Abstract:
Agriculture forms the backbone of third world economies. The global agricultural sector
has been experiencing major challenges including an increasing risk of disease, high
production costs due to the high cost of fertilizer and pesticides, threats to agricultural
production from changing weather patterns and a growing demand for healthy, safe
food.
The use of nanomaterials for the controlled delivery of fertilizers and pesticides is
nascent technology that has the potential to increase the efficiency of food production
and decrease pollution. In this study, the prospect of mesoporous silica nanoparticles
(MSN) and purified montmorrilonite (MMT) for storage and controlled release of
fertilizer and fungicide molecules was investigated. A series of MSNs with particle
sizes, Barrett-Joyner-Halenda (BJH) pore diameters, Brunauer-Emmett-Teller (BET)
surface areas and BJH total pore volumes ranging between 50 nm – 900 nm, 2.4 nm -
4.4 nm, 589 m2g-1 - 1013 m2g-1 and 0.61 cm3g-1 – 0.81 cm3g-1, respectively were
synthesized via Liquid Crystal Templating Mechanism (LCT) by varying the molar
ratio of reagents. Urea, as a model fertilizer molecule was loaded into the carrier
matrices by a simple immersion technique using concentrated aqueous urea solution
while metalaxyl, as a model fungicide was loaded by a rotar - vapor method. Successful
loading was confirmed by infrared (IR) spectral analysis, x-ray diffraction (XRD)
patterns and N2 sorption studies. The loaded amounts of agrochemicals were evaluated
by thermogravimetric analysis (TGA/ DTA). About 15.5 % (w/w) of urea was
entrapped into the MSN pores and ~21.4 % w/w intercalated into MMT interlayer
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space. Metalaxyl entrapment/ intercalation content were 14 % w/w and 8.1 % w/w for
MSN and MMT, respectively. Adsorption processes were mainly by physical forces.
The release process of urea-loaded mesoporous silica nanoparticles (UMSN) and urealoaded
montmorillonite (UMMT) in water and soil indicated a sustained slow releaseprofile.
The findings for soil release studies of UMSN revealed at least fivefold
improvement in the release period while MMT retarded the release of urea significantly.
Release of the fungicide entrapped in the MSN and intercalated into MMT matrix also
revealed sustained release behaviour. About 76 % of the free metalaxyl was released in
soil within a period of 30 days while only 11.5 % and 11.9 % of the metalaxyl
contained in MSN and MMT carriers, respectively were released within the same
period. Our study showed that MSN and MMT can be used to successfully store
agrochemical molecules and significantly delay their release in soil.