Unexpectedly efficient ion desorption of graphene-based materials.

Ion desorption is extremely challenging for adsorbents with superior performance, and widely used conventional desorption methods involve high acid or base concentrations and large consumption of reagents. Here, we experimentally demonstrate the rapid and efficient desorption of ions on magnetite-graphene oxide (M-GO) by adding low amounts of Al3+. The corresponding concentration of Al3+ used is reduced by at least a factor 250 compared to conventional desorption method. The desorption rate reaches ~97.0% for the typical radioactive and bivalent ions Co2+, Mn2+, and Sr2+ within ~1 min. We achieve effective enrichment of radioactive 60Co and reduce the volume of concentrated 60Co solution by approximately 10 times compared to the initial solution. The M-GO can be recycled and reused easily without compromising its adsorption efficiency and magnetic performance, based on the unique hydration anionic species of Al3+ under alkaline conditions. Density functional theory calculations show that the interaction of graphene with Al3+ is stronger than with divalent ions, and that the adsorption probability of Al3+ is superior than that of Co2+, Mn2+, and Sr2+ ions. This suggests that the proposed method could be used to enrich a wider range of ions in the fields of energy, biology, environmental technology, and materials science.

Airy transform of Laguerre-Gaussian beams.

Airy transform of Laguerre-Gaussian (LG) beams is investigated. As typical examples, the analytic expressions for the Airy transform of LG01, LG02, LG11, and LG12 modes are derived, which are special optical beams including the Airy and Airyprime functions. Based on these analytical expressions, the Airy transform of LG01, LG02, LG11, and LG12 modes are numerically and experimentally investigated, respectively. The effects of the control parameters α and ß on the normalized intensity distribution of a Laguerre-Gaussian beam passing through Airy transform optical systems are investigated, respectively. It is found that the signs of the control parameters only affect the location of the beam spot, while the sizes of the control parameters will affect the characteristics of the beam spot. When the absolute values of the control parameters α and ß decrease, the number of the side lobes in the beam spot, the beam spot size, and the Airy feature decrease, while the Laguerre-Gaussian characteristic is strengthened. By altering the control parameters α and ß, the performance of these special optical beams is diversified. The experimental results are consistent with the theoretical simulations. The Airy transform of other Laguerre-Gaussian beams can be investigated in the same way. The properties of the Airy transform of Laguerre-Gaussian beams are well demonstrated. This research provides another approach to obtain special optical beams and expands the application of Laguerre-Gaussian beams.

Beam propagation factor and kurtosis parameter of hollow vortex Gaussian beams: an alternative method.

Based on the second-order moments, an analytical and concise expression of the beam propagation factor of a hollow vortex Gaussian beam has been derived, which is applicable for an arbitrary topological charge $m$m. The beam propagation factor is determined by the beam order $n$n and the topological charge $m$m. With increasing the topological charge $m$m, the beam propagation factor increases. However, the effect of the beam order $n$n on the beam propagation factor is associated with the topological charge $m$m. By using the transformation formula of higher-order intensity moments, an analytical expression of the kurtosis parameter of a hollow vortex Gaussian beam passing through a paraxial and real $ABCD$ABCD optical system has been presented. The kurtosis parameter is determined by the beam order $n$n, the topological charge $m$m, and the position of observation plane $ \eta $η. The influence of the beam order $n$n on the kurtosis parameter is related with the topological charge $m$m and the position parameter $ \eta $η. When the beam order $n$n is larger than 1, the kurtosis parameter in different observation $\eta$η-planes decreases and tends to a stable value with increasing the topological charge $m$m. When $m = \pm {2}n$m=±2n, the kurtosis parameter is independent of the position parameter $ \eta $η and keeps unvaried during the beam propagation. Regardless of the values of $n$n and $m$m, the kurtosis parameter must tend to a saturated value or a stable value as the position parameter $ \eta $η increases to a sufficiently large value. This research is beneficial to the practical application of a hollow vortex Gaussian beam.

ß-FeSe nanorods composited g-C3N4 with enhanced photocatalytic efficiency.

