Surface Adsorption Research Articles

Mercury Capture Performance and Kinetics of CCl4-Adsorbed Activated Carbon Pretreated by the Mechanochemical Method.

In the present work, CCl4-adsorbed activated carbon pretreated by the mechanochemical method (CCl4-AC) was produced for gas-phase mercury capture. The physicochemical properties of the CCl4-AC sorbent were analyzed via N2 adsorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The mercury capture performance of the CCl4-AC sorbent under different flue gas components was investigated in a fixed-bed experimental device. The programmed temperature desorption of mercury was used to determine the mercury capture product of the spent CCl4-AC. Finally, the mass transfer factor model proposed by Fulazzaky was used to analyze mercury capture on the CCl4-AC for clarifying its characteristics. The results showed that the prepared CCl4-AC can be used as a mercury sorbent because of its high mercury capture performance. Mercury capture by the CCl4-AC was interfered by SO2 and promoted by O2 and H2O. Hg-temperature programmed desorption (Hg-TPD) analysis indicated that the main mercury capture products of the CCl4-AC were HgCl2 and HgO. Because of the presence of SO2 in flue gas, there was a little Hg2SO4 formation on the sorbent. XPS analysis showed that the functional group of C-Cl played the dominant role in Hg0 capture, and part of the C-Cl groups were converted into Cl- after mercury capture. The mercury desorption energy of the spent CCl4-AC was 50.49 kJ/mol and stronger compared with that of raw activated carbon. Mass transfer analysis displayed that surface adsorption was the main form at the beginning of mercury adsorption, and the external mass transfer was the mercury adsorption rate-controlling step. Then, mercury adsorption entered the second stage; internal diffusion adsorption stage with internal mass transfer became the adsorption rate control step.

Key Role of Oxidising Species for Water Oxidation on Iridium Oxides Revealed By Time-Resolved Optical and X-Ray Spectroscopies

Iridium oxide is the state-of-the-art electrocatalyst for water oxidation in polymer electrolyte membrane (PEM) electrolysers, crucial for green hydrogen production. Despite its extensive industrial use, the water oxidation mechanism on this metal oxide and the key factors controlling the reaction rate remain unclear. Understanding these controls at a fundamental level on such benchmark metal oxides is vital for designing more active and stable electrocatalysts for water oxidation in PEM electrolysers.In this talk, I will present our research on probing oxygen evolution reaction (OER) relevant species on iridium-based catalysts. This involves a combination of time-resolved operando optical spectroscopy, soft and hard X-ray absorption spectroscopy (XAS), and electrochemical mass spectrometry. Initially, I will discuss the intermediate and catalytically active states of iridium oxides. This is based on correlating optically detected states with oxygen molecular products identified through on-chip electrochemical mass spectrometry. Subsequently, I will demonstrate how we used optical spectroscopy to quantify these states as a function of potential. The nature of these states, including the Ir oxidation state and surface adsorbates on iridium sites, will be elucidated using a combination of time-resolved Ir-L edge XAS, O-K edge XAS, and supported by Density Functional Theory (DFT).With these quantification results of active species for OER, I will compare the intrinsic kinetics of two state-of-the-art iridium oxide structures - amorphous IrOx versus crystalline rutile IrO2.[1] The effect of the electrolyte on the intrinsic activity of iridium oxides will also be discussed.[2] Finally, based on this molecular-level understanding, I will present a modified volcano model for OER catalyst design. This model considers the impact of adsorbate-adsorbate interactions on binding energetics, demonstrating critical design principles for high intrinsic activity OER catalysts.The authors acknowledge the funding support from the Imperial College-Chinese Scholarship Council Studentship and bp-ICAM 92, which made this research possible.[1] Caiwu Liang, Reshma Rao, Karine Svane et al. Unravelling the effects of active site densities and energetics on the water oxidation activity of iridium oxides, 07 March 2023, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-2605628/v1][2] Caiwu Liang, Yu Katayama, Yemin Tao, Asuka Morinaga, Benjamin Moss, Verónica Celorrio, et al. Role of electrolyte pH on water oxidation for iridium oxides. ChemRxiv. Cambridge: Cambridge Open Engage; 2023

