Application of PLA/GO/ZnO and PLA/GO/Cu₂O as sensor

Polylactic acid modified with graphene oxide (PLA/GO) is proposed to interact with ZnO through 6 different schemes. Density functional theory at B3LYP/LANL2DZ level was utilized to calculate total dipole moment (TDM), HOMO/LUMO energy gap (ΔE) and to map the molecular electrostatic potential (MESP). Results indicated that PLA/GO interacted with ZnO through O-atom forming PLA/GO/OZn composite. This composite interacts with methane, hydrogen sulfide, humidity (H₂O), carbon dioxide and ethanol. The same gases were supposed to interact further with PLA/GO/Cu₂O. Adsorption energy for the interaction between each composite and the proposed gases were calculated. Both PLA/GO/OZn and PLA/GO/Cu₂O composites interacted favorably with H₂O. Adsorption energy for interaction of other gases with studied structures are generally low compared to H₂O. PLA/GO/OZn have adsorption energy slightly higher than that of PLA/GO/Cu₂O. PLA/GO/OZn has higher TDM values than those of PLA/GO/Cu₂O, indicating a more polar material. Conversely, PLA/GO/Cu₂O exhibited larger ΔE values than those of PLA/GO/OZn. TDM and energy gap results for both studied structures indicated good sensing capabilities. Further insights come from analyzing the calculated density of states (DOS) and partial density of states (PDOS). PLA/GO/Cu₂O exhibited high peak for copper in its DOS and PDOS spectra compared to zinc and oxygen in case of PLA/GO/OZn. This means a higher density of available electronic states associated with Cu.