Separation was rapid with visual clarity of the aqueous phase achieved over 10 minutes of separation time (Figure , ESI). The PR activity of the HGM/CNx|Pt was found to decrease by a small degree with each cycle in each substrate solution (Figure ; SI Table ), reaching a final areal activity of (82.3 ± 1.0)% in EG (Figure ), (38.9 ± 12.2)% in PET (Figure ), and (67.5 ± 11.4)% in cellulose (Figure ). Except for PET, the percent decrease in activity approximates the percent mass loss of HGM/CNx composite. Overall, the consistent activity of the HGM/CNx|Pt samples points to the CNx|Pt system as capable of maintaining photoreforming performance over multiple trials, with loss in activity attributable to loss of the composite material itself (either through aspiration between trials or breakage and sinking of the composite). In the small reactor trials, a meniscus effect in the 2.5 cm diameter cylindrical reactor caused the floating composite to move into a ring formation in the absence of stirring, clinging to the walls of the reactor over the 2 h irradiation period, and the speed of this separation may have affected the H2 yield and may have been affected by solution characteristics such as surface tension.