Enhanced photocatalytic hydrogen production from Y2O3/TiO2 nano-composites: A comparative study on hydrothermal synthesis with and without an ionic liquid

Article abstract of DOI:10.1039/c5nj03711e

Hetero-junction Y₂O₃/TiO₂ nano-composite (NC) photocatalysts were synthesized using a conventional hydrothermal method (Y₂O₃/TiO₂ NC_(HM)) and an ionic liquid assisted hydrothermal method (Y₂O₃/TiO₂ NC_(ILAHM)). The composite nature and physico-chemical properties of the photocatalysts prepared through both routes as a function of thermal treatment were investigated via thorough characterization. A comparison of the photocatalytic hydrogen production via water splitting is provided. It was found that the concentration of Y₂O₃ in the TiO₂ matrix and the post thermal treatment have obvious effects on the hydrogen production activity, and they were fine-tuned for enhancement of the hydrogen production. The required synergy between Y₂O₃ and TiO₂ was found to occur at an optimum concentration of 25 wt% Y₂O₃ in the TiO₂ matrix, with the sample prepared at 400 °C for 1 h. The optimized NC i.e. 25 wt% Y₂O₃/TiO₂ NC_(ILAHM) produced a promising hydrogen evolution of 1380 μmol g^-1 that was almost 2-fold the production from 25 wt% Y₂O₃/TiO₂ NC_(HM). The enhancement was attributed to the porous surface morphology, higher surface area and quantum yield of the NC prepared using the ionic liquid assisted hydrothermal method.

Full text of DOI:10.1039/c5nj03711e

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Enhanced photocatalytic hydrogen production from Y2O3/TiO2 nano-
composites: A comparative study on hydrothermal synthesis with and without
ionic liquid
T. N. Ravishankar ab, M. de Oliveira Vaz b, S. Khan b, T. Ramakrishnappa*a c, S. R.
Teixeira*b , Geetha. R. Balakrishnaa, G. Nagaraju d, J. Dupont ef
a Centre for Nano and Material Sciences, Jain Global Campus, Jain University, Jakkasandra
(Postꢀ 562112), Kanakapura (T), Bangalore, Karnataka, India.
b Laboratory of Thin Films and Nanostructure Fabrication (L3F nano), Institute of Physics,
Universidade Federal do Rio Grande do Sul, UFRGS, Avenida Bento Gonçalves 9500, P.O. Box
15051, 91501ꢀ970 Porto Alegre, RS, Brazil.
c Dayananda Sagar Academy of Technology and Management, Udayapura, Opp Art of Living,
Kanakapura road, Bangaloreꢀ560082
d Department of Chemistry, SIT Tumkur, Karnataka (India)
e Laboratory of Molecular Catalysis, UFRGS, Porto Alegre, RS, Brazil.
f Department of Sustainable Chemistry, School of Chemistry, University of Nottingham,
Nottingham, U.K.
*Corresponding authors Emails: swadheshi26@gmail.com (Dr.T. Ramakrishnappa, Fax: +91ꢀ80ꢀ
27577199; Tel: +91ꢀ75ꢀ27506270) and srgrbrtxr@gmail.com (Dr. S.R. Teixeira, Fax: +55ꢀ3308ꢀ
6498; Tel: +55ꢀ5133087286)

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Abstract
Heteroꢀjunction Y2O3/TiO2 nanoꢀcomposite (NC) photocatalysts were synthesized by
conventional hydrothermal method (Y2O3/TiO2 NC(HM)) and by ionic liquid assisted
hydrothermal method (Y2O3/TiO2 NC(ILAHM)). The composite nature and physicoꢀchemical
properties of the photocatalysts prepared by both routes as a function of thermal treatment were
investigated via thorough characterizations. A comparison of the photocatalytic hydrogen
production via water splitting is provided. It was found that the concentration of Y2O3 in TiO2
matrix and post thermal treatment have an obvious effects on the hydrogen production activity
that were fineꢀtuned for the enhancement. The synergy between Y2O3 and TiO2 has an optimum
for concentration of 25 wt% of Y2O3 in TiO2 matrix prepared at 400°C for 1 h. The optimized
NC i.e 25 wt % Y2O3/TiO2 NC(ILAHM) has produced promising hydrogen evolution of 1380 µ
mol/g that was almost 2–fold the production from 25 wt % Y2O3/TiO2 NC(HM). The enhancement
was attributed to porous like surface morphology, higher surface area and quantum yield of the
NC prepared by ionic liquid assisted hydrothermal method.
Keywords: Ionic liquid assisted hydrothermal method, Y2O3 modified TiO2 nanoꢀcomposites,
hydrogen evolution via water splitting, thermal treatment, photocatalysis.

