Co-doped TiO2 Photocatalyst Research Articles

Study on Treatment of Ciprofloxacin in Water with Co, N Co-doped TiO2 Photocatalysts on Vermiculite

This paper presents the results of the treatment of ciprofloxacin in water with Co, N-doped TiO2 photocatalysts on a vermiculite background. Vermiculite (Ver) material after activation with HNO3 at three concentrations of 10%, 30%, and 40% exhibits a rougher surface. The 40% HNO3 activated material has the higest porosity and has a surface area greater than 79.4 times the total surface area of ​​the raw material. Co- and N-doped TiO2 photocatalysts on vermiculite were prepared by sol-gel method, using a mixture of tetraisopropylorthotitanate Ti(OC3H7)4 (TTIP), ethanol (EtOH), diethanolamine C4H11NO2 (DEA), and Co(NO3)2.6H2O. The influence of doped cobalt on the structure, surface morphology, and photocatalytic properties of N,Cox-TiO2/Ver (x=0.04;0.06;0.08 mol) was studied through scanning electron microscopy (SEM) and UV-Vis absorption spectroscopy. The SEM image shows that anatase-TiO2 crystals are evenly coated on the surface of Ver and the spherical particles are evenly dispersed on the surface of the material. The absorption spectrum shows that the band gap of the sample N,Cox-TiO2/Ver (x=0.04, 0.06, 0.08 mol) decreases from 3.32 eV to 2.64 eV. We implemented the preliminary experiments to test the efficiency of our synthesized material to treat the antibiotic ciprofloxacin in hospital wastewater. N,Co0,08-TiO2/Ver materials showed over 80% efficiency of removing the ciprofloxacin in these hospital wastewater samples.

Degradation of Methylene Blue by Sol-Gel One-Step Method with B-W Co-doped TiO2

In this work, B-W co-doped TiO2 photocatalysts were synthesized by a sol-gel method using ammonium metatungstate and boric acid as W and B sources, respectively. The effects of W/Ti and B/Ti ratios on the photocatalytic activities were investigated. When W/Ti = 3.5/100 and B/Ti = 5/100, the degradation rate of a 40 mg/L methylene blue solution reached 82.45% within 120 min and the quasi-first-order kinetic constants were 12.39 times and 1.89 times of the quasi-first-order kinetic constants of pure TiO2 and 3.5%W-TiO2, respectively. The characterization results showed that the modified TiO2 crystal type obtained by W and B co-doping was anatase, and the gel was calcined to produce substituted W doping and interstitial B doping (Ti-O-B-Ti). W and B doping can form impurity energy levels below the conduction band and above the valence band, respectively; under their synergistic effect, the bandgap of 5%B-3.5%W-TiO2 was reduced to 2.65 eV, which lowered the the compounding efficiency of the hole-electron pairs and improved the photocatalytic performance.

Upcycling of waste EPS beads to immobilized codoped TiO2 photocatalysts for ciprofloxacin degradation and E. coli disinfection under sunlight

The emerging global problem of antimicrobial resistance needs immediate attention. In this regard, this work demonstrates the use of expanded polystyrene waste in the synthesis of immobilized photocatalytic films for the treatment of antibiotics as well as for bacterial disinfection. A boron–cerium codoped TiO2 catalyst (of specific composition: B0.8Ce0.2TiO2) was immobilized in an expanded polystyrene (EPS) film prepared from waste EPS beads. These films were studied for the degradation of ciprofloxacin (CIP) and disinfection of E. coli under sunlight. The film with a catalyst loading of 20 wt% showed a maximum degradation of 89% in 240 min with a corresponding TOC reduction of 84%. A 7.4 and 6.3 log reduction from the bacterial inactivation studies in the presence and absence of antibiotics, respectively, was obtained. The EPS film was stable after five times of reuse, and no significant chemical changes in the used film were observed from FTIR analysis. The average thickness of the prepared film was found from FESEM analysis to be 1.09 mm. These EPS films were also tested for degradation of other antibiotics, such as norfloxacin, levofloxacin and moxifloxacin. The EPS films were tested in two different reactor volumes at optimum conditions. Also, the effectiveness of B0.8Ce0.2TiO2/EPS film in real water samples indicates its potential in large-scale and real-world applications. Thus, these B0.8Ce0.2TiO2/EPS films can be effectively employed for both degradation of ciprofloxacin and the disinfection of E. coli under solar light to solve the increasing problem of antimicrobial resistance.

