Effective mineralization of organic pollutants in real shale gas flowback water via Fenton reactions over CuNiAl LDHs catalysts

CuNiAl layered double hydroxides (LDHs) were synthesized as Fenton catalysts to mineralize organics in a shale gas flowback water (FW). Cu+/Cu2+ and Ni2+/Ni3+ are present in LDHs due to the synergistic effect between Ni and Cu, which could induce the electron transfer from Ni2+ to Cu2+. The increase in the Cu/Ni ratio leads to an increase in the Cu+ content but a slight decrease in the Cu+ percentage. The most active Cu1.5Ni0.5Al catalyst can mineralize 79.8 % organics in the FW under pH of 6.2, 71 mM H2O2 and 0.2 g‧L–1 catalyst, with a low leaching of Cu (1.1 mg‧L–1) due to its pH buffer ability. Its activity exceeds that of reference catalysts including binary CuAl and NiAl LDHs, some ternary Cu-containing LDHs, CuSO4, CuO, and Cu2O. Moreover, it achieves higher mineralization ability under near circumneutral pH, less H2O2 and catalyst dosage than the catalysts reported in references. Aromatics, esters, alkanes, phenols, and haloalkanes dominate organics in the FW. After reaction, aromatics and haloalkanes are removed completely, while esters and phenols are reduced significantly, moreover, more oxygen-containing organics are formed. Both HO• and O2•− are responsible for the mineralization of organics. HO• is generated from the reaction between H2O2 and Cu+ in the catalyst. O2•− may originate from oxygen vacancies (OVs) on the surface of the catalyst, while OVs may be caused by heterometal doping in LDHs. CuNiAl LDHs may offer a promising and facile approach to mineralize organics in FW under industrially favorable conditions. [Display omitted] ●CuNiAl LDHs as Fenton catalysts to mineralize organics in shale gas flowback water.●79.8 % TOC removal is achieved at circumneutral pH with low catalyst dosage.●Higher activity is obtained under milder conditions than reported catalysts.●HO• from Cu+ and O2•– from OVs are dominant reactive species.