Absorb them: Sponge nanoparticles enhance photocatalysis


May 12, 2023

(Nanowerk News) Exciton Science researchers have created a new type of highly absorbent material that can help increase the efficiency of photocatalysis for hydrogen production and water purification.

Based at RMIT University, the team combined silver nanoparticles with a molecular organic cage to develop a new material that acts like a sponge, absorbing sunlight and chemical reactants in beneficial ways.

When tested, this combination resulted in a two-fold increase in the efficiency of splitting water using solar power, which is a critical step in the creation of green hydrogen.

The results, which were achieved in collaboration with the University of Melbourne and Deakin University, have been published in the journal Applied chemistry (“Photo-Initiated Energy Transfer in Porous Cage Stabilized Silver Nanoparticles”). The nanoparticles act as photosensitizers for the porphyrin cage by transferring excited state energy to the porphyrins The new material containing plasmonic silver nanoparticles was synthesized using only a porphyrin-based porous organic cage as the ligand, which decorates the surface of the nanoparticles. The nanoparticles act as photosensitizers for the porphyrin cage by transferring excited state energy to the porphyrins. The photosensitizing effect and porosity of the ligands allow for superior photoelectrochemical water separation compared to the individual components. (© Wiley-VCH Verlag)

First author Michael Wilms of RMIT said: “By increasing the surface area of ​​highly reactive nanoparticles, we greatly increase the conversion of water to hydrogen using only light.”

What is photocatalysis?

Photocatalysis holds promise for harnessing sunlight, a nearly limitless source of energy, in useful chemical transformations, including water purification and the production of sustainable industrial chemical feedstocks and fuels, such as hydrogen and methane.

Efficient light harvesting for these applications requires the development of high performance materials capable of efficiently absorbing and converting light energy into chemicals.

Metal nanoparticles are excellent absorbers of sunlight, but are not suitable by themselves for water and CO2 conversion2 into chemical fuels.

This is because the ligands (molecules that help stabilize these particles) also hinder their ability to carry out chemical reactions on their surface, the most reactive part of the nanoparticle.

Associate Professor Daniel Gomez of RMIT, senior author on the paper and Exciton Science Associate Investigator, said: “In this work we used a truly porous ‘molecular cage’ to synthesize and stabilize highly light-absorbing nanoparticles.”

The molecular cage itself is highly light absorbing and can receive light energy absorbed by metal nanoparticles, making it a ‘sponge’ for light.

Its porosity allows reactants such as water to easily diffuse within metal molecules and nanoparticles, significantly increasing the efficiency of converting water to hydrogen.

“The next step is to use semiconductor materials instead of metal nanoparticles which could increase the efficiency of water separation and allow us to test this new material in CO conversion.2 too,” said Michael.

“We are also actively exploring replacing silver with low-cost semiconductor materials such as zinc oxide and perovskite.”


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