Nitrate Uptake from Water Using Amine‐Functionalized Meso‐ and Macroporous Carbons

Meso‐ and macroporous carbon materials modified with protonated amino groups (−NH3+Cl−) for aqueous nitrate (NO3−) uptake were prepared by surface functionalization with aminopropylsilane. Although the silane coupling treatment decreased the specific surface area of the carbons, surface modification with the −NH3+Cl− group improved the NO3− uptake capacity of both meso‐ and macroporous carbons. The amount of NO3− adsorbed depends on the specific surface area of the adsorbent; an adsorbent with a larger specific surface area exhibits a larger uptake capacity. Enhanced NO3− adsorption onto the NH3+Cl−‐modified surface occurred through an ion‐exchange mechanism. Changes in the pH of the sample solutions before and after NO3− uptake revealed the competitive exchange of NO3− and OH−. NO3− uptake is inhibited by the coexistence of anions other than NO3− (excess Cl−, SO42−, CO32− and HCO3−) and/or OH− at high pH. In particular, the influence of excess Cl− reveals that NO3− uptake through ion exchange is not irreversible, and the adsorption capacity is determined based on the ion exchange equilibrium. The effect of the surface modification of porous carbons with −NH3+Cl− groups on their NO3− uptake capacity was investigated in detail. The surface modification markedly improved the NO3− uptake capacity. The NO3− uptake was affected by the acid‐base properties of the solution and the existence of anions other than NO3−.