Stable Ti 3+ Defects in Oriented Mesoporous Titania Frameworks for Efficient Photocatalysis

Construction of Molecularly Dispersed Polyoxometalate-Alumina Hybrid Hollow Nanoflowers via Water-Induced Kirkendall Effect

Hybrid nanomaterials with controllable structures and diverting components have attracted significant interest in the functional materials field. Here, we develop a solvent evaporation-induced self-assembly (EISA) strategy to synthesize nanosheet-assembled phosphomolybdic acid (H3PMo)-alumina hybrid hollow spheres. The resulting nanoflowers display a high surface area (up to 697 m2 g-1), adjustable diameter, high chemical/thermal stability, and especially molecularly dispersed H3PMo species. By employing various microscopic and spectroscopic techniques, the formation mechanism is elucidated, revealing the simultaneous control of the morphology by heteropoly acids and water through the water-induced Kirkendall effect. The versatility of the synthesis method is demonstrated by varying surfactants, heteropoly acids, and metal oxide precursors for the facile synthesis of hybrid metal oxides. Spherical hybrid alumina serves as an attractive support material for constructing metal-acid bifunctional catalysts owing to its advantageous surface area, acidity, and mesoporous microenvironment. Pt-loaded hollow flowers exhibit excellent catalytic performance and exceptional stability in the hydrodeoxygenation of vanillin with recyclability for up to 10 cycles. This research presents an innovative strategy for the controllable synthesis of hybrid metal oxide nanospheres and hollow nanoflowers, providing a multifunctional platform for diverse applications.

Photosensitized Reduction and Polymerization for One-Step Preparation of Leucomethylene Blue Hydrogel as a Visual Indicator for Both Gaseous and Dissolved Oxygen

Oxygen is crucial for many chemical and biological processes, and its facile detection is of great significance in our daily lives. In this study, we report a leucomethylene blue (LMB)-encapsulated hydrogel visual indicator for the detection of both gaseous and dissolved Oxygen (DO). The photosensitization of methylene blue (MB) not only lead to its reduction to colorless LMB but also resulted in hydrogel polymerization, thus allowing the one-step preparation of the LMB-hydrogel. Meanwhile, the photosensitized reduction of MB was quite fast (5000-fold faster than the classical glucose reduction). In this manner, the blue color of MB could be completely decayed within only 1 min. Also, the efficient polymerization triggered by MB photosensitization ensured the rapid preparation of LMB hydrogels within 10 min. By placing the oxygen indicator in air or water, oxygen can specifically oxidize the colorless LMB-hydrogel to the blue MB-hydrogel. When coupled with a smartphone, the oxygen indicator exhibited a linear response to DO in the range 0.23-10 mg/L with a detection limit of 0.077 mg/L. The LMB-hydrogel indicator was successfully explored for visual evaluation of vacuum degree during food packaging. The LMB-hydrogel, with the advantages of low cost, ease of preparation, as well as facile use, is a promising visual indicator for both gaseous and dissolved oxygen, especially for in-house usage.

Super-Assembled Multilayered Mesoporous TiO2 Nanorockets for Light-Powered Space-Confined Microfluidic Catalysis

In the field of sustainable chemistry, it is still a significant challenge to realize efficient light-powered space-confined catalysis and propulsion due to the limited solar absorption efficiency and the low mass and heat transfer efficiency. Here, novel semiconductor TiO2 nanorockets with asymmetric, hollow, mesoporous, and double-layer structures are successfully constructed through a facile interfacial superassembly strategy. The high concentration of defects and unique topological features improve light scattering and reduce the distance for charge migration and directed charge separation, resulting in enhanced light harvesting in the confined nanospace and resulting in enhanced catalysis and self-propulsion. The movement velocity of double-layered nanorockets can reach up to 10.5 μm s-1 under visible light, which is approximately 57 and 119% higher than that of asymmetric single-layered TiO2 and isotropic hollow TiO2 nanospheres, respectively. In addition, the double-layered nanorockets improve the degradation rate of the common pollutant methylene blue under sustainable visible light with a 247% rise of first-order rate constant compared to isotropic hollow TiO2 nanospheres. Furthermore, FEA simulations reveal and confirm the double-layered confined-space enhanced catalysis and self-propulsion mechanism.

