Removal of cationic dyes by poly(acrylamide-co-acrylic acid) hydrogels in aqueous solutions

Poly(acrylamide-co-acrylic acid (poly(AAm-co-AAc)) hydrogels prepared by irradiating with γ-radiation were used in experiments on swelling, diffusion, and uptake of some cationic dyes such as Safranine-O (SO) and Magenta (M). Poly(AAm-co-AAc) hydrogels irradiated at 8.0 kGy have been used for swelling and diffusion studies in water and cationic dye solutions. The maximum swellings in water, and SO, and M solutions observed are 2700%, 3500%, and 4000%, respectively. Diffusions of water and cationic dyes within hydrogels have been found to be non-Fickian in character. Adsorption of the cationic dyes onto poly(AAm-co-AAc) hydrogels is studied by the batch adsorption technique. The adsorption type was found Langmuir type in the Giles classification system. The moles of adsorbed dye for SO and M per repeating unit in hydrogel (binding ratio, r) have been calculated as 3834×10⁻⁶ and 1323×10⁻⁶, respectively. These results show that poly(AAm-co-AAc) hydrogels can be used as adsorbent for water pollutants such as cationic dyes.     

Adsorption of methyl violet in aqueous solutions by poly(N-vinylpyrrolidone-co-methacrylic acid) hydrogels

N-vinylpyrrolidone(VP)/methacrylic acid (MAA) monomer mixtures containing different quantities of methacrylic acid were irradiated with gamma-radiation to form hydrogels. Mixtures which contain 5, 10, 15% and irradiated with 3.4 kGy were used for swelling and diffusion studies in water and solutions of methyl violet and for the adsorption of methyl violet from aqueous solutions. Diffusion of water and methyl violet within hydrogels were found to be of non-Fickian character. In the dye adsorption experiments, the effects of pH, concentration of aqueous solution of dye and the composition of hydrogels on the adsorption process were investigated. When the pH and concentration of aqueous solutions of dye and the MAA content in hydrogels increased, the adsorption increased.     

Ultrafiltration of mixed protein solutions of lysozyme and lactoferrin: role of modified inorganic membranes and ionic strength on the selectivity

Ultrafiltration of either single protein solutions (lysozyme 14,300 g mol⁻¹, pI=11; lactoferrin 80,000 g mol⁻¹, pI=8–9) or mixed protein solution was performed with inorganic membranes (MMCO 300,000 g mol⁻¹, pore radius 14 nm) chemically modified in order to bear either pyrophosphate (PP, anionic) or ethylenediamine (EDA, cationic) groups.The electrophoretic mobility of modified and unmodified zirconia particles fouled with proteins was similar whatever the grafted groups, meaning that the membrane surface was always made of adsorbed proteins during UF. In spite of that, for the UF of lysozyme/lactoferrin mixed solution, the maximum selectivity (S=lysozyme transmission/lactoferrin transmission=165) was observed with the EDA membrane and allowed an instantaneous purity of lysozyme in the permeate close to 100% to be achieved. Such high selectivitiy was mainly due to the negligible transmission of lactoferrin with the membrane modified with the EDA groups in the ionic strength range 0–100 mmol l⁻¹ of NaCl at pH 7 (achieved either for mixed and single solutions).     

Layer-by-layer assembled DNA functionalized single-walled carbon nanotube hybrids for arsenic(III) detection

Based on layer-by-layer assembled DNA functionalized single-walled carbon nanotube hybrids, a DNA biosensor for the detection of arsenic(III) in a nearly physiological pH environment was developed. The redox process between arsenic(III) and arsenic(0) on the biosensor was proved. The growth of those hybrids on glassy carbon electrode was monitored by detecting arsenic(III). The arsenic(III) current on the biosensor was similar over a broad pH range (3.0–8.0) and the limit of detection (S/N = 3) was 0.05 μg L⁻¹ at pH 7.0. The biosensor can be reused up to 16 times.     

