Preparation of novel special wettable materials for water remediation

Materials with special wettability have attracted tremendous research attention in recent decades in many fields of applications, such as energy storage and conversion, medicine and healthcare, nanoparticle synthesis and environment remediation. Particularly, the special wettable material has been regarded as one of the most promising materials for water remediation and purification, due to its controllable affinity towards water and various water contaminants. Thanks to the extensive research effort, significant progress has been achieved in the fundamental understanding of the surface wetting phenomenon, the synthesis of special wettable materials, and the potential applications in various fields. The practical implementation of such materials requires the development of novel materials from low-cost precursors through sustainable preparation methods, which unfortunately has not been sufficiently explored and researched. In this thesis, I will present my research works on two novel low-cost and sustainable special wettable materials, and demonstrate their promising application in oily water remediation. The mainly adopted material development strategy is to convert waste materials into functional special wettable materials. In the first project, a novel hydrophobic and oleophilic carbon aerogel is developed using waste pomelo peels as raw materials. The resulted carbon aerogels possess a three-dimensional interconnected porous structure with light density. The carbon aerogels are used as absorbents to selectively absorb water-immiscible oils and organics from oil/water mixtures. The low-cost and sustainable preparation approach and the high oil absorption capacity make the carbon aerogel a promising material for cleaning up oil spills. In the second project, a novel inorganic superhydrophilic and underwater superoleophobic mesh is developed using waste soda-lime glass as starting material. Due to the high surface tension and surface roughness, the resulted mesh shows high affinity toward water in air, and extremely low affinity toward oils under water. Therefore, it can selectively and continuously separate oil/water mixtures through filtration by allowing water permeation while blocking oils. In addition, the as-developed inorganic mesh shows the excellent stability against various harsh environments and the multifunctional water remediation characteristics, making it highly promising for practical water remediation applications.Doctor of Philosophy (IGS

Atmospheric Water Harvesting with Metal-Organic Frameworks and Their Composites: From Materials to Devices

Clean water scarcity is deteriorating because of the growing population and water pollution. New methods to harvest freshwater from non-traditional water sources are urgently required to address this global issue. The atmosphere contains abundant water resources. Harvesting fresh water from the air has become an emerging and attractive approach, among which sorption-based atmospheric water harvesting (AWH) is the most promising method, as it demonstrates high water producibility, wide applicability and low energy consumption. Metal-organic frameworks (MOF) are a class of emerging porous materials characterized by their large specific surface area, adjustable pore structures and chemistry. Recently, hydrolytically stable MOFs have been used as sorbents in AWH, and several MOF-based prototyping devices have been demonstrated with great practical potential. In this review, we briefly summarize the recent progress on the MOFs and their derived composites as AWH sorbents. Then, we introduce several most representative devices using MOFs for practical applications. Finally, the challenges and perspectives of this emerging field are discussed

Novel structured transition metal dichalcogenide nanosheets

Ultrathin two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their unique properties and great potential in a wide range of applications. Great efforts have been devoted to the preparation of novel-structured TMD nanosheets by engineering their intrinsic structures at the atomic scale. Until now, a lot of new-structured TMD nanosheets, such as vacancy-containing TMDs, heteroatom-doped TMDs, TMD alloys, 1T'/1T phase and in-plane TMD crystal-phase heterostructures, TMD heterostructures and Janus TMD nanosheets, have been prepared. These materials exhibit unique properties and hold great promise in various applications, including electronics/optoelectronics, thermoelectrics, catalysis, energy storage and conversion and biomedicine. This review focuses on the most recent important discoveries in the preparation, characterization and application of these new-structured ultrathin 2D layered TMDs.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore

Two-Dimensional Metal-Organic Framework Nanosheets

Two-dimensional (2D) metal–organic framework (MOF) nanosheets are attracting increasing research interest due to their unique properties originating from their ultrathin thickness and large surface area with highly accessible active sites. Here, the aim is to provide recent advances in the synthesis of 2D MOF nanosheets by using the top-down and bottom-up methods, including sonication exfoliation, interfacial synthesis, three-layer synthesis, and surfactant-assisted synthesis methods. In addition, the recent progress in 2D-MOF-nanosheet-based nanocomposites is also introduced. The synthesis of 2D MOF nanosheets should lead to new kinds of functional nanomaterials for a wide range of applications.MOE (Min. of Education, S’pore

