Single Dye Solutions Research Articles

Dye Sorption from Mixtures on Chitosan Sorbents.

This article presents studies on the sorption of the anionic dyes Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84) from solutions of single dyes and from dye mixtures onto three chitosan sorbents-chitin, chitosan DD75% and chitosan DD95%. In this work, the influence of pH on sorption efficiency, the sorption equilibrium time for the tested anionic dyes and the sorption capacity in relation to the individual dyes and their mixtures were determined. It has been found that the sorption process for both dyes was most effective at pH 3 for chitin and chitosan DD75 and at pH 4 for chitosan DD95%. The obtained results were described by the double Langmuir equation (Langmuir 2). The obtained constants made it possible to determine the affinity of the tested dyes for the three sorbents and the sorption capacity of the sorbents. For RB5, the highest sorption capacity for chitosan DD95% was achieved with sorption from a single solution-of 742 mg/g DM and with sorption from mixed dyes-of 528 mg/g DM. For RY84, the highest efficiency was also achieved for chitosan DD95% and was 760 mg/g DM for a single dye solution and 437 mg/g DM for a mixture of dyes.

Visible-light-driven BiOI and GO/BiOI photocatalysts for organic pollutants degradation and hydrogen production using low power sources

BiOI and (3 wt%)GO/BiOI visible-light-driven photocatalysts were obtained by a one-pot solvothermal method and successfully applied to the degradation of single and binary dye solutions of rhodamine B (RhB) and methylene blue (MB) and H2 production using very low-power sources. The GO/BiOI with hierarchical flower morphologies exhibited the highest activity, achieving RhB and MB photodegradation percentages (%Xdye) of 100% and 80%, respectively, in 240 min employing a simple 19 W white LED array. Furthermore, GO/BiOI dosage and RhB initial concentration play an essential role in dye degradation, and scavenger assays confirmed that holes and superoxides are the main species causing RhB oxidation. TOC analysis determined an efficiency of 70%, and after three uses, the GO/BiOI attained a %XRhB of 84%. The H2 evolution was performed under 2 W UV light, yielding 323.25 μmol/h∙g of H2 for BiOI, and the addition of GO nanosheets increased the photoactivity of GO/BiOI up to 63% (509.61 μmol/h∙g). The catalytic activity of GO/BiOI is superior to values reported in the literature considering nominal power consumption (kWh) vs. efficiency of RhB degradation or H2 production.

Removal of Methyl Violet 2B and Direct Black 22 from Single and Binary System Using a Magnetic Zeolite/MgO/Starch/Fe3O4 Nanocomposite

This study focuses on the preparation and characterization of magnetic zeolite (FSM-Zeo) using starch, magnesium oxide, and Fe3O4. Various analyses, including BET, FTIR, SEM, EDS, XRD, Zeta potential, and VSM, were conducted to assess the properties of FSM-Zeo. The adsorption capacity of FSM-Zeo was investigated for methyl violet (MV-2B) and direct black 22 (DB-22) in both single and binary dye solutions. Key parameters such as adsorbent amount, initial dye concentration, contact time, temperature, initial pH, and ionic strength were examined in the single system. Kinetic and isotherm studies revealed that DB-22 and MV-2B adsorption followed the pseudo-second-order model. Moreover, Freundlich and Langmuir models were confirmed for MV-2B and DB-22 adsorption on FSM-Zeo, respectively. In the binary system, the presence of MV-2B enhanced the adsorption of DB-22, resulting in higher removal compared to the single dye solution. A synergistic effect was observed due to the interaction between DB-22 and MV-2B, promoting the adsorption of DB-22 on FSM-Zeo.

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.

