Unveiling the correlation of Fe3O4 fractions upon the adsorption behavior of sulfamethoxazole on magnetic activated carbon

Influence of the iron-oxide mass fractions of magnetic powdered activated carbon on its hexavalent chromium adsorption performance in water

Magnetic powdered activated carbon (Mag-PAC) is an effective adsorbent to remove hexavalent chromium (Cr(VI)) from water and can be recovered for reuse. However, the tradeoff between the adsorption performance of Cr(VI) and magnetic properties of Mag-PAC remains unclear. Herein, we prepared a series of Mag-PAC adsorbents containing various iron-oxide mass fractions with FeSO4·7H2O as the precursor, using a facile wet-chemical precipitation route and conducted batch experiments to evaluate the Cr(VI) adsorption performance. Results revealed that Mag-PAC was functionalized by magnetic iron oxide comprising crystalline goethite and magnetite structures. Furthermore, its adsorption performance was highly dependent on pH and was most effective at an initial solution pH of 2. Both the sorption rate constant and Cr(VI) adsorption capacity were greatly influenced by magnetization, and they gradually decreased as the iron-oxide mass fraction increased. Among the prepared adsorbents, Mag-PAC-75 (∼32% wt iron) exhibited not only an excellent Cr(VI) adsorption performance (Langmuir adsorption capacity: 75.76 mg/g) but also effective magnetic properties (saturation magnetization: 9.66 emu/g). Coexisting anions had a negligible competitive effect on Cr(VI) removal by Mag-PAC-75 at an initial pH of 2, whereas the presence of tannic acid markedly improved the Cr(VI) elimination. The presence of trivalent chromium on the surface of Mag-PAC-75 confirmed via X-ray photoelectron spectroscopy indicated that some synergistic redox reactions may occur during the sorption process. After five regeneration cycles using NaOH, Mag-PAC-75 continued to exhibit a high Cr(VI) removal efficiency and magnetic stability. These findings indicate that optimizing the adsorption performance and magnetic properties is a key factor for realizing the practical application of Mag-PAC for Cr(VI) removal. Overall, Mag-PAC may have been a promising application prospect for Cr(VI) removal from water due to its high adsorption capacity and magnetic properties, coupled with its good reusability and magnetic stability after regeneration cycles.

Performance and mechanism of sulfadiazine and norfloxacin adsorption from aqueous solution by magnetic coconut shell biochar

In this study, magnetic coconut shell biochar loaded with spherical Fe3O4 and γ-Fe2O3 particles was successfully synthesized using a chemical coprecipitation method. The magnetic biochar exhibited a good magnetic separability and environmental security. The maximum sulfadiazine (SDZ) and norfloxacin (NOR) removal efficiencies were 94.8% and 92.3% at pH 4 and 25 °C with adsorbent dosage of 2.5 g/L, respectively. When antibiotic concentrations ranged from 5 to 50 mg/L, the theoretical maximum adsorption capacities of SDZ and NOR were 16.7 mg/g and 25.8 mg/g, respectively. The Langmuir isotherm and pseudo-second-order kinetic models could better describe the adsorption process of both antibiotics, implying the monolayer chemical adsorption. The thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. The ionic strength had no significant effect on the adsorption behavior of either antibiotic. Combined with BET, FTIR, and XPS results, the dominant mechanisms for SDZ and NOR adsorption were pore filling, π-π electron-donor-acceptor interaction, hydrogen bonds and surface complexation. Moreover, Lewis acid-base interaction also contributed to SDZ adsorption.

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.

A review on carbon-based biowaste and organic polymer materials for sustainable treatment of sulfonamides from pharmaceutical wastewater

Frequent detection of sulfonamides (SAs) pharmaceuticals in wastewater has necessitated the discovery of suitable technology for their sustainable remediation. Adsorption has been widely investigated due to its effectiveness, simplicity, and availability of various adsorbent materials from natural and artificial sources. This review highlighted the potentials of carbon-based adsorbents derived from agricultural wastes such as lignocellulose, biochar, activated carbon, carbon nanotubes graphene materials as well as organic polymers such as chitosan, molecularly imprinted polymers, metal, and covalent frameworks for SAs removal from wastewater. The promising features of these materials including higher porosity, rich carbon-content, robustness, good stability as well as ease of modification have been emphasized. Thus, the materials have demonstrated excellent performance towards the SAs removal, attributed to their porous nature that provided sufficient active sites for the adsorption of SAs molecules. The modification of physico-chemical features of the materials have been discussed as efficient means for enhancing their adsorption and reusable performance. The article also proposed various interactive mechanisms for the SAs adsorption. Lastly, the prospects and challenges have been highlighted to expand the knowledge gap on the application of the materials for the sustainable removal of the SAs.

