Effect of Fe-N modification on the properties of biochars and their adsorption behavior on tetracycline removal from aqueous solution

Enhanced adsorption of tetracycline by lanthanum/iron co-modified rice shell biochar: Synthesis, adsorption performance, site energy distribution and regeneration

A novel La/Fe co-modified biochar derived from rice shell (La/Fe@RSBC) was prepared and employed in tetracycline (TC) adsorption from water. The characterizations, kinetics, isotherms, thermodynamics, and site energy distribution (SED) were studied to investigate TC adsorption behaviors. La/Fe@RSBC exhibited the maximum adsorption capacity towards TC of 414.84 mg/g, which was 1.27-2.41 folds than that of RSBC, La@RSBC, and Fe@RSBC. The possible adsorption mechanism of TC dominantly involved H bond, surface complexation, pore filling, electrostatic attraction, and π-π electron donor-acceptor (EDA) interaction. Moreover, TC adsorption behavior was spontaneous and endothermic, significantly related to the compositions and dosage of La/Fe@RSBC, initial pH, and solution temperature. Additionally, SED results promulgated that co-loaded Fe and La synergistically enhanced the affinity of biochar and provided more adsorption sites for TC at a higher temperature. The residual TC after regeneration by ethanol dominantly inhibited the third stage of adsorption, that is, the adsorption of TC on the inner surface of La/Fe@RSBC in next run. Importantly, H2O2 combined with La/Fe@RSBC-mediated advanced oxidation process could effectively clear residual TC after ethanol desorption, which obviously improved the service life of La/Fe@RSBC. In addition, the swine wastewater treatment demonstrated that La/Fe@RSBC had a promising potential application in practical application.

Magnetic nanoparticle modified moss Biochar: A novel solution for effective removal of enrofloxacin from aquaculture water

The presence of residual antibiotics in water constitutes a potential threat to aquatic environments. Therefore, designing environmentally friendly and efficient biochar adsorbents is crucial. Aquaculture by-product moss (bryophyte) was transformed into biochar, which can eliminate antibiotics from wastewater through adsorption. This study successfully fabricated moss biochar (BC) and magnetically modified moss biochar (MBC), and explored their adsorption performance for enrofloxacin (ENR). Characterization analyses revealed that the specific surface area, total pore volume, and the quantity of functional groups of the MBC were significantly larger than those of the BC. The Langmuir isotherm model suggests that the maximum adsorption capacities of BC and MBC for ENR are 7.24 mg g⁻1 and 11.62 mg g⁻1. The adsorption process conforms to a pseudo-second-order kinetic model. Studies carried out at different temperatures disclose the spontaneous and endothermic thermodynamic characteristics of the system. Under neutral conditions, the adsorption efficiency attains its peak. The existence of various coexisting ions in water exerts a negligible influence on the adsorption process; furthermore, when the concentration of humic acid (HA) ranges from 0 to 20 mg/L, the removal rate remains above 90%. In actual water samples, the antibiotic removal rate can be as high as 96.84%. After three cycles of reuse, the structure of MBC remains unchanged while maintaining a high removal efficiency. The primary mechanisms for antibiotic adsorption by MBC involve electrostatic interactions, hydrophobic interactions, pore-filling effects, hydrogen bonding, and π-π interactions. This reusable magnetic moss biochar provides a promising research direction for effectively eliminating antibiotics from water sources.

Effect of Pyrolysis Temperature on the Carbon Sequestration Capacity of Spent Mushroom Substrate Biochar in the Presence of Mineral Iron

The preparation of biochar typically involves the pyrolysis of waste organic biomass. Iron-rich magnetic biochar not only inherits the characteristics of high specific surface area and porous structure from biochar but also possesses significant advantages in easy separation and recovery, which has shown great application potential in various fields such as soil improvement and water resource remediation. This study aims to explore the influence of mineral iron on the carbon sequestration capability of biochar during the pyrolysis process. Experiments were conducted by using spent mushroom substrates as raw materials to prepare biochar at different temperature intervals (300 to 600 °C). The addition of exogenous iron has been found to significantly enhance the carbon retention rate (12.2-44.5%) of biochar across various pyrolysis temperatures and, notably, improves the carbon stability of biochar at 300 °C, 400 °C, and 600 °C. Through the analysis of thermogravimetric mass spectrometry (TG-MS) and X-ray photoelectron spectroscopy (XPS), we discovered that iron catalyzes the thermochemical reactions and inhibits the release of organic small molecules (C2-C5) through both physical blocking (FexOx) and chemical bonding (C=O and O-C=O). The results of Raman spectroscopy and infrared spectroscopy analyses indicate that the addition of iron significantly promotes the graphitization process of carbon and enhances the thermal stability of biochar within the temperature range of 300 to 500 °C. When exploring the retention and stability of carbon during pyrolysis, it was found that under the conditions of 600 °C and the presence of iron, the maximum carbon sequestration rate of biochar can reach 60.6%. Overall, this study highlights the critical role of iron and pyrolysis temperature in enhancing the carbon sequestration capacity of biochar.

Preparation of red mud-modified sludge char through microwave-assisted one-step pyrolysis and steam activation and its adsorption properties for hydrogen sulfide

To improve the hydrogen sulfide (H2S) adsorption performance of sludge-derived char, a type of red mud-modified sludge char (RSC) was prepared through microwave-assisted one-step pyrolysis and steam activation of sludge and red mud (RM). The effects of pyrolysis temperature, RM mass percentage, and steam flow rate on the cumulative adsorption capacity of H2S were systematically investigated using response surface method. The results indicated that the sludge char showed a significant increase in cumulative adsorption capacity from 1.47 mg/g to 22.83 mg/g when it was modified with RM at a pyrolysis temperature of 625 °C, a mass percentage of RM of 20%, and a steam flow rate of 0.46 mmol/min. The XRD and XPS analysis results indicated that the RM doping generated abundant iron oxides on the surface of RSC, which is beneficial for the adsorption of H2S. Adsorption thermodynamics, isotherm fitting and thermodynamic calculations indicate that the adsorption mechanism of H2S on the RSC surface was attributed to the combined effects of physisorption and chemisorption. Additionally, the material exhibited reliable reusability, retaining more than 80% of its initial breakthrough capacity after three adsorption-regeneration cycles. Therefore, the RSC prepared in this study can be regarded as a promising adsorbent due to its low cost, effective adsorption capabilities, and reusability. The developed method is promising as it achieves environmental remediation through the utilization of waste sludge and RM.

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.

Enhanced sorption and destruction of PFAS by biochar-enabled advanced reduction process

The biochar-enabled advanced reduction process (ARP) was developed for enhanced sorption (by biochar) and destruction of PFAS (by ARP) in water. First, the biochar (BC) was functionalized by iron oxide (Fe3O4), zero valent iron (ZVI), and chitosan (chi) to produce four biochars (BC, Fe3O4-BC, ZVI-chi-BC, and chi-BC) with improved physicochemical properties (e.g., specific surface area, pore structure, hydrophobicity, and surface functional groups). Batch sorption experimental results revealed that compared to unmodified biochar, all modified biochars showed greater sorption efficiency, and the chi-BC performed the best for PFAS sorption. The chi-BC was then selected to facilitate reductive destruction and defluorination of PFAS in water by ARP in the UV-sulfite system. Adding chi-BC in UV-sulfite ARP system significantly enhanced both degradation and defluorination efficiencies of PFAS (up to ∼100% degradation and ∼85% defluorination efficiencies). Radical analysis using electron paramagnetic resonance (EPR) spectroscopy showed that sulfite radicals dominated at neutral pH (7.0), while hydrated electrons (eaq-) were abundant at higher pH (11) for the efficient destruction of PFAS in the ARP system. Our findings elucidate the synergies of biochar and ARP in enhancing PFAS sorption and degradation, providing new insights into PFAS reductive destruction and defluorination by different reducing radical species at varying pH conditions.

