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Carbohydrate Polymer Technologies and Applications 2 (2021) 100134
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Carbohydrate Polymer Technologies and Applications
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Nanocrystalline cellulose derived from melon seed shell (Citrullus
colocynthis L.) for reduction and stabilization of silver nanoparticles:
Synthesis and catalytic activity
Segun A. Ogundare a, b, Vashen Moodley a, James F. Amaku c, Abdulrazaq O. Ogunmoye b,
Odunayo C. Atewolara-Odule b, Oseyemi O. Olubomehin b, Kehinde N. Awokoya d,
Nurudeen O. Sanyaolu b, Adeola A. Ibikunle b, Werner E. van Zyl a, *
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban, 4000, South Africa
Department of Chemical Sciences, Olabisi Onabanjo University, P. M. B. 2002, Ago-Iwoye, Nigeria
Department of Chemistry, Michael Okpara University of Agriculture, Umudike, Nigeria
Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria
Melon seed shell
Nanocrystalline cellulose
Ammonium persulphate
Silver nanoparticles
Nitrobenzene reduction
Melon seed shells (MSS) are a hazard to the environment as they host disease vectors. To alleviate the effect, we
explored melon seed shells (MSS) as a new source of nanocrystalline cellulose (NCC) with reducing- and sta­
bilizing capacity for the synthesis of silver nanoparticles (AgNPs). The isolation of NCC from discarded MSS
served the dual purpose of a reducing- and stabilizing agent in the synthesis of AgNPs. The isolated needle-like
crystals (MSS-NCC) had a mean length 204 nm, width 7 nm and aspect ratio 30. The NCC had crystallinity index
of 94% with surface rich in –OH and –COOH functionality. The obtained AgNPs covered the surface of the MSSNCC and catalysed the reduction of nitrobenzene to aniline using NaBH4. The process of the reduction monitored
via UV-vis spectroscopy was completed within 12 min. with a rate constant 0.04 min− 1 as revealed by the kinetic
1. Introduction
Melons are fruit plants that belong to the family of Cucurbitaceace
with approximately 1000 known species and are well adapted to the
warm regions of the world, where they are mostly cultivated for their
fruits (Chomicki, Schaefer & Renner, 2020; Giwa & Akanbi, 2020).
There are many varieties of melons with edible fruits, however, a few
others with inedible fruits but with seeds of dietary and medicinal
importance do exist (Patel & Rauf, 2017). Citrullus colocynthis is one of
the species of melons cultivated in West Africa for its seed, which is rich
in edible oil, protein, carbohydrate and fiber (Falade, Otemuyiwa,
Adekunle, Adewusi & Oluwasefunmi, 2020; Ogundele, Sanni, Oshodi,
Okuo & Amoo, 2015). One of the stages preceding the extraction of the
nutritional components of the seed is the shelling of the seeds. This leads
to the generation of a large quantity of melon seed shells (MSS), which
constitute an environmental concern (obnoxious odor, respiratory dis­
ease, etc.) in open-air dumpsites as a post-harvest waste by attracting
rodents and other disease vectors (Falade et al., 2020; Giwa & Akanbi,
2020). MSS are lignocellulosic waste from which cellulose can be
extracted and nanocrystalline cellulose (NCC) subsequently isolated.
Cellulose is regarded as the most abundant biopolymer and renewable
material on earth and one of the most important glucans, which consists
β-D-glucopyranose units linked by the β− 1, 4-glycosidic bond to form
linear chains (Ogundare & Van Zyl, 2019b). The chains are organized
into fibres that combine with other components (mainly lignin and
hemicellulose) to form the integral components of plants (Moon, Mar­
tini, Nairn, Simonsen & Youngblood, 2011). Cellulose fibres are made of
two distinct regions based on the organization of the repeating units.
The regular ordering of the repeating units leads to formation of crys­
talline regions, which are alternately separated by less ordered amor­
phous regions (Jonoobi et al., 2015).
