Syntheses of U3O8 nanoparticles form four different uranyl complexes: Their catalytic performance for various alcohol oxidations

Article abstract of DOI:10.1016/j.ica.2017.03.020

Two dinuclear complexes namely [(UO₂)₂(L1)₂(DMSO)₂] (1) and [(UO₂)₂(L2)₂(DMSO)₂] (2) of two Schiff base ligands 2-[(2-hydroxy-3-methoxy-benzylidene)-amino]-2-hydroxymethyl propane-1,3-diol (HL1) and 2-[(3,5-dichloro-2-hydroxy-benzylidene)-amino]-2-hydroxymethyl-propane-1,3-diol (HL2) obtained by condensation of the aldehydes 2-hydroxy-3-methoxy-benzaldehyde and 3, 5-dichloro salicylaldehyde with tris(hydroxymethyl)aminomethane ammine, have been synthesized. On the other hand, when the two aldehydes were treated with uranyl nitrate two mononuclear complexes, [(UO₂)(L3)₂(DMSO)₂] (3) and [(UO₂)(L4)₂(DMSO)₂] (4), are obtained. The complexes are then heated at 800?°C in open atmosphere to obtain the U₃O₈ nanomaterials as the final product. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to characterize the so obtained the U₃O₈ nanoparticles. Studies shows the synthesized U₃O₈ nanoparticles obtained from different complexes were different as far as morphology and size are concerned. All four different U₃O₈ nanoparticles explored as oxidising catalyst to oxidize alcohols where morphology of the nanoparticles controls the catalytic efficiency.

Full text of DOI:10.1016/j.ica.2017.03.020

Accepted Manuscript
Research paper
Syntheses of U3O8 nanoparticles form four different uranyl complexes: their
catalytic performance for various alcohol oxidations.
Ishani Majumder, Sourav Chatterjee, Roland C. Fischer, Swarup Kumar Neogi,
Franz A. Mautner, Tanmay Chattopadhyay
PII:
S0020-1693(16)31066-0
http://dx.doi.org/10.1016/j.ica.2017.03.020
ICA 17480
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
28 December 2016
14 March 2017
15 March 2017
Please cite this article as: I. Majumder, S. Chatterjee, R.C. Fischer, S.K. Neogi, F.A. Mautner, T. Chattopadhyay,
Syntheses of U3O8 nanoparticles form four different uranyl complexes: their catalytic performance for various
alcohol oxidations., Inorganica Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.03.020
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Syntheses of U3O8 nanoparticles form four different uranyl complexes:
their catalytic performance for various alcohol oxidations.
a
Ishani Majumder, Sourav Chatterjee, Roland C. Fischer, Swarup Kumar
b
c
d
*,e
Neogi, Franz A. Mautner, TanmayChattopadhyay,*,b
a
Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata-700 009, India
b
Department of Chemistry, Panchakot Mahavidyalaya, Sarbari, Purulia, Pin-723121, India,E-
mail:tanmayc2003@gmail.com
c
Institut fuer Anorganische Chemie, Technische Universitaet Graz, A-8010 Graz, Austria.
dDepartment
of
Physics,
Adamas
University,
Barasat
Barrackpore
Road,
P.O. Jagannathpur, Kolkata-700126, West Bengal,India
e
Institut fuer Physikalische and Theoretische Chemie, Technische Universitaet Graz, A-8010,
Graz, Austria, E-mail:mautner@tugraz.at
ABSTRACT
Two Dinuclear complexes namely [(UO ) (L1) (DMSO) ] (1) and [(UO (L2) (DMSO) ] (2) of
2 2 2)2
2
2
2
2
two Schiffbase ligands2-[(2-Hydroxy-3-methoxy-benzylidene)-amino]-2-hydroxymethyl propane-
1,3-diol (HL1) and 2-[(3,5-Dichloro-2-hydroxy-benzylidene)-amino]-2-hydroxymethyl-propane-1,3-
diol (HL2) obtained by condensation of the aldehydes 2-Hydroxy-3-methoxy-benzaldehyde
and
3, 5-Dichloro salicylaldehyde with Tris(hydroxymethyl)aminomethane ammine, have
been synthesized. On the other hand, when the two aldehydes were treated with uranyl nitrate two
mononuclear complexes, [(UO2)(L3)2(DMSO)2] (3) and [(UO2)(L4)2(DMSO)2] (4), are obtained.
The complexes are then heated at 800°C in open atmosphere to obtain the U3O8 nanomaterials as the
final product. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission
electron microscopy (TEM) were employed to characterize the so obtained the U3O8
.
nanoparticles
Studies shows the synthesized U3O8 nanoparticles obtained from different complexes were different
as far as morphology and size are concerned. All four different U3O8 nanoparticles explored as

oxidising catalyst to oxidize alcohols where morphology of the nanoparticles controls the catalytic
efficiency.
Keywords: Schiff-base; Uranyl nitrate; Nanoparticles,Alcohol Oxidation, Morphology dependent
catalysis
1. Introduction
An unusual and remarkable characteristic of metal oxide nano particles is that their surface
energies per unit volume can be easily tuned or controlled just by slight modification in thermal and
chemical conditions. Therefore synthesis of these nanoparticles having various phases and
morphologies has become prime interest to interest to researchers, as it is possible to direct the
physical/chemical properties of these materials just by regulating their phase and morphology. As
a result they have vast and potential applications in various fields like optics, electronics,
magnetics, and catalysis[1]. Among the above mentioned fields, here we are specially interested
towards the application of nano materials as catalyst because catalysts are the vital requirement for
proficient conversion of raw materials into different essentials of modern livelihood. And also
nano materials can be considered as potential catalyst due to their active surface and interfacial
atom effect, high reactivity, low catalyst loading, environmentally gentle nature, easy recovery
and reusability [2-11]. Here we have chosen Uranium as the metal for the preparation of metal oxide
nano particles because it may demonstrate ways for re-consumption of vast amount of depleted
uranium, resulted from enrichment manufacture[12-14].Although there are plenty of reports in
literature that uranium oxide nanoparticles can exhibit admirable catalytic actions for demolition of
volatile organic compounds (VOCs) and for selective reduction of NO at suitable
temperatures[12,15-16], but there are lack of information for using it in catalytic purposes in
synthetic chemistry [17]. Also the reported synthetic procedure for Uranium oxide nano particles
are infrequent in comparison with main group elements,3d elements or 4f elements. All of this lack
of investigations therefore motivated us towards our present work where we synthesize the uranium
oxide nanoparticles by very simple but effective manner just by employing the pyrolytic reaction to
our four synthesized complexes [(UO ) (L1) (DMSO) ] (1), [(UO (L2) (DMSO) ]
2)2
(2),
2
2
2 2
2
2
[(UO (L3) (DMSO) ] (3), [(UO (L4) (DMSO) ] (4). Where the ligands L1 and L2 are
2) 2)
2
2
2
2
Schiff bases and L3 and L4 are their corresponding aldehydes. Interestingly, all of the

