Langmuir Methods Research Articles

Study of the adsorption mechanism of certain dyes from wastewater on commercial activated carbon using the Langmuir and Freundlich methods

In today's society, there is significant emphasis on environmental protection, with research focused on reducing pollution and developing effective depollution techniques. A growing concern is the presence of colored discharges in wastewater, which contain high levels of toxic substances that pose substantial risks to ecosystems. To mitigate these risks, various methods are employed to remove pollutants from industrial effluents, with adsorption being one of the most effective. Among the adsorbents used, activated carbon is the most commonly utilized due to its high surface area and adsorption capacity. This study aims to enhance the understanding of how two organic dyes, Methyl Red and Methylene Blue, can be removed from aqueous media through adsorption onto commercial activated carbon. The adsorption kinetics and isotherms were employed to elucidate the mechanisms involved in the elimination of these dyes from water. The kinetics were investigated using a stirred reactor, with experiments designed to vary parameters such as the initial dye concentration, the mass of the adsorbent, and the contact time. The experimental data were modeled using kinetic equations of first and second order. The results indicated that the adsorption of both Methyl Red and Methylene Blue onto activated carbon followed a pseudo-second-order kinetic model, as evidenced by large regression coefficients, signifying a good fit. This suggests that the adsorption process is likely controlled by chemisorption, involving valency forces through sharing or exchange of electrons between adsorbent and adsorbate. Additionally, the adsorption isotherms were analyzed to further understand the adsorption mechanisms and capacity. The results showed that the adsorption of both dyes onto commercial activated carbon conformed well to the Freundlich isotherm model. This model implies that adsorption occurs on a heterogeneous surface with a non-uniform distribution of adsorption heat over the surface. Overall, this study provides valuable insights into the adsorption behavior of Methyl Red and Methylene Blue on activated carbon, highlighting the effectiveness of this adsorbent in removing organic dyes from wastewater. The findings underscore the potential of using commercial activated carbon in the treatment of industrial effluents, contributing to the development of more efficient and sustainable water purification methods.

The Adsorption Studies for the Removal of Lead (Pb2+) from Paint Industrial Wastewater using Avocado Seed Activated Carbon (ASAC)

The rapid increase in industrial activities in Nigeria has led to the high contamination of water bodies with heavy metals such as Lead, Cadmium, Zinc etc from wastewater disposal. Previous techniques adopted for this wastewater treatment such as ion exchange, biosorption, solvent extraction and precipitation etc are highly expensive and capital intensive; hence, the need for cheaper technologies that utilizes locally available biomass as a precursor for the preparation of activated carbon. This study aims to utilize avocado seed for the production of activated carbon to treat paint industrial wastewater containing heavy metals such as Lead (Pb2+) and to evaluate the adsorption isotherm and kinetic models that best fit the equilibrium data obtained from the batch adsorption experiment. The avocado seed activated carbon (ASAC) was prepared by carbonizing the sample at a temperature of 700 °C and activating it with a 30 % v/v Concentration of H3PO4 acid at a temperature of 500 °C for 6 hours in a muffle furnace. The batch adsorption studies were done by investigating the varying effect of metal ion concentration (0.5-3.0 mg/L), contact time (15-180 mins) and adsorbent dosage (0.5-3.0 g). The data obtained were analysed using six adsorption isotherms such as Langmuir, Freundlich, Temkin, Toth, Sips and Redlich-Peterson methods. Freundlich isotherm model with an R2 value of 0.94 and adsorption capacity of 0.1965 mg/g showed the highest percentage removal of Lead (Pb2+) to be > 97 %. The kinetic studies revealed that the experimental data fitted well to the pseudo-first-order model with a high correlation coefficient of 0.980 when compared to other models like pseudo-second-order, intra-particle diffusion and Boyd model, thus; signifying that the adsorption’s mechanism was physiosorption. Thus, optimum activation conditions would produce higher activated carbon from avocado seeds that could be used for the removal of heavy metal ions from industrial wastewater, which will aid in eliminating the challenge of agricultural waste accumulation in the environment.

The Effect of Selected Flavonoids and Lipoic Acid on Natural and Model Cell Membranes: Langmuir and Microelectrophoretic Methods.

