Facet-engineered anatase TiO₂ nanocrystals with co-exposed {112}, {100}, and {101} facets for enhanced photocatalysis

Synthesis of anatase TiO₂ nanocrystals (NCs) exposing high-index facets remains challenging. Herein, anatase TiO₂ NCs co-exposing high and low index facets were synthesized by varying the volume ratio of TBAH and DMF. Among the synthesized samples, TiO₂-30, prepared using 30 mL TBAH and 30 mL DMF, exhibited the highest proportion of rod-like NCs exposing {112}, {100}, and {101} facets. In contrast, TiO₂-20, synthesized using 20 mL TBAH and 40 mL DMF, predominantly exhibited cube-like NCs exposing {001} and {100} facets. TiO₂-40, prepared using 40 mL TBAH and 20 mL DMF, retained a rod-like morphology but contained a higher proportion of spherical NCs exposing {101} facets, while TiO₂-50, synthesized using 50 mL TBAH and 10 mL DMF, primarily consisted of spherical NCs. The photocatalytic activities of the synthesized samples were evaluated using methyl orange (MO) degradation, nitro blue tetrazolium (NBT) reduction, and photocatalytic conversion of toluene to benzaldehyde. Among all the samples, TiO₂-30 exhibited the highest photocatalytic activity, with rate constants of 11.3 × 10^-2 min^-1 for MO degradation and 12.7 × 10^-3 min^-1 for NBT reduction, together with a benzaldehyde production rate of 9.92 mg h^-1 g^-1. These values are 4.52-, 2.54-, and 1.70-fold higher, respectively, than those obtained using commercial P25 (Degussa). Structural and photoelectrochemical analyses revealed that TiO₂-30 possesses the highest crystallinity, a lower point of zero charge (ZPC), a more negative flat-band potential, and suppressed charge-carrier recombination compared with the other samples. These characteristics collectively contribute to the superior photocatalytic performance of TiO₂-30.