Tannin-based adsorbents from green tea for removal of monoaromatic hydrocarbons in water: Preliminary investigations

In this study, we report the adsorption of benzene and toluene from water using rarely reported tannin adsorbents. Tannin gel and tannin powder were synthesized by adding formaldehyde to green tea extract, while iron nanoparticles were synthesized by the addition of FeSO₄?·?7H₂O. The surface morphology of the synthesized adsorbents was determined using SEM and FTIR prior to application to contaminated water. The results show up to 88% removal of benzene and toluene in a batch system after 30?min of reaction time, with a higher rate of removal of toluene compared to benzene. A low pH value of 2 had an adverse effect on the tannin gel, reducing the total adsorption of benzene to approx. 37.5%. On the other hand, iron nanoparticles were least affected by the pH with an adsorption of 62.9% for benzene and 83.3% for toluene.     

Performance of acrylic monomer based terpolymer/montmorillonite nanocomposite hydrogels for U(VI) removal from aqueous solutions

Acrylic monomer based terpolymer/montmorillonite nanocomposite hydrogels (NH-MMTs) synthesized using 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), 2-acrylamido-2-methlypropane sulfonic acid (AMPS) and 2-hydroxyethyl methacrylate (HEMA) in the aqueous montmorillonite (MMT) suspension were employed as adsorbents for U(VI) removal from aqueous solutions. Adsorption efficiency of the NH-MMTs was strongly enhanced by increasing pH in the range of 3–6. Adsorption capacity of the NHs increased with the MMT weight ratio up to 1% and the complete removal of U(VI) from 1 mmol/L aqueous solutions was achieved by 2 g/L polymer but further increase of MMT up to 6% caused a gradual decrease in adsorption percentage up to 57%. Nearly 98% of U(VI) loaded on the adsorbents could be recovered by 0.1 M HNO₃. Consecutive adsorption/desorption cycles showed that the NH-MMTs are re-usable. Kinetic results were analyzed using Paterson's and Nernst Planck approximation's based on homogeneous solid phase diffusion (HSPD). Experimental data were fitted to equilibrium isotherm models, Langmuir, Freundlich, Dubinin–Radushkevich and Temkin. SEM, and FTIR analysis of bare and U(VI) loaded adsorbents were used to elucidate adsorption mechanisms. The results showed that the NH-MMTs tested in this study are very promising for the recovery of U(VI) from water.     

Preparation of natural gas adsorbents from high-sulfur petroleum coke

HSPC (high-sulfur petroleum coke) has been used as precursor in the preparation of natural gas adsorbents with chemical activation. The effects of activating parameters, such as activating temperature and duration, on the pore-structure of adsorbents and methane uptake were investigated systematically in this study. The results show that the adsorbents derived from HSPC have comparable pore-structural characteristics and methane uptake to that derived from LSPC (low-sulfur petroleum coke). As evidenced by methane adsorption measurements, the highest deliverable capacity of methane, 129.7 v/v at 3.5 MPa and 25 °C, is obtained on HSR4 prepared at activating agent/coke mass ratio of 4:1. Furthermore, sulfur distribution analyses show that the sulfur in HSPC was almost removed by chemical activation and that sulfur content of as-synthesized adsorbent was as low as 0.18 wt% for HSR4. This study shows that HSPC could be used potentially as a good precursor to prepare high quality adsorbents with lower cost.     

Comparison of Basic Dye Crystal Violet Removal from Aqueous Solution by Low-Cost Biosorbents

