Microporous Hydrophobic Membrane Research Articles

Evaluating the feasibility of direct contact membrane distillation and nanofiltration in ground water treatment through a techno-economic analysis

This study delves into the realm of water treatment by conducting a comprehensive techno-economic evaluation of direct contact membrane distillation (DCMD) and nanofiltration (NF) processes. While previous research has explored the technical aspects of membrane distillation (MD) and nanofiltration, there remains a notable gap in economic analyses. Our research aims to bridge this gap by assessing the financial feasibility of employing MD and NF technologies for water desalination. Specifically, we scrutinize the performance of hydrophobic microporous flat sheet membranes crafted from polytetrafluoroethylene (PTFE) supported by non-woven polypropylene (PP) in desalinating brackish water through DCMD and NF processes. By varying operating conditions such as flow rate and feed temperature, we evaluate the membrane's efficacy. Employing an analytical model based on heat and mass transfer equations, we predict process performance across diverse scenarios. Our model demonstrates a high level of accuracy, with flux predictions deviating by less than 10% when utilizing the Knudsen-molecular mechanism model. Furthermore, through a detailed design and economic analysis of industrial-scale units for both processes, we reveal that the cost of permeated water is lower with NF compared to DCMD. Specifically, our calculations indicate a water cost of 1.34 USD/m3 for DCMD at a feed temperature of 65 °C with an 80% recovery rate, positioning it as a competitive option among conventional desalination methods. Notably, our financial assessment highlights that steam cost constitutes the primary expense in DCMD operations, contingent upon heating value and fuel prices. Noteworthy findings suggest that natural gas emerges as the most cost-effective fuel for steam production in a DCMD plant. This study underscores the economic viability and potential cost efficiencies associated with NF over DCMD in water treatment applications.

Green photocatalytic mixed matrix membranes for simultaneous arsenic photo-oxidation and water recovery via membrane distillation

This work proposes an innovative integration of Membrane Distillation (MD) and photo-oxidation for a continuous recovery of water from arsenic (As) contaminated solutions coupled with the oxidation of arsenite (As(III)) into arsenate (As(V)). Polyvinylidene fluoride (PVDF) mixed matrix membranes (MMMs) containing titanium dioxide nanoparticles (TiO2 NPs) as photocatalyst were developed. A systematic study elucidated the effect of TiO2 NPs on membranes’ morphology prepared via non-solvent-induced phase separation (NIPS) using triethyl phosphate (TEP) as a green solvent for PVDF solubilization. Vacuum membrane distillation (VMD) tests carried out by irradiating the MMMs with ultraviolet (UV) radiation demonstrated the possibility of recovering up to 80 % of the water from As-contaminated synthetic and real multi-ions aqueous solutions from Sila Massif (Italy). The distillate was recovered at a rate of 6.9–7.2 kg·m−2·h−1 (feed inlet temperature of 60 °C), while the presence of 7 wt% of TiO2 in PVDF membranes enabled the photo-oxidation of 95 % of the As(III) to As(V) at a first order kinetic constant of 0.0106 min−1. After 5 cycles of As-remediation experiments, post-hoc mechanical testing on the membrane suggested the emergence of polymer embrittlement induced by UV radiation (total irradiation time of 7.5 h), highlighting the urgent need for developing photocatalytic membranes with long-term stability.Overall, this study elucidates at laboratory scale the performance of a coupled and continuous Membrane Distillation (MD) and photo-oxidation system for arsenic (As) remediation, employing microporous hydrophobic green membranes doped with a photocatalyst.

Numerical Modelling and Performance Evaluation of Vacuum Membrane Distillation for Energy-Efficient Seawater Desalination: Towards Energy-Efficient Solutions