Magnetic activated carbon from spent coffee grounds: iron-catalyzed CO2 activation mechanism and adsorption of antibiotic lomefloxacin from aqueous medium

The facile fabrication of low-cost adsorbents possessing high removal efficiency and convenient separation property is an urgent need for water treatment. Herein, magnetic activated carbon was synthesized from spent coffee grounds (SCG) by Fe-catalyzed CO2 activation at 800 °C for 90 min, and magnetization and pore formation were simultaneously achieved during heat treatment. The sample was characterized by N2 adsorption-desorption, XRD, VSM, SEM, and FTIR. Batch adsorption experiments were conducted using lomefloxacin (LMO) as the probing pollutant. Preparation mechanism was revealed by TG-FTIR and XRD. Experimental results showed that Fe3O4 derived from Fe species can be reduced to Fe by carbon at high temperatures, followed by subsequent reoxidation to Fe3O4 by CO2, and the redox cycle between Fe and Fe3O4 favored the formation of pores. The promotion effects of Fe species on CO2 activation can be quantitatively reflected by the yield of CO as the signature gaseous product, and the suitable activation temperate range was determined to be 675 to 985 °C. The BET surface area, total pore volume, and saturated magnetization value of the product were 586 m2 g-1, 0.327 cm3 g-1, and 11.59 emu g-1, respectively. The Langmuir model was applicable for the adsorption isotherm data for LMO with the maximum adsorption capacity of 95 mg g-1, and thermodynamic analysis revealed that the adsorption process was endothermic and spontaneous. This study demonstrated that Fe-catalyzed CO2 activation was an effective method of converting SCG into magnetic separable adsorbent for LMO removal from aqueous medium.

Three-dimensional graphene aerogel mitigated the toxic impact of chloramphenicol wastewater on microorganisms in an EGSB reactor

Anaerobic treatment of chloramphenicol wastewater holds significant promise due to its potential for bioenergy generation. However, the high concentration of organic matter and residual toxic substances in the wastewater severely inhibit the activity of microorganisms. In this study, a three-dimensional graphene aerogel (GA), as a conductive material with high specific surface area (114.942 m2 g-1) and pore volume (0.352 cm3 g-1), was synthesized and its role in the efficiency and related mechanism for EGSB reactor to treat chloramphenicol wastewater was verified. The results indicated that synergy effects of GA for Chemical Oxygen Demand (COD) removal (increased by 8.17 %), chloramphenicol (CAP) removal (increased by 4.43 %) and methane production (increased by 70.29 %). Furthermore, GA increased the average particle size of anaerobic granular sludge (AGS) and promoted AGS to secrete more redox active substances. Microbial community analysis revealed that GA increased the relative abundance of functional bacteria and archaea, specifically Syntrophomonas, Geobacter, Methanothrix, and Methanolinea. These microbial species can participate in direct interspecific electron transfer (DIET). This research serves as a theoretical foundation for the application of GA in mitigating the toxic impact of refractory organic substances, such as antibiotics, on microorganisms during anaerobic treatment processes.