A waste-to-wealth conversion of plastic bottles into effective carbon-based adsorbents for removal of tetracycline antibiotic from water

Currently, plastic waste and antibiotic wastewater are two of the most critical environmental problems, calling for urgent measures to take. A waste-to-wealth strategy for the conversion of polyethylene terephthalate (PET) plastic bottles into value-added materials such as carbon composite is highly recommended to clean wastewater contaminated by antibiotics. Inspired by this idea, we develop a novel PET-AC-ZFO composite by incorporating PET plastic-derived KOH-activated carbon (AC) with ZnFe2O4 (ZFO) particles for adsorptive removal of tetracycline (TTC). PET-derived carbon (PET-C), KOH-activated PET-derived carbon (PET-AC), and PET-AC-ZFO were characterized using physicochemical analyses. Central composite design (CCD) was used to obtain a quadratic model by TTC concentration (K), adsorbent dosage (L), and pH (M). PET-AC-ZFO possessed micropores (d ≈ 2 nm) and exceptionally high surface area of 1110 m2 g-1. Nearly 90% TTC could be removed by PET-AC-ZFO composite. Bangham kinetic and Langmuir isotherm were two most fitted models. Theoretical maximum TTC adsorption capacity was 45.1 mg g-1. This study suggested the role of hydrogen bonds, pore-filling interactions, and π-π interactions as the main interactions of the adsorption process. Thus, a strategy for conversion of PET bottles into PET-AC-ZFO can contribute to both plastic recycling and antibiotic wastewater mitigation.

Activation of peroxymonosulfate by Fe,N co-doped walnut shell biochar for the degradation of sulfamethoxazole: Performance and mechanisms

Fe and N co-doped walnut shell biochar (Fe,N-BC) was prepared through a one-pot pyrolysis procedure by using walnut shells as feedstocks, melamine as the N source, and iron (III) chloride as the Fe source. Moreover, pristine biochar (BC), nitrogen-doped biochar (N-BC), and α-Fe2O3-BC were synthesized as controls. All the prepared materials were characterized by different techniques and were used for the activation of peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). A very high degradation rate for SMX (10 mg/L) was achieved with Fe,N-BC/PMS (0.5 min-1), which was higher than those for BC/PMS (0.026 min-1), N-BC/PMS (0.038 min-1), and α-Fe2O3-BC/PMS (0.33 min-1) under the same conditions. This is mainly due to the formation of Fe3C and iron oxides, which are very reactive for the activation of PMS. In the next step, Fe,N-BC was employed for the formation of a composite membrane structure by a liquid-induced phase inversion process. The synthesized ultrafiltration membrane not only exhibited high separation performance for humic acid sodium salt (HA, 98%) but also exhibited improved self-cleaning properties when applied for rhodamine B (RhB) filtration combined with a PMS solution cleaning procedure. Scavenging experiments revealed that 1O2 was the predominant species responsible for the degradation of SMX. The transformation products of SMX and possible degradation pathways were also identified. Furthermore, the toxicity assessment revealed that the overall toxicity of the intermediate was lower than that of SMX.

A thorough investigation into the adsorption behavior of sophorolipid-modified fly ash towards compound pollution of lead and tetracycline

Heavy metal ions and antibiotics were simultaneously detected in authentic water systems. This research, for the first time, employed synthesized sophorolipid-modified fly ash(SFA) to eliminate tetracycline(TC) and lead(Pb2+) from wastewater. Various characterization techniques, including SEM-EDS, FTIR, XPS, BET, and Zeta, were employed to investigate the properties of the SFA. The results showed that the sophorolipid modification significantly improved the fly ash's adsorption capacities for the target pollutants. The static adsorption experiments elucidated the adsorption behaviors of SFA towards TC and Pb2+ in single and binary systems, highlighting the effects of different Environmental factors on the adsorption behavior in both types of systems. In single systems, SFA exhibited a maximum adsorption capacity of 128.96 mg/g for Pb2+ and 55.57 mg/g for TC. The adsorption of Pb2+ and TC followed pseudo-second-order kinetics and Freundlich isotherm models. The adsorption reactions are endothermic and occur spontaneously. SFA demonstrates varying adsorption mechanisms for two different types of pollutants. In the case of Pb2+, the primary mechanisms include ion exchange, electrostatic interaction, cation-π interaction, and complexation, while TC primarily engages in hydrogen bonding, π-π interaction, and complexation. The interaction between Pb2+ and TC has been shown to improve adsorption efficiency at low concentrations. Additionally, adsorption-desorption experiments confirm the reliable cycling performance of modified fly ash, highlighting its potential as a cost-effective and efficient adsorbent for antibiotics and heavy metals.

Sustainable efficient utilization of magnetic porous biochar for adsorption of orange G and tetracycline: Inherent roles of adsorption and mechanisms

Iron-doped biochar has been widely used as an adsorbent to remove contaminants due to the high adsorption performance, but it still suffers from complicated preparation methods, unstable iron loading, unsatisfactory specific surface area, and uneven distribution of active sites. Here, a novel magnetic porous biochar (FeCS800) with nanostructure on surface was synthesized by one-pot pyrolysis method of corn straw with K2FeO4, and used in orange G (OG) and tetracycline (TC) adsorption. FeCS800 exhibited outstanding adsorption capacities for OG and TC after K2FeO4 activation and the adsorption data were fitted satisfactorily to Langmuir isotherm and Pseudo-second-order kinetic model. The maximum adsorption capacities of FeCS800 for OG and TC were around 303.03 mg/g and 322.58 mg/g, respectively, at 25 °C and pH 7.0, which were 16.27 and 24.61 times higher than that before modification. Thermodynamic studies showed that the adsorption of OG/TC by FeCS800 were thermodynamically favorable and highly spontaneous. And the adsorption capacity of OG and TC by FeCS800 remained 77% and 81% after 5 cycles, respectively, indicating that FeCS800 had good stability. The outstanding adsorption properties and remarkable reusability of FeCS800 show its great potential to be an economic and environmental adsorbent in contaminants removal.

Recent advances in catalyst design, performance, and challenges of metal-heteroatom-co-doped biochar as peroxymonosulfate activator for environmental remediation

The escalation of global water pollution due to emerging pollutants has gained significant attention. To address this issue, catalytic peroxymonosulfate (PMS) activation technology has emerged as a promising treatment approach for effectively decontaminating a wide range of pollutants. Recently, modified biochar has become an increasingly attractive as PMS activator. Metal-heteroatom-co-doped biochar (MH-BC) has emerged as a promising catalyst that can provide enhanced performance over heteroatom-doped and metal-doped biochar due to the synergism between metal and heteroatom in promoting PMS activation. Therefore, this review aims to discuss the fabrication pathways (i.e., internal vs external doping and pre-vs post-modification) and key parameters (i.e., source of precursors, synthesis methods, and synthesis conditions) affecting the performance of MH-BC as PMS activator. Subsequently, an overview of all the possible PMS activation pathways by MH-BC is provided. Subsequently, Also, the detection, identification, and quantification of several reactive species (such as, •OH, SO4•-, O2•-, 1O2, and high valent oxo species) generated in the catalytic PMS system by MH-BC are also evaluated. Lastly, the underlying challenges associated with poor stability, the lack of understanding regarding the interaction between metal and heteroatom during PMS activation and quantification of radicals in multi-ROS system are also deliberated.

