Visible Light Responsive TiO2 Research Articles

A Visible Light-Responsive TiO2 Photocathode Achieved by a Rh Dopant.

Developing an efficient and stable photocathode material for photoelectrochemical solar water splitting remains challenging. Herein, we demonstrate the potential of rutile TiO2 as a photocathode by Rh doping with visible light absorption up to 640 nm and an onset potential of 0.9 V versus the reversible hydrogen electrode. The dopant transforms the rutile host from an n-type semiconductor to a p-type one, as confirmed by the Mott-Schottky curve and kelvin probe force microscopy. Physical and photoelectrochemical analyses further suggest that the doping mechanism is dependent on concentration. Lower levels of dopants generate localized Rh3+, while higher levels favor Rh4+ that interacts more strongly with the O 2p orbitals. The latter is found not only to extend the visible light absorption range but also to facilitate charge transport. This work elucidates the role of the Rh dopant in adjusting the photoelectrochemical behavior of TiO2, and it provides a promising photocathode material for solar energy conversion.

Green synthesis of xanthene derivatives through visible light-driven photocatalysis using blackberry dye-sensitized TiO2

Researchers are actively exploring novel approaches to sustainable chemistry, aiming to reduce environmental harm while optimizing efficiency. One promising approach is visible light photocatalysis, which enables organic transformations under mild conditions. This research investigation focuses on the synthesis of xanthene derivatives (12-Aryl/hetroaryl-8,9,10,12-tetrahydrobenzo [a] xanthen-11-oness) via a three-component, one-pot condensation reaction of 2-naphthol, dimedone, and aldehydes using visible light-responsive TiO2 nanoparticles sensitized with blackberry dye. A comparative analysis was conducted between pristine TiO2 nanoparticles and blackberry dye-sensitized TiO2 (BB dye-TiO2) to evaluate their photocatalytic activities. The results unequivocally demonstrated the superior photocatalytic activity of BB dye-TiO2 compared to pristine TiO2 nanoparticles. The study determined the optimal operating conditions for achieving an efficient photocatalytic synthesis of xanthene derivatives and proposed a mechanism for the photocatalytic process. The optimized conditions for photocatalytic synthesis with a yield of 98% included a reaction time of 30 min, a light intensity of 100 mW/cm2, and a photocatalyst concentration of 1 g/L. Moreover, the reusability test revealed that the BB dye-TiO2 maintained its photocatalytic activity for up to four runs, with only a slight decrease observed. This study highlights the immense potential of natural dye sensitization and visible light photocatalysis for sustainable chemical synthesis, effectively bridging the realms of green chemistry and synthetic organic chemistry.

Tailoring surface defects in Plasma Electrolytic Oxidation (PEO) treated 2-D black TiO2: Post-treatment role, and intensification by peroxymonosulfate activation in visible light-driven photocatalysis

Herein, we have developed a visible light-responsive black TiO2 photocatalytic coating with controlled formation of oxygen vacancies (OV) and Ti3+ species, crucial for enhancing photocatalytic reactions. The rational control of these semiconductor defects was achieved through plasma electrolytic oxidation (PEO), followed by NaOH post-treatment. The coating's effectiveness was evaluated by tetracycline (TC) degradation. The surface defects function as traps, reducing electron/hole recombination and forming mid-gap/localized-donor states, narrowing the band gap. Rigorous material characterization confirmed unaffected morphology and PEO coating phases, while increasing the density of OVs and Ti3+ species. As a result, TC photo-degradation was ∼3.5 times higher compared to plain PEO coatings. The material demonstrated exceptional stability and efficiency, while it was successfully intensified via peroxymonosulfate (PMS) activation, leading to high synergies (2.10). Scavenger tests revealed the existence of both radical/non-radical pathways, indicating the prevailing photocatalytic mechanism and the key differences achieved through this novel process.

