Removal of uranium (VI) from water by the action of microwave-rapid green synthesized carbon quantum dots from starch-water system and supported onto polymeric matrix

Microbial etch: A novel construction method of functionalized biochar for enhanced uranium extraction in radioactive wastewater

Nuclear energy is playing an increasingly important role on the earth, but the nuclear plants leaves a legacy of radioactive waste pollution, especially uranium-containing pollution. Straw biochar with wide sources, large output, low cost, and easy availability, has emerged as a promising material for uranium extraction from radioactive wastewater, but the natural biomass with suboptimal structure and low content of functional groups limits the efficiency. In this work, microbial etch was first came up to regulate the biochar's structure and function. The surface of the biochar becomes rougher and more microporous, and the mineral contents (Ca, P) indirectly increased by microbial etch. The biochar was modified by calcium phosphate and exhibited a remarkable uranium extraction capacity of 590.8 mg g-1 (fitted value). This work provides a cost-effective and sustainable method for preparing functionalized biochar via microbial etch, which has potential for application to uranium extraction from radioactive wastewater.

Progress and Obstacles in Employing Carbon Quantum Dots for Sustainable Wastewater Treatment

We explored the potential of carbon quantum dots (CQDs) as novel materials for wastewater treatment and their role towards environmental sustainability. The advantages of CQDs over other carbon-based materials, when synthesized using the same precursor material and for the same contaminant, are discussed, enabling future researchers to choose the appropriate material. CQDs have demonstrated exceptional adaptability in various wastewater treatment, acting as efficient adsorbents for contaminants, exhibiting excellent photocatalytic properties for degradation of organic pollutants, and functioning as highly sensitive sensors for water quality monitoring. We found that bottom-up approach has better control over particle size (resulting CQDs: 1-4 nm), whereas top-down synthesis approach (resulting CQDs: 2-10 nm) have more potential for large scale applications and tunability. Transmission electron microscopy (TEM) remains the most expensive characterization technique, which provides the best resolution of the CQD's surface. The study emphasizes on the environmental impact and safety considerations pertaining to CQDs by emphasizing the need for thorough toxicity evaluation, and necessary environmental precautions. The study identifies the lacunae pertaining to critical challenges in practical implementation of CQDs, such as scalability, competition of co-existing contaminants, and stability. Finally, future research directions are proposed, advocating green synthesis approaches, tailored surface functionalization, and, lowering the overall cost for analysis, synthesis and application of CQDs.

Carbon and graphene quantum dots based architectonics for efficient aqueous decontamination by adsorption chromatography technique - Current state and prospects

Aquatic ecosystems and potable water are being exploited and depleted due to urbanization and the encouragement of extensive industrialization, which induces the scarcity of pure water. However, current decontamination methods are limited and inefficient. Various innovative remediation strategies with novel nanomaterials have recently been demonstrated for wastewater treatment. Carbon dots (C-dots) and graphene quantum dots (GQ-dots) are the most recent frontiers in carbon nanomaterial-based adsorption studies. C-dots are extremely small (1-10 nm) quasi-spherical carbon nanoparticles (mostly sp3 hybridized carbon), whereas GQ-dots are fragments of graphene (1-20 nm) composed of primarily sp2 hybridized carbon. This article highlights the function of C-dots and GQ-dots with their specifications and characteristics for the efficient removal of organic and inorganic contaminants in water via adsorption chromatography. The alteration of adsorption attributes with the hybrid blending of these dots has been critically analyzed. Moreover, various top-down and bottom-up approaches for synthesizing C-dots and GQ-dots, which ultimately affect their morphology and structure, are described in detail. Finally, we review the research deficit in the adsorption of diverse pollutants, fabrication challenges, low molecular weight, self-agglomeration, and the future of the dots by providing research prospects and selectivity and sensitivity perspectives, the importance of post-adsorption optimization strategies and the path toward scalability at the tail of the article.

The efficient uptake of uranium by amine-functionalized β-cyclodextrin supported fly ash composite from polluted water

