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Weizmannia coagulans with high temperature tolerance and stability was selected for the production of exopolysaccharides (EPS) at the fermentation temperature of 52 °C. The weak basic anion exchange resin was employed in the fermentation for the construction of buffer system to neutralize some lactic acid and form intermolecular hydrogen bonds with hydroxyl groups on capsular polysaccharides of bacteria via tertiary amine groups, resulting in the increased growth space for capsular polysaccharides. In addition, the fermentation at relatively high temperature significantly decreased the adsorption of Ca2+ derived from CaO used for pH adjustment to the resin and sustained the ion exchange capability of the resin available for the formation of intermolecular hydrogen bonds with capsular polysaccharides. The concentration of EPS obtained achieved up to 19.8 g/L, which was increased by approximately 20-fold as compared to the concentration of EPS obtained by conventional fermentation. The conversion rate of carbohydrates to EPS reached up to 35.1%. The EPS produced under the optimized fermentation condition included neutral and acidic heteropolysaccharides with a molecular mass of 3.4 × 104–1.5 × 106 Da. The concentration and molecular mass distribution of EPS exhibited good reproducibility. This study provides a novel method for the industrial production of EPS. • It is the first that anion exchange resins were employed for EPS production. • Total ion exchange capacity and pH were the key parameters for EPS production. • The concentration of EPS was dramatically increased up to 19.8 g/L. [ABSTRACT FROM AUTHOR]

Four slow pyrolyzed biochars produced from wood (WDB), corncobs (CCB), rice husks (RHB) and sawdust (SDB) were evaluated for adsorption, desorption and regeneration of phosphate (PO 4 3− -P) from anaerobically digested liquid swine manure. The PO 4 3− -P adsorption capacity increased followed by initial concentrations increasing. Maximum PO 4 3− -P adsorptions at initial 150 mg/L of PO 4 3− -P (highest load) were average of 7.67, 6.43, 5.73 and 5.41 mg/g for WDB, CCB, RHB and SDB, respectively. Pseudo second order kinetics model could best fit PO 4 3− -P adsorption, which indicated the chemisorption via precipitation was the main mechanism for PO 4 3− -P removal. The sorption process was reversible and the adsorbed PO 4 3− -P could be desorbed in both neutral (57–78%) and acidic solution environments (75–88%) for all biochars. Meanwhile, regenerated biochar could re-adsorb up to 5.62 mg/g at the highest initial PO 4 3− -P of 150 mg/L. The present finding implied biochar could be effectively used to recover PO 4 3− -P from anaerobic digestate. [ABSTRACT FROM AUTHOR]

Excessive phosphate in wastewater should be removed to control eutrophication of water bodies. The potential of employing amorphous zirconium (Zr) hydroxide to remove phosphate from synthetic wastewater was studied in batch adsorption experiments and in a submerged membrane filtration adsorption hybrid (MFAH) reactor. The adsorption data satisfactorily fitted to Langmuir, pseudo-first order and pseudo-second order models. Langmuir adsorption maxima at 22 °C and pHs of 4.0, 7.1, and 10.0 were 30.40, 18.50, and 19.60 mg P/g, respectively. At pH 7.1 and temperatures of 40 °C and 60 °C, they were 43.80 and 54.60 mg P/g, respectively. The thermodynamic parameters, ΔG° and ΔS° were negative and ΔH° was positive. FTIR, zeta potential and competitive phosphate, sulphate and nitrate adsorption data showed that the mechanism of phosphate adsorption was inner-sphere complexation. In the submerged MFAH reactor experiment, when Zr hydroxide was added at doses of 1–5 g/L once only at the start of the experiment, the removal of phosphate from 3 L of wastewater containing 10 mg P/L declined after 5 h of operation. However, when Zr hydroxide was repeatedly added at 5 g/L dose every 24 h, satisfactory removal of phosphate was maintained for 3 days. [ABSTRACT FROM AUTHOR]

