Introduction: 4-chlorophenol is a toxic and corrosive matter which the Environmental Protection Agency of America (EPA) has reported as one of the priority pollutants. This study is carried out to investigate the efficiency of multi-walled carbon nanotubes oxidized with a mixture of H₂SO₄/HNO₃ in removal of 4-chlorophenol from aqueous solutions.

Materials & methods: This research was an experimental study which was conducted in the first half of 1393 in environmental health engineering research center, Kerman University of medical sciences. Firstly, multi-walled carbon nanotubes were oxidized with a mixture of H₂SO₄/ HNO₃  then effective parameters on phenol removal from aqueous solutions such as the initial concentration of 4-chlorophenol, contact time, amount of adsorbent and pH were studied. Actual wastewater of coal-cleaning with predetermined quality was also studied. SPSS-16 software and Pearson correlation were used for data analysis.

Findings: Removal efficiency of 4-chlorophenol in optimum conditions including pH= 7, contact time= 10 minutes, amount of adsorbent= 0.3 g, the initial concentration of adsorbent= 15 mg/L, was 91.8 percent. Study of the kinetic and isotherm equations showed that the process of adsorption followed the second order kinetic and Freundlich isotherm.

Discussion & conclusions: Multi-walled carbon nanotubes oxidized with a mixture of H₂SO₄/HNO₃ was a good adsorbent for removal of 4-chlorophenol from aqueous solutions and is able to remove this matter from the actual sewage with an efficiency rate equal to 78%, so it can be used as an effective adsorbent for treatment of polluted water and wastewater.