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1. Introduction
Recently, renewable techniques to harvest energy have been emerged as research hot topic since
the conventionally used fossil fuels are costly and present environmental limitations [1ꢀ3]. In this
regard, photocatalytic and photoelectrochemical hydrogen production via water splitting posses
enormous potential for sustainable development of society [4ꢀ6]. Several semiconductors have
been utilized for photocatalytic hydrogen production [7ꢀ9]. Amongst these; TiO2 has been widely
used as a photocatalyst for hydrogen generation via water splitting [10ꢀ12]. Numerous
methodologies have been employed to fine tune the properties of TiO2 for improved
photocatalytic activity [13ꢀ14]. Heteroꢀjunctioning the TiO2 with oxide semiconductors has
proven to enhance hydrogen production compare to bare TiO2 nanomaterials. Nanocomposites
(NCs) of Y2O3/TiO2 are promising candidates as photocatalysts [15ꢀ16]. In Y2O3/TiO2 NC; the
Y2O3 acts as electrons drain and minimizes the recombination of electron/hole pairs [17ꢀ18].
Various preparation methods such as, solꢀgel, coꢀprecipitation and combustion have been
used for the syntheses of Y2O3/TiO2 NCs [19ꢀ20]. Room temperature ionic liquids (RTILs)
hydrothermal method has received extensive attention for both academic research and industrial
investigations over the past two decades for the syntheses of oxide materials [13, 21, 22]. RTILs
possess unique properties such as wide liquid temperature range, high thermal stability, high
ionic conductivity and wide electrochemical window [23]. An important aspect of the interaction
of RTILs with nanoparticle (NP) precursors involves the nucleation and growth of NPs that helps
to control the morphology of the NPs [24]. Ionic liquids possess following special physical
properties that render them interesting as potential solvents for inorganic synthesis; (1) they are
good solvents for a wide range of inorganic materials and they can help bring the unusual
combinations of reagents into the same phase, (2) their compositions of poorly coordinated ions

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make them highly polar yet non coordinating solvents and (3) they are nonvolatile having low
vapor pressure so that they may be used in highꢀvacuum systems [25ꢀ26]. With these tremendous
properties; the ILs are very attractive to be used as additional solvent and surface directing
agents for the hydrothermal synthesis of many other materials [21,22]. However, to date, there is
no report on the syntheses of Y2O3/TiO2 NCs employing RTIL hydrothermal method.
Herein, we have proposed for the first time a simple single step RTIL assisted
hydrothermal method to synthesize Y2O3/TiO2 NCs. For the sake of comparison, a conventional
hydrothermal method without ionic liquids is applied for the synthesis of the photocatalysts. The
NCs are optimized by thermal treatment and by varying the concentration of Y2O3 for improved
photocatalytic hydrogen production via water splitting.
2. Materials
Titanium tetrachloride (TiCl4) and Yttrium nitrate (Y(NO3)3 .6H2O) were purchased from Sigma
Aldrich, Sodium hydroxide (NaOH) was purchased from Merck, India.1ꢀ(2ꢀmethoxyethyl)ꢀ3ꢀ
methylimidazolium methanesulfonate ionic liquid was prepared by previously developed method
[27]. Double distilled water was used throughout the experiments.
3. Experimental section and instrumentation
3.1. Ionic liquid assisted hydrothermally derived photocatalysts
For the syntheses of pristine Y2O3 and TiO2 nanoparticles (NPs), 0.05 M Y(NO3)3 .6H2O and 5.5
mL of TiCl4, respectively were used as precursors. In the first step, each precursor was added
separately in Teflon tube having 2.5 mL 1ꢀ(2ꢀmethoxyethyl)ꢀ3ꢀmethylimidazolium methane
sulfonate as IL and 3.5 mL of 0.1 M NaOH solution as mineralizer. The system was left for
homogenization under a constant stirring and after that; 8 mL of water was added for the
hydrolysis to occur. Furthermore, the precipitate in Teflon tube was put into the stainless

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autoclave followed by hydrothermal treatment at 130 °C for one day. After the reaction, the
system was cooled to room temperature naturally. In the second step, the obtained product was
mixed with acetonitrile and stirred overnight to remove the IL´s residue. Finally, Y2O3 and TiO2
nanoparticles were retrieved from centrifugation; thereby, post calcinations step was followed.
The Y2O3 incorporated TiO2 NCs were prepared by following the similar procedures and
post calcinations except for the first step once we mixed different concentrations (25, 50 and 75
wt %) of Yttrium nitrate with a fixed volume of Titanium tetrachloride (5.5 mL).
For the NCs synthesized by conventional hydrothermal method similar procedures were
followed except for the addition of IL in the first step of the synthesis.
The NCs prepared by both techniques were post annealed at 400°–800°C for 1–3 hours of
calcination times.
3.2. Photocatalytic H2 production
Photocatalytic activities were evaluated by measuring hydrogen production using gas
chromatography at room temperature in water ethanol system. The reaction was carried out in a
closed gas circulating system in an inner irradiation type reactor. Different photocatalysts (10
mg) were sonicated for 20 min to disperse in 7.5 mL aqueous solution. After sonication, 2.5 mL
ethanol was added as a sacrificial reagent. Prior to irradiation, the system was deaerated by
bubbling argon for 10−15 min to reduce the oxygen content. During the entire experiment, the
reaction temperature was kept at 25 °C by eliminating the contribution of IR radiation with the
circulation of water in the outer jacket of the reactor. A 300 W Xenon/Mercury lamp has been
used as light source. Analyses were conducted using Agilent 6820 GC Chromatograph equipped
with a thermal conductivity detector (TCD) and a 5 Å molecular sieve packed column with argon

