Piezoelectric Polyvinylidene Fluoride Membranes with Self-Powered and Electrified Antifouling Performance in Pressure-Driven Ultrafiltration Processes

Light-enhanced ion transport and fouling resistance properties of metal/semiconductor heterojunction nanochannel membranes for osmotic energy recovery in real-world conditions

Osmotic energy, abundant in seawater and high-salinity industrial wastewater, is a highly promising renewable "blue energy". However, practical osmotic energy recovery has been hindered by challenges such as membrane fouling caused by complex aqueous environment. In this study, we developed light-activated heterogeneous nanochannel membranes by continuous stacking two-dimensional semiconducting and metal-like nanosheets, significantly enhancing both ion transport efficiency and stability in complex, real-world aqueous environments. By leveraging light to create temperature gradients and built-in electric fields, solar energy was efficiently converted into a powerful driving force, markedly boosting ion transport efficiency. More importantly, the membrane continuously generated free radicals via photoexcitation and storage, effectively mitigating membrane fouling-even in low-light and nighttime conditions. As a result, while power density initially decreased by maximum of 87 % within 12 h due to organic contamination, it not only recovered to its original level under light exposure but also achieved a twofold increase, demonstrating robust energy recovery performance. Over 60 days of testing in Bohai Sea water, coal chemical wastewater from Shaanxi, and Da Qaidam Salt Lake brine, the system maintained stable power densities of up to 5.43 W/m2 with a membrane area of 0.2 mm2. This work marks a significant leap from the conceptual stage to the practical application of osmotic energy recovery, offering valuable insights into its scalability and real-world potential.

Fast-selective electro-driven membrane reactor in fluoride/silica crystallization for microelectronic wastewaters recycling

Rapid growth of the microelectronic industry leads to a significant increase in the generation of microelectronic wastewaters containing complex pollutants. Resource recovery technologies offer promising solutions for effective wastewater reuse in the microelectronics sector. However, how to simultaneously achieve high-efficiency crystallization and high crystal purity of ionic resources from complex wastewater remains a challenge. Here, for the first time, we propose an electro-driven membrane reactor (EMR) for the ex-situ crystallization of fluoride/silica from microelectronic wastewaters as high-purity fluorosilicates. This EMR with independent chambers combines a bipolar membrane to produce protons for SiF62- generation from the reaction between fluoride and silica. An internal ultrafiltration membrane is used to reject nanoparticles/organics while providing ion channels for protons and SiF62- migration. Selective recovery of Na2SiF6 from the coexisting ions (Cl-, SO42-, NO3- and PO43-)/nanoparticles (SiO2, Al2O3 and CeO2)/organics (tetramethylammonium hydroxide, isopropyl alcohol, bovine serum albumin, sodium alginate and humic acid) is demonstrated. Over 99.5 % Na2SiF6 purity and 64.5 % crystallization rate are verified under the optimal conditions (voltage of 8 V, UH050 membrane, operation mode Ⅰ, and forward permeate flux of 1 mL min-1). This EMR with the advantages of accurate capture capability may be an innovative strategy for enlarging the scale of pollutant elimination, ionic resources and fresh water recovery from micro-electronic wastewaters.

Pressure-induced piezoelectric response for mitigating membrane fouling in surface water treatment: Insights from continuous operation and biofouling characterization

Organic fouling and biofouling represents a critical challenge encountered by the membrane-based water treatment process. Herein, a piezoelectric PVDF membrane (PEM), capable of generating electrical responses to hydraulic pressure stimuli, was synthesized and employed for mitigating the fouling in surface water treatment. The surface-hydrophobilized PEM demonstrated sensitive and enhanced underwater output performance in response to increasing transmembrane pressure (TMP) during constant-flux filtration, with signals reaching up to ∼800 mV at a TMP of ∼80 kPa. This in-situ piezoelectric response significantly reduced TMP growth in both short-term (1 h) and long-term (15 days) filtration trials, demonstrating a strong capability to mitigate membrane fouling. Moreover, continuous piezoelectric stimulation effectively inhibited microbial activity and the accumulation of extracellular polymeric substances (EPS) on PEM surface, surpassing the dominant electrokinetic repulsion mechanisms observed in short-term trials. Microbial community analysis suggests that this evolution is primarily due to the targeted impact of piezoelectric stimulation on microbial metabolic behavior. The piezoelectric-induced electrical microenvironment inhibited the growth of microbes associated with high EPS production while promoting the proliferation of electrically active microbes involved in biopolymer digestion. In addition, the PEM demonstrated enhanced permeate quality throughout the filtration process, with DOC and UV254 removal rates increasing from 11.7 % and 15.6 % initially to 28.6 % and 19.5 % by the 15th day, respectively. Given the performance and self-powered capability of PEM compared to current electrified antifouling methods that require an external power supply, these attributes are anticipated to hold practical significance in developing innovative and energy-efficient strategies for mitigating both organic fouling and biofouling.

