Adsorption of azo dye Congo red on the Sn-doped TiO2 surface

Abstract

In this paper, the effect of SnO2 impurity on the surface charge and adsorption properties of TiO2 samples is investigated. The experimental value of the zero charge point for TiO2 with 3%, 6% and 12% of SnO2 equals 3.53, 3.97 and 3.2, respectively. The adsorption activity of the samples was studied on model solutions of the anionic dye – Congo red. The maximum adsorption capacity (qexp) equals 24.6 mg/g for 3Sn/TiO2, 25.0 mg/g for 6Sn/TiO2 and 39.1 mg/g for 12Sn/TiO2. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to describe the adsorption mechanism of Congo red dye on the surface of Sn/TiO2 samples. Based on the results of the studies of Congo red adsorption by the surface of titanium dioxide doped with Sn, all samples agree best with the Langmuir model. The correlation coefficients for the Langmuir isotherms are in the range of 0.9927 - 0.9996, while the values ​​of R2 for the Freundlich and Dubinin-Radushkevich isotherms are in the range of 0.721 - 0.8329 and 0.8283 - 0.9433, respectively. Experimental data obtained from adsorption isotherms show that the TiO2 sample containing 12% SnO2 is the most active. The best result of Congo red removal occurred at a concentration of Co = 5 mg/l (% of removed dye ≈ 83% for 12Sn/TiO2; 81% for 6Sn/TiO2 and 71% for 3Sn/TiO2). Therefore, the studied samples of TiO2 doped with SnO2 can be used as effective adsorbents of Congo red from aqueous solutions.

Флуоресцентне Кількісне Визначення Адсорбції Пептидів На Діоксиді Титану

“…The qmax value obtained for the peptide was about 50 % higher than one for the small organic molecule Congo red studied under similar conditions [17]. It can be explained by the relatively large size of the peptide that can cover TiO2 forming a thicker layer than smaller molecule of the dye.…”

“…The fluorescence-based method for investigating peptide binding to sorbent surface allows to work at relatively low concentrations of peptides and low sample volumes. Namely, to measure sorbtion at one condition we used approximatwelly 9.43•10 -5 mol of peptide while adsorption-based measurements described in previous works [17] approximately 100-fold larger volumes and larger molar concentrations were used that resulted in consumption of about 0.07 mol of dye per one experimental conditions. We believe that a fluorescence-based approach would be very useful for further studies of peptide adhesion since it combines robust read-out, fast measurement times and cost-efficiency.…”