Photoassisted Reduction of Carbon and Nitrogen Compounds with Semiconductors

Abstract

ABSTRACT. The conversion of visible light into the stored energy of chemical fuel was studied, using semiconductors as photosensi tizers. The reactions investigated were the reduction of carbonate ions to organic compounds and of nitrogen oxyanions to ammonia. Using suspensions of CdS, ZnS-CdS or Ti0 2 in 1M KOH and O.lM Na 2 S at 61 0 C, illuminated with a 150W Xe-Ia~~, w~!ound that there was a slow release of ammonia, 0.014 micromol h cm (illuminated area) which was the same whether the mixture was purged with argon or nitrogen gas. Addition of 0.2M potassium nitrate did not change the rate of release of ammonia. However, addition of potassium ni tri te caused a marked increase in the rate of production of ammonia. Using O. 13M potassium nitrite in 1M KOH, O.lM sodium ~ulfide at 61 0 C, the production rate of ammonia was 0.97 micromol/(h cm ) in th~ presence of Ti0 2 (70mg in 70ml reaction solution), 0.60 micromol/(h cm ~ in the presence of CdS (same concentration), and 0.55 micromol/(h cm ) in the presence of ZnS-CdS (70mg -50mg mixture). In the absence of sodium sulfide, and if sodium sulfite was substituted for sodium sulfide, the above photoassisted reduction of nitrite ions to ammonia was negligible. Also, there was no reaction in the dark. With CdS -ZnS in 0.5M potassium carbonate -O.lM sodium sulfide, illumination caused th:'9 producti2~ of ammoni~~ methanol a~d formaldehyde, at rates of 7.1xl0 ,1.5xl0 and 0.2xl0 mol h-cm-, respectively.

Recent advances in heterogeneous TiO2 photocatalysis

“…By using this microsensor, the formation of H 2 0 2 was found to be more efficient on the ITO surface than on the TiO 2 surface. This observation indicates that H 2 0 2 was produced mostly at ITO, i.e., by reduction of dissolved oxygen (16), rather than by oxidation of water (15), even in the absence of an electron donor. The possible paths for the formation of H 2 02 by reduction of molecular oxygen were reported earliera:…”