ZnCl2 modified biochar derived from aerobic granular sludge for developed microporosity and enhanced adsorption to tetracycline

Polydopamine coating for enhanced electrostatic adsorption of methylene blue by multiwalled carbon nanotubes in alkaline environments

The removal of dye molecules in alkaline environments is an issue that should receive increased attention. In this study, the interaction mechanism between polydopamine-modified multiwalled carbon nanotubes (P-MWCNTs) and multiwalled carbon nanotubes (MWCNTs) with the cationic dye methylene blue (MB) in alkaline environments was explained in depth by adsorption, spectroscopy, and density functional theory (DFT). The mechanism of action and dominant forces between the adsorbent and adsorbate were analyzed graphically by introducing energy decomposition analysis (EDA) and an independent gradient model (IGM) into the DFT calculations. In addition, the force distribution was investigated through an isosurface. Moreover, batch adsorption studies were conducted to evaluate the performance of MWCNTs and P-MWCNTs for MB removal in alkaline environments. The maximum MB adsorption capacities of the MWCNTs and P-MWCNTs in solution were 113.3 mg‧g-1 and 230.4 mg‧g-1, respectively, at pH 9. The IGM and EDA showed that the better adsorption capacity of the P-MWCNTs originated from the enhancement of the electrostatic effect by the proton dissociation of polydopamine. Moreover, the adsorption of MB by MWCNTs and P-MWCNTs in alkaline environments was governed by dispersion and electrostatic effects, respectively. Through this study, it is hoped that progress will be made in the use of DFT to explore the mechanism of adsorbent-adsorbate interactions.

Desorption hysteresis of antibiotics on biochar produced at high temperature: The role of amine groups and amidation reaction

Knowledge of antibiotic desorption from high-temperature biochar is essential for assessing their environmental risks, and for the successful application of biochar to remove antibiotics. In previous studies, irreversible pore deformation, formation of charge-assisted hydrogen bonds or amide bonds were individually proposed to explain the desorption hysteresis of antibiotics on biochars, leading to a debate on hysteresis mechanism. In this study, desorption of sulfamethoxazole (SMX), ciprofloxacin (CFX) and tetracycline (TET) on a wood chip biochar produced at 700 °C (WBC700) and its oxidized product (O-WBC700) was investigated to explore the underlying hysteresis mechanism. Significant desorption hysteresis was observed for SMX, CFX and TET on WBC700 and O-WBC700. Hysteresis index (HI) of each antibiotic was higher on O-WBC700 with more oxygen-containing groups than WBC700, and was higher at lower equilibrium concentration. HI of antibiotics on WBC700 (or O-WBC700) increased in the order of SMX < CFX < TET. The calculated adsorption enthalpy of each antibiotic on WBC700 was positive, indicating an endothermic process. These phenomena together with FTIR, XPS spectra confirmed that the desorption hysteresis mechanism of antibiotics on high-temperature biochar is the formation of amide bonds by amidation reaction, but not the pore deformation or the hydrogen bond. Moreover, antibiotic can form amide bonds with WBC700 only if the amine group with pKa > 4.0, and the HI values were positively correlated with their pKa values. Amine group of antibiotics with higher pKa value show more nucleophilicity and could form stronger amide bonds with carboxyl group of biochar. The obtained results could help to solve the debate on desorption hysteresis mechanism of antibiotics on high-temperature biochars, and provide a new insight into the role of amine groups and amidation reaction on the hysteresis.

Mapping Photogenerated Electron-Hole Behavior of Graphene Oxide: Insight into a New Mechanism of Photosensitive Pollutant Degradation

The use of graphene oxide (GO) photogenerated electron-hole (e-h+) pairs to degrade pollutants is a novel green method for wastewater treatment. However, the interaction between photosensitive pollutants and a GO-light system remains unclear. In this work, the mechanism of degradation of photosensitive pollutant tetracycline (TC) promoted by GO photogenerated e-h+ pairs was studied. Our studies encompassed the determination of TC removal kinetics, analysis of active substances for TC degradation, identification of degradation products, and computational modeling. Clear evidence shows that a new reaction mechanism of enhanced adsorption and induced generation of reactive oxygen species (ROS) was involved. This mechanism was conducive to significantly enhanced TC removal. Kinetic studies showed a first-order behavior that can be well described by the Langmuir-Hinshelwood model. Radical scavenging experiments confirmed that 1O2, •O2-, and holes (h+) were the main active substances for TC degradation. Electron spin resonance analysis indicated that photoexcited TC molecules may transfer electrons to the conduction band of GO to induce the generation of additional ROS. A major transformation product (m/z 459) during TC degradation was identified with liquid chromatography-mass spectrometry. Density functional theory calculation indicated a stronger adsorption between TC and GO under photoirradiation. This mechanism of photo-enhanced adsorption and synergistic induced generation of ROS provides a new strategy for the removal of emerging pollutants in water. Overall, the new mechanism revealed in this work expands the knowledge of applying GO to wastewater treatment and is of great reference value for research in this field.

Removal of tetracycline in the water by a kind of S/N co-doped tea residue biochar

Tetracycline (TC) is widely present in the environment, and adsorption technology is a potential remediation method. S/N co-doped tea residue biochar (SNBC) was successfully prepared by hydrothermal carbonization method using tea residue as raw material. S was doped by Na2S2O3·5H2O, and N was doped by N in tea residue. The adsorption efficiency of SNBC could reach 94.16% when the concentration of TC was 100 mg L-1. The adsorption effect of SNBC on TC was 9.38 times more than that of unmodified biochar. Tea biochar had good adsorption effect at pH 4-9. The maximum adsorption capacity of 271 mg g-1 was calculated by the Langmuir isotherm model. The adsorption mechanism involved many mechanisms such as pore filling, π-π interaction and hydrogen bonding. The adsorbent prepared in this study could be used as an effective adsorbent in the treatment of TC wastewater.

One-Pot Preparation of Layered Double Hydroxide-Engineered Boric Acid Root and Application in Wastewater

Heavy metals and organic pollutants are prevalent in water bodies, causing great damage to the environment and human beings. Hence, it is urgent to develop a kind of adsorbent with good performance. Anion interlacing layered double hydroxides (LDHs) are a promising adsorbent for the sustainable removal of heavy metal ions and dyes from wastewater. Using aluminum chloride, zinc chloride and ammonium pentaborate tetrahydrate (NH4B5O8 · 4H2O, BA) as raw materials, the LDHs complex (BA-LDHs) of B5O8- intercalation was prepared by one-step hydrothermal method. The BA-LDHs samples were characterized by a X-ray powder diffractometer (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR) and the Brunauer-Emmett-Teller (BET) method. The results showed that B5O8- was successfully intercalated. Adsorption experimental results suggested that BA-LDHs possess a maximum adsorption capacity of 18.7, 57.5, 70.2, and 3.12 mg·g-1 for Cd(II), Cu(II), Cr(VI) and Methylene blue (MB) at Cs = 2 g·L-1, respectively. The adsorption experiment conforms to the Langmuir and Freundlich adsorption models, and the kinetic adsorption data are well fitted by the pseudo-second-order adsorption kinetic equation. The as-prepared BA-LDHs have potential application prospects in the removal of heavy metals and dyes in wastewater. More importantly, they also provide a strategy for preparing selective adsorbents.

