Fabrication and characterization of adenine-grafted carbon-modified amorphous ZnO with enhanced catalytic activity

Article abstract of DOI:10.1002/aoc.6013

Sustainability has become a countersign and guiding rule for current field of nanocatalysis. Herein, we report a cost-effective, greener, clean, and proficient process for the formation of adenine-grafted carbon-modified amorphous ZnO nanocatalyst (ZnO@AC

Full text of DOI:10.1002/aoc.6013

Received: 14 May 2020
DOI: 10.1002/aoc.6013
Revised: 10 August 2020
Accepted: 19 August 2020
F U L L P A P E R
Fabrication and characterization of adenine-grafted carbon-
modified amorphous ZnO with enhanced catalytic activity
Bushra Chowhan
| Monika Gupta
| Neha Sharma
Department of Chemistry, University of
Jammu, Jammu, 180006, India
Sustainability has become a countersign and guiding rule for current field of
nanocatalysis. Herein, we report a cost-effective, greener, clean, and proficient
process for the formation of adenine-grafted carbon-modified amorphous ZnO
nanocatalyst (ZnO@AC) derived from garment industry waste (waste cotton
cloth). Due to adenine functionality, catalyst provides consistent dispersion of
ZnO providing catalytically active sites for the synthesis of pyrano[2,3-d]pyrim-
idines and bis(pyrazol-5-ole) and alters the electron–hole pair recombination
without notable mass-transfer limitation. The photocatalytic evaluation of
ZnO@AC was performed on methyl orange (MO) dye under UV light and
87.3% degradation efficiency resulted in 75 min. Moreover, the catalyst was
recyclable and could be reused up to eight runs, making it more sustainable.
The morphology of ZnO@AC remained intact with the slight agglomeration of
ZnO nanoparticles (nps) after eight recoveries according to the transmission
electron microscopy (TEM) image of the used catalyst.
Correspondence
Monika Gupta, Department of Chemistry,
University of Jammu, Jammu 180006,
India.
Email: monika.gupta77@rediffmail.com
Funding information
HRDG-CSIR, New Delhi, India, Grant/
Award Number: (SRF, File. No.: 09/100
(0199)/2017-EMR-1)
K E Y W O R D S
adenine, bis(pyrazol-5-ol)s, methyl orange, pyridine derivatives, waste cotton cloth
1 | INTRODUCTION
carbon.[9] Thus, the synthesized carbon finds applications
in composite materials, electrocatalysis, pollution control
Catalysis has become a contemporary revitalization field of
interest in devising and developing catalysts procured from
low-cost and earth-abundant materials, that is, non-
platinum group metals (NPGMs), intending to improve the
general sustainability of catalytic processes.[1] The synthesis
of heterogeneous catalysts from waste materials has
become more and more popular over the past two
decades to make the system more cost-effective and
sustainable.[2] Among the most copious sources are waste
biomass from agriculture, sewage, mining and metal
fabrication, and the iron, steel, and textile industry.[3–7]
Among various waste biomass, carbon, in particular, has
an exceptional research focus.[8] Traditionally, activated
carbon is synthesized by carbonization of petroleum coke,
wood, and coconut at a high temperature under insuffi-
cient air and even from carbohydrate, leading to sp2
treatment, energy storage, water treatment, gas separations,
and as support for heterogeneous catalysts.[10–12] Carbon as
heterogenous support has been used for the dispersion of
an active metal component, but the leaching is the limit-
itation.[13] Such a major problem can be dodged by grafting
various functional groups onto the surface of carbon. Zinc
oxide (ZnO) has a wide band gap (3.37 eV) at room temper-
ature, which makes it a semiconductor, and its high elec-
tron mobility (200–300 cm−2 V−1 s−1) promotes its electron
transfer efficiency.[14] Nano-ZnO of various morphologies
has seen tremendous applications as catalysts in different
organic reactions that include Knoevenagel condensation,
Mannich
reaction,
and
in
various
organic
transformations, such as the synthesis of antiplatelet
drug (clopidogrel), β-acetamido ketones/esters, phospho-
nomalonates, ferrocenylphosphonates, O-acylation of
Appl Organomet Chem. 2020;e6013.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6013

