Flexible hybrid structure piezoelectric nanogenerator based on ZnO nanorod/PVDF nanofibers with improved output

A Sunlight-Driven Self-Cleaning CuCo-MOF Composite Membrane for Highly Efficient Emulsion Separation and Water Purification

The fouling phenomenon of membranes has hindered the rapid development of separation technology in wastewater treatment. The integration of materials into membranes with both excellent separation performance and self-cleaning properties still pose challenges. Here, a self-assembled composite membrane with solar-driven self-cleaning performance is reported for the treatment of complex oil-water emulsions. The mechanical robustness of the composite membrane is enhanced by the electrostatic attraction between chitosan and metal-organic frameworks (MOF) CuCo-HHTP as well as the crosslinking effect of glutaraldehyde. Molecular dynamics (MD) simulations also revealed the hydrogen bonding interaction between chitosan and CuCo-HHTP. The composite membrane of CuCo-HHTP-5@CS/MPVDF exhibits a high flux ranging from 700.6 to 2350.6 L∙m-2∙h-1∙bar-1 and excellent separation efficiency (>99.0%) for various oil-water emulsions, including crude oil, kerosene, and other light oils. The addition of CuCo-HHTP shows remarkable photothermal effects, thus demonstrating excellent solar-driven self-cleaning capability and antibacterial performance (with an efficiency of ≈100%). Furthermore, CuCo-HHTP-5@CS/MPVDF can activate peroxomonosulfate (PMS) under sunlight, quickly removing oil-fouling and dyes. Density functional theory (DFT) calculations indicate that the bimetallic sites of Cu and Co in CuCo-HHTP effectively promoted the activation of PMS. This study provides distinctive insights into the multifaceted applications of MOFs-derived photothermal anti-fouling composite membranes.

Electrospun polarity-controlled molecular orientation for synergistic performance of an artifact-free piezoelectric anisotropic sensor

Anisotropy in mechanical, optical and thermal sensors in a spatial direction has many applications in health care, robotics, aerospace, and tissue engineering. In particular, wearable and implantable sensors respond to stretching and bending strains that probe mechanical energy and track physiological signals. Hence, the development of anisotropic pressure sensors with true piezoelectric (PE) signals is of utmost importance to achieve efficient devices. Herein, a simple and efficient method is developed for high longitudinal and transverse responses, with an approach to isolating a true piezoelectric signal. The electrospun (ES) polarity of oriented dipoles inside flexible fibers gives rise to a high longitudinal/transverse PE response of both lateral and transverse strains. Nanofibers of poly(vinylidene-chlorotrifluoroethylene) copolymers contain poled dipoles, up to 86%, that promote an enhanced PE coefficient of 42 pm V-1 in the case of negative polarity-based electrospinning. It is 40% higher in composition than the commonly adopted positive polarity-biased electrospinning process. We demonstrated the advantage of such a high PE coefficient by the enhanced sensitivity of the longitudinal (VLs = 0.3 V kPa-1, ILs = 0.07 μA kPa-1) as well as transverse (VTs = 1.0 V kPa-1, ITs = 0.8 μA kPa-1) PE response. To counter the ambiguity of high transverse response as compared to longitudinal in electrospun fiber-based devices, a facile method is proposed to isolate the ferroelectret, triboelectric and piezoelectric signals in a fiber-based hybrid device with their independent charge generation mechanisms.

A Review of Plasma-Synthesized and Plasma Surface-Modified Piezoelectric Polymer Films for Nanogenerators and Sensors

In this review, we introduce recently developed plasma-based approaches for depositing and treating piezoelectric nanoparticles (NPs) and piezoelectric polymer films for nanogenerator (NG) and sensor applications. We also present the properties and an overview of recently synthesized or modified piezoelectric materials on piezoelectric polymers to highlight the existing challenges and future directions of plasma methods under vacuum, low pressure, and ambient air conditions. The various plasma processes involved in piezoelectric NGs and sensors, including plasma-based vapor deposition, dielectric barrier discharge, and surface modification, are introduced and summarized for controlling various surface properties (etching, roughening, crosslinking, functionalization, and crystallinity).