Understanding the carbendazim adsorption from water using biochar derived from apple pomace and industrial wastewater sludge: experimental and DFT approaches

Biochars derived from apple pomace (AP-BC) and industrial wastewater sludge (IS-BC) were used to investigate adsorption performance and mechanism for removing carbendazim from water and compare its performance with commercial biochar (commercial BC). The results showed that the adsorption capacity of AP-BC and IS-BC were 76 mg g-1 and 82 mg g-1 respectively that was comparable with the commercial BC (80 mg g-1). The adsorption kinetics and isotherms were best described by the Pseudo-second-order and Langmuir models. Thermodynamic analysis suggested that higher temperatures can enhance the mobility of molecules, increased mobility facilitates more frequent and stronger interactions between the adsorbate molecules and the surface of the adsorbent material, leading to greater adsorption capacity. Density functional theory (DFT) calculations confirmed carbendazim's weak electrophilic nature, supporting the primary physisorption mechanism. Even after five cycles of recycling, both biochars maintained a consistent carbendazim removal efficiency of around 82%, highlighting their high reusability. In this study, the examination of waste-derived biochar's economic feasibility revealed that using biochars derived from waste biomass for large-scale wastewater treatment applications is an economically viable choice.

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.

Biomass hydrothermal carbonization solution-assisted synthesis of intercalation-expanded core-shell structured molybdenum disulfide for efficient adsorption of Cr (VI) in electroplating wastewater treatment

Cr (VI) is a common heavy metal pollutant in electroplating wastewater. This study introduces the liquid-phase product from the hydrothermal reaction of coffee grounds (CGHCL) into the synthesis process of molybdenum disulfide, assisting in the fabrication of an intercalated, expanded core-shell structured molybdenum disulfide adsorbent (C-MoS2), designed for the adsorption and reduction of Cr (VI) from electroplating wastewater. The addition of CGHCL significantly enhances the adsorption performance of MoS2. Furthermore, C-MoS2 exhibits exceedingly high removal efficiency and excellent regenerative capability for Cr (VI)-containing electroplating wastewater. The core-shell structure effectively minimizes molybdenum leaching to the greatest extent, while the oleophobic interface is unaffected by oily substances in water, and the expanded interlayer structure ensures the long-term stability of C-MoS2 in air (90 days). This study provides a viable pathway for the resource utilization of biomass and the application of molybdenum disulfide-based materials in wastewater treatment.

Amino-functionalized cellulose composite for efficient simultaneous adsorption of tetracycline and copper ions: Performance, mechanism and DFT study

A novel cellulose composite (denoted as PEI@MMA-1) with porous interconnected structure was prepared by adsorbing methyl cellulose (MC) onto microcrystalline cellulose (MCC) and cross-linking polyethyleneimine (PEI) with MCC by the action of epichlorohydrin, which had the excellent adsorption property, wettability and elasticity. The performances of PEI@MMA-1 composite for removing tetracycline (TC), Cu2+ and coexistent pollutant (TC and Cu2+ mixture) were systematically explored. For single TC or Cu2+ contaminant, the maximum adsorption capacities were 75.53 and 562.23 mg/g at 30 °C, respectively, while in the dual contaminant system, they would form complexes and Cu2+ could play a "bridge" role to remarkably promote the adsorption of TC with the maximum adsorption capacities of 281.66 and 253.58 mg/g for TC and Cu2+. In addition, the adsorption kinetics, isotherms and adsorption mechanisms of single-pollutant and dual-pollutant systems have been thoroughly investigated. Theoretical calculations indicated that the amide group of TC molecule with the assistance of Cu2+ interacted with the hydroxyl group of PEI@MMA-1 composite to enhance the TC adsorption capacity. Cycle regeneration and fixed bed column experiments revealed that the PEI@MMA-1 possessed the excellent stability and utility. Current PEI@MMA-1 cellulose composite exhibited a promising application for remediation of heavy metals and antibiotics coexistence wastewater.

Preparation of highly adsorptive biochar by sequential iron impregnation under refluxing and pyrolysis at low temperature for removal of tetracycline

Iron-doping modification is a prevailing approach for improving adsorption capability of biochar with environmental friendliness, but usually requires high temperature and suffers from iron aggregation. Herein, a highly adsorptive biochar was manufactured via sequential disperse impregnation of iron by refluxing and pyrolysis at low temperature for eliminating tetracycline (TC) from aqueous solution. Iron oxides and hydroxides were impregnated and stably dispersed on the carbon matrix as pyrolyzed at 200 °C, meanwhile abundant oxygen and nitrogen functional groups were generated on surface. The iron-doped biochar exhibited up to 891.37 mg/g adsorption capacity at pH 5, and could be recycled with high adsorption capability. The adsorption of TC should be mostly contributed to the hydrogen bonding of N/O functional groups and the hydrogen bonding/coordination of iron oxides/hydroxides. This would provide a valuable guide for dispersedly doping iron and conserving functional groups on biochar, and a super iron-doped biochar was prepared with superior recyclability.

Seeking the adsorption of tetracycline in water by Fe-modified sludge biochar at different pyrolysis temperatures

The composite material SBC-Fe-x with sludge and Fe3+ was developed by different calcination temperatures (600, 700, and 800 °C) for the removal of tetracycline (TC). The adsorption rates of SBC-Fe-600, SBC-Fe-700, and SBC-Fe-800 were 77.5%, 89%, and 91%, respectively. Furthermore, the Langmuir model indicated that the maximum adsorption capacity of SBC-Fe-700 (157.93 mg/g) was three times greater than that of SBC-Fe-600. The conclusions were confirmed by a series of characterizations that SBC-Fe-700 showed a larger specific surface area, well-developed pore structure, rich oxygen-containing functional groups and a high degree of graphitization. The results of pH experiments indicated the broad applicability of SBC-Fe-700 for TC adsorption. In addition, SBC-Fe-700 suggested outstanding performance in different water environments. This work produced a feasible adsorbent for the removal of TC, and a new direction for sludge resource utilization was proposed.

Efficient removal of tetracycline and Cu2+ by honeycomb derived magnetic carbon: Adsorption mechanism and advanced oxidation regeneration mechanism

The honeycomb magnetic carbons (xFe@HCNs) were prepared by sacrificial template method novelty using polyacrylamide resin (PAAS) as template and ammonium pyrrolidine dithioate/Fe3+ complex (APDC-Fe) as carbon skeleton and metal source. Tetracycline (TC) and copper (Cu2+) as target pollutants were used to investigate the adsorption properties of xFe@HCNs in single or binary TC and Cu2+ systems. The adsorption capacity sequence for TC among the adsorbents was (mmol·g-1): 2Fe@HCNs (0.088) > 8Fe@HCNs (0.061) > HCNs (0.054) > RC (0.036), and for Cu2+ was (mmol·g-1): 2Fe@HCNs (1.120) > 8Fe@HCNs (1.026) > RC (0.792) > HCNs (0.681). 2Fe@HCNs demonstrated notable affinity for adsorbing both TC and Cu2+. Additionally, the influence of hydrochemical factors (i.e., cation species, anion species, and pH) on the adsorption properties of 2Fe@HCNs. Combined with advanced oxidation technology, the regeneration methods of magnetic adsorbent were explored using oxidizing agents (e.g., H2O2 and peroxymonosulfate) as eluents which could increase the adsorption sites of magnetic carbon adsorbents during the regenerating process, which was the novelty of the study. Furthermore, the regeneration mechanisms of H2O2 as eluent were investigated. This study discussed the application and regeneration methods of magnetic adsorbents in water treatment, offering new insights into environmental remediation using magnetic materials.

