Novel in-situ electroflotation driven by hydrogen evolution reaction (HER) with polypyrrole (PPy)-Ni-modified fabric membrane for efficient oil/water separation

Bio-Inspired Underwater Superoleophobic Aramid Nanofiber-Based Aerogel Membranes for Highly Efficient Removal of Emulsified Oils and Organic Dyes

Effective elimination of insoluble emulsified oils and soluble organic dyes has received extensively attention in wastewater treatment. In this work, a chitosan and polydopamine @ aramid nanofibers (CS&PDA@ANFs) aerogel membrane was fabricated through an integration methodology consisting of phase inversion and successive deposition of PDA and CS. The as-prepared aerogel membrane possessed a satisfactory three-dimensional interpenetrating network architecture with high porosity and desirable mechanical property. Furthermore, due to the synergistic effect of hydrophilic CS and PDA, the resultant membrane exhibited good superhydrophilicity and underwater superoleophobicity associated with favorable oil resistance/antioil fouling properties. The combination of the interconnected porous structures and super wettability endowed the aerogel membranes with desirable oil-in-water emulsion separation performance. Particularly, an extremely high permeation flux (3729 L/m2/h) and a rejection rate (99.3%) were achieved for the CS&PDA@ANFs membrane. Moreover, diverse dyes could be also adsorbed by the resultant membrane, and the equilibrium adsorption capacity of cationic dye malachite green could reach 36 mg/g, with a high rejection rate over 97%. This study indicated that the CS&PDA@ANFs aerogel membrane held great promise for practical applications in complex wastewater remediation.

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.

Superior performance of a membrane bioreactor through innovative in-situ aeration and structural optimization using computational fluid dynamics

The optimization of membrane bioreactors (MBRs) involves a critical challenge in structural design for mitigation of membrane fouling. To address this issue, a three-dimensional computational fluid dynamics (CFD) model was utilized in this study to simulate the hydrodynamic characteristics of a flat sheet (FS) MBR. The optimization of the membrane module configuration and operating conditions was performed by investigating key parameters that altered the shear stress and liquid velocity. The mixed liquor suspended solids (MLSS) concentration was found to increase the shear stress, leading to a more uniform distribution of shear stress. By optimizing the appropriate bubble diameter to 5 mm, the shear stress on the membrane surface was optimized with relatively uniform distribution. Additionally, extending the side baffle length dramatically improved the uniformity of the shear stress distribution on each membrane. A novel in-situ aeration method was also discovered to promote turbulent kinetic energy by 200 times compared with traditional aeration modes, leading to a more uniform bubble streamline. As a result, the novel in-situ aeration method demonstrated superior membrane antifouling potential in the MBR. This work provides a new approach for the structural design and optimization of MBRs. The innovative combination of the CFD model, optimization techniques, and novel in-situ aeration method has provided a substantial contribution to the advancement of membrane separation technology in wastewater treatment.

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.

Rh metallene with functionalized polypyrrole surface for hydrogen evolution over a wide pH range

Interface engineering of two-dimensional (2D) materials by conductive polymer modification is one of the valid methods to promote hydrogen evolution reaction (HER) performance. Herein, we report a simple and universal strategy for the synthesis of polypyrrole (PPy) modified Rh metallene (Rh@PPy metallene) towards an efficient pH-universal HER. Due to the unique ultrathin 2D metallene structure and the optimized electronic structure between the metallene-PPy surfaces, the as-prepared Rh@PPy metallene not only exhibits excellent HER activity with low overpotentials of 16, 39 and 42 mV in 0.5 M H₂SO₄, 1 M KOH, and 1 M phosphate buffer solution at current density of 10 mA cm^-2, but also displays outstanding stability and durability. This work provides a well-founded pathway to constructe metallene-organic interfaces for various electrocatalytic applications.

