Rapid visualization of fingerprints on various surfaces using ZnO superstructures prepared via simple combustion route

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Original Article

Rapid visualization of

fingerprints on various surfaces using ZnO

superstructures prepared via simple combustion route

N.H. Deepthi

a

, R.B. Basavaraj

a

, S.C. Sharma

b,c

, J. Revathi

d

, Ramani

e

, S. Sreenivasa

f

,

H. Nagabhushana

a,*

a_{C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumkur, 572 103, India}

b_{Department of Mechanical Engineering, Jain University, Jain Group of Institutions, Bangalore, India}

c_{Avinashilingam Institute for Home Science and Higher Education for Women University, Coimbatore, 641043, India}

d_{Department of Biomedical Instrumentation Engineering, Avinashilingam Institute for Home Science and Higher Education for Women University,}

Coimbatore, 641043, India

e_{Department of Food Processing and Preservation Technology, Avinashilingam Institute for Home Science and Higher Education for Women University,}

Coimbatore, 641043, India

f_{Department of Studies and Research in Chemistry, Tumkur University, Tumakuru, 572103, India}

a r t i c l e i n f o

Article history:

Received 12 November 2017

Received in revised form
31 January 2018
Accepted 31 January 2018
Available online 10 February 2018

Keywords:
Zinc oxide
Barbiturates
Photoluminescence
Latentfingerprint

a b s t r a c t

A simple solution combustion route has been used to prepare ZnO nanopowders (NPs) using different
barbiturates (Barbituric acid, 1, 3-dimethyl barbiturates and 2-thiobarbiturates) as fuels. The obtained
product was well characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM),
ultraviolet-visible Spectroscope (UV-Vis) and Photoluminescence (PL). The PXRD results confirm the
hexagonal phase of the material. The detailed structural analysis is performed by Rietveld refinement
method. The energy band gap of NPs is found to be in the range of 3.31 - 3.49 eV. The growth mechanism
for the formation of 3D micro-architectures is discussed in detail. The PL emission spectrum shows a
broad emission peak at 502 nm upon an 406 nm excitation wavelength. The ZnO NPs can be used for the
visualization of latentfinger prints (LFPs) under normal light on various porous and non-porous surfaces.
In this case, the visualized LFPs are found to be excellent compared to the commercially available
powders.

© 2018 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />

1. Introduction

In recent years, inorganic nanostructured materials have been

attracted intensively in controlling the morphology and size due to
the fact that they play important roles in determining optical,
electrical and other physiochemical properties[1e4].

Nanostructured Zinc oxide (ZnO) is a versatile semiconducting
material with a wide band gap (3.37 eV) and a binding energy of
~60 meV at room temperature. It is non-toxic in nature and a low
cost material. Furthermore, it finds a wide range of applications
such as photocatalysis, UV lasers, Light Emitting Diodes (LEDs),
Solar cells, optoelectronic devices[5e9].

The latent finger prints (LFPs) have long been exploited as
authoritative physical evidence, providing added donor
informa-tion, namely gender, occurrence of human metabolites, and
evi-dence of contact with explosives. In most of the cases, LFPs are not
simply visualized owing to their poor optical contrast when
observed with the naked eye. Hence, some advanced techniques
are required to enable their detection. Till date, numerous methods
were utilized for the detection of LFPs, namely powder dusting,
metal deposition, cyanoacrylate/iodine fuming, andfluorescence
staining etc. Among these methods, powder dusting is the simple
and effective method for LFP detection on diverse surfaces,
employing luminescent, metallic, and magnetic materials as
la-beling agents. Although this method is effective for the
develop-ment of LFPs under some prevalent conditions, it is still subject to
several limitations such as difficulty in applications for several
surfaces, low contrast, low selectivity, high background
interfer-ence, and toxicity. Therefore, the aforementioned problems of the
powder-dusting method have to be addressed. With this

* Corresponding author.

E-mail address:(H. Nagabhushana).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect

Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j s a m d

/>

2468-2179/© 2018 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license
( />

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in attention, composite core-shell fluorescent nanomaterials are
attractive alternatives owing to their ease of preparation, unique
physical and chemical properties such as tunable particle size, good
photochemical stability, and highfluorescence intensity[10e17].