complexes give U3O8 nanoparticles with various morphologies as the end product of the pyrolytic
reaction. The synthesis, characterization of the metal complexes and metal oxide nanoparticles and
the morphology dependent catalytic oxidation of the nanoparticles towards aromatic alcohols are
vividly portrayed in thismanuscript.
Scheme 1.
2. Experimental Section
2.1. Physical Methods and Materials.
The chemicals used for this work were purchased from commercial agencies and used as
obtained. Solvents were distilled and dried according to standard procedure before using in the
experiment. Water used in all physical measurement and experiments was Milli-Q grade.3,5-Dichloro
salicylaldehyde, 2-Hydroxy-3-methoxy-benzaldehyde,Tris(hydroxymethyl)aminomethane, Benzyl
alcohol and other alcohols were purchased from Aldrich and used in oxidation experiments without
further purification. Uranyl nitrate hexahydrate was also purchased from Sigma.
PerkinElmer 240C analyzer was used for elemental analysis (carbon, hydrogen and
nitrogen).
Shimadzu FT-IR 8400S and PerkinElmer Spectrum Express Version was used for recording
-1
Infrared spectra (4000-400 cm ) using KBr pellets as mediums. Shimadzu UV-2450PC
spectrophotometer with multiple cell-holders and thermostat were used to supervise the UV-
1
13
visible spectra. Bruker AV300 Supercon NMR spectrometer was used for recording H and
C
NMR spectra (300 MHz) in CDCl and using the solvent signal as the internal standard in a 5 mm
3
BBO probe. Waters Xevo GT S Q-TOF mass spectrometer was used for recording the
electrospray ionization massspectra.
Mettler Toledo (TGA/SDTA851) thermal analyzer was used for thermo gravimetric analysis
(TG-DTA) in flowing dinitrogen (flow rate: 30 cm3min-1). JEOL JSM-6700F field-emission
microscope was utilized to carry out the Field Emission Scanning Electron Microscopic (FE-
SEM) measurement. JEOL (Japan) JEM2100 high-resolution transmission electron microscope was
employed for Transmission Electron
Microscopic
(TEM)
measurement. XPERT-PRO
Diffractometer monochromated Cu-Ka radiation (40.0 kV, 30.0 mA) was used for X-ray powder
diffraction (PXRD) at room temperature. Zetasizer Nano ZS; Malvern Instruments, Malvern, UK was
used to execute dynamic Light Scattering experiments (DLS). Micromeritics Tristar 3000 surface
area analyzer was utilized for the BETanalysis.

2.2. Synthesis of the complex
For preparation of all the four complexes the subsequent common template synthetic procedures were
taken on. Firstly the ligand solution were prepared in situ via condensation of 3,5-Dichloro-2-
hydroxy-benzaldehyde and 2-Hydroxy-3-methoxy-benzaldehyde as the aldehydes with the
corresponding amine as (Tris-(hydroxymethyl)aminomethane) with maintaining the same molar ratio
and then the methanolic solution of uranyl nitrate hexahydrate was added in this mixture to obtain
the complexes 1 and 2. The other two complexes (i.e complex 3 and 4) were prepared just by reaction
with the aldedydes (HL3 and HL4) with uranyl nitrate hexahydrate solution. Their synthesis,
composition and other physicochemical characteristics are specified underneath.
2.2.1 [(UO2)2(L1)2(DMSO)2] (1)
A methanolic solution (5 mL) of Tris(hydroxymethyl)aminomethane (91 µL,1 mmol) was added
to a methanolic solution (5 mL) of 2-Hydroxy-3-methoxy- benzaldehyde (0.152 g,1 mmol) in a drop
wise mode and the resulting solution was refluxed for about 30 mins. Then a methanolic solution (5
mL) of uranyl nitrate hexahydrate (0.502 g, 1 mmol) was added to this ligand and further refluxed for
about 30 mins. The resulting dark orange colored solution was filtered and kept in a CaCl2 desiccator.
The crude product so obtained after evaporation of the solvent was collected, washed and further
recrystalised in DMSO medium. The dark orange colored single crystals appropriate for the X-Ray
diffraction were achieved from this recrystalisation procedure (yield 75%). Anal. Calcd for
C28H42N2O16S2U2: C, 27.95; H, 3.49; N, 2.32. Found: C, 27.87; H, 3.86; N, 2.27. IR (KBr): ν(C=N)
1625 cm−1; ν (skeletal vibration) 1532 cm−1; UV/vis (DMSO): λmax/nm (ε/dm3mol−1cm−1) =
267(3676), λmax/nm (ε/dm3mol−1cm−1) = 405(1778).
2.2.2 [(UO2)2(L2)2(DMSO)2] (2)
A methanolic solution (5 mL) of Tris(hydroxymethyl)aminomethane (91 µL,1 mmol) was added
to a methanolic solution (5 mL) of 3,5-Dichloro-2-hydroxy benzaldehyde (0.191 g, 1mmol) in a drop
wise mode and the resulting solution was refluxed for about 30 mins. Then a methanolic solution
(5 mL) of uranyl nitrate hexahydrate (0.502 g, 1 mmol) was added to this ligand and further
refluxed for about more 30 mins. The resulting dark orange colored solution was filtered and kept
in a CaCl desiccator. The crude product so obtained after evaporation of the solvent was
2
collected, washed and further recrystalised in DMSO medium. Which were further recrystalised
from ethanol for purification of the compound (yield 70%). Anal. Calcd for C26H34N2O14S2U2Cl4: C,

