Adsorption of chlorine and oxygen atoms on clean and defective rutile–TiO2 (110) and MgO (100) surfaces

Two-Dimensional Material-Based Electrochemical Sensors/Biosensors for Food Safety and Biomolecular Detection

Two-dimensional materials (2DMs) exhibited great potential for applications in materials science, energy storage, environmental science, biomedicine, sensors/biosensors, and others due to their unique physical, chemical, and biological properties. In this review, we present recent advances in the fabrication of 2DM-based electrochemical sensors and biosensors for applications in food safety and biomolecular detection that are related to human health. For this aim, firstly, we introduced the bottom-up and top-down synthesis methods of various 2DMs, such as graphene, transition metal oxides, transition metal dichalcogenides, MXenes, and several other graphene-like materials, and then we demonstrated the structure and surface chemistry of these 2DMs, which play a crucial role in the functionalization of 2DMs and subsequent composition with other nanoscale building blocks such as nanoparticles, biomolecules, and polymers. Then, the 2DM-based electrochemical sensors/biosensors for the detection of nitrite, heavy metal ions, antibiotics, and pesticides in foods and drinks are introduced. Meanwhile, the 2DM-based sensors for the determination and monitoring of key small molecules that are related to diseases and human health are presented and commented on. We believe that this review will be helpful for promoting 2DMs to construct novel electronic sensors and nanodevices for food safety and health monitoring.

Introducing catalysis in photocatalysis: What can be understood from surface science studies of alcohol photoreforming on TiO2

Mechanisms in heterogeneous photocatalysis have traditionally been interpreted by the band-structure model and analogously to electrochemistry. This has led to the establishment of 'band-engineering' as a leading principle for the discovery of more efficient photocatalysts. In such a picture, mainly thermodynamic aspects are taken into account, while kinetics are often ignored. This holds in particular for chemical kinetics, which are, other than those for charge carrier dynamics, often not at all considered for the interpretation of the catalysts' photocatalytic performance. However, while being usually neglected in photocatalyis, they are a traditional and powerful tool in thermal catalysis and are still applied with great success in this field. While surface science studies made substantial contributes to thermal catalysis, analogous studies in heterogeneous photocatalysis still play only a minor role. In this review, the authors show that the photo-physics of defined materials in well-defined environments can be correlated with photochemical events on a surface, highlighting the importance of well-characterized semiconductors for the interpretation of mechanisms in heterogeneous photochemistry. The work focuses on contributions from surface science, which were obtained for the model system of a titania single crystal and alcohol photo-reforming. It is demonstrated that only surface science studies have so far enabled the elucidation of molecularly precise reaction mechanisms, the determination of reaction intermediates and assignment of reactive sites. As the identification of these properties remain major prerequisites for a breakthrough in photocatalysis research, the work also discusses the implications of the findings for applied systems. In general, the results from surface science demonstrate that photocatalytic systems shall also be approached by a perspective originating from heterogeneous catalysis rather than solely from an electrochemical point of view.

Cl2 Production by Photocatalytic Oxidation of HCl over TiO2

We studied the photocatalytic aerobic oxidation of HCl over TiO₂ for producing Cl₂ . Steady-state Cl₂ production rates were determined with a photocatalytic fixed-bed gas-phase reactor equipped with UV light-emitting diodes (LEDs) using iodometric titration as online analytics. We found stable Cl₂ production rates of up to 16 mmol h^-1  m^-2 for commercial anatase TiO₂ Hombikat UV100. The rate increased linearly with temperature from 21 to 140 °C, indicating the acceleration of the limiting desorption rate of the coupled product water. Comparing different TiO₂ polymorphs revealed that anatase possesses higher activity than rutile. The adsorption of HCl was monitored in situ by IR spectroscopy. The IR spectra indicated that HCl chemisorption chlorinates the surface of TiO₂ under the reaction conditions, suggesting it to be the first step of the reaction mechanism. High stability opens up the opportunity of developing a promising photocatalytic process of HCl recycling at lower temperatures suitable for reaching full conversion.