Self-assembly synthesis of hollow double silica @ mesoporous magnesium silicate magnetic hierarchical nanotubes with excellent performance for fast removal of cationic dyes
Introduction
Organic dyes, which are extensively applied in textile industries, raise much concern because they have harmful enviromental and toxic effects on ecological systems [1], [2], [3], [4], [5], [6], [7], [8]. And these dyes are very stable due to the synthetic origin and complex aromatic molecular structures [9], [10], [11], [12], [13], [14]. Therefore, the removal of dyes is of vital importance. Many conventional wastewater treatment technologies, such as membrane separation, biochemical oxidation, photodegradation and adsorption, have been used for the removal of dyes to reduce the impact on the enviroment [15], [16], [17], [18], [19], [20], [21], [22], [23]. Among these techniques, adsorption has been found to be commomly used to remove organic dyes owing to easy operation, low costs and high efficiency [24], [25], [26], [27], [28], [29], [30]. Many adsorbents, such as carbon nanotubes and alumina, have been reported to remove orangic pollutions [31], [32], [33], [34], [35]. However, adsorbents left in the solution may cause secondary pollution. Therefore, it reamins a challenge to develop a low-cost and enviromental adsorbent.
Considering their low cost, environmentally benign nature and stability, silicate materials have been widely applied in catalysis and adsorption [36], [37], [38], [39]. Magnesium silicate nanomaterial, one of a series of metal silicates, is considered as a highly effective scavenger of organic pollutants and heavy metals [40], [41]. Recently, most researchers focus on preparing hollow nanospheres and nanotubes via different methods, which have excellent adsorption performance [42], [43]. Magnesium silicates have often been synthesized by the surfactant-assisted approach or nanocasting method [42], [44]. Mesorpous silica materials play a key role in synthesizing magnesium silicates via the surfactant-assisted method. Thus, it is very imorptant to find a suitable silica support.
As a kind of excellenet materials, mesporous silica has been topic of interest due to their excellent properties. Up to now, many reaearchers have synthesized the silica materials with controlling their structural characteristics, such as SBA-15, MCM-41 and KCC-1, which have significant effects on their properties [45], [46], [47], [48]. Mesoporous silica materials, have shown excellent features in catalysis, delivery and adsorption [49], [50], [51], [52], [53], [54]. Recently, Cui et al. have successfully prepared magnetic elongated hollow mesoporous silica nanocapsules (MSNCs) [55]. Considering excellent structure properties, MSNCs are chosen as the assisted-templated for preparing low-cost and enviromental magnetic magnesium silicates.
Inspired by the aforementioned considerations, we have successfully synthesized the novel hollow double silica @ mesoporous magnesium silicate magnetic hierarchical nanotubes using mesoporous silica nanocapsules as the assisted templates to remove two kinds of cationic dyes. MgSNTs have excellent adsorption capacities for the removal of methylene blue and rodamine B owing to large specific surface area, pore volume and pore size. In addition, it could be easily recovered from solution with the help of γ-Fe2O3 in the inner chamber. Moreover, the adsorption capacity, adsorption kinetics, the influence of pH and adsorption mechanism were also carefully and comprehensively investigated.
Section snippets
Experimental section
The synthesis route of MSNCs, the key of the whole synthesis process, was shown in Scheme 1. MgSNTs were synthesized by using mesoporous silica nanocapsules as the assisted templates. The detailed synthesis process was as follows.
Characterization of MgSNTs
The morphology of MWCNTs, Fe3O4/MWCNTs, MWCNTs/Fe3O4@SiO2 and MSNCs was analyzed by TEM as shown in Fig. 1. TEM images of Fig. 1b showed that Fe3O4 nanoparticles were uniformly dispersed on the surface of MWCNTs. SiO2 with thin layers was successfully distributed on the surface of Fe3O4/MWCNTs (Fig. 1c), which was then obtained MSNCs (Fig. 1d) by calcining at 550 °C in air. The shell of MSNCs was about 100 nm in thickness. Fig. 2 showed the TEM images of MgSNTs and MSNCs. Fig. 2b–c showed clearly
Conclusions
In summary, we have successfully prepared novel MgSNTs with high specific surface, high average pore width and pore volume for the first time. To the best of our knowledge, the specific surface is larger than that of previous reported magnesium silicates. Moreover, the adsorption capacity, the influence of pH, adsorption kinetics and adsorption mechanism are also carefully investigated. Compared to adsorption capacities previous reported magnesium, the adsorbent we prepare has high removal
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