Graphitic Carbon Nitride/Chitosan Composite for Adsorption and Electrochemical Determination of Mercury in Real Samples

Application of gold nanoclusters in fluorescence sensing and biological detection

Gold nanoclusters (Au NCs) exhibit broad fluorescent spectra from visible to near-infrared regions and good enzyme-mimicking catalytic activities. Combined with excellent stability and exceptional biocompatibility, the Au NCs have been widely exploited in biomedicine such as biocatalysis and bioimaging. Especially, the long fluorescence lifetime and large Stokes shift attribute Au NCs to good probes for fluorescence sensing and biological detection. In this review, we systematically summarized the molecular structure and fluorescence properties of Au NCs and highlighted the advances in fluorescence sensing and biological detection. The Au NCs display high sensitivity and specificity in detecting iodine ions, metal ions, and reactive oxygen species, as well as certain diseases based on the fluorescence activities of Au NCs. We also proposed several points to improve the practicability and accelerate the clinical translation of the Au NCs.

Graphitic carbon nitride-based electrochemical sensors: A comprehensive review of their synthesis, characterization, and applications

Graphitic carbon nitride (g-C3N4) has garnered much attention as a promising 2D material in the realm of electrochemical sensors. It contains a polymeric matrix that can serve as an economical and non-toxic electrode material for the detection of a diverse range of analytes. However, its performance is impeded by a relatively limited active surface area and inherent instability. Although electrochemistry involving metal-doped g-C3N4 nanomaterials is rapidly progressing, it remains relatively unexplored. The metal doping of g-C3N4 augments the electrochemically active surface area of the resulting electrode, which has the potential to significantly enhance electrode kinetics and bolster catalytic activity. Consequentially, the main objective of this review is to provide insight into the intricacies of synthesizing and characterizing metal-doped g-C3N4. Furthermore, we comprehensively delve into the fundamental attributes of electrochemical sensors based on metal-doped g-C3N4, with a specific focus on healthcare and environmental applications. These applications encompass a meticulous exploration of detecting biomolecules, drug molecules, and organic pollutants.

An innovative electrochemical sensor for brinzolamide detection in athletes' urine using a mercury-phen complex: a step forward in anti-doping

Brinzolamide (BRZ) is an antiglaucoma drug also used by athletes for doping purposes; therefore, it is prohibited by the World Anti-Doping Agency. Consequently, the presence of BRZ or its metabolites in athletes' urine constitutes a violation of anti-doping rules. The current work presents a novel electrochemical method that assesses the effectiveness of mercury oxide nanoparticles (HgO-NPs) and a mercuric chloride-1,10-phenanthroline complex (HgCl2-Phen complex) as sensors for BRZ analysis. A comparative analysis revealed that the synthesized HgCl2-Phen complex exhibited superior sensitivity and efficiency in determining BRZ levels. The properties of the modifiers were extensively characterized using elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). Furthermore, electrochemical characterization was conducted using square wave voltammetry (SWV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The electrode showed a good response for SWV evaluations of BRZ in a concentration range of 0.1 to 6.0 μmol L-1, with very low limits of detection (0.01 μmol L-1) and quantitation (0.031 μmol L-1). The method's applicability was validated by detecting BRZ in urine samples from healthy human volunteers and in pharmaceutical eye drops. Additionally, the practical effectiveness of the method was assessed using the blue applicability grade index (BAGI). The key advantages of this sensor include its simple manufacturing process, as well as its remarkable sensitivity and selectivity.

A Pd-containing ionic liquid modified magnetic graphene oxide nanocomposite (Fe3O4/GO-IL-Pd) as a powerful catalyst for the reduction of nitrobenzenes

A novel palladium-containing ionic liquid-modified magnetic graphene oxide nanocomposite (Fe3O4/GO-IL-Pd) is synthesized and its catalytic performance is studied in the reduction of nitrobenzenes. The Fe3O4/GO-IL-Pd nanocomposite was characterized by using FT-IR, PXRD, SEM, EDS, VSM, and TG analyses. These analyses showed good magnetic properties and high stability of the designed composite. Different derivatives of nitrobenzenes were applied as substrates, giving corresponding anilines in high to excellent yields (89-96%) at short reaction times (10-15 minutes). Also, the stability, reproducibility, and reusability of the Fe3O4/GO-IL-Pd nanocomposite were investigated under applied conditions. A leaching experiment was also performed to study the nature of the Fe3O4/GO-IL-Pd catalyst under the conditions used.

