Nano-hydroxyapatite modified biochar: Insights into the dynamic adsorption and performance of lead (II) removal from aqueous solution

Adsorption of heavy metals by biochar in aqueous solution: A review

Heavy metal pollution (e.g., Cd, Hg, Pb, Cu, Ni, Zn, As and Cr) has become a crucial issue worldwide. Among various remediation strategies, adsorption is widely recognized for its environmental sustainability, cost-effectiveness, and operational simplicity. In this context, biochar has gained significant attention due to its promising adsorption performance. To systematically support adsorption studies, this review compiled essential models for adsorption experiments, including commonly used adsorption kinetics models, isotherm models, and thermodynamic analysis methods. Moreover, we systematically analyzed key factors affecting heavy metal adsorption by biochar, such as its physicochemical properties, environmental pH, temperature, initial concentration, dosage, and the presence of coexisting ions, to identify the conditions that govern adsorption capacity. In addition, the adsorption performance of biochar toward eight significant heavy metals is reviewed in detail, with a focus on elucidating the underlying mechanisms, including complexation, ion exchange, cation-π bonding, electrostatic interactions, and precipitation. Finally, based on identified research gaps and critical challenges, we discuss emerging research tools, including machine learning and advanced surface modifications, to guide the targeted design of biochar materials for enhanced adsorption capacity.

Effective removal of Pb (II) from wastewater by zinc-iron bimetallic oxide-modified walnut shell biochar: A combined experimental and DFT calculation approach

The modified walnut shell biochar (WBC) was prepared through zinc-iron bimetallic oxide modification (ZF@WBC) at 600 °C under oxygen-limited conditions in this study. Through adsorption experiments, characterization analyses, and density functional theory (DFT) calculations, the adsorption properties of ZF@WBC to Pb (II) were investigated and the mechanism underlying such adsorption was elucidated. Characterization results showed that the surface area (375.9709 m2/g) and total pore volume (0.205319 cm3/g) of ZF@WBC were significantly greater than those of walnut shell biochar. The maximum adsorption capacity of ZF@WBC for Pb (II) was found to be 104.26 mg/g, which is 2.57 times higher than that of WBC according to the adsorption experiments conducted. The observed adsorption behavior followed both the pseudo-second-order (PSO) kinetic model and Langmuir isothermal adsorption model, suggesting that chemisorption plays a major role in the absorption process. Based on SEM, XRD, XPS, FTIR characterizations along with DFT calculations performed in this study, it can be concluded that surface complexation, ion exchange, electrostatic attraction, physical absorption are among the main mechanisms responsible for absorption of Pb (II) by ZF@WBC. Furthermore, even in the presence of interfering ions at different concentrations, ZF@WBC exhibited a removal rate above 70% for Pb (II). Therefore, ZF@WBC has great potential as an effective absorbent for removing Pb (II) from wastewater, while also offering opportunities for biomass waste resource utilization.

Mechanism of clay mineral modified biochar simultaneously immobilizes heavy metals and reduces soil carbon emissions

Heavy metal pollution in farmland soil has become increasingly severe, and multi-element composite pollution has brought enormous harm to human production and life. Environmental changes in cold regions (such as freeze-thaw cycles and dry-wet alternations) may increase the potential physiological toxicity of heavy metals and exacerbate pollution risks. In order to reveal the effectiveness of sepiolite modified biochar in the remediation of the soil contaminated with lead (Pb), cadmium (Cd), and chromium (Cr), the rice husk biochar pyrolyzed at 500 and 800 °C were selected for remediation treatment (denoted as BC500 and BC800). Meanwhile, different proportions of sepiolite were used for modification (biochar: sepiolite = 1: 0.5 and 1: 1), denoted as MBC500/MBC800 and HBC500/HBC800, respectively. The results showed that modified biochar with sepiolite can effectively improve the immobilization of heavy metals. Under natural conservation condition, the amount of diethylenetriaminepentaacetic acid (DTPA) extractable Pb in BC500, MBC500, and HBC500 decreased by 5.95, 12.39, and 13.55%, respectively, compared to CK. Freeze-thaw cycles and dry-wet alternations activated soil heavy metals, while modified biochar increased adsorption sites and oxygen-containing functional groups under aging conditions, inhibiting the fractions transformation of heavy metals. Furthermore, freeze-thaw cycles promoted the decomposition and mineralization of soil organic carbon (SOC), while sepiolite hindered the release of active carbon through ion exchange and adsorption complexation. Among them, and the soil dissolved organic carbon (DOC) content in HBC800 decreased by 49.39% compared to BC800. Additionally, the high-temperature pyrolyzed biochar (BC800) enhanced the porosity richness and alkalinity of material, which effectively inhibited the migration and transformation of heavy metals compared to BC500, and reduced the decomposition of soil DOC.

