Investigation of ZnTiO3/TiO2 composites and their application in photocatalysis European Journal of Chemistry 10 (1) (2019) 7-11 European Journal of Chemistry View Journal Online View Article Online Investigation of ZnTiO3/TiO2 composites and their application in photocatalysis Zhenzhao Pei *, Pei Wang and Zhiguo Li Department of Chemical Engineering, Faculty of College of Materials Science and Engineering, Hebei University of Engineering, Handan, 056038, China peizhenzhaophd@126.com (A.P.), wangpeihbgcdx@126.com (P.W.), 18231024595@163.com (Z.L.) * Corresponding author at: Department of Chemical Engineering, Faculty of College of Materials Science and Engineering, Hebei University of Engineering, Handan, 056038, China. Tel: +86.0310.3161792 Fax: +86.0310.3161792 e-mail: peizhenzhaophd@126.com (Z. Pei). 10.5155/eurjchem.10.1.7-11.1824 Received: 07 December 2018 Received in revised form: 09 January 2019 Accepted: 11 January 2019 Published online: 31 March 2019 Printed: 31 March 2019 In this work, we report that ZnTiO3/TiO2 composites, which were synthesized by hydrothermal method possessed photocatalytic and potential spraying properties. The obtained ZnTiO3/TiO2 composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction techniques (XRD). Photocatalytic activities of ZnTiO3/TiO2 composites were evaluated by using Rhodamine B (RhB) as a model pollutant under visible light irradiation. The experimental results showed that the as-prepared ZnTiO3 (2%)/TiO2 composite exhibited better photocatalytic activity than that of pure TiO2. Composites ZnTiO3/TiO2 Rhodamine B Photocatalysis Spraying properties Hydrothermal synthesis Cite this: Eur. J. Chem. 2019, 10(1), 7-11 Journal website: www.eurjchem.com 1. Introduction Over the past decades, titanium dioxide (TiO2) has attracted considerable scientific interest in the field of photocatalysis, due to the outstanding properties such as low cost, photochemical stability and security [1,2]. However, due to its large band gap (TiO2 ~3.2 eV) [3], TiO2 can only work under UV irradiation, which greatly restricts the use of sunlight as an energy source for photoreactions since only about 3-4% of the solar spectrum falls within the UV range [4- 6]. In addition, high recombination rate of electron-hole pairs lowers its photocatalytic efficiency [7]. Up to now, many methods have been proposed to extend the spectral response of TiO2 to the visible-light region, including doping with metal/non-metal ions [8-10] and coupling with other oxide semiconductors [11-15]. In general, doping with metal/non- metal ions can affect the band gap and extend the light absorption range [16], coupling with an oxide semiconductor can improve the charge separation and extend its photo- responsive range [17]. After years of research, many composite systems have been successfully synthesized, such as V2O5/TiO2, SnO2/TiO2, CdO/TiO2, and ZnO/TiO2 [18]. Liang and his coworkers synthesized ZnTiO3-TiO2 heterojunction exhibiting photo- catalytic activity [19]. Subsequently, ZnTiO3-TiO2 was synthesized by solid state dispersion method and sol-gel technique, which could degrade 4-chlorophenol under sunlight [20,21]. Then, Tian et al. [22] found that ZnTiO3-TiO2 could be used for photocatalytic H2 production under visible light. To date, spraying process has been successfully applied to produce many protective coatings for wear, erosion and heat resistance [23,24]. In recent years, numerous studies have been conducted to synthesize spraying materials, such as Al2O3-Al composite, Fe2O3-Al composite, Cr2O3, Al2O3-Cr2O3 composite and ZrO2-Al2O3 composite. Song et al. [25] reported that the FeAl-Al2O3 composite showed excellent wear resistance under dry sliding wear test conditions. Tao and his coworkers [26] found that the coexistence of metal Al phase and Al2O3 ceramic phase could effectively improve the toughness, strength and wear resistance of coatings. However, compared to the gained great progress on spraying materials and photocatalysis, there are no research reports that ZnTiO3/TiO2 composite possessed photocatalytic and spraying properties. In this paper, it was firstly found that ZnTiO3/TiO2 composites showed photocatalytic activity and potential ABSTRACT RESEARCH ARTICLE KEYWORDS European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2019 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. http://dx.doi.org/10.5155/eurjchem.10.1.7-11.1824 http://dx.doi.org/10.5155/eurjchem.10.1.7-11.1824 https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.10.1.7-11.1824&domain=pdf&date_stamp=2019-03-31 http://www.eurjchem.com/ http://dx.doi.org/10.5155/eurjchem.10.1.7-11.1824 mailto:peizhenzhaophd@126.com mailto:wangpeihbgcdx@126.com mailto:18231024595@163.com mailto:peizhenzhaophd@126.