Dear Dr Shaheen

A positive adsorption energy value indicates that the adsorption of the gas molecule onto the metal oxide surface is not favorable energetically. In other words, the gas molecule is not strongly attracted to the surface, and there might be weak interactions between the gas and the surface. While negative adsorption energy values typically indicate stronger binding and favorable adsorption, positive values are not uncommon and can still provide valuable insights into the interaction between the gas and the surface. Here's how you can interpret and explain a positive adsorption energy in your study of formaldehyde on a metal oxide monolayer:

In summary, a positive adsorption energy is acceptable and can provide valuable information about weak interactions between gas molecules and surfaces. It's crucial to carefully interpret the results in the context of the specific system you're studying and consider multiple factors that might contribute to the observed behavior.