Preparation of nickel@polyvinyl alcohol (PVA) conductive membranes to couple a novel electrocoagulation-membrane separation system for efficient oil-water separation

Biomimetic materials for efficient emulsion separation: Based on the perspective of energy

Purifying emulsified oily wastewater is particularly crucial for solving environmental pollution and water scarcity. Membrane separation shows great potential for emulsified wastewater treatment. However, realizing continued effective emulsion separation remains a significant challenge. Fortunately, various kinds of creative schemes have been proposed to overcome the current dilemma. In this paper, biomimetic emulsion separation materials with unique wettability are introduced. Besides, This article summarizes the recently advanced emulsion separation strategies. First, we analyze the typical wettability theory and explore the trade-off between separation flux and efficiency. After that, based on emulsion types, the current common emulsion separation materials are summarized and analyzed. Notably, the integration of natural biological inspiration has made separation materials full of potential. Further, from the perspective of external energy input or no-external energy input, this article provides an overview of advanced emulsion separation materials and analyzes the potential separation mechanism. Encouragingly, efficient emulsion separation can be realized by membrane characteristics (microstructure, superwettability, electrostatic interaction) or the appropriate external stimulus (photo, electricity, magnetic). Finally, the challenges and trends are summarized. We hope that this article will provide inspiration for the advancement of novel generations of separation materials.

Leveraging the potential of antibacterial biomolecules in antibiofouling membrane design: A review

Biofouling, a prevalent issue in membrane technology, compromises the effectiveness and efficiency of membrane-based separation processes. The bottleneck prompts significant research into improving the antibacterial and antibiofouling characteristics of membrane. This review seeks to offer a thorough analysis and discussion on the utilization of biomolecules such as polysaccharides, fatty acids and enzymes for developing antibacterial and antibiofouling membranes. This review discusses the properties, advantages, and limitations of employing antibacterial biomolecules, along with their development and performance in membrane applications. A comprehensive elaboration is crucial to grasp the potential of these antibacterial biomolecules in enhancing membrane performance. This review is expected to offer insights into how these antibacterial biomolecules can optimize membrane performance by reducing biofouling, enhancing operational efficiency, ensuring water quality, and lowering costs. This review concludes that antibacterial polysaccharides and enzymes can serve as promising candidate to enhance the antibacterial properties of membranes. The review also addresses challenges and outlines future research directions concerning antibacterial biomolecules. The future directions outlined in the review focus on striking a balance between achieving strong antibacterial action and preserving essential membrane surface properties, thereby encouraging the creation of eco-friendly environment.

Analysis of Metal-Organic Framework and Polyamide Interfaces in Membranes for Water Treatment and Antibacterial Applications

Integrating biocidal nanoparticles (NPs) into polyamide (PA) membranes shows promise for enhancing resistance to biofouling. Incorporating techniques can tailor thin-film nanocomposite (TFN) membranes for specific water purification applications. In this study, silver-based metal-organic framework Ag-MOFs (using silver nitrate and 1,3,5-benzentricarboxylic acid as precursors) are incorporated into PA membranes via three different methods: i) incorporation, ii) dip-coating, and iii) in situ ultrasonic techniques. The characterizations, such as top-surface and cross-section scanning and transmission microscopy, reveal that the incorporation methods for the modified TFN membranes substantially control morphology and surface characteristics. For example, the in situ ultrasonically interlayered Ag-MOFs showed the largest pores (average pore diameter of 14 Å ± 0.1), resulting in the highest water permeance (water flux of 10.9 LMH/bar for Na2SO4). It also show superior antifouling and anti-biofouling performance, with a flux recovery ratio (FRR) of 94.1% in both fouling tests due to its improved surface hydrophilicity and the antibacterial properties of incorporated Ag-MOFs. Conversely, the surface-grafted dip-coated Ag-MOFs offered the highest salt rejection, attributed to its highly negatively charged surface and a dense PA network with narrow pores (average pore diameter of 10 Å ± 0.06).

Superhydrophilic membrane coupled with hydroxide ion-assisted bubbles for efficient separation of surfactant-stabilized oil/water emulsions

Developing a feasible and efficient membrane for the purification of surfactant-stabilized emulsions is urgently needed but impeded by the issues of membrane fouling and the inherent trade-off between separation efficiency and permeation flux. A superhydrophilic conductive membrane was developed by coating MXene/carbon nanotubes layer and polydopamine-hydrogel molecular layer, which as cathode integrates feasible hydroxide ion-assisted bubbles on its surface by electrolysis of water. These bubbles are more effective than conventional ones in removing surfactant-stabilized oil droplets because the hydroxide ions significantly promote the aggregation of oil droplets and bubbles by reducing their Debye length. In this way, the oil droplets even the small-sized ones assisted by these bubbles are quickly detached from the membrane surface, avoiding the oil accumulation and penetration, significantly mitigating the membrane fouling and trade-off challenges. Therefore, the membrane has outstanding separation efficiency (99.57 %), permeation flux (2065 L m-1 h-1 bar-1), antifouling ability and durability in surfactant-stabilized oil/water emulsion separation. Besides, this membrane coupled with hydroxide ion-assisted bubbles is easily manageable and eco-friendly, which provides a promising solution and valuable insights for efficient emulsion separation and wastewater remediation.

