Magnetic biochar serves as adsorbents and catalyst supports for the removal of antibiotics from wastewater: A review

Numerous antibiotics are being released into the natural environment through wastewater. As antibiotic usage increases annually, its detrimental impact on the environment is escalating. Addressing environmental sustainability and human health requires significant attention towards antibiotic removal. In recent years, magnetic biochar (MBC) has gained widespread application in water treatment due to its exceptional adsorption and catalytic degradation capabilities. Antibiotics such as sulfamethoxazole (SMX), tetracycline (TC), ciprofloxacin (CIP), and others commonly exhibit an adsorption capacity by MBC ranging from 5 mg/g to 900 mg/g. Moreover, MBC typically removes over 90% of these antibiotics within 60 min. The effectiveness of antibiotic removal is significantly influenced by various preparation and modification methods. Furthermore, the incorporation of magnetism enables the material to be recycled and reused multiple times, thereby reducing consumption costs. This article discusses recent studies on antibiotic removal using MBC. It has been observed that variations in the selection of raw material and preparation procedures significantly affect antibiotic removal, while the mechanisms involved in antibiotic removal remain ambiguous. Additionally, it has been noted that the removal process may lead to secondary pollution and high preparation costs. Therefore, this review comprehensively outlines the utilization of MBC in the removal of antibiotics from wastewater, including aspects such as modification, preparation, removal mechanism, and factors influencing removal, and providing recommendations for antibiotic development. The aim is to offer researchers a clear understanding to advance the field of MBC materials.

Preparation of magnetic activated carbon fibers@Fe3O4 by electrostatic self-assembly method and adsorption properties for methylene blue

Nano-Fe3O4 was loaded onto coconut-based activated carbon fibres (CACF) using an electrostatic self-assembly method. The effects of the mass ratio of CACF to nano-Fe3O4, loading time, pH and temperature on the loading effect were investigated and ideal loading conditions were determined. To study the adsorption performance of MACF@Fe3O4 for methylene blue, the effects of the initial concentration, pH and time on the adsorption were investigated and the working conditions of adsorption were established. MACF@Fe3O4 was systematically characterized. Adsorption kinetics were investigated under ideal conditions. The ideal loading conditions for MACF@Fe3O4 were as follows: mass ratio of 1:1, 20 min, pH 9.36, 22.5°C. The saturation magnetization of MACF@Fe3O4 was 48.2263 emu·g-1, which could be quickly separated under an external magnetic field. When the dosage was 0.010 g, the adsorption rate reached 97.29% and the maximum adsorption capacity was 12.1616 mg·g-1. The adsorption process conformed to pseudo-first-order kinetics during the first 15 min and pseudo-second-order kinetics during 20-120 min. The equations wereln( Q e - Q t )=2.2394-0.0689t andt Q t =0.0774 + 0.5295t , respectively. The isothermal adsorption model showed that MACF@Fe3O4 was more in line with the Langmuir model, indicating that the adsorption process was mainly monolayer adsorption. The thermodynamic analysis results showed that the adsorption process of MB by MACF@Fe3O4 was an endothermic process. In this study, MACF@Fe3O4 with high adsorption capacity and easy separation from coconut palm fibres has good application prospects in the field of adsorption, which can promote the high-value utilization of coconut palms.

Biochar-supported nZVI for the removal of Cr(VI) from soil and water: Advances in experimental research and engineering applications

Over the past decade, biochar-supported nZVI composites (nZVI/biochar) have been developed and applied to treat various pollutants due to their excellent physical and chemical properties, especially in the field of chromium (VI) removal. This paper reviewed the factors influencing the preparation and experiments of nZVI/biochar composites, optimization methods, column experimental studies and the mechanism of Cr(VI) removal. The results showed that the difference in raw materials and preparation temperature led to the difference in functional groups and electron transfer capabilities of nZVI/biochar materials. In the experimental process, pH and test temperature can affect the surface chemical properties of materials and involve the electron transfer efficiency. Elemental doping and microbial coupling can effectively improve the performance of nZVI/biochar composites. In conclusion, biochar can stabilize nZVI and enhance electron transfer in nZVI/biochar materials, enabling the composite materials to remove Cr(VI) efficiently. The study of column experiments provides a theoretical basis for applying nZVI/biochar composites in engineering. Finally, the future work prospects of nZVI/biochar composites for heavy metal removal are introduced, and the main challenges and further research directions are proposed.

Sustainable Synthesis of Nanoscale Zerovalent Iron Particles for Environmental Remediation

Nanoscale zerovalent iron (nZVI) particles represent an important material for diverse environmental applications because of their exceptional electron-donating properties, which can be exploited for applications such as reduction, catalysis, adsorption, and degradation of a broad range of pollutants. The synthesis and assembly of nZVI by using biological and natural sustainable resources is an attractive option for alleviating environmental contamination worldwide. In this Review, various green synthesis pathways for generating nZVI particles are summarized and compared with conventional chemical and physical methods. In addition to describing the latest environmentally benign methods for the synthesis of nZVI, their properties and interactions with diverse biomolecules are discussed, especially in the context of environmental remediation and catalysis. Future prospects in the field are also considered.

