Two-dimensional g-C3N4/Ca2Nb2TaO10 nanosheet composites for efficient visible light photocatalytic hydrogen evolution

Scalable g-CN nanosheet powder catalyst was prepared by pyrolysis of dicyandiamide and ammonium chloride followed by ultra-sonication and freeze-drying. Nanosheet composite that combines the g-CN nanosheets and CaNbTaO nanosheets with various ratios were developed and applied as photocatalysts for solar hydrogen generation. Systematic studies reveal that the g-CN/CaNbTaO nanosheet composite with a mass ratio of 80:20 shows the best performance in photocatalytic H evolution under visible light-irradiation, which is more than 2.8 times out-performing bare g-CN bulk. The resulting nanosheets possess a high surface area of 96\ua0m/g, which provides abundance active sites for the photocatalytic activity. More importantly, the g-CN/CaNbTaO nanosheet composite shows efficient charge transfer kinetics at its interface, as evident by the photoluminescence measurement. The intimate interfacial connections and the synergistic effect between g-CN nanosheets and CaNbTaO nanosheets with cascading electrons are efficient in suppressing charge recombination and improving photocatalytic H evolution performance

Multiple resolution seismic attenuation imaging at Mt. Vesuvius

A three-dimensional S wave attenuation tomography of Mt. Vesuvius has been ob- tained with multiple measurements of coda-normalized S-wave spectra of local small magnitude earthquakes. We used 6609 waveforms, relative to 826 volcano-tectonic earthquakes, located close to the crater axis in a depth range between 1 and 4 km (below the sea level), recorded at seven 3-component digital seismic stations. We adopted a two-point ray-tracing; rays were traced in an high resolution 3-D velocity model. The spatial resolution achieved in the attenuation tomography is comparable with that of the velocity tomography (we resolve 300 m side cubic cells). We statisti- cally tested that the results are almost independent from the radiation pattern. We also applied an improvement of the ordinary spectral-slope method to both P- and S-waves, assuming that the di¤erences between the theoretical and the experimental high frequency spectral-slope are only due to the attenuation e¤ects.We could check the coda-normalization method comparing the S attenuation image obtained with the two methods. The images were obtained with a multiple resolution approach. Results show the general coincidence of low attenuation with high velocity zones. The joint interpretation of velocity and attenuation images allows us to interpret the low attenuation zone intruding toward the surface until a depth of 500 meters below the sea level as related to the residual part of solidi ed magma from the last eruption. In the depth range between -700 and -2300 meters above sea level, the images are consistent with the presence of multiple acquifer layers. No evidence of magma patches greater than the minimum cell dimension (300m) has been found. A shallow P wave attenuation anomaly (beneath the southern ank of the volcano) is consitent with the presence of gas saturated rocks. The zone characterized by the maximum seismic energy release cohincides with a high attenuation and low velocity volume, interpreted as a cracked medium

Dual modification of TiO2 nanorods for selective photoelectrochemical detection of organic compounds

Selective detection of organic compounds in water body is both desirable and challenging for photoelectrocatalytic (PEC) sensors. In this work, tunable oxidation capability is designed and achieved by modifying titanium dioxide nanorod arrays (TiO) photoelectrodes with nano-sized plasmonic gold (Au) particle deposition and subsequent hydrogenation treatment (i.e. Au@H-TiO). The effective incorporation of Au nanoparticles onto the TiO nanorods induces a plasmonic effect and extends light absorption from ultraviolet (UV) to the visible light range while the hydrogenation process dramatically improves PEC oxidation activity. Under visible light, the Au@H-TiO electrode exhibits selective detection capability to labile organic compounds. This excellent selectivity is demonstrated by a wide linear relationship between photocurrent and the concentration of different types of sugars, including glucose, fructose, sucrose and lactose in the presence of various concentrations of the aromatic compound potassium hydrogen phthalate (KHP). Furthermore, the modified electrode can also undiscriminately detect all kinds of organic compounds in a rapid manner under UV irradiation due to the strong oxidation capability. Such a unique feature of the tunable oxidation capability bestows the Au@H-TiO photoelectrodes a new generation of the PEC sensors for selective and collective degradation of organic compounds

