Electrostatic Attractive Forces Research Articles

Electrospray Deposition: A Breakthrough Technique for Proton Exchange Membrane Fuel Cell Catalyst Layer Fabrication

This Spotlight article presents the state-of-the-art of electrospray deposition technique applied to the fabrication of proton exchange membrane fuel cell (PEMFC) components, mainly focusing on catalyst layers in gas diffusion electrodes. The atomization of a suspension of particles over a substrate under the influence of a strong electric field results in the growth of a film with macroporous morphology and many interesting properties. This so-called electrospray deposition has reported many noteworthy beneficial effects for the fabrication of the catalyst layers of gas diffusion electrodes of PEMFCs. The electrosprayed catalyst layers prepared from suspensions of catalyst particles and ionomers present a dendritic macroporous morphology with superhydrophobic character that improves the water management inside the cell and increases the performance by ∼20% with respect to standard electrodes prepared by airbrushing. Other interesting effects observed with electrosprayed catalyst layers are increased catalyst utilization and water absorption capabilities of the ionomer, improved performance under nonhumidified conditions, and a reduction in catalyst degradation. In addition, the electrospray deposition decreases platinum losses during fabrication thanks to the attractive electrostatic forces between the ion mist and the substrate compared with regular ink-based spray methods.

Adsorption and recovery of lithium ions from groundwater using date pits impregnated with cellulose nanocrystals and ionic liquid

The study aims to prepare a novel low-cost and environmentally friendly adsorbent by using date pits (DP) impregnated with cellulose nanocrystals (CNCs) and ionic liquid (IL), named IL-CNC@DP. The batch adsorption of lithium onto IL-CNC@DP and DP were studied at different pH values, initial lithium concentrations, and temperatures. The thermodynamics constants of the adsorption process showed that the IL-CNC@DP was exothermic, did not favor a high level of disorder, and spontaneous in nature. At pH 6, there is a significant increase in the removal efficiency where it increased to 90%. This also could be explained by the fact that electrostatic attraction forces and hydrogen bonding existed between the protonated Li+ and the less protonated IL-CNC@DP adsorbent surface, which enhanced the percentage of Li+ removal. A strong inter- and intra-hydrogen bonding (O-H) stretching absorption is seen at 3311 cm−1 that occurs in cellulose components. In conclusion, the IL-CNC@DP in comparison to the DP confirmed exceptional results proving that the modification enhanced the remediation of the Li+ from water. Furthermore, the selectivity of IL-CNC@DP towards real groundwater samples isolated in Qatar depends upon the physicochemical characteristics of each element.

Facile fabrication of MgO/graphene oxide composite as an efficient adsorbent for rapid removal of aqueous organic dyes: Performance evaluation and mechanistic investigation

Aqueous dyes are major environmental contaminants. Herein, a facile solvothermal method is introduced for the fabrication of an MgO/graphene oxide (MgO/GO) nanocomposite. The as-fabricated MgO/GO has been characterized and employed as an adsorbent to remove aqueous methyl blue (MB) and malachite green (MG). The removal performance has been evaluated through batch adsorptions. More importantly, interactions between MgO/GO and MB or MG have been analyzed in detail, allowing the proposal of a plausible adsorption mechanism. Adsorptions of MB (initial concentration 100 mg L−1) and MG (initial concentration 650 mg L−1) on MgO/GO (dosage 500 mg L−1) reached equilibrium in 12 min and 10 min, respectively; the removal efficiency and adsorption capacity of MB were 85.95% and 171.90 mg g−1, and those of MG were 98.08% and 1275.00 mg g−1. Both adsorption processes conformed well to the Freundlich model and the pseudo-second-order model, whereby adsorption rate is controlled by chemical adsorption. The adsorption mechanism involves electrostatic attraction, hydrogen bonding, π-π interactions, and van der Waals forces. The facile preparation and high adsorption efficiency may make MgO/GO a potential adsorbent for aqueous dyes.