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CHOWHAN ET AL.
alcohol, enamination of 1,3-dicarbonyls, and β-amino
carbonyl compounds.[15] Rajesh et al. synthesized reduced
GO-ZnO nanocomposite for the synthesis of 3-substituted
indoles and compared it with ZnO nanoparticles (NPs),
concluding that reduced GO-ZnO nanocomposite showed
much superiority over ZnO NPs.[16] ZnO is suitable for
short wavelength optoelectronic applications because of its
wide band gap. In ZnO, there is a generation of electron–
hole pair recombination, which is the major limitation of
photocatalytic activity. Pondering all these facts, there is a
huge scope to explore and to attain an alternate method for
the synthesis of ZnO loaded, functionalized, thermally
stable, and active carbon support from readily available
waste material for altering the limitations and achieving
high catalytic activity.
Pyrano[2,3-d]pyrimidines are annulated uracils,
available as key structural units in some natural
products such as polyethers, antibiotics, carbohydrates,
pheromones, iridoids, and alkaloids.[17,18] Pyrano[2,3-d]
pyrimidines are building blocks of various natural
products that are also used as a drug for insomnia
treatment.[19] They also exhibit various biological
and pharmacological properties such as antitumor,
cardiotonic, antihypertensive, bronchiodilator, anti-
bronchitic, antimicrobial, antihepatotoxicity, antimalar-
ial, analgesic, antiviral, and antifungal activities.[18,20–29]
An already reported method for the synthesis of pyrano
[2,3-d]pyrimidines using cyclodextrin, 1,4-diazabicyclo
[2.2.2]octane (DABCO), taurine, etc., suffers from cer-
tain downsides involving less yield, high reaction tem-
perature, and more time for the completion of the
reaction.[30–32] Similarly, pyrazoles are again a notable
five-membered N-fused class with a wide range of bio-
logical activities.[33] Pyrazoles are present in numerous
drug molecules such as gastric secretion stimulatory,
environment.[54,55] Methyl orange (MO), from the group
of azo dyes, cannot be degraded easily in the environ-
ment because of its stable structure, and it persists for a
longer period of time.[56] There are various methods for
the removal of toxic dyes from industrial waste water
such as ultrafiltration, adsorption, reverse osmosis,
photocatalytic degradation, and ion exchange.[57-60] But
photocatalytic degradation is an advanced oxidation
process (AOP) for the decomposition of organic
pollutants, which do not create any secondary contami-
nation.[61] The utilization of visible/UV light into AOPs
provide a green method for the degradation of dyes. A
large number of reports are there on the photocatalytic
degradation of MO such as N-doped ZnO, CuO/BiFeO3,
CeO2, SnO2, and nano–ZnO, but the time period required
for the degradation of MO was very high and efficiency
of degradation was very low.[62-65] The present work is an
attempt to reduce the time required for the degradation
of MO under UV irradiation.
This work deals with the synthesis of carbon material
by carbonization of waste cotton cloth collected from the
garment industry and then its covalent functionalization
by organoamine, that is, adenine, for the first time. Zinc
oxide, a cheaper and earth-abundant metal oxide, was
immobilized over the organoamine-functionalized carbon
to obtain a sustainable catalyst. The catalytic activity was
examined for pyrano[2,3-d]pyrimidines and bis(pyrazol-
5-ole) synthesis and in photodegradation of MO.
2 | EXPERIMENTAL
2.1 | Materials and characterization
techniques
anti-inflammatory,
antipyretic,
antidepressant,
Anhydrous ZnCl2 (99.99% pure), ammonium hydroxide
solution, potassium hydroxide, and sodium hydroxide
were purchased from Sigma-Aldrich. All the organic
substrates were also purchased from Sigma-Aldrich.
Waste cotton cloth was collected from a local garment
industry. The morphology of the catalyst was charac-
terized by field emission gun-scanning electron micros-
copy (FEG-SEM), elemental mapping (JSM-7600F,
JEOL, 30 kV), and high-resolution transmission
electron microcopy (HR-TEM) (Tecnai G2, F30, FEI;
300 kV). Fourier transform infrared (FTIR) spectros-
antibacterial, antifilarial agent, analgesic, antifungal,
antianxiety, and antitumor.[34–43] In coordination chem-
istry, pyrazoles as a ligand can differently bond with
metals and can also form strong bridge.[44,45] The litera-
ture survey for the synthesis of pyrazole derivatives
reveals
various
catalysts,
namely,
pyridine
trifluoroacetate, sodium dodecyl sulfate, nanostructured
diphosphate, N-methylimidazolium perchlorate, lemon
juice, triethyl-benzyl ammonium chloride, alpha-casein,
and triphenylphosphine.[46-53] The above catalysts have
their own weaknesses such as high-priced reagents and
catalysts, reagents, tiresome steps, strict reaction condi-
tion, strongly basic or acidic condition, and long
reaction time.
copy was recorded on
a Shimadzu spectrometer
(400–4,000 cm−1). Powder X-ray diffraction was carried
out on Smart lab, 9 kW rotating anode, Cu Kα radia-
tion λ = 1.5148 Å with a scanning rate of 2ꢀ min−1
from 20ꢀC–80ꢀC to establish the crystalline nature of
Different industries, such as leather, pharmaceuticals,
textiles, and paper making are the major sources of dye
pollutants, which are hazardous for humans and the
the samples. Super Nova
E (dual) diffractometer
system was used for single crystal diffraction. Labram

