Adsorption of phosphate and nitrate anions on ammonium-functionnalized mesoporous silicas

Surface modified mesostructured silica materials represent potential adsorbents offering an opportunity to remediate several important water pollutants. In the present work, ammonium-functionnalized MCM-41, MCM-48 and SBA-15 mesoporous silica materials were synthesized via post-synthesis grafting and co-condensation. Their efficiency to remove nitrate and phosphate anions in aqueous solutions was investigated. The adsorbent materials showed high adsorption capacities reaching 46.5 mg NO₃⁻/g and 55.9 mg H₂PO₄⁻/g under the operating conditions explored. The mesoporous silica materials functionalized via post-synthesis grafting method exhibited higher performances in terms of percentage pollutant removal and adsorption capacities if compared to their analogs synthesized according to the co-condensation strategy.     

The electrosorption of phenol onto activated carbon

The electrosorption isotherms of phenol on an activated carbon were measured over a concentration range of 0 to 100mg⁻¹1⁻¹ at 25°C and pH=7.7, 6.5, 4.1 and 1.9. Cathodic polarizations relative to the open circuit potential decreased the amount of phenol adsorbed while anodic polarizations apparently increased the amount adsorbed; however, electro-oxidation of phenol masked adsorption at anodic polarizations. Electro-regeneration of spent activated carbon beds was studied. Within defined potential limits, the electro-regenerated bed maintains its virgin capacity. Application of a cathodic polarization to the bed enhanced the degree to which it was regenerated relative to that in a nonpolarized bed; the effect is, however, modest.     

Adsorption behaviors of the aminated chitosan adsorbent

Using inverse suspension technology, a novel aminated chitosan adsorbent with higher adsorption ability for metal cations and metal anions was prepared. Through cross-linking amination reaction, the content of amidocyanogen of aminated chitosan adsorbent was enhanced four times than that of chitosan cross-linked adsorbent. As can be seen from the results, the adsorption ability of the novel aminated chitosan adsorbent for (Nicit)⁻ and Cr(VI) was enhanced remarkably. When the initial concentration of metallic ion was 1,000 mg/L, the adsorption capacity of the novel aminated chitosan adsorbent for nickel citrate and Cr(VI) was up to 30.2 mg/g and 28.7 mg/g, respectively. And the adsorption capacity of the novel aminated chitosan adsorbent for Ni²⁺ was still higher. So the new aminated chitosan adsorbent offers not only a higher uptake for metal cations but also a better adsorption capacity for metal anions.     

Phosphate removal from water using an iron oxide impregnated strong base anion exchange resin

Removing phosphate from water is important as it causes eutrophication, which in turn has a harmful effect on aquatic life, resulting in a reduction in biodiversity. On the other hand, recovery of phosphate from phosphorus containing wastewater is essential for developing an alternative source of phosphorus to overcome the global challenge of phosphorus scarcity. Phosphate removal from aqueous solutions was studied using an iron oxide impregnated strong base anion exchange resin, Purolite FerrIX A33E in batch and fixed-bed column experiments. Phosphate adsorption in the batch study satisfactorily fitted to the Langmuir isotherm with a maximum adsorption capacity of 48 mg P/g. In the column study, increase in inlet phosphate concentration (5–30 mg P/L), and filtration velocity (2.5–10 m/h) resulted in faster breakthrough times and increase in breakthrough adsorption capacities. Increase in bed height (3–19 cm) also increased adsorption capacity but the breakthrough time was slower. The breakthrough data were reasonably well described using the empirical models of Bohart–Adams, Thomas, and Yoon–Nelson, except for high bed heights. Phosphate adsorbed was effectively desorbed using 1 M NaOH and the adsorbent was regenerated after each of three adsorption/desorption cycles by maintaining the adsorption capacity at >90% of the original value. Greater than 99.5% of the desorbed P was recovered by precipitation using CaCl₂.     

