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![Charge-transfer-complex-mediated mechanism for TiO 2 -assisted photodegradation of colorless aromatic pollutants under visible illumination (Figure taken from [156]).](profile/Jeet-Varia/publication/275674130/figure/fig2/AS:391772309082118@1470417205431/Fig-2-Charge-transfer-complex-mediated-mechanism-for-TiO-2-assisted-photodegradation.png)
Charge-transfer-complex-mediated mechanism for TiO 2 -assisted photodegradation of colorless aromatic pollutants under visible illumination (Figure taken from [156]).
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This review is focused on studies related to the elimination of organic pollutants present in aqueous systems by titanium dioxide photocatalyst under visible light illumination. The titanium dioxide semi-conductor has emerged as a very promising technology for the oxidation and mineralization of aqueous organic pollutants because of its properties...
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... on the electronic property of TiO 2 (mixed phases, co-doped or multi-doped TiO 2 , crystallite size, etc.) and the molecular structure of the organic compounds. In visible- light irradiation the photocatalytic degradation of colorless aromatic pollutants by anatase TiO 2 powders proceeded via a charge- transfer-complex (CTC)-mediated pathway (Fig. 2) and a correla- tion between the chemical structure and the degradation rate of these pollutants was observed [156,157]. Wang et al., [156] found that an electron-donating substituent in benzene ring, which raises the highest occupied molecular orbital and lowers the ionization potential of the organic compound, was favorable to the ...
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Citations
... Compared to bulk rutile TiO2, both ER-TiO2 and CR-TiO2 samples had wider band gaps, which may be attributed to the quantum size effect from their nano-size feature [43]. ...
... Nanostructured semiconductors, such as SnO2, ZnO, and TiO2, can be used to detect a wide range of organic pollutants [7][8][9][10][11]. Tin (IV) Oxide (SnO2) is an n-type transparent semiconductor with a wide bandgap of 3.6 eV at 300 K [12,13]. ...
Metal oxide gas sensors have many advantages over other solid-state gas monitoring devices, including low cost, ease of manufacture, and small design. However, the shape and structure of sensing materials have a considerable impact on the performance of such sensors, posing a significant challenge for gas sensing properties on materials or dense films to attain high-sensitivity characteristics. Various tin dioxide (SnO2) nanostructures have been devised to increase gas sensing characteristics such as sensitivity, selectivity, and response time, among other characteristics. An overview of the most well-known techniques for synthesizing gas-sensing films, as well as the influence of doping with various metal oxides, nanoparticle size, and operating temperature on the gas-sensing properties of such films, is discussed in this work. The gas sensing mechanisms and the gas detection techniques are presented in detail. The metal oxide doped SnO2 showed a strong response for SO2 and NO2 gases, whereas nanoparticle doping plays a crucial effect in increasing SnO2 sensitivity towards H2, H2S, NO2, CO, Ethanol, etc. Furthermore, the effect of operating temperature on SnO2 response is discussed in this report. SnO2 has a high sensitivity over a wide temperature range (100-350 C).
... In order to resolve these problems modification of the band energy of TiO 2 is preferred, either by doping with metal/non-metal elements or by dye photosensitization [11][12][13]. In this context, one of the most efficient strategies for increasing TiO 2 photocatalytic efficiency is transition metal doping, which lowers the energy barrier from 3.2 eV to below 3.0 eV [14]. This decrease in the energy gap shifts the photocatalytic activities from UV light to the visible light region. ...
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Nickel-doped titanium dioxide nanoparticles (NDT) deposited on pine cone activated carbon (PAC) have been successfully synthesized by a hydrothermal method. The as synthesized nanocomposite was characterized by X-ray diffraction pattern (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron (XPS), Fourier transform infrared (FT-IR), UV-visible diffuse reflectance spectra (UV-vis DRS), Photoluminescence (PL), BET surface area, and pHzpc. The characterization results of the prepared nanocomposite revealed that Ni-TiO2 was loaded on the surface of PAC, and had a higher surface area and narrower bandgap than TiO2 nanoparticles. The visible-light photocatalytic activity of the Ni-TiO2@C nanocomposite towards anthracene degradation was found to be 99.9% in 50 mins leading to end products of (1E, 3Z)-hexa-1,3,5-trien-1-ol (1a; m/z = 96), and (1E, 3E)-penta-1,3-dien-1-ol. The synthesized Ni-TiO2@C nanocomposite exhibited a better photocatalytic activity towards the photocatalytic degradation of anthracene as compared to the TiO2 nanomaterial (22.5%) and TiO2/activated carbon nanocomposite (31%) under similar conditions. The photodegradation of anthracene followed the pseudo first-order rate kinetics. The Ni-TiO2@C nanocomposite had excellent regeneration properties till the fifth cycle of use during which it degraded around 73% anthracene.
... Nanostructured semiconductors, such as SnO2, ZnO, and TiO2, can be used to detect a wide range of organic pollutants [7][8][9][10][11]. Tin (IV) Oxide (SnO2) is an n-type transparent semiconductor with a wide bandgap of 3.6 eV at 300 K [12,13]. ...
