Hybrid nanoarchitecturing of hierarchical zinc oxide wool-ball-like nanostructures with multi-walled carbon nanotubes for achieving sensitive and selective detection of sulfur dioxide

This work reports a facile glycerol-assisted solvothermal method for synthesizing hierarchical three-dimensional (3D) wool-ball-like zinc oxide (ZnO) nano structures and their subsequent modifications with multi-walled carbon nanotubes (MWCNTs) as modifiers for achieving sensitive and selective detection of toxic sulfur dioxide (SO2) gas. Structurally, the as-synthesized 3D wool-ball-like ZnO is assembled of two-dimensional (2D) plate-like structures, which themselves are arranged by numerous small nanopartides. Furthermore, in this work we observed an interesting new phenomenon in which when a high concentration of MWCNTs is introduced, many small nanorods grew on the surface of the plate-like structures which assemble the 3D wool-ball-like ZnO nanostructures. When evaluated for SO2 detection, the ZnO/MWCNTs (10:1) composite (ZnO:MWCNTs =10:1) shows a high response of 220.8 to 70 ppm of SO2 gas (approximately three times higher than the response of pure wool-ball-like ZnO) at an optimum operating temperature of 300 degrees C. Additionally, the composite also displays good stability and selectivity to SO2 with the response to 50 ppm of SO2 being 7-14 times higher than the responses to other tested gases at a similar concentration. The excellent sensing performance of the wool-ball-like ZnO/MWCNTs (10:1) composite is mainly attributed to: (i) the formation of p-n heterojunctions at the ZnO/MWCNTs interfaces, which greatly enhance the resistance changes upon exposure to SO2 gas and (ii) the increased amount of adsorption sites for O-2 and SO2 gas molecules owing to the larger surface area of the composite and defects sites generated by the functionalization process of MWCNTs. (C) 2018 Elsevier B.V. All rights reserved

Soft-templated synthesis of mesoporous nickel oxide using poly(styrene-block-acrylic acid-block-ethylene glycol) block copolymers

In this work, we report the soft-templated preparation of mesoporous nickel oxide using an asymmetric poly(styrene-block-acrylic acid-block-ethylene glycol) (PS-b-PAA-b-PEG) triblock copolymer. This block copolymer forms a micelle consisting of a PS core, a PAA shell and a PEG corona in aqueous solutions, which can serve as a soft template. Specifically, the PS block forms the core of the micelles on the basis of its lower solubility in water. The anionic PAA block interacts with the cationic Ni ions present in the solution to generate the shell. The PEG block forms the corona of the micelles and stabilizes the micelles by preventing secondary aggregation through steric repulsion between the PEG chains. In terms of textural characteristics, the as-synthesized mesoporous NiO exhibits a large average pore size of 35 nm with large specific surface area and pore volume of 97.0 m g and 0.411 cm g, respectively. It is expected that the proposed soft-templated strategy can be expanded to other metal oxides/sulfides in the future for potential applications in gas sensors, catalysis, energy storage and conversion, optoelectronics, and biomedical applications

One-step synthetic strategy of hybrid materials from bimetallic metal–organic frameworks for supercapacitor applications

This work reports a facile one-step method for the synthesis of new hybrid porous materials using bimetallic NiCo-MOF-74 as the starting precursor. By controlling the calcination atmosphere and temperature, the bimetallic NiCo-MOF-74 particles can be converted into a series of hybrid materials consisting of carbon, metal, and metal oxides. The direct carbonization of the bimetallic NiCo-MOF-74 particles at 800 degrees C under N-2 atmosphere results in the formation of graphitic carbon/NixCo1-x composites (termed NC-800). In contrast, the heat treatment of NiCo-MOF-74 in air at 350 degrees C (termed NC-350) yields NixCo1-x/NixCo1-xO composites (with a small trace of carbon) as the product. When evaluated as electrode materials for supercapacitors, NC-800 and NC-350 exhibit high specific capacitances of 715 and 513 F g(-1) respectively, at a high current density of 1 A g(-1). Furthermore, these hybrid materials also show good cycling stability with no visible degradation in their specific capacitance after 2,500 cycles. The excellent electrochemical performance of these hybrid materials may be attributed to (i) the synergistic effect of the graphitic carbon and binary mixed metals which can enhance the conductivity of the composites, (ii) the presence of mesopores which can facilitate easy diffusion of electrolyte, and (iii) their large surface area and pore volume which can provide significantly more electroactive sites. The outstanding electrochemical properties of these MOF-derived hybrid materials indicate their promising potential as electrode materials for high-performance supercapacitors

