TiO2 photocatalysis: Design and applications

Enhanced visible light photocatalytic activity of the needle-like SrMoO4 decorated g-C3N4 heterostructure for degradation of tetracycline

Photocatalytic mechanism diagram of SrMoO4/g-C3N4.

Investigation of the Sn4+-distribution and photocatalytic performance of Sn4+/TiO2 hollow fiber nanomaterials

Tin ion-doped TiO2 fibers were smartly prepared, and the distribution depth of Sn4+ influences the photocatalytic performance of TiO2.

Graphene-based materials for metronidazole degradation: A comprehensive review

Due to its cytotoxic effect, metronidazole (MNZ) is a drug commonly used to treat bacterial, protozoal, and microaerophilic bacterial infections. After consumption, it undergoes a series of metamorphic reactions that lead to the degradation of oxidized, acetylated, and hydrolyzed metabolites in the environment. To eliminate such pollutants, due to their high potential, adsorption and photocatalysis extensive processes are used in which graphene can be used to improve efficiency. This review analyses the use of graphene as an absorbent and catalyst with a focus on absorption and photocatalytic degradation of MNZ by graphene-based materials (GBMs). The parameters affecting the adsorption, and photocatalytic degradation of MNZ are investigated and discussed. Besides, the basic mechanisms occurring in these processes are summarized and analyzed. This work provides a theoretical framework that can direct future research in the field of MNZ removal from aqueous solutions.

Porous Mixed-Metal Oxide Li-Ion Battery Electrodes by Shear-Induced Co-assembly of Precursors and Tailored Polymer Particles

Due to their various applications, metal oxides are of high interest for fundamental research and commercial usage. Per applications as catalysts or electrochemical devices, the tailored design of metal oxides featuring a high specific surface area and additional functionalities is of the utmost importance for the performance of the resulting materials. We report a new method for preparing free-standing films consisting of hierarchically porous metal oxides (titanium and niobium based) by combining emulsion polymerization and shear-induced monodisperse particle self-assembly in the presence of sol-gel precursors. After thermal treatment, the resulting porous materials can be used as electrodes in Li-ion batteries. The titanium and niobium sol-gel precursors were partially immobilized to the surface of organic core-interlayer particles featuring hydroxyl groups to obtain hybrid organic-inorganic particles through the melt-shear organization process. Free-standing particle-based films, in analogy to elastomeric opal films and colloidal crystals, can be prepared in a convenient one-step preparation process. After thermal treatment, ordered pores are obtained, while the pristine metal oxide precursor shell can be converted to the (mixed) metal oxide matrix. Heat treatment under CO₂ leads to mixed-TiNb oxide/carbon hybrid materials. The highly porous derivative structure enhances electrolyte permeation. When tested as Li-ion battery electrodes, it shows a specific capacity of 335 mAh·g^-1 at a rate of 10 mA·g^-1. After 1000 cycles at 250 mA·g^-1, the electrodes still provided a specific capacity of 191 mAh·g^-1.

Synthesis of Nanostructured TiO2 Microparticles with High Surface Area

Hydrothermal reactions represent a simple and efficient method for the preparation of nanostructured TiO2 particles that could be of interest as photocatalysts or catalytic supports. Although the particle size is in the range of 2–5 µm, the nanostructures composing the particles ensure a large specific surface area with values above 100 m2/g. The effects of the different synthesis parameters on the morphology, photocatalytic activity, and stability of the prepared material were studied. The surface morphology of the prepared TiO2 powders was studied by scanning electron microscopy (SEM). To further characterize the samples, the specific surface area for different morphologies was measured and the photocatalytic activity of the prepared powders was tested by degrading model pollutants under UV irradiation. The results show that the initial morphology had little effect on the photocatalytic properties. On the other hand, the final calcination temperature significantly increased the degradation rates, making it comparable to that of P25 TiO2 (particle size 20–30 nm).

Copper phosphide decorated g-C3N4 catalysts for highly efficient photocatalytic H2 evolution

Designing functional heterojunctions to enhance photocatalytic hydrogen evolution is still a key challenge in the field of efficient solar energy utilization. Copper phosphides become an ideal material to serve as the cocatalysts during photocatalytic hydrogen evolution by virtue of the lower prices. In this study, we synthesized graphitic carbon nitride (g-C₃N₄) based catalysts loaded with copper phosphide (Cu₃P, Cu₉₇P₃), which exhibit superior performance in photocatalytic H₂ evolution. Ultraviolet (UV)-visible spectroscopy illustrated that the absorption of light strengthened after the loading of copper phosphide, and the time-resolved transient photoluminescence (PL) spectra showed that the separation and transfer of the photoexcited carriers greatly improved. Moreover, both copper phosphide/g-C₃N₄ photocatalysts exhibited a relatively high H₂ evolution rate: Cu₃P/g-C₃N₄ (maximum 343 μmol h^-1 g^-1), Cu₉₇P₃/g-C₃N₄ (162.9 μmol h^-1 g^-1) while copper phosphide themself exhibit no photocatalytic activity. Thus, the copper phosphides (Cu₃P, Cu₉₇P₃) work as a cocatalyst during photocatalytic H₂ evolution. The cycling experiments illustrated that both copper phosphide/g-C₃N₄ photocatalysts perform excellent stability in the photocatalytic H₂ evolution. It is worth noting that while the NaH₂PO₂ was heated in the tube furnace for phosphorization to obtain Cu₃P, the excessive PH₃ could pass through the solution of CuSO₄ to obtain Cu₉₇P₃ at the same time, which significantly improved the utilization of PH₃ and reduced the risk of toxicity. This work could provide new strategies to design photocatalysts decorated with copper phosphide for highly efficient visible-light-driven hydrogen evolution.