Removal of arsenic from aqueous solution using polyaniline/rice husk nanocomposite

The present study deals with the adsorption of arsenic ions from aqueous solution on polyaniline/rice husk (PAn/RH) nanocomposite. Batch studies were performed to evaluate the influence of various experimental parameters like pH, adsorbent dosage, contact time and the effect of temperature. Optimum conditions for arsenic removal were found to be pH 10, adsorbent dosage of 10 g/L and equilibrium time 30 minutes. Adsorption of arsenic followed pseudo-second-order kinetics. The equilibrium adsorption isotherm was better described by Freundlich adsorption isotherm model. The adsorption capacity (q _max ) of PAn/RH for arsenic ions in terms of monolayer adsorption was 34.48 mg/g. The change of entropy (ΔS⁰) and enthalpy (ΔH⁰) was estimated at −0.066 kJ/(mol K) and −22.49 kJ/mol, respectively. The negative value of the Gibbs free energy (ΔG⁰) indicates feasible and spontaneous adsorption of arsenic on PAn/RH.     

Ammonia Removal from Aqueous Solutions by Iranian Natural Zeolite

Abstract

The capability of Iranian natural clinoptilolite for ammonia removal from aqueous solutions has been thoroughly studied. Both batch and continuous (column) experiments were carried out. The viability of this natural zeolite in reducing the leakage of ammonia to the environment through waste water streams was a main focus of this research. Through the batch experiments, the effect of process variables such as the size of zeolite particles, pH, and ammonia concentration of the feed solution on the kinetics of ammonia uptake were investigated. Ammonia removal occurred rapidly and within the first 15 minutes of contact time, a major part of ammonia was removed from the solution. An adsorption capacity about 17.8 mg NH₄ ⁺/g zeolite at feed ammonia concentration of 50 mg/L was obtained and the optimum range for pH was achieved about 5.5–7.6. The adsorption capacity of clinoptilolite in the continuous mode was about 15.16 and 15.36 mg NH₄ ⁺/g zeolite for the original and regenerated types of clinoptilolite, respectively, where feed ammonium concentration was 50 mg/L. Increasing the feed ammonium concentration to 100 mg/L did not reduce the capability of the column for its ammonium removal and up to a bed volume (BV) of 85, there was only less than 1 mg/L ammonium in the column outlet. Presence of cations such as Ca²⁺, Mg²⁺ and Na⁺ in the feed solution reduced the clinoptilolite adsorption capacity to about 11.68 mg NH₄ ⁺/g zeolite. Regeneration experiments were carried out using concentrated sodium chloride solutions, as well as tap water. Where tap water was used as the regenerant, gradual release of ammonium from exhausted clinoptilolite was observed.     

Kinetics and Equilibrium Studies for the Removal of Cobalt,Manganese, and Silver in Ethanol using Dowex 50W-x8 Cation Exchange Resin

Organic solvents such as ethanol, find a wide range of applications in fuel, pharmaceutical industries, food industries, and paint formulations, among others. The removal of Ag(I), Co(II), and Mn(II) ions in ethanol by cation exchange resin, Dowex 50W-x8, was investigated. The adsorption characteristics of metal ions onto Dowex 50W-x8 resin were described by Langmuir isotherms. The maximum sorption exchange capacities at 298 K were obtained as 47.4 mg g^?1, 52.6 mg g^?1, and 58.5 mg g^?1 for Ag(I), Co(II), and Mn(II), respectively. The data was also fitted to Temkin and Dubinin-Radushkevich adsorption isotherm models to evaluate other adsorption properties. The ion exchange of silver, cobalt, and manganese on cation exchange resin followed pseudo-second-order kinetics, and the intraparticle diffusion was rate-determining step. The thermodynamic parameters indicated that the sorption of metal ions onto Dowex 50W-x8 resin was spontaneous (negative ΔG°) and endothermic in nature (positive ΔH°) implying that the adsorption capacity increased with increasing temperature. The resin can be regenerated by eluting metal ions with 3.0 mol L^?1 HNO₃ followed by washing it with 10 mL of Millipore water and 10 mL of 2.0 M NaOH, respectively. The proposed method was applied for metal ion removal in real ethanol samples.     

