Mixed Dye Research Articles

Remediation of charged organic pollutants—binding motifs for highly efficient water cleaning with nanoparticles

AbstractMany charged organic molecules behave as persistent and hazardous pollutants with harmful effects on human health and ecosystems. They are widely distributed related to their charged molecular structure that provides water solubility. In order to track the fate and behavior of such pollutants, charged dyes with specific absorption in the visible spectra serve as convenient model compounds. We provide a platform of smart adsorbers that efficiently remediate positively and negatively charged dyes (crystal violet and Amaranth) from water. Metal oxide nanoparticles serve as a core with an intrinsically large surface area. The surface potential was tuned towards positive or negative by decorating the cores with self‐assembled monolayers of dedicated long‐chained phosphonic acid derivatives. Selective remediation of the dyes was obtained with corresponding oppositely charged core‐shell nanoparticles. Mixed dye solution can be cleaned by a cascade approach or by applying both particle systems simultaneously. The removal efficiency was determined as a function of particle concentration via UV‐spectroscopy. The results of remediation experiments at different pH values and using superparamagnetic iron oxide nanoparticle cores lead to a simple process with recycling capability.

Applicability and Freshness Control of pH-Sensitive Intelligent Label in Cool Chain Transportation of Vegetables.

Freshness is one of the main factors affecting consumers' purchase of food. The freshness indicator labels of packaged fresh green bell pepper (Capsicum annuum L.) and greengrocery (Brassica chinensis L.) were constructed, and pH-sensitive indicator labels based on the dye of anthocyanin and the mixing dye of methyl red and bromothymol blue were prepared in this study. At the same time, the color, chlorophyll content and vitamin C content of vegetables were measured in order to explore the applicability of indicator labels in the cool chain transportation of vegetables. Compared with the nature dye, the chemical dye-type indicator labels are more sensitive to pH changes. The results showed that the mixed indicator intelligent label had the best indication effect, and the MB 2 (mixing 1 g/L methyl red and bromothymol blue solutions at a ratio of 3:2 with a concentration of 70 mL/L in indicator film solution) indicator label could effectively indicate the freshness changes in vegetables during storage. Meanwhile, the color changes of the MB 2-type indicator label were correlated with the colors change of the sample, changes in nutrients, and changes in CO2 content inside the packaging. In addition, freshness detection models for green bell pepper and greengrocery by using color information of MB 2 intelligent labels were established. Hence, this pH-sensitive label can be applied as a promising intelligent packaging for non-destructively monitoring the freshness of respiratory and non-respiratory climacteric vegetables.

A parametric study on intensified degradation of textile dye water using hydrodynamic cavitation based hybrid technique

In this paper, a detailed investigation of the treatment of model textile dye wastewater (MTDW) by applying a hybrid approach of hydrodynamic cavitation (HC) coupled with UV light and different oxidants is reported. A distinct hybrid strategy of HC combined with inline UV and different oxidants was employed to treat model textile dye wastewater comprising mixed dyes under neutral to alkaline conditions and in the presence of salt and detergent, which form significant components of textile wastewater. The model textile dye wastewater was made of three dyes: Reactive Yellow 84, Reactive Black 8, and Reactive Violet 5 with 100 ppm of total concentration. Effects of various operating conditions, such as feed pressure at the venturi inlet, initial pH, process time, and different oxidizing agents, on percentage COD reduction were investigated. The extent of dye decolourization using HC combined with different oxidizing agents, viz., hydrogen peroxide (H2O2), sodium persulfate (NaPS), and potassium peroxymonosulfate (PPMS), were studied. HC coupled with UV and potassium peroxymonosulfate (PPMS) oxidant produced maximum decolourization of dyes to the extent of 100 % at pH 7. A maximum COD reduction of 87.7 % was obtained at the optimized operation conditions of hydrodynamic cavitation (HC) coupled with UV and PPMS. The treatment of model dye wastewater utilizing a hybrid strategy of HC+UV+PPMS achieved a synergetic index of 1.92, which was significantly better than standalone treatments. The current work contributes significantly to our understanding of the performance of cavitation-based systems for treating complicated textile effluent.