A novel polyethyleneimine/polydopamine-functionalized β-cyclodextrin supported fly ash adsorbent (PEI/PDA/β-CD/FA) had been synthesized to uptake uranium from polluted water. At pH = 5.0 and T = 298 K, the uranium uptake efficiency and capacity of PEI/PDA/β-CD/FA reached to 98.7 % and 622.8 mg/g, respectively, which were much higher than those of FA (71.4 % and 206.7 mg/g).The excellent uranium uptake properties of PEI/PDA/β-CD/FA could be explained by three points: (1) using β-CD as a supporting material could effectively avoid the aggregation of FA and improve the hydrophily of FA; (2) the unique cavity structure of β-CD could form chelates with uranyl ions; (3) the formation of PEI/PDA co-deposition coating on FA further enhanced the affinity of FA to UO22+. With the presence of interfering ions, the uptake efficiency of PEI/PDA/β-CD/FA for uranium was still up to 94.5 % after five cycles, indicating the high selectively and recoverability of PEI/PDA/β-CD/FA. In terms of the results of characterizations, uranium was captured by PEI/PDA/β-CD/FA via electrostatic attraction, hydrogen bond, coordination and complexation. To sum up, PEI/PDA/β-CD/FA was expected to be used for actual sewage treatment owing to its excellent uranium uptake efficiency/capacity, selectivity, cycle stability and feasibility of actual application.

Carbon quantum dots assisted BiFeO3@BiOBr S-scheme heterojunction enhanced peroxymonosulfate activation for the photocatalytic degradation of imidacloprid under visible light: Performance, mechanism and biotoxicity

A novel S-scheme heterojunction photocatalyst carbon quantum dots (CQDs)/BiFeO3/BiOBr (CBB) was synthesized via a facile hydrothermal method, which was highly effective in activating peroxymonosulfate (PMS) to photodegrade imidacloprid (IMD) (one of the typical neonicotinoid insecticides (NEOs)) under visible light irradiation. Based on the physicochemical and photoelectrochemical analysis, the super photocatalytic performance of the CBB photocatalyst was contributed to the enhanced separation and transfer of photogenerated electrons (e-) and holes (h+), the activation of PMS by reactive species, and the wider light absorption range induced by CQDs. Moreover, the intermediate products and possible photodegradation pathways of IMD were confirmed through high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS) detection and density functional theory (DFT) calculations. Although the photodegradation of IMD in the CBB/PMS/Vis system can be affected by the water quality parameters (i.e., acid group anions, pH, and the presence of humic acid (HA)), the synthesized CBB photocatalyst showed excellent photocatalytic performance in multiple natural water samples. This study provides a new idea to construct an effective and efficient heterojunction photocatalyst, which may have great advantages in photocatalytic degradation of NEOs and possibly other emerging contaminants in the aquatic environment.

Enhanced removing of phosphate ions from agricultural drainage wastewater by using microwave-assisted synthesized attapulgite (Fullers earth) @carboxymethylcellulose nanocomposite

Contamination of various water resources with phosphate pollutant owing to the excessive use of phosphate fertilizers was labeled by dangerous consequences. Most of the water remediation methods are not efficient for phosphate recovery and always generate secondary wastes. Therefore, the current study is aimed to prepare a novel ecofriendly and sustainable APT500@CMC nanocomposite via simple covalent binding of thermally treated attapulgite clay at 500 °C (APT500) with carboxymethyl cellulose (CMC) using microwave irradiation process. The assembled nanocomposite was confirmed by diverse techniques. The optimum conditions for efficient 10, 25 and 50 mg/L PO43- removal were detected at pH 3, time 30 min, temperature 25 °C and mass 200 mg. The kinetic and isotherms were fitted both to a combination of pseudo 1st - 2nd orders and Langmuir model, while thermodynamic parameters verified PO43- removal via spontaneous and exothermic reaction behavior. The mode of interaction and binding of PO43- ions onto the surface of APT500@CMC were suggested via ion-pair interaction process. Excellent PO43- recovery (98.8 %) from real agricultural drainage wastewater was established. The explored APT500@CMC afforded good stability for five regeneration cycles. Therefore, the collected results confirm the validity of APT500@CMC for excellent removal of PO43- from real agricultural drainage wastewater.

Cr(VI) and doxorubicin adsorptive capture by a novel bionanocomposite of Ti-MOF@TiO2 incorporated with watermelon biochar and chitosan hydrogel

Biodegradable polymers, biochars and metal organic frameworks (MOFs) have manifested as top prospects for elimination of harmful pollutants. In the current study, Ti-MOF was synthesized and decorated with TiO2 nanoparticles, then embedded into watermelon peel biochar and functionalized with chitosan hydrogel to produce Ti-MOF@TiO2@WMPB@CTH. Various instruments were employed to assure the effective production of the bionanocomposite. The HR-TEM and SEM studies referred to excellent surface porosity and homogeneity of Ti-MOF@TiO2@WMPB@CTH bionanocomposite, with 51.02-74.23 nm. Based on the BET analysis, the mesoporous structure has a significant surface area of 366.04 m2 g-1 and a considerable total pore volume of 11.38 × 10-2 cm3 g-1, with a mean pore size of 12.434 nm. Removal of doxorubicin (DOX) and hexavalent chromium (Cr(VI)) was examined under various experimentations. Pseudo-second order kinetic models in addition to Langmuir isotherm offered the best fitting. Thermodynamic experiments of the two contaminants demonstrated spontaneous and endothermic interactions. After five subsequent adsorption and desorption cycles, Ti-MOF@TiO2@WMPB@CTH bionanocomposite demonstrated an exceptional recyclability for the elimination of DOX and Cr(VI) ions, reaching 97.96 % and 95.28 %, respectively. Finally, the newly designed Ti-MOF@TiO2@WMPB@CTH bionanocomposite demonstrated a high removing efficiency of Cr(VI) ions and DOX from samples of real water.

