Semiconductor Photocatalysis for Water Purification

doi:10.1016/B978-0-12-813926-4.00030-6

Nanoscale Materials in Water Purification

Micro and Nano Technologies

2019, Pages 689-705

Nanoscale Materials in Water Purification

https://doi.org/10.1016/B978-0-12-813926-4.00030-6 Get rights and content

Abstract

Nanosemiconductor materials have been widely used for photocatalytic degradation of all kinds of organic pollutions in water system due to the advantages such as high specific surface area, abundant reactive sites, and excellent photochemical performance. However, their application in the photocatalytic field is restricted as a result of the fast combination of photo-induced electron-holes pairs and limited visible-light absorption. Considerable strategies have been developed in the past decades. In this chapter, the development and importance of semiconductor-based photocatalysts in environmental treatment are summarized. The improvement via doping, morphology control, design of photocatalytic reactors, and porous material support are emphasized. Additionally, the design of highly efficient photoelectrocatalysis processes and their reactors are also discussed. Meanwhile, discoveries in the underlying mechanisms of the interfacial electron transfer and electron-holes separation are presented. Highlights of the challenges and proposed strategies in developing advanced nanosemiconductor photocatalysts for the application in degradation of pollutants are proposed.

References (0)

Cited by (22)

Recent progress in red phosphorus-based photocatalysts for photocatalytic water remediation and hydrogen production
2022, Applied Materials Today
Citation Excerpt :
This technique has the potential to degrade the various types of pollutants present in wastewater as well as produce a green energy source like H2 by using semiconducting materials, all by utilizing solar energy which is available in abundance in nature [4,5,6,7,8]. Photocatalysis has many advantages over other techniques such as environment-friendliness, use of ambient conditions, water utility as a solvent, and the absence of formation of any secondary pollutants [9,10,11] . Photocatalysts, semiconducting materials, forms the basis of this technique that can generate electron-hole (e−/h+) when light possessing a minimum energy (greater than or equal to the band-gap energy) of the semiconductor is incident on their surface.
Elemental red phosphorus (RP) photocatalyst has drawn considerable attention to solve the problem of water and energy scarcity because of its availability in abundance, wide response in the visible region, low cost, non-toxicity, and tunable band gap (1.5 eV-2.4 eV). Additionally, it possesses some interesting structural and photocatalytic properties which make it a potential photocatalyst. However, it possesses lower charge carrier mobility because of the presence of charge trapping sites on its surface which restricted its photocatalytic activity in comparison to other traditional photocatalysts. Therefore, various strategies such as preparation of crystalline and nanostructured RP, cocatalyst loading, and construction of heterojunction with RP have been explored to enhance the photocatalytic performance of RP. Over the past few years, significant efforts have been done to develop various RP-based photocatalysts using these strategies. These materials have broad applications in photocatalytic wastewater treatment and water splitting. This review seeks to provide an overview of the progress made so far in photocatalytic water treatment and hydrogen generation applications using RP-based photocatalysts. It starts off with a discussion of the fundamentals and mechanisms of photocatalysis technique, followed by a discussion on the structural, photocatalytic properties and its applications for wastewater treatment and hydrogen production. Finally, it concludes with proposed challenges and perspectives for the future development of advanced RP-based photocatalysts.
Solar reclamation of groundwater and agro-wastewater polluted with pesticide residues using binary semiconductors and persulfates for their reuse in crop irrigation
2022, Pesticides Remediation Technologies from Water and Wastewater