Magnetic nanocellulose-based adsorbent for highly selective removal of malachite green from mixed dye solution

Herein, a novel magnetic adsorbent (BC/AA/MN@Fe3O4) was successfully prepared from waste bamboo fiber tissue and montmorillonite, and subsequently applied for the highly selective removal of malachite green (MG, removal efficiency = 97.3 %) from the mixed dye solution of MG with methyl orange (MO, removal efficiency = 4.5 %). The magnetic adsorbent has a high porosity with abundant mesopores. In the single dye MG solution, the adsorbent could effectively remove MG over a wide pH range from 4 to 10, and the maximum adsorption capacity (qmax) was 2282.3 mg/g. Moreover, the magnetic adsorbent could remove MG from various solutions including mixed dye solution, high salinity solution, and real river water dye solution. The thermodynamic results proved that the adsorption process of MG was spontaneous and endothermic. The adsorption of MG was due to the comprehensive effects of electrostatic attraction, hydrogen bonding interactions and ions exchange, between the adsorbent and MG. Furthermore, the BC/AA/MN@Fe3O4 exhibited an excellent reusability with adsorption efficiency above 53.4 % after five consecutive cycles. Therefore, the prepared magnetic nanocellulose-based adsorbent was expected to be a promising material for highly selective adsorption and separation of MG from mixed dye solution.

Technical aesthetic in the works of Alberto Buri

The artistic technique has an important role in the constructive analyzes of the plastic visual achievements according to the relationship of the artistic elements and the mechanisms of their operation with each other, so the artist deliberately shows the aesthetics of these techniques through his own artistic and technical style according to his conscious ability to move away from the classical traditions. The research consists of four chapters, the chapter included The first is on the methodological framework of the research, so the problem was summed up by the following question: What are the technical aesthetics in the works of Alberto Buri? As for its importance, it was represented by studying the works of the artist (Alberto Buri) for his stylistic and technical uniqueness among the artists of his era. As for the spatial borders (Europe and the United States of America), the temporal borders of the period (1949-1960). Among the results reached by the researcher: The (Buri) style was associated with the technique of existing objects, as it took the collection of dilapidated materials in order to liberate the artwork from all classical constraints and adopt contemporary techniques He mixed dyes with other materials to form different surfaces that were strange.

Direct sunlight induced room temperature synthesis of anticancer and catalytic silver nanoparticles by shrimp shell waste derived chitosan

The use of marine waste derived chitosan (CS) for the synthesis of nanomaterials is considered as one of the effective routes for bio-waste management and recovering functional products. Herein, CS capped silver nanoparticles (Ag NPs-CS) with potential anticancer and dye pollutants adoption properties have been synthesized photochemically under direct sunlight. To obtain, CS, shrimp shell waste was subjected to a serious of standard demineralization, deproteinization and deacetylation processes. The electronic absorption peak (400 nm) denoting surface plasmonic resonance of Ag NPs and infrared peaks relevant to CS (3364 cm−1 of OH/NH2, 2932 cm−1 of CH, and 1647 cm−1 of -CO) exhibited peaks confirmed the formation of CS-Ag NPs. Ag NPs-CS exhibited anticancer activity against Human lung adenocarcinoma cell lines (A549), the maximum cell death noticed at the concentration of 20 μg/mL and 70 μg/mL was 20 and 52 %, respectively. An aqueous Ag NPs-CS (100 μg/mL) was degraded ≥95 % of mixed dye target solution (25 mg/mL) containing equal volume of cationic dye (Methylene blue and Rhodamine B) and anionic dye (methyl orange). Therefore, these findings suggest that the shrimp shell waste derived CS can be used for the synthesis of CS-Ag NPs with potential biomedical and environmental applications.

