Bio-Inspired Synthesis Of Nanostructured Materials On Substrates For Environmental And Energy Applications

It is still a challenging task to develop simple methods for facile synthesis of functional nanostructures on substrates under mild conditions without using expensive instruments. We have successfully developed a bio-inspired method using simple diaphragm-assisted system to synthesize functional nanostructures on various substrates under mild conditions. We have systematically studied the effects of experimental parameters on the formation of nanostructures under controlled conditions. The fundamental mechanism involved has been systematically studied and revealed. By growing the unique networks of nanostructures on a piece of substrate, a double-rough surface, with structures at both nanoscale and microscale, has been achieved, showing interesting roughness-induced superhydrophobicity in air and superoleophobicity in water. The double rough substrates will find important environmental applications. Additionally, nanostructures formed on substrates have been used as integrated and binder-free electrodes for energy storage. The unique structures with a large exposed surface enable the electrodes to demonstrate dramatically improved performances. Moreover, some chemically active substrates were used to build up composite materials to enhance their applications. The method and ideas outlined in the dissertation, based on diaphragm-assisted systems, will have impacts, in principle, on the synthesis of numerous functional materials or precursors under mild conditions

Hydrothermal synthesis and characterisation of α-Fe2O3 nanorods

The hydrothermal synthesis (HS) of α-Fe2O3 nanorods (NRs) is investigated using a combination of complementary analytical techniques. The construction of an HS ‘process map’ as a function of temperature, time and phosphate (PO43-) concentration provides insight into the nature of intermediate β-FeOOH NR precipitation, dissolution and subsequent α-Fe2O3 growth, along with the effect of PO43- anion concentration on the development of α-Fe2O3 particle shape. An HS processing temperature of 200˚C and an Fe3+ : PO43- molar ratio of 31.5 yielded crystalline acicular α-Fe2O3 NRs with an aspect ratio of ~ 7 (~ 420 nm long, ~ 60 nm wide). The additional effects of FeCl3 concentration, pH, stage of phosphate addition and α-Fe2O3 seed content on the growth of α-Fe2O3 NRs is investigated. The development of a novel valve-assisted pressure autoclave is described, facilitating the rapid quenching of hydrothermal suspensions into liquid nitrogen, providing ‘snapshots’ closely representative of the in situ physical state of the synthesis reaction products. Examination of the samples acquired as a function of reaction time and known reaction temperature provides fundamental insight into the anisotropic crystal growth mechanism of the acicular α-Fe2O3 NRs. It is considered that the release of Fe3+ ions back into solution through intermediate β-FeOOH dissolution supplies the nucleation and growth of primary α-Fe2O3 nanoparticles (NPs) (< 10 nm) which subsequently coalescence through a mechanism of oriented attachment (OA) with increasing temperature, into larger, acicular α-Fe2O3 NRs. Fourier transform infra-red spectroscopy investigation of the quenched reaction products provides evidence for PO43- absorption on the α-Fe2O3 NPs, in the form of mono or bi-dentate (bridging) surface complexes, on surfaces normal and parallel to the crystallographic α-Fe2O3 c-axis, respectively. The balance between bi-dentate and mono-dentate phosphate absorption is considered to be critical in mediating the acicular shape of the α-Fe2O3 NRs. A feasibility study on the incorporation of ferromagnetic cobalt, Co3O¬4 NPs or CoFe2O4 NPs into α-Fe2O3 NRs during HS is presented. In all cases, there is no evidence for the incorporation of cobalt within the α-Fe2O3 NRs or the formation of hetero-nanostructures with the Co3O4 or CoFe2O4 NPs. The overall growth mechanism of single crystalline acicular α-Fe2O3 NRs involves the anisotropic growth and dissolution of intermediate β-FeOOH NRs, governed by its crystallographic structure, and the OA of primary α-Fe2O3 NPs, mediated by the preferential absorption of phosphate surfactant

Synthesis and Electrochemical Performance of Hydrothermally Synthesized Co3O4 Nanostructured Particles

