The hydrothermal synthesis of zeolites: precursors, intermediates and reaction mechanism

Hierarchically porous carbons (HPCs) with 1D to 3D network are attracting vast interest due to their potential technological application profile ranging from electrochemical capacitors, lithium ion batteries, solar cells, hydrogen storage systems, photonic material, fuel cells, sorbent for toxic gas separation and so on. Natural raw-materials such as biomass-biopolymer derived hierarchical nanostructured carbons are especially attractive for their uniform pore dimensions which can be adjustable over a wide range of length scales. Good electrical conductivity, high surface area, and excellent chemical stability are unique physicochemical properties which are responsible for micro/nanostructured porous carbon to be highly trusted candidate for emerging nanotechnologies. This review focuses on the ‘out-of-the-box’ synthetic techniques capable of deriving HPC with superior application profiles. The article presents the promising scope of accessing HPCs from (1) hard-templating, soft-templating, and non-templating routes, (2) biopolymers with a major focus on non-templating strategies. Subsequently, emerging strategies of hetero-atom doping in porous carbon nanostructures are discussed. The review will highlight the contribution of synergistic effect of macro–meso–micropores on a range of emerging applications such as CO2 capture, carbon photonic crystal sensors, Li–S batteries, and supercapacitor. Mechanism of ion transport and buffering, electrical double layer enhancement have been discussed in the context of pore structure and shapes. We will also show the differences of HPC and ordered mesoporous carbon (OMC) in terms of their synthesis strategies and choices of template for self-assembly. How the remarkable mechanical strength of the HPCs can be achieved by selecting self-assembling template, whereas collapse of mesostructure via decomposition of framework occurs due to poor thermal stability or high N-content of the carbon source will be discussed.

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Hierarchically porous carbon derived from polymers and biomass: effect of interconnected pores on energy applications

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties becom...

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices

Over the last decade, significant effort has been devoted to the applications of hierarchically structured porous materials owing to their outstanding properties such as high surface area, excellent accessibility to active sites, and enhanced mass transport and diffusion. The hierarchy of porosity, structural, morphological and component levels in these materials is key for their high performance in all kinds of applications. The introduction of hierarchical porosity into materials has led to a significant improvement in the performance of materials. Herein, recent progress in the applications of hierarchically structured porous materials from energy conversion and storage, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine is reviewed. Their potential future applications are also highlighted. We particularly dwell on the relationship between hierarchically porous structures and properties, with examples of each type of hierarchically structured porous material according to its chemical composition and physical characteristics. The present review aims to open up a new avenue to guide the readers to quickly obtain in-depth knowledge of applications of hierarchically porous materials and to have a good idea about selecting and designing suitable hierarchically porous materials for a specific application. In addition to focusing on the applications of hierarchically porous materials, this comprehensive review could stimulate researchers to synthesize new advanced hierarchically porous solids.

Applications of hierarchically structured porous materials from energy storage and conversion, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine

Volumetric performance, a much more reliable and precise parameter for evaluating the charge-storage capacity of supercapacitors compared with gravimetric performance, has aroused more and more interest in recent years owing to the rapid development of miniaturized, portable and wearable electronic devices as well as electric vehicles. Various carbon materials are widely used as electrode materials in supercapacitors. However, their intrinsically low specific capacitance and relatively low bulk density lead to a relatively low volumetric performance, significantly limiting their future application. This critical review points out the crucial importance of volumetric performance and reviews recent achievements of high volumetric performances obtained through the rational design and development of novel carbon-based materials. Particular emphasis is focused on discussing the factors influencing the volumetric performance of carbon materials from a structural design point of view. We then make an in-depth summary of various promising approaches used to make significant research breakthroughs in recent years. Current challenges, future research directions and opportunities in this fascinating field of supercapacitors with high gravimetric and volumetric performances are also discussed.

