Adsorptive removal of Cd(II) from contaminated water via hexavalent molybdenum-containing layered double hydroxide: Ni/Mo-LDH

This article states the first application of nickel/molybdenum-layered double hydroxide (LDH) as a new adsorbent for the removal of cadmium ions [Cd(II)] from aqueous solutions. The essential structure of Ni/Mo-LDH of di and hexavalent cations was elucidated by X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transmission infrared spectroscopy. The maximum adsorption capacity of adsorbent is 53.6 mg g^?1 at a temperature of 298 K, pH of 5.5, mass of 0.5 g L^?1, time of 105 min, and initial concentration of 175 mg L^?1. This adsorbent was distinguished by self and fast separation from adsorption media due to its layered, mesoporous structure and the presence of hexavalent molybdenum cation.     

改性蛋壳材料对重金属离子的去除机理研究

以废弃蛋壳为主要原料,通过微波法和铁改性法分别合成吸附材料ME和FE,采用扫描电镜、X射线衍射以及比表面积分析仪进行表征,并考察材料对废水中Cu~(2+)、Cd~(2+)、Pb~(2+)的吸附性能及其影响因子(反应时间、吸附剂投加量、重金属离子初始质量浓度以及溶液pH)。结果表明:ME对Cu~(2+)、Cd~(2+)的吸附效果较好,当废水中Cu~(2+)、Cd~(2+)的初始质量浓度为50 mg·L~(-1)、ME的投加量为0.6 g·L~(-1)、pH=4时,反应20 min后,ME对Cu~(2+)、Cd~(2+)的去除率均高达100%,其饱和吸附量分别为179.2、183.6 mg·g~(-1);FE对Pb~(2+)的吸附效果较好,当废水中Pb~(2+)的初始质量浓度为50 mg·L~(-1)、pH=6时,FE对Pb~(2+)的饱和吸附量可达87.23 mg·g~(-1),Langmuir吸附等温方程可较好地描述该吸附过程。     

Chromium(VI) Adsorption by Brown Coals

The ability of brown coals (leonardites) to remove chromium(VI) from aqueous solutions was studied as a function of pH, contact time, adsorbent nature, and concentration of metal solutions. The adsorption of Cr(VI) was higher between pH 2.0 and 3.0 for all brown coals and maximum sorption was observed at pH 3.0. The Langmuir adsorption isotherm was used to describe observed sorption phenomena, and the constants were evaluated. The maximum adsorption capacity of 0.92 mmol of Cr(VI)/g for YK, 0.98 mmol of Cr(VI)/g for KK was found from experimental data. KK was the best among the selected adsorbents for the sorption of Cr(VI) at pH 3 and the sorption was 81% out of 100 ppm Cr(VI) after 120 min of stirring.     

Use of adsorbents for thermal energy storage of solar or excess heat: improvement of energy density

The current paper describes the design of a prototype system to explore the feasibility of the adsorption thermal energy storage. Water was chosen as the adsorbate, and three different adsorbents were tested. Zeolite 13X, NaLSX zeolite, and an activated alumina (AA)/zeolite 13X composite adsorbent were used as adsorbents. Experiments were performed at varying flow rates and different relative humidities to determine the optimal operating conditions for the system. The regeneration of the adsorbents also was explored by performing repeated runs on the same adsorbent sample. The results indicate that complete regeneration was achieved. A maximum energy density of 160 kWh/m³ has been achieved with the AA/13X adsorbent, and this adsorbent was chosen for further studies. After this adsorbent screening, the system was modified to improve the data recording and system performance. Tests were performed on AA/13X, and a maximum energy density of 200 kWh/m³ was achieved, which was much higher than the maximum energy density reported in the literature for adsorption thermal energy storage systems (165 kWh/m³). Copyright © 2012 John Wiley & Sons, Ltd.     