Evaluating the stability and performance of a novel core-shell ZVI@C-montmorillonite particle for anaerobic treatment of chloramphenicol wastewater

ZVI@C-MP is a novel composite particle consisting of zero-valent iron (ZVI) enclosed within a carbon shell. The purpose of this composite material is to enhance the anaerobic treatment of wastewater containing chloramphenicol (CAP). This approach aims to address the initial challenge of excessive corrosion experienced by ZVI, followed by its subsequent passivation and inactivation. ZVI@C-MP was synthesized through a hydrothermal process and calcination, with montmorillonite as binder, it exhibits stability, iron-carbon microelectrolysis (ICME) properties, and strong adsorption for CAP. Its ICME actions include releasing iron ions (0.70 mg/L) and COD (11.3 mg/L), generating hydrogen (3.82%), and raising the pH from 6.30 to 7.71. With minimal structural changes, it achieved release equilibrium. ZVI@C-MP boasts high removal efficiency of CAP (98.96%) by adsorption, attributed to surface characteristics (surface area: 167.985 m2/g; pore volume: 0.248 cm3/g). The addition of ZVI@C-MP increases COD removal (10.16%), methane production (72.86%), and reduces extracellular polymeric substances (EPS) from 70.58 to 52.72 mg/g MLVSS. It reduces microbial by-products and toxic effects, enhancing CAP biodegradation and microbial metabolic activity. ZVI@C-MP's electrical conductivity and biocompatibility bolster functional flora for interspecies electron transfer. It's a novel approach to antibiotic wastewater treatment.

Efficient photocatalytic degradation of ciprofloxacin by graphite felt-supported MnS/Polypyrrole composite: Dominant reactive species and reaction mechanisms

The accumulation of antibiotics in aquatic environments poses a serious threat to human health. Photocatalytic degradation is a promising method for removing antibiotics from water, but its practical implementation requires improvements in photocatalyst activity and recovery. Here, a novel graphite felt-supported MnS/Polypyrrole composite (MnS/PPy/GF) was constructed to achieve effective adsorption of antibiotics, stable loading of photocatalyst, and rapid separation of spatial charge. Systematic characterization of composition, structure and photoelectric properties indicated the efficient light absorption, charge separation and migration of the MnS/PPy/GF, which achieved 86.2% removal of antibiotic ciprofloxacin (CFX), higher than that of MnS/GF (73.7%) and PPy/GF (34.8%). The charge transfer-generated 1O2, energy transfer-generated 1O2, and photogenerated h+ were identified as the dominant reactive species, which mainly attacked the piperazine ring in the photodegradation of CFX by MnS/PPy/GF. The •OH was confirmed to participate in the defluorination of CFX via hydroxylation substitution. The MnS/PPy/GF-based photocatalytic process could ultimately achieve the mineralization of CFX. The facile recyclability, robust stability, and excellent adaptability to actual aquatic environments further confirmed MnS/PPy/GF is a promising eco-friendly photocatalyst for antibiotic pollution control.

3D porous carbon-embedded nZVI@Fe2O3 nanoarchitectures enable prominent performance and recyclability in antibiotic removal

Overcoming the instability and poor recyclability during the practical applications of contaminant scavengers is a challenging topic. Herein, a three-dimensional (3D) interconnected carbon aerogel (nZVI@Fe₂O₃/PC) embedding a core-shell nanostructure of nZVI@Fe₂O₃ was elaborately designed and fabricated via an in-situ self-assembly process. The porous carbon with 3D network architecture exhibits strong adsorption towards various antibiotic contaminants in water, where the stably embedded nZVI@Fe₂O₃ nanoparticles not only serve as magnetic seeds for recycling, but also avoid the shedding and oxidation of nZVI in the adsorption process. As a result, nZVI@Fe₂O₃/PC efficiently captures sulfamethoxazole (SMX), sulfamethazine (SMZ), ciprofloxacin (CIP), tetracycline (TC) and other antibiotics in water. In particular, an excellent adsorptive removal capacity of 329 mg g^-1 and a rapid capture kinetics (99% of removal efficiency in 10 min) under a wide pH adaptability (2-8) are achieved using nZVI@Fe₂O₃/PC as an SMX scavenger. nZVI@Fe₂O₃/PC displays exceptional long-term stability given that it shows excellent magnetic property after it is stored in water solution for 60 d, making it an ideal stable scavenger for contaminants in an etching-resistant and efficient manner. This work would also provide a general strategy to develop other stable iron-based functional architectures for efficient catalytic degradation, energy conversion and biomedicine.

