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In this study, activated carbon (AC) was prepared from agro-waste betel nut husks (BNH) through the chemical activation method. Different characterization techniques described the physicochemical nature of betel nut husks activated carbon (BNH-AC) through FTIR, BET, SEM, and pH point of zero charge. Later, the produced AC was used for methylene blue (MB) adsorption via numerous batch experimental parameters: initial concentrations of MB dye (25–250 mg/L), contact time (0.5–24 hours) and initial pH (2–12). Dye adsorption isotherms were also assessed at three temperatures where the maximum adsorption capacity (381.6 mg/g) was found at 30 °C. The adsorption equilibrium data were best suited to the non-linear form of the Freundlich isotherm model. Additionally, non-linear pseudo-second-order kinetic model was better fitted with the experimental value as well. Steady motion of solute particles from the boundary layer to the BNH-AC's surface was the possible reaction dynamics concerning MB adsorption. Thermodynamic study revealed that the adsorption process was spontaneous and exothermic in nature. Saline water emerged as an efficient eluent for the desorption of adsorbed dye on AC. Therefore, the BNH-AC is a very promising and cost-effective adsorbent for MB dye treatment and has high adsorption capacity.

In recent years, different biomaterials have garnered more research attention due to their usefulness as adsorbents. The present study focuses on a chemical treatment process to improve the adsorption capacity of betel nut husk fibers for a textile effluent (methylene blue). The fibers of chemically modified material were assessed using Fourier transform infrared (FTIR) spectrometer and Brunauer–Emmett–Teller (BET) analyzer to determine the existing surface functional groups and surface area, respectively. Parameters including contact time, dye concentration, temperature, effects of pH and desorption efficiency were also evaluated to identify optimum adsorption performance. Adsorption followed the Freundlich isotherm model and pseudo-first-order kinetics, indicating physisorption was responsible for adsorption and its occurrence on multilayers. Adsorption capacity was 149.921 mg/g, 149.874 mg/g and 145.462 mg/g at 30, 40 and 50, respectively, and was best at 30 °C. ΔH° was found to be − 1.494 which suggests adsorption is exothermic in nature and thus satisfying the findings that the physical process of adsorption took place in this study.

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