Photocatalytic Applications of Metal Oxides for Sustainable Environmental Remediation

Abstract

Along with industrialization and rapid urbanization, environmental remediation is globally a perpetual concept to deliver a sustainable environment. Various organic and inorganic wastes from industries and domestic homes are released into water systems. These wastes carry contaminants with detrimental effects on the environment. Consequently, there is an urgent need for an appropriate wastewater treatment technology for the effective decontamination of our water systems. One promising approach is employing nanoparticles of metal oxides as photocatalysts for the degradation of these water pollutants. Transition metal oxides and their composites exhibit excellent photocatalytic activities and along show favorable characteristics like non-toxicity and stability that also make them useful in a wide range of applications. This study discusses some characteristics of metal oxides and briefly outlined their various applications. It focuses on the metal oxides TiO2, ZnO, WO3, CuO, and Cu2O, which are the most common and recognized to be cost-effective, stable, efficient, and most of all, environmentally friendly for a sustainable approach for environmental remediation. Meanwhile, this study highlights the photocatalytic activities of these metal oxides, recent developments, challenges, and modifications made on these metal oxides to overcome their limitations and maximize their performance in the photodegradation of pollutants.

Metal Oxide-Based Photocatalytic Paper: A Green Alternative for Environmental Remediation

“…They are water-soluble, with some being toxic and causing severe impacts on human health [34]. Moreover, these contaminants have a catastrophic effect on the environment and animals, interfering with the reoxygenation capacity of water bodies and blocking sunlight that will directly influence photosynthesis processes [35]. Rhodamine B, methylene blue, methyl orange, congo red, and other azo dyes are examples of model dyes tested in photocatalysis studies [19,[35][36][37][38][39].…”

Recent Advances in Biopolymer-Based Dye Removal Technologies

“…AOP technologies mainly involve photocatalytic processes, Fenton-like processes, ozonation processes, semiconductor photocatalysis, catalytic oxidation (non-iron), ultrasound irradiation, electronic beam irradiation or a combination of two or more processes. Examples of most widely used AOPs include photocatalytic oxidation (UV, UV/H 2 O 2 , UV/Fe 2 + , UV/H 2 O 2 /Fe 2 + , UV/O 3 , UV/S 2 O 8 2− , UV/Cl 2 ), ozonation (O 3 , O 3 /ultraviolet (UV), O 3 /H 2 O 2 , O 3 /H 2 O 2 /UV), semiconductor photocatalytic oxidation (UV/TiO 2 , UV/ZnO, UV/SnO 2 , UV/CeO 2 , UV/ Bi 2 O 3 , UV/WO 3 , UV/NiO, UV/CuO), catalytic homogeneous oxidation (oxides of Mn, Cu, Ru, Ag, and Co), catalytic heterogeneous oxidation (NiO/Al 2 O 3 , Cu/Li 2 O/γ-Al 2 O 3 ), colloidal metal nanoparticles (Au, Ag, and Pd), ultrasound irradiation, Fenton reactions (Fe 2 + /H 2 O 2 , Fe 2 + /H 2 O 2 /UV, Fe 3 + /H 2 O 2 /UV) and electrochemistry (anodic oxidation and electro-Fenton) [ 26 , 79 , 80 , 81 , 82 , 83 ].…”

“…The key advantages and disadvantages of AOPs are summarized in Table 4 [25]. [26,[79][80][81][82][83].…”

Photocatalytic activity of MnTiO3 perovskite nanodiscs for the removal of organic pollutants

“…The most cost-effective photocatalyst is expected to be non-poisonous, reusable, and highly durable. Therefore, various metal oxides and sulfides of Ni, Ti, Zn, W, Cu, and Mo are explored for photocatalytic dye-degradation [ 5 , 6 , 7 , 8 ]. However, oxidative degradation observed from metal oxides, without any substantial alterations in their properties, on exposure to the visible light has the potentials to serve in real-time applications, hence attracting the scientific community [ 9 ].…”