Singlet Oxygen Photogeneration at Surface Modified Titanium Dioxide

Photogeneration of singlet oxygen catalyzed by hexafluoroisopropanol for selective degradation of dyes

Singlet oxygen (¹O₂) shows great potential for selective degradation of dyes in environmental remediation of wastewater. In this study, we showcased that ¹O₂ can be effectively generated from an anion complex composed of deprotonated hexafluoroisopropanol anion ([HFIP_-H]^‒) with hydroperoxyl radical (⋅HO₂) via ultraviolet (UV) photodetachment. Electronic structure calculations and cryogenic negative ion photoelectron spectroscopy unveil critical proton transfer upon complex formation and electron ejection, effectively photoconverting prevalent triplet ground state ³O₂ to long-lived excited ¹O₂, stabilized by nearby HFIP. Inspired by this spectroscopic study, a novel "photogeneration" strategy is proposed to produce ¹O₂ with the incorporation of atmospheric O₂ and HFIP, acting as a catalyst. Conceptually, the designed catalytic cycle upon UV irradiation and electron injection is able to achieve different degradations of dye molecules in a controllable fashion from decolorization to complete mineralization, shedding new light on potential water purification.

Differentiation of Superoxide Radical Anion and Singlet Oxygen and Their Concurrent Quantifications by Nuclear Magnetic Resonance

While there have been various techniques, assays, and commercial kits developed to measure reactive oxygen species (ROS) with varying degrees of success, there is a lack of innovative methods to differentiate and quantify them simultaneously. In this work, we demonstrate a ¹⁹F nuclear magnetic resonance (NMR)-based method to differentiate two important types of ROS, superoxide radical anion and singlet oxygen, and to quantify them concurrently. By taking advantage of the unique chemical reactivity of two fluorine-containing molecules, 4-fluoro-3-methylphenyl boronic acid and 4-fluoro-3-methylphenol, serving as ¹⁹F NMR probes, we are able to differentiate and quantify, for the first time, superoxide radical anion and singlet oxygen generated by photosensitizers (PSs) concurrently. The results reveal that relative amounts of superoxide radical anion and singlet oxygen generated by a PS under light illumination are oftentimes sensitive to the environment, such as the presence or absence of electron donors. This method provides a means to identify the type of mechanism by which a PS functions under a given condition. We envision that this relatively simple, yet robust, method would be beneficial to a broad range of ROS-pertinent studies, such as photodynamic therapy and photoredox reactions.

Precisely Tailoring Heterometallic Polyoxotitanium Clusters for the Efficient and Selective Photocatalytic Oxidation of Hydrocarbons

Photocatalysis is a promising yet challenging approach for the selective oxidation of hydrocarbons to valuable oxygenated chemicals with O₂ under mild conditions. In this work, we report an atomically precise material model to address this challenge. The key to our solution is the rational incorporation of Fe species into polyoxotitanium cluster to form a heterometallic Ti₄ Fe₁ cocrystal. This newly designed cocrystal cluster, which well governs the energy and charge transfer as evidenced by spectroscopic characterizations and theoretical calculations, enables the synergistic process involving C(sp³ )-H bond activation by photogenerated holes and further reactions by singlet oxygen (¹ O₂ ). Remarkably, the cocrystal Ti₄ Fe₁ cluster achieves efficient and selective oxidation of hydrocarbons (C₅ to C₁₆ ) into aldehydes and ketones with a conversion rate up to 12 860 μmol g^-1  h^-1 , 5 times higher than that of Fe-doped Ti₃ Fe₁ cluster. This work provides insights into photocatalyst design at atomic level enabling synergistic catalysis.

Facet synergy dominant Z-scheme transition in BiOCl with enhanced 1O2 generation

BiOCl powders with different morphology were obtained through self-assembling. Their photocatalytic performance was tested through degradation of organic dye and mechanism of photocatalytic for obtained samples were investigated. Relevant characterization demonstrated that facet synergy was a main reason of photocatalytic performance promotion due to changed facet exposure and proportion under self-assembling. Theory and experimental analysis manifested that synergistic facet stimulated Z scheme transition in samples with lower (001) facet proportion, which provided favorable condition of ¹O₂ generation and simultaneously generated prominent charge separation. This work unveiled the facet synergy dominant photocatalytic performance improvement in self-assembling system of BiOCl and verified decisive role of facet proportion in constructing Z-scheme facet junction, which also prompted possibility of improving ¹O₂ generation through facet engineering under self-assembling.

