Facile Synthesis of Potassium-Doped Titanium Oxide Nanostructure (KTiO x s)/AlO(OH) Composites for Enhanced Photocatalytic Performance

: Generally, nanoparticles (NPs) are used as photocatalysts, which sometimes results in difﬁculties in the separation and recycling of photocatalysts from suspensions after their application in water and wastewater treatment, which hinders industrial applications of NPs that are too ﬁne to be removed by gravitational settling. This can be solved by using support NPs to overcome these problems. -OH enrich AlO(OH), which is produced by a steam coating process, has been could be used as a possible support, because the -OH groups on the surface can interact with foreign molecules; thus, various composite functional materials can be prepared. Potassium doped titanium oxide NPs, which are produced by a wet corrosion process, namely KTiO x s, have been selected as photocatalysts, because KTiO x s have sufﬁcient K + ions, thereby expecting the chemical bonding with -OH group from AlO(OH). This study fabricated a novel photocataysis system made by combining KTiO x s as catalysts and AlO(OH) as the catalysts’ support, namely KTiO x s/AlO(OH) composites. The KTiO x s nanowires, obtained from 10 mol/L of a KOH solution treated with Ti and AlO(OH) at 280 ◦ C for 24 h through a steam coating process, yielded the highest surface area and the highest photocatalytic performance.


Introduction
The optical and electrical properties and catalytic performance of materials strongly depend on their morphology and structure. The high quality of nanostructures with controlled crystalline, grain, and surface architectures is of great fundamental and technological interest because of their promising new properties, which can be valuable for advanced materials [1][2][3][4][5][6][7][8]. In particular, the hierarchical self-assembly of nanoscale materials (e.g., particles, cluster, wires, belts, sheets, and tubes) into novel architectures of a higher dimensionality is highly desirable because these structures could have new properties that can be meaningful for the fabrication of advanced nanodevices and in other nanotechnology applications [9,10]. Several researchers have studied the optical and electrical properties and catalytic performances of materials using different semiconductors, including single catalysts like TiO 2 and ZrO 2 ; double catalysts, like Cu-Fe/TiO 2 -SiO 2 , and Cu-ZnO/Pt-K 2 Ti 6 O 13 ; and metal and compound oxides, such as CuO, LaCoO 3 , Ga 2 O 3 , and ATaO 3 , where A represents Na, Li, and K [11][12][13][14][15][16][17].
Titanium oxide (TiO x ) materials have attracted considerable interest in many fields of research, including the fields of photovoltaic and photocatalysis [18][19][20][21]. In particular, the photocatalysis of a TiO x semiconductor has been actively studied and applied in environmental decontamination, such as air purification, water disinfection, hazardous waste remediation, and water purification, because of its biological and chemical inertness, AlO(OH) is one of the main hydroxide layers synthesized through this process. It is another big challenge to apply this method for photocatalyst support.
This study aimed to fabricate a novel photocataysist system made using a combination of KTiO x s as the catalyst and AlO(OH) as the catalyst support, namely KTiO x s/AlO(OH) composites, in order to easily separate them from their suspension after their application in water and wastewater treatment. In addition, this study systematically investigated the best optimized conditions for photocatalysis within this system using various conditions of KTiO x s/AlO(OH) composites. Figure 1 shows the FE-SEM images of the surfaces of the Al substrates after a steam coating process at 180 • C and 280 • C for 24 h. A thin film was clearly observed on the surface after applying the steam coating process at 180 • C for 24 h (Figure 1a). However, a crystalized thick film was observed on the surface after being subjected to a steam coating process at 280 • C for 24 h (Figure 1b). Both of the films fully covered the surface, and the distribution of the crystal size was small, regardless of the process conditions. The average length and width of the crystals of the thin film was < 220 ± 80 nm and < 20 ± 30 nm, respectively, while the average length and width of the lath-like crystal of thick film was < 650 ± 75 nm and < 65 ± 30 nm, respectively. Note that these values were calculated using n = 20 within the FE-SEM images. It is worthwhile that both the length and width can be controlled spontaneously according to the steam coating process temperature.

