V. Babel, B. L. Hiran
amount of reducing agents in presence of metal catalyst
based on gold, palladium, rhodium, ruthenium, and iridium
with PANI. The catalytic enhancement is due to the synergic
eꢀect between Ag, Pd and PANI. The improved activity is
because of electron delocalization between the d orbitals
of Pd and the PANI π-conjugated ligand. The PANI coat-
ing also protects the MOF support from direct exposure to
the corrosion and leaching. Several advantages of PANI
coating is also there. First AgPd NPs supported on PANI
is quite stable, furthermore the method of growing NPs is
awfully simple. In this work a series of MOF composites
were synthesized.
[
4–6]. However, a disadvantage of commercially oꢀered Pd
catalysts is their lack of chemo-selectivity. These catalytic
systems are unfortunately related with environmental issues
or formation of enormous undesired by-products. Supple-
mentary alteration of noble metals with suitable additives
was essential to improve the selectivity, but not at cost of
activity. While, the existence of other reducible functional
groups in the nitroarenes creates the dual necessities of activ-
ity and selective reduction of nitro group pretty challenging.
Leaching of metal from catalyst is also a major issue. The
degree of leaching is strongly sensitive to the nanoparticle
size, support material and most importantly reaction media
and conditions. Although amazing improvements have been
achieved but still the development of novel catalysts with
broad functional group tolerance and high activity signiꢁes
an important challenge.
Herein, we reported heterogeneously catalysed selective
reduction of nitroarenes using green reductant formic acid as
the source of hydrogen. We synthesised MOF-PANI-Metal
alloy composite (UiO-66-D-PANI-AgPd). In the ꢁrst step,
MOF (Zr based metal organic framework UiO-66) particles
were prepared by hydrothermal route. MOF was decarboxy-
lated by silver etching path. Then PANI was coated on the
surface of decarboxylated MOF (UiO-66-D) by chemical
(oxidative) polymerization method. In conclusion, AgPd
nanoalloy grown on the PANI coated MOF surface.
Recently, metal organic frameworks (MOFs) have estab-
lished as a promising class of porous materials with very
large precise surface area, high porosity, and chemical tun-
ability [7]. Because of these advantages and facile synthesis
of MOFs, have been accepted for common applications in
many ꢁelds, including gas storage, gas separation, lumi-
nescence, drug delivery, and catalysis [8–12]. MOFs allow
access to guest molecules similar to their pore size. A variety
of approaches have been taken to create comparatively large
pores in MOFs, including use of longer linkers, modula-
tors, defective crystallization, and templates [13–18] but the
silver-catalysed decarboxylation (silver etching) [7] is quite
interesting. It creates heterogeneous pores, even in highly
stable MOFs, without changing the unique structure. This
alteration in MOFs generates meso porosity which can allow
comparatively large guest molecules.
1.1 Silver Etching Method
5 mL Acetonitrile solution of UiO-66 (100 mg), Potassium
persulfate (135 mg, 0.5 mmol) and Silver nitrate (50 mg,
0.3 mmol) were allowed to react in Teꢂon-lined autoclave,
and placed in a preheated silicon oil bath at 120 ℃ for 1 h.
Decarboxylated MOF was centrifuged and washed three
times with water and acetone. It was activated by keep-
ing under vacuum for 1 h at 120 °C. This method was ꢁrst
introduced by Joeng et al. [7], they have described selective
breaking of carboxylic bond during modiꢁcation of MOFs,
this will create pores in MOFs.
To defeat the leaching obstruction and to improve the
performance of catalyst, alternative support materials must
be developed to achieve high dispersion, utilization, activ-
ity, and stability. To fulꢁl these requirements intrinsically
conducting polymer (ICP) class has attracted signiꢁcant
attention. After intensive research it is found that among all
ICPs polyaniline (PANI) is a ꢁnest choice because of con-
trollable conductivity, good chemical stability, high conduc-
tive property via doping with acids and, easy synthesis using
tremendously simple chemical oxidation of the low price
monomer (aniline) in aqueous solutions [19]. For PANI, It
is expected that the N atoms in carbon matrix may not only
act as an electron donor but also serve as anchoring sites for
the precursor.
1.2 Preparation of Catalyst
Preparation of UiO-66-D-PANI-AgPd: Decarboxylated
MOF (UiO-66-D) solution (250 mg, in 50 mL water) and
Aniline solution (93 µL, 1 mmol in 50 mL water with 5 mg
Sodium dodecyl sulphate SDS) were sonicated separately
for 1 h. Then both the solutions were mixed together on
an ice bath and acidic solution of Ammonium persulfate
(APS) (229 mg, 1 mmol in 25 mL 1 M HCl) was added
drop wise with continuous stirring. Solution remained on
stirring until green colour appeared. In this green suspension
10 mL aqueous solution of AgNO (10% by weight of MOF)
3
was added and stirred for 1 h. Further 10 mL aqueous solu-
tion of Pd(NO ) (10% by weight of MOF) was added and
3
2
AgPd nanoparticles (NPs) are found to be promising in
catalytic dehydrogenation of formic acid in aqueous medium
stirred for another 1 h, followed by addition of Hydrazine
hydrate (3 mL, 65%). Suspension was maintained at 90 °C
for 4 h with stirring. Catalyst was collected by centrifuga-
tion, washed three times with water and acetone and ꢁnally
activated by keeping under vacuum for 1 h at 120 °C.
[
20–22]. The AgPd NPs was supported on metal organic
framework for preparation of a heterogeneous nanocatalyst.
To enhance the activity of catalyst MOF is ꢁrstly coated
1
3
Babel, Vikram
