Sulfur Dioxide Degradation by Composite Photocatalysts Prepared by Recycled Fine Aggregates and Nanoscale Titanium Dioxide

Abstract

To alleviate the heavy burden on landfilling, construction and demolition wastes (C&DWs) are recycled and reused as aggregates in cementitious materials. However, the inherent characteristics of recycled fine aggregates (RFA), such as the high crushing index and high-water absorption, magnify the reusing difficulty. Nevertheless, attributing to the high porosity and high level of calcium hydroxides existing in the old mortar, RFA is featured with a high specific surface area and a high alkalinity. These features are useful to augment the total photo-degradation of SO2 by nano-TiO2 (NT) intermixed mortar, leading RFA to be an excellent potential carrier to load nano-TiO2 and prepare the composite photocatalyst. Hence, this study proposed to load NT onto the surface of RFAs and river sands (RSs) (the control) by the soaking method, preparing composite photocatalysts denoted as NT@RFA and NT@RS, respectively. The prepared composite photocatalysts were then utilized as sands in photocatalytic mortar to evaluate for SO2 degradation. Experiments identified a 50% higher amount of NT was loaded onto the surface of FRA relative to the control. This higher loading amount plus higher alkalinity ultimately translated into a higher photocatalytic activity. In addition, the mortar containing NT@RFA exhibited 46.3% higher physiochemical absorption and 23.9% higher photocatalytic activity than that containing NT@RS. In addition, the durability, embodied by the reuse and anti-abrasive properties, of NT@RFA exceeded that of NT@RS. The overall findings reveal that the NT@RFA not only garners beneficial effect from the high porosity but also generates positive effect from the high alkalinity. Though a number of studies deal with building materials with NT, this study is the first to load NT onto RFA and prepare composite photocatalysts which were then used as fine aggregates in building materials. Consequently, this study proves the potential high-added-value reusability of RFA in green construction materials and provides a low-cost, high-efficiency approach to degrade atmospheric SO2.

Experimental Investigation and Modeling of the Sulfur Dioxide Abatement of Photocatalytic Mortar Containing Construction Wastes Pre-Treated by Nano TiO2

“…The result was the average plus the standard deviation of three parallel samples. Two approaches are commonly available to calculate the sulfur dioxide removal, as shown in Equations ( 6) and (7). The relationship between R and r is plotted in Figure 4.…”

“…Some researchers have attempted to crush and sieve RCs into recycled concrete aggregates (RCA) for the preparation of new concrete [2][3][4] and think of new approaches to raise the added value of RCAs, particularly recycled fine aggregates (RFA) that have a grading size of less than 5 mm. Relative to natural fine aggregates, RFAs have two main features of high porosity [5] and high alkalinity [6,7]. The former is attributed to micro cracks brought about by the mechanical crushing process; whilst the latter originates from calcium hydroxide [Ca(OH)2] that exists in the old mortar attached to the surface of virgin aggregates.…”

Oxidative Desulfurization of Petroleum Distillate Fractions Using Manganese Dioxide Supported on Magnetic Reduced Graphene Oxide as Catalyst

“…Each of these catalytic ODS systems follows different oxidation mechanisms of sulfur compounds [ 18 ]. Sulfur removal has also been investigated by photooxidation using various photocatalysts [ 19 , 20 ].…”

Enhancing Functionality of Epoxy–TiO2-Embedded High-Strength Lightweight Aggregates

“…For instance, TiO 2 , a representative photocatalytic material, was applied to LWAs to impart NO x and SO x reduction functionality [ 11 , 12 , 13 , 14 , 15 ]. It is well known that TiO 2 is superior to other photocatalytic materials, such as ZnO, SnO 2 , Fe 2 O 3 , CuO, NiO, and CeO 2 , in its ability to remove NO x and SO x by the photo-decomposition principle under UV light irradiation [ 16 , 17 ]. In addition, the enhanced photodegradation performance of a cement-based composite by controlling the content of TiO 2 in the cement-based composite [ 18 ], the impregnation and coating of sodium silicate on LWAs to provide self-healing properties [ 19 ], the improved skid-resistance of LWAs by controlling aggregate morphology through micro-surfacing [ 20 ], the hydrophobicity control of LWAs modified with sewage sludge [ 21 ], and the embedment of phase change materials into LWAs to improve thermal energy storage characteristics and reduce damage mitigation [ 9 , 22 ] have been studied.…”