Applications of engineered biochar in remediation of heavy metal(loid)s pollution from wastewater: Current perspectives toward sustainable development goals

Environmental pollution of heavy metal(loid)s (HMs) caused adverse impacts, has become one of the emerging concerns and challenges worldwide. Metal(loid)s can pose significant threats to living organisms even when present in trace levels within environmental matrices. Extended exposure to these substances can lead to adverse health consequences in humans. Removing HM-contaminated water and moving toward sustainable development goals (SDGs) is critical. In this mission, biochar has recently gained attention in the environmental sector as a green and alternative material for wastewater removal. This work provides a comprehensive analysis of the remediation of typical HMs by biochars, associated with an understanding of remediation mechanisms, and gives practical solutions for ecologically sustainable. Applying engineered biochar in various fields, especially with nanoscale biochar-aided wastewater treatment approaches, can eliminate hazardous metal(loid) contaminants, highlighting an environmentally friendly and low-cost method. Surface modification of engineered biochar with nanomaterials is a potential strategy that positively influences its sorption capacity to remove contaminants. The research findings highlighted the biochars' ability to adsorb HM ions based on increased specific surface area (SSA), heightened porosity, and forming inner-sphere complexes with oxygen-rich groups. Utilizing biochar modification emerged as a viable approach for addressing lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and chromium (Cr) pollution in aqueous environments. Most biochars investigated demonstrated a removal efficiency >90 % (Cd, As, Hg) and can reach an impressive 99 % (Pb and Cr). Furthermore, biochar and advanced engineered applications are also considered alternative solutions based on the circular economy.

Mechanistic investigation of Pb2+ adsorption on biochar modified with sodium alginate composite zeolitic imidazolate framework-8

For the serious situation of heavy metal pollution, the use of cheap, clean, and efficient biochar to immobilize heavy metals is a good treatment method. In this paper, SA@ZIF-8/BC was prepared for the adsorption of Pb2+ in solution using sodium alginate (SA) and zeolitic imidazolate framework-8 (ZIF-8) modified corn cob biochar. The results showed that the specific surface area of modified biochar was greatly improved, with good adsorption capacity for Pb2+, strong anti-interference ability, and good economy. At the optimal adsorption pH of 5, the adsorption model of Pb2+ by SA@ZIF-8/BC was more consistent with the pseudo-second-order kinetic model and Langmuir isotherm model. This indicates that the adsorption of Pb2+ by SA@ZIF-8/BC is chemisorption and monolayer adsorption. The maximum adsorption of modified biochar was 300 mg g-1, which was 2.38 times higher than that of before modified BC (126 mg g-1). The shift in binding energy of functional groups before and after adsorption of SA@ZIF-8/BC was studied by XPS, and it was found that hydroxyl and carboxyl groups played an important role in the adsorption of Pb2+. It was demonstrated that this novel adsorbent can be effectively used for the treatment of Pb pollution in wastewater.

