Superabsorbent hydrogels based on N,N-dimethylacrylamide and maleic acid for applications in agriculture as water purifier and nitrogen carrier

To reduce water pollution caused by fertilizers in agricultural irrigation, highly swelling crosslinked hydrogels (p(DMAAm-co-MA) or DM1) based on N,N-dimethylacrylamide (DMAAm) and maleic acid (MA) were prepared using a chemical initiator with the redox polymerization technique. Negative and positive surface modifications of DM1 were achieved using hydrochloric acid (HCl) (p(DMAAm-co-MA)/HCl or DM2) and sodium hydroxide (NaOH) (p(DMAAm-co-MA)/NaOH or DM3), respectively. The synthesized hydrogels were named DM1, DM2 and DM3, respectively. The swelling properties, urea sorption and urea release kinetics of synthesized hydrogels were analyzed in deionized water at different pHs. The sorption isotherms and sorption parameters were investigated thoroughly for all hydrogels and the Langmuir (L) isotherm showed the best fit. In order to examine the urea release mechanism from all hydrogels, four mathematical models of zero-order kinetic model (Z-O), first-order kinetic model (F-O), Higuchi (H) and the Korsmeyer–Peppas power law (K-P) were studied to fit the experimental data. The hydrogels exhibited swelling and releasing properties that were highly dependent on their functional groups and the ionic forces in the medium. Cumulative urea release values for DM1, DM2 and DM3 were calculated as 100% at pH 10, 100% at pH 8 and 100% at pH 8 within 48, 41 and 18 h, respectively. It was confirmed by experimental studies that the prepared hydrogels and their derivatives can be used as carriers for fertilizers, particularly urea, as well as controlled water release sources. As a result, the use of the synthesized hydrogels to prevent contamination of water resources with agricultural products and to provide a nitrogen source that plants require comprise the innovative and original aspect of the article.