Comparative Study of Morphological and Molecular Characters Between Two Sponge Specimens (Porifera: Demosponge: Axinella) with Pharmacologically Active Compounds from the South China Sea

Abstract.-The Phylum Porifera is an economically important group of marine animals. Considerable research and development has been done for the purpose of discovery and sustainable supply of pharmaceutical products from sponges. Although an important resource for natural products,the taxonomic position of many sponges still lacks clarification. Two alkaloids debromohymenialdisine (DBH) and hymenialdisine (HD) with pharmacological activities have been isolated for treating Alzheimer disease from two common yellow sponges from the South China Sea. Although the external morphologies of these sponges are different, they were both classified into the genus Axinella on the basis of morphological characters such as skeleton architecture, spicules, and cell types. Molecular approaches of gene sequence analysis (Cytochrome C oxidase COI, 18S ribosomal RNA ,18S rRNA) demonstrate that both morphotypes are identical species

Modified photoanode based on zinc oxide nanorods for photoelectrochemical water splitting

Among the rich variety of photoelectrode materials, zinc oxide (ZnO) is one of the most promising candidates due to its high electrochemical stability, suitable conduction/valence band edges, high electron mobility and lower recombination of electrons and holes. However, the relatively low photocurrent density and low photocurrent-hydrogen conversion efficiency of ZnO largely limit its practical application in water splitting. This work aims to improve the photoelectrochemical (PEC) properties of ZnO-based photoelectrode from two aspects: substrate modification and ZnO functionalization. On substrate modification, two kinds of substrates had been modified. Firstly, ZnO nanorod arrays were prepared on a V-grooved silicon (Si) substrate and used as the photoanode of PEC cell. The light trapping and overall PEC cell performance were greatly enhanced. Secondly, ZnO nanorods grown on polyethylene terephthalate (PET) flexible substrate were used as the photoanode. The effects of plasmonic enhanced absorption, surface recombination inhibition and improved charge transport were investigated and further optimized by varying the silver (Ag) thickness and the curvature of the PET substrates. On functionalization ZnO nanorods, firstly, multi-walled carbon nanotubes (MWCNTs) were introduced to improve the PEC cell performance. Secondly, Ag nanoparticles were used to decorate ZnO nanorods with the assistance of polydopamine. Modified photoelectrode achieves excellent light harvesting and charge-carriers transportation. All designed modifications were potential strategies to realize the practical use of ZnO as photoelectrode material.Doctor of Philosophy (MAE

Silicon nanoparticles confined in thin carbon network : the free-standing anode of lithium ion batteries with high performance and easy recyclability

Si is a promising anode candidate of lithium ion batteries with exceptionally high theoretical capacity, however, has fatal issues including large volume expansion-induced instability and poor electrical conduction during the charging/discharging process. The stabilization of the Si anode through buffering its volume expansion meanwhile maintaining its structure/morphology integrity is currently the major strategy to overcome the issues. In this work, commercially available Si nanoparticles were confined within the network of thin graphitized carbon layer (from carbonized polydopamine, named as C-PDA) through a straightforward route, forming freestanding flexible and robust mat that can be used as anode directly. Excellent electrochemical performance, i.e., high cycled capacity (about 1750 mAh g−1 after 100 cycles at 100 mA g−1) and rate capacity (around 1600 ∼ 1700, 1200 ∼ 1300, 800 ∼ 900 and 600 ∼ 700 mAh g−1 at 200, 500, 1000 and 2000 mA g−1, respectively), was achieved after optimization due to the C-PDA thin layer that creates electron conduction pathway and the interconnected channels within the C-PDA network that offers free diffusion of electrolyte solution thus smooth transportation of Li ions. Unlike the common sense of accommodating/buffering the volume expansion of Si by carbon phase, the Si NPs collapse into smaller ones upon lithiation at the initial stage and are still trapped within the respective C-PDA frames. The C-PDA network acts as interlock to stabilize the collapsed Si, leading to good electrochemical properties. Recyclability of the used anode was also investigated in this work, implying that taking the advantage of its freestanding nature with no binder and conductive agent used, the used Si NPs with smaller size and maintained crystallinity can be easily recycled through simple solvent soaking after discharge/charge cycling. This work offers a unique and useful strategy of utilizing Si materials in an environment friendly and cost-effective way for energy storage application.Published versio

Influence of thermal treatment on electronic properties of inkjet-printed zinc oxide semiconductor

Additive manufacturing of electronic devices using inkjet printing provides a potential alternative approach in substitution for conventional electronic fabrication processes. However, the complex nature of inkjet printing involves the liquid deposition and film formation from the vaporization of solvent, which makes it different from film created by conventional deposition methods. Inkjet printing of zinc oxide (ZnO), which is a widely utilized semiconductor, produces polycrystalline film composed of nano-size grains, which could significantly influence the properties of printed film. In this study, low-temperature annealing was employed to treat inkjet-printed ZnO for UV photodetection application, and its influence on electrical properties was studied. Band bending was characterized using the Mott-Schottky plot which examines the charge distribution of the films. It is found that the annealing of inkjet-printed polycrystalline ZnO film has improved its electrical properties, which could be attributed to the reduction of band bending due to the merging of grains. The treatment also helps to reduce impurities of the film, such as zinc hydroxide complexes, which is common for solution-derived films. Hence, the study could pay the way for the improvement of electrical properties of inkjet-printed functional materials.Ministry of Education (MOE)Nanyang Technological UniversityPublished versionThis work was supported by Nanyang Technological University and the Ministry of Education of Singapore through a Ph.D. Scholarship and AcRF Tier 1 research grant (RG 96/18)

