Core–Shell Photoanodes for Photoelectrochemical Water Oxidation

Photoelectrochemical (PEC) water splitting into hydrogen and oxygen is a promising solution for the conversion and storage of solar energy. Because sluggish water oxidation is the bottleneck of water splitting, the design and preparation of an efficient photoanode is intensively investigated. Currently, all known photoanode materials suffer from at least one of the following drawbacks: ① low carriers separation efficiency; ② sluggish surface water oxidation reaction; ③ poor long-term stability; ④ insufficient water adsorption and gas desorption. Core–shell configurations can endow a photoanode with improved activity and stability by coating an overlayer that plays energetic, catalytic, and/or protective roles. The construction strategy has an important effect on the activity of a core–shell photoanode. Nonetheless, the mechanism for the improvement of performance is still ambiguous and is worthy of a closer examination. In this review, the successes and challenges of core–shell photoanodes for water oxidation, focusing on synthesis strategies as well as functionalities (facilitating carrier separation, surface reaction promotion, corrosion prevention, and bubble detachment) are explored. Finally, the perspectives of this class of materials in terms of new opportunities and efforts are discussed.     

MBE-grown ZnSSe thin films on ITO substrates for liquid-crystal light valve applications

The MBE growth of ZnSSe alloy thin films on ITO substrates using ZnS and Se sources was studied and various structural and opto-electronic properties of the as-grown thin films were characterised. The XRD rocking curves resulting from these films indicate that the as-grown polycrystalline ZnSSe thin films have a preferred orientation along (1 1 1) direction. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks were found to show a strong growth temperature dependence with the optimised temperature at about 290°C. TEM measurements done on these thin films also indicate a similar growth temperature dependence. The TEM cross-sectional micrograph of the sample grown at the optimised temperature shows a well-defined columnar structure whose nucleation seems to be highly correlated with the ITO grains. UV responsivity as high as 0.01 A/W and more than three orders of magnitude in rejection power for wavelengths longer than 450 nm have been achieved. It was also found that the sample grown at the optimised temperature has the lowest resistivity of 4.3×10¹¹ Ω cm, which provides a good match with that of a liquid-crystal layer. These results indicate that MBE-grown ZnSSe thin film is a promising candidate as the photoconductive material of liquid-crystal light valves for UV imaging applications.     

All‐Cellulose‐Based Quasi‐Solid‐State Sodium‐Ion Hybrid Capacitors Enabled by Structural Hierarchy

Na‐ion hybrid capacitors consisting of battery‐type anodes and capacitor‐style cathodes are attracting increasing attention on account of the abundance of sodium‐based resources as well as the potential to bridge the gap between batteries (high energy) and supercapacitors (high power). Herein, hierarchically structured carbon materials inspired by multiscale building units of cellulose from nature are assembled with cellulose‐based gel electrolytes into Na‐ion capacitors. Nonporous hard carbon anodes are obtained through the direct thermal pyrolysis of cellulose nanocrystals. Nitrogen‐doped carbon cathodes with a coral‐like hierarchically porous architecture are prepared via hydrothermal carbonization and activation of cellulose microfibrils. The reversible charge capacity of the anode is 256.9 mAh g^?1 when operating at 0.1 A g^?1 from 0 to 1.5 V versus Na⁺/Na, and the discharge capacitance of cathodes tested within 1.5 to 4.2 V versus Na⁺/Na is 212.4 F g^?1 at 0.1 A g^?1. Utilizing Na⁺ and ClO₄^? as charge carriers, the energy density of the full Na‐ion capacitor with two asymmetric carbon electrodes can reach 181 Wh kg^?1 at 250 W kg^?1, which is one of the highest energy devices reported until now. Combined with macrocellulose‐based gel electrolytes, all‐cellulose‐based quasi‐solid‐state devices are demonstrated possessing additional advantages in terms of overall sustainability.     

Active Microwave Remote Sensing of an Anisotropic Random Medium Layer

A two-layer anisotropic random medium model has been developed to study the active remote sensing of the Earth. The dyadic Green's function for a two-layer anisotropic medium is developed and used in conjunction with the first-order Born approximation to calculate the backscattering coefficients. It is shown that strong cross-polar-ization occurs in the single scattering process and is indispensable in the interpretation of radar measurements of sea ice at different frequencies, polarizations, and viewing angles. The effects of anisotropy on the angular responses of backscattering coefficients are also illustrated trated.     

