Materials Chemistry and Physics 259 (2021) 124058

Available online 23 November 20200254-0584/© 2020 Elsevier B.V. All rights reserved.

Influence of silver doping on the structure, optical and photocatalytic properties of Ag-doped BaTiO3 ceramics

M.A. Majeed Khan a,*, Sushil Kumar b, Jahangeer Ahmed c, Maqusood Ahamed a, Avshish Kumar d

a King Abdullah Institute for Nanotechnology, King Saud University, Riyadh, 11451, Saudi Arabia b Department of Physics, Chaudhary Devi Lal University, Sirsa, 125055, India c Department of Chemistry, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia d Amity Institute for Advanced Research and Studies, Amity University, Noida, 201313, India

H I G H L I G H T S G R A P H I C A L A B S T R A C T

• Silver doped barium titanate nano-particles were prepared by viable sol-gel technique.

• The structural properties were analyzed by XRD and TEM.

• Mixed valence of Ag was confirmed by XPS.

• Ag-doped BaTiO3 exhibited better pho-tocatalytic activity against organic dyes.

• Mechanism for enhanced photocatalytic activity was established.

A R T I C L E I N F O

Keywords: Ag-doped BaTiO3

X-ray diffraction Dielectric properties Optical band gap Photo-degradation Magnetic measurements

A B S T R A C T

In this paper, an investigation on microstructure, optical, dielectric, photocatalytic and electrochemical prop-erties of monodispersed Ag-doped BaTiO3 nanosized particles modified with different contents of silver (1, 3, 5 mol %) prepared by viable sol-gel technique has been carried out. The obtained samples exhibit tetragonal phase as confirmed by X-ray diffraction and Raman spectra. Using XRD data, the crystallite size of undoped and Ag- doped BaTiO3 nanoparticles (NPs) was found to be in the range of 46–54 nm, and have interplanar spacing of 0.283 nm as confirmed by HRTEM images. The characteristic peaks occurred at 309, 511 and 717 cm− 1 in Raman spectra predicted the formation of tetragonal phase of barium titanate. The calculated band gap energy of BaTiO3 NPs was reduced from 3.87 to 3.47 eV by incorporating the silver ions (5% Ag). Intensity of photoluminescent peaks decrease with increasing Ag content indicating that recombination of electrons-holes was effectively restrained. Dielectric permittivity as well as loss of prepared nanosized particles have been decreased sharply in low frequency region and remained almost constant with low value in high frequency region. Photo-assisted- catalytic property of Ag-doped BaTiO3 NPs towards degradation of hazardous rhodamine B (RhB) dye under visible irradiation (λ ≥ 400 nm) was thoroughly investigated, and a remarkable photocatalytic activity of Ag (5%)-doped BaTiO3 NPs was observed as 79%. On this account, it is promoted as an excellent nanophotocatalyst for the degradation of organic pollutants. C–V analysis depicted that the diffusion coefficient of BaTiO3 NPs increases considerably with Ag incorporation, which is favourable for large–scale energy storage applications.

* Corresponding author. E-mail address: mmkhan@ksu.edu.sa (M.A.M. Khan).

Contents lists available at ScienceDirect

Materials Chemistry and Physics

journal homepage: www.elsevier.com/locate/matchemphys

https://doi.org/10.1016/j.matchemphys.2020.124058 Received 13 August 2020; Received in revised form 5 November 2020; Accepted 17 November 2020

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BET analysis supported the claim of presently prepared materials to be an efficient photocatalyst as well as a potential material for efficient energy storage devices.

1. Introduction

As known to all, barium titanate (BaTiO3) is one of the most important functional dielectric material used for various technological applications in diverse fields such as electronics ferroelectrics, electro-mechanical energy conversion and electro-optic devices [1–3]. BaTiO3 possesses different crystallographic phases, of which the most stable are cubic and tetragonal. In most of synthesis routes, the employed nano-materials preferred low temperature which resulted in the formation of cubic structure [4]. In order to get optimum dielectric constant and ferroelectric properties at room temperature, the tetragonal phase of BaTiO3 is desirable [5]. Some wide band gap oxide semiconductors such as BaTiO3 may generate charge carriers (electron-hole pairs) only if irradiated by band gap matching radiation; and hence exhibit excellent photocatalytic properties under UV radiation [6]. Various parameters such as band gap, light absorption, charge carriers recombination rate, crystal orientation, morphology, and particle size etc. play a vital role on the efficiency of oxide photocatalysists [7,8]. Doping a semiconductor with suitable metal element is a well-known pathway to develop a visible-light-driven photocatalyst [9]. In recent years, the study on metal ions modified oxide semiconductor nanoparticles has received mo-mentum because of the fact that metal ions (such as Ag) in oxide semiconductors (such as BaTiO3) induces the narrowing of band gap, enhancing the visible light absorption and lowering the recombination rate of electron-hole pairs [10,11]. The photo-assisted-catalytic effi-ciency of BaTiO3 could be significantly improved by attaching Ag ions onto the surface of BaTiO3 NPs [12]. It is owing to its narrow bandgap and the diminish e− - h+ recombination rate due to photo induced electron capturing. The dielectric performance of BaTiO3 can easily be improved by adding metallic element (Ag) into it [13], which in turn effectively modified its microwave absorption properties [14].

