Monolayer Coverage Research Articles

Hydrogen adsorption on zinc-terminated ZnO(0001) surface at varying coverages and its effects on electronic and optical properties: A DFT+U Study

Abstract Spin-polarized density functional theory implementing Hubbard corrections (DFT+U) were utilized to study H adsorption of different coverages on Zn-terminated ZnO(0001) surface. Changes in electronic and optical properties were observed upon H adsorption of varying coverages, namely with 0.25 monolayer (ML), 0.50 ML, 1 ML, and 2 ML coverage. In terms of surface structure, H atoms were found to adsorb on top of Zn forming Zn-H bond lengths ranging from 1.54-1.73 Å for certain coverages. On the other hand, O-H bond length values are 2.41 Å and 2.37 Å for 0.50 ML and 2 ML coverage respectively. Additionally, for 0.50 ML, the most stable configuration is when one H atom adsorbs on top of Zn and the other near the hollow site. At low coverage (0.25 ML and 0.50 ML), H prefers to interact with topmost layer Zn atoms resulting to shifts in the electronic bands relative to the pristine surface’s. In addition, at high coverage (1 ML and 2 ML), shifting of bands are observed and are mainly guided by Zn-H atom interaction for 1 ML and weak H-O atom interaction for 2 ML. The observed decrease in band gap as the coverage was increased from 1 ML to 2 ML is supported by the red shift in the absorption plot. However, for low H coverage adsorption, the optical plots deviate due to emergence of flat bands. Changes in electronic properties such as shifts in conduction band minimum (CBM) and decrease in measured band gap occur as guided by the interaction of adsorbed H atoms with the surface atoms and are supported with obtained optical plots. These findings present the tunability of Zn-terminated ZnO(0001) polar surface properties depending on H coverage.

Sequestration of Ni2+ and Zn2+ utilising agricultural biowaste-based amorphous M−SiO2 and modified green M−SiO2/Fe3O4 nano-adsorbents: Modelling and electroplating wastewater performance

This work reports the synthesis of novel amorphous mesoporous silicon dioxide (M−SiO2) nanoparticles and modified hybrid green mesoporous silicon dioxide embedded magnetite (M−SiO2/Fe3O4) nanocomposite by one-pot co-precipitation green approach. The nano-adsorbents’ ability to sequester Ni2+ and Zn2+ ions was investigated in batch experiments using synthetic solutions. The M−SiO2/Fe3O4, having specific surface area of 171.71 m2/g and mesoporous diameters of 6.281 nm, exhibits soft ferromagnetism with a saturation magnetisation of 35.45 emu/g. Specific surface areas and mesoporous diameters of 909 m2/g and 2.288 nm were recorded for M−SiO2. The Langmuir isotherm, pseudo second order kinetic, and Elovich kinetic were found to be best fitted to explain the highest capability of adsorption. The Langmuir monolayer coverage (qmax) of 108.70 and 96.15 mg/g for Ni2+ and Zn2+ by M−SiO2/Fe3O4, respectively, was notably higher than M−SiO2 (80.65 and 72.46 mg/g). The best-fitted kinetics imply that chemisorption predominates on M−SiO2 and M−SiO2/Fe3O4 heterogeneous adsorption surfaces. Thermodynamic parameters confirm endothermic adsorption of cationic metals, and sequestration improved marginally at elevated temperatures. The lab scale cost estimation, magnetic separability and superior metal ions sequestration efficacy of M−SiO2/Fe3O4 nanocomposite up to five ad-desorption cycles with > 90 % regenerability render it an economically feasible and recyclable nano-adsorbent. The feasibility of cationic metals sequestration from electroplating effluent confirms an effective and cost-efficient environmentally friendly nano-adsorbent (M−SiO2/Fe3O4) for treatment of wastewater contaminated with potentially toxic metals.

Unveiling the Composition-Dependent Catalytic Mechanism of Pt-Ni Alloys for Oxygen Reduction: A First-Principles Study.

