Factors affecting the adsorption of stabilisers on to carbon black (flow micro-calorimetry and FTIR studies) Part I Primary phenolic antioxidants

The surface activity of different types of carbon black with phenolic antioxidants is examined using flow micro-calorimetry (FMC), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared spectroscopy (FTIR). Significant differences in both the overall adsorption activity and the levels of probe adsorption are observed. Differences in behaviour between types of carbon black are evident and show that the specific surface area is not the most important factor affecting the adsorption activity, but also the chemical nature of its surface. Essentially, two factors were found to affect the behaviour of phenolic stabilisers: Phenolic hydroxyl and ester groups were found to form the strongest interactions with carbon black. Furthermore, steric hinderance of phenolic hydroxyls by alkyl groups is the main factor which influences adsorption activity. In order to characterise different carbon blacks, FTIR and XPS analysis have been used in an attempt to determine the nature of functional groups present on the surface of the carbon blacks. FTIR analysis also shows that some adsorbed antioxidants on the surface of the carbon black could be successfully detected. This provides valuable information regarding the adsorption mechanisms on to carbon black surfaces. Other techniques included thermogravimetric analysis (TGA), N₂ BET adsorption studies and Karl Fisher analysis. The latter were performed in order to determine differences in the volatile and water contents, respectively, of the carbon black samples.     

Factors affecting the adsorption of stabilisers on to carbon black (flow micro-calorimetry studies) Part III Surface activity study using acid/base model probes

The first and second part of this series of papers investigated the interaction between carbon black and stabilisers (phenolic antioxidants and HALS, respectively) and showed that the mechanism was dependent on both the chemical nature of the carbon black surface and the molecular structure of stabilisers. In this third part, the interactions between model compounds, of varying acidity, and the same four carbon blacks, are investigated using flow micro-calorimetry (FMC) and Fourier transform Infrared spectroscopy (FTIR). As with the first and second parts, differences in adsorption behaviour between the four types of carbon black were evident and were principally related to the chemical nature of the surfaces and the adsorbates. In this study further insight in to the nature of the interactions between the carbon black surface functional groups and the acidic and basic probes has been acquired. The main forms of interaction are hydrogen bonding and Lewis and Bronsted acid/base interactions, formation of proton transfer complexes was also considered possible in cases of strong adsorption. The adsorption behaviour of acid and basic aromatic probes, together with octadecanol and stearic acid, was also found to be dependant on the carbon black surface topography. Flat graphene layers containing minimal heteroatoms favoured adsorption of the latter species as flat adsorption and/or structural ordering was permissable.     

活性炭纤维对铂(Ⅳ)的还原吸附及其影响因素的研究

载铂活性炭纤维在燃料电池催化材料的制备等方面具有重要的应用前景.本文比较了水蒸汽活化和磷酸或氯化锌活化活性炭纤维对水溶液中铂离子的还原吸附性能,并研究了影响活性炭纤维对铂的还原吸附的几种因素.结果表明,不同工艺制备的活性炭纤维,由于其电极电位的差异,其对铂离子的吸附容量也不同;水蒸汽活化和氯化锌活化活性炭纤维由于具有低的电极电位,因而表现出对铂离子更大的还原倾向,在吸附的初期,表现出更快的吸附速度.纤维状的活性炭纤维比颗粒状的活性炭具有更快的吸附速度.溶液的酸度也显著影响活性炭纤维对铂离子的还原吸附能力;低的pH下,活性炭纤维对铂一般具有更强的还原吸附容量.     

Removal of lead(II) by adsorption using treated granular activated carbon: batch and column studies

