A highly efficient strategy for enhancing the adsorptive and magnetic capabilities of biochar using Fenton oxidation

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.

Unlocking the potential of magnetic biochar in wastewater purification: a review on the removal of bisphenol A from aqueous solution

Bisphenol A (BPA) is an essential and extensively utilized chemical compound with significant environmental and public health risks. This review critically assesses the current water purification techniques for BPA removal, emphasizing the efficacy of adsorption technology. Within this context, we probe into the synthesis of magnetic biochar (MBC) using co-precipitation, hydrothermal carbonization, mechanical ball milling, and impregnation pyrolysis as widely applied techniques. Our analysis scrutinizes the strengths and drawbacks of these techniques, with pyrolytic temperature emerging as a critical variable influencing the physicochemical properties and performance of MBC. We explored various modification techniques including oxidation, acid and alkaline modifications, element doping, surface functional modification, nanomaterial loading, and biological alteration, to overcome the drawbacks of pristine MBC, which typically exhibits reduced adsorption performance due to its magnetic medium. These modifications enhance the physicochemical properties of MBC, enabling it to efficiently adsorb contaminants from water. MBC is efficient in the removal of BPA from water. Magnetite and maghemite iron oxides are commonly used in MBC production, with MBC demonstrating effective BPA removal fitting well with Freundlich and Langmuir models. Notably, the pseudo-second-order model accurately describes BPA removal kinetics. Key adsorption mechanisms include pore filling, electrostatic attraction, hydrophobic interactions, hydrogen bonding, π-π interactions, and electron transfer surface interactions. This review provides valuable insights into BPA removal from water using MBC and suggests future research directions for real-world water purification applications.

Mechanisms of adsorption and functionalization of biochar for pesticides: A review

Agricultural production relies heavily on pesticides. However, factors like inefficient application, pesticide resistance, and environmental conditions reduce their effective utilization in agriculture. Subsequently, pesticides transfer into the soil, adversely affecting its physicochemical properties, microbial populations, and enzyme activities. Different pesticides interacting can lead to combined toxicity, posing risks to non-target organisms, biodiversity, and organism-environment interactions. Pesticide exposure may cause both acute and chronic effects on human health. Biochar, with its high specific surface area and porosity, offers numerous adsorption sites. Its stability, eco-friendliness, and superior adsorption capabilities render it an excellent choice. As a versatile material, biochar finds use in agriculture, environmental management, industry, energy, and medicine. Added to soil, biochar helps absorb or degrade pesticides in contaminated areas, enhancing soil microbial activity. Current research primarily focuses on biochar produced via direct pyrolysis for pesticide adsorption. Studies on functionalized biochar for this purpose are relatively scarce. This review examines biochar's pesticide absorption properties, its characteristics, formation mechanisms, environmental impact, and delves into adsorption mechanisms, functionalization methods, and their prospects and limitations.

Oxidative magnetization of biochar at relatively low pyrolysis temperature for efficient removal of different types of pollutants

A novel oxidative magnetization, involving phosphomolybdic acid and Fe(NO3)3 co-promoted pyrolysis, was established to manufacture highly adsorptive magnetic biochars for adsorbing aqueous tetracycline, methylene blue, and Cr6+. The modification of phosphomolybdic acid greatly boosted the formation of γ-Fe2O3 and oxygen containing groups with enhancement of specific surface area and pore volume at 400 °C. Importantly, γ-Fe2O3 was stably fixed on surface in quasi-nanoscale. The oxidized magnetic biochar displayed 631.53, 158.45, 155.13 mg/g adsorption capabilities for tetracycline, methylene blue, and Cr6+ with 22.79 emu/g saturation magnetization, respectively. Oxygen containing groups and quasi-nanoscale γ-Fe2O3 served as key adsorption sites for these pollutants. A general oxidative magnetization was established for manufacturing high-performance magnetic biochar through phosphomolybdic acid/Fe(NO3)3 co-promoted pyrolysis at relatively low temperature.

