Conjugated carbon nitride (CN) is an emerging and promising semiconductor photocatalyst for water photolysis owing to its unique properties. However, the traditional thermally induced polymerization ...of N‐containing precursors typically produces melon‐based CN solids with amorphous or semi‐crystalline structures with only moderate photocatalytic performance. Many strategies have been developed to prepare crystalline CNs (CCNs), such as high‐temperature and high‐pressure routes, ionothermal synthesis, and microwave‐assisted synthesis. In this Minireview, we summarize the progress that has been made in the synthesis of CCNs and their application in photocatalytic water splitting reactions. Three kinds of CCNs are mainly discussed according to their polymeric subunits. Challenges associated with CCNs and their future development are also included.
Polymeric carbon nitride (CN) typically shows a high recombination rate of photogenerated carriers and moderate photocatalytic performance. These issues can be addressed by increasing the crystallinity of this material. In this Minireview, progress in the synthesis of crystalline CN and its application in photocatalytic water splitting is discussed.
As a promising two‐dimensional conjugated polymer, graphitic carbon nitride (g‐C3N4) has been utilized as a low‐cost, robust, metal‐free, and visible‐light‐active photocatalyst in the field of solar ...energy conversion. This Review mainly describes the latest advances in g‐C3N4 photocatalysts for water splitting. Their application in CO2 conversion, organosynthesis, and environmental purification is also briefly discussed. The methods to modify the electronic structure, nanostructure, crystal structure, and heterostructure of g‐C3N4, together with correlations between its structure and performance are illustrated. Perspectives on the challenges and opportunities for the future exploration of g‐C3N4 photocatalysts are provided. This Review will promote the utilization of g‐C3N4 materials in the fields of photocatalysis, energy conversion, environmental remediation, and sensors.
Metal‐free photocatalysis: Recent progress in g‐C3N4 photocatalysis is highlighted. The four fundamental approaches for modification of g‐C3N4 photocatalysts are discussed: electronic structure modulation, nanostructure design, crystal‐structure engineering, and heterostructure construction. The application of g‐C3N4 photocatalysts are briefly summarized and the opportunities and challenges in this field are discussed.
The chemical protonation of graphitic carbon nitride (CN) solids with strong oxidizing acids, for example HNO3, is demonstrated as an efficient pathway for the sol processing of a stable CN colloidal ...suspension, which can be translated into thin films by dip/disperse‐coating techniques. The unique features of CN colloids, such as the polymeric matrix and the reversible hydrogen bonding, result in the thin‐film electrodes derived from the sol solution exhibiting a high mechanical stability with improved conductivity for charge transport, and thus show a remarkably enhanced photo‐electrochemical performance. The polymer system can in principle be broadly tuned by hybridization with desired functionalities, thus paving the way for the application of CN for specific tasks, as exemplified here by coupling with carbon nanotubes.
Going strong: Sol engineering of graphitic carbon nitride solids with strong oxidizing acids (e.g. HNO3) generates a stable colloidal suspension, which can be translated into thin films by dip/disperse‐coating techniques. The polymeric matrix and the reversible hydrogen bonding result in the thin‐film electrodes derived from the sol solution having high mechanical stability with improved conductivity for charge transport.
Aerogel structures have attracted increasing research interest in energy storage and conversion owing to their unique structural features, and a variety of materials have been engineered into ...aerogels, including carbon‐based materials, metal oxides, linear polymers and even metal chalcogenides. However, manufacture of aerogels from nitride‐based materials, particularly the emerging light‐weight carbon nitride (CN) semiconductors is rarely reported. Here, we develop a facile method based on self‐assembly to produce self‐supported CN aerogels, without using any cross‐linking agents. The combination of large surface area, incorporated functional groups and three‐dimensional (3D) network structure, endows the resulting freestanding aerogels with high photocatalytic activity for hydrogen evolution and H2O2 production under visible light irradiation. This work presents a simple colloid chemistry strategy to construct 3D CN aerogel networks that shows great potential for solar‐to‐chemical energy conversion by artificial photosynthesis.
Energy storage and conversion: Self‐supported carbon nitride (CN) aerogels synthesized by self‐assembly of low‐dimensional CN nanostructures are capable of catalyzing H2 and H2O2 evolution reactions under visible‐light irradiation. A simple strategy is used to construct 3D CN aerogel networks that show great potential for solar‐to‐chemical energy conversion by artificial photosynthesis.
Natural photosynthesis serves as a model for energy and chemical conversions, and motivates the search of artificial systems that mimic nature′s energy‐ and electron‐transfer chains. However, ...bioinspired systems often suffer from the partial or even large loss of the charge separation state, and show moderate activity owing to the fundamentally different features of the multiple compounds. Herein, a selenium and cyanamide‐functionalized heptazine‐based melon (DA‐HM) is designed as a unique bioinspired donor–acceptor (D‐A) light harvester. The combination of the photosystem and electron shuttle in a single species, with both n‐ and p‐type conductivities, and extended spectral absorption, endows DA‐HM with a high efficiency in the transfer and separation of photoexcited charge carriers, resulting in photochemical activity. This work presents a unique conjugated polymeric system that shows great potential for solar‐to‐chemical conversion by artificial photosynthesis.
