Hydrothermal synthesis of structurally variable binary CuAl, MnAl and ternary CuMnAl hydroxides for oxytetracycline antibiotic adsorption

Pharmaceuticals are emerging pollutants present mainly in industrial and municipal wastewater. Herein, structurally variable binary and ternary metal hydroxides based on copper, manganese, and aluminum were used for the adsorptive scavenging of the oxytetracycline (OTC) antibiotic. A facile hydrothermal method was used for the synthesis of binary CuAl-hydroxide, MnAl-hydroxide, and ternary CuMnAl-hydroxide. Structural and morphological characteristics of the metal hydroxides (MHs) were studied by X-ray diffraction (XRD), Fourier transformed infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy (SEM) analysis. The adsorptive removal for OTC was found in the order CuMnAl-hydroxide > CuAl-hydroxide > MnAl-hydroxide. The highest removal of OTC by CuMnAl-hydroxide and CuAl-hydroxide was observed at pH 7 while MnAl-hydroxide showed the optimum adsorption at pH 9. All three materials showed different saturation time and equilibrium concentration for OTC adsorption. The mechanism investigation found that strong electrostatic attraction, hydrogen bonding, and anion exchange were mainly responsible for the removal of the OTC and adsorption process followed the pseudo-second-order kinetic model and equilibrium data was best fitted to the Langmuir isotherm model. The adsorption of OTC was influenced by the presence of Cu (II) and Cr (VI) ions in the aqueous solution due to the competitive adsorption of co-ions. Moreover, the adsorption of OTC was endothermic in nature, and maximum adsorption capacity was found to be 250.07 mg/g at 50 degrees C.