Structural, optical and photoelectrochemical properties of TiO2 films decorated with plasmonic silver nanoparticles

Optik 154 (2018) 182–191

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Optik journal homepage: www.elsevier.de/ijleo

Original research article

Structural, optical and photoelectrochemical properties of TiO2 films decorated with plasmonic silver nanoparticles D. Guitoume a,b,∗ , S. Achour c,g , N. Sobti c , M. Boudissa d , N. Souami e , Y. Messaoudi f a

Research Unit on Optics and Photonics, UROP-CDTA, Sétif 1 University, Sétif 19000, Algeria Ceramic Laboratory, Constantine1 University, and national polytechnic school of Constantine 25000, Algeria Materials Science and Applications Unit, Constantine 1 University, Constantine 25000, Algeria d Department of Physics, Sétif 1 University, Sétif 19000, Algeria e Nuclear Research Center of Algiers, 02 Bd Frantz Fanon, BP 399 Alger-Gare, Algiers, Algeria f Laboratoire de Chimie, Ingénierie Moléculaire et Nanostructures, Université de Sétif 1, Sétif 19000, Algérie g National Polytechnic school of Constantine, Constantine 25000, Algeria b c

a r t i c l e

i n f o

Article history: Received 28 June 2017 Received in revised form 20 September 2017 Accepted 29 September 2017 Keywords: TiO2 Thin films Ag nanoparticles Sol-Gel Photodeposition Photoelectrochemical

a b s t r a c t Silver nanoparticles (Ag NPs) were deposited on porous TiO2 films by photodeposition method. TiO2 films were prepared by Sol-Gel dip-coating technique and the porous TiO2 films (PTiO2 ) were elaborated by adding polyethylene glycol (PEG) to the starting solution. The effect of UV irradiation time (t UV ), used for the deposition of Ag NPs, on structural, optical and photoelectrochemical (PEC) properties of silver loaded porous TiO2 films (Ag/PTiO2 ) was studied. The Ag NPs were found to be homogeneously dispersed on PTiO2 films surfaces. The plasmonic effect in Ag/PTiO2 films is evidenced by the drastic change in the visible light absorption. Under simulated solar light, Ag/PTiO2 samples show a higher PEC activity compared with PTiO2 film. The highest PEC activity was obtained for tUV = 15 min and for longer UV illumination PEC response decreased. © 2017 Elsevier GmbH. All rights reserved.

1. Introduction During the last years, titanium dioxide (TiO2 ) thin films have been the subject of a growing number of studies due to their interesting physical and chemical properties. Titanium dioxide is a low cost, nontoxic and corrosion resistant material with high chemical stability [1]. It can be crystalized in three main polymorphs: Anatase, Rutile and brookite [2]. TiO2 is a wide band gap semiconductor (3.26 eV for Anatase phase and 3.05 eV for rutile) [3] with high refractive index (2.75 for Rutile and 2.54 for Anatase at 550 nm wavelength) [4]. These properties make it suitable for a variety of applications such as in dye-sensitized solar cells [5,6], gas sensors [7] and biosensors [8]. Furthermore, TiO2 has been largely studied for its photoinduced properties including photocatalysis [9], superhydrophilicity [10] and antibacterial activity [11]. Due to its low cost, non-toxicity and biocompatibility, TiO2 is considered among other semiconductors to be the most promising and reliable photocatalyst for environmental applications [12]. However, the use of TiO2 as a photocatalyst has two main limitations. The first is the necessity of using UV irradiation to activate the photocatalytic mechanism. The second is the rapid recombination of the photogenerated electron-hole pairs which leads to a reduction in the photocatalytic efficiency

∗ Corresponding author at: Research Unit on Optics and Photonics, UROP-CDTA, Sétif 1 University, Sétif 19000, Algeria. E-mail addresses: [email protected], [email protected] (D. Guitoume). https://doi.org/10.1016/j.ijleo.2017.09.121 0030-4026/© 2017 Elsevier GmbH. All rights reserved.