Proposed approaches for coronaviruses elimination from wastewater: Membrane techniques and nanotechnology solutions

Since the beginning of the third Millennium, specifically during the last 18 years, three outbreaks of diseases have been recorded caused by coronaviruses (CoVs). The latest outbreak of these diseases was Coronavirus Disease 2019 (COVID-19), which has been declared by the World Health Organization (WHO) as a pandemic. For this reason, current efforts of the environmental, epidemiology scientists, engineers, and water sector professionals are ongoing to detect CoV in environmental components, especially water, and assess the relative risk of exposure to these systems and any measures needed to protect the public health, workers, and public, in general. This review presents a brief overview of CoV in water, wastewater, and surface water based on a literature search providing different solutions to keep water protected from CoV. Membrane techniques are very attractive solutions for virus elimination in water. In addition, another essential solution is nanotechnology and its applications in the detection and protection of human and water systems.

Tuning the Interfacial Energetics in WO3/WO3 and WO3/TiO2 Heterojunctions by Nanostructure Morphological Engineering

Nowadays, semiconducting heterojunction-based devices exhibit the best photocatalytic performance, with transition metal oxides such as tungsten (WO₃) and titanium (TiO₂) being the workhorse materials employed in these composites. Contrary to their bulk counterparts, WO₃ and TiO₂ nanostructures offer a huge versatility because their optoelectronic properties (i.e., energy levels) can be tuned by modifying their size, morphology, and composition, thus being, in principle, able to optimize the electron/hole injection barriers inside the device. However, this approach requires a deep fundamental knowledge of their structure-property relationships, which are extremely difficult to access from experiments. In this context, we employed state-of-the-art theoretical methods to determine the size and morphology dependency of the energetic alignment in WO₃/WO₃ and TiO₂/WO₃ nanostructure heterojunctions. Our results demonstrated that any type of alignment can be achieved by the proper choice of the nanostructures involved in the junction, while setting important rules for the design of efficient multicomponent devices.

Enhanced bezafibrate degradation and power generation via the simultaneous PMS activation in visible light photocatalytic fuel cell

A collaborative system including peroxymonosulfate (PMS) activation in a photocatalytic fuel cell (PFC) with an BiOI/TiO₂ nanotube arrays p-n type heterojunction as photoanode under visible light (PFC(BiOI/TNA)/PMS/vis system) was established. Xenon lamp was used as the light source of visible light. A 4.6 times higher pseudo-first-order bezafibrate (BZF) degradation rate constant was achieved in this system compared with the single PFC(BiOI/TNA)/vis system. The radical quenching experiments revealed that the contribution of reactive oxidative species (ROS) followed the order of ¹O₂ ≈ h⁺ >> •OH > SO₄^•- >>O₂^•-. The EPR tests demonstrated that PMS addition enlarged the formation of ¹O₂, •OH and SO₄^•-, but suppressed O₂^•- yield. Interestingly, ¹O₂ was further proved to dominantly originated from the priority reaction between positive photoinduced holes (h⁺) and negatively charged PMS. Besides, N₂-purging tests and density functional theory calculation indicated that PMS probably reacted with residual photoinduced electron (e^-) on the more negative conduction band (CB) of BiOI to form •OH and SO₄^•-, but competed with dissolved oxygen. Other e^- transferred to the less negative CB of TNA through p-n junction will efficiently move to cathode through the external circuit. The greatly promoted power generation of PFC system was observed after PMS addition due to extra h⁺ consumption and efficient e^- separation and transfer. Besides, three possible pathways for BZF degradation were proposed including hydroxylation, fibrate chain substituent and amino bond fracture. This study can provide new insights into the mechanisms of PMS assisted photocatalysis and accompanying energy recovery.

Electrospun Poly(methyl methacrylate)/TiO2 Composites for Photocatalytic Water Treatment

Electrospinning was successfully used for the one-step fabrication of poly(methyl methacrylate) (PMMA) fibers loaded with an inorganic photocatalyst—titanium oxide (TiO₂). By tuning the PMMA/TiO₂ ratio and the electrospinning conditions (applied voltage, needle tip-to-collector distance, and flow rates), PMMA/TiO₂ composites with selected organic/inorganic ratios, tailored designs, and targeted properties were obtained. The morphology of the electrospun composites was affected by the amount of TiO₂ incorporated into the PMMA fibers. In addition, the inorganic photocatalyst had an impact on the wettability, thermal stability, and optical properties of the electrospun composites. In particular, the surface wettability of the composites was strongly influenced by UV light irradiation and from hydrophobic became superhydrophilic. Moreover, PMMA/TiO₂ composites had enhanced tensile strength in comparison with those of bare PMMA mats. The electrospun PMMA/TiO₂ composites showed excellent photocatalytic efficiency against the model organic pollutant—methylene blue—which is very promising for the future development of membranes that are highly efficacious for photocatalytic water treatment.

Fabrication of a UV Photodetector Based on n-TiO2/p-CuMnO2 Heterostructures

The heterojunction based on n-TiO2 nanolayer/p-CuMnO2 thin film was achieved using an efficient two-step synthesis process for the fabrication of a UV photodetector. The first step consisted of obtaining the TiO2 nanolayer, which was grown on titan foil by thermal oxidation (Ti-TiO2). The second step consisted of CuMnO2 thin film deposition onto the surface of Ti-TiO2 using the Doctor Blade method. Techniques such as X-ray diffraction, UV-VIS analysis, SEM, and AFM morphologies were used for the investigation of the structural and morphological characteristics of the as-synthesized heterostructures. The Mott–Schottky analysis was performed in order to prove the n-TiO2/p-CuMnO2 junction. The I-V measurements of the n-TiO2 nanolayer/p-CuMnO2 thin film heterostructure confirm its diode characteristics under dark state, UV and visible illumination conditions. The obtained heterojunction, which is based on two types of semiconductors with different energy band structures, improves the separating results of charges, which is very important for high-performance UV photodetectors.