In this way, there is a good choice of incorporating Ag ions in BaTiO3 so that the dielectric permittivity, electrochemical performance and photocatalytic activity could be significantly enhanced and might be beneficial for the fabrication of energy storage and conversion devices and to act as efficient photocatalyst. There are a number of techniques to synthesize nanosized BaTiO3 particles, out of them, sol-gel method is widely accepted to synthesize nanomaterials due to greater homoge-neity, crystallinity, uniform particle size distribution, considerable low temperature, easy processing and cost effectiveness. Pure and doped nanosized BaTiO3 powders with homogeneity, uniform particle size distribution can be synthesized by wet-chemical method like hydro-thermal method, sol-gel method and/or the combination of these two methods. Taking into consideration all the above facts, authors inves-tigated the influence of silver doping on the structure, optical, dielectric, photocatalytic and electrochemical properties of sol-gel derived BaTiO3 nanosized particles.

2. Experimental details

2.1. Preparation

Ag-doped BaTiO3 nanosized particles were successfully derived by a viable sol-gel protocol, wherein Ag content varied from 1 to 5 mol %. The precursors such as barium acetate (Sigma-Aldrich, 99.999%) and tetrabutyl titanate (Sigma-Aldrich, reagent grade, 97%) were used as the starting materials. Dopant was chosen to be Ag in the form of silver nitrate (Sigma-Aldrich, ACS reagent, ≥ 99.0%). In the present work, the stoichiometric amount of tetrabutyl titanate was dissolved in absolute ethanol (Sigma-Aldrich, reagent grade, 95%), stirring constantly at 3000 rpm for 30 min to attain homogeneous mixing. Then, the

stoichiometric amount of barium acetate and of silver nitrate was simultaneously added into tetrabutyl titanate solution, and magnetically stirred vigorously at room temperature for 1 h to form homogeneous solution. Subsequently the resulting clear transparent solution was put in the water bath at 50 ◦C for a day so that a qualitative dry gel may easily be formed. Finally, the gel powder of samples was calcined at 800 ◦C for 2 h so that Ag-doped BaTiO3 nanosized particles were ob-tained. The heat treatment for calcination of samples was carried out in a temperature controlled furnace without any gas environment and the heating rate was maintained at 5

◦

C/min. All the experiments were performed in normal laboratory ambient conditions.

2.2. Characterization

Structural details of all samples were investigated by XRD (Pan-Alytical X’pert Pro MPD) working at 40 kV and 40 mA using CuKα ra-diation (λ = 1.5406 Å) over 2θ values from 20 to 80◦. FTIR spectra of samples were recorded using IR spectrophotometer (PerkinElmer) in the range 400–3500 cm− 1. The surface composition of undoped and Ag- doped BaTiO3 nanoparticles was determined by ESCA system (VG 3000) with monochromatic MgKα line (1253.6 eV) radiation. Field emission scanning electron microscopy (JEOL, S-5000) and transmission electron microscopy (JEOL, JEM-2010) were performed to examine the microstructure and the particle size of products. Raman spectroscopy was employed to know the existing phase of samples with spectrometer (Perkin-Elmer 400F) using a 514 nm laser beam in the wavenumber range of 200–1000 cm− 1. UV–Visible study was done to find the band gap using UV–visible spectrophotometer (Shimadzu UV-1700) at normal incidence of light in the wavelength range of 250–900 nm. The magnetic measurements were carried out at room temperature with a vibrating sample magnetometer (Quantum Design). The luminescence spectra of prepared samples were recorded using a fluorescent spectrophotometer (Hitachi F-4600) in the wavelength range of 350–550 nm. Dielectric parameters were measured by impedance analyzer in frequency range 0–100000 Hz.

2.2.1. Photocatalytic measurements Activity for photocatalytic action of prepared nanosized particles

was determined as per photocatalytic decomposition of rhodamine B dye in their presence and under the visible light irradiation. In all ex-periments which were carried out at room temperature for different duration of irradiation (0, 15, 30, 45, 60, 75, 90, 105 min), 20 mg of as- prepared nanocatalyst powder was added into 30 ml of RhB aqueous solution (concentration of RhB aqueous solution without catalyst was 20 mg/l) [15]; and the suspension so prepared was magnetically stirred for 30 min in the dark in order to reach at adsorption-desorption equi-librium of RhB dye with the prepared catalyst. The homogeneous sus-pension solution was immersed in a cylindrical vessel (600 ml capacity) and then the solution was irradiated by a 400 W sodium lamp (Philips) with wavelength range of 300–800 nm. After that the suspension was interrogated at above said time intervals by noting absorption variation at the absorption edge (553 nm) of RhB dye employing UV–Vis spec-trophotometer (Shimadzu UV-1700). The catalyst’s degradation effi-ciency can be calculated on the basis of following formula:

Photodegradation (%)=

(

1 −CCo

)

× 100%

where Co is initial concentration of RhB, and C is revised concentration after adsorption of RhB on undoped or Ag-doped BaTiO3 nanosized particles under photo irradiation. The concentration was determined in

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terms of absorption within the limits of the Beer-Lambert law.

3. Results and discussion

3.1. X-ray diffraction analysis

The phase structure of as-synthesized pure and Ag (1, 3, 5 mol %)-doped BaTiO3 nanoparticles has been examined by the XRD patterns in the 2θ range of 20–80◦ as shown in Fig. 1. Main diffraction peaks of all NPs are located at 2θ values of 22.24, 31.56, 38.82, 45.26, 50.92, 56.22, 65.9, 70.46◦, 75.10, and 79.24 corresponding to (001), (110), (111), (200), (210), (211), (220), (300), (103) and (311) crystal planes of tetragonal phase BaTiO3 (JCPDS No. 05–0626). No diffraction peaks of Ag could be observed in recorded XRD patterns. The following Debye- Scherrer equation is used to calculate the crystallite size of prepared samples [16]:

D=0.9 λβcosθ

The estimated crystallite size of BaTiO3 and Ag (1, 3, 5%)-doped BaTiO3 nanoparticles are 46.2, 48.5, 51.4 and 54.2 nm respectively.

