Adsorptive Removal of Phosphate from Water Using Aluminum Terephthalate (MIL-53) Metal–Organic Framework and Its Hollow Fiber Module

The aluminum terephthalate (MIL-53) metal–organic framework (MOF) (MIL-53(Al)) was evaluated as an adsorbent for removing phosphates from aqueous solutions. XRD and FTIR were used to confirm the molecular structure. TGA/DSC was used to measure its stability. The green synthesizing MIL-53(Al) showed good performance as a highly efficient adsorbent. The adsorbed MIL-53(Al) nanoparticles still retain their original morphology according to SEM, allowing it to be easily separated from the aqueous solution via filtration. Additionally, the thermal stability of synthesized MIL-53(Al) is capable of withstanding temperatures up to 500 °C, as confirmed by TGA/DSC. Using different initial concentrations of Na2HPO4 and ICP-OES measurements, we determined the adsorption values of Na2HPO4 by MIL-53(Al) as a function of time. Three kinetic models (pseudo-first-order, pseudo-second-order, and Elovich) and three isotherm models (Langmuir, Freundlich, and Temkin) were used to evaluate the phosphate adsorption behavior of MIL-53(Al) powder in Na2HPO4 aqueous solution. Error functions are used to evaluate various kinetic and isotherm models related to different physical processes. From the analysis of the adsorption experiments, the Elovich model is the best-fitting kinetic model, showing that the adsorption rate decreases with increasing adsorption capacity. Furthermore, error function analysis identified the Freundlich model as the most suitable, indicating that complicated adsorption coexists with physisorption, and chemisorption synergistically drives the adsorption process. The module utilizing MIL-53(Al) hollow fibers also demonstrated preliminary attempts at phosphate adsorption and desorption for the first time. This work demonstrated that MIL-53(Al) is an exceptionally stable adsorbent for removing phosphate from contaminated wastewater.