Studies of 1D ternary nanostructures, in comparison with 1D binary ones, are relatively more meaningful because the ternary nanostructures exhibit not only more complex functions but also properties that are readily tunable by changing the ratio of the component elements. Reports of 1D ternary nanostructures, specifically nanoribbons, however, have been limited because of the considerable difficulty of their synthesis.

Zinc orthogermanate (Zn₂GeO₄) is an important ternary oxide that exhibits negative thermal expansion below ambient temperature. It also exhibits high-wavelength selectivity in UV photodetectors with fast response and recovery time, bright white-bluish luminescence, photocatalytic water splitting, and mineralization of volatile aromatic hydrocarbons. Several solution routes and gas phase evaporation techniques have been developed for the preparation of 1D nanorods and nanowires of Zn₂GeO₄.

Herein we report for the first time the high-yield synthesis of single-crystalline Zn₂GeO₄ nanobelts with lengths of hundreds of micrometers, thickness as small as ~7 nm (corresponding to five repeating cell units), and aspect ratios of up to 10,000 in a binary ethylenediamine (En)/water solvent system using a solvothermal route. The ultralong and ultrathin geometry of the Zn₂GeO₄ nanoribbon greatly improves the photocatalytic activity toward reduction of CO₂ into renewable hydrocarbon fuel (CH₄) in the presence of water vapor.

—Liu et al.

The nanoribbons delivered a CH₄ yield of ~1.5 µmol g^-1 during the first hour under light illumination. Bulk Zn₂GeO₂ obtained by conventional solid-state reaction (SSR) produced only a trace amount of CH₄.

The researchers attributed the higher photocatalytic activity of the nanoribbons toward reduction of CO₂ relative to that of the SSR sample to four reasons:

• Reducing the lateral dimension to the nanometer length scale as in the nanobelts offers a high specific surface area of 28.27 m²/g, which is more than 37 times larger than the area for the SSR material.

• The superb crystal quality excludes the possibility of any grain boundaries and/or other interfaces (which usually act as recombination sites in polycrystalline materials). This should favor improved separation of the photogenerated electron and hole and decrease the electron-hole recombination rate.

• The ultralong longitudinal dimension provides a sufficiently spacious transport channel for charge separation.

• The ultrathin geometry of the nanoribbons allows charge carriers to move rapidly from the interior to the surface to participate in the photoreduction reaction.

The team found that the rate of CH₄ generation over the nanoribbon could be significantly enhanced by loading of Pt or RuO₂ and especially by co-loading of Pt and RuO₂ as a co-catalyst to improve the separation of the photogenerated electron-hole pairs, as demonstrated in photocatalytic water splitting.

Resources

• Qi Liu, Yong Zhou, Jiahui Kou, Xiaoyu Chen, Zhongping Tian, Jun Gao, Shicheng Yan, and Zhigang Zou (200) High-Yield Synthesis of Ultralong and Ultrathin Zn₂GeO₄ Nanoribbons toward Improved Photocatalytic Reduction of CO2 into Renewable Hydrocarbon Fuel. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja1068596