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In this work, a multiplexed colorimetric strategy was initiated for simultaneous and fast visualization of dyes using low-cost and easy-to-prepare indicator papers as sorbents. Response surface methodology (RSM) was employed to model statistically and optimize the process variables for dyes extraction and colorimetric assays. Multiplexed colorimetry was realized by virtue of synchronous color alignments from different dimensions of multiple dyes co-stained colorimetric cards under RSM-optimized conditions, and smartphone-based image analysis was subsequently performed from different modes to double-check the credibility of colorimetric assays. As concept-to-proof trials, simultaneous visualization of dyes in both beverages and simulated dye effluents was experimentally proved with results highly matched to HPLC or spiked amounts at RSM-predicted staining time as short as 50 s ∼3 min, giving LODs as low as 0.97 ± 0.22/0.18 ± 0.08 μg/mL (tartrazine/brilliant blue) for multiplexed colorimetry, which much lower than those obtained by single colorimetry. Since this is the first case to propose such a RSM-guided multiplexed colorimetric concept, it will provide a reference for engineering of other all-in-one devices which can realize synchronous visualization applications within limited experimental steps. [Display omitted] • A multiplexed colorimetry has been initiated for simultaneous visualization of dyes. • Colorimetric conditions were finalized by RSM within limited experimental runs. • Simultaneous colorimetric assays of different dyes could be achieved within 1 min. • Colorimetric sensitivity could be improved by multiplexed colorimetric strategy. • Smartphone-based image analysis was practical for assuring colorimetric results. [ABSTRACT FROM AUTHOR]

Heavy metal ions and organic pollutants discharged into various water bodies have caused serious water pollution, and the efficient removal of these contaminants remains a challenge. Here, we report a novel MXene/poly-melamine-formaldehyde (PMF) composite membrane, in which the PMF particles serve as spacers, and the –NH 2 groups of PMF and the hydroxyl groups of MXene nanosheets have a synergistic effect on the adsorption of pollutants, and the crosslinking of glutaraldehyde inhibits the swelling of the composite membrane. The MXene/PMF composite membrane with 83.7% PMF particle loading displays a water permeability of 381.2 L m−2 h−1 bar−1 (405% that of MXene membrane) and excellent adsorption ability. In static adsorption, the removal rates of Zn2+, Pb2+, phenol, and crystal violet reach 96.2%, 91.7%, 99.1%, and 96.4% respectively, 20∼100% higher than those of MXene membranes. In dynamic adsorption, the breakthrough volumes of the membrane for 2 ppm p-nitrophenol solution and methyl blue solution reach 75 mL (about 8500 times membrane volume) and 350 mL (about 39800 times membrane volume), and the saturation volumes are 1500 mL and 5000 mL, respectively. After cyclic adsorption/desorption for four times, the removal rate of the membranes still maintains above 90%. This work provides an efficient composite membrane for removing pollutants from wastewater. [Display omitted] • A novel MXene/poly-melamine-formaldehyde (PMF) composite membrane are prepared. • The introduction of PMF particles widens the transmission channel and increases water permeance. • PMF and MXene nanosheets have a synergistic effect on the adsorption of pollutants. • Removal rates of Zn2+, Pb2+, phenol and crystal violet by MXene composite membranes are above 90%. • After 4 times of use, the removal rate of pollutant of composite membrane is above 90%. [ABSTRACT FROM AUTHOR]

• Stainless steel and iron are compared as anodes in electrocoagulation. • The removal of Zn2+, Orange II and phosphate is achieved. • The removal efficiency is related to the anode polarisation behaviour. • AISI420 is a promising anode in electrocoagulation. • Cr(VI) is observed in solutions using AISI310 as the anode. Two stainless steel anodes, AISI 420 and AISI 310, and pure iron were compared in an electrocoagulation study for the simultaneous removal of phosphates, Orange II and Zinc ions from a synthetic wastewater at a current density of 11.7 mA cm–2 and a surface area to volume ratio of 19.4 m–1. High removal efficiencies were observed with AISI 420 and pure iron, reaching values between 88% and 99%, while significantly lower values, approximately 30%, were obtained with AISI 310. The AISI 310 performed well in the removal of Zn2+ due to its removal as Zn(OH) 2. The variations in the performance of the steel anodes were attributed to the lower chromium content of the AISI 420, which gives less passive behaviour. This was supported using polarisation data, where a 10–fold increase in the corrosion current was obtained for AISI 420 compared to AISI 310. Furthermore, Cr(VI) was observed in the solution phase when AISI 310 was employed as the anode, illustrating the importance of the alloying concentrations. While rust particles were seen during the non–continuous use of the iron anode, they were not observed with the AISI 420 anode. [ABSTRACT FROM AUTHOR]

• MOFs and their hybrid materials enhance depollution performance. • MOFs as visible photocatalysts promote dyes degradation. • MOFs catalyze Fenton and sulfate radical-based oxidations for depollution. • Iron-based MOFs as sustainable heterogeneous materials efficiently degrade. organics. This paper presents a review on the environmental applications of metal-organic frameworks (MOFs), which are inorganic-organic hybrid highly porous crystalline materials, prepared from metal ion/clusters and multidentate organic ligands. The emphases are made on the enhancement of the performance of advanced oxidation processes (AOPs) (photocatalysis, Fenton reaction methods, and sulfate radical (SO 4 −)-mediated oxidations) using MOFs materials. MOFs act as adsorption and light absorbers, leading to superior performance of photocatalytic processes. More recent examples of photocatalytic degradation of dyes are presented. Additionally, it is commonly shown that Fe-based MOFs exhibited excellent catalytic performance on the Fenton-based and SO 4 •−-mediated oxidations of organic pollutants (e.g., dyes, phenol and pharmaceuticals). The significantly enhanced generation of reactive species such as OH and/or SO 4 − by both homogeneous and heterogeneous catalysis was proposed as the possible mechanism for water depollution. Based on the existing literature, the challenge and future perspectives in MOF-based AOPs are addressed. [ABSTRACT FROM AUTHOR]