Effects of sulfonation on bis-styrylbiphenyl fluorescent whitening agents for polypropylene

Three derivatives of bis-styrybiphenyl with different degrees of sulfonation to be used as fluorescent whitening agents (FWAs) were synthesized. Studies on their spectroscopic properties were performed using a combination of computational methods. Whitening effects of FWAs and the improved thermal stability of polypropylene (PP) were investigated. The morphology of plastic samples was examined by scanning electronic microscopy (SEM). In order to improve the compatibility between FWA and PP, PP grafted with maleic anhydride (MAH) was applied as compatibilizer. The optical properties were further clarified by the results of frontier molecular orbital modeling, which show that the presence of sulfonic sodium group leads to a red shift of maximum UV absorption wavelength and a low HOMO–LUMO energy band gap. It is observed that the addition of 0.010 wt % of the sulfonated FWA would result in the expected whitening effect as well as improved PP thermal stability, while at or above 0.015 wt %, such effects worsen sharply owing to phase separation. Furthermore, the use of MAH-grafted PP as compatibilizer results in improvement of phase behavior and thermal stability. The study provides new insights into the effect of FWA structure on the properties of PP that are related to the whitening of the material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47635.     

Solid superbase derived from lanthanum–magnesium composite oxide and its catalytic performance in the knoevenagel condensation under solvent-free condition

We report for the first time the synthesis of a novel solid superbase that was derived from lanthanum–magnesium composite oxide and KOH through thermal treatment. The as-prepared material shows base strength (H_–) above 26.5 and is a high-efficiency catalyst for solvent-free Knoevenagel condensation at room temperature. The results of the present study open up a new dimension for the use of composite oxides as new support materials in the synthesis of superbases.     

Fast removal of Pb(II) and Cu(II) from contaminated water by groundwater treatment waste: impact of sorbent composition

ABSTRACT

A non-hazardous groundwater treatment waste (GWTW) was examined as a low-cost sorbent for Pb(II) and Cu(II) ions. The content of the dominant elements in GWTW was as follows: 78% Fe₂O₃, 7.4% P₂O₅, 7.4% CaO and 5.2% SiO₂. The removal of Pb(II) and Cu(II) was fast, and more than 67–95% of ions were accumulated by GWTW during the first 3 min. The sorption capacity of GWTW depends on solution pH, concentration and temperature. Equilibrium data fitted well with Langmuir–Freundlich and Langmuir-partition models. The inherently formed nano-adsorbent could be utilized for the treatment of water contaminated with Pb(II) and Cu(II) ions.     

Three-dimensional ordered macroporous bismuth vanadates: PMMA-templating fabrication and excellent visible light-driven photocatalytic performance for phenol degradation

Three-dimension ordered macroporous (3D-OM) bismuth vanadates with a monoclinic crystal structure and high surface area (18-24 m(2) g(-1)) have been prepared using ascorbic acid (AA)- or citric acid (CA)-assisted poly(methyl methacrylate) (PMMA)-templating strategy with bismuth nitrate and ammonium metavanadate as the metal sources, HNO(3) as the pH adjuster and ethylene glycol and methanol as the solvent. The materials were characterized by a number of analytical techniques. The photocatalytic performance of the porous BiVO(4) samples was evaluated for the degradation of phenol in the presence of a small amount of H(2)O(2) under visible light illumination. The effects of the initial phenol concentration and the H(2)O(2) amount on the photocatalytic activity of the photocatalyst were examined. It is shown that the chelating agent, AA or CA, and the amount in which it is added had a significant impact on the quality of the 3D-OM structure, with a "(Bi + V):chelating agent" molar ratio of 2:1 being the most appropriate. Among the as-prepared BiVO(4) samples, the one with a surface area of ca. 24 m(2) g(-1) showed the best visible light-driven photocatalytic performance for phenol degradation (phenol conversion = ca. 94% at phenol concentration = 0.1 mmol L(-1) and in the presence of 0.6 mL H(2)O(2)). A higher phenol conversion could be achieved within the same reaction time if the phenol concentration in the aqueous solution was lowered, but an excess amount of H(2)O(2) was not a favorable factor for the enhancement of the catalytic activity. It is concluded that the excellent photocatalytic activity of 3D-OM BiVO(4) is due to the high quality 3D-OM structured BiVO(4) that has a high surface area and surface oxygen vacancy density. We are sure that the 3D-OM material is a promising photocatalyst for the removal of organics from wastewater under visible light illumination.     

Methane Aromatization over 2 wt% Mo/HZSM-5 in the Presence of O2 and NO

In the non-oxidative aromatization reaction (temperature = 770 C, flow rate = 34 ml min^-1), 2 wt% Mo/HZSM-5 deactivated after 4 h due to severe coking. We observed that with a suitable amount of O₂ (5.3 vol%) in the methane feed, the catalyst could last for more than 6 h with a ca. 4% yield of aromatics at 770 °C. Depending on the concentration of O₂ or the reaction temperature, there are three reaction zones in the catalyst bed: (i) methane oxidation; (ii) methane reforming; and (iii) methane aromatization. CO and H₂ produced in the first two zones are accountable for stability amelioration of the catalyst. The addition of NO exhibited similar effects on the reaction. Further increase in O₂ (8.4 vol%) or NO (14.2 vol%) concentration would result in CO and CO₂ being the predominant carbon-containing products; C₂H₄ and C₂H₆ were generated in small amounts and no aromatics were detected.