Atmospheric CO2 mediated formation of Ag2O-Ag2CO3/g-C3N4 (p-n/n-n dual heterojunctions) with enhanced photoreduction of hexavalent chromium and nitrophenols

Herein a pH-adjusted chemical precipitation method is reported for in-situ formation of ternary Ag2O-Ag2CO3/g-C3N4 (AAG) composites in the presence of atmospheric CO2. For comparison, a Janus Ag2O-Ag2CO3 (AA) composite with fine and narrow size particles of high purity was also fabricated with AgNO3 and NaOH without g-C3N4 (GN). The thermal treatment of the AAG composite by TGA indicates that 14% of atmospheric CO2 was utilized by Ag2O which induced the formation of ternary AAG. The thermal stability of the prepared samples is in the order of GN > AAG > AA. Results from other spectroscopic techniques on AAG affirmed that both Ag2O and Ag2CO3 co-existed on the surface of g-C3N4. Under solar illumination, the constituting particles of AAG realigned at their interfaces to form p-n/n-n dual heterojunctions with improved photocatalytic reduction of nitrophenols (4 and 2-nitrophenols) to aminophenols (4 and 2-aminophenols), and Cr(VI) to Cr(III). The results obtained from this study showed that AAG has higher photoreduction efficiencies compared to AA and GN. The results from the stability runs also showed that AAG has good photo-stability and reusability to catalyze the reduction of nitrophenols and hexavalent chromium under light irradiation with efficiency as high as 89% for five (5) reaction cycles. This study further highlights the significance of Ag2O utilizing CO2 to promote Ag2O/Ag2CO3 formation as a co-catalyst for photocatalytic applications.