Here’s a detailed discussion on NaY zeolite with enhanced adsorption capacity, covering modification methods, key applications, and performance improvements:

1. Enhancing Adsorption Capacity via Structural Modifications

NaY zeolite (a faujasite-type zeolite with a Si/Al ratio ~1.5–3.0) is widely used for gas separation and adsorption due to its large pore size (1.2 nm) and high surface area. However, its native adsorption capacity can be further improved through targeted modifications:

a. Dealumination to Increase Hydrophobicity

• Method: Steam treatment or acid leaching removes framework aluminum, creating mesopores and reducing polar surface sites.
• Effect:
  • Reduces water adsorption (critical for CO₂ capture in humid conditions).
  • Enhances CO₂/N₂ selectivity (e.g., dealuminated NaY shows CO₂ uptake of 4.59 mmol/g at 25°C, 0.1 MPa, compared to ~3.0 mmol/g for untreated NaY).

b. Ion Exchange with Alkali/Alkaline Earth Metals

• Method: Replace Na⁺ with K⁺, Ca²⁺, or Sr²⁺ to adjust pore aperture and surface charge.
• Effect:
  • K⁺-exchanged NaY: Narrower pores improve size-selective adsorption (e.g., separating C₃H₆/C₃H₈).
  • Ca²⁺-exchanged NaY: Higher affinity for CO₂ due to stronger electrostatic interactions (adsorption capacity up to 5.2 mmol/g).

c. Amine Functionalization

• Method: Graft polyethyleneimine (PEI) or 3-aminopropyltriethoxysilane (APTES) onto the zeolite surface.
• Effect:
  • Chemisorption of CO₂ via carbamate formation (e.g., PEI-modified NaY achieves 6.51 mmol/g CO₂ uptake at 25°C, 0.1 MPa).
  • Improves performance in low-pressure applications (e.g., flue gas treatment).

d. Hierarchical Pore Structure Design

• Method: Combine dealumination with template-assisted synthesis to create micro-mesoporous NaY.
• Effect:
  • Faster diffusion of large molecules (e.g., VOCs, dyes).
  • Example: Hierarchical NaY shows 30% higher adsorption capacity for toluene (a common VOC) compared to conventional NaY.

2. Key Applications of Enhanced NaY Zeolites

a. CO₂ Capture

• Modified NaY Advantage:
  • High CO₂/N₂ selectivity (up to 120:1 for amine-functionalized variants).
  • Stable performance under flue gas conditions (humid, low CO₂ concentration).

b. Volatile Organic Compound (VOC) Removal

• Modified NaY Advantage:
  • Hierarchical pores enhance adsorption of benzene, toluene, and xylene (BTX).
  • Example: Steam-dealuminated NaY removes 95% of toluene from air streams at 25°C.

c. Hydrogen Storage

• Modified NaY Advantage:
  • Spillover effects from Pt or Pd nanoparticles deposited on NaY increase H₂ uptake at low pressures (e.g., 1.2 wt% H₂ storage at 77 K).

d. Water Purification

• Modified NaY Advantage:
  • Ion exchange with Ca²⁺ or Mg²⁺ improves removal of heavy metals (e.g., Pb²⁺, Cd²⁺).
  • Example: Ca-exchanged NaY reduces Pb²⁺ concentration in water to <5 ppb.

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