Thermodynamic Study of Adsorption of Methyl Orange and Congo Red from Aqueous Solutions by PVP-Functionalized ZnO

This study has focused on the applications of newly prepared zinc oxide (ZnO) composite with polyvinylpyrrolidone (PVP) for adsorptive removal of methyl orange and Congo red dyes. The performance of ZnO–PVP composite in removing the dyes from aqueous solution is almost double than the simple metal oxide, which signifies the role of PVP in the composite of metal oxide–PVP. The adsorption of methyl orange and Congo red onto ZnO–PVP composite was also conducted as a function of pH of solution, concentration, adsorbent dosage and temperature of the solution. The adsorption of methyl orange and Congo red onto ZnO–PVP composite decreased with the increase in pH of the mixture. The obtained adsorption capacity for methyl orange is higher than Congo red which is related to functional group and size of the dye. The values of ∆H and ∆G designate that adsorption of methyl orange and Congo red is endothermic in nature. The positive values of ∆S for methyl orange and Congo red confirmed a high disorder at the solid/liquid interface.