Highly Efficient Removal of VOCs at Low Concentrations by Low-Cost Biochar-Based Zr-MOF Adsorbents

Despite the low concentrations of volatile organic compounds (VOCs) indoors, they still pose significant health concerns. Therefore, there is an urgent need to prepare adsorbents to remove low-concentration VOCs indoors. In this study, biochar-based MOF composites (UIO-66@PSB and UN-66@PSB) were efficaciously prepared and optimized by a straightforward one-pot method. After being optimized, UIO-66@PSB and UN-66@PSB were characterized by SEM-EDX, XRD, FTIR, XPS, and BET. Toluene and acetaldehyde, as typical indoor pollutants, were chosen as the adsorbates to examine the adsorption performances of UIO-66@PSB and UN-66@PSB adsorbents. The results demonstrated that both UIO-66@PSB and UN-66@PSB exhibited excellent adsorption ability for low-concentration toluene and acetaldehyde while retaining effective adsorption performance even under conditions of high humidity. The PSO model and the Freundlich model were effective in characterizing the adsorption characteristics of toluene, while the PSO model and the Langmuir model were similarly effective in characterizing the adsorption performance of acetaldehyde. Additionally, after 5 adsorption-desorption cycles, UIO-66@PSB and UN-66@PSB can still maintain good adsorption stability. The DFT results revealed that the π-π interaction plays a pivotal role in the adsorption of toluene, with the presence of an amino group shown to augment this phenomenon. Conversely, the electrostatic interaction emerges as the dominant force in the adsorption of acetaldehydes. When the materials were placed in the simulated chamber to observe the adsorption property for the real sample, the removal rates of toluene by UIO-66@PSB and UN-66@PSB could reach 90.85 and 95.73%, respectively. This work indicated that biochar-based MOF composites, which are readily recyclable, have great potential to absorb low concentrations of VOCs in rooms or vehicles.