Bimetallic Au and Pd Nanoparticles Modified WO3 Nanosheets for Enhancing the Sensitivity and Selectivity of Formaldehyde Assessment in Aquatic Products.

Formaldehyde, a common illegal additive in aquatic products, poses a threat to people's health and lives. In this study, a novel metal oxide semiconductor gas sensor based on AuPd-modified WO3 nanosheets (NSs) had been developed for the highly efficient detection of formaldehyde. WO3 NS modified with 2.0% AuPd nanoparticles showed a higher response (Ra/Rg = 94.2) to 50 ppm of formaldehyde at 210 °C, which was 36 times more than the pristine WO3 NS. In addition, the AuPd/WO3 gas sensor had a relatively short response/recovery time of 10 s/9 s for 50 ppm of formaldehyde at 210 °C, with good immunity to other interfering gases and good stability for formaldehyde. The excellent gas-sensitive performance was attributed to the chemical sensitization of Au, the electronic sensitization of Pd, and the synergistic effect of bimetallic AuPd, which facilitated the recognition and response of formaldehyde molecules. Additionally, the high sensitivity and broad application prospect of the 2.0% AuPd/WO3 NS composite-based sensor in real sample detection were also confirmed by using the above sensor for the detection of formaldehyde in aquatic products such as squid and shrimp.

Robust Trajectory Tracking Control for Continuous-Time Nonlinear Systems with State Constraints and Uncertain Disturbances.

In this paper, a robust trajectory tracking control method with state constraints and uncertain disturbances on the ground of adaptive dynamic programming (ADP) is proposed for nonlinear systems. Firstly, the augmented system consists of the tracking error and the reference trajectory, and the tracking control problems with uncertain disturbances is described as the problem of robust control adjustment. In addition, considering the nominal system of the augmented system, the guaranteed cost tracking control problem is transformed into the optimal control problem by using the discount coefficient in the nominal system. A new safe Hamilton-Jacobi-Bellman (HJB) equation is proposed by combining the cost function with the control barrier function (CBF), so that the behavior of violating the safety regulations for the system states will be punished. In order to solve the new safe HJB equation, a critic neural network (NN) is used to approximate the solution of the safe HJB equation. According to the Lyapunov stability theory, in the case of state constraints and uncertain disturbances, the system states and the parameters of the critic neural network are guaranteed to be uniformly ultimately bounded (UUB). At the end of this paper, the feasibility of the proposed method is verified by a simulation example.

Bimetallic Au@Pt Nanocrystal Sensitization Mesoporous α-Fe2O3 Hollow Nanocubes for Highly Sensitive and Rapid Detection of Fish Freshness at Low Temperature.

In this work, we present a new metal oxide semiconductor gas sensor for detecting trimethylamine (TMA) by bimetal Au@Pt-modified α-Fe2O3 hollow nanocubes (NCs) as sensing materials. The structure and morphological characteristics of Au@Pt/α-Fe2O3 were evaluated through multiple analyses, and their gas-sensitive performance was investigated. Compared with the pristine α-Fe2O3 NC sensor, the sensor based on Au@Pt/α-Fe2O3 NCs exhibited faster response time (5 s) and higher response (Ra/Rg = 32) toward 100 ppm TMA gas at a lower temperature (150 °C). Furthermore, we also assessed the Au@Pt/α-Fe2O3 NC sensor for detecting the freshness of Larimichthys crocea which have been observed by headspace solid-phase microextraction and gas chromatography-mass spectrometry. The high performance of the Au@Pt/α-Fe2O3 NCs is attributed to the special hollow morphology with a high specific surface area (212.9 m2/g) and the synergistic effect of the Au@Pt bimetal. The Au@Pt/α-Fe2O3 sensor shows promising application prospects in estimating seafood freshness on the spot.