Search

The catalytic total oxidation of short-chain alkanes released from automobile exhausts is still a big challenge in volatile organic compound (VOC) elimination. The significant degradation of catalytic activity after hydrothermal aging is a widely existing issue. Herein, we report a facile one-pot hydrothermal method to successfully grow TiO2–Al2O3 binary nanoarrays on the 3D channel surfaces of ceramic honeycombs. Such a binary nanoarray was heterogeneously integrated on the cordierite honeycomb channel surface with closely separated nanowire arrays of anatase-TiO2 and mesoporous γ-Al2O3, which exhibited excellent robustness under mechanical vibration and thermal and hydrothermal aging. Moreover, propane conversion with the Pt/TiO2–Al2O3 binary nanoarray catalyst rapidly reached 80% at a temperature as low as 224 °C, suggesting that the binary nanoarray catalyst is a promising candidate for practical applications.

Scalable and cost-effective synthesis and assembly of technologically important nanostructures in three-dimensional (3D) substrates hold keys to bridge the demonstrated nanotechnologies in academia with industrially relevant scalable manufacturing. In this work, using ZnO nanorod arrays as an example, a hydrothermal-based continuous flow synthesis (CFS) method is successfully used to integrate the nano-arrays in multi-channeled monolithic cordierite. Compared to the batch process, CFS enhances the average growth rate of nano-arrays by 125%, with the average length increasing from 2 μm to 4.5 μm within the same growth time of 4 hours. The precursor utilization efficiency of CFS is enhanced by 9 times compared to that of batch process by preserving the majority of precursors in recyclable solution. Computational fluid dynamic simulation suggests a steady-state solution flow and mass transport inside the channels of honeycomb substrates, giving rise to steady and consecutive growth of ZnO nano-arrays with an average length of 10 μm in 12 h. The monolithic ZnO nano-array-integrated cordierite obtained through CFS shows enhanced low-temperature (200 °C) desulfurization capacity and recyclability in comparison to ZnO powder wash-coated cordierite. This can be attributed to exposed ZnO {100} planes, better dispersion and stronger interactions between sorbent and reactant in the ZnO nanorod arrays, as well as the sintering-resistance of nano-array configurations during sulfidation–regeneration cycles. With the demonstrated scalable synthesis and desulfurization performance of ZnO nano-arrays, a promising, industrially relevant integration strategy is provided to fabricate metal oxide nano-array-based monolithic devices for various environmental and energy applications.

The scalable three-dimensional (3-D) integration of functional nanostructures into applicable platforms represents a promising technology for meeting the ever-increasing demands of fabricating high performance devices featuring cost-effectiveness, structural sophistication and multi-functional enabling. Such an integration process generally involves a diverse array of nanostructural entities (nano-entities) consisting of dissimilar nanoscale building blocks such as nanoparticles, nanowires, and nanofilms made of metals, ceramics, or polymers. Various synthetic strategies and integration methods have enabled the successful assembly of both structurally and functionally tailored nano-arrays into a unique class of monolithic devices. The performance of nano-array based monolithic devices is dictated by a few important factors such as materials substrate selection, nanostructure composition and nano-architecture geometry. Therefore, the rational material selection and nano-entity manipulation during the nano-array integration process, aiming to exploit the advantageous characteristics of nanostructures and their ensembles, are critical steps towards bridging the design of nanostructure integrated monolithic devices with various practical applications. In this article, we highlight the latest research progress of the two-dimensional (2-D) and 3-D metal and metal oxide-based nanostructural integrations into prototype devices applicable with ultrahigh efficiency, good robustness and improved functionality. Select examples of nano-array integration, scalable nanomanufacturing and representative monolithic devices such as catalytic converters, sensors and batteries will be utilized as the connecting dots to display a roadmap from hierarchical nanostructural assembly to practical nanotechnology implications ranging from energy, environmental, to chemical and biotechnology areas.

In this study, a cost-effective solution synthesis of commercial scale single crystalline titanium dioxide (TiO2) nanorod arrays has been successfully achieved on the inner walls of cordierite monoliths, which may provide a new class of nanostructured hybrid support for catalysis and energy applications. The morphological evolution has been observed from dandelion TiO2 nanorod clusters to vertically aligned nanorod arrays while increasing the solution treatment time. A heterogeneous nucleation–dissolution–crystallization mechanism is proposed for the growth of the brookite structured TiO2 nanorod arrays on the inner walls of honeycomb monoliths. The brookite structured TiO2 nanorod arrays have a high surface area up to ~250 m2 g−1, with an overall specific surface area in the hybrid nanostructured monolith increasing by 1.8 and 2.5 times after TiO2 nanorods coating for 4 h and 24 h, respectively. The thermal stability tests using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and hydrothermal stability tests under boiling water for 24 h suggest that the TiO2 nanorods coated hybrid monoliths are very stable. An as-prepared 9-cm-long TiO2 nanorod-array monolithic device was demonstrated as a continuous flow fixed-bed absorbent with efficient performance in Rhodamine B removal from aqueous solution.

Amorphous silica nanowires generally grow in either a metal-catalyzed vapour–liquid–solid (VLS) process or a solid–liquid–solid (SLS) process. So far, ordered alignment of impurity-free SiOx (1 < x < 2) nanowires has not been achieved. In this study, without using metal catalysts, laterally aligned amorphous silica nanowire arrays have been successfully synthesized on a Si(100) substrate surface at ∼700–1100 °C. These amorphous silica nanowires have diameters of ∼100–350 nm and lengths of ∼1–20 μm, which are uniformly decorated with ∼4–11 nm SiO nanocrystals as a result of possible thermal decomposition of amorphous silica at high temperature. A carbon-assisted and lattice strain driven mechanism might be responsible for the lateral alignment of these SiO nanocrystal decorated amorphous silica nanowires.