Wastewater treatment by adsorption with electrochemical regeneration using graphite-based adsorbents

An innovative technology for wastewater treatment using adsorption and electrochemical regeneration has been developed at the University of Manchester. The process uses a low capacity graphitic adsorbent material (a graphite intercalation compound, Nyex^TM 1000) which can be regenerated electrochemically. In this study, we investigate the characteristics of a new, partially porous adsorbent material, Nyex^TM 2000 which offers increased surface area in comparison with Nyex^TM 1000. Nyex^TM 2000 was found to have an adsorption capacity of almost three times that of Nyex^TM 1000. The electrical conductivity of a Nyex^TM 2000 was found to be double that of Nyex^TM 1000, enabling improvements in the electrochemical regeneration characteristics. The removal of an anionic azo dye, acid violet 17, from aqueous solution using Nyex^TM 1000 and 2000 was investigated under various operating conditions. The adsorption of acid violet 17 on Nyex^TM 2000 was found to be comparatively fast with 75 % of the equilibrium capacity being achieved within 5 min. The parameters affecting the regeneration efficiency including the charge passed, current density, treatment time, adsorbent bed thickness, and pH were investigated. An electrochemical regeneration efficiency of around 100 % was achieved for a fully loaded Nyex^TM 2000 in a sequential batch electrochemical cell with a regeneration time of 60 min and a charge passed of 100 C g⁻¹ at a current density of 14 mA cm⁻². The charge required for electrochemical regeneration was found to be approximately equal to theoretical charge required for complete oxidation of the adsorbed acid violet 17, making process design relatively simple. Nyex^TM 2000 was found to be an economic adsorbent with relatively small electrical energy consumption required (31 J mg⁻¹ of acid violet 17 treated, compared to 52 J mg⁻¹ of acid violet 17 for Nyex^TM 1000). Multiple adsorption/regeneration cycles presented no loss in adsorptive capacity and material loses over five adsorption/regeneration cycles.     

Study on the Synthesis and Surface Active Properties of a Novel Surfactant with Triple Quaternary Ammonium Groups and Triple Dodecyl Chains Derived from Glycerin

The new triple chain surfactant was firstly prepared by ring-opening and a quaternization reaction with 2-(chloromethyl)-oxirane, tertiary amine and propane-1,2,3-triol as starting materials. The surfactant was characterized by MS and elementary analysis. Air–Liquid surface tension was measured by using a tensiometer at temperatures from 298 to 318 K respectively and in various salt solutions (NaX). The results show that with the increase of temperature, the values of critical micelle concentration (cmc) can achieve a minimum at 308 K. The maximum surface adsorption capacity Γ decreases, while the minimum molecule A _min area increases. With the increase in temperature and the decrease in counterionic diameter, the values of cmc decrease from 8.09 × 10⁻⁵ to 5.52 × 10⁻⁵ mol/L, and the adsorption capacity Γ increase from 1.80 × 10⁻¹⁰ to 2.74 × 10⁻¹⁰ mol/m², while there are almost no influences to surface tension (γ_cmc). The free energy of micelle formation is negative (−85.2 to −92.0 kJ/mol).     

Adsorption characteristics of methylene blue on poplar leaf in batch mode: Equilibrium,kinetics and thermodynamics

Adsorption characteristics of methylene blue (MB) from aqueous solution on natural poplar leaf were investigated. Batch experiments were carried out to study the effects of initial pH, contact time, adsorbent dosage, and initial MB concentration, salt concentration (Ca²⁺ and Na⁺) as well as temperature on MB adsorption. The optimum condition for adsorption was found at pH 6–9 and adsorbent dosage of 2 g L⁻¹. The equilibration time was 240 min. The salt concentration had a negative effect on MB removal. The equilibrium data were analyzed with Langmuir, Freundlich and Koble-Corrigan isotherm models using nonlinear regression method. The adsorption process was more effectively described by Langmuir isotherm based on the values of the correlation coefficient R² and chi-square statistic x². The maximum monolayer adsorption capacity of poplar leaf from the Langmuir model was 135.35 mg g⁻¹ at 293 K. The pseudo second order equation provided a better fit to experimental data in the kinetic studies. Intraparticle diffusion was involved in adsorption process, but it was not the only rate-controlling step. Thermodynamic quantities such as ΔG, ΔH and ΔS were calculated, indicating that the adsorption process was spontaneous and endothermic. Dye-adsorbent interactions were examined by FTIR and SEM analysis. The FTIR results suggested that there were hydroxyl and carboxyl groups on the surface of poplar leaf, which would make MB adsorption possible. The SEM images showed effective adsorption of MB molecules on the adsorbent surface.     

