Quantum Tunneling Enhanced Hydrogen Desorption from Graphene Surface: Atomic versus Molecular Mechanism

We study the desorption mechanism of hydrogen isotopes from graphene surface using first-principles calculations,with focus on the effects of quantum tunneling.At low temperatures,quantum tunneling plays a dominant role in the desorption process of both hydrogen monomers and dimers.In the case of dimer desorption,two types of mechanisms,namely the traditional one-step desorption in the form of molecules(molecular mechanism),and the two-step desorption in the form of individual atoms(atomic mechanism),are studied and compared.For the ortho-dimers,the dominant desorption mechanism is found to switch from the molecular mechanism to the atomic mechanism above a critical temperature,which is∼300K and 200K for H and D,respectively.

Study of the reaction mechanism for preparing powdered activated coke with SO_(2)adsorption capability via one-step rapid activation method under flue gas atmosphere

In this study,the impact of different reaction times on the preparation of powdered activated carbon(PAC)using a one-step rapid activation method under flue gas atmosphere is investigated,and the underlying reaction mechanism is summarized.Results indicate that the reaction process of this method can be divided into three stages:stage I is the rapid release of volatiles and the rapid consumption of O_(2),primarily occurring within a reaction time range of 0-0.5 s;stage II is mainly the continuous release and diffusion of volatiles,which is the carbonization and activation coupling reaction stage,and the carbonization process is the main in this stage.This stage mainly occurs at the reaction time range of 0.5 -2.0 s when SL-coal is used as material,and that is 0.5-3.0 s when JJ-coal is used as material;stage III is mainly the activation stage,during which activated components diffuse to both the surface and interior of particles.This stage mainly involves the reaction stage of CO_(2)and H2O(g)activation,and it mainly occurs at the reaction time range of 2.0-4.0 s when SL-coal is used as material,and that is 3.0-4.0 s when JJ-coal is used as material.Besides,the main function of the first two stages is to provide more diffusion channels and contact surfaces/activation sites for the diffusion and activation of the activated components in the third stage.Mastering the reaction mechanism would serve as a crucial reference and foundation for designing the structure,size of the reactor,and optimal positioning of the activator nozzle in PAC preparation.

Mechanism model for shale gas transport considering diffusion, adsorption/desorption and Darcy flow

To improve the understanding of the transport mechanism in shale gas reservoirs and build a theoretical basic for further researches on productivity evaluation and efficient exploitation, various gas transport mechanisms within a shale gas reservoir exploited by a horizontal well were thoroughly investigated, which took diffusion, adsorption/desorption and Darcy flow into account. The characteristics of diffusion in nano-scale pores in matrix and desorption on the matrix surface were both considered in the improved differential equations for seepage flow. By integrating the Langmuir isotherm desorption items into the new total dimensionless compression coefficient in matrix, the transport function and seepage flow could be formalized, simplified and consistent with the conventional form of diffusion equation. Furthermore, by utilizing the Laplace change and Sethfest inversion changes, the calculated results were obtained and further discussions indicated that transfer mechanisms were influenced by diffusion, adsorption/desorption. The research shows that when the matrix permeability is closed to magnitude of 10^-9D, the matrix flow only occurs near the surfacial matrix; as to the actual production, the central matrix blocks are barely involved in the production; the closer to the surface of matrix, the lower the pressure is and the more obvious the diffusion effect is; the behavior of adsorption/desorption can increase the matrix flow rate significantly and slow down the pressure of horizontal well obviously.

Adsorption and Desorption Mechanisms of Methylene Blue Removal with Iron-Oxide Coated Porous Ceramic Filter

Adsorption and desorption mechanisms of methylene blue (MB) removal with iron-oxide coated porous ce-ramics filter (IOCPCF) were investigated in batch and column mode. The results revealed that MB removal mechanisms included physical adsorption and chemical adsorption, of which chemical adsorption by surface ligand complex reaction played a dominant role after infrared spectrum analysis. Recycling agents were se-lected from dilute nitric acid (pH=3), sodium hydroxide solution (pH=12) and distilled water. Among three agents, dilute metric acid (pH=3) was the best recycling agent. Regeneration rate of IOCPCF arrived at 82.56% at batch adsorption and regeneration was finished in 75min at column adsorption. Adsorp-tion-desorption cycles of IOCPCF after batch and column adsorption were four and three times, respectively. Further, compared with fresh IOCPCF, MB removal rate with these desorbed IOCPCF adsorption only slightly decreased, which suggested that IOCPCF should be used repeatedly.

