Nelson Model Research Articles

Oleic Acid-Tailored Geopolymer Microspheres with Tunable Porous Structure for Enhanced Removal from Tetracycline in Saline Water

Tetracycline (TC) in the water body poses a huge threat to the ecological environment. There is a great challenge to develop highly efficient, green, low-cost and reusable adsorbents for TC removal from saline water. Herein, metakaolin-based geopolymer microspheres (MM) modified by oleic acid were proposed for the enhanced adsorption of TC from saline water. Experimental and characterization results showed that the introduction of oleic acid into the MM effectively adjusted the specific surface area, pore volume and zeta potential of the MM, thus accelerating the adsorption rate and enhancing the TC adsorption capacity of the MM. The adsorption process fitted well to the pseudo-second-order kinetic and Langmuir isothermal models. The Langmuir adsorption capacity of TC by the optimal MM, namely MM3 (0.3%, oleic acid), reached 645.7 mg·g−1 at 298 K, which was higher than many reported adsorbents. The adsorption process was endothermic and spontaneous. The MM3 had good adsorption performance of TC from saline water and regeneration performance. Moreover, the breakthrough curves of the MM3 in a column system were correlative with the Thomas and Yoon–Nelson models. The adsorption mechanisms of TC by the MM3 involved Van der Waals forces, electrostatic interactions, hydrogen–bonding interactions, and ion exchange.

Buckwheat hull-derived biochar immobilized in alginate beads for the adsorptive removal of cobalt from aqueous solutions

Buckwheat hull-derived biochar (BHBC) beads were synthesized by immobilizing biochar powder with alginate. Due to their cation-exchange ability, abundant functional groups, microporous structure, and large surface area, BHBC beads were successfully applied for the removal of cobalt from aqueous solution. The adsorption behavior followed pseudo-second-order kinetics and the Langmuir isotherm model showed a better fit to adsorption data than the Freundlich or Temkin isotherm models. The maximum adsorption capacity of BHBC beads was 24.0 mg/g at pH 5, 35 °C, and an initial cobalt concentration of 1.0 g/L, which was higher than those of previously reported natural resource-based adsorbents. In a fixed-bed column study, the effects of operating parameters such as flow rate, bed height, and bed diameter were investigated. Both the Thomas and Yoon–Nelson models were applied to the experimental data to predict the breakthrough curves using nonlinear regression. Overall, BHBC beads can be used as an efficient adsorbent for removal of radioactive cobalt from aqueous solution.

Exotic interactions mediated by a non-Hermitian photonic bath

Photon-mediated interaction between quantum emitters in engineered photonic baths is an emerging area of quantum optics. At the same time, non-Hermitian (NH) physics is currently thriving, spurred by the exciting possibility to access new physics in systems ruled by non-trivial NH Hamiltonians—in particular, photonic lattices—which can challenge longstanding tenets such as the Bloch theory of bands. Here, we combine these two fields and study the exotic interaction between emitters mediated by the photonic modes of a lossy photonic lattice described by a NH Hamiltonian. We show in a paradigmatic case study that structured losses in the field can seed exotic emission properties. Photons can mediate dissipative, fully non-reciprocal interactions between emitters with range critically dependent on the loss rate. When this loss rate corresponds to a bare-lattice exceptional point, the effective couplings are exactly nearest neighbor, implementing a dissipative, fully non-reciprocal Hatano–Nelson model. Counterintuitively, this can occur irrespective of the lattice boundary conditions. Thus photons can mediate an effective emitter’s Hamiltonian which is translationally invariant despite the fact that the field is not. We interpret these effects in terms of metastable atom–photon dressed states, which can be exactly localized on only two lattice cells or extended across the entire lattice. These findings introduce a paradigm of light-mediated interactions with unprecedented features such as non-reciprocity, non-trivial dependence on field boundary conditions, and range tunability via a loss rate.

