Nitrogen doped hierarchically structured porous carbon fibers with an ultrahigh specific surface area for removal of organic dyes

Recently, tremendous efforts have been devoted to creating inexpensive porous carbon materials with a high specific surface area (SSA) as adsorbents or catalysts for the efficient removal of organic pollutants. Here, activated porous carbon fibers with hierarchical structures were designed and constructed by an electrospinning technique, in situ polymerization, and activation and carbonization processes. Benefiting from the precursor fiber design and subsequent activation techniques, the activated porous carbon fibers (APCFs) derived from a benzoxazine/polyacrylonitrile (BA-a/PAN) precursor exhibited an ultrahigh SSA of 2337.16 m² g⁻¹ and a pore volume of 1.24 cm³ g⁻¹, showing excellent adsorption capacity toward methylene blue (MeB, 2020 mg g⁻¹). Interestingly, the APCFs after pre-adsorption of MeB also display robust activation of peroxymonosulfate (PMS) with singlet oxygen for the ultrafast removal of MeB. Meanwhile, the synergistic effect of adsorption and a catalytic oxidation reaction using APCFs can realize outstanding total organic carbon (TOC) removal in a comparatively short time. Moreover, a synergistic adsorption–oxidation mechanism for promoting the removal of MeB using APCFs was proposed. This study is useful for the design and development of novel metal-free carbon adsorbents, catalysts or catalyst carriers with an ultrahigh SSA for various applications.

Active porous carbon fibers with an ultrahigh specific surface area for the synergistic removal of organic pollutants via adsorption and catalytic oxidation.     

Sulfhydryl functionalized carbon quantum dots as a turn-off fluorescent probe for sensitive detection of Hg2+

Mercury ion (Hg²⁺) is one of the most toxic heavy metal ions and lowering the detection limit of Hg²⁺ is always a challenge in analytical chemistry and environmental analysis. In this work, sulfhydryl functionalized carbon quantum dots (HS-CQDs) were synthesized through a one-pot hydrothermal method. The obtained HS-CQDs were able to detect mercury ions Hg²⁺ rapidly and sensitively through fluorescence quenching, which may be ascribed to the formation of nonfluorescent ground-state complexes and electron transfer reaction between HS-CQDs and Hg²⁺. A modification of the HS-CQD surface by –SH was confirmed using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The HS-CQDs sensing system obtained a good linear relationship over a Hg²⁺ concentration ranging from 0.45 μM to 2.1 μM with a detection limit of 12 nM. Delightfully, the sensor has been successfully used to detect Hg²⁺ in real samples with satisfactory results. This means that the sensor has the potential to be used for testing actual samples.

Schematic presentation of the synthesis of HS-CQDs and the application as a “turn-off” fluorescent probe for Hg²⁺ detection.     

A solvent-dependent chemosensor for fluorimetric detection of Hg2+ and colorimetric detection of Cu2+ based on a new diarylethene with a rhodamine B unit

A novel solvent-dependent chemosensor 1o based on a diarylethene containing a rhodamine B unit has been designed. It could be used as a dual-functional chemosensor for selective detection of Hg²⁺ and Cu²⁺ by monitoring the changes in the fluorescence and UV-vis spectral in different solvents. A striking fluorescence enhancement at 617 nm was observed in DMSO upon the addition of Hg²⁺. However, 1o showed a remarkable absorption band appeared with maximum absorption at 555 nm after the addition of Cu²⁺ in THF. The results of ESI-MS spectra and Job''s plot confirmed a 1 : 1 binding stoichiometry between 1o and the two ions. The limits of detection of Hg²⁺ and Cu²⁺ were determined to be 0.14 μM and 0.51 μM, respectively. A 1 : 2 demultiplexer circuit was constructed by using UV light as data input, Cu²⁺ as the address input, and the absorbance at 555 nm and the absorbance ratio of (A₆₀₃/A₂₇₄) as the dual data outputs.

A novel solvent-dependent chemosensor based on a diarylethene derivative for fluorescent “turn-on” recognition of Hg²⁺ and colorimetric detection of Cu²⁺ was synthesized, its multi-controllable photoswitchable behaviors with light and chemical stimuli were investigated.     

Functionalization of silver nanoparticles with mPEGylated luteolin for selective visual detection of Hg2+ in water sample

A novel colorimetric sensor based on mPEGylated luteolin-functionalized silver nanoparticles (mPEGylated luteolin-AgNPs) in an aqueous solution was prepared. The mPEGylated luteolin-AgNP solution was utilized to detect Hg²⁺ with high sensitivity and selectivity in the presence of other metal cations including Na⁺, K⁺, Mg²⁺, Zn²⁺, Ni²⁺, Mn²⁺, Ba²⁺, Pb²⁺, Sr²⁺, Ca²⁺, Cd²⁺, Al³⁺ and Cu²⁺. The solution could be induced to aggregate, and a color change from yellow-brown to colorless was observed in the presence of Hg²⁺. Meanwhile, the sensor was successfully used to detect Hg²⁺ in tap water with satisfactory recovery ranges using the standard addition method.

