Cellulose

DOI 10.1007/s10570-016-1053-4

ORIGINAL PAPER

An efficient and easily retrievable dip catalyst based

on silver nanoparticles/chitosan-coated cellulose filter paper
Ikram Ahmad . Tahseen Kamal . Sher Bahadar Khan . Abdullah M. Asiri

Received: 19 April 2016 / Accepted: 22 August 2016

Ó Springer Science+Business Media Dordrecht 2016

Abstract Re-use of a catalyst is an important task, X-ray spectroscopy confirmed the formation of the
which is usually achieved by loading it on easily Ag/CH-FP hybrid. Ag/CH-FP morphology was exam-
separable supports such as magnetic substrates. How- ined through scanning electron microscopy analysis,
ever, we demonstrate here the process of easy and fast which showed the presence of Ag nanoparticles
catalyst separation from a reaction medium by loading attached to the cellulose microfibers. The prepared
it onto an economically feasible and microscopically Ag/CH-FP was employed as a dip catalyst for the
high surface substrate of filter paper (FP) made up of degradation of nitroarene compounds of 2-nitophenol
cellulose microfibers as catalyst support. To achieve (2-NP) and 4-nitrophenol (4-NP) by NaBH4. Remark-
the goal, we coated chitosan (CH) on filter paper (CH- ably, the rate constants for 4-NP and 2-NP were
FP) to impart a high affinity of the substrate for metal 3.9 9 10-3 and 1.7 9 10-3 s-1, respectively. In
ion absorption. AgNO3 dissolved in water with a addition, we discussed the ease of the catalyst
0.1 M concentration was used as the Ag ion carrier retrievability from the reaction mixture and its re-
solution, and CH-FP strips with known rectangular usability.
dimensions were submerged into it for the metal ion
absorption. The metal ion-laden CH-FP strips were dip Keywords Silver nanoparticles  Chitosan coating 
treated with sodium borohydride (NaBH4) aqueous Cellulose filter paper  Catalyst  Pollutants
solution to prepare Ag-nanoparticle loaded CH-FP degradation
(Ag/CH-FP). X-ray diffraction and energy dispersive

Electronic supplementary material The online version of Introduction

this article (doi:10.1007/s10570-016-1053-4) contains supple-
mentary material, which is available to authorized users.
Cellulose is a renewable biomass present as the most
I. Ahmad  T. Kamal (&)  S. B. Khan  A. M. Asiri abundant polymeric material on the earth. It is a semi-
Department of Chemistry, Faculty of Science, King
crystalline polymer obtained from higher plants, tuni-
Abdulaziz University, P.O. Box 80203, Jeddah 21589,
Saudi Arabia cates, bacteria and alga (Dhar et al. 2015; Wu et al.
e-mail: tkkhan@kau.edu.sa 2014). Researchers have explored its versatile applica-
tions by preparing its different derivatives due to
I. Ahmad  T. Kamal  S. B. Khan  A. M. Asiri
presence of –OH functional groups on the polymer
Center of Excellence for Advanced Materials Research
(CEAMR), King Abdulaziz University, chain and biodegradable and biocompatible nature
P.O. Box 80203, Jeddah 21589, Saudi Arabia (Kang et al. 2015). Several strategies have been used