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as the carrier gas. Using a gastight syringe with a maximum volume of 50 ꢁL, the amount of
hydrogen produced was measured at each 0.5 h intervals.
3.3. Determination of quantum yield
Quantum yield is a very important factor to evaluate the photocatalytic efficiency of the
photocatalysts. The fluorescence quantum yield (Q) is the ratio of photons absorbed to photons
emitted through fluorescence. The most reliable method for recording Q is the comparative
method of Williams [28], which involves the use of well characterized standard sample (Quinine
sulfite) whose Q value is already known and it was found to be 0.54 [29]. solutions of the
standard and test samples with identical absorbance at the same excitation wavelength can be
assumed to be absorbing the same number of photons. Hence, a simple ratio of the integrated
fluorescence intensities of the two solutions (recorded under identical Conditions) will yield the
ratio of the quantum yield values. Quantum yield of standard (Q known) is known, it is trivial to
calculate the quantum yield of test sample (Q unknown) using following equation:
ꢀꢂꢃꢄꢅꢃ × ꢇꢈꢉꢊꢋ ꢁꢃꢂꢃꢄꢅꢃ × ꢍꢁꢎꢃꢂꢃꢄꢅꢃ
ꢆꢇꢈꢉꢊꢋꢌꢂꢃꢄꢅꢃ × ꢍꢂꢎꢃꢄꢅꢃ
ꢆ
ꢌ
ꢀꢁꢂꢃꢄꢅꢃ
=
Q is quantum yield; η is refractive index of solvent used. Brief procedure is discussed below
(i)
Prepare series of quinine sulfite solutions (0.01 to 0.06 M) in ethanol plus 0.01 % HCl,
note down the absorbance of each solutions using UVꢀVis spectrometer and also record
the integrated fluorescence intensity of each solution using spectrofluorophotometer.
Repeat step 1, for each of the test solutions (prepared photocatalysts) whose Q value has
to be determined.
(ii)

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(iii)
Plot a graph with integrated fluorescence intensity vs absorbance of quinine sulfite and
well as each test solutions and graph is straight line from this graph find out the slope
from this slope and using equation 1, one can determined the Q of the photocatalysts.
3.4. Characterization
Powder Xꢀray diffraction data was recorded on Philips X’pert PRO Xꢀray diffractometer with
graphite monochromatized CuꢀKα (1.5418 Å) radiation operated at 40 kV and 30 mA. Xꢀray
photo electron spectroscopy (XPS) analysis was carried out on an ESCALAB 250 (ThermoꢀVG
Scientific), using Al Kα as the excitation source. The binding energy (BE) from the advantageous
carbon (284.6 eV) was used to calibrate the spectra. The absorption spectra of the samples were
measured by dispersing the nanoparticles in water using Perkin Elmer Lambdaꢀ750 UVꢀVis
spectrometer helping to determine the band gap energy of the prepared photocatalyst using
Kubalkamunk function. Integrated fluorescence intensity of the prepared materials was
determined by using spectrofluorophotometer (Shimadzu, RFꢀ5301PC Series) helping to
determine the quantum yield of the prepared photocatalyts. The morphology was examined using
table top Hitachi 3000 scanning electron microscopy (SEM). Samples were goldꢀcoated prior to
SEM analysis. The nanostructure of the product was observed by transmission electron
microscopy (TEM) performed by JEOL JEM 1200 Ex operating at 100 kV. Samples for TEM
were prepared by dropping the dispersion of 2ꢀpropanol metal oxide nanoparticle on a holey
carbon grid and drying the grids under vacuum for 24 h. BET surface area i.e. N2 adsorptionꢀ
desorption measurements of the samples were measured using Tristar II, Micromeritics. The
water/organic content present in the sample was investigated by thermo gravimetric analysis
(TGA) using a SDT Q600 V20.9 thermo microbalance in N2 atmosphere from room temperature
to 800 °C at a heating rate of 10 °C minꢀ1. For the sake of simplicity, the samples prepared by

