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ARTICLE
RSC Advances
DOI: 10.1039/C4RA12080A
aniline molar ratio 1.0 to 0.2 and irregular agglomerated An aqueous solution of HAuCl4 (1 mM, 10 mL) was taken in a
morphology for 2.0 and 0.1. The mechanism of the culture tube then added 100 µL of distilled aniline ( to maintain
nanostructure formation also established from HRTEM studies HAuCl4 to aniline molar ratio = 1:1) with constant stirring for
and result showed that CA play an important role for worm like 30 min then keep it in dark place without stirring for 12 hs to
nanostructure formation. Optimise the reaction condition for get spherical like composite called Au/PANI@0.0 composite.
nanofibers formation by time dependent UVꢀVis and HRTEM
Synthesis of CA stabilized Au seed solution
studies. The synthesized nanostructure showed good catalytic
efficiency and recyclability to several nitro compounds In the typical experiment 10 mL of 1 mM CA aqueous solution
reduction in aqueous medium. In addition the catalytic was mixed with 1 mM HAuCl4 aqueous solution (v/v=1:1) in a
efficiency of worm like nanofibers is much more than that of culture tube equipped with a magnetic stirrer at room
o
the agglomerated structures under identical condition.
temperature (25 C). After 1 h solution colour changed from
greenish yellow to transparent pinkish violate, this solution
(Auꢀ60) actually considered as a active seed solution for
Au/PANI formation.
Experimental Details
Synthesis of Au/PANI@2.0, Au/PANI@1.0, Au/PANI@0.2 and
Au/PANI@0.1 composite:
Materials
o
Aniline was distilled under reduced pressure and store at 5 C
in dark place and Sodium borohydride (NaBH4) purchased from
Merck chemicals. Au(III) chloride trihydrate (HAuCl4, 3H2O,
ACS reagent, ≥49.0% Au basis) and citric acid (ACS reagent,
≥99.5%) were purchased from SigmaꢀAldrich, and used without
further purification. The nitro aromatics compounds (4ꢀ
nitrophenol, 2,4ꢀdinitrophenol, 2,4,6ꢀtrinitrophenol and 4ꢀ
nitroaniline) were purchased from Loba Chemicals, Mumbai.
All solutions were prepared in deionised water (18 MΩ cm,
Millipore Mili Q water).
To making Au/PANI nanofiber, 20 mL Auꢀ60 aqueous solution
was taken in a culture tube then different amount (in µL) of
distilled aniline monomer was added (Table S1) to Auꢀ60
aqueous solution with constant stirring until dissolving the
aniline at room temperature (25 oC). After adding
aniline,solution colour changed pinkish violate to deep blue to
black immediately indicating Au/PANI composite started to
form. The reaction mixture was kept in dark place without
stirring for 12 hs. Finally products were collected by
centrifugation at rpm 8000 and washed with water several times
o
finally dry under vacuum at 60 C temperature to obtain a dark
Instruments
powder of Au/PANIꢀcomposites.
To observe the surface morphology of composites, little amount
of prepared composites dispersed in Mili Q water then drop
casted on a glass cover slip and dried, at room temperature. We
used JEOL, JSM 6700F instrument, operating at 5 kV. To
reduce the surface potential, samples were coated with platinum
for 90 s due to accumulation of electrostatic charge.
The electron microscopy of Au/PANI nanostructure were
carried out by using HRTEM (JEOL, 2010EX), image were
taken using a CCD at an accelerating voltage of 200 kV.
Samples were spreaded over on a 200 mesh Cuꢀgrid coated
with a holey carbon support film.
Catalytic activity towards nitro compound reduction
For monitoring the reduction process, prepared yellow
aqueous solution of aromatic nitro phenols compounds (4ꢀ
nitrophenol, 4ꢀnitroaniline, 2,4 diꢀnitrophenol, 2,4,6ꢀtriꢀnitro
phenols) of 1 mM and 3 mM concentration of ice cold NaBH4
solution. Then in a quartz UV cell of 1 cm path length took 2
mL of water and added 100µL of aromatic nitrophenols
compounds, water dispersed Au/PANI composites subsequently
added Au/PANI (∼0.3 wt %) as a catalyst then immediately
added 100 µL of 3 mM NaBH4 solution. Now solution was
quickly subjected to UVꢀVis measurement for monitoring
reduction processes.6ꢀ7,22
UVꢀVis spectra of Au/PANI samples were recorded by using a
HewlettꢀPackard UVꢀVis spectrophotometer (model 8453) in a
1.0 cm path length quartz cell.
XRD measurements were performed by using a Bruker AXS
diffractometer (D8 advance) using CuKα radiation (λ=1.54 Å),
a generator voltage of 40 kV and a current of 40 mA. The
scanning rang of the samples 2θ=15ꢀ85o the scan rate was
1s/step with a step width of 0.02.
The FTIR spectra were carried out in a FTIRꢀ8400S instrument
(Shimadzu) using KBr pellets of the samples.
XPS was performed using a focused monochromatized MgꢀKα
Xꢀray source (1253.6 eV) in Omicron NanoꢀTechnology 0571
XPS instrument.
Results and Discussion
Morphological Studies
Nanostructures of Au/PANI were prepared with different
molar ratio of HAuCl4 to aniline and were checked by FESEM
observations (Fig.1). Spherical morphology of Au/PANI@0.0
(in absence of CA) was clearly seen in Fig.1a at equal molar
ratio of HAuCl4 to aniline. Whereas in presence of CA and at
the equal molar ratio of HAuCl4 to aniline, wormꢀlike nanofiber
morphology was observed. Important observation signified that
there were tremendous effects of CA on the formation of
Au/PANI nanostructures. It was also seen that morphology of
Au/PANI depended on the molar ratio of CA to aniline. Fibrous
Synthesis of Au/PANI@0.0 composite:
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012