Unveiling the composition-dependent catalytic mechanism of Pt-based alloy cathodes for the oxygen reduction reaction (ORR) helps improve the proton exchange membrane fuel cells. Using density functional theory calculations, this study investigates the ORR catalytic performance of the Pt-Ni system with various compositions (1.00, ∼0.99, 0.75, 0.50, 0.25, ∼0.01, and 0.00). The ordered solid solution PtNi3(111) system shows activity comparable to Pt(111) and is cost-effective. The Ni1/Pt(111) system, featuring a single Ni atom on the Pt(111) surface as a surface single-atom alloy (SSAA), demonstrates the highest activity with an overpotential of only 0.28, which could be further reduced to 0.21 V by decreasing the surface Ni concentration to 1/16 monolayer coverage. The predicted high activity of Ni1/Pt(111) is confirmed when considering factors such as the implicit solution environment, constant potential conditions, and protonation capability. Moreover, surface-adsorbed oxygen species driven by reaction conditions stabilize these single Ni atoms of Ni1/Pt(111) by preventing segregation and dissolution processes, thereby exhibiting a dual functionality. This study reveals the composition dependence of Pt-based alloys and highlights the stability mechanisms of SSAA catalysts during the ORR.

Appraisal of Characterization and Adsorption Isotherm in the Bioremediation of Cu and Zn Ions from Aqueous Solutions Exploiting Unmodified Corn and Coconut Husk

Environment is contaminated by heavymetals has emerged as a substantial globaly. Conventional remediation methods have proven inadequate and costly in addressing this issue. Hence, there is a pressing need to discover bio-remediation as a cost effective, effectual, and environmentally, a substitute for heavymetal removal. This work investigates the adsorption behaviour of Corn Husk (CH) and Coconut Husk (CCH), an inexpensive adsorbent, towards Cu and Zn ions for potential application in wastewater treatment. The physico-chemical variables of unmodified CH and CCH were appraised, and batch experimental methods were employed to study variables like pH, contact time, size of particle, and preliminary content of metals. The impact of solution pH on metals uptake by the adsorbent was investigated on the pH range of 3 to 8, revealing optimal removal efficiencies at pH 6 for Cu and pH 5 for Zn. Equilibrium adsorption times were determined to be 80 minutes for Cu and 60 minutes for Zn ions onto CH and CCH. adsorption volumes is conforming to mono-layer coverage, attained from the Langmuir plots were 4.792 mg/g and 4.594 mg/g respectively for Cu and Zn metals onto the CH and 4.771 mg/g and 4.400 mg/g for their adsorption onto CCH. Experimental values were confirmed to the Langmuir model and Freundlich model, with the Langmuir model providing the best fit. The CH based adsorbent was generally found to have an increased capacity of adsorption of the metal contents than Coconut husk (CCH). These findings underscore the strength of Corn husk as an active adsorbent to extract cationic heavymetal contents from industrial effluents.

Assessing the Stability and Photocatalytic Efficiency of a Biodegradable PLA‐TiO2 Membrane for Air Purification

AbstractThe potential of a biodegradable polylactic acid (PLA)‐TiO2 membrane for air purification is investigated, utilizing the environmentally friendly solvent Cyrene. Through the integration of TiO2 nanoparticles within a PLA matrix, the membrane is used to degrade ethanol as a model volatile organic compound (VOC) under UV light. Scanning Electron Microscopy (SEM), Energy Dispersive X‐ray Analysis (EDX), and UV–vis spectrophotometry confirm the porous structure of the membrane, the even distribution of TiO2, and its effective band gap of 3.06 eV, respectively. Ethanol adsorption is best described by the Langmuir isotherm model, suggesting monolayer coverage on a homogeneous surface. Photocatalytic tests demonstrate that the membrane decomposes ethanol (6800 ppm) within 14 min under UV light, generating acetaldehyde, acetic acid, formaldehyde, and formic acid as intermediates, and ultimately producing CO2 and water. Reusability tests indicate a decrease in decomposition time over successive cycles due to increased TiO2 exposure from the gradual degradation of PLA. However, this degradation poses challenges for continuous use, compromising the membrane's long‐term durability.

