By Dr Silpaja Chandrasekar, PhDReviewed by Bethan DaviesMar 12 2025A recent study published in Advanced Functional Materials explores a novel method for functionalizing glass using ultrasonication of aryl diazonium salts.
Study: Sonochemical Functionalization of Glass. Image Credit: Rohane Hamilton/ Shutterstock.com
This technique not only eliminates the need for toxic chemicals but also forms stable silicon-oxygen–carbon (Si–O–C) bonds, enhancing resistance to hydrolysis. The resulting polymeric film allows customization of surface properties and demonstrates strong adhesion to microorganisms such as Chlorella vulgaris, Escherichia coli, and Saccharomyces cerevisiae.
With potential applications in enzyme production, filtration, and biofuel technologies, this method addresses key limitations of traditional glass functionalization.
Addressing Previous Challenges
Earlier methods for glass functionalization, such as silane-based coatings and non-covalent approaches, struggled with stability, especially in aqueous environments. Silane-based films degraded due to hydrolysis, while non-covalent coatings like polystyrene exhibited weak adhesion.
Alternative techniques, such as halosilanes, formed siloxane bonds but remained prone to water damage. These challenges underscored the need for a more robust and durable glass functionalization strategy.
Surface Modification and Analysis
To develop this improved approach, researchers modified and characterized silicon and glass surfaces using high-purity chemicals. Solvents like dichloromethane and 2-propanol were distilled before use, and surfaces were cleaned through sonication and dried with argon gas.
Silicon wafers underwent etching with Piranha solution and ammonium fluoride under controlled conditions before being treated with diazonium salts via ultrasonication.
A range of analytical techniques were employed to study the modified surfaces.
Cyclic voltammetry and electrochemical impedance spectroscopy assessed electrical properties using a three-electrode setup. X-ray photoelectron spectroscopy (XPS) provided details of the elemental composition, while water contact angle measurements evaluated surface wettability. Nuclear magnetic resonance (NMR) spectroscopy confirmed chemical modifications and ultraviolet-visible (UV-vis) spectroscopy analyzed absorbance properties across a broad wavelength range.
Testing Biological Applications
To explore potential biological applications, the researchers tested the modified surfaces for microbial adhesion. Chlorella vulgaris was cultured in photobioreactors to assess its growth on coated glass, while Escherichia coli and Saccharomyces cerevisiae adhesion was analyzed through incubation and microscopic imaging.
ImageJ software quantified bacterial and fungal coverage, and zeta potential measurements provided insights into surface charge properties influencing biological interactions.
Computational modeling and statistical analysis complemented the experimental work, offering deeper insights into surface interactions. Density functional theory simulations helped predict bond formation and stability, while statistical tests ensured reproducibility. Image processing techniques provided high-accuracy surface coverage quantification, reinforcing the experimental data's reliability and potential applications.
Sonication and Wettability Control
Water contact angle measurements revealed that sonication significantly altered the wettability of glass surfaces, with effects depending on the probe's proximity. Areas closer to the probe exhibited higher contact angles, peaking after 60 minutes of exposure, while more distant regions had lower angles.
Using 4-heptylbenzene diazonium further increased hydrophobicity, particularly after 90 minutes. Adjusting the probe distance confirmed that closer proximity improved surface coverage. Additionally, increasing the water concentration in acetonitrile enhanced hydrophobicity due to hydrogen radical formation from ultrasonic cavitation.
XPS confirmed the covalent attachment of diazonium salts to the glass surface. The Si 2p spectrum revealed distinct silicon bonds, while the O 1s spectrum suggested interfacial bonding. Comparisons with gold surfaces supported these findings, as gold samples displayed lower peak intensity.
The N 1s spectra confirmed diazonium reduction, leading to new carbon-nitrogen bonds and visible color changes. The C 1s spectrum displayed various carbon bonds, validating sonication as an effective modification method.
To assess stability, the researchers subjected the functionalized surfaces to rigorous washing with hot organic solvents such as tetrahydrofuran, dichloromethane, and toluene. XPS spectra showed no significant changes, indicating that the Si–O–C bonds remained intact.
Water contact angle measurements confirmed stability with minimal variations. However, exposure to tetrabutylammonium fluoride (TBAF) cleaved Si–O–C bonds, forming Si–F bonds. These results demonstrated that while diazonium-derived films are highly stable in organic solvents, they remain susceptible to fluoride treatment.
NMR and UV-vis spectroscopy further confirmed the modification process. Sonication of 4-bromobenzene diazonium for 120 minutes altered the 1H NMR spectra, indicating chemical transformations. Initial spectra displayed doublets at δ 7.8 and δ 8.1, corresponding to aromatic protons. After sonication, signal shifts confirmed successful glass surface modification. These findings reinforce the effectiveness of sonication in controlling surface wettability.
Conclusion
This study introduces an environmentally friendly and scalable method for functionalizing glass through ultrasonication of aryl diazonium salts.
By forming stable Si–O–C bonds, this approach provides superior durability compared to conventional silanization. The ability to fine-tune surface hydrophobicity and charge makes it highly valuable for applications in filtration, environmental remediation, and biofuel production. Hydrophobic surfaces enhance microbial adhesion, while charged surfaces support microalgae attachment, expanding the potential uses of this innovative technique.
Journal Reference
Li, T., et al. Sonochemical Functionalization of Glass. Advanced Functional Materials, 2420485. DOI: 10.1002/adfm.202420485, https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202420485
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