Solar Light-Induced Methylene Blue Removal over TiO2/AC Composites and Photocatalytic Regeneration

TiO₂-containing photocatalysts, which combine TiO₂ with carbon-based materials, are promising materials for wastewater treatment due to synergistic photodegradation and adsorption phenomena. In this work, TiO₂/AC composites were produced by the in situ immobilization of TiO₂ nanoparticles over activated carbon (AC) derived from spent coffee grains, using different TiO₂/AC proportions. The TiO₂/AC composites were tested as adsorbents (dark) and as photocatalysts in a combined adsorption+photocatalytic process (solar irradiation) for methylene blue (MB) removal from ultrapure water, and from a secondary effluent (SecEf) of an urban wastewater treatment plant. All the materials were characterized by XRD (X-ray powder diffraction), N₂ adsorption–desorption isotherms at −196 °C, SEM (scanning electron microscopy), UV-Vis diffuse reflectance, FTIR (Fourier-transform infrared spectroscopy), TPD (temperature programmed desorption), XPS (X-ray photoelectron spectroscopy) and TGA (thermogravimetric analysis). The TiAC60 (60% C) composite presented the lowest band gap (1.84 eV), while, for TiAC29 (29% C), the value was close to that of bare TiO₂ (3.18 vs. 3.17 eV). Regardless of the material, the solar irradiation improved the percentage of MB discolouration when compared to adsorption in dark conditions. In the case of simultaneous adsorption+photocatalytic assays performed in ultrapure water, TiAC29 presented the fastest MB removal. Nevertheless, both TiAC29 and TiAC60 led to excellent MB removal percentages (96.1–98.1%). UV-induced photoregeneration was a promising strategy to recover the adsorption capacity of the materials, especially for TiAC60 and AC (>95%). When the assays were performed in SecEf, all the materials promoted discolouration percentages close to those obtained in ultrapure water. The bulk water parameters revealed that TiAC60 allowed the removal of a higher amount of MB, associated with the overall improvement of the SecEf quality.

Ag/GO/TiO2nanocomposites: the role of the interfacial charge transfer for application in photocatalysis

TiO₂semiconductor nanoparticles (NPs) in the anatase phase have presented limitations of application in photocatalysis, mainly due to the fast recombination of photoexcited electrons. The combination with other nanoparticles/nanostructures has been shown to be a promising solution for increasing photocatalytic efficiency. In this work, titanium dioxide (TiO₂) nanoparticles in different crystalline phases were prepared through a rapid microwave-assisted synthesis and modified by silver nanoparticles (Ag) and graphene oxide (GO). The samples were characterized by x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, infrared spectroscopy and gas adsorption. Crystalline anatase NPs were obtained in basic conditions (pH = 8) while in acidic conditions (pH = 1), single-crystalline rutile NPs were formed. Different previous drying methods: oven and freeze-drying used led to a differentiation in crystallographic phases obtained. Anatase TiO₂and anatase-rutile mixture NPs calcined at 400 °C showed properties as high specific surface area, crystallinity and reduced electron-hole recombination which contributed to an enhanced photocatalytic activity, when compared to the Degussa P25 photoactivity. The effect of silver nanoparticles and GO addition to TiO₂nanopowder was evaluated for photocatalysis activity. An improvement in the methylene blue and rhodamine B dyes photodegradation was observed for both anatase and rutile TiO₂nanocomposites. We noted that anatase TiO₂nanoparticles degraded 53% of rhodamine B, and when functionalized with GO, the photodegradation increased to 69%. Comparatively, the addition of silver nanoparticles to anatase TiO₂increased the dye degradation to 97% in 180 min. Hence, we revel that in the TiO₂nanocomposites, silver nanoparticles showed better interfacial charge transfer than GO, contributing more effectively to the dye photodegradation process.

Significantly enhanced photothermal catalytic hydrogen evolution over Cu2O-rGO/TiO2 composite with full spectrum solar light

Reduced graphene oxide (rGO) has conspicuous photothermal characteristics in photothermal applications. Thus in our previous work, we used reduced graphene oxide (rGO) supported titanium dioxide (TiO₂) nanocomposite (rGO/TiO₂) to absorb the ultraviolet and infrared light in the photothermal hydrogen evolution process. In order to make use of the full spectrum solar energy into other clear energy, the visible light should be also considered in following research. Herein, we report a cuprous oxide (Cu₂O) decorated reduced graphene oxide (rGO) supported titanium dioxide (TiO₂) (Cu₂O-rGO/TiO₂) catalysts, which can absorb full spectrum solar light in an innovative way. The Cu₂O-rGO/TiO₂ catalyst is synthesized through a one-step hydrothermal method. The rates of hydrogen evolution are 17800 μmol·g^-1h^-1 under photothermal condition (90°C), 3800 μmol·g^-1h^-1 under photocatalysis condition only (25°C) and 0 μmol·g^-1h^-1 under thermal catalysis condition only. The result of photothermal catalytic hydrogen evolution rate is about 4.7 times that of the sum of the photocatalytic and thermal reactions. The photothermal synergetic effect promotes the photo-generated electron-holes separation through the rGO due to the temperature rising, and accelerates the reaction rates on the catalyst surface in hydrogen evolution process simultaneously. This work could provide us a new promising way for the conversion of full spectrum solar energy to hydrogen energy.

