Adsorption Kinetics of Blue 5G Dye from Aqueous Solution on Dead Floating Aquatic Macrophyte: Effect of pH, Temperature, and Pretreatment

The textile industry is known to generate large quantities of effluents contaminated with dyes that are not fixed to the fibers during the dyeing process. The available technologies to remove these dyes from the wastewater are expensive and ineffective. Within this context, low-cost, easy-maintenance technologies for the removal of dyes have been studied, such as adsorption on aquatic macrophytes. Thus, the macrophyte Salvinia sp., raw or pretreated with NaOH or H₃PO₄, was used as biosorbent of Blue 5G reactive dye. The study showed that pH and temperature affect the dye removal capacity. The analysis of the infrared spectrum (FTIR) showed that chemical treatment of the Salvinia sp. modified the biomass surface and affected dye adsorption capacity. The pseudo-second-order kinetic model satisfactorily described the experimental data for raw and NaOH-pretreated biomass, and the pseudo-first-order model was more appropriate to describe the experimental data obtained with H₃PO₄-pretreated biomass. The highest capacity of Blue 5G dye removal was obtained with raw biomass, at 333?K and pH?1.0, with 98.35?% adsorption.     

Cuprous Oxide-Modified Diatomite Waste from the Brewery Used as an Effective Adsorbent for Removal of Organic Dye: Adsorption Performance,Kinetics and Mechanism Studies

Cuprous oxide-modified diatomite waste (Cu₂O-DW) as a low-cost and effective adsorbent was prepared via a hydrothermal route combined with acid-alkali treatment. The microstructure and surface properties of the obtained Cu₂O-DW composite was characterized by Brunauer-Emmett-Teller, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The adsorption behaviors of three different types of dyes such as cationic dye methyl blue (MB), anionic dye acid orange (AO), and reactive dye reactive yellow (RY) onto the as-prepared Cu₂O-DW were investigated. Several experimental parameters such as contact time, adsorbent dosage, initial dye concentration, and initial pH values were systematically estimated. The experimental results indicated that as-prepared Cu₂O-DW have a better adsorption performance for MB, AO, and RY. Moreover, the kinetic and isotherm models were also used to account for the adsorption mechanism of dye molecules onto Cu₂O-DW. The results demonstrated that three different dyes are all fitted well with pseudo-first-order kinetic model. Additionally, the Langmuir and Freundlich isotherm model is more suitable for describing the adsorption process of RY and MB on the as-prepared Cu₂O-DW, respectively, and the AO adsorption is propitious to the D-R isotherm model. The value of adsorption energy (E?<?8 kJ mol^?1) confirmed that the physical adsorption is dominator during the adsorption process. The findings of the study demonstrated that the synthesized Cu₂O-DW composite can be a promising adsorbent for the removal of organic dyes from wastewater and it provided a sustainable development method for cycling the diatomite waste from the brewery.     

Equilibrium, Kinetics, and Thermodynamics of Methylene Blue Adsorption by Pine Tree Leaves

The adsorption capacity of pine tree leaves for removal of methylene blue (MB) from aqueous solution was investigated in a batch system. The effects of the process variables, such as solution pH, contact time, initial dye concentration, amount of adsorbent, agitation speed, salt concentration, and system temperature on the adsorption process were studied. The extent of methylene blue dye adsorption increased with increase in initial dye concentration, contact time, agitation speed, temperature, and solution pH but decreased with increased in amount of adsorbent and salt concentration. Equilibrium data were best described by both Langmuir isotherm and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine tree leaves biomass was 126.58?mg/g at 30?°C. The value of separation factor, R _L , from Langmuir equation and Freundlich constant, n, both give an indication of favorable adsorption. The intrapartical diffusion model, liquid film diffusion model, double exponential model, pseudo-first and second order model were used to describe the kinetic and mechanism of adsorption process. A single stage bath adsorber design for the MB adsorption onto pine tree leaves has been presented based on the Langmuir isotherm model equation. Thermodynamic parameters such as standard Gibbs free energy (??G ⁰), standard enthalpy (??H ⁰), and standard entropy (??S ⁰) were calculated.     

