Versatile Synthesis of Mesoporous Crystalline TiO2 Materials by Monomicelle Assembly

Mechanisms underlying the nucleation processes of mesoporous ceria nanoparticles

Mesoporous ceria nanoparticles featuring ordered pores (O-MCNs) have much greater potential than their counterparts featuring interparticle pores (I-MCNs) due to their uniform pore size and interconnected framework structures. However, current methods can only synthesize I-MCNs and fail to achieve O-MCNs. Understanding the mechanisms underlying the formation of pores in I-MCNs can spark ideas for designing new methods to realize the synthesis of O-MCNs. In this study, the details of an established I-MCN synthetic method using 1-octadecene (ODE) and ethanol as a mixed solvent, Ce(NO3)3·6H2O as a precursor and trioctylphosphine oxide (TOPO) as a ligand were explored. The results revealed that six groups of molecules were generated ahead of ceria crystal nucleation, and these molecules played different roles in the formation of I-MCNs. Four steps, namely, ceria crystal nucleation, small ceria nanoparticle formation, small ceria nanoparticle assembly, and I-MCN growth, were involved in the formation of the I-MCNs. The assembly of small ceria nanoparticles driven by the fusion of the (200) plane leaving behind unoccupied spaces was the major reason for the formation of pores in the I-MCNs. These findings provided very useful information for the future design of new methods to achieve O-MCNs.

Black titanium oxide: synthesis, modification, characterization, physiochemical properties, and emerging applications for energy conversion and storage, and environmental sustainability

Since its advent in 2011, black titanium oxide (B-TiOx) has garnered significant attention due to its exceptional optical characteristics, notably its enhanced absorption spectrum ranging from 200 to 2000 nm, in stark contrast to its unmodified counterpart. The escalating urgency to address global climate change has spurred intensified research into this material for sustainable hydrogen production through thermal, photocatalytic, electrocatalytic, or hybrid water-splitting techniques. The rapid advancements in this dynamic field necessitate a comprehensive update. In this review, we endeavor to provide a detailed examination and forward-looking insights into the captivating attributes, synthesis methods, modifications, and characterizations of B-TiOx, as well as a nuanced understanding of its physicochemical properties. We place particular emphasis on the potential integration of B-TiOx into solar and electrochemical energy systems, highlighting its applications in green hydrogen generation, CO2 reduction, and supercapacitor technology, among others. Recent breakthroughs in the structure-property relationship of B-TiOx and its applications, grounded in both theoretical and empirical studies, are underscored. Additionally, we will address the challenges of scaling up B-TiOx production, its long-term stability, and economic viability to align with ambitious future objectives.

Template Evolution Induced Relay Self-Assembly for Mesoporous Carbonaceous Materials via Hydrothermal Carbonization

Constructing carbonaceous materials with versatile surface structures still remains a great challenge due to limited self-assembly methods, especially at high temperatures. This study presents an innovative template evolution induced relay self-assembly (TEIRSA) for the fabrication of large polyoxometalate (POM)-mixed carbonaceous nanosheets featuring surface mesoporous structures through hydrothermal carbonization (HTC). The method employs POM and acetone as additives, cleverly modulating the Ostwald ripening-like process of P123-based micelles, effectively addressing the instability challenges inherent in traditional soft-template methods, especially within the demanding carbohydrate HTC process. Additionally, this method allows for the independent regulation of surface architectures through the selection of organic additives. The resulting nanosheets exhibit diverse surface morphologies, including surface spherical mesopores, 1D open channels, and smooth surfaces. Their unexpectedly versatile properties have swiftly garnered recognition, showing potential in the application of lithium-sulfur batteries.