Coulomb scattering in the massless Nelson model IV. Atom–electron scattering

We consider the massless Nelson model with two types of massive particles which we call atoms and electrons. The atoms interact with photons via an infrared regular form-factor and thus they are Wigner-type particles with sharp mass-shells. The electrons have an infrared singular form-factor and thus they are infraparticles accompanied by soft-photon clouds correlated with their velocities. In the weak coupling regime, we construct scattering states of one atom and one electron, and demonstrate their asymptotic clustering into individual particles. The proof relies on the Cook’s argument, clustering estimatesblack, and the non-stationary phase method. The latter technique requires sharp estimates on derivatives of the ground state wave functions of the fiber Hamiltonians of the model, which were proven in the earlier papers of this series. Although we rely on earlier black studies of the atom–atom and electron–photon scattering in the Nelson model, the paper is written in a self-contained manner. A perspective on the open problem of the electron–electron scattering in this model is also given.

Aminopolycarboxylic Acids-Functionalized Chitosan-Based Composite Cryogels as Valuable Heavy Metal Ions Sorbents: Fixed-Bed Column Studies and Theoretical Analysis.

Over the years, a large number of sorption experiments using the aminopolycarboxylic acid (APCA)-functionalized adsorbents were carried out in batch conditions, but prospective research should also be directed towards column studies to check their industrial/commercial feasibility. In this context, sorption studies of five-component heavy metal ion (HMI) solutions containing Zn2+, Pb2+, Cd2+, Ni2+, and Co2+ in equimolar concentrations were assessed in fixed-bed columns using some APCA-functionalized chitosan-clinoptilolite (CS-CPL) cryogel sorbents in comparison to unmodified composite materials. The overall sorption tendency of the APCA-functionalized composite sorbents followed the sequence Co2+ < Zn2+ < Cd2+ ≤ Pb2+ < Ni2+, meaning that Co2+ ions had the lowest affinity for the sorbent’s functional groups, whereas the Ni2+ ions were strongly and preferentially adsorbed. To get more insights into the application of the composite microbeads into continuous flow set-up, the kinetic data were described by Thomas and Yoon–Nelson models. A maximum theoretical HMI sorption capacity of 145.55 mg/g and a 50% breakthrough time of 121.5 min were estimated for the column containing CSEDTA-CPL cryogel sorbents; both values were much higher than those obtained for the column filled with pristine CS-CPL sorbents. In addition, desorption of HMIs from the composite microbeads in dynamic conditions was successfully achieved using 0.1 M HCl aqueous solution. Moreover, a theoretical analysis of APCA structures attached to composite adsorbents and their spatial structures within the complex combinations with transition metals was systematically performed. Starting from the most stable conformer of EDTA, coordinative combinations with HMIs can be obtained with an energy consumption of only 1 kcal/mole, which is enough to shift the spatial structure into a favorable conformation for HMI chelation.

EFFICIENCY OF ACTIVATED PERIWINKLE CHAR IN THE RECOVERY OF LEAD (II) ION FROM INDUSTRIAL WASTEWATER USING FIXED BED ADSORPTION PROCESS

The discharge of untreated industrial wastewater containing lead and the indiscriminate disposal of periwinkle shell causes lead poisoning and blockage of drainage. The cost of industrial wastewater treatment is demanding; thus the research is focused on creating wealth from waste periwinkle shell as a cheap adsorbent material to reduce the cost of lead removal from industrial wastewater. Therefore, activated periwinkle shell char (APSC) in removal of lead Pb (II) ion from industry wastewater was investigated using fixed-bed adsorption column. APSC was prepared by treating the periwinkle Char with 1M H2SO4 solution. Characterization of the adsorbent before and after continuous adsorption was performed using Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) to show modifications in the surface and chemical structure of APSC after adsorption process. The effect of design variables such as bed height, Influent concentration and withdrawal flowrate were studied.The breakthrough profiles were obtained by an analysis of the column experimental data and the relationship between operating parameters using the Thomas, Clark, Yoon-Nelson and Adams-Bohart models. The equilibrium data was best represented by the Yoon and Nelson model having the highest correlation coefficient (R2) of 0.9751. This suggest that Activated periwinkle shell char is a potential adsorbent for heavy metals removal from industrial wastewater. Keywords: activated, adsorption, char, periwinkle.

