Preparation and photocatalytic activity of TiO2 films ... - Springer Link

J Sol-Gel Sci Technol (2009) 52:267–275 DOI 10.1007/s10971-009-2015-1

ORIGINAL PAPER

Preparation and photocatalytic activity of TiO2 films with Ni nanoparticles E. Ramı´rez-Meneses Æ A. Garcıá-Murillo Æ F. de J. Carrillo-Romo Æ R. Garcıá-Alamilla Æ P. Del Angel-Vicente Æ J. Ramı´rez-Salgado Æ P. Bartolo Pe´rez

Received: 13 March 2009 / Accepted: 5 June 2009 / Published online: 19 June 2009 Ó Springer Science+Business Media, LLC 2009

Abstract Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)2 (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO2 sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO2 films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO2 solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. Highangle annular dark-field images of the Ni/TiO2 system revealed well-dispersed Ni nanoparticles supported on

E. Ramı´rez-Meneses A. Garcıá-Murillo (&) F. de J. Carrillo-Romo Centro de Investigacioń en Ciencia Aplicada y Tecnologıá Avanzada-IPN Unidad Altamira, Km. 14.5 Carretera TampicoPuerto Industrial, C.P. 89600, Altamira, Tamaulipas, Mexico e-mail: [email protected] P. Del Angel-Vicente J. Ramı´rez-Salgado Programa de Ingenierıá Molecular, Instituto Mexicano del Petro´leo, Eje La´zaro Ca´rdenas No. 152, C.P. 07730, Mexico, DF, Mexico R. Garcıá-Alamilla Instituto Tecnolo´gico de Ciudad Madero, Av. 1° de Mayo esq. Sor Juana Ine´s de la Cruz s/n Col. Los Mangos, C.P. 89440 Cd, Madero, Tamaulipas, Mexico P. Bartolo Pe´rez Departamento de Fı´sica Aplicada, CINVESTAV-IPN, Me´rida, Yuc, Mexico

TiO2 and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO2 films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO2. Keywords Sol–gel Thin films Nickel Nanoparticles Organometallic

1 Introduction Titanium oxide has great importance due to its excellent photocatalytic properties [1], as well as the industrial applications related to photo-splitting of water [2], photocatalysis [3], and photovoltaic devices [4]. This is inspired by the potential application of TiO2-based photocatalysts for the degradation of organic compounds [5, 6]. Since Fujishima and Honda discovered the photocatalytic properties of TiO2, a great deal of attention has been focused on applications of TiO2 as a photocatalyst to solve environment problems [7–9]. However, TiO2 exhibits a relatively high energy bandgap (*3.2 eV) and can only be excited efficiently by high energy UV irradiation, which constrains its practical usage. Efforts have been made to extend the energy absorption range of TiO2 from UV to visible light or to improve the photocatalytic activity of nanosized TiO2 powders by adding foreign metallic elements [10, 11]. The main problem with TiO2 powders is collecting the powder after use; the powder itself is a pollutant. Thus, more interest is now focused on the preparation of coatings or films. Yoshinaga et al. achieved Ni nanoparticles on the surface of titania thin film by chemical vapor reductive

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deposition method. The growth of the nanoparticles was based on the specific absorption and heterogeneous nucleation on the surface of a substrate, not via vaporphase formation and subsequent sedimentation. They showed that titania thin film with metallic Ni nanoparticles on its surface exhibited high efficiency in the photocatalysis of hydrogen evolution from decomposition of ethanol [12]. Although many studies of the preparation of metallic nanoparticles from reduced salt metals on substrates, such as SiO2, single-crystal Si or Au, or some highly ordered substrates [13–15] have been carried out, to the best of our knowledge only a few studies are focused on synthesized metallic nanoparticles redispersed into the sol and deposited on films thermally grown by dip-coating or spincoating [16]. The interest in the synthesis of Ni nanoparticles is motivated by the improved characteristics of TiO2 as photocatalyst as was observed in previous reports. Ni and Ni-Zn nanoparticles 1–10 nm diameter synthesized by the liquid-phase selective-deposition method and using Ni and Zn acetylacetonates as precursors were well dispersed and stabilized onto surface TiO2 powders in order to promote the catalytic activity for 1-octene hydrogenation [17–19]. Nevertheless, few investigations dealing with the use of organometallic precursors to prepare well-structured metallic Ni nanoparticles dispersed on ceramic films obtained by sol–gel spin-coating have been reported [20], in contrast with those using transition metal dopants incorporated in the sol precursor [21, 22]. The sol–gel process possesses many merits; specifically, metallic particles can be included homogeneously into the sol, allowing coating onto various materials even pure metals. For this paper, we investigated the feasibility of dispersing Ni nanoparticles from an organometallic precursor Ni(COD)2 (COD = cycloocta-1,5-diene) on TiO2 thin films grown onto commercial glass spheres by sol–gel dip-coating technique with the aim to improve the photocatalytic properties by degrading ethanol under UV-irradiation. The as-deposited Ni/TiO2 films were characterized by XRD, AFM, TEM, HRTEM, HAADF-STEM and XPS analyses.

