Investigation of the adsorption potential of green coffee husks biochar activated with K2CO3 for caffeine removal from water

Abstract

The abundant coffee by-products in Vietnam have great potential for producing environmentally friendly adsorbent materials, increasing the value of processed coffee products, contributing to climate change mitigation. The objective of this study is to evaluate the microstructure of coffee husk biochar (BC) and potassium carbonate-activated biochar (BC-K₂CO₃) revealed the material has rough surface with numerous pores ranging from 100 nm to 300 nm. When used at a dosage of 0.1 g/mL with an adsorption time of 120 minutes and an initial caffeine concentration below 0.025 g/mL, it achieved an adsorption efficiency of over 89.75%. The kinetic caffeine adsorption of BC- K₂CO₃ aligns well with the Freundlich adsorption isotherm model (R² >0.992). BC-K₂CO₃ exhibited a maximum adsorption capacity (Q_m = 33.74 mg/g), significantly higher than the control sample biochar BC (Q_m = 13.99 mg/g), which was produced under the same pyrolysis conditions without K₂CO₃ activation.