Predatory journals are a growing problem in academic fields, and are becoming particularly problematic in the sciences. Unscrupulous publishers take advantage of open access models (publishing models that allow anyone to access journal content without paying subscription costs). However, they publish junk science with questionable methods, results and conclusions. This has the potential to negatively affect future research. The motivations are to make money off of unsuspecting authors by charging them to publish articles, or for authors to unethically increase their publication counts for prestige.
It is important to identify and screen out predatory publishers so that they do not corrupt your literature reviews and research. First, search only reputable library and professional databases such as Medline, PubMed, CINAHL, or Engineering Village. Predatory journals will show up in Google searches. Second, read all research with a critical eye. Read ABOUT the publication, not just the article itself. Ask faculty or a librarian if you are unsure whether an article comes from a reputable journal.