On-substrate joule effect heating by printed micro-heater for the preparation of ZnO semiconductor thin film

Fabrication of printed electronic devices along with other parts such as supporting structures is a major problem in modern additive fabrication. Solution-based inkjet printing of metal oxide semiconductor usually requires a heat treatment step to facilitate the formation of target material. The employment of external furnace introduces additional complexity in the fabrication scheme, which is supposed to be simplified by the additive manufacturing process. This work presents the fabrication and utilization of micro-heater on the same thermal resistive substrate with the printed precursor pattern to facilitate the formation of zinc oxide (ZnO) semiconductor. The ultraviolet (UV) photodetector fabricated by the proposed scheme was successfully demonstrated. The performance characterization of the printed devices shows that increasing input heating power can effectively improve the electrical properties owing to a better formation of ZnO. The proposed approach using the on-substrate heating element could be useful for the additive manufacturing of functional material by eliminating the necessity of external heating equipment, and it allows in-situ annealing for the printed semiconductor. Hence, the integration of the printed electronic device with printing processes of other materials could be made possible.Ministry of Education (MOE)Published versionThis research was funded by Ministry of Education Academic Research Fund, Singapore

Band bending modification of inkjet-printed ZnO thin film for additive manufacturing of electronic devices

Among different approaches for additive manufacturing of electronic devices, inkjet printing is a potential method because it is capable of fabricating multi-material devices with good resolution. Meanwhile, zinc oxide (ZnO) is a wide-bandgap semiconductor, and it is an interesting material for electronic, optoelectronic and gas sensing devices. Hence, inkjet printing of ZnO is an attractive approach for additive manufacturing of functional devices. Band bending, caused by the exchanging of electrons at the surface of the semiconductor, has a significant effect on the performance of semiconductor devices in general and ZnO-based devices in particular. In this work, we present the modification of band bending of inkjet-printed ZnO thin film using thermal annealing. The results show a potential approach to improve the performance of the printed electronic device.Published versio

Erosion of alloys used for the stages of electrical submersible pumps

Judicious selection of the material used for the stages of an electric submersible pump (ESP) is crucial for a prolonged service life. Working in high-velocity fluids carrying solid particles, the stage surfaces are subjected to solid particle impingement and thus erosion defects arise. Moreover, subsequent erosion-corrosion synergy brings additional threats to the ESPs operating in corrosive environments. In this report, jet impingement tests were conducted to evaluate the performance of three alloys under erosive and corrosive conditions. The tested materials include two Ni-Resist cast irons — wear-resistant materials commonly used for ESP stages — and one superduplex stainless steel (SDSS) that is famous for high strength and extraordinary corrosion resistance. The erosion rate of each material, along with its dependence on jet impingement angle, is quantified in terms of overall volume loss and localized depth loss. Tap water and salt solution are used as particle carrier in parallel to study the synergy between erosion and corrosion. The erosion mechanism of different phases, as well as its dependence on particle impingement conditions, are discussed. Finally, the applicability of substituting Ni-Resist cast irons with SDSS to cope with highly corrosive conditions is assessed based on the experiment results.Singapore Maritime Institute (SMI)This research is funded by the Singapore Maritime Institute under the Asset Integrity & Risk Management (AIM) R&D Programme Project SMI-2015-OF-03

Preparing of Interdigitated Microelectrode Arrays for AC Electrokinetic Devices Using Inkjet Printing of Silver Nanoparticles Ink

The surge in popularity of lab-on-chip applications has set a new challenge for the fabrication of prototyping devices, such as electrokinetic devices. In such devices, a micro-electrode is the key component. Currently, microelectromechanical systems (MEMS) processes such as lift-off and etching techniques are employed to prepare the micro-sized conductive patterns. These processes are time-consuming, require a material removal step, clean-room facilities, and the utilisation of harmful chemicals. On the other hand, rapid fabrication is required by researchers designing such devices to test their functionality. Additive manufacturing technology such as the inkjet printing of conductive material is one potential solution to achieve that objective. In this study, we report the utilisation of inkjet printing for the rapid prototyping of alternating current (AC) electrokinetic devices on a rigid glass substrate. The non-lithographical and vacuum-free process for the fabrication of a microfluidic device was demonstrated. The smallest feature size of 60 μm was successfully printed. The crystalline structure of the printed material under different curing temperatures was characterised. It was found that these treatment conditions affect electrical conductivity. Although a low-temperature sintering process was applied, low resistivity was obtained. An AC electrokinetics device for the manipulation of microparticles has been prepared to illustrate such printed silver micro-patterns. The results strongly support the idea that inkjet printing is a powerful and cost-effective prototyping tool for researchers who work with electrokinetic devices.ASTAR (Agency for Sci., Tech. and Research, S’pore)MOE (Min. of Education, S’pore)Published versio

Additive Manufacturing of ZnO Thin Film for Micro Size UV Photodetector

Due to its large bandgap (3.37eV), ZnO is a suitable candidate for sensing material of UV photodetectors with great selectivity to wavelength with high radiation energy. ZnO thin film has been deposited by many methods. However, ZnO thin film created by these techniques, which is compatible with MEMS process, requires the clean-room facilities and photolithography process to remove excessive part of material and form required patterns. In this work, we prepared a solution of Zinc acetate precursor with a simple recipe for additive manufacturing of ZnO thin film. We demonstrated the fully additive manufacturing of photodetector with fast response, less than 0.5 seconds, to UV illumination at a low bias voltage. The all-step additive manufacturing process introduces a highly cost-effective method for fabrication of UV photodetectors. The as-prepared solution may be used for inkjet printing of devices.Published versio