3.2. Microstructural analysis

In order to study the microstructure, particle size and morphology of as-obtained undoped BaTiO3 and Ag-doped BaTiO3 nanoparticles, TEM and HRTEM images were taken into account. Fig. 2(a) and (b) illustrates the representative TEM images of undoped BaTiO3 and Ag (5%)-doped BaTiO3 nanoparticles respectively. The TEM images show that synthe-sized nanoparticles possess spherical morphology with particle sizes of 48–57 nm, besides there exists some agglomerates. The results of TEM observations are well consistent with the calculated values from Debye- Scherer equation. The tetragonal phase of prepared NPs is further approved by the visible lattice fringes in HRTEM images Fig. 2 (c) and

(d). The interplanar spacing of the lattice was about 0.283 nm, which relates to the interplanar distance of (100) plane of tetragonal phase BaTiO3 NPs (JCPDS File No. 812203); whereas lattice fringes of silver (Ag) have interplanar spacing of 0.23 nm which corresponds to wurtzite structure of Ag with (111) as crystallographic plane. EDS spectra was used to explain the chemical and elemental compositions of all the samples which showed only the presence of Ba, Ag and Ti peaks along with O peak, with no indication of contamination Fig. 2 (e) and (f).

3.3. XPS analysis

In order to find the valence state and the chemical composition of as- prepared Ag: BaTiO3 nanoparticles, XPS spectra were recorded and the corresponding results were exhibited in Fig. 3 (a). The base line correction and de-convolution have been performed in the figures. XPS spectra for Ba 3 d signal show two band peaks with Ba 3d5/2 and Ba 3d3/2 located at 781.7 and 797.8 eV (Fig. 3 (b)) and are in excellent coinci-dence with those reported in literature previously for Ba 3 d binding energy [17]. The Ti 2p region is shown in Fig. 3(c) with two bands Ti 2p3/2 and Ti 2p1/2 at 458.7 and 464.8 eV respectively, depicting the valence of Ti in BaTiO3 NPs [18,19]. Fig. 3 (d) reflects Ag 3 d XPS spectra where peaks appeared at 367.2 and 373.1 eV which can be attributed to binding energies for Ag 3d5/2 and Ag 3d3/2, respectively. The O 1s spectra deconvoluted in to two peaks as shown in Fig. 3(e). The deconvoluted peaks at 530.9 and 533.3 eV correspond to oxygen bonded BaTiO3 lattice and surface-adsorbed oxygen atoms respectively [20,21].

3.4. FTIR analysis

To explore the chemical functional groups of pure BaTiO3 and Ag- doped BaTiO3 nanoparticles, FTIR spectra were recorded and shown in Fig. 4. The characteristic bands at 468 cm− 1 is due to Ti–O vibrations in BaTiO3, while the bands centred at 1090 and 1465 cm− 1 is the characteristic band of crystalline barium titanate [22]. The bands

Fig. 1. XRD patterns for undoped and Ag-doped BaTiO3 nanoparticles.

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located at 3412, 2964, 2921, 2851, 1691,1648 and 1554 cm− 1 could be ascribed to bending vibrations and stretching vibrations of hydroxyl groups, respectively. Band bending nature of the material assisted in decreasing the recombination of charge carriers, thereby increasing its photocatalytic performance.

3.5. Raman analysis

Raman spectroscopy is an excellent way to study the impact of doping on the local structure of the samples. The room temperature Raman spectra of pure and Ag-doped BaTiO3 nanoparticles have been analyzed in a wide range of wavenumber 200-1000 cm− 1 displayed in Fig. 5. The peaks located at 309, 511 and 717 cm− 1 are characteristic peaks of tetragonal phase of BaTiO3 [23,24]. The sharp peak at 309 cm− 1 is because of the vibration of TiO6 group. A peak situated at 511 cm− 1 is ascribed to the vibrations produced by displacement of oxygen atom. Moreover, the presence of peak at 717 cm− 1 is attributed to the tetragonality of BaTiO3, which are for identifying the phase transition in undoped and Ag-doped BaTiO3 NPs. The tetragonal phase is desirable for enhanced photocatalytic action of the material. In addition, by

increasing Ag concentration, the intensity of Raman peaks changed, indicating that the higher Ag concentration results in worsening of crystallinity, the same was demonstrated in XRD analysis.

3.6. UV–visible absorption analysis

The optical properties of pure BaTiO3 and Ag doped BaTiO3 NPs were understood by recording the absorption response between 250 and 900 nm wavelength as presented in Fig. 6(a), and then the energy band gap (Eg) was determined as based on Tauc relation [25,26]:

(αhν)=A(hν − Eg

)n

where A is material’s dependent constant, hν being photon energy, n is exponent representing the nature of band transition which depend on the nature of optical transition. Here α is the absorption coefficient estimated by the following relation [27]:

α=Ax

Fig. 2. TEM and HRTEM images. (a,b) TEM images and (c,d) HRTEM images (e,f) EDS spectrum of the as-synthesized undoped BaTiO3 nanoparticles and 5% Ag- doped BaTiO3 nanoparticles.

