Initial Desorption Research Articles

Desorption Kinetics of Legacy Soil Phosphorus: Implications for Non-Point Transport and Plant Uptake

Soil phosphorus (P) solubility and kinetics partly control dissolved P losses to surface water and uptake by plants. While previous studies have focused on batch techniques for measuring soil P desorption kinetics, flow-through techniques are more realistic because they simulate P removal from the system, akin to runoff, leaching, and plant uptake. The objectives were to measure soil P desorption by a flow-through technique at two flow rates and several batch methods, and utilize both for understanding how flow rate impacts the thermodynamics and kinetics of soil P desorption. Desorption obeyed first-order kinetics in two different phases: an initial rapid desorption phase followed by a gradual release. Desorption was limited by equilibrium and the kinetics of physical processes as demonstrated by an interruption test. Dilution-promoted desorption occurred with increasing cumulative volume, which increased desorption rate via first-order kinetics. The batch tests that simulated cumulative solution volume and time of flow-through were similar to the flow-through results; however, the batch methods overestimated the desorption rates due to less limitations to diffusion. Fast flow rates desorbed less P, but at a greater speed than slow flow rates. The differences were due to contact time, cumulative time, and solution volume, which ultimately controlled the potential for chemical reactions to be realized through physical processes. The interaction between these processes will control the quantity and rate of desorption that buffer P in non-point drainage losses and plant uptake.

Temperature-pressure coupling effect on gas desorption characteristics in coal during low-variable temperature process

Accurate determination of coalbed methane (CBM) content can not only prevent and control coal and gas outburst disasters in mines, but also facilitate the prediction of coal seam methane resource reserves, which is significant for injecting carbon dioxide to enhance CBM recovery. The freezing core sampling technique proposed in recent years for accurate determination of the CBM content has faced temperature-pressure coupling effects on gas desorption in coalin a low-variable temperature environment. In this paper, we utilized a self-developed high-low temperature alternating adsorption-desorption experimental device to study the gas desorption process in coal under temperature-pressure coupling conditions in a low-variable temperature environment. The experimental results show that the main promotion and inhibition effects of temperature on the gas adsorption and desorption in coal in a low-temperature environment were consistent with those in an ambient temperature environment, i.e., the decrease of temperature promoted coal gas adsorption, while the increase of the temperature promoted coal gas desorption. It is found that throughout the temperature change process (TCP), there existed a ‘pseudo-desorption’ phenomenon, and the cumulative desorption amount showed a consecutive rising-declining-rising trend and finally stabilized. The whole process can be regarded as consisting of a main desorption process and a retrograde desorption process. In the main desorption process with the same TCP, the cumulative desorption amount and initial desorption rate increased with the increase of initial equilibrium pressure. In the retrograde desorption process, there existed a peak retrograde desorption rate, and the staged retrograde desorption amount conformed to the linear decrease law. A comprehensive analysis of the temperature-pressure coupling effect on gas desorption throughout the TCP was conducted. Thus, we proposed some considerations and precautions for the configuration and supply monitoring of the cold source in the process of the measurement of CBM content using the freeze-coring method.

Mechanism of Gas Desorption in Coal Particles under Different Positive Pressures: Experiments and Numerical Model

The inaccurate calculation of the gas lost is the principal cause of inaccurate determinations of the coalbed methane content via air reverse circulation sampling (ARCS). The positive pressure environment has a significant impact on gas desorption during the sampling process. To obtain the gas desorption mechanism of coal particles under positive pressure, positive pressure desorption experiments were conducted on coal samples with different particle sizes under different adsorption equilibrium pressures using a self-designed positive pressure desorption experimental device. And a positive diffusion model for coal particles was established, in which the diffusion coefficient was calculated based on the results of the positive desorption experiments. The diffusion model was then used to simulate the diffusion capacity of coal particles and compared with the test data. The results show that the responses of the positive pressure desorption and atmospheric pressure desorption to the adsorption equilibrium pressure are similar. The gas desorption velocity increases as the adsorption equilibrium pressure increases. Positive pressure can effectively inhibit gas desorption. The initial gas desorption velocity decreases as the positive pressure and coal particle size increase. Concurrently, the entire sample desorption process during ARCS can be divided into three stages: a slow desorption stage, an accelerated desorption stage, and an atmospheric desorption stage. The relationship between the diffusion coefficient and the positive pressure exhibits an exponential distribution, and the positive pressure diffusion model can describe the gas diffusion from coal particles well. The results of this study could help to establish a gas loss compensation model for the ARCS process.