Preparation and characterization of a novel IPN hydrogel memberane of poly(N-isopropylacrylamide)/carboxymethyl chitosan (PNIPAAM/CMCS)

A novel type of interpenetrating polymer networks (IPN) hydrogel membrane of poly(N-isopropylacrylamide)/carboxymethyl chitosan (PNIPAAm)/(CMCS) was prepared, and the effects of the feed ratio of components, swelling medium and irradiation dose on the swelling and deswelling properties of the hydrogel was systematically studied. The results showed that the introduction of CMCS did not shift the LCST (at 32 °C), which is similar to the pure PNIPAAm. The lowest swelling ratio was at pH 2. There was little influence of irradiation dose on the thermo- and pH-sensitivity of the IPN hydrogel, increasing dose only decreased the swelling ratio. The PNIPAAm:CMCS=1:4 w/w hydrogel was not thermo-sensitive in distilled water, whereas it showed a discontinuous volume phase transition in pH 2 and a continuous one in pH 8 buffer. Consequently, a combination of pH and temperature can be coupled to control the responsive behavior of these hydrogels.     

Recovery and pre-concentration of gold onto poly((N-(Hydroxymethyl)methacrylamide)–1-allyl-2-thiourea) hydrogels synthesized by gamma radiation

Poly((N-(Hydroxymethyl)methacrylamide)–1-allyl-2-thiourea) hydrogels, Poly(NHMMA–ATU), were synthesized by gamma radiation using ⁶⁰Co γ source at different irradiation doses and different ATU content in the irradiated monomer mixture. The swellability of the synthesized hydrogels was changed by irradiation doses and by the content of ATU in the irradiated mixture. These hydrogels were used for the specific gold recovery and pre-concentration from single gold ion solutions and from different natural samples. It has been observed that gold adsorption capacity onto the hydrogels was high at low pHs and reached maximum value at pH = 0.5. Adsorption capacity of the hydrogels for gold at pH = 0.5 was found to be about 698 mg g^− 1 dry hydrogels. Adsorption equilibrium time of gold ions onto the hydrogels was found to be very short and also these hydrogels were showed extremely high selectivity to the gold ions in acidic media when the concentration of the other metal ions were extremely higher than gold. Because of the high specificity of these hydrogels to gold beside the other metal ions at low pHs, all matrix effects were easily eliminated adsorbing gold onto the hydrogels and desorbing into 3 M HCl solution containing 0.8 M thiourea. These hydrogels were found to be highly open pore size. This property of the hydrogels make them attractive due to high adsorption capacity of gold ions on/in the hydrogels penetrating inside and react to all functional groups in the interior surface of the hydrogels.     

Direct electrochemistry of single-stranded DNA on an ionic liquid modified carbon paste electrode

Electrochemical oxidation of thermally denatured single-stranded DNA (ssDNA) was studied on a room temperature ionic liquid N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (IL-CPE). A distinct oxidation peak appeared at +0.772 V (vs. SCE) on the IL-CPE after preconcentration of ssDNA at +0.35 V for 160 s in pH 7.0 phosphate buffer solution (PBS), which was attributed to the oxidation of guanine residue on the ssDNA molecular structure. The results showed an apparent negative shift of the oxidation peak potential and a great enhancement of the oxidation peak current on the IL-CPE compared with that of CPE. The electrochemical parameters of ssDNA on the IL-CPE were further calculated. Under the selected conditions, a linear calibration curve for ssDNA detection was obtained in the concentration range from 10.0 to 110.0 μg mL⁻¹ with the detection limit of 1.5 μg mL⁻¹(3σ).     

Effective scrap iron particles (SIP) pre-treatment for complete mineralization of benzidine based azo dye effluent

This study proposed that hybrid scrap cast iron particles (SIP)-aerobic biodegradation technology could enhance the biodegradability of toxic wastewater. SIP cleaved the azo linkages of Direct Green1 dye to form benzidine, 4-aminophenol, aniline and 1,2,7-triamino-8-hydroxynapthalene-3,6-disulfonic acid. SIP-mediated dye reduction was effective at wide pH range; however, kinetic analysis revealed fastest pseudo-first order dye reduction rate at acidic pH 3 (k_d = 0.549 min⁻¹) followed by pH 9 (k_d = 0.383 min⁻¹) and pH 7 (k_d = 0.318 min⁻¹). The daughter aromatic amines produced were partially adsorbed onto the SIP surface and maximally at neutral pH. The adsorption process followed pseudo-second order adsorption kinetics and Langmuir isotherm. Benzidine was adsorbed more than 4-aminophenol and aniline. BOD₅ of the SIP-treated effluent increased from 0.93 to 12 mg/L showing improved biodegradability. The daughter amines were rapidly mineralized in the aerobic bioreactor within 6 h. Cost-effective SIP pre-treatment could accelerate mineralization and detoxification of recalcitrant wastewater.     

