Commercially used chemical pollutants, such as methylene blue (MB) dye, are dumped into water reservoirs and can potentially harm both humans and aquatic life. To investigate the effect of Cr doping on the morphological, structural, optical, and photocatalytic properties of TiO2, Cr-doped TiO2 nano photocatalysts were synthesized using a simple and cost-effective single-step sol-gel technique. XRD investigations revealed that all of the samples contain only the anatase phase, and the absence of any extra Cr peaks indicates successful Cr doping. Furthermore, Cr doping causes a considerable increase in the average crystallite size of TiO2 nanocrystal from 71.42 to 86.16 nm. The Fourier Transform Infrared (FTIR) spectra revealed the presence of functional groups (Ti-O and H-O) in all of the samples. UV absorbance spectra tauc plots showed that Cr doping caused the TiO2 band gap to shrink from 3.21 eV to 2.90 eV. In addition, the generated Cr-doped TiO2 nano photocatalysts were used to degrade MB dye under direct sunlight irradiation photocatalytically. At optimal conditions, the photo-degradation efficiency of MB dye achieved 21.24%, 31.18%, and 35.76%, for pure, 0.3%, and 0.5% Cr-doped TiO2 respectively. A high rate constant of 2.24 x 10− 3 min− 1 was observed for 0.5% Cr-doped TiO2 nano photocatalyst. An increased photocatalytic activity of Cr-doped TiO2 in visible light makes them ideal candidates for solar-powered water filtration systems.
Research Article
Impact of Cr Doping on the Optical, and Photocatalytic Performances of TiO2 for Solar Drivin Wastewater Treatments
https://doi.org/10.21203/rs.3.rs-4812113/v1
This work is licensed under a CC BY 4.0 License
Version 1
posted
You are reading this latest preprint version
Photocatalytic properties of Cr-doped TiO2
Single-step Solgel
Methylene Blue
Nano photocatalysts
Wastewater Treatment
For the last two decades, metal oxide semiconductors have been widely used as materials for photocatalysis, which is an enhanced oxidation technique to remove organic contaminants from wastewater[1][2][3]. Recently the most reported metal oxide semiconductors include WO3, SnO2, In2O3, and ZnO among all of these Titanium dioxide (TiO2) is one of the most widely used photocatalysts utilized for wastewater treatments, optical devices, sensors, and dye degradation process [4][5][6][7][8][9]. Titanium dioxide has received a lot of interest from material science researchers because of its remarkable features, including chemical and physical stability, non-toxicity, strong oxidative power, low cost, antibacterial activity, environmental friendliness, solar activation, etc [10][11]. Titanium dioxide exists in three crystalline phases: Anatase, Rutile, and Brookite but among these anatase and rutile are the widely used forms of TiO2 because they are more stable than brookite [12][13]. The anatase crystalline structure of TiO2 shows the highest photocatalytic activity and the rutile crystalline structure has the highest refractive index[10]. TiO2 as a photocatalyst has its limitations due to its broadband gap (3.2eV for anatase and 3.2 eV for rutile phases) as well as its substantial charge carrier recombination rate (nanosecond) which significantly affects the use of TiO2 in practical applications due to its limited visible light absorption [4][14][12]. As a result, it is critical to modify the bandgap of the TiO2 nanostructure, to achieve high potential photocatalytic activity [15][16]. Two key factors govern the photocatalytic activity of TiO2: reducing the band gap energy in the visible range and preventing electron-hole recombination rate. There are various ways to improve the photocatalytic activity of TiO2, notably, stimulation, coupling, and encapsulating titanium dioxide and doping with non-metals and metals such as cadmium (Cd) [17], Ruthenium (Ru) [18], gold (Au) [19], palladium (Pd), nickel (Ni) [20][21], copper (Cu) [22], silver (Ag) [23], and chromium (Cr) [24][3][25] seems to be the best options. Currently, various researchers have strived to improve the performance of photocatalysts by employing metal dopants. MohammadSalehi et.al. (2019) successfully synthesized Cr/N-TiO2 nanoparticles via the sol-gel technique and achieved 97.5 % for the photodegradation of methyl orange MO in 75 min [26]. Xuemin Li et.al. (2013) also prepared Cr-doped TiO2 by using the hydrothermal method and utilized it for the photodegradation of p-chlorophenol achieving greater photocatalytic performance as compared to pure TiO2 [27]. In this study, Chromium (Cr) is chosen as a dopant for TiO2 because of its high stability, and electrical and thermal conductivities, which significantly improve its structural and optical qualities. Furthermore, chromium ions actively engage in the breaking of the chemical bonds of various dyes, thus this extraordinary process has benefited the photocatalytic activity of chromium nanoparticles in the generation of radicals. Because of their great oxidative power, these free radicals were utilized to degrade dyes to a great extent and remarkably utilized for wastewater treatments. TiO2 is synthesized by using various methods such as chemical vapor decomposition, hydrothermal method, and sol-gel method [28][29][30][31]. Among various methods, the sol-gel method is the most successful technique for preparing nanocrystalline metallic oxide nanomaterials such as TiO2 [32][33]. The homogeneous properties of the product prepared by this method are very satisfactory [34][31].