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 Cellulose

to extend the applicability of cellulose. The most In the past decades, Ag nanoparticles have attracted
common strategies are (1) chemical modification by unlimited attention because of their distinctive physic-
grafting of a variety of monomers or other functional ochemical properties and potential applications in the
units and (2) physical modification by pre-made poly- optoelectronics, sensor and biomedical fields (Ferreira
mer or polymer nanocomposite coating (Kang et al. et al. 2015). Additionally, they are considered one of
2015). Chemical grafting of cellulose utilizing sophis- the most effective catalysts for a variety of chemical
ticated polymerization techniques such as atom transfer reactions (Schröfel et al. 2014). Similar to other metal
radical polymerization, nitroxide mediated polymeriza- nanoparticles, Ag nanoparticles are generally unsta-
tion and the reversible addition fragmentation chain ble because of their large active surface areas, which
transfer reaction have been discussed (Kang et al. 2015). may result in self-aggregation. Thus, they are usually
Besides controlled radical graft polymerization, free supported on other matrices having high surface areas
radical polymerization grafting techniques are also such as graphene oxide, metal oxides, silica and so on
reported for the chemical modification of cellulose (Haider et al. 2016). Besides these inorganic supports,
(Littunen et al. 2011). The above-mentioned modifica- polymers are known as organic supports and prefer-
tion methods are time consuming and require extraor- entially used because of their easy processing into high
dinary care, skill and a sophisticated experimental surface area materials. Due to these outstanding
facility for successful grafting. Moreover, the main properties, the tendency to take full advantage of
focus of the above-listed studies was to optimize the polymers such as polyvinylalcohol (Huang et al.
reaction conditions without providing the application of 2012), polypyrrole (Wu et al. 2015), polyvinyl
the end product. Recently, cellulose filter paper (FP) has pyrrolidone (Guo et al. 2013) and poly(methyl
been used in various studies because it is easily available methacrylate) (Koo et al. 2016), as catalyst hosting
in laboratories (Haider et al. 2016; Kamal et al. substrates has increased.
2016a, b). Some researchers physically modified cellu- As the emphasis of science and technology is
lose FP, where the modified form was used in various gradually shifting toward environmentally friendly
applications. For instance, Basudeb et al. (Raza and and sustainable resources and processes, green poly-
Saha 2014) prepared multifunctional agarose and silver mers as supporting materials are getting tremendous
nanoparticle-coated cellulose FP where the end product attention from various research groups. In this regard,
was used as a flexible Surface-enhanced Raman scat- cellulose supporting various precious metals and
tering (SERS) sensor. Setyono et al. (Setyono and transition metal nanoparticles is one of the best
Valiyaveettil 2016) physically modified cellulose FP candidates for the fabrication of inorganic-organic
with polyethyleneimine for the easy and effective nanohybrids. Ag nanoparticle deposition on the sur-
removal of hazardous pollutant ions from water. We face of cellulose derivatives provides a new approach
used a ZnO- and TiO2-chitosan nanocomposite coating to hybrid heterogeneous catalysts for organic trans-
onto cellulose FP for wastewater treatment where formation. Cellulose has been presented as a versatile
methyl orange and thymol violet dyes were effectively substrate for catalysts in the grafted [ethylenediamine-
adsorbed and degraded by the nanomaterial (Kamal functionalized cellulose (Keshipour et al. 2013), citric
et al. 2015, 2016a, b). Similarly, TiO2/chitosan/silver acid-modified cotton fibers (Andrade et al. 2015), and
was coated on FP through a layer-by-layer process to carboxymethyl cellulose (Xiao et al. 2015)] and
make antibacterial paper (Xiao et al. 2013). In another nanostructured form [such as cellulose nanocrystals
report, the FP surface was modified by silver nanopar- (Dhar et al. 2015; Yan et al. 2016) and nanofibers
ticles through a mirror reaction to perform the detection (Gopiraman et al. 2015; Jang et al. 2014; Janpetch
and quantification of acetylsalicylic acid by SERS in a et al. 2015; Zhou et al. 2012)]. Carefully examining
commercial tablet (Sallum et al. 2014). An optical these studies, it can be found that cellulose processing
sensor for ascorbic acid was also presented by Daneielle (grafting, nanocrystal formation and nanofiber fabri-
et al. (Ferreira et al. 2015) using Ag ion-coated cellulose cation) has been carried out to provide an affinity for
FP. This brief information from the recent literature the nanoparticles as well as impart a high surface area
clearly manifests the potential of using FP as an for the immobilization of a huge number of nanopar-
effective substrate for designing a wide variety of ticles. As mentioned in the above text, cellulose in the
studies with useful applications. form of common laboratory FP can be utilized as the