The quorum sensing SinI/SinR-TraI/TraR systems promote Pb stabilization by Ensifer adhaerens S24 in the Pb-polluted aquatic environment

In this study, the Pb-resistant Ensifer adhaerens strain S24, which contains quorum sensing (QS) systems responsible for N-acyl homoserine lactone (AHL) production, was investigated for QS system-mediated Pb stabilization and the underlying mechanisms. Whole-genome sequence analysis revealed the QS SinI/R and TraI/R systems in strain S24. Subsequently, strains S24 and the S24∆sinI/R, S24∆traI/R, S24∆traI/R/sinR, and S24∆sinI/R-traI/R/sinR mutants were constructed and compared for QS SinI/SinR-TraI/TraR system-mediated Pb stabilization in the solution and the mechanisms involved. After 5 days of incubation, strain S24 significantly decreased the Pb concentration in the Pb-contaminated solution compared with the mutants. The S24∆sinI/R-traI/R/sinR mutant exhibited reduced Pb stabilization and AHL activity than the other mutants. The S24∆sinI/R-traI/R/sinR mutant had significantly greater Pb concentrations in the solution and lower cell surface-adsorbed and extracellular precipitated Pb (PbS) contents as well as lower expression of H2S-producing genes of metC and sseA than did strain S24. Furthermore, the S24∆sinI/R-traI/R/sinR mutant displayed reduced interactions between the hydroxyl, amino, carboxyl, and ether groups and Pb, compared with strain S24. These findings implied the vital role of the SinI/SinR-TraI/TraR systems in strain S24 for Pb stabilization through enhanced cell surface adsorption and extracellular precipitation in Pb-polluted aquatic environments.

Title: Investigation of Kinetically Favorable Chromium Speciation Distribution for Iron Chromium Redox Flow Batteries

Chromium is a promising active material for redox flow battery (RFB) electrolytes due to its low cost and reduction potential very near the negative limit of the electrochemical window of water. However, many challenges exist with the performance of the Cr3+/2+, most notably sluggish electron-transfer kinetics and parasitic hydrogen evolution during the charge cycle. This presentation will focus on our recent efforts to overcome these challenges by understanding the interplay between electrolyte composition, speciation, and electron-transfer kinetics for the aqueous Cr3+/2+ redox couple.Among the earliest published work on flow batteries was a program based at NASA introducing the iron chromium redox flow battery (ICRFB) [1,2]. These studies were valuable in demonstrating both the promise and the complications of chromium for flow battery electrolytes. The NASA team went to great lengths to enhance chromium redox kinetics and suppress the hydrogen evolution via extensive modification of the carbon negative electrode with Au, Pb, and Bi additives. The present study is based on a key observation from this early work that the electron-transfer rates for Cr-chloride complexes depend strongly on the inner-sphere coordination environment, and specifically the number of chloride ions directly bound to the Cr center.Extensive prior studies from the inorganic coordination chemistry literature further demonstrate that Cr(III) chloride complexes undergo slow equilibration in aqueous solutions to form distributions of four species where the coordination environment around the metal center can be described generally as [CrClx(H2O)6-x](3-x)+ with 0 < x < 3 [3,4]. Each of these species yields a distinct optical absorption signature, enabling quantification of the composition with UV-VIS spectroscopy. Our overarching hypothesis, based on the early NASA work, was that increased chloride coordination (i.e., higher values of x in CrClx(H2O)6-x) would yield enhanced electron-transfer kinetics by reducing inner-sphere reorganization barriers associated with aquo ligands, or by enhancing catalytic mechanisms mediated by chloride surface adsorbates. Thus, we measured optical absorbance and electrochemical reversibility for Cr(III) chloride solutions with HCl, NaCl, and LiCl supporting electrolytes over a range of total chloride concentration from 0.1 to ~10 mol/L.Representative results are summarized in Figure 1 for 0.1 M CrCl3 in aqueous LiCl. Notably, at Au electrodes the reversibility of the Cr3+/2+ redox feature increases dramatically as chloride concentration increases above 5 mol/L (Figure 1a). This shift in reversibility is broadly correlated with UV-VIS results (Figure 1b) demonstrating that the primary Cr(III) species present initially remains the predominant species in the aqueous environment for high concentrations of chloride over time, but the predominant species shifts significantly at lower concentrations of LiCl. Ongoing work, which will be discussed in this presentation, is focused on full quantification of the relationship between speciation and electron-transfer kinetics as well as performance properties for ICRFBs with a range of supporting electrolyte concentrations. We anticipate that understanding the most kinetically favorable speciation distribution will allow us to develop improved electrolytes for functional ICRFBs.