Adsorption and desorption of Cd in reclaimed soil under the influence of humic acid:characteristics and mechanisms

Exogenous humus can change the content and migration activity of cadmium(Cd)in soil.Humic acid(HA)is an important soluble humus component in soil.In order to explore the relationship between cadmium pollution mechanism and ecological environment of humic acid in reclaimed soil,the characteristics of humic acid adsorbing cadmium in alkaline conditions were studied.This study employed reclaimed soil from the Huainan mining area,China.The adsorption and desorption characteristics as well as influence mechanisms on the heavy metal cadmium(Cd)were explored under the influence of HA.The results show that:(1)When Cd concentration was low(0.2–10 mg/L),HA had little effect on Cd adsorption and desorption in reclaimed soil.When the Cd concentration was high(15–80 mg/L),HA had a great influence on the adsorption and desorption of Cd in reclaimed soil.The addition of HA can inhibit the adsorption of Cd by reclaimed soil and effectively improve the desorption capacity of Cd by reclaimed soil.(2)The kinetic curves of Cd adsorption and desorption of reclaimed soil with added HA show that both processes(adsorption and desorption)include two stages:rapid reaction and slow reaction.The adsorption of Cd by reclaimed soil under the influence of HA was 18.18%lower than that of normal reclaimed soil,and the increase of Cd desorption was 50.29%.(3)The factors affecting the adsorption and desorption of Cd in the soil were analyzed with gray theory,and their importance can be ordered as follows:Cd concentration>HA concentration>pH>temperature.Considering the influence of HA,a multi-factor coupling function model of adsorption and desorption of Cd in soil is established.This model provides theoretical guidance for the scientific prediction and evaluation of Cd environmental pollution risks in soil and will be useful for developing a new solution for engineering remediation of high concentration Cd contaminated soil.

Pore structure of low‑permeability coal and its deformation characteristics during the adsorption–desorption of CH4/N2

The pore structure of coal plays a key role in controlling the storage and migration of CH4/N2.The pore structure of coal is an important indicator to measure the gas extraction capability and the gas displacement efect of N2 injection.The deformation characteristic of coal during adsorption–desorption of CH4/N2 is an important factor afecting CH4 pumpability and N2 injectability.The pore structure characteristics of low-permeability coal were obtained by fuid intrusion method and photoelectric radiation technology.The multistage and connectivity of coal pores were analyzed.Subsequently,a simultaneous test experiment of CH4/N2 adsorption–desorption and coal deformation was carried out.The deformation characteristics of coal were clarifed and a coal strain model was constructed.Finally,the applicability of low-permeability coal to N2 injection for CH4 displacement technology was investigated.The results show that the micropores and transition pores of coal samples are relatively developed.The pore morphology of coal is dominated by semi-open pores.The pore structure of coal is highly complex and heterogeneous.Transition pores,mesopores and macropores of coal have good connectivity,while micropores have poor connectivity.Under constant triaxial stress,the adsorption capacity of the coal for CH4 is greater than that for N2,and the deformation capacity of the coal for CH4 adsorption is greater than that for N2 adsorption.The axial strain,circumferential strain,and volumetric strain during the entire process of CH4 and N2 adsorption/desorption in the coal can be divided into three stages.Coal adsorption–desorption deformation has the characteristics of anisotropy and gas-diference.A strain model for the adsorption–desorption of CH4/N2 from coal was established by considering the expansion stress of adsorbed gas on the coal matrix,the compression stress of free gas on the coal matrix,and the expansion stress of free gas on micropore fractures.N2 has good injectability in low-permeability coal seams and has the dual functions of improving coal seam permeability and enhancing gas fow,which can signifcantly improve the efectiveness of low-permeability coal seam gas control and promote the efcient utilization of gas resources.

