Surface Enhanced Infrared Absorption Studies of SiO2–TiO2–Ag Nanofibers: Effect of Silver Electrodeposition Time on the Amplification of Signals

Abstract

Surface Enhanced on Infrared Absorption (SEIRAS) and Raman Spectroscopy (SERS) are nondestructive analytic techniques used to detect low concentrations and recognize the fingerprints of molecules. The recognition of the absorption from samples by conventional infrared spectroscopy (IR) via Attenuated Total Reflection (ATR) is difficult for molecules with a low signal strength. However, developed structures with SERS and SEIRAS effect present problems such as high cost, low stability, and low compatibility. Research into new media to obtain greater amplification is largely based on the creation of nanoscale structures with symmetrical arrangements and reproducible distances, resulting in aggregates of nanoparticles that help generate hot spots which are active for amplification. The sol-gel and electrospinning method for the obtention of ceramics provides an alternative means by which to produce said substrates. Fibers of nanometric scale provide an increase of surface area which allows more contact to occur with analytes. Consequently, in this study, a silica-titania-silver nanostructured support that amplifies signal intensity for Raman and infrared spectroscopy was developed. The silica-titania support was developed by sol-gel and electrospinning techniques, and the as spun fibers were treated at 800 °C. Then, the ceramic fibrous membrane was placed on conductive indium tin oxide plastic to be doped with silver using an electroplating technique, varying the silver nitrate concentration (5, 10 and 20 mM), as well as electrodeposition times (1, 2, 5 and 10 min), with a constant voltage (1 V). Twelve different supports were obtained that showed amplification. The enhancement of infrared signals from pyridine and crystal violet molecules adsorbed on silica-titania-silver (SiO2–TiO2–Ag) nanofibers was studied in situ by Attenuated Total Reflection-Fourier Transformed Infrared Spectroscopy (ATR-FTIR). The highest amplification was obtained by the support doped at 10 min in a 10 mM concentration, with an amplification factor of 2.74 in the band localized at 3301 cm−1. In Raman spectroscopy, the highest amplification factor was 27.03, on the support doped for 5 min at a concentration of 5 mM.

Adsorptive potential of ZnO/SiO2 nanorods prepared via the sol–gel method for the removal of Pb(II) and Cd(II) from petroleum refinery wastewater

“…The peaks at 793 and 1020 cm −1 correspond to the asymmetric vibration mode and symmetric stretching mode of the SiO 2 groups (OSiO), respectively. This result is similar to that of the absorption band reported by Abello‐Ribota et al 43 . The peak at 950 cm −1 is attributed to the presence of asymmetric vibration of SiH bond.…”

“…The peaks at 793 and 1020 cm −1 correspond to the asymmetric vibration mode and symmetric stretching mode of the SiO 2 groups (O Si O), respectively. This result is similar to that of the absorption band reported by Abello-Ribota et al 43 The peak at 950 cm −1 is attributed to the presence of asymmetric vibration of Si H bond. The presence of a peak at 1640 cm −1 is attributed to bending of O H groups of SiO 2 (H bonding) of adsorbed water which is based on the scissor bending vibration of water molecules.…”

Ag Nanoparticle-Decorated SiO2–Al2O3–ZrO2 Composites as a Low-Cost Substrate for Enhanced Signal Infrared Spectroscopy

“…27 Others have suggested that weak interactions occur between silver and pyridine and pyridine and water when in solution, and that this can contribute to the EM enhancement of pyridine. 28 Thus, since the material has an enhancement capacity up to 10, 6 it is possible that the pyridine signal is both enhanced by the charge transfer mechanism and the electromagnetic mechanism. Considering the nature of the ceramic substrate obtained from this research, there is a strong possibility that phonon resonance could also be responsible for the enhancement capabilities as some studies have proven the amplifying capacity of Al 2 O 3 -based materials.…”

“…Integration of ceramic nanofibers in spectroscopic enhancement substrates has been previously studied, where SiO 2 –TiO 2 , and SiO 2 –hydroxyapatite nanofibers were capable of amplifying IR spectroscopic signals with an enhancement factor of up to 2 × 10, , showing promising results regarding a universal substrate capable of amplifying and being reusable, potentially lowering costs and waste. Other uses of ceramics include, for example, substrates composed of TiO 2 , Ag, and ZnO, capable of both amplifying and photocatalysis making the substrate reusable .…”