How Doping Regulates As(III) Adsorption at TiO₂ Surfaces: A DFT + U Study

Area of Science:

• Materials Science
• Environmental Chemistry
• Computational Chemistry

Background:

• Efficient adsorption and removal of highly toxic As(III) from water remain challenging.
• Titanium dioxide (TiO2) shows potential for arsenic removal, but its efficacy requires improvement.
• Understanding the molecular mechanisms of arsenic adsorption on TiO2 is crucial for developing effective remediation strategies.

Purpose of the Study:

• To comprehensively investigate how doping regulates As(OH)3 adsorption over TiO2 surfaces using theoretical calculations.
• To explore the impact of different doping sites and elements on adsorption structures, energies, and mechanisms.
• To provide molecular-level insights for designing efficient arsenic scavengers.

Main Methods:

• Density Functional Theory (DFT) combined with the D3 dispersion correction method (DFT + D3) was employed.
• Simulations were performed on pristine and doped TiO2 surfaces (rutile (110) and anatase (101)).
• Analysis included adsorption structures, binding energies, and electronic properties.

Main Results:

• Doping creates diverse adsorption structures, including bidentate mononuclear and tridentate complexes.
• Doping at oxygen sites (O2c, O3c) is generally more effective than at titanium sites (Ti5c) for enhancing As(OH)3 adsorption.
• Adsorption energies were significantly improved by doping, with specific examples like Mn doping at Ti5c site on rutile (-4.67 eV).
• Arsenic adsorption and removal are crystal-dependent, showing higher efficiency for rutile compared to anatase.
• Auto-oxidation of As(III) to As(V) occurs upon interaction with the TiO2 surface, facilitated by multidentate adsorption.

Conclusions:

• Doping strategies, particularly at oxygen sites, can significantly enhance As(III) adsorption efficacy on TiO2.
• The choice of TiO2 crystal phase (rutile vs. anatase) critically influences adsorption efficiency and arsenic auto-oxidation.
• This study provides fundamental molecular-level understanding for the rational design of advanced TiO2-based adsorbents for arsenic pollution management.