Aerobic Biological Treatment of Chestnut Processing Wastewater

Chestnut agro-industrial companies consume a high volume of water for washing and processing fruit, generating a large volume of wastewater. This work studied the biodegradation of chestnut processing wastewater through aerobic assays, varying substrate, and biomass concentrations. In general, this wastewater presents a good biodegradability, especially in experiments with relatively low chemical oxygen demand (COD) (0.4 and 0.6?g O₂ L^?1) allowing a COD removal of 85?C90?%. The best results were obtained in the reactor initially loaded with 2?g?L^?1 of biomass and 0.4 or 0.6?g O₂ L^?1 of COD. These experiments also showed high COD removal rates: 4.25 and 3.88?g COD g^?1 volatile suspended solids (VSS) h^?1, respectively. The sedimentation rate, evaluated for different initial values of biomass (1, 2, and 3?g?L^?1), always presented higher values in the experiments with 2 and 3?g?L^?1 of biomass, regardless of the initial COD value used. After comparing different kinetic models (Monod, Contois, and Haldane), it was observed that the Haldane inhibition model satisfactorily describes the COD biodegradation. AQUASIM software allowed calculating the kinetic constant ranges: K _s, 1.59?C6.99?g COD L^?1; ?? _max, 25?C40?g COD g^?1 VSS day^?1; and K _i values, 0.07?C0.11. These kinetic constants corresponds to maximum rates (??*) between 1.48 and 4.25?g COD g^?1 VSS day^?1 for substrate concentrations (S*) from 0.38 to 0.88?g COD L^?1.     

Limitations of atp estimates of microbial biomass

Serious limitations were found in the use of ATP measurements as indicators of Pseudomonas paucimobilis biomass and activity in sterilized soil. These limitations were related to effects of moisture stress, nutrient variation and protozoan predation on soil ATP levels and ATP per bacterium. Rewetting dry soil resulted in an increase (2.2-fold) in ATP per bacterium, as did additions of glucose (5.9-fold) and (NH₄)₂SO₄ (2.8-fold). ATP per bacterium also differed between grazed and ungrazed bacteria. Carbon dioxide evolution and ATP concentrations varied independently with time. Thus, except under low nutrient conditions, when neither bacterial numbers nor ATP measurements changed, ATP concentrations did not indicate bacterial population dynamics or respiration. Carbon and nitrogen effects on ATP concentrations were reduced by adding an excess of glucose a few hours before ATP measurements.     

Evaluation of the Fate of Ciprofloxacin and Amoxicillin in Domestic Wastewater

The main objective of this study was to evaluate the contribution of sorption to the removal of two commonly used antibiotics (amoxicillin and ciprofloxacin) from wastewater. These antibiotics are excreted in large quantities with more than 75% of them being unmetabolized and are therefore likely to end up in domestic wastewater in significant quantities. The specific objectives were to determine the sorption behavior in synthetic wastewater (SWW), the effect of pH and contribution of microbial surfaces, to the sorption of these antibiotics. The SWW, adjusted to various pH levels, was used and sorption kinetics conducted at 100 and 250 ??g L^?1 concentrations. Adsorption isotherms were determined at different pH levels. The SWW (pH 6.6) was inoculated with Rhodococcus sp. B30 strain to determine the contribution of microbial surfaces to sorption. Generally, both antibiotics revealed a decrease in sorption with pH increase, suggesting that lowering the solution pH of the wastewater may reduce their amounts in wastewater solution. Comparatively, ciprofloxacin exhibited higher sorption than amoxicillin. The sorption distribution coefficient (K _d) values for ciprofloxacin ranged from 0.4356 to 0.8902 L?g^?1, with pH?=?5.5 exhibiting the highest K _d, while that for amoxicillin ranged from 0.1582 to 0.3858 L?g^?1 with the highest K _d at pH?=?3.5. There was a significant difference (p?<?0.05) in K _d values between various pH levels for both antibiotics except between the pH of 5.5 and 6.6. Both antibiotics were not degraded within 48 h by Rhodococcus sp. B30 strain. These results indicate that degradation may not be the major process of removal of compounds from wastewater treatment plants and hence the importance of sorption as an intervention technique.     

