Accepted Manuscript Molecular mechanism of anionic dyes adsorption on cationized

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Fig. 1. FTIR spectra (a), X-ray diffraction patterns (b) of RH, RHC and CRHC. 
3.2.2 XRD 
Fig.1b shows the X-ray diffraction patterns of RH, RHC and CRHC. For RH and 
RHC, the typical crystallization peaks of type I cellulose (2θ: 15-16 ° [110], 22 ° 
[200], 34 ° [004]) were observed. Likewide, the crystallinity index (CrI) of different 
samples was estimated from the ratio of the peak area to the total area of the spectrum 
including the amorphous response [28]. Compared with RH, the crystallinity index 
(CrI) after the alkali and bleaching treatment increased the progressive removal of the 
amorphous components (lignin and hemicellulose). Moreover, the higher crystallinity 
due to the chemical cellulose structure, where each monomer has three hydroxyl 
groups with the ability to form intra- and inter-molecular hydrogen bonds between 
cellulose chains, resulting in a highly compact system [29]. 
Compared with RHC, the characteristic peaks of CRHC disappeared and a new 
peak emerged at 20.10°, and the crystallinity index (CrI) decreased significantly. In 
the modification process, the alkali treatment increases the stiffness of the fiber as it 
removes the different amorphous fractions. The hydroxy groups on the glycosides of 
RHC are substituted during the cationization process, leading to breakage of hydrogen 
bonds of the original RHC. At the same time, the introduction of quaternary 
ammonium groups disturbs the regularity of the entire molecular chain, causing the 
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crystalline regions in the molecular structure to be destroyed and the amorphous 
regions to increase. However, the spectrum of RHC still shows a characteristic peak at 
2θ = 20.10°, indicating that the crystal structure of cellulose was not completely 
destroyed during the modification process.
3.2.3 SEM 
Fig. 2 shows the SEM micrographs of RHC and CRHC samples at different 
magnifications. For the rice husks cellulose (RHC-500um, RHC-100um, RHC-50um), 
the rough surfaces were clearly observed due to the loss of external non-cellulose 
compounds (hemicellulose, lignin, pectin and wax)
[27]. Fig. 2 also shows 
micrographs of RHC with a short, rod-like structure and many aggregates. These 
aggregates may be attributed to the highly polar surfaces of these fibers, which cause 
aggregations of interfibrillar hydrogen bonds or the strong intermolecular hydrogen 
bonds between the particles [30, 31]. Likewise, the particle morphology and 
aggregation is highly affected by the SEM sample preparation. After the modification, 
it is observed that the rice husks fiber bundles was separated into individual fibers. 
After modification, the surface morphology changed obviously. The CRHC surface is 
less rougher than the RHC surface and appears to have a smoother surface with a 
uniform wrinkled structure. 
Fig. 2. SEM images of RHC and CRHC. 

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