Bacterial cellulose microfilament biochar-architectured chitosan/polyethyleneimine beads for enhanced tetracycline and metronidazole adsorption

This study investigates the potential applications of incorporating 2D bacterial cellulose microfibers (BCM) biochar into chitosan/polyethyleneimine beads as a semi-natural sorbent for the efficient removal of tetracycline (TET) and metronidazole (MET) antibiotics. Batch adsorption experiments and characterization techniques evaluate removal performance and synthesized adsorbent properties. The adsorbent eliminated 99.13 % and 90 % of TET and MET at a 10 mg.L-1 concentration with optimal pH values of 8 and 6, respectively, for 90 min. Under optimum conditions and a 400 mg.L-1 concentration, MET and TET have possessed the maximum adsorption capacities of 691.325 and 960.778 mg.g-1, respectively. According to the isothermal analysis, the adsorption of TET fundamentally follows the Temkin (R2 = 0.997), Redlich-Peterson (R2 = 0.996), and Langmuir (R2 = 0.996) models. In contrast, the MET adsorption can be described by the Langmuir (R2 = 0.997), and Toth (R2 = 0.991) models. The pseudo-second-order (R2 = 0.998, 0.992) and Avrami (R2 = 0.999, 0.999) kinetic models were well-fitted with the kinetic results for MET and TET respectively. Diffusion models recommend that pore, liquid-film, and intraparticle diffusion govern the rate of the adsorption process. The developed semi-natural sorbent demonstrated exceptional adsorption capacity over eleven cycles due to its porous bead structure, making it a potential candidate for wastewater remediation.

Unlocking the potential of Chinese herbal medicine residue-derived biochar as an efficient adsorbent for high-performance tetracycline removal

This study employed hydrothermal carbonization (HTC) in conjunction with ZnCl2 activation and pyrolysis to produce biochar from one traditional Chinese medicine astragali radix (AR) residue. The resultant biochar was evaluated as a sustainable adsorbent for tetracycline (TC) elimination from water. The adsorption performance of TC on two micropore-rich AR biochars, AR@ZnCl2 (1370 m2 g-1) and HAR@ZnCl2 (1896 m2 g-1), was comprehensively evaluated using adsorption isotherms, kinetics, and thermodynamics. By virtue of pore diffusion, π-π interaction, electrostatic attraction, and hydrogen bonding, the prepared AR biochar showed exceptional adsorption properties for TC. Notably, the maximum adsorption capacity (930.3 mg g-1) of TC on HAR@ZnCl2 can be achieved when the adsorbent dosage is 0.5 g L-1 and C0 is 500 mg L-1 at 323 K. The TC adsorption on HAR@ZnCl2 took place spontaneously. Furthermore, the impact of competitive ions behavior is insignificant when coexisting ion concentrations fall within the 10-100 mg L-1 range. Additionally, the produced biochar illustrated good economic benefits, with a payback of 701 $ t-1. More importantly, even after ten cycles, HAR@ZnCl2 still presented great TC removal efficiency (above 77%), suggesting a good application prosperity. In summary, the effectiveness and sustainability of AR biochar, a biowaste-derived product, were demonstrated in its ability to remove antibiotics from water, showing great potential in wastewater treatment application.

Effect of citric acid modification on the properties of hydrochar and pyrochar and their adsorption performance toward methylene blue: crucial roles of minerals and oxygen functional groups

Modification is widely used to enhance the adsorption performance of pristine hydrochar (HBC) and pyrochar (BC). However, comparisons between modified HBC and BC toward pollutant removal have rarely been reported. In this study, pristine HBC and BC derived from rice straw were first produced, and then citric acid (CA) was used as a modifier to synthesize CA-modified HBC (CAHBC) and CA-modified BC (CABC). Furthermore, the adsorption performance of biochars toward methylene blue (MB) was investigated. The results showed that BC exhibits relatively rough surfaces and contains more minerals (ash), whereas HBC has plentiful O-containing functional groups and fewer minerals. CA modification partially removed minerals from the surface of BC, which weakened the ion exchange, surface complexation, and n-π interaction, resulting in a lower adsorption ability toward MB. By contrast, CA produced more O-containing functional groups on the surface of HBC, which strengthened the hydrogen bonding and electrostatic interaction, thus increasing the adsorption capacity toward MB. The two-compartment model showed a good fit to the adsorption process of MB on CAHBC, and the isotherm data for MB adsorption by HBC and CAHBC are suitable for the Freundlich model. The highest adsorption amount of MB using CAHBC was 80.13 mg·g-1, which was 27.66% higher than that for CABC. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the carboxyl groups in the surface functional groups of CAHBC played a crucial role in the MB adsorption process. In addition, CAHBC showed a good performance for a wide range of pH values (4.0-10.0) and under the interference of coexisting ions, and also presented a recycling ability. Furthermore, the adsorption of MB on CAHBC biochar was a spontaneous, exothermic, degree-of-randomness-increasing process. Consequently, CA modification of HBC is a promising strategy and could be used for MB removal from aquatic environments.

Imidacloprid removal by modified graphitic biochar with Fe/Zn bimetallic oxides

Coping with the critical challenge of imidacloprid (IMI) contamination in sewage treatment and farmland drainage purification, this study presents a pioneering development of an advanced modified graphitic white melon seed shells biochar (Fe/Zn@WBC). The Fe/Zn@WBC demonstrates a substantial enhancement in adsorption efficiency for IMI, achieving a remarkable removal rate of 87.69% within 30 min and a significantly higher initial adsorption rate parameter h = 4.176 mg g-1·min-1. This significant improvement outperforms WBC (12.22%, h = 0.115 mg g-1·min-1) and highlights the influence of optimized adsorption conditions at 900 °C and the graphitization degree resulting from Fe/Zn bimetallic oxide modification. Characterization analysis and batch sorption experiments including kinetics, isotherms, thermodynamics and pH factors illustrate that chemical adsorption is the main type of adsorption mechanism responsible for this superior ability to remove IMI through pore filling, hydrogen bonding, hydrophobic interaction, electrostatics interaction, π-π interactions as well as complexation processes. Furthermore, we demonstrate exceptional stability of Fe/Zn@WBC across a broad pH range (pH = 3-11), co-existing ions presence along with humic acid under various real water conditions while maintaining high removal efficiency. This study presents an advanced biochar adsorbent, Fe/Zn@WBC, with efficient adsorption capacity and easy preparation. Through three regeneration cycles via pyrolysis method, it demonstrates excellent pyrolysis regeneration capabilities with an average removal efficiency of 92.02%. The magnetic properties enable rapid separation facilitated by magnetic analysis. By elucidating the efficacy and mechanistic foundations of Fe/Zn@WBC, this research significantly contributes to the field of environmental remediation by providing a scalable solution for IMI removal and enhancing scientific understanding of bimetallic oxides-hydrophilic organic pollutant interactions.

Arsenic and antimony desorption in water treatment processes: Scaling up challenges with emerging adsorbents

The metalloids arsenic (As) and antimony (Sb) belong to the pnictogen group of the periodic table; they share many characteristics, including their toxic and carcinogenic properties; and rank as high-priority pollutants in the United States and the European Union. Adsorption is one of the most effective techniques for removing both elements and desorption, for further reuse, is a part of the process to make adsorption more sustainable and feasible. This review presents the current state of knowledge on arsenic and antimony desorption from exhausted adsorbents previously used in water treatment, that has been reported in the literature. The application of different types of eluents to desorb As and Sb and their desorption performance are described. The regeneration of saturated adsorbents and adsorbate recovery techniques are outlined, including the fate of spent media and possible alternatives for waste disposal of exhausted materials. Future research directions are discussed, as well as current issues including the lack of environmental impact analysis of emerging adsorbents.

Both nanoplastic and iron mineral types determine their heteroaggregation: Aggregation kinetics and interface process

Nanoplastics (NPs) inevitably interact with iron minerals (IMs) after being released into aquatic environments, changing their transport and fate. In this study, batch heteroaggregation kinetics of four types of NPs, i.e., polymethyl methacrylate (PMMA), polystyrene (PS-Bare), amino-polystyrene (PS-NH2), and carboxyl-polystyrene (PS-COOH), with two different IMs (hematite and magnetite) were conducted. We found that the heteroaggregation of NPs and IMs and the associated interfacial interaction mechanisms are both NPs-dependent and IMs-dependent. Specifically, the NPs had stronger heteroaggregation with hematite than magnetite; the heteroaggregation order of two IMs with NPs was PMMA > PS-NH2 > PS-Bare > PS-COOH. Moreover, hydrogen bond, complexation, hydrophobic, cation-π, and electrostatic interaction were involved in the interfacial reaction between NPs and hematite, and electrons were transferred from the NPs to the hematite, causing the reduction of Fe3+ into Fe2+. Furthermore, we first revealed that both pre-homoaggregation of NPs and IMs could affect their subsequent heteroaggregation, and the homoaggregates of IMs could be interrupted by PMMA or PS-COOH NPs introduction. Therefore, the emerging NPs pollution is likely to generate an ecological effect in terms of elemental cycles such as iron cycle. This work provides new insights into assessing the environmental transfer and ecological effects of NPs in aquatic environments.

