Reduced Graphene Oxide Conjugated Cu₂O Nanowire Mesocrystals for High-Performance NO₂ Gas Sensor

TLDR

Reduced graphene oxide promotes nonclassical crystallization of Cu₂O nanowire mesocrystals, where amorphous Cu₂O nanoparticles agglomerate, undergo particle‑mediated growth and Ostwald ripening, and self‑organize into a porous 3D framework interspersed with rGO sheets, with the nanowire architecture tunable by growth conditions. The resulting rGO‑Cu₂O mesocrystals, featuring anisotropic nanowires, octahedral morphology, and high surface area, exhibit superior room‑temperature NO₂ sensitivity compared to Cu₂O nanowire networks or rGO alone, indicating promise for ultrasensitive environmental sensing.

Abstract

Reduced graphene oxide (rGO)-conjugated Cu2O nanowire mesocrystals were formed by nonclassical crystallization in the presence of GO and o-anisidine under hydrothermal conditions. The resultant mesocrystals are comprised of highly anisotropic nanowires as building blocks and possess a distinct octahedral morphology with eight {111} equivalent crystal faces. The mechanisms underlying the sequential formation of the mesocrystals are as follows: first, GO-promoted agglomeration of amorphous spherical Cu2O nanoparticles at the initial stage, leading to the transition of growth mechanism from conventional ion-by-ion growth to particle-mediated crystallization; second, the evolution of the amorphous microspheres into hierarchical structure, and finally to nanowire mesocrystals through mesoscale transformation, where Ostwald ripening is responsible for the growth of the nanowire building blocks; third, large-scale self-organization of the mesocrystals and the reduction of GO (at high GO concentration) occur simultaneously, resulting in an integrated hybrid architecture where porous three-dimensional (3D) framework structures interspersed among two-dimensional (2D) rGO sheets. Interestingly, "super-mesocrystals" formed by 3D oriented attachment of mesocrystals are also formed judging from the voided Sierpinski polyhedrons observed. Furthermore, the interior nanowire architecture of these mesocrystals can be kinetically controlled by careful variation of growth conditions. Owing to high specific surface area and improved conductivity, the rGO-Cu2O mesocrystals achieved a higher sensitivity toward NO2 at room temperature, surpassing the performance of standalone systems of Cu2O nanowires networks and rGO sheets. The unique characteristics of rGO-Cu2O mesocrystal point to its promising applications in ultrasensitive environmental sensors.