Visualization of Adsorption: Luminescent Mesoporous Silica-Carbon Dots Composite for Rapid and Selective Removal of U(VI) and in Situ Monitoring the Adsorption Behavior

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.

Carbon Dots-Embedded Silica Tubes: An Excitation-Independent Yellow-Emitting Turn-On Probe for Simultaneous Detection and Removal of Inorganic Arsenic with In Vivo Tracking in Living Organisms

The environmental monitoring and remediation of highly toxic inorganic arsenic species in natural water are needed for the benefit of the ecosystem. Current studies on arsenic detection and removal often employ separate materials, which exhibit blue luminescence with fluorescence quenching, making them unsuitable for biological and environmental samples. In this study, carbon dot-embedded mesoporous silica tubes functionalized with melamine are synthesized to address these limitations and enable specific and turn-on probing of inorganic arsenic. The newly synthesized material demonstrates excitation-independent yellow luminescence and can effectively detect both As (III) and As (V) at low detection limits (11 × 10-9 m, 11.2 × 10-9 m), well below the prescribed threshold limits in drinking water. It also exhibits a high adsorption capacity (≈125, 159 mg g-1 ) with fast kinetics. The material's applicability in environmental samples is validated through the successful quantification of arsenic in real samples with satisfactory recoveries. Moreover, the material shows recyclability for reuse, as demonstrated by its arsenic adsorption and desorption for several cycles under basic conditions. Additionally, the material's capability for monitoring arsenic in a biological sample (Artemia salina) is demonstrated through fluorescence imaging. The encouraging outcomes underscore the material's potential use in monitoring and mitigating arsenic in aqueous systems.

Recent advancement in nanomaterials for the detection and removal of uranium: A review

Uranyl ions U(VI), are the common by-product of nuclear power plants and anthropogenic activities like mining, excess utilization of fertilizers, oil industries, etc. Its intake into the body causes serious health concerns such as liver toxicity, brain damage, DNA damage and reproductive issues. Therefore, there is urgent need to develop the detection and remediation strategies. Nanomaterials (NMs), due to their unique physiochemical properties including very high specific area, tiny sizes, quantum effects, high chemical reactivity and selectivity have become emerging materials for the detection and remediation of these radioactive wastes. Therefore, the current study aims to provide a holistic view and investigation of these new emerging NMs that are effective for the detection and removal of Uranium including metal nanoparticles, carbon-based NMs, nanosized metal oxides, metal sulfides, metal-organic frameworks, cellulose NMs, metal carbides/nitrides, and carbon dots (CDs). Along with this, the production status, and its contamination data in food, water, and soil samples all across the world are also complied in this work.

High-capacity/high-rate hybrid column for high-performance ion exchange

Herein, a fixed-bed high-capacity/high-rate (HC/HR) hybrid column was developed using commercial ion-exchange beads (IEBs) and ion-exchange fibers (IEFs). The as-fabricated HC/HR hybrid column exhibited excellent breakthrough bed volume (BV) and utilization efficiency of capacity (UEC) at a high service flow rate (SFR) for the adsorption of Cd(II). The IEBs displayed a high adsorption capacity of 235.2 ± 9.8 mg g^-1 and slow adsorption kinetics (k₂ = 0.0001 g mg^-1 min^-1) for the sorption of Cd(II); meanwhile, the IEFs showed a maximum adsorption capacity of only 146.3 ± 7.5 mg g^-1, which is lower than that of the IEBs, but fast kinetics (k₂ = 0.0130 g mg^-1 min^-1). At an SFR of 104.23 BV h^-1, the HC/HR hybrid column showed excellent performance for the sorption of Cd(II), having a high breakthrough BV of 1009.11 and a UEC of 92.86%; these values are much higher than those of the IEB-packed column. Furthermore, at an increased SFR (318.47 BV h^-1), the HC/HR hybrid column maintained its high performance, demonstrating a breakthrough BV of 568.80 and UEC of 83.90%. The regeneration experiment indicates that 97% of the initial capacity was retained. Thus, the HC/HR hybrid column could easily be applied to existing column systems and shows promising performance in ion-exchange processes.