Facile fabrication of polymeric quaternary ammonium salt hydrogel by radiation for dyes removal from aqueous solution

The effluents containing various dyes from the process industries raise esthetic problems and cause toxic impacts on aquatic and human life. Thus, the dye effluent must be adequately treated before being discharged into water-bodies. A cellulose-derived quaternary ammonium salt was treated by radiation to form hydrogel structure. The radiation dose effects on gel fraction and swelling properties were investigated. The hydrogel structure was characterized by IR and SEM analyses. The Zeta potential values at different pH were all greater than +30 mV, which indicating that the hydrogel possessed enough electrostatic attraction force to anionic ions. The adsorption behaviors of the polymeric quaternary ammonium salts hydrogel (PQH) towards methyl orange (MO), Congo red (CR), and Coomassie brilliant blue (CBB) are discussed. The pseudo-second-order mode well fitted the adsorption kinetics for all three dyes. The increasing order of the initial adsorption rate h0 was MO > CR > CBB. The Langmuir model well described the adsorption isotherms were well described by with the maximum adsorption capacity for MO, CR, and CBB being 628.93, 427.35, and 617.28 mg/g, respectively. HCl was used to regenerate the dye-loaded-hydrogel. The adsorption-desorption test demonstrated the good reusability of this hydrogel. Also, the PQH has selective adsorption of MO from RhB/MO mixing solution.

Cationic cobaltammines as anion receptors: Sonochemical synthesis, characterization and comparative account of antibacterial activity of nano and non-nano pentaammineazidocoablt(III) compounds

Sonochemical technique has lead the synthesis of nano-scale cobalt(III) compounds from pentaammineazidocobalt(III) chloride and sodium salts of metal oxoanions (Na2MO4·2H2O, M = Mo or W) in an aqueous medium. These dark red coloured particles have composition [Co(NH3)5N3]MO4 (M = Mo or W) and further characterization by UV–Vis, IR, SEM, Zeta-sizer and PXRD. Through classical method their crystals have also been grown and their characterization has been done by UV–Vis, IR, PXRD and SCXRD. Thermal stability of single crystalline and nano-scale cobalt(III) compounds have been determined by thermal gravimetric analysis. The binding ability of pentaammineazidocobalt(III) cation for oxoanions has been observed (in an aqueous solution) with UV–Vis spectroscopic titrations (log k = 2.35 (MoO42-), 3.76 (WO42-). Single crystal X-ray structures of both the compounds have revealed the presence of one cation and one anion. Electrostatic forces of attraction and strong H-bonding interactions (NH…O) have stabilized crystal lattices in both the structures. All compounds along with sodium salts of oxoanions has further revealed their antibacterial activities using a strain of gram negative bacteria, a strain of gram positive bacteria and acid fast bacteria (Escherichia coli,Bacillus thuringiensis and Mycobacterium smegmatis respectively). This study predicts that these new nano compounds have two-fold more inhibitory activity as compared to the normal crystalline compounds and sodium salts of oxoanions.

Some polymeric imidazolates from alkylimidazolium as corrosion inhibitors of API 5L X52 steel in production water

In this work, the synthesis route and evaluation of two poly(ionic liquids) (PolyILs) derived from alkylimidazolium imidazolate to be used as corrosion inhibitors (CIs) of API 5L X52 steel exposed to oil reservoir production water (PW) are discussed. The corrosion inhibition performance of the PolyILs was investigated by potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). According to the PDP analysis, it was concluded that the PolyILs could be classified as mixed-type CIs with anodic tendency, featuring maximal inhibition efficiency (η) of 80%. The adsorption mechanism occurred through the blocking of active sites by means of electrostatic attraction forces and formation of chemical bonds. The SEM and AFM surface analyses evidenced that the metal surface in the presence of the PolyILs was less damaged by steel corrosion. Finally, the XPS studies confirmed that the CI interaction with the steel surface reduced the amount of produced corrosion products such as FeOOH and/or FeCO3.