Learning Forecast-Efficient Yield Curve Factor Decompositions with Neural Networks

Most factor-based forecasting models for the term structure of interest rates depend on a fixed number of factor loading functions that have to be specified in advance. In this study, we relax this assumption by building a yield curve forecasting model that learns new factor decompositions directly from data for an arbitrary number of factors, combining a Gaussian linear state-space model with a neural network that generates smooth yield curve factor loadings. In order to control the model complexity, we define prior distributions with a shrinkage effect over the model parameters, and we present how to obtain computationally efficient maximum a posteriori numerical estimates using the Kalman filter and automatic differentiation. An evaluation of the model’s performance on 14 years of historical data of the Brazilian yield curve shows that the proposed technique was able to obtain better overall out-of-sample forecasts than traditional approaches, such as the dynamic Nelson and Siegel model and its extensions.

Modeling of linear alkyl benzene sulphonic acid removal from aqueous solution with fixed bed adsorption column: Thomas and Yoon–Nelson methods

AbstractBACKGROUNDIn Turkey, which is one of the world's top walnut producers, the volume of waste shell has increased in recent years as a result of escalating consumption. Globally, including in Turkey, cleaning products are the leading pollutants entering the aquatic environment. This study aimed to address both issues, by investigating the removal of Linear Alkyl Benzene Sulphonic Acid synthetic solution through a fixed‐bed adsorption column system embedded with the composite of a polyaniline‐supported activated walnut shell.RESULTSLinear Alkyl Benzene Sulfonic Acid removal efficiency was evaluated in terms of detergent and chemical oxygen demand (COD) parameters. Column performance increased with low flow rate, increased bed height and high inlet concentration. Optimum conditions were determined as 7.5 cm bed height, 10 mL min−1 flow rate, and 30 mg L−1 inlet solution concentration. Thomas and Yoon–Nelson models were applied to experimental data to estimate the column adsorption behavior. The Yoon–Nelson model (R2 &gt; 0.9) seemed fit to explain the adsorption column behavior. To understand the reuse capacity of the adsorbent a regeneration study was carried out, showing that the maximum adsorption capacity of the adsorbent (qtotal) decreased from 216 mg g−1 before regeneration to 6.4 mg g−1 after the third regeneration cycle.CONCLUSIONThis adsorbent has a high potential for detergent and COD adsorption from anionic aqueous solutions, and would be a good alternative for a pretreatment step. © 2022 Society of Chemical Industry (SCI).

Remarkable adsorption for hazardous organic and inorganic contaminants by multifunctional amorphous core–shell structures of metal–organic framework-alginate composites

• CA-MIL-53-AC were synthesized via a one-pot method for removing DDT, As(V), and F. • Composite beads showed superior textural properties and abundant reactive functional groups. • CA-MIL-53-AC had higher adsorptive capacity than the other beads for DDT, As(V), and F. • Plausible mechanisms were identified to provide insights in the contaminants removal. Novel metal–organic framework-alginate composite beads (CA-MIL-53-AC) were synthesized using sodium alginate (gelling agent) and calcium chloride (complexing agent) via a one-pot and dropping method to selectively remove the dichlorodiphenyltrichloroethane (DDT), arsenate (As(V)), and fluoride in an aqueous solution. To evaluate the characteristics of the synthesized composite beads, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared, X-ray photoelectron spectroscopy, thermal gravimetric analysis, zeta potential, and porosimetry techniques were used in this study. The adsorption kinetics showed that DDT, As(V), and fluoride removal could be described by the pseudo-first-order model. Also, the adsorption isotherms indicated that DDT and As(V)/fluoride removal followed the Langmuir and Freundlich models, respectively. Compared with granular AC and pristine CA, CA-AC, and CA-MIL-53, the CA-MIL-53-AC showed superior adsorption performance for all target contaminants (5.29, 4.89, and 3.18 mg/g for DDT, As(V), and fluoride, respectively). The adsorptive behavior for DDT was spontaneous, exothermic, and highly favorable based on thermodynamics calculations. Furthermore, the regenerated composite beads showed high removal capacity for DDT after the third recycle. The continuous DDT adsorption in the fixed-bed column at different flow rates were well fitted using Thomas, Adams–Bohart, and Yoon–Nelson models. The plausible mechanisms for the DDT, As(V), and fluoride removal by CA-MIL-53-AC were identified as hydrophobic and π–π interactions, ion exchange, surface complexation, and hydrogen bonding. These findings provide significant insight to remove DDT, As(V), and fluoride from water for practical applications.

