ACID-BASE PROPERTIES OF NATURAL AND ACTIVATED ZEOLITES AND THEIR COMPOSITES

This study investigates the acid-base surface characteristics of natural zeolite samples from the Sokyrnytsia deposit (Ukraine). The samples include untreated natural zeolite, its acid-activated form obtained by treatment with nitric acid (HNO3, 2 M) at 40 °C under continuous stirring for 4 hours, and zeolite modified with titanium dioxide, both in its natural and acid-activated forms. The acid-base properties of all zeolite forms and composites were studied using the Hammett indicator method, which involves the selective adsorption of acid-base indicators from solutions onto the surface of solid materials. Significant changes in the distribution of Brønsted acid and base sites on the surface of the investigated zeolite-based samples were observed. X-ray diffraction analysis of the acid-activated natural zeolite revealed that acid treatment induced only minor changes in the phase composition while preserving the crystalline structure of the zeolite compared to the untreated material. The influence of pH on fluoride ion removal efficiency by natural zeolite was also investigated to explain the changes in its surface acid-base properties following acid activation. To confirm the potential redistribution of the electronic configuration on the zeolite surface and the possible blocking of its adsorption properties, additional experiments were conducted on the adsorption removal and photocatalytic degradation of Congo Red dye from solutions using the acid-activated zeolite modified with titanium dioxide. The findings demonstrate the feasibility and practicality of utilizing cost-effective natural Ukrainian zeolites for the development of adsorbents and photocatalysts with tunable acid-base surface properties, which could offer competitive advantages in the removal of various pollutants from water.