On-site H2O2 production with amphiphilic g-C3N4 as photocatalyst in a combined photocatalysis–extraction–separation process

Hydrogen peroxide (H2O2) can be photocatalytically generated by oxygen in water with fatty alcohols as a sacrificial agent; however, it is expensive to separate because of the miscibility of fatty alcohols and water. In this work, H2O2 is directly generated photocatalytically using amphiphilic graphitic carbon nitride (g-C3N4) and oxygen in pure anhydrous oily benzyl alcohol (BA) alone; it is simply extracted by water and separated using a hydrophobic/lipophilic mesh to obtain a high-concentration H2O2 aqueous solution. The results show that the H2O2 concentration in BA after 4 h of photoreaction is 9.45 mM and that of the final solution product can be as high as 70.93 mM in water. Water does not enhance the photoreaction; instead, unexpectedly, it weakens it. However, it is possible to completely extract the H2O2 from the reacted BA. In this study, the H2O2 solution is rapidly separated from the BA with a separation efficiency of 99.97% using a hydrophobic mesh. The photocatalyst g-C3N4 is present at the water/BA interface owing to its amphiphilicity, and it can be caught by the mesh during separation and reused after backwashing. The combined photoreaction, extraction, and separation processes provide a simple, environment-friendly, and rapid H2O2 photogeneration process for the on-site production of a usable H2O2 solution.