Facile Approach for the Syntheses of Ultrafine TiO2 Nanocrystallites with Defects and C Heterojunction for Photocatalytic Water Splitting

Abstract

In this paper, a supercritical water (sc-H2O) reaction medium was employed for the syntheses of ultrafine TiO2 nanocrystallites (at ca. 5 nm) that were linked with lactate species at surface. The resulting hybrid material was then subjected to an aging at ca. 300 °C for 2 h under N2 atmosphere. After subjected to spherical aberration corrected STEM and EPR analyses, it was noted that the aged sample was shown with highly distorted crystal lattice with oxygen vacancies at surface and Ti3+ in the bulk. The anoxic aging also caused incomplete combustion for lactate species, leading to the formation of C heterojunction with TiO2. UV–vis, PL and transient photocurrent (TP) measurements revealed that the resulting surface oxygen vacancies and C heterojunction had conferred a combination of advantages in enhancing visible light absorption and promoting electron–hole pair separation for aged sample, which led to significantly promoted hydrogen production efficiency in photocatalytic water splitting under a full-spectrum irradiation (where the aged TiO2 had yielded ca. 4-fold higher hydrogen production rate than the nonaged one and ca. 40–50-fold higher than commercial Degussa P25). We expected that the work conducted herein could provide a facile and controllable approach to produce simultaneously defects and C heterojunction for ultrafine TiO2 nanocrystallites, which might lead to scale-up production of them for industry.