Environmental applications of metal-organic framework-based three-dimensional macrostructures: a review

Metal-organic frameworks (MOFs) hold considerable promise for environmental remediation owing to their exceptional performance and distinctive structure. Nonetheless, the practical implementation of MOFs encounters persistent technical hurdles, notably susceptibility to loss, challenging recovery, and potential environmental toxicity arising from the fragility, insolubility, and poor processability of MOFs. MOF-based three-dimensional macrostructures (3DMs) inherit the advantageous attributes of the original MOFs, such as ultra-high specific surface area, tunable pore size, and customizable structure, while also incorporating the intriguing characteristics of bulk materials, including hierarchical structure, facile manipulation, and structural flexibility. Consequently, they exhibit rapid mass transfer and exceptional practicality, offering extensive potential applications in environmental remediation. This review presents a comprehensive overview of recent advancements in utilizing MOF-based 3DMs for environmental remediation, encompassing their fascinating characteristics, preparation strategies, and characterization methods, and highlighting their exceptional performance in pollutant adsorption, catalysis, and detection. Furthermore, existing challenges and prospects are presented to advance the utilization of MOF-based materials across various domains, particularly in environmental remediation.

Biomimetic 3D Prototyping of Hierarchically Porous Multilayered Membranes for Enhanced Oil-Water Filtration

This study introduces a biomimetic approach to 3D printing multilayered hierarchical porous membranes (MHMs) using Direct Ink Writing (DIW) technology. Fabricated through a fast layer-by-layer printing process with varying concentrations of pore-forming agents, the produced MHMs mimic the hierarchical pore structure and filtration capabilities of natural soil systems. As a result, the 3D-printed MHMs achieved an impressive oil rejection rate of 99.02% and demonstrated exceptional reusability, maintaining a flux recovery ratio of 99.48% even after hours of continuous filtration. Moreover, the 3D-printed MHMs exhibit superior hierarchical porous architecture and mechanical integrity compared to traditional flat sheet single-layered membranes. This study presents a significant advancement for scalable 3D printing of customized multilayer membranes with tailored porosity and high-performance filtration properties. The simplicity, versatility, and cost-effectiveness of the presented manufacturing method offer a pathway for advanced design and on-demand membrane production.

CB[6]/ZnO chelated superoleophobic-hydrophilic PVDF membranes for one-step remediation of multi-contaminant in wastewater

Industrial wastewater, despite undergoing primary and secondary treatments with conventional methods, continues to pose challenges due to the presence of multiple contaminants. Membrane separation has emerged as an effective solution to streamline the treatment process, yet it often results in surface fouling. This study introduces a single platform designed for simultaneous removal of dyes, oils, and proteins during the tertiary treatment stage, thereby eliminating the need for multiple separation steps. To enhance membrane robustness and address common fouling issues, polyvinylidene fluoride-montmorillonite-cucurbit[6]uril/zinc oxide (PV-M-CB[6]ZnO) mixed-matrix membranes have been developed. The incorporation of montmorillonite (M), cucurbit[6]uril (CB[6]) host-guest encapsulation, and zinc metal chelation significantly improves the membrane's capability in eliminating cationic dyes, treating oil-water emulsions, and separating bovine serum albumin. With an optimal CB[6]/ZnO loading of 1.6 wt%, the PV-M-CB[6]ZnO membranes exhibit superior performance with high water permeability (4114 L/m2.h.bar) and exceptional separation efficiencies: 95.5% for malachite green, 93.2% for methylene blue, and 98.2% for crystal violet, compared to pristine PVDF membranes. Additionally, these membranes demonstrate an impressive oil-water rejection rate of 97.6% and a bovine serum albumin rejection rate of 76%, with a flux recovery ratio exceeding 86% after seven filtration cycles. Thus, the PV-M-CB[6]ZnO membranes offer enhanced hydrophilicity, improved antifouling properties, and increased efficiency for the removal of multiple contaminants from industrial wastewater, providing a promising solution for sustainable environmental remediation.

A critical review of ozone-based electrochemical advanced oxidation processes for water treatment: Fundamentals, stability evaluation, and application

In recent years, electrochemical advanced oxidation processes (EAOPs) combined with ozonation have been widely utilized in water/wastewater treatment due to their excellent synergistic effect, high treatment efficiency, and low energy consumption. A comprehensive summary of these ozone-based EAOPs is still insufficient, though some reviews have covered these topics but either focused on a specific integrated process or provided synopses of EAOPs or ozone-based AOPs. This review presents an overview of the fundamentals of several ozone-based EAOPs, focusing on process optimization, electrode selection, and typical reactor designs. Additionally, the service life of electrodes and improvement strategies for the stability of ozone-based EAOPs that are ignored by previous reviews are discussed. Furthermore, four main application fields are summarized, including disinfection, emerging contaminants treatment, industrial wastewater treatment, and resource recovery. Finally, the summary and perspective on ozone-based EAOPs are proposed. This review provides an overall summary that would help to gain insight into the ozone-based EAOPs to improve their environmental applications.

