Titania Photocatalysts Research Articles

Visible-Light-Induced Oxidative Coupling of Phenols and Alkenylphenols with a Recyclable, Solid Photocatalyst.

A photocatalytic method for phenol and alkenylphenol oxidative coupling is reported using an inexpensive heterogeneous titanium dioxide photocatalyst with air and visible light. During the coupling process, the Ti-substrate complex is activated under visible light through a ligand to metal charge transfer effect, and the diphenol adduct is proposed to form through a radical cation. The heterogeneous TiO2 catalyst remains stable throughout the reaction and can be easily removed and reused multiple times.

Novel Pilot-Scale Photocatalytic Nanofiltration Reactor for Agricultural Wastewater Treatment

Nowadays, the increased agro-industrial activities and the inability of traditional wastewater treatment plants (WWTPs) to eliminate recalcitrant organic contaminants are raising a potential worldwide risk for the environment. Among the various advanced water treatment technologies that are lately proposed for addressing this challenge, the development and optimization of an innovative hybrid photocatalytic nanofiltration reactor (PNFR) prototype emerges as a prominent solution that achieves synergistic beneficial effects between the photocatalytic degradation activity and size exclusion capacity for micropollutant molecules. Both these features can be contemporarily endued to a multitude of membrane monoliths. The physicochemical and the photoinduced decontamination properties of the titania materials were firstly determined in the powder form, and subsequently, the structural and morphological characterization of the obtained titania-modified membrane monoliths were accomplished. The PNFR unit can operate at high water recovery and low pressures, exhibiting promising removal efficiencies against Acetamiprid (ACT) and Thiabendazole (TBZ) pesticides and achieving the recycling of 15 m3/day of real agro-wastewater. The obtained results are very encouraging, demonstrating the integration of titania photocatalysts in a photocatalytic membrane reactor as a feasible technological solution for the purification of agricultural wastewater.

Enhancing the Photocatalytic Activity of TiO2 for the Degradation of Congo Red Dye by Adjusting the Ultrasonication Regime Applied in Its Synthesis Procedure

Recently, the ultrasound-assisted sol-gel synthesis procedure of mesoporous titania (TiO2) photocatalysts caught the researcher’s attention, due to the physicochemical properties enhancement of the resulting titania nanomaterials. Thus, by varying different synthesis parameters particular characteristics could be obtained. In the present study, the ultrasound pulse on/off ratio has been considered and the effect of the envisaged parameter on the textural, morphological, and optical features of titania nanomaterial has been investigated. Therefore, X-ray Diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR), N2-sorption measurements, SEM imaging, and UV-Vis Diffuse Reflectance spectroscopy (UVDR) have been used. And further, the photocatalytic activity of the prepared TiO2 materials was evaluated by the features developed about the applied ultrasound pulse on/off ratio as 1/1, 2/1, 3/1, 4/1, 1/3 and 2/2. It was found that the ultrasound pulse on/off ratio considered in the synthesis procedure of titania leads to TiO2 materials with different textural (SBET = 98–156 m2/g), morphological, and optical (Eg = 3.1–3.2 eV) characteristics. For this reason, TiO2 nanomaterials prepared were found to exhibit suitable features for photocatalytic applications. Thus, the TiO2 4.1 sample prepared at 4/1 ultrasound pulse on/off ratio revealed the highest photodegradation efficiency of Congo Red dye (98.28%) as the results of photocatalytic tests show. More than that, a possible reaction mechanism of the CR photodegradation process through the contribution of reactive oxygen species (·HO, ·O2−), holes (h+), and electrons (e−) of developed titania photocatalyst was proposed.

A Novel Tri-Functionality pH-Magnetic-Photocatalytic Hybrid Organic-Inorganic Polyoxometalates Augmented Microspheres for Polluted Water Treatment.

