Diazonium-Based Covalent Molecular Wiring of Single-Layer Graphene Leads to Enhanced Unidirectional Photocurrent Generation through the p-doping Effect

Abstract

Development of robust and cost-effective smart materials requires rational chemical nanoengineering to provide viable technological solutions for a wide range of applications. Recently, a powerful approach based on the electrografting of diazonium salts has attracted a great deal of attention due to its numerous technological advantages. Several studies on graphene-based materials reveal that the covalent attachment of aryl groups via the above approach could lead to additional beneficial properties of this versatile material. Here, we developed the covalently linked metalorganic wires on two transparent, cheap, and conductive materials: fluorine-doped tin oxide (FTO) and FTO/single-layer graphene (FTO/SLG). The wires are terminated with nitrilotriacetic acid metal complexes, which are universal molecular anchors to immobilize His6-tagged proteins, such as biophotocatalysts and other types of redox-active proteins of great interest in biotechnology, optoelectronics, and artificial photosynthesis. We show for the first time that the covalent grafting of a diazonium salt precursor on two different electron-rich surfaces leads to the formation of the molecular wires that promote p-doping of SLG concomitantly with a significantly enhanced unidirectional cathodic photocurrent up to 1 μA cm–2. Density functional theory modeling reveals that the exceptionally high photocurrent values are due to two distinct mechanisms of electron transfer originating from different orbitals/bands of the diazonium-derived wires depending on the nature of the chelating metal redox center. Importantly, the novel metalorganic interfaces reported here exhibit minimized back electron transfer, which is essential for the maximization of solar conversion efficiency.

Scope and Limitations of Using Microemulsions for the Covalent Patterning of Graphene

“…Control samples of the pure mineral oil, T80 and S80 commercial solutions were previously studied (see Supporting Information, Section S3, Figure S2), with the purpose of identifying their Raman With these four different MEMs (big and small-O/W and big and small-W/O), we based our studies on the free radical addition using aryl diazonium salts as precursors, since it is one of the best known reactions to functionalize graphene, due to its versatility and high reactivity. [6,[31][32][33] Moreover, depending on the nature of the substituents on the aromatic ring, both n and p-doping of G-substrates can be obtained. [32,33] Three different reagents with different doping capabilities were selected: 4methoxybenzenediazonium tetrafluoroborate (MBD), 4-bromobenzenediazonium tetrafluoroborate (BBD) and 4-nitrobenzenediazonium tetrafluoroborate (NBD), as shown in Figure 1.…”

“…[6,[31][32][33] Moreover, depending on the nature of the substituents on the aromatic ring, both n and p-doping of G-substrates can be obtained. [32,33] Three different reagents with different doping capabilities were selected: 4methoxybenzenediazonium tetrafluoroborate (MBD), 4-bromobenzenediazonium tetrafluoroborate (BBD) and 4-nitrobenzenediazonium tetrafluoroborate (NBD), as shown in Figure 1. [12,19,33,34] For each reagent, three different samples were studied: (a) pristine graphene substrates, (pr-G H 2 O), with no functionalization after being submerged in water media (see the Supporting Information, Section S4); (b) fully functionalized graphene substrates as control samples, (f-G, where f is related to the substituent on the salt: MB-G, BB-G and NB-G), using an aqueous solution of each diazonium salt for the functionalization process and (c) patterned graphene substrates, (p-G), which implies functionalization by MEM-patterning (see Supporting Information, Section S5 for both fully functionalized and patterned).…”

“…With these four different MEMs (big and small‐O/W and big and small‐W/O), we based our studies on the free radical addition using aryl diazonium salts as precursors, since it is one of the best known reactions to functionalize graphene, due to its versatility and high reactivity [6,31–33] . Moreover, depending on the nature of the substituents on the aromatic ring, both n and p‐doping of G‐substrates can be obtained [32,33] .…”

Enhanced susceptibility of SARS-CoV-2 spike RBD protein assay targeted by cellular receptors ACE2 and CD147: Multivariate data analysis of multisine impedimetric response

“…Finally, to obtain more atomic-level information, we performed molecular dynamics (MD) studies, (for other computational studies of electrochemical experiments on proteins see [65] , [66] , [67] , [68] ). We prepared models of ACE2 and CD147 receptors on the functionalised sensor (see Methods) and performed 500 ns MD runs.…”