Emerging Aspects of Photo-catalysts (TiO2 & ZnO) Doped Zeolites and Advanced Oxidation Processes for Degradation of Azo Dyes: A Review

Abstract

<jats:sec> <jats:title>Background:</jats:title> <jats:p>Azo dyes are recognized as non-decomposable and recalcitrant compounds and can be depleted into more dangerous secondary products in anaerobic environments. In current scenario different water treatment strategies including adsorption, photo-catalysis and advanced oxidation processes based practices are facing different limitations.</jats:p> </jats:sec> <jats:sec> <jats:title>Method:</jats:title> <jats:p> A literature survey was accomplished by searching the scientific data from different search engines including Scopus, PubMed, Science Direct, Springer, Taylor &amp; Francis,Google Scholar, Blackwell-Synergy, Wiley-Interscience and Research-Gate etc. This article has been compiled after intensively reviewing about 231 research papers, reviews and book chapters in the fields of industrial effluents, hazardous materials and water treatment strategies with their advantages and limitations.</jats:p> </jats:sec> <jats:sec> <jats:title>Results:</jats:title> <jats:p> Molecular oxygen and other active species such as O2•−, HO2•, H2O2 and •OH play a significant role in degradation of dyes in AOPs and photo-catalyst utilizes sunlight energy and accelerates some chemical reactions depending upon the activation energies. Different reaction parameters;calcination temperature, pH, initial dye concentration, and catalyst dosage have significant impact on photo-catalytic degradation performance.Characterization of degradation processes of dye-stuffs could be carried out by state of the art analytical techniques i.e. UV-Visible spectroscopy, powdered XRD, FTIR (ATR), EDX-SEM, BET and differential pulse voltammetry. GC-MS and LC-MS investigation of photo-degradation by-products and intermediates could provide identification and possible degradation pathway for target dye molecules. This review covers research related to photocatalytic degradation of azo dyes by TiO2 and ZnO, widely used photo catalysts and various combination of zeolites. </jats:p> </jats:sec> <jats:sec> <jats:title>Conclusion:</jats:title> <jats:p>It can be concluded that the combination of nano-sorbents (Fly Ash Zeolites) and photo-catalysts not only enhances the degradation but also removes toxic dye molecules and theirby-products, effectively. The review explains the suitability of synergic applications of catalysts (TiO2, ZnO) and catalytic bed (zeolites) for different industrial effluents and waste water treatment as a significant pace towards green technology. </jats:p> </jats:sec>

Enhanced Visible Light Photocatalytic Degradation of Methylene Blue by CdS-ZnS-BiPO4 Nanocomposites Prepared by a Solvent-Assisted Heating Method

“…Photocurrent responses of different nanocomposites are summarized in Figure 6B, in which photocurrent responses of CdS-BiPO 4 and CdS-ZnS-BiPO 4 are higher than those of BiPO 4 and ZnS-BiPO 4 , demonstrating improved charge separation as a result of the p-n junction formed between P-type and N-type semiconductors. A p-n junction can improve the charge separation through the Schottky barrier effect, which is similar to a previous study on electron transfer from a semiconductor to a metal [19]. This contributes to the interfacial charge transfer between the semiconductors, thus improving the photocatalytic activity.…”

“…Thus, a new method of employing photocatalysts in breaking down dyes has been developed as an alternative option for effective treatment of wastewater containing organic dyes [12][13][14][15][16][17][18]. In the pioneer work, TiO 2 catalyst was 2 of 19 attractive due to its nontoxicity, low cost, and high chemical stability [19]. However, with low quantum efficiency (<20%), the photocatalytic activity of TiO 2 is inefficient, leading to high operation cost for industrial applications as high-energy UV light is required for water treatment [20].…”

High-Performance Integrated rGO-[Polymeric Ionic Liquid] [Heteropolyanions] for Catalytic Degradation of Azo Dyes

“…Among these, the catalytic oxidation technology has attracted significant attention due to its ideal degradation efficiency and mild reaction conditions. The dyes decolorized via the above procedure may follow two routes, that is, partially degrade into relevant aromatic intermediates, which can be further mineralized by certain technical means, such as aerobic biodegradation, to eliminate their toxicity or deeply mineralize into oxyacids, CO 2 , and H 2 O. − …”

Effects of Ag Nanoparticles on Zinc Oxide Photocatalytic Performance

“…Among wide-bandgap semiconductors eligible for the process of photocatalysis and dye degradation, special attention has been given to zinc oxide (ZnO) in recent literature due to its special features. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22].…”