Highly fluorescent g-C3N4 nanobelts derived from bulk g-C3N4 for NO2 gas sensing

Using highly water-stable wool keratin/CsPbBr3 nanocrystals as a portable amine-responsive fluorescent test strip for onsite visual detection of food freshness

Perovskite nanocrystals (PNCs) have emerged as promising candidates for fluorescent probes owing to their outstanding photoelectric properties. However, the conventional CsPbBr3 (CPB) NCs are extremely unstable in water, which has seriously limited their sensing applications in water environment. Herein, we present a powerful ligand engineering strategy for fabricating highly water-stable CPB NCs by using a biopolymer of wool keratin (WK) as the passivator and the polyaryl polymethylene isocyanate (PAPI) as the cross-linking agent. In particular, WK with multi-functional groups can serve as a polydentate ligand to firmly passivate CPB NCs by the ligand exchange process in hot toluene; and then the addition of PAPI can further encapsulate CPB NCs by the crosslinking reaction between PAPI and WK. Consequently, the as-prepared CPB/WK-PAPI NCs can maintain ∼ 80 % of their relative photoluminescence (PL) intensity after 60 days in water, and they still maintain ∼ 40 % of their relative PL intensity even after 512 days in the same environment, which is one of the best water stabilities compared previously reported polymer passivation methods. As a proof-of their application, the portable CPB/WK-PAPI NCs-based test strips are further developed as a fluorescent nanoprobe for real-time and visual monitoring amines and food freshness. Among various amine analytes, the as-prepared test strips exhibit higher sensitivity towards conjugated amines, achieving a remarkable detection limit of 18.3 nM for pyrrole. Our research not only introduces an innovative strategy involving natural biopolymers to enhance the water stability of PNCs, but also highlights the promising potential of PNCs for visually and portably detecting amines and assessing food freshness.

Enhancing visible light photocatalytic activity of holmium doped g-C3N4 and DFT theoretical insights

In the search of novel photocatalysts to increase the effect of visible light in photocatalysis, g-C3N4 (CN) has become a shining star. Rare earth metals have been used as dopant material to reinforce the photocatalytic activity of CN due to their unique electron configuration recently. In this present study, the pure and different amounts of Ho-doped g-C3N4 (HoCN) photocatalysts were successfully synthesized using urea as a precursor by the one-pot method. Morphological, structural, optical, and vibrational properties of the synthesized photocatalysts were characterized by SEM, EDX, XRD, TGA, XPS, FTIR, PL, TRPL, Raman, DRS, and BET analyses. In addition, theoretical calculations using density functional theory (DFT) were meticulously carried out to delve the changes in the structural and electronic structure of CN with holmium doping. According to calculations, the chemical potential, electrophilicity, and chemical softness are higher for HoCN, while HOMO-LUMO gap, dipole moment, and the chemical hardness are lower for the pure one. Thus, holmium doping becomes desirable with low chemical hardness which indicates more effectivity and smaller HOMO-LUMO gap designate high chemical reactivity. To determine the photocatalytic efficiency of the pure and doped CN photocatalysts, the degradation of methylene blue (MB) was monitored under visible light. The results indicate that holmium doping has improved the photocatalytic activities of CN samples. Most strikingly, this improvement is noticeable for the 0.2 mmol doped CN sample that showed two times better photocatalytic activity than the pure one.

Cyano-Rich g-C3 N4 in Photochemistry: Design, Applications, and Prospects

Cyano-rich g-C3 N4 materials are widely used in various fields of photochemistry due to the very powerful electron-absorbing ability and electron storage function of cyano, as well as its advantages in improving light absorption, adjusting the energy band structure, increasing the polarization rate and electron density in the structure, active site concentration, and promoting oxygen activation ability. Notwithstanding, there is yet a huge knowledge break in the design, preparation, detection, application, and prospect of cyano-rich g-C3 N4 . Accordingly, an overall review is arranged to substantially comprehend the research progress and position of cyano-rich g-C3 N4 materials. An overall overview of the current research position in the synthesis, characterization (determination of their location and quantity), application, and reaction mechanism analysis of cyano-rich g-C3 N4 materials to provide a quantity of novel suggestions for cyano-modified carbon nitride materials' construction is provided. In view of the prevailing challenges and outlooks of cyano-rich g-C3 N4 materials, this paper will purify the growth direction of cyano-rich g-C3 N4 , to achieve a more in-depth exploration and broaden the applications of cyano-rich g-C3 N4 .

