Advances in Emerging Crystalline Porous Materials

Crystalline porous materials (CPMs) have attracted considerable research attention in recent years for their wide applications in many fields, such as the energy storage and conversion, gas separation and storage, water purification, catalysis, optoelectronics, sensors, drug delivery, etc. The wide applications of CPMs derive from their superiorities of tunable porous structures, abundant functionalities, excellent chemical stability, various species and facile fabrication procedures. By atomically combining organic units with one another through strong covalent bonds or metal ions/clusters via coordination interactions, the design and fabrication of CPMs, including metal–organic frameworks (MOFs), covalent organic frameworks (COFs) and polyoxometalates (POMs), have been subjects of extensive study. In the past century, advances in chemistry and materials science have cultivated diverse CPMs, which are featured by general tendencies in structural evolution from rigid frames to soft dynamic blocks and from low dimensional to multiple dimensional. However, there still exist grant challenges in terms of materials process and practical applications. In this context, it is the right time to organize a special issue themed on CPMs, focusing on the recent progress and challenges in the design, synthesis and applications of CPMs. We have gladly taken the opportunity to serve as the Guest Editors of this special issue. The special issue consists of 16 research papers, 16 reviews, and 1 essay, covering a broad spectrum of the advanced developments of CPMs, mainly involving COFs, MOFs and POMs, as well as other significant crystalline materials including but not limited to perovskites. It encompasses some of the highly important research achievements, efforts and practices of CPMs in many well-established applications and emerging technologies including electrode materials, catalysis, synthesis, gas absorption and separation, chemical sensing, etc. COFs are a type of special porous organic materials, whose frameworks are conjunct with organic building units through covalent bonds. These covalent bond modes move the chemistry of COFs beyond the structures to methodologies, and also endow them with fascinating properties, such as the distinctive electronic properties favorable for the manufacture of electronic devices. Prof. Jian Zhu and co-workers put forward a dedicated summary on the synthesis and applications of conductive 2D COFs (article number 2006043). The interrelations of bonding strategies and the electronic properties of conductive 2D COFs have been discussed comprehensively. Prof. Long Chen et al. provided a review on the predesignable and tailorable 2D COFs with redox activities (article number 2005073). These 2D redox-active COFs have potential to serve as the electroactive materials of supercapacitors for efficient energy storage. Beside the attractive electronic properties for electronics, the special functional groups in COFs can also invest them with the capability of interacting with other species. Prof. Shilun Qiu and co-workers rationally designed and synthesized two 3D thioether-based COFs, JUC-570 and JUC-571, which selectively manifested the efficient adsorption of toxic Hg2+ ions (article number 2006112). In the field of catalysis, Prof. Shengqian Ma and co-workers improved the catalytical activities for selective functionalization of sp2 C–H bond to C–X (X = Br, Cl) or C–O bonds via the strong coordination of bipyridine-based COFs with palladium (article number 2003970). Prof. Yuan-Biao Huang and Prof. Rong Cao improved the electrocatalytic performance of carbon dioxide reduction reaction (CO2RR) by integrating D-A heterojunction units into the COF material (article number 2004933). Prof. Shuangxi Liu and Dr. Lan-Lan Lou provided a review on the advances of chiral COFs and MOFs in the asymmetric catalysis processes (article number 2005686). The design strategies, synthetic pathway and asymmetric catalytic performance of chiral COFs and MOFs have been discussed. Different from COF materials, MOFs are assembled by the coordination interactions between metal-containing nodes and organic linkers, and are also known as porous coordination polymers. Prof. Jing Li and Prof. Hao Wang presented an overview of MOFs based on calcium, whose traits are high thermal stability, nontoxicity, and relatively low density (article number 2005165). Prof. Michael J. Zaworotko and co-workers executed a taxonomic classification based upon taxonomy to supplement topological classification of porous coordination networks (PCNs), and this taxonomic approach has provided a useful guide for crystal engineers (article number 2006351). MOFs and other porous crystalline materials have attracted increasing attention in clean energy applications on account of their permanent