In the present work, we synthesized pure and Cr-doped (0.3 and 0.5) % TiO2 nano photocatalysts by using a single-step sol-gel method. We observed from XRD results that Cr+ 3 ions can promote crystallite formation by lowering internal tensions, promoting atom diffusion which causes a significant increase in the crystallite size, and altering the photocatalytic characteristics of TiO₂ crystals. Chromium doping creates new electronic states in TiO₂, shrinking its bandgap. This enables the material to absorb and use a broader spectrum of natural sunlight, making these nano photocatalysts more effective and energy-efficient for practical tasks.
2.1 Materials and Methods
All the precursor materials, i.e., titanium butoxide IV, chromium nitrate, and aqueous HCL, were purchased from Sigma Aldrich (Germany) and ANALAR was used for the preparation of the un-doped and Cr-doped TiO2 nanoparticles by using single-step sol-gel technique.
2.2 Preparation of Un-doped TiO2
Precursor material 10 ml titanium butoxide (TBO) was mixed with 20 ml distilled water. After 20 minutes of continuous stirring at room temperature (27 0C), a few drops of HCl were added dropwise into the solution, and steering was stopped after 40 minutes. To create xerogel, the warmed samples were dried in an oven at 150 0C for 12 hours. Bulk crystals subsequently developed, indicating that the gel had completely dried. Using a crusher and pestle, the dry gel is modified into fine powder. Calcination at 500 0C for 4 hours was done to remove any potential impurities that deteriorate at high temperatures from the sample.
2.3 Preparation of Cr-doped TiO2 nanocrystals
Titanium butoxide (TBO) 10 ml was added to (0.3 g) Cr (NO3)3, and after 20 minutes of continuously stirring at the ambient temperature (27 0C), 20 ml distilled water and several drops of HCl were poured gradually into the solution, and steering discontinued after 40 minutes. To create xerogel, warm samples were dried in a heated oven at 150 0C for 12 hours. The suspension gel shrunk during this time due to water loss and transformed into a thick paste. Bulk crystals then developed, indicating that the gel had completely dried. The dry gel was then crushed into a fine powder using a mortar and pestle. Calcination at 500 0C for 4 hours of Cr-doped TiO2 was performed to eliminate any suspicious impurities that degraded at high temperatures from the specimen. The same process was used to create a 0.5 g Cr-doped TiO2 sample.
2.4 Photodegradation Activity of all prepared samples
The generated nanocrystals were subsequently exposed to direct sunlight, and the rate of photodegradation using methylene blue (MB) at starting dye concentrations of 10 mg per 500 ml is determined for 0.5 mg of catalysts per 100 ml of dye solution. To measure the photocatalytic ability of the samples, the UV-vis absorption spectra were studied by exposing them to distinct periods of visible light. The available sunlight exposure time was 0 to 120 minutes, with a 15-minute interval.
