Photo-catalytic oxidation of acetone on a TiO2 powder: An in situ FTIR investigation

Outstanding photo-thermo synergy in aerobic oxidation of cyclohexane by bismuth tungstate-bismuth oxychloride high-low heterojunction

The difficulty of achieving both high conversion rate and high selectivity is a huge challenge in the catalytic aerobic oxidation of cyclohexane. In this paper, bismuth tungstate-bismuth oxychloride (Bi2WO6-BiOCl) nanoflower heterojunctions prepared via a one-step solvothermal process were applied in the photo-thermo synergetic catalytic oxidation of cyclohexane in the dried air. With the addition of little water at different reaction temperature, the ratio of bismuth to tungsten and the mass ratio of Bi2WO6 to BiOCl can be precisely tailored in the nanoflower sphere composites with thin nanosheets. Their microscopic morphology, elemental composition, crystal structure, and photoelectrochemical characteristics were explored by different characterization methods. The Bi2WO6-BiOCl composites possessed poor photocatalytic and thermal performances with the low conversion rates of 1.43% and 2.68%, respectively. However, through the photo-thermo catalytic oxidation process, an exceptional conversion rate of 13.32% was achieved with excellent selectivity of 99.22% for cyclohexanone and cyclohexanol (KA oil) using the same Bi2WO6-BiOCl composites. This superior performance outstrips Bi2WO6 flowers, BiOCl nanosheets and Bi2WO6-BiOCl composites with other compounding ratios. The creation of a high-low heterojunction in the Bi2WO6-BiOCl composite was confirmed by band energy analysis. The opto-electronic analysis, band energy analysis, sacrifice experiments, and active radical analysis were employed to elucidate the mechanism for the exceptional photo-thermo catalytic performance in detail. This work offers an exploratory solution to the challenges of high energy consumption and the difficulty in simultaneously achieving high selectivity and high conversion rates in cyclohexane oxidation, thus holding significant value.

TiO2 with controllable oxygen vacancies for efficient isopropanol degradation: photoactivity and reaction mechanism

Flame-synthesized TiO_2−x with controllable defects exhibits a remarkable photooxidation efficiency of gaseous isopropanol with the reaction mechanism investigated.

Photocatalytic Oxidation of Propane Using Hydrothermally Prepared Anatase-Brookite-Rutile TiO2 Samples. An In Situ DRIFTS Study

Photocatalytic oxidation of propane using hydrothermally synthesized TiO₂ samples with similar primary crystal size containing different ratios of anatase, brookite and rutile phases has been studied by measuring light-induced propane conversion and in situ DRIFTS (diffuse reflectance Fourier transform infrared spectroscopy). Propane was found to adsorb on the photocatalysts, both in the absence and presence of light. The extent of adsorption depends on the phase composition of synthesized titania powders and, in general, it decreases with increasing rutile and brookite content. Still, the intrinsic activity for photocatalytic decomposition of propane is higher for photocatalysts with lower ability for propane adsorption, suggesting this is not the rate-limiting step. In situ DRIFTS analysis shows that bands related to adsorbed acetone, formate and bicarbonate species appear on the surface of the photocatalysts during illumination. Correlation of propane conversion and infrared (IR) data shows that the presence of formate and bicarbonate species, in excess with respect to acetone, is composition dependent, and results in relatively low activity of the respective TiO₂. This study highlights the need for precise control of the phase composition to optimize rates in the photocatalytic oxidation of propane and a high rutile content seems to be favorable.

