Biochar Adsorbents with Enhanced Hydrophobicity for Oil Spill Removal

Oil spills cause massive loss of aquatic life. Oil spill cleanup can be very expensive, have secondary environmental impacts, or be difficult to implement. This study employed five different adsorbents: (1) commercially available byproduct Douglas fir biochar (BC) (SA ∼ 695 m²/g, pore volume ∼ 0.26 cm³/g, and pore diameter ∼ 13-19.5 Å); (2) BC modified with lauric acid (LBC); (3) iron oxide-modified biochar (MBC); (4) LBC modified with iron oxide (LMBC); and (5) MBC modified with lauric acid (MLBC) for oil recovery. Transmission, engine, machine, and crude oils were used to simulate oil spills and perform adsorption experiments. All five adsorbents adsorbed large quantities of each oil in fresh and simulated seawater with only a slight pH dependence, fast kinetics (sorptive equilibrium reached before 15 min), and high regression fits to the pseudo-second-order kinetic model. The Sips isotherm model oil sorption capacities for these sorbents were in the range ∼3-11 g oil/1 g adsorbent. Lauric acid-decorated (60-2 wt %) biochars gave higher oil adsorption capacities than the undecorated biochar. Lauric acid enhances biochar hydrophobicity and its water contact angle and reduces water influx into biochar's porosity preventing it from sinking in water for 3 weeks. These features were observed even at 2% wt of lauric acid (sinks only after 2 weeks). Magnetization by magnetite nanoparticle deposition onto BC and LBC allows the recovery of the exhausted adsorbent by a magnetic field as an alternative to filtration. Oil sorption was endothermic. Recycling was demonstrated after toluene stripping. The oil-laden adsorbents' heating values were obtained, suggesting an alternative use of these spent adsorbents as a low-cost fuel after recovery, avoiding waste disposal costs. The initial and oil-laden adsorbents were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmet-Teller surface area, contact angle, thermogravimetric analyses, differential scanning calorimetry, vibrating sample magnetometry, elemental analysis, and X-ray photoelectron spectroscopy.

Fast nitrate and fluoride adsorption and magnetic separation from water on α-Fe2O3 and Fe3O4 dispersed on Douglas fir biochar

α-Fe₂O₃ and Fe₃O₄ dispersed on high surface area (663 m²/g) Douglas fir biochar (BC) was prepared for fast nitrate and fluoride ion removal from water using magnetic separations. This biochar, made originally at 900 °C, was impregnated with FeCl₃ and converted by pyrolysis at 600 °C to magnetic (494 m²/g) biochar (MBC). MBC and its precursor BC were characterized using SEM, SEM-EDX, STEM, S_BET, PZC measurements, XRD analysis, and XPS. Dispersed α-Fe₂O₃ and Fe₃O₄ particles caused magnetization and generated most adsorption sites, causing more nitrate and fluoride uptake than BC. Both nitrate and fluoride adsorption on MBC remained high over a pH range from 2 to 10. Sorption was evaluated from 298 to 318 K using the Langmuir and Freundlich isotherm models. Langmuir adsorption capacities were 15 mg/g for nitrate and 9 mg/g for fluoride, higher capacities than those reported for other biochar and iron oxide adsorbents.

Lead (Pb2+) sorptive removal using chitosan-modified biochar: batch and fixed-bed studies

Chitosan-Modified fast pyrolysis BioChar (CMBC) was used to remove Pb²⁺ from water. CMBC was made by mixing pine wood biochar with a 2% aqueous acetic acid chitosan (85% deacylated chitin) solution followed by treatment with NaOH. The characterizations of both CMBC and Non-Modified BioChar (NMBC) were done using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), scanning electron microscopy (SEM), surface area measurements (S_BET), elemental analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and ζ-potential measurements. Elemental analysis indicated that chitosan accounts for about 25% weight of the CMBC. The Langmuir maximum adsorption capacity of CMBC at pH 5 was 134 mg g⁻¹versus 48.2 mg g⁻¹ for NMBC at 318 K. CMBC column adsorption studies resulted in a capacity of 5.8 mg g⁻¹ (Pb²⁺ conc. 150 mg L⁻¹; pH 5; column dia 1.0 cm; column length 20 cm; bed height 5.0 cm; flow rate 2.5 mL min⁻¹). CMBC removed more Pb²⁺ than NMBC suggesting that modification with chitosan generates amine groups on the biochar surface which enhance Pb²⁺ adsorption. The modes of Pb²⁺ adsorption on CMBC were studied by comparing DRIFTS and X-ray photoelectron spectroscopy spectra before and after Pb²⁺ adsorption.

Batch and fixed-bed column studies for the removal of lead (Pb²⁺) from aqueous solution by chitosan-modified pinewood biochar.