Superior adsorption performance of graphitic carbon nitride nanosheets for both cationic and anionic heavy metals from wastewater

Advancements in effervescent-assisted dispersive micro-solid phase extraction for the analysis of emerging pollutants

Emerging pollutants pose an increasing threat to the environment and human well-being, requiring substantial progress in analytical methodologies. Dispersive micro-solid phase extraction (μ-dSPE) has proven successful in detecting and measuring these contaminants, particularly in trace quantities. However, challenges persist in achieving a uniform sorbent distribution and efficient separation from the sample matrix. To address these issues, effervescent-assisted dispersive micro-solid phase extraction (EA-μ-dSPE) was developed. This method uses on-site produced carbon dioxide as a dispersing agent, eliminating the need for vortexing or ultrasonication. Due to the sorbent dispersion in the sample solution, the contact surface between the analyte and the sorbent increases, resulting in increased extraction efficiency, reduced extraction time, and promotes of sustainability. Several parameters are critical to the successful execution of this procedure to extract the analytes, including the type and structure of sorbent, composition of dispersing agents, sorbent separation procedure, and type and properties of desorption solvents. The sorbent plays a critical role in successful extraction of emerging pollutants. It is clear that for the extraction of the analyte on the sorbent, proper interaction must be established between the analyte and the sorbent via physical and chemical interactions. This review thoroughly evaluates the underlying principles of the approach, its potential, and the significant advancements that have been documented. It explores the method's capacity to analyse and identify emerging pollutants, emphasising its potential across various sample matrices for enhanced pollutant identification and quantification.

Graphitic carbon nitride nanosheets mitigate cadmium toxicity in Glycine max L. by promoting cadmium retention in root and improving photosynthetic performance

Cadmium (Cd) pollution poses a serious threat to plant growth and yield. Nanomaterials have shown great application potential for alleviation of Cd toxicity to plants. In this study, we applied graphitic carbon nitride nanosheets (g-C3N4 NSs) for alleviation of Cd-toxicity to soybean (Glycine max L.). The g-C3N4 NSs supplementation significantly improved plant growth and reduced oxidative damage in the Cd-toxicated soybean seedlings through hydroponic culture. Particularly, the g-C3N4 NSs dynamically regulated the root cell wall (RCW) components by increasing pectin content and modifying its demethylation via enhancing pectin methylesterase (PME) activity, therefore greatly enhanced stronger RCW-Cd retention (up to 82.8%) and reduced Cd migration to the shoot. Additionally, the g-C3N4 NSs reversed the Cd-induced chlorosis, increased photosynthetic efficiency because of enhancement in Fv/Fm ration, Y(II) and sugars content. These results provide new insights into the alleviation of Cd toxicity to plants by g-C3N4 NSs, and shed light on the application of low-cost and environmental-friendly carbon-based NMs for alleviating heavy metal toxicity to plants.

Enhancement of Pb(ii) adsorptive removal by incorporation of UiO-66-COOH into the magnetic graphitic carbon nitride nanosheets

Efficient elimination of Lead (Pb(ii)) from aqueous solutions has become a crucial area of focus in the wastewater treatment industry. In this study, novel mesoporous magnetic g-C3N4/Fe3O4/UiO-66-COOH was synthesized by combining the acid-functionalized metal-organic framework (MOF) of UiO-66-COOH via a facile novel solvothermal method with magnetic graphitic carbon nitride (g-C3N4/Fe3O4) sheets to enhance Pb(ii) adsorption in water. The study investigated various influential adsorption parameters, including pH, dosage, contact time, ion concentration, and temperature. The Langmuir model, which depicts monolayer adsorption on a uniform surface, was a more suitable fit for the adsorption isotherms. The kinetics conformed to the pseudo-second-order model, indicating a chemical adsorption mechanism. According to the Langmuir model, the adsorption capacity of g-C3N4/Fe3O4/UiO-66-COOH is expected to reach a maximum of 285.8 mg L-1. This value is 2.6 times higher than g-C3N4/Fe3O4 and 1.6 times higher than UiO-66-COOH. The enhanced adsorption capacity of g-C3N4/Fe3O4/UiO-66-COOH is attributed to its superior characteristics, such as abundant functional groups and high surface area which is 2.16 times higher than g-C3N4/Fe3O4. The adsorption thermodynamics indicated that the adsorption occurred spontaneously and was characterized as exothermic. g-C3N4/Fe3O4/UiO-66-COOH material exhibited good recyclability for up to five runs.