Results and Discussions
Catalysts 2021, 11, x FOR PEER REVIEW 3 of 15 be applied to components with complicated shapes and large substrates. In addition, the steam coating process does not require any pre-treatment, and so the fabrication step can be reduced. AlO(OH) is one of the main hydroxide layers synthesized through this process. It is another big challenge to apply this method for photocatalyst support. This study aimed to fabricate a novel photocataysist system made using a combination of KTiOxs as the catalyst and AlO(OH) as the catalyst support, namely KTiOxs/AlO(OH) composites, in order to easily separate them from their suspension after their application in water and wastewater treatment. In addition, this study systematically investigated the best optimized conditions for photocatalysis within this system using various conditions of KTiOxs/AlO(OH) composites. Figure 1 shows the FE-SEM images of the surfaces of the Al substrates after a steam coating process at 180 °C and 280 °C for 24 h. A thin film was clearly observed on the surface after applying the steam coating process at 180 °C for 24 h (Figure 1a). However, a crystalized thick film was observed on the surface after being subjected to a steam coating process at 280 °C for 24 h (Figure 1b). Both of the films fully covered the surface, and the distribution of the crystal size was small, regardless of the process conditions. The average length and width of the crystals of the thin film was < 220 ± 80 nm and < 20 ± 30 nm, respectively, while the average length and width of the lath-like crystal of thick film was < 650 ± 75 nm and < 65 ± 30 nm, respectively. Note that these values were calculated using n = 20 within the FE-SEM images. It is worthwhile that both the length and width can be controlled spontaneously according to the steam coating process temperature.  Figure 2 shows the XRD profiles of the obtained AlO(OH) films that were prepared through the steam coating process at 180 °C and 280 °C for 24 h. Several peaks corresponding to aluminum hydroxide, including AlO(OH), were observed in all of the specimens. Compared with the AlO(OH) film that was prepared at 180 °C for 24 h, the crystallinity of the AlO(OH) film that was prepared at 280 °C for 24 h was higher.

Results and Discussions
It can be explained that this phenomenon is the reaction that balanced the water and Al during the chemical reaction of the steam coating process. The chemical reaction between Al and water likely occurs as follows. 2Al It has been reported that AlO(OH) is at its most stable form from around 280 °C [43]. The reaction environment of the steam coating process was balanced by subcritical water  Figure 2 shows the XRD profiles of the obtained AlO(OH) films that were prepared through the steam coating process at 180 • C and 280 • C for 24 h. Several peaks corresponding to aluminum hydroxide, including AlO(OH), were observed in all of the specimens. Compared with the AlO(OH) film that was prepared at 180 • C for 24 h, the crystallinity of the AlO(OH) film that was prepared at 280 • C for 24 h was higher.
It can be explained that this phenomenon is the reaction that balanced the water and Al during the chemical reaction of the steam coating process. The chemical reaction between Al and water likely occurs as follows.
It has been reported that AlO(OH) is at its most stable form from around 280 • C [43]. The reaction environment of the steam coating process was balanced by subcritical water in the liquid phase and saturated steam in the gas phase. Note that the state water is presented in a general pressure-temperature diagram. Subcritical water exists at temperatures between the atmospheric boiling point and the critical temperature of water. Therefore, the most impactful chemical reaction happens through the formation of AlO(OH). Here, this is worthwhile, because the large number of -OH groups on the surface were induced by this reaction, which are expected to interact with foreign molecules in order to fabricate a variety of composite functional materials. Therefore, the steam coating process condition can be completed through this reaction for this work.   Figure 3a shows the 3D images of the obtained AlO(OH) surfaces. After the steam coating process, synthesized crystals are clearly observed compared with the untreated sample. Based on this observation, a high surface area could be achieved by applying a steam coating process at 280 • C for 24 h, because the microstructures of the lath crystals have a bumpy geometry, which could increase the surface area ( Figure 3b). So, we can conclude that a high temperature treatment condition for the steam coating process can increase the surface area.
