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Zinc Orthogermanate Nanoribbons Support Improved Photocatalytic Reduction of CO2 to Renewable Methane

CH4 generation over (a) bulk material, (b) nanoribbons, (c) 1 wt % Pt-loaded nanoribbons, (d) 1 wt % RuO2-loaded nanoribbons, and (e) 1 wt % RuO2 + 1 wt % Pt-coloaded nanoribbons as a function of light irradiation time. Credit: ACS, Liu et al. Click to enlarge.

Researchers at Nanjing University and Anhui Polytechnic University in China have synthesized zinc orthogermanate (Zn2GeO4) ultralong nanoribbons which show promising photocatalytic activity toward the reduction of CO2 into renewable methane (CH4) and water.

The team used a En/H2O binary solvent system for the synthesis, and noted that this binary solvent system may provide a new route for preparing other 1D ternary oxides. A paper on their work was published online 24 September in the Journal of the American Chemical Society.

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.


  • 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



Does this mean that coal burning should be put on hold until such times as CO2 emitted can be converted to liquid fuels or methane gas?

The Goracle


Why do we hate trees so much? Why try to cut back on CO2, food for trees, when there is no evidence that current CO2 levels has any type of impact on the planet's temperatures?

Trees are our friends!!!



Where does the oxygen go in this equation? CO2 + H20 -> CH4 + (2)O2. That's a rather explosive gas mix. One of the advantages of eletrolysis is that it keeps the decomposed gasses isolated from each other. In the article I see no mention at all about the oxygen being released, although the abstract does show oxygen in the graphic. Since it's a subscription site, I'm not curious enough to spend the $30 to find out about this rather important detail.


Goracle: Trees need CO2 but we don't. What is your choice.


Oh yes, the old "CO2 is plant food" joke, how well I remember it. Guess what? So is water, now go ask Pakistan if they want more rain.

More of a good thing is not always a better thing.

A team from the University of Guelph has determined that Trees are soaking up less carbon than expected given the increase in atmospheric CO2. According to the press release, “Scientists and policy-makers hoping to use forests to naturally soak up increasing amounts of carbon dioxide may have overestimated the role of trees as carbon sink”.

“Contrary to expectations, tree growth has declined over the past century despite rising amounts of CO2 in the atmosphere, said Madhur Anand, a professor in Guelph’s School of Environmental Sciences.”


Nice chemistry, but this will never compete with solar-electric combined with watersplitting. These catalysts are extremely expensive and fragile. Adding (never completely pure) water and CO2 to these catalysts over square miles of area, and collecting the gases makes it very complicated and even more fragile, while simply using classical solar or solar-thermal electricity to split water at a central point is comparatively much easier. Even more, if you use electrical water-spliting you can use off-peak electricity of any source.


Alain has it right. Using concentrated solar thermal/electric and efficient electrolysis can make H2 and O2 used in gasification and synthesis of fuels.


Except you'd be much better of using solar to displace natural gas, either through through PV powering air conditioning or using CSP to provide the heat for a steam cycle.


Better is a judgement term. If I gasify biomass and increase yield using solar thermal electric H2 and O2, I can power cars with methanol. I can power 100 million cars with methanol, not 1 million EVs.

By The Way, you don't need PVs to power AC, if you have absorption AC using heat from CHPs. Or just use evacuated tube solar thermal collectors and absorption AC. Either way, seek the most good for the most people using the least resources and you will probably be on the right track.


1.5 micro-mol per gram per hour is about 24 micrograms per gram per hour. It would take about 42,000 hours for these nanoribbons to generate their mass in methane.

Well, it's a start.


I think they wanted to show it could be done, the commercial applications may come later.


I just learned reading Dr. Olah's book Methanol Economy that it is CO2 that is used in making methanol. The CO is shifted to CO2 and that is used in the catalytic reaction.

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