Single-crystal-like black Zr-TiO2 nanotube array film: An efficient photocatalyst for fast reduction of Cr(VI)

Photocatalytic reduction of heavy metal ions offers an eco-friendly approach to wastewater treatment. However, most photocatalysts are suffering from rapid bulk and surface recombination of photo-generated charges, as well as low utilization of visible light. Herein, the simultaneous enhancement of bulk and surface separation of photoinduced charges by combining crystallographic preferred orientation (CPO) and surface oxygen vacancies (OVs) of single crystal-like black Zr doped TiO2 nanotube arrays film (BLK-Zr-NTAs) is reported. The CPO of BLK-Zr-NTAs along [001] direction suppressed the number of recombination centers in bulk, thus driving rapid separation/migration of photo-generated carriers from bulk to the surface. Meanwhile, the large amounts of OVs acted as electron trapping sites to inhibit the charges recombination. Besides, the introduction of OVs widened the light-absorption range, extending up to 1200 nm. The BLK-Zr-NTAs show outstanding photocatalytic performance towards Cr(VI) without using any sacrificial agents or co-catalysts, in so doing emerging as one of the best photocatalysts dedicated to Cr(VI) reduction reported so far.