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.10.1.7-11.1824&domain=pdf&date_stamp=2019-03-31� 8 Pei et al. / European Journal of Chemistry 10 (1) (2019) 7-11 Figure 1. XRD patterns of the corresponding powder samples of pure TiO2 (a) and ZnTiO3 (2, 10, 20 and 30%)/TiO2 composite (b-e). spraying properties. The hydrothermal method was employed to synthesize ZnTiO3/TiO2 composites. Rhodamine B was selected as a model hazardous dye to evaluate the photo- catalytic activity of ZnTiO3/TiO2 composites under visible light irradiation. The experimental results suggested that these ZnTiO3/TiO2 composites could be a promising class of photo- catalyst candidates for organic contaminant degradation and spraying material for wear resistance and metal corrosion prevention. 2. Experimental 2.1. Preparation of ZnTiO3/TiO2 Titanium(IV) sulfate (Ti(SO4)2, CP) was purchased from Sinopharm Chemical Reagent Co., Ltd., Zinc sulfate (ZnSO4·7H2O, AR) was purchased from Tianjin Zhiyuan Reagent Co., Ltd., and hexamethylene tetramine (C6H12N4, AR) was purchased from Beijing Chemical Reagent Co., Ltd. All chemicals applied to the experiment were used fully as received without further purification. Deionized water used was self-made. ZnTiO3/TiO2 composites were synthesized by a relatively simple hydrothermal method. Ti(SO4)2 and ZnSO4·7H2O were used as the source of titanium and source of zinc, respectively. Different ZnTiO3/TiO2 composites varying in the content of ZnTiO3 in the composite were obtained by adding different amounts of ZnSO4·7H2O into a certain amount of Ti(SO4)2. In a typical procedure, a known amount of Ti(SO4)2 and a certain amount of ZnSO4·7H2O were dissolved in 35 mL distilled water. The mole fractions of ZnSO4·7H2O used for synthesizing ZnTiO3/TiO2 composites were 0, 2, 10, 20 and 30%, respect- tively. Then 2 g C6H12N4 was added into the distilled water. Subsequently, the mixed solution was transferred to a 50 mL Teflon lined stainless-steel autoclave under vigorous stirring at ambient temperature, and kept at 220 °C for 5 h in an oven. After cooling to room temperature, the precipitates were collected by centrifugation, washed several times with absolute ethanol and distilled water. The precipitates were dried at 105 °C for 8 h and then calcined in air at 600 °C for 2 h. The as-prepared ZnTiO3/TiO2 composites were corres- pondingly denoted as pure TiO2, ZnTiO3 (2%)/TiO2, ZnTiO3 (10%)/TiO2, ZnTiO3 (20%)/TiO2, and ZnTiO3 (30%)/TiO2. 2.2. Characterization of phase and microstructure The morphologies of the as-prepared ZnTiO3/TiO2 composites with varying ZnTiO3 content were observed by a scanning electron microscopy. The powder X-ray diffraction patterns of the powders were recorded on apparatus (D/Max- 2200, Rigaku) using CuKα irradiation (λ = 1.5408 Å) in the range of 2θ, 10-70°. 2.3. Measurements of photocatalytic performance The photocatalytic activities of the as-prepared ZnTiO3/ TiO2 composites were evaluated by photocatalytic decolori- zation of Rhodamine B in aqueous solution under visible light irradiation. A 500 W Xenon lamp equipped with a special cut- off filter to remove ultraviolet irradiation (λ < 380 nm) was used as a visible light source. Before exposure to the visible light irradiation, 40 mg of the powder photocatalyst was combined with 40 mL of the dye solution in a 50 mL quartz test tube and was stirred for 40 min to reach the adsorption- desorption equilibrium. The samples were then irradiated by a 500 W Xenon lamp. Eight milliliter aliquot was withdrawn at certain time intervals and then centrifuged (8000 rpm, 30 min) to remove the particles. The change of the solution absorbance with the extension of irradiation time was measured by an UV-vis spectrophotometer. 