Vacuum membrane distillation (VMD) is a compelling technique for desalinating water because it exhibits superior pure water permeability at lower operating temperatures compared to other membrane distillation technologies. This leads to reduced energy consumption, lower heat loss via conduction across the membrane surface, and minimal heat transfer through conduction due to the low pressure on the permeate side. Detailed modelling of heat and mass transfer in VMD is essential for optimizing the process as it provides valuable insights that contribute to the advancement and successful implementation of seawater desalination using VMD technology. The aim of this study is to establish a comprehensive numerical model that describes the water vapor transfer across a hydrophobic micro-porous membrane in single-stage and multi-stage VMD processes for seawater desalination. The numerical predictions were compared to experimental data in addition to numerical computations based on an existing literature database, and good agreement has been found. The investigation also conducted a sensitivity analysis of process variables and membrane specifications on the VMD performance, as well as an assessment of the impact of temperature and concentration polarization. The obtained results showed that the permeation flux reached 18.42 kg/m2·h at 35 g/L feed concentration, 65 °C feed temperature, 50 L/h feed flow rate, and 3 kPa vacuum pressure. Moreover, the findings revealed that the feed temperature was the most significant factor, while the feed flow rate was the least important in determining the permeation flux. Additionally, the findings suggested that the effectiveness of the VMD process heavily relies on the composition and permeability of the support materials. Finally, the results confirmed that temperature polarization had a more significant effect on the reduction of the permeate flux than the concentration polarization.

Experimental Investigation of a Plate-Frame Water Gap Membrane Distillation System for Seawater Desalination.

This study presented a detailed investigation into the performance of a plate-frame water gap membrane distillation (WGMD) system for the desalination of untreated real seawater. One approach to improving the performance of WGMD is through the proper selection of cooling plate material, which plays a vital role in enhancing the gap vapor condensation process. Hence, the influence of different cooling plate materials was examined and discussed. Furthermore, two different hydrophobic micro-porous polymeric membranes of similar mean pore sizes were utilized in the study. The influence of key operating parameters, including the feed water temperature and flow rate, was examined against the system vapor flux and gained output ratio (GOR). In addition, the used membranes were characterized by means of different techniques in terms of surface morphology, liquid entry pressure, water contact angle, pore size distribution, and porosity. Findings revealed that, at all conditions, the PTFE membrane exhibits superior vapor flux and energy efficiency (GOR), with 9.36% to 14.36% higher flux at a 0.6 to 1.2 L/min feed flow rate when compared to the PVDF membrane. The copper plate, which has the highest thermal conductivity, attained the highest vapor flux, while the acrylic plate, which has an extra-low thermal conductivity, recorded the lowest vapor flux. The increasing order of GOR values for different cooling plates is acrylic < HDPE < copper < aluminum < brass < stainless steel. Results also indicated that increasing the feed temperature increases the vapor flux almost exponentially to a maximum flux value of 30.36 kg/m2hr. The system GOR also improves in a decreasing pattern to a maximum value of 0.4049. Moreover, a long-term test showed that the PTFE membrane, which exhibits superior hydrophobicity, registered better salt rejection stability. The use of copper as a cooling plate material for better system performance is recommended, while cooling plate materials with very low thermal conductivities, such as a low thermally conducting polymer, are discouraged.

Selected physical and chemical cleanings remove biofilm in seawater membrane distillation without causing pore wetting

Membrane distillation (MD) is an emerging process with a proven ability to recover freshwater from streams with a wide range of salinities. However, MD is susceptible to biofouling. This study explores the efficiency of different cleaning strategies in biofilm removal during seawater MD. Hydraulic cleaning and chemical cleanings with 0.3%w w−1 ethylenediaminetetraacetic acid (EDTA), 0.3%w w−1 NaOCl, and 3%w w−1 citric acid were tested. The results showed that permeate flux recovery increased in the order of hydraulic cleaning <3%w w−1 citric acid <0.3%w w−1 NaOCl ≈0.3%w w−1 EDTA. Membrane cleanings substantially reduced the thickness of the residual biofilm layer and decreased its bacterial concentration and resistance to vapor pressure. The post-cleaning permeate conductivities were low suggesting that employed cleaning protocols did not cause pore wetting of hydrophobic polytetrafluoroethylene microporous (0.22 μm) membrane, and membrane rejection properties remained stable.

Iron Control in Liquid Effluents: Pseudo-Emulsion Based Hollow Fiber Membrane with Strip Dispersion Technology with Pseudo-Protic Ionic Liquid (RNH3+HSO4-) as Mobile Carrier.

