Inactivation of SARS-CoV-2 and photocatalytic degradation by TiO2 photocatalyst coatings

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causative agent of the COVID-19, which is a global pandemic, has infected more than 552 million people, and killed more than 6.3 million people. SARS-CoV-2 can be transmitted through airborne route in addition to direct contact and droplet modes, the development of disinfectants that can be applied in working spaces without evacuating people is urgently needed. TiO₂ is well known with some features of the purification, antibacterial/sterilization, making it could be developed disinfectants that can be applied in working spaces without evacuating people. Facing the severe epidemic, we expect to fully expand the application of our proposed effective approach of mechanical coating technique (MCT), which can be prepared on a large-scale fabrication of an easy-to-use TiO₂/Ti photocatalyst coating, with hope to curb the epidemic. The photocatalytic inactivation of SARS-CoV-2 and influenza virus, and the photocatalytic degradation of acetaldehyde (C₂H₄O) and formaldehyde (CH₂O) has been investigated. XRD and SEM results show that anatase TiO₂ successfully coats on the surface of Ti coatings, while the crystal structure of anatase TiO₂ can be increased during the following oxidation in air. The catalytic activity towards methylene blue of TiO₂/Ti coating balls has been significantly enhanced by the followed oxidation in air, showing a very satisfying photocatalytic degradation of C₂H₄O and CH₂O. Notably, the TiO₂/Ti photocatalyst coating balls demonstrate a significant antiviral activity, with a decrease rate of virus reached 99.96% for influenza virus and 99.99% for SARS-CoV-2.

Bismuth titanate-based UV filters embedded mesoporous silica nanoparticles: Role of bismuth concentration in the self-sealing process

The development of new safe inorganic UV filters to effectively protect the skin from ultraviolet (UV) radiation effects is an emerging issue. Bismuth titanate-based UV filters embedded into mesoporous silica nanoparticles (MSN) represent a new class of inorganic sunscreens, with excellent UVA and UVB shielding properties. In addition, the presence of bismuth ions promotes a self-sealing process, allowing (i) the entrapment of the active phases in the deepest core of the system and (ii) the formation of an external glassy silica layer with a consequent suppression of the photocatalytic activity. In this work, aimed at studying in detail the self-sealing mechanism and accessing the role of bismuth ions in the formation of the system, a series of samples impregnated with a different amount of bismuth were investigated. The self-sealing process already occurs at the lowest content of bismuth and the mechanism is demonstrated to be triggered by the ability of Bi to work as a low-melting point agent for silica. Finally, a sunscreen formulation containing the new UV filter was prepared and the Sun Protection Factor (SPF), the pH and the viscosity were measured, demonstrating the potential of the proposed material for large-scale applications.

Formation and Controlled Growth of Bismuth Titanate Phases into Mesoporous Silica Nanoparticles: An Efficient Self-Sealing Nanosystem for UV Filtering in Cosmetic Formulation

The application of nanosized inorganic UV filters in cosmetic field is limited by their high photocatalytic properties that could induce the degradation or dangerous transformation of the organic molecules in sunscreen formulations. To overcome this problem and simultaneously enlarge the window of filter's absorption, we propose the growth of bismuth titanates Bi_xTi_yO_z into mesoporous silica nanoparticles (MSN). We investigated the chemical-physical properties by means of XRPD, TEM, UV-vis spectroscopy, N₂ physisorption, XPS, and SF-ICP-MS analysis, while the influence on the environment was evaluated through photocatalytic tests. The growing process of this new nanosystem is discussed underlining the key role of the Bi³⁺ ion that, acting as a low-melting point agent for the silica framework, led to a self-sealing mechanism. The excellent UV shielding properties combined with a radical suppression of the photocatalytic activity make the proposed nanosystem a perfect candidate for the development of the next generation nanomaterials for sunscreen formulations.