Social Bots Detection via Fusing BERT and Graph Convolutional Networks

The online social media ecosystem is becoming more and more confused because of more and more fake information and the social media of malicious users’ fake content; at the same time, unspeakable pain has been brought to mankind. Social robot detection uses supervised classification based on artificial feature extraction. However, user privacy is also involved in using these methods, and the hidden feature information is also ignored, such as semi-supervised algorithms with low utilization rates and graph features. In this work, we symmetrically combine BERT and GCN (Graph Convolutional Network, GCN) and propose a novel model that combines large scale pretraining and transductive learning for social robot detection, BGSRD. BGSRD constructs a heterogeneous graph over the dataset and represents Twitter as nodes using BERT representations. Corpus learning via text graph convolution network is a single text graph, which is mainly built for corpus-based on word co-occurrence and document word relationship. BERT and GCN modules can be jointly trained in BGSRD to achieve the best of merit, training data and unlabeled test data can spread label influence through graph convolution and can be carried out in the large-scale pre-training of massive raw data and the transduction learning of joint learning representation. The experiment shows that a better performance can also be achieved by BGSRD on a wide range of social robot detection datasets

An energy-efficient method for mitigating membrane fouling : a novel embodiment of the inverse fluidized bed

A novel inverse fluidized bed (IFB) was developed to improve membrane fouling mitigation vis-à-vis the conventional aeration method. The fluidized media, whose density was less than water and oleophilic, were more effective than bubbles for both feeds containing oil and particulates due to their greater inertia. The key highlights are (i) for all the conditions investigated, IFB consistently gave a lower trans-membrane pressure (TMP) than aeration at the same energy requirement; (ii) IFB performed better even when the energy input was reduced by 87.5%; (iii) IFB provided an impressive enhancement of up to 54 times that of dead-end filtration.MOE (Min. of Education, S’pore)EDB (Economic Devt. Board, S’pore

Carbon-based sorbents with three-dimensional architectures for water remediation

Over the past decade, carbon-based 3D architectures have received increasing attention in science and technology due to their fascinating properties, such as a large surface area, macroscopic bulky shape, and interconnected porous structures, enabling them to be one of the most promising materials for water remediation. This review summarizes the recent development in design, preparation, and applications of carbon-based 3D architectures derived from carbon nanotubes, graphene, biomass, or synthetic polymers for water treatment. After a brief introduction of these materials and their synthetic strategies, their applications in water treatment, such as the removal of oils/organics, ions, and dyes, are summarized. Finally, future perspective directions for this promising field are also discussed

Two-dimensional NiCo2O4 nanosheet-coated three-dimensional graphene networks for high-rate, long-cycle-life supercapacitors

We report the synthesis of two-dimensional (2D) NiCo2O4 nanosheet-coated three-dimensional graphene network (3DGN), which is then used as an electrode for high-rate, long-cycle-life supercapacitors. Using the 3DGN and nanoporous nanosheets, an ultrahigh specific capacitance (2173 F g-1 at 6 A g-1), excellent rate capability (954 F g-1 at 200 A g-1) and superior long-term cycling performance (94% capacitance retention after 14000 cycles at 100 A g-1) are achieved

Wet-chemical synthesis and applications of semiconductor nanomaterial-based epitaxial heterostructures

Semiconductor nanomaterial-based epitaxial heterostructures with precisely controlled compositions and morphologies are of great importance for various applications in optoelectronics, thermoelectrics, and catalysis. Until now, various kinds of epitaxial heterostructures have been constructed. In this minireview, we will first introduce the synthesis of semiconductor nanomaterial-based epitaxial heterostructures by wet-chemical methods. Various architectures based on different kinds of seeds or templates are illustrated, and their growth mechanisms are discussed in detail. Then, the applications of epitaxial heterostructures in optoelectronics, catalysis, and thermoelectrics are described. Finally, we provide some challenges and personal perspectives for the future research directions of semiconductor nanomaterial-based epitaxial heterostructures.Ministry of Education (MOE)Published versionThis work was supported by MOE under AcRF Tier 2 (ARC 19/15, No. MOE2014-T2-2-093; MOE2015T2-2-057; MOE2016-T2-2-103; MOE2017-T2-1-162) and AcRF Tier 1 (2016-T1-001-147; 2016-T1-002-051; 2017-T1001-150; 2017-T1-002-119) and NTU under Start-Up Grant (M4081296.070.500000) in Singapore. We would like to acknowl‑ edge the Facility for Analysis, Characterization, Testing and Simu‑ lation, Nanyang Technological University, Singapore, for use of their electron microscopy (and/or X-ray) facilities. Hua Zhang thanks the support from ITC via Hong Kong Branch of National Precious Metals Material Engineering Research Center, and the Start-Up Grant from City University of Hong Kong