Dynamic Effect of Gas Initial Desorption in Coals with Different Moisture Contents and Energy-Controlling Mechanism for Outburst Prevention of Water Injection in Coal Seams

Dynamic Effect of Gas Initial Desorption in Coals with Different Moisture Contents and Energy-Controlling Mechanism for Outburst Prevention of Water Injection in Coal Seams

Laboratory Study on Changes in Gas Desorption Properties of Anthracite after Cyclic Loading

Coal mass is subjected to cyclic loading during pulsating hydraulic fracturing (PHF), and changes in its gas desorption properties affect gas drainage. Therefore, it is of great importance to correctly understand the influences of cyclic loading on the gas desorption properties of coal mass. Firstly, loading tests with different frequencies and amplitudes were performed on anthracite from Qinshui Basin (Shanxi Province, China) using a fatigue testing machine. Secondly, gas desorption tests were performed to determine the associated curves for each test group at different equilibrium pressures, and the initial desorption capacity and diffusion coefficient of the gas were calculated. Finally, the influence of different loading conditions on the gas desorption laws were analyzed. The test results demonstrate that a greater loading frequency increases the ratio of the initial desorption capacity so that the desorption rate of coal samples is higher, and the gas desorption properties become increasingly better in the initial stage. However, variations in the amplitude have minimal impact on the ratio of the initial desorption capacity. When the amplitude is too large in the initial stage, the diffusion coefficient decreases and the gas desorption properties worsen. In addition, the above test results are used to discuss the selection of the amplitude and frequency in the PHF process from a macroperspective. The contained research results provide an important theoretical basis for the field application of PHF technologies in coal mines.

Study on the mechanism of the influence of HNO3 and HF acid treatment on the CO2 adsorption and desorption characteristics of coal

In order to cooperate with the application of acid fracturing enhanced permeability technology, this paper proposes using CO2 adsorption and desorption system and low-temperature nitrogen adsorption method to conduct experimental research on the changes in the CO2 adsorption and desorption characteristics of coal after treatment with HF solution and HNO3 solution. In addition, Combined with X-ray diffraction experiments, the indirect relationship between mineral dissolution and adsorption and desorption characteristics is analyzed. The research results show that: The acid solution transforms the pore structure of coal through the dissolution of mineral impurities. In the microporous stage, hydrofluoric acid is mainly used for pore formation and nitric acid for pore expansion. Acid treatment changed the adsorption characteristics of the coal sample, reduced the saturated adsorption capacity a, and increased the adsorption constant b. And a and b were linearly related to the specific surface area and pore volume, respectively. This paper has determined that adsorption equilibrium pressure 1.91 MPa and 2.57 MPa are the enhanced adsorption thresholds of hydrofluoric acid and nitric acid, respectively. After exceeding the threshold, acid treatment will no longer play a role in increasing CO2 adsorption. In addition, the acid treatment also changed the desorption characteristics of the coal sample, increased the initial desorption amount and the final desorption amount, shortened the desorption time. The effect of hydrofluoric acid was more evident than that of nitric acid.

The Improvement in Hydrogen Storage Performance of MgH2 Enabled by Multilayer Ti3C2.

