{'fraction_non_alphanumeric': 0.0243117626027887, 'fraction_numerical': 0.003932785126921702, 'mean_word_length': 5.506976744186047, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Introduction and Summary

2 Photocatalysis Semiconductor photocatalysis has received much attention during last three decades as a promising solution for both energy generation and environmental problems. Since the discovering of Fujishima and Honda 1 that water can be photo-electrochemically decomposed into hydrogen and oxygen using a semiconductor (TiO 2) electrode under UV irradiation, extensive works have been carried out to produce hydrogen from water splitting using a variety of semiconductor photocatalysts. In recent years, scientific and engineering interest in heterogeneous photocatalysis has been also focused on environmental applications such as water treatment and air purification. Many review papers on semiconductor photocatalysis can be found in literature. Semiconductor photocatalysis is initiated by electron-hole pairs after bandgap excitation. When a photocatalyst is illuminated by light with energy equal to or greater than band-gap energy, the valence band electrons can be excited to the conduction band, leaving a positive hole in the valence band: The excited electron-hole pairs can recombine, releasing the input energy as heat, with no chemical effect. However, if the electrons (and holes) migrate to the surface of the semiconductor without recombination, they can participate in various oxidation and reduction reactions with adsorbed species such as water, oxygen, and other organic or inorganic species. These oxidation and reduction reactions are the basic mechanisms of photocatalytic water/air remediation and photocatalytic hydrogen production, respectively. A simplified mechanism for photocatalytic process on a semiconductor is presented in Figure 1.1. 3 For photocatalytic water/air remediation as an environmental application, valence band (VB) holes are the important elements that induce the oxidative decomposition of environmental pollutants. The positive hole can oxidize pollutants directly, but mostly they react with water (i.e., hydroxide ion, OH –) to produce the hydroxyl radical (• OH), which is the very powerful oxidant with the oxidation potential of 2.8 V (NHE). • OH rapidly attacks pollutants at the surface and in solution as well and can mineralize them into CO 2 , H 2 O, etc. TiO 2 , the most popular photocatalyst because of its relatively high activity, chemical stability, availability with low production costs, and non-toxicity has been widely studied and proven to have a potential to completely oxidize a variety of organic compounds, including persistent organic pollutants. The reducing conduction band (CB) electrons are more important when photocatalytic reaction is applied for hydrogen production from water splitting. In order to initiate hydrogen production, the conduction band level must be more negative …