Accordion-like multilayer Ti3C2Tx MXene sheets decorated 1D Mn2O3 nanorods-based nanocomposites: An efficient catalyst for swift removal of single and mixed dyes

Ti3C2Tx-MXene-based nanocomposites were prepared with 1D Mn2O3 through the electrostatic self-assembly method. The synthesized nanocomposites are investigated for photocatalytic degradation of individual dye, mixed cationic and anionic dyes under visible light irradiation. The cubic bixbyite structure of 1D Mn2O3 was confirmed in the nanocomposites by the XRD and Raman spectroscopy analyses. The band gap energy of the 1D Mn2O3-Ti3C2Tx MXene (5–20 wt%) nanocomposites was estimated to range from 0.9 eV to 0.2 eV through the Tauc plot, implying their application as a photocatalyst under visible light illumination. The randomly oriented nanorods were decorated on the accordion-like Ti3C2Tx MXene sheets and were confirmed by the SEM, FESEM and TEM analyses. The average diameter of Mn2O3 nanorods (87 nm) and interlayer spacing of Ti3C2Tx MXene sheets (172 nm) were measured from FESEM analysis. The Mn, O, Ti, C and F elemental compositions of the composites were analyzed by the EDAX. The 100% degradation efficiency of methylene blue (MB) dye was achieved in the presence of 1D Mn2O3-Ti3C2Tx (20 wt%) nanocomposite and the same was used to degrade the mixed cationic and anionic dyes. In mixed dyes, methyl orange (MO), rhodamine B (RhB) and methylene blue (MB) achieved degradation efficiencies of 82%, 80% and 96%, respectively. Based on the scavenger's experiment, the hydroxyl radical (OH−) and superoxide anion radicals (O2°−), were the dominant reactive species in the dye degradation.

Application of a Mixed-Ligand Metal–Organic Framework in Photocatalytic CO2 Reduction, Antibacterial Activity and Dye Adsorption

In this paper, a known mixed-ligand MOF {[Co2(TZMB)2(1,4-bib)0.5(H2O)2]·(H2O)2}n (compound 1) was reproduced, and its potential application potential was explored. It was found that compound 1 had high photocatalytic activity for CO2 reduction. After 12 h of illumination, the formation rate of CO, which is the product of CO2 reduction by compound 1, reached 3012.5 μmol/g/h. At the same time, compound 1 has a good antibacterial effect on Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Candida albicans (C. albicans), which has potential research value in the medical field. In addition, compound 1 can effectively remove Congo Red from aqueous solutions and achieve the separation of Congo red from mixed dye solutions.

Construction of hexagonal spindle-shaped Fe-MOFs induced by cationic copolymer and its application for effective wastewater treatment.

The environment and human health are in danger due to the long-term enrichment and buildup of organic pesticides, dyes, and harmful microbes in wastewater. The development of functional materials that are efficient for treating wastewater remains a significant problem. Eco-friendly hexagonal spindle-shaped Fe-MOFs (Hs-FeMOFs) were created in this study under the influence of cationic copolymer (PMSt). The mechanism of crystal growth and development of its unique morphology were described after looking into impact factors for the ideal circumstances and being characterized by XRD, TEM, XPS, and other techniques. It revealed that Hs-FeMOFs possess an enormous supply of adsorption active sites, a strong electropositivity, and the nanometer tip. Then, typical organic pollutants, such as herbicides and mixed dyes, as well as biological pollutants bacteria, were chosen to assess its efficacy in wastewater treatment. It was discovered that the pendimethalin could be quickly removed in wastewater and the removal rate reached 100% within 10min. In separation of mixed dyes, the retention rate of malachite green (MG) reached 92.3% in 5min and with a minimum inhibitory concentration of 0.8mg/mL and demonstrated strong activity due to the presence of cationic copolymers. In actual water matrix, Hs-FeMOF could also play excellent adsorption and antibacterial activity. In summary, a novel, environmentally friendly MOF material with good activity was successfully created by cationic copolymer induction. It offers a fresh approach to develop functional materials in wastewater treatment.

