The Allura red AC (ARAC) dye adsorption onto natural sawdust (NSD) and hexadecylpyridinium bromide-treated sawdust (MSD) was investigated in aqueous solution as a function of contact time, solution pH, particle size, adsorbent dosage, dye concentration, temperature, and ionic strength. The adsorbents were characterized by Fourier transform infrared spectroscopy and X-ray diffraction crystallography. The dye adsorption onto both adsorbents was confirmed by field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The maximum dye adsorption was found within 120 min at pH 2.0 for NSD and pH 3.0 for MSD, respectively, with a particle size of 0–75 μm and an adsorbent dosage of 0.07 g/50 mL ARAC dye solution (50 μmol/L). The batch adsorption kinetic data were followed by the pseudo-second-order kinetic model rather than the pseudo-first-order and Elovich kinetic models. Equilibrium adsorption isotherms were explained by the Langmuir isotherm model, and the maximum extent of adsorption was found to be 52.14 μmol/g for NSD and 151.88 μmol/g for MSD at 55 °C. The values of activation energy (E a) and thermodynamic parameters (ΔG ⧧, ΔH ⧧, ΔS ⧧, ΔG°, ΔH° and ΔS°) proved that the ARAC dye adsorption onto both adsorbents NSD and MSD is a spontaneous-endothermic physisorption process. ARAC (98–99%) was released from dye-loaded adsorbents in aqueous solution (pH ≥ 12) within 120 min. The adsorbents NSD and MSD were reused for a second time without significant loss of their adsorption efficiency.

Phytochemical screening and gas chromatography-mass spectrometry (GC-MS) methods were used to determine the phytochemical components of various extracts of stems and roots of Catharanthus roseus. Preliminary phytochemical screening of n-hexane, chloroform, ethyl acetate and methanol extracts of stems and roots of Catharanthus roseus were carried out to identify the class of compounds present in each extract. The results exhibited that steroids, terpenoids, flavonoids and phenolic compounds were found in every extract of stems and roots. Alkaloids were also found in all extracts except n-hexane. But carbohydrates were absent in all extracts of stems and roots except methanol. The GC-MS analysis of the n-hexane extract of the stems and roots of Catharanthus roseus was done, which allowed the identification and quantification of 30 and 22 n-hexane soluble compounds present in the stems and roots, respectively. In this experiments, D:B-Friedo-B':A'-neogammacer-5-en-3β-ol (10.23%) and Ethyl palmitate (13.63%) identified with the highest concentration in the n-hexane extract of stems and roots, respectively.

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Natural peanut husk (NPH) and hexadecyltrimethylammonium bromide (CTAB)-modified peanut husk (MPH) were used to study the adsorption characteristics of amaranth in aqueous solution. NPH and MPH were characterized by Fourier transform infrared (FTIR) spectroscopy. The pHzpc values of NPH and MPH were estimated to be 5.06 and 5.96, respectively. The adsorption of amaranth onto both adsorbents was confirmed by the observations of field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDX) analysis. Adsorption kinetic experiments were conducted at various contact time, solution pH, initial dye concentration, temperature, and ionic strength, respectively. Dye adsorption kinetics pursued the pseudo-second-order kinetic model. Adsorption isotherms obeyed the Langmuir model with the highest dye adsorption capacity of 20.88 µmol/g for NPH at pH 2, and 117.65 µmol/g for MPH at pH 4. The values of activation energy (Ea) for the adsorption process were determined to be 48.68 kJ/mol for NPH and 16.92 kJ/mol for MPH, respectively. Thermodynamic data confirmed that amaranth adsorption onto both adsorbents was an endothermic spontaneous physisorption process. The release of amaranth from dye-loaded adsorbents was performed in HCl solution (pH 1) and the recycled adsorbents were utilized six times without significant loss of their adsorption capacity.

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