Potential dopant in photocatalysis process for wastewater treatment-a review

Nowadays, too much pollution has happened around us, and one of them is water pollution, which each day has become more severe and worse. One of the sources of water pollution comes from the industry that has used dyes either excessively or not. In case of that, the wastewater needs to be treated before released to the river or environment. In this paper, a review of the wastewater treatment using dopants such as nitrogen and magnesium, will be discussed

Highly Efficient Visible-Light-Induced Photocatalytic Activity of Fe-Doped TiO2 Nanoparticles

Bare TiO2 and nominal 5.0 at% Fe-doped TiO2 nanoparticles were synthesized by the modified sol-gel method. The samples were physically characterized in order to obtain the correlation between structure and photocatalytic properties by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett and Teller (BET), and UV-vis diffuse reflectance spectrophotometry (UV-vis DRS). XRD results indicated that phase structures of bare TiO2 and Fe-doped TiO2 nanoparticles were the mixture of anatase and rutile phases. The content of rutile phase in 5.0 at% Fe-doped TiO2 nanoparticles decreased . TEM images revealed that the shape of bare and 5.0 at% Fe-doped TiO2 was almost spherical and the average particle size was in the range of 10-30 nm. Specific surface areas of the samples were found as 75 and 134 m2/g for bare TiO2 and nominal 5.0 at% Fe-doped TiO2, respectively. The results from UV-vis reflectance spectra clearly indicated the shift of absorption band edge towards visible region upon doping TiO2 with iron. Photocatalytic activity of bare TiO2 and 5.0 at% Fe-doped TiO2 nanoparticles was examined by studying the mineralization of oxalic acid under visible light irradiation and the results clearly showed that Fe-doped TiO2 sample exhibited higher activity than bare TiO2

Synthesis and Characterization of the Novel BiVO4/CeO2 Nanocomposites

Novel BiVO4/CeO2 nanocomposites were synthesized by the hydrothermal method combined with the homogeneous precipitation method. The mole ratios of BiVO4:CeO2 were 0.4:0.6, 0.5:0.5, and 0.6:0.4. The obtained BiVO4/CeO2 nanocomposites were characterized by X-ray diffraction (XRD) for phase composition and crystallinity. Particle sizes, morphology and elemental composition of BiVO4/CeO2 composites were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The Brunauer, Emmett and Teller (BET) adsorption-desorption of nitrogen gas for specific surface area determination at the temperature of liquid nitrogen was performed on all samples. UV-vis diffuse reflectance spectra (UV-vis DRS) were used to identify the absorption range and band gap energy of the composite catalysts. The results indicated that BiVO4/CeO2 samples retained monoclinic scheelite and fluorite structures. The morphologies of nanocomposite samples consisted of rod-like, plate-like and spheroidal shapes. Specific surface area (SSABET) of the novel synthesized catalysts drastically increased from 38 - 150 m2/g whereas an average BET-equivalent particle diameter (dBET) significantly decreased from 30 - 12 nm, upon increasing the amount of CeO2 in the BiVO4/CeO2 composite. The absorption spectra of all nanocomposite samples were shifted to the visible region, suggesting the potential application of this novel composite as an active visible-light driven photocatalyst

Photocatalytic Degradation of Phenol Using Nb-Loaded ZnO Nanoparticles

Niobium-doped Zinc Oxide nanoparticles (Nb-doped ZnO NPs) in the range of 20 and 40 nm were synthesized by Flame Spray Pyrolysis (FSP) technique. The crystalline phase, morphology and size of the nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-vis spectroscopy. The specific surface area of the nanoparticles was measured by nitrogen adsorption (BET analysis). The pure ZnO and Nb-doped ZnO NPs were found to have the clear spherical, hexagonal and rod-like morphologies. To the best of our knowledge, the application of Nb-doped ZnO NPs as a photocatalyst has not been reported yet. In this study, the photocatalytic activities of pure ZnO and Nb-doped ZnO NPs were determined by studying the mineralization of phenol under UV light illumination. The results indicated that all Nb-doped ZnO NPs have better photocatalytic activity than the pure ZnO nanoparticles. It was found that, 0.50 mol% Nb-doped ZnO NPs exhibited the fastest response to the degradation of phenol

Kinetics Study of Photocatalytic Activity of Flame-Made Unloaded and Fe-Loaded CeO 2

Unloaded CeO2 and nominal 0.50, 1.00, 1.50, 2.00, 5.00, and 10.00 mol% Fe-loaded CeO2 nanoparticles were synthesized by flame spray pyrolysis (FSP). The samples were characterized to obtain structure-activity relation by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Brunauer, Emmett, and Teller (BET) nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), and UV-visible diffuse reflectance spectrophotometry (UV-vis DRS). XRD results indicated that phase structures of Fe-loaded CeO2 nanoparticles were the mixture of CeO2 and Fe2O3 phases at high iron loading concentrations. HRTEM images showed the significant change in morphology from cubic to almost-spherical shape observed at high iron loading concentration. Increased specific surface area with increasing iron content was also observed. The results from UV-visible reflectance spectra clearly showed the shift of absorption edge towards longer visible region upon loading CeO2 with iron. Photocatalytic studies showed that Fe-loaded CeO2 sample exhibited higher activity than unloaded CeO2, with optimal 2.00 mol% of iron loading concentration being the most active catalyst. Results from XPS analysis suggested that iron in the Fe3+ state might be an active species responsible for enhanced photocatalytic activities observed in this study

