Solar energy-controlled shape selective synthesis of zinc oxide nanomaterials and its catalytic application in synthesis of glycerol carbonate

Article abstract of DOI:10.1016/j.jssc.2020.121927

In this study, we have synthesized shape selective zinc oxide (ZnO) nanoflower using solar energy and naturally accessible aromatic amino acids like tryptophan, tyrosine and phenylalanine as a photo capping agents. This synthesized material has been characterized by various characterization techniques such as XRD, FE-SEM, EDX, UV–Vis and FTIR. The ZnO nanoflower synthesized using solar energy and photo capping agents exhibited excellent catalytic activity after calcination for the synthesis of glycerol carbonate via urea glycerolysis as compared to the conventional process owing to its shape selective morphology. Further, high resolution XPS studies were performed to explore the valence states and effectiveness of surface engineering of the ZnO catalyst. Such a unique technique of ZnO nanoflowers synthesis represents a novel and environmentally benign route for synthesis of shape selective metal oxide nanoparticles as well as derived nanomaterial after calcination showed excellent activity and potential recyclability for the conversion of waste into valuable products. After calcination ZnO nanomaterials shows 67% yield in the synthesis of glycerol carbonate at 140 ?°C in 4 ?h, at the end a catalytic reaction mechanism was proposed.

Full text of DOI:10.1016/j.jssc.2020.121927

Journal of Solid State Chemistry 295 (2021) 121927
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Solar energy-controlled shape selective synthesis of zinc oxide
nanomaterials and its catalytic application in synthesis of glycerol carbonate
Jayendra Ahire , Bhalchandra M. Bhanage *
Department of Chemistry, Institute of Chemical Technology, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Solar Energy
ZnO
Nanomaterials
Aromatic amino acid
Glycerol carbonate
In this study, we have synthesized shape selective zinc oxide (ZnO) nanoflower using solar energy and naturally
accessible aromatic amino acids like tryptophan, tyrosine and phenylalanine as a photo capping agents. This
synthesized material has been characterized by various characterization techniques such as XRD, FE-SEM, EDX,
UV–Vis and FTIR. The ZnO nanoflower synthesized using solar energy and photo capping agents exhibited
excellent catalytic activity after calcination for the synthesis of glycerol carbonate via urea glycerolysis as
compared to the conventional process owing to its shape selective morphology. Further, high resolution XPS
studies were performed to explore the valence states and effectiveness of surface engineering of the ZnO catalyst.
Such a unique technique of ZnO nanoflowers synthesis represents a novel and environmentally benign route for
synthesis of shape selective metal oxide nanoparticles as well as derived nanomaterial after calcination showed
excellent activity and potential recyclability for the conversion of waste into valuable products. After calcination
ZnO nanomaterials shows 67% yield in the synthesis of glycerol carbonate at 140 ꢀC in 4 h, at the end a catalytic
reaction mechanism was proposed.
1. Introduction
the main objectives of the scientific research community is to develop
innovative and novel practices that use an alternative sustainable en-
Metal and metal oxide nanomaterials are attracting huge com-
mercial and scientific interest due to its superior electronic, mechan-
ical, optical, and chemical properties [1,2]. Due to distinct chemical
and physical properties, it has extensive applications in the domain of
catalysis, adhesives/sealants, automotive, energy, electronics, opto-
electronics, biomedical, aerospace, etc. [3,4]. Numerous reports are
available to synthesize nanomaterials from top-down i.e., lithographic
etching, grinding in the ball mill, and sputtering techniques. Top-down
methods are industrially leading; however, it require specialized in-
struments to control temperature, pressure, vacuum, etc. Moreover,
resulting nanomaterials suffer from surface defects, non-uniform
shapes. In bottom-up techniques like vapor deposition, sole gel, pre-
cipitation, pyrolysis and solvothermal methods, atoms and molecules
are integrated into constituting building blocks to form nanostructures
[5–7]. These methods endow the excellent control of the size, shape,
and composition of nanoparticles through variation in precursor con-
centration and reaction conditions. Owning to the continuously
increasing demands of metal oxide nanomaterials, an economical and
ecologically safe method required for their preparations. Hence, one of
ergy source to prepare these materials with desired properties [8].
