Removal of organic compounds by nanoscale zero-valent iron and its composites

MXenes as emerging nanomaterials in water purification and environmental remediation

Environmental pollution has accelerated and intensified because of the acceleration of industrialization, therefore fabricating excellent materials to remove hazardous pollutants has become inevitable. MXenes as emerging transition metal nitrides, carbides or carbonitrides with high conductivity, hydrophilicity, excellent structural stability, and versatile surface chemistry, become ideal candidates for water purification and environmental remediation. Particularly, MXenes reveal excellent sorption capability and efficient reduction performance for various contaminants of wastewater. In this regard, a comprehensive understanding of the removal behaviors of MXene-based nanomaterials is necessary to explain how they remove various pollutants in water. The eliminate process of MXene-based nanomaterials is collectively influenced by the physicochemical properties of the materials themselves and the chemical properties of different contaminants. Therefore, in this review paper, the synthesis strategies and properties of MXene-based nanomaterials are briefly introduced. Then, the chemical properties, removal behaviors and interaction mechanisms of heavy metal ions, radionuclides, and organic pollutants by MXene-based nanomaterials are highlighted. The overview also emphasizes associated toxicity, secondary contamination, the challenges, and prospects of the MXene-based nanomaterials in the applications of water treatment. This review can supply valuable ideas for fabricating versatile MXene nanomaterials in eliminating water pollution.

Zein adsorbents with micro/nanofibrous membrane structure for removal of oils, organic dyes, and heavy metal ions in aqueous solution

Developing multi-functional media for effectively removing different contaminants coexisted in wastewater system is highly desired. Herein, zein, a natural protein possessing abundant functional groups in molecule, is chosen to be fabricated into micro/nanofibrous membranes as adsorbents and separation media. Zein fibers with novel groove ribbon structures, which possess better structural characteristics, are designed for obtaining good adsorption performance. The adsorption performances of zein fiber membranes are evaluated. The results show that zein fiber membranes have the adsorption capacities up to 94 g/g for motor oil, 168 mg/g for Congo red, and 189 mg/g for Pb²⁺ ion for 1000 mg/L initial solution concentration, showing considerable competitiveness as compared with the reported adsorbents. The zein membrane with groove ribbon fiber morphology exhibits optimal adsorption capability and can be attractive multi-functional separation media.

Synthesis of carbon-based nanomaterials and their application in pollution management

With the fast development of industry, large amounts of organic and inorganic pollutants are inevitably released into the natural environment, which results in the pollution of the environment and are thereby dangerous to human health. The efficient elimination of these pollutants is crucial to environment protection and human health. The high sorption capacity of carbon-based materials and high photocatalytic ability of carbon-based composites result in the application of carbon-based materials in environmental pollution cleanup. In this review article, we summarized recent studies on the synthesis of carbon-based materials, and their application in the sorption of organic and inorganic pollutants, the photocatalytic degradation of organic pollutants, and the in situ photocatalytic reduction-solidification of heavy metal ions. The sorption method is useful to remove pollutants from aqueous solutions. The sorption-photocatalytic degradation of organic pollutants is applicable, especially at low concentrations, whereas the catalytic reduction of metal ions is the best method for the in situ immobilization of high valent metal ions under complicated conditions. The interaction mechanism is discussed using advanced spectroscopy analysis and theoretical calculations, and at the end the challenges in the future are described.

Enhanced antibiotic degradation and hydrogen production of deacetoxycephalosporin C fermentation residue by gamma radiation coupled with nano zero-valent iron

Antibiotic fermentation residue (AFR) has been categorized as hazardous waste in China. Anaerobic biohydrogen fermentation may be a promising technology for handling AFR, which could achieve dual goals of waste treatment and clean energy production at the same time. However, the low hydrogen yield and low removal efficiency of residual antibiotics are two major factors limiting the AFR biohydrogen fermentation process. This work firstly applied gamma radiation (50 kGy) to remove the residual antibiotic in AFR and improve the bioavailability of organic matters, then adding nano zero-valent iron (nZVI) (100-1000 mg/L) to further enhance the AFR biohydrogen fermentation performance. Results showed that residual deacetoxycephalosporin C in AFR was removed with a high efficiency of 98.6%, and hydrogen yield achieved 20.45 mL/g-VS_added with the combined approach of gamma radiation pretreatment and 500 mg/L nZVI addition, which was 139.2% higher compared to the control experimental result. The combined approach also promoted the biohydrogen production rate, decreased the lag phase of hydrogen production, and increased the organics utilization. Microbiological analysis revealed that highly efficient hydrogen-producing genera Clostridium sensu stricto were enriched in much higher abundance with the combined approach, which might be the fundamental mechanism for the enhanced AFR fermentation performance.