Till date, numerous methods have been used for the fabrication
of ZnO hierarchical and complex nano/micro structures[18e26].
However, most of the synthesis techniques which are unfavorable
for the large production in controlled processes. In this context, the
solution combustion route has proven to be simple, less time
consuming, and energy saving. In this method, the fuel plays a vital
role for the formation of the desired product with a well-defined
morphology. The combustion process involves a homogeneous
mixture of precursor's salts and fuel. Normally, precursors are
chosen as metal nitrates due to their easy solubility when
compared to others[27e29].

Barbiturates are organic compounds which contain a carbonyl
group with two amine groups. Further, they are odourless and
soluble in water. The general details and structure of barbiturates
are enumerated inTable 1.

In this paper, for the first time, ZnO NPs were prepared via
barbiturates assisted combustion route. Thefinal product was
well-characterized using Powder X-ray Diffraction (PXRD), Scanning
Electron Microscope (SEM), Ultraviolet-visible Spectroscopy (UV-Vis)
and Photoluminescence (PL). The product was further utilized for
LFPs visualization on various porous and non-porous surfaces.
2. Experimental

2.1. Synthesis of ZnO NPs

Zinc nitrate hexahydrate [(Zn(NO3)2.6H2O)] and Barbituric acid,

1,3-Dimethylbarbituric acid 2-thiobarbituric acid were procured
from sigma Aldrich and used as a starting materials without further
purification. Stoichiometric quantity of Zinc nitrate (2 g) and
bar-bituric acid (0.5 g) were thoroughly mixed in double distilled water
and then stirred for ~30 min until homogeneous mixture was

reached. The obtained reaction mixture was kept in a pre-heated
muffle furnace maintained at 500 ± 10
_{C. The obtained product}

was used for different characterization. Similar procedure was
repeated for 2-thiobarbituric and 1, 3 Dimethyl barbituric acids as
fuels for the preparation of ZnO.

2.2. Characterization

Phase purity and crystallinity of NPs were studied using a PXRD
Shimadzu 7000 using Cuk_a(1.541Å) radiation with nickel filter. The
morphology of the product is analyzed by HITACHI-3000 Table top
SEM. The DRS studies of the samples were recorded on PerkinElmer
(Lambda-35) spectrophotometer. The PL measurements were
per-formed by using Jobin Yvon Spectro_{fluorimeter with 450 W Xenon}
lamp as an excitation source.

3. Results and discussion

Fig. 1(a) shows the PXRD patterns of the as-synthesized ZnO NPs
using barbituric acid, 2-thiobarbituric and 1, 3 Dimethyl barbituric
acids. All the diffraction peaks exhibit a hexagonal phase with the
standard JCPDS Card No. 36-1451[30]. The peaks at the diffraction
angles of 31.70
, 34.40
, 47.65
, 56.70
, 62.96
and 67.99
are
attributed to (100), (002), (101), (102), (110), (103) and (112) planes,
respectively. Furthermore, the sharp and broad peaks indicate that
the prepared samples are highly crystalline in nature. The average
crystallite size of the product was calculated using Scherrer's
equation and Williamson-Hall plots, and the obtained results are
tabulated inTable 2 [31]. The crystallite size and microstrain were
also estimated by WilliamsoneHall approach by putting the factor
‘4 sin

q

’ along x-axis and ‘

b

cos

q

’ along y-axis (Fig. 1(b)). The slope of
the straight line gives the strain and intercept of on y-axis gives
crystallite size (D). The calculated crystallite size and micro strain
are listed inTable 2. As can be evident from this table, the crystallite
size obtained from Barbituric acid as a fuel is lower compared to

2-thiobarbituric and 1, 3 Dimethyl barbituric acids.

Table 1

General details of the fuels.

Chemical name Chemical formula Molar mass g/mol Structure

Barbituric acid C4H4N2O3 128.09

1,3-Dimethylbarbituric acid C6H8N2O3 156.14

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Fig. 1. (a) PXRD profiles and (b) Williamson-Hall plots of ZnO NPs using different barbiturates.
Table 2

Estimated crystallite size, microstrain and energy gap values of ZnO NPs with different barbiturates.

