Nav: Home

Semiconductors combine forces in photocatalysis

January 24, 2019

A significant advance in the photocatalytic activity of conventional materials is demonstrated by a two-dimensional heterostructure comprising nanolayers of two semiconductors: black phosphorus and bismuth tungstate. As researchers have reported in the journal Angewandte Chemie, this catalyst harnesses the energy of visible light to split water and produce hydrogen, and to break down nitrogen monoxide in exhaust gas.

Just as plants use photosynthesis, certain semiconductors are able to absorb the energy of light and use this to power chemical reactions. For example, bismuth tungstate (Bi(2)WO(6)) should, in principle, be suitable for the photocatalytic degradation of nitrogen monoxide (NO) and the production of hydrogen. However, results so far have not been very satisfactory. One approach to improving the performance of this material is to bind two-dimensional nanolayers of the bismuth tungstate into a layered heterojunction with a second nanolayer of a different semiconductor.

A team led by Dongyun Chen and Jianmei Lu at Soochow University, Suzhou, and Jiangsu University, Zhenjiang (China) found that black phosphorus may be a suitable partner for this type of heterostructure. This material demonstrates photocatalytic properties, though it has had limited application to date.

Black phosphorus consists of rippled layers of six-membered rings that can be split into individual atomic layers. The researchers covered these nanolayers evenly with 50 nm chips of bismuth tungstate. The two semiconductors are in very close contact in this simply and efficiently producible heterostructure, resulting in a synergetic effect. The black phosphorus provides a broad absorption range into the spectrum of sunlight. The energy levels of the electrons in the two materials are favorably placed. This allows the light-induced positive and negative charges (electron-hole pairs) to be efficiently separated, transported within the heterostructure, and transferred to molecules. The researchers propose that the charge-transfer mechanism resembles the so-called Z-scheme present in photosynthesis.

As expected, the photocatalytic degradation of NO by the heterostructure was significantly more effective than with other bismuth-based materials. For the photocatalytic production of hydrogen, an additional platinum-based co-catalyst was added. Under irradiation, electrons can move from the heterostructure to platinum atoms, and from there they are able to rapidly reduce the H(+) ions in water to form hydrogen gas. With visible light, the efficiency of the catalytic process was nine times that of pure bismuth tungstate.

The researchers suggest that black phosphorus may have broad applicability that extends to renewable energies and treatment of exhaust gases.
-end-
About the Author

Dr. Jianmei Lu is a Professor at the College of Chemistry, Chemical Engineering and Materials Science, Soochow University, and has been working in the environmental management area for over 30 years.

http://lupolymer.org/en/people/professor-lu/

Wiley

Related Hydrogen Articles:

Paving the way for hydrogen fuel cells
The hype around hydrogen fuel cells has died down, but scientists have continued to pursue new technologies that could enable such devices to gain a firmer foothold.
Keeping the hydrogen coming
A coating of molybdenum improves the efficiency of catalysts for producing hydrogen.
Hydrogen bonds directly detected for the first time
For the first time, scientists have succeeded in studying the strength of hydrogen bonds in a single molecule using an atomic force microscope.
Argon is not the 'dope' for metallic hydrogen
Hydrogen is both the simplest and the most-abundant element in the universe, so studying it can teach scientists about the essence of matter.
Metallic hydrogen, once theory, becomes reality
Nearly a century after it was theorized, Harvard scientists have succeeded in creating metallic hydrogen.
From theory to reality: The creation of metallic hydrogen
For more than 80 years, it has been predicted that hydrogen will adopt metallic properties under certain conditions, and now researchers have successfully demonstrated this phenomenon.
Artificial leaf goes more efficient for hydrogen generation
A new study, affiliated with Ulsan National Institute of Science and Technology has introduced a new artificial leaf that generates hydrogen, using the power of the Sun to mimic underwater photosynthesis.
Hydrogen from sunlight -- but as a dark reaction
The storage of photogenerated electric energy and its release on demand are still among the main obstacles in artificial photosynthesis.
New process produces hydrogen at much lower temperature
Waseda University researchers have developed a new method for producing hydrogen, which is fast, irreversible, and takes place at much lower temperature using less energy.
Hydrogen in your pocket? New plastic for carrying and storing hydrogen
A Waseda University research group has developed a polymer which can store hydrogen in a light, compact and flexible sheet, and is safe to touch even when filled with hydrogen gas.

Related Hydrogen Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#530 Why Aren't We Dead Yet?
We only notice our immune systems when they aren't working properly, or when they're under attack. How does our immune system understand what bits of us are us, and what bits are invading germs and viruses? How different are human immune systems from the immune systems of other creatures? And is the immune system so often the target of sketchy medical advice? Those questions and more, this week in our conversation with author Idan Ben-Barak about his book "Why Aren't We Dead Yet?: The Survivor’s Guide to the Immune System".