porosity, high surface area, and controllable constructions. Prof. Yunhua Xu and co-workers focused on MOF-related materials for alkali metal ion batteries and discussed on the relationship between fundamental characteristics including component/structure design, composite fabrication, morphology engineering and electrochemical performance of cathode materials (article number 2006424). Prof. Jing-Lin Zuo and Prof. Zhong Jin presented experimentally three stable MOFs composed of Zr4+ and tetrathiafulvalene-base ligands, which could effectively facilitate the diffusion of Li+ ions in the lithium-ion capacitors (article number 2005209). Prof. Xue-Ping Gao and Prof. Guo-Ran Li provided a comprehensive survey on the crystalline multi-metal compounds (transition metal composite oxides, binary metal chalcogenides, double or complex salts hybrid metal compounds) as host materials in sulfur cathodes (article number 2005332). The solid materials with the capacity of proton conduction also draw widespread interest in the electrolytes for batteries or fuel cells. Prof. Hiroshi Kitagawa and Prof. Ken-ichi Otake shed light on the controllable proton-conductive behavior within MOFs, and generalized the design strategies and importance of hydrophobicity (article number 2006189). The uniform porosity, the presence of uncoordinated metal sites, and the hybrid organic-inorganic essence make MOFs ideal candidates for chemical catalysis, electrocatalysis, photocatalysis, and thermocatalysis. Prof. Tong-Liang Hu et al. reviewed the development of CPMs-confined active metal species for heterogeneous catalysis, with a particular focus on the synergistic effects between active components (article number 2003971). Prof. Yaping Du and Prof. Jun Zhang payed special attention to the properties and applications of rare-earth (RE)-MOF based catalysts, and summed up the effects of introduction of RE elements on the catalytic conversion (article number 2005371). The pore features of CPMs will result in the confinement effect in the processes of heterogeneous catalysis. The influences of confinement effects resided in CPMs on the diffusion, adsorption/desorption, and catalytic reaction have been discussed by Prof. Hongbo Zhang and colleagues (article number 2005334). Prof. Lifang Jiao payed close attention to the recent process of MOFs-derived carbon-based metal catalysts for general electrocatalytic reactions (article number 2004398). Prof. Kanokwan Kongpatpanich and Prof. Satoshi Horike experimentally improved the catalytic activity in glucose-to-HMF transformation of Brønsted MOFs via incorporating the desirable Al3+ catalytic sites at the organic linker (article number 2006541). Prof. Jian-Rong Li proposed a labile Zr(IV)-MOF with in situ porphyrin substitution for enhanced photocatalytic CO2 reduction (article number 2005357). The incorporation of metalloporphyrin not only awards MOFs with high catalytic activity and selectivity for CO2-to-CO reduction, but also with excellent chemical stability. Prof. Hai-Long Jiang and Prof. Yu-Zhen Chen encapsulated the Cu2O nanocrystals into MOFs to prepare the photothermal catalyst for one-pot cascade reactions (article number 2004481). The gas adsorption and separation are other important practical applications for the active sites in MOFs. Prof. Pingyun Feng designed and manufactured the tunable MOFs from the rare 8-connected trimers building scaffold, and these MOFs with different metals (Zn, Co, Fe) illustrated high uptake capacities for ethane (123 cm3 g−1) and ethylene (113 cm3 g−1) (article number 2003167). Prof. Ryotaro Matsuda and colleagues studied on the oxygen capturing abilities of MOFs with 9,10-Di(4-pyridyl)anthracene (dpa) ligands (article number 2004351). It was revealed that reversible trapping and releasing of dissolved oxygen could be realized under the stimulation of light and heat. CPMs are also the emerging platform for the optics, in both linear and nonlinear optical applications. Prof. Bin Zhao and Prof. Hang Xu explored the optical applications of MOFs in regard of the luminescent sensors for environmental pollutants (article number 2005327). The detected objects of the luminescent MOFs cover the common toxic organics, biotoxics, radioactive ions and heavy metal ions. In the aspect of nonlinear optics, Prof. Jialiang Xu and Prof. Xian-He Bu discussed on the important advances of crystalline porous NLO materials (article number 2006416). The second- and third-order NLOs of CPMs are emphasized, and the impact of chirality in porous materials for second-order NLOs are discussed. Aside from the familiar MOFs and COFs pertaining to the CPMs, there are also some distinct porous materials or crystalline materials with valuable applications in diversified domains. Prof. Zhong-Yong Yuan et al. summarized the synthesis pathways of metal phosphonate nanoporous materials and the diverse