From here, we would like to demonstrate the results of KTiO x s nanowires as photocatalysts. Figure 4 shows the FE-SEM and TEM images of the KTiO x s nanowires obtained by WCP. Compared with the untreated sample, unique nanowires were observed on the surface of the Ti particles after WCP, as in previous works [2,40]. The initial Ti materials were 200 µm in size. After KOH treatment, the nanowires were synthesized on the Ti surface, and each of the nanowires were around 200 nm in size. Based on these results, it can be confirmed that Ti particles can successfully modify nanostructures through WCP. Figure  4d shows a TEM image of the KTiOx nanowires with a diameter in the range of 10-30 nm. The presence of K in the individual KTiOx nanowires was confirmed by STEM-based EDX mapping. A quantitative analysis yielded a K-concentration of about 45±11 wt.%.  From here, we would like to demonstrate the results of KTiOxs nanowires as photocatalysts. Figure 4 shows the FE-SEM and TEM images of the KTiOxs nanowires obtained by WCP. Compared with the untreated sample, unique nanowires were observed on the surface of the Ti particles after WCP, as in previous works [2,40]. The initial Ti materials were 200 µm in size. After KOH treatment, the nanowires were synthesized on the Ti surface, and each of the nanowires were around 200 nm in size. Based on these results, it can be confirmed that Ti particles can successfully modify nanostructures through WCP. Figure 4d shows a TEM image of the KTiOx nanowires with a diameter in the range of 10-30 nm. The presence of K in the individual KTiOx nanowires was confirmed by STEMbased EDX mapping. A quantitative analysis yielded a K-concentration of about 45±11 wt.%.  From here, we would like to demonstrate the results of KTiOxs nanowires as photocatalysts. Figure 4 shows the FE-SEM and TEM images of the KTiOxs nanowires obtained by WCP. Compared with the untreated sample, unique nanowires were observed on the surface of the Ti particles after WCP, as in previous works [2,40]. The initial Ti materials were 200 µm in size. After KOH treatment, the nanowires were synthesized on the Ti surface, and each of the nanowires were around 200 nm in size. Based on these results, it can be confirmed that Ti particles can successfully modify nanostructures through WCP. Figure 4d shows a TEM image of the KTiOx nanowires with a diameter in the range of 10-30 nm. The presence of K in the individual KTiOx nanowires was confirmed by STEMbased EDX mapping. A quantitative analysis yielded a K-concentration of about 45±11 wt.%.  The Raman spectra of the obtained KTiOxs nanowires are presented in Figure 5 New peaks were observed for the potassium titanate phase (280 cm −1 ), namely KTiOxs, caused mainly by the structural changes in TiO2 [44,45]. The synthesis of the KTiOxs involved the rearrangement of the Ti-O bonds. Potassium atoms were inserted in the space between  The Raman spectra of the obtained KTiO x s nanowires are presented in Figure 5 New peaks were observed for the potassium titanate phase (280 cm −1 ), namely KTiO x s, caused mainly by the structural changes in TiO 2 [44,45]. The synthesis of the KTiO x s involved the rearrangement of the Ti-O bonds. Potassium atoms were inserted in the space between the Ti-O bonds. The Ti-O-K bonds were formed with some of the broken Ti-O bonds; the other Ti-O bonds were reserved. The peaks at 445, 660, and 903 cm -1 were assigned to different TiO 2 phases (anatase, rutile, and brookite) [45,46]. Therefore, this indicates that KTiO x s exhibited the characteristics of a (Ti-O-K) structure unit containing TiO 2 phases [45]. A Raman spectroscope with back-scattering configuration was used for examining the structural properties of the films. Raman shifts are affected by the vibration of the electronic polarization of the constituents in the films, which depend on bonding characteristics such as the atomic distance and bonding angle [47]. Therefore, the structure of the product changed when the chemical bond was rearranged. In order to verify the surface chemical composition of the obtained nanostructured oxide films, an X-ray photoelectron spectroscopy (XPS) analysis was performed. The incorporation of K into titanium oxide films could be evidenced by the existence of the K2p peak in the XPS spectrum. The XPS result ( Figure 6) shows that the peak of the K element was observed at about 293.5 eV, which was the region of the compound for K + [2].
