MOF-based Ca-alginate/PAA granulate beads for efficient heavy metal removal from water: Synthesis, performance, and mechanism

Developing high-efficient and easy-to-recover adsorbents for the removal of toxic metals in water is imperative, although it poses a huge challenge. In this study, a sulfur-functionalized metal-organic framework was incorporated into Ca-alginate/polyacrylic acid granulates as an effective adsorbent (abbr. CPZ-SH) for Cu2+ and Cd2+ removal. The physicochemical properties of the obtained CPZ-SH were determined by the integrated characterization techniques (e.g., FTIR, XRD, and SEM). The environmental effects of solution pH, typical background cations (K+, Na+, Mg2+, and Ca2+), and dissolved organic matter were assessed to determine the adsorption behaviors of the granulates. Time-dependent adsorption kinetics suggested that the adsorption process was dominated by an intraparticle diffusion procedure. CPZ-SH exhibited maximum adsorption capacities of 75.8 and 48.4 mg g–1 at 30 ℃, and excellent adsorption reusability with Cu2+ and Cd2+ adsorption efficiencies over 96.0% and 85.1% after 10 cycles, respectively. The extended X-ray absorption fine structure (EXAFS) demonstrated that the functional groups (thiol, carboxyl, and hydroxyl) played a crucial role in adsorption processes. The findings provided an effective strategy to construct nanostructured metal-organic frameworks (MOFs) into granulates as recyclable adsorbents and enable heavy metal removal from water.