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-. image