Surface functionality and optical properties impact of phenol red dye on mesoporous silica matrix for fiber optic pH sensing

Phenol red dye (PR) functionalized mesoporous silica matrix nano-structures/ nano-tubes (MSNs) are synthesized by sol-gel method for pH sensing. FE-SEM analysis revealed formation of different nano-objects (i.e. nano-clusters and nano-tubes) with defined pores, which are arranged into bunch of nanotubes after PR encapsulation. AFM analysis shows the crack-free dense matrices films with low average surface roughness and thickness. XRD and FTIR exhibited the interaction/bonding of phenolic anchoring groups of PR with silica. HRTEM analysis confirms the formation of crystalline nano-tubes after PR encapsulation within silica matrix. TGA/DTA analysis shows PR dye interacts efficiently within the silica matrix species from 300 °C - 1000 °C. N2 adsorption isotherms confirms the meso-porous nature of the PR encapsulated silica matrix have high surface area value of 434 m2/g with a pore volume of 0.96 cm3/g. UV-vis analysis exhibited that silica matrix has transmission of 84% at 550 nm and 1.36 refractive index. However, transmission is reduced to 79% whilst refractive index increased to 1.37 at 550 nm after PR encapsulation. Coated fiber optic displayed dynamic range of 1-10 pH with fast response time (<50 s). In conclusion, these structural, physicochemical, thermal and optical characteristics of synthesized PR encapsulated silica matrix film could serve as a prototype sensing device model leading to functional benefits in pH stimuli response behavior of opto-chemical devices and optical characteristics.