Photocatalytic Activity of Titanium Dioxide Nanotubes Following Long-Term Aging

Anodic titanium dioxide (TiO₂) nanotubes were found to be active photocatalysts. These photocatalysts possess a high surface area, even when supported, rendering them potential candidates for water treatment. In this work, photocatalytic surfaces were produced by anodizing commercially pure Ti plates using two different electrolyte compositions and correspondingly diverse process parameters. Changes in the physical and chemical stability as well as photocatalytic activity were studied over a fifty-two-week aging process. During this period, the nanotubular surfaces were exposed to flowing synthetic greywater, solar irradiation, and the natural environment. The physical and phase stability of the materials anodized using the organic electrolyte were found to be outstanding and no degradation or change in crystalline structure was observed. On the other hand, materials anodized in the aqueous electrolyte proved to suffer from light-induced phase transition from anatase to rutile. Surfaces synthesized in the organic electrolyte were more resistant to fouling and showed a better tendency to recover photocatalytic activity upon cleaning. In conclusion, the nanotubes produced in the organic electrolyte proved to be stable, rendering them potentially suitable for real-life applications.

Impact of TiO2 Surface Defects on the Mechanism of Acetaldehyde Decomposition under Irradiation of a Fluorescent Lamp

TiO2 was placed in heat-treatment at the temperature of 400–500 °C under flow of hydrogen gas in order to introduce some titania surface defects. It was observed that hole centers in TiO2 were created during its heat treatment up to 450 °C, whereas at 500 °C some Ti3+ electron surface defects appeared. The type of titania surface defects had a great impact on the mechanism of acetaldehyde decomposition under irradiation of artificial visible light. Formation of O•− defects improved both acetaldehyde decomposition and mineralization due to the increased oxidation of adsorbed acetaldehyde molecules by holes. Contrary to that, the presence of electron traps and oxygen vacancies in titania (Ti3+ centers) was detrimental for its photocatalytic properties towards acetaldehyde decomposition. It was proved that transformation of acetaldehyde on the TiO2 with Ti3+ defects proceeded through formation of butene complexes, similar as on rutile-type TiO2. Formed acetic acid, upon further oxidation of butene complexes, was strongly bound with the titania surface and showed high stability under photocatalytic process. Therefore, titania sample heat-treated with H2 at 500 °C showed much lower photocatalytic activity than that prepared at 450 °C. This study indicated the great impact of titania surface defects (hole traps) in the oxidation of acetaldehyde and opposed one in the case of defects in the form of Ti3+ and oxygen vacancies. Oxidation abilities of TiO2 seem to be important in the photocatalytic decomposition of volatile organic compounds (VOCs) such as acetaldehyde.

Enhanced solar photocatalysis of TiO2 nanoparticles and nanostructured thin films grown on paper

Titanium dioxide nanoparticles and nanostructured thin films were simultaneously synthesized using a microwave-assisted hydrothermal method. The synthesis formed very fine particles, appearing as nanospheres in the 11 nm size range. As for the nanostructured films, they have displayed similar structural characteristics to the nanoparticles, with thickness of 130 nm. These films covered uniformly and homogenously the Whatman paper, while maintaining its flexibility. The materials processed had their photocatalytic activity assessed from rhodamine B degradation under solar radiation (91% degradation after 40 min for the powder material and 68% after 6 h for the nanostructured thin films). Reusability experiments were also carried out, revealing superior performance concerning the Degussa P25, the most common photocatalyst used. The results of the present work can be thought as an option for the existing photocatalysts activated under solar light, namely for water purification, as it simultaneously produces enhanced photocatalytic powders and photocatalytic papers fully disposable and that can be easily recycled.

Characterization, X-ray Absorption Spectroscopic Analysis and Photocatalytic Activity of Co/Zn Co-Doped TiO2 Nanoparticles Synthesized by One-Step Sonochemical Process

A novel one-step preparation of sonochemical method was applied to synthesize Co/Zn co-doped TiO2 nanoparticles using a sonicator of 750 W, 20 kHz for 30 min at room temperature. The formation of the anatase TiO2 phase for all as-prepared samples was observed from XRD results with a crystalline size in nanoscale. The use of ultrasound allowed for the successful doping of both Co and Zn into the TiO2 lattice, which was confirmed by Synchrotron light including X-ray near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) spectroscopy. Ti K-edge, Co K-edge, and Zn K-edge XANES spectra exhibited the dominating +4, +2, and +2 valence state of Ti, Co, and Zn in as-prepared samples, respectively. A detailed XANES and EXAFS data analysis give strong evidence that the Co/Zn dopants partially replace the Ti atom of the TiO2 host. The Co/Zn co-doping extends the light absorption of the host to the visible region and restricts the e+/h+ recombination. The photocatalytic activity of samples was tested for degradation of Rhodamine B dye solution under visible light irradiation. The as-synthesized of the co-doped catalyst was presented as highly efficient, with 2.5 and 5 times dye degradation compared with single-doped and bare TiO2.

