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Core–shell structures, where the "guest" material is encapsulated within a protective shell, integrate the advantages of different materials to enhance the overall properties of the composite. Covalent–organic frameworks (COFs) are favorable candidates for composing core–shell structures due to their inherent porosity, good activity, excellent stability, and other advantages. In particular, COFs as shells to encapsulate other functional materials are becoming increasingly popular in the fields of environmental remediation and energy conversion. However, there is a lack of reviews on COF‐based core–shell materials. In this context, this review provides a systematic summary of the current research on COF‐based core–shell composites. First, a simple classification is made for COF‐based core–shell composites. The second part of the review describes the main synthesis methods. The changes brought about by the COF shell and core–shell structures on the properties of the composites and their applications in photocatalysis, electrocatalysis, adsorption, sensing, and supercapacitors are then emphasized. Finally, new perspectives on the future development and challenges of composites are presented. The purpose of this study is to provide future insights into the design and application of COF‐based core–shell composites. [ABSTRACT FROM AUTHOR]

In order to solve the problem of environmental health hazards caused by phthalate esters, a series of pure Bi2O2CO3 and light (La, Ce, Pr, Nd, Sm and Eu) and heavy (Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) rare earth-doped Bi2O2CO3 samples were prepared by hydrothermal method. The crystalline phase composition and physical structure of the samples calcined at 300 °C were studied, and we found that the rare earth ion doping promoted the transformation of Bi2O2CO3 to β-Bi2O3 crystalline phase, thus obtaining a mixed crystal phase photocatalyst constituted by rare earth-ion-doped Bi2O2CO3/β-Bi2O3. The Bi2O3/Bi2O2CO3 heterostructure had a lower band gap and more efficient charge transfer. The fabricated samples were applied to the photocatalytic degradation of dimethyl phthalate (DMP) under a 300 W tungsten lamp, and it was found that the rare earth ion doping enhanced the photocatalytic degradation activity of DMP, in which the heavy rare earth of Er-doped sample reached 78% degradation for DMP at 150 min of light illumination. In addition, the doping of rare earths resulted in a larger specific surface area and a stronger absorption of visible light. At the same time, the formation of Bi2O2CO3/β-Bi2O3 heterogeneous junction enhanced the separation efficiency of photogenerated electrons and holes. [ABSTRACT FROM AUTHOR]

