Yongming Fu

Realizing room-temperature self-powered ethanol sensing of ZnO nanowire arrays by combining their piezoelectric, photoelectric and gas sensing characteristics

Room-temperature self-powered ethanol sensing has been realized from ZnO nanowire (NW) arrays by combining their piezoelectric, photoelectric and gas sensing characteristics. Under the assistance of UV illumination, the piezoelectric output of ZnO NWs acts not only as a power source, but also as a response signal to ethanol gas at room temperature. Upon exposure to 700 ppm ethanol at room temperature under 67.5 mW cm−2 UV illumination, the piezoelectric output voltage of ZnO NWs (under 34 N compressive forces) decreases from 0.80 V (in air) to 0.12 V and the response is up to 85. The room-temperature reaction between the UV-induced chemisorbed oxygen ions and ethanol molecules increases the carrier density in ZnO NWs, resulting in a strong piezoelectric screening effect and very low piezoelectric output. Our study can stimulate a research trend on designing new gas sensors and investigating new gas sensing mechanisms.

High Piezo-photocatalytic Efficiency of CuS/ZnO Nanowires Using Both Solar and Mechanical Energy for Degrading Organic Dye

High piezo-photocatalytic efficiency of degrading organic pollutants has been realized from CuS/ZnO nanowires using both solar and mechanical energy. CuS/ZnO heterostructured nanowire arrays are compactly/vertically aligned on stainless steel mesh by a simple two-step wet-chemical method. The mesh-supported nanocomposites can facilitate an efficient light harvesting due to the large surface area and can also be easily removed from the treated solution. Under both solar and ultrasonic irradiation, CuS/ZnO nanowires can rapidly degrade methylene blue (MB) in aqueous solution, and the recyclability is investigated. In this process, the ultrasonic assistance can greatly enhance the photocatalytic activity. Such a performance can be attributed to the coupling of the built-in electric field of heterostructures and the piezoelectric field of ZnO nanowires. The built-in electric field of the heterostructure can effectively separate the photogenerated electrons/holes and facilitate the carrier transportation. The CuS component can improve the visible light utilization. The piezoelectric field created by ZnO nanowires can further separate the photogenerated electrons/holes through driving them to migrate along opposite directions. The present results demonstrate a new water-pollution solution in green technologies for the environmental remediation at the industrial level.

Detecting Liquefied Petroleum Gas (LPG) at Room Temperature Using ZnSnO3/ZnO Nanowire Piezo-Nanogenerator as Self-Powered Gas Sensor.

High sensitivity, selectivity, and reliability have been achieved from ZnSnO3/ZnO nanowire (NW) piezo-nanogenerator (NG) as self-powered gas sensor (SPGS) for detecting liquefied petroleum gas (LPG) at room temperature (RT). After being exposed to 8000 ppm LPG, the output piezo-voltage of ZnSnO3/ZnO NW SPGS under compressive deformation is 0.089 V, much smaller than that in air ambience (0.533 V). The sensitivity of the SPGS against 8000 ppm LPG is up to 83.23, and the low limit of detection is 600 ppm. The SPGS has lower sensitivity against H2S, H2, ethanol, methanol and saturated water vapor than LPG, indicating good selectivity for detecting LPG. After two months, the decline of the sensing performance is less than 6%. Such piezo-LPG sensing at RT can be ascribed to the new piezo-surface coupling effect of ZnSnO3/ZnO nanocomposites. The practical application of the device driven by human motion has also been simply demonstrated. This work provides a novel approach to fabricate RT-LPG sensors and promotes the development of self-powered sensing system.

Hydrothermal synthesis of Co–ZnO nanowire array and its application as piezo-driven self-powered humidity sensor with high sensitivity and repeatability

A high sensitive and repeatable self-powered humidity sensor has been realized from Co-doped ZnO nanowires (NWs). The piezoelectric output of the device acts not only as a power source, but also as a response signal to the relative humidity (RH) in the environment. When the relative humidity is 70% RH at room temperature, the piezoelectric output voltage of the humidity sensor under compressive force decreases from 1.004 (at 20% RH) to 0.181 V. The sensitivity of self-powered humidity sensing based on Co-doped ZnO nanoarrays is much higher than that of undoped ZnO nanoarrays. The device exhibits good repeatability for humidity detection, and the response maintains ∼90% after one month. Such a high performance can be attributed to the piezo-surface coupling effect of the nanocomposites and more active sites introduced by the Co dopants. Our study can stimulate a research trend on exploring composite materials for piezo-gas sensing.

Ultrafast piezo-photocatalytic degradation of organic pollutions by Ag2O/tetrapod-ZnO nanostructures under ultrasonic/UV exposure

Ultrafast degradation of organic pollutions has been realized by the piezo-photocatalytic activity of Ag2O/tetrapod-ZnO nanostructures under ultrasonic/UV exposure. Tetrapod-ZnO (T-ZnO) nanostructures are synthesized in mass production by a thermal evaporation method, and Ag2O nanoparticles are uniformly loaded on the whole surface of T-ZnO nanostructures. Under both ultrasonic and UV exposure, Ag2O/T-ZnO nanostructures can efficiently co-use the mechanical and UV energy to degrade organic pollutions, and the degradation speed is extraordinarily fast. Taking methylene blue (MB) as an example, Ag2O/T-ZnO nanostructures (2 g L−1) can completely degrade an MB aqueous solution (5 mg L−1) within ∼2 min under ultrasonic (200 W) and UV (50 W) exposure. Such a degradation rate is much higher than previous results, and has potential applications in sewage treating techniques at the industrial level. In this process, the piezoelectric field of T-ZnO nanostructures and the build-in electric field of Ag2O/T-ZnO heterojunctions can separate the photogenerated electron–hole pairs, lowering the recombination rate and enhancing the photocatalytic activity. The present results can promote the development of sewage treating techniques for environmental improvement.