3. Results and discussion 3.1. X-ray diffraction analysis The crystal structures of the corresponding pure TiO2 and as-prepared ZnTiO3/TiO2 composites were measured by XRD characterization. XRD pattern of pure TiO2 (Figure 1a) revealed the typical peaks at around 2θ = 25.3, 37.8, 48.0, 53.9, 55.1 and 62.7°, which were attributed to the (101), (004), (200), (105), (211) and (204) planes of TiO2 (JSPDS 21-1272). These peaks conformed to the presence of anatase structure in the pure TiO2 [27]. The pure TiO2 had anatase (101) plane peak but no rutile (100) plane peak was observed, clearly indicating that only the anatase crystalline phase was present. When the ZnTiO3 molar fraction was 2%, no obvious diffraction peak assigned to the crystal phase of ZnTiO3 could be observed in Figure 1b. 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.1.7-11.1824 Pei et al. / European Journal of Chemistry 10 (1) (2019) 7-11 9 Figure 2. SEM image of pure TiO2. Figure 3. SEM images of as-prepared ZnTiO3 (2, 10, 20 and 30%)/TiO2 composites (a-d). However, with the larger content of ZnTiO3 in the ZnTiO3/TiO2 (from 10 to 30% molar fraction), it could be seen that the characteristic peak of anatase TiO2 gradually decreased, which was shown in Figure 1c-e. XRD patterns of ZnTiO3/TiO2 composites (Figure 1c-e) demonstrated that the diffractions at around 2θ = 30.0 and 35.4° were assigned to the (220) and (311) planes of ZnTiO3 (JSPDS 39-0190). Such results clearly indicated that two components (TiO2 and ZnTiO3) coexisted in the composites. 3.2. Morphology and microstructure analysis The morphologies of pure TiO2 and ZnTiO3/TiO2 compo- sites were examined by SEM (Figure 2 and 3). As shown in Figure 2, pure TiO2 exhibited smooth surfaces and ellipsoid- like shape, with an average size diameter around 60.54 µm. Figure 3a-d showed SEM images of ZnTiO3/TiO2 composites prepared by introducing different amounts of ZnSO4 into Ti(SO4)2 to reach a ZnTiO3 molar content of 2, 10, 20 and 30% in the ZnTiO3/TiO2 composites. The morphology depended on the ZnTiO3 content. As the molar content of ZnTiO3 was 2% (Figure 3a), the average size diameter (appropriately 64.12 µm) of ZnTiO3/TiO2 composite became larger, compared to that of pure TiO2. When the ZnTiO3 molar fraction was increased to 10 and 20%, larger average size diameter could be observed, compared to that of ZnTiO3 (2%)/TiO2. Figure 3d illustrated that average size diameter became different with larger diameters and smaller diameters in the composite containing 30% ZnTiO3. Actually, as clearly shown in Figure 3, the as-prepared ZnTiO3/TiO2 composites owned a relatively big particle size, which enabled them to be employed as promising spraying materials for metal corrosion prevention and wear resistance. 3.3. Enhanced photocatalytic performance RhB was used as the target probe molecule for photo- catalytic degradation reactions to evaluate the photocatalytic capability of pure TiO2 and as-prepared ZnTiO3/TiO2 compo- sites under visible light irradiation. Figure 4 displayed the photodegradation of RhB as a function of irradiation time over pure TiO2 and ZnTiO3 (2, 10, 20 and 30%)/TiO2 composites. As clearly shown in Figure 4f, based on a blank experiment without any catalyst, the self-photolysis of RhB under visible light irradiation could be ignored, corroborating the degradation reaction was truly driven by the photocatalytic process. It could be seen from Figure 4 that 62.2, 87.5, 52.5, 27.8 and 36.5% of RhB had been effectively degraded over pure TiO2 and ZnTiO3 (2, 10, 20 and 30%)/TiO2 for 5 h, respectively. It was found that pure TiO2 exhibited photo- catalytic activity under the visible light irradiation, the reason might be that added C6H12N4 in the experiment not only provided an alkaline environment, meanwhile added C6H12N4 acted as the nitrogen source for nitrogen doping into TiO2, so the as-prepared TiO2 exhibited photocatalytic activity under visible light irradiation. ZnTiO3 (2%)/TiO2 exhibited the highest photocatalytic activity among the as-prepared ZnTiO3/ TiO2 composites, which increased photodegradation efficiency by 25.3% compared to the pure TiO2. As the molar fraction of ZnTiO3 increased from 2 to 10%, a decrease in the photo- catalytic activity of ZnTiO3 (10%)/TiO2 composite was observed. With the 20 and 30% content of ZnTiO3, the photocatalytic activities of ZnTiO3 (20%)/TiO2 and ZnTiO3 (30%)/TiO2 could be seen from Figure 4d-e. 