Search

Advanced semiconductor photocatalysts have significant potential for efficient alcohol photooxidation. In this study, a novel 2D/2D g-C3N4/SnS (CNS) S-scheme heterojunction was fabricated via a one-step hydrothermal stripping and assembly method, in which SnS nanosheets were in situ anchored on exfoliated g-C3N4 nanosheets. The as-prepared CNS composites exhibit superior photocatalytic performance in the photooxidation of benzyl alcohol (BA) to benzaldehyde. This is because constructing the 2D/2D heterojunction interface efficiently provided numerous surface Sn vacancies, enhancing light absorption, and encouraging charge separation and transfer. CNS-10 achieved the best photocatalytic activity with a promising formation rate of 1.63 mmolreacted BA gcatal.−1 h−1, which is 4-fold more significant than that of pristine g-C3N4. Femtosecond time-resolved transient absorption spectroscopy (fs-TAS) reveals that the exceptional performance could be attributed to the effective synergistic promotion of shallow electron trapping in g-C3N4 and inhibition of the recombination of photogenerated electrons and holes. Furthermore, the main active species and possible reaction mechanisms during the photocatalytic process were also examined. Overall, this study can offer insights into the rational construction of 2D/2D S-scheme photocatalysts. [ABSTRACT FROM AUTHOR]

We propose a multiband asymmetric acoustic absorption and reflection system constructed from a waveguide and multi-order resonators with different radiant modes. Theoretical and experimental results confirm that the coupling of the dark and bright modes at each resonant frequency enables multiband high-efficiency absorption requiring only two functional units. More interestingly, we demonstrate a hybrid multiband asymmetric system based on customized multi-mode pairs. One side of the hybrid multiband system almost completely absorbs the lower frequency incident sound waves while reflecting the higher frequency ones; conversely, the other side effectively reflects the lower frequency ones and absorbs the higher frequency ones. Our design showcases the flexibility of customized multiband asymmetric absorption and also provides an approach for the design of bidirectional wave-manipulation devices. [ABSTRACT FROM AUTHOR]

Numerous vanadium–titania composites have drawn significant interest as efficient photocatalysts for the photocatalytic oxidation of alcohols into valuable aldehydes or C–C coupling compound intermediates. In this comparative study, the photocatalytic potential of two conformations of vanadium–titania catalysts was analyzed, including a vanadium–titania solid solution of VTiOx and vanadium oxide supported on titania VOx/TiO2. The distinct structural interfaces among the components of these catalysts resulted in notably divergent catalytic performances. The VTiOx catalyst is superior to the corresponding supported VOx/TiO2 catalysts in the photo-oxidation of benzyl alcohol. The vanadium incorporated into the titania lattice influences surface oxygen vacancy defects, examined by a series of technologies, thus distinctly improving the photocatalytic activity. The experimental phenomena supported with density functional theory (DFT) studies indicate that incorporating V into the TiO2 lattice can effectively lower the activation energy for the lattice oxygen, thereby improving the generation and repair of oxygen vacancies and thus promoting photo-oxidation. [ABSTRACT FROM AUTHOR]

As a typical representative of antibiotics, tetracycline is widely used in medicine and aquaculture due to its low cost and strong antibacterial ability. However, it is difficult for humans or animals to metabolize completely, resulting in the aggravation of water pollution in aquatic environments. Therefore, it is urgent to explore advanced photocatalysts for the degradation of antibiotics. In this work, we prepared a spherical manganese dioxide-ceria (MnCeOx) solid solution by a simple one-step hydrothermal method and evaluated its photocatalytic degradation activity towards tetracycline using a Xe lamp. The study of the structure and optical properties showed that doping of Mn cations into a ceria lattice can introduce defect energy levels to narrow the band gap, which can then increase the number of surface oxygen vacancies, so as to improve the adsorption of tetracycline and promote the separation and transfer of photogenerated electrons and holes. MnCeOx-10 with the highest oxygen defect showed the best photocatalytic performance (the promising degradation efficiency was 65% in 90 minutes), which was about 2.3 times and 1.3 times higher than those of the original CeO2 and MnOx/CeO2 catalysts, respectively. In addition, the capture experiment verified that ˙O2− and h+ should be the reasons for enhancing the degradation process. This study provides guidance and a practical basis for the development of an efficient rare-earth photocatalyst system. [ABSTRACT FROM AUTHOR]