Sl. No. Sample Crystallite size (nm) Micro strain ( 103₎ _{Energy gap (eV)}

Scherrer's W-H plot ε W-H

1 Barbituric acid 5 8 6.35 6.75 3.31

2 1, 3-Dimethylbarbituric acid 23 25 1.55 1.79 3.35

3 2-Thiobarituric acid 10 15 3.62 1.51 3.49

Fig. 2. Rietveld refinement of ZnO NPs using (a) Barbituric acid, (b) 1, 3-dimethyl Barbituric acid, (c) 2-thiobarbituric acid, and (d) Packing diagram of ZnO NPs.
N.H. Deepthi et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 18e28

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The Rietveld refinement analysis of ZnO obtained from
Barbi-turic acid, 2-thiobarbiBarbi-turic and 1, 3 Dimethyl barbiBarbi-turic acid fuels
were done using FULLPROF software, which is shown inFig. 2. Tofit
the various parameters to the data, the Pseudo-voigt function is
used. The quality of the performed Rietveld refinement is decided
qualitatively by the profile parameters (Rp, Rwpand

c

2). The refined

parameters are presented inTable 3. The_{fitting parameters namely}
Rp, Rwpand

c

2indicate the good agreement between the refined

and observed PXRD patterns for the hexagonal ZnO phase[32e34].
The packing diagram of ZnO NPs is drawn by using refined values
by Diamond software and shown inFig. 2(d).

Fig. 3(a) depicts the diffuse reflectance spectra of the ZnO NPs
synthesized by using different barbiturates in the wavelength range
from 350 to 1100 nm. The spectra show a broad and maximum peak
at ~380 nm. Kubelkae Munk function is utilized to determine the
band gap energy (Eg) of ZnO NPs [35,36]. The intercepts of the

tangents to the plots of F(R_∞)2versus photon energy (h

n

) is shown
inFig. 3(b). The K-M (Kubelkae Munk) function F(R∞) and photon

energy (h

n

) can be calculated by using Eqs:

FRị ẳ 1  Rị
2

2R (1)

R ẳ 10A (2)

h

n

¼ 1240

_l

(3)

where R∞ is the reflection coefficient of the sample, A is the
absorbance intensity of ZnO NPs, and

l

is the absorption
wave-length. The obtained band gaps of ZnO NPs using different
barbi-turates are tabulated inTable 2. The energy band gap for barbituric
acid is less compared to 2-thiobarbituric and 1, 3 Dimethyl
barbi-turic acids.

Fig. 4(aef) shows the SEM images of the ZnO NPs prepared with
various concentrations (5e30 ml) of Barbituric acid. From the
mi-crographs it clearly shows hexagonal shaped disks-like structures
obtained for the 5 ml conc. (Fig. 4(a)). As the concentration of
barbituric acid fuel increases from 10 to 30 ml, the stacked
hex-agonal disks-like structures are obtained (Fig. 4(bee)). Further,
Fig. 5 shows the SEM micrographs of ZnO NPs prepared with
different concentrations (5e30 ml) of 1, 3-dimethylbarbituric acid.
When the fuel concentration is 5 ml, the pyramidal-like structures
are obtained as shown inFig. 5(a). However, when the fuel
con-centration is increased from 10 to 20 ml, the pyramidal-like
structures start oriented in different direction as shown in
Fig. 5(bed). When the fuel concentration is increased to 25 and
30 ml hexagonal superstructures are formed by the self-assembled

orientation and attachment process (Fig. 5(eef)). The SEM
micro-graphs of ZnO NPs prepared with different concentrations
(5e30 ml) of 2-thiobarbituric acid are shown inFig. 6(aef). As the
fuel concentration is increased from ~5 to 10 ml, the hexagonal

shaped structures are obtained (Fig. 6(a) and (b)). However, with
increasing the fuel concentration from 20 to 30 ml, each of
hex-agonal shaped particles oriented in a particular direction and it
forms a spherical and oval shaped ball-like structure (Fig. 7).

Based on the egg box model, the trapping mechanism can be
explained. The term “egg-box” arises from the resemblance
be-tween the arrangement of the cations into electronegative cavities

Table 3

Rietveld refinement values of ZnO NPs using different barbiturates.

Parameters ZnO

Barbituric acid 1,3-Dimethylbarbituric acid 2-thiobarbituric acid

Crystal system Hexagonal Hexagonal Hexagonal

Space group P63mc P63mc P63mc

Refinement parameters

RP 2.40 1.89 3.54

RWP 3.61 2.43 5.24

RExp 3.92 3.67 4.04

c2 _0.85 _0.44 _1.68

GoF 0.91 0.65 1.30

RBragg 1.87 1.04 2.60

RF 1.38 1.000 1.27

X-ray density (g/cc3₎ _5.807 _5.721 _5.631

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and eggs in an egg-box. Within the“egg-box” domains, the divalent
cations form intermolecular bonds via two hydroxyl groups of one
pyrimidine-chain of the barbituric acid and three carboxylate
groups of another chain. The formation of hexagonal structures can
be related to the interactions between the reducing two amine
groups and three carboxylic groups with the zinc ions. A probable
reason for the change in the morphology of ZnO with the increase
in concentration of barbiturates is mainly due to increased active
components such as ammine groups. By acting like surfactants,
these amine groups control the nucleation mechanism of ZnO,
leading to the controlled growth of the ZnO hexagonal structures.
The exact mechanism between the contents of any plant extract
with metal ions leading to the formation of superstructures is not
reached which thus needs more intensive research activities[37].

