Hydration of TiO₂ Facets Regulates As(III) Adsorption: DFT and DRIFTS Study

Abstract

Hydration of TiO 2 facets controls the reactions occurring at the mineral−water interfaces. However, the underlying mechanism of the facet-dependent hydration and the effect of hydration on contaminant adsorption are still ambiguous. Herein, arsenite [As(III)] adsorption on hydrated {001}, {100}, {101}, and {201} TiO 2 was explored by integrating multiple characterizations and density functional theory (DFT) calculations. Our macroscopic adsorption results show an As(III) adsorption density order of {201} > {100} > {101} > {001}, though As(III) on each facet formed a bidentate binuclear structure, as evidenced by the extended X-ray absorption fine structure analysis. The in situ diffuse reflectance infrared Fourier transform spectroscopy analysis identified distinctive surface hydroxyls on four-faceted TiO 2 upon water adsorption. The hydrated surface regulated the subsequent As(III) adsorption, giving an As(III) adsorption energy order of {201} (−0.95 eV) < {100} (−0.38 eV) < {101} (−0.005 eV) < {001} (0.04 eV) according to DFT calculations. The As(III) adsorption energy on hydrated facets was linearly correlated with the macroscopical As(III) adsorption density (R 2 = 0.99, p < 0.05), revealing that the impregnable water binding highly suppressed the exchange of As(III) molecules with adsorbed water. Our study provided a novel insight into the facet-dependent interfacial adsorption.

Mechanistic Study for Antimony Adsorption and Precipitation on Hematite Facets

“…The Sb adsorption and precipitation experiments were conducted at pH 7.0 ± 0.2 by adding 20 mg of Fe 2 O 3 into 40 mL of 0.04 mol/L NaCl solution with initial Sb­(III) or Sb­(V) concentrations ranging from 0.004 to 3.7 mmol/L. The aqueous solution was purged with N 2 for 30 min to eliminate CO 2 before adding Fe 2 O 3 samples . The solution pH was adjusted with HCl and NaOH.…”

“…The aqueous solution was purged with N 2 for 30 min to eliminate CO 2 before adding Fe 2 O 3 samples. 21 The solution pH was adjusted with HCl and NaOH. After the samples were reacted for 24 h, Sb were measured using inductively coupled plasma optical emission spectroscopy (ICP−OES, Optima 2000 DV, PerkinElmer Co., USA).…”

Theoretical Study of NO Adsorption by Hydroxyl-Containing Char with the Participation of Na/K

“…In this work, all the calculations have been carried out by the GGA-PBE (generalized gradient approximation–Perdew Burke Ernzerh) functional ,, based on the density functional theory − as implemented in the Dmol 3 code, ,, which is similar to those in the literatures. − ,, The wave function of the valence electron was treated by using the DNP (double numerical polarized) basis set with polarization function. All-electron calculations were performed for all atoms in the system, and all calculations were chosen to be spin unrestricted.…”

Facet-Dependent Atomic Distances Shape Vanadate Adsorption Complexes on Hematite Nanocrystals

“…18 These ambiguous results highlight the diversity and complexity of V(V) surface structure, motivating our study for the molecular-level understanding. 19 Previous facet-dependent adsorption results suggested that the oxyanions themselves also contributed to the significant difference in the formation of surface complexes. For instance, on the {001} Fe 2 O 3 facet, As(V) formed the 1 V complex but U(VI) exhibited the 2 E complex.…”

“…Extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) calculations found two V–Fe atomic distances in V­(V) adsorbed samples, 2.8 Å, and 3.2–3.3 Å, corresponding to bidentate edge-sharing ( 2 E) and bidentate corner-sharing ( 2 C) complexes, respectively. , Meanwhile, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra showed multiple bands between 650 and 850 cm –1 , confirming the monodentate mononuclear ( 1 V) complex on Fe 2 O 3 . These ambiguous results highlight the diversity and complexity of V­(V) surface structure, motivating our study for the molecular-level understanding …”