Hexavalent chromium removal from aqueous medium by ternary nanoadsorbent: A study of kinetics, equilibrium, and thermodynamic mechanism

Although many studies have focused on chromium removal from aqueous media by ternary Nano adsorbents, still the integrated kinetics, equilibrium, and thermodynamic mechanisms of chromium removal remain unknown. Thus in this study, we have synthesized a novel ternary oxide nanocomposite comprising iron, manganese, and stannous (Fe2O3-MnO2-SnO2) in a facile method as a promising adsorbent for the removal of Cr(VI) from an aqueous medium. The Fe2O3-MnO2-SnO2 system was firstly characterized by FTIR, XRD, TGA, BET, and SEM/EDX. The effect of parameters, for instance, pH, temperature, initial Cr(VI) intensity, and adsorbent dose, have been examined to optimize the Cr(VI) adsorption performance. The adsorption of Cr(VI) onto Fe2O3-MnO2-SnO2 nanoadsorbent is associated with an adsorption/reduction mechanism. Using an initial Cr(VI) intensity of 50 mg L-1, 200 rpm agitation, 2.5-g L-1 of adsorbent, pH 2, 90 minutes adsorption time, and 298 K temperature, a maximum adsorption capability of 69.2 mg Cr(VI) g-1 for Fe2O3-MnO2-SnO2 was obtained. Models of pseudo-2nd-order kinetics and Langmuir's isotherm were best suited to the investigated data. Besides, thermodynamic parameters show that Cr(VI) adsorption onto Fe2O3-MnO2-SnO2 was random and dominated by entropy. The reusability of Fe2O3-MnO2-SnO2 was found to be consistently high (remaining above 80% for Cr(VI)) over four adsorption-desorption cycles. Chromium adsorption from the tannery wastewater was achieved 91.89% on Fe2O3-MnO2-SnO2. Therefore, Fe2O3-MnO2-SnO2 nanoparticles, being easy to be synthesized, reusable and having improved adsorption capability with higher surface area, could be a desirable option for removing Cr(VI) from aqueous environments.

"Two-in-one" dual-function luminescent MOF hydrogel for onsite ultra-sensitive detection and efficient enrichment of radioactive uranium in water

In consideration of the severe hazards of radioactive uranium pollution and the growing demand of uranium resources, the novel sensor/adsorbent composite was creatively developed to integrate the dual functions for on-site detection of uranium contamination and efficient recovery of uranium resources. By hybridizing the luminescent 3D terbium (III) metal-organic framework (Tb-MOF) with sodium alginate (SA) gel using terbium (III) as cross-linker, the Tb-MOF/Tb-AG was fabricated with multi-luminescence centers and sufficient binding sites for uranium. Notably, the ultra-high sensitivity with detection limit as low as 1.2 ppt was achieved, which was 4 orders of magnitude lower than the uranium contamination standard in drinking water (USEPA) and even comparable to the sensitivity of the ICP-MS. Furthermore, the very wide quantification range (1.0 ×10^-9-5.0 ×10^-4 mol/L), remarkable adsorption capacity (549.0 mg/g) and outstanding anti-interference ability have been achieved without sophisticated sample preparation procedures. Applied in complex natural water samples from Uranium Tailings and the Pearl River, this method has shown good detection accuracy. The ultra high sensitivity and great adsorption capacity for uranium could be ascribed to the synergistic coordination, hydrogen bonding and ion exchange between uranium and Tb-MOF/Tb-AG. The mechanisms were explored by infrared spectroscopy, batch experiments, X-ray photoelectron studies and energy dispersive spectroscopic studies. In addition, the Tb-MOF/Tb-AG can be reused for uranium adsorption.

