Synthesis of strontium ferrite and its role in the removal of methyl orange, phenolphthalein and bromothymol blue from laboratory wastewater

Abstract

The presence of organic chemical pollutants such as methyl orange (MOIn), phenolphthalein (PhIn) and bromothymol blue (BBIn) in laboratory wastewater is a challenge which requires immediate attention. In response to this challenge, strontium ferrite (SrFe2O4) was prepared via co-precipitation method as an adsorbent for the removal of these pollutants from laboratory wastewater. SrFe2O4 was characterized by Fourier Transform Infrared spectrometer (FTIR), X-ray Diffraction analysis (XRD), Energy Dispersive X-Ray Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). FTR, XRD and RDS results confirmed the identity of SrFe2O4. SEM shows particles of SrFe2O4 of different dimensions and shapes, that reveal the coexistence of both monocrystalline and polycrystalline particles. The adsorption of the contaminants from aqueous solutions on SrFe2O4 was studied in a batch system. The results showed that the adsorption is affected by the initial contaminant concentration (1.00–5.00 mg L−1), adsorbent dosage (0.05–0.10 g), adsorption temperature (303–323 K), and pH (2.1–11.0). SrFe2O4 removes the pollutants from water with adsorption capacities (7.00–8.60 mg g−1) and percentage removals (70.00–86.00%) that compared favourably with other previously reported adsorbents. The removal of the pollutants by SrFe2O4 obeys the pseudo-first-order model which can be described by the Langmuir isotherm model. The Gibb's free energy change (∆Go) and enthalpy change (∆Ho) for the sorption process were negative while the entropy change (∆So) was found to be 0.205, 0.282 and -0.221 kJ mol−1K−1 for MOIn, PhIn and BBIn respectively. The adsorption mechanism was considered to occur via electrostatic interaction. Regeneration capacities expressed by SrFe2O4 were above 70% even after the 12th regeneration cycle. The sorption process was further described in molecular terms using computational quantum mechanical modelling, density functional theory (DFT). The use of SrFe2O4 for the treatment of raw laboratory wastewater is effective towards the removal of MOIn, PhIN and BBIn.