A novel colorimetric sensor for selective detection of Hg²⁺ based on mPEGylated luteolin functionalized silver nanoparticles was prepared.     

A novel carbon dot/polyacrylamide composite hydrogel film for reversible detection of the antibacterial drug ornidazole

A carbon dot/polyacrylamide (CDs/PAM) composite hydrogel film with stable fluorescence performance was fabricated by merging a hydrogel film and carbon dots (CDs) with blue fluorescence, which were prepared by hydrothermal synthesis using anhydrous citric acid and acrylamide as carbon sources. The obtained CDs/PAM composite hydrogel film exhibited a good fluorescence quenching effect on ornidazole (ONZ), and can be used for the quantitative detection of ONZ. In the ONZ concentration range of 5–60 μM, a good linear relationship between the fluorescence quenching efficiency of the CDs/PAM composite hydrogel film and the concentration of ONZ solution was obtained with a low detection limit of 2.35 μM. In addition, the detection system has good selectivity and strong anti-interference capacity, and can be used in repeated cycles for detection.

A novel carbon dot/polyacrylamide composite hydrogel film with stable blue fluorescence performance was fabricated by merging a hydrogel film and carbon dots, which was used for highly selective and quantitative detection of ONZ in real samples.     

Construction of a flexible covalent organic framework based on triazine units with interesting photoluminescent properties for sensitive and selective detection of picric acid

Highly emissive two-dimensional (2D) covalent organic frameworks (COFs) have rarely been reported due to the challenge of inhibiting the aggregation-caused quenching (ACQ) caused by π–π stacking between layers. To address this issue, the use of flexible building units is a promising strategy. However, currently reported flexible 2D COFs generally exhibit poor crystallinity, low surface area, etc. and the mechanism of the excellent fluorescence performance for the flexible 2D COFs still needs to be further explored. In this article, a novel flexible 2D COF (DTZ-COF) was synthesized using two π-electron deficient triazine monomers rather than the commonly used one π-electron rich fused aromatic ring under solvothermal conditions. Fortunately, DTZ-COF exhibits excellent crystallinity and high surface area (1276.5131 m² g⁻¹ and 2087.5502 m² g⁻¹ for Brunauer–Emmett–Teller (BET) and Langmuir surface area, respectively), which are rarely observed in previously reported flexible 2D COFs. The increased Lewis basic sites endow DTZ-COF with certain advantages in the separation of CO₂ and N₂. The comparison between flexible DTZ-COF and a non-flexible 2D COF (TPT-TPT-COF) with a similar framework suggests that the introduction of flexible building units can indeed improve the photoluminescence (PL) efficiency. The π-electron deficient DTZ-COF has excellent fluorescence performance and exhibits unique solvent responsiveness, such as fluorescence enhancement in aromatic solvents, and fluorescence quenching in alcohol and water. As a chemical sensor for detection of picric acid (2,4,6-trinitrophenol, TNP), the efficient fluorescence quenching involving both static and dynamic behaviors ensures high selectivity and sensitivity (ppb level).

Construction of a novel two-dimensional covalent organic framework with excellent photoluminescence performance using flexible building blocks.     

1,3,4-Thiadiazol derivative functionalized-Fe3O4@SiO2 nanocomposites as a fluorescent probe for detection of Hg2+ in water samples

5-Amino-1,3,4-thiadiazole-2-thiol was used to synthesize a novel fluorescent functionalizing group on a Fe₃O₄@SiO₂ magnetic nanocomposite surface for detection of heavy metal ions in water samples. The prepared probe was characterized by using X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and a vibrating sample magnetometer. Among various tested ions, the new nanocomposite responded to Hg²⁺ ions with an intense fluorescence “turn-off”. The limit of detection of the probe shows that it is sensitive to the minimum Hg²⁺ concentration of 48.7 nM. Theoretical calculations were done for estimating binding energies of the three possible bonding modes and the visualized molecular orbitals were presented.

VBYT-Fe₃O₄@SiO₂ fluorescent probe was designed for sensitive detection of mercury in water samples.     

Room-temperature preparation of a chiral covalent organic framework for the selective adsorption of amino acid enantiomers

Herein, we have reported the facile room-temperature synthesis of a chiral covalent organic framework (CCOF) for the enantioselective adsorption of amino acids. The prepared CCOF provides various stereoscopic interactions with amino acids for highly selective adsorption of their enantiomers.

