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. 2024 Jul 1;14(1):15032.
doi: 10.1038/s41598-024-58875-1.

Urea intercalated encapsulated microalgae composite hydrogels for slow-release fertilizers

Nada Sarhan  1 , Esraa G Arafa  2 , Nada Elgiddawy  1 , Khaled N M Elsayed  3 , Fatma Mohamed  4   5   6
Affiliations

Urea intercalated encapsulated microalgae composite hydrogels for slow-release fertilizers

Nada Sarhan et al. Sci Rep. .

Erratum in

Abstract

In agriculture, hydrogels can be addressed for effective operation of water and controlled-release fertilizers. Hydrogels have a significant ability for retaining water and improving nutrient availability in soil, enhancing plant growth while reducing water and fertilizer usage. This work aimed to prepare a hydrogel composite based on microalgae and biopolymers including chitosan and starch for use as a soil conditioner. The hydrogel composite was characterized by FTIR, XRD, and SEM. All hydrogel properties were studied including swelling degree, biodegradability, water-holding capacity, water retention, and re-swelling capacity in soil and water. The urea fertilizer loading and releasing behavior of the prepared hydrogels were investigated. The results revealed that the range of the maximal urea loading was between 99 and 440%, and the kinetics of loading was fitted with Freundlich model. The urea release % exhibited 78-95%, after 30 days, and the kinetics of release was fitted with zero-order, Higuchi, and Korsmeyer-Peppas models. Furthermore, the prepared hydrogels obtained a significant water-holding capacity, after blending soil (50 g) with small amount of hydrogels (1 g), the capacity increased in the range of 99.4-101.5%. In sum, the prepared hydrogels have the potential to be applied as a soil conditioner.

Keywords: Hydrogels; Microalgae; Slow-release fertilizer; Water retention.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Schematic diagram illustrates the basic idea.
Figure 2
Figure 2
FTIR spectrum of (A) Starch St, (B) Chitosan CS, (C) Microalgae Sy, (D) Sy-St hydrogel, (E) unloaded Sy-St-CS hydrogel, (F) urea-loaded Sy-St-CS hydrogel, and (G) urea.
Figure 3
Figure 3
XRD of (A) Microalga Sy, (B) unloaded Sy-St-CS hydrogel, and (C) urea-loaded Sy-St-CS hydrogel.
Figure 4
Figure 4
SEM of (A1-3) unloaded Sy-St-CS hydrogel, (B1-2) urea-loaded Sy -St-CS hydrogel, (C1-2) urea-release, and (D1-2) biodegradation of Sy-St-CS hydrogel.
Figure 5
Figure 5
The swelling behavior of hydrogel samples (Sy-St, Sy-CS, Sy-St-CS) with different time intervals.
Figure 6
Figure 6
Loading properties and mechanism of the hydrogels sample (Sy-St; Sy-CS; Sy-St-CS). (A) Loading percentage of urea on hydrogels samples, (B) fitting of the loading results with Langmuir model, and (C) fitting of the loading results with Freundlich model. Suppl. Figure 1: ANOVA residual plots for urea loading through Sy-St-CS hydrogel.
Figure 7
Figure 7
Urea release percentage from Sy-St, Sy-CS, and Sy-St-CS hydrogels, inset showing the release percentage at initial hours for three samples.
Figure 8
Figure 8
Kinetic models of urea release from Sy-St, Sy-CS, and Sy-St-CS, (A) zero-order, (B) first-order, (C) Higuchi, (D) Hixsonn˜ Crowell, and (E) Korsofmeyer–Peppas models. Suppl. Figure 2: ANOVA residual plots for release urea through Sy-St-CS hydrogel.
Figure 9
Figure 9
Biodegradation percentage from Sy-St, Sy-CS, and Sy-St-CS hydrogels.
Figure 10
Figure 10
Water retention in soil percentage from Sy-St, Sy-CS, and Sy-St-CS hydrogels.
Figure 11
Figure 11
Reswelling capacity in soil percentage from Sy-St, Sy-CS, and Sy-St-CS hydrogels during five cycles.
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