Impact of humic acid coated-TiO₂ nanocomposite for fast sorption of Cd(II) and Cr(VI) from aqueous solutions

Abstract

Heavy metals and humic acid (HA) are often found together in aquatic ecosystems. HA has been shown to make nanoparticles (NPs) more stable because of its strong repulsion between particles and high charge density. In this study, soil-based HA nanoparticles coated with nano-TiO₂ (HA-TiO₂ nanocomposite) are used to remove Cd(II) and Cr(VI) ions from aqueous solutions. These particles are stable for 90 days. The zeta potential of HA-TiO₂ (28 ± 2.4 nm) at pH 6.5 was 30.4 mV, and this is significant for environmental remediation because the surface charge can be either negatively or positively charged. The three-factorial Box–Behnken design; BBD with the response surface methodology was utilized for sorption system optimization. At optimal process variables, the highest sorption capacities of HA-TiO₂ for Cd(II) and Cr(VI) ions were 358.4 ± 0.2 and 243.5 ± 0.1 mg.g⁻¹ (169.7 and 127.6 mg.g⁻¹ for native HA), respectively, at pH 6.5 after 30 minutes. To fit the kinetic data, the normalized standard deviation was preferable to the pseudo-second-order model. Thermodynamic parameters revealed endothermicity (ΔH^o = 6.52–4.89 kJ mol⁻¹) and spontaneity (ΔG^o = −6.3–9.5 kJ K⁻¹mol⁻¹) of the sorption processes at (20–40 °C). The ion-exchange sorption mechanism was suggested to take part in the Langmuir model fit. The application of the fabricated nanocomposite for the removal of Cd(II) and Cr(VI) from different environmental water samples was conducted with 98.5 − 99.7% efficiency. All results suggest that HA-TiO₂ can be used as an effective and ecofriendly sorbent for the removal of heavy metal ions in an aqueous environment.

Graphical Abstract

Keywords:

• Nano-titanium dioxide (TiO₂ NPs)
• heavy metals
• response surface methodology
• toxic metals
• sorption
• statistical optimization

Additional information

Funding

This work was funded by the Deanship of Scientific Research (DSR), University of Jeddah, Jeddah under grant No. (563-965-1436/G). The authors, therefore, acknowledge with thanks DSR technical and financial support.