A chiral COF CTzDa was synthesized at room temperature for the selective enantioselective adsorption of amino acids.

Chirality is one of the most common properties of natural compounds including proteins, polysaccharides, nucleic acids and enzymes, and it plays an extremely important role in life activities.^1,2 However, the selective recognition and interaction of their enantiomers with organisms make a huge difference in activity, toxicity, adsorption, transfer, metabolism and elimination. Therefore, the exploration of efficient ways to obtain pure enantiomers becomes more and more urgent; however, this is highly challenging owing to the dramatic similarity of the physicochemical properties of two enantiomers.^3,4 To date, various chiral separation techniques have been proposed such as chromatography,^5,6 crystallization^7,8 and extraction.^9,10 Adsorption separation based on porous materials has shown advantages due to their strong chiral recognition ability, long-term stability, and less complexity.¹¹The exploration of chiral-functionalized porous materials as adsorbents for the highly efficient resolution of enantiomers has received extensive attention; these materials include metal–organic frameworks,^12,13 porous organic cages,^14,15 metal–organic cages^16,17 and composite porous materials.¹⁸ However, the type of adsorbents for enantioselective adsorption was far more enough due to its challengeable preparation. As a consequence, it is necessary to design and prepare more new adsorbents with excellent stability and rapid kinetics for the selective adsorption of enantiomers.Covalent organic frameworks (COFs)^19,20 are crystalline organic porous materials with broad applications in diverse fields including chromatography separation,^21,22 heterogeneous catalysis,^23,24 fluorescence sensing^25,26 and optoelectronic materials.^27,28 The large surface area, excellent stability and the number of duplicate ordered units of COFs allow numerous interactions between the host and guests, such as hydrogen bonding, π–π interactions, hydrophobic interactions and molecular sieving, indicating COFs as a convenient platform for enantioselective adsorption. Chiral covalent organic frameworks (CCOFs) have been explored as the stationary phase in chiral chromatography and as catalysts in asymmetric catalysis.^29–31 However, the application of CCOFs as adsorbents for selective adsorption has been rarely reported.Here, we have reported the design and room-temperature (RT) synthesis of a CCOF, CTzDa, via the post-modification of the COF TzDa for the selective adsorption of the enantiomers of amino acids (AAs). TzDa consisting of 4,4′,4''-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and 1,4-dihydroxyterephthalaldehyde (Da) was chosen as the platform for the preparation of chiral COF due to its high stability, easy synthesis and abundant active groups (–OH).³²d-Camphoric acid was converted to its acid chloride to react with the hydroxyl group of TzDa for obtaining CTzDa. The application of CTzDa as the adsorbent for the chiral separation of AAs was further investigated via detailed experimental characterizations and computational modeling. This work shows high potential of chiral COFs as adsorbents in enantioselective adsorption.The COFs used as adsorbents should possess great stability, high crystallinity and large surface areas. Moreover, the introduction of a chiral environment into the COF structure via a post-modification strategy is a widely accessible way to prepare CCOFs. In this work, TzDa, which possessed a highly ordered and stable structure with abundant active groups (–OH) for further modification, was chosen as the COF platform for preparing CCOF. As shown in Fig. 1, we synthesized TzDa by condensing Tz and Da at RT instead of high temperature and pressure (Fig. S1, ESI^†).Open in a separate windowFig. 1Room-temperature synthesis: (a) TzDa; (b) CTzDa. d-Camphor acid chloride (d-cam-ClO) (Fig. S2 and S3, ESI^†) prepared from d-camphor acid was then applied to react with hydroxyl groups to introduce the chiral moiety into the channel of TzDa for preparing CTzDa.The Fourier transform infrared (FTIR) spectra of TzDa show the C N peak at 1665 cm⁻¹ along with the disappearance of the peaks for the C O and NH₂ bonds for the starting materials, indicating the successful condensation of Tz and Da (Fig. S4, ESI^†). Compared with TzDa, CTzDa exhibited additional peaks at 1805 cm⁻¹, 1741 cm⁻¹ and 1259 cm⁻¹ for the C O bond of the carboxyl group and C O and C–O bonds of the ester group, respectively, but no peaks for the C O bond of acid chloride (Fig. 2a and S5, ESI^†). The result reveals the successful grafting of the chiral d-camphoric acid moiety on TzDa. The modification ratio of d-camphoric acid on TzDA was calculated to be 41% using a toluidine blue O (TBO) dye assay (ESI^†).Open in a separate windowFig. 