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Materials Chemistry for Environmental Appications > L4 - Porous materials for water treatment > Flashcards

L4 - Porous materials for water treatment Flashcards

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1
Q

What are the three main classifications of porous materials?

A

Hybrid porous materials,
Pure organic porous materials
Inorganic porous materials

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2
Q

Give an example of a hybrid porous material.

A

Metal-Organic Frameworks (MOFs)

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3
Q

What are pure organic porous materials composed of?

A

Only organic elements, primarily carbon, hydrogen, nitrogen, and oxygen.

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4
Q

Name two types of pure organic porous materials.

A

Conjugated Microporous Polymers (CMPs)
Covalent Organic Frameworks (COFs).

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5
Q

What are inorganic porous materials commonly used in water treatment?

A

Zeolites, silica, and activated carbon.

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6
Q

Which materials commonly exhibit macroporosity?

A

Rocks and solid foams.

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7
Q

Which materials commonly exhibit mesoporosity?

A

Clays and mesoporous silica.

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8
Q

Name three common microporous materials.

A

Zeolites, activated carbons, and metal-organic frameworks (MOFs).

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9
Q

What is specific surface area in porous materials?

A

The total surface area per unit mass, measured in m²/g.

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10
Q

Why is high specific surface area important in porous materials?

A

It allows greater adsorption capacity.

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11
Q

What does specific pore volume indicate?

A

The volume of pores relative to the mass, measured in cm³/g.

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12
Q

What are the typical sources for producing activated carbon?

A

Coal, biomass, and industrial waste.

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13
Q

What is the typical surface area range for activated carbon?

A

500–3000 m²/g.

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14
Q

Describe the internal structure of activated carbon.

A

Small, disordered stacks or layers of graphene.

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15
Q

What property do oxygenated compounds give to activated carbon surfaces?

A

Both acidic and basic character.

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16
Q

List three applications of activated carbon.

A

Gas separation, water treatment, and supercapacitor electrodes.

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17
Q

Why can activated carbons conduct heat and electricity relatively well?

A

Due to their carbon structure and delocalized π-electrons.

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18
Q

Describe the step-by-step chemical activation process for producing activated carbon, including after-treatment steps.

A
  1. Precursor Selection
  2. Pretreatment
  3. Mixing with Chemical Activator
  4. Activation
  5. After Treatment:
    • Acid and Base Washing
    • High-Temperature Treatment
  6. Drying
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19
Q

What is done during the pretreatment step in chemical activation?

A

Heating the precursor in nitrogen to remove volatile substances.

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19
Q

What is the first step in the chemical activation of activated carbon?

A

Selecting a carbon-rich precursor material.

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19
Q

Which chemicals are commonly used as activators in chemical activation?

A

Phosphoric acid (H₃PO₄), potassium hydroxide (KOH), or zinc chloride (ZnCl₂).

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20
Q

What is the purpose of the high-temperature treatment in the activation process?

A

To develop the pore structure in an inert atmosphere.

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21
Q

What is done in the after-treatment of activated carbon?

A

Acid and base washing, followed by additional high-temperature treatment.

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22
Q

Why is the washing step important in chemical activation of activated carbon?

A

To remove any residual chemicals and ash.

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23
Q

What are zeolites composed of?

A

Aluminosilicate minerals with a microporous structure.

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24
Q

What unique property do zeolites have for water treatment?

A

Ion-exchange capabilities, which allow them to remove hardness ions like calcium and magnesium.

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25
Q

How are zeolites synthesized?

A

By hydrothermal methods in a closed system with high temperature and pressure.

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26
Q

What is the purpose of organic templates in zeolite synthesis?

A

To guide the formation of specific pore shapes and sizes.

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27
Q

What are Metal-Organic Frameworks (MOFs) made of?

A

Metal ions coordinated with organic linkers.

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28
Q

Why are Metal-Organic Frameworks (MOFs) versatile in adsorption applications?

A

They can have hydrophobic and hydrophilic regions and can be customized by selecting different metals and linkers.

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29
Q

What is a primary limitation of MOFs in water treatment?

A

Their thermal stability is generally low, and they can be sensitive to humidity.

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30
Q

What is a π-conjugated system?

A

A structure with alternating single and double bonds, allowing electron delocalization across multiple atoms.

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31
Q

Why are π-conjugated systems useful in materials like Conjugated Microporous Polymers (CMPs)?