The severe water pollution from effluent dyes threatens human health. This study created pH-magnetic-photocatalytic polymer microspheres to conveniently separate the photocatalyst nanoparticles from the treated water by applying an external magnetic field. While fabricating magnetic nanoparticles' (MNPs) microspheres, incorporating 0.5 wt.% iron oxide (Fe3O4) showed the best magnetophoretic separation ability, as all the MNPs microspheres were attracted toward the external magnet. Subsequently, hybrid organic-inorganic polyoxometalates (HPOM), a self-synthesized photocatalyst, were linked with the functionalized magnetic nanoparticles (f-MNPs) to prepare augmented magnetic-photocatalytic microspheres. The photodegradation dye removal efficiency of the augmented magnetic-photocatalytic microspheres (f-MNPs-HPOM) was then compared with that of the commercial titanium dioxide (TiO2) photocatalyst (f-MNPs-TiO2). Results showed that f-MNPs-HPOM microspheres with 74 ± 0.7% photocatalytic removal efficiency better degraded methylene orange (MO) than f-MNPs-TiO2 (70 ± 0.8%) at an unadjusted pH under UV-light irradiation for 90 min. The excellent performance was mainly attributed to the lower band-gap energy of HPOM (2.65 eV), which required lower energy to be photoactivated under UV light. The f-MNPs-HPOM microspheres demonstrated excellent reusability and stability in the photo-decolorization of MO, as the microspheres retained nearly the same removal percentage throughout the three continuous cycles. The degradation rate was also found to follow the pseudo-first-order kinetics. Furthermore, f-MNPs-HPOM microspheres were pH-responsive in the photodegradation of MO and methylene blue (MB) at pH 3 (acidic) and pH 9 (alkaline). Overall, it was demonstrated that using HPOM photocatalysts in the preparation of magnetic-photocatalytic microspheres resulted in better dye degradation than TiO2 photocatalysts.

Doped and immobilized titanium dioxide photocatalysts as a potential source of nitrosamine formation

Immobilized and visible-light-active titanium dioxide (TiO2) is widely used for water treatment. However, the accelerated generation of degradation byproducts is a potential risk of TiO2-based photocatalysis. This study aimed to investigate the structural effect of engineered TiO2 samples on the formation of major nitrosamines during photocatalysis. The nitrogen-containing impurities and leached metal ions from doped-TiO2 samples could exacerbate nitrosamine formation potential (FP) in distilled water, secondary effluent, and chloraminated water. Doped-TiO2 with 2-ethylimidazole, trimethylamine, triethylamine, and N-carbon nanotubes could leach in the range of 47–64 ng L−1 nitrosamines (including N-nitrosomethylethylamine, N-nitrosodiethylamine, N-nitrosodimethylamine, and N-nitrosopyrrolidine) even under dark conditions. Furthermore, we investigated the role of metal dopants on nitrosamine-FP during the chloramination of precursors such as dimethylamine and microcystin-LR. Metal ions such as Cu that leached from the metal-doped catalysts may catalyze the nitrosamine-FP. Therefore, pre-purification (washing) and immobilization of doped-TiO2 samples on substrates are suggested to remove a considerable amount of nitrosamines. However, during the prolonged tryout, the selection of substrates was critical. Polymeric supports, such as polyimide and polyvinylpyrrolidone, can produce up to 85 ng L−1 nitrosamine, whereas TiO2 immobilized onto steel mesh can remove nitrosamine formation during photocatalytic oxidation followed by chloramination. This study systematically screened a diverse range of dopants, supports, and solvents in engineered TiO2 photocatalysts, in 61 samples, and provided novel insights into their effect on nitrosamine formation.

Optimization of process variables for the concurrent removal of aliphatic and aromatic volatile organic compounds over a copper impregnated titanium dioxide photocatalyst

Ultraviolet light assisted photocatalytic removal of aliphatic and aromatic volatile organic compounds in a multicomponent system over copper-impregnated titanium dioxide prepared by wet impregnation method.

Ruthenium and palladium bimetallic nanoparticles achieving functional parity with a rhodium cocatalyst for TiO2-photocatalyzed ring hydrogenation of benzoic acid.