Effect of H2O and O2 on the Adsorption and Degradation of Acetaldehyde on Anatase Surfaces—An In Situ ATR-FTIR Study

The effect of H2O and O2 on the adsorption and degradation of gaseous acetaldehyde on the anatase TiO2 surface has been studied, in the dark and upon UV illumination, at ambient temperatures. The processes occurring at the surface have been elucidated by means of in situ ATR–FTIR (Attenuated Total Reflection—Fourier Transform Infrared) spectroscopy, while gas detectors allowed the analysis of the adducts and products in the gas phase. In the dark and under dry conditions acetaldehyde reacts independently of the atmosphere, upon aldol condensation to crotonaldehyde. However, under humid conditions, this reaction was prevented due to the replacement of the adsorbed acetaldehyde molecules, by water molecules. Upon UV illumination under oxygenic conditions, acetaldehyde was decomposed to acetate and formate. Under an N2 atmosphere, the formation of acetate and formate was observed during the first hour of illumination, until all adsorbed oxygen had been consumed. In the absence of molecular oxygen acetate, methane, and CO2 were detected, the formation of which most likely involved the participation of the bridging O atoms, within the TiO2 lattice.

Insight into the significant roles of microstructures and functional groups on carbonaceous surfaces for acetone adsorption

To understand the roles of pore structures and functional groups on acetone adsorption, activated carbons (ACs) with different properties were obtained by surface modification. XRD, SEM, TEM and nitrogen adsorption were used to identify the structural characteristics of the ACs, while TG-DTA, FTIR, XPS and Boehm titration were applied to analyse the surface chemistries. The microporous surface areas showed a positive linear correlation to the acetone adsorption amounts, and increasing the carboxylic groups could improve the uptake of strongly adsorbed acetone. HNO3 modified AC (AC-N) was found to exhibit an excellent adsorption capacity of 5.49 mmol g-1, which might be attributed to the developed microporous structures and abundant carboxylic groups. The desorption activation energies (E d) of strongly adsorbed acetone on AC-N and AC were both determined to be 81.6 kJ mol-1, indicating the same adsorption sites on different activated carbons, suspected to be carboxylic groups. The possible adsorption mechanism of acetone on carbonaceous surfaces was also proposed.

The Application of Nano-TiO2 Photo Semiconductors in Agriculture

Nanometer-sized titanium dioxide (TiO₂) is an environmentally friendly optical semiconductor material. It has wide application value in many fields due to its excellent structural, optical, and chemical properties. The photocatalytic process of nano-TiO₂ converts light energy into electrical or chemical energy under mild conditions. In recent years, the study and application of nano-TiO₂ in the agricultural sector has gradually attracted attention. The nano-TiO₂ applications of degrading pesticides, plant germination and growth, crop disease control, water purification, pesticide residue detection, etc. are good prospects. This review describes all of these applications and the research status and development, including the underlying principles, features, comprehensive applications, functional modification, and potential future directions, for TiO₂ in agriculture.

Copper NPs decorated titania: A novel synthesis by high energy US with a study of the photocatalytic activity under visible light

The most important drawback of the use of TiO2 as photocatalyst is its lack of activity under visible light. To overcome this problem, the surface modification of commercial micro-sized TiO2 by means of high-energy ultrasound (US), employing CuCl2 as precursor molecule to obtain both metallic copper as well as copper oxides species at the TiO2 surface, is here. We have prepared samples with different copper content, in order to evaluate its impact on the photocatalytic performances of the semiconductor, and studied in particular the photodegradation in the gas phase of some volatile organic molecules (VOCs), namely acetone and acetaldehyde. We used a LED lamp in order to have only the contribution of the visible wavelengths to the TiO2 activation (typical LED lights have no emission in the UV region). We employed several techniques (i.e., HR-TEM, XRD, FT-IR and UV-Vis) in order to characterize the prepared samples, thus evidencing different sample morphologies as a function of the various copper content, with a coherent correlation between them and the photocatalytic results. Firstly, we demonstrated the possibility to use US to modify the TiO2, even when it is commercial and micro-sized as well; secondly, by avoiding completely the UV irradiation, we confirmed that pure TiO2 is not activated by visible light. On the other hand, we showed that copper metal and metal oxides nanoparticles strongly and positively affect its photocatalytic activity.