As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

A review on g-C3N4-based photocatalysts

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has been the hotspot in the materials science as a metal-free and visible-light-responsive photocatalyst. Pure g-C3N4 suffers from the insufficient sunlight absorption, low surface area and the fast recombination of photo-induced electron-hole pairs, resulting in low photocatalytic activity. Element doping is known to be an efficient method to tune the unique electronic structure and band gap of g-C3N4, which considerably broaden the light responsive range and enhance the charge separation. This review summarizes the recent progress in the development of efficient and low cost doped g-C3N4 systems in various realms such as photocatalytic hydrogen evolution, reduction of carbon dioxide, photocatalytic removal of contaminants in wastewater and gas phase. Typically, metal doping, nonmetal doping, co-doping and heterojunction based on doped g-C3N4 have been explored to simultaneously tune the crystallographic, textural and electronic structures for improving photocatalytic activity by enhancing the light absorption, facilitating the charge separation and transportation and prolonging the charge carrier lifetime. Finally, the current challenges and the crucial issues of element doped g-C3N4 photocatalysts that need to be addressed in future research are presented. This review presented herein can pave a novel avenue and add invaluable knowledge to the family of element doped g-C3N4 for the develop of more effective visible-light-driven photocatalysts.

Doping of graphitic carbon nitride for photocatalysis: A reveiw

Metal-organic frameworks (MOFs) are typically highlighted for their potential application in gas storage, separations and catalysis. In contrast, the unique prospects these porous and crystalline materials offer for application in electronic devices, although actively developed, are often underexposed. This review highlights the research aimed at the implementation of MOFs as an integral part of solid-state microelectronics. Manufacturing these devices will critically depend on the compatibility of MOFs with existing fabrication protocols and predominant standards. Therefore, it is important to focus in parallel on a fundamental understanding of the distinguishing properties of MOFs and eliminating fabrication-related obstacles for integration. The latter implies a shift from the microcrystalline powder synthesis in chemistry labs, towards film deposition and processing in a cleanroom environment. Both the fundamental and applied aspects of this two-pronged approach are discussed. Critical directions for future research are proposed in an updated high-level roadmap to stimulate the next steps towards MOF-based microelectronics within the community.

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An updated roadmap for the integration of metal–organic frameworks with electronic devices and chemical sensors

Developing efficient sensor materials with superior performance for selective, fast and sensitive detection of gases and volatile organic compounds (VOCs) is essential for human health and environmental protection, through monitoring indoor and outdoor air pollutions, managing industrial processes, controlling food quality and assisting early diagnosis of diseases. Metal–organic frameworks (MOFs) are a unique type of crystalline and porous solid material constructed from metal nodes (metal ions or clusters) and functional organic ligands. They have been investigated extensively for possible use as high performance sensors for the detection of many different gases and VOCs in recent years, due to their large surface area, tunable pore size, functionalizable sites and intriguing properties, such as electrical conductivity, magnetism, ferroelectricity, luminescence and chromism. The high porosity of MOFs allows them to interact strongly with various analytes, including gases and VOCs, thus resulting in easily measurable responses to different physicochemical parameters. Although much of the recent work on MOF-based luminescent sensors have been summarized in several excellent reviews (up to 2018), a comprehensive overview of these materials for sensing gases and VOCs based on chemiresistive, magnetic, ferroelectric, and colorimertic mechanisms is missing. In this review, we highlight the most recent progress in developing MOF sensing and switching materials with an emphasis on sensing mechanisms based on electricity, magnetism, ferroelectricity and chromism. We provide a comprehensive analysis on the MOF–analyte interactions in these processes, which play a key role in the sensing performance of the MOF-based sensors and switches. We discuss in detail possible applications of MOF-based sensing and switching materials in detecting oxygen, water vapor, toxic industrial gases (such as hydrogen sulfide, ammonia, sulfur dioxide, nitrous oxide, carbon oxides and carbon disulfide) and VOCs (such as aromatic and aliphatic hydrocarbons, ketones, alcohols, aldehydes, chlorinated hydrocarbons and N,N′-dimethylformamide). Overall, this review serves as a timely source of information and provides insight for the future development of advanced MOF materials as next-generation gas and VOC sensors.

