•3D In2O3 nest-like were produced with a two-phase solvothermal method.•This superstructure is composed of nanocuboids and nanobelts.•Porous structures were obtained onto the nanocuboids and nanobelts by annealing.•Two chemical sensors were fabricated with pure nest-In2O3 and Pd NPs@nest-In2O3.•Pd nanoparticles can promote the sensitivity, selectivity and stability.3D hierarchical In2O3 nanoarchitectures with nest-like superstructure were produced successfully with a two-phase solvothermal approach and annealing process for the first time. Nanocuboids and nanosheets with smooth surfaces, which form the 3D nanoarchitectures, can convert to porous In2O3 configurations after annealed at 300 °C for 2 hours. The hierarchical In2O3 materials were applied to make chemical sensors together with Pd nanoparticles. It was found that the devices made with 3D nest-like In2O3 and Pd nanoparticles exhibit enhanced performances in detecting reducing gases, compared to their counterparts fabricated with pure In2O3 materials. Specifically, the sensitivity (S=Ra/Rg) and selectivity of the devices to acetone vapor of 100 ppm can be improved dramatically, after attaching Pd nanoparticles onto the surfaces of the nanoarchitectures.

•Porous In2O3 nanocuboids have been synthesized successfully on a large scale.•In(OH)3 nanocuboids can be first produced in nanoreactors consisting of AOT surfactant and transform to form porous In2O3 nanocuboids topotactically.•The gas sensing performances of the materials are investigated before and after modified with Pd nanoparticles.•The chemical sensors made with Pd@In2O3 nanocuboids show enhanced performances in detecting reduce gases.Porous In2O3 nanocuboids were synthesized successfully on a large scale and characterized with XRD, TG–DTA, BET, FESEM and TEM. The precursors – In(OH)3 nanocuboids, which were first produced in the nanoreactors consisting of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant and In3+ ions, can transform topotactically to form porous In2O3 nanocuboids, after annealed at 300 °C. The gas sensing performances of the materials were also investigated before and after modified with Pd nanoparticles. The chemical sensors made with Pd@In2O3 nanocuboids exhibit enhanced performances in detecting reducing gases such as acetone, compared to those fabricated with pure porous In2O3 nanocuboids.

Porous and single-crystalline Co3O4 nanospheres have been synthesized successfully on a large scale. It was found that the reaction time can dramatically affect the growth of the Co3O4 nanospheres in nanoreactors constructed with AOT− and Co2+ ions. The dynamic evolution of the nanostructures produced in the reaction strongly support a stepwise splitting mechanism proposed to explain the formation of the porous and single crystalline nanospheres. The pseudocapacitors made with the porous and single crystalline Co3O4 nanospheres exhibit excellent charge-storage performance. The enhanced electrochemical properties of the materials can be attributed to their superstructures with pores and single crystalline features.

The direct reactions between ascorbic acid (AA) and palladium salts can produce homogeneous Pd nanoparticles on a large scale by grinding or shaking the two reactants together for ca. 2 minutes at room temperature. The size of homogeneous Pd nanoparticles can be tuned conveniently by using different palladium salts as precursors in the reactions without adding any solvent and organic protectors. Compared to Pd nanoparticles with much smaller sizes of ca. 2.7 nm produced by grinding a solid mixture of AA and Pd(CH3COO)2, homogeneous Pd nanoparticles of 35.6 ± 5 nm can be generated in the direct reaction between AA and Pd(NO3)2·2H2O. It was found that AA can reduce Pd2+ to Pd0 to form Pd nanoparticles directly, accompanied by its oxidation to 2,3-diketogulonic acid (2,3-DKG) and a series of fragment species of 2,3-DKG simultaneously. The small amount of crystalline water in Pd(NO3)2·2H2O can promote the formation of Pd nanoparticles dramatically, compared to the reactions conducted with Pd(CH3COO)2, Pd(NO3)2 and PdCl2 without crystalline water. Based on the experimental results, a two-step reaction mechanism is proposed to understand the formation of Pd nanoparticles. The quasi solid-state features of the direct reactions could lead to defects of high concentration on the surface of the as-prepared Pd nanoparticles, which can be applied to the catalysis of the Suzuki reaction immediately after their formation in the reactions.