Green synthesis of zinc oxide nanoparticles toward highly efficient photocatalysis and antibacterial application

Zinc oxide nanoparticles (ZnO NPs) were successfully synthesized by a green method using rosin and zinc chloride as salt precursors. The phase structure, morphology, and particle size of ZnO were determined by X-ray powder diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The fabricated ZnO NP samples are crystalline with a grain size of 30-100 nm. The ZnO NPs were used as catalysts for the photodegradation of methylene blue (MB) and methyl orange (MO) under visible and UV light. The results indicate that the prepared ZnO material excellently removed MB and MO (c _initial = 10 mg/L) with efficiencies of 100% and 82.78%, respectively, after 210 min under UV radiation with a ZnO NP dose of 2 g/L. The photocatalyst activity of the synthesized material was also tested under visible light radiation with the same conditions; however, it achieved lower efficiencies. In addition, ZnO NPs were also tested regarding their antibacterial activity, and the results showed that the prepared ZnO samples had the highest (i.e., 100%) antibacterial efficiency against E. coli.

Photochemical transformation of hexachlorobenzene (HCB) in solid-water system: Kinetics, mechanism and toxicity evaluation

As one of the first batch of persistent organic pollutants (POPs) included in Stockholm Convention, hexachlorobenzene (HCB) has attracted great attention because of its wide occurrence and great environmental risks. Considering the easy adsorption of HCB on solids and the complexity of natural particles, we systematically investigated the photodegradation of HCB on the surface of silica gel (SG) in aqueous solution in this work to reveal its fate in natural waters. Under mercury lamp irradiation, more than 90% of HCB loaded on SG could be removed after 240 min. Moreover, the effects of solution pH and water constituents were examined, and results showed that the presence of NO₂^-, NO₃^-, Fe³⁺ and humic acid (HA) significantly inhibited the reaction due to the scavenging of ROS and/or competitive absorption of light. According to radical quenching experiments and electron paramagnetic resonance (EPR) spectra, hydroxyl radicals and singlet oxygen generated on the surface of SG could participate in the transformation of HCB, but •OH played a dominant role. Based on products identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS), two main pathways were proposed for the removal of HCB, including dechlorination and hydroxylation which represent direct and indirect photodegradation, respectively, and the occurrence of these two reactions was further supported by density functional theory (DFT) calculations. From the quantitative analysis of penta-chlorobenzene, it was estimated that dechlorination and hydroxylation contributed to approximately 44.4% and 55.6% of initial HCB degradation, respectively. Furthermore, toxicity predictions by the ecological structure-activity relationship model (ECOSAR) suggested that the toxicity of HCB was decreased in the photodegradation process. This study would provide important information for understanding the photochemical transformation mechanism of HCB at the solid/water interface.

Photocatalytic Selective Degradation of Catechol and Resorcinol on the TiO2 with Exposed {001} Facets: Roles of Two Types of Hydroxyl Radicals

Photocatalytic studies on contaminant degradation in water suspension generally suggest that the degradation reaction mainly takes place on the surface of the photocatalysts rather than in the water phase. The mechanism of selective degradation is often difficult to distinguish concerning the contribution of adsorption and radical selectivity. This study is thus designed to investigate the roles of two types of hydroxyl radicals, adsorbed hydroxyl radical (·OHa) and free hydroxyl radical (·OHf), on the selective degradation of catechol (CT) and resorcinol (RE). CT and RE are significantly different in adsorption on a TiO2 photocatalyst with a highly exposed {001} facet. CT can be selectively degraded by TiO2 and was highly correlated with adsorption. Free radical quenching experiment results showed that the degradation of CT can be identified as the combined effect of both ·OHa and ·OHf, while the degradation of RE was mainly due to the ·OHf. Electron paramagnetic resonance coupled with spin trapping agents was used to detect the relative concentration of hydroxyl radicals in all the photocatalytic degradation processes. After a series analysis, we proposed that the mechanism of selective degradation mainly depends on the concentration of ·OHf for the pollutant molecules with weak adsorption on the catalyst surface.

DNA dyes: toxicity, remediation strategies and alternatives

Release of untreated effluent from processing or manufacturing industries and other commercial premises into water bodies is a major threat to environment and human health. In this regard, the effluent generated from laboratories and other research facilities is of great concern. Among other harmful chemicals, the effluent is rich in toxic organic dyes, which get exposed to the environment and pose serious health risk. The dyes used in nucleic acid analysis specially the DNA dyes are known for their teratogenicity and mutagenic potential, which mainly depends upon the organism and circumstances under which it is exposed. Among animals and humans, exposure to theses dyes may lead to irritation in mouth, eyes and respiratory tract and many other possible effects which are yet to be explored. To overcome these problems, dyes present in the effluents from laboratories must be degraded to non-toxic forms. Various strategies have been proposed and investigated for degradation and remediation of contaminated laboratory effluent. As a modern and cost-effective technique, biodegradation using microbes and plants is potentially eco-friendly and sustainable technique for detoxifying these dyes. In this article, we have discussed and reviewed the structure, properties and toxicity profile of prominent nucleic acid dyes, along with the strategies of remediation of laboratory effluents contaminated with these dyes. In addition, we have also discussed the feasibility and limitations of these remediation strategies and identified research gaps that can help researchers to explore more effective solutions to manage this area of great concern. We have also reviewed various less toxic alternatives of these common as safer options of these dyes.