A novel scheme for the utilization of Cu slag flotation tailings in preparing internal electrolysis materials to degrade printing and dyeing wastewater

About 60 million tons of Fe-rich Cu slag (IRCS) are generated annually worldwide during Cu slag flotation and cause irreversible water and soil pollution. Current research provides an environmentally friendly technology, the preparation of internal electrolysis materials (IEMs) through the carbothermal reduction of IRCS, for the degradation of printing and dyeing wastewater. XRD and SEM-EDS indicated that carbothermal reduction could promote the conversion of fayalite to zero-valent iron (ZVI), and ZVI could effectively form IEM with residual carbon. The degradation capacity of IEM for methylene blue (MB) was remarkably improved compared with raw IRCS after roasting for 60 min at 1100 °C with 35% anthracite dosage. MB degradation efficiency improved by increasing the IEM dosage and reaction temperature and decreasing the MB concentration and solution pH. FTIR, XRD, SEM-EDS, and XPS all detected the formation of Fe oxide or Fe hydroxide. UV-vis and TOC demonstrated that the characteristic groups of MB were destroyed and resulted in the mineralization of MB. MB degradation could be attributed to the Fe²⁺, [H], and ·OH produced by the galvanic reaction induced by IEM. Overall, this study offers theoretical guidance in the treatment of printing and dyeing wastewater and the reuse of IRCS.

Conductive-polymer-supported palladium-iron bimetallic nanocatalyst for simultaneous 4-chlorophenol and Cr(VI) removal: Enhanced interfacial electron transfer and mechanism

Nanoscale zerovalent iron (nZVI) reduction offers a wide range of applications in source-zone remediation, but the reactivity of nZVI is largely hampered due to its low electron-transfer ability and tendency to aggregate. Based on the dual function of conductive polymers (CPs) as support and electron transfer carrier, we combined CPs with nZVI and prepared a series of Pd/Fe bimetallic materials that successfully address the challenges of nZVI reduction. These Pd/Fe@CPs particles showed strong catalytic ability for the simultaneous removal of 4-chlorophenol (4-CP) and Cr(VI). The removal rate of 4-CP was significantly enhanced by 1.5-6.2 times after supporting Pd/Fe nanoparticles (NPs) with CPs. The enhanced reactivity of supported Pd/Fe NPs was attributed to their highly stabilized and dispersed state and the promoted electron transfer due to the synergistic effect between CPs and nZVI bimetallic particles. The various catalytic activity over Pd/Fe@CPs was attributed to the distinctive properties of CPs and their different interfacial electron transfer ability. Importantly, this study provides insights into distinguishing both mechanisms of direct electron transfer and atomic-hydrogen-mediated indirect electron transfer, and their quantitative relationship to the dehalogenation performance over Pd/Fe@CPs materials. This work provides better understanding of the remediation process and mechanisms of nZVI reduction.

Surface plasmon resonance allied applications of silver nanoflowers synthesized from Breynia vitis-idaea leaf extract

An environmentally friendly, green synthesis process has been adopted to synthesize silver nanoparticles (AgNPs) in an aqueous solution from a new remedial plant. Breynia vitis-idaea leaves act like natural capping and reducing agents. The resulting AgNPs were characterized and analyzed using different characterization techniques, such as UV-Vis spectroscopy, X-ray diffraction, zeta potential, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The UV-Vis absorption spectrum showed high stability and a surface plasmon resonance (SPR) peak around 430 nm. The effects of several processing variables, such as reaction time, temperature, concentration and pH, were analyzed. High temperature and alkaline pH intensify the ability to form flower-shaped AgNPs with enhanced properties. AgNPs were investigated for antibacterial activity against Gram-negative E. coli bacterial strains with a 10 mm zone of inhibition. These AgNPs showed dye degradation up to 88% when an aqueous crystal violet dye solution was mixed with AgNPs as the catalyst. Further, AgNPs alone were effectively used in the detection of hydrogen peroxide (H2O2) in an aqueous medium with a LOD (limit of detection) of 21 μM, limit of quantification (LOQ) of 64 μM and a decrease in absorption intensity up to 89%. Based on these results, these AgNPs were effectively used in numerous fields, such as biomedical, water purification, antibacterial and sensing of H2O2.