Synthesis, Characterization, and Photocatalytic, Bactericidal, and Molecular Docking Analysis of Cu-Fe/TiO2 Photocatalysts: Influence of Metallic Impurities and Calcination Temperature on Charge Recombination

This research evaluated the potential photocatalytic efficiency of synthesized Cu-Fe/TiO2 photocatalysts against organic contaminants and biocontaminants through various synthesis methods (Cu-to-Fe ratio, metal loading, and calcination temperature) and reaction parameters (photocatalyst dose, irradiation time, and different initial methyl orange (MO) concentrations). In addition, the best photocatalysts were characterized through Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), differential reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS) analysis techniques. The best metal loading was 1 wt % with 5:5 Cu/Fe ratio and 300 °C calcination temperature (5Cu-5Fe/TiO2-300) having 97% MO decolorization. Further analysis indicates that the metal presence does not generate new channels for de-excitation but clearly affects the intensity and decreases charge recombination. The behavior of the photoluminescence intensity is (inversely) proportional to the activity behavior through the series, indicating that the main catalytic effect of Fe and Cu relates to charge recombination and that the Cu-Fe bimetallic catalyst optimizes such function. Moreover, the best-engineered photocatalysts asserted impactful bacteriostatic efficacy toward the tested Escherichia coli strain (in 30 min), and therefore, molecular docking studies were used to predict the inhibition pathway against E. coli β-lactamase enzyme. The photocatalyst had a high negative docking score (-5.9 kcal mol-1) due to intense interactions within the active site of the enzyme. The molecular docking study revealed that the ligand could inhibit β-lactamase from producing its bactericidal activity.

Recyclable self-floating A-GUN-coated foam as effective visible-light-driven photocatalyst for inactivation of Microcystis aeruginosa

In this work, a recyclable self-floating A-GUN-coated (Ag/AgCl@g-C₃N₄@UIO-66(NH₂)-coated) foam was fabricated for effective inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. The floating photocatalyst was able to inactivate 98% of M. aeruginosa within 180 min under the visible-light irrigation, and the floating photocatalyst exhibited a stable performance in various conditions. Moreover, the inactivation efficiency can still maintain nearly 92% after five times recycle experiments, showing excellent photocatalytic stability. Furthermore, effects of A-GUN/SMF floating catalyst on the physiological properties, cellular organics, and algal functional groups of M. aeruginosa were studied. The floating photocatalyst can not only make full use of excellent photocatalytic activities of A-GUN nanocomposite, but also promote contact between catalyst and algae, and realize the effective recovery of the photocatalyst. Finally, possible photocatalytic inactivation mechanisms of algae were obtained, which provides references for removing cyanobacteria blooms in real water bodies.

Rare-Earth-Modified Titania Nanoparticles: Molecular Insight into Synthesis and Photochemical Properties

A molecular precursor approach to titania (anatase) nanopowders modified with different amounts of rare-earth elements (REEs: Eu, Sm, and Y) was developed using the interaction of REE nitrates with titanium alkoxides by a two-step solvothermal-combustion method. The nature of an emerging intermetallic intermediate was revealed unexpectedly for the applied conditions via a single-crystal study of the isolated bimetallic isopropoxide nitrate complex [Ti2Y(iPrO)9(NO3)2], a nonoxo-substituted compound. Powders of the final reaction products were characterized by powder X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL). The addition of REEs stabilized the anatase phase up to ca. 700 °C before phase transformation into rutile became evident. The photocatalytic activity of titania modified with Eu3+ and Sm3+ was compared with that of Degussa P25 titania as the control. PL studies indicated the incorporation of Eu and Sm cations into titania (anatase) at lower annealing temperatures (500 °C), but an exclusion to the surface occurred when the annealing temperature was increased to 700 °C. The efficiency of the modified titania was inferior to the control titania while illuminated within narrow wavelength intervals (445-465 and 510-530 nm), but when subjected to a wide range of visible radiation, the Eu3+- and Sm3+-modified titania outperformed the control, which was attributed both to doping of the band structure of TiO2 with additional energy levels and to the surface chemistry of the REE-modified titania.

Silver-Doped BaSrTiO₃ Nanocomposite: Synthesis, Characterization, Antibacterial and Photocatalytic Activities

In this research, strontium titanate (SrTiO₃), barium titanate (BaTiO₃), barium strontium titanate (BaSrTiO₃), and Ag-doped BaSrTiO₃ nanocomposites with different Ag contents were fabricated using the sol-gel chemical route. The prepared samples were characterized by several techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), differential reflectance spectroscopy (DRS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma spectroscopy (ICP), and Brunauer-Emmett-Teller (BET) measurement. The EDS results indicated that the synthesized nanoparticles had a cube perovskite-like structure. The EDS and ICP results revealed that Ag was doped into the Ba_0.5Sr_0.5TiO₃ structure. The SEM and TEM images demonstrated that the particle size of 15 mol% Ag-doped Ba_0.5Sr_0.5TiO₃ was smaller than that of pure Ba_0.5Sr_0.5TiO₃ as confirmed by surface area results. The photocatalytic properties of undoped titanate samples and Ag-doped Ba_0.5Sr_0.5TiO₃ were studied by the photodecomposition of Eosin yellowish (EY) and methylene blue (MB) dyes. The results illustrated that the photodegradation efficiency of the Ag-doped Ba_0.5Sr_0.5TiO₃ was far higher than the undoped titanate sample, and the optimum Ag doping was 15 mol%. The antibacterial activities of pure Ba_0.5Sr_0.5TiO₃ and Ag-doped Ba_0.5Sr_0.5Ti0₃ were studied against Staphylococcus aureus as Gram-positive (+) and Pseudomonas aeruginosa and Escherichia coli as Gram-negative (-) bacteria. In comparison with the bare Ba_0.5Sr_0.5TiO₃ nanoparticles, the Ag-doped sample showed a significant enhancement in antibacterial activities against both Gram-negative and Gram-positive bacterial strains.

