Textile dyes removal from aqueous solution using Opuntia ficus-indica fruit waste as adsorbent and its characterization

• We use Opuntia ficus-indica fruit waste as adsorbent for the removal of textile dyes.
• Chemical activation increased the adsorption and specific surface area of the adsorbents.
• The adsorbents show cavities of different size and with irregular shape.
• The adsorbent-dye systems adjust themselves better to Freundlich's equation.

For this research, three different adsorbents, one untreated and two chemically activated, were prepared from Opuntia ficus-indica fruit waste. By the construction of adsorption isotherms, its adsorption capabilities and the viability of its use in the removal of textile basic and direct type dyes were determined. It was found that the adsorbent with the most adsorption capacity for basic dyes was the one activated with NaClO, and, for direct dyes, it was the one activated with NaOH. Langmuir and Freundlich equations isotherms were applied for the analysis of the experimental data. It was found that the Freundlich model best described the adsorption behavior. The adsorption capacity was improved when the pH of the dye solution had an acid value. The specific surface area of the adsorbents was calculated by means of methylene blue adsorption at 298 K to stay within a range between 348 and 643 m2 g−1. The FTIR spectroscopic characterization technique, the SEM, the point of zero charge, and the elemental analysis show the chemical and physical characteristics of the studied adsorbents, which confirm the adsorption results obtained.