CR incorporation in mesoporous silica matrix for fiber optic pH sensing.

Highlights • Thermally stable CR immobilization silica matrix is synthesized by sol–gel method for sensing applications. • Microscopic analysis revealed the porous surface with average surface roughness ∼1.98 nm and ultra-thin ∼12 nm thickness. • Synthesized matrix has high surface area of 458 m2/g, high transparency ∼82 % and low refractive index 1.36. • The calculated sensitivity ∼90 (a.u.)/pH at 434 nm and fast response time ∼0.5 s–0.2 s is reported. • Experimental findings shows that the coated matrix has potential for opto-chemical sensing devices. Abstract This research work is concerned with the synthesis of cetyl trimethylammonium bromide (CTAB) assisted silica nanomatrix and creosol red (CR) immobilization in silica nanomatrix. The synthesized nanomatrices are systematically characterized by FESEM/EDS analysis, AFM, FTIR, TGA, BET and UV–vis spectroscopy. FESEM analysis suggests the porous structure network of CTAB assisted silica occupied by CR species after immobilization. Silicon and oxygen signals along with CTAB and CR species by EDS spectra confirm a strong interaction with each other. AFM analysis exhibited the crack-free smooth surface with low average surface roughness ∼2.25 nm which decreased down to ∼1.98 nm. The thickness ∼12 nm is calculated after CR immobilization. FTIR spectroscopy confirmed the presence of silica molecules and CR species bonding after immobilization in silica matrix. BET analysis confirmed the mesoporosity of synthesized matrices with surface area of 458 m2/g, after immobilization. TGA and UV–vis analysis show that thermally stable CR immobilized matrix is 82% transparent and has low refractive index ∼1.38. The proposed sensing device has linear sensitivity ∼90 (a.u.)/pH unit with coefficient of determination (R2) ∼0.98 within pH 1–9. Fast response has been observed at 0.2 s in pH 9 with color change behavior and 98% repeatability identify that the coated matrix has potential in opto-chemical sensing device. [ABSTRACT FROM AUTHOR]