A review of biocompatible polymer-functionalized two-dimensional materials: Emerging contenders for biosensors and bioelectronics applications

Bioelectronics, a field pivotal in monitoring and stimulating biological processes, demands innovative nanomaterials as detection platforms. Two-dimensional (2D) materials, with their thin structures and exceptional physicochemical properties, have emerged as critical substances in this research. However, these materials face challenges in biomedical applications due to issues related to their biological compatibility, adaptability, functionality, and nano-bio surface characteristics. This review examines surface modifications using covalent and non-covalent-based polymer-functionalization strategies to overcome these limitations by enhancing the biological compatibility, adaptability, and functionality of 2D nanomaterials. These surface modifications aim to create stable and long-lasting therapeutic effects, significantly paving the way for the practical application of polymer-functionalized 2D materials in biosensors and bioelectronics. The review paper critically summarizes the surface functionalization of 2D nanomaterials with biocompatible polymers, including g-C3N4, graphene family, MXene, BP, MOF, and TMDCs, highlighting their current state, physicochemical structures, synthesis methods, material characteristics, and applications in biosensors and bioelectronics. The paper concludes with a discussion of prospects, challenges, and numerous opportunities in the evolving field of bioelectronics.

Two-Dimensional Graphitic Carbon Nitride (g-C3N4) Nanosheets and Their Derivatives for Diagnosis and Detection Applications

The early diagnosis of certain fatal diseases is vital for preventing severe consequences and contributes to a more effective treatment. Despite numerous conventional methods to realize this goal, employing nanobiosensors is a novel approach that provides a fast and precise detection. Recently, nanomaterials have been widely applied as biosensors with distinctive features. Graphite phase carbon nitride (g-C3N4) is a two-dimensional (2D) carbon-based nanostructure that has received attention in biosensing. Biocompatibility, biodegradability, semiconductivity, high photoluminescence yield, low-cost synthesis, easy production process, antimicrobial activity, and high stability are prominent properties that have rendered g-C3N4 a promising candidate to be used in electrochemical, optical, and other kinds of biosensors. This review presents the g-C3N4 unique features, synthesis methods, and g-C3N4-based nanomaterials. In addition, recent relevant studies on using g-C3N4 in biosensors in regard to improving treatment pathways are reviewed.

Smartphone-based photoelectrochemical biosensing system with graphitic carbon nitride/gold nanoparticles modified electrodes for matrix metalloproteinase-2 detection

Photoelectrochemical analysis has been widely used in the field of biosensing due to its high sensitivity and strong anti-interference ability. Herein, a portable and versatile smartphone-based photoelectrochemical biosensing platform was developed for the rapid and on-site biomedical analysis. In the system, light excitation and photocurrent measurements were accomplished by a miniaturized and integrated circuit board. Smartphone with a specifically designed application was utilized to wirelessly control the system via Bluetooth. For photoelectrochemical sensor, graphitic carbon nitride (g-C₃N₄) and gold nanoparticles loaded on indium tin oxide electrodes were utilized as photoactive materials and signal amplification elements, respectively. The gold nanoparticles were also used to immobilized matrix metalloproteinase-2 (MMP-2) specific cleavage peptide that modified with bovine serum albumin (BSA) on the terminal. In the presence of MMP-2, the peptide was specifically hydrolyzed and cleaved. Thus, parts of the peptide chain and BSA were detached from the electrode resulting in the decrease of steric hindrance and the increase of photoelectrochemical currents. The photocurrents changed linearly with the logarithm of MMP-2 concentrations ranging from 1 pg/mL to 100 ng/mL in both buffer and artificial serum with correlation coefficient of 0.9943 and 0.9698. The limit of detections were as low as 0.48 pg/mL in buffer and 0.55 pg/mL in artifical serum. It indicated that the biosensor has good linearity and high sensitivity, which also verified the effectiveness of the portable instrument. This system provides a pioneering solution for the development of miniaturized and portable photoelectrochemical analysis instruments used for the field monitoring of different analytes.