Visible light assisted photocatalytic degradation of mixture of reactive ternary dye solution by Zn–Fe co-doped TiO2 nanoparticles

The current study deals with the synthesis of novel Zn, and Fe co-doped TiO2 photocatalyst by the sol-gel method at room temperature. The prepared photocatalysts are characterized by several standard analytical tools. X-ray diffraction (XRD) and Raman analysis verifies the tetragonal anatase phase of TiO2 in all synthesized nanoparticles. The morphology and chemical composition of ZFT_2.5 were confirmed using the Field-Emission Scanning Electron Microscope (FE-SEM) and energy dispersive X-ray (EDAX) analysis respectively. X-ray photoelectron spectroscopy (XPS) measurements verify the binding energies of a host and dopant material. The High resolution transmission electron microscopy (HR-TEM) reveals the presence of spherical nanoparticles in ZFT_2.5 photocatalyst with a diameter ranging from 8 to 20 nm. The absorption spectra of the prepared nanoparticles exhibit strong absorption in visible light. The synergistic effect created by Zn and Fe blocked the light induced charge carriers and delayed the recombination probability. The photocatalyst ZFT_2.5 was tested for photocatalytic degradation against the mixture of the three cationic dyes [rhodamine B (RhB), malachite green (MG), and methylene blue (MB)] under exposure of visible light. Total organic carbon (TOC) study was performed to evaluate the organic character of the photodegradate dye solution.

Enhanced photocatalytic activity in RhB dye degradation by Mn and B co-doped mixed phase TiO2 photocatalyst under visible light irradiation

Here, we report synthesis of undoped, manganese (Mn) doped, boron (B) doped and Mn-B co-doped TiO2 nanoparticles (NPs) by a cost-effective sol-gel method. The structural properties, phase, micro-morphology and particle size of the synthesized nanoparticles have been characterized by X-ray diffraction, Raman spectroscopy, Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) techniques. These studies revealed that undoped and mono (Mn/B) doped TiO2 NPs exhibit only anatase phase, whereas (Mn and B) co-doped TiO2 NPs exhibit anatase and rutile mixed phase structure. Furthermore, co-doping reduces the particle size, agglomeration in aqueous medium and the sample possesses crystal defects. UV–Visible diffusive reflectance spectroscopy (DRS) revealed that the co-doped sample demonstrates extended optical response in the visible wavelength range of the solar spectrum and is red shifted when compared to undoped and mono doped TiO2 NPs. The obtained optical band gap (2.11 eV) and the Urbach energy (1.12 eV) for the Mn and B co-doped TiO2 NPs suggest the formation of mid-gap energy states, which might make this NPs a suitable candidate for photocatalysis in the visible light spectrum. We investigated the photocatalytic degradation of rhodamine B (RhB) dye by the synthesized NPs under visible light irradiation. Our studies revealed that co-doped TiO2 photocatalyst can degrade 99% of RhB dye within 90 min of visible light irradiation and can retain 95% degradation efficiency up to the third consecutive cycles. Finally, we provide a plausible explanation for such enhanced visible light assisted photocatalytic performance.

Synthesis, Characterization and Optimization of Highly Selective Molecularly Imprinted Ni and F Co-Doped TiO2 Photocatalyst for Effective Removal and Photocatalytic Decomposition of Paracetamol

Synthesis, Characterization and Optimization of Highly Selective Molecularly Imprinted Ni and F Co-Doped TiO2 Photocatalyst for Effective Removal and Photocatalytic Decomposition of Paracetamol

C, F co-doping Ag/TiO2 with visible light photocatalytic performance toward degrading Rhodamine B