MgH2 has become a hot spot in the research of hydrogen storage materials, due to its high theoretical hydrogen storage capacity. However, the poor kinetics and thermodynamic properties of hydrogen absorption and desorption seriously hinder the development of this material. Ti-based materials can lead to good effects in terms of reducing the temperature of MgH2 in hydrogen absorption and desorption. MXene is a novel two-dimensional transition metal carbide or carbonitride similar in structure to graphene. Ti3C2 is one of the earliest and most widely used MXenes. Single-layer Ti3C2 can only exist in solution; in comparison, multilayer Ti3C2 (ML-Ti3C2) also exists as a solid powder. Thus, ML-Ti3C2 can be easily composited with MgH2. The MgH2+ML-Ti3C2 composite hydrogen storage system was successfully synthesized by ball milling. The experimental results show that the initial desorption temperature of MgH2-6 wt.% ML-Ti3C2 is reduced to 142 °C with a capacity of 6.56 wt.%. The Ea of hydrogen desorption in the MgH2-6 wt.% ML-Ti3C2 hydrogen storage system is approximately 99 kJ/mol, which is 35.3% lower than that of pristine MgH2. The enhancement of kinetics in hydrogen absorption and desorption by ML-Ti3C2 can be attributed to two synergistic effects: one is that Ti facilitates the easier dissociation or recombination of hydrogen molecules, while the other is that electron transfer generated by multivalent Ti promotes the easier conversion of hydrogen. These findings help to guide the hydrogen storage properties of metal hydrides doped with MXene.

Effect of particle size on gas energy release for tectonic coal during outburst process

Based on the particle size evolution of tectonic coal in formation process, the differences between tectonic coal and intact coal in pore structure and initial gas desorption characteristics were studied. Then, the influences of particle size reduction on pore structure and initial gas desorption characteristics were investigated; and the initial gas energy release model was derived, which was used to calculate the gas expansion energy of tectonic coals with different particle sizes. This study concludes that the particle size of tectonic coal will be reduced under the pulverization effect during the formation process, and the particle sizes of these types of tectonic coal reach millimeter level or even smaller scale under pulverized state. The pore volume and specific surface area of minipores (pore size: 10–100 nm), mesopores (pore size: 100–1000 nm) and macropores (pore size: 1000–10000 nm) in tectonic coal are larger than those in intact coal by over 10 times. Tectonic coal’s average gas desorption rate in the first 10 s reaches up to 11.47 times of that of intact coal. Within the 5 particle size greater than 0.074 mm, the pulverization obviously transforms the minipores and mesopores in coals, but its effect on micropores (pore size: 0.9–10 nm) is limited. When the particles are pulverized to blow 0.074 mm, the micropores are obviously transformed. The initial gas energy release model for coal samples with different particle sizes is derived and verified through the experimental data. As calculated using the initial gas energy release model, the gas expansion energy will be reduced sharply with the particle size reduction when the particle size is smaller than 1 mm. Therefore, the particle size of tectonic coal decides its initial gas desorption capacity, which is of critical significance to the gas energy release in the outburst process. This study will be of great scientific significance for exploring the outburst mechanism and prevention.

Neighboring Pd single atoms surpass isolated single atoms for selective hydrodehalogenation catalysis

Single atom catalysts have been found to exhibit superior selectivity over nanoparticulate catalysts for catalytic reactions such as hydrogenation due to their single-site nature. However, improved selectively is often accompanied by loss of activity and slow kinetics. Here we demonstrate that neighboring Pd single atom catalysts retain the high selectivity merit of sparsely isolated single atom catalysts, while the cooperative interactions between neighboring atoms greatly enhance the activity for hydrogenation of carbon-halogen bonds. Experimental results and computational calculations suggest that neighboring Pd atoms work in synergy to lower the energy of key meta-stable reactions steps, i.e., initial water desorption and final hydrogenated product desorption. The placement of neighboring Pd atoms also contribute to nearly exclusive hydrogenation of carbon-chlorine bond without altering any other bonds in organohalogens. The promising hydrogenation performance achieved by neighboring single atoms sheds light on a new approach for manipulating the activity and selectivity of single atom catalysts that are increasingly studied in multiple applications.

