TiO2 photocatalysis: Design and applications

Visualizing the Interfacial Charge Transfer between Photoactive Microcystis aeruginosa and Hydrogenated TiO2

Exploring photoactive biotic-abiotic conjugations is of great importance for a variety of applications, but it remains difficult to probe the interfacial transfer of photoinduced charge carriers. In this work, Kelvin probe force microscopy, together with fluorescence imaging technique, were used to visually observe the spatial distribution and interfacial behavior of photocarriers in Microcystis aeruginosa/TiO₂ hybrids. Experimental investigations suggested that photosynthetic microalgae cells were prone to trap photoholes from TiO₂ photocatalysts. Oxygen vacancy defects in semiconductor exhibited significant impact on the charge migration, as the surface photovoltage of hydrogenated TiO₂/microalgae hybrid was much higher than the pristine system. Profiting from the bioenhanced charge separation, biotic-abiotic architecture presented remarkably increased activity for photocatalytic inactivation of microalgae microorganisms. This work not only highlights the visual techniques for understanding the charge transfer around biotic-abiotic interface, but also provides a bioenhanced conjugation for the photocatalytic elimination of microorganisms in water treatment applications.

Enhanced visible light photocatalytic activity of Fe2O3 modified TiO2 prepared by atomic layer deposition

In this work, commercial anatase TiO2 powders were modified using ultrathin Fe2O3 layer by atomic layer deposition (ALD). The ultrathin Fe2O3 coating having small bandgap of 2.20 eV can increase the visible light absorption of TiO2 supports, at the meantime, Fe2O3/TiO2 heterojunction can effectively improve the lifetime of photogenerated electron-hole pairs. Results of ALD Fe2O3 modified TiO2 catalyst, therefore, showed great visible light driven catalytic degradation of methyl orange compared to pristine TiO2. A 400 cycles of ALD Fe2O3 (~ 2.6 nm) coated TiO2 powders exhibit the highest degradation efficiency of 97.4% in 90 min, much higher than pristine TiO2 powders of only 12.5%. Moreover, an ultrathin ALD Al2O3 (~ 2 nm) was able to improve the stability of Fe2O3-TiO2 catalyst. These results demonstrate that ALD surface modification with ultrathin coating is an extremely powerful route for the applications in constructing efficient and stable photocatalysts.

Photocatalytic and bactericidal properties and molecular docking analysis of TiO2 nanoparticles conjugated with Zr for environmental remediation

Despite implementing several methodologies including a combination of physical, chemical and biological techniques, aquatic and microbial pollution remains a challenge to this day. Recently, nanomaterials have attracted considerable attention due to their extraordinary prospective for utilization toward environmental remediation. Among several probable candidates, TiO2 stands out due to its potential for use in multifaceted applications. One way to improve the catalytic and antimicrobial potential of TiO2 is to dope it with certain elements. In this study, Zr-doped TiO2 was synthesized through a sol-gel chemical method using various dopant concentrations (2, 4, 6, and 8 wt%). Surface morphological, microstructural and elemental analysis was carried out using FESEM and HR-TEM along with EDS to confirm the formation of Zr-TiO2. XRD spectra showed a linear shift of the (101) anatase peak to lower diffraction angles (from 25.4° to 25.08°) with increasing Zr4+ concentration. Functional groups were examined via FTIR, an ample absorption band appearing between 400 and 700 cm-1 in the acquired spectrum was attributed to the vibration modes of the Ti-O-Ti linkage present within TiO2 nanoparticles, which denotes the formation of TiO2. Experimental results indicated that with increasing dopant concentrations, photocatalytic potential was enhanced significantly. In this respect, TiO2 doped with 8 wt% Zr (sample 0.08 : 1) exhibited outstanding performance by realizing 98% elimination of synthetic MB in 100 minutes. This is thought to be due to a decreased rate of electron-hole pair recombination that transpires upon doping. Therefore, it is proposed that Zr-doped TiO2 can be used as an effective photocatalyst material for various environmental and wastewater treatment applications. The good docking scores and binding confirmation of Zr-doped TiO2 suggested doped nanoparticles as a potential inhibitor against selected targets of both E. coli and S. aureus. Hence, enzyme inhibition studies of Zr-doped TiO2 NPs are suggested for further confirmation of these in silico predictions.

Biomedical Waste Management by Using Nanophotocatalysts: The Need for New Options

Biomedical waste management is getting significant consideration among treatment technologies, since insufficient management can cause danger to medicinal service specialists, patients, and their environmental conditions. The improvement of waste administration protocols, plans, and policies are surveyed, despite setting up training programs on legitimate waste administration for all healthcare service staff. Most biomedical waste substances do not degrade in the environment, and may also not be thoroughly removed through treatment processes. Therefore, the long-lasting persistence of biomedical waste can effectively have adverse impact on wildlife and human beings, as well. Hence, photocatalysis is gaining increasing attention for eradication of pollutants and for improving the safety and clearness of the environment due to its great potential as a green and eco-friendly process. In this regard, nanostructured photocatalysts, in contrast to their regular counterparts, exhibit significant attributes such as non-toxicity, low cost and higher absorption efficiency in a wider range of the solar spectrum, making them the best candidate to employ for photodegradation. Due to these unique properties of nanophotocatalysts for biomedical waste management, we aim to critically evaluate various aspects of these materials in the present review and highlight their importance in healthcare service settings.