3.1.1 XRD
The XRD patterns of undoped TiO2 and Cr-doped TiO2 nanocrystals have been depicted in Fig. 2. All the samples reveal the anatas phase of TiO2 with (JCPDS card no. 00-152-6931) having a Face center cubic (FCC) crystal structure. The diffraction peaks of All the synthesized samples appear at the 2theta angles 25.3◦, 38.0◦, 48.3◦, 55.0◦,63.8◦; with (h,k,l) planes (101), (004), (200), (105) and (211) respectively [35]. There is no substantial difference in the recorded peaks of all the synthesized samples and no creation of extra peaks, indicating that Cr+ 3 ions were successfully incorporated into the TiO2 crystal lattice. The Scherr equation was used to describe the link between crystallite size and peak broadness in XRD, providing an estimate of average crystallite size based on peak broadening.
D = K λ/βcosθ (1)
In the above equation, D is the average crystallite size, K is the Scherer Constant (usually round about 0.9), and λ is the wavelength of the diffracted X-rays (1.5406 A◦). The diffraction angle is denoted by θ, whereas β represents the diffraction peak's full width at half maximum (FWHM). An increase in the concentration of Cr from (0.3 to 0.5) % reveals a significant increase in the average crystallite size of the TiO2 nanocrystal [36]. According to the Scherer equation, the crystalline size (D) is inversely proportional to peak broadening, and crystallite size increases with the sharpness of the peaks (FWHM), which is perfectly satisfied by our XRD results as mentioned in Table 1. The average crystallite size of un-doped TiO2 increases from 71.42 nm to 80.09 and 86.16 nm for (0.3 and 0.5) % Cr-doped TiO2 samples with lattice constant (a = 0.3450, c = 4.3505) [36]. Additionally, a relatively small shift in the XRD peaks of the Cr-doped TiO2 samples might be attributed to the compressive strain induced by the Cr+ 3 ions positioned in the TiO2 crystal lattice [37]. Variations in several other important parameters such as dislocation density and crystallinity percentage with doping of Cr into TiO2 lattice also tabulated in Table 1.
3.1.2 FTIR analysis
Figure 3 shows the FTIR spectra in the range of 400 cm− 1 to 4000 cm− 1 of the undoped and Cr-doped TiO2 nanocrystals. The minor intensity peak at 439 cm− 1 is attributed to the typical Ti-O-Ti vibration [38]. The peak at 1510 cm− 1 indicates the presence of an aromatic ring [39] and the peak at 1697 cm− 1 shows the bending vibration peak of H-O-H due to adsorbed water species [40]. However, these peaks show exclusively in pure TiO2 and are missing in Cr-doped samples it might be due to the annealing process which removes water molecules from doped chromium. Certain peaks in undoped TiO2 can be ascribed to the unique vibrational modes of Ti-O bonds or other functional groups in the material. The broad absorption band at about 2353 cm− 1 results from the CO2 in the atmosphere [41]. The sharp peak at 3724 cm− 1 shows NH2 stretching vibration [42]. The peak at 3856cm− 1 is attributed to the H-O-H vibrations from physiabsorbed water.
3.1.3 UV analysis
Figure 4 displays UV-visible spectroscopy data for all manufactured pure and Cr-doped TiO2 samples. Pure TiO2 exhibits outstanding transparency in the visible area, as well as substitutional absorption in the ultraviolet. Figures (4-b) reveals the significant decrease in the bandgap of the TiO2 with an increase in the concentration of the dopant material Cr. The band gap of the TiO2 nanocrystal decreased from 3.5 eV to 2.9 eV for the 0.5% Cr-doped TiO2 sample. It may be due to the absorption spectra of the Cr-TiO2 sample exhibiting more absorption than TiO2 in the visible range as shown in Figure (4-a) [43], indicating the presence of additional electronic energy states between the valance band and conduction band of the material. The observed red shift in the Cr-doped TiO2 sample correlates with the integration of Cr+ 3 into the titanium crystal lattice [44][36][45].
