Layered double hydroxides/biochar composites as adsorbents for water remediation applications: recent trends and perspectives

Adsorption is an effective technology for wastewater treatment processes. Activated carbons are the adsorbent materials traditionally used in most of the applications but sometimes their use is limited due to the high-cost of synthesis/production and for their partial or difficult regenerability. For these reasons, scientists have turned their interest in synthesizing new and cheaper composites materials with efficient adsorptive properties. In this scenario, layered double hydroxides/biochar composites (LDHs-biochar) have attracted a great interest due to their elevated adsorption performances for a wide spectrum of pollutants, deriving from the synergistic effects arising upon the combination of LDHs with biochar. This review article focuses on the application of LDHs-biochar composites for the removal of pollutants of different nature (i.e. heavy metals, dyes, phosphate, etc.) from aqueous matrixes. Specific emphasis is given to the synthesis and characterization of these materials. Equilibrium and kinetic data are presented together with their modeling analysis and further insights about the thermodynamics of the adsorption are also provided. A specific insight into adsorption mechanisms, including the interpretation of the interactions between the solid matrix and the contaminants, was considered in this review. The review indicated that LDHs-biochar composites are promising materials that can be proficiently applied to wastewater treatment in terms of efficiency and costs demands. However, there is still a need of research efforts in order to establish this class of materials as proficient adsorbents to remove critical contaminants.