Enhanced adsorption for trivalent antimony by nano-zero-valent iron-loaded biochar: performance, mechanism, and sustainability

The discharge of tailing leachate and metallurgical wastewater has led to an increasing trend of water pollution. In this study, nZVI-modified low-temperature biochar was used to adsorb Sb(III) from water. The adsorption capacity and speed of nZVI-BC were better than those of BC, and the best adsorption effect was observed for 4nZVI-BC, with 93.60 mg·g-1 maximum adsorptive capacity, which was 208.61% higher than the original BC. The Langmuir and Temkin models were well fitted (R2 ≥ 0.99), and PSO was more in line with the 4nZVI-BC adsorption process, indicating that the adsorption was a monolayer physico-chemical adsorption. The combination of XRD, FTIR, and XPS characterization demonstrated that the adsorption mechanism predominantly included redox reactions, complexation, and electrostatic interactions. The thermodynamic results demonstrated that 4nZVI-BC adsorption on Sb(III) was a spontaneous endothermic process. Additionally, the order of the influence of interfering ions on 4nZVI-BC was CO32-  > H2PO4-  > SO42-  > Cl-. After three repeated uses and adsorption-desorption, the adsorption ratio of Sb(III) by 4nZVI-BC was still as high as 90% and 65%, respectively. This study provides a theoretical reference for the exploration and development of Sb(III) removal technologies for aquatic environments.

Magnetic hydrochar derived from waste lignin for thallium removal from wastewater: Performance and mechanisms

Waste lignin, such as black liquor (BL) from paper and pulping industries, is an agro-industrial biowaste while its reuse raised global concerns. In this work, a hydrothermal carbonization procedure was employed to convert BL into magnetic lignin-based hydrochar (MLHC) for thallium elimination from wastewater. The results exhibited water purification potential due to a wider working pH window (2-9) with the magnetization intensity of 11.12 emu/g. The maximum adsorption capacity for Tl(III) was 278.9 mg/g, while the contribution of various mechanisms was elucidated with the order: surface precipitation (31.3 %), complexation (20.6 %), physical adsorption (18.2 %), chemical reduction (15.0 %), and ion exchange (14.9 %). This study revealed that hydrothermal treatment could be a potential and promising method to convert waste lignin into magnetic bio-adsorbent to recycle pulping black liquor and apply it for thallium pollution control.

Fenton oxidation of biochar improves retention of cattle slurry nitrogen

Nitrogen (N) losses during fertilization with livestock slurry, mainly in the form of ammonia (NH₃ ), can cause environmental problems and reduce fertilizer efficiency. Leonardite, which is characterized by oxygen-rich functional groups and low pH, has been found to decrease losses of slurry N. However, leonardite, as a byproduct of open-cast lignite mining, is not a renewable resource. The objective of this study was to modify biochar by chemical surface oxidation in order to find a sustainable but similarly effective substitute for leonardite. Biochar was produced from spruce sawdust in a pyrolysis oven at a maximum temperature of 610 °C. Then the biochar was oxidized using the Fenton reaction, with a ratio of Fe²⁺ /H₂ O₂ of 1:1,000, as a source of highly reactive HO· radicals to introduce oxygen-rich functional groups to the biochar surface. The ammonium (NH₄ ⁺ ) adsorption capacity of biochar, oxidized biochar, and leonardite was tested in ammonium sulfate [(NH₄ )₂ SO₄ ] solution, pH-adjusted (NH₄ )₂ SO₄ solution, and cattle slurry. The results showed that biochar had the highest total NH₄ ⁺ adsorption of 1.4 mg N g^-1 in (NH₄ )₂ SO₄ solution, whereas oxidized biochar had the highest reversible NH₄ ⁺ adsorption of 0.8 mg N g^-1 . In the pH-adjusted ammonium solution, all materials reduced NH₃ emissions by ≥90%, and oxidized biochar reduced NH₃ emissions by 99.99%. In contrast, leonardite reduced NH₃ emissions the most in cattle slurry, and oxidation of biochar increased the reduction in NH₃ emissions from 22 to 67% compared with non-oxidized biochar. In conclusion, biochar oxidized by means of the Fenton reaction greatly decreased NH₃ emissions by increased adsorption of NH₄ ⁺ in cattle slurry compared with non-oxidized biochar, indicating the great potential of oxidized biochar for reducing N losses during slurry application.