The influence of kaempferol (K), myricetin (M) and lipoic acid (LA) on the properties of natural erythrocytes, isolated from animal blood and biological membrane models (monolayers and liposomes) made of phosphatidylcholine (PC), cholesterol (CHOL), and sphingomyelin (SM), CHOL in a ratio of 10:9, was investigated. The Langmuir method, Brewster angle microscopy (BAM) and microelectrophoresis were used. The presented results showed that modification of liposomes with kaempferol, myricetin and lipoic acid caused changes in the surface charge density and the isoelectric point value. Comparing the tested systems, several conclusions were made. (1) The isoelectric point for the DPPC:Chol:M (~2.2) had lower pH values compared to lipoic acid (pH~2.5) and kaempferol (pH~2.6). (2) The isoelectric point for the SM-Chol with myricetin (~3.0) had lower pH values compared to kaempferol (pH~3.4) and lipoic acid (pH~4.7). (3) The surface charge density values for the DPPC:Chol:M system in the range of pH 2-9 showed values from 0.2 to -2.5 × 10-2 C m-2. Meanwhile, for the DPPC:Chol:K and DPPC:Chol:LA systems, these values were higher at pH~2 (0.7 × 10-2 C m-2 and 0.8 × 10-2 C m-2) and lower at pH~9 (-2.1 × 10-2 C m-2 and -1.8 × 10-2 C m-2), respectively. (4) The surface charge density values for the SM:Chol:M system in the range of pH 2-9 showed values from 0.5 to -2.3 × 10-2 C m-2. Meanwhile, for the DPPC:Chol:K and DPPC:Chol:LA systems, these values were higher at pH~2 (0.8 × 10-2 C m-2), and lower at pH~9 (-1.0 × 10-2 C m-2 and -1.8 × 10-2 C m-2), respectively. (5) The surface charge density values for the erythrocytes with myricetin in the range of pH 2-9 showed values from 1.0 to -1.8 × 10-2 C m-2. Meanwhile, for the erythrocytes:K and erythrocytes:LA systems, these values, at pH~2, were 1.3 × 10-2 C m-2 and 0.8 × 10-2 C m-2 and, at pH~9, -1.7 × 10-2 C m-2 and -1.0 × 10-2 C m-2, respectively.

Textural, mineralogical and physico-chemical characterization of red clay of Tanout (Zinder-Niger) with a view to its valorization in water treatment

This study aims to determine the textural (specific surface, pore volume and pore size) and mineralogical characteristics of Tanout red clay of Zinder region (Niger) in order to have textural data allowing its use as an adsorbent. The methodology is based on textural analyzes (adsorption of N2 at 77 K by the Brunauer-Emmett-Teller method), mineralogical (X-ray fluorescence, X-ray diffraction, thermo-gravimetric analysis, scanning electron microscopy) and physicochemical (preliminary analyses). The results obtained show that the red clay has a specific surface of 418.4 m2.g-1 and 967.7 m2.g-1 calculated according to the BET and Langmuir methods respectively and a microporous surface of 540 m2.g- 1, with pore volume varying from 0.0389 to 0.2535 cm3.g-1 and pore size varying from 0.3675 to 5.423 nm calculated according to the methods (Barrett-Joyner-Halenda, Dubinin-Radushkevich, Dubinin -A, Horvath-Kawazoe and Saito-Foley). It has slit and cylindrical micro- pores. It has a slightly neutral pH in an aqueous medium and a high cation exchange capacity with low humidity and density, and is mainly composed of SiO2 (83.2%), Al2O3 (7.04%) and Fe2O3 (3.35%) with trace elements, the main ones being: Zr (2490 ppm), Sr (310.21 ppm), Cu (310.1 ppm), V (290.1 ppm) and Zn (140ppm). It consists essentially of Montmorillonite, illite and Kaolinite with impurities such as quartz and rutile. This clay has a high degree of crystallinity. These characteristics make it a promoter material that can be used as an adsorbent.

