Graphitic Carbon Nitride Doped with the s-Block Metals: Adsorbent for the Removal of Methyl Blue and Copper(II) Ions

All-in-One Zinc-Doped Prussian Blue Nanozyme for Efficient Capture, Separation, and Detection of Copper Ion (Cu2+ ) in Complicated Matrixes

Copper is a vital micronutrient for lives and an important ingredient for bactericides and fungicides. Given its indispensable biological and agricultural roles, there is an urgent need to develop simple, affordable, and reliable methods for detecting copper in complicated matrixes, particularly in underdeveloped regions where costly standardized instruments and sample dilution procedures hinder progress. The findings that zinc-doped Prussian blue nanoparticle (ZnPB NP) exhibits exceptional efficiency in capturing and isolating copper ions, and accelerates the generation of dissolved oxygen in a solution of H2 O2 with remarkable sensitivity and selectivity, the signal of which displays a positive correlation with the copper level due to the copper-enhanced catalase-like activity of ZnPB NP, are presented. Consequently, the ZnPB NP serves as an all-in-one sensor for copper ion. The credibility of the method for copper assays in human urine and farmland soil is shown by comparing it to the standard instrumentation, yielding a coefficient of correlation (R2 = 0.9890), but the cost is dramatically reduced. This ZnPB nanozyme represents a first-generation probe for copper ion in complicated matrixes, laying the groundwork for the future development of a practical copper sensor that can be applied in resource-constrained environments.

Exploring the Sensing Potential of g-C3N4 versus Li/g-C3N4 Nanoflakes toward Hazardous Organic Volatiles: A DFT Simulation Study

Ab initio calculations were performed to determine the sensing behavior of g-C3N4 and Li metal-doped g-C3N4 (Li/g-C3N4) quantum dots toward toxic compounds acetamide (AA), benzamide (BA), and their thio-analogues, namely, thioacetamide (TAA) and thiobenzamide (TAA). For optimization and interaction energies, the ωB97XD/6-31G(d,p) level of theory was used. Interaction energies (Eint) illustrate the high thermodynamic stabilities of the designed complexes due to the presence of the noncovalent interactions. The presence of electrostatic forces in some complexes is also observed. The observed trend of Eint in g-C3N4 complexes was BA > TAA > AA > TBA, while in Li/g-C3N4, the trend was BA > AA > TBA > TAA. The electronic properties were studied by frontier molecular orbital (FMO) and natural bond orbital analyses. According to FMO, lithium metal doping greatly enhanced the conductivity of the complexes by generating new HOMOs near the Fermi level. A significant amount of charge transfer was also observed in complexes, reflecting the increase in charge conductivity. NCI and QTAIM analyses evidenced the presence of significant noncovalent dispersion and electrostatic forces in Li/g-C3N4 and respective complexes. Charge decomposition analysis gave an idea of the transfer of charge density between quantum dots and analytes. Finally, TD-DFT explained the optical behavior of the reported complexes. The findings of this study suggested that both bare g-C3N4 and Li/g-C3N4 can effectively be used as atmospheric sensors having excellent adsorbing properties toward toxic analytes.

Photocatalytic degradation of organic pollutants by carbon quantum dots functionalized g-C3N4: A review

Graphitic carbon nitride (g-C₃N₄) has received much attention due to its unique characteristics of stable physicochemical features, facile preparation, and inexpensive cost. However, the bulk g-C₃N₄ has a weak capacity for pollutant degradation and needs to be modified for real application. Therefore, extensive research has been done on g-C₃N₄, and the discovery of the novel zero-dimensional nanomaterials known as carbon quantum dots (CQDs) provided it with a unique modification option. In this review, the development for the removal of organic pollutants by g-C₃N₄/CQDs was discussed. Firstly, the preparation of g-C₃N₄/CQDs were introduced. Then, the application and the degradation mechanism of g-C₃N₄/CQDs were briefly described. And the discussion of the influencing factors on g-C₃N₄/CQDs' ability to degrade organic pollutants came in third. Finally, the conclusions of photocatalytic degradation of organic pollutants by g-C₃N₄/CQDs and future perspectives followed. This review will strengthen the understanding of the photocatalytic degradation of real organic wastewater by g-C₃N₄/CQDs, including their preparation, application, mechanism, and influencing factors.

