Microwave assisted facile green synthesis of silica coated magnetite nanoparticles for fast removal of methylene blue dye from environmental water samples

ABSTRACT

To prepare a magnetic nano-adsorbent for efficient and fast removal of a dye, especially if present in trace concentration, along with a facile green synthetic methodology is a great challenge. The present work realises this task by combining the well-known advantages of both solvent-free microwave approach, nanoscale particle size and the fast magnetic separation. Thus, silica-coated magnetite nanoparticles (Fe₃O₄ NPs@SiO₂) as an important precursor were produced directly via an optimised solid-solid interaction between silica and Fe₃O₄ NPs at 200 watt of microwave irradiation for only 10 min. The as-developed adsorbent was characterised using Fourier Transform Infrared (FT-IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) analysis. Its performance with no further modification for removal of Methylene blue (MB) dye from aqueous solution was achieved in a batch mode as a function of pH, contact time, adsorbent dose and initial dye concentration. The results demonstrate excellent removal efficiency (98.9%) within 5 min, as compared with recent adsorbents synthesised through a multi-steps reaction. Modelling of the experimental data denoting well-fitting with both Langmuir sorption isotherm (monolayer capacity 47.98 mg/g) and pseudo-second-order kinetic model. A possible MB binding mechanism has been proposed taking in account values of dissociation constants of the different forms of silica surface silanol groups. The adsorbent after first was successfully regenerated in situe for five consecutive cycles. Moreover, it was proved to be valid for collecting efficiently trace concentrations of MB spiked environmental water samples to be in the range 92.4–98.8%.

KEYWORDS:

• Methylene blue removal
• Fe₃O₄ NPs@SiO₂
• solvent-less microwave synthesis
• adsorption and kinetics models
• environmental water samples

Disclosure statement

No potential conflict of interest was reported by the author(s).