Abstract
The development of new technologies for securing and recycling water resources are in high demand. A key focus of these technologies is the development of various ion exchangers or adsorbents that are used for the purification of aqueous solutions. Layered sodium titanate is one of the cation exchangers utilised in the removal of heavy metals and radionuclides from wastewater. To enhance the removal efficiency, the precise design of the crystal morphology, structure, and chemical composition is important. Herein, we synthesised a unique seaweed-like sodium titanate mat (SST) using a template-free alkaline hydrothermal process. The Co2+ sorption capacity of SST was investigated by batch testing with cobalt(ii) nitrate. SST, which was synthesised from titanium sulphate in a 10 M NaOH solution at 200 °C, had a seaweed-like structure composed of randomly distributed nanofibres of layered sodium titanate that is approximately 9 nm in diameter. The crystal shape changed from roundish crystals to fibrous crystals as the hydrothermal reaction period increased. The Co2+ sorption isotherm of SST was fitted with the Langmuir isotherm model and the maximum sorption density was 1.85 mmol g−1. The selectivity of the Co2+ sorption on SST was high in comparison to that of Ca2+ and Mg2+. Herein, the Co2+ sorption mechanisms of SST were studied in comparison with commercially available sodium titanate. Results show that controlling the crystal morphology, structure, and Na concentration of the layered titanate that can be ion-exchanged determines the cation sorption properties of sodium titanate.
Highlights
For the conservation of water resources, the development of water management and water treatment technologies are important
seaweed-like sodium titanate mat (SST), which was synthesised from titanium sulphate in a 10 M NaOH solution at 200 C, had a seaweed-like structure composed of randomly distributed nanofibres of layered sodium titanate that is approximately 9 nm in diameter
Previous studies have shown that the X-ray absorption near-edge structure (XANES) spectra of the layered titanate have an A2 peak with a high intensity, which indicates the presence of the veorder coordination of Ti in the layered titanate structure.[28]
Summary
The crystallographic properties of the sorbent are directly related to sorption mechanisms, the design of the surface area, crystal structure, and chemical composition of the sorbents. A seaweed-like sodium titanate (SST) mat with a unique morphology was synthesised using titanium sulphate solution by a simple alkaline hydrothermal synthesis method without the addition of surfactants or templates. Cobalt(II) nitrate hexahydrate (Co(NO3)2$6H2O, FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan) was dissolved in ultra-pure water and diluted to the various concentrations of test solutions without pH adjustment. These results agree with the interlayer distance calculated using a d-value of 200 obtained by XRD analysis.
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