The recent renaissance of black phosphorus (BP) as a two-dimensional (2D)layered

No abstract

We report our investigation on the intrinsic chemical activity of the anatase TiO 2 (001)-(1 × 4) reconstructed surface, using epitaxially grown anatase TiO 2 (001) thin films and using methanol molecules as a probe, characterized by combining scanning tunneling microscopy and temperature-programmed desorption. Our results provide direct evidence that the perfect (1 × 4) lattice sites of the surface are intrinsically quite inert for the reaction of methanol. We obtain that the activation energy for desorption of molecular methanol is about 0.55−0.64 eV, which is in good agreement with our first-principle calculations based on the structural model with 5-fold coordinated Ti atoms at the ridges of (1 × 4) reconstruction. We find that two types of defect sites, that is, reduced Ti pairs and partially oxidized Ti pairs, are responsible for the chemical activity of the surface, evidenced by the desorption of water due to the dehydrogenation of methanol at the defect sites. The methoxy left at the reduced Ti-pair sites further produced CH 3 radical, and the methoxy near the partially oxidized Ti-pair sites produced formaldehyde and methanol through disproportionation reaction. The determination of these intrinsic properties can be important to understanding the conflicting results from this surface in the literature and thus to reveal the actual reaction mechanisms.

No abstract

We investigate the dynamic processes of formaldehyde (HCHO) molecules on 5-fold-coordinated titanium (Ti 5c ) sites of rutile TiO 2 (110) surface using scanning tunneling microscopy (STM) together with density functional theory simulations. Our results show that the adsorbed HCHO molecules at Ti 5c sites are present as two types of protrusions, either centered at Ti 5c rows or centered at bridging oxygen (O b ) rows in the STM images, corresponding to the monodentate adsorption configuration through a O−Ti 5c bond and to the bidentate adsorption configuration through both O−Ti 5c and C−O b bonds, respectively, which can be well supported by the simulated images. It is also observed that the monodentate adsorption tends to spontaneously switch to bidentate adsorption. Our results confirm the existence of the energetically more favored bidentate adsorption for HCHO at Ti 5c sites. We obtain that the energy barriers are approximately 0.28 and 0.75 eV for the adsorbed HCHO molecules switching from monodentate adsorption to bidentate adsorption and reversely switching from bidentate adsorption to monodentate adsorption, respectively, from measurements of their dynamic processes. Our findings can well elucidate the missing signature of the energetically more favored bidentate configuration in some previous experiments and provide insightful understanding of formaldehyde on TiO 2 (110) surface.

When a metal single-atom (SA) catalyst is supported on a semiconducting photocatalyst, the charge transfer of the photoexcited carriers to metal SAs can provide a synergetic activity for the co-catalysts. Here, we report the interfacial electronic coupling of the Au SAs on the TiO2(110) surface using scanning tunneling microscopy/spectroscopy, in combination with first-principles calculations. Distinct energy and spatial distributions of the metal-induced gap states (MIGSs) are experimentally revealed for the Au SAs adsorbed at the terminal Ti sites and the oxygen vacancies. The localized MIGS below the Fermi level provides a dedicated channel for the transfer of a photoexcited hole from the TiO2 substrate to the adsorbed Au SAs. The hole can weaken the Ti–Au bonding and activate the diffusion of Au SAs. Our results shed light on combining the advantages of photocatalysis and metal SA catalysis using a co-catalyst, which is promising to promote chemical reactions at low temperatures.

Rhizospheric and endophytic fungi are key factors which influence plant fitness and soil fertility. Atractylodes macrocephala is one of the best-known perennial herbs used in traditional Chinese medicine. Continuous cropping has been shown to have a negative effect on its growth and renders it more susceptible to microbial pathogen attacks. In this study, we investigated the effects of continuous cropping on the endophytic and rhizospheric fungi associated with A.  macrocephala using culture-independent Illumina MiSeq. Continuous cropping was found to decrease fungal diversity inside plant roots, stems, leaves and tubers. Additionally, we found that the structure and diversity of rhizospheric and endophytic fungal communities were altered by root-rot disease. Fusarium was overrepresented among root-rot rhizospheric and endophytic fungi, indicating that it has a major negative impact on plant health during A.  macrocephala monocropping. Canonical correspondence analysis of the control and diseased samples revealed that pH, hydrolysis N, electrical conductivity and Hg content were well-correlated with fungal community composition during continuous cropping. Taken together, these results highlight the ecological significance of fungal communities in maintaining plant fitness and will guide the development strategies to attenuate the negative impacts of A.  macrocephala continuous cropping.

We here report our investigation on the photocatalytic reactions of methanol on the anatase TiO 2 (001)-(1×4) surface using scanning tunneling microscopy and temperature-programmed desorption. Our results show that in the reduced surface the Ti-pair defect sites are photoinactive, but in the reoxidized surface the partially oxidized defect sites are photoactive to dissociate methanol and methoxy to formaldehyde. The perfect (1×4) lattice sites are photoactive, even though they are inactive in thermally driven reaction. The photocatalytic reaction of methanol (CD 3 OH) at the perfect lattice sites is evidenced by the conversion of CD 3 OH to various other deuterated methanol (CD 3 OD and CD 2 HOH) and a small amount of formaldehyde (CD 2 O) after ultraviolet light irradiation, in contrast with no such conversion reaction in the nonirradiated sample. The production of CD 3 OD and CD 2 HOH can be attributed to the reverse reaction between the produced CD 2 O and the H or D adatoms during or after ultraviolet light irradiation, which also leads to the small amount of formaldehyde in final products. The identification of the site-dependent photocatalytic reactions of methanol, in addition to our recently characterized site-dependent thermally driven reactions, may provide an insightful understanding about the activity and photoactivity of the anatase TiO 2 (001)-(1×4) surface.