After the successful synthesis of nano photocatalysts has been placed in the sunlight, the photodegradation rate using methylene blue (MB) at starting dye concentrations of 10 mg per 500 ml is measured for 0.5 mg of photo-catalysts per 100 ml of dye solution. The samples' UV-vis wavelength spectrum was examined by subjecting them to varying durations of visible light exposure in order to determine their photocatalytic potential. The absorbance of the MB solution is measured at its highest absorption at a longer wavelength, of 465 nm for each distinct period of 15 min. The energy provided by sunlight as a level of intermediate excitation of electrons allowed the electrons in the Cr-doped TiO2 semiconductors to migrate from the valence band to the conduction band. When photogenerated holes and electrons move to the surface of nanocrystals (NCs), oxidative bases are formed. These NCs react by releasing adsorption-reacting agents which form hydroxyl (–OH) radicals, superoxide radicals, anions, and hydrogen peroxide, all of which contribute to the breakdown of dye. As the time frame of being subjected to direct sunlight increased to 120 minutes, a consistent rise in the degradation efficiency was seen for all fabricated samples, including pure, 0.3, and 0.5% Cr-doped TiO2 nanocrystals, as shown in Fig. 5 (a-c). Figures (5-a) illustrates the MB dye's gradual degradation caused by pure TiO2, which causes 21.4% of the dye to deteriorate in 120 minutes when exposed to sunshine. A substantial rise in MB degradation for 0.5% Cr-doped TiO2 nanocrystals is shown in Fig. 5 (c), with a degradation of 35.76% over the same 120-minute period. Figure 5 (d), which depicts the collective photodegradation efficiency of pure, 0.3, and 0.5% Cr-doped TiO2, shows how the MB dye degradation progressively increased over time. The degradation efficiency of all the fabricated samples was determined by using Eq. (2),
% Degradation Efficiency = \(\:\frac{{C}_{0}-\:{C}_{t}}{{C}_{0}}\:\times\:100\:\%\) ………………………… (2)
whereas C0 and Ct stand for the maximum absorbance at 465 nm for each generated sample, recorded under visible direct sunshine, at durations of 0 min and 15 min delay intervals up to 120 min (t). The Cr-doped TiO2 nanocrystals' exceptional photocatalytic performance is caused by their band gap shifting toward the visible spectrum. The TiO2 lattice's Cd doping could prolong the time that charge carriers stay preventing electron/hole recombination for a longer amount of time. Compared to pure TiO2, Cr-doped TiO2 produces new energy levels that increase photocatalytic activity and decrease the bandgap energy of the TiO2 nanocrystals. Cr doping produces oxygen vacancies, which operate as the most active locations for water splitting on the metal-doped TiO2 surfaces despite Cr2+ ions having a lower valency than Ti4+ ions. These reactive species play a major role in the decolorization of MB.
To understand how MB dye degrades photocatalytically, Fig. 6 (a,b) depicts the first-order model reaction kinetics of pure and Cr-doped TiO2. The kinetics of the first-order model is described by formula (3) below.
lnC0 / Ct = kt ……………………………………… (3)
Where C0 and Ct stand for the quantity of MB captured in direct sunlight for a total duration of 120 minutes at increments of 15 min. The symbols t and k stand for the reaction's time and rate constant, respectively. The linear fitting vs irradiation time of the photocatalytic degradation of MB was assessed using a tauc plot, as Fig. 6 (b) illustrates. The value of the predicted kinetic degradation rate constant (k) can be found by analyzing the gradient of the fitting curve. Under direct sunlight, it was observed that the computed values of (k) for pristine TiO2, and Cr-doped TiO2 are, respectively, (1.88, 1.98, and 2. 24) x 10− 3 min− 1 as illustrated in Table 2.
Photodegradation Mechanism
The Cr-doped TiO2 undergoes photoexcitation, which excites the electrons in the valence band (VB) to the conduction band (CB) and leaves the VB containing holes are shown in Fig. 7. Photons are absorbed and electron-hole pairs are generated; the electron-trapping effect of Cr ions prolongs the stability of the charge carriers by lowering the rate of recombination of these pairs. After migrating to the TiO2 particle's surface, the photogenerated electrons can convert molecular oxygen (O2) to produce superoxide radicals (O2•−). While the photogenerated holes move towards the surface, they can oxidize hydroxide ions (OH−) or water (H2O) and produce hydroxyl radicals (•OH). The methylene blue molecules are attacked by the hydroxyl radicals (•OH) and superoxide radicals (O2•−), which cause the complex organic structure of MB to break down into less destructive or environment-friendly molecules like CO2, H2O, and other least harmful inorganic ions. In the presence of Cr-doped TiO2, the entire photocatalytic degradation of methylene blue can be described by the following reaction:
MB + hν + O2 → CO2 + H2O + less destructive ions
The addition of Cr+ 3 ions to the TiO2 crystal lattice increases the pace of methylene blue breakdown overall because of enhanced charge carrier separation and extended light absorption towards the visible spectrum.
