Graphene Membrane - Nanotechnology - Lecture Slides, Slides of Nanotechnology

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Group 3: Krista Melish, Phillip Keller,

James Kancewick, Micheal Jones

Gas Separation in Industry

 Hydrogen separation

○ From Nitrogen in ammonia plants ○ From hydrocarbons in petrochemical applications

 CO2 and water removal from natural gas

 Nitrogen separation from air

 Hydrogen Recovery From Tail Gases

 Air & natural gas drying

 Vapor removal

 Hydrocarbon Separations

 Helium recovery from natural gas

Pharmaceuticals

Food processing, packaging, and storing

Limitations of Common Membranes

 Energy intensive

 Expensive

 Lack efficiency and productivity

 Break easily

 The material plugs too easily and becomes resistant to flow

Properties of a Good Membrane

 High flux rate (permeability)

 High selectivity

 Ideal pore size

 High surface area

 Low manufacturing cost

 Small thickness

 Mechanically Stable

Mechanisms for Gas

Separation in Membranes

Relationships Among Membranes

Fick’s Law

The Flux rate (J) is inversely proportional to membrane thickness (x)

Selectivity vs. Permeability

of Membranes

Properties of Graphene

 Tear-resistant

 Thermal conductor

 Very Thin

 Very stiff, but also flexible

 Mechanically Strong

 Stronger than a diamond

 Electronically conducting

 100 times faster than the silicon in computer chips

 Ductile

Graphene Becomes a Membrane

 Graphene is impermeable to all gases due to the electron density of its Aromatic rings

 In order to create a membrane, must create pores synthetically

http://www.physics.upenn.edu/~drndic/group/research.ht ml

 TEM

 Puncture holes by removing carbon rings by electric beam

 The unsaturated carbons are passivated by nitrogen

○ Control pore

size

Graphene Membrane

 Thinnest possible membrane (1 atom thick)

 Over 20,000 x thinner than other membranes

 Ideal pore size for separation

 Improvement of 500x compared to other

membranes

 Large surface area

 (Up to areas of 1 mm ^2)

 Resistant to oxidation

 (for temperature less than 450 celsius)

 Very mechanically stable

Article Overview

 Inspiration for Research  No prior research on graphene as a separation membrane ○ Massive possible efficiency gains in the gas separation field

 Goals  Use first principles models to mathematically prove the viability of graphene as the ultimate membrane for gas separation  Encourage future research and experimentation

 Method

 Density Functional Theory

 Simulation Results

 Further Research and Experimentation Ideas

Research Inspiration

 Graphene first isolated in 2004

 Although there has been a boom of graphene research lately, no efforts have been put into analyzing its usefulness as a gas separation membrane.

 Gas separation is very energy intensive currently  Huge opportunities to increase efficiency

 Application to other fields  Proton Exchange Membranes for fuel cells  Carbon sequestration from flue gases  Gas sensors in instrumentation

Research Method

 Density Functional Theory based modeling using  Plane wave base ○ 300 and 680 eV kinetic energy cutoffs  Periodic boundary conditions

 Initial Static Calculations  2 methods used  Perdew, Burke, and Erzenhoff functional form of the generalized gradient approximation (PBE)  Rutgers-Chalmers van der Waals density function for exchange and correlation (vdW-DF) ○ Good at evaluating strength of dispersion interactions between neutral non polar molecules

Model: Nitrogen Functionalized

 Hexagonal cell made of

graphene  15 H 2 or CH 4 molecules placed inside the cell for dispersion calculations

 One face of the cell

contains the nano-pore  Nano-pore created by removing two cells (a), leaving 8 dangling carbons  Functionalized with 4 hydrogens and 4 nitrogens (b)