Application of Semiconductor Photocatalytic Materials for the Removal of Inorganic Compounds from Wastewater

Abstract

A wide range of inorganic pollutants are sensitive to photochemical transformation on the surface of catalysts. The major inorganic wastewater pollutants treated by this process include cyanide-containing waste and heavy metal pollutants, such as arsenic species and hexavalent chromium. Heterogeneous photocatalysis has been explored as an alternative technology for inorganic ion removal offering satisfactory results. The photocatalytic removal of inorganic pollutants usually has two types of mechanisms: oxidation and reduction.In this chapter, the photocatalytic activities of various semiconductor materials for inorganic ion removal have been compiled and reviewed. The key advancements on the preparation of semiconductor materials tested for the removal of inorganic ions at low-level concentrations from natural water evaluating the matrix effects are also highlighted and discussed. In particular, the chapter focuses on enhancing the degradation efficiency; maximizing the use of illumination wavelength in the visible light region to develop solar active photocatalysts; the ease of separation from treated water, which is always of great interest; and improving the retrieval and reuse of semiconductors.

Fe doped TiO 2 photocatalyst for the removal of As(III) under visible radiation and its potential application on the treatment of As-contaminated groundwater

“…Alternatively, the heterogeneous photocatalysis using TiO 2 /UV has been shown a relatively inexpensive, and environmentally benign way to achieve the oxidation of As(III) into As(V) [2,[4][5][6][7][8]. TiO 2 is a promising material for arsenic removal from water due to its physical and photo-chemical stability, non-toxicity, the resistance to corrosion as well as strong oxidizing power [2].…”

“…TiO 2 is a promising material for arsenic removal from water due to its physical and photo-chemical stability, non-toxicity, the resistance to corrosion as well as strong oxidizing power [2]. However, TiO 2 has a low surface area and low adsorption capacity, resulting in the inefficient removal of As(V) [2,7]. Many efforts have been taken to improve the adsorption capacity of TiO 2 by increasing the specific surface area [6] or incorporating adsorbing materials into it with both great photocatalytic ability and high adsorption capacity [9][10][11][12][13].…”

Recent Developments in the Photocatalytic Treatment of Cyanide Wastewater: An Approach to Remediation and Recovery of Metals

“…This reductive mechanism can decrease the oxidation state of inorganic ions and metals in solution, leading to smaller forms or their zero-valence state. This promotes the precipitation on the semiconductor surface; nevertheless, it is required that the standard potential of the level of the conduction band of the electron is sufficiently negative for generating the reduction half-reaction of the metal [77]. Figure 4 shows the different conduction and valence bands of some metal sulfides and oxides with semiconductor properties.…”