Solar energy is a ubiquitous component but often neglected in the
synthesis of nanomaterials. Light assisted methods can provide effi-
cient control over particle size, shape, and composition [9–12].
Recently, solar energy assisted the synthesis of nanomaterials taking
intense attention in the synthesis of plasmonic nanoparticles [13,14].
Furthermore, it provides new tools for the manipulation of
light-induced particle nucleation and growth, which induce shape
selectivity. However, the requirement of very strong absorbance
limited this attractive approach to plasmonic materials. During the
synthesis of transition metal oxides, solar energy is not provided
control over the shape and size of nanomaterials. This unexplored
opportunity of solar energy to control the shape and size of
non-plasmonic nanomaterials not only provides new paths for the
synthesis of different non-plasmonic materials but also gives a new
approach for large scale and sustainable synthesis of nanomaterials.
Aromatic amino acids act as an excellent capping agent for the
synthesis of plasmonic nanomaterials and non-plasmonic nano-
materials using the hydrothermal method [15,16]. Although amino
* Corresponding author. Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai, 400019, India.
E-mail addresses: Jayendra.ahire9@gmail.com (J. Ahire), bm.bhanage@ictmumbai.edu.in (B.M. Bhanage).
https://doi.org/10.1016/j.jssc.2020.121927
Received 22 August 2020; Received in revised form 15 December 2020; Accepted 16 December 2020
Available online 6 January 2021
0022-4596/© 2020 Elsevier Inc. All rights reserved.

J. Ahire, B.M. Bhanage
Journal of Solid State Chemistry 295 (2021) 121927
Scheme 1. (a) Structures of aromatic amino acids used as capping reagents, (b) Reaction mechanism for the formation of ZnO nanoflower under sunlight.
acid application as a photo reducing agent is explored for plasmonic
nanomaterials [17], the use of amino acid as a photocopying agent for
nonplasmonic nanomaterials is not explored yet.
2.2. ZnO nanoflowers synthesis/catalyst synthesis
To synthesize the ZnO nanoflowers, 1 mmol Zinc acetate, 1 mmol L-
tyrosine were added to 15 ml water. Then, the solution was stirred for 15
min, followed by the dropwise addition of aqueous NaOH (600 mg in 10
ml) solution. After precipitation, the reaction mixture was kept under
sunlight at 11 am Indian time (temperature range of 40–45 ꢀC) for 80 min
(Scheme 1). The deionized water is used to wash the resulting precipi-
tated product and later ethyl alcohol. Further, precipitant dried in an
oven at 100 ꢀC for 10 h. This as-synthesized material then designated as
tyrosine (ZnO- TYRS), phenylalanine (ZnO-PHYS), and tryptophan (ZnO-
TRPS). To compare the study at normal reaction conditions, a similar
experiment was performed without sunlight at 40–45 ꢀC for 80 min with
the same experimental conditions. Catalytic activity of resultant precip-
itant is explore after calcination for 4 h in air atmosphere at 500 ꢀC in
muffle furnace (see Scheme 2).
By considering the photo capping ability of aromatic amino acids in
the synthesis of non-plasmonic nanomaterials, we envisioned to use
the aromatic amino acids as photocapping agent and natural sunlight
as an alternative energy source for the shape and size-selective syn-
thesis of nanomaterials. The ZnO flower nanostructures were synthe-
sized under solar energy using aromatic amino acids like tyrosine,
tryptophan, and phenylalanine. The solar energy initiated a capping
mechanism with the structural evolution of ZnO nanoflowers has been
illustrated through controlled synthesis with UV–Vis spectroscopy. The
underlying mechanism of nanostructure growth has been established
through observation of the hyperchromic redshift in UV–vis spectra of
synthesized ZnO nanoparticles. Further, the catalytic activity of
calcined ZnO nanoflowers investigated for the synthesis of glycerol
carbonate from glycerol and urea at mild reaction conditions.
