New carbon composite adsorbents for the removal of textile dyes from aqueous solutions: Kinetic,equilibrium, and thermodynamic studies

New carbon composite materials were prepared by pyrolysis of mixture of coffee wastes and red mud at 700 °C with the inorganic: organic ratios of 1.9 (CC-1.9) and 2.2 (CC-2.2). These adsorbents were used to remove reactive orange 16 (RO-16) and reactive red 120 (RR-120) textile dyes from aqueous solution. The CC-1.9 and CC-2.2 materials were characterized using Fourier transform infrared spectroscopy, Nitrogen adsorption/desorption curves, scanning electron Microscopy and X-ray diffraction. The kinetic of adsorption data was fitted by general order kinetic model. A three-parameter isotherm model, Liu isotherm model, gave the best fit of the equilibrium data (298 to 323 K). The maximum amounts of dyes removed at 323 K were 144.8 (CC-1.9) and 139.5 mg g^?1 (CC-2.2) for RO-16 dye and 95.76 (CC-1.9) and 93.80 mg g^?1 (CC-2.2) for RR-120 dye. Two simulated dyehouse effluents were used to investigate the application of the adsorbents for effluent treatment.     

Selective thermal recycling for graphene growth on natural substrates: A comparative study on life cycle assessment,energy consumption,and mechanical performance in recompounding

Manufacturing of carbon-based materials from waste thermoplastics is a keystone to reduce adverse environmental impacts. There are numerous attempts for sustainable graphene manufacturing from various waste sources by thermal treatment but there is no clear distinction on the effective conversion process by addressing reliable CO₂ footprints. This study provides a comprehensive benchmarking study on the conversion of waste polypropylene plastics coming from yogurt containers into graphene on the substrate of talc by applying two upcycling techniques of catalytic carbonization (CC) and flash pyrolysis (FP) by comparing energy and speed of the processes and a dimensional stability and physical characteristics of the produced graphene substances by adopting a comparative life cycle assessment. FP led to the sphericalization of graphenes due to fast dehydration, cross-linking, and carbonization of aromatic structures. On the other hand, gradual heating in CC caused the formation of tubular-like graphene structures. In addition, FP became advantageous by resulting in 52% of CO₂ emission compared with CC process. On the other hand, graphenes separated from talcs exhibited a remarkable 70% reduction in global warming potential compared with conventional graphene production from graphite. In order to complete the value chain and circularity, the mechanical performance of two different hybrid additives produced by selective thermal recycling in recompounding with copolymer polypropylene was examined, and additives from CC enhanced the flexural and tensile properties two times better than the one from FP. With this study, it becomes possible to compare analysis of graphene growth on natural substrates by exploring life cycle assessment, energy consumption, and mechanical performance with selective thermal recycling and recompounding.     

Electrocatalytic reduction of bromate ion using a polyaniline-modified electrode: An efficient and green technology for the removal of BrO3 in aqueous solutions

The electrocatalytic reduction of bromate ion (BrO₃⁻) was investigated in a three-electrode system using polyaniline (PANI) as the electrode material. Bromate ion reduction and Br⁻ removal were observed during electrochemical treatment because of the catalytic and doping capabilities of the PANI film. BrO₃⁻ removal efficiency in the 0.10 mol L⁻¹ Na₂SO₄ supporting electrolyte achieved 99% at pH 7 in 25 min, with no bromide ion detected in the solution. Optimal removal was found in pH range 6-7, and the pH of the solution had a significant impact on bromate reduction. A reduction mechanism was also discussed by analyzing the cyclic voltammograms of the reduction process and X-ray photoelectron spectra of the main elements (N 1s and Br 3d) on the PANI surface. We propose that during the electrocatalytic reduction process, bromate is reduced to bromide because of the loss of electrons from the nitrogen atoms on the PANI chains. The doping of the resultant Br⁻ ions in the PANI film has an important role in avoiding further oxidation of Br⁻ to BrO₃⁻. The used PANI film can be regenerated by de-doping the Br⁻ ions with a 0.5 mol L⁻¹ H₂SO₄ solution. Thus the process can be considered efficient and green.     