Selecting molecular or surface centers in carbon dots-silica hybrids to tune the optical emission: A photo-physics study down to the atomistic level

In this work, we unveil the fluorescence features of citric acid and urea-based Carbon Dots (CDs) through a photo-physical characterization of nanoparticles synthesized, under solvent-free and open-air conditions, within silica-ordered mesoporous silica, as a potential host for solid-state emitting hybrids. Compared to CDs synthesized without silica matrices and dispersed in water, silica-CD hybrids display a broader emission in the green range whose contribution can be increased by UV and blue laser irradiation. The analysis of hybrids synthesized within different silica (MCM-48 and SBA-15) calls for an active role of the matrix in directing the synthesis toward the formation of CDs with a larger content of graphitic N and imidic groups at the expense of N-pyridinic molecules. As a result, CDs tuned in size and with a larger green emission are obtained in the hybrids and are retained once extracted from the silica matrix and dispersed in water. The kinetics of the photo-physics under UV and blue irradiation of hybrid samples show a photo-assisted formation process leading to a further increase of the relative contribution of the green emission, not observed in the water-dispersed reference samples, suggesting that the porous matrix is involved also in the photo-activated process. Finally, we carried out DFT and TD-DFT calculations on the interaction of silica with selected models of CD emitting centers, like surface functional groups (OH and COOH), dopants (graphitic N), and citric acid-based molecules. The combined experimental and theoretical results clearly indicate the presence of molecular species and surface centers both emitting in the blue and green spectral range, whose relative contribution is tuned by the interaction with the surrounding media.

Antibacterial Carbon Dots-Based Composites

The emergence and global spread of bacterial resistance to conventionally used antibiotics have highlighted the urgent need for new antimicrobial agents that might replace antibiotics. Currently, nanomaterials hold considerable promise as antimicrobial agents in anti-inflammatory therapy. Due to their distinctive functional physicochemical characteristics and exceptional biocompatibility, carbon dots (CDs)-based composites have attracted a lot of attention in the context of these antimicrobial nanomaterials. Here, a thorough assessment of current developments in the field of antimicrobial CDs-based composites is provided, starting with a brief explanation of the general synthesis procedures, categorization, and physicochemical characteristics of CDs-based composites. The many processes driving the antibacterial action of these composites are then thoroughly described, including physical destruction, oxidative stress, and the incorporation of antimicrobial agents. Finally, the obstacles that CDs-based composites now suffer in combating infectious diseases are outlined and investigated, along with the potential applications of antimicrobial CDs-based composites.

Preparation of Fluorescent Carbon Dots Composites and Their Potential Applications in Biomedicine and Drug Delivery-A Review

Carbon dots (CDs), a new member of carbon nanostructures, rely on surface modification and functionalization for their good fluorescence phosphorescence and excellent physical and chemical properties, including small size (<10 nm), high chemical stability, biocompatibility, non-toxicity, low cost, and easy synthesis. In the field of medical research on cancer (IARC), CDs, a new material with unique optical properties as a photosensitizer, are being applied to heating local apoptosis induction of cancer cells. In addition, imaging tools can also be combined with a drug to form the nanometer complex compound, the imaging guidance for multi-function dosage, so as to improve the efficiency of drug delivery, which also plays a big role in genetic diagnosis. This paper mainly includes three parts: The first part briefly introduces the synthesis and preparation of carbon dots, and summarizes the advantages and disadvantages of different preparation methods; The second part introduces the preparation methods of carbon dot composites. Finally, the application status of carbon dot composites in biomedicine, cancer theranostics, drug delivery, electrochemistry, and photocatalysis is summarized.

Prospective application of phosphorylated carbon nanofibers with a high adsorption capacity for the sequestration of uranium from ground water

In this study carbon nanofibers (CNF) were phosphorylated by using ortho-phosphoric acid and applied for adsorptive remediation of uranium from water. The phosphorylated carbon nanofibers (PCNF) showed 96% removal of uranium as compared to 79% by CNF. The adsorption data from batch adsorption studies fitted well with the Langmuir model and a maximum adsorption capacity of 512.8 mg g⁻¹ was obtained at pH 6.0 while the adsorption followed pseudo second order kinetics. A detailed characterisation of the adsorbent has been carried out using various analytical and spectroscopic tools. The application of the adsorbent to ground water samples exhibited promising results even in the presence of other interfering cations and anions which is imperative considering the toxic effects of uranium in ground water.

Adsorption of uranium at pH 6.0 using phosphorylated carbon nanofibers.

One-step solvent-free synthesis of carbon dot-based layered composites exhibiting color-tunable photoluminescence

We here report a practical and green approach to the development of luminescent composites through in situ solvent-free formation of carbon dots on layered inorganic compounds. The composites exhibit higher solid-state photoluminescence than those prepared by mixing of synthesized carbon dots and layered clay minerals. Tuning of the emission color of the composites has also been achieved by the addition of small molecules into phloroglucinol as starting materials for carbonization. The carbon dots synthesized in clay compounds in the solvent-free conditions are well-dispersed to obtain homogeneous composites. Furthermore, we have demonstrated that highly luminescent carbon dots are formed by carbonization in the presence of layered inorganic compounds. The one-step solvent-free approach presented in this work may allow not only facile, economical, and sustainable production of nanostructured carbon dot-based composites but also improvement of their luminescence properties.

