Stable Cuprous Hydroxide Nanostructures by Organic Ligand Functionalization

Abstract

Copper compounds have been extensively investigated for diverse applications. However, studies of cuprous hydroxide (CuOH) have been scarce due to structural metastability. Herein, a facile, wet-chemistry procedure is reported for the preparation of stable CuOH nanostructures via deliberate functionalization with select organic ligands, such as acetylene and mercapto derivatives. The resulting nanostructures are found to exhibit a nanoribbon morphology consisting of small nanocrystals embedded within a largely amorphous nanosheet-like scaffold. The acetylene derivatives are found to anchor onto the CuOH forming CuC linkages, whereas CuS interfacial bonds are formed with the mercapto ligands. Effective electronic coupling occurs at the ligand-core interface in the former, in contrast to mostly non-conjugated interfacial bonds in the latter, as manifested in spectroscopic measurements and confirmed in theoretical studies based on first principles calculations. Notably, the acetylene-capped CuOH nanostructures exhibit markedly enhanced photodynamic activity in the inhibition of bacteria growth, as compared to the mercapto-capped counterparts due to a reduced material bandgap and effective photocatalytic generation of reactive oxygen species. Results from this study demonstrate that deliberate structural engineering with select organic ligands is an effective strategy in the stabilization and functionalization of CuOH nanostructures, a critical first step in exploring their diverse applications.

Keywords: acetylene; antimicrobial activity; cuprous hydroxide; interfacial electronic coupling; mercapto ligands.

Figure 1.

Representative TEM images of the organically capped CuOH samples: (a, d, g) CuOH-EPA, (b, e, h) CuOH-HC16, (c, f, i) CuOH-EPT. Scale bars are (a-c) 200 nm, (d-f) 20 nm, and (g-i) 5 nm. (j) AFM topograph of CuOH-EPA and (k) the corresponding height profile along the red line in panel (j). (l) XRD patterns of CuOH-EPA, simulated CuOH-EPA, traditional Cu-alkyne polymer (CCDC-242490), CuOH (cuprice), and Cu₂O. (m and n) Simulated CuOH-EPA structure. (o) FTIR spectra of CuOH-EPA, CuOH-HC16, and CuOH-EPT nanostructures, and the corresponding ligand monomers (light-colored curves).

Figure 2.

High-resolution XPS spectra of the (a) Cu 2p, (c) O 1s, (d) S 2p, and (e) C 1s electrons of the CuOH-EPT, CuOH-EPA, and CuOH-HC16 samples (from bottom to top). The corresponding (b) EPR and (f) VBM spectra.

Figure 3.

(a) Cu K-edge normalized XANES profiles of CuOH-EPA, CuOH-HC16, CuOH-EPT, Cu foil, Cu₂O, and CuO, and (b) their corresponding FT-EXAFS spectra. Inset to panel (a) is the corresponding first-order derivative of the pre-edge region.

Figure 4.

Optimized structure of (a) CuOH-EPA and EPA ligand, (c) CuOH-HC4 and HC4, (e) CuOH-EPT and EPT with corresponding bond distances (black) and Bader charges in |e| (blue). Charge density difference isosurfaces of (b) CuOH-EPA, (d) CuOH-HC4, and (f) CuOH-EPT (±0.0016|e|). Yellow, positive representing electron gains; cyan, negative for electron loss.

Figure 5.

Photographs of different organically capped CuOH nanostructures (a) in ambient light (dispersed in DCM) and under 365 nm photoirradiation (b) when dispersed in DCM and (c) as solid films). The colors of the CuOH-EPA, CuOH-HC16 and CuOH-EPT dispersions in DCM are all yellowish, while the photoluminescence is red, yellow, and orange, respectively when dispersed in DCM or solid films. (d, f, h) UV-vis (solid curves) and PL spectra (dotted curves) of the ligands-functionalized CuOH nanostructures at the excitation at 395 nm, and (e, g, i) the excitation-dependent PL profiles of (e) CuOH-EPA, (g) CuOH-HC16, and (i) CuOH-EPT.

Figure 6.

(a) Projected local density of states of CuOH-EPA (top) and CuOH-HC4 (bottom). (b) Proposed PL mechanism. (c) TDDFT-based UV-vis spectrum of CuOH-EPA, where the asterisks denote experimental values. (d) Natural transition orbitals (NTO) analysis of CuOH-EPA.

Figure 7.

Antibacterial study of CuOH samples series. (a) Study under UV photoirradiation for 40min. Gram negative bacteria E. coli is a control for comparison with CuOH containing samples. (b) Study under blue Light (465 nm) for 200 min. Antibacterial studies under blue light photoirradiation. E. coli in PBS 1X (black line) is a control. Error bars are included as the study was done in triplicate. (c) Photographs depicting E. coli grown on LB agar plates at different photoirradiation time points (i.e., 0, 30, 60, 90, 120, 150, 180 and 210 min) under blue light (465 nm) in the absence of CuOH and the presence of CuOH-EPA, CuOH-HC16, and CuOH-EPT. (d) Loss of GSH after treatment by materials at different time points. (e) EPR hyperfine splitting patterns in the presence of DMPO after 10 minutes of photoirradiation at 465 nm.