Synergistic Effect of Cu,F‐Codoping of Titanium Dioxide for Multifunctional Catalytic and Photocatalytic Studies

Abstract

This material has been used as a photo catalyst for water splitting since 1972 when Fujishima and Honda reported its ability to generate hydrogen and oxygen from water molecules. [1] Titanium dioxide is normally used in advanced oxidation processes, [2] in systems capable of elimi nating a wide variety of chemicals in air and water, as well as solar fuel production (such as H 2 ). [3,4] The photoactivated pro cesses of titanium dioxidebased photo catalysts are achieved when the irradiation energy is higher than its band gap. This generates electrons in the conduction band and holes in valence band, which rapidly migrate to the TiO 2 surface and provoke the generation of extremely reactive spe cies. For example, H 2 O 2 and the radicals OH • , O 2-• formed after the electron and the holes reach the external surface of titanium dioxide, are very important for the photodecomposition of organic pol lutants to CO 2 and H 2 O, which is true for the most active titanium dioxidebased materials. [5,6] The band gap value has a direct impact on the rate of electronhole (e --h +) recombination during the photocatalytic processes. In the case of titanium dioxide, the relatively large band gap, means there is a slow recombination rate compared to most of the other photocatalysts. [7] Three main phases are present in TiO 2 : 1) Anatase (tetrag onal, a = b = 3.785 Å, c = 9.54 Å), 2) brookite (orthorhombic, a = 5.143 Å, b = 5.456 Å, c = 9.182 Å), and 3) rutile (tetragonal a = b = 4.593 Å, c = 2.959 Å). [8,9] The thermodynamically meta stable phases, anatase, and brookite, irrevocably pass into the stable phase of rutile at high temperatures. [7] Each of these phases show its own morphological characteristics and band gap value: In the case of anatase the band gap is of 3.2 eV, while rutile and brookite have band gaps of 3.0 and 3.3 eV, respec tively. In general, anatase shows the most attractive photocata lytic behavior due to its versatility and textural properties. [10][11][12] However, the anatase phase, due to its band gap, can only be activated by UV light, which accounts for approximately only 4% of the solar spectrum. Thus, in order to stabilize the anatase phase at elevated temperatures, and to utilize UV and visible light for photocatalysis, chemical modifiers and dopants are generally employed for the modification of the photocatalytic Titanium dioxide nanomaterials with improved catalytic and photo catalytic properties through codoping with copper and fluorine are synthesized and contain optimal textural and compositional properties, which are not possible without doping or with a single doping of Cu or F separately. The codoped systems promote the generation of a synergistic effect increasing activity of the systems in photocatalytic processes of both potential environmental or energy interest. The photocatalysts show very effective degradations of industrial and emerging contaminants such as ciprofloxacin (80% degradation) and naproxen (72% degradation) using UV light (300 W) in short periods of up to 15 min. An ad...

Modulation of the photocatalytic activity and crystallinity of F-TiO2 nanoparticles by using green natural carboxylic acids

“…S7 of the ESI †), one can observe that the F-doped material does not show peaks corresponding to brookite, promoting the formation of a material composed mainly of the anatase phase. Therefore, as confirmed previously for analogous systems, 25,26 F-doping inhibits the formation of brookite. Even though the calcinations at temperatures higher than 550 °C favour the transition to rutile, 25,26,40 in the case of F-TiO 2 -NA-500 with a calcination temperature below 550 °C, the anatase phase seems to be the unique crystalline phase.…”

“…Therefore, as confirmed previously for analogous systems, 25,26 F-doping inhibits the formation of brookite. Even though the calcinations at temperatures higher than 550 °C favour the transition to rutile, 25,26,40 in the case of F-TiO 2 -NA-500 with a calcination temperature below 550 °C, the anatase phase seems to be the unique crystalline phase. Furthermore, the presence of fluorine lowers the crystallite size when compared with the non-doped material TiO 2 -NA-500, which is related to the presence of Ti 3+ centres.…”

“…It seems that F-doping is associated with a growth in the porosity of the system, as previously reported by our group 25,72 and with an increase in the pore diameter (D p ) and pore volume (V p ), compared with its non-doped analogue. This fact is in agreement with the photocatalytic results which show a higher photodegradation activity in F-doped systems.…”

“…In addition, our interest is also focused on preparing F-doped TiO 2 materials as these preferentially form ultrareactive {001} facets [20][21][22] and exhibit optimal structural properties for applications in photocatalysis. [23][24][25][26] Suzuki-Miyaura and similar cross-coupling reactions (Heck, Buchwald-Hartwig, etc.) are versatile tools for specific organic syntheses in both academic and industrial contexts.…”

“…[33][34][35] Usually, these supports play only a structural role in the catalytic process, although there are occasions in which their role is also crucial. 25 The active metal-support strength has a significant effect on catalyst performance. Depending on the material used, it can influence the electronic environment of the active sites, affecting their morphology and activity.…”