POCS AFP

What does POCs stand for

Porous organic cages

generally what type of material are POCs

a type of crystalline microporous materials

What are the desirable properties of POCs

uniform micropores, high surface areas, and thermal and chemical stability

What differentiates POCs from other conventional porous materials, such as zeolites, metal organic frameworks, porous polymers, and carbon molecular sieves.

The unique structure of POCs and their distinctive solid state molecular packing

generally, what do POCs consist of and what can they do

They consist of covalently bonded organic cages that can assemble into crystalline microporous materials displaying three-dimensional connectivity and uniform pore size.

What are the general characteristics of POCS

Discrete organic building blocks
Intrinsic cavities
Extrinsic voids
Imine linked tetrahedral structure

What are the general advantages of POCs

Dissolvable in common organic solvents
Thermal stability
Chemical stability
High surface areas (~40-800 m2/g)

How are POCs typically synthesized

via [4+6] cycloimination reactions. Depending
on the amine and trialdehyde employed different cages can be formed.

what is the most studied prototypical type of POC.

CC3

How is CC3 formed

by the coordination of 1,3,5-triformylbenzene with trans-1,2-diaminocyclohexane,

What is the limiting pore size (window diameter) of CCS

~3.6 Ǻ

What has CC3 been used fo r

- to separate mesitylene from 4-ethyl toluene,
- separation of rare gases, including Xe and Kr ,
- sulfur hexafluoride separation
- gas chromatography separations involving chiral alcohols
- as membrane for the separation of several binary gases (ideal selectivites)
- as proton conductor
- as a noble metal catalytic support.

What in the XRD indicates a decrease in the
interplanar spacing.

displacement to higher 2 theta angles

What may be related to small changes in the unit cell volume of CC3

the displacement of XRD peaks as a function of synthesis time

What suggest different degrees of packing of CC3 as well a contraction-expansion within this POC

The flexible nature of the CC3 crystals together with these changes in interplanar spacings

How many growth regimes are there for the crystal size of CC3

Three main growth regimes observed

When does the first regime occur

from 8hr to 18hr

what happens in the first regime

rapid crystal growth
amorphous agglomerates densify and transform into larger irregular crystals

when does the second regime happen

from 18 hr to 60 hr

what happens during the second regime

there is an intermediate stage in which crystal size decreases gradually with time

what might be causing the crystal size to decrease in the second growth regime

crystal fragmentation (most likely based on SEM)
crystal dissolution,
crystal dissolution,

When does the last regime take place

60 hr to 360 hr

what happens during the last regime

there is a regrowth stage
a progressive increase in crystals size as a function of synthesis time

What is likely responsible for the continuous crystal growth in the final regime

Ostwald ripening mechanism in which small crystals disappear at expense of growing larger crystals which are favored energetically

What happens during the fragmentation event

crystals detach from larger crystals

When regarding crystal fragmentation what may explain the decrease in crystal size

The regular hexagonal voids left by fragmented crystals with comparable sizes of those crystals synthesized at 30 h

What is CO2 uptake highly dependent on from CC3

crystal size

How does the concentration of solute change for the stirring and non-stirring case

in the non-stirring case the concentration of solutes is high, and gradually decreases

in the stirring case, this concentration rapidly decreases and become steady.

What should affect the overall crystallization process affecting the resultant crystal size, shape, and distribution

The kinetics of the stirring/non-stirring concentration gradient

In principle what is the most thermodynamically stable and simplest form that a colloidal particle can adopt in solution during nucleation and growth

spherical

Why is the spherical shape likely preferred in the non-stirring case

the higher concentration of solutes leads to:

faster supersaturation (solute concentration/solubility ratio)

lower local thermal energy associated to the stagnant solution (non-stirred case) leading to the lowest energy spherical shape configuration.

What are the different formation stages for different crystal formation stages for CC3

rapid crystal growth stage
intermediate stage in which crystal size decreased with time.
regrowth stage leading to a continuous crystal size increase.

Adsorption properties of the resultant CC3 phases for CO2 and N2 were highly dependent on what

synthesis time.

What are the advantages of the microwave synthesis of POCs

• Narrow size distribution of crystals
• Higher heating rates vs conventional heating
• No contact between energy source and chemicals
• No wall or heat diffusion effects
• Selectively heats
• No “hotspots”

What were the conclusions of the microwave synthesis of POCs

• Microwave irradiation greatly reduced crystallization time for two prototypical POCs: CC3 and CC2.
• Size control of CC3α achieved
• Highly crystalline at short times!
• Typical reported surface areas obtained
• Microporous topology maintained

What the proposed steps for the formation of CC3 via EISA

initial homogenous solution on Al foil.
homogenous solution on Al Foil. High RH
MSE
Flexible State
POC Nanocrystalline islands

What were the conclusions of CC3 formed by EISA

- The solvent diffusion rate was controlled by the relative humidity in the system.
- Novel synthetic method for the formation of a prototypical type of porous organic cage denoted as CC3.
- The formation of CC3 crystals was promoted via EISA approach which relies on the gradual evaporation of dichloromethane from a diluted concentration of CC3 precursors deposited on
aluminum foil.
- The slow solvent evaporation allowed enough time for the organization and formation of CC3 porous organic cage.
- HRTEM, SAED, SEM, and XRD patterns were used as key techniques to follow the formation of this porous organic cage.

What are the uses of high purity Xe

Buildings - Commercial lighting
Automotive – Head lights
Space Industry – Propellant
Medical – Anesthesia, Imaging
Science – NMR

What are the advantages of membranes

Low energy consumption
Continuous process
No phase changes
No chemical additives

What is the importance of separation processes

Chemical separations account for
about half of US industrial energy
use and up to 15% of the nation’s
total energy consumption.

Why would you want to use POCs as membranes

they should display the most desirable properties of polymers (facile processability and flexibility) and inorganic materials (hierarchically ordered pores with molecular sieving properties) leading to highly selective and permeable membranes

Why was CC3 chosen as the POC membrane for Xe separation

its limiting pore aperture is ~3.6 A can be used as a molecular sieve
Xe has a kinetic diameter ~4.1 A
He, CO2, Kr, and CH4 have kinetic
~ 2.6 Å, 3.3 Å, 3.6Å, and 3.8 Å respectively

draw how CC3 membranes were made by secondary seeded growth

What is the key factor that leads to a higher-than-expected selectivity for Ch4/Xe

pore shape selectivity based on molecular configuration
leading potentially to entropic selectivity

What are the factors that affected the separation mechanism

molecular sieving,
adsorption,
diffusivity differences **

What were the conclusion of CC3 as separation membranes for Xe

-The quality of the membranes was dependent on the crystal size, and size distribution of the seeds employed for membrane synthesis. Smaller CC3 seeds with narrow size distribution led to enhanced membrane separation performance.

-Mechanistically, the membranes separated He, CO2, Kr, and CH4 from Xe mainly via differences in diffusivities.

-CC3 membranes displayed low to moderate ideal selectivities of the light gas over Xenon and unprecedented high gas permeances in the 773 to 2114 GPUs range.

-These membranes may be promising for extracting Xenon from different important gas sources, including air, natural gas, and nuclear based mixtures

How might POCS be used for hydrogen isotope separations

Quantum size effects are observed when the difference between the size of the molecule and pore diameter is comparable to the De Broglie wavelength.

Quantum size effects are observed when the difference between the size of the molecule and pore diameter is comparable to the De Broglie wavelength.