Simultaneous redox transformation and removal of Cr(Ⅵ) and As(Ⅲ) by polyethyleneimine modified magnetic mesoporous polydopamine nanocomposite: Insights into synergistic effects and mechanisms

Application of a superior magnetic hydroxy iron material for arsenic removal from soil

Magnetic removal technology enable rapid removing arsenic from soil. However, the high cost of magnetic arsenic removal materials folimited its application. A magnetic arsenic removal material which is much less costly was introduced in this study. CTAB@β-FeOOH@Fe3O4 (C-M-MFe), a composite modified montmorillonite, was synthesized and investigated for its adsorption performance, mechanism, and remediation efficacy in arsenic-contaminated soil. The results indicate that the maximum theoretical adsorption capacities of the material for As(Ⅴ) and As(Ⅲ) are 74.90 mg g-1 and 67.81 mg g-1, respectively. The adsorption mechanism involves electrostatic attraction, inner-sphere complexation, and precipitation. Moreover, our findings suggest that the potential synergistic oxidation of As(Ⅲ) facilitated by Fe(Ⅲ) in β-FeOOH and structural Fe(Ⅱ) in magnetite, may contribute to adsorption efficiency. Under the conditions of 1:1 (g:g) of soil slurry solid-liquid ratio, 1% of adsorbent dosage, and more than 12 h of treatment duration, C-M-MFe could strongly reduce 92.14% of available arsenic and also 44.09% of specifically adsorbed arsenic in the soil. Finally, the total arsenic removal rate reached 10.83%, with an adsorbent recovery rate of 92.44%. Compared with other magnetic arsenic removal materials, the C-M-MFe developed in this study is an efficient adsorbent of arsenic with low cost. Plus that we found that As(Ⅲ) might be oxidized by β-FeOOH in adsorption process, which contribute to solve the tough problem of As(Ⅲ) removal. The results of this paper offered a promising potential method for arsenic removal from contaminated soils. ENVIRONMENTAL IMPLICATIONS: This research developed a cost-effective adsorbent for arsenic removal, which possesses both magnetic and catalytic oxidation properties. Our study elucidated the primary adsorption mechanism and evaluated its application effectiveness in contaminated soil. By leveraging the adsorption and catalytic oxidation capabilities of β-FeOOH, we achieved an enhancement in the removal of As(III). This approach offers a promising strategy to improve As(III) removal efficiency while minimizing the required adsorbent dosage, thus holding potential for practical applications in remediating arsenic-contaminated soils.

Integrated electrochemical identification and detoxification of chromium oxyanion by dual amino functionalized carboxymethyl cellulose material

Precise identification and detoxification of chromium pollution is important in effectively safeguarding ecological security and human health, while achieving the dual objectives of pollution prevention and resource regeneration. Herein, we synthesized dual-amine-functionalized carboxymethyl cellulose (CMC) material to develop a non-metal based integrated electrochemical process for centralized Cr(VI) detection, adsorption and reduction. Polyethyleneimine (PEI) and 5-aminosalicylic acid (5-ASA) were selected as amine-functionalizing additives. PEI was primarily employed to construct a three-dimensional network structure, optimizing mass transfer during the electrochemical process. 5-ASA, which possessed more negative electrostatic potential, greatly enhanced the adsorption capacity and reducibility of CMC by promoting electron transfer, changing the surface chemical environment and reducing the energy barrier of reduction reaction. The adsorption of Cr(VI) (354.6 mg/g) was dominated by charge attraction, chelation and electrostatic attraction interactions, while the reduction of chromium (54 %) was triggered by electrochemical and electro reduction process. The electrode also exhibited a Cr(VI) detection sensitivity of 0.00256 μA/ppb and limit of 1.2471 ppb, respectively. This research developed a metal-free environmentally friendly electrochemical material for advancing the efficiency and intelligence of environmental management.

