Negative Enthalpy Change Research Articles

Structural Insight into Groove Binding of Yohimbine with Calf Thymus DNA: A Spectroscopic, Calorimetric, and Computational Approach.

A variety of anticancer and antibacterial drugs target DNA as one of their primary intracellular targets. Understanding ligand-DNA interactions and developing new, promising bioactive molecules for clinical use are greatly aided by elucidating the interaction between small molecules and natural polymeric DNAs. Small molecules' ability to attach to and inhibit DNA replication and transcription provides more information on how drugs impact the expression of genes. Yohimbine has been broadly studied in pharmacological properties, while its binding mode to DNA has not been explicated so far. In this study, an attempt was made to explore the interaction between Yohimbine (YH) and calf thymus (CT-DNA) by using varying thermodynamics and in silico approaches. Minor hypochromic and bathochromic shifts of fluorescence intensity were observed, suggesting the binding of YH to CT-DNA. The Scatchard plot analysis using the McGhee-von Hipple method revealed noncooperative binding and affinities in the range of 105 M-1. The binding stoichiometry value is 2:1 (2 molecules of YH were span by 1 base pair) and was determined by Job's plot. The thermodynamic parameters suggested exothermic binding, which was favored by negative enthalpy and positive entropy changes from both isothermal titration calorimetry and temperature-dependent fluorescence experiment. Salt-dependent fluorescence suggested that the interaction between the ligand and DNA was governed by nonpolyelectrolytic forces. Kinetics experiment confirmed the static type of quenching. The results of iodide quenching, urea denaturation assay, dye displacement, DNA melting, and in silico molecular docking (MD) suggested groove binding of YH to CT-DNA. Circular dichroism spectra confirmed minimal perturbation of CT-DNA with YH binding via groove region. Therefore, the groove binding mechanism of interaction was validated by biophysical techniques and in silico, MD approaches. The findings supported here may contribute to the development of new YH therapeutics possessing better efficacy and lesser side effects.

Understanding the molecular interaction of BSA protein with antibiotic sulfa molecule(s) for novel drug development

Sulfonamide/ sulfa drug (SN) are extensively studied due to their potential antibiotic property. The study of the interaction of bio-macromolecules and small molecules has been a subject of significant interest with varied applications in drug development and modification. The present study aimed to determine the structure, binding characteristics and thermodynamic aspects into binding of sulfamolecules (sulfadiazine and sulfamethazine) towards plasma protein - bovine serum albumin (BSA). The spectrofluorometric titrations study indicates that SN is bound non-cooperatively to BSA protein with the binding affinities and the binding stoichiometry (n) to be in the order of 104 M-1and 1:1 respectively. The quenching constants were observed to decrease with increase in temperature, indicating static quenching mechanism. The negative molar Gibbs energy suggested the spontaneity of the interaction process. The negative enthalpy and positive entropy change(s) indicated towards the involvement of both electrostatic and hydrophobic forces during association process. Salt dependent fluorescence study revealed major contributions from non-poly-electrolytic and less poly-electrolytic forces. Thermal denaturation, circular dichroism (CD), synchronous fluorescence, small angle neutron scattering (SANS) and zeta (ζ)-potential result indicates minor structural change of BSA upon association with sulfa drug. Molecular docking (MD) study further supports the experimental results and shows the ligand binding at Pocket-I of the active site of BSA. The results obtained thus advance our insights into drug-protein interaction patterns which provide help and guidance to biomedical and pharmaceutical researchers for the rational designing of drugs and for the development of more effective and targeted therapies.

Solvent extraction of gold from a chloride-hypochlorite leached solution of waste printed circuit boards

ABSTRACT This study reveals the reclamation process of gold from a brine-leached solution of waste printed circuit boards (WPCBs) after the maximum leaching of base metals in a nitric acid medium. The brine leaching performed in the presence of hypochlorite yielded leach liquor of 152 ppm Au, 86 ppm, Cu, and 62 ppm Ni that underwent solvent extraction with tri-butyl phosphate (TBP) in Exxol D80. The gold extraction process was observed to be selective over base metal impurities, while the effect of TBP concentration, equilibrium pH, temperature, and organic-to-aqueous phase ratio was optimized. Experimental results showed the formation of complex into the extraction phase with the negative enthalpy change value of −98.7 kJ/mol. Thiosulphate mobilized stripping of gold from the loaded-TBP could give about 99% recovery efficiency of the solvent extraction process along with a good regeneration of the organic extractant to be re-used.