Influence of Zinc and Humic Acids on Dye Adsorption from Water by Two Composts

Searching for alternative low-cost biosorbents for the removal of textile dyes from wastewater is currently an important subject of research. In this work, we have investigated how the presence of other contaminants in textile wastewaters can affect dye adsorption by biosorbents. We tested the adsorption of three dyes of different types: Basic Violet 10 (BV10), Acid Blue 113 (AB113) and Direct Blue 71 (DB71) by two different composts-municipal solid waste compost and pine bark compost-in the presence of Zn (5 mg L-1) or dissolved organic matter (100 mg humic acids L-1) in batch experiments. Dye adsorption capacity for both composts followed the following sequence: BV10 > AB113 > DB71. In general, dye sorption at the equilibrium was adequately described by the Freundlich model, but not always by the Langmuir model, which did not allow for the estimation of maximum retention capacities in all cases. In general, these were around 1 mg g-1 for DB71, 2 mg g-1 for AB113, and 40 mg g-1 for BV10. Municipal solid waste compost had slightly higher affinity than pine bark compost for the anionic dyes AB113 and DB71, whereas for the cationic dye BV10, pine bark compost presented a much higher adsorption capacity (41.7 mg g-1 versus 6.8 mg g-1). The presence of Zn or dissolved organic matter in the solutions at typical wastewater concentrations did not decrease the dye adsorption capacity of the composts. This result is positive both for the real application of composts to real textile wastewaters and for the validity of the results of biosorbent performance obtained with single-dye solutions.

Simultaneous Removal of Cationic Crystal Violet and Anionic Reactive Yellow Dyes using eco-friendly Chitosan Functionalized by Talc and Cloisite 30B

Designing adsorbent materials that can effectively remove many types of organic dyes is crucial because of the wide diversity of synthetic dyes found in wastewater. Thus, this study presents the synthesis of economic and eco-friendly adsorbent composites composed of chitosan (Cs), talc (T), and Cloisite 30B clay (C) to remove both cationic crystal violet (CV) and anionic reactive yellow 145 (RY) dyes for the first time. Cs was functionalized with T and subsequently the CsTC1 and CsTC2 composites were prepared by sensitizing the obtained CsT with different weight ratios of Cloisite 30B (C). X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), N2 adsorption–desorption isotherm, and zeta potential analysis were employed to characterize the materials. The addition of T to Cs matrix improves the thermal stability, pore size, and pore volume with respect to pure Cs. The effect of C inclusion was examined by measuring the affinity of the prepared composites towards adsorption of cationic CV and anionic RY dyes in comparison to pure Cs and CsT composite. The adsorption results in a single dye solution revealed that the CsTC1 composite is the most effective adsorbent for removal of RY dye with 76.9 mg/g adsorption capacity, whereas the CsTC2 composite exhibited the highest adsorption activity for CV dye (37.03 mg/g). Furthermore, RY and CV co-adsorption on CsTC composites was tested from a mixed dye solution. The adsorption kinetics of RY and CV adsorption followed the pseudo second order model. Langmuir isotherm model described the experimental adsorption data better than the Freundlich, Dubinin–Radushkevich, and Temkin isotherm models, indicating a monolayer sorption process for both dyes. The proposed mechanism for RY and CV adsorption using CsTC composites was investigated.

Co-sintering of ceramic ultrafiltration membrane with gradient pore structures for separation of dye/salt wastewater

Robust ceramic membranes with low fabrication cost and high separation performance are particularly suitable for the separation of dye wastewater containing high salinity. In this work, a co-sintering process was employed to fabricate alumina tight ultrafiltration (UF) membranes with gradient pore structures on the alumina supports that could decrease the sintering consumption and improve the separation efficiency simultaneously. It was revealed that the phase compositions of the alumina support, alumina intermediate layer, and separation layer were all α phase, demonstrating a high acid/alkali resistance. The resulting alumina membranes produced from the co-sintering process exhibited a mean pore size of ∼5 nm and water permeance of 72 L m−1 h−1 bar−1. As a result, the membranes reject nearly 99% of dyes and allow most salts (above 99%) to pass through the membranes in treating the single dye solution, single salt solution, and mixed dye/salt solution. Finally, a concentration-diafiltration process was designed and conducted to separate and recover the saltwater and dyes from the dye/salt mixture. The results showed that Na2SO4 content in the retentate decreased from 21 g/L to 0.5 g/L while maintaining the dye concentration above 980 mg/L. This work provided a cost-effective method to prepare high-performance ceramic UF membranes for the separation of dye/salt solution.

CNTs Intercalated LDH Composite Membrane for Water Purification with High Permeance.