KHCO3-activated high surface area biochar derived from brown algae: A case study for efficient adsorption of Cr(VI) in aqueous solution

The current study aimed to assess the effectiveness of biochar formed from algae in the removal of Cr(VI) through the process of impregnating brown algae Sargassum hemiphyllum with KHCO3. The synthesis of KHCO3-activated biochar (KBAB-3), demonstrating remarkable adsorption capabilities for Cr(VI), was accomplished utilizing a mixture of brown algae and KHCO3 in a mass ratio of 1:3, followed by calcination at a temperature of 700 °C. Based on the empirical evidence, it can be observed that KBAB-3 shown a significant ability to adsorb Cr(VI) within a range of 60-160 mg g-1 across different environmental conditions. In addition, the KBAB-3 material demonstrated the advantageous characteristic of easy separation, allowing for the continued maintenance of a high efficiency in removing Cr(VI) even after undergoing numerous cycles of reuse. In conclusion, the application of KBAB-3, a novel adsorbent, exhibits considerable prospects for effective removal of Cr(VI) from diverse water sources in the near future.

Norfloxacin adsorption by urban green waste biochar: characterization, kinetics, and mechanisms

Biochar, as a potential adsorbent, has been widely employed to remove pollutants from sewage. In this study, a lignin-based biochar (CB-800) was prepared by a simple high-temperature pyrolysis using urban green waste (Cinnamomum camphora leaves) as a feedstock to remove norfloxacin (NOR) from water. Batch adsorption test results indicated that CB-800 had a strong removal capacity for NOR at a wide range of pH values. The maximum adsorption achieved in the study was 50.90 ± 0.64 mg/g at 298 K. The pseudo-first and second-order kinetic models and the Dubinin-Radushkevich isotherm fitted the experimental data well, indicating that NOR adsorption by CB-800 was a complex process involving both physi-sorption and chemi-sorption. The physical properties of CB-800 were characterized by SEM and BET. The mesoporous structures were formed hierarchically on the surface of CB-800 (with an average pore size of 2.760 nm), and the spatial structure of NOR molecules was more easily adsorbed by mesoporous structures. Combined with Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis, it was showed that the main NOR adsorption mechanisms by CB-800 included ion exchange, π-electron coordination, hydrogen bonding, and electrostatic adsorption. Meanwhile, the reduction of C = O and pyridine nitrogen, and the presence of C-F2, also indicated the occurrence of substitution, addition, and redox. This study not only determined the reaction mechanism between biochar and NOR, but also provides guidance to waste managers for the removal of NOR from water by biochar. It is envisaged that the results will broaden the utilization of urban green waste.

Denitrification driven by additional ferrous (Fe2+) and manganous (Mn2+) and removal mechanism of tetracycline and cadmium (Cd2+) by biogenic Fe-Mn oxides

Zoogloea sp. MFQ7 achieved excellent denitrification of 91.71% at ferrous to manganous ratio (Fe/Mn) of 3:7, pH of 6.5, nitrate concentration of 25 mg L-1 and carbon to nitrogen ratio of 1.5. As the Fe/Mn ratio increasd, the efficiency of nitrate removal gradually decreased, indicating that strain MFQ7 had a higher affinity for Mn2+ than Fe2+. In situ generated biogenic Fe-Mn oxides (BFMO) contained many iron-manganese oxides (MnO2, Mn3O4, FeO(OH), Fe2O3, and Fe3O4) as well as reactive functional groups, which play an significant part in tetracycline (TC) and cadmium (Cd2+) adsorption. The adsorption of TC and Cd2+ by BFMO can better fit the pseudo-second-order and Langmuir models. In addition, multiple characterization results of before and after adsorption indicated that the removal mechanism of BFMO on TC and Cd2+ was probably surface complexation adsorption and redox reactions.

3D electro-Fenton augmented with iron-biochar particle electrodes derived from waste iron bottle caps and sugarcane bagasse for the remediation of sodium dodecyl sulphate

The present work demonstrates a novel strategy of synthesizing iron-biochar (Fe@BCSB) composite made with the waste iron bottle cap and sugar cane bagasse for implementation in the three-dimensional electro-Fenton (3DEF) process. The catalytic ability of the Fe@BCSB composite was explored to remediate the sodium dodecyl sulphate (SDS) surfactant from wastewater at neutral pH. At the optimum operating condition of Fe@BCSB dose of 1.0 g L-1, current density of 4.66 mA cm-2, and Na2SO4 dose of 50 mM, nearly 92.7 ± 3.1% of 20 mg L-1 of SDS abatement was attained during 120 min of electrolysis time. Moreover, the Fe@BCSB showed significant recyclability up to six cycles. Besides, other organics were successfully treated with more than 85% abatement efficiency in the proposed Fe@BCSB-supported 3DEF process. The total operating cost obtained during SDS treatment was around 0.31 US$ m-3 of wastewater. The phytotoxicity test revealed the positive impact of the 3DEF-treated effluent on the germination of the Vigna radiata. The electron paramagnetic resonance conveyed •OH as the prevailing reactive species for the oxidation of SDS in the 3DEF process. Further, about 81.3 ± 3.8% of SDS and 53.7 ± 4.1% of mineralization efficacy were acquired from the real institutional sewage.

Efficient Adsorbent Derived from Phytolith-Rich Ore for Removal of Tetracycline in Wastewater

In recent decades, the tetracycline (TC) concentration in aquatic ecosystems has gradually increased, leading to water pollution problems. Various mineral adsorbents for the removal of tetracyclines have garnered considerable attention. However, efficient adsorbents suitable for use in a wide pH range environment have rarely been reported. Herein, a phytolith-rich adsorbent (PRADS) was prepared by a simple one-step alkali-activated pyrolysis treatment using phytolith as a raw material for effectively removing TC. PRADS, benefiting from its porous structure, which consists of acid- and alkali-resistant, fast-adsorbing macroporous silica and mesoporous carbon, is highly desirable for efficient TC removal from wastewater. The results indicate that PRADS exhibited excellent adsorption performance and stability for TC over a wide pH range of 2.0-12.0 under the coexistence of competing ions, which could be attributed to the fact that PRADS has a porous structure and contains abundant oxygen-containing functional groups and a large number of bonding sites. The adsorption mechanisms of PRADS for TC were mainly attributed to pore filling, hydrogen bonding, π-π electron-donor-acceptor, and electrostatic interactions. This work could offer a novel preparation strategy for the effective adsorption of pollutants by new functionalized phytolith adsorbents.

One-step synthesis of iron and nitrogen co-doped porous biochar for efficient removal of tetracycline from water: Adsorption performance and fixed-bed column

Here, Fe/N co-doped porous biochars (FeNKBCs) were obtained by grinding corncob, CH3COOK, FeCl3·6H2O, and C3H6N6 via one-step synthesis and were applied to remove antibiotics from wastewater. Notably, CH3COOK had an excellent porous activation ability. The developed nanotubular structure of Fe1N2KBC had a high pore volume (Vtotal) (1.2131 cm3/g) and specific surface areas (SSA) (2083.54 m2/g), which showed outstanding sorption abilities for TC (764.35 mg/g), OTC (560.82 mg/g), SMX (291.45 mg/g), and SMT (354.65 mg/g). The adsorption process of TC was controlled by chemisorption. Moreover, Fe1N2KBC has an excellent dynamic adsorption performance (620.14 mg/g) in a fixed-bed column. The properties of SSA, Vtotal, and the content of graphite N and Fe-N were positively correlated with TC adsorption capacity. The high performance of TC removal was related to π-π stacking, pore-filling, hydrogen bond, and electrostatic interaction. Fe1N2KBC possessed stable sorption amounts in pH 2-12 and actual water, and well reuse performance. The results of this work present an effective preparation method of Fe/N porous biochar for TC-contaminated water remediation.

