H2O2 is an environmentally friendly chemical for wide water treatments and H2 is regarded as an ideal substitute for traditional fossil energy. The industrial production of H2O2 is via the anthraquinone oxidation process, which, however, consumes extensive energy and produces pollution. Herein, based on the density functional theory (DFT) calculations, we report a green and sustainable piezocatalytic intermediate water splitting (IWS) process to simultaneously obtain H2O2 and H2 using C-doped KNbO3 nano single crystals as catalysts. The KNbO3 catalysts doped with suitable amounts of carbon show an enhanced water splitting rate, which could be attributed to the decreased reaction barriers on the C-KNbO3 surface and improved polarized built-in electric field, as evidenced by DFT simulations and PFM measurements. Remarkably, the piezocatalytic H2 evolution efficiency of 0.5 : 1 C-KNbO3 reaches 524.51 μmol g−1 h−1. Additionally, 0.5 : 1 C-KNbO3 could generate H2 and H2O2 simultaneously through two-electron piezocatalytic IWS reactions. This improved catalytic efficiency is attributed to the promoted piezo-response of KNbO3 after C doping, as revealed by PFM tests.
Membrane distillation (MD) shows great potential in hypersaline water treatment, but it is invariably constrained by temperature polarization. Conductive heating vacuum membrane distillation (CHVMD), a single-pass system without recirculating feed, effectively alleviates temperature polarization by introducing a thermal conducting layer that enhances the transfer of external heat to the membrane-water interface. However, this process exacerbates concentration polarization, raising the scaling potential. Gypsum scaling, a common issue in MD, has been effectively alleviated by using carboxyl antiscalants. However, the mechanisms by which different carboxyl antiscalants influence gypsum scaling in MD remain poorly understood. In this study, the performance and mechanism of three carboxyl antiscalants—polyacrylic acid (PAA), polymethacrylic acid (PMAA) and hydrolyzed polymaleic anhydride (HPMA)—in CHVMD using gypsum solution as the feed were investigated. The results show that these carboxyl antiscalants enhance the membrane durability in the single-pass CHVMD system, while improving both initial and stabilized flux in the order: PAA > HPMA > PMAA. PAA exhibits a more pronounced effect on reducing the evaporation enthalpy of water through the formation of intermediate water, and lowering the resistance to heat and mass transfer with the formation of vertical, large lamellar gypsum crystals, achieving an initial flux of 12.79 kg/m 2 h and a stabilized flux of 10.20 kg/m 2 h. For PMAA, increasing feed salinity significantly reduces the evaporation enthalpy, and lowers the transfer resistance by the formation of larger needle-like gypsum crystals, thereby obtaining the highest initial flux of 15.45 kg/m 2 h and stabilized flux of 11.35 kg/m 2 h.
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