Durable Nano-Flower Structured Foam Coupled with Electrically-Driven in Situ Aeration Enable High-Flux Oil/Water Emulsion Separation with Dynamic Antifouling Ability

The conventional membranes used for separating oil/water emulsions are typically limited by the properties of the membrane materials and the impact of membrane fouling, making continuous long-term usage unachievable. In this study, a filtering electrode with synchronous self-cleaning functionality is devised, exhibiting notable antifouling ability and an extended operational lifespan, suitable for the continuous separation of oil/water emulsions. Compared with the original Ti foam, the in situ growth of NiTi-LDH (Layered double hydroxide) nano-flowers endows the modified Ti foam (NiTi-LDH/TF) with exceptional superhydrophilicity and underwater superoleophobicity. Driven by gravity, a rejection rate of over 99% is achieved for various emulsions containing oil content ranging from 1% to 50%, as well as oil/seawater emulsions. The flux recovery rate exceeds 90% after one hundred cycles and a 4-h filtration period. The enhanced separation performance is realized through the "gas bridge" effect during in situ aeration and electrochemical anodic oxidation. The internal aeration within the membrane pores contributes to the removal of oil foulants. This study underscores the potential of coupling foam metal filtration materials with electrochemical technology, providing a paradigm for the exploration of novel oil/water separation membranes.

Magnetic Hyperporous Elastic Material with Excellent Fatigue Resistance and Oil Retention for Oil-Water Separation

Oily wastewater has caused serious threats to the environment; thus, high-performance absorbing materials for effective oil-water separation technology have attracted increasing attention. Herein, we develop a magnetic, hydrophobic, and lipophilic hyperporous elastic material (HEM) templated by high internal phase emulsions (HIPE), in which free-radical polymerization of butyl acrylate (BA) and divinylbenzene (DVB) is employed in the presence of poly(dimethylsiloxane) (PDMS), lecithin surfactant, and modified Fe3O4 nanoparticles. The adoption of the emulsion template with nanoparticles as both stabilizers and cross-linkers endows the HEM with biomimetic hierarchical open-cell micropores and elastic cross-linked networks, generating an oil absorbent with outstanding mechanical stability. Compressive fatigue resistance of the HEM is demonstrated to endure 2000 mechanical cycles without plastic deformation or strength degradation. By exploiting the synergistic effect of hierarchical structures and low-surface-energy components, the resulting HEM also possesses excellent and robust hydrophobicity (water contact angle of 164°) and good oil absorption capacity, in which Fe3O4 nanoparticles lead to convenient magnetically controlled oil recyclability as well. Notably, the unique biomimetic microporous structure demonstrates superior oil retention capacity (>95% at 1000 rpm and >60% at 10,000 rpm) over the state-of-the-art porous materials for a diverse variety of oils to reduce the risk of secondary oil leakage, along with good recoverability by squeezing owing to the excellent compression resilience. These excellent performances of our HEM provide broad prospects for practical applications in oil-water separation, energy conversion, and smart soft robotics.

Investigation of different molecular weight Polyvinylidene Fluoride (PVDF) polymer for the fabrication and performance of braid hollow fiber membranes

In the current study, braid reinforced membranes were fabricated from polyvinylidene fluoride (PVDF) polymers with two different molecular weights, and the blending of the polymers in a 1:1 ratio to upgrade the performance of the membrane. Characterization, filtration studies, and membrane bioreactor (MBR) application were done to evaluate membrane performance by applying the same operation conditions on each membrane. Characterization studies indicated that the fabricated membrane from blending polymers was a hydrophilic structure with a contact angle of 50.78° and smoother surface properties compared to the other fabricated membranes. According to the MBR results, at the end of the operation process, TMP levels of the membrane from the blending method are found 150 mbar, membrane from high molecular weight PVDF polymer had 250 mbar, and membrane from low molecular weight PVDF polymer had 800 mbar. As a consequence of the investigation, it is seen that the hydrophilic structure of the membrane allows the pollutant to adsorb less to the blend membrane surface, and the lower roughness is also a factor in reducing fouling.