Temperature Jump Methods for Measuring the Pme of RuO2

The potential of maximum entropy (PME) is used to understand the structure and charging of the electrochemical double layer. Closely related to the potential of zero charge (PZC), the PME occurs when disorder of the solvent molecules at the surface reaches a maximum. Using a laser induced temperature jump (LITJ) to measure the PME has been shown to be a convenient method for metal electrodes. We present experiments using LITJ to investigate a metal oxide thin film and film thickness. The PME of these thin films appears to change with thickness, correlating with surface strain where a thinner film shifts the PME closer to OER potentials in turn reducing the overpotentials required. Our experiments are shown to be reproducible and independent of sweep rate or the vertex potentials selected. Interestingly we observe a hysteresis with scan direction, of 100-250 mV which we nominally attribute to surface adsorbates. Our results highlight the link between excess surface charge and catalytic activity and how this may be tuned via surface strain. Figure 1

Adsorption of Sudan II dye onto fly ash/polyacrylic acid/melamine composite: Factorial design optimization, reusability performance and removal mechanism

This study aims to develop fly ash (FA) modified with melamine (M) and polyacrylic acid (PAA) for strong adsorption of Sudan II dye from aquatic media. Surface functionality and morphological characteristics of the prepared FA/PAA/M composite were characterized using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) techniques. A factorial design model was applied to estimate the influence of adsorption and interactions of adsorption parameters such as contact time, pH, adsorbent dose, and initial dye solution. The significant interactions among these factors were investigated by analysis of variance (ANOVA). The isotherm modeling data indicated the Langmuir adsorption capacity for raw FA and FA/PAA/M composite as 57.4 and 142.3 mg/ g, respectively. This means that the Sudan II dye adsorption capacity of FA was boosted more than one time after modification with PAA/M polymer due to increased affinity towards the dye molecules by amide and hydroxyl groups onto the surface of the composite adsorbent. The adsorption kinetic evaluation revealed that the Sudan II dye adsorption by the composite was well-defined by the pseudo-second-order model. The produced FA/PAA/M showed a reasonable regeneration performance of 72/66 % after the adsorption/desorption processes were repeated four times. The adsorption mechanism between dye molecules and surface functional groups of the composite was described by hydrogen bonding interactions, π- π interactions, metal-π interaction and electrostatic attractions. The results indicated that the composite could be a promising adsorbent for dye removal from industrial wastewater due to its strong adsorption capacity, easy preparation, and good reusability performance.

Carbonization of golden shower pods to high surface area biochar for decontamination of cationic dyes and regeneration study by gamma radiations

