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Zinc ion, one of the most important transition metal ions in living organisms, plays a crucial role in the homeostasis of the organism. The disorder of zinc is associated with many major diseases. It is highly desirable to develop selective and sensitive methods for the real-time detection of zinc ions. In this work, double-emitting fluorescent carbon dots (CDs) are prepared by a solvothermal method using glutathione, L-aspartic acid, and formamide as the raw materials. The carbon dots specifically recognize zine ions and produce a decrease in fluorescence intensity at 684 nm and an increase at 649 nm, leading to a ratiometric fluorescent sensor for zinc detection. Through surface modification and spectral analysis, the surface groups including carboxyl, carbonyl, hydroxyl, and amino groups, and C=N in heterocycles of CDs are revealed to synergistically coordinate Zn2+, inducing the structural changes in the emission site. The CDs can afford a low limit of detection of ~5 nM for Zn2+ detection with good linearity in the range of 0.02-5 µM, showing good selectivity as well. The results from real samples including fetal bovine serum, milk powder, and zinc gluconate oral solution indicated the good applicability of the CDs in the determination of Zn2+.

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Introduction: Dopamine is one of the most significant neurotransmitters and plays an important role in the management of cognitive functions such as learning, memory, and behavior. The disorder of dopamine is associated with many major mental diseases. It is necessary to develop selective methods for the detection of dopamine. Methods: In this work, carbon dots (CDs) were synthesized by a solvothermal route using glutathione, L-histidine, and formamide as sources. Results: Under light irradiation, The CDs convert dissolved oxygen to singlet oxygen (1O2), which could oxidize TMB. When reduced dopamine was present, it suppressed the catalysis of CDs, then the absorption of the CDs-coupled TMB complex at 652 nm was diminished. Furthermore, it was revealed that the surface groups including hydroxyl, amino, carbonyl, and carboxyl groups of CDs were related to their light-responsive catalytic activity by surface modification. In the range of 0.5-15 µM, the CDs could afford a LOD of 0.25 µM for dopamine detection with fine linearity, also showing good selectivity. Discussion: The results from fetal bovine serum indicated the good applicability of the CDs in the determination of dopamine.

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Surface-modified porous silica is a well-established composite material. To improve its embedding and application behavior, adsorption studies of various probe molecules have been performed using the technique of inverse gas chromatography (IGC). For this purpose, IGC experiments were carried out in the infinite dilution mode on macro-porous micro glass spheres before and after surface modification with (3-mercaptopropyl)trimethoxysilane. To provide information about the polar interactions between probe molecules and the silica surface, in particular, eleven polar molecules have been injected. In summary, the free surface energy for pristine silica ( γ S t o t a l = 229 mJ/m2) and for (3-mercaptopropyl)trimethoxysilane-modified silica ( γ S t o t a l = 135 mJ/m2) indicates a reduced wettability after surface modification. This is due to the reduction of the polar component of the free surface energy ( γ S S P ) from 191 mJ/m2 to 105 mJ/m2. Simultaneously, with the reduction of surface silanol groups caused by surface modification of silica and, therefore, the decrease in polar interactions, a substantial loss of Lewis acidity was observed by various IGC approaches. Experiments with all silica materials have been conducted at temperatures in the range from 90°C to 120°C to determine the thermodynamic parameters, such as adsorption enthalpy ( Δ H a d s ) and adsorption entropy ( Δ S a d s ), using the Arrhenius regression procedure evaluating the IGC data. With the help of the enthalpy-entropy compensation, two types of adsorption complexes are assumed between polar probe molecules and the silica surface because of different isokinetic temperatures. Identical adsorption complexes with an isokinetic temperature of 370°C have been assigned to alkanes and weakly interacting polar probes such as benzene, toluene, dichloromethane, and chloroform. Polar probe molecules with typical functional groups such as OH, CO, and CN, having the ability to form hydrogen bonds to the silica surface, exhibit a lower isokinetic temperature of 60°C. Quantum chemical calculations of the probe molecules on a non-hydroxylated and hydroxylated silica cluster supported the formation of hydrogen bonds in the case of a strong polar adsorption complex with a bonding distance of 1.7 nm-1.9 nm to the silica surface.