Buffer standards for the physiological pH of the zwitterionic compound of 3-(N-morpholino)propanesulfonic acid (MOPS) from T = (278.15 to 328.15) K

This paper reports the pH values of five NaCl-free buffer solutions and 11 buffer compositions containing NaCl at I = 0.16 mol · kg⁻¹. Conventional pa_H values are reported for 16 buffer solutions with and without NaCl salt. The operational pH values have been calculated for five buffer solutions and are recommended as pH standards at T = (298.15 and 310.15) K after correcting the liquid junction potentials. For buffer solutions with the composition m₁ = 0.04 mol · kg⁻¹, m₂ = 0.08 mol · kg⁻¹, m₃ = 0.08 mol · kg⁻¹ at I = 0.16 mol · kg⁻¹, the pH at 310.15 K is 7.269, which is close to 7.407, the pH of blood serum. It is recommended as a pH standard for biological specimens.     

Swelling and thermodynamic studies of temperature responsive 2-hydroxyethyl methacrylate/itaconic acid copolymeric hydrogels prepared via gamma radiation

The copolymeric hydrogels based on 2-hydroxyethyl methacrylate (HEMA) and itaconic acid (IA) were synthesized by gamma radiation induced radical polymerization. Swelling and thermodynamic properties of PHEMA and copolymeric P(HEMA/IA) hydrogels with different IA contents (2, 3.5 and 5 mol%) were studied in a wide pH and temperature range. Initial studies of so-prepared hydrogels show interesting pH and temperature sensitivity in swelling and drug release behavior. Special attention was devoted to temperature investigations around physiological temperature (37 °C), where small changes in temperature significantly influence swelling and drug release of these hydrogels. Due to maximum swelling of hydrogels around 40 °C, the P(HEMA/IA) hydrogel containing 5 mol% of IA without and with drug-antibiotic (gentamicin) were investigated at pH 7.40 and in the temperature range 25–42 °C, in order to evaluate their potential for medical applications.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

VO2 nano-sheet negative electrodes for lithium-ion batteries

Vanadium dioxide (VO₂) nano-sheets were directly synthesized via a continuous hydrothermal process and were investigated as electrodes in a wide potential range of 0.05–3 V vs. Li/Li⁺. The nano-sheets showed excellent capacity retention, with a specific capacity of 350 mAh g^− 1 at an applied current of 0.1 A g^− 1 and 95 mAh g^− 1 at 10 A g^− 1. Further electrochemical testing suggested that a significant proportion of the charge storage in the cells was due to pseudocapacitive processes.     

Swelling and drug release properties of acrylamide/carboxymethyl cellulose networks formed by gamma irradiation

Hydrogels based on acrylamide monomer (AM) and different ratios (5–20 wt%) of carboxymethyl cellulose (CMC) were synthesized by gamma irradiation. The hydrogels were characterized in terms of gel content, swelling and drug release characters. The effect of temperature and pH on the degree of swelling was also studied. The results showed that the gel fraction of AM/CMC hydrogels decreases greatly with increasing the contents of CMC in the initial feeding solution. The kinetic study showed that the swelling of all the hydrogels tends to reach the equilibrium state after 5 h. However, the swelling of AM/CMC hydrogels was greater than the hydrogel based on pure AM. On the other hand, it was found that the swelling of all the hydrogels changes within the temperature range 30–40 °C and within the pH range 4–8. The AM/CMC hydrogels was evaluated for the possible use in drug delivery systems. In this respect, the release properties of methylene blue indicator, as a drug model, was investigated. It was found that the percentage release from the hydrogels increase with time to reach ～80% after 3 h at pH of 2 compared to ～100% at pH of 8.     