Self-activation of potassium/iron citrate-assisted production of porous carbon/porous biochar composites from macroalgae for high-performance sorption of sulfamethoxazole

Excellent biochar properties are crucial for sorption performance, and a developed pore structure is especially important. Herein, novel porous carbon/porous biochar (PC/PB) composites, in which the porous biochar and porous carbon were prepared at the same time, were synthesized via a green method from algal biomass with the help of the self-activation of citrate for the first time, and the composites were evaluated for the sorption of sulfamethoxazole (SMX). Many micro/meso/macropores were introduced into the PC/PB composites, which showed high specific surface areas (up to 1415 m²/g) and pore volumes (up to 1.08 cm³ g^-1). The PC/PB composites displayed excellent SMX sorption capacities, which reached 844 mg g^-1. Pore filling played a crucial role in determining the sorption capacity, and hydrogen bonding, electrostatic interactions and π-π stacking controlled the sorption rate. This study provides an improved method for preparation of porous biochar.

Green synthesis of Ag2O nanoparticles using Punica granatum leaf extract for sulfamethoxazole antibiotic adsorption: characterization, experimental study, modeling, and DFT calculation

Silver oxide (Ag₂O) nanoparticles (NPs) were generated by synthesizing green leaf extract of Punica granatum, and afterwards they were used as adsorbent to remove the antibiotic additive sulfamethoxazole (SMX) from aqueous solutions. Prior of their use as adsorbent, the Ag₂O NPs were characterized by various methods such as X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), scanning electron microscopy/energy-dispersive X-ray (SEM-EDX), and transmission electron microscopy (TEM). The Ag₂O NPs were found to be spherically shaped and stabilized by the constituents of the extract. Further, at SMX antibiotic concentration of 100 mg L^-1, the Ag₂O NPs achieved almost complete removal of 98.93% within 90 min, and by using 0.8 g L^-1 of adsorbent dose at pH=4 and temperature T=308 K. In addition, the experimental data were well fitted with the theoretical Langmuir model indicating homogeneous adsorbed layer of the SMX antibiotic on the Ag₂O NPs surface. The maximum uptake capacity was 277.85 mg g^-1. A good agreement was also found between the kinetic adsorption data and the theoretical pseudo-second-order model. Regarding the thermodynamic adsorption aspects, the data revealed an endothermic nature and confirmed the feasibility and the spontaneity of the adsorption reaction. Furthermore, the regeneration study has shown that the Ag₂O NPs could be efficiently reused for up to five cycles. The geometric structures have been optimized and quantum chemical parameters were calculated for the SMX unprotonated (SMX^+/-) and protonated (SMX⁺) using density functional theory (DFT) calculation. The DFT results indicated that the unprotonated SMX^+/- reacts more favorably on the Ag₂O surface, as compared to the protonated SMX⁺. The SMX binding mechanism was predominantly controlled by the electrostatic attraction, hydrogen bond, hydrophobic, and π-π interactions. The overall data suggest that the Ag₂O NPs have promising potential for antibiotic removal from wastewater.

Efficient Gold Recovery from Cyanide Solution Using Magnetic Activated Carbon

Activated carbon has been used for gold recovery in the gold mining industry commercially for decades. The high specific surface area and porosity, good affinity to aurocyanide ions, and abundant resources make activated carbon an efficient and economical material for the adsorption of aurocyanide. However, the separation of activated carbon from the slurry is usually a challenge, and the adsorption rate of activated carbon is limited by the coarse particle size. Herein, a simple and sustainable way to recover gold from cyanide solution using magnetic activated carbon synthesized via a solvothermal method has been developed. The synthesized magnetic activated carbon possesses good magnetism (44.57 emu/g) and specific surface area equal to 249.7 m²/g. The magnetic activated carbon showed 99.1% recovery efficiency of gold from 10 mg/L solution within 5 h, which is much faster compared to the commercial granular activated carbon, and the magnetic activated carbon can be easily separated from the solution with an external magnet. The adsorption ability of this magnetic activated carbon has been tested under different conditions in the cyanide solution, the adsorption isotherm and kinetics are also investigated. The magnetic activated carbon was also recycled in the adsorption-desorption tests and showed good reusability.

