Fig. 1. FTIR spectra of starch (a) and SAP (b)

Fig. 2. SEM images of Starch (a) and SAP (b)

Fig. 3. TG (a) and DTG (b) curves of Starch and SAP

Fig. 4. Effect of absorbed dose on water absorption of SAP

Fig. 5. Effect of MBA content on water absorption of SAP

Fig. 6. Effect of starch to AA feed ratio on water absorption of SAP

Fig. 7. Released PO₄^3- (a) and K⁺ (b) concentrations of SAP versus time curves

Fig. 8. (a) Water absorption of K⁺@SAP versus time curves in solutions with different concentrations of sodium chloride; (b) water absorption of K⁺@SAP versus time curves images in three times; (c) quality of K⁺@SAP after water absorption versus time curves at room temperature; (d) quality of K⁺@SAP after water absorption versus time curves in different temperatures