Ordered mesoporous transition metal oxides have attracted considerable research attention due to their unique properties and wide applications. The preparation of these materials has been reported in ...the literature using soft and hard templating pathways. Compared with soft templating, hard templating, namely, nanocasting, is advantageous for synthesizing rigid mesostructures with high crystallinity and has already been applied to numerous transition metal oxides such as Co3O4, NiO, Fe2O3, and Mn3O4. However, nanocasting is often complicated by the multiple steps involved: first, the preparation of ordered mesoporous silica as the hard template, then infiltration of the metal precursor into the pores, and finally, formation of the metal oxide and removal of the hard template. In this paper, we provide a complete protocol that covers the preparation of most widely used ordered mesoporous silica templates (MCM-41, KIT-6, SBA-15) and the nanocasting process for obtaining ordered mesoporous metal oxides, with emphasizing cobalt oxide as an example. Characterization of the products is presented, and the factors that can potentially affect the process are discussed.
Inspired by natural processes, there is an enormous interest in light-driven water splitting to convert solar energy into electrical and chemical energy. This approach is thought to be able to ...eventually solve the main energy problem that society will face more dramatically in the near future. The water oxidation reaction is widely considered a major barrier for utilizing solar energy in artificial photosynthesis. Due to the relatively high overpotential and slow kinetics of the reaction, numerous efforts are made on the development of non-noble metal oxygen evolution catalysts such as transition metal oxides. Among them, cobalt-oxide-based materials have shown decent activity and thus present themselves as a promising candidate. In this perspective, we summarize the state of the art in synthesis of cobalt-oxide-based materials and application as water oxidation catalysts through electrochemical, photochemical, and photoelectrochemical approaches. Additionally, we state the future challenges that are critical to overcome to push the catalyst performance one step further.
Glycerol is a highly versatile molecule because of its three hydroxyl groups and can be transformed to a plethora of different value-added fine chemicals and products. It is an important byproduct in ...biodiesel production and, hence, produced in high amounts, which resulted in a high surplus flooding the market over the last decades. Thus, glycerol is regarded as a potential platform chemical, and many research efforts were devoted to find active catalysts to transform glycerol to various products via different catalytic processes. The selective oxidation reaction is one of the most promising reaction pathways to produce valuable fine chemicals used in the chemical and pharmaceutical industry. This Review describes the recent developments in selective glycerol oxidation to value-added products over heterogeneous catalysts. Particular emphasis is placed not only on newly developed catalysts based on supported noble-metal nanoparticles but also on catalysts containing nonprecious metals. The idea of using cost-efficient non-noble metals for glycerol oxidation is appealing from an economic point of view. Numerous parameters can influence the catalytic performance of the materials, which can be tuned by various synthetic approaches. The reasons for enhancements in activity are critically examined and put into perspective among the various studies. Moreover, during the past decade, many research groups also reported photocatalytic and, more scarcely, electrocatalytic pathways for glycerol oxidation, which are also described in detail herein and have otherwise found little attention in other reviews.
Conspectus The global energy landscape is undergoing significant change. Hydrogen is seen as the energy carrier of the future and will be a key element in the development of more sustainable industry ...and society. However, hydrogen is currently produced mainly from fossil fuels, and this needs to change. Alkaline water electrolysis with advanced technology has the most significant potential for this transition to produce large-scale green hydrogen by utilizing renewable energy. The assembly of industrial electrolyzer plants is more complex on a larger scale, but it follows a basic working principle, which involves two half-cells of anode and cathode sites where the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) occur. Out of the two reactions, the OER is more challenging both thermodynamically and kinetically. Besides having access to renewable electricity, developing durable and abundant electrocatalysts for the OER remains a challenge in large-scale alkaline water electrolysis. Among different physicochemical properties, the electrocatalyst surface and its interaction with water and reaction intermediates, as well as formed molecular hydrogen and oxygen, play an essential role in the catalytic performance and the reaction mechanism. In particular, the binding strengths between the catalyst surface and intermediates determine the rate-limiting step and electrocatalytic performance. This Account gives some insights into the status of the hydrogen economy and basic principles of alkaline water electrolysis by covering its fundamentals as well as industrial developments. Further, the HER and OER reaction mechanisms of alkaline water electrolysis and selected electrocatalyst progress for both half-reactions are briefly discussed. The Adsorbate Evolution Mechanism and the Lattice Oxygen Mechanism for the OER are explained with specific references. This Account also deliberates on the author’s selected contributions to the development of transition metal-based electrocatalysts for alkaline water electrolysis with an emphasis on OER. The focus is particularly given to the enhancement of intrinsic activity, the role of eg-filling, phase segregation, and defect structure of cobalt-based electrocatalysts for OER. Structural modification and phase transformation of the cobalt oxide electrocatalyst under working conditions are further deliberated. In addition, the creation of new active surface species and the activation of cobalt- and nickel-based electrocatalysts through iron uptake from the alkaline electrolyte are discussed. In the end, this Account provides a brief overview of challenges related to large-scale production and utilization of green hydrogen.