F- Serve as Surface Trapping Sites to Promote the Charge Separation and Transfer of TiO2

Finding an effective strategy to promote the charge transfer and separation of TiO₂ is urgently needed. Herein, a surface fluorination (F^-)-modified TiO₂ (denoted as TO-xF, where x represents the volume of HF added in the solution) catalyst has been prepared by a mild and facile post-treatment method. The changes induced by surface F^- on the morphological, structural, and surface electronic features and the charge separation and transfer efficiency of TiO₂ were specifically examined. Compared with pristine TO, TO-0.4F exhibits enhanced photocatalytic degradation of methyl orange and phenol, production of hydroxyl radicals, and photocurrent response. The enhanced photocatalytic activities of TO-0.4F can be attributed to the role of surface F^- as surface trapping sites in effectively boosting the charge transfer and separation processes, which is verified by the steady-state and time-resolved fluorescence spectroscopy, electrochemical impedance spectroscopy, Bode plot, transient photocurrent response, and open-circuit voltage measurements. This study emphasizes the role of surface F^- in promoting the charge transfer and separation and improving the photocatalytic activity of TiO₂.

Photocatalytic Activity of TiO2-Doped Fe, Ag, and Ni with N under Visible Light Irradiation

Doping with noble metal ions or doping with nitrogen has been attempted to prepare TiO2 that reacts even in visible light. In this study, TiO2 was doped with nitrogen and various metal ions instead of noble metals. The TiO2 photocatalysts doped with metal ions (Fe, Ag, Ni) and nitrogen were prepared by a sol-gel method. Their physicochemical properties were characterized and their photocatalytic activities were investigated under visible light irradiation. In TiO2 doped with metal ions and nitrogen, the light absorption region was extended to visible light. The photoluminescence intensity was much greater in N/Ni/TiO2 than in N/Ag/TiO2 and N/Fe/TiO2. The photolysis activities of N/Ni/TiO2 were the highest in formaldehyde decomposition and methylene blue decomposition. The sterilization efficiency of N/Ni/TiO2 was the highest in the evaluation test for the inhibition of the proliferation of Pseudomonas aeruginosa. The bandgap of N/Ni/TiO2 was 2.4 eV, which was significantly lower than that of anatase TiO2 (3.2 eV). The N/Ni/TiO2 had a much higher optical intensity than other metal ion-doped TiO2, so it was highly active under visible light irradiation.

Wavelength Dependence of the Transformation Mechanism of Sulfonamides Using Different LED Light Sources and TiO2 and ZnO Photocatalysts

The comparison of the efficiency of the commercially available photocatalysts, TiO2 and ZnO, irradiated with 365 nm and 398 nm light, is presented for the removal of two antibiotics, sulfamethazine (SMT) and sulfamethoxypyridazine (SMP). The •OH formation rate was compared using coumarin, and higher efficiency was proved for TiO2 than ZnO, while for 1,4-benzoquinone in O2-free suspensions, the higher contribution of the photogenerated electrons to the conversion was observed for ZnO than TiO2, especially at 398 nm irradiation. An extremely fast transformation and high quantum yield of SMP in the TiO2/LED398nm process were observed. The transformation was fast in both O2 containing and O2-free suspensions and takes place via desulfonation, while in other cases, mainly hydroxylated products form. The effect of reaction parameters (methanol, dissolved O2 content, HCO3- and Cl-) confirmed that a quite rarely observed energy transfer between the excited state P25 and SMP might be responsible for this unique behavior. In our opinion, these results highlight that "non-conventional" mechanisms could occur even in the case of the well-known TiO2 photocatalyst, and the effect of wavelength is also worth investigating.

