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Reduction of aqueous carbonate photocatalysed by treated semiconductors
Author(s) -
Khalil Laila B.,
Youssef Nabil S.,
Rophael Magdy W.,
Moawad Mona M.
Publication year - 1992
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/jctb.280550415
Subject(s) - phthalocyanine , photocatalysis , quantum yield , aqueous solution , semiconductor , yield (engineering) , chemistry , coating , irradiation , photochemistry , materials science , metal , inorganic chemistry , organic chemistry , catalysis , fluorescence , metallurgy , optoelectronics , physics , quantum mechanics , nuclear physics
Heterogeneous photocatalysed reduction of aqueous Na 2 CO 3 solution (1 m) was achieved by using phthalocyanine‐coated semiconductor powders (1–3% coating) as well as bare semiconductors. The suspensions were irradiated with 254 nm light from a low‐pressure mercury lamp in a nitrogen atmosphere. The phthalocyanine dyes (Fe 2+ ‐Pc or Co 2+ ‐Pc) absorb > 80% of the 254 nm radiation and thus sensitize the semiconductor. The products of reduction (CH 3 OH and HCHO) were determined spectrophotometrically. The CH 3 OH yields obtained are much higher than the HCHO yields, due to a photocatalysed reduction of HCHO to CH 3 OH. The CH 3 OH yields from coated titania increased linearly with irradiation time over the period 6–18 h. However, the straight line does not pass through the origin, and it seems that a slowing‐down occurs at times > 6 h. Titania coated with both dyes gave an optimum CH 3 OH yield at 2% surface coating. At higher coating percentages, phthalocyanine screens the surface, thus reducing the light reaching the semiconductor. Changing the redox potential of the phthalocyanine dye by changing its central metal from Fe to Co affects the CH 3 OH yields. The bare MoS 2 photocatalyst gave a much higher CH 3 OH yield due to the characteristic behaviour of the semiconducting layer‐type disulphide, distinguished from that of classical semiconducting materials. In the various semiconductors studied, it seems that there is no correlation between the position of the conduction band and the yield of CH 3 OH. Such correlation was argued. Generally, a decrease in the yield of CH 3 OH was observed as the band gap width of the semiconductor increased. The yields of the photoproduced CH 3 OH generally increased with the percentage of light absorbed at 254 nm by the various semiconductors. Irradiation leads to the production of electrons in the conduction band of the semiconductor. It is likely that the photoproduced electrons reduce CO 3 2 ‐ initially to HCOO‐ and then to HCHO and CH 3 OH.