Enhancing the linear dynamic range of a mode-localized MEMS mass sensor with repulsive electrostatic actuation

This letter demonstrates the linear dynamic range enhancement of a mode-localized microelectromechanical systems sensor based on two weakly coupled cantilevers under electrostatic actuation resulting in a repulsive force. An analytical model is proposed to design the sensor, and the expression of the electrostatic force is obtained using a finite element simulation. Compared to attractive electrostatic actuation, the intensity of the resulting force is less sensitive to the change in the cantilever’s displacement, with negligible electrostatic nonlinearities. This result is confirmed by experimental measurements showing linear vibrations up to 70% of the gap, which is almost three times higher than the electrostatic critical amplitude of a similar device using attractive electrostatic force. Finally, the mass sensing capability is highlighted by depositing a few picograms of platinum on the sensor.

Physico-chemical and electrostatic surface characterisation of mica mineral and its applicability on the adsorption of Safranin Orange and Reactive Black 5 dyes

ABSTRACT The combined approach of specific surface area (SSA), porosity, microprobe analysis (EMPA), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with EDX and infrared spectroscopy (FTIR) provided the mica mineral physico-chemical and morphological characterisation. The electrostatic surface properties were assessed through the determination of the Point of Zero Charge (pHPZC) by the drift method and the electrokinetic mica mineral features represented by the Isoelectric Point (pHIEP) which was carried out through zeta potential measurements. Adsorption tests were performed to correlate the surface charge behaviour of the mica mineral and its influence on the adsorption efficiency of two different dyes, namely: Safranin Orange (SO), as a cationic dye and Reactive Black 5 (RB5), as an anionic dye. The higher adsorption capacity SO dye was observed at pH 9 and achieved almost 83% of removal, while RB5 dye adsorption on mica surface had the highest result, about 45% of removal efficiency, on pH of 3. In both cases, the main mechanism identified that drove this results is the electrostatic force of attraction between the adsorbent edge surface charge (pH-dependent) and the ionic nature (anionic or cationic) of the pollutant dyes particles. The preliminary adsorption experiments demonstrated that the raw grounded mica mineral has a greater potential associated with its application on cationic dye removal in wastewater. The present study aimed to detail the main characteristics of the mica mineral in order to evaluate the potential use of such mineral residues in the removal efficiency of contaminated wastewater.

Highly efficient nano-Fe/Cu bimetal-loaded mesoporous silica Fe/Cu-MCM-41 for the removal of Cr(VI): Kinetics, mechanism and performance

Zero valent iron (Fe0) can reduce Cr(VI) in water, where Fe0 and Fe(Ⅱ) are possible electron donors, but passivation and aggregation easily occur to Fe0. To improve the performance of Fe0, a new hybridization strategy of Fe/Cu bimetal and silica-based mesoporous molecular sieve MCM-41 for the removal of Cr(VI) from water has been proposed. The results show that the two-dimensional mesoporous structure of MCM-41 can provide skeleton support for Fe0, improve the mass transfer rate, and overcome the aggregation bottleneck of Fe0. The Cr(VI) removal rate reached 98.98% (pH = 2) after 40 min. The analytical results revealed Cr(VI) removal process: Cr(VI) adsorbed onto Fe/Cu-MCM-41 by electrostatic attraction and other molecular inter-atomic forces. The second metal, Cu, can inhibit the passivation of Fe0 and promote Fe(Ⅱ)through the formation of Fe/Cu battery, thereby promoting the electron transfer. The resulting Cr(Ⅲ) is precipitated as FeCr2O4 and CrxFe1−x(OH)3.

Influence of soil properties, temperature and pH on adsorption-desorption of imazamox in Indian aridisols

ABSTRACT As adsorption-desorption behaviour of herbicide plays an important role in determining leachability, release rate and availability to target species, the present study aims to evaluate the influence of soil properties, temperature and ionic state of imazamox on its adsorption-desorption behaviour. The sorption was significantly influenced by above evaluated parameters and Freundlich adsorption coefficient varied from 0.24 × 103 to 7.60 × 103 mg1−1/n kg−1 L1/n. In soils with pH in the range of 6.4–9.5, sorption of imazamox decreased with increase in solution pH while in acidic soil (pH 2.3 to 5.9), adsorption increased with increase in solution pH. At low solution pH adsorption occurs mainly through cationic form while at high solution pH adsorption was predominantly through anionic form. The presence of electrostatic attractive and repulsive forces, ∏→∏ charge transfer, hydrogen bonding and van der waals forces was key mechanism affecting the adsorption of imazamox. Greater adsorption hysteresis was observed in soils having pH in the range of 6.2–9.5 suggesting relatively less adsorption and difficult desorption of imazamox in these soils. Due to irreversible binding in high pH soil, it can be speculated that it may enhance the chances of crop injury in these soils.

