Graphene-based nanostructures as catalysts for wet peroxide oxidation treatments: From nanopowders to 3D printed porous monoliths

Abstract

This paper explores the catalytic behaviour of different graphene-based nanostructures for the treatment of wastewater using Catalytic Wet Peroxide Oxidation (CWPO) processes. In a first stage, graphene-based nanopowders with distinct physical-chemical characteristics are tested in the CWPO of phenol using the following standard operating conditions: [Phenol]0 = 1 g·L−1, [H2O2]0 = 5 g L−1 and 80 °C. Graphene nanoplatelets with the lowest oxygen content exhibit the highest catalytic activity. The typical phenol oxidation by-products are detected in the liquid phase while CO and CO2 appear in the gas phase. Afterwards, three dimensional (3D) porous graphene monoliths (D ∼ 11.5 mm, H ∼ 4 mm, Dopen ∼ 0.68 mm and δw =0.36 cm, 75 cells·cm−2, εgraphene skeleton = 41%) based on those nanoplatelets are additive manufactured using a direct ink writing technique and, then, tested under similar CWPO conditions. The results evidence that the 3D graphene-based structures are catalytically active, though they undergo a progressive deactivation due to the deposition of organic matter. The graphene-based monoliths can be regenerated by thermal treatments, allowing their use at industrial scale by means of reaction-thermal regeneration cycles.