Synthesis of nitrogen doped carbon quantum dots/magnetite nanocomposites for efficient removal of methyl blue dye pollutant from contaminated water

XG and CS-based self-assembled nanocomposite hydrogel embedding fluorescent NCQDs capable of detection and adsorptive removal of the polar MO and Cr(VI) pollutants

Aiming at dealing with organic and inorganic pollutants dissolved in aquatic environments, we introduce self-assembled fluorescent nanocomposite hydrogel based on a binary polysaccharide network (xanthan gum/chitosan) embedding nitrogen-doped carbon quantum dots not only as a hybrid solid optical sensor for detecting Cr(VI) ions but also to remove anionically charged contaminants Cr(VI) and methyl orange (MO) by acting as an adsorbent. This fluorescent nanocomposite achieved a detection limit of 0.29 μM when used to detect Cr(VI) and demonstrated a fluorescence quantum yield of 59.7 %. Several factors contributed to the effectiveness of the adsorption of Cr(VI) and MO in batch studies, including the solution pH, dosage of the adsorbent, temperature, initial contamination level, and contact time. Experimental results showed 456 mg/g maximum adsorption capacity at pH 4 for MO compared to 291 mg/g at pH 2 for Cr(VI) at 25 °C. In addition to conforming to Langmuir's model, Cr(VI) and MO's adsorption kinetics closely matched pseudo-second-order. Using thermodynamic parameters, the results indicate that Cr(VI) and MO adsorb spontaneously and exothermically. Recycling spent adsorbent for Cr(VI) and MO using NaOH at 0.1 M was possible; the respective adsorption efficiency remained at approximately 82.2 % and 83 % after the fifth regeneration cycle.

Development of folate-conjugated polypyrrole nanoparticles incorporated with nitrogen-doped carbon quantum dots for targeted bioimaging and photothermal therapy

PPy nanoparticles are widely employed as PTT agents, because of their exceptional near-infrared absorption properties. Nonetheless, the efficacy of PTT with PPy nanoparticles is hindered by a challenge, specifically, a lack of precise targeting. In this study, a PTT imaging agent was developed by combining NCQDs having bright green fluorescent properties with PPy nanoparticles along with the masking of folic acid to overcome the challenge of targeting. The synthesized PPy:NCQDs:FA nanocomposite, characterized by extraordinary photothermal property, was utilized for imaging of folate receptor positive (FA+) MCF-7 cancer cells through the emission of green fluorescence by NCQDs incorporated within the nanocomposite. Additionally, these nanoparticles demonstrated a good level of cell viability, exceeding 82 %, even at a concentration of 600 μg mL-1. Even the in vivo toxicity inspection of the nanocomposite exemplified no observed acute toxicity at experimental dosages of 1 and 3 mg per kg body weight. By subjecting MCF-7 cells, inoculated with 100 μg mL-1 of nanocomposite, to NIR laser irradiation for 5 min, a significant decline in cell viability was witnessed, establishing the photothermal therapeutic potency of the nanocomposite. The death of cancer cells induced by nanocomposite was verified through MTT assay, imaging of cells by NCQDs alone, with nanocomposite, and by live/dead cell Calcein AM/PI staining assay. Quantification of induced apoptosis post-laser treatment is conducted through staining with Annexin V-FITC/PI. These findings establish potential use of PPy:NCQDs:FA nanocomposite as versatile theranostic agents, capable of targeted bioimaging and treatment for cancer cells exhibiting folate receptors.

Fluorescence Carbon Dots from Blood-Berries for Sensing Cr6+ Ions in Water and Application in White Light Emitting Diode

Conventional techniques for identifying heavy metal ions in water are laborious and time-consuming. Therefore, it is necessary to create innovative sensing technologies that can detect with greater sensitivity and speed. Although there have been reports of optical-based assays utilising fluorescent nanomaterials, these assays usually rely on variations in signal strength. However, this approach has significant drawbacks when it comes to environmental monitoring. Fluorescence carbon dots (CDs) have been prepared by facile synthesis from Blood berries. A homemade heavy metal optical detector is constructed to accurately identify heavy metal ions, exclusively Cr6+ ions in a water medium. Their optical emission signature varies based on the specific chromium ions in solution, and the emission intensity also changes depending on its concentration. The quenching behaviour is attributed to the interaction between the metallic cations and the fluorescent surface states of the carbon dots. Another application is the encapsulation of CDs in PVDF polymer to form a flexible film and use it as a phosphor for LED conversion.

