High-Performance Sensing of Formic Acid Vapor Enabled by a Newly Developed Nanofilm-Based Fluorescent Sensor

Abstract

Although it is widely used in industry and food products, formic acid can be dangerous owing to its corrosive properties. Accurate determination of formic acid would not only benefit its qualified uses but also be an effective way to avoid corrosion or injury from inhalation, swallowing, or touching. Herein, we present a nanofilm-based fluorescent sensor for formic acid vapor detection with a wide response range, fast response speed, and high sensitivity and selectivity. The nanofilm was synthesized at a humid air/dimethyl sulfoxide (DMSO) interface through dynamic covalent condensation between two typically designed building blocks, de-tert-butyl calix[4]arene-tetrahydrazide (CATH) and 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)tetra-benzaldehyde (ETBA). The as-prepared nanofilm is uniform, flexible, fluorescent, and photochemically stable. The thickness and fluorescence intensity of the nanofilm can be facilely adjusted by varying the concentration of the building blocks and the sensing performance of the nanofilm can be optimized accordingly. Based on the nanofilm, a fluorescent sensor with a wide response range (4.4 ppt−4400 ppm) for real-time and online detection of formic acid vapor was built. With the sensor, a trace amount (0.01%) of formic acid in petroleum ether (60−90 °C) can be detected within 3 s. Besides, fluorescence quenching of the nanofilm by formic acid vapor can be visualized. It is believed that the sensor based on the nanofilm would find real-life applications in corrosion and injury prevention from formic acid.

Polymeric Emissive Materials Based on Dynamic Covalent Bonds

“…The Hirsch group reported the pH-dependent morphology and optical property of a lysine-derived polymer [ 45 ]. Wu et al developed a fluorescent polymer nanofilm based on acylhydrazone bonds [ 46 ]. The nanofilm could act as a fluorescent sensor with wide response range for real time detection of formic acid.…”

An amino-type halogen-bonded organic framework for the selective adsorption of aliphatic acid vapors: insight into the competitive interactions of halogen bonds and hydrogen bonds

“…Aliphatic acids at low concentrations are oen used in food products as a preservative, while they are very dangerous at high concentrations. 50,51 In addition, owing to the volatile and ammable nature of shortchain aliphatic acids, their vapors have a strong stimulating effect on the eyes and nose. Short-chain aliphatic acid vapors at high concentrations mixed with air could be explosive.…”

Film Nanoarchitectonics of Pillar[5]arene for High-Performance Fluorescent Sensing: a Proof-of-Concept Study

“…Considering the high porosity and uniformity, it is expected that the nanofilms may be used as a new kind of substrates for sensing film development as they are not only facilitating mass transfer, but also favoring to minimize "coffeering effect", a general factor affecting the quality of fluorescent sensing films. 26 As a proof-of-concept study, herein, a flexible and uniform nanofilm was prepared via confined condensation of a newly synthesized acyl-hydrazine derivative of pillar [5]arene (BHCP5A) with a commercially available triformyl-benzene (TFB) at the air/DMSO interface. BHCP5A is chosen as it possesses a rigid cavity, which is expected to inhibit stacking between layers, endowing the nanofilm with rich porosity.…”

“…However, development of the fluorescent nanofilms is very time-consuming as creation of reactive fluorophores is a prerequirement, which hinders the application of the strategy, particularly when sensor array is to be developed. Considering the high porosity and uniformity, it is expected that the nanofilms may be used as a new kind of substrates for sensing film development as they are not only facilitating mass transfer, but also favoring to minimize “coffee-ring effect”, a general factor affecting the quality of fluorescent sensing films …”