Therefore, these results can be expected to make a chemical bonding with -OH group from AlO(OH). The Raman results confirmed that the amount and crystallinity of the obtained KTiO x s nanowires increased at a high concentration for the KOH solution. This result may explain the generation of more chemical bonding between OH − and K + for suitable composites for photocatalysis. Figures 7 and 8 show the FE-SEM images and EDX analysis of the obtained KTiO x s/AlO(OH) composites. In the case of the KTiO x s obtained from the 1 mol/L-KOH treatment, it is hard to see the combination of KTiO x s and AlO(OH); however, the composites formed with KTiO x s obtained from the 10 mol/L-KOH treatment are clearly observed. It can be assumed that the K + ion site hs less 1 mol/L-KOH treated Ti compared with the 10 mol/L-KOH treated Ti, based on the Raman results. Unique nanowires of KTiO x s were observed so, it can be said that this composite was of a combination of KTiO x s and AlO(OH). In detail, an EDX analysis was carried out to confirm this composite. The Ti component is clearly shown in the EDX mapping analysis, indicating that KTiO x s/AlO(OH) composites were successfully obtained during the reaction (Figure 8).  Therefore, these results can be expected to make a chemical bonding with -OH group from AlO(OH). The Raman results confirmed that the amount and crystallinity of the obtained KTiOxs nanowires increased at a high concentration for the KOH solution. This result may explain the generation of more chemical bonding between OH − and K + for suitable composites for photocatalysis. Figures 7 and 8 show the FE-SEM images and EDX analysis of the obtained KTiOxs/AlO(OH) composites. In the case of the KTiOxs obtained from the 1 mol/L-KOH treatment, it is hard to see the combination of KTiOxs and AlO(OH); however, the composites formed with KTiOxs obtained from the 10 mol/L-KOH treatment are clearly observed. It can be assumed that the K + ion site hs less 1 mol/L-KOH treated Ti compared with the 10 mol/L-KOH treated Ti, based on the Raman results. Unique nanowires of KTiOxs were observed so, it can be said that this composite was of a combination of KTiOxs and AlO(OH). In detail, an EDX analysis was carried out to confirm this composite. The  Therefore, these results can be expected to make a chemical bonding with -OH group from AlO(OH). The Raman results confirmed that the amount and crystallinity of the obtained KTiOxs nanowires increased at a high concentration for the KOH solution. This result may explain the generation of more chemical bonding between OH − and K + for suitable composites for photocatalysis. Figures 7 and 8 show the FE-SEM images and EDX analysis of the obtained KTiOxs/AlO(OH) composites. In the case of the KTiOxs obtained from the 1 mol/L-KOH treatment, it is hard to see the combination of KTiOxs and AlO(OH); however, the composites formed with KTiOxs obtained from the 10 mol/L-KOH treatment are clearly observed. It can be assumed that the K + ion site hs less 1 mol/L-KOH treated Ti compared with the 10 mol/L-KOH treated Ti, based on the Raman results. Unique nanowires of KTiOxs were observed so, it can be said that this composite was of a combination of KTiOxs and AlO(OH). In detail, an EDX analysis was carried out to confirm this composite. The Ti component is clearly shown in the EDX mapping analysis, indicating that KTiOxs/AlO(OH) composites were successfully obtained during the reaction (Figure 8).    