CHOWHAN ET AL.
3 of 13
HR-Evolution Raman Spectrometer was used for
photoluminescence (PL) using a laser of 352 nm. Light
irradiation in photodegradation experiment was con-
ducted out by illuminating a UV–Visible spectrometer
(PG instrumentation, US T-90). X-ray photoelectron
spectroscopy (XPS) was performed on PHI 5000 Versa
Prob II for the determination of oxidation states
and chemical compositions of the catalyst. Ther-
mogravimetric analysis (TGA) was conducted on
Perkin Elmer diamond TG/DTA with a heating rate of
5ꢀC min−1 from 25ꢀC to 800ꢀC under a nitrogen
atmosphere. The characterization of the product
synthesized by nuclear magnetic resonance (NMR) was
performed on Bruker Avance III (400 and 100 MHz).
TEM was scanned by FP 5022/22-Tecnai G2 20
S-TWIN, FEI.
in activating agent for 10 h with the weight ratio of the
activating agent and cotton cloth as 2.5:1. The cotton
cloth was washed with distilled water and dried in an
oven at 90ꢀC. The activation and carbonization were
performed by mixing infiltrated cotton cloth (10 g) and
H2SO4 (2 ml) at 100ꢀC in an oven for 10 min. The carbon-
ized and activated cotton cloth was then washed with
distilled water to neutralize the pH. After being dried in
an oven at 80ꢀC, the product formed was grounded in
agate mortar to obtain the CS.
2.2.2 | Synthesis of –COCl functionalized
carbon
For acid chloride functionalization of carbon, the above
prepared CS (1 g) was dispersed and reflexed in SOCl2
(250 ml) at 80ꢀC in the presence of DMF (N,N-dimethyl
formamide, 6.5 ml) for 24 h, which gave neon green color
to the solution. The excess of SOCl2 was distilled off, and
dried –COCl functionalized carbon (CCl) was collected
for further functionalization.
2.2 | Synthesis of ZnO NP-immobilized
adenine-functionalized carbon
nanocatalyst (ZnO@AC)
2.2.1 | Synthesis of carbon structure
The carbon structure (CS) was obtained by activation of
cotton cloth using KOH. First, the cotton cloth was
washed with NaOH (1 M) solution to dispose of oils and
fats. The activating agent was prepared using KOH (20%)
and distilled water (80%). The cotton cloth was infiltrated
2.2.3 | Synthesis of adenine-functionalized
carbon
As-synthesized CCl powder (1 g) was allowed to react
with adenine (6.66 mmol) in dry tetrahydrofuran (THF,
SCHEME 1 Scheme for
the synthesis of ZnO@AC from
waste cotton cloth

4 of 13
CHOWHAN ET AL.
6.66 ml) at 90ꢀC for 12 h. The prepared adenine-
functionalized carbon (AC) was filtered and then washed
with distilled water and ethanol. AC was dried at 50ꢀC
under vacuum.
muffle furnace at 200ꢀC for 1 h. During the adjustment of
pH value, NH4OH reacted with zinc chloride and
converted to Zn (OH)2 and by heating filtered solid in air
convert Zn (OH)2 to ZnO NPs.
2.2.4 | Synthesis of ZnO NP-decorated AC
2.3 | Production of pyrano[2,3-d]
pyrimidines
The ZnO NP-decorated AC (ZnO@AC) was synthesized
by hydrolysis of zinc chloride (Scheme 1). Zinc chloride
(ZnCl2/0.136 g/1 mmol) was first dissolved in an appro-
priate amount of ethanol in which ZnCl2 got dissolved
and followed by the addition of AC (1 g) to it. The pre-
pared solution was stirred for 10 min, and NH4OH was
added until the solution was neutralized. The solution
was further stirred for 30 min and filtered using sintered
glass crucible. The solid obtained was dried at 80ꢀC using
an oven for 5 h. The final catalyst, that is, ZnO NP-
decorated AC, was obtained by heating the solid in a
To a round-bottomed flask was added aldehyde (1 mmol),
barbituric acid (1 mmol), aniline (1 mmol), and
malononitrile (1 mmol) in EtOH/H2O (1:1) (3 ml) and
ZnO@AC (0.050 g). The mixture was stirred at room tem-
perature and monitored by thin-layer chromatography
using petroleum ether:ethylacetate. After the completion of
the reaction, hot ethanol was added to the reaction mixture
to filter out the catalyst in order to obtain the product. The
filtrate was evaporated to obtain a crude product. The pure
product was crystallized from the crude product using hot
FIGURE 1 Field emission gun–
scanning electron microscopy (FEG-
SEM) at high and low magnifications (a,
b); high-resolution transmission electron
microscopy (HR-TEM) at high and low
magnifications (c–e); SEAD pattern (f)
of immobilized ZnO@AC