Phosphate adsorption on chemically modified sugarcane bagasse fibres

Integral sugarcane bagasse fibres of about 2 cm length that were pre-treated for removal of greases and sugars were carboxymethylated on their surface, retaining about 20% of impurities (as insoluble material and water). The fibres were doped with Fe²⁺ ion, by dipping in aqueous iron chloride solutions of different concentrations. This material was used to remove phosphate from water. Thermal analyses (differential scanning calorimetry – DSC) and infrared spectroscopy – FTIR show the occurrence of important changes on carboxymethylated fibres after incorporation of Fe²⁺ and PO₄^3-. Non-carboxymethylated fibres, also treated with the iron solutions, also showed a good level of capture of phosphate from an aqueous solution. The chemical modification increases Fe²⁺ ion adsorption on the fibre surface, increasing the efficiency of phosphate adsorption. Apparently, the process of modification, without incorporation of Fe²⁺, also improves phosphate retention. When about 4% of iron is adsorbed on the fibres, 97% of phosphate is captured on the carboxymethylated material and 94% on the non-carboxymethylated material. The absorption data fit both the Langmuir and Freundlich isotherm. When quantified by measuring the monolayer adsorption in the Langmuir isotherm model, the presence of Fe²⁺ ions on the surface fibres increases the phosphate adsorption capacity by about 45%. Our results (Q max = 152 mg/g) are far superior or in the same order of magnitude, when compared with literature data, with the advantage be the raw material, waste of biomass, only somewhat changed chemically and even after the modifications compose materials harmless to the environment.     

Gaseous mercury removal using biogenic porous silica modified with potassium bromide

Rice husk, as an abundant agricultural waste and renewable biomass, is adopted to produce porous silica which is used as a potential carbon-free adsorbent for mercury emission control of coal-fired power plants. The rice husk derived porous silica (RHS) exhibits a good Hg⁰ adsorption capability with Hg⁰ removal efficiency above 80% in the temperature range of 60–140 °C, which is plausibly due to the big specific surface area and mesoporous structure. The mercury removal performance of RHS can be evidently reinforced by KBr modification. The optimal KBr loading value and reaction temperature are 2 wt% and 140 °C, respectively. Acidic gas components, such as NO and SO₂, both show slight inhibitive effects on Hg⁰ adsorption process probably owing to the competitive adsorption or the elimination of adsorption sites.     

Adsorption Kinetics Emulation With Lattice Gas Cellular Automata

ABSTRACT

Lattice gas cellular automata (LGCA), as a fluid dynamic simulation method, are conceptually simple and can be applied to deal with thermal interface effects to a wide array of boundary conditions. Based on LGCA, the lattice Boltzmann method has been successfully used to model a number of typical continuous fluid dynamic problems. In this research, however, we extend the general Frisch, Hasslacher, and Pomeau method from LGCA to the microscopic scale to emulate the surface adsorption process. Specifically, hexagonal grids topology and geometry are applied in two dimensions with 6-bit digits to represent different states of each grid node. The rule space is then determined as 6⁶. A two-dimensional porous network is constructed for simulating a practical adsorbent material structure. The lattice gas collision and movement are implemented within periodic space boundary conditions. Local rules of lattice gas interaction with network surface are defined and examined. The adsorption probabilities on each adsorptive site, corresponding to adsorption potential with relationship to temperature, are taken into account. As a result, an intuitive visualization of physical surface adsorption kinetics is achieved.     

A parametric study on isobaric adsorption process in a closed adsorbent bed

A numerical study on heat and mass transfer in an annular adsorbent bed filled with adsorbent granules for an isobaric adsorption process is performed. In order to reduce the number of independent parameters that influences heat and mass transfer in the bed, the governing equations and related initial and boundary conditions for the problem are non-dimensionalized and this yields two dimensionless parameters as G and Γ. The G dimensionless parameter is the ratio of heat of adsorption to sensible heat stored by adsorbent particle and Γ parameter compares mass diffusion within the adsorbent particle and heat diffusion in the radial direction of the adsorbent bed. The obtained results show that the total dimensionless time for an adsorption process can be reduced by increasing of Γ value. The total dimensionless time is independent from G for low values of Γ (i.e. Γ = 10^− 5). The results also show that the instantaneous equilibrium model can provide accurate results only for an adsorbent bed with a low value of Γ (i.e. Γ = 10^− 5). The present study is performed for Γ values from 10^− 5 to 1 and G value from 1 to 100.     

