Potassium hydroxide-treated walnut shell residue biochar for wastewater treatment: phenol adsorption and mechanism study

Abstract

Using walnut shell as raw material and potassium hydroxide as an activating agent, the walnut shell carbon (denoted as WSC) was prepared for phenol adsorption. The prepared biocomposite adsorbent structure was investigated using N2 adsorption–desorption analysis, Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy techniques. Adsorption efficiency of the prepared samples were investigated in various conditions such as activator ratio, initial phenol concentration, activation temperature, pH and adsorption reaction temperature. Also the kinetic and thermodynamic studies were carried out. The Brunauer–Emmett–Teller surface of the best WSC is 435.98 m2 g–1 and the maximum pore volume is 0.299 cm3 g–1, also it has a layered structure and porosity. When the mass ratio of WSC to KOH is 1:0.1, the amount of WSC (700°C, 2 h) is 2.0 g L–1 and the initial concentration of phenol is 20 mg L–1, the adsorption properties show that the prepared WSC has good adsorption performance with the phenol removal rate of 98.78% in 60 min. The kinetic study illustrates that the phenol adsorption on WSC fits the non-linear pseudo-first-order. It indicates that the phenol adsorption on WSC is accompanied by mainly physical adsorption.