CHOWHAN ET AL.
5 of 13
1
ethanol. The obtained product was characterized using H
NMR and 13C NMR techniques.
MO in water using UV light. ZnO@AC (100 mg) was
dispersed in a 100-ml MO (0.03 mmol) solution, after
which it was stirred for 30 min in the dark. This
established adsorption/desorption equilibrium between
the surface of ZnO@AC and MO molecules. Subse-
quently, the mixture was flashed with UV light
(254 nm). Four-milliliter samples were taken from the
above mixture after every 15 min, and the catalyst was
separated by centrifugation and then decantation for its
complete removal to quench the degradation. The
obtained samples were then analyzed using UV–Vis
spectroscopy (rangeꢁ250–600 nm). MO gave absorbance
maxima at 456 nm, which diminished with time under
UV light.
2.4 | Production of bis(pyrazol-5-ole)
To a stirred mixture of hydrazine hydrate (2.0 mmol),
ethyl acetoacetate (2.0 mmol), and ZnO@ AC (0.050 g) as
catalyst in EtOH/H2O (1:1) (3 ml) was added aromatic
aldehyde (1.0 mmol) after 1 min. The reaction mixture
above was stirred at room temperature for the required
time. Thin-layer chromatography was used to monitor
the reaction. To the reaction mixture, hot ethanol (5 ml)
was added and filtered to separate the catalyst. Finally,
the crude product was by evaporation. Recrystallization
of the solid product was done by ethanol. The pure
1
product was then characterized using H NMR and 13C
NMR techniques.
3 | RESULT AND DISCUSSION
3.1 | Characterization
2.5 | Photodegradation MO
The FEG-SEM revealed the rough surface of the prepared
catalyst, and no ordered porosity is observed in high mag-
nification of SEM (Figure 1a,b). The ZnO particles were
spherical and had a consistent distribution. To obtain
The prepared nanocatalyst (ZnO@AC) was evaluated for
photocatalytic activity by measuring photodegradation of
FIGURE 2 The elemental map for C, O, N, and Zn showing uniform dispersion for each element (a–e); Fourier transform infrared
(FTIR) spectrum of ZnO@AC (f); X-ray diffraction pattern (XRD) pattern of ZnO@AC (g)

6 of 13
CHOWHAN ET AL.
more details about the structures of catalyst, HR-TEM
measurements were carried out. The catalyst was first
dispersed in the ethanol, ultrasonicated, and then cast on
the TEM grid. The grid was then dried under IR lamp.
The representative TEM images taken for the catalyst
(Figure 1c–e) corresponded to the high-resolution magni-
fication morphologies of the catalyst showing ZnO immo-
bilization over adenine-grafted carbon. Insets are the
higher magnification of green square areas in Figure 1e.
From these images, we can recognize that ZnO NPs were
in the shape of nanospheres having an average size of
4.68 nm. Figure 1e demonstrated that the distinct lattice
fringes of d = 0.26 nm matched with (002) planes of
ZnO. The selected area electron diffraction (SAED)
pattern (Figure 1f) showed an amorphous halo for the
prepared catalyst.
uniform distribution of ZnO over the adenine grafted
carbon. Figure 2b–e shows elemental maps for C, O, N,
and Zn, respectively. The FTIR spectrum of ZnO@AC
(Figure 2f) showed a peak at 470 cm−1 and a strong peak
at 1,188 cm−1 corresponding to Zn–O stretching bond
and the amide C–N bond, respectively. The peak at
1,684 cm−1 was a characteristic peak of the CO stretch in
the amide group. The peaks at 1,560 and 1,618 cm−1 are
typical peaks of graphitic carbon. The broad hump in the
range of 3,100–3,500 cm−1 was owed to the merging of
O–H and N–H stretching bands. These results demon-
strated that the adenine molecules were linked to carbon
covalently by amide linkage. Along with these peaks, a
high intensity absorption band was observed at 404 cm−1
,
which corresponds to the E2 mode of hexagonal ZnO
supporting the synthesis of ZnO at 200ꢀC. X-ray diffrac-
tion (XRD) analysis revealed the presence of amorphous
zinc oxide over AC (Figure 2g). There was no diffraction
peak detected in the XRD pattern, revealing legible
The elemental mapping technique was performed on
the prepared catalyst for the presence and distribution of
elements (Figure 2a–e). The images confirmed the
FIGURE 3 Thermogravimetric
analysis (TGA) spectra for CS
(black), CCl (red), AC (green) and
ZnO@AC (blue) (a);
thermogravimetric–differential
thermal analysis (TG-DTA) graph of
ZnO@AC (b); X-ray photoelectron
spectroscopy (XPS) of ZnO@AC
showing the presence of Zn as ZnO
(c–e); photoluminescence
(PL) spectra of ZnO@AC with a near
edge emission band at 322 nm and a
red emission at 644 nm (f)

