Waste to Value through Rice Hull to Nano-silica: A Novel Paradigm of Sustainable Agronomy

Abstract

Although Silicon (Si) in its bulk phases has long been used as a fertilizer in agriculture, specifically for those in the Poaceae family, the unique role their nanoscale counterparts may adopt in modern day agriculture remains mostly unknown. Oryza sativa (rice) is among the main agricultural crops in Sri Lanka. The rice plants accumulate and greatly benefit from Si, where it is deposited beneath the cuticle as cuticle-Si double layer in the form of silicic acid. Further, Si may also interact favorably with other applied nutrients, hence improving the agronomic performance, crop yield, as well as the tolerance of rice plants to abiotic and biotic stresses, thus making Si essential in sustainable rice production. The hull, or the hard protective layer of the rice grain, is mostly regarded as a bulk-scale waste produced during the post-harvest processing of rice. Nevertheless, it is notable that Si is a prominent constituent in rice hull. Hence, there have been recent attempts to utilize rice hull as a precursor for producing Si nanoparticles. However, such approaches, still being in their infancy, requires further systematic investigations to optimize the nanoparticle preparation, in terms of the ensuing nanoparticle properties (i.e., size, morphology, and porosity etc.) as well as the process economies themselves. Hence, in this study, a novel, facile, efficient, and scalable strategy was systematically developed for the preparation of Si nanoparticles from waste rice hull. Notably, preprocessing conditions, synthetic parameters, and the chemical usages were optimized to allow scalability and sustainability to ensue. Initial characterization of the nanoparticles synthesized under aptly optimized conditions indicated the ability of this novel approach to synthesize nanoparticles of smaller dimension that could be stably suspended in aqueous media for prolonged durations without any signs of instability. Further investigations are ongoing in terms of creating and controlling the porosity of these nanomaterials, which will further enhance their carrier properties and thus the applicability as an effective nano-fertilizer. Overall, the knowledge imparted by this study will be significant in intensifying agricultural practices, specifically in many developing parts of the world, where rice remains to be a prominent crop, thus indicating a novel paradigm of sustainable agronomy.