什么是吸附？
吸附的研究有相当长的历史。关于吸附的第一份文献是Fontana在1777年发表的关于炭吸附行为的研究。1814年，N.T.Saussure在木炭上做了很多吸附实验。现在，他的吸附装置在英国国家历史博物馆展出。如今吸附技术广泛应用于工业过程（如气体和蒸汽分离）和粉体材料的表征。 一个吸附的例子如下。这个图没有显示化学吸附和物理吸附的区别。一般来说，如果吸附质与吸附剂之间的相互作用较强（如氢键或酸碱吸附），而且这个作用力在给定的吸附温度或室温下可以阻止真空引起的吸附质解吸，则成为化学吸附。而物理吸附则主要是由范德华力引起的弱相互作用。吸附剂可以很容易地在真空下解吸。最近我们不再使用“物理吸附”这个术语了和“化学吸附”这两种说法，而是换成了“可逆”和“不可逆”。
吸附状态
Gas adsorption is a fundamental analytical technique for evaluating the surface characteristics and internal structure of solid materials. Used across industries such as catalysis, pharmaceuticals, energy storage, and environmental engineering, gas adsorption reveals critical data on surface area, pore size distribution and porosity - key factors in performance and functionality.
Microtrac offers advanced gas adsorption analyzers and adsorption equipment designed to deliver precise, reproducible measurements that comply with international standards such as ISO 9277 and ISO 15901-2. Our instruments serve both R&D and quality control applications, enabling users to better understand and optimize materials.
Why Gas Adsorption?
Gas adsorption involves the adherence of gas molecules onto the surface of a solid. This physical interaction, known as physisorption, forms the basis for characterizing materials with porous or high surface-area structures. By studying how much gas is adsorbed at different pressures, engineers and researchers can derive:
- Specific surface area (via BET method and more)
- Pore size distribution (via classical methods like BJH, or novel methods like GCMC or DFT models)
- Total pore volume
These metrics are vital across multiple applications:
- In adsorbents like activated carbon, surface area correlates with adsorption capacity
- In catalysis, higher surface area typically means more active sites for chemical reactions
- In batteries and fuel cells, pore volume and structure influence energy density and ion transport
- In pharmaceuticals, particle surface area affects dissolution rate and bioavailability
气体吸附分析中的行业
催化与石化工程
催化剂效率在很大程度上取决于表面积和可及孔隙率。气体吸附分析仪有助于量化氧化铝、沸石和活性炭等催化剂载体的有效性。准确的BET表面积测量有助于质量控制、化学反应器的优化和延长催化剂寿命。
药品
受 USP <846> 等汇编规范的约束，药物物质的表面积分析对于控制产品行为至关重要。气体吸附提供了实现一致释放曲线、生物利用度和片剂性能所需的数据。
储能与转换
电池电极、超级电容器和储氢材料需要在比表面积和孔隙可及性之间取得平衡。气体吸附是评估多孔碳和金属有机框架（MOFs）等材料以实现最佳充放电效率的关键。
环境技术
气体吸附测量用于开发捕获或分离气体（如CO2或VOCs）的材料。从室内空气净化器到工业洗涤器，吸附剂性能由总气体吸附量、表面积和孔结构分析驱动。
建筑与先进材料
在建筑、陶瓷和过滤介质中，孔隙率影响强度、耐久性和流体渗透性。气体吸附技术被用于表征气凝胶、砂浆和多孔陶瓷等材料，这些材料既应用于结构领域也应用于热力学领域。
Core Technique: Volumetric Gas Adsorption
Core Technique: Volumetric Gas Adsorption
The most usual form of gas adsorption measurement is volumetric (manometric) physisorption. This method involves dosing a known volume of adsorptive gas (typically nitrogen or argon) into an evacuated sample cell and monitoring pressure changes as the gas adsorbs onto the sample's surface. The resulting adsorption isotherm—gas volume adsorbed vs. relative pressure (P/P0)—forms the basis for analytical models.
Key steps:
- Degassing (Outgassing): Prior to analysis, samples are heated under vacuum to remove moisture and contaminants.
- Cryogenic cooling: Most measurements use liquid nitrogen (77 K) or liquid argon (87 K) to maintain stable, low temperatures ideal for physisorption.
