Synthesis and enhanced photocatalytic activity of nitrogen-doped triphasic TiO2 nanoparticles
Introduction
Titanium dioxide (TiO2) nanopowders containing two or more polymorphs are of interest for photocatalytic and photovoltaic applications due to the enhanced photoactivity resulting from the synergistic effect of the mixed phases [[1], [2], [3]]. In the last decade, the synergistic effect of anatase and rutile heterojunctions has been studied extensively [4,5]. However, mixtures including the brookite phase have been overlooked due to the lesser photocatalytic activity and rather low thermodynamic stability of brookite.
TiO2 has three common polymorphs, namely anatase, rutile, and brookite. The phase transformation among the polymorphs of TiO2 depends on different factors, such as particle size, surface acidity and energy, and solution chemistry [6,7]. The transformation enthalpies of anatase to rutile and brookite to rutile suggest that the thermodynamic phase stability of the three polymorphs is in the order of rutile, brookite, and anatase [8]. In addition, calorimetric data suggest that anatase either transforms directly to rutile or transforms first to brookite and then to rutile. Nevertheless, it is not certain whether anatase transforms to brookite or vice versa.
The photocatalytic performance of TiO2 powders largely depends on their synthesis method and conditions, which affect the morphology, grain size, crystallite size, surface area, distribution of phases, and other additives [[9], [10], [11], [12]]. Anatase is considered to have better photocatalytic activity than either rutile or brookite does. Especially, the mixed phase of anatase/rutile TiO2 has synergistic effects with interfacial electron transfer and higher photocatalytic activity compared with the pure anatase or rutile phase [5]. A mixture of anatase and brookite or rutile and brookite, as well as three-phase anatase, brookite, and rutile, has also been observed to exhibit high photocatalytic activity [[13], [14], [15]]. Anatase, brookite, and rutile mixtures are photoactive for the degradation of methyl orange (MO) [16], methylene blue (MB) [17], acetaldehyde [18], 4-nitrophenol [19], 4-chlorophenol [20], and NOx [21]. However, there have been few studies on the evolution of TiO2 powders containing ternary mixtures of the anatase, brookite, and rutile phases by the hydrothermal process. Further research is needed for clarifying the ambiguity concerning the formation and phase transformation among the three phases of TiO2 and understanding the effect of three-phase-containing TiO2 nanoparticles on the photodegradation of organic substances.
In this study, N-doped TiO2 nanoparticles containing anatase, brookite, and rutile mixtures were synthesized using a one-step HNO3-assisted hydrothermal process for enhancing the photocatalytic activity of TiO2 particles. The results revealed that the present phases and their proportions in the nanoparticles could easily be tuned by changing the temperature of the hydrothermal dwell. N doping was established for all the samples in different amounts, depending on the phases present. Enhanced photoactivity was obtained using triphasic TiO2 with the highest amount of N as an interstitial dopant.
Section snippets
Synthesis
The N-doped TiO2 nanoparticles were synthesized through a procedure described previously in [22], although major modifications were made. The synthesis started with diluting concentrated HNO3 (Aldrich 70%) using distilled water to obtain 1 M HNO3 solution (0.06 HNO3/H2O volume ratio). Following this, 10 mL of titanium tetra isopropoxide (TTIP; Aldrich 97%) was added dropwise to the freshly prepared, diluted HNO3 solution. The mixture was continuously stirred at 300 rpm for 15 min; the solution
XRD, Raman, and XPS analysis
The XRD patterns of the TiO2 nanoparticles synthesized via 1 M HNO3–assisted hydrothermal treatment at different temperatures are shown in Fig. 1a. The nanoparticles show the characteristic peaks corresponding to the anatase (PDF no. 12-1272), brookite (PDF no. 29-1360), and/or rutile (PDF no. 21-1276) phase, depending on the synthesis conditions. No peaks belonging to other TiO2 phases or contaminations were detected. It should be noted that the synthesis temperature had a major effect on the
Conclusions
It is possible to synthesize N-doped TiO2 nanoparticles containing only the anatase phase, binary anatase–brookite phases, and ternary anatase–brookite–rutile phases via a facile, one-step hydrothermal process using a HNO3 catalyzer. The hydrothermal synthesis temperature has a profound effect on the type and amount of the TiO2 nanoparticles synthesized. N doping is mostly related to the crystal structure of the particles. Increasing the N placement in the structure may enhance the
Acknowledgements
This work was carried out for the KONNECT Joint Call on “Resources and Sustainability: Strengthening STI Cooperation between the EU and Korea.” The authors would like to thank the Scientific and Technological Council of Turkey (TUBITAK), project number 216M391, for providing the partial grant. This work was also partially supported by project VEGA 2/0010/18 (Slovak Republic).
References (33)
- et al.
Low-temperature synthesis of anatase-brookite composite nanocrystals: the junction effect on photocatalytic activity
J. Colloid Interface Sci.
(2005) - et al.
Highly photocatalytic activity of brookite/rutile TiO2 nanocrystals with semi-embedded structure
Appl. Catal. B Environ.