Fig. 8(a) shows the PL emission spectra of ZnO NPs using
different barbiturates upon an excitation wavelength of 406 nm.
These spectra exhibit a broad emission peak at ~502 nm. This is due
to the kind of oxygen related defects occurring in the ZnO NPs.
Najafi. et al.[38]have reported that the visible emission from ZnO
consisted of blue (447 nm), green (555 nm), and red (668 nm)

re-gions, which corresponds to Zinc interstitial (Zni), Oxygen vacancy

(Vo), and oxygen interstitial (Oi) defect levels, respectively. The blue

peak is attributed to recombination between the Znito the valence

band level. The green emission corresponds to the singly ionized
oxygen vacancy in ZnO, resulting from the recombination of a
photon generated hole with the single ionized charge state of this
defect. These emission peaks indicates the existence of large
number/deep level of surface defects in ZnO NPs due to oxygen

Fig. 4. (aef) SEM micrographs of ZnO NPs prepared with different concentrations (5e30 ml) of Barbituric acid.

Fig. 5. (aef) SEM micrographs of ZnO NPs prepared with different concentrations (5e30 ml) of 1, 3-dimethyl Barbituric acid.
N.H. Deepthi et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 18e28

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deficiencies and zinc interstitials. It was believed that this
phe-nomenon was due to band transition from Znito Vodefect levels in

ZnO. The PL excitation spectra of ZnO NPs obtained by various
barbiturates are shown inFig. 8(b) upon monitoring an 600 nm
emission wavelength. It was observed from thefigure that there is
a broad peak around ~406 nm along with the small intense peaks
observed at 437, 448, 466, 479, and 489 nm.

The Commission International de I'Eclairage (CIE) 1931 x-y
chromaticity diagram of ZnO nanostructures synthesized using
different barbiturates is shown inFig. 8(c). The corresponding CIE
values are given in the insets ofFig. 8(c). From the CIE chromaticity

values, the color coordinates are located in the yellow region as

indicated by star (*). The color appearance of the light changes
when heated to a certain temperature. It can be estimated with the
reference source of light and given by the correlated color
tem-perature (CCT) parameter [39]. The transforming the (x, y)
co-ordinates of CIE to (Ul, Vl) of CCT can be performed by using the Eqs
(4and5)[40]:

U0ẳ_{2x ỵ 12y ỵ 3}4x (4)

V0ẳ_{2x ỵ 12y þ 3}9y (5)

Fig. 6. (aef) SEM micrographs of ZnO NPs prepared with different concentrations (5e30 ml) of 2-thiobarbituric acid.

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The obtained result of the CIE diagram is presented inFig. 8(d).
Also, the superiority of the white light in terms of CCT is evaluated

by McCamy empirical formula CCTẳ 437n3_ỵ

3601n2_{ 6861n ỵ 5514:31 (theoretical) where n ẳ x  x}
cị=

y  ycị; the inverse slope line and chromaticity epicenter is at

xcẳ 0.3320 and yc¼ 0.1858[41]. Generally, a CCT value greater than

5000 K indicates the cold white light used for commercial lighting
purpose and the CCT value less than 5000 K indicates the warm
white light used for home appliances. The obtained CCT value

(3070 K) for the near white light emitting phosphor agrees with the
CCT value of standard daylight at noon (D65, 6500 K), which is
suitable for cold near white light emission. The results indicate that

the present NPs can be used as a component in warm sources of
light emitting diodes.

All the eccrine LFPs are collected from a single donor by
adequately washed his hands with soap and wiped gently. Then,
thefingers are pressed in a medium pressure on different surfaces
including porous and non-porous materials. It turned out from the
PXRD results that the crystallite size is lesser in barbituric acids
used as a fuel, hence this product has been taken as a labeling agent
in the powder dusting method.