24.37; H, 2.65; N, 2.18. Found: C, 24.17; H, 2.86; N, 2.17. IR (KBr): ν(C=N) 1625 cm−1; ν
−1
−1
−1
3
(skeletal vibration) 1512 cm ; UV/vis (DMSO): λmax/nm (ε/dm mol cm )= 257(3338), λmax/nm
−1
−1
3
(ε/dm mol cm ) = 428(2233).
2.2.3 [(UO2)(L3)2(DMSO)2] (3)
A methanolic solution (5 mL) of uranyl nitrate hexahydrate (0.502 g, 1 mmol) was added in a drop
wise mode to a methanolic solution (5 mL) of 2-Hydroxy-3-methoxy-benzaldehyde (0.152 g, 1
mmol) followed by 30 min reflux. The resulting dark red solution was then filtered and kept in a
CaCl2 desiccator. The crude product so obtained after evaporation was collected, washed and further
recrystalised in DMSO medium. Which were further recrystalised from ethanol for purification of the
compound. Anal. Calcd for C20H26O10S2U1: C, 32.96; H, 3.43; Found: C, 32.36; H, 3.22; IR (KBr):
ν(C=N) 1695 cm−1; ν (skeletal vibration) 1535 cm−1. UV/vis (DMSO): λmax/nm (ε/dm3mol−1cm−1)
= 264(3642), λmax/nm (ε/dm3mol−1cm−1) = 449(1303).
2.2.4[(UO2)(L4)2(DMSO)2](4)
A methanolic solution (5 mL) of uranyl nitrate hexahydrate (0.502 g, 1 mmol) was added in a
drop wise mode to a solution (5 mL) of 3,5-Dichloro-2-hydroxy benzaldehyde (0.191 g, 1 mmol)
followed by 30 min reflux. The resulting dark red solution was then filtered and kept in a CaCl
2
desiccator. The crude product so obtained after evaporation was collected, washed and further
recrystalised in DMSO medium. The dark red colored single crystals appropriate for the X-Ray
diffraction were achieved from this recrystalisation procedure (yield 70%). Anal. Calcd for
C18H18O8S2U1Cl4: C, 26.79; H, 2.23; Found: C, 26.87; H, 2.06; IR (KBr): ν(C=N) 1625 cm−1; ν
−1
−1
(skeletal vibration) 1532 cm−1; UV/vis (DMSO): λmax/nm (ε/dm mol cm ) = 262(4937), λmax/nm
3
(ε/dm3mol−1cm−1) = 429(1706).
2.3 Alcohol oxidation study of catalysts
To 1 mmol solution of the aromatic alcohol in EDC solvent, 1.25 mmol of PhI(OAc)2 and 300 mg
of the MgSO4 along with 0.01 mmol of Uranium oxide nanoparticles were added. The mixture was
stirred about 8 to 10 hrs at 45°C using TLC to monitor the sequence. After completion of the reaction,
it was filtered, the solvent was then evaporated, the crude was purified by coloum chromatography
and the final product was characterized by 1H-NMR spectroscopy.

2.4. X-ray data collection and crystal structure determination:
The X-ray single-crystal data of compounds 1 and 4 were collected on a Bruker-AXS APEX-II CCD
and Bruker-AXS microsource diffractometer. The crystallographic data, conditions retained for the
intensity data collection and some features of the structure refinements are listed in Table 1.
The intensities were collected with Mo-Kα radiation (λ= 0.71073 Å). Data processing, Lorentz-
polarization and absorption corrections were performed using SAINT, APEX and the SADABS
computer programs [18]. The structures were solved by direct methods and refined by full-matrix
2
least-squares methods on F , using the SHELXTL [19] program package. All non-hydrogen atoms
were refined anisotropically. The hydrogen atoms were located from difference Fourier maps
assigned with isotropic displacement factors and included in the final refinement cycles by use of
geometrical constraints. Molecular plots were performed with the Mercury [20] program with a
version of 3.8.
CCDC 1500829-500830 contain the supplementary crystallographic data for this paper. These data
can be obtained free charge from the Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/5datarequest/cif.
Table 1.
3. Results and Discussion
3.1. Synthesis, Rationalization, and Characterization of the Metal-Complexes
Complex 1 and 2 were prepared by general template synthetic procedure. Firstly the Schiff
base ligands were synthesized by combining between 2-Hydroxy-3-methoxy-benzaldehyde(HL1),
2,5-Dichloro-2-hydroxy
benzaldehyde
(HL2)
and
the
corresponding
ammine
(Tris(hydroxymethyl)aminomethane), then a methanolic solution of uranyl nitrate hexahydrate was
added to obtain the complexes. On the other hand, complex 3 and 4 are synthesized just by treating
the aldehydes with the methanolic solution of Uranyl nitrate. In some cases for complex 1 and 4 single
crystals suitable for X ray diffraction analysis were obtained.
3.2. IR and UV-Visible Spectra of the complexes
The FTIR spectra of compounds 1-4 are shown in Fig. S1-S4. Complexes 1 and 2 show bands
-1
due to C=N stretch in the region 1625 cm and complexes 3 and 4 show bands in the region of
-1
1693-1695 cm due aldehydic C=O stretch. All the complexes show skeletal vibration in the region