Detoxification of water resources is the need of the hour and a number of environment friendly materials are proposed by scientist to deal with water pollution issues. The present study deals with preparation and characterization of porous activated carbon from golden shower pods, a waste ligno-cellulosic biomass, for the removal of dye contaminants from aqueous solution. The synthesized material, golden shower biochar (GSBC) was characterized using various analytical techniques to confirm the presence of active sites. The BET analysis of GSBC revealed high surface area of 1120 m2/g with total pore volume of 1.099 cm3/g and average pore radius 19.618 Å. Operational parameters were optimized using batch studies by taking GSBC dose of 50 mg which showed complete removal of target dyes with an initial dye concentration of 200 mg/L with just 60 min interaction time; based on these results, a fixed bed column of GSBC was designed and column studies were performed. Adsorption isotherm studies were carried out using Langmuir and Freundlich models, of which Langmuir model was found to be best-fit with maximum adsorption capacities of 208.86 mg/g, 284.35 mg/g and 327.56 mg/g for Crystal violet, Brilliant green and Methylene blue dyes respectively. Analysis of kinetics and thermodynamics revealed that the best-fit model was pseudo second-order with spontaneous reaction course and exothermic nature. Regeneration was carried out using gamma irradiation of dye loaded GSBC, followed by leaching in alcohol. It was observed that a 30 KGy dose was just sufficient to completely degrade the dye on the adsorbent surface. GSBC has shown immense potential for eradication of dyes from water effluents and it is easily recovered with negligible loss in efficacy.

Unveiling Ion Dynamics in the Electric‐Double Layer Under Piezoionic Actuation of Chemo‐Mechanical Energy Harvesters

AbstractUnderstanding the ion dynamics within the electric double layer (EDL) is crucial for maximizing the potential of chemo‐mechanical energy harvesters. This study elucidates the electrochemical response of EDL to the compressive mechanical stimulation of carbon nanotube (CNT) yarns from the perspective of ion adsorption. The results revealed that H3O+ contributed to the ionic capacitance of the EDL by forming a polarized layer with Cl− on the outer Helmholtz plane. The unique molecular shape, compatible with spx hybridized orbitals of CNTs also enhance surface adsorption properties. In contrast, Cl− provides a strong electrostatic potential to the electrode, which has electronic structures incompatible with the spx hybridized orbitals of CNTs. The differing dynamic behaviors of these two ions jointly induce delamination of the cationic and anionic layers, as well as unipolarization of the EDL under mechanical compression of the microstructure. The ion dynamics revealed by multiscale simulations satisfactorily explain the experimentally observed high ion capacitance and energy conversion process of the HCl‐based EDL.

Optimizing Nitrate Reduction to Ammonia via Modulating Adsorption-Desorption Dynamics with High-Entropy CuNiCoZnMn Alloy Catalysts.

NO3RR synthesis of ammonia is a complex eight-electron reaction involving multiple steps and intermediates, in which NO3- adsorption and NH3 desorption are crucial. The Cu-based high entropy quinary alloy catalyst has good surface adsorption and desorption ability for the reduction of nitric acid to ammonia. Here, the catalytic sites were coordinated by constructing CuNiCoZnMn alloys to adjust the electronic structure of the catalytic sites to facilitate the reaction of the substrate and thus optimize the whole reaction path. Based on the ternary alloy CuNiCo, the introduction of the Zn element continues to reduce the desorption energy barrier, and the introduction of the Mn element continues to enhance the initial adsorption energy so that the target product can be quickly held and released to accelerate the production of ammonia. The NH3 yield and Faraday efficiency obtained for the quinary CuNiCoZnMn alloy catalyst reached 723.7 μmol h-1 cm-2 and 96.6%, respectively, at -0.35 V vs RHE potential. The density functional theory calculations showed that the quinary CuNiCoZnMn alloy (NO3- to *NO3-) initial adsorption-free energy change and (*NH3 to NH3) NH3 desorption-free energy change are -2.50, 0.072 eV, respectively, which are significantly better than those of the ternary CuNiC and quaternary CuNiCoZn of -2.02, 0.544 eV and -1.97, 0.217 eV.

Adsorption characteristics and mechanisms of bisphenol A on novel nitrogen-modified biochar derived from waste masks and biomass.

