New S-g-C3N4 based photocatalytic mortar with long-term photocatalytic performance by constructing three-dimensional structure Mg-Al layered double hydroxides

The weak long-term photocatalytic performance of photocatalytic cementitious materials under real-life service conditions has always been one of the main factors restricting their large-scale application. A novel stable three-dimensional structure of S-g-C3N4/MgAl-LDH was constructed by composing S-g-C3N4 with MgAl-LDH, aiming to improve its compatibility with cement mortar to achieve ideal long-term photocatalytic performance under natural exposure. Taking S-g-C3N4 as reference, the possible contributions of MgAl-LDH on improving the mechanical strength and long-term photocatalytic performance of mortar was analyzed by XRD, TG/DTG, SEM-EDX and isothermal calorimetry. The result shows that since the high specific surface area and refinement of MgAl-LDH, the dense surface morphology and fewer surface defects jointly promote the improvement of strength. When the content of S-g-C3N4/MgAl-LDH is 6 %, the 28d compressive strength of composite mortar is excellent, which is 28.7 % higher than the pure cement mortar. More importantly, under the stimulation of the calcium-rich layer on the surface of S-g-C3N4/MgAl-LDH, the accumulation of a large amount of gelling hydration products is beneficial to the stable long-term photocatalytic performance of S-g-C3N4/MgAl-LDH doped mortar. After 180 days of natural exposure, the NOx removal rate of the CMSL-8 % sample can still remain at 68.3 % of the original value (328 μmol·m−2·h−1). This research provides a new theoretical basis for photocatalytic cementitious materials to achieve ideal long-term photocatalytic performance.