Microfluidically synthesized Au, Pd and AuPd nanoparticles supported on SnO2 for gas sensing applications

Abstract

Monometallic Au and Pd nanoparticles (NPs) and homogeneous AuPd nanoalloy particles were synthesized in a continuous flow of reactants (HAuCl4, K2PdCl4, NaBH4 and polyvinylpyrrolidone (PVP)) using a microfluidic reactor with efficient micromixers. The obtained ultrasmall NPs were subsequently deposited onto SnO2 supports with different surface area (32.7 and 3.6 m 2 g-1). Samples with 1.0 and 0.1 wt.% metal loading were prepared. After calcination at 380 °C for 1 h the supported NPs aggregated to some extent. SnO2 supported AuPd nanoalloys with low (0.1 wt.%) metal loadings showed the smallest NP diameters (~ 5-7 nm) and the narrowest size distribution among the samples. The gas sensing performance of the materials was investigated at 300 °C in four different gas atmospheres containing either CO, CH4, ethanol or toluene using dry and humid conditions. They exhibited a distinct variation in the response patterns and selectivity toward the test gases depending on composition and metal loading: Au increased the sensor signals compared to pristine SnO2 in all cases and decreased the interference of water vapor; the supported Pd NPs showed a weak response to toluene, strong sensitivity in CO sensing and slightly better response in ethanol sensing in humid air compared to dry air. However, they showed a high selectivity toward CH4 when used in dry air; AuPd alloy particles provided lower sensor signals compared to pristine SnO2 and no remarkable CH4 selectivity, in contrast to the Pd system. Operando diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS) indicates a strong band bending in the case of Pd and AuPd NPs, whereas in the case of Au no band bending occured, indicating a strong electronic interaction between the support and Pd-containing NPs (Fermi-level control mechanism), and a weak electronic interaction between SnO2 and Au NPs (spill-over mechanism).

Hollow WO3/SnO2 Hetero-Nanofibers: Controlled Synthesis and High Efficiency of Acetone Vapor Detection

“…Finally, in Figure 5D, W 4f in the WO 3 /SnO 2 (0.3%) composite gives a spin orbital dipole with two binding energies of 36.38 and 38.48 eV, respectively. The calculation results show that the spin orbit jet energy is 2.1 eV, which reaches a similar agreement with the theoretical calculation value (Nayak et al, 2015; Bai et al, 2016; Tofighi et al, 2019). According to the XPS results, interaction with the decoration of WO 3 is clearly witnessed, leading to the modification of the chemical state of the WO 3 /SnO 2 (0.3%) composite.…”

Acetone Sensing and Catalytic Conversion by Pd-Loaded SnO2

“…In particular, temperature effects on sensing are not always thoroughly investigated in sensor development. Often, the crystal size and composition as well as the noble metal loading are varied to optimize the performance of the sensor while operating it at a fixed temperature (typically between 300 and 400 • C) [12]. Only after this optimization, usually, the performance of the best sensor composition is evaluated at different operating temperatures, yielding the ideal one, typically close to the initial temperature [13].…”

Sensor Micro and Nanoparticles for Microfluidic Application

“…In the presence of metallic nanoparticles on the sensor surface, chemical reactions of the gas are affected by gas activation on the nanoparticle surface [63]. G. Tofighi et al [64] presented a one-step microfluidic synthesis of colloidal nanoparticles that were deposited onto the SnO 2 surface for gas sensing. Monodisperse nanocolloids of gold (Au), palladium (Pd) and homogeneous AuPd nanoparticles in aqueous suspension were produced in a continuous flow microfluidic reactor by using aqueous solution of metal precursors (HAuCl 4 , K 2 PdCl 4 ) with polyvinylpyrrolidone (PVP)) and NaBH 4 with PVP solution as the reducing agent.…”