Selective adsorption of gold ion in wastewater with competing cations by novel thiourea-reduced graphene oxide

In this study, selective adsorption experiments of Au were carried out using graphene oxide (GO) and thiourea-reduced GO (TU-rGO). Adsorption experiments using Au, Cu, Pb, and Zn were performed with GO and TU-rGO in order to selectively adsorb Au from simulated waste electric and electronic equipment leachate or printed circuit board wastewater. Optimal adsorption conditions were determined, adsorption isotherm models were fitted, and desorption and regeneration experiments were performed. Additionally, GO and TU-rGO were characterized to better understand the material and propose the adsorption and desorption mechanisms for TU-rGO. It was found that TU-rGO could selectively adsorb Au, achieving a high efficiency of 95‒99% at initial Au concentrations of 0.1‒10 mg L−1 with little to no adsorption of Cu, Pb, and Zn. Moreover, the desorption efficiency of Au by ammonium thiosulfate reached 94% with the adsorption efficiency of TU-rGO decreasing from 99 to 78% after five adsorption and desorption cycles. Isotherm adsorption experiments indicated that the Langmuir model better fitted the adsorption of Au than the Freundlich model. This implied that the adsorption process was mainly controlled by monolayer coverage, with a high Au adsorption capacity of approximately 833 mg g−1 for TU-rGO.

Fabrication of electrospun ion exchanger adsorbents with morphologies designed for the separation of proteins and plasmid DNA

Electrospun cellulose adsorbents are an emergent class of materials applied to a variety of bioprocess separations as an analogue to conventional packed bed chromatography. Electrospun adsorbents have proven to be effective as rapid cycling media, enabling high throughput separation of proteins and viral vectors without compromising selectivity and recovery. However, there is a current lack of knowledge in relation to the manipulation and control of electrospun adsorbent structure with function and performance to cater to the separation needs of emerging, diverse biological products.In this study, a series of electrospun cellulose adsorbents were fabricated by adjusting their manufacturing conditions. A range of fiber diameters (400 to 600 nm) was created by changing the electrospinning polymer solution. Additionally, a range of porosities (0.4 to 0.7 v/v) was achieved by varying the laminating pressures on the electrospun sheets. The adsorbents were functionalized with different degrees of quaternary amine ligand density to create 18 prototype anion exchangers. Their morphology was characterized by BET nitrogen adsorption surface area, X-ray computed tomography, capillary flow porometry and scanning electron microscopy measurements.The physical characteristics of the adsorbents were used in an adapted semi-empirical model and compared to measured permeability data. Permeabilities of prototypes ranged from 10−2 to 10−4 mDarcy. The measured data showed good adherence to modelled data with possible improvements in acquiring wet adsorbent characteristics instead of dried material. Finally, the electrospun adsorbents were characterized for their binding capacity of model proteins of different sizes (diameters of 3.5 nm and 8.9 nm) and plasmid DNA. Static binding capacities ranged from 5 mg/ml to 25 mg/ml for the proteins and plasmid DNA and showed <20 % deviation from monolayer coverage based on BET surface area. Therefore, it was concluded that the electrospun adsorbents most likely adsorb monolayers of proteins and plasmid DNA on the surface with minimal steric hindrance.

Binding energies of CD4 and fragment species to Pt(111): Implications for measurements of anion electron stimulated desorption.

We consider the electron stimulated desorption, via dissociative electron attachment, of anionic species from thin condensed CD4 films deposited on a Pt substrate and compare experimentally observed desorption yields with density functional theory calculations of the binding energies of various anionic and neutral moieties to Pt(111). Certain species (which can be considered chemisorbed) exhibit very high binding energies and large charge transfer with the substrate. Other "physisorbed" species have much lower binding energies. Species that chemisorb have lower desorption yields than those that physisorb, especially at 1-2 monolayer coverage of the Pt substrate. The binding energy of D- to Pt is the weakest, and experimentally, the desorption yield is the highest regardless of the thickness of CD4. The calculations show that the formation and desorption of anionic species at a distance of 16Å from the substrate, which is equivalent to the thickness of CD4 films of four monolayers, are not influenced by the short-range interactions between the substrate and the molecule and DEA products.

Surface anchoring requirements for vanadia clusters on titanium oxide surfaces and their impact on activity for oxidative dehydrogenation of ethanol

Titanium oxide site requirements for the anchoring of catalytically active forms of dispersed vanadia species are investigated. Using a series of oxygen-modified titanium nitride materials, we systematically modify the available vanadia-anchoring moieties on the titanium-bearing support surface. This strategy in turn results in a very narrow size distribution of well-dispersed vanadia clusters anchored on the support. This synthesis technique ensures that only highly dispersed vanadia is present on the catalyst surface even at nominal monolayer coverages. A deeper insight into the catalytic behavior for ethanol partial oxidation of the active vanadia species is obtained by comparing intrinsic kinetic and thermodynamic parameters of kinetically relevant reaction steps (heat of ethanol adsorption, hydrogen abstraction activation energy, and the energetics of catalyst reoxidation). It is found that these parameters are dependent on the relative amount of oxygen in the titanium-bearing support and the resulting distribution of vanadia species, which validates the premise of a potential participation of lattice oxygen atoms of the titania support into the catalytic activity of active vanadia species.