The photocatalytic wastewater hydrogen production process with superior performance to the overall water splitting

The utilization of a cost-free sacrificial agent is a novel approach to significantly enhance the efficiency of photocatalytic hydrogen (H2) production by water splitting. Wastewater contains various organic pollutants, which have the potential to be used as hole sacrificial agents to promote H2 production. Our studies on different pollutants reveals that not all pollutants can effectively promote H2 production. However, when using the same pollutants, not all photocatalysts achieved a higher H2 evolution rate than pure water. Only when the primary oxidizing active species of the photocatalyst are •OH radicals, which are generated by photogenerated holes, and when the pollutants are easily attacked and degraded by •OH radicals, can the production of H2 be effectively promoted. It is noteworthy that the porous brookite TiO2 photocatalyst exhibits a significantly higher H2 evolution rate in Reactive Red X-3B and Congo Red, reaching as high as 26.46 mmol⋅g-1⋅h-1 and 32.85 mmol⋅g-1 ⋅h-1, respectively, which is 2-3 times greater than that observed in pure water and is 10 times greater than most reported studies. The great significance of this work lies in the potential for efficient H2 production through the utilization of wastewater.

Comparative study of reactive oxygen species and tetracycline degradation pathways in catalytic peroxodisulfate activation by asymmetric mesoporous TiO2 and the corresponding controlled-release materials

The removal of trace amounts of antibiotics from water environments while simultaneously avoiding potential environmental hazards during the treatment is still a challenge. In this work, green, harmless, and novel asymmetric mesoporous TiO2 (A-mTiO2) was combined with peroxodisulfate (PDS) as active components in a controlled-release material (CRM) system for the degradation of tetracycline (TC) in the dark. The formation of reactive oxygen species (ROS) and the degradation pathways of TC during catalytic PDS activation by A-mTiO2 powder catalysts and the CRMs were thoroughly studied. Due to its asymmetric mesoporous structure, there were abundant Ti3+/Ti4+ couples and oxygen vacancies in A-mTiO2, resulting in excellent activity in the activation of PDS for TC degradation, with a mineralization rate of 78.6%. In CRMs, ROS could first form during PDS activation by A-mTiO2 and subsequently dissolve from the CRMs to degrade TC in groundwater. Due to the excellent performance and good stability of A-mTiO2, the resulting constructed CRMs could effectively degrade TC in simulated groundwater over a long period (more than 20 days). From electron paramagnetic resonance analysis and TC degradation experiments, it was interesting to find that the ROS formed during PDS activation by A-mTiO2 powder catalysts and CRMs were different, but the degradation pathways for TC were indeed similar in the two systems. In PDS activation by A-mTiO2, besides the free hydroxyl radical (·OH), singlet oxygen (1O2) worked as a major ROS participating in TC degradation. For CRMs, the immobilization of A-mTiO2 inside CRMs made it difficult to capture superoxide radicals (·O2-), and continuously generate 1O2. In addition, the formation of sulfate radicals (·SO4-), and ·OH during the release process of CRMs was consistent with PDS activation by the A-mTiO2 powder catalyst. The eco-friendly CRMs had a promising potential for practical application in the remediation of organic pollutants from groundwater.

Catalyzing Artificial Photosynthesis with TiO2 Heterostructures and Hybrids: Emerging Trends in a Classical yet Contemporary Photocatalyst

Titanium dioxide (TiO2) stands out as a versatile transition-metal oxide with applications ranging from energy conversion/storage and environmental remediation to sensors and optoelectronics. While extensively researched for these emerging applications, TiO2 has also achieved commercial success in various fields including paints, inks, pharmaceuticals, food additives, and advanced medicine. Thanks to the tunability of their structural, morphological, optical, and electronic characteristics, TiO2 nanomaterials are among the most researched engineering materials. Besides these inherent advantages, the low cost, low toxicity, and biocompatibility of TiO2 nanomaterials position them as a sustainable choice of functional materials for energy conversion. Although TiO2 is a classical photocatalyst well-known for its structural stability and high surface activity, TiO2-based photocatalysis is still an active area of research particularly in the context of catalyzing artificial photosynthesis. This review provides a comprehensive overview of the latest developments and emerging trends in TiO2 heterostructures and hybrids for artificial photosynthesis. It begins by discussing the common synthesis methods for TiO2 nanomaterials, including hydrothermal synthesis and sol-gel synthesis. It then delves into TiO2 nanomaterials and their photocatalytic mechanisms, highlighting the key advancements that have been made in recent years. The strategies to enhance the photocatalytic efficiency of TiO2, including surface modification, doping modulation, heterojunction construction, and synergy of composite materials, with a specific emphasis on their applications in artificial photosynthesis, are discussed. TiO2-based heterostructures and hybrids present exciting opportunities for catalyzing solar fuel production, organic degradation, and CO2 reduction via artificial photosynthesis. This review offers an overview of the latest trends and advancements, while also highlighting the ongoing challenges and prospects for future developments in this classical yet rapidly evolving field.