Design and simulation of a solar chemical reactor for the thermal reduction of metal oxides: Case study of zinc oxide dissociation

A laboratory-scale solar reactor was designed and simulated for the thermal reduction of metal oxides involved in water-splitting thermochemical cycles for hydrogen production. This reactor features a cavity-receiver directly heated by concentrated solar energy, in which solid particles are continuously injected. A computational model was developed by coupling the fluid flow, heat and mass transfer, and the chemical reaction. The reactive particle-laden flow was simulated, accounting for a multiphase model (solid-gas flow). A discrete phase model based on a Lagrangian approach was developed. The kinetics of the chemical reaction was considered in the specific case of zinc oxide dissociation for which reliable data are available. The complete model predicts temperature and gas velocity distributions, species concentration profiles inside the reactor, particle trajectories and fates, and conversion rate assessing the reaction degree of completion. The reaction extent is highly dependent on temperature of the radiation-absorbing particles. Initial diameter of injected particles is also a key parameter because it determines the available surface area for a given particle mass feed rate. The higher the particle surface area, the higher the conversion rate. As a result, reaction completion can be achieved when particle temperature exceeds 2200 K for a initial particle diameter.     

Supported photocatalysis as a pre‐treatment prior to biological degradation for the removal of some dyes from aqueous solutions; Acid Red 183, Biebrich Scarlet,Methyl Red Sodium Salt,Orange II

BACKGROUND: The aim of this study was to assess the feasibility of coupling photocatalysis and a biological treatment for the removal of azo dyes from aqueous effluents. Biological processes do not always appear relevant for dyes removal, owing to the low or total absence of biodegradability of this class of pollutants. RESULTS: During photocatalysis pre‐treatment, a decrease in the chemical oxygen demand (COD) indicated oxidation of the target compound and thus a change in the chemical structure; better biodegradability or less toxicity could then be expected. However, the concomitant decrease in dissolved organic carbon (DOC), characteristic of a high mineralization yield, led to nearly constant COD:DOC ratios, which was unfavorable for an increase in biodegradability. It was confirmed by the low values found for the ratios biological oxygen demand (BOD₅) to COD, which remained in the range 0.09–0.19, namely below 0.4 after photocatalytic reaction. Moreover, toxicity increased or remained at a high level after irradiation of the azo dyes for 3 h, and decreased only for Orange II, from toxic (EC₅₀ = 53%) to moderately toxic (EC₅₀ = 76%). CONCLUSION: An integrated process involving photocataysis and biological treatment to treat azo dyes appeared unsuitable under the conditions tested and may only be considered for Orange II among the four dyes tested. Copyright © 2010 Society of Chemical Industry     

Reduction of metal ions in dilute solutions using a GBC-reactor: Part I: Experimental study on the laboratory scale reduction of ferric ions

To reduce metal ions in dilute solutions a new type of electrochemical reactor has been developed: the GBC-reactor. This reactor consists of a gas diffusion electrode coupled with a packed bed electrode. The working principle of the reactor is based upon two main reactions: the catalytic oxidation of hydrogen gas in the gas diffusion electrode and the simultaneous reduction of metal ions on the packed bed electrode. This process occurs spontaneously without the need for an external power supply when the Gibbs free energy of the total reaction is negative. To study the behaviour of the reactor the reduction of ferric ions was used as a model system. The experimental results, obtained from varying a number of key process parameters, could be described using a very simple macroscopic rate equation. It is concluded that the reduction of ferric ions in a GBC-reactor is controlled by both mass transfer and electrochemical kinetics. To carry out scale-up and optimization studies a reactor model incorporating the potential distribution in the packed bed electrode is, however, necessary.     

