Enhancing Spray Charge and Abaxial Deposition on Hydrophilic Substrates Using Hypervalent Oxometallate Salt KMnO₄

The pursuit of innovative and excellent additives that augment the negative charges of sprayed droplets is crucial due to their potential applications in agricultural, industrial, and daily sterilization/disinfection processes. However, traditional additives have shown limited efficacy in enhancing the electrification of water droplets. Herein, we introduce hypervalent oxometallate salts (HOMs) as innovative additives to address this challenge. Notably, KMnO₄ exhibits a remarkable effect on spray charge properties, enhancing the abaxial deposition efficiency on hydrophilic substrates by a factor of 4-fold compared to pure water spraying. This enhancement is attributed to the distinctive features of [MnO₄]^-, such as low energy band gap and electrostatic and zeta potentials, strong electron acceptance ability, and low binding energy with water molecules. These properties significantly promote the polarization of water molecules and amplify the spray charge capacity. Additionally, the underlying mechanisms of promoting abaxial deposition on a hydrophilic substrate are attributed to the interface reactions on the adaxial side and an increase in positive charge on the abaxial surface. This work introduces an additive for enhancing the negative charge of a spray, marking a pivotal improvement in the utilization efficiency of chemicals in the agricultural and industrial sectors.