Removal of Bromide from Surface Water: Comparison Between Silver-Impregnated Graphene Oxide and Silver-Impregnated Powdered Activated Carbon

Abstract

Abstract

This study demonstrates that silver (Ag⁺) impregnated graphene oxide (GO) reduces anion and natural organic matter (NOM) competition for bromide (Br⁻) adsorption sites compared with Ag⁺ impregnated powdered activated carbon (PAC). We impregnated two GO (Tour and Modifier Hummers [MH] method) and one PAC with silver ions. Batch studies were conducted to assess Br⁻ removal in model waters with Br⁻, chloride (Cl⁻), bicarbonate (HCO₃⁻), and/or NOM and natural surface waters. In buffered ultrapure water, Tour-Ag, MH-Ag, and PAC-Ag all removed >85% of Br⁻, while sorbents without Ag⁺ removed <3% of Br⁻. In all water matrices, Tour-Ag removed >75% of Br⁻, MH-Ag removed >50%, and PAC-Ag removed >30%, highlighting that GO-Ag is more effective at removing Br⁻ from water than PAC-Ag (p < 0.05). Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis show that Br⁻ is evenly dispersed on the surface of GO-Ag, indicating possible attachment to oxygen groups and silver on the GO surface. A leaching test of GO-Ag in buffered water showed that ∼20% of Ag⁺ loaded onto GO leaches into solution, of which only 1–3% remains when Br⁻ is spiked into solution, indicating possible complexation and precipitation as AgBr. GO-Ag and PAC-Ag were introduced separately in combination with alum during coagulation and flocculation operations. Both MH-Ag and Tour-Ag showed high removal of Br⁻, demonstrating that GO-Ag could supplement current technologies used in water treatment facilities when Br⁻ removal is needed.