• Pollutants were removed from wastewater through electrocoagulation (EC). • The optimal values for EC were pH 9, time of 10 min, and current density of 8 mAcm-2. • The maximum removal of color, turbidity and COD were 86%, 82% and 59% respectively. • The treated wastewater with EC can be reused in process of wool dyeing. The possibility of using electrocoagulation for efficient removal of pollutants in the industrial liquid waste of a textile industry was studied. The performance of the process was evaluated through the analysis of color, turbidity, and chemical oxygen demand (COD). The analysis was first done with the wastewater coming from the process of dyeing linen, which is the most polluting of all effluents that reach the residual effluent pool (REP). For the analysis, the MODDE 7.0 software was used to construct a statistical model. With the results obtained from this model and the experimental measurements, response surfaces were obtained. These response surfaces predicted the behavior of electrocoagulation for different values of the studied variables (pH, current density, and treatment time). Based on the obtained results, the wastewater coming from the REP was treated using the optimum values for the operational variables. After the treatment it was possible to remove 86% color, 82% turbidity, and 59% COD. It was demonstrated that reusing the treated water in the process of wool dyeing does not have a negative effect on the quality of the dyed fabric. Thus, it is possible to implement the process in the textile industry to reduce the consumption of water. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The low-cost calcium lignosulfonate waste was reused. • The Fe 3 O 4 /C-ACLS was prepared using Fe 3 O 4 as magnetic source. • The Fe 3 O 4 /C-ACLS was used as an excellent adsorbent for the removal of azo dyes. • The Fe 3 O 4 /C-ACLS can be recycled. Abstract The magnetic lignin-based adsorbent (Fe 3 O 4 /C-ACLS) has been successfully prepared and applied to adsorbing azo dyes Congo red, Titan yellow and Eriochrome blue black R. The samples were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), X-ray powder diffraction (XRD), vibration sample magnetometer (VSM), Raman spectroscopy and elemental analysis. In the process of adsorption, five kinds of influencing factors and recycling regeneration were discussed, and the adsorption mechanisms such as kinetics, isotherm, thermodynamics were explored. The results show that Fe 3 O 4 /C-ACLS can remove 98%, 92% and 99% of Congo red, Titan yellow and Eriochrome blue black R, respectively. Under the same conditions, the removal rate was 87%, 84% and 88% after 5 times adsorption cycle, respectively. Pseudo-first-order, pseudo-second-order kinetics, Elovich model and intraparticle diffusion model were studied, and the results show that the adsorption process conforms to pseudo-second-order kinetics model, and the diffusion rate is controlled by many steps. The results of isotherm model and thermodynamics show that the adsorption process is consistent with Langmuir model and is mainly a spontaneous chemical endothermic process of monolayer. [ABSTRACT FROM AUTHOR]

The removal of brilliant green (BG), a toxic organic and cationic dye, has been examined by UV/S 2 O 8 2− (PS), UV/HSO 5 − (PMS) and UV/H 2 O 2 processes. BG showed insignificant direct photolysis at 254 nm (i.e., 8.6% after 30 min). However, enhanced BG degradation was observed in UV/PS, UV/PMS and UV/H 2 O 2 systems as revealed from 63.1, 47.0 and 34.8% BG degradation, respectively, at 30 min of reaction time, using 0.05 mM BG and 1.0 mM oxidant initial concentration. The bimolecular rate constants of OH and SO 4 − with BG were determined to be 2.35 × 10 9 and 2.21 × 10 9 M −1 s −1 , respectively. Electrical energy per order (EE/O) values for UV/PS, UV/PMS and UV/H 2 O 2 processes were calculated to be 5.4, 6.8, and 7.8 KWh/m 3 /order, respectively. The addition of humic acid (HA) and inorganic anions inhibited the degradation of BG by UV/PS in the order of NO 2 −  > HA > HCO 3 −  > Cl −   > NO 3 −  ≈ SO 4 2− . The results of frontier electron densities (FEDs) showed that C-atom holding the three rings (C7), and C-atoms at para positions to N-alkyl groups of the two rings (C4 and C14) are the predominant sites for radical addition. Furthermore, nine degradation products (DPs) of BG were detected experimentally using LC/MS/MS. [ABSTRACT FROM AUTHOR]

Here we demonstrate, a simple and solvent-free synthetic route for the production of FeS/Fe(0) functionalized graphene nanocomposite (G-Fe) via a one-step pyrolysis of seaweed biomass ( Ulva fasciata ). It is proposed that the natural abundance of both inorganic and organic sulfur in the seaweed induces the reduction of exfoliated graphitic sheets at elevated temperatures. FeCl 3 was employed both as the iron precursor as well as the templating agent. Iron doping played a dual-faceted role of exfoliating as well as activating agent, producing composite with high adsorption capacity for Pb 2+ (645 ± 10 mg/g), CR (970 mg/g), CV(909 mg/g), MO (664 mg/g), MB (402 mg/g) dyes and good recyclability (8 cycles). Pb 2+ adsorption was irreversible even at low pH values and the spent composite (G-Fe-Pb) was utilized for efficient Cr(IV) removal (̴100 mg/g). The adsorption data followed the pseudo second order kinetics while the equilibrium data fitted perfectly into the Langmuir adsorption equation. Further, a thin layer of composite was deposited on a filter paper by vacuum filtration which was tested under continuous filtration mode for RB5 dye removal. Preliminary results highlight the potential of this composite to be used in pretreatment steps in hybrid membrane processes for filtration of complex wastewater feeds. [ABSTRACT FROM AUTHOR]

Catalysts are known to activate peroxides to generate active radicals (i.e., hydroxyl radical ( OH) and sulfate radical (SO 4 − )) under certain conditions, but the activation of peroxides in the absence of catalysts under visible light irradiation has been rarely reported. This work demonstrates a catalyst-free activation of peroxides for the generation of OH and/or SO 4 − through photoexcited electron transfer from organic dyes to peroxides under visible LED light irradiation, where Rhodamine B (RhB) and Eosin Y (EY) were selected as model dyes. The formation of OH and/or SO 4 − in the reactions and the electron transfer from the excited dyes to peroxides were validated via electron paramagnetic resonance (EPR), photoluminescence (PL) spectra and cyclic voltammetry (CV). The performance of the peroxide/dye/Vis process was demonstrated to be altered depending on the target substrate. Meanwhile, the peroxide/dye/Vis process was effective for simultaneous decolorization of dyes and production of active radicals under neutral even or basic conditions. The findings of this study clarified a novel photoexcitation pathway for catalyst-free activation of peroxides under visible light irradiation, which could avoid the secondary metal ion (dissolved or leached) pollution from the metal-based catalysts and expand the application range of the peroxide-based catalytic process. [ABSTRACT FROM AUTHOR]

An environmental friendly hydrogel adsorbent (DEC@GEL) was successfully manufactured by a facile free-radical polymerization method. Multiple characterizations demonstrated that the adsorbent was rich in functional groups and porous structures. The batch and multisystem adsorption experiments were applied to systematically investigate the adsorption properties of methylene blue (MB), malachite green (MG), indigo sodium dimethyl sulfonate (IC) and tartrazine (TR) in wastewater. The experimental results proved that the kinetic and isotherms of four dyes were more consistent with the pseudo-second-order and Langmuir model, respectively. Notably, the maximum adsorption capacities of MB, MG, TR and IC at 318 K were 2186.85, 2302.53, 1766.13 and 2301.75 mg/g, respectively, which were higher than many adsorbents that had been reported. Recycle experiment demonstrated the high reusability of the DEC@GEL. The selectivity and adsorption column experiments proved that DEC@GEL was not only widely applicable to various dyes, but also provided a positive start for the industrial application. Moreover, the simulated adsorption experiments further demonstrate that DEC@GEL had the prospect of application in real industrial conditions. Finally, four adsorption mechanisms had been proposed. Various adsorption experiments had shown that DEC@GEL was not only efficient in processing dyes, but also had great potential for practical industrial applications. [Display omitted] • An environmental friendly hydrogel adsorbent was successfully manufactured. • various tests revealed that hydrogel had abundant functional groups, pores, good acid and base resistance. • The maximum adsorption capacities of MB, MG, TR and IC were 2186.85, 2302.53, 1766.13 and 2301.75 mg/g, respectively. • Selectivity, continuity, circulation and simulation experiments revealed the practical application of adsorbent. • Adsorption mechanisms included electrostatic, hydrogen bonding, Π-Π and host-guest interactions. [ABSTRACT FROM AUTHOR]