Green citric acid in the sorption process of rare earth elements

In this study the effects of citric acid (CA) as a biodegradable complexing agent in the sorption process of La(III), Nd(III) and Ho(III) ions (single component systems) on various types of ion exchangers (chelating ion exchangers, cation exchanger, strongly and weakly basic polystyrene and polyacrylate anion exchangers) were investigated. The effects of pH, Ln(III):CA molar ratio, phase contact time and initial concentrations as well as temperature on the adsorption capacity were analysed. The optimal process conditions were also determined which varied depending on the ion exchanger and the metal ion. The process was fast in all systems (up to 60 min). The sorption data was analysed using the pseudo-first order (PFO), pseudo-second order (PSO), intraparticle diffusion (IPD), Boyd and Dumwald–Wagner (DW) kinetic models as well as the Langmuir, Freundlich, and Temkin isotherm models. Among the studied adsorbents, the highest adsorption capacity was obtained for the Purolite S957 chelating ion exchanger which was 162.04 mg/g for the La(III) complexes, 142.65 mg/g for the Nd(III) complexes and 180.26 mg/g for the Ho(III) complexes. Reusability of ion exchangers in the desorption studies was also evaluated as a sustainable approach. Moreover, dynamic experiments were performed using the columns set. The Thomas, Adams–Bohart, Yoon–Nelson and Wolborska models were applied to the experimental data to predict the dynamic behaviour of fixed bed columns. The physicochemical properties of adsorbents were characterized by scanning electron microscopy (SEM), pHpzc, and Fourier transform infrared spectroscopy (FTIR). The binary complexes of Ln(III) ions with CA at various metal:ligand ratios were investigated using the potentiometric method. The overall stability constants of the complexes were determined.

Efficient dichloromethane and toluene removal via lignin derived oxygen and nitrogen-containing activated carbons with well-developed micro-mesopore structure

Industrial lignin is a promising carbon precursor because it is abundant and renewable, with high carbon content. However, a large amount of lignin is used as low-value burning fuel, and even considered as environmental pollutant in some circumstances. In this work, a family of the porous activated carbon (PAC) are synthesized utilizing alkali lignin as the precursor by carbonization-activation methods. The obtained PAC display high specific surface area (2923 m2·g−1), large pore volume (1.51 cm3·g−1), and interconnected micro-mesopore structure as well as rich surface heteroatom content (7.53–10.22 at.% oxygen, 1.17–2.29 at.% nitrogen, and 0.84–0.96 at.% sulfur). When used as adsorbent for volatile organic compound (VOC) removal, the PAC show outstanding adsorption capacity of dichloromethane (171 mg·g−1) and toluene (518 mg·g−1). The porous characteristics of PAC improved along with the fluctuation of the proportions of carbonization temperature, activation temperature, and lignin/KOH mass ratio. In addition, the correlation between adsorption properties and pore structure suggests that the dichloromethane and toluene adsorption capacity are determined by nanopores (0.5–1.0 nm) and micropores (<2 nm) respectively. The Yoon and Nelson (YN) model of adsorption breakthrough curve reveals that PAC have the high adsorption rate k and fast mass transfer rate. The positive linear relationship (R2 > 0.80) between the k and mesopore confirms that mesopores play the role of mass transfer channel.

Continuous fixed-bed column study and adsorption modeling removal of Ni2+, Cu2+, Zn2+ and Cd2+ ions from synthetic acid mine drainage by nanocomposite cellulose hydrogel

Heavy metal ions are widely recognized for their harmful effects on human health and the environment. Heavy metal ions removal using nanocomposite hydrogel is a promising method for industrial applications and process development owing to their utilization in both kinematic and dynamic adsorption process. There is a need to develop simple, low-cost water purification techniques that use biodegradable bio-based natural polymers like cellulose nanocrystal that have been modified with nanomaterials. These innovative functional cellulose nanocrystals-based nanomaterials have been shown to successfully remove a variety of contaminants from wastewater to acceptable levels. Due to their capacity to hold water in their porous structures, hydrogels are the most commonly used 3D polymer mesh materials for environmental remediation. The application of potential hydrogel for the absorption of Cu2+, Ni2+, Zn2+ and Cd2+ ions from an aqueous solution in a packed bed adsorption column was studied in this work. The adsorbent was studied using FTIR, SEM, XRD and TGA. The influence of breakthrough factors such as bed height (10, 17 and 25 cm) influent concentration (10, 20 and 50 mg/L) and the feed flow rate (10, 20 and 30 mL/min) was assessed. Bed Depth Service Time, Thomas and Yoon–Nelson models were used to fit the experimental data. With an increase in bed height, breakthrough and exhaustion time, the removal efficiency rose to 99.42 ± 0.12 for Cu2+, 99.23 ± 1.16 for Ni2+, 99.36 ± 0.89 for Cd2+ and 98.94 ± 0.48 for Zn2+, but declined with increased flow rate and influent concentration. Better performance was observed at a bed height of 25 cm, an influent metal ion concentration of 10 mg/L and a flow velocity of 10 mL/min. The BDST and Yoon–Nelson models were both successfully used to predict the breakthrough curves of heavy metal ions removal.

