Multifunctional hierarchical cabbage-like nZVI-Fe 3 O 4 /C composites for efficient chromium (VI) removal

Insights into the Mechanism of Efficient Cr(VI) Removal from Aqueous Solution by Iron-Rich Wheat Straw Hydrochar: Coupling DFT Calculation with Experiments

Agricultural solid waste has become one of the raw materials for hydrothermal carbon production, promoting resource utilization. This study synthesized two types of ball-milling carbons (Fe-MHBC vs MHBC) with and without FeCl3 modification using wheat straw hydrochars. Cr(VI) adsorption on these two types of ball-milling carbons was investigated. According to Langmuir's maximum adsorption capacity analysis, Fe-MHBC had a capacity of 116.29 mg g-1. The thermodynamic analysis based on isothermal adsorption reveals the spontaneous process of the reaction between the two materials. The adsorption of Cr(VI) on Fe-MHBC exhibited excellent agreement with the pseudo-second-order kinetics model. Furthermore, X-ray photoelectron spectroscopy analysis showed that Fe(II) in the material reduced Cr(VI) when it participated in the reaction. The acidic conditions facilitate the elimination of Cr(VI). The Fe-MHBC has a higher zeta potential, which enhances the electrostatic attraction of Cr(VI) particles. Even with a starting pH of 10, the removal rate can be consistently maintained at over 64%. The adsorption of Cr(VI) was inhibited by various anions and higher ion concentrations. Density functional theory demonstrates that the presence of Fe enhances the adsorption capacity and electron transfer flux of Cr(VI). Fe-MHBC effectively eliminates Cr(VI) by the process of electrostatic adsorption, redox, and complexation reactions. This study demonstrated that hydrochar materials modified by FeCl3 through a ball-milling process show considerable potential as effective adsorbents in the treatment of Cr(VI) pollution, offering a viable and environmentally friendly solution for mitigating this prevalent environmental issue.

Fabrication of Iron-Containing Biochar by One-Step Ball Milling for Cr(VI) and Tetracycline Removal from Wastewater

Simple ball milling technology can simultaneously improve the adsorption performance of adsorbents for heavy metals and organic pollutants and has attracted increasing attention. Iron-modified biochar (Fe@MBC) was prepared by one-step ball milling, and the characterization results proved that FeCl3 was successfully loaded on biochar. The removal rates of Cr(VI) and tetracycline hydrochloride (TC) by Fe@MBC were increased by 88.27% and 82.64% compared with BC. The average pore size, oxygen-containing functional groups and graphitization degree of Fe@MBC are higher than those of BC, which is more conducive to promoting adsorption. The adsorption isotherms show that the adsorption of Cr(VI) and TC on the Fe@MBC surface conforms to the Langmuir type of single-layer adsorption and the Freundlich model of multilayer adsorption, respectively. The maximum adsorption capacities of Cr(VI) and TC are 25.46 and 66.91 mg·g-1, respectively. Kinetic experiments show that the adsorption process is more consistent with the pseudo-second-order model of chemical adsorption. The adsorption process of Cr(VI) and TC on the Fe@MBC surface is a spontaneous endothermic process that becomes more obvious as the temperature increases. The increase in solution pH has a significant impact on the removal rate of Fe@MBC. When the pH value increased from 3 to 11, the adsorption rates decreased by 53.74% and 17.16%, respectively. The presence of PO43-, CO32-, K+, and Cu2+ significantly affects the adsorption of TC by Fe@MBC, and PO43- and CO32- also affect the adsorption of Cr(VI). Mechanistic studies show that ion exchange, electrostatic interaction, pore filling, and hydrogen bonding contribute to the removal of Cr(VI) and TC by Fe@MBC. The removal mechanism of Cr(VI) also involves complexation and redox reactions, and the removal mechanism of TC involves π-π bonds and van der Waals forces. The results show that Fe@MBC is a green and efficient adsorbent.

Multifunctional modified polyvinyl alcohol: A powerful biomaterial for enhancing bioreactor performance in nitrate, Mn(II) and Cd(II) removal

The co-existence of multiple pollutants in wastewater such as nitrate and heavy metal, is of high concern due to the potential environmental impact. In this study, a novel biomaterial PPy@Fe₃O₄/PVA was synthesized as a multifunctional bacteria immobilized carrier, to enhance simultaneous denitrification, Cd(II) and Mn(II) removal efficiency in bioreactor environments. The morphology and main components of the PPy@Fe₃O₄/PVA material were characterized by SEM and XRD. Using PPy@Fe₃O₄/PVA as a carrier, the maximum removal efficiencies for nitrate (0.207 mg L^-1·h^-1), Mn(II) (90.98%) and Cd(II) (98.78%) were increased by 27.05%, 30.27%, and 16.48%, respectively, compared to in the absence of PPy@Fe₃O₄/PVA. Regeneration experiments were performed, demonstrating the excellent stability and reusability of the PPy@Fe₃O₄/PVA material. Furthermore, effects of key factors were investigated on the performance of the PPy@Fe₃O₄/PVA bioreactor in simultaneous denitrification, Mn(II) and Cd(II) removal. Experimental results indicate that the highest nitrate, Mn(II) and Cd(II) removal efficiencies were obtained under the conditions of HRT of 10 h, initial Mn(II) concentration of 40 mg/L and initial Cd(II) concentration of 10 mg/L. Gas chromatography analysis indicated that N₂ was the mainly final gaseous product. Moreover, the bioreactor community diversity was markedly influenced by the initial concentration of Cd(II) and Pseudomonas sp. H117 played a primary role in the process of simultaneous denitrification, Mn(II) and Cd(II) removal.

Preparation of magnetic carbon/Fe3O4 supported zero-valent iron composites and their application in Pb(II) removal from aqueous solutions

Nanoscale zero-valent iron (NZVI) was first assembled on magnetic carbon/Fe₃O₄ (CM) with a combination of hydrothermal and liquid phase reduction methods. The novel NZVI@CM magnetic nanocomposites have the merits of large surface area, unique magnetic property, low cost and environmental friendliness. They can be used for Pb(II) removal in aqueous solution. The materials were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) adsorption. The various parameters, such as reaction time, dosage of catalyst, solution pH and acid ions concentrations were studied. The removal efficiency of Pb(II) can be obviously increased by the combination of appropriate CM and NZVI. The removal efficiency of Pb(II) is 99.7% by using 60 mg of NZVI@CM at pH 7. The kinetics study indicates that the Pb(II) removal accords to pseudo-second-order kinetics model.

Macadamia nutshells-derived activated carbon and attapulgite clay combination for synergistic removal of Cr(VI) and Cr(III)

A physical mixture of Macadamia-derived activated carbon and cationic attapulgite clay was investigated for total chromium removal in aqueous solution. The parameters influencing the adsorption of chromium on the sorbents were investigated, and it was shown that pH 3, contact time 2 hours, concentration 50 mg L−1 and calculated adsorption capacity of 96.28 mg g−1 were the optimal parameters. The process of adsorption was better described by Freundlich adsorption isotherm, and the kinetic modelling data suggested a chemisorption mechanism described by pseudo-second-order (PSO) rate model. Ionic strength studies demonstrated that the removal of anionic Cr(VI) species was mostly affected by the presence of anions like Cl− and [Formula: see text], while the removal of the cationic Cr(III) species was affected largely by cations [Formula: see text]>Na+>K+. Overall, the removal mechanism involved adsorption, reduction and ion exchange processes.