Synergistic Effect of BiVO4/P-g-C3N4 Heterojunction with Enhanced Optoelectronic Properties on Synthetic Colorants under Visible Light

Environmental remediation in the presence of robust semiconductor photocatalysts by utilizing renewable energy sources is of keen interest among researchers. In this study, we synthesize a BiVO4/P-g-C3N4 semiconductor heterojunction photocatalytic system through a hydrothermal route followed by utilizing a total-solvent evaporation method. The optical and electronic properties of the as-prepared heterojunction are characterized via various spectroscopic techniques. Rhodamine B (RhB) and Congo Red (CR) are used as synthetic colorants to evaluate the photocatalytic performances of BiVO4/P-g-C3N4. In addition, the chemical environment of the photocatalyst and its mechanistic pathways are confirmed through X-ray photoelectron spectroscopy and electrochemical Mott–Schottky analysis. The BiVO4/P-g-C3N4 photocatalyst shows higher photodegradation (96.94%) of the mixed synthetic dyes under simulated solar-light irradiation. The as-synthesized BiVO4/P-g-C3N4 heterojunction significantly promotes the quick separation of photoexcited carriers due to the excellent synergetic properties, the extended light absorption, and the photoelectrochemical response. Furthermore, a possible type-II charge transfer mechanism is adopted for the BiVO4/P-g-C3N4 system after investigating the band potentials, active species, and charge carrier migration over the heterojunction interface.

Unusual, hierarchically structured composite of sugarcane pulp bagasse biochar loaded with Cu/Ni bimetallic nanoparticles for dye removal

Biochar-supported nanocatalysts emerged as unique materials for environmental remediation. Herein, sugarcane pulp bagasse (SCPB) was wet-impregnated with Cu(NO3)23H2O and Ni(NO3)26H2O, then pyrolyzed at 500 °C, under N2, for 1 h. We specifically focused on sugarcane pulp instead of SCB and biochar materials. The metal nitrate to biomass ratio was set at 0.5, 1, and 2 mmol/g, with Cu/Ni initial ratio = 1. The process provided hierarchically structured porous biochar, topped with evenly dispersed 40 nm-sized CuNi alloy nanoparticles (SCPBB@CuNi). The biochar exhibited an unusual fishing net-like structure induced by nickel, with slits having a length in the 3–12 μm range. Such a fishing net-like porous structure was obtained without any harsh acidic or basic treatment of the biomass. It was induced, during pyrolysis, by the nanocatalysts or their precursors. The CuNi nanoparticles form true alloy as proved by XRD, and are prone to agglomeration at high initial metal nitrate concentration (2 mmol/g). Stepwise metal loading was probed by XPS versus the initial metal nitrate concentration. This is also reflected in the thermal gravimetric analyses. The SCPBB@CuNi/H2O2 (catalyst dose: 0.25 g/L) system served for the catalyzed removal of Malachite Green (MG), Methylene Blue (MB), and Methyl Orange (MO) dyes (concentration = 0.01 mmol/L). Both single and mixed dye solutions were treated in this advanced oxidation process (AOP). The dyes were removed in less than 30 min for MG and 3 h for MB, respectively, but 8 h for MO, therefore showing selectivity for the degradation of MG, under optimized degradation conditions. The catalysts could be collected with a magnet and reused three times, without any significant loss of activity (∼85%). AOP conditions did not induce any nanocatalyst leaching.To sum up, we provide a simple wet impregnation route that permitted to design highly active Fenton-like biochar@CuNi composite catalyst for the degradation of organic pollutants, under daylight conditions.

