Synthesis and characterization of novel photochromic and pH-sensitive colorimetric hydrogel based on azobenzene

Abstract

This article reports the synthesis of new Dye A from the reaction of 4-methyl 2-nitroaniline, NaNO2/H+, and sodium 1-naphtholate. Dye A responded with an obvious colour change visible to naked eyes to pH, ultraviolet light, and fluoride ion and was studied by UV–vis spectroscopy. Next, the reaction of Dye A with crotonic anhydride leads to the formation of MDye A. Subsequently, synthesis of a new type of photochromic and pH-sensitive colorimetric hydrogel consisting of a new azobenzene (MDye A), acrylic acid, acrylamide, N,N'-methylenebisacrylic amide as a crosslinking agent, and sodium acrylate in the presence of 2,2′-azobis(isobutyronitrile) as initiator and sorbitan monostearate (Span 60) as the dispersant or under a LED lamp (400 nm, 20 W) in the presence of CdS nanorods and β-cyclodextrin was studied. The products were characterized using 1H NMR,13C NMR, TGA, DTG, SEM, TEM, and FTIR spectroscopy. The synthesized new hydrogel showed good pH responsiveness and photoresponsiveness, which was investigated by UV–vis spectroscopy. Also, the effects of parameters such as amounts of CdS nanorods, cross-linker, and water, duration of pre-oxygenation, light intensity on the swelling of gel, and polymerization rate in the synthesis of hydrogel were investigated.