Co-adsorption behaviors and mechanisms of Cd(Ⅱ), Pb(Ⅱ), and Cr(Ⅵ) on sodium dodecyl sulfate modified attapulgite clay-supported nano zero-valent iron: Competitive or synergistic effect?

Cadmium(Ⅱ), plumbum(Ⅱ), and chromium(Ⅵ) universally co-exist in the environment, greatly aggravating their environmental risks and elevating the difficulty of remediation. Herein, a novel sodium dodecyl sulfate modified attapulgite clay-supported nano zero-valent iron (SDS@ATP/nZVI) was exploited as the synchronous adsorbent of Cd(Ⅱ), Pb(Ⅱ), and Cr(Ⅵ) composite pollution. With the aid of the carrier SDS@ATP, nZVI was highly dispersed and became the primary active ingredient. The adsorption kinetics results showed that there existed a strong competitive effect between Cd(Ⅱ) and Pb(Ⅱ), while the co-existence of Cr(Ⅵ) accelerated the removal of Cd(Ⅱ) on SDS@ATP/nZVI. The adsorption capacity (qmax) of Cd(Ⅱ) in their binary system was only 71.3 mg/g and 0.34 times that of single Cd(Ⅱ) adsorption under pH = 6.0 and 298 K, whereas that of Pb(Ⅱ) (qmax = 558.7 mg/g) was almost equivalent, supporting that Pb(Ⅱ) adsorption had the priority and quickly reduced to Pb0 by Fe0. Meanwhile, residue Pb(Ⅱ) and Cd(Ⅱ) mightily competed for active sites of surface chemical adsorption of iron hydroxide. Similarly, the qmax of Cd(Ⅱ) and Cr(Ⅵ) in their binary system were 238.7 and 70.9 mg/g, which was 1.12 and 0.94 times to those of individual Cd(Ⅱ) and Cr(Ⅵ) adsorption, implying a synergistic effect of Cr(Ⅵ). Cr(Ⅵ) species firstly was reduced and simultaneously facilitated the generation of iron hydroxide, of which both free Cd(Ⅱ) and newly reduced Cr(Ⅲ) with iron hydroxide co-precipitated to constitute the amorphous Fe-Cr(Ⅲ)-Cd(Ⅱ) sediment. These findings also provide exhaustive inspiration and strategy for the remediation of multiple composite pollution.

The efficient uptake of uranium by amine-functionalized β-cyclodextrin supported fly ash composite from polluted water

A novel polyethyleneimine/polydopamine-functionalized β-cyclodextrin supported fly ash adsorbent (PEI/PDA/β-CD/FA) had been synthesized to uptake uranium from polluted water. At pH = 5.0 and T = 298 K, the uranium uptake efficiency and capacity of PEI/PDA/β-CD/FA reached to 98.7 % and 622.8 mg/g, respectively, which were much higher than those of FA (71.4 % and 206.7 mg/g).The excellent uranium uptake properties of PEI/PDA/β-CD/FA could be explained by three points: (1) using β-CD as a supporting material could effectively avoid the aggregation of FA and improve the hydrophily of FA; (2) the unique cavity structure of β-CD could form chelates with uranyl ions; (3) the formation of PEI/PDA co-deposition coating on FA further enhanced the affinity of FA to UO22+. With the presence of interfering ions, the uptake efficiency of PEI/PDA/β-CD/FA for uranium was still up to 94.5 % after five cycles, indicating the high selectively and recoverability of PEI/PDA/β-CD/FA. In terms of the results of characterizations, uranium was captured by PEI/PDA/β-CD/FA via electrostatic attraction, hydrogen bond, coordination and complexation. To sum up, PEI/PDA/β-CD/FA was expected to be used for actual sewage treatment owing to its excellent uranium uptake efficiency/capacity, selectivity, cycle stability and feasibility of actual application.