A comparative study for the removal of reactive red 49 (RR49) and reactive yellow 15 (RY15) using a novel electrode by electrocoagulation technique

The present work deals with the investigation of the efficiency of the electrocoagulation (EC) technique in the removal of two different reactive dyes as a simple, durable, and cost-effective technique for wastewater treatment. The difference in structure between Reactive Red 49 (RR49) and Reactive Yellow 15 (RY15) is explored during the treatment process through the use of a novel design of electrodes. The optimum conditions obtained were 80 and 60 mg/L of initial dye concentrations, pH of 5.9 and 4 for RR49 and RY15, respectively, 0.5 g of NaCl electrolyte, and 900 and 500 rpm of stirring rate for RR49 and RY17 dyes respectively, which led to the highest percent removal (98.5%) for both dyes. The suitable temperatures were 20 and 30 °C for RR49 and RY15, respectively. The thermodynamic parameters were designated, and it was a spontaneous process for both dyes. The removal process was designated to pseudo- second-order for the RR49 dye and pseudo- first-order for the RY15 dye and fitted to the Langmuir model. Analysis of Variance (ANOVA) was presented to assess the variation of the outcomes attained from each factor.

Green and rapid synthesis of biomass carbon dot-based fluorescence sensing for the sensitive determination of oxytetracycline

Eco-friendly biomass carbon dots (CDs) with blue fluorescence emission were rapidly synthesized by a microwave method. Based on the inner filter effect (IFE) between oxytetracycline (OTC) and CDs, the fluorescence of CDs could be selectively quenched by OTC. Therefore, a simple and time-saving fluorescence sensing system for the detection of OTC was established. Under optimal experimental conditions, the concentration of OTC showed a good linear relationship with fluorescence quenching values (ΔF) in the range of 4.0-100.0 μmol L^-1, a corresponding correlation coefficient (r) of 0.9975, and a detection limit of 0.12 μmol L^-1. The method has the advantages of low cost, time-saving, and green synthesis that could be used for the determination of OTC. Moreover, possessing high sensitivity and specificity, this fluorescence sensing method was successfully applied for detecting OTC in milk, indicating its potential applications in food safety.

Sustainable removal of uranium from acidic wastewater using various mineral raw materials

Various types of plutonic and volcanic rocks and their alteration products from Greece (serpentinite, magnesite and andesite), have been used for sustainable removal of Uranium (U) from the acidic drainage of Kirki mine, as well as for the pH increase of the polluted solutions. In this light, this study aims at the further understanding and improvement of the ecofriendly reuse of sterile, natural raw materials (including those remaining through industrial processing and engineering testing of aggregate rocks), for remediation of acid mine drainage. The selected rocks constitute such residues of sterile materials were used as filters in experimental continuous flow devices in the form of batch-type columns, in order to investigate acidic remediation properties with special focus on U removal. The initial pH of the wastewater was 2.90 and increased after seven (7) days of experimental application and more specifically from the fourth day onwards. Uranium removal became quantitatively significant once pH reached the value of 5.09. The volcanic rocks appeared to be more effective for U removal than the plutonic ones because of microtextural differences. However, optimum U removal was mainly achieved by serpentinite: while the raw materials rich in Mg strongly reacted and remediated the pH of the drainage water waste. Furthermore, the increase of pH values due to the presence of mineral raw materials, provided increased oxidation potential which deactivated the toxic load of metals, particularly U. Consequently, batch-type serpentinite reaction with the tailing fluid caused a drop in U concentration from an initial value of 254 ppb to the one of 8 ppb, which corresponds to 97% of removal. Andesite presented the second best reactant for experimental remediation, especially when it was mixed with magnetically separated mineral fractions. Despite the fact that the proposed methodology is currently at a relatively low Technology Readiness Level (TRL), it carries the potential to become an extremely effective and low-cost alternative to conventional environmental restoration technologies.

Polysaccharide-based C-dots and polysaccharide/C-dot nanocomposites: fabrication strategies and applications

C-dots are a new class of materials with vast applications. The synthesis of bio-based C-dots has attracted increasing attention in recent years. Polysaccharides being the most abundant natural materials with high biodegradability and no toxicity have been the focus of researchers for the synthesis of C-dots. C-dots obtained from polysaccharides are generally fabricated via thermal procedures, carbonization, and microwave pyrolysis. Small size, photo-induced electron transfer (PET), and highly adjustable luminosity behavior are the most important physical and chemical properties of C-dots. However, C-dot/polysaccharide composites can be introduced as a new generation of composites that combine the features of both C-dots and polysaccharides having a wide range of applications in biomedicines, biosensors, drug delivery systems, etc. This review demonstrates the features, raw materials, and methods used for the fabrication of C-dots derived from different polysaccharides. Furthermore, the properties, applications, and synthesis conditions of various C-dot/polysaccharide composites are discussed in detail.