2(a) FTIR spectra of TaDa and CTzDa. (b) PXRD patterns of TaDa and CTzDa. (c) Zeta potential of TzDa and CTzDa. (d) PXRD patterns of CTzDa after immersing in various solvents.The powder X-ray diffraction (PXRD) pattern of TzDa prepared via the RT approach not only matched well with the simulated PXRD pattern, but also showed all the characteristic peaks of TzDa obtained with the solvothermal approach, indicating the formation of the reported ordered structure of TzDa (Fig. S6, ESI^†). All the PXRD peaks of TzDa remained after modification with d-cam-ClO, indicating no change in the crystal structure. The coupling reaction of camphoric acid with its hydroxyl group prevents the formation of intramolecular hydrogen bonds between the hydroxyl groups (Da) on formaldehyde (Tz), which results in a decrease in the crystallinity of the synthesized CTzDa (Fig. 2b and S7, ESI^†).The grafting of d-cam made the zeta potential of COF more negative from −8.2 mV (TzDa) to −47.3 mV (CTaDa) due to the introduction of the hydroxyl group of d-cam (Fig. 2c; Table S1, ESI^†). There was no variation in the PXRD patterns and FTIR spectra of CTzDa after immersing in various solvents including tetrahydrofuran (THF), acetonitrile (ACN), dimethyl formamide (DMF), water, 0.1 M HCl and 0.1 M NaOH for 1 day, demonstrating the high chemical stability of CTzDa (Fig. 2d and S8, ESI^†). The prepared CTzDa also had high thermal stability up to 200 °C (Fig. S9, ESI^†).The transmission electron microscopy (TEM) images show a layer-like structure for both TzDa and CTzDa and no obvious change in morphology after the grafting of d-camphor acid onto TzDa (Fig. S10, ESI^†). The scanning electron microscopy (SEM) images indicate that the surface of CTzDa is rougher than that of TzDa (Fig. S11, ESI^†). The Brunauer–Emmett–Teller (BET) surface area and the pore size of TzDa were calculated to be 1380 m² g⁻¹ and 3.2 nm, respectively, while those of CTzDa decreased to 403 m² g⁻¹ and 1.8 nm, respectively, due to the introduction of d-camphor acid (Fig. S12 and Table S2, ESI^†).The introduction of a chiral moiety caused various stereoscopic interactions in the COF, which could improve the enantioselective ability of CTzDa. Thus, we employed the synthesized porous material CTzDa for the selective adsorption of chiral AAs (tryptophan (Trp), histidine (His), aspartic acid (Asp) and serine (Ser)). The effect of the concentration of AAs on the adsorption capacity indicated the appropriate concentrations of AAs in adsorption (Fig. S13, ESI^†). The effect of pH on the AAs adsorption showed that the adsorption process was favorable near the isoelectric point (Fig. S14, ESI^†). In comparison with TzDa, CTzDa exhibited obviously higher enantioselectivity and adsorption capacity to l-AAs than d-AAs (Fig. 3 and S15, ESI^†).Open in a separate windowFig. 3Time-dependent enantioselective adsorption of AAs on CTzDa at 293 K: (a) d-Trp and l-Trp (50 mg L⁻¹); (b) d-His and l-His (20 mg L⁻¹); (c) d-Asp and l-Asp (red, 20 mg L⁻¹); (d) d-Ser and l-Ser (20 mg L⁻¹).We further investigated the kinetics and adsorption isotherms of AAs on CTzDa. The time-dependent adsorption capacity (q_t) of AAs at three initial concentrations at 293 K showed that the adsorption equilibrium of AAs on CTzDa was achieved within 30 min, indicating the rapid adsorption of AAs on CTzDa (Fig. S16, ESI^†). The adsorption followed the pseudo-second-order kinetic model rather than the pseudo-first-order kinetic model (Fig. S17 and S18, ESI^†). The larger k₂ values of d-AAs than those of l-AAs indicate different interactions of CTzDa with d-AAs and l-AAs (Table S3, ESI^†).