The amorphous regions within the cellulose fibres are susceptible to
hydrolysis. The hydrolysis of cellulose fibres leads to isolation of NCC,
which contain large proportion of crystalline components. Cellulose
* Corresponding author.
E-mail address: [email protected] (W.E. van Zyl).
Received 23 April 2021; Received in revised form 20 July 2021; Accepted 2 August 2021
Available online 4 August 2021
2666-8939/© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (
S.A. Ogundare et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100134
hydrolysis has been achieved by the use of mineral acids (H2SO4, HCl,
H3PO4) (Habibi, Lucia & Rojas, 2010; Mohamed, Salleh, Jaafar, Asri &
Ismail, 2015; Ogundare, Moodley, & van Zyl, 2017; Tang et al., 2015),
organic acid (oxalic acid, maleic acid) (Chen, Zhu, Baez, Kitin & Elder,
2016; Cherian et al., 2010; Xu et al., 2017) and oxidants (2,2,6,6-tet­
ramethylpyperidine-1-oxyl (TEMPO), ammonium persulphate (APS),
periodate) (F. Jiang & Hsieh, 2014a; Leung et al., 2011; Yang & van de
Ven, 2016; Yao, Wang, Cai & Wang, 2016). The characteristics and the
surface functional groups of the isolated NCC depend on the source of
the cellulose and the type of reagent(s) employed. APS has been reported
as a unique reagent with the advantage of isolating NCC directly from
lignocellulosic material without pretreatment, unlike the use of other
hydrolyzing agents, where such pretreatment is indispensable for suc­
cessful isolation of NCC (Castro-Guerrero & Gray, 2014). Under suitable
conditions (temperature 60–80 ◦ C and pH 1.0), APS generates SO4‾
(S2O82− → 2SO4‾), HSO4‾ and H2O2 (S2O82− + 2H2O → 2HSO4‾ + H2O2
(Goh, Ching, Chuah, Abdullah, & Liou, 2016)). The generated compo­
nents have the capacity to hydrolyze the amorphous region and also
oxidize the lignin and hemicellulose present (Leung et al., 2011). The
oxidative hydrolysis introduces carboxylic and aldehyde functional
groups on the NCC surface and the presence of these functional groups
alongside hydroxyl groups make the NCC an ideal reducing- and stabi­
lizing agent in the synthesis of metal nanoparticles.
Metal nanoparticles of group 11 (Cu, Ag and Au) have interesting
properties when compared to their corresponding bulk metal state due
to increased surface plasmon resonance (Wang, Gao, Chen, Chen &
Chen, 2017). Free surface electrons can interact in different environ­
ments and account for the suitability of nanoparticles in applications
such as catalysis, sensing, antimicrobial agents, drug design and drug
delivery, cancer diagnostics and therapeutics (Ahmed & Aljaeid, 2016;
Cai & Yao, 2013; Edison, Sethuraman & Lee, 2016; Elemike, Onwudiwe,
Ekennia, Ehiri & Nnaji, 2017; He et al., 2015; May & Oluwafemi, 2016;
Ogundare & Van Zyl, 2019b; Shen, Huang, Li, Chen & Wu, 2019; Zong
et al., 2018). As a catalyst, silver nanoparticles (AgNPs) have shown
tremendous performance in the degradation of dyes (methyl orange and
methylene blue) and reduction of nitroarenes, whose accumulation in
water bodies can cause harmful effects on aquatic life (Kaushik &
Moores, 2016; Wu et al., 2013). More recently, the drive to green
chemistry principles has led to the use of renewable and abundant
nature-based materials such as NCC in the synthesis of metal nano­
particles (Ogundare & van Zyl, 2018; Wu et al., 2014). The importance
of the green synthesis of metal nanoparticles with NCC and other
biogenic-based materials is that the nanoparticles derived are biocom­
patible, less toxic, environmentally friendly and relatively cheap in
comparison with those derived by using conventional synthetic re­
agents, which often limited the biocompatibility and consequently the
biomedical applications of the nanoparticles (Makvandi et al., 2020;
Ogundare & Van Zyl, 2019b; Zare et al., 2020). MSS are sustainably
generated annually in large quantities and can be used to form NCC,
which is currently one of the most sought-after nanotechnological ma­
terials based on its numerous applications (Abitbol et al., 2016; Zhu
et al., 2016). Although the potential of using MSS as adsorbent material
have been explored for the removal of dyes, heavy metals and phar­
maceutical wastes from contaminated water (Ahile et al., 2018; Foo &
Hameed, 2012; Giwa & Akanbi, 2020; Rahimdokht, Pajootan & Arami,
2016), there is no report on the isolation of NCC from MSS.