In order to figure out the chemical bonding of the KTiOxs/AlO(OH) composites obtained here, FTIR was carried out (Figure 9). The strong band at 3000-3400 cm −1 and the weak band at 1600-1700 cm −1 can be assigned to the stretching and bending modes of the adsorbed water [48]. Other absorption peaks were observed at around 480-500 cm −1 after In order to figure out the chemical bonding of the KTiO x s/AlO(OH) composites obtained here, FTIR was carried out (Figure 9). The strong band at 3000-3400 cm −1 and the weak band at 1600-1700 cm −1 can be assigned to the stretching and bending modes of the adsorbed water [48]. Other absorption peaks were observed at around 480-500 cm −1 after the steam coating process, which could be attributed to Al-O symmetric stretching and ring vibration mode in Al-O tetraheda formed through the oxygen atom [49]. In particular, the KTiO x s/AlO(OH) composite reveled the stretching vibration mode of Ti-O (580 cm −1 ) and Ti-O-Ti (720 cm −1 ) with Al-O bonding [50]. On the basis of these results, K + from KTiO x s and the -OH group from AlO(OH) could undergo chemical bonding to fabricate the composite. Therefore, it can be assumed that the initial concept to make the composite using AlO(OH) as a support for KTiO x s is successfully achieved.
Catalysts 2021, 11, x FOR PEER REVIEW 9 of 15 the steam coating process, which could be attributed to Al-O symmetric stretching and ring vibration mode in Al-O tetraheda formed through the oxygen atom [49]. In particular, the KTiOxs/AlO(OH) composite reveled the stretching vibration mode of Ti-O (580 cm −1 ) and Ti-O-Ti (720 cm −1 ) with Al-O bonding [50]. On the basis of these results, K + from KTiOxs and the -OH group from AlO(OH) could undergo chemical bonding to fabricate the composite. Therefore, it can be assumed that the initial concept to make the composite using AlO(OH) as a support for KTiOxs is successfully achieved. In order to examine the photocatalytic activity of the obtained KTiOxs nanowires, the photodegradation of methylene blue (MB) was evaluated under UV light irradiation. The band gap of the obtained KTiOxs is around 2.8~2.9 eV. The UV-VIS absorption spectra presented in Figure 10A demonstrate the decomposition of MB dye, leading to decolorization. For comparison, the absorption spectra of the untreated sample are also presented. The major absorption peaks appeared at about 612 and 664 nm, which is characteristic for In order to examine the photocatalytic activity of the obtained KTiO x s nanowires, the photodegradation of methylene blue (MB) was evaluated under UV light irradiation. The band gap of the obtained KTiO x s is around 2.8~2.9 eV. The UV-VIS absorption spectra presented in Figure 10A demonstrate the decomposition of MB dye, leading to decolorization. For comparison, the absorption spectra of the untreated sample are also presented. The major absorption peaks appeared at about 612 and 664 nm, which is characteristic for MB dye [51]. The major absorption peaks appeared and were used as a direct indication of photocatalytically activated dye degradation. Indeed, all of the obtained KTiO x s specimens showed a higher photocatalytic activity than the untreated samples. This observation was in agreement with the remarkable photocatalytic properties reported for nanostructured titanium oxide materials with an enhanced surface area and increased electron transfer ability [2,52]. Interestingly, the 10 mol/L-KOH-treated Ti specimen showed a higher photocatalytic activity than the 1 mol/L-KOH-treated Ti. The intensity of the MB peaks of the 10 mol/L-KOH treated Ti decreased to a blank level after 30 min of UV exposure. The degradation rate of the 10 mol/L-KOH treated Ti was almost 99% in this study. This