In situ observation of shrinking and swelling of normal and compression Chinese fir wood at the tissue, cell and cell wall level

The shrinking and swelling of wood due to moisture changes are intrinsic material properties that control and limit the use of wood in many applications. Herein, hygroscopic deformations of normal and compression wood of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) were measured during desorption and absorption processes. The dimensional changes were observed in situ by an environmental scanning electron microscope and analyzed at different hierarchical levels (tissue, cell and cell wall). The relationship between moisture variation and hygroscopic deformation was measured. During initial desorption periods from 95 to 90 or 75% RH, an expansion of the lumen and a shrinkage of the cell wall were observed, revealing a non-uniform and directional deformation of single wood cells. The variation of shrinking or swelling at different hierarchical levels (tissue, cell and cell wall) indicates that the hygroscopic middle lamella plays a role in the deformation at the tissue level. Higher microfibril angles and helical cavities on the cell wall in compression wood correlate with a lower shrinking/swelling ratio. Normal wood showed a more pronounced swelling hysteresis than compression wood, while the sorption hysteresis was almost the same for both wood types. This finding is helpful to elucidate effects of micro- and ultrastructure on sorption. The present findings suggest that the sophisticated system of wood has the abilities to adjust the hygroscopic deformations by fine-tuning its hierarchical structures.

CO2 absorption and desorption using phase-separation gel

Phase-separation absorbent has attracted much attention to reduce energy consumption for CO2 capture, storage and utilization. In this work, to improve handling of the absorbents, we have developed a new semi-solid absorbent, phase-separation gel, which became clouded gel by CO2 absorption and returned to transparent by CO2 desorption. We measured amounts of CO2 absorption at 50 ˚C and desorption at 90 ˚C with 10 vol% CO2 gas mixed with N2 gas. A cyclic capacity defined by the CO2 desorption amount of a phase-separation gel with solvent of 2-(ethylamino)ethanol/diethylene glycol diethyl ether was larger than those of the other homogeneous gels with 2-(ethylamino)ethanol/diethylene glycol monoethyl ether or diethylene glycol. Furthermore, the initial desorption flux of the phase-separation gel was larger than that of the absorbent solvent, suggesting that the phase-separation absorbent fixed inside the gels improves the initial desorption flux because of the larger interfacial area between the CO2-rich and CO2-lean phases inside the gel.

Dynamic Characterization during Gas Initial Desorption of Coal Particles and Its Influence on the Initiation of Coal and Gas Outbursts

The law of gas initial desorption from coals is greatly important for understanding the occurrence mechanism and predicting coal and gas outburst (hereinafter referred to as ‘outburst’). However, dynamic characterization of gas initial desorption remains to be investigated. In this study, by monitoring the gas pressure and temperature of tectonically deformed (TD) coal and primary-undeformed (PU) coal, we established the evolution laws of gas key parameters during the initial desorption. The results indicate that the gas pressure drop rate, mass flow rate, initial desorption rate, and gas velocity increase with increasing gas pressure, with stronger gas dynamic effect, generating a high pressure gradient on the coal surface. Under the same gas pressure, the pressure gradient formed on the TD coal surface is greater than that formed on the surface of the PU coal, resulting in easily initiating an outburst in the TD coal. Moreover, the increased gas pressure increases temperature change rates (falling rate and rising rate) of coal mass. The minimum and final stable temperatures in the TD coal are generally lower compared to the PU coal. The releasing process of gas expansion energy can be divided into two stages exhibiting two peaks which increase as gas pressure increases. The two peak values for the TD coal both are about 2–3 times of those of the PU coal. In addition, the total gas expansion energy released by TD coal is far greater than that released by PU coal. The two peaks and the total values of gas expansion energy also prove that the damage of gas pressure to coal mass increases with the increased pressure, more likely producing pulverized coals and more prone to initiate an outburst.

