Efficient removal of both antimonite (Sb(iii)) and antimonate (Sb(v)) from environmental water using titanate nanotubes and nanoparticles

Abstract

Increasing attention has been focused on antimony (Sb) pollution and remediation in aquatic ecosystems, where efficient removal technologies for Sb compounds, particularly Sb(III) and Sb(V), from environmental water are urgently needed. Thus, herein, a mesoporous material, titanate nanotubes (3 nm, TiO₂ NTs) with a large surface area was synthesized and used to remove both Sb(III) and Sb(V) from various natural waters. Furthermore, it was characterized via adsorption isotherm and kinetic experiments, and its mechanisms were investigated using various techniques, including Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and density functional theory (DFT) models. The results show that the maximum amounts of Sb(III) and Sb(V) adsorbed on the TiO₂ NTs (250.0 mg g⁻¹ and 56.3 mg g⁻¹) were due to electrostatic interactions and complexation, which were 20- and 7-fold greater than that on TiO₂ NPs of 12.0 mg g⁻¹ and 8.6 mg g⁻¹, respectively. The removal efficiencies for the TiO₂ NMs using tap water, natural surface water and wastewater were satisfactory, which were nearly 100% for Sb(III) and 100%, 98% and 56%, respectively, for Sb(V) with 5 mg/50 mL TiO₂ and spiked with Sb (200 μg L⁻¹). The TiO₂ NTs showed excellent reusability with 0.5 mol L⁻¹ sodium hydroxide as a desorbing agent. The FTIR and XPS results suggested that the hydroxyl groups play a significant role in the adsorption processes. Based on DFT calculations, it was found that Sb(III) preferred to form O–Ti bonds, Sb(V) formed O–Ti bonds on the {101} facet of the anatase TiO₂ NPs, and Sb(V) preferred to adsorb on the {001} facet. However, for Sb(III), there was no preference between the {101} and {001} facets. This study demonstrates that TiO₂ NTs are promising, easily synthesizable and environmentally friendly adsorbents for both Sb(III) and Sb(V), and can be potentially applied in wastewater treatment.