A porous trimetallic Au@Pd@Ru nanoparticle system: Synthesis, characterisation and efficient dye degradation and removal

Article abstract of DOI:10.1039/c5ta03959b

A facile room temperature one-pot synthesis of trimetallic porous Au@Pd@Ru nanoparticles (Au@Pd@RuNPs) has been developed. The trimetallic nanoparticles have been prepared by the successive sacrificial oxidation of cobalt nanoparticles (CoNPs). The average particle size of Au@Pd@RuNPs is 110 nm. The porous nature and the presence of Au, Pd and Ru have been confirmed via TEM, FE-SEM and EDS analyses. The trimetallic nanoparticles have shown excellent catalytic activity towards the reduction of p-nitrophenol and efficient degradation of various azo dyes. This has been further extended towards the removal of colour from waste water via the catalytic degradation of azo dyes. Moreover, the produced amine can be eliminated from the waste water via its sorption on an industrial solid waste dolochar.

Full text of DOI:10.1039/c5ta03959b

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Materials Chemistry A
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A porous trimetallic Au@Pd@Ru nanoparticle
system: synthesis, characterisation and efficient
dye degradation and removal†
Cite this: DOI: 10.1039/c5ta03959b
Anupam Sahoo, Suman Kumar Tripathy, Niranjan Dehury and Srikanta Patra*
A
facile room temperature one-pot synthesis of trimetallic porous Au@Pd@Ru nanoparticles
(Au@Pd@RuNPs) has been developed. The trimetallic nanoparticles have been prepared by the
successive sacrificial oxidation of cobalt nanoparticles (CoNPs). The average particle size of
Au@Pd@RuNPs is 110 nm. The porous nature and the presence of Au, Pd and Ru have been confirmed
via TEM, FE-SEM and EDS analyses. The trimetallic nanoparticles have shown excellent catalytic activity
towards the reduction of p-nitrophenol and efficient degradation of various azo dyes. This has been
further extended towards the removal of colour from waste water via the catalytic degradation of azo
dyes. Moreover, the produced amine can be eliminated from the waste water via its sorption on an
industrial solid waste dolochar.
Received 1st June 2015
Accepted 14th August 2015
DOI: 10.1039/c5ta03959b
www.rsc.org/MaterialsA
1
5,32,37–42
features of bimetallic nanoparticles derived from Au–Pd,
Introduction
32,43–49
50–52
Au–Ru
or Pd–Ru
have been extensively studied.
The development of multimetallic core–shell or alloy nano- However, heterotrimetallic nanoparticles consisting of Au, Pd
particles has gained a signicant attention in recent decades and Ru in a solid or porous form have not yet been explored.
both from the fundamental as well as application perspec- Thus, the present article intends to highlight the development
1–11
tives.
This is primarily because of the fact that multimetallic of trimetallic porous structured Au@Pd@Ru nanoparticles
nanoparticles oen provide unique optoelectronic, electro- (Au@Pd@RuNPs) and to study their reactivity towards catalytic
chemical, chemical and catalytic properties which are signi- p-nitrophenol (PNP) reduction and azo dye degradation.
1,12–19
cantly different from their monometallic counterparts.
Herein, we describe a facile room-temperature synthesis of
Addition of a second metal onto the existing metal enhances its trimetallic porous Au@Pd@RuNPs via stepwise spontaneous
properties like activity, stability and selectivity by an ensemble oxidation of cobalt nanoparticles (CoNPs). The porous structure
1
,17,18,20,21
or ligand effect.
particles can also be manipulated by varying the chemical by FE-SEM and TEM analysis. In addition, the synthesised
composition.
The properties of multimetallic nano- of the synthesised core–shell nanoparticles has been conrmed
1
4–16,22–27
The activity of nanoparticles can be nanoparticles have been subjected to test the catalytic activity
16,27–29
further enhanced by making porous structures.
