Lamda 25 uv vis spectrophotometer

All experiments were performed using the batch process. Four linearized forms of the isotherm models were used, namely Langmuir, Freundlich, Dubinin-Radushkevish, and Temkin to evaluate the adsorption capacity. A fixed amount of the geopolymer GEO-MSWBA or GEO-MSWFA (0.05 g) was added to a 50 mL of the MB solution at different pH values, temperatures, and initial MB concentrations, and placed in a temperature-controlled shaker at 130 rpm (shaking Incubator, MODEL: SSI10R-2, Orbital-Shaking). To ensure quality, control blank and two trials were prepared. Each solution concentration was measured under 663 nm [44 (link)] using a visible spectrophotometer (PerkinElmer Lamda 25UV/VIS spectrophotometer). The removal efficiency was calculated using Eq 1:
$\mathrm{Removal}\mathrm{percentage}(\%)=\frac{C_0-C_{eq}}{C_0}\mathrm{x}100$
Where, C₀ and C_eq are the initial and equilibrium of MB concentrations (mg/L), respectively.
The adsorption capacity was calculated using Eq 2:
$\mathrm{Adsorption}\mathrm{capacity}\left({\mathrm{q}}_{\mathrm{e}}\right)=\frac{\left(C_0-C_{eq}\right)\times V}{m}$
Where q_e is the amount of MB adsorbed by the geopolymer (mg/g), V is the volume (L), and m is the mass of the prepared geopolymer (g).

An MB stock solution of 1000 ppm was prepared by adding 1 g of MB in a 1 L volumetric flask, then filling it with distilled water till the mark. The MB (C₁₆H₁₈N₃SCl, molecular weight: 319.85 g/mol) standard powder was obtained from Fluka Chemia (number, 66721) and was packed in Switzerland. Distilled water was added slowly to the volumetric flask while shaking it gently to allow the MB to completely solubilize. A linear calibration curve of MB was conducted by preparing MB concentrations of 0, 1, 2, 3, 4, and 5 ppm. The absorbance was measured under the maximum wavelength of 663 nm using a visible spectrophotometer (PerkinElmer Lamda 25 UV/VIS spectrophotometer). The absorbance of each concentration was recorded and a curve of MB concentration vs. absorbance was plotted.

The desorption studies were carried out by adding the spent black and green olive stones (MB-loaded; initial MB concentration of 600 mg/L) to 50 mL of acidic mixtures of acetic acid and ethanol (%vol) (10:1, 5:1, and 1:1). The mixture was then shaken at 25 °C and 150 rpm for 24 h. The supernatants were then filtered and analyzed using a visible spectrophotometer (PerkinElmer Lamda 25 UV/VIS spectrophotometer) to determine the final dye concentration.