A practical and green approach to the development of color-tunable luminescent composites through in situ solvent-free synthesis of carbon dots on layered inorganic compounds is reported.

Synthesis of carbon-based nanomaterials and their application in pollution management

With the fast development of industry, large amounts of organic and inorganic pollutants are inevitably released into the natural environment, which results in the pollution of the environment and are thereby dangerous to human health. The efficient elimination of these pollutants is crucial to environment protection and human health. The high sorption capacity of carbon-based materials and high photocatalytic ability of carbon-based composites result in the application of carbon-based materials in environmental pollution cleanup. In this review article, we summarized recent studies on the synthesis of carbon-based materials, and their application in the sorption of organic and inorganic pollutants, the photocatalytic degradation of organic pollutants, and the in situ photocatalytic reduction-solidification of heavy metal ions. The sorption method is useful to remove pollutants from aqueous solutions. The sorption-photocatalytic degradation of organic pollutants is applicable, especially at low concentrations, whereas the catalytic reduction of metal ions is the best method for the in situ immobilization of high valent metal ions under complicated conditions. The interaction mechanism is discussed using advanced spectroscopy analysis and theoretical calculations, and at the end the challenges in the future are described.

Application of carbon dots and their composite materials for the detection and removal of radioactive ions: A review

Radioactive ions with high-heat release or long half-life could cause long-term influence on environment and they might enter the food chain to damage human body for their toxicity and radioactivity. It is of great importance to develop methods and materials to detect and remove radioactive ions. Carbon dots and their composite materials has been applied widely in many fields due to their plentiful raw materials, facile synthesis and functional process, unique optical property and abundant functional groups. This comprehensive review focuses on the preparation of CDs and composite materials for the detection and adsorption of radioactive ions. Firstly, the recent-developed synthetic methods for CDs were summarized briefly, including hydrothermal/solvothermal, microwave, electrochemistry, microplasma, chemical oxidation methods, focusing on the influence of CDs properties. Secondly, the synthetic methods for CDs composite materials were classified to four categories and summarized generally. Thirdly, the application of CDs for radioactive ions detection and adsorption were explored and concluded including uranium, iodine, europium, strontium, samarium et al. Finally, the detection and adsorption mechanism for radioactive ions were searched and the perspective and outlook of CDs for detection and adsorption radioactive ions have been proposed based on our understanding.

Synthesis and modification of carbon dots for advanced biosensing application

There has been an explosion of interest in the use of nanomaterials for biosensing applications, and carbonaceous nanomaterials in particular are at the forefront of this explosion. Carbon dots (CDs), a new type of carbon material, have attracted extensive attention due to their fascinating properties, such as small particle size, tunable optical properties, good conductivity, low cytotoxicity, and good biocompatibility. These properties have enabled them to be highly promising candidates for the fabrication of various high-performance biosensors. In this review, we summarize the top-down and bottom-up synthesis routes of CDs, highlight their modification strategies, and discuss their applications in the fields of photoluminescence biosensors, electrochemiluminescence biosensors, chemiluminescence biosensors, electrochemical biosensors and fluorescence biosensors. In addition, the challenges and future prospects of the application of CDs for biosensors are also proposed.

N, S doped carbon quantum dots inside mesoporous silica for effective adsorption of methylene blue dye

This study aimed to develop non-metal elements for doping carbon quantum dots (CQDs) with nitrogen and sulfur (N, S-CQDs), which loaded inside hexagonal mesoporous silica (HMS) in order to effectively remove methylene blue dye (MB) from an aqueous solution. The histidine and cysteine amino acids were used as the source for synthesis N, S-CQDs through the hydrothermal method. Morphology and structure of the N, S-CQDs, and adsorbent (N, S-CQDs/HMS) were characterized by using different microscopic and spectroscopic techniques. The adsorption parameters such as adsorbent dosage (0.25–1 g/L), pH (2–10), contact time (15–75 min), and initial MB dye concentration (20–300 mg/L) were investigated. The maximum adsorption capacity and removal efficiency of MB were determined at 370.4 mg/g and 97%, respectively, under optimum conditions at 303 K. The adsorption isotherm studies were fitted with the Freundlich isotherm equation, and the dye removal kinetics of the adsorbent followed the pseudo-second-order model. Thermodynamic studies showed that the adsorption process had exothermic and spontaneous behavior. The removal of MB next to the Rhodamine B and Reactive Black 5 dyes indicated that the N, S-CQDs/HMS had excellent selective behavior for MB absorption. This prepared adsorbent could be well recycled with suitable activity after four repeated adsorption–desorption cycles. Results revealed that the porous characters, surface area, charge properties, reduction in the bandgap, and quantum yield of the N, S-CQDs/HMS were essential factors that affected dye adsorption.