Abstract

The removal of basic dye crystal violet by low-cost biosorbents was investigated in this study using a batch experimental system. The adsorption of crystal violet onto various adsorbents was solution pH-dependent and the maximum removal occurred at basic pH 10.0. The kinetic experimental data were analyzed using pseudo-first-order and pseudo-second-order equations to examine the adsorption mechanism and the intraparticle diffusion model to identify the potential rate controlling step. These results suggested that the adsorption of crystal violet onto various adsorbents was best represented by the pseudo-second-order equation. The suitability of the Langmuir and Freundich adsorption isotherms to the equilibrium data was also investigated at various temperatures for all four sorbents and the adsorption isotherms exhibited Freundlich behavior. The Freundlich constant K_f was 1.55 for alligator weed, 2.33 for Laminaria japonica, 9.59 for rice bran and 5.38 (mg/g)/(mg/L)^1/n for wheat bran, respectively at adsorbent concentration 5 g/L, pH 10.0 and 20°C. The thermodynamic parameters (ΔH, ΔG, and ΔS) were calculated and the results showed that the adsorption process for various adsorbents was spontaneous, endothermic, with an increased randomness, respectively. The particle size and the reaction temperature exhibited an insignificant impact on the adsorption equilibrium of crystal violet. The adsorbents investigated could serve as low-cost adsorbents for removing the crystal violet from aqueous solution.     

Various carbon-based MgAl2O4 adsorbents and their removal efficiency of CR dye and antibiotics in aqueous media: High selective adsorption capacity,performance prediction and mechanism insight

Various carbon -based MgAl₂O₄ (MAO) adsorbents were synthesized by a simple ultrasound irradiation technology with the activated carbon (AC), carbon quantum dots (CQDs), C₃N₄ (CN) and graphene oxide (GO) as carbon sources. The optimum synthesis conditions for the carbon -based MAO adsorbents were determined by the study of the addition of different types of carbon and different mass ratios of m_{Various carbon}: m_MAO = 2.5%, 5.0%, 7.5% and 10%. The carbon -based MAO adsorbents were used for the adsorption of Congo red (CR) dye, tetracycline hydrochloride (TCH), oxytetracycline hydrochloride (OCH), ciprofloxacin (CIP), naproxen sodium (NPS) and tetrabromobisphenol A (TBBPA) and the seven factors affecting the adsorption behavior were discussed, including the type of carbon, AC content, initial dye concentration (C_CR), adsorbent dosage (C_{carbon -based MAO adsorbents}), adsorption time (A_t), pH value and reaction temperature (T). The corresponding adsorption isotherm models such as Langmuir, Tempkin, Koble-Corrigan, Toth and Freundlich models and thermodynamics of carbon -based MAO adsorbents for the adsorption of CR dye were also studied. When pH = 7.8, C_CR = 200 mg/L, A_t = 90 min, T = 287 K and C_{AC 5.0 wt%-MAO} = 1 g/L, the removal rate of CR dye reaches 89.7%. The back propagation (BP) neural network model was used to predict the adsorption percentage of carbon-based MAO adsorbents, which was consistent with the experimental results. The high adsorption capacity of AC 5.0 wt%-MAO adsorbents for the adsorption of CR dye can be assigned to the synergistic effects of electrostatic interaction, intermolecular force, n-π interaction and hydrogen bonding, while for the adsorption of TCH, OCH and CIP can be ascribed to the electrostatic interaction. This study demonstrated a huge potential of carbon -based MAO adsorbents as an eco-friendly adsorbent for the adsorption of dyes and drugs.     

Adsorption of anionic dye on eco-friendly synthesised reduced graphene oxide anchored with lanthanum aluminate: Isotherms,kinetics and statistical error analysis

In the present study we made an effort to deploy eco-friendly synthesized reduced graphene oxide/Lanthanum Alluminate nanocomposites (RGO-LaAlO₃) and Lanthanum Alluminate (LaAlO₃) as adsorbents to remove dye from the synthetic media. XRD, SEM, BET surface area and EDX have been used to characterize the above-mentioned adsorbents. The impacts of different factors like adsorbent dosage, the concentration of adsorbate and PH on adsorption were studied. The best fit linear and nonlinear equations for the adsorption isotherms and kinetic models had been examined. The sum of the normalized errors and the coefficient of determination were used to determine the best fit model. The experimental data were more aptly fitted for nonlinear forms of isotherms and kinetic equations. Pseudo-second-order and Freundlich isotherm model fits the equilibrium data satisfactorily. Methyl orange (MO) has been used as model dye pollutant and maximum adsorption capacity was found to be 469.7 and 702.2 mg g^?1 for LaAlO₃ and RGO-LaAlO₃, respectively.     