QSAR modeling could be a promising tool for guiding the development of novel and cost-effective environmental technologies. As an example, it could be widely used to analyze the degradation rules of organic pollutants in various decomposition methods. However, a lack of systematic research on a particular removal method is significant in revealing the decomposition rule of pollutants more accurately and guiding industrial applications. In this study, six coagulation systems (MnO 2 /Fe(OH) 3 /AlCl 3 /FeCl 3 /CaCl 2 /MgCl 2) were used as examples to remove 38 dyes under three pH conditions, and the characteristics and differences of these systems were explored by QSAR modeling. The results showed that the removal effect by MnO 2 under acidic and neutral conditions and Fe(OH) 3 under acidic conditions were quantitatively described mainly by bond order (BO) and Fukui index (f (+) and f (0)), which reflected that oxidative degradation dominated. In contrast, most of the critical parameters of other systems were molecular descriptors represented by ∑q(O) (the total charge of all the oxygen atoms in the molecule) and SAA (surface area of a molecule), which reflected that electrostatic adsorption and hydrogen-bond adsorption processes dominated. [Display omitted] • The most key parameters of the MnO 2 /Fe(OH) 3 system such as BO x and f (+) n. • The most key parameters of the AlCl 3 /FeCl 3 /CaCl 2 /MgCl 2 system such as SAA and ∑q(H). • The MnO 2 /Fe(OH) 3 system is dominated by oxidative degradation, and various interface adsorptions coexist. • The AlCl 3 /FeCl 3 /CaCl 2 /MgCl 2 system is dominated by electrostatic adsorption, supplemented by hydrogen bond adsorption. [ABSTRACT FROM AUTHOR]

A bifunctional photocatalyst-Fe-benzenedicarboxylate (MIL-53(Fe)) has been synthesized successfully via a facile solvothermal method. The resulting MIL-53(Fe) photocatalyst exhibited an excellent visible light ( λ ≥ 420 nm) photocatalytic activity for the reduction of Cr(VI), the reduction rate have reached about 100% after 40 min of visible light irradiation, which has been more efficient than that of N-doped TiO 2 (85%) under identical experimental conditions. Further experimental results have revealed that the photocatalytic activity of MIL-53(Fe) for the reduction of Cr(VI) can be drastically affected by the pH value of the reaction solution, the hole scavenger and atmosphere. Moreover, MIL-53(Fe) has exhibited considerable photocatalytic activity in the mixed systems (Cr(VI)/dyes). After 6 h of visible light illumination, the reduction ratio of Cr(VI) and the degradation ratio of dyes have been exceed 60% and 80%, respectively. More significantly, the synergistic effect can also be found during the process of photocatalytic treatment of Cr(VI) contained wastewater under the same photocatalytic reaction conditions, which makes it a potential candidate for environmental restoration. Finally, a possible reaction mechanism has also been investigated in detail. [ABSTRACT FROM AUTHOR]

Periodic mesoporous organosilicas (PMOs) with benzene bridging groups in the silica wall were functionalized with a tunable content of phosphonic acid groups. These bifunctional materials were synthesized by co-condensation of two different organosilane precursors, that is, 1,4-bis(triethoxysilyl)benzene (BTEB) and sodium 3-(trihydroxysilyl)propyl methyl phosphate (SPMP), under acidic conditions using nonionic surfactant Brij-S10 as template. The materials exhibited well-ordered mesostructures and were characterized by X-ray diffraction, nitrogen sorption, TEM, TGA, FTIR, and solid-state NMR measurements. The materials thus obtained were employed as adsorbents to remove different types of dyes, for example, cationic dyes methylene blue and phenosafranine, anionic orange II, and amphoteric rhodamine B, from aqueous solutions. The materials exhibited a remarkably high adsorption capacity than activated carbon due to their ordered mesostructures, a large number of phosphonic acid groups, and high surface areas. The adsorption was mainly governed by electrostatic interaction, but also involved π-π stacking interaction as well as hydrogen bonding. The adsorption kinetics can be better fitted by the pseudo-second order model. The adsorption process was controlled by the mechanisms of external mass transfer and intraparticle diffusion. The materials retained more than 97% dye removal efficiency after use for five consecutive cycles. [ABSTRACT FROM AUTHOR]

Highlights: [•] ACF-supported hemin allowed enhanced decomposition of dyes compared with bare hemin. [•] Hemin-ACF exhibited excellent pH tolerance over a wide pH range from acidic to alkaline. [•] The introduction of ACF accelerated the generation of reactive species by electron transfer from ACF to hemin. [Copyright &y& Elsevier]

Highlights: [•] Porous carbon nanospheres via a convenient synthesis of ZnCl2 chemical activation. [•] This material owns an extremely high surface area and tunable pore structure. [•] It possesses an excellent adsorption property and superior recycling property. [Copyright &y& Elsevier]

Abstract: The electrochemical oxidation of textile effluents over a boron-doped diamond anode was investigated in the present study. Experiments were conducted with a multi-component synthetic solution containing seventeen dyes and other auxiliary inorganics, as well as an actual effluent from a textile dyeing process. The effect of varying operating parameters, such as current density (4–50mA/cm2), electrolyte concentration (0.1–0.5M HClO4), initial solution pH (1–12.3) and temperature (22–43°C), on process efficiency was investigated following changes in total organic carbon (TOC), chemical oxygen demand (COD) and color. Complete decolorization accompanied by significant mineralization (up to 85% depending on the conditions) could be achieved after 180min of treatment. Performance was improved at higher electrolyte concentrations and lower pH values, while the effect of temperature was marginal. Energy consumption per unit mass of COD removed was favored at lower current densities, since energy was unnecessarily wasted to side reactions at higher densities. [Copyright &y& Elsevier]

Abstract: Here we report the use of a thiol-functionalized silica-gel to prepare supported CdS nanocrystals by a facile one-step procedure. Upon changing the relative proportion of the matrix we obtained nanocrystals with different average sizes and size distributions, as evidenced by spectroscopic measurements as well as TEM images. Photoluminescence spectra also indicated that the main effect of the matrix is related to the size control since the spectral profiles were found to be strongly dependent on the excitation wavelength. The performance of the material in the photocatalytic degradation of two commercial dyes (methylene blue and rhodamine 6G) has been tested under sunlight radiation, showing promising results. Almost complete decolorization has been observed after 80min of exposure, with no adsorption on the silica surface. [Copyright &y& Elsevier]

Abstract: We report the simultaneous adsorption of acid blue 25 dye (AB25) and heavy metals (Zn2+, Ni2+ and Cd2+) on a low-cost activated carbon, whose adsorption properties have been improved via a surface chemistry modification using a calcium solution extracted from egg shell wastes. Specifically, we have studied the removal performance of this adsorbent using the binary aqueous systems: AB25–Cd2+, AB25–Ni2+ and AB25–Zn2+. Multi-component kinetic and equilibrium experiments have been performed and used to identify and characterize the synergic adsorption in the simultaneous removal of these pollutants. Our results show that the presence of AB25 significantly favors the removal of heavy metals and may increase the adsorption capacities up to six times with respect to the results obtained using the mono-cationic metallic systems, while the adsorption capacities of AB25 are not affected by the presence of metallic ions. It appears that this anionic dye favors the electrostatic interactions with heavy metals or may create new specific sites for adsorption process. In particular, heavy metals may interact with the –SO3 − group of AB25 and to the hydroxyl and phosphoric groups of this adsorbent. A response surface methodology model has been successfully used for fitting multi-component adsorption data. [Copyright &y& Elsevier]

