Oxygen-plasma-assisted formaldehyde adsorption mechanism of SnO2 electrospun fibers

Abstract: Chemisorbed oxygen acts a crucial role in the redox reaction of semiconductor gas sensors, and which is of great significance for improving gas sensing performance. In this study, an oxygen-plasma-assisted technology is presented to enhance the chemisorbed oxygen for improving the formaldehyde sensing performance of SnO2 electropun fiber. An inductively coupled plasma device was used for oxygen plasma treatment of SnO2 electrospun fibers. The surface of SnO2 electrospun fibers was bombarded with high-energy oxygen plasma for facilitating the chemisorption of electronegative oxygen molecules on the SnO2 (110) surface to obtain an oxygen-rich structure. Oxygen-plasma-assisted SnO2 electrospun fibers exhibited excellent formaldehyde sensing performance. The formaldehyde adsorption mechanism of oxygen-rich SnO2 was investigated using density functional theory. After oxygen plasma modification, the adsorption energy and the charge transfer number of formaldehyde to SnO2 were increased significantly. And an unoccupied electronic state appeared in the SnO2 band structure, which could enhance the formaldehyde adsorption ability of SnO2. The gas sensing test revealed that plasma-treated SnO2 electrospun fibers exhibited excellent gas sensing properties to formaldehyde, low operating temperature, high response sensitivity, and considerable cross-selectivity. Thus, plasma modification is a simple and effective method to improve the gas sensing performance of sensors.

Research Progress of Adsorption and Photocatalysis of Formaldehyde on TiO2/AC

Based on the increasingly serious formaldehyde pollution, effective degradation of formaldehyde has become a practical problem that humans urgently need to solve. Among many treatment methods, activated carbon has the advantages of large specific surface area, high adsorption efficiency, and uniform pore size distribution. As a kind of clean photocatalytic material for formaldehyde degradation, titanium dioxide supported by activated carbon has become a research hotspot to develop adsorption-catalytic materials for formaldehyde degradation. In this paper, the research progress of activated carbon and its modification, the photocatalytic principle and modification of titanium dioxide, and TiO2/AC materials are reviewed. The results show that the pore size distribution gradient and acidic oxygen-containing functional groups of activated carbon play key roles in the formaldehyde adsorption process. TiO2 doped with metal ions and nonmetal ions can significantly improve the photocatalytic activity. The TiO2/AC material can greatly improve the photocatalytic rate and achieve the technical goal of efficient and clean degradation for formaldehyde.

Mechanical and Adsorptive Properties of Foamed EVA-Modified Polypropylene/Bamboo Charcoal Composites

Due to its excellent adsorption and humidity control function, bamboo charcoal (BC) has often been mixed with polypropylene (PP) to produce PP/BC composites for interior paneling applications. However, due to the poor foaming quality of PP, PP/BC composites suffer as a result of their high density, which limits their scope of use. Here, to improve its foaming quality, PP was modified with ethylene vinyl acetate (EVA), and then the EVA-modified PP (E-PP) was mixed with different contents of BC (0 wt.%–50 wt.%), as well as foaming agent (Azodicarbonamide, AC) and its auxiliaries (ZnO, Znst), in a twin-screw extruder, followed by hot-pressing at high temperature to obtain foamed E-PP/BC composites. The resulting composites showed good porosity and pore distribution with an increase of BC content by up to 20%. Further increase in the BC content seemed to cause the foaming performance to decrease significantly. The product density and adsorption rate increased, while the mechanical strength decreased with increasing BC content. At a BC content of 40 wt.%, the foamed E-PP/BC composite showed the best combined performance, with a density of 0.90 g/cm3, 24-h formaldehyde adsorption rate of 0.48, and bending strength of 11.59 MPa.

Investigation of Formaldehyde Adsorption on Carbon Nanotubes by Density Functional Theory

Background: Formaldehyde (HCOH) is the most abundant airborne carbonyl indoor volatile organic compound (VOC), which is well-known to cause serious health effects such as respiratory system disease, immune system disorders, and central nervous system damage. Methods: The interaction between HCOH and intrinsic, congeners of Au, Ag, Cu-doped SWCNTs were investigated by density functional theory (DFT) to evaluate the detection of formaldehyde. Results: The results demonstrated that the less adsorption on the surface of intrinsic SWCNT, an HCOH molecule tended to be chemisorbed to the Au, Ag, and Cu atoms of doped SWCNT with larger binding energy of 0.4-0.8 eV and smaller binding distance of 1.9-2.3 Å. Furthermore, charge transfer and density of state studies indicated tha t the electronic properties changed evidently in the most stable HCOH-doped SWCNT systems, mainly at the region of -5.5 to -4.5 eV and Fermi level. Conclusion: More importantly, the adsorption of HCOH affected the electronic conductance of doped SWCNT. It is expected that the results obtained in this study could provide a useful theoretical guidance for the investigation of molecular films interface bonding and design of HCOH sensing devices.