Ordered Mesoporous Crystalline Frameworks Toward Promising Energy Applications

Ordered mesoporous crystalline frameworks (MCFs), which possess both functional frameworks and well-defined porosity, receive considerable attention because of their unique properties including high surface areas, large pore sizes, tailored porous structures, and compositions. Construction of novel crystalline mesoporous architectures that allows for rich accessible active sites and efficient mass transfer is envisaged to offer ample opportunities for potential energy-related applications. In this review, the rational synthesis, unique structures, and energy applications of MCFs are the main focus. After summarizing the synthetic approaches, an emphasis is placed on the delicate control of crystallites, mesophases, and nano-architectures by concluding basic principles and showing representative examples. Afterward, the currently fabricated components of MCFs such as metals, metal oxides, metal sulfides, and metal-organic frameworks are described in sequence. Further, typical applications of MCFs in rechargeable batteries, supercapacitors, electrocatalysis, and photocatalysis are highlighted. This review ends with the possible development and synthetic challenges of MCFs as well as a future prospect for high-efficiency energy applications, which underscores a pathway for developing advanced materials.

Silanol-Assisted High-Yield Nanofabrication of SnO2 Single Crystals with Highly Tunable and Ordered Mesoporosity

Highly ordered mesoporous materials with a single-crystalline structure have attracted broad interest due to their wide applications from catalysis to energy conversion/storage, but constructing them with good controllability and high yields remains a highly daunting task. Herein, we construct a new class of three-dimensionally ordered mesoporous SnO2 single crystals (3DOm-SnO2) with well-defined facets and excellent mesopore tunability. Mechanism studies demonstrate that the silanol groups on ordered silica nanospheres (3DO-SiO2) can induce the efficient heterogeneous crystallization of uniform SnO2 single crystals in its periodic voids by following the hard and soft acid and base theory, affording a much higher yield of ∼96% for 3DOm-SnO2 than that of its solid counterpart prepared in the absence of 3DO-SiO2 (∼1.5%). Benefiting from its permanent ordered mesopores and favorable electronic structure, Pd-supported 3DOm-SnO2 can efficiently catalyze the unprecedented sequential hydrogenation of 4-nitrophenylacetylene to produce 4-nitrostyrene, then 4-nitroethylbenzene, and finally 4-aminoethylbenzene. DFT calculations further reveal the favorable synergistic effect between Pd and 3DOm-SnO2 via moderate electron transfer for realizing this sequential hydrogenation reaction. Our work underlines the crucial role of silanol groups in inducing the high-yield heterogeneous crystallization of 3DOm-SnO2, shedding light on the rational design and construction of various 3DO single crystals that are of great practical significance.

Preparation of uniform lignin/titanium dioxide nanoparticles by confined assembly: A multifunctional nanofiller for a waterborne polyurethane wood coating

We report a facile synthesis for lignin/titanium dioxide (TiO2) nanoparticles (LT NPs) at room temperature by confining assembly of lignin macromolecules. The LT NPs had a uniform nanosize distribution (average diameter ∼ 68 nm) and were directly employed as multifunctional nanofillers to reinforce a waterborne polyurethane wood coating (WBC). X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy revealed the mechanism by which formed TiO2 confined lignin assembly. The LT NPs considerably increased the tensile strength of a WBC film from 16.3 MPa to 28.1 MPa. The WBC-LT NPs exhibited excellent ultraviolet (UV) A and UVB blocking performances of 87 % and 98 %, respectively, while maintaining 94 % transmittance in the visible region. Incorporating LT NPs into the WBC enhanced the coating performance (the hardness, adhesion, and abrasion resistance) on wood substrates. A quantitative color and texture analysis revealed that the LT NPs increased the decorativeness of actual wooden products. After nearly 1800 h of UV irradiation, wood coated with the WBC-LT NPs exhibited good color stability, where the original color remained unchanged or even became brighter. In this study, value-added valorization of lignin is enabled by using organic-inorganic nanofillers and insights are gained into developing multifunctional WBCs.