Morphology adjustment is a feasible method to change the physicochemical properties of photocatalysts. The issue that excessively thick tube wall of tubular g-C 3 N 4 is not conducive to the electron migration from inside to the surface thus inhibiting the separation of photogenerated carriers has always been ignored. Potassium ions were used to regulate the structure of the tubular supramolecular precursor by breaking hydrogen bonds, thereby promoting the synthesis of delaminated laminar tubular g-C 3 N 4 (K-CN), which not only shortened the transfer distance of photogenerated electrons but also provided abundant reaction active sites. Experiments and DFT calculations were combined to reveal the details of the physicochemical properties of K-CN. The photocatalytic capacity of K-CN for tetracycline hydrochloride (TCH) degradation and H 2 O 2 generation were 83% and 133 μM, respectively. This work not only synthesized a novel delaminated tubular g-C 3 N 4 but also provided a strategy and inspiration for structure and performance optimization for tubular g-C 3 N 4. [Display omitted] • Supramolecular self-assembly produced tubular g-C 3 N 4 precursors. • Potassium ions was influenced on the supramolecular self-assembly. • Destruction of the hydrogen bond induced delamination of tubular g-C 3 N 4. • Experiment and DFT calculation were combined to reveal the properties of K-CN. • Delamination promoted K-CN showed strong photocatalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Supramolecular self-assembly produced tubular g-C 3 N 4 precursors. • H 2 O 2 impregnated precursors achieve the multi-mesoporous filling in tubular g-C 3 N 4. • Endogenous gas release promoted the formation of porous structures. • Investigating the physicochemical properties by experiment and DFT calculation. The problem that the hollow part with macroporous size in the hollow tubular g-C 3 N 4 is difficult to function in photochemical reactions has been neglected for a long time. To address this issue, tubular g-C 3 N 4 with mesoporous-rich non-hollow ant nest-like filling (AN-TCN) was prepared by calcining supramolecular precursors impregnated with hydrogen peroxide solution. The endogenous gas released from the wet rod-like supramolecular precursor during thermal polymerization contributed to the construction of a mesoporous filling structure inside the AN-TCN, which not only increased the reactive sites, but also enhanced the ability of visible light response and facilitated the separation and transfer of photoinduced charges. Experiments and theoretical calculations were conduct together to reveal the physicochemical characteristics of AN-TCN. The photocatalytic capacity of AN-TCN-4.5 for tetracycline hydrochloride (TCH) reached to 86 % under visible radiation within 30 min. This study afforded a new thinking and strategy for morphology regulation and performance optimization of g-C 3 N 4 -based photocatalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bifunctional KHCO 3 template-mediated synthesis of porous and well-structured g-C 3 N 4. • Cyano defects and K intercalation are introduced into g-C 3 N 4 framework. • Catalysts owns tunable band structure, optimized charge transfer. • The mechanism is well studied by experiments and theoretical calculations. • The photocatalyst exhibits an excellent ability to produce H 2 O 2 under visible light. The photocatalytic method to produce hydrogen peroxide (H 2 O 2) as a substitute for fossil fuels has become a hot research topic. We herein propose cyano defect and potassium intercalation modified g-C 3 N 4 photocatalysts in which the porous structure and crystallinity can be maintained relatively well. Simultaneously, the photocatalysts possess adjustable band structure, enhanced carrier transfer efficiency and highly selective dual-electron O 2 reduction. The physicochemical properties and reaction mechanisms are well studied through the effective combination of experiments and theoretical calculations. The H 2 O 2 yield of KDCN-0.2 (278.9 μmol L-1h−1) is approximately 4.3 times higher than that of original CN (65.2 μmol L-1h−1), and the energy conversion efficiency is also higher than many current CN-based photocatalysts. This work deepens the understanding of the mechanism of photocatalytic O 2 reduction for H 2 O 2 production and points out the promising direction for the design of novel CN-based photocatalysts with ideal properties in energy conversion and environmental applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfur doped hollow tubular g-C 3 N 4 was prepared through molecular self-assembly. • A noval 2D/1D BOC/SCN hierarchical heterostructure was constructed. • BOC/SCN composites exhibited outstanding photocatalytic activity and stability for TCH degradation. • A possible Z-scheme charge transfer pathway and degradation mechanism were proposed. The construction of heterojunction photocatalysts was considered to be an effective strategy to tackle refractory pollutants. However, most of the reported composites lacked precise control of their morphology, resulting in unsatisfactory catalytic activity. In this work, we successfully fabricated sulfur doped g-C 3 N 4 hollow tubes (SCN) via molecular self-assembly, and then grew the Bi 2 O 2 CO 3 nanoflakes (BOC) in situ parallel on the surface of SCN to construct 2D/1D interfacial phase. Within 30 min visible light irradiation, the robust BOC/SCN-3 heterostructure showed considerable improvement for tetracycline degradation (82.6%) compared with individual components. This enhanced photocatalytic performance derived from the synergistic effect of S doping and heterojunction interface contact. The tubular structure formed by S doping not only narrowed the bandgap and thus boosting the visible light harvesting of CN, but also promoted electrons to travel along the 1D longitudinal and radial directions. In addition, the built-in electric field between BOC and SCN effectively achieved the spatial separation of electron-hole pairs. Mechanism analysis revealed that the h+ and •O 2 − radicals played the dominating contribution in the photocatalytic process, and a possible Z-scheme mechanism was proposed. It was expected that such design route could provide a new perspective on hierarchical heterostructure for pollutant removal. [ABSTRACT FROM AUTHOR]

• Melamine self-assembly can adjust the shape and structure of the material. • Melamine self-assembly is an effective measure to synthesize high-performance g-C 3 N 4 -based materials. • The type, mechanism, influencing factors and recent advances of self-assembly are highlighted. • Provides guidance for scientific researchers to develop and design high-performance g-C 3 N 4 -based materials. The increasing pollution of the environment and the depletion of energy are currently facing and urgently need to be resolved. In recent years, various technologies have been exploited to try to solve these problems. Researchers are mainly committed to developing high-performance materials. This review discusses the construction of ordered graphitic carbon nitride (g-C 3 N 4)-based materials by melamine self-assembly. Firstly, the self-assembly types, corresponding synthesis strategies, characteristics and recent advances are reviewed from the perspectives of material source and product shape. Meanwhile, the effects of molecular structure, solution environment, synthesis methods and the presence of other substances on the self-assembly behavior are also discussed. In addition, we present the synthesis mechanisms from multiple sides. Finally, the applications in environment and energy are summarized, and the future research directions are also proposed. This review provides new insights into the design and construction of high-performance ordered g-C 3 N 4 -based materials for environment and energy. [ABSTRACT FROM AUTHOR]