Sustainable utilization metal ions of acid leaching clay wastewater to fabricate adsorbents for high-efficient removing Congo red and Methyl violet

Recycling waste into efficient adsorbents to remove pollutants again provides a compatible solution for the sustainable development of water resources. Here, Mg2+, Al3+, and Fe3+ metal ions from oxalic acid leaching mixed-dimensional palygorskite clay wastewater were successfully converted into mixed metal oxides (MMOs) through a simple precipitation-calcination process. MMOs prepared under different precipitation pH conditions or different washing schemes were used to remove the anionic dye Congo red (CR) and cationic dye Methyl violet (MV). The relatively pure Mg-Al-Fe MMO obtained at pH 13 with thorough washing had ultrahigh adsorption capacity for CR, up to 1369 mg/g. In the presence of sodium oxalate byproducts without washing, the prepared MMOs containing Fe3O4, sodium carbonate, and carbon byproducts had higher removal capacities for cationic dye MV, with a maximum of 1098 mg/g. Moreover, the series of MMOs exhibited strong removal capability for CR + MV mixed dyes and satisfactory cycle stability. This work provided a new perspective on the sustainable utilization of mineral resources and water resources.

Enhanced simultaneous degradation of simulated dyes using ZnO/GCN heterojunction photocatalyst.

The scarcity of water leads to research nowadays to focus on techniques for treating wastewater. Photocatalysis emerged as a technique of interest due to its nature of friendliness. It utilizes light and catalyst to degrade the pollutants. One of the popular catalysts to be used is zinc oxide (ZnO), but its usage is limited due to the high recombination rate of electron-hole pair. Herein, in this study, ZnO is modified with graphitic carbon nitride (GCN), and the GCN loading amount was varied to study the impact on photocatalytic degradation of mixed dye solution. To the best of our knowledge, this is the first work that reports on the degradation of mixed dye solution using modified ZnO with GCN. Structural analysis showed that GCN is present in the composites which proves the success of the modification. Photocatalytic activity revealed that the composite with 5 wt% loading of GCN showed the best activity at a catalyst dosage of 1 g/L with degradation rates of 0.0285, 0.0365, 0.0869, and 0.1758 min-1 for methyl red, methyl orange, rhodamine B, and methylene blue dyes, respectively. This observation is expected due to the formation of heterojunction between ZnO and GCN which creates a synergistic effect and thus led to an improvement in the photocatalytic activity. Based on these results, ZnO modified with GCN has a good potential to be used in the treatment of textile wastewater which consists of various dye mixtures.

Preparation of paramagnetic ferroferric oxide-calcined layered double hydroxide core–shell adsorbent for selective removal of anionic pollutants

Adsorption is one of the most common methods of pollution treatment. The selectivity for pollutants and recyclability of adsorbents are crucial to reduce the treatment cost. Layered double hydroxide (LDH) materials are one type of adsorbent with poor recyclability. Prussian blue (PB) is a sturdy and inexpensive metal–organic framework material that can be used as the precursor for synthesizing paramagnetic ferroferric oxide (Fe3O4). It is intriguing to build some reusable adsorbents with magnetic separation by integrating LDH and PB. In this work, paramagnetic Fe3O4-calcined LDH (Fe3O4@cLDH) core–shell adsorbent was designed and prepared by the calcination of PB-ZnAl layered double hydroxide (PB@LDH) core–shell precursor, which exhibits high anionic dyes selectivity in wastewater solutions. The paramagnetism and adsorption capability of Fe3O4@cLDH come from the Fe3O4 core and calcined ZnAl-LDH shell, respectively. Fe3O4@cLDH shows an adsorption capacity of 230 mg g−1 for acid orange and a high selectivity for anionic dyes in cation–anion mixed dye solutions. The regeneration process indicates that the high selectivity for anions is related to the specific hydration recovery process of ZnAl-LDH. The synergistic effect of the paramagnetic Fe3O4 core and calcined ZnAl-LDH shell makes Fe3O4@cLDH an excellent magnetic separation adsorbent with high selectivity to anions.