Modeling the kinetics of potentially toxic elements desorption in sediment affected by a dam breakdown disaster in Doce River - Brazil

On November 5th, 2015, a mining dam spilled a huge plume of mining waste in the Doce River. Even though many studies have reported the environmental impact from the Doce River's tragedy, the transport of potentially toxic elements (PTE) by kinetic modeling to determine how long the basin takes to achieve the natural balance has not been described. Therefore, samples of sludge, sediment, and water were collected along the Doce River basin, to assess the elements' total leaching by kinetic modeling. The elements Fe, Al, Mn, Cu, Ag, Pb, Cd, and As were evaluated. An innovative mobilization factor (FS/D) indicated that Mn2+, Ag+, and Cd2+ can be mobilized about 80, 89, and 57 times more than its initial concentration. Besides, in low pH, the Al and Pb ions can be mobilized. The desorption kinetics showed a lower rate constant (k) and higher initial desorption constant (h) for Mn2+ than Cd2+ and Ag+, suggesting both high- and low-affinity interaction sites for Mn2+. The exponential decay demonstrated that metals can leach for months or years. Thus, the long-lasting release of metals from mining tailing waste in concentrations that endanger the ecosystem and human health makes clear the need for long-term monitoring.

Adsorption/desorption performance of Pb2+ and Cd2+ with super adsorption capacity of PASP/CMS hydrogel.

Super-absorbent polyaspartic acid/carboxymethyl Salix psammophila powder (PASP/CMS) hydrogel was prepared by aqueous solution polymerization. PASP/CMS hydrogel was characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that PASP/CMS hydrogel is prepared by graft copolymerization of the -COOH of polyaspartic acid (PASP) and the -CH2OH of CMS. The surface of the hydrogel became dense from loose porosity, and Pb2+ and Cd2+ were adsorbed onto the surface of hydrogel. The crystallinity of CMS was destroyed by the addition of PASP. The initial concentration of Pb2+ and Cd2+, pH, adsorption time and adsorption temperature on the adsorption effect were studied through experiments. Results showed that hydrogel has a good removal effect on Pb(II) and Cd(II) ions. Pseudo-second-order kinetics and Langmuir isotherm models are represented in the process, which are spontaneous, exothermic and decreased in randomness, and it is a single layer chemical adsorption. At the same time, the effect of desorption experimental parameters (HNO3 initial concentration, desorption time, and desorption temperature) on the experiment was studied and optimized.

Evaluating Energy-Efficient Solutions of CO2 Capture within Tri-solvent MEA+BEA+AMP within 0.1+2+2–0.5+2+2 mol/L Combining Heterogeneous Acid–Base Catalysts

To reduce the extensive energy penalty of CO₂ desorption process of amine-based CO₂ capture technology, the combination of “coordinative effect” with “heterogeneous catalysis” was adopted into “MEA+BEA+AMP” tri-solvents at special concentrations (0.1–0.5+2+2 mol/L) with solid base catalysts “CaCO₃” and various solid acid catalysts “γ-Al₂O₃, H-ZSM-5, and blended γ-Al₂O₃/H-ZSM-5”. Experiments were performed to evaluate if there were synergetic effects within the optimization of amine blend concentrations and catalyst selections. Reaction schemes were investigated within the tri-solvents to understand the absorption and desorption mechanisms of coordinative effect. CO₂ absorption was performed at 40 °C, and CO₂ desorption was performed at 90 °C. Five tri-solvent compositions with various catalysts were investigated in terms of initial absorption rate (Iₐbₛ), initial desorption rate (Idₑₛ), heat duty (H), and cyclic capacities, which were categorized into absorption–desorption parameters systematically. The results indicated that tri-solvents with catalysts were highly energy-efficient. The optimized tri-blend was 0.3+2+2 mol/L MEA+BEA+AMP, which performed better than the 2+2 mol/L BEA+AMP benchmark on both absorption and desorption. The optimized regeneration performance of tri-blends was 0.3+2+2 mol/L, and its relative heat duty was 32.9% of that of 5 M MEA and 66.5% of that of 2+2 M BEA+AMP. Results manifested that the combination of solid acid–base catalysts with tri-solvents containing “coordinative effects” was a promising solution to further optimize the energy efficiency of CO₂ absorption–desorption within industrial amine-based CO₂ capture processes.

