1. Microscopic model for pH sensing mechanism in zinc-based nanowalls
- Author
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Guglielmo G. Condorelli, Salvatore Mirabella, Elena Bruno, Antonino Scandurra, and M. G. Grimaldi
- Subjects
Materials science ,Nanostructure ,Photoemission spectroscopy ,Scanning electron microscope ,chemistry.chemical_element ,02 engineering and technology ,Zinc ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,chemistry.chemical_compound ,Zinc nitrate ,Zinc oxide ,Materials Chemistry ,Non-Nernstian response ,Electrical and Electronic Engineering ,Zinc hydroxynitrate ,Instrumentation ,Nanowalls ,Metals and Alloys ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,pH sensors ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Chemical engineering ,Electrode ,Hydroxide ,0210 nano-technology - Abstract
Zinc based nanostructures are very promising material for pH sensing since they allow the realization of low-cost, sustainable, and high sensitivity electrodes. The pH sensitivity reported in literature for different ZnO nanostructures spreads from sub- to super-Nernstian, with the microscopic mechanism behind the H+ detection often unrevealed. In this work we synthesize by hydrothermal process and thermal annealing two zinc based nanowalls (NWLs) consisting of layered hydroxide zinc nitrate Zn5(OH)8(NO3)2·2H2O (as grown) and zinc oxide ZnO (annealed) phases, respectively. Scanning electron microscopy, micro Raman spectroscopy, X-ray photoemission spectroscopy were used to characterize the morphology and structure of NWLs. Electrochemical chronopotentiometric analysis in standard buffer solutions (pH 4 to 9) was used to study the response towards pH. Despite the two zinc based NWLs have the same morphology (interconnected sheets 10-20 nm thin, 1.4–1.7 μm wide), truly different behavior as pH sensitive electrodes are evidenced. As grown NWLs show a super-Nernstian response (+83.7 mV/decade), whereas annealed NWLs show a sub-Nernstian response (+27.1 mV/decade). The data are satisfactorily modeled by considering the crystallographic structures and assuming that layered hydroxide zinc nitrate NWLs is sensitive to only H+ (with two simultaneous and independent mechanisms), while zinc oxide NWLs is simultaneously and independently sensitive to both H+ and OH−. These data and the proposed modeling are useful to further develop the pH sensitivity of electrodes based on ZnO nanostructures.
- Published
- 2019