Understanding association between methylene blue dye and biosorbent: Palmyrah sprout casing in adsorption process in aqueous phase

Water pollution caused by industrial dyes has become a severe problem in the modern world. Biosorbents can be used in an eco-friendly manner to remove industrial dyes. In this study, five biosorbents were selected: palmyrah sprout casing (PSC), manioc peel, lime peel, king coconut husk, and coconut kernel. Batch adsorption experiments were conducted to identify the best biosorbent with the highest ability to adsorb methylene blue (MB) from wastewater. The detailed mechanisms of PSC used in the adsorptive removal of MB in aqueous phase were investigated. Of the five biosorbents, PSC exhibited the best removal performance with an adsorption capacity at equilibrium (qe) of 27.67 mg/g. The qe values of lime peel, king coconut husk, manioc peel, and coconut kernel were 24.25 mg/g, 15.29 mg/g, 10.84 mg/g, and 7.06 mg/g, respectively. To explain the mechanisms of MB adsorption with the selected biosorbents, the Fourier transform infrared (FTIR) spectrometry and X-ray diffraction (XRD) analyses were performed to characterize functional properties, and isotherm, kinetic, rate-limiting, and thermodynamic analyses were conducted. The FTIR analysis revealed that different biosorbents had different functional properties on their adsorptive surfaces. The FTIR and XRD results obtained before and after MB adsorption with PSC indicated that the surface functional groups of carbonyl and hydroxyl actively participated in the removal process. According to the isotherm analysis, monolayer adsorption was observed with the Langmuir model with a determination coefficient of 0.998. The duration to reach the maximum adsorption capacity for MB adsorption with PSC was 120 min, and the adsorption process was exothermic due to the negative enthalpy change (−9.950 kJ/mol). Moreover, the boundary layer thickness and intraparticle diffusion were the rate-limiting factors in the adsorption process. As a new biosorbent for MB adsorption, PSC could be used in activated carbon production to enhance the performance of dye removal.

Adsorption of sulfur on Lanxess Lewatit® AF 5 resin during the acidic albion leaching process for chalcopyrite

Elemental sulfur is one of the major byproducts of the acidic Albion leaching process for chalcopyrite. It is a challenging component in the leach solution as it impedes gold recovery from the residue. Lanxess Lewatit® AF 5 (AF 5) is a microporous carbon-based resin, which is being investigated for the removal of elemental sulfur during this leaching process. In the current research, a series of leaching experiments were performed as a function of temperature, agitation speed and concentrate to AF 5 ratio. Using these results, the adsorption isotherms, the kinetics and the thermodynamics of sulfur removal were studied. One hundred percent of the elemental sulfur could be adsorbed by the AF 5 resin from the acidic Albion leaching process for chalcopyrite. Adsorption isotherms at various temperatures were determined using the Langmuir and Freundlich models. The maximum sorption capacity of AF 5 at 95 °C was 488 mg/g. The kinetic data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models and it was shown that the PFO model was best suited to describe the results. The rapid kinetics of sulfur adsorption were attributed to the open pore structure of the AF 5. The Gibbs free energy, enthalpy and entropy of sulfur adsorption by AF 5 were determined as follows: ΔGadso = −1.9 kJ/mol, ΔHadso = −9.1 kJ/mol, and ΔSadso = −0.1 kJ/(mol K). The negative free energy and enthalpy changes demonstrated that the adsorption of elemental sulfur was both spontaneous and exothermic over the temperature range studied.

