Effective Enhancement of the Degradation of Oxalic Acid by Catalytic Ozonation with TiO2 by Exposure of {001} Facets and Surface Fluorination

Ferromanganese oxide-functionalized TiO2 for rapid catalytic ozonation of PPCPs through a coordinated oxidation process with adjusted composition and strengthened generation of reactive oxygen species

Ferromanganese oxide (MFOx) was first utilized to functionalize TiO2 and an MFOx@TiO2 catalyst was developed for catalytic ozonation for rapid attack of pharmaceutical and personal care products (PPCPs) with adjusted reactive oxygen species (ROSs) composition and strengthened ROSs generation. Unlike Al2O3, which strongly relied on adsorption and was significantly influenced by MFOx loading, synergistic catalytical effects of MFOx and TiO2 were observed, and optimal MFOx doping of 2 wt% and MFOx@TiO2 dosage of 500 ppm were obtained for catalyzing ozonation. In ibuprofen (IBP) degradation, MFOx@TiO2-catalyzed ozonation (MFOx@TiO2/O3) obtained 2.0-, 4.7- and 6.9-folds the kobs of TiO2/O3, MFOx/O3 and bare ozonation (B/O3). Stronger O3 decomposition was observed by MFOx@TiO2 over bare TiO2 with the participation of redox pairs Fe(II)/Fe(III) and Mn(II)/Mn(III)/Mn(IV) and increased surface oxygen vacancies (SOVs) from 9.8 % to 33.7 % was detected. The results revealed that Fe(II), Mn(II) and Mn(III) with low valance accelerated Ti(III) generation from Ti(VI), obtaining an unprecedented high Ti(III) composition occupying 35.3 % of the total Ti atoms. Ti(III) catalyzed the direct reduction of SOVs-O2 to •O2-, and it accelerated the formation of Ti(VI)-OH and Ti(VI)-O which catalyzed O3 decomposition into •O2-. •O2- was found to primarily initiate IBP degradation with nucleophilic addition and dominated over 66 % IBP removal. The enhanced •O2- generation further strengthened •OH and 1O2 production. MFOx@TiO2/O3 obtained 17 %, 21 % and 30 % higher TOC removal over TiO2/O3, MFOx/O3 and B/O3, respectively. Acute toxicity tests confirmed the effective toxicity control of organics by MFOx@TiO2/O3 process (inhibition rate: 10.9 %). Degradation test of atenolol and sulfamethoxazole confirmed the catalytic effects of MFOx@TiO2. MFOx@TiO2 performed strong resistance to water matrix in application test and showed good stability and reusability. The study proposed an effective catalyst for strengthening the ozonation process on PPCPs degradation and provided an in-depth understanding of the mechanisms and characteristics of the MFOx@TiO2 catalyst and MFOx@TiO2/O3 process.

A review on recent advancements in extraction, removal and recovery of phenols from phenolic wastewater: Challenges and future outlook

Water pollution is the major problem seen in today's scenario and even pollutants at low concentration harms our environment. In industrial sector usage of phenol is seen even at low concentrations. The interaction of phenol in the environment provides adverse effects to living beings. This review focuses on the toxicity of phenol and its impact towards environment and human health. The treatment techniques such as distillation, extraction, wet air oxidation, membrane process, electrochemical oxidation, biological treatment and finally adsorption techniques were discussed. Among many treatment techniques so far utilized in the treatment of phenol, adsorption was considered as one of the best technique due to its advantages such as reusability, ease in operation, large availability etc., This review also highlights the adsorption technique for the cleaner removal of phenol from aqueous solution with novel as well as low-cost adsorbents in the removal of phenolic compounds. This review also discusses about the drawbacks and issues related with adsorption of phenolic compounds.

