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Research on functionalized covalent organic framework (COF) materials with good hydrophilic characteristics is significant on account of their application in the removal of dyes in wastewater. In this work, two anionic COF materials (TFPB-Pa-SO3H COF and TFPB-BDSA COF) were successfully synthesized with sulfonated modification as dyestuff sorbents to be used for the adsorption of cationic dyes. The two prepared COF materials exhibited predominant hydrophilicity with lower water contact angles (35° and 27°) than reported COF materials. The sulfonated groups on the COFs can efficiently adsorb cationic dyes via electrostatic interaction, which can moderately ameliorate their adsorptive capacity toward hydrosoluble dyes. TFPB-Pa-SO3H COF and TFPB-BDSA COF showed superfast adsorption equilibrium with methylene blue (1 and 2 min) and high adsorption uptakes of crystal violet (1559 and 1288 mg g−1), which manifested that the adsorption rate may be closely related to the solubilities of the host COF materials as well as the guest dye molecule in aqueous solution. Meanwhile, the adsorption stability between the COF materials and dye molecule adsorbed on the COF skeleton accounted for the highly effective adsorption of the target dye in a large quantity. In addition, TFPB-Pa-SO3H COF as an adsorbing material was successfully applied for the removal of dye molecules in real water samples. [ABSTRACT FROM AUTHOR]

This study was performed to investigate the potential application of a chitosan (CS) and quinoa polysaccharide (QS) composite aerogel for the adsorption of dyes from water. The properties of the synthesized CSQS composite aerogel were characterized by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), the Brunauer–Emmett–Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). Results showed that the CSQS composite aerogel possesses a porous, loose and flexible structure with a mesoporous nature and high hydrophobicity. Meanwhile, various factors such as the initial concentration, temperature, contact time, and pH have been investigated for evaluation of the optimum adsorption for the removal of Congo red (CR) and methylene blue (MB) in batch sorption experiments, and experimental results showed that the maximum adsorption capacity was found to be 342 mg g−1 for CR and 57.80 mg g−1 for MB under the optimum conditions. The adsorption kinetics of CR and MB on the CSQS composite aerogel were found to be well modeled by pseudo-second-order and pseudo-first-order kinetic models, respectively. In addition, the experimental equilibrium data were represented well by the Langmuir isotherm model. The results in this article demonstrated that the obtained aerogel is suitable for application in drinking water purification. The entire synthesis process of the CSQS aerogel is green and economical without additional need for toxic agents, which allows the process to greatly reduce the discharge of secondary pollution to the environment. The facile, scalable and general strategy presented here can be extended to the preparation of other polysaccharide-based aerogel materials, and has a good prospects for application in the removal of dyes from water. [ABSTRACT FROM AUTHOR]

The ion-exchange process is usually influenced by the surface properties of the adsorbents. In particular, the prophase adsorption/desorption process is confined by different crystal facets. In this research, spinel Li4Ti5O12 nanosheets with an exposed (1−14) high-index facet were prepared by a hydrothermal method followed by calcination treatment. Then, a H4Ti5O12 adsorbent was obtained, covered with the same (1−14) facets, after treatment with 0.2 M HCl. This special facet-exposed H4Ti5O12 has high cycling ability, with the adsorption uptake remaining at 96.84% after four cycles, a fast adsorption equilibrium time (equilibrium time < 60 min), excellent ion adsorption selectivity for Li+ uptake (separation factor: Li+ > K+ > Ca2+ > Na+ > Mg2+), and good adsorption capacity for Li+ uptake (21.57 mg g−1). With the help of X-ray photoelectron spectroscopy analyses, the Li+ adsorption process on the H4Ti5O12 nanosheets is shown to be an ion-exchange process. In addition, the coordination relationship between lithium and oxygen ions was investigated, illustrating that the four-coordinated structure is more stable than other complexes. These results indicate that hydrogen ions are exchanged for lithium ions at tetrahedral 8a sites, leading to the H4Ti5O12 structure with high stability in the adsorption–desorption cycling process. [ABSTRACT FROM AUTHOR]

Lithium-rich spinel lithium manganese oxide (LMO) compounds are one kind of promising adsorbents for lithium recovery from brine due to their high capacity and low Mn dissolution; Li1.6Mn1.6O4 is one of them. However, Mn3+ exists in the Li1.6Mn1.6O4 precursor due to incomplete reaction during syntheses, and the disproportionation reaction of Mn3+ inevitably results in Mn dissolution during lithium adsorption and desorption. The stable recycling and structural stability of Li1.6Mn1.6O4 were improved in aqueous lithium resources through K-gradient doping (LMO-K). The dissolution of Mn is reduced to 4.0% from 5.4% (before doping) and the adsorption capacity is kept at high capacity (31.6 mg g−1) at a low Li+ concentration of 12 mmol L−1. In addition, first-principles calculations further confirm that K substitutes for Li at 16d sites, leading to the stabilization of the Mn cations in the compound. With the help of K doping, the undesired dissolution of Mn in the cycle process is inhibited, which may be due to the reduction in the content of Mn3+ and improvement in the structural stability of the adsorbent. [ABSTRACT FROM AUTHOR]