Synthesis, characterization, magnetic properties and catalytic performance of iron orthoborate

Article abstract of DOI:10.14233/ajchem.2016.19681

The structural properties of iron orthoborate samples prepared by different synthetic approaches were comparatively investigated. The structural properties of the product were characterized by powder XRD, FT-IR, UV-Vis-NIR and SEM methods and the thermal

Full text of DOI:10.14233/ajchem.2016.19681

Asian Journal of Chemistry; Vol. 28, No. 6 (2016), 1325-1329
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19681
Synthesis, Characterization, Magnetic Properties and Catalytic Performance of Iron Orthoborate
*
ENGIN MEYDAN and ÖMER FARUK ÖZTÜRK
Department of Chemistry, Faculty of Art & Sciences, Çanakkale Onsekiz Mart University, Çanakkale, Turkey
*Corresponding author: E-mail: ofozturk@comu.edu.tr
Received: 17 October 2015;
Accepted: 21 January 2016;
Published online: 29 February 2016;
AJC-17801
The structural properties of iron orthoborate samples prepared by different synthetic approaches were comparatively investigated. The
structural properties of the product were characterized by powder XRD, FT-IR, UV-Vis-NIR and SEM methods and the thermal stability
was analyzed by the TGA/DTA technique. The room temperature magnetic properties of the product were investigated using the vibrating
sample magnetometer technique. Fe2(SO4)3·H2O was used as iron source and H3BO3 and B2O3 were used as boron sources. High temperature
solid state synthesis method was used and the experiments were performed at Fe:B = 1:2, 1:3 and 1:4 mole ratios. High purity (99 %) iron
orthoborate (Fe3BO6) was obtained from iron(III) sulfate and boric acid at 1:3 ratio. The product was observed to crystallize into orthorhombic
crystal structure (Norbergite type) and cell parameters were determined as a = 10.046(2) Å, b = 8.532(2) Å and c = 4.467(1) Å values from
ICDD data base. The use of Fe3BO6 in the catalytic reaction for the oxidation of benzyl alcohol under solvent-free conditions was tested
without employing any oxidant. Benzaldehyde, dibenzyl ether and benzyl benzoate were observed to be the three main products.
Keywords: Iron borate, High temperature synthesis, Solid state reactions, Magnetic properties, Benzyl alcohol oxidation.
physical and magnetic properties and the catalytic performance
of iron orthoborate are investigated.
INTRODUCTION
Transition metal borates have some properties which are
strongly dependent on their exact chemical composition and
their microscopic physical structure. The materials, which
are synthetic materials with potential uses due to electronic,
magnetic and optical properties, are of continuing interest.
Transition metal borates also display the important property
of catalytic activity [1-3]. Borates are divided into two groups:
orthoborate and metaborate. Both of the borate groups contain
isolated trigonal BO33- (∆) and tetrahedral BO45- (T). In the
metaborates, simple units (∆ or T) join together to form a
variety of polymeric chain and ring structures. The other form,
orthoborates, have discrete ∆ or T imbedded in a metal oxide
framework. The orthoborates can be subdivided into three groups
which correspond to the crystal modifications of CaCO3:
aragonite-type structure (MnBO3 and Fe3BO6), calcite-type
structure (CrBO3) and vaterite-type structure (YBO3) [4-9].
In the traditional process, the iron borate compounds are
usually prepared by solid-state reaction of anhydrous borate
materials carried out by means of a high temperature reaction
between finely-milled oxide powders and metal. The influence
of various iron precursors (metallic Fe, Fe2O3) and boron
sources (B2O3, H3BO3) on iron orthoborate synthesis has been
reported [10-13]. In this paper, we prepare Fe3BO6 using a
different precursor. The correlations between the structural,
EXPERIMENTAL
The initial materials employed for the solid-state syntheses
included Fe2(SO4)3·H2O (Sigma, 99 %), H3BO3 (Aldrich,99.9 %)
and B2O3 (Sigma, 99 %). Benzyl alcohol (Riedel, 99 %) was
used for the catalytic performance of iron orthoborate. The
experimental procedure involves; (i) Mixing and grinding of
the different precursors, (ii) Heating the mixture to about 900 °C
and (iii) Regrinding. Five experiments were prepared using
different combinations for iron orthoborate.
Experiment 1: Fe2(SO4)3·H2O and H3BO3 were mixed in
Fe:B = 1:2 ratio and manually ground in an agate mortar for
30 min. The mixture was heated in an ash-oven (900 °C, 9 h).
The product (A1) was dried in a vacuum oven after washing
with distilled water and ethanol.
Experiment 2: Fe2(SO4)3·H2O and H3BO3 were mixed in
Fe:B = 1:3 ratio and manually ground in an agate mortar for
30 min. The mixture was heated in an ash-oven (900 °C, 9 h).
The product (A2) was isolated as described in experiment 1.
Experiment 3: Fe2(SO4)3·H2O and H3BO3 were mixed in
Fe:B = 1:4 ratio and manually ground in an agate mortar for
30 min. The mixture was heated in an ash-oven (900 °C, 9 h).
The product (A3) was isolated as described in experiment 1.