Applications of functionalized magnetic biochar in environmental remediation: A review

Magnetic biochar (MBC) is extensively applied on contaminants removal from environmental medium for achieving environmental-friendly remediation with reduction of secondary pollution owing to its easy recovery and separation. However, the summary of MBC synthesis methods is still lack of relevant information. Moreover, the adsorption performance for pollutants by MBC is limited, and thus it is imperative to adopt modification techniques to enhance the removal ability of MBC. Unfortunately, there are few reviews to present modification methods of MBC with applications for removing hazardous contaminants. Herein, we critically reviewed (i) MBC synthetic methods with corresponding advantages and limitations; (ii) adsorption mechanisms of MBC for heavy metals and organic pollutants; (iii) various modification methods for MBC such as functional groups grafting, nanoparticles loading and element doping; (iv) applications of modified MBC for hazardous contaminants adsorption with deep insight to relevant removal mechanisms; and (v) key influencing conditions like solution pH, temperature and interfering ions toward contaminants removal. Finally, some constructive suggestions were put forward for the practical applications of MBC in the near future. This review provided a comprehensive understanding of using functionalized MBC as effective adsorbent with low-cost and high-performance characteristics for contaminated environment remediation.

Recent developments in the use of activated charcoal in medicine

One of the raw forms of graphite is activated charcoal which has an extensive surface area allowing for the adsorption of a wide range of chemicals. It possesses the strongest physical adsorption forces of the available materials, as well as the largest volume of adsorbing porosity. Activated charcoal acts as an adsorbent, collecting and storing substances in the gastrointestinal tract, reducing or blocking absorption in the bloodstream. The ingested toxins interact with charcoal by recycling toxins in the intestinal cavity. In cases where the drug has not been absorbed from the abdominal system, it is recirculated through the liver and intestines or by means of passive diffusion or active secretion. The article aims to review the most recent advances in the use of the activated charcoal, including the dose, how charcoal acts in the body, the mechanism of action, administration, contraindications, as well as the impact of various factors on the adsorption process. In addition, we also discussed numerous medical applications of activated charcoal.

Removal of fluconazole from aqueous solution by magnetic biochar treated by ball milling: adsorption performance and mechanism

The problem of low adsorption capacity of pristine magnetic biochar for organic pollutants always occurs. It is of great significance to select a suitable method to improve the adsorption performance of magnetic biochar. In this study, magnetic biochar was treated by ball milling and tested for its fluconazole adsorption capacity. The maximum adsorption capacity of ball-milled magnetic biochar (BMBC) for fluconazole reached nearly 15.90 mg/g, which was approximately five times higher than that of pristine magnetic biochar (MBC). Fluconazole adsorption by BMBC was mainly attributed to π-π interactions, hydrogen bonding, and surface complexation with oxygen-containing functional groups. The enhancement in fluconazole adsorption by BMBC was attributed to an increase in oxygen-containing functional groups. Batch adsorption experiments also illustrated that BMBC could be successfully applied in a wide range of pH values. The high efficiency of fluconazole removal confirmed that ball milling was an effective strategy to enhance the adsorptive performance of magnetic biochar.

Preparation of magnesium Ferrite-Doped magnetic biochar using potassium ferrate and seawater mineral at low temperature for removal of cationic pollutants

Magnetic biochar has captured a great interest for remediation of environment as an easily separable carbonous adsorbent. Herein, a highly adsorptive magnetic biochar was manufactured through seawater mineral and K₂FeO₄ co-promoted pyrolysis of jackfruit peel at 300 °C for removal of different cationic pollutants, and characterized by element analysis, FTIR, SEM-EDS, XRD, XPS and so on. MgFe₂O₄ was generated without external base and a 19.42 emu/g saturation magnetization was achieved. Simultaneously, iron oxides and oxygen containing groups were introduced. The magnetic biochar exhibited 61.30 mg/g, 129.61 mg/g, and 1238.30 mg/g adsorption capacities for Cu²⁺, methylene blue (MB), and malachite green (MG) at 25 °C, respectively, and remarkably surpassed the corresponding pristine biochar. The adsorption of MB and MG was mainly realized by electrostatic interaction, hydrogen bonding, complexation, and π-π electron-donor-acceptor interaction, and that of Cu²⁺ was attributed to electrostatic interaction, hydrogen bonding, and complexation.

