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The graphitic carbon nitride (g-C3N4) is regarded as a powerful support for constructing heterojunction. How to rationally design high-performance g-C3N4-based heterojunction remains a great challenge. In this work, a kind of spatial distribution heterojunction is prepared by in situ growing ZnIn2S4 (ZIS) nanosheets on g-C3N4 microtubes (T-CN). To highlight the advantage of such a structure design, g-C3N4 bulk (B-CN) and g-C3N4 nanosheets (S-CN) are also used as the supports to obtain B-CN/ZIS bulk heterojunction and S-CN/ZIS 2D/2D heterojunction, respectively. T-CN/ZIS spatial distribution heterojunction combines the hierarchical core/shell structure of B-CN/ZIS and ultrathin structure of S-CN/ZIS, which is much favorable for photocatalytic CO2 reduction. It is found that the gas yield from CO2 reduction is highest over T-CN/ZIS, which is 3.5 and 1.5 times higher than B-CN/ZIS and S-CN/ZIS. The experimental results manifest that the spatial distribution of ZIS nanosheets on T-CN induces stronger photoabsorption, faster interfacial charge transfer, and larger CO2 adsorption, all of which are responsible for the best catalytic activity. It is expected that this work will provide an instructive guideline for designing g-C3N4-based heterojunction.

Polluted water and exhaust gas released from industrial activities cause a series of environmental issues such as heavy metals accumulation and greenhouse effect. Here, we have proposed an “adsorbent-to-photocatalyst” conversion strategy to bridge water remediation with photocatalytic CO2 reduction. Harmful heavy metals in polluted water are removed and collected by adsorbents, which are converted into valuable photocatalysts for CO2 reduction without secondary treatment. Calcium silicate hydrate (CSH) nanosheets are prepared as an ideal “bridge”. Their ultrathin thickness (2.8 nm), ultrahigh surface area (637.2 m2 g−1), and abundant surface hydroxyls are much favorable for both heavy metals removal and photocatalysis processes. Four typical heavy metals including Cu2+, Zn2+, Ni2+, and Pb2+ are selected for studies. Interestingly enough, in the case of Ni2+ removal, CSH nanosheets undergo phase change and they are spontaneously converted into a new semiconductor nickel silicate hydroxide. The nickel silicate hydroxide has a suitable energy level for reducing CO2 into CO. And its strong CO2 adsorption and abundant exposed Ni2+ sites contribute to efficient and selective photocatalytic CO2 reduction. The CO yield is up to 1.71 × 104 μmol g−1 h−1 with 99.2% selectivity under visible light.

The present work investigated the effects of the thermal cycles in air on the tensile properties of a 2.5 dimensional carbon fiber reinforced silicon carbide composite (2.5D-C/SiC) in weft and warp direction, prepared by low-pressure chemical vapor infiltration. The composite was exposed to different thermal cycles between 900 °C and 300 °C in air. The fracture morphologies of the failed composite were examined by a scanning electron microscope to investigate the underlying damage mechanisms. It is found that the composite can retain its tensile strength within 40 thermal cycles. Comparatively, the modulus of 2.5D-C/SiC decreases with increasing thermal cycles. Extensive pullout of fibers on the fractured surface and interface debonding suggest that the damage caused by the thermal cycles involves weakening of the bonding strength of coating/composite and fiber/matrix. The above damage supply the channel for the oxidation of PyC and carbon fibers in the composites.In addition, the degradation in warp direction is faster than that in weft direction.

To reveal the shear properties of SiC matrix composites, interlaminar shear strength (ILSS) of three kinds of silicon carbide matrix composites was investigated by compression of the double notched shear specimen (DNS) at 900 °C in air. The investigated composites included a woven plain carbon fiber reinforced silicon carbide composite (2D-C/SiC), a two-and-a-half-dimensional carbon fiber-reinforced silicon carbide composite (2.5D-C/SiC) and a woven plain silicon carbon fiber reinforced silicon carbide composite (2D-SiC/SiC). A scanning electron microscope was employed to observe the microstructure and fracture morphologies. It can be found that the fiber type and reinforcement architecture have significant impacts on the ILSS of the SiC matrix composites. Great anisotropy of ILSS can be found for 2.5D-C/SiC because of the different fracture resistance of the warp fibers. Larger ILSS can be obtained when the specimens was loaded along the weft direction. In addition, the SiC fibers could enhance the ILSS, compared with carbon fibers. The improvement is attributed to the higher oxidation resistance of SiC fibers and the similar thermal expansion coefficients between the matrix and the fibers.

The tension –tension fatigue properties were investigated for a 2.5D-C/SiC composite in warp and weft direction. The fatigue experiments were carried out at room temperature (RT) and 900 C in laboratory air. The tensile properties of the specimens survived 10 6 cycles were determined to explore the damage mechanisms. The fracture surfaces were examined by a scannin g electron mic roscope. The composite exhib its excellent fatigue resistance at RT. The fatigue limits in both directions are about 85% of the ultimate tensile strength. The tensile stren gth and failure strain of the C/SiC can be enhanced for the survived comp osite at RT. The fatigue limits of the composite at 900 C are much lower than those at RT in both directions . Examination of the fracture surfaces revealed that the failure is closely related to the propagation of the cracks originated from the crossover of the bundles and produc ed within the bundles. The cracks also offered the chan nels for the oxygen to penetrate into the composite and are responsible for the oxidization of the carbon fibers in the composite. The oxidization of the fibers plays a critical key role in decreasing the fatigue limits at 900 C.