In this work we aim to demonstrate for the first time that it is possible
to isolate and characterize nanocrystalline cellulose (NCC) from melon
seed shells (MSS), and then to use the NCC for both the reduction and
stabilization of silver nanoparticles, and finally to use the nano­
composite as a catalyst in the reduction of nitrobenzene to aniline as a
suitable application. This report posts three major highlights which
include i) isolation of NCC from MSS via APS hydrolysis to furnish the
surface of the isolated NCC with carboxylate functional group alongside
the inherent hydroxyl functional group, ii) the synthesis of AgNPs using
the isolated NCC as the hydroxyl groups serve as the site of reduction of
the precursor ion (Ag+) and the carboxylate groups provide support for
the AgNPs to prevent excessive aggregation, and iii) the demonstration
of the AgNPs as suitable catalyst for the reduction of nitrobenzene to
2. Experimental
2.1. Materials
The MSS of Citrullus colocynthis were obtained from Ilora town, Oyo
State, Nigeria. Ammonium persulphate (NH4)2S2O8, sodium hydroxide
pellets (NaOH), sodium chlorite (NaClO2), silver nitrate (AgNO3), so­
dium borohydride (NaBH4), nitric acid, glacial acetic acid, nitroben­
zene, toluene and ethanol were procured from Sigma-Aldrich and used
as received.
2.2. Extraction of cellulose from MSS
Cellulose was extracted from the obtained MSS by using a procedure
described previously (Bano & Negi, 2017; Lu & Hsieh, 2012) with slight
modification. The MSS were initially separated from extraneous matter,
washed with double distilled water and dried in an oven at 60 ◦ C for 48
h. The dried sample was ground and screened using a 100-μm sieve. The
screened sample was dewaxed for 24 h using 2:1 v/v of toluene: ethanol
(20 mL/g) via a soxhlet extraction process. The dewaxed sample was
subsequently bleached and delignified for 5 h using 1.5 w/v% NaClO2
(20 mL/g) at 70 ◦ C with the pH adjusted to 3.0 using glacial acetic acid.
This was followed by washing to neutral pH and drying. Further treat­
ment was carried out to dissolve the hemicellulose by using 1 M NaOH
(20 mL/g) at 70 ◦ C for 2 h. The dissolved hemicellulose was filtered off
and the obtained cellulose (MSS-Cel) was washed to neutral pH and
dried at 60 ◦ C for 24 h. The yield was subsequently determined as pre­
sented in Eq. (1).
% Yield of MSS − Cel =
Mass of extracted MSS − Cel (g)
× 100%
Mass of MSS used (g)
2.3. Isolation of NCC from MSS-Cel
NCC was isolated from MSS-Cel using 100 mL/g (volume of APS
solution per mass of MSS-Cel) of 1 M APS at 60 ◦ C for 16 h under
vigorous stirring (Leung et al., 2011). The suspension obtained was
cooled down to room temperature and diluted (dilution factor: 20) with
double distilled water. The NCCs were separated by centrifugation using
OHAUS Frontier 5706 at 6000 rpm with relative centrifugal force =
4427 × g for 20 min. This procedure was repeated 5 times to reduce the
concentration of the oxidant. The isolated MSS-NCC solution was soni­
cated to minimize aggregation using an ultrasonicator (UP400S,
Hielscher, Germany) at 50% amplitude and a 0.5 cycle for 20 min. The
MSS-NCC was then dialyzed to neutral pH. A film of MSS-NCC for
characterization was obtained by drying at room temperature. The yield
of MSS-NCC was determined gravimetrically as presented in Eq. (2).