Potassium-iron rice straw biochar composite for sorption of nitrate, phosphate, and ammonium ions in soil for timely and controlled release

In this study, potassium-iron rice straw biochar composite (KRSB) was produced and compared with rice straw biochar (RSB) for the sorption of NO₃^-, PO₄^3-, and NH₄⁺ in aqueous medium and soil column. RSB was produced by pyrolyzing rice straw at 400 and 600 °C in a slow pyrolysis unit. KRSB was produced through chemical and hydrothermal treatments of rice straw biochar produced at 400 and 600 °C. Batch experiment results indicate that the KRSB showed better sorption capacity for nitrate, phosphate, and ammonium ions compared to pristine RSB. The sorption isotherms of all three nutrients (NO₃^-, PO₄^3-, and NH₄⁺) were better-explained by the Langmuir-Freundlich isotherm model. The column leaching experiment showed that the KRSB loaded soil reached maximum sorption capacity for PO₄^3- and NO₃^- within six and eight days, respectively but, it showed poor sorption capacity for NH₄⁺. The soil fertility index in the 400 and 600 KRSB amended soils were significantly increased by 50.68 and 52.85%, respectively compared to the control. Results indicated that KRSB could be utilized in the soil in two ways: first, to keep the nutrients attached to its surface and second, to release the nutrients in a phased and timely manner to increase their availability for plants.

Magnetic palm kernel biochar potential route for phenol removal from wastewater

The pollution of water resources due to the disposal of industrial wastes that have organic material like phenol is causing worldwide concern because of their toxicity towards aquatic life, human beings and the environment. Phenol causes nervous system damage, renal kidney disease, mental retardation, cancer and anaemia. In this study, magnetic palm kernel biochar is used for removal of phenol from wastewater. The effect of parameters such as pH, agitation speed, contact time and magnetic biochar dosage are validated using design of experiments. The statistical analysis reveals that the optimum conditions for the highest removal (93.39%) of phenol are obtained at pH of 8, magnetic biochar dosage of 0.6 g, agitation speed at 180 rpm and time of 60 min with the initial concentration of 10 mg/L. The maximum adsorption capacities of phenol were found to be 10.84 mg/g and Langmuir and Freundlich isotherm models match the experimental data very well and adsorption kinetic obeys a pseudo-second order. Hence, magnetic palm kernel can be a potential candidate for phenol removal from wastewater.

Multifunctional iron-biochar composites for the removal of potentially toxic elements, inherent cations, and hetero-chloride from hydraulic fracturing wastewater

This paper evaluates a novel sorbent for the removal of potentially toxic elements, inherent cations, and hetero-chloride from hydraulic fracturing wastewater (FWW). A series of iron-biochar (Fe-BC) composites with different Fe/BC impregnation mass ratios (0.5:1, 1:1, and 2:1) were prepared by mixing forestry wood waste-derived BC powder with an aqueous FeCl₃ solution and subsequently pyrolyzing them at 1000 °C in a N₂-purged tubular furnace. The porosity, surface morphology, crystalline structure, and interfacial chemical behavior of the Fe-BC composites were characterized, revealing that Fe chelated with CO bonds as COFe moieties on the BC surface, which were subsequently reduced to a CC bond and nanoscale zerovalent Fe (nZVI) during pyrolysis. The performance of the Fe-BC composites was evaluated for simultaneous removal of potentially toxic elements (Cu(II), Cr(VI), Zn(II), and As(V)), inherent cations (K, Na, Ca, Mg, Ba, and Sr), hetero-chloride (1,1,2-trichlorethane (1,1,2-TCA)), and total organic carbon (TOC) from high-salinity (233 g L^-1 total dissolved solids (TDS)) model FWW. By elucidating the removal mechanisms of different contaminants, we demonstrated that Fe-BC (1:1) had an optimal reducing/charge-transfer reactivity owing to the homogenous distribution of nZVI with the highest Fe⁰/Fe²⁺ ratio. A lower Fe content in Fe-BC (0.5:1) resulted in a rapid exhaustion of Fe⁰, while a higher Fe content in Fe-BC (2:1) caused severe aggregation and oxidization of Fe⁰, contributing to its complexation/(co-)precipitation with Fe²⁺/Fe³⁺. All of the synthesized Fe-BC composites exhibited a high removal capacity for inherent cations (3.2-7.2 g g^-1) in FWW through bridging with the CO bonds and cation-π interactions. Overall, this study illustrated the potential efficacy and mechanistic roles of Fe-BC composites for (pre-)treatment of high-salinity and complex FWW.