The transport of iron(III) from aqueous solutions through pseudo-emulsion-based hollow fiber with strip dispersion (PEHFSD) was investigated using a microporous hydrophobic hollow fiber membrane module. The pseudo-protic ionic liquid RNH3HSO4- dissolved in Solvesso 100 was used as the carrier phase. This pseudo-protic ionic liquid was generated by the reaction of the primary amine Primene JMT (RNH2) with sulphuric acid. The aqueous feed phase (3000 cm3) containing iron(III) was passed through the tube side of the fiber, and the pseudo-emulsion phase of the carrier phase (400 cm3) and sulphuric acid (400 cm3) were circulated through the shell side in counter-current operational mode, using a single hollow fiber module for non-dispersive extraction and stripping. In the operation, the stripping solution (sulphuric acid) was dispersed into the organic membrane phase in a tank with a mixing arrangement (a four-blade impeller stirrer) designed to provide strip dispersion. This dispersed phase was continuously circulated from the tank to the membrane module in order to provide a constant supply of the organic solution to the fiber pores. Different hydrodynamic and chemical parameters, such as feed (75-400 cm3/min) and pseudo-emulsion phases (50-100 cm3/min) flows, sulphuric acid concentration in the feed and stripping phases (0.01-0.5 M and 0.5-3 M, respectively), metal concentration (0.01-1 g/L) in the feed phase, and PPILL concentration (0.027-0.81 M) in the carrier phase, were investigated. From the experimental data, different diffusional parameters were estimated, concluding that the resistance due to the feed phase was not the rate-controlling step of the overall iron(III) transport process. It was possible to concentrate iron(III) in the strip phase using this smart PEHFSD technology.

Review of Waterproof Breathable Membranes: Preparation, Performance and Applications in the Textile Field.

Waterproof breathable membranes (WBMs) characterized by a specific internal structure, allowing air and water vapor to be transferred from one side to the other while preventing liquid water penetration, have attracted much attention from researchers. WBMs combine lamination and other technologies with textile materials to form waterproof breathable fabrics, which play a key role in outdoor sports clothing, medical clothing, military clothing, etc. Herein, a systematic overview of the recent progress of WBMs is provided, including the principles of waterproofness and breathability, common preparation methods and the applications of WBMs. Discussion starts with the waterproof and breathable mechanisms of two different membranes: hydrophilic non-porous membranes and hydrophobic microporous membranes. Then evaluation criteria and common preparation methods for WBMs are presented. In addition, treatment processes that promote water vapor transmission and prominent applications in the textile field are comprehensively analyzed. Finally, the challenges and future perspectives of WBMs are also explored.

Book Review Hollow Fiber Membrane Contactors: Module Fabrication, Design and Operation, and Potential Applications

The latest developments and applications of hollow fiber membrane contactors (HFMCs) were discussed in this recent published book. Membrane contactor provides gas–liquid or liquid–liquid contact without dispersion of one phase in another, which gives a higher mass transfer coefficient compared to the conventional contactors. Using a microporous hydrophobic or hydrophilic membrane, one of the fluids is immobilized in the pores where the mass transfer is occurred based on the concentration gradient. HFMC technology has been implemented in various applications including gas separation, fermentation, pharmaceuticals, wastewater treatment, chiral separation, semiconductor manufacturing, carbonation of beverages, metal ion extraction, protein extraction, VOC removal from waste gas, and osmotic distillation.

New Materials and Phenomena in Membrane Distillation

In recent decades, membrane-based processes have been extensively applied to a wide range of industrial processes, including gas separation, food industry, drug purification, and wastewater treatment. Membrane distillation is a thermally driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. At the operational level, the performance of membrane distillation is negatively affected by wetting and temperature polarization phenomena. In order to overcome these issues, advanced membranes have been developed in recent years. This review, which focuses specifically on membrane distillation presents the basic concepts associated with the mass and heat transfer through hydrophobic membranes, membrane properties, and advances in membrane materials. Photothermal materials for solar-driven membrane distillation applications are also presented and discussed.

Membrane distillation by novel Janus-enhanced membrane featuring hydrophobic-hydrophilic dual-surface for freshwater recovery

Membrane distillation (MD) is a promising membrane process with nearly 100% salt rejection, which can can realize freshwater recovery and reuse. However, wetting and low permeate flux are major concern for the hydrophobic microporous membrane during MD operation. To address this concern, a simple and effective method to fabricate anti-wetting and high permeate flux Janus-enhanced membranes with double-sided spraying was developed. The spraying materials on both sides of the polytetrafluoroethylene (PTFE) membrane were prepared by crosslinking reactions. Sulfosuccinic acid (SSA) crosslinked MXene was used in the permeate side to construct hydrophilic nanochannels, consequently improving the permeate flux. Methyltriethoxysilane (MTES) crosslinked polydimethylsiloxanes (PDMS) was used in the feed side to reduce surface energy and enhance the anti-wetting ability of the membrane. The optimal water contact angles for the feed and permeate side were 135° and 71.8°, respectively. During direct contact membrane distillation (DCMD) experiments of seawater desalination, Janus-enhanced membrane proved to be stable after 60 h with an average permeate flux as high as 33.5 kg/(m2·h). Therefore, this study provided a novel insight on preparing a MD membrane with simultaneous enhanced permeability and wetting resistance for freshwater recovery.