J Sol-Gel Sci Technol (2009) 52:267–275

formation of a dark gray colloid, Eq. (1). The reaction is slow at lower temperatures [23]. The obtained solution was concentrated by solvent evaporation before hexane addition to promote colloid precipitation, and the supernatant solution was removed by filtration. Finally, the resulting solution was evaporated in a vacuum until the residue was completely dry. NiðCODÞ

H 2 ð3barÞ;70 C 1;3diaminopropane StabilisedNicolloid ð1Þ

2.2 Synthesis of the titanium oxide ‘‘sol’’ with the addition of Ni nanoparticles Figure 1 shows the schematic flowchart of the experimental procedure. Titanium tetraisopropoxide (Ti(OiPr)4 (99.9%, Aldrich) was mixed with isopropanol (iPrOHFermont) and stabilized in presence of acetic acid (AcOHFermont), with a molar ratio AcOH/Ti = 5.8, as reported previously [25]. The obtained solution was diluted with methanol. The solution was then stirred at room temperature for 1 h. After the reaction time, a stable gray ‘‘sol’’ was obtained. Then, the metallic nanoparticles were redispersed in 2 mL of THF, forming a colloid, and dispersed into the titanium ‘‘sol,’’ yielding a gray colloidal stable solution. The obtained solution was stirred 1 h before the deposition stage. The initial step is followed by the condensation of the hydrolyzed species. Each new alcoxolation step was accompanied by the formation of an i-propanol molecule [26]. The final material before calcining has the following chemical composition, where every titanium

Ti(OC3 H7)4

CH 3COOH

i

PrOH MeOH Mixing and stirring Ni nanoparticles mixing dip-coating

TEM, HRTEM observations

drying

2 Experimental 2.1 Synthesis of metallic nanoparticles The reaction was carried out as a standard procedure in a Fischer–Porter bottle, using a typical procedure reported by Cordente et al. [23] and elsewhere [24]. 200 mg of Ni(COD)2 (Aldrich) were dissolved in THF and decomposed under H2 atmosphere in presence of five equivalents of 1,3-diaminopropane (99%, Aldrich) leading to the

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heating at 100 ºC for 1h calcining at 400 ºC for 3 h Ni/TiO 2 system AFM, HRTEM, HAADF observations

photocatalysis evaluation

Fig. 1 Flowchart of the experimental procedures

XRD and XPS studies


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atom is forming part of the network: Ti(OC3H7 or OH)2-y(O)y, where y can be one or two. 2.3 Elaboration of Ni/TiO2 thin films by ‘‘dip-coating’’ technique Commercial glass spheres were used as substrates (three different diameter sizes: 6, 4 and 3 mm) and carefully cleaned with methanol and oven dried before being wetted uniformly with the Ni/TiO2 sol using a withdrawal speed of 2.5 cm min-1. After the film deposition stage, the sample was heat treated in an oven at 100 °C for 15 min, with the aim of removing the most volatile organic compounds, and a second coating was done. The deposited thin film underwent solvent evaporation, solute condensation and thermal decomposition, which resulted in the formation of titanium dioxide films. Finally, the sample was thermally treated at 400 °C for 3 h in order to densify and promote the crystallization of the film. After calcinations, every oxygen atom is bonded with a Ti atom, and a pure and highly homogeneous oxide network is obtained (TiO2). For this step, Eq. (2) is proposed, when every Ti atom is surrounded by three O atoms and one –OH bond or one –OR group, in the network of the hydrolyzed gel.