Dyeing sludge-derived biochar for efficient removal of antibiotic from water

Adsorption is one of the most effective methods for ecotoxic antibiotics removal, while developing high-performance adsorbents with excellent adsorption capacity is indispensable. As the unavoidable by-product of wastewater, sewage sludge has dual properties of pollution and resources. In this study, dyeing sludge waste was converted to biochar by KOH activation and pyrolysis, and used as an efficient adsorbent for aqueous antibiotics removal. The optimized dyeing sludge-derived biochar (KSC-8) has excellent specific surface area (1178.4 m2/g) and the adsorption capacity for tetracycline (TC) could reach up to 1081.3 mg/g, which is four and five times higher than those without activation, respectively. The PSO (pseudo-second-order) kinetic model and the Langmuir isotherm model fitted better to the experimental data. The obtained KSC-8 has stabilized adsorption capacity for long-term fixed-bed experiments, and maintained 86.35% TC removal efficiency after five adsorption-regeneration cycles. The adsorption mechanism involves electrostatic attraction, hydrogen bonding, π-π interactions and pore filling. This work is a green and eco-friendly way as converting the waste to treat waste in aiming of simultaneous removal of antibiotics and resource recovery of dyeing sludge.

Magnetic biochar enhanced copper immobilization in agricultural lands: Insights from adsorption precipitation and redox

Biochar has exceeded expectations for heavy metal immobilization and has been prepared from widely available sources and inexpensive materials. In this research, coconut shell biochar (CSB), bamboo biochar (BC), magnetic coconut shell charcoal (MCSB), and magnetic bamboo biochar (MBC) were manufactured via co-pyrolysis, and their adsorption properties were tested. The pseudo-secondary (R2 = 0.980-0.985) adsorption kinetic fittings for the four biochas were superior to the pseudo-primary kinetics (R2 = 0.969-0.982). Unmodified biochar adsorption isotherms were more consistent with the Freundlich model, while magnetic biochar fitted Langmuir models better. The maximum adsorption capacity of MCSB for Cu(Ⅱ) reached 371.50 mg g-1. The adsorption mechanisms quantitatively analysis of the biochar indicated that chemical precipitation and ion exchange contributed to the adsorption, in which the magnetic biochar metal-π complexation also enhanced the adsorption. The pot experiment revealed that MCSB (2.0 %DW) significantly enhanced the biomass of lettuce, and facilitated the immobilization of DTPA-Cu (p < 0.05). SEM-EDS, XPS, and FTIR were utilized for morphological characterization and functional group identification, and the increased active adsorption sites (-OH, -COOH, CO, and Fe-O) of MCSB enhanced chemisorption and π-π EDA complexation with Cu(Ⅱ). EEM-PARAFAC and RDA analysis further elucidated that magnetic biochar immobilized copper and reduced biotoxicity (efficiency: 76.12%) by adjusting soil pH, phosphate, and SOM release (negative correlation). The presence of iron oxides (FeOx) promoted in situ adsorption of metallic copper and offered new insights into soil remediation.

Precursor-oriented design of nano-alumina for efficient removal of antibiotics

Rapid and efficient removal of environmental antibiotics is vital to curb bacterial resistance. Through rational precursors-oriented design, we attain the best Al2O3 absorbent by 500 °C calcination of ammonium aluminium carbonate hydroxide (AACH) precursor from NH4HCO3 route (AACH-NH4HCO3-500) for fast and efficient removal of tetracycline (TC) and other antibiotics from environmental waters including high-salinity wastewater. AACH-NH4HCO3-500 (0.25 g·L-1) can remove (69.92 ± 1.78)% of aqueous TC (0.025 g·L-1) within 5 min and (97.62 ± 2.75)% within 2 h, and the adsorption capacity is 444.4 mg·g-1, which is the highest qmax of TC for the 2 h-adsorptions among numerous adsorbents. AACH-NH4HCO3-500 has fine tolerance to the coexisting substances, and can be easily regenerated and reused, and has no harm even discarded. The relations among the synthetic methods, the structural features, and the adsorption functions of Al2O3 are disclosed through a systematic comparison of the commercial Al2O3 and different Al2O3 nanomaterials attained from three precursors produced by five different routes. The reasons behind the exceptional adsorption performance are discussed throughout. Our findings would facilitate the development of excellent adsorbents for removal of other pollutants.

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.

Simultaneous removal of phosphate and tetracycline using LaFeO3 functionalised magnetic biochar by obtained ultrasound-assisted sol-gel pyrolysis: Mechanisms and characterisation

Excessive phosphate and tetracycline (TC) contaminants pose a serious risk to human health and the ecological environment. As such exploring the simultaneous adsorption of phosphate and TC is garnering increasing attention. In this study, an efficient lanthanum ferrate magnetic biochar (FLBC) was synthesised from crab shells using an ultrasound-assisted sol-gel method to study its performance and mechanisms for phosphate and TC adsorption in aqueous solutions in mono/bis systems. According to the Langmuir model, the developed exhibited a maximum adsorption capacity of 65.62 mg/g for phosphate and 234.1 mg/g for TC (pH:7.0 ± 0.1, and 25 °C). Further, it exhibited high resistance to interference and pH suitability. In practical swine wastewater applications, whereby the concentrations of phosphate and TC are 37 and 19.97 mg/L, respectively, the proposed material demonstrated excellent performance. In addition, electrostatic adsorption, chemical precipitation and ligand exchange were noted to be the main mechanisms for phosphate adsorption by FLBC, whereas hydrogen bonding and π-π interaction were the main adsorption mechanisms for TC adsorption. Therefore, this study successfully prepared a novel and efficient adsorbent for phosphate and TC.

Adsorption characterization of tetracycline antibiotics on alkali-functionalized rice husk biochar and its evaluation on phytotoxicity to seed germination

This work presented adsorption characteristics of tetracycline antibiotics (TCs) on KOH-functionalized rice husk biochar pyrolyzed at 700 °C (KBC700) and evaluation on phytotoxicity of TCs-adsorbed aqueous phase to seed germination. Specifically, KBC700 gained eightfold rise in specific surface area by KOH activation. Predominant monolayer chemisorption helped KBC700 control TCs, and spontaneous and exothermic features were identified by thermodynamic studies. KBC700 could efficiently work in a wide pH range (4.5 ~ 9.5), as well as in simulated eutrophic water and co-existing cationic solution. Humic acid exerted negative impact on TCs disposal. Outstanding regeneration capability and stability were also found during adsorption-desorption cycles. Mechanism discussion implied predominant pore filling and π-π interaction accompanied by hydrogen bonding and electrostatic interaction involved in TCs-removal process. Importantly, less phytotoxicity to seed germination was found in TCs-adsorbed aqueous phase. Collectively, these findings contribute to adsorption properties recognition and subsequent application for KOH-modified rice rusk biochar in environmental TCs remediation.

Carbon-based materials as efficient adsorbents for the removal of antibiotics: The real contributions of carbon edge sites

Disclosing the effect of edge defects in carbon-based materials on antibiotic removal remains a great challenge. In this study, carbon-based adsorbents (DC-s) with different degrees of edge defects were synthesized on a large scale via a direct calcination of sodium citrate (SC) and their adsorption performance to antibiotics were explored. The experimental results suggested that the edge defects of DC-s samples were the active sites for the adsorption of tetracycline (TC) and norfloxacin (NOR). The adsorption capacity of the optimal sample DC-900 for TC and NOR was 155.8 and 168.0 mg g-1, respectively. Density functional theory (DFT) calculations further revealed that zigzag edge defects rather than armchair edge defects were crucial to the excellent adsorption performance of DC-s samples for antibiotics, and the natures for the difference in the adsorption performance of the two edge defects for antibiotics were their different electronic structures. In addition, DC-900 also showed stable adsorption efficiency for antibiotics in the interferences, dynamic adsorption, and cycle experiments, suggesting its good environmental application potential. This study provides new insight into clarifying the natures of edge defects with carbon-based adsorbents for high-efficiency removal of antibiotics, which may guide the exploration of cost-effective carbon-based adsorbents.