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In this paper, the chemical microstructure of coal samples is quantitatively analyzed experimentally before and after liquid nitrogen cold soaking, by using elemental analyzer, X-ray diffractometer, and Fourier infrared spectrometer, including the reverse side of chemical composition of elements, organic matter, and functional groups. It was found that with the increase of coal metamorphism, the contents of carbon, nitrogen, and sulfur elements gradually increase, while those of hydrogen and oxygen elements gradually decrease. In addition, as the degree of metamorphism increases, the graphitization phenomenon of coal becomes weaker, the interlayer spacing of aromatic rings (d002) increases, the structure of coal crystal nucleus is loose, its order is weakened, the crystal volume becomes smaller, and the void structure unit increases. The FTIR spectra of each coal sample could be divided into four absorption bands, i.e., the aromatic structure, oxygen-containing functional group, aliphatic group, and hydroxyl absorption band. After cold soaking of liquid nitrogen, the peak intensity areas of aromatic and aliphatic structures decrease, while those of oxygenated functional groups and hydroxyl groups increase, and the values of A(C = O)/A(C-O) increase and those of A(CH3)/A(CH2) decrease, mainly due to the gradual decrease of methylene side chains and increase of methylene straight chains. The present results are helpful to further reveal the mechanism of adsorption-resolution deformation of coal body due to cold immersion of liquid nitrogen.

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It is well known that two-dimensional (2D) MXene-derived quantum dots (MQDs) inherit the excellent physicochemical properties of the parental MXenes, as a Chinese proverb says, "Indigo blue is extracted from the indigo plant, but is bluer than the plant it comes from." Therefore, 0D QDs harvest larger surface-to-volume ratio, outstanding optical properties, and vigorous quantum confinement effect. Currently, MQDs trigger enormous research enthusiasm as an emerging star of functional materials applied to physics, chemistry, biology, energy conversion, and storage. Since the surface properties of small-sized MQDs include the type of surface functional groups, the functionalized surface directly determines their performance. As the Nobel Laureate Wolfgang Pauli says, "God made the bulk, but the surface was invented by the devil," and it is just on the basis of the abundant surface functional groups, there is lots of space to be thereof excavated from MQDs. We are witnessing such excellence and even more promising to be expected. Nowadays, MQDs have been widely applied to catalysis, whereas the related reviews are rarely reported. Herein, we provide a state-of-the-art overview of MQDs in catalysis over the past five years, ranging from the origin and development of MQDs, synthetic routes of MQDs, and functionalized MQDs to advanced characterization techniques. To explore the diversity of catalytic application and perspectives of MQDs, our review will stimulate more efforts toward the synthesis of optimal MQDs and thereof designing high-performance MQDs-based catalysts.

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A simple heat treatment method was used to optimize the three-dimensional network structure of the hydrophobic aerogel, and during the heat treatment process at 200-1000 °C, the thermal conductivity of the aerogel reached the lowest to 0.02240 W/m·K between 250 °C and 300 °C, which was mainly due to the optimization of microstructure and pyrolysis of surface groups. Further Fluent heat-transfer simulation also confirmed the above results. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to finely measure the pyrolysis process of aerogels, and the pyrolysis process of aerogel was divided into four stages. (I) Until 419 °C, as the temperature continued to rise, surface methyl groups were oxidized to form hydroxyl. (II) As the temperature reached to 232 °C, the oxidation proceeded. In addition, inside the aerogel, because of lacking oxygen, the reaction produced CH4 and C-Si bonds would form. (III) After 283 °C, Si-OH groups began to condense to form Si-O-Si, which optimized the three-dimensional network structures to be beneficial to improve the thermal insulation performance of silica aerogel. (IV) When it reached 547 °C, the chemical reaction was terminated, and all the primary particles gradually fused into secondary particles and sintered to form clusters.

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Fluorine (F) in water has a negative effect on the environment and human health. Schwertmannite has potential remediation to contamination in solution. In this study, the adsorption mechanism and influencing factors of synthetic schwertmannite for low-concentration F were studied through batch experiments. The results suggested that the adsorption of F by schwertmannite reached equilibrium after about 60 min, and the adsorption efficiency exceeded 94%. The experimental data can be best-fit by the pseudo-second-order kinetic and Langmuir models well. Schwertmannite showed effective adsorption at pH 4, dosage 1.5 g L-1, low temperature, and low concentration of co-existing anion. The adsorption process was a spontaneous and exothermic reaction, which was dominated by chemical adsorption. FT-IR and XPS spectra analysis revealed that F adsorption on schwertmannite through the surface complexation and anion exchange reaction between SO42- and OH- with F-, especially the primary role of OH-. The results can provide theoretical support for the schwertmannite application in the treatment of F-containing wastewater.