Degradation of carbamazepine by UVA/WO3/hypochlorite process: Kinetic modelling, water matrix effects, and density functional theory calculations

The rapid recombination of electron/hole pairs is a major setback in the application of WO₃-based photocatalysis in water treatment. In this study, hypochlorite (ClO^-) was used as an electron acceptor to enhance the photocatalytic degradation of carbamazepine (CBZ) using UVA-excited WO₃. The results showed that CBZ degradation in the UVA/WO₃/ClO^- system followed a pseudo-first order reaction kinetic model. The addition of 0.1 mM ClO^- to the UVA/WO₃ system at pH values of 8.2 and 6.2 increased the rate constant (k_obs) of the degradation process 5.3- and 11.5-fold, respectively. Further, increasing the WO₃ dosage or decreasing the initial CBZ concentration resulted in an increase in k_obs. However, at high concentrations, ClO^- inhibited CBZ degradation. Based on the kinetic model, it could be suggested that ClO played a dominant role in the degradation process. Furthermore, the water matrix effects were as follows: the optimal pH was 6.2; humic acid, chloride, bicarbonate, and ammonium exhibited inhibitory effects on CBZ degradation; and sulfate ion significantly enhanced the degradation. Density functional theory (DFT) calculations indicated a strong affinity between ClO^- and the WO₃ surface. Specifically, the electrical energy per order that was associated with the use of ClO^- varied in the range of 0.100-1.617 kWh/m³. In summary, this study shows that ClO^- is an excellent electron acceptor for excited WO₃, while clarifying the CBZ degradation-enhancing effect of ClO^- as well as the kinetic model and DFT calculations. These findings can be employed in the degradation of recalcitrant contaminants in a cost-effective manner, while being significant for the development of more effective catalysts of UV-assisted advanced oxidation processes.

A Study on TiO2 Surface Texturing Effect for the Enhancement of Photocatalytic Reaction in a Total Phosphorous Concentration Measurement System

Powerful sunlight, a high water temperature, and stagnation in the water flow induce eutrophication in rivers and lakes, which destroys the aquatic ecosystem and threatens the downstream water supply systems. Accordingly, it is very important to perform real-time measurements of nutrients that induce algal growth, especially total phosphorus, to preserve and manage the aquatic ecosystem. To conduct quantitative analysis of the total phosphorus in the aquatic ecosystem, it is essential to perform a pretreatment process and quickly separate the phosphorus, combined with organic and inorganic materials, into a phosphate. In this study, the sandblasting process was used for the physical etching of the wafer, and photocatalytic materials were deposited on the surface with various roughness in order to improve the photocatalytic reaction surface and efficiency. The photocatalytic reaction was applied to combine the pretreated sample with the coloring agent for color development, and the absorbance of the colored sample was analyzed quantitatively to compare and evaluate the characteristics, followed by the surface increase in the photocatalytic materials. In addition, the pretreatment and measurement parts were materialized in a single chip to produce a small and light total phosphorus analysis sensor.

Kinetics and energetic analysis of the slow dispersive electron transfer from nano-TiO2 to O2 by in situ diffusion reflectance and Laplace transform

Electron transfer to O₂ is a universally existing process for the physiochemistry of many materials. Electron transfer to O₂ is also an inevitable process for photocatalytic reactions over TiO₂ and other materials. In the present research, a diffusion reflectance system was developed to measure in situ optical diffusion reflectances caused by photoinduced electrons in nano-TiO₂ under a steady light illumination; in situ absorption decays can be obtained to study the electron transfer from their trapped states to O₂. It is seen that the kinetics of electron transfer to O₂ is persistent and dispersive; this lasts for several minutes and approximately agrees with a stretched exponential kinetics. The result implies that variable apparent energy barriers (E_is) are involved in the electron transfer. The effects of O₂ amount, light intensity, and temperature are studied and the results mean the trap-filling effect should be involved in the electron transfer to O₂. A Laplace transform is used to derive the E_i distributions. It is found that the E_i dispersion shape almost does not change; this indicates that the physical reason causing the E_i dispersion is the same for different experimental conditions and possibly comes from the trap-filling effect. It is shown that the slow kinetics of the electron transfer is also dependent on the slow rate for an electron transferring from a trap to O₂, in additional to the trapping-filling effect. The results indicate that the photocatalytic activity can be increased through a modulation in trap distribution.

Microplastic degradation methods and corresponding degradation mechanism: Research status and future perspectives

Microplastics (MPs) pollution has become a global environmental concern because of their severe threat to biota. However, limited studies on the elimination of MPs pollution were reported. The conventional treatment methods were not suitable for MPs owing to their smaller size than plastic items. Hence many methods for MPs treatment have been examined. This review summarized the recently reported MPs degradation methods including AOPs (direct photodegradation, photocatalytic oxidation, and electrochemical oxidation) and biodegradation, corresponding degradation mechanism as well as current development state. The characteristics and limitations of each technique were discussed in detail. We found that all of them achieved almost satisfying degradation performance of MPs, but most of them exhibited that MPs can only be degraded partially into useful products or even CO₂ and H₂O under lab conditions. Given these, some recommendations for future research directions were proposed based on the knowledge gaps in these reported literatures. The aim of this review is to give a comprehensive introduction of several MPs degradation methods and acquaint the readers with the current research status of MPs degradation.

Does Symmetry Control Photocatalytic Activity of Titania-Based Photocatalysts?

Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morphology seem to be responsible for the efficiency of water oxidation, methanol dehydrogenation and oxidative decomposition of acetic acid, respectively. For the discussion on the dependence of the photocatalytic activity on the morphology and/or the symmetry other titania-based photocatalysts have also been analyzed, that is, octahedral anatase particles (OAP), commercial titania P25, inverse opal titania with and without incorporated gold NPs in void spaces and plasmonic photocatalysts (titania with deposits of gold). It has been concluded that though the morphology governs photocatalytic activity, the symmetry (despite its importance in many cases) rather does not control the photocatalytic performance.