Na/N Co-doped Seaweed Biochar Composite for Efficient Removal of Aqueous Pb(II) and Cu(II)

Pollution from harmful heavy metal ions such as Pb(II) and Cu(II) is causing serious environmental and health problems. In this study, Sodium and nitrogen co-doped porous carbon material (Na/NABc) was successfully prepared from seaweed, sodium hydroxide, and dicyandiamide. The experimental results showed that Na/NABc is an excellent adsorbent for the effective removal of Pb(II) and Cu(II) from water bodies. Specifically, 99.8% of Pb(II) and 64.6% Cu(II) (100 mg/L) were removed within 12 h using 10 mg Na/NABc(10%) at 25 °C. The adsorption of Pb(II) and Cu(II) in aqueous solution by Na/NABc(10%) was efficient and rapid in the first stage. The theoretical maximum removal capacities of Na/NABc for Pb(II) and Cu(II) were 959.6 and 299.1 mg/g, respectively. Pb(II) and Cu(II) ions were adsorbed quickly in the first 60 min, and the kinetics data were generally consistent with a pseudo-second-order model. Na/NABc(10%) had a large distribution coefficient for Pb(II) (8.38 L/mg) and Cu(II) (1.17 L/mg). The possible mechanisms were precipitation, Ion exchange, and surface complexation. The removal rate can reach about 70% after five cycles, and the release of sodium meets the standard. The results of this study demonstrate the potential applicability of Na/NABc(10%) for adsorption of heavy metals from aqueous solution.

Selenium-phosphorus modified biochar reduces mercury methylation and bioavailability in agricultural soil

Biochar is a frequently employed for solidifying and stabilizing mercury (Hg) contamination in soil. However, it often results in an elevated presence of soil methylmercury (MeHg), which introduces new environmental risks. Consequently, there is a necessity for developing a safer modified biochar for use in Hg-contaminated soil. This study employed sodium selenite (at a safe dosage for soil) and hydroxyapatite to modify straw biochar (BC) based on the interaction between selenium (Se) and phosphorus (P). This process led to the formation of Se-modified biochar (Se-BC), P-modified biochar (P-BC), and Se and P co-modified biochar (Se-P-BC). Additionally, solvent adsorption experiments and pot experiments (BC/soil mass ratio: 0.5 %) were conducted to investigate the impacts of these soil amendments on soil Hg methylation and bioavailability. Se and P co-modification substantially increased the surface area, pore volume, and Hg adsorption capacity of BC. BC treatment increased the simulated gastric acid-soluble Hg, organo-chelated Hg, and MeHg in the soil. Conversely, Se-P-BC significantly reduced these forms of Hg in the soil, indicating that Se-P-BC can transform soil Hg into less bioavailable states. Among the different biochar treatments, Se-P-BC exhibited the most pronounced reductions in soil MeHg, total Hg, and MeHg in water spinach, achieving reductions of 63 %, 71 %, and 70 %, respectively. The co-modification of Se and P displayed a synergistic reduction effect in managing soil Hg pollution, which is associated with the increase of available Se in the soil due to phosphorus addition. The significantly reduced dissolved organic carbon and the abnormally high SO42- concentration in the soil of Se-P-BC treatment also inhibited Hg methylation and bioavailability in the soil. In summary, Se-P-BC substantially increased reduction percentage in plant Hg content while mitigating the risk of secondary pollution arising from elevated soil MeHg.

Biochar and nano biochar: Enhancing salt resilience in plants and soil while mitigating greenhouse gas emissions: A comprehensive review

Salinity stress poses a significant challenge to agriculture, impacting soil health, plant growth and contributing to greenhouse gas (GHG) emissions. In response to these intertwined challenges, the use of biochar and its nanoscale counterpart, nano-biochar, has gained increasing attention. This comprehensive review explores the heterogeneous role of biochar and nano-biochar in enhancing salt resilience in plants and soil while concurrently mitigating GHG emissions. The review discusses the effects of these amendments on soil physicochemical properties, improved water and nutrient uptake, reduced oxidative damage, enhanced growth and the alternation of soil microbial communities, enhance soil fertility and resilience. Furthermore, it examines their impact on plant growth, ion homeostasis, osmotic adjustment and plant stress tolerance, promoting plant development under salinity stress conditions. Emphasis is placed on the potential of biochar and nano-biochar to influence soil microbial activities, leading to altered emissions of GHG emissions, particularly nitrous oxide(N2O) and methane(CH4), contributing to climate change mitigation. The comprehensive synthesis of current research findings in this review provides insights into the multifunctional applications of biochar and nano-biochar, highlighting their potential to address salinity stress in agriculture and their role in sustainable soil and environmental management. Moreover, it identifies areas for further investigation, aiming to enhance our understanding of the intricate interplay between biochar, nano-biochar, soil, plants, and greenhouse gas emissions.