Abstract: We synthesized mefenamic acid (MA) derived gold nanoparticles (MA-AuNps) in aqueous solution (MA-Au sol). Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) of the sol at 1, 5, 15 and 60min showed changes in size and shape of formed AuNps. Fourier Transform Infrared (FTIR) Spectroscopy revealed the interaction between AuNps and MA. Each Au sol exhibited exceptional catalytic activity for the reduction of Methylene Blue (MB), Rose Bengal (RB) and Eosin B (EB) dye individually as well as collectively. However, complete reduction of dye(s) was accomplished by Au sol of 5min in just 15s. The catalytic performance of Ma-Au sol was far superior to that adsorbed on glass. AuNps were recovered with the help of water insoluble room temperature ionic liquid and reused with enhanced catalytic potential. This finding is a novel, rapid and highly economical alternative for environmental safety against pollution by dyes and extendable for control of other reducible contaminants as well. [Copyright &y& Elsevier]

Abstract: In this paper, we found that the acidic and basic dyes were easily decolorized by a bis-ions coexistence system of NH4 + and NO3 − under UV light irradiation. The coexistence of NH4 + and NO3 − is a necessary condition for the photocatalytic decolorization of soluble dyes. The photocatalytic decolorization of methyl orange (MO) and methylene blue (MB) follows the first order rate kinetics. The location of an absorption peak in the visible region is blue-shifted with the increase in the illumination time. It is proposed that the photocatalytic decolorization of soluble dyes in the bis-ions coexistence system of NH4 + and NO3 − is a photoreduction reaction, in which the ammonium nitrate acts as a photocatalyst. The chromophore of acidic and basic dyes reacts with hydrogen and then results in their rapid decolorization. [Copyright &y& Elsevier]

Abstract: Porous SnIn4S8 microspheres were initially synthesized through a facile solvothermal approach and were investigated as visible-light driven photocatalysts for dyes degradation in polluted water. The photocatalysts were characterized by XRD, SEM, TEM, N2 adsorption–desorption, and UV–vis diffuse reflectance techniques. Results demonstrated that the as-synthesized SnIn4S8 was of a new tetragonal polymorph, showing a band-gap of 2.5eV, a specific surface area of 197m2 g−1, and an accessible porous structure as well. The photocatalytic activity of the porous SnIn4S8 was evaluated by decomposition of several typical organic dyes including methyl orange, rhodamine B, and methylene blue in aqueous solution under visible light irradiation. It is demonstrated that porous SnIn4S8 was highly photoactive and stable for dyes degradation, showing photocatalytic activity much higher than binary constituent sulfides like In2S3, SnS2, or even ternary chalcogenide ZnIn2S4 photocatalyst. The excellent photocatalytic performance of porous SnIn4S8 is the consequence of its high surface area, well-defined porous texture, and large amount of hydroxyl radicals. [Copyright &y& Elsevier]

Abstract: Photodegradation of persistent organic dyes (Rhodamine B (RhB), Malachite Green Oxalate (MG) and Crystal Violet 10B (CV)) is studied with Fe(III)-salen complex (λ max 494nm), and hydrogen peroxide under visible light irradiation (λ ≥400nm). The complete decolourization of the dyes (60mg/L each) was achieved in the aqueous medium. The pseudo-first-order degradation rate constants of RhB, MG, CV were found to be 2.83×10−3 s−1, 1.57×10−3 s−1 and 1.34×10−3 s−1, respectively. The effect of various parameters like concentration of H2O2, pH of the medium, and influence of electrolytes are investigated on the degradation of RhB. A modified benzoic acid hydroxylation method has been used to detect the active oxygen species (OH radicals) in this study. The hydroxyl radical production is increased with the increase in irradiation time. Interestingly, even an excess amount of scavenger could not arrest the degradation of the dyes. This may be due to the formation of some secondary oxidants. Here, active ferryl ion was identified as the secondary oxidant. Degradation products of the dye (RhB) were determined by GC–MS, and phthalic acid was identified as the major one. From the results, a possible photodegradation mechanism has been proposed. [Copyright &y& Elsevier]

Abstract: Removal of Acid Red 73 (AR 73) and Reactive Red 24 (RR 24) onto modified wheat straw (MWS) from aqueous solutions was investigated. Sorption experiments were carried out as function of MWS dosage, contact time, initial concentration, pH and temperature. Characterizations of MWS were measured and a mass of amine groups were observed in the framework of MWS. The equilibrium sorption data were well represented by the Langmuir isotherm equation, and the calculated thermodynamic parameters indicated a spontaneous and endothermic nature for sorption process. It was shown that pseudo-second-order kinetic equation could best describe the adsorption kinetics. More over, the high maximum sorption capacity (q e max, 714.3mgg−1 for AR 73 and 285.7mgg−1 for RR 24) and low cost (1.24US$kg−1) of MWS provided strong evidence of the potential of MWS for the technological applications of anionic dyes removal from aqueous solutions. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the stoichiometry of decolorization of four dyes (Basic Yellow 28, Malachite Green, Reactive Black 5 and Reactive Red 198) was investigated using ozonation processes. The decolorization of Basic Yellow 28 (BY28) and Malachite Green (MG) was optimal at an acidic pH value of 3, whereas decolorization of Reactive Black 5 (RB5) and Reactive Red 198 (RR198) was optimal at a basic pH of 10. Stoichiometric Ratios (SR) between ozone and dyes were calculated to be 3.5, 7.1, 11 and 16.1 for BY28, MG, RB5 and RR198, respectively. The correlation between ozone-double bond (DB) with the best linear fit and the least relative error (ɛ (%)) was between aromatic ring number () and SR, with regression coefficients of 0.993 and 4.6, respectively. Also, the relationship between total double bond number (DBN T)–SR had respective values of 5.1 and 0.983 for the ɛ (%) and regression coefficient. Additionally, the pseudo-first order decolorization rate constants, k′, were decreased from aromatic ring number 2 () to aromatic ring number 5 (). [Copyright &y& Elsevier]

Abstract: The ambient sonocatalytic degradation of congo red, methyl orange, and methylene blue by titanium dioxide (TiO2) catalyst at initial concentrations between 10 and 50mg/L, catalyst loadings between 1.0 and 3.0mg/L and hydrogen peroxide (H2O2) concentrations up to 600mg/L is reported. A 20kHz ultrasonic processor at 50W was used to accelerate the reaction. The catalysts were exposed to heat treatments between 400 and 1000°C for up to 4h to induce phase change. Sonocatalysts with small amount of rutile phase showed better sonocatalytic activity but excessive rutile phase should be avoided. TiO2 heated to 800°C for 2h showed the highest sonocatalytic activity and the degradation of dyes was influenced by their chemical structures, chemical phases and characteristics of the catalysts. Congo red exhibited the highest degradation rate, attributed to multiple labile azo bonds to cause highest reactivity with the free radicals generated. An initial concentration of 10mg/L, 1.5g/L of catalyst loading and 450ppm of H2O2 gave the best congo red removal efficiency of above 80% in 180min. Rate coefficients for the sonocatalytic process was successfully established and the reused catalyst showed an activity drop by merely 10%. [Copyright &y& Elsevier]

