Studies on low-carbon designed adsorbents for Cr(VI) and tetracycline removal: Insight into the diverse activation and adsorption mechanism

It is of great significance to identify adsorption mechanisms for designing low-carbon adsorbents to treat complex pollutants. The adsorption of biochar is greatly influenced by its surface functional groups. Various functional Typha biochars activated using KOH (KTBs) and ZnCl 2 (ZTBs) through an integrated method exhibited different removal capabilities when treating inorganic (hexavalent chrome) and organic (tetracycline) pollution. Specifically, KTBs presented a better removal efficiency of 99.24 % for TC, while ZTBs exhibited a superior efficiency of 99.20 % for Cr(VI) removal. In conjunction with studies on morphologies and adsorbabilities, the adsorption mechanisms were thoroughly investigated using XPS and density functional theory (DFT) simulation. The adsorption of TC is mainly influenced by hydrogen bonding and π-π interactions, while the removal of Cr(VI) is primarily attributed to surface potential electrostatic attraction and functional groups containing zinc. Based on the adsorption mechanism, CrO 4 2- and/or Cr(OH) 3 were selectively extracted and concentrated from the complex hybrid wastewater by simply controlling the pH values of the solution. This novel approach presents a new method for recovering secondary resources through adsorption and desorption processes. The study offers a low-carbon feasible method for synthesizing suitable biochars for various specific targets and provides an effective solution for emergency wastewater treatment . • Functionalized biochars are assembled using optimized activation strategies. • Adsorption abilities and characteristics were studied to reveal the underlying mechanisms. • Various functional groups play distinct roles in the adsorption of Cr(VI) and tetracycline. • DFT is deployed to address the interaction mechanism between adsorbent and adsorbate. • Deep and accurate mechanistic analyses help in the design of specialized adsorbents.