Human Health Risk Assessment of the Photocatalytic Oxidation of BTEX over TiO2/Volcanic Glass

This study demonstrates rapid photocatalytic oxidation of a benzene, toluene, ethylbenzene, and xylene (BTEX) mixture over TiO2/volcanic glass. The assessment of the photocatalytic oxidation of BTEX was conducted under conditions simulating those found in indoor environments affected by aromatic hydrocarbon release. We show, under UV-A intensities of 15 mW/cm2 and an air flow rate of 55 m3/h, that low ppmv levels of BTEX concentrations can be reduced to below detectable levels. Solid-phase microextraction technique was employed to monitor the levels of BTEX in the test chamber throughout the photocatalytic oxidation, lasting approximately 21 h. Destruction of BTEX from the gas phase was observed in the following sequence: o-xylene, ethylbenzene, toluene, and benzene. This study identified sequential degradation of BTEX, in combination with the stringent regulatory level set for benzene, resulted in the air quality hazard indexes (Total Hazard Index and Hazard Quotient) remaining relatively high during the process of photocatalytic oxidation. In the practical application of photocatalytic purification, it is crucial to account for the slower oxidation kinetics of benzene. This is of particular importance due to not only its extremely low exposure limits, but also due to the classification of benzene as a Group 1 carcinogenic compound by the International Agency for Research on Cancer (IARC). Our study underscores the importance of taking regulatory considerations into account when using photocatalytic purification technology.

Indoor Air Pollutant (Toluene) Reduction Based on Ultraviolet-A Irradiance and Changes in the Reactor Volume in a TiO2 Photocatalyst Reactor

This study experimentally confirmed the effect of TiO2 photocatalysts on the removal of indoor air pollutants. In the experiment, toluene, a representative indoor air pollutant, was removed using a coating agent containing TiO2 photocatalysts. Conditions proposed by the International Organization for Standardization (ISO) were applied mutatis mutandis, and a photoreactor for an experiment was manufactured. The experiment was divided into two categories. The first experiment was conducted under ISO conditions using the TiO2 photocatalyst coating agent. In the second experiment, the amount of ultraviolet-A (UV-A) light was varied depending on the lamp's service life, and the volume of the reactor was varied depending on the number of contaminants. The results showed that the TiO2 photocatalytic coating agent reduced the effect of toluene. This reduction effect can be increased as a primary function depending on the changes in the amount of UV-A light and reactor volume. However, because toluene is decomposed in this study, additional organic pollutants such as benzene and butadiene can be produced. Because these pollutants are decomposed by the TiO2 photocatalysts, the overall reduction performance may change. Nonetheless, TiO2 photocatalysts can be used to examine the effect of indoor pollutant reduction in indoor ventilation systems and building materials.

TiO2-Photocatalyst-Induced Degradation of Dog and Cat Allergens under Wet and Dry Conditions Causes a Loss in Their Allergenicity

Allergies to dogs and cats can cause enormous damage to human health and the economy. Dog and cat allergens are mainly found in dog and cat dander and are present in small particles in the air and in carpets in homes with dogs and cats. Cleaning houses and washing pets are the main methods for reducing allergens in homes; however, it is difficult to eliminate them completely. Therefore, we aimed to investigate whether a TiO2 photocatalyst could degrade dog and cat allergens. Under wet conditions, exposure to the TiO2 photocatalyst for 24 h degraded Can f1, which is a major dog allergen extracted from dog dander, by 98.3%, and Fel d1, which is a major cat allergen extracted from cat dander, by 93.6-94.4%. Furthermore, under dry conditions, the TiO2 photocatalyst degraded Can f1 and Fel d1 by 92.8% and 59.2-68.4%, respectively. The TiO2 photocatalyst abolished the binding of dog and cat allergens to human IgE by 104.6% and 108.6%, respectively. The results indicated that the TiO2 photocatalyst degraded dog and cat allergens, causing a loss in their allergenicity. Our results suggest that TiO2 photocatalysis can be useful for removing indoor pet allergens and improving the partnership between humans and pets.