1326 Naseem et al.
Asian J. Chem.
Experiment 4: Fe2(SO4)3·H2O and B2O3 were mixed in
(Fig. 1) [4]. The norbergite structure is distorted hexagonal
close-packing of oxygen that can be written as “Fe2B2/3O4”
from which it is clearly comparative to A2BO4 (olivine).
Fe:B = 1:2 ratio and manually ground in an agate mortar for
30 min. The mixture was heated in an ash-oven (900 °C, 9 h).
The product (A4) was isolated as described in experiment 1.
Experiment 5: Fe2(SO4)3·H2O and B2O3 were mixed in
Fe:B = 1:3 ratio and manually ground in an agate mortar for
30 min. The mixture was heated in an ash-oven (900 °C, 9 h).
The product (A5) was isolated as described in experiment 1.
Characterization: Formation of Fe3BO6 was analyzed in
terms of XRD pattern which was recorded on a Rigaku (model
DMAX2200) diffractometer with filtered 1.5418 Å Cu lamp.
The diffractograms were recorded in the range of 20-80°with
a step size of 0.04 °/s. The purity of the products was determined
by using the software CRYSFIRE [14] in correlation with
ICCD card of Fe3BO6 (70-0880). The best result was obtained
from iron sulfate and boric acid (A2, Fe:B = 1:3) where pure
Fe3BO6 form was created (≥ 99 %). Iron and B contents were
analyzed on an Oxford (model ED2000) XRF instrument. For
A2 (%): Fe 62.38 0.05, (B+O) 37.62 0.02; calculated Fe
61.08, (B + O) 38.92.
b
c
a
Density of the product was measured by a Mettler Toledo
density kit at room temperature and calculated according to
the Archimedes’ principle [15] with the following equation:
ρρ = [Wair/(Wair – Wn-hexane)]·ρn-hexane
)
where ρρ is the density of product, ρn-hexane is density of n-
hexane, Wair is the weight of the product in air and Wn-hexane is
the weight of the product in n-hexane.
The thermogravimetry (TG) and differential thermal analysis
(DTA) was carried out on a Shimadzu DTG-60H instrument,
typically heating a 10.00 mg sample from room temperature
to 900 °C at a heating rate of 20 °C/min under nitrogen flow
(15 mL/min). FT-IR transmittance spectra were measured at
room temperature in KBr pellet with a powder sample by a
using Perkin Elmer spectrum one model spectrophotometer
in the frequency range 4000-450 cm-1. The electronic spectra
were recorded on Shimadzu UV-3600/UV-Vis-NIR spectro-
photometer equipped with Praying Mantis attachment. The
magnetic susceptibility measurement was carried out using
AlfaAesor magnetic susceptibility Balance. The structure and
morphology of the product was investigated by scanning electron
microscopy (SEM; Philips XL-30S FEG 12-24 kV).
M(T) (magnetization vs. applied field) measurement was
performed by a vibrating sample magnetometer (VSM) with
the quantum desing physical property measurement system
(PPMS). M(T) measurement was done at room temperature
with curves measured with steps of 100 Oe in the 5 kOe
range and with steps of 1 kOe in higher field ranges.
The solid catalyst was then separated and the reaction
products were analyzed by a Shimadzu GCMS-QP5050A
instrument (optima column-5-1.0 µm, 50 m × 0.32 mm),
temperature range: 8-250 °C (20 °C/min), carrier gas: helium
(1 mL/min).
Fig. 1. Norbergite structure
Structure: The powder XRD pattern of Fe3BO6 (99 %) is
shown in Fig. 2. Impurity phase has been observed as an FeOx
phase [15]. Three sharp peaks were observed at 2θ values of
31° (2 2 1), 35° (2 3 0) and 53° (6 0 0); and smaller peaks at
48° (3 1 2), 61° (6 2 1) and 63° (3 5 1), in the order of decreasing
intensity. The results matched properly with the reported data
for Fe3BO6 [ICDD 70-0880]. XRD analyses revealed that the
sample prepared has norbergite structure.
1000
800
600
400
200
0
20
40
60
80
2θ (°)
Fig. 2. XRD patterns of Fe3BO6 (*Impurity oxide phase: FeOx)
Table-1 gives the lattice parameters a = 10.048(2) Å, b =
8.531(2) Å and c = 4.466(1) Å, calculated from refined
parameters indexed with the Pnma system. The measured
density of Fe3BO6 is consistent with four formula units per
distorted hexagonal structure [4,15].
RESULTS AND DISCUSSION
The iron(III) borate phase can be prepared by a high
temperature solid state reaction between various iron(III) and
boron sources: Fe3BO6 with the orthorhombic crystal structure