Utilizing different types of biomass materials to modify steel slag for the preparation of composite materials used in the adsorption and solidification of Pb in solutions and soil

This study utilized discarded steel slag (SS) as raw material and prepared modified steel slag materials (SS-SBC, SS-NBC, SS-BHA) through modification with biomass materials such as straw biochar (SBC), nutshell biochar (NBC), and biochemical humic acid (BHA). These materials were then applied for the removal of Pb from both solution and soil. The physical and chemical properties of the materials were analyzed using characterization techniques such as SEM, EDS, XRD, and BET. The specific surface area of the modified materials increased from the original 3.8584 m2/g to 34.7133 m2/g, 181.7329 m2/g, and 7.7384 m2/g, respectively. The study then explored the influence of different adsorption conditions on the adsorption capacity of Pb in solution, determining the optimal conditions as follows: initial concentration of 200 mg/L, adsorbent mass of 0.04 g, temperature of 15 °C, and pH = 2. To further investigate the adsorption process, kinetic and isotherm models were established. The results indicated that the adsorption process for all three materials followed a pseudo-second-order kinetic model and Freundlich isotherm model, suggesting a multi-layer chemical adsorption. Thermodynamic analysis revealed that the adsorption process was an exothermic spontaneous reaction. Soil cultivation experiments were conducted to explore the effects of different material addition amounts and cultivation times on the passivation of Pb-polluted soil. Analysis of heavy metal forms in the soil revealed that the addition of modified materials reduced the acid-extractable form of Pb in the soil and increased the residual form, which is beneficial for reducing the migration of Pb in the soil. FT-IR and XPS analyses were employed to study the functional groups, element composition, and valence states before and after adsorption passivation of Pb by the three materials. The results confirmed that the adsorption mechanisms of SS-SBC, SS-NBC, and SS-BHA mainly involved electrostatic adsorption, ion and ligand exchange, and surface precipitation. This study not only provides a new material for adsorbing and immobilizing heavy metals in soil and water but also offers a new approach for the resource utilization of steel slag waste.

Hydroxyapatite and its composite in heavy metal decontamination: Adsorption mechanisms, challenges, and future perspective

Nanohydroxyapatite (n-HAP), recognized by its peculiar crystal architecture and distinctive attributes showcased the underlying potential in adsorbing heavy metal ions (HMI). In this paper, the intrinsic mechanism of HMI adsorption by n-HAP was first revealed. Subsequently, the selectivity and competitiveness of n-HAP for HMI in a variety of environments containing various interferences from cations, anions, and organic molecules are elucidated. Next, n-HAP was further categorized according to its morphological dimensions, and its adsorption properties and intrinsic mechanisms were investigated based on these different morphologies. It was shown that although n-HAP has excellent adsorption capacity and cost-effectiveness, its application is often challenging to realize due to its inherent fragility and agglomeration, the technical problems required for its handling, and the difficulty of recycling. Finally, to address these issues, this paper discusses the tendency of n-HAP and its hybridized/modified materials to adsorb HMI as well as the limitations of their applications. By summarizing the limitations and future directions of hybridization/modification HAP in the field of HMI contamination abatement, this paper provides insightful perspectives for its gradual improvement and rational application.

A novel porous lignocellulosic standing hierarchical hydroxyapatite for enhanced aqueous copper(II) removal

Potentially toxic metal-polluted water resources are a heavily discussed topic the pollution by potentially toxic metals can cause significant health risks. Nanomaterials are actively developed towards providing high specific surface area and creating active adsorption sites for the treatment and remediation of these polluted waters. In an effort to tackle the limitations of conventional type adsorbents, nano-hydroxyapatite (HAp) was developed in this study by in situ generation onto wood powder, resulting in the formation of uniform hybrid powder (HAp@wood composite) structure consisting of HAp nanoparticles that showed the removal efficiency up to 80 % after 10 min; the maximum adsorption capacity for Cu(II) ions (98.95 mg/g-HAp) was higher compared to agglomerated nano-HAp (72.85 mg/g-HAp). The adsorption capacity of Cu(II) remained stable (89.85-107.66 mg/g-HAp) during the four adsorption-desorption cycles in multi-component system, thereby demonstrating high selectivity for Cu(II). This approach of using nanoparticle is relatively simple yet effective in improving the adsorption of potentially toxic metals and the developed approach can be used to develop advanced nanocomposites in commercial wastewater treatment.

