Novel biochar-filled hydrogel composites: Assessment of multifunctionality and potential in environmental applications.

Hydrogels (HGs) are hydrophilic 3D-cross-linked polymers applied, inter alia, to improve soil resistance to drought. Their combination with biochar (BC), a product of biomass pyrolysis, can result in obtaining specific composites characterized by the advantages of both initial materials. The BC introduction into HG can double its swelling degree and increase their sorption capacity by more than threefold compared to the pure HG. Furthermore, the composites are able to increase plants biomass (up to 160%), even under heavy metal contamination, and are characterized by lower nutrient release rate (up to 25%) in comparison to the pure hydrogels. This review explores the properties of biochar-filled hydrogel composites, including swelling degrees and ability to absorb heavy metals and other toxic compounds. Additionally, it discusses their agricultural applications as soil conditioners and slow-release fertilizers, covering their effects on water and nutrient retention in the soil, soil microbial activity, as well as plant performance under contamination and drought stress. Finally, the cost-economic assessment and future prospects of these novel materials were proposed. The BC-filled HGs were considered as highly promising soil amendments, but their application potential depended entirely on the development of new production technologies and the investigation of interactions occurring between the composites and the selected soil components.