Titanium (99.7%, in area 10 cm × 3 cm) was purchased from the Far East Ti Equipment Co., Shanghai, China. RB, titanium tetraisopropoxide (TTIP), ethanol, acetic acid, nickel chloride and other chemical reagents were purchased from E. Merck (Indonesia). All reagents were of analytical reagent grade quality. All solutions were prepared with doubly distilled water.

X-ray data were collected by using a D8ADVANCE X-ray diffractometer (Bruker axs Co., Germany) based on CuKα radiation. The 2θ (two-theta) angle of the diffractometer was stepped from 10˚ to 80˚ by 0.03˚ increments. Transmission Electron microscope (TEM) was obtained by a JOEL JEM 1400 (Japan) with an in-column energy filter. Electrochemical experiments were performed with a Potentiostat (Jiangsu Electroanalytical Co., China). The two electrode system consisted of a Ti/TiO₂-NiO electrode as the working electrode, electrode and a Ti/TiO₂ as the counter electrode. The radiation source was a halogen lamp (300 W, Osram).

The TiO₂ film has been synthesized by procedures that have been published previously [40] . A 10 mL solution of TTIP was hydrolysed in the 100 mL acetic acid glacial solution and mixed under vigorous stirring in an ice water-bath (10˚C - 15˚C) until a clear yellow solution of TiO₂ nanocrystals was formed. The solution was heated at 90˚C for 2 h when it became a gel, which was then placed in an oven at 150˚C for 24 h to undergo an aging process. Next, the TiO₂ xerogel was ground and pulverized into a fine powder and calcined in a muffle furnace at 400˚C for 2 h at a heating rate of 10˚C∙min⁻¹. Then, ethanol was added to the TiO₂ powder before dip-coating to the Ti mesh. The TiO₂-coated Ti mesh was then dried at 100˚C for 5 min. The coating and drying treatments was repeated three times.

1.145 grams of synthesized xerogel TiO₂ (previous procedure) was added in 0.81 grams of NiNO₃∙6H₂O that has dissolved in 25 ml of distilled water. The mixed solution was stirred with magnetic stirrer to fuse. Then, the uniform mixture was dried at 110˚C for 3 h. To improve the crystalline TiO₂-NiO after the green suspension was formed, it was calcinated at various temperature of 150˚C, 300˚C, 400˚C, 500˚C, 600˚C, and 700˚C for 4 hours at 10˚C/min. The crystalline TiO₂-NiO composite was superimposed onto a SnO₂F conductive glass and was dried at 110˚C for 3 h. The coating and drying treatments was repeated three times.

In order to investigate the photoelectrocatalytic (PEC) activity of the prepared sensitized TiO₂ thin film, a series of degradation experiments of Rhodamine B in aqueous solutions were performed. The initial concentration of Rhodamine B was 5 mg∙L⁻¹, with 0.05 mol∙L⁻¹ of NaCl used as the supporting electrolyte. The total volume of the solution was 10 mL. Experiments were carried out in an optical quality quartz cell equipped with a two- electrode system. A copper wire as well as Ti plate was used as the counter electrode. The front of the working electrode was irradiated with a 300 W visible light lamp (Halogen lamp, Osram) and the progress of the photoelectrocatalytic degradation was recorded at defined intervals by UV-VIS spectroscopy. The PEC degradation of RB was performed at voltages of 1.0 V to +10.0 V and at various pH values.

The TiO₂ films prepared by sol-gel from titanium tetraisopropoxide precursor were characterized by XRD, as shown in Figure 2. The present work, the sol-gel method was carried out under acidic conditions with acetic acid as solvent. The use of acetic acid as the solvent, as well as activating the formation of Ti(OCOCH₃)(OⁱPr)₂ complexes, permits control of both the degree of condensation and the oligomerisation and induces preferential

crystallisation of TiO₂ in the anatase phase. In the first case, a spherical and relatively monodisperse aggregates of nanocrystallites could be obtained. The growth kinetics of the aggregates is determined by the stability of the colloid. The TiO₂ particles formed are relatively stable and a white suspension is gradually formed due to the precipitation of large aggregates.

However, under the acetic acid conditions using the Ti(OⁱPr)₄ precursor, the complexes formation was occur as described in the equation below [40] .

