Upcycling pharmaceutical capsules into porous activated carbon and activated carbon ash for efficient emerging contaminant removal

Abstract

The management of pharmaceutical waste remains a significant challenge and presents opportunities for the development of value-added materials. In this study, discarded pharmaceutical gelatin capsules were converted into activated carbons and Ti-rich inorganic residues through sequential carbonization (700 °C), CO2 activation (850 °C), and calcination, enabling the simultaneous valorization of both the carbonaceous and inorganic fractions of the waste. The resulting activated carbons (ACHC and ACSC) exhibited well-developed micro/mesoporous structures and oxygen and nitrogen-containing surface functionalities, while the inorganic residues retained Ti-containing phases derived from capsule excipients. ACSC exhibited the highest surface area (675 m2 g−1) and adsorption capacities toward methylene blue, acetaminophen, and bisphenol A (225, 380, and 112 mg g−1, respectively). Adsorption equilibrium data were best described by the Sips and Redlich–Peterson models, indicating heterogeneous adsorption behavior and a distribution of adsorption sites. The calcined ash fractions exhibited photocatalytic activity toward methylene blue degradation under UV irradiation, with ACHC ash achieving approximately 70% removal after 350 min. Dark adsorption control experiments demonstrated negligible methylene blue uptake by the ash materials, indicating that the observed removal under irradiation was predominantly associated with photocatalytic degradation. The results demonstrate that both the carbonaceous and inorganic fractions generated during the thermal conversion of pharmaceutical capsule waste can be further utilized as functional materials for contaminant removal, highlighting the potential of this approach as an integrated waste valorization strategy. Graphical abstract