Chamorn Chawengkijwanich

This study explored the influence of high silver (Ag) loading (5–10 mol%) on the photocatalytic performance of zirconium (Zr) co-doped TiO₂ (AZT) with a low Zr content. Although various Ag/Zr ratios have been reported, the effect of high Ag loading combined with low Zr content remains largely unrevealed, particularly in low-temperature synthesis where the role of Zr as a phase inhibitor is less critical. To address this gap, the AZT photocatalyst was fabricated via a solvothermal method combined with organic-free peroxy route. Characterization indicated Zr⁴⁺ incorporated into the TiO₂ lattice, inducing structural distortions and promoting Ti³⁺ defect states. Simultaneously, silver existed as ternary Ag species, which functioned as visible light responsive co-catalysts that enhanced light absorption via Surface Plasmon Resonance (SPR) and facilitated efficient charge separation. Photocatalytic performance was evaluated through Methylene Blue (MB) decolorization under household LED lamp. The optimized 7% Ag loaded catalyst achieved 99.4% removal efficiency within 6 h, with a reaction rate ten times higher than the Zr-doped sample. This superior activity was attributed to a p-n heterojunction and the SPR effect, narrowing the optical band gap to 2.60 eV. Radical scavenger experiments confirmed that the process was primarily driven by photogenerated holes.

Binary zinc oxide (ZnO) nanocomposites with different noble metals, silver (Ag) and ruthenium (Ru), were prepared from an aqueous leaf extract of Callistemon viminalis. The biosynthesized photocatalysts were characterized and examined for their photocatalytic disinfection against Escherichia coli isolated from hospital wastewater. The influence of the different noble metals showed a difference in physicochemical characteristics and photocatalytic efficiency between Ag–ZnO and Ru–ZnO. The photocatalytic degradation of methylene blue and photocatalytic disinfection were found to be in the order Ag–ZnO > Ru–ZnO > ZnO. The photocatalytic disinfection of Ag–ZnO reached a 75% reduction in 60 min, compared to 34 and 9% reductions of Ru–ZnO and ZnO, respectively. The kinetic reaction rate for the photocatalytic disinfection of Ag–ZnO was found to be 2.8 times higher than that of Ru–ZnO. The outstanding photocatalytic activity of Ag–ZnO over Ru–ZnO was attributed to higher crystallinity, greater UVA adsorption capacity, smaller particle size, and the additional antimicrobial effect of Ag itself. The C. viminalis-mediated Ag–ZnO nanocomposites can be a potential candidate for photocatalytic disinfection of drug-resistant E. coli in hospital wastewater.

Struvite and hydroxyapatite are byproducts of phosphorus removal from wastewater that can be used as phosphate fertilizers. Due to their low water solubility, especially in alkaline soils, their use is currently limited. The use of phosphate-solubilizing bacteria to enhance the dissolution of struvite and hydroxyapatite could be an attractive solution for expanding their use, but literature reports on this are limited. In this study, Arthrobacter sp. (TBRC 5201), Azotobacter vinelandii (TBRC 7231), and Bacillus megaterium (TBRC 1396) were evaluated for their ability to dissolve struvite and hydroxyapatite on agar media with struvite or hydroxyapatite as the sole source of phosphorus. Only B. megaterium (TBRC 1396) was able to use struvite and hydroxyapatite for growth. After 14 d of incubation in liquid medium, B. megaterium (TBRC 1396) dissolved phosphorus from struvite up to 835.45 ± 11.76 mg P/l compared with 196.08 ± 3.92 mg P/l in a control without cells, whereas the dissolution of hydroxyapatite by B. megaterium was minimal. B. megaterium (TBRC 1396) was also capable of dissolving phosphorus from swine wastewater-derived struvite. Both free cells and alginate-encapsulated cells of B. megaterium (TBRC 1396) were able to rapidly dissolve phosphorus from swine wastewater-derived struvite, resulting in soluble phosphorus concentrations that reached 400 mg P/l within 2 days, compared with those without cells that required 12 days. In conclusion, the application of struvite with phosphate-solubilizing bacteria is a promising tool for green sustainable agriculture.