Reduction of metal ions in dilute solutions using a GBC-reactor: Part I: Experimental study on the laboratory scale reduction of ferric ions

To reduce metal ions in dilute solutions a new type of electrochemical reactor has been developed: the GBC-reactor. This reactor consists of a gas diffusion electrode coupled with a packed bed electrode. The working principle of the reactor is based upon two main reactions: the catalytic oxidation of hydrogen gas in the gas diffusion electrode and the simultaneous reduction of metal ions on the packed bed electrode. This process occurs spontaneously without the need for an external power supply when the Gibbs free energy of the total reaction is negative. To study the behaviour of the reactor the reduction of ferric ions was used as a model system. The experimental results, obtained from varying a number of key process parameters, could be described using a very simple macroscopic rate equation. It is concluded that the reduction of ferric ions in a GBC-reactor is controlled by both mass transfer and electrochemical kinetics. To carry out scale-up and optimization studies a reactor model incorporating the potential distribution in the packed bed electrode is, however, necessary.     

Protection of lyocell fibres against fibrillation; mechanism for the poor crosslinking performance of reactive dyes on lyocell fibres and the influence of a colourless crosslinking agent as co‐applicant

Sandospace R and five multi‐functional reactive dyes have been applied to lyocell fibre, by exhaust methods. A comparison has been made of the number of mmoles of each species covalently bonded to the fibre, with cross‐linking efficiency (NSF values). None of the dyes studied was able to achieve levels of cross‐linking found in non‐fibrillating grades of lyocell, unless unrealistically high levels were applied. Sandospace R readily matched the NSF values found in commercially produced non‐fibrillating fibres. An explanatory mechanism based on differences in size between Sandospace R and the reactive dyes has been proposed. Fitting the experimental NSF data to an Arrhenius model confirmed the increasing gradient of the NSF curves with increasing millimolar concentration of species fixed. The chroma of the agent‐plus‐dye fibre samples remained relatively constant being either at the same level or above that of those fibre samples treated only with dye. Co‐application of Sandospace R with the reactive dyes has achieved levels of cross‐linking found in commercial non‐fibrillating lyocell fibres.     

Pheromone biosynthetic pathways: Conversion of ipsdienone to (−)-ipsdienol,a mechanism for enantioselective reduction in the male bark beetle,Ips paraconfusus

The enantiomeric composition of the pheromone components (+)-ipsdienoI, e.e. 87.6%, and (–)-ipsenol, e.e. 93.8%, produced by the male bark beetleIps paraconfusus (Scolytidae) under natural conditions was determined by HPLC separation of their diastereomeric ester derivatives. Males confined in an atmosphere of ipsdienone produced (–)-ipsdienol, e.e. 28%, and (–)-ipsenol, e.e. 86%, indicating an enantiomeric selectivity in the conversion of the ketone to the alcohols. These findings demonstrate an enantioselective conversion mechanism in the biosynthetic pathway to the pheromones from myrcene, a host-plant terpene.     

A methodology for characterizing reactive coatings: Time–temperature–transformation (TTT) analysis of the competition between cure,evaporation, and thermal degradation for an epoxy-phenolic system

A methodology, in terms of a macroscopic isothermal time–temperature–transformation (TTT) diagram, is presented for characterizing the changes that occur isothermally in a reactive thermosetting system in which evaporation, cure, and thermal degradation occur. Iso-weight loss contours show the progress of the loss of volatile material (mostly solvent). The gelation contour corresponds to the macroscopic viscosity rising to a definite level. The vitrification contour corresponds to the glass transition temperature (T_g) rising to the temperature of cure (T_cure). Iso-T_g contours show the progress of cure in terms of the easily measured T_g (rather than chemical conversion). The iso-T_g contours also show the influence of thermal degradation competing with cure. Degradation is responsible for difficulties in assigning the glass transition temperature of the fully cured material (i.e., T_g∞).     