Soil humic acid and arsenite binding by isothermal titration calorimetry and Dynamic Light Scattering: Thermodynamics and aggregation

The arsenite-humic acid binding process was investigated using Isothermal Titration Calorimetry (ITC), Dynamic Light Scattering and Laser Doppler Electrophoresis techniques. The ITC data were successfully (R2 = 0.996–0.936) interpreted by applying the MNIS model, enabling thermodynamic parameters to be determined. The MNIS model was adjusted to the arsenite-HA binding process assuming that hydrogen bonding is the dominant type of interaction in the system. Negative enthalpy change values indicated the arsenite-HAs binding as an exothermic process. Negative ΔG values (-(26.83–27.00) kJ mol−1) pointed out to spontaneous binding reaction, leading to the formation of the arsenite-HA complexes. The binding constant values ((7.57–5.02) 105 M−1) clearly demonstrate pronounced binding affinity. As ΔS values are obviously positive but close to zero, and ΔH>ΔS, the reaction can be considered enthalpy driven. Reaction heats and ΔH values (-(18.96–15.64) kJ mol−1) confirmed hydrogen bonds as the most ascendant interaction type in the arsenite-HA complex. Negative zeta potential values (−45 to −20 mV) had shown that arsenite-HA aggregates remained negatively charged in the whole molar charge ratio range. The HAs' aggregate size change is evident but not particularly pronounced (Zav = 50–180 nm). It can be speculated that aggregation during the titration process is not expressive due to repulsive forces between negatively charged arsenite-HA particles. Thermodynamic and reaction parameters clearly indicated that arsenite-HA complexes are formed at common soil pH values, confirming the possible influence of humic acids on increased As mobility and its reduced bioavailability.

Experimental investigation of a novel evaporative cooling pad made of cement-free porous concrete

Greenhouse overheating is a major problem for dry climate agricultural setups during the summer months. Evaporative cooling is a convenient solution for controlling indoor temperature on hot and dry days. However, conventional evaporative cooling pad materials such as polymers, cellulose, and organic fibres present problems in terms of high carbon footprint, after-use disposal, and/or very limited lifespan. In this study, porous concrete was tested as a novel evaporative cooling pad material in an experimental wind tunnel with different inlet air temperatures at a constant air velocity (2.5 m s−1). The porous concrete evaporative cooling pad demonstrated the highest evaporative cooling capacity at −11.46 kW sensible cooling with 10.17 kW m−2 °C−1 cooling coefficient. It further exhibited an evaporation rate of 5.84 g s−1 with an evaporation coefficient of 1.56 m s−1. The average cooling effectiveness was obtained as 0.97, where some inlet air conditions demonstrated negative enthalpy changes after evaporation. However, the maximum average enthalpy change was 10.97 kJ kg−1. This novel evaporative cooling pad material showed the highest effectiveness when compared to conventional evaporative cooling pad systems reported in other studies.

DNA Strand Displacement with Base Pair Stabilizers: Purine-2,6-Diamine and 8-Aza-7-Bromo-7-Deazapurine-2,6-Diamine Oligonucleotides Invade Canonical DNA and New Fluorescent Pyrene Click Sensors Monitor the Reaction.

Purine-2,6-diamine and 8-aza-7-deaza-7-bromopurine-2,6-diamine 2'-deoxyribonucleosides (1 and 2) were implemented in isothermal DNA strand displacement reactions. Nucleoside 1 is a weak stabilizer of dA-dT base pairs, nucleoside 2 evokes strong stabilization. Strand displacement reactions used single-stranded invaders with single and multiple incorporations of stabilizers. Displacement is driven by negative enthalpy changes between target and displaced duplex. Toeholds are not required. Two new environmental sensitive fluorescent pyrene sensors were developed to monitor the progress of displacement reactions. Pyrene was connected to the nucleobase in the invader or to a dendritic linker in the output strand. Both new sensors were constructed by click chemistry; phosphoramidites and oligonucleotides were prepared. Sensors show monomer or excimer emission. Fluorescence intensity changes when the displacement reaction progresses. Our work demonstrates that strand displacement with base pair stabilizers is applicable to DNA, RNA and to related biopolymers with applications in chemical biology, nanotechnology and medicinal diagnostics.

