Fused multifunctional fibrous SiO2/activated carbon composites for SERS and selective pollutant adsorption

Surface enhanced Raman scattering (SERS) is a powerful technique for detecting dye molecules at trace levels. The removal of these dyes through adsorption using efficient substrates remains equally critical for environmental applications. In this study, paper (P) strips were fabricated by decorating fibrous SiO₂ (FSO) and activated carbon (AC) composites with silver nanoparticles (Ag NPs). The P-Ag@FSO/AC-5 composite effectively detected methylene blue (MB) at levels as low as 10⁻⁹ M, exhibiting a high SERS enhancement factor (EF) of 2.88 × 10⁷. These paper strips could also detect rhodamine B (10⁻⁸ M) and methyl orange (10⁻⁶ M) effectively. The fibrous morphology of FSO facilitated Ag NPs entrapment, creating efficient SERS-active “hotspots,” while the porous structure of AC enhanced MB adsorption near the Ag surface. As a result, P-Ag@FSO/AC-5 exhibited stronger Raman signals (EF: 1.86 ×10⁴) compared to P-Ag@FSO (EF: 1.66 × 10⁴) when tested using 10⁻⁵ M MB solution. In adsorption studies, FSO/AC-5 removed 95 % of MB within 80 min, with a capacity of 207.46 mg g⁻¹. Its selective adsorption efficiency for MB over methyl orange in mixed dye systems reached 85.07 %. Furthermore, MB-loaded FSO/AC-5 functioned as a visual sensor for Cucurbit[7]uril (CB[7]), detecting it at 10⁻⁶ M. Thus, FSO/AC-based composites, when functionalized with plasmonic silver nanoparticles, demonstrate dual functionality as efficient adsorbents for dye removal and as sensitive SERS substrates for molecular detection.