Carbon black co-adsorbed ZnO nanocomposites for

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Apr 3, 2018 - *Dr. M.M. Rahman, ... conductive oxide with 3.3 eV band gap energy, 60 meV exciton binding energy, high range of resistivity ((10-3 ..... [35] M.A. Subhan, P.C. Saha, M.-M. Alam, A.M. Asiri, M. Al-Mamun, M.M. Rahman, J.

Accepted Manuscript Title: Carbon black co-adsorbed ZnO nanocomposites for selective benzaldehyde sensor development by electrochemical approach for environmental safety Authors: Mohammed M. Rahman, M.M. Alam, Abdullah M. Asiri PII: DOI: Reference:

S1226-086X(18)30216-8 https://doi.org/10.1016/j.jiec.2018.04.041 JIEC 3982

To appear in: Received date: Revised date: Accepted date:

21-1-2018 3-4-2018 29-4-2018

Please cite this article as: Mohammed M.Rahman, M.M.Alam, Abdullah M.Asiri, Carbon black co-adsorbed ZnO nanocomposites for selective benzaldehyde sensor development by electrochemical approach for environmental safety, Journal of Industrial and Engineering Chemistry https://doi.org/10.1016/j.jiec.2018.04.041 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Carbon black co-adsorbed ZnO nanocomposites for selective benzaldehyde

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sensor development by electrochemical approach for environmental safety

Mohammed M. Rahmana,b,*, M.M. Alamc, Abdullah M. Asiria,b

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Chemistry Department, King Abdulaziz University, Faculty of Science, Jeddah 21589, P.O. Box 80203,

Saudi Arabia. b

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Center of Excellence for Advanced Material Research (CEAMR), King Abdulaziz University, Jeddah

Department of Chemical Engineering and Polymer Science, Shahjalal University of Science and

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c

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21589, P.O. Box 80203, Saudi Arabia.

*Corresponding

address:

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*Dr. M.M. Rahman,

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Technology, Sylhet 3100, Bangladesh

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Email: [email protected] Phone: +966596421830

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Graphical abstract

ABSTRACT

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ZnOO/CNT nanocomposites prepared by facile wet-chemical method at low temperature Highly sensitive Benzaldehyde chemi-sensor by reliable I-V method Chemi-sensor exhibits the lower detection limit within short response time Practically analyzed the real environmental samples Effective chemi-sensor for health care and environmental fields

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    

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Research highlights:

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The nanocomposites (NCs) of carbon black (CB) co-adsorbed ZnO nanomaterials were synthesized by facile wet-chemical process at low temperature. The prepared NCs were

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characterized by UV/vis., EDS, TEM, FTIR, EIS, XPS, and powder XRD. In this research approach, a newly developed benzaldehyde (BH) chemical sensor with active ZnO/CB is studied

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by electrochemical method. A uniform thin layer of ZnO/CB NCs was deposited on a glassy carbon electrode (GCE) with conducting binder to result the working electrode for BH chemical sensor. The proposed chemical sensor is displays good selectivity with lower detection limit, long-term stability and enhanced electrochemical responses. The calibration plot is found to be

linear (r2=0.9965) over the concentration (LDR) range of 0.1 nM 0.1 mM mM. The sensitivity (5.0633 µAµM-1cm-2) and detection limit (18.75 ±0.94 pM) of projected BH chemical sensor were estimated from the slope of calibration plot. Based on sensing performance of ZnO/CB

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NCs/binder/GCE, this chemical sensor is introduced a well-organized route of efficient detection of hazardous and carcinogenic chemicals to safe the environmental and healthcare sectors in broad scales.

Keywords: ZnO/CB Nanocomposites; Benzaldehyde sensor; Wet-chemical process; Optical

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properties; Structural analysis; Environmental analysis

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Introduction

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Due to the increase of the application areas of chemical sensor such as control of

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intelligent, diagnosis of medical and biomedical, detection of leakages of inflammable toxic gases and monitoring the environmental contamination, the sensor technology is an important

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issue in this decade [1-5].The benzaldehyde is a volatile organic compound (VOC) and it has

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industrial importance to produce pharmaceuticals, flavors, perfume, foods, plastic additives and

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fragrances [6]. In United Sate of America (USA) and European Union (EU), the benzaldehyde is used as safe food additive and flavoring ingredients [7]. Recently, some researchers claimed that