Hydrophobic and visible-light responsive TiO2 as an efficient photocatalyst for promoting hydrogen peroxide production in a two-phase system

Photocatalytic synthesis of hydrogen peroxide (H2O2) coupled with benzyl alcohol (BA) oxidation reaction is preferred based on the economic consideration. Herein, we developed a hydrophobic TiO2 material (DNOPA-TiO2), co-modified with 2,3-dihydroxynaphthalene (2,3-DN) and octadecylphosphonic acid (OPA), which enables H2O2 synthesis under visible-light-irradiation in a two-phase system consisting of BA and water. This system allows the separation of generated H2O2 in the aqueous phase from benzaldehyde (BAL), the product of BA oxidation, present in the organic phase. The hydrophobic DN2OPA2-TiO2 exhibited higher and more stable H2O2 production (3522 μmol L−1) over an 8-hour reaction under visible light (λ > 450 nm). The addition of 2,3-DN facilitates visible light harvesting and donates electrons to TiO2 through the formation of charge-transfer complexes, which promotes the O2 reduction reaction (ORR) and improves H2O2 production. Moreover, the remarkable stability of DN2OPA2-TiO2 is originated from the hydrophobic nature of the catalysts thanks to OPA modification. This modification allows TiO2 to exist in the organic phase with better dispersion, inhibiting the decomposition of H2O2 resulting from direct contact between produced H2O2 and TiO2.

A strategy to improve the performance of TiO2 nanotube array film photocatalysts by magnetron-sputtered amorphous BiFeO3

Amorphous BiFeO3/TiO2 nanotube array thin films were prepared on indium tin oxide glass using an anodic oxidation technique coupled with magnetron sputtering. The morphology, structure, optical properties, photoelectrochemical properties, and photocatalytic activity of heterostructured nanotube array thin films with different morphologies of BiFeO3 were studied. HRTEM observations show the interface between amorphous BiFeO3 and anatase TiO2. The amorphous BiFeO3/TiO2 nanotube array thin films show enhanced visible-light absorption and outstanding separation and transfer of photoinduced charges. The BFO3-TNA sample shows excellent photocatalytic activity. By using it, 97.6% of chromium (VI) can be removed in 60 min under visible-light illumination. This work will provide a feasible route to further enhance the photocatalytic activities of visible-light responsive TiO2 nanotube array thin films as photocatalysts for rapidly removing chromium (VI) from water.

Visible light responsive S-Doped TiO2 nanoparticles: synthesis, characterization and photocatalytic degradation of pollutants

Visible light responsive S-Doped TiO2 nanoparticles: synthesis, characterization and photocatalytic degradation of pollutants

Photocatalytic degradation of malachite green dye using nitrogen/sodium/iron-TiO2 nanocatalysts

Enhanced visible light-responsive TiO2 modified with nitrogen, sodium, and iron was synthesized using an integration of green synthesis and wet impregnation method. The prepared nanocatalysts were characterized using some analytical tools like UV–visible spectrometry (UV–visible), photoluminescence (PL), High-resolution transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller N2 adsorption–desorption process, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy, The photocatalytic activity of N/Na/Fe–TiO2 and bared TiO2 for the degradation of Malachite green (MG) dye in aqueous solution under visible light was investigated. The response surface methodology (RSM) based on Box Benhken Design was used to evaluate the interaction between three important independent variables (reaction time, catalyst dosage, and dye solution pH). The XRD results of the prepared samples showed that the crystal phase was anatase irrespective of the modifiers. The BET surface areas of the tri-doped TiO2 nanocatalysts (80.165 m2/g) were higher than the undoped TiO2 (10.25 m2/g). XPS analysis confirmed the existence of Ti in + 4 oxidation states with or without the dopants. The MG removal efficiency was pH and catalyst dosage-dependent, and maximum MG degradation (96.57 %) was obtained using N/Na/Fe tri-doped TiO2 nanocatalyst under optimum experimental conditions of 0.11 g catalyst dosage, 25.83 min reaction time, and pH of 9.89. The N/Na/Fe-TiO2 nanocatalyst was reusable for up to 5 cycles without significant loss of photocatalytic activity.