Preparation of Ni@UiO-66 incorporated polyethersulfone (PES) membrane by magnetic field assisted strategy to improve permeability and photocatalytic self-cleaning ability

Metal-organic frameworks (MOFs) have been considered as promising nanofillers to fabricate mixed matrix membranes for water treatment. However, manipulating distribution of MOFs nanoparticles in the membrane matrix remains a great challenge. In this study, UiO-66 was firstly coated by magnetic Ni via an in-situ reduction reaction, and then incorporated into polyethersulfone (PES) membrane matrix to prepare PES-Ni@UiO-66 membrane. The magnetic Ni allowed to manipulate the distribution of magnetic Ni@UiO-66 in the phase-inversion process by an external magnetic field. The hydrophilic Ni@UiO-66 can be pulled onto membrane surface by the magnetic force, endowing the prepared membrane with rather higher hydrophilicity. The prepared membrane exhibited superior water permeability with a pure water flux of 611.5 ± 19.8 L·m^-2·h^-1 and improved antifouling performance. Moreover, benifiting from photocatalytic activity of the exposed Ni@UiO-66 on membrane surface, the obtained PES-Ni@UiO-66 membrane demonstrated excellent photocatalytic self-cleaning ability with a flux recovery rate (FRR) higher than 95% under UV irradiation. Analyzing by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory indicated that the improved antifouling performance could be attributed to less attractive or even repulsive interaction between the prepared membrane and pollutants. This work provided valuable guidance for structural regulation and development of high-performance MOFs-based membranes for water treatment.

Slippery Mechanism for Enhancing Separation and Anti-fouling of the Superhydrophobic Membrane in a Water-in-Oil Emulsion: Evaluating Water Adhesion of the Membrane Surface

Water removal from water-in-oil emulsions with superhydrophobic microporous membranes is an important industrial process, where the interface property between the membrane and feed becomes critical. Here, superhydrophobic isotactic polypropylene (iPP) microporous membranes with the "lotus effect" and "rose-petal effect" were prepared via utilizing micromolding phase separation, where the former surface exhibited a water contact angle of 153° and a sliding angle of 3.2°, while the latter surface exhibited a water contact angle of 151° and adhesive characteristics. Surface topography and wettability analysis revealed that surface hydrophobicity and water adhesion could be improved by reducing the periodic distance and diameter and increasing the height of the micron-scale structure. When treating both water-in-oil emulsions and water-in-oil emulsions containing BSA pollutants, the iPP membrane with the "lotus effect" was superior to that with the "rose-petal effect" in terms of oil permeate flux, separation efficiency, anti-fouling ability, and recyclability (20 cycles). To explain this phenomenon, a "slippery" mechanism was introduced that correlated the sliding angle to the slippery surface of the iPP membrane with the "lotus effect" and its anti-water adhesion property. This work proposed a theoretical platform for investigating the effect of water adhesion on superhydrophobic membranes in terms of oil-water separation efficiency and anti-fouling ability, thereby providing a definite basis for preparing superhydrophobic membranes with efficient separation and fouling resistance capabilities.

Structured sludge derived multifunctional layer for simultaneous separation of oil/water emulsions and anions contaminants

The effective treatment of complex oily wastewater is of great significance but still a considerable challenge, since single-function, expensive reagents, and complicated process have emerged as shackles for practical applications. Herein, with the objective to waste-control-waste, we proposed a facile and sustainable strategy to fabricate a low-cost multifunctional layer from hazardous waste aluminum sludge (WAS) for complex oily wastewater management. The as-designed layered double oxides/WAS (LDOs/WAS) layer with three-dimensional (3D) hierarchical rough surface exhibited excellent underwater superoleophobicity even under corrosive conditions and low adhesion to oil without any chemical modification reagent treatment. Significantly, the layer can be applied to gravity-directed simultaneous efficient oil-in-water emulsions and anions (taking phosphate as an example) separation with a separation efficiency for emulsion and phosphate up to 99.4% and 99.1%, respectively, and a high separation flux of above 2585 L m^-2 h^-1. Notably, the flux can be controlled simply and flexibly by adjusting the thickness of the layer. Furthermore, the layer also displayed excellent thermal stability, chemical stability, durability and recyclability. Therefore, this work not only presents a promising approach to design sludge-based multifunctional materials for complex oily wastewater remediation, but also shows great potential and value in environmental pollutions reduction and industrial applications.

