Nonstoichiometric Doping of La0.9FexSn1-xO3 Hollow Microspheres for an Ultrasensitive Formaldehyde Sensor.

Oxygen vacancies play an essential role in gas-sensitive materials, but the intrinsic oxides are poorly controlled and contain low oxygen vacancy concentrations. In this work, we prepared La0.9Fe1-xSnxO3 microspheres with high sensitivity and controllability by a simple hydrothermal method, and then, we demonstrated that it has many oxygen ion defects by X-ray photoelectron spectroscopy and electron paramagnetic resonance characterization. The gas sensor exhibited ultrahigh response, specific recognition of formaldehyde gas, and excellent moisture resistance. By comparing the composites with different doping ratios, it was found that the highest catalytic activity was reached when x = 0.75, and the response value of La0.9Fe0.75Sn0.25O3 hollow microspheres at 200 °C reached 73-10 ppm of formaldehyde, which is 188% higher than that of intrinsic LaFeO3 hollow microspheres. On the one hand, due to the absence of A-site La3+ and the replacement of B-site Fe3+ by Sn4+, a large number of oxygen vacancies are induced on the surface and in the interior of the materials; on the other hand, it is also related to the large specific surface area and gas channels caused by the particular structure.

Etching dopant elements to construct active-site-rich Mo2C for the hydrogen evolution reaction.

We propose a strategy to etch dopants to construct Mo2C with more unsaturated coordination of Mo atoms and lattice distortion for enhanced catalytic activity. It is more effective than doping and etching pure Mo2C and provides a novel strategy for the preparation of catalysts with high catalytic activity.

Pd-SnO2/In2O3 with a Unique Structure for the Ultrasensitive Detection of Triethylamine near Room Temperature.

Triethylamine (TEA) is a serious threat to people's health, and it is still a challenge to detect TEA at ppb level near room temperature (RT). Herein, we developed a simple, low-cost, low-temperature, and ultra-sensitive TEA sensor based on Pd-SnO2/In2O3 composites. First, SnO2 nanoparticles were obtained by the pyrolysis of Sn-MOF@SnO2 precursor (MOF: metal organic framework), and Pd-SnO2/In2O3 composites were prepared by further compounding and doping. The results show that the Pd-SnO2/In2O3 sensor is highly sensitive to TEA gas at near RT (at 60 °C, the sensor response to 10 ppm TEA is 12,000, the response/recovery (res/rec) time is 51 s/493 s, and at 30 °C, the response value also reaches 1380, the res/rec time is 66 s/610 s), along with good selectivity, stability, and moisture resistance. Even at 10 °C operating temperature and 75% relative humidity (RH) in a low-temperature and high-humidity environment, it still maintains a high sensitivity of over 1000 to 10 ppm TEA, which shows great application potential in TEA detection. The reason for the enhanced performance of the 0.5%Pd-SnO2/In2O3 sensor can be attributed to a large number of adsorbed oxygens on the unique structure of the material, the good charge transfer ability of the n-n-type heterojunction between SnO2 and In2O3, the chemical sensitization and electronic sensitization of Pd nanoparticles, and the catalytic spillover effect. This work will provide a new approach for preparing sensors with good comprehensive properties, making full use of the advantages of the material structure-activity relationship.

Ultrasensitive Formaldehyde Sensor Based on SnO2 with Rich Adsorbed Oxygen Derived from a Metal Organic Framework.

SnO2 has been a commonly researched gas-sensing material due to its low cost, good performance, and good stability. However, gas sensors based on pure SnO2 usually show a low response or high working temperature. In this work, laminar SnO2 was obtained by using a Sn-based metal organic framework(Sn-MOF)@SnO2 as a precursor. Sn-MOF@SnO2 is prepared at low temperatures using water and dimethylformamide as a solvent, which is simple, low cost, and easily reproducible. After sintering, Sn-MOF@SnO2 is derived to SnO2 with rich adsorbed oxygen, large specific surface area, and unique nanoparticle piled pores, thus showing excellent gas-sensing properties. The prepared SnO2 has an ultrahigh response value of 10,000 to 10 ppm formaldehyde at an optimal working temperature of 120 °C, a fast response/recovery time of 33 s/142 s, and an actual detection limit of lower than 10 ppb as well as high selectivity and high stability. Density functional theory calculations show that the exposed (110) plane of oxygen-rich vacancies in laminar SnO2 can effectively increase the coadsorption capacity of O2 and formaldehyde molecules, thereby improving the formaldehyde gas-sensing performance of the material. The present original approach paves the way to design advanced materials with excellent gas-sensing properties as well as broad application prospects in formaldehyde monitoring.