Hydrogen Evolution Activity of Nitrogen-Rich g-C3-xN4+x Synthesized by Solid-Gas Interface Method

Synthesis of a metal-free carbon nitride (g-C3N4) photocatalyst in the form of nitrogen-rich g-C3-xN4+x derivatives is desirable for efficient solar to hydrogen conversion and remains a challenging task to achieve. Herein we report the development of homogeneous sheets of nitrogen-rich graphitic carbon nitride samples from melamine by a solid-gas interface approach. Using this method, pure g-C3N4 (CN), g-C3-xN4+x under ammonia flow (CN-NH3) and g-C3-xN4+x under nitrogen flow (CN-N2) are prepared. The g-C3-xN4+x (CN-NH3) sample shows better surface conductivity, wide optical absorbance in the visible region, reduced recombination and high electron donor density, and higher performance toward photoelectrochemical hydrogen evolution (HER). The g-C3-xN4+x (CN-NH3) generates a photocurrent of 2.06 μA cm-2, which is 2.5 times higher than that of the pure g-C3N4 (CN) sample (0.85 μA cm-2). It also shows higher photocatalytic water splitting ability compared to the CN and CN-N2 samples, generating 634 μmol g-1 hydrogen without cocatalyst and 1163 μmol g-1 of hydrogen with Pt cocatalyst. Density functional calculations suggest that the progressive band gap reduction with the increase in the N-dopant percentage can be attributed to the gradual increase in the partial π-occupations, which can lead to a significant stabilization of the conduction band minima. The theoretical modeling, however, indicates a saturation in the band gap effect after 75% of N-dopant. The onset potential of g-C3-xN4+x for HER appears at η = 0.43 V in dark and η = 0.34 V vs Ag/AgCl under solar light illumination of 1 sun.

Graphitic carbon nitride (g-C3N4)-assisted materials for the detection and remediation of hazardous gases and VOCs

Graphitic carbon nitride (g-C3N4)-based materials are attracting attention for their unique properties, such as low-cost, chemical stability, facile synthesis, adjustable electronic structure, and optical properties. These facilitate the use of g-C3N4 to design better photocatalytic and sensing materials. Environmental pollution by hazardous gases and volatile organic compounds (VOCs) can be monitored and controlled using eco-friendly g-C3N4- photocatalysts. Firstly, this review introduces the structure, optical and electronic properties of C3N4 and C3N4 assisted materials, followed by various synthesis strategies. In continuation, binary and ternary nanocomposites of C3N4 with metal oxides, sulfides, noble metals, and graphene are elaborated. g-C3N4/metal oxide composites exhibited better charge separation that leads to enhancement in photocatalytic properties. g-C3N4/noble metal composites possess higher photocatalytic activities due to the surface plasmon effects of metals. Ternary composites by the presence of dual heterojunctions improve properties of g-C3N4 for enhanced photocatalytic application. In the later part, we have summarised the application of g-C3N4 and its assisted materials for sensing toxic gases and VOCs and decontaminating NOx and VOCs by photocatalysis. Composites of g-C3N4 with metal and metal oxide give comparatively better results. This review is expected to bring a new sketch for developing g-C3N4-based photocatalysts and sensors with practical applications.

