Chitosan nanocomposites (CS NCs) have exceptional reinforcement qualities due to the high surface-to-volume ratio of nanomaterials. In a recent article published in Environmental Research, the authors synthesized reinforced CS NCs with activated carbon nanoparticles (ACNPs), nonactivated carbon nanoparticles (n-ACNPs), and lignocellulose nanofibers (LCNFs).
Study: Potential of chitosan/carbon nanoparticles and chitosan/lignocellulose nanofiber composite as growth media for peatland paddy seeds. Image Credit: AlanMorris/Shutterstock.com
It was demonstrated that CNPs and LCNFs derived from oil palm biomass have potential as growth media for peatland paddy. Furthermore, CS NCs exhibited a synergetic fertilizing effect against mycorrhiza and fungi.
Reinforcing CS with CNPs and LCNFs
CNPs have high electrical conductivity, superior absorption capacity, chemical stability, unique surface properties, and good transmittance. Similarly, LCNFs have good absorption capacity, good mechanical properties, high thermal conductivity, and high crystallinity. CNPs and LCNFs derived from oil palm trunk (OPT) fibers and oil palm empty fruit bunch (EFB) waste have unique properties and are harnessed as biofertilizers to control or promote growth in various plants.
However, the blending of CNPs and LCNFs with polymer materials remains unexplored. Moreover, their sole use is ineffective, expensive, and difficult to handle. The use of the nanomaterials at higher concentrations causes nanotoxicity in plants, hindering nutrient transport. Thus, surface modification and functionalization of these nanomaterials can alleviate the toxic effects.
CS is an abundant biopolymer and serves as a superior nanocomposite matrix by exhibiting nontoxicity, excellent mechanical properties, antibacterial properties, and biodegradation when reinforced with CNPs and LCNFs. CNPs, LCNFs, and CS have a synergic effect in regulating plant growth and aid the controlled release of certain fertilizers such as potassium nitrate (KNO3) and nitrogen, phosphorus, and potassium (NPK). However, no studies have reported on applying CNPs and LCNFs to reinforce CS biopolymer and use them as a growth media for paddy grown in peatlands.
CS NCs as Growth Promoters
In the present study, the authors investigated the efficiency of solvent-casted CS NCs reinforced with CNPs and LCNFs as growth media for peatlands cultivated paddy varieties. The nanomaterials include EFB activated/nonactivated CNPs (EFB ACNPs/ EFB n-ACNPs), OPT nonactivated CNPs (OPT n-ACNPs), and OPT lignocellulose nanofibers (OPT LCNFs). The authors observed the highest pore volume and specific surface area for EFB ACNPs.
Furthermore, they also confirmed that the Dendang paddy variety had the best growth patterns due to CS NCs.The Indragiri paddy variety showed the best growth pattern in the greenhouse test. All CS NCs had a synergetic effect on mycorrhiza and fungi. The obtained results confirm the potential of CS NCs to accelerate peatland restoration in tropical areas and as growth regulators for peatland paddy varieties.
OPT n-ACNPs, EFB ACNPs, and EFB n-ACNPs were particle-like with irregular and uneven shapes that aggregated easily to form clusters, while LCNFs had long fiber-like structures individually, which entangled with each other in a web-like network. The clusters formed by CNP aggregates had a porous structure, favorable for water storage and diffusion, promoting growth and germination in paddy.
The aggregates of activated and nonactivated EFB CNPs had a diameter greater than 500 nanometers, while LCNFs diameter was less than 20 nanometers. However, the length measurement in LCNFs was difficult due to entanglement. EFB ACNPs had the highest surface area, pore-volume, pore width, and surface-to-volume ratio favorable for increasing the bioavailability, surface reactiveness, and dissolution rate.
The porous structure of these NPs enhanced the accessibility of the surface area. The increase in these properties in EFB ACNPs was due to potassium hydroxide (KOH)-activation treatment, which favored different functional groups (hydroxyl, carboxyl, and carbonyl groups) on the surface of activated carbon. The elastic modulus and tensile strength test revealed that the addition of CNFs and LCNFs did not affect the elastic modulus and tensile strength compared to neat CS composites. However, LCNF-reinforced CS biopolymers had higher tensile strength than CS biopolymers reinforced with CNF.
Crystallography of the synthesized nanomaterials revealed the highest crystallinity in OPT LCNFs, followed by OPT n-ACNPs, EFB ACNPs, and EFB n-ACNPs, which explains the enhanced elastic modulus and tensile strength of CS/ OPT LCNFs over other CNPs.
Moreover, the synergetic effect of EFB ACNPs reinforced CS NCs resulted in enhanced germination rate, height growth, and maximum growth potential in paddy varieties.
Additionally, the hydrophilicity of CS aided in easy water absorption and water transportation in plants, and the activation of EFB CNPs enhanced the pore volumes in individual ACNP and increased the specific surface area resulting in good water transportation. CNPs or LCNFs-filled CS NCs aided in the controlled release of certain nutrients in peatlands, enhancing the growth performance in paddy varieties grown in peatlands.
The authors observed that CS NCs were more suitable for Dendang and Indragiri paddy over Batanghari paddy. While the presence of CNP and LCNF aggregates as nano and micro-sized structures enhances the water transportation to paddy plants, their presence impeded the antifungal properties against Trichoderma species, Serratia marcescens, and Stenotrophomonas maltophilia as observed in images from transmission electron microscope (TEM) and scanning electron microscope (SEM). Although the free positive charge of CS allows chemical functionalization and surface modification, their reinforcement with CNPs/LCNFs reduced antifungal or antibacterial properties.
In conclusion, CS NCs are potential growth mediums for paddy varieties cultivated in peatland, which can be grown either in the greenhouse or in a germinator. Compared to the CS NCs, EFB ACNP-reinforced CS NCs showed better growth patterns in the germination test. Similarly, compared to sole CS NCs, their reinforcement with OPT n-ACNPs resulted in the highest growth rate, growth natality, and height average in the greenhouse. The authors in the present work demonstrated that CNP- and LCNF-reinforced CS NCs could be alternative growth regulators or stimulators for paddy cultivated in peatlands.
Hartoyo, A. P. P., Octaviani, E. A., Syamani, F. A., Mulsanti, I. W., & Solikhin, A. Potential of chitosan/carbon nanoparticles and chitosan/lignocellulose nanofiber composite as growth media for peatland paddy seeds. (2022) Environmental Research, 113235. https://www.sciencedirect.com/science/article/abs/pii/S001393512200562X