Chemisorption Mechanism Research Articles

Corrosion inhibition performance of protein derived carbon quantum dots as corrosion inhibitors on low carbon steel in sulfuric acid solution

Protein derived carbon quantum dots (PCQDs) were successfully fabricated via a hydrothermal method with shrimp meat as the precursor. Subsequently, their corrosion-inhibiting performance on mild steel (L-steel) in a 0.5 mol/L H2SO4 solution was evaluated. Electrochemical impedance spectroscopy (EIS) tests demonstrated that at a concentration of 250 mg/L, the corrosion inhibition efficiency of PCQDs exceeded 90 %. Potentiodynamic polarization (PDP) tests indicated that when the concentration of PCQDs reached 500 mg/L, the corrosion inhibition efficiency was as high as 97.45 %. Comprehensive characterizations of the PCQDs, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible spectroscopy (UV–Vis), verified the existence of functional groups such as carboxyl, hydroxyl, and aromatic rings within the PCQDs. These groups are conducive to forming a strong adsorption force on the surface of L-steel and creating a protective layer. Surface morphology analyses carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the surface of L-steel treated with PCQDs was significantly smoother in comparison to untreated samples exposed to acidic conditions. Adsorption studies disclosed a mixed physical and chemical adsorption behavior, and theoretical calculations showed that the N and S atoms in PCQDs preferentially adsorb in a parallel direction. The addition of PCQDs led to a reduction in the diffusion coefficient, indicating that the diffusion of corrosive ions was effectively hindered. The distribution function of PCQDs was 3.48 Å, which suggested that the chemisorption mechanism played a dominant role in the inhibition process.

Efficient adsorption of antibiotics using MXene nanosheet delaminated by Taylor vortex flow

MXenes are emerging as a promising class of two-dimensional (2D) adsorbents suitable for various environmental applications. The present study explores the use of Ti3C2Tx MXene nanosheet, delaminated by Taylor vortex flow (TVF), namely d-MXene-CT, as an efficient adsorbent for fluoroquinolones (FQs). The TVF induced in the gap between two coaxial cylinders of the Couette-Taylor reactor enhances the delamination process, yielding larger and thinner MXene nanosheets with a specific surface area 12 fold higher than that of nanosheets delaminated by turbulent eddy flow (TEF), namely d-MXene-MT in a conventional mixing tank (MT) reactor. As a result, the d-MXene-CT exhibited superior adsorption performance, with removal capacity for ciprofloxacin (CIP) of 349 mg/g and for levofloxacin (LEV) of 290.51 mg/g, representing 40 ∼ 60 % improvement over d-MXene-MT (249 mg/g for CIP and 180.22 mg/g for LEV). The adsorption process follows the pseudo-second-order kinetics model and fits the Langmuir isotherm, indicating the involvement of a monolayer chemisorption mechanism. Further investigation revealed that the removal of CIP and LEV was mainly driven by electrostatic attraction between oxygen functionality of MXene and protonated nitrogen group of FQs. The study highlights the potential of d-MXene-CT as a promising adsorbent for treating (FQs) from contaminant water.

Potential-dependent kinetics of oxygen chemisorption as the crucial step of oxygen reduction reaction: GCDFT study

Nitrogen-doped carbon materials (NCMs) are widely regarded as promising alternatives to expensive platinum-based electrocatalysts for the oxygen reduction reaction (ORR). While NCMs exhibit considerable electrochemical activity in alkaline media, their performance in acidic environments remains a significant challenge. However, acidic conditions are commercially desirable for ORR’s catalysis in proton-exchange membrane fuel cells (PEMFCs). The dramatic pH dependence of NCM effectiveness has sparked ongoing debate, with several factors under consideration, including surface protonation, variations in hydrogen binding energy, differences in proton donors, and interface structure. In this work, we present a grand canonical density functional theory (GCDFT) study of the chemisorption step on pristine and nitrogen-doped graphene. Through nudged elastic band (NEB) calculations at various electrode potentials, we propose a potential-dependent (and thus pH-dependent) mechanism of oxygen chemisorption at graphitic nitrogen (Ngr) defects, offering new insights into the pH dependency of the onset potential in NCM catalysts.