A

They provide electronic conductivity, making CMPs useful in applications like gas storage and catalysis.

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32
Q

Which porous materials are commonly used for water treatment?

A

Activated carbon, zeolites, alumina, and MOFs.

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33
Q

Why is activated carbon effective for removing organic pollutants in water treatment?

A

Due to its high surface area and versatile pore structure.

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34
Q

How do zeolites help in softening water?

A

By exchanging ions like calcium and magnesium with sodium ions.

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35
Q

What is a primary use of alumina in water treatment?

A

Removing fluoride and arsenic ions.

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36
Q

Which adsorbent is used for removing dissolved organic matter in water treatment?

A

Activated carbon.

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37
Q

Which adsorbent is suitable for organic micropollutants in water treatment?

A

Activated carbon.

38
Q

What are the primary adsorbents used for arsenic removal in water treatment?

A

Aluminium oxide and iron hydroxide.

39
Q

Which adsorbents are effective for removing phosphates from water?

A

Aluminium oxide and iron hydroxide.

40
Q

Name the adsorbent suitable for micropollutants like phenol, chlorinated hydrocarbons, pesticides, and pharmaceuticals.

A

Activated carbon.

41
Q

Which type of adsorbent is used for organic substances in water treatment?

A

Polymeric adsorbents.

42
Q

Why is adsorption on porous materials relevant in industrial wastewater treatment?

A

It is used for the removal and recycling of organic substances, often with desorption using solvents.

43
Q

What challenge is associated with adsorbing pollutants on porous materials?

A

Competition between pollutants; organic matter is adsorbed together with micropollutants.

44
Q

What pollutants can activated carbon remove in water treatment?

A

Dissolved organic matter
organic micropollutants
micropollutants like phenol
chlorinated hydrocarbons
pesticides
pharmaceuticals

45
Q

Which pollutants can aluminium oxide remove from water?

A

Arsenic and phosphates.

46
Q

Which pollutants can iron hydroxide adsorb in water treatment?

A

Arsenic and phosphates.

47
Q

What types of pollutants do polymeric adsorbents target in water treatment?

A

Organic substances.

48
Q

Why is activated carbon effective for a wide range of organic pollutants?

A

It has a high surface area and versatile pore structure that can adsorb dissolved organic matter, organic micropollutants, and various micropollutants

49
Q

What contaminants are removed in drinking water treatment?

A

Dissolved organic matter, organic micropollutants, and arsenic.

50
Q

What are the main pollutants targeted in urban wastewater treatment?

A

Phosphate and micropollutants.

51
Q

Adsorbents for water treatment

A

*Activated Carbon
*Zeolites
*Alumina
*Mesoporous silica
*Hypercrossliked polymers
*Metal organic frameworks
*Biobased adsorbents

52
Q

Precursors for activated carbon

A

*Coal, peat, and wood
*Agriculture biomass
*Industrial waste

53
Q

Activated carbon forms/shapes

A

powder, granular, tablet (monolith)

54
Q

What factors influence the pore size distribution in activated carbon?

A

The precursor material, the temperature, and the activation method used.

55
Q

How does the uptake and sedimentation of pollutants differ when using powdered activated carbon?

A

The uptake of pollutants and organics is fast, but sedimentation is slow.

56
Q

What equipment is commonly used with powdered activated carbon to manage slow sedimentation?

A

Sedimentation tanks.

57
Q

How does the uptake of pollutants differ when using granulated activated carbon?

A

The uptake is slower compared to powdered activated carbon.

58
Q

What equipment is commonly used with granulated activated carbon for adsorption processes?

A

Columns.

59
Q

How does the heat of adsorption on activated carbon compare to other sorbents?

A

It is generally lower, resulting in lower energy requirements for regeneration of the sorbent.

60
Q

What is an advantage of activated carbon’s hydrophobic nature?

A

It does not require moisture removal prior to purification and separation processes.

61
Q

What type of molecules does activated carbon adsorb more effectively than other sorbents?

A

Non-polar and weakly polar organic molecules.

62
Q

What is the primary method used to synthesize zeolites?

A

Hydrothermal or solvothermal synthesis.

63
Q

What distinguishes solvo-thermal synthesis from hydrothermal synthesis?

A

In solvo-thermal synthesis, water is replaced by other solvents.

