Ion Current Rectification in High-Salt Environment from Mesoporous TiO2 Microplug in Situ Grown at the Tip of a Micropipette Induced by Space-Confined Evaporation.

In this work, in situ growth of a titanium dioxide microplug (TDMP) having mesoporous channels at the tip of a glass micropipette induced by space-confined evaporation is reported. Moreover, clear ion current rectification (ICR) of a single-material nanopore in a saturated potassium chloride solution is observed for the first time. TDMP presents an asymmetrical channel structure with the top and bottom apertures of 12.3 ± 6.1 and 42.6 ± 19.7 nm, respectively. TDMP exhibits outstanding ICR capability as the ions get transported through it due to the applied potential. The values for the rectification coefficient (r = log2|I+1 V/I-1 V|) in a saturated KCl solution under acidic (pH of 3.0) and alkaline (pH of 10.0) environments are 1.32 and -0.84, respectively. The intensity and direction of ICR can be adjusted by pH or through the modification of citric acid. Meanwhile, the length and ion transport behavior of TDMP under different growth conditions (time and diameter) were also investigated. TDMP with asymmetric mesoporous channels, maintaining ICR in a saturated salt solution, is expected to expand the application of nanopores in high-salt environments. Furthermore, growth of mesoporous material in the micropipette facilitates the miniaturization of the nanopore device, which further promotes its application potential.