Adsorption capacity of sodium dodecyl sulfate activation okara for methylene blue on aqueous solution

Agricultural waste okara (OA) was selected as a precursor to prepare low-cost adsorbent for the removal of methylene blue (MB). Sodium dodecyl sulfate (SDS), as a kind of anionic surfactant, was loaded onto okara (SOA) to achieve high adsorption ability. Scanning electron microscopy, Fourier transform infrared spectrometer and X-ray diffraction were investigated for the materials characterization. The effect of pH, contact time, initial concentration, adsorbent dose and ionic strength was determined to explore the adsorption properties. The adsorption kinetics, adsorption isotherms, cost analysis of adsorbent and adsorption mechanism were discussed. And the adsorption equilibrium data fitted well with Langmuir model, while the calculated maximum adsorption capacity was 238.10 mg g−1 for OA and 334.83 mg g−1 for SOA, respectively. The kinetics data followed the pseudo-second-order model. Thermodynamic parameters (ΔHo, ΔGo and ΔSo) indicated the spontaneous and exothermal nature. This research reveals that SOA is an effective, low-cost and promising adsorbent on the adsorption of MB on aqueous solution.