Metal-organic frameworks (MOFs), a class of porous crystalline framework materials, are linked by strong bonds between inorganic and organic building blocks. [1-3] In the past two decades, MOFs have rapidly grown as a star material due to their exceptional performance in areas such as storage, separation and catalysis. [4] The outstanding performance of MOFs in applications benefits from their intrinsically porous structures and highly tunable pore environment. [5-7] The creation and modification of pore space with optimized size, functionality and diversity can be precisely tuned at the molecular level by rationally designing building blocks and synthetic procedures. [8,9] The diversity of MOFs can be enriched by expanding the library of organic linkers with varying lengths, geometries, and functional groups. [10] Additionally, very diverse metal cations are applied to MOF synthesis, ranging from monovalent (Ag + , Cu + , etc.), divalent (Mg 2+ , Fe 2+ , Co 2+ , Ni 2+ , etc.), trivalent (Al 3+ , Sc 3+ , V 3+ , Cr 3+ , etc.), to tetravalent (Ti 4+ , Zr 4+ , Hf 4+ , etc.) cations. [11] In this review, we mainly focus on MOFs with group 3 and 4 metals, including Y, lanthanides (Ln, from La to Lu), actinides (An, from Ac to Lr), Ti, and Zr (Figure 1). Group 3 metal cations are generally found in the oxidation state of +3 in the MOF structures, while group 4 metal cations mainly exist in the oxidation state of +4, leading to the formation of much stronger coordination bonds with carboxylates. [12] Therefore, group 4 metal-based MOFs (M IV-MOFs) generally have enhanced stability compared with MOFs constructed from metals of group 3 and other groups. This series of MOFs stands out because the involved metals can generally coordinate with carboxylates to form frameworks with strong coordination bonds, according to the Pearson's hard/soft acid/base principle, where group 3 and 4 metal cations are regarded as hard acids while carboxylate ligands are hard bases. [11] One remarkable feature of MOFs with group 3 and 4 metals is that they generally can form phases containing M 6 O 8 (M = Y, Ln, An, Zr and Hf) clusters, regardless of their atomic numbers, charges and radius. This series of M 6-based MOFs is best represented by UiO series such as UiO-66 with fcu topology. [13] Under different synthetic conditions, UiO-66(M, M = An, Zr and Hf) constructed from [M 6 (μ 3-O) 4 (μ 3-OH) 4 ] clusters and linear carboxylates can be obtained, while UiO-66(M, M = Y, Ln) is assembled from Metal-organic frameworks (MOFs) based on group 3 and 4 metals are considered as the most promising MOFs for varying practical applications including water adsorption, carbon conversion, and biomedical applications. The relatively strong coordination bonds and versatile coordination modes within these MOFs endow the framework with high chemical stability, diverse structures and topologies, and interesting properties and functions. Herein, the significant progress made on this series of MOFs since 2018 is summarized and an update on the current status an...

No abstract

attention owing to its clean and high energy density property. [2c,d,3a,4] To facilitate the photocatalytic activity, most of the photocatalytic systems were conducted by adding various SEDs, namely triethylamine, monoethanolamine, diethanolamine, triethanolamine (TEOA), methanol, ethanol, L-ascorbic acid, ethylenediamine, tetraacetic acid, and phenol. These SEDs are believed to eliminate the photoinduced holes and in return promote the photoinduced electrons for hydrogen generation. [5] The introduction of hazardous organic scavengers for photoinduced holes not only enhances the cost of the photocatalytic reaction, but also brings extra pollution or wastes. Therefore, extensive endeavors should be devoted to the overall water splitting process without any organic sacrificial reagents. Although great progress has been made for overall water splitting, [6] their quantum efficiency is far lower than industrial application. It is more interesting to develop dual-functional photocatalysts for hydrogen evolution on one side and make full use of SEDs consumption or oxygen evolution for organic oxidation on the other side. [7,8] It is a very meaningful procedure to oxidative couple the amines to form imines, which possesses multiple applications as one of the biologically active nitrogencontaining organic compounds. Therefore, combining the PHE Photocatalytic hydrogen evolution (PHE) over semiconductor photocatalysts is usually constrained by the limited light-harvesting and separation of photogenerated electron-hole pairs. Most of the reported systems focusing on PHE are facilitated by consuming the photoinduced holes with organic sacrificial electron donors (SEDs). The introduction of the SEDs not only causes the environmental problem, but also increases the cost of the reaction. Herein, a dual-functional photocatalyst is developed with the morphology of sandwichedlike hollowed Pd@TiO 2 @ZnIn 2 S 4 nanobox, which is synthesized by choosing microporous zeolites with sub-nanometer-sized Pd nanoparticles (Pd NPs) embedded as the sacrificial templates. The ternary Pd@TiO 2 @ZnIn 2 S 4 photocatalyst exhibits a superior PHE rate (5.35 mmol g −1 h −1 ) and benzylamine oxidation conversion rate (>99%) simultaneously without adding any other SEDs. The PHE performance is superior to the reported composites of TiO 2 and ZnIn 2 S 4 , which is attributed to the elevated light capture ability induced by the hollow structure, and the enhanced charge separation efficiency facilitated by the ultrasmall sized Pd NPs. The unique design presented here holds great potential for other highly efficient cooperative dual-functional photocatalytic reactions.

Organic-free MnO2 aerogels with ultralow density have been achieved by self-assembly of two dimensional MnO2 nanosheets via an ice-templating approach.