The Effectiveness of Activated Carbon-Based PET Bottle Waste Modified With Iron Oxide Toward Congo Red Removal
Laelatul Fadilah1,a* and Lina Mahardiani2,b

1Department of Chemistry Education, Faculty of Teacher Training and Eductaion, Universitas Sebelas Maret, Jl. Ir. Sutami 36A Surakarta, Indonesia
alaelatulfadilah[at]student.uns.ac.id, bmahardiani.lina[at]staff.uns.ac.id

Abstract

Water pollution caused by synthetic dyes such as Congo Red (CR) is a serious environmental problem due to their toxic, persistent, and non-biodegradable nature. Meanwhile, the accumulation of polyethylene terephthalate (PET) bottle waste continues to rise and contributes to plastic pollution. This study integrates these two issues by utilizing PET waste as a raw material for activated carbon modified with Fe3O4 to produce an effective, easily separable, and reusable magnetic adsorbent for the removal of Congo Red from aqueous solutions. The synthesized adsorbents include PET-AC, PET-AC/Fe3O4 Oven, and PET-AC/Fe3O4 Furnace, which were characterized using FTIR, XRD, and N&#8322- Adsorption-Desorption Isotherms. The characterization results indicate the formation of characteristic functional groups of activated carbon and Fe-O bands in the modified adsorbents. XRD analysis confirmed the formation of a semi-crystalline Fe3O4 phase with a crystallinity of 6.90% in PET-AC/Fe3O4 Oven and 18.47% in PET-AC/Fe3O4 Furnace. BET analysis showed a surface area of PET-AC of 622.7830 m2/g, which decreased to 323.7633 m2/g and 228.2129 m2/g after Fe3O4 modification due to partial pore closure of the adsorbent. Nevertheless, both modified adsorbents exhibited high adsorption capacity for CR, with PET-AC/Fe3O4 Furnace providing the best performance across all test variations. After four regeneration cycles, the PET-AC/Fe3O4 Furnace still maintained a removal efficiency of 96.729%. Isotherm studies indicate that adsorption follows the Langmuir model (R2 = 0.9770 and 0.9944), while kinetic studies follow the pseudo-second-order model (R2 = 0.9948 and 0.9971), suggesting monolayer adsorption dominated by chemisorption mechanisms. The results of this study indicate that Fe3O4-modified PET waste-based activated carbon has the potential to serve as an effective and sustainable adsorbent for dye wastewater treatment while supporting the utilization of plastic waste within the circular economy concept.

Keywords: Activated Carbon, PET, Fe3O4, Adsorption, Congo Red

Topic: Physical Chemistry