The pursuit of improved water purification technology has motivated extensive research on novel membrane materials to be carried out. In this paper, one-dimensional carboxylated carbon nanotubes (CNTs) were intercalated into the interlayer space of layered double hydroxide (LDH) to form a composite membrane for water purification. The CNTs/LDH laminates were deposited on the surface of the hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane through a vacuum-assisted assembly strategy. Based on the characterization of the morphology and structure of the CNTs/LDH composite membrane, it was found that the intercalation of CNT created more mass transfer channels for water molecules. Moreover, the permeance of the CNTs/LDH membrane was improved by more than 50% due to the low friction and rapid flow of water molecules in the CNT tubes. Additionally, the influence of preparation conditions on the separation performance was investigated using Evans blue (EB). Optimized fabrication conditions were given (the concentration of CoAl-LDH was 0.1 g/L and the weight ratio of CNTs was 2 wt.%). Next, the separation performances of the prepared CNTs/LDH composite membrane were evaluated using both single and mixed dye solutions. The results showed that the composite membrane obtained possessed a retention of 98% with a permeance of 2600 kg/(m2·h·MPa) for EB, which was improved by 36% compared with the pristine LDH composite membrane. Moreover, the stability of the CNTs/LDH composite membrane was investigated in 100 h with no obvious permeance drop (less than 13%), which exhibited its great potential in water purification.

Sorption of cationic dyes from aqueous solutions by moss Rhytidiadelphus squarrosus: Kinetics and equilibrium studies

With the aim to investigate sorption properties of natural sorbent prepared from moss Rhytidiadelphus squarrosus we elucidated biosorption of cationic dyes Malachite green (BG4), Auramine O (BY2) and Thioflavine T (BY1) from aqueous solutions. The removal of dyes by moss biosorbent was found to be rapid at an initial stage and the equilibrium was reached within 1-2 hours. The pseudo-n-order kinetic model was successfully applied to the kinetic data and the order of adsorption reaction was calculated in the range from 1.7 to 2.6. The value of rate constant kn' ranged from 0.001 to 0.039 [min-1]/[μmol/g]1-n. The equilibrium data were fitted to the adsorption isotherms. The Freundlich isotherm was found to represent the measured sorption data of BG4, BY1 and BY2 well. The maximum sorption capacities of moss biomass from single dye solutions calculated by Langmuir equation were 354 μmol/g for BG4, 310 μmol/g for BY1 and 382 μmol/g for BY2. These results showed that the prepared biomass presents low-cost, natural and easy available sorbent which may be potentially used for removal of dyes from environment and also may be an alternative to more costly materials such as activated carbon.

Understanding the physicochemical properties of Zn\u2013Fe LDH nanostructure as sorbent material for removing of anionic and cationic dyes mixture

In our work, the removal of cationic and anionic dyes from water was estimated both experimentally and computationally. We check the selectivity of the adsorbent, Zn–Fe layered double hydroxide (LDH) toward three dyes. The physical and chemical properties of the synthesis adsorbent before and after the adsorption process were investigated using X-ray photoelectron spectroscopy, energy dispersive X-ray, X-ray diffraction, FT-IR, HRTEM, and FESEM analysis, particle size, zeta potential, optical and electric properties were estimated. The effect of pH on the adsorption process was estimated. The chemical stability was investigated at pH 4. Monte Carlo simulations were achieved to understand the mechanism of the adsorption process and calculate the adsorption energies. Single dye adsorption tests revealed that Zn–Fe LDH effectively takes up anionic methyl orange (MO) more than the cationic dyes methylene blue (MB) and malachite green (MG). From MO/MB/MG mixture experiments, LDH selectively adsorbed in the following order: MO > MB > MG. The adsorption capacity of a single dye solution was 230.68, 133.29, and 57.34 mg/g for MO, MB, and MG, respectively; for the ternary solution, the adsorption capacity was 217.97, 93.122, and 49.57 mg/g for MO, MB, and MG, respectively. Zn–Fe LDH was also used as a photocatalyst, giving 92.2% and 84.7% degradation at concentrations of 10 and 20 mg/L, respectively. For visible radiation, the Zn–Fe LDH showed no activity.