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the benzaldehyde is carcinogenic and mutagenic substance [8]. The exposure of benzaldehyde at very low concentration level is a potential risk to human and animal health [9]. Therefore, it is

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urgently needed to detect benzaldehyde, particularly at ppm level concentration to attentive the people. There are some old and traditional methods such as high performance liquid chromatography (HPLC), gas chromatography (GC) and electroanalytical methods to detect BH [10-12]. But the existing methods have difficulties such as expensive, time consuming, uneasy to

portable and complicated detection system. Presently, the chemical sensors based on electrochemical approach (I-V method) is widely adopted due to its attractive facilities such as low cost, easy to handle, possess high sensitivity with lower detection limit, long time stability in

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chemical environment [13,14]. The oxides of transition metal (doped/undoped/composited) such as SnO2 [15, 16] ZnO [17,18], In2O3 [19,20], Fe2O3 [21], Co3O4 [22], TiO2 [23], WO3 [24] have been investigated as active nanomaterial in sensor applications. Among these metal oxides, ZnO is an important semiconductive oxide with 3.3 eV band gap energy, 60 meV exciton binding energy, high range of

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resistivity ((10-3  105  cm) and transparency in visible wave region [25-32]. Thus, ZnO

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exhibits outstanding Optical, electrical and piezo-electrical properties, which make the ZnO as an

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efficient active material in sensor application [33, 34]. As sensing element, ZnO has been found

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potential candidate to detect bisphenol A [35], acetone [36], 4-aminophenol [37], and ethanol [38] in phosphate buffer medium successively. The carbonaceous nanostructured carbon black

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(CB) processes very attractive electrochemical properties such as high chemical stability, large

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surface area, and excellent conductivity. Therefore, CB has been applied as sensing material to

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detect amoxicillin, nimesulide [39], estradiol [40], acetaminophen, folic acid, propranolol, caffeine [41], and hydrazine [42]. Therefore, this research approach is to development of a

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chemical sensor based on nanocomposite of ZnO-CB. Herein, the desire electrochemical sensor based on I-V method was prepared using wet-

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chemically synthesized ZnO/CB NCs. The working electrode of proposed chemical sensor was fabricated by a GCE coated with ZnO/CB NCs as uniform very thin layer with conducting nafion (5% nafion suspension in ethanol) binder and applied to detect BH in phosphate buffer medium successively. As an outcome of this research, the projected BH chemical sensor has been

showed good sensitivity with lower detection limit, a broad linear dynamic range, and precious reproducibility performance with short response time. Therefore, it can be concluded that this noble research approach might be simple and reliable way to development of electrochemical

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sensor using I-V method in the field of environmental sector in broad scale.

Experimental sections Materials and Methods

The laboratory grade chemicals such as 3-chlorophenol (3-CP), 3-methylaniline (3-MA),

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ammonium hydroxide (AH), tetrahydrofuran (THF), chloroform (Chl), benzaldehyde (BH),

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methanol (MeOH), 2,4-dinitrophenol (2,4-DNP), melamine (MEL), pyridine, nafion (5%

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ethanolic solution), monosodium phosphate and disodium phosphate were purchased from the

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Sigma-Aldrich company and used directly without any purification. FTIR (Madison, WI, USA)

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and UV-vis (thermo scientific) analysis were implemented on prepared nanomaterials to result

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FTIR and UV-vis spectrums. To quantify binding energy with corresponding oxidation states of species exiting, the synthesized nanomaterials were investigated by XPS analysis, on a K-α1

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spectrometer (thermo scientific, K-α1 1066) with an excitation radiation source (A1 Kα1, Beam spot size = 300.0 μm, pass energy = 200.0 eV, pressure ̴ 10-8 torr). The structural morphology,

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molecular arrangement and particles size of ZnO/CB NCs were examined by TEM (JEOL, Japan) analysis. The crystallinity of prepared nanocomposites were identified by execution of

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XRD (powder x-ray diffraction) investigation. The electrochemical (I-V) measurement was carried out using USA originated Keithley electrometer (6517A, USA).