Monomicelle-Directed Engineering of Strained Carbon Nanoribbons as Oxygen Reduction Catalyst

To date, precisely tailoring local active sites of well-defined earth-abundant metal-free carbon-based electrocatalysts for attractive electrocatalytic oxygen reduction reaction (ORR), remains challenging. Herein, the authors successfully introduce a strain effect on active C-C bonds adjacent to edged graphitic nitrogen (N), which raises appropriate spin-polarization and charge density of carbon active sites and kinetically favor the facilitation of O2 adsorption and the activation of O-containing intermediates. Thus, the constructed metal-free carbon nanoribbons (CNRs-C) with high-curved edges exhibit outstanding ORR activity with half-wave potentials of 0.78 and 0.9 V in 0.5 m H2 SO4 and 0.1 m KOH, respectively, overwhelming the planar one (0.52 and 0.81 V) and the N-doped carbon sheet (0.41 and 0.71 V). Especially in acidic media, the kinetic current density (Jk ) is 18 times higher than that of the planar one and the N-doped carbon sheet. Notably, these findings show the spin polarization of the asymmetric structure by introducing a strain effect on the C-C bonds for boosting ORR.

Chelated Ion-Exchange Strategy toward BiOCl Mesoporous Single-Crystalline Nanosheets for Boosting Photocatalytic Selective Aromatic Alcohols Oxidation

The photoresponse and photocatalytic efficiency of bismuth oxychloride (BiOCl) are greatly limited by rapid recombination of photogenerated carriers. The construction of porous single-crystal BiOCl photocatalyst can effectively alleviate this issue and provide accessible active sites. Herein, a facile chelated ion-exchange strategy is developed to synthesize BiOCl mesoporous single-crystalline nanosheets (BiOCl MSCN) using acetic acid and ammonia solution respectively as chelating agent and ionization promoter. The strong chelation between acetate ions and Bi³⁺ ions introduces acetate ions into the precipitated product to exchange with Cl^- ions, resulting in large lattice mismatch, strain release, and formation of void-like mesopores. The prepared BiOCl MSCN photocatalyst exhibits excellent catalytic performance with 99% conversion and 98% selectivity for oxidation of benzyl alcohol to benzaldehyde and superior general adaptability for various aromatic alcohols. The theoretical calculations and characterizations confirm that the superior performance is mainly attributed to the abundant oxygen vacancies, plenty of accessible adsorption/active sites and fast charge transport path without grain boundaries.

Solid-Phase Synthesis of Titanium Dioxide Micro-Nanostructures

Titanium dioxide (TiO₂) micro-nanostructures are widely utilized in photochemical applications due to their unique band gaps and are of huge demand in scientific research and industrial manufacture. Herein, this work reports a controllable, facile, economical, and green solid-phase synthesis strategy to prepare TiO₂ with governable morphologies containing 1D nanorods, 3D microbulks, and irregular thick plates. Specifically, Ti powders are transformed into TiO₂ micro-nanostructures through dispersing them into a solid NaOH/KOH mixture with a low eutectic point, followed by grinding, heating, ion exchange, and calcination. As no solvents are utilized in the alkali treatment process, the usage of solvents is decreased and high vapor pressure is avoided. Moreover, the band gaps of TiO₂ micro-nanostructures can be regulated from 3.02 to 3.34 eV through altering the synthetic parameters. Notably, the as-prepared TiO₂ micro-nanostructures exhibit high photocatalytic activities in the degradation of rhodamine B and methylene blue under simulated solar light illumination. It is believed that the solid-phase synthesis strategy will be of huge demand for the synthesis of TiO₂ micro-nanostructures.