Effects of different pyrolysis temperatures on the structural tuning of cerium-based metal-organic frameworks and adsorption performance of tetravalent selenium

Selenium dioxide (SeO₂) is a carcinogenic pollutant that must be effectively removed to ensure the safety of the water supply. In this study, a series of Ce–MOFs adsorbents and their derivatives with different structures and properties were successfully prepared by using microwave digestion and anaerobic carbonisation techniques. The pyrolysed Ce–MOFs exhibit excellent adsorption capabilities, with their Se(Ⅳ) adsorption properties and efficiencies significantly outperforming the majority of data presented in the existing literature. For example, the Ce–MOFs obtained by pyrolysis at 300 ℃ and 600 ℃ reached adsorption equilibrium in only 9 min at solution pH 8 and 4, and the maximum adsorption capacity could reach 331.12 and 354.61 mg/g, respectively. The adsorption kinetics and isotherms indicated that the primary mechanisms involved were chemisorption and liquid film diffusion. Additionally, Ce–MOFs demonstrated the capacity to effectively adsorb phosphate, sulfate, and silicate, exhibiting good reusability. The application of characterisation techniques, including XRD, SEM, FTIR and XPS, has demonstrated that the carbon skeleton underwent a gradual detachment, accompanied by significant alterations to the morphology, pore size distribution and surface functional groups. This resulted in the exposure of an increased number of CeO₂ lattices and oxygen vacancies, which in turn led to the formation of a greater number of adsorption sites. The aforementioned adsorption sites are more favourable for Se(Ⅳ) adsorption through electrostatic attraction and ligand exchange, among other mechanisms. This study provides a scientific basis for the application of Ce–MOFs in the field of environmental remediation, as well as valuable data for further optimising the design and preparation of adsorbents, and new ideas and methods for solving the problem of water environmental pollution.