Controlled aggregation of methylene blue in silica–methylene blue nanocomposite for enhanced 1O2 generation

Abstract

Organic photosensitizers can facilitate photochemical singlet-oxygen (1O2) production, providing a promising strategy for photocatalysis, photodynamic therapy, and environmental protection. Unfortunately, most organic photosensitizers tend to self-aggregate because of their hydrophobicity and conjugated π–π electronic structure, leading to the inactivation of their photosensitizing capabilities. Thus, the controlled aggregation of organic photosensitizers is critical for photosensitizer’s applications. We report a nanocomposite of porous silica nanoaggregates and the organic photosensitizer methylene blue (P-SiOx NAs/MB) that allows the aggregation control of methylene blue (MB). This nanocomposite-photosensitizer consists of highly dispersed MB in P-SiOx NAs and enhances 1O2 production under light irradiation without the inactivation of the photosensitizing ability of MB. The enhanced 1O2 generation rate of P-SiOx NAs/MB is 1.36 times larger than that of free MB. This behavior is contrasted with the inactivation of the photosensitizing ability of MB-encapsulated organo-silica nanoparticles, due to MB self-aggregation within the particles. This study provides a strategy for creating an efficient photosensitizer via suppression of MB self-aggregation to enhance the generation of 1O2.