Research Progress in the Synthesis of Carbon Dots and Their Application in Food Analysis

Food safety is connected to public health, making it crucial to protecting people's health. Food analysis and detection can assure food quality and effectively reduce the entry of harmful foods into the market. Carbon dots (CDs) are an excellent choice for food analysis and detection attributable to their advantages of good optical properties, water solubility, high chemical stability, easy functionalization, excellent bleaching resistance, low toxicity, and good biocompatibility. This paper focuses on the optical properties, synthesis methods, and applications of CDs in food analysis and detection, including the recent advances in food nutritional composition analysis and food quality detection, such as food additives, heavy metal ions, foodborne pathogens, harmful organic pollutants, and pH value. Moreover, this review also discusses the potentially toxic effects, current challenges, and prospects of CDs in basic research and applications. We hope that this review can provide valuable information to lay a foundation for subsequent research on CDs and promote the exploration of CDs-based sensing for future food detection.

Polymeric biomolecules based nanomaterials: Production strategies and pollutant mitigation as an emerging tool for environmental application

The ever-exploding global population coupled with its anthropogenic impact has imparted unparalleled detrimental effects on the environment and mitigating them has emerged as the prime challenge and focus of the current century. The niche of nanotechnology empowered by composites of biopolymers in the handling of xenobiotics and environmental clean-up has an unlimited scope. The appositeness of biopolymer-nanoparticles (Bp-NPs) for environmental contaminant mitigation has received unique consideration due to its exclusive combination of physicochemical characteristics and other attributes. The current review furnishes exhaustive scrutiny of the current accomplishments in the development of Bp-NPs and biopolymer nanomaterials (Bp-NMs) from various polymeric biomolecules. Special attention was provided for polymeric biomolecules such as cellulose, lignin, starch, chitin, and chitosan, whereas limited consideration on gelatin, alginate, and gum for the development of Bp-NPs and Bp-NMs; together with coverage of literature. Promising applications of tailored biopolymer hybrids such as Bp-NPs and Bp-NMs on environmentally hazardous xenobiotics handling and pollution management are discussed as to their notable environmental applications.

Adsorptive removal of Ag/Au quantum dots onto covalent organic frameworks@magnetic zeolite@arabic gum hydrogel and their catalytic microwave-Fenton oxidative degradation of Rifampicin antibiotic

Recent progress in nanotechnology via incorporation of small particle size as quantum dots (QDs) (1-10 nm) in many industrial activities and commercial products has led to significant undesired environmental impacts. Therefore, QDs removal from wastewater represents an interesting research topic with a lot of challenges for scientists and engineers nowadays. In this work, the coagulative removal of metal quantum dots as silver and gold from industrial water samples is explored. A novel biosorbent was assembled via binding of covalent organic frameworks (COFs) with magnetic zeolite and Arabic gum hydrogel (COFs@MagZ@AGH) as a promising removal material for Ag-QDs and Au-QDs. This was fully characterized by EDX, SEM, TEM, FT-IR, XPS, XRD and surface area and applied in coagulative removal of Au-QDs and Ag-QDs in presence of several experimental factors as pH, presence of other electrolytes, stirring time, initial QDs concentration, coagulant dosage, and temperature in order to optimize the removal processes. At optimum conditions, COFs@MagZ@AGH was able to recover 99.19% and 87.57% of Ag-QDs and Au-QDs QDs, respectively via chemical adsorption mechanism with perfect fitting to pseudo-second order model. Reuse of the recovered Ag/Au-QDs@COFs@MagZ@AGH as efficient catalysts in catalytic degradation of Rifampicin antibiotic (Rf) from water was additionally investigated and optimized via microwave-Fenton catalysts with excellent oxidative degradation efficiency (100%). Reusability and applicability of the biosorbent (COFs@MagZ@AGH) and catalysts (Ag/Au-QDs@COFs@MagZ@AGH) in real industrial water samples were also explored and successfully accomplished.

Covalent and Non-covalent Functionalized Nanomaterials for Environmental Restoration

Nanotechnology has emerged as an extraordinary and rapidly developing discipline of science. It has remolded the fate of the whole world by providing diverse horizons in different fields. Nanomaterials are appealing because of their incredibly small size and large surface area. Apart from the naturally occurring nanomaterials, synthetic nanomaterials are being prepared on large scales with different sizes and properties. Such nanomaterials are being utilized as an innovative and green approach in multiple fields. To expand the applications and enhance the properties of the nanomaterials, their functionalization and engineering are being performed on a massive scale. The functionalization helps to add to the existing useful properties of the nanomaterials, hence broadening the scope of their utilization. A large class of covalent and non-covalent functionalized nanomaterials (FNMs) including carbons, metal oxides, quantum dots, and composites of these materials with other organic or inorganic materials are being synthesized and used for environmental remediation applications including wastewater treatment. This review summarizes recent advances in the synthesis, reporting techniques, and applications of FNMs in adsorptive and photocatalytic removal of pollutants from wastewater. Future prospects are also examined, along with suggestions for attaining massive benefits in the areas of FNMs.