^33,34The adsorption isotherms were evaluated in an initial concentration range of 10–100 mg L⁻¹ at four different temperatures (20–50 °C) (Fig. S19, ESI^†). The adsorption isotherms of AAs could be better described by the Langmuir model than the Freundlich model (Table S4, ESI^†), indicating monolayer adsorption of AAs on CTzDa. The calculated maximum adsorption capacities (q_m) of l-AAs were higher than those of d-AAs, indicating the selective adsorption of chiral AAs on CTzDa. The adsorption enantioselectivity values of CTzDa were 4.20, 2.59, 2.60 and 1.62 for the enantiomers of Trp, His, Asp and Ser, respectively (Table S5, ESI^†). Compared with previous adsorbents, the developed CTzDa exhibited higher enantioselectivity (Table S6, ESI^†), showing the great potential of CTzDa as an adsorbent in the enantioselective adsorption of AAs.Efficient desorption and reusability are essential for adsorbents. Different types of eluents were used for the desorption of AAs from CTzDa at 60 °C under ultrasonication for 5 min (Fig. S20^†). The results showed that organic solvents were not favourable for AA desorption. The adsorbed AAs could be well desorbed from CTzDa with water (pH = 4 or 8) (Fig. S20, ESI^†) due to the increase in the hydrophilicity of AAs.³⁵ After five adsorption–desorption cycles, CTzDa exhibited no significant decrease in adsorption capacity, indicating the good reusability of CTzDa for the adsorption of AAs (Fig. S21, ESI^†). There was no obvious change in the PXRD pattern and FTIR spectra after five adsorption–desorption cycles, suggesting that CTzDa was stable during adsorption and desorption (Fig. S22, ESI^†).The adsorption thermodynamics was assessed by the change in Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) (Fig. S23, S24 and Table S7, ESI^†). The negative ΔG value indicated that the adsorption of AAs on CTzDa was thermodynamically spontaneous. The negative ΔH value suggested the presence of an exothermic process, which was related to the decrease in adsorption capacity at high temperatures. The negative ΔS value demonstrated the AAs lost freedom during the adsorption process.AutoDock Vina (ADVina) was used to perform docking calculations.^36,37 The calculated binding energy (BE, kcal mol⁻¹) represents the generated energy in adsorption (Table S8, ESI^†). The existing interaction modes between CTzDa and AAs are shown in Fig. 4. The binding interactions between AAs and the building unit mainly included π–π interactions, C–H⋯π interactions and H-bonds, but the strengths related to the stereoscopic interactions were different, which originally resulted in distinct adsorptions. For Trp, the carboxyl and amino groups of l-Trp could both form hydrogen bonds with CTzDa, while the different stereoscopic positions of d-Trp led to only carboxyl group forming aromatic H-bonds with CTzDa (Fig. 4a). The carboxyl group of l-His or l-Ser formed hydrogen bonds with CTzDa. On the contrary, the corresponding hydrogen bond of d-His or d-Ser between the carboxyl group and CTzDa was absent due to the large distance (Fig. 4b and d). The hydrogen bond length between l-Asp and CTzDa (1.95 Å) was shorter than that between d-Asp and CTzDa (2.61 Å) (Fig. 4c). The above-mentioned different stereoscopic interactions made the BE between the main framework and racemic AAs follow the order l-AAs > d-AAs, indicating the stronger adsorption of l-AAs than that of d-AAs on CTzDa (Table S8^†). The K_L/K_D ratios were 1.97, 1.66, 1.18 and 1.40 for Trp, His, Aps and Ser, respectively. K_L/K_D > 1 also indicated that CTzDa exhibited stronger adsorption of l-AAs than that of d-AAs.Open in a separate windowFig. 4Molecular docking modes between CTzDa and AAs: (a) Trp; (b) His; (c) Asp; (d) Ser. The receptor COF unit is displayed with thin stick style by marking C in yellow, O in red, N in blue and H in white. The AAs are displayed with thick stick style by marking C in green, O in red, N in blue and H in white. Blue, green and yellow dotted lines represent the π–π interaction, n–π interaction and hydrogen bond between CTzDa and AAs, respectively. Thin figure represents the distance of atoms.In summary, we have designed and synthesised the chiral COF CTzDa through introducing a chiral selector (d-cam) in the COF TzDa at room temperature in a facile manner. The prepared CTzDa showed good stability in various solvents, which was favourable for adsorption. CTzDa also exhibited rapid kinetics and high selectivity for the adsorption separation of the enantiomers of amino acids. Docking calculations showed that the difference in the stereoscopic hydrogen bonds between l-AAs and d-AAs is the key interaction for the enantioselective adsorption of AAs on CTzDa. This work provides a facile strategy for highly selective adsorption of AA enantiomers. Further research will focus on the potential of CTzDa in the chiral chromatographic separation of AAs.     

