Photocatalysts for degradation of dyes in industrial effluents: Opportunities and challenges

Abstract

Discharging dye contaminants into water is a major concern around the world. Among a variety of methods to treat dye-contaminated water, photocatalytic degradation has gained attention as a tool for treating the colored water. Herein, we review the recent advancements in photocatalysis for dye degradation in industrial effluents by categorizing photocatalyst materials into three generations. First generation photocatalysts are composed of single-component materials (e.g., TiO 2 , ZnO, and CdS), while second generation photocatalysts are composed of multiple components in a suspension (e.g., WO 3 /NiWO 4 , BiOI/ZnTiO 3 , and C 3 N 4 /Ag 3 VO 4 ). Photocatalysts immobilized on solid substrates are regarded as third generation materials (e.g., FTO/WO 3 -ZnO, Steel/TiO 2 -WO 3 , and Glass/P-TiO 2 ). Photocatalytic degradation mechanisms, factors affecting the dye degradation, and the lesser-debated uncertainties related to the photocatalysis are also discussed to offer better insights into environmental applications. Furthermore, quantum yields of different photocatalysts are calculated, and a performance evaluation method is proposed to compare photocatalyst systems for dye degradation. Finally, we discuss the present limitations of photocatalytic dye degradation for field applications and the future of the technology.

New Insight on Photoisomerization Kinetics of Photo-Switchable Thin Films Based on Azobenzene/Graphene Hybrid Additives in Polyethylene Oxide

“…Methyl red is of those azo dyes which contain one or more azo groups (–N=N–) as a chromophore group that is influenced by UV absorption. Recently, 2D carbon as graphene and graphene oxides were used as support materials for photocatalytic processes [ 20 , 21 ].…”

Anion-Exchange-Mediated Internal Electric Field: Boosting Photogenerated Carrier Separation and Utilization

“…Notably, these active species could, under green and mild conditions, participate in a variety of organic reactions, including hydrogenation 5,6 , epoxidation 7,8 , alcohol oxidation 9,10 , selective oxidation of aromatic compounds 11,12 , and even some reactions that are rather challenging in thermal catalysis. Yet still, currently for heterogeneous photocatalysts, there exist the common issues of rapid recombination of photocarriers and the resulting low e ciency of carrier separation and utilization, which would hamper the high-performance catalysis of sophisticated organic reactions, and thus their applications have so far been limited primarily to environment-related aspects such as degradation of organics, air puri cation and water photolysis [13][14][15][16][17] . A strategy extensively adopted to boost the carrier separation e ciency is to construct composite materials featuring heterojunctions, in which the internal electric eld (IEF), resulting from the different band structures at the interface, is expected to facilitate the carrier separation and migration 18,19 .…”

Visible Light Induced Photocatalytic Dye Degradation by Cobalt Oxide Nanoparticles

“…The semiconductor material based photocatalytic dye degradation mechanisms are well established in the literature [23,24,49,50] . The basic mechanism of photocatalytic degradation of dyes is illustrated in Figure 15.…”