Photocatalysts photocatalytic activity

Table 1 Surface area, band gap energies and photocatalytic activities for H2 evolution from an electrolsde solution over single CdS and CdS-based composite photocatalysts.

The photocatalytic activity of 20mesh wire-net photocatalyst was observed to be nearly equal to that of 350mesh one under the same amount of titanium dioxide loading (1.88 g). 

Some other studies showed that the combination of the three polymorphs with reduced crystallite size and high surface area can lead to the best photocatalysts for 4-chlorophenol degradation [37], or that particles in the dimension range 25-40 nm give the best performances [38]. Therefore, many elements contribute to the final photocatalytic activity and sometimes the increased contribution of one parameter can compensate for the decrease of another one. For example, better photocatalytic activity can be obtained even if the surface area decreases, with a concomitant increase in the crystallinity of the sample, which finally results in a higher number of electron-hole pairs formed on the surface by UV illumination and in their increased lifetime (slower recombination) [39]. Better crystallinity can be obtained with the use of ionic liquids during the synthesis [39], with a consequent increase of activity. 

The photocatalytic activity of ZnO nanomaterials for the degradation of some organic pollutants in water [173] (e.g., dyes [174]) was explored by several groups to achieve environmental benefits. Recent studies have indicated that ZnO can be used under acidic or alkaline conditions with the proper treatment [175,176]. ZnO nanomaterials were used as photocatalysts for the degradation of phenol [177] and chlorinated phenols such as 2,4,6-trichlorophenol [178]. ZnO nanomaterials were also used for the degradation of Methylene Blue [179], direct dyes [180], Acid Red [181], and Ethyl Violet [182],... 

ZnO photocatalyst can also be coupled with other materials in order to improve its chemical and physical properties [183] and photocatalytic activity [184]. Nanosized ZnO was immobilized on aluminum foil for the degradation of phenol [185]. Lanthanum and ZnO were combined to degrade 2,4,6-trichlorophenol [186]. Compared with Ti02 nanomaterial, ZnO nanomaterial generally absorbs a significant amount of the solar spectrum in the visible range therefore, ZnO nanomaterials were combined with Ti02 nanomaterials used as a photocatalyst [187]. 

Ohno, T., Akiyoshi, M., Umebayashi, T., Asai, K., Mitsui, T., and Matsumura, M., Preparation of S-doped Ti02 photocatalysts and their photocatalytic activities under visible light, Appl. Catal. A Gen., 265,115, 2004. 

A. Kudo, H. Kato, S. Nakagawa, Water splitting into H2 and O2 on new Sr2M207 (M — Nb and Ta) photocatalysts with layered perovskite structures Factors affecting the photocatalytic activity, J. Phys. Chem. B 104 (2000) 571-575. 

Wang, P., et al., A one-pot method for the preparation of graphene-Bi2Mo06 hybrid photocatalysts that are responsive to visible-light and have excellent photocatalytic activity in the degradation of organic pollutants. Carbon, 2012. 50(14) p. 5256-5264. 

Ge, L, C. Han, and J. hiu, In situ synthesis and enhanced visible light photocatalytic activities of novel PANI-g-C3N4 composite photocatalysts. Journal of Materials Chemistry, 2012. 22(23) p. 11843-11850. 

Chen, Q. Shi, H. Shi, W. Xu, Y. Wu, D., Enhanced visible photocatalytic activity of titania-silica photocatalysts effect of carbon and silver doping. CataLScience Techn. 2012,2 1213-1220. 

Kudo, A., Kato, H., Nakagawa, S. 2000. Water splitting into Hj and Oj on new StjMjO, (M=Nb and Ta) photocatalysts with layered perovskite structures factors affecting the photocatalytic activity. J Phys Chem B 104 571-575. 

Zou Z, Ye J, Sayama K, Arakawa H (2001) Direct splitting of water under visible light irradiation with an oxide semiconductor photocatalyst. Nature 414 625-627 Konta R, Ishii T, Kato H, Kudo A (2004) Photocatalytic activities of noble metal ion doped SrTiOs under visible light irradiation. J Phys Chem 108 8992-8995 Kato H, Kudo A (2002) Photocatalytic activities of noble metal ion doped SrTiOs under visible light irradiation. J Phys Chem B 106 5029-5034... 

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