Adsorption of Rhodamine b by Sulfocalix(4)Arene thin films for dye removal application

This study investigates the potential of Sulfocalix[4]arene (SC[4]) thin film for the removal and molecular-level adsorption of Rhodamine B dye (RhB), focusing on its performance in extraction and adherence. SC[4] thin films with 5, 10, 15, and 20 layers were fabricated using the spin coating method and subsequently characterised for its optical and topographical properties. Optical characterisation using Ultraviolet-Visible Spectroscopy (UV-Vis) at wavelengths from 260 to 300 nm revealed a progressive increase in absorbance across layers, notably at 277 nm and 283 nm peaks. Topographical analysis was conducted using Atomic Force Microscopy (AFM) to determine thickness and surface roughness. Results indicated a linear correlation between film thickness and the number of layers, with measurements of 58.175 nm for 5 layers, 77.626 nm for 10 layers, 84.608 nm for 15 layers, and 94.806 nm for 20 layers. Surface roughness, quantified via root mean square roughness (Rq), was significantly influenced by the number of layers. Adsorption studies of SC[4] thin films immersed in RhB dye solutions, characterised by UV-Vis, indicated that adsorption is the primary mechanism, evidenced by consistent, stable absorbance and dye concentration under both dark and visible light environments. The films demonstrated stable adsorption without prompting degradation of the RhB solution. Thicker films exposed to visible light showed a slight decrease in absorbance over time, suggesting environmental factors could affect adsorption depending on film thickness. A slight redshift in RhB_s absorption peak from 554 to 560 nm on SC[4] surfaces, along with a gradual increase in absorbance over immersion time, implies effective adsorption driven by Van der Waals forces. Among the examined thin films, the 5-layer SC[4] film demonstrated the most effective performance, providing reliable adsorption capability and stability under diverse light environments. These findings highlight the potential of SC[4] thin films as efficient adsorbents for RhB dye removal from textile wastewater.