Mercury Removal from Aqueous Solution Using ETS-4 in the Presence of Cations of Distinct Sizes

Bis-Schiff base cellulosic nanocrystals for Hg (II) removal from aqueous solution with high adsorptive capacity and sensitive fluorescent response

Mercury pollution in aqueous solutions is a severe problem in environmental protection and the contaminated water may cause serious risks to human health. Based on the constant development of adsorptive materials, adsorption technique is widely applied as an efficient and convenient approach to eliminate mercury species from waters. In this work, we report a one-pot procedure to prepare a bis-Schiff base cellulosic adsorbent to integrate the advantages of large adsorptive capacity and excellent fluorescent recognition towards mercury ions. The adsorption experiments demonstrate that sulfydryl-contained cellulosic nanocrystals exhibit specific affinity with mercury species and the adsorption capacity reaches as high as 624.8 mg/g at room temperature. Besides, the introduction of rhodamine moiety endows the material a 19 times enhancement of selective "off-on" fluorescent sensing while exposed to mercury. Additionally, the bifunctional adsorbent material shows high sensitivity towards mercury ions in aqueous solution with detection limits of as low as 8.29 × 10^-8 M for fluorescence and 5.9 × 10^-9 M for UV-vis spectrum, respectively. The fitting results of the adsorption models indicate a monolayer adsorption during the uptake of mercury ions and the removal process follows the pseudo-second order kinetics. Moreover, density functional theory studies are employed to further understand the adsorptive and responsive mechanisms.

Vibrational Spectral Analysis of Natisite (Na2TiSiO5) and its Structure Evolution in Water and Sulfuric Acid Solutions

Natisite (Na₂TiSiO₅) is a layered sodium titanosilicate containing TiO₅ square pyramids. The structure evolution of natisite in water and acid solutions is the basis for its potential applications. With Na₂SiO₃ as the silicon source, natisite with the shape of the square sheet was selectively prepared from the hydrothermal method with 14.3 mol/L NaOH solution at 240 °C. Natisite has 20 Raman active modes and 22 infrared active modes from the first-principles calculations within density functional theory, and the calculated Raman and infrared spectra agree well with the experimental ones. The characteristic Raman peak at 844 cm⁻¹ is caused by the symmetric stretching of the apical Ti–O bond in the TiO₅ unit, assigning to A_1g and B_2g modes. Natisite remains relatively stable in water with a sodium leaching percentage of lower than 6%. When washing with sulfuric acid solutions, the interlayer spacing of natisite is reduced due to the extensive removal of sodium ions, and an intermediate composed of SiO₄ and newly formed TiO₆ units may be formed. Moreover, after washing with water and acid solutions, 95.5%, 63.4%, and 35.2% of Na, Si, and Ti in natisite can be leached in total, respectively, resulting in the structural disintegration of natisite.