Jingna Zhao

Enhanced photocatalytic activity of ZnO nanotetrapods

The photocatalytic characteristics of the tetrapod-branched ZnO nanostructures synthesized by thermal evaporation method are investigated. The fitting of absorbance maximum plot versus time indicates an exponential decay, suggesting the photodegradation of Rhodamine B catalyzed by the ZnO nanotetrapod is a pseudo first-order reaction. These results demonstrate that the photocatalytic activity of ZnO nanotetrapod is much better than that of P25 TiO2 and ZnO powders. The slow electron/hole recombine rate due to the abundant surface states, as well as the high surface-to-volume ratio will effectively enhance the photocatalytic activity of the ZnO nanotetrapod.

Electro‐Induced Mechanical and Thermal Responses of Carbon Nanotube Fibers

The electromechanical and electrothermal responses of carbon nanotube fibers provide new ways to use energy conversion, including the modulation of assembly structures by alternative densification and relaxation. The most efficient way to strengthen the tensile strength up to 2.32-2.50 GPa is shown as well as a microscale, nanotube-based Chinese calligraphy brush.

Continuous electrodeposition for lightweight, highly conducting and strong carbon nanotube-copper composite fibers

Carbon nanotube (CNT) fiber is a promising candidate for lightweight cables. The introduction of metal particles on a CNT fiber can effectively improve its electrical conductivity. However, the decrease in strength is observed in CNT-metal composite fibers. Here we demonstrate a continuous process, which combines fiber spinning, CNT anodization and metal deposition, to fabricate lightweight and high-strength CNT-Cu fibers with metal-like conductivities. The composite fiber with anodized CNTs exhibits a conductivity of 4.08 × 10(4)-1.84 × 10(5) S cm(-1) and a mass density of 1.87-3.08 g cm(-3), as the Cu thickness is changed from 1 to 3 μm. It can be 600-811 MPa in strength, as strong as the un-anodized pure CNT fiber (656 MPa). We also find that during the tensile tests there are slips between the inner CNTs and the outer Cu layer, leading to the drops in electrical conductivity. Therefore, there is an effective fiber strength before which the Cu layer is robust. Due to the improved interfacial bonding between the Cu layer and the anodized CNT surfaces, such effective strength is still high, up to 490-570 MPa.

Enhanced carbon nanotube fibers by polyimide

The performance of carbon nanotube (CNT) fibers is limited by the intertube characteristics. Here we report a direct method of curing to improve mechanical properties of poly(amic acid)-infiltrated fibers. After curing at 190 °C for 60 min the fibers composed of double- and triple-walled CNTs, their strength is stably improved by 30.3%, from 1.58 to 2.06 GPa. The enhancement arises from the increase in shear stress between tube surfaces, by measuring the static frictional force of CNT fibers. Due to the existence of CNTs, the imidization temperature of polyimide drops greatly from 218 to 157 °C.

Bio-Inspired Aggregation Control of Carbon Nanotubes for Ultra-Strong Composites

High performance nanocomposites require well dispersion and high alignment of the nanometer-sized components, at a high mass or volume fraction as well. However, the road towards such composite structure is severely hindered due to the easy aggregation of these nanometer-sized components. Here we demonstrate a big step to approach the ideal composite structure for carbon nanotube (CNT) where all the CNTs were highly packed, aligned, and unaggregated, with the impregnated polymers acting as interfacial adhesions and mortars to build up the composite structure. The strategy was based on a bio-inspired aggregation control to limit the CNT aggregation to be sub 20–50 nm, a dimension determined by the CNT growth. After being stretched with full structural relaxation in a multi-step way, the CNT/polymer (bismaleimide) composite yielded super-high tensile strengths up to 6.27–6.94 GPa, more than 100% higher than those of carbon fiber/epoxy composites, and toughnesses up to 117–192 MPa. We anticipate that the present study can be generalized for developing multifunctional and smart nanocomposites where all the surfaces of nanometer-sized components can take part in shear transfer of mechanical, thermal, and electrical signals.