2.3. Characterization of ZnO nanoflowers
2. Experimental section
Absorption spectra were recorded on UV–Visible spectrophotometer
(Shimadzu UV-2450) with a quartz cuvette of optical path length 1.0 cm.
X-ray diffraction using Shimadzu XRD-6100 with 40 kV and 30 mA
2.1. Chemicals
Various chemicals such as glycerol (99%) were purchased from
Sigma-Aldrich Pvt. Ltd., Mumbai. Urea, zinc acetate, L-tyrosine, L-tryp-
tophan, L-phenylalanine and sodium hydroxide were procured from
Merck, India Pvt. Ltd., Mumbai.
diffractometer, CuK radiation using Cu-Kα of k ¼ 1.5405 Å employed and
the analysis was conducted between 10◦ and 80◦. The shape and size of
the prepared samples were determined using field emission scanning
electron microscopy (FEG-SEM) on Tescan MIRA 3 model instrument.
Scheme 2. ZnO catalyzed synthesis of glycerol carbonate.
2

J. Ahire, B.M. Bhanage
Journal of Solid State Chemistry 295 (2021) 121927
3. Results and discussion
High UV light absorbance is an essential property for a molecule to
utilize it as a photo capping agent. Hence, we select aromatic amino acids
because it shows high UV light absorbance due to the presence of aro-
matic functional groups along with amine and carboxylic acids. The
UV–Visible spectrum of aromatic side-chain has a characteristic absor-
bance peak at 280 nm, 275 nm, 258 nm of tryptophan, tyrosine, and
phenylalanine, respectively. The peak at lower wavelengths in the range
of 230–240 nm is caused by the absorbance of carboxylic acid moieties in
the compounds [18].
The X-ray diffraction (XRD) patterns of the ZnO synthesized using
tyrosine (ZnO-TYRS), phenylalanine (ZnO-PHYS) and tryptophan (ZnO-
TRPS) under solar energy are shown in Fig. 1. The crystalline nature was
confirmed by XRD patterns, which presented sharp and intense diffrac-
tion peaks at θ of 31.7, 34.3, 36.2, and 47.4 attributed to (100), (002),
(101) and (102) planes of hexagonal structure of ZnO. It confirms the
presence of the wurtzite structure of ZnO (JCPDS card no. 36–1451) in all
three samples (Fig. 1). It is observed that the XRD pattern of ZnO-PHYS
has the highest intensity resulting from a high crystallinity of ZnO
nanoflower made of nanorod with compared with other morphologies.
It was observed that tryptophan has the highest absorptivity in the
UV–Vis region as compared to the Tyrosine and lowest to the phenylal-
anine (Fig. 2(c)). The ZnO nanoparticles synthesis via solar energy
assisted reaction shows a hyperchromic redshift at 274 nm in UV–Vis
spectra due to the formation of the ZnO-AAA complex shown in the
yellow region of Fig. 2 (c, f, i) [19]. Moreover, ZnO of solar energy
assisted reactions also showed significantly high absorbance in range of
300–350 nm due to a higher quantity of ZnO nanoparticles (Fig. 2(c, f, i))
Fig. 1. X-ray diffraction (XRD) pattern of ZnO using tyrosine (ZnO-TYRS: Blue),
phenylalanine (ZnO-PHYS: Red) and tryptophan (ZnO-TRPS: Green). (For
interpretation of the references to colour in this figure legend, the reader is
referred to the Web version of this article.)
Fourier- Transform Infrared (FTIR) spectra were recorded on Bruker
Perkin Elmer-100 spectrometer. X-ray photoelectron spectroscopy (AXIS
Supra) was used to probe the oxidation state of synthesized ZnO nano-
flowers. The binding energies were corrected for the charge shift using
the C1 peak of graphitic carbon. (B.E. ¼ 284.6 eV) as a reference.