Highly Efficient and Reversible Carbon Dioxide Capture by Carbanion-Functionalized Ionic Liquids.

Due to the active unstable nature of carbon anions, it is challenging to develop carbanion-functionalized ionic liquids (ILs) for efficient and reversible carbon dioxide (CO2) capture. Here, a series of carbanion-based ILs with large conjugated structures were designed and a promising system was achieved through tuning the nucleophilicity of carbanions and screening the cation. The ideal carbanion-functionalized IL trihexyl(tetradecyl)phosphonium N,N-diethycyanoacetoamide ([P66614][DECA]) showed equimolar chemisorption of CO2 ( up to 0.98 mol CO2/mol IL) under ambient pressure and excellent absorption rate. What's more, the combined CO2 can be released easily, leading to excellent reversibility due to high stability of anion conjugated structures. More importantly, the presence of water had negligible effect on the absorption capacity, which makes it potential to be applied to the CO2 capture in industrial flue gas. The chemisorption mechanism of the carbanion and CO2 was confirmed by spectroscopic investigations and DFT calculations, where carboxylic acid product was formed through proton transfer after the carbanions reacted with CO2. Considering that high capacity, quick rate as well as excellent reversibility, these carbanion-functionalized ILs should certainly represent competitive candidates for further scale up and practical application in CO2 capture.

Biosorption of Cr(VI) by Theobroma cacao pericarp.

This paper reports a comprehensive study of Theobroma cacao pericarp (TCP) residues, which has been prepared, characterized, and tested as an inexpensive and efficient biosorbent of Cr(VI) from aqueous solutions. The maximum adsorption capacity of TCP obtained at optimal conditions (pH = 2, dose = 0.5g L-1, C0 = 100mg L-1) was qmax = 48.5mgg-1, which is one of the highest values reported by the literature. Structural and morphological characterization has been performed by FTIR, SEM/EDX, and pHPZC measurements. FTIR analysis revealed the presence of O-H, -NH, -NH2, C = H, C = O, C = C, C-O, and C-C functional groups that would be involved in the Cr(VI) biosorption processes. The experimental equilibrium data of biosorption process were successfully fitted to non-linear Langmuir (R2 = 0.95, χ2 = 11.0), Freundlich (R2 = 0.93, χ2 = 14.8), and Temkin (R2 = 0.93, χ2 = 14.7) isotherm models. Kinetics experimental data were well adjustment to non-linear pseudo-2nd (R2 = 0.99, χ2 = 2.08)- and pseudo-1st-order kinetic models (R2 = 0.98, χ2 = 2.25) and also to intra-particle Weber-Morris (R2 = 0.98) and liquid film diffusion (R2 = 0.99) models. These results indicate that Cr(VI) biosorption on heterogeneous surfaces as well as on monolayers of TCP would be a complex process controlled by chemisorption and physisorption mechanisms. The thermodynamic results indicate that the Cr(VI) biosorption on TCP is a feasible, spontaneous, and endothermic process. TCP can be regenerated with NaOH and reused up to 3 times.

