A transparent TMPyP/TiO2 composite thin film as an HCl sensitive optochemical gas sensor

Abstract

a b s t r a c tTetracationic porphyrin (TMPyP) molecules were incorporated into an optically transparent TiO 2 thin film, prepared by Glancing Angle Physical Vapour Deposition (GAPVD), by simple infiltration (at pH 6.4). The preparation of optically transparent TMPyP/TiO 2 composite thin films provides a method for the integration of the porphyrin molecules into photonic devices for direct monitoring of gases. Previously, UV-visible and fluorescence spectral techniques have been used to study the reversible protonation of TMPyP in aqueous solution. The optical spectrum of TMPyP shows an intense Soret band at 423 nm with a 22 nm red shift upon protonation by HCl. The experimental conditions for monitoring the concentration of HCl gas by absorption spectroscopy have been optimized. The maximum absorbance change was observed at the Soret band wavelength. A selected temperature of 80 • C and a 300 s recovery period were found to be the optimum operating parameters (response time t 50 = 16.8 ± 0.7 s). The composite with smaller surface concentration of TMPyP ( = 0.3 × 10 −9 mol cm −2 ) presented the best detection limit (0.1 ppm). The response of the composite sensor was highly stable for several months.

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…Modeling the OAD thin film microstructure and growth by Monte Carlo (MC) simulation and other numerical methods has been carried out to better understand the evolution of porosity as a function of the deposition angle [93,228], with Suzuki et al [62] deducing that evaporated OAD thin films should present a maximum surface area at an evaporation angle of 70°. Interestingly, experiments exploring different adsorptions from the liquid phase have confirmed a maximum surface adsorption capacity at this ''magic deposition angle" [63,[229][230][231].…”

“…In the liquid phase of a photonic sensor incorporating dye molecules in transparent OAD thin films (see Section 5.4), we have observed that the pH of the medium greatly modifies the adsorption capacity of cationic or anionic organic molecules from the rhodamine and porphirine families [229,230,[242][243][244][245][246][247][248]. To account for this pH dependent behavior, we have used the classical zero point of charge concept (zpc), which is widely used in colloidal chemistry [249].…”

“…Our group has widely investigated this procedure and developed different composite sensor systems based on this principle. For instance, acid vapors can be detected from the change in optical absorption and fluorescence of OAD TiO 2 films with tetracationic metal-free porphyrin incorporated in their pores [229,244]. Typically, the selectivity of these hybrid systems is mainly determined by the chemical reactivity of the anchored molecules.…”

Application of the electronic spectra of porphyrins for analytical purposes: The effects of metal ions and structural distortions

“…Moreover, porphyrins in films and membrans are widely used for sensing of gases: e.g. oxygen [28,49,50], nitrogen oxides [28,51,52,53], carbon monoxide [52], carbon dioxide [54], hydrogen chloride [55], and ammonia [56]. The simultaneous determination of oxygen and carbon dioxide [54], oxygen and temperature [49] as well as oxygen and hydrogen peroxide [50] can be implemented too.…”

Elucidating the Reaction Kinetics of Hydrophobic Porphyrin Nanoaggregates Dispersed in PVA Films Exposed to HCl Vapors

“…One of these undesirable compounds, whose use is nowadays strictly regulated in many countries, is hydrogen chloride (HCl), a residual product from some industrial processes that interacts with the environment and natural biosystems. Optochemical sensing of HCl vapors can be accomplished through the use of organic dyes that change their absorption properties under the action of this acid at room temperature, with sensitivity at the ppm level or less .…”