STUDY ON THE CO\(_2\) ADSORPTION PROPERTIES OF ACTIVATED CARBON PRODUCED FROM CORN COB

Activated carbon (AC) prepared from corn cobs was used as an adsorbent for CO2 capture under different temperatures. The characterization by Boehm titration and TGA showed that the total acidic groups of AC were significantly higher than the total basic groups, and the increasing activated temperature resulted in increases in the total basicity and decreases in the total acidity. The CO2 adsorption behavior of AC was predicted by four isotherm models. It was found that the suitable order was Sips &gt; Tóth &gt; Freudlich &gt; Langmuir. The maximum monolayer coverage capacity and isosteric heat of adsorption were in the range of 6.28 - 10.92 mmol g-1 and 26.48 - 21.55 kJ mol-1, respectively. High specific surface area and high amount of carboxylic groups were found to be in favor of CO2 capture.

The effective treatment of dye-containing simulated wastewater by using the cement kiln dust as an industrial waste adsorbent

This study compares the adsorption behavior of both Methylene Blue (MB) and Congo Red (CR) dyes on the surfaces of cement kiln dust (CKD) powder from the experimentally simulated wastewater solution. The cement kiln dust powder was characterized using X-ray Fluorescence (XRF), X-ray diffraction (XRD), N2 adsorption–desorption Brunauer–Emmett–Teller (BET), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) tests. The adsorption for such dyes was studied under varying mixing contact times, temperatures, and pH as well as various initial concentrations of both dyes and adsorbent using the batch mode experiments. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were applied, and the results revealed that the pseudo-second-order fitted well to the kinetic data. Thermodynamic parameters stated that the adsorption process was endothermic. Studying Linear and nonlinear forms of Langmuir and Freundlich's adsorption isotherms revealed that the adsorption process was followed by both homogeneous mono-layer and heterogeneous multilayer coverage on the active sites of cement kiln dust particles. The data showed that the adsorption capacities of the methylene blue and Congo red dyes were 58.43 and 123.42 mg/g, respectively and cement kiln dust is an adsorbent with little cost for the treatment of wastewater.

Acid Treatment on Bentonite Clay for the Removal of Fast Green FCF Dye from Aqueous Solution

ABSTRACTThe bentonite clay has been activated by acid treatment and utilized as a lower‐cost and eco‐friendly adsorbent required to remove Fast Green FCF dye from the aqueous solution. At first acid activated bentonite clay minerals were analyzed by various analytical techniques like Fourier Transform Infrared Spectroscopy (FTIR), x‐ray diffraction (XRD), and x‐ray fluorescence (XRF) analysis. The batch adsorption research was performed to investigate the Fast Green FCF dye adsorption onto the acid‐treated (Bent) bentonite clay. Sorption studies investigated the impacts of adsorbent dosage, initial pH, and time of contact on Fast Green FCF color elimination. The adsorption capacity decreased as the pH was above 7 and then remained almost the same after a pH value of 9. At acidic conditions (below pH value 7), the capacity of adsorption diminished by a decrease in the pH of the solution. The results indicated that the maximum capacity of adsorption has been obtained at an adsorbent dosage of 0.1 g. As the dosage of the adsorbent was improved, several active sites that were available at the time of the dye adsorption increased. As a result, the dye percentage that was removed from the clay increased. Besides these, adsorption kinetics, adsorption equilibrium isotherm, and thermodynamics studies have been also conducted. While studying the adsorption kinetics pseudo‐2nd‐order kinetics has been seen to be more appropriate as compared to pseudo‐1st‐order model. The experimental findings indicated that the attachment of the dye to the clay surface followed the “Langmuir adsorption” isotherm rather than the Freundlich adsorption isotherm with a monolayer coverage of 18.93 mg/g. From the thermodynamics study, it was revealed that the process of adsorption takes place instantly at high temperatures.

