B/N-Codoped Carbon Nanosheets Derived from the Self-Assembly of Chitosan-Amino Acid Gels for Greatly Improved Supercapacitor Performances

This work presents an efficient strategy for preparing chitosan (CS)-derived boron (B), nitrogen (N)-codoped porous carbon (C) nanosheets by using three amino acids with different acidities and the help of boric acid. Amino acids act not only as a N sources but also as the structure-directing agents through the interaction with CS to induce the formation of special morphology and structure. Boric acid serves both as the B source and as the reactive template, improving activition efficiency to creat more pores. When amino acids with different acidities are added, the morphology of the prepared samples changes from large bulks to thin nanosheets. In particular, the as-prepared carbon formed by a CS-aspartic acid gel precursor shows thin curved nanosheets. After adding KOH and boric acid, the samples possess loose and cross-linked morphologies with porous structure, which is favorable for ion transport and has benefit for the supercapacitor (SC) performance. As a result, the obtained B/N-codoped porous carbons show enhanced electrochemical performance. The sample CS/His-B prepared with basic amino acid shows the superior capacitance of 478 F g^-1. Meanwhile, the assembled symmetric SC achieves a maximum energy density of 30.1 Wh kg^-1 when the power density is 225.1 W kg^-1 and demonstrates an ultralong cycling life for which the retention of capacitance is approximately 100% after 100 000 cycles. The maximum area capacitance is up to 12.7 F cm^-1 with 50 mg of active material loaded. For an all-solid-state SC using KOH-polyvinyl alchydroohol (PVA) electrolyte, the device owns a wide potential range of 1.4 V, which shows an excellent maximum energy density of 14.4 Wh kg^-1 and still remains 4.4 Wh kg^-1 at the power density of 1049.5 W kg^-1. B/N-codoped carbon nanosheets derived from the self-assembly of chitosan-amino acid gels represent a promising route for preparing carbon materials for high-performance SCs.

Preparation of brookite TiO2 nanoparticles with small sizes and the improved photovoltaic performance of brookite-based dye-sensitized solar cells

Brookite TiO₂ nanoparticles with small sizes (hereafter denoted as BTP particles) were synthesized through the hydrothermal treatment of TiCl₄ solution with Pb(NO₃)₂ as an additive. The obtained BTP particles have a large specific surface area (∼122.2 m² g^-1) and relatively uniform particle sizes (∼10 nm) with the coexistence of a small quantity of nanorods with a length of ∼100 nm. When used as a photoanode material for dye-sensitized solar cells (DSSCs), the BTP particles show a much higher dye-loading content than the brookite TiO₂ quasi nanocubes (denoted as BTN particles) with a mean size of ∼50 nm and a specific surface area of ∼34.2 m² g^-1 that were prepared through a similar hydrothermal process but without the addition of Pb(NO₃)₂. The fabricated BTP film-based solar cell with an optimized film thickness gives a conversion efficiency up to 6.36% with a 74% improvement when compared to the BTN film-based one (3.65%) under AM 1.5G one sun irradiation, while the corresponding bilayer brookite-based solar cell by using brookite TiO₂ submicrometer particles as an overlayer of the BTP film displays a significantly enhanced efficiency of 7.64%. Both of them exceed the current record (5.97%) for the conversion efficiency of pure brookite-based DSSCs reported in the literature. The present results not only demonstrate a really simple synthesis of brookite TiO₂ nanoparticles with both high phase purity and a large surface area, but also offer an efficient approach to improve the photovoltaic performance of brookite-based solar cells by offsetting brookite's inherent shortages such as lower dye-loading and poor conductivity as compared to anatase.

Engineering disorder into exotic electronic 2D TiO2nanosheets for enhanced photocatalytic performance

We successfully prepared exotic electronic 2D TiO₂nanosheets and then engineered disorder into them to obtain black TiO₂nanosheets.

Ni2+ and Ti3+ co-doped porous black anatase TiO2 with unprecedented-high visible-light-driven photocatalytic degradation performance

A black Ni doped porous TiO₂ were fabricated via an in situ solid-state chemical reduction approach, which exhibited excellent visible-light-driven performance.

Large-scale, three-dimensional, free-standing, and mesoporous metal oxide networks for high-performance photocatalysis

Mesoporous nanostructures represent a unique class of photocatalysts with many applications, including splitting of water, degradation of organic contaminants, and reduction of carbon dioxide. In this work, we report a general Lewis acid catalytic template route for the high-yield producing single- and multi-component large-scale three-dimensional (3D) mesoporous metal oxide networks. The large-scale 3D mesoporous metal oxide networks possess large macroscopic scale (millimeter-sized) and mesoporous nanostructure with huge pore volume and large surface exposure area. This method also can be used for the synthesis of large-scale 3D macro/mesoporous hierarchical porous materials and noble metal nanoparticles loaded 3D mesoporous networks. Photocatalytic degradation of Azo dyes demonstrated that the large-scale 3D mesoporous metal oxide networks enable high photocatalytic activity. The present synthetic method can serve as the new design concept for functional 3D mesoporous nanomaterials.