result is superior to the reported results (high score of the reported results was 90%) [29,53,54]. Generally, the photocatalytic activity leading to the degradation of dyes depends on the catalyst concentration. The high surface area exerts a synergistic effect on the catalyst concentration. As the higher catalyst concentration creates an increase in adsorbed dye molecules, and a higher photocatalytic performance can be expected [55]. Normally, the photocatalytic process is based on the photogeneration of electronhole pairs, which will initiate redox reactions with the species adsorbed on the surface of the catalysts. In the photocatalytic process, OH radicals originating from the oxidation of OH-or H2O through the photogenerated electron-hole pairs in the presence of oxygen have been considered as the major reactants responsible for the photocatalytic oxidation of organic materials and the degradation of pollutants [22,23,56]. Consequently, improved electronic properties can be linked to an enhanced photocatalytic activity. In our work, the electronic properties are governed by the amount of Ti-O-K components. From these results, we can conclude that an efficient charge/energy transfer occurs in the KOHtreated samples under photo-irradiation and leads to an improved photocatalytic activity, as evidenced by the drastic diminishment of the UV absorption peaks. These results clearly demonstrate that KTiOx can be a cost-effective, highly efficient, and environmental-friendly photocatalyst. Normally, the photocatalytic process is based on the photogeneration of electron-hole pairs, which will initiate redox reactions with the species adsorbed on the surface of the catalysts. In the photocatalytic process, OH radicals originating from the oxidation of OHor H 2 O through the photogenerated electron-hole pairs in the presence of oxygen have been considered as the major reactants responsible for the photocatalytic oxidation of organic materials and the degradation of pollutants [22,23,56]. Consequently, improved electronic properties can be linked to an enhanced photocatalytic activity. In our work, the electronic properties are governed by the amount of Ti-O-K components. From these results, we can conclude that an efficient charge/energy transfer occurs in the KOH-treated samples under photo-irradiation and leads to an improved photocatalytic activity, as evidenced by the drastic diminishment of the UV absorption peaks. These results clearly demonstrate that KTiOx can be a cost-effective, highly efficient, and environmental-friendly photocatalyst.
In order to optimize the best composite conditions for the photocatalytic effect, we prepared four different KTiO x s/AlO(OH) composites, as shown in Figure 11. For comparison, the absorption spectra of bare AlO(OH) specimens prepared by a steam coating process at 180 • C and 280 • C for 24 h were also presented as the control samples. From the results, at first, we can confirm that the KTiO x s/AlO(OH) composites showed a higher photocatalytic activity compared with the bare AlO(OH) specimens because of the existence of KTiO x s. Among the KTiO x s/AlO(OH) composites, the 10 mol/L-KOH treated Ti and the steam coating AlO(OH) composite treated at 280 • C for 24 h showed a remarkable enhanced photocatalytic activity because both the KTiO x s and AlO(OH) had a high surface area. Once again, we assume that a high surface area executes a synergistic effect on the catalyst concentration, because a large amount of dye molecules can be loaded on the surface, resulting in a higher photocatalytic performance [57,58].