-1
1516-1532 cm . Electronic spectra of all the complexes have been studied in DMSO medium
(Fig. S5-S8). Two distinct peaks have been recognized in all the cases. The first ones in the region
of 257-267 nm which are due to the π-π* transition of the imine group [21]. The red-shifted peak
around the region of 405-450 nm are due to the LMCT (5f of Uranium to Oxygen 2p) [21].
3.3. Solution studies: Mass Spectrometry
For better understanding of the solution phase structure or composition of the complexes Mass
spectral study has been executed (Figures S9-S12). The spectral analysis reveals that complexes
1 and 2 exhibit similar solution structure as both of them shows a base peak at 564.1184 amu
and 602.9757 amu respectively, which corroborates well with the dinuclear uranium species
[(UO (L1/L2) (H O) ].2Na+, (calc.m/z 564.0860 amu and 602.9640 amu respectively). Complexes
)
2 2
2
2
2
3 and 4 also behave similarly in solution and show the base peaks at 441.5513 and 497.8875 amu
respectively which corroborates well with the mononuclear species [(UO )(L1/L2)(H O)2]+, (calc.
2
2
m/z 441.5800 and 497.8860 amu respectively).
3.4.Crystal Structure Descriptions.
Single crystal structural analyses reveal that 1 consists of four crystallographically indipendent
neutral centrosymmetric dinuclear [UO2(L1)(DMSO)]2 subunits, whereas 4 consists of mononuclear
complexes [UO2(L4)2(DMSO)2]. Since the four dinuclear [UO2(L1)(DMSO)]2 units in the unit cell
have similar geometries (Table 2), we describe here only one dinuclear entity as representative (Fig.
1). In this complex the metal is coordinated by N(1) and six oxygen donor atoms. The UO6N
chromophore may be described as compressed pentagonal bipyramid with the uranyl oxygen atoms
O(6) and O(7) located in the axial sites [U(1)-O(6) = 1.792(9), U(1)-O(7) = 1.813(10) Å, O(6)-U(1)-
O(7) = 178.8(4)°]. The L1 ligand is chelating the U(1) via O(1) and N(1) donors [U(1)-O(1) =
2.278(7), U(1)-N(1) = 2.590(10) Å, O(1)-U(1)-N(1) = 69.6(3)°] and bridging U(1) and
centrosymmetric U(1’) [(‘) –x,2-y,1-z] via O(3) donor atom to generate the dinuclear subunit. The
bond parameters within the four membered planar U2O2 ring are: U(1)-O(3) = 2.351(7), U(1)-O(3’) =
2.341(7), U(1)…U(1’) = 3.8930(7) Å, U(1)-O(3)-U(1)’ = 112.1(3); O(3)-U(1)-O(3’) = 67.9(3)°].
Coordination number seven is completed by O(8) donor atom of a terminal DMSO molecule located in
equatorial site [U(1)-O(8) = 2.360(9) Å]. Oxygen atoms O(2), O(4) and O(5) of L1 molecule are not
ligated to uranium centers, but are involved in hydrogen bonds of type O-H…O to generate a
supramolecular 2D system oriented along the a- and b-axis of the triclinic unit cell (Table S1).

The equatorial sites of pentagonal bipyramid around U(1) of mononuclear complex 4 (Fig. 2) are
occupied by O(1) and O(2) donor atoms of a chelating ligand molecule L2 [U(1)-O(1) = 2.314(2),
U(1)-O(2) = 2.517(2) Å O(1)-U(1)-O(2) = 68.58(8)°], O(3) donor of a second L2 molecule which
act only as terminal ligand [U(1)-O(3) = 2.308(2) Å], and O(5) and O(6) donor atoms of two
terminal DMSO molecules [U(1)-(O5) = 2.367(2), U(1)-O(6) =2.402(2) Å]. The axial sites of the
UO7 chromophore are occupied by the uranyl oxygen atoms O(7) and O(8) [U(1)-O(7) = 1.779(3),
U(1)-O(8) = 1.785(3) Å, O(7)-U(1)-O(8) = 175.73(11)°] (Table 3).
Table 2.
Fig. 1
Table 3.
Fig. 2
3.5. Synthesis, Rationalization, and Characterization of the Metal-Oxide Nanoparticles.
3.5.1. Synthesis of U O Nanoparticles.
3 8
For the typical preparation of U3O8 nanoparticles, all the four complexes (1-4) were placed
inside in a Teflon lined stainless steel autoclave sealed in platinum crucible and heated for 3 hr at
800ºC temperature. After 3 hr the crucible was left to cool at room temperature. After cooling the
final product was collected and washed a number of times with ethanol and vacuum dried.
3.5.2. Characterization of theNanoparticles.
3.5.2.1. Thermogravimetric Analysis.
Thermogravimetric analysis was employed to evaluate the thermal behavior of the complexes
which are used as precursors of the nanoparticles. Detailed analysis of the thermogramms (Fig.
S15a) reveal that Complex 1 and 2 gives U3O8 as stable end product directly as evident from the
pyrolytic reaction [exp.weight loss = 29.93% (calcd 29.95%) for complex 1] and [exp. weight loss
= 36.24% (calcd 34.21%) for complex 2]. But for Complex 3 and 4 the end product of the thermal
reaction is the UO nano particles as evident from the TG diagram (Fig. S15b) [exp.weight loss =
2
59.26% (calcd 61.21%) for complex 3 and [exp. Weight loss = 65.24% (calcd 66.34%) for complex 4].
The UO nano particles so formed is then readily transformed into U O nano particles through
2
3
8