% Yield of MSS − NCC =
Mass of isolated MSS − NCC (g)
× 100%
Mass of MSS − Cel used (g)
2.4. Synthesis of silver nanoparticles
The isolated MSS-NCC was used as a reducing- and stabilizing agent
in the synthesis of AgNPs by following our previous report (Ogundare,
Moodley, & van Zyl, 2017). The synthesis was conducted at 80 ◦ C using
10 mL of 0.1 wt% of MSS-NCC dispersion sonicated for 15 min with pH
adjusted to 10 using 0.1 M NaOH. A 1 mL sample of freshly prepared 0.3
M of AgNO3 was added to a stirring solution of MSS-NCC with temper­
ature maintained at 80 ◦ C for 75 min. The obtained brown colloid was
washed with double distilled water and centrifuged at 6000 rpm with
S.A. Ogundare et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100134
relative centrifugal force = 4427 × g for 30 min. This procedure was
repeated 5 times to remove the unreacted AgNO3 completely. Dry
sample for characterization was obtained by drying at 50 ◦ C for 24 h in
an oven. The percentage of silver in the colloid was determined by
inductive coupled plasma optical emission spectroscopy (ICP-OES) after
microwave digestion.
0.15 mL of the synthesized AgNPs (equivalent to ca. 0.3 μmol of Ag) in a
quartz cuvette of 1 cm path length. The reduction was monitored at
intervals of 3 min with a UV-3600 Plus UV-VIS-NIR spectrophotometer
(Shimadzu, Japan).
2.5. Characterization
3.1. Isolation of MSS-NCC and synthesis of MSS-NCC/AgNPs
The optical study of the synthesized AgNPs was carried out using a
UV-3600 Plus UV-VIS-NIR spectrophotometer (Shimadzu, Japan). The
concentration of the synthesized AgNPs was determined using three
separate samples of a mixture of the synthesized AgNPs and HNO3 (69%
w/w) in volume ratio 1:10 (sample: acid) digested in a MARS 6 (CEM,
USA) microwave system. The digested samples were subsequently
analyzed for the concentration of Ag+ ions using an Optima 5300 DV
ICP-OES (Perkin Elmer, USA). The analysis was preceded with calibra­
tion using freshly prepared standard solutions (1.0–0.05 ppm) of Ag+
ions from a 100 ppm stock solution by serial dilution. A FTIR spectro­
scopic study was used to analyze functional groups present in MSS, MSSCel, MSS-NCC and the synthesized AgNPs. The FTIR spectra were
recorded using a Spectrum 100 infrared spectrometer equipped with an
ATR accessory (Perkin Elmer, USA) in the range 380–4000 cm− 1 at 4
cm− 1 resolution. Microscopic studies were used to examine the shape,
size and dispersity of the synthesized AgNPs. The dimension and
morphological transition of MSS to MSS-NCC were also established
using microscopic studies. Transmission electron microscopy (TEM) and
high-resolution TEM were carried out on a JEOL 1010 (Japan) trans­
mission electron microscope (TEM), and a JEOL 2100 (Japan) high
resolution transmission electron microscope (HRTEM), respectively. A
Zeiss Ultra Plus field emission gun scanning electron microscope (FEG­
SEM) (Germany) was used for the SEM study. The particle size distri­
butions of MSS-NCC and AgNPs were obtained using ImageJ 1.42 and
OriginPro 8 software. Thermal stability of the nanoparticles was deter­
mined on a STA 6000 (Perkin Elmer, USA). The thermogravimetric
analysis (TGA) was conducted at a temperature range of 25–600 ◦ C with
a steady heating rate of 10 ◦ C/min under N2 gas at a flow rate of 20 mL/
min. The TGA plots were used to determine the decomposition pattern
and the percentage residual products. The diffraction patterns of the
MSS-NCC and the synthesized AgNPs were recorded in the range
10–90 ◦ C using a Bruker AXS D8 Advance (Germany) equipped with CuKα radiation source (wavelength = 0.154 nm) operating at 40 kV and 40
mA. The crystallinity index (CI) of the MSS-NCC and the crystallite sizes
(Dhkl) of the nanoparticles were determined using Segal’s (Eq. (3)) (Lu &
Hsieh, 2012; Segal, Creely, Martin & Conrad, 1959) and Debye-­
Scherrer’s (Eq. (4)) (Debye, 1915; F. Jiang & Hsieh, 2013) equations,
respectively. The CI of the MSS-NCC composite was calculated using the
peak associated with the maximum intensity of both amorphous and
crystalline region (I002) at 2θ = 23.1◦ and the peak associated with the
intensity of the amorphous region (Iam) at 2θ = 18.0◦ The parameters
used for the determination of the Dhkl were: wavelength (λ = 0.154 nm),
the angular full width at half maximum intensity (β) obtained through
the Gaussian fit of the peaks and the Bragg angle (θ) using crystallo­
graphic plane of (111) for the AgNPs and (002) for the MSS-NCC.
