H2O2-assisted photocatalysis for removal of natural organic matter using nanosheet C3N4-WO3 composite under visible light and the hybrid system with ultrafiltration

In this study, a nano-sheet C3N4-WO3 composite (nsCW21) was applied as a visible-light active photocatalyst to degrade natural organic matter (NOM). The nsCW21 photocatalyst exhibited a higher removal efficiency for NOM than the bare host and other composite counterparts due to the effective separation of the charge carriers in the Z-scheme pathway. The addition of H2O2 resulted in the enhanced photocatalytic performance via the generation of hydroxyl radicals from the catalyst with an NOM removal rate of up to 71% for 5 h. The catalyst showed a considerable stability, which held a good NOM degradation efficiency during five cycle runs. The complex NOM removal behavior was unraveled by using a fluorescence excitation emission matrix-parallel factor analysis and a two-dimensional correlation spectroscopy (2D-COS) combined with Fourier-transform infrared spectroscopy (FT-IR). The large sized and the terrestrial humic-like component exhibited a high adsorption tendency toward the catalyst and was degraded primarily by h(+), while a typical humic-like component, which is mainly removed by .OH, displayed a high degradation rate constant (k = 0.159 h(-1)). The 2D-COS revealed the sequence of the preferable removal among the different NOM functional groups in the nsCW21 system with H2O2 addition, which occurred in the order of open ring reaction oxygenated functional groups > the transformation into aliphatic compounds/inorganic moieties. Meanwhile, the hybrid system that employed ultrafiltration as a post-treatment demonstrated synergetic effects on the improved effectiveness for NOM removal in the overall system, which was a total of 91%, of the residuals from the precedent photocatalysis as well as alleviating the membrane fouling.