Click-chemistry synergic MXene-functionalized flexible skeleton membranes for accurate recognition and separation

Membrane-based technology with accurate-recognition and specific-transmission has been regarded as one of the most promising strategies in environmental protection and energy conservation. However, membrane technique still faces challenges of "trade-off effect" between high selectivity and permeation flux within organic-aqueous mixed matrix. Here, well-intergrown click-chemistry synergic MXene-functionalized flexible skeleton membranes has been prepared in this strategy, enabling size-exclusion&structure selectivity by uniform location array imprinting unit and transport performance towards specific medicinal molecules of artemisinin (Ars). The well-assembled ultrathin cascade-type MXene layer guarantees the narrow interlayer nanochannels and the flexible skeleton modified mesoporous SiO2 nanoparticles provide active reaction platform for the construction of selective recognition space. The resulting membranes demonstrated outstanding selective separation performance with permeability factor that artesunate (Aru) /Ars and dihydro-artemisinin (d-Ars) / Ars of 3.17 and 2.89 and permeation flux of 1173.25 L·m-2·h-1·bar-1. Besides, combined with antibacterial durability, recycling performance, high separation performance in mobile phase stability of CMFMs, it is anticipated that this work hopefully opens a new avenue for efficient chiral separation to medicinal molecules, exhibiting broad potential for practical application.

A sustainable solution for organic pollutant degradation: Novel polyethersulfone/carbon cloth/FeOCl composite membranes with electric field-assisted persulfate activation

Sulfate radical-based advanced oxidation processes (SR-AOP) and ultrafiltration (UF) membranes have demonstrated effectiveness in treating wastewater. This investigation illuminated a pioneering two-stage procedure for fabricating polyethersulfone/carbon cloth/FeOCl (PES/CC/FeOCl) composite catalytic membranes, exhibiting proficiency in persulfate activation. Evidenced by their distinctively high degradation rates and superior stability, these innovative composite membranes efficaciously obviate tetracycline (TC), showcasing a striking TC degradation rate, with an unparalleled removal ratio peaking at 93% under applied electrical fields. The process underlying persulfate activation and TC degradation was meticulously explored through electron paramagnetic resonance (EPR) and quenching trials. These evaluations unveil that hydroxyl radicals (•OH) and sulfate radicals (SO4•-) primarily drive the eradication of diminutive organic molecules. Subsequent studies emphasized the noteworthy rejection ratio of the PES/CC/FeOCl composite membranes (90%) for sodium alginate (SA), further revealing their exceptional on-line cleansing efficiency in an electrofiltration-associated in-situ oxidation system. In essence, this study proposed a novel approach for the synthesis of composite membranes adept at the catalytic degradation of organic pollutants. This paradigm-shifting research imparted a unique lens to perceive the integration of membrane separation technology, enriching the domain of advanced wastewater treatment strategies.

A comprehensive review on the behavior and evolution of oil droplets during oil/water separation by membranes

Membrane separation technology has significant advantages for treating oil-in-water emulsions. Understanding the evolution of oil droplets could reveal the interfacial and colloidal interactions, facilitate the design of advanced membranes, and improve the separation performances. This review on the characteristic behavior and evolution of oil droplets focuses on the advanced analytical techniques, and the subsequent fouling as well as demulsification effects during membrane separation. A detailed introduction is provided on microscopic observations and numerical simulations of the dynamic evolution of oil droplets, featuring real-time in-situ visualization and accurate reconstruction, respectively. Characteristic behaviors of these oil droplets include attachment, pinning, wetting, spreading, blockage, intrusion, coalescence, and detachment, which have been quantified by specific proposed parameters and criteria. The fouling process can be evaluated using Hermia and resistance models. The related adhesion force and intrusion pressure as well as droplet-droplet/membrane interfacial interactions can be accurately quantified using various force analysis methods and advanced force measurement techniques. It is encouraging to note that oil coalescence has been achieved through various effects such as electrostatic interactions, mechanical actions, Laplace pressure/surface free energy gradients, and synergistic effects on functional membranes. When oil droplets become destabilized and coalesce into larger ones, the functional membranes can overcome the limitations of size-sieving effect to attain higher separation efficiency. This not only bypasses the trade-off between permeability and rejection, but also significantly reduces membrane fouling. Finally, the challenges and potential research directions in membrane separation are proposed. We hope this review will support the engineering of advanced materials for oil/water separation and research on interface science in general.

Green Synthesis of a Carbon Quantum Dots-Based Superhydrophobic Membrane for Efficient Oil/Water Separation