Development of a high-speed bioaerosol elimination system for treatment of indoor air

We developed a high-speed filterless airflow multistage photocatalytic elbow aerosol removal system for the treatment of bioaerosols such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human-generated bioaerosols that diffuse into indoor spaces are 1-10 μm in size, and their selective and rapid treatment can reduce the risk of SARS-CoV-2 infection. A high-speed airflow is necessary to treat large volumes of indoor air over a short period. The proposed system can be used to eliminate viruses in aerosols by forcibly depositing aerosols in a high-speed airflow onto a photocatalyst placed inside the system through inertial force and turbulent diffusion. Because the main component of the deposited bioaerosol is water, it evaporates after colliding with the photocatalyst, and the nonvolatile virus remains on the photocatalytic channel wall. The residual virus on the photocatalytic channel wall is mineralized via photocatalytic oxidation with UVA-LED irradiation in the channel. When this system was operated in a 4.5 m³ aerosol chamber, over 99.8% aerosols in the size range of 1-10 μm were removed within 15 min. The system continued delivering such performance with the continuous introduction of aerosols. Because this system exhibits excellent aerosol removal ability at a flow velocity of 5 m/s or higher, it is more suitable than other reactive air purification systems for treating large-volume spaces.

SARS-CoV-2 Disinfection of Air and Surface Contamination by TiO2 Photocatalyst-Mediated Damage to Viral Morphology, RNA, and Protein

SARS-CoV-2 is the causative agent of COVID-19, which is a global pandemic. SARS-CoV-2 is transmitted rapidly via contaminated surfaces and aerosols, emphasizing the importance of environmental disinfection to block the spread of virus. Ultraviolet C radiation and chemical compounds are effective for SARS-CoV-2 disinfection, but can only be applied in the absence of humans due to their toxicities. Therefore, development of disinfectants that can be applied in working spaces without evacuating people is needed. Here we showed that TiO2-mediated photocatalytic reaction inactivates SARS-CoV-2 in a time-dependent manner and decreases its infectivity by 99.9% after 20 min and 120 min of treatment in aerosol and liquid, respectively. The mechanistic effects of TiO2 photocatalyst on SARS-CoV-2 virion included decreased total observed virion count, increased virion size, and reduced particle surface spike structure, as determined by transmission electron microscopy. Damage to viral proteins and genome was further confirmed by western blotting and RT-qPCR, respectively. The multi-antiviral effects of TiO2-mediated photocatalytic reaction implies universal disinfection potential for different infectious agents. Notably, TiO2 has no adverse effects on human health, and therefore, TiO2-induced photocatalytic reaction is suitable for disinfection of SARS-CoV-2 and other emerging infectious disease-causing agents in human habitation.

Response Surface Methodology: Photocatalytic Degradation Kinetics of Basic Blue 41 Dye Using Activated Carbon with TiO2

Water decontamination still remains a major challenge to some developing countries not having centralized wastewater systems. Therefore, this study presents the optimization of photocatalytic degradation of Basic Blue 41 dye in an aqueous medium by an activated carbon (AC)-TiO₂ photocatalyst under UV irradiation. The mesoporous AC-TiO₂ synthesized by a sonication method was characterized by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy for crystal phase identification and molecular bond structures, respectively. The efficiency of the AC-TiO₂ was evaluated as a function of three input variables viz. catalyst load (2-4 g), reaction time (15-45 min) and pH (6-9) by using Box-Behnken design (BBD) adapted from response surface methodology. Using color and turbidity removal as responses, a 17 run experiment matrix was generated by the BBD to investigate the interaction effects of the three aforementioned input factors. From the results, a reduced quadratic model was generated, which showed good predictability of results agreeable to the experimental data. The analysis of variance (ANOVA), signposted the selected models for color and turbidity, was highly significant (p < 0.05) with coefficients of determination (R²) values of 0.972 and 0.988, respectively. The catalyst load was found as the most significant factor with a high antagonistic impact on the process, whereas the interactive effect of reaction time and pH affected the process positively. At optimal conditions of catalyst load (2.6 g), reaction time (45 min), and pH (6); the desirability of 96% was obtained by a numerical optimization approach representing turbidity removal of 93% and color of 96%.

