Recently, under the circumstances of pandemic of COVID-19 much attention has been paid to titanium dioxide TiO2 as bactericidal agent; however, conventional TiO2 requires ultraviolet radiation or visible light to exercise its photocatalytic properties and its induced antimicrobial activity. In order to expand its applications directed at wide civil life, antibacterial TiO2 being usable under dark conditions has been demanded. The present paper describes the powder characterization of newly developed potassium K and phosphorous P co-doped nanometer-size anatase TiO2 powders using X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM & TEM), Brunauer-Emmett-Teller method (BET), fourier-transform infrared spectroscopy (FT-IR), X-ray absorption fine structure (XAFS), electron spin resonance (ESR) and chemiluminescence (CL). It was found for the first time that thus prepared anatase TiO2 could submit much reactive oxygen species (ROS) even in the dark, which has close relation with bactericidal activity in light interception.

The photocatalytic activities of reduced titanium dioxide (TiO2) materials have been investigated by measuring their ability to produce hydroxyl radicals under UV and visible light irradiation. Degussa P25 TiO2 was doped with nitrogen (N), fluorine (F), and/or phosphorus (P) and then subjected to surface modification employing a thermo-physicochemical process in the presence of reducing agent sodium borohydride (NaBH4). The reduced TiO2 materials were characterized by a number of X-ray, spectroscopic and imaging methods. Surface doping of TiO2 was employed to modulate the band gap energies into the visible wavelength region for better overlap with the solar spectrum. Hydroxyl radical generation, central to TiO2 photocatalytic water purification applications, was quantitated using coumarin as a trap under UV and visible light irradiation of the reduced TiO2 materials. At 350 nm irradiation, the yield of hydroxyl radicals generated by the reduced forms of TiO2 was nearly 90% of hydroxyl radicals generated by the Degussa P25 TiO2. Hydroxyl radical generation by these reduced forms of TiO2 was also observed under visible light irradiation (419 and 450 nm). These results demonstrated that simple surface modification of doped TiO2 can lead to visible light activity, which is important for more economical solar-driven applications of TiO2 photocatalysis.

Nitrogen-doped titanium dioxide (N-dopedTiO2) photocatalyst was synthesized from nanotube titanic acid (denoted as NTA; molecular formulaH2Ti2O5·H2O) precursorviaa hydrothermal route in ammonia solution. As-synthesized N-dopedTiO2catalysts were characterized by means of X-ray diffraction, transmission electron microscopy, diffuse reflectance spectrometry, X-ray photoelectron spectroscopy, electron spin resonance spectrometry and Fourier transform infrared spectrometry. It was found that nanotube ammonium titanate (NAT) was produced as an intermediate during the preparation of N-dopedTiO2from NTA, as evidenced by the N1sX-ray photoelectron spectroscopic peak ofNH4 +at 401.7 eV. The catalyst showed much higher activities to the degradation of methylene blue and p-chlorophenol under visible light irradiation than Degussa P25. This could be attributed to the enhanced absorption of N-dopedTiO2in visible light region associated with the formation of single-electron-trapped oxygen vacancies and the inhibition of recombination of photo-generated electron-hole pair by doped nitrogen.

OH radicals as reactive oxygen species in an organism were applied to assay antioxidant capacity since the obtained results present high biological relevance. As a proper photocatalyst, titanium dioxide was employed to generate OH radicals under ultraviolet light irradiation. However, ultraviolet light can damage molecular probe (DNA or protein) during the detection of antioxidant capacity, which interferes with the results. In this article, a novel composite graphene oxide-titanium dioxide (GO-TiO2) nanostructure was synthesized, which can generate numerous OH radicals just under visible light irradiation. In addition, a novel electrochemical antioxidant capacity sensor was designed with GO-TiO2 composites as source of OH radicals and DNA as a molecular probe. Antioxidants were measured by using the suppression of the decline of reduction current of methylene blue used as an intercalating agent for DNA after irradiation and ˙OH-mediated DNA damage. Using gallic acid (GA) as a mode antioxidant species, the detection of GA at levels as low as 0.85 mg L(-1) was possible. The antioxidant capacity of other antioxidants was also assayed. Finally, the novel sensor was applied to the determination of antioxidant capacity in tea.

This article provides an overview of current research into the development, synthesis, photocatalytic bacterial activity, biocompatibility and cytotoxic properties of various visible-light active titanium dioxide (TiO2) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO2 NPs are doped with metal and non-metal elements, modified with carbonaceous nanomaterials, and coupled with other metal oxide semiconductors. Transition metals introduce a localized d-electron state just below the conduction band of TiO2 NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO2 NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO2 NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO2 NPs with carbon nanotubes and graphene sheets also achieve the efficient creation of ROS under visible light irradiation. Furthermore, titanium-based alloy implants in orthopedics with enhanced antibacterial activity and biocompatibility can be achieved by forming a surface layer of Ag-doped titania nanotubes. By incorporating TiO2 NPs and Cu-doped TiO2 NPs into chitosan or the textile matrix, the resulting polymer nanocomposites exhibit excellent antimicrobial properties that can have applications as fruit/food wrapping films, self-cleaning fabrics, medical scaffolds and wound dressings. Considering the possible use of visible-light active TiO2 nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.