Promotion effects of microwave heating on coalbed methane desorption compared with conductive heating

As a clean energy resource, coalbed methane (CBM) has drawn worldwide attention. However, the CBM reservoir has strong adsorption capacity and low permeability and thus requires stimulation. As a means to stimulate coalbed methane recovery, thermal injection faces geological and economic challenges because it uses conventional conductive heating (CH) to transfer heat. Realized by the conversion of the electromagnetic energy into the thermal energy, microwave heating (MH) may be a sound stimulation method. Although previous research suggested that MH had potential as a stimulation method for coalbed methane recovery, it is not clear if MH is superior to CH for enhancing coalbed methane recovery. This paper compares the effect of MH and CH on methane desorption from coal using purpose-built experimental equipment. To compare the MH and CH experimental results, the desorption temperature for each CH desorption test was set to the maximum temperature reached in the correlative MH desorption test. The results show that although the cumulative desorbed volume (CDV) of methane under MH was less than that desorbed by CH in the initial desorption stage, the final total CDV under MH for the three different power settings was ~ 12% to ~ 21% more than that desorbed by CH at the same temperatures. CH and MH both change the sample’s microstructure but MH enlarges the pores, decreases methane adsorption, promotes methane diffusion, and improves permeability more effectively than CH. Rapid temperature rise and the changes in the coal’s microstructure caused by MH were the main reasons for its superior performance. These findings may provide reference for selecting the most appropriate type of heating for thermal injection assisted coalbed methane recovery.

A widespread mechanism in ectomycorrhizal fungi to access nitrogen from mineral-associated proteins.

A large fraction of nitrogen (N) in forest soils is present in mineral-associated proteinaceous compounds. The strong association between proteins and minerals limits microbial accessibility to this source, which is a relatively stable reservoir of soil N. We have shown that the ectomycorrhizal (ECM) fungus Paxillus involutus can acquire N from iron oxide-associated proteins. Using tightly controlled isotopic, spectroscopic and chromatographic experiments, we demonstrated that the capacity to access N from iron oxide-associated bovine serum albumin (BSA) is shared with the ECM fungi Hebeloma cylindrosporum and Piloderma olivaceum. Despite differences in evolutionary history, growth rates, exploration types and the decomposition mechanisms of organic matter, their N acquisition mechanisms were similar to those described for P. involutus. The fungi released N from mineral-associated BSA by direct action of extracellular aspartic proteases on the mineral-associated BSA, without initial desorption of the protein. Hydrolysis was suppressed by the adsorption of proteases to minerals, but this adverse effect was counteracted by the secretion of compounds that conditioned the mineral surface. These data suggest that the enzymatic exudate-driven mechanism to access N from mineral-associated proteins is found in ECM fungi of multiple lineages and exploration types.

Rapid gas desorption and its impact on gas-coal outbursts as two-phase flows

Coal and gas outbursts are a violent release of energy in part driven by rapidly desorbing gas from the fragmenting coal. We present a coupled two-phase model of coal and gas outbursts to define the timing, rate and magnitude of gas desorption and its contribution to the resulting energetics. The model involves a fragmenting ejection of the outburst from an overpressurized coal that retreats omnidirectionally from a point and develops a deepening crater. This model is applied to represents both experiments and in situ observations. These results indicate that the outburst is initially driven by free gas before desorbing gas rate exceeds this free gas liberation rate early into the outburst (at ∼17 s in our model). The cumulative mass of desorbed gas only exceeds the free gas later into the event at approximately double this duration (at ∼29 s in our model). During the outburst, ∼55 % of the expansion energy is contributed by desorbing gas. Using the initial gas emission rates for both non-tectonic and tectonic coals defines a power-law relationship between the initial gas desorption rate and the desorption gas contribution (∼14 %–92 %), indicating that the desorbing gas plays a decisive role in outburst development. Furthermore, taking the gas emission model as a boundary conditions for numerical simulations, the gas pressure potential energy (GPPE) released in the first millisecond at the maximum gas emission rate is derived to characterize its effects on the dynamic characteristics of the outburst two-phase flow. The maximum energy release intensity considering gas desorption is ∼5 times that without gas desorption for non-tectonic coal. For tectonic (mylonitized) coals the energy release is a further ∼4 times greater than that of non-tectonic coals. This paper presents a novel quantitative study defining the role of gas desorption in outbursts and contributes to the understanding of causal mechanisms and precursory phenomena preceding catastrophic outbursts.