Carbon dots@metal–organic frameworks as dual-functional fluorescent sensors for Fe3+ ions and nitro explosives

Two novel dual-functional fluorescent composites were prepared, which exhibit excellent fluorescence sensing capabilities for Fe³⁺, p-NT and 2,4-DNP.

Phosphate functionalized layered double hydroxides (phos-LDH) for ultrafast and efficient U(VI) uptake from polluted solutions

Elimination of U(VI) from polluted solutions is important for human health and environmental safety. In this work, a relatively low-cost 3D flower-like phosphate-functionalized layered double hydroxides (phos-LDH) was fabricated by a one-pot hydrothermal method. The prepared phos-LDH inherited the structure of 3D flower-like layered double hydroxides (LDH), and had a higher specific surface area (∼203.4 m²⋅g^-1) than that of LDH. The kinetic process indicated that U(VI) adsorption onto phos-LDH achieved equilibrium within 15 min and obeyed general order model. The adsorption isotherms of phos-LDH illustrated that the U(VI) adsorption obeyed Langmuir model, the adsorption capability of phos-LDH can reach 923.1 mg⋅g^-1 at 298 K. The U(VI) adsorption was a spontaneous and endothermic process according to the thermodynamic data. There was the electrostatic attraction between U(VI) and phos-LDH at pH = 5.0. FTIR and XPS analyses educed that the hydroxyl and phosphate groups played a very useful role for the complexation between U(VI) and phos-LDH. In addition, the excellent selective adsorption capability for U(VI) in competitive cation and anion solutions further confirmed the practical application of phos-LDH in real wastewater treatment.

Carbon Dots in Porous Materials: Host-Guest Synergy for Enhanced Performance

Carbon dots (CDs) are emerging as a new class of carbon nanomaterials, which have inspired growing interest for their widespread applications in anti-counterfeiting, sensing, bioimaging, optoelectronic and energy-related fields. In terms of the concept of host-guest assembly, immobilizing CDs into porous materials (PMs) has proven to be an effective strategy to avoid the aggregation of bare CDs in solid state, in particular, the host-guest synergy with both merits of CDs and PMs affords composites promising properties in afterglow and tunable emissions, as well as optimizes their performance in optics, catalysis, and energy storage. This Minireview summarizes the recent progress in the research of CDs@PMs, and highlights synthetic strategies of constructing composites and roles of porous matrices in boosting the applications of CDs in diverse areas. The prospect of future exploration and challenges are proposed for designing advanced CDs-based functional nanocomposite materials.

Polymer Nanorings with Uranium Specific Clefts for Selective Recovery of Uranium from Acidic Effluents via Reductive Adsorption

Nanostructured polymeric materials, functionalized with an appropriate receptor, have opened up newer possibilities for designing a reagent that shows analyte-specific recognition and efficient scavenging of an analyte that has either a detrimental influence on human physiology and environment or on its recovery for further value addition. Higher active surface area, morphological diversity, synthetic tunability for desired surface functionalization, and the ease of regeneration of a nanostructured material for further use have provided such materials with a distinct edge over conventional reagents. The use of a biodegradable polymeric backbone has an added significance owing to the recent concern over the impact of polymers on the environment. Functionalization of biodegradable sodium alginate with AENA (6.85% grafting) as the receptor functionality led to a unique open framework nanoring (NNRG) morphology with a favorable spatial orientation for specific recognition and efficient binding to uranyl ions (U) in an aqueous medium over a varied pH range. Nanoring morphology was confirmed by transmission electron microscopy and atomic force microscopy images. The nanoscale design maximizes the surface area for the molecular scavenger. A combination of all these features along with the reversible binding phenomenon has made NNRG a superior reagent for specific, efficient uptake of UO₂²⁺ species from an acidic (pH 3-4) solution and compares better than all existing UO₂²⁺-scavengers reported till date. This could be utilized for the recovery of uranyl species from a synthetic acidic effluent of the nuclear power. The results of the U uptake experiments reveal a maximum adsorption capacity of 268 mg of U per g of NNRG in a synthetic nuclear effluent. X-ray photoelectron spectroscopy studies revealed a reductive complexation process and stabilization of U(IV)-species in adsorbed uranium species (U@NNRG).