Multilayer Graphene Oxide Supported ZIF-8 for Efficient Removal of Copper Ions

To address the performance deterioration of ZIF-8 for the adsorption of copper ions caused by powder volume pressure and particle aggregation, we employed multilayer graphene oxide (MGO) as a support to prepare composite adsorbents (MGO@ZIF-8) by using the in situ growth of ZIF-8 on MGO. Due to a good interfacial compatibility and affinity between ZIF-8 and graphene nanosheets, the MGO@ZIF-8 was successfully prepared. The optimal Cu²⁺ adsorption conditions of MGO@ZIF-8 were obtained through single factor experiments and orthogonal experiments. Surprisingly, the Cu²⁺ adsorption capacity was significantly improved by the integration of MGO and ZIF-8, and the maximum Cu²⁺ adsorption capacity of MGO@ZIF-8 reached 431.63 mg/g under the optimal adsorption conditions. Furthermore, the kinetic fitting and isotherm curve fitting confirmed that the adsorption law of Cu²⁺ by MGO@ZIF-8 was the pseudo-second-order kinetic model and the Langmuir isotherm model, which indicated that the process of Cu²⁺ adsorption was monolayer chemisorption. This work provides a new approach for designing and constructing ZIF-8 composites, and also offers an efficient means for the removal of heavy metals.

Gram-Scale Synthesis of Graphitic Carbon Nitride Quantum Dots with Ultraviolet Photoluminescence for Fe3+ Ion Detection

A method for gram-scale synthesis of graphitic carbon nitride quantum dots (g-C₃N₄QDs) was developed. The weight of the g-C₃N₄QDs was up to 1.32 g in each run with a yield of 66 wt%, and the purity was 99.96 wt%. The results showed that g-C₃N₄QDs exhibit a stable and strong ultraviolet photoluminescence at a wavelength of 365 nm. More interestingly, the g-C₃N₄QDs can be used as a high-efficiency, sensitive, and selective fluorescent probe to detect Fe³⁺ with a detection limit of 0.259 μM.

Synergistic effects of the hybridization between boron-doped carbon quantum dots and n/n-type g-C3N4 homojunction for boosted visible-light photocatalytic activity

Dye wastewater has raised a prevalent environmental concern due to its ability to prevent the penetration of sunlight through water, thereby causing a disruption to the aquatic ecosystem. Carbon quantum dots (CQDs) are particularly sought after for their highly tailorable photoelectrochemical and optical properties. Simultaneously, graphitic carbon nitride (g-C₃N₄) has gained widespread attention due to its suitable band gap energy as well as excellent chemical and thermal stabilities. Herein, a novel boron-doped CQD (BCQD)-hybridized g-C₃N₄ homojunction (CN) nanocomposite was fabricated via a facile hydrothermal route. The optimal photocatalyst sample, 1-BCQD/CN (with a 1:3 mass ratio of boron to CQD) accomplished a Rhodamine B (RhB, 10 mg/L) degradation efficiency of 96.8% within 4 h under an 18 W LED light irradiation. The kinetic rate constant of 1.39 × 10^-2 min^-1 achieved by the optimum sample was found to be 3.6- and 2.8-folds higher than that of pristine CN and un-doped CQD/CN, respectively. The surface morphology, crystalline structure, chemical composition and optical properties of photocatalyst samples were characterized via TEM, FESEM-EDX, XRD, FTIR, UV-Vis DRS and FL spectrometer. Based on the scavenging tests, it was revealed that the photogenerated holes (h⁺), superoxide anions (∙O₂^-) and hydroxyl radicals (∙OH) were the primary reactive species responsible for the photodegradation process. Overall, the highly efficient 1-BCQD/CN composite with excellent photocatalytic activity could provide a cost-effective and robust means to address the increasing concerns over global environmental pollution.