The organic pollutants in industrial wastewater continuously endanger human health. Therefore, effective treatment of organic pollutants is very urgent. Photocatalytic degradation technology is an excellent solution to remove it. TiO2 photocatalysts are easy to prepare and have high catalytic activity, unfortunately, TiO2 only absorbs ultraviolet light limiting its utilization of visible light. In this study, a facile environmentally friendly synthesis of Ag-coated on micro-wrinkled TiO2-based catalysts in order to extend the absorption of Visible light. Firstly, a fluorinated titanium dioxide precursor was prepared by a one-step solvothermal method, and the precursor was calcined at high temperature in a nitrogen atmosphere to form a carbon dopant, and then a surface silver-deposited carbon/fluorine co-doped TiO2 photocatalyst C/F–Ag–TiO2 was prepared by a hydrothermal method The results showed that the Ag was coated on the wrinkled TiO2 layer and C/F–Ag–TiO2 photocatalyst was synthetized successfully. Benefit from the synergistic effect of doped carbon and fluorine atoms in combination with the quantum size effect of the surface silver nanoparticles, the band gap energy of C/F–Ag–TiO2 (2.56 eV) is obviously lower than anatase (3.2eV). The photocatalyst achieved an impressive degradation rate of 84.2% for Rhodamine B in 4 h, with a degradation rate constant of 0.367 h−1, which was 17 times higher than that of P25 under visible light. Therefore, the C/F–Ag–TiO2 composite is a promising candidate as a highly efficient photocatalyst for environmental remediation.

Enhancing CO2 photoconversion activity of TiO2 via synergistic effects of La-doping and ammonia vapor heat treatment

A novel, sample and economical method was used to prepare the new co-doped TiO2 photocatalysts and evaluated for CO2 photoconversion under visible-light irradiation. The La(NO3)3-TiO2 photocatalyst was obtained by the sol–gel method and then was heat treated with different concentrations of ammonia vapor. It was found that the synergistic modification of TiO2 photocatalyst by La(NO3)3 and ammonia vapor could improve its photocatalytic performance under visible light. The photocatalytic assessment presented a significantly amelioration in CO2 photoconversion, giving 3.078 μmol CH4 production in 4 h. The structures and properties of the photocatalysts were characterized and analyzed by means of XRD, SEM-EDS, HRTEM, BET, XPS, FTIR, ICP-AES, UV–vis DRS and theoretical calculation. The performance of the photocatalyst could be correlated to contributions of various phenomena such as larger specific surface area and the co-exposed (101) and (001) facets of anatase TiO2. Finally, the most likely substituted structures were obtained. The results of DFT + U theoretical calculation showed that La and N could modify TiO2 by replacing surface Ti atoms and internal O atoms, respectively.

Optimization by central composite design (CCD)-response surface methodology (RSM) of the highly selective molecularly imprinted Ni and F co-doped TiO2 photocatalyst for photocatalytic degradation of bisoprolol

In this study, photocatalytic degradation of bisoprolol in aqueous solution, employing high selective synthesized molecularly imprinted Ni–F–TiO2 has been optimized by CCD-RSM under both LED lamps and sunlight.

Photocatalytic degradation of chlorazol yellow dye under sunlight irradiation using Ce, Bi, and N co-doped TiO2 photocatalyst in neutral medium.

Chlorazol yellow (CY) is a commonly used anionic, toxic, mutagenic, and potentially carcinogenic azo dye, which is menacing to the environment, aquatic system, food chain, and human health as well. To remove CY dye molecules from an aqueous medium, a series of Ce, Bi, and N co-doped TiO2 photocatalysts were prepared by varying the composition of the dopants. Under sunlight irradiation, the resultant 5 wt% (Ce-Bi-N) co-doped TiO2 composite catalyst was found to show the best catalytic activity. Hence, the required characterization of this catalyst was performed systematically using energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) techniques. From the thorough investigation, it is revealed that the CY molecules reached adsorption-desorption equilibrium onto the surface of the catalyst within 30min following second-order kinetics. Herein, the catalyst attained 97% degradation when exposed to sunlight at neutral (pH ~ 7, [CY] = 5mg L-1) medium. The developed catalyst can destruct CY molecules with a maximum rate of 23.1µg CY g-1min-1 and the photodegradation kinetics follows first-order kinetics below 23.5mg L-1, a fractional order between 23.5 and 35.0mg L-1, and a zeroth order above 35.0mg L-1 of CY concentration. Finding from scavenging effect implies that [Formula: see text] and [Formula: see text] radicals have significant influence on the degradation. A suitable mechanism has been proposed with excellent stability and verified reusability of the proposed photocatalyst.