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[13]. Therefore, many methods have been developed to overcome these constraints by doping with metallic or non-metallic elements [14], co-doping [15,16], coupling with other semiconductors in composite materials [17], surface decorating with noble metals nanoparticles [18] and with silver based nanocomposites such as Ag/AgBr [19] and Ag/AgCl [20].Among these strategies, loading TiO2 films with noble metals nanoparticles (Au, Ag, Pt and Pd) seems to be one of the most interesting approaches to increase the photoactive efficiency in the visible region [21]. The localized surface plasmonic resonance effect (LSPR) of noble metallic nanoparticles contributes to an increase of the absorption in the visible region [22], which is very benefic for enhancing the photoinduced properties efficiency using solar light. Compared to other noble metals, Ag has attracted much interest due to its low cost and abundance [23], making it suitable for industrial applications [24]. In addition, Ag exhibits an antibacterial activity and a higher performance in the decomposition of aqueous phase pollutants [25]. Ag NPs are usually prepared from colloidal solutions via chemical routes. The main drawback of these methods is the necessity of adding organic stabilizing agents and the instability of the colloid solutions over time [26]. Photodeposition synthesis of silver nanoparticles, which is the technique adopted in this work, is based on the irradiation of photocatalically active support in order to reduce silver ions. This method seems to be an interesting alternative due to its simplicity and low cost. It is also considered as an environment-friendly technique because it offers the possibility of preparing silver nanoparticles without the use of organic additives. Recently, many studies reported on the photocatalytic degradation of organic pollutants using Ag loaded TiO2 films. However, a fewer number focused on their PEC activity. The surface morphology of TiO2 films has a great influence on the PEC response. Among the various morphologies of TiO2 , nanotubes have been intensively studied due to their larger specific surface area and vertical orientation leading to a high PEC activity. The idea of this work is to use simple and low cost techniques (Sol-Gel dip-coating for TiO2 and photodeposition for Silver nanoparticles) to obtain silver loaded TiO2 films with PEC response comparable to that obtained from Ag loaded TiO2 nanotubes prepared by the relatively complex and expensive anodization process. To obtain TiO2 films with high specific surface area, PEG was added to the Sol-Gel starting solution. PEG is decomposed during the annealing process leading to the formation of a rough and porous surface. In this work, we studied the structural, optical and PEC properties of porous TiO2 films decorated with Ag NPs. A mechanism explaining the effect of UV irradiation time, during silver photodeposition process, on the PEC response is suggested. 2. Experimental 2.1. TiO2 films preparation The TiO2 films were prepared by sol-gel dip-coating technique. The starting solution was made of titanium tetraisopropoxide (TTIP, Sigma-Aldrich 97%) as a precursor, isopropanol (2-PrOH) as a solvent, distilled water, hydrochloric acid (HCl, 36–38%) as a catalyst, and polyethylene glycol 300 (PEG) as an organic additive which was incorporated to obtain crack free and porous films. TIIP:2-PrOH:H2 O:HCl:PEG molar ratio was equal to 1:20:1:1:0.02. Firstly, a mixture of isopropanol and HCl was prepared then distilled water was added. After that, TTIP was dissolved in the as prepared solution under continuous stirring and finally PEG was added. The obtained solution was vigorously stirred for 1 h until the formation of a homogeneous and transparent solution. Another solution with the same composition, but without adding PEG, was prepared following the same procedure. The prepared films were deposited on glass substrates (microscope glass slides) and on ITO substrates. The glass substrates were cleaned in ultrasonic bath by acetone and ethanol, then rinsed with distilled water while the ITO substrates were cleaned by isopropanol and distilled water. Subsequently, the glass and ITO substrates were dipped and withdrawn in the prepared solutions with a speed of 1 mm/s. The as deposited films were then dried at 70 ◦ C for 10 min and the dipping-withdrawing cycles were repeated 6 times for each sample. Finally, the obtained films were annealed in air at 520 ◦ C for 1 h. 2.2. Silver nanoparticles deposition on TiO2 films Silver nanoparticles were deposited on the prepared PTiO2 films by the photodeposition technique. A silver nitrate (AgNO3 ) solution with a molarity of 1 mM was prepared by dissolving AgNO3 in distilled water. The prepared solution was then cast on the surface of the annealed TiO2 films and irradiated by a UV–365 nm 20W BLB lamp for 10,15 and 25 min. The distance between the samples and the UV lamp was set to 5 cm. Finally, the obtained samples were abundantly rinsed with distilled water and dried in air. The prepared samples were labeled as following: PTiO2 (porous films) and TiO2 for the samples prepared with and without PEG, respectively. PTiO2 -10, PTiO2 -15 and PTiO2 -25 are Ag loaded PTiO2 films prepared with 10, 15 and 25 min of UV irradiation time, respectively. 2.3. Analysis The crystalline phase identification was performed using grazing incidence X ray diffraction (GIXRD) and Raman spectroscopy. The XRD patterns were obtained by means of Philips XPERT PRO MPD using Cu K␣ radiation (␭ = 1.5406 Å). Raman spectra were recorded using Bruker Senterra R200L with argon ion laser (532 nm) as an excitation source. The samples were illuminated with 20 mW of laser power and the spectral data were collected in the continuous scan mode. Surface morphology of the samples was studied by scanning electron microscopy (SEM). The SEM micrographs were obtained in the