Mechanistic insight into lead immobilization on bone-derived carbon/hydroxyapatite composite at low and high initial lead concentration

The contamination of heavy metal lead has a serious impact on the natural environment and organisms. Among various materials for lead removal, animal bone derived hydroxyapatite has received extensive attention. However, there are different opinions among researchers regarding the mechanism of lead removal by hydroxyapatite, possibly due to varying initial lead concentrations used in different studies and lack of accuracy in the study of lead removal mechanisms. In present work, we synthesized a carbon-containing hydroxyapatite (CHAP) through pyrolysis of bovine bone with excellent lead removal efficiency, and further investigated the lead removal mechanism of CHAP under high and low initial lead concentrations by combining XRD Rietveld refinement, FTIR, XPS, HRTEM etc. methods. The results showed that under low initial Pb2+ concentration condition, the main mechanism of lead removal by CHAP was chemical precipitation (94.1 %), with small contributions of lead complexation with carbon functional groups and cation-π interactions on the amorphous carbon in CHAP, and surface adsorption on the precipitates. Under high initial Pb2+ concentration condition, chemical precipitation remained the main mechanism (74.68 %), but the contributions of the other three mechanisms increased, and ion exchange appeared in the later stage of the removal process. This study provides new insights on the lead immobilization mechanism by CHAP at different initial Pb2+ concentrations in water.

Simultaneous immobilization of lead and arsenic and improved phosphorus availability in contaminated soil using biochar composite modified with hydroxyapatite and oxidation: Findings from a pot experiment

Multi-metals/metalloids contaminated soil has received extensive attention because of their adverse health effects on the safety of the food chain and environmental health. In order to provide additional insight and aid in mitigating environmental risks, a pot experiment was directed to assess the impacts of biochars derived from rice straw (BC), and modified biochars i-e., hydroxyapatite modified (HAP-BC) and oxidized biochars (Ox-BC) on the redistribution, phytoavailability and bioavailability of phosphorus (P), lead (Pb), and Arsenic (As), as well as their effects on the growth of maize (Zea mays L.) in a Lead (Pb)/Arsenic (As) contaminated soil. The results showed that HAP-BC increased the soil total and available P, compared with raw biochar and control treatment. HAP-BC improved soil properties by elevating soil pH and electric conductivity (EC). The Hedley fractionation scheme revealed that HAP-BC enhanced the labile and moderately labile P species in soil. Both HAP-BC and Ox-BC assisted in the P build-up in plant roots and shoots. The BCR (European Community Bureau of Reference) sequential extraction data for Pb and As in soil showed the pronounced effects of HAP-BC towards the transformation of labile Pb and As forms into more stable species. Compared with control, HAP-BC significantly (P ≤ 0.05) decreased the DTPA-extractable Pb and As by 55% and 28%, respectively, subsequently, resulting in reduced Pb and As plant uptakes. HAP-BC application increased the plant fresh and dry root/shoot biomass by 239%, 72%, 222% and 190%, respectively. The Pb/As immobilization by HAP-BC was mainly driven by precipitation, ion exchange and surface complexation mechanisms in soil. In general, HAP-BC application indicated a great capability to be employed as an effective alternative soil amendment for improving P acquisition in soil, simultaneously immobilizing Pb and As in the soil-plant systems.

