A new type of SnO2@β-Fe(Zr)OOH hollow nanosphere as a bifunctional adsorbent for removing nitrate from water: kinetics, isotherm, and thermodynamic studies

A SnO 2 @β-Fe(Zr)OOH nanocomposite, β-FeOOH doped with Zr on SnO 2 hollow spheres, was synthesized by two-step hydrothermal method to solve the problem of nitrate pollution in sewage. The structure and properties of samples which synthesized in this work were analyzed by means of XRD, SEM, TEM, XPS, BET and Zeta potential systematically. Moreover, the effects of initial nitrate concentration, pH, time and temperature on nitrate removal were also investigated. The amount of nitrate nitrogen adsorbed by the SnO 2 @β-Fe(Zr)OOH nanocomposite was 14.0 mg/g in the first 30 min. Based on the analysis of the nitrate adsorption kinetic model of SnO 2 @β-Fe(Zr)OOH nanocomposite in water, the adsorption was in line with the second-order kinetic model and belonged to chemical adsorption. It showed that the Langmuir adsorption isotherm model fitting results are superior to the Freundlich isothermal adsorption model through fitting the adsorption isotherm. With the increase of temperature, the maximum adsorption capacity showed the same trend, which indicated that the adsorption process is an endothermic process. In addition, adsorption thermodynamic studies were carried out to prove that the reaction process is a spontaneous reaction. After six adsorption–desorption cycles, the composite still has an adsorption capacity of 80%. Graphic abstract