In this study, successful Sol-gel synthesis of Cr-doped TiO2 nanophotocatalysts was done for the photodegradation of a commercially used pollutant Methylene Blue dye. All the fabricated nanophotocatalysts were characterized through various nanomaterials characterization techniques i.e. XRD, FTIR, and UV, which confirms the successful doping of Cr into TiO2 crystal lattice with various modifications in its optical, structural, and photocatalytic properties. In addition, the generated nano photocatalysts were tested for the photodegradation of MB and achieved significantly improved photodegradation results during exposure to direct sunlight. Overall the doping of Cr shrank the Band gap and significantly enhanced the photodegradation efficiency of the TiO2 semiconductor making it a remarkable candidate for practical use in photocatalysis-efficient Solar Energy devices and cost-free wastewater treatment processes.
Data Availability Statement:
The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.
- T. R. Ahammad, S. Z.; Gomes, J.; Sreekrishnan, “Wastewater treatment forproductionofH2S-free biogas,” J. Chem. Technol. Biotechnol., vol. 83, no. May, pp. 1163–1169, 2008, doi: 10.1002/jctb.
- R. Nainani, P. Thakur, and M. Chaskar, “Synthesis of silver doped TiO2 nanoparticles for the improved photocatalytic degradation of methyl orange Synthesis of Silver Doped TiO 2 Nanoparticles for the Improved Photocatalytic Degradation of Methyl Orange,” 2012. [Online]. Available: https://www.researchgate.net/publication/284803185
- J. Bansal et al., “Performance analysis of anomalous photocatalytic activity of Cr-doped TiO2 nanoparticles [Cr(x)TiO2(1−x)],” Appl. Phys. A Mater. Sci. Process., vol. 126, no. 5, pp. 1–10, 2020, doi: 10.1007/s00339-020-03536-z.
- A. López Ortiz, M. Meléndez Zaragoza, J. Salinas Gutiérrez, M. Marques Da Silva Paula, and V. Collins-Martínez, “Silver oxidation state effect on the photocatalytic properties of Ag doped TiO2 for hydrogen production under visible light,” Int. J. Hydrogen Energy, vol. 40, no. 48, pp. 17308–17315, 2015, doi: 10.1016/j.ijhydene.2015.09.058.
- D. Jocelyn, R. Gutiérrez, N. Rose, and S. Silva, “Journal of Photochemistry and Photobiology A : Chemistry Photocatalytic activity enhancement of TiO 2 thin films with silver doping under visible light,” "Journal Photochem. Photobiol. A Chem., vol. 262, pp. 57–63, 2013, doi: 10.1016/j.jphotochem.2013.04.021.
- Y. Deng, “Sensing Mechanism and Evaluation Criteria of Semiconducting Metal Oxides Gas Sensors,” in Semiconducting Metal Oxides for Gas Sensing, Springer Singapore, 2019, pp. 23–51. doi: 10.1007/978-981-13-5853-1_2.
- M. Samadi, M. Zirak, A. Naseri, M. Kheirabadi, M. Ebrahimi, and A. Z. Moshfegh, Design and tailoring of one-dimensional ZnO nanomaterials for photocatalytic degradation of organic dyes: a review, vol. 45, no. 4. Springer Netherlands, 2019. doi: 10.1007/s11164-018-03729-5.
- D. Meng et al., “Low-temperature formaldehyde gas sensors based on NiO-SnO2 heterojunction microflowers assembled by thin porous nanosheets,” Sensors Actuators, B Chem., vol. 273, pp. 418–428, Nov. 2018, doi: 10.1016/j.snb.2018.06.030.
- A. Gupta, P. K. Parida, and P. Pal, “Functional Films for Gas Sensing Applications: A Review,” in Energy, Environment, and Sustainability, Springer Nature, 2019, pp. 7–37. doi: 10.1007/978-981-13-3290-6_2.