Piezoelectricity induced by pulsed hydraulic pressure enables in situ membrane demulsification and oil/water separation

Recovering oil from oily wastewater is not only for economic gains but also for mitigating environmental pollution. However, demulsification of oil droplets stabilized with surfactants is challenging because of their low surface energy. Although the widely used oil/water separation membrane technologies based on size screening have attracted considerable attention in the past few decades, they are incapable of demulsification of stabilized oil emulsions and the membrane concentrates often require post-processing. Herein, the piezoelectric ceramic membrane (PCM), which can respond to the inherent transmembrane pressure in the pressure-driven membrane processes, was employed to transform hydraulic pressure pulses into electroactive responses to in situ demulsification. The pulsed transmembrane pressure on the PCM results in the generation of considerable rapid voltage oscillations over 3.2 V and a locally high electric field intensity of 7.2 × 10⁷ V/m, which is capable of electrocoalescence with no additional stimuli or high voltage devices. Negative dielectrophoresis (DEP) force occurred in this membrane process and repelled the large size of oil after demulsification away from the PCM surface, ensuring continuous membrane demulsification and oil/water separation. Overall, PCM provides a further opportunity to develop an environmentally friendly and energy-saving electroresponsive membrane technology for practical applications in wastewater treatment.

In-situ synthesis of non-phase-separated boron carbon nitride for photocatalytic reduction of CO2

Non-phase-separated hexagonal boron carbon nitride (h-BCN) is an emerging type of promising metal-free photocatalyst, but the synthesis of this material remains quite challenging. Here, h-BCN without phase separation was obtained through a novel organic-inorganic hybrid precursor pyrolysis method using boric acid and ethylenediamine as raw materials. The resultant BCN-1 exhibited excellent photocatalytic activity for CO₂ reduction, as confirmed by a CO generation rate of 13.97 μmol g^-1 h^-1 under visible light illumination with no co-catalyst or sacrificial agent. This rate was 9.4 times higher than that of g-C₃N₄ (2.1 μmol g^-1 h^-1) under the same experimental condition. The pre-existing C-N-B bond is essential for mediating the growth kinetics and diminishing the thermodynamically preferred C and BN phase-segregation structure, while ammonia is crucial for C-N-B bond fixation and pore formation during the pyrolysis process. This finding of a facile method for synthesizing non-phase-separated BCN has positive effects on the study of photocatalytic CO₂ reduction by sustainable metal-free catalysts.

Surface-engineered polyethersulfone membranes with inherent Fe-Mn bimetallic oxides for improved permeability and antifouling capability

In recent years, bimetallic oxide nanoparticles have garnered significant attention owing to their salient advantages over monometallic nanoparticles. In this study, Fe₂O₃-Mn₂O₃ nanoparticles were synthesized and used as nanomodifiers for polyethersulfone (PES) ultrafiltration membranes. A NIPS was used to fabricate asymmetric membranes. The effect of nanoparticle concentration (0-1 wt.%) on the morphology, roughness, wettability, porosity, permeability, and protein filtration performance of the membranes was investigated. The membrane containing 0.25 wt% nanoparticles exhibited the lowest water contact angle (67°) and surface roughness (10.4 ± 2.8 nm) compared to the other membranes. Moreover, this membrane exhibited the highest porosity (74%) and the highest pure water flux (398 L/m² h), which was 16% and 1.9 times higher than that of the pristine PES membrane. The modified PES membranes showed an improved antifouling ability, especially against irreversible fouling. Bovine serum albumin protein-based dynamic five-cycle filtration tests showed a maximum flux recovery ratio of 77% (cycle-1), 67% (cycle-2), and 65.8% (cycle-5) for the PES membrane containing 0.25 wt% nanoparticles. Overall, the biphasic Fe₂O₃-Mn₂O₃ nanoparticles were found to be an effective nanomodifier for improving the permeability and antifouling ability of PES membranes in protein separation and water treatment applications.

Insights into the impact of polydopamine modification on permeability and anti-fouling performance of forward osmosis membrane

