Improving preparation method of TiO2-NiO composite materials for self-cleaning glass

TiO2-NiO Composite have been synthesized as self-cleaning material on glass. TiO2 was prepared using titanium tetraisopropoxide (TTIP) by sol gel method, while TiO2-NiO composite was prepared from TiO2 synthesized with additional Ni(NO3)2.6H2O precursor. TiO2 synthesized powder was added to Ni2+ concentrated solution in aquadest so it formed crystalline layer on TiO2 powder. Core shell composite of TiO2-NiO was obtained through the drying process at 110 °C and calcined at 700 °C. Identification and characterization of NiOTiO2 composite were carried out using X-Ray Diffraction (XRD), and X-Ray Fluoresecence (XRF). XRD diffractograms show the appearance of TiO2 and NiO peaks. Another analysis with XRF showed that composition of TiO2-NiO composite are 2:1; 1:1 and 1:2 (w/w). The electronic spectrum from TiO2-NiO core shell result showed an increasing response in visible light so it can be applied as coating material in manufacturing technology of self cleaning glass.


Introduction
Glass is a non-crystalline solid object that is usually transparent and has a variety of practical, technological and decorative uses in things like window panels, cutting tools, optoelectronics and others. Scientifically, the term "glass" is often defined in a broader sense, including every solid object. which has a non-crystalline structure (amorphous) on the atomic scale and shows the transition from glass when heated to a liquid state [1]. Along with the development of the times, there have been many researches on the modification of glass substrate to have several advantages, including anti-bacterial, anti-fungal, anti-UV, not easily dirty and easy to clean. Glass is often installed in locations that are difficult to reach so there are obstacles to clean glass. In skyscraper buildings, there is a high risk of accidents in the process of cleaning the outer glass of the building. Therefore, self-cleaning glass is needed in order to reduce the risk of workplace accidents during glass cleaning.
Titanium dioxide (TiO2) has been widely used in various fields of application especially as photocatalytic for self-cleaning [2], water treatment [3], antibacterial [4], and air purification [5]. In addition TiO2 has been used for sensors [6], solar energy conversion [7], and as an antiultraviolet (UV) agent [8].TiO2 also has the ability of photocatalysts to absorb UV light (200-380 nm) with a band gap energy of 3-3.2 eV but the effectiveness of TiO2 in photocatalysts is still low, this is due to the high band gap energy that can only absorb ultra violet light, 4 % of all sunlight energy reaches the earth's surface [9].
TiO2 photocatalytic activity can be increased through the process of doping metal ions. The use of doping methods is more beneficial than the impregnation method. This is due to the use of  [10].
Nickel oxide (NiO) is one of the active catalysts for photocatalytic reactions. The addition of NiO into the photocatalyst can increase the decomposition of water, where hydrogen gas is formed on the surface of nickel oxide while oxygen gas is released from the photocatalyst surface [11]. In the study, Nickel metal was tested as a dopant to increase the efficiency of TiO2 photocatalysts in visible light regions and reduction of band gap on TiO2 [12]. The anatase transformation to rutile due to the addition of dopants depends not only on the nature of the metal dopant (ionic radius), but also by the concentration of dopants [13]. In this paper, the addition of NiO to TiO2 is expected to increase TiO2 photocatalytic activity so that it can be better for self-cleaning applications.

Methods 2.2.1. Synthesis of TiO2
The titanium (IV) isopropoxide solution was hydrolyzed using a glacial acetic acid solution (temperature 10-14 ºC) at a ratio of 1: 10 (v / v) and then stirred continuously using a magnetic stirrer until a white sol gel was obtained, then stirred and heated at 90 ºC until white gel (sol gel TiO2) obtained [14]. And then, sol gel TiO2 was roasted at 150 ºC for 24 hours until formed the xerogel TiO2 Xerogel TiO2 was further treated by calcined at 400 ºC for 2 hours with a speed of 10 ºC / minute. The resulting TiO2 crystalline powder was analyzed by XRD.

Results and Discussion
Synthesis of TiO2 with the addition of NiO metal was carried out using the sol-gel method [14]. The addition of metal is expected to replace several positions of Ti atoms in TiO2. The calcination process was carried out at 700 o C for 2 hours. X-ray diffractograms of TiO2 and TiO2-NiO are shown in Figure  1. Figure 1. (A) shows the diffraction pattern of the synthesized TiO2 is indicated by the presence of characteristic peaks that appear at a certain diffraction angle (2θ). The peaks include (2θ) = 25.46°    From the table 1 shows the percentage of degradation of Methylene Blue, in TiO2 the degradation of Methylene Blue in the 5 minutes was 31.76962% while in the 20 minute it was 45.44908%. In TiO2-NiO composite the highest degradation of methylene blue was 64.01827% within 20 minutes on TiO2-NiO composite (1:1). This is consistent with research [16] which explains the duration of irradiation affects the degradation of Methylene Blue which proves that the longer the visible light irradiation time will have an increasing effect on composite photocatalytic activity. This is because the longer the visible light radiation, the more electrons continue to be excited and play a role in the photodegradation activity of Methylene Blue.  The contact angle measurements were carried out by using water droplets. The contact angle between water and the material was analyzed using ImageJ software. Small contact angles can reach stable hydroxyl forms grouped on the surface. Therefore, it can be done with this hydroxyl group. The results obtained from this process are shown in Figure 4-5. Based on measurements of TiO2-NiO composite contact angles obtained contact angle on glass without coating before irradiation was obtained 59.8° ( Figure 4A) and after irradiation 58.9° ( Figure 5A) almost no change in this indicates the absence of photocatalytic activity on glass without coating so that the glass does not have selfcleaning properties. In glass/TiO2, the contact angle before irradiation was 81.56° ( Figure 4B) and after irradiation 63.59° ( Figure 5B), whereas in glass/TiO2-NiO the contact angle before irradiation was 68.65° ( Figure 4C) and after irradiation 58.31° ( Figure 5C). In glass/TiO and glass/TiO2-NiO the decrease in contact angle increases the hydrophilic properties of the glass which indicates photocatalytic activity so that the glass has self-cleaning properties.

Conclusion
TiO2-NiO composite was successfully synthesized and applied for self-cleaning glass. The longer irradiation time, so that the greatest of decrease in absorbance of Methylene Blue, which shows that the photocatalytic activity of the composite TiO2-NiO is increasing. The maximum dye degradation of Methylene blue achieved was 64.01827% for 20 minutes. In the hydrophobicity test, the contact angle of glass/TiO2 after UV irradiation was obtained 63.59 ºC and glass/TiO2 -NiO 58.31 ºC.