Efficient removal of heavy metals from polluted water with high selectivity for Hg(ii) and Pb(ii) by a 2-imino-4-thiobiuret chemically modified MIL-125 metal–organic framework

A highly porous adsorbent based on a metal–organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal. MIL-125 was densely decorated by 2-imino-4-thiobiuret functional groups, which generated a green, rapid, and efficacious adsorbent for the uptake of Hg(ii) and Pb(ii) from aqueous solutions. ITB-MIL-125 showed a high adsorption affinity toward mercury(ii) ions of 946.0 mg g⁻¹ due to covalent bond formation with accessible sulfur-based functionality. Different factors were studied, such as the initial concentration, pH, contact time, and competitive ions, under same circumstances at the room temperature. Moreover, the experimental adsorption data were in excellent agreement with the Langmuir adsorption isotherm and pseudo-second order kinetics. At a high concentration of 100 ppm mixture of six metals, ITB-MIL-125 exhibited a high adsorption capacity, reaching more than 82% of Hg(ii) compared to 62%, 30%, 2%, 1.9%, and 1.6% for Pb(ii), Cu(ii), Cd(ii), Ni(ii), and Zn(ii), respectively.

A highly porous adsorbent based on a metal–organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal.     

Manganese(ii) enhanced fluorescent nitrogen-doped graphene quantum dots: a facile and efficient synthesis and their applications for bioimaging and detection of Hg2+ ions

Manganese ion (Mn²⁺) bonded nitrogen-doped graphene quantum dots (Mn(ii)-NGQDs) with water solubility have been successfully synthesized by a simple, one-pot hydrothermal carbonization, using sodium citrate, glycine and manganese chloride as raw materials. The photoluminescence (PL) characteristics of Mn(ii)-NGQDs were studied in detail. The resulting Mn(ii)-NGQDs show a remarkably enhanced PL intensity and quantum yield (QY = 42.16%) compared with the product without Mn(ii)-doped (named as NG, QY = 27.06%) and the product doped with other metal ions. The Mn(ii)-NGQDs not only display low toxicity and high cellular uptake efficiency for fluorescence live cell imaging in biological evaluations but also exhibit a fast, highly selective and sensitive fluorescence quenching effect toward Hg²⁺ ions, with a detection limit of 3.4 × 10⁻⁸ mol L⁻¹.

Manganese ion (Mn²⁺) bonded nitrogen-doped graphene quantum dots (Mn(ii)-NGQDs) with water solubility have been successfully synthesized by a simple, one-pot hydrothermal carbonization, using sodium citrate, glycine and manganese chloride as raw materials.     

TiO2-Based photocatalyst modified with a covalent triazine-based framework organocatalyst for carbamazepine photodegradation

A novel fluorine-doped TiO₂ (TiO_2−XF_X) heterojunction semiconductor photocatalyst was synthesised using covalent triazine-based frameworks (CTFs) at different weight ratios. X-ray photoelectron spectroscopy revealed that doping with CTFs shifts the value of the TiO_2−XF_X catalyst to a lower binding energy, which led to the bandgap narrowing. From the results of the photocatalytic activity and Fourier-transform infrared spectroscopy, a rise in carbamazepine (CBZ) adsorption under dark conditions and an increased intensity of characteristic triazine units after exfoliation were observed, which indicated that the addition of nanosheet CTFs would increase the number of active sites. Furthermore, the results showed that the TiO_2−XF_X/CTFs photocatalyst was almost 5.5 times better than pure TiO_2−XF_X in the removal of CBZ under visible light owing to the narrowed bandgap, the increased active sites, the quick separation of photo-generated carriers, and improved light absorption. A mechanism for photodegradation of CBZ with the TiO_2−XF_X/CTFs photocatalyst was proposed.

A novel fluorine-doped TiO₂ (TiO_2−XF_X) heterojunction semiconductor photocatalyst was synthesised using covalent triazine-based frameworks (CTFs) at different weight ratios.     

A sensitive fluorescent sensor for the detection of trace water in organic solvents based on carbon quantum dots with yellow fluorescence

The quantitative analysis of trace water in organic solvents has always been a research hotspot, and it is still in the development stage and needs to be continuously developed. In this study, a facile and rapid approach was developed for the preparation of carbon quantum dots (CQDs) with yellow fluorescence emission and ultrahigh absolute fluorescence quantum yields (92.6%). Compared to traditional organic fluorescent molecules, the preparation of CQDs is simpler, faster and more environmentally friendly. It is found that the fluorescent properties of CQDs are excellent in organic solvents and could be quenched by trace water, which makes them a promising material used without any modification for the detection of water in organic solvents. As a result, the as-prepared CQDs were adopted as fluorescent probes for the detection of water in organic solvents (ethanol, tetrahydrofuran, and 1,4-dioxane). The limit of detection was as low as 0.01%. To the best of our knowledge, this is the first time that CQDs have been used as water sensing fluorescent probes in organic solvents. The possible mechanism for trace water detection of the as-prepared CQDs in organic solvents is attributed to the specific water–fluorophore interaction and partially to the increase in polarity of the solvent caused by an increase in water concentration.