Efficient photosensitive light harvesting dye sensitized solar cell using hibiscus and rhodamine dyes

Co-sensitization is a powerful technique for achieving photosensitive light harvesting and enhancing dye sensitized solar cell (DSSC) performance. In this article, potential of extracted natural dye from Hibiscus sabdariffa and synthetic organic dye from Rhodamine as single dye source and mixed dyes are used to examine the performance of cells. The UV–Vis absorption spectra showed that examined dye mixture has cumulative absorption properties, such that its absorption spectra overlapped the spectral area. Moreover, DSSCs are characterized using UV–Vis Spectroscopy and Scanning electron microscopy (SEM). FTIR study was used to observe the functional groups of dye molecules to ensure the anchoring ability of dye to adsorb onto TiO2 layer. X-Ray diffraction spectrum analysis (XRD), Photovoltaic performance of cells, Energy dispersive spectroscopy (EDS), and Electrochemical impedance spectroscopy (EIS) were also conducted on the cells. The impedance spectra of dyes show minimum impedance of 17.5 Ω in case of mixed dye. XRD analysis recognizes small crystalline size that reveals anatase crystal phase of TiO2. Co-sensitized dye solar cell shows highest current density (Jsc) of 4.02mA and power conversion efficiency of 1.23%. The outcomes can be attributed to the light harvesting, the good optical condition, and the appropriate energy levels of the co-sensitized dye. Moreover, the homogenous dispersion causes effective dye loading on the surface of semiconductor.

Selective adsorption and separation of methylene blue by facily preparable xanthan gum/amantadine composites

In this work, xanthan gum-based composites were successfully graft-modified by amantadine (XG-Fe3+/AM) with higher adsorption capacity and selectivity on recycling cationic dye (methylene blue, MB) from aqueous solution. The adsorption equilibrium of MB could be achieved approximately within 5 min when the initial concentration was 100 mg/L, and the maximum adsorption capacity was up to 565 mg/g. After 5 desorption-regeneration cycles, the removal rate of XG-Fe3+/AM for MB could still be as high as 95 % with slight decrement. Additionally, the effects of pH, contact time, temperature and initial dye concentration on the adsorption performance of MB were systematically examined. Furthermore, the adsorbent was characterized by FT-IR, BET and XPS analysis. In mixed anionic and cationic dyes, the adsorption selectivity of XG-Fe3+/AM on MB in the mixture of MB and methyl orange (MO) reached up to 99.69 %. Molecular dynamics simulation revealed that the trend of adsorption energy for dyes was in good agreement of the experimental order of adsorption capacities and molecular sizes among seven anionic and cationic dyes based on molecular matching effect and electrostatic interaction. Therefore, XG-Fe3+/AM is an eco-friendly, facile-synthesis and high-selectivity adsorbent, which remove cationic dyes in multi-component systems through electrostatic interaction and molecular matching effect.

Mussel-inspired in-situ metallization of nano-Ag on ceramic membrane for catalytic degradation of dye wastewater

Catalytic membranes supported with nano-catalysts have been widely used for wastewater treatment. The traditionally catalyst immobilization methods, such as physical blending, chemical deposition and impregnation et al., involve complex preparation steps. Herein, Ag nanoparticles were in-situ immobilized on a ceramic microfiltration substrate by a mussel-inspired facile metallization process. Firstly, dopamine was deposited onto the substrate (∼200 nm) to form a uniform polydopamine coating. Then, Ag nanoparticles were in-situ metalized and immobilized on the polydopamine decorated ceramic membrane. The preparation conditions were relatively simple without sintering. FTIR, XRD, FESEM and EDS characterizations demonstrate the successful immobilization of the Ag nanoparticles. The obtained membrane exhibits good hydrophilicity and permeability (606.08 L m−2 h−1 at 0.1 MPa). The degradation rate of methyl orange achieves ∼95.6% within 20 min. The apparent reaction rate constant reaches the highest value of 568.1 min−1 at 0.5 MPa, which is several orders of magnitude higher than that of the feed side. The composite membrane can degrade mixed dyes. The catalytic membrane also shows excellent stability and antifouling property. In conclusion, this research provides a convenient and effective way for preparing a kind of composite catalytic membrane with high performance, which has potential applications in environmental remediation.