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where A is absorbance and x is thickness of sample. The energy band gap could be obtained by extrapolating the slope line of (αhν)2 vs. hν plot as shown in Fig. 6(b). The direct band gap energy of BaTiO3 without doping is 3.87 eV and with 5% Ag doping is 3.47 eV. It is demonstrated that the band gap decreases with increase of silver ions concentration, which resulted in the decrement of recombination rate of photogenerated electrons and holes, and support the improvement in the photocatalytic activity of Ag-doped BaTiO3 nanoparticles.

3.7. Photoluminescence analysis

Photoluminescence (PL) provides information about recombination rate of photogenerated pairs of electrons and holes in semiconductors [28]. Room temperature PL spectra of undoped and Ag-doped BaTiO3 nanoparticles in 350–550 nm region with 350 nm as excitation wave-length is presented in Fig. 7. The emission peaks at 394, 449 and 524 nm are observed for all the samples. Moreover, the intensity of doped BaTiO3 nanoparticles decreases with increasing Ag concentration and

ultimately Ag (5%)-doped BaTiO3 NPs exhibit PL intensity as lowest when compared with undoped BaTiO3 NPs, and hence indicates that the recombination rate of electrons-holes is effectively restrained. It may be predicted that in case of smaller size nanoparticles, more photo gener-ated electrons and holes easily migrate from inner part of particles to the surface so that they can take part in surface redox reactions, which promote the photocatalytic activity. Therefore, Ag (5%) doped BaTiO3 nanoparticles has revealed the superior photocatalytic performance in the photodegradation of Rh B under the UV light irradiation.

3.8. Magnetic hysteresis analysis

To investigate the effect of metal ions substitution on the magnetic characteristics, magnetization versus magnetic field (M − H) loops recorded at room temperature for pure and Ag-doped BaTiO3 are pre-sented in Fig. 8. It is observed that all the samples with different Ag concentration exhibit ferromagnetic behaviour. The ferromagnetism is likely to be related to oxygen vacancies, secondary phase, and induced

Fig. 3. (a) XPS survey scan spectrum of Ag doped BaTiO3 nanoparticles (b) Ba3 and 3d5, (c) Ti 2p1/2 and 2p2/3 (d) Ag 3 d (e) O1s XPS spectra.

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defects [29]. The saturation magnetization (Ms) of pure BaTiO3 and Ag (5%)-doped BaTiO3 nanoparticles are 6.62 × 10− 4 and 10.87 × 10− 4

emu/g respectively. The increased values of Ms may be due to Ag-doping

induced defects resulted in effective ferromagnetic exchange coupling.

Fig. 4. FTIR spectra of pure BaTiO3 and Ag-doped BaTiO3 nanoparticles.

Fig. 5. Raman Spectroscopy for undoped BaTiO3 and Ag-doped BaTiO3 nanoparticles.

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3.9. Dielectric analysis

The dielectric spectroscopy is the most reliable technique which give indepth information about structure of nanosized particles, grains, grain boundaries, transport phenomena and charge storage capacity of di-electrics which depend on chemical composition, preparation tech-niques etc. [30]. The frequency dependence of complex dielectric permittivity of undoped and Ag-doped BaTiO3 was studied at room

temperature as given by the following formula [31]:

ε∗ = ε′

+ iε′′

where ε′ is real part known as dielectric constant describing the stored energy and ε˝ is imaginary part called as dielectric loss describing the dissipated energy. ε′ and ε˝ of pure and Ag-doped BaTiO3 nanoparticles can be obtained using the following equations:

Fig. 6. UV–visible absorption spectra vs wavelength of (a) undoped and Ag–doped nano-BaTiO3 system (b) corresponding Tauc plots of (αhν)2 versus photon energy hν for estimation of optical band gaps.

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ε′

=CptAεo

and

ε˝ = ε′ tanδ

where Cp is capacitance of sample, t is thickness and A is cross-sectional area of sample. The effect of frequency of applied field on dielectric constants (real & imaginary) for undoped BaTiO3 and Ag doped BaTiO3 nanoparticles with various Ag concentrations in frequency range 0–100,000 Hz at room temperature are shown in Fig. 9 (a) and (b). From

Fig. 7. Room temperature photoluminescence spectra of undoped and Ag-doped BaTiO3 nanoparticles.

Fig. 8. Room temperature magnetic hysteresis loop of the BaTiO3 nanoparticles doped with different content of Ag from 1% to 5 mol%.

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these figures it can be seen that ε′ and ε′ ′ of all samples show similar behaviour with frequency. At lower frequency range, ε′ and ε′ ′ are reduced very sharply with increase in frequency, whereas remains low and constant at higher frequency range as a common feature of semi-conducting materials. Further, silver ions put their signature on the processing of BaTiO3 nanoparticles as grain boundary mobility mini-mizes with Ag doping concentration as induced defects resulted in segregation at grain boundaries. This observed frequency dependent

dielectric response is as per interfacial polarization as predicted by Maxwell and Wagner and is in consonance with phenomenological theory given by Koops [32].

3.10. Electric modulus analysis

The electric modulus theory is an important way that can be used to analyze the electrical conductivity and space charge relaxation process

Fig. 9. Frequency dependent of dielectric constant (a) and dielectric loss (b) of the BaTiO3 nanoparticles doped with different content of Ag from 1% to 5 mol%.

