The effects of functional groups on the adsorption efficiency of nitrate and nitrite from water by carbon cloth were investigated. The carbon cloth was treated by sulfuric acid and used for the adsorption of nitrate and nitrite from water samples at nearly neutral solutions. The concentrations of ions in the solution were monitored using in situ UV spectroscopy. Acid treatment caused a significant increase in the adsorption rate of ions and the adsorption capacity of the adsorbent.