Weak Electrostatic Interaction Enabled Highly Oriented Assembly of Gold Nanorods onto Ultrathin Flagella Bionanofibers

Biological substrates are generally considered unfavored for electrostatic uptake of nanoparticles due to their low surface charges. Herein, the electrostatic interaction between weakly charged ultrathin flagella bionanofibers and gold nanorods (AuNRs) is investigated. It is discovered that compared with the reported AuNRs assembly onto one‐dimensional (1D) templates of strong charges, the weak electrostatic interaction here can generate more ordered 1D AuNRs array. Under strong attraction force, AuNRs can bind firmly on templates by either narrow heads or long sidewalls, resulting in less ordered 1D structure. While under weak attraction force, AuNRs can be captured only if interacting with flagella using their long sidewalls to obtain accumulative strong enough force. Another discovery is that under weak AuNRs–flagella electrostatic attraction force, the relatively stronger AuNRs–AuNRs repulsion force plays a significant role in determining the interparticle gap and the single‐ or double‐string pattern of AuNRs on ultrathin flagella. Advantage is also taken of the bio‐origin of flagella by assembling AuNRs onto flagella that are still attached to living bacterium. Such a capability makes our approach highly feasible for potential device fabrication, as individual nanoarray is hard to manipulate, but would be greatly facilitated if it is associated with a micron‐sized base, like bacteria.

Coupling adsorption and in-situ Fenton-like oxidation by waste leather-derived materials in continuous flow mode towards sustainable removal of trace antibiotics

The gap of pollutant concentration between simulated sewage (mg/L level) and actual water (μg/L level) strongly limits the application of advanced oxidation processes (AOPs) in natural waters. By coupling adsorption for gathering trace organic contaminants and in-situ catalytic oxidation for recovering adsorption capability, adsorptive catalysts can build a bridge between theoretical research and practical application to promote scientific progress of AOPs. Here, waste leather derived biochar based adsorptive catalysts (WLBC) can effectively adsorb trace sulfamethoxazole (SMX) via electrostatic attraction, hydrophobic interaction, π-π interaction, and Van der Waals forces, moreover, the subsequent in-situ oxidation of surface SMX by hydroxyl radical (•OH) generated from WLBC mediated Fenton-like reaction will recover the adsorption capability of WLBC. Compared with persulfate-driven AOPs, •OH-dominated oxidation is nonselective for various pollutants and effective for adsorbent regeneration. In addition, the pathway of SMX degradation was proposed based on the results of liquid chromatography-quadrupole time of flight-mass spectrometer (LC-QTOF-MS), involving four stages of 1) nitration, hydroxylation, and hydrolytic reaction of SMX, 2) cleavage of S-N and S-C bonds, 3) ring-opening, 4) mineralization. The adsorption and in-situ Fenton-like oxidation system established by WLBC is capable of efficiently degrading trace pollutants and regenerating adsorbent for long-scale operation, which immunes largely from coexisting substances (e.g. anions, cations, and humic acid) with extremely low metal leaching and relatively low cost. Therefore, this study proposes a strategy for sustainable removal of trace organic pollutant in natural waters based on coupling WLBC induced adsorption and in-situ Fenton-like oxidation.