Electron and Energy Transfer Mechanisms: The Double Nature of TiO2 Heterogeneous Photocatalysis

Photocatalytic chemical transformations in the presence of irradiated TiO₂ are generally considered in terms of interfacial electron transfer. However, more elusive energy-transfer-driven reactions have been also hypothesized to occur, mainly on the basis of the indirect evidence of detected reaction products whose existence could not be justified simply by electron transfer. Unlike in homogeneous and colloidal systems, where energy transfer mechanisms have been investigated deeply for several organic syntheses, understanding of similar processes in heterogeneous systems is at only a nascent level. However, this gap of knowledge can be filled by considering the important achievements of synthetic heterogeneous photocatalysis, which bring the field closer to industrial exploitation. The present manuscript summarizes the main findings of previous literature reports and, also on the basis of some novel experimental evidences, tentatively proposes that the energy transfer in TiO₂ photocatalysis could possess a Förster-like nature.

Progress on photocatalytic semiconductor hybrids for bacterial inactivation

Due to its use of green and renewable energy and negligible bacterial resistance, photocatalytic bacterial inactivation is to be considered a promising sterilization process. Herein, we explore the relevant mechanisms of the photoinduced process on the active sites of semiconductors with an emphasis on the active sites of semiconductors, the photoexcited electron transfer, ROS-induced toxicity and interactions between semiconductors and bacteria. Pristine semiconductors such as metal oxides (TiO₂ and ZnO) have been widely reported; however, they suffer some drawbacks such as narrow optical response and high photogenerated carrier recombination. Herein, some typical modification strategies will be discussed including noble metal doping, ion doping, hybrid heterojunctions and dye sensitization. Besides, the biosafety and biocompatibility issues of semiconductor materials are also considered for the evaluation of their potential for further biomedical applications. Furthermore, 2D materials have become promising candidates in recent years due to their wide optical response to NIR light, superior antibacterial activity and favorable biocompatibility. Besides, the current research limitations and challenges are illustrated to introduce the appealing directions and design considerations for the future development of photocatalytic semiconductors for antibacterial applications.

Rational design of type I photosensitizers based on Ru(ii) complexes for effective photodynamic therapy under hypoxia

Photodynamic therapy (PDT) has been widely used in conjunction with molecular oxygen to cause cancer cell death. Hypoxia, the inherent property in solid tumors, is the obstacle during the process of PDT. It is urgent to develop PDT photosensitizers independent of the oxygen concentration. Herein, triphenylamine-modified Ru(ii) complexes have been used as photosensitizers to produce superoxide anions (O2-˙) and hydroxyl radicals (˙OH) through a type I photochemical process. Ru(ii) complexes with triphenylamine can provide a possibility to drive the reactive oxygen species production through low oxidation potential and good light-harvesting abilities. The investigation on light-mediated radical production showed that Ru4 could produce abundant ˙OH and O2-˙ compared to Ru1-Ru3 under hypoxic environments owing to the strong absorption. These radicals exhibit potent toxicity, which can damage the neighbouring biomolecules and cause the apoptosis of cancer cells. The PDT effect was evaluated in vitro under hypoxia, suggesting that Ru4 could maintain excellent performance in inducing a sharp decrease in the activity of cancer cells.

Coupling Strategy for CO2 Valorization Integrated with Organic Synthesis by Heterogeneous Photocatalysis

Photocatalytic reduction of CO₂ to solar fuels and/or fine chemicals is a promising way to increase the energy supply and reduce greenhouse gas emissions. However, the conventional reaction system for CO₂ photoreduction with pure H₂ O or sacrificial agents usually suffers from low catalytic efficiency, poor stability, or cost-ineffective atom economy. A recent surge of developments, in which photocatalytic CO₂ valorization is integrated with selective organic synthesis into one reaction system, indicates an efficient modus operandi that enables sufficient utilization of photogenerated electrons and holes to achieve the goals for sustainable economic and social development. In this Review we discuss current advances in cooperative photoredox reaction systems that integrate CO₂ valorization with organics upgrading based on heterogeneous photocatalysis. The applications and virtues of this strategy and the underlying reaction mechanisms are discussed. The ongoing challenges and prospects in this area are critically discussed.

Supramolecular agents for combination of photodynamic therapy and other treatments

Photodynamic therapy (PDT) is a promising treatment for cancers such as superficial skin cancers, esophageal cancer, and cervical cancer. Unfortunately, PDT often does not have sufficient therapeutic benefits due to its intrinsic oxygen dependence and the limited permeability of irradiating light. Side effects from "always on" photosensitizers (PSs) can be problematic, and PDT cannot treat tumor metastases or recurrences. In recent years, supramolecular approaches using non-covalent interactions have attracted attention due to their potential in PS development. A supramolecular PS assembly could be built to maximize photodynamic effects and minimize side effects. A combination of two or more therapies can effectively address shortcomings while maximizing the benefits of each treatment regimen. Using the supramolecular assembly, it is possible to design a multifunctional supramolecular PS to exert synergistic effects by combining PDT with other treatment methods. This review provides a summary of important research progress on supramolecular systems that can be used to combine PDT with photothermal therapy, chemotherapy, and immunotherapy to compensate for the shortcomings of PDT, and it provides an overview of the prospects for future cancer treatment advances and clinical applications.

