Self-assembled hierarchical phenolphthalein encapsulated silica nanoparticles: structural, optical and sensing response

Abstract

Exploration of novel meso-materials with higher surface areas is a major challenge in the rapidly expanding field of opto-chemical sensor devices. Therefore, synthesis and growth mechanism of surfactant CTAB assisted sol-gel based silica and phenolphthalein encapsulated silica nanoparticles (NPs) and their optical and pH sensing activities is reported at low temperature in this present communication. Hierarchical/ordered structures/architectures are observed after encapsulation of phenolphthalein by FE-SEM analysis. AFM analysis exhibits the formation of porous nanostructures with average surface roughness Ra ∼5.15 nm which is reduced to Ra ∼4.98 nm after encapsulation of phenolphthalein, whereas, particle size increased from 8 nm to 13 nm. N2 adsorption isotherms explain the meso-porous nature of the matrix with high surface area value of 443 m2/g with a pore volume of 0.93 cm3/g and pore diameter of 85.59 Å. Experimental findings show that the prepared meso-silica-phenolphthalein frameworks have high thermal stability, low refractive index (1.33) with good optical transparency of 83%. Furthermore, the evanescent wave is used to selectively excite the phph molecules encapsulated in silica matrix and deposited on the Plastic Clad Silica fiber as cladding for sampling the aqueous media (pH solutions 2–12) surrounding the fiber. Highest sensing response is optimized for pH 12 within 1s with pink color indication. The improved structural and optical characteristics identify that the prepared optochemical nanosensor device has potential for fast detection of pH at dynamic range.