Mechanochemical Forces as a Synthetic Tool for Zero- and One-Dimensional Titanium Oxide-Based Nano-photocatalysts

Tuning the physicochemical features of titanium oxide nanomaterials by ultrasound: Elevating photocatalytic selective partial oxidation of lignin-inspired aromatic alcohols

The research for "green" and economically feasible approaches such as (photo)catalysis especially for biomass valorization such as selective oxidation of biomass derived compounds like aromatic alcohols to corresponding aldehyde by avoiding the harsh reaction conditions and the addition of reagents concentrate the focus of attention the last years. Hence, design and development of novel photocatalyst for the partial selective oxidation is highly desirable. In this research work, ultrasonication of different frequencies (22, 40, 80 kHz) and different amplitudes was utilized as synthesis tool in order to obtain novel materials by precipitation method. The synthesized samples were characterized by using different techniques such as N₂ sorption, TEM, XPS, XRD, thermal analysis, and diffuse reflectance spectroscopy. The synthesized sample by using low ultrasound frequency (22 kHz) and amplitude showed a mixed morphological and structural nature consisting of asymmetric 1-dimensional (nanorods-like), layered nano-structures and not well-defined areas, leading to elevate for metal oxide specific surface areas up to 155 m²/g. The observed 1-D nanostructures have diamentions in the range of 20-60 nm. This sample revealed the highest photo-oxidation efficiency for the selective conversion of two biomass-derived, and more specifically lignin-inspired model compounds, benzyl alcohol and cinnamyl alcohol to benzaldehyde and cinnamyl aldehyde, respectively, and hence the highest yield towards the desired aldehydes. The selective photo-oxidation activity was retained even after 5 photocatalytic cycles, while no leaching of Ti was recorded.

Mechanochemical Synthesis of TiO2-CeO2 Mixed Oxides Utilized as a Screen-Printed Sensing Material for Oxygen Sensor

TiO₂ and CeO₂ are well known as oxygen sensing materials. Despite high sensitivity, the actual utilization of these materials in gas detection remains limited. Research conducted over the last two decades has revealed synergistic effects of TiO₂-CeO₂ mixed oxides that have the potential to improve some aspects of oxygen monitoring. However, there are no studies on the sensing properties of the TiO₂-CeO₂ obtained by mechanochemical treatment. We have tested the applicability of the mechanochemically treated TiO₂-CeO₂ for oxygen detection and presented the results in this study. The sensing layers are prepared as a porous structure by screen printing a thick film on a commercial substrate. The obtained structures were exposed to various O₂ concentrations. The results of electrical measurements showed that TiO₂-CeO₂ films have a significantly lower resistance than pure oxide films. Mixtures of composition TiO₂:CeO₂ = 0.8:0.2, ground for 100 min, have the lowest electrical resistance among the tested materials. Mixtures of composition TiO₂:CeO₂ = 0.5:0.5 and ground for 100 min proved to be the most sensitive. The operating temperature can be as low as 320 °C, which places this sensor in the class of semiconductor sensors working at relatively lower temperatures.

Ultrasonically-assisted synthesis of CeO2 within WS2 interlayers forming type II heterojunction for a VOC photocatalytic oxidation

Here, we investigate the band structure, density of states, photocatalytic activity, and heterojunction mechanism of WS₂ with CeO₂ (CeO₂@WS₂) as a photoactive heterostructure. In this heterostructure, CeO₂'s growth within WS₂ layers is achieved through ultrasonicating WS₂ and intercalating CeO₂'s precursor within the WS₂ interlayers, followed by hydrothermal treatment. Through a set of density functional calculations, we demonstrate that CeO₂ and WS₂ form an interface through a covalent bonding that can be highly stable. The electrochemical impedance spectroscopy (EIS) found that the CeO₂@WS₂ heterostructure exhibits a remarkably higher conductivity (22.23 mS cm^-2) compared to either WS₂ and CeO₂, assignable to the interface in CeO₂@WS₂. Furthermore, in a physically mixed CeO₂-WS₂ where the interaction between particles is noncovalent, the resistance was significantly higher (0.67 mS cm^-2), confirming that the heterostructure in the interface is covalently bonded. In addition, Mott-Schottky and the bandgap measurements through Tauc plots demonstrate that the heterojunction in CeO₂ and WS₂ is type II. Eventually, the CeO₂@WS₂ heterostructure indicated 446.7 µmol g ^-1 CO₂ generation from photocatalytic oxidation of a volatile organic compound (VOC), formic acid, compared to WS₂ and CeO₂ alone.