Feasibility assessment of bioethanol production from humic acid-assisted alkaline pretreated Kentucky bluegrass (Poa pratensis L.) followed by downstream enrichment using direct contact membrane distillation

The effective fractionation of structural components of abundantly available lignocellulosic biomass is essential to unlock its full biorefinery potential. In this study, the feasibility of humic acid on the pretreatment of Kentucky bluegrass biomass in alkaline condition was assessed to separate 70.1% lignin and hydrolyzable biocomponents. The humic acid-assisted delignification followed by enzymatic saccharification yielded 0.55 g/g of reducing sugars from 7.5% (w/v) pretreated biomass loading and 16 FPU/g of cellulase. Yeast fermentation of the biomass hydrolysate produced 76.6% (w/w) ethanol, which was subsequently separated and concentrated using direct contact membrane distillation. The hydrophobic microporous flat-sheet membrane housed in a rectangular-shaped crossflow module and counter-current mode of flow of the feed (hot) and distillate (cold) streams yielded a flux of 11.6 kg EtOH/m2/24 h. A modular, compact, flexible, and eco-friendly membrane-integrated hybrid approach is used for the first time to effectively valorize Kentucky bluegrass biomass for sustainable production of biofuel.

Facile preparation of robust anti-wetting membrane by simple two-step FeOOH and fluorosilane membrane modification

A membrane contactor system using a hydrophobic microporous membrane can effectively harvest valuable gaseous compounds, such as NH3, CH4, H2, and volatile fatty acids, in waste streams. However, widespread implementation of membrane contactor-based resource recovery is still hindered by membrane wetting, which lowers selectivity and decreases mass transfer rate during membrane contactor operation. Herein, for the first time, we present a facile and scalable approach for preparing membrane with superior hydrophobicity and physico-chemical robustness by simple two-step membrane modification using only three chemicals: n-butanol, FeCl3·6H2O, and fluorosilane. Firmly grafted re-entrant FeOOH nanostructure and fluorosilane were confirmed by scanning electron microscopy, energy dispersive X-ray spectrometry, Fourier transform infrared spectroscopy, and X-ray diffractometry. The superior wetting resistance of the modified membrane was confirmed by liquid entry pressure (LEP) and contact angle (CA) analysis (LEP = 2.92 bar & CA = 149.1°). In addition, the modified membrane exhibited excellent resistance to harsh acid–base exposure, and great tensile strength of 5.8 MPa. The modified membrane achieved ammonia recovery flux of 1.02 g/m2h without wetting occurrence from feed solution containing 5.00 g/L of sodium dodecyl sulfate surfactant. We expect that the membrane modification procedure developed in this study will widen the potential of membrane contactor-based recovery of valuable gaseous compounds from various waste streams.

Interpreting contact angles of surfactant solutions on microporous hydrophobic membranes

Almost every single experimental study regarding membranes involves the measurement of contact angle (CA) to quantify the membrane wetting property. However, the interpretation of CA can sometimes be tricky. In this study, we investigate an interesting phenomenon about the CA of a surfactant solution on a microporous hydrophobic membrane. Specifically, a surfactant solution with a very low surface tension can have an unexpectedly high CA on a microporous hydrophobic membrane. In contrast, a water/ethanol mixture with the same surface tension completely wicks the membrane (i.e., zero CA). The drastic difference in CA between the two types of liquid of the same surface tension results from the rapid adsorption of surfactants at the wetting frontier which substantially reduces the local surfactant concentration and increases the local surface tension. The same theory can also be applied to explain the striking difference between the two liquids in capillary rise and liquid entry pressure. The results from this study cast significant doubt on the role of surface tension in understanding the wetting behavior of surfactant solutions when they are in contact with solid with large specific area and raise important questions regarding the utility of measuring CA for surfactant solutions on microporous hydrophobic membranes.

