The phrase "is mentioned that" is correct and usable in written English.
It is typically used to introduce a statement about what someone has said or indicated, and it may be followed by a quotation or paraphrase. For example: It is mentioned that "The most important thing is to stay positive."
Vinterberg allows himself a touch of asperity when the word "comeback" is mentioned: "That implies I've been away.
The hearing will be broadcast here on a short time delay (in case anything is mentioned that might jeopardise national security), and I will live blog it.
Any time an artist is mentioned that is on tour, Bandsense automatically creates a link to the artist page on songkick so the reader can find out more.
Another article is mentioned that is supposed to link technology use and increased obesity.
It is mentioned that the three-dimensional structures of proteins are dictated by their linear sequences of amino acids.
It is mentioned that the actor's lawyers had likened his time filming on location to serving in Afghanistan.
In "Discovering the Universe" by Comins and Kaufmann, it is mentioned that cool main sequence stars have broader absorption lines than hot main sequence stars.
In literature, it is mentioned that the buildings, masonry structures included, should have a ductile behavior when subjected to earthquake loads.
It is mentioned that the first four types make use of K+ channels specially attuned to metabolic changes to transduce stimuli.
It is mentioned that the industrial application of the RF hollow anode is based on the surface modification as yielded in-situ/in-vacuo almost immediately after treatment.
It is mentioned that physiology of prokaryotic cells arose extremely early in evolution and have diverged to cover a tremendously broad spectrum of metabolic and molecular alternatives.