applications involving adsorption and separation, energy conversion and storage, heterogeneous catalysis, membrane engineering, and biomaterials (article number 2005304). Prof. Dan Wang and Prof. Ranbo Yu realized the overall water splitting under visible light with the assistance of multishelled structured SrTiO3 (article number 2005345). The solar-to-hydrogen efficiency was boosted to 0.08% for the La/Rh Co-doping SrTiO3. Prof. Zhen Zhou et al. offered a systematic review on the electrocatalysis of 3D graphene macrostructures (3D GMs) and introduced on the preparation strategies and methods for functional modifications (article number 2005255). Prof. Tiehong Chen and Zhipeng Su summarized the developments of porous noble metal electrocatalysts in the past decades, and investigated the impact of porous noble metal structure on the electrocatalytic performance, including accessibility of active sites, connectivity of skeleton structures, channels dimensions, and hierarchical structures (article number 2005354). Prof. Shigeyuki Masaoka and Prof. Mio Kondo reported a facile channel to adjust the catalytic activity of iron porphyrin for CO2 reduction via modulating the self-assembly (article number 2006150). Prof. Banglin Chen and co-workers fabricated hierarchically oriented carbon-structured composites via combining the confined pyrolysis strategy and disparate bond environments within MOFs simultaneously (article number 2002811). The resultant composites display fascinating catalytic activity in Knoevenagel condensation-hydrogenation reaction, and enhanced capacity and cycling stability in Li-S batteries. Prof. Jian Zhang and Prof. Huabin Zhang developed C-Mo-S triatomic coordination in hybrid ZIF for electrochemical reducing oxygen efficiently and steadily (article number 2003256). Prof. Xian-He Bu and Prof. Wei Li designed two isostructural perovskite ferroelectrics and examine the corresponding elastic properties and high-pressure behaviors (article number 2006021). Prof. Mitsuhiko Shionoya reported on the molecular recognition concerning amino acid and other peptide derivatives with the help of abundant hydrogen bonding in a porous metal-macrocycle framework (article number 2005803). Prof. Dan Ding designed pure organic phosphorescent crystals based on carbazole. The alkyl modification of organic blocks boosted room temperature phosphorescence lifetime and luminescence efficiency (article number 2005449). Although the themed special issue might not be exhaustive, it does highlight some of major advances in the developments and applications of crystalline porous materials. We hope that this special issue will be timely, meaningful and valuable in providing a significative reference and perspective for the research community working in this emerging field. In addition, we expect to trigger active interest of more scientists to join in this field. We would like to thank Dr. José Oliveira (Editor-in-Chief) and Dr. Jovia Jiang (Deputy Editor) for giving us the opportunity to organize this special issue. Our appreciation extends to the editorial team of Small, for their professionalism throughout the editing process. We are also greatly indebted to all the contributing authors for their efforts and enthusiastic supports. Jialiang Xu is a Professor of Materials Chemistry at Nankai University. He obtained his PhD from ICCAS in 2010 under the supervision of Prof. Yuliang Li, and then worked as Marie-Curie Fellow at Radboud University, Nijmegen, hosted by Prof. Alan Rowan and Prof. Theo Rasing. In 2013, he was awarded the NWO-VENI grant, with which he developed his research line at the interface between Chemistry and Physics to study the coupling between light and (supra)molecular materials. He joined Tianjin University in 2015, and relocated to Nankai University in 2018. Yunhua Xu is a professor in the School of Materials Science and Engineering of Tianjin University. He received PhD degree in Materials Physics and Chemistry from South China University of Technology in 2008. Prior to joining Tianjin University, he worked as a researcher at the University of California, Santa Barbara, Iowa State University and the University of Maryland, College Park, from 2006 to 2015. His research interests focus on electrochemical storage materials and devices. Xian-He Bu is a Cheung Kong Scholar Professor of Chemistry at Nankai University (from 2004). He obtained his BS and PhD degrees from Nankai University in 1986 and 1992 under the supervision of Prof. Rong-Ti Chen. Since 1995, he has been a full professor at Nankai University. He now serves as the dean of School of Material Science and Engineering, and a director of Tianjin Key Lab of Metal and Molecule-Based Material Chemistry. His current research focuses on the syntheses and applications of multifunctional coordination compounds, crystal engineering, magnetic materials, etc.