Titania-Clay Mineral Composites for Environmental Catalysis and Photocatalysis

The use of titania-based composite materials in the field of heterogeneous catalysis and photocatalysis has a long and rich history. Hybrid structures combining titania nanoparticles with clay minerals have been extensively investigated for nearly four decades. The attractiveness of clay minerals as components of functional materials stems primarily from their compositional versatility and the possibility of using silicate lamellae as prefabricated building blocks ready to be fitted into the desired nanoconstruction. This review focuses on the evolution over the years of synthetic strategies employed for the manufacturing of titania–clay mineral composites with particular attention to the role of the adopted preparative approach in shaping the physical and chemical characteristics of the materials and enabling, ultimately, tuning of their catalytic and/or photocatalytic performance.

Octahedral Shaped PbTiO3-TiO2 Nanocomposites for High-Efficiency Photocatalytic Hydrogen Production

In this work, octahedral shaped PbTiO₃-TiO₂ nanocomposites have been synthesized by a facile hydrothermal method, where perovskite ferroelectric PbTiO₃ nanooctahedra were employed as substrate. The microstructures of the composites were investigated systemically by using XRD, SEM, TEM and UV-Vis spectroscopy. It was revealed that anantase TiO₂ nanocrystals with a size of about 5 nm are dispersed on the surface of the {111} facets of the nanooctahedron crystals. Photocatalytic hydrogen production of the nanocomposites has been evaluated in a methanol alcohol-water solution under UV light enhanced irradiation. The H₂ evolution rate of the nanocomposites increased with an increased loading of TiO₂ on the nanooctahedra. The highest H₂ evolution rate was 630.51 μmol/h with the highest concentration of TiO₂ prepared with 2 mL tetrabutyl titanate, which was about 36 times higher than that of the octahedron substrate. The enhanced photocatalytic reactivity of the nanocomposites is possibly ascribed to the UV light absorption of the nanooctahedral substrates, efficient separation of photo-generated carriers via the interface and the reaction on the surface of the TiO₂ nanocrystals.

Biochar Nanoparticles over TiO2 Nanotube Arrays: A Green Co-Catalyst to Boost the Photocatalytic Degradation of Organic Pollutants

Biochar nanoparticles (BC NPs), produced by low temperature pyrolysis (350 °C) of microalgae (Nannochloropsis sp.) and nutshells, are proposed as low-cost and sustainable co-catalysts to promote the photocatalytic activity of TiO2 nanotube (NT) arrays towards the degradation of methylene blue (MB) used as an organic pollutant model molecule. BC NPs (size < 25 nm) were obtained by treating bulk BC (i.e., biomass after pyrolysis) by sonication–centrifugation cycles in a water solution. The filtered BC NPs dispersion was deposited by simple drop-casting on the TiO2 NT support. The BC loading was varied by performing multiple depositions. Photocatalytic experiments under UV light (365 nm) revealed that the decoration with BC NPs significantly improves the TiO2 photoactivity. Such enhancement is mainly influenced by the amount of BC deposited; upon optimizing the BC deposition conditions, the rate of photocatalytic degradation of MB increases approximately three times with respect to bare TiO2, almost irrespective of the nature of the raw material. The greater photocatalytic activity of BC-TiO2 can be attributed to the synergistic combination of reactant/product adsorption and catalytic degradation of the adsorbed organic pollutant, as well as an improved charge carrier separation and electron transfer.

Mesoscale Confinement Effects and Emergent Quantum Interference in Titania Antidot Thin Films

The effect of confinement on electron and ion transport in oxide films is of interest both fundamentally and technologically for the design of next-generation electronic devices. In metal oxides with mobile ions and vacancies, it is the interplay of the different modes of charge transport and the corresponding current-voltage signatures that is of interest. We developed a patterned structure in titania films, with feature sizes of 11-20 nm, that allow us to explore confined transport. We describe how confinement changes the competing charge transport mechanisms, the patterned antidot array leads to displacement fields and confines the charge density that results in modified and emergent electron transport with an increase in conductivity. This emergent behavior can be described by considering electron interference effects. Characterization of the charge transport with electron holography and impedance spectroscopy, and through comparison with modeling, show that nanoscale confinement is a way to control quantum interference.

Multiphoton Upconversion Materials for Photocatalysis and Environmental Remediation

Solar-driven photocatalysis holds great potential for energy conversion, environmental remediation, and sustainable chemistry. However, practical applications of conventional photocatalytic systems have been constrained by their insufficient ability to harvest solar radiation in the infrared spectrum. Lanthanide-doped upconversion materials possess high photostability, tunable absorption, and the ability to convert low-energy infrared radiation into high-energy emission, making them attractive for infrared-driven photocatalysis. This review highlights essential principles for rational design of efficient photocatalysts. Particular emphasis is placed on current state-of-the-arts that offer enhanced upconversion luminescence efficiency. We also summarize recent advances in lanthanide-doped upconversion materials for photocatalysis. We conclude with new challenges and prospects for future developments of infrared-driven photocatalysts.