The Adsorption Behaviors and Mechanisms of Humic Substances by Thermally Oxidized Graphitic Carbon Nitride

Thermal oxidation is efficient for enhancing the photocatalysis performance of graphitic carbon nitride (g-C₃N₄), while its effect on adsorption performance has not been fully studied, which is crucial to the application of g-C₃N₄ as adsorbents and photocatalysts. In this study, thermal oxidation was used to prepare sheet-like g-C₃N₄ (TCN), and its application for adsorption of humic acids (HA) and fulvic acids (FA) was evaluated. The results showed that thermal oxidation clearly affected the properties of TCN. After thermal oxidation, the adsorption performance of TCN was enhanced significantly, and the adsorption amount of HA increased from 63.23 (the bulk g-C₃N₄) to 145.35 mg/g [TCN prepared at 600 °C (TCN-600)]. Based on fitting results using the Sips model, the maximum adsorption amounts of TCN-600 for HA and FA were 327.88 and 213.58 mg/g, respectively. The adsorption for HA and FA was markedly affected by pH, alkaline, and alkaline earth metals due to electrostatic interactions. The major adsorption mechanisms included electrostatic interactions, π-π interactions, hydrogen bonding, along with a special pH-dependent conformation (for HA). These findings implied that TCN prepared from environmental-friendly thermal oxidation showed promising prospects for humic substances (HSs) adsorption in natural water and wastewater.

Charge transport and heavy metal removal efficacy of graphitic carbon nitride doped with CeO2

Doping of graphitic carbon nitride (g-C₃N₄) with semiconductors prevents electron-hole recombination and enhances adsorption capacity. This work investigates the synthesis of a water remediation material using g-C₃N₄ doped with CeO₂ using two different techniques. The chemical structures of the doped g-C₃N₄ samples were confirmed using FTIR, XRD, XPS and their morphology was studied using SEM-EDX. Charge transport through the doped materials was illustrated by a comprehensive dielectric study using broadband spectroscopy. The ability of doped g-C₃N₄ to adsorb heavy metals was investigated thoroughly in the light of applying different parameters such as temperature, pH, time, and concentration. The results showed that the mode of doping of g-C₃N₄ by CeO₂ strongly affected its adsorption capacity. However, g-C₃N₄ doped with CeO₂ using the first mode adsorbed 998.4 mg g^-1 in case of Pb²⁺ and 448 for Cd²⁺. Kinetic study revealed that the adsorption process obeyed PSORE as its q ^exp _e is close to its q ^cal _e and the rate-controlling step involved coordination among the synthetic materials and the heavy metal ions. The recovery of Pb²⁺ and Cd²⁺ ions from various sorbents was investigated by utilizing different molar concentrations of HNO₃ and indicated no significant change in the sorption capability after three different runs. This study has demonstrated an efficient method to obtain a highly efficient adsorbent for removing heavy metals from waste water.

Potential of waste mangosteen shell in the removal of cadmium ions: Effects of pH, contact time, and temperature

In this study, waste biomass adsorbents produced from mangosteen shells (MGS) were prepared (denoted as MGS500 and MGS1000). The physical and chemical characteristics, such as scanning electron microscopy, thermogravimetric-differential thermal analysis, specific surface area, pore volumes, surface functional groups, and point of zero charge of the prepared MGS samples were determined, and the adsorption capacity of cadmium ions from aqueous media was assessed. The effects of pH, adsorption time, temperature, and coexistence on adsorption were carefully assessed using an inductively coupled plasma optical emission spectrometer under several experimental conditions. The adsorption capacity decreased in the order, MGS < MGS500 < MGS1000. The optimal pH for cadmium ion removal was 5.0. The amount of cadmium ions adsorbed gradually increased with time, and adsorption equilibrium was achieved within 24 h after adsorption. Additionally, the amount of adsorbed cadmium ions increased with increasing adsorption temperature. To elucidate the adsorption mechanism in detail, the elemental distribution and X-ray photoelectron spectra of the prepared adsorbents were analyzed. Finally, desorption solutions such as HNO3, H2O, and NaOH were used to desorb the absorbed cadmium ions from MGS1000. Under our experimental conditions, the desorption percentage of cadmium ions was approximately 98.8% using HNO3. In conclusion, MGS1000 exhibited a good adsorption capacity of 12.0 mg/g for adsorbing cadmium ions from aqueous media and desorption capacity with HNO3 at 1000 mmol/L.