In the present study, a deeper understanding of adsorption behavior of Pb(II) from aqueous systems onto activated carbon and treated activated carbon has been attempted via static and column mode studies under various conditions. It probes mainly two adsorbents that is, activated carbon (AC) and modified activated carbon (AC-S). Characterization of both the adsorbents was one of the key focal areas of the present study. This has shown a clear change or demarcation in the various physical and chemical properties of the modified adsorbent from its precursor activated carbon. Both the adsorbents are subjected to static mode adsorption studies and then after a comparison based on isotherm analysis; more efficient adsorbent is screened for column mode adsorption studies. The lead removal increased for sample of treated carbon. The extent of Pb(II) removal was found to be higher in the treated activated carbon. The aim of carrying out the continuous-flow studies was to assess the effect of various process variables, viz., of bed height, hydraulic loading rate and initial feed concentration on breakthrough time and adsorption capacity. This has helped in ascertaining the practical applicability of the adsorbent. Breakthrough curves were plotted for the adsorption of lead on the adsorbent using continuous-flow column operation by varying different operating parameters like hydraulic loading rate (3.0-10.5 m3/(hm2)), bed height (0.3-0.5 m) and feed concentrations (2.0-6.0 mg/l). At the end, an attempt has also been made to model the data generated from column studies using the empirical relationship based on Bohart-Adams model. This model has provided an objective framework to the subjective interpretation of the adsorption system and the model constant obtained here can be used to achieve the ultimate objective of our study that is, up scaling and designing of adsorption process at the pilot plant scale level. AC-S column regeneration using 0.5 and 1.0M concentration of HNO3 has been investigated. It has shown a regeneration efficiency of 52.0% with 0.5 M HNO3.     

Prediction of simultaneous adsorption of Cu(II) and Pb(II) onto activated carbon by conventional Langmuir type equations

Removal of Cu(II) and Pb(II) by adsorption onto activated carbon was examined in single- and binary-component aqueous solutions representative of contaminated solutions containing heavy metals. Reversibility of adsorption of the heavy metals on the activated carbon was evaluated by desorption experiments. The number of the maximum adsorption sites and adsorption equilibrium constants of Cu(II) and Pb(II) were estimated by the results of single-component systems assuming the Langmuir adsorption model. The adsorption sites per gram of activated carbon resulted in similar values for Cu(II) and Pb(II) from the isotherms. The adsorption constant for Pb(II) was nearly 1.8 times greater than that of Cu(II). Rate constants of adsorption and desorption were also estimated from the kinetic analysis. Using the single set of common parameters obtained from the single-component systems, the experimental results for a binary-component system were quantitatively predicted. Competitive adsorption of Cu(II) and Pb(II) on the same adsorption sites was confirmed by both experimental and predicted results of adsorption in the binary mixture.     

影响活性炭纤维动态吸附氙性能的因素

应用正交设计方法研究了活性炭纤维动态吸附氙的性能.主要考察了吸附温度、原料气浓度和原料气流量及空白未知因素对活性炭纤维动态吸附氙平衡吸附量的影响.结果表明：吸附温度、原料气浓度以及原料气流量为影响平衡吸附量的最重要的因素.其中,吸附温度对平衡吸附量的影响最大,其次是原料气的浓度和原料气的流量.     

Adsorption of Pb(II) and Pb(II)-citric acid on sawdust activated carbon: Kinetic and equilibrium isotherm studies

The removal of Pb(II) and Pb(II)-citric acid (Pb(II)-CA) from aqueous solutions by sawdust activated carbon (SDAC) was investigated. The higher adsorptive removal of Pb(II) from aqueous solutions containing Pb(II)-CA than Pb(II) only was observed due to the presence of CA in the former system. The mechanism of adsorption process was studied by conducting pH as well as kinetic studies. Batch adsorption experiments were conducted to study the effect of adsorbent dose, initial concentration and temperature for the removal of Pb(II) from Pb(II) only and Pb(II)-CA aqueous systems. The adsorption was maximum for the initial pH in the range of 6.5-8.0 and 2.0-5.0 for Pb(II) and Pb(II)-CA, respectively. The solution pH, zero point charge (pH(zpc)) and species distribution of Pb(II) and Pb(II)-CA were found to play an important role in the adsorption of Pb(II) and Pb(II)-CA onto SDAC from water and wastewaters. SDAC exhibited very high adsorption potential for Pb(II) ions in presence of CA than when Pb(II) ions alone were present. The kinetic and equilibrium adsorption data were well modeled using pseudo-first-order kinetics and Langmuir isotherm model, respectively.     

