Recent research published in Angewandte Chemie International Edition reveals that gamma radiation can convert methane into a wide array of chemical products at room temperature, offering insights into both cosmic processes and industrial applications. Led by Weixin Huang at the University of Science and Technology of China (Hefei), this study uncovers how gamma radiation—high-energy photons commonly found in cosmic rays and unstable isotope decay—can drive chemical reactions that transform simple molecules like methane (CH4) into more complex organic compounds. These findings have important implications for understanding the formation of organic molecules in the universe and the potential origins of life.
Methane is abundant in the interstellar medium, present in space as a key component of molecular clouds and icy mantles surrounding dust grains. The researchers propose that gamma radiation provides the energy necessary for driving chemical reactions in these environments, leading to the formation of more complex organic molecules. While most studies of cosmic processes have focused on simulating extremely low temperatures and vacuum conditions found in outer space, Huang’s team deviated from this approach by investigating reactions involving methane under more Earth-like conditions—namely, at room temperature. They exposed methane to gamma radiation from a cobalt-60 emitter in both gas and aqueous phases, a setting more representative of the conditions found in space.
The results of their experiments demonstrate that gamma radiation can initiate the conversion of methane into a variety of organic products, though the yield and types of products vary depending on the experimental conditions. When pure methane was exposed to gamma radiation, it produced small amounts of ethane, propane, and hydrogen. However, when oxygen was added to the reaction, the conversion rate increased significantly, leading to the formation of carbon dioxide (CO2), carbon monoxide (CO), ethylene, and water. This suggests that the presence of oxygen in the interstellar medium could be crucial in facilitating more complex chemical processes.
Interestingly, the addition of water in the reaction led to the formation of acetone and tertiary butyl alcohol in the aqueous phase, while in the gas phase, ethane and propane were still predominant. When both water and oxygen were introduced, the reactions accelerated even further. In the aqueous phase, this combination led to the formation of formaldehyde, acetic acid, and acetone. The most remarkable finding, however, was that when ammonia was also added to the mix, acetic acid could be further converted into glycine, an amino acid that has been found in space. This discovery is significant because glycine is one of the building blocks of life, and its formation under these conditions suggests that similar processes could have played a role in the emergence of life on Earth—or elsewhere in the universe.
Huang and his team developed a reaction scheme to explain the mechanisms behind these transformations. Oxygen and hydroxyl (∙OH) radicals are central to the process, and their role is not dependent on temperature. This finding is important because it implies that such reactions could occur under the cold and low-pressure conditions present in space, further supporting the idea that complex organic molecules might form naturally in the interstellar medium.
The researchers also discovered that the presence of various solid particles commonly found in interstellar dust, such as silicon dioxide, iron oxide, magnesium silicate, and graphene oxide, affected the selectivity of the methane conversion. For example, silicon dioxide led to a more selective conversion of methane into acetic acid. This suggests that the varying compositions of interstellar dust could influence the types of molecules formed in space and help explain the uneven distribution of organic compounds observed in different regions of the universe.
The implications of this study extend beyond the realm of astrophysics. The researchers point out that gamma radiation is a readily available, safe, and sustainable source of energy that could be harnessed for industrial applications. The ability to efficiently convert methane into high-value products, such as glycine, acetic acid, and acetone, under mild conditions (room temperature) could offer a new avenue for utilizing methane, a potent greenhouse gas, as a raw material for industrial synthesis. This presents a promising strategy for methane recycling, one of the longstanding challenges in industrial chemistry.
Source: Wiley