Biodegradation of 3,4-Dichloroaniline by a Novel Myroides odoratimimus Strain LWD09 with Moderate Salinity Tolerance

A Gram-negative bacterium strain LWD09, capable of growing aerobically on 3,4-dichloroaniline (DCA) as the sole carbon and energy source, was isolated from the farm field. This bacterium was identified as Myroides odoratimimus strain by morphological, physiological, and biochemical characteristics as well as 16S rDNA sequence. Analysis of culture pH, temperature, cells growth, and DCA concentration demonstrated that strain LWD09 could effectively degrade DCA without a lag phase. The kinetics of DCA degradation was well described using the Andrews equation, and the kinetic parameters were as follows: q _max?=?1.74?h^?1, K _s?=?43.5?mg?L^?1, and K _i?=?230.3?mg?L^?1. In addition, strain LWD09 was found to be moderately halophilic and showed the highest power of DCA degradation in 5% NaCl (w/w, %). With initial concentrations of 30, 100, and 200?mg?L^?1, 100%, 80.4%, and 33.2% of DCA were transformed after 96?h in 5% NaCl, respectively. These results suggest that strain LWD09 has the potential to degrade DCA in saline wastewater. To date, this is the first report on the degradation of DCA by a M. odoratimimus strain with moderate salinity tolerance.     

Kinetic,Thermodynamic, and Adsorption Behavior of Cationic and Anionic Dyes onto Corn Stigmata: Nonlinear and Stochastic Analyses

The potential to remove methylene blue (MB) basic dye and indigo carmine (IC) acidic dye, from wastewater treatment systems using corn stigmata through biosorption was investigated in batch experiments. The effects of contact time, solution pH, biosorbent dosage, initial dye concentration, salts, and temperature were sought. Results showed that the maximal uptakes of MB were 106.3 mg g^?1 at pH?=?7 and 63.7 mg g^?1 for IC at pH?=?2. In order to determine the properties and surface structure of the biomass physicochemical properties (pH_pzc, elemental analysis, Boehm’s titration, and chemical composition), spectral (FTIR analysis) and morphological characteristics (SEM) were investigated. Random distribution of the active sites was described by the new biosorption fractal model of Brouers–Sotolongo. The thermodynamic study demonstrated the favorable character of the biosorption of MB and of IC, which was inhibited by the presence of salts. The elucidation of the biosorption mechanism showed that the biosorption of MB onto corn stigmata was mainly controlled by chemisorption and the biosorption of IC was described by physisorption.     

Adsorption of Natural Estrogens and Their Conjugates by Activated Sludge

Adsorption to biomass is a key mechanism which results in the elimination of natural estrogens and their conjugates from sewage. Freundlich model showed that the adsorption capacities of estrone and 17β-estradiol to activated sludge were the highest at neutral pH. The lower capacities at pH 2 and 11.5 could be due to the competition of sludge adsorption sites by cations or electrostatic repulsion from particles of similar charges. The lowest adsorption capacity at pH 11.5 was attributable to electrostatic repulsion, and the highest capacity at pH 2 might be due to the increased sulfate adsorbability. For estrogen conjugates such as estrone-3-sulfate and 17β-estradiol-3-sulfate, adsorption performances were similar at pH 5, 7, and 9. It was observed that mean values of log K _D were 2.78, 2.61, 1.67, and 1.94 l kg TSS^?1; log K _OM were 2.96, 2.79, 1.77, and 2.04 l kg VSS^?1 and those of log K _OC were 3.31, 3.12, 2.21, and 2.46 l kg OC^?1 for estrone, 17β-estradiol, estrone-3-sulfate, and 17β-estradiol-3-sulfate, respectively.     