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Cellulose

best candidate for the immobilization of metal 2-nitrophenol were obtained from BDH Chemicals,
nanoparticles because of its easy availability in almost England. Acetic acid was purchased from NTN Ltd.,
all research laboratories (Khan et al. 2016). Another UK.
advantage of using cellulose FP is that its separation
and reutilization can be easily accomplished.
Nitrophenols are pollutants found in industrial Methods
wastewater from the dye, explosive, pesticide, plasti-
cizer and herbicide industries and in agricultural Surface modification of filter paper
wastewater (Bera et al. 2015; Chi et al. 2013).
Although 4-nitrophenol (4-NP) is one of the most We relied on physical modification of the cellulose FP
intractable toxins, upon its nitro group transformation by CH. This physical modification involved the
to an amino group, the product called 4-aminophenol following simple procedure.
(4-AP) is an important intermediate used in the CH aqueous solution was prepared in dilute acetic
synthesis of several analgesic and antipyretic drugs. acid (2 %V/V) with a concentration of 1 wt% fol-
Therefore, catalytic transformation of 4-NP to 4-AP is lowed by the introduction of FP with a diameter of
an important process and is often chosen as a model 12.5 cm into this solution. FP was kept for about 3 h in
reaction when testing of the catalyst is required. The this state, and, after being taking out, it was dried for
transformation of nitrophenols to aminophenols has further use.
been carried out using noble metal nanoparticles as
reported in vast literature, but we investigated the In-situ Ag nanoparticle synthesis
effect of the substrate used for the in situ preparation of
the Ag nanoparticles for complete and easy CH-FP was incorporated into a pre-made AgNO3
recyclability. aqueous solution with a concentration of 0.1 M.
In this article we chose cellulose FP as the substrate Before incorporation into Ag salt solution, CH-FP
for preparation of Ag nanoparticles. FP was first was cut into three types of strips with dimensions of
coated with chitosan (CH) to enhance the substrate X 9 Y cm2 (where X = 0.4 cm and Y were varied
affinity for Ag ions. The Ag ion-loaded CH-FP was from 2 to 4 cm). These strips were taken out of the
treated with NaBH4 aqueous solution for the conver- AgNO3 solution after 4 h during which the maximum
sion of Ag? to Ag0 nanoparticles. We carried out amount of Ag ions was immobilized by a CH coating
characterization of the synthesized materials by var- layer. The Ag ion-laden CH-FPs were dipped into
ious analytical techniques, all favoring the successful freshly prepared 0.1 M NaBH4 aqueous solution. This
formation of Ag nanoparticles present on the FP. The treatment quickly changed the strips color from white
synthesized material’s catalytic activity was tested in to dark brown. The dark brown Ag/CH-FP strips were
the transformation of nitrophenols to aminophenols by freshly used in catalytic transformations of nitrophe-
NaBH4. nols to aminophenols.

Catalytic transformation reactions

Experimental
We tested the performance of Ag/CH-FP in transfor-
Materials mation reactions of two types of nitrophenols, i.e.,
2-nitrophenol (2-NP) and 4-nitrophenol (4-NP). The
Cellulose filter papers with dimensions of 12.5 cm description of the catalytic transformation is exempli-
diameter and 0.3 mm thickness were purchased from fied with the case of 2-NP as detailed below.
Whatman company. Chitosan [specifications: degree Two NaBH4 and 2-NP aqueous solutions in DI
of deacetylation [75 % and high molecular weight water were prepared with concentrations of 0.1 M and
(800–2000 cP, 1 wt% in 1 % acetic acid (25 °C, 0.01 M, respectively. Then, 0.2 ml of 2-NP was
Brookfield)] was purchased from Sigma-Aldrich. poured into a cuvette containing 2.5 ml DI water.
Silver nitrate (AgNO3) was obtained from Merck. Afterwards, 0.4 ml of 0.1 M NaBH4 was added, and
Sodium borohydride (NaBH4), 4-nitrophenol and the cuvette was placed in a UV-visible

