Photocatalytic Production of Hypochlorous Acid over Pt/WO₃ under Simulated Solar Light

Abstract

The production of hypochlorous acid (HClO) over a visible-light active photocatalyst was achieved for the first time in an aqueous solution of NaCl under simulated solar light. Approximately 17.6 μM of HClO was accumulated after 1 h of photoirradiation by employing the photocatalytic oxidation of Cl– with O2 reduction over the Pt cocatalyst-loaded WO3. The quantum efficiency of the HClO production was 2.3% at 420 nm. Moreover, the photoelectrochemical HClO production on the WO3 photoanode was also investigated to elucidate the photocatalytic reaction mechanism. The initial faradaic efficiency of the process reached 96%, indicating high selectivity toward the production of HClO over the WO3 surface in an aqueous NaCl solution. It was found that the highly photocatalytic performance over Pt-loaded WO3 was primarily attributed to the higher oxygen reduction and lower H2O2 formation abilities in comparison to other cocatalysts.

Enhanced HClO production from chloride by dual cocatalyst loaded WO3 under visible light

“…In our previous work, we have reported that the Pt cocatalyst works as the active site for the O 2 reduction reaction during the photocatalytic production of HClO over Pt/WO 3 , both H 2 O and H 2 O 2 could be produced, and the H 2 O 2 was easy to react with HClO which led to a decrease in the concentration of the accumulated HClO (eqn (11)). 22 2Cl − → Cl 2 + 2e − , E 0 = +1.39 V vs. NHE (at pH = 0.0)Cl 2 + H 2 O ↔ H + + HClO + Cl − O 2 + 4H + + 4e − → 2H 2 O, E 0 = +1.23 V vs. NHE (at pH = 0.0)O 2 + 2H + + 2h + → H 2 O 2 , E 0 = +0.68 V vs. NHE (at pH = 0.0)HClO + 2e − + H + → Cl − + H 2 OHClO + H 2 O 2 → H + + Cl − + H 2 O + O 2 …”

“…Additionally, H 2 O and H 2 O 2 will be competitively produced during the ORR, and the production of H 2 O 2 will lead to the decomposition of HClO, as shown in eqn (10). 22 Therefore, we investigated the production of H 2 O 2 on Mn, Pt, and Pt-Mn during the oxidative photoelectrochemical HClO production using the WO 3 /FTO electrode as the photoanode and MnO x /FTO, Pt/FTO, or Pt-Mn/FTO as the cathode in a two-compartment cell. Gaseous N 2 was bubbled into the anode chamber and O 2 was bubbled into the cathode chamber at a flow rate of 1 mL min −1 .…”

“…In our previous work, we firstly reported the photocatalytic oxidation of Cl − to Cl 2 , using Pt/WO 3 as the powder photocatalyst and solar light as the energy source. 22 However, due to the use of Pt as a cocatalyst, the production of Pt/WO 3 is economically burdensome for practical applications. Recently, some articles have reported that Pt–M (M = Ni, Co, Mn, Cu, etc. )…”

Impact of Reaction Parameters and Water Matrices on the Removal of Organic Pollutants by TiO2/LED and ZnO/LED Heterogeneous Photocatalysis Using 365 and 398 nm Radiation

“…Opposite to the TiO 2 , the Cl − are adsorbed well on the ZnO surface, having a positive charge [ 83 , 84 , 85 ] and enhancing the formation rate of ROS due to the hindered recombination of photoinduced e CB − and h VB + [ 83 ]. Significant conversion of Cl − by h VB + to HClO has been reported in some cases [ 82 , 86 , 87 ]. The degradation of HClO via reaction with e CB − , or superoxide radical anions (O 2 •− ) also results in the formation of • OH [ 87 , 88 ], which may explain the increased r 0 7-HC for ZnO.…”

“…Significant conversion of Cl − by h VB + to HClO has been reported in some cases [ 82 , 86 , 87 ]. The degradation of HClO via reaction with e CB − , or superoxide radical anions (O 2 •− ) also results in the formation of • OH [ 87 , 88 ], which may explain the increased r 0 7-HC for ZnO. Active chlorine species formation and photocatalytic reactions are complex, depending on many parameters [ 88 , 89 , 90 ], and require further investigation.…”