Amino-containing polymer-coated magnetite nanoparticles as nano-adsorbents for bisphenol A: Synthesis, kinetic and thermodynamic study

Magnetite nanoparticles coated with poly(dimethyl aminoethyl methacrylate) (PDMAEMA@MNPs) and their quarternized form (PQDMAEMA@MNPs) were successfully synthesized and used as nano-adsorbents for bisphenol A (BPA). The particles were spherical with the average particle size between 10 and 20 nm in diameter with a moderate degree of nanoclustering (ca.150-200 particles/cluster). In terms of adsorption properties, the PDMAEMA@MNPs exhibited a higher BPA adsorption capacity (1.05 mg/g MNP at pH 9) than the quaternized form (0.50 mg/g MNP at pH 9). Equilibrium isotherm, kinetic, and thermodynamic characteristics of BPA adsorption on the PDMAEMA@MNPs were investigated. It was found that the BPA adsorption on the MNPs reached an equilibrium within 5 min and the maximum adsorption capacity (qe) was 9.88 mg/g. The adsorption isotherm study results indicated that the BPA adsorption process on PDMAEMA@MNPs exhibited the best fit with the Freundlich model, and the adsorption kinetics followed the pseudo-second order model with the R2 value of 1.00. The thermodynamic data exhibited a negative enthalpy change (ΔH◦ = -2585.571 J/mol), indicating exothermic BPA adsorption, and a negative Gibbs free energy (ΔG◦), implying a spontaneous BPA adsorption process.

Hydroxyl-functionalized hypercrosslinked polymers with ultrafast adsorption rate as an efficient adsorbent for phenol removal

In the present study, the adsorptive potential of hypercrosslinked polymers (HCPs) was investigated for the removal of phenol from aqueous solutions. Herein, two HCPs were one-step synthesized by the Friedel-Crafts reaction using 4,4′-biphenyldiol (BPD) or hydroquinone (HQ) as the building unit and 1,4-bis(chloromethyl)benzene (DCX) as the external crosslinker. The results showed that the HCPs, derived from BPD and DCX (called as BPD-D), exhibited more excellent pore structures with the higher surface area of 697 m2 g−1 and the micropore volume of 0.23 cm3 g−1 and allowed for the extremely fast equilibrium adsorption of phenol, attributed to the hierarchical pore structure and the great hydrophilicity; meanwhile, the maximum adsorption capacity of BPD-D towards phenol was calculated to be 156.74 mg g−1. Moreover, the adsorption equilibrium and kinetic processes of BPD-D towards phenol were well described by the Freundlich model (R2 > 0.99) and the pseudo-second-order kinetic model (R2 > 0.9999) at 303 K. Moreover, negative changes in Gibbs free energy and enthalpy reflect that the adsorption of BPD-D for phenol is a spontaneous and exothermic process. In addition, adsorption performances were investigated under different conditions, e.g., the initial concentrations of phenol, the dosage of the BPD-D, the initial pH of phenol aqueous solution and recyclability. Our finding demonstrates that HCPs show potential application prospects in the removal of organic pollutants from wastewater.

The recycle of spent Zn–C batteries and the synthesis of magnetic nanocomposite from graphene nanosheets and ferrite and its application for environmental remediation

