Enhanced adsorption of tetracycline from wastewater using MgAl-layered double hydroxides on MWCNTs: influence of humic acid and fluorescence quenching

Abstract

In this paper, the MgAl-layered double hydroxide supported on multiwalled carbon nanotubes (MgAl LDH@MWCNT) nanocomposite was successfully synthesised and characterised for respective analytical methods to elucidate the new structure and composite functional groups. MgAl LDH@MWCNT nanocomposite was applied for the interaction and adsorption of tetracycline from water in the presence of humic acid. The remediation of tetracycline by MgAl LDH@MWCNT nanocomposite for 25, 50 and 100 mg/L concentrations was 94.4%, 90% and 85%, respectively, and 90 minutes of contact time was optimum for adsorption. Remediation of tetracycline was 96.8%, 95.2% and 89% for 25, 50 and 100 mg/L at pH 4. Ultrasonically assisted remediation of tetracycline without the addition of humic acid for 25, 50, and 100 mg/L was 87%, 82% and 76%, respectively, within 5 minutes. Fluorescence quenching indicates that the sorption process is a single-step quenching for humic acid with tetracycline, and quenching intensity was increased with increasing tetracycline concentration. Quenching study revealed that the interaction between the humic acid and tetracycline was static quenching, which means that the non-fluorescent complex was formed. The binding constant K<inf>b</inf> was obtained as 6.775 × 103 L mol−1, and the number of binding sites for tetracycline with humic acid was 1.447. 3D fluorescence spectra show a shoulder peak appearance at Ex/Em = 480–575 nm/550–630 nm, which is due to the formation of a stable complex between the interaction of humic acid and tetracycline in the presence of MgAl LDH@MWCNT nanocomposite. Tetracycline adsorption was controlled by electrostatic interaction, which involved electron sharing. Multilayer adsorption on the surface of MgAl LDH@MWCNT was observed, which is due to the sharing of electrons and π-π stacking. © 2025 Informa UK Limited, trading as Taylor & Francis Group.