Preparation of ZnO/CB NCs by wet-chemical process

To synthesis of ZnO/CB NCs, zinc chloride (ZnCl2), carbon black (CB) and ammonium hydroxide (NH4OH) were used. The reliable and simple wet-chemical process (co-precipitation) was executed to prepare this NCs. The co-precipitation process is an efficient and easy system to

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the preparation of nanomaterials and the resultant nanomaterials (doped/undoped/composited) using hydrothermal process are smaller in grain size and phase. Following this method, the prepared 100.0 mL of 0.1 M ZnCl2 solution in di-ionized water was taken in 250.0 mL conical flask and the measured amount of carbon black (CB) was added in this conical flask. Then, the

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whole mixture was kept on a hot plat at 80˚C temperature with contentious magnetic string

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system. To precipitate the metal ion in form of metal hydroxide, 0.1 M NH4OH was added

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dropwise to increase the pH of solution gradually up to 10.5. At pH 10.5, all the metal ions were

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precipitated out quantitatively with CB in the form of Zn(OH)2●CB●nH2O crystal. At this conditions, the process was kept for 6 hours and after that, the precipitate was separated from the

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aqueous medium and washed with acetone and de-ionized water. Thus, the resulted mass was

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kept inside a low temperature oven at 110 ˚C temperature for overnight. This analogous system of formation of nanocrystal has been reported earlier [43,44]. The proposed reactions in conical

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flask are supposed as in bellow.

(i)

ZnCl2(s) → Zn2+(aq) + 2Cl-(aq)

(ii)

Zn2+(aq)+ CB(dis)+ OH- + nH2O⇆ Zn(OH)2.●CB●nH2O ↓

(iii)

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NH4OH(l) ⇆ NH4+ (aq) + OH- (aq)

Finally, the dehydrated Zn(OH)2.●CB●nH2O sample was subjected to calcine at 300 ˚C

temperature for 6 hours into a high temperature muffle furnace and due to the presence of atmospheric oxygen, the metal hydroxides were converted to metal oxides of ZnO●CB. But at

this temperature, CB was not oxidized (thermal stability of CB is above 500˚C and oxidation of Zn(OH)2 is below 300 ˚C temperature) [45,46]. The proposed reactions inside the muffle furnace are as follows. Zn(OH)2●CB+ O2→ ZnO●CB + H2O (v)

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(iv)

Fabrication of GCE with ZnO/CB NCs:

To fabricate the working electrode of desire chemical sensor, the commercial GCE with 0.0316 cm2 surface area was used. A slurry of ZnO/CB NCs was prepared in ethanol and used to

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coat on the GCE as uniform thin layer. Then, the modified GCE was dried at room condition. To

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enhance the binding properties between NCs and GCE, a drop of nafion (5% ethanolic solution

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of nafion) was added onto dried GCE. Finally, the assembled working electrode (ZnO/CB

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NCs/binder/GCE) was dried inside an oven at 35C for a time adequate enough to dry the

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conducting film entirely. An electrochemical cell was assembled with Keithley electrometer,

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where ZnO/CB NCs /binders/GCE was acted as working and Pt-wire as counter electrode. The BH solutions based on concentration ranging from 0.1 M to 0.1nM were prepared and used as

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analyte to electrochemical investigate in the desire phosphate buffer system. A calibration plot as current vs. concentration of BH was prepared. Considering the maximum linearity (r2) of

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calibration curve, the linear dynamic range (LDR) was identified. The sensitivity and detection

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limit of desired chemical sensor were estimated from the slop of calibration curve. The used electrometer (Keithley electrometer, 6517A, USA) is simple two electrodes system. Amount of 0.1 M PBS (phosphate buffer solution) was kept constant as 10.0 mL throughout the electrochemical investigation.

Results and discussions Binding energy analysis The synthesized NCs of ZnO/CB were investigated by the XPS analysis and the core level XPS spectrum of ZnO/CB NCs is represented in Fig. 1. As it is illustrated in Fig. 1(a), the

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observed spin orbitals of Zn2p3/2 and Zn2p1/2 are centered at 1022.0 and 1045.0 eV respectively. The spin energy separation between the two peaks of Zn2p level is 23.0 eV, and indicated to existence of Zn2+ in ZnO/CB NCs [47-51]. The core level orbit of O1s is shown an intense peak at 532.0 eV as demonstrated in Fig. 1(b). Therefore, it can be ascribed as existence of O2- in

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lattice position of sample ZnO/CB NCs [52-54]. From this observation, it is confirmed that ZnO

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existed into the nanocomposite of ZnO/CB. The high relational of XPS spectrum of C1s is

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illustrated in Fig. 1(c) and as it is observed from Fig. 1(c), the C1s is fitted with two peaks at

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Optical and structural analyses

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284.20 and 288.12 eV corresponding with C-C/C=C and C=O bonds respectively [55-58].