In this research work, the well-known manganese zinc ferrite Mn0.8Zn0.2Fe2O4 (MZF) magnetic material ferrite was prepared using an eco-friendly method from spent Zn–C batteries (SZCBs) and doped with the high surface area graphene oxide (GO) nanosheets to form MZF/GO magnetic nanocomposite. The prepared MZF/GO magnetic nanocomposite was characterized using DTA-TG, XRD, FT-IR, TEM, and VSM techniques for examining the morphological structure, functional groups, and magnetic properties of the prepared nanocomposite. The characterization results indicated the formation of the Mn0.8Zn0.2Fe2O4 ferrite, and GO, and the homogenous distribution of the ferrite on the GO nanosheets. MZF/GO magnetic nanocomposite was then used as a solid adsorbent for removing Acid Red (AR) dye from water. The results presented the suitability of the pseudo-second-order kinetic model, exothermic, electrostatic, and the physical nature adsorption process, with a removal capacity of 49.9 mg AR dye per g MZF/GO magnetic nanocomposite. The thermodynamics of the adsorption process showed the spontaneity of the process, with a negative entropy change value of −63.7 J/mol.K, negative enthalpy change value of −34.5 kJ/mol, and negative Gibbs free energy change value of −17.5 kJ/mol, indicating that the adsorption of the AR dye by MZF/GO magnetic nanocomposite is enthalpy-driven-process. Moreover, MZF/GO magnetic nanocomposite could be used for the remediation of real environmental water polluted with AR dye, and also could be used for five consecutive cycles with high efficacy for times for the adsorption/removal of AR dye.

β-cyclodextrin encapsulation of curcumin elicits an altered mode of angiogenin inhibition: In vitro and in vivo studies

The interaction of curcumin (Cur) with human angiogenin (hAng), a potent blood vessel inducer responsible for angiogenesis is found to change following encapsulation within the β-cyclodextrin (βCD) cavity. The enhanced bioavailability and increase in the binding stoichiometry of hAng:Cur-βCD (1:2) leads to increased affinity, hence an increase in the association constant. The altered mode of hAng inhibition of Cur from a non-competitive (KI = 23.7 ± 2.2 μM) to a mixed type (KI = 19.8 ± 1.4 μM), after encapsulation provides an insight into interaction patterns. Isothermal titration calorimetry (ITC) experiments indicate the formation of multiple favorable non-covalent interactions (also confirmed by docking studies), which implies negative enthalpy changes (−ΔHo) and restriction in the dynamic mobility of the free protein molecule resulting in a very less positive entropy change (TΔSo). This leads to a medium magnitude for the spontaneous free energy change associated with the interaction/binding process. The spontaneity of binding indicates a more favorable value for the Cur-βCD (ΔGo = −7.75 kcal/mol) compared to Cur (ΔGo = −7.49 kcal/mol). In vivo studies also demonstrate the anti-angiogenic effect of Cur/Cur-βCD confirmed by the significant decrease in blood vessel density and branching index.

Biophysical and molecular modeling evidences for the binding of sulfa molecules with hemoglobin

The molecular mechanism of the heme protein, hemoglobin (Hb) interaction with sulfa molecule, sulfadiazine (SDZ) has been investigated through spectroscopic, neutron scattering and molecular modeling techniques. Absorption and emission spectroscopic studies showed that SDZ molecules were bound to Hb protein, non-cooperatively. The binding affinityof SDZ-Hb complex at standard experimental condition was evaluated to be around (4.2 ± 0.07) ×104, M−1with 1:1 stoichiometry. Drug induced structural perturbation of the 3 D protein moiety was confirmed through circular dichroism (CD), synchronous fluorescence and small angle neutron scattering methods. From the temperature dependent spectrofluorometric studies, the negative standard molar Gibbs energy change suggested the spontaneity of the reaction. The negative enthalpy and positive entropy change(s) indicated towards the involvement of both electrostatic and hydrophobic forces during the association process. Salt dependent fluorescence study revealed major contributions from non-poly-electrolytic forces. Molecular modeling studies determined the probable binding sites, types of interaction involved and the conformational alteration of the compactness of the Hb structure upon interaction with SDZ molecule. Overall, the study provides detailed insights into the binding mechanism of SDZ antibiotics to Hb protein. Communicated by Ramaswamy H. Sarma

Deciphering binding affinity, energetics, and base specificity of plant alkaloid Harmane with AT and GC hairpin duplex DNA.

