New composite materials based on g-C3N4 loaded with Copper(I) oxalate as promoters of C-C coupling in CO2-H2O co-processing under solar irradiation

New composites made of copper(I)oxalate mixed with g-C3N4 by High Energy Milling (HEM) (at 800 rpm) in various w/w percentage (10, 20, 50 % w/w) and for different milling times (30–90 min) are shown to be active as gas-phase photocatalysts in coprocessing “CO2 and H2O” under solar irradiation (0.1 W cm−2) at room temperature to afford ethene or acetone in the range of 20–50 μmol g−1 h−1. The materials have been characterized by UV–VIS DRS, FTIR, elemental analyses, XRD, SEM, Band-gap and chopped photocurrent. The CO2RPs have been identified through GC, GC-MS and multinuclear NMR. Materials have been tested for over 15 h in gas-phase photochemical reactions and shown to be stable towards: the exchange with 13CO2, used to exclude “false positives”, disproportionation to afford CO and CO32-, and oxalate anion reduction. Cu(I)-oxalate modifies the properties of g-C3N4 and most likely is even implied in C-C coupling, as the Cu-Cu distance (255 pm, as determined by XRD in this work) is suited for promoting C-C coupling and is kept constant during operation by the backbone-action of the oxalate anion, which avoids Cu-centres random distribution, that would cause C-C coupling regression.