recorded on a ESCA/SAM (560, Perkin–Elmer) photoelectron spectrometer with a system selecting Al radiation. All the binding energies were referenced to the adventitious C 1s peak at 284.6 eV. The photocatalytic performances of the nanocrystallized TiO2 and Ni/TiO2 films were evaluated by the degradation of ethanol using a 25-W UV-mercury lamp (Trojans) (*380 nm) as a visible source. The experiments were carried out in the aqueousphase using a mixture of 90% water/10% ethanol as feedstock. This mixture was maintained at *10 °C and transported to the photocatalytic reactor with a nitrogen flow rate of 25 mL min-1. The feeding gas mixture was pre-heated to 100 °C and introduced to the reactor containing 100 g glass spheres films and irradiated under UV radiation placed at a distance of 10 cm from the glass reactor. The condensable products (ethanol and acetaldehyde) were collected in a trap with cold water. Two microliter aliquots of the solution were periodically withdrawn to measure the concentration of acetaldehyde as a function of time. Identification of acetaldehyde was performed by gas chromatography (GC) using a Agilent 6890 chromatograph equipped with HP-5 Phenyl Methyl Capillary 30 m 9 250 lm 9 0.25 lm.

air;400 C

2½Ti(OC3 H7 or OH(O)Þ ! 2TiO2 þ 3CO2 " þ4H2 O " ð2Þ

3 Results and discussion 3.1 Phase composition

2.4 Characterization techniques The phase of the sample was determined by XRD (D8 Advance Bruker), using Cu Ka radiation with grazing angle configuration operating at a voltage of 30 kV and an emission current of 25 mA. Data were obtained in step times of 1.0 s and step sizes of 0.01° (2h) from 20 to 100°. Atomic force microscopy (AFM) observations were carried out at room temperature using a Nanoscope IV (Veeco D3100). Specimens for transmission electron microscopy (TEM) analysis were prepared by the slow evaporation of a drop of the colloidal solution (after the purification process) deposited onto a holey carbon-covered copper grid. TEM experiments were performed on a JEOL-2000 FXII electron microscope, operating at 200 kV. HRTEM observations were performed on a JEOL 2010 FasTem field emission microscope, and high-angle annular dark-field HAADF-STEM was performed by using a JEOL JEM 2200FS with a Schottky-type field emission gun, operating at 200 kV and integrated with a CEOS aberration corrector. The elemental composition was determined by Energy dispersive X-ray spectroscopy (EDS) with a NORAN spectrometer fitted to the TEM. The images were obtained using a CCD camera and Digital Micrograph Software from GATAN. X-Ray Photoelectron Spectra (XPS) were

Figure 2 shows the XRD patterns of heat treated TiO2 and Ni/TiO2 films. It was found that the TiO2 film pattern and the Ni/TiO2 film (Fig. 2a, b, respectively) exhibited a nanocrystalline anatase-TiO2 phase (JCPDS 21-1272) associated with broad XRD diffraction peaks. This can be further confirmed by SAED measurements from HRTEM observations. It was also noticed that no additional XRD peaks corresponding to Ni addition were revealed. This may be attributed to the well-dispersed nanocrystalline Ni particles in the TiO2 matrix, which are not large enough for XRD detection. The XRD not reveal any other characteristic peaks of a mixed oxide phase being formed due to an interaction between Ni and TiO2 support. Similar behavior was also reported by Chang et al. [27]. 3.2 AFM studies AFM top-view images of TiO2 and Ni/TiO2 films are shown in Fig. 3a, b, respectively. Figure 3a shows the AFM image corresponding to TiO2 film heat treated at 400 °C for 3 h. The brightness of a small region in Fig. 3a corresponds to its height. Dark points are given by a depth or by the presence of pores. Using the AFM studies, we found that the TiO2 film is characterized for a mean

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(312)

(215) (312)

(004) (200) (105) (211) (204) (116) (220)

Intensity (a.u.)