Electrochemical Performance and Hydrogen Storage of Ni–Pd–P–B Glassy Alloy

The search for hydrogen storage materials is a challenging task. In this work, we tried to test metallic glass-based pseudocapacitive material for electrochemical hydrogen storage potential. An alloy ingot with an atomic composition of Ni60Pd20P16B4 was prepared via arc melting of extremely pure elements in an Ar environment. A ribbon sample with a width of 2 mm and a thickness of 20 mm was produced via melt spinning of the prepared ingot. Electrochemical dealloying of the ribbon sample was conducted in 1 M H2SO4 to prepare a nanoporous glassy alloy. The Brunauer-Emmett-Teller (BET) and Langmuir methods were implemented to obtain the total surface area of the nanoporous glassy alloy ribbon. The obtained values were 6.486 m2/g and 15.082 m2/g, respectively. The Dubinin-Astakhov (DA) method was used to calculate pore radius and pore volume; those values were 1.07 nm and 0.09 cm3/g, respectively. Cyclic voltammetry of the dealloyed samples revealed the pseudocapacitive nature of this alloy. Impedance of the dealloying sample was measured at different frequencies through use of electrochemical impedance spectroscopy (EIS). A Cole-Cole plot established a semicircle with a radius of ~6 Ω at higher frequency, indicating low interfacial charge-transfer resistance, and an almost vertical Warburg slope at lower frequency, indicating fast diffusion of ions to the electrode surface. Charge-discharge experiments were performed at different constant currents (75, 100, 125, 150, and 200 mA/g) under a cutoff potential of 2.25 V vs. Ag/AgCl electrode in a 1 M KOH solution. The calculated maximum storage capacity was 950 mAh/g. High-rate dischargeability (HRD) and capacity retention (Sn) for the dealloyed glassy alloy ribbon sample were evaluated. The calculated capacity retention rate at the 40th cycle was 97%, which reveals high stability.

Physico-chemical, mineralogical and structural characterization of a clay of Tanout (Zinder-Niger)

The objective of this study is to identify the different mineral phases, the structural and textural properties of natural clay of Tanout in Zinder region (Niger) in order to have mineralogical data allowing its valuation. The methodology is based on a physicochemical characterization by coupling several analysis techniques (preliminary analyses, X-ray fluorescence, X-ray diffraction, thermos- gravimetric analysis, scanning electron microscopy, Brunauer-Emmett-Teller by adsorption of N2 at 77 K). The results from these analyzes show that this clay has a low humidity rate, a low density, a slightly neutral pH in an aqueous medium and a high cation exchange capacity and is mainly composed of SiO2 (68.1%), Al2O3 (17.02%) and Fe2O3 (7.6%) with trace elements, the most important of which are: Zr (4150.6 ppm), Sr (470 ppm), Cu (380.2 ppm) and V (320ppm). It essentially consists of Kaolinite and Montmorillonite with impurities such as quartz and microclines. It has a specific surface of 441.1 m2.g-1 and 2288 m2.g-1 calculated according to the BET and Langmuir methods respectively, with porous volume varying from 0.0157 to 0.2597 cm3.g-1 and of pore size which varies from 1.847 to 6.182 nm calculated according to the methods (Barrett-Joyner-Halenda, Dubinin-Radushkevich, Dubinin-A, Horvath-Kawazoe and Saito-Foley). This clay has an important degree of crystallinity. These characteristics make it a potential material that can be used in water pollution control.

Adsorption of Chromium Using Apu Wood (Pistia stratiotes L) Root Bioadsorbent and Modification of Apu Wood Root

The adsorbent is a material used for the adsorption process. One alternative used in the selection of adsorbents is biological materials. One type of plant that can be used to adsorb heavy metals is Apu Wood. This study aims to examine the effect of Cr (VI) concentration on the adsorption capacity of adsorbent, examine the time adjustment to the adsorption capacity of adsorbent, examine the characterization of adsorbent using SEM and FTIR, assess the adsorption equilibrium using the Langmuir and Freundlich methods and the kinetics of the adsorption reaction using pseudo order 1 and pseudo order 2. In this study, variables are the concentration of initial solution Cr(VI) of 2, 4, 6, 8, and 10 ppm and contact time of 15, 30, 45, 60, and 75 minutes. The result of this research is the capacity of adsorption increases in line with the increase in the initial concentration of Cr(VI) solution as adsorbate. Contact time affects the capacity of adsorption where the longer the contact time, the adsorption capacity increases until it reaches equilibrium at 70 minutes. In SEM and FTIR analysis both tests showed that aluminum adsorbtion using apu wood adsorbent and its modification changed the composition of the function group and the structure of the adsorbent surface area. The Langmuir Isoterm model produces a greater value R2 than the Freundlich isotherm model which indicates that the adsorbent surface is in direct contact with adsorbate and adsorbate attaches to the active site of the adsorbent of only one layer (monolayer). Kinetics adsorption pseudo order 1 produces a value of R2 greater than kinetics adsorps pseudo order 2 which indicates the mechanism that occurs is the transfer of mass in addition to the use of electrons together between heavy metals Cr (VI) with apu wood root.

