The field of photocatalysis currently witnesses an increasing interest in the development of various selective chemical conversions beyond hydrogen production via water splitting, in particular due to the growing concerns regarding the economical viability of photo(electro)catalytic water splitting, and especially since the photocatalytic production of high-value compounds from low-cost chemical feedstock holds promise for commercially viable applications on a more immediate time scale as compared to the photocatalytic production of hydrogen. One of the most attractive compounds that can be photocatalytically obtained by a simple two-electron reduction of dioxygen is hydrogen peroxide, a highly versatile and environmentally benign oxidizing agent used in a number of important industrial processes. Although photocatalytic H2O2 peroxide production from pure water and oxygen has been reported, the reaction rates were usually too low to accumulate high concentrations of the product, making the presence of additional electron donors like aliphatic or aromatic alcohols practically indispensable to achieve reasonable reaction rates. Notably, this approach appears even more attractive if also the oxidation product of this reaction has a higher value than the substrate, as it is the case for the conversion of biomass-derived feedstock. Polymeric carbon nitrides (PCNs) whose photocatalytic activity was first reported by Wang et al. are known for their excellent performance in light-driven H2O2 production from oxygen. The ionic form of this material comprising stacks of 2D heptazine-based networks and alkali metal cations and/or protons, poly(heptazine imide) (PHI), otherwise known as CNx-NCN, KSCN-or alkali metal modified carbon nitride, typically outperforms the conventional, non-ionic, melon polymer in this reaction. The superior activity of PHI can be explained, among other factors, by partial substitution of the terminal NH2-groups for -N --CN species in PHI, resulting in fewer hydrogen bond interactions and better dispersibility of the material in polar solvents. A major challenge in carrying out such reactions in suspension is the effective separation of the dissolved reduction and oxidation products for their subsequent use, in order to avoid the decomposition of H2O2 on the surface of the photocatalyst by photoredox decomposition or by its disproportionation in the dark. The H2O2 decomposition would lead to the loss of the overall reaction yield, a problem that typically becomes even more prominent at higher H2O2 concentration in the reaction medium.