A mesoporous tin phosphate-graphene oxide hybrid toward the oxygen reduction reaction

We report a one-pot synthetic strategy for the production of an efficient oxygen reduction reaction (ORR) electrocatalyst by the hybridization of hexagonally ordered mesoporous/crystalline tin phosphate (mesoSnPi) nanoflakes with thin layers of graphene oxide (GO). In the electrocatalytic measurements, the obtained nanocomposite (SnPi@GO) exhibited a superior electrocatalytic performance for ORR over mesoporous tin phosphate (mesoSnPi), bulk tin phosphate (bulkSnPi), bulk tin oxide (bulkSnO), various transition metal phosphate nanomaterials and most state-of-the-art manganese oxides

Synthesis and fundamental understanding of metal oxide nanostructures for gas-sensing applications

Gas sensors are indispensable aspects of our life as it warns us about the dangerous gases in our environment. Semiconducting oxide gas sensors are by far the most popular type of sensors, because of their simple processing and low fabrication cost. The early metal oxide-based sensor materials however often exhibit several undesirable characteristics, such as poor selectivity, sensitivity to moisture, long-term signal drift and, slow response time. Hence, the development of fast-responding gas sensors with high sensitivity and selectivity is highly desirable. The introduction of nanotechnology has attracted large interests in gas-sensing research, largely because nanoscale particles offer a larger high surface area to volume ratio and enhanced functionalities compared to bulk particles. In particular, the synthesis of metal oxide nanostructures with controlled morphology is highly attractive because the properties of nanostructure depend not only on their composition, but also on their structure, phase, shape, size, and size distribution. Many efforts have been carried out to improve the „3S‟: sensitivity, selectivity, and stability of semiconductor gas sensors by utilizing metal oxide nanostructures. However, some challenges still exist in both synthesis and fundamental understanding of the gas-sensing mechanism of nanoscale metal oxides.This thesis aims to explore the use of nanostructures based on n-type semiconducting oxides as gas sensor materials for the detection of VOCs and to develop different ways to enhance the sensitivity of these metal oxide nanostructures through means of structuraliiicontrol, surface engineering and introduction of additives such as metal oxides and noble metals. Our research method involves the use of various microscopy, diffraction, and spectroscopy techniques to characterize the achieved metal oxide nanostructures or nanocomposites. To gain a further insights understanding of the metal oxide/gas interactions during the sensing process, it is important to use multi-scale theoretical methods validated by experimental techniques. The findings will benefit the design and construction of gas sensors with desirable properties/performance (sensitivity, selectivity and stability) for potential applications in environmental monitoring and detection

Spatial-controlled etching of coordination polymers

Nanoarchitectonics provide versatile opportunities for modifying theproperties of coordination polymers (CP) other than molecular engineering. Spatial-controlled etching represents a specific category which focuses on disassembly of the frameworks under control. It showssignificant power in tailoring the properties and functions of the CPs. Here, we discuss the mechanism for controlled etching of the CPs and summarized the two main strategies utilized so far. Several examples are illustrated to demonstrate recent developments in this area. Moreover, advantages of the etched CPs are summarized in several important applications, including energy storage, catalysis, and nanomedicine