Synthesis of a novel magnetic biomass-MOF composite for the efficient removal of phosphates:Adsorption mechanism and characterization study

The adverse effects of eutrophication have prompted the use of various remediation techniques for phosphate(PO_(4)^(3-))removal owing to it being the major causative agent.Herein,the influence of different solvents and ratios of 2-aminoterepthalicacid on the efficiency of magnetic biomass metal-organic framework composites based on the in situ growth of NH_(2)-MIL-101(Fe)onto magnetized peanut husks towards PO_(4)^(3-)removal was assessed via the adsorption technique.The magnetic biocomposite labelled as MPN@NH2-MIL-101(Fe)exhibited the best efficiency owing to its mesoporous structures and presence of abundant oxygen and nitrogen possessing functional groups.Adsorption results confirmed MPN@NH2-MIL-101(Fe)to have a high adsorption capacity of(14.0±0.3)mg·L^(-1)at a PO43-concentration of 20 mg·L^(-1)with an associated high stability within pH 2-10.The adsorption kinetics for the process was well described by both Elovich and pseudo-second-order kinetic models and was mediated by both internal diffusion and liquid film diffusion.The Temkin and Freundlich models fitted the equilibrium data well signifying occurrence of both physical and chemical adsorption on a heterogeneous surface.It is concluded that MPN@NH2-MIL-101(Fe)is a promising adsorbent for the effective removal of phosphate from a water body.

Experimental and Numerical Research on Water Transport during Adsorption and Desorption in Cement-Based Materials

The durability of cement-based materials is related to water transport and storage in their pore network under different humidity conditions.To understand the mechanism and characteristics of water adsorption and desorption processes from the microscopic scale,this study introduces different points of view for the pore space model generation and numerical simulation of water transport by considering the“ink-bottle”effect.On the basis of the pore structure parameters(i.e.,pore size distribution and porosity)of cement paste and mortar with water-binder ratios of 0.3,0.4 and 0.5 obtained via mercury intrusion porosimetry,randomly formed 3D pore space models are generated using two-phase transformation on Gaussian random fields and verified via image analysis method of mathematical morphology.Considering the Kelvin-Laplace equation and the influence of“ink-bottle”pores,two numerical calculation scenarios based on mathematical morphology are proposed and applied to the generated model to simulate the adsorption-desorption process.The simulated adsorption and desorption curves are close to those of the experiment,verifying the effectiveness of the developed model and methods.The obtained results characterize water transport in cement-based materials during the variation of relative humidity and further explain the hysteresis effect due to“ink-bottle”pores from the microscopic scale.

Biomass Carbon Improves the Adsorption Performance of Gangue-Based Ceramsites:Adsorption Kinetics and Mechanism Analysis

The large accumulation of coal gangue,a common industrial solid waste,causes severe environmental problems,and green development strategies are required to transform this waste into high-value-added products.In this study,low-cost ceramsites adsorbents were prepared from waste gangue,silt coal,and peanut shells and applied to remove the organic dye methylene blue from wastewater.We investigated the microstructure of ceramsites and the effects of the sintering atmosphere,sintering temperature,and solution pH on their adsorption performance.The ceramsites sintered at 800℃under a nitrogen atmosphere exhibited the largest three-dimensional-interconnected hierarchical porous structure among the prepared ceramsites;further,it exhibited the highest methylene blue adsorption performance,with an adsorption capacity of 0.954 mg·g^(−1),adsorption efficiency of over 95%,and adsorption equilibrium time of 1 h at a solution pH of 9.The removal efficiency remained greater than 75%after five adsorption cycles.The adsorption kinetics data were analyzed using various models,including the pseudosecond-order kinetic model and Langmuir equation,and the adsorption was attributed to electrostatic interactions between the dyes and ceramsites,n-interactions,and hydrogen bonds.The prepared coal gangue ceramsites exhibited excellent adsorption capacities,removal rates,and cyclic stabilities,demonstrating their promising application prospects for the comprehensive utilization of solid waste and for wastewater treatment.