Forward osmosis (FO) has drawn wide attention as a promising method to address world-wide water crisis due to the advantages of low-energy consumption and easy separation operation. Unfortunately, the trade-off between permeability and selectivity as well as membrane fouling hindered the application of forward osmosis. Surface modification is a feasible method to address these issues. However, there is a lack of systematic evaluation about the effect of modification position on FO performance due to the asymmetric structure of thin film composite (TFC) FO membrane. To provide new insights into the design of FO membrane with satisfied permeability and fouling resistance, novel TFC FO membranes were fabricated by introducing polydopamine (PDA) on the support layer (TFC-I) or active layer (TFC-S), respectively. The surface morphology, chemical composition and wettability of the fabricated membrane were studied. It was found that the surface wettability of the modified membrane was improved greatly compared to pristine TFC membrane (TFC-C). Moreover, TFC-S membrane displayed a rougher surface than that of TFC-I membrane. As a result, a superior TFC-S membrane with a water flux of 60.95 ± 3.15 L m^-2h^-1 in AL-DS mode was obtained, which was 72.61% and 17.87% higher than that of TFC-C and TFC-I membrane, respectively. In addition, the TFC-S membrane also presented an excellent fouling resistance and membrane regeneration performance during the three organic fouling cycle experiments. The results indicated that the introduction of PDA as a surface coating for TFC membranes modification guaranteed the high-performance and fouling resistance. Especially, the PDA coating on the support layer surface resulted in an enhancement in permeability, while both the permeability and anti-fouling performance were significantly improved with the PDA coating on the polyamide active layer surface. This study provides new insights into the development of modification TFC-FO membranes for practical applications in water treatment.

Polymeric Membranes for Oil-Water Separation: A Review

This review is devoted to the application of bulk synthetic polymers such as polysulfone (PSf), polyethersulfone (PES), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF) for the separation of oil-water emulsions. Due to the high hydrophobicity of the presented polymers and their tendency to be contaminated with water-oil emulsions, methods for the hydrophilization of membranes based on them were analyzed: the mixing of polymers, the introduction of inorganic additives, and surface modification. In addition, membranes based on natural hydrophilic materials (cellulose and its derivatives) are given as a comparison.

Self-assembled supramolecule for synthesizing highly thermally conductive Cellulose/Carbon nitride nanocomposites with improved flame retardancy

The fabrication of polymer composites with excellent thermal conductivity typically involves complex matrix or fillers modifications. This study proposed a simple technique based on precursor selection for obtaining highly thermally conductive cellulose nanofiber (CNF)/supramolecule-synthesized carbon nitride (SCN) composites. Fourier-transform infrared tests demonstrated the construction of hydrogen bonds between CNF and SCN; a highly ordered structure and relatively compact in-plane stacking were confirmed via scanning electron microscopy and X-ray diffraction characterizations. Consequently, the resultant CNF/SCN composites exhibited remarkable in-plane thermal conductivity of 11.83 ± 0.41 W m^-1 K^-1 at 30 wt% SCN content, which was attributed to the significantly reduced interfacial phonon scattering. It also showed evident improvements in electrical insulation and flame retardancy compared with the pure CNF film, where the volume resistivity, peak heat release rate, and total heat release were remarkably enhanced by 1242% and reduced by 59.9% and 15.8%, respectively. Further analysis of char residuals revealed a relatively dense surface, high concentration of carbon materials, and a high degree of graphitization, indicating that the char residual functioned as a robust physical barrier to effectively inhibit combustion. This study provides a facile approach to achieving high-efficiency improvements in thermal conductivity and flame retardancy, and simultaneously facilitating broader applications of carbon nitride in thermal management.

A novel composite membrane for simultaneous separation and catalytic degradation of oil/water emulsion with high performance

It is of great significance to develop novel membranes with dual-function of simultaneously separating oil/water emulsion and degrading the contained water-miscible toxic organic components. To meet this requirement, a dual-functional Ni nanoparticles (NPs)@Ag/C-carbon nanotubes (CNTs) composite membrane was fabricated via electroless nickel plating strategy in this study. The as-prepared composite membrane possessed superhydrophilicity with water contact angle of 0° and splendid underwater oleophobic property with oil contact angle of 142°. When the membrane was applied for separation of surfactant stabilized oil-in-water emulsion, high permeate flux (about 97 L m^-2·h^-1 under gravity), oil rejection (about 98.8%) and antifouling property were achieved. Benefitting from the NiNPs@Ag/C-CNTs layer on membrane surface, the composite membrane exhibited high catalytic degradation activity for water-miscible toxic organic pollutant (4-nitrophenol) with addition of NaBH₄ in a flow-through mode. Meanwhile, the NiNPs@Ag/C-CNTs composite membrane possessed excellent durability, which was verified by the good structural integrity even under ultrasonic treatment. The cost-efficiency, high separation and degradation performance of the prepared membrane suggested its great potential for treatment of oily wastewater.