(2016) - et al.
Photocatalytic activity of nanocrystalline TiO2 (brookite, rutile and brookite-based) powders prepared by thermohydrolysis of TiCl4 in aqueous chloride solutions
Colloids Surf. A
(2008) - et al.
Synthesis and enhanced photocatalytic activity of molybdenum, iron, and nitrogen triple-doped titania nanopowders
Ceram. Int.
(2016) - et al.
Hydrothermal synthesis of 3D TiO2 nanostructures using nitric acid: characterization and evolution mechanism
Ceram. Int.
(2016) - et al.
Factors influencing the photocatalytic degradation of Rhodamine B by TiO2-coated non-woven paper
J Photochem. Photobiol. A: Chem
(2008) - et al.
Self-induced synthesis of phase-junction TiO2 with a tailored rutile to anatase ratio below phase transition temperature
Sci. Rep.
(2016) - et al.
Enhancement of dye-sensitized solar cells efficiency using mixed-phase TiO2 nanoparticles as photoanode
Scanning.
(2017) - et al.
Synthesis and catalytic applications of non-metal doped mesoporous titania
Inorganics
(2017) - et al.
Synergistic effect between TiO2 sol-gel and degussa P25 in dye photodegradation
J. Solgel Sci. Technol.
(2013)
Synergistic effect between anatase and rutile TiO2 nanoparticles in dye-sensitized solar cells
Dalton Trans.
Study of the anatase to rutile transformation kinetics of the modified TiO2
Pol. J. Chem. Technol.
Phase stability and transformation in titania nanoparticles in aqueous solutions dominated by surface energy
J. Phys. Chem. C
J. Energetics of nanocrystalline TiO2
Colloquium
Preparation of porous TiO2 photocatalyts with different crystal phases and high catalytic activity by simple calcination of titanate nanofibers
RSC Adv.
Synthesis, characterization and photocatalytic activity of mesoporous Na-Doped TiO2 nano-powder prepared via a solvent-controlled non-aqueous sol–gel route
RSC Adv.
Cited by (17)
Nitrogen doped titanium dioxide (N-TiO<inf>2</inf>): Electronic band structure, visible light harvesting and photocatalytic applications
2023, Journal of Water Process EngineeringA critical review on N-modified TiO<inf>2</inf> limits to treat chemical and biological contaminants in water. Evidence that enhanced visible light absorption does not lead to higher degradation rates under whole solar light
2022, Journal of Hazardous MaterialsCitation Excerpt :In contrast, the sol-gel method has another variant. This variant consists in utilizing Teflon-lined stainless-steel autoclaves, which allow thermal treatment at temperatures below 220 °C for hours or days in the presence of water, thereby obtaining crystalline materials with interesting textural characteristics (Marques et al., 2019; Peng et al., 2008; Ramacharyulu et al., 2015; D’Arienzo et al., 2009; Erdogan et al., 2019; Wu et al., 2010; DArienzo et al., 2010). Herein, a combined synergistic effect of temperature and pressure creates favorable conditions for obtaining crystalline materials of TiO2.
Effects of fluorination and thermal shock on the photocatalytic activity of Bi<inf>2</inf>O<inf>3</inf> nanopowders
2021, Colloids and Surfaces A: Physicochemical and Engineering AspectsElucidation of the photocatalytic degradation mechanism of an azo dye under visible light in the presence of cobalt doped TiO<inf>2</inf> nanomaterials
2021, ChemosphereCitation Excerpt :The photocatalytic efficiency of TiO2 photocatalyst is closely depending on the recombination rate of the photogenerated electron-hole pairs (Chen et al., 2015). In order to have an efficient photocatalyzed reaction and thus improve the effectiveness of the photocatalyst, the recombination of the (e−/h+) pairs following to the initial charge separation should be decelerated as much as possible (Schneider et al., 2014; Peng et al., 2017; Erdogan et al., 2019; Bouziani et al., 2020). Therefore, in a quest of the improvement of the photosensitization of TiO2 in the visible domain, the modification of the electronic structure by doping TiO2 with transition metal ions (Liu et al., 2017; Cerdán-Pasarán et al., 2019; Komaraiah et al., 2019) is one of the methods used by many research groups to overcome this problem.
Evolution of the physicochemical and photocatalytic properties of BaO embedded in bismuth phosphovanadates glasses
2021, Chemical Physics LettersInfluence of Sr-doping on structural, optical and photocatalytic properties of synthesized Ca<inf>3</inf>(PO<inf>4</inf>)<inf>2</inf>
2020, Journal of Colloid and Interface ScienceCitation Excerpt :The key advantage of this method is that it can generate hydroxyl radicals (OH•) in aqueous medium. Therefore, they are the major contributor for organic pollutant oxidation and their final mineralization into carbon dioxide and water [14–19]. In this regard, phosphates have gained tremendous attention due to their uniqueness in electrical, optical, magnetic and catalytic behavior [20–22].