Contin- towards the reduction of PNP and various azo compounds.
uous efforts have been made towards the development of such Furthermore, the activity of the Au@Pd@RuNPs is extended to
materials in order to achieve the desired properties and activi- decolorise the coloured waste water (synthetic and industrial) via
ties. In this context, several bimetallic core–shell type nano- catalytic decomposition of the azo bond and possible remedia-
materials of both solid and porous structures have been tion from the produced toxic amine by efficient sorption using
11–13,15–19,26,30–32
developed and extensively studied.
In contrast, dolochar (an industrial solid waste) to purify waste water.
heterotrimetallic nanoparticles are relatively less common,
although they can show interesting properties as compared to
their monometallic and bimetallic counterparts.
Moreover, the trimetallic porous structured nanoparticles are The trimetallic porous Au@Pd@RuNPs have been prepared by
yet to be explored.
the stepwise galvanic displacement of CoNPs (Scheme 1) (see
Results and discussion
3,19,21,33–36
Au, Pd and Ru are well known for their excellent catalytic and the Experimental section). The CoNPs have been prepared by
electrocatalytic properties. The catalytic and electrocatalytic the reduction of an aqueous CoCl solution by a strong reducing
2
2
7,28
agent NaBH
formed CoNPs. Addition of the as synthesised CoNP solution to
the aqueous solution of HAuCl leads to the spontaneous
4
.
Citrate acts as a capping agent to stabilise the
School of Basic Sciences, Indian Institute of Technology Bhubaneswar,
Bhubaneswar-751007, India. E-mail: srikanta@iitbbs.ac.in; Tel: +91-674-2576053
4
3
+
0
reduction of Au ions to Au by the sacricial oxidation of
Co /Co (EAu3+/Au
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c5ta03959b
0
2+
1
0
+ 0.994 V and ECo2+/Co
0
ꢀ 0.277 V versus SHE).
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The dark blackish brown colour of the solution changes to violet
indicating the formation of porous Au nanoparticles (AuNPs). A
0.1% polyvinylpyrrolidone (PVP) was added to the solution for
better stabilisation. Aer allowing sufficient time, the oxidised
2
+
4
Co ions in solution were further reduced by NaBH and core–
shell type Au@CoNPs were obtained. Palladium was spontane-
ously deposited onto the porous AuNPs by the sacricial
oxidation of the Co layer of Au@CoNPs using an aqueous
solution of K
quently, a third metal ruthenium is deposited (using an
aqueous solution of RuCl $3H O (E + 0.68 V versus SHE))
2
[PdCl
4
] (EPd2+/Pd
0
+ 0.915 V versus SHE). Subse-
Ru3+/Ru0
3
2
by repeating a similar procedure and trimetallic porous
Au@Pd@RuNPs are obtained (Scheme 1).
The formation of porous AuNPs, porous Au@PdNPs and
porous Au@Pd@RuNPs is realised by the distinct colour change
using UV-Vis spectroscopy. Fig. 1 represents the UV-Vis spectra
Fig. 1 UV-Vis spectra of porous AuNPs, porous Au@PdNPs and
of the nanoparticles in solution. The spontaneous reduction of porous Au@Pd@RuNPs in water.
3
+
0
0
Au / Au by Co is witnessed by the generation of a surface
plasmon resonance (SPR) band at 667 nm indicating the
formation of porous Au nanospheres. The disappearance of the
characteristic SPR band of porous AuNPs upon addition of
nanoparticles, standard p-nitrophenol (PNP) reduction by
NaBH was conducted. The disappearance of the distinct band
4
0
second or third metals Pd or Ru by sacricial oxidation of Co
at 400 nm during the reduction of PNP in the presence of the
catalysts has been monitored by UV-Vis spectroscopy (Fig. 3a). It
is well documented that this reaction can be catalysed by noble
indicates the deposition of Pd or Ru onto the Au surface (Fig. 1).