Removal of thiophenic compounds from liquid fuel by different modified activated carbon cloths

The adsorption behavior of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from n-heptane was investigated onto activated carbon cloth (ACC) and its modified forms at 30 °C in batch condition. ACC was modified by HNO₃, (NH₄)₂S₂O₈, H₂SO₄, HCl and NaOH at ambient temperature. The adsorbents were characterized using nitrogen adsorption/desorption. It was found that the adsorbents are mainly microporous but differ in their surface chemistry, which is related to the effect of oxidizing agent. The adsorption process was studied from both equilibrium and kinetics point of view. The equilibrium experimental data were fitted to the Langmuir, Freundlich and Langmuir-Freundlich by non-linear method. Among the tested adsorbents, the modified ACC with HNO₃ (ACC-HNO₃) had the highest capacity for adsorption of DBT. Kinetic characterization of the adsorption process indicated that the mixed-order and modified pseudo-n-order models can describe the kinetics of adsorption of thiophenic compounds onto ACCs. The ACC and ACC-HNO₃ were used to test the removal efficiency of total sulfur contents (BT, DBT and DMDBT, 150 ppmw for each of them), too. The effect of shaking and ultrasound methods and also temperature and time on the regeneration of saturated ACC-HNO₃ with DBT was studied.     

Adsorption of carbon dioxide, ethane, and methane on titanosilicate type molecular sieves

The separation of carbon dioxide from light hydrocarbons is a vital step in multiple industrial processes that could be achieved by pressure swing adsorption (PSA), if appropriate adsorbents could be identified. To compare candidate PSA adsorbents, carbon dioxide, methane, and ethane adsorption isotherms were measured for cation exchanged forms of the titanosilicate molecular sieves ETS-10, ETS-4, and RPZ. Mixed cation forms, such as Ba/H-ETS-10, may offer appropriate stability, selectivity, and swing capacity to be utilized as adsorbents in CO₂/CH₄ PSA processes. Certain cation exchanged forms of ETS-4 were found to partially or completely exclude ethane by size, and equivalent RPZ materials were observed to exclude both methane and ethane, while allowing carbon dioxide to be substantially adsorbed. Adsorbents such as Ca/H-ETS-4 and Ca/H-RPZ are strong candidates for use in PSA separation processes for both CO₂/C₂H₆ and CO₂/CH₄, potentially replacing current amine scrubber systems.     

Fast removal of ammonium nitrogen from aqueous solution using chitosan-g-poly(acrylic acid)/attapulgite composite

In this work, a novel composite adsorbent with three-dimensional cross-linked polymeric networks based on chitosan (CTS) and attapulgite (APT) was prepared via in situ copolymerization in aqueous solution, and its efficacy for removing ammonium nitrogen (NH₄⁺-N) from synthetic wastewater was investigated using batch adsorption experiments. In the adsorption test, the pH effect, adsorption kinetics, isotherms, and desorbability were examined. A comparison between as-prepared adsorbent and clay, powdered activated carbon (PAC), and other reported adsorbents was also carried out. The results indicate that as-prepared composite adsorbent is pH-dependent and has faster adsorption kinetics and higher adsorption capacity. At natural pH, the composite adsorbent with 20 wt.% APT can adsorb 21.0 mg NH₄⁺-N per gram, far higher than the other adsorbents involved. The adsorbed NH₄⁺-N can be completely desorbed by 0.1 mol/L NaOH within 10 min. All information obtained give an indication that the composite can be used as a novel type, fast-responsive and high-capacity sorbent material for NH₄⁺-N removal.     

Statistical condensation adsorption isotherms of gas molecules adsorbed on porous adsorbents, surface monolayer adsorption isotherms and hysteresis phenomena

