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Constructing robust catalysts by growing nanostructure arrays directly onto honeycomb monoliths is a promising technology for fabricating highly active reactors with low materials usage and cost-effectiveness. In this study, catalytically active NiO nanosheet arrays were uniformly grown onto the channel surfaces of cordierite honeycombs to form monolithic catalysts with ultra-low loading. Ce doping was found to significantly enhance the catalytic propane oxidation performance of pristine NiO nanosheet arrays. With a Ce doping of ∼4 wt.% in NiO, a conversion of 90 % propane oxidation into CO2 was achieved at 440 °C, a ∼40 °C decrease compared to the pristine NiO under a space velocity of 24,000 h−1. With the promoting effect of Ce, the Ce-doped NiO nanosheet arrays exhibited a much better thermal stability, with only 1.1 % loss of conversion after a 48 h operation at 425 °C, in comparison with a 21.5 % loss over the pristine NiO catalyst.

One-dimensional titanium dioxide (TiO2) nanostructure arrays (nanoarrays) are important metal oxide nanomaterials that can be synthesized via facile solvothermal methods. The properties of the organic solvents can impose significant effects on the microstructures and properties of the final products. However, the discussions were limited to the homogeneously nucleated TiO2 nanomaterials in free-standing powder form, while the solvent effects are less understood during the heterogeneous growth of TiO2 nanoarrays on a substrate surface. In this work, six organic compounds, namely 2-butanone, n-decane, n-hexane, toluene, ethylene glycol and ethanol, were selected as the solvents for the solvothermal synthesis of TiO2 nanoarrays on the cordierite monolithic substrates. Special attentions are paid to the morphology, crystallinity, specific surface area, and porosity of the samples. The heterogeneous growth of TiO2 nanoarrays on substrate surfaces is found to favor the solvents with moderate dielectric constants, which can be partially dissolved in the aqueous solution and modulate the reaction rate during the solvothermal synthesis. Organic solvents with low dielectric constants may result in a complete separation between the precursors and aqueous solution, and therefore slow down the overall reaction, causing the insufficient growth of the nanoarrays. The TiO2 nanoarrays are obtained with optimum morphology from the combination of 2-butanone and titanium (IV) butoxide as solvent and precusor, respectively, with a high specific surface area up to 56 m2/g including cordierite substrate given a micron thickness. When loaded with Pt catalyst, the TiO2 nanoarray-based monolithic catalysts show excellent low-temperature catalytic activity and hydrothermal stability for the CO and hydrocarbon oxidation under the simulated exhausted conditions. This work shall shed light on a better understanding of the growth mechanism and rational design of TiO2 nanoarrays for high-performance catalytic converters.

Photoabsorption, charge separation efficiency and surface reactive catalytic sites are three critical factors in semiconductor photocatalytic process, which determine the photocatalytic activity. For bulk g-C3N4 derived from direct pyrolysis of C/N rich precursors, reactive sites distributed on the lateral edges are very scarce. In this work, we report the template-free preparation of three novel structured g-C3N4, namely, porous tubular (PT) g-C3N4, porous tubular yolk-shell (PTYS) g-C3N4, and porous split yolk-shell (PSYS) g-C3N4, by an unprecedented precursor microstructure regulation of melamine crystals in a gas-pressure mediated re-crystallization process. Enhanced photoabsorption, increased surface area, largely improved separation and migration efficiencies of photoinduced charge carriers are simultaneously realized in these g-C3N4 structures. Noticeably, selective photo-deposition test uncovers that the porous outer-walls and inner-rods of PTYS g-C3N4 are enriched by abundant reductive reactive sites, which consumedly boost the photo-reduction activity. Collectively promoted by these advantages, PTYS g-C3N4 shows not only an efficient H2 production activity with a high apparent quantum efficiency (AQE) of 11.8% at λ = 420 ± 15 nm, but also a superior CO2 reduction for CO production than bulk g-C3N4 by a factor 5.6, which is verified by the 13C isotopic labeling. This work develops precursor microstructure engineering as a promising strategy for rational design of unordinary g-C3N4 structure for renewable energy production.

