Xiaoyang Shi

Columbia University | CU · Earth and Environmental Sciences Ph.D. Program

The distributed consensus mechanism is the backbone of the rapidly developing blockchain network. Blockchain platforms consume vast amounts of electricity based on the current consensus mechanism of Proof-of-Work (PoW). Here, we point out a different consensus mechanism named Proof-of-Stake (PoS) that can eliminate the extensive energy consumption...

The distributed consensus mechanism is the backbone of the rapidly developing blockchain network. Blockchain platforms consume vast amounts of electricity based on the current consensus mechanism of Proof of Work. Here, we point out an advanced consensus mechanism named Proof of Stake that can eliminate the extensive energy consumption of the curre...

Hydration of ions/molecules in nanometer-sized clusters or nanoscopic pores is ubiquitous and plays a key role in many chemical and physical systems. In this work, guanidine-H2O reactions with n = 1-8 water molecules were systematically studied by ab initio methods. The result suggests that the reduced availability of water molecules greatly inhibi...

Global warming effect caused by excessive emission of greenhouse gases, such as CO2 from modern industries, are emerging as serious environmental problem nowadays. Many strategies have been developed to address this issue, including solar energy utilization, green plants cultivation and coal desulfurization. These existing strategies always need so...

Purification/separation of CO2 stream from carbon capture or other carbon source is highly energy consuming process. However, oxidative impurity of O2 either deactivates catalysts in most carbon reduction systems, and thus reduces CO2 conversion efficiency. Here we report an effective method for splitting O2-containing CO2 into CO, through a chemic...

The moisture-swing sorbent of amine-based anion exchange resins is one of the most promising materials for direct carbon capture from ambient air to alleviate excessive emissions of CO2. In this study, how physical and chemical properties of the amine-based anion exchange resins affect their carbon capture performances is studied systematically, th...

An energy-saving system containing ion-exchange or nanoporous materials and carbonate ions is proposed, which is capable of capturing CO 2 from ambient air simply by controlling the amount of water (moisture) in contact with the sorbent. The system binds CO 2 from the air when the surrounding is dry, whereas it desorbs CO 2 when it is wet. A design...

Ion hydration is well known as a fundamental process in many natural phenomena. To capture CO2 efficiently, this study explores a novel “moisture-driven CO2 sorbent” based on diffusion of ions and the structure of ion hydration complexes forming inside water-laden resin structures. We present a quantitative analysis, with atomistic modeling, to inv...

Ion exchange membrane (IEM) loaded with CO_3^(2-) ions was developed for reversible SO2 removal by humidity-swing based on the hydrolysis of CO_3^(2-) and SO_3^(2-) ions. The dry environment promotes the hydrolysis of CO_3^(2-) in IEM to generate OH^- which binds SO2 to form HSO_3^-, and HCO_3^- that reacts with SO2 to form HSO_3^- and CO2. The abs...

The urgency to address global climate change induced by greenhouse gas emissions is growing. In particular, the rise in atmospheric CO2 levels is generating alarm. Technologies to remove CO2 from ambient air, or “direct air capture” (DAC), have recently demonstrated that they can contribute to “negative carbon emission.” Recent advances in surface...

The urgency to address global climate change induced by greenhouse gas emissions is growing. In particular, the rise in atmospheric CO2 levels is generating alarm. Technologies to remove CO2 from ambient air, or “direct air capture” (DAC), have recently demonstrated that they can contribute to “negative carbon emission.” Recent advances in surface...

We propose a novel approach to synthesize graphene sheets with fine quality by calcinating the composites intercalated with montmorillonite (MMT) and asphaltene. The graphene sample thus fabricated could reach 10.79 μ m long, with smooth and continuous morphology and with little defects. By analyzing the XRD patterns of graphene/MMT composites at d...

Reversible CO2 capture from ambient air by humidity swing has shown great potential in mitigating the greenhouse effect. In this work, we developed a new humidity-swing absorbent based on PO_4^(3-)/HPO_4^(2-)/H_2 PO_4^- ions exhibiting superior CO2 absorption capacity and kinetics compared to that of CO_3^(2-)/ HCO_3^--based absorbent. After ion ex...

A rigorous dynamic adsorption model, considering the realistic diffusion-reaction processes of CO2 adsorption onto the amine functionalized mesoporous silica, was proposed in this work. Three fundamental adsorption steps at different length scales were took into account in model development and a numerical algorithm was developed to solve the coupl...

Pimple is one of the most common skin diseases for humans, whose growth cause pain yet the corresponding mechanical analysis is lacking. A finite element model is developed to quantify the deformation field with the expansion of follicle, and then the mechanical stimulus is related to the sensation of pain during the development of pimple. Parametr...

There is a rich diversity of surface topologies controllably engineered by patterning cavities embedded beneath the surface of soft materials. Upon external compression, the surface undergoes the reversible transformation from the flat surface to various surface topographies, including a periodic checkerboard pattern with alternate convex and conca...