Diclofenac degradation properties of a La-doped visible light-responsive TiO2 photocatalyst

Diclofenac (DCF), which is detected in the aquatic environment, can act as a harmful factor to the ecosystem and human health, but it is difficult to remove it with existing water treatment methods. DCF can be removed using the TiO2 photocatalysis process, and in this study, a method for removing it using visible light was sought. A visible-light reactive TiO2 photocatalyst doped with lanthanum (La) was synthesized using an LPP (Liquid Phase Plasma) process, and the photocatalytic activity was investigated by decomposing diclofenac. La was doped uniformly into the TiO2 powder, and the content of doped La increased with increasing concentration of the initial precursor. The La dopant was in the form of La2O3, and the bandgap and photoluminescence intensity decreased with increasing amount of doped La. In the photolysis experiment using a UV light source, the La-doped TiO2 photocatalysts (LDTPs) showed slightly higher activity than the bare TiO2, but the photocatalyst activity of the LDTPs under the visible light irradiation was superior. In the degradation experiment of DCF by LDTP, four major by-product intermediates were detected. Moreover, it was estimated that degradation proceeded through two pathways: hydroxylation and ring closure.

Visible light responsive rutile TiO2 photocatalysts mixed with cement: Enhancement effect driven by TiO2/cement interfaces

Naked rutile TiO2 as well as commercial rutile TiO2 with Al2O3 and ZrO2 capping layers both with particle size of 100 ~ 300 nm were tested as additives to cements with a goal of fabricating building materials that can remove harmful NO and volatile organic compounds from the atmosphere. The commercial TiO2 is widely used as pigment and very cost-effective. Generally, the activities of photocatalysts were enhanced by mixing with cement. Moreover, originally less active capped TiO2 yielded comparable or even superior activity than bare rutile in the composite with cement. Our results suggest that the activity of the photocatalyst/cement is overwhelmingly governed by the active TiO2/cement interfaces rather than the intrinsic surface structural properties of photocatalysts. Based on various analyses results including x-ray absorption spectroscopy, emphasis is placed on the unique adsorption properties of the interface sites, which are driven by the lattice distortion of TiO2 at this interface.

Visible light responsive TiO2 - graphene oxide nanosheets - Zn phthalocyanine ternary heterojunction assisted photoelectrocatalytic degradation of Orange G

Herein, we report on the successful fabrication of a visible light-responsive TiO2 - graphene oxide nanosheets – Zn phthalocyanine (TiO2@GONS@ZnPc) ternary structure for the photoelectrochemical degradation of Orange G azo dye. The characterization of TiO2@GONS@ZnPc composite was achieved using various spectroscopic and microscopic techniques. Our results show that the TiO2@GONS@ZnPc surface hybrid heterojunction promotes charge separation and electron migration, significantly improving the degradation efficiency with an applied potential. For the first time, we show the existence of a non-radical activation route for persulfate (PS) using such π electron-rich ZnPc-GONS catalysts. The degradation kinetics were found to follow pseudo first order kinetics. Electron spin resonance analyses suggested that neither hydroxyl radicals nor sulfate radicals were produced therein, and therefore were not responsible for the persulfate-driven oxidation of the OG dye. These findings suggest that both which GONS and ZnPc play a critical role in mediating the eventual charge transfer mediated PS activation. The results illustrate the remarkable capacity of the TiO2@GONS@ZnPc composite to rapidly degrade Orange G by a coupled TiO2@GONS@ZnPc-persulfate system.