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

Carbon quantum dots (CQDs) are a new class of carbon nanoparticles with superior advantages as small particle size, excellent biocompatibility and low toxicity which advance their recent applications in biotechnology, bioimaging and biosensing. The use of free CQDs in water treatment is greatly rendered by their high solubility in water. Therefore, this work is aimed to rapidly synthesize CQDs in only 10 min via microwave irradiation pyrolysis of starch-water system. The maximum fluorescence emission of CQDs was detected at 526 nm throughout the excitation wavelength (390 nm). The CQDs have been targeted to occupy the surface and pores of a polymeric material based on poly(anthranilic acid-formaldehyde-phthalic acid) (PAFP) to produce a novel CQDs@PAFP nanobiosorbent. The surface area of CQDs@PAFP was detected (28.79 m² g^-1 BET) and the nanoparticle size was confirmed (TEM). The highest removals of U(VI) by CQDs@PAFP nanobiosorbent were 95.5-98.0 % for 30-90 mg L^-1. The sorption mechanism was designated to the pseudo-second-order model and closely tailored with Freundlich model. CQDs@PAFP was emerged as an excellent nanobiosorbent for U(VI) removal from wastewater (97.3 %) and sea water (96.0 %). CQDs@PAFP confirmed its excellent reusablity for efficient multi- recovery of U(VI) from different water samples.

Specific Recognition of Uranyl Ion Employing a Functionalized Nanochannel Platform for Dealing with Radioactive Contamination

Radioactive contamination is a highly concerning global environmental issue along with the development of the nuclear industry. On account of sophisticated operations and high cost of instrument detection methods, numerous efforts have been focused on rapid and simple detection of pollution elements and uranium is the most common one. It is an enormous challenge to push the limit of determination as low as possible while carrying out ultrasensitive detection. Here, we report an intelligent platform based on functionalized solid nanochannels to monitor ultratrace uranyl ions. The platform has a detection limit of 1 fM, which is far below the value that traditional instrumental methods can reach. What is more, the system also exhibits uranyl removal property. The mesenchymal stem cells cultivated in media containing uranyl can achieve excellent viability in the presence of the membranes. This work provides a new choice for handling global radioactive contamination of water.

Carbon Dots-in-Matrix Boosting Intriguing Luminescence Properties and Applications

As a new class of luminescent nanomaterials, carbon dots (CDs) have aroused significant interest because of their fascinating photoluminescence properties and potential applications in biological, optoelectronic, and energy-related fields. Strikingly, embedding CDs in host matrices endow them with intriguing luminescent properties, in particular, room temperature phosphorescence and thermally activated delayed fluorescence, due to the confinement effect of the host matrix and the H-bonding interactions between CDs and the matrix. Here, the state-of-the-art strategies for introducing CDs in various host matrices are summarized, such as nanoporous materials, polyvinyl alcohol, polyurethane, potash alum, layered double hydroxides, amorphous silica, etc. The resultant luminescent properties of the composites and their emission mechanisms are discussed. Their applications in bioimaging, drug delivery/release, sensing, and anticounterfeiting are also presented. Finally, current problems and challenges of CDs-based composites are noted for future development of such luminescent materials.

Petroleum pitch-based porous aromatic frameworks with phosphonate ligand for efficient separation of uranium from radioactive effluents

Porous aromatic frameworks with structural/pore controllability and rigid skeletons present a series of emerging materials for solid phase extraction. However, the complicated monomers or noble metal catalyst, and cumbersome synthetic strategies result in high-cost engineering application of porous aromatic frameworks. Herein, a simple synthetic strategy of porous aromatic frameworks with phosphonate is reported for efficient separation of uranium from radioactive effluents, and petroleum pitch, a low-cost and widely available material, was used as the building block. 4-Vinylbenzylphosphonic acid diethyl ester monomer is introduced to chelate uranium and to improve the aqueous dispersibility of sorbents. The phosphonate functionalized PPAFs take 40 min to achieve adsorption equilibrium, and the maximum sorption capacity reaches 147 mg U/g at pH 1.0. PPAFs exhibit good selectivity over various competing ions and excellent radioresistance in acidic solution. Besides, PPAFs remain almost 100% sorption efficiency and intact structure over 5 sorption-desorption cycles with alkaline eluent. This work not only applies a low-cost material for uranium extraction, but a new idea for the utilization of waste and recycling of resources.

Spectrographic sensors for uranyl detection in the environment

More and more severe energy problem triggers extensive application of nuclear energy, and the adverse effects brought by nuclear materials such as uranyl to the environment are becoming the concern, as it has become a threat to human's health. Therefore, the detection of uranyl is increasingly important, which aims to make the application of uranium under surveillance and protection. A lot of detection methods employing varying materials based on different techniques for uranyl have been proposed including those using expensive and complicated instruments such as ICP-MS, ESI-MS, and neutron activation analysis etc. Those methods based on expensive instruments often provide quite low limit of detection (LOD) and excellent validity and repeatability, however, methods that are low-cost, convenient and rapid are in demand because these are satisfied characters for on-site and in-time determination. In the review, we discuss uranyl sensors based on spectrographic techniques, which is facile and promising for rapid assessment of uranium content in practical application. Spectrographic techniques including fluorescence, UV-vis spectrophotometry, resonance light scattering (RLS) and surface enhanced Raman scattering (SERS) are evaluated. In detail, the core materials that playing extremely important roles in detection performance are stated consisting of small molecule, biomolecule, polymer and nanomaterial.