Using a Dopamine‐Modified Magnetic Nano‐flower Material for the Solid Phase Extraction of Cyromazine and Melamine in Food Samples

AbstractThis work reported a simple method to prepare MGO@PDA@MoS2 nano‐flower by in situ growth of MoS2 on the poly‐dopamine (PDA) modified Fe3O4@GO (MGO) nanosheets. The novel material was composed of PDA modified MGO nanosheets and flower‐like MoS2 microspheres which two‐dimension ultrathin MoS2 nanosheets were grown in situ on the surface of MGO@PDA and self‐assembled. The material could be used as a new adsorbent for magnetic solid phase extraction (m‐SPE). The nano‐composite was characterized by TG, VSM, SEM, TEM, XRD, XPS and FT‐IR. The extraction parameters were investigated, including initial concentration, extraction time, pH, ionic strength and desorption conditions. The adsorption behaviors of the material were explored via isotherm and kinetic adsorption experiments, which demonstrated that Langmuir adsorption isotherm model and pseudo‐second‐order kinetic model were more appropriate to describe the adsorption process on MGO@PDA@MoS2. A rapid, safe, sensitive, easy, and effective method has been developed for detecting cyromazine and melamine simultaneously in real samples including beef, protein powder and milk by combining with HPLC. Under optimized conditions, the proposed method has a good trueness, wide linear range of 0.1‐100 μg mL−1, low limits of detection (LOD), satisfactory repeatability and reproducibility. Excellent recoveries for the determination of cyromazine and melamine were obtained in spiked real samples. In a word, the nano‐composite material has the advantages of magnetic separation and high adsorption affinity for cyromazine and melamine, and it is a promising adsorbent for extracting cyromazine and melamine from real samples.

Isotherms, kinetics and thermodynamics of pb(ii) adsorption by crosslinked chitosan/sepiolite composite

A novel composite adsorbent was prepared from chitosan (Ch) and sepiolite (S) for removal of Pb(II) from aqueous solution. The Ch-S composite beads were successfully synthesized by crosslinking epichlorohydrin (ECH) and tripolyphosphate (NaTPP). A number of physicochemical parameters such as, pH, initial Pb(II) concentration, temperature, contact time and desorption have been studied during the adsorption process. Experimental data acquired from batch adsorption tests have been analyzed by three isotherm models (Langmuir, Freundlich and Dubinin–Radushkevich), and three kinetic models including the pseudo-first-order, the pseudo-second-order and intraparticle diffusion equations using nonlinear regression technique. Langmuir isotherm was the best to fit the experimental data (R2 = 0.971). The maximum adsorption capacity was 0.158 mol kg−1 from Langmuir isotherm model. Maximum removal efficiency was found approximately 66% for the initial Pb(II) concentration of 1000 mg/L, adsorbent dosage of 100 mg and agitation speed of 150 rpm at pH 4.5. The adsorption free energy was found as EDR (15.8 kJ mol−1), which indicated that Pb(II) adsorption process onto Ch-S composite was chemically performed. The kinetic studies have shown that the best fitted kinetic model is the pseudo-first order (R2 = 0.979). Adsorption enthalpy value was determined as 18.7 kJ mol−1, adsorption entropy was found as 106 J mol−1 K−1, and Gibbs free energy was found as 12.9 kJ mol−1. The thermodynamic parameters showed that the adsorption of Pb(II) on Ch-S was endothermic, possible and spontaneous.