The filaments of electron-irradiated silver have better bactericidal, photoluminescent and photodegradation properties than material synthesized through other means

New material has improved bactericidal, photoluminescent and photodegradation properties
2013-05-15

The filaments of electron-irradiated silver may have important applications in areas such as the food industry.

New material has improved bactericidal, photoluminescent and photodegradation properties

The filaments of electron-irradiated silver may have important applications in areas such as the food industry.

2013-05-15

The filaments of electron-irradiated silver have better bactericidal, photoluminescent and photodegradation properties than material synthesized through other means

 

By Elton Alisson

Agência FAPESP – Researchers from the Universidade Estadual Paulista’s Chemistry Institute (IQ-UNESP) in Araraquara have discovered a material with bactericidal, photoluminescent and photodegradation properties that may have important applications in many areas such as the food industry. The study was published in Scientific Reports, part of the Nature group.

The research group is also part of the Multidisciplinary Center for Development of Ceramic Materials (CMDC)—a FAPESP Research, Innovation and Dissemination Center (CEPID). The researchers obtained metallic silver filaments in a compound formed by silver oxide and tungsten (tungstate) using a new material synthesis process.

“These filaments have increased properties compared to conventional material and were obtained through an unprecedented method, which until then was landmark and without description in scientific literature,” said Elson Longo, one of the authors of the article, in an interview with FAPESP. Other study participants included scientists from the Department of Chemistry at the Universidade Federal de São Carlos and the Department of Chemistry at the Universitat Jaume I.

Longo is the coordinator of CMDC and the National Institute of Sciences and Technology on Nanotechnology Materials (INCTMN), also funded by FAPESP, both with headquarters in Unesp’s Chemistry Institute. In the past two years, Longo and other CMDC researchers have initiated a project to examine some of the optical properties—such as photoluminescence—of the silver tungstate through field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM).

During the study, the group verified exponential growth in the filaments of metallic silver on nanometric and micrometric scales in different regions of the surface of tungstate crystals. “At first, we thought the filaments were carbon. After five months of analyzing samples of tungstate crystals, we found that, in fact, silver filaments were growing on the surface of the material,” explained Longo.

Upon studying the growth mechanism and the photoluminescent properties of silver filaments, through a project conducted with FAPESP funding, the researchers found that the electrons of the FE-SEM and HRTEM that fall on tungstate crystals induce a chemical reaction in the materials that lead to the growth of metallic silver filaments.

According to Longo, the interaction of the electrons generated by the microscopes—mainly FE-SEM, whose particles are more energetic—with silver tungstate ions promotes a reduction in metallic silver. “We saw filaments of metallic silver grow on the tungstate in a clear manner in a sequence of short images. These images are published on the internet in the Scientific Reports article,” explained Longo.

“The greater the interaction between the electrons with silver ions, the greater the growth of metallic silver filaments, and it is possible to observe this through scanning or transmission microscopes,” he explained.

According to the researcher, the effect of electron synthesis on silver filaments that they observed is similar to the reaction that causes the photoelectric effect described by Albert Einstein (1879–1955) in 1905, for which he was awarded the Nobel Prize in Physics in 1921.

While the photoelectric effect is the photon of electromagnetic radiation—such as light—which, after contact with the metal, can eject electrons from the material, depending on its energy, when it comes to electron synthesis, it is the electron that, upon contact with metallic material—in this case, tungstate—provokes a chemical reaction, redox.

“This phenomenon that in the article we called ‘electron-driven synthesis of silver filament’ is very innovative, and no one had previously managed to explain it,” commented José Arana Varela, full professor at Unesp’s Chemistry Institute and one of the authors of the study and the article.

“In the article, we explained how this redox reaction is induced by the electrons irradiated from the scanning and transmission microscopes,” affirmed Varela, who is also the FAPESP’s CEO.

New material

According to the Unesp researchers, other international research groups have managed to obtain metallic silver filaments from silver tungstate through other synthesis methods. One of these methods is a hydrothermal method in which pressure and temperature are applied to obtain the product.

However, until now, no research group has attempted to obtain the material through electron irradiation on tungstate, as the Brazilian group did, which increases the photoluminescent, photodegradation and bactericidal properties of the metallic silver filaments, in comparison to the same product obtained through other methods.

“This new material presents advantages in relation to the current bactericide methods, in which silver is deposited in materials—such as polymers—to give them this property,” said Longo. Electron irradiation increases the bactericidal properties of the silver filaments threefold in comparison to the current method of deposition.

Because of this property, the technology for which the group requested the patent has begun to generate interest among manufacturers of bactericides for food packaging. Other possible applications for the new material are photodegradation of organic compounds in water and applications in the areas of ceramics, microelectronics and chemicals.

“We are now studying how to grow these metallic silver filaments in other systems, such as molybdates. We have already found that in molybdates, the material grows utilizing a similar process. We want to see what electron energy limit is enough to induce this reaction and if they improve the applications of existing systems,” said Varela.

The article “Direct in situ observation of the electron-driven synthesis of Ag filaments on α-Ag2 WO4 crystals” (doi: 10.1038/srep01676) by Longo and others, can be read at www.nature.com/srep/2013/130417/srep01676/full/srep01676.html.
 

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