In this study, the effect of nanoparticle size on adsorption thermodynamics was investigated. The results of theoretical and experimental studies show that particle size significantly affects the equilibrium constant and thermodynamic properties of nanoadsorption. Relationships between the equilibrium constant, thermodynamic properties and particle size were derived using the thermodynamic theory of nanoadsorption. The equilibrium constant and thermodynamic properties were obtained by investigating the adsorption of Cu 2+ onto different sizes of nano-ZnO and the adsorption of Ag + onto different sizes of nano-TiO 2 . Good agreement was achieved between results obtained by experiments and predicted by theoretical analyses. The equilibrium constant and the molar Gibbs free energy of nanoadsorption were found to increase with smaller nanoparticle size. However, the effects of particle size on the molar enthalpy and the molar entropy are uncertain. In addition, the molar Gibbs free energy, the molar enthalpy, the molar entropy and the logarithm of the equilibrium constant are linearly related to the reciprocal of the diameter of the nanoparticle . The thermodynamic properties revealed in this study may provide important guidelines for research and application in the field of nanoadsorption. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption properties of olive wood (OW) toward phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2-nitrophenol, 4-nitrophenol and 2,4-dinitrophenol, were improved by washing OW with some organic solvents (ethanol, tetrahydrofuran, ether, dichloromethane or hexane). Adsorption isotherms were classified according to Giles and Smith classification, in which L2-shape was obtained after OW washing. The adsorption data were modeled using Langmuir and Freundlich isotherm equations and it was found that adsorption capacity and affinity have increased after OW washing. Thermodynamic (ΔG°, ΔH° and ΔS°), kinetic and intra-particle diffusion parameters were estimated before and after OW washing. It was found that the adsorption of phenols on OW was of physical nature, spontaneous, exothermic and followed second order rate equation. After OW washing, adsorption spontaneity has increased. Both pore diffusion and kinetic resistances have most likely affected the adsorption process. The results presented in this work suggested that washing OW with any one of the tested solvents would enhance uptake of the tested phenols into OW sorbent. Discussing some economical and environmental aspects suggested that the use of ethanol might be preferred. [Copyright &y& Elsevier]

Abstract: Benzoic acid removal is important for the water treatment, and adsorption is an efficient treatment process. Three kinds of modified bentonites, hydroxy-aluminum pillared bentonite (Al(OH)-Bent), octadecyl trimethyl ammonium chloride modified bentonite (OTMAC-Bent), and both octadecyl trimethyl ammonium chloride and hydroxy-aluminum modified bentonite (Al(OH)-OTMAC-Bent) were prepared and characterized by XRD, FTIR, and BET analysis. Experiments were conducted on the adsorption of benzoic acid by the prepared modified bentonites at different temperatures in batch experiments. The results show benzoic acid adsorption capabilities of Na-Bent and Al(OH)-Bent are even low, but high for OTMAC-Bent and Al(OH)-OTMAC-Bent. Optimal conditions for the adsorption of benzoic acid on OTMAC-Bent and Al(OH)-OTMAC-Bent were as follows: pH of 3.5, 0.04g/mL adsorbent, and contact time of 90min. Increased adsorption with temperature indicates that the adsorptions of benzoic acid onto Al(OH)-OTMAC-Bent and OTMAC-Bent are spontaneous and endothermic. The adsorption data could be well interpreted by the Langmuir model and Temkin Equation. The adsorption efficiency was higher than 85%, suggesting that OTMAC-Bent and Al(OH)-OTMAC-Bent are excellent adsorbents for effective benzoic acid removal from water. [Copyright &y& Elsevier]