Mitigation of Cd(II) contamination in aqueous solution and soil by multifunctional hydroxyapatite/sludge biochar composite

Biochar with well-developed pore structure is an ideal carrier for easily agglomerated hydroxyapatite (HAP). Hence, a novel multifunctional hydroxyapatite/sludge biochar composite (HAP@BC) was synthesized by chemical precipitation method and used for mitigating Cd(II) contamination form aqueous solution/soil. Compared to sludge biochar (BC), HAP@BC exhibited rougher and more porous surface. Meanwhile, the HAP was dispersed on the sludge biochar surface, which reduced the agglomeration of HAP. The adsorption performance of HAP@BC on Cd(II) was better than that of BC under the influence of different single-factor batch adsorption experiments. Moreover, the Cd(II) adsorption behavior by BC and HAP@BC was uniform monolayer adsorption, and this reaction process was endothermic and spontaneous. The Cd(II) maximum adsorption capacities of BC and HAP@BC were 79.96 and 190.72 mg/g at 298 K, respectively. Moreover, the Cd(II) adsorption mechanism on BC and HAP@BC included complexation, ion exchange, dissolution-precipitation and Cd(II)-π interaction. According to the semi-quantitative analysis, ion exchange was the main mechanism for Cd(II) removal by HAP@BC. Notably, HAP played a role in the Cd(II) removal by dissolution-precipitation and ion exchange. This result suggested that there was a synergistic effect between HAP and sludge biochar for the Cd(II) removal. HAP@BC reduced the leaching toxicity of Cd(II) in soil better than BC, indicating that the HAP@BC was able to mitigate Cd(II) contamination in soil more effectively. This work demonstrated that sludge biochar was an ideal carrier for dispersed HAP and provided an effective HAP/biochar composite for the mitigation of Cd(II) contamination in aqueous solution/soil.

Effect of iron impregnation ratio on the properties and adsorption of KOH activated biochar for removal of tetracycline and heavy metals

The effect of iron impregnation ratio on magnetic biochars (MBCs) prepared by biomass pyrolysis accompanied by KOH activation has been less reported. In this study, MBCs were produced by one-step pyrolysis/KOH-activation of walnut shell, rice husk and cornstalk with different impregnation ratios (0.3-0.6). The properties, adsorption capacity and cycling performance for Pb(II), Cd(II) and tetracycline of MBCs were determined. MBCs prepared with low impregnation ratio (0.3) showed stronger adsorption capacity on tetracycline. The adsorption capacity of WS-0.3 toward tetracycline was up to 405.01 mg g^-1, while that of WS-0.6 was only 213.81 mg g^-1. It is noteworthy that rice husk and cornstalk biochar with an impregnation ratio of 0.6 were more effective in removing Pb(II) and Cd(II), and the content of Fe⁰ crystals on surface strengthened the ion exchange and chemical precipitation. This work highlights that the impregnation ratio should be changed according to the actual application scenarios of MBC.

Adsorption of Pb(II) from wastewater using a red mud modified rice-straw biochar: Influencing factors and reusability

Efficient environmental remediation of toxic chemicals using effective sorbents has received considerable attention recently. For the present study, the synthesis of a red mud/biochar (RM/BC) composite was performed from rice straw with the aim of achieving Pb(II) removal from wastewater. Characterization was performed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), Zeta potential analysis, elemental mapping, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results showed that RM/BC had higher specific surface area (S_BET = 75.37 m² g^-1) than raw biochar (S_BET = 35.38 m² g^-1). The Pb(II) removal capacity (q_e) of RM/BC was 426.84 mg g^-1 at pH 5.0, and the adsorption data well fitted pseudo second order kinetics (R² = 0.93 and R² = 0.98), as well as the Langmuir isotherm model (R² = 0.97 and R² = 0.98) for both BC and RM/BC. Pb(II) removal was slightly hindered with the increasing strength of co-existing cations (Na⁺, Cu²⁺, Fe³⁺, Ni²⁺, Cd²⁺). The increase in temperatures (298 K, 308 K, 318 K) favored Pb(II) removal by RM/BC. Thermodynamic study indicated that Pb(II) adsorption onto BC and RM/BC was spontaneous and primarily governed by chemisorption and surface complexation. A regeneration study revealed the high reusability (>90%) and acceptable stability of RM/BC even after five successive cycles. These findings indicate that RM/BC evidenced special combined characteristics of red mud and biochar, hence its use for Pb removal from wastewater offers a green and environmentally sustainable approach fitting the "waste treating waste" concept.