Carbon and metal based magnetic porous materials - Role in drug removal: A Comprehensive review

Development of effective adsorbents for the removal of contaminants from wastewater is indispensable due to increasing water scarcity and a lack of pure drinking water, which are prevailing as a result of rapid industrialization and population growth. Recently, the development of new adsorbents and their effective use without generating secondary waste is receiving huge consideration. In order to protect the environment from primary and secondary pollution, the development of adsorbents from wastes and their recycling have become conventional practices aimed at waste management. As a result, significant progress has been made in the synthesis of new porous carbon and metal-organic frameworks as adsorbents, with the objective of using them for the removal of pollutants. While many different kinds of pollutants are produced in the environment, drug pollutants are the most vicious because of their tendency to undergo significant structural changes, producing metabolites and residues with entirely different properties compared to their parent compounds. Chemical reactions involving oxidation, hydrolysis, and photolysis transform drugs. The resulting compounds can have detrimental effects on living beings that are present in soil and water. This review stresses the development of adsorbents with adjustable porosities for the broad removal of primary drug pollutants and their metabolites, which are formed as a result of drug transformations in environmental matrices. This keeps adsorbents from building up in the environment and prevents them from becoming significant pollutants in the future. Additionally, it stops secondary pollution caused by the deterioration of the used adsorbents. Focus on the development of effective adsorbents with flexible porosities allows for the complete removal of coexisting contaminants and makes a substantial contribution to wastewater management. In order to concentrate more on the development of flexible pore adsorbents, it is crucial to comprehend the milestones reached in the research and applications of porous magnetic adsorbents based on metal and carbon, which are discussed here.

Iron Oxide-Doped Carbon Nanoparticles Stabilised with Functionally Modified Hyperbranched Polyglycerol for Cd2+ Sensing and Photodynamic Antibacterial Therapeutic Applications

Nanoscale materials are being developed from individual particles to multi-component assemblies, with carbon nanomaterials being particularly useful in bioimaging, sensing, and optoelectronics due to their unique optical properties, enhanced by surface passivation and chemical doping. Noble metals are commonly used in conjunction with carbon-based nanomaterials for the synthesis of nanohybrids. Carbon-based materials can function as photosensitizers and effective carriers in photodynamic therapy, enabling the use of combined treatment approaches. The hydrophobicity and agglomeration tendency of carbon nanoparticles pose a drawback. This study is an attempt to overcome these limitations, which involved the synthesis of iron oxide-doped carbon nanoparticles through the carbonisation of citric acid and hexamethylene tetramine, followed by doping them with iron oxide. The as synthesized iron oxide-doped carbon nanoparticles were stabilised with fluorescently modified hyperbranched polyglycerol. The efficacy of these nanoparticles in photodynamic antibacterial therapy and Cd (II) ion sensing was investigated. The selectivity of stabilised nanoparticles against Cd2+ ion is presented in the current study. The current study also compares the antibacterial efficacy of undoped, iron oxide-doped and stabilised nanoparticle systems. The possible toxic effects of the synthesised nanosystems were investigated in order to assess their suitability for biomedical applications and establish their safety profile.

Fe3+-induced luminescence quenching in carbon dots - mechanism unveiled

Carbon dot (CD)-based fluorimetric sensors have attracted immense attention for the detection of metal ions. Among the available works in this direction, more than 70% of the studies reported the detection of Fe3+ through luminescence quenching. Ferric ions are significant species from environmental and biological point of view. Excited-state electron transfer from carbon dots to ferric ions is suggested as the reason for the luminescence quenching. However, to date, no solid proof was provided to demonstrate this electron transfer process. Herein, N-doped blue luminescent carbon dots prepared via hydrothermal carbonization are used to demonstrate the exact mechanism operating in the above-mentioned detection strategy. The carbon dots possessed an average size of 4.9 nm, and exhibited good aqueous solubility as well as an excitation wavelength-dependent emission. Fe3+-mediated luminescence quenching was quantitatively achieved at the micromolar level, with a detection limit of 1.426 μM. The CD-mediated reduction of ferric ions is confirmed by spectral analysis. Fe3+-induced luminescence quenching was partially restored in the presence of ascorbic acid, enabling the sub-micromolar level monitoring of this analyte, with the lowest detection amount of 276 nM. Turnbull's blue method is adopted for confirming the reducing role of ascorbic acid, which eventually increased the luminescence of the system, evoking a turn-on response.

