Controlled biocide release from hierarchically-structured biogenic silica: surface chemistry to tune release rate and responsiveness

Bruno D Mattos,Wido H Schreiner,Orlando J Rojas,Mohammadi Pezhman,Blaise L Tardy,Washington L E Magalhães,Markus Linder,Tero Kämäräinen

doi:10.1038/s41598-018-23921-2

Bruno D Mattos, Wido H Schreiner + Show 6 more

Open Access

https://doi.org/10.1038/s41598-018-23921-2

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Abstract

Biocides are essential for crop protection, packaging and several other biosystem applications. Therein, properties such as tailored and controlled release are paramount in the development of sustainable biocide delivery systems. We explore the self-similar nano-organized architecture of biogenic silica particles to achieve high biocide payload. The high surface area accessibility of the carrier allowed us to develop an efficient, low energy loading strategy, reaching significant dynamic loadings of up to 100 mg·g−1. The release rate and responsiveness were tuned by manipulating the interfaces, using either the native hydroxyl surfaces of the carrier or systems modified with amines or carboxylic acids in high density. We thoroughly evaluated the impact of the carrier-biocide interactions on the release rate as a function of pH, ionic strength and temperature. The amine and carboxyl functionalization strategy led to three-fold decrease in the release rate, while higher responsiveness against important agro-industrial variables. Key to our discoveries, nanostructuring thymol in the biogenic silica endowed systems with controlled, responsive release promoting remarkable, high and localized biocidal activity. The interfacial factors affecting related delivery were elucidated for an increased and localized biocidal activity, bringing a new light for the development of controlled release systems from porous materials.

Highlights

Biocides are essential in agro-industrial applications to improve the yields in crop production and to extend the active life of biodegradable compositions[1,2]
We have shown that the top-down route for isolation of biogenic silica particles results in a polydisperse dispersion[27]
Acid media could act as a catalyst for hydrolysis of ester bonds, which hypothetically could have occurred between thymol and the SiCOOH carrier[39,40]. Considering this to be true, we propose that the highest release rate of thymol from the SiCOOH@Thy system would be at pH 5, which was the experimental observation

Summary

Introduction

Biocides are essential in agro-industrial applications to improve the yields in crop production and to extend the active life of biodegradable compositions[1,2]. By promoting different carrier/biocide interface interactions through surface modifications, the release rates can be tuned They can render BDS more responsive to external stimuli such as pH, temperature and ionic strength. Through specific surface modifications of biogenic silica, we propose and develop a generic strategy to obtain “green” BDS with a tunable and responsive release. Such features are essential in order to minimize the amount of biocides delivered for efficient pest control as a function of soil or crop type as well as climatic conditions. A significantly more focused and pronounced biocidal activity is demonstrated for thymol-loaded biogenic silica when compared with unloaded systems

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Conclusion