Effects of Surface Heterogeneity of α-Quartz and α-Cristobalite on Adsorption of Crystal Violet

Silica minerals are a kind of important minerals and widespread on the earth’s surface. They play an irreplaceable role in the whole geochemistry and environment processes. The diversity in the crystal structure of SiO2 polymorphs might lead to the heterogeneity in their surface microstructures and properties. As two common SiO2 polymorph minerals in soil and sediments, α-quartz and α-cristobalite have been studied for the effects of their surface heterogeneity on adsorption behaviors toward crystal violet (CV) by batch adsorption experiments in different specific surface areas (SSAs) and at different pH values and temperatures, as well as by X-ray photoelectron spectroscopy (XPS) investigation. Owing to the larger surface site density, the saturated adsorption amount of α-quartz was larger than that of α-cristobalite. It was also indicated by the larger slope of adsorption lines as a function of SSA. The adsorption capacity of both increased with increasing pH and temperature. In the thermodynamic study, the negative ΔG indicated that the adsorption of CV on the surface was spontaneous and the positive ΔH suggested that the reaction was endothermic. The well-fitted Langmuir adsorption isotherms suggested that the CV adsorption was monolayer adsorption. The adsorption interaction force was mainly involved in electrostatic attraction force between the negatively charged surface reactive sites and positively charged N atoms in the dimethylamino groups of CV. The XPS spectra of N 1s showed that the stoichiometric ratio of Nlow/Nhigh changed from lower than 2:1 to about 2:1 as the adsorption changed from the unsaturated to saturated state. The change reflected that the spatial arrangement of adsorbed CV monomer on the mineral surface could be readjusted by lifting the average tilt angle between the average plane of the CV monomer and the sample surface during the adsorption process. Surface heterogeneity of α-quartz and α-cristobalite controlled the different distributions and postures of adsorbed CV monomers on the surface. The CV monomers adsorbed on α-quartz presented a larger average tilt angle because of its larger surface reactive site density, while α-cristobalite did conversely.

GREEN SYNTHESIS OF SILVER NANOPARTICLES USING MICROALGAL EXTRACT AND ITS APPLICATION IN METAL ION REMOVAL FROM AQUEOUS SOLUTION

Heavy metal pollution is of great concern and cannot be ignored as heavy metals are highly mobile in soil and are recalcitrant. Nanotechnology provides a novel sustainable approach for synthesizing materials of desired properties, composition, and structure, it is however expected to adsorb heavy metals and play a significant role in water treatment. Green chemistry is the cost-effective, non-toxic, and environment friendly approach that involves the use of biological components as reducing and stabilizing agents for the synthesis of nanoparticles. In the present study, heavy metals such as cadmium (Cd II) and lead (Pb II) were successfully removed from its aqueous solution by an adsorption process using the silver nanoparticles of size ~15nm biosynthesized using freshwater algal extract. The adsorption peak at 411 nm confirms the formation of silver nanoparticles. The maximum value of metal ion adsorption capacity (23.98 mg/g) was observed for Pb (II). The higher value of R2 showed that the experimental data were fitted best with Langmuir isotherm. The rate kinetics study showed that Pb (II) adsorption on Ag nanoparticles followed pseudo-second order kinetics (R2>0.9) indicating that Pb (II) was attached to the nanoparticles surface through electrostatic force of attraction, also referred to as chemisorption whereas Cd (II) adsorption on Ag nanoparticles followed pseudo-first order kinetics (R2 >0.8) indicating physical adsorption between adsorbate and adsorbent.

Mechanistic study on methyl orange and congo red adsorption onto polyvinyl pyrrolidone modified magnesium oxide

This study reported a new water stable magnesium oxides (MgO) composite with polyvinyl pyrrolidone (PVP) prepared by one-pot hydrothermal method for the efficient elimination of both methyl orange and congo red from aqueous solutions. The as-prepared composite material shows new exposed crystalline surfaces and additional peaks for hydrogen bond formation which are confirmed from FTIR and X-ray diffraction analysis. The surface area of MgO-PVP composite (85 m2 g−1) was clearly higher than plain MgO (67 m2 g−1). The dye removal capacity of MgO-PVP composite was significantly higher than plain MgO. The adsorption mechanism study illustrated that the dye removal by MgO-PVP composite not only due to the electrostatic force of attraction, but also involved the ion exchange amid hydroxide group and dye molecules. The adsorption kinetic mechanism of dyes was mainly controlled by film diffusion, and pseudo-second-order kinetic equation was found to be best applicable to the current experiential data. Langmuir and DR isotherms were well fitted with current experimental results. The adsorption of methyl orange and congo red onto the composite was also conducted as a function of initial concentration, pH of solution, temperature of the solution and adsorbent dosage. Dye adsorption capacity was decreased with the increasing of initial pH value. The negative values of (∆G) for both the dyes show the spontaneous adsorption process.