Removal of organic pollutant from wastewater using Nano Carbon synthesized from wood waste biomaterial as an adsorbent

With the help of eco-friendly waste materials like Manila tamarind tree bark and shells (Pithecellobium Dulce), the malachite green dye has been removed from wastewater in this investigation. The maximum adsorption of dye was achieved at pH 6.7 in the research work. The removal percentage of Malachite green dye was found to be dependent on the initial concentration of dye solution, and the maximum removal percentage was found to be 85% at 25 mg/L of Malachite green dye. The experimental methods were carried out using the batch adsorption technique. The pH parameter, temperature, adsorption dose, and contact time for the removal of Malachite green dye were studied. The Freundlich, Langmuir, and Temkin methods were used to calculate equilibrium adsorption data. The thermodynamic parameters such as a change in free energy (G0 ), enthalpy (H0 ), and entropy (S0 ) were determined. The negative values of G0 indicated that the process of dye removal was spontaneous at all values of temperature. Further, the values of H0 indicated the endothermic nature of the process of dye removal from the wastewater.

Modification of mesoporous structure of silver-doped bioactive glass with antibacterial properties for bone tissue applications

Silver-containing mesoporous bioglasses powders with SiO2–CaO–P2O5–Ag2O composition have been successfully synthesized by sol-gel and evaporation-induced self-assembly (EISA) methods in presence of various amounts of surfactant (Pluronic-F127). The morphology and crystal structure of the powders were characterized by scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD). Also, the textural properties of samples have been evaluated by adsorption-desorption, Langmuir and BET methods. Accordingly, powders had a smooth surface morphology with cubic mesoporous structure and a desired surface area and pore volume. The in vitro bioactivity was assessed by SEM, XRD and Fourier transform infrared spectroscopy (FTIR) analyses. All samples enhance the formation of HA after soaking the material in simulated body fluid (SBF) solution. The antibacterial property of samples was evaluated to investigate the effect of silver content in chemical composition. The results showed an adequate antibacterial activity of the samples against Escherichia coli, Salmonella and Listeria monocytogenes.

Conifer Cone (Pinus resinosa) as a Green Corrosion Inhibitor for Steel Rebar in Chloride-Contaminated Synthetic Concrete Pore Solutions.

The present study has been focused on the environment-friendly corrosion inhibitor. Conifer cone (Pinus resinosa) has been used as a novel corrosion inhibitor to mitigate the corrosion of steel rebars in simulated concrete pore solutions (SCPS) in the presence and absence of chloride ions. The corrosion inhibitor is extracted by simple chemical methods. The functional groups present in the extracted conifer cone (ECC) powder are characterized as well as the surface morphology of ECC has been examined. The corrosion inhibition performance has been evaluated by the electrochemical and weight loss methods. The experimental results indicate that ECC possesses a corrosion inhibition efficiency of 81.2% at a dosage of 1000 mg·L-1, after 720 h of immersion in chloride-contaminated SCPS. Adsorption isotherm and their standard Gibbs free energy (ΔGads0) values are calculated by Langmuir, Freundlich, and Temkin isotherm methods, and the results indicate that the ECC is initially adsorbed on the steel rebar surface by physisorption and then it turns to chemisorption. The steel rebar surfaces have been characterized after exposure to the ECC containing SCPS, and the results indicate that the ECC containing cationic adsorbate molecules, which interact with steel rebar, leads to retardation of metal dissolution in corrosive chloride medium.

Synthesis and Characterization of Aero-Eutectic Graphite Obtained by Solidification and Its Application in Energy Storage: Cathodes for Lithium Oxygen Batteries

Aero-eutectic graphite can be defined as a new light material with hierarchically structured porosity. It is obtained from the solidification of gray cast irons, followed by the dissolution of the ferrous matrix by an acidic sequence. The result is a continuous and interconnected network of graphite sheets with varied dimensions randomly oriented. X-ray diffraction characterization has revealed graphite crystallographic planes (002), (100), (101), (102) and (004), while the surface area measured by BET and Langmuir methods has been determined in the order of 90 m2 g−1 and 336 m2 g−1, respectively. The process of obtaining eutectic aero-graphite also allows the deposit of Cu nanofilms and TiC particles. Aero-eutectic graphite has been tested as cathode in Li–O2 batteries as it has been prepared, without the addition of binders or conductive carbons, showing an appropriate contact with the electrolyte, so that the oxygen reduction and evolution reactions may develop satisfactorily. In the discharge-charge galvanostatic tests, the battery accomplishes 20 complete cycles with area capacity limited to 1.2 mAh cm−2.