(101)

Fig. 2 XRD patterns of the a TiO2 and b Ni/TiO2 films

(a)

(b) 20

40

60

80

100

2θ (°)

roughness (Ra) of 1.7 nm and an RMS (Rq) of 2.2 nm. The TiO2 film showing nanosized grains formed on the glass surface was found to be 18.1 nm. Ni nanoparticles obtained on TiO2 (Fig. 3b) have a very fine size, with good uniformity in structure and composition. The mean roughness (Ra) was 0.3 nm and the RMS (Rq) was 0.4 nm. The change in roughness is attributed to the presence of Ni. The Fig. 3 Top-view of AFM topography micrographs of a TiO2, b Ni/TiO2 and c AFM phase imaging of Ni/TiO2

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average grain size of Ni/TiO2 has a diameter of 5 nm (Fig. 3b). Phase Imaging is a powerful extension of TappingModeTM AFM. It provides nanometer-scale information about surface structure and properties not often revealed by other SPM techniques. By mapping the phase of the cantilever oscillation during the TappingMode scan, phase


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imaging goes beyond simple topographical mapping to detect variations in composition, adhesion, friction, viscoelasticity, and numerous other properties. This is because the interaction force that exists between the tip and surface contains chemical and viscoelastic information about the sample [20, 21]. The contrast in phase images can be strongly dependent on the magnitude of the tip sample interaction force. A strong contrast between different regions can be obtained in phase images, even for topographically flat surfaces where no contrast is obtained. Phase imaging was used in both samples (TiO2 and Ni/TiO2). In the first one, no phase contrast was found, indicating the presence of one compound, in contrast with the second, in which the phase contrast becomes visible, as shown in Fig. 3c. Mapping of different components in composite materials, as with the Ni/TiO2 sample, is shown in Fig. 3c. In this figure, the light areas in the phase image seem related to Ni nanoparticles. Additionally, these areas could be also due to the presence of NiO2 formed during heat treatment. The size of these light areas, probably associated with Ni nanoparticles, is an average of 14 nm. The particle distribution of Ni in the TiO2 is nearly homogeneous.

shows HRTEM micrographs of Ni/TiO2 film. Figure 5a shows Ni/TiO2 film exhibiting agglomerated nanoparticles with an average size of 15 nm. The grain size is in good agreement with AFM measurements. Figure 5b shows clearly the lattice planes of monocrystal TiO2. Interplanar spacings d were determined by Fast Fourier Transform (FFT). The space between the lattice plane was 0.352 nm, which corresponds well to the d value of the (101) plane for anatase, in agreement with the theoretical data. Figure 6a is an HAADF-STEM image of Ni/TiO2 powders showing the size and distribution of well-dispersed Ni nanoparticles. The visibility of these particles supported on TiO2 depends on the metal and support element atomic numbers. The shape of the nanoparticles is often overshadowed by the phase contrast of the support. The contrast of the metal particles can be observed (indicated by arrows). The composition of the as-synthesized Ni/TiO2 powders was further confirmed by EDX, as seen in Fig. 6b. The typical EDX spectrum displays Ti (71.69% wt), O (26.48% wt), Ni (1.83% wt) without including Cu from the TEM grid. According to HAADFSTEM images, it was not possible to distinguish the formation of NiO2 from TiO2 probably formed during the Ni/TiO2 film heat treatment carried out in air conditions.

3.3 TEM and HRTEM studies 3.4 XPS analyses

Number of particles

TEM micrographs (Fig. 4a) of Ni nanoparticles before mixing with the TiO2 solution revealed the formation of nearly monodispersed Ni nanostructures. HRTEM observations revealed an average particle size of 5 nm, as well as the presence of traces of NiO2 on the surface of Ni nanoparticles as can be observed in Fig. 4b. Figure 5

XPS was used to determine the elemental surface composition and the electronic state of elements. Figure 7 shows the XPS spectra of the Ni/TiO2 samples for O 1s, C 1s, Ti 2p and Ni 2p. Figure 7a depicts the presence of O 1s and C 1s around 540 and 380 eV, respectively [28]. The signals

100 80

dm = 2.9 nm

60 40 20 0 0

2

4

6

8

5 nm

Diameter (nm)

(a)

(b)

Fig. 4 a TEM and b HRTEM images of Ni nanoparticles prepared from Ni(COD)2 in THF in presence of 5 equiv. 1,3-diaminopropane