Diesel soot combustion suffers from ignition temperatures (T10) as high as > 450 °C in the absence of catalysts, which are unavailable in diesel exhaust during normal driving cycles (normally 200–400 °C). A catalytic diesel particulate filter (CDPF) could decrease T10 greatly, but it is often inadequate due to the poor contact associated with the solid (catalyst)-solid (soot) interactions. Herein, a highly significant T10, as low as ˜200 °C, was achieved on noble metal-free ultrathin MnO2-x nanosheet array fabricated by in situ etching of a La layer from LaMnO3 under loose contact conditions in a NO-containing atmosphere. A number of advantages were found with such a system including the improved reducibility. Then, the nanosheet array ensures high dispersion of soot on the catalyst. Finally, high NO-to-NO2 oxidation activity further facilitates contact between catalyst and soot via NO2, a stronger oxidant than O2.

A new, surfactant-free hydrothermal method has been developed for the growth of CeO2-based nanoflake arrays onto three-dimensional-channeled cordierite honeycomb substrates. Herein, a leaching-crystallization mechanism was proposed where the hydrothermal reaction, only involving cerium nitrate and water, leached the cordierite surface slightly and induced the formation of CeO2 nanoparticles subsequently. Further continued reaction reincorporated Al and Si atoms leached from cordierite into CeO2, finally recrystallizing Ce-Al-Si composite nanoflake structures. By using atomic layer deposition process, well-dispersed, size-controlled Pt nanoparticles were uniformly decorated on the CeO2-based nanoflakes to form the Pt/ CeO2 nano-array-based monolithic catalyst. Despite 5-50 times reduction in the active material usage compared with the traditional wash-coated catalyst, the Pt/CeO2 nano-array monolithic catalyst exhibited good catalytic oxidation activities over various individual gases, such as propylene, propane, CO, and NO oxidation, with 90% conversion efficiencies at temperatures below 200 °C. Under the simulated exhaust condition of low-temperature diesel combustion (LTC-D) developed by US DRIVE, the monolithic catalyst with low Pt loading (˜1 g/l) exhibits 90% conversion of catalytic oxidation over CO and hydrocarbonsat temperatures as low as ˜180 °C, much superior to the performance of traditional washcoated catalysts.

High performance of an ultra-low Pt loading diesel oxidation catalyst can be achieved by using a combination of novel nano-array structured support, precise control of ultrafine active Pt particles, and an addition of H2 as a promoter into the exhausts. Highly stable mesoporous rutile TiO2 nano-array was uniformly grown on three-dimensional (3-D) cordierite honeycomb monoliths using a solvothermal synthesis. Atomic layer deposition was employed for precise dispersion of ultrafine Pt particles (0.95 ± 0.24 nm) on TiO2 nano-array with a Pt loading of 1.1 g/ft3. Despite low Pt loading, the Pt/TiO2 nano-array catalyst shows impressive low-temperature oxidation reactivity, with the conversion of CO and total hydrocarbon (THC) reaching 50% at 224 and 285 °C, respectively, in the clean diesel combustion (CDC) simulated exhaust conditions. The excellent activity is attributed to the unique nano-array structure that promotes gas-solid interaction and ultra-small Pt particle dispersion that increase surface Pt atoms. We also demonstrate that addition of more H2 into the exhaust can lower light-off temperature for CO and THC by up to ∼60 °C and ∼30 °C, respectively.

Channel surfaces of 3-D cordierite honeycomb were readily etched with basic solution and became rougher with formation of a uniform layer of silicate nanosheet array structures. The reaction between KMnO4 and Co(NO3)2 was applied for integrating Mn-Co-O nanosheet array on both blank and modified cordierite honeycombs. The etched cordierite channels can induce the Mn-Co-O arrays with larger unit size, higher density and thickness. Compared to the blank cordierite, the Mn-Co-O array on etched cordierite has much better catalytic performance in oxidation of hydrocarbons, which can be due to its varied features such as more abundant porosity, higher surface area, more Mn4+, Co3+ and adsorbed oxygen species. This study provides an efficient way for tuning the nanostructures of Mn-Co composite oxide nano-array based monolith, further boosting their catalytic activities in combustion of hydrocarbons.