Banana peels as a green bioadsorbent for removing metals ions from wastewater

Bioadsorption using agricultural waste offers a promising approach for removing toxic metals from wastewater. This study explores the potential of chemically activated banana peels (BPs) as a green and cost-effective bioadsorbent for Cu(II) and Zn(II) removal. Fourier-transform infrared (FTIR) spectroscopy revealed the presence of functional groups like alcohols, phenols, and amino acids on activated BPs, potentially responsible for metal ion binding. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of cavities on the BPs surface and the existence of oxygen and potassium. The adsorption capacity of BPs was investigated under various conditions, including pH, contact time, sorbent dosage, metal concentration, and temperature. This study used Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich (D–R) isotherm models to describe the equilibrium results of Cu (II) and Zn (II) adsorption. The Langmuir isotherm model best described the adsorption process, suggesting monolayer coverage of metal ions on the BPs surface. Maximum adsorption capacities were 3.2 mg g−1 for Cu(II) and 2.8 mg g−1 for Zn(II), demonstrating the effectiveness of BPs in metal removal. Kinetic studies indicated pseudo-first-order (PFO) behavior for Cu(II) and pseudo-second-order (PSO) behavior for Zn(II) adsorption. Thermodynamic analysis revealed a spontaneous and exothermic process (negative Gibbes free energy (ΔG°) and enthalpy (ΔH°) with decreased randomness [negative entropy (ΔS°)] at the biosorption interface. Finally, the BPs sorbent was successfully applied to remove different metal ions from real wastewater samples collected from the El Wadi drain.

Modification of PVA Nanofiber by Simple Hot Water Treatment and Application on the Removal of Malachite Green Dye From Aqueous Solutions.

In this study, the crosslinking of PVA nanofiber was increased using solvent vapor treatment. Then, Fe3O4 nanoparticles were synthesized by a simple hot water technique and composited with the nanofiber. The study focuses on applying the modified PVA nanofibers to remove malachite green (MG) from water using different pH, contact times, and dye initial concentrations. The surface morphology of the nanofiber was determined using SEM, FTIR, and XRD techniques. SEM showed that the crosslinking was increased, and Fe3O4 nanoparticles appeared as agglomerates on the surface of the nanofiber. The removal percentages at optimal pH and contact time were 99.76%, and 99.5%, respectively. Thereafter, kinetics was studied by the linear pseudo-first order, pseudo-second order, Elovich equation, and Intraparticle diffusion models. Results demonstrated that the adsorption kinetics follow the pseudo-second order. Moreover, the adsorption isotherm was discussed using Langmuir and Freundlich equations. The Langmuir equation best described the adsorption with R2 value of 0.9771, and the maximum removal was 128.205 mg/g. As a result, the MG dye molecules covered the PVA nanofiber/Fe3O4 nanoparticles in a monolayer and homogenous coverage. The results of this study are significant for industries' wastewater treatment as they provide a potential solution for the removal of MG dye from textile, paper, cosmetics, food, and aquaculture industries' wastewater.

Selective adsorption/reduction of Au in electronic waste recycling wastewater by self-assembled thiourea-crosslinked reduced graphene oxide framework ball

The increased production of electrical and electronic waste (E-waste) has resulted in a greater Au presence in E-waste than in ores. As such, it is imperative to selectively recover Au from the wastewater of E-waste. In this work, a designed self-assembled thiourea-crosslinked reduced graphene oxide framework (TU-rGOF) balls for fixed-bed reactors was successfully synthesized via a facile crosslinking reaction between thiourea (TU) and graphene oxide (GO), in which TU simultaneously transforms GO into reduced graphene oxide (rGO) during the heating process. This material exhibits excellent adsorption performance and reduced Au(III) into Au0 in aqueous solution. The adsorption efficiency reaches 95 % between pH 1 and 3. Most importantly, the TU-rGOF ball demonstrated high selectivity toward Au(III) among coexisting metal ions, including Cu(II), Pb(II), Zn(II), and Ni(II). 99 % of Au(III) at a low concentration (1 or 10 mg/L Au(III)) in a highly acidic solution (pH 2.0) was removed, yielding a maximum Langmuir adsorption capacity of 97.09 mg g−1 (TU-rGOF ball) and 833.3 mg g−1 (TU-rGO only). The best adsorption fitting to the Langmuir model also suggests monolayer coverage of Au on the TU-rGOF ball surface. Based on scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses, Au(III) adsorption by TU-rGOF ball was proposed to be governed by chelation and redox. Furthermore, TU-rGOF balls also exhibited excellent selective adsorption performance (∼90 % Au adsorption at an Au concentration ∼ 1 mg/L) in real E-waste wastewater (pH = 0.07) containing significant amounts of competitive ions. This study provides novel implications for applying TU-rGOF balls to fixed-bed reactors for low-concentration Au(III) recovery from complex recycled E-waste solutions.