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

Self-assembly of block copolymers (BCPs) provides a versatile strategy for controllable preparation of a broad range of functional materials with different ordered structures. In recent decades, this softtemplating strategy has been widely utilized for preparing a wide range of mesoporous materials. These porous materials have attracted tremendous interest in energy storage and conversion (ESC) applications in view of their ability to absorb, store, and interact with guest species on their exterior/interior surfaces and in the pore space. Compared with other synthetic approaches, such as template-free and hardtemplating methods, BCP soft-templating protocols show great advantages in the construction of large mesopores with diameters between 10–60 nm, which are suitable for applications requiring the storage or hosting of large-sized species/molecules. In addition, this strategy shows incomparable merits in the flexible control of pore size/architecture/wall thickness, which determines the final performance of mesoporous materials in ESC devices. In the last decade, rapid development has been witnessed in the area of BCP-templated mesoporous materials. In this review paper, we overview the progress of this field over the past 10 years, with an emphasis on the discussions of synthetic methodologies, the control of materials structures (including morphology and pore size/shape), and potential applications particularly in rechargeable batteries, supercapacitors, electro-/photocatalysis, solar cells, etc.Self-assembly of block copolymers (BCPs) provides a versatile strategy for controllable preparation of a broad range of functional materials with different ordered structures. In recent decades, this softtemplating strategy has been widely utilized for preparing a wide range of mesoporous materials. These porous materials have attracted tremendous interest in energy storage and conversion (ESC) applications in view of their ability to absorb, store, and interact with guest species on their exterior/interior surfaces and in the pore space. Compared with other synthetic approaches, such as template-free and hardtemplating methods, BCP soft-templating protocols show great advantages in the construction of large mesopores with diameters between 10–60 nm, which are suitable for applications requiring the storage or hosting of large-sized species/molecules. In addition, this strategy shows incomparable merits in the flexible control of pore size/architecture/wall thickness, which determines the final performance of mesoporous materials in ESC devices. In the last decade, rapid development has been witnessed in the area of BCP-templated mesoporous materials. In this review paper, we overview the progress of this field over the past 10 years, with an emphasis on the discussions of synthetic methodologies, the control of materials structures (including morphology and pore size/shape), and potential applications particularly in rechargeable batteries, supercapacitors, electro-/photocatalysis, solar cells, etc

One-Step Synthetic Strategy of Hybrid Materials from Bimetallic Metal–Organic Frameworks for Supercapacitor Applications

This work reports a facile one-step method for the synthesis of new hybrid porous materials using bimetallic NiCo-MOF-74 as the starting precursor. By controlling the calcination atmosphere and temperature, the bimetallic NiCo-MOF-74 particles can be converted into a series of hybrid materials consisting of carbon, metal, and metal oxides. The direct carbonization of the bimetallic NiCo-MOF-74 particles at 800 °C under N₂ atmosphere results in the formation of graphitic carbon/Ni<i>_x</i>Co_1−<i>x</i> composites (termed NC-800). In contrast, the heat treatment of NiCo-MOF-74 in air at 350 °C (termed NC-350) yields Ni_<i>x</i>Co_1−<i>x</i>/Ni_<i>x</i>Co_1−<i>x</i>O composites (with a small trace of carbon) as the product. When evaluated as electrode materials for supercapacitors, NC-800 and NC-350 exhibit high specific capacitances of 715 and 513 F g^–1, respectively, at a high current density of 1 A g^–1. Furthermore, these hybrid materials also show good cycling stability with no visible degradation in their specific capacitance after 2,500 cycles. The excellent electrochemical performance of these hybrid materials may be attributed to (i) the synergistic effect of the graphitic carbon and binary mixed metals which can enhance the electrical conductivity of the composites, (ii) the presence of mesopores which can facilitate easy diffusion of electrolyte, and (iii) their large surface area and pore volume which can provide significantly more electroactive sites. The outstanding electrochemical properties of these MOF-derived hybrid materials indicate their promising potential as electrode materials for high-performance supercapacitors

Two-dimensional mesoporous vanadium phosphate nanosheets through liquid crystal templating method toward supercapacitor application

Mesoporous vanadium phosphate (VOPO) nanosheets have been successfully synthesized through an easy and reproducible lyotropic liquid crystals (LLC) templating approach for the first time. Using the triblock copolymer (P123) as a surfactant, VOPO precursor with a well-developed 2D hexagonal mesostructure can be obtained. Following complete removal of the template by calcination, crystallized VOPO frameworks with less-ordered mesostructure are achieved. The as-prepared mesoporous VOPO nanosheets exhibit superior pseudocapacitive performance (767 F g at 0.5A g) by virtue of the favorable mesostructure that gives rise to abundant easily accessible redox active sites as well as reinforced charge transfer and ion diffusion properties. The charge storage mechanism of the mesoporous VOPO nanosheets has been experimentally demonstrated to be based on the reversible two-step redox reactions between V(V) and V(III) in acidic medium. This advantageous LLC templating strategy is expected to open up a new route for designing various mesoporous metal phosphates with superior electrochemical performance for utilization in energy storage devices