Thermodynamics,a good theory for the study of electrochemistry in non-isothermal systems. A specific application: thermal diffusion

We present here a short survey on general non-equilibrium thermodynamics when the external forces are especially of electrostatical nature. Such a development provides a very well-adapted frame to analyse many irreversible processes as thermal diffusion in ionic media. This phenomena, so-called Soret effect in fluid mixtures, has greatly been studied by various experimental methods. Among these, the electrochemical ones give valuable information on quantities such as entropies and heats of transfer.     

Blends of cardanol-based epoxidized novolac resin and CTBN for application in surface coating: a study on thermal,mechanical, chemical,and morphological characteristics

Blend samples of cardanol-based epoxidized novolac resin and different weight percentages of carboxyl-terminated butadiene acrylonitrile (CTBN) were developed and cured with stoichiometric amounts of aliphatic amine. The formation of various products during the curing of blend samples has been studied by Fourier-transform infrared spectroscopy. The dynamic differential scanning calorimeter scans showed that the pure epoxies and their blend samples with CTBN cured in the temperature range of 100–150°C. The blend sample containing 15 wt% CTBN showed the least cure time (at 120°C) among all other blend samples. Upon evaluation, it was found that blend samples exhibit better properties compared to pure epoxy resin in terms of increase in impact strength and elongation-at-break of the casting and gloss, scratch hardness, adhesion, and flexibility of the film. The improvement in these properties indicates that the rubber modified resin would be more durable than the epoxy based on cardanol. Chemical and morphological properties of the formulated resins were also determined. The thermal stability of the blend samples containing 15 wt% CTBN in epoxy resin was the highest among all other prepared systems. The blend morphology, studied by scanning electron microscope, showed the presence of precipitated discrete rubber particles, which dispersed throughout the epoxy matrix—i.e., they revealed the presence of two-phase morphological features.     

Accessibility of man-made cellulosic fibres. Part 2: Examination of the exhaustion profiles of a series of reactive dyes on never-dried and dried lyocell, viscose and modal fibres in the presence of varying electrolyte concentrations

Reactive dyes exhibit a higher level of initial exhaustion, in the presence of small concentrations of electrolyte, on never-dried lyocell than on never-dried viscose and modal. This difference is particularly noticeable in the case of high substantivity bis-monochloro- s -triazinyl reactive dyes, which exhibit the same differentiated performance on the corresponding dried fibres. Low salt quantities (comparable to those used for applying direct dyes to cellulosic substrates) can therefore be used for applying high substantivity dyes and effect chemicals by an exhaustion process to both never-dried and dried lyocell substrates.     

Effect of bis[2-(methacryloyloxy)ethyl] phosphate as a crosslinker on poly(AAm-co-AMPS)/Na-MMT hydrogel nanocomposite as potential adsorbent for dyes: kinetic,isotherm and thermodynamic study

In the present study, synthesis of poly(AAm-co-AMPS)/Na-MMT hydrogel nanocomposite with different amount of bis[2-(methacryloyloxy)ethyl] phosphate as a crosslinker was successfully carried out for the removal of crystal violet (CV), methylene blue (MB) and methyl red (MR) from aqueous solution. Hydrogel nanocomposite was characterized by FT-IR, SEM, EDS, XRD and TGA analysis. Several important parameters were investigated to obtain maximum adsorption capacity. Adsorption behavior of hydrogel nanocomposite was investigated for the adsorption of dyes and it was found to remove about 80% for CV, 89% for MB and 51% for MR in 50 mg/L of dyes solutions at pH 7 and about 86% for CV, 93% for MB and 23% for MR at pH 12. Kinetic studies revealed that the applicability of pseudo-first-order and pseudo-second-order model for the adsorption of CV, MB and MR. The adsorption isotherm was studied in 25, 35, 45 and 55 °C using Langmuir, Freundlich, Temkin and Jovanovic models and the adsorption data were well described by Freundlich isotherm model. Hydrogel nanocomposite showed 155, 176 and 113 mg/g maximum adsorption capacity for CV, MB and MR respectively. Negative values of ΔG⁰ for all three dyes suggested the feasibility of dyes removal and support for spontaneous adsorption of CV, MB and MR on hydrogel nanocomposite. Desorption of dyes from the dye loaded hydrogel nanocomposite was simply done in ethanol. The results indicate that the prepared poly(AAm-co-AMPS)/Na-MMT hydrogel nanocomposite is an efficient adsorbent with high adsorption capacity for the aforementioned dyes.