Removal of Cu2+ and Pb2+ in aqueous solutions by fly ash

In this study, the removal of Cu²⁺ and Pb²⁺ ions by precipitation from aqueous solutions by using six fly ashes with different compositions was achieved. The effect of four parameters on the removal of Cu²⁺ and Pb²⁺, which are contact time, fly ash composition, pH of the solution and fly ash concentration, were investigated. The fly ash concentrations required to achieve maximum Cu²⁺ and Pb²⁺ removal were found to vary between 0.2–10 and 0.075–3.5 g/l, respectively. It was also observed that both the Cu²⁺ and Pb²⁺ removal capacities of the fly ashes depend strongly on their CaO content.     

Effect of synthesis methods on magnetic Kans grass biochar for enhanced As(III,V) adsorption from aqueous solutions

Magnetic biochar is increasingly known as a multi-functional material and the appropriate synthesis method further increase its efficient applications. In this study, the effects of synthesis methods on the fabrication of Kans grass straw/biochar (KGS/KGB) with Fe³⁺/Fe²⁺ by chemical co-precipitation and subsequently pyrolyzing at 500 °C for 2 and 4 h were studied in details, and compared their As(III, V) adsorption potentials under different operating conditions. Magnetic biochars (MKGB3 and MKGB4) prepared from KGS revealed of superior Fe₃O₄ loading, higher As(III, V) adsorption efficiency and saturation magnetization (45.7 Am² kg⁻¹) than that of KGB (MKGB1 and MKGB2). Moreover, Thermogravimetric analysis (TGA) demonstrated three stages of decomposition and the MKGB3 and MKGB4 generated higher residual mass (>60%) at stage 3 (1000 °C) due to greater Fe₃O₄ composite in biochar matrix and turned to be thermally more stable. As(III) and As(V) adsorption equilibrium data well fitted in Langmuir model and followed the order: MKGB4 > MKGB3 > MKGB2 > MKGB1. The maximum As(III) and As(V) adsorption capacities were about 2.0 mg g⁻¹ and 3.1 mg g⁻¹, respectively. The data best fitted in pseudo-second-order (R² > 0.99) rather than pseudo-first-order kinetics model indicating of more complex mechanism. The adsorption of As(III) and As(V) was found to decrease with increasing in ionic strength of competing ions and PO₄³⁻ was found to strongly inhibit arsenic adsorption. Highest desorption was achieved at pH 13.5 using NaOH. This study suggests that selective adsorbent synthesis method could be useful to prepare effective adsorbent for toxic metals immobilization.     

A dimensionless analysis of heat and mass transport in an adsorber with thin fins; uniform pressure approach

A numerical study on heat and mass transfer in an annular adsorbent bed assisted with radial fins for an isobaric adsorption process is performed. A uniform pressure approach is employed to determine the changes of temperature and adsorbate concentration profiles in the adsorbent bed. The governing equations which are heat transfer equation for the adsorbent bed, mass balance equation for the adsorbent particle, and conduction heat transfer equation for the thin fin are non-dimensionalized in order to reduce number of governing parameters. The number of governing parameters is reduced to four as Kutateladze number, thermal diffusivity ratio, dimensionless fin coefficient and dimensionless parameter of Γ which compares mass diffusion in the adsorbent particle to heat transfer through the adsorbent bed. Temperature and adsorbate concentration contours are plotted for different values of defined dimensionless parameters to discuss heat and mass transfer rate in the bed. The average dimensionless temperature and average adsorbate concentration throughout the adsorption process are also presented to compare heat and mass transfer rate of different cases. The values of dimensionless fin coefficient, Γ number and thermal diffusivity ratio are changed from 0.01 to 100, 1 to 10^− 5 and 0.01 to 100, respectively; while the values of Kutateladze number are 1 and 100. The obtained results revealed that heat transfer rate in an adsorbent bed can be enhanced by the fin when the values of thermal diffusivity ratio and fin coefficient are low (i.e., α^? = 0.01, Λ = 0.01). Furthermore, the use of fin in an adsorbent bed with low values of Γ number (i.e. Γ = 10^− 5) does not increase heat transfer rate, significantly.     