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occurring in the sample. The study of electrical relaxation in these sys-tems is carried out by following expression relating electric modulus (M*) and dielectric permittivity (ε∗) given as [33];

M* =M′

+ jM˝ =1ε*

where

M ′

=ε′

[(ε′

)2+ (ε˝)2]

M˝ =ε˝

[(ε′

)2+ (ε˝)2]

where M′ and M˝ are real and imaginary parts of complex electric modulus and are expressed mathematically in terms of the real and imaginary parts (ε′ and ε′′) of dielectric permittivity. The frequency dependence of M′and M˝ for undoped BaTiO3 as well as Ag-doped BaTiO3 nanoparticles at room temperature is depicted in Fig. 10(a) and (b) respectively. From Fig. 10 (a), it is observed that M′ exhibits

Fig. 10. Variation in the (a) real and (b) imaginary part of the electric modulus as a function of frequency at room temperature.

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almost constancy at low frequencies which may be related to lacking in restoring force governing the motion of charge carriers under the in-fluence of induced electric field. Further, M′ is negligibly small in low frequency range suggesting the less electrode polarization in the nano-material [34]. The step-like transition relative to the frequency reach an asymptotic value which reflects the strong capacitive nature of samples. The plot of M˝ as a function of frequency of applied field exhibits a well-defined single relaxation peak, indicating that the charge carriers experience a relaxation. However, in low frequency region, the ions are capable to move long distances, and in high frequency region, ions are confined in potential wells, and hence they are limited to localized movement only [35].

3.11. Photocatalytic activity

Photocatalytic activity of undoped and Ag-doped BaTiO3 nano-particles was evaluated through the degradation of Rhodamine B dye in UV–visible light illumination and the results are presented in Fig. 11 (a, b, c, d). All the prepared samples exhibit RhB absorption peak at 553 nm which show decrement as time spent and finally lost in about 105 min indicating the complete decomposition of RhB molecules. A blank test has been carried out in the absence of photocatalyst and found that there was no significant degradation under identical illumination conditions.

The decomposition efficiency of a photocatalyst has been calculated on the basis of relation [36] as given in experimental section. The degradation profiles clearly exhibit that the photocatalytic activity of BaTiO3, 1% Ag@ BaTiO3, 3% Ag@ BaTiO3 and 5% Ag@ BaTiO3 nano-particles after 105 min of UV–visible irradiation, and are numerically found to be 41, 46, 58 and 79% respectively (Fig. 12). The enhanced photocatalytic activity of Ag-doped BaTiO3 nanoparticles can be attributed to lower electron-hole recombination rate, decreased band

gap and high specific surface area of Ag-doped BaTiO3 nanoparticles with Ag doping level [36].

3.11.1. Photocatalytic degradation mechanism The photocatalytic performance of a catalyst mainly depends on the

generation, separation and transfer of electron-hole pairs. The appro-priate band positions of a semiconductor material produces space charge depletion/accumulation at the interfaces, which help in the effective separation of photo generated charge carriers [37]. The band edge po-tentials of BaTiO3 and Ag-doped BaTiO3 NPs were estimated as based on the following empirical formulae

EVB = χ − Ee + 0.5Eg

ECB =EVB − Eg

where Ee is the energy of free electrons on the hydrogen scale (about 4.5 eV) and χ is the electronegativity of the semiconductor (5.12 eV for BaTiO3 and 5.02 eV for Ag (5%)-doped BaTiO3 NPs respectively) [38].

Herein, ECB and EVB band edge potential of BaTiO3 were calculated as − 1.31 and 2.56 eV, whereas for Ag (5%)-doped BaTiO3 these were calculated as − 1.21 and 2.26 eV respectively. The photocatalytic mechanism of Ag doped BaTiO3 nanoparticles has been proposed in Fig. 13. The equal number of electrons and holes were produced when the photo catalyst was illuminated by UV–visible light irradiation. These excited electrons can easily be trapped by the Ag nanoparticles as the Fermi level of Ag/BaTiO3 lies in between conduction band and Fermi level of pure BaTiO3 resulted in the formation of Schottky junction at the Ag/BaTiO3 interface and enhanced the separation of photogenerated charge carriers thereby decreasing the recombination rate [39]. There-fore, photogenerated charge carriers can be separated efficiently and were found to have highest photocatalytic activity of Ag (5%)-doped

Fig. 11. UV–visible absorption spectra of photodegradation of rhodamine B (RhB) dye through (a) undoped BaTiO3 (b) 1% Ag-doped BaTiO3 (c) 3% Ag-doped BaTiO3 (d) 5% Ag-doped BaTiO3 under visible light irradiation.

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BaTiO3 NPs as compared to undoped BaTiO3 NPs using rhodamine B (RhB) dye.

3.11.2. Reusability of photocatalyst To inspect the stability and reusability of Ag (5%)-doped BaTiO3

nanoparticles photocatalyst, recycling processes were carried out for the photodegradation of RhB dye as shown in Fig. 14. At the end of each experiment the used Ag-doped BaTiO3 NPs were separated by centrifu-gation and cleaned with deionized water and then dried at 100 ◦C for 2 h. The degradation efficiency of Ag (5%)-doped BaTiO3 photocatalyst after six cycles is found to be slightly reduced from 79 to 77%, indicating the stability of prepared photocatalyst. The slight decrease in the pho-tocatalytic activity might be due to the adsorption of intermediate species of degraded RhB on the nanoparticles. These results revealed that the prepared nanophotocatalyst can easily be reused for continuous

treatment of wastewater.