Unraveling the potential of N-butyl imidazolium tetrafluoroborate-modified sulfonated polyether ether ketone polymer composite for ciprofloxacin removal

This study focused on characterization and assessing the adsorption capabilities of sulfonated polyether ether ketone (SPEEK) and ionic liquid incorporated SPEEK (SPEEK-BIM) composite adsorbents for removing ciprofloxacin (CIP) from water. Fourier-transform infrared (FTIR) analysis verified successful sulfonation and interaction between the polymer and ionic liquid. Scanning electron microscopy (SEM) revealed structural changes, indicating increased surface roughness and the formation of pores after sulfonation. Thermogravimetric analysis (TGA) showed thermal stability and multiple degradation steps. Adsorption experiments demonstrated SPEEK and SPEEK-BIM's effectiveness, with maximum removal efficiencies of 75.8 % and 92.9 % respectively, at a solid/liquid ratio of 0.6 g/L. Equilibrium was reached within 300 min for SPEEK and 180 min for SPEEK-BIM, with pH 7–9 yielding optimal adsorption due to CIP's zwitterionic form. Calculated maximum adsorption capacities were found as 303.03 mg g−1 and 500.0 mg g−1 for SPEEK and SPEEK-BIM, respectively. Langmuir isotherm modeling indicated monolayer coverage, while pseudo second-order kinetics described chemisorption with active sites involvement. Thermodynamic analysis suggested spontaneous, endothermic adsorption favored at higher temperatures. Desorption studies demonstrated reusability, especially in basic conditions. Water medium affected adsorption, with reduced efficiency in drinking and tap water compared to distilled water. Comparisons with literature data highlighted competitive adsorption capacities. In conclusion, SPEEK and SPEEK-BIM composite adsorbents hold promise for CIP removal, with potential applications in water treatment and environmental remediation.

Biomass-derived sustainable mesoporous activated carbon as an efficient and recyclable adsorbent for the adsorption of hazardous dyes

The use of activated carbon obtained from biomass in wastewater treatment has grown in popularity due to its sustainability and low manufacturing cost. Mesoporous activated carbon (MAC), with a large surface area (480 m2/g) and remarkable adsorption capacity, was produced at 550 °C using affordable Ficus religiosa leaf as a biomass precursor. The developed MAC was used to adsorb the hazardous contaminants of acid blue 9 (AB9) and malachite green (MG) from wastewater. To characterize MAC, various analytical techniques were used, including XRD, Raman, HR-SEM, HR-TEM, EDAX, FTIR, BET surface area analysis, XPS, TGA, and the associated DTA. The observed data confirms the production of the graphitic framework in the synthesized MAC but also demonstrates the dispersion of mesopores with a diameter of 4 nm. Also, BET, HR-SEM, and HR-TEM images confirmed the presence of high pore density and dye adsorption surface area. MAC dye adsorption capacity with optimum adsorbent dosage of 0.2g and 0.3g was estimated as 1.552 × 10−4 (mol/g) (123.04 mg/g) and 1.495 × 10−4 (mol/g) (138.58 mg/g) for AB9 and MG respectively at equilibrium of 120 min. The regression coefficients derived from the Freundlich, Langmuir, and D-R adsorption isotherms peak are compared, and the R2 value of 0.99 reported by Langmuir suggests that the adsorption of AB9 and MG adheres to the Langmuir adsorption isotherm by best fitting the equilibrium, recommending monolayer coverage. The chemisorption mechanism is defined by the combination of adsorption kinetics and a pseudo-second-order model. Besides, the sustainability was shown for five adsorptions–desorption cycles judge the utility and economic viability of the adsorption process. The plausible adsorption mechanism of MAC over AB9 and MG is mediated by synergetic interactions such as π-π interactions, hydrogen bonding, and electrostatic interactions. Therefore, exceptional stability, sustainability, and reliability for up to five adsorption run cycles of MAC justify its superiority over other adsorbents in the adsorption of AB9 and MG from wastewater.