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.

Mesoporous TiO2 Single-Crystal Particles from Controlled Crystallization-Driven Mono-Micelle Assembly as an Efficient Photocatalyst

Mesoporous materials with crystalline frameworks have been widely explored in many fields due to their unique structure and crystalline feature, but accurate manipulations over crystalline scaffolds, mainly composed of uncontrolled polymorphs, are still lacking. Herein, we explored a controlled crystallization-driven monomicelle assembly approach to construct a type of uniform mesoporous TiO2 particles with atomically aligned single-crystal frameworks. The resultant mesoporous TiO2 single-crystal particles possess an angular shape ∼80 nm in diameter, good mesoporosity (a high surface area of 112 m2 g-1 and a mean pore size at 8.3 nm), and highly oriented anatase frameworks. By adjusting the evaporation rate during assembly, such a facile solution-processed strategy further enables the regulation of the particle size and mesopore size without the destruction of the oriented crystallites. Such a combination of ordered mesoporosity and crystalline orientation provides both effective mass and charge transportation, leading to a significant increase in the hydrogen generation rate. A maximum hydrogen evolution rate of 12.5 mmol g-1 h-1 can be realized, along with great stability under solar light. Our study is envisaged to extend the possibility of mesoporous single crystal growth to a range of functional ceramics and semiconductors toward advanced applications.

Cooperative and Orthogonal Switching in the Solid State Enabled by Metal-Organic Framework Confinement Leading to a Thermo-Photochromic Platform

Cooperative behavior and orthogonal responses of two classes of coordinatively integrated photochromic molecules towards distinct external stimuli were demonstrated on the first example of a photo-thermo-responsive hierarchical platform. Synergetic and orthogonal responses to temperature and excitation wavelength are achieved by confining the stimuli-responsive moieties within a metal-organic framework (MOF), leading to the preparation of a novel photo-thermo-responsive spiropyran-diarylethene based material. Synergistic behavior of two photoswitches enables the study of stimuli-responsive resonance energy transfer as well as control of the photoinduced charge transfer processes, milestones required to advance optoelectronics development. Spectroscopic studies in combination with theoretical modeling revealed a nonlinear effect on the material electronic structure arising from the coordinative integration of photoresponsive molecules with distinct photoisomerization mechanisms. Thus, the reported work covers multivariable facets of not only fundamental aspects of photoswitch cooperativity, but also provides a pathway to modulate photophysics and electronics of multidimensional functional materials exhibiting thermo-photochromism.

Superexchange-induced Pt-O-Ti3+ site on single photocatalyst for efficient H2 production with organics degradation in wastewater

Efficient photocatalytic H2 production from wastewater instead of pure water is a dual solution to the environmental and energy crisis, but due to the rapid recombination of photoinduced charge in the photocatalyst and inevitable electron depletion caused by organic pollutants, a significant challenge of dual-functional photocatalysis (simultaneous oxidative and reductive reactions) in single catalyst is designing spatial separation path for photogenerated charges at atomic level. Here, we designed a Pt-doped BaTiO3 single catalyst with oxygen vacancies (BTPOv) that features Pt-O-Ti3+ short charge separation site, which enables excellent H2 production performance (1519 μmol·g-1·h-1) while oxidizing moxifloxacin (k = 0.048 min-1), almost 43 and 98 times than that of pristine BaTiO3 (35 μmol·g-1·h-1 and k = 0.00049 min-1). The efficient charge separation path is demonstrated that the oxygen vacancies extract photoinduced charge from photocatalyst to catalytic surface, and the adjacent Ti3+ defects allow rapid migration of electrons to Pt atoms through the superexchange effect for H* adsorption and reduction, while the holes will be confined in Ti3+ defects for oxidation of moxifloxacin. Impressively, the BTPOv shows an exceptional atomic economy and potential for practical applications, a best H2 production TOF (370.4 h-1) among the recent reported dual-functional photocatalysts and exhibiting excellent H2 production activity in multiple types of wastewaters.