The Equilibria in Lipid-Lipoic Acid Systems: Monolayers, Microelectrophoretic and Interfacial Tension Studies.

In this examination, we investigated the effect of lipoic acid (LA) on the properties of biological membrane models (monolayers, bilayers, and liposomes) formed from phosphatidylcholine (PC) or phosphatidylserine (PS) using the Langmuir, microelectrophoresis, and interfacial tension methods. The Langmuir technique allowed us to calculate the π–A isotherms and determine the molecular surface areas of pure and mixed monolayers. Using mathematical equations, we established that LA and the lipids formed complexes at a 1:1 ratio. The interfacial tension method was based on Young and Laplace’s equation. We assumed the formation of a 1:1 complex in the PC–LA system. Using the mathematical relationships, we derived the parameters characterizing the resulting complex, i.e., the surface occupied by the complex and the interfacial tension and stability constant of the formed complex. The microelectrophoretic method was used to determine the dependence of the zeta potential of the lipid membranes as a function of the pH (pH 2 to 10) of the electrolyte solution. The results indicate that modification of PC or PS membranes with LA affects changes in the zeta potential and the isoelectric point values.

Comparison of Activated Carbons Produced from Zonguldak Kozlu and Zonguldak Karadon Hard Coals for Hydrogen Sorption

ABSTRACT A series of activated carbons prepared using hard coals from two different mines, Kozlu and Karadon in Zonguldak, with heat treatment and chemical activation (KOH, NaOH, ZnCl,2 and H3PO4) were evaluated for their hydrogen sorption performances at −196°C. The analysis of the porous structure of the resulting activated carbons was accomplished through the use of the BET, Langmuir, DFT, and t-plot methods utilizing the nitrogen adsorption-desorption data (−196°C). The analysis results have shown that the carbons, according to the type of the applied chemical activation could be ranked in the order H3PO4 < ZnCl2 < NaOH < KOH in terms of their yielded surface area and total pore volume. Heat treatment only without any chemical treatment yielded the smallest pore volume and surface area, on the other hand, highly microporous structure containing microporores in between 74.84% and 97.78% occured by chemical activation. The effects of pore volume and surface area on hydrogen sorption were examined. The highest hydrogen sorption capacity attained was 5.43 wt% and 5.21 wt% for the samples obtained from Zonguldak Karadon hard coal with KOH treatment at 700°C, and with ZnCl2 activation at 400°C, respectively.

Application of low-cost material for adsorption of dye from aqueous solution

ABSTRACT Cationic dyes are one of the aromatic compounds that cause major environmental problems. The adsorption process has attracted a lot of attention in recent years. In this study, the seeds were used as a low-cost adsorbent for the removal of cationic Blue 41 dye from aquatic environments. The studied parameters included the effect of adsorbent dosage, pH of the solution, contact time, and the initial concentration of Cationic Blue 41 dye. The removal efficiency in optimal conditions for Cationic Blue 41 with Salvia seeds (concentration = 50 mg/L, dose = 2 g/L, reaction time = 120 min and pH = 9) was obtained 70%. The data were evaluated using Freundlich and Langmuir methods. The structure and characteristics of the seeds were determined by Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FT-IR) and Brunauer-Emmett-Teller (BET) techniques. The SBET and total pure volume for the Salvia seeds were 3.053 m2/g and 0.684 cm3/g. The results showed that the adsorption process follows Langmuir model with an adsorption capacity of 19.16 mg/g. According to the result of the pseudo-first and pseudo-second kinetic study, it was found that the process of dye adsorption on the low-cost seeds best described by pseudo-second kinetic. The findings showed that the Salvia seeds can be used as a natural absorbent, environmentally friendly and affordable treatment for water and wastewater, especially those containing cationic dyes.

