No abstract

Volatile organic compounds (VOCs) exert a serious impact on the environment and human health. The development of new technologies for the elimination of VOCs, especially those from non-industrial emission sources, such as indoor air pollution and other low-concentration VOCs exhaust gases, is essential for improving environmental quality and human health. In this study, a monolithic photothermocatalyst was prepared by stabilizing manganese oxide on multi-porous carbon spheres to facilitate the elimination of formaldehyde (HCHO). This catalyst exhibited excellent photothermal synergistic performance. Therefore, by harvesting only visible light, the catalyst could spontaneously heat up its surface to achieve a thermal catalytic oxidation state suitable for eliminating HCHO. We found that the surface temperature of the catalyst could reach to up 93.8 °C under visible light, achieving an 87.5% HCHO removal efficiency when the initial concentration of HCHO was 160 ppm. The microporous structure on the surface of the carbon spheres not only increased the specific surface area and loading capacity of manganese oxide but also increased their photothermal efficiency, allowing them to reach a temperature high enough for MnOx to overcome the activation energy required for HCHO oxidation. The relevant catalyst characteristics were analyzed using XRD, measurement of BET surface area, scanning electron microscopy, HR-TEM, XPS, and DRS. Results obtained from a cyclic performance test indicated high stability and potential application of the MnOx-modified multi-porous carbon sphere.

Mason pine-derived hydrochar (MPHC), cedarwood-derived hydrochar (CHC), bamboo-derived hydrochar (BHC), coconut shell-derived hydrochar (CSHC), pecan shell-derived hydrochar (PSHC), wheat straw-derived hydrochar (WSHC), maize straw-derived hydrochar (MSHC), and rice straw-derived hydrochar (RSHC) were synthesized by hydrothermal carbonization (HTC). The physicochemical properties of these hydrochars were characterized by various techniques, and the adsorption behavior of methylene blue (MB) on hydrochars from an aqueous solution was also investigated. The characterization results suggested that the hydrochars possessed various oxygen-containing functional groups (e.g., ether and hydroxyl groups, etc.). Thermodynamic parameters demonstrated that adsorption was spontaneous for all produced hydrochars. The adsorption was endothermic for CHC, BHC, CSHC, PSHC, WSHC, MSHC, RSHC, and exothermic for MPHC. The Langmuir model best described the adsorption process. MB adsorption capacity is ranked as MPHC > PSHC > CSHC > CHC > MSHC> WSHC > RSHC > BHC. The saturated adsorption value for MB on these hydrochars at 15 ℃ was 155. 14, 109.24, 93.15, 91.71, 88.11, 86.36, 70.01, and 64.43 mg/g, respectively; the difference in adsorption value indicates that the type of biomass affects MB adsorption. This high adsorption capacity for MB suggests that the produced hydrochars could be utilized as a promising new adsorbent in wastewater treatment.