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Limited avenues are available for property control of carbonized polymer dots (PDs) owing to the unsatisfactory understanding of PDs" formation. Herein, a de novo "polymer template" strategy is presented for PDs with customizable functional surface groups (FSG), size, and underlying fluorescence, with a detailed mechanism. The strategy relies on novel di-active site polymers (DASPs) prepared from alkenyl azides via [3+2] cycloaddition and guanidino hydrolysis. Benefiting from these specific reactions, the DASPs were convenient for mass production and stable for storage, and could be transformed to PDs upon addition of nucleophilic agents through nucleophilic addition and substitution at 70 °C. By regulating the types of alkenyl azides, nucleophilic agents, and reaction conditions, the as-prepare PDs could be tailored with controlled types of core, FSG, and particle size, as well as fluorescence properties of quantum yield from 8.2-55.6 %, and emission maximum from 380-500 nm. These specialties make this "polymer template" strategy a promising start for building PDs-based sensor platforms. Moreover, the strategy could further our understanding towards PDs' formation, and open up a new way to customize PDs for specific needs in the fields of analysis, catalysis, images, etc.

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Fluoride has an adverse effect on both the environment and industrial production. In particular, wastewater from smelting systems containing high concentrations of fluoride is a major cause of fluoride pollution. Based on the characteristics of such wastewater, a targeted and integrated method for removal fluoride using schwertmannite is proposed. The schwertmannite, prepared from the oxidation of Fe(II) by KMnO4 (Ksw) and MnO2(Msw), effectively removed fluoride within 30 min under certain conditions. Under most experimental conditions, the removal efficiency of F ion by Ksw was always 13 % higher than that by Msw, which is attributed to the different concentrations of OH- and SO42- for ion exchange. The calculations showed that the chemical formulas of Ksw and Msw are Fe8O8(OH)5.42±0.04(SO4)1.29±0.02 and Fe8O8(OH)5.28±0.04(SO4)1.36±0.02, respectively. In the Ksw system, 0.70 mol of OH- and 0.30 mol of SO42- were released per mole of F ions sorbed; those released for the Msw system were 0.69 mol and 0.31, respectively. The results showed that OH- played a primary role in the ion exchange and the schwertmannite showed good practicability for actual industrial wastewater.

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Four types of carbon dots (CDs) with various color (blue, green, yellow, and red) emissions have been synthesized under solvent-free conditions from citric acid and different nitrogen sources (DMF, urea, ethanamide, and formamide). By detailed characterization and comparison, it is confirmed that the graphitized sp2 conjugated domain and surface functional groups such as C-O and C=N play synergetic roles in adjusting the fluorescence properties. Notably, the size effect is not the dominant mechanism to achieve multi-color fluorescence emissions in this work. The structural configuration of the carbon dots further influences the energy band structure, as demonstrated in simplified energy level diagrams. An absorption peak at approximately 560 nm appears in the visible light region for red-emitting CDs, assigned to an n→π* transition of the aromatic structure, thus introducing a new surface state energy level, resulting in a reduction in the energy of electron transition and the expansion into the visible region of the UV/Vis spectrum. Taking advantage of the diverse absorption and emission properties, different CDs/TiO2 binary composites are obtained for photocatalytic degradation of organic dyes, and it is found that the absorption range in terms of visible light and the band gap of the carbon dots make a difference to the photocatalytic performance of the composites.