Surface Modification of Magnesium Ferrite Nanoparticles for Selective and Sustainable Remediation of Congo Red

Surface modification of silica-coated magnesium ferrite nanoparticles (MgFe2O4@SiO2 NPs) by 3-aminopropyltriethoxysilane (APTES) shows enhanced selectivity for the removal of Congo Red (CR) from both single and binary aqueous dye solutions. Before coating the surfaces of amine-functionalized magnesium ferrite nanoparticles (MgFe2O4–NH2 NPs) with silica, control studies of the adsorption of cationic, neutral, and anionic dyes were performed using both single and binary dye systems. The studies found that the MgFe2O4–NH2 nanoadsorbent favors the adsorption of indigo carmine (IC) and CR in single dye solutions (>90% removal efficiencies). However, MgFe2O4–NH2 NPs preferentially adsorb CR in binary dye solutions. Interestingly, the selectivity of CR over IC depends on the initial concentration of IC/CR in the IC/CR binary systems. A further enhancement in the selective removal of CR in both single and binary dye solutions was achieved by coating the MgFe2O4–NH2 NPs with silica followed by modification with APTES (i.e., APTES-modified MgFe2O4@SiO2 NPs). The highly selective adsorption capacity for CR on the APTES-modified MgFe2O4@SiO2 nanoadsorbent was attributed to the mixture of polar functional groups (i.e., −OH and −NH2) on the surface of the nanoadsorbent, which facilitates adsorbent–adsorbate interactions such as electrostatic and hydrogen-bonding interactions, which are amplified for CR with its more numerous polar functional groups (i.e., amine, azo, and sulfonate groups). From the results, the APTES-modified MgFe2O4@SiO2 nanoadsorbent offers an effective, inexpensive, and reusable/sustainable system for the selective removal and remediation of Congo Red from wastewaters.

Visible light‐assisted degradation of binary mixture of dyes using purple tea‐mediated zinc oxide nanoparticles

AbstractThis work presents completely a new, green, and non‐expensive route of synthesis of zinc oxide (ZnO) nanoparticles (NPs) using purple tea leaves. The crystalline nature of purple tea‐mediated ZnO NPs (PT‐ZnO NPs) was confirmed by XRD and SAED analyses. Further characterizations of PT‐ZnO NPs were done using UV‐vis spectroscopy, FTIR spectroscopy, SEM‐EDX, and TEM. The size of synthesized NPs was calculated to be 15.1 nm which presented spherical morphology with some sorts of agglomeration. The PT‐ZnO NPs when applied as visible light‐driven photocatalyst for degradation of dyes, Malachite green (MG) and Rhodamine B (RB) showed that degradation was found to be higher in their binary solution (MG‐RB) than in their single solution (MG/RB). MG 95% and RB 35% was degraded in their binary solution where as in their respective single dye solution MG 89% and RB 22% got degraded within the experimental time. The highly pure, PT‐ZnO NPs are considered to have comparable photocatalytic activity with respect to most of the reported works and hence might find a way for its practical application for waste water treatment in the real world. The PT‐ZnO NPs could be reused at least for five times without any significant loss in degradation efficiency.

Structural Characterization and Adsorption Properties of Dunino Raw Halloysite Mineral for Dye Removal from Water.

In this work, raw halloysite mineral from Dunino (Poland) has been characterized and tested as an efficient and low-cost adsorbent for dye removal from water. The morphology and structure of this clay were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the chemical composition was evaluated by means of X-ray fluorescence spectroscopy (XRF), energy dispersive X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS). The results showed that it is made up of both platy and tubular structures, mainly composed of Si, Al, and O. Iron oxide particles covering the platy structures were also observed. The surface charge of halloysite was measured by z-potential measurements and by the evaluation of the point of zero charge. The clay was tested as an adsorbent for the removal of positively and negatively charged dye molecules, i.e., methylene blue (MB) and methyl orange (MO), both separately and in a mixed-dye solution. Halloysite showed the ability to efficiently and selectively remove MB molecules by adsorption, both in a single-dye solution and in a mixed one. The adsorption of positive dyes on the clay surface mainly occurred through ion exchange at negatively charged sites on its surface. The possibility of regenerating the clay for further dye removal processes is also shown.