High efficiency removal of methyl blue using phytic acid modified graphene oxide and adsorption mechanism

Phytic acid modified graphene oxide (PGO) has encouraging prospect in environmental application. Herein, PGO was fabricated with a simple hydrothermal method and used as adsorbent to remove methyl blue (MB). Elaborate inspection based on the hard-soft acid-base (HSAB) principle, spectroscopic characterization, as well as batch adsorption and fitting were conducted to unravel the adsorption mechanism. Results show, PGO efficiently adsorbs 89.08 mg·g-1 of MB in 22 min. HSAB principle proposes, high electron transfer (ΔN) and energy lowering (ΔE) induce covalent bond (chemical interaction), while low ΔN and ΔE induce electrostatic effect (physical interaction). Accordingly, both the first and second strongest interaction occurs between PA moiety and MB: π electrons of MB flows towards O atom in OH and O(-O-) of PA, respectively. Yet the third strongest interaction happens between GO moiety and MB: electron of O atom in OH group of GO flows towards N atom of MB. Above top three interactions are characterized by prominent ΔN and ΔE implying the formation of covalent bond. However, other interactions yield low ΔN and ΔE, suggesting the presence of electrostatic effect. HSAB principle conclusion was substantiated by FTIR and UV-Vis analyses. These findings confirm that PA modification enhances the adsorption affinity of graphene oxide. Thereby, chemical adsorption induced by physical interaction is proposed. This work may inspire the design of efficient adsorbent based on PGO framework for environmental restoration.

Superior capacity and easy separation of zirconium functionalized chitosan melamine foam for antimony(III/V) removal

Nowadays, highly toxic antimony has severely posed threat to water sources and jeopardized human health. Fabricating adsorbents with the capability of easy separation, high efficiency and large adsorption capacity remains a major challenge. In this paper, zirconium functionalized chitosan melamine foam (ZCMF) was fabricated with zirconium and chitosan crosslinked onto melamine foam, then utilized for the removal of antimony(III/V) in water. The characterization of SEM and EDS collectively showed that ZCMF has a porous structure which could boost the mass transfer rate and zirconium ions on the surface could provide plentiful active adsorption sites. Systematic adsorption experiments demonstrated that the experimental data of Sb(III) and Sb(V) were consistent with the pseudo-second-order and Elovich kinetic models, respectively, and the Langmuir maximum adsorption capacities were separately 255.35 mg g-1 (Sb(III)) and 414.41 mg g-1 (Sb(V)), which displayed prominent performance among adsorbents derived from biomass. Combining the XPS and FTIR characterization with experimental data, it is rational to speculate that ZCMF could remove Sb from aqueous solution through ligand exchange, electrostatic attraction, and surface complexation mechanisms. ZCMF exhibited excellent performance, including large adsorption capacity, easy separation, facile preparation and eco-friendliness. It could be a promising new adsorbent for the treatment of antimony-containing wastewater.

Efficient Adsorptive Removal of Methylene Blue Dye from Aqueous Solution Using Eragrostis Teff Biomass-Derived Nitrogen and Phosphorus-Codoped Carbon Quantum Dots

Carbon quantum dots have a great application potential in environmental protection via adsorption technology due to their large specific surface area and negative zeta potential. In this work, nitrogen and phosphorus-codoped carbon quantum dots (NP-CQDs) with a large specific surface area and negative zeta potential were successfully synthesized by a single-step hydrothermal synthesis. Batch adsorption studies were utilized to assess the adsorbent's capacity to remove common methylene blue (MB) dye contaminants from an aqueous solution. The experiment showed that MB dye could be removed in 30 min under optimum experimental conditions, with a removal efficiency of 93.73%. The adsorbent's large surface area of 526.063 m2/g and negative zeta potential of -12.3 mV contribute to the high removal efficiency. The Freundlich isotherm model fits the adsorption process well at 298 K, with R2 and n values of 0.99678 and 4.564, respectively, indicating its applicability. A kinetic study demonstrated that the pseudo-second-order model, rather than the pseudo-first-order model, is more suited to represent the process of MB dye adsorption onto NP-CQDs. This research established a simple and cost-effective method for developing a highly efficient NP-CQD adsorbent for organic dye degradation by adsorption.

Treating waste with waste: Adsorption of anionic dyes in wastewater with surfactant-modified phosphogypsum

Phosphogypsum (PG) is a solid waste generated during the wet process of phosphoric acid production. The environmental-friendly disposal and recycling of PG is vital in the field of environmental solid waste treatment. In this study, PG is used for adsorbent of dyes in wastewater to achieve the goal of recycling waste with waste. Surfactant-modified phosphogypsum (ODBAC@PG) was prepared using octadecyl dimethyl benzyl ammonium chloride (ODBAC) as modifier. ODBAC@PG exhibits high adsorption capability for anionic dyes (methyl blue (MeB) and indocyanine carmine (IC)). The pseudo-second-order kinetic model fits the kinetic experimental data for the adsorption of two organic anionic dyes. Langmuir adsorption isotherm fits the adsorption characteristics of MeB and IC on ODBAC@PG, exhibiting a monolayer adsorption pattern. Thermodynamic parameters indicate the spontaneous and exothermic properties of MeB and IC on ODBAC@PG. MeB and IC have antagonistic effects on each other in binary adsorption system. High adsorption capacity after six cycles of experiments demonstrates the high reusability of ODBAC@PG. The nature for the adsorption includes electrostatic interaction, hydrogen bond and hydrophobic interaction. Using ODBAC@PG for dyes wastewater treatment can accomplish the goal of treating waste with waste and turning waste into treasure.

