Investigating the synergistic effects in tourmaline/TiO2-based heterogeneous photocatalysis: Underlying mechanism insights

• Tourmaline/TiO2 composites showed improved photoactivity toward BPA degradation.
• Hydroxyl radical dominated BPA decomposition with a high mineralization.
• Efficient electron–hole separation was achieved with higher carrier density induced.
• Tourmaline spontaneous polarization caused the changed band bending of TiO2.

We proposed to combine a polarized mineral tourmaline and TiO2 nanosemiconductor to form a hybrid photocatalyst, to simultaneously optimize the photocatalytic efficiency and macroscopic aggregation of nano-TiO2. Photoactivity assessment toward bisphenol A (BPA) degradation indicated the optimal T(20%)-TiO2 catalyst exhibited higher performance than the bare TiO2 or the mechanical mixtures. In view of the reactive species scavenging results and intermediate identification, a hydroxyl radical-initiated oxidation as the dominating BPA decomposition pathway was proposed. The results of photoluminescence spectra and photocurrent measurements along with electrochemical impedance spectra and Mott–Schottky analyses led us to a better understanding of the photocatalytic process involving the facilitated charge transfer and higher carrier density induced owing to tourmaline incorporation. The synergistic effects in tourmaline-involved photocatalysis would be attributed to the fact that the internal dipolar field, originating from tourmaline spontaneous polarization, resulted in spatially varied energy levels of the bands and changed band bending of TiO2 semiconductor, which lowered the potential barrier for photoelectrons or holes to readily migrate to the surface and retarded electron–hole recombination. The concept of engineering internal field in heterogeneous photocatalysis using a polarized mineral of low cost will shed new light on applied photochemistry and development of nanotechnology enabled approaches for water treatment.

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