A simple fluorescent sensor for water content based on carbon quantum dots with yellow fluorescence was first demonstrated.     

Efficient removal of humic acid in water using a novel TiO2 composite with biochar doping

Titanium dioxide modified with biochar (Ti–C) was prepared by a sol–gel method for the degradation of humic acid (HA) in aqueous solutions. Under identical conditions, Ti–C contained less TiO₂ and showed better HA degradation capacity than that of pure TiO₂, and had ca. 20% higher HA removal rate than that of simple Ti–C adsorption. Photocatalytic degradation of HA with Ti–C had an efficient removal rate of 50% at pH = 3, which was ca. 28% higher than that at pH = 7 (HA = 10 mg L⁻¹), while a higher reaction temperature, longer lighting time and larger Ti–C dosage were conducive to HA photocatalytic degradation. SEM micrographs showed that Ti–C had a much rougher surface than the original biochar, and EDS results of Ti–C indicated that its carbon content increased up to 26.2% after biochar doping. Ti–C had an evident anatase structure and a typical SiO₂ structure, as revealed by XRD analysis. TOC and GC-MS analysis indicated that HA was effectively degraded and transformed into harmless carbon dioxide. Superoxide radicals were the main active radicals produced for the efficient degradation of humic acid, while hydroxyl radicals and electron–holes also contributed to HA decomposition in Ti–C systems. This work is expected to be helpful for the innovative preparation of titanium dioxide as a low-cost photocatalyst for the degradation of humic acid in water.

Titanium dioxide modified with biochar (Ti–C) was prepared by a sol–gel method for the degradation of humic acid (HA) in aqueous solutions.     

Bis-BODIPY linked-triazole based on catechol core for selective dual detection of Ag+ and Hg2+

Herein, we introduced a new chemosensor, bis-BODIPY linked-triazole based on catechol (BODIPY-OO) prepared by bridging two units of BODIPY fluorophore/triazole binding group with a catechol unit. A solution of this compound displayed 4- and 2-fold enhancements in fluorescence intensity after adding a mole equivalent amount of Ag⁺ and Hg²⁺ ions in methanol media, respectively. ¹H NMR titrations of BODIPY-OO with Ag⁺ and Hg²⁺ suggested that the triazole was involved in the recognition process. BODIPY-OO showed high sensitivity toward Ag⁺ and Hg²⁺ over other metal ions with detection limits of 0.45 μM and 1 μM, respectively. It can also distinguish Hg²⁺ from Ag⁺ by addition of an EDTA. This compound can therefore be employed as practical fluorescent probe for monitoring the presence of Ag⁺ and Hg²⁺ ions.

BODIPY–triazole–catechol combination serves as a “turn-on” fluorescent probe for dual detection and differentiation of Hg²⁺ and Ag⁺ ions.     

A colorimetric and fluorescent chemosensor for Hg2+ based on a photochromic diarylethene with a quinoline unit

A new colorimetric and fluorescent ‘on–off’ chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized. The chemosensor 1O demonstrated selective and sensitive detection of Hg²⁺ ions in the presence of other competitive metal ions in acetonitrile. The stoichiometric ratio of the sensor 1O for Hg²⁺ was determined to be 1 : 1, and the limit of detection of the probe 1O was calculated to be 56.3 nM for Hg²⁺. In addition, a molecular logic circuit with four inputs and one output was successfully constructed with UV/vis light and metal-responsive behavior. ESI-MS spectroscopy, Job''s plot analysis, and ¹H NMR titration experiments confirm the binding behavior between 1O and Hg²⁺.

A new colorimetric and fluorescent ‘on–off’ chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized.     

A highly selective colorimetric fluorescent probe for detection of Hg2+ and its application on test strips

An efficient fluorescent probe Pyr-Rhy based on pyrazole was developed, which can detect Hg²⁺ in water. Its fluorescence properties were studied by UV-vis and fluorescence spectroscopy, and the study results indicated that this probe can selectively detect Hg²⁺via complexation reaction, and then cause a remarkable color change from colorless to pink and a strong fluorescence enhancement can be observed. Furthermore, this probe showed high sensitivity with the detection limit down to 2.07 × 10⁻⁸ M, and its stoichiometric ratio toward Hg²⁺ ions was 1 : 1. The sensing mechanism was investigated by Job''s plot ¹H NMR titrations, and FT-IR spectra analysis, which demonstrated a chelation-enhanced fluorescence (CHEF) mechanism. More importantly, obvious color changes of sensor Pyr-Rhy can be observed when it was impregnated on filter paper testing strips and immersed in Hg²⁺ solution (water as solution), indicating its potential application for trace Hg²⁺ detection in environmental samples.