Adsorption of FFA in crude catfish oil onto chitosan,activated carbon,and activated earth: A kinetics study

The feasibility of using chitosan, activated carbon, and activated earth to remove FFA from crude catfish visceral oil, and the adsorption kinetics of the procedure were evaluated. The effect of adsorbents on water activity and the 18∶3 and 22∶6 content of crude catfish visceral oil was also studied. The initial adsorption kinetic coefficients of FFA (mL g⁻¹ min⁻¹) were 0.1, 0.07, and 0.03 for chitosan, activated carbon, and activated earth, respectively. The external film mass-transfer coefficient (0.001 mL s⁻¹) was similar for the three adsorbents. The adsorption capacity of FFA at saturation (mg g⁻¹) was 71.2 for chitosan, 65.5 for activated carbon, and 57.0 for activated earth. The intraparticular diffusion coefficients (mg mL⁻¹ min^−0.05) were 0.14, 0.12, and 0.09 for chitosan, activated carbon, and activated earth, respectively. Water activity of the crude oil decreased with increased contact time of the adsorbents. Results indicated that chitosan was a better adsorbent than activated carbon and activated earth for FFA removal from crude catfish visceral oil.     

Water-in-oil microemulsion as mobile phase in thin-layer chromatographic retention studies of anions

A water-in-oil (W/O) microemulsion, consisting of sodium dodecyl sulphate (SDS)/1-pentanol/water/heptane, has been used as mobile phase for the separation of inorganic anions from their binary mixtures, for example, IO ₄ ⁻ -NO ₂ ⁻ , IO ₄ ⁻ -BrO ₃ ⁻ , IO ₄ ⁻ -I⁻, MnO ₄ ⁻ -BrO ₃ ⁻ , MnO ₄ ⁻ -NO ₂ ⁻ , and MnO ₄ ⁻ -Br⁻. The weight ratio, SDS/n-pentanol was kept constant at 1/2.46 for all compositions. The retention efficiency of anions on layers of silica gel G, alumina, microcrystalline cellulose, kieselguhr G, and mixtures of kieselguhr and cellulose in 4:1 and 3:2 ratios has been examined with the W/O microemulsion system as a mobile phase. Thin layers of kieselguhr were most useful for differential migration of anions. Quantitative separation of IO ₄ ⁻ from accompanying ions, limits of identification, and dilution of few anions are reported. The effects of amines, phenols, and heavy metals on the separation efficacy of IO ₄ ⁻ also have been investigated.     

An EPR study of Cu adsorption by clinoptilolite from Cl<Superscript>−</Superscript>, NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> and SO<Stack><Subscript>4</Subscript><Superscript>2−</Superscript></Stack> solutions

The concentration and the type of Cu²⁺ species adsorbed on a natural zeolite (Clinoptilolite) was measured and studied by using Electron Paramagnetic Resonance Spectroscopy (EPR). The EPR results together with macroscopic sorption data indicate that the solution ionic strength as well as, the type of electrolyte anion (Cl⁻, NO₃⁻ and SO₄²⁻ ions were examined) affect the amount of Cu adsorbed and the type of Cu surface complexes. The increasing in solution pH affects Cu adsorption quantitatively whereas; the type of surface complexes formed depends mainly on solution ionic strength. For low solution ionic strength, when the inhibition from solution species is limited, the adsorbed Cu is characterized by more than one type of chemical environment. On the contrary, for high solution ionic strength the Cu adsorption is inhomogeneous and EPR spectra show only one type of surface complex. When the anions of the background electrolytes are different, but of equal normality, the results indicate that in the presence of SO₄²⁻ discernible Cu surface complexes are formed whereas, for Cl⁻ and NO₃⁻ these surface formations are obtained only for high Cu adsorbed concentrations.     