Kinetics Analysis of Crystal Violet Adsorption from Aqueous Solution onto Flamboyant Pod Biochar

The increasing presence of presistent synthetic dyes, like crystal violet (CV), in wastewater poses a significant threat to aquatic ecosystems and human health due to its genotoxicity and carcinogenicity. Biochar derived from agricultural waste offers a promising, cost-effective, and eco-friendly approach for dye removal. This study explores the potential of flamboyant pod biochar (FPB) as a novel and sustainable adsorbent for CV removal. FPB offers a unique advantage as it utilizes readily available flamboyant pod waste, promoting waste valorization and a cost-effective approach. FPB was synthesized through a simple process involving milling, sun-drying, and pyrolyzing flamboyant pod waste at 300 °C. Batch adsorption experiments were conducted to evaluate the influence of contact time and initial dye concentration on removal efficiency. Kinetic modeling using pseudo-first-order and pseudo-second-order models explored the underlying mechanisms governing the adsorption process. The pseudo-second-order kinetic model exhibited a superior fit (R² > 0.87) compared to the pseudo-first-order model, suggesting a chemisorption mechanism governing the adsorption process. These findings demonstrate the potential of FPB as a low-cost, sustainable adsorbent for CV removal from wastewater.

Simultaneous removal of heavy metals and Escherichia coli from water using silver-doped hydroxyapatite-coated activated carbon nano composite-alginate beads

The scarcity of clean water due to heavy metal and microbial contamination is a global issue. In many parts of the world, heavy metals such as Pb, Cd, and U, along with bacteria like Escherichia coli, have been found to exceed permissible limits in groundwater and other water sources that the public depends on for daily drinking water. To address this, we have synthesized a novel composite material consisting of Ag-impregnated hydroxyapatite-coated activated carbon nanoparticles embedded in alginate beads, for the simultaneous removal of heavy metals (U, Pb, and Cd) and Escherichia coli from drinking water. The material's efficiency was evaluated through a series of batch and column experiments. Batch studies indicate 90 % sequestration of U within 5 hours and Pb and Cd within 7 hours, while Escherichia coli (107 cfu/mL) was eradicated instantly. The study confirms that sorption follows pseudo-second-order kinetics via chemisorption and ion-exchange mechanisms. Fixed-bed column studies, using a logistic growth model, showed strong agreement between theoretical and experimental parameters for the Bohart-Adams, Thomas, and Yoon-Nelson models. The beads demonstrated a high affinity for heavy metals, achieving complete removal and disinfection within an empty bed contact time of 1.12 minutes. Reusability studies indicate that even after the third regeneration and reuse cycle, removal efficiency remained about 95 % for U and Pb, and 85 % for Cd. Furthermore, the effects of variations in water quality parameters such as pH, dissolved carbonates, humic acid, and ionic strength (except for Cd) on removal efficiency were minimal. In summary, the study revealed that the Ag-impregnated hydroxyapatite-coated activated carbon nanoparticles embedded in alginate beads are an efficient, sustainable, and cost-effective material for the simultaneous removal of Pb, Cd, U, and Escherichia coli from water with diverse physicochemical properties.

Highly efficient and sustainable polyacrylic acid-polyacrylamide double-network hydrogels prepared by cross-linking of waste residues for heavy metals ions removal

In this paper, an adsorbent composite called S-PEMR, which consists of electrolytic manganese residues (EMR)- silicate minerals-based polyacrylic acid-polyacrylamide double-network hydrogels, has been developed. The successful synthesis was confirmed by the characteristic peaks of COO, amide I, CO, -CH2, C-N group vibration in FTIR spectra as well as amorphous carbon in XRD patterns. This composite tackles the issue of harnessing EMR, which consists of layered silicate minerals and additional elements. These elements have potential value but are difficult to be effectively and safely utilized. It was observed that the adsorption process agreed with the quasi-secondary model and the Langmuir isotherm, the adsorption process is controlled by a chemisorption mechanism with the occurrence of electron sharing or electron transfer (establishment of covalent bonds) between the S-PEMR and the adsorbate. The S-PEMR was found to be recyclable up to four times. In the initial experiment, the concentrations of Ni, Cu, Cd, and Pb in a natural wastewater were recorded as 645.84, 906.21, 378.15, and 8.29 μg/L, respectively. The composites used in the study exhibited high removal efficiency for Ni (42.06 %), Cu (93.14 %), Cd (89.68 %), and Pb (77.02 %). The S-PEMR can be recycled up to four times with only a moderate reduction in adsorption performance. The removal mechanism primarily involved chelation or coordination, ion exchange, functional groups containing elements such as O and N, as well as the interaction of Si-O and Al-O with the heavy metal ions. This research establishes S-PEMR as a highly effective adsorbent for removing harmful contaminants from water.