In further hydrolysis and condensation steps, the Ti(OCOCH₃)(OⁱPr)₂ product will produce nanotitania. In this research, nano-TiO₂ was prepared from stock solutions of 110 mL solution containing titanium tetraisopropoxide and acetic acid solution in a volume ratio of 1:10 in a water bath (10˚C - 15˚C). The anatase of TiO₂ was obtained after an annealing process at 400˚C (annealing rate of 10˚C min). Figure 2 shows that the XRD pattern of the TiO₂ thus prepared exhibits strong diffraction peaks at 2θ = 25.35˚ (d₁₀₁ = 3.51 Å), 2θ = 37.90˚ (d₀₀₄ = 2.37 Å), 2θ = 48.11˚ (d₂₀₀ = 1.89 Å), 2θ = 54.16˚ (d₁₀₅ = 1.69 Å), and 2θ = 54.96˚ (d₂₁₁ = 1.67 Å), indicating that TiO₂ is formed by the anatase phase. All peaks are in good agreement with the standard spectrum (JCPDS No.: JCPDS # 782-484). This result suggested that the nano-TiO₂ powder was irregularly polycrystalline. The XDR pattern shows that only the anatase phase is formed.

In addition, TEM was used to further examine the crystallite/particle size, crystallinity, and morphology of the samples. Clear spherical and non-homogeneous structures can be seen in Figure 3(a), with the average size of the primary particle approximately 10 nm, which is in good agreement with the value determined by XRD. The particle of TiO₂ in the anatase phase has a mostly spherical morphology (Figure 2(a)). The area selected for electron diffraction pattern analysis (SAED), confirming that the TiO₂ nanoparticles are highly crystalline in the anatase phase, in good agreement with the standard JCPDS # 782-484 and XRD result.

The composite of TiO₂-NiO was obtained after an annealing process at 700˚C (annealing rate of 10˚C min). Figure 4 shows that the XRD pattern of the TiO₂-NiO thus prepared exhibits strong diffraction peaks at 2θ = 27.45˚ (d₁₁₀ = 3.2452 Å ), 2θ = 36.10˚ (d₁₀₁ = 2.4849 Å ), 2θ = 39.20˚ (d₂₀₀ = 2.2952 Å), 2θ = 41.25˚ (d₁₁₁ = 2.1858 Å), 2θ = 44.05˚ (d₂₁₀ = 2.0531 Å ), 2θ = 54.36˚ (d₂₁₁ = 1.6858), and 2θ = 56.66˚ (d₂₂₀ = 1.6227 Å) which are the characterization of rutile TiO₂ according to the standard JCPDS No. 870-710. There are also several peaks indicates the anatase phase at 2θ = 25.40˚ (d₁₀₁ = 3.5023 Å), 2θ = 37.90˚ (d₀₀₄ = 2.3709 Å), and 2θ = 48.15˚ (d₂₀₀ = 1.8874 Å) according to the standard JCPDS No. 782-486. Peaks characteristic of NiTiO₃ are peaks at the 2θ = 24˚ (d₀₁₂ = 3.6584 Å), 2θ = 33˚ (d₁₁₀ = 2.6911 Å), 2θ = 49˚ (d₀₂₄ = 1.8356 Å), and 2θ = 57˚ (d₀₁₈ = 1.5969 Å). All peaks are in good agreement with the standard spectrums JCPDS No. 753-757.

TEM was used to further examine the crystallite/particle size, and morphology of the TiO₂-NiO composites samples. Clear spherical and non-homogeneous structures can be seen in Figure 5(a), with the average size of

the primary particle approximately 20 - 30 nm, which is in good agreement with the value determined by XRD. The particle of TiO₂ in the anatase phase has a mostly spherical morphology (Figure 5(a)). The area selected for electron diffraction pattern analysis (SAED) (Figure 5(b)), confirming that the TiO₂-NiO nanoparticles are also highly crystalline in the anatase phase, rutile phase and TiNiO₃.