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ionic liquid assisted method are labeled adding subscript
whereas others without IL are
(ILAHM)
labeled by (HM)
4. Results and discussion
4.1. Y2O3/TiO2 NCs(ILAHM)
XRD is mainly used to know the phase composition and crystallite size of the prepared
materials. Fig.1 showed the XRD patterns of the pristine photocatalysts, calcinated at 400°C for
1h. The diffractograms are in good agreement with JCPDS #s. 41ꢀ1105 and 2ꢀ387, that clearly
confirm the formation of Y2O3 and TiO2, respectively. Once Y2O3 NPs were incorporated to
TiO2 NPs; the XRD patterns become broader and presence of tetragonal anatase TiO2 and cubic
Y2O3 phases can be clearly seen (Fig. 1). The relative intensity of the peak at 2θ = 29.2 related to
(222) plane of cubic Y2O3 is increasing with concentration of Y2O3. The crystallite size, BET
surface area, band gap energy and quantum yield for 25, 50, 75 wt % Y2O3/ TiO2 NCs(ILAHM) and
pristine NPs of TiO2(ILAHM) and Y2O3(ILAHM) are calculated and are shown in the Table 1. It can
be seen that the NC materials present higher surface area compared to the pristine Y2O3 and TiO2
NPs. In addition, 25 wt% Y2O3/TiO2 NC(ILAHM) presents the highest surface area compared to all
other photocatalysts. Furthermore, comparing the quantum yields of Y2O3/ TiO2 NCs(ILAHM) and
pristine nanoꢀmaterials the NC materials seems to be more attractive for photolysis as compared
to their pristine NPs (Table 1). The optical properties were characterized at room temperature
using a UV–Vis spectrophotometer in the wavelength range between 200–800 nm and the band
gap energies of the NCs were calculated from diffused reflectance spectra using Tauc plot
function and the results are indicated in Table 1, corresponding UV–Vis spectra and Tauc Plot
function for determination of band gap of different photocatalyts synthesized via ILAHM and
HM are showed in supplementary file as Fig S1, Fig S2, Fig S3 and Fig S4,(S stands for

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supporting information). The band gap of pristine Y2O3 and TiO2 were found to be 4.5 and 3.2
eV and upon heteroꢀjunctioning the band gaps of the NCs were decreased. These results clearly
show that light absorption of the heteroꢀjunction NCs in increased
Fig. 1 XRD patterns of (a) pristine Y2O3(ILAHM) NPs,(b) pristine TiO2(ILAHM) NPs, (c) 25 wt% (d)
50 wt% and (e) 75 wt% Y2O3/ TiO2 NCs(ILAHM), (A= Anatase TiO2 and Y = Y2O3) and the
samples are calcinated at 400°C for 1 h.
The pristine Y2O3 (ILAHM) & TiO2 (ILAHM) NPs, and Y2O3/TiO2 NCs (ILAHM) were subsequently
applied for hydrogen evolution in water–ethanol system. Fig. 2 compares the gas
chromatography results of the photocatalysts. It can be seen that the pristine NPs prepared in the
current study have shown enhanced photoactivity compared to the commercially available
powders that highlights the importance of the RTILs synthesis route. Furthermore, the
photocatalytic activity of NC materials is better than the pristine Y2O3(ILAHM) and TiO2(ILAHM)
NPs presenting NC as promising photocatalysts. For the Y2O3/TiO2 NCs(ILAHM), the

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concentration of Y2O3 in TiO2 matrix has an obvious effect on the H2 evolution activity that has
an optimum for 25 wt% concentration of Y2O3 evolving 1380 µ mol/g of H2. On the other hand,
the H2 evolution rate dropped to 890 µ mol/g for 75 wt% Y2O3/TiO2 NC(ILAHM)
.
Table 1 Crystalline size, BET surface area, quantum yield and band gap energies of the
differentphotocatalysts synthesized via ionic liquid assisted hydrothermal method (ILAHM) and
hydrothermal method (HM).
Y2O3
content
(wt %)
Crystalline size (nm)
BET surface
area (m2/g)
Quantum
yield
Band gap
(eV)
Samples
ILAHM
HM
ILAHM
HM
ILAHM
HM
ILAHM HM
TiO2 NPs
0
33.3 for (101) 32.7
32.1
29.4
40.6
0.21
0.20
0.41
3.34
2.10
3.32
2.15
Y2O3/TiO2
NCs
25
41.3 for (101)
ꢀꢀꢀꢀꢀ
50.6
35.7
0.51
0.45
50
75
42.1 for (101)
33.7
30.3
18.4
0.35
0.31
0.08
2.00
1.97
4.50
2.07
1.99
4.50
ꢀꢀꢀꢀꢀ
42.6 for (101)
ꢀꢀꢀꢀꢀ
32.8
20.4
0.41
0.09
Y2O3 NPs
100
28.6
29.8
The enhanced photocatalytic activity of Y2O3/TiO2 NCs (ILAHM) can be explained as follow; water
splitting is an uphill reaction that needs the standard Gibbs free energy change of ꢂGº of 237
kJ/mol or 1.23 eV. Therefore, the band gap energy (Eg) of the photocatalyst should straddle the
water redox potentials and it should be between 1.23 eV < Eg < 3.26 eV [30,31].

