Nanoparticle-Reinforced Silica Gels with Enhanced Mechanical Properties and Excellent pH-Sensing Performance

Silica gels offer excellent wear resistance, high chemical stability, good insulation, and light transmittance, are therefore promising to engineer 2D sensing films. However, their practical applications are greatly hampered by their poor structural stability, low sensitivity, reliability, and repeatability. Incorporation of nanoelements into glasses and ceramics is a promising new pathway to tackle these challenges. Unfortunately, it is difficult to disperse nanoparticles uniformly in any glass and ceramics. Herein, a facile sol–gel approach is applied to synthesize novel silica gel nanocomposites with dispersed nanoparticles (NPs) as additives and thymol blue as an indicator. Titanium dioxide (TiO₂) NPs with a diameter of 5 nm can be dispersed uniformly in the silica gel, with enhanced modulus and hardness (up to 230% and 138%, respectively) and good alkaline resistance. The addition of nanoparticles improves the film's stability, sensitivity, and repeatability of spectral responses (in pH 1–12), and reduces the indicator leakage. The interaction of indicator with silica gel substrate, nanoparticles, and H⁺ is analyzed to elucidate the principle of reversible color change. This novel simplified method to produce glass-like functional materials under much lower temperatures is groundbreaking in materials science and engineering.