The porous nature of the nanoparticles has been conrmed
by the FE-SEM and TEM analyses (Fig. 2 and S1†). The FE-SEM
images of all the nanoparticles have shown a blackberry like
structure. The bimetallic Au@PdNPs and trimetallic Au@Pd@
RuNPs are formed via the deposition of smaller sized PdNPs
and RuNPs onto the surface of AuNPs and Au@PdNPs, respec-
tively (Fig. 2a and S1a and b†). The FE-SEM images have further
revealed that the formed AuNPs, Au@PdNPs and Au@P-
d@RuNPs are moderately monodispersed and the average sizes
of the nanoparticles are 90 nm, 105 nm and 110 nm, respec-
tively (Fig. 2, S1 and S2†). Furthermore, the TEM images of
AuNPs, Au@PdNPs and Au@Pd@RuNPs have also revealed
porous structures with moderately good monodispersity (Fig. 2b
and S1†). The EDS analysis of the selected region of nano-
particles indicates the presence of Au, Pd and Ru metals in
AuNPs, Au@PdNPs and Au@Pd@RuNPs (Fig. 2c, and S1e
and f†).
16,53–56
metals.
To understand the variation of reactivity of the
nanoparticles (porous AuNPs, porous Au@PdNPs and porous
Au@Pd@RuNPs) kinetic measurements of reduction of 0.1 mM
PNP in the presence of 10 mM NaBH and a xed amount of
4
synthesised nanoparticles has been studied (Fig. 3). It is
observed that all the synthesised nanoparticles catalysed the
reduction of PNP efficiently; however, the rate of the reaction
signicantly varies between the nanoparticles (Fig. 3b). The
trimetallic Au@Pd@RuNPs have shown better reactivity than
the corresponding dimetallic Au@PdNPs and monometallic
AuNPs (porous Au@Pd@RuNPs > porous Au@PdNPs > porous
AuNPs) indicating the importance of the second or third metal
in the nanoparticle system. The observed rate of reaction is
pseudo-rst order with respect to PNP. The calculated rate
constants vary signicantly for different nanoparticles (Table 1).
Interestingly, the trimetallic Au@Pd@RuNPs were able to
complete at least six more catalytic cycles with comparable
efficiency during the repeated addition of PNP into the same
reaction vessel aer the completion of the rst catalytic cycle.
The AuNPs, PdNPs, RuNPs and their bimetallic analogues
are well known for their catalytic and electrocatalytic activi-
53–63
ties.
To test the catalytic activity of the synthesised
Scheme 1 Schematic representation of the preparation of porous AuNPs, porous Au@PdNPs and porous Au@Pd@RuNPs.
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Fig. 3 (a) UV-Vis spectra of the catalytic reduction of PNP in the
presence of Au@Pd@RuNPs and (b) normalised time dependent
catalytic reduction of PNP at 400 nm in the presence of Au@P-
d@RuNPs, Au@PdNPs and AuNPs in a Tris buffer (pH 9.0). [PNP] ¼ 0.1
mM; [NPs] ¼ 0.5 pM; and [NaBH ] ¼ 10 mM.
4
degradation of CR in the presence of Au@Pd@RuNPs (linear
dependence of ln(A /A ) vs. time) suggests rst order reaction
with respect to the dye.
0
t
To test the generality of the dye degradation, other dyes such
as reactive red (RR-120) and reactive black (RB-5) were used
(Scheme S1†). Fig. 5 represents the degradation of various azo
dyes at pH 9.0 using a specic concentration of the nano-
catalyst. It is observed that all the dyes are efficiently degraded
Fig. 2 (a) FE-SEM images, (b) TEM images, and (c) EDS spectra of
Au@Pd@RuNPs. The inset of (c) represents the region selected for
recording the EDS spectra.