Mechanism of tetracycline sorption on carbon-bentonite

Antibiotics increased industrial production is the reason of their occurrence in wastewater, soils, groundwater, and drinking water. In this regard, treating the environment for pharmaceuticals is one of the urgent environmental challenges. Synthesis of adsorbents using different types of raw materials by the methods of mechanochemical activation makes it possible to significantly increase their sorption capacity due to the accumulation of various kinds of defects in the crystal structure of the adsorbent. We obtained the bentonite-carbon composite using roller-ring vibratory mill with coal-bentonite ratio of 30 : 70 and 50 : 50. However, the nature of the interaction between carbon and bentonite correlates with changes of surface area and porosity. The porous structure parameters of the samples show the mechanochemical activation of the mixture involves their components interactions. The authors studied the structural and chemical changes during the modification of bentonite with activated carbon by analysing the vibrational spectra of carbon, initial, and modified aluminosilicate samples. According to infrared spectroscopy of adsorbents, absorption bands characteristic of Si-O-C bond vibrations occurred. The paper investigates the sorption capacity of mechanochemically modified natural clay mineral Dash-Salakhli bentonite towards tetracycline hydrochloride. Research investigates the kinetics of the process and rapid sorption of tetracycline. The paper provides possible mechanisms of chemisorption due to donor-acceptor interaction and ion-exchange processes.

Selective extraction of Lead from Chelator-Rich effluents using a Biomass-Based sorbent

The efficient removal of lead (Pb) from waste streams containing chelators presents a significant challenge due to the high stability and mobility of Pb-chelator complexes. This study investigates a novel approach utilizing a biomass-based sorbent, proline-incorporated dithiocarbamate-modified cellulose with epoxy-cross-linkage (DMC-Pro-Epo6), to extract Pb from effluents with excess chelators. DMC-Pro-Epo6 exhibited exceptional Pb(II) sorption performance under controlled and various chelator-rich conditions. The sorbent maintained high sorption efficiency even with 100-fold excess chelator concentration and competing metal ions. DMC-Pro-Epo6 also outperformed commercially-available ion-selective sorbents in terms of separation efficiency. The sorption kinetics followed a pseudo-second order model, demonstrating rapid sorption with equilibrium reached within 20 min. The maximum sorption capacities of DMC-Pro-Epo6 obtained from the Langmuir isotherm model were 1267 and 659 µmol/g in Pb(II)-containing aqueous solution and Pb(II)-containing EDTA solution, respectively. X-ray photoelectron and absorption spectroscopy analyses, along with sorption parameters, confirmed a chemisorption mechanism for Pb(II) sorption onto DMC-Pro-Epo6. Validation of the protocol using real waste samples with complex chelator and base metal ion matrices resulted in a quantitative and selective extraction of 92 to 99 % of Pb(II). This success suggests the potential for scaling up the developed process. Compared to conventional treatment methods, the proposed technique offers a more efficient and streamlined process for separating metal ions and chelators from effluents.