Review of Piezoelectric Properties and Power Output of PVDF and Copolymer-Based Piezoelectric Nanogenerators

The highest energy conversion efficiencies are typically shown by lead-containing piezoelectric materials, but the harmful environmental impacts of lead and its toxicity limit future use. At the bulk scale, lead-based piezoelectric materials have significantly higher piezoelectric properties when compared to lead-free piezoelectric materials. However, at the nanoscale, the piezoelectric properties of lead-free piezoelectric material can be significantly larger than the bulk scale. The piezoelectric properties of Poly(vinylidene fluoride) (PVDF) and Poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) lead-free piezoelectric nanomaterials are reviewed and their suitability for use in piezoelectric nanogenerators (PENGs) is determined. The impact of different PVDF/PVDF-TrFE composite structures on power output is explained. Strategies to improve the power output are given. Overall, this review finds that PVDF/PVDF-TrFE can have significantly increased piezoelectric properties at the nanoscale. However, these values are still lower than lead-free ceramics at the nanoscale. If the sole goal in developing a lead-free PENG is to maximize output power, lead-free ceramics at the nanoscale should be considered. However, lead-free ceramics are brittle, and thus encapsulation of lead-free ceramics in PVDF is a way to increase the flexibility of these PENGs. PVDF/PVDF-TrFE offers the advantage of being nontoxic and biocompatible, which is useful for many applications.

Wearable Electrospun Piezoelectric Mats Based on a PVDF Nanofiber-ZnO@ZnS Core-Shell Nanoparticles Composite for Power Generation

This work adopted a strategy to use new functional high-performance piezoelectric materials for sustainable energy production in wearable self-powered electrical devices. An innovative modification in electrospinning was used to produce highly aligned nanofibers. In the nanogenerator, the flexible membrane constituents were tunefully combined. The novel composite nanofibers were made of Poly (vinylidene fluoride) PVDF, loaded with ZnO@ZnS core-shell nanoparticles to achieve a non-brittle performance of the hetero nanoparticles and piezoelectric polymer. A nanofiber mat was inserted between two thermoplastic sheets with conductive electrodes for application in wearable electronic devices. Complete spectroscopic analyses were performed to characterize the nanofiber's material composition. It is shown that the addition of 10 wt % ZnO@ZnS core-shell nanoparticles significantly improved the piezoelectric properties of the nanofibers and simultaneously kept them flexible due to the exceedingly resilient nature of the composite. The superior performance of the piezoelectric parameter of the nanofibrous mats was due to the crystallinity (polar β phase) and surface topography of the mat. The conversion sensitivity of the PVDF device recorded almost 0.091 V/N·mm3, while that of the PVDF-10 wt % ZnO@ZnS composite mat recorded a sensitivity of 0.153 V/N·mm3, which is higher than many flexible nano-generators. These nanogenerators provide a simple, efficient, and cost-effective solution to microelectronic wearable devices.

Sandwich-type double-layer piezoelectric nanogenerators based on one- and two-dimensional ZnO nanostructures with improved output performance

Piezoelectric nanogenerators (PENGs) have attracted great interest owing to their broad range application in environmental mechanical energy harvesting to power small electronic devices. In this study, novel flexible and high-performance double-layer sandwich-type PENGs based on one-dimensional (1-D) and two-dimensional (2-D) zinc oxide (ZnO) nanostructures and Ni foam as the middle layer have been developed. The morphology and structure of 1- and 2-D ZnO nanostructures have been studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). To investigate the effect of structural design on the piezoelectric performance, single-layer PENGs were also fabricated. The piezoelectric output of all prepared PENGs were evaluated under different human impacts at various forces and frequencies. The double-layer designed PENGs showed a two times larger voltage output compared to the single-layer PENGs, and the use of Ni foam as middle-layer and of 2-D ZnO nanosheets (compared to 1-D nanorods) was also found to increase the performance of the designed PENGs. The working mechanism of the prepared PENGs is also discussed. The design of nanogenerators as double-layer sandwich structures instead of two integrated single-layer devices reduces the overall preparation time and processing steps and enhances their output performance, thus opening the gate for widening their practical applications.