A Review on Resource Utilization of Spent V-W-Ti Based Selective Catalytic Reduction Catalysts

To address the environmental pollution caused by nitrogen oxides, V₂O₅-WO₃/TiO₂ is widely used as a catalyst based on selective catalytic reduction (SCR) technology. However, spent SCR catalysts pose a potential hazard to the environment due to the presence of heavy metals. This problem continues to plague countries with predominantly thermal power generation, and landfills as the dominant disposal method wastes significant metal resources. Previous research into the recovery of these metal resources has received considerable attention. Here, we summarise the methods of recovery and find that research trends are beginning to move towards improving the added value of recovered products. One very promising application is photocatalysts; however, the atomic efficiency of current methods is not satisfactory. Therefore, this review first focuses on the regeneration of spent SCR catalysts and the processes used for elemental extraction to clarify what forms of V, W and Ti can be obtained from existing processes. This is followed by providing directions for the conversion of spent SCR catalysts into photocatalysts with improvements based on such processes. From a different perspective, this also provides a new resource for photocatalysts and is expected to significantly reduce the cost of photocatalyst production.

A Nanobody‐on‐Quantum Dot Displacement Assay for Rapid and Sensitive Quantification of the Epidermal Growth Factor Receptor (EGFR)

Biosensing approaches that combine small, engineered antibodies (nanobodies) with nanoparticles are often complicated. Here, we show that nanobodies with different C‐terminal tags can be efficiently attached to a range of the most widely used biocompatible semiconductor quantum dots (QDs). Direct implementation into simplified assay formats was demonstrated by designing a rapid and wash‐free mix‐and‐measure immunoassay for the epidermal growth factor receptor (EGFR). Terbium complex (Tb)‐labeled hexahistidine‐tagged nanobodies were specifically displaced from QD surfaces via EGFR‐nanobody binding, leading to an EGFR concentration‐dependent decrease of the Tb‐to‐QD Förster resonance energy transfer (FRET) signal. The detection limit of 80±20 pM (16±4 ng mL⁻¹) was 3‐fold lower than the clinical cut‐off concentration for soluble EGFR and up to 10‐fold lower compared to conventional sandwich FRET assays that required a pair of different nanobodies.

One-dimensional titanate nanotube materials: heterogeneous solid catalysts for sustainable synthesis of biofuel precursors/value-added chemicals-a review

One-dimensional (1D) titanate nanotubes materials (protonated titanate nanotube (HTNT) and sodium titanate nanotube (NaTNT)) have been reported as low-cost and efficient catalytic materials in chemical syntheses for the production of biofuel precursors with interesting catalytic performance exhibited, even better than some commonly used zeolites, H-MOR, H-β, SO4 2-/Al2O3, and H-ZSM-5 solid catalysts with environmental benign in focus when compared with homogeneous catalytic materials. This mini-review expressly revealed the significance and potential of using HTNT and NaTNT as sustainable and environmentally benign solid catalysts/supports in various chemical reactions. The critical assessment of biomass valorization and titanate nanostructured materials as catalysts/supports via Green Chemistry approach, #7 (use of renewable feedstocks), #9 (use of catalyst against stoichiometry) and United Nations (UN) Sustainable Development Goals (SDGs), #7 (affordable and clean energy; ensure access to inexpensive, reliable, sustainable, and new energy), is presented as integrated pathways to meet environmental benign technology toward sustainability. Hence, this work follows in the pattern of recent formulated features reported for solid catalysts-'PYSSVR' concept, which means P-production cost, Y-yield, S-stability, S-selectivity, V-versatility, and R-reusability.