While the part of photoanoda TiO₂-NiO composite shows that TiO₂-NiO materials were deposited on the Ti contained on porous amorphous silica (Figure 6). The conductivity character of those composite is shown in Figure 7. The profile shows that the composite photoanoda Ti/TiO₂-NiO quite well as electron generation. Based on the bar graph in Figure 8, that shows the percentage of formation of NiO in a variety of temperatures, as well as the byproducts NiTiO₃. NiTiO₃ arises due to the formation of NiO and TiO₂. Percentage of NiO in the composite achieving optimum condition at 500˚C reached 22.78%. Another product is a composite of NiTiO₃ that appears on composite roasted at 600˚C and roasted at 700˚C composite. Increased temperature and addition of NiO dopants were affecting the TiO₂ crystalization. Increased temperature and the addition of NiO dopants

were affecting TiO₂ crystal structure transformation. The addition of these dopants was found to suppress the transformation of anatase into rutile (compared with no addition of dopand, Table 1). The occurrence of these structural transformations will change the photoactivity of TiO₂ and further explained in TiO₂-NiO composite activity for photodegradation of Rhodamine B.

This experiment was carried out at different pH values of 2.0, 4.0, 6.0, 8.0 and 10.0, respectively, in order to investigate the process of RB photoelectrocatalytic degradation. The experimental results were shown in Figure 9. It demonstrated that the efficiency of the photoelectrode on the photoelectrocatalytic degradation of RB was

improved with the increase in pH value and the rate constant of the photoelectrocatalytic degradation of RB was also increased at the same time. The results showed that the photoelectrocatalytic activity of the photoelectrode was increased due to the increase in pH value. The study of the effect of pH value on the efficiency of photoelectrocatalytic degradation of organic dye was valuable but complicated. Firstly, pH value had significant effect on the absorption behavior of the organic dye on the catalyst surface. The point of zero charge of the TiO₂ that was the catalyst was at pH 6.4. Thus, the TiO₂ surface was positively charged in the media with pH less than 6.4, whereas it was negatively charged under the conditions with the pH greater than 6.4. The value of pH could also influence the charge carried by the molecule [40] , the molecule of RB was cationic form at lower than 4. When the pH value was less on the catalyst surface became difficult because of an electrostatic repulsive force. When the pH value was greater than 4, the molecule of RB was in the zwitterionic form and a certain part of the molecule was attracted by the catalyst surface due to the electrostatic attraction [16] . As a result, the efficiency of the photoelectrocatalytic degradation of RB was relatively low with the pH less than 4 while the efficiency was increased with the pH greater than 4. Secondly, the change of pH had an important effect on modifying the position of the TiO₂ conduction band (60 mV per pH unit) [35] . Thus, the oxidizing ability of photogenerated holes was raised, i.e. the hydroxyl radical production was facilitated in the oxidation of water (or hydroxide ions) by photogenerated holes. The more alkaline, the more readily water (or hydroxide ions) underwent oxidation to generate hydroxyl radicals on the catalyst surface. Therefore, the photoelectrocatalytic degradation of RB was more efficient due to the increase in pH value. The pH value of 10 was selected in subsequent experiments.

When the potential was 3.0 V, the rate of photoelectron transport process was lower and controlled the overall PEC oxidation. Thus, the photocurrent increased within the potential of 3.0 - 5.0 V. Once the applied bias exceeded 5.0 V, the interfacial oxidation, which was slower than the photoelectron transport, became the rate-de- termining step of the overall process. Under this condition the photocurrent saturated gradually. The anodic potential was an important parameter in the process of photoelectrocatalytic degradation of RB. The effect of applied potential was determined by using a series of potentials. To study the key factors affecting the photodegradation of RB, a series of tests were executed under different experimental conditions in which the deduction of Vis absorbance was estimated.

After 5 min degradation (batch system), about 96.3% of RB was removed. Photoelectrocatalytic (PEC) experiment 1 was carried out under halogen lamp irradiation using the Ti/TiO₂-NiO photoelectrode with a potential voltage of +10.0 V. It was obvious that the degradation rate was very fast. But their applied potential voltages make the electrode surface damage rapidly. Furthermore, the continuous systems were done with applied potential bias of 4, 5, and 6 volts. The results are shown in Table 2. However, RB could not undergo complete degradation to produce CO₂ and H₂O, as a result, the intermediates were produced during the process [40] . Therefore, PEC method showed high complete mineralization activity in the RB degradation reaction. Figure 10 shows no prominent peak in the UV region around 370 nm as an indication of an intermediate peak of rhodamine.

Compared the photoelectrocatalytic oxidation using the Ti/TiO₂ electrode by batch system as well as by single photoanode (Table 2), the photoelectrocatalytic oxidation process using integrated photoanode can enhance the RB degradation, respectively, as shown in Table 3. The experimental results also demonstrated that the reaction rate of RB degradation using several electrode by continuous system was higher than that by single photoanode.