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The XRD spectra of synthesized ZnO/CB NCs are shown in Fig. 2(a).The XRD diffraction is recorded by the radiation source of Cu-K1 (= 1.54178A˚) ranging from 10–80˚ with

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scanning speed of 2◦/min. As it is demonstrated in Fig. 2(a), the synthesized ZnO/CB NCs are consist of well assorted phases of ZnO and CB. The observed diffracted peaks of ZnO are (100),

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(002), (101), (102), (200), (112), (201) and (004) crystal planes. This resultant peaks of ZnO

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have a great similarities with the JCPDS no. 036-1451 and previous authors [59-63]. The additional characteristic peaks of CB such as (100), (004) and (110) are also demonstrated in Xray diffraction spectrum and well matched with reported articles [64,65] and JCPDS no. 440141. Using following equation (v), the crystal size of the synthesized nanocomposite is

calculated from peak ZnO (101) and the resulted crystal diameter of ZnO/CB NCs is close to 14.57 nm. D=0.9λ/(βcosө)

(v)

Here,  is representing the wavelength (X-ray radiation = 1.5418 Å) and β is width at half,

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corresponding to highest intense peak, and  is the diffracting angle [66].

The FTIR investigation was executed on the synthesized NCs to determine the functional groups existing in ZnO/CB NCs. The resultant FTIR spectrum is represented in Fig. 2(b) and the

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identical peaks are observed at 706, 831, 1374, 1514 and 2365 cm-1. The peaks at 706 and 831

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cm-1 are associated with Zn–O stretching vibration [67]. Besides this, the observed peaks at 1374

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and 1514 cm-1 are due to the symmetric and asymmetric stretching vibration of C=O group in

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prepared NCs [68,69]. Moreover, the peak at 2358 cm-1 is raised from atmospheric CO2 [70, 71]. The photo sensitivity of synthesized nanocomposite (NCs) is an important measurable features.

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Therefore, ZnO/CB NCs were investigated by the UV-vis spectrum scanning with the visible

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light source. As it is illustrated in Fig. 2(c), a broad peak at 293 nm is observed, and is identical characteristic absorption band of ZnO/CB NCs [72-74]. The UV-vis spectrum is allows us to

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estimate the optical band gap Ebg using equation (vi) and it is found to be 4.23 eV.

Ebg=1240/ λmax

(vi)

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Here, Ebg is band gape energy and λmax is maximum absorbed wave length.

TEM analyses The morphology of ZnO/CB nanocomposites was evaluated by implementation of TEM analysis. As it is observed from Fig. 3, the accumulated round-spherical-shaped morphology is exhibited by ZnO/CB nanocomposites. The TEM images (Fig. 3a-b) are displayed that the

aggregated ZnO nanoparticles are adsorbed on the surface of CB and formed as a nanocomposites. The red-circle indicates the CB is existed in the aggregated ZnO/CB (indicated by arrow). Therefore, it is very clear from the TEM images, the nanocomposites is assembled as

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round shaped ZnO-spherical-particle-like morphology adsorbed onto CB, which represent to the co-adsorption and particles-aggregation as nanocomposite materials.

Applications: Detection of BH by ZnO/CB NCs

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The proposed BH chemical sensor based on NCs of ZnO/CB was implemented to detect

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BH in phosphate buffer medium. The chemical sensor with ZnO/CB NCs /binder/GCE is first

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stage and as per author knowledge any report regarding of this is not available. To fabricate the

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working electrode of BH chemical sensor, GCE (0.0316 cm2 surface area) was coated with the

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ethanolic slurry of ZnO/CB NCs as uniform thin layer. The binding strength between layer of

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ZnO/CB NCs and GCE was enhanced by addition of a drop of nation solution (5% ethanolic nafion solution). The use of nafion as conducting binder is improved the stability, conductivity

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and electron transfer rate of proposed chemical sensor due to its synergistic effect [75, 76]. Therefore, the BH chemical sensor has been exhibited the useful advantages such as long-tern

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stability and inertness in chemical environment, and enhanced electrochemically activities during sensing performance. The electrochemical (I-V) responses were measured on the thin film of

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ZnO/CB NCs/binder/GCE during sensing experiment of BH and it was observed that the intensity of I-V responses were decreased with increasing of BH concentration in the measuring phosphate buffer medium. The perceived decreasing tendency of I-V responses were due to the acceptation of electrons from applied current by BH and BH was reduced to benzylic alcohol.