Enhanced Piezoelectricity of PVDF-TrFE Nanofibers by Intercalating with Electrosprayed BaTiO3

Over the past few decades, flexible piezoelectric devices have gained increasing interest due to their wide applications as wearable sensors and energy harvesters. Poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE), as one of piezoelectric polymers, has caught considerable attention because of its high flexibility, high thermal stability, and biocompatibility. However, its relatively lower piezoelectricity limits its broader applications. Herein, we present a new approach to improving the piezoelectricity of PVDF-TrFE nanofibers by integrating barium titanate (BTO) nanoparticles. Instead of being directly dispersed into PVDF-TrFE nanofibers, the BTO nanoparticles were electrosprayed between the nanofiber layers to create a sandwich structure. The results showed that the sample with BTO sandwiched between PVDF-TrFE nanofibers showed a much higher piezoelectric output compared to the sample with BTO uniformly dispersed in the nanofibers, with a maximum of ∼ 457% enhancement. Simulation results suggested that the enhanced piezoelectricity is due to the larger strain induced in the BTO nanoparticles in the sandwich structure. Additionally, BTO might be better poled during electrospraying with higher field strength, which is also believed to contribute to enhanced piezoelectricity. The potential of the piezoelectric nanofiber mats as a sensor for measuring biting force and as a sensor array for pressure mapping was demonstrated.

Piezoelectric Nanogenerators Fabricated Using Spin Coating of Poly(vinylidene fluoride) and ZnO Composite

In this context, the open-circuit voltage generated by either poly (vinylidene fluoride) or PVDF and ZnO composite sample before being enhanced to 4.2 V compared to 1.2 V for the samples of pure PVDF. The spin coating method was used to create a composite film, which served as a piezoelectric nanogenerator (PNG). Zinc oxide (ZnO) nanoparticles and PVDF serve as the matrix for the coating structure. Thin films were created that employed the spin coating method to achieve the desired results of ZnO's non-brittle outcome and piezoelectric characteristics, as well as PVDF for use in self-powered devices. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and fourier transform infrared (FT-IR) were used to evaluate the properties of these formations. The electrical properties of the film were measured using an oscilloscope. Results indicated that by adding ZnO nanoparticles to the PVDF samples, piezoelectric capabilities were enhanced compared to samples containing PVDF only. These results point to promising uses for various wearable devices, such as water strider robot systems and self-operating equipment.

A Flexible Piezoelectric Device for Frequency Sensing from PVDF/SWCNT Composite Fibers

Polymer piezoelectric devices have been widely studied as sensors, energy harvesters, and generators with flexible and simple processes. Flexible piezoelectric devices are sensitive to external stimuli and are attracting attention because of their potential and usefulness as acoustic sensors. In this regard, the frequency sensing of sound must be studied to use flexible piezoelectric devices as sensors. In this study, a flexible piezoelectric device composed of a polymer and an electrode was successfully fabricated. Polyvinylidene fluoride, the active layer of the piezoelectric device, was prepared by electrospinning, and electrodes were formed by dip−coating in a prepared single−walled carbon nanotube dispersion. The output voltage of the external sound was matched with the input frequency through a fast Fourier transform, and frequency matching was successfully performed, even with mechanical stimulation. In a high−frequency test, the piezoelectric effect and frequency domain peak started to decrease sharply at 300 Hz, and the limit of the piezoelectric effect and sensing was observed from 800 Hz. The results of this study suggest a method for developing flexible piezoelectric-fiber frequency sensors based on piezoelectric devices for acoustic sensor systems.

Nanoscale mapping of surface strain in tapered nanorods using confocal photoluminescence spectroscopy

The strain occurs spontaneously at the heterogeneous interfaces of virtually all crystalline materials. Consequently, the analysis across multiple interfaces requires a complementary characterization scheme with a resolution that fits the deformation scale. By implementing two-photon confocal laser scanning nanoscopy with an axial resolution of 10 nm, we extract the surface strain from the photoluminescence (PL) spectra, epitomized by a 2-fold enhancement at the tapered tips in comparison to the substrate of ZnO nanorods. We firstly traced the well-established contribution from quantum confinement (QC) to PL shift in three geometrically classified regions: (I) a strongly tapered region where the diameter increases from 3 to 20 nm; (II) a weakly tapered region with a gradually increasing diameter from 20 to 58 nm; (III) round cylindrical region interfacing the sapphire substrate. The measured PL shift influenced by the deformation is significantly stronger than the attained QC effect. Particularly, surface strain at the strongly tapered region turned out to drastically increase the PL shift which matches well with the analysis based on the surface to volume ratio incorporating mechanical parameters such as the compliance tensor component, strain dislocation constant, and surface stress. The surface strain increased at a lower temperature, further disclosing its inherent dependence on the thermal expansion coefficients in clear contrast to the temperature-invariant characteristics of QC.