Novel nano-engineered environmental sensor based on polymelamine/graphitic-carbon nitride nanohybrid material for sensitive and simultaneous monitoring of toxic heavy metals

Heavy metal ions (HMIs) pollution is always a serious issue worldwide. Therefore, monitoring HMIs in environmental water is an important and challenging step to ensure environmental health and human safety. In this study, we spotlight an effortless, single-step in-situ electrochemical polymerization deposition technique to fabricate a novel, low-cost, efficient, nano-engineered poly(melamine)/graphitic-carbon nitride nanonetwork (PM/g-C₃N₄) modified screen-printed carbon electrode (SPE) for sensitive, selective, and simultaneous electrochemical monitoring of toxic HMIs in environmental waters. g-C₃N₄ nanomaterial was prepared using melamine as a precursor via pyrolysis technique. As-prepared g-C₃N₄ and melamine monomer were electrochemically in-situ polymerized/deposited over pre-anodized SPE (ASPE) using cyclic voltammetry technique. XRD, XPS, and SEM were engaged to characterize the developed electrode. The fabricated PM/g-C₃N₄/ASPE was applied as an environmental sensor to selective and simultaneous electrochemical detection of Pb²⁺ and Cd²⁺ ions using differential pulse voltammetry technique. The developed sensor displayed excellent selectivity and sensitivity towards Pb²⁺ and Cd²⁺ with limit of detections of 0.008 µM and 0.02 µM, respectively. The fabricated PM/g-C₃N₄/ASPE sensor exhibits superior stability, repeatability, good anti-interference, and applicability for recognition of Pb²⁺ and Cd²⁺ ions in real water samples. These results proved that developed environmental sensor is low-cost, efficient, practical platform for rapid, selective, simultaneous monitoring of HMIs in the environment.

Application of Nanotechnology in Analysis and Removal of Heavy Metals in Food and Water Resources

Toxic heavy metal contamination in food and water from environmental pollution is a significant public health issue. Heavy metals do not biodegrade easily yet can be enriched hundreds of times by biological magnification, where toxic substances move up the food chain and eventually enter the human body. Nanotechnology as an emerging field has provided significant improvement in heavy metal analysis and removal from complex matrices. Various techniques have been adapted based on nanomaterials for heavy metal analysis, such as electrochemical, colorimetric, fluorescent, and biosensing technology. Multiple categories of nanomaterials have been utilized for heavy metal removal, such as metal oxide nanoparticles, magnetic nanoparticles, graphene and derivatives, and carbon nanotubes. Nanotechnology-based heavy metal analysis and removal from food and water resources has the advantages of wide linear range, low detection and quantification limits, high sensitivity, and good selectivity. There is a need for easy and safe field application of nanomaterial-based approaches.

Deep eutectic solvent-based manganese molybdate nanosheets for sensitive and simultaneous detection of human lethal compounds: comparing the electrochemical performances of M-molybdate (M = Mg, Fe, and Mn) electrocatalysts