Melon motifs: Biomimetic donor–acceptor motifs were introduced in melon‐based carbon nitride semiconductors to promote exciton dissociation and charge separation. This work presents a simple version of a biomimetic polymeric system that shows great potential for solar‐to‐chemical energy conversion through artificial photosynthesis, and it provides the structural basis for designing photochemical conversion systems having bioinspired functions.
Stimuli‐responsive photoluminescent (PL) materials have been widely used as fluorescent ink for data security applications. However, traditional fluorescent inks are limited in maintaining the ...secrecy of information because the inks are usually visible by naked eyes either under ambient light or UV‐light illumination. Here, we introduced metal‐free water‐soluble graphitic carbon nitride quantum dots (g‐CNQDs) as invisible security ink for information coding, encryption, and decryption. The information written by the g‐CNQDs is invisible in ambient light and UV light, but it can be readable by a fluorescence microplate reader. Moreover, the information can be encrypted and decrypted by using oxalic acid and sodium bicarbonate as encryption reagent and decryption reagent, respectively. Our findings provide new opportunities for high‐level information coding and protection by using water‐soluble g‐CNQDs as invisible security ink.
Secret communication: The information written by using carbon nitride dots as security ink is invisible under illumination with both ambient light and UV light. The encoded information is readable by a fluorescence microplate reader, and it can be further encrypted and decrypted by quenching and recovering the fluorescence of the security ink using H2CO4 and NaHCO3, respectively.
The generation of sustainable and stable semiconductors for solar energy conversion by photoredox catalysis, for example, light-induced water splitting and carbon dioxide reduction, is a key ...challenge of modern materials chemistry. Here we present a simple synthesis of a ternary semiconductor, boron carbon nitride, and show that it can catalyse hydrogen or oxygen evolution from water as well as carbon dioxide reduction under visible light illumination. The ternary B-C-N alloy features a delocalized two-dimensional electron system with sp(2) carbon incorporated in the h-BN lattice where the bandgap can be adjusted by the amount of incorporated carbon to produce unique functions. Such sustainable photocatalysts made of lightweight elements facilitate the innovative construction of photoredox cascades to utilize solar energy for chemical conversion.
Abstract
Oxynitride photocatalysts hold promise for renewable solar hydrogen production via water splitting owing to their intense visible light absorption. Cocatalyst loading is essential for ...activation of such oxynitride photocatalysts. However, cocatalyst nanoparticles form aggregates and exhibit weak interaction with photocatalysts, which prevents eliciting their intrinsic photocatalytic performance. Here, we demonstrate efficient utilization of photoexcited electrons in a single-crystalline particulate BaTaO
2
N photocatalyst prepared with the assistance of RbCl flux for H
2
evolution reactions via sequential decoration of Pt cocatalyst by impregnation-reduction followed by site-selective photodeposition. The Pt-loaded BaTaO
2
N photocatalyst evolves H
2
over 100 times more efficiently than before, with an apparent quantum yield of 6.8% at the wavelength of 420 nm, from a methanol aqueous solution, and a solar-to-hydrogen energy conversion efficiency of 0.24% in Z-scheme water splitting. Enabling uniform dispersion and intimate contact of cocatalyst nanoparticles on single-crystalline narrow-bandgap particulate photocatalysts is a key to efficient solar-to-chemical energy conversion.
Solar‐powered one‐step‐excitation overall water splitting (OWS) using semiconducting materials is a simple means of achieving scalable and sustainable hydrogen production. While tantalum oxynitride ...(TaON) is one of the few photocatalysts capable of promoting OWS via single‐step visible‐light excitation, the efficiency of this process remains extremely poor. The present work employed 15 nm amorphous Ta2O5⋅3.3 H2O nanoparticles as a new precursor together with Zr doping and an optimized nitridation duration to synthesize a TaON‐based photocatalyst with reduced particle sizes and low defect densities. Upon loading with Ru/Cr2O3/IrO2 cocatalysts, this material exhibited stoichiometric water splitting into hydrogen and oxygen, with an order of magnitude improvement in efficiency. Our findings demonstrate the importance of inventing/selecting the appropriate synthetic precursor and of defect control for fabricating active OWS photocatalysts.
By the invention of an amorphous Ta2O5⋅3.3 H2O nanopowder precursor together with Zr doping as the main strategies, detrimental TaIII defect species and grain boundaries were eliminated in the resultant TaON particles. These effects have improved the photocatalytic overall water splitting efficiency of TaON by an order of magnitude.
Nontuberculous mycobacteria (NTM) infection is similar to Mycobacterium tuberculosis (MTB) infection. Early clinical identification and differentiation of NTM and MTB infections continues to be a ...major challenge. Nucleic acid amplification tests (NAATs) have the ability to efficiently and rapidly detect pathogens and are widely used in mycobacterial infections. The objective of this study is to estimate the diagnostic accuracy of NAATs for NTM.
We will search candidate studies that assessing the accuracy of NAATs for diagnosis of NTM through PubMed, Embase and the Cochrane Library until May 2021. Studies with full text that meet the inclusion criteria will be included. Following a revised tool for Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2), two researchers will independently evaluate the study quality. The STATA software (version 15.0) will be used to carry out meta-analyses. When heterogeneity is observed, subgroup analyses and meta-regression analyses will be used to explore sources of heterogeneity. Sensitivity analyses will be used to check the robustness of analyses.
We hope that this study will provide meaningful evidence for the early and rapid diagnosis of NAATs for NTM, which will help to guide the treatment of NTM and improve the prognosis of patients.
PDF
