra-high adsorption capacity of MgO/SiO2 composites with rough surfaces for Congo red removal from water. J Colloid Interface Sci 510:111–117CrossRefGoogle Scholar
  36. 36.
    Huang X, Men Y, Wang J, An W, Wang Y (2016) Highly active and selective binary MgO–SiO2 catalysts for the production of 1,3-butadiene from ethanol. Catal Sci Technol 7:168–180CrossRefGoogle Scholar
  37. 37.
    Stöber W, Fink A, Bohn E (1968) Controlled growth of monodisperse silica spheres in the micron size range. J Colloid Interface Sci 26:62–69CrossRefGoogle Scholar
  38. 38.
    Cui ZM, Chen Z, Cao CY, Song WG, Jiang L (2013) Coating with mesoporous silica remarkably enhances the stability of the highly active yet fragile flower-like MgO catalyst for dimethyl carbonate synthesis. Chem Commun 49:6093CrossRefGoogle Scholar
  39. 39.
    Salem KJ, El Nahhal MI, Hammad MT, Hempelmann R (2015) Optical and fluorescence properties of MgO nanoparticles inmicellarsolution of hydroxyethyl laurdimonium chloride. Chem Phys Lett 636:26–30CrossRefGoogle Scholar
  40. 40.
    Venkataraman NV, Vasudevan S (2001) Conformation of methylene chains in an intercalated surfactant bilayer. J Phys Chem B 105:1805–1812CrossRefGoogle Scholar
  41. 41.
    Oh MH, Kim KW, Choi S, Singh RK (2010) Preparation of monodispersed magnesia coated silica particles through a surface-induced precipitation method. Powder Technol 204:154–158CrossRefGoogle Scholar
  42. 42.
    Li YS, Church JS, Woodhead AL, Moussa F (2010) Preparation and characterization of silica coated iron oxide magnetic nano-particles. Spectrochim Acta Part A 76:484–489CrossRefGoogle Scholar
  43. 43.
    Venkatesha TG, Nayaka YA, Chethana BK (2013) Adsorption of Ponceau S from aqueous solution by MgO nanoparticles. Appl Surf Sci 276:620–627CrossRefGoogle Scholar
  44. 44.
    Gaashani RAI, Radiman S, Al Douri Y, Tabet N, Dauda AR (2012) Investigation of the optical properties of Mg(OH)2 and MgO nanostructures obtained by microwave-assisted methods. J Alloys Compd 521:71–76CrossRefGoogle Scholar
  45. 45.
    Popov IA, Shirmane L, Pankratov V, Lushchik A, Kotlov A, Serga EV, Kulikova DL, Chikvaidze G, Zimmermann J (2013) Comparative study of the luminescence properties of macro- and nanocrystalline MgO using synchrotron radiation. Nucl Instrum Methods B 310:23–26CrossRefGoogle Scholar
  46. 46.
    Chen Y, Chen H, Guo L, He Q, Chen F, Zhou J, Feng J, Shi J (2009) Hollow/rattle-type mesoporous nanostructures by a structural difference-based selective etching strategy. ACS Nano 4:529–539CrossRefGoogle Scholar
  47. 47.
    Zhang X, Wu T, Zhang Y, Ng DHL, Zhao H, Wang G (2015) Adsorption of Hg2+ by thiol functionalized hollow mesoporous silica microspheres with magnetic cores. RSC Adv 5:51446–51453CrossRefGoogle Scholar

Copyright information

© The Tunisian Chemical Society and Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Issa M. El-Nahhal
    • 1
  • Fawzi S. Kodeh
    • 1
    Email author
  • Jamil K. Salem
    • 1
  • Talaat Hammad
    • 2
  • Sylvia Kuhn
    • 3
  • Rolf Hempelmann
    • 3
  • Sara Al Bhaisi
    • 1
  1. 1.Department of ChemistryAl-Azhar University-GazaGazaPalestine
  2. 2.Department of PhysicsAl-Azhar University-GazaGazaPalestine
  3. 3.Physical ChemistrySaarland UniversitySaarbrückenGermany

Personalised recommendations