Radiation Synthesis of Poly(Acrylamide-Acrylic Acid-Dimethylaminoethyl Methacrylate) Resin and Its Use for Binding of Some Anionic Dyes

Poly(acrylamide-acrylic acid-dimethylaminoethyl methacrylate) P(AAm-AA-DMAEMA) resin was prepared by the template copolymerization. PAAm was used as a template for the copolymerization of DMAEMA and AA in aqueous solution using gamma rays. The adsorption of indigo carmine and eriochrome black-T anionic dyes from aqueous media on P(AAm-AA-DMAEMA) has been investigated. The adsorption behavior of this resin has been studied under different adsorption conditions: dye concentrations (50?C500 mg l^?1), contact times, temperature (30?C55°C), and pH values (2?C7). The amount of dye adsorbed increased with increasing resin content, but it had a little change with temperature and decreased slightly with increasing pH. Adsorption data of the samples were modeled by the pseudo-first-order and pseudo-second-order kinetic equations in order to investigate dye adsorption mechanism. It was found that the adsorption kinetics of the resin followed a pseudo-second-order model with rate constant (k ₂) of 2.5?×?10^?3 and 1.8?×?10^?2 g (mg^?1 min^?1) for indigo carmine and eriochrome black-T, respectively. Equilibrium isotherms were analyzed using the Langmuir and Freundlich isotherms. It was seen that the Freundlich model fits the adsorption data better than the Langmuir model.     

Sequential Microaerophilic-Oxic Phase Mineralization of Azo Dyes by a Monoculture of Pseudomonas Aeruginosa Strain AWF Isolated from Textile Wastewater

A novel dye degrading bacterium capable of decolorizing and mineralizing four different dyes (Methyl red, Orange II, Direct red 80, and Direct blue 71) was isolated from textile industrial wastewater using the selective enrichment technique. The bacterium was identified as Pseudomonas aeruginosa. More than 80 % decolorization of Direct red 80 was obtained under microaerophilic conditions in 48 h, whereas only 10 % color removal was obtained under oxic conditions at the same time. Subsequent aeration of the decolorized medium resulted in the mineralization of the metabolic intermediates generated after azo bond cleavage by P. aeruginosa as confirmed by total organic carbon content and high-performance liquid chromatography analyses. The degradation products were characterized by Fourier transform infrared spectrometer and nuclear magnetic resonance techniques whereas the biotoxicity profile of the samples were evaluated using the brine shrimp lethality test assay. Data from this study provide evidence of dye mineralization and detoxification by a monoculture of P. aeruginosa in successive microaerophilic/oxic stages.     

Solubility of cinnabar (red HgS) and implications for mercury speciation in sulfidic waters

New experiments have been conducted to determine the speciation of dissolved mercury (Hg) over wide pH (1–12) and sulfide concentration ranges (0.5–30 mM) and in the presence of elemental sulfur (S⁰) or Hg⁰, conditions that encompass those of near-bottom and pore waters of sediments. Samples containing synthetic red mercuric sulfide (HgS, cinnabar), buffer solution, aliquots of bisulfide (HS^?1) solution, and, in special cases, S⁰ or Hg⁰ were prepared anaerobically and allowed to equilibrate for several months. Filtered samples were analyzed for pH, total sulfide (ΣS^2?), and total mercury [Hg]_tot. Plots of [Hg]_tot values vs. pH at varying ΣS^2? verified the formation of three previously known mercury-sulfide complexes (HgS₂H_n ^n?2) and revealed that a new Hg₂SOH⁺ complex is important at low pH and low ΣS^2?. Our constants for ionic strength (I) 0.7 and 25⁰ C are as follows: K₁=10^{?5.76(+0.71, ?1.02)} for HgS_cinn+H₂S ? HgS₂H₂ ⁰; K₂=10^{?4.82(+0.72, ?1.10)} for HgS_cinn+HS^? ? HgS₂H^?; K₃=10^{?13.41(+0.76, ?0.93)} for HgS_cinn+HS^? ? HgS₂ ^2?+H⁺; K₄=10^{?8.36(+0.71, ?0.93)} for 2HgS_cinn+H⁺+H₂O ? Hg₂SOH⁺+H₂S. With decreasing pH, below 1, Hg solubility decreased sharply, indicating the formation of a new solid phase, inferred to be corderoite (Hg₃S₂Cl₂). From our solubility data, we calculated the free energy of formation (ΔG_f ^o) of Hg₃S₂Cl₂ to be ?396 (+3, ?11) kJ/mol. In experiments where excess S⁰(s) was present, a new mercury-polysulfide dimer was identified; its formation constant is K₅=10^{?1.99(+0.69, ?1.27)} for 2HgS_cinn+2HS^? + nS⁰ ? Hg₃S₄ ^IIS_n ^oH₂ ^2?. Data from experiments where Hg⁰(aq) was added confirmed the reversibility of HgS dissolution. An application of our mercury-sulfide speciation model to a natural anoxic basin, Saanich Inlet, British Columbia, is discussed.     