Our previous study showed that a rhodium (Rh) cocatalyst is indispensable for ring hydrogenation of benzoic acid over a titanium(IV) oxide (TiO2) photocatalyst. In this study, we explored ring hydrogenation under an Rh-free condition by using two kinds of cocatalyst that were inactive for this reaction when used solely. Cyclohexanecarboxylic acid as the ring hydrogenation product was successfully obtained when ruthenium (Ru) and palladium (Pd) were simultaneously loaded on TiO2, indicating that this bimetallic system can be used in place of an Rh cocatalyst in ring hydrogenation. The state and distribution of Ru and Pd in particles loaded on TiO2 were investigated by transmission electron microscopy, X-ray photon spectroscopy, and X-ray absorption near edge structure analysis. The functions of Ru and Pd as cocatalysts are discussed on the basis of results of characterization and activity tests. The effects of different contents of Ru and Pd in Ru-Pd/TiO2 prepared by a two-step photodeposition method on catalytic activity and the features of the reaction system were investigated in detail.

Cationic vacancy engineering of p-TiO2 for enhanced photocatalytic nitrogen fixation.

Defect engineering is one of the effective strategies to regulate and control catalyst properties. Constructing appropriate catalytically active centers effectively tunes the electronic and surface properties of the catalyst to achieve further enrichment of photogenerated electrons, enhances the electronic feedback of the catalytically active center to the anti-bonding orbitals of the nitrogen molecule, and enhances N2 adsorption while weakening the NN bond. In this study, titanium vacancy (VTi)-rich undoped anatase p-TiO2 was successfully synthesized to investigate the effect of its metal vacancies on photocatalytic nitrogen reduction reaction (NRR) performance. The cation vacancies of VTi-rich p-TiO2 lead to local charge defects that enhance carrier separation and transport while trapping electrons to activate N2, allowing effective reduction of the excited electrons to NH3. This work provides a viable strategy for driving the efficiency of photocatalytic nitrogen fixation processes by altering the structural properties of semiconductors through cationic vacancies, offering new opportunities and challenges for the design and preparation of titanium dioxide-based materials.

A band-to-band transition visible-light-responsive anatase titania photocatalyst by N,F-codoping for water splitting and CO2 reduction

A band-to-band transition visible-light-responsive N,F-codoped anatase TiO2 photocatalyst with low Ti3+ defects is prepared for water oxidation/reduction, CO2 reduction and Z-scheme overall water splitting under visible-light irradiation.

Pyridyl anchoring squaraine as a near-infrared dye sensitizer for effective sensitized hydrogen production over a titanium dioxide photocatalyst in water medium

Pyridyl anchoring squaraine as a near-infrared dye sensitizer for effective sensitized hydrogen production over a titanium dioxide photocatalyst in water medium

Photoacoustic Spectroscopic Analysis of Electron-Trapping Sites in Titanium(IV) Oxide Photocatalyst Powder Treated by Ball Milling

Photoacoustic Spectroscopic Analysis of Electron-Trapping Sites in Titanium(IV) Oxide Photocatalyst Powder Treated by Ball Milling

Chemometric study in plasmonic photocatalytic efficiency of gold nanoparticles loaded mesoporous TiO2 for mineralization of ibuprofen pharmaceutical pollutant: Box Behnken Design conception

In this study gold nanoparticles loaded mesoporous TiO2 (Titania) photocatalyst for mineralization of ibuprofen (IBP) pharmaceutical pollutant has been investigated in aqueous heterogeneous suspension. A Box-Behnken Design (BBD) on Response Surface Methodology (RSM) based on a three variables-model with three levels was used to optimize the photocatalytic process. The interaction effects of wavelength irradiation, IBP concentration and metal supported on Titania concentration on the mineralization of pharmaceutical pollutant were analyzed. IBP mineralization efficiency was modeled by a polynomial regression with a coefficient of determination R2 equal to 0.9974. An optimum efficiency of IBP mineralization of 98.50 % was achieved at optimized experimental conditions of wavelength irradiation equal to 366 nm, and 29.46 mg.L−1 as a value of IBP concentration and a metal concentration of 0.5 wt%. Overall, the results indicate that gold nanoparticles supported on mesoporous Titania at low concentration (0.5Au-TiO2) have a very interesting performance and exhibit good conditions as a photodriven catalyst for mineralization of pharmaceutical pollutant in wastewater.