Abstract: Sahara desert sand (SaDeS) was employed as a mineral sorbent for retaining organic dyes from aqueous solutions. Natural sand has demonstrated a strong affinity for organic dyes but significantly lost its adsorption capacity when it was washed with water. Therefore, characterization of both natural and water washed sand was performed by XRD, BET, SEM and FTIR techniques. It was found that water-soluble kyanite, which is detected in natural sand, is the dominant factor affecting adsorbance of cationic dyes. The sand adsorbs over 75% of cationic dyes but less than 21% for anionic ones. Among the dyes studied, Methylene Blue (MB) demonstrated the strongest affinity for Sahara desert sand (Q e =11.98mg/g, for initial dye solution concentration 3.5×10−5 mol/L). The effects of initial dye concentration, the amount of the adsorbent, the temperature and the pH of the solution on adsorption capacity were tested by using Methylene Blue as model dye. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied. It was concluded that adsorption of Methylene Blue on Sahara desert sand followed pseudo-second order kinetics. Gibbs free energy, enthalpy change and entropy change were calculated and found −6411J/mol, −30360J/mol and −76.58J/molK, respectively. These values indicate that the adsorption is an exothermic process and has a spontaneous nature at low temperatures. [Copyright &y& Elsevier]

Abstract: Copolymer hydrogels composed of poly(vinyl alcohol) (PVA) and carboxymethyl cellulose (CMC) was prepared by using electron beam irradiation as crosslinking agent. The copolymers were characterized by FTIR and the physical properties such as gelation. The thermal behavior and swelling properties of the prepared hydrogels were investigated as a function of PVA/CMC composition. The factors effecting adsorption capacity of acid, reactive and direct dyes onto PVA/CMC hydrogel, such as CMC content, pH value of the dye solution, initial concentration and adsorption temperature for dyes were investigated. Thermodynamic study indicated that the values the negative values of ΔH suggested that the adsorption process is exothermic. The value of ΔH (38.81kJ/mol) suggested that the electrostatic interaction is the dominant mechanism for the adsorption of dyes on hydrogel. [Copyright &y& Elsevier]

Abstract: The adsorption process of two dyes as a function of pH on three different adsorbents (goethite, Co-goethite, and magnetite) has been analyzed. Typical anionic adsorption behavior was observed for both dyes onto goethite and Co-goethite. The adsorption level was practically constant in the range of pH studied when the adsorbent was magnetite. The constant capacitance model (CCM) was employed to fit the experimental results. The surface complexes proposed from the adsorption data were in agreement with the patterns obtained from FTIR spectroscopy and a molecular mechanics calculation. Goethite has very good performance as adsorbent of Alizarin and Eriochrome Blue Black R. The presence of a foreign cation in Co-goethite does not improve the adsorption abilities of goethite. At low pH, the amounts of Alizarin and Eriochrome Blue Black R adsorbed on goethite and Co-goethite are similar. However, a higher dependence with the increase of pH is observed by Eriochrome Blue Black R. On magnetite, the dye adsorption shows less affinity for both dyes. Electronic and steric considerations can explain the trends found in the adsorption of the two dyes on the three iron oxides studied in this work. [Copyright &y& Elsevier]

This review evaluates a number of different agricultural waste adsorbents and types of dyes. Certain wastewater containing different dye contaminants causes serious environmental problems. Recently, growing research interest in the production of carbon based has been focused on agricultural by-products. Low cost adsorbents derived from agricultural wastes have demonstrated outstanding capabilities for the removal of dyes from wastewater. Therefore, low cost agricultural waste adsorbents can be viable alternatives to activated carbon for the treatment of contaminated wastewater. The use of cheap and eco-friendly adsorbents have been studied as an alternative substitution of activated carbon for the removal dyes from wastewater. The dye adsorption capacities of agricultural waste adsorbents vary, depending on the characteristics of the individual adsorbent, the extent of surface modification and the initial concentration of adsorbate. [Copyright &y& Elsevier]

Synthetic dyes are a major part of our life. Products ranging from clothes to leather accessories to furniture all depend on extensive use of organic dyes. An unfortunate side effect of extensive use of these chemicals is that huge amounts of these potentially carcinogenic compounds enter our water supplies. Various advanced oxidation processes (AOPs) including the use of high-energy radiation have been developed to degrade these compounds. In this review, dye decoloration and degradation as a result of its exposure to high energy radiation such as gamma radiation and pulsed electron beam are discussed in detail. The role of various transient species such as yph name="rad" />OH and eaq − are taken into account as reported by various researchers. Literature citations in this area show that eaq − is very effective in decolorization but is less active in the further degradation of the products formed. The degradation of the dyes is initiated exclusively by on electron-rich sites of the dye molecules. Additionally, various parameters that affect the efficiency of radiation induced degradation of dyes, such as effect of radiation dose, oxygen, pH, hydrogen peroxide, added ions and dye classes are also reviewed and summarized. Lastly, pilot plant application of radiation for wastewater treatment is briefly discussed. [Copyright &y& Elsevier]

Kaolinite, a low-costly material, is the most abundant phyllosilicate mineral in highly weathered soils. In this work, the adsorption kinetics of maxilon yellow 4GL (MY 4GL) and maxilon red GRL (MR GRL) dyes on kaolinite from aqueous solutions was investigated using the parameters such as contact time, stirring speed, initial dye concentration, initial pH, ionic strength, acid-activation, calcination and solution temperature. The equilibrium time was 150min for both dyes. The results showed that alkaline pH was favorable for the adsorption of MY 4GL and MR GRL dyes and physisorption seemed to play a major role in the adsorption process. It was found that the rate of adsorption decreases with increasing temperature and the process is exothermic. The adsorption kinetics followed the pseudo-second-order equation for both dyes investigated in this work with the k 2 values lying in the region of 1.79×104 to 107.87×104 g/molmin for MY 4GL and 3.44×104 to 72.09×104 g/molmin for MR GRL. The diffusion coefficient values calculated for the dyes were in the range of 3.76×10−9 to 62.50×10−9 cm2/s for MY 4GL and 1.98×10−9 to 44.00×10−9 cm2/s for MR GRL, and are compatible with other studies reported in the literature. The thermodynamic activation parameters such as the enthalpy, entropy and free energy were determined. The obtained results confirmed the applicability of this clay as an efficient adsorbent for cationic dyes. [Copyright &y& Elsevier]