Insights into binding efficacy and thermodynamic aspects of small molecules are important for rational drug designing and development. Here, the interaction of Harmane (Har), a very important bioactive indole alkaloid, with AT and GC hairpin duplex-DNAs has been reported using various biophysical tools. Detailed molecular mechanism with special emphasis on binding nature, base specificity, and thermodynamics have been elucidated via probing nucleic acids with varying base compositions. Har bound to both the DNA strands exhibited hypochromic effect in absorbance whereas bathochromic and hypochromic effects in fluorescence spectra. The binding constants estimated were in the order of 105 M-1 (higher for GC sequence compared with AT) with 1:1 stoichiometry. Noncooperative binding mode has been observed via intercalation in both the cases. The thermodynamic profile was obtained from temperature-dependent fluorescence experiments. Both Har-AT and Har-GC complexations were exothermic in nature associated with positive entropy and negative enthalpy changes. Salt-dependent studies revealed that the binding interaction was governed by nonpolyelectrolytic and hydrophobic interaction forces. The ligand-induced structural perturbation of the DNA structures was evident from the circular dichroism data. Molecular modelling data indicated towards the involvement of hydrophobic forces and hydrogen bonding.

Targeting Natural Polymeric DNAs with Harmane: An Insight into Binding and Thermodynamic Interaction Through Biophysical Approach.

DNA is one of the major molecular targets for a broad range of anticancer drugs. Hence, interaction studies involving cellular DNA and small molecules can be highly beneficial as they often lead to rational and efficient drug design. In this study, the binding interaction of Harmane (a naturally occurring, bioactive indole alkaloid) with two natural polymeric DNAs, that is, Calf thymus (CT) DNA and Herring testis (HT) DNA has been elucidated using biophysical techniques. A ground state, 1:1 complexation, was revealed by steady-state fluorescence spectroscopy. The thermodynamic profile and energetics of the associated reaction were evaluated by temperature-dependent fluorescence spectroscopy. The spontaneity of the binding was confirmed by the negative ΔG° values in both cases. Negative enthalpy change, along with stronger positive entropic contribution, indicated the dominant electrostatic nature of the interaction and finally the entropy-driven exothermic binding process throughout. Salt-dependent studies further demonstrated the significant contribution of electrostatic interactions in ligand binding toward DNA. Infrared data substantiated the structural information of the said interactions, leading to the exploration of the structure-function relationship.

Pressure-Induced Polymerization: Addition and Condensation Reactions.

Under pressure of 1–100 GPa, unsaturated organic molecules tend to form covalent bond to each other for a negative enthalpy change, which often produces polymeric materials with extended carbon skeleton. The polymerization reactions typically happen in crystal, which promotes the topochemical process. This review summarized the topochemical polymerization processes of several alkynes, aromatics, and alkynylphenyl compounds, including the critical crystal structures before the reaction, bonding process, and the structure of the products. Secondly, this review also summarized the condensation reaction identified in the polymerization process, including the elimination of small molecules such as NH3, etc.

Entropy Versus Enthalpy Controlled Temperature/Redox Dual-Triggered Cages for Selective Anion Encapsulation and Release.

New C3 -symmetric imidazole ligands were designed with phosphine and phosphine oxide linkers (LP and LPO , respectively) to demonstrate a dual-triggered dynamic closed coordination cage. Both LP and LPO form discrete Zn4 L4 -closed cages (1P and 1PO , respectively) with excellent selectively for BPh4 - , whereas 1P and 1PO encapsulate neither a slightly larger size anion [B(C6 H4 CH3 )4 - ] nor smaller size anions (BF4 - , PF6 - , SbF6 - , and OSO2 CF3 - ). 1PO exhibits more negative enthalpy and entropy changes upon anion encapsulation, thus releasing almost all of the encapsulated anions at high temperature (343 K) (trigger 1: BPh4 - ⊂1PO 1PO +BPh4 - ). In contrast 1P has less negative enthalpy and entropy changes, thus preserving the captured anion over a wide range of temperatures (298 K to 343 K). The 1P cage can be quantitatively oxidized to the 1PO cage by a mild oxidant (Ox.=H2 O2 ), and therefore the captured anion can be released by a redox triggering event (trigger 2: BPh4 - ⊂1P +Ox.→1PO +BPh4 - ).