Diffuse pesticide contribution into groundwater is mainly due to leaching (i.e., the movement of pesticides through the soil profile to groundwater). In many areas of the world, groundwater is used for drinking and irrigation purposes, and its use is seriously threatened by pesticide pollution. Therefore, operational, low-cost, and environmentally friendly methods to detoxify groundwater are required to avoid damage to the environment and human health, significantly earlier to the reuse of reclaimed water. Thereby, research developed on thr decontamination of water polluted with pesticide residues has been focused on the expansion of advanced oxidation processes (AOPs) being solar heterogeneous photocatalysis of actual interest amongst these technologies. In this process, semiconductor materials absorb directly or indirectly UV-Vis irradiation generating mainly hydroxyl radicals (HO^•), a strong oxidizing species, and other radicals. Moreover, the addition of oxidizing agents to a water slurry such as persulfates (HSO₅⁻ or S₂O₈⁼) generally entails an increase in the photodegradation rate of pesticides because they can generate sulfate radical anion (SO₄^•−), also with high oxidation capacity. Therefore, this technology has recently gained considerable attention to transform biorecalcitrant pollutants like many pesticides into less detrimental compounds finally getting the mineralization of the parent substances to CO₂ and H₂O. With this aim, the effect of binary semiconductors (mainly ZnO and TiO₂) to detoxify groundwater and agro-wastewater for their use as irrigation water is reviewed in this chapter since most of these materials are able to absorb a significant part of the Earth’s solar radiation spectrum.
Synthesis of pure and doped SnO<inf>2</inf> and NiO nanoparticles and evaluation of their photocatalytic activity
2022, Materials Chemistry and Physics
Citation Excerpt :
When the semiconductor is irradiated by a photon having energy equal to/greater than its band gap, electrons will be excited to the conduction band (possess strong oxidation ability) leaving holes (possess strong reduction ability) in the valence band and creating e‒/hole+ pair which so-called exciton. Generally, the more positive is the valence band and the more negative is the conduction band, the more efficient is the photocatalyst [34]. The photogenerated charged species migrate to the oxide surface, react with the surface adsorbed water and oxygen molecules and form reactive oxygen components like OH.-, .
This paper presents a comparative experimental study between sol-gel and sonochemical approaches for the synthesis of SnO₂ and NiO nanoparticles. In addition, the doping effect on the structural, optical properties and the photocatalytic activity of the synthesized oxides was studied. The XRD results revealed the high purity of the prepared oxides and the well incorporation of the dopant elements into the host structure. Morphological characterization by HR-TEM showed ultrafine nanoparticles with an average size <10 nm for the oxides calcined at 250 °C. The particle size increased upon calcination reaching about 30–40 nm for the samples calcined at 750 °C. The EDX results of the doped samples ensured the existence of the dopant elements without any impurities. Diffuse reflectance spectroscopy UV-DR results of the doubly doped tin oxide Sn_0.094Ti_0.03Ni_0.03O₂ and nickel oxide Ni_0.094Ti_0.03Sn_0.03O exhibited lower band gap energies 3.24 eV and 3.27 eV, respectively, than that of their corresponding pure oxides. The fluorescence probe method and the photodegradation of Coomassie Brilliant Blue dye R (CBBR) showed higher photodegradation rate constants over the oxides prepared by sonochemical than sol-gel routes. The photocatalytic activity process using five real industrial wastewater samples was explored and the results revealed that these oxides could be feasible candidates for the photodegradation of organic pollutants.
Solvent controlled synthesis of quercetin loaded CuS nanostructure: A versatile treatment against harmful bacteria and carcinogenic organic moiety in water
2021, Journal of Molecular Liquids
Citation Excerpt :
This concept suffers from the defects of cost-effectiveness, complex nature and high maintenance [12]. The nanomaterial semiconductor photocatalysis is an emerging platform for water purification and gaining popularity due to its high surface area, heterogeneous nature (easily separable), reproducibility and high selectivity [13,14]. The catalytic activity of nanomaterial is strongly influenced by particle size, morphology (hollow, needle, sphere flower etc.) and stoichiometry ratio of the material [15].