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Fig. 1. XRD patterns of PTiO2 and Ag/PTiO2 films deposited on ITO substrates.

backscattering mode by means of Philips XL30 ESEM FEG SEM with an accelerating voltage of 20 KV. The RMS surface roughness values of the prepared films were measured using MFP-3D Oxford Instruments company Atomic Force Microscopy (AFM). UV–visible absorption spectra were obtained using Jasco V570 UV–Vis-NIR spectrophotometer. PEC measurements were performed in a Solarton analytical SI 1287 electrochemical workstation with a standard three electrodes system using a quartz cell. The working electrode consisted of the prepared samples, Pt wire coil as the counter electrode and saturated calomel electrode (SCE) as the reference electrode. The used electrolyte was composed of 0.01 M NaOH + 0.1 M Na2 SO4 . The illumination source was a solar simulator with AM 1.5 illumination (100 mW/cm2 ). Cyclic voltammetry measurements were recorded in the range −1 to 1 V with a scan rate of 20 mV. 3. Results and discussion 3.1. Structural properties 3.1.1. XRD analysis The XRD spectra of PTiO2 and Ag/PTiO2 thin films deposited on ITO substrates are displayed in Fig. 1. All the films present five strong diffraction peaks located at 21.51◦ , 30.57◦ , 35.40◦ , 51.04◦ and 60.70◦ . These peaks are attributed to the ITO substrate. We also note the presence of two small peaks at 25.28◦ and 37.80◦ which are assigned to TiO2 Anatase (101) and (004) planes, respectively (JCPDS No. 21-1272). No diffraction peak of silver is detected which can be explained by the dominance of the ITO peaks in the spectrum with their high intensities, making it difficult to detect silver existing in low amounts. To confirm silver deposition, the films deposited on glass substrates were studied by GIXRD. XRD patterns of PTiO2 and Ag/PTiO2 films deposited on glass substrates are shown in Fig. 2. All the samples exhibit an intense peak located at 25.28◦ , which is related to TiO2 Anatase (101) plane (JCPDS. No. 21–1272). No characteristic peaks of other TiO2 phases besides Anatase were detected, indicating that the prepared samples are pure TiO2 Anatase which is known for its high photocatalytic reactivity [27]. A diffraction peak located at 38.18◦ was detected only for Ag/PTiO2 films and not for PTiO2 . This peak is assigned to silver (111) plane (JCPDS No. 04-0783). In addition, the intensity of Ag (111) peak increases with tUV increasing which is ascribed to the growth of the loaded silver amount. It is worthy to note that no diffraction peak of silver oxides phases was detected, indicating that the photodeposited particles are pure metallic silver without traces of silver oxides. 3.1.2. RAMAN analysis Fig. 3 shows Raman spectra of PTiO2 and Ag/PTiO2 films deposited on ITO substrates. All the films present a peak at 144 cm−1 corresponding to the (Eg ) TiO2 Anatase vibrational mode [28]. We note that the intensity of the Anatase peak of both PTiO2 -10 and PTiO2 -15 films is higher than that of PTiO2 film. This Raman signal amelioration can be attributed to the surface enhanced Raman spectra (SERS) properties of Ag [29]. No amelioration of Raman spectrum intensity is observed for

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Fig. 2. XRD patterns of PTiO2 and Ag/PTiO2 films deposited on glass substrates.

glass

PTiO2 PTiO2-10

10000 8000

PTiO2-15

Anatase

PTiO2-25

6000 4000 2000 0 50

100 150 200 250 300 350 400 450 -1

Fig. 3. Raman spectra of PTiO2 and Ag/PTiO2 films deposited on ITO substrates.