Resource utilization of waste masks has become an urgent scientific issue. In this work, with sustainably, waste masks and biomass were co-pyrolysis with oxygen limitation to prepare mask-based biochar (MB). Then, urea was introduced to prepare novel nitrogen modified mask-based biochar (NMB) via a one-step hydrothermal synthesis method. The adsorption characteristics of NMB on the emerging environmental pollutant, bisphenol A (BPA), were evaluated via batch adsorption tests. Moreover, the physicochemical properties of the materials were characterized with various advanced techniques. Also, the roles of waste masks and nitrogen modification were explored. The adsorption mechanisms of NMB on BPA were revealed as well as the performance differences between different adsorbents. The results showed that waste masks participated in thermochemical reactions, shaped the microsphere structure of biochar, and increased the types of surface functional groups. The nitrogen modification enriched the surface elemental composition and activated the specific surface area via the mesopore. These would enhance the adsorption performance. The maximum adsorption of BPA by NMB was 62.63mg·g-1, which was approximately 2.35-5.58 times higher than that of the control materials. Temkin model and pseudo-second-order model optimally simulate the isothermal and kinetic adsorption, respectively. The adsorption mechanisms are jointly by physical and chemical adsorption, which mainly includes π-π interaction, hydrogen bonding, intraparticle diffusion, surface adsorption, and ion exchange. After discussion and evaluation, NMB has lower preparation process cost (7.21 USD·kg-1) and safety, with potential for environmental applications. This study aims to expand new ideas for the comprehensive utilization of waste masks and the preparation of eco-friendly materials. Moreover, it provides a theoretical basis for the removal of BPA.

Prosopis juliflora biochar for adsorption of sulfamethoxazole and ciprofloxacin from pharmaceutical wastewater

This study aimed to synthesize the biochar of Prosopis juliflora (PJ) and apply it to the adsorption of antibiotic residues sulfamethoxazole (SMZ) and ciprofloxacin (CIX) from pharmaceutical industry wastewater. The PJ biochar was synthesized using the pyrolysis method and characterized by proximate analysis, TGA, SEM-EDX, FTIR, XRD, and BET methods. The moisture content, volatile matter, ash content, and fixed carbon were found to be 6.4 %, 72.3 %, 3.0 %, and 18.3 %, respectively. Moreover, biochar characteristics were described by a high BET surface area of 875 m2/g, various FTIR peaks with different functional groups, high TGA thermal stability at increasing temperature, amorphous XRD structure, and high SEM surface morphology, and major EDX carbon compositions of 97 %. These analysis results demonstrated insights into the potential and nature of biochar adsorbent. The maximum adsorption of SMZ and CIX was found to be 98.7 % and 97.8 %, respectively, at a contact time of 120 min, initial concentration of 50 mg/L, pH (5 for CIX and 8 for SMZ), and adsorbent dose of 1 g/L for a synthetic solution. On the other hand, COD and TOC of real wastewater were reduced from 2498 to 514 mg/L and 1050 to 124 mg/L during the real wastewater treatment. Target pollutants concentration in real wastewater was found to be 8.29 and 5.3 mg/L for CIX and SMZ and their removal efficiency was obtained as 80.4 % and 76.7 % respectively. The obtained experimental data were best fitted with the Langmuir isothermal model at R2 = 0.999, implying the adsorbent surface is homogeneous and monolayer. Similarly, the adsorption kinetics process was well described by a pseudo-second-order kinetics model for both SMZ and CIX at R² = 0.999. Finally, the non-linear intra-particle diffusion graphs suggest that chemical adsorption is the main influencing factor for overall kinetics. In conclusion, using PJ biochar is a promising precursor in advancing adsorbents for removing contaminants from industrial wastewater to address environmental pollution challenges.