Fabrication of visible-light responsive TiO2@C photocatalyst with an ultra-thin carbon layer to efficiently degrade organic pollutants

Titanium dioxide (TiO2) is considered a promising photocatalyst due to its remarkable properties, such as photostability, low energy consumption and non-toxicity. However, some intrinsic drawbacks of TiO2 including high band gap energy and easy recombination of electron-hole pairs seriously hinder its practical application in photocatalysis. In this study, a 1-nm-thick carbon coating layer was introduced onto the surface of TiO2 (TiO2@C) by carbonizing kraft lignin to improve the photocatalytic performance. Compared with TiO2, TiO2@C shows absorption in both visible-light and UV-light regions, a decrease in band gap energy from 3.31 to 3.27 eV and excellent electronic conductivity, which favour the generation and separation of photo-generated carriers. In addition, the ultra-thin carbon coating can guarantee the penetration of sunlight, and TiO2@C, which remains afloat on the water, can contact with wastewater and absorb sufficient sunlight due to the hydrophobicity and loose structure. The investigation of photocatalytic degradation towards methylene blue (MB) and tetracycline (TC) under artificial visible-light irradiation demonstrates that the prepared TiO2@C has relatively superior photocatalytic activity. The absorbed MB and TC are almost completely degraded by TiO2@C within 10 min and 35 min, respectively. Given the simple modification and excellent photocatalysis, the prepared TiO2@C exhibits great potential applications in contaminated water treatment. This study provides a feasible carbon-coating strategy to improve the photocatalytic performance of TiO2, which can be extended to the rational design of other photocatalysts.

A phase separation in a protonated layered nickel titanate to form Ni-doped anatase/rutile TiO2 nanocomposite with efficient visible-light responsive photocatalytic activity

ABSTRACT We report a simple methodology for the preparation of an efficient visible-light responsive TiO2 photocatalyst through acid treatment of a lepidocrocite-type layered nickel cesium titanate (Cs0.7Ti1.65Ni0.35O4) for interlayer protonation and subsequent calcination at different temperatures (400–600°C) to induce structural transformation. The Ni-doped anatase/rutile nanocomposite possessing a morphology similar to that of protonated layered nickel titanate is obtained at all calcination temperatures. The sample obtained at 600°C exhibits the highest visible-light responsive photocatalytic activity for decomposition of the aqueous methylene blue dye under visible-light (λ > 420 nm) irradiation. The activity is 14 times higher than that of P25 (standard TiO2 photocatalyst) modified with Ni2+ and 3 times higher than that of NiTiO3 (visible-light responsive photocatalyst). The efficient visible-light responsive photocatalytic activity is ascribable to the visible-light absorption ability of the TiO2 phase owing to Ni-doping. Also, an efficient electron transfer across anatase–rutile interfaces for inhibition of charge recombination could be responsible for the activity. This methodology is a new route for efficient visible-light responsive photocatalysts based on TiO2 doped with various elemental species. This is because lepidocrocite-type layered titanates are available in a variety of chemical compositions.

Biological renewable hemicellulose-template for synthesis of visible light responsive sulfur-doped TiO2 for photocatalytic oxidation of toxic organic and As(III) pollutants

Sulfur-doped TiO2 catalysts using biological renewable hemicellulose template (S/TiO2-T) were synthesized and characterized with different instruments. The photocatalytic activities of the resulting S/TiO2-T photocatalysts with different amounts of S-doped TiO2 were investigated through the decomposition of toxic nitrobenzene, p-chlorophenol, and phenol organic compounds and oxidation of As(III) pollutant under visible light irradiation. The highest photocatalytic activity was obtained from S/TiO2-T catalyst prepared with the n(TiCl4)/n(Thiourea) precursor molar ratio of 4/2 after calcinations at 600 °C to achieve the complete removal of nitrobenzene within 40 min. However, only 75.2%, 8.8%, and 7.9% were removed by S/TiO2, TiO2-T, and P25-TiO2, respectively. It was also observed that the S/TiO2-T(4/2) catalyst had higher catalytic efficiency for oxidation of As(III) under visible light irradiation. The complete oxidation of 250 ml (50 mg/L) of As(III) solution was achieved within 20 min under visible light irradiation by 125 mg S/TiO2-T(4/2) catalyst. The hemicellulose aided synthesis led to high dispersion, small grain size, and high specific surface area of S/TiO2-T catalysts. Moreover, the S-doping of TiO2 is also the key factor for the visible light responsive degradation of toxic organic compounds and oxidation of As(III), and using the template in the synthesis further improves the catalytic performances.