Facile Synthesis of "Boron-Doped" Carbon Dots and Their Application in Visible-Light-Driven Photocatalytic Degradation of Organic Dyes

Carbon dots (C-dots) were facilely fabricated via a hydrothermal method and fully characterized. Our study shows that the as-synthesized C-dots are nontoxic, negatively charged spherical particles (average diameter 4.7 nm) with excellent water dispersion ability. Furthermore, the C-dots have a rich presence of surface functionalities such as hydroxyls and carboxyls as well as amines. The significance of the C-dots as highly efficient photocatalysts for rhodamine B (RhB) and methylene blue (MB) degradation was explored. The C-dots demonstrate excellent photocatalytic activity, achieving 100% of RhB and MB degradation within 170 min. The degradation rate constants for RhB and MB were 1.8 × 10⁻² and 2.4 × 10⁻² min⁻¹, respectively. The photocatalytic degradation performances of the C-dots are comparable to those metal-based photocatalysts and generally better than previously reported C-dots photocatalysts. Collectively considering the excellent photocatalytic activity toward organic dye degradation, as well as the fact that they are facilely synthesized with no need of further doping, compositing, and tedious purification and separation, the C-dots fabricated in this work are demonstrated to be a promising alternative for pollutant degradation and environment protection.

Microplastic pollution reduction by a carbon and nitrogen-doped TiO2: Effect of pH and temperature in the photocatalytic degradation process

Microplastics (MPs) are pollutants formed by plastics ≤ 5 mm and are present in marine and terrestrial environments. Due to their large surface to volume ratio and chemical surface properties, MPs adsorb hazardous chemicals from their surrounding environment. When MPs are consumed by fauna, they transfer those substances through the trophic chain. An essential issue of MPs is their disposal. Due to their size, the disposal methods commonly used for plastic items are not suited for MPs. Here, photocatalysis in an aqueous medium is proposed as an alternative to fight MPs pollution. Although the photocatalysis of MPs has been reported, the effect of operating variables in the process has not been investigated. To fill this gap, the impact of pH and temperature on the degradation process of HDPE MPs was investigated using C,N-TiO₂ and visible light. Degradation was followed by mass loss, carbonyl index calculation and microscopy. It was found that photocatalysis at low temperature (0 °C) increases MPs' surface area by fragmentation, and low pH value (pH 3) favours hydroperoxide formation during photooxidation. By using the design of experiments tool, it was demonstrated that there is a combined effect of pH and temperature in the photocatalysis of HDPE MPs.

Hot-carrier generation from plasmons in an antenna-spacer-mirror nanostructure

By introducing Au-nanodisk antennas, we conveniently got hot carriers from decay of surface plasmons (SPs) on planar interface in an Au-antennas/TiO₂-spacer/Au-mirror (ASM) structure without an additional phase-matching process for SP generation. The presence of hot carriers from SPs is distinguished by opposite photocurrents compared with a similar structure without an Au mirror. Analyzed by extinction spectra and electrodynamics simulations, reflection between an Au nanodisk layer and an Au mirror induces an optical response of cavity mode, which excites SPs on an Au-mirror interface and significantly enhances the light harvesting, thus leading to a relatively high hot-carrier density from SP decay. The peak of incident photon-to-electron conversion efficiencies at different wavelength also well matches the optical response of the structure.

Pilot-Scale Testing of UV-A Light Treatment for Mitigation of NH3, H2S, GHGs, VOCs, Odor, and O3 Inside the Poultry Barn

Poultry farmers are producing eggs, meat, and feathers with increased efficiency and lower carbon footprint. Technologies to address concerns about the indoor air quality inside barns and the gaseous emissions from farms to the atmosphere continue to be among industry priorities. We have been developing and scaling up a UV air treatment that has the potential to reduce odor and other gases on the farm scale. In our recent laboratory-scale study, the use of UV-A (a less toxic ultraviolet light, a.k.a. “black light”) and a special TiO₂-based photocatalyst reduced concentrations of several important air pollutants (NH₃, CO₂, N₂O, O₃) without impact on H₂S and CH₄. Therefore, the objectives of this research were to (1) scale up the UV treatment to pilot scale, (2) evaluate the mitigation of odor and odorous volatile organic compounds (VOCs), and (3) complete preliminary economic analyses. A pilot-scale experiment was conducted under commercial poultry barn conditions to evaluate photocatalyst coatings on surfaces subjected to UV light under field conditions. In this study, the reactor was constructed to support interchangeable wall panels and installed on a poultry farm. The effects of a photocatalyst's presence (photocatalysis and photolysis), UV intensity (LED and fluorescent), and treatment time were studied in the pilot-scale experiments inside a poultry barn. The results of the pilot-scale experiments were consistent with the laboratory-scale one: the percent reduction under photocatalysis was generally higher than photolysis. In addition, the percent reduction of target gases at a high light intensity and long treatment time was higher. The percent reduction of NH₃ was 5–9%. There was no impact on H₂S, CH₄, and CO₂ under any experimental conditions. N₂O and O₃ concentrations were reduced at 6–12% and 87–100% by both photolysis and photocatalysis. In addition, concentrations of several VOCs responsible for livestock odor were reduced from 26 to 62% and increased with treatment time and light intensity. The odor was reduced by 18%. Photolysis treatment reduced concentrations of N₂O, VOCs, and O₃, only. The initial economic analysis has shown that LEDs are more efficient than fluorescent lights. Further scale-up and research at farm scale are warranted.