The fibres of MSS-Cel (extracted after dewaxing, bleaching and
delignification of MSS) were hydrolyzed using APS to isolate MSS-NCCs.
The MSS-NCCs were furnished with surface carboxylic functional groups
resulting from the oxidation of the C6 primary hydroxyl groups. The
gravimetric analysis showed that MSS yielded 35% of MSS-Cel, which on
hydrolysis gave 37% (equivalent to ca. 13% of MSS). The percentage
yield (13%) of the isolated MSS-NCC is comparable to 12% and 14% for
NCC isolated from groundnut shell (Bano & Negi, 2017) and bacterial
cellulose (Leung et al., 2011) using H2SO4 and APS, respectively.
However, it is lower than 22–23% (cotton and Cellulose Ashless Clipping
Filter Aids, Whatman (Castro-Guerrero & Gray, 2014)) and 28% (Flax)
(Leung et al., 2011) reported for NCC isolated using APS directly on
materials with less lignin content. The synthesis of the MSS-NCC/AgNPs
using the isolated MSS-NCC as an effective reducing- and stabilizing
agent was initially indicated by the formation of an intense yellowish
colloidal solution (Inset: Fig. 1), which showed optical absorbance with
a narrow spectrum centered at 412 nm wavelength (Fig. 1). Generally,
this is a unique characteristic indicating the formation of AgNPs and it is
associated with localized surface plasmon resonance of the electrons at
the surface of the synthesized AgNPs (Mochochoko, Oluwafemi, Jum­
bam & Songca, 2013; Ogundare & van Zyl, 2018, 2019a; Oluwafemi
et al., 2016). The result of the triplicate ICP-OES analysis of the micro­
wave digested samples of MSS-NCC/AgNPs showed that the concen­
tration of Ag metal in the colloid was 225.36 ± 12.37 mg/L. The colloid
was stable without precipitation over a period of 6 months.
CI (%) =
I002 − Iam
× 100%
Dhkl (nm)
3. Results and discussion
3.2. FTIR study
The vibrational absorption bands in the FTIR spectrum (Fig. 2) of the
MSS assigned (ν/cm− 1) as: 3330 (O–H), 1647 (H–O–Hbend), 1457 (–CH2–
(C6)bend), 1024 (C–O–C) and 892 (C1–O–C4deform.) showed the unique
characteristics of cellulose, which indicated cellulose as one of the
components of the MSS (Bano & Negi, 2017; Ogundare & van Zyl,
2019a; M. Rosa et al., 2010). These bands prominently appeared in the
spectra of the extracted MSS-Cel, MSS-NCC and the synthesized AgNPs.
However, the weak bands at (ν/cm− 1): 1749 and 1714 in the spectrum of
2.6. Catalytic study
The performance of the synthesized AgNPs as catalyst for the
reduction of nitrobenzene (NB) using NaBH4 as reducing agent was
evaluated using 0.01 mM of NB (2 mL), 10 mM of NaBH4 (1 mL) and
Fig. 1. Optical spectra and images (inset) of MSS-NCC and MSS-NCC/AgNPs.
