Novel Al-doped UiO-66-NH2 nanoadsorbent with excellent adsorption performance for tetracycline: Adsorption behavior, mechanism, and application potential

Metal doping, an alternative strategy to enhance the adsorption performance of metal-organic frameworks (MOFs), is a hot research direction of MOF modification. However, the commonly used doping metals are mostly rare metals, which increase the cost and may lead to secondary pollution. Thus, the practical application of metal doping in MOF modification is limited. Herein, Aluminum (Al), an abundant, cheap, and environmentally friendly metal, was doped in UiO-66-NH2 to prepare Al-UiO-66-NH2 to adsorb tetracycline (TC) effectively. The optimal Al doping ratio for preparing Al-UiO-66-NH2 was determined, and the physicochemical characteristics of the prepared Al-UiO-66-NH2 were obtained. Adsorption performance and reusability were investigated. Furthermore, the possible adsorption mechanisms were explored, and the anti-interference adsorption ability and application potential were evaluated. The optimal Al doping ratio was 1:1 (Zr/Al molar ratio), and the adsorption capacity of Al-UiO-66-NH2 was 6.86 times higher than that of UiO-66-NH2. Compared with UiO-66-NH2, Al-UiO-66-NH2 had smaller particle size, larger specific surface area and pore size, and more coordinated NH2-BDC. For TC adsorption, the process was spontaneous and endothermic and fitted well with the pseudo -second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity obtained by the Langmuir model was 520 mg/g. Pore filling, electronic interaction, H-bonding interaction, complexation, 7C-7C interaction, and Lewis acid-base interaction took part in the adsorption. Al-UiO-66-NH2 could be reused, while exhibiting high water stability and a certain anti-interference performance for TC adsorption. Overall, Al-UiO-66-NH2 was an alternative MOF adsorbent for the treatment of wastewater containing TC with desirable application potential.