Abstract: It was found that Rh, Pd and Pt contained in the spent ceramic automotive catalysts could be effectively extracted by dry chlorination with chlorine. In order to concentrate Pd(II) contained in the chloride solution obtained from the dry chlorination process, thermodynamic and kinetics studies for adsorption of Pd(II) complexes from the chloride solutions on anionic exchange resin Diaion WA21J were carried out. It was found that Pd, Pt, Rh, Al, Fe, Si, Zn and Pb from the chloride solution could be adsorbed on the resin. The isothermal adsorption of Pd(II) was found to fit Freundlich, Langmuir and Dubinin–Kaganer–Radushkevich models under the adsorption conditions. The adsorption of Pd(II) on the resin was favorable according to the values of 1/n and RL from Freundlich and Langmuir adsorption isotherms, respectively. The maximum monolayer adsorption capacities Q max based on Langmuir adsorption isotherms were 5.70, 4.84 and 4.05mg/g and the corresponding value Xm based on Dubinin–Kaganer–Radushkevich were 5.55, 4.69 and 4.01mg/g at temperatures 18°C, 28°C and 40°C, respectively. The apparent adsorption energies (Ead ) based on Dubinin–Kaganer–Radushkevich isotherm were −15.43, −16.22 and −23.57kJ/mol for the temperatures 18°C, 28°C and 40°C, respectively. Chemical adsorption was a main mechanism involved in the adsorption process. Pd(II) adsorption on the resin could be accelerated by increasing the adsorption temperature. The adsorption of Pd(II) from the chloride solution on the resin underwent pseudo-first order kinetic process and the apparent adsorption activation energy Ea was 15.0kJ/mol. The intra-particle diffusion was a main rate controlling step in the Pd(II) adsorption process under the adsorption conditions. [Copyright &y& Elsevier]

Abstract: Present study explored the adsorptive characteristics of Indigo Carmine (IC) dye from aqueous solution onto rice husk ash (RHA). Batch experiments were carried out to determine the influence of parameters like initial pH (pH0), contact time (t), adsorbent dose (m) and initial concentration (C 0) on the removal of IC. The optimum conditions were found to be: pH0 =5.4, t =8h and m =10.0g/l. The pseudo-second-order kinetic model represented the adsorption kinetics of IC on to RHA. Equilibrium isotherms were analyzed by Freundlich, Langmuir, Temkin and Redlich–Peterson models using a non-linear regression technique. Adsorption of IC on RHA was favorably influenced by an increase in the temperature of the operation. The positive values of the change in entropy (ΔS 0) and heat of adsorption (ΔH 0); and the negative value of change in Gibbs free energy (ΔG 0) indicate feasible and spontaneous adsorption of IC on to RHA. [Copyright &y& Elsevier]

Abstract: Two macroporous crosslinked poly(styrene-co-divinylbenzene) resins functionalized with methoxy and phenoxy groups, PVBME and PVBPE were prepared and their adsorption characteristics for phenol were studied in hexane as well as in aqueous solution. It was shown that the equilibrium adsorption capacity of phenol onto PVBPE was a little larger than that onto PVBME at the same temperature and equilibrium concentration. The adsorption onto PVBME in hexane can be correlated to Langmuir isotherm model, whereas the semi-empirical Freundlich isotherm model characterized the adsorption onto PVBPE better. The adsorption thermodynamic parameters were calculated and it was found that the adsorption enthalpy, adsorption free energy, and adsorption entropy were all negative, and the adsorption thermodynamic parameters onto PVBPE were more negative than the corresponding ones onto PVBME. The relationship of the adsorption capacity with the equilibrium concentration was linear in aqueous solution. The adsorption was hypersensitive to the solution pH in aqueous solution, and the optimum pH was determined to be 6.0. The adsorption dynamics of phenol onto PVBPE in aqueous solution was investigated and it was seen that the adsorption can be well fitted by the pseudo-first-order rate equation. [Copyright &y& Elsevier]

