KIT-5-Assisted Synthesis of Mesoporous SnO2 for High-Performance Humidity Sensors with a Swift Response/Recovery Speed

Starch valorization: Direct conversion of starch to hexyl levulinate over SO4/ZrO2-KIT5 composite

Valorization of biomass for the synthesis of valuable chemicals is a promising toolbox for replacing fossil fuel consumption. Long-chain hexyl levulinate (HL) is one of the attractive high-value chemicals obtained from biomass valorization. The current paper investigates the synthesis of KIT5-supported SO4/ZrO2 and its application in the successive hydrolysis and dehydration of starch to HL. The acidity of the prepared catalyst was modified, and its effect on the conversion of starch and HL yield was thoroughly studied. The parameters effective on the reaction yield and selectivity were optimized, and the possibility of 5-((hexyloxy)methyl) furan-2-carbaldehyde formation was explored. The prepared SO4/ZrO2-KIT5 can be used at least in four successive runs with a slight decrease in its reactivity. The HL yield was increased to a maximum of 28 %, while the starch conversion increased to a maximum of 100 % by conducting the reactions at 220 °C for 10 h. The accessibility and low cost of the starting materials as well as the method's simplicity, can give a practical outlook of its possible industrial application.

Highly Selective and Fast Response/Recovery Cataluminescence Sensor Based on SnO2 for H2S Detection

In the present work, three kinds of nanosized SnO2 samples were successfully synthesized via a hydrothermal method with subsequent calcination at temperatures of 500 °C, 600 °C, and 700 °C. The morphology and structure of the as-prepared samples were characterized using X-ray diffraction, transmission electron microscopy, selected area electron diffraction, Brunauer-Emmett-Teller analysis, and X-ray photoelectron spectroscopy. The results clearly indicated that the SnO2 sample calcined at 600 °C had a higher amount of chemisorbed oxygen than the SnO2 samples calcined at 500 °C and 700 °C. Gas sensing investigations revealed that the cataluminescence (CTL) sensors based on the three SnO2 samples all exhibited high selectivity toward H2S, but the sensor based on SnO2-600 °C exhibited the highest response under the same conditions. At an operating temperature of 210 °C, the SnO2-600 °C sensor showed a good linear response to H2S in the concentration range of 20-420 ppm, with a detection limit of 8 ppm. The response and recovery times were 3.5 s/1.5 s for H2S gas within the linear range. The study on the sensing mechanism indicated that H2S was oxidized into excited states of SO2 by chemisorbed oxygen on the SnO2 surface, which was mainly responsible for CTL emission. The chemisorbed oxygen played an important role in the oxidation of H2S, and, as such, the reason for the SnO2-600 °C sensor showing the highest response could be ascribed to the highest amount of chemisorbed oxygen on its surface. The proposed SnO2-based gas sensor has great potential for the rapid monitoring of H2S.

Ultra-Sensitive and Fast Humidity Sensors Based on Direct Laser-Scribed Graphene Oxide/Carbon Nanotubes Composites

In this paper, the relative humidity sensor properties of graphene oxide (GO) and graphene oxide/multiwalled nanotubes (GO/MWNTs) composites have been investigated. Composite sensors were fabricated by direct laser scribing and characterized using UV-vis-NIR, Raman, Fourier transform infrared, and X-ray photoemission spectroscopies, electron scanning microscopy coupled with energy-dispersive X-ray analysis, and impedance spectroscopy (IS). These methods confirm the composite homogeneity and laser reduction of GO/MWNT with dominant GO characteristics, while ISresults analysis reveals the circuit model for rGO-GO-rGO structure and the effect of MWNT on the sensor properties. Although direct laser scribing of GO-based humidity sensor shows an outstanding response (|ΔZ|/|Z| up to 638,800%), a lack of stability and repeatability has been observed. GO/MWNT-based humidity sensors are more conductive than GO sensors and relatively less sensitive (|ΔZ|/|Z| = 163,000%). However, they are more stable in harsh humid conditions, repeatable, and reproducible even after several years of shelf-life. In addition, they have fast response/recovery times of 10.7 s and 9.3 s and an ultra-fast response time of 61 ms when abrupt humidification/dehumidification is applied by respiration. All carbon-based sensors' overall properties confirm the advantage of introducing the GO/MWNT hybrid and laser direct writing to produce stable structures and sensors.