Photocatalytic Degradation of Dye Acid Orange Seven on Titanium Dioxide Photocatalysts Immobilized on Stainless Steel Coated Layers: Role of Catalyst Loading and Ultrasonic Treatment

Supported titanium dioxide (TiO2) was investigated for potential application in photocatalytic degradation of dye acid Orange 7 in textile wastewater. Two commercial powder photocatalysts, Degussa (P25) and Precheza (AV01), were immobilized on stainless steel plates of dimensions (75 mm × 25 mm) through Electrophoretic Deposition Process (EPD) from aqueous colloidal suspensions of n-TiO2, c=10 g.L-1 produced in methanol. Two sets of coated layers were prepared - using ultrasonically treated TiO2 colloidal suspensions and without ultrasonic treatment. The prepared coated layers were fitted onto a four-hole photocatalytic reactor operating under batch-mode conditions. As a source of UV light, Sylvania LynxS, 11W UV lamps emitting light of wavelength between 320-400 nm with maximum wavelength at λ=355 nm was used. The current study aimed to evaluate the effect of ultrasonic treatment on the catalyst’s colloidal suspension and electrophoretic deposition loading (mg/cm2) on its surface area on the resultant photocatalytic degradation of dye Acid Orange 7. The photocatalytic degradation of the dye was monitored by changes in dye absorbance for 120 minutes at an interval of 30 minutes. Changes in dye concentration were determined by ultraviolet spectrophotometry at λ = 485 nm. The initial concentration of dye Acid Orange 7 used in the experiments was c=1×10-4 mol. L-1. The findings show that 61.1 % of dye mineralization was achieved after 120 minutes of photocatalytic degradation. The optimum catalytic loading for maximum photocatalytic degradation was determined at 0.75 mg/cm2 for the two commercial powder catalysts - TiO2 (P25/AV01) in ultrasonically treated TiO2 (P25) and non-ultrasonically treated TiO2 (AV01). Ultrasonic treatment of TiO2 (P25) colloidal suspensions before immobilisation positively influenced its photocatalytic activity, whereas ultrasonic treatment negatively affected the photoactivity of TiO2 (AV01). Overall, TiO2 (AV01) proved to be more efficient by 28.6%, compared to TiO2 (P25). The results show the potential application of UV-TiO2 treatment model in the remediation of coloured dye Acid Orange textile wastewater.

Front Cover: Hydrogen‐Free Hydrogenation of a Nitrogen‐Containing Ring of Quinolines in an Alcoholic Suspension of a Titanium(IV) Oxide Photocatalyst Modified with Metal Cocatalysts (ChemCatChem 22/2022)

The Front Cover shows hydrogen-free hydrogenation of a nitrogen-containing ring of quinolines (Qns) in an alcoholic suspension of a TiO2 photocatalyst modified with metal cocatalysts. In their Research Article, H. Kominami and co-workers show that hydrogenation competed with H2 evolution over the cocatalyst, and the use of a Rh cocatalyst resulted in a large 1,2,3,4-tetrahydroquinoline (THQn) yield and a much larger H2 yield. In contrast, the use of an inexpensive Cu cocatalyst resulted in a relatively large THQn yield with greatly suppressed evolution of H2, and the hydrogenation was greatly accelerated at slightly elevated temperatures. Hydrogenation over Cu-TiO2 under solar light was investigated in addition to the expandability and reusability of Cu-TiO2. More information can be found in the Research Article by H. Kominami and co-workers.

Enhancement in the visible light induced photocatalytic and antibacterial properties of titanium dioxide codoped with cobalt and sulfur

In this study, the sol-gel technique was used to develop Cobalt Sulfur codoped Titanium Dioxide (Co–S codoped TiO2) photocatalysts. For structural analysis of the prepared resultant TiO2 samples, XRD, FTIR, UV–Vis DRS, SEM, HR-TEM and EDX measurements were used to describe the produced photocatalysts. The characterization findings indicate that the synthesized nanoparticles possessed great crystallinity, high purity, and superior optical characteristics. For the methylene blue (MB) degradation process, Co–S codoped TiO2 nanoparticles were tested for their photocatalytic degradation performance. The Co–S codoped TiO2 nanoparticles had improved catalytic activity when compared with pure, Co-doped, S-doped TiO2 and decomposed 93% of MB in 120 min. When compared to pure and doped TiO2, the catalysts of Co–S codoped TiO2 showed a synergistic effect and improved the performance of the catalysts. Furthermore, the antibacterial applications of synthesized Co–S codoped TiO2 nanoparticles was studied against E. coli (Gram negative) and S. aureus (Gram positive) bacteria and exhibited strong antibacterial activity against the selected strains.