A new 2D crystal, P2S3, is found based on extensive evolutionary algorithm driven structural search. Furthermore, P2S3 is confirmed to be stable by the computed phonon spectrum and ab initio molecular dynamics simulations. This 2D crystalline phase of P2S3 corresponds to the global minimum in the Born-Oppenheimer surface of the phosphorus sulfide m...

The mechanical behaviors for a series of two-dimensional (2-D) crystals X3M2 (X=S, Se; M=N, P, As) are explored through density functional theory (DFT) calculations. Two atomic structures exist for X3M2, namely α-heart and β-heart, which exhibit different out-of-plane Negative Poisson’s Ratio (NPR) phenomena. For α-heart structure, general out-of-p...

Wrinkle formation followed by sharp strain localization is commonly observed in compressed stiff film/soft substrate systems. However, cavities or defects beneath the film may directly trigger the formation of local ridges and then folding configurations at a relatively small compressive strain, and a mixture of wrinkles and folds upon further comp...

Ion hydration is a fundamental process in many natural phenomena. This paper presents a quantitative analysis, based on atomistic modeling, of the behavior of ions and the impact of hydration in a novel CO2 sorbent. We explore moisture-driven CO2 sorbents focusing on diffusion of ions and the structure of ion hydration complexes forming inside wate...

Thermal energy storage capacity of working fluid can be enhanced by using energy conversion of adsorption/desorption process of working fluid in nanoporous materials. Molecular simulation including molecular dynamics and grand canonical Monte Carlo are employed to investigate the energy storage of CO2/IRMOF-1 (isoreticular metal organic framework)...

The phase transition of monolayer black phosphorene (MBP, α-P) to β-P and γ-P are explored by density functional theory (DFT) calculations and molecular dynamics (MD) simulations using reactive force field. It is found that MBP can transfer to a mixed phase of β-P and γ-P under biaxial strain, while the Stone–Wales defect (SW-2) in MBP can serve as...

Developing inexpensive and high efficient CO2 air capture technologies is an important solution for solving the greenhouse problem. In this work, we used the low cost quaternized chitosan (QCS)/poly (vinyl alcohol) (PVA) hybrid aerogels with quaternary ammonium groups and hydroxide ions to reversibly capture CO2 from ambient air by humidity swing....

Two-dimensional materials have attracted tremendous attention for their fascinating electronic, optical, chemical, and mechanical properties. However, the band gaps of most reported two-dimensional (2D) materials are smaller than 2.0 eV, which has greatly restricted their optoelectronic applications in the blue and ultraviolet range of the spectrum...

A new phosphorous allotrope, closed-edged bilayer phosphorene nanoribbon, is proposed via radially deforming armchair phosphorene nanotubes. Using molecular dynamics simulations, the transformation pathway from round phosphorene nanotubes falls into two types of collapsed structures: arc-like and sigmoidal bilayer nanoribbons, dependent on the numb...

The hydration of ions in nanoscale hydrated clusters is ubiquitous and essential in many physical and chemical processes. Here we show that the hydrolysis reaction is strongly affected by relative humidity. The hydrolysis of CO32- with n = 1-8 water molecules is investigated by ab initio method. For n = 1-5 water molecules, all the reactants follow...

To reveal the mechanism of energy storage in the water/graphene system and water/grapheme-oxide system, the processes of rapid evaporation of water molecules on the sheets of graphene and graphene-oxide are investigated by molecular dynamics simulations. The results show that both the water/graphene and water/grapheme-oxide systems can store more e...

A polymeric ionic liquid (PIL), with quaternary ammonium ions attached to the polymer matrix, displays CO2 affinity controlled by moisture. This finding led to the development of moisture swing absorption (MSA) for direct air capture (DAC) of CO2. This work aims to elucidate the role of water in MSA. For some humidity range, CO2 absorption is an en...

We developed ReaxFF parameters for phosphorus and hydrogen to give a good description of the chemical and mechanical properties of pristine and defected black phosphorene. ReaxFF for P/H is transferable to a wide range of phosphorus and hydrogen containing systems including bulk black phosphorus, blue phosphorene, edge-hydrogenated phosphorene, pho...

This study reports a preparation method of a new moisture swing sorbent for CO2 capture from air. The new sorbent components include ion exchange resin (IER) and polyvinyl chloride (PVC) as a binder. The IER can absorb CO2 when surrounding is dry and release CO2 when surrounding is wet. The manuscript presents the studies of membrane structure, kin...

Half time and absorption capacity of CO2 absorbent. (DOCX)

The self-assembly mechanism of one-end-open carbon nanotubes (CNTs) suspended in an aqueous solution was studied by molecular dynamics simulations. It was shown that two one-end-open CNTs with different diameters can coaxially self-assemble into a nanocapsule. The nanocapsules formed were stable in aqueous solution under ambient conditions, and the...