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Fig. 2 Hydrogen generation of different photocatalysts synthesized via ILAHM and commercial
TiO2 (Degussa Pꢀ25).
In addition, the photocatalyst should be efficient enough to separate the photogenerated carriers
and to transport them to their reactive sites in order to decrease the electronꢀhole pair
recombination. In heteroꢀjunction photocatalysts that possess appropriate band gap energetics the
CB electrons of one semiconductor are injected to other thereby; achieving a wide electronꢀhole
separation (Fig. 3) [33]. The CB of TiO2 and Y2O3 are positioned at ca. – 0.7 and – 0.35 V,
respectively more negative than that of water reduction potential and VB of TiO2 lies closed to
the water oxidation potential compared to the VB of Y2O3 [33,34].

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−
C
e
H
e
h
e
C
e
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
H
.ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ.
h
. O /H O (+ 1.23 VV)
V
+
Fig. 3 Electron transportation in Y2O3/ TiO2 NCs for photocatalytic hydrogen generation.
Therefore, owing the advantage of heteroꢀjunctioning of Y2O3 and TiO2, under illumination;
electrons are excited from VB to CB of TiO2, thereof transferred to the CB of Y2O3, thereby;
reducing water to hydrogen. On the other hand holes from the VB of TiO2 oxidize water.
Therefore, the heteroꢀjunction formed between TiO2 and Y2O3 efficiently separates the
photoexcited electronꢀhole pairs, and thus hinders the charge recombination and improve the
photocatalytic performance of NC materials compared to the pristine Y2O3 and TiO2 NPs. Since
we are changing the concentration of Y2O3 that evidently affects the capture of photoexcited
electrons from the CB of TiO2. If concentration of Y2O3 is large, the light absorption from TiO2;

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will be small thereby inhibiting the generation of electronꢀhole pairs in TiO2 that is the main
reason of decreasing H2 evolution rate of high content incorporation of Y2O3 such as that 75 wt%
of Y2O3 in TiO2 matrix [16]. In the absence of Y2O3, most of these charges tend to recombine
rapidly as the pristine TiO2 NPs present lower photocatalytic hydrogen generation. Therefore, the
synergy for improved photocatalytic activity can be obtained only for a certain concentration of
Y2O3 in TiO2 matrix. In the current work that synergy is achieved for the 25 wt% Y2O3/TiO2 NC.
Therefore, the optimum concentration of Y2O3 in TiO2 matrix not only optimize the light
absorption but also increase the BET surface area and quantum yield (Table 1) which than
synergize 25 wt% Y2O3/TiO2 NC for enhanced photocatalytic activity compared to all other
samples.
4.2. Y2O3/TiO2(HM)
For the sake of comparison, the Y2O3/ TiO2 NCs(HM) were prepared by hydrothermal method
without the presence of IL. Fig.4 shows the XRD patterns of different photocatalysts, calcinated
at 400 °C for 1h. The diffractograms of the pristine photocatalysts are in good agreement with
JCPDS #s. 41ꢀ1105 and 2ꢀ387, that clearly confirm the formation of Y2O3 and TiO2,
respectively. Once Y2O3(HM) NPs were incorporated to TiO2(HM) NPs; the XRD patterns become
broader compared to those observed for NCs prepared by ILAHM (Fig. 1). These results suggest
the presence of amorphism in the NC(HM) matrix; therefore it is hard to determine the crystalline
grain from the Scherre´s equation. On the other hand, in case of ILAHM synthesis, well defined
peaks can be observed these results clearly indicate that the presence of ionic liquid in the
hydrothermal synthesis helps to improve the crystalline structure of the photocatalysts. As
compared to pristine Y2O3(HM) and TiO2(HM) NPs the NCs(HM) present higher surface area (Table
1). In addition, 25 wt% Y2O3/ TiO2 NC(HM) present the highest surface area and quantum yield