- J. Bahadur, S. Agrawal, V. Panwar, A. Parveen, and K. Pal, “Antibacterial properties of silver doped TiO2 nanoparticles synthesized via sol-gel technique,” Macromol. Res., vol. 24, no. 6, pp. 488–493, Jun. 2016, doi: 10.1007/s13233-016-4066-9.
- G. Y. Nigussie et al., “Antibacterial Activity of Ag-Doped TiO 2 and Ag-Doped ZnO Nanoparticles,” Int. J. Photoenergy, vol. 2018, pp. 1–7, 2018, doi: 10.1155/2018/5927485.
- D. R. Eddy et al., “Heterophase Polymorph of TiO2 (Anatase, Rutile, Brookite, TiO2 (B)) for Efficient Photocatalyst: Fabrication and Activity,” Nanomaterials, vol. 13, no. 4, p. 704, Feb. 2023, doi: 10.3390/nano13040704.
- A. H. Navidpour, S. Abbasi, D. Li, A. Mojiri, and J. L. Zhou, “Investigation of Advanced Oxidation Process in the Presence of TiO2 Semiconductor as Photocatalyst: Property, Principle, Kinetic Analysis, and Photocatalytic Activity,” Catalysts, vol. 13, no. 2, p. 232, Jan. 2023, doi: 10.3390/catal13020232.
- J. Qaderi, C. R. Mamat, and A. A. Jalil, “Preparation and Characterization of Copper, Iron, and Nickel Doped Titanium Dioxide Photocatalysts for Decolorization of Methylene Blue,” Sains Malaysiana, vol. 50, no. 1, pp. 135–149, 2021, doi: 10.17576/jsm-2021-5001-14.
- A. K. Gupta, P. Srivastava, and L. Bahadur, “Improved performance of Ag-doped TiO2 synthesized by modified sol–gel method as photoanode of dye-sensitized solar cell,” Appl. Phys. A Mater. Sci. Process., vol. 122, no. 8, 2016, doi: 10.1007/s00339-016-0241-2.
- M. B. Suwarnkar, R. S. Dhabbe, A. N. Kadam, and K. M. Garadkar, “Enhanced photocatalytic activity of Ag doped TiO2 nanoparticles synthesized by a microwave assisted method,” Ceram. Int., vol. 40, no. 4, pp. 5489–5496, May 2014, doi: 10.1016/j.ceramint.2013.10.137.
- Y. Li, Y. Guo, Y. Li, and X. Zhou, “Fabrication of Cd-Doped TiO2 Nanorod Arrays and Photovoltaic Property in Perovskite Solar Cell,” Electrochim. Acta, vol. 200, pp. 29–36, May 2016, doi: 10.1016/j.electacta.2016.03.091.
- S. M. Al-Shomar, “Investigation the effect of doping concentration in Ruthenium-doped TiO2 thin films for solar cells and sensors applications,” Mater. Res. Express, vol. 7, no. 3, 2020, doi: 10.1088/2053-1591/ab815b.
- V. S. Katta, V. R. Chappidi, and S. S. K. Raavi, “Plasmonic AU Npcs Embedded Ytterbium-Doped Tio2 Nanowire Photoanodes for Efficient Indoor Photovoltaic Devices,” SSRN Electron. J., 2022, doi: 10.2139/ssrn.4233066.
- T. Rajaramanan, D. Velauthapillai, P. Ravirajan, and M. Senthilnanthanan, “A facile impregnation synthesis of Ni-doped TiO2 nanomaterials for dye-sensitized solar cells,” J. Mater. Sci. Mater. Electron., vol. 34, no. 10, p. 916, Apr. 2023, doi: 10.1007/s10854-023-10347-4.
- M. Irfan, M. I. Khan, M. Al Huwayz, and N. Alwadai, “Synthesis, characterization, and photodegradation assessment of Ni and Cd-doped TiO2 nanocrystals via sol-gel method for methylene blue under sunlight,” Dig. J. Nanomater. Biostructures, vol. 19, no. 2, pp. 953–966, 2024, doi: 10.15251/DJNB.2024.192.953.
- M. M. Abbas and M. Rasheed, “Solid State Reaction Synthesis and Characterization of Cu doped TiO2Nanomaterials,” in Journal of Physics: Conference Series, IOP Publishing Ltd, Mar. 2021. doi: 10.1088/1742-6596/1795/1/012059.