Recent Development in Non-Metal-Doped Titanium Dioxide Photocatalysts for Different Dyes Degradation and the Study of Their Strategic Factors: A Review

Semiconductor titanium dioxide in its basic form or doped with metals and non-metals is being extensively used in wastewater treatment by photocatalysis due to its versatile nature. Other numerous characteristics including being environmentally friendly, non-pernicious, economical, multi-phase, highly hydrophilic, versatile physio-chemical features, chemical stability, suitable band gap, and corrosion-resistance, along with its low price make TiO2 the best candidate in the field of photocatalysis. Commercially, semiconductor and synthesized photocatalysts—which have been investigated for the last few decades owing to their wide band gap—and the doping of titania with p-block elements (non-metals) such as oxygen, sulfur, nitrogen, boron, carbon, phosphorus, and iodine enhances their photocatalytic efficiency under visible-light irradiation. This is because non-metals have a strong oxidizing ability. The key focus of this review is to discuss the various factors affecting the photocatalytic activity of non-metal-doped titania by decreasing its band gap. The working parameters discussed are the effect of pH, dyes concentration, photocatalyst’s size and structure, pollutants concentration and types, the surface area of photocatalysts, the effect of light intensity and irradiation time, catalyst loading, the effect of temperature, and doping impact, etc. The mechanism of the photocatalytic action of several non-metallic dopants of titanium dioxide and composites is a promising approach for the exploration of photocatalysis activity. The various selected synthesis methods for non-metallic-doped TiO2 have been reviewed in this study. Similarly, the effect of various conditions on the doping mode has been summarized in relation to several sorts of modified TiO2.

Evaluation of Antifungal Properties of Titania P25.

Commercial titania photocatalyst—P25 was chosen for an antifungal property examination due to it exhibiting one of the highest photocatalytic activities among titania photocatalysts. Titania P25 was homogenized first (HomoP25) and then annealed at different temperatures. Additionally, HomoP25 was modified with 0.5 wt% or 2.0 wt% of platinum by a photodeposition method. The obtained samples were characterized by diffuse-reflectance spectroscopy (DRS), X-ray photoabsorption spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy. Moreover, photocatalytic activity was tested for methanol dehydrogenation under UV/vis irradiation. The spore-destroying effect of photocatalysts was investigated against two mold fungal species, i.e., Aspergillus fumigatus and Aspergillus niger. Both the mycelium growth and API ZYM (estimation of enzymatic activity) tests were applied for the assessment of antifungal effect. It was found that annealing caused a change of surface properties of the titania samples, i.e., an increase in the noncrystalline part, a growth of particles and enhanced oxygen adsorption on its surface, which resulted in an increase in both the hydrogen evolution rate and the antifungal effect. Titania samples annealed at 300−500 °C were highly active during 60-min UV/vis irradiation, inhibiting the germination of both fungal spores, whereas titania modification with platinum (0.5 and 2.0 wt%) had negligible effect, despite being highly active for hydrogen evolution. The control experiments revealed the lack of titania activity in the dark, as well as high resistance of fungi for applied UV/vis irradiation in the absence of photocatalysts. Moreover, the complete inhibition of 19 hydrolases, secreted by both tested fungi, was noted under UV/vis irradiation on the annealed P25 sample. It is proposed that titania photocatalysts of large particle sizes (>150 nm) and enriched surface with oxygen might efficiently destroy fungal structures under mild irradiation conditions and, thus, be highly promising as covering materials for daily products.

