Hierarchical FeTiO3-TiO2 hollow spheres for efficient simulated sunlight-driven water oxidation

A Review of Metal-Organic Frameworks Derived Hollow-Structured Photocatalysts: Synthesis and Applications

Photocatalysis is a most important approach to addressing global energy shortages and environmental issues due to its environmentally friendly and sustainable properties. The key to realizing efficient photocatalysis relies on developing appropriate catalysts with high efficiency and chemical stability. Among various photocatalysts, Metal-organic frameworks (MOFs)-derived hollow-structured materials have drawn increased attention in photocatalysis based on advantages like more active sites, strong light absorption, efficient transfer of pho-induced charges, excellent stability, high electrical conductivity, and better biocompatibility. Specifically, MOFs-derived hollow-structured materials are widely utilized in photocatalytic CO2 reduction (CO2RR), hydrogen evolution (HER), nitrogen fixation (NRR), degradation, and other reactions. This review starts with the development story of MOFs, the commonly adopted synthesis strategies of MOFs-derived hollow materials, and the latest research progress in various photocatalytic applications are also introduced in detail. Ultimately, the challenges of MOFs-derived hollow-structured materials in practical photocatalytic applications are also prospected. This review holds great potential for developing more applicable and efficient MOFs-derived hollow-structured photocatalysts.

Enhanced Organic Pollutant Removal Efficiency of Electrospun NiTiO3/TiO2-Decorated Carbon Nanofibers

A nanocomposite comprised of nickel titanate/titania nanoparticles decorated with carbon nanofibers (NiTiO₃/TiO₂-decorated CNFs) is successfully synthesized via electrospinning and further utilized for methylene blue (MB) photodegradation. The morphology, phase, structural and chemical composition of the nanocomposite is investigated via scanning electron microscope, X-ray diffraction and transmission electron microscope equipped with energy dispersive X-ray. A mathematical model is developed to predict the photocatalytic activity of the produced nanocomposite by considering parameters such as initial dye concentration, light intensity, reaction temperature, and catalyst dosage. The reaction rate constant K₁ decreased from 0.0153 to 0.0044 min^-1 with an increase in the MB concentration from 5 to 15 mg L^-1, while K₂, K₃, and K₄ were found to increase with the increase in reaction temperature (0.0153 to 0.0222 min^-1), light intensity (0.0153 to 0.0228 min^-1) and catalyst dose concentration (0.0153 to 0.0324 min^-1), respectively. The results obtained are found to be in good agreement with the modeling results and showed effective photodegradation activity. The performance of our catalyst is found to be better compared to other catalysts previously reported in the literature. The recyclability data of the synthesized NiTiO₃/TiO₂-decorated CNFs catalyst for four runs show that the catalyst is quite stable and recyclable. This nanocomposite photocatalyst offers a low-cost solution for wastewater pollution problems and opens new avenues to further explore the electrospinning method for the synthesis of nanocomposites.

Heterogeneous Fenton-like removal of tri(2-chloroisopropyl) phosphate by ilmenite (FeTiO3): Kinetic, degradation mechanism and toxic assessment

Tri(2-chloroisopropyl) phosphate (TCPP), a common organophosphate flame retardant, was frequently detected in the environment and posed threats to human health. In this work, the main component of ilmenite FeTiO₃ was synthesized by the sol-gel method and employed as the catalyst for the degradation of TCPP by activating persulfate (PS) under UV irradiation. The degradation processes were fitted by the pseudo-first-order kinetic. The k_obs value in UV/FeTiO₃/PS system was up to 0.0056 min^-1 and much higher than that in UV/PS (0.0014 min^-1), UV/FeTiO₃ (0.0012 min^-1) and FeTiO₃/PS (0.0016 min^-1) systems, demonstrating a distinct synergistic effect in TCPP removal. The degradation efficiency of TCPP increased with the increase of UV intensity, PS concentration and catalyst dosage, and with the decrease of pH. By quenching experiment and EPR analysis, ·OH was confirmed to be the dominant radical in the reaction of the UV/FeTiO₃/PS system. The possible degradation pathways of TCPP were dechlorination, dealkylation, and further oxidation of alkyl groups based on the theoretical calculation of frontier molecular orbits. The toxicity of degradation intermediates evaluated by luminescence inhibition rate of photoluminescence was higher than TCPP. Thus, TCPP can be degraded in the UV/FeTiO₃/PS system effectively at the premise of introducing controlling measures to reduce the toxicity of degradation intermediates.

FeTiO3 Perovskite Nanoparticles for Efficient Electrochemical Water Splitting

The use of water splitting has been investigated as a good alternate for storing electrical energy. While the general interest in developing non-toxic, high-performance, and economically feasible catalysts for oxygen evolution reaction (OER) is noteworthy, there is also significant interest in water splitting research. Recently, perovskite-type oxides have performed as an alternative to non-precious metal catalysts and can act as a new class of effective catalysts in water splitting systems. Herein, a perovskite-structured FeTiO3 was prepared via a facile one-step solvothermal method using ionic liquid as templates. The results of structural and morphological studies have supported the formation of FeTiO3 perovskite. Furthermore, FeTiO3 perovskite demonstrated OER activity with a lower onset potential of 1.45 V vs. RHE and Tafel slope value of 0.133 V.dec−1 at 1 M KOH solution using mercury/mercurous oxide (Hg/HgO) were used as working electrodes.