Determination of kinetic and equilibrium parameters of the batch adsorption of Mn(II), Co(II), Ni(II) and Cu(II) from aqueous solution by black carrot (Daucus carota L.) residues

In this study, the effect of temperature on the adsorption of Mn(II), Ni(II), Co(II) and Cu(II) from aqueous solution by modified carrot residues (MCR) was investigated. The equilibrium contact times of adsorption process for each heavy metals-MCR systems were determined. Kinetic data obtained for each heavy metal by MCR at different temperatures were applied to the Lagergren equation, and adsorption rate constants (kads) at these temperatures were determined. These rate constants related to the adsorption of heavy metal by MCR were applied to the Arrhenius equation, and activation energies (Ea) were determined. In addition, the isotherms for adsorption of each heavy metal by MCR at different temperatures were also determined. These isothermal data were applied to linear forms of isotherm equations that they fit the Langmuir adsorption isotherm, and the Langmuir constants (qm and b) were calculated. b constants determined at different temperatures were applied to thermodynamic equations, and thermodynamic parameters such as enthalpy (Delta H), free energy (Delta G), and entropy (Delta S) were calculated and these values show that adsorption of heavy metal on MCR was an endothermic process and process of adsorption was favoured at high temperatures.     

Study on adsorption of Co(II) and Ni(II) onto mesoporous Ti-containing MCM-48

Ti-containing MCM-48 (Ti-MCM-48) material with mesoporous structure was synthesized and characterized, and the absorption processes of Co(II) and Ni(II) on the material were investigated in detail in the present study. The Ti- MCM-48 was synthesized by hydrothermal reaction and characterized by XRD, FT-IR and nitrogen sorption methods. Optimum pH value for maximum adsorption rate is 8.0, and the saturated adsorption capacities of Ti-MCM-48 for Co(II) and Ni(II) are 9.870 and 22.94 mg g(-1) respectively, which are greater than those of the reported materials Adsorption isotherms of Co(II) and Ni(II) on Ti-MCM-48 accord well with the Langmuir adsorption models. Kinetic data of adsorption reactions and the adsorption equilibrium parameters were also determined, and the obtained data correlated linearly with the pseudo-second order equation.     

Effect of the adsorbate (Bromacil) equilibrium concentration in water on its adsorption on powdered activated carbon. Part 2: Kinetic parameters

The application of several monosolute equilibrium models has previously shown that Bromacil adsorption on SA-UF (Norit) powdered activated carbon (PAC) is probably effective on two types of sites. High reactivity sites were found to be 10–20 less present in a carbon surface than lower reactivity sites, according to the q_m values calculated by isotherm models. The aims of this work were trying, primarily, to identify the kinetic-determinant stage of the sorption of Bromacil at a wide range of initial pesticide concentrations (5 to 500 μg L⁻¹ at pH 7.8), and secondly, to specify the rate constants and other useful design parameters for the application in water treatment. It was therefore not possible to specify a priori whether the diffusion or surface reaction is the key step. It shows that many of the tested models which describe the stage of distribution or the surface reaction are correctly applied. However, the diffusivity values (D and D₀) were found to be constant only constants for some specific experimental concentrations. The HSDM model of surface diffusion in pores was also applied but the values of the diffusion coefficient of surface (D_s) were widely scattered and reduce significantly with the initial concentration or the equilibrium concentration in Bromacil. The model of surface reaction of pseudo-second order fitted particularly well and led to constant values which are independent of the equilibrium concentration, except for the low concentrations where the constants become significantly more important. This last observation confirms perfectly the hypothesis based on two types of sites as concluded by the equilibrium data (part 1).     

Effect of the adsorbate (Bromacil) equilibrium concentration in water on its adsorption on powdered activated carbon. Part 1. Equilibrium parameters

This study was carried out to investigate the adsorption equilibrium and kinetics of a pesticide of the uracil group on powdered activated carbon (PAC). The experiments were conducted at a wide range of initial pesticide concentrations (5 μg L⁻¹ to 500 μg L⁻¹ at pH 7.8), corresponding to equilibrium concentrations of less than 0.1 μg L⁻¹ for the weakest, which is compatible with the tolerance limits of drinking water. Such a very broad range of initial solute concentrations resulting powdered activated carbon (PAC) concentrations (0.1–5 mg L⁻¹) is the main particularity of our study. The application of several monosolute equilibrium models (two, three or more parameters) has generally shown that Bromacil adsorption is probably effective on two types of sites. High reactivity sites (K_L  10³ L mg⁻¹) which are 10–20 less present in a carbon surface than lower reactivity sites (K_L  10 L mg⁻¹), according to the q_m values calculated by two- or three-parameter models. The maximum capacity of the studied powdered activated carbon (PAC), corresponding to monolayer adsorption, compared to the Bromacil molecule surface, would be between 170 mg g⁻¹ and 190 mg g⁻¹. This theoretical value is very close to the experimental q_m values obtained when using linearized forms of Langmuir, Tóth and Fritz–Schluender models.     

