Cd-Doped Amorphous TiO Hollow Spheres for Robust and Ultrasensitive Photoelectrochemical Sensing of Hydrogen Sulfide.

Hydrogen sulfide is a highly toxic molecule to human health, but high-performance detection of it remains a challenge. Herein, we report an ultrasensitive photoelectrochemical (PEC) sensor for HS by modifying indium tin oxide (ITO) electrodes with Cd-doped amorphous TiO hollow spheres, which are prepared by templating against colloidal silica particles followed by a cadmium-sodium cation exchange reaction. The amorphous TiO hollow spheres act as both the probing cation carrier and the photoelectric beacon. Upon exposure to sulfide ions, the photocurrent of the functionalized photoanode proportionately decreases in response to the formation of CdS nanoparticles. The decreased photocurrent could be attributed to the mismatching bandgap between the amorphous TiO and CdS nanoparticles: the photoexcited electrons and holes from amorphous TiO are transferred to the conduction band and valence band of CdS, respectively, and then recombined. The decrease in photocurrent is linear with the concentration of sulfide ions in the range from 1 to 10 000 pmol L with a detection limit of 0.36 pmol L. Enabled by a unique sensitization mechanism, this PEC sensor features excellent performance in a wide linear range, high selectivity and sensitivity, high stability, and low fabrication cost.