Application of artificial neural network for prediction of particle size in pharmaceutical cocrystallization using mechanochemical synthesis

Milling by mechanical means is vital unit operation in pharmaceutical processing which can be used for controlling particle size reduction. This approach can be also used for mechanochemical synthesis of pharmaceutical cocrystals. However, controlling the particle size of cocrystal during the milling process is challenging due to complexity of the process and different mechanisms involved. In this study, artificial neural network (ANN) approach was performed to predict the size of particles during mechanochemical synthesis of pharmaceutical cocrystals in ball milling operation. Theophylline was used as active pharmaceutical ingredient (API) and 4-aminobenzoic acid as co-former in the experiments. Different types of excipients including hydroxypropylmethylcellulose (HPMC), lactose, microcrystalline cellulose (MCC) polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) were used to see the effect of excipients on the cocrystals particle size. ANN was developed considering excipient type, excipient percentage, jar size, milling time as inputs, while median particle size (d50) was considered as the response, and representative of particle size. Two hidden layers were considered in developing ANN, and a combination of linear and nonlinear functions was used as transfer function. ANN was trained and validated with measured data, and R2 greater than 0.99 was obtained for the training and validation, with RMSE values of 1.06 and 3.89 for training and validation, respectively. The results were used to provide a design space for understanding the cocrystal particle size variation during ball milling process. It was indicated that the largest particles were formed using PEG as excipient, and increase in particle size over the milling time. The latter was attributed to the electrostatic attraction forces between the particles, thus aggregation and agglomeration of particles as the milling time exceeds a threshold. Furthermore, larger particles were obtained with the larger jar size. It turned out that faster cocrystallization rate occurred after only 5 min of milling in 25 mL jar compared to 25 min in 10 mL milling jar. The developed methodology has been shown to be robust and can be used as predictive tool for designing pharmaceutical cocrystallization using ball milling, and controlling the particle size during size reduction process.

RETRACTED ARTICLE: A novel biosensor for gabapentin drug detection based on the Pd-decorated aluminum nitride nanotube

Density functional theory calculations were performed to inspect the potential application of pristine AlN nanotube (AlNNT) as well as Pd-decorated AlNNT (Pd@AlNNT) in recognition of gabapentin (GB) drug. The sensing response of AlNNT to the GB drug is very small (~ 5.2 at 298 K) attributed to the small adsorption energy (AE) of −0.16 eV. Molecular orbital energy decomposition method (EDA) showed that the contributions of electrostatic attraction, Pauli repulsion, orbital relations, and dispersion forces in the AE are about −0.21, 0.19, −0.11, and −0.09 eV, respectively. A Pd atom preferentially adsorbed over an Al–N bond of the AlNNT, releasing the energy of 2.93 eV. We found that the GB strongly adsorbed on the Pd@AlNNT with AE of −1.29 eV and the sensing response increased to 524.6 by the Pd decoration. Based on the results, the main stabilization contribution to the AE of GB on the Pd@AlNNT comes from the electrostatic attraction based on the EDA analysis. The recovery time was achieved to be 1.8 s for the GB desorption from the Pd@AlNNT surface. Finally, we concluded that the Pd@AlNNT can transform the presence of GB molecules into electrical signal, and it may potentially be applied as an electronic sensor for GB drug detection.

Multivalent Ion-Mediated Attraction between Like-Charged Colloidal Particles: Nonmonotonic Dependence on the Particle Charge.