Nanoencapsulation of Acetamiprid by Sodium Alginate and Polyethylene Glycol Enhanced Its Insecticidal Efficiency

Nanoformulation has been considered one of the newly applied methods in integrated pest management strategies. In this research, a conventional neonicotinoid insecticide acetamiprid was nanoencapsulated via AL (Sodium Alginate) and PEG (Polyethylene Glycol) and tested against the elm leaf beetle Xanthogaleruca luteola. The synthesized particles had spherical-like morphology and nanoscale based on TEM (Transmission Electron Microscopy) and DLS (Dynamic Light Scattering). The encapsulation efficiency and loading percentages of acetamiprid in AL and PEG were 92.58% and 90.15%, and 88.46% and 86.79%, respectively. Leaf discs treated with different formulations by the leaf-dipping method were used for oral toxicity assays. The LC₅₀ values (Lethal Concentration to kill 50% of insect population) of acetamiprid and Al- and PEG-nanoencapsulated formulations on third-instar larvae were 0.68, 0.04, and 0.08 ppm, respectively. Based on the highest relative potency, AL-encapsulated acetamiprid had the most toxicity. The content of energy reserve protein, glucose, and triglyceride and the activity of detoxifying enzymes esterase and glutathione S-transferase of the larvae treated by LC₅₀ values of nanoformulations were also decreased. According to the current findings, the nanoencapsulation of acetamiprid by Al and PEG can increase its insecticidal performance in terms of lethal and sublethal toxicity.

Photo-supercapacitors based on nanoscaled ZnO

In this study, zinc oxide (ZnO) powders in two different morphologies, nanowire (NW) and nanoflower (NF), have been synthesized by the hydrothermal method. The eligibility of the pristine ZnO nanopowders as a photo-active material has been revealed by designing P-SC devices via the facile drop-casting method on both glass and plastic substrates in large-area applications. The impact of physical properties and especially defect structures on photo-supercapacitor (P-SC) performance have been explored. Although the dark Coulombic efficiency (CE%) of both NW and NF-based P-SC were very close to each other, the CE% of NW P-SC increased 3 times, while the CE% of NF P-SC increased 1.7 times under the UV-light. This is because the charge carriers produced under light excitation, extend the discharge time, and as confirmed by electron paramagnetic resonance, photoluminescence, and transmission electron microscopy analyses, the performance of P-SCs made from NF powders was relatively low compared to those produced from NW due to the high core defects in NF powders. The energy density of 78.1 mWh kg⁻¹ obtained for NF-based P-SCs is very promising, and the capacitance retention value of almost 100% for 3000 cycles showed that the P-SCs produced from these materials were entirely stable. Compared to the literature, the P-SCs we propose in this study are essential for new generation energy storage systems, thanks to their ease of design, adaptability to mass production for large-area applications, and their ability to store more energy under illumination.

Collaborative Filler Network for Enhancing the Performance of BaTiO3/PDMS Flexible Piezoelectric Polymer Composite Nanogenerators

Wearable sensors are gaining attention in human health monitoring applications, even if their usability is limited due to battery need. Flexible nanogenerators (NGs) converting biomechanical energy into electrical energy offer an interesting solution, as they can supply the sensors or extend the battery lifetime. Herein, flexible generators based on lead-free barium titanate (BaTiO₃) and a polydimethylsiloxane (PDMS) polymer have been developed. A comparative study was performed to investigate the impact of multiwalled carbon nanotubes (MWCNTs) via structural, morphological, electrical, and electromechanical measurements. This study demonstrated that MWCNTs boosts the performance of the NG at the percolation threshold. This enhancement is attributed to the enhanced conductivity that promotes charge transfer and enhanced mechanical property and piezoceramics particles distribution. The nanogenerator delivers a maximum open-circuit voltage (V_OC) up to 1.5 V and output power of 40 nW, which is two times higher than NG without MWCNTs. Additionally, the performance can be tuned by controlling the composite thickness and the applied frequency. Thicker NG shows a better performance, which enlarges their potential use for harvesting biomechanical energy efficiently up to 11.22 V under palm striking. The voltage output dependency on temperature was also investigated. The results show that the output voltage changes enormously with the temperature.

