Tribological Properties of MoS2 on Semiconducting and Metallic Surfaces

It is of great interest to seek lubrications for friction minimization in order to save energy and thus reduce cost. Two dimensional MoS₂ exhibits promising friction reduction and anti-wear properties. Moreover, the use of single layer MoS₂ (SLM) in nano-devices receives significant research interest because it has remarkable electronic and optical properties compared to bulk MoS₂. Therefore, it is important to investigate the tribological behavior of SLM under various conditions. My study is divided into three projects. The first project investigated the mechanical and tribological behavior of MoS₂ nanoflakes on nanoscopically rough substrates. Single- and multi- layer MoS₂ nanoflakes were prepared on SiO₂ nanoparticle films, followed by Atomic Force Microscopy (AFM) characterization to reveal their conformity on nanoparticle films and tribological properties. The second project aimed at studying the adhesion and friction between MoS₂ and selected molecules. In this study, silicon tips were modified with two kinds of silane molecules terminated with - NH₂ and -SH groups. Modified AFM probes were utilized to obtain the friction and adhesion on single layer and bulk MoS₂. In the third project, tribological properties of MoS₂ are tuned by modifying its surface. Radical reactions between 4- nitrobenzenediazonium tetrafluoroborate (4-NBD) and MoS₂ in aqueous solution have been previously investigated as a means for facile modification, but a detailed study has yet to be carried out to reveal the nature of its chemical reactivity with MoS₂ on Au(111) substrates in terms of layer thicknesses. Here, the chemical and wear properties of single and multilayer (bulk) MoS₂ on Au(111) substrates were investigated with AFM before and after being functionalized with 4-NBD in aqueous solution. The study of the mechanical and tribological properties of MoS₂ on different substrates provides insightful perspective of using 2D material boundary lubricants under different conditions. In addition, tribological, chemical and optical properties of MoS₂ can be further tuned by manipulating its surface via chemical surface modification

Tribological Properties of MoS2 on Semiconducting and Metallic Surfaces

It is of great interest to seek lubrications for friction minimization in order to save energy and thus reduce cost. Two dimensional MoS₂ exhibits promising friction reduction and anti-wear properties. Moreover, the use of single layer MoS₂ (SLM) in nano-devices receives significant research interest because it has remarkable electronic and optical properties compared to bulk MoS₂. Therefore, it is important to investigate the tribological behavior of SLM under various conditions. My study is divided into three projects. The first project investigated the mechanical and tribological behavior of MoS₂ nanoflakes on nanoscopically rough substrates. Single- and multi- layer MoS₂ nanoflakes were prepared on SiO₂ nanoparticle films, followed by Atomic Force Microscopy (AFM) characterization to reveal their conformity on nanoparticle films and tribological properties. The second project aimed at studying the adhesion and friction between MoS₂ and selected molecules. In this study, silicon tips were modified with two kinds of silane molecules terminated with - NH₂ and -SH groups. Modified AFM probes were utilized to obtain the friction and adhesion on single layer and bulk MoS₂. In the third project, tribological properties of MoS₂ are tuned by modifying its surface. Radical reactions between 4- nitrobenzenediazonium tetrafluoroborate (4-NBD) and MoS₂ in aqueous solution have been previously investigated as a means for facile modification, but a detailed study has yet to be carried out to reveal the nature of its chemical reactivity with MoS₂ on Au(111) substrates in terms of layer thicknesses. Here, the chemical and wear properties of single and multilayer (bulk) MoS₂ on Au(111) substrates were investigated with AFM before and after being functionalized with 4-NBD in aqueous solution. The study of the mechanical and tribological properties of MoS₂ on different substrates provides insightful perspective of using 2D material boundary lubricants under different conditions. In addition, tribological, chemical and optical properties of MoS₂ can be further tuned by manipulating its surface via chemical surface modification

Further insight into systemic sclerosis from the vasculopathy perspective

Systemic sclerosis (SSc) is an autoimmune disease characterized by immune dysfunction, vascular system dysfunction, and tissue fibrosis. Vascular injury, vascular remodeling, and endothelial dysfunction are the hallmark pathological changes of the disease. In the early stages of SSc development, endothelial cell injury and apoptosis can lead to vascular and perivascular inflammation, oxidative stress, and tissue hypoxia, which can cause clinical manifestations in various organs from the skin to the parenchymal organs. Early diagnosis and rational treatment can improve patient survival and quality of life. Ancillary examinations such as nailfold capillaroscopy as well as optical coherence tomography can help early detect vascular injury in SSc patients. Studies targeting the mechanisms of vascular lesions will provide new perspectives for treatment of SSc

Efficient Removal of Methyl Orange and Alizarin Red S from pH-Unregulated Aqueous Solution by the Catechol–Amine Resin Composite Using Hydrocellulose as Precursor