Functional metal–organic frameworks as effective sensors of gases and volatile compounds

Nitrogen self-doped graphitic carbon nitride (C3N4+x) was successfully synthesized by the co-thermal condensation of the precursor with a nitrogen-rich additive. The resultant self-doped semiconductor was characterized by X-ray photoelectron spectroscopy (XPS), which indicated that the nitrogen atom substituted the sp2 carbon atom. The photocatalytic hydrogen evolution was systematically evaluated under visible light irradiation (λ > 400 nm). The average hydrogen evolution rate for C3N4+x was 1.8 times higher than that of pristine graphitic carbon nitride, and the superiority lay in greatly improved optical, emission and electronic properties of the nitrogen modified carbon nitride. This study filled the research gap of self-doping for 2D polymeric carbon nitride and will stimulate intensive investigations in the further improvement of photocatalytic hydrogen evolution.

Nitrogen self-doped graphitic carbon nitride as efficient visible light photocatalyst for hydrogen evolution

Zinc oxide (ZnO) and zeolitic imidazolate framework-8 (ZIF–8) core–shell heterostructures were obtained by using the self-template strategy where ZnO nanorods not only act as the template, but also provide Zn2+ ions for the formation of ZIF–8 shell. The ZIF–8 shell was uniformly deposited to form ZnO@ZIF–8 nanorods with core–shell heterostructures at 70 °C for 24 h as the optimum reaction time by the hydrothermal synthesis. Transmission electron microscopy (TEM) images revealed that the ZnO@ZIF–8 heterostructures are composed of ZnO as core and ZIF–8 as shell. Nitrogen (N2) sorption isotherms demonstrated that the as-prepared ZnO@ZIF–8 nanorods are a typical microporous material. Additionally, the ZnO@ZIF–8 nanorods sensor exhibited distinct gas response for reducing gases with different molecule sizes. The selectivity of the ZnO@ZIF–8 nanorods sensor was obviously improved for the detection of formaldehyde owing to the limitation effect of the aperture of ZIF–8 shell. This study demonstrated that semicon...

Zeolitic Imidazolate Framework Coated ZnO Nanorods as Molecular Sieving to Improve Selectivity of Formaldehyde Gas Sensor

Ternary solid solutions of (1 − x)(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)– xNaNbO3 (BNKT–xNN) lead-free piezoceramics were fabricated using a conventional solid-state reaction method. Pure BNKT composition exhibited an electric-field-induced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric-to-relaxor temperature TF-R shifted down below room temperature as the substitution of NN, a compositionally induced nonergodic-to-ergodic relaxor transition was presented, which featured the pinched-shape polarization and sprout-shape strain hysteresis loops. A strain value of ~0.445% (under a driving field of 55 kV/cm) with large normalized strain of ~810 pm/V was obtained for the composition of BNKT–0.04NN, and the large strain was attributed to the reversible electric-field-induced transition between ergodic relaxor and ferroelectric phase.

Composition- and Temperature-Dependent Large Strain in (1−x)(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)– xNaNbO3 Ceramics

Intrinsic electric field assisted polymeric graphitic carbon nitride coupled with Bi4Ti3O12/Bi2Ti2O7 heterostructure nanofibers toward enhanced photocatalytic hydrogen evolution

Ag/BiPO4 heterostructures were synthesized by a hydrothermal method combined with an impregnation technique. The heterostructures exhibit much higher activity than pure BiPO4 for degradation of methylene blue, which may be primarily ascribed to highly efficient photogenerated electron–hole pair separation. They also show good recyclability and slightly strong absorption in the visible region. In addition, the possible mechanism for the enhanced photocatalytic properties of Ag/BiPO4 heterostructures is discussed. Moreover, radical scavengers experiments confirmed that holes are the main active species instead of hydroxyl radicals when coupled with the BiPO4 surface by the noble nanocrystalline metal Ag.

Mengmeng Li

Papers

Nitrogen self-doped graphitic carbon nitride as efficient visible light photocatalyst for hydrogen evolution

Zeolitic Imidazolate Framework Coated ZnO Nanorods as Molecular Sieving to Improve Selectivity of Formaldehyde Gas Sensor

Composition- and Temperature-Dependent Large Strain in (1−x)(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)– xNaNbO3 Ceramics

Intrinsic electric field assisted polymeric graphitic carbon nitride coupled with Bi4Ti3O12/Bi2Ti2O7 heterostructure nanofibers toward enhanced photocatalytic hydrogen evolution

Ag/BiPO4 heterostructures: synthesis, characterization and their enhanced photocatalytic properties.