Effect of lithological substrate on microbial biomass and enzyme activity in brown soil profiles in the northern Apennines (Italy)

The aim of the present study was to investigate the microbial activity along forest brown soil profiles sequence developed on different lithological substrates (carbonate or non-carbonated cement in sandstone formations) at different altitudes. The main question posed was: does carbonate affect the biochemical activity of brown soil profiles at different altitudes? For the purpose of this study, four soil profiles with different amounts and compositions of SOM developed on different lithological substrates were selected: two with carbonate (MB and MZ) and the other two with non-carbonated cement in the sandstone formations (MF1 and MF2). Chemical and biochemical properties of soil were analysed along soil profiles in order to assess the SOM quantity and quality, namely total organic C (C_org), water extractable organic C (WEOC) and humification indices (HI, DH, HR). Microbial biomass (C_mic and N_mic) content, as well as the specific activities of acid phosphatase, β-glucosidase and chitinase enzymes were chosen as indicators of biochemical activity. The soil biochemical properties provided evidence of better conditions for microorganisms in MB than in MF1, MF2 and MZ soil profiles, since patterns of microbial biomass content and activity might be expected in response to the amount and quality of organic substances. The different lithological substrates did not show any clear effect on soil microbial biomass content, since similar values were obtained in MF1, MF2 (with non-carbonated cement) and MZ (with carbonate). However, the specific activities of acid phosphatase (per unit of C_org and per unit of C_mic) were higher in soils with no carbonate (MF1 and MF2) than in soils with carbonate (MB and MZ). In conclusion, the biochemical activity along brown soil profiles was mainly regulated by different soil organic matter content and quality, while the two different lithological substrates (with carbonate or non-carbonated cement in the sandstone formations) did not show any direct effect on microbial biomass and its activity. However, the activity of acid phosphatase per unit of C was particularly enhanced in soil with non-carbonate cement in the sandstone formations.     

Photo-Degradation of Some Dyes using Ag-Loaded Titaniumdioxide

The photocatalytic degradation of organic dyes using TiO₂ andsilver-loaded TiO₂ has beenstudied. The dyes which were chosen (methyl violet, a cationicdye; Cibacron Blue FMR, areactive dye; and Maxilon Red GRL, a mono azo basic dye)represent the major structuralfamilies of organic dyes. Ag-loading dramatically reduceddegradation time. While theundoped TiO₂ degraded about 63% of the total amount ofmethyl violet within 4 min,degradation rose to 95% with Ag-loaded TiO₂ within the sametime period. The photo-decomposition of dyes was monitored as a function of pH anddissolved organic and inorganic matters.     

