Ecological biopolymers of natural origin are multifunctional, stable, and biocompatible materials. Polysaccharides, such as carboxymethyl cellulose, chitosan, gums, and glucans, are key components of biomass and are characterized by stability, availability, and the ability for structural modification. The exceptional properties of biopolymers hold great potential for the development of new biocompatible nanomaterials. Recently, biopolymers have been actively studied as materials for the synthesis of metal oxide nanoparticles. Metal oxide nanomaterials based on biopolymers hold significant potential in addressing environmental issues, particularly in water purification, which is one of the key environmental challenges. Biopolymer-based catalysts demonstrate high efficiency in removing organic, inorganic, and biological pollutants from wastewater. This review summarizes the latest data on the development of materials based on polysaccharides and the study of their catalytic properties. Special attention is given to nanocomposites based on spinel ferrites, which are used as Fenton-like catalysts for water purification from bacteria, dyes, antibiotics, and other organic compounds.