The verb “to suggest” never governs the infinitive. (However the noun, “suggestion”, does). The verb “to suggest” governs the subjunctive (a type of noun clause), or a any kind of noun (including the gerund) or noun phrase.
Subjunctive: The teacher suggested (that) Joe study harder.
Noun: The teacher suggested harder study (or, for a more natural sentence, use the gerund, “studying harder”).
By the way, “research” is uncountable, so it has no plural. A countable alternative would be “study”, or we could say a “piece of research”.