Microwave Synthesis of Pt Clusters on Black TiO2 with Abundant Oxygen Vacancies for Efficient Acidic Electrocatalytic Hydrogen Evolution

Oxygen vacancies-enriched black TiO₂ is one promising support for enhancing hydrogen evolution reaction (HER). Herein, oxygen vacancies enriched black TiO₂ supported sub-nanometer Pt clusters (Pt/TiO₂ -O_V ) with metal support interactions is designed through solvent-free microwave and following low-temperature electroless approach for the first time. High-temperature and strong reductants are not required and then can avoid the aggregation of decorated Pt species. Experimental and theoretical calculation verify that the created oxygen vacancies and Pt clusters exhibit synergistic effects for optimizing the reaction kinetics. Based on it, Pt/TiO₂ -O_V presents remarkable electrocatalytic performance with 18 mV to achieve 10 mA cm^-2 coupled with small Tafel slope of 12 mV dec^-1 . This work provides quick synthetic strategy for preparing black titanium dioxide based nanomaterials.

Charge Separation by Creating Band Bending in Metal-Organic Frameworks for Improved Photocatalytic Hydrogen Evolution

Metal-organic frameworks (MOFs) have been intensively studied as a class of semiconductor-like materials in photocatalysis. However, band bending, which plays a crucial role in semiconductor photocatalysis, has not yet been demonstrated in MOF photocatalysts. Herein, a representative MOF, MIL-125-NH₂ , is integrated with the metal oxides (MoO₃ and V₂ O₅ ) that feature appropriate work functions and energy levels to afford the corresponding MOF composites. Surface photovoltage results demonstrate band bending in the MOF composites, which gives rise to the built-in electric field of MIL-125-NH₂ , boosting the charge separation. As a result, the MOF composites present 56 and 42 times higher activities, respectively, compared to the pristine MOF for photocatalytic H₂ production. Upon depositing Pt onto the MOF, ∼6 times higher activity is achieved. This work illustrates band bending of MOFs for the first time, supporting their semiconductor-like nature, which would greatly promote MOF photocatalysis.

Versatile Synthesis of Mesoporous Crystalline TiO2 Materials by Monomicelle Assembly

Mesoscale TiO₂ structures have realized many technological applications-ranging from catalysis and biomedicine to energy storage and conversion-because of their large mesoporosities offering desirable accessibility and mass transport. Tailoring mesoporous TiO₂ structures with novel mesoscopic and microscopic configurations is envisaged to offer ample opportunities for further applications. In this Review, we explain how to synthesize novel mesoporous TiO₂ materials and present recent examples. An emphasis is placed on a "monomicelle assembly" strategy as an emerging and powerful approach to direct the formation of mesostructured TiO₂ with precise control over its structural orientations and architectures. Furthermore, typical examples of mesoporous TiO₂ for applications in batteries and photocatalysis are highlighted. The Review ends with an outlook towards the synthesis of mesoporous TiO₂ with tailored architectures by self-assembly, which could pave the way for developing advanced energy conversion and storage devices.

Modulation of Z-Scheme Heterojunction Interface between Ultrathin C3N5 Nanosheets and Metal-Organic Framework for Boosting Photocatalysis

Fabricating heterojunction photocatalysts for H2 production is promising for the development of clean energy. For boosting the photocatalytic activity, modulating the heterojunction interface can facilitate the electron-hole separation and solar energy utilization, but it is highly challenging in synthesis. In this work, by facilely exfoliating the bulk C3N5, ultrathin C3N5 nanosheets (N-CN) with large surface area, improved light absorption, and efficient charge transport were synthesized and further applied to the construction of NH2-UiO-66/N-CN heterojunctions. The optimized NH2-UiO-66/N-CN-2 exhibits high hydrogen evolution rate and cycling stability with Pt as the cocatalyst. Combined with the experimental results, the density functional theory calculation reveals that the high photocatalytic performance is attributed to the promoted photogenerated carrier transfer by the formation of well-contacted and stable Z-scheme heterojunction interface. This contribution renders an insight into the modulation of the heterojunction interface for enhancing the activity of MOF-based photocatalysts.