The efficient separation of oil and water is a significant challenge worldwide due to the increasing frequency of industrial oily wastewater. Previous work by our group utilizes biological metal-organic framework-based superhydrophobic (S.P) textile fabric for oil/water separation. However, this system is limited due to the low mechanical stability, so there is a need for producing a more robust S.P membrane for oil/water separation. In this study, we report on the synthesis of carbon quantum dots (CQD) from banana leaves via a hydrothermal process and their application in producing a robust S.P coating on textile fabric for oil/water separation. The CQDs were characterized using various techniques including TEM, XRD, absorbance spectroscopy, and the BET method. The TEM images showed that the CQDs were circular in shape with a size of 4.4 nm, while the XRD micrograph indicated that the CQDs were crystalline in nature. The UV-vis graph showed a peak at a wavelength of 278 nm, suggesting strong absorption in the ultraviolet region. The BET-specific surface area of the prepared CQDs is 845 m2/g, with a pore volume of 0.33 cm3/g, and a mean pore diameter of 1.62 nm. We examined the surface wettability, morphology, composition, oil absorption capacity, oil/water separation performance, flux rate, chemical stability, and mechanical stability of the S.P membrane. Our findings indicate that the developed CQD-based S.P membrane possesses excellent S.P properties, displaying high water contact angles of 163° and low water sliding angles of 1°. The membrane demonstrated superior oil absorption capacity, separation efficiency, and flux rate towards three different oils-petroleum ether, n-hexane, and silicone oil. Petroleum ether has the highest separation efficiency (99.5%), and flux rate (13,500 L m-2 h-1), while silicone oil has the lowest. However, silicone oil has the highest absorption capacity (218.9 g/g) and petroleum ether has the lowest (194.8 g/g). For the absorption capacity and separation efficiency, a one-way ANOVA test was conducted. The statistical analyses revealed significant differences in absorption capacity and separation efficiency for the three oils, highlighting the efficacy of the superhydrophobic membrane for tailored oil/water separation. Additionally, the S.P membrane exhibited good mechanical (the membrane maintains its superhydrophobicity until an abrasion length of 850 cm) and chemical stability (the membrane maintains its superhydrophobicity in pH range 1-13), withstanding abrasion and immersion in solutions of varying pH values. The CQD-based S.P membrane shows great potential as a promising material for oil/water separation applications, with excellent performance and stability under various environmental conditions.

Efficient oily wastewater treatment by a novel electroflotation-membrane separation system consisting a Ni-Cu-P membrane prepared by electroless nickel plating

Electroflotation-membrane separation system with a conductive membrane has recently emerged as a promising technology for oily wastewater treatment. However, the conductive membrane prepared by electroless plating often suffers the problems of low stability and high activation cost. To solve these problems, this work proposed a new strategy regarding surface metallization of polymeric membrane by surface nickel-catalyzed electroless nickel plating of nickel‑copper‑phosphorus alloys for the first time. It was found that, addition of copper source remarkably enhanced the membranes' hydrophilicity, corrosion resistance and fouling resistance. The Ni-Cu-P membrane had an underwater oil contact angle of up to 140°, and simultaneously possessed rejection rate > 98 % with rather high flux of 65,663.0 L·m^-2·h^-1 and excellent cycling stability when separating n-hexane/water mixtures under gravity drive. The permeability is higher than the state-of-the-art membranes for oil/water separation. The Ni-Cu-P membrane as the cathode can be assembled into an electroflotation-membrane separation system, allowing to separate oil-in-water emulsion with 99 % rejection. Meanwhile, the applied electric field significantly improved membrane flux and fouling resistance (flux recovery up to 91 %) when separate kaolin suspensions. Polarization curve and Nyquist curve analysis further confirmed that addition of Cu element obviously enhanced corrosion resistance of the Ni modified membrane. This work provided a novel strategy to make up high-efficiency membranes for oily wastewater treatment.

Mitigation of protein fouling by magnesium ions and the related mechanisms in ultrafiltration process

Although protein is an important membrane foulant in the water body that may be significantly affected by the coexisting common cation magnesium (Mg²⁺), the effect of Mg²⁺ on protein fouling is rarely reported. In this context, this study selected bovine serum albumin (BSA) as the model foulant, and investigated its fouling characteristics at different Mg²⁺ concentrations (0-100 mM). Filtration tests showed that the protein fouling can be significantly mitigated by adding Mg²⁺, and the specific filtration resistance (SFR) of pure BSA (3.56 × 10¹⁴ m kg^-1) was at least 5 times that of BSA-Mg²⁺ solutions (0.5-100 mM). In addition, an optimal Mg²⁺ concentration exists, which can achieve the lowest BSA SFR. A series of characterizations indicated that the main contributors to the differences in BSA SFR were the changes in BSA adhesion capacity and the thickness and structure of the foulant layer. Basically, the above results were attributed to the hydration repulsion effect of Mg²⁺, which prevented tight adhesion of foulants to the membrane. Moreover, the lowest BSR SFR at 1 mM Mg²⁺ was achieved not only by the hydration repulsion effect but also by the particle size compression due to the conformational change of BSA molecules. This combined effect led to the lowest foulant retention on the membrane surface and delivered to the lowest SFR. This study conducts a thorough inspection into the specific effect of Mg²⁺ on protein fouling and provides a fresh insight into protein fouling control in the UF process.

Fine-tuning of carbon nanostructures/alginate nanofiltration performance: Towards electrically-conductive and self-cleaning properties

Electrically-conductive membranes became the center of attention owing to their enhanced ion selectivity and self-cleaning properties. Carbon nanostructures (CNS) attain high electrical conductivity, and fast water transport. Herein, we adopt a water-based, simple method to entrap CNS within Alginate network to fabricate self-cleaning nanofiltration membranes. CNS are embedded into membranes to improve the swelling/shrinkage resistivity, and to achieve electrical-conductivity. The CaAlg PEG-formed pores are tuned by organic-inorganic network via silane crosslinking. Flux/rejection profiles of Na₂SO₄ are studied/optimized in reference to fabrication parameters. 90% Na₂SO₄ rejection (7 LMH) is achieved for silane-CaAlg₂₀₀-10% CNS membranes. Membranes exhibit outstanding electrical conductivity (∼2858 S m^-1), which is attractive for fouling control. CaAlg/CNS membranes are tested to treat dye/saline water via two-stage filtration, namely, dye/salt separation and desalination. A successful dye/salt separation is achieved at the first stage with a rejection of 100%-RB and only 3.1% Na₂SO₄, and 54% Na₂SO₄ rejection in the second stage.

