Degradation of organic pollutants using metal-doped TiO2 photocatalysts under visible light: a comparative study (original) (raw)
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Preparation of Mg-doped TiO2 nanoparticles for photocatalytic degradation of some organic pollutants
Studia Universitatis Babeș-Bolyai Chemia, 2019
In this study, the sol-gel method was used to prepare Mgdoped TiO2 nanoparticles from titanium tetraisopropoxide and magnesium sulfate as the dopant precursors. Mg-doped TiO2 shows the formation of anatase phase with polyhedral and spherical particles with an average size of 25-30 nm. X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and photoluminescence were used to characterize the prepared material. The photocatalytic degradation performance of rhodamine B, nonylphenol ethoxylates, pseudoephedrine hydrochloride, and nicotine on Mg-doped TiO2 was studied under UV irradiation. The photocatalytic degradation shows that 98.92, 98.00, 98.00 and 97.95% of rhodamine B, nonylphenol ethoxylates, pseudoephedrine hydrochloride, and nicotine was decomposed by Mg-doped TiO2, respectively.
M-doped TiO 2 (M = Ag 2? , Al 3? , Ce 4? , Nb 5? ) with different dopant contents have been prepared by the Pechini method using titanium IV isopropoxide as precursor. The effect of doping concentration on the photocatalytic activity for methyl orange (MO) photodegradation was investigated using UV radiation. The photocatalysts were characterized by surface area, X-ray diffraction and UV-Vis diffuse reflectance spectroscopy. An increase in the photoactivity of TiO 2 nanoparticles was confirmed by MO photocatalytic degradation experiments, when the transition metal ions were incorporated into the semiconductor crystalline lattice, which could be attributed to an increase in the charge separation and reduction of e -/h ? recombination as a function of the substitutional defect generated at very low levels.
2013
Titanium dioxide (Titania; TiO 2) is one of the most widely used metal oxide semiconductor in the field of photocatalysis for removal of pollutants. It has been noted that titanium dioxide is a research friendly material as its physico-chemical and catalytic properties can be easily altered as per specific application. Since many years, researchers have tried to modify the properties of titanium dioxide by means of doping with metals and non-metals to improve its performance for photocatalytic degradation (PCD) applications. The doping of various metal ions like Ag, Ni, Co, Au, Cu, V, Ru, Fe, La, Pt, Cr, Ce, etc. in titanium dioxide have been found to be influencing the band gap, surface area, particle size, thermal property, etc. and therefore the photocatalytic activity in PCD. Moreover, photocatalytic activity of doped titanium dioxide has been observed in visible light range (i.e., at wavelength >400 nm). In this review, different synthesis route for doping of metal ions in titanium dioxide have been emphasised. The effect of metal dopant on the structural, textural and photocatalytic properties of titanium dioxide has been reviewed.
Revista Facultad …, 2011
In this work, TiO 2 photocatalysts were synthesized using a conventional sol-gel and hydrothermal synthesis methods with steam pressure treatment. Photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS) and N 2 adsorption-desorption. The photoactivity of the samples was analyzed towards the photooxidation of the azo dye Orange II (Or-II) and phenol using different illumination setups to compare the activity features of photocatalysts. The effect of the synthesis variables such as the synthesis route, water/alcoxide and alcohol/alcoxide ratios, as well as the alcohol type was analyzed. TiO 2 photocatalysts obtained by hydrothermal synthesis have a better photoactivity than the particles synthesized by the chosen sol-gel route, reaching the Or-II degradation photoactivity of the commercial TiO 2 P25. On the other hand, the water/alcoxide ratio and alcohol type have a marked effect on the photoactivity of the hydrothermal synthesized TiO 2 , whereas the alcohol/alcoxide ratio does not have a relevant effect on the Or-II degradation photoactivity.
Abstract In this study the efficiency of different bare, doped and composite photocatalysts were compared, under UV and visible light irradiation in order to show a detailed picture of the relative performance of the best photocatalysts developed in our laboratories and the mostly investigated reference titanias. The syntheses of our photocatalysts were optimized in order to achieve maximum photocatalytic activity under UV and visible light irradiation. Non doped commercial (Aeroxide P25, Aldrich anatase) and synthesized titanias (produced by sol-gel and flame hydrolysis techniques) and nitrogen, iron, iodine doped and silver or gold deposited titanium dioxides were investigated with two model pollutants (phenol and oxalic acid) under identical experimental conditions. The material properties of these selected photocatalysts were thoroughly characterized by X-ray diffraction, diffuse reflectance spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy and BET methods. The highest degradation rate of phenol was determined for the flame made titania sample with relatively low specific surface area (20 m2/g) when UV irradiation was applied. In contrast with that, our nitrogen doped photocatalyst with high specific surface area (139 m2/g) was the best for phenol degradation under visible light irradiation. Although the most efficient oxalic acid mineralization occurred with noble metal photodeposited samples under UV irradiation, this type of modification was detrimental when VIS irradiation is applied. The decomposition rate of oxalic acid was maximum under VIS irradiation using the iron and nitrogen doped photocatalysts. For both substrates and irradiation conditions our best photocatalysts were found to be significantly more active than Aeroxide P25 TiO2. Intermediate studies revealed that phenol degradation resulted in dihydroxy benzene intermediates, such as pyrocatechol and hydroquinone both under UV and visible light irradiation with our TiO2-N photocatalyst. The results of this comparative study could promote the determination of the optimal synthesis conditions of titanium dioxide based photocatalysts for a given organic pollutant in water.