(ꢁ4 minutes) in the presence of trimetallic nanocatalyst
Au@Pd@RuNPs (Fig. 5). The rate of degradation of the dyes
follow the order: RB-5 > CR > RR-120. The results suggest that
the trimetallic Au@Pd@RuNP nanocatalyst system could be
This observation signies high efficiency and repeatability of useful for the degradation of various azo based dyes. Notably,
the present catalytic system for the decomposition of PNP. the same Au@Pd@RuNP trimetallic nanocatalyst is able to
We next extend the catalytic activity of the nanoparticles repeat the catalytic cycles at least six times with comparable
towards the degradation of azo compounds. It is well known efficiency for all the three dyes.
that the effluents containing azo dyes cause severe problems to
We next study the removal of the produced aromatic amines
aquatic life. The dyes discharged as industrial waste from the from the reaction mixture (Scheme S1†). The aromatic amines
textile or other related industries not only cause water pollution are also well-known carcinogenic agents which cause severe
64
76–78
but also pose a health risk to humans. The dyes are very stable problems in both aquatic as well as human life.
In general,
and are not degraded easily. Thus, facile catalytic degradation enzymatic reduction (using the enzymes tyrosinase, oxido-
of dyes could be a viable option to get rid of the dye based reductase, laccases, etc.) or aerobic/anaerobic biodegradation
pollution. Reductive cleavage of azo dyes could eliminate the (using different types of micro-organisms) of amines are
73,79–89
colour from the solution. It is well documented that the commonly used for the removal of aromatic amines.
degradation of azo (–N]N–) bonds can be efficiently done by Nevertheless, the methods are tedious, cost inefficient and need
6
5–75
various metal nanoparticles.
Thus, to test the reactivity of special precaution towards culturing microbial media and
90–92
our synthesised nanocatalysts towards the degradation of azo maintaining the activity of enzymes.
To overcome these
dyes Congo red (CR) was taken as the reference. The kinetics of limitations we adopted a simple and milder strategy for the
CR dye degradation (disappearance of the band at 498 nm) was removal of amines via their sorption onto a porous substrate.
monitored by UV-Vis spectroscopy (Fig. 4). The degradation of Dolochar is a carbonaceous solid waste obtained from sponge
93
CR is monitored both in neutral (pH 7.0) as well as in Tris iron industry. It has requisite porosity and large surface area.
buffer (pH 9.0) solutions. In both cases the degradation of CR Dolochar has thus been used for the efficient removal of various
2
+
6+
3ꢀ
93,94
in the presence of a trimetallic Au@Pd@RuNP nanocatalyst ions such as Cd , Cr , PO
4
, etc.
It is therefore assumed
was completed in approximately 4 minutes and the rates of that dolochar can also sorb amines efficiently. To test the
degradation of CR were almost the same. Considering the sorption of amine on dolochar various aromatic amines such as
controlled decomposition of NaBH
4
in an alkaline medium, pH benzidine, 2-aminophenol, 4-aminophenol and 3,4-dimethoxy-
9.0 has been selected for further studies. The corresponding aniline have been used (Fig. 6). The UV-Vis spectra of the
bimetallic Au@PdNPs and monometallic AuNPs have shown amines showing the bands around 300 nm and 250 nm
much inferior reactivity than the trimetallic nanoparticles (Fig. 6(i)) have diminished signicantly aer the treatment of
(Fig. 4b and Table 1) indicating the importance of second or dolochar (Fig. 6(ii)) suggesting their sorption into porous
third metals into the catalyst system. The kinetic analysis of the dolochar.