Nitrogen-doped carbon dots encapsulated in the mesoporous channels of SBA-15 with solid-state fluorescence and excellent stability

A simple and low-cost approach is developed, by which nitrogen-doped carbon dots (NCDs) with a negative potential are assembled inside the mesoporous channels of SBA-15 via capillary force. The unique confined microenvironment leads to a strong interaction between confined NCDs and the inner surface of SBA-15, thus effectively avoiding the aggregation of NCDs. The resultant composite (NCDs-in-SBA-15) exhibits blue fluorescence similar to the NCD aqueous solution, and shows excellent structural, thermal and photostability. Solid NCDs-in-SBA-15 still emits fluorescence even after heat treatment at 400 °C under ambient atmosphere. In addition, NCDs-in-SBA-15 possesses remarkable resistance to acid/alkali solvents. Furthermore, NCDs-in-SBA-15 shows superior selectivity and adsorption capacity to Fe3+. The facile approach and these advantageous performances could make CDs meet the requirements of fluorescent materials in the solid state and then have wider applications.

Highly efficient immobilization of uranium(VI) from aqueous solution by phosphonate-functionalized dendritic fibrous nanosilica (DFNS)

A novel phosphonate assisted fabrication dendritic fibrous nanosilica (DFNS)-based adsorbing material was successfully synthesis via organic modification with 3-aminopropyltriethoxysilane (KH550), epichlorohydrin (ECH) and phytic acid (PA) on the grounds of hard-soft-acid-base theory, in which organic phosphorous can be applied for efficient chelating uranium(VI) (U(VI)). The adsorption properties can be evaluated by setting a series parameters (pH, adsorbent dose, contact time, initial U(VI) concentration). It is clear that uranium as a "hard" lewis acid can easily form chelating bond with "hard" donor-ligands so that as-papered PA-DFNS has an excellent adsorption capacity (q_m = 1106 mg g^-1, 298.15 K), which exhibits a 163% increment compared with that of original DNFS under the same condition. In the meantime, the adsorption equilibrium time of PA-DNFS (t = 60 min) was shortened by 33% compared with that of pristine DNFS. Besides, the PA-DFNS exhibited good removal efficiency and stability under the 0.1 M HNO₃ after 6 cycles, extending the application of PA-DFNS in the field of adsorption.

Luminescent Sol-Gel Glasses from Silicate–Citrate–(Thio)Ureate Precursors

Recent advancements in synthesis and analysis of the composites based on silica and carbon quantum dots have revealed great potential of such systems in bioimaging, sensor, as well as solid-state lighting applications. Most of the synthetic methods for obtaining such materials are still relatively complex and costly. The aim of this work was to study the luminescent properties of silica-based composites prepared by the simple sol-gel method using low-cost silicate–citrate–(thio)ureate precursors. The glassy composites were prepared by acid hydrolysis of ethyl silicate (40%) in aqueous solution of citric acid ureates or thioureates with the citric acid-to-(thio)urea molar ratio of 1:1, 1:1.5 or 1:3. The results of spectrofluorimetric analysis have shown that heat-treated at 270 °C such silica gels upon UV excitation (with an optimum at λexc = 360 nm) emit light in a visible spectrum (400–600 nm). Upon this, photoluminescence efficiency of ureate-derived glasses (quantum yield 70.53% for 1:1.5 sample) appeared to be much higher than that for thioureate-derived glasses (quantum yield 11.25% for 1:3 sample) suggesting that the preparation conditions to obtain the glasses with optimal photoluminescence characteristics are quite different in case of urea and thiourea. Thus, citrate–ureate-derived silica glasses already demonstrate very good potential to be efficient materials for different fluorescence-related applications.