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 Cellulose

spectrophotometer to measure the absorbance spectra. weight loss against temperature was recorded under
An Ag/CH-FP strip with known dimensions was nitrogen atmosphere with a heating rate of 10 °C/min
added to this cuvette in such a way that most of the up to 800 °C. The residual concentrations of 2-NP and
path was free for the UV-visible beam to pass through 4-NP in catalytic reduction studies were measured
it. The reduction reaction started, and the absorption using a Thermo Scientific Evolution 300 UV-visible
spectra were continuously recorded. For the sake of spectrophotometer.
comparison, FP and CF-FP were also investigated. To
test the recyclability, three catalytic transformation
reactions of nitrophenols were tested by using same Results and Discussion
0.6 9 4 cm2 Ag/CH-FP strip. Similar experimental
protocols were followed for the 4-NP catalytic Preparation of catalyst strips
transformation.
Scheme 1 shows the preparation process of the Ag/
Characterizations CH-FP dip-catalyst. First, FP strips were treated with
1 wt% CH aqueous solution (2 % v/v of acetic acid in
The morphologies of the FP, CH-FP and Ag/CH-FP DI water). Excess solution was removed to avoid the
were characterized by a field emission scanning blocking of pores by film formation over the FP. CH-
electron microscope (FESEM) with a JEOL JSM- FP strips were then immersed in 0.1 M AgNO3
7600F, Japan. Samples were stuck with carbon tape aqueous solution for 1 h. As a result, Ag ions were
onto a 1-cm-diameter stub and coated with Pt prior to trapped in the CH coating layer over cellulose
SEM observations. Crystal structures of samples were microfibers of FP. Previous studies have shown that
analyzed by performing X-ray diffraction (XRD) on a the –OH and –NH2 functional groups of CH have good
PANalytical diffractometer with a Cu Ka radiations affinity for various metallic ions (Zhang et al. 2016).
(k = 0.154 nm) source. The instrument was operated Polyethyleneimine and polyvinylalchol have been
at 40 kV and 50 mA, and data were obtained at a scan used by some researchers as coating polymers to
rate of 1°–2° 2h min-1. The percentage crystallinities increase the entrapment of metallic ions/nanoparticles
(Cr (%)) of bare FP, CH-FP and Ag/CH-FP samples over FP microfibers and nanofibrils because of the
were calculated from the XRD patterns using the presence of either amine or hydroxyl functional groups
following equation, in those polymers (Liu et al. 2012, 2015; Zheng et al.
Ið200Þ  Iam 2015). When the strips were given longer time to
Cr ð%Þ ¼  100 ð1Þ remain in the AgNO3 solution, their color changed
Ið200Þ
from white to brown, indicating that Ag ions were
where I(200) and Iam represent the intensity of the (200) transformed into nanoparticles. However, we gave the
peak and intensity of the amorphous halo, respec- strips a 1-h staying time, after which, they were taken
tively. For the cellulose I, the diffraction intensity at out of the salt solution and gently washed with DI water
2h = 18° was chosen as the Iam. to remove the loosely bound and un-reacted Ag? ions
Crystallite sizes of Ag nanoparticles and cellulose on the CH surface. All the strips were dipped into
were calculated using the following Scherrer formula, freshly prepared 0.1 M NaBH4 solution to reduce the
Ag ions to Ag nanoparticles. During this step, the strips
Kk
s¼ ð2Þ turned deep brown. No release of the brown matter to
b cos h
the NaBH4 solution was detected by visual inspection
where s, k, b and h are respectively, the crystallite size, during this step, which indicated that almost all
wavelength of X-rays, full width of the peak at half nanoparticles were firmly bound to the CH-FP.
maximum (FWHM) and scattering angle of the peak.
FWHM was calculated from XRD patterns by Fityk Structure and morphology
software. Thermogravimetric analysis was performed
on 10 mg of sample using a TGA Q500 instrument. X-ray diffraction analysis was carried out to determine
Samples were placed in aluminium pans and kept on the crystalline nature of the samples used in this study.
the auto-sampler stage of the TGA instrument. Their The XRD patterns of FP, CH-FP and Ag/CH-FP are

