Large-Scale Nanofiber Manufacturing| Bilayer cascade of WO: nanofbers/Ag@CeO, nanosheetsfor ppb-level xylene detection under the catalysis-gassensitivity synergistic mechanism

Prof. Wang Ding & Assoc. Prof. Li Huijun from University of Shanghai for Science and Technology: Bilayer Cascade WO3 Nanofibers/Ag@CeO2 Nanosheets for ppb-Level Xylene Detection

Benzene series (BTEX) refers to benzene and its derivatives, including toluene, ethylbenzene, xylene and other highly toxic aromatic volatile organic compounds. Xylene has been classified as a Group 3 carcinogen by the International Agency for Research on Cancer (IARC). Short-term exposure to high concentrations of xylene may cause central nervous system depression, mild dizziness, nausea, chest tightness and fatigue, and in severe cases may lead to coma or even death due to respiratory and circulatory failure. Therefore, rapid, efficient and accurate detection of xylene at ppb levels is of great significance in health, environmental protection and medical fields.

Recently, Prof. Wang Ding and Assoc. Prof. Li Huijun's team from University of Shanghai for Science and Technology published their latest research "Bilayer cascade of WO3 nanofibers/Ag@CeO2 nanosheets for ppb-levels xylene detection under the catalysis-gas sensitivity synergistic mechanism" in the journal Rare Metals. The researchers prepared WO3 nanofibers by electrospinning as the bottom gas-sensing layer. The effects of reaction temperature, reaction time, Ag doping amount and acetic acid content on the morphological evolution of Ag@Ce-BDC were investigated to explore its growth and morphology control mechanism.The constructed WO3/Ag@CeO2 bilayer sensor exhibited excellent gas-sensing performance, showing a response value of 32.13 to 10 ppm xylene gas at an operating temperature of 160°C. Additionally, the sensor's detection limit for xylene was as low as 1 ppb, highlighting its great potential in detecting trace xylene gas.

Figure 1: Schematic of synthesis process and morphology analysis of Ag@Ce-BDC and Ag@CeO2 nanosheets

SEM was used to study the effect of Ag ion addition on morphology. The results showed that as Ag doping increased, Ce-BDC transformed from initial nanoplate morphology to nanoflower morphology assembled by nanosheets (1.5%). When Ag doping was excessive (7%), the nanoflowers gradually disintegrated. After calcination, Ag@CeO2 nanomaterials maintained their original morphology.

Figure 2: Gas-sensing performance of WO3 NFs, WO3/CeO2 and WO3/Ag@CeO2 gas sensors

Figure 2A confirmed that the WO3/1.5%Ag@CeO2 sensor showed the highest sensitivity to 5 ppm xylene at 160°C, reaching 32.13. The sensor demonstrated good cycling stability, fast response/recovery time (80/17.7 s) and low detection limit (1 ppb). Furthermore, while the WO3 NF sensor showed comparable responses to acetone and benzene, the bilayer WO3/CeO2 and WO3/(0.5%-3%)Ag@CeO2 sensors exhibited distinct selectivity for BTEX.

Figure 3: Gas sensing mechanism analysis of WO3/Ag@CeO2 bilayer gas sensor

The gas-sensing characteristics of the bilayer gas sensor are attributed to the synergistic effect between catalysis and gas sensitivity, achieved by separating the gas-sensing layer (bottom) from the catalytic overlayer (top) (Figure 3A). To verify the catalytic-induced sensing mechanism, online mass spectrometry analysis was employed. The results showed that xylene molecules could be catalytically cleaved by Ag@CeO2 at 160°C into two radicals: toluene radical (m/z = 92) and methyl radical (m/z = 15).It is well known that BTEX with benzene rings are stable, while other interfering gases are more reactive. Interestingly, non-aromatic interfering gases are completely oxidized to inactive substances (CO2 and H2O) when passing through the CeO2 overlayer, while low-activity BTEX gases are not completely oxidized when passing through the CeO2 overlayer, resulting in the high selectivity of the bilayer sensor.To verify the hypothesized mechanism, experiments were conducted on the xylene catalytic performance of 1.5%Ag@CeO2 nanomaterials. As shown in Figure 3D, at 160°C, both xylene conversion rate and CO2 production were at low levels, indicating that the more stable xylene was not completely oxidized at this operating temperature.

Paper Link: https://doi.org/10.1007/s12598-025-03286-y