ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Rapid and selective sorption of organic dyes using Na₂Ti(PO₄)₂⋅H₂O synthesized from natural Ilmenite

Ashen I. Mapa, Kusal D. Mendis, Nethmini Rajakaruna, Lalinda Palliyaguru, Ushan S. Kulathunga, Avon P. Jayaweera, Atsushi Nakamura, and Pradeep M. Jayaweera

Dept. of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka

E-mail: pradeep@sjp.ac.lk

Received: 6 March 2025  Accepted: 17 November 2025

Abstract:

The sorption behaviors of acridine orange (AO), crystal violet (CV), methylene blue (MB), tetrabromophenol blue (TBPB), and rhodamine B (RhB) on Na₂Ti(PO₄)₂.H₂O (Na₂TiP) were studied experimentally. The average removal efficiencies of \(\:94.5\%,\:73.5\%,\:\text{a}\text{n}\text{d}\:57.4\%\:\)were reported for AO, CV, and MB, respectively. For TBPB and RhB, the averaged removal efficiencies remained below \(\:3\%.\:\:\)The effect of pH on the sorption of each of the five dyes on Na₂TiP was tested and the results indicated a negligible effect of pH in the tested range from 5 to 10 on the sorption properties of any of the dyes. To test the selective sorption by Na₂TiP, three dye mixtures, each containing AO/RhB/MB (dye mixture I), CV/TBPB/MB (dye mixture II), and AO/TBPB (dye mixture III), were used separately. The results showed high sorption capacities for AO, CV, and MB against TBPB and RhB, which are in good agreement with individual dye sorption experiments. Adsorption data was fitted to Langmuir and Freundlich isotherm models and the adsorption nature of AO, CV and MB can be best described by the Langmuir isotherm model. The reusability of the sorption material, Na₂TiP was confirmed after the removal of dyes from Na₂TiP through thermal decomposition at 300 °C. The sorption material, Na₂TiP, was characterized using EDX, XPS, and FTIR techniques. Geometry optimization of all the dye molecules was carried out with the Density Functional Theory (DFT) method. The length dimensions of the dye molecules were then compared with the interlayer spacing of Na₂TiP to determine the reason for the observed selectivity.

Keywords: Disodium titanium phosphate; Methylene blue; Crystal violet; Acridine orange; Tetrabromophenol blue; Rhodamine B; Selective sorption

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04524-4

Chemical Papers 80 (3) 2451–2465 (2026)