In this study, a new type of lean NOx traps (LNT) based on Pt:La0.8Sr0.2MnO3 (LSMO) nanoparticles decorated on ZnO nanorod array integrated monoliths have been successfully designed and demonstrated. Compared to the commercial catalyst, the nanorod array based catalyst demonstrates competitive NO oxidation activity, and exceptional hydrothermal stability and recoverability after sulfur poisoning. With uniform distribution of perovskite and Pt nanoparticles, the ZnO nanorod array retains its structure after long-time exposure to the reducing gaseous atmosphere. The H2 treatment induces the surface Mn4+ reduction to Mn3+ and subsequently to Mn2+, affecting oxygen mobility, and decreasing the amount of surface lattice oxygen on the LSMO perovskite, thus leading to the catalyst performance decay according to a Mars-Van Krevelen reaction mechanism. Such surface state change was found to be reversible, with the catalytic performance fully recovered after O2 re-treatment, making it suitable for NOx storage and reduction (NSR). The complete lean NOx traps are formulated with rationally-designed sequential BaCO3 and Pt loading, improving NOx storage capacity. The ZnO nanorod array supported LNT shows good water compatibility under simulated exhaust. The nanorod array catalysts may be potentially suitable for vehicular NOx emission control.

Rational modification of interfacial structure and chemistry can help effectively tailor the reactivity and stability of heterogeneous catalysts regardless of their elemental or compound natures. Herein, a diluted acidic treatment was designed and utilized to modify the surface structure and chemistry of spinel Co3O4 nanoparticles. Such a chemical leaching strategy has significantly promoted the propane oxidation activity of the PGM-free Co3O4 nanocrystal aggregates. With a much higher activity than the commercial Al2O3 supported Pt and Pd catalysts, these leached nanoparticle aggregates exhibited much more abundant defects, surface Co2+ and chemisorbed oxygen species. Such surface-modified Co3O4 nanocatalysts have displayed excellent and stable propane oxidation efficiency independent of both O2 and C3H8 concentrations, where the activities of both commercial Pt (or Pd)/Al2O3 and self-made Pt (or Pd)/CeO2 catalysts were greatly affected by different O2 and C3H8 concentrations. Meanwhile, the Co3O4 nanocrystal aggregates catalyst exhibited good performance in presence of water or sulfur dioxide. This facile chemical leaching based technique provides a potential means to make highly active and stable oxide catalysts.

Stranded Natural Gas (SNG) flaring has increased over the last decade resulting in additional Green House Gas (GHG) emissions and underutilization of our finite fossil fuel resources. However, utilization of SNG is difficult due to its low volume, inconsistent composition, and intermittent flow. In this paper, intensified Chemical looping for Ammonia Synthesis (CLAS) is explored as a process suitable for remote deployment at SNG sites. CLAS mediate ammonia synthesis by using compounds that carry nitrogen and hydrogen in stepwise reactions, allowing ammonia synthesis under milder conditions and smaller, more flexible processes. The challenge in CLAS is to find a feasible combination of materials and process conditions that yield ammonia at economically acceptable rates. We propose a framework that systematically evaluates CLAS to determine their suitability for SNG deployment. CLAS reaction schemes are reviewed and organized based on the mediating compounds used to synthesize ammonia. Different compounds are evaluated for each CLAS in search of a thermodynamically spontaneous pair. Spontaneous CLAS flowsheets are, then, optimized to maximize ammonia output at equilibrium. The results are ranked against performance metrics of energy intensity, efficiency, and cost. Chemical loops with Ca3N2/CaH2, SrH2/Sr3N2, MnO2/Mn5N2 and MoO2/Mo2N are found to have favorable performance, along with literature-reported evidence and are recommended for further evaluation toward a distributed ammonia synthesis solution.

Significant reduction of noble metal catalyst loading and simplification of electrode fabrication are urgently needed in order to lower the cost of proton exchange membrane electrolyzer cells (PEMECs) for large-scale hydrogen production. Herein, we report an integrated electrode design comprising in-situ grown platinum nanowires (PtNW) on ultrathin titanium liquid/gas diffusion layers (LGDLs) via a cost-effective and green chemical synthesis approach. The ultrathin integrated PtNW electrodes showed a low cell voltage of 1.643 V and high efficiency of 90.08% at 1000 mA cm−2 using about 15 times lower catalyst loadings than a conventional catalyst-coated membrane in PEMEC tests. Ex-situ electrochemical characterizations and microscale visualizations further reveal that PtNW electrodes display highly efficient hydrogen evolution reactions and excellent electrode durability due to high active surface area, favorable bubble detachment, and structural stability. This work provides new insights into catalyst layer design and facile ultrathin electrode fabrication for more compact and low-cost PEM electrolyzers, fuel cells and other systems.