Effect of Na2CO3, HF, and CO2 Treatment on the Regeneration of Exhausted Activated Carbon Used in Sintering Flue Gas

The method of continuous treatment with Na₂CO₃ solution, HF solution, and CO₂ was proposed for the regeneration of the exhausted activated carbon (EAC) produced in the sintering flue gas purification process. In order to obtain the optimal operation conditions, the effect of key parameters such as Na₂CO₃ solution concentration, HF solution concentration, and CO₂ activation temperature on the sulfur conversion rate and regeneration efficiency was analyzed. Also, the N₂ adsorption, Brunauer-Emmett-Teller analysis, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, X-ray fluorescence, and Fourier transform infrared spectroscopy were adopted to investigate the deactivation reason and the change of the physical-chemical properties. The results showed that the deactivated EAC was mainly due to the deposition of inorganic compounds such as CaSO₄, SiO₂, and KCl to block the pores. Continuous treatment with Na₂CO₃ solution and HF solution could remove the inorganic compounds effectively. CO₂ activation treatment further developed the blocked porosity and decreased the surface acidity. The optimal conditions for the regeneration of EAC were a Na₂CO₃ concentration of 0.5 mol/L, an HF concentration of 0.8 mol/L, and a CO₂ activation temperature of 1073 K with the activation time of 1 h, corresponding to the specific surface area of 607.91m²/g. In the fourth regeneration cycle, the adsorption performance during the successive adsorption-regeneration process could still maintain a high level and the regeneration efficiency was 95.31%.

Porous carbon aerogel derived from bacterial cellulose with prominent potential for efficient removal of antibiotics from the aquatic matrix

The development of adsorption methods for the remediation of antibiotics pollution in water is hindered by the lack of high-performance sorbents. In this study, a nanofiber carbon aerogel was prepared using bacterial cellulose and its adsorption performances for three common antibiotics (norfloxacin, sulfamethoxazole, and chloramphenicol) in water were evaluated. The as-prepared nanofiber carbon aerogel showed a higher adsorption capacity toward target antibiotics compared to other adsorbents reported in the literature. The maximum adsorption capacities for norfloxacin, sulfamethoxazole, and chloramphenicol were 1,926, 1,264, and 525 mg/g, respectively at 298 K. Notably, the nanofiber carbon aerogel was able to adsorb 80% of the equilibrium adsorption capacity within 1 min and reach equilibrium within 15 min. After five regeneration cycles, the adsorption capacity still reached 1,166, 847, and 428 mg/g for norfloxacin, sulfamethoxazole, and chloramphenicol, respectively. The characterization results showed that the carbon aerogel exhibited a high specific surface area (1,505 m²/g) and a layered porous network structure. Furthermore, the mechanistic study reveals that the enhanced antibiotic adsorption by the as-prepared nanofiber carbon aerogel was attributed to the pore filling effect, hydrogen bonding, hydrophobic effect, electrostatic interaction, and π-π interactions. Overall, these results imply that low-cost and green nanofiber carbon aerogels may be promising adsorbents for the remediation of antibiotic-contaminated wastewater. The materials prepared from natural and readily available bacterial cellulose can adsorb antibiotics efficiently, which provides a reference for the development of adsorbent materials using natural substances.

Preparation of sludge-based activated carbon for adsorption of dimethyl sulfide and dimethyl disulfide during sludge aerobic composting

Emission of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) during sludge aerobic composting has limited the use and development of this economical sludge treatment process. In this study, cheap and easily available sludge was used as raw material for the preparation of adsorbents to eliminate DMS and DMDS. A series of sludge-based activated carbons (SACs) were prepared by acid or base activation, and coconut shell mix was also assessed. The results revealed that SAC preparation by KOH activation without coconut shell mix could significantly enhance the surface area and pore volume of SAC, and showed the maximum adsorption capacity for DMS (53.45 mg g^-1) and DMDS (151.28 mg g^-1). In addition, SAC had a good adsorption effect on a mixture of DMS and DMDS. The SAC adsorbents could efficiently adsorb DMS and DMDS after four cycles of regeneration. Thermodynamic and kinetic analyses demonstrated that adsorption between the SAC and DMS/DMDS was via physical adsorption. The SAC developed in this study utilized waste in a useful way that could significantly reduce the cost of adsorbents and use them for odor elimination during sludge aerobic composting.