The holding period in the electrometer was set at 1 sec and a proposed reduction mechanism of BH is illustrated in Scheme 1(a). As it is represented in the reactions (vii) and (viii), the two electrons are necessary to reduce BH. As a result, a deficiency of electrons in measuring Thus, it is responsible to

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phosphate buffer system is observed and it is fulfil by applied I-V.

reduce the intensity of I-V responses. Consequently, with increasing of analyte (BH) concentration, the I-V response is decreased. The similar electrochemical reduction of BH was

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reported previously [77-79].

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A thin film of ZnO/CB NCs was deposited on GCE with conducting binder to result a

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working electrode of BH chemical sensor and it was implemented to detect BH in environmental

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sample with various concentration of BH. The reduction reaction was involved in detection performance as stated in equation (vii) and (viii).

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H 2O  H   OH 

(viii)

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C 6H 5CHO  2H   2e   C 6H 5CH 2OH

(vii)

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On the other hand, ZnO is semiconductor material blending with CB to make NCs. Here, during the chemi-sorption, the dissolved oxygen is converted to ionic species (such as O2−and

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O−) by gaining electrons from the conduction band of aggregated NCs which improve and enhance the current responses against potential during the I-V measurement at room conditions

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(Eq ix & x). The aqueous BH sensing mechanism of ZnO/CB/GCE NCs sensors based on the semiconductors oxides is presented, where the oxidation or reduction of the semiconductor oxide itself according to the dissolved O2 in bulk-solution or surface-air of the surrounding atmosphere. e- (ZnO/CB/GCE NCs) + O2 → O2-

(ix)

e- (ZnO/CB/GCE NCs) + O2- → 2O-

(x)

These reactions are taken place in bulk-solution or air/liquid interface or surrounding air due to the low carrier concentration, which effect the resistance. BH sensitivity toward

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ZnO/CB/GCE NCs could attribute to the higher oxygen deficiency and defect density leads to increase oxygen adsorption. Larger the amount of oxygen adsorbed on the surface, larger would be the oxidizing capability and faster would be the oxidation of BH. The reactivity of BH would have been very large as compared to other chemical with the surface under identical condition. When BH reacts with the adsorbed O2 on the conjugated-surface of the film of ZnO/CB, it was

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liberated the free electrons in the conduction band. The free-electrons are functioned with the

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hydrolyzed proton (H+) to enhance the reduction of BH as per the equation (vii & viii). The

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fabricated working electrode of desired chemical sensor was not equally responsive in all buffer

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medium (pH of 5.7, 6.5, 7.0, 7.5 and 8.0). Therefore, the assembled working electrode with ZnO/CB NCs was tested to measure I-V response for the pH optimization. It was found to

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maximum response at pH 8.0 (alkaline buffer), which is represented in Fig. 4(a). To investigate

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the selectivity of proposed sensor based on ZnO/CB NCs/binder/GCE, a number of toxins at

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micro-level concentration and applied potential 0+1.5 were investigated. The electrochemical (I-V) responses of 3-CP, 3-MA, AH, THF, Chl, BH, MeOH, 2,4-DNP, pyridine, and MEL are

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demonstrated in Fig. 4(b). As it is observed from Fig. 4(b), the benzaldehyde (BH) shows the highest I-V response. The capability to produce replicated I-V responses in an identical

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conditions is an important analytical performance of chemical sensor. Therefore, the reproducibility test of desire electrochemical sensor based on ZnO/CB NCs/binder/GCE was executed at 0.1 µM concentration of BH and applied potential 0+1.5V. As it is represented in Fig. 4(d), the five runs are practically indistinguishable and the electrochemical (I-V) responses are not changed even washing of electrode after each run. Obviously, this performance provides the evidence of reliability

of projected BH chemical sensor. To measure the accuracy of electrochemical responses of reproducibility performance, the percentage of relative standard (%RSD) deviation of current data was estimated at applied potential +1.5V. A highly precious RSD (1.01%) is obtained. The response time is another analytical performance to identify the efficiency of electrochemical sensor. Thus, this

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performance was executed at 0.1µM concentration of BH in optimized phosphate buffer medium as represented in Fig. 4(c). As it is illustrated in Fig. 4(c), an appreciable result of response time 13.0 sec is obtained.

