Enhanced Arsenic Adsorption in Groundwater Using Zirconium MOF-Modified Granular Activated Carbon

Many Americans still rely on unregulated private wells for drinking water, where arsenic concentrations often exceed regulatory limits. Arsenic poses a serious public health risk due to its toxicity even at low concentrations. While granular activated carbon (GAC) is widely used to remove organic contaminants, improve taste and odor, and limit microbial growth, it is largely ineffective for arsenic removal. Recently, metal–organic frameworks (MOFs) have emerged as promising materials for arsenic adsorption due to their high surface area and tunable functionality. Combining MOFs with GAC enhances arsenic removal by integrating the adsorption performance of MOFs with GAC’s operational benefits over powdered activated carbon (PAC), such as better flow and system compatibility. This study investigates the incorporation of metal–organic frameworks (MOFs), specifically UiO-66 and UiO-66-NH2, into GAC to enhance arsenic adsorption. The modified composites achieved 6–10 wt % zirconium (Zr) loading and 25–30% UiO-66 content. Batch experiments demonstrated that higher Zr content significantly improved arsenic removal, reaching up to 111 mg As/g GAC–UiO-66, based on the MOF content in the composite material. The best-performing material was synthesized using a solvothermal method with ZrCl4, resulting in strong As–O–Zr coordination that contributed to the high adsorption efficiency. Characterization data suggest that chemical interactions, rather than surface area or pore structure, primarily drive arsenic uptake. The adsorption behavior aligns best with the Freundlich model, indicating heterogeneous surface binding on the Zr-functionalized GAC. Importantly, incorporating Zr-based MOFs into granular activated carbon improves structural integrity and reusability, addressing key scalability and cost challenges of powdered MOFs for practical water treatment applications.