Characterization of Polyvinylidene Difluoride-based Energy Harvesting with IDE Circuit Flexible Cantilever Beam

Piezoelectric energy harvesting is the process of extracting electrical energy using energy harvester devices. Any stress in the piezoelectric material will generate induced voltage. Previous energy harvester device with stiff cantilever beam was generated low harvested energy. A flexural piezoelectric energy harvester is proposed to improve the generated harvesting energy. Polyvinylidene difluoride is a polymer piezoelectric material attached to a flexible circuit made of polyimide. Four interdigitated electrode circuits were designed and outsourced for fabrication. The polyvinylidene difluoride was then attached to the interdigitated electrode circuit, and a single clear adhesive tape was used to bind them. Four piezoelectric energy harvesters and ultrasonic ceramic generators were experimentally tested using a sieve shaker. The sieve shaker contains a two-speed oscillator, with M1=0.025 m/s and M2=0.05 m/s. It was used to oscillate the energy harvester devices. The resulting induced voltages were then measured. Design 4, with the widest width of electrode fingers and the widest gap between electrode fingers, had the highest power generated at an output load of 0.745 µW with the M2 oscillation speed. The oscillation speed of the sieve shaker impacted the energy harvester devices as a higher oscillation speed gave higher generated power.

Fiber Surface/Interfacial Engineering on Wearable Electronics

Surface/interfacial engineering is an essential technique to explore the fiber materials properties and fulfil new functionalities. An extensive scope of current physical and chemical treating methods is reviewed here together with a variety of real-world applications. Moreover, a new surface/interface engineering approach is also introduced: self-assembly via π-π stacking, which has great potential for the surface modification of fiber materials due to its nondestructive working principle. A new fiber family member, metal-oxide framework (MOF) fiber shows promising candidacy for fiber based wearable electronics. The understanding of surface/interfacial engineering techniques on fiber materials is advanced here and it is expected to guide the rational design of future fiber based wearable electronics.

Understanding the Origin of Enhanced Piezoelectric Response in PVDF Matrices with Embedded ZnO Nanoparticles, from Polarizable Molecular Dynamics Simulations

The pervasive use of portable electronic devices, powered from rechargeable batteries, represents a significant portion of the electricity consumption in the world. A sustainable and alternative energy source for these devices would require unconventional power sources, such as harvesting kinetic/potential energy from mechanical vibrations, ultrasound waves, and biomechanical motion, to name a few. Piezoelectric materials transform mechanical deformation into electric fields or, conversely, external electric fields into mechanical motion. Therefore, accurate prediction of elastic and piezoelectric properties of materials, from the atomic structure and composition, is essential for studying and optimizing new piezogenerators. Here, we demonstrate the application of harmonic-covalent and reactive force fields (FF), Dreiding and ReaxFF, respectively, coupled to the polarizable charge equilibration (PQEq) model for predicting the elastic moduli and piezoelectric response of crystalline zinc oxide (ZnO) and polyvinylidene difluoride (PVDF). Furthermore, we parametrized the ReaxFF atomic interactions for Zn-F in order to characterize the interfacial effects in hybrid PVDF matrices with embedded ZnO nanoparticles (NPs). We capture the nonlinear piezoelectric behavior of the PVDF-ZnO system at different ZnO concentrations and the enhanced response that was recently observed experimentally, between 5 and 7 wt % ZnO concentrations. From our simulation results, we demonstrate that the origin of this enhancement is due to an increase in the total atomic stress distribution at the interface between the two materials. This result provides valuable insight into the design of new and improved piezoelectric nanogenerators and demonstrates the practical value of these first-principles based modeling methods in materials science.

Recent advances in nanogenerators-based flexible electronics for electromechanical biomonitoring

Electromechanical biomonitoring is essential in human health evaluation, diseases prevention and life quality improvement. Nanogenerators (NGs) have demonstrated exceptional performances and versatility in self-powered flexible electronics including piezoelectric and electrostatic sensors. Combined with artificial intelligent (AI), five generation (5G) and internet-of-thing (IoT) technologies, the NGs-based flexible electronics are paving a new way for creating intelligent electromechanical biomonitoring systems which are also capable of analyzing, transmitting, and deciding. In this review, we cover the recent remarkable developments in monitoring electromechanical physiological signals using NGs-based flexible electronics. We begin by covering the fundamentals of NGs from the perspective of mechanisms, materials, device structures, and manufacturing methods. We then give an overview of NGs-based flexible electronics in various wearable and implantable sensing applications. Finally, the present limitations and future developing trends of this field are discussed and prospected.