Bengal gram seed husk as an adsorbent for the removal of dyes from aqueous solutions – Column studies

A continuous fixed bed (column) study was carried out by using seed husk of Bengal gram (Cicer arietinum) (SHBG) as a biosorbent for the removal of direct dye, Congo red (CR) from aqueous solutions. The effects of important factors, such as the value of initial pH, the flow rate, the influent concentration of CR, bed depth, particle size of SHBG, foreign ions and regeneration of CR were studied. The effect of similar type of direct dyes like direct turquoise blue 86 (DTB) and direct black 38 (DB) on the adsorption of CR in column containing SHBG is also studied by keeping other parameters constant. The studies confirmed that the breakthrough curves were dependent on flow rate, initial dye concentration, size of SHBG, initial pH of solution of CR and bed depth. The bed depth service time analysis (BDST) model was applied at different bed depths to predict the breakthrough curves. The model is found suitable for describing the biosorption process of the dynamic behaviour of the SHBG column and the data were in good agreement with BDST model. When the flow rate was 0.67 mL/min and the influent concentration of CR was mg L⁻¹, the column capacity was 6.572 mg g⁻¹. The removal capacity of SHBG was more in case of CR (6.572 mg g⁻¹) compared to other similar direct dyes of DTB (1.984 mg g⁻¹) and DB (1.612 mg g⁻¹). The removal of CR was enhanced in the presence of foreign ion potassium (8.308 mg g⁻¹) and decreased in the presence of calcium (5.58 mg g⁻¹). 120 ml of acetone is required for the completion of regeneration of the column and the total amount of CR recovered in this case. All the results suggested SHBG as a potential adsorbent for removal of CR from aqueous solution so that the rate of bio-sorption process is rapid.     

Diffusion of ferrocene methanol in super-cooled aqueous solutions using cylindrical microelectrodes

The diffusion of ferrocene methanol in super-cooled aqueous solutions containing sucrose has been studied, using disk and cylindrical microelectrodes, over a wide viscosity range. The solution viscosity and the reduced temperature T/T_g (T_g being the glass transition temperature) were varied by changing the sucrose concentration and the temperature of the system. The voltammetric limiting current obtained with a disk microelectrode and the i(t) response on a cylindrical microelectrode after a potential step were used to determine diffusion coefficients from 7 × 10⁻⁶ cm² s⁻¹ down to 2 × 10⁻¹¹ cm² s⁻¹. The electrochemical procedure described in this work allows a simple and accurate measurement of the dynamics of electroactive solutes in glass-forming liquids.     

Buffer standards for the physiological pH of N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine (TRICINE) from T = (278.15 to 328.15) K

The pH values of two buffer solutions without NaCl and seven buffer solutions with added NaCl, having ionic strengths (I = 0.16 mol · kg⁻¹) similar to those of physiological fluids, have been evaluated at 12 temperatures from T = (278.15 to 328.15) K by way of the extended form of the Debye–Hückel equation of the Bates–Guggenheim convention. The residual liquid junction potentials (δE_j) between the buffer solutions of TRICINE and saturated KCl solution of the calomel electrode at T = (298.15 and 310.15) K have been estimated by measurement with a flowing junction cell. For the buffer solutions with the molality of TRICINE(m₁) = 0.06 mol · kg⁻¹, NaTRICINE(m₂) = 0.02 mol · kg⁻¹, and NaCl(m₃) = 0.14 mol · kg⁻¹, the pH values at T = 310.15 K obtained from the extended Debye–Hückel equation and the inclusion of the liquid junction correction are 7.342 and 7.342, respectively. These are in excellent agreement. The zwitterionic buffer TRICINE is recommended as a secondary pH standard in the region for clinical application.     