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This paper is focused on the effect of the stabilizing component SiO2 on the type and concentration of active sites in SnO2/SiO2 nanocomposites compared with nanocrystalline SnO2. Previously, we found that SnO2/SiO2 nanocomposites show better sensor characteristics in CO detection (lower detection limit, higher sensor response, and shorter response time) compared to pure SnO2 in humid air conditions. Nanocomposites SnO2/SiO2 synthesized using the hydrothermal method were characterized by low temperature nitrogen adsorption, XRD, energy dispersive X-ray spectroscopy (EDX), thermo-programmed reduction with hydrogen (TPR-H2), IR-, and electron-paramagnetic resonance (EPR)-spectroscopy methods. The electrophysical properties of SnO2 and SnO2/SiO2 nanocomposites were studied depending on the oxygen partial pressure in the temperature range of 200-400 °C. The introduction of SiO2 results in an increase in the concentration of paramagnetic centers Sn3+ and the amount of surface hydroxyl groups and chemisorbed oxygen and leads to a decrease in the negative charge on chemisorbed oxygen species. The temperature dependences of the conductivity of SnO2 and SnO2/SiO2 nanocomposites are linearized in Mott coordinates, which may indicate the contribution of the hopping mechanism with a variable hopping distance over local states.

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Carbon dots (CDs) display tunable photoluminescence and excitation-wavelength dependent emission. The color of fluorescence is affected by electronic bandgap transitions of conjugated π-domains, surface defect states, local fluorophores and element doping. In this review (with 145 refs.), the studies performed in the past 5 years on the relationship between the fluorescence mechanism and modes for modulating the emission color of CDs are summarized. The applications of such CDs in sensors and assays are then outlined. A concluding section then gives an outlook and describes current challenges in the design of CDs with different emission colors. Graphical abstract Schematic representation of the relationship between the color-emitting (blue, green, yellow, red and multicolor) modulation of carbon dots and fluorescence mechanism including bandgap transitions of conjugated π-domains and surface defect states.

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Nanocomposites SnO2/SiO2 with a silicon content of [Si]/([Sn] + [Si]) = 3/86 mol.% were obtained by the hydrothermal method. The composition and microstructure of the samples were characterized by EDX, XRD, HRTEM and single-point Brunauer-Emmet-Teller (BET) methods. The surface sites were investigated using thermal analysis, FTIR and XPS. It is shown that the insertion of silicon dioxide up to the value of [Si]/([Sn] + [Si]) = 19 mol.% stabilizes the growth of SnO2 nanoparticles during high-temperature annealing, which makes it possible to obtain sensor materials operating stably at different temperature conditions. The sensor properties of SnO2 and SnO2/SiO2 nanocomposites were studied by in situ conductivity measurements in the presence of 10-200 ppm CO in dry and humid air in the temperature range of 150-400 °C. It was found that SnO2/SiO2 nanocomposites are more sensitive to CO in humid air as compared to pure SnO2, and the sample with silicon content [Si]/([Sn] + [Si]) = 13 mol.% is resistant to changes in relative air humidity (RH = 4%-65%) in the whole temperature range, which makes it a promising sensor material for detecting CO in real conditions. The results are discussed in terms of the changes in the composition of surface-active groups, which alters the reactivity of the obtained materials.

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Building on work by Stallings, Jaco, and Hempel in three dimensions and a more recent four-dimensional analog by Abrams, Kirby, and Gay, we show how the splitting homomorphism and group trisection constructions can be extended to functors between appropriate categories. This further enhances the bridge between smooth four-dimensional topology and the group theory of free and surface groups.

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Surface functional groups strongly affect the properties of carbon dots (CDs). Amino, carboxy, and hydroxy groups are most commonly encountered in CDs, and they can be introduced via covalent and noncovalent modification. This article (with 116 refs.) reviews the progress made in the past few years. Following an introduction into the field, a large section covers methods for covalent modification (via amide coupling reactions, silylation, and other reactions including esterification, sulfonylation and copolymerization). Next section reviews methods for noncovalent modifications (π interactions, complexation/chelation, and electrostatic interactions). The resulting modified CDs are powerful nanomaterials for targeting and extracting analytes, and in drug release. The modification of the surface also affects fluorescence quantum yields, complexation capacity, the color of fluorescence, and their quenching capability. Current challenges are critically assessed in the concluding section. Graphical abstract The modification methods of carbon dots (CDs) includes covalent and noncovalent. Covalent modifications include amidation, silylation, esterification, sulfonylation and copolymerization reaction. Noncovalent modifications include electrostatic interactions, complexation and π interactions.

