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With the increased application of batteries in powering electric vehicles as well as potential contributions to utility-scale storage, there remains a need to identify and develop efficient and sustainable active materials for use in lithium (Li)- and sodium (Na)-ion batteries. Organic cathode materials provide a desirable alternative to inorganic counterparts, which often come with harmful environmental impact and supply chain uncertainties. Organic materials afford a sustainable route to active electrodes that also enable fine-tuning of electrochemical potentials through structural design. Here, we report a bis-anthraquinone-functionalized s-indacene-1,3,5,7(2H,6H)-tetraone (BAQIT) synthesized using a facile and inexpensive route as a high-capacity cathode material for use in Li- and Na-ion batteries. BAQIT provides multiple binding sites for Li- and Na-ions, while maintaining low solubility in commercial organic electrolytes. Electrochemical Li-ion cells demonstrate excellent stability with discharge capacities above 190 mAh g-1 after 300 cycles at a 0.1C rate. The material also displayed excellent high-rate performance with a reversible capacity of 142 mAh g-1 achieved at a 10C rate. This material affords high power capabilities superior to current state-of-the-art organic cathode materials, with values reaching 5.09 kW kg-1. The Na-ion performance was also evaluated, exhibiting reversible capacities of 130 mAh g-1 after 90 cycles at a 0.1C rate. This work offers a structural design to encourage versatile, high-power, and long cycle-life electrochemical energy-storage materials.

SrTiO3 cubes with tunable sizes of 160–290 nm have been synthesized by mixing TiCl4, SrCl2, and LiOH in pure ethanol or a water/ethanol mixed solution at just 70 °C for 3 h. Replacing water/ethanol...

Ag3PO4 nanoparticles were lightly deposited on Cu2O cubes, octahedra, and rhombic dodecahedra for facet-dependent photocatalytic degradation of methyl orange. Cu2O cubes remain inactive after loadi...

ZnS particles were grown over Cu2O cubes, octahedra, and rhombic dodecahedra for examination of their facet-dependent photocatalytic behaviors. After ZnS growth, Cu2O cubes stay photocatalytically inactive. ZnS-decorated Cu2O octahedra show enhanced photocatalytic activity, resulting from better charge carrier separation upon photoexcitation. Surprisingly, Cu2O rhombic dodecahedra give greatly suppressed photocatalytic activity after ZnS deposition. Electron paramagnetic resonance spectra agree with these experimental observations. Time-resolved photoluminescence profiles provide charge-transfer insights. The decrease in the photocatalytic activity is attributed to an unfavorable band alignment caused by significant band bending within the Cu2O(110)/ZnS(200) plane interface. A modified Cu2O-ZnS band diagram is presented. Density functional theory calculations generating plane-specific band energy diagrams of Cu2O and ZnS match well with the experimental results, showing that charge transfer across the Cu2O(110)/ZnS(200) plane interface would not happen. This example further illustrates that the actual photocatalysis outcome for semiconductor heterojunctions cannot be assumed because interfacial charge transfer is strongly facet-dependent.

Development of layered perovskites for sunlight-driven catalysis has gained a lot of attention in contemporary inorganic materials research. While the compositional modifications of three-dimensional perovskites are ubiquitous, they are infrequent in the case of layered perovskites particularly with niobates when the perovskite layer thickness is low. We report here the solid state synthesis of a series of lead-free double-layer Aurivillius niobates, LaBi2Nb1.5M0.5O9 (M = Cr, Mn, Fe, Co), by adopting a heterovalent coupled substitution strategy with SrBi2Nb2O9. Rietveld structure refinements of the compounds using P-XRD data suggest the formation of 3dn transition metal incorporated double-layer Aurivillius niobates in the non-centrosymmetric A21am space group, isostructural with the parent. The compounds show optical absorption in the visible region with the absorption tail extending up to ∼650 nm and band gaps ranging from 2.25–2.94 eV. While the compounds show paramagnetic behaviour with no indication of magnetic phase transition or ordering in the temperature range 5–300 K, the Mn compound stabilizes with a low-spin (LS) configuration in contrast to all others (Cr, Fe and Co compounds), which adopt a high-spin (HS) configuration. The stabilization of the LS configuration (t42g) of the Mn compound occurs with eg → t2g electron redistribution due to the suppression of first-order Jahn–Teller (FOJT) distortion by the dominating second-order Jahn–Teller (SOJT) distortion of Nb5+ (4d0). The compounds exhibit photocatalytic rhodamine B degradation at pH 2 within 50–110 minutes under natural sunlight-irradiation and remain stable after five consecutive degradation cycles maintaining their activity largely intact. The heterovalent coupled substitution strategy adopted here will open up possibilities for transforming many other UV-active layered niobates into sunlight-active compounds without using toxic Pb or expensive Ag, while the paramagnetic nature of the compounds will be helpful in post-catalytic magnetic separation of the catalysts. It is believed that the electronic instability of the t32ge1g configuration of Mn due to competing FOJT and SOJT effects may have far-reaching consequences in modifying its magneto-structural and electron transport properties.