Mesoporous manganese doped cerium oxide catalysts were prepared by an inverse micelle method with different manganese loadings. These materials exhibited superior activity for epoxidation of alkenes with molecular oxygen. Highest active 10MnCe material showed an activity of 80 % conversion and >99 % selectivity for cyclooctene epoxidation. The fluorite crystal structure which facilitates the high oxygen mobility, low temperature reducibility, homogeneous distribution of manganese on ceria, nanoparticle nature, higher number of oxygen vacancies, low valent states of manganese and cerium, and the ability to generate reactive oxygen species of the manganese doped cerium oxide could be correlated to the high catalytic activity. The reaction followed first order kinetics with a rate constant of 0.31 h−1 at 100 °C, and the activation energy turned out to be 10.5 kJ/mol. The mechanistic study revealed that the reaction proceeds via a unique mechanism which involves in situ generated superoxide and singlet oxygen species.

Reducing the mass transfer resistance globally of a catalyst is a key to enhancing the catalytic reaction kinetics and fully utilizing the catalyst activity. Despite the success in tailoring the external mass transfer in the widely studied washcoat monoliths, the internal mass transfer resistance is difficult to be reduced due to the requirement of increasing macroporosity while maintaining high specific surface area and mechanical stability. Therefore, nanostructured array-based monolithic catalysts (nanoarray catalysts) have been developed in the past decade as a promising class of structured catalysts that may complement or substitute washcoat catalysts. This work fundamentally elucidates the enhanced mass transport properties of the nanoarray monolithic catalysts by a combination of experimental measurements and theoretical modeling. Using a low-dimensional model, the relative contributions of resistances were quantified in terms of chemical kinetics, internal and external mass transfers based on a probe model of C2H4 oxidation over the TiO2 supported Pt-based monolithic catalysts. The nanoarray catalysts displayed a lower internal mass transfer resistance than the washcoat counterparts as a result of the high macroporosity and small thickness of nanoarray layers. The nanoarray configuration provides a new pathway towards designing high-performance monolithic reactors and catalysts with low internal diffusion limitations for various gas phase reactions.

Low temperature propane oxidation has been achieved by Co3O4-based nano-array catalysts featuring low catalytic materials loading (15 mg under flow rate of 150 mL/min). The increased Ni doping into the Co3O4 lattice has led to 100% propane conversion at low temperature (

Atomically-thin two-dimensional (2D) nanostructure, an emerging class of nanomaterials, has achieved tremendous progress in the past decade and will remain a significant research topic in the near future Apart from the discoveries of various 2D nanomaterials, remarkable attentions have been paid to the rational design and alteration of architectures based on pristine 2D materials to meet demands of next-generation functional applications in the near term Herein, this review intends to provide an instant survey over the recent key advances on the structural engineering strategies of 2D nanomaterial-based architectures for new sensing capabilities and opportunities Through intrinsic or extrinsic alterations, the pristine 2D nanostructures of some unique intrinsic properties could be modified and functionalized in a predictable pattern to overcome existing drawbacks and obtain synergistic abilities, demonstrating a great potential in promoting sensing device performance In parallel with the review of latest development of structural engineering strategies and related highly functionalized sensor devices including sensing capabilities towards Covid-19 antigens, the underlying mechanisms of these designs are revealed to offer a unique insight in understandings of architecture design and property tailoring for boosting new sensing capabilities and performances

Gas flaring in oil/gas drilling and gas leakage in natural gas power plant lead to significant energy loss and environmental burden. Here, solar-driven efficient methane oxidation was demonstrated under high velocity continuous flow over the ZnO/La0.8Sr0.2CoO3 (ZnO/LSCO) heterojunctions. The ZnO/LSCO heterojunctions enable a unique epitaxial hetero-interface, which effectively regulates the electron transfer between Zn 3d-O 2p hybrid orbital in ZnO and Co eg orbital in LSCO and promotes the rapid generation and refill of oxygen vacancy with unpaired electron (Vo ), thus enhancing the activity and mobility of surface lattice oxygen in ZnO/LSCO. Under solar illumination, the synergy of photothermal and photocatalytic effect boosts the reversible electron transfer in the interface, which further activates surface lattice oxygen, resulting in a ∼2 times higher methane oxidation activity. Such a solar-driven system not only enables a promising pathway for emitted methane utilization, but also provides an advanced catalyst design concept of epitaxial interface construction.