Morphological effects of nanoparticles are crucial in many solid-catalyzed chemical transformations. We herein prepared two manganese-ceria solid solutions, well-defined MnCeOx nanorods and MnCeOx-nanocubes, exposing preferentially (111) and (100) facets of ceria, respectively. The incorporation of Mn dopant into ceria lattice strongly enhanced the catalytic performance in the NO reduction with CO. MnCeOx (111) catalyst outperformed MnCeOx (100) counterpart due to its higher population density of oxygen vacancy defects. In-situ infrared spectroscopy investigations indicated that the reaction pathway over MnCeOx and pristine CeO2 is similar and that besides the direct pathway, an indirect pathway via adsorbed hyponitrite as an intermediate cannot be ruled out. X-ray photoelectron and Raman spectroscopies as well as first-principles density functional theory (DFT) calculations indicate that the enhanced catalytic performance of MnCeOx can be traced back to its "Mn—OL(VÖ)—Mn—OL(VÖ)—Ce" connectivities. The Mn dopant strongly facilitates the formation of surface oxygen vacancies (VÖ) by liberating surface lattice oxygen (OL) via CO* + OL → CO2* + VÖ and promotes the reduction of NO, according to NO* + VÖ → N* + OL and 2N* → N2. The Mn dopant impact on both the adsorption of CO and activation of OL reveals that a balance between these two effects is critical for facilitating all reaction steps. [ABSTRACT FROM AUTHOR]

In this work, an InVO4/TiO2 heterojunction composite catalyst was successfully synthesized through a facile hydrothermal method. The structural and optical characteristics of InVO4/TiO2 heterojunction composites are investigated using a variety of techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and spectroscopy techniques. The addition of InVO4 to TiO2 considerably enhanced the photocatalytic performance in selective photo-oxidation of benzyl alcohol (BA). The 10 wt% InVO4/TiO2 composite photocatalyst provided a decent 100% BA conversion with over 99% selectivity for benzaldehyde, and exhibited a maximum conversion rate of 3.03 mmol g−1 h−1, which is substantially higher than bare InVO4 and TiO2. The excellent catalytic activity of the InVO4/TiO2 photocatalyst is associated with the successful assembly of heterostructures, which promotes the charge separation and transfer between InVO4 and TiO2. [ABSTRACT FROM AUTHOR]

Monolithic silica and polymer capillary columns with ultrahigh column efficiencies were prepared. Permeability and electrochromatography performances of these two kinds of columns were compared. Monolithic silica columns bear higher permeability than polymer counterparts by two orders of magnitude. Furthermore, the van Deemter plots of alkylbenzenes on these two kinds of columns demonstrate that monolithic silica columns produce much lower plate heights of alkylbenzes than polymer columns do. Within the range of electroosmotic flow (EOF) velocity investigated, no uptrend of plate height with the increase of EOF was observed suggesting the great capacity of fast separation and high efficiency. The plate height of thiourea on monolithic silica columns is as low as 2.67 μm, representing its corresponding column efficiency is over 430,000 plates/m. As far as we know, it is the highest ever column efficiency reported in the literature. Moreover, the separation of butylbenzene isomers was obtained on the monolithic silica column. [ABSTRACT FROM AUTHOR]

This study demonstrates the synthesis of an efficient photocatalyst, CuO/TiO2 heterojunction, for selective aerobic photo-oxidation of methanol to methyl formate. The CuO nanoparticles (size: 3.5 ± 1.0 nm) are particularly deposited at the {101} facet of anatase TiO2 nanosheets to minimize recombination of photo-generated electrons/holes. The photocatalysts are characterized by different methods, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy, and hydrogen temperature-programmed reduction (H2-TPR). The heterojunction catalysts exhibit an excellent photocatalytic performance under mild conditions (i.e., 25–45 °C and gas reactions under UV irradiation with a wavelength of 365 nm) for the selective photo-oxidation of methanol using 0.5 vol% oxygen (O2) as an oxidizing agent. The 5 wt% CuO/TiO2 photocatalyst exhibits a decent 95% methanol conversion with over 85% selectivity towards the formation of methyl formate. The by-product of the reaction is found to be merely CO2, which can be readily eliminated from the product. The formation rate for the methyl formate is 10.8 mmol g−1 h−1 at 25 °C, which is considerably higher than that for the corresponding CuO and TiO2 nanosheets as well as for conventional catalysts. The superior catalytic activity of the CuO/TiO2 is associated with its unique electronic structure and the synergistic effects at the interface of the photocatalysts' components. The results of this study offer guidelines for design of a new synthetic strategy for preparation of efficient photocatalysts for selective oxidation of methanol to methyl formate and related reactions. [ABSTRACT FROM AUTHOR]