Spinel Co3O4 exhibit remarkable photo and electro-chemical properties. Combined with its cost effectiveness and wide abundance, Co3O4 has emerged as a promising candidate for pseudocapacitor, fuel cell, lithium ion batteries, water splitting and energy applications. It is well documented in the literature that the pseudocapacitive performance of oxides depends on many factors such as type of oxide, surface area and morphology, electrolyte, temperature etc. In view of this, the present work delineates efforts to understand the effect of morphology on the electrocapacitive behavior of Co3O4 nanostructured particles. The systematic morphological changes in Co3O4 is achieved by varying hydrolyzing agent, urea content during the hydrothermal synthesis of particles. Morphology and size analysis using scanning electron microscopy (SEM), show hierarchical structures namely plate like architecture and brush like structures of particles. The electrochemical measurements are performed using standard three-electrode system with 3M KOH electrolyte via cyclic voltammetry and galvanostatic charge-discharge methods. Amongst the Co3O4 studied, Co3O4-U0.37 displayed moderate surface area (50.10 m2/g), highest specific capacitance (764 F/g at 5mV/s) and energy density (19.56 Wh/kg). The specific capacitance of all Co3O4 decreased with the increase in scan rate. The cyclic stability of Co3O4-U0.37 is studied up to 5,000 cycles and about 64% retention in charge storage capacity was observed. The superior electro-capacitive behavior of the Co3O4-U0.37 is attributed to high surface area, brush like structure, and high electrical conductivity amongst studied Co3O4. In conclusion, it is demonstrated that high specific capacitance is achievable in the same oxide material by the tight control of morphology of the material. The low hydrolyzing concentration aided in producing high surface area architecture

II-VI Semiconductor Nanowire Array Sensors Based on Piezotronic, Piezo-Phototronic and Piezo-Photo-Magnetotronic Effects

With the rapid progress of nanotechnologies, there are two developing trends for the next generation of sensors: miniaturization and multi-functionality. Device miniaturization requires less power consumption, or even self-powered system. Multi-functional devices are usually based on multi-property coupling effects. Piezoelectric semiconductors have been considered to be potential candidates for self-powered/multi-functional devices due to their piezotronic coupling effect. In this dissertation, ZnO and CdSe nanowire arrays have been synthesized as the piezoelectric semiconductor materials to develop the following self-powered/multi-functional sensors: (1) self-powered gas sensors of ZnO/SnO2, ZnO/In2O3, ZnO/WO3 and CdSe nanowire arrays have been assembled. All these gas sensors are capable of detecting oxidizing gas and reducing gas without any external power supply owing to piezotronic effect which can convert mechanical energies to electrical energy to power the sensors; (2) a self-powered ZnO/ZnSe core/shell nanowire array photodetector has been fabricated. This photodetector is able to detect the entire range of the visible spectrum as well as UV light because of its type II heterostructure. The absolute sensitivity and the percentage change in responsivity of the photodetector were significantly enhanced resulting from the piezo-phototronic effect. The photodetector also exhibited self-powered photodetection behavior; (3) three dimensional nanowire arrays, such as ZnO and ZnO/Co3O4, have been synthesized to investigate piezo-magnetotronic and piezo-photo-magnetotronic effects. Under magnetic field, the magnetic-induced current of ZnO nanowire array decreased as magnetic field increased, and the current difference was magnified by one order of magnitude caused by piezo-magnetotronic effect through applying a stress. In contrast, under UV light illumination, the current response increased with an increment of magnetic field. The current difference was enhanced by at least two orders of magnitude attributed to piezo-photo-magnetotronic effect. Furthermore, ZnO/Co3O4 core/shell structure was employed to further improve the magnetic-induced current difference. This phenomenon projects a potential for multi-functional piezo-magnetotronic and piezo-photo-magnetotronic device development

Synthesis and Electrochemical Performance of Hydrothermally Synthesized Co3O4 Nanostructured Particles