Ultrasound-assisted adsorption approach for desulfurization of n-heptane using nitrogen-doped magnetic carbon dot nanocomposite

Desulfurization is an important process that not only affects the quality and performances of fuels but also is of great importance from environmental aspects. In this research, nitrogen-doped magnetic carbon dots nanocomposite was synthesized and characterized, and it's potential in adsorptive removal of thiophenes (i.e., thiophene, benzothiophene, and dibenzothiophene) from n-heptane (i.e., as model fuel) was investigated. After optimization of adsorption process, the removal efficiency was obtained above 95% for all of studied thiophenes. Besides that, it was concluded that using ultrasound during the adsorption process could enhance the maximum adsorption capacity. Langmuir model was able to appropriately describe the adsorption isotherm data, where the maximum equilibrium adsorption capacities for thiophene, benzothiophene and dibenzothiophene were obtained as 90.22, 96.51 and 100.38 mgg-1, respectively. The analysis of kinetic data also revealed that all thiophenes were being adsorbed following Pseudo-second-order model. To regenerate the adsorbent, the desorption process was also investigated using different solvents under different conditions, methanol was found as effective solvent for regeneration. The proposed adsorbent was used successfully for the removal of pollutants in a gasoline sample.

Reusable flexible poly(vinyl alcohol)/chitosan-based polymer carbon dots composite film for acid blue 93 dye adsorption

The design and synthesis of water-insoluble chitosan-based polymer carbon dots [P(CS-g-CA)CDs] are described. A polyvinyl alcohol/chitosan-based polymer carbon dot [PVA/P(CS-g-CA)CDs] composite film was prepared using a simple casting method to be used in dye adsorption. The composite film was characterized using FT-IR, XPS, transparency, contact angle, and mechanical properties tests, which showed the successful incorporation of P(CS-g-CA)CDs into the film and also revealed that hydrogen bonding improved the mechanical properties of the PVA film. Furthermore, the composite film displayed substantially enhanced hydrophobicity, making it suitable for use in aqueous environments. In addition, the composite film exhibited stable adsorption of acid blue 93 (AB93) at pH 2-9, with an enhanced adsorption capacity of 433.24 mg/g. The adsorption obeyed Langmuir law with an efficiency of more than 89% even after five cycles. Therefore, the PVA/P(CS-g-CA)CDs film is a promising material for the treatment of organic dye-polluted wastewater.

Dual Emission Carbon Dots for Simultaneous Detections of Pb2+ and Fe3+ Ions in Water Via Distinct Sensing Mechanisms

Herein, dual-emission carbon dots (DE-CDs) were synthesized using a one-pot hydrothermal method. DE-CDs exhibited two well-separated peaks at 433 and 513 nm under ultraviolet excitation. The prepared DE-CDs offer selective detection of Fe3+ ions via inner filter effect (IFE) and Pb2+ ions via aggregation-induced enhancement (AIE). The obtained DE-CDs showed a good affinity for both Fe3+ and Pb2+ ions in the presence of various interfering ions. The limits of detection were 0.797 ppm and 4.739 ppm for Pb2+ and Fe3+, respectively. The finding reveals the huge potential of DE-CDs for the selective detection of multiple targets in one solution.

Photocatalytic Degradation of Methylene Blue Using N-Doped ZnO/Carbon Dot (N-ZnO/CD) Nanocomposites Derived from Organic Soybean

