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

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 approximate to 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.