Metals free MWCNTs@TiO2@MMT heterojunction composite with MMT as a mediator for fast charges separation towards visible light driven photocatalytic hydrogen evolution

Constructing heterojunctions with low-cost materials functional under solar energy is an important way for efficient hydrogen production for energy management applications. In this study, multiwall carbon nanotubes (MWCNTs) modified TiO2 1D/0D heterojunction dispersed in 2D montmorillonite (MMT) nanoclay was designed and fabricated using a facile sol-gel and wet impregnation approach. The samples were characterized by XRD, Raman, FESEM, HRTEM, FTIR, UV-vis and PL-spectroscopy techniques. Dispersing 1D/0D MWCNTs/TiO2 on the 2D MMT structure extends visible light absorption, shorten charges migration distance and provides abundant active sites. The performance of samples was investigated for dynamic photocatalytic H-2 evolution with different sacrificial reagents under visible light irradiations. The MWCNTs/TiO2/MMT heterojunction composite exhibits the highest H-2 evolution rate of 1888 ppm h(-1), which is about 1.49, 3.07 and 7.12 folds higher than MWCNTs/TiO2, MMT/TiO2 and pure TiO2 samples, respectively. Among the different sacrificial reagents, highest H-2 production was obtained using glycerol-water mixture due to the presence of alpha-hydrogen atoms attached to carbon atoms. Next, the photocatalytic turn-over productivity (PTOP) was estimated which demonstrated the molecular H2 production rate with the photon-energy utilization. The maximum PTOP for H-2 production was achieved over MWCNTs/TiO2/MMT heterojunction composite, 5.94 times higher than using bare TiO2 NPs. The improved charges efficiency due to the synergistic effect between MWCNTs/TiO2/MMT in 1D/OD/2D heterojunctions is critical for enhanced and dynamic H-2 evolution. The ternary composite exhibited excellent and stable performance for H-2 production. This study suggests that constructing heterojunction of low cost coupling materials with TiO2 can provide an efficient way for H-2 production under solar energy.