Harnessing Temperature-Dependent Breathing Behaviour in Aluminium-Based MOF for Enhanced Congo Red Dye Removal

Abstract

A novel and efficient strategy for dye adsorption is provided by unlocking the temperature-dependent breathing behaviour of aluminium-based metal–organic frameworks (Al-MOF). Distinct from conventional MOF adsorption studies, this research uniquely elucidates the dynamic structural adaptations of Al-MOFs that enable the accommodation of large dye molecules, specifically Congo red (CR). Hydrothermally synthesised Al-MOFs—extensively characterised to confirm exceptional crystallinity, high porosity (BET surface area of 173 m² g⁻¹), and thermal stability—exhibit a remarkable temperature-responsive ‘breathing’ mechanism. Elevated temperatures induce reversible phase transitions from narrow to large pores, resulting in a significant expansion of pore volume that dramatically enhances CR adsorption, achieving a maximum capacity of 223.8 mg g⁻¹. The adsorption behaviour conforms to the Langmuir model (R² > 0.990) and follows pseudo–second-order kinetics (R² = 0.993), confirming homogeneous chemisorption. Thermodynamic analysis indicates that the adsorption process is both spontaneous (ΔG° < 0 at ≥ 303 K) and endothermic (ΔH° = +82.06 kJ mol⁻¹, ΔS° = +271.7 J mol⁻¹ K⁻¹), further substantiating the role of the breathing mechanism. Importantly, the Al-MOF demonstrates outstanding reusability, retaining over 90% adsorption efficiency after five cycles. These findings firmly establish temperature-responsive breathing Al-MOFs as transformative, thermodynamically favourable, and highly reusable adsorbents, offering a promising solution for the advanced environmental remediation of hazardous dye pollutants.