The prepared ZnO NPs are effectively used to visualize the LFPs
on various non-porous surfaces such as blade, metal scale and
stapler (Fig. 9). To check the background hindrance, we developed

Fig. 8. (a) PL emission spectra, (b) excitation spectra, (c) CIE diagram, (d) CCT diagram, (e) Inset diagram of CIE coordinates, and (f) Inset diagram of CCT values of ZnO NPs using
different barbiturates.

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LFPs on various porous surfaces with different backgrounds as
shown in Fig. 10. It can be observed from the _{figure that the}
developed LFPs are clearly visible without any background
hin-drance of the porous surfaces. All the above results evidence that
the prepared ZnO NPs can be effectively used as labeling agents to

visualize the LFPs on various porous and non-porous surfaces. It
turns out from the_{figure that all the three levels (whorl, lake,}

bi-furcation, ridge end, island and sweat pores) of LFPs are clearly
visible. Fig. 11shows the developed individual and complex
fin-gerprints on the surface of glass. The figure shows the LFP with

Fig. 9. Latentfingerprint images of ZnO NPs on non-porous surfaces such as (a) blade, (b) metal scale, and (c) stapler with (d) its room-in portion.

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clearer ridge patterns consisting of all the three levels of ridge
features.

The enhanced LFPs are photographed under 254 nm UV light
range by using a Canon digital camera. Detailed LFPs ridge
char-acteristics of ZnO NPs taken on the glass surface shows the Level I,
Level II and Level III LFPs ridge characteristics (Fig. 12). The

superiority of enhanced LFPs on various porous and non-porous
surfaces was evaluated by using Bandey scale developed by UK
Home Office[42]. Thisfive point scale system was extensively used
to estimate the quality of LFPs only in research circumstance not in
legal procedures (Table 4). According to Bandey system, grade 3 or
grade 4 LFPs are considered for explicit identification of individuals.

Fig. 11. Developed individual and complex LFPs on glass surface.

Fig. 12. Detailedfingerprint ridge characteristics of ZnO NPs taken on the glass surface showing Level I, Level II, and Level III fingerprint ridge characteristics.
N.H. Deepthi et al. / Journal of Science: Advanced Materials and Devices 3 (2018) 18e28

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It was found that in the previous reports authors have prepared LFP
labeling agents with the addition of various rare earth elements
and then visualized the LFP characteristics[43e46]. In the present
work, however, we have prepared the ZnO NPs without any

external dopants. It was observed that by using the ZnO NPs, level II
(bi-furcation, ridge end, crossover, island, eye etc.) and level III
(sweat pores and scar), the LFP ridge details were clearly studied on
various porous surfaces. The results obtained on various porous
surfaces were also not discussed in earlier reports.

4. Conclusion

The ZnO NPs have been prepared by the simple solution
com-bustion method using different barbiturates as fuel to study the
structural and photometric properties. The PXRD results confirm
the hexagonal phase. The estimated crystallite size for barbituric
acid-based NPs is found to be lesser compared to the other
barbi-turates based NPs. The estimated energy band gap of ZnO NPs is
found to be in the range of 3.31e3.49 eV. The morphology of the
product can be tuned by varying the concentration of different
barbiturates. The broad emission peak at ~502 nm was due to the
oxygen defects crated in the prepared ZnO NPs. The CIE color
co-ordinates indicate that the obtained product exhibits the yellow
color. The estimated average CCT value (3070 K) reveals that the
material can be used for the fabrication of cool LEDs. The ZnO NPs
prepared with barbituric acid show smaller crystallite sizes. Hence,
it is used for the detection and enhancement of latentfingerprints
on various porous and non-porous material surfaces. The
finger-print images were clear with high-contrast and low-background
interference, and even showed the minute details which help
individualization. Therefore, the prepared ZnO NPs are are a
promising candidate for the fabrication of white LEDs, as well as for
the forensic applications.

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Table 4

Bandeyfingerprint grading scheme.
Grade Description
0 No description

1 No continuous ridges; all discontinuous or dotty
2 One third of the mark comprised of continuous ridges;

remainder either show no development or dotty
3 Two thirds of the mark comprised of continuous ridges;

remainder either show no development or dotty

</div>
<span class='text_page_counter'>(11)</span><div class='page_container' data-page=11>

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[42] H.L. Bandey, Fingerprint Development and Imaging Newsletter: The Powders
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Home Office, Sandridge, UK, 2004.

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cyclohexyl-1,2-diamino based organic ligands, J. Sci. Adv. Mater. Devices 2
(2017) 156e164.

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