Effects of Fe-N co-modified biochar on methanogenesis performance, microbial community, and metabolic pathway during anaerobic co-digestion of alternanthera philoxeroides and cow manure

The performance of anaerobic digestion (AD) is susceptible to disturbances in feedstock degradation, intermediates accumulation, and methanogenic archaea activity. To improve the methanogenesis performance of the AD system, Fe-N co-modified biochar was prepared under different pyrolysis temperatures (300,500, and 700 °C). Meanwhile, pristine and Fe-modified biochar were also derived from alternanthera philoxeroides (AP). The aim was to compare the effects of Fe-N co-modification, Fe modification, and pristine biochar on the methanogenic performance and explicit the responding mechanism of the microbial community in anaerobic co-digestion (coAD) of AP and cow manure (CM). The highest cumulative methane production was obtained with the addition of Fe-N-BC500 (260.38 mL/gVS), which was 42.37 % higher than the control, while the acetic acid, propionic acid, and butyric acid concentration of Fe-N-BC were increased by 147.58 %, 44.25 %, and 194.06 % compared with the control, respectively. The co-modified biochar enhanced the abundance of Chloroflexi and Methanosarcina in the AD system. Metabolic pathway analysis revealed that the increased methane production was related to the formation and metabolism of volatile fatty acids and that Fe-N-BC500 enhanced the biosynthesis of coenzyme A and the cell activity of microorganisms, accelerating the degradation of propionic acid and enhancing the hydrogenotrophic methanogenesis pathway. Overall, Fe-N co-modified biochar was proved to be an effective promoter for accelerated methane production during AD.

Bimetal doped Cu-Fe-ZIF-8/g-C3N4 nanocomposites for the adsorption of tetracycline hydrochloride from water

Bimetal doped Cu-Fe-zeolitic imidazole framework-8 (ZIF-8)/graphitic carbon nitride (GCN) (Cu-Fe-ZIF-8/GCN) nanocomposites were prepared via one-pot and ion-exchange methods. The main influencing factors, such as adsorbent concentration, TC concentration, initial pH, and coexisting ions, were evaluated in detail. Due to the suitable pore structures and the presence of multiple interactions on the surface, the nanocomposite showed a high adsorption capacity up to 932 mg g-1 for tetracycline hydrochloride (TC), outperforming ZIF-8 by 4.8 times. The adsorption kinetics and adsorption isotherm were depicted in good detail using pseudo-second-order kinetic and Langmuir models, respectively. Thermodynamic calculation revealed that the adsorption of the nanocomposite under experimental conditions was a spontaneous heat absorption process, and was primarily driven by chemisorption. After four cycles of use, the nanocomposite retained 87.2% of its initial adsorption capacity, confirming its high reusability and broad application prospects in removing tetracycline-type pollutants from wastewater.

Synthesis and application of wetland plant-based functional materials for aqueous antibiotics removal

Wetlands have been widely used in wastewater treatment and restoration of water bodies due to their ecological characteristics and functions. However, large amounts of plant residues are produced in wetlands every year and their treatment are facing large challenge. Synthesis of wetland plant-based functional materials (WPBFMs) has emerged as promising method for treating and recycling wetland plant residues. These functional materials have been demonstrated to effectively remove aqueous pollutants, such as antibiotics and dyes in wastewater. This article provides a comprehensive review on synthesis and application of WPBFMs for aqueous antibiotics removal and gives guidance for future research in treatment and recycling of wetland plant residues. It is shown that emergent plant residues are the mostly used raw materials for WPBFMs synthesis. The main products are biochar and its composites, cellulose and its modified materials, which are synthesized by slow pyrolysis and alkali treatment-bleaching treatment method, respectively. The removal pathways and mechanisms for aqueous antibiotics by WPBFMs are also discussed. Finally, the challenges and perspectives are discussed for synthesis and application of WPBFMs for antibiotics removal.

Phosphoric acid activation of cow dung biochar for adsorbing enrofloxacin in water: Icing on the cake

In this study, we used different concentrations of H3PO4 to activate pristine biochar (BC) derived from cow dung (BC and BC modified with phosphoric acid at concentrations of 10% (10P-BC), 30% (30P-BC), and 50% (50P-BC)) in order to obtain cheap, high-performance adsorbents. Brunauer-Emmett-Teller analysis, scanning electron microscopy, X-ray diffraction, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, organic element composition determination, and other analyses showed that activation with H3PO4 increased the porosity and hydrophilicity compared with the original BC, thereby enhancing the adsorption properties. The Langmuir isotherm model obtained the best fit and the maximum capacities for adsorbing enrofloxacin by BCs were 12.66 mg/g for BC, 51.90 mg/g for 10P-BC, 63.61 mg/g for 30P-BC, and 26.79 mg/g for 50P-BC. The main mechanisms responsible for antibiotic loading on BC were hydrogen bonding, π-π electron donor-acceptor interactions, pore filling, and electrostatic interactions. Calculations of fixed carbon retention before and after pyrolysis, and adsorption showed that activated BC had a good carbon fixation capacity and it was more capable of adsorbing enrofloxacin compared with the original BC, thereby providing a new method for removing organic pollutants from the environment and reducing carbon emissions. The cost efficiency was analyzed using the improved fuzzy comprehensive evaluation model based on the entropy method. Removal efficiency and utilization efficiency indicators were calculated for the different phosphoric acid activated BCs. The pollutant removal efficiencies were better for 10P-BC and 30P-BC, and the optimal removal efficiency was determined for 30P-BC. Given the current global climate change situation, using 10P-BC and 30P-BC could also help to meet China's carbon neutrality goals by reducing emissions of pollutants containing carbon.

Enhanced Adsorptive Removal of Tetracycline by Phosphomolybdic Acid-Modified Low-Temperature Sludge Biochar

Increasing the adsorption capacity and reducing the energy consumption of sludge biochar during preparation is important. In this study, a new modification method was developed to prepare phosphomolybdic acid-modified sludge biochar through the low-temperature pyrolysis of sewage sludge using phosphomolybdic acid as a modifier. Tetracycline was used to assess the adsorption performance of sludge biochar, and phosphomolybdic acid-modified sludge biochar was prepared at different temperatures. The results showed that the adsorption capacity of sludge biochar improved from 84.49 to 120.86 mg/g through modification with phosphomolybdic acid at 200 °C. The maximum adsorption capacities of phosphomolybdic acid-modified sludge biochar (200 °C pyrolysis temperature) at 298, 308, and 318 K were 283.87, 421.39, and 545.48 mg/g, respectively. Both liquid film and intraparticle diffusion were the main rate-limiting steps of tetracycline adsorption by phosphomolybdic acid-modified sludge biochar. Furthermore, the adsorption of tetracycline by phosphomolybdic acid-modified sludge biochar was mainly attributed to π-π interactions, electrostatic interactions, hydrogen bonding, and pore filling.