Thiamethoxam adsorption by ZnCl2 modified cow manure biochar: Mechanism and quantitative prediction

The overuse of thiamethoxam (THM) has threatened the survival of living organisms and it is necessary to find an environmentally friendly material to remove THM frequently detected in water. Biochar prepared from cow manure modified with ZnCl2 (Zn-CBC) was used to remove THM. Compared to the unmodified cow manure biochar (CBC), the removal ratio of THM by Zn-CBC was enhanced 35 times. In the mechanistic analysis, SEM and BET showed that Zn-CBC had a good pore structure and its specific surface area (166.502 m2 g-1) increased to 17 times that of CBC, indicating that Zn-CBC had good pore adsorption properties. The adsorption kinetic and isotherm implied that the main mechanism was chemisorption including π-π interaction and H-bonding. Furthermore, the stable graphitized structure of Zn-CBC allowed for efficient adsorption and reusability. In addition, this study constructed an intelligent prediction model using batch experiment data, and the high R2 (0.978) and low RMSE (0.057) implied that the model could accurately and quantitatively predict the adsorption efficiency. This paper provides a novel perspective to simultaneously remove the neonicotinoid insecticides and realize the resource utilization of cow manure.

Removing DOM from chloride modified hydrochar could improve Cu2+ adsorption capacity from aqueous solution

The behavior and composition of hydrochar-based dissolved organic matter (DOM) would affect the efficiency of copper (Cu) removal from wastewater through adsorption. In this study, the reed was hydrolyzed in the presence of feedwater with and without ZnCl2, FeCl3, and SnCl4 to produce pristine hydrochars (PHCs), which were named H2O-HC, ZnCl2-HC, FeCl3-HC, and SnCl4-HC. After removal of DOM, washed hydrochars (WHCs) were obtained, labelled as W-H2O-HC, W-ZnCl2-HC, W-FeCl3-HC, and W-SnCl4-HC. The release dynamics of DOM from PHCs were analyzed, and the adsorption behaviors of Cu2+ on both PHCs and WHCs were investigated. The results showed that chloride-modifications were beneficial for the porosity, specific surface area (SSA), and functional groups of WHCs. Meanwhile, the quantity of hydrochar-based DOM was significantly affected by chloride-modifications. In particular, the relative contents of Ar-P and Fa-L in the DOM released from hydrochars varied with time and modification. Furthermore, the Qe of Cu2+ adsorption on WHCs followed the order of W-SnCl4-HC > W-FeCl3-HC > W-ZnCl2-HC > W-H2O-HC at 15 °C. Compared to PHCs, the adsorption capacity of Cu2+ on WHCs was improved by 7.15-119.77% at the temperature of 35 °C. Simultaneously, the adsorption capacity of Cu2+ in WHCs showed a significant correlation with the SSA via physical adsorption (P < 0.05). Moreover, XPS analysis revealed that Cu2+ adsorption also occurred via complexation and chelation through newly formed Cu-O group between W-SnCl4-HC and Cu2+. Notably, the increase of Cu2+ adsorption in WHCs was significantly correlated with the release of Fa-L and Ar-P from PHCs (P < 0.05). This study found that the content and composition of hydrochar-based DOM could be a major driving factor for Cu2+ adsorption.

Adsorption properties and mechanism of suaeda biochar and modified materials for tetracycline

Adsorption was an available way to eliminate Tetracycline (TC) from waste water. Suaeda biochar (800SBC) and iron modified biochar (Fe-800SBC) were prepared using pyrolysis under oxygen-limiting conditions. BET and SEM showed that the surface of Fe-800SBC was rougher, and the specific surface area (SBET) was 7 times that of 800SBC. There existed pore filling, ion exchange, metal ion complexation, hydrogen bonds and cation-π interaction mechanism. Both 800SBC and Fe-800SBC conformed to quasi-second-order kinetics model, belonged to chemisorption. Fe-800SBC conformed to Elovich model too. The adsorption process of 800SBC conformed to Freundlich and Sips L-F models, Fe-800SBC conformed to the Sips L-F and Temkin models, identifying the presence of physical and chemical adsorption during adsorption. Response surface method (RSM) was used to optimize important process parameters. The quadratic model was sufficient to predict TC removal response in the range of studied parameters.

Eco-friendly remediation of tetracycline antibiotic from polluted water using waste-derived surface re-engineered silica sand

A new green reactive adsorbent (calcium ferric oxide silica sand (CFO-SS)) made from wastepaper sludge ash and ferric ions was synthesised and shown to remove tetracycline antibiotics (TC) from contaminated water effectively. The synthesised sand was dried at 95 °C, and a series of batch and fixed bed experiments were performed to determine the optimum operating conditions. Results showed that the adsorption capacity of the CFO-SS increases with the concentration gradient between the solid and liquid phases. 0.3 g of the new adsorbent was proven sufficient to remove more than 90% of the TC at a pollutant dose of 50 mg/L in 50 mL of simulated groundwater with an agitation speed of 200 rpm for 3 h. The adsorption isotherm followed the Langmuir isotherm model, with a loading capacity of 21.96 mg/g at pH 7, while the Pseudo second-order model best described the absorption kinetics. The adsorption mechanisms proposed included electrostatic interaction, intraparticle diffusion, hydrogen bonding, and cation-π interactions. Characterisation investigations revealed that the newly precipitated oxides on silica sand play an essential role in TC adsorption support. In fixed-bed experiments, it was discovered that reducing the flow rate and inflow concentration of TC and increasing the sorbent mass significantly extended the lifetime of the produced sorbent in the packed column. The measured breakthrough curves were best fit with the Adams-Bohart and the Clark models, as they provided the highest square root number (R2) values. Finally, considering the efficacy of CFO-SS in TC adsorption performance, it can be noted that the novel synthesised reactive material is an efficient and environmentally friendly material for TC removal, and it presents a potential solution to resolving the challenge of TC-rich groundwater.

Cadmium and lead removal by Mg/Fe bimetallic oxide-loaded sludge-derived biochar: batch adsorption, kinetics, and mechanism

Biochar is a valuable adsorbent for the removal of heavy metals from water, and it is important to explore ways to increase its heavy metal adsorption capacity. In this study, Mg/Fe bimetallic oxide was loaded onto sewage sludge-derived biochar to enhance its heavy metal adsorption capacity. Batch adsorption experiments for the removal of Pb(II) and Cd(II) were performed to evaluate the removal efficiency of Mg/Fe layer bimetallic oxide-loaded sludge-derived biochar ((Mg/Fe)LDO-ASB). The physicochemical properties of (Mg/Fe)LDO-ASB and corresponding adsorption mechanisms were studied. The maximum adsorption capacities of (Mg/Fe)LDO-ASB for Pb(II) and Cd(II), which were calculated by isotherm model, were 408.31 and 270.41 mg/g, respectively. Adsorption kinetics and isotherms analysis showed that the dominant adsorption process of Pb(II) and Cd(II) uptake by (Mg/Fe)LDO-ASB was spontaneous chemisorption and heterogeneous multilayer adsorption, and film diffusion was the rate-limiting step. SEM-EDS, FTIR, XRD, and XPS analyses revealed that the Pb and Cd adsorption processes of (Mg/Fe)LDO-ASB involved oxygen-containing functional group complexation, mineral precipitation, electron-π-metal interactions, and ion exchange. The order of their contribution was as follows: mineral precipitation (Pb: 87.92% and Cd: 79.91%) > ion exchange (Pb: 9.84% and Cd: 16.45%) > metal-π interaction (Pb: 0.85% and Cd: 0.73%) > oxygen-containing functional group complexation (Pb: 1.39% and Cd: 2.91%). Mineral precipitation was the main adsorption mechanism, and ion exchange played a crucial role in Pb and Cd adsorption.