Biosorptive removal of Pband Cd onto novel biosorbent: Defatted Carica papaya seeds

Carica papaya seeds, an agricultural waste in Nigeria, were defatted to obtain defatted C. papaya seed biosorbent. The Fourier Transformed Infrared spectrum of defatted C. papaya seed biosorbent suggests the presence of CO, OH of carboxylic acid, lactonic and amide band functional groups. The adsorption of metal ion onto defatted C. papaya seed biosorbent led to small shifts in the IR bands. The adsorption capacity of defatted C. papaya seed biosorbent was evaluated to be 1666.67 mg/g for Pb²⁺ and 1000.00 mg/g for Cd²⁺. In binary metal ion solution, the defatted C. papaya seeds showed decreased adsorption capacity for either metal ion. The influence of different particle sizes was found to have negative impact on the adsorption capacity of C. papaya seed biosorbent in the removal of Pb²⁺ and Cd²⁺ from aqueous solution. The adsorption of both metal ions was observed to follow the Freudlich model better than the Langmuir model suggesting that the adsorption of both metal ions was on multisites on the defatted C. papaya seed biosorbent. The adsorption was found to be highly feasible, spontaneous and exothermic in nature. Optimization results suggests 5 m³ of 100 mg/L of Pb²⁺ and Cd²⁺ requires 43.3 and 49.2 kg of defatted C. papaya seeds to remove 95% of the metal ions from aqueous solution.     

Hydrogen purification using compact pressure swing adsorption system for fuel cell

Adsorption of CO and CO₂ in mixtures of H₂/CO/CO₂ was achieved using compact pressure swing adsorption (CPSA) system to produce purified hydrogen for use in fuel cell. A CPSA system was designed by combining four adsorption beds that simultaneously operate at different processes in the pressure swing adsorption (PSA) process cycle. The overall diameter of the cylindrical shell of the CPSA is 35 cm and its height is 40 cm. Several suitable adsorbent materials for CO and CO₂ adsorption in a hydrogen stream were identified and their adsorption properties were tested. Activated carbon from Sigma–Aldrich was the adsorbent chosen. It has a surface area of 695.07 m²/g. CO adsorption capacity (STP) of 0.55 mmol/g and CO₂ at 2.05 mmol/g were obtained. The CPSA system has a rapid process cycle that can supply hydrogen continuously without disruption by the regeneration process of the adsorbent. The process cycle in each column of the CPSA consists of pressurization, adsorption, blowdown and purging processes. CPSA is capable of reducing the CO concentration in a H₂/CO/CO₂ mixture from 4000 ppm to 1.4 ppm and the CO₂ concentration from 5% to 7.0 ppm CO₂ in 60 cycles and 3600 s. Based on the mixture used in the experimental work, the H₂ purity obtained was 99.999%, product throughput of 0.04 kg H₂/kg adsorbent with purge/feed ratio was 0.001 and vent loss/feed ratio was 0.02. It is therefore concluded that the CPSA system met the required specifications of hydrogen purity for fuel cell applications.     

Study of thermal conductivity,permeability, and adsorption performance of consolidated composite activated carbon adsorbent for refrigeration

Composite adsorbents, comprising activated carbon and expanded natural graphite, have been developed, and their thermal conductivity, permeability and adsorption performance were tested. The thermal conductivity varied with the ratio of activated carbon to expanded natural graphite. Thermal conductivity increased as the ratio of expanded graphite increased. Considering that the density of activated carbon for the composite adsorbent should not be lower than 200 kg/m³, otherwise the volumetric cooling capacity would be unacceptably low, the highest thermal conductivity obtained from experiments was 2.47 W m^?1 K^?1. The permeability was also measured, and the best result obtained was 4.378 × 10^?12 m². In order to evaluate the influence of heat and mass transfer on adsorption performance, the adsorption rate was tested using a Rubotherm magnetic suspension balance, and results showed that for the freezing conditions lower than ?10 °C the performance of granular activated carbon was better than that of solidified adsorbent because of the reduced mass transfer of ammonia at low saturated pressure. The adsorption performance of consolidated adsorbents increased rapidly when the evaporating temperature was higher than ?10 °C. When the evaporating temperature was 8 °C, the adsorption rate of consolidated adsorbent was improved by 29% if compared with that of granular adsorbent.     