thermal treatment in air as we have kept the Platinum crucible in 800°C for few hours in the
preparation of nano particles. Because of the high temperature the nano crystalline UO2 particles re-
crystallize and further oxidized into the more stable U3O8 form, as reported by other groups [17, 22-
23]
3.5.2.2. Powder X-ray DiffractionAnalysis.
The nanoparticles are named as UNP1, UNP2, UNP3 and UNP4 according to their synthetic
precursors respectively. Fig. 3 corresponds to the XRD patterns of all the U3O8 compounds. It reveals
that all of the samples are polycrystalline in nature. The observed peaks in this XRD pattern
corroborates well with those of the orthorhombic α-U3O8 structure[24]. It is reported in literature
that U3O8 exists as mixed-valent Uranium (V/VI) compound in a molar ratio of 2 : 1. In general,
the compound U3O8 crystallizes into three different polymorphs: (i) conventional orthorhombic α-
U O and two high- temperature variations (ii) hexagonal U O (iii) orthorhombic β-U O [25-26].
3 8
3
8
3
8
However, in the present work, the peaks observed in the XRD pattern represented in Fig. 3 can be
indexed with that of orthorhombic α-U3O8 structure[26]. So, in contrast with the reported XRD pattern
of the orthorhombic α-U3O8 [21] the XRD pattern of our compound UNP1 (U3O8) demonstrates
almost comparable intense (001) and (130) reflections. But for the other two compounds U3O8 (UNP2)
and U O (UNP3), (001) reflection is comparatively more intense than the other (130) peak,
3 8
suggesting these two compounds [U3O8 (UNP2) and U3O8 (UNP3)] the particles are
preferentially oriented along a definite direction. However, in case of U O (UNP4), intensities of
3 8
the (001) and (130) reflections are equivalent along with some additional reflections (highlighted in the
Fig. 3). Those additional reflections do not match with reflections of β-U O and γ-U O phases hence
;
3
8
3
8
we can conclude that these reflections are due to another α-U3O8 phase with somewhat different lattice
constants. As no additional peaks of impurity have been found in the entire XRD pattern, signifies
that the obtained nano-crystalline U O via this synthesis method are absolutely pure in nature.
3 8
Moreover, it is evident from the XRD pattern that the broadening of the diffraction peaks indicates
small size of the particles in thesecompounds [27].
Fig. 3

3.5.2.3. Scanning Electron Microscopy Analysis.
The Scanning electron microscopic (SEM) analysis helps us to evaluate the morphology and
particle size of the metal oxide nanoparticles so prepared (Fig. 4). It is evident from the
micrograph that the nano materials exist in different morphological shapes with an average size range
of 50-100 nm. Detail assessment of the micrograph reveals that UNP1 have irregular shape
morphology, while UNP2 have very small granule like structure. UNP3 have particle like
morphology whereas UNP4 have distinct petals like structure. The roughened edges of the
surface of the particles as noticed from the respective SEM images indicating the slow growth of the
nano particles by a process of oriented accumulation of small primary nanocrystals.
Fig. 4
3.5.2.4. Dynamic Light Scattering.
Dynamic light scattering experiment was carried out to determine of the hydrodynamic
size of the NPs. The representative DLS graph so obtained, indicates the formation of stable and non
aggregated particles with
a
mean diameter of 70 20 nm and 50 20 nm for all U3O8
(UNP1,UNP2,UNP3 and UNP4)nanoparticles respectively (Fig. 5). Thef our types of nano
particles (UNP1, UNP2, UNP3 and UNP4) are indexed with the PDI values of 0.616, 0.465,
0.515, 0.475 respectively. The estimated size distribution histograms (Fig. 5 and Fig. S16) and the
PDI values authenticated their size distribution and good stability in waterrespectively.
Fig. 5
3.5.2.5. Transmission Electron MicroscopyAnalysis.
Transmission Electron Microscopic analysis were performed to obtained the actual size i.e the
diameter of the nano particles in solid state. Thorough examination of the TEM images in Fig. 6 of
the four nano particles demonstrates that all the nano particles exhibit nearly spherical geometry.
UNP1, UNP3 and UNP4 nano particles display a mean size of 30 10 nm. Whereas for UNP2, the
average diameter becomes smaller compared to the other and exhibits a diameter of 5 2 nm. Both
the TEM and DLS experiments measure the diameter of the nano particles, but the diameter obtained
from TEM analysis is found to be quite smaller with respect to the diameter obtained from DLS,
which is quite obvious as TEM analysis gives the size of the nano’s in dried state whereas, DLS gives
the hydrated diameter. Actually, from the Transmission electron microscopy, the images we obtained

is for single particle, whereas for DLS gives the hydrodynamic diameter which is biased toward the
larger-size end of the populationdistribution.
Fig. 6
3.5.2.6. Energy-Dispersive X-ray Spectroscopy.
EDX spectrum of the NPs are represented in Fig. S17 and S18.U and O signals come from
the U3O8 nanoparticles. Small signals of other elements are due to presence of those elements in
water. And for UNP3 the EDX spectrum gives a signal of copper which is due to the copper grid. The
Platinum (Pt) signals come from the coating material of the instrument.
3.6. Catalytic Oxidation ofAlcohols.
Fractional oxidation of benzyl alcohol in various solvent employing UOx/MCM-41
materials as the catalyst has been previously reported.[28] But incorporation of these solvents in the
catalytic reaction produces by-products in the reaction system and thereby it is becoming hard to
separate the preferred material from the solvent. To avoid this complication in product separation
and to minimise the formation of by-products, solvent-free conditions are employed by other
groups.[28] But in all of the above cases generally t-BuOOH or H2O2 are used as the oxidant in
catalytic reaction which sometimes leads to chemical transformation of the UO nano species.[17,28]
x
Therefore, to avoid or minimise the above mentioned problems, in our present case, using our
synthesized uranium nanoparticles as catalyst we employed PhI(OAc) as a very simple but effective
2
oxidant and EDC (ethylenedichloride) as the solvent employing the similar oxidation methods as
reported by other groups using Mn O as catalyst.[29]
2 3
The method of oxidation was followed as same as reported earlier. [29] The 1 mmol of the benzyl
alcohol as the precursor was mixed with 0.01 mmol of the Urenium Oxide nanoparticles , 1.25 mmol
of PhI(OAc)2 and 300 mg of the MgSO4 using 25 mL ethylenedichloride (EDC) as solvent. The
resulting mixture was stirred in a magnetic stirrer maintaining 45°C temperature until the reaction
reached completion. The conversion was monitored by doing TLC of the reaction mixture at a definite
time interval. After completion of the reaction the mixture was filtered through a sintered funnel, the
residue was collected and washed with the mother solvent (EDC). Then the combined filtrate was
transferred in a separating funnel and extracted with water and the extract was collected over activated
MgSO4 for absorption of excess moisture. The EDC was then evaporated under rotary evaporator. The

