A sunlight assisted dual purpose photoelectrochemical cell for low voltage removal of heavy metals and organic pollutants in wastewater

• Principle and demonstration of a novel dual purpose photo-electrochemical cell.
• Simultaneous removal of heavy metals and organic pollutants from wastewater.
• Metal removal on cathode with nearly 100% current efficiency.
• Sunlight assisted anodic decomposition of organic pollutant.
• 60% Reduction of the working voltage of the photo-electrochemical cell.

Photoelectrochemical cells that consisted of a Pt (small cells) or Ti (large cells) cathode and a sunlight responsive WO3 photoanode were built for simultaneous removal of heavy metal ions and organic pollutants. Synthetic wastewater samples containing 0.5 M of NaCl, 10 ppm of methylene blue (MB, organic pollutant), 500 ppm of Cu2+ or 500 ppm Ni2+ were tested as the first examples for demonstration of the principle, device and process. The results showed that upon irradiation of simulated sunlight on the photoanode, metal ions (Cu2+ and Ni2+) can be recovered as metals or hydroxide at the cathode. MB was simultaneously decomposed at the photoanode without using any additional chemicals as sacrificial agents. The cell voltage required for this dual purpose process was as much as 71% or 60% lower than that required for conventional electrodeposition of Cu or Ni respectively with an inert anode. Charge efficiency was close to 100% for the cathodic processes, and over 70% for the photoanodic degradation of MB through a combined mechanism of partial oxidation and mineralisation according to UV–Vis spectroscopic evidence and reaction pathway analysis.