Vol. 28, No. 6 (2016)
Synthesis, Characterization, Magnetic Properties and Catalytic Performance of Iron Orthoborate 1327
TABLE-1
CRYSTALLOGRAPHIC DATA FOR Fe3BO6
Spectroscopic and magnetic studies: The lowest energy
term for the free ion is 6S, which splits in a weak octahedral
field to give 6A1g as the ground state for d5. In the d5 ground
state (6A1g) octahedral complex, all transitions are not only
Laporte forbidden but also spin forbidden [16]. No electronic
transition is observed on UV-spectrum which d5 electron confi-
guration indicates is similar to high spin sequence. Experimental
magnetic susceptibility result (µeff = 5.38 µB) is compatible
with the electronic spectrum.
The IR spectrum of Fe3BO6 is shown in Fig. 4 where the
isolated metal orthoborates allow us to easily establish the
presence of the BO3 and BO4 groups in the structure [17-19].
All the experimental results are collected in Table-2. The OH
vibration peak observed at 3300 cm-1 belongs to moisture on
the face similar to during cooling.
Empirical formula
Molecular weight (g/mol)
Sample form
Crystal system
Space group
Fe3BO6
274
Soft gray, powder
Norbergite
Pnma
Unit cell dimensions (Å)
a = 10.048.(2); b = 8.531.(2);
c = 4.466 (1).
382.82
Volume (Å3)
Z
4
Calculated density (g/cm3)
Experimental density (g/cm3)
Refinement method
Data range
4.756
4.813 ( 0.01)
CRYSFIREE
20-80°
The morphology of Fe3BO6 was also analyzed by scanning
electron microscopy. The low magnification image in Fig. 3a
shows the panoramic morphology.An enlarged image (Fig. 3b)
shows clear norbergite/distorted hexagonal shapes.
64
60
55
50
45
40
35
30
25
20
15
10
5
0
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600450
Wavelength (cm–1)
Fig. 4. FT-IR spectrum of Fe3BO6
TABLE-2
INFRARED BAND WAVENUMBERS (cm-1) OF Fe3BO6
Wavenumber
(cm-1)
Wavenumber
(cm-1)
Wave type
Wave type
1460
805
1194
570
884
576
479
–
ν(BO3)
ν2(BO3)
ν3(BO3)
ν4(BO3)
ν1(BO4)
ν4(BO4)
ν(Fe-O)
–
The temperature and magnetic field dependencies of the
magnetization of iron orthoborate sample were measured.
Fig. 5 shows σ(H) curves of Fe3BO6 at 300 K. The σ value
obtained at 300 Oe is 0.98 emu/g. The sample shows weakly
ferromagnetic behaviour at room temperature, the σ(H) curve
(370 Oe) indicates some magnetic impurity contribution [20].
Catalytic studies: Fe3BO6 was tested for the first time as
a heterogeneous catalyst and benzyl alcohol oxidation reaction
was chosen as the test reaction (Scheme-I). The experiments
were performed in solvent-free conditions without employing
any oxidizing agent other than the air present in the reflux
atmosphere.
The oxidation reaction was performed in a magnetically-
stirred three-neck flask equipped with thermometer and reflux
condenser. The reaction in the flask was charged with benzyl
alcohol (10 mL) and a prescribed amount of catalyst (0.5 g)
was added so that the conversion of benzyl alcohol increased
regularly with the amount of the catalyst until BzOH/Fe3BO6
ratio at 165°C. The system was heated at a prescribed temperature
Fig. 3. (a) Low magnification (b) Enlarged SEM images of Fe3BO6
Significant mass loss was not observed in the TGA and
DTA curves throughout the long temperature range up to 900
°C. DTA curve indicated that no structural phase transitions
(neither endothermic nor exothermic) take place. This behaviour
verifies the thermal stability of the product.