- Equilibrium dosing: Gas is introduced incrementally until equilibrium is reached at each pressure step.
Microtrac's instruments support full automation of these steps with integrated degassing stations and precision dosing systems.
Standard Models for Data Analysis
BET Theory (ISO 9277)
The Brunauer–Emmett–Teller (BET) method is the gold standard for calculating specific surface area. It assumes multilayer adsorption and is applied to the linear region of the isotherm (typically P/P0 = 0.05–0.30; except type I isotherm). BET surface area is calculated from the monolayer capacity using:
- Molecular cross-sectional area of the adsorbate (e.g. 0.162 nm² for N2)
- Avogadro’s number
- Ideal gas law constants (such us molar volume of gas at STP)
Microtrac systems support both single-point and multi-point BET analysis as per ISO 9277 and ASTM D6556.
BJH Method (ISO 15901-2)
The Barrett–Joyner–Halenda (BJH) method is used to determine mesopore size distribution by analyzing the desorption branch of the isotherm. BJH applies the Kelvin equation to correlate pressure changes with pore diameters, assuming cylindrical pore geometry.
Ideal for:
- Silica gels
- Porous glass
- Mesoporous oxides
DFT, NLDFT & QSDFT
Density Functional Theory (DFT), non-local DFT (NLDFT), and quenched solid DFT (QSDFT) are advanced methods that model gas adsorption in porous materials based on statistical mechanics. Unlike BJH, which relies on certain assumptions about pore geometry and is limited in analyzing micropores, DFT-based methods can accurately account for a range of pore shapes and sizes, making them ideal for characterizing microporous materials such as activated carbon and metal-organic frameworks (MOFs).
- Provides high-resolution pore size distributions
- Applicable to a range of adsorbates and pore geometries
- Built-in libraries in Microtrac software enhance accuracy
Choice of Adsorbate Gases
The selection of gas affects sensitivity and pore accessibility:
- Nitrogen (N2, 77 K): Standard for BET and mesopore analysis. Well-characterized and widely accepted.
- Argon (Ar, 87 K): Preferred for micropore analysis due to its non-polar nature and smoother adsorption behavior.
- Krypton (Kr, 77 K): Used for low surface area materials (<1 m²/g). Its low saturation pressure increases sensitivity for small sample surfaces.
- Carbon Dioxide (CO2, 273 K or 298 K): Ideal for probing ultra-micropores (<0.7 nm), which are often inaccessible to nitrogen at 77 K due to kinetic restrictions and slower diffusion rates.
Microtrac’s BELSORP series supports all of these gases, enabling flexible, accurate analysis across materials.
Microtrac Gas Adsorption Analyzers: Engineered for Precision
Microtrac’s portfolio of gas adsorption analyzers is designed to deliver maximum reliability, compliance, and ease of use. Key features include:
Conclusion: Precise Gas Adsorption Measurement for Confident Material Design
Gas adsorption is not just a laboratory technique - it is a gateway to understanding how materials behave in real-world applications. Accurate surface area and porosity data can inform:
- Material selection
- Product formulation
- Regulatory approval
- Performance optimization
Microtrac’s gas adsorption analyzers empower users to obtain this information quickly, reliably, and in full compliance with international standards. Whether you're testing catalysts, refining pharmaceutical powders, or exploring next-generation adsorbents, we have the adsorption equipment to support your goals.
Learn more about our Gas Adsorption Measurement instruments and how we can help you bring material innovation to life.
氣體吸附測量 - FAQ
What is gas adsorption used for?
Gas adsorption is used to determine surface area, pore size distribution, and gas-solid interactions. It is essential for industries like catalysis, energy, and pharmaceuticals.
What is the difference between physisorption and chemisorption?
Physisorption involves weak van der Waals forces and is reversible, while chemisorption involves stronger chemical bonds and is often irreversible. Both are studied using gas adsorption methods.
How do gas adsorption analyzers work?
Gas adsorption analyzers measure the quantity of gas adsorbed on a solid material at varying pressures. This data is used to calculate surface area and porosity using models such as BET or BJH.
What gases are commonly used in gas adsorption?
Nitrogen is the most common gas due to its inertness and consistency. Other gases like argon, CO2, or krypton may be used for specific materials and applications.