Three-dimension hierarchical composite via in-situ growth of Zn/Al layered double hydroxide plates onto polyaniline-wrapped carbon sphere for efficient naproxen removal

In this work, a novel adsorbent, 3D hierarchical CS@PANI@ZnAl-LDH composite, has been successfully fabricated through the hydrothermal synthesis of the carbon sphere, oxidative polymerization of polyaniline, and in-site growth of ZnAl-layered double hydroxides, simultaneously applied for the naproxen removal from aqueous solutions. The dynamics and isotherms fit better with the pseudo-second-order and Langmuir model, demonstrating the chemisorption, monolayer, and endothermic process. In addition, the high uptake capacities of CS@PANI@ZnAl-LDH for naproxen was 545.5 mg/g at 298 K when the pH was 5.0, outperforming most previously reported materials. Moreover, after five adsorption-desorption cycles, the spent CS@PANI@ZnAl-LDH maintains high removal efficiency and structural composition, revealing excellent recyclability and stability. Furthermore, Fourier transformed infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses indicate electrostatic interactions, π-π interactions, and hydrogen bonding between CS@APNI@ZnAl-LDH and naproxen. Quantitative analyses, Localized orbit locator (LOL)-π isosurface, and Independent Gradient Model further verify the adsorption mechanisms mentioned above, indicating the synergistic effects between PANI and ZnAl-LDH improve the elimination ability for naproxen. Significantly, Hirshfeld surface analyses reveal that naproxen behaves as the H-bond acceptor, and the ZnAl-LDH acts as the H-bond donor. This work provided a feasible way to design purification materials for wastewater treatment.

Understanding of the Dual Roles of Phosphorus in Atomically Distributed Fe/Co-N4P2 over Carbon Nitride for Photocatalytic Debromination from Tetrabromobisphenol A

Atomically dispersed Fe and Co on carbon nitride under an external phosphine (PH₃) atmosphere (P-Fe₁Co₁/CN) are prepared. Combined with the results of calculations and experiments, the formed P-induced bimetallic single atoms of Fe/Co-N₄P₂ can provide more reactive sites to enhance optical performance. Meanwhile, the introduced P can coordinate with Fe and Co and change the sole nitrogen coordination environment via the bridging effect. Herein, on the one hand, the structure of Fe-P-Co enhances interactions of single atoms in heterogeneous metals, and, on the other hand, the formed Fe/Co-N₄P₂ effectively changes the electron configuration in coordination centers. All of the abovementioned findings can enhance the photocatalytic performance of P-Fe₁Co₁/CN, achieving 96% removal and 51% debromination rates from tetrabromobisphenol A under visible light irradiation. The two efficiencies can be further improved under UV-vis light irradiation. The findings of this work reveal the dual roles of P in bimetallic single-atom catalysts, provide a facile method to synthesize P-assisted bimetal single-atom photocatalysts, and highlight the great potential of carbon nitride-based single atoms as photocatalysts.

Novel NbCo-MOF as an advanced peroxymonosulfate catalyst for organic pollutants removal: Growth, performance and mechanism study

Multivariate metal-organic frameworks (MTV-MOFs) are expected as catalyst to apply to the advanced oxidation processes (AOPs) based on sulfate radical (SO₄·^-) to treat wastewater containing organic pollutants. Mixing metals de novo method was combined with stringent solvothermal conditions to synthesize macaroon-like NbCo-MOF catalyst. NbCo-MOF catalyst prepared with different atom ratios and growth time presented various morphology, structure, performance, and distinctive MTV-MOFs growth law which were confirmed by SEM, TEM, EDS, XRD, FTIR, raman spectra and UV-vis spectra. Besides, optimum peroxymonosulfate (PMS) catalytic activation conditions were studied. Furthermore, the effects of anions (Cl^-, NO₃^-, HCO₃^-, and C₂O₄^2-) on NbCo-MOF catalytic activation were explored which were proved very limited. Particularly, the Co²⁺/Co³⁺ cycle combining with the Nb⁴⁺/Nb⁵⁺ cycle for PMS activation were verified by XPS. EPR and quenching experiment results indicated exists non-radical pathway (¹O₂), but radical pathways are dominant (SO₄·^- O₂·^-, and ·OH). Moreover, the TC removal rate exhibited no significant reduce after three times run. Furthermore, NbCo-MOF exhibited excellent decomposing ability towards methylene blue, tylosin tartrate, rhodamine B, and tetracycline with the removal rate reaching to 100%, 98.4%, 99.7%, and 99.7% in 30 min respectively and also maintained good performance in actual water environment.