Boosted Inner Surface Charge Transfer in Perovskite Nanodots@Mesoporous Titania Frameworks for Efficient and Selective Photocatalytic CO2 Reduction to Methane

Exploring high-efficiency and stable halide perovskite-based photocatalysts for the selective reduction of CO₂ to methane is a challenge because of the intrinsic photo- and chemical instability of halide perovskites. In this study, halide perovskites (Cs₃ Bi₂ Br₉ and Cs₂ AgBiBr₆ ) were grown in situ in mesoporous TiO₂ frameworks for an efficient CO₂ reduction. Benchmarked CH₄ production rates of 32.9 and 24.2 μmol g^-1  h^-1 with selectivities of 88.7 % and 84.2 %, were achieved, respectively, which are better than most reported halide perovskite photocatalysts. Focused ion-beam sliced-imaging techniques were used to directly image the hyperdispersed perovskite nanodots confined in mesopores with tunable sizes ranging from 3.8 to 9.9 nm. In situ X-ray photoelectronic spectroscopy and Kelvin probe force microscopy showed that the built-in electric field between the perovskite nanodots and mesoporous titania channels efficiently promoted photo-induced charge transfer. Density functional theory calculations indicate that the high methane selectivity was attributed to the Bi-adsorption-mediated hydrogenation of *CO to *HCO that dominates CO desorption.

Degradable mesoporous semimetal antimony nanospheres for near-infrared II multimodal theranostics

Metallic and semimetallic mesoporous frameworks are of great importance owing to their unique properties and broad applications. However, semimetallic mesoporous structures cannot be obtained by the traditional template-mediated strategies due to the inevitable hydrolytic reaction of semimetal compounds. Therefore, it is yet challenging to fabricate mesoporous semimetal nanostructures, not even mention controlling their pore sizes. Here we develop a facile and robust selective etching route to synthesize monodispersed mesoporous antimony nanospheres (MSbNSs). The pore sizes of MSbNSs are tunable by carefully controlling the partial oxidation of Sb nuclei and the selective etching of the as-formed Sb₂O₃. MSbNSs show a wide absorption from visible to second near-infrared (NIR-II) region. Moreover, PEGylated MSbNSs are degradable and the degradation mechanism is further explained. The NIR-II photothermal performance of MSbNSs is promising with a high photothermal conversion efficiency of ~44% and intensive NIR-II photoacoustic signal. MSbNSs show potential as multifunctional nanomedicines for NIR-II photoacoustic imaging guided synergistic photothermal/chemo therapy in vivo. Our selective etching process would contribute to the development of various semimetallic mesoporous structures and efficient multimodal nanoplatforms for theranostics.

Photo-assisted sequential assembling of uniform metal nanoclusters on semiconductor support

Dispersing metal nanoclusters on the oxide supports is attracting close attention in heterogeneous catalysis, but great challenges still lie in controlling the size and dispersion of nanoclusters due to the inevitable agglomeration. Here, we propose a sequential photochemical deposition strategy named “first store, and then release” to uniformly fabricate the size-controlling noble metal nanoclusters on semiconductor oxides. Using the typical semiconductor TiO₂, the photoexcited electrons can be first stored as reduced species (e.g. Ti³⁺) under irradiation and the Ti³⁺ species can optimize both the nucleation and growth processes in dark reaction, resulting in a uniform dispersing of various noble metals (Au, Pt, Ag etc.) with size diameters of ∼1 nm. The nanoclusters catalysts exhibited superior performance in catalytic oxidation of HCHO compared with that of nanoparticles. This work brings a new and useful strategy to construct size-controlling noble metals on the oxide supports for heterogeneous catalysis and the related fields.

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Metal nanoclusters were deposited on semiconductors via sequential photodeposition

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Ti³⁺ species store the photoelectrons and optimize the nucleation and growth processes

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The catalysts exhibit superior performance in catalytic oxidation of HCHO

Crystal Facet Engineering and Hydrogen Spillover-Assisted Synthesis of Defective Pt/TiO2-x Nanorods with Enhanced Visible Light-Driven Photocatalytic Activity