Synthesis, characterization, and adsorption properties of collagen and attapulgite‐filled copolymer biocomposites: Batch and column studies

AbstractSeveral biocomposites were synthesized by copolymerizing hydroxyethyl methacrylate (HEMA) and itaconic acid (IA) at varied molar ratios in the presence of different wt% of collagen (CLG) and attapulgite (APG) clay. The structure and properties of the biocomposite adsorbents were characterized by Fourier transform infrared apectroscopy, nuclear magnetic resonance, X‐ray photo electron spectroscopy, X‐ray diffraction, scanning electron microscope, transfer electron microscopy, energy‐dispersive X‐ray analysis, differential thermal analysis–thermogravimetric analysis, point zero charge analysis, mechanical properties, and pH reversibility tests. The synthesis variables were optimized with a central composite design of response surface methodology (RSM). The biocomposite prepared with an optimized composition of 1.5 wt% CLG, 1.7 wt% APG, and 5:1 molar ratio of HEMA:IA showed an adsorption capacity (Qe, mg/g) of 674.4/602.4 for methylene blue (MB)/Rose Bengal (RB) dye from a feed containing 200 mg/L of MB + RB dye mixture in batch mode. In a fixed bed in column mode, the optimized biocomposite showed a removal% of 82.8/71.3 for 100 mg/L inlet concentration, 20 ml/min flow rate, and 20 mm bed height with a breakthrough time of 23/31 min and a mass transfer coefficient (kmtc × 105 cm/s) of 8.36/7.67 for MB/RB as single dye solution.

Identification of adsorption or degradation mechanism for the removal of different ionic dyes with iron-carbon micro-electrolysis process

The Fe-C micro-electrolysis materials (Fe-C MEM) are thought to be a good candidate in dyes removal. In this work, two Fe-C MEM (M1 and M2) with different physiochemical properties were compared in the dyes removal. Three cationic dyes (Three cationic dyes (malachite green (MG), crystal violet (CV), methylene blue (MB)), as well as two anionic dyes (methyl orange (MO), sunset yellow (SY)), were chosen in the study. The results showed that the M2 exhibited a better porosity with higher ZVI content, contributing to a higher dyes removal efficiency for all five dyes. Meanwhile, the cationic dyes had a higher dyes removal efficiency than anionic dyes. When the dyes were mixed together, CV had a higher removal efficiency than MG, although MG was the highest in the single dye solution. The removal mechanism of the five dyes was different. The two cationic triphenylmethane dyes (CV and MG) could be degraded while the two anionic azo dyes (MO, SY) were not degraded but adsorbed on Fe-C MEM. MB was removed mainly based on adsorption and coagulation.

Tert-butylamine/oleic acid-assisted morphology tailoring of hierarchical Bi4Ti3O12 architectures and their application for photodegradation of simulated dye wastewater

Herein we report the morphology tailoring of hierarchical Bi4Ti3O12 architectures by using tert-butylamine (TB) and oleic acid (OA). It is demonstrated that the content of TB and OA has an important effect on the morphologies of as-derived Bi4Ti3O12 samples. When adding 12 mmol TB and 6 mmol OA (with respect to 1 mmol Bi4Ti3O12) to the precursor solution, rod-like hierarchical architectures (length 2–15 μm, diameter 0.5–1.7 μm) are obtained. The hierarchical microrods are composed of nanosheets of 20–50 nm in thickness and 300–1700 nm in diameter. The addition of other amounts of TB and OA results in the formation of nanoflake-assembled hierarchical hollow microspheres with size of several micrometres; however the sizes of the microspheres and their sub-nanoflakes depend on the TB/OA amounts. Rhodamine B (RhB), methyl orange (MO) and methylene blue (MB) aqueous solutions, as well as RhB/MO/MB mixture solution (simulated dye wastewater), were used to evaluate the photodegradation performances of the as-prepared Bi4Ti3O12 samples under simulated sunlight irradiation. It is demonstrated that the nanosheet-assembled hierarchical microrods possess a photodegradation activity preponderating over the other morphologies. Moreover, the photocatalytic experiments reveal an interesting photodegradation process of RhB/MO/MB in the mixture solution, which is different from the photodegradation of single dye solution. The photodegradation mechanism of the Bi4Ti3O12 photocatalysts was investigated and discussed.