An efficient fluorescent probe Pyr-Rhy based on pyrazole was developed, which can detect Hg²⁺ in water.     

Rapid electrochemical quantification of trace Hg2+ using a hairpin DNA probe and quantum dot modified screen-printed gold electrodes

Rapid, simple, sensitive and specific approaches for mercury(ii) (Hg²⁺) detection are essential for toxicology assessment, environmental protection, food analysis and human health. In this study, a ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quaternary Zn–Ag–In–S quantum dot (QD) on screen-printed gold electrodes (SPGE), referred to as the HP-QDs-SPGE electrochemical biosensor in this study, was developed for Hg²⁺ detection. Based on the “turn-off” reaction of a hairpin DNA probe binding with a mismatched target and Hg²⁺ through the formation of T–Hg²⁺–T coordination, the HP-QDs-SPGE electrochemical biosensor can rapidly quantify trace Hg²⁺ with high ultrasensitivity, specificity, repeatability and reproducibility. The conformational change of the hairpin DNA probe caused a significant decrease in electrochemical intensity, which could be used for the quantification of Hg²⁺. The linear dynamic range and high sensitivity of the HP-QDs-SPGE electrochemical biosensor for the detection of Hg²⁺ was studied in vitro, with a broad linear dynamic range of 10 pM to 1 μM and detection limits of 0.11 pM. In particular, this HP-QDs-SPGE electrochemical biosensor showed excellent selectivity toward Hg²⁺ ions in the presence of other metal ions. More importantly, this biosensor has been successfully used to detect Hg²⁺ in deionized water, tap water, groundwater and urine samples with good recovery rate and small relative standard deviations. In summary, the developed HP-QDs-SPGE electrochemical biosensor exhibited promising potential for further applications in on-site analysis.

A ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quantum dot on screen-printed gold electrodes, was developed for Hg²⁺ detection.     

ZIF-8 metal organic framework materials as a superb platform for the removal and photocatalytic degradation of organic pollutants: a review

Metal organic frameworks (MOFs) are attracting significant attention for applications including adsorption, chemical sensing, gas separation, photocatalysis, electrocatalysis and catalysis. In particular, zeolitic imidazolate framework 8 (ZIF-8), which is composed of zinc ions and imidazolate ligands, have been applied in different areas of catalysis due to its outstanding structural and textural properties. It possesses a highly porous structure and chemical and thermal stability under varying reaction conditions. When used alone in the reaction medium, the ZIF-8 particles tend to agglomerate, which inhibits their removal efficiency and selectivity. This results in their mediocre reusability and separation from aqueous conditions. Thus, to overcome these drawbacks, several well-designed ZIF-8 structures have emerged by forming composites and heterostructures and doping. This review focuses on the recent advances on the use of ZIF-8 structures (doping, composites, heterostructures, etc.) in the removal and photodegradation of persistent organic pollutants. We focus on the adsorption and photocatalysis of three main organic pollutants (methylene blue, rhodamine B, and malachite green). Finally, the key challenges, prospects and future directions are outlined to give insights into game-changing breakthroughs in this area.

Metal organic frameworks (MOFs) are attracting significant attention for applications including adsorption, chemical sensing, gas separation, photocatalysis, electrocatalysis and catalysis.     

A novel water-soluble naked-eye probe with a large Stokes shift for selective optical sensing of Hg2+ and its application in water samples and living cells

A water-soluble and colorimetric fluorescent probe with a large Stokes shift (139 nm) for rapidly detecting Hg²⁺, namely Hcy-mP, was synthesized by using an indole derivative and 2,4-dihydroxybenzaldehyde as starting materials. This probe demonstrates good selectivity for Hg²⁺ over other metal ions including Ag⁺, Pb²⁺, Cd²⁺, Cr³⁺, Zn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, K⁺, Na⁺, Mg²⁺, and Ca²⁺ in aqueous solution. With the increase in concentration of Hg²⁺, the color of the solution changed from pale yellow to pink and the fluorescence intensity decreased slightly. When 5-equivalents of EDTA were added to the solution with Hg²⁺, the fluorescence intensity of this probe was restored. The probe has been applied to the detection of Hg²⁺ in real water samples. Moreover, this probe was confirmed to have low cytotoxicity and excellent cell membrane permeability. The effect of Hcy-mP–Hg²⁺ towards living cells by confocal fluorescence was also investigated.

A water-soluble and colorimetric fluorescent probe with a large Stokes shift (139 nm) for rapidly detecting Hg²⁺, namely Hcy-mP, was synthesized by using an indole derivative and 2,4-dihydroxybenzaldehyde as starting materials.