Poly(allyl alcohol-co-vinyl acetate)-grafted concrete waste for adsorptive removal of As(III)

This study focused on the synthesis of concrete waste grafted with a polymer of allyl alcohol and vinyl acetate as a novel nano adsorbent and the investigation of its ability in the adsorptive removal of Arsenic (As(III)) from aqueous solutions. The prepared nano adsorbent was characterized using X-ray diffraction, thermogravimetric analysis, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. Various parameters were optimized by response surface methodology and central composite design model to achieve the highest As(III) removal efficiency, including the solution's temperature, contact time, and pH. The model predicted a maximum removal efficiency of 92 % under the optimal conditions (temperature = 25 °C, contact time = 24 min, and pH = 7), resulting in a sorption capacity of 6.81 mg g−1. The zero point of charge for the nano adsorbent was obtained at about 6.5. The experimental data for As(III) sorption onto the nano adsorbent was well-fitted by the Freundlich isotherm and pseudo-1st-order kinetic models. This suggests that the adsorption process involves the formation of a multilayer of As(III) on the adsorbent surface, and it occurs through physical interactions rather than chemical reactions. The reusability of the nano adsorbent was evaluated, demonstrating a removal efficiency exceeding 72 % even after seven recycling cycles. The presence of interfering cations influenced the removal efficiency in the following order: Pb2+>Mn2+>Cu2+>Zn2+>Ni2+. The prepared nano adsorbent showed significant efficiency in removing As(III) from well water and river water samples, with a repeatability range of 1.09–2.51 %.

Synthesis and characterization of porous silica and composite films for enhanced CO₂ adsorption: A circular economy approach

This study explores the synthesis and application of carbon-negative technology that leverage circular economy and environmentally friendly methodologies. Porous silica using plant-derived silica sources and self-assembled lignin templates were prepared, achieving an impresive surface area of up to 104.76 m2/g. Additionally, we prepared porous composite films via a freeze-drying process incorporating polyvinyl alcohol (PVA). These films demonstrated enhanced tensile properties, with a tensile strength reaching 285.72 kPa. Notably, the film surfaces engaged in a third-body tribology mechanism, which endowed them with excellent abrasion resistance and a low friction coefficient. The specific surface area of the films was measured at 20.15 m2/g, making them ideal substrates for CO₂ adsorption functionalization. The functionalized films showcased outstanding CO₂ adsorption capabilities, with a maximum uptake of 29.38 mg/g. Furthermore, they retained over 90% of their adsorption capacity after five adsorption/desorption cycles. Under high CO₂ conditions, these composite films combine the desirable attributes of both solid and liquid adsorbents—high surface area, low volatility, and adsorption stability—contributing significantly to greenhouse gas mitigation and the pursuit of carbon neutrality.

Mechanism of arsenic removal using brown seaweed derived impregnated with iron oxide biochar for batch and column studies

Water contaminated with arsenic presents serious health risks, necessitating effective and sustainable removal methods. This article proposes a method for removing arsenic from water by impregnating biochar with iron oxide (Fe2O3) from brown seaweed (Sargassumpolycystum). After the seaweed biomass was pyrolyzed at 400 °C, iron oxide was added to the biochar to increase its adsorptive sites and surface functional groups, which allowed the binding of arsenic ions. Batch studies were conducted to maximize the effects of variables, including pH, contact time, arsenic concentration, and adsorbent dosage, on arsenic adsorption. The maximum arsenic adsorption efficiency of 96.7% was achieved under optimal conditions: pH 6, the adsorbent dosage of 100 mg, the initial arsenic concentration of 0.25 mg/L, and a contact time of 90 min. Langmuir and Freundlich’s isotherms favored the adsorption process, while the kinetics adhered to a pseudo-second-order model, indicating chemisorption as the controlling step. Column studies revealed complete saturation after 200 min, and the adsorption behavior fits both the Adams–Bohart and Thomas models, demonstrating the potential for large-scale application. The primary mechanism underlying the interaction between iron-modified biochar and arsenic ions is surface complexation, enhanced by increased surface area and porosity. This study highlights the significant contribution of iron-modified biochar derived from macroalgae as an effective and sustainable solution for arsenic removal from water.