This study reports on successful synthesis of carbon dots (CDs), nitrogen-doped zinc oxide (N-ZnO), and N-ZnO/CD nanocomposites as photocatalysts for degradation of methylene blue. The first part was the synthesis of CDs utilizing a precursor from soybean and ethylenediamine as a dopant by a hydrothermal method. The second part was the synthesis of N-ZnO with urea as the nitrogen dopant carried out by a calcination method in a furnace at 500 °C for 2 h in an N2 atmosphere (5 °C min-1). The third part was the synthesis of N-ZnO/CD nanocomposites. The characteristics of CDs, N-ZnO, and N-ZnO/CD nanocomposites were analyzed through Fourier transform infrared (FTIR), UV-vis absorbance, photoluminescence (PL), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), thermal gravimetry analysis (TGA), field-emission scanning electron microscopy energy-dispersive spectroscopy (FESEM EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analysis. Based on the HR-TEM analysis, the CDs had a spherical shape with an average particle size of 4.249 nm. Meanwhile, based on the XRD and HR-TEM characterization, the N-ZnO and N-ZnO/CD nanocomposites have wurtzite hexagonal structures. The materials of N-ZnO and N-ZnO/CD show increased adsorption in the visible light region and low energy gap E g. The E g values of N-ZnO and N-ZnO/CDs were found to be 2.95 and 2.81 eV, respectively, whereas the surface area (S BET) values 3.827 m2 g-1 (N-ZnO) and 3.757 m2 g-1(N-ZnO/CDs) belonged to the microporous structure. In the last part, the photocatalysts of CDs, N-ZnO, and N-ZnO/CD nanocomposites were used for degradation of MB (10 ppm) under UV-B light irradiation pH = 7.04 (neutral) for 60 min at room temperature. The N-ZnO/CD nanocomposites showed a photodegradation efficiency of 83.4% with a kinetic rate of 0.0299 min-1 higher than N-ZnO and CDs. The XRD analysis and FESEM EDS of the N-ZnO/CDs before and after three cycles confirm the stability of the photocatalyst with an MB degradation of 58.2%. These results have clearly shown that the N-ZnO/CD nanocomposites could be used as an ideal photocatalytic material for the decolorization of organic compounds in wastewater.

Carbon dots decorated magnetite nanocomposite obtained using yerba mate useful for remediation of textile wastewater through a photo-Fenton treatment: Ilex paraguariensis as a platform of environmental interest-part 2

Two carbon dots (CD) with diameters of 4.9 ± 1.5 and 4.1 ± 1.2 nm were successfully synthesized through an acid ablation route with HNO₃ or H₂SO₄, respectively, using Ilex paraguariensis as raw material. The CD were used to produce magnetite-containing nanocomposites through two different routes: hydrothermal and in situ. A thorough characterization of the particles by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) indicates that all nanomaterials have spherical-like morphology with a core-shell structure. The composition of this structure depends on the route used: with the hydrothermal route, the shell is composed of the CD, but with the in situ process, the CD act as nucleation centers, and so the iron oxide domains are in the shell. Regarding the photocatalytic mechanism for the degradation of methyl orange, the interaction between the CD and the magnetite plays an important role in the photo-Fenton reaction at pH 6.2, in which ligand-to-metal charge transfer processes (LTMCT) allow Fe²⁺ regeneration. All materials (100 ppm) showed catalytic activity in the elimination of methyl orange (8.5 ppm), achieving discoloration of up to 98% under visible irradiation over 400 nm in 7 h. This opens very interesting possibilities for the use of agro-industrial residues for sustainable synthesis of catalytic nanomaterials, and the role of the interaction of iron-based catalysts with organic matter in heterogeneous Fenton-based processes.

Metal-doped carbon dots as robust nanomaterials for the monitoring and degradation of water pollutants

The contamination of the environment by domestic and industrial discharges is a relevant and persistent problem that needs novel solutions. Innovations in the detection, adsorption, and removal or in-situ degradation of toxic components are urgently required. Various effective techniques and materials have been proposed to address this problem, in which carbon dots (CDs) stand out because of their unique properties and low-cost and abundant nature. Their combination with different metals results in the enhancement of their innate properties. Metal-doped CDs have shown excellent results and competitive advantages in recent times. Considering the above useful critiques and CDs notable potentialities, this review discusses different approaches in detail to sense, adsorb, and photodegrade different pollutants in water samples. It was found that altering the electronic structure of CDs via metal doping has a great potential to enhance the optical, electrical, chemical, and magnetic capabilities of CDs, which in turn is beneficial for wastewater treatment.

Doped Carbon Quantum Dots/PVA Nanocomposite as a Platform to Sense Nitrite Ions in Meat

A sensor device based on doped-carbon quantum dots is proposed herein for detection of nitrite in meat products by fluorescence quenching. For the sensing platform, carbon quantum dots doped with boron and functionalized with nitrogen (B,N-Cdot) were synthesized with an excellent 44.3% quantum yield via a one-step hydrothermal route using citric acid, boric acid, and branched polyethylenimine as carbon, boron, and nitrogen sources, respectively. After investigation of their chemical structure and fluorescent properties, the B,N-Cdot at aqueous suspensions showed high selectivity for NO₂^- in a linear range from 20 to 50 mmol L^-1 under optimum conditions at pH 7.4 and a 340 nm excitation. Furthermore, the prepared B,N-Cdots successfully detected NO₂^- in a real meat sample with recovery of 91.4-104% within the analyzed range. In this manner, a B,N-Cdot/PVA nanocomposite film with blue emission under excitation at 360 nm was prepared, and a first assay detection of NO₂^- in meat products was tested using a smartphone application. The potential application of the newly developed sensing device containing a highly fluorescent probe should aid in the development of a rapid and inexpensive strategy for NO₂^- detection.

