Thermally Controlled Benzene Sorption Using PDMS-Infused Macroporous Silicon Matrices

Exposure to benzene, toluene, ethylbenzene, and xylene (BTEX) presents substantial health risks. Among BTEX, benzene poses health risks at much lower concentrations, underscoring the need for sensors capable of detecting it at trace levels. Existing small and portable sensor technologies cannot selectively distinguish between molecularly similar gases, such as BTEX, highlighting the need for the development of cost-effective, selective, and sensitive sensors. Gas preconcentration can improve sensitivity and, in some cases, selectivity, particularly when a preconcentrator is engineered to maintain a uniform temperature within the sorbent, enabling precise sorption control and enhancing sensor performance during volatile organic compound (VOC) desorption. However, preconcentrator materials suffer from poor thermal conductivity, limiting their ability to achieve homogeneous heating especially when dynamic temperature changes are required. This study presents a composite macroporous silicon (Si)-polydimethylsiloxane (PDMS) preconcentrator, where the Si matrix encloses PDMS and thus facilitates homogeneous temperature distribution of the sorbent. Utilizing a photoionization detector (PID) to measure benzene, macroporous Si-PDMS preconcentrators with pore diameters of 1, 2, 5, and 8 μm were evaluated against two controls: a thin layer of equivalent mass PDMS on Si, and a 525 μm thick PDMS sample. The thin PDMS on Si exhibits the highest desorption peak heights due to enhanced gas diffusion flux through the sorbent, whereas the 1 μm macroporous Si-PDMS preconcentrator exhibits the sharpest thermal desorption peaks across all concentrations, ramp rates, and adsorption times, indicating rapid attainment of homogeneous temperature of the PDMS sorbent. These findings support the potential of macroporous Si-PDMS composites as practical preconcentrators for low-cost VOC sensors.