Enhanced photocatalytic reduction of CO2 into CH4 over N, Eu co-doped TiO2: Insight into the synergistic effect of N and Eu

The synthesis of photocatalysts with good activity and strong product selectivity is of strategic importance for photocatalytic reduction of carbon dioxide (CO2). In this study, an improved sol-gel method was employed for the synthesis of N-doped TiO2, Eu-doped TiO2, and N, Eu co-doped TiO2 photocatalysts. The phase structures, optical and electrical properties of the catalysts were thoroughly investigated by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller Surface area analysis, Ultraviolet-visible diffuse reflectance spectroscopy, Photoluminescence spectroscopy, and electrochemical measurements. The experimental results of photocatalytic CO2 reduction indicated that both N and Eu doping could effectively improve the photoresponse of TiO2, but the synergistic effect of N and Eu made the N, Eu co-doped TiO2 exhibit superior photocatalytic activity and product selectivity, the formation rate of methane (CH4) by photocatalytic reduction of CO2 using N-Eu/TiO2 as the catalyst could reach 13.48 μmol·gcat−1·h−1, which was about 12 times higher than that of pure TiO2, and the selectivity reached nearly 100%. Finally, this synergistic effect was explained using DFT calculation and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and the possible mechanism of photocatalytic CO2 reduction over N-Eu/TiO2 was elucidated.

Development of immobilised sunlight active W-Mo/Mo-V/V-W co-doped TiO2 photocatalyst by plasma electrolytic oxidation

W-Mo/Mo-V/V-W co-doped TiO2 photocatalyst for the effective degradation of MB (methylene blue) dye under sunlight irradiation was successfully prepared by one-step Plasma Electrolytic Oxidation (PEO) process. The XRD, XPS, and EDS results revealed that W/Mo/V were co-doped in the TiO2 lattice. The highest redshift in the light absorption edge is recorded for the sample MV (Mo-V co-doped TiO2) with a bandgap of 2.51 eV, whereas the bandgaps for WM (W-Mo co-doped TiO2) and VW (V-W co-doped TiO2) are recorded as 2.96 eV and 2.58 eV, respectively. The co-doped photocatalysts show a typical PEO structure with a high degree of porosity favouring the dye adsorption ability. EIS, LSV, and PL analysis confirmed that the co-doped coatings pose a high degree of charge separation, suppressed charge carriers' recombination, and increased the ability to produce photocurrent. Under direct sunlight irradiation, the sample MV showed the highest photocatalytic efficiency, confirmed by MB dye degradation, then the other co-doped and undoped TiO2. This can be attributed to the synergetic effects of intense visible light absorption in the solar spectrum and the reduced charge carriers' recombination rate by acting as the trapping sites for photogenerated electrons and holes. Finally, this immobilised co-doped photocatalyst developed by the PEO process is a promising system in the quest to establish a renewable energy-assisted strategy for textile wastewater treatment application. • Developed direct sunlight active W-Mo/Mo-V/V-W co-doped TiO 2 on Cp-Ti by PEO. • Mo-V co-doped TiO 2 (Eg of 2.41 eV) shows the highest redshift in light absorption. • Immobilised Mo-V co-doped TiO 2 shows the highest dye degradation and mineralisation. • Low Eg and e + /h − recombination rate is due to the synergetic effect of V and Mo.

Removal of the Hazardous Congo Red Dye through Degradation under Visible Light Photocatalyzed by C,N Co-Doped TiO2 Prepared from Chicken Egg White.

The C,N co-doped TiO2 photocatalyst was prepared by interacting the chicken egg white having various weights (1, 2, and 4 g) with 1 g of TiO2 in an autoclave through the hydrothermal process at 150°C. The C,N co-doped TiO2 photocatalysts were characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), specular reflectance UV/visible (SRUV/Vis), and transmission electron microscope (TEM) instruments. The photocatalytic activity of the co-doped TiO2 was evaluated by monitoring the photo-decolorization of Congo red dye under visible light through a batch experiment. The characterization results assigned that the C and N atoms from the chicken egg white have been successfully co-doped into TiO2 through interstitial and substitutional combination, which could notably narrow their band gap energy entering into the visible region. In line with the gap narrowing, the co-doping C,N into TiO2 could remarkably improve the photocatalytic activity under visible light in the dye photo-decolorization. The enhancement of the photocatalyst activity of TiO2-C,N was controlled by the weight of the egg white introduced, and 2 g of the egg white resulted in the highest activity. Further, the best dye photo-decolorization, which was about 98%, of 10 mg/L Congo red dye in 100 mL of the solution under visible irradiation could be reached by applying TiO2-C,N prepared from 2 g of the egg white, within 45 min, at pH 7, and 50 mg of the photocatalyst mass.

