Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Materials Chemistry for Environmental Appications > L2 - Adsorption and associated concepts, materials and characterisation > Flashcards

L2 - Adsorption and associated concepts, materials and characterisation Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What is adsorption?

A

The process where molecules (adsorbates) attach to the surface of a solid (adsorbent), involving physical or chemical attachment.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is desorption?

A

The process where adsorbed molecules detach from the surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is an adsorbate?

A

A molecule that attaches to the surface of an adsorbent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is an adsorbent?

A

A highly porous solid with a large surface area that adsorbates attach to.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are kinetics in adsorption?

A

Calculations of how quickly adsorption occurs, often as a function of time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is an adsorption isotherm?

A

A mathematical relationship describing adsorption equilibrium, often dependent on adsorbate concentration or pressure at a given temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is physisorption?

A

A type of adsorption involving weak van der Waals forces, reversible, forms multilayers, and usually occurs at low temperatures.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is chemisorption?

A

A type of adsorption involving strong chemical bonds, typically irreversible, forms a monolayer, and requires higher temperatures.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the key differences between physisorption and chemisorption?

A

Physisorption is reversible, involves van der Waals forces, and forms multilayers, while chemisorption is irreversible, forms chemical bonds, and forms a single layer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why does physisorption decrease with increasing temperature?

A

Higher temperatures give molecules more kinetic energy, making it easier for them to escape the adsorbent’s surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is Henry’s Law in the context of adsorption?

A

An adsorption model where the amount adsorbed is linearly related to concentration or pressure, assuming low molecule interactions and low adsorbate uptake.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the Langmuir Isotherm?

A

An adsorption model for monolayer adsorption, assuming uniform adsorption sites and no interaction between adsorbed molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When is the BET (Brunauer-Emmett-Teller) theory used?

A

For multilayer adsorption, especially with nitrogen on mesoporous surfaces.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does the Freundlich Isotherm describe?

A

Adsorption on a heterogeneous surface with interaction between adsorbed molecules, where adsorption energy decreases as sites fill up.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What determines the adsorption loading (q) in gas adsorption?

A

It depends on partial pressure
𝑝 and temperature 𝑇 in the form
q=f(p,T).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What factors influence adsorption from liquid solutions?

A

Adsorption depends on solute concentration
c and temperature T in the form
q=f(c,T)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the separation factor in adsorption?

A

A measure of the adsorbate’s concentration in adsorbed vs. fluid phases, calculated as
r=x/(1−x).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why is the BET model less accurate for very small pores (micropores)?

A

Because in very small pores, there isn’t enough space for multiple layers to form, leading to potential inaccuracies.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What pore size range is considered too small for accurate BET analysis due to the multilayer assumption?

A

Micropores, which are less than 2 nm in size.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What factors influence the amount of material adsorbed according to the Freundlich isotherm?

A

The amount adsorbed depends on the adsorbent’s characteristics, the adsorbate’s concentration in the solution, and the temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How is adsorbent size typically measured?

A

Through sieve analysis, which separates particles by size.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Why does adsorbent size matter in adsorption?

A

Smaller particles often increase adsorption rate due to more surface area and also impact the pressure needed to push fluid through a fixed bed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What does adsorbent density represent?

A

The mass per unit volume of adsorbent particles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Why is adsorbent density important in adsorption design?

A

It helps determine the height of the adsorbent bed, as adsorption is often measured per unit mass of adsorbent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What does adsorbent porosity indicate?

A

The fraction of void space within each adsorbent particle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Why is adsorbent porosity ε important for adsorption?

A

It affects how much adsorbate the adsorbent can hold internally.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How is specific pore volume (Vpore) calculated and what does it represent?

A

V (pore)=ϵ /ρ
; it represents the pore volume per unit mass of adsorbent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How does adsorbent particle size affect the pressure needed to maintain fluid flow in a fixed-bed operation?

A

Smaller particles increase the pressure drop due to higher resistance, while larger particles reduce the pressure drop by allowing easier fluid flow (more space between particles).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are the four main steps in adsorption kinetics?

A
  1. Movement from bulk solution to boundary film
  2. Diffusion to adsorbent surface
  3. Transfer to active sites
  4. Chemical adsorption via bonding or ion exchange
30
Q

Why are adsorption kinetics important?

A

They help understand the adsorption mechanism and identify potential rate-controlling steps in the process.

31
Q

Why is adsorbent size important?

A

Smaller adsorbent size increases surface area and adsorbate uptake, affecting adsorption rate.

32
Q

What is adsorbent porosity?

A

The fraction of void space in an adsorbent, affecting adsorption capacity.

33
Q

How are adsorbent pore sizes classified?

A

Micropores (< 2 nm)
Mesopores (2-50 nm)
Macropores (> 50 nm)

34
Q

How does pore size affect adsorption?

A

Different pore sizes control adsorption properties, with micropores being best for gases and large pores ideal for larger molecules.

35
Q

Why is specific surface area critical in adsorption?

A

Because adsorption occurs on the surface, a larger surface area increases adsorption capacity.

36
Q

How is the BET method used in adsorption?

A

It measures surface area by calculating how much gas can adsorb onto a surface under specific pressures.

37
Q

What are some common engineered adsorbents?