ZnO twin-spheres topologically exposed in ±(001) polar facets have been successfully produced on a large scale. The fragmentary and hexagonal ±(001) facets of ZnO tilt and assemble gradually for 8–12 generations to form supercrystals. The surfactant effect on the formation of ZnO supercrystals reveals that their structure stepwise evolves from prisms to dumbbells to twin-spheres exposed in ±(001) facets and eventually to twin-spheres covered with dots. A hollow ring around a prism, which connects two hemispheres of the supercrystals, is finally sealed inside each of the twin-spheres. Based on the experimental observations, a stepwise self-assembly mechanism is proposed to understand the formation of the supercrystals. It is also observed that the ZnO twin-spheres exhibit anisotropic blue emission in intensity attributed to their special surfaces exposed in ±(001) facets. Novel devices could be designed and fabricated through carefully tailoring the microstructure of ZnO supercrystals.Keywords: ±(001) facets; anisotropic emission; self-assembly growth; supercrystals; ZnO twin-spheres

Porous and single crystalline ZnO nanosheets, which were synthesized by annealing hydrozincite Zn5(CO3)2(OH)6 nanoplates produced with a water/ethylene glycol solvothermal method, are used as building blocks to construct functional Pd–ZnO nanoarchitectures together with Pd nanoparticles based on a self-assembly approach. Chemical sensing performances of the ZnO nanosheets were investigated carefully before and after their surface modification with Pd nanoparticles. It was found that the chemical sensors made with porous ZnO nanosheets exhibit high selectivity and quick response for detecting acetone, because of the 2D ZnO nanocrystals exposed in (100) facets at high percentage. The performances of the acetone sensors can be further improved dramatically, after the surfaces of ZnO nanosheets are modified with Pd nanoparticles. Novel acetone sensors with enhanced response, selectivity and stability have been fabricated successfully by using nanoarchitectures consisting of ZnO nanosheets and Pd nanoparticles.Keywords: acetone sensors; enhanced performances; nano-architectures; Pd nanoparticles; self-assembly; ZnO nanosheets;

Free-standing and porous hierarchical nanoarchitectures constructed with cobalt cobaltite (Co3O4) nanowalls have been successfully synthesized in large scale by calcining three dimensional (3D) hierarchical nanostructures consisting of single crystalline cobalt carbonate hydroxide hydrate – Co(CO3)0.5(OH)·0.11H2O nanowalls prepared with a solvothermal method. The step-by-step decomposition of the precursor can generate porous Co3O4 nanowalls with BET surface area of 88.34 m2 g−1. The as-prepared Co3O4 nanoarchitectures show superior specific capacitance to the most Co3O4 supercapacitor electrode materials to date. After continuously cycled for 1000 times of charge–discharge at 4 A g−1, the supercapacitors can retain ca 92.3% of their original specific capacitances. The excellent performances of the devices can be attributed to the porous and hierarchical 3D nanostructure of the materials.Highlights► Free-standing and porous Co3O4 nanowalls have been synthesized on large scale. ► The step-by-step decomposition of precursor generates porous nanoarchitectures. ► Supercapacitors made with the materials exhibit excellent performances.

An in situ growth strategy has been developed for the large scale production of novel nanoarchitectures consisting of single crystalline Co3O4 particles strung together by multi-walled carbon nanotubes (MWCNTs). Both Co3O4 plum-like and octahedra crystals have been grown on and around MWCNTs to form necklace-like structures. Solvents used in the reaction can dramatically affect the size and morphology of Co3O4 single crystals. Plum-like Co3O4 crystals are readily converted to octahedra, after changing the volume ratio of ethylene glycol (EG) to water. The size of Co3O4 single crystals also decreases on lowering the volume ratio of EG to water due to the enhanced polarity of the solvents. The MWCNTs are routinely oriented through the (400) planes of Co3O4 octahedra. This preferred growth orientation can be attributed to a lattice match between the MWCNTs and single crystalline Co3O4 particles.

The direct reactions between ascorbic acid (AA) and palladium salts can produce homogeneous Pd nanoparticles on a large scale by grinding or shaking the two reactants together for ca. 2 minutes at room temperature. The size of homogeneous Pd nanoparticles can be tuned conveniently by using different palladium salts as precursors in the reactions without adding any solvent and organic protectors. Compared to Pd nanoparticles with much smaller sizes of ca. 2.7 nm produced by grinding a solid mixture of AA and Pd(CH3COO)2, homogeneous Pd nanoparticles of 35.6 ± 5 nm can be generated in the direct reaction between AA and Pd(NO3)2·2H2O. It was found that AA can reduce Pd2+ to Pd0 to form Pd nanoparticles directly, accompanied by its oxidation to 2,3-diketogulonic acid (2,3-DKG) and a series of fragment species of 2,3-DKG simultaneously. The small amount of crystalline water in Pd(NO3)2·2H2O can promote the formation of Pd nanoparticles dramatically, compared to the reactions conducted with Pd(CH3COO)2, Pd(NO3)2 and PdCl2 without crystalline water. Based on the experimental results, a two-step reaction mechanism is proposed to understand the formation of Pd nanoparticles. The quasi solid-state features of the direct reactions could lead to defects of high concentration on the surface of the as-prepared Pd nanoparticles, which can be applied to the catalysis of the Suzuki reaction immediately after their formation in the reactions.