Semiconductor photocatalysis under natural sunlight is an emergent area in contemporary materials research, which has attracted considerable attention toward the development of catalysts for environmental remediation using solar energy. A series of five-layer Aurivillius-phase perovskites, Bi5ATi4FeO18 (A = Ca, Sr, and Pb), are synthesized for the first time. Rietveld refinements of the powder X-ray diffraction data indicated orthorhombic structure for the Aurivillius phases with Fe largely occupying the central octahedral layer, whereas the divalent cations (Ca, Sr, and Pb) are statistically distributed over the cubo-octahedral A-sites of the perovskite. The compounds with visible-light-absorbing ability (Eg ranging from ∼2.0 to 2.2 eV) not only exhibit excellent collective photocatalytic degradation of rhodamine B–methylene blue (MB) and rhodamine B–rhodamine 6G mixture at pH 2 but also show almost 100% photocatalytic selective degradation of MB from the rhodamine B–MB mixture at pH 11 under natural solar irradiation. The selectivity in the alkaline medium is believed to originate from the combined effect of the photocatalytic degradation of MB by the Aurivillius-phase perovskites and the photolysis of MB. Although a substantial decrease in MB adsorption from the mixed dye solution (MB + RhB) together with slower MB photolysis at the neutral pH makes the selective MB degradation sluggish, the compounds showed excellent photocatalytic degradation activity and chemical oxygen demand removal efficacy toward individual RhB (at pH 2) and MB (at pH 11) under sunlight irradiation. The catalysts are exceptionally stable and retain good crystallinity even after five successive cyclic runs without any noticeable loss of activity in both the acidic and alkaline media. The present work provides an important insight into the development of layered perovskite photocatalysts for collective degradation of multiple pollutants and selective removal of one or multiple pollutants from a mixture. The later idea may open up new possibilities for recovery/purification of useful chemical substances from the contaminated medium through selective photocatalysis.

Wurtzite CdS nanoparticles have been lightly deposited on Cu2O cubes, octahedra, and rhombic dodecahedra to examine facet effects on the interfacial charge transfer in a photocatalytic reaction. Instead of an expected photocatalytic activity enhancement on the basis of a favorable band alignment at the heterojunction, CdS-decorated Cu2O octahedra and rhombic dodecahedra show drastically reduced photocatalytic activities. Further increasing the CdS deposition amount leads to complete suppression of photocatalytic activity. Cu2O cubes remain inactive even after CdS deposition. Transmission electron microscopy analysis reveals epitaxial growth of the (101) planes of CdS on the (110) planes of a Cu2O rhombic dodecahedron, whereas the (110) planes of CdS align parallel to the (111) planes of a Cu2O octahedron. Because facet-dependent photocatalytic activity can be understood from different degrees of band bending at the crystal surfaces, significantly upward bending for the CdS-contacting planes can explain th...

Synthesis of new semiconductors responsive under visible light/sunlight has been considered as an elegant strategy of photocatalyst development for efficient solar light harvesting applications. In the present study, new La-substituted layered Sillen-Aurivillius oxyhalide intergrowths, Bi 3 LaNbO 8 X (X=Cl, Br), have been prepared by solid state reaction. The compounds are characterized by powder X-ray diffraction ( p -XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) studies. The P-XRD data revealed formation of Sillen-Aurivillius hybrid perovskites isostructural to the parent compounds, Bi 4 NbO 8 X (X = Cl, Br), and the FE-SEM-EDS confirmed the morphology to be agglomerates of submicron-sized particles with desired compositions as expected. The band gap for all the pristine oxyhalides lie in range 2.43–2.54 eV indicative of their sunlight active nature. The sunlight-driven photocatalytic activity studies through Rhodamine B (RhB) degradation unveiled excellent dye degradation efficiencies over Bi 3 LaNbO 8 Cl and Bi 3 LaNbO 8 Br in the acidic medium. The enhanced photocatalytic activities are attributed to superior charge carrier separation and dye adsorption in the La-substituted phases. Scavenger tests demonstrated the active role of hole and hydroxyl radical as key species in the RhB degradation under sunlight in presence of Bi 3 LaNbO 8 Br. The demonstration of enhanced activity under natural sunlight is significant in future development of environmental remediation technologies by harvesting solar energy.