123
Cellulose

FP and CH-FP had diffractions at 2h = 14.8, 16.2,

22.5 and 34.4°. These peaks correspond to the
cellulose-I crystal structure, which can be indexed as
(-110) (110), (200) and (004). Such results also
suggest that the physical modification of FP by CH
does not alter the crystal structure of cellulose and CH
is present in the form of an amorphous coating layer on
the FP surface. On the other hand, Ag/CH-FP showed
numbers of Bragg reflections that were not present in
either the FP or CH-FP XRD patterns. These reflec-
tions were located at 2h values of 38. 28°, 44.04°,
64.34° and 77.28° and may be indexed on the basis of
the face-centered cubic structure of Ag. Moreover, the
crystal size and crystallinity information of cellulose
crystals are listed in the supporting information
(Table SI-1). All the samples had nearly the same
crystallinity and crystal size as the cellulose crystals.
The XRD results clearly demonstrated that the Ag
nanoparticles were formed by the reduction of Ag? -
ions adsorbed by NaBH4. The calculated average size
from the XRD data (using the Debye-Scherrer equa-
tion) was approximately 23 nm.
Figure 2 represents the FE-SEM images of samples
in this investigation. The left side images in (a–c) are
the low-magnification images of FP, CH-FP and Ag/
CH-FP. No considerable difference can be found
among these images. Such results indicate that FP
processing to Ag/CH-FP might involve very minor
changes to the surface morphology. The right side
images in (a–c) are the high-magnification images of
the corresponding FP, CH-FP and Ag/CH-FP samples.
A closer look of the images in (a) and (b) reveals that
initially individual cellulose microfibers are somehow

Scheme 1 Preparation of the Ag/CH-FP catalyst

illustrated in Fig. 1. All the XRD patterns had

numbers of Bragg diffractions confirming the exis-
tence of crystals in the samples. The XRD patterns of Fig. 1 XRD patterns of FP, CH-FP and Ag/CH-FP