Fig. 2. FE-SEM analysis of ZnO nanostructures under sunlight using (a) tryptophan, (d) tyrosine (g) phenylalanine, and without sunlight (b, e, h) respectively. UV–Vis
absorbance spectra of ZnO synthesis using (c) tryptophan, (f) tyrosine, (i) phenylalanine with sunlight (Blue) and without sunlight (Red). (For interpretation of the
references to colour in this figure legend, the reader is referred to the Web version of this article.)
3

J. Ahire, B.M. Bhanage
Journal of Solid State Chemistry 295 (2021) 121927
Fig. 3. (a) Overall XPS survey spectrum, (b) FTIR spectra synthesis under sunlight using tyrosine (ZnO TYRS: Blue), Phenylalanine (ZnO PHYS: Red) and tryptophan
(ZnO TRPS: Green), (c) Zn 2p spectra of samples tyrosine (ZnO TYRS: Blue), Phenylalanine (ZnO PHYS: Red) and tryptophan (ZnO TRPS: Green), XPS spectra of O 1s of
ZnO TYRS (d); ZnO PHYS (e) and ZnO TRPS (f). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of
this article.)
[20]. Solar energy assisted synthesis ZnO nanomaterials shows higher
absorbance in the range of 230–240 nm by presence of carboxylic acid
moieties.
organic ligand.
Fig. 3(d–f) displays XPS spectra of O 1s region of ZnO TYRS, ZnO
PHYS, and ZnO TRPS. From Fig. 3(c), the Zn 2p core-level of ZnO
nanoflowers has two fitting peaks located at about 1042.6 and 1019.6 eV
attributed to Zn 2p1/2 and Zn 2p3/2, respectively. The decrease in BE
ascribed with the amino acid interaction with ZnO nanoparticles. These
results indicate that the chemical valence of Zn at the surface of three
nanoflower morphologies of ZnO is þ2 oxidation state. The binding en-
ergy difference between the Zn 2p1/2 and Zn 2p3/2 is 23 eV for all three
samples of ZnO, which is in agreement with the literature [22].
In O1s core-level spectrum of ZnO TYRS shows three different forms
of oxygen shown in Fig. 3 (d). Three fitting Gaussians peaks marked as
O1s (1), O1s (2) and O1s (3) were used to fit the experimental data. Peak
O1s (1), positioned at the lower binding energy of 529.15 eV is assigned
to O2- ions in lattice oxygen, which contributes to the perfect hexagonal
structure of ZnO lattice. The peak O1s (2) located at 530.55 eV belongs to
O2- ion present in the Zn–O bonding of ZnO. Peaks located at O1s (3) can
The structural features of all nanostructure synthesized using sunlight
were further analyzed using FEG-SEM. The FEG-SEM images of ZnO-
TRPS, ZnO-TYRS, and ZnO-PHYS (Fig. 2 (a, d, g)) show that the nano-
flower shape is selectively grown in ZnO nanoparticles when synthesis is
performed in the presence of sunlight. The synthesis of the ZnO nano-
particles without sunlight using tryptophan (ZnO-TRP) and tyrosine
(ZnO-TYR) showed the irregular shapes of these nanoparticles. While the
use of phenylalanine (ZnO-PHY) gave nanorods as shown in Fig. 2 (b, e,
h) respectively. The ZnO prepared under sunlight using tryptophan and
tyrosine shows nanoflower with rod and needle shape petals (Fig. 2 (a,
b)). Controlled size (1μm–2μm) of nanoflower with petals diameter from
50 nm-200nm of nanoflower is obtained when sunlight is provided for
80 min. The rod and needle type of petals are 300 nm–600nm in range of
length. A highly dense nanoflower structure obtained when phenylala-
nine is used as a capping agent under solar (Fig. 2. g).
