Removal of arsenic with reduced graphene oxide-TiO₂-enabled nanofibrous mats

Arsenic contamination is found at dangerous levels in drinking water around the world and is many times treated with an oxidation step from arsenite [As(III)] to the more easily adsorbed and less toxic arsenate [As(V)]. Herein, electrospun nanofibrous mats made of poly(lactic-co-glycolic) acid and chitosan are coated with reduced graphene oxide (rGO) and titanium dioxide (TiO₂) for enhanced oxidation of arsenic. We compared the oxidative properties of UV-irradiated rGO-TiO₂ nanocomposite-enabled fibers (rGO-TiO₂@fibers) to both their non-reduced counterpart (GO-TiO₂@fibers) and TiO₂ nanoparticles in suspension. The rGO-TiO₂@fibers have a rate constant an order of magnitude larger, and oxidize 2.5 times more As(III), per mass of TiO₂ as compared to GO-TiO₂@fibers. When bound to UV-illuminated TiO₂, GO—and especially the more-conductive rGO—accept electrons from TiO₂’s valence band, inhibiting electron-hole recombination and increasing production of hydroxyl radicals (⋅OH) that oxidize As(III). Hydroxyl radical generation was correlated with As(III) oxidation and used to determine radical-scavenging of the fibers. TiO₂ paired with rGO achieved the highest levels of radical production both when bound to fibers and when in suspension, illustrating a synergistic relationship between rGO and TiO₂. Reuse properties and titanium leaching of the rGO-TiO₂@fibers and GO-TiO₂@fibers were evaluated over the course of six oxidative cycles, illustrating limited leaching and consistent enhanced oxidative performance by the rGO-TiO₂@fibers. Nanocomposites of rGO-TiO₂ have not yet been reported as a surface coating on electrospun fibrous scaffolds, and their applications are typically in dye degradation, bacteria inactivation, and electrochemistry. Through their superior oxidative performance, “green” synthesis, and facile recyclability, rGO-TiO₂@fibers herein are an example of nano-enabled technology being strategically leveraged to address water treatment challenges around the world.