3.12. Cyclic voltammetry (C–V) analysis

In order to understand the electrochemical behaviour of prepared samples, cyclic voltammetry (C–V) has been carried out. Fig. 15 (a, b, c & d) represents typical voltammograms of undoped BaTiO3 and Ag- doped BaTiO3 nanoparticles. The standard three electrode cell system at ambient temperature was used which have electrodes dipped in 0.1 M aqueous H2SO4 electrolyte, applied potential in the range of − 1 to +1 V and various scan rates of 25, 50, 75, 100 mV/s. It is observed that anode peak current increases with the scan rate and anodic peak shift to lower potential while cathodic peak shift to high potential with increasing scan rate. Fig. 15(c) and (d) depicts that the peak current (Ip) have linear relationship with the square root of scan rate (ν1/2). The following

Fig. 12. Change in the concentration of Rh B dye in the presence of different photocatalysts.

Fig. 13. Proposal photocatalytic degradation mechanism of Rh B decomposition over 5% Ag-doped BaTiO3 nanoparticles under visible light irradiation.

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equations may be used to calculate the diffusion coefficient of lithium ions [40]:

ip = 2.69 x 105n3/2AD1/2cν1/2

where A (cm2) is electrode surface area, ν (V/s) is voltage scan rate, n is number of transferred electrons, Ip (A) is anodic or cathodic peak cur-rent, c is concentration of substrate and D (cm2/s) is diffusion coeffi-cient. The diffusion coefficient was estimated to be 9.68 × 10− 13 and 2.57 × 10− 12 cm2/s for BaTiO3 and Ag (5%)-doped BaTiO3 nano-particles, respectively. The diffusion coefficient of Li+ ions is found maximum for Ag (5%)-doped BaTiO3 among all prepared samples,

which may be attributed to fair particle dispersion as well as improved conductive network among nanoparticles as connected by Ag ions and therefore leading to enhanced electrochemical performance. The cyclic voltammetric technique used in the present study shows that sol-gel derived Ag (5%)-doped BaTiO3 NPs is very much suitable for energy storage device application. S. Mondal et al. [41,42] have fabricated and demonstrated highly sensitive and robust gate-controllable electronic trap detection in ZrO2 and HfO2 dielectric based MIS devices employable in charge-trapping memory devices.

Fig. 14. Reusability assay of 5% Ag-doped BaTiO3 nanoparticles for photodegradation of RHB dye under visible light irradiation.

Fig. 15. Cyclic voltammograms curve of (a) undoped BaTiO3 (b) 1% doped (c) 3% doped (d) 5% doped BaTiO3 nanoparticles at various voltage scan rates.

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3.13. Specific surface area and BET analysis

The Brunauer-Emmett-Teller (BET) surface area of pure BaTiO3 and Ag-doped BaTiO3 nanoparticles were estimated by using N2 adsorption- desorption isothermals and are shown in Fig. 16. As illustrated in Fig. 16 (a and b), the adsorption-desorption isothermals proved that undoped

and Ag-doped BaTiO3 nanoparticles represent the typical IV type isothermal profile, suggesting the existence of mesoporous structure as per IUPAC classification [43]. BET analysis showed that Ag (5%)-doped BaTiO3 nanoparticles has surface area of 20.1 m2 g-1, which is higher than that of pure BaTiO3 nanoparticles (15.4 m2 g− 1). The high surface area of Ag (5%)-doped BaTiO3 nanoparticles is a favourable reason for

Fig. 16. (a & b) Nitrogen adsorption-desorption isothermal of the as-synthesized undoped BaTiO3 and 5% Ag-doped BaTiO3 nanoparticles.

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better adsorption of rhodamine B dye as compared to undoped BaTiO3 NPs [44].

4. Conclusion

In summary, sol-gel derived Ag-doped BaTiO3 NPs proved their po-tential applications in photocatalytic degradation of organic pollutants and in energy storage devices. TEM images revealed nanosized particles (48–57 nm), depicting that Ag-doping in BaTiO3 enhances the size of particles. Magnetization curves reveal the room temperature ferro-magnetic behaviour of all Ag-doped BaTiO3 NPs. Raman spectral peaks revealed the formation of BaTiO3 nanoparticles. The band gap energy decreased from 3.87 to 3.47 eV with increment in Ag content. At lower frequency range, ε′ and ε˝ is reduced sharply, while remained low and constant at higher frequency range as a common feature of semi-conducting materials. Photocatalytic activity of Ag (5%)-doped BaTiO3 nanoparticles demonstrated the highest (79%) visible light driven pho-tocatalytic degradation of rhodamine B dye as compared to undoped BaTiO3 NPs (41%). The enhanced diffusion coefficient 2.57 × 10− 12

cm2/s of Ag (5%)-doped BaTiO3 NPs is favourable for energy storage device application.

CRediT authorship contribution statement

M.A. Majeed Khan: Conceptualization, Methodology, Validation, Investigation, Funding acquisition. Sushil Kumar: Formal analysis, Investigation, Methodology, Validation, Visualization, Software, Data curation. Jahangeer Ahmed: Data curation, Formal analysis, Project administration, administration, Resources, Writing - review &; editing. Maqusood Ahamed: Conceptualization, Data curation, Investigation, Formal analysis, Resources. Avshish Kumar: Methodology, Validation, Visualization, Investigation, Formal analysis.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors extend their sincere appreciation to Researchers Sup-porting Project Number (RSP-2020/130), King Saud University, Riyadh, Saudi Arabia for funding this research.

References

[1] Y.L. Wang, X.L. Chen, H.F. Zhou, L. Fang, L.J. Liu, H. Zhang, Evolution of phase transformation behavior and dielectric temperature stability of BaTiO3–Bi (Zn0.5Zr0.5)O3 ceramics system, J. Alloys Compd. 551 (2014) 365–369.