Halogen-Doped Carbon Dots: Synthesis, Application, and Prospects

Carbon dots (CDs) have many advantages, such as tunable photoluminescence, large two-photon absorption cross-sections, easy functionalization, low toxicity, chemical inertness, good dispersion, and biocompatibility. Halogen doping further improves the optical and physicochemical properties of CDs, extending their applications in fluorescence sensors, biomedicine, photocatalysis, anti-counterfeiting encryption, and light-emitting diodes. This review briefly describes the preparation of CDs via the “top-down” and “bottom-up” approaches and discusses the preparation methods and applications of halogen (fluorine, chlorine, bromine, and iodine)-doped CDs. The main challenges of CDs in the future are the elucidation of the luminescence mechanism, fine doping with elements (proportion, position, etc.), and their incorporation in practical devices.

A Strategic Review on Carbon Quantum Dots for Cancer-Diagnostics and Treatment

The understanding of the genesis of life-threatening cancer and its invasion calls for urgent development of novel technologies for real-time observations, early diagnosis, and treatment. Quantum dots (QDs) grabbed the spotlight in oncology owing to their excellent photostability, bright fluorescence, high biocompatibility, good electrical and chemical stability with minimum invasiveness. Recently, carbon QDs (CQDs) have become popular over toxic inorganic QDs in the area of bioimaging, biosensing, and drug delivery. Further, CQDs derived from natural sources like biomolecules and medicinal plants have drawn attention because of their one-pot, low-cost and ease of synthesis, along with remarkable tunable optical properties and biocompatibility. This review introduces the synthesis and properties of CQDs derived from natural sources, focusing on the applicability of CQD-based technologies as nano-theranostics for the diagnosis and treatment of cancer. Furthermore, the current issues and future directions for the transformation of CQDs-based nanotechnologies to clinical applications are highlighted.

Iron phosphonate for highly efficient capture of U(VI) from acidic solution

In this study, a novel, high surface area iron phosphonate (IP) for highly efficient adsorption of uranyl ion in acidic medium was described. The as-prepared IP was amorphous with its specific surface area and total pore volume as high as 268 m²/g and 1.04 cm³/g, respectively. Particularly, the as-prepared IP with ferrous ions and oxygen, nitrogen-bearing functional groups prove excellent U(VI) adsorption capacity (154.6 mg/g) as compared to that of amorphous FePO₄ (67.3 mg/g) and Fe₃(PO₄)₂(H₂O)₈ (33.8 mg/g). Surprising, the saturation adsorption capacity could achieve up to 353.9 mg/g. Besides, the IP also had a fast adsorption rate for attaining adsorption equilibrium within 20 min, and followed pseudo-second-order kinetic and Freundlich models. Moreover, both the Dubinin-Radushkevich isotherm adsorption model and the value of enthalpy indicated a chemisorption process. Otherwise, the Na⁺-independent U(VI) adsorption on IP and the adsorption-desorption isotherm studies revealed that inner-layer surface complexation is the control step for U(VI) adsorption process, and the adsorbent featured an irreversible adsorption process. The structure and functional groups of the adsorbent remained unchanged after capture of U(VI). Further, X-ray photoelectron spectra (XPS) analysis demonstrated that the capture mechanism of U(VI) on IP from acidic aqueous solution was due to not only redox reaction, but also ascribed to the coordinated chemical adsorption.

Adsorption behavior of silver quantum dots by a novel super magnetic CoFe2O4-biochar-polymeric nanocomposite

