An ecological self-purification pathway: Natural lava-Rhodopseudomonas palustris synergy enables spontaneous photobioelectrocatalysis for efficient dye degradation

Persistent synthetic dyes such as crystal violet pose substantial challenges to environmental remediation due to their high structural stability and toxicity. Here, we report a natural photobioelectrocatalytic strategy for dye removal by coupling the photosynthetic bacterium Rhodopseudomonas palustris K7 with natural volcanic lava. Characterization results demonstrated that the lava is an N-type semiconductor with a band gap of 3.32 eV and a flat-band potential of −0.87 V, enabling photoinduced charge generation under illumination. Under simulated light irradiation at 28°C (1000 lux, 300 W xenon lamp), the “strain K7-lava” co-culture system (100 mg lava mixed with 40 mL bacterial suspension at OD660 = 1.0) removed 54.9% of 10 mg L−1 CV within 48 h. This performance was markedly higher than that of “lava-alone” or “bacteria-alone” treatment controls, demonstrating a significant synergistic effect of microbe and lava in dye degradation. The degradation process followed pseudo-first-order kinetics, with an apparent rate constant of 0.01226 h−1 under illumination, substantially exceeding that of “strain K7 alone” (0.00023 h⁻¹) or “lava alone” (0.00195 h⁻¹). In the co-culture system, photoexcited lava generated “photoelectron-oxidative hole pairs” that produced reactive oxygen species (ROS) capable of oxidatively decomposing the dye. Meanwhile, photogenerated electrons were accepted by strain K7, significantly enhancing its electrochemical activity and elevating intracellular energy and reducing power levels, thereby further accelerating dye degradation. Our study reveal a synergistic interaction between naturally occurring semiconductor minerals and environmental microorganisms in pollutant removal, offering a new perspective on natural self-purification processes. Moreover, this study proposes a green, low-cost strategy for the treatment of low-to moderate-strength dye-containing wastewater.