Potentially hazardous chemical contaminants endanger the environment and human well-being, challenging scientists and policy makers to develop holistic alternative approaches for remediation. The addition or accumulation of these chemicals can have a series of far-reaching consequences and have direct and indirect effects at multiple levels of ecological organization. Therefore, the development of a sensitive tool for the comprehensive evaluation of chemical concentrations is highly relevant. Herein, we thus report the simultaneous electrochemical detection of highly toxic hydroquinone (HQ), Hg²⁺, and nitrite (NO₂^-) compounds using nanostructured metal molybdate (M = Mg, Fe and Mn) catalysts. These functional nanomaterials are synthesized using a deep eutectic solvent (DES) modified hydrothermal method that provides sustainable aspects and energy efficient synthesis strategies. Choline chloride (ChCl)-urea DES used in this study exhibits an all-in-one behaviour by simultaneously acting as a template, reducing agent, and homogeneous means for stabilizing metal ions. This stimulates the fabrication of hierarchical structures of metal molybdates with high surface activities that cause their remarkable properties with minimal waste generation. The structural, morphological, catalytic, and electrochemical capacities of the as-synthesized MgMoO₄, Fe₂(MoO₄)₃, and MnMoO₄ materials are explored through various techniques and comparatively, MnMoO₄ presents superior characterization features such as a reduced particle size, increased surface area and hierarchical architectures. Owing to the exceptional physicochemical attributes, the MnMoO₄ modified glassy carbon electrode (GCE) demonstrates superior electrochemical activities towards the individual and simultaneous detection of HQ, Hg²⁺, and NO₂^-. Well-defined and separate peaks are observed for the simultaneous detection of HQ, Hg²⁺, and NO₂^- which is influenced by the binding energies of these pollutants. Furthermore, the modified electrode exhibits a high sensitivity of 23.8, 17.7 and 10.2 μA μM^-1 cm^-2 with a limit of detection (LOD) of 0.026, 0.05, and 0.01 μM for HQ, Hg²⁺, and NO₂^- respectively under ideal conditions. Also, the reproducibility and anti-interference ability reinforce the application potential of the MnMoO₄ modified electrode for the simultaneous electrochemical detection of HQ, Hg²⁺, and NO₂^- in real samples with better recoveries, thus assessing the effect of these hazardous chemicals on humanity.

Ultrasonically assisted synthesis of barium stannate incorporated graphitic carbon nitride nanocomposite and its analytical performance in electrochemical sensing of 4-nitrophenol

We describe the ultrasonic assisted preparation of barium stannate-graphitic carbon nitride nanocomposite (BSO-gCN) by a simple method and its application in electrochemical detection of 4-nitrophenol via electro-oxidation. A bath type ultrasonic cleaner with ultrasonic power and ultrasonic frequency of 100 W and 50 Hz, respectively, was used for the synthesis of BSO-gCN nanocomposite material. The prepared BSO-gCN nanocomposite was characterized by employing several spectroscopic and microscopic techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infra-red, field emission scanning electron microscopy, and high resolution transmission electron microscopy, to unravel the structural and electronic features of the prepared nanocomposite. The BSO-gCN was drop-casted on a pre-treated glassy carbon electrode (GCE), and their sensor electrode was utilized for electrochemical sensing of 4-nitrophenol (4-NP). The BSO-gCN modified GCE exhibited better electrochemical sensing behavior than the bare GCE and other investigated electrodes. The electroanalytical parameters such as charge transfer coefficient (α = 0.5), the rate constant for electron transfer (k_s = 1.16 s^-1) and number of electron transferred were calculated. Linear sweep voltammetry (LSV) exhibited increase in peak current linearly with 4-NP concentration in the range between 1.6 and 50 μM. The lowest detection limit (LoD) was calculated to be 1 μM and sensitivity of 0.81 μA μM^-1 cm^-2_. A 100-fold excess of various ions, such as Ca²⁺, Na⁺, K⁺, Cl^-, I^-, CO₃^2-, NO₃, NH₄⁺ and SO₄^2- did not able to interfere with the determination of 4-NP and high sensitivity for detecting 4-NP in real samples was achieved. This newly developed BSO-gCN could be a potential candidate for electrochemical sensor applications.

Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency

Cr(VI) contamination has posed great threat to both the ecosystem and human health for its carcinogenic and mutagenic nature. A highly effective adsorbent for the removal of Cr(VI) was prepared and its adsorption mechanism was thoroughly discussed in this study. In detail, magnetic BiFeO₃ and kenaf biochar were loaded on cross-linked chitosan to obtain chitosan-kenaf biochar@BiFeO₃ (CKB) for improving adsorption capacity towards Cr(VI). The adsorption process of Cr(VI) onto CKB was evaluated as a function of the pH, the existence of competing ions, the initial concentration of Cr(VI) and contact time. The results show that CKB exhibits the highest adsorption capacity under the optimal pH 2.0. The presence of competing ions such as Ca²⁺, NO₃⁻, SO₄²⁻, and Cl⁻ decreases the adsorption capacity; among them, Ca²⁺ and NO₃⁻ show the greatest hindrance. By studying the effect of initial Cr(VI) concentration on the adsorption capacity, it was found that CKB in the solution was enough to remove Cr(VI) for all treatments (10–200 mg/L). The adsorption experimental data were well fitted with pseudo-first-order model, suggesting that chemisorption is not the dominant rate-limiting step. Freundlich isotherm model can better explain the adsorption process, indicating a non-ideal adsorption towards Cr(VI) on a heterogeneous surface of CKB. A 2^5-1 Fractional Factorial Design (FFD) showed that pH and initial concentration of Cr(VI) have significant influence on Cr(VI) adsorption in our reaction system. In general, excellent adsorption efficiency of CKB indicates that it may be a good candidate for the remediation of Cr(VI)-contaminating wastewater.

Chitosan-induced enhanced expression and activation of alternative oxidase confer tolerance to salt stress in maize seedlings

This study aimed to investigate the possible alleviating effect of chitosan on salt-induced growth retardation and oxidative stress and to elucidate whether this effect is linked to activation of mitochondrial respiration on the basis of alternative respiration in maize seedlings. Salt stress significantly reduced root length and plant height in comparison to the control, whereas foliar application of chitosan ameliorated the adverse effect of salinity to a certain degree. Moreover, chitosan resulted in plant growth promotion as compared to unstressed seedlings. The separate applications of chitosan and salt had a stimulatory effect on the activities of antioxidant enzymes; however, combined application of chitosan and salt were more effective than that of chitosan or salt alone. Similarly, mitochondrial total respiration rate (V_t) and alternative respiration capacity (V_alt) were increased by separate applications of chitosan and salt; however, the combination of chitosan and salt gave the highest values for these parameters. The highest values of V_alt/V_t was recorded at seedlings treated with salt plus chitosan. Similarly, cytochrome respiration capacity was also increased by chitosan in both stress-free and stressed conditions. In addition, AOX1, encoding alternative oxidase, was significantly upregulated by chitosan and/or salt. The maximum transcript level was recorded at seedlings treated with salt plus chitosan. Chitosan also significantly decreased superoxide anion and hydrogen peroxide contents and lipid peroxidation level under normal and the stressed conditions. These results suggest that the mitigating effect of chitosan on salt stress is linked to activation of alternative respiration at biochemical and molecular level.

Voltammetric determination of adefovir dipivoxil by using a nanocomposite prepared from molecularly imprinted poly(o-phenylenediamine), multi-walled carbon nanotubes and carbon nitride

An electrochemical sensor for adefovir dipivoxil (ADV) detection was prepared by electropolymerization of o-phenylenediamine in the presence of ADV on a glassy carbon electrode modified with multi-walled carbon nanotubes and carbon nitride. The electrode was characterized by field emission scanning electron microscopy and differential pulse voltammetry. The performance was optimized by response surface methodology. The changes in differential pulse voltammetric peak currents of the redox probe, ferricyanide, were linear to ADV concentrations in the range from 0.1 to 9.9 μmol L^-1, with the detection limit of 0.05 μmol L^-1 (S/N = 3). The sensor was applied to the determination of ADV in drug formulations, human serum and urine samples. It is selective due to the use of an imprinted material, well reproducible, long-term stable, and regenerable. Graphical abstract By merging the unique properties of carbon nitride with intrinsic properties of MWCNTs, and molecularly imprinted polymers, a novel electrochemical sensor with selective binding sites was prepared for determination of adefovir dipivoxil in pharmaceutical and biological samples.