Abstract: A critical review of the adsorption and catalysis of n- and methylalkanes demonstrates that the interior surface of TON- and MTT-type zeolites dominates both adsorption and catalysis, and that the contribution from the exterior surface is negligible. For both n- and methylalkane isomers, the experimental Henry constants at the interior TON-type zeolite surface are more than an order of magnitude greater than those at the exterior surface. Molecular simulations on exclusively interior TON-type silica surface reproduce the adsorption isotherms of n- and methylalkane isomers remarkably well and suggest that even an isomer as bulky as 2,3-dimethylpentane could have access to the interior TON-type zeolite surface. Only the reference state used in solution thermodynamics affords an equitable comparison between internal and external surface thermodynamics. It indicates that methylalkanes adsorb in a structured fashion at the exterior TON-type zeolite surface when the interior surface is inaccessible. But the entropic penalty for this organized exterior surface “pore mouth” or “key-lock” adsorption is high, so that methylalkanes prefer adsorption at the interior surface when it is accessible. We speculate that CHA- and ERI-type sieves exhibit exterior surface catalysis in long n-alkane conversion, but the database remains too small to allow investigation of the full potential of shape selectivity in exterior zeolite surface catalysis. [Copyright &y& Elsevier]

Abstract: A surface tension technique was used to determine the critical aggregation concentration (cac) of a yellow and a red dye in relation to the presence of the anionic surfactant sodium dodecylbenzene sulfonate (DBS) and to temperature changes in buffered aqueous solutions. The cac values of the yellow dye increase from 25 to 45 °C (from 41.37 to 50.32 mg L−1) and decrease from 45 to 55 °C (from 50.32 to 38.72 mg L−1). The cac values for the red dye/DBS aggregates decrease (from 124.52 to 88.50 mg L−1) from 25 to 55 °C. Adsorption of the two dyes onto a mesoporous aminopropyl silica (Sil–NH2) was also studied. The adsorption of the yellow dye increases with an increase in temperature from 25 to 55 °C. In the presence of DBS the adsorption on Sil–NH2 for the yellow dye decreases, and for the red dye increases from 25 to 55 °C. Adsorptions occurred below and above the cac of the anionic dyes/DBS aggregates. Adsorption of the dyes onto Sil–NH2 fitted well to the Langmuir, Freundlich, and Redlich–Peterson adsorption models. However, in the presence of DBS, only the Freundlich model fit the experimental adsorption data at low dye concentrations (less than 400 mg L−1). In this case, the Redlich–Peterson model was only fitted to the red dye adsorption data. The magnitude of the Dubinin–Radushkevich energetic parameters (E, from 7.00 to 15.00 kJ mol−1) indicates that the adsorption of the dyes onto Sil–NH2, in the absence and in the presence of DBS, is controlled by water adsorbed/dye in solution ion-exchange interactions. It is observed that the values of are positive for both dyes and the values are quite similar to each other. The exception is the adsorption of the yellow dye in the presence of DBS, which is slightly exothermic. The values are all negative. However, the interactions of the dyes with Sil–NH2 silica are more spontaneous in the presence of the surfactant. The positive adsorption entropy values () for the interaction of the dyes suggest that entropy is a driving force of the dye adsorptions. However, the entropic contribution is higher for the adsorptions in the presence of DBS. It was suggested that the chemical structures of the dyes play an important role in the formation of the dye/DBS aggregates and in dye adsorption onto the aminopropyl silica. [Copyright &y& Elsevier]

Abstract: A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m2 g−1 with a pore size of 3.5 nm, a pore volume of 0.564 cm3 g−1, and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5–67.5 kJ mol−1 depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption. [Copyright &y& Elsevier]

