Selective adsorption of Cr(VI) by nitrogen-doped hydrothermal carbon in binary system.

Selective adsorption of heavy metal ions from industrial effluent is important for healthy ecosystem development. However, the selective adsorption of heavy metal pollutants by biochar using lignin as raw material is still a challenge. In this paper, the lignin carbon material (N-BLC) was synthesized by a one-step hydrothermal carbonization method using paper black liquor (BL) as raw material and triethylene diamine (TEDA) as nitrogen source. N-BLC (2:1) showed excellent selectivity for Cr(VI) in the binary system, and the adsorption amounts of Cr(VI) in the binary system were all greater than 150 mg/g, but the adsorption amounts of Ca(II), Mg(II), and Zn(II) were only 19.3, 25.5, and 6.3 mg/g, respectively. The separation factor (SF) for Cr(VI) adsorption was as high as 120.0. Meanwhile, FTIR, elemental analysis and XPS proved that the surface of N-BLC (2:1) contained many N- and O- containing groups which were favorable for the removal of Cr(VI). The adsorption of N-BLC (2:1) followed the Langmuir model and its maximum theoretical adsorption amount was 618.4 mg/g. After 5th recycling, the adsorption amount of Cr(VI) by N-BLC (2:1) decreased about 15%, showing a good regeneration ability. Therefore, N-BLC (2:1) is a highly efficient, selective and reusable Cr(VI) adsorbent with wide application prospects.

Amine-functionalized magnetic microspheres from lignosulfonate for industrial wastewater purification.

Amine-functionalized magnetic microspheres (LS-Fe-NMA) were successfully prepared from lignosulfonate by magnetization and amine modification to remove Cr(VI) from industrial wastewater. In addition to SEM, FTIR, XPS, magnetic hysteresis curves and other characterizations, the adsorption tests were performed in real Cr(VI)-containing industrial wastewater. The experimental influencing factors, such as adsorbent types, LS content in the composites, adsorption time, dosages of adsorbent and adsorption temperature were systematically explored. The results of adsorption models fitting proved that the adsorption conformed to the Langmuir model and the pseudo-second-order kinetic model. At 45 °C, the calculated equilibrium adsorption amount by LS-Fe-NMA in industrial wastewater was 642.11 mg/g. In addition, the adsorption process followed the principle of spontaneous endothermic reaction. It was found that electrostatic interaction, redox and complexation existed during the adsorption process. The excellent adsorption performance and reusability of LS-Fe-NMA for Cr(VI) demonstrates its practical application value in real Cr(VI)-containing industrial wastewater.

One-pot preparation of magnetic nitrogen-doped porous carbon from lignin for efficient and selective adsorption of organic pollutants.

Organic pollutants pose a serious threat to water environment, thus it is essential to develop high-performance adsorbent to remove them from wastewater. Herein, nitrogen-doped magnetic porous carbon (M-PLAC) with three-dimensional porous structure was synthesized from lignin to adsorb methylene blue (MB) and tetracycline (TC) in wastewater. The calculated equilibrium adsorption amount by M-PLAC for MB and TC was 645.52 and 1306.00 mg/g, respectively. The adsorption of MB and TC on M-PLAC conformed to the pseudo-second-order kinetic model. The removal of MB by M-PLAC showed fast and efficient characteristics and exhibited high selectivity for TC in a binary system. In addition, M-PLAC was suitable for a variety of complex water environments and had good regeneration performance, demonstrating potential advantages in practical wastewater treatment. The organic pollutant adsorption by M-PLAC was attributed to electrostatic interaction, hole filling effect, hydrogen bonding, and the π-π interaction.

Magnetic biochar based on furfural residue as an excellent candidate for efficient adsorption of Tetracycline, Bisphenol A, Congo red, and Cr6.

Magnetic porous adsorbent materials are widely favored for their large specific surface area, good adsorption performance, and ease of separation. This work provided a magnetic biochar derived from furfural residue (M-FRAC) with excellent adsorption properties for various pollutants, including Congo red (CR), Tetracycline (TC), Bisphenol A (BPA), and Cr6+. The influence of experimental parameters, such as pollutant concentration, contact time, and pH, on the adsorption properties of M-FRAC was studied in detail. The adsorption process was highly dependent on pH and initial contaminant concentration. All pollutant adsorption was favorable under acidic conditions. The optimal pH of the CR, TC, and Cr6+ adsorption was 5, 4, and 2, respectively, while that of BPA was in the range of 2-5. The experimental equilibrium adsorption amount of CR, TC, BPA, and Cr6+ by M-FRAC was 110.89, 602.81, 157.76, and 265.31 mg/g, respectively. The adsorption processes of pollutants on M-FRAC were in accordance with the Langmuir isotherm model. The adsorption kinetics fitted the pseudo-second-order (PSO) kinetics model. In addition, M-FRAC could be readily separated from solution by applying an external magnetic field. Therefore, the M-FRAC has a good application prospect in practical industrial wastewater treatment.