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nm

Fig. 5 a TEM and b HRTEM of Ni/TiO2 film micrographs heat-treated at 400 °C for 3 h

0.2 µm

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

0.352 nm danatase(101)

6

8

10

12

14

16

18

20

22

24

26

28

nm

(a) Fig. 6 a HAADF micrograph of Ni/TiO2 showing the spatial and size distribution of the Ni nanoparticles and b EDX analysis of Ni/TiO2 powders heat-treated at 400 °C for 3 h

(a)

(b)

EDX eds-1

(b)

Ni Nps

50 nm

of Ni are weak, due to the low quantity of nickel nanoparticles. Figure 7b displays the binding energy, indicating that for Ni 2p was assigned to Ni 2p3/2 and Ni 2p1/2 in Ni2O3 around 855 and 869 eV, respectively, in agreement with the literature [22, 29, 30]. The spectrum also displays an additional peak, about 3 eV lower binding energy than the peak Ni 2p3/2 corresponding to metallic Ni (853 eV) [31, 32]. This indicates that some of zerovalente nickel nanoparticles changed into Ni2O3 in the thermal treatment. As shown in Fig. 7b, the Ti 2p1/2 and Ti 2p3/2 spin-orbital splitting photoelectrons for Ni/TiO2 powders are around 464.5 and 458 eV, respectively, which are in good agreement with the values of Ti4? in pure TiO2 [28, 33]. The O 1s core level spectra of Ni/TiO2 samples is around 525 eV, and is due to O2- ions in the TiO2 lattice (–Ti–O–Ti) [28, 34]. These energies seem unaffected by the presence of nickel nanoparticles. From these results it was concluded that nickel atoms (BE = 855 eV) existed in the form of Ni2O3, dispersed on the surface of TiO2.

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Element Ti O Ni

weight % 71.69 26.48 1.83 100

3.5 Photocatalytic activity of anatase films Figure 8 shows schematically the system of reaction used for the evaluation of the materials. Experimental results of the photocatalytic activity are presented in Fig. 9. As can be seen in this figure, TiO2 films in presence of Ni nanoparticles and the small crystal size of anatase have enhanced the photocatalytic activity of the TiO2 films. After 4 h of UV illumination in ethanol aqueous solution, Ni/TiO2 films (Fig. 9a) showed a photocatalytic efficiency 12.1% higher than pure anatase TiO2 films (Fig. 9b). The predominant reaction was the dehydrogenation of the ethanol, producing (essentially) acetaldehyde and hydrogen. The photocatalytic decomposition of ethanol has been reported by Huan-Lin Kuo et. al. [35], using TiO2 (1% wt Pt.) nanotubes as powders crystallized in anatase phase introduced into a batch reactor with an oxygen-free atmosphere and two 15-W UV lamps (k = 315–400 nm). Those results revealed the formation of 700 lmoles of


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Fig. 7 XPS spectra of the Ni/TiO2 powders: a O 1s, b Ti 2p and c Ni 2p N(E) (a. u.)

O(A)

(a) O 1s

Ni 2p

Ti 2p C 1s Ti 3s Ti 3p

1000

800

600

400

200

0

Binding energy (eV) Ti 2p3/2

Ti 2p1/2

465

Ni 2p3/2

N(E) (a. u.)

N(E) (a. u.) 470

(c)

Ni 2p1/2

(b)

TiO2

460

455

450

Ni2O3 metallic Ni

875

870

Binding energy (eV)

865

860

855

850

Binding energy (eV)

Fig. 8 Experimental set up used in the gas-phase decomposition of ethanol: a synthetic air, b water–ethanol reservoir, c plug flow glass reactor, d reactor containing the glass spheres and e water reservoir to collect acetaldehyde and dihydrogen, f chromatograph analysis

hydrogen as the principal product in the gaseous phase but, additionally, acetaldehyde (l) as product of ethanol dehydrogenation. According to the authors [35], the formation of acetaldehyde, representing the photocatalytic decomposition of ethanol, indicates that its dehydrogenation produces acetaldehyde (l) and hydrogen (g) in an equimolar ratio following the global Eq. (3):