Dye Removal Ability of Pure and Doped Graphitic Carbon Nitride

Background:

Rapid escalation in textile, paper, pesticides, pharmaceuticals and several other chemical based manufacturing industries due to amplification in human requirements have proportionately contributed to the extreme contamination of water ecosystem, resulted from the discharge of toxic pollutants from industries. Effluents from textile industries are comprised of coloured dyes like Rhodamine B, Methyl Orange, Methylene Blue and phenolic compounds which deserve special mention owing to their non-biodegradable, carcinogenic and severe detrimental nature. Urgent needs to ameliorate this fast declining environmental situation are of immense necessity in current scenario.

Objectives:

Objectives: In this regard, graphitic carbon nitride (GCN) is a distinguished material for water purification-based applications because of its exclusive characteristics making it highly prospective for degradation of toxic dyes from water by catalysis and adsorption techniques. GCN has been a material of conspicuous interest in recent times owing to its two dimensional sheets like structure with favourable surface area, and cost-effective synthesis approaches along with high production yield. This article presents a detail study of different aspects of GCN as a material of potential for water purification. Through extensive literature survey it has been shown that GCN is an effective material to be used in the fields of application. Several effective procedures like catalysis or adsorption for removal of dyes from water have been discussed with their basic science behind.

Conclusions:

This systematic effort shows that GCN can be considered to be one of the most efficient water purifier with further advantages arising from its easy and cost effective large scale synthesis.

Insight into Organic Pollutant Adsorption Characteristics on a g-C3N4 Surface by Attenuated Total Reflection Spectroscopy and Molecular Dynamics Simulation

Herein the adsorption characteristics of zwitterionic dye pollutant Rhodamine B (Rh⁺B^-) on a g-C₃N₄ surface were investigated by both an attenuated total reflection spectroscopy (ATRS) experiment and a molecular dynamics simulation (MDS). For experimental investigation, g-C₃N₄ was coated on a silica optical fiber (SOF) surface to fabricate an adsorption film. According to the ATRS response, adsorption thermodynamics and thermodynamics results were in situ obtained and evaluated. The isothermal Langmuir model was used to calculate the adsorption equilibrium constants (K_ads) and adsorption energies (ΔG_ads) for Rh⁺B^- as 27.25 × 10⁴ M^-1 and -31.01 kJ mol^-1, respectively, which indicated the spontaneous adsorption behavior of Rh⁺B^- at the g-C₃N₄ surface. Using dynamic Elovich modeling, the rate constants of Rh⁺B^- were found to be k₁ = 0.0063 min^-1 and k₂ = 0.0004 min^-1, which indicated two-stage adsorption at the g-C₃N₄ surface. For theoretical simulation, adsorption configurations and adsorption energies were systematically calculated by a molecular dynamics simulation (MDS) . Rh⁺B^- molecules were inclined to orient in a parallel position at the g-C₃N₄ surface during low concentration but a perpendicular position at the g-C₃N₄ surface during high concentration. Combined with experimental and calculation results, this work revealed the microscopic adsorption performance and elucidated the intermolecular interaction between localized interfaces of g-C₃N₄ and hazardous dye pollutant. We propose an adsorption model to explain the process of surface interaction, which is based on molecular orientation and a force-driven mechanism. Electrostatic attraction and π-π interaction dominated the adsorption interaction with an adsorption energy of ΔG_low(ads) = -38.96 kJ mol^-1 for low Rh⁺B^- concentration, and electrostatic attraction dominated the adsorption interaction with an adsorption energy of ΔG_high(ads) = -25.76 kJ mol^-1 for high Rh⁺B^- concentration. This work can provide a fundamental basis for a dye-pollutants removal application by g-C₃N₄ in both adsorption and photocatalyzation.

