Removal of methylene blue using MnO2@rGO nanocomposite from textile wastewater: Isotherms, kinetics and thermodynamics studies

Tshimangadzo S Munonde; Azile Nqombolo; Siphosethu Hobongwana; Anele Mpupa; Philiswa Nosizo Nomngongo

doi:10.1016/j.heliyon.2023.e15502

Removal of methylene blue using MnO₂@rGO nanocomposite from textile wastewater: Isotherms, kinetics and thermodynamics studies

Heliyon. 2023 Apr 17;9(4):e15502. doi: 10.1016/j.heliyon.2023.e15502. eCollection 2023 Apr.

Authors

Tshimangadzo S Munonde^{1

2}, Azile Nqombolo^{1

2

3}, Siphosethu Hobongwana², Anele Mpupa^{1

2}, Philiswa Nosizo Nomngongo^{1

2

4}

Affiliations

¹ Department of Chemical Sciences, University of Johannesburg, Doornfontein Campus, P.O. Box 17011, Doornfontein, 2028, South Africa.
² Department of Science and Innovation-National Research Foundation South African Research Chair Initiative (DSI-NRF SARChI) in Nanotechnology for Water, University of Johannesburg, Doornfontein, 2028, South Africa.
³ Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.
⁴ DSI/Mintek Nanotechnology Innovation Centre, University of Johannesburg, Doornfontein, 2028, South Africa.

Abstract

In this study, the adsorptive removal of methylene blue dye, which is commonly used in textile industries, was investigated using the MnO₂@reduced graphene oxide (rGO) adsorbent. The sonication-assisted synthesis from rGO nanosheets and MnO₂ nanoparticles resulted to the MnO₂@rGO nanocomposite with improved physicochemical properties. The characterization results showed the improved surface area, porous structure and adsorption sites from the nitrogen adsorption-desorption studies, improved morphology from the Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) and the improved crystal structure from X-ray powder diffraction (XRD). The improved physicochemical properties on the MnO₂@rGO nanocomposite played a significant role in enhancing the dye removal in textile wastewater. The equilibrium experimental data was best described by the Langmuir isotherm model with a maximum adsorption capacity of 156 mg g^-1, suggesting a monolayer adsorption. The kinetic data best fitted the pseudo-second order kinetic model, suggesting a chemisorption adsorption process. The thermodynamic data (ΔG°, ΔH° and ΔS°) confirmed the feasibility, randomness and spontaneous nature of the adsorption process. The mechanism of adsorption involved the hydrogen bonding, π-π interactions and electrostatic interactions. The removal of methylene blue using MnO₂@rGO nanocomposite in spiked textile wastewater yielded a 98-99% removal. The method demonstrated competitiveness when compared with literature reported results, paving way for further investigations towards industrial scale applications.

Keywords: Chemisorption; Isotherms; Kinetics; Methylene blue; MnO2@rGO nanocomposite; Textile wastewater.