Nanohybrid materials of titania nanosheets and plasmonic gold nanoparticles for effective hydrogen evolution

A new type of nanocomposites containing titania and gold were prepared via the coupling between exfoliated TiO nanosheets and surfactant-capped Au nanoparticles, followed by flocculation and calcination. After hybridization with TiO nanosheets, octahedral Au nanoparticles were embedded intimately into the matrix of titania, leading to a broad absorption peak assigned to surface plasmon resonance (SPR) effect in the visible region. The obtained nanocomposite exhibited remarkably improved photocatalytic hydrogen evolution performance compared to naked titania and conventional titania with photodeposited Au co-catalyst, due to the special SPR effect of the relatively large octahedral Au nanoparticles. Through control experiments, we demonstrated that the octahedral Au nanoparticles mainly functioned as local light intensifier and photon scattering agent

Recent progress on visible light responsive heterojunctions for photocatalytic applications

Photocatalysis has attracted much attention in recent years due to its potential in solving energy and environmental issues. Even though numerous achievements have been made, the photocatalytic systems developed to date are still far from practical applications due to the low efficiency and poor durability. Efficient light absorption and charge separation are two of the key factors for the exploration of high performance photocatalytic systems, which is generally difficult to be obtained in a single photocatalyst. The combination of various materials to form heterojunctions provides an effective way to better harvest solar energy and to facilitate charge separation and transfer, thus enhancing the photocatalytic activity and stability. This review concisely summarizes the recent development of visible light responsive heterojunctions, including the preparation and performances of semiconductor/semiconductor junctions, semiconductor/cocatalyst junctions, semiconductor/metal junctions, semiconductor/non-metal junctions, and surface heterojunctions, and their mechanism for enhanced light harvesting and charge separation/transfer

Characteristics of PM10 Levels Monitored in Bangkok and Its Vicinity Areas, Thailand

The ambient air concentrations of PM10 were observed in Bangkok and its vicinity areas including Nonthaburi and Nakhon Pathom, Thailand. The selected study areas are located near heavy-traffic roads with a high concentration of traffic-related air pollution. The ambient air samples were collected in the winter season (October 2019 to February 2020). The highest average level of PM10 was found in Nonthaburi (66.63 µg/m3), followed by Bangkok (56.79 µg/m3) and Nakhon Pathom (40.18 µg/m3), respectively. The morphology of these particles is typically spherical and irregular shape particles. At the sampling site in Bangkok, these particles are primarily composed of C, O, and Si, and a certain amount of metals such as Fe, Cu, and Cr. Some trace amount of other elements such as Ca, Na, and S are present in minor concentration. The particles collected from Nakhon Pathom and Nonthaburi sampling sites contain the main abundant elements C, O, and Si, followed by Cu, Cr, S, Fe, Ca, and Na, respectively. These particles are an agglomeration of carbon particles resulting from the incomplete combustion of organic matter. Their origin may be associated with road dust, vehicle emission, and the erosion of building products. It can be noted that the levels and characteristics of PM10 are key factors in understanding the behavior of the particles in not only atmospheric visibility but also human health risks

Controllable synthesis of concave cubic gold core-shell nanoparticles for plasmon-enhanced photon harvesting

Well-defined core-shell nanoparticles (NPs) containing concave cubic Au cores and TiO2 shells (CA@T) were synthesized in colloidal suspension. These CA@T NPs exhibit Localized Surface Plasmon Resonance (LSPR) absorption in the NIR region, which provides a unique property for utilizing the low energy range of the solar spectrum. In order to evaluate the plasmonic enhancement effect, a variety of CA@T NPs were incorporated into working electrodes of dye-sensitized solar cells (DSSCs). By adjusting the shell thickness of CA@T NPs, the plasmonic property can be tuned to achieve maximum photovoltaic improvement. Furthermore, the DSSC cells fabricated with the CA@T NPs exhibit a remarkably plasmonic assisted conversion efficiency enhancement (23.3%), compared to that (14.8%) of the reference cells assembled with spherical Au@TiO2 core-shell (SA@T) NPs under similar conditions. Various characterizations reveal that this performance improvement is attributed to the much stronger electromagnetic field generated at the hot spots of CA@T NPs, resulting in significantly higher light harvesting and more efficient charge separation. This study also provides new insights into maximizing the plasmonic enhancement, offering great potential in other applications including light-matter interaction, photocatalytic energy conversion and new-generation solar cells