Ion-mediated effective interactions are important for the structure and stability of charged particles such as colloids and nucleic acids. It has been known that the intrinsic electrostatic repulsion between like-charged particles can be modulated into effective attraction by multivalent ions. In this work, we examined the dependence of multivalent ion-mediated attraction between like-charged colloidal particles on the particle charge in a wide range by extensive Monte Carlo simulations. Our calculations show that for both divalent and trivalent salts, the effective attraction between like-charged colloidal particles becomes stronger with the increase of the particle charge, whereas it gradually becomes weakened when the particle charge exceeds a “critical” value. Correspondingly, as the particle charge is increased, the driving force for such effective attraction transits from an attractive electrostatic force to an attractive depletion force, and the attraction weakening by high particle charges is attributed to the transition of electrostatic force from attraction to repulsion. Our analyses suggest that the attractive depletion force and the repulsive electrostatic force at high particle charges result from the Coulomb depletion which suppresses the counterion condensation in the limited region between two like-charged colloidal particles. Moreover, our extensive calculations indicate that the “critical” particle charge decreases apparently for larger ions and smaller colloidal particles due to stronger Coulomb depletion and decreases slightly at higher salt concentrations due to the slightly enhanced Coulomb depletion in the intervening space between colloidal particles. Encouragingly, we derived an analytical formula for the “critical” particle charge based on the Lindemann melting law.

Hydrothermal synthesis of hydroxyapatite-reduced graphene oxide (1D–2D) hybrids with enhanced selective adsorption properties for methyl orange and hexavalent chromium from aqueous solutions

The presence of organic dye molecules and heavy metal ions in water causes ecological and public health problems. Therefore, remediation of water/wastewater contaminated with organic dye molecules and toxic metal ions is of importance. Herein, a reduced graphene oxide (RGO)–hydroxyapatite (Hat) (1D–2D) hybrid composite was fabricated through a hydrothermal process and applied for the adsorption of methyl orange (MO) and hexavalent chromium (Cr(VI)) from water. The as-fabricated RGO–Hat hybrids were characterized using FTIR, XRD, HR-TEM, SEM, XPS, EDAX, and TGA-DSC analytical techniques. The influencing parameters of adsorption performance, namely solution pH, contact time, and co-interfering ions, were explored to obtain the maximum adsorption capacity of contaminants from the solid–liquid interface. Batch studies revealed that MO and Cr(VI) adsorption followed the pseudo-second-order kinetic and the Langmuir isotherm models. The adsorption capacity was 49.14 and 45.24 mg g−1 for MO and Cr(VI), respectively. The adsorption of such ions over RGO–Hat hybrids was mainly driven by several uptake mechanisms viz, electrostatic force of attraction, π–π interactions, and hydrogen bonding. Thus, this study demonstrated that the RGO–Hat hybrid is a potential candidate for the treatment of MO and Cr(VI) from water.

Synthesis of highly porous activated carbon derived from kernel oil treatment by-products of Argania Spinosa as a recyclable adsorbent for amoxicillin removal from real wastewater

The widespread occurrence of drugs in the aquatic environment has raised concerns over the last decades about the mechanisms to be used to remove these emerging contaminants because of their harmful effects on the water quality and human health. This current research was aimed to explore the preparation of an activated carbon from kernel oil treatment residues of Argania Spinosa for the removal of amoxicillin (AMX) from water. The conditions for synthesizing the activated carbon (AC-RS) were used: an impregnation weight ratio of char to KOH 1:1 at activation temperature of 800 °C for 1 h of activation time, which gave a BET surface area and total pore volume of 1618 m2 g−1 and 0.763 cm3 g−1, respectively. The effect of AMX/AC-RS interactions as well as the operating conditions (time, solution pH, initial concentration, and temperature) on the adsorption capacity was also studied. The adsorption of AMX onto AC-RS, with maximum adsorption capacity of 303.03 mg g−1, is much higher compared to several adsorbents reported in the literature. The high amount of AMX absorbed by AC-RS at pH 6 mainly results from the adsorption sites involved in the electrostatic attraction force, π-π hydrophobic interaction, and hydrogen bonding. The regeneration study ascertained the fact that AC-RS was reusable even after four consecutive cycles and the efficiency remains higher than 70%. Therefore, the optimized batch parameters were employed for the AMX removal in real wastewater, a percentage of 77.2% was obtained.