A sensitive Potentiometric resolved ratiometric Photoelectrochemical aptasensor for Escherichia coli detection fabricated with non-metallic nanomaterials

In this work, a sensitive potentiometric resolved ratiometric photoelectrochemical aptasensor for Escherichia coli (E. coli) detection was successfully fabricated with non-metallic nanomaterials. To avoid the use of precious metals or heavy metals, three-dimensional graphene hydrogel-loaded carbon quantum dots (C-dots/3DGH) and graphene-like carbon nitride (g-C₃N₄) with excellent PEC activity and matched potential were prepared. These two materials were modified onto two adjacent areas on the ITO electrode. By applying different bias voltage, the cathodic current generated by C-dots/3DGH and the anodic current generated by g-C₃N₄ can be clearly distinguished and would not interfere with one another. Then E. coli aptamer was modified onto the surface of C-dots/3DGH. In the presence of targets, the binding of E. coli with aptamer lead to the steric hindrance greatly increased and the cathodic current decreased significantly. Meanwhile, the anodic current generated by g-C₃N₄ was not influenced and it can serve as a stable reference to evaluate the environmental factors. Therefore, the concentration of E. coli can be quantified by the ratio of cathodic current to anodic current, which can effectively eliminate these analyte-independent factors and provide a more precise analysis. In addition, this ratiometric PEC biosensor also showed a good sensitivity and a wide linear range (2.9 cfu/mL to 2.9 × 10⁶ cfu/mL).

Construction of Chitosan-Zn-Based Electrochemical Biosensing Platform for Rapid and Accurate Assay of Actin

This work reports a study on the development of a sensitive immunosensor for the assay of actin, which is fabricated using sensing material chitosan-Zn nanoparticles (NPs) and anti-actin modified on glassy carbon electrode respectively. The prepared materials were characterized using transmission electron microscope (TEM), fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) spectra, and circular dichroism (CD) techniques. Meanwhile, the electrochemical properties were studied by linear sweep voltammetric (LSV), electrochemical impedance spectra (EIS), and differential pulse voltammetry (DPV). According to the experiments, under the optimum conditions, the linear fitting equation was I (μA) = −17.31 + 78.97c (R² = 0.9948). The linear range was from 0.0001 to 0.1 mg/mL and the detection limit (LOD, S/N = 3) was 21.52 ng/mL. The interference studies were also performed for checking the sensors’ selectivity to actin. With better properties of the chitosan-Zn NPs, the modified electrode is considered as a better candidate than Western blot or immunohistochemical method for real-time usability. The detection limit reported is the lowest till date and this method provides a new approach for quality evaluation.

An Electrochemical Sensor of Poly(EDOT-pyridine-EDOT)/Graphitic Carbon Nitride Composite for Simultaneous Detection of Cd2+ and Pb2

In this study, poly(2,5-bis(3,4-ethylenedioxythienyl)pyridine)/graphitic carbon nitride composites (poly(BPE)/g-C₃N₄) were prepared by an in situ chemical polymerization method. Composites were characterized by using Fourier transform infrared spectroscopy (FT-IR), ultraviolet⁻visible absorption spectra (UV⁻vis), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, electrochemical sensors were applied for the electrochemical determination of Cd²⁺ and Pb²⁺ using the differential pulse voltammetry (DPV) method. The results indicated that 10 wt % poly(BPE)/g-C₃N₄ composite-modified electrode exhibited linear detection ranging from 0.12 to 7.2 μM and 0.08 to 7.2 μM for Cd²⁺ and Pb²⁺, with detection limits (S/N = 3) of 0.018 μM and 0.00324 μM. Interference analysis suggested that the 10 wt % poly(BPE)/g-C₃N₄-modified electrode can be applied for the detection of the Cd²⁺ and Pb²⁺ in real samples.

Fabrication of g-C3N4/NiO heterostructured nanocomposite modified glassy carbon electrode for quercetin biosensor

Herein, we report a one-pot synthesis of structurally uniform and electrochemically active graphitic carbon nitride/nickel oxide (g-C₃N₄/NiO) nanocomposite and an investigation on the electrocatalytic oxidation of quercetin (QR). The synthesized g-C₃N₄/NiO nanocomposite has uniform surface distribution, which was characterized with scanning electron microscopy (SEM). Moreover, the composition of synthesized g-C₃N₄/NiO nanocomposite was characterized by UV-vis-spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR spectra), BET, SEM and HRTEM. The g-C₃N₄/NiO was electrochemically treated in 0.1 MPBS solution through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The peak current response increases linearly with QR concentration from 0.010 μM to 250 µM with a fast response time of less than 2 s and a detection limit of 0.002 μM. To further evaluate the feasibility of using this sensor for real sample analysis, QR content in various real samples including green tea, green apple, honey suckle were determined and satisfactory results were achieved.