Synergistic effect of F and triggered oxygen vacancies over F-TiO2 on enhancing NO ozonation

Oxidation-absorption technology is a key step for NO_x removal from low-temperature gas. Under the condition of low O₃ concentration (O₃/NO molar ratio = 0.6), F-TiO₂ (F-TiO₂), which is cheap and environmentally friendly, has been prepared as ozonation catalysts for NO oxidation. Catalytic activity tests performed at 120°C showed that the NO oxidation efficiency of F-TiO₂ samples was higher than that of TiO₂ (about 43.7%), and the NO oxidation efficiency of F-TiO₂-0.15 was the highest, which was 65.3%. Combined with physicochemical characteristics of catalysts and the analysis of active species, it was found that there was a synergistic effect between F sites and oxygen vacancies on F-TiO₂, which could accelerate the transformation of monomolecular O₃ into multi-molecule singlet oxygen (¹O₂), thus promoting the selective oxidation of NO to NO₂. The oxidation reaction of NO on F-TiO₂-0.15 follows the Eley-Rideal mechanism, that is, gaseous NO reacts with adsorbed O₃ and finally form NO₂.

Ultrasonic Auxiliary Ozone Oxidation-Extraction Desulfurization: A Highly Efficient and Stable Process for Ultra-Deep Desulfurization

For ultra-deep desulfurization of diesel fuel, this study applied the ultrasound-assisted catalytic ozonation process to the dibenzothiophene (DBT) removal process with four Keggin-type heteropolyacids (HPA) as catalysts and acetonitrile as extractant. Through experimental evaluations, H₃PMo₁₂O₄₀ was found to be the most effective catalyst for the oxidative removal of DBT. Under favorable operating conditions with a temperature of 0 °C, H₃PMo₁₂O₄₀ dosage of 2.5 wt.% of n-octane, and ultrasonic irradiation, DBT can be effectively removed from simulated diesel. Moreover, the reused catalyst exhibited good catalytic activity in recovery experiments. This desulfurization process has high potential for ultra-deep desulfurization of diesel.

Catalytic ozonation with vanadium oxide-doped TiO2 nanoparticles for the removal of di-2-ethylhexyl phthalate

Among various plastic additives, di-2-ethylhexyl phthalate (DEHP) has been a great concern due to its high leaching potential and harmful effects on both human and the ecosystem. For the effective oxidation and mineralization of DEHP by ozone in the existing TiO₂ catalytic processes, the heterogeneous catalyst, vanadium oxide (V₂O₅)-incorporated TiO₂ (V₂O₅/TiO₂), was synthesized. The generation of hydroxyl radicals was promoted by cyclic redox reactions of vanadium atoms in V₂O₅/TiO₂ via the increase of surface oxygen vacancies by the replacement of V⁵⁺ species in the lattice of TiO₂. The catalytic ozonation in the presence of V₂O₅/TiO₂ exhibited the significantly higher degradation of DEHP with the pseudo-second-order kinetic constant of 1.7 × 10⁵ mM^-1min^-1 and the removal efficiency of 58.7% after 60 s in 2 mg/L of ozone. The degradation of DEHP was initiated by the shortening of the alkyl-side chain followed by the opening of esterified benzene moieties.

Selective Fluoride Transport in Subnanometer TiO2 Pores

Synthesizing nanopores which mimic the functionality of ion-selective biological channels has been a challenging yet promising approach to advance technologies for precise ion-ion separations. Inspired by the facilitated fluoride (F^-) permeation in the biological fluoride channel, we designed a highly fluoride-selective TiO₂ film using the atomic layer deposition (ALD) technique. The subnanometer voids within the fabricated TiO₂ film (4 Å < d < 12 Å, with two distinct peaks at 5.5 and 6.5 Å), created by the hindered diffusion of ALD precursors (d = 7 Å), resulted in more than eight times faster permeation of sodium fluoride compared to other sodium halides. We show that the specific Ti-F interactions compensate for the energy penalty of F^- dehydration during the partitioning of F^- ions into the pore and allow for an intrapore accumulation of F^- ions. Concomitantly, the accumulation of F^- ions on the pore walls also enhances the transport of sodium (Na⁺) cations due to electrostatic interactions. Molecular dynamics simulations probing the ion concentration and mobility within the TiO₂ pore further support our proposed mechanisms for the selective F^- transport and enhanced Na⁺ permeation in the TiO₂ film. Overall, our work provides insights toward the design of ion-selective nanopores using the ALD technique.