Smart fibers for energy conversion and storage

Fibers have played a critical role in the long history of human development. They are the basic building blocks of textiles. Synthetic fibers not only make clothes stronger and more durable, but are also customizable and cheaper. The growth of miniature and wearable electronics has promoted the development of smart and multifunctional fibers. Particularly, the incorporation of functional semiconductors and electroactive materials in fibers has opened up the field of fiber electronics. The energy supply system is the key branch for fiber electronics. Herein, after a brief introduction on the history of smart and functional fibers, we review the current state of advanced functional fibers for their application in energy conversion and storage, focusing on nanogenerators, solar cells, supercapacitors and batteries. Subsequently, the importance of the integration of fiber-shaped energy conversion and storage devices via smart structure design is discussed. Finally, the challenges and future direction in this field are highlighted. Through this review, we hope to inspire scientists with different research backgrounds to enter this multi-disciplinary field to promote its prosperity and development and usher in a truly new era of smart fibers.

Fabrication of Piezoelectric ZnO Nanowires Energy Harvester on Flexible Substrate Coated with Various Seed Layer Structures

Flexible piezoelectric nanogenerators (PENGs) are very attractive for mechanical energy harvesting due to their high potential for realizing self-powered sensors and low-power electronics. In this paper, a PENG that is based on zinc oxide (ZnO) nanowires (NWs) is fabricated on flexible and transparent Polydimethylsiloxane (PDMS) substrate. The ZnO NWs were deposited on two different seed layer structures, i.e., gold (Au)/ZnO and tin-doped indium-oxide (ITO)/ZnO, using hydrothermal synthesis. Along with the structural and morphological analyses of ZnO NWs, the electrical characterization was also investigated for ZnO NWs-based flexible PENGs. In order to evaluate the suitability of the PENG device structure, the electrical output performance was studied. By applying a periodic mechanical force of 3 N, the ZnO NWs-based flexible PENG generated a maximum root mean square (RMS) voltage and average power of 2.7 V and 64 nW, respectively. Moreover, the comparison between the fabricated device performances shows that a higher electrical output can be obtained when ITO/ZnO seed layer structure is adopted. The proposed ZnO NWs-based PENG structure can provide a flexible and cost-effective device for supplying portable electronics.

Flexible Nanogenerator from Electrospun PVDF-Polycarbazole Nanofiber Membranes for Human Motion Energy-Harvesting Device Applications

Poly(vinylidene difluoride) (PVDF) has become the polymer matrix of choice for fabrication of wearable electronics and physiological monitoring devices. Despite possessing a high piezoelectric constant, additives are required to increase the charge transfer from PVDF matrix to connected signal readout units. Many of these additives also stabilize the β-phase of PVDF, which is associated with highest piezoelectric coefficients. However, most of the additives used are often brittle ceramic-phase materials resulting in decreased flexibility of the devices and offsetting the gain in β-phase content. Intrinsically conducting polymers (ICP), on the other hand, are ideal candidates to improve the device-related properties of PVDF, due to their higher flexibility than ceramic fillers as well as ability to form conducting network in PVDF membranes. This work reports the performance and device feasibility of PVDF-polycarbazole (PCZ) electrospun nanofiber membranes. A higher β-phase was observed by FTIR spectroscopy in PVDF/PCZ compared to other PVDF phases. Moreover, a higher open-circuit potential was recorded over PVDF/polyaniline composites, which were studied for comparison. The addition of PCZ reduced the flexibility of pure PVDF nanofibers by 20% only. Besides, the work investigated the bacterial biofouling and cell compatibility of the matrix, as essential properties to examine any putative medical device application. PVDF/PCZ membranes were then used to develop a nanogenerator, which was capable of instantly lighting an entire LED array employing the rectified output power, and charged up a 2.2 μF capacitors using a bridge rectifier through a vertical compressive force applied periodically. Finally, the nanogenerator demonstrated electrical energy harvesting from movements of various parts of the human body, such as toe and heel movement and wrist bending. In conclusion, PCZ can be considered as an attractive, biocompatible, and anti-biofouling conducting polymer for electrical actuation and flexible electronic device applications.

Optimization, characterization and evaluation of ZnO/polyvinylidene fluoride nanocomposites for orthopedic applications: improved antibacterial ability and promoted osteoblast growth

