This study evaluated the potential of using raw Maclura pomifera and wild carob for the treatment of methylene blue (MB) and crystal violet (CV) as part of the search for new, abundant, and cost-effective natural materials applicable for wastewater treatment. Additionally, it explored the impact of washing water temperature on the adsorption performance of these raw organic materials. The physicochemical properties of the materials were characterized using BET, SEM/EDS, and FTIR analyses. The effects of various experimental parameters were investigated through batch adsorption experiments. The results demonstrated that the influence of washing water temperature was material-dependent. For Maclura pomifera, the maximum adsorption capacity of methylene blue and crystal violet decreased from 134.4 and 136.6 mg g⁻¹ for MPC to 67.1 and 90.5 mg g⁻¹ for MPH. In contrast, the adsorption capacities of wild carob biosorbents remained consistent, with the maximum amounts adsorbed for methylene blue and crystal violet by CC, CW, and CH being close, around 78.8 and 98.9 mg g⁻¹, respectively, indicating a minimal effect of washing temperature on this material. The adsorption of both dyes onto the adsorbents was positively affected by increasing the pH, contact time, and initial dye concentration and was negatively affected by increasing adsorbent dose or ionic strength. Adsorption isotherms and kinetics were modeled using various mathematical approaches. The kinetic data were accurately described by a pseudo-second-order model, with a significant contribution from intraparticle diffusion. The Sips and Redlich–Peterson models provided the best fit for the adsorption isotherms of both dyes on the biosorbents. These findings confirm that the selected biomaterials are excellent adsorbents for the removal of cationic dyes.

The aim of this research work was to optimize the chemical treatment of two biomass materials, spent coffee grounds (SCGs) and date pits (DPs), for their use as adsorbents in the removal of methylene blue (MB). The treatment was carried out using sodium hydroxide (NaOH) following a two-level full factorial design, varying the activating solution concentration, activation time, and activation temperature. Only the model based on SCG proved statistically significant. The optimal pretreatment conditions (0.2 M, 5.5 h, 22 °C) yielded an adsorption capacity of 140.23 mg·g⁻¹. The optimal material was characterized by FTIR, BET, SEM, and pHpzc analyses. The effects of pH (1–11), initial concentration (5–300 mg·L⁻¹), adsorbent dose (0.25–2 g·L⁻¹), contact time (0–420 min), and temperature (22–50 °C) on MB adsorption onto the optimal adsorbent were investigated. Adsorption was enhanced by increasing the pH, contact time, and initial concentration, but decreased with higher adsorbent dose and temperature. Kinetic analysis revealed that the pseudo-second-order model best described the data (R² = 0.96), with a notable contribution from intraparticle diffusion (R² = 0.98). The Sips model (R² = 0.99) adequately represented the adsorption isotherm. These findings confirm the strong potential of this biosorbent for the removal of cationic dyes from aqueous solutions.