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.1.7-11.1824 10 Pei et al. / European Journal of Chemistry 10 (1) (2019) 7-11 Figure 4. Photocatalytic activities of blank (without catalyst), pure TiO2, and as-prepared ZnTiO3/TiO2 composites on the degradation of RhB under visible light irradiation. 3.4. Photocatalytic reaction mechanism of ZnTiO3/TiO2 The reason for the improved photocatalytic performance might be that electrons and holes induced in ZnTiO3 were separated and pushed to the side of TiO2, and those generated active electrons and holes could act in the reduction of oxygen molecules to radicals and oxidation of water molecules to hydroxyl radicals [28]. Generally, organic molecules such as RhB could be efficiently degraded by these generated active radicals. So, ZnTiO3 (2%)/TiO2 exhibited higher photocatalytic activity than pure TiO2. However, the increase of molar fraction of ZnTiO3 led to the increase of particle size, which could be seen from Figure 3a-c. The larger particle size resulted in the longer migration distance of photo-generated electrons and holes, which could improve the recombination of photo-generated carriers and decrease the photocatalytic activity. The particle size of ZnTiO3 (30%)/TiO2 became different with larger diameters and smaller diameters, which led to lower photodegradation efficiency than ZnTiO3 (10%)/TiO2 and higher photodegradation efficiency than ZnTiO3 (20%)/TiO2. 4. Conclusions In summary, ZnTiO3/TiO2 composites were synthesized via a facile hydrothermal method exhibited photocatalytic activity. By tuning the different amounts of ZnSO4, different ZnTiO3/TiO2 composites were successfully obtained. ZnTiO3 (2%)/TiO2 composite exhibited the superior photocatalytic activity with 87.5% RhB degradation rate (compared to pure TiO2 of 62.2%) under the visible light irradiation. Therefore, use of ZnTiO3/TiO2 composites showed advantages of low cost, re-usability and enhanced photocatalytic activity. In addition, the as-prepared ZnTiO3/TiO2 composites owned a relatively big particle size, which enabled them to be employed as promising spraying materials for metal corrosion prevention and better photocatalytic applications. This study could promote the synthesis of photocatalysts that exhibited high photodegradation efficiency and further application in the spraying fields. Acknowledgments This work was financially supported by Open Foundation of Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Chinese Academy of Sciences (PCOM201126), Key Program of Educational Commission of Hebei Province of China (ZH2011224). Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors contributed equally to this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Zhenzhao Pei http://orcid.org/0000-0003-4298-7539 Pei Wang http://orcid.org/0000-0001-6382-6182 Zhiguo Li http://orcid.org/0000-0002-9446-2091 References [1]. Siddiqa, A.; Sabir, S.; Hussain, S. T.; Muhammad, B. Eur. J. Chem. 2013, 4(4), 388-395. [2]. Gaya, U. I. Eur. J. Chem. 2011, 2(2), 163-167. [3]. Xu, Y.; Schoonen, M. A. A. Am. Mineral. 2000, 85, 543-556. [4]. Aboul-Gheit, A. K.; Ahmed, S. M.; El-Desouki, D. S.; Abdel-Azeem, S. M.; El-Shahat, M. F. Eur. J. Chem. 2011, 2(1), 104-108. [5]. Kaur, S.; Singh, V. Ultrason. Sonochem. 2007, 14, 531-537. [6]. Liu, W.; Chen, S. F.; Zhao, W.; Zhang, S. J. Desalination 2009, 249, 1288-1293. [7]. Liu, G.; Wang, L. Z.; Yang, H. 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This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). 2019 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.10.1.7-11.1824 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Preparation of ZnTiO3/TiO2 2.2. Characterization of phase and microstructure 2.3. Measurements of photocatalytic performance 3. Results and discussion 3.1. X-ray diffraction analysis 3.2. Morphology and microstructure analysis 3.3. Enhanced photocatalytic performance 3.4. Photocatalytic reaction mechanism of ZnTiO3/TiO2 4. Conclusions Acknowledgments Disclosure statement ORCID References Graphical Abstract PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: