Adsorption of 2,4-dichlorophenoxyacetic acid over Fe–Zr-based metal-organic frameworks: Synthesis, characterization, kinetics, and mechanism studies

Biochar produced by thermal decomposition of biomass under oxygen-limited conditions has received increasing attention as a cost-effective sorbent to treat metal-contaminated waters. However, there is a lack of information on the roles of different sorption mechanisms for different metals and recent development of biochar modification to enhance metal sorption capacity, which is critical for biochar field application. This review summarizes the characteristics of biochar (e.g., surface area, porosity, pH, surface charge, functional groups, and mineral components) and main mechanisms governing sorption of As, Cr, Cd, Pb, and Hg by biochar. Biochar properties vary considerably with feedstock material and pyrolysis temperature, with high temperature producing biochars with higher surface area, porosity, pH, and mineral contents, but less functional groups. Different mechanisms dominate sorption of As (complexation and electrostatic interactions), Cr (electrostatic interactions, reduction, and complexation), Cd and Pb (complexation, cation exchange, and precipitation), and Hg (complexation and reduction). Besides sorption mechanisms, recent advance in modifying biochar by loading with minerals, reductants, organic functional groups, and nanoparticles, and activation with alkali solution to enhance metal sorption capacity is discussed. Future research needs for field application of biochar include competitive sorption mechanisms of co-existing metals, biochar reuse, and cost reduction of biochar production.

Proton conducting materials have garnered immense attention for their role as electrolytes in fuel cells. Metal Organic Frameworks (MOFs) and coordination polymers have recently been investigated as possible candidates for proton-conducting applications. Their crystallinity, chemically functionalizable pores and options for systematic structural variation are some of the factors that allow for the targeted design of better proton conductors operating over a wide variety of temperatures and/or humidity conditions. This review will examine selected examples from this nascent field, and will focus on the design and synthesis of proton conducting MOFs, their properties and conditions under which they operate.