Spinel Co3O4 exhibit remarkable photo and electro-chemical properties. Combined with its cost effectiveness and wide abundance, Co3O4 has emerged as a promising candidate for pseudocapacitor, fuel cell, lithium ion batteries, water splitting and energy applications. It is well documented in the literature that the pseudocapacitive performance of oxides depends on many factors such as type of oxide, surface area and morphology, electrolyte, temperature etc. In view of this, the present work delineates efforts to understand the effect of morphology on the electrocapacitive behavior of Co3O4 nanostructured particles. The systematic morphological changes in Co3O4 is achieved by varying hydrolyzing agent, urea content during the hydrothermal synthesis of particles. Morphology and size analysis using scanning electron microscopy (SEM), show hierarchical structures namely plate like architecture and brush like structures of particles. The electrochemical measurements are performed using standard three-electrode system with 3M KOH electrolyte via cyclic voltammetry and galvanostatic charge-discharge methods. Amongst the Co3O4 studied, Co3O4-U0.37 displayed moderate surface area (50.10 m2/g), highest specific capacitance (764 F/g at 5mV/s) and energy density (19.56 Wh/kg). The specific capacitance of all Co3O4 decreased with the increase in scan rate. The cyclic stability of Co3O4-U0.37 is studied up to 5,000 cycles and about 64% retention in charge storage capacity was observed. The superior electro-capacitive behavior of the Co3O4-U0.37 is attributed to high surface area, brush like structure, and high electrical conductivity amongst studied Co3O4. In conclusion, it is demonstrated that high specific capacitance is achievable in the same oxide material by the tight control of morphology of the material. The low hydrolyzing concentration aided in producing high surface area architecture

Controlling the morphology of metal–organic frameworks and porous carbon materials: metal oxides as primary architecture-directing agents

Owing to their large ratio of surface area to mass and volume, metal–organic frameworks and porous carbons have revolutionized many applications that rely on chemical and physical interactions at surfaces. However, a major challenge today is to shape these porous materials to translate their enhanced performance from the laboratory into macroscopic real-world applications. In this review, we give a comprehensive overview of how the precise morphology control of metal oxides can be transferred to metal–organic frameworks and porous carbon materials. As such, tailored material structures can be designed in 0D, 1D, 2D, and 3D with considerable implications for applications such as in energy storage, catalysis and nanomedicine. Therefore, we predict that major research advances in morphology control of metal–organic frameworks and porous carbons will facilitate the use of these materials in addressing major needs of the society, especially the grand challenges of energy, health, and environment

Template-free hierarchical trimetallic oxide photocatalyst derived from organically modified ZnCuCo layered double hydroxide

High-performance photocatalysts have considerable potential to address energy and environmental issues. In this study, dodecylbenzenesulfonate (DBS) modified ZnCuCo layered double hydroxide (DBS-ZnCuCo LDH) microspheres were synthesized through the facile template-free hydrothermal method. Subsequently, ZnCuCo mixedmetal oxides (MMOs) with morphological features of the DBS modified LDH, enhanced surface area, increased light absorption and effective charge separation were prepared by the calcination of the as-synthesized LDH at 650 degrees C. Structural, morphological, and photoelectrochemical properties of ZnCuCo and DBS-ZnCuCo LDHs and the corresponding MMOs (ZnCuCo MMO1 and ZnCuCo MMO2) were investigated. SEM and TEM images revealed that DBS-ZnCuCo LDH and ZnCuCo MMO2 possess 3D flower-like hierarchical morphologies with interlaced petal-like nanosheets. Although ZnCuCo LDH was inactive for photocatalytic H-2 production under visible light irradiation, ZnCuCo MMO2 exhibited a high H2 production rate (3700 mu mol g(-1) h(-1)), benefiting from the synergy of the ZnO, CuO, and Co3O4. Furthermore, 95% sulfamethazine (SMZ) degradation was obtained after 60 min of photocatalysis, which is considerably higher than the degradation efficiency of ZnCuCo LDH (24%) and ZnCuCo MMO1 (58%). Based on the photoelectrochemical tests, Z-scheme and double charge transfer mechanisms were proposed to explain the enhanced photocatalytic H-2 production and degradation of SMZ. Scavenging tests revealed that O-2(center dot-) radicals were the main reactive species in the photodegradation of SMZ. A possible degradation pathway was proposed based on the detection of intermediate products.Peer reviewe