Polydopamine-Mediated Ag and ZnO as an Active and Recyclable SERS Substrate for Rhodamine B with Significantly Improved Enhancement Factor and Efficient Photocatalytic Degradation

Abstract

We demonstrate the development of an active multicomponent Ag/PDA/ZnO@GMF surface-enhanced Raman scattering (SERS) substrate via introducing bio-inspired polydopamine (PDA) in between a noble metal (AgNPs) and ZnO nanorods. The insertion of PDA enabled efficient charge redistribution between metal and semiconductor through their aromatic cores. The substrate exhibited a high enhancement factor (EF) of 1010 for the organic pollutant dye Rhodamine B (RhB). Subsequent exposure of a RhB-loaded substrate to an external UV light source developed an efficient pathway for RhB degradation and replenished the substrate for multiple usage cycles with remarkable photostability. Thus, enhanced performance of the substrate in terms of light-harvesting capability and high charge-separation efficiency was observed. In addition, the much larger surface area of the branched ZnO nanostructures served as a template for PDA assisted synthesis and controlled deposition of AgNPs, which further improved the SERS effect. Our work seeks to understand the contributions of the noble metal and semiconductor components and the synergistic effects of combining them with a facile charge transport medium to enable the fabrication of highly efficient SERS substrates for use in industrial and environmental applications.

Zinc oxide nanostructures for fluorescence and Raman signal enhancement: a review

“…A film with fluffy sponge-like morphology was obtained, pointing out its high specific surface area and showing uniform distribution of all elements. A more exotic strategy for developing SERS substrates based on ZnO and Ag was investigated by Chin et al by employing a long-range π-conjugated segment, namely polydopamine, as an adhesive layer that can provide effective charge redistribution between the metal and semiconductor [ 53 ]. Additionally, the polydopamine layer assured a large number of functional groups, which served as anchors for controlled distribution and growth of Ag NPs, durability of the substrate, and biocompatibility.…”

“…Chin et al [ 53 ] fabricated polydopamine-ZnO–based substrates using increasing Ag NP deposition times and observed a gradually decrease of the detected concentration of rhodamine 6G with increasing deposition time. However, for longer deposition times, which resulted in a high metal coverage of the ZnO nanorods, the limit of detection decreased ( Figure 3 ).…”

“… SEM images of silver nanoparticle–ZnO–polydopamine substrates and the SERS spectra of different rhodamine B concentrations acquired from each substrate. The deposition time of silver nanoparticles was varied for each substrate: (a) 2 h, (b) 4 h, (c) 6 h, (d) 8 h, (e) 10 h, and (f) 12 h. Figure 3 was adapted from [ 53 ] (© 2021 Chin, H.-K. et al, published by MDPI, distributed under the terms of the Creative Commons Attribution 4.0 International License, https://creativecommons.org/licenses/by/4.0). …”

“…Since metal-based SERS substrates are disposable after being used, the photocatalytic property of ZnO would ensure reduced consumption of resources and costs when used as a SERS substrate. The self-cleaning ability of ZnO alone or ZnO–noble metal-based nanostructured substrates has been shown under UV or visible irradiation via the photocatalytic degradation of the organic molecules attached to the substrate [ 8 , 34 , 53 ]. For instance, [ 75 ] presented Au-coated roughened ZnO nanostructures, which enabled photocatalytic degradation of adsorbed analytes and the reuse of the substrate.…”

“…The rhodamine 6G adsorbed on Ag–ZnO–Au film showed a fast photocatalytic degradation due to higher surface area and the presence of a metal–semiconductor junction by this 3D hybrid structure [ 68 ]. Additionally, it was observed that metal-based substrates did not exhibit any catalytic degradation, while those that incorporated ZnO led to a significant decrease in the SERS intensity under the same irradiation conditions [ 53 ]. A typical experiment to test the reusability of an Au–ZnO substrate consisted of immersing the substrate in a dye solution for 12 h and characterizing it by SERS.…”