Abstract
Magnesium silicate as a high-performance adsorption material has attracted increasing attention for the removal of organic dye pollution. Here, we prepared a series of magnesium silicate hydrates (MSH) in a hydrothermal route, and carefully investigated the corresponding adsorption behavior towards methylene blue (MB) as well as the effect of surface charge on adsorption capacity. The results show that surface charge plays a key role in the adsorption performance of MSH for MB, a negative surface charge density follows the increase of Si/Mg feeding ratio from 1.00 to 1.75, and furthermore the higher negative charge favors the improvement of the adsorption capacity. Among four investigated samples (MSH = 1.00, 1.25, 1.50, and 1.75), MSH-1.75 has the highest negative surface charge and shows the largest adsorption capacity for MB. For example, the equilibrium adsorption quantity is 307 mg·g−1 for MSH-1.75, which is 35% higher than that of 227 mg·g−1 for MSH-1.00. Besides, for MSH-1.75, the as-prepared sample with negative charge exhibits ca. 36% higher adsorption quantity compared to the sample at the zero point of charge (pHZPC). Furthermore, magnesium silicate hydrate material with Si/Mg feeding ratio = 1.75 demonstrates the promising removal efficiency of beyond 98% for methylene blue in 10 min, and the maximum adsorption capacity of 374 mg·g−1 calculated from the Langmuir isotherm model.
Highlights
Various synthetic dyes have been developed and have played an important role in modern life
The chemical composition of four samples were further determined by ICP and energy-dispersive X-ray spectroscopy (EDX), and the corresponding results were summarized in Table 1 and Figure S1 (Supporting Information), respectively
One observes that all the four samples have similar chemical composition while the determined Si/Mg ratios slightly increase with the same trend as the Si/Mg feeding ratios, which are in the Si/Mg ratio range of the reported in the literature [24]
Summary
Various synthetic dyes have been developed and have played an important role in modern life. Magnesium silicate as a high-performance and sustainability adsorption material has attracted increasing interest to remove heavy metal ions and various kinds of dyes [4,5]. The surface properties play crucial roles in enhancing the adsorption capacity [12,13,14,15,16]. We fabricated a series of magnesium silicate hydrate (MSH) adsorbents with different surface charge density by adjusting the Si/Mg feeding ratio in a hydrothermal route, and carefully investigated the corresponding adsorption behavior for methylene blue as well as the relationship between surface charge density and adsorption capacity
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