Probing the formation and optical properties of Ti3+–TiO2 with (001) exposed crystal facet by ethanol-assisted fluorination

(001)-faceted TiO₂ with Ti³⁺ defects that are exclusively embedded in the bulk lattice near the surface was synthesized.

Engineering Z-system hybrids of 0D/2D F-TiO2 quantum dots/g-C3N4 heterostructures through chemical bonds with enhanced visible-light photocatalytic performance

A Z-system hybrid of F-TiO₂ quantum dots/g-C₃N₄ nanosheets with an effective pathway (C–O bond) for charge transfer and selective recombination was constructed.

Zinc-iron silicate for heterogeneous catalytic ozonation of acrylic acid: efficiency and mechanism

This research aimed at researching the degradation of acrylic acid (AA) in aqueous solution, by catalytic and non-catalytic ozonation processes performed in a semi-continuous reactor. Zinc–iron silicate was synthesized and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) analysis, Fourier transformation infrared (FT-IR) and energy dispersive spectrometry (EDS). The characterization studies showed that Fe–Si binary oxide, Zn–Si binary oxide, ZnO and Fe₂O₃ deposits were formed on the surface of poor crystallinity zinc–iron silicate which contained abundant functional groups. Catalytic ozonation test results revealed that zinc–iron silicate exhibited high catalytic activity and stability in catalytic ozonation of AA in aqueous solution. The inclusion of zinc–iron silicate in the ozonation process enhanced AA decomposition by 28.7% and TOC removal by 20%, compared to the ozonation alone. The main AA removal mechanisms involved direct oxidation by ozone and indirect oxidation by hydroxyl radicals generated by the ozone chain reaction accelerated by zinc–iron silicate. The surface characteristics and chemical composition are significant factors determining the catalytic activity of zinc–iron silicate.

Zinc–iron silicate was synthesized, and exhibited high activity and stability for catalytic ozonation under semi-continuous conditions.

The role of surface hydroxyl concentration on calcinated alumina in catalytic ozonation

Alumina has been used as a catalyst for ozonation, surface hydroxyl on which is regarded as the active center for ozone attack, but the influences of hydroxyl generation are still vague. Here, we prepared alumina with different hydroxyl concentrations by adjusting calcination temperatures, of which the catalytic activity was evaluated with the mineralization degree of phenol, and then revealed the active sites of hydroxyl generation with characterization of XRD, Py-IR, and NH₃-TPD. The results show that the greater the hydroxyl concentration, the higher the catalytic activity, demonstrating that surface hydroxyl contributes to its catalytic activity. The effect of calcination temperatures on hydroxyl concentration and catalytic activity is in accordance with the amount of weak Lewis acid sites on the surface of alumina, illustrating the surface hydroxyl derived from the decomposition of water adsorbed on weak Lewis acid sites. However, the catalytic performance of the alumina decreases slowly in a long-term reaction owing to the active center reduction resulted from the coverage by organic acids from phenol degradation. The present work reveals the influences of hydroxyl generation which are beneficial for adjusting surface hydroxyl regarded as active site for ozone attack and the reason of catalyst deactivation, which provides guideline for the rational design of catalyst.