A comparison of vacuum and direct contact membrane distillation for phosphorus and ammonia recovery from wastewater

Recovery of ammonia (NH3) and phosphorous (P) from municipal wastewater is important to minimize the environmental impact of their discharge and to comply with the concept of circular economy. Technologies have been established to recover P in form of struvite (MgNH4PO4·6H2O) for its use as a fertilizer. NH3 is usually converted to molecular nitrogen and released to the atmosphere; however, NH3 recovery in form of NH3/H2O mixture is relevant for numerous applications such as manufacturing of cleaning agents, sanitizers and liquid fertilizers. Membrane distillation (MD), a process driven by the partial vapor pressure across a microporous hydrophobic membrane, has demonstrated the potential for concentrating the non-volatiles while, at the same time, recovering volatiles from a solution. Among various configurations of MD, vacuum and direct contact MD (DCMD) have been extensively studied. The current study compares the performance of DCMD and vacuum MD (VMD) for simultaneous recovery of NH3 and P from wastewater in form of NH3/H2O mixture and struvite, respectively. The study finds that while both the configuration are equally effective to concentrate P, the control over removal efficiency of NH3 in the two configurations becomes the bottleneck for struvite recovery under different pH conditions. For wastewater with high pH, VMD almost completely removes NH3 before reaching substantial P concentration, thereby eliminates the possibility of struvite formation. DCMD on other hand, only partly removes NH3 while concentrating P, therefore, for struvite recovery from a high pH wastewater, DCMD is better option. For low pH wastewater, VMD is preferred choice as it recovers NH3 more effectively than DCMD but still leaves ample NH3 in the wastewater for struvite formation.

Non-solvent Flux Augmentation of an LDPE-Coated Polytetrafluoroethylene Hollow Fiber Membrane for Direct Contact Membrane Distillation.

Membrane distillation (MD) is a thermal technology for the desalination process that requires a hydrophobic microporous membrane to ensure that the membrane can maintain the liquid–vapor interface. This work aims to enhance the water permeation flux of the previously coated membrane by modifying the surface of the polytetrafluoroethylene hollow fiber (PTFE HF) membrane with a selected non-solvent such as acetone, cyclohexanone, and ethanol in low-density polyethylene as a polymeric coating solution. However, the modification using acetone and cyclohexanone solvents was unsuccessful because a reduction in membrane hydrophobicity was observed. The modified PTFE HF membrane with ethanol content exhibits high wetting resistance with a high water contact angle, which can withstand pore wetting during the direct contact MD process. Since MD operates under a lower operating temperature range (50–90 °C) compared to the conventional distillation, we herein demonstrated that higher flux could be obtained at 7.26 L m–2 h–1. Thus, the process is economically feasible because of lower energy consumption. Performance evaluation of the modified PTFE HF membrane showed a high rejection of 99.69% for sodium chloride (NaCl), indicating that the coated membrane preferentially allowed only water vapor to pass through.

Single-sided and integrated polyaniline/ poly(vinylidene fluoride) flexible membrane with micro/nanostructures as breathable, nontoxic and fast response wearable humidity sensor

Harmless and breathable flexible humidity sensor has important applications in continuous and real-time detection of human physiological activities. In this work, with hydrophobic poly (vinylidene fluoride) (PVDF) membrane as both the template and substrate and cetyltrimethylammonium bromide as a structure regulator, polyaniline (PANI) was unilaterally deposited on a PVDF microporous membrane to facilely fabricate a single-sided integrated flexible humidity sensor (IFHS). Such IFHS is featured with unique micro/nano structure and good air permeability. Moreover, it exhibits good humidity sensing properties at room temperature including fast response, small hysteresis and stable response even under bending deformation. The flexible sensor could realize non-contact monitoring of human respiration and speaking activities. Unilateral deposition of PANI and good breathability of IFHS avoids direct contact between PANI and human skin, thus averting harms to human and minimizing the deterioration of humidity sensing properties of PANI layer. The simple method is universal to the preparation of single-sided, integrated, breathable, nontoxic and fast response wearable humidity sensors based on PANI and hydrophobic microporous polymer membranes, offering useful references for the construction of advanced flexible sensors.

