Alternatives for Epoxides in Graphene Oxide.

The structural mystery of the long-known graphene oxide (GO) unfolds as one of the most abstract conceptual problems among nanomaterials. Generally construed as the oxidized form of graphene, it is proposed to host a variety of functional groups with oxygen and hydrogen. Theoretical studies are abundant on the highly strained epoxides, while larger cyclic ethers having one or more oxygen atoms and vinylogous carbonyls are paid scant attention even though they are predicted by several structural models. The nature of the geometric and electronic structures of these alternative functional groups, the preferred distribution on the graphene lattice, comparative stability, etc., remain unexplored. Our systematic inquiry into the impact of hexagonal and periodic constraints on these mystic functional groups unveils several surprises. Among those that retain the hexagonal carbon backbone, epoxides are surprisingly more stable than larger ethers despite the excessive strain associated with their acute triangular geometry. Epoxidation conserves the planarity of the carbon backbone, which allows their optimal distribution on the lattice by reducing the repulsive interactions from oxygen lone pairs and π-electrons. These findings categorically rule out the possibility of 1,3-ethers in GO and settle the longstanding debate on its existence. They face severe steric repulsion even in low-dimensional systems that tear the σ-skeleton of graphene completely apart, reducing its dimensionality. We show that selective breaking of the σ-bonds is preferred over that of epoxides if backed by cyclic delocalization of electrons. Particularly, 1,6-diones in trans orientation are thermodynamically favored and justify the large holes experimentally observed through microscopic imaging.

Effective corrosion inhibition of mild steel using novel 1,3,4-oxadiazole-pyridine hybrids: Synthesis, electrochemical, morphological, and computational insights.

An easy synthesis of two 1,3,4-oxadiazole derivatives, namely, 2-phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazole (POX) and 2-(4-methoxyphenyl)-5-(pyridin-3-yl)-1,3,4-oxadiazole (4-PMOX), and their corrosion-inhibition efficacy against mild steel corrosion in 1 N HCl, is evaluated using weight loss from 303 to 323 K, Electrochemical Impedance Spectroscopy (EIS), Potentiodynamic Polarization (PDP), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), UV-Vis spectroscopy, along with theoretical evaluation. Both POX and 4-PMOX exhibit excellent inhibition efficiency, with values reaching 97.83% and 98% at 500 ppm, respectively. The PDP analysis reveals that both derivatives act as mixed-type inhibitors. The Langmuir adsorption isotherm provides insights into the adsorption phenomena, demonstrating that 4-PMOX exhibits superior adsorption behavior on the mild steel surface compared to POX. This finding is further supported by SEM, DFT, RDF, and MSD analyses. Quantum mechanical parameters, including EHOMO, ELUMO, dipole moment (µ), energy gap (ΔE), etc., are in good agreement with the effectiveness of inhibition performance revealing ΔE values of 3.10 and 2.75 for POX and 4-PMOX, respectively. The results obtained from this study hold significant implications for researchers aiming to design more efficient organic inhibitors to combat metal corrosion.

Topological Impact of Delocalization on the Stability and Band Gap of Partially Oxidized Graphene.

Strategic perturbations on the graphene framework to inflict a tunable energy band gap promises intelligent electronics that are smaller, faster, flexible, and much more efficient than silicon. Despite different chemical schemes, a clear scalable strategy for micromanaging the band gap is lagging. Since conductivity arises from the delocalized π-electrons, chemical intuition suggests that selective saturation of some sp2 carbons will allow strategic control over the band gap. However, the logical cognition of different 2D π-delocalization topologies is complex. Their impact on the thermodynamic stability and band gap remains unknown. Using partially oxidized graphene with its facile and reversible epoxides, we show that delocalization overwhelmingly influences the nature of the frontier bands. Organic electronic effects like hyperconjugation, conjugation, aromaticity, etc. can be used effectively to understand the impact of delocalization. By keeping a constant C4O stoichiometry, the relative stability of various π-delocalization topologies is directly assessed without resorting to resonance energy concepts. Our results demonstrate that >C=C< and aromatic sextets are the two fundamental blocks resulting in a large band gap in isolation. Extending the delocalization across these units will increase the stability at the expense of the band gap. The band gap is directly related to the extent of bond alternation within the π-framework, with forced single/double bonds causing the large gap. Furthermore, it also establishes the ground rules for the thermodynamic stability associated with the π-delocalization in 2D systems. We anticipate that our findings will provide the heuristic guidance for designing partially saturated graphene with the desired band gap and stability using chemical intuition.