Uptake of Metal Ions on Humic Acids

The kinetics, the sorption capacities, pH and temperature dependence of sorption of humic acids (HAs) of Turkish brown coals with respect to Zn(II), Cu(II), Ni(II), Co(II) and Pb(II) ions were investigated, and the roles of the carboxylic and phenolic groups in the adsorption of metals ion on HAs were searched in this work. These metal ions are able to form complex compounds with carboxylic and phenolic groups of HAs. Adsorption equilibrium was achieved in between 50 and 60 min for all studied cations. HAs extracted from different brown coals have been characterized by chemical and physical methods. The chemical properties of HAs showed differences depending on the source from which they were obtained. The sorption of metals on the surface of HAs depends strongly on the pH, and sorption decreases with decreasing pH. Maximum removal of metal ions was demonstrated at pH values of 4.1–5.0. The Langmuir adsorption isotherm was used to describe observed sorption phenomena. The Δ G ⁰ became negative as the temperature increased, and so the equilibrium constant decreased slightly. The investigation proved that the HAs are suitable materials for the studied heavy metal ion removal from aqueous solution and could be considered as potential material for purification of effluent polluted with toxic metal ions.     

Charcoal-methanol adsorption refrigerator powered by a compound parabolic concentrating solar collector

A compound parabolic concentrating solar collector (CPC) of concentration ratio 3.9 and aperture area 2.0 m² was used to power an intermittent solid adsorption refrigerator and ice maker using activated charcoal (carbon) as the adsorbing medium and methanol as the working fluid. The copper tube receiver of the CPC was packed with 2.5 kg of imported adsorbent 207E3, which was only utilised when the performance of activated charcoal (ACJ1, produced from local coconut shells) was found to be inferior to the imported adsorbent. Up to 1 kg of ice at an evaporator temperature of −6°C was produced, with the net solar coefficient of performance (COP) being of the order of 0.02. Maximum receiver/adsorbent temperature recorded was 154°C on a day when the insolation was 26.8 MJ/m⁻². Temperatures in excess of 150°C are undesirable since they favour the conversion of methanol to dimethyl ether, a noncondensable gas which inhibits both condensation and adsorption. The major advantage of this system is its ability to produce ice even on overcast days (insolation 10 MJ/M⁻²).     

Photocatalytic degradation and hydrogen evolution using bismuth tungstate based nanocomposites under visible light irradiation

In this work, Bi₂WO₆/PANI composites were synthesized for efficient removal of ciprofloxacin (CIP) from urban wastewater and production of hydrogen energy in the absence of sacrificial agents. The experimental study visualizes the formation of 2D based nanostructures and perceived that these nanostructures could provide more photocatalytic active-sites for removal of CIP and also increase the oxidation/reduction of water for hydrogen energy production. The PXRD showed excellent crystallinity/orthorhombic structure with crystallite size 10–23 nm. The Bi₂WO₆/PANI composites, compared to Bi₂WO₆, exhibited higher efficiency and stability for degradation of CIP and production of hydrogen energy. CIP was effectively degraded 98% by Bi₂WO₆/PANI (5%) and the effect of different parameters such as pH, catalyst-concentration, and effect of CIP-concentration was also analyzed. The hydrogen energy rate was 490.56 h⁻¹g⁻¹ by using Bi₂WO₆/PANI (5%). The improved photocatalytic performance of Bi₂WO₆/PANI composite was mainly ascribed to the unique hierarchical structures, harvesting extended absorption of visible light, higher surface area, and higher crystallinity. The current findings may provide new insights to fabricate nanomaterials for environmental and energy issues.     