Condensation adsorption isotherms of type IV (or V) according to BDDT classification on porous adsorbents composed of one or two groups of adsorption sites are derived statistically. When Β_c1 (or Β_c2) is less than unity, the isotherm becomes type IV, and when it is greater than unity, the isotherm becomes type V. It is understood that the negative sign(-) of the additional adsorption energy, q, in the nth layer in deriving those theoretical isotherms plays a decisive role on the horizontally flat approach to the axis of the isotherm near the saturation vapor pressure. The values of the surface area can be calculated easily. The pore radii of all the adsorbents which we have obtained by using the derived isotherms with respect to the appropriately selected experimental data agree with those obtained by using the Kelvin equation. Many surface mono-layer adsorption isotherms are obtained in the process of deriving the various adsorption isotherms. From them we can learn that the surface sites are not adsorbed completely even near the saturated vapor pressure, and we can find the range of error by comparing them with v_ms of the BET equation. We could mention through judging the results of a great deal of the experimental isotherm data of types IV and V that “the cause of hysteresis phenomena of the condensation adsorption-desorption of gases is originated from the deviation from the thermodynamically reversible adsorption-desorption process in the condensation adsorption-desorption of gases”.     

ADSORPTION,KINETICS, AND EQUILIBRIUM STUDIES ON REMOVAL OF 4,4-DDT FROM AQUEOUS SOLUTIONS USING LOW-COST ADSORBENTS

The removal of a chlorinated pesticide (4,4-DDT) from aqueous solutions by a batch adsorption technique using different low-cost adsorbents was investigated. Two adsorbents, wood sawdust (A) and cork wastes (B), were used to determine adsorption efficiency. The influence of the adsorbent particle size and the organic matter of water (humic acids) on the removal process was studied. The obtained results were compared to those obtained with a commercial powdered activated carbon (PAC, F400, Chemviron) (C). Kinetic studies were performed to understand the mechanistic steps of the adsorption process. The rate of the adsorption kinetics of 4,4-DDT on the low-cost adsorbents was found best fitted with a pseudo-second-order kinetic model. This is in contrast to the rate of the adsorption kinetics of the PAC F400, which was best fitted with the Lagergren model. The application of the Morris-Weber equation showed that the adsorption process of 4,4-DDT on these adsorbents was complex. Both the adsorption on the surface and the intraparticle diffusion were the rate-controlling mechanisms. Langmuir and Freundlich adsorption isotherms were applicable to the adsorption process and their constants were evaluated. The adsorption capacity (q_m) calculated from the Langmuir isotherm (69.44 mg·g^?1, 19.08 mg·g^?1, and 163.90 mg·g^?1, respectively, for A, B, and C) showed that the process is highly particle size dependent, that the organic matter influenced the adsorption process negatively, and that wood sawdust is the most effective adsorbent for the removal of 4,4-DDT from aqueous solutions. The adsorbents studied exhibited a possible application in water decontamination, as well as in treatment of industrial and agricultural waste waters.     

煤层气在活性炭和炭分子筛上变压吸附分离

变压吸附分离是有效的气体分离提纯方法,采用合适的吸附剂可对煤层气(CH4/N2混合气体)进行高效分离,节约能耗。在单床吸附装置上测量了CH4/N2混合气体在3种活性炭和4种炭分子筛吸附柱上的穿透曲线,并进行实验研究再生条件对吸附剂分离性能的影响。实验结果表明,7种吸附剂均对CH4/N2混合气具有一定程度的分离能力,且高温真空再生后吸附效果更好;但仍需开发出更有效的吸附剂。     

Adsorption of Methyl Chloride on Molecular Sieves,Silica Gels,and Activated Carbon

Adsorption of methyl chloride (CH₃Cl or MeCl) on five different types of adsorbents was investigated experimentally at increasing pressures and room temperature. Prior to adsorption, all adsorbents were analyzed to assess their physical and chemical characteristics. The experimental data was then used to determine the adsorption isotherms, heats of adsorption, adsorption rates, and their respective theoretical models. The MeCl adsorption capacity was found to reasonably correlate with the adsorbent's surface area. The MeCl adsorption isotherm and adsorption rates were fitted for the first time to a Freundlich isotherm model and pseudo first-/second-order kinetic models, respectively. The range of heat of adsorption indicated a physisorption type of bonding; hence, the investigated adsorbents can potentially be regenerated for cyclic adsorption.     

