Biochar-supported Fe/Ni bimetallic nanoparticles for the efficient removal of Cr(VI) from aqueous solution

Advances in Fe-modified lignocellulosic biochar: Impact of iron species and characteristics on wastewater treatment

Lignocellulosic biomass is an attractive feedstock for biochar production owing to its high abundance and renewability. Various modified biochars have been extensively studied for wastewater treatment to improve the physical and chemical properties of lignocellulosic biochar (L-BC). Particularly, Fe-modified L-BCs have garnered attention owing to the abundance and eco-friendliness of Fe and the outstanding ability to remove various organic and inorganic contaminants via adsorption, oxidation, reduction, and catalytic reactions. Different iron species (e.g., Fe(0), Fe (hydr)oxide, Fe sulfide, and Fe-Metal) are formed during the preparation of Fe-L-BCs, which can completely differentiate the physical and chemical properties of BCs. This review discusses the advances in the synthesis of different Fe-L-BCs, specific changes in the physical and chemical properties of Fe-L-BCs upon Fe addition, and their impacts on wastewater treatment. The results of this review can demonstrate the unique advantages and drawbacks of Fe-L-BCs for the removal of different types of pollutants.

Transport of nZVI/copper synthesized by green tea extract in Cr(IV)-contaminated soil: modeling study and reduced toxicity

In this study, nano-zero-valent iron/copper was synthesized by green tea extracts (GT-nZVI/Cu) and produced a stable suspension than nano-zero-valent iron synthesized by green tea extracts (GT-nZVI) injected into Cr(VI)-containing soil column. The equilibrium 1D-CDE model was successfully used to fit the penetration curves of Fe(tot), Fe(aq), and Fe(0) in order to determine the relevant parameters. The hydrodynamic dispersion coefficient of chromium-contaminated soil was 0.401 cm2·h-1, and the pore flow rate was 0.144 cm·h-1. The stable C/C0 of Fe(tot), Fe(aq), and Fe(0) in the effluent were retarded to 0.39, 0.79, and 0.11, respectively, compared to a ratio of 1 for the concentration of the tracer Cl- in the effluent to the concentration in the influent. Additionally, the 1D-CDE model describes the migration behavior of Cr(VI) with a high R2 (> 0.97). The obtained blocking coefficients declined gradually with increasing concentration of GT-nZVI/Cu suspension and decreasing concentration of Cr(VI). The content of reduced chromium in the soil decreased from 2.986 to 1.121 after remediation, while the content of more stable oxidizable chromium and residual chromium increased from 2.975 and 20.021 to 16.471 and 27.612. The phytotoxicity test showed that mung bean seeds still had a germination rate of 90% (control of 100%), root length of 29.63 mm (control of 35.25 mm), and stem length of 17.9 cm (control of 18.96 cm) after remediation with GT-nZVI/Cu. These indicated that GT-nZVI/Cu was effective in immobilizing Cr(VI) in the soil column and reduced the ecological threat. This study provides an analytical basis and theoretical model for the migration of chromium-contaminated soil in practical application.

A novel Ce-Ni@biochar nanocomposite with enhanced photocatalytic activity towards organic dyes degradation: impact of process variables and water matrices

The intent of this research work is to implement a biogenic, affordable, and highly effective Ce-Ni@biochar catalyst in order to study its photoactivity in the removal of crystal violet and malachite green oxalate. The catalyst was synthesized using liquid phase reduction method where cerium and nickel nanoparticles are embedded on the rice husk biochar for photocatalytic degradation of organic dyes in the presence of sunshine. Various characterization techniques were conducted on fabricated catalyst for adequate evaluation of the chemical composition as well as morphological and topographical properties of the formed compound. The nanoparticles embedded on biochar persuade increased charge separation that resulted in a substantial decrease in electron-hole recombination rate. The synergistic actions of the catalyst resulted in a high level of photocatalytic activity. The fabricated nanocatalyst showed excellent photoactivity that caused 96 and 99% degradation of crystal violet and malachite green oxalate, a growing industrial pollutant, within 35 and 25 min, respectively. A persuasive mechanism and kinetics are well presented. A series of investigations were done on other factors, such as contact duration, catalyst dosage, starting concentration, interfering ions, and pH, to know its degradation pursuance. The impacts of different water matrices were also investigated. The removal effectiveness of the synthesized catalyst persisted after five consecutive cycles. Marking the burgeoning industrial effluents as a result of rapid industrialization and also focusing on easy availability and low-cost source as well as high efficiency, reusability of the catalyst imparts its novelty and need of this research work.

A novel PEI-grafted N-doping magnetic hydrochar for enhanced scavenging of BPA and Cr(VI) from aqueous phase

Herein, polyethyleneimine (PEI)-grafted nitrogen-doping magnetic hydrochar (PEI_MW@MNHC) was synthesized for hexavalent chromium (Cr(VI)) and bisphenol A (BPA) elimination from water. Characterizations exhibited that abundant amino functional groups, intramolecular heterocyclic N, azo and Fe-N_X structures were successfully introduced into the inherent structure of hydrochar. The obtained PEI_MW@MNHC presented maximum uptake of 205.37 and 180.79 mg/g for Cr(VI) and BPA, respectively, and was highly tolerant to various co-existing ions. Mechanism investigation revealed that the protonated amino, intramolecular heterocyclic N and Fe(II) participated in Cr(VI) reduction, and the N/O-containing groups and Fe(III) fixed Cr(III) onto PEI_MW@MNHC by the formation of complexes and precipitates. On the other hand, azo, Fe-N_X and graphitic N structures contributed to the removal of BPA via pore filling, hydrogen bonding and π-π interactions. Additionally, PEI_MW@MNHC maintained over 85.0% removal efficiency for Cr(VI) and BPA after four cycles, manifesting that PEI_MW@MNHC was an ideal adsorbent with outstanding practical application potential.

Insight into the Fe-Ni/biochar composite supported three-dimensional electro-Fenton removal of electronic industry wastewater

For the efficient removal of the bio-refractory organic pollutants in the electronic industry wastewater, the Ni-Fe (oxides) modified three-dimension (3D) particle electrode was applied in electro-Fenton system (3D/EF), where iron ions were released from anode and deposited onto algal biochar (ABC) to prepare composite catalyst during reaction process. Firstly, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis were applied to confirm successful fabrication of the 3D particle electrode materials. Secondly, COD removal efficiency could reach about 80%, which was about 20% higher than that in 2D/EF system, under the optimized conditions as 2.0 g/L of Ni-ABC particle electrodes, initial pH of 3, 100 mL/min of aeration intensity and 20 mA/cm² of applied current density. Thirdly, characterized using three-dimensional fluorescence spectroscopy and GC-MS analysis, it seemed that most of the macromolecular substances could be degraded, whereas mono-2-ethylhexyl phthalate (MEHP) was identified as the most abundant and representative compound. Finally, possible degradation pathway of MEHP in 3D/EF system was proposed including dealkylation, cleavage of C-O bond, and demethylation. Therefore, this study provides a new strategy in designing EF system employing bimetal doped biochar composite for an efficient elimination of organic pollutants within electronic industry wastewater.