S.A. Ogundare et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100134
Fig. 2. FTIR spectra and vC=O bands (inset) of the MSS, MSS-Cel, MSS-NCC and MSS-NCC/AgNPs.
the MSS indicated the presence of acetyl and esters of lignin and
hemicellulose and other non-cellulosic components (Bano & Negi, 2017;
Goh, Ching, Chuah, Abdullah, & Liou, 2016; Hu et al., 2014). The
disappearance of these bands in the spectrum of the MSS-Cel showed the
effect of the extraction process on the removal of lignin, hemicellulose
and other non-cellulosic components. Seemingly related weak bands
were observed and assigned (ν/cm− 1) as: 1730 (C = O of carboxylic
acid) and 1725 (COO‾) in the FTIR spectra of the MSS-NCC isolated
using APS and the synthesized AgNPs, respectively. These bands were
due to partial oxidation of the C6 primary hydroxyl groups on the
Fig. 3. Representative TEM micrographs of MSS-NCC (A), TEM (B)/HRTEM (C) (inset: corresponding SAED) micrographs of MSS-NCC/AgNPs, SEM micrographs of
MSS-Cel (D), MSS-NCC (E) and MSS-NCC/AgNPs (F).
S.A. Ogundare et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100134
MSS-Cel by APS used for the hydrolysis and the corresponding carbox­
ylate moiety formed which served as the anchor site for the synthesized
nanoparticles (Castro-Guerrero & Gray, 2014; Cheng et al., 2014; Leung
et al., 2011; Wu et al., 2013)
Table 1
Sources and hydrolyzing agent for isolation of NCC with the dimension analysis.
3.3. Morphological study
A TEM micrograph of the isolated MSS-NCC is shown in Fig. 3A,
which revealed the presence of needle-like particles with nanoscale di­
mensions. The analysis of the dimensions of 140 randomly selected
nanocrystals showed a mean length 204 ± 73 nm, width 7 ± 2 nm and
aspect ratio 30 ± 15. The nanocrystals were poly-dispersed as indicated
by the high standard deviation of the dimensions (Fig. S1). The isolated
MSS-NCC showed a resemblance both in morphology and dimensions to
NCCs isolated from other cellulosic materials such as groundnut shell
(Bano & Negi, 2017), rice husk (S. M. Rosa, Rehman, de Miranda,
Nachtigall & Bica, 2012), flax fiber (Leung et al., 2011), filter paper
(Ogundare & van Zyl, 2019a) and cigarette filters (Ogundare, Moodley,
& van Zyl, 2017). Similarly, the effect of the APS hydrolysis on the
extracted MSS-Cel was clearly evident as shown by the SEM micrographs
(Fig. 3D and E), which revealed the transformation of the cellulose
aggregate (Fig. 3D) into a loosely entangled network of nanocrystals
(Fig. 3E) on drying. The isolated MSS-NCC displayed its reducing and
stabilizing capacities as the Ag+ ions were reduced to atomic silver
which assembled as nanoparticles on the surface of the MSS-NCC, as
shown in the representative TEM (Fig. 3B) and HRTEM (Fig. 3C) mi­
crographs. The AgNPs adopted a quasi-spherical morphology with a
calculated mean diameter 18 ± 6 nm from the analysis of 230 randomly
selected AgNPs (Fig. S2). The selected area electron diffraction (SAED)
pattern (insect; Fig. 3C) of the AgNPs revealed their polycrystalline
nature as indicated by the distinct diffraction rings typical of crystalline
Ag (Ogundare & van Zyl, 2018; Pastoriza-Santos & Liz-Marzán, 2008).
