Engineering Nanostructured Catalysts for Structural Evolution and Textural Maturation in Co-Pyrolyzed Polystyrene–Biomass Carbons for Efficient Tetracycline Removal

The sustainable valorization of non-recyclable synthetic polymers alongside agricultural residues into high-value carbonaceous materials represents an imperative pathway for environmental remediation and waste management. In this study, a nanostructured Ru/CeO2 catalyst was successfully synthesized via a hydrothermal route followed by chemical reduction, and its catalytic influence on the co-pyrolysis of waste polystyrene (PS) and corn stalks (CS) was systematically investigated. Powder X-ray diffraction (XRD) confirmed the formation of pure cubic fluorite CeO2 (JCPDS No. 34-0394) with highly dispersed Ru nanoparticles. Incorporating Ru/CeO2 into the PS/CS blend (mass ratio 1:2) during co-pyrolysis at 500 ∘C for 1.5 h significantly enhanced the structure and porous architecture of the resulting biochar. Nitrogen physisorption analysis revealed a substantial increase in the Brunauer–Emmett–Teller specific surface area (SBET) from 58.74 m2/g (non-catalytic) to 115.94 m2/g (catalytic), alongside concurrent improvements in micropore volume (Vmicro from 0.027 cm3/g to 0.049 cm3/g) and total pore volume (Vtotal from 0.058 cm3/g to 0.117 cm3/g). Mechanistically, the active Ru species are proposed to facilitate structural transformation and volatile cracking, while the redox couple is hypothesized to regulate the local oxygen micro-atmosphere, thereby favoring the formation of microporous polycyclic aromatic structures is strongly supported by ex situ characterizations such as BET, SEM, XRD, and FTIR observations in this work and previous literature. More importantly, the evaluation of tetracycline (TC) removal efficiency from wastewater was conducted to compare the performance of activated carbons synthesized with and without the addition of the Ru/CeO2 catalyst during the co-pyrolysis stage. At the treatment tests (C0=50 mg/L, 0.5 g/L dosage, 100 min), Ru/CeO2-AC demonstrated outstanding performance, achieving 95.9% Tetracycline removal versus 89.6% for the non-catalyzed counterpart (AC0). These findings demonstrate that Ru/CeO2-assisted co-pyrolysis provides an effective strategy for engineering high-performance microporous carbon materials from mixed organic waste.