C2 H5 OH ! CH3 CHO þ H2

ð3Þ

In our study, the photocatalytic decomposition of ethanol was performed using Ni/TiO2 films coated on glass spheres introduced in a semi-batch reactor and an oxygen free atmosphere. The effluent of the reactor was trapped in water and thereafter analyzed by chromatography

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4 Conclusions

40

(a) 35

Yield % H2

30 25

(b) 20 15 10 0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Time (h)

Fig. 9 Photocatalytic activity of ethanol degradation on the deposited films: a Ni/TiO2 and b TiO2

technique. By means of GC studies, the presence of acetaldehyde was determined, allowing (indirectly) the estimation of hydrogen, taking into account Eq. (3). The photocatalytic reaction occurs by the absorption of one energy photon by TiO2, creates a hole and an electron. The interaction of 2 positive charges directly produces acetaldehyde and dihydrogen. The photocatalytic process of the reaction during ethanol dehydrogenation can be written as follows: TiO2 þ hm ! hþ þ e þ

C2 H5 OH þ 2H ! CH3 CHO þ 2H

ð4Þ þ

ð5Þ

2Hþ þ 2e ! H2

ð6Þ

CH3 CHO þ 2C2 H5 OH ! CH3 CHðOC2 H5 Þ2 þ H2 O

ð7Þ

CH3 CHO þ CH3 COOH ! CH4 þ CO2

ð8Þ

Additionally, there are some main causes that may explain the differences observed in the photocatalytic activity of these films. In the current study, the entrapment of the metallic particles on the surface of TiO2 films was studied with TEM measurements, and after thermal treatment it was found that Ni nanoparticles appeared well distributed on the TiO2 surface. According to TEM, the isolated Ni nanoparticles, before being added into TiO2 films, presented a mean size between 5 and 10 nm, while HR-TEM analysis of the TiO2 films after the addition of Ni nanoparticles showed that these particles, as well as the TiO2 particles, presented an average size of 14 nm. The metal actually modifies the photocatalytic properties of the semiconductor by changing the distribution of electrons.From these results, we conclude that Ni/TiO2 films synthesized by the proposed procedure show enhanced photocatalytic efficiency. The ethanol photodegradation was found to be strongly dependent on the crystalline nature and grain size of the Ni/TiO2 system.

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In this study, we prepared nanocrystalline TiO2 and Ni/TiO2 composite thin films by sol–gel dip-coating technique. These films, calcined at 400 °C, exhibited an anatase phase as determined by XRD. Microstructural observations by AFM analysis revealed a porous appearance in the absence of Ni, whereas the presence of Ni evidenced a decrease in roughness and showed a homogeneous distribution of Ni nanoparticles. HAADF-STEM micrographs also confirmed that Ni nanoparticles appeared well distributed on the TiO2 surface, inducing the formation of clusters with TiO2 during the dipping process and revealing that Ni nanoparticles with an average size between 5 and 10 nm remain dispersed after heat treatment at 400 °C. In the process of calcination, nickel is presented on the surface of TiO2 in the form of metallic nickel and Ni2O3, as confirmed by XPS studies. Nickel species could enhance the charge carrier trapping, diminishing the recombination of photo-generated electron-hole pairs and expanding light absorption of TiO2 towards the visible region. This study demonstrates that Ni nanoparticles obtained by an organometallic approach can be incorporated into the formation of a TiO2 matrix by sol–gel process, showing stability in terms of size and dispersion. The small crystal size of Ni nanoparticles well distributed on TiO2 surface enhanced the photocatalytic activity of the anatase dip-coated films to an efficiency 12.1% higher than pure anatase TiO2 films. In order to extend the utility of Ni/TiO2 materials, further studies related to TiO2 and Ni/TiO2-based nanocomposites at different calcination temperatures are now in progress. These films show a high potential for practical applications. Acknowledgments This work was supported by CONACyT 47279, 59408 and 59921 Projects. The authors thank Hector Dorantes Rosales (ESIQIE-IPN) for TEM analysis, V. Montiel Palma (CIQ-UAEM) and Benito Barrera Garcia for their support on the experimental work. The authors would like to thank David Nentwick for his editing work on this paper. The authors would also like to thank M. Garcıá Murillo for her assistance.

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