[2] C.C. Homes, T. Vogt, Doping for superior dielectrics, Nat. Mater. 12 (2013) 782. [3] L. Zhang, P. Wu, Y. Li, Z.Y. Cheng, J.C. Brewer, Preparation process and dielectric

properties of Ba0.5Sr0.5TiO3–P(VDF–CTFE) nanocomposites, Compos. Eng. B 56 (2014) 284.

[4] W.W. Lee, W.H. Chung, W.S. Huang, W.C. Lin, W.Y. Lin, Y.R. Jiang, C.C. Chen, Photocatalytic activity and mechanism of nano-cubic barium titanate prepared by a hydrothermal method, J. Taiwan Inst. Chem. E 44 (2013) 660–669.

[5] T. Ahmad, G. Kavitha, C. Narayana, A.K. Ganguli, Nanostructured barium titanate prepared through a modified reverse micellar route: structural distortion and dielectric properties, J. Mater. Res. 20 (2005) 1415–1421.

[6] K. Maeda, Photocatalytic water splitting using semiconductor particles: history and recent developments, J. Photochem. Photobiol., A C 12 (2011) 237–268.

[7] X.R. Xiong, R.M. Tian, X. Lin, D.W. Chu, S.A. Li, Formation and photocatalytic activity of BaTiO3 nanocubes via hydrothermal process, Nanomaterials 692182 (2015) 6.

[8] T.B. Nguyen, M.J. Hwang, K.S. Ryu, Appl. Surf. Sci. 258 (2012) 7299–7305. [9] A. Kudo, Y. Miseki, Heterogeneous photocatalyst materials for water splitting,

Chem. Soc. Rev. 38 (2009) 253–278. [10] V. Vaiano, O. Sacco, D. Sannino, P. Ciambelli, S. Longo, V. Vendittob, G. Guerrab,

J. Chem. Technol. Biotechnol. 89 (2014) 1175–1181. [11] K. Li, H. Wang, C. Pan, J. Wei, R. Xiong, J. Shi, Int. J. Photoenergy (2012) 1–8,

398508.

[12] R. Su, Y.J. Shen, L. Li, Dawei zhang, guang yang, chuanbo gao, silver-modified nanosized ferroelectrics as a novel photocatalyst, Small 11 (2015) 202–207.

[13] P. Yu, B. Cui, Z. Chang, Preparation and characterization of Ag-doped BaTiO3 based X7R ceramics, Mater. Res. Bull. 44 (2009) 893–897.

[14] Meng Zhang, Ji Zhengn, Liang Lu, Fei Jiang, Ying Wang, Preparation and microwave absorption properties of Ag-doped BaTiO3 nanocomposites, J. Magn. Magn Mater. 368 (2014) 198–201.

[15] Rui-Xia Wang, Quing Zhu, Wan-Sheng Wang, Cong-Min Fan, An-Wu Xu, BaTiO3- graphene nanocomposites: synthesis and visible light photocatalytic activity, New J. Chem. 39 (2015) 4407–4413.

[16] M.A. Majeed Khan, Wasi Khan, M. Naziruddin Khan, Abdulaziz N. Alhazaa, Enhanced visible light-driven photocatalytic performance of Zr doped CeO2 nanoparticles, J. Mater. Sci. Mater. Electron. 30 (2019) 8291–8300.

[17] Yan-Jun Wan, Peng-Li Zhu, Yu Shu-Hui, Wen-Hu Yang, Rong Sun, Ching- Ping Wong, Wei-Hsin Liao, Barium titanate coated and thermally reduced graphene oxide towards high dielectric constant and low loss of polymeric composites, Compos. Sci. Technol. 141 (2017) 48–55.

[18] L. Makhova, R. Hesse, M. Ullrich, R. Denecke, I. Konovalov, Surface potential of BaTiO single crystal near the Curie temperature, Phys. Rev. B 83 (2011) 115–407.

[19] P.M. Nithya, L. Gomathi Devi, Effect of surface Ag metallization on the photocatalytic properties of BaTiO3: surface plasmon effect and variation in the Schottky barrier height, Surf. Interfaces 15 (2019) 205–215.

[20] D.P. Dutta, M. Roy, N. Maiti, A.K. Tyagi, Phase evolution in sonochemically synthesized Fe3+ doped BaTiO3 nanocrystallites : structural, magnetic and ferroelectric characterisation, Phys. Chem. Chem. Phys. 18 (2016) 9758.

[21] I.C. Amaechi, G. Kolhatkar, A. Hadj Youssef, D. Rawach, S. Sun, A. Ruediger, B-site modified photoferroic Cr3+-doped barium titanate nanoparticles: microwave- assisted hydrothermal synthesis, photocatalytic and electrochemical properties, RSC Adv. 9 (2019) 20806.

[22] Y. Ni, H. Zheng, N. Xiang, K. Yuan, J. Hong, Simple hydrothermal synthesis and photocatalytic performance of coral-like BaTiO3 nanostructures, RSC Adv. 5 (10) (2015) 7245–7252.

[23] Tesfakiros Woldu, B. Raneesh, M. V. Ramana Reddy, Nanda kumar kalarikkal, RSC Adv. 6 (2016) 7886.

[24] P. Hermet, M. Veithen, P. Ghosez, Raman scattering intensities in BaTiO3 and PbTiO3 prototypical ferroelectrics from density functional theory, J. Phys. Condens. Matter 21 (2009) 215901.

[25] M.A. Majeed Khan, Sushil Kumar, Mohamad S. AlSalhi, Synthesis and characteristics of spray deposited CuInS2 nanocrystals thin films for photovoltaic applications, Mater. Res. Bull. 48 (2013) 4277–4282.