crude so collected was then further purified by column chromatography to obtain the aldehyde as the
final product. EDC was used as the suitable solvent for the oxidation because the other solvents like
water, methanol, ethanol, acetoniltrile, DCM, chloroform or THF are found to be not so much efficient
for the conversion. The schematic representation of the alcohol oxidation was represented in the
following scheme.
Scheme 2.
First the benzyl alcohol was used as substrate for the oxidation purpose using UNP1 to UNP4 as the
catalyst. Among the obtained U3O8 nanoparticles, UNP1 and UNP2 displays significant activities for
the catalytic oxidation of benzyl alcohol into benzaldehyde compared with the other two nanoparticles
(UNP3 and UNP4). When the reaction achieves the maximum time (i.e. 8 hr) the UNP2 leads to 60%
oxidation of benzyl alcohol, where as the UNP1 shows 55% oxidation. The other nano particles
UNP3 and UPN4 shows 30% and 35% conversion respectively. Here conversion of the benzyl
alcohol has been plotted against the reaction time at 45°C (Figure 7). To demonstrate the
recyclability of the catalyst the experiments were repeat about five times as described in later section.
Fig. 7
To further analyse the higher catalytic activity of UNP2 among the others, the textural properties i. e.
surface area of all the four nano particles were investigated by Brunauer–Emmett–Teller (BET)
gas-sorption measurements performed at 77 K for the as-dried powder sample under vacuum, as
shown in Fig. S19. The BET adsorption isotherm for the determination of surface area of finely
divided solid is given by according to the following equation [30].
……………………..(1)
Where, W= weight of gas adsorbed, P/P = relative pressure, Wm = weight of adsorbate as
0
monolayer, C = BET constant. From the plot of 1/(W((Po/P)-1)) vs P/P the specific surface area of
0
2
2
2
UNP2 (30.02 m /gm) and UNP1 (27.35 m /gm) is found to be higher than UNP3(15.37m /gm)
2
and UNP4 (16.55 m /gm). Generally, it is considered that the higher the surface area, the higher is the
catalytic performance if the same material is used as a catalyst. This corroborates well with the

experimental data obtained from the benzyl alcohol oxidation. As UNP2 has the smallest size and
highest surface area according to the TEM analysis and BET data, so it is reasonable why it
becomes the most efficient catalyst among the rest. The good catalytic activity of the UNP2 was
further estimated employing various types of alcohols under the above mentioned reaction
conditions (Table 4). The benzyl alcohols having activated and deactivated groups were used as
substrates in this oxidation to obtain the aldehyde as the main product. And negligible amount acids as
side product are also obtained (Table 4). Amusingly, it is observed that the deactivated alcohol
demonstrating the highest rate of conversion over the other activated and normal benzyl alcohol as
also reported in case of Mn O nano particles by others[29].
2 3
Table 4.
3.7. Reusability and Recyclability of the Nanoparticles asCatalyst
The recycling effectiveness i.e reuse in several cycles is an important criterion for an
excellent catalyst. For this very purpose we have chosen benzyl alcohol as a substrate and UNP2 as
catalyst as a representative case for these recycling experiments. After each reaction cycle the catalysts
are recovered and then washed thoroughly with acetonitrile and dried at 100°C for 2h. At the end of
the 5th cycle the used catalyst has been further characterized by Powder XRD study, Scanning
electron microscopy as well as by Transmission electron microscopy (Fig. 8). Comparing all the
experimental results of the used catalyst with original one it is easy to conclude that no
significant change has been takes place in the catalyst after oxidation reaction.Taking into account
the catalyst loss during the recycling, the catalytic performance of the samples is quite stable,
especially for the recycled samples. In other words the catalysts are recyclable as well as reusable.
Fig. 8
4. Conclusions
We successfully synthesized U3O8 nanoparticles form four different Uranyl-Schiff-base
complexes in high yields through a facile pyrolytic route. The prepared U3O8 nanoparticles showed
different morphological shapes with average size ranges of 50-100 nm. Catalytic testing revealed that
the catalytic activity of the porous U3O8 nanoparticle (UNP2) was distinctly superior to that
of other U3O8 nanoparticles for the oxidation of various alcohols to corresponding aldehydes.

The present results propose that the catalytic performance of U3O8 nanoparticles is morphology-
dependent.
Acknowledgement
Financial support by the Science and Engineering Research Board (a statutory body under DST, New
Delhi, India (F. No. SB/FT/CS-185/2013 dt. 30-06-2014) is gratefully acknowledged by TC.
F.A.M acknowledges partial support by NAWI Graz. I. M is thankful to UGC, India
[UGC/689/Jr Fellow(Sc) Upgradation ] for providing fellowship.
References
[1] C. Burda, X. Chen, R. Narayanan, M. A. El-Sayed, Chem. Rev. 105 (2005) 1025.
[2] V.Polshettiwar, J.M. Basset, ChemSusChem. 5 (2012) 6.
[3] B. C. Ranu, D. Saha, D. Kundu, N. Mukherjee, Wiley-VCH. (2013).
[4] R. S. Varma, Sustainable Chem. Processes. 2 (2014) 11.
[5] Z. Chen, Z. Jiao, D. Pan, Z. Li, M. Wu, C.H. Shek, C. M. L. Wu, K. L. L. Joseph, Chem. Rev. 112
(2012) 3833.
[6] W. Weifeng, C. Xinwei, C. Weixing, G. I. Douglas, Chem. Soc. Rev. 40 (2011)1697.
[7] O. Giraldo, S. L. Brock, W. S. Willis, M. Marquez, S. L. Suib, S. Ching, J. Am. Chem. 427 Soc.
122 (38) (2000) 9330.
[8] V. Polshettiwar, B. Baruwati, R. S. Varma, ACS Nano. 3 (2009) 728.
[9] Z. Hao, C. Gaoping, W. Zhiyong, Y. Yusheng, S. Zujin, G. Zhennan, Nano Lett. 8 (2008) 430
2664.
[10] Y. Hirao, C. Yokoyama, M. Makoto, Chem. Commun. (1996) 597.
[11] E. A. Kotomin, Y. A. Mastrikov, E. Heifets, J. J. Maier, Chem. Chem. Phys. 10 (2008)