GRAPHICAL ABSTRACT

Effect of temperature and humidity on the sensing performance of TiO2nanowire-based ethanol vapor sensors

In this paper, we study the influence of two key factors, temperature, and humidity, on gas sensors based on titanium dioxide nanowires synthesized at 4 different temperatures and with different morphology. The samples' structure are investigated using SEM, XRD and FTIR analysis. The effects of humidity and temperature are studied by measuring the resistance and gas response when exposed to ethanol. At room temperature, we observed a 15% sensitivity response to 100 ppm of ethanol vapor and by increasing the operating temperature up to 180 °C, the response is enhanced by two orders of magnitude. The best operating temperature for the highest gas response is found to be around 180 °C. Also, it was observed that every nanowire morphology has its own optimum operating temperature. The resistance of sensors is increased at higher Relative Humidity (RH). Besides, the response to ethanol vapor experiences a gradual increase when the RH rises from 10% to 60%. On the other hand, from 60% to 90% RH the gas response decreases gradually due to different mechanisms of interaction of the TiO₂with H₂O and ethanol molecules.

Insights into the Mechanism of the Mechanochemical Formation of Metastable Phases

The mechanochemical reaction kinetics of sulfur with copper to form a metastable copper sulfide phase at room temperature is investigated in ultrahigh vacuum by modifying the properties of the copper during cleaning in vacuum. The measured kinetics is in agreement with a theory first proposed by Karthikeyan and Rigney that predicts that the rate depends linearly both on the contact time and on the strain-rate sensitivity of the substrate. The mechanism for this process was investigated using thin samples of copper fabricated using a focused-ion-beam and by measuring the crystal structure and elemental composition of the copper subsurface region by electron microscopy after reaction. The measured sulfur depth distributions produced by shear-induced surface-to-bulk transport were in good agreement with values calculated using rate constants that also model the reaction kinetics. Sulfur was found both in crystalline regions and also concentrated along grain boundaries, implying that formation of metastable phases is facilitated by both the presence of dislocations and by grain boundaries.

The many flavours of mechanochemistry and its plausible conceptual underpinnings

Mechanochemistry describes diverse phenomena in which mechanical load affects chemical reactivity. The fuzziness of this definition means that it includes processes as seemingly disparate as motor protein function, organic synthesis in a ball mill, reactions at a propagating crack, chemical actuation, and polymer fragmentation in fast solvent flows and in mastication. In chemistry, the rate of a reaction in a flask does not depend on how fast the flask moves in space. In mechanochemistry, the rate at which a material is deformed affects which and how many bonds break. In other words, in some manifestations of mechanochemistry, macroscopic motion powers otherwise endergonic reactions. In others, spontaneous chemical reactions drive mechanical motion. Neither requires thermal or electrostatic gradients. Distinct manifestations of mechanochemistry are conventionally treated as being conceptually independent, which slows the field in its transformation from being a collection of observations to a rigorous discipline. In this Review, we highlight observations suggesting that the unifying feature of mechanochemical phenomena may be the coupling between inertial motion at the microscale to macroscale and changes in chemical bonding enabled by transient build-up and relaxation of strains, from macroscopic to molecular. This dynamic coupling across multiple length scales and timescales also greatly complicates the conceptual understanding of mechanochemistry.

Improvements in Catalyst Synthesis and Photocatalytic Oxidation Processing Based on the Use of Ultrasound

The efficacy of photocatalysis strongly depends on the activity of the catalysts and the operational factors, especially factors associated with mass transfer and the possibility of catalyst deactivation. The use of ultrasound has great potential to enhance catalyst activity, during both the synthesis and actual oxidation processes due to the cavitational effects of turbulence and liquid streaming. This article presents an overview of the application aspects of ultrasound, both in the synthesis of the photocatalyst and applications for wastewater treatment. A review of the literature revealed that the use of ultrasound in the synthesis processes can result in a catalyst with a lower mean size and higher surface area as well as uniform size distribution. The application of ultrasound in the actual photocatalytic oxidation facilitates enhancement of the oxidation capacity, leading to higher degradation rates, sometimes synergistic results and definitely lower treatment times. This article also presents guidelines for the selection of the best operating conditions for the use of ultrasound in photocatalytic systems and includes a discussion on the possible reactor configurations suitable for large-scale operations. Overall, a combination of ultrasound with photocatalytic oxidation or the optimized application of ultrasound in catalyst synthesis can yield significant benefits.