Mechanisms of polystyrene nanoplastics adsorption onto activated carbon modified by ZnCl2

In this study, the adsorption capacity of activated carbon was enhanced after zinc chloride activation. The effects of pore filling, n-π and π-π interaction and electrostatic interaction on the adsorption of polystyrene nanoplastics (PSNPs) by activated carbon were determined by SEM, BET, Raman spectrum, FTIR and surface Zeta potential. Pore filling, electrostatic interaction and n-π interaction and π-π interaction all played a role in the adsorption process, but n-π interaction and π-π interaction was not the decisive role. The adsorption of PSNPs on activated carbon conformed to the pseudo-second-order kinetics and Langmuir isotherm, and there was spontaneous physical adsorption process driven by entropy in the adsorption process. Further, the effects of common anions SO₄^2-, HCO₃^-, and Cl^- in water on the adsorption of PSNPs by activated carbon were investigated, and the results showed that the presence of these ions could increase the adsorption capacity to some extent. ZCAC has a stable adsorption capacity under tap water, but its adsorption capacity is affected under lake water. In addition, the reuse of activated carbon was investugated, and the adsorption capacity of activated carbon was fully recovered after high temperature calcination. This study provided a direction for materials modification of adsorbed nanoplastics and a feasible method for removal of nanoplastics in drinking water treatment plants.

One-pot preparation of layered double oxides-engineered biochar for the sustained removal of tetracycline in water

Tetracycline (TC) and sugarcane bagasse had both exerted enormous strain on environmental security. In this work, new composite adsorbent designed by impregnating bio-waste bagasse with magnesium-aluminum layered double oxides (BC-MA) was innovatively brought forward for TC removal. Benefiting from the abundant adsorption sites supplied by developed pores structure (0.308 cm³·g^-1), enlarged surface area (256.8 m²·g^-1) and reinforced functional groups, the maximum adsorption amount of BC-MA for TC reached 250.6 mg g^-1. Moreover, BC-MA displayed desirable adsorption capacity in diverse water environments coupled with excellent sustainable regeneration ability. The absorption process of TC by BC-MA was spontaneous and endothermic, and the pivotal rate-limiting stage pertained to intraparticle diffusion. The mechanisms proposed here mainly concerned π-π interactions, pore filling, complexation and hydrogen bonding. These findings suggested that the synthesis of modified biochar from bagasse would offer new opportunities for simultaneous waste resource reuse and water pollution control.

Modified biochar prepared from Retinervus luffae fructus for dyes adsorption and aerobic sludge granulation

Retinervus luffae fructus biochar (RLFB) and ZnCl2 pretreated Retinervus luffae fructus biochar (ZRLFB) were prepared by pyrolysis. The as-prepared biochar was investigated for its applicability as a dye adsorber using sunset yellow (SY) and basic red 46 (BR46) dyes. Additionally, ZRLFB was used for the experimental cultivation of granular sludge. The results indicated that the adsorption effect of ZRLFB on the two dyes was higher than RLFB. The adsorption of RLFB to SY was related to the Langmuir and Freundlich models, whereas the adsorption of RLFB-BR46, ZRLFB-SY, and ZRLFB-BR46 was more in line with the Langmuir model. The adsorption process of dyes on two kinds of biochars can be described using pseudo-second-order mechanisms. The maximum adsorption capacity obtained was 1.9586 (RLFB-SY), 6.1286 (RLFB-BR46), 49.2611 (ZRLFB-SY), and 181.4882 mg g^-1 (RLFB-BR46). The result of the SBR operation showed that ZRLFB can potentially be applied as the core of aerobic granular sludge.

Development of sludge-based activated char sorbent with enhanced hydrophobicity for oil spill cleanup

Recovery of oil spilled on surface waters by the use of sorbents remains one of the primary oil spill response options available. To improve on this response measure, we have successfully fabricated an activated char (AC) sorbent material by pyrolysis of sewage sludge (SS), a readily available waste product generated across the world from wastewater treatment plants. The inherent Fe-minerals in SS texture were converted to magnetic Fe₃O₄ particles during the pyrolysis reaction. The AC provided a unique means to recover the sorbent after the oil sorption process with a magnetic field. Meanwhile, a superhydrophobic sorbent material with a water contact angle of 152.2° was created by the treatment of AC with myristic acid which could float on the water surface. Feasibility studies at the laboratory-scale were conducted with motor oil and light crude oil to evaluate its potential use in spill response operations. Results showed a sorption capacity of about 8.5 and 10.7 g/g for motor oil and light crude oil, respectively. Following the recovery of the test oils by ethanol stripping, the material could be recycled up to 5 times with trivial loss in sorption capacity. This research proposes a framework for the development of a highly efficient sorbent material for oil spill response operations from SS waste.

Activated ZnCl2 biochar and humic acid as additives in monoammonium phosphate fertilizer: Physicochemical characterization and agronomic effectiveness

Activated zinc biochar (ZnBC) and humic acid (HA) were used as coating agents in a soluble monoammonium phosphate (MAP) to modify phosphorus (P) use efficiency by altering adsorption/desorption kinetics between the granule region and the soil. The coated treatments MAPZnBC and MAPHA were compared with MAP through P diffusivity, kinetics, and agronomic evaluation. Eucalyptus sawdust was used as biomass for biochar synthesis, and a pre-pyrolysis treatment with zinc chloride (ZnCl₂) was applied. The P diffusivity was evaluated in the fertosphere zone. Adsorption and desorption potential of the ZnBC compared with control biochar (BC) was evaluated separately. Desorption kinetics of P from soil was assessed after incubation with MAPZnBC and MAPHA. The shoot dry matter yield (SDM), P uptake, and P use efficiency (PUE) were evaluated with a pot experiment in a clay Oxisol sown with maize and soybeans as successive plant trials, under glasshouse conditions. Surface area values of 940 and 305 m² g^-1 combined with adsorption capacities of 106 and 53 mg P g^-1 for ZnBC and BC, respectively, confirm the increased capacity of activated biochar to adsorb P. Both MAPZnBC and MAPHA decreased P diffusivity compared to MAP after 20 days of incubation. Moreover, MAPZnBC and MAPHA presented 20% and 34% more water-soluble phosphorus recovery. MAPZnBC expressed an increase in SDM while MAPHA highlighted P uptake and PUE compared with MAP. Both kinetic studies and agronomic evaluations showed that ZnBC and HA are suitable as coatings for phosphate fertilizers in terms of increasing P efficiency in the fertosphere on high P-fixing soils.

