Multi-responsive dual-purpose smart starch-based hydrogel reinforced with activated carbon for agricultural applications

Abstract

This work evaluates the effect of incorporating different amounts of activated carbon (AC) modified with glycidyl methacrylate (GMA; ^GMAAC) into a hydrolyzed or not hydrogel matrix based on starch-g-GMA (^GMASt) and N,N’-dimethyl acrylamide (DMAAm). FTIR and XRD results suggests that ^GMAAC has little effect on the hydrogel matrix. However, it increases their thermal stability, the diameter of pores, and the amorphous character of the non-hydrolyzed matrices. As a mechanical enhancer, ^GMAAC is more effective in the non-hydrolyzed matrices than in the hydrolyzed ones. The matrices show responsiveness towards pH, ionic strength, and temperature variations, reaching a swelling degree of (438.2 ± 41.60) g g⁻¹ for the hydrolyzed sample containing the highest amount of ^GMAAC (0.5 %; ionic strength of 1 ×10⁻⁵ M and T = 25 °C). Statistical results suggest that the efficiency of the matrices would not be suppressed at higher ionic strengths. As fertilizer-releasing devices, the matrices would promote a controlled and sustained release of urea for more than 3 h, and the urea loaded onto ^GMAAC would only be released after the degradation of the matrix. Recycling tests suggest that the ^GMAAC-containing matrices would not have their performance compromised for at least 15 consecutive cycles of swelling and drying. However, a thorough and careful study of the degradation behavior and potential environmental impacts is a prospect of this work.