Polyethyleneimine-modified iron-doped birnessite as a highly stable adsorbent for efficient arsenic removal

Remediation of arsenic contamination is of great importance given the high toxicity and easy mobility of arsenic species in water and soil. This work reports a new and stable adsorbent for efficient elimination of arsenic by coating polyethyleneimine (PEI) molecules onto the surface of iron-doped birnessite (Fe-Bir). Characterization results of surface microstructure and crystalline feature (scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS), etc.) suggest that Fe-Bir/PEI possesses a fine particle structure, inhibiting the agglomeration of birnessite-typed MnO2 and offering abundant active sites for arsenic adsorption. Fe-Bir/PEI is capable of working in a wide pH range from 3 to 11, with an efficient removal capacity of 53.86 mg/g at initial pH (pH0) of 7. Meanwhile, commonly coexisting anions (NO3-, SO42-, and Cl-) and cations (Na+, K+, Ca2+ and Mg2+) pose no effect on the arsenic removal performance of Bir/PEI. Fe-Bir/PEI exhibits a good reusability for arsenic removal with low Mn and Fe ions leaching after 5 cycles. Besides, Fe-Bir/PEI possesses efficient remediation capability in simulated As-contaminated soil. The modification of PEI in Fe-Bir/PEI can adsorb newly formed As(V), which is impossible for the adsorbent without PEI. Further, the arsenic removal mechanism of Fe-Bir/PEI is revealed with redox effect, electrostatic attraction and hydrogen bonding.

CdBi2S4-Decorated Aminated Polyacrylonitrile Nanofiber for Photocatalytic Treatment of Cr(VI) and Tetracycline Wastewater

The significant threat posed by the high toxicity of heavy metals and antibiotics in water pollutants has prompted a growing emphasis on the development of highly efficient removal methods for these pollutants. In this paper, flexible electrospinning polyacrylonitrile (PAN) nanofiber-supported CdBi2S4 was synthesized via a hydrothermal method, followed by amination treatment with diethylenetriamine (DETA). The as-prepared CdBi2S4/NH2-PAN nanofiber, enriched with sulfur vacancies, demonstrated outstanding visible-light trapping ability and a suitable band gap, leading to efficient separation and transport of photogenerated carriers, ultimately resulting in exceptional photocatalytic capability. The optimal 3-CdBi2S4/NH2-PAN nanofiber achieved impressive reduction rates of 92.26% for Cr(VI) and 96.45% for tetracycline hydrochloride (TCH) within 120 min, which were much higher than those for CdS/NH2-PAN, Bi2S3/NH2-PAN, and CdBi2S4/PAN nanofibers. After five cycles, the removal rate of the CdBi2S4/NH2-PAN nanofiber consistently remained above 90%. Their ease of separation and recovery from the application environment contributes to their practicality. Additionally, compared with conventional suspended particle catalyzers, the composite nanofiber exhibited remarkable flexibility and self-supporting properties.

Recent progress in magnetic polydopamine composites for pollutant removal in wastewater treatment

Various water pollution issues pose a significant threat to human water safety. Magnetic polydopamine composites (MPCs), which can be separated by magnetic fields after the adsorption process, exhibit outstanding adsorption capacity and heterogeneous catalytic properties, making them promising materials for water treatment applications. In particular, by modifying the polydopamine (PDA) coating, MPCs can acquire enhanced high reactivity, antibacterial properties, and biocompatibility. This also provides an attractive platform for further fabrication of hybrid materials with specific adsorption, catalytic, antibacterial, and water-oil separation capabilities. To systematically provide the background knowledge and recent research advances in MPCs, this paper presents a critical review of MPCs for water treatment in terms of both structure and mechanisms of effect in applications. Firstly, the impact of different PDA positions within the composite structure is investigated to summarize the optimization of properties contributed by PDA when acting as the shell, core, or bridge. The roles of various secondary modifications of magnetic materials by PDA in addressing water pollution problems are explored. It is anticipated that this work will be a stimulus for further research and development of magnetic composite materials with real-world application potential.