Thermodynamic and kinetic studies for the adsorption of Hg(II) by nano-TiO2 from aqueous solution

Titanium dioxide nanocrystals were employed, for the first time, for the sorption of Hg(II) ions from aqueous solutions. The effects of varying parameters such as pH, temperature, initial metal concentration, and contact time on the adsorption process were examined. Adsorption equilibrium was established in 420 min and the maximum adsorption of Hg(II) on the TiO₂ was observed to occur at pH 8.0. The adsorption data correlated with Freundlich, Langmuir, Dubinin–Radushkevich (D–R), and Temkin isotherms. The Freundlich isotherm showed the best fit to the equilibrium data. The Pseudo-first order and pseudo-second-order kinetic models were studied to analyze the kinetic data. A second-order kinetic model fit the data with the (k₂ = 2.8126 × 10^?3 g mg^?1min^?1, 303 K). The intraparticle diffusion models were applied to ascertain the rate-controlling step. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were calculated which showed an endothermic adsorption process. The equilibrium parameter (R_L) indicated that TiO₂ nanocrystals are useful for Hg(II) removal from aqueous solutions.     

Isotherm studies of lead(II), manganese(II), and cadmium(II) adsorption by Nigerian bentonite clay in single and multimetal solutions

This study was aimed at evaluating the isotherm of lead(II), manganese(II), and cadmium(II) adsorption in single and multimetal solutions using Nigerian bentonite. The natural and calcined clays were characterized for specific surface area, surface morphology, elemental composition, and cation exchange capacity (CEC). The adsorption data were analyzed and interpreted using isotherm models. The natural bentonite exhibits a specific surface area of 23.5?m²/g and a CEC value of 47.7 mEq/100?g and displays a higher adsorption capacity of all heavy metals in both single and multimetal solutions than the calcined bentonite. The removal of lead(II) by natural bentonite in single-component system is 0.0448?mmol/g. The order of selectivity is lead(II)?>?cadmium(II)?>?manganese(II). Result also shows that both clays demonstrate a preferable adsorption toward lead(II). Lead(II) adsorption is less affected by the presence of counter cations in multimetal solution. The adsorption of heavy metals onto Dijah-Monkin bentonite is site selective and site specific, and the adsorption data are well presented by the Langmuir model. The CEC could be the primary mechanism for the uptake of heavy metals, and the removal capacity was shown to depend on the ionic radius of metal ions.     

Decomposition of carbon dioxide to carbon by hydrogen-reduced Ni(II)-bearing ferrite

Hydrogen-activated Ni(II)-bearing ferrite, Ni _0.37 ²⁺ Fe _0.49 ²⁺ Fe _2.09 ³⁺ O_4.00, showed a high rate of decomposition of carbon dioxide to carbon at 300°C. This is based on the redox process of the Ni(II)-bearing ferrite with the spinel type of crystal structure. The rates of both activation by hydrogen gas and oxidation in carbon dioxide gas were much improved in the Ni (II)-bearing ferrite. The rate of decomposition was 0.178 mol h^–1 for the activated Ni(II)-bearing ferrite and 0.005 92 mol h^–1 for the activated magnetite in the batch mode, being 30 times larger. The rate of carbon dioxide decomposition was 16 times higher in the flow system in comparison with that of the activated magnetite.     

