Adsorption of methyl orange onto yellow passion fruit peel (Passiflora edulis sims) modified with nitric acid and sodium hydroxide.

• DOI: https://doi.org/10.22533/at.ed.9162429112

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• Abstract: Brazil is the world's largest producer of passion fruit, and its peel is a residue of the juice production industries. This material is rich in pectin, which, when removed by acid or basic treatments, leaves behind a lignocellulosic residue that can be utilized as an adsorbent. In this study, we examined the utilization of passion-fruit peel treated with nitric acid and sodium hydroxide as an adsorbent for acidic dyes. The adsorption of methyl orange was studied in batch, varying the initial concentration of dye from 100 to 1000 mg L -1 and the temperature from 298 to 348 K. The passion fruit peel proved to be 2 a promising adsorbent for the methyl orange dye, with adsorption capacities ranging from 263.16 to 322.58 mg of dye per gram of adsorbent Treating the sample with either acid or base enhanced the adsorption capacity, with the basic treatment proving more effective. The adsorption process follows the Langmuir model, and its kinetics can be mathematically described by the pseudo-second order equation. Diffusion studies revealed that the diffusion within the solution influences the results, serving as the rate- limiting step of the process. The adsorption of methyl orange onto passion fruit peel is an exothermic process. It occurs with decreasing entropy, and the Gibbs free energies obtained indicate that the process is spontaneous at temperatures near room temperature. The enthalpy values indicate that the adsorption of methyl orange over passion fruit peel is a physical process.