Constructing Highly Stable CoAl-LDH-Coupled g-C3N4 2D/2D Heterojunctions for Solar Energy-Driven Conversion of Flared Gas to Syngas through Dry-/Bireforming of Methane

Fabricating highly stable CoAl-layered double hydroxide (LDH)-anchored graphitic carbon nitride (g-C3N4) 2D/2D heterojunction composites for photocatalytic flared gas (methane) reduction with CO2 through methane dry reforming (MDR) and methane bireforming has been investigated. The self-assembly growth of CoAl-LDH flakes with layered g-C3N4 sheets enables proficient charge carrier separation to provide good photoactivity and stability. The optimized 15 wt % CoAl-LDH/g-C3N4 exhibited efficient syngas production, in which H2 and CO yield rates were 4.8 and 3.8 folds higher than those of pure CoAl-LDH, respectively. This activity enhancement can be attributed to strong interfacial interaction, higher light absorption, acidic/basic characteristics, and an improved charge-transfer process. With different feed ratios (CH4/CO2), the highest syngas production was achieved with a ratio of 1.0, confirming efficient adsorption of both reactants due to the basic characteristics of composites to uptake CO2/CH4. During photocatalytic CO2 reduction with CH4/H2O through the bireforming of methane, lower photoactivity for CO/H2 production was observed than using MDR due to a competing sorption process. The quantum yield further confirms higher photon flux utilization for continuous CO and H2 evolution, as evidenced by good recyclability in multiple cycles. This study provides a new opportunity to construct CoAl-LDH-coupled g-C3N4 heterojunctions to utilize natural gas flaring toward syngas production through the dry reforming process. Photocatalytic MDR technology proves to be an excellent option for flared gas utilization for syngas (CO and H2) production in a cleaner environment.