PTiO2 -25 film indicating that the sample does not present SERS effect. On the contrary, the PTiO2 -25 spectrum intensity is lower than that of PTiO2 . The PTiO2 -25 Raman signal intensity decrease might be ascribed to the high amount of silver deposited on the film’s surface which will screen the exciting laser from reaching the film in Ag particles deposition sites. Consequently, the Raman spectrum intensity decreases due to the less interaction between the exciting laser and the film crystals. 3.2. Morphological study SEM micrographs of the prepared samples are illustrated in Fig. 4. For TiO2 film, the surface morphology is smooth and homogeneous, while for PTiO2 film (with 2% PEG) the surface becomes rough and porous. The difference in surface morphology is explained by the formation of pores in PTiO2 films resulting from the thermal decomposition of PEG during the annealing process. PEG is completely decomposed at 520 ◦ C [30], which is the annealing temperature of the prepared samples. For the silver loaded films we observe the presence of homogeneously dispersed white spots which represent the silver nanoparticles photocatalytically grown. When TiO2 film is illuminated with a radiation having an energy corresponding to its band gap, electron-hole pairs are formed. The photogenerated electrons will then reduce the adsorbed silver ions Ag+ into metallic Ag0 silver [31]: TiO2 + h → h+ + e−

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Fig. 4. SEM micrographs of: (a) TiO2 film, (b) PTiO2 film, Ag/PTiO2 films photodeposited with: (c) tUV = 10 min and (d) tUV = 25 min.

Ag+ ads + e− → Ag0 Other photocatalytically formed chemical species, beside electrons and holes, including • OH radicals, O2 − ions, H2 O2 and O2 might also be involved in the silver deposition mechanism [26]. In addition, Ag particles size increases with increasing ´ UV irradiation time from 10 to 25 min. Similar results were reported by Piwonski et al. [26] and Chen et al. [32], indicating ´ et al. [26], an increase of the photodeposited silver particles size with UV irradiation time increasing. According to Piwonski the growth of the initially formed silver clusters is more favored than the growth from other adsorbed Ag+ active sites which explains the silver particles size increasing for longer UV illuminations. The silver particles size can be controlled by monitoring the photodeposition parameters including the intensity, duration and nature of the irradiation (continuous or pulsed) [26] and also the chemical composition of the used silver precursor [33]. The roughness of Ag/PTiO2 surface films has a considerable influence on the PEC response of the prepared films. The roughness root mean square values (RMS) of TiO2 , PTiO2 , PTiO2 -10, PTiO2 -15, and PTiO2 -25 are 1.0, 3.8, 10.4, 7.8 and 9.5 nm, respectively. We note that the roughness of PTiO2 film is higher than that of TiO2 which is due the decomposition of PEG during the annealing process. We also note that all the silver loaded PTiO2 films present a higher roughness compared with PTiO2 film which will contribute in the enhancement of the PEC response. 3.3. Optical properties Fig. 5 depicts the UV–vis absorption spectra of PTiO2 and Ag/PTiO2 films. For all the films we observe the presence of high absorption region below 400 nm which is due to the intrinsic TiO2 band gap transition from the valence band formed by 2p orbitals of the oxide anions to the conduction band formed by 3d t2g orbitals of Ti4+ cations [34]. Compared with PTiO2 film, Ag loaded PTiO2 films exhibit an enhancement of the absorption in the entire visible region. This absorption amelioration is ascribed to the localized surface plasmon resonance (LSPR) in Ag NPs [22,32,35]. The LSPR excitation is achieved when the time varying electric field of the incident light drives a collective oscillation of the Ag NPs free electrons. At a particular

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Fig. 5. UV–vis absorption spectra of PTiO2 and Ag/PTiO2 films deposited on ITO substrates.

Fig. 6. Cyclic voltammograms of TiO2 and PTiO2 films in dark and under simulated solar light.

frequency, the oscillating electrons will be in resonance with the incident light resulting in a strong oscillation of the surface electrons which is characterized by an enhancement of visible light absorption and the presence of a peak in the absorption spectrum. We also note that the absorption increases with tUV increase from 10 to 15 min which is attributed to the increase of the loaded Ag amount. The absorption spectra of PTiO2 -10 and PTiO2 -15 films exhibit a broad absorption peaks centered at 400 and 483 nm corresponding to their LSPR frequencies, respectively. The absorption peak maximum presents a red shift with tUV increasing which might be attributed to silver particles size increasing [36,37]. As it can be observed, the absorption in the visible region decreased for PTiO2 -25 film. According to Rycenga et al. [22] and Wu et al. [37], LSPR extinction (the sum of light absorption and scattering) for silver nanoparticles is dominated by absorption for smaller silver particles. As the particles size increases, the scattering takes over. In this work, we think that absorption predominates the LSPR extinction behavior for PTiO2 -10 and PTiO2 -15. However with the increase in Ag particles size, as for PTiO2 -25, the scattering takes over. Consequently, a decrease of the absorption is noticed for PTiO2 -25 film. Similar results are reported by Chen et al. [32] indicating a decrease of the visible light absorption for TiO2 nanotubes decorated with Ag NPs photodeposited with longer UV irradiation times. 3.4. Electrochemical properties In to order investigate the effect of PEG addition and silver nanoparticles loading on PEC response of the prepared TiO2 films, cyclic voltammetry was performed. The cyclic voltamogramms of PTiO2 and TiO2 films in dark and under simulated solar light irradiation are displayed in Fig. 6.

