Applications of Two-Dimensional Nanomaterials in Energy and Devices

Author:Yang Dong

Supervisor:xiong yu jie changning wang


Degree Year:2019





Since the discovery of graphene in 2004,two-dimensional(2D)nanomaterials have shown broad prospects in many fields such as energy,physics,chemistry and electronic devices.In recent years,with the unique characteristics of 2D nanomaterials,high-efficiency photocatalysts,high-performance optoelectronic devices and flexible electronic devices have become the research highlights of 2D materials.Specifically,the high surface-to-volume ratio of two-dimensional materials introduces unbeatable advantages in the preparation of high-efficiency photocatalysts.The ultra-thin characteristics of 2D nanomaterials provide the possibility to fabricate micro-and nano-scale devices.The superior mechanical properties of two-dimensional nanomaterials enable excellent performance in wearable electronics.Although 2D nanomaterials have varieties of excellent properties,there are still several problems to be solved toward applications.The first problem lies on the preparation of large-area nanomaterials with high performance.The 2D nanomaterials prepared by chemical synthesis method are small in size,and the ones prepared by vapor deposition method have defects in electrical properties.Secondly,the applications are limited by the synthesis and device processing of high-performance 2D nanomaterials.For example,the electrons and holes in the catalytic process of C3N4 are easily recombined,leading to low catalytic activity.The graphene-based Schottky solar cell still has poor photoelectric conversion efficiency in the near-infrared band.In the meantime,the fabrication of the biological device with excellent mechanical properties and good biological activity is another challenge.Since the surface of human organs is extremely soft,researchers are keep finding ways to utilize these 2D nanomaterials so that the devices can be perfectly combined in the human body and organs without damaging human tissues.Finally,the combination of 2D nanomaterials and novel information technology is required to obtain data more effectively and more reliable.In this thesis,we have prepared a variety of devices based on 2D nanomaterials by chemical synthesis,vapor deposition,transfer printing and metal-assisted exfoliation.The properties of the nanomaterials have been improved by doping and forming composites.By employing the characteristics of plasmonic elements,we improve the performance of related optoelectronic devices.A variety of wearable and implantable bioelectronic devices have been fabricated and tested with their performance and toxicity.The devices are able to wirelessly transmit data with Bluetooth.Finally,devices are successfully embedded with artificial intelligence and data acquisition.The main achievements are as follows:1.The application of 2D C3N4 nanosheets in photocatalytic hydrogen production.A novel high-performance non-metal photocatalyst was prepared by binding melem to g-C3N4,constructing a g-C3N4/melem heterostructure.The heterojunction can effectively suppress the recombination of electrons and holes.In addition,there is also a synergistic effect of interfacial charge polarization,which greatly improves the catalytic hydrogen production efficiency.The introduction of the oligomer increases the hydrogen production activity of the polymer compared to the original g-C3N4.The maximum hydrogen production rate of this heterojunction is up to 23 mmol/g/h,which is twice that of melem and doubled compared with g-C3N4;2.The application of the graphene in plasmonic devices.A shaped Ag nanopore periodic array(Ag NH)was first prepared by micro-nano fabrication processing,and then a gold-graphene-NH sandwich structure was successfully constructed by introducing graphene,forming an alkene film-nanopore sandwich structure.The sandwich structure realized a sub-20 nm distribution between the Ag NH in the horizontal direction and a sub-nanometer distribution between the Au NP and Ag NH structures in the vertical direction.The graphene-silicon nanowire photovoltaic device was constructed by using graphene.According to the plasmonic absorption band of Ag,a theory that a plasmonic element can inject hot electrons into the Si nanowire array was successfully proven.3.The application of 2D silicon nanomaterials in implantable neural devices.The ultra-thin 2D silicon nano-films was successfully transferred through PDMS stamps,and a new 3D implantable neural array device was fabricated.The device is a multi-layer stacking structure,each of which has two silicon-based photoelectric sensors,and a neuron device has a layer of Fe therein,so that the device has magnetic actuated performance.The 3D implantable neural device has spatial light intensity distribution mapping capability,which provides a good idea for developing complex integrated neural devices.4.The application of two-dimensional MoSe2 nanomaterials in wireless gas sensors.The large-area 2D MoSe2 was successfully transferred through gold-assisted mechanical exfoliation.This method enables excellent electrical properties.The exfoliated MoSe2 has a lateral size of up to several hundred microns,which makes it possible to construct complex devices.The epidermal electronics of the sandwich structure were fabricated based on the large piece of MoSe2.The device has a high sensitivity and selectivity to NH3 and NO2 and is capable of maintaining a fast response(<200 S)to gases as low as one part per million(ppm).The device,combined with cloud information systems,wirelessly transmits data and stores it in the cloud terminal,providing a new strategy for environmental monitoring and toxic gas detection.5.The application of MoS2 on stretchable electronic.Gold-assisted exfoliation was used to prepare large-scale MoS2 nanosheets.Using MoS2 nanosheets as the active layer,a stretchable electronic integrated with photodetector,temperature sensor is fabricated.The system greatly improves the stretchability of the device by the Chinese traditional papercut structure.This work provides a reference for the development of novel stretchable electronic.6.Research on 2D nanomaterial intelligent device based on neural network.A gold-assisted exfoliated large-area MoSe2 nanosheet was used to prepare a wearable gas smart watch with excellent response to NO2.By introducing Ag nanoparticles,the sensing performance was improved,and the integration with smart watches further proved the wearability and portability of the system.Combining neural network algorithm-based machine learning and cloud data sharing,a method for predicting pollution sources in complex wind paths was constructed.This provides an idea for building complex 2D nano-smart devices.