Effective removal of tetracycline antibiotics from water by magnetic functionalized biochar derived from rice waste

The effective removal of tetracycline antibiotics (TCs) from water is of great significance and remains a big challenge. In this work, a novel magnetized biochar (magnetic functionalized carbon microsphere, MF-CMS) was prepared by the coupling hydrothermal carbonization and pyrolysis activation of starch-rich rice waste using ZnCl₂ and FeCl₃ as activators. As the MF-CMS dose was 2.0 g/L, the initial concentration of TCs was 100 mg/L, the removal rates of tetracycline, doxycycline, oxytetracycline, and chlortetracycline were 96.02%, 96.10%, 96.52%, and 85.88%, respectively. The best modeled on pseudo second order, Langmuir adsorption model, and intraparticle diffusion kinetic models suggested that both chemisorption and physisorption occurred in all removal processes, in which chemisorption dominated. TCs were efficiently adsorbed through the combined effects of pore filling, electrostatic attraction, π-π interactions, and complexation reactions of surface functional groups (such as γ-Fe₂O₃ and FeOOH). The removal rates of TCs after five cycles approximately decreased by 20%. And the cycling and metal ion release experiments of MF-CMS indicated that MF-CMS had good reusability, stability, and safety. The estimated cost of preparing MF-CMS is 5.91 USD per kg, and 1 kg of MF-CMS (consuming 8 kg of waste rice) can approximately treat 0.55 tons of TCs wastewater. Overall, the magnetic biochar derived from starch-rich rice waste as an adsorbent has promising and effective for the removal of TCs from water, but also provides a new idea for the resourceful treatment of solid waste.

Removal of Ciprofloxacin from Water by a Potassium Carbonate-Activated Sycamore Floc-Based Carbonaceous Adsorbent: Adsorption Behavior and Mechanism

In this study, a porous carbonaceous adsorbent was prepared from sycamore flocs by pyrolysis method and K₂CO₃ activation. The effects of preparative conditions of the material on its adsorptive property were explored. The optimal material (SFB_2-900) was obtained with a K₂CO₃/biochar mass ratio of 2:1 at an activation temperature of 900 °C, possessing a huge surface specific area (1651.27 m²/g). The largest adsorption capacity for ciprofloxacin on SFB_2-900 was up to 430.25 mg/g. The adsorption behavior was well described by the pseudo-second-order kinetic model and the Langmuir isothermal model. Meanwhile, this process was spontaneous and exothermic. The obtained material showed excellent adsorption performance in the conditions of diverse pH range, ionic strength, and water quality of the solution. The optimum adsorption conditions (pH = 7.01, dosage = 0.6 g/L, and C₀ = 52.94 mg/L) determined based on the response surface methodology were in accordance with the practical validation consequences. The good regeneration effect of SFB_2-900 manifested that this material had great practical application potential. Combining the experimental results and density functional theory calculation results, the adsorption mechanisms mainly included pore filling, π-π EDA interactions, electrostatic interactions, and H-bonds. The material could be regarded as a novel and high-efficiency adsorbent for antibiotics. Additionally, these findings also provide reference for the reuse of waste biomass in water treatment.

Hydrothermal and pyrolytic conversion of sunflower seed husk into novel porous biochar for efficient adsorption of tetracycline

In this study, sunflower seed husk biochar prepared by ZnCl₂-activated and hydrothermal carbonization (HZSF) was studied for its effectiveness in removing tetracycline (TC) from an aqueous solution. The physical and chemical properties of materials were characterized by different methods of surface analysis. The specific surface area of HZSF is significantly enhanced over 1200 times compared with non-modified biochar (HZSF: 1578.3 m²·g^-1, SF-700: 1.3 m²·g^-1), which has an enhancement effect on the TC adsorption capacity. The HZSF showed that the Langmuir isotherm and pseudo-second-order kinetic models could properly characterize the adsorption processes. In the Langmuir isotherm model, HZSF exhibited effective adsorption performance with q_max of 673.0 mg·g^-1 at 298 K for 24 h. The possible mechanisms for the adsorption process were the monolayer, chemical adsorption, and the participation of strong intermolecular forces. In general, HZSF has the potential to be a useful adsorbent for the elimination of antibiotics from water-based solutions.

A Stable Fe-Zn Modified Sludge-Derived Biochar for Diuron Removal: Kinetics, Isotherms, Mechanism, and Practical Research

To remove typical herbicide diuron effectively, a novel sludge-derived modified biochar (SDMBC600) was prepared using sludge-derived biochar (SDBC600) as raw material and Fe-Zn as an activator and modifier in this study. The physico-chemical properties of SDMBC600 and the adsorption behavior of diuron on the SDMBC600 were studied systematically. The adsorption mechanisms as well as practical applications of SDMBC600 were also investigated and examined. The results showed that the SDMBC600 was chemically loaded with Fe-Zn and SDMBC600 had a larger specific surface area (204 m²/g) and pore volume (0.0985 cm³/g). The adsorption of diuron on SDMBC600 followed pseudo-second-order kinetics and the Langmuir isotherm model, with a maximum diuron adsorption capacity of 17.7 mg/g. The biochar could maintain a good adsorption performance (8.88-12.9 mg/g) under wide water quality conditions, in the pH of 2-10 and with the presence of humic acid and six typical metallic ions of 0-20 mg/L. The adsorption mechanisms of SDMBC600 for diuron were found to include surface complexation, π-π binding, hydrogen bonding, as well as pore filling. Additionally, the SDMBC600 was tested to be very stable with very low Fe and Zn leaching concentration ≤0.203 mg/L in the wide pH range. In addition, the SDMBC600 could maintain a high adsorption capacity (99.6%) after four times of regeneration and therefore, SDMBC600 could have a promising application for diuron removal in water treatment.

Adsorption Performance of Methylene Blue by KOH/FeCl3 Modified Biochar/Alginate Composite Beads Derived from Agricultural Waste

In this study, high-performance modified biochar/alginate composite bead (MCB/ALG) adsorbents were prepared from recycled agricultural waste corncobs by a high-temperature pyrolysis and KOH/FeCl3 activation process. The prepared MCB/ALG beads were tested for the adsorption of methylene blue (MB) dye from wastewater. A variety of analytical methods, such as SEM, BET, FTIR and XRD, were used to investigate the structure and properties of the as-prepared adsorbents. The effects of solution pH, time, initial MB concentration and adsorption temperature on the adsorption performance of MCB/ALG beads were discussed in detail. The results showed that the adsorption equilibrium of MB dye was consistent with the Langmuir isothermal model and the pseudo-second-order kinetic model. The maximum adsorption capacity of MCB/ALG−1 could reach 1373.49 mg/g at 303 K. The thermodynamic studies implied endothermic and spontaneous properties of the adsorption system. This high adsorption performance of MCB/ALG was mainly attributed to pore filling, hydrogen bonding and electrostatic interactions. The regeneration experiments showed that the removal rate of MB could still reach 85% even after five cycles of experiments, indicating that MCB/ALG had good reusability and stability. These results suggested that a win-win strategy of applying agricultural waste to water remediation was feasible.