Recent advances of carbon-based nanomaterials (CBNMs) for wastewater treatment: Synthesis and application

Carbon-based nanomaterials (CBNMs) have attracted significant alert due to the affluent science underpinning their implementations associated with a novel mixture of high aspect proportions, greater thermal and electrical performance, outstanding optical features, and high exterior area. CBNMs not only bear assurance in a broad range of implementations in medication, nano and microelectronics, and ecological remedies but may also be utilized in practical laboratory determinations. More specifically, CBNMs perform as an outstanding adsorbent in terminating heavy metal ions (HMI) from wastewater. There is presently a deficiency of powerful threat inspection instruments owing to their complex detection and related deficit in the health risk database. Therefore, our present review concentrates on spreading CBNMs to release pollutants from wastewater. The article wraps the effect of these contaminants and photocatalytic strategies towards treating these mixtures in wastewater, along with their restrictions and challenges, convincing resolutions, and possibilities of these approaches.

In Vitro Study: Synthesis and Evaluation of Fe3O4/CQD Magnetic/Fluorescent Nanocomposites for Targeted Drug Delivery, MRI, and Cancer Cell Labeling Applications

In the present study, first, Fe₃O₄ nanoparticles were functionalized using glutaric acid and then composited with CQDs. Doxorubicin (DOX) drug was loaded to evaluate the performance of the nanocomposite for targeted drug delivery applications. The XRD pattern confirmed the presence of characteristic peaks of CQDs and Fe₃O₄. In the FTIR spectrum, the presence of carboxyl functional groups on Fe₃O₄/CQDs was observed; DOX (positive charge) is loaded onto Fe₃O₄/CQDs (negative charge) by electrostatic absorption. FESEM and AFM images showed that the particle sizes of Fe₃O₄ and CQDs were 23-75 and 1-3 nm, respectively. The hysteresis curves showed superparamagnetic properties for Fe₃O₄ and Fe₃O₄/CQDs (57.3 and 8.4 emu/g). The Fe₃O₄ hysteresis curve showed superparamagnetic properties (Ms and Mr: 57.3 emu/g and 1.46 emu/g. The loading efficiency and capacity for Fe₃O₄/CQDs were 93.90% and 37.2 mg DOX/g MNP, respectively. DOX release from Fe₃O₄/CQDs in PBS showed pH-dependent release behavior where after 70 h at pH 5 and 7.4, about 50 and 21% of DOX were released. Fluorescence images of Fe₃O₄/CQD-treated cells showed that Fe₃O₄/CQDs are capable of labeling MCF-7 and HFF cells. Also, T₂-weighted MRI scans of Fe₃O₄/CQDs in water exhibited high r₂ relaxivity (86.56 mM^-1 S^-1). MTT assay showed that DOX-loaded Fe₃O₄/CQDs are highly biocompatible in contact with HFF cells (viability = 95%), but they kill MCF-7 cancer cells (viability = 45%). Therefore, the synthesized nanocomposite can be used in MRI, targeted drug delivery, and cell labeling.

Effects of nitrogen/bismuth-doping on the photocatalyst composite of carbon dots/titanium dioxide nanoparticles (CDs/TNP) for enhanced visible light-driven removal of diclofenac

The present work demonstrates the coupling of titanium dioxide, TiO₂ nanoparticles (TNP) with N-doped, Bi-doped, and N-Bi co-doped rice husk-derived carbon dots (CDs) via a facile dispersion method, forming respective photocatalyst composites of CDs/TNP, N-CDs/TNP, Bi-CDs/TNP and N-Bi-CDs/TNP. Characterization analyzes verified the successful incorporation of respective CDs samples into TNP, forming photocatalyst composite with narrowed band gap and quenched photoluminescence intensity. Photocatalytic activity of TNP and the respective composites was investigated for photodegradation of diclofenac (DCF) under both simulated sunlight and natural sunlight irradiation. The as-prepared N-Bi-CDs/TNP composite showed the best photocatalytic performance among all composites, able to completely degrade 5 ppm of DCF within 60 min and 180 min under both types of visible light irradiation, respectively. The N-Bi-CDs/TNP composite also showed a TOC removal efficiency up to 87.63%. N-Bi-CDs, worked as photosensitizer and electron reservoir, contributed to the outstanding photocatalytic activity of N-Bi-CDs/TNP, whereby the recombination was prolonged and light absorption was shifted towards the visible light region. Furthermore, the composite of N-Bi-CDs/TNP also demonstrated good stability and reusability over repeated degradation cycles. The photodegradation of DCF resulted into several intermediates, which were identified from LC-MS analysis. The present work could provide an insight on the application of heteroatoms doped and co-doped carbon dots in semiconductor oxide as high performance photocatalysts.