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compared to all other photocatalysts. Interestingly, same sample when prepared by the ILAHM
has presented the highest surface area as well as the quantum yield when compared to other
samples (Table 1). These results show that the concentration of Y2O3(HM) in TiO2(HM) is a critical
factor for higher surface area that has an optimum of 25 wt % in the current study. The band gap
energies (Table 1) obtained from the absorption spectra presented the similar trend as observed
for different concentration of Y2O3 prepared by ILAHM
Fig. 4 XRD patterns of (a) pristine Y2O3(HM) NPs,(b) pristine TiO2(HM) NPs, (c) 25 wt% (d) 50
wt% and (e) 75 wt% Y2O3/ TiO2 NCs(HM), (A= Anatase TiO2 and Y = Y2O3) and the samples are
calcinated at 400°C for 1 h.
Fig. 5 compares the gas chromatography results of the prepared photocatalysts. The
photocatalytic hydrogen production for NCs(HM) materials is far better than the pristine Y2O3(HM)
and TiO2(HM) NPs. The highest hydrogen production (890 µmol /h/g) was observed for 25 wt%

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Y2O3/ TiO2 NC(HM). However, all of the NCs prepared by ILHAM (Fig. 2) have presented
improve photocatalytic activity compare to the best NC prepared by HM. Comparing the samples
prepared by two methods in Table 1; clearly the higher surface area and quantum yield can be
observed for ILAHM synthesized NCs. These results show that the addition of ionic liquid in the
hydrothermal synthesis not only results in improved crystalline structure but also other physicoꢀ
chemical properties that are vital for improved photocatalytic activity of the NCs.
Fig. 5 Hydrogen generation of different photocatalysts synthesized via HM and commercial TiO2
(Degussa Pꢀ25).
4.3. Effect of temperature on photocatalytic hydrogen production
In the above discussion the samples were calcinated at 400°C for 1 h. Once we optimized the
concentration of the Y2O3 in TiO2 i.e.25 wt %, we further investigated the effect of thermal
treatment on the photocatalytic performance of the NCs. Fig. 6 displays the XRD patterns of 25

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wt% Y2O3/ TiO2 NC(ILAHM) calcinated at temperatures (from 500 – 800 °C) for 1 h. The presence
of anatase phase of TiO2 along with cubic Y2O3 can be seen up to 600°C. Further increasing
temperature from 700°C and above, the intensity of anatase phase decreases and at 800 °C
complete transformation to the rutile phase can be confirmed.
Fig. 6 XRD patterns of 25 wt% Y2O3/ TiO2 NC(ILAHM), calcinated at different temperatures (A=
Anatase TiO2, R= Rutile TiO2 and Y = Y2O3).
Usually, due to increase in the temperature the particles agglomerate thereby the surface area is
decreased. The crystallite size for anatase phase of TiO2 for (101) peak and BET surface area at
different temperatures are calculated from Scherrer’s equation and are shown in the Table S1 the
crystalline size gradually decreases with increasing the temperature. After heat treatment, the
above photocatalysts were subjected to photocatalytic hydrogen production (Fig. S5). In the set
of these samples the NC prepared at 500°C has shown improved photocatalytic activity (1280
µmol/g) compared to other samples. However, compared to the sample prepared at 400°C (Fig.
2) the photocatalytic activity is clearly decreased. Once the rutile TiO2 has found to decrease the

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photocatalytic performance of TiO2 [35]; therefore, we suggest that the formation of rutile phase
in the crystalline structure is the main reason to decrease the photocatalytic activity of the NC.
For 25 wt % Y2O3/ TiO2 NC(HM) prepared by HM without IL (Fig. 7) same thermal
treatments were followed. The XRD patterns have followed the similar trend as that of Fig. 6.
The BET surface area obtained at different thermal treatments is shown in the Table S1. It can be
seen that the surface area decreases with increasing temperature that is clearly related to the
agglomeration of the NCs as well as the formation of rutile phase of TiO2.
Fig. 7 XRD patterns of 25 wt% Y2O3/ TiO2 NC(HM) calcinated at different temperatures (500 –
800 °C for 1h ),(A= Anatase TiO2, R= Rutile TiO2 and Y = Y2O3).
After heat treatment, the above photocatalysts were applied to photocatalysis (Fig. S6)
Comparing the photocatalytic activity of this set of samples one can observe that the sample
prepared at 500°C has shown the best performance (470 µmol/g). However, compared to the NC
prepared at 400°C it has shown a phenomenal decrease in the photocatalytic activity that is