Photonic Crystals for Plasmonic Photocatalysis

Noble metal (NM)-modified wide-bandgap semiconductors with activity under visible light (Vis) irradiation, due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively studied over the last few years. Despite the novelty of the topic, a large number of reports have already been published, discussing the optimal properties, synthesis methods and mechanism clarification. It has been proposed that both efficient light harvesting and charge carriers’ migration are detrimental for high and stable activity under Vis irradiation. Accordingly, photonic crystals (PCs) with photonic bandgap (PBG) and slow photon effects seem to be highly attractive for efficient use of incident photons. Therefore, the study on PCs-based plasmonic photocatalysts has been conducted, mainly on titania inverse opal (IO) modified with nanoparticles (NPs) of NM. Although, the research is quite new and only several reports have been published, it might be concluded that the matching between LSPR and PBG (especially at red edge) by tuning of NMNPs size and IO-void diameter, respectively, is the most crucial for the photocatalytic activity.

Highly Active Rutile TiO2 Nanocrystalline Photocatalysts

The controllable synthesis of rutile TiO₂ single crystal particles with the preferential orientation of {111} facets still remains a scientific and technological challenge. Here, we developed a facile route for fabrication of rutile TiO₂ nanorod crystals (RTiO₂NRs) having high ratios of oxidative {111} to reductive {110} surfaces. RTiO₂NRs were synthesized using a peroxo-titanium complex (PTC) approach, which was controlled by changing the Ti/H₂O₂ ratio. The thus obtained RTiO₂NRs revealed a high tendency to agglomerate through orientation-dependent attachment along the {110} facets. This resulted in an increased {111}/{110} surface ratio and led to a markedly improved photocatalytic activity of RTiO₂NR aggregates. The reported findings illustrate the rich potential of the herein proposed facile and energy-efficient synthesis of nanostructured rutile TiO₂-based photocatalysts.

Enhanced Pollutant Adsorption and Regeneration of Layered Double Hydroxide-Based Photoregenerable Adsorbent

Efforts to combine photocatalysts with organic and inorganic adsorbents in engineered composite materials have been pursued extensively to harness sunlight for a green, sustainable regeneration of exhausted adsorbent. Recent advances combining benchmark photocatalyst, titanium dioxide (TiO₂), with an inorganic adsorbent, layered double hydroxides (LDHs), have shown potential for an inorganic adsorbent-photocatalyst system but faced critical limitations in realizing practical applications: low adsorption capacity and slow, inefficient photocatalytic regeneration. This study presents an enhanced TiO₂/LDH based material that demonstrates a dramatically increased efficiency for both decontamination through adsorption and subsequent solar, photocatalytic regeneration. The combination of delamination and high temperature treatment of LDH is utilized to drastically enhance the adsorption capacity toward model contaminant Methyl Orange to 1450-1459 mg/g, which is even higher than most commercial and lab-synthesized carbon-based adsorbents. Light-active plasmonic nanoparticles are employed to increase the photocatalytic regeneration performance, and experimental results show that the synthesized composite material regains above 97% of its adsorption capacity for 5 cycles of regeneration and readsorption. Overall, the results of this study demonstrate potential for the development of inorganic multifunctional adsorbents that can harness a variety of chemical reactions without the loss of adsorptivity over long-term use.

Fabrication of Ce3+ substituted nickel ferrite-reduced graphene oxide heterojunction with high photocatalytic activity under visible light irradiation

In the current investigation, graphene (rGO)-supported cerium substituted nickel ferrite (NiCe_yFe_2-yO₄ y = 0.05) photocatalyst was prepared via two-step wet chemical approach. The resulting NiCe_yFe_2-yO₄/rGO nanocomposite exhibited excellent photocatalytic performance and stability. Moreover, the photocatalytic activity of NiCe_yFe_2-yO₄/rGO nanocomposite was also investigated comparatively with NiCe_yFe_2-yO₄ nanoparticles. As compared to the NiCe_yFe_2-yO₄ nanoparticles, NiCe_yFe_2-yO₄/rGO nanocomposite showed superior photocatalytic efficiency and recycling stability for MB degradation, which is two times that of bare NiCe_yFe_2-yO₄ nanoparticles. After visible light irradiation for 70 min, 94.67 % of MB dye was removed by NiCe_yFe_2-yO₄/rGO nanocomposite whereas only 50 % of MB dye was removed by NiCe_yFe_2-yO₄ nanoparticles. The increase in photocatalytic performance is mainly ascribed to formation of NiCe_yFe_2-yO₄/rGO heterojunction which not only assist in separation of photo-induced charge carriers, but also sustain a strong redox ability. Moreover, the photo-corrosion of NiCe_0.05Fe_1.95O₄ nanoparticles is inhibited through transfer of photo-induced electrons of NiCe_0.05Fe_1.95O₄ nanoparticles to rGO. A possible photo-degradation mechanism based on reactive species trapping experiments has been proposed. The effect of various factors like pH, temperature and catalyst dosage has also been explored. Facile synthesis method, excellent photocatalytic performance for organic pollutants and superior reusability suggest that NiCe_yFe_2-yO₄/rGO photocatalyst possesses high potential for large-scale pollutant treatment.