The SEM micrograph (Fig. 3F) of the synthesized AgNPs showed that the
nanoparticles retained their morphology as they assembled on drying,
which indicated the stabilizing effect of the MSS-NCC (Ogundare & van
Zyl, 2018, 2019a).
size (nm)
index (%)
Flax/ APS
7/ 204
4/ 144
Hemp/ APS
6/ 148
Cotton/ APS
7/ 109
Bamboo/ APS
6/ 143
This study
(Leung et al.,
(Leung et al.,
& Gray, 2014)
(Hu et al., 2014)
8/ 144
Lyocell fiber/
Rice straw/
(Cheng et al.,
(F. Jiang & Hsieh,
Moodley, & van
Zyl, 2017)
presents comparative data of this study on isolated NCC with other
related studies and it revealed that the calculated CI (94%) of the
MSS-NCC was comparable with 93% and relatively higher than 75%
obtained from lyocell and flax, respectively, using APS hydrolysis, and it
indicated that the APS hydrolysis was effective in the removal of the
amorphous region of the cellulose aggregate (Cheng et al., 2014; Leung
et al., 2011). The calculated Dhkl (4 nm) of the MSS-NCC was approxi­
mately half of the mean width (7 nm) of the nanocrystals as determined
from the TEM micrograph which showed that the nanocrystals con­
tained at least two units of elementary crystallites laterally aligned in
colloidal solution (Brito, Pereira, Putaux, & Jean, 2012; Elazzouzi-Ha­
fraoui et al., 2008). The intensities of the peaks associated with the
MSS-NCC were observed to decrease in the diffractogram of the
MSS-NCC/AgNPs which showed intense peaks at 2θ = 38.0◦ (111), 44.2◦
(200), 64.3◦ (220), 77.4◦ (311) and 81.5◦ (222) characteristic of metallic
silver with face centered cubic (FCC) crystal structure (F. Jiang & Hsieh,
2014b; Ogundare & van Zyl, 2019a). The calculated crystallite size
(17.70 nm) of the AgNPs correlated with the mean diameter (18 nm) of
the AgNPs as determined by TEM. This indicated that the MSS-NCC
stabilized the AgNPs and prevented excessive agglomeration during
3.4. Powder X-ray diffraction study
The analysis of the X-ray diffraction pattern (Fig. 4) of the isolated
MSS-NCC revealed a characteristic cellulose I crystalline composition
with intense peaks at 2θ = 15.2◦ (101) and 22.9◦ (002) (Bano & Negi,
2017; Ogundare & van Zyl, 2019a). This showed that the crystalline
phase of the native cellulose in MSS was not affected at any stage of the
chemical treatment (Y. Jiang, Zhao, Feng, Fang & Shi, 2016). Table 1
3.5. TGA/DTA study
The thermogram of the MSS-NCC showed two pyrolytic stages
characteristic of cellulose with peak temperature at 176 and 366 ◦ C
(Table S1). The initial weight loss (2.0%) below 110 ◦ C accounted for the
absorbed moisture on the MSS-NCC (Bano & Negi, 2017; Ogundare &
van Zyl, 2019a). The first pyrolytic stage associated with the dehydra­
tion of the anhydroglucose chain segments (Bano & Negi, 2017; F. Jiang
& Hsieh, 2013) accounted for 13.8% weight loss. The second stage
which involved the decomposition of the polymeric chains and oxidative
degradation (Ogundare, Moodley, & van Zyl, 2017; S. M. Rosa et al.,
2012) led to the generation of volatile components (CO, CO2, H2 and
CH4) and accounted for approximately half of the weight loss at 366 ◦ C,
see Fig. 5. The thermal profile of the MSS-NCC/AgNPs showed two py­
rolytic stages comparable to MSS-NCC but at relatively lower tempera­
ture which was attributed to the presence of AgNPs with higher thermal
conductivity. The difference in residual mass of MSS-NCC (30.4) and
MSS-NCC/AgNPs (78.6) at 600 ◦ C accounted for the AgNPs.
4. Catalytic reduction of nitrobenzene (NB) using MSS-NCC/
The catalytic activity of the MSS-NCC/AgNPs was studied by
Fig. 4. Powder XRD diffractograms of MSS-NCC and MSS-NCC/AgNPs.