We report a novel composite absorbent prepared by the simple method that catechol-amine resin coats the hydrocellulose based on the adhesion property like polydopamine. The composite which contains many chelating groups on its surface was characterized by scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), etc. The obtained adsorbents were investigated to remove Methyl Orange (MO) and Alizarin Red S (AR) from pH-unregulated aqueous system by batch experiments, including the affected factors of adsorbent dosage, contact time, initial concentration, and temperature. Results showed the adsorption processes belonged to the chemisorption and exhibited a spontaneous and endothermic nature. Besides, the removal performances fitted with the Langmuir isotherm model and pseudo-second order kinetic model very well. The maximum adsorption amounts of MO and AR were 189.39 and 284.09 mg/g at 303 K, respectively. The difference about adsorption amounts may be caused by the strong effect of π–π conjugation and hydrogen bonding between adsorbent and AR. Furthermore, the adsorption processes exhibited a spontaneous and endothermic nature. The recycling test indicated that the adsorbent stayed stable for the removal of both dyes by desorbed three times. Accordingly, the adsorbent with high adsorption capacity and rapid removal rate should be a promising material for the removal of anionic dyes from sewage

Mapping Catalytically Relevant Edge Electronic States of MoS2.

Molybdenum disulfide (MoS2) is a semiconducting transition metal dichalcogenide that is known to be a catalyst for both the hydrogen evolution reaction (HER) as well as for hydro-desulfurization (HDS) of sulfur-rich hydrocarbon fuels. Specifically, the edges of MoS2 nanostructures are known to be far more catalytically active as compared to unmodified basal planes. However, in the absence of the precise details of the geometric and electronic structure of the active catalytic sites, a rational means of modulating edge reactivity remain to be developed. Here we demonstrate using first-principles calculations, X-ray absorption spectroscopy, as well as scanning transmission X-ray microscopy (STXM) imaging that edge corrugations yield distinctive spectroscopic signatures corresponding to increased localization of hybrid Mo 4d states. Independent spectroscopic signatures of such edge states are identified at both the S L2,3 and S K-edges with distinctive spatial localization of such states observed in S L2,3-edge STXM imaging. The presence of such low-energy hybrid states at the edge of the conduction band is seen to correlate with substantially enhanced electrocatalytic activity in terms of a lower Tafel slope and higher exchange current density. These results elucidate the nature of the edge electronic structure and provide a clear framework for its rational manipulation to enhance catalytic activity

Structure and dynamics of urban freight truck movements: A complex network theory perspective

Knowledge of the core structure and inherent dynamics of urban freight transport systems is important for the development of policies, aimed at improving the livability and sustainability of cities. The past decade has witnessed a great deal of efforts into analyzing the geographic structure of urban freight transport systems. However, in-depth studies on the system core structure and underlying dynamics are still absent. This study contributes to the field by analyzing large scale freight truck trip data from Chinese cities, using complex network analysis. We empirically reconstruct and characterize the urban freight truck mobility networks and reveal the underlying spatial interaction patterns. We develop a spatial network growth model which explains how hub-and-spoke core structure of urban freight transport systems are formed. The developed model captures the essential interaction dynamics of freight locations, and explains the effects of spatial distance, economic size and business pattern replication. Inspired by the model, we provide policy implications for land-use planning, transportation planning and sustainable urban development.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport and Plannin

Removal and Recovery of Zn²⁺ and Pb²⁺ by Imine-Functionalized Magnetic Nanoparticles with Tunable Selectivity

This research investigated the adsorption of zinc and lead from binary metal solution with tunable selectivity. A nano adsorbent was prepared by introducing imine groups onto the surface of stability enhanced magnetic nanoparticles and then characterized by TEM and FTIR. Binary metal components adsorption was carried out in different concentration of metal and EDTA solution. Due to the interaction between metals and adsorbent in the presence of EDTA, the selective adsorption of zinc and lead could be achieved with 100% selectivity. To only remove zinc from binary metals, the solution condition was [EDTA]/[M²⁺] = 0.7 with pH of 6, and its saturated adsorption capacity was 1.25 mmol/g. For selective adsorption of lead, an equilibrium adsorption capacity of 0.81 mmol/g was obtained under the condition of [EDTA]/[M²⁺] = 0.7 and pH of 2. The exhausted adsorbent could be regenerated by simple acid or alkali wash, and high purity lead and zinc salt solutions were recovered and concentrated

Mapping Catalytically Relevant Edge Electronic States of MoS₂

Molybdenum disulfide (MoS₂) is a semiconducting transition metal dichalcogenide that is known to be a catalyst for both the hydrogen evolution reaction (HER) as well as for hydro-desulfurization (HDS) of sulfur-rich hydrocarbon fuels. Specifically, the edges of MoS₂ nanostructures are known to be far more catalytically active as compared to unmodified basal planes. However, in the absence of the precise details of the geometric and electronic structure of the active catalytic sites, a rational means of modulating edge reactivity remain to be developed. Here we demonstrate using first-principles calculations, X-ray absorption spectroscopy, as well as scanning transmission X-ray microscopy (STXM) imaging that edge corrugations yield distinctive spectroscopic signatures corresponding to increased localization of hybrid Mo 4d states. Independent spectroscopic signatures of such edge states are identified at both the S L_2,3 and S K-edges with distinctive spatial localization of such states observed in S L_2,3-edge STXM imaging. The presence of such low-energy hybrid states at the edge of the conduction band is seen to correlate with substantially enhanced electrocatalytic activity in terms of a lower Tafel slope and higher exchange current density. These results elucidate the nature of the edge electronic structure and provide a clear framework for its rational manipulation to enhance catalytic activity