Biochar-based nanocarriers: fabrication, characterization, and application as 2,4-dichlorophenoxyacetic acid nanoformulation for sustained release.

Biochar prepared from rice husk (rBC) was used as a nanosorbent for the sustained delivery of 2,4-dichlorophenoxyacetic acid (2,4-D) and for its potential use as an eco-friendly nanoherbicide formulation. For the biochar-based 2,4-D nanoformulation (DrBC), the loading efficiency of the herbicide onto the rBC nanocarrier was checked at various weight ratios, where a weight ratio of 1:0.25 (rBC:2,4-D) was found optimum. Further experiments were carried out to understand the 2,4-D sorption characteristics of rice husk biochar (rBC) and its sustained herbicidal release property in soil and water. When the adsorption mechanism was analyzed, the Freundlich isotherm and pseudo-second-order kinetic equation were found to be the best. The sustained release of 2,4-D from the DrBC nanoformulation was detected for about 26 days. The release profile of 2,4-D from DrBC was found to be a controlled diffusion mechanism based on Korsmeyer-Peppas model fit. The size of the DrBC nanoformulation was found to be 256.5 nm using dynamic light scattering (DLS) with a negative zeta potential of 28.8 mV. Fourier transform infrared spectroscopy (FT-IR) results indicated the involvement of carboxyl, aromatic carbon, and siloxane in 2,4-D adsorption onto rBC. The additional chlorine in the EDAX spectrum of scanning electron microscope (SEM) indicated the herbicide adsorption onto the rBC carrier. The DrBC nanoformulation exhibited enhanced herbicidal activity against the tested Brassica sp., but did not affect the growth of the non-target plant (Zea mays). The present study could be promising for achieving high herbicidal loading, sustained release, and reduced leaching of 2,4-D for its effectual usage in an eco-friendly fashion.