Roll-to-Roll Manufacturing of Robust Superhydrophobic Coating on Metallic Engineering Materials

Creating a robust superhydrophobic surface on the conventional engineering materials at mass production is of great importance for self–cleaning, anti–icing, non–wetting surface and low flow resistance in industrial applications. Herein, we report a roll–to–roll strategy to create durable and robust superhydrophobic surfaces with designed micro–/nano– scale hierarchical structures on many conventional engineering materials by combining electrical discharge machining, coating of carbon nanoparticles, and followed by oil penetration and drying. The treated surface shows good superhydrophobic properties with static water contact angle of 170±2o and slide angle of 3±1o. The treated surface also exhibits good resilience and maintains the performance after tested in various harsh conditions including water flushing for several days, sand abrasion, scratching with sandpapers and corrosive solution. Significantly, the superhydrophobic surfaces also shows a high efficiency of self–cleaning properties even after oil–contamination during applications

Ternary NiCoTi-layered double hydroxide nanosheets as a pH-responsive nanoagent for photodynamic/chemodynamic synergistic therapy

Combining photodynamic therapy (PDT) with chemodynamic therapy (CDT) has been proven to be a promising strategy to improve the treatment efficiency of cancer, because of the synergistic therapeutic effect arising between the two modalities. Herein, we report an inorganic nanoagent based on ternary NiCoTi-layered double hydroxide (NiCoTi-LDH) nanosheets to realize highly efficient photodynamic/chemodynamic synergistic therapy. The NiCoTi-LDH nanosheets exhibit oxygen vacancy-promoted electron-hole separation and photogenerated hole-induced O2-independent reactive oxygen species (ROS) generation under acidic circumstances, realizing in situ pH-responsive PDT. Moreover, due to the effective conversion between Co^{3+} and Co^{2+} caused by photogenerated electrons, the NiCoTi-LDH nanosheets catalyze the release of hydroxyl radicals (∙OH) from H2O2 through Fenton reactions, resulting in CDT. Laser irradiation enhances the catalyzed ability of the NiCoTi-LDH nanosheets to promote the ROS generation, resulting in a better performance than TiO_{2} nanoparticles at pH 6.5. In vitro and in vivo experimental results show conclusively that NiCoTi-LDH nanosheets plus irradiation lead to efficient cell apoptosis and significant inhibition of tumor growth. This study reports a new pH-responsive inorganic nanoagent with oxygen vacancy-promoted photodynamic/chemodynamic synergistic performance, offering a potentially appealing clinical strategy for selective tumor elimination

Synthesis, assembly and applications of novel two-dimensional metal chalcogenide nanomaterials

The ability to prepare novel two-dimensional (2D) metal chalcogenide nanosheets and heteronanostructures or construct novel nanostructures via self-assembly by using 2D metal chalcogenides as basic building blocks is of great importance for the further exploration of their properties and varying potential applications. In the light of this, my aim in this thesis is to synthesize novel 2D metal chalcogenide nanosheets and heteronanostructures or assemble 2D metal chalcogenide nanosheets into new nanostructures and then explore their potential applications in fluorescent biosensors, dye-sensitized solar cells, Li-ion batteries and digital data storage devices. First, I prepared two solution-dispersed ultrathin 2D ternary metal chalcogenide nanosheets, i.e. Ta2NiS5 and Ta2NiSe5, in high-yield and large scale in liquid phase by exfoliating their layered bulk crystals via the electrochemical Li-intercalation and exfoliation method. The sizes of the Ta2NiS5 and Ta2NiS5 nanosheets are 0.05-2 μm. Significantly, the yield for the single-layer Ta2NiS5 nanosheet reached up to ca. 86%. The single-layer Ta2NiS5 nanosheet was used as a novel sensing platform to construct fluorescent biosensor for DNA detection. Second, I achieved the high-yield and scalable production of single-layer alloyed MoS2xSe2(1-x) and MoxW1-xS2 nanosheets with high concentration (~66%) of metallic 1T phase by exfoliation of their micro-sized 2H-phase layered bulk crystals using the electrochemical Li-intercalation and exfoliation method. The MoS2xSe2(1-x) nanosheet thin film casted on a fluorine-doped tin oxide (FTO) substrate by the drop-casting method was directly used as an efficient electrocatalyst for the tri-iodide reduction at counter electrode in a dye-sensitized solar cell without any post-treatments. A power conversion efficiency of 6.5% was achieved on the MoS2xSe2(1-x) nanosheet thin film electrode, which is higher than that of 2H-phase MoS2xSe2(1-x) (5.4%). Third, I prepared three kinds of 2D metal chalcogenide heteronanostructures in liquid phase by an electrochemical method by using metal foils and bulk TiS2 crystal as precursors, in which metal sulphide nanoplates, including CuS, ZnS and Ni3S2, were epitaxially grown on ultrathin TiS2 nanosheet. TEM analyses revealed that these metal sulphide nanoplates were aligned on the TiS2 with perfect epitaxial alignment effect to vertical 2D epitaxial heteronanostructures. Moreover, when used as the anode in a Li ion battery, the CuS-TiS2 heteronanostructure-based electrode exhibited good performance. Last, I developed a facile and universal approach for the high-yield and scalable preparation of chiral nanofibers by the self-assembly of various ultrathin 2D nanomaterials, including single-layer graphene oxide (GO), MoS2, TaS2, TiS2, few-layer TaSe2, WSe2 and Pt nanoparticle-decorated reduced graphene oxide (Pt-rGO) or MoS2 (Pt-MoS2), in vigorously stirred polymeric solutions. These chiral nanofibers can be further transformed into same-handed helical nanorings with a diameter of 400-800 nm via a second assembly process. Chiral MoS2 nanofiber with P123 was integrated into a resistive memory device as the active layer. Impressively, the fabricated memory device presented a non-volatile flash memory behavior with excellent reproducibility and good stability.DOCTOR OF PHILOSOPHY (MSE

