Nickel phthalocyanine-catalyzed ammonia detection on a TiO2 photoelectrochemical sensor with ZIF-67 enrichment for environmental water analysis
Wenru Wu, Nuoxuan Xiong, Yue Lin, Fang Luo, Cuiying Lin, Bin Qiu, Zhenyu Lin, Jiang Zhou, Jian Wang
Abstract
A novel photoelectrochemical sensor based on TiO 2 /NiPc/ZIF-67 composite was developed for ammonia (NH 3 ) detection in water, showing exceptional sensitivity and selectivity. The sensor was fabricated by depositing TiO 2 , NiPc, and ZIF-67 onto an ITO electrode. Under optimized conditions, it achieved an ultra-low detection limit of 0.031 nM, surpassing previous reports. A strong linear correlation (R 2 = 0.998) was observed between the relative value of the photocurrent and the logarithm of NH 3 concentration over the range of 0.1 nM to 10 µM. TiO 2 ensured stable photocurrent generation, while ZIF-67, a metal-organic framework with polyhedral morphology, adjustable pore size, high surface area (758.6 m 2 /g BET), and microporous structure, selectively enriched NH 3 . In competitive adsorption experiments, NH 3 exhibited a slower adsorption rate compared to gases like CO, CH 4 , N 2 , and O 2 , minimizing interference. NiPc, a p-type semiconductor with an 18π-electron conjugated structure, coordinated with NH 3 to promote NH 3 oxidation and accelerate the reaction rate. The synergistic effect of NiPc and ZIF-67 enhanced the sensor performance, as demonstrated by cyclic voltammetry, which showed that the electrode potential of the oxidation process shifts negatively when both materials were modified on a glassy carbon electrode upon NH 3 addition. In real water samples, the sensor displayed high selectivity, with minimal response to common interfering ions such as Cu 2+ , Mg 2+ , and Ca 2+ , ensuring accurate NH 3 detection in complex environments.