Photocatalytic degradation of the tire-derived chemical 1,3-diphenylguanidine in stormwater using a biochar-supported NZn doped TiO2 catalyst

The global challenge of declining raw water availability for potable and irrigation uses, especially in semi-arid areas, calls for alternative raw water sources such as urban stormwater. However, stormwater contains potentially harmful chemicals, such as tire rubber additives, that can threaten human and ecosystem health. This study investigated the use of a visible light-activated photocatalyst to degrade diphenylguanidine (DPG), a synthetic rubber additive commonly found in stormwater. The photocatalyst was a composite of nitrogen- and zinc-doped TiO 2 on phosphorus-treated canola straw biochar. This composite exhibited better photocatalytic activity than pristine TiO 2 , with enhanced visible-light absorption. The biochar provided a high surface area and adsorption capacity, preventing semiconductor agglomeration and reducing electron-hole recombination, thereby enhancing degradation efficiency. Adding 2 wt% nitrogen and zinc, respectively, and 10 wt% biochar increased the surface area to 213.2 m 2 /g (up from 144.6 m 2 /g for TiO 2 ). This increase led to inhibited TiO 2 crystal growth, improved photon absorption, and a reduction in the band-gap energy from 3.19 eV to 2.68 eV. Complete DPG degradation was achieved under visible light at pH 7, with an initial concentration of 250 μg/L, in 80 min. The findings confirm the synergistic effect of the catalyst and visible light. This composite material has strong potential for treating stormwater in real-world applications. This study highlights the value of innovative materials derived from renewable resources and powered by visible light to combat environmental pollution.