Efficient Mesoporous MgO/g-C3N4 for Heavy Metal Uptake: Modeling Process and Adsorption Mechanism

Removing toxic metal ions arising from contaminated wastewaters caused by industrial effluents with a cost-effective method tackles a serious concern worldwide. The adsorption process onto metal oxide and carbon-based materials offers one of the most efficient technologies adopted for metal ion removal. In this study, mesoporous MgO/g-C₃N₄ sorbent is fabricated by ultrasonication method for the uptake Pb (II) and Cd (II) heavy metal ions from an aqueous solution. The optimum conditions for maximum uptake: initial concentration of metal ions 250 mg g^-1, pH = 5 and pH = 3 for Pb⁺⁺ and Cd⁺⁺, and a 60 mg dose of adsorbent. In less than 50 min, the equilibrium is reached with a good adsorption capacity of 114 and 90 mg g^-1 corresponding to Pb⁺⁺ and Cd⁺⁺, respectively. Moreover, the adsorption isotherm models fit well with the Langmuir isotherm, while the kinetics model fitting study manifest a perfect fit with the pseudo-second order. The as fabricated mesoporous MgO/g-C₃N₄ sorbent exhibit excellent Pb⁺⁺ and Cd⁺⁺ ions uptake and can be utilized as a potential adsorbent in wastewater purification.

Removal of nutrients from pulp and paper biorefinery effluent: Operation, kinetic modelling and optimization by response surface methodology

This study investigated the effectiveness of extended aeration system (EAS) and rice straw activated carbon-extended aeration system (RAC-EAS) in the treatment of pulp and paper biorefinery effluent (PPBE). RAC-EAS focused on the efficient utilization of lignocellulosic biomass waste (rice straw) as a biosorbent in the treatment process. The experiment was designed by response surface methodology (RSM) and conducted using a bioreactor that operated at 1-3 days hydraulic retention times (HRT) with PPBE concentrations at 20, 60 and 100%. The bioreactor was fed with real PPBE having initial ammonia-N and total phosphorus (TP) concentrations that varied between 11.74 and 59.02 mg/L and 31-161 mg/L, respectively. Findings from the optimized approach by RSM indicated 84.51% and 91.71% ammonia-N and 77.62% and 84.64% total phosphorus reduction in concentration for EAS and RAC-EAS, respectively, with high nitrification rate observed in both bioreactors. Kinetic model optimization indicated that modified stover models was the best suited and were statistically significant (R² ≥ 0.98) in the analysis of substrate removal rates for ammonia-N and total phosphorus. Maximum nutrients elimination was attained at 60% PPBE and 48 h HRT. Therefore, the model can be utilized in the design and optimization of EAS and RAC-EAS systems and consequently in the prediction of bioreactor behavior.

Coffee Husk and Lignin Revalorization: Modification with Ag Nanoparticles for Heavy Metals Removal and Antifungal Assays

This study presents the use of the modified coffee husk and coffee lignin as sorbents in the heavy metal ions sorption of Pb(II), Cd(II), Cr(III), and Cu(II) in an aqueous solution. The modification of sorbents was carried out by the impregnation method, using silver nitrate (AgNO3) and sodium borohydride (NaBH4) as a nanoparticles’ (NPs) precursor, and reducing agent, respectively. The obtained nanocomposite material was morphologically characterized by electron microscopy. In addition, an evaluation of metal ions’ sorption, pseudo-first-order, and pseudo-second-order kinetics modeling was performed. Finally, antifungal activity was evaluated on different Candida species. Coffee and lignin modified with AgNPs increased the extraction capacity with the highest sorption for Pb ions with 2.56 mg/g and 1.44 mg/g, respectively.