Utilization of waste PET-derived metal–organic framework grafted polyaniline composite for heavy metal adsorption from aqueous solution

In this research, we used waste polyethylene terephthalate (PET) bottles as a source to develop an iron-based MOF-supported polyaniline (Fe-MOF@PANI) composite, which was then applied for the adsorptive removal of cadmium (Cd(II)) and lead (Pb(II)) ions from aqueous environment. A comprehensive characterization of the Fe-MOF@PANI composite was conducted using several analytical techniques including FTIR, PXRD, SEM, EDX with mapping, and XPS analysis, which provided significant insights into its functionality, crystalline structure, surface morphology, and elemental composition. The synthesized Fe-MOF exhibited a spindle-shaped morphology that was evenly distributed over the surface of the PANI composite, as confirmed by SEM analysis. Additionally, the porous characteristics of the Fe-MOF@PANI composite were proven through BET analysis. The Fe-MOF@PANI composite exhibited remarkable adsorption efficiencies for selected metal cations, achieving adsorption capacities of 143.36 mg/g and 258.59 mg/g for Cd(II) and Pb(II) ions, respectively. The findings of the isotherm and kinetic studies demonstrated that the adsorption process fitted well with Langmuir and pseudo-second-order kinetics, indicating that adsorption of both metal cations occurs in a monolayer formation and includes chemisorption mechanisms, respectively. This research paves the way for further development and application of post-functionalized PET-derived MOF adsorbents to remove Cd(II) and Pb(II) ions from water efficiently.

Rapid and selective separation of heavy metal ions from aquatic medium using a bidentate functionalized hybrid material

Low-cost mesoporous silica material, functionalized with a bidentate pyrazolyl pyridine metal acceptor and presenting a high specific surface area of 417 m²/g, was synthesized (mSi-L3) using a two-step procedure and characterized in detail to confirm the successful covalent binding onto silica surface. Notably, mSi-L3 exhibited strong selectivity for PbII among CdII and CuII ions, and displayed rapid metal ion removal, typically less than 10 min, from water samples.The influence of various environmental parameters on the adsorption process, such as pH, contact time and temperature, was systematically investigated. Optimal adsorption of metal ions was achieved at pH 6, as lower pH values reduced the availability of active sites due to competitive hydronium ion presence. Kinetic studies indicated that the adsorption process adhered to the pseudo-second-order model, suggesting a chemisorption mechanism. Temperature significantly influenced the adsorption capacity, with increased temperatures enhancing metal ion removal and confirming the endothermic nature of the process. The isotherm study suggests that the Langmuir model accurately describes the adsorption process, confirming that CuII, CdII and PbII ions are adsorbed as a monolayer on the homogeneous surface of m-SiL3 material, implying that the material has uniform adsorption sites where each metal ion occupies a distinct site without interaction with neighbouring ions. These findings underscore the importance of optimizing environmental conditions to maximize the efficiency of mSi-L3 for heavy metal removal. Also, mSi-L3 demonstrated excellent stability, with only a slight (∼1−3 %) decrease in functional groups on its surface after multiple regeneration cycles. Extensive analytical studies conducted with real water samples provided further evidence of the stability and effectiveness of mSi-L3 for the separation of metal trace elements of lead, copper and cadmium.

A theoretical simulation of carbon dioxide adsorption capture on amine-functionalized graphene oxides

Amine-functionalized graphene oxides (AFGOs) are potential candidates for CO2 capture applications, as the amine functional groups could act as effective sites, promoting CO2 adsorption strength and selectivity. However, the CO2 adsorption mechanism on AFGO appears to be ambiguous, particularly with no explicit identification of the chemically bonded species. In this work, density functional theory and microkinetic simulations were carried out to investigate the physical and chemical adsorption mechanisms and behavior between AFGO and CO2. Our findings indicate that the van der Waals and hydrogen bonding (HB) interactions constitute physical binding modes between the aminated GO and CO2. The chemical adsorption pathways on AFGO materials have been revealed by the transition state search method, in which the relevant CO2 adsorption species, including carbamic acid and carbamate, and their formation conditions were theoretically identified on AFGOs. The chemisorption mechanisms have been recognized to be the nucleophilic interaction between GO-supported amines and CO2, simultaneously assisted by the cooperative effect of multiple HB interactions. More specifically, the surface hydroxyl groups and water molecules can serve as proton transfer media and offer HB interactions, thus regulating the reaction activity and chemical adsorption species. This theoretical work presents a new insight into CO2-AFGO interaction mechanisms, which is valuable for designing aminated GO adsorbents.