Recent industrial development and research progress in nanotechnology have led to the release of a number of nanomaterials with particle sizes (1-10 nm) which are categorized as quantum dots (QDs) in aquatic system. Disposal away of such QDs will cause potential pollution to the environment. Therefore, removal of disposed QDs from wastewater represents a challenging research subject for scientists and engineers. Hence, the objective of this study is devoted to assess the process of coagulative removal of silver quantum dots (Ag-QDs), as an example, from water by a novel super magnetic nanocomposite. Such material was aimed to prepare from the chemical combination and reaction of a generated Citrus sinensis and Citrus reticulata peels biochar (SMCsr-B) with spinel cobalt ferrite (CoFe₂O₄) as a super-magnetic source. The produced (SMCsr-B) was then crosslinked with polyurea-formaldehyde polymer (PUF) using EDA in only two minutes via microwave irradiation to produce (SMCsr-B/PUF). The SEM, EDX, FT-IR, XRD, and XPS analyses of the assembled (SMCsr-B/PUF) nanocomposite were acquired to confirm surface morphology and chemical structure. Controlling experimental factors were investigated as pH, time, and Ag-QDs pollutant concentration using microwave irradiative removal technique to establish the efficiency of coagulative adsorption of Ag-QDs onto (SMCsr-B/PUF). The solution (pH 5) was proved to exhibit the higher removal percentages of Ag-QDs in 15-25 s. SMCsr-B/PUF nanocomposite exhibited high removal efficiency as 93.12%, 92.39% and 92.48% upon using 20, 40 and 60 mg L^-1 of Ag-QDs, respectively in presence of 10 mM NaCl. The kinetic and equilibrium adsorption data were best fitted to Freundlich model. The prepared SMCsr-B/PUF was successfully utilized as an efficient super magnetic nanocomposite for removal and recovery of Ag-QDs from aqueous environment.

Graphene-based materials for the adsorptive removal of uranium in aqueous solutions

Ground water contamination by radioactive elements has become a critical issue that can pose significant threats to human health. Adsorption is the most promising approach for the removal of radioactive elements owing to its simplicity, effectiveness, and easy operation. Among the plethora of functional adsorbents, graphene oxide and its derivatives are recognized for their excellent potential as adsorbent with the unique 2D structure, high surface area, and intercalated functional groups. To learn more about their practical applicability, the procedures involved in their preparation and functionalization are described with the microscopic removal mechanism by GO functionalities across varying solution pH. The performance of these adsorbents is assessed further in terms of the basic performance metrics such as partition coefficient. Overall, this article is expected to provide valuable insights into the current status of graphene-based adsorbents developed for uranium removal with a guidance for the future directions in this research field.

Highly fluorescent carbon dots as novel theranostic agents for biomedical applications

As an emerging fluorescent nanomaterial, carbon dots (CDs) exhibit many attractive physicochemical features, including excellent photoluminescence properties, good biocompatibility, low toxicity and the ability to maintain the unique properties of the raw material. Therefore, CDs have been intensively pursued for a wide range of applications, such as bioimaging, drug delivery, biosensors and antibacterial agents. In this review, we systematically summarize the synthesis methods of these CDs, their photoluminescence mechanisms, and the approaches for enhancing their fluorescence properties. Particularly, we summarize the recent research on the synthesis of CDs from drug molecules as raw materials and introduce the representative application aspects of these fascinating CDs. Finally, we look into the future direction of CDs in the biomedical field and discuss the challenges encountered in the current development.

Two Fascinating Polysaccharides: Chitosan and Starch. Some Prominent Characterizations for Applying as Eco-Friendly Food Packaging and Pollutant Remover in Aqueous Medium. Progress in Recent Years: A Review

The call to use biodegradable, eco-friendly materials is urgent. The use of biopolymers as a replacement for the classic petroleum-based materials is increasing. Chitosan and starch have been widely studied with this purpose: to be part of this replacement. The importance of proper physical characterization of these biopolymers is essential for the intended application. This review focuses on characterizations of chitosan and starch, approximately from 2017 to date, in one of their most-used applications: food packaging for chitosan and as an adsorbent agent of pollutants in aqueous medium for starch.

Gold nanoparticles-mediated ratiometric fluorescence aptasensor for ultra-sensitive detection of Abscisic Acid

Herein, a novel ratiometric aptasensor based on carbon quantum dots@2-Methylimidazole zinc salt (CQDs@ZIF-8) and aptamer-functionalized gold nanoparticles (Apt-AuNPs) was developed for highly sensitive detection of ABA by fluorescence spectrometry. The CQDs@ZIF-8 nanomaterials displayed dual-emission properties at 490 nm and 657 nm with excitation at 420 nm were synthesized for the first time. ZIF-8 not only served as an anchor point for CQDs but also acted as a modulator to regulate fluorescence signals of CQDs. Interestingly, introduction of ZIF-8 changed the quenching properties of the AuNPs on CQDs. The AuNPs quenched the fluorescence of CQDs@ZIF-8 at 490 nm but not at the second peak of 657 nm. Few studies have been reported on the ineffectiveness of AuNPs in fluorescence quenching as far as we know. In this study, we found that incorporation of ABA triggered the aggregation of AuNPs due to the specific ABA-aptamer recognition and this changed the fluorescence intensity of the ratiometric probe (CQDs@ZIF-8@Apt-AuNPs). The proposed probe increased the sensitivity and selectivity of determining ABA levels in rice seeds in the range of 0.100-150 ng/mL with an LOD of 30.0 ng/L. Importantly, the method proposed here offers a new unique strategy for the construction of ratiometric probes and ultra-sensitive measurement of biomolecules.