Environmental risk of nanomaterials and nanoparticles and EPR technique as an effective tool to study them-a review

Nanotechnologies and different types of nanomaterials belong in present day to intensively studied materials due to their unique properties and diverse potential applications in, e.g., electronics, medicine, or display technologies. Together with the investigation of their desired beneficial properties, a need to investigate and evaluate their influence on the environment and possible harmful effects towards living organisms is growing. This review summarizes possible toxic effects of nanomaterials on environment and living organisms, focusing on the possible bioaccumulation in organisms, toxicity, and its mechanisms. The main goal of this review is to refer to potential environmental risks rising from the use of nanomaterials and the necessity to deal with the possible toxic effects considering the growing interest in the wide-scale utilization of these materials. Electron paramagnetic resonance spectroscopy as the only analytical technique capable of detecting radical species enables detection, quantification, and monitoring of the generation of short-lived radicals often coupled with toxic effects of nanomaterials, which makes it an important method in the process of nanotoxicity mechanism determination.

Pickering Emulsions of Fluorinated TiO2: A New Route for Intensification of Photocatalytic Degradation of Nitrobenzene

Fluorination of the TiO₂ surface has been often reported as a tool to increase the photocatalytic efficiency due to the beneficial effects in terms of production of oxidizing radicals. Moreover, it is shown that the unique amphiphilic properties of the fluorinated TiO₂ (TiO₂-F) surface allow one to use this material as a stabilizer for the formulation of Pickering emulsions of poorly soluble pollutants such as nitrobenzene (NB) in water. The emulsions have been characterized in terms of size of the droplets, type of emulsion, possibility of phase inversion, contact angle measurements, and optical microscopy. The emulsified system presents micrometer-sized droplets of pollutant surrounded by the TiO₂-F photocatalyst. Consequently, the system can be considered to be composed of microreactors for the degradation of the pollutant, which maximize the contact area between the photocatalyst and substrate. The enhanced photocatalytic activity of TiO₂-F was confirmed in the present paper as the apparent rate constants of NB photodegradation were 16 × 10^-3 and 12 × 10^-3 min^-1 for fluorinated and bare TiO₂, respectively. At NB concentrations largely exceeding its solubility, the rate constant was 0.04 × 10^-3 min^-1 in the presence of both TiO₂ and TiO₂-F. However, unlike TiO₂, TiO₂-F stabilized NB/water emulsions and, under these conditions, the efficiency of NB photocatalytic degradation in the emulsified system was ca. 18 times higher than in the nonemulsified one. This result is relevant also in terms of practical applications because it opens the route to one-pot treatments of biphasic polluted streams without the need of preliminary physical separation treatments.

"Tailoring the TiO2 phases through microwave-assisted hydrothermal synthesis: Comparative assessment of bactericidal activity"

Nanocrystalline titania (TiO₂) is one of the most investigated crystalline nanostructured systems in the field of materials science. The technological applications of this material are related to its optoelectronic and photocatalytic properties, which in turn are strongly dependent on the crystal phase (i.e., anatase, brookite, and rutile), particle size, and surface structure. However, systematic comparative studies of all its crystal phases are scarce in literature due to difficulties in providing a controlled synthesis, which is primarily important in obtaining the brookite phase. In this report, the synthesis of TiO₂ nanoparticles in the anatase, brookite, and rutile structures was explored, using amorphous TiO₂ as a common precursor under microwave-assisted hydrothermal conditions. The influence of parameters such as temperature, acidity, and precursor concentration on phase crystallization were investigated. The TiO₂ materials (amorphous and crystalline phases as well as commercial Degussa P25) were systematically characterized using Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-visible reflectance spectroscopy, and dynamic and electrophoretic light scattering. The bactericidal activity and photocatalytic antibacterial effectiveness of each material were evaluated through the determination of the minimum inhibitory and bactericidal concentrations, and via the mortality kinetic method under ultraviolet (UV) illumination under similar conditions with two bacterial groups of unique cellular structures: Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). The results are discussed with particular emphasis on the relationship between the synthesis parameters (acidity, precursor concentration, temperature and reaction time) and the bactericidal properties.

