This study primarily aims to understand the adsorption mechanism of urea, creatinine, and uric acid on spherical activated carbon. The adsorption of urea, creatinine, and uric acid onto spherical activated carbon underwent with a pseudo-second-order rate and in accordance with the Halsey formula. The adsorption of urea may have occurred because of interaction between the urea dipole and the dipole induced in the porous surface by the urea as well as because of dipole–dipole interaction between surface oxygen groups on the spherical activated carbon surface and the urea. The interaction among urea molecules, such as hydrogen bonding, induced multilayer adsorption. The adsorption model of creatinine was similar to that of urea. Because uric acid molecules are very strongly hydrophobic, their adsorption onto spherical activated carbon is caused by attractive forces between the hydrophobic surface of activated carbon and the similarly hydrophobic uric acid molecules, in addition to van der Waals forces. Moreover, uric acid molecules adsorbed onto spherical activated carbon and uric acid molecules in water are considered to undergo additional multilayer adsorption because of hydrophobic interactions.
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