Statistical approach to synthesise biogenic silica nanoparticles from rice husk and conjugated with Justicia adhatoda extract as green, slow-release biocide.

Biogenic silica synthesised from rice husk was used as a controlled release system of an eco-friendly biocide consisting of a Justicia adhatoda extract. Fourier-transform infrared spectroscopy (FTIR) indicated the presence of ester bonds between the silica support and the conjugated Justicia adhatoda extract. Surface area analysis and microscopy confirmed a high level of Justicia adhatoda extract loading in the silica support. The phytochemical investigation of Justicia adhatoda was done by Gas chromatography-mass spectrometry (GC-MS) spectroscopy. Moreover, compared with the naked biogenic silica nanoparticles, a better thermal stability was determined for the conjugated system of the extracted compounds. Trial of kinetic release of silica: Justicia adhatoda ∼29% of loaded Justicia adhatoda was released within 1 h and then the rate of release became slow. Net release of Justicia adhatoda was observed up to 50% within 7 h. The Justicia adhatoda compounds released from silica also showed the improved mortality rate against stored product pest rice weevil (Sitophilus oryzae).