Herein, electrospun zinc oxide nanoparticle/poly (vinylidene fluoride) (ZnONP/PVDF) composite fiber membranes were designed, fabricated, and tested for improved orthopedic applications. A single factor screening study was conducted to determine the optimal ZnONP/PVDF formulation based on osteoblast (bone forming cells) proliferation and antibacterial properties. Further, ZnONP/PVDF materials were characterized for their morphology, crystallinity, roughness, piezoelectric properties, and chemistry to understand such cell results. The optimal concentration of high molecular weight PVDF (18%, w/v) and a low concentration of ZnONPs (1 mg/ml) were identified for electrospinning at room temperature in order to inhibit bacterial colonization (without resorting to antibiotic use) and promote osteoblast proliferation. Compared to no ZnO/PVDF scaffold without Piezo-excited group,the study showed that on the 1 mg/ml ZnO/PVDF scaffolds with piezo-excitation, the density of SA and E.coli decreased by 68% and 56%.The density of osteoblasts doubled within three days(compared to the control). In summary, ZnONP/PVDF composite fiber membranes were formulated by electrospinning showing an exceptional ability to eliminate bacteria colonization while at the same time promote osteoblast functions and, thus, they should be further studied for a wide range of orthopedic applications.

Laser Ablation-Assisted Synthesis of Poly (Vinylidene Fluoride)/Au Nanocomposites: Crystalline Phase and Micromechanical Finite Element Analysis

In this research, piezoelectric polymer nanocomposite films were produced through solution mixing of laser-synthesized Au nanoparticles in poly (vinylidene fluoride) (PVDF) matrix. Synthetization of Au nanoparticles was carried out by laser ablation in N-methyle-2-pyrrolidene (NMP), and then it was added to PVDF: NMP solution with three different concentrations. Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were carried out in order to study the crystalline structure of the nanocomposite films. Results revealed that a remakable change in crystalline polymorph of PVDF has occurred by embedding Au nanoparticles into the polymer matrix. The polar phase fraction was greatly improved by increasing the loading content of Au nanoparticle. Thermogravimetric analysis (TGA) showed that the nanocomposite films are more resistant to high temperature and thermal degradation. An increment in dielectric constant was noticed by increasing the concentration of Au nanoparticles through capacitance, inductance, and resistance (LCR) measurement. Moreover, the mechanical properties of nanocomposites were numerically anticipated by a finite element based micromechanical model. The results reveal an enhancement in both tensile and shear moduli.

Chitosan-ZnO Nanocomposites Assessed by Dielectric, Mechanical, and Piezoelectric Properties

The aim of this work is to structurally characterize chitosan-zinc oxide nanoparticles (CS-ZnO NPs) films in a wide range of NPs concentration (0-20 wt.%). Dielectric, conductivity, mechanical, and piezoelectric properties are assessed by using thermogravimetry, FTIR, XRD, mechanical, and dielectric spectroscopy measurements. These analyses reveal that the dielectric constant, Young's modulus, and piezoelectric constant (d33) exhibit a strong dependence on nanoparticle concentration such that maximum values of referred properties are obtained at 15 wt.% of ZnO NPs. The piezoelectric coefficient d33 in CS-ZnO nanocomposite films with 15 wt.% of NPs (d33 = 65.9 pC/N) is higher than most of polymer-ZnO nanocomposites because of the synergistic effect of piezoelectricity of NPs, elastic properties of CS, and optimum NPs concentration. A three-phase model is used to include the chitosan matrix, ZnO NPs, and interfacial layer with dielectric constant higher than that of neat chitosan and ZnO. This layer between nanoparticles and matrix is due to strong interactions between chitosan's side groups with ZnO NPs. The understanding of nanoscale properties of CS-ZnO nanocomposites is important in the development of biocompatible sensors, actuators, nanogenerators for flexible electronics and biomedical applications.

Study of Sputtered ZnO:Ga2O3 Films for Energy Harvesting Applications

Thin films of ZnO:Ga2O3 (ZGO) were deposited by radio frequency (RF) sputtering at voltages of 0.5, 0.9 and 1.1 kV. The films were studied with respect to their suitability in flexible piezoelectric nanogenerators. The analysis of the spectroscopic and microscopic results showed that piezoelectric features were revealed for the films grown at all sputtering voltages, but the most favorable morphology in terms of low roughness was achieved at 1.1 kV. The effect of the sputtering voltage on the films crystallinity and lattice strain was studied. It was found that the increasing sputtering voltage promoted the films crystallization. Additionally, the presence of oxygen vacancies in the piezoelectric films was negligible as it is not a major factor affecting their performance. The electrical measurements of the Ag/ZnO:Ga2O3/Ag harvester on a flexible substrate in the low-frequency range showed a piezoelectric voltage of 414 mV, a current of 10.4 µA and an electric power output of 1.4 µW at a mass load of 100 g. These results were achieved by a simple architecture of a single piezoelectric layer with a relatively small size of 3 cm2 and small piezoelectric film thickness (600 nm) containing lead-free material. It was proven that the sputtered ZGO films are suitable for energy harvesting elements and their performance could be tuned by the sputtering voltage. Another possible application of the proposed device, excluding low-frequency vibrational harvesting, could be a pressure sensor or strain gauge, due to the good linearity of the electrical parameter dependences on the strain.

