UV-Vis spectroscopy in the characterization and applications of smart microgels and metal nanoparticle-decorated smart microgels: a critical review

Abstract

Smart microgels (SMGs) and metal nanoparticles (MNPs)-decorated smart microgels have garnered significant attention because of their responsive behavior. Both SMGs and their hybrids are extensively used in adsorption, drug delivery, and catalysis, which can be characterized with expensive instruments. UV-Vis spectroscopy is a technique that can easily monitor these processes, and it can also identify the presence of noble metal nanoparticles, like Ag and Au, in smart microgels with the help of the surface plasmon resonance wavelength of these metals. This technique is widely employed to determine the size and shape of MNPs present in microgels. Additionally, UV-Vis spectroscopy enables the investigation of optical behaviors of noble metal nanoparticles under various stimuli. Time-dependent UV-Vis spectroscopy can monitor the kinetics of swelling and deswelling in MGs and HMGs. It also facilitates the study of metal nanoparticle growth within polymer networks or the growth of polymer networks around metal nanoparticle cores. Furthermore, UV-Vis spectroscopy can be used to explore numerous applications of microgels and hybrid substances in photonics, sensing, catalysis, and adsorption. This tutorial review highlights the use of UV-Vis spectroscopy in the characterization and applications of both smart microgels and their hybrids in adsorption and catalysis, considering the recent research advancements in these fields.

Fig. 1. Swelling/deswelling behavior of microgels and hybrid microgels.

Fig. 2. Adsorbate content impact on the adsorption capacity of both microgels and hybrids (red arrows stand for the functional groups and green dots correspond to pollutants).

Fig. 3. Pictorial representation of the porosity of microgels.

Fig. 4. Availability of the empty space in microgels depends on the microgel content.

Fig. 5. UV-Vis spectrum of both P(S@NIPMAM–MAA) and Ag–P(S@NIPMAM–MAA) (reproduced from ref. with permission from Elsevier, copyright 2021).

Fig. 6. UV-Vis spectra of Au nanorod-containing microgels and pure MGs (reproduced from ref. with permission from Elsevier, copyright 2019).

Fig. 7. Au NPs stability in P(S@NIPMAM) microgels (reproduced from ref. with permission from Elsevier, copyright 2022).

Fig. 8. λ _SPR value shifting of Ag–P(S@NIPMAM–MAA) with (A) increasing pH, (B) increasing temperature, and (C) decreasing temperature (reproduced from ref. with permission from Wiley, copyright 2021).

Fig. 9. The k_obs value depending on the NPs content in microgels.

Muhammad Arif

Hamid Raza

Toheed Akhter