Removal of malachite green (a toxic dye) from water by cobalt ferrite silica magnetic nanocomposite: Herbal and green sol-gel autocombustion synthesis

Cobalt ferrite-silica nanocomposites were synthesized in the presence of various amounts of Salix alba bark extract via the self-propagating sol-gel process. The structure, morphology and magnetic property of nanostructures was investigated and the adsorbent ability for the removal of malachite green (MG) dye from water through CoFe₂O₄SiO₂ has been reported. The products were characterized by XRD, SEM, TEM, FTIR and VSM techniques. The samples that were synthesized in the presence of more extract (20 mg extract) revealed no trace of impurity in XRD pattern and indicated more spherical and agglomerated particles on SEM images; in contrast other samples indicated Co₃O₄ as impurity besides rough and irregular spherical shapes. TEM images for sample SA20 (15.41 ± 0.65 nm size) illustrated narrow size distribution which is consistent with the SEM analysis. The saturation magnetization values continuously increase with the increasing Salix alba bark extract amount and reaches to 2.89 emu/g for SA20 sample. Investigation on MG adsorption isotherm and kinetic onto the nanocomposites were carried out as well. The experimental data best fitted to the Langmuir model and revealed a monolayer adsorption capacity of 75.5 ± 1.21 mg g^?1. The adsorption kinetic was found to follow pseudo-second-order kinetic model. Consequently, prepared nanocomposite can be used as an effective magnetic adsorbent for the MG removal from water.     

NOx reduction by CO over ASC catalysts in a simulated rotary reactor: Effect of reaction conditions

A rotary reactor, separated the NO_x removal process into adsorption stage and reduction stage, was utilized to remove the NO_x from the flue gas. The influences of various reaction conditions on the reactor were tested, i.e., oxygen concentration in the adsorption zone, time ratio of adsorption and reduction, gas hourly space velocity (GHSV) of the reactor, GHSV of the reduction zone and effect of H₂O and SO₂. The results showed that the synthesized ASC catalyst had higher deNO_x efficiency with the increasing of oxygen concentration in flue gas. Meanwhile, the GHSV of the reactor had an obvious influence on NO_x adsorption, and high NO_x adsorption and reduction efficiencies were observed at 10,000 h^?1. The optimal reaction conditions in this research were concluded as follows: oxygen concentration was 8%, time ratio of adsorption and reduction was 60 s: 60 s, GHSV of the adsorption zone was 10,000 h^?1 and GHSV of the reduction zone was 12,000 h^?1. While the water and SO₂ tolerance of catalysts was weak, and the catalysts would be inactivated when exposed to 100 ppm SO₂ in 1.5 h. Free nitrate ions were the main nitrate species on the catalyst surface. In situ DRIFT study showed that a large amount of free nitrate ions was released from the catalyst surface when the reduction time was increased from 30 s to 60 s, and much NO_x was adsorbed on the catalyst surface in the form of free nitrate ions when the oxygen concentration was 8%.     

Cu-Co-Al类水滑石的制备及其电催化还原硝酸盐研究

通过共沉淀法制备不同摩尔比的Cu-Co-Al类水滑石化合物,采用X射线衍射、场发射扫描电子显微镜对类水滑石物质进行表征。结果表明,Cu、Co、Al摩尔比即n(Cu~(2+)):n(Co~(2+)):n(Al~(3+))=2:1:1、1:2:1、1:1:2和1:1:1时均能形成结构良好的水滑石类化合物。将所制备的材料制成涂膜电极,利用线性伏安扫描法研究其电催化还原硝酸盐的效果,结果表明n(Cu~(2+)):n(Co~(2+)):n(Al~(3+))=2:1:1时电催化还原硝酸盐效果最好,其还原峰电流与硝酸盐浓度及扫描速率呈正相关。研究结果表明,Cu-Co-Al类水滑石涂膜电极可以用于硝酸盐的电化学检测与去除工艺过程中。