Carbon quantum dots embedded mesoporous silica for rapid fluorescent detection of acidic gas

A fluorescent composite consisting of an ordered mesoporous material (MCM-41) and carbon quantum dots (CQDs) was successfully prepared and designated as MCM/CQDs. CQDs with citric acid as a carbon source and diethylenetriamine as a nitrogen doping agent were directly synthesized in MCM-41 via a hydrothermal method and the reaction conditions were optimized. The MCM/CQDs prepared at the optimized condition showed different fluorescent properties (as indicated by the fluorescent emission wavelength and fluorescent response to acid) compared to the CQDs formed in water. It was found that the preparation of MCM/CQDs caused changes in the characteristics (i.e., surface and pore properties) of MCM-41, which in turn could impact the formation of CQDs in MCM-41. The prepared MCM/CQDs combined the porous nature of MCM-41 and the fluorescent properties of CQDs, and can be applied to the rapid detection of acetic acid (HAc) as a model organic volatile compound. The detection was more sensitive for HAc gas (detection limit: 0.2 μmol/L) than for HAc solution (detection limit: 3 μmol/L). The reason was explained by the physical adsorption of HAc gas by MCM-41, which increased the HAc concentration in the MCM/CQDs and therefore enhanced the fluorescent response. This study expanded the potential application of CQDs embedded mesoporous silica in gas sensing, especially in the rapid and sensitive detection of acetic acid as a representative of acidic volatile compounds.

The efficient immobilization of uranium(vi) by modified dendritic fibrous nanosilica (DFNS) using mussel bioglue

Herein, a dendritic fibrous nanosilica (DFNS)-based adsorbent was constructed through bio-inspired bifunctional stimulation as a rapid and efficient trap for uranium(vi).

Novel Ion-Imprinted Carbon Material Induced by Hyperaccumulation Pathway for the Selective Capture of Uranium

The development of nuclear energy is significant for resource sustainability. Uranium is the main nuclear fuel, and its effective absorption has captured the attention of researchers. In this study, the green technologies hyperaccumulation effect of the plant and ion-imprinted technology were used to prepare the uranium ion-imprinted hierarchically porous carbon material (II-HPC). At the same time, a nonimprinted hierarchically porous carbon (HPC) was prepared for comparison. The adsorption isotherm was fitted to the Langmuir model and maximum sorption capacity of II-HPC was 503.64 mg g^-1 at 298 K. The kinetic data followed the pseudo-second-order model, indicating a dominant role of chemisorption. Initial studies were performed on a lab-scale simulated continuous-flow system for the adsorption kinetics testing of II-HPC in simulated seawater. The results showed that the amount of uranium adsorbed after 35 days was 0.379 mg g^-1, which determined that II-HPC adsorbent is a potential material for enrichment of U(VI) from the seawater.

Synthesis of Microporous Covalent Phosphazene-Based Frameworks for Selective Separation of Uranium in Highly Acidic Media Based on Size-Matching Effect

On the basis of high stability of phosphorus-oxygen linkage, we constructed two microporous covalent phosphazene-based frameworks (CPFs), for the first time, by choosing hexachlorocyclotriphosphazene as a core unit and polyhydroxy aromatic compounds (hydroquinone or phloroglucinol) as monomers, named CPF-D and CPF-T, respectively. Characterization studies by using Fourier transform infrared, nuclear magnetic resonance, thermal gravimetric analysis, ⁶⁰Co γ-ray irradiation, and so forth, demonstrated that both of the CPF materials have excellent acid and radiation stability and relatively higher thermal stability. The results of batch adsorption experiments show that CPF-T is significantly more capable of sorbing uranium than CPF-D. In a pure uranium system with higher acidity (pH 1), the uranium sorption amount of CPF-T can reach up to 140 mg g^-1. Distinctively, in mixed-metal solution with 12 coexisting cations, CPF-T shows relatively stable and excellent uranium adsorption capability over a wide range of acidity (pH 4 to 3 M HNO₃), and the difference in uranium sorption amounts is less than 30% with the maximum of 0.26 mmol g^-1 at pH 4 and the minimum of 0.20 mmol g^-1 at 3 M HNO₃, which is far superior to that of the conventional solid-phase extractant (SPE) materials previously reported. The research results suggested that the sorption model based on the speculated mechanism of size-matching plus hydrogen bond network has played a dominant role in the process of uranium adsorption. The proposed strategy for the one-pot fabrication of an acid-resistant microporous framework materials by bridging the aromatic monomers via P-O bonds provides an alternative approach for the design and synthesis of new SPE materials with size-matching function desired for effective separation of uranium or other valuable metals from highly acidic environments.

Functionalized Sugarcane Bagasse for U(VI) Adsorption from Acid and Alkaline Conditions

The highly efficient removal of uranium from mine tailings effluent, radioactive wastewater and enrichment from seawater is of great significance for the development of nuclear industry. In this work, we prepared an efficient U(VI) adsorbent by EDTA modified sugarcane bagasse (MESB) with a simple process. The prepared adsorbent preserves high adsorptive capacity for UO22+ (pH 3.0) and uranyl complexes, such as UO2(OH)+, (UO2)2(OH)22+ and (UO2)3(OH)5+ (pH 4.0 and pH 5.0) and good repeatability in acidic environment. The maximum adsorption capacity for U(VI) at pH 3.0, 4.0 and 5.0 is 578.0, 925.9 and 1394.1 mg/g and the adsorption capacity loss is only 7% after five cycles. With the pH from 3.0 to 5.0, the inhibitive effects of Na+ and K+ decreased but increased of Mg2+ and Ca2+. MESB also exhibits good adsorption for [UO2(CO3)3]4- at pH 8.3 from 10 mg/L to 3.3 μg/L. Moreover, MESB could effectively extract U(VI) from simulated seawater in the presence of other metals ions. This work provided a general and efficient uranyl enriched material for nuclear industry.