Hydrogen spillover can assist the introduction of defects such as Ti³⁺ and concomitant oxygen vacancies (V_O) in a TiO₂ crystal, thereby inducing a new level below the conduction band to improve the conductivity of photogenerated electrons and the visible light absorption property of TiO₂. Meanwhile, crystal facet engineering offers a promising approach to achieve improved activity by influencing the recombination step of the photogenerated electrons and holes. In this study, with the aim of achieving enhanced visible light-driven photocatalytic activity, rutile TiO₂ nanorods with different aspect ratios were synthesized by crystal facet engineering, and Pt-deposited TiO_2-x nanorods (Pt/TNR) were then obtained via reduction treatment assisted by hydrogen spillover. The reduction treatment at 200 °C induced the formation of surface Ti³⁺ exclusively, whereas surface Ti³⁺ and V_O were formed by performing the reduction at 600 °C. The Pt/TNR with a higher aspect ratio reduced at 200 °C exhibited the highest activity in photocatalytic H₂ production under visible light irradiation owing to the synergistic effect of the introduction of Ti³⁺ defects and the spatial charge carrier separation induced by crystal facet engineering.

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Microcystis@TiO2 Nanoparticles for Photocatalytic Reduction Reactions: Nitrogen Fixation and Hydrogen Evolution

Solar-driven photocatalysis has been known as one of the most potential technologies to tackle the energy shortage and environmental pollution issues. Utilizing bio-pollutants to prepare functional materials has been considered as a green option. Herein, we used Microcystis aeruginosa as a bio-template to fabricate a Microcystis@TiO2 photocatalyst using a calcination method. The as-prepared Microcystis@TiO2 showed prominent ability as well as favorable stability for photocatalytic reduction reactions including hydrogen evolution and nitrogen fixation. Under light illumination, Microcystis@TiO2 calcined at 550 °C exhibited optimal photo-reduced activity among all samples, with the highest hydrogen evolution (1.36 mmol·g−1·h−1) and ammonia generation rates (0.97 mmol·g−1·h−1). This work provides a feasible approach to prepare functional materials from disposed pollutants.

Defect Engineering of Pt/TiO2-x Photocatalysts via Reduction Treatment Assisted by Hydrogen Spillover

Defect engineering of metal oxides is a facile and promising strategy to improve their photocatalytic activity. In the present study, Pt/TiO_2-x was prepared by a reduction treatment assisted by hydrogen spillover to pure rutile, anatase, and brookite and was subsequently used for hydrogen production from an aqueous methanol solution. With increasing reduction temperature, the photocatalytic activity of the rutile Pt/TiO_2-x increased substantially, whereas the activity of anatase Pt/TiO_2-x decreased and that of brookite Pt/TiO_2-x was independent of the treatment temperature. Electron-spin resonance analysis revealed that rutile and brookite possess similar defect sites (Ti³⁺ and concomitant oxygen vacancy) after the reduction at 600 °C, whereas different resonance signals were observed for anatase after the reduction at 600 °C. During the reduction process, electrons donated from spillover hydrogen migrate between the conduction band and the inherent midgap states. This research demonstrates that the depth of the inherent midgap states, depending on the crystal phases, influences the generation of defects, which play a key role in the photocatalytic performance of Pt/TiO_2-x.

Rich oxygen vacancies, mesoporous TiO2 derived from MIL-125 for highly efficient photocatalytic hydrogen evolution

Here we report a mesoporous TiO₂ with a large specific surface area and rich oxygen vacancies using a Ti-based MOF (MIL-125) as a precursor through high-temperature annealing. Such integration of a unique mesoporous structure and oxygen vacancies provides effective carrier transport channels, increases surface active sites, and enhances photocatalytic activity for the hydrogen evolution reaction.