A

Activated carbon, polymeric adsorbents, and oxidic adsorbents like Al₂O₃ and silica.

38
Q

How are molecular sieve zeolites unique as adsorbents?

A

They have “cages” that selectively trap specific molecules based on size.

39
Q

What is the main application of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs)?

A

They are used for gas storage, adsorption, catalysis, and sensor applications due to their high porosity and stability.

40
Q

Why are activated carbons and MOFs effective for VOC removal?

A

They have large surface areas and pore structures that capture volatile organic compounds (VOCs) efficiently.

41
Q

What makes PFAS adsorption challenging?

A

PFAS compounds are highly persistent and require special adsorbents and models to effectively capture them from solutions.

42
Q

What gas is commonly used in the Barrett-Joyner-Halenda (BJH) method for pore size characterization?

A

Nitrogen gas.

43
Q

In the Barrett-Joyner-Halenda (BJH) method, what happens to nitrogen gas when the relative pressure reaches 1?

A

The nitrogen gas fills the pores, reaching full saturation.

44
Q

What is desorption in the Barrett-Joyner-Halenda (BJH) method?

A

The gradual removal of nitrogen gas from the pores by slowly lowering the pressure.

45
Q

How does the Barrett-Joyner-Halenda (BJH) method measure pore sizes?

A

By tracking the desorption of nitrogen gas as the pressure decreases, revealing the volume and size of each pore.

46
Q

In the Barrett-Joyner-Halenda (BJH) method, what happens to smaller pores during desorption?

A

Smaller pores empty at lower pressures, while larger pores require higher pressures to empty.

47
Q

What does the Barrett-Joyner-Halenda (BJH) method reveal about a material?

A

It reveals the pore size and pore volume distribution in mesoporous materials.

48
Q

How is activated carbon produced?

A

Activated carbon is produced by carbonizing materials like coconut shells, coal, lignite, wood, etc., followed by activation with air or steam.

49
Q

What are common uses of activated carbon?

A

Activated carbon is used for recovering organic vapor, decolorizing liquid solutions, and treating and purifying water supplies and wastewater.

50
Q

How are polymeric adsorbents made?

A

Polymeric adsorbents are made by polymerizing styrene and divinyl benzene or acrylic esters.

51
Q

What types of substances do polymeric adsorbents adsorb?

A

Polymeric adsorbents are used to adsorb nonpolar organics from water or polar solutes, depending on the polymer used.

52
Q

Why are polymeric adsorbents typically more expensive and selective?

A

Their production costs are higher, so they are used selectively for specific applications.

53
Q

How is activated alumina (Al₂O₃) prepared?

A

Activated alumina is prepared by removing water from colloid alumina.

54
Q

What is a primary use of activated alumina?

A

It is mainly used as a desiccant for removing water vapor from gases and liquids.

55
Q

How can activated alumina be reused?

A

It can be reactivated after use for reuse as a desiccant (drying agent).

56
Q

How is activated silica prepared?

A

Activated silica is prepared from gel precipitated by acid treatment of a sodium silicate solution.

57
Q

What are the main uses of activated silica?

A

Activated silica is used for dehydrating air and removing toxic species, commonly in personal protection equipment like gas masks.

58
Q

Name 5 natural adsorbents commonly used for low-cost adsorption.

A

Clay, natural zeolites, chitosan, peat, wood

59
Q

What contaminants are natural zeolites effective at adsorbing?

A

Ammonium, heavy metals, and other contaminants.

60
Q

How are coconut shells used as low-cost adsorbents?

A

When carbonized, they are effective for adsorbing organic contaminants and odors.

61
Q

What is fly ash, and what is it used for in adsorption?

A

A byproduct of coal combustion, used for adsorbing dyes, heavy metals, and oil.

62
Q

What are the three main categories of low-cost adsorbents?

A

Natural materials, agricultural wastes/by-products, and industrial wastes/by-products.

63
Q

What are examples of low-cost adsorbents derived from agricultural wastes/by-products?

A

Shells, hulls, stones from fruits and nuts, sawdust, corncob waste, sunflower stalks, and straw.

64
Q

List some examples of industrial waste/by-product adsorbents.

A

Fly ash, bagasse, palm oil ash, shale oil ash, and red mud.

65
Q

Name some applications of nanopolymers.

A

Gas separation, gas storage, heterogeneous catalysts, sensors, biomedical uses, and electronic energy storage.

66
Q

What are the main advantages of nanopolymers?

A

Diverse chemistry, potentially inexpensive, post-modification possible, and can be processed into membranes.

67
Q

What are some key features of nanopolymers?

A

Cross-linked, rigid and conjugated, covalently bonded, physiochemically stable, and highly porous.

68
Q

Give examples of Volatile Organic Compounds (VOCs).

A

aldehydes,
aromatic compounds,
alcohols,
alkanes,
ethers
ketones,
olefins,
Halogenated hydrocarbons
polycyclic aromatic hydrocarbons

69
Q

Why are Volatile Organic Compounds significant in environmental studies?

A

VOCs can easily evaporate and may contribute to air pollution and health issues due to their volatility and potential toxicity.

70
Q

What are the two modes of operation in adsorption systems?

A

Batch and continuous systems.

Materials Chemistry for Environmental Appications (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions