Key Role In Adsorption Research Articles

Synthesis of ultrathin hybrid membranes via the co-polymerization of acrylic acid, styrene and molybdenum disulfide and their high adsorption selectivity for lead(II) in the mixture of metal ions

Lead(II) is a potential carcinogen of heavy-metal ions (HIs). With the wide application of Pb-bearing products including lead alloy products, and new-energy lead-ion batteries, lead pollution has become a tricky problem. To solve such a difficulty, novel ultrathin MoS2-vinyl hybrid membranes (MVHMs) with a “spring” effect were synthesized via co-polymerization of acrylic acid, styrene and molybdenum disulfide (MoS2) and their adsorptions for HIs were explored. The “spring” effect derived from the interaction between the tendency of the short polyacrylic acid (PAA) chain connected with MoS2 to spread outward and the coulomb force between layers from MoS2 (s-MoS2), which enlarge the spacing of MoS2 layers without changing the number of layers after membrane formation, which changes the swelling membrane to a dense membrane and reduces the original thickness from 0.5 cm to 0.011 mm in the thickness direction. The adsorption experiment revealed that these MVHMs had super adsorption performance and high selectivity for Pb2+ by comparison with other five metal ions: Cu2+, Cd2+, Ni2+, Cr3+ and Zn2+. Especially, the adsorption quantity of MVHMs for Pb2+ could approach 2468 mg/g and the maximum adsorption ratio of qe[Pb2+]/qe[Cu2+] can reach 10.909. These values were much larger than the data obtained with the adsorbents reported in the last decade. A variety of models are applied to evaluate the effect of ionic groups. It was confirmed that –COOH plays a key role in adsorption of HIs and s-MoS2 also has a certain contribution. Conversely, ion exchange plays only a minor role during the period of adsorption process. Effective diffusion coefficient (Deff) of Pb(II) had the largest values among these metal ions. Hence, these hybrid membranes are promising adsorbents for the removal of Pb2+ from water containing various ions.

Prediction of Biochar Yield and Specific Surface Area Based on Integrated Learning Algorithm

Biochar is a biomaterial obtained by pyrolysis with high porosity and high specific surface area (SSA), which is widely used in several fields. The yield of biochar has an important effect on production cost and utilization efficiency, while SSA plays a key role in adsorption, catalysis, and pollutant removal. The preparation of biochar materials with better SSA is currently one of the frontiers in this research field. However, traditional methods are time consuming and laborious, so this paper developed a machine learning model to predict and study the properties of biochar efficiently for engineering through cross-validation and hyper parameter tuning. This paper used 622 data samples to predict the yield and SSA of biochar and selected eXtreme Gradient Boosting (XGBoost) as the model due to its excellent performance in terms of performance (yield correlation coefficient R2 = 0.79 and SSA correlation coefficient R2 = 0.92) and analyzed it using Shapley Additive Explanation. Using the Pearson correlation coefficient matrix revealed the correlations between the input parameters and the biochar yield and SSA. Results showed the important features affecting biochar yield were temperature and biomass feedstock, while the important features affecting SSA were ash and retention time. The XGBoost model developed provides new application scenarios and ideas for predicting biochar yield and SSA in response to the characteristic input parameters of biochar.

Preparation of microporous carbon materials using residual coal from oxidative degradation of lignite as the carbon source and the mechanism and dynamics of its methyl orange adsorption

The preparation of coal-based carbon materials traditionally uses anthracite as the carbon source. In the present study, two types of porous carbon materials were prepared, one by tube furnace heating (CM1) and one by microwave processing (CM2), through the KOH activation method using the residue (YNC1) from the oxidative degradation of lignite. The structure-function relationships of the obtained materials were explored by studying the dynamic law and mechanism of methyl orange adsorption. Results showed that both CM1 and CM2 contained aromatic and hydroxyl (secondary alcohol) moieties but no carboxyl groups, ketone groups or long-chain aliphatic hydrocarbons. Both materials were dominated by micropores and mesopores, with a greater proportion of micropores than mesopores. The micropore content was higher in CM2 than in CM1. Additionally, structural characterisation revealed that the microwave-based KOH activation could open aromatic structures. Studies on the adsorption of methyl orange by the carbon materials indicated that the secondary hydroxyl groups on the surface of the carbon materials were active sites for chemical adsorption and played the key role in adsorption, leading to monolayer chemical adsorption. Furthermore, the distribution pattern of hydroxyl groups produced by the polarity selection of the microwave field was more favourable for chemical adsorption. The dynamic law of CM1 and CM2 adsorption of methyl orange conformed to the quasi-second-order kinetic model. The adsorption process comprised two stages: external surface adsorption, followed by the diffusion of methyl orange in pores.

Insights into the sandwich-like ultrathin Ni-doped MoS2/rGO hybrid as effective sulfur hosts with excellent adsorption and electrocatalysis effects for lithium-sulfur batteries

Dual redox mediator based on a novel ultrathin sandwich-type Ni-doped MoS 2 /rGO with rich MoS 2 -defect accelerate the electrochemical kinetics for high performance lithium-sulfur batteries. • The sandwich-type Ni-MoS 2 /rGO is developed as sulfur host via hydrothermal method. • The rich MoS 2 -defect plays key role in adsorption and redox kinetics of LiPSs. • Adsorption-electrocatalysis synergy enhances the electrochemical properties. • The S@Ni-MoS 2 /rGO cathode has high specific capacity and long cycle stability. The design of sulfur hosts with high conductivity, large specific surface area, strong adsorption and electrocatalytic ability is crucial to advance high performance lithium-sulfur batteries. Herein, a novel ultrathin sandwich-type Ni-doped MoS 2 /reduced graphene oxide (denote as Ni-doped MoS 2 /rGO) hybrid is developed as a sulfur host through a simple one-step hydrothermal route. The two-dimensional layered structure Ni-doped MoS 2 /rGO hybrid with heterostructure and heteroatom architecture defects not only plays a key role in adsorption of lithium polysulfide but also catalyzes on redox kinetics of sulfur and polysulfide species. Meanwhile, it can contribute to the large specific surface area for Li 2 S/S 8 deposition, fast Li-ion and electron transportation, thus enhancing the electrocatalytic properties, as confirmed firstly by cyclic voltammetry (CV) results. Due to the adsorption-catalytic synergistic effect, the Ni-doped MoS 2 /rGO cathode exhibits high specific capacity (1343.6 mA h g −1 at 0.2 C, 921.6 mA h g −1 at 1 C), high coulombic efficiency and an outstanding cycle stability (with the low attenuation rate of 0.077% per cycle over 140 cycles at 0.5 C and 0.11% per cycle over 400 cycles at 1 C, respectively). This work proposes some inspiration for exploring the construction of advanced lithium-sulfur batteries through the rational design defects of atomic structure and electronic states of MoS 2 as sulfur host.

Efficient removal of Sb(V) in textile wastewater through novel amorphous Si-doped Fe oxide composites: Phase composition, stability and adsorption mechanism

The development of amorphous iron oxide-based composites for the Sb(V) removal is limited by their easy phase transformation, aggregation, and unstable nature. Herein, novel modified Si-doped Fe oxide composites (SFOC) were prepared to break through the current obstacle. Characterization results of SFOC with a suitable amount of doped Si indicated that the coordination interaction between Si-OH and Fe-OH blocked the crystal growth sites in both Si and Fe oxide, and the crystal unit cells of same element were difficult to contact with each other. Hence, the crystal growth of Si and Fe oxide was retarded and their unit particle size became smaller. Meanwhile, the crystal phase transformation of amorphous ferrihydrite was prevented and the aggregation extent of Fe oxide was greatly decreased after Si doping. These changes caused that more Fe vacancies were generated on the surface of amorphous Fe oxide unit and the surface area of SFOCs also increased, resulting in the great increasement of exposed Fe hydroxyl groups in SFOC. As compared to pristine Fe oxide, the optimal SFOC10 with Fe/Si molar ratio of 10:1 exhibited the highest surface area of 363.9 m2/g, the maximum Sb(V) removal capacity of 176.1 mg/g, and higher selective Sb(V) adsorption performance. The introduction of Si oxide also endowed SFOC10 with much better phase stability and Sb(V) removal capacity during the long cyclic adsorption-desorption process. Moreover, the inner-sphere complexation of Fe-OH and Sb(OH)6− played a key role in adsorption. Furthermore, optimal SFOC10 was sufficient for the Sb(V) removal from real textile wastewater in both the batch and dynamic column adsorption processes.

Efficient removal of diclofenac and cephalexin from aqueous solution using Anthriscus sylvestris-derived activated biochar

The objective of this study was to investigate the adsorption of diclofenac (DF) and cephalexin (CPX) by Anthriscus sylvestris-derived activated biochar. The raw biochar (R-BC) and activated biochar (ACT-B) were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and elemental analyses techniques to obtain information regarding the morphology, functional groups and elements of the adsorbents. Batch studies were carried out to examine the effect of various operational parameters. The maximum adsorption capacity of ACT-B was 392.94 mg g−1 for DF and 724.54 mg g−1 for CPX. The removal of DF and CPX was influenced by temperature and the co-existing ions. The kinetic data fitted well with the pseudo-second-order kinetic model, whereas the isotherm data showed the best correlation with Langmuir isotherm model. Electrostatic adsorption, hydrophobic interaction and π-π bonding play a key role in adsorption of both adsorbates by ACT-B. Additionally, column studies were conducted using ACT-B at different flow rates and different concentrations of DF and CPX to investigate the practical applicability of ACT-B in removal of the target contaminants. Thus, this study provides a feasible approach to synthesize activated biochar that can minimize pharmaceuticals pollution in water bodies.

Functional adjustment and cyclic application of Fe–Mn bimetal composite for Sb(V) removal: Transformation of iron oxides forms and a stable regeneration method

In this work, the surface properties, functional groups and stability of Fe–Mn bimetal composite (FMBC) was modified through sintering to improve the weaknesses of pristine FMBC, such as poor separation performance, high amount of dissolved Fe and Mn, and easy phase transformation. Characterization analysis indicated that 2-line ferrihydrite in sintered FMBC (SFMC) gradually transformed into hematite with the phase-transition temperature of 450 °C. With the increasing sintering temperature and time, the dehydroxylation reaction enhanced and gradually became irreversible, while the BET surface area and porosity of SFMC firstly increased and then decreased, resulting in the initial increase and then sharp decrease of the amount of exposed hydroxyl groups on SFMC. The sintering treatment greatly improved the separation performance and stability of SFMC. 350 °C and 2 h were determined as the optimal sintering conditions of SFMC in this study and the calculated maximum adsorption capacity of optimal SFMC reached up to 95 mg/g. Freundlich model and pseudo-second-order kinetics model can describe the Sb(V) adsorption data well. As compared to pristine FMBC, optimal SFMC presented larger BET surface area and porosity, better separation performance and stability, lower dissolved Fe and Mn amount, larger cyclic adsorption efficiency and enough ability for Sb(V) removal in real textile wastewater. Furthermore, the inner sphere complexation between Sb(OH)6- and exposed hydroxyl groups played a key role in adsorption. Additionally, the NaCl + NaOH elution exhibited greater Sb(V) desorption performance and effectively retarded the phase transformation of SFMC than NaOH solution.

Promotional effects of B-terminated defective edges of Ni/boron nitride catalysts for coking- and sintering-resistant dry reforming of methane

It is urgent to develop highly sintering- and coking-resistance nickel-based catalysts for efficient dry reforming of methane (DRM). Here, we rationally designed and originally developed boron nitride defect-confined Ni catalysts (Ni/d-BN) for DRM by sonication-assisted alcoholysis and chemical peeling techniques. Ni/d-BN catalysts which exposed more B terminal sites exhibited very high catalytic activity, excellent stability and coking-resistance. The defect sites of BN were found to play a key role in adsorption and activation of reaction gases. The B-terminal sites in d-BN can be directly used as active sites for DRM reaction and it also can effectively promote the formation of B-O H*, thus increasing the rate of conversion of carbonate species and CHx* species into formate species, greatly promoting the formation of CO and effectively preventing coke deposition. This work paves the way for design of catalysts with simultaneous coking- and sintering-resistant of supported Ni-based catalysts for DRM applications.

KOH-activated hydrochar with engineered porosity as sustainable adsorbent for volatile organic compounds

The pore structure of materials plays a key role in adsorption, and it is of great significance to regulate the porosity of adsorbent for specific adsorbate. Herein, porous carbons (PCs) with engineered porosity were synthesized as adsorbents for volatile organic compounds (VOCs), which employed sucrose-based hydrochar via KOH activation. Surface area of 2604 m2/g together with pore volume of 1.685 cm3/g could be reached when KOH/hydrochar ratio was 3. The adsorption capacities of three typical VOCs were in the order of toluene > acetic ether > acetone, with the vapor pressure had greatest effect on adsorption among the properties of adsorbates. Influence of carbon porosity was further investigated, showing that micropores in the range of 1–3 times of the VOC diameter were crucial to the adsorption process. In addition, more than 90 % of the initial adsorption capacity could be reached after four regeneration cycles. Considering economic and environmental aspects, we demonstrated porous carbons derived from hydrothermal carbonized sucrose could be promising materials in adsorption. This work could also provide guidance for the porosity regulation of adsorbents for different VOCs.

Interaction of anionic dyes with polyaniline implanted cellulose: Organic π-conjugated macromolecules in environmental applications

The selective response of most of the adsorbents towards a particular dye creates problem in launching them as adsorbent in real field applications. Owing to that we have synthesized organic macromolecule of polyaniline implanted cellulose through vapor phase polymerization method. Polyaniline implanted cellulose was found as a cationic charge transport medium and thus enthusiastically chosen to observe its interaction with anionic dyes as adsorbent media. The prepared material was found crystalline in X-ray diffraction (XRD) measurement. Field emission scanning electron microscopy (FESEM), Raman spectroscopy and optical absorbance, measurements were carried out to explore its physical properties. The polyaniline implanted cellulose substrate has shown excellent adsorptive response with anionic dyes of methyl orange (MO) and eosin yellow (EY). More than 97% removal efficiency was observed at optimum experimental conditions for both the dyes and the MO dye adsorption process followed Langmuir isotherm strictly. However, Freundlich isotherm model has shown better fit for equilibrium adsorption data of EY dye onto polyaniline implanted paper. Kinetic analysis indicated the applicability of second order kinetic model with involvement of intra-particle diffusion. The polaron and bipolaron charged defect states in the polyaniline chain played the key role in adsorption of anionic dyes through chemical interaction. Thus it appeared as an efficient adsorbent for anionic dyes with wide range of selectivity.

Catalytic ozonation of Orange-G through highly interactive contributions of hematite and SBA-16 – To better understand azo-dye oxidation in nature

Hematite-SBA-16 mixture (HS) exhibited high catalytic activity in Orange-G (OG) ozonation in water. Total OG discoloration was achieved in half the time required with hematite or SBA-16 alone, all UV–Vis bands disappeared in less than 2 min. Liquid chromatography- Mass spectrometry (LC-MS) revealed that OG ozonation triggers via both hydroxylation and desulfonation of the aromatic rings into specific intermediates. Prolonged ozonation in the presence of hematite and SBA-16 alone resulted in different distributions of common derivatives. The latter were not detected after 25 min ozonation with HS. Stochastic modeling of the evolution in time of the UV–Vis bands of OG revealed strong binary interaction between the initial pH and catalyst concentration. This was explained in terms of reciprocal contributions of: i. the catalytic properties of hematite in spite of its low porosity; ii. the high specific surface area of SBA-16 for adsorption and surface reaction notwithstanding its low intrinsic catalytic activity. The weak basicity of SBA-16 surface seems to play a key-role in adsorption. These findings are of great interest for envisaging flexible oxidative treatments, where Fe3+ containing soils or mixtures of sand and rust may also act as catalyst for total mineralization of various azo-dyes, regardless to their structures.

Molecular-Level Investigation of the Adsorption Mechanisms of Toluene and Aniline on Natural and Organically Modified Montmorillonite.

The present work reports the adsorption mechanisms of aniline and toluene in dry and hydrated montmorillonite (MMT-Na and MMT-Na-W) and tetramethylammonium-cation-modified MMT (MMT-TMA) as determined through density functional theory. These theoretical investigations explicitly demonstrate that cation-π interactions between Na(+)/TMA(+) cations and aromatics play the key role in adsorption of organics over MMT-Na and MMT-TMA. Weak hydrogen bonds between the H atoms of organics and basal O atoms of tetrahedral silicate also stabilize the location of organics. The combination of interactions between water and basal O atoms and between organics and water molecules in hydrated MMT complexes strengthens the adsorption of organics on MMT, resulting in higher formation energies in hydrated organically intercalated MMTs than in the corresponding dry complexes. The adsorption of organics also changes frontier orbital distributions and consequently promotes the preferential occurrence of reactions on the organics rather than on the MMT layers. These adsorption mechanisms predicted by theoretical investigation can be used to explicate the adsorption of aromatic organics on aluminosilicates with different external environment.

A cluster DFT study of NH3 and NO adsorption on the (MoO2)2+/HZSM-5 surface: Lewis versus Brønsted acid sites

A systematic DFT study was carried out to investigate NH3 and NO adsorption on both Lewis and Brønsted acid sites of (MoO2)2+/HZSM-5 catalyst by using cluster models. The adsorption energy results indicate that NH3 could strongly adsorb on both Lewis and Brønsted acid sites in the form of coordinated NH3 and NH4+, respectively, whereas NO represents poorer adsorption ability. It is also found that Lewis and Brønsted acid sites are competitive energetically for NH3 adsorption. According to the difference in the proposed mechanisms for NH3 adsorption on different acid sites, particular attention has been focused on the first dissociation of coordinated NH3 for Lewis acid site and the effect of Mo site on the introduction of NO for Brønsted acid site. For the coordinated NH3 on Lewis acid site, the more electron donation from NH3 is, the greater its adsorption stability is and the higher active its H atoms are. In addition, DOS results show that stability of the H atoms is enhanced by interacting with framework oxygen and especially the H atoms chemical-bonded with framework oxygen. For the NH4+ on Brønsted acid site, reduced-state Mo5+ holds stronger reducibility and oxidizability than terminal oxygen, which is suggested to play a key role in adsorption and activation of NOx together with the adsorbed NH4+.

Important roles of enthalpic and entropic contributions to CO2 capture from simulated flue gas and ambient air using mesoporous silica grafted amines.

The measurement of isosteric heats of adsorption of silica supported amine materials in the low pressure range (0-0.1 bar) is critical for understanding the interactions between CO2 and amine sites at low coverage and hence to the development of efficient amine adsorbents for CO2 capture from flue gas and ambient air. Heats of adsorption for an array of silica-supported amine materials are experimentally measured at low coverage using a Calvet calorimeter equipped with a customized dosing manifold. In a series of 3-aminopropyl-functionalized silica materials, higher amine densities resulted in higher isosteric heats of adsorption, clearly showing that the density/proximity of amine sites can influence the amine efficiency of adsorbents. In a series of materials with fixed amine loading but different amine types, strongly basic primary and secondary amine materials are shown to have essentially identical heats of adsorption near 90 kJ/mol. However, the adsorption uptakes vary substantially as a function of CO2 partial pressure for different primary and secondary amines, demonstrating that entropic contributions to adsorption may play a key role in adsorption at secondary amine sites, making adsorption at these sites less efficient at the low coverages that are important to the direct capture of CO2 from ambient air. Thus, while primary amines are confirmed to be the most effective amine types for CO2 capture from ambient air, this is not due to enhanced enthalpic contributions associated with primary amines over secondary amines, but may be due to unfavorable entropic factors associated with organization of the second alkyl chain on the secondary amine during CO2 adsorption. Given this hypothesis, favorable entropic factors may be the main reason primary amine based adsorbents are more effective under air capture conditions.