Removal of methyl orange from water by Fenton oxidation of magnetic coconut-clothed biochar

Water pollution has become a serious environmental problem to date. Advanced oxidation processes (AOP) have been widely applied in water treatments.

Magnetic biochar derived from rice straw and stainless steel pickling waste liquor for highly efficient adsorption of crystal violet

Reducing the preparation cost of magnetic biochar is necessary for its large-scale application as an adsorbent. In this study, stainless steel pickling waste liquor and rice straw were successfully applied to synthesize of magnetic biochar (SPWL-MBC). Several iron oxides adhered on the biochar matrix, mainly Fe₃O₄, Fe₂O₃ and FeO. SPWL-MBC exhibited superparamagnetism, and its specific surface area was 274.29 m²/g. The material was able to adsorb a model contaminant, crystal violet (CV), with a maximum adsorption capacity of approximately 111.48 mg/g. Adsorption mechanism analysis showed that iron oxides, π-π interaction, hydrogen bonding and electrostatic interaction were responsible for the adsorption of CV. The CV adsorption efficiency of SPWL-MBC remained 71.91% after three adsorption-regeneration cycles. These outcomes illustrate that the magnetic biochar prepared from stainless steel pickling waste liquor can effectively remove CV from wastewater.

Dual roles of biochar redox property in mediating 2,4-dichlorophenol degradation in the presence of Fe3+ and persulfate

Recent studies suggested that biochars could mediate the degradation of organic contaminants. The role of biochars in mediating organic contaminant degradation could be amplified in a Fenton-like reaction, and comparing biochars with varied properties may provide insightful information to understand the reaction mechanisms. In this study, biochar was applied in a Fenton-like reaction system with Fe³⁺ and persulfate (PS) to degrade 2,4-dichlorophenel (2,4-DCP). Biochars with different intensities of persistent free radicals (PFRs), oxygen-containing functional groups (OFGs), and redox properties were investigated regarding their roles in 2,4-DCP removal. Compared to biochar system, PS addition increased 2,4-DCP degradation and Fe³⁺ addition increased its sorption. The combination of PS and Fe³⁺ promoted 2,4-DCP degradation over 2 times higher. Various reactive oxygen species (ROS), including SO₄^•-, HO^•, and O₂^•-, were involved in 2,4-DCP degradation, contributing to around 50% of the overall 2,4-DCP degradation. The direct electron transfer between biochar particles and 2,4-DCP contributed to the rest of 2,4-DCP degradation. A significant positive correlation was observed between 2,4-DCP degradation and electron donating capacity (EDC) or Fe²⁺. We thus concluded that EDC-involved structures in biochars could either directly donate electron to 2,4-DCP, or reduce Fe³⁺ to Fe²⁺, which activated PS to generate ROS. This dual roles of biochar should be well considered in biochar application and production. This study provided a useful theoretical basis for manipulating biochar redox properties to enhance their application potential in pollution control.

An Efficient Strategy for Enhancing the Adsorption Capabilities of Biochar via Sequential KMnO4-Promoted Oxidative Pyrolysis and H2O2 Oxidation

In this study, sequential KMnO4-promoted oxidative pyrolysis and H2O2 oxidation were employed to upgrade the adsorption capacities of durian shell biochar for methylene blue (MB) and tetracycline (TC) in an aqueous solution. It was found that the KMnO4/H2O2 co-modification was greatly influenced by pyrolysis temperature and the optimal temperature was 300 °C. Moreover, a low concentration of H2O2 enabled the improvement of the adsorption capabilities greatly with the catalysis of pre-impregnated manganese oxides, addressing the shortcoming of single H2O2 modification. The co-modified biochar exhibited high adsorption capabilities for MB and TC, remarkably surpassed KMnO4- and H2O2- modified biochars as well as pristine biochar. The increase of adsorption capabilities could be mainly contributed to the incorporation of MnOx and carboxyl by KMnO4-promoted oxidative decomposition and Mn-catalyzed H2O2 oxidation. This would provide a novel and efficient method for preparing highly adsorptive biochar using sequential KMnO4-promoted oxidative pyrolysis and H2O2 oxidation.