123
 Cellulose

covered with a thin CH layer, which are partly Fig. 2 FESEM images of a bare FP, b CH-FP and c Ag/CH-FP. c
connecting the fibers. However, most of the fibers The left and right column images in (a–c) are low- and high-
magnification images of the corresponding samples, respec-
are segregated from each other, pointing to the fact tively. The EDX spectrum of Ag/CH-FP with a table of the
that the CH thin layer might be wrapping these fibers. elemental composition (d)
The high magnification image of the Ag/CH-FP shows
that there are numerous light bright spots (indicated by
small circles to guide the reader’s eyes) on the Catalytic properties
cellulose microfibers. These bright spots appeared
because of the formation of the Ag nanoparticles, 4-NP transformation to 4-AP
which were already confirmed by XRD analysis. For
further confirmation of the successful in situ synthesis Figure SI-1 shows the UV-visible spectra of 4-NP
of Ag nanoparticles as well as their approximate before and after addition of NaBH4. The kmax of the
loading onto the FP cellulose microfibers, an EDX initial solution’s red shifted from 317 nm to 400 nm.
spectrum was recoded from the high-magnification Visual inspection of this experiment suggests that the
image of the Ag/CH-FP. An EDX spectrum in Fig. 2d solution color changed from an initial pale yellow to
clearly shows signals of the Ag along-with carbon, bright yellow. Previous reports stated that this color
oxygen and platinum. The carbon and oxygen signals change was due to the formation of 4-nitrophenolate
were detected because of the organic nature of the CH ions under alkaline conditions (Kumar and Deka 2014;
and FP, and platinum signals appeared because of its Wu et al. 2012). The bright yellow color of the solution
coating during sample preparation for FESEM anal- did not change for a couple of days even though a large
ysis. In our previous report (Kamal et al. 2016c), we excess of NaBH4 was incorporated, which indicated
found that increasing the CH solution concentration that the NaBH4 alone could not reduce the 4-NP. The
from 1 to 5 wt% results in the formation of its thick reduction of 4-NP to 4-AP by NaBH4 is considered to
layer over cellulose FP, which also blocks the original be thermodynamically favorable because the differ-
pores in the FP. ence in their standard electrode potentials is greater
Figure 3 shows TGA thermograms of FP, CH-FP than zero, i.e., DE0 ¼ Eð4NP=4APÞ
0 0
 EðH 3 BO3 =BH4 Þ
¼
and Ag/CH-FP. While increasing the temperature to 0:76  ð1:33Þ ¼ 0:67 V. However, this reduction
100 °C, all the samples lost around 6.7 % of their reaction is kinetically limited when a suitable and
original weight. This weight loss was the result of efficient catalyst is not present in the system. Catalysts
moisture elimination from the samples. A further huge based on noble metal nanoparticles are famous for
and apparent weight reduction between 230 and catalyzing the 4-NP hydrogenation reaction by NaBH4
375 °C was due to the depolymerization, oxidation (Wu et al. 2012), while organic supports such as filter
and evolution of gases in the main organic components paper act as adsorbents for the 4-NP and do not show
in the sample (cellulose and CH). While comparing any catalytic activity toward 4-NP hydrogenation (Liu
the virgin nanoparticles and those containing samples et al. 2015). Figure 4a shows three-dimensional (3D)
for the main weight reduction event, it was found that plots of UV-visible spectra of the 4-NP solution as
the thermal stability of the Ag/CH-FP was lowest. In functions of time, having 0.6 9 2 cm2 Ag/CH-FP
contrast to the previous report on nanomaterial- strip. The peak intensity at kmax = 400 nm decreased
embedded polymer matrices, which showed high with the passage of time and completely vanished after
thermal stability (Kamal et al. 2016c), a decrement 1740 s. This disappearance of the peak intensity was
in the thermal stability of the Ag/CH-FP might be due correlated to the reduction of the 4-NP. At the expense
to the catalytic nature of the Ag nanoparticles. of the peak disappearance at 400 nm, a new peak at
Usually, catalytic nanoparticles decrease the activa- 300 nm appeared, which is commonly observed in the
tion energy and increase the depolymerization during event of 4-AP formation. Similarly, Fig. 4b–c shows
the thermal event (Khan et al. 2015, 2016; Kim et al. 3D UV-visible spectral plots as functions of time for
2012, 2013). It was found from the TGA results that the 4-NP solutions, where 0.6 9 3 cm2 and
0.6 9 2 cm2 Ag/CH-FP strips contained 1.15 mg of 0.6 9 4 cm2 Ag/CH-FP strips were used as catalysts,
Ag nanoparticles. respectively. The only difference among the three

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Cellulose

(a)

(b)

(c)

(d) Element Weight% Atomic%

CK 41.06 52.21
OK 48.80 46.58
Ag L 6.60 0.93
Pt M 3.53 0.28

Totals 100.00

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 Cellulose

120 peak located at 344 nm shifted to 417 nm upon

FP addition of NaBH4 because of the formation of
100 CH-FP
Ag/CH-FP
2-nitrophenolate ions under alkaline conditions (Fig-
Weight loss (%)

