Adsorption Properties of MgO(111) Nanoplates for the Dye Pollutants from Wastewater

Nanoplates of MgO possessing the polar (111) facet as the primary surface were studied as adsorbents for dye pollutants removal from wastewater. The thickness of the MgO(111) nanoplates is (3 to 5) nm, with an average specific surface area (SSA) of 198 m(2.).g(-1). Congo red and reactive brilliant red X3B are used as model azo dyes, and their adsorption is studied at different dye concentrations, solution pH, salt concentration, and temperatures in a batch reactor. The experimental results indicate that the MgO nanoplates with polar (111) surfaces exhibited much more favorable adsorption properties than a conventionally decomposition prepared MgO powder (CP-MgO, SSA = 30 m(2).g(-1)) and activated carbon (SSA = 1500 m(2).g(-1)) for Congo red solution with the initial concentration of 100 mg.L-1 in 30 min. The maximum adsorption capability of Congo red on MgO (111) nanosheets reached 131.3 mg.g(-1) in 30 min, while the maximum adsorption capabilities of Congo red on CP-MgO and activated carbon were only (61.9 and 17.7) mg.g(-1), respectively. Two common models, the Langmuir and Freundlich isotherms, are used to explicate the interaction of dye and MgO(111). The isotherm evaluations revealed that the Langmuir model attained better fits to the experimental equilibrium data than the Freundlich model. The maximum predicted adsorption capacities were (303.0 and 277.8) mg.g(-1) for Congo red and reactive brilliant red X3B, respectively. In addition, adsorption kinetic data followed a pseudosecond-order rate for both dyes. Furthermore, compared to activated carbon, the adsorbent MgO(111) has the advantage in that it can be readily regenerated by a simple calcination process and reused without loss of activity. Therefore, it may be well suited for dealing with the removal of dyes from wastewaters.