Synthesis of Mg-Doped TiO2 nanoparticles under different conditions and its photocatalytic activity
Photochemistry and photobiology
In this study, TiO(2)- and Mg-doped TiO(2) nanoparticles with different dopant contents were prepared by sol-gel method. The prepared photocatalysts were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) and diffuse reflectance spectroscopy (DRS) techniques. The results of BET analysis indicated a pore diameter of 8 nm and surface area of 48.5 m(2) g(-1). XRD patterns of pure and doped TiO(2) nanoparticles at 450 °C revealed that all phases are anatase. The particle size obtained from TEM was less than 20 nm. The band gap energy of Mg-doped TiO(2) nanoparticles was lower than that of TiO(2) . The photocatalytic activity of the pure and doped nanoparticles has been compared in the removal of C.I. Acid Red 27 (AR27). The photocatalytic activity of Mg-doped (0.2 mol%) TiO(2) for the degradation of AR27 was higher than that of bare TiO(2) nanoparticles. Results of total organic carbon anal...
Materials Today: Proceedings, 2019
The application of heterogeneous photocatalysis is described as an advanced oxidation process (AOP) for the degradation of the diazo reactive dye using immobilized TiO 2 as a photocatalyst. Starting TiO 2 solutions were prepared with and without the addition of polyethylene glycol (PEG) and TiO 2 films were directly deposited on a borosilicate glass substrate using the sol-gel dip-coating method. The surface morphology and the nanoscale roughness of TiO 2 films were studied by means of atomic force microscopy (AFM). Structural properties of TiO 2 were identified by Xray diffraction (XRD). The decomposition behaviour of organic compounds from the gels was investigated using thermal gravimetry (TG) and differential scanning calorimetry (DSC). Photocatalytic activities of TiO 2 films in the process of degradation of the commercial diazo textile dye Congo red (CR), used as a model pollutant, were monitored by means of UV/vis spectrophotometry. The kinetics of the degradation of the CR dye was described with the Langmuir-Hinshelwood (L-H) kinetic model. The addition of PEG to the TiO 2 solution resulted in the changes in the film surface morphology, and affected the ratio of anatase-rutile crystal phases and the photocatalytic activity of TiO 2. The TiO 2 film prepared with PEG is characterized by higher roughness parameters (R a , R max , R q , R z and Z max), a lower amount of the rutile phase of TiO 2 , a higher amount of the anatase phase of TiO 2 and a better photocatalytic activity compared to the TiO 2 film without the addition of PEG.
Journal of Analytical Science and Technology, 2016
Background: A simple hydrothermal process was applied to synthesize the doped TiO 2 particles with different concentrations as well as different metal ions (Mn, Ce and La). Methods: The synthesis of Mn-doped-TiO 2 nanoparticles was done by using a hydrothermal method from hydrolysis of titanium tetrachloride in aqueous solution. The photocatalytic activities were checked by studying the degradation of two model organic pollutants. Results: The material was characterized by X-ray diffraction, scanning electron microscopy, and UV-Visible spectroscopy. The X-ray diffraction pattern studied for doped TiO 2 particles suggests the anatase phase with a crystalline nature. Doped TiO 2 particles showed a porous and complex nature with a highly rough surface. The photocatalytic activity of Mn-Ce-and La-doped TiO 2 with different metal-ion concentrations of 0.15-0.60% show that the degradation rate of all of the pollutants increases with an increase in the dopant concentration from 0.15 to 0.45%, and a further increase in the dopant concentration decreased the degradation rate. Conclusions: The results indicate that TiO2 with a concentration of 0.45% for all metal ions (Mn, Ce and La) shows the highest activity. Among studied dopent TiO2 with Mn (0.45%) showed the best degradation activity.
Egyptian Journal of Petroleum, 2014
M-doped TiO 2 nanoparticles (M = Cu, Zn) were prepared by the sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and UV-vis spectroscopy techniques were used to characterize the samples. Photocatalytic activities of samples for methyl orange (MO) degradation and the chemical oxygen demand (COD) were investigated. XRD results confirmed the formation of the anatase phase for the TiO 2 nanoparticles, with crystallite sizes in the range of 9-21 nm. The small crystallite size and doping ions (Cu and Zn) inhibited any phase transformation and promoted the growth of the TiO 2 anatase phase. The optical study showed that doping ions lead to an increase in the absorption edge wavelength, and a decrease in the band gap energy of TiO 2 nanoparticles. The doped TiO 2 nanoparticles in general showed higher photocatalytic activities than the pure ones. The Cu doped TiO 2 nanoparticles showed the best photocatalytic activity based on the measured COD values.
Enhanced photocatalytic activity of multi-doped TiO2 for the degradation of methyl orange
Applied Catalysis A: General, 2012
We report the synergistic effect of dopants like Gd, N and S in enhancing the photocatalytic activity of TiO 2. Nanosized TiO 2 doped at both cationic and anionic sites by Gd, N and S exhibited increased photocatalytic activity compared to TiO 2 doped with either Gd or N and S. All the doped TiO 2 existed as anatase phase and no separate phase due to Gd 2 O 3 was seen up to a Gd concentration of 2%. The particle size as seen from the transmission electron micrograph was ∼25 nm. The optical absorption property of TiO 2 was improved by doping and redshift of the absorption edge is seen for all doped samples compared to pristine TiO 2. The red shift of the absorption edge was the highest for the multiple ion-doped sample. Presence of bonded N and S in TiO 2 was detected by X-ray photoelectron spectroscopy. Fluorescence lifetime studies indicated an enhanced lifetime for the charge carriers in the doped system compared to pristine TiO 2. Photocatalytic activity study showed that the multi-doped sample has the highest activity for the degradation of methyl orange compared to Gd-TiO 2 , NS-TiO 2 and pristine TiO 2. The enhanced photocatalytic activity of the multi-doped TiO 2 is attributed to factors such as improved optical absorption property and improved lifetime of the charge carriers.