An evaluation of average values of both r2 and RMS shows that phenylalanine adsorption was better described by Langmuir and Tempkin models. Langmuir model is associated to homogeneous and monolayer adsorption. The homogeneous nature of the adsorption process is confirmed by the Tempkin model, which is characterized by a uniform distribution of binding adsorption energies. Regarding Freundlich isotherm, the slope 1/n ranging between 0 and 1 is a measure of adsorption intensity. A value for 1/n below one indicates a normal Langmuir isotherm while 1/n above one is indicative of cooperative adsorption. An average value of 0.46 was observed for 1/n, corroborating the homogeneous nature

of the adsorbent surface, consistent with the good Langmuir

and Tempkin fits. Maximum PHE uptake capacity, based Oligomycin A on Langmuir model, was 69.5 mg g−1, a comparable value to other adsorbents reported in the literature for PHE adsorption ( Table 4). The adsorption capacity was either equivalent or higher than more expensive adsorbents such as zeolites and polymeric resins. The study of single component adsorption, e.g., phenylalanine, is relevant to establish the adsorption mechanisms that occur in the studied system thus allowing the adsorption conditions to be set in order to favor its removal in multi-component systems, e.g., in protein hydrolysates where other amino acids compete for adsorption. This study showed that PHE was predominantly adsorbed by hydrophobic interactions, in which the phenyl ring is Montelukast Sodium the main portion of the molecule interacting with the surface of the adsorbent, probably with its constitutive graphene rings. Also, Doulia et al. (2001) demonstrated that the phenolic Target Selective Inhibitor Library amino acids tryptophan, phenylalanine and tyrosine will be preferably adsorbed when in solution with other amino acids due to their higher hydrophobicity. Thus, the multi-component adsorption of amino acids in a solution where only the phenolic ones are present should provide a reasonable scenario of what would happen to the phenylalanine when present in solution with other amino acids, phenolic or not, and it is the

scope of an ongoing work. Defective coffee press cake was thermally and chemically treated and successfully used as an adsorbent for the removal of phenylalanine from aqueous solutions. The adsorbent was essentially microporous, with an adequate chemical make-up at the surface. The predominant adsorption mechanism was evaluated as of a hydrophobic type, but others were also observed depending on the solution pH. The adsorption equilibrium data were better described by the Langmuir equation, indicating homogeneous adsorption. The maximum value of uptake capacity for the adsorbent/adsorbate system studied was comparable to values encountered in the literature for other types of adsorbents. The results herein presented indicate that PHE removal from aqueous solutions can be satisfactorily accomplished by a residue-based adsorbent.