Physicochemical and bacteriological status of a local textile mill effluent showed considerably high values of temperature (40°C), pH (9.50), EC (3.57μs/m), BOD (548mgl−1), COD (1632mgl−1), TSS (5496mgl−1), TDS (2512mgl−1), heavy metals ions (0.28–6.36mgl−1) and color above the prescribed fresh water limits. However, a considerable decline in almost all pollution indicators from source to sink indicated signs of natural remediation. Ten bacteria strains isolated from effluent showed comparatively higher resistance (MRL) (mgl−1) (average) for 10 heavy metals than against four structurally different dyes tested on solid media of mineral salt. Overall bacterial resistance was quite high against Fe3+ (2820), Cr3+ (1203), Zn2+ (1122), Mn2+ (804) and Pb2+ (435), whereas, it varied amid 300–500 in four dyes. Bacterial decolorization/degradation of dyes indicated on solid media was confirmed through experiments carried out in liquid broth. [Copyright &y& Elsevier]

The purpose of this paper is to establish the experimental conditions for removal of several textile dyes from aqueous solutions by sorption on beech wood sawdust, an industrial waste lignocellulosic product. From the six dyes tested, the sorbent shows preference for three dyes: Direct Brown, Direct Brown 2 and Basic Blue 86. Sorption of dyes on the beech wood sawdust is dependent on the nature of dye, pH, dyes concentration, contact time, and amount of sorbent. By comparative kinetic studies, the rate of sorption was found to conform with good correlation to pseudo-second-order kinetics. The parameters that characterize the sorption were determined on the basis of Langmuir isotherms. The preference of beech sawdust for dyes increases as follows: Basic Blue 86−1 for Direct Brown. [Copyright &y& Elsevier]

The decolourisation of dye solutions by oxidation with H2O2, using activated carbon as catalyst, is studied. For this purpose, three different samples, mainly differing in the respective surface chemistries, were prepared and characterized. Moreover, this work involved three pH levels, corresponding to acid, neutral and alkaline solutions, and six dyes belonging to several classes. The catalytic decolourisation tests were performed in a laboratorial batch reactor. Adsorption on activated carbon and non-catalytic peroxidation kinetic experiments were also carried out in the same reactor, in order to compare the efficiencies of the three processes. The non-catalytic reaction is usually inefficient and, typically, adsorption presents a low level of decolourisation. In these cases, the combination of activated carbon with hydrogen peroxide may significantly enhance the process, since the activated carbon catalyses the decomposition of H2O2 into hydroxyl radicals, which are very reactive. Based on the experiments with the different activated carbon samples, which have similar physical properties, it is proved that the surface chemistry of the catalyst plays a key role, being the basic sample the most active. This is discussed considering the involvement of the free electrons on the graphene basal planes of activated carbon as active centres for the catalytic reaction. Additionally, it is shown that the decolourisation is enhanced at high pH values, and a possible explanation for this observation, based on the proposed mechanism, is given. [Copyright &y& Elsevier]

Layered double hydroxides (LDHs) and layered double oxides (LDOs) are desirable adsorption materials for printing and wastewater treatment owing to their outstanding anion exchange abilities, abundant active sites, and eco-friendly nature. In this study, a versatile LDO hybrid coated with carbon dots (CDs@MgAl-LDO) was constructed by modifying sodium dodecylbenzene sulfonate on the surface of MgAl-LDH as a carbon precursor, followed by ligand carbonization and hydrotalcite dehydration at 450 °C under N 2 flow. CDs@MgAl-LDO displayed a hexagonal lamellar architecture with a plate lateral size of approximately 500 nm. It had a higher BET specific surface area (28.61 m2/g) than MgAl-LDO (11.48 m2/g). X-ray diffraction analysis revealed that CDs@MgAl-LDO maintained the "memory effect" of LDOs and could retrieve the original structure when dispersed in water. Moreover, the modified carbon dots change the intrinsically hydrophilic nature of LDOs and help to improve the affinity for organic contaminants, including both cationic and anionic dyes. The adsorption of dyes on CDs@MgAl-LDO followed a pseudo-second-order kinetic model with correlation coefficients (R2) ranging from 0.9901 to 0.9911 and exhibited Freundlich-type heterogeneous adsorption. It showed superior adsorption performance for three dyes, with the maximum adsorption capacity of 3628.9–5174.1 mg/g, thereby outperforming previously reported LDH-based adsorbents. This work developed a facile approach for preparing new carbon dots-LDH hybrids for the highly efficient removal of multiple dyes. [Display omitted] • A versatile LDO hybrid coated with CDs was constructed. • CDs were in-situ transformed from SDBS on the surface of LDH by carbonization. • The hybrid exhibited superior adsorption capacity for both cationic and anionic dyes. • The adsorption was heterogeneous and followed pseudo-second-order kinetic model. [ABSTRACT FROM AUTHOR]

In this research, the adsorptive performance of a starch-magnesium/aluminum layered double hydroxide (S-Mg/Al LDH) composite was investigated for different organic dyes in single-component systems by conducting a series of batch mode experiments. S-Mg/Al LDH composite showed preferential adsorption of anionic dyes than cationic dyes. The marked impact of key process variables (e.g., contact time, adsorbent dosage, pH, and temperature) on its adsorption was investigated. Multiple isotherms, kinetics, and thermodynamic models were applied to describe adsorption behavior, diffusion, and uptake rates of the organic dyes over S-Mg/Al LDH composite. A better fitting of the non-linear Langmuir model reflects the predominance of monolayered adsorption of dye molecules on the composite surface. Partition coefficients (mg g−1 μM−1) for S-Mg/Al LDH were observed in the following descending order: Amaranth (665) > Tartrazine (186) > Sunset yellow (71) > Eosin yellow (65). Furthermore, comparative evaluation of the adsorption enthalpy, entropy, and Gibbs free energy values indicates that the adsorption process is spontaneous and exothermic. S-Mg/Al LDH composite maintained a stable adsorption/desorption recycling process over six consecutive cycles with the advantages of low cost, chemical/mechanical stability, and easy recovery. The results of this study are expected to expand the application of modified LDHs toward wastewater treatment. [Display omitted] • Starch-magnesium/aluminum layered double hydroxide (S-Mg/Al LDH) is used as adsorbent. • The mechanism of anionic dye adsorption on S-Mg/Al LDH composite was studied. • Equilibrium dye adsorption partition coefficients ranged from 65 to 665 mg/g μM−1. • The efficacy of S-Mg/Al LDH was regenerable up to at least six cycles. • The adsorption of dye molecules by S-Mg/Al LDH was spontaneous and exothermic. [ABSTRACT FROM AUTHOR]

Industrial contaminants such as dyes and intermediates are released into water bodies, making the water unfit for human use. At the same time large amounts of food wastes accumulate near the work places, residential complexes etc. polluting the air due to putrefaction. The need of the hour lies in finding innovative solutions for dye removal from wastewater streams. In this context, the article emphasizes adoption or conversion of food waste materials, an ecological nuisance, as adsorbents for the removal of dyes from wastewaters. Adsorption, being a well-established technique, the review critically examines the specific potential of food waste constituents as dye adsorbents. The efficacy of food waste-based adsorbents is examined, besides addressing the possible adsorption mechanisms and the factors affecting phenomenon such as pH, temperature, contact time, adsorbent dosage, particle size, and ionic strength. Integration of information and communication technology approaches with adsorption isotherms and kinetic models are emphasized to bring out their role in improving overall modeling performance. Additionally, the reusability of adsorbents has been highlighted for effective substrate utilization. The review makes an attempt to stress the valorization of food waste materials to remove dyes from contaminated waters thereby ensuring long-term sustainability. [Display omitted] • Adsorption technology points to suitability of dye removal from contaminated waters. • Food waste materials are ideal adsorbents for dye removal from wastewaters. • Information and communication technologies assist in dye adsorption modeling. • Emphasis on adsorbent regeneration focusing on sustainability is required. [ABSTRACT FROM AUTHOR]