433 4644.
[12] G. J. Hutchings, C. S. Heneghan, I. D. Hudson, S. H. Taylor, Nature. 384 (1996) 341.
[13] S. H. Taylor, C. S. Heneghan, G. J. Hutchings, I. D. Hudson, Catal. Today. 59 (2000)
436 249.
[14] K. Vidya, S. E. Dapurkar, P. Selvam, S. K. Badamali, D. Kumar, N.M. Gupta, J. Mol.
438 Catal. 181 (2002) 91.
[15] T. Campbell, M. A. Newton, V. Boyd, J. Phys. Chem. B. 109 (2005) 2885.
[16] H. Madhavaram, H. Idriss, J. Catal. 224 (2004) 358.
[17] Q.Wang, G-D. Li, S. Xu, J-X. Li, J-S Chen, J. Mater. Che. 18 (2008) 1146.
[18] Bruker (2005) SAINT v. 7.23; Bruker (2008) APEX; Bruker AXS Inc. Madison, Wisconsin,
USA.
[19] G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112.
[20] C.F. Macrae, P.R. Edington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, , T. Towler, J.
Streek, J. Appl. Cryst. 39 (2006) 453.
[21] M. S. Bharara, K. Strawbridge, J. Z. Vilsek, T. H. Bray, A. E. V. Gorden, Inorg. Chem. 46
(2007) 8309.
[22] F. Valdivieso, M. Pijolat, M. Soustelle, J. Jourde, J. Sol. State Ionics. 117 (2001) 141.
[23] F. Valdivieso, V. Francon, F. Byasson, M. Pijolat, A. Feugier, V. Peres, J. NuclearMaterials.
354 (2006) 85.
[24] Q. Wang, G. Dong Li, S. Xu, J. X. Li, J. S. Chen, J. Mater. Chem. 18 (2008) 1146.
[25]
[26]
J. Selbin, J. D. Ortego, Chem. Rev. 69 (1969) 657.
H. R. Hoekstra, S. Siegel, L. H. Fuchs, J. J. Katz, J. Phys. Chem. 59 (1955) 136.
[27] Z. Tohidiyan, I. Sheikhshoaie, M. Khaleghib, J. Appl. Chem. 10 (2016) 71.

[28] D. Kumar, R. P. Bhat, S. D. Samant, N. M. Gupta, Catal. Commun. 6 (2005) 627.
[29] H. Rahaman, R. M. Laha, D. K. Maiti, S. K. Ghosh, RSC Adv. 5 (2015) 33923.
[30] S. Brunauer, P. H. Emmett, E. Teller, J. Am. Chem. Soc. 60 (1938) 309.

1
Scheme 1. Schematic representation of the four ligands.
Fig. 1 Perspective view of a representative dinuclear unit of 1 together with the atom numbering
scheme. Symmetry code: (‘) –x, 2-y,1-z

1
Fig. 2 Perspective view of 4 together with the atom numbering scheme.
Fig. 3 Powder XRD pattern of different U3O8 nanoparticles.

1
Fig. 4 Scanning Electron Micrograph images of (A) UNP1, (B) UNP2, (C) UNP3, (D)UNP4.
Fig. 5 Dynamic light scattering of (A) UNP1 and (B) UNP3

2
Fig. 6 Transmission electron microscopy images of (A) UNP1 (B) UNP2 (C) UNP3 (D) UNP4.
Scheme 2. Schematic representation of the alcohol oxidation.

2
Fig. 7 The oxidation conversion of benzyl alcohol measured as a function of reaction time at 45°C
using different uranium oxide materials as catalysts.
Fig. 8 Comparison data of oxidation of different alcohols by UNP2.

2
Table 1. Crystallographic Data and Details of Refinement for Complexes 1 and 4.
pound
1
4
irical formula
H42N2O16S2U2
1202.82
18Cl4O8S2U
mula mass
.39
nic
em
triclinic
e group
P-1
)
)
)
10.4511(5)
16.9286(8)
20.3307(9)
92.359(2)
91.594(2)
90.387(2)
3592.4(3)
4
06(2)
411(3)
181(4)
851(1)
819(1)
81(1)
3
)
.32(6)
)
100(2)
2)
m-1)
9.194
0
(Mg/m3)
2.224
8
collected
18601
8
ue refl. / rint
meters / restraints
dness-of-fit on f2
wr2 (all data)
wr2 (confidence factors)
dual extrema (e/å3)
18601 / 0.000
932 / 20
/ 0.0263
0
1.053
5
0.0606 / 0.1630
0.0898/0.1441
3.94 / -5.22
73 / 0.0638
96/0.0446
/ -0.94
Table 2. Selected Bond Lengths (Å) and Angles (°) for Compound 1.
U(1)-O(6)
U(1)-O(7)
U(1)-O(1)
1.792(9)
1.813(10)
2.278(7)
U(3)-O(31)
U(3)-O(30)
U(3)-O(25)
1.778(9)
1.796(8)
2.257(7)

