Assessment of the possibility of the prediction and regulation of sorption properties of composite coatings of piezoquartz sensors

Abstract

The synthesis and application of new compounds as sorbents, including in the creation of sensors, is rapidly developing. To ensure high performance characteristics in combination with sensitivity and selectivity, various approaches are used to create composite sensor coatings. The study of sorption processes is the basis for the creation and development of analytical application of gas sensor systems, including those based on piezoquartz resonators. When developing new coatings for their further successful analytical application, it is important to create a model or theory for predicting their sorption properties. Therefore, the study is devoted to assessing the possibility of predicting the sorption properties of composite coatings of piezoquartz sensors based on sorbents of various natures.

As sorbents for the formation of sorption films and composite coatings (in the ratio of 1: 1 by weight, designation (sorbent1+sorbent2)) on the electrode surface of piezoquartz resonators (PCR) with a base oscillation frequency of 14.0 MHz, substances of different nature (chitosan, 18-crown-6, amorphous silicon oxide, lanolin, dihydroquercetin, carbon nanotubes, micellar casein concentrate (MCC)) were used. The study of sorption of compounds on individual and composite coatings of sensors was carried out in static mode using a MAG-8 device. As the sorption properties of coatings, the characteristics reflecting the efficiency (specific mass sensitivity) and kinetics (desorption coefficient, sorption rate) of the sorption of substances were calculated. The method of projections onto latent structures was used for the prediction of the sorption properties of coatings. As a result of the research, the previously established influence of the degree of dispersion of the sorbent on the mass sensitivity of the micro-weighing of vapours of substances was confirmed, with an increase in particle size, the specific mass sensitivity increased. It has been shown that an increase in the specific mass sensitivity of the microweighing of substance vapours using composite coatings (MCC + stabilizing sorbent) was observed with an increase in the affinity of the stabilizing sorbent for water vapour. Moreover, with an increase in the length of the hydrocarbon radical by C₂H₅- in a homologous series of carboxylic acids and alcohols, the rate of increase in the specific mass sensitivity of microweighing increased by an order of magnitude. Also, with an increasing polarity of sorbed compounds, the sorption rate increased on all composite coatings (MCC + stabilizing sorbent). It has been established that the specific mass sensitivity of the microweighing of substance vapours on chitosan-based composite coatings increased for vapours of volatile compounds with a small hydrocarbon radical with increasing affinity of the sorbent for water. Also, with an increasing polarity of sorbate molecules, the rate of sorption on all composite coatings based on chitosan decreased, which is consistent with the change in the rate of sorption on its individual film. An approach was proposed for assessing the sorption characteristics of composite coatings based on the considered types of sorbents with the determination of coefficients using the regression method on latent structures with an error of 5%. The considered trends in changes in the sorption properties of coatings depending on various factors can be used to create composite coatings of gas piezosensors with specified sorption properties.