Recent progress in TiO2-biochar-based photocatalysts for water contaminants treatment: strategies to improve photocatalytic performance

Toxic organic pollutants in wastewater have seriously damaged human health and ecosystems. Photocatalytic degradation is a potential and efficient tactic for wastewater treatment. Among the entire carbon family, biochar has been developed for the adsorption of pollutants due to its large specific surface area, porous skeleton structure, and abundant surface functional groups. Hence, combining adsorption and photocatalytic decomposition, TiO2-biochar photocatalysts have received considerable attention and have been extensively studied. Owing to biochar's adsorption, more active sites and strong interactions between contaminants and photocatalysts can be achieved. The synergistic effect of biochar and TiO2 nanomaterials substantially improves the photocatalytic capacity for pollutant degradation. TiO2-biochar composites have numerous attractive properties and advantages, culminating in infinite applications. This review discusses the characteristics and preparation techniques of biochar, presents in situ and ex situ synthesis approaches of TiO2-biochar nanocomposites, explains the benefits of TiO2-biochar-based compounds for photocatalytic degradation, and emphasizes the strategies for enhancing the photocatalytic efficiency of TiO2-biochar-based photocatalysts. Finally, the main difficulties and future advancements of TiO2-biochar-based photocatalysis are highlighted. The review gives an exhaustive overview of recent progress in TiO2-biochar-based photocatalysts for organic contaminants removal and is expected to encourage the development of robust TiO2-biochar-based photocatalysts for sewage remediation and other environmentally friendly uses.

Significant Differences in the Effects of Nitrogen Doping on Pristine Biochar and Graphene-like Biochar for the Adsorption of Tetracycline

To improve the adsorption efficiency of pollutants by biochar, preparing graphene-like biochar (GBC) or nitrogen-doped biochar are two commonly used methods. However, the difference in the nitrogen doping (N-doping) effects upon the adsorption of pollutants by pristine biochar (PBC) and GBC, as well as the underlying mechanisms, are still unclear. Take the tetracycline (TC) as an example, the present study analyzed the characteristics of the adsorption of TCs on biochars (PBC, GBC, N-PBC, N-GBC), and significant differences in the effects of N-doping on the adsorption of TCs by PBC and GBC were consistently observed at different solution properties. Specifically, N-doping had varied effects on the adsorption performance of PBC, whereas it uniformly improved the adsorption performance of GBC. To interpret the phenomenon, the N-doping upon the adsorption was revealed by the QSAR model, which indicated that the pore filling (VM) and the interactions between TCs with biochars (Ead-v) were found to be the most important two factors. Furthermore, the density functional theory (DFT) results demonstrated that N-doping slightly affects biochar's chemical reactivity. The van der Waals (vdWs) and electrostatic interactions are the main forces for TCs-biochars interactions. Moreover, N-doping mostly strengthened the electrostatic interactions of TCs-biochars, but the vdWs interactions of most samples remained largely unaffected. Overall, the revealed mechanism of N-doping on TCs adsorption by biochars will enhance our knowledge of antibiotic pollution remediation.

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.

Improvement of the specific surface area of biochar by calcium-precipitated nanoparticles synthesized by microbial induction as a template skeleton: Removal mechanism of tetracycline in water

The template method is an effective means to improve the specific surface area and porosity of biochar, but the synthesis of template agents and the way they are integrated with biomass materials still need further development. Therefore, the free Pseudomonas sp. Y1 was used to synthesize calcium-precipitated nanoparticles (CPN) on sludge as a fused template skeleton to enlarge the surface area of sludge biochar facilitating the adsorption of tetracycline (TC) in this work. The modified biochar (FBC) showed excellent specific surface area (448.55 m2 g-1) and porosity (0.0053 cm³ g-1), stable morphological structure, abundant active functional groups, and appreciable adsorption capacity (65.43 mg g-1) based on several characterization and adsorption experiments. Moreover, the adsorption model postulated that the removal of TC is mainly a chemisorption-based heat-trapping, disordered multilayer interaction. In detail, this process involved the joint contribution from electrostatic interactions, ligand exchange, hydrogen bonding, π-π bonding, complexation, and pore filling. Meanwhile, the adaptability and stability of FBC were examined by pH and coexisting substances. This template skeleton induced by microorganisms can provide new insight into the modification of biochar with the template method.

Biochar-Associated Free Radicals Reduce Soil Bacterial Diversity: New Insight into Ecoenzymatic Stoichiometry

The toxicity of environmentally persistent free radicals (EPFRs), often generated during biochar production, on soil bacteria is still not truly reflected when considering the conditions in real soil. Herein, the influence of free radicals within biochar on soil bacteria was investigated from the perspectives of enzyme activity, community structure, and ecoenzymatic stoichiometry. Biochar addition enhanced the contents of EPFRs and derived hydroxyl radicals (•OH) in the soil, while it reduced bacterial alpha diversity by 5.06-35.44%. The results of redundancy analysis and inhibition experiments collectively demonstrated the key role of EPFRs and •OH in reducing the bacterial alpha diversity. Specifically, EPFRs and •OH increased the stoichiometric imbalance by promoting the release of dissolved organic carbon and ammonium N, thus aggravating the P limitation in soil. This was further confirmed by increased alkaline phosphatase activity from 702 to 874 nmol g-1 h-1. The P limitation induced by EPFRs and •OH decreased the bacterial alpha diversity, as evidenced by the negative correlation between P limitation and bacterial alpha diversity (r2 = -0.931 to -0.979, P < 0.01) and the structural equation model. The obtained results demonstrate a ubiquitous but previously overlooked mechanism for bacterial toxicity of biochar-associated free radicals, providing scientific guidance for safe utilization of biochar.

Recent advances in the synthesis and application of magnetic biochar for wastewater treatment

Magnetic biochar (MBC) is a novel bio-carbon material with both desired properties as adsorbent and magnetic characteristics. This review provides an up-to-date summary and discussion on the latest development of MBC, which covers the progress on its synthesis, application, and techno-economic analysis. The review indicates that the direct hydrothermal synthesis has been catching more research attention to produce MBC due to its mild reaction conditions. Instead of the Fe-loaded MBC, there is a trend of using Mn for the magnetization. For the MBC application, how to improve its adsorption performance for water decontamination, ideally to match that of the biochar (BC) or activated carbon, is important. In addition, more studies on the environmental impacts of MBC and life-cycle assessment decoding the process optimization options are necessary. This review will provide valuable references for the development of MBC and MBC-based materials for wastewater treatment.

Efficient removal of cesium ions using Prussian blue loaded on magnetic porous biochar synthesized by one-step calcination

Prussian blue (PB) is widely used for the selective removal of radioactive cesium ions (Cs+) from aqueous solutions. Due to its small size and easy dispersion in water, PB requires a carrier that is both inexpensive and easily separable. Magnetic porous biochar (MPBC) was formed by activating starch with FeCl3 through a one-step calcination method. MPBC can be used as a carrier for Prussian blue, which is easily separated from the solution. This composite material (PB/MPBC) has a rich pore structure and maintains effective surface area, which can facilitate the penetration of Cs+ into the adsorbent. Besides, PB/MPBC exhibits high selectivity and good adsorption capacity achieving a large removal capacity of 101.43 mg/g. Thus, this study provides a novel approach for preparing composites with efficient removal of Cs+.

Experimental and theoretic mechanism of successive adsorption of oppositely charged Cu(II) and Cr(VI) onto amine-rich cellulose adsorbent

A novel layer-by-layer adsorption was proposed and used for adsorption of Cu(II) and Cr(VI) on the pre-bleached sawdust cellulose coated with polyethylenimine (PSC-PEI). It was found that PSC-PEI loaded with Cu(II) cations was favorable for Cr(VI) anions adsorption. The maximum adsorption capacities estimated by Langmuir model for Cu(II) and Cr(VI) were 80.0 and 93.5 mg/g, respectively. The kinetic regression results, as fitted by the pseudo-second order model, revealed that the rate constant (k2) for Cr(VI) at 0.07 g/mg/min is significantly greater than that observed for Cu(II) at 0.02 g/mg/min, indicating that PSC-PEI exhibited a stronger affinity towards Cr(VI). The first-layer adsorption mechanism for Cu(II) involved the formation of copper-amine complex. Zeta potential and XPS results revealed that the second-layer adsorption of Cr(VI) mainly involved electrostatic attraction and redox reaction. The simulated results for dynamic column test showed good agreement between the theoretical values and the experimental values. The mass transfer mechanism indicated that Cu(II) adsorption was dependent on external mass transfer process, while the internal mass transfer is the rate-determining step for Cr(VI) adsorption. The saturated adsorbent was regenerated by washing with 5% NaOH and 5% H2SO4 solutions and the adsorption ability of more than 70% was sustained after three cycles of regeneration. This study demonstrated that the oppositely charged Cu(II) cations and Cr(VI) anions could be effectively removed by amine-rich cellulose adsorbent from wastewater through layer-by-layer adsorption.