The comparative study of two kinds of β-Bi2O3/TiO2 binary composite and their removal of 17ɑ-ethynylestradiol

In this work, we used TiO₂ nanobelts and P25 particles as titanium sources to combine with β-Bi₂O₃ to form β-Bi₂O₃/TiO₂ and β-Bi₂O₃/P25 composites. The prepared samples were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and UV-vis absorbance spectroscopy and fluorescence spectroscopy. The structure and performance of two composites were comparatively investigated, and the β-Bi₂O₃ molar ratios in them were optimized and their roles in them were studied. The results showed that the TiO₂ nanobelts and commercial TiO₂ (P25) particles combined with β-Bi₂O₃ nanosheets. The optimal molar ratios of Bi to Ti element in two kinds of composites are 1:1. The β-Bi₂O₃ in P25/β-Bi₂O₃ makes more contribution to the improvement of photocatalytic activity of them than that in β-Bi₂O₃/TiO₂ because P25 particles are distributed on β-Bi₂O₃ nanosheet more uniformly. The photocatalytic activities of β-Bi₂O₃/TiO₂ (0.02275 min^-1) and β-Bi₂O₃/P25 (0.02382 min^-1) are 3.72 times and 3.90 times than that of pure β-Bi₂O₃ (0.0061 min^-1) for EE2 removal. The enhanced photocatalytic activities of two kinds of composites are ascribed to photo-induced interfacial charge transfer on the heterojunction between β-Bi₂O₃ and TiO₂ or P25. From the economic view, β-Bi₂O₃/P25 composites are better than β-Bi₂O₃/TiO₂ because TiO₂ nanobelts in the β-Bi₂O₃/TiO₂ composite are obtained from P25 via extra hydrothermal treatment in strong alkaline environment. The free radical capture experiment indicated that the dominant reactive species are h⁺ and •O^-₂ for EE2 removal by TiO₂/β-Bi₂O₃ and P25/β-Bi₂O₃ composites.

Reactive Oxygen Species and Catalytic Active Sites in Heterogeneous Catalytic Ozonation for Water Purification

Heterogeneous catalytic ozonation (HCO) processes have been widely studied for water purification. The reaction mechanisms of these processes are very complicated because of the simultaneous involvement of gas, solid, and liquid phases. Although typical reaction mechanisms have been established for HCO, some of them are only appropriate for specific systems. The divergence and deficiency in mechanisms hinders the development of novel active catalysts. This critical review compares the various existing mechanisms and categorizes the catalytic oxidation of HCO into radical-based oxidation and nonradical oxidation processes with an in-depth discussion. The catalytic active sites and adsorption behaviors of O₃ molecules on the catalyst surface are regarded as the key clues for further elucidating the O₃ activation processes, evolution of reactive oxygen species (ROS) or organic oxidation pathways. Moreover, the detection methods of the ROS produced in both types of oxidations and their roles in the destruction of organics are reviewed with discussion of some specific problems among them, including the scavengers selection, experiment results analysis as well as some questionable conclusions. Finally, alternative strategies for the systematic investigation of the HCO mechanism and the prospects for future studies are envisaged.

Development and Study of Biocompatible Polyurethane-Based Polymer-Metallic Nanocomposites

INTRODUCTION

In this work we selected components, developed technology and studied a number of parameters of polymer nanocomposite materials, remembering that the material would have high optical and good mechanical characteristics, good sorption ability in order to ensure high value of the optical signal for a short time while maintaining the initial geometric shape. In addition, if this nanocomposite is used for medicine and biology (biocompatible or biocidal materials or the creation of a sensor based on it), the material must be non-toxic and/or biocompatible. We study the creation of polymer nanocomposites which may be applied as biocompatible materials with new functional parameters.

MATERIAL AND METHODS

A number of polymer nanocomposites based on various urethane-acrylate monomers and nanoparticles of gold, silicon oxides, zinc and/or titanium oxides are obtained, their mechanical (microhardness) properties and wettability (contact angle) are studied. The set of required, biology-related properties of these materials, such as toxicity and sorption of microorganisms are also investigated in order to prove their possible applicability.

RESULTS AND DISCUSSION

The composition of the samples influences their microhardness and the value of contact angle, which means that varying with the monomer and the metallic, oxide nanoparticles composition, we could change these parameters. Besides it, the set of required, biology-related properties of these materials, such as toxicity and sorption of microorganisms were also investigated in order to prove their possible applicability. It was shown that the materials are non-toxic, the adhesion of microorganisms on their surface also could be varied by changing their composition.

CONCLUSION

The presented polymer nanocomposites with different compositions of monomer and the presence of nanoparticles in them are prospective material for a possible bio-application as it is biocompatible, not toxic. The sorption of microorganism could be varied depending on the type of bacterias, the monomer composition, and nanoparticles.

