Magnetised nanocomposite mesoporous silica and its application for effective removal of methylene blue from aqueous solution
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Silanol
Physisorption
Specific surface area
Physisorption
MCM-41
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Macropore
Capillary condensation
Carbon fibers
Physisorption
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In this study, we have investigated the thermal and hydrothermal stability of a dual mesostructured silica and of a macro‐mesoporous silica. Concerning the thermal stability, results obtained by SAXS, nitrogen adsorption‐desorption analysis and infrared spectroscopy show that, the macro‐mesoporous material is stable up to 550 °C, the mesostructure being only slightly damaged, but a contraction of both the macropores and the mesopores is observed upon calcination. Considering the dual mesoporous silica, regardless the calcination temperature, the matrix with small pores is completely degraded whereas the one with the larger pores is only weakly damaged. With regard to hydrothermal stability, all the investigated hierarchical porous silica are damaged when they are plunged into boiling water because of the hydrolysis of the superficial Si–O–Si linkages, involved by water molecules adsorbed on the silanol groups. The extracted and calcined macro‐mesoporous material is stable for one hour in boiling water, whereas the non‐calcined sample is stable for only 30 minutes. The collapse reaches only the mesopores, the macropores remain unaltered. The dual mesostructured silica is also sensitive to boiling water, but two kinetics of degradation, which correspond to each matrix, are observed. The network having small pores disintegrates after 3 hours, while the matrix having large pores begins to collapse after 8 hours. This behavior has been attributed to the difference in the mesopore wall thickness between the two matrixes.
Silanol
Thermal Stability
Macropore
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Clays are widely used as sorbents for heavy metals due to their high specific surface areas, low cost, and ubiquitous occurrence in most soil and sediment environments. However, the low loading capacity for heavy metals is one of their inherent limitations. In this work, a novel SiO2–Mg(OH)2 nanocomposite was successfully prepared via sequential acid–base modification of raw sepiolite. The structural characteristics of the resulting modified samples were characterized by a wide range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nitrogen physisorption analysis. The results show that a hierarchical nanocomposite constructed by loading the Mg(OH)2 nanosheets onto amorphous SiO2 nanotubes can be successfully prepared, and the nanocomposite has a high surface area (377.3 m2/g) and pore volume (0.96 cm3/g). Batch removal experiments indicate that the nanocomposite exhibits high removal efficiency toward Gd(III), Pb(II), and Cd(II), and their removal capacities were greatly enhanced in comparison with raw sepiolite, due to the synergistic effect of the different components in the hierarchical nanocomposite. This work can provide a novel route toward a hierarchical nanocomposite by using clay minerals as raw material. Taking into account the simplicity of the fabrication route and the high loading capacities for heavy metals, the developed nanocomposite also has great potential applications in water treatment.
Physisorption
Sepiolite
Specific surface area
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Large quantities of waste slags are produced during the preparation of electrical manganese, causing serious pollution to the environment. The recycling and utilization of electrolytic manganese slag (EMS) is a serious challenge to the industry. Here, we report the utilization of EMS in preparation of high-performance mesoporous silica using amino-ended hyperbranched polyamide (AEHPA) as template. The effects of AEHPA content and molecular weight on properties of mesoporous silica, including the specific surface area, pore diameter, pore volume, size, and distribution, have been investigated. On the basis of 0.3 wt % AEHPA-2 during the preparation of silica, the specific surface area, pore volume, and pore diameter of the produced amorphous mesoporous silica are 451.34 m2 g–1, 0.824 cm3 g–1, and 7.09 nm, respectively, showing remarkable improvements over the silica without AEHPA in specific surface area (271.05 m2 g–1), pore volume (1.167 cm3 g–1), and pore diameter (17.43 nm). The formation mechanism of mesoporous silica has been supposed and substantiated by FT-IR, XRD, XPS spectra, and SEM micrographs. This preparation method of mesoporous silica from EMS may open a new avenue for recycling and utilization of manganese slag.
Specific surface area
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Boehmite
Specific surface area
Polyethylenimine
Physisorption
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Specific surface area
Particle (ecology)
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Carboxymethyl cellulose
Physisorption
Mesoporous organosilica
Particle (ecology)
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A range of polyviologens synthesized by the Menshutkin reaction have been successfully incorporated into silica hybrids using the hydrolytic sol−gel route. Transparent hybrids can be obtained with up to 75% polyviologen content, indicating a likely nanoscale morphology. Hybrids were calcined at 650 °C to remove the polymer, forming porous amorphous silica products. Nitrogen adsorption−desorption studies have been undertaken on the hybrids and the calcination products, and the results are analyzed by the modeless method of Brunauer et al. for mesopore size distributions and a micropore analysis method based on t-curves. The hybrids are mostly mesoporous solids, but porosities are very low at high polymer contents. Calcination leads to silicas which are mainly mesoporous with varying degrees of microporosity depending on the nature and concentration of the polyviologen (PV) used. Poly(hexyl viologen ditosylate) produces high surface area silicas with >98% mesoporosity. The results may provide evidence for an influence of the PV on the structure of the forming silica, which is proposed to occur through electrostatic interactions between the quaternary nitrogen atoms of the polymer and the silanol oxygen atoms in the growing silica network.
Silanol
Hybrid material
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