Yongfeng Qi

Preparation and Characterization of Titanium-Based Photocatalysts

We prepared a series of mole percentage of modified titanium dioxide materials. The crystalline phases of as-prepared nanocomposites were characterized by using the X-ray diffraction (XRD) of Cu Kα radiation (BRUKER D8 ADVANCE Diffractometer, Germany), in which the scanning angle range begins from 10° to 90° (the scanning rate is 2°min−1). In order to further identify the element composition, the AIK alpha X ray (HM = 1486.6 eV) radiation operated under 250 W (PHI5300, USA) was used to carry out the X ray photoelectron spectroscopy (XPS) analysis. In order to observe the surface structure and morphology, scanning electron microscope (SEM, Phillips XL-30 FEG/NEW) was used. Transmission electron microscopy (TEM, Philips Model CM200) confirmed the shape and microstructure. The crystal structures of the prepared samples were characterized by high resolution TEM (HRTEM). Energy dispersive X ray spectroscopy (EDS) was used to confirm the composition of the samples. According to the Brunauer-Emmett-Teller (BET) method (Micromeritics ASAP 2020), the error line of the specific surface area of the sample prepared from the N2 adsorption/desorption data is 1% of the measurement result. Fourier transform infrared (FTIR) spectra were obtained by using Nicolet Nexus spectrometer in the range of 4000–400 cm−1 using potassium bromide. The optical absorption properties of the samples prepared in 350–800 nm range were collected on UV-vis DRS (SHIMADZU UV-3600 Plus). BaSO4 is used as the reflectivity standard in UV-vis DRS experiment. Photoluminescence (PL) measurements of samples were carried out on SHIMADZU RF5301 (Japan), and data recorded in the range of 350–600 nm were recorded. The prepared samples were excited at 310 nm.

Foundations of Photocatalytic

Semiconductor photocatalysis technology is a green technology being developed rapidly in recent years by using solar energy for energy conversion and environmental purification, which has important application in both energy and environment. Photocatalysis has gradually been considered as a promising way to solve energy and environmental problems since Fujishima achieved hydrogen production from cracking water using titanium dioxide (titanium dioxide) in 1972. This field is becoming a hot topic and has attracted a lot of scientists’ attention and research. Semiconductor catalyst is driven by light to convert light energy into electrical or chemical energy without additional pollution. Furthermore, it is a technology to produce environmental friendly clean energy only with sunlight and can solve the ever increasing environmental pollution problems. In recent years, the depletion of fossil fuel and requirement of clean environment push the development of renewable energy including solar energy, which provides a good platform for the photocatalytic technology to accomplish the dream of blue sky and white cloud and sustainable developing. This chapter focuses on the development of photocatalytic technology for decades and expounds its development from the advent to the prosperous.

Photocatalytic Denitrification in Flue Gas

NOX and SO2 emission from power plants during the coal burning process has been one of the major problems that result in adverse effect on the environment and human health. In general, ammonia based selective catalytic reduction (NH3-SCR) and calcium-based wet flue gas desulfurization (WFGD-Ca) processes have been applied to flue gas treatment of coal-fired power plants on a large scale, but they have not been able to achieve the comprehensive removal of a variety of pollutants. The combination of NH3-SCR and WFGD-Ca processes is mainly used to remove both simultaneous NOX and SO2, but the high capital operating costs limit its use in developing countries. In recent years, the study on the degradation of wastewater and gaseous pollutants by titanium dioxide has received extensive attention and has obtained good results in basic research and application-oriental research. Fe3O4-titanium dioxide composites were prepared by hydrothermal method, and the titanium dioxide layer was coated on the surface of Fe3O4. Because of the benefits of photocatalytic method, it has been paid attention to control NOx and other pollutant in the flue gas. The main principle of photocatalytically treating NOx is to photocatalytically oxidize NO into NO2, which is soluble and may be captured by WFGD through liquid absorption.

The Photocatalytic Removal of Mercury from Coal-Fired Flue Gas

Mercury in the flue gas of coal combustion exists in three chemical forms: elemental mercury (Hg0), particle-bounded mercury (Hgp), and oxidized mercury (Hg2+). Hg2+ is water-soluble, so it can be removed by wet scrubbers and the Hg2+ removal efficiency can reach up to 90%. In addition, Hgp can be easily removed by electrostatic precipitator (ESP) or fabric filter (FF). However, elemental mercury is difficult to remove because of its volatility, insolubility and chemical stability. So the most critical step is to control elemental mercury. There are two main methods for elemental mercury control: adsorption and oxidation. Activated carbon injection has proven to be an effective adsorption method for elemental mercury removal in flue gas. However, its high operation cost and negative effect on fly ash quality may restrict its industrial application. The drawbacks associated with the use of particulate adsorbents make the oxidation method more attractive. In recent years, the progress in the photocatalytic oxidation of elemental mercury has aroused wide interests among researchers. Compared with other methods, photocatalytic oxidation possesses higher oxidation ability and no secondary pollution, therefore it is a promising technology for oxidation of elemental mercury. We set up a chemical reactor system to evaluate the photocatalytic performance on mercury in the simulated flue gas, and studied the mercury oxidation efficiency of different photocatalysts, including morphology controlled photocatalysts, metal or nonmetal modified titanium dioxide photocatalysts and others photocatalysts, such as BiOIO3 and ZnO. The morphology controlled photocatalysts include hollow titanium dioxide photocatalyst and anatase titanium dioxide with co-exposed (001) and (101) facets. The metal modified titanium dioxide photocatalysts include CuO/titanium dioxide and V2O5/titanium dioxide photocatalysts, and the nonmetal modified titanium dioxide photocatalysts include carbon spheres supported CuO/titanium dioxide photocatalysts and carbon decorated In2O3/titanium dioxide photocatalysts. These studies are helpful to observe the characteristics and performance of different kinds of photocatalysts.

The Photocatalytic Technology for Wastewater Treatment

In order to maintain the balance of desulfurization slurry material circulation system, prevent the soluble part of the chlorine concentration in flue gas to exceed a specified value, and ensure the quality of gypsum, discharge from the system is necessary, including a certain amount of waste water, which is mainly from gypsum dehydration and cleaning system. The impurities in waste water mainly include suspended, supersaturated sulfites, sulfates, and heavy metals, many of which are the primary pollutants required to be strictly controlled by national environmental standards. The photocatalysis showed great superiority on wastewater treatment. Based on the photocatalytic mechanism and the kinetics, the photocatalytic process includes primary reaction process and secondary reaction process, and the wastewater degraded with photocatalysts is studied in this chapter. Through the analysis of traditional method on degrading wastewater, it is a universal view that photocatalysis is a promising method with industrialized value. At last, several future developing views of the application of photocatalysts on wastewater treatment were put forward, which included efficiency priority, combining immobilization, mechanism in microcosmic, and application in macroscopic.

Preparation and Characterization Other Photocatalysts

A series of zinc-based photocatalyst and bismuth-based photocatalyst were prepared. Several preparation methods and their characteristics of zinc-based photocatalyst are given. BiOIO3 nanosheets are studied systematically, which possess superior photocatalytic properties. The fabricated CSs-BiOI/BiOIO3 composites with heterostructures show the enhanced photocatalytic performance than BiOIO3. The physical and chemical properties of the as-prepared materials are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, high resolution TEM, Brunauer-Emmett-Teller, Fourier transform infrared, UV-vis diffuse reflectance spectra, and Photoluminescence.