Engineered Magnetic Carbon-Based Adsorbents for the Removal of Water Priority Pollutants: An Overview

This review covers the preparation, characterization, and application of magnetic adsorbents obtained from carbon-based sources and their application in the adsorption of both inorganic and organic pollutants from water. Different preparation routes to obtain magnetic adsorbents from activated carbon, biochar, hydrochar, graphene, carbon dots, carbon nanotubes, and carbon nanocages, including the magnetic phase incorporated on the solid surface, are described and discussed. The performance of these adsorbents is analyzed for the removal of fluoride, arsenic, heavy metals, dyes, pesticides, pharmaceuticals, and other emerging and relevant water pollutants. Properties of these adsorbents and the corresponding adsorption mechanisms have been included in this review. Overall, this type of magnetic adsorbents offers an alternative for facing the operational problems associated to adsorption process in water treatment. However, some gaps have been identified in the proper physicochemical characterization of these adsorbents, the development of green and low-cost preparation methods for their industrial production and commercialization, the regeneration and final disposal of spent adsorbents, and their application in the multicomponent adsorption of water pollutants.

Enhanced removal of As(III) and As(V) from water by a novel zirconium-chitosan modified spherical sodium alginate composite

Most nano-scaled adsorbents have trouble in separating from aqueous solution, thus, a need for new materials of facile separation and predominant adsorption performance has arisen. This present study focused on a novel segregative zirconium-chitosan modified sodium alginate (Zr-CTS/SA) composite preparation and its performance for As(III/V) removal from aqueous solution. The obtained composite presented a spherical structure with a diameter of 2.0-3.0 mm and favorable thermal stability. Experimental data showed that Zr-CTS/SA had considerable adsorbability for As(III) and As(V), the adsorption capacities were enhanced about at least 20 and 6 times separately compared with pristine SA beads. The adsorption processes of As(III) and As(V) could both be described with Langmuir isotherm model and the maximum adsorption capacities reached 43.19 and 76.78 mg g^-1, respectively. The kinetic data of As(III) followed the intra-particle diffusion model while As(V) fitted the pseudo-first-order model. Moreover, the adsorption mechanisms of As(III/V) involved ligand exchange with Cl on the surface of Zr-CTS/SA, another reaction pathway for As(V) was the electrostatic attraction with protonated -OH and -NH₂ groups. Note that the employment of Zr-CTS/SA in low-concentration arsenic solution exhibited a residue concentration as low as the 10 μg L^-1 WHO guideline for drinking water.

Enhanced photocatalytic degradation of Rhodamine B, antibacterial and antioxidant activities of green synthesised ZnO/N doped carbon quantum dot nanocomposites

In order to explore an alternative photocatalyst for environmental remediation, we report a two-step process for the synthesis of zinc oxide/nitrogen doped carbon quantum dot nanocomposites (ZnO@NCQD NCs).

Abidin Z. Sustainable Development of Enhanced Luminescence Polymer-Carbon Dots Composite Film for Rapid Cd2+ Removal from Wastewater

As a remedy for environmental pollution, a versatile synthetic approach has been developed to prepare polyvinyl alcohol (PVA)/nitrogen-doped carbon dots (CDs) composite film (PVA-CDs) for removal of toxic cadmium ions. The CDs were first synthesized using carboxymethylcellulose (CMC) of oil palms empty fruit bunch wastes with the addition of polyethyleneimine (PEI) and then the CDs were embedded with PVA. The PVA-CDs film possess synergistic functionalities through increasing the content of hydrogen bonds for chemisorption compared to the pure CDs. Optical analysis of PVA-CDs film was performed by ultraviolet-visible and fluorescence spectroscopy. Compared to the pure CDs, the solid-state PVA-CDs displayed a bright blue color with a quantum yield (QY) of 47%; they possess excitation-independent emission and a higher Cd2+ removal efficiency of 91.1%. The equilibrium state was achieved within 10 min. It was found that adsorption data fit well with the pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption uptake was 113.6 mg g-1 at an optimal pH of 7. Desorption experiments showhe that adsorbent can be reused fruitfully for five adsorption-desorption cycles using 0.1 HCl elution. The film was successfully applied to real water samples with a removal efficiency of 95.34% and 90.9% for tap and drinking water, respectively. The fabricated membrane is biodegradable and its preparation follows an ecofriendly green route.