Adsorption of hydrogen sulfide, carbon dioxide, methane, and their mixtures on activated carbon

H2S and CO2 are acid contaminants of natural gas and biogas, which removal have been studied using adsorption data for monocomponent and binary mixtures. However, equilibrium adsorption data for H2S + CO2 + CH4 mixture has not been investigated yet. In this work, H2S and CO2 partition coefficients (K) and activated carbon (AC) selectivity (S) for H2S + CO2 + CH4 mixture separation at high-pressure and different temperatures were determined. To reach this goal, monocomponent isotherms for H2S, CO2 and CH4 on Brazilian babassu coconut hush AC were experimentally determined at different temperatures and pressures. Then, obtained data were correlated by Langmuir and Tóth models, and multicomponent adsorption was predicted using Extended Langmuir, Extended Tóth and Ideal Adsorption Solution Theory (IAST) methods. Results indicate AC captures approximately 26 wt% of H2S or CO2. K values for CO2 and H2S reached more than 3 and 26, respectively, depending on the predictive model utilized and were higher for diluted mixtures (high CH4 content in gas phase). S values for CO2 and H2S can reach values greater than 25 for Tóth + IAST. Furthermore, selectivity toward H2S is approximately 5.6 times greater than CO2. The effect of temperature on multicomponent results indicate K and S values decrease as temperature increases. Therefore, results obtained herein show that is possible to separate H2S and CO2 from mixture containing CH4 using this AC as adsorbent and better separation performance was observed for low H2S and CO2 concentrations and lower temperatures.

Aqueous-phase aerosols on the air-water interface: Response of fatty acid Langmuir monolayers to atmospheric inorganic ions.

Atmospheric aerosol particles composed of a mixture of organic and inorganic compounds are common and constitute an important fraction of air pollutants. In this study, the activities of common atmospheric inorganic ions (Ag+, Zn2+, Fe3+, Fe2+, Ca2+ and Al3+) and fatty acid molecules (stearic acid and arachidic acid) at air-aqueous interface were investigated by Langmuir methods and infrared reflection-absorption spectroscopy (IRRAS). In the presence of different inorganic ions, surface pressure-area isotherms of the Langmuir films showed compressed or expanded characteristics. IRRAS spectra confirmed that the existence of inorganic ions in the fatty acid monolayer changes the surface properties of aqueous-phase aerosols. Formation of different coordination types of carboxylates at the air-water interface alters the dissolution and partitioning behavior, which has significant influence of Raoult effect on nucleating cloud droplets. Our work displays the relationship between structure and surface properties for aqueous-phase aerosols and implies an efficient method for further understanding of their formation mechanism and potential atmospheric implications.

Recyclable Mesoporous Ceria Supported Gold Nanoparticles Based Catalyst for O-Arylation of Phenols.

Ceria supported gold nanoparticles (Au-CeO2 NPs) were prepared by a simple deposition-precipitation method. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and Raman analysis indicated the formation of gold nanoparticles over phase pure cerianite ceria support. The presence of gold nanoparticles was well identified by UV-DRS study. In addition, the field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HR-TEM) images revealed that the maximum number of particles having spherical shape were approximately 10 nm size. Subsequently, surface area of the catalyst determined from BET, Langmuir and DFT methods were found to be 83.1, 134 and 85.2 m2 g(-1) respectively. N2 absorption-desorption measurement revealed that Au-CeO2 NPs was mesoporous in nature. Au-CeO2 NPs proved to be an efficient catalyst for the O-arylation reactions. The reaction conditions were optimized using 2,6-dimethoxyphenol and 1-chloro-4-nitrobenzene as a model substrate by changing the solvent, base, quantity of catalyst, and temperature. The scope of the work was extended to various substituted phenols and aryl halides (F, Cl and Br) and reusability of catalyst was tested for four cycles which showed no loss in its activity.

Model-based approaches to investigate the interactions between unmodified gold nanoparticles and DNA strands

Model-based techniques were used to resolve fluorescence datasets related to the interactions of two complementary oligonucleotides (which were tagged by fluorescein and Texas red respectively) in the presence of 13nm gold nanoparticles (AuNPs). This system was selected as an example to demonstrate the advantages of model-based techniques in studying interactions of nanoparticles and biomolecules, and providing better insight to such nano-bio systems which is in turn helpful for designing more efficient sensor/delivery systems. The adsorption isotherms were analyzed by model-based Scatchard and Langmuir methods and the results were the adsorption constants of the oligonucleotides on AuNPs and the number of binding sites on AuNPs. This is the first reported application of Scatchard method where DNA is the adsorbate. The main part of the study is focused on the application of more sophisticated model-based techniques to analyze complex three-way excitation–emission fluorescence data sets recorded through the adsorption/hybridization process. A novel model-based restricted Tucker3 method is also proposed to estimate the hybridization constant. An advantage of this technique is the estimation of the concentration profiles of all involving chemical components, even those without a fluorescence signal.