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Fig. 7. Cyclic voltammograms of PTiO2 and Ag/PTiO2 films under simulated solar light.

As expected, in dark conditions the current density values of both of TiO2 and PTiO2 films are negligibly small and practically identical. Under light conditions a photogneretaed current is observed with a current density value higher than that in dark. The presence of a current under light conditions is attributed to the transfer of photogenerated electrons, excited by the small UV fraction present in the simulated solar light spectrum, to the ITO substrate and then injected in the outer circuit. Furthermore, the photocurrent generated from PTiO2 film is higher than that generated from TiO2 film which can be explained by the porous surface morphology of PTiO2 film leading to a higher specific surface area. Cyclic voltammograms of PTiO2 and Ag/PTiO2 films under simulated solar light are illustrated in Fig. 7. All the samples present a cathodic peak PC1 which is attributed to hydrogen evolution [32]. Anodic peaks PA1 , PA2 and cathodic shoulder PC2 are observed only for Ag/PTiO2 films and not for PTiO2 . PA1 and PA2 are related to the oxidation of silver leading to the formation of Ag2 O on different Ag crystalline planes [38] and the cathodic shoulder PC2 is assigned to the reduction of the anodically formed oxide. Ag is oxidized by OH− ions present in the solution as described by the following reaction [39]: 2Ag + 2OH− ↔ Ag2 O + H2 O + 2e− Gross et al. [38] performed electrochemical measurements for Ag loaded TiO2 nanotubes under the same experimental conditions and using the same electrolyte composition (0.01 M NaOH + 0.1 M Na2 SO4 ). The Ag oxidation peak was obtained at −0.22 V vs MSE (Mercury sulfate electrode), this value corresponds to 0.22 V vs SCE which is practically the same value obtained in our work for the anodic peak PA1 . In addition, the intensity of the oxidation peak PA2 for PTiO2 -25 film is higher than that of PA1 which is due to the increase of the loaded silver amount. Furthermore, the value of the photocurrent generated from all Ag/PTiO2 films is higher than that generated from PTiO2 . The photocurrent density increases with tUV increase reaching its highest value for tUV = 15 min. After that it decreases for tUV = 25 min. The saturated photocurrent density values of PTiO2 , PTiO2 -10, PTiO2 -15 and PTiO2 -25 are about 17.60, 32.28, 41.87 and 28.81 ␮Acm−2 , respectively. These photocurrent values are higher than those obtained by Gross et al. for Ag loaded TiO2 nanotubes under visible light illumination [38] and they are comparable to the values obtained by Jiao et al. [40] for silver decorated TiO2 nanotubes. Cyclic voltammetry was carried out for PTiO2 -15 (the film with the highest PEC response) using 0.5 M Na2 SO4 as electrolyte. Cyclic voltammograms of PTiO2 -15 in dark and under simulated solar light are presented in Fig. 8. As expected, the dark current density is negligible. Upon irradiation, an important increase in the photocurrent density is observed. The saturated photocurrent density of PTiO2 -15 film is about 65 ␮Acm−2 , which is slightly higher than that obtained by Chen et al. for Ag NPs decorated TiO2 nanotubes with PEC measurements performed using the same electrolyte composition [32]. In order to explain the photoelectrochemical activity enhancement in Ag NPs loaded TiO2 films many mechanisms have been reported. Nishanthi et al. [34] suggested that the photocurrent density increase is attributed to the amelioration of electron-hole pairs separation efficiency. Silver NPs play the role of charge separation centers where photogenerated electrons are transferred to silver nanoparticles and therefore suppressing their recombination. This mechanism does not take into account the effect of visible light absorption amelioration, due to LSPR, on the PEC activity. Awazu et al. [41] have deposited TiO2 film on nanoparticles comprising Ag core covered with silica SiO2 shell (Ag@SiO2). Although no electronic transfer is possible between Ag and TiO2 , the TiO2 coated Ag@SiO2 core-shell structure displayed an enhancement of methylene blue decomposition by a factor of 7 under near UV Irradiation. According to Awazu et al., the amelioration of the photocatalytic activity is ascribed to the delay of electron-hole pairs recombination owing to the enhancement of the electric field amplitude on the surface of Ag NPs due to the LSPR effect. In contrast with the mechanism suggested by S.T. Nishanthi et al., a different mechanism was reported by Tatsuma et al. [42], Chen et al. [32] and Jiao et al. [40] suggesting that

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Fig. 8. Cyclic voltammograms of PTiO2 -15 film in dark and under simulated solar light using 0.5 M Na2 SO4 as electrolyte.