- V. Soni, A. N. Singh, P. Singh, and A. Gupta, “Photocatalytic dye-degradation activity of nano-crystalline Ti1−xMxO2−δ (M =Ag, Pd, Fe, Ni and x = 0, 0.01) for water pollution abatement,” RSC Adv., vol. 12, no. 29, pp. 18794–18805, 2022, doi: 10.1039/d2ra02847f.
- H. Zhu, T. Jie, and D. Xiang, “Preparation and photoelectrochemical activity of Cr-doped TiO2 nanorods with nanocavities,” J. Phys. Chem. C, vol. 114, no. 7, pp. 2873–2879, 2010, doi: 10.1021/jp9085987.
- J. Bansal et al., “Performance analysis of anomalous photocatalytic activity of Cr-doped TiO2 nanoparticles [Cr(x)TiO2(1−x)],” Appl. Phys. A, vol. 126, no. 5, p. 363, May 2020, doi: 10.1007/s00339-020-03536-z.
- H. Mohammad-Salehi, M. Hamadanian, and H. Safardoust-Hojaghan, “Visible-Light Induced Photodegradation of Methyl Orange via Palladium Nanoparticles Anchored to Chrome and Nitrogen Doped TiO2 Nanoparticles,” J. Inorg. Organomet. Polym. Mater., vol. 29, no. 5, pp. 1457–1465, Sep. 2019, doi: 10.1007/s10904-019-01109-z.
- X. Li, Z. Guo, and T. He, “The doping mechanism of Cr into TiO2 and its influence on the photocatalytic performance,” Phys. Chem. Chem. Phys., vol. 15, no. 46, p. 20037, 2013, doi: 10.1039/c3cp53531b.
- A. Jasim and O. Salman, “The Effect of Solvent Variation on Structural, Optical, and Electrical Properties of TiO2 Films Prepared by Hydrothermal Method,” J. Appl. Sci. Nanotechnol., vol. 3, no. 2, pp. 59–69, Jun. 2023, doi: 10.53293/jasn.2023.5562.1191.
- A. Chakraborty, Samriti, O. Ruzimuradov, R. K. Gupta, J. Cho, and J. Prakash, “TiO2 nanoflower photocatalysts: Synthesis, modifications and applications in wastewater treatment for removal of emerging organic pollutants,” Environ. Res., vol. 212, p. 113550, Sep. 2022, doi: 10.1016/j.envres.2022.113550.
- M. Patricia, B. Vega, M. H. Aracely, H. J. Luis, G. Mar, and V. R. L. Hinojosa-reyes, “Visible light photocatalytic activity of sol – gel Ni-doped TiO 2 on p - arsanilic acid degradation,” J. Sol-Gel Sci. Technol., 2018, doi: 10.1007/s10971-018-4579-0.
- R. Nainani and P. Thakur, “Synthesis of silver doped TiO2 nanoparticles for the improved photocatalytic degradation of methyl orange,” no. March, 2016.
- A. Khlyustova, N. Sirotkin, T. Kusova, A. Kraev, V. Titov, and A. Agafonov, “Doped TiO2: The effect of doping elements on photocatalytic activity,” Mater. Adv., vol. 1, no. 5, pp. 1193–1201, 2020, doi: 10.1039/d0ma00171f.
- S. M. Al-Shomar, “Investigation the effect of doping concentration in Ruthenium-doped TiO 2 thin films for solar cells and sensors applications,” Mater. Res. Express, vol. 7, no. 3, p. 036409, Mar. 2020, doi: 10.1088/2053-1591/ab815b.
- M. Harikishore, M. Sandhyarani, K. Venkateswarlu, T. A. Nellaippan, and N. Rameshbabu, “Effect of Ag Doping on Antibacterial and Photocatalytic Activity of Nanocrystalline TiO 2,” Procedia Mater. Sci., vol. 6, no. Icmpc, pp. 557–566, 2014, doi: 10.1016/j.mspro.2014.07.071.
