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. 2025 Jan 16;11(2):e42036.
doi: 10.1016/j.heliyon.2025.e42036. eCollection 2025 Jan 30.

Preparation of slow-release fertilizer derived from rice husk silica, hydroxypropyl methylcellulose, polyvinyl alcohol and paper composite coated urea

Idayatu Dere  1 , Daniel T Gungula  2 , Semiu A Kareem  1 , Fartisincha Peingurta Andrew  3   4 , Abdullahi M Saddiq  5 , Vadlya T Tame  2 , Haruna M Kefas  1 , David O Patrick  1 , Japari I Joseph  6
Affiliations

Preparation of slow-release fertilizer derived from rice husk silica, hydroxypropyl methylcellulose, polyvinyl alcohol and paper composite coated urea

Idayatu Dere et al. Heliyon. .

Abstract

There is a growing trend toward utilizing agricultural waste to create value-added products, addressing environmental concerns associated with their disposal. This study focuses on developing slow-release fertilizers (SRFs) using amorphous silica derived from rice husk, hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), waste paper, and urea. Experimental optimization was carried out using the response surface methodology central composite design (RSM-CCD). The optimal formulation included 8.63 g of silica, 1.04 g of HPMC, and 0.27 g of PVA. Two SRFs were prepared under these conditions: SRF1, consisting of silica, HPMC, and PVA, and SRF2, which additionally incorporated coated waste paper. Characterization techniques such as Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD) Scanning Electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis were used to examine the materials. The rice-husk-derived silica exhibited a pore size of 2.140 nm and a BET surface area of 690 m2/g, providing an excellent surface for nutrient encapsulation. Although the addition of coated waste paper minimally influenced the slow-release behaviour of SRF2, however the other components effectively reduced nutrient leakage by trapping the nutrients. The swelling behaviour of the SRFs was analyzed in different media after 72 h, showing values of 2.66, 2.54 (g/g) in distilled water, 2.20, 2.58 (g/g) in pH 4, and 1.86, 3.09 (g/g) in pH 9 solutions. The swelling kinetics aligned with Scott's second-order kinetic model. Urea release tests in water revealed a release of 94 % and 97 % at 24 h for SRF1 and SRF2, respectively, compared to 98 % release of pure urea within 1 h. SRF2 demonstrated optimal nutrient release after 48 h. The release kinetics followed the first-order kinetic model for both SRF1 and SRF2, highlighting their potential as effective slow-release fertilizers.

Keywords: Central composite design; Coated silica; Hydroxypropyl methylcellulose; Polyvinyl alcohol; Rice husk; Slow release fertilizer.

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Conflict of interest statement

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Prof. Daniel T. Gungula reports financial support was provided by Tertiary Education Trust Fund. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Response surface combined effect plots of formulation variables for SRF
Fig. 2
Fig. 2
FTIR spectra of blended paper (a), PVA (b), HPMC (c), silica (d), urea (e) and overlay spectra of SRF1 and SRF2 (f).
Fig. 3
Fig. 3
Sem Images of silica (a), HPMC (b), SRF1(c) and SRF2 (d).
Fig. 4
Fig. 4
Xrd pattern of blended paper, HPMC, silica, silica Intercalated, SRF1 and SRF2.
Fig. 5
Fig. 5
Swelling Behaviours of SRF1 (a) and SRF2 (b) in Solution medium.
Fig. 6
Fig. 6
Swelling kinetics (t/St) of SRF in solution media as a function of time.
Fig. 7
Fig. 7
Release behavior of Urea, SRF1 and SRF2.
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