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Activated carbons (ACs) are widely used in the purification of drinking water without almost any knowledge about the adsorption mechanisms of the persistent organic pollutants. Chlordecone (CLD, Kepone) is an organochlorinated synthetic compound that has been used mainly as agricultural insecticide. CLD has been identified and listed as a persistent organic pollutant by the Stockholm Convention. The selection of the best suited AC for this type of contaminants is mainly an empirical and costly process. A theoretical study of the influence of AC surface groups (SGs) on CLD adsorption is done in order to help understanding the process. This may provide a first selection criteria for the preparation of AC with suitable surface properties. A model of AC consisting of a seven membered ring graphene sheet (coronene) with a functional group on the edge was used to evaluate the influence of the SGs over the adsorption. Multiple Minima Hypersurface methodology (MMH) coupled with PM7 semiempirical Hamiltonian was employed in order to study the interactions of the chlordecone with SGs (hydroxyl and carboxyl) at acidic and neutral pH and different hydration conditions. Selected structures were re-optimized using CAM-B3LYP to achieve a well-defined electron density to characterize the interactions by the Quantum Theory of Atoms in Molecules approach. The deprotonated form of surface carboxyl and hydroxyl groups of AC models show the strongest interactions, suggesting a chemical adsorption. An increase in carboxylic SGs content is proposed to enhance CLD adsorption onto AC at neutral pH conditions.

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Although reports have shown shifts in carbon dot emission wavelengths resulting from varying the excitation wavelength, this excitation-dependent emission does not constitute true tuning, as the shifted peaks have much weaker intensity than their dominant emission, and this is often undesired in real world applications. We report for the first time the synthesis and photoluminescence properties of carbon dots whose peak fluorescence emission wavelengths are tunable across the entire visible spectrum by simple adjustment of the reagents and synthesis conditions, and these carbon dots are excited by white light. Detailed material characterization has revealed that this tunable emission results from changes in the carbon dots' chemical composition, dictated by dehydrogenation reactions occurring during carbonization. These significantly alter the nucleation and growth process, resulting in dots with either more oxygen-containing or nitrogen-containing groups that ultimately determine their photoluminescence properties, which is in stark contrast to previous observations of carbon dot excitation-dependent fluorescence. This new ability to synthesize broadband excitable carbon dots with tunable peak emissions opens up many new possibilities, particularly in multimodal sensing, in which multiple analytes and processes could be monitored simultaneously by associating a particular carbon dot emission wavelength to a specific chemical process without the need for tuning the excitation source.

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The "capacitive mixing" (CAPMIX) is one of the techniques aimed at the extraction of energy from the salinity difference between sea and rivers. It is based on the rise of the voltage between two electrodes, taking place when the salt concentration of the solution in which they are dipped is changed. We study the rise of the potential of activated carbon electrodes in NaCl solutions, as a function of their charging state. We evaluate the effect of the modification of the materials obtained by adsorption of charged molecules. We observe a displacement of the potential at which the potential rise vanishes, as predicted by the electric double layer theories. Moreover, we observe a saturation of the potential rise at high charging states, to a value that is nearly independent of the analyzed material. This saturation represents the most relevant element that determines the performances of the CAPMIX cell under study; we attribute it to a kinetic effect.

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Activated carbon (AC) is employed in drinking water purification without almost any knowledge about the adsorption mechanism of persistent organic pollutants (POPs) onto it. Hexachlorocyclohexane (HCH) is an organochlorinated contaminant present in water and soils of banana crops production zones of the Caribbean. The most relevant isomers of HCH are γ-HCH and ß-HCH, both with great environmental persistence. A theoretical study of the influence of AC surface groups (SGs) on HCH adsorption is done in order to help to understand the process and may lead to improve the AC selection process. A simplified AC model consisting of naphthalene with a functional group was used to assess the influence of SGs over the adsorption process. The Multiple Minima Hypersurface (MMH) methodology was employed to study γ-HCH and ß-HCH interactions with different AC SGs (hydroxyl and carboxyl) under different hydration and pH conditions. The results obtained showed that association of HCH with SGs preferentially occurs between the axial protons of HCH and SG's oxygen atom, and the most favorable interactions occurring with charged SGs. An increase in carboxylic SGs content is proposed to enhance HCH adsorption onto AC under neutral pH conditions. Finally, this work presents an inexpensive computer aided methodology for preselecting activated carbon SGs content for the removal of a given compound.

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