The current study aimed to assess the effectiveness of biochar formed from algae in the removal of Cr(VI) through the process of impregnating brown algae Sargassum hemiphyllum with KHCO3. The synthesis of KHCO3-activated biochar (KBAB-3), demonstrating remarkable adsorption capabilities for Cr(VI), was accomplished utilizing a mixture of brown algae and KHCO3 in a mass ratio of 1:3, followed by calcination at a temperature of 700 °C. Based on the empirical evidence, it can be observed that KBAB-3 shown a significant ability to adsorb Cr(VI) within a range of 60-160 mg g-1 across different environmental conditions. In addition, the KBAB-3 material demonstrated the advantageous characteristic of easy separation, allowing for the continued maintenance of a high efficiency in removing Cr(VI) even after undergoing numerous cycles of reuse. In conclusion, the application of KBAB-3, a novel adsorbent, exhibits considerable prospects for effective removal of Cr(VI) from diverse water sources in the near future.

A new strategy that simultaneous use of KHCO3 activated biochar and nano-MgO incorporation for Pb2+ and Cd2+ removal from water was raised. After activating by KHCO3, the BC showed a higher surface area and could carry more MgO nanoparticles the BC owned. The synthesized MgO-K-BC had a large adsorption capacity for Pb2+ (1625.5 mg/g) and Cd2+ (480.8 mg/g). Multiple characterization and comparative test have been performed to demonstrate that ion-exchange, precipitation, and complexation are the main mechanisms for Pb2+ and Cd2+ removal by MgO-K-BC. In order to further explore the adsorption mechanism in-depth, the density functional theory (DFT) calculation combined with experimental results were performed. The O-top of MgO was the most stable adsorption site for Pb2+/Cd2+ adsorption compared with other adsorption sites (Mg-top, bridge, and hollow). In addition, the results of charge density maps and projected density of state (PDOS) showed that the overlap of electron cloud and orbits between MgO and Pb2+ were denser than Cd2+, indicating that MgO-K-BC had a stronger affinity for Pb2+ than Cd2+, so that, MgO-K-BC had a higher adsorption capacity for Pb2+ than Cd2+. This work provides a deep understand of the mechanism for heavy metals adsorption by metal oxide and a practical and theoretical guidance for adsorbent preparation with high adsorption ability for heavy metal.