Study on the adsorption efficiency and mechanism of Sb(V) in aqueous solutions using enhanced surfactant-modified iron-calcium composite

The presence of Sb(V) in aqueous solutions poses a significant threat to the surrounding environment, and current treatment methods are inadequate. In this study, a magnetic surfactant (CTAB)-modified iron-calcium composite (CTAB-IC) was successfully synthesized using iron-calcium composite as the base material. This novel composite was used for the efficient removal of Sb(V) from textile wastewater solutions. Characterization analyses revealed that the CTAB-IC material exhibits a rich long-prismatic structure and superparamagnetic properties, classifying it as a soft magnetic material. Post-adsorption particle agglomerates were found to comprise Ca, S, and O. Sequential batch experiments demonstrated a maximum adsorption capacity of 54.05 mg/g, with adsorption kinetics data fitting the pseudo-second-order model. The intraparticle diffusion model indicated the presence of multiple diffusion steps during the adsorption process. Additionally, the adsorption of Sb(V) by CTAB-IC was identified as a heterogeneous surface adsorption process, best described by the Freundlich model. The primary adsorption mechanisms involved the formation of surface Ca-O-Sb complexes and inner-sphere Fe-O-Sb complexes, as well as amorphous surface precipitation and electrostatic adsorption. Notably, the treatment of textile wastewater often results in iron-calcium-rich sludge, which is challenging to manage and valorize. This study explored the potential for resource recycling by utilizing CTAB to harness the Fe elements in textile wastewater sludge, thereby promoting waste-to-resource conversion.

The roles of amorphous phase on Ca–Mg carbonate mineralization under the action of bacteria and EPS

Amorphous Ca–Mg carbonate (ACMC) is an important precursor phase of carbonate, and it is of great significance for understanding the process of microbial induced carbonate mineralization and the synthesis of new biomimetic mineral materials. Currently, the biomineralization role of ACMC remains controversial. Therefore, this study conducted experiments on ACMC-induced mineralization under the action of bacteria and their extracellular polymeric substances (EPS). The results show that bacteria and their secretion of EPS contributed to the formation and stability of hydrated Mg-rich ACMC, and affected the polymorphism and morphology of minerals. Bacterial cells and EPS could provide nucleation sites for ACMC precipitation, and they could also be easily adsorbed or encapsulated by ACMC and mineral particles. EPS, Mg2+, or both were conducive to the formation of aqueous amorphous phase, and could stabilize ACMC through surface adsorption and incorporation. The results of this study help to reveal the biomineralization role of ACMC and promote understanding of the formation and transformation process of Ca-Mg carbonate.

Synergistic effect of CaCO3 particles and porous carbon towards the removal of Zn2+ ions in aqueous solutions

This work describes the preparation of an adsorbent containing CaCO3 particles dispersed in activated carbon and its use for the removal of Zn2+ ions from aqueous solutions. The combination of the large porosity of the activated carbon support with the easy ion exchange occurring at the surface of the carbonate particles led to the achievement of fast adsorption kinetics and excellent ion removal capacity for the composite adsorbent. The material was synthesized by wet impregnation of the porous carbon support with an aqueous solution of Ca(NO3)2, followed by evaporation of the solvent with subsequent heat treatment in an inert atmosphere. X-ray diffraction results demonstrated the presence of CaCO3 crystals in the material, but with broad and low intensity diffraction peaks, corresponding to an average crystallite size of 20 nm; solid-state 13C NMR spectroscopy confirmed the presence of this phase by means of the identification of the signal relative to the 13C nuclei of the CO32− group at ∼170 ppm. The carbon-based adsorbent containing the CaCO3 particles showed excellent ability to remove Zn2+ ions from aqueous solutions, with essentially all ions removed after 30 min of contact time. In addition, the kinetic analysis data were properly fitted using the pseudo-second order model, pointing to the occurrence of chemisorption as the rate limiting of the process. The equilibrium adsorption isotherms were correctly described by the Langmuir model, indicating that the adsorption takes place with the formation of a monolayer on the adsorbent surface. The results evidenced a synergistic effect of the porous carbon and the CaCO3 particles regarding the Zn2+ ions removal, with a fast adsorption kinetics at the initial stage of adsorption attributed to the high availability of the dispersed CaCO3 particles on the carbon surface.