Modeling the coverage of MoS2 and WS2 thin films using in-situ spectroscopic ellipsometry

In-situ spectroscopic ellipsometry (SE) was used to analyze monolayer and few-layer samples of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. MoS2 and WS2 film growth times ranged from 5 – 40 min to achieve a range of film coalescence and surface coverage from less than a monolayer to considerable bilayer and additional layers. Post-growth measurements using atomic force microscopy, photoluminescence and Raman spectroscopy were used to assess the evolution of surface morphology and film properties with growth time to determine the areal coverage of monolayer, bilayer, multilayer and void regions. The room temperature SE spectra were modeled using an effective medium approximation to obtain the monolayer and bilayer dielectric functions of MoS2 and WS2. Using these distinct dielectric functions, changes in ellipsometry parameters associated with partial to full coverage of monolayers and bilayers were simulated. Such simulations will enable improved control of the layer-by-layer deposition of MoS2 and WS2 by monitoring in-situ spectroscopic ellipsometry.

Acid-activated corn silk as a promising phytosorbent for uptake of Malachite green and Cd (II) ion from simulated wastewater: equilibrium, kinetic and thermodynamic studies

Malachite green (MG) dye and cadmium metal ion are toxic pollutants that should be removed from aqueous environment. The recent study aimed to examine the adsorption behavior of MG dye and Cd (II) from wastewater onto low-cost adsorbent prepared by activating corn silk with nitric acid (ACS) and characterized by SEM, FTIR, XRD, BET and TGA. The optimum MG and Cd (II) adsorption was observed at pH 7 and pH 9 and maximum uptake of both pollutants was at 0.5 g dosage, 60 mins contact time and 20 mg/L initial concentration. The retention of dye and metal ion by the studied adsorbent was best fit to Langmuir isotherm and Pseudo-second order kinetics. The maximum monolayer coverage capacity of ACS for MG dye and Cd (II) ion was 18.38 mg/g and 25.53 mg/g, respectively. Thermodynamic studies predicted a spontaneous reaction with exothermic process for MG dye whereas an endothermic and spontaneous process was confirmed for Cd ion based on estimated parameters. The adsorption mechanism of MG dye and Cd (II) uptake was by combination of electrostatic interaction, pore diffusion, ion exchange, pie-pie attraction, hydrogen bonding, and complexation. The adsorbed pollutants were effectively desorbed with significant regeneration efficiency after successive five cycles that proved the potential of low-cost biosorbent for selective sequestration of cationic dye and divalent metal ion from effluents.

Exploring the sustainable synthesis pathway and comprehensive characterization of magnetic hybrid alumina nanoparticles phase (MHAl-NPsP) as highly efficient adsorbents and selective copper ions removal

This study introduces a novel method for producing magnetic hybrid alumina nanoparticles phase (MHAl-NPsP) tailored specifically for efficient copper (II) ion removal from wastewater. The synthesized MHAl-NPsP underwent comprehensive characterization, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) revealing its rough and porous surface morphology, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) analysis, BET analysis for surface area measurements, TGA analysis confirming high thermal stability, vibrating sample magnetometry (VSM) analysis confirming successful synthesis through detection of magnetic properties, and X-ray Photoelectron Spectroscopy (XPS) analysis. Remarkably, MHAl-NPsP demonstrated an exceptional adsorption capacity of 52.5 mg/g under optimized conditions of pH 3.5 and an initial copper concentration of 30 mg/L, surpassing previous results significantly. Detailed investigation into adsorption kinetics revealed a pseudo-second-order model, suggesting a predominant chemisorption mechanism. Moreover, analysis using the Langmuir isotherm model showed excellent fitting with an R² value of 0.994, indicating monolayer coverage as the primary adsorption mode. Notably, pH dependency studies indicated enhanced adsorption efficiency with decreasing pH levels, highlighting the significant role of electrostatic interactions. This study underscores the effectiveness and environmental sustainability of the green synthesis approach employed for MHAl-NPsP. Utilizing their magnetic properties, MHAl-NPsP facilitate easy separation and retrieval of adsorbed copper ions, making them highly promising for practical applications in wastewater treatment. The findings advocate for the development of eco-friendly adsorbents to tackle water pollution challenges, providing promising solutions for sustainable environmental remediation.