Preparation of hydrogels from hydrochloric acid modified attapulgite for environmentally responsive fertilizers

The inefficiency of traditional fertilizers in nutrient utilization has led to various ecological and environmental problems. Green agriculture requires environmentally friendly fertilizers that can respond to environmental changes to regulate nutrient release. In this study, N-isopropylacrylamide (NIPAm) and sodium alginate (SA) were utilized as monomers sensitive to temperature and pH variations, while hydrochloric acid-modified attapulgite (ATP) served as an inorganic filler to prepare composite hydrogels (SPAA) with environmentally responsive properties, and these composite hydrogels were used as carriers for the preparation of hydrogel fertilizers for urea. The results showed that the compositing of modified ATP could enhance the swelling properties of hydrogels. Compared with the blank sample, the maximum water absorption capacity of the ATP-composite hydrogel was enhanced by about 75.4%, and the water preserved by the ATP-composite hydrogel was about 2.75 times of that of the blank sample under drying condition of 30°C for 6 h. Meanwhile, hydrogel fertilizers SPAA-U(S) and SPAA-U(P) were prepared by solubilization adsorption and polymerization embedding in this study, and both fertilizers possessed slow-release characteristics, with nutrient release time in water exceeding 30 h. The nutrient release behavior of the fertilizers responded to the environment, and the slow-release effect was optimal under the conditions of 20°C and pH = 7. Under acidic, alkaline and high temperature conditions, the ability of the hydrogel to immobilize water molecules decreases, which also leads to easier release of urea from the hydrogel matrix along with water molecules. The hydrogel fertilizer developed in this work can improve the utilization of fertilizer and promote the high quality and sustainable development development of agriculture.