Access to safe drinking water is a global health issue. Human exposure to drinking water contaminants, such as arsenic, has been linked to cancer, neurological, cardiovascular and pulmonary health problems. The arsenic levels in 8% of private wells in Iowa were determined to be greater than the EPA’s drinking water standards of 10 ppb (0.01 mg/L).  Therefore, it is critical, both globally and locally, to develop improved methods for removing and analyzing arsenic in water. Mesoporous silica has well-defined pores of 1.5-10 nm and very high surface areas. Mesoporous silica can be readily modified through surface functionalization. In this study, functionalized mesoporous silica will be tailored to optimize arsenic adsorption. Specifically, mesoporous silica will be functionalized with thiol and/or amine functional groups which are expected to selectively adsorb As(III) or As(V) species, respectively. Magnetic iron oxide nanoparticles will be incorporated into the mesoporous silica to facilitate magnetic recovery from solution.