Effect of physical properties of construction wastes based composite photocatalysts on the sulfur dioxide degradation: Experimental investigation and mechanism analysis

The reducing, reusing, and recycling of construction and demolition wastes (C&DWs) is an imperative aspect of sustainable development. Recycled aggregates (RAs) originated from C&DWs therefrom are applied to the field of building materials for preparing new constructions. The study herein aims to by the photocatalytic technology endow RAs with the photocatalysis and by that achieves the upcycling of RAs with high-added value. Three typical types of RAs were used, which are respectively recycled clay brick sands (RCBS), recycled glass sands (RGS), and recycled fine concrete aggregates (RFA). The sulfur dioxide was identified as the target pollutant; whilst the degradation of sulfur dioxide was the specific embodiment of the photocatalytic performance. RAs were used as carriers to load and absorb nanoscale titanium dioxide (NT), preparing composite photocatalysts (CPs). The CPs were subsequently used as fine aggregates in substituting natural fine aggregates, resulting in the photocatalytic mortar. The particle size of RCBS, the color of RGS, and the origin of RFA were identified as emblematic characteristics that affected the photocatalytic performance of produced photocatalytic mortar. Results unveiled that: (1) RCBS with a smaller particle size absorbs more NT and possesses a higher sulfur dioxide degradation; whilst the utility of per gram NT of 2.36–4.75 mm RCBS is c.a. 2 times than that of 0.6–1.18 mm RCBS. (2) RGS that is black has the lowest sulfur dioxide degradation; whilst the RGS that is transparent has the highest value. RGS with other colors at varying extents exhibited a reduced degradation, with no discernible rules to follow. (3) RFA derived from recycled concrete with normal strength has a better performance. The paper at the end also in an attempt probed into the enhancement mechanisms of photocatalytic efficiency triggered by RA-based CPs.