Effective adsorption of sulfate ions with poly(m-phenylenediamine) in aqueous solution and its adsorption mechanism

Sulfate adsorption by poly（m-phenylenediamine）s（PmPDs） with various oxidation states synthesized through chemically oxidative polymerization was investigated.Series of sorption experiments were conducted,and the adsorption mechanism and the relationship between oxidation state and adsorption performance were studied with the characterization of Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,pH tracking and energy calculation.The results show that the adsorption performance in acidic solution is improved with the decrease of oxidation state of poly（m-phenylenediamine）（PmPD）.The rate constant is as high as 425.5 mg/（g·min） in the short equilibrium time of 30 min.The estimated highest adsorptivity of sulfate ions is 95.1%.According to the Langmuir equation,the adsorbance is 108.5 mg/g.The sulfate desorption efficiency is about 95% and the accumulative adsorbance is up to 487.95 mg/g in 5 cycles.

Study on the Effects of Polyacrylamide on Phosphorus Adsorption and Desorption Characteristics of Soil Aggregates

[Objective]The research aimed to provide scientific reference for reasonable utilization of polyacrylamide(PAM).[Method]After PAM treatment,the soil aggregates were classified through dry sieve analysis and the adsorption capacity and desorption capacity of all soil aggregates to phosphorus at different phosphorus concentrations were analyzed.[Result] The phosphorus adsorption and desorption of soil sample treated by PAM declined. The amount of phosphorus adsorption increased with the increase of phosphorus concentration and this increase was fast in low phosphorus concentration area but slow in high phosphorus concentration area.At different phosphorus concentrations,adsorption showed a へ shape changing trend.The phosphorus adsorption was related to phosphorus concentration and the 2-3 mm aggregate had the highest desorption rate while 0.1-0.25 mm aggregate and 0.45-1 mm aggregate had lowest desorption rate.[Conclusion]The PAM treatment generated significant influence on phosphorus adsorption and analytic features of aggregate in all size fractions.

Characterization of adsorptive capacity and mechanisms on adsorption of copper, lead and zinc by modified orange peel

A novel adsorbent was prepared by modifying orange peel with sodium hydroxide and calcium chloride. The morphological and characteristics of the adsorbent were evaluated by infrared spectroscopy （IR）, scanning electron microscopy （SEM） and N2-adsorption techniques. The adsorption behavior of Cu^2＋, Pb^2＋ and Zn^2＋ on modified orange peel （SCOP） was studied by varying parameters like pH, initial concentration of metal ions. Equilibrium was well described by Langmuir equation with the maximum adsorption capacities for Cu^2＋, Pb^2＋ and Zn^2＋ of 70.73, 209.8 and 56.18 mg/g, respectively. Based on the results obtained in batch experiments, breakthrough profiles were examined using a column packed with SCOP for the separation of small concentration of Pb^2＋ from an excess of Zn^2＋ followed by elution tests. Ion exchange with Ca^2＋ neutralizing the carboxyl groups of the pectin was found to be the predominant mechanism.

Adsorption mechanism of 2-mercaptobenzothiazole on chalcopyrite and sphalerite surfaces:Ab initio and spectroscopy studies

Interaction mechanism of the collector,2-mercaptobenzothiazole（MBT）,with chalcopyrite and sphalerite surfaces were investigated by Fourier transform infrared（FTIR） and density functional theory,Results of FTIR showed that some characteristic peaks of MBT were observed on the chalcopyrite surface,including C=N,C=N-S and C-S stretching vibration peaks,and the adsorption product was CuMBT.But there were no characteristic peaks of MBT on the sphalerite surface.The thione molecular form of MBT was the most efficient and stable,N and exocyclic S were the more favourable reactive sites for nucleophilic attacked by metal atoms.Compared with ZnS（110）,MBT is more readily adsorbed on CuFeS2（112）.Attachment of MBT occurs due to strong bonding through exocyclic S p and s orbits with Cu d orbit on CuFeS2（112） and electron transfer from Cu atom to S atom.Under the vacuum condition,MBT in the form of thione molecular cannot be adsorbed on ZnS（110） spontaneously.