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Table 1 Summary of the observed rate constants toward the reduction of PNP and degradation of various dyes in the presence of nanocatalysts
in a Tris buffer solution (pH 9.0). [PNP] ¼ 0.1 mM, [NaBH ] ¼ 10 mM, [NP] ¼ 0.5 pM; and [dye] ¼ 0.1 mM
4
ꢀ1
Rate constant (s
PNP
)
Nanoparticles
CR
RR-120
RB-5
ꢀ3
ꢀ3
ꢀ2
ꢀ4
ꢀ4
ꢀ2
AuNPs
Au@PdNPs
Au@Pd@RuNPs
1.99 ꢂ 0.04 ꢃ 10
5.09 ꢂ 0.34 ꢃ 10
2.42 ꢂ 0.12 ꢃ 10
1.74 ꢂ 0.49 ꢃ 10
7.20 ꢂ 0.12 ꢃ 10
2.49 ꢂ 0.65 ꢃ 10
—
—
—
—
ꢀ2
ꢀ2
1.34 ꢂ 0.29 ꢃ 10
9.49 ꢂ 0.74 ꢃ 10
Fig. 4 (a) UV-Vis spectra of the catalytic reduction of CR in the
presence of Au@Pd@RuNPs and (b) time dependent catalytic degra-
dation of CR at 498 nm in the presence of Au@Pd@RuNPs, Au@PdNPs
and AuNPs in a Tris buffer (pH 9.0). [CR] ¼ 0.1 mM; [NPs] ¼ 0.5 pM; and
[
4
NaBH ] ¼ 10 mM.
We next extend this strategy to sorb the produced amines
during the catalytic degradation of CR and other dyes. It is
observed that during the degradation of CR new bands around
3
2
50 nm and 300 nm developed (Fig. 4a) which is due to the Fig. 6 UV-Vis spectra of 1.0 mM (10 cm ) solutions of (a) 2-amino-
95
formation of corresponding amines (Scheme S1†). Dolochar phenol, (b) benzidine, (c) 4-aminophenol and (d) 3,4 dimethoxyaniline
before (i) and after (ii) their sorption on 1000 mg dolochar for 12 h and
was added into the reaction mixture aer the degradation of the
dye and stirred overnight. The UV-Vis spectra of the solution
showed that the bands corresponding to aromatic amines
(iii) blank in a Tris buffer (pH 9.0).
(ꢁ250 nm and ꢁ300 nm) disappeared suggesting the signicant
sorption of amines (Fig. S3a†). Furthermore, the EDS analysis of behaviour of amines from other decomposed dyes (RR-120 and
the treated dolochar also showed peaks related to nitrogen RB-5) was also tested and similar sorption behaviour was
indicating the sorption of amines (Fig. S4d†). The sorption observed (Fig. S3b and c†).
Next, we extended this to study the treatment of synthetic
waste water. The trimetallic nanocatalyst Au@Pd@RuNPs has
shown efficient dye degradation followed by removal of in situ
generated amines from the solution by using dolochar (Fig. 7a).
This encouraging result has prompted us to examine the
decolourisation of real industrial waste water (see the Experi-
mental section) using a Au@Pd@RuNP nanocatalyst followed
by the sorption of produced amines in dolochar. It is observed
that the synthesised nanocatalyst efficiently decolorises col-
oured waste water and removes corresponding amines (Fig. 7b).
The present one-pot method for the degradation of azo dyes is
much simpler and removal of produced amines does not
require any tedious biological methods. Moreover, the present
method generates solid waste from an aqueous solution by
using another waste dolochar. Handling solid waste is much
convenient than handling the liquid waste. Thus, the present
report would be very useful for the efficient removal of colour
and corresponding amines from the textile based waste water.
Fig. 5 Normalised time dependent catalytic degradation of CR at
4
98 nm, RR-120 at 535 nm and RB-5 at 595 nm in the presence of a
Au@Pd@RuNP nanocatalyst in a Tris buffer (pH 9.0). [dye] ¼ 0.1 mM;
NPs] ¼ 0.5 pM; and [NaBH ] ¼ 10 mM.
[
4
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Pollution Control Board and processed by following a reported
94
procedure. The synthetic waste water was prepared as per the
94,98
reported procedure.
The industrial waste water was collected
from the local textile industry at Khordha Industrial Area,
Khordha, Orissa, India.