Super porous TiO2 photocatalyst: Tailoring the agglomerate porosity into robust structural mesoporosity with enhanced surface area for efficient remediation of azo dye polluted waste water

The low surface area of TiO₂ (50 m²g^-1 - Degussa P25) due to randomly oriented, agglomerated nanostructures and charge carrier recombination tendency, has till date been its major limitation for photocatalytic remediation of polluted wastewater. This study presents an innovative process to design super porous TiO₂ nanostructures with high effective surface area (238 m²g^-1), robust, structurally ordered mesoporosity via a simple sol-gel assisted reflux method. Detailed material characterization studies suggest that the higher degree of intermolecular ligation in novel templates such as butanetetracarboxylic or tricarballylic acid modified titanium hydroxide gels resulted in retainment of the porous structure during the urea assisted combustion synthesis. The induction of robust structural porosity is accompanied by a reduction in pore size distribution, an increase in pore volume leading to significantly higher total surface area of the synthesized TiO_2. Detailed investigation of dye adsorption kinetics and photocatalytic degradation kinetics, complemented by kinetic modeling analysis confirmed that the super porous TiO₂ with robust mesoporous structure outperforms the rest of synthesized TiO₂ catalyst (having only agglomerate porosity) in terms of its superior adsorption capacity, faster diffusion kinetics and photocatalytic activity for degradation of Amaranth dye. Thus, the super porous TiO₂ shows promising potential for application in sustainable photocatalytic technology for remediation of wastewater contaminated with azo dyes.

Exploration of TiO2 nanoparticle mediated microdynamic therapy on cancer treatment

Radical therapy takes advantage of the reactive oxygen species produced in greater quantities within tumor cells than in normal cells. Here, for the first time, we explore a TiO₂ nanoparticle mediated microwave induced radical therapy (termed as Microdynamic Therapy) as a new cancer treatment method. The experiments in vitro and in vivo demonstrate that colloidal TiO₂ nanoparticles could significantly suppress the growth of osteosarcomas, even under low power (5 W) microwave (MW) irradiation for 5 min. The high photocatalytic activity of TiO₂ nanoparticles efficiently utilizes the microwave-induced plasmonic effect for the formation of reactive oxygen species (ROS). Furthermore, TiO₂ nanoparticles exhibit a higher cytotoxicity on cancer cells (osteosarcoma UMR-106 cells) than on normal cells (mouse fibroblast L929 cells). The effectiveness of TiO₂ nanoparticles for microwave induced radical therapy demonstrates that this is a new landmark approach to treating cancers.

Influence of Surface-Related Phenomena on Mechanism, Selectivity, and Conversion of TiO2 -Induced Photocatalytic Reactions

Heterogeneous photocatalysis is the result of an inextricable connection of several factors differently contributing to the overall process. Photon absorption is the "sine qua non" condition for the reaction to occur. In fact, photons can be considered as immaterial reactants, and all of the phenomena related to the interaction of light-matter play a prominent role. However, other factors contribute in a concerted way to address the reaction, so that the relative contribution of each of them is often difficult to evaluate. In this framework, the present paper highlights some aspects of the interaction of TiO₂ surface-adsorbate species that could be underestimated and their influence on the conversion, selectivity, and mechanisms of photocatalytic reactions. To this aim, some paradigmatic examples on the adsorption of water and organics on TiO₂ are reported.

Application of metal oxide semiconductors in light-driven organic transformations

Herein, we provide an up-to-date overview of metal oxide semiconductors (MOS) as versatile and inexpensive photocatalysts to enable light-driven organic transformations.

Enhanced removal of arsenite and arsenate by a multifunctional Fe-Ti-Mn composite oxide: Photooxidation, oxidation and adsorption

In order to attain a high-efficiency and low-cost adsorbent for both arsenate (As(V)) and arsenite (As(III)) removal from As-contaminated water, a novel nanostructured Fe-Ti-Mn composite oxide (FTMO) was fabricated through a one-step simultaneous oxidation and co-precipitation method. Batch control experiments and series of spectroscopy detection technologies were carried out to investigate the surface change of the FTMO adsorbent and the respective role of Fe, Ti and Mn content in the arsenic adsorption process. The results showed that the FTMO adsorbent had a high adsorption capacity for both As(V) and As(III) (especially for the latter one) via the formation of inner-sphere complexes at the water/oxide interface under both darkness and light conditions. The material could effectively oxidize As(III) to As(V) and light illumination could further apparently enhance the As(III) oxidation, thus achieving high adsorption efficiency of As(III). Combined with the characterizations from FTIR, ESR and XPS, it was assumed that the predominant As(III) removal mechanism could be attributed to the coupling of various processes including photooxidation, oxidation and adsorption. The Ti and Mn contents were dominant for the As(III) oxidation, while the Fe content mainly played an important role for the adsorption of newly formed As(V). However, the involvement of surface hydroxyl groups and the formation of inner-sphere surface complexes were primarily responsible for the As(V) adsorption mechanism. Moreover, the successful removal of arsenic from real water matrices made the FTMO a potentially attractive adsorbent for both As(V) and As(III) removal.