Biochar facilitates methanogens evolution by enhancing extracellular electron transfer to boost anaerobic digestion of swine manure under ammonia stress

This study explored the mechanisms by which biochar mitigates ammonia inhibition in anaerobic digestion (AD) of swine manure. Findings show 2-8 g/L exogenous ammonia dosages gradually inhibited AD, leading to decreases in the efficiencies of hydrolysis, acidogenesis and methanogenesis by 3.4-70.8%, 6.0-82.0%, and 4.9-93.8%, respectively. However, biochar addition mitigated this inhibition and facilitated methane production. Biochar enhanced microbial activities related to electron transport and extracellular electron transfer. Moreover, biochar primarily enriched Methanosarcina, which, consequently, upregulated the genes encoding formylmethanofuran dehydrogenase and methenyltetrahydromethanopterin cyclohydrolase for the CO2-reducing methanogenesis pathway by 26.9-40.8%. It is believed that biochar mediated direct interspecies electron transfer between syntrophic partners, thereby enhancing methane production under ammonia stress. Interestingly, biochar removal did not significantly impact the AD performance of the acclimated microbial community. This indicated the pivotal role of biochar in triggering methanogen evolution to mitigate ammonia stress rather than the indispensable function after the enrichment of ammonia-resistance methanogen.

Enhanced adsorption of roxarsone on iron-nitrogen co-doped biochar from peanut shell: Synthesis, performance and mechanism

Efficient removal of organic arsenic (roxarsone, ROX) from wastewater is highly demanded on the purpose of human health and environmental protection. This work aims to prepare Fe-N co-doped biochar (Fe-N-BC) via one-pot hydrothermal method using waste peanut shell, FeCl3·6H2O and urea, followed by pyrolysis. The effect of Fe-N co-doping on biochar's physicochemical properties, and adsorption performance for ROX were systematically investigated. At the pyrolysis temperature of 650 °C, Fe-N-BC-650 shows a significantly increased specific surface area of 358.53 m2/g with well-developed micro-mesoporous structure. Its adsorption capacity for ROX reaches as high as 197.32 mg/g at 25 °C, with > 90 % regeneration efficiency after multiple adsorption-desorption cycles. Correlation and spectral analysis revealed that the pore filling, π-π interactions, as well as hydrogen bonding play the dominant role in ROX adsorption. These results suggest that the Fe-N co-doped biochar shows great potential in the ROX removal from wastewater with high efficiency.

Enhanced adsorption of Congo red from urea/calcium chloride co-modified biochar: Performance, mechanisms and toxicity assessment

Adsorbents with excellent physicochemical properties and green synthetic routes are desired for efficient removal of Congo red (CR) wastewater. Hence, a novel approach was proposed within this work. Biochar NCBC obtained from Medulla Tetrapanacis was synthesized through co-modification with urea/calcium chloride. NCBC exhibited an enormous surface area (750.09 m2/g) and a micro-mesoporous composite structure. Higher nitrogen content was detected on the surface of NCBC (8.17%) compared to that of urea directly modified biochar (4.63%). Nitrogen observed on the surface of NCBC was presented as graphitic N, pyrrolic N, amine N as well as pyridinic N. Kinetic and isothermal investigations revealed the active sites on NCBC to be homogeneous and bind to CR mainly by chemisorption. Calculated maximum sorption of CR on NCBC was 2512.82 mg/g basing on Langmuir model. Moreover, the practicality of NCBC was further proved by the cultivation of Nelumbo nucifera Gaertn. and Penicillium.

Tetracycline Adsorption Performance and Mechanism Using Calcium Hydroxide-Modified Biochars

Tetracycline is frequently found in various environments and poses significant ecological risks. Calcium hydroxide-modified biochar has shown potential as a material for removing multiple classes of pollutants from wastewater streams. The tetracycline-adsorption performance and mechanism of alkali-modified biochars derived from nine wastes (corn straw, rice straw, swine manure, cypress powder, wheat straw, peanut shell, walnut shell powder, soybean straw, and corncobs) were investigated in the study. Among the four alkalis tested, calcium hydroxide exhibited the most effective modification effects at a pyrolysis temperature of 500 °C. Straw biomass was most suitable to be modified by calcium hydroxide, and calcium hydroxide-modified biochar showed the highest adsorption performance for tetracycline. The maximum adsorption capacities were 8.22 mg g-1 for pristine corn straw biochar and 93.46 mg g-1 for calcium hydroxide-modified corn straw biochar. The tetracycline adsorption mechanism by calcium hydroxide-modified corn straw biochar involved hydrogen bonding, oxygen-containing functional groups, Ca2+ metal complexation, and electrostatic attraction. Consequently, calcium hydroxide-modified corn straw biochar emerges as an environment-friendly, cost-effective, and efficient tetracycline adsorbent.

Intensive adsorption of tetracycline by cobalt oxide quantum dots-loaded mineral carbon

Spent bleaching earth (SBE), a waste by-product produced from the bleaching step of edible oil by montmorillonite clays (bleaching earth), causes serious public health and environmental problems. Accordingly, in this study, SBE was pyrolyzed to yield mineral carbon materials (SBE@C) and cobalt oxide (Co3O4) was loaded to improve the active site of those materials. Due to the carrier function of SBE@C, ultra-fine Co3O4 quantum dots (QDs) (2-6 nm) were homogeneously and robustly immobilized onto SBE@C. The obtained adsorbent exhibited high regeneration performance and an outstanding adsorption capacity (253.36 mg/g). It can be attributed to the surface complexation of cobalt with TC being the dominant process contributing to adsorption behavior. Further, Co3O4 QDs-SBE@C still maintained adequate sorption capacity at a broad range of pH values and in the presence of co-occurring ions. These results suggested the significant application potential of SBE and demonstrated the efficiency of using Co3O4 QDs-SBE@C for wastewater remediation.

Synthesis and applications of biomass-derived porous carbon materials in energy utilization and environmental remediation

Renewable biomass and its waste are considered among the most promising applications materials owing to the depletion of fossil fuel and concerns about environmental pollution. Notably, advanced porous carbon materials derived from carbon-rich biomass precursors exhibit controllable pore structures, large surface areas, natural microstructures, and abundant functional groups. In addition, these three-dimensional structures provide sufficient reaction sites and fascinating physicochemical properties that are conducive to heteroatom doping and functional modification. This review systematically summarizes the design methods and related mechanisms of biomass-derived porous carbon materials (BDPCMs), discusses how the synthesis conditions influence the structure and performance of the carbon material, and emphasizes the importance of its use in energy utilization and environmental remediation applications. Current BDPCMs challenges and future development strategies are finally discussed to provide systematic information for further synthesis and performance optimization, which are expected to lead to novel ideas for the future development of bio-based carbon materials.

