Towards Viable Eco-friendly Matrices for Controlled Pesticide Delivery: Adsorptive Behaviour of Cow Dung Ash and Starch Towards Organophosphorus Pesticides

Abstract

The work reported herein explores the viability of cow dung as a matrix for controlled pesticide delivery, by comparing its adsorptive characteristics towards two organophosphorus pesticides with those of starch, conventionally utilized in designing controlled pesticide delivery systems. Characterization of cow dung ash (CDA) was by Fourier transform infrared (FTIR) spectroscopy and powder X-ray diffraction (PXRD). Pesticide adsorption data on the surfaces correlate well with Langmuir and Freundlich isotherms, with the former isotherm giving a slightly better fit (R2 \(\ge\) 0.90) than the latter (R2 \(\ge\) 0.81). Values of the adsorption parameters KL and RL indicate favourable pesticide adsorption on both surfaces. Desorption is the microscopic reverse of adsorption; both processes obey pseudo-second-order kinetics, implicating a mechanism in which adsorbate diffusion to the polymer surface and its transport into the polymer interior are important events. The isothermal and kinetic ratios \(\frac{{K}_{L}^{CDA}}{{K}_{L}^{Starch}}\)= 3.8 and 4.0, \(\frac{{k}_{2}^{CDA}}{{k}_{2}^{Starch} }\) = 1.3 and 0.6, and \(\frac{{k}_{-2}^{CDA}}{{k}_{-2}^{Starch}}\) = 5.2 and 1.0 at pH 7 and 27oC, compare the adsorptive behaviour of diazinon and dichlorvos, respectively, on CDA and starch. These parameters are of the same order of magnitude, signalling that CDA is as potentially viable as starch for use as a matrix for pesticide-controlled delivery.