Instrumentation
UV-Vis spectra were obtained by using a Perkin Elmer Lambda
3
5 spectrophotometer. The Dynamica Velocity 18R refrigerated
Fig. 7 Absorption spectra of (a) synthetic waste water and (b) industrial centrifuge instrument was used for the separation of nano-
waste water (i) before and (ii) after the reduction by NaBH in the particles. FE-SEM images and EDS analysis were carried out
presence of Au@Pd@RuNPs and (iii) after the treatment of dolochar for
2 h and (iv) blank. [NPs] ¼ 0.5 pM; [NaBH ] ¼ 50 mM and dolochar ¼
50 mg for (a) and 1500 mg for (b). The volume of synthetic and
4
using Zeiss Merlin compact Microscope and Oxford instru-
ments, respectively. TEM analysis was conducted using a JEOL
2000 FX-II Transmission Electron Microscope.
1
7
4
3
industrial waste water taken for this experiment was 10 cm .
Synthesis of trimetallic nanoparticles
Preparation of porous gold nanoparticles (AuNPs). Co
Conclusions
3
nanoparticles were prepared by adding 0.1 cm of 0.4 M CoCl
2
3
In conclusion, we have developed a facile room temperature solution into 100 cm deaerated aqueous solution containing
method for the preparation of a trimetallic porous Au@Pd@ 8 mM NaBH and 1.0 mM sodium citrate. During the course of
4
RuNP nanocatalyst system via the successive sacricial oxida- reaction, the purple coloured solution turned brownish black
tion of CoNPs. The porous nature and elemental composition of indicating the formation of CoNPs. Stirring was continued till
the nanocatalyst have been conrmed by TEM and FE-SEM the evolution of H gas ceased. Nitrogen was purged to the
2
studies, and EDS analysis. The nanocatalyst has shown excel- solution throughout the reaction to avoid the oxidation of the
3
lent catalytic reactivity towards the reduction of PNP and formed CoNPs. In parallel, 60 cm of 0.44 mM aqueous HAuCl4
degradation of azo based dyes. Furthermore, the toxic amines was deaerated during this time. When the H2 gas evolution
produced during degradation of azo dyes have been removed via ceased, the HAuCl solution was transferred to the CoNP solu-
4
the sorption on solid industrial waste dolochar. The nano- tion via a cannula. As soon as the solution was added, the colour
catalyst has shown efficient removal of colours and in situ of the solution changed to deep blue and then violet indicating
generated toxic amines from industrial waste water are elimi- formation of porous AuNPs. A required amount of PVP (nal
nated by simple sorption on a porous solid waste (dolochar) concentration: 0.1%) was added and the solution was stirred for
ꢄ
which is much more convenient than the traditional biological 2 h at 50 C. The AuNP solution was marked as solution A. A part
ꢄ
processes. Furthermore, the present report demonstrates the of solution A was centrifuged at 4 C at 12 000 rpm for
generation of solid waste from waste water which is convenient 15 minutes to remove the oxidised cobalt. The supernatant was
for waste management. This is the rst example of the trime- decanted and resuspended in 0.1% PVP. This process was
tallic porous Au@Pd@RuNP system which is important both repeated thrice to obtain pure porous AuNPs. This porous AuNP
from the synthetic and catalytic points of view. Moreover, we solution was used for further characterisation and to study the
believe that the present report would be an important addition catalytic activity.
towards the nanocatalyst based efficient removal of azo-based
dyes and treatment of textile waste water.
Preparation of porous Au@Pd nanoparticles (Au@PdNPs).
To a 25 cm deaerated solution A, 0.4 cm of 0.5 M NaBH
4
3
3
solution was added. Immediately, the blue coloured solution
turned brownish black indicating the deposition of a CoNP
layer onto the AuNPs. The solution was then allowed to stir at
Experimental
Materials
room temperature until the evolution of hydrogen gas ceased.
