Valorization of expired carvedilol-based pharmaceuticals into porous carbon materials via pyrolysis and sonication-assisted acid etching.

Expired pharmaceuticals have become an environmental concern due to inappropriate disposal and the lack of sustainable waste valorization strategies. In this study, expired carvedilol tablets were utilized as a pharmaceutical waste-derived precursor for producing porous carbon materials through the integration of controlled pyrolysis and probe-sonication-assisted acid etching. Pyrolysis was performed at 700-900 °C under an inert atmosphere to promote devolatilization, aromatization, and pore formation, followed by acid etching under different conditions to tailor surface chemistry and pore structure. The materials were characterized using CHNO elemental analysis, Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy with Energy-Dispersive X-ray analysis (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analyses. CHNO analysis revealed that carbon content increased from 76.61% to 86.14% with increasing pyrolysis temperature, indicating progressive carbonization and aromatization. Pyrolysis at 800 °C provided an optimal compromise between structural integrity and surface functionality, whereas moderate acid etching conditions (1 M H_2SO_4, 60 min) promoted pore development while preserving the carbon framework. BET analysis revealed increased surface area and pore restructuring after etching, while FTIR, SEM-EDX, XPS, and CHNO analyses confirmed carbon enrichment, controlled surface modification, and improved structural homogeneity. Furthermore, probe-type sonication promoted controlled surface modification and pore development under the optimized etching conditions. Overall, the systematic integration of controlled pyrolysis and probe-sonication-assisted acid etching provides an effective strategy for transforming expired pharmaceutical waste into porous carbon materials. This approach offers a sustainable pathway for pharmaceutical waste valorization while supporting functional carbon materials for environmental and adsorption-related applications within a circular economy framework.