Perchlorate removal in aqueous solutions using periodic mesoporous organosilicas (PMOs) functionalized with quaternary ammonium groups

Perchlorate anion (ClO₄⁻) in water has become an environmental issue of concern because it can impair proper functioning of the thyroid gland. For the removal of perchlorate anions from water, adsorption using anionexchange resins has been generally used as the most suitable method. In this work, we prepared periodic mesoporous organosilica materials (PMOs) functionalized with quaternary ammonium ligands, and used them for the removal of perchlorate anions from aqueous solutions. The physical and chemical properties of prepared samples were measured using nitrogen adsorption-desorption measurement, elemental analyses, X-ray diffractometer, and infrared spectrometer. We also investigated equilibrium isotherms for the measurement of adsorption capacities and kinetic performance of the prepared samples.     

Adsorption and desorption of m-xylene vapor on organically modified montmorillonite

m-Xylene vapor was adsorbed to organically modified montmorillonite (organoclay). Hexadecyltrimethylammonium (HDTMA) was used to modify the surface of the clay. In adsorption experiments, the organoclay, along with the non-modified (washed) clay, was used. m-Xylene was adsorbed from a gaseous phase by using a fixed adsorption bed. The adsorption breakthrough curves and the adsorption isotherms were determined at three different temperatures (24, 34, and 44 °C). The adsorption data were modeled with the BET isotherm equation. It was found that the adsorption isotherms of washed clay exhibited a favorable Type I behavior, which implies that the adsorption capacity is strongly dependent on vapor concentration at low concentration ranges. In regards to the organoclay, isotherms showed a marginally favorable Type II behavior with a reduced adsorption capacity at low concentrations, and exhibited a linear increase at elevated vapor concentrations. The adsorption capacity of both washed clay and organoclay obviously decreased with the temperature. The desorption of m-xylene from the clays was also performed by using pure nitrogen, and the desorption rate constant k was on the order of 10⁻⁵ min⁻¹ for all types of clay.     

Granulation of Fe-Al-Ce nano-adsorbent for fluoride removal from drinking water by spray coating on sand in a fluidized bed

A technology for the granulation of Fe-Al-Ce nano-adsorbent (Fe-Al-Ce) in a fluidized bed was developed. The coating reagent, a mixture of Fe-Al-Ce and a polymer latex, was sprayed onto sand in a fluidized bed. The granule morphology, coating layer thickness, granule stability in water and adsorption capacity for fluoride was investigated by analyzing samples for different coating time. The coating amount was from 3% to 36%. With increasing coating amount, granule stability decreased and adsorption capacity increased. FTIR analysis showed that the latex can react with active hydroxyl on the Fe-Al-Ce adsorbent, which led to a decrease of the adsorption capacity. Coated granules with a coating amount of 27.5% had a fluoride adsorption capacity of 2.22 mg/g (coated granules) at pH 7 and initial fluoride concentration of 0.001 M. A column test showed that 300 bed volumes can be treated with the effluent under 1.0 mg/L at an initial fluoride concentration of 5.5 mg/L, space velocity of 5 h^− 1 and pH of 5.8. The coating granulation of the Fe-Al-Ce adsorbent can produce granules that can be used in a packed bed for the removal of fluoride from drinking water.     