[26] M.A. Majeed Khan, Wasi Khan, Avshish Kumar, Abdulalziz N. Alhazaa, Plasma enhanced chemical vapour deposition growth and physical properties of single- walled carbon nanotubes, Mater. Lett. 219 (2018) 269–272.

[27] Sushil Kumar, M. A. Majeed Khan, Morphological, optical and DC conduction properties of a-GaSe semiconductor nanoparticle thin films, J. Mater. Sci. Technol. 29 (12) (2013) 1151–1155.

[28] L. Gomathi Devi, P.M. Nithya, Preparation, characterization and photocatalytic activity of BaTiF6 and BaTiO3: a comparative study, J. Environ. Chem. Eng. 6 (2018) 3565–3573.

[29] N. Sharma, A. Gaur, U.K. Gaur, R.K. Kotnala, Multiferroicity in Ba0. 97La0. 03Ti1−xNixO3 (0.03≤ x≤ 0.07) ceramics, J. Alloys Compd. 615 (2014) 135–140.

[30] M.D. Rahaman, M.D. Mia, M.N.I. Khan, A.K.M. Akther Hossain, Study the effect of sintering temperature on structural, microstructural and electromagnetic properties of 10% Ca-doped Mn0.6Zn0.4Fe2O4, J. Magn. Magn Mater. 404 (2016) 238–249.

[31] M. Mehedi Hassan, Wasi Khan, Ameer Azam, A.H. Naqvi, Influence of Cr incorporation on structural, dielectric and optical properties of ZnO nanoparticles, J. Industrial Eng. Chem. 21 (2015) 283–291.

[32] M.A. Majeed Khan, Rahul Siwach, Sushil Kumar, Maqusood Ahmed, Jahangeer Ahmed, Investigations on microstructure, optical, magnetic, photocatalytic, and dielectric behaviours of pure and Co-doped ZnO NPs, J. Mater. Sci. Mater. Electron. 31 (2020) 6360–6371.

[33] A.K. Pradhan, T.K. Nath, S. Saha, Impedance spectroscopy and electric modulus behavior of Molybdenum doped Cobalt–Zinc ferrite, Mater. Res. Express 4 (2017), 076107.

[34] K.S. Hemalatha, G. Sriprakash, M.V.N. Ambika Prasad, R. Damle, K. Rukmani, Temperature dependent dielectric and conductivity studies of polyvinyl alcohol- ZnO nanocomposite films by impedance spectroscopy, J. Appl. Phys. 118 (2015) 154103.

[35] Nitin Kumar, Alok Shukla, Nripesh Kumar, R.N.P. Choudhary, Ajeet Kumar, Structural, electrical, and multiferroic characteristics of lead-free multiferroic: Bi (Co 0.5 Ti 0.5) O3–BiFeO3 solid solution, RSC Adv. 8 (2018) 36939.

[36] M.A. Majeed Khan, Rahul Siwach, Sushil Kumar, Abdulaziz N. Alhazaa, Role of Fe doping in tuning photocatalytic and photoelectrochemical properties of TiO2 for photodegradation of methylene blue, Optic Laser. Technol. 118 (2019) 170–178.

[37] F. Jiang, T. Yan, H. Chen, A. Sun, C. Xu, X. Wang, A g-C3N4–CdS composite catalyst with high visible-light-driven catalytic activity and photostability for methylene blue degradation, Appl. Surf. Sci. 295 (2014) 164–172.

[38] Yong-Por Ong, Li-Ngee Ho, Soon-An Ong, Johar Banjuraizah, Abdul Haqi Ibrahim, Sin-Li Lee, Noradiba Nordin, A synergistic heterostructured ZnO/BaTiO3 loaded carbon photoanode in photocatalytic fuel cell for degradation of Reactive Red 120 and electricity generation, Chemosphere 219 (2019) 277–285.

[39] S. Kuriakose, V. Choudhary, B. Satpati, S. Mohapatra, Facile synthesis of Ag–ZnO hybrid nanospindles for highly efficient photocatalytic degradation of methyl orange, Phys. Chem. Chem. Phys. 16 (2014) 17560–17568.

M.A.M. Khan et al.

Materials Chemistry and Physics 259 (2021) 124058

16

[40] M.A. Majeed Khan, Sushil Kumar, Tansir Ahamad, Abdulaziz N. Alhazaa, Enhancement of photocatalytic and electrochemical properties of hydrothermally synthesized WO3 nanoparticles via Ag loading, J. Alloys Compd. 743 (2018) 485–493.

[41] Sandeep Mondal, Tathagata Paul, V. Arindam Ghosh, Venkataraman, Gate- controllable electronic trap detection in dielectrics, IEEE Electron. Device Lett. 41 (2020) 717–720.

[42] S. Mondal, V. Venkataraman, All inorganic spin coated nanoparticle-based capacitive memory devices, IEEE Electron. Device Lett. 37 (2016) 396–399.

[43] A.M. Pourrahimi, D. Liu, V. Strom, M.S. Hedenqvist, R.T. Olsson, U.W. Gedde, Heat treatment of ZnO nanoparticles: new methods to achieve high-purity nanoparticles for high-voltage applications, J. Mater. Chem. 3 (2015) 17190.

[44] S. Vignesh, S. Suganthi, J.K. Sundar, V. Raj, P.R. Indra Devi, Highly efficient visible light photocatalytic and antibacterial performance of PVP capped Cd:Ag:ZnO photocatalyst nanocomposites, Appl. Surf. Sci. 479 (2019) 914–929.

M.A.M. Khan et al.