Development of composites from titanate nanotubes, layered double hydroxides, and oyster shells for the enhanced removal of methylene blue, acid red 1, and congo red from aqueous solutions

Abstract

The composite adsorbent derived from titanate nanotubes (TNTs), layered double hydroxides (LDHs) and oyster shell (OS) were used to removal cationic and anionic dyes. Scanning electron microscopy confirmed the successful integration of TNTs, LDHs, and OS, displaying distinct rod-like and hexagonal structures, as well as a rough surface. Energy dispersive spectroscopy identified essential elements such as calcium, sodium, oxygen, titanium, and aluminum, critical for the composite’s functionality. X-ray diffraction revealed characteristic peaks corresponding to anatase-phase titanium dioxide, LDHs, and calcium carbonate, validating TLO’s structural integrity. Fourier-transform infrared spectroscopy detected functional groups vital for adsorption, including OH-, Ti-O, and Ca-O bonds. BET surface area analysis (BET) showed a significantly larger surface area of 82.11 m²/g for TLO compared to its individual components, enhancing its adsorption capacity. Zeta potential analysis demonstrated a variable surface charge across a range of pH values, enabling TLO to effectively adsorb both cationic and anionic pollutants. Methylene blue, acid red 1, and congo red, in pH 3 to 9 solutions, showed high capacities, with maximum values of 1111 mg/g for methylene blue, 357 mg/g for acid red 1, and 192 mg/g for congo red. These results highlight TLO’s strong electrostatic attraction and ion exchange for cationic dyes, and surface precipitation for anionic dyes, particularly in neutral to alkaline environments. TLO is regarded as an effective material for advanced wastewater treatment.