1328 Naseem et al.
Asian J. Chem.
0.4
Raising the temperature to 100 °C led to a consistent enhance-
ment in conversion. Optimum reaction temperature for highest
benzaldehyde selectivity was 110 °C. Substantial amounts
of dibenzyl ether and benzaldehyde are produced at higher
temperatures (Fig. 7).
0.10
0.3
0.05
0.00
0.2
-0.05
0.1
90
-0.10
-1000
-500
0
500
1000
0.0
Benzaldehyde
80
Organic
70
60
50
40
30
20
10
0
-0.1
-0.2
Alcohol
-0.3
-0.4
-20000
-10000
0
10000
20000
Magnetic alan (Oe)
Fig. 5. Magnetization (M) vs. applied field (H) loops of Fe3BO6
100
110
125
150
OH
Temperature (°C)
H
O
CH2
C
Fig. 7. Effect of reaction temperature on the product selectivities
O2
Conclusion
Catalyst
In summary, Fe3BO6 was prepared in 99 % pure form by
a solid state reaction between Fe2(SO4)3·H2O and H3BO3 after
a series of experiments to investigate the effect of reaction
conditions on the formation of Fe3BO6. Rietveld refinement
of powder XRD data shows the structure has a norbergite
(distorted hexagonal) system with four formula units in the
unit cell for the pycnometric density of Fe3BO6. Magnetization
measurements revealed that Fe3BO6 is weakly ferromagnetic
at room temperature. Further studies are needed to investigate
the complex magnetism of iron orthoborate at low temperature.
The use of iron orthoborate in catalytic reactions was investi-
gated for the first time. The solvent-free partial oxidation of
benzyl alcohol to benzaldehyde proceeded with moderate
conversion. The acidic nature of the catalyst promotes the
sequential reactions of the reactants and products and the
selectivity. Further research is needed to achieve better perfor-
mance for other organic solvents and other catalytic reaction
types.
Scheme-I: Oxidation of C6H5CH2OH
(25-150 °C) for a period of 10 h. At higher loadings no further
increase in the conversion was noticed. While conversion
remained almost constant, the decrease in the selectivity for
benzaldehyde was correlated with the increase in the selecti-
vities of second generation products (dibenzyl ether and benzal-
dehyde) from benzaldehyde. Best performance was achieved
for a reaction period of 4-5 h. Benzyl alcohol conversion
increased while selectivity for benzaldehyde decreased during
the longer reaction time (Fig. 6).
60
50
40
ACKNOWLEDGEMENTS
25
50
This work was supported by TUBITAK (The Scientific
and Technological Research Council of Turkey/Project No:
113Z022).
75
30
20
10
0
100
110
125
150
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