Facile synthesis and life cycle assessment of Iron oxide-Douglas fir biochar hybrid for anionic dye removal from water

Development of low-cost and safe IONPs-based biochar hybrids with efficient multiple pollutant removal abilities is critical. In the present study, we studied the potential of an Fe3O4-modified wood-based biochar (FDBC) composite to remove an aqueous anionic dye, bromophenol blue (BPB) via simple magnets. Smaller surface area (1.5 times) and a smaller pore volume (∼2 times) of FDBC over the original biochar (DBC) does not impede the BPB uptake by FDBC. The Langmuir monolayer BPB adsorption capacities of FDBC and DBC are 448.0 and 451.0 mg/g (removal percentages, 89.8 % vs. 90.3 %) (adsorbent dose 50 mg, 25 mL of 1000 mg/L BPB concentration, 2 h, pH 5.0). The larger surface area (248 m2/g) and abundant nano Fe3O4 (11.0 nm) sites account for FDBC's excellent BPB removal compared to recent IONPs-based adsorbents. At pH 5.0–8.0, the BPB is bound to the FDBC (points of zero charge = 8.2) via H-bonding and π-π stacking, as confirmed by pH, desorption, and thermodynamic studies. Compared to NaOH and H2O2, methanol desorbs more BPB from the spent adsorbent at pH 7.0. Moreover, this composite removes even the BPB residuals from real wastewater, becoming an ideal adsorbent for BPB removal. A limited life cycle assessment of FDBC's synthesis revealed a higher impact for global warming (2.38 kg CO2eq) per kg of the adsorbent, whereas the lower impacts for ozone depletion, particulate matter emissions, and air quality. The FDBC is more economical because of its green and facile synthesis, excellent dye removal capacity, easy and fast recovery. Efficient multiple dye uptake of FDBC produces large concentration of recovered dyes, which can be possibly reused in various economic applications.