Phase-Selective and Localized TiO2 Coating on Additive and Wrought Titanium by a Direct Laser Surface Modification Approach

Titanium has been the material of interest in biological implant applications due to its unique mechanical properties and biocompatibility. Their design is now growing rapidly due to the advent of additive manufacturing technology that enables the fabrication of complex and patient-customized parts. Titanium dioxides (TiO2) coatings with different phases (e.g., anatase, rutile) and morphologies have shown to be effective in enhancing osteointegration and antibacterial behavior. This enhanced antibacterial behavior stems from the photocatalytic activity generated from crystalline TiO2 coatings. Anatase has commonly been shown to be a more photocatalytic oxide phase compared to rutile despite its larger band gap. However, more recent studies have suggested that a synergistic effect leading to increased photocatalytic activity may be produced with a combination of oxides containing both anatase and rutile phases. Here, we demonstrate the selective and localized formation of TiO2 nanostructures on additive and wrought titanium parts with anatase, rutile, and mixed phases by a laser-induced transformation approach. Compared to conventional coating processes, this technique produces desired TiO2 phases simply by controlled laser irradiation of titanium parts in an oxygen environment, where needed. The effects of processing conditions such as laser power, scanning speed, laser pulse duration, frequency, and gas flow on the selective transformation were studied. The morphological and structural evolutions were investigated using various characterization techniques. This method is specifically of significant interest in creating phase-selective TiO2 surfaces on titanium-based bioimplants, including those fabricated by additive manufacturing technologies.

Enhanced Visible-Light Driven Photocatalytic Activity of Ag@TiO2 Photocatalyst Prepared in Chitosan Matrix

Ag doped TiO2 photocatalysts (Ag@TiO2) were prepared with an aim to extend the absorption range of TiO2 into the visible region, for tentative application under solar irradiation. Photocatalyst synthesized by the novel method using chitosan for reduction of Ag+ to Ag0 nanoparticles was compared to similar catalysts previously reported. The photocatalytic activity of Ag@TiO2 obtained by a simple novel method was evaluated based on degradation of salicylic acid as a model compound. The higher activity under visible irradiation can be attributed to the surface plasmon resonance and suppression of the electron-hole recombination when deposition of Ag nanoparticles on TiO2 was achieved using chitosan. The photocatalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDXS), selected area diffraction (SAED), and diffuse reflectance spectroscopy (DRS). The photochromism of Ag was observed and explained.

Doping TiO2 with CuSO4 enhances visible light photocatalytic activity for organic pollutant degradation

Photocatalysis is one of the most promising advanced oxidation processes due to the capability of solid catalyst to continuously produce oxidant species under light irradiation. The use of conventional UV lamps is high cost intensive, which undermines the possible implementation in developing countries. Visible light active photocatalysts can overcome these challenges and find a market opportunity for competitive technology implementation. This work proposes the synthesis of visible light active catalyst following a facile sol-gel synthesis that introduces CuSO₄ as dopant in TiO₂. Results present complete abatement of methylene blue in 120 min of treatment under 50 mW cm^-2 of blue light (λ = 450 nm), while commercial P25 TiO₂ presented null abatement under identical conditions. Synthesis parameters including dopant level and calcination temperature allowed defining optimum synthesis conditions based on material characteristics modification and catalytic activity enhancement. A doping level of 0.21 mol% CuSO₄ was identified as optimum condition to enable visible light photocatalysis of doped TiO₂ catalysts calcined at 300 °C. Finally, operational parameters were evaluated defining a wide range of pH operation under 3.0 g L^-1 of catalyst dose to treat up to 20 g L^-1 of highly recalcitrant phenothiazine dye. These optimum conditions allowed complete dye removal under visible light after 120 min of treatment.

Environmental factors affecting degradation of perfluorooctanoic acid (PFOA) by In2O3 nanoparticles

Nanophotocatalysts have shown great potential for degrading poly- and perfluorinated substances (PFAS). In light of the fact that most of these catalysts were studied in pure water, this study was designed to elucidate effects from common environmental factors on decomposing and defluorinating perfluorooctanoic acid (PFOA) by In₂O₃ nanoparticles. Results from this work demonstrated that among the seven parameters, pH, sulfate, chloride, H₂O₂, In₂O₃ dose, NOM and O₂, the first four had statistically significant negative effects on PFOA degradation. Since PFOA is a strong acid, the best condition leading to the highest PFOA removal was identified for two pH ranges. When pH was between 4 and 8, the optimal condition was: pH = 4.2; sulfate = 5.00 mg/L; chloride = 20.43 mg/L; H₂O₂ = 0 mmol/L. Under this condition, PFOA decomposition and defluorination were 55.22 and 23.56%, respectively. When pH was between 2 and 6, the optimal condition was: pH = 2; sulfate = 5.00 mg/L; chloride = 27.31 mg/L; H₂O₂ = 0 mmol/L. With this condition, the modeled PFOA decomposition was 97.59% with a defluorination of approximately 100%. These predicted results were all confirmed by experimental data. Thus, In₂O₃ nanoparticles can be used for degrading PFOA in aqueous solutions. This approach works best when the target contaminated water contains low concentrations of NOM, sulfate and chloride and at a low pH.