We report a self-limiting growth method of ultrasmall Pd-containing bimetallic nanocatalysts supported on carbon through under temperature reduction (UTR). The UTR phenomenon is observed for the (co)reduction of a second base metal precursor (M = Co, Ni, and Zn) below its thermodynamic reduction temperature in the presence of Pd. The origin of the UTR phenomenon lies in the hydrogen spillover of Pd to drive the (co)reduction of the base metal at the temperature below its thermodynamic reduction temperature; while, the further reduction is shut down simultaneously to limit the overgrowth of nanoparticles when forming nanoalloys. Using nitrided carbon as a support, we demonstrate the self-limiting growth of three Pd-containing nanoalloys, including Pd1.7Co, Pd1.6Ni and Pd2Zn, with average sizes around 1.5 nm using UTR. Sub-2 nm Pd-containing bimetallic nanoalloys exhibited excellent catalytic properties in both methanol electrooxidation and selective hydrogenation of cinnamaldehyde.

A hydrothermal strategy combined with colloidal deposition synthesis was successfully used to grow ZnO/perovskite (LaBO 3 , B = Mn, Co, Ni) core–shell nanorod arrays within three dimensional (3-D) honeycomb cordierite substrates. A facile sonication assisted colloidal wash coating process is able to coat a uniformly dispersed perovskite nanoparticles onto the large scale ZnO nanorod arrays rooted on the channel surfaces of the 3D cordierite substrate achieved by hydrothermal synthesis. Compared to traditional wash-coated perovskite catalysts, an enhanced catalytic performance was observed for propane oxidation with 25 °C lower light-off temperature than powder-form coated perovskite catalyst of similar LaMnO 3 loading (4.3 mg). Temperature programmed reduction and desorption under H 2 and O 2 atmosphere, respectively, were used to study the reducibility and oxygen activity of these core–shell nanorod array based monolithic catalysts, revealing a catalytic activity sequence of LaCoO 3 > LaMnO 3 > La 2 NiO 4 at the initial stage of catalytic reaction. The good dispersion and size control in La-based perovskite nanoparticles and their interfaces to ZnO nanorod array support may contribute to the enhancement of catalytic performance. This work may provide a new type of Pt-group metals (PGM) free catalysts with improved catalytic performance for hydrocarbon oxidations at low temperature.

Monolithic catalysts, also known as structured catalysts, represent an important catalyst configuration widely used in automotive, chemical, and energy industries. However, several issues associated with washcoat based monolithic catalyst preparation are ever present, such as compromised materials utilization efficiency due to a less-than-ideal wash coating process, difficulty in precise and optimum microstructure control and lack of structure–property correlation. In this mini-review, we introduce the concept of nano-array catalyst, a new type of monolithic catalyst featuring high catalyst utilization efficiency, good thermal/mechanical robustness, and catalytic performance tunability. A comprehensive overview is presented with detailed discussion of the strategies for nano-array catalyst preparation and rational catalytic activity adjustment enabled by the well-defined nano-array geometry. Specifically their scalable fabrication processes are reviewed in conjunction with discussion of their various catalytic oxidation reaction performances at low temperature. We hope this review will serve as a timely and useful research guide for rational design and utilization of the new type of monolithic catalysts.

A variety of stannate nanostructures have been fabricated for UV photocatalysis, including zinc- and cadmium-based stannates. As the template nanostructures, high surface-area mesoporous metal hydroxystannate [ZnSn(OH) 6 and CdSn(OH) 6 ] nanoparticles (>100 m 2 /g) have been synthesized using a simple, low-temperature substitution chemical process with controlled porosity, morphology and crystallinity. Post-synthetic thermal treatments were employed to obtain amorphous ZnSnO 3 , CdSnO 3 , ilmenite CdSnO 3 , and crystalline Zn 2 SnO 4 –SnO 2 nanoparticles. As a result, the band gaps can be tuned from 5.4 eV to 3.3 eV and from 4.9 eV to 2.1 eV for Zn-based and Cd-based stannates, respectively. Amorphous ZnSnO 3 porous nanoparticles showed highest activity toward dye degradation under UV illumination followed by the Zn 2 SnO 4 -SnO 2 and ilmenite CdSnO 3 nanostructures due to their beneficial band structure alignment, high conductivities, and high specific surface areas. This study may provide an important strategy for high throughput synthesis and screening of functional complex metal oxide nanomaterials, while the enabled stannate nanomaterials could be utilized in various applications.

