Synthesis of optically active bromophenol blue encapsulated mesoporous silica–titania nanomatrix: structural and sensing characteristics

Abstract

Mesostructured silica-titania (ST) and bromophenol blue encapsulated silica–titania (BPB-ST) nanomatrices are synthesized by sol–gel method at low temperature. FESEM analysis shows uniform crack-free porous surface of ST matrix. EDX mapping analysis shows that the BPB species are uniformly distributed/immobilized throughout the ST matrix lattices. AFM images reveal 45.68 nm thick film with low average surface roughness ~1.27 nm, after encapsulation of BPB dye in ST matrix. TEM analysis exhibits uniform interior titania core and silica shell network, with average particle size 2.4 ± 0.4 nm for ST sample which reduced to 0.8 ± 0.3 nm after BPB encapsulation. Mesoporous high surface area 488 m2/g and pore volume of 0.55 cm3/g encapsulated matrix is found to be beneficial for sensing analysis. Transparent (67%) mesoporous nanoparticles with low refractive index 1.41 is obtained for encapsulated nanomatrix. The synthesized sensing material is fast responsive <1 sec and found to be linear for pH 3–12. High pKa value of 7.57 at 580 nm for ST-BPB leads to the broader sensitivity range, repetitive, easy-to use, and color indication system. The ability to change color in response to external stimulus makes ST-BPB a potential sensing material in food.