Oil sands process water (OSPW), generated during bitumen extraction in northern Alberta, is produced in very large volumes and contains a complex mixture of inorganic salts, suspended solids, residual hydrocarbons, and organic contaminants. Among these, naphthenic acids (NAs) are recognized as the primary contributors to OSPW toxicity due to their structural diversity, persistence, and resistance to conventional treatment. In the absence of approved discharge regulations, OSPW is stored in tailings ponds, leading to steadily increasing volumes and significant environmental and public health concerns. Advanced oxidation processes (AOPs) such as UVC/H2O2 and ozonation have been investigated but are often energy‑intensive and depend on continuous chemical inputs, motivating the development of more sustainable, solar‑driven treatment technologies.
This work investigates tin oxide (SnO2)–based photocatalysts modified with silver (Ag) for solar‑driven degradation of NAs in real OSPW. SnO2 is an attractive photocatalyst owing to its strong oxidative potential, chemical stability, low toxicity, and favorable electronic properties. Ag is incorporated to form SnO2/Ag heterojunctions with the objective of enhancing charge separation and suppressing electron–hole recombination. Material characterization confirmed successful heterojunction formation and uniform Ag dispersion.
Photocatalytic performance was assessed using synchronous fluorescence spectroscopy to monitor fluorescent organic compounds and conventional NA analysis to quantify removal. Raw OSPW exhibited characteristic fluorescence peaks associated with single‑ and multiring aromatics. Under simulated solar irradiation, photolysis and unmodified SnO2 produced minimal changes in fluorescence intensity, indicating limited degradation. In contrast, an optimally Ag‑modified SnO2/Ag catalyst produced a pronounced reduction in all major fluorescence peaks, particularly those linked to multi‑ring aromatics, demonstrating substantially enhanced photocatalytic activity. NA degradation followed similar trends, with simpler O2‑substituted NAs being more readily oxidized than more complex and highly oxidized species. Performance decreased at both lower and higher Ag contents, with excessive Ag loading leading to increased charge recombination and light‑shielding effects, consistent with photoluminescence results. Kinetic analysis indicated pseudo‑first‑order behavior, and dark adsorption controls confirmed that removal was dominated by photocatalytic oxidation rather than sorption.
Mechanistic studies using radical scavengers identified hydroxyl radicals (•OH) as the primary reactive species driving NA degradation. The optimized SnO2/Ag catalyst maintained high removal efficiency over multiple reuse cycles with minimal Ag leaching, indicating good stability and reusability under solar irradiation. Toxicological assessment of treated OSPW showed a strong reduction in immunotoxic responses, demonstrating that the process not only removes target organics but also substantially mitigates biological effects. In addition, two new performance indicators were introduced to support more robust comparison of photocatalytic systems for complex industrial effluents such as OSPW.
Overall, this study demonstrates that optimally engineered SnO2/Ag photocatalysts can deliver efficient, solar‑driven degradation of NAs and significant toxicity reduction in real OSPW. At an optimum catalyst dose of 0.5 g/L, the SnO2/Ag (5%) catalyst achieved around 90% removal of the O₂‑NAs and a strong decrease in immunotoxic responses. These results highlight SnO2/Ag photocatalysis as a promising and more sustainable pathway for tailings water remediation.
Oil sands process water (OSPW), generated during bitumen extraction in northern Alberta, is produced in very large volumes and contains a complex mixture of inorganic salts, suspended solids, residual hydrocarbons, and organic contaminants. Among these, naphthenic acids (NAs) are recognized as the primary contributors to OSPW toxicity due to their structural diversity, persistence, and resistance to conventional treatment. In the absence of approved discharge regulations, OSPW is stored in tailings ponds, leading to steadily increasing volumes and significant environmental and public health concerns. Advanced oxidation processes (AOPs) such as UVC/H2O2 and ozonation have been investigated but are often energy‑intensive and depend on continuous chemical inputs, motivating the development of more sustainable, solar‑driven treatment technologies.
This work investigates tin oxide (SnO2)–based photocatalysts modified with silver (Ag) for solar‑driven degradation of NAs in real OSPW. SnO2 is an attractive photocatalyst owing to its strong oxidative potential, chemical stability, low toxicity, and favorable electronic properties. Ag is incorporated to form SnO2/Ag heterojunctions with the objective of enhancing charge separation and suppressing electron–hole recombination. Material characterization confirmed successful heterojunction formation and uniform Ag dispersion.
Photocatalytic performance was assessed using synchronous fluorescence spectroscopy to monitor fluorescent organic compounds and conventional NA analysis to quantify removal. Raw OSPW exhibited characteristic fluorescence peaks associated with single‑ and multiring aromatics. Under simulated solar irradiation, photolysis and unmodified SnO2 produced minimal changes in fluorescence intensity, indicating limited degradation. In contrast, an optimally Ag‑modified SnO2/Ag catalyst produced a pronounced reduction in all major fluorescence peaks, particularly those linked to multi‑ring aromatics, demonstrating substantially enhanced photocatalytic activity. NA degradation followed similar trends, with simpler O2‑substituted NAs being more readily oxidized than more complex and highly oxidized species. Performance decreased at both lower and higher Ag contents, with excessive Ag loading leading to increased charge recombination and light‑shielding effects, consistent with photoluminescence results. Kinetic analysis indicated pseudo‑first‑order behavior, and dark adsorption controls confirmed that removal was dominated by photocatalytic oxidation rather than sorption.
Mechanistic studies using radical scavengers identified hydroxyl radicals (•OH) as the primary reactive species driving NA degradation. The optimized SnO2/Ag catalyst maintained high removal efficiency over multiple reuse cycles with minimal Ag leaching, indicating good stability and reusability under solar irradiation. Toxicological assessment of treated OSPW showed a strong reduction in immunotoxic responses, demonstrating that the process not only removes target organics but also substantially mitigates biological effects. In addition, two new performance indicators were introduced to support more robust comparison of photocatalytic systems for complex industrial effluents such as OSPW.
Overall, this study demonstrates that optimally engineered SnO2/Ag photocatalysts can deliver efficient, solar‑driven degradation of NAs and significant toxicity reduction in real OSPW. At an optimum catalyst dose of 0.5 g/L, the SnO2/Ag (5%) catalyst achieved around 90% removal of the O₂‑NAs and a strong decrease in immunotoxic responses. These results highlight SnO2/Ag photocatalysis as a promising and more sustainable pathway for tailings water remediation.