Sugarcane juice derived carbon dot-graphitic carbon nitride composites for bisphenol A degradation under sunlight irradiation

Carbon dots (CDs) and graphitic carbon nitride (g-C3N4) composites (CD/g-C3N4) were successfully synthesized by a hydrothermal method using urea and sugarcane juice as starting materials. The chemical composition, morphological structure and optical properties of the composites and CDs were characterized using various spectroscopic techniques as well as transmission electron microscopy. X-ray photoelectron spectroscopy (XPS) results revealed new signals for carbonyl and carboxyl groups originating from the CDs in CD/g-C3N4 composites while X-ray diffraction (XRD) results showed distortion of the host matrix after incorporating CDs into g-C3N4. Both analyses signified the interaction between g-C3N4 and CDs. The photoluminescence (PL) analysis indicated that the presence of too many CDs will create trap states at the CD/g-C3N4 interface, decelerating the electron (e-) transport. However, the CD/g-C3N4(0.5) composite with the highest coverage of CDs still achieved the best bisphenol A (BPA) degradation rate at 3.87 times higher than that of g-C3N4. Hence, the charge separation efficiency should not be one of the main factors responsible for the enhancement of the photocatalytic activity of CD/g-C3N4. Instead, the light absorption capability was the dominant factor since the photoreactivity correlated well with the ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) results. Although the CDs did not display upconversion photoluminescence (UCPL) properties, the π-conjugated CDs served as a photosensitizer (like organic dyes) to sensitize g-C3N4 and injected electrons to the conduction band (CB) of g-C3N4, resulting in the extended absorption spectrum from the visible to the near-infrared (NIR) region. This extended spectral absorption allows for the generation of more electrons for the enhancement of BPA degradation. It was determined that the reactive radical species responsible for the photocatalytic activity were the superoxide anion radical (O2•-) and holes (h+) after performing multiple scavenging tests.

A high sensitive visible light-driven photoelectrochemical aptasensor for shrimp allergen tropomyosin detection using graphitic carbon nitride-TiO2 nanocomposite

Herein, for the first time a visible-light-driven photoelectrochemical (PEC) aptasensor for shrimp tropomyosin determination was fabricated by using graphitic carbon nitride (g-C₃N₄) and titanium dioxide (TiO₂) as photoactive nanomaterials, ascorbic acid (AA) as electron donor and ruthenium (III) hexaammine (Ru(NH₃)₆³⁺) as signal enhancer. The surface of an ITO electrode was first modified with g-C₃N₄, TiO₂, and polyethyleneimine (PEI) and then the amine terminal aptamer_TROP probe was attached to PEI by the use of glutaraldehyde (GA) as cross-linker. After that, Ru(NH₃)₆³⁺ was adsorbed on aptamer to enhance the photocurrent signal. The principle of proposed PEC aptasensor is based on the formation of a selective complex between tropomyosin and immobilized aptamer_TROP probe on the surface of ITO/g-C₃N₄-TiO₂/PEI/aptamer_TROP-Ru(NH3)₆⁺³. After the incubation of tropomyosin with TROP aptamer probe, the photocurrent signal decreased due to releasing adsorbed Ru(NH₃)₆³⁺ on aptamer and preventing AA from scavenging photogenerated holes to the photoactive modified electrode. Under the optimized conditions, the fabricated PEC aptasensor was used for the determination of shrimp tropomyosin in the concentration range of 1-400ngmL^-1 with a limit of detection of 0.23ngmL^-1. The proposed PEC aptasensor exhibited high selectivity, sensitivity, and good stability.

Two isomeric solid carbon nitrides with 1 : 1 stoichiometry which exhibit strong mechanical anisotropy

Two isomeric layered carbon nitride polymorphs are characterized using reliable theoretical methods. The NCNC phase, which is predicted for the first time, has a number of differences with the isomeric NCCN polymorph in its electronic, spectral and mechanical properties.