The Use of Tunable Optical Absorption Plasmonic Au and Ag Decorated TiO2 Structures as Efficient Visible Light Photocatalysts

Exploring solar-excited heterogeneous photocatalysts by taking advantage of surface plasmon resonance (SPR) has drawn growing research attention. As it could help to pave the way for global sustainable development. The decoration of TiO2 particles with noble metals possessing SPR effects is regarded as one of the most effective solutions. The perfect match of the SPR absorption band with the spectrum of incident light is an essential factor for plasmonic enhancement. However, modifying with sole noble metal is often limited as it tunes wavelength of only several nanometers. To overcome this drawback, an alternative approach can be offered by decoration with more than one noble metal. For instance, Au-Ag co-decoration displays greatly adjustable, composition-dependent SPR agent over a broad range of the visible light spectrum (ca. from 415 to 525 nm). Hence Au-Ag complex is a remarkable candidate for tuning the photo adsorption of TiO2 from UV to visible light. This study presents a novel and tailored method for the fabrication of Au-Ag co-modified TiO2 particles, and how Au-Ag dependent SPR was applied as the visible light-responsive TiO2 based photocatalysts in a simple but reliable way. The fabricated Au-Ag co-decorated TiO2 (AuxAg(1−x)/TiO2) was characterized and proved to own excellent stability and large specific surface area. The optimization of these particles against the wavelength of maximal solar light intensity was confirmed by photo degradation of methylene blue under visible light radiation. This work may provide further insight into the design of TiO2-based composites with improved photocatalytic properties for environmental remediation and renewable energy utilization.

Visible light responsive TiO2 photocatalysts for degradation of indoor acetaldehyde.

Photocatalysis is a promising technique for developing sustainable and environmentally friendly materials to improve indoor air quality. Visible-light-responsive TiO2 has been widely investigated but there are inconsistent results because photocatalytic properties depend strongly on synthetic methods. Herein, we synthesize TiO2 doped with 10 different metal ions (M–TiO2) by conducting a dialysis in a sol–gel method to obtain the best photocatalyst for the degradation of acetaldehyde under LED irradiation. Purification of a sol by dialysis enables us to discuss pure effects of dopants on the photocatalytic activity because impurities such as counter ions of metal salts are removed before sintering. Only Cr–, Pt–, V–, and Fe–TiO2 show photocatalytic activity and the optimal doping amounts are 0.50–1.7, 0.10, 1.0, and 0.10 atom%, respectively. Such differences in the optimal amounts can be explained in terms of the dopant ions having different valence states, suggesting the formation of oxygen vacancies. The Cr–TiO2 powder exhibits high activity even at the doping amount of 4.2 atom%. We also demonstrate that the Cr–TiO2 film prepared on a glass substrate can be used to degrade acetaldehyde by changing the film thickness and the LED intensity depending on the degree of the indoor contamination.

Visible light-responsive Fe-loaded TiO2 photocatalysts for total oxidation of acetaldehyde: Fundamental studies towards large-scale production and applications

Various Fe loadings were applied onto P25 TiO2 using temperature-controlled vapour deposition and the resulting structures were subsequently annealed at 750 °C. As-received TiO2 was nearly photo-catalytically inactive for acetaldehyde decomposition under visible light, but when a very small amount of Fe below the threshold was loaded, the activity became maximized. Control of Fe loading is critical to prepare high-performing Fe-TiO2 photocatalysts since a larger amount of Fe forms larger iron oxide particles, which induces non-radiative recombination of the optically excited electron-hole pairs, thereby reducing the photocatalytic activity. Regarding the reaction mechanism, fast oxidation of acetaldehyde into CO2 and a slower path via acetic acid to CO2 were identified, where almost no evolution of secondary pollutant vapour was identified. A strategy towards large-scale production and stable fixation of photocatalyst powder on surfaces of construction materials for real air purification applications are discussed.