ObjectiveTo develop an aesthetic resin composite using a nitrogen-doped titanium dioxide (NTiO2) filler that possesses antimicrobial properties against cariogenic bacteria. MethodsN-TiO2 powder was manufactured by calcining commercial TiO2 with urea. Free radical release from the N-TiO2 powder under visible light irradiation was analysed using UV-Vis spectrophotometry. The N-TiO2 powder was incorporated into a dental resin and the photocatalytic activity assessed using a dye under both visible light and dark conditions. Using XTT assay to measure the cellular metabolic activity, the antibacterial properties of the N-TiO2 /resin composite discs were tested using Streptococcus mutans. ResultsDoping nitrogen of TiO2 resulted in a band gap shift towards the visible light spectrum, which enabled the powder to release reactive oxygen species when exposed to visible light. When incorporated into a dental resin, the N-TiO2/resin composite still demonstrated sustained release of reactive oxygen species, maintaining its photocatalytic activity and showing an antibacterial effect towards Streptococcus mutans under visible light conditions. SignificanceN-TiO2 filled resin composite shows great promise as a potential aesthetic resin based adhesive for orthodontic bonding.

Nanosized titanium dioxide (nano-TiO2) is widely used in the chemical, electrical, and electronic industries. Nanosized TiO2 has been reported to be an efficient photocatalyst, which is able to produce reactive oxygen species (ROS) under UVA irradiation. In the present work, we evaluate the effect of mitochondrial respiratory chain on the generation of ROS and cytotoxicity in keratinocyte (HaCaT) cells induced by nano-TiO2 under UVA irradiation. HaCaT cells were pretreated with different inhibitors of mitochondrial respiratory chain and followed by treatment with 200 µg/mL nano-TiO2, then exposed to UVA (365 nm) for 1 hour and cultured for 24 hours. Our results demonstrated that the complexes I and III of the mitochondrial respiratory chain are the major site in the ROS generation induced by nano-TiO2 Our results also demonstrated that the uncouplers of mitochondrial oxidative phosphorylation resulted in obvious changes in the production of intracellular ROS induced by nano-TiO2 The ROS sources of lipoxygenase, cyclooxygenase, and nicotinamide adenine dinucleotide phosphate oxidase had no significant effect on the ROS production. To some extent, nitric oxide synthase had effect on the ROS production. These results indicated that mitochondrial respiratory chain may be the main source of intracellular ROS production induced by nano-TiO2.

Titanium oxide sulfate, the raw material for one of the industrial preparation methods of titanium dioxide (TiO2), and urea as the nitrogen source were used to synthesize N-modified TiO2 materials (N-TiO2) with different chemical bonding of N elements by a relatively simple homogeneous co-precipitation method, providing a theoretical basis and experimental foundation for the industrial preparation of N-TiO2 photocatalytic materials. According to the analysis of its microscopic morphology, structural composition, and optoelectronic properties, the material consisted of porous spherical clusters formed by the aggregation of spherical nanoparticles. Nitrogen atoms were uniformly distributed on the surface of the material, causing a red shift in its optical response range and a reduction in the electron-hole recombination rate, which contributed to the photocatalytic performance of the material. The conducted photocatalytic degradation experiments of methyl orange and rhodamine B revealed that both dyes can be effectively degraded under visible-light conditions. Methyl orange interacted with the oxygen vacancies and Brønsted acid sites on the surface of the material, converting from an azo structure to a more degradable quinoid structure. In antibacterial experiments, N-TiO2 demonstrated excellent antibacterial properties, which led to a preliminary discussion of its antibacterial mechanism. According to electron paramagnetic resonance investigations and reactive oxygen species (ROS) scavenging experiments, the material can generate multiple ROS at the same time, among which·OH is the key active substance.

Previous reports of some studies have described that nitrogen (N)-doped titanium dioxide (TiO2 ) exhibits photocatalytic antibacterial activity under visible light irradiation and that reactive oxygen species (ROS) is involved in its activity. For prevention and treatment of peri-implantitis, an inflammatory lesion caused by the bacterial infection of plaque adhering to the circumference of an implant, we considered that applying N-doped TiO2 to dental implant surfaces can be effective. For this study, we aimed at evaluating visible light-induced antibacterial activity of titanium (Ti) treated with NaOH and hot water, and subsequently heated in an ammonia (NH3 ) gas atmosphere at 500°C for 3 hr to quantify the generated amount of ROS available for antibacterial activity. N-doped anatase-type titania (TiO2 -xNx) is formed on the Ti substrate surface. Under visible light, markedly more hydroxyl radicals were generated with a nitrogen-doped titanium dioxide plate than with a pure titanium plate. Hydrogen peroxide exhibited the same tendency. Furthermore, it showed visible light-induced antibacterial effects over Escherichia coli. Results demonstrate that N-doped TiO2 can be useful as a dental implant surface with low risk of postoperative infection when using visible light irradiation.

A carbon and nitrogen TiO2 (C/N-TiO2) photocatalyst has been obtained modifying a commercial TiO2 using ammonium citrate. The photocatalyst has been tested in two photocatalytic tests under visible light, NOx abatement in gas phase and phenol degradation in liquid phase monitoring in parallel the formation of reactive oxygen species (ROS) via EPR. We achieved a deep insight about its activity, which relies on superoxide and singlet oxygen (O2−• and 1O2) with no role of OH• radicals. The singlet oxygen (1O2) is exclusively a result of the excitation of the surface carbonaceous species and it is essential to oxidize phenol but limits the abatement of nitric oxide. The photocatalyst activity can be modulated according to its actual application tuning the carbon content. The oxidation of phenol in liquid environment is favoured by the presence of the carbonaceous phase while NO abatement is favoured by its partial removal.