The adsorption of Congo red from solution was carried out using calcium-rich fly ash with different contact times, concentrations, temperatures, and pHs. While the amount of dye adsorbed per unit weight of fly ash increases with increasing concentration and temperature, it decreases slightly with increasing pH. The adsorption was between 93 and 98% under the conditions studied. Kinetic studies showed that the adsorption process obeyed the pseudo-second-order kinetic model. It was also determined that the adsorption isotherm followed Freundlich and Dubinin–Radushkevich models. From thermodynamic studies, it was seen that the adsorption was spontaneous and endothermic. Desorption studies suggested that desorption was 29.18% in the presence of 0.1 N HCl and was 47.21% in the presence of CH3COOH (50% v/v). This indicated that most of the dye was held by fly ash via chemisorption as well as ion exchange. Furthermore, FTIR study also shows that a chemisorption process occurs between CR and fly ash, probably indicating dye/fly ash complexing. [Copyright &y& Elsevier]

The present study was designed to produce novel cross-linked Chitosan and Chitosan/β-Cyclodextrin beads and study the adsorption of Indigo Carmine. Both adsorbents were characterized by SEM and FTIR techniques. Batch experiments were conducted in order to evaluate the effect of initial adsorbent's concentration, dye's initial concentration, initial pH and temperature. In all cases Chitosan/β-Cyclodextrin crosslinked beads exhibited higher removal efficiency of Indigo Carmine. Higher removal rates of Indigo Carmine were observed at low values of dye's initial concentration, pH and temperature, and high concentrations of adsorbent. The equilibrium adsorption data were a good fit for both Langmuir and Freundlich models and maximum adsorption capacity was 500.0 and 1000.0 mg IC /g adsorbent for Chitosan and Chitosan/β-Cyclodextrin crosslinked beads, respectively. Adsorption of Indigo Carmine was found to follow the pseudo-second order. The negative values of ΔGo, ΔHo and ΔSo indicate that the adsorption process is exothermic, spontaneous and favorable at low temperatures. • Crosslinked chitosan and β-cyclodextrin/chitosan beads were produced. • Study of Indigo Carmine's adsorption on the produced beads. • Maximum adsorption capacity of IC on chitosan beads was 500.0 mg/g. • Maximum adsorption capacity of IC on β-cyclodextrin/chitosan beads was 1000.0 mg/g. • Adsorption of Indigo Carmine was found to follow the pseudo-second order. [ABSTRACT FROM AUTHOR]

The release of synthetic food dyes, like Sunset yellow, into industrial effluents can cause serious environmental and health problems. Due to its aromatic structure, it is recalcitrant towards degradation into non -toxic intermediates and its removal by efficient adsorption represents a cheap and efficient method. Herein we propose the use of thermally reduced graphene oxide (TRGO) as effective Sunset yellow dye adsorbent with an adsorption maximum capacity comparable with other sophisticated, chemically synthesized carbon-based nanomaterials. The reduced graphene oxide and the Sunset yellow adsorbed one were characterized by FT-IR, XPS and XRD spectroscopy, N 2 adsorption-desorption isotherm and TGA analysis. BET surface area reduced from 274.1 m2/g (for TRGO) to 39.9 m2/g (for TRGO-SY) showing that Sunset Yellow molecules occupied the corresponding active sites while the number of sheets resulted from the XRD spectra – from 3 to 8 in TRGO to 5 in TRGO-SY indicates the ordered intercalations in the graphene structure. The adsorption isotherm experimental data were better fitted with the Langmuir model than the Freundlich model, with the maximum adsorption capacity of the SY dye monolayer of 243.3 mg/g at pH = 6.0 and 189.0 mg/g from synthetic wastewater. The kinetic study revealed a perfect fit following the Pseudo-second order model with an equilibrium achieved within 30 min. The lack of adsorption on the starting graphene oxide is indicative for π-π interactions between the adsorbate and adsorbent. Image 1 • Green and easily available adsorbent for anionic synthetic dyes. • Thermally reduced graphene oxide-an effective Sunset yellow dye adsorbent. • Perfect fit following the Pseudo-second order model. • Very rapid rate of SY removal, reaching the equilibrium after 30 min. [ABSTRACT FROM AUTHOR]