Pyrolysis temperature affects the physiochemical characteristics of lanthanum-modified biochar derived from orange peels: Insights into the mechanisms of tetracycline adsorption by spectroscopic analysis and theoretical calculations

Biochar (BC) derived from orange peels was modified using LaCl₃ to enhance its tetracycline (TC) adsorption capacity. SEM-EDS, FT-IR, XRD, and BET were used to characterize the physiochemical characteristics of La-modified biochar (La-BC). Batch experiments were conducted to investigate the effects of several variables like pyrolysis temperature, adsorbent dosage, initial pH, and coexisting ions on the adsorption of TC by La-BC. XPS and density functional theory (DFT) were used to elucidate the TC adsorption mechanism of La-BC. The results demonstrated that La was uniformly coated on the surface of the La-BC. The physiochemical characteristics of La-BC highly depended on pyrolysis temperature. Higher temperature increased the specific surface area and functional groups of La-BC, thus enhancing its TC adsorption capacity. La-BC prepared at 700 °C (BC@La-700) achieved the maximum adsorption capacity of 143.20 mg/g, which was 6.8 and 4.6 times higher than that of BC@La-500 and BC@La-600, respectively. The mechanisms of TC adsorption by La-BC were most accurately described by the pseudo-second-order kinetic model. Furthermore, the adsorption isotherm of La-BC was consistent with the Freundlich model. BC@La-700 achieved good TC adsorption efficiencies even at a wide pH range (pH 4-10). Humic acid significantly inhibited TC adsorption by La-BC. The presence of coexisting ions (NH₄⁺, Ca²⁺, NO₃^-) did not significantly affect the adsorption capacity of La-BC, particularly BC@La-700. Moreover, BC@La-700 also exhibited the best recycling performance, which achieved relative high adsorption capacity even after 5 cycles. The XPS results showed that π-π bonds, oxygen-containing functional groups, and La played a major role in the adsorption of TC on La-BC. The result of DFT showed that the adsorption energy of La-BC was the greatest than that of other functional groups on biochar. Collectively, our findings provide a theoretical basis for the development of La-BC based materials to remove TC from wastewater.

Mesoporous Activated Biochar from Crab Shell with Enhanced Adsorption Performance for Tetracycline

In this study, three mesoporous-activated crab shell biochars were prepared by carbonation and chemical activation with KOH (K-CSB), H₃PO₄ (P-CSB), and KMnO₄ (M-CSB) to evaluate their tetracycline (TC) adsorption capacities. Characterization by SEM and a porosity analysis revealed that the K-CSB, P-CSB, and M-CSB possessed a puffy, mesoporous structure, with K-CSB exhibiting a larger specific surface area (1738 m²/g). FT-IR analysis revealed that abundant, surface ox-containing functional groups possessed by K-CSB, P-CSB, and M-CSB, such as -OH, C-O, and C=O, enhanced adsorption for TC, thereby enhancing their adsorption efficiency for TC. The maximum TC adsorption capacities of the K-CSB, P-CSB, and M-CSB were 380.92, 331.53, and 281.38 mg/g, respectively. The adsorption isotherms and kinetics data of the three TC adsorbents fit the Langmuir and pseudo-second-order model. The adsorption mechanism involved aperture filling, hydrogen bonding, electrostatic action, π-π EDA action, and complexation. As a low-cost and highly effective adsorbent for antibiotic wastewater treatment, activated crab shell biochar has enormous application potential.

Novel hydrophilic straw biochar for the adsorption of neonicotinoids: kinetics, thermodynamics, influencing factors, and reuse performance

Nitenpyram (NIT) is the most water-soluble neonicotinoid (NEO). It has been shown to pose a serious threat to human health and the environment but was always ignored due to its limited market share. There were few experts who studied NIT's transport behavior on biochar. In this study, two types of biochar were co-activated separately using zinc chloride combined with phosphoric acid and potassium hydroxide combined with acetic acid, marked as ZBC and KBC. Characterizations suggested that hydrophilic ZBC and KBC had more surface functional groups than unmodified biochar (BC), and specific surface areas of ZBC (456.406 m²·g^-1) and KBC (750.588 m²·g^-1) were significantly higher than of BC (67.181 m²·g^-1). The pore structures of KBC and ZBC were hierarchical porous structures with different pore sizes and typical microporous structure, respectively. The adsorption performance of either NIT or IMI on KBC was better than that on ZBC. Only 0.4 g·L^-1 of KBC can absorb 89.62% of NIT in just 5 min. The equilibrium adsorption amounts of NIT on ZBC and KBC were 17.995 mg·g^-1 and 82.910 mg·g^-1. Elovich and Langmuir models were used to evaluate the whole adsorption process, which was attributed to the chemisorption mechanism. In addition, removal rates of NIT were negatively correlated to NIT's initial concentration and positively correlated to the dose of biochar. pH had almost no effect on adsorption, but the presence of salt ions can inhibit the removal of NIT. Long-term stabilities of biochars were also acceptable. These findings will promote the development in the preparation of biochar fields and provide a positive reference value for NEO removal.

Chemically activated carbon preparation from natural rubber biosludge for the study of characterization, kinetics and isotherms, thermodynamics, reusability during Cr(VI) and methylene blue adsorption

Alkaline leachate, dust generation, and foul smell during the stacking process of natural rubber biosludge (NRBS) can pollute surrounding water, soil, and air. In this study, natural rubber chemically activated carbon (NRCAC) has been synthesized for the first time from NRBS by pyrolysis using ZnCl₂ at 700 °C for adsorptive removal of Cr(VI) and methylene blue (MB) from aqueous solutions. Both NRBS and NRCAC were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Brunauer-Emmett-Teller (BET), and thermogravimetric analyzer (TGA). FTIR and SEM-EDS suggested significant functional and morphological transformations in NRCAC. Experimental investigations of different process parameters, such as pH, concentration, contact time, salt concentration, etc., were conducted to study their influences on adsorption. Adsorption and desorption kinetics followed a pseudo-second-order model, while adsorption equilibrium followed Liu isotherm. Maximum uptake calculated from the Liu model was 81.28 and 211.90 mg/g for Cr(VI) and MB, respectively. Thermodynamic analysis established spontaneous and endothermic adsorption. Up to five adsorption/desorption cycles were conducted using eluents such as 1 M NaOH and water for Cr(VI) and MB, respectively. Electrostatic attraction and ion-exchange favored Cr(VI)/MB adsorption, while hydrogen bonding and π-π stacking were significant in MB uptake. Overall findings suggest that NRBS (a renewable agro-industrial, abundant, and freely available) could be employed to synthesize biochar for adsorptive removal of wastewater containing Cr(VI)/MB.

A review of antibiotics and antibiotic resistance genes (ARGs) adsorption by biochar and modified biochar in water

Antibiotics have been used in massive quantities for human and animal medical treatment, and antibiotic resistance genes (ARGs) are of great concern worldwide. Antibiotics and ARGs are exposed to the natural environment through the discharge of medical wastewater, causing great harm to the environment and human health. Biochar has been widely used as a green and efficient adsorbent to remove pollutants. However, pristine and unmodified biochars are not considered sufficient and efficient to cope with the current serious water pollution. Therefore, researchers have chosen to improve the adsorption capacity of biochar through different modification methods. To have a better understanding of the application of modified biochar, this review summarizes the biochar modification methods and their performance, particularly, molecular imprinting and biochar aging are outlined as new modification methods, influencing factors of biochar and modified biochar in adsorption of antibiotics and ARGs and adsorption mechanisms, wherein adsorption mechanism of ARGs on biochar is found to be different than that of antibiotics. After that, the directions of biochar and modified biochar worthy of research and the issues that need attention are proposed. It can be noted that under the current dual carbon policy, biochar may have wider application prospects in future.

Fe-Al bimetallic oxides functionalized-biochar via ball milling for enhanced adsorption of tetracycline in water

The clusters formed by modified materials on its surface makes the application of functionalized biochars in adsorption face a great challenge. Here, a facile ball milling technology was innovatively proposed to tailor Fe-Al oxides-laden bagasse biochar to fabricate a novel adsorbent (BMFA-BC). Benefited from the increased exposure of Fe-Al oxides and, more importantly, enhanced functional groups by ball milling, the adsorption capacity of BMFA-BC for aqueous tetracycline reached up to 116.6 mg g^-1 at 298 K. And the adsorption performance was temperature-dependent. Characterization analysis, batch sorption (thermodynamics, kinetics, isotherms, chemical factors) as well as data modeling illustrated that this superior adsorption ability could be attributed to π-π conjugation, H-bonding, complexation as well as pore filling. BMFA-BC displayed good adsorption capacity in multiple aqueous environments. The excellent regeneration ability, magnetic susceptibility ensured its viability for sustainable pollutants removal. These superiorities revealed that BMFA-BC was a suitable sorbent for antibiotics elimination.