Preparation of Zr/Y co-doped TiO2 photocatalyst and degradation performance of hydroquinone

Preparation of Zr/Y co-doped TiO2 photocatalyst and degradation performance of hydroquinone

Graphene quantum dot and iron co-doped TiO2 photocatalysts: Synthesis, performance evaluation and phytotoxicity studies

The present study reports the synthesis, photocatalytic decolorization of reactive black 5 dye and phytotoxicity of graphene quantum dots (GQDs) and iron co-doped TiO2 photocatalysts via modified sol gel method. GQDs were synthesized by direct pyrolysis of citric acid (CA). Scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS), Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), Brunauer–Emmett–Teller (BET) and photoluminescence spectroscopy (PL) were used to determine the physicochemical properties of the best performing photocatalysts. The results indicated improved physicochemical properties of GQD-0.1Fe-TiO2-300 with root mean square roughness (Rz) (33.82 nm), higher surface area (170.79 m2 g−1), pore volume (0.08 cm3 g−1), and bandgap (2.94 eV). Moreover, GQD-0.1Fe co-doping of TiO2 greatly improved the photocatalytic decolorization efficiency for RB5 dye. The photocatalytic reaction followed the pseudo first order reaction with gradual decrease in Kapp values for increment in RB5 concentration. The KC value was obtained as 2.45 mg L−1 min−1 while the KLH value was 0.45 L mg−1 indicating the heterogeneous reaction system followed the Langmuir-Hinshelwood isotherm and simultaneously occurring adsorption and photocatalytic processes. Photocatalytic reaction mechanism studies exhibited the holes and OH radicals as the main active species in the GQD-0.1Fe-TiO2-300 responsible for the decolorization of RB5. The proposed reaction pathway showed that both Fe-TiO2 and GQDs play important role in generation of electrons and holes. Additionally, GQD-0.1Fe-TiO2-300 were durable up to four cycles. Phytotoxicity assay displayed that treated water and best performing photocatalysts had no effect on Lycopersicon esculentum seed germination. Therefore, the proposed system can pave a viable solution for safe usage of dye loaded wastewater and effluent for irrigation after treatment.

Facile one-pot hydrothermal method to prepare Sn(II) and N co-doped TiO2 photocatalyst for water splitting under visible light irradiation

Facile one-pot hydrothermal method to prepare Sn(II) and N co-doped TiO2 photocatalyst for water splitting under visible light irradiation

Visible light active Fe-Pr co-doped TiO2 for water pollutants degradation

Fe–Pr co-doped TiO2 photocatalysts are synthetized by sol–gel method using titanium tetraisopropoxide, praseodymium nitrate and iron acetylacetonate as precursors of titania, praseodymium and iron, respectively. The chemical-physical properties of all prepared samples are analysed by X-ray diffraction (XRD), Raman spectroscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), photoluminescence (PL) spectroscopy and N2 adsorption at −196 °C. XRD patterns show the main peaks of anatase phase in all photocatalysts and evidence that Fe and Pr ions are effectively introduced into the TiO2 lattice. UV–vis DRS spectra indicate the reduction of the band gap value of Fe-Pr co-doped TiO2 with respect to TiO2 and Pr-doped TiO2 thank to co-doping of TiO2 with Pr and Fe ions. The photocatalytic performances of all prepared samples are investigated for the degradation of Acid Orange 7 azo dye (AO7) and also of phenol under visible light irradiation. Photocatalytic efficiency obtained using Fe–Pr co-doped TiO2 markedly increases compared to un-doped TiO2, Pr-doped TiO2 and Fe-doped TiO2 photocatalysts. Fe-Pr co-doped TiO2 prepared with 8.5 mg of praseodymium nitrate gave the best photocatalytic activity. The enhanced photocatalytic activity should be associated with the simultaneous doping of TiO2 with Pr3+ and Fe3+ ions that induces a marked decrease of band gap value together with an enhanced generation of oxygen vacancies, which can trap electrons, and therefore reducing their recombination with photogenerated positive holes. Indeed, using the optimized Fe-Pr co-doped TiO2, the dye discoloration and mineralization is about 87 and 80 %, respectively, after 60 min of LEDs visible light irradiation, underlining the best performances of the optimized Fe–Pr co-doped TiO2 in terms of treatment time. Finally, the optimized Fe-Pr co-doped TiO2 is tested for visible light degradation of phenol in aqueous solution, confirming the absence of possible sensitization phenomena of photocatalyst surface by the AO7 dye.