Hybrid micro-/nano-structures derived from metal–organic frameworks: preparation and applications in energy storage and conversion

Metal–organic frameworks (MOFs), an important class of inorganic–organic hybrid crystals with intrinsic porous structures, can be used as versatile precursors or sacrificial templates for preparation of numerous functional nanomaterials for various applications. Recent developments of MOF-derived hybrid micro-/nano-structures, constructed by more than two components with varied functionalities, have revealed their extensive capabilities to overcome the weaknesses of the individual counterparts and thus give enhanced performance for energy storage and conversion. In this tutorial review, we summarize the recent advances in MOF-derived hybrid micro-/nano-structures. The synthetic strategies for preparing MOF-derived hybrid micro-/nano-structures are first introduced. Focusing on energy storage and conversion, we then discuss their potential applications in lithium-ion batteries, lithium–sulfur batteries, supercapacitors, lithium–oxygen batteries and fuel cells. Finally, we give our personal insights into the challenges and opportunities for the future research of MOF-derived hybrid micro-/nano-structures.MOE (Min. of Education, S’pore

25th anniversary article : hybrid nanostructures based on two-dimensional nanomaterials

Two-dimensional (2D) nanomaterials, such as graphene and transition metal dichalcogenides (TMDs), receive a lot of attention, because of their intriguing properties and wide applications in catalysis, energy-storage devices, electronics, optoelectronics, and so on. To further enhance the performance of their application, these 2D nanomaterials are hybridized with other functional nanostructures. In this review, the latest studies of 2D nanomaterial-based hybrid nanostructures are discussed, focusing on their preparation methods, properties, and applications

Non-volatile resistive memory devices based on solution-processed ultrathin two-dimensional nanomaterials

Ultrathin two-dimensional (2D) nanomaterials, such as graphene and MoS2, hold great promise for electronics and optoelectronics due to their distinctive physical and electronic properties. Recent progress in high-yield, massive production of ultrathin 2D nanomaterials via various solution-based methods allows them to be easily integrated into electronic devices via solution processing techniques. Non-volatile resistive memory devices based on ultrathin 2D nanomaterials have been emerging as promising alternatives for the next-generation data storage devices due to their high flexibility, three-dimensional-stacking capability, simple structure, transparency, easy fabrication and low cost. In this tutorial review, we will summarize the recent progress in the utilization of solution-processed ultrathin 2D nanomaterials for fabrication of non-volatile resistive memory devices. Moreover, we demonstrate how to achieve excellent device performance by engineering the active layers, electrodes and/or device structure of resistive memory devices. On the basis of current status, the discussion is concluded with some personal insights into the challenges and opportunities in future research directions.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Published versio