Tuning the reactivity of tri-s-triazine, trinitro-tri-s-triazine and ternary tri-s-triazine graphitic C3N4 quantum dots through H-functionalized and B-doped complexes: A density functional study

Modifying the structures and doping are proven to be effective methods to tune the structural and electrical properties of g-C₃N₄ quantum dots. Hence, in this study, tri-s-triazine and tri-nitro tri-s-triazine have been studied by functionalizing their edges with hydrogen. The H-functionalized tri-nitro tri-s-triazine quantum dot displays a buckled structure with a band gap of 1.988 eV, whereas the tri-s-triazine demonstrates a planner structure with a band gap of 1.636 eV. The obtained results have been compared with the previous results. The absorbance spectrum of H-functionalized trinitro tri-s-triazine falls under the visible region with a peak value of 488 nm, and the absorption spectrum of tri-s-triazine falls at 790 nm. The planarity of the tri-nitro tri-s-triazine structure is improved by doping the B atom in the N site, and the band gap of H-functionalized B doped tri-nitro tri-s-triazine is 1.143 eV. The absorbance spectrum of H-functionalized B doped tri-nitro tri-s-triazine is 508 nm. The reactivity of the structure is increased by doping B atoms, and it is confirmed by the electrophilicity index. Similarly, the H-functionalized B doped tri-s-triazine exhibits a band gap of 1.328 eV. Further, the tri-s-triazine structures are arranged in ternary form, and the properties are studied by increasing the number of B atoms in the tri-s-triazine rings. The outcome presents that the structures are planar, and band gap values are reduced further. Also, the reactivity of the sheets is increased, which is confirmed by the electrophilicity index. It is proposed that the sheets with a high reactivity can be used for the removal of hazardous ions and molecules from the industrial wastage.

Synthesis, Cr(VI) removal performance and mechanism of nanoscale zero-valent iron modified potassium-doped graphitic carbon nitride

A novel composite (nZVI@K-GCN) was firstly synthesized by liquid phase reducing nanoscale zero-valent iron (nZVI) on potassium-doped graphitic carbon nitride (K-GCN). The results of Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) suggested that nZVI@K-GCN possessed abundant active functional groups such as terminal amino-groups (-NH or -NH₂ groups) and -OH, and the specific surface area and pore volume from BET of nZVI@K-GCN were 4.7 times and 3.7 times higher than that of graphitic carbon nitride (GCN), respectively. These properties showed that the composite was especially suitable for heavy metal treatment. The application of the composite in the removal of chromium(VI) from aqueous solution showed that the maximum adsorption capacity of nZVI@K-GCN towards Cr(VI) was 68.6 mg/g at 308 K when the initial concentration of Cr(VI) was 30 mg/L, and more than 99% removal was obtained at pH = 3. This adsorption was an endothermic and spontaneous process. XPS patterns and batch experiments proved that complexation, electrostatic attraction and reduction precipitation were the main adsorption mechanism for Cr(VI) on nZVI@K-GCN.

Next-Generation Multifunctional Carbon-Metal Nanohybrids for Energy and Environmental Applications

Nanotechnology has unprecedentedly revolutionized human societies over the past decades and will continue to advance our broad societal goals in the coming decades. The research, development, and particularly the application of engineered nanomaterials have shifted the focus from "less efficient" single-component nanomaterials toward "superior-performance", next-generation multifunctional nanohybrids. Carbon nanomaterials (e.g., carbon nanotubes, graphene family nanomaterials, carbon dots, and graphitic carbon nitride) and metal/metal oxide nanoparticles (e.g., Ag, Au, CdS, Cu₂O, MoS₂, TiO₂, and ZnO) combinations are the most commonly pursued nanohybrids (carbon-metal nanohybrids; CMNHs), which exhibit appealing properties and promising multifunctionalities for addressing multiple complex challenges faced by humanity at the critical energy-water-environment (EWE) nexus. In this frontier review, we first highlight the altered and newly emerging properties (e.g., electronic and optical attributes, particle size, shape, morphology, crystallinity, dimensionality, carbon/metal ratio, and hybridization mode) of CMNHs that are distinct from those of their parent component materials. We then illustrate how these important newly emerging properties and functions of CMNHs direct their performances at the EWE nexus including energy harvesting (e.g., H₂O splitting and CO₂ conversion), water treatment (e.g., contaminant removal and membrane technology), and environmental sensing and in situ nanoremediation. This review concludes with identifications of critical knowledge gaps and future research directions for maximizing the benefits of next-generation multifunctional CMNHs at the EWE nexus and beyond.