Insoluble matrix proteins from shell waste for synthesis of visible-light response photocatalyst to mineralize indoor gaseous formaldehyde

HCHO is the most concerned indoor air pollutant that photocatalytic degradation is a feasible approach. To achieve efficient and complete degradation of HCHO under visible light irradiation, heteroatoms are usually doped in TiO2. But using natural materials as a dopant instead of expensive and toxic chemicals to fertilize TiO2 remains challenging. This paper proposes a sustainable and green approach to synthesize an efficient N, Ca co-doped TiO2 photocatalyst (TIMP) by using the insoluble matrix proteins (IMPs) extracted from abalone shell. TIMP-0.8 achieves near completely degradation HCHO within 45 min under visible light at ambient temperature and exhibits superior stability after 7 cycles. TIMP-0.8 has monodispersity with smaller diameter, high porosity, abundant defects and high adsorption affinity for surface hydroxyls compared with pure TiO2. With the assistance of IMPs, the rate-determining step of HCHO degradation changes from −COOH oxidation to spontaneous decomposition of HCO3−, significantly facilitating the elimination and mineralization of HCHO. Overall, IMPs from abalone shell are natural surfactant, bio-templet, and dopant for TiO2 modification, contributing to desirable visible-light photocatalytic performance for HCHO degradation. This paper provides new insight for high-value utilization of waste shell and photocatalytic indoor purification.

Visible-light harvesting innovative W6+/Yb3+/TiO2 materials as a green methodology photocatalyst for the photodegradation of pharmaceutical pollutants.

In this work, we report on the synthesis of a new-age reusable visible-light photocatalyst using a heterojunction nanocomposite of W6+/Yb3+ on a mixed-phase mesoporous network of monolithic TiO2. The structural properties of the monolithic photocatalysts are characterized using p-XRD, SEM-EDAX, TEM-SAED, XPS, PLS, UV-Vis-DRS, FT-IR, micro-Raman, TG-DTA, and N2 isotherm analysis. The electron microscopic analysis reveals a mesoporous network of ordered worm-like monolithic design, with a polycrystalline mixed-phase (anatase/rutile) TiO2 composite, as indicated by diffraction studies. The UV-Vis-DRS analysis reveals a redshift in the light absorption characteristics of the mixed-phase TiO2 monolith as a function of W6+/Yb3+ co-doping. It is observed that the use of (8.0mol%)W6+/0.4 (mole%)Yb3+ co-doped monolithic TiO2 photocatalyst, with an energy bandgap of 2.77eV demonstrates superior visible-light photocatalysis, which corroborates with the PLS studies in terms of voluminous e-/h+ pair formation. The practical application of the photocatalyst has been investigated through a time-dependent dissipation of enrofloxacin, a widely employed antimicrobial drug, and its degradation pathway has been monitored by LC-MS-ESI and TOC analysis. The impact of physio-chemical parameters such as solution pH, sensitizers, drug concentration, dopant/codopant stoichiometry, catalyst quantity, and light intensity has been comprehensively studied to monitor the process efficiency.

Optimized preparation and characterization of Co-N codoped TiO2 with enhanced visible light activity: An insight into effect of dopants on surface redox reactions of photogenerated charge carriers for hydroxyl radical formation

In this study, a statistical experiment design approach using response surface methodology was applied in the optimization of preparing Co-N codoped TiO2 photocatalyst. The prepared Co-N codoped TiO2 significantly enhanced the photocatalytic degradation of dye Congo Red under visible light irradiation, as compared to undoped and N, Co monodoped TiO2. As proved by various characterizations, the enhanced photocatalytic activity of Co-N codoped TiO2 can be attributed to the narrowing of energy band structure and the existence of surface oxygen vacancies (OVs) and Co ions as the charge traps, thus resulting in the improvement of visible light absorption and charge transfer. The electron spin resonance and fluorescence measurements confirmed that the formation of hydroxyl radicals (•OH) can be promoted during Co-N codoped TiO2 photocatalysis, due to the more efficient generation and separation of electron–hole pairs. Moreover, it was found that the oxidation of H2O by holes is the relatively major pathway of •OH formation, and OVs could effectively reduce the electron competition between dissolved O2 and Co dopants to ensure the hole- and electron-induced surface redox reactions to proceed smoothly. Based on the above results, a more comprehensive mechanism of Co-N codoping for enhancing TiO2-assisted photocatalysis was thereby proposed.