A novel bilayer is introduced, consisting of a stiff film adhered to a soft substrate with patterned holes beneath the film and substrate interface. To uncover the transition of surface patterns, two dimensional plane strain simulations are performed on the defected bilayer subjected to uniaxial compression. Although the substrate is considered as...

Pimple is one of the most common skin diseases for humans. The mechanical modeling of pimple growth is very limited. A finite element model is developed to quantify the deformation field with the expansion of follicle, and then the mechanical stimulus is related to the sensation of pain during the development of pimple. Through these models, parame...

Based on extensive evolutionary algorithm driven structural search, we propose a new diphosphorus trisulfide (P2S3) 2D crystal, which is dynamically, thermally and chemically stable as confirmed by the computed phonon spectrum and ab initio molecular dynamics simulations. This 2D crystalline phase of P2S3 corresponds to the global minimum in the Bo...

Ion hydrations are ubiquitous in natural and fundamental processes. A quantitative analysis of a novel CO2 sorbent driven by ion hydrations was presented by molecular dynamics (MD). We explored the humidity effect on the diffusion and structure of ion hydrations in CO2 sorbent, as well as the working mechanism of the moisture-swing CO2 sorbent. The...

The hydration of ions in nanoscale hydrated clusters is ubiquitous and essential in many physical and chemical processes. Here we show that the hydrolysis reaction is strongly affected by relative humidity. The hydrolysis of CO32- with n = 1-8 water molecules is investigated by ab initio method. For n = 1-5 water molecules, all the reactants follow...

ReaxFF provides a method to model reactive chemical systems in large-scale molecular dynamics simulations. Here, we developed a ReaxFF potential for phosphorus-hydrogen systems. This potential is transferable to a wide range of phosphorus-hydrogen systems, including the P-H molecules, bulk black phosphorus, the atomic-thin black phosphorus layers,...

A novel system containing nanoporous materials and carbonate ions is proposed, which is capable to capture CO2 from ambient air simply by controlling the amount of water (humidity) in the system. The system absorbs CO2 from the air when the surrounding is dry, whereas desorbs CO2 when wet. A design of such a CO2 absorption/desorption system is inve...

The coalescence, the initial stage of sintering, of two contacted Cu nanoparticles is investigated under different heating rates of 700, 350 and 233 K/ns. The nanoparticles coalesced rapidly at the initial stage when the temperature of the system is low. Then, the nanoparticles collided softly in an equilibrium period. After the system was increase...

We have examined theoretically the stability of porous phosphorene and its application in hydrogen separation from gas mixture by employing first-principles calculations. The self-passivated pore of phosphorene was designed by removing six phosphorous atoms, reaching to the formation of covalent bonds among marginal atoms spontaneously. The gas per...

A great deal of information exists concerning the hydration of ions in bulk water. Much less noticeable, but equally ubiquitous is the hydration of ions holding on to several water molecules in nanoscopic pores or in natural air at low relative humidity. Such hydration of ions with a high ratio of ions to water molecules (up to 1:1) are essential i...

Several thermostat methods, including Nose-Hoover method, Berendsen method, Langevin method and Velocity rescaling method are employed to investigate the coating process using molecular dynamics simulations. The coating system consists of Au atoms depositing onto Cu substrate. The temperature profiles of the particles indicate Nose-Hoover thermosta...

Two-dimensional materials have attracted tremendous attention for their fascinating electronic, optical, chemical and mechanical properties. However, the band gaps of most 2D materials reported are smaller than 2.0 eV, which greatly restricted their optoelectronic applications in blue and ultraviolet range of the spectrum. Here, we propose a new st...

Today, 2D semiconductor materials have been extended into the nitrogen group: phosphorene, arsenene, antimonene and even nitrogene. Motivated by them, based upon first-principles density functional calculations, we propose a new two-dimensional phosphorus nitride (PN) structure that is stable well above the room temperature, due to its extremely hi...

Water confined in nanoscopic pores is essential in determining the energetics of many physical and chemical systems. Herein, we report a recently discovered unconventional, reversible chemical reaction driven by water quantities in nanopores. The reduction of the number of water molecules present in the pore space promotes the hydrolysis of CO3 (2-...

Flocculation treatment processes play an important role in water and wastewater pretreatment. Here we investigate experimentally and theoretically the possibility of using graphene oxide (GO) as a flocculant to remove methylene blue (MB) from water. Experimental results show that GO can remove almost all MB from aqueous solutions at its optimal dos...

The interfacial properties of hydrate and its ambient play an important role in hydrate technique. In this paper, the molecular characteristics of H2O in hydrate/ice/liquid water mixture system are investigated based on molecular dynamics (MD) simulations. The structure I (sI) methane hydrate is partially heated to obtain the studied system. The pr...

Scrubbing CO2 directly from the ambient air (air capture) by sorbent is an emerging technology to address climate change due to anthropic emission of greenhouse gases. A good understanding of thermodynamics and reaction kinetics under ultra-low CO2 concentration and variable humidity is fundamental to the design of economic air capture. In this stu...