Thermodynamic and isotherm studies of the biosorption of Cu(II), Pb(II), and Zn(II) by leaves of saltbush (Atriplex canescens)

The Freundlich and Langmuir isotherms were used to describe the biosorption of Cu(II), Pb(II), and Zn(II) onto the saltbush leaves biomass at 297 K and pH 5.0. The correlation coefficients (R²) obtained from the Freundlich model were 0.9798, 0.9575, and 0.9963 for Cu, Pb, and Zn, respectively, while for the Langmuir model the R² values for the same metals were 0.0001, 0.1380, and 0.0088, respectively. This suggests that saltbush leaves biomass sorbed the three metals following the Freundlich model (R² > 0.9575). The K_F values obtained from the Freundlich model (175.5 · 10⁻², 10.5 · 10⁻², and 6.32 · 10⁻² mol · g⁻¹ for Pb, Zn, and Cu, respectively), suggest that the metal binding affinity was in the order Pb > Zn > Cu. The experimental values of the maximal adsorption capacities of saltbush leaves biomass were 0.13 · 10⁻², 0.05 · 10⁻², and 0.107 · 10⁻² mol · g⁻¹ for Pb, Zn, and Cu, respectively. The negative ΔG^∘ values for Pb and the positive values for Cu and Zn indicate that the Pb biosorption by saltbush biomass was a spontaneous process.     

Studies on radiation synthesis of polyethyleneimine/acrylamide hydrogels

Polyethyleneimine(PEI)/acrylamide(AAM) hydrogels were synthesized by γ-radiation-induced polymerization/crosslinking of aqueous mixtures containing different ratios of PEI and AAM. The gel percentage and equilibrium degree of swelling (EDS) of the synthesized hydrogels were investigated. The compositions of the hydrogels produced were found to be different from the feed composition. Ion-chromatography technique was used to determine the amount of Pb (II) and Cd (II) absorbed by the hydrogel. The maximum binding capacity of the PEI/AAM hydrogels, for Pb and Cd was found to be 19 and 12.6 mg/g, respectively, (at 100 ppm). PEI/AAM hydrogels had better metal uptake efficiency than the pure AAM hydrogel at concentrations less than 50 ppm. Pure PEI was observed to be highly degrading type polymer on exposure to gamma radiation. TGA and FT-IR techniques were used to characterize the prepared hydrogels.     

γ-irradiated chitosan-polyvinyl pyrrolidone hydrogels as pH-sensitive protein delivery system

The effects of pH of the buffer solution and the composition of the hydrogel system on the bovine serum albumin (BSA) adsorption capacity of chitosan (CS)–polyvinyl pyrrolidone (PVP) (CSPVP) hydrogels and release of BSA were investigated. Poly-electrolyte CSPVP hydrogels with different compositions were prepared by irradiating CS/PVP/water mixtures with γ-rays at ambient temperature. The adsorption capacity of hydrogels was found to increase from 0 to 350 mg BSA/g dry gel, by changing external stimuli and hydrogel composition. The adsorption of BSA within CSPVP hydrogels increased with increase in CS content in the hydrogels. When the irradiation doses of hydrogel increased, the adsorption of BSA decreased. The maximum adsorption of BSA was observed at pH 5. A significant amount of the adsorbed BSA (up to 95%) was eluted in the phosphate medium containing 0.1 M NaCl at pH 7.4.     

Electrochemical properties of Li(Li(1−x)/3CoxMn(2−2x)/3)O2 (0 ⩽ x ⩽ 1) solid solutions prepared by poly-vinyl alcohol (PVA) method

The whole range of solid solutions Li(Li_(1−x)/3Co_xMn_(2−2x)/3)O₂ (0 ⩽ x ⩽ 1) was firstly synthesized by an aqueous solution method using poly-vinyl alcohol as a synthetic agent to investigate their structure and electrochemical properties. X-ray diffraction results indicated that the synthesized solid solutions showed a single phase without any detectable impurity phase and have a hexagonal structure with some additional peaks caused by monoclinic distortion, especially in the solid solutions with a low Co amount. In the electrochemical examination, the solid solutions in the range between 0.2 ⩽ x ⩽ 0.9 showed higher discharge capacity and better cyclability than LiCoO₂ (x = 1) on cycling between 2.0 and 4.6 V with 100 mA g⁻¹ at 25 °C. For example, Li(Li_0.2Co_0.4Mn_0.4)O₂ (x = 0.4) exhibited a high discharge capacity of 180 mA h g⁻¹ at the 50th cycle. By synthesizing the solid solution between Li₂MnO₃ and LiCoO₂, the electrochemical properties of the end members were improved.