Catalysis is at the core of almost every established and emerging chemical process and also plays a central role in the quest for novel technologies for the sustainable production and conversion of ...energy. Particularly since the early 2000s, a great surge of interest exists in the design and application of micro- and nanometer-sized materials with hollow interiors as solid catalysts. This review provides an updated and critical survey of the ever-expanding material architectures and applications of hollow structures in all branches of catalysis, including bio-, electro-, and photocatalysis. First, the main synthesis strategies toward hollow materials are succinctly summarized, with emphasis on the (regioselective) incorporation of various types of catalytic functionalities within their different subunits. The principles underlying the scientific and technological interest in hollow materials as solid catalysts, or catalyst carriers, are then comprehensively reviewed. Aspects covered include the stabilization of catalysts by encapsulation, the introduction of molecular sieving or stimuli-responsive “auxiliary” functionalities, as well as the single-particle, spatial compartmentalization of various catalytic functions to create multifunctional (bio)catalysts. Examples are also given on the applications which hollow structures find in the emerging fields of electro- and photocatalysis, particularly in the context of the sustainable production of chemical energy carriers. Finally, a critical perspective is provided on the plausible evolution lines for this thriving scientific field, as well as the main practical challenges relevant to the reproducible and scalable synthesis and utilization of hollow micro- and nanostructures as solid catalysts.
Herein, we demonstrate that a perfect replication of a desired composition is not only related to the degree of interconnectivity of the double gyroid ordered mesoporous silica template, there is ...also an enormous effect from the nature of precursor and its composition. For the first time, the symmetry of ordered mesoporous Co3O4 was tuned with iron doping by using the same batch of cubic ordered mesoporous silica (KIT-6) as a hard template. Nanocasting of the pure Co3O4 results in a negative replica of the silica template that has a monomodal pore size distribution and a dense coupled structure, while incorporation of a small amount of iron lowers the mesostructural symmetry and alters the pore system of the replica. The effect of this remarkable observation was further investigated for electrochemical water oxidation where superior catalytic activities were observed when Co3O4 was doped with small amounts of iron. Furthermore, iron incorporated Co3O4 indicated comparable water oxidation activity with noble metal and cobalt based electrocatalysts. This kind of abundant transition metal based mesostructured material has the potential to be used as promising electrocatalysts for water oxidation.
The outstanding performance of halide perovskites in optoelectronic applications can be partly attributed to their high absorption coefficient and long carrier lifetime, which are also desirable for ...photocatalysts. Herein, we report that cesium lead iodide perovskite quantum dots (CsPbI3 QDs) can be used as catalysts to promote the polymerization of 2,2′,5′,2″-ter-3,4-ethylenedioxythiophene under visible light illumination while preserving the quantum dot in the desirable cubic crystal phase. Simultaneously, the generated conducting poly(3,4-ethylenedioxythiophene), PEDOT, encapsulates and stabilizes the morphology of the CsPbI3 QDs. The photocatalytic polymerization clearly depends on the concentration of the CsPbI3 QDs, and the CsPbI3 QDs maintain the desirable perovskite phase when the concentration of the QD increases. Molecular oxygen and 1,4-benzoquinone can serve as electron acceptors during the photocatalytic polymerization reaction. When molecular oxygen is used, the structure of the CsPbI3 QD transforms from cubic to orthorhombic, while usage of 1,4-benzoquinone preserves the cubic phase of CsPbI3 QD. This novel approach enables the one-step formation of CsPbI3/PEDOT composite, which could be promising for the preparation of novel optoelectronic materials and high performance devices.
Direct selective oxidation of hydrocarbons to oxygenates by O2 is challenging. Catalysts are limited by the low activity and narrow application scope, and the main focus is on active C−H bonds at ...benzylic positions. In this work, stable, lead‐free, Cs3Bi2Br9 halide perovskites are integrated within the pore channels of mesoporous SBA‐15 silica and demonstrate their photocatalytic potentials for C−H bond activation. The composite photocatalysts can effectively oxidize hydrocarbons (C5 to C16 including aromatic and aliphatic alkanes) with a conversion rate up to 32900 μmol gcat−1 h−1 and excellent selectivity (>99 %) towards aldehydes and ketones under visible‐light irradiation. Isotopic labeling, in situ spectroscopic studies, and DFT calculations reveal that well‐dispersed small perovskite nanoparticles (2–5 nm) possess enhanced electron–hole separation and a close contact with hydrocarbons that facilitates C(sp3)−H bond activation by photoinduced charges.
Better with bismuth: A range of mesoporous‐silica‐supported small bismuth halide perovskite nanoparticles were prepared. They were found to be very promising photocatalysts for selective aromatic and aliphatic C−H bond activation under visible‐light illumination.
Halide perovskites have prompted the evolution of the photovoltaic field and simultaneously demonstrated their great potential for application in other optoelectronic devices. A fundamental ...understanding of their structure-property relationship is essential to fabricate novel materials and high-performance devices. This review gives a perspective on different synthetic methodologies for the preparation of halide perovskites and highlights the effects of structural factors such as crystal structure, grain size, nanoscale dimensionality, patterned arrangement, and hierarchical structure on their optoelectronic properties. The main emphasis is given to 0D, 1D and 2D nanostructured materials including their common synthesis methods and key structural properties. Structural factors should be precisely controlled during the material preparation and device fabrication to improve the performance of targeted applications.
This review gives a perspective on different synthetic methodologies for the preparation of halide perovskites and highlights the structural effects on their optoelectronic properties.
The controlled synthesis of a series of ordered mesoporous composite materials via solid–solid reaction of ordered mesoporous Co3O4 with various transition metal precursors is reported. This ...versatile methodology allows preparation of a range of composites with precisely controllable material compositions. The textural parameters of the heterostructured compounds are highly dependent on the oxidation state of the dopant. Electrocatalytic activities of the prepared materials were investigated as oxygen evolution catalysts for the electrolysis of water. Among the ordered mesoporous composite materials, Co3O4–CuCo2O4 shows a significant enhancement for electro-catalytic water splitting with a lower onset potential and higher current density. Following these results, a series of ordered mesoporous composite materials based on cobalt and copper oxides with different atomic ratios were prepared through a nanocasting route. Enhanced electrocatalytic performance was obtained for all composite samples in comparison with Co3O4.
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