Metal-doped carbon-supported/modified titanate nanotubes for perfluorooctane sulfonate degradation in water: Effects of preparation conditions, mechanisms, and parameter optimization

Metal-doped, activated carbon (AC) supported titanate nanotubes (Me/TNTs@AC) have been shown promising for photocatalytic degradation of per- and polyfluoroalkyl substances (PFAS). However, the preparation recipe of the adsorptive photocatalysts has not yet been optimized in terms of type and content of precursor ACs and the metal dopants as well as synthesizing conditions. In this work, the photocatalytic performance of Me/TNTs@AC was evaluated based on the effectiveness in defluorination of pre-sorbed perfluorooctane sulfonic acid (PFOS) after 4-h UV irradiation. Based on the experimental results, the highest photocatalytic mineralization efficiency (66.2 %) of PFOS was achieved using Ga/TNTs@AC prepared under the following conditions: Filtrosorb-400® = 50 wt%, Ga = 2 wt%, hydrothermal treatment temperature = 130 °C, hydrothermal duration = 72 h, and calcination temperature = 550 °C. To understand the underlying mechanisms, selected materials were characterized via X-ray diffraction, the BET surface area and pore volume, UV-vis diffuse reflectance spectrometry, and photoluminescence. The results revealed that the superior photoactivity of Ga/TNTs@AC is attributed to the Ga-facilitated formation of pure crystallized anatase phase during the calcination, high UV light absorption, formation of microscale hybrid AC-anatase-Ga phases, and oxygen defects induced by Ga³⁺. The information can facilitate preparation and optimization of composite photocatalysts for efficient adsorption and photocatalytic degradation of PFAS in water.

Mechanistic insights into sulfate and phosphate-mediated hexavalent chromium removal by tea polyphenols wrapped nano-zero-valent iron

Nano zero-valent iron via green synthesis (g-nZVI) has great potential in removing toxic hexavalent Cr(VI) from industrial wastewater. Sulfate and phosphate in wastewater can influence Cr(VI) removal by g-nZVI. In this study, the Cr(VI) removal kinetics by different g-nZVI materials were investigated with the existence of sulfate and/or phosphate, and the corresponding mechanisms were first revealed using multiple characterizations, including X-ray absorption near-edge spectra (XANES) and X-ray photoelectron spectroscopy (XPS). The results showed that Cr(OH)₃ was the dominant species initially formed on the surface of g-nZVI particles before transforming to Cr₂O₃ during the reaction of g-nZVI with Cr(VI). Sulfate in wastewater can promote the reduction from Cr(VI) to Cr(OH)₃ by g-nZVI, because sulfate triggers the release of Fe(II) and tea polyphenols (from tea extracts) from the g-nZVI surface due to the corrosion of Fe⁰ core, which is in line with an obvious increase in pseudo-second-order rate constant (k₂) and subtle change in Cr(VI) removal capacity (q_e). However, phosphate impedes the g-nZVI corrosion and inhibits q_e because of the inner-sphere complexation of phosphate onto g-nZVI decreasing the released Fe(II) for Cr₂O₃ production. When sulfate and phosphate coexisted in contaminated water, the inhibition effect of phosphate in Cr(VI) removal by g-nZVI was stronger than the promotion of sulfate. Accordingly, q_e value of g-nZVI declined from 93.4 mg g^-1 to 77.5 mg g^-1, while k₂ remained constant as the molar ratio of phosphate/sulfate increased from 0.1 to 10 in water. This study provides new insights into applying g-nZVI in efficient Cr(VI) removal from contaminated water with enrichment of sulphates and phosphates.

Molecular insights into membrane fouling caused by polysaccharides with different structures in polyaluminum chloride coagulation-ultrafiltration process