Facile synthesis of orange fluorescence multifunctional carbon dots for label-free detection of vitamin B12 and endogenous/exogenous peroxynitrite

In this work, orange emission fluorescent multifunctional carbon dots (O-CDs) were designed for the label-free detection of vitamin B₁₂ (VB₁₂)，endogenous/exogenous peroxynitrite (ONOO^-) sensing, cell imaging, and fluorescent flexible film preparation. The O-CDs with excitation-independent were prepared using safranine T and ethanol as precursors via one-step hydrothermal process. VB₁₂ was utilized as a quencher to quench the fluorescence of O-CDs due to the internal filtration effect (IFE). Two-segment linear ranges are 1-65 μM and 70-140 μM, and the detection limit was calculated as 0.62 μM. Besides, ONOO^- can reduce the fluorescence intensity of O-CDs based on static quenching (SQ). The linear ranges are 0.3-9 μM and 9-48 μM, and the detection limit was 0.06 μM. Moreover, the O-CDs were exploited as a cellular imaging reagent for intracellular VB₁₂ and endogenous/exogenous ONOO^- imaging owing to its great biocompatibility, low toxicity and strong photostability. These results indicate that O-CDs have the potential to be used as a sensitive fluorescence probe to rapidly monitor VB₁₂ and endogenous/exogenous ONOO^- with high selectivity in living cells. Also, the as-proposed O-CDs can be employed to fabricate O-CDs/PVA composites as fluorescent flexible films. All of the above prove that the O-CDs present great prospect in multiple applications such as biosensing, cellular labeling, biomedical optical imaging, and fluorescent films.

The synthesis of a novel titanium oxide aerogel with highly enhanced removal of uranium and evaluation of the adsorption mechanism

A TiO2 aerogel with a high removal percentage and adsorption capacity was manufactured via template synthesis. Subsequently, the as-prepared TiO2 aerogel was characterized by various techniques and applied as an adsorbent for the removal of U(vi). The results revealed that the U(vi) adsorption was very rapid and reached apparent equilibrium within 100 min. The maximum removal percentage was 97.1%, which was calculated using the pseudo-second-order kinetic model (T = 298 K, t = 180 min, pH = 5, m/V = 0.1 g L-1 and C0 = 10 mg g-1). The Langmuir isotherm model was used to determine the maximum adsorption capacity and it achieved 638.0 mg g-1 (T = 298 K, pH = 5 and m/V = 0.1 g L-1). In addition, the removal of U(vi) on the TiO2 aerogel was relatively good in acidic solution and the removal behavior was independent of the influence of ionic strength. The removal percentage of the as-prepared TiO2 aerogel was higher than 90% after five cycles. Due to these excellent properties such as easy recovery, fast adsorption kinetics, high adsorption capacity and high removal percentage, the TiO2 aerogel might become an extremely employable adsorbent for the extraction of U(vi) in seawater.

Application of polyamide thin-film composite layered on polysulfone-GO/TiO2 mixed matrix membranes for removal of nitrotoluene derivatives from petrochemical wastewaters

Release of harmful organic intermediates or byproducts during the manufacture of petrochemical compounds is a serious problem in petrochemical plants. In this work, polysulfone membranes blended with GO/TiO₂ nanocomposite were synthesized by phase inversion method and coated with a polyamide layer formed by interfacial polymerization to prepare a thin-film composite (TFC) sample. Analysis and characterization of the sample were carried out by XRD, FE-SEM, BET, FTIR/ATR, AFM, TGA, and zeta potential. Results indicated that incorporation of GO/TiO₂ into the membrane structure enhanced porosity, surface roughness, and macrovoid formation along the cross-section of the sublayer and permeability of the membrane. The TFC membranes were applied to remove mononitrotoluene (MNT) and dinitrotoluene (DNT) as the basic intermediates of toluene diisocyanate (TDI). The membranes demonstrated high efficiency (> 90%) for the removal of MNT and DNT according to the charge exclusion mechanism and Donnan effect. Application of the TFC membrane for treatment of wastewater in the TDI plant showed that the removal of pollutants is variable in the range of 45-65% and 53-69% for the membrane with the highest flux and highest rejection in different transmembrane pressure, respectively.