Synthesis of a high-performance silver silicate (Ag6Si2O7)/silver bromide (AgBr) photocatalyst with enhanced visible light catalytic activity for refractory organic pollutants

In this study, a novel, efficient, environmentally friendly mediator-free Z-scheme Ag6Si2O7/AgBr photocatalyst was designed and successfully developed for the first time. A series of studies have shown that Ag6Si2O7/AgBr heterojunction photocatalysts display significantly enhanced photocatalytic activity towards degradation of phenol, methyl orange (MO) and rhodamine (RhB) compared to pristine Ag6Si2O7 and AgBr under visible light irradiation. In this system, the introduction of Ag6Si2O7 greatly increases the specific surface area, expands the visible light response region, and extends the charge carrier lifetime, thus enhancing the reducing and oxidizing ability of Ag6Si2O7/AgBr composite photocatalyst. Brunauer-Emmett-Teller (BET), UV-vis diffraction spectra (DRS), Photoluminescence (PL) spectroscopy, and photoelectrochemical measurements were used to confirm these results. Meanwhile, field scanning electron microscope (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) results from the samples before and after use show that the obtained sample has high physical and chemical stability. This ensures that the Ag6Si2O7/AgBr photocatalyst maintains high catalytic activity, degrading 90% of MO within 8 min, even after 5 cycles. Moreover, superoxide free radicals (O-center dot(2)-) and photogenerated holes (h(+)) are the primary active species produced during photocatalytic degradation of MO over 1:18 Ag6Si2O7/AgBr, which was verified through a free radical scavenging experiment and from electron spin resonance spectra (ESR). Moreover, experimental gas chromatography-mass spectrometry (GS-MS) results and total organic carbon (TOC) content show that the 1:18 Ag6Si2O7/AgBr photocatalyst provides high mineralization for organic pollutants. Finally, a possible Z-scheme photocatalytic mechanism is proposed based on energy band theory calculations and experimental results.