Defective Dopant-Free TiO2 as an Efficient Visible Light-Active Photocatalyst

Pristine and modified/doped titania are still some of the most widely investigated photocatalysts due to its high activity, stability, abundance and proper redox properties to carry out various reactions. However, modifiers and/or dopants resulting in visible-light activity might be expensive or work as recombination centers under UV irradiation. It seems that defective titania, known as “self-doped” TiO2, might be the best solution since it can be obtained under mild conditions without the addition of expensive materials and methods. This review discusses various methods of defective titania preparation, characterization of defect types, their localization (surface vs. bulk) and their function, as well as proposed mechanisms of photocatalytic reactions in the presence of self-doped titania. Although many kinds of defective titania samples have already been prepared with different colors, color intensities and defect kinds (mainly Ti3+ and oxygen vacancies), it is difficult to conclude which of them are the most recommended as the preparation conditions and activity testing used by authors differ. Furthermore, activity testing under solar radiation and for dyes does not clarify the mechanism since bare titania can also be excited and sensitized, respectively, in these conditions. In many reports, authors have not considered the possible influence of some impurities originated from the synthesis method (e.g., H, Al, Zn, Cl, F) that could co-participate in the overall mechanism of photocatalytic reactions. Moreover, some reports indicate that defective titania, especially black ones, might decrease activity since the defects might work as recombination centers. Despite some unproven/unclear findings and unanswered questions, there are many well-conducted studies confirmed by both experimental and theoretical studies that defective titania might be a promising material for various photocatalytic reactions under both UV and visible-light irradiation. Based on available literature, it could be proposed that optimal defects’ concentration, the preferential role of surface defects, a higher surface-to-bulk ratio of defects in rutile than in anatase, and the beneficial impact of disordered surface are the most important aspects to be considered during the preparation of defective titania.

Synthesis of sulfonated lignin-derived ordered mesoporous carbon for catalytic production of furfural from xylose

Sulfonated lignin-derived ordered mesoporous carbon (OMC-SO₃H) solid acid was synthesized through solvent evaporation induced self-assembly (EISA) method followed by sulfonation, using lignin as carbon precursor and glyoxal as cross-linking agent during the preparation process. The as-synthesized OMC-SO₃H exhibited a typical 2D hexagonal meso-structure (space group p6mm) and showed a good catalytic performance for the catalytic conversion of hemicellulose-derived xylose to furfural. A highest furfural yield of 76.7% with 100% xylose conversion was achieved at 200 °C for 45 min in γ-valerolactone (GVL)-water (85:15 v/v%) mixture. The lignin-derived OMC-SO₃H solid acid catalyst showed superior stability and reusability, and was also applicable to the catalytic production of furfural from xylan. This work provides a promising strategy for the synthesis of ordered mesoporous carbon solid acid from green and sustainable lignin biomass resource, which has wide range of applications in the utilization of cellulose and hemicellulose.

A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis

Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO₂ reduction to CH₄. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.

Surface defects induced charge imbalance for boosting charge separation and solar-driven photocatalytic hydrogen evolution

Low charge separation efficiency of semiconductor materials is the main obstacle for high-performance photocatalyst. Herein, we report surface defects engineered uniform mesoporous TiO₂ nanospheres (DMTNSs) through surfactant-mediated self-assembly solvothermal approach combined with hydrogenation strategy to promote charge separation. The surface defects induced charge imbalance result in the formation of built-in field, which can promote photogenerated charge separation efficiently and be confirmed by experimental and density functional theory (DFT) calculations. Under AM 1.5G irradiation, the photocatalytic hydrogen evolution of DMTNSs is ~3.34 mmol h^-1 g^-1, almost 3.5 times higher than that of pristine non-defective TiO₂ nanospheres (0.97 mmol h^-1 g^-1), due to the engineered surface defects narrowing the bandgap (~3.01 eV) and inducing charge imbalance to boost spatial charge separation and extend visible-light response. The defect induced charge imbalance strategy opens a new valuable perspective for fabricating other high-efficient oxide photocatalysts.

Trace-Level Fluorination of Mesoporous TiO2 Improves Photocatalytic and Pb(II) Adsorbent Performances

Fluorination is an effective way of tuning the physicochemical property and activity of TiO₂ nanocrystallites, which usually requires a considerable amount of hydrofluoric acid (or NH₄F) for a typical F/Ti molar ratio, R_F, of 0.5-69.0 during synthesis. This has consequential environmental issues due to the high toxicity and hazard of the reactants. In the present work, an environmentally benign fluorination approach is demonstrated that uses only a trace amount of sodium fluoride with an R_F of 10^-6 during synthesis. While it maintained the desirable high surface area (102.4 m²/g), the trace-level fluorination enabled significant enhancements on photocatalytic activities (e.g., a 56% increase on hydrogen evolution rate) and heavy metal Pb(II) removal (31%) of the mesoporous TiO₂. This can be attributed to enriched Ti³⁺ and localized spatial charge separation due to fluorination as proved by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and density functional theory (DFT) analyses.