Hydrophilic magnetic Ti3C2Tx-based nanocomposite as an efficient boron adsorbent: Synthesis, characterization, and application

It is widely recognized that wastewater containing boron is an environmental issue. Therefore, the development of adsorbents with excellent adsorption capacity, stability, and recyclability is essential in water treatment applications. A Fe3O4/PDA/Ti3C2Tx/PEI/DHHA nanocomposite has been prepared that can be used to separate and recover boric acid by adjusting the pH of the solution, based on the affinity theory of boric acid and cis-diol. Through series characterization, it was determined that the adsorbent possessed good magnetic properties, high hydrophilicity and high loading capacities. In this study, 4-formylphenylboronic acid (FPBA) was selected as the model compound. The nanocomposite exhibited an adsorption equilibrium time of 10 h and an adsorption capacity of 98.99 mg/g at pH = 8.5 and 25 °C. The Langmuir isothermal model and the quasi-secondary kinetic model are both appropriate for describing the adsorption process. Thermodynamic results suggest that adsorption is a spontaneous chemisorption process. Furthermore, the nanocomposite retains good regeneration performance after five adsorption-desorption cycles.

Novel efficient capture of hexavalent chromium by polyethyleneimine/amyloid fibrils/polyvinyl alcohol aerogel beads: Functional design, applicability, and mechanisms

The harmful effects of hexavalent chromium (Cr(VI)) on the environment and human health have aroused wide public concern. In this study, bulk spherical aerogel beads (PAP) were synthesized from polyethyleneimine (PEI), protein amyloid fibrils (AFL), and polyvinyl alcohol (PVA) through green technology and its removal of Cr(VI) from wastewater was comprehensively studied. The results showed that although the bulk PAP beads (∼ 5 mm) only had an average pore size of 16.88 nm and a BET surface area of 12 m²/g, its maximum adsorption capacity for Cr(VI) reached 121.44 mg/g (at 298 K). Cr(VI) adsorption onto PAP conformed to pseudo-second-order adsorption kinetics and was endothermic. The adsorption of Cr(VI) decreased stepwise with the increase of solution alkalinity (pH = 2: 91.97%; pH = 10: 0.04%). Importantly, PAP showed high selectivity towards Cr(VI) in mixed heavy metal solutions (Cr(VI) > Pb(II) > Ni(II) > Cu(II) > Cd(II)) and good reusability (removal efficiency > 88% after 5 cycles). PAP had excellent anti-interference ability against FA and HCO₃^- with the overall removal rate exceeding 87% in the presence of 5 - 25 mg/L of these ions. Cations such as Na⁺, Mg²⁺, and other heavy metal ions at high concentrations could promote the removal efficiency of Cr(VI). The removal rates of Cr(VI) and Cr(III) by PAP in a tannery wastewater were 34.4% and 59.3%, respectively. Meanwhile, the removal rates of Cr(VI) in a electroplating wastewater and a contaminated soil leachate reached 84.4∼89.7%, showing high practicability. Mechanism studies revealed that electrostatic attraction, hydrogen bonding, reduction, and complexation were the main reactions for Cr(VI) removal by PAP. In general, the study of PAP provides a new insight into using bulk monolith materials for treating Cr(VI) contaminated wastewater.