Novel F-doped carbon nanotube@(N,F)-co-doped TiO2-δ nanocomposite: Highly active visible-light-driven photocatalysts for water decontamination

The development of a facile strategy to prepared titanium oxide with reduced band gap, high electrical conductivity together with good chemical and structural stability that can be widely applied for photocatalysis under visible light holds great appeal. Herein, we reported a novel F-doped carbon nanotube@(N,F)-co-doped TiO2-δ nanocomposite, which was prepared simply by depositing titanium oxide onto electrospun PAN nanofibers containing NH4F via solvothermal synthesis, and the following thermal treatment process. The optimally synthesized nanocomposite shows outstanding photocatalytic performance by removing 77.2% of RhB, 84.1% of MB and 66.2% of Cr(VI) under visible light from a 5 W LED lamp within 60 min, which are approximately 33.6, 6.5 and 6.0 times those over the commercially available pure TiO2 powders, respectively. The greatly improved photocatalytic activity could be attributed to the facts that the co-doping of N and F together with oxygen deficiency enhanced the visible light absorption, and the F-doped carbon nanotube facilitated the exposure of active sites and the separation of photogenerated electrons and holes. This work provides a simple, feasible method for designing and fabricating high-performance titanium oxide photocatalysts.

Is Black Titania a Promising Photocatalyst?

Five different (commercial and self-synthesized) titania samples were mixed with NaBH4 and then heated to obtain black titania samples. The change in synthesis conditions resulted in the preparation of nine different photocatalysts, most of which were black in color. The photocatalysts were characterized by various methods, including X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), photoacoustic and reverse-double beam photoacoustic spectroscopy (PAS/RDB-PAS). The photocatalytic activity was tested for oxidative decomposition of acetic acid, methanol dehydrogenation, phenol degradation and bacteria inactivation (Escherichia coli) under different conditions, i.e., irradiation with UV, vis, and NIR, and in the dark. It was found that the properties of the obtained samples depended on the features of the original titania materials. A shift in XRD peaks was observed only in the case of the commercial titania samples, indicating self-doping, whereas faceted anatase samples (self-synthesized) showed high resistance towards bulk modification. Independent of the type and degree of modification, all modified samples exhibited much worse activity under UV irradiation than original titania photocatalysts both under aerobic and anaerobic conditions. It is proposed that the strong reduction conditions during the samples’ preparation resulted in the partial destruction of the titania surface, as evidenced by both microscopic observation and crystallographic data (an increase in amorphous content), and thus the formation of deep electron traps (bulk defects as oxygen vacancies) increasing the charge carriers’ recombination. Under vis irradiation, a slight increase in photocatalytic performance (phenol degradation) was obtained for only four samples, while two samples also exhibited slight activity under NIR. In the case of bacteria inactivation, some modified samples exhibited higher activity under both vis and NIR than respective pristine titania, which could be useful for disinfection, cancer treatment and other purposes. However, considering the overall performance of the black titania samples in this study, it is difficult to recommend them for broad environmental applications.

Construction of biomass derived carbon quantum dots modified TiO2 photocatalysts with superior photocatalytic activity for methylene blue degradation

Titanium dioxide (TiO2) photocatalyst has been extensively studied due to its high photocatalytic activity under UV radiation, chemical stability, and low cost. However, its photocatalytic efficiency is limited by the low harvest of visible light due to larger energy band gap (Eg =3.2 eV) and the rapid recombination of photo-generated carriers. Herein, N-doped carbon quantum dots (NCQDs) were utilized to decorate TiO2 via a facile hydrothermal-calcination synthesis approach, wherein NCQDs were prepared using spent coffee grounds as biomass carbon source and urea as nitrogen source. The NCQDs increase the absorption of visible light, and facilitate electron transfer and separation of photo-generated electron-hole pairs. A very low NCQDs content of 3 wt% (3- NCQDs/TiO2) resulted in 2.25 times faster photodegradation rate for methylene blue (MB) than pristine TiO2. 3-NCQDs/TiO2 exhibited efficient and stable photocatalytic degradation over MB with photodegradation rate of 93.1% within 60 min and more than 86% after 4 cycles. Besides, it shows enhanced degradation performance in alkaline conditions. This work provides a new attempt to boost the photocatalytic activities of the photocatalysts by biomass-derived NCQDs for water remediation.