Additionally, impedance spectroscopy is studied and included in the Electronic

Supplemental Information (ESI).

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As it is demonstrated in Fig. 5(a), the electrochemical (I-V) responses based on ZnO/CB

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NCs/binder/GCE sensor are varied with corresponding concentration of BH solution from higher

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to lower. Therefore, it can be concluded that the I-V responses are inversely proportional to the

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concentration of BH. That means, the lower concentration of BH exhibits highest I-V response.

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A number of BH solution based on concentration ranging from 1.0 mM to 0.1 nM were prepared

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in de-ionized water and used as analyte to execute corresponding I-V response as illustrated in Fig. 5(a). This performances was executed at applied potential 0+1.5V in phosphate buffer

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medium with pH 8.0. The current data from Fig. 5(a) at applied potential +1.5 V are collected and a new Fig. 5(b) as current vs. concentration of BH is plotted known as calibration curve. The

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resulted calibration curve is found to be linear over concentration range of 0.1 nM  0.1 mM

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identified as linear dynamic range (LDR) and LDR is really very wide range of concentration. The analytical performance sensitivity of projected BH chemical sensor is estimated from the slop of calibration curve and surface area of GCE (0.0316 cm2) and it is equal to 5.0633 µAµm1

cm-2, a result might be satisfactory. Similarly, the detection limit (DL) of BH chemical sensor is

calculated from slop of calibration curve and signal to noise ratio at 3. The obtained DL is 18.75

± 0.94 pM, a value is very lower concentration. To find out the linearity of calibration curve in between the linear dynamic range, the current data are plotted against the corresponding concentration of BH in logarithmic scale as Fig. 5(b) inset and the current data is fitted with

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regression co-efficient value r2=0.9965, which provides the conformation of linearity of calibration curve in between LDR.

To optimize the validity of BH chemical sensor based on ZnO/CB NCs/binder /GCE, a

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number of test was executed as represented in Fig. 6. As it is perceived from Fig. 6(a), the

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resulted seven electrochemical (I-V) responses (seven consecutive days with the similar

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fabricated electrode with ZnO/CB NCs) at 0.1µM concentration of BH and applied potential

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0+1.5V are indistinguishable. Thus, this investigation provides information of long-term stability of BH chemical sensor using nafion binder and ability to produce similar

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electrochemical responses with constant (%RSD = 1.40) results for long duration in identical

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conditions. To establish the logical support for using ZnO/CB NCs as BH chemical sensor, the

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three electrochemical (I-V) responses for three fabricated electrodes are represented in Fig. 6(b).

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Obviously, ZnO/CB NCs/binder/GCE shows the supreme I-V response.

As it is demonstrated in Fig. 5(a), the electrochemical responses of BH chemical sensor

based on ZnO/CB NCs/binder/GCE vary with the concentration of BH in phosphate buffer system. At initial, the small surface coverage due to adsorption of few molecules of BH on the surface of ZnO/CB NCs/binder /GCE electrode and the reduction reaction of BH is started

progressively. With time, the surface coverage of anticipated electrode is enhanced as well as the reaction and approach to its steady state equilibrium state. With further enrichment of molecules on surface of working electrode, the surface coverage is become saturated and attained

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steady state current density in sensing medium. Fig. 5(b) is represented such steady state current data and the current data are consistency distributed along the linear plot. Thus, this evidence shows the reliability of method. As it is shown in Fig. 4(c), the response time of projected BH chemical sensor is 13.0 sec. Thus, this time is necessary by the BH chemical sensor to produce the steady state equilibrium electrochemical (I-V) response. In short, the projected BH chemical

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sensor with ZnO/CB NCs/binder/GCE has been exhibited good sensitivity with broad LRD, very

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lower DL, long-term stability with high accuracy, and quick response ability. A comparison of

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similar researches are illustrated in Table 1 [80-84]. So, the fabricated BH chemical sensor is

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simple and efficient to detect BH by applying current vs. potential electro-chemical approaches.

Real sample analysis

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To examine real time applicability of BH chemical sensor, the projected ZnO/CB

NCs/binder/GCE sensor was investigated in real samples collected from extract of PC-baby bottle, PC-water bottle, PVC-food packaging bag and waste effluent of industry. This experiment was executed using recovery method as demonstrated in Table 2 and the obtained results are quite satisfactory.

