1 Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC, H4B 1R6, Canada; Quebec Centre for Advanced Materials, Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, H4B 1R6, Canada.
2 Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC, H4B 1R6, Canada; Quebec Centre for Advanced Materials, Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, H4B 1R6, Canada. Electronic address: adedapo.adeola@concordia.ca.
3 Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC, H4B 1R6, Canada; Quebec Centre for Advanced Materials, Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, H4B 1R6, Canada. Electronic address: rafik.naccache@concordia.ca.

Rapid global urbanization and population growth have ignited an alarming surge in emerging contaminants in water bodies, posing health risks, even at trace concentrations. To address this challenge, novel water treatment and reuse technologies are required as current treatment systems are associated with high costs and energy requirements. These drawbacks provide additional incentives for the application of cost-effective and sustainable biomass-derived activated carbon, which possesses high surface area and low toxicity. Herein, we synthesized microporous activated carbon (MAC) and its magnetic derivative (m-MAC) from tannic acid to decaffeinate contaminated aqueous solutions. Detailed characterization using SEM, BET, and PXRD revealed a very high surface area (>1800 m²/g) and a highly porous, amorphous, heterogeneous sponge-like structure. Physicochemical and thermal analyses using XPS, TGA, and EDS confirmed thermal stability, unique surface moieties, and homogeneous elemental distribution. High absorption performance (>96 %) and adsorption capacity (287 and 394 mg/g) were recorded for m-MAC and MAC, respectively. Mechanistic studies showed that the sorption of caffeine is in tandem with multilayer and chemisorptive mechanisms, considering the models' correlation and error coefficients. p-p stacking and hydrogen bonding were among the interactions that could facilitate MAC-Caffeine and m-MAC-Caffeine bonding interactions. Regeneration and reusability experiments revealed adsorption efficiency ranging from 90.5-98.4 % for MAC and 88.6-93.7 % for m-MAC for five cycles. Our findings suggest that MAC and its magnetic derivative are effective for caffeine removal, and potentially other organic contaminants with the possibility of developing commercially viable and cost-effective water polishing tools.