Enrichment of Methylocystis dominant mixed culture from rice field for PHB production

Presence of methanotrophs in diverse environmental habitats helps to reduce emissions of greenhouse gas like methane. Isolation and culture of undiscovered wealth of methanotrophic organisms can help in exploitation of these organisms in value added products. The present study focuses on the enrichment of methanotroph dominated mixed microbial community by use of three stage strategy of revival, proliferation, and segregation. During the enrichment process amplicon sequencing of 16 s rRNA V3-V4 region showed relative abundance of mixed culture comprising single methanotrophic species of Methylocystis genus (88.92%) along with only three other species. Methylocystis dominant mixed culture (MMI-11) was observed to produce polyhydroxyalkanoates (PHA). During studies to identify favourable culture conditions, nitrate was found to be preferred nitrogen source for growth and PHA production. Cell growth ability to produce PHA was also evaluated at 14 L fermentor by supplying gas using continuous bubbling and through pressurization in the headspace. The mixed methanotrophic culture was found to accumulate maximum of 22.20% polyhydroxybutyrate (PHB) under nitrate limited condition. The molecular weight of PHB was found to be 2.221 × 10⁵ g mol^-1 with polydispersity of 1.82.

Multi-parameter optimization maximizes the performance of genetically engineered Geobacillus for degradation of high-concentration nitroalkanes in wastewater

Nitroalkanes are important toxic pollutants for which there is no effective removal method at present. Although genetic engineering bacteria have been developed as a promising bioremediation strategy for years, their actual performance is far lower than expected. In this study, important factors affecting the application of engineered Geobacillus for nitroalkanes degradation were comprehensively optimized. The deep-reconstructed engineered strains significantly raised the expression and activity level of catalytic enzymes, but failed to fully enhance the degradation efficiency. However, further debugging of a variety of key parameters effectively improved the performance of the engineering strains. The increased cell membrane permeability, trace supplementation of vital nutritional factors, synergy of multifunctional enzyme engineered bacteria, switch of oxygen-supply mode, and moderate initial biomass all effectively boosted the degradation efficiency. Finally, a low-cost and highly effective bioreactor test for high-concentration nitroalkanes degradation proved the multi-parameter optimization mode helps to maximize the performance of genetically engineered bacteria.

Bioremediation of trichloroethylene-polluted groundwater using emulsified castor oil for slow carbon release and acidification control

In this study, the emulsified castor oil (ECO) substrate was developed for a long-term supplement of biodegradable carbon with pH buffering capacity to anaerobically bioremediate trichloroethylene (TCE)-polluted groundwater. The ECO was produced by mixing castor oil, surfactants (sapindales and soya lecithin [SL]), vitamin complex, and a citrate/sodium phosphate dibasic buffer system together for slow carbon release. Results of the emulsification experiments and microcosm tests indicate that ECO emulsion had uniform small droplets (diameter = 539 nm) with stable oil-in-water characteristics. ECO had a long-lasting, dispersive, negative zeta potential (-13 mv), and biodegradable properties (viscosity = 357 cp). Approximately 97% of TCE could be removed with ECO supplement after a 95-day operational period without the accumulation of TCE dechlorination byproducts (dichloroethylene and vinyl chloride). The buffer system could neutralize acidified groundwater, and citrate could be served as a primary substrate. ECO addition caused an abrupt TCE adsorption at the initial stage and the subsequent removal of adsorbed TCE. Results from the next generation sequences and real-time polymerase chain reaction (PCR) indicate that the increased microbial communities and TCE-degrading bacterial consortia were observed after ECO addition. ECO could be used as a pH-control and carbon substrate to enhance anaerobic TCE biodegradation effectively. PRACTITIONER POINTS: Emulsified castor oil (ECO) contains castor oil, surfactants, and buffer for a slow carbon release and pH control. ECO can be a long-term carbon source for trichloroethylene (TCE) dechlorination without causing acidification. TCE removal after ECO addition is due to adsorption and reductive dechlorination mechanisms.

