No abstract

It remains a big challenge to develop high-efficiency and low-cost adsorption materials to remove toxic heavy metal ions in water. Here, we developed a template-free synthesis method to fabricate high surface area and large pore size magnesium silicate hierarchical nanostructures in a mixed solvent of ethanol and water and carefully investigated the corresponding adsorption behavior for Pb2+, Zn2+, and Cu2+ in aqueous solution. The results reveal that the ethanol volume fraction in the solvent plays an important role to optimize the pore structure, which directly determines the adsorption capacity and the adsorption rate for heavy metal ions. When the ethanol volume fraction is beyond 50%, the obtained magnesium silicate presents a flowerlike structure with a hierarchical pore distribution: 0.5–2, 2–30, and 30–200 nm. When the ethanol volume faction is 90%, for example, the sample exhibits a maximum adsorption capacity of 436.68, 78.86, and 52.30 mg/g for Pb2+, Zn2+, and Cu2+ ions, which has a BET surface area of 650.50 m2/g and an average pore diameter of 6.89 nm, respectively. Also, the sample presents excellent repeated adsorption performance after three elutions. The obtained materials show widely promising and practical applications in water treatment in a wide pH range from 2.8 to 5.8.

No 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.

It is of great and increasing interest to explore porous adsorption films to reduce heavy metal ions in aqueous solution. Here, we for the first time fabricated carbon paper@magnesium silicate (CP@MS) composite films for the high-efficiency removal of Zn and Cu by a solid-phase transformation from hydromagnesite-coated CP (CP@MCH) precursor film in a hydrothermal route and detailedly examined adsorption process for Zn and Cu as well as the adsorption mechanism. The suitable initial pH range is beyond 4.0 for the adsorption of the CP@MS to remove Zn under the investigated conditions, and the adsorption capacity is mainly up to the pore size of the porous film. The composite film exhibits excellent adsorption capacity for both of Zn and Cu with the corresponding maximum adsorption quantity of 198.0 mg g for Zn and 113.5 mg g for Cu, which are advantageous over most of those reported in the literature. Furthermore, the adsorption behavior of the CP@MS film follows the pseudo-second-order kinetic model and the Langmuir adsorption equation for Zn with the cation-exchange mechanism. Particularly, the CP@MS film shows promising practical applications for the removal of heavy metal ions in water by an adsorption-filtration system.