A comprehensive study on the adsorption-photocatalytic processes using CoFe2O4/SiO2/MnO2 magnetic nanocomposite as a novel photo-catalyst for removal of Cr (VI) under simulated sunlight: Isotherm, kinetic and thermodynamic studies

Purpose

The present study aimed to investigate the efficiency of CoFe₂O₄/SiO₂/flower-like MnO₂ nanoparticles as a catalyst for Cr (VI) adsorption-photocatalytic processes.

Methods

The magnetic nanocomposite used was first synthesized and then characterized using TEM, SEM, EDX, XRD, FTIR, XRF and BET advanced techniques. The removal of the Cr (VI) was performed through a batch adsorption approach and the effects of sample pH (A; 2–6), initial chromate concentration (B; 50–100 ppm) and adsorbent weight to sample volume ratio (C; 1–3 mg ml⁻¹), hole scavenger (0.1 -0.3%w/v) and time (E; 30–60 min), to evaluate the individual and interactive effects under ultraviolet light conditions, were also studied by the central composite design in the photocatalytic process of adsorption.

Results

The adsorption-photocatalytic performance of the CoFe₂O₄/SiO₂/MnO₂ composite was high in which 98.1% of Cr(VI) after 30 min of photocatalytic treatment in optimum conditions (i.e. pH = 3, catalyst concentration = 2 mg L⁻¹, Cr(VI) concentration = 200 mg L⁻¹, and hole scavenger concentration = 0.4% (w/ v), At laboratory temperature, speed = 400 rpm, under UV radiation).Under optimum conditions, Cr(VI) reductive followed pseudo—second—order kinetics and followed the Langmuir and Temkin isotherms, also, positive value of ΔH° indicates endothermic nature.

Conclusions

The results showed that the synthesized CoFe₂O₄/SiO₂/MnO₂ magnetic nanocomposite holds a great potential for use as a photocatalyst to remove Cr (VI) in adsorption reactions. It can be used as an effective catalyst in the eradication of Cr (VI) wastewater.

Graphical abstract