Novel quantification of formation trend and reaction efficiency of hydroxyl radicals for investigating photocatalytic mechanism of Fe-doped TiO2 during UV and visible light-induced degradation of acid orange 7

A detailed mechanistic investigation of the hydroxyl radical (•OH) formation and organic pollutant degradation over transition metal-doped and undoped TiO₂ photocatalysts was performed by the quantitative measurement of •OH and the identification of intermediate products under various experimental conditions. The Fe-doped TiO₂ as a typical subject was prepared, characterized and used to degrade an azo dye Acid Orange 7 (AO7). It is indicated that the enhanced photocatalytic activity of Fe-doped TiO₂ for AO7 degradation was attributed to the increase in surface area, the facilitated charge transfer via Fe-dopant, and a red shift of absorbable wavelength, maintaining a great formation of •OH under visible irradiation. The oxidation of H₂O by holes was estimated as the major pathway of •OH formation rather than the reduction of dissolved O₂ by electrons, and their formation trends reached to approximately 75% and 25%, respectively. Meanwhile the synergistic effect of Fe-dopant produced nearly 10% of extra •OH by visible light photoactivation. The intermediate products and pathways of AO7 degradation varied greatly with different photocatalysts and conditions of the process, involving several reaction mechanisms such as the azo bond cleaving, naphthalene oxidation, desulfonation, and hydroxylated products generation. Through the quantification of •OH-reacted efficiency we proposed, a stoichiometry of •OH affecting overall reaction mechanisms in the TiO₂-assisted photodegradation of AO7 was further established. This study can provide new insights on how to better clarify the variation regularity of organic pollutant degradation from different treatments of the •OH-based advanced oxidation processes.

Recent Progresses on Metal Halide Perovskite-Based Material as Potential Photocatalyst

Recent years have witnessed an incredibly high interest in perovskite-based materials. Among this class, metal halide perovskites (MHPs) have attracted a lot of attention due to their easy preparation and excellent opto-electronic properties, showing a remarkably fast development in a few decades, particularly in solar light-driven applications. The high extinction coefficients, the optimal band gaps, the high photoluminescence quantum yields and the long electron–hole diffusion lengths make MHPs promising candidates in several technologies. Currently, the researchers have been focusing their attention on MHPs-based solar cells, light-emitting diodes, photodetectors, lasers, X-ray detectors and luminescent solar concentrators. In our review, we firstly present a brief introduction on the recent discoveries and on the remarkable properties of metal halide perovskites, followed by a summary of some of their more traditional and representative applications. In particular, the core of this work was to examine the recent progresses of MHPs-based materials in photocatalytic applications. We summarize some recent developments of hybrid organic–inorganic and all-inorganic MHPs, recently used as photocatalysts for hydrogen evolution, carbon dioxide reduction, organic contaminant degradation and organic synthesis. Finally, the main limitations and the future potential of this new generation of materials have been discussed.

New Insights into the Fundamental Principle of Semiconductor Photocatalysis

Although photocatalysis has been studied for many years as an attractive way to resolve energy and environmental problems, its principle still remains unclear. Some confusions and misunderstandings exist in photocatalytic studies. This research aims to elaborate some new thoughts on the fundamental principle of semiconductor photocatalysis. Starting from the basic laws of thermodynamics, we first defined the thermodynamic potential of photocatalysis. A concept, the Gibbs potential landscape, was thus then proposed to describe the kinetics of photocatalysis. Photocatalysis is therefore defined as a light-driven chemical reaction that still needs heat activation, in that light and heat play their different roles and interact with each other. Photocatalysis should feature an activation energy functioning with both light and heat. The roles of light and heat are correlative and mutually inhibit at both levels of thermodynamics and kinetics, so it is impossible for an intrinsic light-heat synergism to happen. Two criteria were further proposed to determine an intrinsic light-heat synergism in photocatalysis. Experiments were also carried out to calculate the thermodynamic potential and can agree well with the theory. Experimental results proved that there is no intrinsic light-heat synergism, in accordance with our theoretical prediction. This research clarified some misunderstandings and gained some new insights into the nature of photocatalysis; this is important for the discipline of semiconductor photocatalysis.