Synthesis of bifunctional polymeric adsorbent and its application in purification of stevia glycosides

Polymeric adsorbents with both functions of adsorption and decolorization were synthesized by introducing quaternary ammonium groups (e.g. –N⁺(CH₃)₃ groups) into conventional resinic adsorbent used to adsorb stevia glycosides in production. The relation between the adsorption capacity of the bifunctional adsorbents for stevia glycosides and the structure of adsorbents, and that between the decolorization efficiency and the structure were investigated. The results revealed that the adsorption capacity for stevia glycosides decreased somewhat as the increase of the content of quaternary ammonium groups in the adsorbent, while the decolorization efficiency increased. Adsorbents containing about 0.6–0.8 mmol/g of –N⁺(CH₃)₃ groups showed both high adsorption capacity and high decolorization efficiency, and showed adsorptive selectivity for the small-sized components of stevia glycosides. Mechanism of adsorption and decolorization was also studied, and revealed that adsorption of stevia glycosides was based on hydrophobic interactions, but decolorization was based on both ion exchange and hydrophobic interactions. Introduction of –N⁺(CH₃)₃ groups into polymeric adsorbent also changed the adsorption selectivity for various stevia glycosides, and thus the bifunctional adsorbent could be used to prepare stevia glycosides with high content of rebaudioside A.     

Synthesis of electrically conducting composite adsorbents for wastewater treatment using adsorption & electrochemical regeneration

Electrically conducting adsorbent materials called Nyex™ 1000 & 2000 have already been reported with comparatively low adsorption capacity for various organic, biologically non-degradable and toxic compounds. Two composite adsorbents called CA₁ & CA₂ were synthesized using synthetic graphite-carbon black and expanded graphite-carbon black respectively. The aim of developing the new adsorbents was to increase the adsorption capacity along with good electrical properties. The developed adsorbents were characterized using N₂ adsorption for specific surface area, Boehm surface titration for surface chemistry, bed electrical conductivity, laser size analyzer for average particle size, and scanning electron microscope (SEM) for particle morphology and shape. Then both the composite adsorbents were tested for the adsorption of acid violet 17 followed by an electrochemical regeneration. The adsorption study revealed that both the adsorbents had almost similar kinetic behavior with a significant increase in adsorption capacity for acid violet 17 (300 & 26 mg g⁻¹ respectively) when compared with the adsorption capacity of previously developed electrically conducting materials called Nyex™ 1000 & 2000 (3.5 and 9 mg g⁻¹ respectively). The composite adsorbent CA₂ was successfully electrochemically regenerated by passing an electric charge of 138 C g⁻¹ at a current density of 14 mA cm⁻² for a treatment time of 60 min, whereas, the composite adsorbent CA₁ could not be regenerated successfully. The regeneration efficiencies of CA₂ were obtained at around 120% during five adsorption–regeneration cycles. The amount of actual charge passed of 138 C g⁻¹ for achieving 100% regeneration efficiency was found to be similar with stoichiometrically calculated amount of charge. The amount of electrical energy required to oxidize each mg of adsorbed acid violet onto CA₂ (24 J mg⁻¹) was found to be significantly lower to that of Nyex™ 1000 & 2000 adsorbents (52 J mg⁻¹ & 32 J mg⁻¹ respectively).     

Deep desulfurization of gasoline using ion-exchange zeolites: Cu(I)- and Ag(I)-beta

Solid adsorbents Cu(I) and Ag(I) metal exchanged beta zeolites were prepared by solid-state ion-exchange (SSIE) method. Crystallographic structure of the prepared adsorbents has been characterized by XRD analysis. The texture of the prepared adsorbents was investigated using N₂ sorption. Pyridine IR measurements have been carried out to investigate the nature of the acid sites of the adsorbents. The deep-desulfurization performance of such adsorbents has been evaluated through fixed-bed adsorption technique with model gasoline containing thiophene and benzothiophene at ambient temperature and pressure. The obtained results revealed that the breakthrough capacities of Cu(I)- and Ag(I)-beta zeolite with the optimized Cu⁺ or Ag⁺ content are 0.239 mmol S/g and 0.237 mmol S/g, respectively. The remaining sulfur in the desulfurized gasoline is less than 1 ppmw. Their desulfurization capacity for actual FCC gasoline blend is reduced about 30% due to the competitive adsorption from olefins and aromatics. However, The capacity regeneration of Cu(I)- and Ag(I)-beta zeolite sorbents was carried out for 9 times. It is more than 95% recovery of desulfurization after the first regeneration, and it keeps little reduction after subsequent 8 times of regeneration. Such studies included the effect factors on desulfurization performance, such as metal exchange content, SiO₂/Al₂O₃ ratio, acidity, and other texture properties of the zeolite etc.     