CHOWHAN ET AL.
7 of 13
crystalline phase. The XRD spectrum consisted of struc-
tured amorphous halo, which confirmed the amorphous
form of the prepared catalyst. Both XRD and SEAD pat-
tern confirmed the ZnO NPs are amorphous form
supporting the greater catalytic activity.
peaks corresponding to C1s, O1s, N1s, Zn3p, Zn3s, and
Zn2p were detected (Figure 3c). The Zn2p and Zn3p
spectra (Figure 3e) showed a typical ZnO profile. The
valence state of zinc in the catalyst was confirmed by the
two binding energy peaks located at 1,042.85 eV
(Zn2p1/2) and 1,019.85 eV (Zn2p3/2), which correspond to
core levels of the zinc(II) ions. The binding energy
difference between the two lines is 23.0 eV, which con-
firms that the Zn atoms are in a completely oxidized state
in the catalyst. Figure 3d shows the O1s high-resolution
XPS spectra of ZnO. The peak at around 530.18 eV is
attributed to the oxidized metal ions in the NPs, namely,
O–Zn in the ZnO lattice. XPS further confirmed the
conversion of zinc hydroxide into zinc oxide at 200ꢀC.
The quantum confinement alters the electronic band
structure of semiconductor materials; it is anticipated
that for small sizes of nanostructures, the PL properties
will be altered. The PL properties of ZnO@AC demon-
strated a relative intensity emission between the UV–
Visible emissions when the spectrum was recorded at
room temperature with the excitation wavelength of
320 nm. It was found that the PL of the catalyst was
dominated by the peak near-band-edge UV emission. A
dominant, sharp, and intense peak at 322 nm in the UV
region was observed (Figure 3f). Also, an emission band
in the visible region in the region 644 nm was observed,
The catalyst was designed and functionalized with
adenine in order to create a more heat-stable catalyst.
The TGA (Figure 3a) of CS, CCl, AC and ZnO@AC indi-
cated that the oxygen-based groups in CS generated from
waste cotton were converted into heat-stable structures
via covalent bonding with the adenine moieties. More-
over, the immobilization of ZnO further delayed the ther-
mal decomposition. According to Figure 3b, there was a
continuous decomposition of catalyst with the rise in
temperature under nitrogen atmosphere. Moreover, the
loss of 7.83% weight up to 176ꢀC of synthesized catalyst
was due to the removal of trapped gases and solvent.
Further, the decomposition of the catalyst was due to
thermal destruction of oxygen-containing groups in CS
initially and then due to the thermal disruption of the
adenine moieties and carbon skeleton. The differential
thermal (DT) analysis curve (Figure 3b) showed conti-
nuous evolution of heat, indicating exothermic reaction
taking place through the entire course of heating. XPS
was employed to determine the elemental composition
and valence state of zinc in ZnO@AC. In XPS spectrum,
TABLE 1 Optimization experiments for the synthesis of pyrano[2,3-d]pyrimidinesa
Entry
Catalyst (g)
ZnO@AC
ZnO@AC
ZnO@AC
ZnO@AC
ZnO@AC
ZnO@AC
ZnO@AC
AC
Solvent
Temperature (ꢀC)
Time
24 h
24 h
24 h
24 h
4 h
Yield (%)b
1
Ethanol
Reflux
Reflux
Reflux
Reflux
Reflux
r. t.
73
72
10
80
91
94
58
—
—
—
—
2
H2O
3
CH3CN
4
Methanol
5
Ethanol:H2O (1:1)
Ethanol:H2O (1:1)
—
6
15 min
24 h
24 h
24 h
24 h
24 h
7
r. t.
8
Ethanol:H2O (1:1)
Ethanol:H2O (1:1)
Ethanol:H2O (1:1)
Ethanol:H2O (1:1)
r. t.
9
CCl
r. t.
10
11
C
r. t.
—
r. t.
aReaction condition: 3-nitrobenzaldehyde (1 mmol), malononitrile (1 mmol), barbituric acid (1 mmol), catalyst (0.05 g), solvent (5 ml).
bIsolated yield.