Probe decorated porous silica and polymer monoliths as solid-state optical sensors and preconcentrators for the selective and fast recognition of ultra-trace arsenic ions

In this work, we manifested a new approach in designing solid-state colorimetric sensors for the selective optical sensing of As³⁺. The sensor fabrication is modulated using, (i) a cubic mesopores of ordered silica monolith, and (ii) a bimodal macro-/meso-porous polymer monolith, as hosting templates that are immobilized with a tailor-made chromoionophoric probe (DFBEP). The surface morphology and structural dimensions of the monolith templates and the sensor materials are characterized using p-XRD, XPS, FE-SEM-EDAX, HR-TEM-SAED, FT-IR, TGA, and BET/BJH analysis. The sensing components such as pH, probe content, sensor dosage, kinetics, temperature, analyte concentration, linear response range, selectivity, and sensitivity are optimized to arrive at the best sensing conditions. The silica and polymer-based monolithic sensors show a linear spectral response in the concentration range of 2-300 and 2-200 ppb, with a detection limit of 0.87 and 0.75 ppb for As³⁺, respectively. The real-time ion-monitoring propensity of the sensors is tested with spiked synthetic and real water samples, with a recovery efficiency of ≥99.1% (RSD ≤1.57%). The sensors act as both naked-eye optical sensors and preconcentrators, with a response time of ≤2.5 min. The molecular and photophysical properties of the DFBEP-As³⁺ complex are studied by TD-DFT calculations, using the B3LYP/6-31G (d,p) method.

Characterizing membrane fouling formation during ultrafiltration of high-salinity organic wastewater

High-salinity organic wastewater usually consists of diverse highly concentrated ions such as Na⁺, Ca²⁺ and Al³⁺ etc., which may significantly influence the fouling propensity when membrane technique is employed for contaminants removal. The current work investigated the effects of high salinity especially high-concentration Na⁺, Ca²⁺ and Al³⁺ on UF fouling characteristics, where 2 M Na⁺ and 0.5-1.0 M Ca²⁺ or Al³⁺ were applied according to the general composition of high-salinity wastewater. The results demonstrated that the presence of high-concentration Na⁺ alone benefited the ultrafiltration of bovine serum albumin (BSA) solution, but posed adverse effects on the ultrafiltration of humic acid (HA) solution. Further addition of Ca²⁺ or Al³⁺ on the basis of Na⁺ was found to aggravate the development of BSA fouling. Such differentiated behaviors were further elucidated by the comprehensive fouling characterizations in terms of foulant properties, specific resistances, filtration modelling and fouling layer observations. Correlation analysis suggested that irreversible fouling had strong relationship with Al³⁺ addition, while reversible fouling seemed to be primarily influenced by foulant size. Meanwhile, membrane rejection in the presence of various salts remarkably decreased, which was negatively correlated with zeta potential. Consequently, this study should shed light on the membrane fouling formation for treating high-salinity organic wastewater using membrane techniques.

Anti-fouling and protein separation of PVDF-g-PMAA@MnO2 filtration membrane with in-situ grown MnO2 nanorods

MnO₂ nanorods with controllable scale were grown in the PVDF-g-PMAA modified membrane to form PVDF-g-PMAA@ MnO₂ membrane through the in situ redox reaction of KMnO₄ solution, which is confirmed by scanning electron microscopy (SEM) and X-ray energy-dispersion spectroscopy (EDX). The pore size of the membrane decreased with the increase of KMnO₄ solution concentration. The thermodynamic stability and the hydrophilicity of the membrane were also enhanced by the MnO₂ nanorods. The water flux, bovine serum albumin (BSA)/Lysozyme protein solution flux and rejection, flux recovery, etc. showed effective improvement of the anti-fouling performance of the PVDF-g-PMAA@ MnO₂ membrane. More importantly, it can effectively separate BSA from lysozyme, which provided a potential application in the field of biology, food, and other industrial fields for the requirement of separation and purification.

