Biogenic silica nanoparticles loaded with neem bark extract as green, slow-release biocide

Biogenic silica derived from Equisetum arvense was used as a carrier of an eco-friendly biocide consisting of a neem bark extract cross-linked with polycarboxylic acids. Infrared spectroscopy indicated the presence of ester bonds between the silica support and the loaded bark extract. Surface area analysis, porosimetry and microscopy confirmed a high level of biocide loading in the silica support. Furthermore, compared with the unloaded biogenic silica nanoparticles, a better thermal stability was determined for the system carrying the extracted compounds. Experiments consisting of three sequential release profiles showed full mass release after 20 days of unloaded neem while the extract loaded in the solid support reached only 60–75% released after 30 days. A four-fold improvement in the neem extract stability was observed in aqueous media if loaded in the silica support. The neem compounds released from silica showed a satisfactory scavenging activity over 50% of DPPH free radical, and could cause the mortality of the major workers of Acromyrmex crassispinus ant specie.