In this study, mechanisms of membrane fouling caused by polysaccharides with different molecular structures in polyaluminum chloride (PACl) coagulation-ultrafiltration (C-UF) process were explored. Carrageenan and xanthan gum were chosen for model foulants of straight chain and branched chain polysaccharides, respectively. Filtration experiments showed that, with PACl dosage of 0-5 mM, specific filtration resistance (SFR) of carrageenan and xanthan solution showed a unimodal pattern and a continuous decrease pattern, respectively. A series of experimental characterizations indicated that the different SFR pattern was closely related to structure of foulants layer. Density functional theory (DFT) calculation suggested that Al³⁺ preferentially coordinating with the terminal sulfonyl groups of carrageenan chains to promote gel layer formation at low PACl concentration (0.15 mM). There existed a chemical potential gap between bound water in gel layer and free water in the permeate, so that, filtration through gel layer corresponded to rather high SFR for overcoming this gap. In contrast, Al³⁺ coordinating with the non-terminal sulfonyl groups of carrageenan at high PACl concentration caused transition from gel layer to cake layer, leading to SFR decrease. However, xanthan gum itself can form a dense gel layer with a complex polymer network by virtue of the interlacing of main chains and branches. Al³⁺ coordinating with the carboxyl groups on branched chains of xanthan gum resulted in clusters of polymer chains and flocculation, corresponding to the reduced SFR. This proposed molecular-level mechanism well explained membrane fouling behaviors of polysaccharides with different molecular structure, and also facilitated to optimize C-UF process for water treatment.

Impacts of Calcium Addition on Humic Acid Fouling and the Related Mechanism in Ultrafiltration Process for Water Treatment

Humic acid (HA) is a major natural organic pollutant widely coexisting with calcium ions (Ca²⁺) in natural water and wastewater bodies, and the coagulation-ultrafiltration process is the most typical solution for surface water treatment. However, little is known about the influences of Ca²⁺ on HA fouling in the ultrafiltration process. This study explored the roles of Ca²⁺ addition in HA fouling and the potential of Ca²⁺ addition for fouling mitigation in the coagulation-ultrafiltration process. It was found that the filtration flux of HA solution rose when Ca²⁺ concentration increased from 0 to 5.0 mM, corresponding to the reduction of the hydraulic filtration resistance. However, the proportion and contribution of each resistance component in the total hydraulic filtration resistance have different variation trends with Ca²⁺ concentration. An increase in Ca²⁺ addition (0 to 5.0 mM) weakened the role of internal blocking resistance (9.02% to 4.81%) and concentration polarization resistance (50.73% to 32.17%) in the total hydraulic resistance but enhanced membrane surface deposit resistance (33.93% to 44.32%). A series of characterizations and thermodynamic analyses consistently suggest that the enlarged particle size caused by the Ca²⁺ bridging effect was the main reason for the decreased filtration resistance of the HA solution. This work revealed the impacts of Ca²⁺ on HA fouling and demonstrated the feasibility to mitigate fouling by adding Ca²⁺ in the ultrafiltration process to treat HA pollutants.

Superhydrophobic nanofibrous sponge with hierarchically layered structure for efficient harsh environmental oil-water separation

Oil leakage has posed serious threat to the environment, but still remain a great challenge to be solved especially for harsh environmental conditions. Herein, robust superhydrophobic nickel hydroxide grown by hydrothermal method and stearic acid modification on a blow-spun polyacrylonitrile (PAN)/Al₂O₃ nanofibrous sponge was proposed, so that the nickel hydroxide-modified polyacrylonitrile sponge (NPAS) was successfully obtained for efficient oil-water separation. The porous NPAS with a distinctive hierarchically layered structure, which exhibited excellent separation efficiency and mechanical elasticity. Due to its superhydrophobic and high porosity, the absorption capacity of NPAS could reach as high as 45 g g^-1. It could not only separate a series of oil-water mixture with a high steady flux of 12,413 L m^-2 h^-1 (dichloromethane-water), but also separate stabilized emulsions with a superior flux 2032 L m^-2 h^-1 (water-in-dichloromethane) under gravity, all of that with above 99.92% separation efficiencies, which was higher than that of the most reported sponges. Most importantly, its strong acid/alkali resistance enable it is suitable for hazardous materials treatment applications in harsh environmental conditions. This novel NPAS via facile large-scale blow-spinning provide an efficient strategy for oil-containing wastewater treatment and environmental protection.

Mechanistic insights into Ca-alginate gel-associated membrane fouling affected by ethylene diamine tetraacetic acid (EDTA)

While transparent exopolymer particles (TEP) is a major foulant, and ethylene diamine tetraacetic acid (EDTA) is a strong chelating agent frequently used for fouling mitigation in membrane-based water treatment processes, little has been known about TEP-associated membrane fouling affected by EDTA. This work was performed to investigate roles of EDTA addition in TEP (Ca-alginate gel was used as a TEP model) associated fouling. It was interestingly found that, TEP had rather high specific filtration resistance (SFR) of 2.49 × 10¹⁵ m^-1·kg^-1, and SFR of TEP solution firstly decreased and then increased rapidly with EDTA concentration increase (0-1 mM). A series of characterizations suggested that EDTA took roles in SFR of TEP solution by means of changing TEP microstructure. The rather high SFR of TEP layer can be attributed to the big chemical potential gap during filtration described by the extended Flory-Huggins lattice theory. Initial EDTA addition disintegrated TEP structure by EDTA chelating calcium in TEP, inducing reduced SFR. Continuous EDTA addition decreased solution pH, resulting into no effective chelating and accumulation of EDTA on membrane surface, increasing SFR. It was suggested that factors increasing homogeneity of TEP gel will increase SFR, and vice versa. This study revealed the thermodynamic mechanism of TEP fouling behaviors affected by EDTA, and also demonstrated the importance of EDTA dosage and pH adjustment for TEP-associated fouling control.