Combined Application Effects of Arbuscular Mycorrhizal Fungi and Biochar on the Rhizosphere Fungal Community of Allium fistulosum L

Arbuscular mycorrhizal fungi (AMF) are widespread soil endophytic fungi, forming mutualistic relationships with the vast majority of land plants. Biochar (BC) has been reported to improve soil fertility and promote plant growth. However, limited studies are available concerning the combined effects of AMF and BC on soil community structure and plant growth. In this work, a pot experiment was designed to investigate the effects of AMF and BC on the rhizosphere microbial community of Allium fistulosum L. Using Illumina high-throughput sequencing, we showed that inoculation of AMF and BC had a significant impact on soil microbial community composition, diversity, and versatility. Increases were observed in both plant growth (the plant height by 8.6%, shoot fresh weight by 12.1%) and root morphological traits (average diameter by 20.5%). The phylogenetic tree also showed differences in the fungal community composition in A. fistulosum. In addition, Linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed that 16 biomarkers were detected in the control (CK) and AMF treatment, while only 3 were detected in the AMF + BC treatment. Molecular ecological network analysis showed that the AMF + BC treatment group had a more complex network of fungal communities, as evidenced by higher average connectivity. The functional composition spectrum showed significant differences in the functional distribution of soil microbial communities among different fungal genera. The structural equation model (SEM) confirmed that AMF could improve the microbial multifunctionality by regulating the rhizosphere fungal diversity and soil properties. Our findings provide new information on the effects of AMF and biochar on plants and soil microbial communities.

Simultaneous adsorption of ciprofloxacin and Cu2+ using Fe and N co-doped biochar: Competition and selective separation

The treatment of combined antibiotics and heavy metals pollution is a critical challenge. Herein, iron and nitrogen co-doped biochar (Fe/N-BC) was synthesized using rape straw as precursor, and applied for the adsorption of ciprofloxacin (CIP) and Cu2+ in single and binary systems. The qmax for CIP and Cu2+ were 46.45 mg g-1 and 30.77 mg g-1, respectively. Adsorption decreased in a binary matrix, indicating that there was a competitive effect between CIP and Cu2+, which might be due to CIP and Cu2+ sharing similar active adsorption sites on Fe/N-BC. Interestingly, CIP and Cu2+ co-adsorption was a pH-dependent process. Fe/N-BC has potential to highly selectively separate CIP/Cu2+ from mixed solutions through adjusting pH values. Furthermore, adsorption mechanisms were systematically investigated in this research. This research could help to provide a deeper understanding of the synchronously removing specific antibiotics and heavy metals by biochar adsorbents.

Removal of tetracycline in aqueous solution by iron-loaded biochar derived from polymeric ferric sulfate and bagasse

In this study, the tetracycline (TC) removal performance of iron-loaded biochar (BPFSB) derived from sugarcane bagasse and polymerized iron sulfate was investigated, and the mechanism of TC removal was also explored by study of isotherms, kinetics and thermodynamics and characterization of fresh and used BPFSB (XRD, FTIR, SEM and XPS). The results showed that under optimized conditions (initial pH 2; BPFSB dosage 0.8 g·L-1; TC initial concentration 100 mg·L-1; Contact time 24 h; temperature 298 K), the removal efficiency of TC was as high as 99.03%. The isothermal removal of TC followed well the Langmuir, Freundlich, and Temkin models, indicating that multilayer surface chemisorption dominated the TC removal. The maximum removal capacity of TC by BPFSB at different temperatures was 185.5 mg·g-1 (298 K), 192.7 mg·g-1 (308 K), and 230.9 mg·g-1 (318 K), respectively. The pseudo-second-kinetic model described the TC removal better, while its rate-controlling step was a combination of liquid film diffusion, intraparticle diffusion, and chemical reaction. Meanwhile, TC removal was also a spontaneous and endothermic process, during which the randomness and disorder between the solid-liquid interface was increased. According to the characterization of BPFSBs before and after TC removal, H-bonding and complexation were the major interactions for TC surface adsorption. Furthermore, BPFSB was efficiently regenerated by NaOH. In summary, BPFSB had the potential for practical application in TC removal.

Adsorption Characteristics of Heavy Metals Pb2+ and Zn2+ by Magnetic Biochar Obtained from Modified AMD Sludge

Acid mine drainage (AMD) sludge can be used to prepare adsorbent materials for the removal of heavy metals in water, which is an effective means for its resource utilization. Magnetic modified biochar (MMB), which can be recovered by magnetic separation, was prepared from sludge generated from the carbonate rock neutralization treatment of AMD and rice straw agricultural waste. Unmodified biochar (UMB) was obtained from rice straw and chemically modified and treated by ultraviolet radiation to produce MMB. The Pb²⁺ and Zn²⁺ adsorption capacities of UMB and MMB were investigated. Simultaneously, the materials were characterized by SEM, FTIR, BET, and ZETA. The results showed that the specific surface area (130.89 m²·g^-1) and pore volume (0.22 m²·g^-1) of MMB were significantly increased compared to those of UMB (9.10 m²·g^-1 and 0.05 m²·g^-1, respectively). FTIR images showed that MMB was successfully loaded with Fe₃O₄. The adsorption process of Pb²⁺ and Zn²⁺ onto MMB was consistent with the Langmuir adsorption isotherm and second-order kinetic models, with maximum adsorption capacities of 329.65 mg·g^-1 and 103.67 mg·g^-1, respectively. In a binary system of Pb²⁺ and Zn²⁺, MMB preferentially binds Pb²⁺. The adsorption efficiencies of MMB reached >80% for Pb²⁺ and Zn²⁺.

Remediation of cadmium contaminated soil using K2FeO4 modified vinasse biochar

The remediation of cadmium (Cd) contaminated soil is challenging for agricultural practices. In this study, a novel vinasse biochar modified by potassium ferrate (K₂FeO₄) was synthesized to immobilize Cd in agricultural soil. Three biochars [i.e., vinasse biochar (BC), KMnO₄ modified vinasse biochar (MnBC), and K₂FeO₄ modified vinasse biochar (FeBC)] were applied to compare their efficiencies of Cd immobilization. The results showed that the orders of pH, ash content, and functional groups in different biochar were the same following BC < MnBC < FeBC. Scanning electron microscope images showed that the FeBC has more micropores than MnBC and BC. X-ray diffraction identified manganese oxides and iron oxides within MnBC and FeBC, indicating that Mn and Fe were well loaded on the biochar. In the soil-based pot experiment, both MnBC and FeBC significantly reduced soil available Cd by 23-38% and 36-45% compared with the control, respectively (p < 0.05). In addition, the application of BC, MnBC, and FeBC significantly increased the yield, chlorophyll, and vitamin C of Chinese cabbage (p < 0.05), and decreased its Cd uptake compared with the control. Notably, shoot Cd significantly reduced when 2% FeBC was applied (p < 0.05). Overall, using K₂FeO₄ to modify vinasse biochar enriched the surface functional groups and minerals as well as reduced Cd availability in soil and its uptake by the plant. Our study showed that K₂FeO₄ modified vinasse biochar could be used as an ideal amendment for the remediation of Cd-contaminated soil.

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.

Fe-modified fly ash/cotton stalk biochar composites for efficient removal of phosphate in water: mechanisms and green-reuse potential

Excessive phosphate content input into natural water can lead to the waste of resource and eutrophication. Biochar is a kind of low-cost adsorbent. However, its adsorption capacity for phosphate is low. In order to solve this problem, Fe compound-modified fly ash/cotton stalk biochar composites (Fe-FBC) were prepared through co-pyrolyzed fly ash and cotton stalk at 800℃, followed by infiltration of FeSO₄ solution. The samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, and zeta potential. After modification, the hydrophilicity and polarity of Fe-FBC increased. In addition, the pore volume, specific surface area, and surface functional groups were significantly improved. The adsorption behavior of Fe-FBC for the removal of phosphate from water can be well fitted by the pseudo-second-order kinetic and Sips isotherm adsorption model, with a maximum adsorption capacity of 47.91 mg/g. Fe-FBC maintained a high adsorption capacity in the pH range of 3-10. The coexisting anions (NO₃^-, SO₄^2-, and Cl^-) had negligible effects on phosphate adsorption. The adsorption mechanisms of Fe-FBC include electrostatic attraction, ligand exchange, surface complexation, ion exchange, chemical precipitation, and hydrogen bonding. Moreover, the desorption process of phosphate was investigated, indicating that the phosphate-saturated Fe-FBC could use as slow-release phosphate fertilizer. This study proposed a potentially environmental protection and recycling economy approach, which consists of recycling resources and treating wastes with wastes.