–
–
be ascribed to the presence of C O bonding originated from the surface
Further, the FTIR analysis of ZnO was carried out to perceive the role
of aromatic amino acid as a photocapping agent (Fig. 3 (b)). The peak in
range of 1500–1550 cmꢁ1 is from the bonding between the COOH
moiety and the Zn2þ ions on the ZnO surface. The symmetric stretching
of carboxylate ions (COOꢁ) is noticed by a peak at 1406 cmꢁ1 [21]. The
characteristic peak of ZnO was observed at 480–500 cmꢁ1 in all ZnO
samples. Hence, the appearance of these peaks recognizes the role of
amino acid as photocapping agent, which is adsorbed on the surface of
ZnO nanostructures.
To obtain a detail information from the composition of the structures
of the prepared ZnO nanoparticles and chemical state after calcination,
XPS analysis was carried out. Fig. 3(a) shows an XPS survey spectrum of
the sample ZnO TYRS (blue), ZnO PHYS (red), ZnO TRPS (green). The
XPS survey spectrum reveals peaks corresponding to Zn, O, and C. The C
1s peak is correlated to atmospheric carbon as well as the carbon sub-
strate. All binding energies were calibrated by referencing the C 1s peak
(BE ¼ 284.6 eV). After calcination of ZnO TYRS and ZnO TRPS transition
of nanoflower structure into rod shape structure is took place by loss of
adsorbed amino acid molecule [23,24].
Similarly, in the ZnO PHYS case of Fig. 3 (e), three fitting Gaussians
peaks located at 529.34, 530.85, and 532.31. Lower binding energy peak
is confirmed by the presence of a peak O1s (1) at 529.34 is assigned to O1
in Zn–O bonding. A peak of O1s (2) at 530.85 is attributed to O2- ions in
the Zn–O bonding of the wurtzite structure of ZnO. The contribution at
532.31 eV of O1s (3) is usually ascribed to molecular water or to
carboxylate- or carbonate-type species. In the case of ZnO TRPS of Fig. 3
(f), two deconvoluted peaks are located at binding energies 529.76,
530.45. Here, the lower binding energy peak of O1s (1)) is attributed to
the Zn–O bonding of the wurtzite structure of ZnO, the presence of a
middle peak of O1s(2) at binding energy 530.45 eV is ascribed to the
Zn–O bonding in ZnO.
A recent study shows that peak at 530.45 eV from O2ꢁ ion in ZnO is
associated to Zn–O bonding in ZnO strongly correlated to higher catalytic
active sites for activation of glycerol leading to high catalytic activity of
porous ZnO nanoparticles in urea glycerolysis, [25]. We observed that,
highest intensity of peak of O2 from O2ꢁ is found in ZnO TRPS followed
4

J. Ahire, B.M. Bhanage
Journal of Solid State Chemistry 295 (2021) 121927
Fig. 4. (a) ZnO TYRS,(b) ZnO PHYS, (c) ZnO TRPS after calcination at 500 ꢀC.
donation from photoionization of aromatic amino acids [31].
by ZnO TYRS and ZnO PHYS sequentially. The lower intensity might be
attributed to some amino acid species still remain on the ZnO surface
together with surface carbon resulting from decomposition of the amino
acid. High area ratio of O1s (2)/O1s (3) can correlated with more
available catalytic active sites due to low amount of adsorbed amino acid
on ZnO [26]. Area ratio of peaks O1s (2)/O1s (3) is highest for ZnO TRPS
followed by ZnO TYRS and ZnO PHYS. It shows presence of amino acid
adsorbed on ZnO is in order of ZnO PHYS > ZnO TYRS > ZnO TRPS.
Further in this study, the higher catalytic activity of ZnO TYRS and ZnO
TRPS can be attributed to peak from O2- ions in the Zn–O at 530.55 and
530.45 respectively. After calcination of precipitant ZnO TYRS ZnO
TRPS, ZnO PHYS shows shapes of nansoflakes, nanorod and irregular
shape respectively. ZnO TYRS show highest catalytic activity due to
higher active sites and high available surface area from nanoflakes
structure (Fig. 4).