• Hollow tubular g-C 3 N 4 isotype heterojunction (SCN-CN) was synthesized. • SCN-CN performed a high visible-light photodegradation efficiency for TCH and RHB. • This work provides a theoretical basis for CN isotype heterojunction. • Electronic, optical, and work function properties were calculated based on DFT. A highly reactive hollow tubular g-C 3 N 4 isotype heterojunction (SCN-CN) was designed to enhance visible light absorption and manipulate the directed transfer of electrons and holes. The results of UV–vis DRS, XPS valence band and DFT theoretical calculations indicated S doping increases the visible-light absorption capacity and changed the ba nd gap structure of g-C 3 N 4 (CN), resulting in the transfer of electrons from the CN to the SCN and holes from the SCN to the CN under visible light. In addition, the tubular structure of the SCN-CN facilitated the transfer of electrons in the longitudinal direction, which reduced charge carrier recombination. Furthermore, the optical properties, electronic structure, and electron transfer of SCN-CN were also studied by experiments and theoretical calculations. The antibiotic tetracycline hydrochloride (TCH) and dye Rhodamine B (RHB) were subjected to evaluate the photocatalytic performance of SCN-CN. The scavenger tests and ESR data showed that the h+, ·O 2 − and ·OH worked together in the photocatalytic process. Moreover, the photocatalytic degradation pathway was analyzed by LC-MS. This study synthesized a hollow tubular CN isotype heterojunction with high visible-light photocatalytic performance and provided a theoretical basis for CN isotype heterojunction. [ABSTRACT FROM AUTHOR]

• Recent advances in photocatalysts modified with fullerene and its derivatives are overviewed. • Exclusive properties and photocatalytic mechanisms of fullerene and its derivatives. • Main synthesis strategies and affecting factors are discussed. • Excellent photocatalytic applications of photocatalysts modified with fullerene and its derivatives. • Challenges and directions on future design, synthesis and applications. Fullerenes possess high chemical stability, large specific surface area, good electrical conductivity and unique three-dimensional structure. In this paper, we provide a general overview of the latest research results of fullerene-based photocatalysts. Firstly, the current status of semiconductor materials and fullerenes in photocatalytic applications are briefly introduced. Secondly, introduced action mechanisms of photocatalysts modified by fullerene C 60 and its derivatives, including basic structure, exclusive properties and its effect in photocatalysis and material preparation process. Thirdly, factors affecting material effectiveness and the synthesis strategy of composite photocatalyst modified by fullerene are introduced. Meanwhile, the application advances of the photocatalysts are introduced, including in the degradation of pollutants, organic synthesis, hydrogen production, antibacterial and disinfection in water. Finally, the development trends of fullerenes and their derivatives in photocatalysis are also summarized, including theoretical calculations, the morphological structure control, stable derivatives and increase the selectivity, and new other types of fullerene materials. [ABSTRACT FROM AUTHOR]

• Synthesis methods, structures and properties of QD-MOF composites. • Progress of QD-MOF composites in environmental remediation and energy production. • Detailed photocatalytic mechanism of QD-MOF composites. • The presents challenges of QD-MOF composites and the prospects for their future development. Photocatalysis is an efficient technology for energy production and environmental remediation. The composites of metal organic frameworks (MOFs) combined with quantum dots (QDs) allow high photocatalytic ability. Recently, these composites have been applied increasingly in the fields of energy production and environmental remediation. Even so, QD-MOF composites still have some shortcomings in the field of photocatalysis. In this review, the synthesis methods and structures as well as the applications of QD-MOF composites in water splitting for hydrogen production, carbon dioxide (CO 2) reduction to produce methane (CH 4), organic dye degradation, Cr(VI) reduction, and nitric oxide (NO) oxidation are discussed. The mechanisms of these processes are also described in detail. Finally, new insights into the future development and challenges of the composite are proposed to advance further development of the research area. [ABSTRACT FROM AUTHOR]