Insights into removal of tetracycline by persulfate activation with peanut shell biochar coupled with amorphous Cu-doped FeOOH composite in aqueous solution

Peanut shell biochar (BC) supported on Cu-doped FeOOH composite (Cu–FeOOH/BC) was synthesized using a facile and scalable method. The Cu–FeOOH/BC samples were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy equipped with an energy-dispersive spectrometer (SEM-EDS), x-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) techniques. Novel catalytic composites with different Cu/Fe molar ratios were compared systematically by activating persulfate (PS) for the tetracycline (TC) degradation. 0.5Cu–1FeOOH/BC (Cu/Fe molar ratio = 0.5:1) was confirmed as the optimum activation material and the removal of TC reached 98.0% after 120 min by combining with 20 mM PS at pH 7.0 and 25 °C. The influencing factors including catalyst loading, PS dosage, water matrix species, and pH on the performance system of 0.5Cu–1FeOOH/BC-PS were investigated, respectively. Reaction rate constants (Kobs) on catalyst dosages (0.05, 0.10, 0.20, and 0.30 g L−1) were 0.0072, 0.0101, 0.0244, and 0.0144 min−1, and 0.0090, 0.0146, 0.0244, and 0.0178 min−1 for the change of PS concentrations (5, 10, 20, and 30 mM), which indicated that increasing the concentrations of catalyst and PS appropriately improved TC degradation, but excessive dosages inhibited the reaction process of TC removal. The TC removal rate was inhibited by inorganic anions with the following order of HCO3− > Cl− > HPO42− > SO42− > NO3−. Free radical quenching and capture experiments under different pH values revealed that sulfate radicals existed predominantly in acidic conditions and hydroxyl radicals in alkaline conditions. The catalyst showed an excellent recyclability and stability and the removal efficiency of TC still remained over 90% after five consecutive uses. To conclude, coupling of 0.5Cu–1FeOOH/BC and PS can be successfully applied as an effective and stable technique for the treatment of refractory organic pollutants in wastewater.