Development of Sn-doped ZnO based ecofriendly piezoelectric nanogenerator for energy harvesting application

In this work, we have a demonstrated zinc oxide (ZnO) polymer-based ecofriendly piezoelectric nanogenerator (PENG) on a paper substrate for an energy harvesting application. The ZnO thin film is developed on the paper substrate, where different doping concentrations of Sn have been investigated systematically to validate the effect of doping towards enhancing the device performance. The piezoelectric potential of the fabricated device is evaluated by applying three different loads (4 N, 8 N, 22 N), where the source of the corresponding mechanical loads is based on the object of a musical drum stick. The results suggest that the pristine ZnO PENG device can generate a maximum output voltage and current of 2.15 V and 17 nA respectively. Moreover, the ZnO PENG device doped with 2.5% Sn achieved an even higher voltage (4.15 V) and current (36 nA) compared to pristine ZnO devices. In addition, the hydrothermal growth technique used to develop Sn-doped ZnO has the benefits of high scalability and low cost. Hence, the Sn-doped PENG device is a suitable candidate for energy harvesting applications operating in both uniform and non-uniform loading conditions.

Fiber/Fabric-Based Piezoelectric and Triboelectric Nanogenerators for Flexible/Stretchable and Wearable Electronics and Artificial Intelligence

Integration of advanced nanogenerator technology with conventional textile processes fosters the emergence of textile-based nanogenerators (NGs), which will inevitably promote the rapid development and widespread applications of next-generation wearable electronics and multifaceted artificial intelligence systems. NGs endow smart textiles with mechanical energy harvesting and multifunctional self-powered sensing capabilities, while textiles provide a versatile flexible design carrier and extensive wearable application platform for their development. However, due to the lack of an effective interactive platform and communication channel between researchers specializing in NGs and those good at textiles, it is rather difficult to achieve fiber/fabric-based NGs with both excellent electrical output properties and outstanding textile-related performances. To this end, a critical review is presented on the current state of the arts of wearable fiber/fabric-based piezoelectric nanogenerators and triboelectric nanogenerators with respect to basic classifications, material selections, fabrication techniques, structural designs, and working principles, as well as potential applications. Furthermore, the potential difficulties and tough challenges that can impede their large-scale commercial applications are summarized and discussed. It is hoped that this review will not only deepen the ties between smart textiles and wearable NGs, but also push forward further research and applications of future wearable fiber/fabric-based NGs.

The effect of ZnO/ZnSe core/shell nanorod arrays photoelectrodes on PbS quantum dot sensitized solar cell performance

ZnO nanorod (NR) based inorganic quantum dot sensitized solar cells have gained tremendous attention for use in next generation solar cells. ZnO/ZnSe-core/shell NR arrays (NRAs) with various densities were grown on an Au@ZnO seed layer (Au = 0.0, 4.0, 8.0 and 16.0 nm) on glass supported fluorine-doped tin oxide (FTO) substrates using low cost hydrothermal and ion-exchange approaches. PbS quantum dots (QDs) were loaded into the ZnO/ZnSe core/shell NRAs via a successive ionic layer adsorption and reaction (SILAR) method. The morphology, structural and optical properties of the core/shell NRAs were investigated using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis spectroscopy measurements. It was observed that the density of the ZnO/ZnSe NRAs decreases with increasing Au buffer layer thickness. The absorption decreases along with a decrease in the ZnO/ZnSe NRA density. The ZnO NRs/PbS QD photoelectrode performs poorly; however, after introducing a ZnSe shell on the core-ZnO, the solar cells parameters changed according to the ZnO/ZnSe NRA density. Values of η = ∼0.88%, J SC = 14.60 mA cm-2, and V OC = 190 mV, and η = ∼0.25%, J SC = 6.77 mA cm-2, and V OC = 115 mV were obtained for the highest and lowest NRA densities, respectively. Although the photovoltaic performance of these photoelectrodes is still inferior, further improvement of the device would be possible by suppressing surface defects, and through quality optimization of the ZnO/ZnSe NRAs, PbS QDs, counter electrode and electrolyte.