Fig. 9. Schematic showing the charge transfer in Ag/PTiO2 films.

the photocurrent density and photocatalytic enhancement in Ag and Au loaded TiO2 films can be attributed to the transfer of electrons from plasmonic photoexcited Ag NPs, upon irradiation by visible light, to the conduction band of TiO2 . In this work, the enhancement of PEC response of Ag/PTiO2 films is attributed to both of their high specific surface area (due to their higher surface roughness compared with PTiO2 film) and to the plasmonic properties of Ag nanoparticles. For the plasmonic contribution, we suggest that the enhancement of the PEC response is attributed to a synergic effect of both of the local electric field enhancement in vicinity of Ag NPs and to the transfer of electrons from photoexcited Ag NPs to TiO2 . Beside the charge carriers generated from TiO2 excited by the UV fraction present in the simulated solar light spectrum, the electric field amplitude enhancement on Ag NPs surface will not only delay the electron-hole pairs recombination [41], but it will also promote the generation of more electron-hole pairs in TiO2 [43]. Moreover, upon resonance with the incoming light at a particular frequency, a collective electron oscillation is created in silver nanoparticle surface (LSPR). Many of the oscillating electrons have a sufficient energy allowing their direct transfer to TiO2 conduction band and consequently increasing the photoelectrochemical response. Mubeen et al. [44] and Chen et al. [32] reported that electrons are transferred from Au and Ag NPs to TiO2 by quantum tunneling. However, Zhang et al. [43] suggested that the resort to the tunneling effect is not necessary to explain the transfer of electrons from Au NPs to TiO2 conduction band. In our case, the minimum value of the required exciting photon energy must be greater than the difference between the top bent of TiO2 conduction band Ecbb and silver Fermi level Ef (Fig. 9) which is equal to 0.55 eV [38]. As mentioned in

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Section 3.3, the PTiO2 -10 and PTiO2 -15 samples present plasmon resonance peaks located at 400 and 483 nm, respectively. The energy values of these wavelengths are much higher than 0.55 eV and photoexcited electrons can easily be transferred from Ag to TiO2 . Therefore, tunneling effect is not necessary to explain the electronic transfer from Ag to TiO2 . Furthermore, PTiO2 -15 film presents a higher PEC activity compared with PTiO2 -10 which can be attributed to the higher visible light absorption in an extended range of the visible spectrum from 450 to 800 nm. PTIO2 -25 film displays a lower PEC response than both of PTiO2 -10 and PTiO2 -15, which can be explained by its lower absorption in the visible region compared with the two other samples and as a result a reduced number of electrons are being excited and transferred to TiO2 conduction band. Similar results were obtained by Chen et al. [32] and Nishanthi et al. [34] indicating a decrease in PEC response of Ag loaded TiO2 prepared with longer UV irradiation time. The PEC activity results are in well agreement with the UV–vis absorption spectra confirming that the PEC response enhancement is due to the plasmonic effect in Ag nanoparticles. 4. Conclusion Plasmonic Silver nanoparticles have successfully been deposited on porous Sol-Gel PTiO2 films by photodeposition technique with different UV irradiation times. Porous PTiO2 films can easily be prepared by adding PEG to the Sol-Gel starting solution. It was found that PTiO2 films present a higher photoelectrochemical response compared with TiO2 film. Ag loaded PTiO2 films exhibit an enhancement in visible light absorption due to the LSPR effect. The effect of UV irradiation time, during the Ag NPs photodeposition, on the PEC activity was investigated. It was found that Ag/PTiO2 films present a higher PEC activity compared with bare PTiO2 films. The highest PEC response was obtained for the sample with 15 min of UV irradiation time. It was found that longer UV illumination will lead to a decrease in PEC activity. The photocurrent values of the Sol-Gel prepared Ag/PTiO2 films are comparable to those obtained for Ag NPs loaded TiO2 nanotubes elaborated with the relatively complex metallic Ti anodization technique. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29]

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