Entropy Versus Enthalpy Controlled Temperature/Redox Dual‐Triggered Cages for Selective Anion Encapsulation and Release

AbstractNew C3‐symmetric imidazole ligands were designed with phosphine and phosphine oxide linkers (LP and LPO, respectively) to demonstrate a dual‐triggered dynamic closed coordination cage. Both LP and LPO form discrete Zn4L4‐closed cages (1P and 1PO, respectively) with excellent selectively for BPh4−, whereas 1P and 1PO encapsulate neither a slightly larger size anion [B(C6H4CH3)4−] nor smaller size anions (BF4−, PF6−, SbF6−, and OSO2CF3−). 1PO exhibits more negative enthalpy and entropy changes upon anion encapsulation, thus releasing almost all of the encapsulated anions at high temperature (343 K) (trigger 1: BPh4−⊂1PO 1PO+BPh4−). In contrast 1P has less negative enthalpy and entropy changes, thus preserving the captured anion over a wide range of temperatures (298 K to 343 K). The 1P cage can be quantitatively oxidized to the 1PO cage by a mild oxidant (Ox.=H2O2), and therefore the captured anion can be released by a redox triggering event (trigger 2: BPh4−⊂1P+Ox.→1PO+BPh4−).

Potential application of graphene oxide and Aspergillus niger spores with high adsorption capacity for recovery of europium from red phosphor, compact fluorescent lamp and simulated radioactive waste

The recovery of rare earth elements (REEs) is a global challenge and the mining of rare earths has serious environmental implications due to the toxic waste released post mining. Hence, the rising demand for rare earths and their far reaching electronic applications necessitates an effective strategy to recover the REEs from more viable sources. In this work, the graphene oxide–Aspergillus niger spores (GO–A. niger spores) blend was utilized for adsorptive recovery of a precious rare earth Eu(III) and the adsorption variables like pH of the medium, adsorbent dosage, sorption kinetics, thermodynamics, and isotherm were optimized for the developed biosorbent. The adsorption process suits the Langmuir isotherm model with a maximum adsorption capacity of 147.3 mg/g. The pseudo–second–order kinetics is a perfect fit to describe the adsorption process. The results obtained through the Van't Hoff plot show negative free energy change (ΔG0) which implies the spontaneity of the adsorption process. The negative standard enthalpy change (ΔH0) values show that the nature of the adsorption process is exothermic. The analytical characterizations including Fourier transform infrared spectroscopy (FTIR), Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), thermal gravimetric analysis (TGA), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) were employed to study the biosorbent. The features of GO–A. niger spores biosorbent were applied to recover Eu(III) from real samples such as fluorescent lamp phosphor, red phosphor powder, and a simulated radioactive waste solution.

Chelating solid-phase polymeric adsorbent for the removal of Hg2+ ions from aqueous solutions: preparation, characterization and adsorption optimization studies

In this article, preparation, characterization and application of a chelating amino-grafted solid-phase polymeric adsorbent for the removal of Hg2+ ions from contaminated aqueous solutions were discussed. Functional groups identification and surface morphology studies were carried out using FTIR, XRD, and SEM techniques. Batch adsorption methodology was used to explore the influence of solution’s pH, shaking time, adsorbent dose, Hg2+ ions initial concentration, and temperature on the adsorption capacity of the prepared adsorbent. A maximum adsorption capacity of 120 mg Hg2+/g adsorbent was achieved at pH 7.0, shaking time 120 min and adsorbent dose of 0.4 g/L. Based on non-linear modeling and error functions analysis, the current adsorption process is well described by Langmuir isotherm and pseudo-second order models; suggesting a chemisorption reaction between the Hg2+ ions and the amino groups on the adsorbent surface via complexation. Moreover, the adsorption process is carrying out spontaneously with a negative enthalpy change. Finally, the adsorbent regeneration and reusability were studied and an accumulative uptake capacity of 464 mg Hg2+/g adsorbent was achieved.