Mechanistic study on methyl orange and congo red adsorption onto polyvinyl pyrrolidone modified magnesium oxide

This study reported a new water stable magnesium oxides (MgO) composite with polyvinyl pyrrolidone (PVP) prepared by one-pot hydrothermal method for the efficient elimination of both methyl orange and congo red from aqueous solutions. The as-prepared composite material shows new exposed crystalline surfaces and additional peaks for hydrogen bond formation which are confirmed from FTIR and X-ray diffraction analysis. The surface area of MgO-PVP composite (85 m(2) g(-1)) was clearly higher than plain MgO (67 m(2) g(-1)). The dye removal capacity of MgO-PVP composite was significantly higher than plain MgO. The adsorption mechanism study illustrated that the dye removal by MgO-PVP composite not only due to the electrostatic force of attraction, but also involved the ion exchange amid hydroxide group and dye molecules. The adsorption kinetic mechanism of dyes was mainly controlled by film diffusion, and pseudo-second-order kinetic equation was found to be best applicable to the current experiential data. Langmuir and DR isotherms were well fitted with current experimental results. The adsorption of methyl orange and congo red onto the composite was also conducted as a function of initial concentration, pH of solution, temperature of the solution and adsorbent dosage. Dye adsorption capacity was decreased with the increasing of initial pH value. The negative values of ( increment G) for both the dyes show the spontaneous adsorption process.

Automated summary

A new water stable MgO-PVP composite was prepared by hydrothermal method, showing higher surface area and adsorption capacity than plain MgO. The adsorption mechanism involved electrostatic force and ion exchange, with kinetic mainly controlled by film diffusion. Langmuir and DR isotherms were well fitted with experimental results, and dye removal capacity decreased with increasing initial pH value. The negative ΔG values indicated a spontaneous adsorption process.