Room-Temperature Optoelectronic Gas Sensor Based on Core-Shell g-C3N4@WO3 Heterocomposites for Efficient Ammonia Detection

The ever-growing modern industry promotes the evolution of gas sensors for environmental monitoring and safety inspection. However, traditional chemiresistive gas sensors still suffer from drawbacks of high power consumption and detection limit, mainly due to the insufficient charge-transfer ability of gas-sensing materials. Here, an optoelectronic gas sensor that can detect ppb-level ammonia at room temperature is constructed based on core-shell g-C3N4@WO3 heterocomposites. The growth of WO3 nanosheets on graphitic g-C3N4 nanosheets was precisely controlled, achieving well-defined g-C3N4@WO3 core-shell architectures. Based on the synergism between light activation and the amplification effect of in situ-formed heterojunctions, the g-C3N4@WO3 sensor exhibits improved sensing characteristics for reliable ammonia detection. As compared with the pristine g-C3N4 sensor, the sensor response toward ammonia is enhanced 21 times and the detection limit is reduced from 308 to 108 ppb. This work provides a successful approach for the in situ formation of core-shell g-C3N4@WO3 interfacial composites and offers an easy solution for the rational design of advanced optoelectronic gas sensors.

Multi-layered g-C3N4 as a Fluorescent Probe for Hg2+ Detection

Hg²⁺ is one of the most toxic heavy metal ions that exist in the environment and it forms large numbers of toxic binary compounds. Accurate and rapid detection of the concentration of heavy metal ions is a prerequisite technology to achieve pollution control and prevention. Fluorescent probes have attracted extensive attention because of their high sensitivity, prominent precision, convenient and fast visualization of heavy metals. Herein, we report multi-layered graphitic carbon nitride via a simple thermopolymerization treatment as a very effectual fluorescent probe for sensitive and selective detection of Hg²⁺ with a limit of detection as low as 1.14 nM.

Boosting the Quantum Yield of Oxygen-Doped g-C3N4 via a Metal-Azolate Framework-Enhanced Electron-Donating Strategy for Highly Sensitive Sulfadimethoxine Tracing

Two of the most persistent challenges for the sensing applications of luminescent carbon nitride-based materials are poor quantum yields and aggregation-induced luminescence quenching in aqueous environments. Herein, a highly emissive oxygen-doped carbon nitride composite (OCNP@M7) was synthesized, with a metal-azolate framework (MAF-7) serving as a luminous booster. Both experimental studies and theoretical calculations suggest that the MAF-enhanced electron-donating effect dramatically promoted the electron density on the π-structure of oxygen-doped carbon nitride. In addition, the structural rigidity of MAF-7 effectively inhibits both aggregation and nonradiative energy dissipation. Consequently, OCNP@M7 exhibits strong and stable blue emission under UV light irradiation and an absolute quantum yield up to 95.2%, which is, as far as we know, the highest value among fluorescent carbon nitride materials in solution ever reported. OCNP@M7 could further function as a high-efficiency fluorescent probe for the sensitive detection of sulfadimethoxine residues in complex environments. It is anticipated that this strategy can be extended to fabricate various carbon nitride-based antibiotic monitoring systems with tailor-made functions.

Current advances on g-C3N4-based fluorescence detection for environmental contaminants

The development of highly-sensitive fluorescence detection systems for environmental contaminants has become high priority research in the past years. Special attention has been paid to graphitic carbon nitride (g-C₃N₄)-based nanomaterials, whose unique and superior optical property makes them promising and attractive candidates for this purpose. It is necessary to enhance the current understanding of the various classes of g-C₃N₄-based fluorescence detection systems and their mechanisms, as well as find suitable approaches to improve detection performance for environmental monitoring, protection, and management. In this review, the recent progresses on g-C₃N₄-based fluorescence detections for environmental contaminants, mainly including their basic principles, mechanisms, applications, modification strategies, and conclusions, are summarized. A particular emphasis is placed on the design and development of modification strategies for g-C₃N₄ with the objective of improving detection performance. High photoluminescence quantum yield, tunable fluorescence emission characteristics, and strong adsorption capacity of g-C₃N₄ could ensure the ultrasensitivity and selectivity of fluorescence detection of environmental contaminants. Concluding perspectives on the challenges and opportunities to design highly efficient g-C₃N₄-based fluorescence detection system are intensively put forward as well.