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

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 me[r]

Original Article

Rapid visualization of fingerprints on various surfaces using ZnO

superstructures prepared via simple combustion route

N.H Deepthia, R.B Basavaraja, S.C Sharmab,c, J Revathid, Ramanie, S Sreenivasaf,

H Nagabhushanaa,*

aC.N.R Rao Centre for Advanced Materials, Tumkur University, Tumkur, 572 103, India

bDepartment of Mechanical Engineering, Jain University, Jain Group of Institutions, Bangalore, India

cAvinashilingam Institute for Home Science and Higher Education for Women University, Coimbatore, 641043, India

dDepartment of Biomedical Instrumentation Engineering, Avinashilingam Institute for Home Science and Higher Education for Women University,

Coimbatore, 641043, India

eDepartment of Food Processing and Preservation Technology, Avinashilingam Institute for Home Science and Higher Education for Women University,

Coimbatore, 641043, India

fDepartment 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 (http://creativecommons.org/licenses/by/4.0/)

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:bhushanvlc@gmail.com(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

https://doi.org/10.1016/j.jsamd.2018.01.007

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 (http://creativecommons.org/licenses/by/4.0/)

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

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 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 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, 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 Cuka(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 Spectrofluorimeter 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, 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 [31] The crystallite size and microstrain were also estimated by WilliamsoneHall approach by putting the factor ‘4 sinq’ along x-axis and ‘bcosq’ 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 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, Dimethyl barbituric acids

Table

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

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

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 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 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 (2018) 18e28

The Rietveld refinement analysis of ZnO obtained from Barbi-turic acid, 2-thiobarbiBarbi-turic and 1, Dimethyl barbiBarbi-turic acid fuels were done using FULLPROF software, which is shown inFig 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, Rwpandc2) The refined

parameters are presented inTable Thefitting parameters namely Rp, Rwpandc2indicate 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 (hn) is shown inFig 3(b) The K-M (Kubelkae Munk) function F(R∞) and photon

energy (hn) can be calculated by using Eqs:

FRị ẳ  Rị

2R (1)

R∞ ¼ 10A (2)

hn ¼ 1240l (3)

where R∞ is the reflection coefficient of the sample, A is the absorbance intensity of ZnO NPs, andlis the absorption wave-length The obtained band gaps of ZnO NPs using different barbi-turates are tabulated inTable The energy band gap for barbituric acid is less compared to 2-thiobarbituric and 1, 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 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 shows the SEM micrographs of ZnO NPs prepared with different concentrations (5e30 ml) of 1, 3-dimethylbarbituric acid When the fuel concentration is 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

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

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

Fig (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 (2018) 18e28

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]:

U0ẳ2x ỵ 12y ỵ 34x (4)

V0ẳ2x þ 12y þ 39y (5)

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

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 437n3ỵ

3601n2 6861n ỵ 5514:31 (theoretical) where n ẳ x  x cÞ=

ðy  ycÞ; the inverse slope line and chromaticity epicenter is at

xc¼ 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 (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

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 thefigure 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 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

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 or grade 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 (2018) 18e28

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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Bandeyfingerprint grading scheme Grade Description No description

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

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

remainder either show no development or dotty

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