There is a well-known relationship between porous materials performance in a given process and their textural properties. These properties include specific surface area, among others, where the most widely used experimental technique to determine them is gas adsorption. Although the most used adsorptive gas is N₂ at 77 K up to atmospheric pressure, its quadrupole moment generates specific interactions with surface groups, as silanols in silica materials, causing a preferential orientation effect on the adsorbed N₂ molecule affecting the specific surface area value. In this sense, we analyzed the adsorption–desorption isotherms at 77 K of nanoporous silica materials using different adsorptives. From these data, we obtained the specific surface area (S_BET) values of the samples by applying the BET method with the IUPAC recommendations for each gas. The selected materials were MCM-41, MCM-48, SBA-15, and SBA-16, and the adsorptives used were Ar, O_2, and CH₄, along with N_2. Among the chosen adsorptives, Ar and CH₄ do not have a quadrupole moment, whereas this value is present for N₂ and O₂, being the latter four times smaller than nitrogen. In addition, at 77 K, both Ar and CH₄ are below their triple-point temperature, while N₂ and O₂, which are above their triple-point temperature, are in the same thermodynamic state. Taking the S_BET obtained by Ar at 77 K as the referential value of each sample, the corresponding molecular transversal areas of the other adsorptives were estimated. It was found that the variation of transversal area for the N₂ molecule at 77 K on silica materials was between 0.133 and 0.149 nm² (below its common value of 0.162 nm²). In contrast, in the case of the O₂ molecule at 77 K, this value was almost constant, with an average of 0.123 nm². These results showed that the quadrupole moment of the O₂ does not play an important role in the interaction with surface silanol groups present in the samples, making oxygen at 77 K a potential and reliable adsorptive to determine the specific surface area of silica materials.

在给定过程中的多孔材料性能与其质地特性之间存在众所周知的关系。这些特性包括比表面积等，其中最广泛使用的确定它们的实验技术是气体吸附。虽然最常用的吸附气体是77 K 至大气压下的N ₂，但其四极矩会与表面基团产生特定的相互作用，如二氧化硅材料中的硅烷醇，对吸附的 N ₂分子产生优先取向效应，从而影响比表面积值. 从这个意义上说，我们使用不同的吸附剂分析了纳米多孔二氧化硅材料在 77 K 下的吸附-解吸等温线。从这些数据中，我们获得了比表面积（S _BET) 样品的值，通过对每种气体应用具有 IUPAC 建议的 BET 方法。所选择的材料是MCM-41，MCM-48，SBA-15，SBA和-16，和adsorptives用过是氩，O- _2，和CH ₄，用N沿着_2.在所选择的adsorptives，Ar和CH ₄做不具有四极矩，而该值存在于 N ₂和 O ₂，后者比氮小四倍。此外，在 77 K 时，Ar 和 CH ₄都低于其三相点温度，而高于其三相点温度的 N ₂和 O ₂处于相同的热力学状态。以S以 Ar 在 77 K 下获得的_BET作为每个样品的参考值，估计其他吸附剂的相应分子横截面积。发现二氧化硅材料上77K下N ₂分子的横截面积的变化在0.133和0.149 nm ^{2 之间}（低于其0.162 nm ^{2 的}共同值）。相反，在77 K的 O ₂分子的情况下，该值几乎恒定，平均为 0.123 nm ²。这些结果表明 O ₂的四极矩 在与样品中存在的表面硅烷醇基团的相互作用中没有发挥重要作用，使 77 K 的氧气成为确定二氧化硅材料比表面积的潜在和可靠的吸附剂。