Simultaneous electrochemical sensing of heavy metal ions based on a g-C3N4/CNT/NH2-MIL-88(Fe) nanocomposite

The presence of Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ in drinking-water can be harmful to human health, even if their concentration is fairly low. Hence, it is significant to detect these heavy metal ions in sewage to evaluate the quality of water. Herein, amino-functionalized metal-organic frameworks (NH₂-MIL-88(Fe)) embedded with graphitic carbon nitride (g-C₃N₄) nanosheets and acid-functionalized carbon nanotubes were prepared via a one-pot synthesis. The composite can be directly modified on the surface of glass carbon electrodes without the assistance of Nafion or other binders. The modified glass carbon electrodes can be used to simultaneously detect Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ in water via square wave stripping voltammetry. The doping of g-C₃N₄ in the composite, rich in N-containing functional groups, participates in the adsorption of metal ions on the surface of the electrodes. The porous composite provides accommodation room for metals generated by electro-reduction. The detection limit for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ is 39.6 nM, 7.6 nM, 11.9 nM, and 9.6 nM, respectively. And the sensitivity for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ is 0.0789 mA μM^-1 cm^-2, 0.4122 mA μM^-1 cm^-2, 0.2616 mA μM^-1 cm^-2, and 0.3251 mA μM^-1 cm^-2, respectively. This work not only enriches the functional design of Fe-MOF materials, but also develops a method for the determination of metal ions using the adsorption sites in g-C₃N₄.

Development of Absorbent Using Amylose-Graphite Composite Electrode for Removal of Heavy Metals

Amylose of Phragmites Australis captures heavy metals in a box consisting of sugar chains. However, its absorption rate is low in the period of the month scale. Therefore, the electrochemical driving force was used to promote the absorption rate in this research. Amylose was doped with TiO₂ porous graphite electrode. The composted absorbent was characterized using XRD(X-ray diffraction), SEM (Scanning Electrode Microscopy), Raman spectroscopy, and electrochemical methods. The affinity and maximum absorption amount were calculated using the isotherm method. In this study, Pb²⁺, Cu²⁺, Cd²⁺, and Cr⁶⁺ were chosen to demonstrate because these heavy metals are significant pollutants in Japan’s surface water. It was found that the maximum absorption was Cu²⁺ (56.82-mg/L) > Pb²⁺ (55.89-mg/L) > Cr⁶⁺ (53.97-mg/L) > Cd²⁺ (52.83.68-mg/L) at −0.5 V vs. Ag/AgCl. This is approximately the same order as the hydration radius of heavy metals. In other words, the absorption amounts were determined by the size of heavy metal ions. Subsequently, the mixed heavy metal standard solution was tested; the maximum absorption amount was 21.46 ± 10.03 mg/L. It was inferred that the electrochemical driving force could be shown as the ion size effect in the mixed solution. Despite there being no support for this hypothesis at this time, this study succeeded in showing that the electrochemical driving force can improve the ability of the absorbent.

Advances in the Synthesis and Application of Anti-Fouling Membranes Using Two-Dimensional Nanomaterials

This article provides a comprehensive review of the recent progress in the application of advanced two-dimensional nanomaterials (2DNMs) in membranes fabrication and application for water purification. The membranes fouling, its types, and anti-fouling mechanisms of different 2DNMs containing membrane systems are also discussed. The developments in membrane synthesis and modification using 2DNMs, especially graphene and graphene family materials, carbon nanotubes (CNTs), MXenes, and others are critically reviewed. Further, the application potential of next-generation 2DNMs-based membranes in water/wastewater treatment systems is surveyed. Finally, the current problems and future opportunities of applying 2DNMs for anti-fouling membranes are also debated.

Graphitic Carbon Nitride (C3N4) Reduces Cadmium and Arsenic Phytotoxicity and Accumulation in Rice (Oryza sativa L.)