In this work, we report a strategy for synthesizing morphology-controlled hierarchical self-assembled, three dimensional (3D) porous wool ball (W-ball) like zinc oxides (ZnO) with excellent catalytic performance. A precursor, hydrozincite (Zn 5 (CO 3 ) 2 (OH) 6 ), was first synthesized via a green urea-glycerol assisted template-free hydrothermal approach, which was calcined to form crystalline 3D porous ZnO having nanostructured morphology. The effect of synthesis process parameters which control the morphology of ZnO were studied. ZnO was found to possess tunable pore characteristics with comparatively high specific surface area of 68 m 2 g −1 , and excellent acid-base surface properties. Prepared catalysts exhibited excellent photocatalytic performance for the treatment of highly toxic rhodamine B (RhB) dye under UV radiation. Zeta (ζ)-potential and dye adsorption tests were performed. Reusability experiments showed that after five cycles, catalysts exhibited 87% removal efficiency without any noticeable loss of the activity.

ZnS particles were grown over Cu

Recent studies on the electrical conductivity and photocatalytic activity properties of semiconductor nanocrystals such as Cu2O, Ag2O, TiO2, PbS, and Ag3PO4 exposing well-defined surfaces have revealed strong facet effects. For example, the electrical conductivity of Cu2O crystals can vary from highly conductive to nonconductive, and they can be highly photocatalytically active or inactive depending on the exposed faces. The crystal surfaces can even tune their light absorption wavelengths. Our understanding is that the emergence of these unusual phenomena can be explained in terms of the presence of an ultrathin surface layer having different band structures and degrees of band bending for different surfaces, which affects charge transport and photons into and out of the crystals. This review uses primarily results from our research on this frontier area of semiconductor properties to illustrate the existence of semiconductor facet effects. A simple adjustment to normal semiconductor band diagram allows ...

An absorption edge in the visible region and a slow recombination of photogenerated electron–hole pairs in semiconductors are desirable for efficient sunlight-driven photocatalysis. One of the strategies to harvest visible-light instead of ultraviolet is to identify or develop new semiconductors with a band gap below 3 eV. The five-layer Aurivillius phase perovskites, Bi6–xLaxTi3Fe2O18 (x = 0, 1), where the band gap ranges from ∼2.02–2.57 eV, have been identified as potential members. The compounds, Bi6–xLaxTi3Fe2O18 (x = 0, 1), are synthesized by solid state reaction and characterized by PXD, FE-SEM, EDS, UV–vis DRS, and PL spectroscopy. La-substitution into Bi6Ti3Fe2O18 results in a sluggish recombination of photogenerated electron–hole pairs in Bi5LaTi3Fe2O18 as compared to the parent. The compounds showed remarkable photocatalytic performance toward Rhodamine B (RhB) degradation (more than 96%) within 30 min of sunlight-irradiation under mild acidic medium. Dye degradation is found to be coincident wi...

Aurivillius phase layered perovskites, Bi5–xLaxTi3FeO15 (x = 1, 2) are synthesized by solid-state reaction. The compounds are characterized by powder X-ray diffraction (PXD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), UV–vis diffuse reflectance (UV–vis DRS), and photoluminescence (PL) spectroscopy. UV–vis DRS data revealed that the compounds are visible light absorbing semiconductors with band gaps ranging from ∼2.0–2.7 eV. Photocatalytic activity studies by Rhodamine B (RhB) degradation under sun-light irradiation showed that these layered oxides are very efficient photocatalysts in mild acidic medium. Scavenger test studies demonstrated that the photogenerated holes and superoxide radicals (O2•–) are the active species responsible for RhB degradation over the Aurivillius layered perovskites. Comparison of PL intensity, dye adsorption and ζ-potential suggested that a slow e––h+ recombination and effective dye adsorption are crucial for the degradatio...

Aurivillius phase layered perovskites, Bi5-xLaxTi3FeO15 (x = 1, 2) are synthesized by solid-state reaction. The compounds are characterized by powder X-ray diffraction (PXD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), UV-vis diffuse reflectance (UV-vis DRS), and photoluminescence (PL) spectroscopy. UV-vis DRS data revealed that the compounds are visible light absorbing semiconductors with band gaps ranging from ∼2.0-2.7 eV. Photocatalytic activity studies by Rhodamine B (RhB) degradation under sun-light irradiation showed that these layered oxides are very efficient photocatalysts in mild acidic medium. Scavenger test studies demonstrated that the photogenerated holes and superoxide radicals (O2(•-)) are the active species responsible for RhB degradation over the Aurivillius layered perovskites. Comparison of PL intensity, dye adsorption and ζ-potential suggested that a slow e(-)-h(+) recombination and effective dye adsorption are crucial for the degradation process over these photocatalysts. Moreover, relative positioning of the valence and conduction band edges of the semiconductors, O2/O2(•-), (•)OH/H2O potential and HOMO-LUMO levels of RhB appears to be responsible for making the degradation hole-specific. Photocatalytic cycle tests indicated high stability of the catalysts in the reaction medium without any observable loss of activity. This work shows great potential in developing novel photocatalysts with layered structures for sun-light-driven oxidation and degradation processes largely driven by holes and without any intervention of hydroxyl radicals, which is one of the most common reactive oxygen species (ROS) in many advanced oxidation processes.