Adsorptive removal of antipsychotic drug by carbon nanofibers in a batch and fixed bed column system

Carbon nanofibers are promising green materials for sustainable technology within a wide range of applications including environment, energy, health and high-technology. Accordingly, drug adsorption is an important subject in connection with its environmental and pharmaceutical applications. This study aims to investigate the adsorption performance of carbon nanofibers in batch and fixed bed column processes. Carbon nanofibers were used as adsorbent to remove triflupromazine hdyrochloride from aqueous solutions. Adsorption kinetics were studied using Lagergren first order and Pseudo second order models. Intraparticle diffusion graph was plotted using kinetic data and showed that intraparticle diffusion is the single step controlling the adsorption rate. Experimental equilibrium data was modeled by using Langmuir and Freundlich equations and has a better fit to the Langmuir model. Triflupromazine adsorption on carbon nanofibers was found to be H-type according to Giles classification. The effect of temperature and the effect of pH on adsorption were studied to determine optimum adsorption conditions. Adsorption capacity of carbon nanofibers was decreased with increasing temperature due to the exothermic and physical nature of the process. Thermodynamic parameters confirmed the exothermic nature of the adsorption. Results showed the effective adsorption of drug molecules by carbon nanofibers. Maximum adsorption capacity was calculated as 165.41 mg/g at pH 9 using Langmuir equation. Modeling of the fixed bed column data was done by using Thomas model and Yoon–Nelson model. Results showed the important effect of the operating conditions on the removal performance of carbon nanofibers. Removal capacity was increased with an increase in the flow rate and the increase in the fixed bed length.

Importance of spectroscopic and static gravimetric studies for exploring adsorption behavior of propan-2-ol vapor in a fixed-bed column

The exploration of the vapor–solid adsorption mechanism based on goodness-of-fit kinetic models raises many doubts because most of them do not consider the influence of adsorbent heterogeneity on the adsorption kinetics. Thus, results should be verified by independent studies. In this work, the mechanism of propan-2-ol (IPA) vapor adsorption on BPL 4 × 6 activated carbon was investigated using static gravimetric and column studies. Several kinetic and simplified dynamic models were used to fit experimental data. It was shown that the pseudo-second-order model provided the best agreement with the kinetic data at 0.5 g m−3, while the double-exponential model was better at higher concentrations which indicated a complex adsorption mechanism. The Yoon–Nelson and Thomas models well predicted breakthrough curves, and the overall mass transfer coefficients were approximately an order of magnitude lower than the adsorption rates determined from the kinetic models. FTIR analysis showed that the increase in IPA loading caused a change in carbon surface chemistry. This phenomenon was most pronounced at low surface coverage, suggesting that specific interactions between adsorbate and surface oxygen groups affected the process mechanism, the adsorbent capacity, and regenerability. This is in line with the results of thermodynamic studies.

Highly Effective Cow Bone Based Biocomposite for the Sequestration of Organic Pollutant Parameter from Palm Oil Mill Effluent in a Fixed Bed Column Adsorption System.

The reduction of chemical oxygen demand (COD) from palm oil mill effluent (POME) is very significant to ensure aquatic protection and the environment. Continuous adsorption of COD in a fixed bed column can be an effective treatment process for its reduction prior to discharge. Adsorption capacity of bone derived biocomposite synthesized from fresh cow bones, zeolite, and coconut shells for the reduction in the organic pollutant parameter was investigated in this study in a fixed bed column. The effect of influent flow rate (1.4, 2.0, and 2.6 mL/min) was determined at an influent pH 7. The optimum bed capacity on the fabricated composite of surface area of 251.9669 m2/g was obtained at 1.4 mL/min at breakthrough time of 5.15 h influent POME concentration. The experimental data were fitted to Thomas, Adams–Bohart, and Yoon–Nelson models fixed bed adsorption models. It was revealed that the results fitted well to the Adams Bohart model with a correlation coefficient of R2 > 0.96 at different influent concentration. Adsorption rate constant was observed to increase at lower flow rate influent concentration, resulting in longer empty bed contact time (EBCT) for the mass transfer zone of the column to reach the outlet of the effluent concentration. In general, the overall kinetics of adsorption indicated that the reduction in COD from POME using a bone-biocomposite was effective at the initial stage of adsorption. The pore diffusion model better described the breakthrough characteristics for COD reduction with high correlation coefficient. Shorter breakthrough time compared to EBCT before regeneration indicated that the bone composite was suitable and effective for the reduction in COD from POME using fixed bed column adsorption.

Continuous Fixed-Bed Column Studies on Congo Red Dye Adsorption-Desorption Using Free and Immobilized Nelumbo nucifera Leaf Adsorbent.

The adsorption of Congo red (CR), an azo dye, from aqueous solution using free and immobilized agricultural waste biomass of Nelumbo nucifera (lotus) has been studied separately in a continuous fixed-bed column operation. The N. nucifera leaf powder adsorbent was immobilized in various polymeric matrices and the maximum decolorization efficiency (83.64%) of CR occurred using the polymeric matrix sodium silicate. The maximum efficacy (72.87%) of CR dye desorption was obtained using the solvent methanol. Reusability studies of free and immobilized adsorbents for the decolorization of CR dye were carried out separately in three runs in continuous mode. The % color removal and equilibrium dye uptake of the regenerated free and immobilized adsorbents decreased significantly after the first cycle. The decolorization efficiencies of CR dye adsorption were 53.66% and 43.33%; equilibrium dye uptakes were 1.179 mg g–1 and 0.783 mg g–1 in the third run of operation with free and immobilized adsorbent, respectively. The column experimental data fit very well to the Thomas and Yoon–Nelson models for the free and immobilized adsorbent with coefficients of correlation R2 ≥ 0.976 in various runs. The study concludes that free and immobilized N. nucifera can be efficiently used for the removal of CR from synthetic and industrial wastewater in a continuous flow mode. It makes a substantial contribution to the development of new biomass materials for monitoring and remediation of toxic dye-contaminated water resources.

Alternative Materials for the Enrichment of Biogas with Methane.

Carbonaceous adsorbents have been pointed out as promising adsorbents for the recovery of methane from its mixture with carbon dioxide, including biogas. This is because of the fact that CO2 is more strongly adsorbed and also diffuses faster compared to methane in these materials. Therefore, the present study aimed to test alternative carbonaceous materials for the gas separation process with the purpose of enriching biogas in biomethane and to compare them with the commercial one. Among them was coconut shell activated carbon (AC) as the adsorbent derived from bio-waste, rubber tire pyrolysis char (RPC) as a by-product of waste utilization technology, and carbon molecular sieve (CMS) as the commercial material. The breakthrough experiments were conducted using two mixtures, a methane-rich mixture (consisting of 75% CH4 and 25% CO2) and a carbon dioxide-rich mixture (containing 25% CH4 and 75% CO2). This investigation showed that the AC sample would be a better candidate material for the CH4/CO2 separation using a fixed-bed adsorption column than the commercial CMS sample. It is worth mentioning that due to its poorly developed micropore structure, the RPC sample exhibited limited adsorption capacity for both compounds, particularly for CO2. However, it was observed that for the methane-rich mixture, it was possible to obtain an instantaneous concentration of around 93% CH4. This indicates that there is still much potential for the use of the RPC, but this raw material needs further treatment. The Yoon–Nelson model was used to predict breakthrough curves for the experimental data. The results show that the data for the AC were best fitted with this model.

Competitive adsorption of Ni(II) and Cu(II) ions from aqueous solution by vermiculite-alginate composite: batch and fixed-bed column studies

The present study introduces vermiculite-Alginic composite (VMT-ALG) as a low-cost adsorbent for the uptake of Ni(II) and Cu(II). The fabricated composite was characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) analysis. The different process parameters such as contact time, pH, initial heavy metal concentration, and temperature were optimized. According to the experimental data, the Freundlich adsorption model with the coefficient determination of 0.9945 and 0.9925 is the best isotherm model to describe the adsorption of Cu(II) and Ni(II) by VMT-ALG, respectively. Also, the equilibrium study confirmed the heterogeneous adsorption for Ni(II) and Cu(II). Kinetic studies indicate that intra-particle diffusion would be the significant rate-limiting step of the adsorption process. Thermodynamic studies indicated that the adsorption process was physisorption and endothermic. Research on fixed-bed column (20 cm length and 1.0 cm inner diameter) has been carried out under different volumetric flow rates (10 and 20 ml/min) and different initial concentrations of Cu(II) and Ni(II) (250, 500, and 750 mg/l). The results of column data were successfully explained using the Thomas and Yoon–Nelson models. Finally, continuous adsorption studies for Cu(II) and Ni(II) simultaneous uptake from aqueous solutions were conducted by VMT-ALG composite. The results indicated that the adsorption capacity of Cu(II) and Ni(II) both increased with an increase in the concentration of metal ions, and decreased with an increase in the flow rate.

Pathways to student engagement: beyond triggers and mechanisms at the engagement interface

This paper, while conceptual in nature, is informed by both research and practice. Exploring the “engagement interface” as the site for student engagement (SE), we offer a conceptual contribution in engaging with the Kahu and Nelson (2018) model by bringing in a fuller understanding of SE grounded in the higher education context rather than being uncritically transplanted from a compulsory education context. This involves consideration of the multiple facets of SE as well as the dynamic, shifting and multilocal nature of the construct. The paper then proceeds to enhance the details of the model, grounding them in a finer-grained reading of the literature and relating educational constructs to the model’s proposed “mechanisms” in a conceptually substantiated way. This further extends Kahu and Nelson’s aim of illuminating the “black box” of SE. Our third contribution is to practice by proposing tactics: informed by the literature, we invite practitioners to consider ways in which they can increase the likelihood of facilitating engagement with, and by, students more constructively.

Fabrication of MNPs/rGO/PMMA Composite for the Removal of Hazardous Cr(VI) from Tannery Wastewater through Batch and Continuous Mode Adsorption.

Herein, we report the synthesis of magnetic nanoparticle (MNP)-reduced graphene oxide (rGO) and polymethylmethacrylate (PMMA) composite (MNPs/rGO/PMMA) as adsorbent via an in situ fabrication strategy and, in turn, the application for adsorptive removal and recovery of Cr(VI) from tannery wastewater. The composite material was characterized via XRD, FTIR and SEM analyses. Under batch mode experiments, the composite achieved maximum adsorption of the Cr(VI) ion (99.53 ± 1.4%, i.e., 1636.49 mg of Cr(VI)/150 mg of adsorbent) at pH 2, adsorbent dose of 150 mg/10 mL of solution and 30 min of contact time. The adsorption process was endothermic, feasible and spontaneous and followed a pseudo-2nd order kinetic model. The Cr ions were completely desorbed (99.32 ± 2%) from the composite using 30 mL of NaOH solution (2M); hence, the composite exhibited high efficiency for five consecutive cycles without prominent loss in activity. The adsorbent was washed with distilled water and diluted HCl (0.1M), then dried under vacuum at 60 °C for reuse. The XRD analysis confirmed the synthesis and incorporation of magnetic iron oxide at 2θ of 30.38°, 35.5°, 43.22° and 57.36°, respectively, and graphene oxide (GO) at 25.5°. The FTIR analysids revealed that the composite retained the configurations of the individual components, whereas the SEM analysis indicated that the magnetic Fe3O4–NPs (MNPs) dispersed on the surface of the PMMA/rGO sheets. To anticipate the behavior of breakthrough, the Thomas and Yoon–Nelson models were applied to fixed-bed column data, which indicated good agreement with the experimental data. This study evaluates useful reference information for designing a cost-effective and easy-to-use adsorbent for the efficient removal of Cr(VI) from wastewater. Therefore, it can be envisioned as an alternative approach for a variety of unexplored industrial-level operations.