2
U(1)-O(3’)
U(1)-O(3)
U(1)-O(8)
U(1)-N(1)
U(2)-O(14)
U(2)-O(15)
U(2)-O(9)
U(2)-O(11)
U(2)-O(11a)
U(2)-O(16)
U(2)-N(2)
U(1)...U(1’)
U(2)...U(2a)
O(7)-U(1)-O(6)
O(6)-U(1)-O(1)
O(7)-U(1)-O(1)
O(6)-U(1)-O(3’)
O(3’)-U(1)-O(7)
O(3’)-U(1)-O(1)
O(6)-U(1)-O(3)
O(7)-U(1)-O(3)
O(3)-U(1)-O(1)
O(3)-U(1)-O(3’)
O(3)- U(1)- N(1)
O(6)-U(1)-U(2)
O(3)-U(1)-U(2)
O(8)-U(1)-U(2)
2.341(7)
2.351(7)
2.360(9)
2.590(10)
1.794(10)
1.795(10)
2.249(9)
2.343(8)
2.352(9)
2.378(10)
2.608(10)
3.8930(7)
3.8707(8)
178.8(4)
86.1(3)
92.7(3)
92.1(3)
89.1(3)
158.3(3)
85.6(3)
95.2(3)
133.3(3)
67.9(3)
132.0(3)
88.6(3)
34.01(19)
109.6(2)
U(3)-O(27)
U(3)-O(27b)
U(3)-O(32)
U(3)-N(3)
U(4)-O(23)
U(4)-O(22)
U(4)-O(17)
U(4)-O(19)
U(4)-O(19c)
U(4)-O(24)
2.341(7)
2.356(7)
2.383(9)
2.589(11)
1.793(9)
1.797(9)
2.260(9)
2.336(9)
2.359(9)
2.368(10)
2.577(10)
3.8980(7)
3.8987(8)
92.6(4)
82.3(3)
76.0(3)
142.8(3)
94.4(4)
85.0(4)
69.6(3)
65.4(3)
151.7(3)
87.4(4)
92.5(2)
U(4)-N(4)
U(3)...U(3b)
U(4)...U(4c)
O(7)-U(1)-O(8)
O(8)-U(1)-O(1)
O(8)-U(1)-O(3’)
O(8)-U(1)-O(3)
O(6)-U(1)-N(1)
O(7)-U(1)-N(1)
O(1)-U(1)-N(1)
O(3’)-U(1)-N(1)
O(8)-U(1)-N(1)
O(6)-U(1)-O(8)
O(7)-U(1)-U(1)
O(1)-U(1)-U(2)
O(3)-U(1)-U(2)
N(1) –U(1)-U(2)
166.7(2)
33.85(19)
98.69(19)
Symmetry codes: (‘) –x,2-y,1-z; (a) 1-x,1-y,1-z; (b) 1-x,1-y,-z; (c) –x,1-y,-z.
Table 3. Selected Bond Lengths (Å) and Angles (°) for Compound 4.
U(1)-O(7)
U(1)-O(8)
U(1)-O(3)
U(1)-O(1)
1.779(3)
1.785(3)
2.308(2)
2.314(2)
175.73(11)
U(1)-O(5)
U(1)-O(6)
U(1)-O(2)
2.367(2)
2.402(2)
2.517(2)
O(7)-U(1)-O(8)
O(6)-U(1)-O(3)
75.73(8)

2
O(3)-U(1)-O(8)
O(7)-U(1)-O(1)
O(1)-U(1)-O(8)
O(3)-U(1)-O(1)
O(7)-U(1)-O(5)
O(5)-U(1)-O(8)
O(5)-U(1)-O(3)
O(5)-U(1)-O(1)
O(7)-U(1)-O(6)
O(7)-U(1)-O(3)
90.11(11)
90.89(10)
89.88(10)
146.79(8)
90.96(10)
93.29(11)
73.19(8)
73.65(8)
87.97(10)
91.54(10)
O(6)-U(1)-O(1)
O(6)-U(1)-O(5)
O(7)-U(1)-O(2)
O(8)-U(1)-O(2)
O(2)-U(1)-O(3)
O(1)-U(1)-O(2)
O(5)-U(1)-O(2)
O(6)-U(1)-O(2)
O(6)-U(1)-O(8)
137.47(8)
148.86(8)
85.82(10)
90.56(11)
144.63(8)
68.58(8)
142.02(8)
68.94(8)
88.63(10)
Symmetry codes: (‘) –x,2-y,1-z; (a) 1-x,1-y,1-z; (b) 1-x,1-y,-z; (c) –x,1-y,-z.
Table 4. Catalytic activity of U3O8 nanoparticles using various alcohols as substrate.
Acid (3)
Entry
Alcohol (1)
Catalyst
Reagent & conditions
Conversion
(%)
Desired
aldehyde (2)
Yield
(%, 2 : 3)
60
1.
UNP2 (0.01 mol %)
PhI(OAc)2, EDC, 45 °C ,8.0 h
60
(29:1)
2a:58%
2b:56%
3a:2%
3b:4%
48
2.
3.
UNP2 (0.01 mol %)
UNP2 (0.01 mol %)
PhI(OAc)2, EDC, 45 °C ,10.0 h
PhI(OAc)2, EDC, 45 °C ,7.0 h
50
65
(14:1)
62
(11:1)
3c:5%
3d:4%
2c:55%
2d:56%
58
4.
UNP2 (0.01 mol %)
PhI(OAc)2, EDC, 45 °C ,8.0 h
59
(14:1)

2
Graphical Abstract (Picture):
Graphical Abstract (Synopsis):
Four uranyl complexes have been synthesized and characterized, then undergone to pyrolytic
reaction to produce U3O8 nanoparticles of different shape and morpholgy which affect their
catalytic efficiency.

2
Highlights:
(1) Syntheses of Uranium Oxide nano particles by very simple but effective manner just by
employing the pyrolytic reaction to our four synthesized complexes.
(2) Formation of U3O8 and UO2 nano crystals from the respective precursors and then
conversation of UO2 to U3O8 nano materials of different shape and morphology.
(3) Well characterizations of the nano particles by means of X-ray diffraction (XRD), scanning
electron microscopy (SEM), and transmission electron microscopy (TEM).
(4) Appreciable oxidation of benzyl alcohol by using PhI(OAc)2 as a very simple but effective
oxidant instead of regular t-BuOOH or H2O2, which minimizes formation of by-products and
chemical transformation of the UOx nano species.
(5) Finally four different U3O8 nanoparticles was explored as oxidising catalyst to oxidise
alcohols where morphology of the nanoparticles controls the catalytic efficiency.