Adsorption Behaviour of Basic Dyes on the Humic Acid Immobilized Pillared Clay

In this work, the adsorption of three basic dyes, namely methylene blue (MB), crystal violet (CV) and rhodamine B (RB) on the humic acid (HA) immobilized pillared clay (PILC) (HA-PILC) was studied. The adsorption capacity of dyes at 30 °C using HA–PILC was foundto be 2.6, 2.0 and 2.3 times greater than that using PILC for the removal of MB, CV and RB, respectively for an initial concentrationof 250 μmol dm^-3. The adsorption process was pH dependent. The maximum dye adsorption on HA-PILC was observed at a pH of 5.0–7.0 (removal of 95.2–99.2% for MB, 92.7–97.3% for CV and 83.4–91.0% for RB) with no significant increase in removalsbeyond a pH of 7.0. The adsorption process could be best describedby the Urano and Tachikawa model showing that particle diffusion controlled adsorption. Equilibrium adsorption data were analyzed using the Langmuir, Freundlich and Redlich-Peterson isotherms. Dye adsorption was best described by the Freundlich model. The monolayer adsorption capacities of HA-PILC calculated using the Langmuir isotherm were 608.4, 484.7 and 413.1 μmol g^-1 for MB, CV and RB, respectively. The linear Sheindorf-Rebhun-Sheintuch equation (Multicomponent Freundlich-type), was applied to the isotherm data obtained for each binary-solute combination of MB, CV and RB. The study showed that HA-PILC was an excellent media for the removal of basic dyes from aqueous solutions, based on adsorption kinetics and capacity.     

Cu(II) Biosorption and Competitive Studies in Multi-ions Aqueous Systems by Arthrobacter sp. Sphe3 and Bacillus sphaericus Cells: Equillibrium and Thermodynamic Studies

Arthrobacter sp. Sphe3 and Bacillus sphaericus cells were used for Cu(II) biosorption. The effect of contact time, biosorbent dose, equilibrium pH, temperature and the presence of other ions on the efficiency of the process were extensively studied. Optimum pH value and biomass concentration were determined at 5.0 and 1.0?g/l, whereas contact time was found to be 5 and 10?min for Arthrobacter sp. Sphe3 and Bacillus sphaericus biomass, respectively. Equilibrium data fitted very well to Freundlich model (R ²?=?0.996, n?=?2.325, K _f?=?8.141) using Arthrobacter sp. Sphe3. In the case of B. sphaericus, a Langmuir adsorption model [R ²?=?0.996, Q _max?=?51.54?mg-Cu(II)/g] showed to better describe the results. Potentiometric titration and Fourier transform infrared (FTIR) spectroscopy showed that amine, carboxyl and phosphate groups participate in Cu(II)-binding. The calculated thermodynamic parameters indicated the spontaneous and feasible nature of Cu(II) biosorption on both biosorbents. Selectivity of Cu(II) biosorption was examined in binary and multi-ions systems with various anions and cations which are commonly found in municipal and industrial wastewater. A specificity towards Cu(II) was observed in binary mixtures with Cl^-, CO ₃ ^-2 , NO ₃ ^- , SO ₄ ^-2 , PO ₄ ^-3 , Mg⁺² and Ca⁺², and As(V) with the maximum uptake capacity remaining constant even at high competitive ion??s concentrations of 200?mg/l. Desorption studies showed that Cu(II) could be completely desorbed from Cu(II)-loaded Arthrobacter strain Sphe3 and B. sphaericus biomass using 1.0 and 0.8?M HCl, respectively, and both bacterial species could be effectively reused up to five cycles, making their application in wastewater detoxification more attractive.     