This study describes the synthesis of a new bioadsorbent with zwitterionic characteristics and its successful application for removal of a cationic dye (crystal violet, CV) and an anionic dye (orange II, OII) from single component aqueous systems. The new bi-functionalized cellulose derivative (MC3) was produced by chemical modification of cellulose with succinic anhydride and choline chloride to introduce carboxylic and quaternary ammonium functional groups on the cellulose surface. MC3 was characterized by several wet chemical and spectroscopic methods. The effects of solution pH, contact time, and initial solute concentration on removal of CV and OII by MC3 were investigated. Studies of the desorption and re-adsorption of the dyes were also carried out. The isotherms for adsorption of CV and OII on MC3 were satisfactorily fitted using the Konda and Langmuir models. MC3 showed experimental maximum adsorption capacities of 2403 mg g-1 for CV and 201 mg g-1 for OII. The desorption and re-adsorption results showed that MC3 could be reused in successive adsorption cycles, which is essential for minimizing process costs and waste generation. The findings showed that MC3 is a versatile biosorbent capable of efficiently removing both cationic and anionic dyes. [Display omitted] • A new bi-functionalized biosorbent (MC3) was synthetized from cellulose (C). • Modification of C was performed using succinic anhydride and choline chloride. • MC3 removed a cationic and an anionic dye from monocomponent solutions efficiently. • MC3 showed very high adsorption capacity for crystal violet and orange II. • MC3 is a versatile biosorbent that can be reused in new adsorption cycles. [ABSTRACT FROM AUTHOR]

In order to promote the application of membrane technology in the treatment of textile wastewater containing small molecule dye, fabricating a hollow fiber loose nanofiltration (LNF) with a thin and compact separation layer and deepening the understanding of compactness-tailoring mechanism in chemical crosslinking are essential. Firstly, the mechanisms of synergistic crosslinking of PEI-70K and PEI-10K, along with a weakening of the PEI hydration by ethanol, were expounded in primary crosslinking. Then, some LNF separation layers with different compactness were prepared through crosslinking with different crosslinkers to further reduce pore size, which resulted in the efficient removal (~100%) of a small molecular dye (methyl orange (MO), M = 327 g mol–1). The removal of methyl orange is mainly caused by size sieving. The relationship among the pore size, the M w of the secondary crosslinkers, and the pore size reduction rate was interpreted by comparing the pore size reduction rate of three secondary crosslinkers with different molecular weights. In addition, the as-prepared separation layer exhibited excellent dimensional stability and solvent resistance. This paper not only provides a reference for fabricating hollow fiber LNF with better purification performance, but also shows their potential in developing solvent resistant nanofiltration [Display omitted] • The synergistic effect of PEIs with two Mw on membrane microstructure was expounded. • The influence of weakening PEI hydration by ethanol on compactness was revealed. • The relationship among the pore size, the M w of crosslinkers and the reduction rate of pore size was interpreted. • Chemical crosslinking reduced pore size and enhanced the rejection of MO effectively. • Chemical crosslinking improved the dimensional stability and solvent resistance. [ABSTRACT FROM AUTHOR]

Abstract: A factorial design was employed to evaluate the quantitative removal of an anionic red dye from aqueous solutions on epichlorohydrin-cross-linked chitosan. The experimental factors and their respective levels studied were the initial dye concentration in solution (25 or 600mgL−1), the absence or the presence of the anionic surfactant sodium dodecylbenzenesulfonate (DBS) and the adsorption temperature (25 or 55°C). The adsorption parameters were analyzed statistically using modeling polynomial equations. The results indicated that increasing the dye concentration from 25 to 600mgL−1 increases the dye adsorption whereas the presence of DBS increases it. The principal effect of temperature did not show a high statistical significance. The factorial results also demonstrate the existence of statistically significant binary interactions of the experimental factors. The adsorption thermodynamic parameters, namely Δads H, Δads G and Δads S, were determined for all the factorial design results. Exothermic and endothermic values were found in relation to the Δads H. The positive Δads S values indicate that entropy is a driving force for adsorption. The Δads G values are significantly affected by an important synergistic effect of the factors and not by the temperature changes alone. [Copyright &y& Elsevier]

Electrochemical oxidation of synthetic wastewater containing acid blue 22 on a boron-doped diamond electrode (BDD) was studied, using cyclic voltammetry and bulk electrolysis. The influence of current density, dye concentration, flow rate, and temperature was investigated, in order to find the best conditions for COD and colour removal. It was found that, during oxidation, a polymeric film, causing BDD deactivation, was formed in the potential region of water stability, and that it was removed by anodic polarisation at high potentials in the region of O2 evolution. Bulk electrolysis results showed that the electrochemical process was suitable for completely removing COD and effectively decolourising wastewaters, due to the production of hydroxyl radicals on the diamond surface. In particular, under optimal experimental conditions of flow rates (i.e. 300dm3 h−1) and current density (i.e. 20mAcm−2), 97% of COD was removed in 12h electrolysis, with 70kWhm−3energy consumption. [Copyright &y& Elsevier]

Abstract: In this study, the surface coverage ratio (S c/S p) and monolayer cover adsorption amount per unit surface area (q mon/S p) were employed to investigate the adsorption isotherm equilibrium of the adsorption of dyes (AB74, BB1 and MB) on NaOH-activated carbons (FWNa2, FWNa3 and FWNa4); the adsorption rate of the Elovich equation (1/b) and the ratio of 1min adsorption amount of adsorbate to the monolayer cover amount of adsorbate (q 1/q mon) were employed to investigate adsorption kinetics. The q mon/S p of NaOH-activated carbons was better than that of KOH-activated carbons prepared from the same raw material (fir wood). The S c/S p values of the adsorption of all adsorbates on adsorbent FWNa3 in this study were found to be higher than those in related literature. Parameters 1/b and q 1 of the adsorption of dyes on activated carbons in this study were higher than those on KOH-activated carbons; the q 1/q mon value of FWNa3 was the highest. The pore structure and the TPD measurement of the surface oxide groups were employed to explain the superior adsorption performance of FWNa3. A high surface activated carbon (FWNa3) with excellent adsorption performance on dyes with relation to adsorption isotherm equilibrium and kinetics was obtained in this study. Several adsorption data processing methods were employed to describe the adsorption performance. [Copyright &y& Elsevier]

Batch and column kinetics of methylene blue adsorption on calcium chloride, zinc chloride, magnesium chloride and sodium chloride treated beech sawdust were simulated, using untreated beech sawdust as control, in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. The adsorption capacity, estimated according to Freundlich''s model, the Langmuir constant K L and the adsorption capacity coefficient values, determined using the Bohart and Adams’ bed depth service model indicate that salts treatment enhanced the adsorption properties of the original material. Since sawdust is an industrial waste/byproduct and the salts used can be recovered as spent liquids from various chemical operations, this process of adsorbent upgrading/modification might be considered to take place within an ‘Industrial Ecology’ framework. [Copyright &y& Elsevier]

