Zirconium based metal organic frameworks (Zr-MOFs) have become popular in engineering studies due to their high mechanical stability, thermostability and chemical stability. In our work, by using a theoretical kinetic adsorption isotherm, we can exert MOFs to an acid dye adsorption process, experimentally exploring the adsorption of MOFs, their external behavior and internal mechanism. The results indicate their spontaneous and endothermic nature, and the maximum adsorption capacity of this material for acid orange 7 (AO7) could be up to 358 mg·g−1 at 318 K, estimated by the Langmuir isotherm model. This is ascribed to the presence of an open active metal site that significantly intensified the adsorption, by majorly increasing the interaction strength with the adsorbates. Additionally, the enhanced π delocalization and suitable pore size of UiO-66 gave rise to the highest host–guest interaction, which further improves both the adsorption capacity and separation selectivity at low concentrations. Furthermore, the stability of UiO-66 was actually verified for the first time, through comparing the structure of the samples before and after adsorption mainly by Powder X-ray diffraction and thermal gravimetric analysis.

Isostructural zirconium-based metal–organic frameworks (Zr-MOFs) have attracted the attention of researchers because of their remarkable stability at high temperatures and high pressures and their chemical stabilities against acids and bases. Due to this stability, Zr-MOFs can be utilized in adsorption research, and the adsorption performance of a Zr-MOF depends on the pore size and the surroundings of the MOF. In this study, as the dimensions changed and the adsorption was carried out, the Zr-MOF material remained stable, and the adsorption of the best state was achieved at 235 mg/g. Through the simulation of theoretical kinetic models of Zr-MOFs, we initially postulated that the adsorption capacity is proportional to the pore size and that acid orange 7 (AO7) was adsorbed by the MOFs. Afterwards, we verified our hypotheses through a series of Brunauer–Emmett–Teller (BET) data analysis; non-local density function theory (NLDFT) was mainly used to analyze the data. Moreover, we determined that physical adsorption occurs on the surface of the MOFs during the adsorption process, while chemisorption occurs in the form of dye molecules combining with active sites. Ultimately, we concluded that the larger the pore size, the stronger the adsorption capacity, and this contribution casts a new light on the issue of wastewater treatment.

a b s t r ac tWater pollution is a serious threat to the human beings' survival and development and a universal problem across community society. In this work, a novel β-cyclodextrin (β-CD) hydrogel was successfully synthesized by polycondensation reaction using epichlorohydrin (EPI) and β-CD under basic condition, and the swelling ratio at room temperature was up to 181%. The adsorption behavior and adsorption mechanism of EPI crosslinked β-CD were evaluated by using acid orange 7 (AO7) as a model dye. We found that the adsorption process obeyed the pseudo-second-order kinetic model, and the maximum adsorption capacity of AO7 was estimated to be 132 mg g -1 , which is much higher than the bamboo charcoal, titanium dioxide and so on. Moreover, intraparticle diffusion model indicates that the adsorption process can be divided into three stages: diffusion of the AO7 to β-CD hydrogel surface, intraparticle diffusion, establishment of the adsorption equilibrium, and the host-guest interaction between the hydrophobic naphthyl group and the cavity of β-CD plays the decisive role in the adsorption of AO7 onto β-CD hydrogel.

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