Enhanced mineralization of atrazine by surface induced hydroxyl radicals over light-weight granular mixed-quartz sands with ozone

A light-weight granular mixed-quartz sand (denoted as L-GQS) combined with stirring-assisted bubble column reactor was firstly applied in catalytic ozonation of atrazine. The L-GQS, with a density of 2.36 g cm^-3 and average diameter of ca. of 4 mm, was readily churned up and uniformly distributed within the solution in the reactor. The introduction of L-GQS was found to exhibit enhanced catalytic ozonation of atrazine, with the increase in degradation rate and the dissolved organic carbon (DOC) removal being more than 2-fold for the catalytic process (L-GQS dosage = 5 g L^-1, [atrazine]₀ = 50 μM, [O₃] = 25 mg L^-1, gas flow = 0.2 L min^-1, at pH 7.0 and 293 K). The L-GQS settled at the bottom of the reactor after experimentation, allowing its easy separation from the solution. A complete characterization of the material (XRD, XPS, FTIR, FE-SEM/EDS, BET and pH_pzc) revealed that L-GQS consisted of α-quartz, β-cristobalite, anorthoclase and small amount of iron oxy-hydroxides. Hydroxyl groups, Bronsted acid sites and Lewis acid sites on the surface of L-GQS all contributed to the atrazine adsorption, ozone decomposition and ·OH generation. The L-GQS catalyzed ozonation exhibited superior atrazine degradation and mineralization rates in a wide range of pH (3.0-9.0) and reaction temperatures (278 K-293 K). Also, an enhancement of DOC abatement was observed both in presence of natural organic matter isolates and natural water matrices (river water) when L-GQS was used. Finally, the degradation mechanism was proposed, based on the intermediates and by-products formation analyzed by LC-QTOF-MS/MS and ionic chromatography. Our results indicate that the L-GQS combined with stirring-assisted bubble column reactor could be utilized as an enhancement of ozone-based advanced oxidation processes.

Ozone facilitated degradation of caffeine using Ce-TiO2 catalyst

The ozone initiated oxidation of 1,3,7-trimethylxanthine (caffeine), commonly found in wastewaters as model compound is reported using cerium (Ce)/titanium dioxide (TiO₂) as catalyst. The effect of pH and loading of ceria on titania were investigated. Effect of reaction conditions on degradation of caffeine based on their pseudo first-order rate constants were compared. The combination of catalyst Ce-TiO₂ and ozone aeration significantly enhanced the degradation of caffeine compared to uncatalysed ozonation. The oxidation of caffeine ensued via the free radical mechanism, through enhanced ozone decomposition into OH radicals. Ce/TiO₂(0.5 wt%) showed good activity in degradation of caffeine at pH 6, in both natural stream and river water samples showing about 60% total organic carbon removal in 2 h ozonation period. Using liquid chromatography-mass spectroscopy, degradation products were analysed. A reaction intermediate and one final product were positively identified. Nano-catalysts with different loadings of Ce on TiO₂ synthesized by sol-gel route were characterized by scanning electron microscope, transmission electron microscopy, BET and powder X-ray diffraction spectrum techniques. The results showed that the material retained a highly ordered mesoporous structure and possessed large surface area.

Hollow TiO2 spheres with improved visible light photocatalytic activity synergistically enhanced by multi-stimulative: Morphology advantage, carbonate-doping and the induced Ti3

Great efforts have been devoted to improve the photocatalytic activity of TiO₂ in the visible light region. Rational design of the external structure and adjustment of intrinsic electronic status by impurity doping are two main effective ways to achieve this purpose. A facile one-pot synthetic approach was developed to prepare C-doped hollow TiO₂ spheres, which simultaneously realized these advantages. The synthesized TiO₂ exhibits a mesoporous hollow spherical structure composed of fine nanocrystals, leading to high specific surface area (~180m²/g) and versatile porous texture. Carbonate-doping was achieved by a post-thermal treatment at a relatively low temperature (200°C), which makes the absorption edge red-shifted to the visible region of the solar spectrum. Concomitantly, Ti³⁺ induced by C-doping also functions in improving the visible-light photocatalytic activity by reducing the band gap. There exists a synergistic effect from multiple stimulatives to enhance the photocatalytic effect of the prepared TiO₂ catalyst. It is not out of expectation that the as-prepared C-doped hollow TiO₂ spheres exhibits an improved photocatalytic activity under visible light irradiation in organic pollutant degradation.