8 of 13
CHOWHAN ET AL.
which is generally assigned to deep level defects, such as
oxygen vacancies and interstitials of zinc and oxygen
(Figure 3f). It can be attributed to increasing the total sur-
face area in the particle ensemble volume resulting from
the decrease of the individual particle surface affects the
shift of peaks.[66] Here, Figure 3f shows the blue shift of
the UV peak from classical 380 to 322 nm. The blue shift
behavior was explained by the probable quantum con-
finement, which shifts the energy levels between valence
band and conduction band apart, causing a blue shift.[67]
experiment were conducted to study the behavior of
ZnO@AC. Initially, 3-nitrobenzaldehyde (1 mmol),
malononitrile (1 mmol), and barbituric acid (1 mmol)
were taken as model substrates for optimization in a con-
trolled environment to explore the catalytic behavior of
ZnO@AC (Table 1). Ethanol–water, which is a greener
solvent, was found to be the best medium for the reaction
at room temperature. The reaction was also tried in other
solvents such as H2O, ethanol, methanol, and CH3CN
and solvent-free condition, but the yield was less in all
these solvents (Table 1, Entries 1–7). After optimizing sol-
vent, temperature was optimized (Table 1, Entries 5 and
6). For 3-nitrobenzaldehyde, the 94% product was formed
with catalyst (0.05 g). If the amount of catalyst was
reduced (0.04 g), the yield was also reduced to 78%, and if
the amount of catalyst increased (0.06 g), yield remained
the same; moreover, the time for the reaction to complete
also remained unchanged. The reaction was tried with
various catalytic parallels but there was on recation.
shown in Table 1 (Entries 8–10).
3.2 | Application of catalyst
3.2.1 | Synthesis of pyrano[2,3-d]
pyrimidines
The as-prepared catalyst was investigated using three-
component synthesis of pyrano[2,3-d]pyrimidines, which
act as a heterogeneous catalyst. Various controlled
TABLE 2 Substrate scope for ZnO@CA catalyzed synthesis of pyrano[2,3-d]pyrimidinesa
Entry
R
Product
4a
Time (min)
Yield (%)b
M. pt/lit. M. pt (ꢀC)
200–202/198–200[68]
228–230/230–235[68]
285–290/285–288[68]
226–230/226–228[32]
280–284/280–282[68]
204–208/200–205[68]
286–289/290–296[68]
285–290/285–290[68]
285–287/288–290[68]
163–169/165–170[68]
—
1
H
10
8
91
94
93
89
86
87
87
88
86
85
—
—
2
3-NO2
4-NO2
2-NO2
4-Cl
4b
3
4c
6
4
4d
10
10
10
12
12
12
12
240
240
5
4e
6
4-Br
4f
7
4-CH3
4-OCH3
3,4-OCH3
4-OH
CH3CHO
4 g
4 h
4i
8
9
10
11
12
4j
—
—
—
aReaction condition: aromatic aldehyde (1 mmol), malononitrile (1 mmol), barbituric acid (1 mmol), catalyst (0.05 g), Ethanol: H2O (1:1,
3 ml), room temperature.
bIsolated yield.