Improved charge separation and carbon dioxide photoreduction performance of surface oxygen vacancy-enriched zinc ferrite@titanium dioxide hollow nanospheres with spatially separated cocatalysts

Here, we describe the fabrication of surface oxygen vacancy-enriched ZnFe₂O₄@TiO₂ double-shell hollow heterostructure nanospheres (ZnFe₂O₄@H-TiO_2-x) coupled with spatially separated CoO_x and Au-Cu bimetallic cocatalysts. The ZnFe₂O₄@TiO₂ heterojunction and spatially separated dual cocatalysts can significantly promote the separation of photoinduced charge carriers. Combined with the unique hollow double-shell heterostructure characteristics and improved surface state properties, the hybrid nanospheres can efficiently adsorb and activate CO₂ molecules. These advantages cause the optimized catalyst to exhibit remarkably higher gas-phase photocatalytic CO₂ reduction activity than the control CoO_x/ZnFe₂O₄/Au-Cu and ZnFe₂O₄@H-TiO_2-x double-shell hollow nanospheres loaded with a single cocatalyst. Meanwhile, the Au-Cu bimetal effect boosts the CO₂ conversion rate and CH₄ selectivity. The optimized hybrid catalyst with a Au/Cu ratio of 1:1 provides a CH₄ yield of 21.39 μmol g^-1 h^-1 with 93.8% selectivity. This work provides a rational photocatalyst design to improve CO₂ conversion and CH₄ selectivity.

MOF-derived core/shell C-TiO2/CoTiO3 type II heterojunction for efficient photocatalytic removal of antibiotics

A novel core/shell C-TiO₂/CoTiO₃ type II heterojunction was successfully synthesized via a direct calcination method by using MIL-125/Co core-shell nanocakes as a sacrificial template and precursor. In the calcination process, the organic ligand in MIL-125 acts as an in-situ carbon doping source to form a carbon-doped TiO₂ core (C-TiO₂). At the same time, CoTiO₃ nanoparticles are formed on the surface of C-TiO₂ by an in-situ solid-state reaction between the C-TiO₂ and Co²⁺ shell of MIL-125/Co. Due to such delicate core/shell structural features, carbon doping and type II heterojunctions, C-TiO₂/CoTiO₃ core/shell composites can effectively harvest visible light, facilitate the interfacial separation and suppress the recombination of photogenerated electron-hole pairs, leading to the remarkable photocatalytic activity for removal of ciprofloxacin (CIP). In particular, C-TiO₂/CoTiO₃-3 exhibits the best photocatalytic degradation activity of CIP with a degradation efficiency of 99.6% and a total carbon content removal percentage of 76% under visible-light illumination for 120 min. In addition, the proposed photocatalytic mechanism study illustrated that the main radical species in the photocatalytic degradation of CIP using C-TiO₂/CoTiO₃ as the photocatalyst is •OH. This work provides a new approach and insight for synthesizing core/shell heterojunction-based photocatalysts for various applications.

Synthesis of a novel one-dimensional Bi2O2CO3–BiOCl heterostructure and its enhanced photocatalytic activity

A novel one-dimensional Bi₂O₂CO₃–BiOCl heterostructure was synthesized. BiOCl nanosheets uniformly and vertically grew onto the Bi₂O₂CO₃ porous rods via crystallographic oriented epitaxial nucleation and growth. Bi₂O₂CO₃–BiOCl displayed excellent photocatalytic activity.

Photocatalytic Oxygen Evolution from Water Splitting

Photocatalytic water splitting has attracted a lot of attention in recent years, and O2 evolution is the decisive step owing to the complex four-electrons reaction process. Though many studies have been conducted, it is necessary to systematically summarize and introduce the research on photocatalytic O2 evolution, and thus a systematic review is needed. First, the corresponding principles about O2 evolution and some urgently encountered issues based on the fundamentals of photocatalytic water splitting are introduced. Then, several types of classical water oxidation photocatalysts, including TiO2, BiVO4, WO3, α-Fe2O3, and some newly developed ones, such as Sillén-Aurivillius perovskites, porphyrins, metal-organic frameworks, etc., are highlighted in detail, in terms of their crystal structures, synthetic approaches, and morphologies. Third, diverse strategies for O2 evolution activity improvement via enhancing photoabsorption and charge separation are presented, including the cocatalysts loading, heterojunction construction, doping and vacancy formation, and other strategies. Finally, the key challenges and future prospects with regard to photocatalytic O2 evolution are proposed. The purpose of this review is to provide a timely summary and guideline for the future research works for O2 evolution.