A simple and effective synthesis of magnetic γ-Fe2O3@SiO2@TiO2-Ag microspheres as a recyclable photocatalyst: dye degradation and antibacterial potential

PURPOSE AND METHODS

In this study, an effective technique for synthesizing γ-Fe₂O₃@SiO₂@TiO₂-Ag magnetically separable photocatalyst was introduced by combining co-precipitation, sol-gel, and photo-deposition methods. A series of analyses including FTIR, SEM, EDS, XRD, and VSM were applied to characterize the prepared materials and the investigations on photocatalytic activity of the prepared composites were accomplished.

RESULTS

Compared to bare γ-Fe₂O₃@SiO₂@TiO₂, the Ag-doped composite was more active in terms of photocatalytic characteristics. By applying γ-Fe₂O₃@SiO₂@TiO₂-Ag, the decomposition rate of the Basic blue 41 reached to about 94% after 3 h of UV irradiation; this rate was 63% for pure γ-Fe₂O₃@SiO₂@TiO₂. The results indicated that the dye degradation kinetics followed first-order kinetic model. During the five cycles of separation, it was observed that the Ag-doped composite was greatly effective and stable in terms of recycling. Moreover, the results indicated that antibacterial activity of γ-Fe₂O₃@SiO₂@TiO₂-Ag was remarkably stronger than that of pure Fe₂O₃@SiO₂@TiO₂ particles.

CONCLUSION

It was concluded that by modifying magnetic TiO₂ by silver nanoparticles, charge separation was eased by catching photo-generated electrons, resulted in an enhanced photo- and biological activity. Graphical abstract.

Synthesis of Mesoporous TiO2-B Nanobelts with Highly Crystalized Walls toward Efficient H2 Evolution

Mesoporous TiO2 is attracting increasing interest due to properties suiting a broad range of photocatalytic applications. Here we report the facile synthesis of mesoporous crystalline TiO2-B nanobelts possessing a surface area as high as 80.9 m2 g-1 and uniformly-sized pores of 6-8 nm. Firstly, P25 powders are dissolved in NaOH solution under hydrothermal conditions, forming sodium titanate (Na2Ti3O7) intermediate precursor phase. Then, H2Ti3O7 is successfully obtained by ion exchange through acid washing from Na2Ti3O7 via an alkaline hydrothermal treatment. After calcination at 450 °C, the H2Ti3O7 is converted to a TiO2-B phase. At 600 °C, another anatase phase coexists with TiO2-B, which completely converts into anatase when annealed at 750 °C. Mesoporous TiO2-B nanobelts obtained after annealing at 450 °C are uniform with up to a few micrometers in length, 50-120 nm in width, and 5-15 nm in thickness. The resulting mesoporous TiO2-B nanobelts exhibit efficient H2 evolution capability, which is almost three times that of anatase TiO2 nanobelts.

Ti-Based Catalysts and Photocatalysts: Characterization and Modeling

This perspective article aims to underline how cutting-edge synchrotron radiation spectroscopies such as extended X-ray absorption spectroscopy (EXAFS), X-ray absorption near edge structure (XANES), high resolution fluorescence detected (HRFD) XANES, X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) have played a key role in the structural and electronic characterization of Ti-based catalysts and photocatalysts, representing an important additional value to the outcomes of conventional laboratory spectroscopies (UV-Vis, IR, Raman, EPR, NMR etc.). Selected examples are taken from the authors research activity in the last two decades, covering both band-gap and shape engineered TiO₂ materials and microporous titanosilicates (ETS-10, TS-1 and Ti-AlPO-5). The relevance of the state of the art simulation techniques as a support for experiments interpretation is underlined for all the reported examples.