CHOWHAN ET AL.
9 of 13
The substrate scope for the reaction was explored after
from about 10 to 15 min in the minimum solvent
environment (Table 3).
optimization (Table 2). Generally, among various
aldehydes, electron-donating groups (EDG, –CH3, and
–OCH3) gave lower yields (Table 2, Entries 7–10) than
electron-withdrawing groups (EWG and –NO2) (Table 2,
Entries 2–4). The position of the substituent had an
obvious effect on the reaction, which was noticeable. The
lower yield was obtained when aromatic aldehydes
bearing ortho EWG were used (Table 2, Entry 4). The plau-
sible mechanism for the synthesis of Pyrano[2,3-d]pyrimi-
dines is provided in the Supporting Information (ESI).
The ortho and para-nitro benzaldehydes cor-
responded to the respective product with higher yields
within 10 min due to the electron-withdrawing proper-
ties of nitro groups (Table 4, Entries 2 and 4).
Products having methoxy, methyl, hydroxyl, and –N
(CH3)2 groups (Table 4, Entries 6–8) took longer time
for the conversion because of their electron-donating
character. Heterocyclic aldehyde was also successfully
converted into the corresponding product (Table 4,
Entry 9). One new product is synthesized for
bis(pyrazol-5ole) (Table 4, Entry 10). The mechanism
for the synthesis of bis(pyrazol-5-ole) is provided in
the Supporting Information (ESI).
3.2.2 | Synthesis of bis(pyrazol-5-ols)
As depicted in Table 3, the reaction was optimized for
the amount of catalyst, temperature of reaction, and
solvent system. Our goal was to achieve bis(pyrazol-
5-ols) formation at room temperature. It was aimed to
provide the required products in a short time where
ethanol/H2O mixture was used as an environment-
friendly solvent for high yield. Eventually, ethyl
acetoacetate (2 mmol), 4-nitrobenzaldehyde (1 mmol),
hydrazine hydrate (2 mmol), and catalyst (0.05 g) gave
sufficient performance with 3 ml of water:ethanol (1:1)
(Table 3, Entry 3). Bis(pyrazol-5-ols) was quantitatively
obtained at room temperature for periods ranging
3.2.3 | Photodegradation of MO
ZnO@AC was investigated for photodegradation of MO
azo dye, which contains a chromophore consisting of azo
(–N=N–) and sulphonate (SO3−) group using direct UV
illumination. The orange color of the dye gradually faded
using the prepared nanocatalyst because of the destruc-
tion of the chromophore and photodecomposition of
organic dye. The UV–Visible spectrum (250–600 nm)
further confirmed the degradation (Figure 4a). To
TABLE 3 Optimization of reaction condition for the synthesis of bis(pyrazol-5-ole)a
Entry
Catalyst (g)
ZnO@AC (0.05 g)
ZnO@AC (0.05 g)
ZnO@AC (0.05 g)
ZnO@AC (0.04 g)
ZnO@AC (0.06 g)
AC
Solvent
Temperature (ꢀC)
Time
24 h
Yield (%)b
1
2
3
4
5
6
7
8
9
Ethanol
Reflux
Reflux
r. t.
81
90
96
68
76
—
—
—
—
Ethanol: H2O (1:1)
Ethanol: H2O (1:1)
Ethanol: H2O (1:1)
Ethanol: H2O (1:1)
Ethanol: H2O (1:1)
Ethanol: H2O (1:1)
Ethanol: H2O (1:1)
Ethanol: H2O (1:1)
24 h
10 min
24 h
Reflux
Reflux
r. t.
24 h
24 h
CCl
r. t.
24 h
C
r. t.
24 h
—
r. t.
24 h
aReaction condition: 4-nitrobenzaldehyde (1 mmol), hydrazine hydrate (2 mmol), ethyl acetoacetate (2 mmol), catalyst, solvent (3 ml).
bIsolated yield.

10 of 13
CHOWHAN ET AL.
TABLE 4 Substrate scope for ZnO@MAC catalyzed synthesis of bis (pyrazol-5-ole)a
Entry
R
Product
8a
Time (min)
Yield (%)b
M. pt/lit. M. pt (ꢀC)
205–207/207–208[69]
270–272/269–271[69]
255–260/254–257[69]
241–242/240–241[69]
215–217/215–217[69]
198–201/200–203[45]
196–198/197–198[69]
254–256/255–257[69]
239–243/239–241[69]
231–233/This work
—
1
H
14
10
12
12
15
15
15
15
15
15
240
240
91
96
96
96
91
90
91
84
89
92
—
—
2
4-NO2
3-NO2
2-NO2
4-Cl
8b
3
8c
4
8d
5
8e
6
4- OCH3
4-CH3
4-OH
8f
7
8 g
8 h
8i
8
9
Thiophene-2-
4-N (CH3)2
CH3CHO
10
11
12
8j
—
—
—
aReaction condition: aldehyde (1 mmol), hydrazine hydrate (2 mmol), ethyl acetoacetate (2 mmol), catalyst (0.05 g), ethanol: H2O (1:1, 3 ml),
room temperature.
bIsolated yield.
evaluate the photocatalyst activity of ZnO@AC, the MO
solution was subjected to UV light as a blank, which
showed only 6% degradation and about 25% degradation
was observed when the nanocatalyst was added in dark.
This suggested that both catalyst and UV light was
required for photocatalytic reaction. Figure 4b showed
strong absorption maxima at 456 nm due to the chromo-
phore in MO dye, and it diminished as the time of UV
illumination increased up to 75 min and attains about
87.3% degradation efficiency. Figure 4b showed a plot for
relative concentration of dye (C/CO) verses time.
Figure 4c showed the plot of ln(Co/Ct) versus time;
linear plots were observed, which attested that
photodegradation of MO obeys pseudo-first-order
kinetics. MO was photodegraded significantly because of
proficient oxidation by hydroxyl radicals produced in
photocatalysis under UV light and converting azo group
of MO to nontoxic forms with amine groups. The
mechanism of photodegradation of MO is provided in the
Supporting Information (ESI).
3.3 | Stability of catalyst
The stability of ZnO@AC was also examined. The cata-
lyst was reusable up to eight runs, and loss in the yield
can be tolerated (Figure 5a). There is no noticeable loss
of ZnO even after the eight cycles confirmed by the hot
filtration test. In Figure 5b, the TEM images of recycled
catalyst depicted the agglomeration of ZnO NPs, which
led to the decrease in yield after the eighth cycle of reus-
ability. The performance of an as-prepared catalyst has
been compared with the pervious reported catalysts
known in literature for both the reactions, and ZnO@AC
has shown the superior performance compared with the
other reported catalyst (Table 5).