Alkali-cation-incorporated and functionalized iron oxide nanoparticles for methyl blue removal/decomposition

Enhancing the rate of decomposition or removal of organic dye by designing novel nanostructures is a subject of intensive research aimed at improving waste-water treatment in the textile and pharmaceutical industries. Despite radical progress in this challenging area using iron-based nanostructures, enhancing stability and dye adsorption performance is highly desirable. In the present manuscript alkali cations are incorporated into iron oxide nanoparticles (IONPs) to tailor their structural and magnetic properties and to magnify methyl blue (MB) removal/decomposition capability. The process automatically functionalizes the IONPs without any additional steps. The plausible mechanisms proposed for IONPs incubated in alkali chloride and hydroxide solutions are based on structural investigation and correlated with the removal/adsorption capabilities. The MB adsorption kinetics of the incubated IONPs is elucidated by the pseudo second-order reaction model. Not only are the functional groups of -OH and -Cl attached to the surface of the NPs, the present investigation also reveals that the presence of alkali cations significantly influences the MB adsorption kinetics and correlates with the cation content and atomic polarizability.

Linear and nonlinear behavior of crosslinked chitosan/N-doped graphene quantum dot nanocomposite films in cadmium cation uptake

In this research, crosslinked nanocomposite (NC) films involving chitosan (CS) and various percentages of nitrogen-doped graphene quantum dot (NGQD) were prepared via ultrasonic acoustic accompanied by adding glutaraldehyde as a crosslinking agent (henceforth nominated as CCS/NGQD NC). The objective of this study is the design of a safe adsorbent of CCS/NGQD NC under easy and low-cost conditions to investigate the mechanisms of Cd(II) ion sorption and find an appropriate model for the kinetics of removal. By comparing adsorption ability of CCS/NGQD NC films 2, 5 and 8 wt% under the same conditions, the CCS NC film with 5 wt% of NGQD was selected as the best mass ratio to investigate the adsorption process. To understand the nature of the sorption behavior, the experimental data were used to calculate pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic models, and various isotherm models in linear and nonlinear regression. In addition, some error functions were applied to detect, either linear or nonlinear model is suitable to examine the experimental data and prevent any huge mistakes. The linear Freundlich equation well describes the uptake of Cd(II) ion by CCS film and CCS/NGQD NC film 5 wt%. Based on linear Langmuir, the maximum adsorption capacities of CCS film and CCS/NGQD NC film 5 wt% were 34.46 and 35.00 mg·g^-1, respectively. Kinetic analysis indicates that the mechanism of removal is described by nonlinear pseudo-second order model for CCS film and linear pseudo-second order model for the CCS/NGQD NC film 5 wt%. Also, thermodynamic parameters were analyzed in different temperatures. The obtained thermodynamic values prove that Cd(II) ion adsorption on both adsorbents is feasible, spontaneous and endothermic.

Nitrogen-Doped Nanoporous Carbon Nanospheroids for Selective Dye Adsorption and Pb(II) Ion Removal from Waste Water

In the presence of melamine and block copolymers, namely, F108, F127, and P123, nitrogen-doped nanoporous carbon nanospheroids (N@CNSs) were synthesized by the hydrothermal process. The F127-modified sample (CNF127) exhibits the maximum Brunauer-Emmett-Teller (BET) surface area of 773.4 m2/g with a pore volume of 0.877 cm3/g. The microstructural study reveals that nanospheroids of size 50-200 nm were aggregated together to form a chainlike structure for all triblock copolymer-modified samples. The X-ray photoelectron spectroscopy study shows the binding energies of 398.33 and 400.7 eV attributed to sp2 (C-N=C)- and sp3 (C-N)-hybridized nitrogen-bonded carbons, respectively. The synthesized N@CNS samples showed selective adsorption of organic dye methylene blue (MB) in the presence of methyl orange (MO) as well as Pb(II) ion removal from contaminated water. The adsorptions for MB and Pb(II) ions followed pseudo-first-order and pseudo-second-order kinetic models, respectively. The sample CNF127 showed the highest adsorption of 73 and 99.82 mg/g for MB and Pb(II) adsorptions, respectively. The adsorption capacity for MB of the copolymer-modified samples follows the order CNF127 > CNP123 > CNF108, which corroborated with the mesoporosity as well as nitrogen content of the corresponding samples. The maximum % adsorption of Pb(II) follows the order CNF127 (99.82%) > CNF108 (98.74%) > CNP123 (91.82%), and this trend is attributed to the BET surface area of the corresponding samples. This study demonstrates multicomponent removal of water pollutants, both organic dyes and inorganic toxic metal ions.