High removal efficiency of industrial toxic compounds through stable catalytic reactivity in water treatment system

We identified optimal conditions for the disposal of high concentration of organic contaminants within a short time using a hybrid advanced oxidation process (AOP) combining various oxidizing agents. Plasma-treated water (PTW) containing many active species, that play dominant roles in the degradation of organic substances like hydroxyl radicals, atomic oxygen, ozone, and hydrogen peroxide, was used in this study as a strategy to improve degradation performance without the use of expensive chemical reagents like hydrogen peroxide. In particular, the optimal decomposition conditions using PTW, which were combined with 10 mg/h ozone, 2 g/L iron oxide, and 4 W UV light, demonstrated excellent removal abilities of a high concentration of reactive black 5 (RB5; 100 mg/L, >99%, [k] = 4.15 h^-1) and tetracycline (TC; 10 mg/L, >96.5%, [k] = 3.35 h^-1) for 25 min, approximately 1.5 times higher than that without PTW (RB5; 100 mg/L, 94%, [k] = 2.80 h^-1). These results confirmed that the production of strong reactive hydroxyl radicals from the decomposition process, as well as various reactive species included in PTW efficiently attacked pollutant substances, resulting in a higher removal rate. This suggests that a water treatment system with this optimal condition based on complex AOP systems using PTW could be useful in critical environmental and biomedical applications.

Applications of water-stable metal-organic frameworks in the removal of water pollutants: A review

Because the pollutants produced by human activities have destroyed the ecological balance of natural water environment, and caused severe impact on human life safety and environmental security. Hence the task of water environment restoration is imminent. Metal-organic frameworks (MOFs), structured from organic ligands and inorganic metal ions, are notable for their outstanding crystallinity, diverse structures, large surface areas, adsorption performance, and excellent component tunability. The water stability of MOFs is a key requisite for their possible actual applications in separation, catalysis, adsorption, and other water environment remediation areas because it is necessary to safeguard the integrity of the material structure during utilization. In this article, we comprehensively review state-of-the-art research progress on the promising potential of MOFs as excellent nanomaterials to remove contaminants from the water environment. Firstly, the fundamental characteristics and preparation methods of several typical water-stable MOFs include UiO, MIL, and ZIF are introduced. Then, the removal property and mechanism of heavy metal ions, radionuclide contaminants, drugs, and organic dyes by different MOFs were compared. Finally, the application prospect of MOFs in pollutant remediation prospected. In this review, the synthesis methods and application in water pollutant removal are explored, which provide ways toward the effective use of water-stable MOFs in materials design and environmental remediation.

Recent advances in metal-organic framework membranes for water treatment: A review

Among many separation membranes reported to date, the favorable polymer affinity and unique physio-chemical performances of metal-organic frameworks (MOFs) including ultra-high surface area, regular and highly controlled porosity have drawn widespread attention in industrial and academic communities. In this comprehensive review, the developmental timeline of MOF containing membranes for water treatment were clarified. The removal efficiencies, elimination mechanisms, as well as possible influencing factors of various MOF containing membranes that applied to water treatment were systematically summarized. The excellent removal performances of MOF containing membranes for various pollutants were determined by the size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding and so on. Since the progress of engineered MOF containing membranes for practical wastewater treatment applications lags, we further analyzed the potential environmental application of MOF containing membranes from four aspects (stability of MOFs, antifouling performance of membranes, compatibility between MOF fillers and polymer matrix, dispersity of MOF nanoparticles in matrix), hoping to provide some meaningful insights.

Fabrication and Characterization of Co-Doped Fe2O3 Spindles for the Enhanced Photo-Fenton Catalytic Degradation of Tetracycline

