Prof. HUANG Qing's group from the Hefei Institutes of Physical Science (HFIPS) developed a surface-enhanced Raman spectroscopy (SERS) gas sensor to detect aldehyde with high sensitivity and selectivity, which provided a new detection method for studying the adsorption of gas molecules on porous materials. The relevant research results have been published in Analytical Chemistry. 

Adsorption technology is one of the main technologies for treating Volatile organic compounds (VOCs). Over the past years, metal-organic frameworks (MOFs) have attracted high interest for their outstanding adsorption property. Closely related to MOFs, layered double hydroxides (LDHs), also known as hydrotalcite-like systems or anionic clays, have received special attention for their improved adsorption properties due to the enhanced porosity and chemical affinity at multiple active sites.

In this study, silver nanocubes (AgNCs) and Co-Ni LDH composite nanomaterials were prepared in template sacrifice method, and modified with 4-aminophenol (4-ATP) for both trapping and probe functions. Based on the as-prepared composite material, researchers constructed a high-efficiency gas sensor for selective detection of aldehyde gas.

"This SERS sensor has ultrahigh sensitivity for aldehyde gas," said XU Di, the first author of this paper, "we verified its accuracy, repeatability and selectivity in the experiment."

Combined with principal component analysis method, they successfully identified and analyzed the similar SERS spectrum of aldehyde gases with the sensor, indicating application value.

They further investigated the adsorption kinetics and thermodynamic process of benzaldehyde molecules on Co-Ni LDH with the sensor. The kinetic adsorption process could be fitted better by the pseudo-first-order kinetics with a higher correlation coefficient than by a pseudo-second-order model. The isotherm adsorption fits the Langmuir isotherm model, and its adsorption constant is 6.25 × 106 L/mol, indicating that the adsorption sites of the composites were homogeneous and dominated by monolayer chemisorption.

This study established a new measurement method for probing the adsorption process with extremely low consumption of both adsorbates and adsorbents, but also may lay the groundwork for the construction of rapid and ultra-sensitive SERS sensors for probing VOCs in the future.

This work was supported by the National Natural Science Foundation of China.

Figure. Schematic illustration of the synthetic route of AgNCs@Co-Ni LDH and procedure for the SERS detection of trace benzaldehyde. (Image by XU Di)