CHOWHAN ET AL.
11 of 13
FIGURE 4 UV–Vis spectra of
photocatalytic degradation of MO with
ZnO@AC (absorbance vs. wavelength (a),
plot showing relative concentration verses
time (b), and photocatalytic degradation of
dye with time (c))
FIGURE 5 Recyclability graph
for ZnO@AC using
4-nitrobenzaldehyde as a test
substrate for both the reactions (a);
transmission electron microscopy
(TEM) image of recycled catalyst
after the eighth run showing
agglomeration of catalytic
structure (b)
TABLE 5 Comparison of catalytic activity of designed catalyst with some recent published work
Product
Catalyst
Reaction time
30 min
Reaction condition
H2O:EtOH, r. t.
H2O, 90ꢀC
Yield (%)
References
DABCO
83
91
85
95
93
Bhat et al.[31]
Taurine
18 min
Daneshvar et al.[32]
Rajinder et al.[68]
Fatahpour et al.[69]
This work
Ni NPs @N-doped TiO2
Al-HMS-20
ZnO@AC
85 min
MeOH,65ꢀC
12 h
EtOH, r. t.
6 min
H2O/EtOH(1:1), r. t.
Pyridine trifluoroacetate
Methylimidazolium perchlorate
-
12 h
H2O, 70ꢀC
85
90
85
88
95
96
Alshakova et al.[45]
Khaligh et al.[49]
Xu-dong et al.[71]
Wang et al.[47]
Milan et al.[72]
This work
20 min
6 h
50ꢀC, solvent-free
H2O, reflux
Sodium dodecyl sulfate
α-Casein
1 h
H2O, reflux
15 min
10 min
H2O/EtOH
ZnO@AC
H2O/EtOH(1:1), r. t.

12 of 13
CHOWHAN ET AL.
4 | CONCLUSIONS
Monika Gupta https://orcid.org/0000-0001-5265-0388
Neha Sharma https://orcid.org/0000-0003-2468-3419
Waste cotton cloth from the garment industry was suc-
cessfully used as support for the synthesis of heteroge-
neous catalysts (ZnO@AC), which was an efficient
catalyst for the synthesis of pyrano[2,3-d]pyrimidines and
bis(pyrazol-5-ols) and photodegradation of MO under
green and clean conditions. The uniform dispersion of
amorphous ZnO and size was confirmed by FEG-SEM,
HR-TEM, and elemental mapping. FTIR, XRD, XPS, and
TGA confirmed the amorphous nature of ZnO, the oxida-
tion state of ZnO, and the increased thermal stability of
the catalyst, respectively. Further, the formation of ZnO
at 200ꢀC was confirmed by FTIR and XPS. The PL spectra
showed a blue shift due to quantum confinement. To
check the sustainability and economic reliability, the
nano–micro combination of ZnO@AC was recycled for
numerous cycles without an obvious loss of activity. The
recycled catalyst after the eighth cycle was characterized
by transmission electron spectroscopy and showed a
slight agglomeration of catalyst. Moreover, the applica-
tion toward other reactions using the nanocatalyst is
under process. The photocatalyst was also favored by
immobilizing ZnO over AC, which prevented the
electron–hole recombination and hence enhanced the
catalytic activity.
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AUTHOR CONTRIBUTIONS
Bushra Chowhan: Conceptualization; data curation;
formal analysis; funding acquisition; investigation; meth-
odology; software. Monika Gupta: Conceptualization;
data curation; formal analysis; investigation; methodol-
ogy; project administration; software; supervision; valida-
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SUPPORTING INFORMATION
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How to cite this article: Chowhan B, Gupta M,
Sharma N. Fabrication and characterization of
adenine-grafted carbon-modified amorphous ZnO
with enhanced catalytic activity. Appl Organomet
Chem. 2020;e6013. https://doi.org/10.1002/aoc.
6013
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