Effects of core titanium crystal dimension and crystal phase on ROS generation and tumour accumulation of transferrin coated titanium dioxide nanoaggregates

Radionuclide-stimulated therapy (RaST), which is enhanced by Cherenkov radiation, has enabled deep tissue stimulation of UV photosensitizers, providing a new path for cancer treatment. Previous reports have shown UV-active titanium dioxide (TiO₂) nanoparticles (NPs) modified with transferrin inhibit tumour growth after orthogonal treatment with Cherenkov radiation-emitting radionuclides such as ¹⁸F-fluorodeoxyglucose (FDG). However, poor understanding of TiO₂ NP parameters on reactive oxygen species (ROS) generation and particle distribution limits effective therapy. Here we sought to delineate the effects of crystal phase and core TiO₂ crystal dimension (cTd) on ROS production and particle morphology. We prepared Transferrin (Tf)-TiO₂ nanoaggregates (NAGs) using solvothermally synthesized cTd sizes from 5 to 1000 nm diameter and holo- or apo-transferrin. Holo-transferrin was unable to stabilize TiO₂ NPs while apo-transferrin stabilized TiO₂ into uniform nanoaggregates (NAGs), which were invariant with differing cTd, averaging 116 ± 1.04 nm for cTds below 100 nm. ROS production increased from 5 to 25 nm cTd, attaining a peak at 25 nm before decreasing with larger sizes. The supra-25 nm ROS production decrease was partially driven by a ~1/r ³ surface area decline. Additionally, amorphous TiO₂ of equal core size exhibited a 2.6-fold increase in ROS production compared to anatase NAGs, although limited stability halted further use. Although both 5 and 25 nm anatase cTds formed similarly sized NAGs, 5 nm anatase showed a four-fold higher tumour-to-muscle ratio than the 25 nm NPs in tumour-bearing mice, demonstrating the intricate relationships between physical and biological properties of NAGs. The combined in vivo and ROS results demonstrate that anatase crystals and cTd size of 25 nm or less are ideal particle parameters to balance biodistribution with ROS production efficiency.

Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO2 ceramics: from polarons to Nb-Nb dimers

Rutile is the most common and stable polymorph form of titanium oxide TiO2 at all temperatures. The doping of rutile TiO2 with a small amount of niobium is reknown for being responsible for a large increase of the electrical conductivity by several orders of magnitude, broadening its technological interest towards new emerging fields such as the thermoelectric conversion of waste heat. The electronic conduction has been found to be of a polaronic nature with strongly localized charges around the Ti3+ centers while, on the other side, the relatively high value of the thermal conductivity implies the existence of lattice heat carriers, i.e. phonons, with large mean free paths which makes the nanostructuration relevant for optimizing the thermoelectric efficiency. Here, the use of a high-pressure and high-temperature sintering technique has allowed to vary the grain size in rutile TiO2 pellets from 300 to 170 nm, leading to a significant reduction of the lattice thermal conductivity. The thermoelectric properties (electrical conductivity, Seebeck coefficient and thermal conductivity) of Nb-doped rutile nanostructured ceramics, namely NbxTi1-xO2 with x varying from 1 to 5%, are reported from room temperature to ∼900 K. With the incorporation of Nb, an optimum in the thermoelectric properties together with an anomaly on the tetragonal lattice constant c are observed for a concentration of ∼2.85%, which might be the fingerprint of the formation of short Nb dimers.

Crystallization of TiO2-MoS2 Hybrid Material under Hydrothermal Treatment and Its Electrochemical Performance

Hydrothermal crystallization was used to synthesize an advanced hybrid system containing titania and molybdenum disulfide (with a TiO₂:MoS₂ molar ratio of 1:1). The way in which the conditions of hydrothermal treatment (180 and 200 °C) and thermal treatment (500 °C) affect the physicochemical properties of the products was determined. A physicochemical analysis of the fabricated materials included the determination of the microstructure and morphology (scanning and transmission electron microscopy—SEM and TEM), crystalline structure (X-ray diffraction method—XRD), chemical surface composition (energy dispersive X-ray spectroscopy—EDS) and parameters of the porous structure (low-temperature N₂ sorption), as well as the chemical surface concentration (X-ray photoelectron spectroscop—XPS). It is well known that lithium-ion batteries (LIBs) represent a renewable energy source and a type of energy storage device. The increased demand for energy means that new materials with higher energy and power densities continue to be the subject of investigation. The objective of this research was to obtain a new electrode (anode) component characterized by high work efficiency and good electrochemical properties. The synthesized TiO₂-MoS₂ material exhibited much better electrochemical stability than pure MoS₂ (commercial), but with a specific capacity ca. 630 mAh/g at a current density of 100 mA/g.

Porous Hybrid Materials Based on Mesotetrakis(Hydroxyphenyl) Porphyrins and TiO2 for Efficient Visible-Light-Driven Hydrogen Production