Effect of PFDTS/TiO2 Coating on Microstructure and Wetting Behavior of Phosphogypsum.

Phosphogypsum (PG) constitutes a form of solid byproduct emanating from the manufacturing process of wet-process phosphoric acid. The fabrication of one metric ton of wet-process phosphoric acid entails the generation of approximately five tons of phosphogypsum, a highly prolific and economically viable waste stream. If we can effectively solve the problem of poor hydrophobicity of phosphogypsum, it is possible to replace cement and other traditional cementitious materials. In this way, we can not only improve the utilization rate of phosphogypsum but also obtain significant economic and environmental benefits. In the present investigation, hydrophobic surface coatings were synthesized and applied onto the surface of α-hemihydrate phosphogypsum (α-HPG) utilizing sol-gel processing and impregnation techniques. After hydroxylating α-HPG with alkaline solution (OH-α-HPG), titanium dioxide nanoparticles (TiO2) hybridized with perfluorodecyltriethoxysilane (PFDTS) were grafted on its surface. The assessment of the hydrophobic properties of the coatings was conducted through water contact angle measurements, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) analyses. The contact angle remained above 124.2° after strong acidic and alkaline immersion and 50 tape adhesion experiments with good chemical stability and durability, and the mechanism of surface hydrophobicity modification was discussed. The experimental outcomes demonstrated a notable increase in the hydroxyl group concentration on the α-HPG surface following hydroxylation, significantly enhancing the attachment rate of PFDTS and TiO2 onto the HPG surface. PFDTS and TiO2 can undergo chemical interaction with hydroxyl groups, facilitating their robust adsorption onto the surface of OH-α-HPG through chemisorption mechanisms. After bonding the OH-α-HPG surface with PFDTS and TiO2 via hydrogen bonding, the otherwise hydrophilic α-HPG surface acquired excellent hydrophobicity (OH-α-HPG-PT, contact angle (CA) = 146.7°). The surface modification of α-HPG through hydroxylation and hydrophobicity enhancement significantly augmented the compatibility and interfacial interplay between α-HPG and PT. This research successfully enhanced the hydrophobic properties of α-HPG, profoundly showcasing its immense potential within the construction industry and the realm of comprehensive solid waste utilization.

Methylene Blue and Rhodamine B Dyes' Efficient Removal Using Biocarbons Developed from Waste.

The preparation of biocarbons from cellulose fibres utilised in the production of baby nappy mats (sourced from Feniks Recycling company, Poland) for the removal of methylene blue and rhodamine B dyes has been documented. A Brunauer, Emmett and Teller analysis revealed a surface area within the range of 384 to 450 m2/g. The objective of this study was to investigate the removal efficiency of dyes from aqueous solutions by biocarbons, with a particular focus on the influence of various parameters, including pH, dye concentration, adsorbent dosage, shaking speed, contact time, and temperature. The maximum adsorption capacity of the dyes onto the biocarbons was found to be 85 mg/g for methylene blue and 48 mg/g for rhodamine B, respectively. The Langmuir equation proved to be the most suitable for interpreting the sorption of organic dyes. The adsorption process was found to exhibit a chemisorption mechanism, effectively mirroring the pseudo-second-order kinetics. Furthermore, the adsorption of dyes was observed to be endothermic (the enthalpy change was positive, 9.1-62.6 kJ/mol) and spontaneous under the tested operating conditions. The findings of this study indicate that biocarbons represent a cost-effective option for the removal of methylene blue and rhodamine B. The adsorption method was observed to be an effective and straightforward approach for the removal of these dyes. The results of the Boehm titration analysis and zero charge point value indicated that the synthesised biomaterials exhibited a slightly basic surface character.