Co-doped Fe2O3 spindles with different Co contents were successfully fabricated by a facile one-step hydrothermal method. The crystalline structure, morphology, optical properties, and chemical state of the as-prepared catalysts before and after photo-Fenton reaction were characterized. Co2+ incorporated into the Fe2O3 lattice was confirmed by the above characterizations. Also, the photocatalytic and photo-Fenton catalytic performances of the samples were evaluated by the degradation of tetracycline (TC) under visible light irradiation in the absence/presence of H2O2. The results demonstrated that Co-doped Fe2O3 spindles exhibited better catalytic degradation performance in comparison with single Fe2O3 spindles, and the sample of Co(5%)-Fe2O3 spindles displayed the highest activity and best stability. The improvement of photo-Fenton activity might be attributed to two reasons: On the one hand, Co-doped Fe2O3 spindles not only formed the Fe vacancies to reduce the band gap but also could build up an internal electric field, which inhibits electron/hole pair recombination and facilitates the transfer of photoexcited charge carriers. On the other hand, the intrinsic Co2+/Co3+ redox cycling can accelerate the circulation between Fe2+ and Fe3+ in Co(5%)-Fe2O3 spindles to facilitate H2O2 consumption and produce more ·OH radicals for TC degradation.

Mechanism of Oxytetracycline Removal by Coconut Shell Biochar Loaded with Nano-Zero-Valent Iron

In this paper, coconut shell biochar (BC), pickling biochar (HBC), and nano-zero-valent iron-loaded biochar (nZVI-HBC) were prepared; these were used to remove oxytetracycline (OTC), and the removal mechanism and degradation product were analyzed. These biochars were characterized using SEM, XRD, FTIR, and XPS. The effects of biochar addition amount, pH, ion type, and ion concentration on OTC adsorption were studied by a batch adsorption experiment. Under the optimal conditions, the equilibrium adsorption capacity of nZVI-HBC to OTC was 196.70 mg·g-1. The adsorption process can be described by Langmuir isothermal adsorption equations, conforming to the pseudo-second-order dynamics model, indicating that adsorption is dominated by single-molecule chemical adsorption, and a spontaneous process of increasing heat absorption entropy. Mass spectrometry showed that the OTC removal process of nZVI-HBC included not only adsorption but also degradation. These results provide a practical and potentially valuable material for the removal of OTC.

Study on the Adsorption Performance of Casein/Graphene Oxide Aerogel for Methylene Blue

Casein (CS) and graphene oxide (GO) were employed for the fabrication of a casein/graphene oxide (CS/GO) aerogel by vacuum freeze drying. Fourier transform infrared spectroscopy, scanning electron microscopy, surface area and micropore analysis (BET), and thermogravimetric analysis were used to characterize the specific surface area, structure, thermal stability, and morphology of the CS/GO aerogel. The influence of experimental parameters such as the GO mass fraction in the aerogel, metering of the adsorbent, pH, contact time, and temperature on the adsorption capacity of the CS/GO aerogel on methylene blue (MB) was also investigated. According to Langmuir isotherm determination, the maximum removal rate of MB from the CS/GO aerogel was 437.29 mg/g when the temperature was 293 K and pH was 8. Through kinetic and thermodynamic studies, it is found that adsorption follows a pseudo-second-order reaction model and is also an exothermic and spontaneous process.

Environmental risks and toxicity of surfactants: overview of analysis, assessment, and remediation techniques

This work comprehensively reviewed the toxicity and risks of various surfactants and their degraded products in the environmental matrices, various analytical procedures, and remediation methods for these surfactants. The findings revealed that the elevated concentration of surfactants and their degraded products disrupt microbial dynamics and their important biogeochemical processes, hinder plant-surviving processes and their ecological niche, and retard the human organic and systemic functionalities. The enormous adverse effects of surfactants on health and the environment necessitate the need to develop, select, and advance the various analytical and assessment techniques to achieve effective identification and quantification of several surfactants in different environmental matrices. Considering the presence of surfactants in trace concentration and environmental matrices, excellent analysis can only be achieved with appropriate extraction, purification, and preconcentration. Despite these pre-treatment procedures, the chromatographic technique is the preferred analytical technique considering its advancement and shortcomings of other techniques. In the literature, the choice or selection of remediation techniques for surfactants depends largely on eco-friendliness, cost-implications, energy requirements, regeneration potential, and generated sludge composition and volume. Hence, the applications of foam fractionation, electrochemical advanced oxidation processes, thermophilic aerobic membranes reactors, and advanced adsorbents are impressive in the clean-up of the surfactants in the environment. This article presents a compendium of knowledge on environmental toxicity and risks, analytical techniques, and remediation methods of surfactants as a guide for policymakers and researchers.