A series of highly robust nano-micro hybrid materials based on meso-tetra(4-hydroxyphenyl) porphyrins (M = H, Pd, Zn) and titanium dioxide (denoted as THPP-TiO2, THPP-Pd-TiO2, and THPP-Zn-TiO2) have been prepared by a facile sol-gel method for the first time. When Pt nanoparticles are incorporated in these hybrids, Pt/THPP-Pd-TiO2 achieves good H2 production activity (2025.4 μmol g−1 h−1 and 12.03 μmol m−2 h−1), higher than that of Pt/THPP-Zn-TiO2 (1239.8 μmol g−1 h−1 and 7.46 μmol m−2 h−1) and Pt/THPP-TiO2 (576.8 μmol g−1 h−1 and 4.02 μmol m−2 h−1), owing to the different central metal ions in porphyrins. The best activity of Pt/THPP-Pd-TiO2 would be attributed to the two-center catalysis from coordination Pd metal ions and Pt nanoparticles, while the higher activity of Pt/THPP-Zn-TiO2 than Pt/THPP-TiO2 could be ascribed to the more effective light harvesting and electron transfer between THPP-Zn and TiO2. In addition, the hybridized Pt/THPP-Pd-TiO2 catalyst exhibits unattenuated hydrogen production stability even after recycling the experiment 10 times (cumulative turnover number of 5111 after 50 h), far superior to that of the surface-sensitized Pt/THPP-Pd/TiO2 catalyst with analogous components, due to the more stable Ti-O bonds between four phenols in porphyrins and TiO2 for the hybrid system. The present study provides a promising approach for constructing stable organic–inorganic hybrid systems with unique hierarchical structures for efficient light absorption and electron transfer.

The Photocatalytic Activity of Titania Coatings Produced by Electrochemical and Chemical Oxidation of Ti6Al4V Substrate, Estimated According to ISO 10678:2010The Photocatalytic Activity of Titania Coatings Produced by Electrochemical and Chemical Oxidation of Ti6Al4V Substrate, Estimated According to ISO 10678:2010

The last twenty years have been a period of intense investigations of materials based on titanium dioxide, which have unique properties and functionalities, and which can be used in various areas of medicine. As a part of this issue, the results of our works for the assessment of the photocatalytic activity of titanium dioxide nanocoatings of different nanoarchitecture (nanoporous, nanotubular, nanosponge-like and nanofibrous examples), which were earlier checked in terms of their biocompatibility and usability for the modification of medical devices' surfaces, are presented. The studied materials were produced on the surface of Ti6Al4V substrates using electrochemical and chemical oxidation methods. The activity of produced titania materials was studied on the base of the methylene blue (MB) degradation effect, in accordance to ISO 10678:2010. In our works, we have focused on the analysis of the correlation between the photocatalytic activity of nanoarchitecturally different TiO₂ coatings, their morphology and structure. The obtained results prove that all studied coatings, both amorphous and amorphous containing crystalline domains, revealed photocatalytic activity in the photoinduced degradation of the organic pollution standard. This activity may be an additional advantage of medical device coatings, being adequate for use in sterilization processes applying UVA light.

Functionalized Graphene Derivatives and TiO2 for High Visible Light Photodegradation of Azo Dyes

Functionalized graphene derivatives including graphene oxide (GO), reduced graphene oxide (rGO), and heteroatom (nitrogen/sulphur (N/S) or boron (B))-doped graphene were used to synthesize composites with TiO₂ (T). The photocatalytic performance of composites was assessed for the degradation of Orange G dye (OG) under simulated solar light. All the prepared graphene derivatives—TiO₂ composites showed better photocatalytic performance than bare TiO₂. A higher photocatalytic activity was found for the composites containing GO and N/S co-doped rGO (k_app = 109.2 × 10⁻³ and 48.4 × 10⁻³ min⁻¹, for GO-T and rGONS-T, respectively). The influence of both initial solution pH and the reactive species involved in the OG degradation pathway were studied. The photocatalytic activity of the samples decreased with the increase of the initial pH (from 3.0 to 10.0) due to the occurrence of electrostatic repulsive forces between the photocatalysts surface and the molecules of OG, both negatively charged. The use of selective scavengers showed that although the photogenerated holes dominate the degradation mechanism, radicals and singlet oxygen also participate in the OG degradation pathway. In addition, reutilization experiments indicated that the samples were stable under the reaction conditions used.

A comparative study on emergent pollutants photo-assisted degradation using ruthenium modified titanate nanotubes and nanowires as catalysts

Several methods have been used to tailor nanomaterials structure and properties. Sometimes, slight changes in the structure outcomes expressive improvements in the optical and photocatalytic properties of semiconductor nanoparticles. In this context, the influence of the metal doping and the morphology on a catalyst performance was studied in this work. Here, ruthenium doped titanate nanotubes (RuTNT) were synthesised for the first time using an amorphous Ru-containing precursor. Afterwards, the photocatalytic performance of this sample was compared to the one obtained for ruthenium titanate nanowires (RuTNW), recently reported. Two samples, RuTNW and RuTNT, were produced using the same Ru-containing precursor but distinct hydrothermal methodologies. The powders were structural, morphological and optical characterized by X-ray diffraction and fluorescence, transmission electron microscopy, Raman, X-ray photoelectron and photoluminescence spectroscopies. Distinct variations on the structural and optical properties of the RuTNT and RuTNW nanoparticles, due to ruthenium incorporation were observed. Their potential use as photocatalysts was evaluated on the hydroxyl radical photo-assisted production. Both samples were catalytic for this reaction, presenting better performances than the pristine counterparts, being RuTNT the best photocatalyst. Subsequently, the degradation of two emergent pollutants, caffeine and sulfamethazine, was studied. RuTNT demonstrated to be better photocatalyst than RuTNW for caffeine but identical performances were obtained for sulfamethazine. For both catalysts, the degradation mechanism of the pollutants was explored through the identification and quantification of the intermediate compounds produced and several differences were found. This indicates the importance of the structural and morphological aspects of a material on its catalytic performance.