Desalination of dye utilizing carboxylated TiO2/calcium alginate hydrogel nanofiltration membrane with high salt permeation

In order to recover dyes from textile wastewater, a self-supported carboxylated titanium dioxide/calcium alginate (TiO2-COOH/CaAlg) hydrogel nanofiltration membrane was prepared using TiO2-COOH as the reinforcing agent. The Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDX) mapping scanning spectra were employed to characterize the distribution of TiO2-COOH nanoparticles on the membrane surface. The pore size distribution, zeta potential and mechanical performance of the membrane were evaluated. The rejections for single dye solutions, salt solutions and dye/salt mixture solutions were also examined. The results indicate that the TiO2-COOH nanoparticles are dispersed uniformly on the membrane surface. Compared to CaAlg membrane, the tensile strength of 20 wt% TiO2-COOH/CaAlg membrane is enhanced by 328%. At the operating pressure of 0.1 MPa, the rejection ratios of 20 wt% TiO2-COOH/CaAlg membrane for 100 mg/L Brilliant blue G250, Direct black 38 and Congo red are 98.4%, 96.8% and 95.9% respectively, and the permeate flux is about 14.1 L·m−2·h−1. Meanwhile, this membrane possesses the low rejection ratios for inorganic salts (16.1%, 15.6%, 12.3% and 9.0% for MgSO4, Na2SO4, MgCl2 and NaCl, respectively), excellent dye anti-fouling property and good stability in the long-term filtration for dye/salt mixture solution.

Spectrofluorometer: the excitation beam intensity calibration using a single standard solution

The accurate, periodically updated excitation beam intensity correction is essential for conducting fluorescence spectroscopy research. This article describes a simple and inexpensive approach to reevaluate the excitation calibration curve of a spectrofluorometer using a single dye solution. The method shows excellent agreement with the data obtained using a certified calibration detector for the broad spectral range from 290 nm to 700 nm.

Color-mixing effects of photosensitive organic dyes initiated by superoxide anion radicals under visible-light irradiation

Water pollution by dyes is a major health and environmental issue. Photosensitive organic dyes produce hydrated electrons, eaq−, singlet oxygen, 1O2, and superoxide anion radicals, O2·−. O2·− catalyzes H2O2 transformation into hydroxyl radicals ·OH, which can be used to degrade wastewater under sunlight. Here, we measured eaq−, 1O2, O2·− and ·OH generated under visible light irradiation of photosensitive organic dyes in the presence of the auxiliary Fe3+, the 1,5-diphenylcarbazide molecular probe, the NH2OH molecular probe and the dimethyl sulphoxide probe. Results show that single photosensitive organic dyes are not degraded in the visible light/H2O2 system. However, they were degraded when mixed in a certain proportion to produce a brown coloration, a phenomenon named the ‘color-mixing effect.’ Likewise, the average yields of O2·− in single photosensitive organic dye solutions were lower, of 0.015 (ΔA510), than that in mixed brown solutions, of 0.113. The color-mixing effect is explained mainly by higher ·OH generation from increased O2·− production. Findings imply that sunlight irradiation is a promising way to clean colorful and dye-containing wastewater.

Bio-inspired co-deposited preparation of GO composite loose nanofiltration membrane for dye contaminated wastewater sustainable treatment

The fully separation of dye/salt through loose nanofiltration membranes is of great significance for the sustainable development paradigm of textile wastewater. However, the current loose nanofiltration membranes suffer low separation efficiency and complex preparation. Herein, by one-step co-deposition, we develop graphene oxide (GO) composite loose nanofiltration membranes with low negatively charged surface. Our membrane possesses unconventional high pure water permeation of 71.7 LMH/bar, 92.9 % rejection for Methyl blue (MB) and 98.8 % rejection for Congo red (CR). Benefiting from the large interlayer distance of GO nanosheets and low negatively charged surface, membrane achieves high dyes/salts separation with satisfactory permeation to salts (94.3 % of Na2SO4, 97.6 % of MgSO4, 98.3 % of MgCl2 and 99.0 % of NaCl). The CR/salt mixed solutions exhibit similar removal rates to their constituents’ single dye or salt solutions (CR rejection is up to more than 97 % and the permeations of all salts are above 93 %). At the same time, binary dyes mixtures (Congo red and Methyl orange) can also be effectively separated. Furthermore, the membrane shows a relatively desirable antifouling property. The flux recovery still remains at 85.9 % after three cycling filtrations. This study provides a facile approach to prepare highly-efficient loose nanofiltration membranes for wastewater sustainable remediation.