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Graphical abstract Graphical abstract illustrating the preparation and dye adsorption processes of the poly(AAm-co-AMPS)/Na-MMT hydrogel nanocomposite

     

The roles of polymer relaxation phenomena,aqueous dye solubility and the physical properties of water in the mechanism of adsorption of a disperse dye on poly(ethylene terephthalate) fibres: part 5 analysis of polymer relaxation phenomena for different polymers

The temperature dependent uptake of a commercial disperse dye on cotton and polyamide 66 fabrics at dyeing temperatures between 30°C and 130°C adhered to the Williams–Landel–Ferry equation, insofar as, very good correspondence was observed between plots of experimentally determined colour strength data points (log1/f_k) and the respective structural relaxation times of the cellulose and nylon 66 polymers (loga_T data points), as a function of the parameter (T − T_g). Adsorption of the dye on both types of fibre therefore concurs with the fundamental precept of the free volume model of dye diffusion. Comparison of the adherence of the uptake of the commercial dye on cotton and polyamide 66 fabrics with that secured on polyester fabric revealed that despite the major chemical and physical differences between the three types of fibre, the same dyeing mechanism likely applies to each fibre type. The marked temperature dependent uptake of the commercial grade disperse dye each of the three types of substrate is the consequence of two, different, but inherently interconnected, thermally activated phenomena, namely the relaxation times of the molecular rearrangements occurring within the respective cellulose, nylon 66 or poly(ethylene terephthalate) macromolecule, in which polymer glass transition assumes the principal role, and the aqueous solubility of the commercial grade disperse dye.     

Multiwalled CNTs for Cr(VI) removal from industrial wastewater: An advanced study on adsorption,kinetics, thermodynamics for the comparison between the embedded and non‐embedded carboxyl group

The adsorption capabilities of multiwalled carbon nanotubes (MWCNTs) with and without the embedded carboxyl group for the removal of parts per million levels of hexavalent chromium were examined as a function of several parameters, namely contact time, pH of initial solution, initial concentration of Cr(VI), adsorbent dosage as well as temperature of solution. Adsorption isotherms have been utilized to explain the adsorption mechanism. Ion exchange, intra‐particle diffusion, and electrostatic interactions are found to be the fundamental mechanisms describing the adsorption of Cr(VI). The maximum adsorption capacities of Cr(VI) ion by raw MWCNTs and functionalized MWCNTs were found to be 84.75 and 78.13 mg · g^?1, respectively, as calculated by the Langmuir adsorption isotherm model. This is with regard to the electron‐rich atoms inside the functional group which repels the negatively charged dichromate ions. Kinetic studies were performed, and the data was found in good agreement with the pseudo‐second‐order.     