3
All chemicals were purchased from commercial sources and An aqueous solution of 0.31 cm (20 mM) K [PdCl ] was added
2
4
used as received. All glassware was cleaned with aqua-regia and to the reaction mixture and stirred for 6 h at room temperature
ꢄ
thoroughly rinsed with copious amounts of doubly distilled and additional 2 h at 50 C. This black coloured solution was
water. All aqueous solutions and buffers were prepared by marked as solution B. The pure PVP stabilised Au@PdNPs were
doubly distilled water. All the inert atmospheric reactions were obtained by following a procedure similar to that described for
conducted under a dinitrogen atmosphere using the standard porous AuNPs.
Schlenk technique. Nitrogen gas was purged throughout during
Preparation of porous Au@Pd@Ru nanoparticles (Au@Pd@
the preparation of nanoparticles. All the reactions were carried RuNPs). A similar synthesis procedure was adopted for the
ꢄ
out at 25 C unless specied. The molar concentration of preparation of porous Au@Pd@RuNPs from solution B as
nanoparticles in solution was calculated by following the mentioned for the preparation of Au@PdNPs. An aqueous
1
6,96,97
previously reported procedure and is found to be ꢁ5.0 pM.
3 2
solution of 0.166 mM (nal concentration) RuCl $3H O was
The solid waste dolochar was collected from the Orissa used for the preparation of Au@Pd@RuNPs.
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Reduction of p-nitrophenol (PNP). The reduction of
p-nitrophenol (PNP) using synthesised nanoparticles was
Acknowledgements
monitored by following the procedure reported by Pradhan This work was supported by the CSIR (Letter No. 01(2692)/12/
56
3
et al. Briey, in a standard 1.0 cm quartz cuvette (with 1 cm EMR-II dated 03/10/2012) New Delhi. AS, SKT and ND are
path length) nanocatalyst (100 mL, 5.0 pM), excess NaBH
thankful to DST (Inspire programme), CSIR and UGC, New
100 mL, 100 mM) and 700 mL Tris buffer (pH 9.0) were taken and Delhi, India, respectively, for their fellowship. The authors
4
(
ꢄ
the solution was kept at 25 C for 5 minutes. A 100 mL (1 mM) sincerely acknowledge Dr Mrinmoy De, Indian Institute of
solution of PNP was added to the reaction mixture and the Science, Bangalore for his kind help in recording TEM images of
reduction of PNP was monitored by recording the time-course our samples. We are grateful to reviewers for their critical
spectra at 400 nm.
Degradation of azo dyes. Nanocatalyst (100 mL, 5.0 pM) and manuscript.
excess NaBH (100 mL, 100 mM) were taken in 700 mL Tris buffer
comments and valuable suggestion to improve the quality of the
4
3
(
1
pH 9.0) solution in a standard 1.0 cm quartz cuvette having
cm path length and kept for 5 minutes at 25 C. A 100 mL
ꢄ
Notes and references
(1 mM) solution of CR was then added and the time course
spectra of the decomposition of CR were recorded at 498 nm.
The time course spectra for RB-5 (595 nm) and RR-120 (535 nm)
dyes were also recorded by following a procedure similar to CR.
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Sorption of aromatic amines on dolochar. To a 10 cm Tris
buffer (pH 9.0) solution of 1 mM aromatic amine (2-amino-
phenol) 1000 mg dolochar was added. The solution was then
stirred for 12 h at room temperature. The solution was allowed
to settle, ltered and the UV-Vis spectrum was recorded. A
similar procedure was followed for other aromatic amines
(benzidine, 4-aminophenol and 3,4 dimethoxyaniline).
Sorption of generated aromatic amines on dolochar. The
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sorption of reduced products (aromatic amines) of Congo red
3
dye onto dolochar was carried out by taking 10 cm ,
ꢀ
3
7
00 mg dm CR. Before treatment with dolochar the solution
was reduced by trimetallic porous Au@Pd@Ru nanocatalyst
100 mL, 5.0 pM) and 100 mM NaBH . Aer complete decol-
(
4
ourisation and decomposition of NaBH4 (12 h), dolochar
400 mg) was added to the reaction mixture. The mixture was
stirred overnight at 250 rpm at room temperature. The sorption
(
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