Preparation, characterisation, and dye adsorption potential of quaternised cellulose materials

<p class="MsoNormal" style="margin-bottom:0cm;text-align:justify;line-height:115%"><span lang="EN-GB" style="font-size:10pt;line-height:115%;font-family:&#39;times new roman&#39; , serif">Cellulose-based adsorbents are attractive candidates
for water treatment, yet their performance is governed not only by surface
functionalisation but also by the structural accessibility of adsorption sites.
In this work, we establish structure-adsorption relationships in cellulose
materials by correlating pretreatment-controlled morphology, textural
properties, and various quaternisation routes with dye uptake behavior.
Microcrystalline cellulose was subjected to sulphuric acid hydrolysis and
ultrasonication, followed by freeze-drying to generate porous cellulose
precursors, which were subsequently quaternised appropriately with
glycidyltrimethylammonium chloride or related reagents with different alkyl
chain lengths. The synthesis was optimised to obtain a reproducible precursor
with a well-developed architecture, and the resulting materials were subjected
to physicochemical characterisation. The most favourable precursor was a
material with substantially enhanced specific surface area and pore volume
relative to the starting microcrystalline cellulose. Quaternisation effectively
altered the surface chemistry and morphology, with a visible decrease in
specific surface area and pore volume. Adsorption experiments with methyl
orange, Congo Red, and methylene blue revealed a dependence of adsorption
performance on both dye chemistry and adsorbent structure. No meaningful
adsorption was observed for methyl orange, and hydrogels were ineffective for
all dyes examined. Congo Red was adsorbed only to a limited extent by microcrystalline
cellulose and the quaternised aerogel, whereas methylene blue exhibited high
uptake exclusively on quaternised aerogel, consistent with a heterogeneous
adsorption surface and multiple interaction pathways. Altogether, these
findings show that adsorption in quaternised cellulose systems is dictated by
the interplay between pore architecture, surface functionality, specific
interactions, rather than by cationization alone. </span><span lang="EN-GB" style="font-size:10pt;line-height:115%"></span></p>