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clearly related to the combined effect of higher crystallinity and surface area (Table 1) of the
sample. The heat treatment results presented above have clearly shown that for the current study
400°C is an optimum temperature. To further investigate how time can affect the photocatalytic
activity of the 25 wt% Y2O3/ TiO2 NC(ILAHM) is heat treated at 400°C for 1, 2 and 3 h duration.
Comparing. Fig. S7; with Fig 2 it is clear that the best photocatalytic performance throughout the
current study is observed for 25 wt% Y2O3/ TiO2 NC(ILAHM) prepared at 400 °C for 1h. It seems
that the synergizing heteroꢀjunction NCs the concentration of Y2O3 and thermal treatment are
critical steps that not only affects the crystalline structure but also other physicoꢀchemical
properties of the photocatalysts.
In above discussion we have comprehensively compared the photocatalytic activity of the
samples prepared by ILAHM and HM and evidently the samples prepared by ILAHM have
improved performances. Consider now the formation mechanism of the NCs employing
hydrothermal method with and without adding IL. According to the literature when NPs are
synthesized via HM; the important aggregation mechanisms to be considered are (1) Diffusion
limited aggregation (DLA) and (2) Reaction limit aggregation (RLA) [36]. DLA occurs upon
high collision between the NPs that traverse relatively low energy barrier due to the absence of
structural directing agent. As a result the particles will be aggregated and morphology will not be
controllable thereby the active surface area will decrease that is the case of HM synthesis without
IL. The surface morphology of the prepared photocatalysts were analyzed using SEM. The SEM
image of NC(HM) in Fig. 8 (a) is evident to follow that mechanism due to the formation of
irregular size agglomerates. On the other hand, in RLA the presence of self assembling template
does not let the particles collide due to high energy barrier that let them to stay apart. Therefore,
the morphology will be controllable and porous structure will be presented, thereby; the surface

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area will increase [37]. In the literature, the mechanism to the formation of NPs prepared by
ILAHM is not completely understood [38]. However, based on the selfꢀassembling template
nature of ionic liquid we suggest that in the current study the formation of NC(ILAHM) is prevailed
by RLA. The anionic part of the IL i.e methanesulfonate possesses large hydrophilicity that will
preferentially interact with water molecules in solution through hydrogen bonding. The cationic
part of IL i.e 1ꢀ(2ꢀmethoxyethyl)ꢀ3ꢀmethylimidazolium ring will array in the opposite direction
to pile up possibly by π–π interactions or other nonꢀcovalent interactions (hydrogen bonding, van
der Waals forces, and electrostatic forces) between imidazolium rings [39]. This implies that IL
successfully participates in the reaction as a selfꢀassembling template. Consequently, the
titanium and yttrium precursors will be hydrolyzed and condensed around the selfꢀassembled IL
structure at a controlled rate thereby the collision between the particles will be constraint due to
the presence of these templates, which leads to the formation of porous structure with high
surface area. Fig. 8 (b) clearly indicates voluminous porous network with voids indicated by the
arrows that will help to facilitate water adsorption, penetration and improved photocatalytic H2
evolution. Scheme S1 presents the suggested mechanism to the formation of NCs via HM and
ILAHM. Scheme S2 presents the structure of 1ꢀ(2ꢀmethoxyethyl)ꢀ3ꢀmethylimidazolium
ꢀ1
methanesulfonate (MOEMI.CH3SO3 ).

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(b
(a
Fig. 8 SEM images of (a) 25 wt% Y2O3/TiO2 NC synthesized via HM and (b) 25 wt%
Y2O3/TiO2 NC synthesized via ILAHM heat treated at 400°C for 1 h.
Being best in all aspects in the current study from now onwards we will characterize 25 wt%
Y2O3/ TiO2 NC
comprehensively. Samples for TEM were prepared by dropping a
(ILAHM)
dispersion of metal oxide nanoparticles in 2ꢀpropanol on a holey carbon grid and drying the grids
under vacuum for 24 h. Fig. 9 (a) shows the TEM image, the average particle size was found to
be 55 nm. The lattice spaces of 0.35 nm, 0.30 nm and 0.53 nm can be observed in HRTEM
image (Fig. 9 (b)), that are in good agreement with (101) plane for anatase TiO2, (222) and (200)
planes for cubic Y2O3. The corresponding SAED spectrum is shown in Fig. 9 (c) that further
indicates the presence of Y2O3 and TiO2.

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Fig. 9 (a) TEM image, (b) HRTEM image and (c) SAED pattern of the 25 wt% Y2O3/TiO2 NC
synthesized via ILAHM.
The surface chemical composition and the oxidation state for the synthesized samples are
investigated by XPS measurements. From the survey spectrum (not shown) the presence of C, S,
Ti, Y and O elements was recorded. The high resolution deconvoluted XPS spectra of O 1s, Ti
2p, Y 3d and S 2p regions are displayed in Fig 10. In Ti 2p region (Fig. 10 (a)) the binding
energies of 458.6 and 464.1 eV are indicative of Ti 2p3/2 and Ti 2p1/2 which correspond to Ti4+
[40]. In O 1s region (Fig.10 (b)) the peak centered at 529.6 eV is related to the oxygen in TiO2
and Y2O3 lattice. However, the adjacent peak at 531.4 eV can be regarded as the presence of

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surface hydroxide species that were found to be advantageous for improved hydrogen generation
[41], in Y 3d region (Fig. 10 (c)), the binding energies for Y 3d5/2 and Y 3d3/2 are observed at ca.
155.82 and 158 eV, respectively, with a spinꢀorbit splitting of 1.74 eV. These results match with
the previous reports on Y2O3 [42]. In addition, another peak in the middle of Y 3d5/2 and Y 3d3/2
was also observed that might be related to some lower oxidation state of Y. A nominal amount of
sulphur was registered in the XPS spectra and the corresponding S 2p3/2 and S 2p1/2 peaks are
centered at 166.80 and 168.30 eV, respectively (Fig. 10 (d)). The presence of sulphur in the NCs
is related to the syntheses step itself as the source of that is the CH3SO4 anion in the ionic liquid
[43].