A potential threat from biodegradable microplastics: mechanism of cadmium adsorption and desorption in the simulated gastrointestinal environment

It has been demonstrated that microplastics (MPs) can accumulate heavy metals from the environment and transfer them into organisms via the food chain. However, adsorption and desorption capacities for biodegradable MPs relative to those for conventional MPs remain poorly understood. In this study, cadmium (Cd(II)) adsorption and desorption characteristics of polylactic acid (PLA), a typical biodegradable MP, were investigated. Two conventional MPs, i.e., polypropylene (PP) and polyamide (PA) were used for comparison. The maximum Cd(II) adsorption capacities of the MPs studied in the adsorption experiments decreased in the order PA (0.96 ± 0.07 mg/g) > PLA (0.64 ± 0.04 mg/g) > PP (0.22 ± 0.03 mg/g). The Pseudo-second-order kinetic model and Freundlich isothermal model described the Cd(II) adsorption behaviors of PLA MPs well. X-ray photoelectron spectroscopy and two-dimensional Fourier transform infrared correlation spectroscopy analysis indicated that oxygen functional groups were the major and preferential binding sites of PLA MPs, which contributed to their high Cd(II) adsorption capacities. Simulated gastric and intestinal fluids both significantly enhanced the desorption capacities of the examined MPs. Notably, degradation of the PLA MPs during in vitro human digestion made the Cd(II) on the PLA MPs more bioaccessible (19% in the gastric phase and 62% in the intestinal phase) than Cd(II) on the PP and PA MPs. These results indicate the remarkable capacities of biodegradable MPs to accumulate Cd(II) and transfer it to the digestive system and show that biodegradable MPs might pose more severe threats to human health than conventional nonbiodegradable MPs.

Adsorption and Desorption Characteristics of Cadmium and Lead in Typical Paddy Soils of Jiangxi Province and Its Environmental Risk Assessment

[Objective] This study aimed to investigate the adsorption and desorption characteristics of cadmium and lead in typical paddy soils of Jiangxi Province. [Method] Gleyed paddy soil and waterloggogenic paddy soil were collected from Jiangxi Province and used as experimental materials to investigate single and com- petitive adsorption and desorption behaviors of cadmium and lead by batch equilib- rium method. The environmental risk of the presence of cadmium and lead in paddy soils was assessed using distribution coefficients. [Result] Under equal ratio condi- tions, the adsorption capacity of lead by two types of paddy soils was higher than that of cadmium, and the adsorption rate in waterloggogenic paddy soil was higher than that in gleyed paddy soil. The desorption capacity of cadmium by two types of paddy soils was higher than that of lead, and the desorption rate in gleyed paddy soil was higher than that in waterloggogenic paddy soil. Under competitive condi- tions, the adsorption capacity of cadmium and lead by paddy soils was significantly reduced compared with single ion system, while the desorption rate was remarkably improved. The potential environmental risk of cadmium contamination was greater than that of lead in paddy soils. Moreover, environmental risks of cadmium and lead were reduced with the increase of pH, which increased significantly under the coex- istence state. [Conclusion] In the coexistence of cadmium and lead, cadmium con- tamination should be controlled and avoided compared with lead contamination in paddy soils.

Adsorption and Desorption of Natural Zeolite on NH_4^+

The adsorption and desorption kinetic of natural zeolite on NH4＋ was stud-ied by lab analysis. The results showed that the adsorption and desorption kinetic of natural zeolite on NH4＋ coincided with the first-order kinetics, modified Freundlich equation, parabolic diffusion model, and heterogeneous diffusion model. The desorp-tion of the adsorbed NH4＋ was far rapider than the adsorption, which can be fin-ished within 60 min.