Green synthesis of porous three-dimensional nitrogen-doped graphene foam for electrochemical applications

A facile and green approach was developed for the production of porous three-dimensional (3D) nitrogen-doped graphene with a foam structure. In comparison with conventional methods, this green approach uses environmental precursors in the preparation of graphene products. The resulting crystalline graphene foam product exhibited a uniform structure with large surface area. These appealing features render the prepared graphene foam product a prospective backbone for producing 3D charge-transport networks. The 3D graphene foam products were employed as the skeleton with an interconnected network for lithium-ion batteries. The lithium-ion batteries with the 3D porous foam structure exhibit superior cycling stability and good rate capability. There is no capacity loss after 800 cycles because the capacity stabilized for the first few cycles, and the lithium-ion batteries with 3D graphene foam showed a discharge capacity of 180 mA h g(-1) at a current density of 1000 mA g(-1). This superior cycling stability and good rate capability was ascribed to the 3D structure with an interconnected porous network and the nitrogen-doping strategy for improved conductive properties of graphene foam, which produces an efficient 3D charge-transport network. The configuration of this 3D transport network in lithium-ion cells not only can improve the electron-transport efficiency but also can suppress the volume effect during charge/discharge cycling. Besides, nitrogen doping could enhance the formation of chemical bonding between carbon and the nearby nitrogen atoms, which could accelerate the diffusion of lithium ions through the whole graphene network

Efficient and Rapid Photocatalytic Degradation of Methyl Orange Dye Using Al/ZnO Nanoparticles

ZnO and Aluminum doped ZnO nanoparticles (Al/ZnO NPs) were successfully synthesized by the sol-gel method. Together with the effect of calcination temperatures (200, 300 and 400 °C) and Al dosage (1%, 3%, 5% and 10%) on structural, morphological and optical properties of Al/ZnO NPs, their photocatalytic degradation of methyl orange (MO) dye was investigated. The calcination temperatures at 200, 300 and 400 °C in forming structure of ZnO NPs led to spherical nanoparticle, nanorod and nanoflake structures with a well-crystalline hexagonal wurtzite, respectively. The ZnO NPs calcined at 200 °C exhibited the highest specific surface area and light absorption property, leading to the MO removal efficiency of 80% after 4 h under the Ultraviolet (UV) light irradiation. The MO removal efficiency was approximately two times higher than the nanoparticles calcined at 400 °C. Furthermore, the 5% Al/ZnO NPs exhibited superior MO removal efficiency of 99% in only 40 min which was approximately 20 times enhancement in photocatalytic activity compared to pristine ZnO under the visible light irradiation. This high degradation performance was attributed to the extended light absorption, narrowed band gap and effective suppression of electron–hole recombination through an addition of Al metal

Hierarchical macro/mesoporous NiO as stable and fast-charging anode materials for lithium-ion batteries

A new type of hierarchical macro/mesoporous NiO is prepared from a simple thermolysis of nickel dimethylglyoxime complex, of which the drastic mass loss enables the formation of hierarchical porous structure in the crystalline NiO. The products exhibit excellent performance as anodes for lithium-ion batteries, delivering a remarkable discharge capacities of 911.1\ua0mA\ua0h g after 200 charging/discharging cycles at a current density of 0.5\ua0A\ua0g, and 558\ua0mA\ua0h g after 1000 cycles at 2\ua0A\ua0g. Such superior performance of the materials over other NiO counterparts is associated with markedly reduced internal resistance endowed by a large proportion of macropores in the hierarchical structure