Effects of NOM properties on copper release from model solid phases

This study examined impacts of concentrations and properties of natural organic matter (NOM) on copper release from characteristic copper solid model phases such as tenorite CuO and malachite Cu2(OH)2CO3. Unaltered Aldrich humic acid (AHA) and standard Suwannee River fulvic acid (SRFA) strongly increased copper release from the model phases but NOM alteration by chlorination or ozonation gradually suppressed or, at higher oxidant doses, eliminated these effects. The nature of NOM changes induced by chlorination and ozonation was examined using differential absorbance spectroscopy (DAS) and high-performance size-exclusion chromatography (HPSEC). The data of these methods show that NOM molecules with higher apparent molecular weight (AMW), higher aromaticities and contributions of protonation-active phenolic and carboxylic groups play a key role in adsorption and colloidal dispersion of the model solids. The data also show that metal release from model phases was well correlated with a number of spectroscopic parameters characterizing NOM properties, notably SUVA254, spectral slopes of NOM absorbance, and differential absorbance at wavelength of 280 nm and 350 nm that is indicative of the contributions of carboxylic and phenolic functional groups. Changes of ζ-potential of the model solid phases were the strongest predictor of the enhancement of copper release especially in the system controlled by malachite. While effects of NOM on the ζ-potential of tenorite and malachite were prominent for unaltered NOM, its oxidation by chlorine and ozone was accompanied by a gradual decrease and ultimately disappearance of its surface activity.

Synthesis of an innovative calcium-alginate magnetic sorbent for removal of multiple contaminants

A new calcium-alginate magnetic sorbent has been prepared by an electrostatic extrusion technique. The sorbent has the calcium alginate as a bio-polymeric shell and iron oxides as magnetic cores. It is characterized by a multifunctional property: ease in separation via magnetic force, and effective adsorption of arsenic(V) and copper ions. It has been found that the equilibrium time of copper and arsenic(V) can be attained in less than 3 and 25 h, respectively. The maximum adsorption capacities of arsenic and copper ions are 6.75 and 60.24 mg/g, respectively, which are much higher than those of commercial adsorbents. Solution pH plays a key role in adsorption. The adsorption of arsenic increases as the pH is decreased. On the other hand, higher pH can enhance adsorption of copper ions.

Adsorption of atrazine and metolachlor in three soils from Blue Creek wetlands, Waterville, Ohio

Atrazine and metolachlor are extensively used pesticides in agricultural activities in northwest Ohio. Adsorption coefficients are often used to model pesticide fate and transport. Many physical-chemical parameters, such as organic matter, clay content, pH, and ionic strength, affect pesticide adsorption. Adsorption kinetics and adsorption isotherms were studied by batch experiment. Effects of humic acid, solution pH, and ionic strength on atrazine and metolachlor adsorption were also approached. After 24 h, both atrazine and metolachlor reached adsorption equilibrium in three local soils. Adsorption isotherms were described by Freundlich equations. The Freundlich coefficient (Kf) ranged from 0.14 to 4.47 (L kg−1) for atrazine, and 0.04 to 5.30 (L kg−1) for metolachlor. Adsorption capacity decreased in the order Sloan loam > Del Rey loam > Ottokee fine sand. Koc values varied considerably for both pesticides: metolachlor > in Sloan loam, atrazine ≥ metolachlor in Del Rey loam, and atrazine > metolachlor in Ottokee fine sand. In addition to organic matter content, clay played a key role in adsorption in the Del Rey loam and Ottokee fine sand. Higher adsorption was observed at pH 5 for both pesticides. As pH decreased to 3 and increased to 11, adsorption decreased. Adsorption increased as ionic strength increased.