Development of cellulose-based biosorbents from the residue of the peach palm agribusiness and simulation of industrial scale-up for copper removal from Brazilian spirit.

Cachaça (Brazilian spirit) is an alcoholic beverage of cultural and economic importance in Brazil. Its artisanal production is usually conducted in copper alembics, which results in contamination. The development of effective biosorbents from cheap matrices is an alternative to minimize both solid waste generation and copper levels in cachaça. The present work evaluates the obtention of nanocellulose-based materials from the major residue generated during the processing of palm heart from the Brazilian peach palm, through different processing techniques. Materials were characterized by physicochemical composition and their sorbent capacities for copper removal from aqueous solutions, and a simulation was conducted to evaluate potential application in the adequacy of cachaça to meet Brazilian legislation requirements. The different processing methods resulted in different cellulose concentrations, with the highest concentration in the bleached material (B3, 694 g kg-1 of cellulose), and different specific surface areas (1.02-12.4 m2 g-1). Copper adsorption onto nanocellulose obtained from peach palm external sheath is fast, with a predominance of a chemisorption mechanism. Isotherms were best represented by Langmuir's model, suggesting a monolayer adsorption. Simulations indicate that B3 is a suitable material for the removal of copper from cachaça, and small amounts of biosorbent (733.5 g) are required for the reduction of copper concentrations (10 to 3 mg L-1) in 1000 L of cachaça. This study demonstrated that the obtention of biosorbents from peach palm solid residues is promising and this nanocellulose-based material can be used for copper removal from contaminated cachaça. © 2024 Society of Chemical Industry.

Enhanced methylene blue dye sequestration by carbon-embedded mesoporous zinc oxide nanoparticles fabricated utilizing Aloe barbadensis miller biowaste: Batch optimization, simulation modeling, and textile effluent feasibility

The present study reports novel carbon-embedded mesoporous zinc oxide nanoparticles (ZnO/C NPs) utilizing Aloe barbadensis miller (Aloe vera) biowaste extract as size-reducing agent and bio-stabilizer via a one-pot green fabrication approach. The fabricated nanoparticles were carbonized at 250 °C and characterized using FTIR, UV-Vis, ZPA, TEM, SEM/EDX, XRD, BET, and TGA techniques. Using Brunauer, Emmett, and Teller's theory, the ZnO/C NPs specific surface area was determined to be 63.25 m2/g, and the average pore diameter (3.46 nm) was in the mesoporous range. Fabricated ZnO/C NPs have an un-uniform size distribution, with an average crystallite size of 17.37 nm. The methylene blue (MB) dye adsorption of mesoporous ZnO/C NPs was studied in batch mode experiments at 37 °C using an aqueous solution. Detailed isotherms and kinetics modeling were performed, and it established that the Langmuir isotherm and Pseudo second order kinetic correctly fit the optimized MB dye adsorption data due to their higher correlation coefficients than other analyzed models. The Langmuir isotherm-based monolayer adsorption was found to be 105.26 mg/g. The pseudo second order kinetic best explains the adsorption reaction, indicating that the chemisorption mechanism is more likely to regulate the MB dye adsorption. Further, thermodynamics parameters showed that the MB dye adsorption onto ZnO/C NPs was spontaneous, endothermic, and accompanied by increased entropy. The ZnO/C NPs demonstrated remarkable MB dye sequestration from aqueous solution upto four reusability cycles, with regenerability of ≥84.52 %. Furthermore, feasibility study revealed an outstanding decolorization efficacy of MB dye upto 58.18 % from textile effluent, establishing mesoporous ZnO/C NPs as viable, environment-friendly, and cost-effective remedies for textile wastewater treatment.