Conclusions The NCs of ZnO/CB was prepared using wet-chemical process at low temperature. FTIR, UV-Vis, XRD, XPS and TEM were implemented to details characterization of prepared NCs. A

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uniform thin layer was deposited on GCE with conducting nafion binder. The proposed chemical sensor is found as high selectivity (5.0633 µAµM-1cm-2) with lower detection limit (18.75 ± 0.94 pM), long term stability with precious electrochemical responses and enhanced electrochemical activity. The current to concentration of BH is found to be linear (r2 = 0.9965) over LDR (0.1 nM  0.1 mM). The projected BH chemical sensor based on ZnO/CB NCs is capable to analysis of

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environmental real sample efficiently. It might be introduced an efficient route for the detection

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of environmental unsafe chemicals by electrochemical approach to protect the healthcare and

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environmental fields in broad scales.

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Acknowledgements

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Center of Excellence for Advanced Materials Research (CEAMR), Chemistry

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Department, King Abdulaziz University, Jeddah, Saudi Arabia is highly acknowledged for

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financial supports and research facilities.

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Fig. 1. Binding energy analysis by XPS study of

ZnO/CB NCs. (a) spin orbit Zn2p, (b) O1s

A

CC

EP

level, (c) spin orbit of C1s level, and (d) full spectrum of ZnO/CB NCs

SC RI PT U N A M D TE EP

Fig. 2. Optical and morphological evaluation by (a) XRD pattern of the ZnO/CB NCs (b) FTIR,

A

CC

and (c) UV spectrum

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A

CC

EP

TE

D

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A

N

U

Fig. 3. (a-b) TEM analysis from high to low magnified images of ZnO/CB NCs.

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A

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EP

Fig. 4. Optimization of BH chemical sensor based on ZnO/CB NCs/binder/GCE (a) pH optimization, (b) selectivity, (c) response time, and (d) repeatability.

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Fig. 5. (a) Concentration variation of BH chemical sensor based on ZnO/CB NCs/binder /GCE by I-V method, (b) calibration curve (Inset: log [BH Conc.] vs. Current)

A

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Fig. 6: The optimization of BH chemical sensor based on ZnO/CB NCs/binder /GCE in electrochemical approach. (a) Inter-day validity and (b) the validity of ZnO/CB NCs/binder /GCE sensor.

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Scheme 1. (a) Schematic of fabricated GCE with ZnO/CB NCs using conducting nafion binder

A

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TE

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and electrochemical (I-V) response.

Table 1. Comparative performance of BH chemical sensor by various nanomaterials DL

LDR

Sensitivity

Ref

P-TP-3,4,5-TC acid

0.54 µM

31000 µM,

------------------

[80]

Carbon Nanodots (CDs)

0.3 µM.

----------------

-----------------

[81]

Y2O3 NPs

0.90 µM

1.8 µM–10.8 mM

---------------

[82]

NiO materials

-----

--------

---------

[83]

PED coupled LC

5.1 ng

--

---

[84]

ZnO/CB NCs/GCE

18.75 pM

0.1 nM 0.1 mM

5.0633 µAµMcm-2

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Materials

N

U

This work

A

* DL (Detection limit), LDR (Linear dynamic range), µM (Micromole), nM (Nanomole).

M

Table 1. Measured concentration of BH analytes in real sample Added BH Determined BH Recoveryb concentration concentrationa by ZnO/CB (%) NCs/GCE

D

Sample

A

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EP

TE

0.1000 µM 0.0948 µM 94.8 Industrial effluent 0.1000 µM 0.0987 µM 98.7 0.1000 µM 0.0991µM 99.1 Plastic baby 0.1000 µM 0.0971 µM 97.1 bottle 0.1000 µM 0.0969 µM 96.9 0.1000 µM 0.0988 µM 98.8 Plastic water 0.1000 µM 0.0975 µM 97.5 bottle 0.1000 µM 0.0949 µM 94.9 0.1000 µM 0.0953 µM 95.3 PVC food 0.1000 µM 0.0991 µM 99.1 packaging bag 0.1000 µM 0.0947 µM 94.7 0.1000 µM 0.0942 µM 94.2 a Mean of three repeated determination (signal to noise ratio 3) with ZnO/CB NCs/GCE. b Concentration of BH determined/ Concentration of BH taken. c Relative standard deviation value indicates precision among three repeated determinations.

RSDc (%) (n=3) 2.44

1.07

1.46

2.81

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