Gallic acid grafting modulates the oxidative potential of ferrimagnetic bioactive glass-ceramic SC-45

Magnetite-containing glass-ceramics are promising bio-materials for replacing bone tissue after tumour resection. Thanks to their ferrimagnetic properties, they generate heat when subjected to an alternated magnetic field. In virtue of this they can be employed for the hyperthermic treatment of cancer. Moreover, grafting anti-cancer drugs onto their surface produces specific anti-neoplastic activity in these biomaterials. Gallic acid (GA) exhibits antiproliferative activity which renders it a promising candidate for anticancer applications. In the present paper, the reactivity of ferrimagnetic glass-ceramic SC-45 grafted with GA (SC-45+GA) was studied in terms of ROS release, rupture of the C-H bond of the formate molecule and Fenton reactivity by EPR/spin trapping in acellular systems. The ability of these materials to cause lipid peroxidation was assessed by UV-vis/TBA assay employing linoleic acid as a model of membrane lipid. The results, compared to those obtained with SC-45, showed that GA grafting (i) significantly enhanced the Fenton reactivity and (ii) restored the former reactivity of SC-45 towards both the C-H bond and linoleic acid which had been completely suppressed by prolonged contact with water. Fe²⁺ centres at the surface are probably implicated. GA, acting as a pro-oxidant, reduces Fe³⁺ to Fe²⁺ by maintaining a supply of Fe²⁺ at the surface of SC-45+GA.

Free-radical chemistry as a means to evaluate lunar dust health hazard in view of future missions to the moon

Lunar dust toxicity has to be evaluated in view of future manned missions to the Moon. Previous studies on lunar specimens and simulated dusts have revealed an oxidant activity assigned to HO· release. However, the mechanisms behind the reactivity of lunar dust are still quite unclear at the molecular level. In the present study, a complementary set of tests--including terephthalate (TA) hydroxylation, free radical release as measured by means of the spin-trapping/electron paramagnetic resonance (EPR) technique, and cell-free lipoperoxidation--is proposed to investigate the reactions induced by the fine fraction of a lunar dust analogue (JSC-1A-vf) in biologically relevant experimental environments. Our study proved that JSC-1A-vf is able to hydroxylate TA also in anaerobic conditions, which indicates that molecular oxygen is not involved in such a reaction. Spin-trapping/EPR measures showed that the HO· radical is not the reactive intermediate involved in the oxidative potential of JSC-1A-vf. A surface reactivity implying a redox cycle of phosphate-complexed iron via a Fe(IV) state is proposed. The role of this iron species was investigated by assessing the reactivity of JSC-1A-vf toward hydrogen peroxide (Fenton-like activity), formate ions (homolytic rupture of C-H bond), and linoleic acid (cell-free lipoperoxidation). JSC-1A-vf was active in all tests, confirming that redox centers of transition metal ions on the surface of the dust may be responsible for dust reactivity and that the TA assay may be a useful field probe to monitor the surface oxidative potential of lunar dust.

Lignin coating to quench photocatalytic activity of titanium dioxide nanoparticles for potential skin care applications

Ultraviolet light can cause photodamage to the skin, such as sunburn and melanomas.

Anode-selective coating of titanium(iv) oxide (TiO2) using electrophoretic sulfone-containing click polyester

We synthesized aliphatic and aromatic poly(ester-sulfide)s, via a thiol–ene click polymerization of ester-containing dialkenes with dithiols. Subsequent Oxone oxidation led to the corresponding poly(ester-sulfone). We then prepared a composite with TiO₂ using electrophoretic deposition. The composite was selectively deposited onto a stainless-steel anode.

Singlet oxygen plays a key role in the toxicity and DNA damage caused by nanometric TiO2 in human keratinocytes

Nanometric TiO2 has been reported to be cytotoxic and genotoxic in different in vitro models when activated by UV light. However, a clear picture of the species mediating the observed toxic effects is still missing. Here, a nanometric TiO2 powder has been modified at the surface to completely inhibit its photo-catalytic activity and to inhibit the generation of all reactive species except for singlet oxygen. The prepared powders have been tested for their ability to induce strand breaks in plasmid DNA and for their cytotoxicity and genotoxicity toward human keratinocyte (HaCaT) cells (100-500 μg mL(-1), 15 min UVA/B exposure at 216-36 mJ m(-2) respectively). The data reported herein indicate that the photo-toxicity of TiO2 is mainly triggered by particle-derived singlet oxygen. The data presented herein contribute to the knowledge of structure-activity relationships which are needed for the design of safe nanomaterials.