Preparation of carbon nanomaterials and their application in water purification

Water contamination is a severe problem faced by the whole world. With the rapid growth in global population, this problem is even worsening. Fullerene and TiO2 are promising photocatalysts for water purification owing to their intrinsically high photocatalytic activity. Yet, a lot of weaknesses (e.g. large bandgap of TiO2, hydrophobicity of fullerene, etc.) unfortunately inhibit them from fulfilling their potential in water purification. In this thesis, different strategies were designed to synthesize and functionalize various carbon nanomaterials. Afterwards, these specifically designed and prepared carbon nanomaterials were employed to overcome the intrinsic weaknesses of both fullerene and TiO2. Great improvement in photodynamic performance was witnessed in both photocatalysts. Their potential in water purification was hence proved. Firstly, C60 was functionalized with pyrene moieties via Prato Reaction. The as-prepared C60 derivatives exhibited clearly improved absorption in visible range. The apparent photodynamic activity of these C60 derivatives in both organic and aqueous solutions suggested their potential application in water purification. Secondly, an eco-friendly way to harvest multi-layer graphene with low defect density and low oxidation degree was established. Moreover, a modified Hummers Method for controllably oxidizing graphene towards different oxidation degree was developed. The combination of these two designs enabled the finding of the graphene material with the optimal oxidation degree, which not only can boost the synergistic effect between the substrate and the photocatalyst in composites, but also can maintain original properties of the graphene material to the greatest degree. Subsequently, a facile method for producing Fullerene/Graphene and Fullerene/Graphene Oxide composites was established. The strong interaction within composites between fullerene and graphene substrates was identified by Raman. The great improvement in fullerene’s photocatalytic activity in these composites was witnessed in photodynamic test. Fullerene’s excellent photodynamic performance, which was much better than that of commercial anatase TiO2, further confirmed its application potential in water purification. Finally, different composites between graphene materials and anatase TiO2 were prepared by three strategies. Photocatalysts with enhanced photocatalytic activity were successfully synthesized and several important factors which control the final photodynamic performance of materials were identified. Overall, good progress was made in both the material preparation and the understanding of different underlying factors limiting the photodynamic performance of photocatalysts. This work brings the application of fullerenes and TiO2 for water purification, one step closer

Polarity-induced oxygen vacancies at LaAlO3|SrTiO3 interfaces

Using first-principles density functional theory calculations, we find a strong position and thickness dependence of the formation energy of oxygen vacancies in LaAlO3|SrTiO3 (LAO|STO) multilayers and interpret this with an analytical capacitor model. Oxygen vacancies are preferentially formed at p-type SrO|AlO2 rather than at n-type LaO|TiO2 interfaces; the excess electrons introduced by the oxygen vacancies reduce their energy by moving to the n-type interface. This asymmetric behavior makes an important contribution to the conducting (insulating) nature of n-type (p-type) interfaces while providing a natural explanation for the failure to detect evidence for the polar catastrophe in the form of core level shifts

Noncollinearity-modulated electronic properties of the monolayer CrI3_3

Introducing noncollinear magnetization into a monolayer CrI$_3$ is proposed to be an effective approach to modulate the local electronic properties of the two-dimensional (2D) magnetic material. Using first-principles calculation, we illustrate that both the conduction and valence bands in the monolayer CrI$_3$ are lowered down by spin spiral states. The distinct electronic structure of the monolayer noncollinear CrI$_3$ can be applied in nanoscale functional devices. As a proof of concept, we show that a magnetic domain wall can form a one-dimensional conducting channel in the 2D semiconductor via proper gating. Other possible applications such as electron-hole separation and identical quantum dots are also discussed

JDsearch: A Personalized Product Search Dataset with Real Queries and Full Interactions

Recently, personalized product search attracts great attention and many models have been proposed. To evaluate the effectiveness of these models, previous studies mainly utilize the simulated Amazon recommendation dataset, which contains automatically generated queries and excludes cold users and tail products. We argue that evaluating with such a dataset may yield unreliable results and conclusions, and deviate from real user satisfaction. To overcome these problems, in this paper, we release a personalized product search dataset comprised of real user queries and diverse user-product interaction types (clicking, adding to cart, following, and purchasing) collected from JD.com, a popular Chinese online shopping platform. More specifically, we sample about 170,000 active users on a specific date, then record all their interacted products and issued queries in one year, without removing any tail users and products. This finally results in roughly 12,000,000 products, 9,400,000 real searches, and 26,000,000 user-product interactions. We study the characteristics of this dataset from various perspectives and evaluate representative personalization models to verify its feasibility. The dataset can be publicly accessed at Github: https://github.com/rucliujn/JDsearch.Comment: Accepted to SIGIR 202

Balanced Coarsening for Multilevel Hypergraph Partitioning via Wasserstein Discrepancy

We propose a balanced coarsening scheme for multilevel hypergraph partitioning. In addition, an initial partitioning algorithm is designed to improve the quality of k-way hypergraph partitioning. By assigning vertex weights through the LPT algorithm, we generate a prior hypergraph under a relaxed balance constraint. With the prior hypergraph, we have defined the Wasserstein discrepancy to coordinate the optimal transport of coarsening process. And the optimal transport matrix is solved by Sinkhorn algorithm. Our coarsening scheme fully takes into account the minimization of connectivity metric (objective function). For the initial partitioning stage, we define a normalized cut function induced by Fiedler vector, which is theoretically proved to be a concave function. Thereby, a three-point algorithm is designed to find the best cut under the balance constraint