Heat and mass transfer in a counter flow parallel plate membrane-based absorption heat pump (PMAHP)

Membrane-based absorption heat pumps (MAHP) operate based on the working principle of the absorption refrigeration system (ARS), which could be used to recover and transform low-temperature waste heat into useable heat sources with higher temperatures. This work focuses on the performance study of a counter-flow parallel-plate membrane-based absorption heat pump (PMAHP) to recover low-temperature waste heat from used cooling water at 40 °C. It consists of refrigerant (water) and absorbent (LiCl solution) streams flowing in neighboring channels formed by hydrophobic microporous membranes with air gaps sandwiched in between these channels. Air-gap design is incorporated to minimize the sensible heat loss through conduction between the two streams. Water vapor molecules travel from the water stream to the solution stream through the membrane and air gaps. As the water molecules are absorbed by the solution, they condense to release the latent heat of absorption and dilution. The recovered heat can be used subsequently for fluid heating or air-conditioning purposes. A three-dimensional, steady-state model based on the finite element method is used to study the conjugate heat and mass transfer mechanisms. Model validation results agree with experimental data with a general discrepancy of within 10%. Parametric studies on the performance of the PMAHP are carried out. Scaling analysis is applied to study the effects of geometrical parameters on the heat and mass transfer dimensionless parameters, fluid flow behavior, heat, and mass transport within the PMAHP. The optimal air gap width is determined to achieve maximum solution temperature lift, which shows an improvement of 99.6% compared to the base case. The findings of this study provide an insight regarding the potential aspects to be focused on for further enhancement in the PMAHP heat and mass transfer performance.

Combined macroscopic and pore scale modeling of direct contact membrane distillation with micro-porous hydrophobic membranes

The transport processes of a direct contact membrane distillation (DCMD) module are investigated with a multiscale approach in this study. A stochastic, numerical reconstruction algorithm is first developed to generate 3D virtual membranes based on the membrane's pore size and fiber orientation distributions. Pore-scale simulations are then performed on the reconstructed membrane model. The membrane's effective thermal conductivity and mass diffusivity are computed using AVIZO software and OpenFOAM solver, respectively. A 2D macroscopic, multiphysics model considering the conservation of mass, species, momentum, and energy is developed, where the effective transport properties obtained from pore-scale simulations are utilized, to study the heat and mass transfer through the membrane. Two commercially available polytetrafluoroethylene (PTFE) membranes (GE-Osmonics/0.22 μm and MS-3010/0.45 μm) are chosen as examples for the present multiscale approach. The computed transport properties of the membranes are found to yield good distillate flux predictions with data reported in the literature. The MS-3010/0.45 μm membrane is found to produce 24% higher freshwater on average than GE-Osmonics/0.22 μm membrane. Finally, the performance of DCMD of three hypothetical membranes with different specifications is compared to the reconstructed MS-3010/0.45 μm membrane to study the factors that need to be taken into account for optimal design of the membrane for DCMD applications.

Building a Differential Electrochemical Mass Spectrometry (DEMS): A Powerful Toll for Investigation of (photo)Electrochemical Processes