The characterisation of slow-heated inertinite- and vitrinite-rich coals from the South African coalfields

Abstract The development of coal char structures with pyrolysis has been extensively investigated but has traditionally been focused on the carboniferous coals in the northern Hemisphere. In this investigation, the properties of pyrolysis chars generated from inertinite- and vitrinite-rich coals (81% and 91% mmb by volume, respectively) collected from selected South African coalfields were determined. Chars were generated at 450, 700 and 1000 °C. The properties of coals and chars were examined using the chemical, physical, petrographic, solid-state 13 C NMR and X-ray diffraction analytical techniques. The objective was to generate results for further studies including molecular modelling and atomistic reaction kinetics. A good correlation was found between the total maceral scan (rank) and aromaticity as the pyrolysis temperature increased, as well as between the aromaticity measurements with XRD and NMR techniques. The chemical structure of the intertinite-rich and vitrinite-rich chars at 700–1000 °C was remarkably similar in terms of the proximate, ultimate, total maceral scan and aromaticity values. Greater transition occurred in the vitrinite-rich coal, implying a thermally more activated coal. Differences in the physical structure of the chars at these temperatures were observed in terms of the surface area using the Dubinin–Radushkevich (D–R), the Brunauer–Emmet–Teller (BET) and Langmuir methods as well the microporosity from the CO 2 adsorption method. The macerals were not distinguishable at 700–1000 °C. However, the differences in maceral composition of the coals resulted in substantially different char forms during thermal conversion. The intertinite-rich coal formed more denser chars and higher proportions of thicker-walled networks (60–65% by volume). The vitrinite- rich coal showed higher proportions of isotropic “coke” (91–95% by volume), which contributes to a high distribution of surface area and micropores. Therefore, on a chemical level, the high temperature chars were similar. Differences existed in the physical structure at high temperatures. The physical structures, char forms and crystallite diameter ( L a ) significantly distinguished the chars at high temperatures, where L a for inertinite-rich chars was 37.6 A compared with 30.7 A for the vitrinite-rich chars. The L a property, in particular, played a significant role in investigations for the molecular structural properties of the inertinite- and vitrinite-rich chars, including their reactivity behaviour with carbon dioxide gas.

Influence of pH and antibiotic solubility on the removal of ciprofloxacin from aqueous media using montmorillonite

The ciprofloxacin (CPX) is a fluoroquinolone antibiotic that has been found in soils and aqueous media due to its vast use in both, human and veterinary health care. As a consequence the removal of this kind of compounds is widely studied. However, there are a few studies about the CPX removal from aqueous media by adsorption.This work is focused on the study of CPX removal by adsorption using an Argentinian montmorillonite (Mt). The influence of the pH media and the consequent antibiotic solubility in the adsorption process was analyzed. The experimental curve of CPX solubility versus pH media showed a strong correlation between them where the lowest value of solubility was obtained for the zwitterion species (CPX±). This result points out the fact that the solubility of the CPX species must be considered in adsorption experiments because of the antibiotic precipitation and the consequent overestimation of the adsorbent adsorption capacities. CPX adsorption kinetics and adsorption isotherms at different pH values showed that the adsorption processes obey pseudo-second order kinetics. The CPX adsorption capacity of the Mt, the affinity of the species towards its surface and the possible mechanisms involved in the adsorption process were assessed by Langmuir, Freundlich and Scatchard methods. The results showed that the adsorption mechanism of CPX on Mt is pH dependent, obtaining a negative cooperative mechanism at pH3, 6 and 7.5 and a positive cooperative mechanism at pH10. The highest CPX adsorption capacity on Mt was obtained at pH6. Infrared spectroscopy and X-ray diffractograms of the complexes obtained after the adsorption process provided information about the interaction between the functional groups of CPX and the adsorption sites on Mt and the changes in the basal space related with the molecular arrangements of the CPX on the sample, respectively. The CPX removal by this clay mineral is remarkably higher when it is compared with other materials and quite similar to previous data obtained with other bentonites.