Preparation of Fe/Ni Bimetallic Oxide Porous Graphene Composite Materials for Efficient Adsorption and Removal of Sulfonamides

An iron-nickel bimetallic oxide porous graphene composite material (Fe/Ni-PG) was prepared by a simple partial combustion method, which can be used to effectively remove sulfonamides (SAs) from an aqueous solution. The adsorption performance of Fe/Ni-PG, Fe-PG, and Ni-PG on six kinds of SAs was compared, and the influence of time, temperature, pH, and initial concentration of SAs on the adsorption behavior of SAs of Fe/Ni-PG in an aqueous solution was studied. The adsorption kinetics and thermodynamics exhibited that the Langmuir model and pseudo-second-order kinetics model can describe the adsorption isotherm and kinetics. The maximum adsorption capacities of sulfadiazine (SD), sulfamerazine (SM), sulfamethazine (SDM), sulfathiazole (STZ), sulfapyridine (SPD), and sulfisoxazole (SIZ) calculated by the Langmuir model were 26.3, 50.3, 42.2, 27.3, 34.5, and 41.7 mg/g, respectively, which exceeded those of most reported adsorbents. In the adsorption process, hydrogen bonding, π-π electron donor-acceptor, electrostatic interaction, and bimetallic synergies play a major role, and the entire adsorption process is spontaneously endothermic. In addition, the material has excellent stability, and the Fe/Ni-PG after desorption is consistent with the raw material. This work provides a favorable way for the removal of SAs in the environment.

Enhanced refractory organics removal by sponge iron-coupled microbe technology: performance and underlying mechanism analysis

Sponge iron (SFe) is a zero-valent iron (Fe⁰) composite with a high-purity and porous structure. In this study, SFe was coupled with microorganisms that were gradually domesticated to form a Fe⁰/iron-oxidizing bacteria system (Fe⁰-FeOB system). The enhancement effect of the Fe⁰-FeOB system on refractory organics was verified, the mechanism of its strengthening action was investigated, and the relationship and influencing factors between the Fe⁰ and microorganisms were revealed. The average removal rates of the Fe⁰-FeOB system were 8.98%, 5.69%, and 40.67% higher than those of the SBR system for AF, AN, and NB wastewater treatment, respectively. With the addition of SFe, the microbial community structure was gradually enhanced with a large number of FeOB were detected. Moreover, the bacteria with strong iron corrosion and Fe(II) oxidation abilities plays a critical role in improving the Fenton-like effect. Interestingly, the variation trend of ⋅OH was fairly consistent with that of Fe(II). Thus, the main drivers of the Fenton-like effect are biological corrosion and metabolism. Consequently, microbial degradation and Fenton-like effect contributed to the degradation performance of the Fe⁰-FeOB system. Among them, the microbial degradation accounted for 96.09%, of which the biogenic Fenton effect accounted for 8.9%, and the microbial metabolic activity accounted for 87.19%. However, the augmentation of the Fe⁰-FeOB system was strongly dependent on SFe for the strengthening effect of microorganisms disappeared after leaving the SFe 35 days.

Encapsulation of iron nanoparticles with magnesium hydroxide shell for remarkable removal of ciprofloxacin from contaminated water

The rapid evolution of antimicrobial resistant genes (AMRs) in water resources is well correlated to the persistent occurrence of ciprofloxacin in water. For the first time, encapsulated nanoscale zerovalent iron (nZVI) with a shell of magnesium hydroxide (Mg/Fe⁰) was used to adsorb ciprofloxacin from water. Optimization of the removal conditions exhibited that 5% was the optimum mass ratio between magnesium hydroxide and nZVI [Mg(OH)₂/nZVI)] as more than 96% of 100 mg L^-1 of ciprofloxacin was removed. In addition, 0.5 g L^-1 of Mg/Fe⁰ showed an extraordinary performance in removing ciprofloxacin over a wide range of pH (3-11) with removal efficiencies exceeded 90%. Kinetic analysis displayed that the kinetic data was well described by both Pseudo first-order and second-order models. Also, the equilibrium data was well fitted by Freundlich isotherm model. In addition, thermodynamic analysis evidenced that the removal of ciprofloxacin by Mg/Fe⁰ was exothermic, and spontaneous. The experiments also revealed that physisorption and chemisorption were the responsible mechanisms for ciprofloxacin removal. The proposed treatment system remediated 10 litters of 100 mg L^-1 of ciprofloxacin solution with 100% overall removal efficiency. This treatment system could be a promising and practical solution to decrease ciprofloxacin concentration in different water bodies.