Nanotechnology-based photoimmunological therapies for cancer

Phototherapy is a non-invasive or minimally invasive therapeutic strategy. Immunotherapy uses different immunological approaches, such as antibodies, vaccines, immunoadjuvants, and cytokines to stimulate the host immune system to fight against diseases. In cancer treatment, phototherapy not only destroys tumor cells, but also induces immunogenic tumor cell death to initiate a systemic anti-tumor immune response. When combined with immunotherapy, the effectiveness of phototherapy can be enhanced. Because of their special physical, chemical, and sometimes immunological properties, nanomaterials have also been used to enhance phototherapy. In this article, we review the recent progress in nanotechnology-based phototherapy, including nano-photothermal therapy, nano-photochemical therapy, and nano-photoimmunological therapy in cancer treatment. Specifically, we focus on the immunological responses induced by nano-phototherapies.

The Ability of Functionalized Fullerenes and Surface-Modified TiO2 Nanoparticles to Photosensitize Peroxidation of Lipids in Selected Model Systems

Photochemical properties of a new class of inorganic nanoparticles, namely a cationic C₆₀ fullerene substituted with three quaternary pyrrolidinium groups (BB6) and a surface-modified nanocrystalline TiO₂ with bromopyrogallol red (Brp@TiO₂ ) were examined for their effectiveness in photogenerating singlet oxygen and free radicals. In particular, their ability to photosensitize peroxidation of unsaturated lipids was analyzed in POPC:cholesterol liposomes and B16 mouse melanoma cells employing a range of spectroscopic and analytical methods. Because melanoma cells typically are pigmented, we examined the effect of melanin on the photosensitized peroxidation of lipids in liposomes and B16 melanoma cells, mediated by BB6 and Brp@TiO₂ nanoparticles. The obtained results suggest that peroxidation of unsaturated lipids, photosensitized by BB6 occurs mainly, although not exclusively, via Type II mechanism involving singlet oxygen. On the other hand, if surface-modified TiO₂ is used as a photosensitizer, Type I mechanism of lipid peroxidation dominates, as indicated by the predominant formation of the free radical-dependent cholesterol oxidation products. The protective effect of melanin was particularly evident when BB6 was used as a photosensitizer, suggesting that melanin could efficiently interfere with Type II processes.

Generation of hydroxyl radicals and singlet oxygen by particulate matter and its inorganic components

Particulate matter (PM) can strongly affect redox biochemistry and therefore induce the response of the immune system and aggravate the course of autoimmune diseases. Nanoparticles containing transition metal compounds possessing semiconductor properties (TiO₂, ZnO) may act as photocatalysts and accelerate the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). In this study, the NIST standard reference material, SRM 1648a, has been analyzed in terms of this consideration. Organic compounds present in SRM 1648a were removed by cold oxygen plasma treatment. Samples of SRM 1648a with removed organic content (<2% of organic carbon, <1% of nitrogen) were obtained within 2 h of this treatment. The treatment did not affect the morphology of the powder. The reference material and PM2.5 collected in Kraków are composed of smaller particles and nanoparticles forming aggregates. The efficiency of (photo)generation of hydroxyl radicals and singlet oxygen was compared for original and organics-free samples. The analyzed samples showed the highest activity towards ROS generation when exposed to UV-vis-NIR light, moderate under UV irradiation, and the lowest in dark. Data collected in the present study suggest that the organic fraction is mostly responsible for singlet oxygen generation, as almost twice higher efficiency of ¹O₂ generation was observed for the original NIST sample compared to the material without the organic fraction. However, particulate matter collected in Kraków was found to have a five times higher activity in singlet oxygen generation (compared for original NIST and Kraków dust samples).

Photocatalytic partial oxidation of limonene to 1,2 limonene oxide

The silylation of crystalline TiO₂ P25, commonly used for photocatalytic degradation of pollutants, results in an exceptionally selective catalyst for the aerobic limonene epoxidation to 1,2-limonene oxide under solar light irradiation. The hypothesized mechanism involves the singlet oxygen generated through energy transfer from the excited TiO₂ to adsorbed O₂ molecules. The reaction product is the valued precursor of bio-based poly(limonene carbonate), a thermoplastic polymer of superior thermal and optical properties whose industrial production is in need of an efficient green synthesis of limonene oxide.