Multifunctionalization of carbon nanotube fibers with the aid of graphene wrapping

Carbon nanotube (CNT) fibers are promising candidates for developing multifunctional textiles. The direct introduction of functional guests within or around CNT fibers meets problems due to the rough fiber surface and weak interfacial bindings. To improve the functionality and performance stability, we report a new method to modify the surface roughness and level of functionalization of CNT fibers, by wrapping graphene oxide (GO) or reduced graphene (RG) around them. Besides the functional groups on the graphene sheets, the introduction of a graphene layer also has smoothing and shield effects, resulting in higher tensile strength and improved and stabilized performance. The electrochemical and photocurrent applications were exploited by depositing polyaniline around GO-wrapped CNT fibers and TiO2 around RG-wrapped fibers, with a capacitance up to 229.5 F cm−3 and a photocurrent density of 132 μA cm−2, respectively. The present technique has the advantage that the mechanical and functional properties can be optimized by simply modifying the core CNT fiber via polymer infiltration during the fiber spinning.

Enhancing interfacial adhesion and functionality of carbon nanotube fibers with depolymerized chitosan

The infiltration of high molecular weight polymers into carbon nanotube (CNT) fibers to strengthen them is strongly restricted. By depolymerizing chitosan with H2O2 in an acidic environment, the molecular weight was significantly decreased to below 7.5 × 104 g mol−1, resulting in improved infiltration. The CNT fiber containing depolymerized chitosan was as strong as 1.81 GPa, double the strength of the ethanol-densified fiber. The strengthening ability was greater than that of polyvinyl alcohol, and was attributed to the amino and hydroxyl groups. These groups also provided the composite fiber with multifunctionality, and we provided two examples. After the adsorption of Cu(II), the fibers electrical conductivity was increased by 86 S cm−1. The chitosan-infiltrated fiber induced the efficient deposition of CdS nanoparticles, and thus became photoluminescent.

Electro-optic effect in Ba1−xPbxTiO3 films

High quality Ba1−xPbxTiO3 (x=0–0.25) films were grown on R-Al2O3 in a wide thickness range of 0.5–3 μm. Significant improvement of the films’ crystallinity and optical quality was observed in the presence of lead oxide for the films prepared at 650–700 °C. Strong texture of (110) type was observed in these films. The material is transparent at 350–2000 nm, indicating the possibility of its application in light controlling devices at wavelengths used in optical communication: 1300 and 1500 nm. Maximum field induced relative phase shift of 0.22 rad was measured in the film with composition of Ba0.9Pb0.1TiO3 under a field strength of 3×106 V/cm.

Wide‐Range Tunable Dynamic Property of Carbon‐Nanotube‐Based Fibers

A carbon nanotube (CNT) fiber is formed by assembling millions of individual tubes. The assembly feature provides the fiber with rich interface structures and thus various ways of energy dissipation, as reflected by the nonzero loss tangent (>0.028-0.045) at low vibration frequencies. A fiber containing entangled CNTs possesses higher loss tangents than a fiber spun from aligned CNTs. Liquid densification and polymer infiltration, the two common ways to increase the interfacial friction and thus the fibers tensile strength and modulus, are found to efficiently reduce the damping coefficient. This is because the sliding tendency between CNT bundles can also be well suppressed by a high packing density and the formation of covalent polymer cross-links within the fiber. The CNT/bismaleimide composite fiber exhibits the smallest loss tangent, nearly the same as that of carbon fibers. At a higher level of the assembly structure, namely a multi-ply CNT yarn, the interfiber friction and sliding tendency obviously influence the yarns damping performance, and the loss tangent can be tuned within a wide range, similar to carbon fibers, nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow new applications ranging from high quality factor materials to dissipative systems.

Bio-inspired Design and Fabrication of Super-Strong and Multifunctional Carbon Nanotube Composites

Carbon nanotubes (CNTs) are ideal scaffolds to design and architect high-perform‐ ance composites at high CNT volume fractions. In these composites, the CNT align‐ ment determines the level of aggregation and the structure morphology, and thus the load transfer efficiency between neighboring CNTs. Here, we discuss two major solutions to produce high-volume fraction CNT composites, namely the layer-bylayer stacking of aligned CNT sheets and the stretching of entangled CNT webs (networks). As inspired by the growth procedure of natural composites, the aggrega‐ tion of CNTs can be well controlled during the assembling process. As a result, the CNTs can be highly packed, aligned, and importantly unaggregated, with the impregnated polymers acting as interfacial adhesion or mortars to build up the composite struc‐ ture. The CNT/bismaleimide composites can yield a super-high tensile strength up to 6.27–6.94 GPa and a modulus up to 315 GPa.