Self-powered, stretchable, fiber-based electronic-skin for actively detecting human motion and environmental atmosphere based on a triboelectrification/gas-sensing coupling effect

A new self-powered, stretchable, fiber-based electronic-skin (e-skin) has been fabricated for actively detecting human motion and environmental atmosphere. Several bundles of carbon fibers (coated with polydimethylsiloxane (PDMS) or polypyrrole (Ppy)) were woven together, forming a flexible fiber-based e-skin. The triboelectric current of the e-skin was dependent on the strain deformation and the environmental atmosphere. The e-skin can actively detect various human motions, such as finger touch, joint motion, skin deformation and slight stretching. Each PDMS–Ppy crossing point can be employed as an independent unit, and these units can output triboelectric current individually, realizing the tactile perception. The e-skin can also monitor volatile organic compounds in the atmosphere with high sensitivity, recovery and selectivity, (e.g. upon exposure to 1200 ppm methanol vapor, the triboelectric current of the e-skin decreased from 41.17 (in air) to 15.12 nA). The working mechanism is based on the triboelectrification/gas-sensing coupling effect. This new device architecture and material system can promote the development of a self-powered multifunctional e-skin.

A self-powered flexible vision electronic-skin for image recognition based on a pixel-addressable matrix of piezophototronic ZnO nanowire arrays

The emerging electronic-skins (e-skins) are designed to mimic the comprehensive properties of human perception via flexible device techniques, and the achievement of a vision e-skin for image recognition is a highly interesting topic for applications in bionic organs and robots. In this paper, a new self-powered flexible vision e-skin has been realized from a pixel-addressable matrix of piezophototronic ZnO nanowire arrays. Under applied deformation, the e-skin can actively output piezoelectric voltage (piezoelectric effect), and the output piezoelectric voltage can be significantly influenced by UV illumination. The piezoelectric output can be regarded as both a photodetecting signal and electrical power for driving the device (no external power source is needed). The working mechanism is based on the optoelectronic/piezoelectric coupling effect (piezophototronic effect) of ZnO. The photo-generated carriers inside the ZnO nanowires can partially screen the piezoelectric field, affecting the piezoelectric output. The e-skin device has a 6 × 6 pixel-addressable matrix structure, and can map multi-point UV-stimuli through a multichannel data acquisition method, realizing image recognition. This new device structure and working mechanism may provoke a new research direction for the development of multi-functional e-skins.

A self-powered brain-linked biosensing electronic-skin for actively tasting beverage and its potential application in artificial gustation

A new self-powered brain-linked biosensing electronic-skin (e-skin) for detecting pH value and alcoholicity of beverages has been realized based on polydimethysiloxane/polypyrrole (PDMS/Ppy) nanostructures. This e-skin (linking brain and transmitting signal to the specific encephalic region) can work as an artificial gustation system for gustatory perception substitution without an external electricity source. The sensing units on the e-skin can efficiently convert mechanical energy (human motion) into triboelectric impulse. The triboelectric output can be influenced by pH value and alcohol concentration in common beverages (acidic, alkaline or alcoholic drinks), which can be treated as the bio-chemical sensing signal. The bio-chemical sensing behavior arises from the triboelectrification/bio-chemical-sensing coupling effect. The biosensing e-skin is simply linked to the brain of a mouse at the primary motor cortex area, and the inputting signal can take part in the mouse perception, thus realizing behavior interventions, e.g., shaking of legs. This study provides a novel approach for developing artificial gustation e-skin and self-powered brain-machine interaction system with low cost.

A self-powered electronic-skin for real-time perspiration analysis and application in motion state monitoring

A new self-powered electronic-skin (e-skin) for real-time perspiration analysis has been fabricated from a polyaniline (PANI) triboelectric-biosensing unit matrix, which can also work as a self-powered visualization system for preventing exercise injury (dehydration). The biosensing units on the e-skin can be driven by body motion through efficiently converting mechanical energy into triboelectric current. After surface modification with enzymes and a drop-cast chitosan film, the triboelectric output of the biosensing units can be influenced by the target biomarkers, acting as a biosensing signal. This new triboelectrification/enzymatic-reaction coupling effect has been demonstrated in different biosensing units that can detect the urea, uric acid, lactate, glucose, Na+ and K+ concentration in perspiration without any external electricity power. The e-skin can be linked to a visualization panel, and the input triboelectric current can show the motion state of the human body during exercise. This work can provoke a new research direction for developing wearable healthcare diagnosis systems and self-powered visualization systems. This new technique could also reduce medical expenses and facilitate application in low-income regions.