Cobalt oxide (Co3O4), a low-cost transitional metal oxide, has been widely studied for catalytic total oxidation of CO and hydrocarbons. However, much less attention has been paid to the poisoning effect due to alkali metals in such oxidation catalysts despite the ease of access to such poisons in both mobile and stationary combustion sources. In this study, the alkali metals such as Na, K and Li were readily deposited onto a Co3O4 catalyst to study their poisoning effect on CO and propane oxidation. 1% doping onto Co3O4 was found to increase the light-off temperature by 50 °C in CO oxidation and over 160 °C in propane oxidation. It is also noted that alkali metals exhibited a ‘locking-effect’ on oxygen of Co3O4, leading to poor oxygen mobility of alkali metal doped catalysts. During the reaction, alkali metals can significantly promote the adsorption of CO2 to form robust surface carbonate species even at high temperature, another reason for the poisoning effect of alkali metals on Co3O4 nanocatalysts for catalytic oxidation.

Manganese oxide (OMS-2), a promising exhaust treatment catalyst, has been successfully integrated onto the channel wall surfaces of cordierite honeycombs in the form of a nanoarray forest. To further improve their catalytic carbon monoxide (CO) oxidation activity, a series of different metal oxide nanocoatings were uniformly grown on the surface of OMS-2 nanoarrays by utilizing a facile and fast microwave-assisted synthesis method. The manganese-cobalt oxide core-shell nanoarray based monolithic catalysts exhibit the highest catalytic performance with a 100% CO conversion at 150 °C, in a sharp contrast with 325 °C for the bare OMS-2 nanoarrays. Different growth mechanisms of the layered Co(OH)2 and spinel Co3O4 induced by different cobalt precursors are used to explain the morphology evolution of the manganese-cobalt oxide core-shell nanoarrays. The Co3+ distributed on the surface of the nanoarrays acts as the active sites for CO oxidation. The small grain size, abundant surface-adsorbed oxygen, and interfacial effects between MnO2 and Co3O4 were found to favor the observed high catalytic activity. A thermal annealing study showed that high temperature induces the sintering of the nanoarray catalyst, which further affects the CO oxidation activity. This fast, cost-effective, and scalable method will provide a new route for synthesizing efficient core-shell nanoarray monolithic catalysts for low temperature catalysis.

Constructed with parallel or honeycomb channels micrometer to millimeter in diameter, monolithic catalysts and reactors have been utilized in various business sectors ranging from mechanical, automotive, fine chemicals, pharmaceutical, to biotechnology industries. However, the performance of state-of-the-art washcoating monolithic catalysts in industry suffers from some long-standing problems such as mediocre-uniformity, need for high catalyst loading, low materials utilization, random catalytic sites, poor washcoat adhesion, short life-time, degradation tendency, all of which lead to much compromised and less-than desirable catalytic performance. In this work, we significantly mitigated these issues and reduced precious metal and metal oxide usages by 10–40 folds, by directly integrating bare monolith structures with ultra-efficient, thermally stable, and physically and chemically well-defined nanostructure arrays. The well-defined nanostructure array monolithic catalysts represent a new and effective model platform for bridging catalytic nanomaterials science and engineering with the practical industrial catalysis.

Ordered TiO 2 /(La,Sr)MnO 3 composite nanorod array catalysts have been successfully fabricated by using a combination of hydrothermal synthesis and radio-frequency (RF) magnetron sputtering method on Si and glass substrates. Electron microscopy, energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) method are used to characterize the structure, morphology, composition and surface area of the as-prepared nanorod arrays. The TiO 2 /(La,Sr)MnO 3 core–shell nanorod arrays exhibit an enhanced CO oxidation activity compared to TiO 2 nanorods, which might be due to the lattice oxygen in (La,Sr)MnO 3 . The TiO 2 /(La,Sr)MnO 3 composite nanorod array may provide a promising class of nanocatalysts for energy and environment applications.

CuxO (x = 1, 2) nanocrystals have been synthesized by the composite-hydroxide-mediated approach. The obtained nanocrystals were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrum. The morphology of the nanocrystals changed from sphere-shaped nanostructures to flower-shaped nanostructures, and finally to nanowires associated with phase transformation from CuO to Cu2O by increasing the temperature. The possible phase transformation mechanism was discussed. The catalytic degradation activity of the CuxO (x = 1, 2) nanocrystals to methyl orange was also investigated. The photocatalytic ability of the sphere-shaped nanostructures is much higher than that of the nanowires, owing to its absorption of wider range of light energy. This work provides a new facile synthesis route of CuxO (x = 1, 2) nanocrystals and suggests their possible application in organic pollutants removal.