64
Q

What are structure-directing agents (SDAs) in porous material synthesis?

A

SDAs are specific organic molecules that stabilize unique structures during synthesis, such as crown ether 18-crown-6 for the EMT structure.

65
Q

How does templating influence the structure of zeolites?

A

Templating guides the zeolite structure to adopt geometric and electronic configurations that are unique to the templating molecule.

66
Q

How do organic templates help control pore size and shape in porous materials?

A

Different templates lead to different pore sizes and shapes, allowing precise control over the final pore structure.

67
Q

How do organic templates create pores in porous materials?

A

Organic templates fill spaces within the forming structure, creating channels or cavities that remain as pores once the template is removed.

68
Q

What are the main roles of organic templates in shaping the structure of porous materials?

A

Influencing gelation and nucleation, lowering chemical potential, and filling space.

69
Q

How do organic templates influence the gelation and nucleation process in porous material synthesis?

A

They guide the initial formation by helping particles come together in a stable structure.

70
Q

What does it mean for organic templates to lower chemical potential in porous material synthesis?

A

The template makes it easier and more stable for the structure to form, acting like a “blueprint” for the lattice.

71
Q

What effect does the hydrophobicity of organic templates have in porous material synthesis?

A

Hydrophobic templates repel water, which creates larger, open spaces around them, forming bigger pores.

72
Q

Why does the repulsion of hydrophobic templates from water lead to larger pores?

A

The templates “push” the material around them, creating more open space and larger pores as the template avoids interaction with the surrounding water.

73
Q

Why are larger pores created by hydrophobic templates important in certain applications?

A

Larger pores are beneficial in applications like gas separation and catalysis, as they can trap or interact with larger or specific types of molecules.

74
Q

What type of framework do zeolites have, and what ions are present in their pores?

A

Zeolites have a negatively charged framework with cations (positively charged ions) present in their pores.

75
Q

What ions are zeolites particularly useful in removing from wastewater?

A

Ammonium ions.

76
Q

What are some drawbacks of using alumina in water treatment?

A

It has challenges with regeneration and is pH-dependent.

77
Q

Which contaminants is alumina particularly effective at removing from water?

A

Fluoride and arsenic.

78
Q

What is alumina, and what is its primary function in water treatment?

A

Alumina is a highly porous form of aluminum oxide that acts as an adsorbent.

79
Q

How does the three-dimensional structure of zeolite-templated activated carbons affect their properties?

A

It provides high electrical conductivity, which is useful for applications like energy storage.

80
Q

What happens to the structure of activated carbon when the zeolite template is removed?

A

The activated carbon retains some of the ordered structure of the template.

81
Q

How does using a zeolite Y template affect the diffraction lines in activated carbon?

A

Only one diffraction line is usually seen, indicating a less ordered structure.

82
Q

How does using an EMT zeolite template affect the diffraction lines in activated carbon?

A

Multiple diffraction lines appear, indicating a more ordered structure is retained.

83
Q

In soft templating, what type of state and materials are used?

A

A fluid-like state with surfactants or block copolymers.

84
Q

In hard templating, what kind of materials are typically used?

A

Solid-state and rigid materials, often nanostructured.

85
Q

How is the template removed in a soft templating process?

A

By heat treatment.

86
Q

How is the template removed in a hard templating process?

A

By etching with toxic hydrofluoric acid (HF).

87
Q

What is the advantage of soft templates in terms of pore structure and surface properties?

A

Soft templates allow tunable pore structure and surface properties.

88
Q

What is the main limitation of pore size control in hard templating?

A

It is fixed and constrained by the hard template’s pre-formed structure.

89
Q

How does the pore size distribution differ between soft and hard templates?

A

Soft templates produce highly uniform, narrowly distributed pores, while hard templates result in relatively wider pores than the original template.

90
Q

Which template type is considered low-cost, convenient, and suitable for large-scale production?

A

Soft template.

91
Q

Why is hard templating considered unsuitable for large-scale production?

A

It is expensive and involves complicated preparation steps.

92
Q

What is the main mechanism involved in soft templating?

A

Micelle formation, self-assembly, and mesoporous product formation.

93
Q

What is the primary mechanism involved in hard templating?

A

Mesoporous templating, nanocasting, and mesoporous product replication.

Materials Chemistry for Environmental Appications (8 decks)

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