The present work demonstrates the successful synthesis of solvent controlled copper sulfide nanoparticles (CuS NP's) and nanotubes (CuS NT's) using a facile and green microwave irradiation method. Ethylene glycol and a mixture of water and ethylene glycol (1:1) were used as solvents for the preparation of CuS NT's and NP's, respectively. The catalytic and bactericidal attributes of the fabricated nano structures were measured and compared vividly. The formation of CuS nano structures was monitored using simple techniques like UV–visible absorption spectroscopy, IR spectroscopy, XRD and then finally confirmed by TEM analysis. After complete structural elucidation, biologically active quercetin molecule was successfully loaded into both nano-modules and confirmed using UV, TGA and IR techniques. The respective loading efficiency in CuS NP's and NT's was estimated to be 9.59 ± 3% and 12.5 ± 3%. The release of quercetin drug using both CuS nano-modules at two different pH conditions (pH 2.2 and 7.4) was further investigated. Owing to the inherent bactericidal properties of nanostructures and quercetin, the synergistic effect of quercetin and CuS was also examined. Further, the catalytic efficiency of CuS NP's and NT's were tested on the removal of toxic carcinogenic dyes (Methyl orange and crystal violet) in solar light. The catalytic degradation study of methyl orange demonstrated 91.72% degradation ability with CuS NP's and 96.62% with CuS NT's in 30 min. Moreover, the percentage degradation of crystal violet with CuS NP's and NT's was found to be 96.92 and 97.23%, respectively.
Heterojunction Cr<inf>2</inf>O<inf>3</inf>-Ag<inf>2</inf>O nanocomposite decorated porous polymer monoliths a new class of visible light fast responsive heterogeneous photocatalysts for pollutant clean-up
2021, Journal of Environmental Chemical Engineering
Citation Excerpt :
To overcome these challenges, the photo-induced catalytic oxidation processes have gained considerable attention for wastewater treatment [15–18]. In this process, the use of solar energy and a photoactive semiconductor (TiO2, ZnO, WO3, CdS, ZnS, etc.) as the heterogeneous catalyst proves to be a viable and sustainable approach for the dissipation of organic pollutants [19–22]. However, the use of nanoparticle-based semiconductor materials is associated with a potential drawback in terms of its nanotoxicology, which continues to be a debatable issue [23,24].
We report a unique Cr₂O₃-Ag₂O nanocomposite that is homogeneously dispersed on a polymer monolith by solvothermal assisted polymerization method. The surface morphology and structural features of the visible light responsive photocatalyst is characterized using FE-SEM-EDAX, HR-TEM-SAED, p-XRD, XPS, PLS, FT-IR, UV-Vis-DRS, TGA, BET/BJH and PEC measurements. The characterization data reveals a voluminous macro-/meso-porous monolithic framework with superior surface properties that promotes photocatalytic activity through the uniformly dispersed Cr₂O₃-Ag₂O nanocomposites. Electrochemical and spectroscopic studies reveal a lower recombination rate of the photogenerated charges for (60:40) Cr₂O₃-Ag₂O nanocomposite, with an energy band gap of 2.35 eV. A comprehensive analysis of physicochemical parameters such as solution pH, catalyst quantity, dopant stoichiometry, dye concentration, electron acceptors, illumination time and intensity reveals superior photocatalytic efficacy in dissipating organic dye (Reactive Brown-10) pollutants, within 1 h of visible light (300 W/cm²) irradiation. The high surface area of the Cr₂O₃-Ag₂O dispersed polymer monolith facilitates effectual dissipation of massive organic pollutants using a nominal photocatalyst quantity (100 mg), in the optimized pH range of 3.0–4.0. The monolithic photocatalyst ensures easy transport of pollutants to the photoactive sites, thereby ensuring ≥ 99% dye degradation, through superoxide anion radical species. The proposed photocatalyst is environmentally benign with excellent durability and reusability.
Visible light photocatalysis: Case study (process)
2021, Handbook of Nanomaterials for Wastewater Treatment: Fundamentals and Scale up Issues
The release of toxic wastewater into the surface and ground water has created global clean water crisis. With global warming, rapid urbanization, and industrialization, it's a worldwide challenge to provide clean and potable water to the ever-growing population. The technological innovation for wastewater remediation should not only be efficient but also cost-effective because the population density is high in poor countries. Among the several methods, wastewater treatment by visible light photocatalytic process is an attractive technology for large-scale wastewater remediation. However, photocatalytic process alone may not provide the ultimate solution to the wastewater problem. Combining the photo and nonphoto advanced oxidation processes together and designing a hybrid process have a high potential for complete remediation of wastewater. Herein, the development of photocatalytic and hybrid processes has been discussed.

View all citing articles on Scopus

View full text

Chapter 24 - Semiconductor Photocatalysis for Water Purification

Abstract