The roles of polymer relaxation phenomena,aqueous dye solubility and the physical properties of water in the mechanism of adsorption of a disperse dye on poly(ethylene terephthalate) fibres: Part 3 physical properties of water and water-derived fibre properties

In the absence of published information regarding the temperature dependency of water-derived poly(ethylene terephthalate) fibre properties, the findings reported for the thermally regulated interactions between water and 100% amorphous poly(ethylene terephthalate) materials were interpreted from the perspective of the amorphous domains that reside within semi-crystalline polyester textile fibres. This analysis suggests that the pronounced temperature dependent uptake of a commercial grade disperse dye on poly(ethylene terephthalate) fabric achieved during an aqueous dyeing process at temperatures between 30 and 130°C is the likely result of the combination of three separate, but inherently inter-related, thermally activated phenomena, namely, polymer structural relaxation, in which polymer glass transition assumes a dominant role, dissolution of disperse dye in the aqueous dyebath, as well as various water–fibre interactions, in the guise of water sorption, water molecule diffusivity, water-induced swelling and water-induced plasticisation. Although thermally regulated macromolecular relaxation processes adopt the principal role in dye uptake, temperature dependent dye solubility and water-derived fibre properties nevertheless likely provide crucially important supportive roles.     

The roles of polymer relaxation phenomena,aqueous dye solubility and the physical properties of water in the mechanism of adsorption of a disperse dye on poly(ethylene terephthalate) fibres: Part 4 further aspects related to polymer relaxation phenomena

To further investigate the contribution of polymer relaxation times to the mechanism of disperse dye adsorption on poly(ethylene terephthalate) fibres, the temperature-dependent uptake of Teratop Yellow HL-G 150% on both cotton and polyamide 66 fabrics at temperatures between 30 and 130°C was compared with that on poly(ethylene terephthalate) fabric. Although uptake of the commercial grade dye on polyester fabric is governed by the thermally regulated, broad glass transition of the water-saturated poly(ethylene terephthalate) substrate, as this was not observed for either cotton or nylon 66 fabrics, the respective cellulose or polyamide 66 polymer glass transition does not present a major thermal impediment to dye uptake over the wide range of dyeing temperatures used. This is because the onset and end-set temperatures of the glass transition of the water-plasticised poly(ethylene terephthalate) material reside within the range of dyeing temperatures employed, whereas those of the water-plasticised cotton and polyamide materials occur below the lowest dyeing temperature examined (30°C). The thermal dependency of disperse dye solubility also likely makes a meaningful contribution to the temperature-dependent dye uptake observed for each type of fibre.     

Generalized analytical expressions for Tafel slope,reaction order and a.c. impedance for the hydrogen evolution reaction (HER): mechanism of HER on platinum in alkaline media

Following the generally accepted mechanism of the HER involving the initial proton discharge step to form the adsorbed hydrogen intermediate, which is desorbed either chemically or electrochemically, generalized expressions for the Tafel slope, reaction order and the a.c. impedance for the hydrogen evolution reaction are derived using the steady-state approach, taking into account the forward and backward rates of the three constituent paths and the lateral interactions between the chemisorbed intermediates. Limiting relationships for the Tafel slope and the reaction order, previously published, are deduced from these general equations as special cases. These relationships, used to decipher the mechanistic aspects by examining the kinetic data for the HER on platinum in alkaline media, showed that the experimental observations can be consistently rationalized by the discharge-electrochemical desorption mechanism, the rate of the discharge step being retarded on inactive platinum compared to the same on active platinum.Nomenclature C _d double-layer capacity (µF cm^–2) - E _rev reversible electrode potential (V) - F Faraday number (96 487 C mol^–1 ) - R gas constant - T temperature (K) - Y _f Faradaic admittance (^–1 cm^–2) - Y _t Total admittance (^–1 cm^–2) - Z _f Faradaic impedance ( cm²) - i _f total current density (A cm^–2) - i _nf nonfaradaic current density (A cm^–2) - j - k ₀ ¹ rate constant of the steps described in Equations 1 to 3 (mol cm^–2 s^–1 ) - j - qmax saturation charge (µC cm^–2) - Laplace transformed expressions for i, and E - _{1 3} symmetry factors for the Equations 1 and 3 - saturation value of adsorbed intermediates (mol cm^–2) - overpotential - coverage by adsorbed intermediates - angular frequency This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribution to electrochemistry.