A series of ß-FeSe nanorods composited g-C3N4 were prepared. The structure, morphology, chemical state, photocatalytic activity, electrochemical impedance and photoluminescence of ß-FeSe/g-C3N4 composites were well characterized. It is found that the decolourization rate of 3 wt% ß-FeSe/g-C3N4 composites reaches 4.4 times than that of g-C3N4. The improved photocatalytic properties could be ascribed to the reduced recombination of photogenerated electrons and holes, which is derived from the excellent ability of ß-FeSe to capture and transfer electrons. This work provides an alternative co-catalyst for decolourizing organic matter.

Improved oxygen evolution activity of IrO2 by in situ engineering of an ultra-small Ir sphere shell utilizing a pulsed laser.

Noble metal-based catalysts are vital electrocatalysts for the oxygen evolution reaction (OER), which is a half reaction among multiple renewable energy-related reactions. To fully exploit their potential as efficient OER catalysts, we developed a fast one-step strategy to engineer a unique nanostructure for the benchmark catalyst IrO2 utilizing an ultra-fast pulse laser, through which a shell of ultra-small Ir spheres with a diameter of ca. 2 nm is in situ engineered around the IrO2 core. The creation of the Ir sphere shell not only increases the electrochemical surface area, but also improves the electrical conductivity of the electrocatalyst. The as-engineered IrO2@Ir architecture exhibits extremely high electrocatalytic activity towards the OER, revealing an overpotential of 255 mV at 10 mA cm-2 and Tafel slope of 45 mV dec-1. These values are much lower than those observed for the unmodified structure. Furthermore, the catalytic performance is the best among all the noble metal-based OER catalysts. This work may open a new avenue to efficiently improve the catalytic activity of noble metal-based catalysts and significantly advance the development in the energy industry.

Durable Broadband and Omnidirectional Ultra-antireflective Surfaces.

Light reflection from surfaces is ubiquitous in nature. Diverse optoelectronic devices need durable, omnidirectional, and transparent ultra-antireflective surfaces. Here, we engineered antireflective transparent surfaces composed of silica nanocaps through a simple thermal treatment of a silica-coated monolayer colloidal crystal template. The relationship between the structure and the antireflective performance of the silica nanocaps was systematically studied both experimentally and numerically. On the basis of the understanding of the structure-antireflection relationships, ultra-antireflection coatings with a transmittance of ∼98.75 ± 0.15% in the visible wavelength range were prepared by fabricating two differently sized silica nanocaps. More importantly, the antireflection of the coatings formed by two differently sized nanocaps demonstrated poor dependence on the angle of the incident light (i.e., omnidirectionality). The reflection is <2.5% even at an incident angle of 60°. The prepared ultra-antireflective silica nanocap coatings outperform state-of-the-art transparent antireflective coatings regarding the antireflection performance, the wavelength range, and the omnidirectionality. The silica nanoshells were welded together with the underlying fused silica. Therefore, they can sustain common mechanical friction and scratching, demonstrating extraordinary mechanical durability as verified by sand abrasion tests. Further, the silanized silica nanocaps turned out to be hydrophobic with an outstanding self-cleaning performance without prominently influencing the transmittance. The durable and omnidirectional ultra-antireflective transparent silica nanocaps will have promising applications in solar energy conversion and storage, displays, optical lenses, and a wide range of optoelectronic devices.

Pseudopotential generation.

Different classes of first-principle pseudopotentials are compared and various schemes for pseudopotential generation based on norm conservation are discussed in this paper. BHS (Bachelet, Hamann, and Schlüter)-scheme and V (Vanderbilt)-modifications are used to derive the KB (Kleinman and Bylander)-pseudopotentials and pseudo wave functions of bismuth. Quality test of pseudopotentials shows that no ghost states occur in the logarithmic derivatives of pseudo wave functions of Bismuth. The obtained bond length of bismuth dimer with this type of pseudopotentials is in good agreement with previous accurately calculated ab initio quantum chemical result.