Removal of hexachlorocyclohexane isomers from wastewater using activated carbon from Musa paradisiaca peel: Adsorption isotherms, kinetic, and thermodynamic studies

The potential usage of activated carbon from plantain peel (Musa paradisiaca) (TPPC) and unactivated carbon from plantain peel (UPPC) for the removal of Hexachlorocyclohexanes (HCHs) from water systems was investigated. The TPPC and UPPC were characterized using Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Adsorption experiments were conducted as a function of adsorbent weight (2 – 10 g), temperature (30 -50 °C), and solution pH (2 - 9) under an adsorbent packed column. The Optimum removal efficiency of 98.23 % was achieved in the column studies under the following conditions: pH = 5, the dosage of adsorbent = 5 g/100 mL, temperature = 30 °C. The batch adsorption process was employed to evaluate the kinetics, equilibrium, and thermodynamics of the adsorption processes. The equilibrium study showed that Langmuir among other isotherm models applied performed better in fitting the data. Additionally, the kinetic data was best described by the pseudo-second-order model (R2 > 0.97), indicating a chemisorption mechanism. Furthermore, the thermodynamic calculations of the adsorption process suggest that HCH adsorption was exothermic (ΔH = -110.87) and spontaneous (-ΔG).

Chemisorption of hydrogen on metal oxides with palladium (II) oxide additives

Chemisorption can lead to a change in electrical conductivity, which allows using semiconductor materials to create gas sensors. On the other hand, semiconductor sensors can be used as devices for studying the chemisorption of gases. In this work, we set two tasks. The first of them was to create a sensor for the selective determination of hydrogen in air, including in a mixture with other gases. The second task was to determine the mechanism of hydrogen chemisorption on the surface of metal oxides with palladium (II) oxide additives. We obtained and characterised nanodispersed materials based on SnO2 and WO3 with additions of 3% PdO by weight. We compared the electrical characteristics of these materials in stationary temperature conditions as well as with temperature modulation in the presence of hydrogen, methane, and their mixtures. The specific features of hydrogen chemisorption were determined on the surface of metal oxide semiconductors based on SnO2 and WO3 with PdO additives in the temperature modulation mode of the sensor. It was shown that the extrema in the dependence of the sensor’s electrical conductivity on temperature can be explained by the contribution of proton transfer to the total electrical conductivity. The presence of extrema in the electrical conductivity of sensors, which were observed in thermal modulation mode in the presence of hydrogen, allows conducting qualitative and quantitative analysis of not only single-component gas systems, but also of mixtures of hydrogen with other analyte gases. In particular, this work demonstrated that it was possible to determine the composition of a hydrogen-methane mixture in air using a single metal oxide sensor. The advantage of this approach is that multidimensional data arrays can be easily processed.

Enhanced removal of methylene blue and procion deep red H-EXL dyes from aqueous environments by modified-bentonite: Isotherm, kinetic, and thermodynamic

This study aims to enhance local bentonite's effectiveness in removing methylene blue and procion deep red dyes from aqueous media through organic modification with cetyltrimethylammonium bromide surfactant. Raw and modified bentonites were analyzed using XRF, XRD, FTIR, BET/BJH, and DSC techniques. The modified bentonite showed a crystalline structure and mesoporous morphology with a heterogeneous surface. Optimal adsorption conditions for MB dye were 0.2 g adsorbent dose, 60 min contact time, 60 mg/L initial concentration, and pH 8, achieving a maximum sorption capacity of 6.418 mg/g. For PDR dye, optimal conditions were a 0.125 g adsorbent dose, 40 mg/L initial concentration, 30 min contact time, and acidic pH, with a maximum adsorption capacity of 8.503 mg/g. Isotherm analysis indicated the Langmuir model best fits the adsorption data, suggesting a mono-layer adsorption process. Kinetic investigations revealed that the adsorption follows a pseudo-second-order model, indicating a chemisorption mechanism. Thermodynamic results showed exothermic adsorption for MB and endothermic adsorption for PDR. This work highlights the potential of surfactant-modified bentonite as a cost-effective sorbent for treating polluted aqueous systems, effectively removing both cationic and anionic dyes.