80
ure SI-3). The peak intensity at kmax did not change as
long as there was no catalyst. As explained in our
60 earlier report (Kamal et al. 2016a, b), the organic
component of the catalyst (CH-FP) has no activity for
40
the transformation of the 2-NP to 2-AP or in the
20
presence of CH-FP. Around 5 % loss of the pollutants
was observed by the adsorption process. Figure 5a–c
0 shows the evolution of UV-visible spectra of 2-NP as a
200 400 600 800
function of time in the presence of 0.6 9 2 cm2,
Temperature (oC)
0.6 9 3 cm2 and 0.6 9 4 cm2 Ag/CH-FP strips. A
Fig. 3 TGA thermograms of FP, CH-FP and Ag/CH-FP clear decrease in intensity at kmax = 417 nm was
observed in all cases, indicating the reduction of the
plots was that the 4-NP hydrogenation was completed 2-NP (see Figure SI-4). Figure 5d shows the absor-
within a short time for the catalytic strip having a high bance ratios (Ln(At/A0) of the peak at 417 nm versus
surface area (0.6 9 4 cm2). Obviously, the amount of time for 2-NP aqueous solutions, where 0.6 9 2 cm2,
Ag nanoparticles was greater in the 0.6 9 4 cm2 strip 0.6 9 3 cm2 and 0.6 9 4 cm2 were used as catalysts.
than in the rest of the strips, which led to faster In all cases, the time taken for the completion of the
completion of the hydrogenation reaction (see Fig- reaction was on the order of 0.6 9 4 cm2 [ 0.6 9 3 -
ure SI-2). Since an excess amount of NaBH4 was used cm2 [ 0.6 9 2 cm2. Moreover, all the data of (Ln(At/
in the 4-NP transformation reaction, the reaction might A0) versus time have linear regions, indicating that the
follow the pseudo-first order kinetic. It is expressed as reactions proceeded with the pseudo-first-order kinet-
follows, ics. The reaction rates were 0.002, 0.0019 and
0.0017 s-1 for 0.6 9 2 cm2, 0.6 9 3 cm2 and
LnðAt =A0 Þ ¼ kapp t ð3Þ
0.6 9 4 cm2 catalysts. It should be mentioned here
where At is the kmax absorbance value at the designated that there was a small induction period over all the Ag/
time, Ao is the absorbance at time (t) = 0, and kapp is CH-FP catalysts. The induction period is generally
the apparent rate constant of the reaction. considered to be due to the diffusion of the 2-nitro-
In order to determine the kapp, the (Ln(At/A0) values phenolate ions to be adsorbed onto the surface of the
for each graph in Fig. 4a–c were plotted against time. catalyst prior to the start of the reaction (Zeng et al.
It can be observed from the data presented in Fig. 4d 2010).
that for any individual experiment, the data points did Besides the effect of the catalyst amount on the
not follow the exact linearity given by line. This was reaction rate constant of 4-NP and 2-NP reduction
due to the fact that all the catalytic experiments were reactions, the effect of the initial concentration of the
conducted in UV cuvettes whereby bubbles were nitrophenols was tested, where a constant amount of
continuously produced and deposited on the catalyst catalyst (0.6 9 4 cm2) was used. These data are
strip. Such deposition prohibited the 4-NP ions from presented in Figures SI-5 and -6. A general trend of
reaching the catalyst surface. However, when the data a decreasing rate of the reaction was found with
points (from initial to last) were fitted with the linear increasing nitrophenol concentration.
equation, the kapp of 0.002, 0.0028 and 0.0039 s-1 was Based on the results described in the above text, the
observed. conversion mechanism of nitrophenols to aminophe-
nols over Ag/CH-FP is speculated in Fig. 6. The
2-NP transformation to 2-AP nitophenolate ions are first adsorbed by the organic
component of the catalyst; at the same time, BH4-ions
In addition to 4-NP catalytic reduction, Ag/CH-FP react with the inorganic component of the catalyst. As
strips were also tested in 2-NP reduction. An aqueous a result of this reaction, adsorbed hydrogen species
solution of 2-NP has two kmax = 280 and 344 nm. The and electrons on the catalyst surface are transferred to

123
Cellulose

(a) (b)

3.0 3.0

2.5 2.5

. u.)
. u.)

Absorbance (a
Absorbance (a

2.0 2.0

1.5 1.5

1.0 1.0
0 0
0.5 500 0.5
500

)
)
(s

(s
0.0 1000 0.0

e
250 200 1000

m
300 250
350 1500 300

Ti

Ti
400 350
450 400
450
Wave 500 2000 Wave 500 1500
lengt 550 lengt 550
h (nm h (nm
) )

(c) (d)

3.0

2.5
. u.)
Absorbance (a

2.0

1.5

1.0
0
0.5 200
)
(s

0.0 400
e

200
m

300 600
Ti

400
800
Wave 500
lengt
h (nm
)