Spherical CuO was synthesized by a simple hydrothermal reaction with the yield as high as ∼90%. The size of the CuO spheres can be facilely and selectively controlled to range from several hundred nanometers to a few micrometers simply by adjusting the concentration of the reactants. The CuO spheres consist of many small and uniform nanoneedles with tips about tens of nanometers in diameter. Interestingly, it was found that the initial concentration of reactants plays an important role in the formation of spherical CuO with different size. A growth mechanism of spherical CuO was also proposed based on the observed results. The cyclic voltammogrametry reveals that CuO nanospheres exhibit a remarkable electrocatalytic activity for the oxidation/reduction of H 2 O 2 . This study provides a promising route for the facile and cost-effective synthesis of inorganic nano- and micromaterials, and the synthesized CuO shows great promise in electrochemical applications.

Growth of vertically aligned ZnO nanowire arrays has been extensively studied on a variety of important semiconductor substrates, such as SiC and GaN. Systematic experiments were carried out to investigate the effect of growth parameters to the quality of the nanowires. In addition, the growth of nanowalls connecting individual aligned nanowires was studied and a growth mechanism was proposed. These conductive and interconnected nanowalls are indispensable for nanodevices to be fabricated on nonconductive substrates for serving as a common electrode. Finally, these nanowire arrays have been integrated as ultra violet detectors, which show good optical performance.

The ZnO nanobelts were synthesized by a hydrothermal method. The XRD spectrum indicates that the sample is wurtzite (hexagonal) structured ZnO with lattice constants of a = 3.249 A , c = 5.206 A . SEM and TEM images show the nanobelts to have lengths of 10–20 μm, widths of 50–500 nm, thicknesses of about 30–60 nm, and growth direction of [0001]. Gas sensitivity experiments on ZnO nanobelts were carried out under different temperatures. The results indicated high sensitivities with an operating temperature of only 220 ∘C for the oxidative gas O2, and 305 ∘C for the gas N2. The mechanism of gas sensitive effects is analyzed in detail.

The mechanical resonance behavior of a ZnO nanowire/nanorod at ambient condition has been studied under optical microscope by cutting its length using focused ion beam microscopy. Nanobalance using a ZnO nanowire as the cantilever has been demonstrated for measuring the mass in the order of pico-grams in working atmosphere (see optical microscopy images). The measurement limit of the balance is estimated to be ∼1 pg. The technique demonstrated here has potential for commercial applications in general laboratories, especially for measuring the mass of wet biological cells or species.

Polar surface induced asymmetric growth of single-side teethed ZnO nanocombs was attributed to the self-catalysis of the Zn-terminated (0 0 0 1) surface (Z.L. Wang, X.Y. Kong, J.M. Zuo, Phys. Rev. Lett. 91 (2003) 185502). In this Letter, nanocombs of ZnO with double-sided teeth have been observed. This symmetric growth of the fish-ribbon like teeth has been identified due to the existence of an inversion domain boundary along the ribbon, so that both side surfaces of the ribbon are terminated with the chemically active Zn-(0 0 0 1) plane. A model is also given about the formation of � 110� double-sided nanocombs based on the nucleus composed of multiply twinned pyramids. The data show that the Zn-terminated (0 0 0 1) surface is responsible for the formation of the teeth, while the oxygen-terminated (0 0 0 1) surface is chemically inactive and does not grow teeth. � 2005 Elsevier B.V. All rights reserved.

In this Letter, three-dimensional (3D) interconnected networks of ZnO nanowires and nanorods are synthesized by a high temperature solid–vapor deposition process. The nanorods and nanowires have diameters of 20–100 nm and they grow along the c-axis. Due to the diverse orientation of the nanowires grown from a polycrystalline substrate, the networks are formed by a sintering process of the crossed nanowires during growth. The thickness of the multilayer nano-network could be as thick as � 30 lm. The sharp nanowire tips, the high degree of networking, and high surface area of these unique nanonetworks make them a potential candidate for field emission, ultra-sensitive gas sensing, catalysts and filtering. � 2005 Elsevier B.V. All rights reserved.