Construction of a Molecularly Imprinted Sensor Modified with Tea Branch Biochar and Its Rapid Detection of Norfloxacin Residues in Animal-Derived Foods

Norfloxacin (NOR) is a common antibiotic used in humans and animals, and its high levels can cause intolerance or poisoning. Therefore, NOR levels in animal-derived foods must be monitored due to potential side effects and illegal use phenomena. This research centered on the development of an environmentally friendly electrochemical sensor for NOR detection. Potassium carbonate activated tea branch biochar (K-TBC) as an efficient use of waste was coated on the surface of glassy carbon electrode (GCE), and a molecular-imprinted polymer (MIP) layer was subsequently electropolymerized onto the modified electrode. NOR was used as template molecule and o-phenylenediamine (o-PD) and o-aminophenol (o-AP) were used as bifunctional monomers. The electrochemical sensor was built and its electrochemical behavior on NOR was investigated. The sensor demonstrated an excellent linear current response to NOR concentrations in the ranges of 0.1-0.5 nM and 0.5-100 nM under ideal experimental circumstances, with a detection limit of 0.028 nM (S/N = 3). With recoveries ranging from 85.90% to 101.71%, the designed sensor was effectively used to detect NOR in actual samples of milk, honey, and pork. Besides, the fabricated sensor had low price, short detection time, good selectivity and stability, which can provide a theoretical and practical basis for the actual monitoring of NOR residues.

Applying fulvic acid for sediment metals remediation: Mechanism, factors, and prospect

Fulvic acid (FA) has been shown to play a decisive role in controlling the environmental geochemical behavior of metals. As a green and natural microbial metabolite, FA is widely used in environmental remediation because of its good adsorption complexation and redox ability. This paper introduces the reaction mechanism and properties of FA with metals, and reviews the progress of research on the remediation of metal pollutant by FA through physicochemical remediation and bioremediation. FA can control the biotoxicity and migration ability of some metals, such as Pb, Cr, Hg, Cd, and As, through adsorption complexation and redox reactions. The concentration, molecular weight, and source are the main factors that determine the remediation ability of FA. In addition, the ambient pH, temperature, metal ion concentrations, and competing components in sediment environments have significant effects on the extent and rate of a reaction between metals and FA during the remediation process. Finally, we summarize the challenges that this promising environmental remediation tool may face. The research directions of FA in the field of metals ecological remediation are also prospected. This review can provide new ideas and directions for the research of remediation of metals contaminants in sediments.

Adsorption-reduction coupling mechanism and reductive species during efficient florfenicol removal by modified biochar supported sulfidized nanoscale zerovalent iron

Sulfidized nanoscale zerovalent iron (S-nZVI) was a promising material for degrading halogenated contaminants, but the easy aggregation limits its application for in-situ groundwater remediation. Hence, S-nZVI was decorated onto modified biochar (mBC) to obtain better dispersity and reactivity with florfenicol (FF), a widely used antibiotic. Uniform dispersion of S-nZVI particles were achieved on the mBC with plentiful oxygen-containing functional groups and negative surface charge. Thus, the removal rate of FF by S-nZVI@mBC was 2.5 and 3.1 times higher than that by S-nZVI and S-nZVI@BC, respectively. Adsorption and dechlorination of FF showed synergistic effect under appropriate mBC addition (e.g., C/Fe mass ratio = 1:3, 1:1), probably due to the enrichment of FF facilitates its reduction. In contrast, the contact between FF and S-nZVI could be hindered under more mBC addition, significantly decrease the reduction rate of FF and the reduction capacity of per unit Fe⁰. In addition, sulfur dose altered the surface species of surface Fe and S, and removal rates of FF correlated well with surface reductive species, i.e., FeS (r = 0.90, p < 0.05) and Fe⁰ (r = 0.98, p < 0.01). These mechanistic insights indicate the importance of rational design for biochar supported S-nZVI, which can lead to more efficient FF degradation.