Publication: Preparation, characterization and functional evaluation of agricultural waste-derived nanocelluloses
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Date
2024-09-01
Authors
Lim, Kah Yee
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Abstract
Nanocelluloses (NCs), the fundamental natural building block of cellulosic based fibres, have fore-fronted to be a new generation of functionalized materials,
which have attracted tremendous attention in the nanotechnology community.
Specifically, the functional roles of NCs represent the interplay between the surface
compositions, crystalline structure, charge density, structural transitions, and their
hydration/ dehydration behaviour, that give rise to different characteristics. In this
work, the preparation of multifunctional nanocelluloses (NCs) from coffee residue
(Coffea robusta L.) (CR), rice husk (Oryza sativa) (RH) and tangerine peel (Citrus
unshiu) (TP) via three major synthesis techniques, notably hydrothermal, microwave
and enzymatic hydrolysis synthesis approaches have been succeeded. The unique
characteristics of NCs were evaluated with respect to the scanning electron
microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform
infrared spectroscopy, thermogravimetric analysis, zeta potential measurement,
chemical composition, elemental analysis, surface charge and degree of substitution
(DS). The adsorptive performance of NCs were examined by batch adsorption
experiments using both cationic and anionic model adsorbates, methylene blue (MB)
and chlorpyrifos (CPF), and simulated by the non-linear isotherm models. Their
unique antimicrobial functions were tested against both gram-positive
(Staphylococcus aureus and Bacillus subtilis) and gram-negative (Escherichia coli and Salmonella typhi) bacterial species using in-vitro colony-forming unit count
method. The particle length and diameter, aspect ratio, crystallinity index, zeta
potential, surface functional charge and DS of these newly prepared rod-shaped CR CNCs, whisker-shaped RH-CNWs and entangled microfiber network TP-CNFs were
identified to be 264.35-649.97 nm, 22.07-25.26 nm, 10.47-29.46, 65.9-75.0 %, -30.2-
-44.5 mV, 0.21-0.23 mmol/g and 0.135-0.148, respectively. The characteristic
profiles of CR-CNCs, RH-CNWs and TP-CNFs displayed lattice crystallographic
planes of cellulose Type-Iβ polymorphs, signifying the successive isolation of nano sized fragments from the matrix of amorphous and non-cellulosic materials. The
equilibrium data were found to be in good agreement with the Langmuir isotherm
model, with the monolayer adsorption capacities (Qo) for MB and CPF of 283.42-
429.51 mg/g and 98.29-192.99 mg/g, respectively. The adsorption process was
driven mainly by the hydrogen bonding, electrostatic attraction, π-π and ion-dipole
interactions, and the synergistic interplay of Lewis-base reaction and hydrophobic
forces between model adsorbates with the functionalized NCs. Excellent inhibition
efficiencies against both gram-positive S. aureus and B. subtilis and gram-negative
E. coli and S. typhi have been detected, with the inhibition rates of 81-95 % for CR CNCs, 88-98 % for RH-CNWs and 72-93 % for TP-CNFs, respectively. The
antibacterial actions marked the leakage of protein (4.47-42.90 µg/mL) and nucleic
acid (0.68-16.25 µg/mL) from the bacterial cells. The unique features and multi functional roles of different NCs have been well-elucidated, which would allow an
integral valorisation of currently undervalued biomass waste feedstock, and
contribute to a “zero-waste” and “circular economic model”.