S.A. Ogundare et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100134
Fig. 5. The thermograms and DTA curves of MSS-NCC and MSS-NCC/AgNPs.
monitoring the reduction of NB in the presence of excess NaBH4 (500
fold) via UV/vis spectrophotometer. A gradual decline in the intensity of
the peak absorbance at 265 nm with time indicated the progression of
the reaction (Farooqi, Naseem, Ijaz & Begum, 2016; Li et al., 2015). The
reduction of NB usually will not progress without a catalyst due to the
high energy barrier. The AgNPs on MSS-NCC showed a strong affinity for
NB and BH4‾ attraction to the surface providing a channel for electron
transfer with minimum energy barrier (Tada et al., 2005). However, the
AgNPs showed less affinity for the product of the reduction (aniline)
which diffused from its surface. A pseudo first-order rate constant (k) for
the reaction kinetics was calculated from a plot of ln (At/Ao) against time
(t) based on the relationship: ln (At/Ao) = kt, where At and Ao are the
absorbance at a time (t) and initial absorbance respectively (Farooqi
et al., 2016; Li et al., 2015). Fig. 6 (A and B) shows the UV-vis spectra of
the reduction at interval and the kinetic plot with a slope (0.04 min− 1)
corresponding to the rate constant. This showed the significance of
MSS-NCC/AgNPs as catalyst obtained from relatively cheap and easily
accessible material derived from agricultural waste. This study demon­
strates for the first time the capacity of AgNPs synthesized using NCC as
Table 2
AgNPs with applications synthesized using NCC from different sources.
reducing agent
dimension of
Spherical/ 7–34
Spherical/ ~ 1
Spherical/ 1–30
20–50 nm
This study
(Kaushik et al., 2016)
(Ogundare & van
Zyl, 2018)
(Shi et al., 2015)
Spherical/ 1–20
Spherical/ 1–10
NCC (cotton)
NCC (cigarette
NCC (CelluForce
Inc.)/ Dopamine
NCC (filter paper)/
NCC (cotton)
Fig. 6. UV-visible spectra (A) and kinetic plot (B) for the reduction of NB using MSS-NCC/AgNPs as catalyst.
(Lokanathan, Uddin,
Rojas & Laine, 2013)
(Xiong, Lu, Zhang,
Zhou & Zhang, 2013)
S.A. Ogundare et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100134
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5. Conclusion
This study explored the potential of MSS as a source of NCC, which
was employed as a reducing- and stabilizing agent in the synthesis of
AgNPs. The TEM micrograph of the obtained nanocomposite (MSSNCC/AgNPs) showed the surface of the needle-like crystals of the NCC
adorned with well dispersed spherical AgNPs (mean diameter: 18 nm).
The AgNPs were polycrystalline as revealed by SAED obtained from
HRTEM and adopted a FCC crystal structure as shown by XRD analysis.
The nanocomposite catalyzed the reduction of NB to aniline using
NaBH4 as oxidant. The kinetic plot revealed a pseudo-first order mech­
anism with a rate constant 0.04 min− 1. In summary, the initial aims set
out at the start was achieved, namely i) to isolate nanocrystalline cel­
lulose (NCC) from melon seed shells (MSS), that ii) NCC derived from
MSS can then be used for both the reduction and stabilization of silver
nanoparticles, and iii) to use the nanocomposite as a catalyst. Finally, we
believe that an alternative and noteworthy use for discarded MSS, which
constitute an environmental and safety annoyance and host several
disease vectors at dumpsites, have been established.
SAO thanks Messrs. K. Oladejo and S. Oladejo for assistance on data
collection. MSS, SAO, VM and WEVZ thank the University of KwaZuluNatal (UKZN) for providing facilities used in this research work. SAO,
AOO, OCA, OOO, NOS, and AAI thank Olabisi Onabanjo University,
Ago-Iwoye, for providing support and infrastructure required for the
successful completion of this work. This research did not receive any
specific grant from funding agencies in the public, commercial, or notfor-profit sectors.
Supplementary materials
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