A cost-effective quick-making strategy for visible light-responsive titanium dioxide

The formation of anatase structure usually requires high-temperature heat treatment at 450–500 °C for 30–150 min, which causes energy waste, particle agglomeration and significant loss of photocatalytic performance of TiO2. In this paper, we proposed a low-temperature quick-making strategy for visible light-responsive TiO2, which involves ultrahigh electron density cold plasma spraying combined with rapid heating (CPRH) treatment at a quite lower temperature than traditional methods. We explored the effect of calcination temperature and time on the crystallization behavior of the plasma sprayed TiO2. Anatase crystal structures are found in CPRH samples calcined at 275 °C in 10 min. The decrease of Ti3+, the increase of N-doping, and the preservation of –OH groups are detected in CPRH-300 samples. Also, the higher visible-light photoactivity than the conventional sol-gel TiO2 crystallized at 450 °C is obtained. The proposed cost-effective CPRH strategy demonstrates significant practical value for energy conservation.

Homogeneous Doping of Substitutional Nitrogen/Carbon in TiO2 Plates for Visible Light Photocatalytic Water Oxidation

AbstractExtending the light absorption range of wide‐bandgap photocatalysts into the visible light region is significant in terms of fully harvesting and converting solar light. The desirable band‐to‐band redshift of the absorption edge of semiconducting binary metal oxides such as prototypical photocatalyst TiO2 by doping is long targeted but remains a challenge, up to date. Here, by taking the advantage of abundant 1D diffusion channels with rhombus‐like cross‐sections along the c‐axis in the crystal structure of titanium oxalate hydrate to promote the entrance of nitrogen dopant species into the bulk and subsequent thermal topotactic transition in an atmosphere of gaseous ammonia, homogeneous doping of substitutional carbon/nitrogen for oxygen in the TiO2 decahedral plates with a dominant anatase phase is obtained for the first time. The resultant TiO2−x(CN)y with an unusual band‐to‐band visible light absorption spectrum can induce photocatalytic water oxidation to release oxygen under visible light irradiation. This study provides not only a promising visible light–responsive TiO2 photocatalyst, but also an important strategy for developing other solar‐driven photocatalysts.

Synthesis of visible light responsive iodine-doped mesoporous TiO2 by using biological renewable lignin as template for degradation of toxic organic pollutants

The visible light responsive I-doped mesoporous TiO2 (I/TiO2-T) catalysts were synthesized by facile hydrolysis method with lignin as a template. The resulting I/TiO2-T catalysts synthesized from different amounts of I as a dopant and lignin as a template were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The photocatalytic activities of the resulting catalysts were investigated by the degradation of p-chlorophenol under artificial visible light irradiation. The results showed that the lignin-templated TiO2 with a suitable amount of I-doping (I/TiO2-T) had higher catalytic activity than the catalyst prepared form I-doped TiO2 without lignin template (I/TiO2). Complete degradation of p-chlorophenol was achieved by I/TiO2-T with suitable amount of I-doping at 60 min. However, 95.7, 10.7, and 5.5% of the p-chlorophenol was degraded with I/TiO2, TiO2-T, and P25 catalysts, respectively, under 140 min visible light irradiation. The enhanced catalytic activities of the samples with template and I-doping may be due to the small grain size and high specific surface area of the catalysts. The band gap and the electrical properties of TiO2 also could be adjusted with I-doping. The I-doped TiO2 with the extrinsic I5+-to-Ti4+ and the iodine-to-oxygen donor defects could be excited by visible irradiation for efficient pollutants degradation. A possible photocatalytic mechanism for the degradation of the pollutants with I/TiO2-T under visible light irradiation was also proposed.

Visible light responsive TiO2 nanotubes synthesized by electrochemical anodization method

Visible light responsive TiO2 nanotubes synthesized by electrochemical anodization method