Organophilicity of Graphene Oxide for Enhanced Wettability of ZnO Nanorods.

Interfacing two-dimensional graphene oxide (GO) platelets with one-dimensional zinc oxide nanorods (ZnO) would create mixed-dimensional heterostructures suitable for modern optoelectronic devices. However, there remains a lack in understanding of interfacial chemistry and wettability in GO-coated ZnO nanorods heterostructures. Here, we propose a hydroxyl-based dissociation-exchange mechanism to understand interfacial interactions responsible for GO adsorption onto ZnO nanorods hydrophobic substrates. The proposed mechanism initiated from mixing GO suspensions with various organics would allow us to overcome the poor wettability (θ ∼ 140.5°) of the superhydrophobic ZnO nanorods to the drop-casted GO. The addition of different classes of organics into the relatively high pH GO suspension with a volumetric ratio of 1:3 (organic-to-GO) is believed to introduce free radicals (-OH and -COOH), which consequently result in enhancing adhesion (chemisorption) between ZnO nanorods and GO platelets. The wettability study shows as high as 75% reduction in the contact angle (θ = 35.5°) when the GO suspension is mixed with alcohols (e.g., ethanol) prior to interfacing with ZnO nanorods. The interfacial chemistry developed here brings forth a scalable tool for designing graphene-coated ZnO heterojunctions for photovoltaics, photocatalysis, biosensors, and UV detectors.