## 1 Introduction
The sol-gel process is significantly influenced by the presence of acids or bases [12], playing a fundamental role in shaping the characteristics of the resulting gel, impacting various aspects such as reaction speed, gel architecture, and the ultimate properties of the material synthesized. In particular, the acids act as catalysts by accelerating the hydrolysis reaction through electrophilic mechanisms. This acceleration promotes the rapid formation of hydroxyl groups, which are essential for subsequent polymerization reactions [17; 18]. In addition, the acid affects the microstructure and properties of the dried and fired gel by favoring linear chain structures [19]. However, the use of acid catalysts, such as nitric acid, can introduce potential drawbacks such as altering the structure and stability of encapsulated bioactive molecules, generating hazardous waste, and posing safety concerns during handling and synthesis [20; 21]. Therefore, exploring acid-free synthesis methods is useful for developing safer, more environmentally friendly, and potentially more effective biomaterials. In this study, silica-based hybrid materials were synthesized by incorporating 5% quercetin (Q5), a flavonoid renowned for its anti-inflammatory, antioxidant, and antibacterial properties [22; 23; 24]. These properties are mainly due to the presence and placement of the ortho-dihydroxy or catechol group in B-ring, as well as the presence of a 2,3-double bond and a hydroxyl substitution at position 3 and 5 (see structure in Figure 1). Two systems were produced by employing two sol-gel-based approaches: one using nitric acid as a catalyst and the other without any acid. This dual approach aimed to investigate the impact of the acidic environment on the structural integrity of quercetin and the overall bioactivity of the hybrid materials. The rationale behind synthesizing biomaterials with a 5% flavonol content depends on our prior research findings. Through our investigations, we determined that this concentration yielded the most efficient drug release compared to the higher-concentration hybrid materials that we studied. Furthermore, theoretical analyses supported our experimental outcomes, suggesting that at lower drug concentrations, flavonoid is well absorbed into the SiO\({}_{2}\) surface with slow mobility. This facilitates the formation of abundant hydrogen bonds between quercetin molecules and the SiO\({}_{2}\) surface, thereby mitigating the formation of agglomerates typically observed at higher concentrations [25; 26]. Structural characterization was performed using Fourier transform infrared (FTIR) spectroscopy, while the antibacterial efficacy was assessed through the Kirby-Bauer antibacterial sensitivity test. Additionally, the bioactivity and release kinetics of quercetin from the silica matrices were studied to evaluate their potential as drug delivery systems. Similar studies have demonstrated the effectiveness of the sol-gel technique for drug delivery, such as the encapsulation of antibiotics in silica matrices to control infection, the release of anti-inflammatory drugs for sustained therapeutic effects, and the incorporation of anticancer agents to target tumor cells [27; 28; 29]. The findings from this research could contribute to the development of more effective biomaterials for biomedical applications, particularly in tissue engineering and infection control.