Gemini Surfactant as a Template Agent for the Synthesis of More Eco-Friendly Silica Nanocapsules

Olga Kaczerewska,Joana Figueiredo,João Tedim,Susana Loureiro,Roberto Martins,Isabel Sousa

doi:10.3390/app10228085

Abstract

Silica mesoporous nanocapsules are a class of “smart” engineered nanomaterials (ENMs) applied in several fields. Recent studies have highlighted that they can exert deleterious effects into marine organisms, attributed to the use of the toxic cationic surfactant N-hexadecyl-N,N,N-trimethylammonium bromide (CTAB) during the synthesis of ENMs. The present study reports the successful synthesis and characterization of novel gemini surfactant-based silica nanocapsules. The gemini surfactant 1,4-bis-[N-(1-dodecyl)-N,N-dimethylammoniummethyl]benzene dibromide (QSB2-12) was chosen as a more environmentally-friendly replacement of CTAB. Nanocapsules were characterized by scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), dynamic light scattering (DLS), thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherms. Short-term exposure effects of new ENMs were evaluated in four marine species (Nannochloropsis gaditana, Tetraselmis chuii and Phaeodactylum tricornutum) and the microcrustacean (Artemia salina). The replacement of the commercial cationic surfactant by the gemini surfactant does not change the structure nor the environmental behaviour in seawater of the newly synthesised silica nanocontainers. Additionally, it is demonstrated that using gemini surfactants can reduce the toxicity of novel silica nanocapsules towards the tested marine species. As a result, environmentally-friendly ENMs can be obtained based on a safe-by-design approach, thereby fitting the concept of Green Chemistry.

Highlights

Engineered nanomaterials (ENMs) have been proposed as new solutions for encapsulation of active compounds, such as corrosion inhibitors, antifouling agents, pH indicators, drugs or dyes [1,2,3,4,5,6,7].Nanocapsules are core–shell structures with diameter generally ranging between 100–500 nm [8], and one of the most used nanocapsules are based on mesoporous silica, typically with a diameter of 100–200 nm [9]
QSB2-12 will not change the thermogravimetric profile synthesis [14]. These results suggest that replacing CTAB with QSB2-12 will not change the ofthermogravimetric silica nanocapsules
This study demonstrates that developing greener silica mesoporous nanocapsules by replacing cationic surfactants used during Silica nanocapsules nanocapsules (SiNC) synthesis, may lead to less toxic alternatives

Summary

Introduction

Nanocapsules are core–shell structures with diameter generally ranging between 100–500 nm [8], and one of the most used nanocapsules are based on mesoporous silica, typically with a diameter of 100–200 nm [9]. This cutting-edge immobilization technique has assumed a relevant role in the field of smart coatings, by providing a controlled release of encapsulated molecules, reducing their toxicity (compared to the free forms), preventing direct interaction with coating matrices, reducing leakages and increasing the coating’s service life [3,10,11]. Recent studies have revealed that the silica nano-form or the formation of agglomerates in artificial saltwater, over time, is not necessarily the

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