Photocatalytic Mineralization of Organic Acids over Visible-Light-Driven Au/BiVO 4

Au/BiVO4 visible-light-driven photocatalysts were synthesized by coprecipitation method in the presence of sodium dodecyl benzene sulfonate (SDBS) as a dispersant. Physical characterization of the obtained materials was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), UV-Vis diffuse reflectance spectroscopy (DRS) and Brunauer, and Emmett and Teller (BET) specific surface area measurement. Photocatalytic performances of the as-prepared Au/BiVO4 have also been evaluated via mineralizations of oxalic acid and malonic acid under visible light irradiation. XRD and SEM results indicated that Au/BiVO4 photocatalysts were of almost spherical particles with scheelite-monoclinic phase. Photocatalytic results showed that all Au/BiVO4 samples exhibited higher oxalic acid mineralization rate than that of pure BiVO4, probably due to a decrease of BiVO4 band gap energy and the presence of surface plasmon absorption upon loading BiVO4 with Au as evidenced from UV-Vis DRS results. The nominal Au loading amount of 0.25 mol% provided the highest pseudo-first-order rate constant of 0.0487 min−1 and 0.0082 min−1 for degradations of oxalic acid (C2) and malonic acid (C3), respectively. By considering structures of the two acids, lower pseudo-first-order rate constantly obtained in the case of malonic acid degradation was likely due to an increased complexity of the degradation mechanism of the longer chain acid

Role of Gd in Enhancing the Charge Carrier Mobility of Spray Deposited BiVO4 Photoanodes

The emergence of bismuth vanadate BiVO4 as one of the most promising photoanodes for solar water splitting is largely driven by the successful efforts of dopant introduction and optimization to improve its photoelectrochemical PEC performance. To this end, although less commonly used, several trivalent ions e.g., Sm3 , In3 , Gd3 that substitute Bi3 have also been demonstrated to be effective dopants, which can increase the photocurrent density of BiVO4 photoanodes. However, the main factor behind such improvement is still unclear, as various explanations have been proposed in the literature. Herein, Gd3 is introduced to substitute Bi3 in spray deposited BiVO4 films, which enables up to a 2 fold increase in the photocurrent density. Further PEC analysis suggests that Gd doping enhances the charge carrier separation in the BiVO4 films and does not affect the catalytic and optical properties. Indeed, time resolved microwave conductivity TRMC measurements reveal that the charge carrier mobility of BiVO4 is increased by 50 with the introduction of Gd while the charge carrier lifetime is unaffected. This increase of mobility is rationalized to be a result of a higher degree of monoclinic lattice distortion in Gd doped BiVO4, as evident from the X ray diffraction and Raman spectroscopy data. Overall, these findings provide important insights into the nature and the underlying role of Gd in improving the photoelectrochemical performance of BiVO4 photoanode

Preferential adsorption of NH3 gas molecules on MWCNT defect sites probed using in situ Raman spectroscopy

The preferential adsorption of NH3 gas molecules on multiwalled carbon nanotubes (MWCNTs) was studied using in situ Raman spectroscopy. It was observed that the full widths at half maximum of the G band and the intensity ratio I2D/IG of the MWCNTs decreased significantly during NH3 gas adsorption at elevated temperatures. These observations were explained in terms of suppressed second-order-defect associated Raman vibrations resulting in a lower disorder Raman band due to ammonia adsorption on the defect sites. Another corresponding effect was a temporary increase in electron doping levels due to ammonia adsorption. This behaviour was accompanied by a drop of ca. 2% in the resistance of the MWCNTs corresponding to the occupancy of most of the defect sites. We suggest preferential adsorption of ammonia gas molecules on the thermally activated defect sites of MWCNTs as an appropriate gas sensing mechanism. This knowledge can be used to design and tune the selectivity of ammonia gas sensor

Cocaine by-product detection with metal oxide semiconductor sensor arrays

A range of n-type and p-type metal oxide semiconductor gas sensors based on SnO2 and Cr2O3 materials have been modified with zeolites H-ZSM-5, Na-A and H–Y to create a gas sensor array able to successfully detect a cocaine by-product, methyl benzoate, which is commonly targeted by detection dogs. Exposure to vapours was carried out with eleven sensors. Upon data analysis, four of these that offered promising qualities for detection were subsequently selected to understand whether machine learning methods would enable successful and accurate classification of gases. The capability of discrimination of the four sensor array was assessed against nine different vapours of interest; methyl benzoate, ethane, ethanol, nitrogen dioxide, ammonia, acetone, propane, butane, and toluene. When using the polykernel function (C = 200) in the Weka software – and just five seconds into the gas injection – the model was 94.1% accurate in successfully classifying the data. Although further work is necessary to bring the sensors to a standard of detection that is competitive with that of dogs, these results are very encouraging because they show the potential of metal oxide semiconductor sensors to rapidly detect a cocaine by-product in an inexpensive way