The potential of adsorptive removal of basic dyes with titanate nanotubes (TNTs) and acid dyes with surfactant (hexadecyltrimethylammonium (HDTMA) chloride)-modified TNTs were investigated. TNTs were prepared via a hydrothermal method and subsequently washed with HCl aqueous solutions of different concentrations. The prepared TNTs were then mediated by the HDTMA ions through the cation exchange process. Effects of acid washing and HDTMA-modified process on the revolution of microstructure and surface chemistry characteristics of TNTs were characterized with XRD, nitrogen adsorption–desorption isotherms, and FTIR. The adsorption capacities of two basic dyes (two acid dyes) on TNTs (their HDTMA-modified version) at initial dye concentration of 2000mg/L were measured. It was experimentally concluded that if the amount of Na+ in the TNTs was not very low, the TNTs and their HDTMA-modified version might be a good adsorbent for the removal of basic and acid dyes from aqueous solution through the cation and anion exchange mechanism, respectively. The adsorption capacity for basic and acid dyes could reach 380 and 400mg/g, respectively. [Copyright &y& Elsevier]

The adsorption of three basic dyes (Rhodamine B (RB), Crystal Violet (CV), and Methylene Green (MG)) and two acid dyes (Acid Red 1 (AR1) and Erioglaucine (EG)) onto MCM-41 was studied to examine the potential of MCM-41 for the removal of dyes from water solution. The revolution of pore structure and surface chemical characteristics of MCM-41 induced by dyes adsorption was characterized based on the analyses of XRD patterns, FTIR spectra, and nitrogen adsorption–desorption isotherms. The adsorption capacity of MCM-41 for the five dyes followed a decreasing order of RB>CV>MG>EG∼AR1. It was experimentally concluded that if the dyes adsorption did not introduce a serious disorder on the pore structure of MCM-41 (such as RB adsorption), MCM-41 might be a good adsorbent for the removal of basic dyes from water solution. The fitness of both Langmuir and Freundlich adsorption model on describing the equilibrium isotherms of three basic dyes was examined. The suitability of both pseudo-second-order kinetic model and the intraparticle diffusion model for the description of the kinetic data was investigated, from which the adsorption mechanism was examined. [Copyright &y& Elsevier]

This paper deals with the application of wheat shells (WS), an agricultural by-product, for the removal of direct blue 71 (DR) from aqueous solution. The characteristics of WS surface, such as surface area, Bohem titration and scanning electron microscopy (SEM) were obtained. The removal of direct blue 71 onto WS from aqueous solution was investigated by using parameters, such as pH, temperature, adsorbent dose, contact time and initial concentration. The adsorption process attains equilibrium within 36h. The extent of dye removal decreased with increasing adsorbent dosage and also increased with increasing contact time, temperature, in solution concentration. Optimum pH value for dye adsorption was determined between 6 and 8. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. It was found that the Langmuir equation fit better than the Freundlich equation. Maximum adsorption capacity (Q m) was calculated as at different temperatures (293, 303 and 313K) 40.82, 45.66 and 46.30mgg−1, respectively. In addition, the adsorption data obtained at different temperatures of DR by WS were applied to pseudo first-order, pseudo second-order and Weber–Morris equations, and the rate constants of first-order adsorption (k 1), the rate constants of second-order adsorption (k 2) and intraparticle diffusion rate constants (k 3) at these temperatures were calculated, respectively. The rates of adsorption were found to conform to pseudo second-order kinetics with good correlation (R 2 ≥0.9904). Also, free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were determined to predict the nature of adsorption. Furthermore, the results indicate that WS could be employed as a low-cost alternative to other adsorbents in the removal of direct blue 71 from aqueous solution. [Copyright &y& Elsevier]

Abstract: Adsorption of industrially important dyes namely bromophenol blue, alizarine red-S, methyl blue, methylene blue, eriochrome black-T, malachite green, phenol red and methyl violet from aqueous media on activated charcoal has been investigated. The effect of shaking time, pH and temperature on the adsorption behaviour of these dyes has been studied. It was noted that adsorption of all the dyes on activated charcoal decreases with an increase in the pH and the temperature. The adsorption isotherms at different temperatures were found to be of L-type. Adsorption data was fitted to Freundlich, BET and Langmuir isotherms and various adsorption parameters have been calculated. The thermodynamic parameters such as ΔG, ΔH and ΔS were calculated from the slopes and intercepts of the linear variation of ln K against 1/T, where K is the adsorption coefficient obtained from Langmuir equation, was used. The calculated values for the heat of adsorption and the free energy indicate that adsorption of dyes is favored at low temperatures and the dyes are chemisorbed on activated charcoal. [Copyright &y& Elsevier]

Abstract: Ozonation experiments were carried out under continuous operation in a bubble column. The effect of several parameters (inlet dye concentration, applied ozone dose, pH and conductivity) in colour and TOC removal of an acid dye solution was investigated with the aim to optimize the operation conditions. The ozone consumption was measured in each experiment. Ozonation was found to be effective for decolourisation of an acid dye; however, it only has a slight effect on TOC removal. Increasing the inlet dye concentration leads to a decrease in the decolourisation efficiency and an increase in the ozone consumption. The decolourisation increases with the applied ozone dose. Colour removal efficiencies for different ozone doses were between 76 and 100%. In the pH range 5–9, the decolourisation efficiency decreases with pH only when buffered solutions were used. The presence of salt decreases the decolourisation efficiency. Several dyes of different classes were also studied and ozonation was found to be effective for decolourisation but considerably less efficient for TOC removal. Under the conditions tested, only the disperse and sulphur dyes presented a colour removal lower than 86%. Practical application of this process was validated by treating two industrial textile effluents collected after two different biological treatments. [Copyright &y& Elsevier]

Abstract: The electrochemical oxidation of textile effluents over a titanium–tantalum–platinum–iridium anode was investigated. Batch experiments were conducted in a flow-through electrolytic cell with internal recirculation at current intensities of 5, 10, 14 and 20A, NaCl concentrations of 0.5, 1, 2 and 4% and recirculation rates of 0.81 and 0.65L/s using a highly colored, synthetic effluent containing 16 textile dyes at a total concentration of 361mg/L and chemical oxygen demand (COD) of 281mg/L. Moreover, an actual dyehouse effluent containing residual dyes as well as various inorganic and organic compounds with a COD of 404mg/L was tested. In most cases, quantitative effluent decolorization was achieved after 10–15min of treatment and this required low energy consumption; conversely, the extent of mineralization varied between 30 and 90% after 180min depending on the operating conditions and the type of effluent. In general, treatment performance improved with increasing current intensity and salinity and decreasing solution pH. However, the use of electrolytes not containing chloride (e.g. FeSO4 or Na2SO4) suppressed degradation. Although the acute toxicity of the actual effluent to marine bacteria Vibrio fischeri was weak, it increased sharply following treatment, thus suggesting the formation of persistent toxic by-products. [Copyright &y& Elsevier]