Effect of the preparation method and metal content on the synthesis of metal modified titanium oxide used for the removal of salicylic acid under UV light

Titanium dioxide modified with Ag and Fe was synthesized using two preparation methods, characterized and applied to the photocatalytic degradation of salicylic acid in aqueous solution. The modified TiO₂ samples were prepared by the sol-gel and wet impregnation methods starting from titanium(IV) isopropoxide and using AgNO₃ and Fe(NO₃)₃·9H₂O as precursors of the modifiers, with their content varying between 0 and 5 wt.%. Catalysts characterization was based on powder X-ray diffraction (PXRD), nitrogen physisorption at 77 K, temperature programmed reduction (H₂-TPR), chemisorption of NH₃ at 343 K and X-ray photoelectron spectroscopy (XPS). The photocatalytic degradation of salicylic acid by modified TiO₂ was investigated under ultraviolet irradiation at 298 K considering various concentrations of the catalyst, between 100 and 1000 mg_catalyst/dm³, and of the organic molecule, between 0 and 15 mg/dm³. The catalysts most active in the degradation of salicylic acid were those having the highest Fe content.

Development of Porous Titania Structure with Improved Photocatalytic Activity: Response Surface Modeling and Multi-Objective Optimization

Porous titania was successfully synthesized by an ultrasound-assisted sol-gel route. The synthesis process was empirically modeled and optimized using the response surface methodology (RSM). Input variables adopted for optimization dealt with the weight ratio of precursors (r) and the sonication time (t), representing the used factors in the synthesis procedure. With regard to application, the synthesized TiO₂ samples were tested for the photodegradation of two water-soluble organic pollutants under UV-Vis irradiation. Optimal conditions for the efficient pollutants' photodegradation were found to involve a precursors ratio of 3 and a sonication time of 60 min. Thus, the M5 sample prepared under the founded optimal conditions yielded the maximal removal efficiencies of 98.4% and 46.3% for the photodegradation of CR dye and 2,4-D herbicide, respectively. In addition, the photodegradation kinetics revealed the pseudo first-order rate constants, showing the photodegradation of CR (k₁ = 8.86 × 10^-2 min^-1) by M5 sample is about 1.3-fold faster than the photodegradation of 2,4-D pesticide (k₂ = 6.84 × 10^-2 min^-1).

Aqueous solution photocatalytic synthesis of p-anisaldehyde by using graphite-like carbon nitride photocatalysts obtained via the hard-templating route

Graphite-like carbon nitride (GCN)-based materials were developed via the hard-templating route, using dicyandiamide as the GCN precursor and silica templates. That resulted in urchin-like GCN (GCN-UL), 3D ordered macroporous GCN (GCN-OM) and mesoporous GCN (GCN-MP). The introduction of silica templates during GCN synthesis produced physical defects on its surface, as confirmed by SEM analysis, increasing their specific surface area. A high amount of nitrogen vacancies is present in modified catalysts (revealed by XPS measurements), which can be related to an increase in the reactive sites available to catalyse redox reactions. The textural and morphological modifications induced in GCN an enhanced light absorption capacity and reduced electron/hole recombination rate, contributing to its improved photocatalytic performance. In the photocatalytic conversion of p-anisyl alcohol to p-anisaldehyde in deoxygenated aqueous solutions under UV-LED irradiation, the GCN-UL was the best photocatalyst reaching 60% yield at 64% conversion for p-anisaldehyde production after 240 min of reaction. Under oxygenated conditions (air), the process efficiency was increased to 79% yield at 92% conversion only after 90 min reaction. The GCN-based photocatalyst kept its performance when using visible-LED radiation under air atmosphere. Trapping of photogenerated holes and radicals by selective scavengers showed that under deoxygenated conditions, holes played the primary role in the p-anisaldehyde synthesis. Under oxygenated conditions, the process is governed by the effect of reactive oxygen species, namely superoxide radicals, with a significant contribution from holes.

Covalent organic framework photocatalysts: structures and applications

In the light of increasing energy demand and environmental pollution, it is urgently required to find a clean and renewable energy source. In these years, photocatalysis that uses solar energy for either fuel production, such as hydrogen evolution and hydrocarbon production, or environmental pollutant degradation, has shown great potential to achieve this goal. Among the various photocatalysts, covalent organic frameworks (COFs) are very attractive due to their excellent structural regularity, robust framework, inherent porosity and good activity. Thus, many studies have been carried out to investigate the photocatalytic performance of COFs and COF-based photocatalysts. In this critical review, the recent progress and advances of COF photocatalysts are thoroughly presented. Furthermore, diverse linkers between COF building blocks such as boron-containing connections and nitrogen-containing connections are summarised and compared. The morphologies of COFs and several commonly used strategies pertaining to photocatalytic activity are also discussed. Following this, the applications of COF-based photocatalysts are detailed including photocatalytic hydrogen evolution, CO₂ conversion and degradation of environmental contaminants. Finally, a summary and perspective on the opportunities and challenges for the future development of COF and COF-based photocatalysts are given.