Effluent organic matter removal from reverse osmosis feed by granular activated carbon and purolite A502PS fluidized beds

Applying pre-treatments to remove dissolved organic matter from reverse osmosis (RO) feed can help to reduce organic fouling of the RO membrane. In this study the performance of granular activated carbon (GAC), a popular adsorbent, and purolite A502PS, an anion exchange resin, in removing effluent organic matter (EfOM) from RO feed collected from a water reclamation plant located at Sydney Olympic Park, Australia were evaluated and compared through adsorption equilibrium, kinetics and fluidized bed experiments. The maximum adsorption capacity (Q_max) of GAC calculated from the Langmuir model with RO feed was 13.4 mg/g GAC. The operational conditions of fluidized bed columns packed with GAC and purolite A502PS strongly affected the removal of EfOM. GAC fluidized bed with a bed height of 10 cm and fluidization velocity of 5.7 m/h removed more than 80% of dissolved organic carbon (DOC) during a 7 h experiment. The average DOC removal was 60% when the bed height was reduced to 7 cm. When comparing GAC with purolite A502PS, more of the later was required to remove the same amount of DOC. The poorer performance of purolite A502PS can be explained by the competition provided by other inorganic anions present in RO feed. A plug flow model can be used to predict the impact of the amount of adsorbent and of the flow rate on removal of organic matter from the fluidized bed column.     

Equilibrium,kinetic and thermodynamic study of removal of reactive orange 12 on platinum nanoparticle loaded on activated carbon as novel adsorbent

The proposed research describes the synthesis and characterization of platinum nanoparticles loaded on activated carbon (Pt-NP-AC) and its efficient application as novel adsorbent for efficient removal of reactive orange 12 (RO-12). The influences of effective parameters following the optimization of variables on removal percentages, their value was set as 0.015 g Pt-NP-AC, pH 1, contact time of 13 min. At optimum values of all variables at 25 and 50 mgL⁻¹ of RO-12 enthalpy (ΔH⁰) and entropy (ΔS⁰) changes was found to be 59.89 and 225.076, respectively, which negative value of ΔG⁰ shows a spontaneous nature, and the positive values of ΔH⁰ and ΔS⁰ indicate the endothermic nature and adsorption organized of dye molecule on the adsorbent surface. Experimental data was fitted to different kinetic models including first-order, pseudo-second-order, Elovich and intra-particle diffusion models, and it was seen that the adsorption process follows pseudo-second-order model in consideration to intra-particle diffusion mechanism. At optimum values of all variables, the adsorption process follows the second-order kinetic and Langmuir isotherm model with adsorption capacity 285.143 mg g⁻¹ at room temperature.     

The antioxidant properties of lycopene concentrate extracted from tomato paste

Lycopene concentrate (LC) containing 50 wt% lycopene was extracted from tomato paste. The antioxidant properties of LC were evaluated by means of chemiluminescence in four models. The four models were superoxide anions generated from pyrogallol autoxidation, hydroxyl radicals from Fenton reaction, singlet oxygens from OH⁻−NaClO−H₂O₂, and lipid peroxidation from 2,2′-azobis(2-amidinopropane)dihydrochloride-induced γ-linolenic acid. LC was an effective scavenger toward superoxide anions, hydroxyl radicals, and singlet oxygens, and also it could effectively reduce lipid peroxidation. The 50% efficient concentrations (EC₅₀) toward superoxide anions, hydroxyl radicals, lipid peroxidation and singlet oxygen were 0.75, 0.05, 0.1, and 1 mg/mL, respectively. In addition, changes of antioxidant behaviors with time were investigated. The time requirements of LC for effectively scavenging superoxide anions, hydroxyl radicals, and inhibiting lipid peroxidation were not higher than 6, 6, and 18 s, respectively.     

An ultrasound assisted reductive method for preparation of MnO2: modification of XAD and application in removal of arsenic

ABSTRACT

A sonochemical reduction method of permanganate (MnO₄^?) was utilized for preparation of manganese dioxide (MnO₂) coating on the surface of XAD-4 resin. Characterization of the modified MnO₂-coated XAD-4 resin (MX-4) was done and sorption studies were carried out using arsenic (⁷⁶As) radiotracer. The adsorption capacity for As(III) and As(V) using MX-4 were 5.5 mg/g and 7.6 mg/g, respectively. The MX-4 resin was successfully applied for quantitative removal of arsenic from two ground water samples collected from arsenic contaminated regions of North 24 Parganas, West Bengal, India. A schematic mechanism of removal of arsenic by MX-4 beads was also suggested.