Enhanced charge transfer and separation of hierarchical hydrogenated TiO2 nanothorns/carbon nanofibers composites decorated by NiS quantum dots for remarkable photocatalytic H2 production activity

Hierarchical core/shell hydrogenated TiO₂ (H-TiO₂) nanothorns/carbon nanofibers (CNFs) composites were produced through a solvothermal method, followed by ordinal calcination and hydrogenation treatments using the prepared carbon nanofiber as electron-transporting substrate material. The hierarchical H-TiO₂/CNFs composites possess more exposed surface active sites and offer efficient charge transport paths. NiS quantum dots as excellent electron acceptors and cocatalysts were anchored on the hierarchical H-TiO₂/CNFs composites by a wet chemical deposition method. The synergistic effects of the surface defects (oxygen vacancies), NiS cocatalyst, and carbon nanofibers greatly improve charge transfer and separation, increase the accessible surface area and surface donor density of the composites and also extend the photoresponse from the ultraviolet to the visible light region. By taking advantage of these features and because of its unique architecture, the optimal NiS quantum dots-decorated H-TiO₂/CNFs composite exhibited a remarkable solar-driven hydrogen generation rate (75.92 μmol h^-1, 30 mg^-1) in the absence of a Pt cocatalyst under AM 1.5 irradiation, which is about 12.3 times that of TiO₂/CNFs nanostructures.

Synthesis of one-dimensional Bi2O3–Bi5O7I heterojunctions with high interface quality

One-dimensional Bi₂O₃–Bi₅O₇I heterostructures with high interface quality were first synthesized by calcining of BiOI–Bi(OHC₂O₄)·2H₂O precursors. And the obtained Bi₂O₃–Bi₅O₇I heterostructures exhibit outstanding photocatalytic activity for degrading methyl orange and phenol with high concentration.

Ta3N5 nanoparticles/TiO2 hollow sphere (0D/3D) heterojunction: facile synthesis and enhanced photocatalytic activities of levofloxacin degradation and H2 evolution

A novel 0D/3D Ta₃N₅ nanoparticles/TiO₂ hollow sphere heterojunction with efficient solar-light-driven levofloxacin degradation and H₂ evolution is fabricated.

Synthesis of Bi2O3–Bi4V2O11 heterojunctions with high interface quality for enhanced visible light photocatalysis in degradation of high-concentration phenol and MO dyes

Bi₂O₃–Bi₄V₂O₁₁ heterostructures with high interface quality were synthesized by calcining Bi₂VO_5.5–Bi(OHC₂O₄)·2H₂O precursors. The Bi₂O₃–Bi₄V₂O₁₁ heterostructure exhibits outstanding photocatalytic activity for degrading phenol and MO dyes with high concentration under visible light irradiation.

Titanocene dichloride (Cp2TiCl2) as a precursor for template-free fabrication of hollow TiO2 nanostructures with enhanced photocatalytic hydrogen production

A one-pot and template-free strategy for synthesizing hollow TiO₂ nanostructures (HTSs) is developed by using titanocene dichloride as a titanium source, acetone as a solvent, and ammonia as a basic source. Transmission electron microscopy (TEM) observations demonstrate that the morphology transformation undergoes solid, yolk-shell and then hollow structures, typical of an Ostwald ripening process. Comparative experiments suggest that the mismatched hydrolysis rate of chloride anion and organic cyclopentadiene in unique titanocene dichloride (Cp₂TiCl₂) molecules should be responsible for the formation of HTSs. The TiO₂ nanostructures exhibit controllable morphologies and tunable sizes by mainly adjusting the amounts of the titanium precursor or ammonia. The HTSs show much improved photocatalytic performance as compared with samples of other morphologies in water splitting application, due to the remarkably increased surface area and active sites, and enhanced mass transfer. Our findings reported herein may offer new perspectives in materials chemistry, and energy- and environment-related applications.

Facile synthesis of a heterogeneous Li2TiO3/TiO2 nanocomposite with enhanced photoelectrochemical water splitting

A novel Li₂TiO₃/TiO₂ nanocomposite was synthesized by a combination of anodization and hydrothermal processes and an enhanced photoelectrochemical response was demonstrated.

Light absorption modulation of novel Fe2TiO5 inverse opals for photoelectrochemical water splitting

Fe₂TiO₅ inverse opals with modulated light absorption were prepared. Enhanced light absorption and superior charge separation resulted in high photocurrent.

R. S, Nair BN, Karunakaran V, Mohamed AP, Warrier KGK, Hareesh US. A facile one pot synthetic approach for C3N4–ZnS composite interfaces as heterojunctions for sunlight-induced multifunctional photocatalytic applications

Herein, we report a facile one pot synthetic protocol for the creation of C₃N₄–ZnS composite interfaces by the co-pyrolysis of a precursor mix containing zinc nitrate, melamine, and thiourea at 550 °C in air.

Shape-selective synthesis of Bi2WO6 hierarchical structures and their morphology-dependent photocatalytic activities

Various morphologies of Bi₂WO₆ were synthesized using l-lysine as surfactant and the possible formation mechanisms were proposed.

Enhanced photocatalytic activity of Bi25FeO40–Bi2WO6 heterostructures based on the rational design of the heterojunction interface

Based on the rational design of heterojunction interface, a novel and efficient Bi₂₅FeO₄₀–Bi₂WO₆ heterostructure photocatalyst was successfully constructed by a facile hydrothermal process.