In solar energy assisted pathway the resultant precipitant is majorly
ZnO-AAA nanomaterial compared to precipitant synthesis in absence of
solar energy, confirm by UV–Vis spectra (Fig. 2 (c,f,i)) (Scheme 1: Step-
4). After the formation of ZnO-AAA complex, transportation of Zn from
solution to the crustal surface resulting in the ripening of ZnO nanorod
[32]. Thus, soluble ZnO-AAA complex species in the solution phase
adsorb on sites with high surface energy, i.e. (0002) plane of ZnO. This,
in turn, results in a rapid increase in the size of nanoparticles when solar
energy is used.
In the absence of solar energy, competitive coordination between zinc
with OH and aromatic amino acid is dominated by OH-. After the satu-
ration of growth species [Zn (OH)4]2- in solution, the formation of ZnO
seeds takes place (Scheme 1: Step-3). In the growth of ZnO nanoparticle,
after ZnO seeds are formed, [Zn(OH)4]2- adsorb on positively charged
(0001) plane of ZnO lattice. In the absence of solar energy, aromatic
amino acid shows poor capping ability. Whereas, in the case of tyrosine
and tryptophan without solar energy, the agglomerated structure of ZnO
is observed due to limited capping potential. The small amount of rod-
like nanostructure attributed to the limited role of tyrosine and trypto-
phan for the growth of ZnO. In the case of phenylalanine, higher con-
centration [Zn (OH)4]2- complexes on ZnO seed could lead to the
formation of the nanorod.
3.1. Reaction mechanism for growth of ZnO nanostructures
In solar energy-controlled growth of ZnO nanostructure, an aromatic
amino acid is an active tool to control seed assisted growth due to its dual
role as surface-capping and surface-directing agents. Based on the above
results, we proposed a reaction mechanism for the formation of ZnO
nanoflower under sunlight.
The synthesis of ZnO nanoflower has been carried out through sun
light-assisted activation of aromatic amino acid through photoionization
(electron ejection) in alkaline condition) [27,28]. After the addition of
aqueous alkaline solution formation of [Zn(OH)4]2- complex takes place
(Scheme 1: Step-1, 2).
In next step, the reaction solution was kept under solar energy. Here,
ejection of the electron due to the interaction of a photon with the aro-
matic ring of amino acid takes place with the formation of cation radical.
Later, the formation of neutral radicals takes place by losing protons from
cation species. The formation of [Zn(OH)4]2- -AAA is followed by pre-
cipitation of ZnO-AAA nuclei initiated (Scheme 1: Step-4).
The photoionization process is monophotonic in an alkaline envi-
ronment and results in the formation of the neutral radical and solvated
electron [29]. In the competitive process of ZnO nuclei formation,
photoionization accelerates the process of formation and growth of ZnO
nuclei from Zn (II). The higher rate of nucleation and growth of nano-
particles can be confirmed via UV–Vis spectroscopy of ZnO [20]. In the
UV–Vis absorption spectrum of the ZnO, hyperchromic redshifts (5–10
nm) in range of 310–350 nm were observed for ZnO TRPS and ZnO TYRS
containing zinc and aromatic amino acid with sunlight as compared to
without sunlight (Fig. 2 (c, f, i) green region). The hyperchromic redshifts
indicate the acceleration of nucleation and growth of ZnO nanoparticles
synthesis under solar energy due to the Zn-AAA complex [30]. The
positive and negative charges of solar energy activated aromatic amino
acid can adsorbs on (1010) plane, resulting in the formation of nanorod
