Photocatalysts in Advanced Oxidation Processes for Wastewater Treatment

Elvis Fosso-Kankeu, Sadanand Pandey, Suprakas Sinha Ray, Elvis Fosso-Kankeu, Sadanand Pandey, Suprakas Sinha Ray

• Publisher: Wiley-Scrivener
• Year: 2020
• Print ISBN: 9781119631392
• eBook ISBN: 9781119631446
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Photocatalysts in Advanced Oxidation Processes for Wastewater Treatment comprehensively covers a range of topics aiming to promote the implementation of photocatalysis at large scale through provision of facile and green methods for catalysts synthesis and elucidation of pollutants degradation mechanisms. This book is divided into two main parts namely "Synthesis of effective photocatalysts" (Part I) and "Mechanisms of the photocatalytic degradation of various pollutants" (Part II). The first part focuses on the exploration of various strategies to synthesize sustainable and effective photocatalysts. The second part of the book provides an insights into the photocatalytic degradation mechanisms and pathways under ultraviolet and visible light irradiation, as well as the challenges faced by this technology and its future prospects.

Part 1
SYNTHESIS OF EFFECTIVE PHOTOCATALYSTS

1
Biogenic Synthesis of Metal Oxide Nanoparticle Semiconductors for Wastewater Treatment

Nkgaetsi M. Ngoepe^1,2, Mpitloane J. Hato^1,3*, Kwena D. Modibane¹ and Nomso C. Hintsho-Mbita^1,2†

¹Department of Chemistry, School of Physical and Mineral Sciences, University of Limpopo (Turfloop), Sovenga, Polokwane, South Africa

²DST/NRF Centre of Excellence in Strong Materials, South Africa

³Department of Environmental Sciences, College of Agriculture and Environmental Sciences, University of South Africa (UNISA), Florida Science Campus, Johannesburg, South Africa

Abstract
Water quality has become a priority worldwide, for every living organism to sustain life. Pollution created by textile dyeing operations has attracted an enormous amount of interest owing to the release of effluent containing complex mixture of coloured and potentially noxious compounds to the environment. However, industrial projects tend to produce large amounts of wastewater which are mostly used for economic purposes. Development of dyes and dyeing conditions to minimize the amount of residual dye contained in any effluent has been one of the promising route to minimise the environmental impact. Unfortunately, the presence of coloured discharge cannot be totally eliminated using only this route. Therefore, several methods such adsorption, membrane technology and photocatalysis have been developed to address the environmental pollution. Among these methods, photocatalytic degradation has gained attention as a tool for treating the coloured water. In particular, nanostructured materials such as titanium tioxide (TiO₂) and zinc oxide (ZnO) have been identified as the most promising and suitable photocatalytic semiconductors thus far, as compared to other nanoparticles. However, these nanoparticles possess wide bandgap values of 3.37 eV and 3.2 eV, respectively. Due to this high values, both TiO₂ and ZnO possess some drawbacks in degrading organic pollutants in wastewater. In addition, their chemical synthesis methods require hazardous solvents and generate toxic by-products, which therefore results in their limitation for their use in degrading a larger scale of pollutants. In this chapter, the focus will be on the synthesis of TiO₂ and ZnO using green materials such as plant, and bacteria and their use as potential photocatalysts in wastewater treatment. The challenges and future perspectives are also highlighted in this chapter.

Keywords: Metal oxides, dyes, photocatalytic degradation, wastewater

1.1 Introduction

Environmental remediation has become a concern for researchers, thus alternative treatment methods such as nanotechnology are being explored to provide for safe and quality water. Industries such as cosmetics, papers, and leather produce wastewater containing a number of organic dyes such as methylene blue (MB), methyl orange (MO), and rhodamine blue (RhB) [1, 2]. These effluents contaminate natural reservoirs such as rivers, lakes, and dams. The need for exploring reliable economic methods for treating water has risen greatly. Several methods such as microbial degradation, reverse osmosis, adsorption and photo catalysis to mention a few, have been used to eliminate organic dyes from wastewater. These methods have one form of a drawback or the other, for example microbial degradation is time consuming, ineffective with some of the dyes, and carcinogenic materials can be produced [3]. While, in reverse osmosis pre-treatment of the membrane is required before use [4]. Other methods such as adsorption, though they have been highly explored, they tend to be costly and the regeneration process is complicated [5]. However, a common drawback among all these methods is that they transform organic dyes from one phase to another and do not eliminate these pollutants completely, thereby creating secondary pollutants. In photocatalysis, the main advantage it has over other methods is that it dissociates organic dyes to less harmful intermediates. This is an advanced oxidation process that is mostly used since it is inexpensive and eco-friendly [6]. In this method, semiconductor materials are the preferred candidates for advanced oxidation process [7].

Semiconductor materials often consist of physicochemical properties such as generation of electron-hole pair under irradiation wavelength, redox potential, and adsorption ability which makes them suitable for photocatalytic degradation [8]. There are two types of semiconductors, namely; p-type and n-type. The p-types are extrinsic semiconductors which can conduct even at room temperature, whereby holes are the majority carrier and electrons are a minority. They tend to suffer from instability, photocorrosion, and reconstruction of self during photocatalysis [9, 10] thus their use is limited. Normally, semiconductors which are mostly used are the...

Table of contents

• Cover
• Table of Contents
• Preface
• Part 1: SYNTHESIS OF EFFECTIVE PHOTOCATALYSTS
• Part 2: MECHANISMS OF THE PHOTOCATALYTIC DEGRADATION OF VARIOUS POLLUTANTS
• Index
• End User License Agreement