Colour Removal from Synthetic Dye Wastewater Using a Bioadsorbent

Removal of dyes (Crystal Violet, Methylene Blue, Malachite Greenand Rhodamine B) from aqueous solutions at differentconcentrations, pH and temperatures by Neem sawdust has beencarried out successfully. The percentage of the dye adsorbed byNeem sawdust decreased from 91.56 to 78.94 and 84.93 to 71.25 for Crystal Violet and Malachite Green, respectively, when the concentration of the dye was increased from 6 to 12 mg L^-1 at atemperature 30 ± 1 °C and pH 7.2. Adsorption ofother dyes (Methylene Blue and Rhodamine B) also decreased withincreasing concentration of the dye in solutions. The values ofthe rate constant of adsorption (k _ad) of Crystal Violet at25, 35 and 45 °C were found to be 10.80, 10.52 and 10.25 × 10^-2 min^-1, respectively. The values of the Langmuir constant for adsorption capacity (Q ^o) of Crystal Violet on the adsorbent varied from 4.44 to3.99 mg g^-1, respectively, with the increase of temperaturebetween 25 to 45 °C. The equilibrium data followed theLangmuir model of adsorption. The variation in the extent ofremoval with pH has been explained on the basis of surfaceionisation and complexation. Thermodynamic parameters(ΔG, ΔH and ΔS) have also been determinedto explain the results.     

Biosorption of Methylene Blue from Aqueous Solutions by Hazelnut Shells: Equilibrium, Parameters and Isotherms

This paper presents a study on the batch adsorption of a basic dye, methylene blue (MB), from aqueous solution onto ground hazelnut shell in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. A contact time of 24 h was required to reach equilibrium. Batch adsorption studies were carried out by varying initial dye concentration, initial pH value (3–9), ionic strength (0.0–0.1 mol L^?1), particle size (0–200 μm) and temperature (25–55°C). The extent of the MB removal increased with increasing in the solution pH, ionic strength and temperature but decreased with increase in the particle size. The equilibrium data were analysed using the Langmuir and Freundlich isotherms. The characteristic parameters for each isotherm were determined. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by Langmuir isotherm equation. The maximum adsorption capacities for MB were 2.14?×?10^?4, 2.17?×?10^?4, 2.20?×?10^?4 and 2.31?×?10^?4 mol g^?1 at temperature of 25, 35, 45 and 55°C, respectively. Adsorption heat revealed that the adsorption of MB is endothermic in nature. The results indicated that the MB strongly interacts with the hazelnut shell powder.     

TiO2-Assisted Photodegradation of Direct Blue 78 in Aqueous Solution in Sunlight

The photodegradation of azo dyes aqueous solution has been investigated using TiO₂ as catalyst in sunlight. The effect of amount of catalyst, concentration of dye, and pH value on the degradation of Direct Blue 78 was observed. A complete degradation of 100 mg/L Direct Blue 78 solution under solar irradiation was achieved in 6 h at pH?3.0, dosage of TiO₂ 1.0 g/L. A possible pathway for the photodegradation of Direct Blue 78 in sunlight was proposed.     

Does 2-ketogluconate chelate calcium in the pH range 2.4 TO 6.4?

The dissolution of synthetic hydroxyapatite was studied as a function of pH in the presence of 10 mM 2-ketogluconate, acetate, citrate, and EDTA. In the pH range 5.7–7.7, the relative effectiveness for the dissolution of hydroxyapatite increased in the order 2-ketogluconate ? g acetate < citrate < EDTA. The dissociation constants for gluconic acid (pK_a = 3.41 at μ = 0.2, 25°C) and 2-ketogluconic acid (pK_a = 2.66, at μ = 0.2, 25°C) were measured potentiometrically and used to determine the 1:1 stability constant for the corresponding calcium complexes. The observed calcium-stability constant for the gluconate ion (log K₁₁ = 1.19 at μ = 0.2, 25°C) is in accord with an earlier determination made under similar conditions, however, the calcium stability constant for the 2-ketogluconate ion, which has not previously been reported was found to be less than or equal to the experimental error in the determination (log K₁₁ < 0 at μ = 0.2, 25°C). The negligible value for the calcium stability constant for 2-ketogluconate, confirms the dissolution observations and refutes previous qualitative assumptions in the literature suggesting that 2-ketogluconic acid is an effective chelating agent for calcium ions. It was concluded that 2-ketogluconic, the major acid component of wheat-seedling rhizosphere products is one of the strongest monobasic carboxylic acids and as such acts as a readily available source of hydrogen ions for the dissolution of hydroxyapatite. This dissolution does not involve chelation of calcium ions.