Comparative Photocatalytic Degradation of Methylene Blue Using Plant-Based Pigments: Turmeric, Spinach, and Green Tea Extracts

Synthetic dyes such as methylene blue are persistent environmental pollutants resistant to conventional wastewater treatment. This study investigated whether aqueous extracts of three plant-based materials—turmeric (curcumin), spinach (chlorophyll), and green tea (polyphenols)—could serve as photocatalysts for methylene blue degradation under visible light. Absorbance at 670 nm was measured continuously using a spectrophotometer over approximately ten minutes per condition. Turmeric extract produced a statistically meaningful decrease in methylene blue absorbance of approximately 12.8% (initial: 2.511 AU; final: 2.189 AU; linear fit slope = −5.29 × 10⁻⁴ AU s⁻¹, r = −0.912), while spinach and green tea extracts showed no measurable change (|r| < 0.025). The methylene blue light control also exhibited no degradation, confirming that light alone was insufficient. These findings suggest that curcumin in turmeric acts as a more effective visible-light photocatalyst than chlorophyll or polyphenols under the tested conditions.