Morphology Control Studies of MnTiO3 Nanostructures with Exposed {0001} Facets as a High-Performance Catalyst for Water Purification

Novel single-crystal hexagonal MnTiO₃ nanosheets with exposed {0001} facets have been synthesized via a simple one-pot hydrothermal method using NaOH as a mineralizer and tetraethylammonium hydroxide (TEAH) as a morphology controller. The intermediate morphologies of MnTiO₃ nanostructures such as nanoparticles, nanowires, nanorods, and nanodiscs are trapped kinetically by adjusting the synthesis conditions. This approach enables us to elucidate the growth mechanisms of MnTiO₃ nanosheets based on the tetraethylammonium cation adsorption abilities on different MnTiO₃ crystal facets combined with density functional theory calculations. Dissolution and recrystallization processes are involved during the MnTiO₃ crystallization. The surface-controlled MnTiO₃ has been found to be effective as a catalyst for ozonation in the degradation of 4-chlorophenol (4-CP). Within typical experimental conditions (catalyst dosage = 0.3 g L^-1, [4-CP]₀ = 50 mg L^-1, [O₃] = 20 mg L^-1, gas flow = 0.1 L min^-1, pH 6.8, and T = 293 K), the total organic carbon (TOC) removal efficiency of 4-CP in catalytic ozonation with well-structured MnTiO₃ (MnTiO₃-180-10 sample) was 76.3% after 60 min, compared with only 22.1 and 38.5% TOC removal in the absence of catalyst and with uncontrolled MnTiO₃ (MnTiO₃-no TEAH sample), respectively. Benefiting from the high exposure percentage of {0001} facet, mixed-valences of manganese, surface hydroxyl groups, and the enrichment Lewis acid sites provided by Mn and Ti, the morphology-controlled MnTiO₃ nanosheets can be applied as heterogeneous catalytic ozonation catalysts which exhibit excellent pollutant degradation. We anticipate that MnTiO₃ can be a promising candidate material for the application in remediation of organic pollutants in water.

Synthesis of petal-like δ-MnO2 and its catalytic ozonation performance

Petal-like δ-MnO₂ microspheres were successfully synthesized by a very simple hydrothermal method with potassium permanganate (KMnO₄) as the only raw material.

Low-temperature NOx(x = 1, 2) removal with ˙OH radicals from catalytic ozonation over a RGO–CeO2nanocomposite: the highly promotional effect of oxygen vacancies

CeO₂grown on a reduced graphene oxide nanocomposite (RGO–CeO₂) was successfully synthesized by a facile alkaline hydrothermal method with the addition of ethylene glycol.

Enhanced catalytic ozonation over reduced spinel CoMn2O4 for NOx removal: active site and mechanism analysis

In this paper, CO atmosphere reduced cobalt manganate (CoMn₂O₄/CO), prepared by a hydrothermal method, was successfully utilized in catalytic ozonation for NO_x removal.

Hierarchical rattle-like N-doped anatase TiO2 superstructure: one-pot synthesis, morphological evolution and superior visible light photocatalytic activity

A novel N-doped rattle-like hierarchical anatase superstructure with a spherical porous core and hierarchical shell composed of ultrathin nanosheets was synthesized via a facile template-free method, which exhibits enhanced photocatalytic activity under visible light illumination.

Self-fluorinated Bi3Ti2O8F formed by cross-linked nanosheets as a superior dye-sensitized photocatalyst

A new semiconductor photocatalyst Bi₃Ti₂O₈F (BTOF) has been prepared by a hydrothermal method, whose surface is highly fluorinated by the intrinsic F ions.

Engineering a high energy surface of anatase TiO2 crystals towards enhanced performance for energy conversion and environmental applications

Great progress has been made in surface engineering of anatase TiO₂ crystals at the atomic level so as to fundamentally understand the surface-dependent properties. Herein, we summarize important achievements in this field, focusing on facets with high surface energy.