In order to optimize the best conditions for the composites, a degradation level calculated by the intensity of the MB was used in this system. The composites used in this study are listed in Table 1. First, in order to figure out the effect of the surface area of KTiOxs, a higher surface area of AlO(OH) substrates was used. This indicated that the degradation function of MB with 10 mol/L-KOH treated Ti was four times higher than for the 1 mol/L-KOH treated Ti (Figure 11b). From these results, it can be seen that the 10 mol/L-KOH treated Ti catalyst is suitable for a higher photocatalysis performance because of its high surface area. Second, in order to figure out the effect of the surface area of AlO(OH), we used the 10 mol/L-KOH treated Ti as a high performance photocatalyst. From this comparison, a large surface area of AlO(OH) could contain the large amounts of KTiOxs, thereby increasing the photocatalytic activity (Figure 11c). On the basis of these results, the K + from KTiOxs and OH-from AlO(OH) could create a chemical reaction to make the composite successful, and the best composite condition for the photocatalysis was to use a high surface area for KTiOxs and AlO(OH). Briefly, it can be explained that the best condition for the KTiOxs/AlO(OH) composite is using 10 mol/L-KOH treated Ti as a photocatalyst and steam coating processed AlOOH treated at 280 °C for 24 h as a catalyst support. Figure 11. Analysis of the photocatalytic activity: (a) UV-VIS absorption spectra took from the original MB dye, and from the dye exposed to various conditions of KTiOx/AlO(OH) composites In order to optimize the best conditions for the composites, a degradation level calculated by the intensity of the MB was used in this system. The composites used in this study are listed in Table 1. First, in order to figure out the effect of the surface area of KTiO x s, a higher surface area of AlO(OH) substrates was used. This indicated that the degradation function of MB with 10 mol/L-KOH treated Ti was four times higher than for the 1 mol/L-KOH treated Ti (Figure 11b). From these results, it can be seen that the 10 mol/L-KOH treated Ti catalyst is suitable for a higher photocatalysis performance because of its high surface area. Second, in order to figure out the effect of the surface area of AlO(OH), we used the 10 mol/L-KOH treated Ti as a high performance photocatalyst. From this comparison, a large surface area of AlO(OH) could contain the large amounts of KTiO x s, thereby increasing the photocatalytic activity (Figure 11c). On the basis of these results, the K + from KTiO x s and OH-from AlO(OH) could create a chemical reaction to make the composite successful, and the best composite condition for the photocatalysis was to use a high surface area for KTiO x s and AlO(OH). Briefly, it can be explained that the best condition for the KTiO x s/AlO(OH) composite is using 10 mol/L-KOH treated Ti as a photocatalyst and steam coating processed AlOOH treated at 280 • C for 24 h as a catalyst support.

Preparation of KTiO x s/AlO(OH) Composites for Photocatalysis System
An Al-Mg-Si alloy with a size of 10 mm X 10 mm was used as the substrate for synthesizing AlO(OH) as a support. The chemical composition of the Al alloy is shown in Table 2. The chemical composition is the same as that of AA6061. The steam coating process was carried out with press micro reactor (MMS-100 OMlabotech) with a volume of 10 m 3 using a Teflon container with a 100-mL capacity. AA6061 substrates were placed on a substrate stage, which was made of Teflon tape, 10 mL of ultrapure water was added to the bottom of a Teflon container to produce steam. The autoclave process was carried out by heating up to 180 • C and 240 • C for 24 h, and then was cooled down naturally at room temperature.
In order to synthesize the K-incorporated Ti (KTiO x s) as photocatalysts, Ti microspheres (purity >99.8% and diameter of 125-250 µm) were purchased from Sigma-Aldrich in Japan. The Ti particles were soaked in 5 mL KOH solution with a concentration of 1 and 10 mol/L at room temperature for 24 h. Note that this process is called as WCP. After WCP, all particles were washed with deionized water and dried. These particles contained a Ti core and a shell of KTiO x s nanowires forming a network.
In order to synthesize the KTiO x s/AlO(OH) composites for the photocatalysis system, the obtained the AlO(OH) substrates were attached by a carbon type on the bottom of the container (UG Yamayu, Tokyo, Japan) and mixed with 0.75g of KTiO x s with 4 mL of H 2 O at 200 rpm for 24 h with shaking. After 24 h, the samples were washed with H 2 O to remove the unattached KTiO x s. In order to figure out the effect of the surface area of KTiO x s and AlO(OH), we prepared four different composites as follows. The sample names of the composites were recorded in the order of the condition of KTiO x s/AlO(OH), as follows: 1 mol/L-KOH treated Ti/180 • C for 24 h treated Al, 1 mol/L-KOH treated Ti/280 • C for 24 h treated Ti, 10 mol/L-KOH treated Ti/180 • C for 24 h treated Al, and 10 mol/L-KOH treated Ti/180 • C for 24 h treated Ti.

