Construction of pH-responsive chlorpyrifos hydrogels system and its controlled-release property

Traditional pesticides are susceptible to environmental factors and their early degradation leads to a low utilization rate. It is an effective measure to improve the utilization rate of pesticides by using responsive controlled release technology. In this study, dopamine-modified attapulgite/chlorpyrifos/calcium alginate composite hydrogels (PRCH) with a specific response to alkaline conditions were prepared using dopamine-modified attapulgite loaded with chlorpyrifos (CPF) and alginate was used as coating material by extrinsic extrusion method and crosslinking with Ca²⁺. The morphology and structure of PRCH were characterized by scanning electron microscope (SEM), Zeta-potential, and BET specific surface area tests. The sustained-release and swelling properties of PRCH in different pH environments were studied, and the stability of PRCH under UV light and different temperatures were explored. The results showed that the loading rate of PRCH with chlorpyrifos was as high as 85%. PRCH could absorb water and swell under alkaline conditions, resulting in the opening of calcium alginate channels and even structural collapse to release chlorpyrifos. The release mechanism of PRCH was explained by fitting the curve with Korsmeyer-Peppas model equation: The release rate of PRCH in buffer solution with pH 5.5 was determined by both drug diffusion and hydrogel swelling. When the buffer pH is 7.0, the pesticide transport process is dominated by the cleavage rate of hydrogels. At pH 8.5, the diffusion of pesticide itself played a major role in the release of chlorpyrifos, but the fragmentation of the hydrogels accelerated the spread of chlorpyrifos. In addition, we found that PRCH has stronger UV stability and temperature stability than industrial grade chlorpyrifos. Collectively, PRCH has the advantages such as excellent drug loading rate, pH-specific response characteristics and being environmentally friendly. Therefore, the system has great application prospects in improving the stability and efficacy of traditional pesticides.