Metal oxide gas sensors have many advantages over other solid-state gas monitoring devices, including low cost, ease of manufacture, and small design. However, the shape and structure of sensing materials have a considerable impact on the performance of such sensors, posing a significant challenge for gas sensing properties on materials or dense films to attain high-sensitivity characteristics. Various tin dioxide (SnO2) nanostructures have been devised to increase gas sensing characteristics such as sensitivity, selectivity, and response time, among other characteristics. An overview of the most well-known techniques for synthesizing gas-sensing films, as well as the influence of doping with various metal oxides, nanoparticle size, and operating temperature on the gas-sensing properties of such films, is discussed in this work. The gas sensing mechanisms and the gas detection techniques are presented in detail. The metal oxide doped SnO2 showed a strong response for SO2 and NO2 gases, whereas nanoparticle doping plays a crucial effect in increasing SnO2 sensitivity towards H2, H2S, NO2, CO, Ethanol, etc. Furthermore, the effect of operating temperature on SnO2 response is discussed in this report. SnO2 has a high sensitivity over a wide temperature range (100-350 C).
... It is important to note that some studies have demonstrated that photocatalytic processes are not characterized by a linear evolution of efficiency-irradiation. In view of this, to optimize the design of the processes it is important to adjust the flow of photons and sources of irradiation to the catalyst substrate and type of pollutant [56]. Globally, in most cases, high efficiency is observed by using UV radiation in the presence of TiO 2 catalysts for the abatement of CEC from water [51]. ...
... Aiming industrial processes applications, the photocatalyst should be active under the visible light spectrum since this is the largest fraction of sunlight radiation [56,58]. The mechanism for photocatalytic activity of TiO 2 under visible light radiation depends on the electronic properties of TiO 2 (crystalline phases, co-doped or multidoped, crystallite size, etc.) and the molecular structure of the organic compounds to be degraded [59,60]. ...
The application of TiO2 as a slurry catalyst for the degradation of contaminants of emerging concern (CEC) in liquid effluents has some drawbacks due to the difficulties in the catalyst reutilization. Thus, sophisticated and expensive separation methods are required after the reaction step. Alternatively, several types of materials have been used to support powder catalysts, so that fixed or fluidized bed reactors may be used. In this context, the objective of this work is to systematize and analyze the results of research inherent to the application of ceramic materials as support of TiO2 in the photocatalytic CEC removal from liquid effluents. Firstly, an overview is given about the treatment processes able to degrade CEC. In particular, the photocatalysts supported in ceramic materials are analyzed, namely the immobilization techniques applied to support TiO2 in these materials. Finally, a critical review of the literature dedicated to photocatalysis with supported TiO2 is presented, where the performance of the catalyst is considered as well as the main drivers and barriers for implementing this process. A focal point in the future is to investigate the possibility of depurating effluents and promote water reuse in safe conditions, and the supported TiO2 in ceramic materials may play a role in this scope.
... Nanostructured materials are widely used in various fields because of their unique properties. Nowadays, nanostructured titania has received much attention due to its high potential in photocatalytic applications, self-cleaning coatings, photovoltaic, heavy metal removal from industrial effluents, ceramic membranes, and gas sensors [1]. Among nanostructured materials, TiO 2 as a semiconductor is very useful in these applications. ...
In this study, several TiO2 mesoporous nanoparticles with different mol% of niobium and silver were synthesized using the sol–gel method. The crystalline phase, chemical state, photocatalytic and optical properties, specific surface area, and morphology of mesoporous nanoparticles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis reflective spectroscopy (UV–Vis), Brunauer–Emmett–Teller-specific surface area (BET) and field emission scanning electron microscopy (FESEM). With increasing calcination temperature, the photocatalytic activity of the samples gradually increased due to the improvement of crystallization of the anatase and rutile phases. Nb/Ag codoping sample calcined at 550 °C has reduced the band gap energy (3.17 eV to 3.06 eV) and improved the photocatalytic properties of samples under visible light (xenon lamp, 200 W for 1 h and 2 h). Doped TiO2 mesoporous nanoparticles were shown to have the highest photocatalytic activity as compared with the pure TiO2 nanoparticles. The best photocatalytic efficiency of codoped TiO2 mesoporous nanoparticles was observed for the TNA3 sample calcined under 550 °C, containing molar contents of Nb (0.5 mol%) and Ag (1 mol%) dopant ions with 95.60% efficiency.
Synthesis of Nb/Ag-codoped TiO2 (TNA) nanoparticles by sol–gel method
... The direct reaction of electrons or holes with the contaminants can also occur. However, the electron-hole pairs formation only takes place when energy is equal or higher than the band-gap energy (E g ), which usually ranges between 3.0 and 3.2 eV, 7,8 and that is attained only with UV radiation (wavelengths ≤400 nm). The greener irradiation process is using sunlight but it has only less than 8% of UV radiation in its spectrum. ...
