Adsorption of creatinine on active carbons with nitric acid hydrothermal modification

• Modification with 4 M HNO3 decreased BET surface area by 26 m2 g−1.
• 4 M HNO3 modification decreased the total pore volume for 0.04 cm3 g−1.
• The creatinine adsorption capacity increased 29% after HNO3 treatment at 180 °C.
• The generated oxygen-containing functional group increased the creatinine adsorption.

The adsorption of creatinine on active carbons was studied. Original active carbon (AC) and AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb creatinine. The pore structure and surface properties of the AC samples were characterized by N2 adsorption, temperature programmed desorption (TPD), Fourier Transform Infrared spectroscopy (FTIR), and X-ray photoelectron spectrometer (XPS). It indicated that 4 M HNO3 hydrothermal modification with 180 °C was an efficient method in improvement of the creatinine adsorption. The improved adsorption capacity can be attributed mainly to an increase in the acidic oxygen-containing functional groups. The adsorption of creatinine over AC may involve an interaction with the acidic oxygen-containing groups on AC. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constants. Equilibrium data fitted very well to the Freundlich model in the entire saturation range (3.58–59.08 mg L−1). The maximum adsorption capacities of AC modified with 180 °C is 62.5 mg g−1 according to the Langmuir model. Pseudo first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model, which indicates that the chemical adsorption was the rate-limiting step, instead of mass transfer.

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