- S. Demirci, T. Dikici, M. Yurddaskal, and S. Gultekin, “Applied Surface Science Synthesis and characterization of Ag doped TiO 2 heterojunction films and their photocatalytic performances,” Appl. Surf. Sci., vol. 390, pp. 591–601, 2016, doi: 10.1016/j.apsusc.2016.08.145.
- H. M. Yadav et al., “Enhanced visible light photocatalytic activity of Cr3+-doped anatase TiO2 nanoparticles synthesized by sol–gel method,” J. Mater. Sci. Mater. Electron., vol. 27, no. 1, pp. 526–534, 2016, doi: 10.1007/s10854-015-3785-6.
- C. C. Pan and J. C. S. Wu, “Visible-light response Cr-doped TiO2-XNX photocatalysts,” Mater. Chem. Phys., vol. 100, no. 1, pp. 102–107, 2006, doi: 10.1016/j.matchemphys.2005.12.013.
- X. F. Lei, X. X. Xue, and H. Yang, “Applied Surface Science Preparation and characterization of Ag-doped TiO 2 nanomaterials and their photocatalytic reduction of Cr ( VI ) under visible light,” Appl. Surf. Sci., vol. 321, pp. 396–403, 2014, doi: 10.1016/j.apsusc.2014.10.045.
- K. M. Joshi and V. S. Shrivastava, “Photocatalytic degradation of Chromium (VI) from wastewater using nanomaterials like TiO2, ZnO, and CdS,” Appl. Nanosci., vol. 1, no. 3, pp. 147–155, 2011, doi: 10.1007/s13204-011-0023-2.
- X. Yang, S. Wang, H. Sun, X. Wang, and J. Lian, “Preparation and photocatalytic performance of Cu-doped TiO 2 nanoparticles,” Trans. Nonferrous Met. Soc. China, vol. 25, no. 2, pp. 504–509, 2015, doi: 10.1016/S1003-6326(15)63631-7.
- S. G. M. A. Behnajady, “Chromium ( VI ) adsorption from aqueous solution by prepared biochar from Onopordom Heteracanthom,” Int. J. Environ. Sci. Technol., vol. 13, no. 7, pp. 1803–1814, 2016, doi: 10.1007/s13762-016-0978-3.
- M. H. Gomaa, A. Ibrahim, K. El‐Sayed, and Z. A. Hamid, “Boosting the hydrophobicity of eco‐friendly polyaniline coating using TiO 2 and ZnO nanoparticles,” Surf. Interface Anal., vol. 56, no. 3, pp. 147–159, Mar. 2024, doi: 10.1002/sia.7280.
- F. Hasan, “Synthesis of Cr Doped TiO2 Using Sol-Gel Technique and Calculation of its Photocatalytic Activity * Address for Correspondence Synthesis of Cr Doped TiO 2 Using Sol-Gel Technique and Calculation of its Photocatalytic Activity,” vol. 9, no. June, pp. 15242–15249, 2019.
- Y. H. Peng, G. F. Huang, and W. Q. Huang, “Visible-light absorption and photocatalytic activity of Cr-doped TiO 2 nanocrystal films,” Adv. Powder Technol., vol. 23, no. 1, pp. 8–12, 2012, doi: 10.1016/j.apt.2010.11.006.
- X. Li, Z. Guo, and T. He, “The doping mechanism of Cr into TiO2 and its influence on the photocatalytic performance,” Phys. Chem. Chem. Phys., vol. 15, no. 46, pp. 20037–20045, 2013, doi: 10.1039/c3cp53531b.
- D. Maučec, A. Šuligoj, A. Ristić, G. Dražić, A. Pintar, and N. N. Tušar, “Titania versus zinc oxide nanoparticles on mesoporous silica supports as photocatalysts for removal of dyes from wastewater at neutral pH,” Catal. Today, vol. 310, no. February, pp. 32–41, 2018, doi: 10.1016/j.cattod.2017.05.061.
- M. Jahdi, S. B. Mishra, E. N. Nxumalo, S. D. Mhlanga, and A. K. Mishra, “Smart pathways for the photocatalytic degradation of sulfamethoxazole drug using F-Pd co-doped TiO2 nanocomposites,” Appl. Catal. B Environ., vol. 267, no. October 2019, p. 118716, 2020, doi: 10.1016/j.apcatb.2020.118716.
No competing interests reported.