Multiple fouling dynamics, interactions and synergistic effects in brackish surface water distribution systems

Dissolved salts, colloidal particles, and active microorganisms in brackish surface water distribution systems (BSWD) cause multiple fouling, poses potential threat to the environmental pollution, and raising technical and economic issues as well. So far, the co-occurrence and interactions of multiple fouling remains largely unknown. Multiple fouling behaviors were assessed in agriculture BSWD under different nitrogen (N) fertilizers. X-ray diffraction, Rietveld refinement analysis, 16S rRNA, and microbial network analysis were conducted to determine the fouling characteristics. Statistical analysis was applied to reveal the relative contributions and interaction of multiple fouling. Our results demonstrated, multiple fouling of precipitates, particulates and biofoulings were co-occurred. Fouling growth was largely attributed to the strong interactions of different fouling. The binary interactions of precipitates - particulates contributed 51.1%, and ternary interactions of precipitates - particulates - biofouling contributed 25.4% to explain the decline of system performance, while the contribution of each single type fouling was minimal. Thereby indicating the significant role of calcium silica, biomineralization and bio-silicates in fouling. The lower acid N fertilizer broken the interaction of multiple fouling by increasing the precipitate crystal parameters and repulsive forces amongst particulates, as well as destroyed microbial interactions in biofouling. Overall, this study open frontier for multiple fouling in-depth profiling and antifouling guidance for effective utilization of BSWD.

FeNi2P three-dimensional oriented nanosheet array bifunctional catalysts with better full water splitting performance than the full noble metal catalysts

The 3D (three-dimensional) oriented nanosheet array FeNi₂P electrocatalyst grown on carbon cloth (FeNi₂P/CC) is explored in this work. This unique 3D oriented nanosheet array structure can expose more catalytic active sites, promote the penetration of electrolyte solution on the catalyst surface, and facilitate the transfer of ions, thus speeding up the kinetic process of Hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER). At the current densities of 10 mA/cm² in 1 M KOH solution, the HER overpotential (71 mV) of the FeNi₂P/CC self-supporting electrode is very close to that of noble metal HER catalyst of 20% Pt/C (54 mV), and its OER overpotential (210 mV) is 34% lower than that of the precious metal OER catalyst of RuO₂ (318 mV), demonstrating the excellent electrocatalytic performance of the FeNi₂P/CC catalyst. Moreover, the cell voltage for full water splitting (at 10 mA/cm² current densities) of the FeNi₂P/CC bifunctional electrode cell is 1.52 V, which is 3.8% lower than that of the full noble-metal electrode reference cell (RuO₂ || Pt/C, 1.58 V), suggesting that this FeNi₂P/CC bifunctional catalyst is likely to replace precious metals to reduce the costs in full water splitting application. According to density functional theory (DFT) calculation results, the introduction of iron atom can change the electronic structure of the Ni₂P, so it can reduce the adsorption energy of hydrogen and oxygen, and facilitate the adsorption and desorption of hydrogen and oxygen on the surface of the catalyst, improving its performance of HER and OER.

Effects of High Salinity on Alginate Fouling during Ultrafiltration of High-Salinity Organic Synthetic Wastewater

Ultrafiltration is widely employed in treating high-salinity organic wastewater for the purpose of retaining particulates, microbes and macromolecules etc. In general, high-salinity wastewater contains diverse types of saline ions at fairly high concentration, which may significantly change foulant properties and subsequent fouling propensity during ultrafiltration. This study filled a knowledge gap by investigating polysaccharide fouling formation affected by various high saline environments, where 2 mol/L Na⁺ and 0.5–1.0 mol/L Ca²⁺/Al³⁺ were employed and the synergistic influences of Na⁺-Ca²⁺ and Na⁺-Al³⁺ were further unveiled. The results demonstrated that the synergistic influence of Na⁺-Ca²⁺ strikingly enlarged the alginate size due to the bridging effects of Ca²⁺ via binding with carboxyl groups in alginate chains. As compared with pure alginate, the involvement of Na⁺ aggravated alginate fouling formation, while the subsequent addition of Ca²⁺ or Al³⁺ on the basis of Na⁺ mitigated fouling development. The coexistence of Na⁺-Ca²⁺ led to alginate fouling formed mostly in a loose and reversible pattern, accompanied by significant cracks appearing on the cake layer. In contrast, the fouling layer formed by alginate-Na⁺-Al³⁺ seemed to be much denser, leading to severer irreversible fouling formation. Notably, the membrane rejection under various high salinity conditions was seriously weakened. Consequently, the current study offered in-depth insights into the development of polysaccharide-associated fouling during ultrafiltration of high-salinity organic wastewater.