with cementing effects [21]. From these steps, it is ascertaining that
several petals of ZnO integrate into ZnO nanoflower due to electron
3.2. Catalytic activity of ZnO nanoparticles
The transportation sector contributes about 20% of total CO2 emis-
sions in the world, predict to increase by double the current level in 2050
[33]. Therefore, biodiesel from vegetable oil and animal fat is a sus-
tainable alternative to petrol and diesel; however, during the production
of biodiesel, it produces glycerol of about 10–20% by volume [25]. The
increasing demand for biodiesel and unidentified application of glycerol
contributes to a decline in the price of glycerol. Glycerol carbonate has a
wide range of applications in chemical industries, e.g., raw materials for
the synthesis of polymers including polyester, polyurethane and poly-
amide, surfactants, and lubricating oils [34–37]. Consequently, the sci-
entific community of catalysis and chemistry are in search of new
catalysts and pathways for this transformation. In the conventional
process, the use of phosgene or energy-intensive epoxide in the synthesis
of dimethyl carbonate, propylene carbonate, or ethylene carbonate also
limits the application of transesterification with glycerol [38]. The CO2
and CO utilization for the synthesis of glycerol carbonate is not
economically feasible due to low conversion, the high value of catalyst
[39–42]. Furthermore, the synthesis of glycerol carbonate using glycerol
and urea is an attractive approach due to the reuse of generated ammonia
in the synthesis of urea. Hence, an efficient catalyst with a simple and
sustainable synthetic approach is highly desirable. In these contexts, we
intended to use the intrinsic property of synthesized ZnO nanomaterial
by calcination to remove the capping agent and develop an active and
stable catalyst.
5

J. Ahire, B.M. Bhanage
Journal of Solid State Chemistry 295 (2021) 121927
Table 1
Summary of catalytic activity of different catalysts with reaction conditions for the synthesis of glycerol carbonate.
Entry
Catalyst
Temp (ꢀC)
Time
Conversion (%)
Selectivity
(%)
Yield
(%)
Ref.
(hr)
Catalytic activity of Different Catalyst
1
2
3
4
5
6
ZnO-TRP
ZnO-TYR
ZnO-PHY
ZnO-TRPS
ZnO-TYRS
ZnO-PHYS
150
150
150
150
150
150
4
4
4
4
4
4
52
55
51
69
75
70
90
87
88
88
91
89
47
48
45
61
68
62
This
Work
This
Work
This
Work
This
Work
This
Work
This
Work
Effect of Temperature
7
8
9
ZnO-TYRS
120
140
160
4
4
4
47
72
83
85
93
90
40
67
74
This
Work
This
Work
This
ZnO-TYRS
ZnO-TYRS
Work
Effect of Reaction Time
10
ZnO-TYRS
140
140
2
6
53
84
58
89
31
75
This
Work
This
11
ZnO-TYRS
Work
Comparison of Catalytic activity with reported catalyst
12
13
14
15
16
17
18
(CH3COO)2Zn.H2O
ZnOSO4
Zn/MCM-41
Cu/MCM
Ni/MCM
2.5 wt%Au/ZnO
MgO
130
130
140
145
145
150
150
3
3
5
3
3
4
4
65
81
84
66
60
88
69
80
92
98
68
89
56
37
52
75
82
49
53
49
26
[43]
[44]
[45]
[45]
[45]
[44]
[44]
temperature variations from 140-120 ꢀC (Table 1, entry 7–9). At 140 ꢀC,
maximum selectivity (93%) is observed. Hence we select 140 ꢀC as
temperature for further study.
Furthermore, reaction time varies to analyze impacts on yield. The
highest catalytic performance of 75% yield for glycerol carbonate was
achieved after 6 h, but the maximum selectivity was recorded at 4 h with
a yield of 67% (Table 1, entry 9, 11, 12). Hence, we used 4 h as a reaction
duration for further study. Further, recyclability study of the catalyst was
performed. The recycling experiment with a yield of 57 % (Fig. 5)
showed the reliability of the catalyst up to the 3 cycles.