The present study investigated the role of graphitic carbon nitride (C₃N₄) in alleviating cadmium (Cd)- and arsenic (As)-induced phytotoxicity to rice (Oryza sativa L.). A high-temperature pyrolysis was used to synthesize the C₃N₄, which was characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, and dynamic light scattering. Rice seedlings were exposed to C₃N₄ at 50 and 250 mg/L in half-strength Hoagland’s solution amended with or without 10 mg/L Cd or As for 14 days. Both Cd and As alone resulted in 26–38% and 49–56% decreases in rice root and shoot biomass, respectively. Exposure to 250 mg/L C₃N₄ alone increased the root and shoot fresh biomass by 17.5% and 25.9%, respectively. Upon coexposure, Cd + C₃N₄ and As + C₃N₄ alleviated the heavy metal-induced phytotoxicity and increased the fresh weight by 26–38% and 49–56%, respectively. Further, the addition of C₃N₄ decreased Cd and As accumulation in the roots by 32% and 25%, respectively, whereas the metal contents in the shoots were 30% lower in the presence of C₃N₄. Both As and Cd also significantly altered the macronutrient (K, P, Ca, S, and Mg) and micronutrient (Cu, Fe, Zn, and Mn) contents in rice, but these alterations were not evident in plants coexposed to C₃N₄. Random amplified polymorphic DNA analysis suggests that Cd significantly altered the genomic DNA of rice roots, while no difference was found in shoots. The presence of C₃N₄ controlled Cd and As uptake in rice by regulating transport-related genes. For example, the relative expression of the Cd transporter OsIRT1 in roots was upregulated by approximately threefold with metal exposure, but C₃N₄ coamendment lowered the expression. Similar results were evident in the expression of the As transporter OsNIP1;1 in roots. Overall, these findings facilitate the understanding of the underlying mechanisms by which carbon-based nanomaterials alleviate contaminant-induced phyto- and genotoxicity and may provide a new strategy for the reduction of heavy metal contamination in agriculture.

The transport of graphitic carbon nitride in saturated porous media: Effect of hydrodynamic and solution chemistry

Understanding transport behavior of graphitic carbon nitride (g-C₃N₄) in porous media plays an important role in preventing its possible causing the underground environmental problems. The transport behavior of g-C₃N₄ in porous media were investigated by packed column experiments at different flow rates, ionic strengths (ISs), pHs and multivalent cations. The experimental results showed that the transport ability of g-C₃N₄ decreased with the IS increasing, and most of the g-C₃N₄ was retained in the sand column for the IS greater than 0.0001 M. The flow rate had little effect on the transport behavior of g-C₃N₄, and the recovery of g-C₃N₄ increased slightly with increasing flow rate. In addition, the migration ability of g-C₃N₄ under acidic conditions was drastically reduced compared with neutral alkaline conditions. Moreover, it was found that 1.51%, 30.33%, 34.91%, and 60.54% of g-C₃N₄ was retained in the column when g-C₃N₄ was leached through the quartz sand column at Al³⁺, Ca²⁺, Mg²⁺, and K⁺, which was consistent with the Schulze-Hardy rule. Finally, FTIR spectrum showed that the infrared absorption peak of the g-C₃N₄ mixed quartz sand were shifted to certain degrees under different conditions, which confirmed that hydrogen bond was formed in the transport of carbon nitride with the quartz sand surface. This study provides a new perspective on the role of hydrogen bond in the transport and fate of nanomaterials.

Density functional theory based studies on the adsorption of rare-earth ions from hydrated nitrate salt solutions on g-C3N4 monolayer surface

This article represents density functional theory (DFT) based comparative analysis on six trivalent rare-earth ions (RE³⁺; RE: Y, La, Ce, Sm, Eu and Gd) absorption, from the respective nitrate-hexahydrate salts, on graphitic carbon nitride (g-C₃N₄) 2D monolayer, and the photocatalytic properties of the RE³⁺ adsorbed g-C₃N₄ systems (g-C₃N₄/RE³⁺) based on the ground-state electronic structure calculations. Structure, stability and coordination chemistry of two configurations of each hydrated RE-salt system are discussed in detail. Both DFT (B3LYP/SDD) and semi-empirical (Sparkle/PM7) calculations identify the central N₆ vacancy of pristine g-C₃N₄ as the most suitable site for RE³⁺ adsorption. Bader's QTAIM, Mayer bond order and charge population analyses (ADCH, CHELPG and DDEC) are performed to describe the bond characteristics within the systems under study. Thermochemical calculations suggest that the adsorption process is thermodynamically more feasible for higher atomic number (Z) RE³⁺ [Sm³⁺, Eu³⁺ and Gd³⁺], compared to lower-Z RE³⁺ [Y³⁺, La³⁺ and Ce³⁺] ions. Besides, the better photocatalytic properties of higher-Z RE³⁺ adsorbed g-C₃N₄ systems are revealed from better HOMO-LUMO delocalization, decreased HOMO-LUMO gap, increased softness, higher electrophilicity and electron transfer parameter, compared to pristine or lower-Z RE³⁺ adsorbed g-C₃N₄ systems, as obtained from Hirshfeld orbital compositions, density of states and condensed Fukui function analyses.