The development of electrochemical devices more efficient for energy conversion and storage are a challenge for modern society. Among this class of devices, fuel cells, batteries, and photovoltaic cells stand out. Despite their importance and practicality, the electrochemical processes that take place in these devices are not always easily understood. In addition, the detection and identification of the products and intermediaries, as well as the reaction paths usually are extremely complex, due to the different species produced and also several reaction steps that take place simultaneously in this type of system. In this context, analytical techniques have been combined to electrochemistry systems to investigate the electrochemical processes in real-time. FTIR (infrared spectroscopy with Fourier transform), MS (mass spectrometry) are some of examples that coupled techniques. Therefore, these setups provide great opportunities for the electrochemistry field, which also includes catalysts design improvement and reaction investigations under different experimental conditions.1-3 The electrochemical mass spectrometry (EMS) technique has stood out as an important tool for the identification and analyses of qualitatively/quantitatively gaseous, volatile intermediates, and products generated during electrochemical reactions. The interface between the mass spectrometer’s high-vacuum system and the electrochemical cell’s room pressure was composed of a hydrophobic porous membrane connected to the inlet system. The ionic current intensity associated with the products was monitored and correlated to the faradaic current3. In 1984 Wolter and Heitbaum4 refined the Electrochemical Mass Spectroscopy technique, employing a new vacuum system design consisting of two pumping stages, giving high sensitivity to the technique and allowing the on-line detection of gaseous with response-time ≤ 0.5 s, four times faster than the first setup developed. The Wolter and Heitbaum’s method was called Differential Electrochemical Mass Spectroscopy (DEMS). Here, differential pumping is related to a two-stage pressure reduction, where the gas flow is initially expanded to a low vacuum and later to a high vacuum, where the mass spectrometer is located4. This work presents the instrumental design used to construct a DEMS to investigate and elucidate (photo)electrochemical reactions. The DEMS design selected was composed of a two-stage differentially pumped vacuum system (Figure 1(I)). The instrument is composed of three main sections: electrochemical cell; hydrophobic microporous membrane, and mass spectrometer, including the vacuum system (turbomolecular and pre-vacuum pumps). The electrochemical cell used, was employed initially by Baltruschat5, this cell use a modified Polytetrafluoroethylene (PTFE) porous membrane interface as the working electrode, which is prepared by metal sputtering onto a microporous membrane.An example of the relation between cyclic voltammogram (CV) and mass-spectrum cyclic voltammograms (MSCV) using the DEMS constructed in this work is shown in Fig. 1((II)a-b), respectively (CVs only in H2SO4 is presented as an insert in Fig. 1(a)). The working electrode was sputtered of platinum (50 nm thickness) onto the PTFE microporous membrane interface. The counter electrode was a platinum mesh with a high surface area, the reference electrode was a reversible hydrogen electrode (RHE). The electrochemical cell was directly attached to the pre-vacuum chamber of the mass spectrometer High purity N2 was used to de-aerate the solution.The cyclic voltammograms were recorded at a sweep rate of 10 mV s-1. While the faradaic current and the ion mass current for the generated product, CO2 (m/z = 44 (CO2 +), were monitored at the same time. Fig. 1(c-e) shows the faradaic (d) and ionic currents (e) profiles vs. time obtained for 6 CVs, the potential is also presented. As can be observed, the faradaic current has an excellent correlation with the ionic current, conducting to a great synchronization between the voltammetric scans and the ionic signal profile. Besides, the results show a significant deactivation of the electrocatalyst, which is followed by the ionic signal (m/z = 44). As reported in the literature6, the formic acid electrooxidation produces a poison intermediate, which is formed from the dissociative adsorption of formic acid on the electrode surface, this poison specie was posteriorly identified as CO. Therefore, the DEMS technique can provide important information to determine the reaction mechanisms. Bashyam, R.; Zelenay, P., Nature 2006, 443 (7107), 63-66. Bruckenstein, S.; Gadde, R. R., Journal of the American Chemical Society 1971, 93 (3), 793-794. Chen, A.; Lipkowski, J., The Journal of Physical Chemistry B 1999, 103 (4), 682-691. Wolter, O.; Heitbaum, J., 1984, 88 (1), 2-6. Baltruschat, H., Journal of the American Society for Mass Spectrometry 2004, 15 (12), 1693-1706. Herrero, E.; et al.., Journal of Electroanalytical Chemistry 1993, 350 (1), 73-88. Figure 1

Comb-like structural modification stabilizes polyvinylidene fluoride membranes to realize thermal-regulated sustainable transportation efficiency

Hydrophobic micro-porous membrane such as polyvinylidene fluoride (PVDF) with excellent thermal-/chemical-stability and low surface energy has received extensive attention in industrial water treatment and sustainable energy conversion. However, undesirable contaminants caused by inevitable proteins or microorganisms adhesion may lead to a rapid loss of separation efficiency, which significantly deteriorate their porous structures and eventually limit their practical performance. Herein, we present a scalable approach for fabricating comb-like copolymer modified PVDF membranes (PVDF-PN@AgNPs) that prevent bacteria from proliferating on the surface and temperature-controlled release of adhered contaminants. Comb-like structured copolymers were imparted to a polydopamine (PDA)-treated PVDF membrane by Michael addition reaction, which enabled a covalent binding of comb-like structured copolymers to the membrane. Such unique structural design of grafted copolymer, containing hydrophilic side chain and temperature-responsive chain backbone, stably prevents bacteria adhesion and provides reversible surface wettability. Therefore, the resultant membranes were evaluated to prevent bacterial adhesion, high touch-killing efficiency and temperature-controlled contaminants release (~99% of protein and ~75% of bacteria). Moreover, with the collapse and stretch of grafted copolymer chain backbone, the synthetic membrane further reversibly adjusted inner micro-porous structure and surface wettability, which eventually helped to achieve variable water fluid transport efficiency. This study not only provides a feasible structural design for stably coping with the challenging of antifouling and subsequent contamination adhesion of PVDF membrane, but also potentially answers the significant gap between lab research advances and practical application, particularly in the industrial membrane field.