Thenoyltrifluoroacetone (TTA)-Carbon Dot/Aerogel Fluorescent Sensor for Lanthanide and Actinide Ions

Contamination of groundwater with radioactive substances comprising actinides and lanthanides is a significant environmental hazard and thus the development of selective, sensitive, and easy-to-apply sensors for water-soluble actinide and lanthanide ions is highly sought. We constructed a new selective fluorescent sensor for UO2 2+, Sm3+, and Eu3+ based on a carbon dot (C-dot)-aerogel hybrid prepared through in situ carbonization of 2-thenoyltrifluoroacetone (TTA), a high-affinity heavy metal chelator. The TTA-C-dot-aerogel enabled the detection of UO2 2+ ions, which induced a significant red fluorescence shift, whereas Eu3+ and particularly Sm3+ ions gave rise to pronounced fluorescence quenching. Importantly, the lanthanide/actinide ion-selective TTA-C-dots could be synthesized only in situ inside the aerogel pores, indicating the crucial role of the aerogel host matrix both in enabling the formation of the C-dots and in promoting the adsorption and interactions of the lanthanide and actinide metal ions with the embedded C-dots.

Ion-Imprinted Mesoporous Silica for Selective Removal of Uranium from Highly Acidic and Radioactive Effluent

It is strategically important to recycle uranium from radioactive liquid wastes for future uranium supply of nuclear energy. However, it is still a challenge to adsorb uranium selectively from highly acidic and radioactive waste. In this paper, we report a novel strategy for effective uranium removal from highly acidic and radioactive media by surface ion-imprinted mesoporous silica sorbent. The sorbent was successfully synthesized by a co-condensation method with uranyl as the template ion and diethylphosphatoethyltriethoxysilane as the functional ligands. The pseudo-second-order model and Langmuir model showed better correlation with the sorption kinetic and isotherm data, and the sorption equilibrium could be reached within 40 min, the maximum adsorption capacity from Langmuir model was 80 mg/g in 1 mol/L nitric acid (HNO₃) solution at 298.15 K. The sorbent showed faster kinetics and higher selectivity toward uranium over other ions compared with nonimprinted mesoporous and other previous sorbents. Furthermore, the ion-imprinted materials exhibited remarkable radioresistance stability and could be regenerated efficiently after five cycles. This work may provide a new approach for highly efficient sorption of uranium from strong HNO₃ and radioactive media.

Adsorption of Uranium over NH2-Functionalized Ordered Silica in Aqueous Solutions

The aim of this work was to obtain an in-depth understanding of the U(VI) adsorption mechanism over amino-functionalized mesoporous silica SBA-15 and highlights its high efficiency in aqueous media for U(VI) removal and preconcentration. The samples were synthesized and functionalized by both grafting and co-condensation methods, using different alkyl-substituted amine groups and were characterized using X-ray diffraction, N₂ physisorption, Fourier transform infrared spectroscopy, and elemental C-H-N-S analyses. The properties for U(VI) adsorption were evaluated under discontinuous conditions, with the determination of the effect of several parameters (initial pH, contact time, initial U(VI) concentration, functionalization method, and organic moiety composition). U(VI) adsorption over grafted materials reached equilibrium at around 30 min, with a maximum adsorption capacity of 573 mg_U·g_ads^-1 for the most efficient material at its optimal adsorption pH (equal to 6) at 20 °C. Functionalized materials by grafting exhibit better adsorption capacities than co-condensed samples because of higher function surface density and function availability. U(VI) adsorption mechanisms were also studied by measuring the electrophoretic mobilities of the particles, aqueous U(VI) speciation, in situ attenuated total reflection infrared and Raman spectroscopies, and transmission electron microscopy analysis. U(VI) adsorption occurred through the formation of an inner sphere complex. The localization of adsorbed U(VI) has also been determined inside of the mesopores, with the formation of several particles on the nanometer scale, in the size of U-hydroxy phases. Besides, the study of the reusability of amino-functionalized SBA-15 by applying adsorption-desorption cycles was also conducted. The adsorption capacity of the material remains stable for at least four adsorption-desorption cycles without any noticeable capacity decrease.