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.

This paper describes a simple and low-cost process for the degradation of 4-Chlorophenol (4-CP) from aqueous solution, using natural Tunisian Hematite (M₁) and Siderite (M₂). Two natural samples were collected in the outcroppings of the Djerissa mining site (Kef district, northwestern Tunisia). Both Hematite and Siderite ferrous samples were characterized using several techniques, including X-Ray Diffraction (XRD), Nitrogen Physisorption (BET), Infrared Spectroscopy (FTIR), H₂-Temperature Programmed Reduction (H₂-TPR), Scanning Electronic Microscopy (SEM) linked with Energy Dispersive X-ray (EDS) and High-Resolution Transmission Electron Microscopy (HRTEM). Textural, structural and chemical characterization confirmed the presence of Hematite and Siderite phases with a high amount of iron on the both surface materials. Their activity was evaluated in the oxidation of 4-CP in aqueous medium under heterogeneous photo-Fenton process. Siderite exhibited higher photocatalytic oxidation activity than Hematite at pH 3. The experimental results also showed that 100% conversion of 4-CP and 54% TOC removal can be achieved using Siderite as catalyst. Negligible metal leaching and catalyst reutilization without any loss of activity point towards an excellent catalytic stability for both natural catalysts.