Study of the adsorption of phenol by two soils based on kinetic and isotherm modeling analyses

Various natural adsorbents, which have been in used for removal of pollutants, in general, and phenol, in particular, are mostly directed towards improving the adsorption capacity of the adsorbents by various pretreatments (chemical, thermal or biological), which necessarily lead to increase in the cost as well as in the level of difficulties in regeneration/disposal of the adsorbent. The present studies, on the other hand, are aimed towards evaluating the feasibility of using two common soils as potential low-cost adsorbents for the removal of phenol from its aqueous solution, in their natural forms (i.e., without any pretreatment). Accordingly, experiments were carried out (in batch mode) for optimization of the adsorption parameters (such as pH, contact time, equilibrium time and adsorbent dosage), for varying initial phenol concentrations. The results showed that the maximum phenol adsorption capacity was found at pH ~6, under a constant temperature of 30 ± 2 °C (at 6-hour equilibrium period). Several kinetic models (viz. Lagergren first-order, pseudo-second-order, Elovich and intra-particle diffusion) as well as isotherm models (Langmuir, Freundlich, Redlich and Peterson and Sip) were applied to the experimental data. The pseudo-second-order model was found to be the most suitable model describing the adsorption of phenol by two soils (which indicated this adsorption as a chemisorption process). On analysis of equilibrium isotherms for the adsorption of phenol by two soils, Redlich-Peterson and Sip isotherms were found to be the best representative for phenol-sorption on two selected, soil adsorbents.     

Adsorption of Congo Red from Aqueous Solutions Using Chitosan Hydrogel Beads Formed by Various Anionic Surfactants

The structural organization of chitosan hydrogel beads (CSBs) formed by various anionic surfactants, sodium dodecyl sulfate (SDS), sodium decyl sulfate (DS), dodecyl benzenesulfonic acid sodium salt (SDBS), and dioctyl sulfosuccinate sodium salt (DSS), and their applications as adsorbents for environmental purifications were investigated using Congo red (CR) as a model dye. The adsorption capacities of CSB as a function of surfactant concentration revealed that CSBs formed by 5 g/L anionic surfactant were the most effective for CR adsorption. The structure of CSBs and their adsorption capacities for CR depend on the nature of anionic surfactants. The maximum adsorption capacities of CSB_SDS, CSB_DS, CSB_SDBS, and CSB_DSS obtained from the Langmuir isotherm model were 186.02, 209.28, 207.25, and 113.83 mg/g, respectively, indicating that CSB_DS was the best adsorbent for CR.     

Adsorptive interaction of bisphenol A with mesoporous titanosilicate/reduced graphene oxide nanocomposite materials: FT-IR and Raman analyses

Nanocomposite materials containing graphene oxide have attracted tremendous interest as catalysts and adsorbents for water purification. In this study, mesoporous titanosilicate/reduced graphene oxide composite materials with different Ti contents were employed as adsorbents for removing bisphenol A (BPA) from water systems. The adsorptive interaction between BPA and adsorption sites on the composite materials was investigated by Fourier transform infrared (FT-IR) and Raman spectroscopy. Adsorption capacities of BPA at equilibrium, q _e (mg/g), decreased with increasing Ti contents, proportional to the surface area of the composite materials. FT-IR observations for fresh and spent adsorbents indicated that BPA adsorbed onto the composite materials by the electrostatic interaction between OH functional groups contained in BPA and on the adsorbents. The electrostatic adsorption sites on the adsorbents were categorized into three hydroxyl groups: Si-OH, Ti-OH, and graphene-OH. In Raman spectra, the intensity ratios of D to G band were decreased after the adsorption of BPA, implying adsorptive interaction of benzene rings of BPA with the sp² hybrid structure of the reduced graphene oxide.