Barbituric acid derived covalent organic framework and its CNT composite as high-performance adsorbents for organic dye removal

Herein, we report for the first time, the synthesis of Barbituric acid (BA) based Covalent Organic Framework (COF) and its composite with Carbon NanoTubes (CNT), for efficient and selective dye removal. The adsorbents were characterized using solid state 13C NMR, PXRD, FT-IR, BET, FEG-SEM and TGA. Higher porosity and surface area facilitates efficient adsorption process. Batch experiments for dye adsorption were performed for Malachite Green (MG) and Methyl Orange (MO) as well as mixed dye to determine the adsorption capacity, removal efficiency and adsorption mechanism. The experimental results best fits Langmuir isotherm model and follows Pseudo second order kinetics. The maximum adsorption capacity was as high as 553.55 mg/g and 226.12 mg/g for MG and MO respectively, using COF. The COF-CNT composite showed even higher values viz. 603.91 mg/g and 234.57 mg/g for MG and MO. Moreover, the adsorption performance of these adsorbents in binary dye mixture exhibited the potential of COF for dye separation and that of COF-CNT for simultaneous dye removal. Thermodynamic studies demonstrated endothermic and spontaneous adsorption process. The regeneration studies reveal the potential of these adsorbents to be reused for multiple cycles. These adsorbents with high adsorption efficiency can act as promising and recyclable materials for practical wastewater treatment.

Hollow polyphosphazene microcapsule with rigid-flexible coupling cationic skeletons for highly efficient and selective adsorption of anionic dyes from water

An amino-rich hollow polyphosphazene microcapsule with rigid-flexible coupling cationic skeleton (HTCM) was facilely prepared by one-step polycondensation from hexachlorocyclotriphosphazene and tetraethylenepentamine. The systematic adsorption studies for six single dye systems and three binary mixed dye systems showed that HTCM possessed a highly-efficient and selective adsorption behavior towards anionic dyes from water. Especially, the adsorption capacity of HTCM towards methyl orange (MO) at equilibrium reached 1009.66 mg g−1 at 25 °C, and the relative separation factors of anionic dye MO for three cationic dyes (methylene blue, Crystal violet and Rhodamine B) was up to 124.22, 124.87 and 136.35, respectively. The adsorption rate of MO onto HTCM was very rapid, attaining 68.6 % of adsorption equilibrium capacity for MO within the first 30 min. The adsorption kinetics, isotherm and thermodynamic analysis revealed that the uptake behavior of HTCM towards MO obeyed pseudo-second-order kinetic model, intraparticle diffusion model and Langmuir model, and the uptake process was spontaneous and endothermic. As verified from FT-IR and XPS analysis for HTCM before and after MO adsorption, the adsorption mechanism of HTCM for MO involved electrostatic interaction and hydrogen bonding. The present study promises the potential of HTCM for highly selective separation of anionic dyes from wastewater.

Donnan Effect-Engineered Covalent Organic Framework Membranes toward Size- and Charge-Based Precise Molecular Sieving.

Covalent organic frameworks (COFs), with ordered pores and well-defined topology, are ideal materials for nanofiltration (NF) membranes because of their capacity of transcending the permeance/selectivity trade-off predicament. However, most reported COF-based membranes are focused on separating molecules with different sizes, resulting in low selectivity to similar molecules with different charges. Here, the negatively charged COF layer was fabricated in situ on a microporous support for the separation of molecules with different sizes and charges. Ultrahigh water permeance (216.56 L m-2 h-1 bar-1) was obtained because of the ordered pores and excellent hydrophilicity, which exceeds that of most membranes with similar rejections. For the first time, we used multifarious dyes with different sizes and charges, for the investigation of the selectivity behavior caused by the Donnan effect and size exclusion. The obtained membranes represent superior rejections to negatively and neutrally charged dyes larger than 1.3 nm, while positively charged dyes with a size of 1.6 nm can pass through the membrane, resulting in the separation of negative/positive mixed dyes with similar molecular sizes. This strategy of combining the Donnan effect and size exclusion in nanoporous materials may evolve into a generic platform for sophisticated separation.