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Fig. 10 High resolution deconvoluted XPS spectra of (a) Ti 2p (b) O 1s, (c) Y 3d and (d) S 2p
regions in 25 wt% Y2O3/ TiO2 NC synthesized via ILAHM.
Furthermore, EDS was used to identify the elements present in the prepared materials (Fig. S8).
In case of both of the pristine Y2O3(ILAHM) and TiO2(ILAHM) NPs, O was found along with their
corresponding Y and Ti elements (Fig. S8 (a & b)). However, 25 wt% Y2O3/ TiO2 NC(ILAHM); the
presence of all of three elements can be observed in Fig. S4 (c), confirming the existence of
Y2O3 content in the TiO2 matrix.

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FTꢀIR spectroscopy is mainly used to check the presence of functional groups present in the
synthesized nanomaterial, Fig.S9 contrasts the FTꢀIR spectra of pristine Y2O3, TiO2 NPs and 25
wt% Y2O3/ TiO2 NC(ILAHM). The significant characteristic peak for Y2O3 is observed at ca.
421cm–1 (Fig.S9 (a)) that can be assigned to stretching vibration modes of YꢀO [44], and spectral
region centered at ca. 3500 cm–1 can be assigned to vibrational modes of H2O molecules on the
surface of Y2O3/TiO2 NC [45]. Fig. S9 (b) shows the significant characteristic peak at ca. 400
cm–1 due to the TiꢀO stretching vibration modes in TiO2 [46]. For 25 wt% Y2O3/ TiO2 NC (ILAHM)
,
these peaks can be observed at ca. 478 cm–1 and ca. 668 cm–1 i.e shifted to higher wavenumber
compared to pristine Y2O3 & TiO2 NPs (Fig.S9 (c)), from these analyses, the formation of
Y2O3/TiO2 NC can be confirmed and the shift in the wavenumber in Y2O3/TiO2 NC compared to
Y2O3 and TiO2 may be related to the composite nature of the material.
TG analysis was employed to determine the thermal stability of the asꢀprepared materials.
Thermal stability of the as prepared 25 wt% Y2O3/ TiO2 NC (ILAHM) was studied by TGA analysis
(Fig. 11). Two obvious weight loss stages can be observed. The first stage from room
temperature to 100 °C and the second from 100 °C to 420 °C are attributed to the dehydration of
water content and thermal decomposition of organic substances, respectively. Furthermore,
beyond 420 °C there is no change in the shape of the curve (no weight loss) that indicates the
prepared NC is thermally stable at high temperatures [47].

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Fig. 11 Thermo gravimetric analysis of 25 wt% Y2O3/ TiO2 NC(ILAHM)
.
5. Conclusions
We have successfully synthesized pristine Y2O3 and TiO2 and Y2O3/TiO2 NCs via simple ionic
liquid assisted hydrothermal method for the first time. The photocatalytic activities of the NCs
were compared to the samples prepared via hydrothermal methods in the absence of ionic liquid.
Compared to the hydrothermal method the NCs prepared by ionic liquid assisted hydrothermal
method have improved the photocatalytic hydrogen production from water splitting that
highlights the importance of ionic liquid in the synthesis procedure. The hydrogen production
was optimized via thermal treatment and the synergy for the enhanced was obtained for 25 wt%
of Y2O3 /TiO2 (ILAHM) calcinated at 400°C for 1 h. The same sample when prepared in the absence
of ionic liquid has resulted into decrease in the photocatalytic activity. The enhancement can be
understood from the largest BET surface area, highest quantum yield and adequate surface
morphology of the sample. The methodology provided here clearly indicates the importance of

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ionic liquid assisted hydrothermal method for the syntheses of NCs. In the absence of IL the
particles agglomerate due to diffusion limited aggregation. On the other hand, selfꢀassembling
template nature of IL prevails the reaction limit aggregation mechanism that helps to improve the
physicoꢀchemical preoperties of the NCs for enhanced hydrogen production.
Acknowledgement: One of the authors, T.N. Ravishankar wishes to acknowledge Centre for
Nano and Material Sciences, Jain University, CNPqꢀTWAS, DSTꢀSERB and DST Nanomission
for financial support and Laboratory of Thin Films and Nanostructure Fabrication (L3F nano),
Institute of Physics, UFRGS, Brazil for research facilities.
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