Fig. 4 Effect of the amount of the catalyst on the 4-NP presented in the plots (a–c) (0.2 ml of [4-NP] = 0.001 M, 1 ml
conversion to 4-AP: UV-visible spectra of 4-NP at different of [NaBH4] = 0.1 M, 2 ml DI water and UV cuvette as reaction
intervals of time where a 0.6 9 2, b 0.6 9 3 and c 0.6 9 4 cm2 vessel)
catalyst strips were used. d Ln(At/A0) versus time of the data

the nitrophenols, thereby resulting in the –NO2 group percentage of the reactant transformation is plotted
reduction to the –NH2 group. against the number of experimental runs, as shown in
Since the catalytic properties of the noble metal Fig. 7. Above 90 % transformation of both the
nanoparticles have been explored extensively, we nitrophenols was observed, which indicates that high
present here that using large, bendable and nanoscop- catalytic activity of the Ag/CH-FP was retained even
ically high surface area polymeric support of FP might after its repeated use.
help in easy recovery of the loaded Ag nanoparticle
catalyst from the system. The recovery of Ag
nanoparticles was completed by simply pulling the Conclusions
strip from the reaction medium. We used the same Ag/
CH-FP strip in the four-times transformation of the We succeeded in developing a conceptually different
2-NP and 4-NP to corresponding phenols and the method to synthesize and immobilize the Ag

123
 Cellulose

(a) (b)
2.0 2.0
. u.)

. u.)
1.5 1.5
Absorbance (a

Absorbance (a
1.0 1.0

0.5 0 0.5 0
500
500

)
(s

(s
0.0 1000 0.0

e
m

m
300 1500 300 1000

Ti

Ti
400 400
Wave 500 2000 Wave 500
lengt lengt
h (nm h (nm
) )

(d)
(c)
2.0
. u.)

1.5
Absorbance (a

1.0

0.5 0
200
)
(s

0.0 400
e
m

300 600
Ti

400
Wave 500 800
lengt
h (nm
)

Fig. 5 Effect of the amount of the catalyst on the 4-NP presented in the plots (a–c) (0.2 ml of [2-NP] = 0.001 M, 1 ml
conversion to 4-AP: UV-visible spectra of 4-NP at different of [NaBH4] = 0.1 M, 2 ml DI water and UV cuvette as reaction
intervals of time where a 0.6 9 2, b 0.6 9 3 and c 0.6 9 4 cm2 vessel)
catalyst strips were used. d Ln(At/A0) versus time of the data

nanoparticles in a CH coating layer over FP in situ. species and electrons, resulting in the transformation
Ag/CH-FP strips exhibited good activities for the of the –NO2 group of nitrophenols to the –NH2
transformation of nitrophenols to aminophenols. group. The Ag nanoparticle recovery process was
Furthermore, the prepared Ag/CH-FPs were struc- easy because it involved the pulling of the dipped
turally and morphologically characterized by XRD, Ag/CH-FP strip from the reaction medium. We
TGA and FE-SEM, respectively. In Ag/CH-FP, the believe that the current approach will provide a
organic components of polysaccharides act as an simple, cost-effective and scalable method to pro-
adsorbent for nitrophenols, while Ag nanoparticles duce different noble and transition metals supported
react with BH4- ions and transfer a surface hydrogen onto polysaccharide fibers.

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Cellulose

OH OH
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Ferreira DCM et al (2015) Optical paper-based sensor for
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Kamal T, Anwar Y, Khan SB, Chani MTS, Asiri AM (2016a)
Acknowledgments The authors are grateful to the Center Dye adsorption and bactericidal properties of TiO2/Chi-
of Excellence for Advanced Materials Research (CEAMR) tosan coating layer. Carbohydr Polym. doi:10.1016/j.
and Chemistry Department at King Abdulaziz University carbpol.2016.04.042
for providing the research facilities. Kamal T, Khan SB, Asiri AM (2016b) Nickel nanoparticles-
chitosan composite coated cellulose filter paper: an effi-
cient and easily recoverable dip-catalyst for pollutants
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