Investigation of cadmium removal using tin oxide nanoflowers through process optimization, isotherms and kinetics

Abstract

The present study demonstrates a treatment approach that utilizes flower-shaped tin oxide nanoparticles for the removal of cadmium from synthetic wastewater by adsorption. Tin oxide nanoparticles were synthesized using a simple and eco-friendly method and employed for the removal of cadmium ions from wastewater. The nanoflowers were successfully characterized using Fourier Transform Infrared Spectroscopy, X-Ray Diffraction Analysis, Scanning Electron Microscope and Brunauer-Emmett-Teller (BET) surface area analysis. The batch adsorption process was optimized by response surface methods to investigate the influential parameters of the adsorption process. Optimal removal efficacy was achieved at a pH value of 9.0, a mixing time of 20 min, and an adsorbent amount of 15 mg. The results indicated that the adsorbent achieved a maximum removal efficiency of 99.14 ± 0.10% for Cd(II)ions in domestic wastewater. The adsorption equilibrium process was elucidated by Langmuir, Freundlich, Sips and Toth isotherm models using nonlinear regression. In addition, error functions such as Chi-square (X², Average Relative Error (ARE), Root Mean Squared Error (RMSE) and HYBRID were used to test the validity of the nonlinear models. The results indicated that the Sips model, with an R² value of 0.9894, accurately matched the experimental data and adsorption capacity of 57.12 mg g^{- 1} for Cd(II) was calculated respectively. The sorption kinetics were well characterized by a pseudo-second-order kinetic model. The results demonstrated that adsorption of cadmium onto the surface of SnO₂ nanoparticles is influenced by both monolayer adsorption and multi-site interactions. These findings indicate that SnO₂ nanoparticles are suitable for removing cadmium from aqueous solutions in batch processes.

Keywords: Adsorption isotherms; Experimental design; Heavy metal removal, domestic wastewater, nanoflowers.

Fig. 1

Schematic representation of the experimental procedure for the SnO₂ based removal method.

Fig. 2

(a) FT-IR, (b) XRD spectra and c-d) SEM images and e) pHpzc analysis of of tin oxide nanoflowers.

Fig. 2

(a) FT-IR, (b) XRD spectra and c-d) SEM images and e) pHpzc analysis of of tin oxide nanoflowers.

Fig. 3

(a) Comparison of experimental and predicted values using a parity plot and (b) 3D-RSP showing the effects of adsorbent amount and pH of aqueous medium on the removal of cadmium.

Fig. 4

Two and three parameter isotherms obtained using the nonlinear method for the adsorption of Cd(II) onto tin oxide nanoflowers (constructed by Matplot Library of Python).

Fig. 5

PSO and WM-IPD plots for the adsorption Cd(II) onto tin oxide nanoflowers (constructed by Matplot Library of Python).

Fig. 6

The reusability graph for Cd(II) ion removal with tin oxide nanoflowers. Reaction conditions: temp 298 K, concentration of Cd(II) ion (30 mg/L), pH 9.0 buffer, mixing time (20 min), shaking speed (250 rpm).