Evaluation of Photocatalytic Activity of KTiO x s/AlO(OH) Composites
First, in order to evaluate the photocatalytic activity of the KTiO x s that were treated with 1 and 10 mol/L-KOH, with treated Ti as the photocatalysts, 2g of KTiO x s were mixed with 2 mL of methylene blue organic dye (MB; 125 mg/L) solutions. For the photocatalysis, UV irradiation (UV light; GrassyLeDio RX122, Volxjapanv, Tokyoy, Japan) with a 10 cm working distance was carried out for 10, 20, and 30 min. Note that the UV light can react under a 500 nm wavelength. During UV exposure, the mixtures (KTiO x s and MB solutions) were stirred continuously. After we confirmed the activity of the KTiO x s, the photocatalytic activity of the KTiO x s/AlO(OH) composites were carried out. Here, 300 mL of MB dye was drop wised on the surface of KTiO x s/AlO(OH) composites for UV irradiation for 10, 20, and 30 min.

Characterizations
Changes in the surface structure, shape, and size of the obtained AlO(OH) and KTiO x s nanowires were observed using a field emission scanning electron microscope (FE-SEM; JSM-7610, JEOL Ltd., Tokyo, Japan), which was operated at 15 kV. The crystal phase of the obtained AlO(OH) film was identified using X-ray diffraction (XRD; Smart Lab, Rigaku, Tokyo, Japan), with Cu K radiation (40 kV, 30 mA) within a range of 5 • -90 • and at a scanning rate of 2θ = 4 • /min. The surface area was measured using atomic force microscopy (AFM; AFM5000, HITACHI, Tokyo, Japan) with DFM mode at 20 µm × 20 µm. A Raman spectroscope was used for examining the structural properties of the obtained KTiO x s nanowires. A laser Raman spectrometer (NRS-5100, JASCO, Tokyo, Japan) was used within a range of 100-1500 cm −1 at a 532 nm laser wavelength. For the identification and visualization of the obtained KTiO x s/AlO(OH) composites, an energydispersive X-ray (SEM-EDX; JSM-7610, JEOL Ltd., Tokkyo, Japan) analysis was carried out at 20 kV. To investigate the structural properties of the obtained KTiO x s/AlO(OH) composites, Fourier-transform infrared spectroscopy (FT-IR; IRAffinity-1S, Shimadzu Co., Tokyo, Japan) was performed, which was recorded within the range of 400-4000 cm −1 , with 20 scans at a resolution of 4 cm −1 . After UV irradiation, the photocatalytic activity was evaluated by collecting the UV-VIS absorption spectra (UV-VIS Spectrophotometer; V-630Bio Spectrophotometer, JASCO, Tokyo, Japan) of the solution. The degradation efficiency was recorded as the decreased absorption peak.

Conclusions
The preparation of KTiO x s/AlO(OH) composites for photocatalysis was demonstrated. In order to overcome the separation after photocatalysis and water purification using particles catalysts, a support to contain the particle catalysts is needed. Herein, KTiO x s nanoparticles were selected as the photocatalysts, because nanostructured KTiO x s was a promising candidate for photocatalysis in previous work. Based on this concept, AlO(OH) was considered as a support, because the enriched −OH group has a higher potential to create a chemical reaction with the K + from KTiO x s. In particular, our strategic plan for this project was to enhance the photocatalytic activity as follws: (1) to make a large surface area of support to load more catalysts and (2) to make a large surface area of catalysts to enlarge the concentration of dye molecules. In this contribution, AlO(OH) as a support was prepared by a steam coating process at 180 • C and 280 • C for 24 h to fabricate the different surface areas, and the KTiO x s nanowires were prepared using WCP with 1 and 10 mol/L-KOH solution treatments to elongate the different surface areas. The photocatalytic activity of KTiO x s/AlO(OH) composites was successfully studied as a function of the surface