Boosting Demulsification and Antifouling Capacity of Membranes via an Enhanced Piezoelectric Effect for Sustaining Emulsion Separation

Traditional superwettable membranes for demulsification of oil/water emulsions could not maintain their separation performance for long because of low demulsification capacity and surface fouling during practical applications. A charging membrane could repel the contaminants for a while, the charge of which would gradually be neutralized during the separation progress. Here, a superhydrophilic piezoelectric membrane (SPM) with sustained demulsification and antifouling capacity is proposed for achieving prolonged emulsion separation, which is capable of converting inherent pulse hydraulic filtration pressure into pulse voltage. A pulse voltage up to -7.6 V is generated to intercept the oil by expediting the deformation and coalescence of emulsified oil droplets, realizing the demulsification. Furthermore, it repels negatively charged oil droplets, avoiding membrane fouling. Additionally, any organic foulants adhering to the membrane undergo degradation facilitated by the generated reactive oxygen species. The separation data demonstrate a 98.85% efficiency with a flux decline ratio below 14% during a 2 h separation duration and a nearly 100% flux recovery of SPM. This research opens new avenues in membrane separation, environmental remediation, etc.

Advancing piezoelectric 2D nanomaterials for applications in drug delivery systems and therapeutic approaches

Precision drug delivery and multimodal synergistic therapy are crucial in treating diverse ailments, such as cancer, tissue damage, and degenerative diseases. Electrodes that emit electric pulses have proven effective in enhancing molecule release and permeability in drug delivery systems. Moreover, the physiological electrical microenvironment plays a vital role in regulating biological functions and triggering action potentials in neural and muscular tissues. Due to their unique noncentrosymmetric structures, many 2D materials exhibit outstanding piezoelectric performance, generating positive and negative charges under mechanical forces. This ability facilitates precise drug targeting and ensures high stimulus responsiveness, thereby controlling cellular destinies. Additionally, the abundant active sites within piezoelectric 2D materials facilitate efficient catalysis through piezochemical coupling, offering multimodal synergistic therapeutic strategies. However, the full potential of piezoelectric 2D nanomaterials in drug delivery system design remains underexplored due to research gaps. In this context, the current applications of piezoelectric 2D materials in disease management are summarized in this review, and the development of drug delivery systems influenced by these materials is forecast.

Membrane processes enhanced by various forms of physical energy: A systematic review on mechanisms, implementation, application and energy efficiency

Membrane technologies in water and wastewater treatment have been eagerly pursued over the past decades, yet membrane fouling remains the major bottleneck to overcome. Membrane fouling control methods which couple membrane processes with online in situ application of external physical energy input (EPEI) are getting closer and closer to reality, thanks to recent advances in novel materials and energy deliverance methods. In this review, we summarized recent studies on membrane fouling control techniques that depend on (i) electric field, (ii) acoustic field, (iii) magnetic field, and (iv) photo-irradiation (mostly ultraviolet or visible light). Mechanisms of each energy input were first reported, which defines the applicability of these methods to certain wastewater matrices. Then, means of implementation were discussed to evaluate the compatibility of these fouling control methods with established membrane techniques. After that, preferred applications of each energy input to different foulant types and membrane processes in the experiment reports were summarized, along with a discussion on the trends and knowledge gaps of such fouling control research. Next, specific energy consumption in membrane fouling control and flux enhancement was estimated and compared, based on the experimental results reported in the literature. Lastly, strength and weakness of these methods and future perspectives were presented as open questions.

Triboelectric Nanogenerator-Based Near-Field Electrospinning System for Optimizing PVDF Fibers with High Piezoelectric Performance

Electrospinning is an effective method to prepare polyvinylidene fluoride (PVDF) piezoelectric fibers with a high-percentage β phase. However, as an energy conversion material for micro- and nanoscale diameters, PVDF fibers have not been widely used due to their disordered arrangement prepared by traditional electrospinning. Here, we designed a near-field electro-spinning (NFES) system driven by a triboelectric nanogenerator (TENG) to prepare PVDF fibers. The effects of five important parameters (PVDF concentration, needle inner diameter, TENG pulse DC voltage (TPD-voltage), flow rate, and drum speed) on the β phase fraction of PVDF fiber were optimized one by one. The results showed that the electrospun PVDF fibers had uniform diameter and controllable parallel arrangement. The β phase content of the optimized PVDF fiber reached 91.87 ± 0.61%. For the bending test of a single PVDF fiber piezoelectric device, when the strain is 0.098%, the electric energy of the single PVDF fiber device of NFES reaches 7.74 pJ and the energy conversion efficiency reaches 13.5%, which is comparable to the fibers prepared by the commercial power-driven NFES system. In 0.5 Hz, the best matching load resistance of a PVDF single fiber device is 10.6 MΩ, the voltage is 6.1 mV, and the maximum power is 3.52 pW. Considering that TENG can harvest micromechanical energy in the low frequency environment, the application scenario of the NFES system can be extended to the wild or remote mountainous areas without traditional high-voltage power supply. Therefore, the electrospun PVDF fibers in this system will have potential applications in high-precision 3D fabrication, self-powered sensors, and flexible wearable electronic products.