Removal of Organic Dyes from Water and Wastewater Using Magnetic Ferrite-Based Titanium Oxide and Zinc Oxide Nanocomposites: A Review

Heterogeneous photocatalysis using titanium dioxide (TiO2) and zinc oxide (ZnO) has been widely studied in various applications, including organic pollutant remediation in aqueous systems. The popularity of these materials is based on their high photocatalytic activity, strong photosensitivity, and relatively low cost. However, their commercial application has been limited by their wide bandgaps, inability to absorb visible light, fast electron/hole recombination, and limited recyclability since the nanomaterial is difficult to recover. Researchers have developed several strategies to overcome these limitations. Chief amongst these is the coupling of different semi-conductor materials to produce heterojunction nanocomposite materials, which are both visible-light-active and easily recoverable. This review focuses on the advances made in the development of magnetic ferrite-based titanium oxide and zinc oxide nanocomposites. The physical and magnetic properties of the most widely used ferrite compounds are discussed. The spinel structured material had superior catalytic and magnetic performance when coupled to TiO2 and ZnO. An assessment of the range of synthesis methods is also presented. A comprehensive review of the photocatalytic degradation of various priority organic pollutants using the ferrite-based nanocomposites revealed that degradation efficiency and magnetic recovery potential are dependent on factors such as the chemical composition of the heterojunction material, synthesis method, irradiation source, and structure of pollutant. It should be noted that very few studies have gone beyond the degradation efficiency studies. Very little information is available on the extent of mineralization and the subsequent formation of intermediate compounds when these composite catalysts are used. Additionally, potential degradation mechanisms have not been adequately reported.

Nanocrystalline ferrihydrite activated peroxymonosulfate for butyl-4-hydroxybenzoate oxidation: Performance and mechanism

Heterogeneous catalysts activated peroxymonosulfate (PMS) for degradation of refractory organic contaminants has been recognized as a promising removal technology for the environmental remediation. In this study, nanocrystalline ferrihydrite (NFH) was prepared to activate PMS for the degradation of butyl-4-hydroxybenzoate (BHB). XPS analysis indicates that calcination process played a key role in regulating the surface oxygen species of NFH, thus control its activation ability toward PMS. NFH exhibits excellent stability (the released concentration of Fe ions < 0.13 mg/L) and desirable reusability. Increasing solution temperature and NFH dosage exerted a positive role in PMS activation for BHB removal, while such positive correlation was not found in the case of increasing initial pH. Increasing the static solution dissolved oxygen remarkably enhanced BHB oxidation kinetics. However, continuous N₂ and air blowing caused a significant decline in BHB removal. Reaction mechanism study showed that SO₄^‒, OH, O₂^‒, and ¹O₂ were the main reactive oxygen species for degrading BHB by NFH/PMS. LC/MS analysis indicated BHB was degraded by the pathways of hydroxylation, carboxylation, decarboxylation, dehydrogenation, ring cleavage and chain cleavage reaction. This work suggests the ferrihydrite might be a promising catalyst to activate PMS to destroy refractory organic pollutants in the environmental remediation.

Metallic Active Sites on MoO2(110) Surface to Catalyze Advanced Oxidation Processes for Efficient Pollutant Removal

Advanced oxidation processes (AOPs) based on sulfate radicals (SO₄^⋅−) suffer from low conversion rate of Fe(III) to Fe(II) and produce a large amount of iron sludge as waste. Herein, we show that by using MoO₂ as a cocatalyst, the rate of Fe(III)/Fe(II) cycling in PMS system accelerated significantly, with a reaction rate constant 50 times that of PMS/Fe(II) system. Our results showed outstanding removal efficiency (96%) of L-RhB in 10 min with extremely low concentration of Fe(II) (0.036 mM), outperforming most reported SO₄^⋅−-based AOPs systems. Surface chemical analysis combined with density functional theory (DFT) calculation demonstrated that both Fe(III)/Fe(II) cycling and PMS activation occurred on the (110) crystal plane of MoO₂, whereas the exposed active sites of Mo(IV) on MoO₂ surface were responsible for accelerating PMS activation. Considering its performance, and non-toxicity, using MoO₂ as a cocatalyst is a promising technique for large-scale practical environmental remediation.

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The degradation rate of PMS/Fe(II)/MoO₂ system is 50 times higher than that without MoO₂

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Fe(III)/Fe(II) cycle on (110) surface of MoO₂ in PMS/Fe(II)/MoO₂ system was confirmed

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The metal active sites exposed to MoO₂ (110) surface are responsible for PMS activation

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Compared with MoS₂, MoO₂ co-catalytic system has less toxicity and no release of H₂S

Sonocatalytic degradation of butylparaben in aqueous phase over Pd/C nanoparticles

In the present work, the sonocatalytic degradation of butylparaben was investigated using Pd immobilized on carbon black as the sonocatalyst. The presence of 25 mg/L 10Pd/C significantly increased the removal rate of butylparaben and the observed kinetic constant increased from 0.0126 to 0.071 min^-1, while the synergy index between sonolysis and adsorption was 70.7%. The BP degradation followed pseudo-first-order kinetics with the apparent kinetic constant decreased from 0.071 to 0.030 min^-1 when the initial concentration of butylparaben increased from 0.5 to 2 mg/L. The process was being favored slightly under alkaline conditions. The presence of organic matter (20 mg/L humic acid) reduced the apparent kinetic constant more than two times. The addition of chlorides up to 250 mg/L did not significantly reduce the rate of reaction, while the presence of 250 mg/L bicarbonates reduced the observed kinetic constant from 0.071 to 0.0472 min^-1. The prepared catalyst retains the efficiency after five subsequent experiments since the apparent kinetic constant was only slightly decreased from 0.071 to 0.059 min^-1.

Alcohol-assisted self-assembled 3D hierarchical iron (hydr)oxide nanostructures for water treatment

Self-assembled 3D hierarchical iron (hydr)oxides are synthesized with different alcohol additives for water treatment.

Highly efficient removal of organic contaminants based on peroxymonosulfate activation by iron phthalocyanine: mechanism and the bicarbonate ion enhancement effect

The development of catalytic oxidation processes with high efficiency based on peroxymonosulfate (PMS) activation is a promising yet challenging research topic in the environmental catalysis field.

Magnetism in CoFe2O4nanoparticles produced at sub- and near-supercritical conditions of water

Size and size distribution investigation of magnetic CoFe₂O₄, hydrothermally synthesized using three different heating rates from 0.15 °C s⁻¹to ∼500 °C s⁻¹.

Augmenting the catalytic performance of spinel nanoferrites (CoFe2O4 and NiFe2O4) via incorporation of Al into the lattice

Augmentation in the catalytic performance via incorporation of Al³⁺ ions into the lattice of spinel nanoferrites owing to the synergistic interactions among the metal ions present in the surface exposed catalytically active octahedral sites.

Preparation of a macroporous CuAl2O4 spinel monolith and its rapid selective adsorption towards some anionic dyes

Macroporous CuAl₂O₄ spinel, which was first synthesized, showed excellent selective adsorption performance towards some anionic dyes.