3.3. Reaction mechanism
Based on the previous reports, a reaction mechanism has been
postulated for the ZnO-promoted glycerolysis of urea (Scheme 3)
[44–46]. At the outset, urea and glycerol adsorb on the surface of zinc
oxide, which comprises lewis acid-base functions. On the Lewis basic
sites, urea molecule is activated by OH groups of glycerol. Then, the
carbonyl group of urea attack to the adsorbed glycerol moiety on ZnO
with the release of NH3. Next, the secondary –OH group of activated
glycerol attack on urea carbonyl carbon to generate a five-membered
cyclic glycerol carbonate. This step simultaneously involve the loss of
the second molecule of NH3. Ammonia formed during the reaction vent
out by continuous N2 supply, it moves the equilibrium to a maximum
conversion. In the final step of the reaction path, glycerol carbonate re-
leases from catalytic surface.
Fig. 5. Recyclability study of ZnO-TYRS for glycerol carbonylation (Reaction
conditions: glycerol/urea ¼ 1:1, catalyst: 5.0 wt %, Temperature: 140 ꢀC, N2 of
20 ml/hr flow to remove NH3 formed during reaction, Time: 4 h).
After calcination of synthesized ZnO from solar energy, we observed a
change in morphology. This can be described because of the loss of
organic ligands. We used catalyst at 5.0 wt% of glycerol with N2 of 20 ml/
hr flow to remove NH3 formed during the reaction. At the outset, cata-
lytic activity investigated of all calcined catalysts at 150 ꢀC (Urea:
Glycerol ¼ 1:1). We observed that solar energy assisted synthesis nano-
materials in showing higher catalytic activity (Table 1, Entry 4–6) than
without solar energy (Table 1, Entry 1–3). It was observed that ZnO-TYRS
showed a higher conversion than ZnO-PHYS and ZnO-TRPS. Next, the
catalytic performance of calcined ZnO-TYRS has been investigated with
4. Conclusion
We developed a sustainable and economically competent method for
the shape of selective synthesis of ZnO nanomaterials under solar energy
using aromatic amino acids as photo-capping agents. Aromatic amino
6

J. Ahire, B.M. Bhanage
Journal of Solid State Chemistry 295 (2021) 121927
Scheme 3. Proposed reaction mechanism for ZnO catalyzed glycerol carbonylation with urea.
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acids, such as tyrosine, tryptophan, and phenylalanine, demonstrated as
highly efficient photocapping agents under solar energy for the synthesis
of ZnO nanoflowers. Further, calcined ZnO nanomaterial showed excel-
lent catalytic activity for the carbonylation of glycerol by using the urea
as a green chemical for the efficacious synthesis of glycerol carbonate.
CRediT authorship contribution statement
Jayendra Ahire: Conceptualization, Methodology, Investigation,
Visualization, Writing - original draft, Formal analysis. Bhalchandra M.
Bhanage: Conceptualization, Supervision, Validation, Resources,
Writing - review & editing, Funding acquisition.
[11] C.K. King’ondu, A. Iyer, E.C. Njagi, N. Opembe, H. Genuino, H. Huang, R.A. Ristau,
S.L. Suib, Light-assisted synthesis of metal oxide heirarchical structures and their
catalytic applications, J. Am. Chem. Soc. 133 (2011) 4186–4189, https://doi.org/
10.1021/ja109709v.
Declaration of competing interest
[12] T. Dexin, W. Yanli, G. Ying, Facile visible-light-assisted synthesis, optical, and
electrochemical properties of Pd nanoparticles with single-crystalline and multiple-
twinned structures, Rare Met. Mater. Eng. 46 (2017) 2065–2069, https://doi.org/
10.1016/S1875-5372(17)30180-7.
[13] K. Dubey, B.G. Anand, R. Badhwar, G. Bagler, P.N. Navya, H.K. Daima, K. Kar,
Tyrosine- and tryptophan-coated gold nanoparticles inhibit amyloid aggregation of
insulin, Amino Acids 47 (2015) 2551–2560, https://doi.org/10.1007/s00726-015-
2046-6.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgment
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The author is thankful to the Council of Scientific and Industrial
Research, New Delhi, for its financial support for the award of Senior
Research Fellowship. The author is also grateful to Dr. Vithal Saptal,
Pohang University of Science and Technology for his writing assistance.
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