Facile Preparation of Montmorillonite/Crosslinked Chitosan Containing Potassium Nitrate Nanocomposites as Eco-Friendly Slow Release Fertilizers

Abstract

Montmorillonite/tripolyphosphate crosslinked chitosan containing potassium nitrate nanocomposites (MMT/CS-KNO3-TPP) were synthesized by facile incipient wetness impregnation method. The MMT was impregnated stepwise with a mixture of protonated chitosan and KNO3, followed by a TPP solution to ionically crosslink with chitosan, resulting in MMT/CS-KNO3-TPP nanocomposites. The initial quantity of KNO3 to MMT was varied from 0 to 10, 20, and 30 wt%, and the TPP crosslinker was varied according to TPP:chitosan weight ratios of 0:5, 1:5, and 3:5. The resultant MMT/CS-KNO3-TPP nanocomposites composed of the K+ and NO3− ions embedded in crosslinked chitosan which intercalated in the MMT basal spacing and covered on MMT external surface. The structure of these nanocomposites could effectively slow the K+ and NO3− releases, with the 72- hours cumulative released values (%R) ranging from 20–34% for K+ to 0.4–1.0% for NO3−. The MMT/CS-KNO3-TPP nanocomposites with higher TPP concentration could extend the K+ and NO3− release times. Total K+ release times were predicted to be in the range of 128–204 days. The presence of MMT/CS-KNO3-TPP nanocomposites in RD43 rice cultivation could promote the growth of RD43 seedlings and roots. Furthermore, the TPP crosslinked chitosan showed physical changes in distilled water, indicating its potential as a long-term nitrogen (N) and phosphorus (P) source for plant nutrients.