Carbon materials for high volumetric performance supercapacitors: design, progress, challenges and opportunities

The phase transformation of zirconia from tetragonal to monoclinic is characterized by UV Raman spectroscopy, visible Raman spectroscopy, and XRD. Electronic absorption of ZrO2 in the UV region makes UV Raman spectroscopy more sensitive at the surface region than XRD or visible Raman spectroscopy. Zirconia changes from the tetragonal phase to the monoclinic phase with calcination temperatures elevated and monoclinic phase is always detected first by UV Raman spectroscopy for the samples calcined at lower temperatures than that by XRD and visible Raman spectroscopy. When the phase of zirconia changes from tetragonal to monoclinic, the slight changes of the phase at very beginning can be detected by UV Raman spectroscopy. UV Raman spectra clearly indicate that the phase transition takes place initially at the surface regions. It is found that the phase change from tetragonal to monoclinic is significantly retarded when amorphous Zr(OH)4 was agglomerated to bigger particles and the particle agglomeration of ...

Phase Transformation in the Surface Region of Zirconia Detected by UV Raman Spectroscopy

Characterization of aluminosilicate zeolites by UV Raman spectroscopy

Hierarchically porous carbons with variable pore sizes at multi-length-scale, a nitrogen and boron co-doped and local graphitized framework, and high mechanical strength were synthesized through the self-assembly of poly(benzoxazine-co-resol) with ionic liquid C16mimBF4 and a carbonization process. In this synthesis, the ionic liquid acts both as a structure directing agent and a heteroatom precursor. The obtained porous carbons have a specific surface area lower than 376 m2 g−1 and thus a high skeleton density. With such heteroatom doped skeleton structures and fully interconnected macropores, mesopores and micropores, the hierarchically porous carbon shows outstanding electrochemical performance, e.g. a superior high gravimetric capacitance (Cg) of 247 F g−1, an interfacial capacitance (CS) of 66 μF cm−2 (calculated based on the discharge curve with a constant current density of 0.5 A g−1), whilst a high volumetric capacitance (Cv) of 101 F cm−3 compared to those reported in the literature. Cycling stability tests indicate that the carbon exhibits a capacitance retention of ∼96.2% after 4000 charge–discharge cycles, strongly reflecting an excellent long-term cyclability of the electrode. Due to its unique skeleton structure and high conductivity, such hierarchically porous carbon shows promise as an electrode material for supercapacitors.

Ionic liquid C16mimBF4assisted synthesis of poly(benzoxazine-co-resol)-based hierarchically porous carbons with superior performance in supercapacitors

Framework titanium atoms in titanium-substituted silicalite (TS-1) can be identified by UV resonance Raman spectroscopy since the associated Raman bands at 1125, 530, and 490 cm−1 (see figure) are observed only when the charge transfer transition associated with the framework Ti atoms is excited by a UV laser. Thus, framework Ti atoms can be distinguished from nonframework Ti atoms and other defect sites. This method can be applicable to identifying transition metal atoms in the frameworks of other molecular sieves.

UV Resonance Raman Spectroscopic Identification of Titanium Atoms in the Framework of TS-1 Zeolite

Framework titanium in Ti-silicalite-1 (TS-1) zeolite was selectively identified by its resonance Raman bands using ultraviolet (UV) Raman spectroscopy. Raman spectra of the TS-1 and silicalite-1 zeolites were obtained and compared using continuous wave laser lines at 244, 325, and 488 nm as the excitation sources. It was only with the excitation at 244 nm that resonance enhanced Raman bands at 490, 530, and 1125 cm-1 appeared exclusively for the TS-1 zeolite. Furthermore, these bands increased in intensity with the crystallization time of the TS-1 zeolite. The Raman bands at 490, 530, and 1125 cm-1 are identified as the framework titanium species because they only appeared when the laser excites the charge-transfer transition of the framework titanium species in the TS-1. No resonance Raman enhancement was detected for the bands of silicalite-1 zeolite and for the band at 960 cm-1 of TS-1 with any of the excitation sources ranging from the visible to UV regions. This approach can be applicable for the ide...

Guang Xiong

Papers

Phase Transformation in the Surface Region of Zirconia Detected by UV Raman Spectroscopy

Characterization of aluminosilicate zeolites by UV Raman spectroscopy

Ionic liquid C16mimBF4assisted synthesis of poly(benzoxazine-co-resol)-based hierarchically porous carbons with superior performance in supercapacitors

UV Resonance Raman Spectroscopic Identification of Titanium Atoms in the Framework of TS-1 Zeolite

Identifying framework titanium in TS-1 zeolite by UV resonance Raman spectroscopy