Enhancing the photocatalytic activity of Ag-TiO2/SiO2 and its potential application in water treatment

Ag-doped TiO2/SiO2 with visible light response was prepared by a simple sol-gel method using titanium w-butoxide (TNB), tetraethoxysilane (TEOS) as precursors, and silver nitrate (AgNO3). The synthesized Ag-TiO2/SiO2 were characterized by SEM, XRD, PL (photoluminescence) emission and UV-Vis absorption spectroscopy. Their photocatalytic activities were evaluated by treating aqueous solutions of phenol under simulated visible light illumination. The role of silver doped was investigated in the range 1% – 5% (molar ratio), resulting in the best bandgap value of 2.93 eV for Ag(3%)-TiO2/SiO2 compared to 3,18 eV for the un-doped TiO2/SiO2. Consequently, the best phenol treating yield – about 97% after 4 hours – was obtained using Ag(3%)-TiO2/SiO2. So the synthesized Ag(3%)-TiO2/SiO2 might serve as a potential photocatalyst for water treatment using visible lights.

Au@CoS-BiVO4 {010} Constructed for Visible-Light-Assisted Peroxymonosulfate Activation

A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. Au@CoS, when doped on monoclinic BiVO4 {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO4 {010} and {110} facets. The visible-light response of m-BiVO4 was enhanced, which was attributed to the SPR effect of Au. And the photogenerated electrons were transferred from the m-BiVO4 {010} facet to Au via a Schottky junction. Owing to higher work function, CoS was able to capture these photoelectrons with acceleration of the Co(Ⅱ)/Co(Ⅲ) redox, enhancing peroxymonosulfate conversion to sulfate radical (Co2+ + HSO5−→ Co3+ + •SO4− + OH−). On the other hand, holes accumulated on m-BiVO4 {110} facets also contributed to organics oxidation. Thus, more than 95% of RhB was degraded within 40 min, and, even after five cycles, over 80% of RhB could be removed. The radical trapping experiments and EPR confirmed that both the sulfate radical and photogenerated hole were the main species for organics degradation. UV-vis DRS, photoluminescence (PL) and photoelectrochemical analyses also confirmed the enhancement of the visible-light response and charge separation. In a pilot scale experiment (PMS = 3 mM, initial TOC = 151 mg/L, reaction time = 4 h), CoS-Au-BiVO4 loaded on glass fiber showed a high mineralization rate (>60%) of practical wastewater.