Herein, we report the synthesis and characterization of Ce(iii)-doped UiO-66 nanocrystals, revealing their potential to efficiently remove organic dyes such as methylene blue (MB), methyl orange (MO), Congo red (CR), and acid chrome blue K (AC) from aqueous solutions. Specifically, the room-temperature adsorption capacities of Ce(iii)-doped UiO-66 equaled 145.3 (MB), 639.6 (MO), and 826.7 (CR) mg g, exceeding those reported for pristine UiO-66 by 490, 270, and 70%, respectively. The above behavior was rationalized based on zeta potential and adsorption isotherm investigations, which revealed that Ce(iii) doping increases the number of adsorption sites and promotes π-π interactions between the adsorbent and the adsorbate, thus improving the adsorption capacity for cationic and anionic dyes and overriding the effect of electrostatic interactions. The obtained results shed light on the mechanism of organic dye adsorption on metal-organic frameworks, additionally revealing that the synergetic interplay of electrostatic, π-π, and hydrophobic interactions results in the operation of two distinct adsorption regimes depending on adsorbate concentration.
The solubilities and the refractive indices of the MgBr 2 −MgSO 4 −H 2 O system at 333.15 K were studied with the isothermal equilibrium solubility method. The phase diagram and refractive index diagram were plotted for this system at 333.15 K. The system belongs to hydrate II type. The phase diagram is constituted of three invariant points cosaturated with two salts, four univariant solubility isotherms saturated with one salt, and four stable crystallization fields in the ternary system corresponding to MgSO 4 · 6H 2 O (Hex), MgSO 4 ·4H 2 O (Tet), MgSO 4 ·H 2 O (Kie), and MgBr 2 ·6H 2 O (Mb). The calculated refractive index data agree well with the experimental results. Combining the experimental solubility data of the ternary system, the Pitzer binary parameters for MgBr 2 and MgSO 4 , and the Pitzer mixing ion-interaction parameter θ Br,SO 4 , the Pitzer parameter ψ Mg,Br,SO 4 and the solubility equilibrium constants K sp of solid phases in the ternary system at 333.15 K were fitted using the Pitzer and Harvie−Weare (HW) model. Then the solubilities for the ternary system at 333.15 K were calculated. A comparison between the experimental and calculated solubilities illustrates that the predicted data obtained with the model are in accordance with experimental results.
The densities and pH values in the system NaBO2–Na2SO4–H2O at 298.15 K and 323.15 K were investigated. Combining the equilibrium constants for different boron species, the distributions of six boron species in the mixed solution were calculated with total boron concentration and pH values. The molar fractions of the six boron species are mainly affected by the total boron concentration and temperature, but rarely affected by the concentration of SO42–. The dominant boron species in the mixed solution at the two temperatures is B(OH)4‒. The mole fraction of B(OH)3, B5O6(OH)4‒, and B3O3(OH)4‒ can be neglected. The polyborate ions are easier to form as the temperature increases. The results of distribution for boron species in this study and those with the Pitzer model can both be used to describe the distribution of boron species in the mixed solution.
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