Insights into carbon dioxide sequestration into coal seams through coupled gas flow-adsorption-deformation modelling

Injecting carbon dioxide(CO_(2))into coal seams may unlock substantial carbon sequestration potential.Since the coal acts like a carbon filter,it can preferentially absorb significant amounts of CO_(2).To explore this further,desorption of the adsorbed gas due to pressure drop is investigated in this paper,to achieve an improved understanding of the long-term fate of injected CO_(2) during post-injection period.This paper presents a dual porosity model coupling gas flow,adsorption and geomechanics for studying coupled processes and effectiveness of CO_(2) sequestration in coals.A new adsorption?desorption model derived based on thermodynamics is incorporated,particularly,the desorption hysteresis is considered.The reliability of the proposed adsorption-desorption isotherm is examined via validation tests.It is indicated that occurrence of desorption hysteresis is attributed to the adsorption-induced pore deformation.After injection ceases,the injected gas continues to propagate further from the injection well,while the pressure in the vicinity of the injection well experiences a significant drop.Although the adsorbed gas near the well also decreases,this decrease is less compared to that in pressure because of desorption hysteresis.The unceasing spread of CO_(2) and drops of pressure and adsorbed gas depend on the degree of desorption hysteresis and heterogeneity of coals,which should be considered when designing CO_(2) sequestration into coal seams.

Collecting performances of N-dodecylethylene-diamine and its adsorption mechanism on mineral surface

The collecting performances of N-dodecylethylene-diamine （ND） to quartz and hematite were studied via single mineral flotation. Experimental results show that ND has stronger collecting ability to quartz than hematite. Different floatability of quartz and hematite was presented in the existence of depressant. Compared with lauryl amine, ND has stronger collecting performances to quartz. Satisfied separation result of artificially mixed sample was acquired with iron grade of concentrate of 59.92% and iron recovery of 88.85% when pulp pH value was 7.27 with 41.7 mg/L collector and 3.33 mg/L starch. Polar group properties calculation results indicated that ND has stronger collecting capability and better selectivity than lauryl amine. Measurement results of zeta-potentials and infrared spectrum showed that hydrogen bonding adsorption and electrostatic adsorption occur between the surface of ND and quartz.

A new liquid membrane diffusion model for characterizing the adsorption kinetics of europium by using a continuous measurement of adsorption platform

To explore the kinetic adsorption under continuous and nonequilibrium states, an integration of continuous measurement and adsorption platform kinetics method was proposed, which was initially called the ICM-AP kinetics method, and a corresponding kinetic adsorption experimental method was developed. Adsorption experiments of europium(Eu) on Ca-bentonite,Na-bentonite, and the D231 cation exchange resin were performed using the ICM-AP kinetics method and continuous measurements. Because the kinetic experimental results observed in this study were different from those of traditional batch adsorption data, pseudo-first-order or pseudo-second-order kinetic models were unsuitable for fitting the experimental data.Hence, a liquid membrane diffusion(LMD) model was developed based on the assumption of simultaneous adsorption/desorption to discuss the mechanism of kinetic adsorption. The kinetic adsorption mechanism was also studied by using XPS.The results indicated that the proposed adsorption model can fit the experimental data more suitably, and the adsorption/desorption behaviors of Eu on bentonite and the D231 resin were simultaneously observed, suggesting that the adsorption kinetics of Eu(Ⅲ) was mainly dominated by hydrated Eu(Ⅲ) ions on the liquid membrane.

Adsorption/desorption behavior between a novel amphoteric granular lignin adsorbent and reactive red K-3B in aqueous solutions

A novel amphoteric granular lignin adsorbent(AGLA) was prepared using magnesium lignosulfonate as a raw material which was provided by a straw sulfite pulp mill in Guangdong Province, China. A reactive dye(red K-3B) was used as an adsorbate to investigate the adsorption behavior by static and mobile ways. The removal of reactive red K-3B was found to be initially pH and concentration dependent. Moreover, an increase of solution temperature ranging from 5℃ to 60℃ helped to enhance the rate of intraparticle diffusion of adsorbate and changes in the size of the pores of the adsorbent and thus to reduce the adsorption time. The total breakthrough adsorption capacity was 531 mg/g, and the saturated adsorption capacity was 560 mg/g, which prevailed over the activated carbons evidently. The reactive red K-3B adsorbed on AGLA could be recovered with a mixture of alcohol, NaCl and HCl aqueous solutions. The recovery percentage could reach 92.4%.