BET Surface Area & Pore Size Analysis

Scope

Gas adsorption BET/BJH analysis covers the measurement of specific surface area and pore size distribution of solid porous and non-porous materials using nitrogen physisorption at 77 K. Full adsorption and desorption isotherms are collected across a defined relative pressure range, and the data are analyzed using the BET and BJH theoretical frameworks.

The measurement covers:

• BET surface area – multipoint analysis across the P/P₀ range of 0.05–0.30; reported in m²/g, encompassing both external surface area and internal pore wall area accessible to nitrogen
• BJH pore size distribution – derived from the desorption isotherm using Kelvin equation-based analysis; reports pore volume (cm³/g), average pore diameter (nm), and differential pore volume distribution across the mesopore range (2–50 nm)
• Total pore volume – measured from the quantity of nitrogen adsorbed at P/P₀ ≈ 0.99, representing total accessible pore space
• t-plot analysis – separates micropore area from total BET surface area; relevant for microporous materials such as zeolites and activated carbons
• Isotherm type classification – IUPAC isotherm classification (Types I–VI) provides qualitative information on pore geometry (cylindrical, slit-shaped, inkbottle) and material porosity type

Applications

• Catalyst characterisation – surface area and pore size directly govern catalyst activity, selectivity, and mass transfer; BET/BJH is standard practice for characterising fresh, used, and regenerated catalysts across refining, petrochemical, and fine chemical industries
• Activated carbons and adsorbents – pore structure determines adsorption capacity for gases, liquids, and contaminants; BET surface area and BJH pore distribution are key specifications for activated carbon used in water treatment, air purification, and energy storage
• Ceramic and refractory powders – surface area measurement for process control in sintering, coating, and powder compaction; higher surface area powders sinter at lower temperatures and require different binder loading
• Battery and energy materials – electrode materials (cathodes, anodes, separators) and solid electrolytes in lithium-ion and next-generation batteries where interfacial surface area affects rate capability and cycle life
• Metal-organic frameworks (MOFs) and zeolites – extremely high surface area materials (500–7000 m²/g) where BET surface area is a primary performance specification
• Membrane and filtration media – characterisation of porous polymer, ceramic, and carbon membranes for gas separation, ultrafiltration, and nanofiltration applications

Benefits

• Gives both surface area and pore structure in one measurement run – a single nitrogen adsorption/desorption isotherm yields BET surface area, BJH pore size distribution, total pore volume, and average pore diameter without additional sample preparation
• Relevant across a wide range of materials and surface areas – from dense powders at 0.1 m²/g to high-surface-area carbons and MOFs at thousands of m²/g; krypton adsorption extends the method further for very low surface area sintered materials
• Pore size distribution identifies both mesopore volume and geometry – BJH output shows not just average pore size but how pore volume is distributed, which matters for selectivity in separation and catalysis
• Non-destructive and requires small sample quantities – typically 0.05 to 1 g of material depending on surface area; sample is recovered after outgassing in most cases
• Widely accepted across industries and regulatory frameworks – BET surface area data generated per ASTM or ISO methods is accepted in pharmaceutical filings, catalyst specifications, and materials procurement standards worldwide