Development of a mesoporous ZrO2-coating for sensing applications using ATR-FTIR spectroscopy

Abstract

Mesoporous silica is an extensively studied material and has been used in ATR-IR sensing schemes due to its high surface area and tuneable surface chemistry. However, the poor chemical stability in aqueous solutions at pH values higher than 8 as well as the strong absorption below 1200 cm-1 limits the range of applications. Therefore, a mesoporous zirconia coating was developed to circumvent these problems.A precursor solution was deposited on Si- and Ge-ATR elements utilising the evaporation induced self-assembly process. The prepared coatings were analysed with XRD, GI-SAXS, Raman and FTIR spectroscopy to evaluate the influence of reaction, coating and ageing parameters. The film thickness and, additionally, the thermal and chemical stability of different coatings were analysed. The pristine coating was used for enrichment studies of the ionic species cetyltrimethylammonium bromide and potassium dihydrogenphosphate. The surface was then chemically modified with silanes and characterised by FTIR spectroscopy, XRD and contact angle measurements. The modified coatings were used for the enrichment of benzonitrile, valeronitrile and benzene.Mesoporous zirconia coatings were successfully prepared and an optimised ageing process developed. Calcination of the coatings at 500°C was necessary to remove the surfactant of the precursor solution and to obtain cubic mesostructures. The mesoporous structure was still present after heating to 900°C in atmospheric conditions and after keeping the coating in aqueous solution at a pH value of 12 for 72 h. Enrichments with ionic species were successful, but not applicable for sensing schemes as the analytes could not be completely removed after enrichment. For potassium dihydrogenphosphate, enrichments with concentrations of 5 mg L-1 were achieved. Fast enrichments of 10 mg L-1 benzonitrile, 25 mg L-1 valeronitrile and 12 mg L-1 benzene were achieved as well as the complete removal of these analytes proving the applicability of these coatings for sensing applications.Further characterisation of the mesoporous zirconia coatings and enrichments of various analytes are necessary to determine possible applications of these coatings.