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.

The fiber length has a significant impact on the fiber bridging capacity and the mechanical properties of high ductility cementitious composites (HDCCs), which is related to fiber/matrix interfacial bonding. However, this fundamental knowledge of HDCCs design has rarely been investigated systematically. To this end, this study deeply investigates the effect of the fiber length on the bridging stress and the complementary energy with various fiber/matrix interfacial bonds in theory. Then, the mechanical performances of HDCCs with various fiber lengths and compressive strengths were evaluated experimentally. In micromechanical design, longer fibers can achieve stronger bridging stress and more sufficient complementary energy regardless of the fiber/matrix interfacial bonding properties. However, it should be noted that the increase in bridging capacity was quite slow for the overlong fibers and excessive interfacial bonding. The experiments indicated that overlong fibers (18 mm and 24 mm) easily twined on the mixer blade and were hard to disperse evenly. The HDCCs with shorter fibers displayed better workability. The compressive strength was less affected by the fiber length, and most striking differences were less than 5.0%, while the flexural properties and the tensile properties first increased and then decreased when the fiber length ranged from 6 mm to 24 mm. Consequently, the fibers with lengths of 9 mm and the fibers with lengths of 12 mm were better candidates for the HDCCs with compressive strengths of 30 MPa to 80 MPa, and fibers with lengths of 9 mm caused the HDCCs to exhibit higher ductility properties in general.

Modified micromechanical bridging model is established with consideration of the fiber rupture effect at debonding and slipping stages. The bridging model includes the debonding and slipping rupture of fibers and establishes the fiber/matrix interfacial parameters (friction τ 0 , chemical bonding force G d , slip-hardening coefficient β ). A different interfacial bonding can cause fiber rupture. The influence of the interfacial conditions on the fiber rupture risk was investigated. In the modified bridging model, the effective bridging stress, the debonding rupture stress, and the slipping rupture stress were clearly identified. Finally, single-fiber pullout tests with different embedded lengths were carried out to validate the bridging model. The relationship between the fiber bridging stress and the crack opening predicted by the bridging model was consistent with the experimental results. This modified micromechanical bridging model can be used to quantitatively calculate the actual fiber bridging capacity and to predict the ductility of the high ductility cementitious composites reinforced by different types of fibers.