RETRACTED ARTICLE: NiO nanoparticles for enhanced removal of methyl orange: equilibrium, kinetics, thermodynamic and desorption studies

In this work, a green hydrothermal method was utilised to synthesise NiO nanoparticles (NiO-NPs) as an effective and low cost adsorbent for dye adsorption from aqueous medium. The product was characterised using powder XRD, FTIR and SEM techniques and the adsorption behaviour of NiO-NPs was assessed using methyl orange (MO) dye. The maximum removal (97.56 mg/g) of MO onto NiO-NPs was observed at pH 4, adsorbent amount 0.03 g and temperature 40°C. Thence, on evaluating and optimising the factors affecting the adsorption, the results exhibited that 95% dye removal was reached in first 30 min, additionally the adsorption equilibrium, kinetics and thermodynamics models were investigated. The results showed that the adsorption followed Langmuir model and pseudo second order model. The thermodynamic assessment of adsorption of MO onto NiO-NPs indicated the feasibility, endothermic and spontaneous nature with enthalpy and entropy of the system being positive (∆H° = 8.661 KJ/mol, ∆S° = 7.310 J/mol K). Also, the order of magnitude of ∆G° and ∆H° revealed the reversibility of reaction that reflects the adsorbent could be regenerated and potential contender for dyes removal form textile wastes.

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