Defective Dopant-Free TiO2 as an Efficient Visible Light-Active Photocatalyst

Pristine and modified/doped titania are still some of the most widely investigated photocatalysts due to its high activity, stability, abundance and proper redox properties to carry out various reactions. However, modifiers and/or dopants resulting in visible-light activity might be expensive or work as recombination centers under UV irradiation. It seems that defective titania, known as “self-doped” TiO2, might be the best solution since it can be obtained under mild conditions without the addition of expensive materials and methods. This review discusses various methods of defective titania preparation, characterization of defect types, their localization (surface vs. bulk) and their function, as well as proposed mechanisms of photocatalytic reactions in the presence of self-doped titania. Although many kinds of defective titania samples have already been prepared with different colors, color intensities and defect kinds (mainly Ti3+ and oxygen vacancies), it is difficult to conclude which of them are the most recommended as the preparation conditions and activity testing used by authors differ. Furthermore, activity testing under solar radiation and for dyes does not clarify the mechanism since bare titania can also be excited and sensitized, respectively, in these conditions. In many reports, authors have not considered the possible influence of some impurities originated from the synthesis method (e.g., H, Al, Zn, Cl, F) that could co-participate in the overall mechanism of photocatalytic reactions. Moreover, some reports indicate that defective titania, especially black ones, might decrease activity since the defects might work as recombination centers. Despite some unproven/unclear findings and unanswered questions, there are many well-conducted studies confirmed by both experimental and theoretical studies that defective titania might be a promising material for various photocatalytic reactions under both UV and visible-light irradiation. Based on available literature, it could be proposed that optimal defects’ concentration, the preferential role of surface defects, a higher surface-to-bulk ratio of defects in rutile than in anatase, and the beneficial impact of disordered surface are the most important aspects to be considered during the preparation of defective titania.

Efficient elimination of the pollutants in eutrophicated water with carbon strengthened expanded graphite based photocatalysts: Unveiling the synergistic role of metal sites

Metal sites (Ni, Bi or Ag) were introduced into carbon strengthened expanded graphite (CEG) based photocatalysts, and performed as a novel strategy to enhance the elimination of Microcystis aeruginosa and microcystin-LR from water. Results show that metal doping can efficiently improve the adsorption of harmful algae and enhance the photocatalytic activities in inactivation of harmful algae and degradation of MC-LR. Among the CEG catalysts, Ni-CEG can achieve the highest removal rate up to 90.6% for algal cells with 5 h visible light irradiation, while Bi-CEG catalyst provides the best performance for MC-LR degradation with the removal rate of 80.9% in 6 h visible light irradiation. In general, considering the coexistence of algal cells and microcystin-LR, Bi-CEG is proved to be an excellent candidate for the remediation of eutrophicated waters since it can achieve the efficient removal of both harmful algae and MC-LR. DFT calculations indicate that metal doping can transform the photocatalysts into n-type semiconductor, and provide the mid-gap state. In addition, the partial charge density distribution near Fermi level was mainly composed by the metal dopants, which can enhance the interaction with harmful algae and MC-LR.

Effects of Reaction Temperature on the Photocatalytic Activity of TiO2 with Pd and Cu Cocatalysts

The aim of this study was to investigate the effects of reaction temperature on the photocatalytic activity of TiO2 with Pd and Cu cocatalysts. N2 sorption, transmission electron microscopy and high-resolution transmission electron microscopy were used to characterize the specific surface area, pore volume, pore size, morphology and metal distribution of the catalysts. The photocatalytic destruction of methylene blue under UV light irradiation was used to test its activity. The concentration of methylene blue in water was determined by UV-vis spectrophotometer. Pd/TiO2 catalyst was more active than Cu/TiO2 and TiO2. At 0–50 °C reaction temperature, the activity of TiO2 and Pd/TiO2 increased with an increase of reaction temperature. When the temperature was as high as 70 °C, the reaction rate of TiO2 drop slightly and Pd/TiO2 became less effective. In contrast, Cu/TiO2 was more active at room temperature than the other temperatures. The results indicate that the photocatalytic activity of the catalyst is influenced by the reaction temperature and the type of cocatalyst. When the reaction temperature is higher than 70 °C, the recombination of charge carriers will increase. The temperature range of 50–80 °C is regarded as the ideal temperature for effective photolysis of organic matter. The effects of reaction temperature mainly influence quantum effect, i.e., electron-hole separation and recombination.

The Photocatalysis-Enhanced TiO2@HPAN Membrane with High TiO2 Surface Content for Highly Effective Removal of Cationic Dyes

The elimination of dye pollutants from wastewater is a significant concern that has prompted extensive research into the development of highly efficient photocatalytic membranes. A novel method was proposed to prepare photocatalysis-enhanced poly(acrylonitrile-methyl acrylate) (PAN-based) membranes in this study. In detail, the blended membrane containing SiO₂@TiO₂ nanoparticles with a shell-core structure was first prepared via thermal-induced phase separation. The SiO₂ nanoshells were dissolved, and the released TiO₂ nanoparticles migrated to the membrane surface during a simple hydrolysis process, which prevents the TiO₂ nanoparticles from directly contacting or interacting with the polymer matrix. The hydrogen bonds bind the exposed TiO₂ with the PAN membrane surface, resulting in the formation of the TiO₂@HPAN hybrid membrane. The photocatalytic efficiency of the TiO₂@HPAN membrane doubled compared with that of nonhydrolyzed membranes. In the presence of UV light, the hybrid membrane can degrade 99.8% of methylene blue solution in less than 2 h, compared to only 86.1% for the blended membranes. Further, the TiO₂@HPAN membrane showed excellent photocatalytic activity for cationic dyes due to electrostatic attraction. Moreover, the high-flux recovery rate and recycling stability of the TiO₂@HPAN membrane lead to an excellent antifouling property. The facile preparation method proposed in this work shows extraordinary potential for the development of highly efficient selective photocatalytic materials for cationic dyes to be used in wastewater treatment applications.