Selectively sequestrating aqueous Bi(III) with titanium pyrophosphate polyhedral submicro-particles

Titanium pyrophosphate (TiP 2 O 7 ) adsorbent was prepared by sol–gel combined with sintering method. The products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), Raman, transmission and scan electron microscope (TEM/SEM) technologies. The results showed that the cubic phase of TiP 2 O 7 has a uniform polyhedral morphology, and most particles are 200–600 nm in size. The submicron scale TiP 2 O 7 particles were first assessed to adsorb aqueous Bi(III) ions. It is found that TiP 2 O 7 micro-particles exhibited excellent capture capability ( Q m  = 42.54 mg g −1 , 298.5 K), fast adsorption rates (>99 % within 30 min) for toxic Bi(III) and high Bi(III) selectivity ( K d Bi  = 5.6 × 10 4 mL g −1 ) in the presence of various competitive ions, with the order of Bi(III) ≫ Pb(II) ≫ Cu(II) > Fe(II) > Al(III) > Zn(II). The adsorption kinetics conformed to the pseudo-second-order model, equilibrium adsorption satisfied the Langmuir equation, and the adsorption process was thermodynamically spontaneous. Chemisorption was inferred as the adsorption mechanism, and surface hydroxylated functional groups were considered the adsorptive sites. The reusability and testing of actual samples demonstrated the practicality of TiP 2 O 7 adsorbents in water environment treatment.