... To accomplish these goals, some strategies have been proposed, such as metal and non-metal doping, or combination with other functional materials. 7,[9][10][11][12][13] Composites of TiO 2 with graphene-family materials have been pointed as very efficient photocatalysts. [14][15][16][17] Graphene is a two-dimensional carbon nanomaterial with a honeycomb structure made of sp 2 carbons. ...
Formalin or hydrate of formaldehyde, a common disinfectant used in aquaculture, is not able to absorb sunlight, therefore its photodegradation must be catalyzed. To take advantage of sunlight for its photodegradation, TiO2-reduced graphene oxide (TiO2-rGO) nanocomposites with different GO contents (0.25-3.0wt%) were synthesized and characterized by scanning electron microscopy (SEM), UV-vis and ATR-FTIR spectroscopies. Additionally, their specific surface areas (SBET), pore volume and size were determined. The photocatalysts efficiency for formaldehyde (FM) degradation under simulated sunlight was assessed in aqueous solution. Among the nanocomposites considered, TiO2-rGO 0.5wt% was the most efficient, achieving 93.8±4.6 % of FM photodegradation in 90 min. The same irradiation conditions were applied in natural water matrices (aquaculture's freshwater and saltwater) to evaluate the influence of natural water constituents on photocatalysis. The photodegradation percentages obtained were 63.7±0.6 % and 16.0±1.4 % in aquaculture's freshwater and saltwater, respectively. This lower efficiency to photodegrade FM in natural aqueous matrices is attributed to the inhibition of photocatalytic oxidation of organic compounds caused by dissolved organic matter (DOM) and inorganic ions existing in the aquatic environment. Nevertheless, the results obtained for photocatalytic efficiency in natural waters are promising, suggesting a great potential of application in green photocatalysis to remove FM from contaminated freshwater.
... Higher concentrations of H 2 O 2 were produced with activated sludge in the anode chamber and the addition of the electron mediator ADQS to the anode. Cr 3+ reduction could occur via direct electrochemical reduction or via electrochemically-produced H 2 O 2 [186]. H 2 O 2 was shown to be a superior reducer because when H 2 O 2 was not formed (i.e., when the chamber was gassed with N 2 ), Cr 6+ was reduced at lower rates and lower removal efficiencies (42.5% with nitrogen after 12 h vs. about 100% with air after 4 h). ...
... ) and H 2 O 2 [186], which might also have contributed to the higher Cr 6+ reduction rates. ...
... Higher concentrations of H 2 O 2 were produced with activated sludge in the anode chamber and the addition of the electron mediator ADQS to the anode. Cr 3+ reduction could occur via direct electrochemical reduction or via electrochemically-produced H 2 O 2 [186]. H 2 O 2 was shown to be a superior reducer because when H 2 O 2 was not formed (i.e., when the chamber was gassed with N 2 ), Cr 6+ was reduced at lower rates and lower removal efficiencies (42.5% with nitrogen after 12 h vs. about 100% with air after 4 h). ...
... ) and H 2 O 2 [186], which might also have contributed to the higher Cr 6+ reduction rates. ...
Raw metals are fundamental to the global economy as they are essential to maintain the quality of our life as well as industrial performance. A number of metal-bearing aqueous matrices are appealing as alternative supplies to conventional mining, like solid industrial and urban waste leachates, wastewaters and even some natural extreme environments (e.g. deep marine sediments, geothermal brines). Some of these sources are already managed for recovery, while others are not suitable either because they are too low in content of recoverable metals or they contain too many impurities that would interfere with classical recovery processes or would be cost-prohibitive. Microbial electro-metallurgy, which results from the interactions between microorganisms, metals and electrodes, in which the electron transfer chain associated with microbial respiration plays a key role, can contribute to overcome these challenges. This review provides the state of the art on this subject, and summarizes the general routes through which microbes can catalyse or support metal recovery, leading to nano- and macro-scale materials. Competing sorption and electrochemical technologies are briefly revisited. The relevant sources of metals are highlighted as well as the challenges and opportunities to turn microbial electro-metallurgy into a sustainable industrial technology in the near future. Finally, an outlook to pursue functional materials through microbial electrometallurgy is provided.
... Therefore, the development of photocatalysts showing a high activity under visible light irradiation is needed in order to be able to use the sunlight or rays from artificial sources more effectively in photocatalytic reactions. Many studies have attempted to develop visible light-sensitive photocatalysts using, for example, TiO 2 doped with metallic nanoparticles (NPs) such as Au, Ag or Cu [2][3][4][5]. This approach seems to be of interest for improving the photocatalytic effect in visible light due to the localized surface plasmon resonance band (LSPR) of the metallic NPs, which induces a high absorption in the visible range. ...
The microstructuring of the distribution of silver nanoparticles (NPs) in mesoporous titania films loaded with silver salts, using two-beam interference lithography leading to 1 Dimension (1D) grating, induces variations in the photocatalytic efficiency. The influence of the structuration was tested on the degradation of methyl blue (MB) under ultraviolet (UV) and visible illumination, giving rise to a significant improvement of the photocatalytic efficiency. The periodic distribution of the NPs was characterized by transmission electron microscopy (TEM), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscopy (SEM).