Molecular Characterization and Biocompatibility of Exopolysaccharide Produced by Moderately Halophilic Bacterium Virgibacillus dokdonensis from the Saltern of Kumta Coast

The use of natural polysaccharides as biomaterials is gaining importance in tissue engineering due to their inherent biocompatibility. In this direction, the present study aims to explore the structure and biocompatibility of the EPS produced by Virgibacillus dokdonensis VITP14. This marine bacterium produces 17.3 g/L of EPS at 96 h of fermentation. The EPS was purified using ion exchange and gel permeation chromatographic methods. The porous web-like structure and elemental composition (C, O, Na, Mg, P, S) of the EPS were inferred from SEM and EDX analysis. AFM analysis revealed spike-like lumps with a surface roughness of 84.85 nm. The zeta potential value of −10 mV indicates the anionic nature of the EPS. Initial molecular characterization showed that the EPS is a heteropolysaccharide composed of glucose (25.8%), ribose (18.6%), fructose (31.5%), and xylose (24%), which are the monosaccharide units in the HPLC analysis. The FTIR spectrum indicates the presence of functional groups/bonds typical of EPSs (O-H, C-H, C-O-H, C-O, S=O, and P=O). The polymer has an average molecular weight of 555 kDa. Further, NMR analysis revealed the monomer composition, the existence of two α- and six β-glycosidic linkages, and the branched repeating unit as → 1)[α-D-Xylp-(1 → 2)-α-D-Glcp-(1 → 6)-β-D-Glcp-(1 → 5)]-β-D-Frup-(2 → 2)[β-D-Xylp-(1 → 4)]-β-D-Xylp-(1 → 6)-β-D-Fruf-(2 → 4)-β-D-Ribp-(1 →. The EPS is thermally stable till 251.4 °C. X-ray diffraction analysis confirmed the semicrystalline (54.2%) nature of the EPS. Further, the EPS exhibits significant water solubility (76.5%), water-holding capacity (266.8%), emulsifying index (66.8%), hemocompatibility (erythrocyte protection > 87%), and cytocompatibility (cell viability > 80% on RAW264.7 and keratinocyte HaCaT cells) at higher concentrations and prolongs coagulation time in APTT and PT tests. Our research unveils the significant biocompatibility of VITP14 EPS for synthesizing a variety of biomaterials.

Impact of sulfur-impregnated biochar amendment on microbial communities and mercury methylation in contaminated sediment

S-impregnation of biochar through elemental S streaming is known to increase its sorption performance against Hg and methyl mercury (MeHg). However, the effects of %S-loading on biochar's mechanism and sorption capacities for MeHg, and its consequent impact when used as an amendment material for Hg-contaminated sediments, are poorly understood, and thus, were investigated in this work. Our results showed that a minimum sulfur loading of 1% was the most effective in reducing MeHg levels in sediments. At higher %S-loading (3-20%), the reduction in surface area, pore blockage due to unreacted sulfur particles, and presence of poorly bound sulfur species resulted in lowered effectiveness for MeHg control. Increasing S-functionalization during impregnation shifted the sorption process of MeHg from Hg-O to Hg-S in S-impregnated biochar (BCS). Our 60-day slurry experiment showed a significant reduction in pore water THg (40-70%) and MeHg (30-55%), as well as sediment MeHg (50-60%) in biochar-amended sediments. The reduction in the bioavailable Hg resulted in lowered Hg methylation, as supported by the suppression of both the Fe- and SO₄^2--reduction activities in the amended sediments. The microbial community structure in BCS-amended sediments showed a shift towards sulfur-consuming, iron-reducing, thiosulfate-oxidizing, and sulfate-reducing bacterial populations. At the genus level, the overall relative abundance of principal Hg methylators was also lower in the BCS treatment than in the unamended sediments. This study highlights the application of BCS as a promising strategy for remediation of Hg-contaminated sediments.

Optimized production conditions and activation of biochar for effective promotion of long-chain fatty acid degradation in anaerobic digestion

Engineered biochar production and utilization in anaerobic digestion (AD) potentially overcome its limited application to the treatment of slowly degradable or inhibitory substrates. Here an attempt was made to develop an optimized biochar production procedure for use in AD to stimulate palmitic acid biodegradation via direct interspecies electron transfer (DIET). The electrical conductivity of biochar was greatly increased with an elevated pyrolysis temperature and K₂CO₃ activation, and the conductivity reached a comparable level (0.6-1.4 S/cm) to that of carbon black at 800 °C. In addition, the K₂CO₃ activation greatly improved biochar wettability. When using K₂CO₃-activated biochar produced at 800 °C, the maximum methane production rate from palmitic acid was 1.3 times that of a control without biochar addition.