Ecotoxicological characteristics and properties of zinc-modified biochar produced by different methods

Despite the dynamic progress of BC engineering, there is a lack of knowledge on the toxicity and environmental impact of modified BC. The aim of this study was the ecotoxicological evaluation of BC modified with zinc (Zn) using different methods: impregnation of feedstock with Zn before pyrolysis (PR), impregnation with Zn after pyrolysis (PS) and impregnation with Zn after pyrolysis with an additional calcination step (PST). The ecotoxicological assessment was based on tests with invertebrates (Folsomia candida, Daphnia magna) and bacteria (Aliivibrio fischeri). The post-treated and calcined composites had a higher content of total (C_tot) PAHs (144-276 μg kg^-1) than pre-treated BC-Zn (68-157 μg kg^-1). All BC-Zn treatments stimulated the reproduction of F. candida at the lowest BC dose (0.5%) by 4-24%. Increasing the biochar dose to 1% and 3% retained the stimulating effect of the pre-modified biochars (from 19 to 41%). Pre-modified BC-Zn reduced the luminescence of A. fischeri from 40% to 80%. Post-treated BCs reduced bacterial luminescence by 99%, but the calcination step limited the toxic effects to the level observed for the control. Post-treated BCs had a toxic effect on D. magna, with EC50 values ranging from 433 to 783 mg L^-1. The ecotoxicity of composites depends on modification methods, BC dose and pyrolysis temperature. The application of limiting conditions for HM leaching (i.e., pre-modification, calcination) increased the safety of using Zn-biochar composites.

Properties and mechanism of Cr(VI) removal by a ZnCl2-modified sugarcane bagasse biochar-supported nanoscale iron sulfide composite

A ZnCl₂-modified biochar-supported nanoscale iron sulfide composite (FeS-ZnBC) was successfully prepared to address the easy oxidization of FeS and enhance Cr(VI) removal from water. The material was characterized by SEM, XRD, FTIR, and XPS. The effects of FeS:ZnBC mass ratio, FeS-ZnBC dosage, solution pH, initial Cr(VI) concentration, and reaction time on the adsorption performance were investigated. The results revealed that the optimum adsorption capacity of FeS-ZnBC (FeS:ZnBC = 1:2) for Cr(VI) was 264.03 mg/g at 298 K (pH = 2). A Box-Behnken design (BBD) was applied to optimize the input variables that affected the adsorption of Cr(VI) solution. The results revealed that the highest removal (99.52%) of Cr(VI) solution was achieved with a Cr(VI) initial concentration of 150.59 mg/L, FeS-ZnBC adsorbent dosage of 2 g/L, and solution pH of 2. The sorption kinetics could be interpreted using a pseudo-second-order kinetic model. The isotherms were simulated using the Redlich-Peterson isotherm model, indicating that Cr(VI) removal by the FeS-ZnBC composites was a hybrid chemical reaction-sorption process. The main mechanisms of Cr(VI) removal by FeS-ZnBC were adsorption, chemical reduction, and complexation. This study demonstrated that FeS-ZnBC has potential application prospects in Cr(VI) removal.

Enhanced adsorption capacity of tetracycline on porous graphitic biochar with an ultra-large surface area†

Excessive tetracycline in the water environment may lead to the harming of human and ecosystem health. Removing tetracycline antibiotics from aqueous solution is currently a most urgent issue. Porous graphitic biochar with an ultra-large surface area was successfully prepared by a one-step method. The effects of activation temperature, activation time, and activator dosage on the structural changes of biochar were investigated by scanning electron microscopy, Brunauer–Emmett–Teller, X-ray powder diffraction, and Raman spectroscopy. The effect of the structure change, adsorption time, temperature, initial pH, and co-existing ions on the tetracycline removal efficiency was also investigated. The results show that temperature had the most potent effect on the specific surface area, pore structure, and extent of graphitization. The ultra-large surface area and pore structure of biochar are critical to the removal of tetracycline. The q_e of porous graphitic biochar could reach 1122.2 mg g⁻¹ at room temperature. The calculations of density functional theory indicate that π–π stacking interaction and p–π stacking interaction can enhance the tetracycline adsorption on the ultra-large surface area of graphitic biochar.

1. A ultra-large surface area of porous graphitic biochar was successfully using corn starch and ZnCl₂ by a one-step method. 2. The adsorption capacity of tetracycline on the biochar could get 1122.2 mg g⁻¹ at room temperature.

Selective adsorption of antibiotics on manganese oxide-loaded biochar and mechanism based on quantitative structure-property relationship model

In this study, MnCl₂-impregnated biomass was oxygen-limited pyrolyzed to produce manganese oxide-loaded biochar (MBC), its adsorption behaviors and influencing factors on tetracycline (TTC), norfloxacin (NOR), and sulfamethoxazole (SMX) were systematically investigated. Three antibiotics exhibited enhanced adsorption behavior on MBC, with maximum adsorption capacity as accurately described by Sips isotherm: TTC (534 mg/g) > NOR (67 mg/g) > SMX (28 mg/g). Hydrogen bonding, n/π-π interactions, electrostatic interaction, surface coordination, and hydrophobic interaction are the major mechanisms for the improved adsorption. Manganese oxide particles on MBC promoted surface coordination and hydrogen bonding. Antibiotic molecules with more hydroxyl oxygen-containing functional groups are more susceptible to migrate to biochar surfaces and to be adhered. Moreover, the quantitative structure-property relationship (QSPR) model was constructed and revealed that hydrogen bonding and π-π interactions were crucial for tetracycline antibiotics selective adsorption. Hence, MBC was a prospective adsorbent with promising applications for antibiotic removal in sewage processing.

Vitamin C modified crayfish shells biochar efficiently remove tetracycline from water: A good medicine for water restoration

In this study, crayfish shell biochar (CSB) was modified by introducing vitamin C (VC) with abundant surface functional groups. CSB was impregnated with VC at different ratios and its capacity to adsorb tetracycline (TC) from water was analyzed. The physicochemical properties of CSB were determined by N₂ adsorption-desorption isotherm analysis, X-ray diffraction, and Fourier transform infrared spectroscopy. The effects of various factors on adsorption such as the pH, TC concentration, time, and salt ion concentrations were also investigated. Based on the chemical structure of VC, VC can provide CSB with more oxygen-containing functional groups such as hydroxyl groups. The results showed that the CSB modified with VC (CSB-VC) exhibited excellent adsorption of TC, and CSB-VC₂ with an impregnation ratio of 2 (gVC/gCSB) had the greatest adsorption performance (saturated adsorption capacity, Q_m = 293.36 mg/g), whereas the adsorption performance of CSB alone was about 50% lower (Q_m = 172.16 mg/g). The optimal impregnation ratio VC improved the adsorption performance of CSB after modification to 70.4% of the original. Hydrogen bonding, p-p conjugation, pi-pi electron donor-acceptor effect, and π-π interactions were identified as the main adsorption mechanisms. CSB-VC₂ was highly effective over a wide range of pH values and at high ion concentrations. Experiments demonstrated the effective regeneration of the adsorbent after multiple cycles, thereby indicating its excellent reusability. It should be noted that the adsorption capacity was good under different water quality conditions, and thus it should exhibit stable adsorption performance under complex water environment conditions.