Removal of methylene blue dye from aqueous solution using coffee silverskin biomass as a low-cost adsorbent

The search for effective and low-cost adsorbents to remove dyes from industrial effluents has promoted the demand for new research aimed to mitigate negative impacts caused to the environment. In this sense, this work aimed to evaluate the potential of coffee silver skin (PPC) as a low-cost adsorbent in the removal of methylene blue (MB) dye from aqueous solutions through studies of kinetics and adsorption equilibrium. Subsequently, the material was subjected to physicochemical characterization, specific surface area (BET), presence of functional groups (FTIR), elemental analysis (CHNS-O), point of zero charge (pH(PZC)), and crystallinity (XRD). The results showed that PPC presented a predominantly amorphous structure composed of holocellulose (38.36%), lignin (34.97%). and minerals (potassium. calcium. and magnesium). The low specific surface area (0.383 m(2)/g) was compensated by the diversity of surface functional groups containing oxygen. confirmed by the predominance of carbon (55.93%), oxygen (32.91%), and hydrogen (6.37%). The pH(PZC) analysis showed that the point of zero charge of the PPC was 6.49. The equilibrium time of the adsorption process was 24 h, following kinetics described by the Elovich model (R-(aj.)(2) = 0.999; chi(2) = 0.233), which represented an initial adsorption rate (alpha) and desorption rate (beta) corresponding to 2.405 mg/g.min and 0.587 mg/g, respectively. The adsorption equilibrium data were better fitted by the Langmuir model (R-(aj.)(2) = 0.991; chi(2) = 99.176). indicating that the adsorption of MB by PPC occurred on the monolayer. The adsorption of MB by PPC was favorable, presenting separation factors (R-L) between 0.58 and 0.03. The maximum adsorption capacity of PPC (Q(max) = 313.69 mg/g) was superior to other types of low-cost adsorbents reported in the literature, thus demonstrating its potential use as an adsorbent for the removal of cationic dyes from aqueous solution.