Mussel inspired synthesis of polydopamine/polyethyleneimine-grafted fly ash composite adsorbent for the effective separation of U(VI)

Polydopamine/polyethyleneimine-grafted fly ash composite (PDA/PEI/FA), an efficient multifunctional adsorbent for U(VI) with excellent separation efficiency (94.5 %) and capacity (422.5 mg/g), was synthesized by grafting PDA and PEI on FA via Mussel inspiration and Michael addition reaction. The introduction of PDA and PEI had brought numerous functional groups with fine affinities to uranium, like catechol, amino and imino, causing good U(VI) separation performances. Langmuir and Pseudo-second-order models were well matched with experimental data, illustrating the U(VI) separation on PDA/PEI/FA was a homogeneous chemical adsorption process. After five cycles, the U(VI) adsorption efficiency for PDA/PEI/FA was still up to 90.2 %, implying that PDA/PEI/FA possessed good stability and reusability. Besides, the good dynamic adsorption performances of PDA/PEI/FA further demonstrated that PDA/PEI/FA was an ideal adsorbent for the practical wastewater treatment. According to the characterization results, U(VI) was absorbed by PAD/PEI/FA through complexation, redox reaction, electrostatic attraction and hydrogen bonding. Given the above, PDA/PEI/FA showed good practical application prospect in U(VI) separation.

Fe-biochar for simultaneous stabilization of chromium and arsenic in soil: Rational design and long-term performance

Excess chromium (Cr) and arsenic (As) coexist in soil such as chromated copper arsenate (CCA) contaminated sites, leading to high risks of pollution. Fe-biochar with adjustable redox activity offers the possibility of simultaneous stabilization of Cr and As. Here, a series of Fe-biochar with distinct Fe/C structure were rationally produced for the remediation of Cr and As contaminated soil (BCX-Fe, X represented the biomass/Fe ratio). Adsorption tests showed that maximal adsorption of BC5-Fe for Cr(VI) and As(III) reached 73.7 and 81.3 mg/g. A 90-day soil remediation experiment indicated that the introduction of 3% (w/w) Fe-biochar reduced the leaching state of Cr(VI) by 93.8-99.7% and As by 75.2-95.6%. Under simulated groundwater erosion for 10 years and acid rain leaching for 7.5 years, the release levels of Cr(VI) and As in the BC5-Fe remediated soil could meet the groundwater class IV standard in China (Cr(VI)<0.1 mg/L, As<0.05 mg/L). Accelerated aging tests demonstrated that BC5-Fe had long-term Cr and As stabilization ability. The quenching experiment, EPR, and XPS suggested that the corrosion products of Fe dominated the adsorption and redox reactions, while the O groups acted as electron transfer stations and constituted redox microcirculation in the synchronous uptake of Cr/As. Based on these insights, we believe that our study will provide meaningful information about the application potential of Fe-biochar for the heavy metal contaminated soil remediation.

Polyethylenimine-grafted nitrogen-doping magnetic biochar for efficient Cr(VI) decontamination: Insights into synthesis and adsorption mechanisms

Herein, polyethylenimine (PEI)-grafted nitrogen (N)-doping magnetic biochar (PEI_MW@MNBC_BM) was synthesized, and characterization results showed that the microwave-assisted PEI grafting and ball milling-assisted N doping introduced abundant amino, pyridine N and pyrrole N structures onto biochar, which possessed high affinity to Cr(VI) in the anion form. The as-prepared PEI_MW@MNBC_BM displayed pH-dependence adsorption performance and high tolerance to co-existing ions with maximum uptake capacity of Cr(VI) identified as 183.02 mg/g. Furthermore, PEI_MW@MNBC_BM could bind Cr(VI) through electrostatic attraction, complexion, precipitation, reduction and pore filling. Especially, effective reduction of Cr(VI) was ascribed to cooperative electron transfer of partial oxygen-containing functional groups, intramolecular pyridine/pyrrole N, protonated amino and Fe²⁺ on the adsorbent, while oxygen-containing and amino functional groups from N-doping biochar and PEI synergistically complexed Cr(III) via providing lone pair electrons to form coordinate bonds. Furthermore, the stable precipitation was formed between Fe³⁺ and Cr(III). Additionally, the Cr(VI) elimination efficiency could maintain 95.83% even after four adsorption-desorption cycles, suggesting PEI_MW@MNBC_BM as a high-performance adsorbent for Cr(VI) contaminated water remediation.