Error analysis of equilibrium studies for the almond shell activated carbon adsorption of Cr(VI) from aqueous solutions

In this study, the preparation of activated carbon from almond shell with H2SO4 activation and its ability to remove toxic hexavalent chromium from aqueous solutions are reported. The influences of several operating parameters such as pH, particle size and temperature on the adsorption capacity were investigated. Adsorption of Cr(VI) is found to be highly pH, particle size and temperature dependent. Four adsorption isotherm models namely, Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich were used to analyze the equilibrium data. The Langmuir isotherm provided the best correlation for Cr(VI) onto the almond shell activated carbon (ASC). Adsorption capacity was calculated from the Langmuir isotherm as 190.3 mg/g at 323 K. Thermodynamic parameters were evaluated and the adsorption was endothermic showing monolayer adsorption of Cr(VI). Five error functions were used to treat the equilibrium data using non-linear optimization techniques for evaluating the fit of the isotherm equations. The highest correlation for the isotherm equations in this system was obtained for the Freundlich isotherm. ASC is found to be inexpensive and effective adsorbent for removal of Cr(VI) from aqueous solutions.     

Kinetic studies of adsorption of Pb(II), Cr(III) and Cu(II) from aqueous solution by sawdust and modified peanut husk

Sawdust and modified peanut husk were used as adsorbents to remove Pb(II), Cr(III) and Cu(II) from aqueous solution. Results of kinetic experiments demonstrated that the adsorption was effective and rapid. Three different kinds of kinetic models (i.e., intraparticular diffusion model, Lagergren-first-order and second-order equations) were used to investigate the adsorption mechanisms. The adsorption of heavy metals on sawdust and modified peanut husk is not an intraparticular diffusion control. The kinetic adsorption data can be described by the second-order equation and the adsorption might be a rate-limiting control. The suitability of the adsorbent was tested by fitting the adsorption data with Langmuir and Freundlich isotherms, which gave good fits with both isotherms.     

On the energy transfer to small disturbances in fluid flow (Part I)

Acta Mechanica - The “energy in a small disturbance” in a viscous compressible heat-conductive medium is defined as a positive definite quantity characterizing the mean level of...     

Characteristics of equilibrium, kinetics studies for adsorption of Hg(II), Cu(II), and Ni(II) ions by thiourea-modified magnetic chitosan microspheres

Magnetic chitosan microspheres were prepared and chemically modified with thiourea (TMCS) for adsorption of metal ions. TMCS obtained were investigated by means of X-ray diffraction (XRD), IR, magnetic properties and thermogravimetric analysis (TGA). The adsorption properties of TMCS toward Hg(2+), Cu(2+), and Ni(2+) ions were evaluated. Various factors affecting the uptake behavior such as contact time, temperature, pH and initial concentration of the metal ions were investigated. The kinetics was evaluated utilizing the pseudo-first-order, pseudo-second-order, and the intra-particle diffusion models. The equilibrium data were analyzed using the Langmuir, Freundlich, and Tempkin isotherm models. The adsorption kinetics followed the mechanism of the pseudo-second-order equation for all systems studied, evidencing chemical sorption as the rate-limiting step of adsorption mechanism and not involving a mass transfer in solution. The best interpretation for the equilibrium data was given by Langmuir isotherm, and the maximum adsorption capacities were 625.2, 66.7, and 15.3mg/g for Hg(2+), Cu(2+), and Ni(2+) ions, respectively. TMCS displayed higher adsorption capacity for Hg(2+) in all pH ranges studied. The adsorption capacity of the metal ions decreased with increasing temperature. The metal ion-loaded TMCS with were regenerated with an efficiency of greater than 88% using 0.01-0.1M ethylendiamine tetraacetic acid (EDTA).     

Influence of cationic surfactant on adsorption of Cr(VI) onto activated carbon

The effect of a cationic surfactant on the adsorption of Cr(VI) on activated carbon was investigated using cetylpyridinium chloride (CPC). At a concentration below the critical micelle concentration (CMC) of CPC, the adsorption of CPC and Cr(VI) reached equilibrium within 60 min, while it took 180 min at the concentration above CMC. CPC decreased the adsorption rate of Cr(VI) and increased the adsorption amount of Cr(VI) onto activated carbon. To analyze adsorption phenomena of Cr(VI), adsorption kinetic and isotherm were used and fitted well with the pseudo-second order kinetic model and Langmuir adsorption model, respectively. CPC introduced a cationic functional group on the surface of activated carbon and provided an adsorption site for Cr(VI).