Improved Cupressus sempervirens L. galls for methylene blue removal: adsorption kinetics optimisation using the DA-LS algorithm, characterisation, and machine learning modeling

ABSTRACT In this study, an investigation was conducted on the effectiveness of three bioadsorbents – galbuli of Cupressus sempervirens L. almond shells, and Luffa – for removing methylene blue (MB) from water. Various activation techniques and operational conditions were employed to enhance the adsorption capacity. The study focused on adsorption kinetics and equilibrium capacity. The results showed that microwave-dried galbuli of Cupressus sempervirens L. exhibited the highest adsorption capacity of 38.05 mg/g with an adsorption efficiency of 17.4%. To improve this capacity, the Dragonfly Algorithm-integrated least squares (DA-LS) was proposed to optimise the fitting of 32 adsorption isotherm models, which included a proposed modified Langmuir model. After optimisation, the sixth chemical treatment of Cupressus sempervirens L. reached a Langmuir isotherm qmax value of 84.44 mg/g, suggesting the high efficiency of the bioadsorbent compared to previous studies. Characterisation using microscopy and ATR-FTIR techniques revealed that chemical modifications led to rougher, microporous cellulose fibres and significant changes in the chemical structure, potentially enhancing the surface area and adsorption efficiency. To predict the adsorption capacity, the Support Vector Machine for Regression with DA (SVMR-DA) was utilised, achieving a root mean square error (RMSE) of 1.357 and an R2 of 0.9913. This high accuracy indicates a reliable model with a robust error distribution. These results suggest that Cupressus sempervirens L. can be an effective bioadsorbent for water treatment, with significant potential for industrial application.

Green and eco-friendly scalable synthesis of chitosan-carbon nanocomposite for efficient dye removal

The integration of activated carbon with chitosan (CS) for dye removal offers a multitude of benefits, making this hybrid material a promising and efficient solution for water purification. Activated carbon (C) was synthesized from fruit wastes and then mixed with CS for the preparation of chitosan‑carbon nanocomposite (CSCNC) using ball milling technique. XRD and ATR-FTIR techniques affirmed the preparation of CSCNC. Additionally, the findings obtained from TEM and SEM analyses signifying the deposition of activated carbon onto the surface of CS. The majority of particle size and polydispersity index (PdI) for CSCNC were found to be 162.8 nm and 0.483, respectively as displayed from DLS technique. The current research work was examined the adsorption and desorption behaviors of Methylene Blue (MB) using CSCNC. Adsorption experiments reveal a time-dependent process characterized by an initial rapid phase and gradual approach to equilibrium, with the pseudo-second-order kinetics model providing the best fit. The adsorption capacity exhibited a rising pattern as pH increased, reaching its peak value of 912.4 mg/g. Both Langmuir and Freundlich isotherm models explained the equilibrium relationship between MB and the nanocomposite, offering insights into maximum adsorption capacity and surface characteristics. Desorption studies explored the nanocomposite's regenerative potential under varying conditions. The findings contributed to the sustainable design of water treatment technologies, emphasizing the nanocomposite's efficiency, scalability, and regenerative capabilities.

Adsorption of amitriptyline from aqueous solutions using magnetic graphene-based material: Isotherm, kinetics, and thermodynamic study

Amitriptyline (AMT) is an antidepressant often found in water environments. Due to its toxicity, in this work, AMT adsorption was proposed using graphene oxide (GO) and magnetic GO (GO·Fe3O4 1:1). The adsorbent characterizations were accomplished by FTIR, SEM, EDS, Raman spectroscopy, XRD, and VSM revealed the typical characteristics of the pristine GO and GO·Fe3O4 1:1. In the batch adsorption study, GO·Fe3O4 1:1 showed the highest adsorption capacity (91.84 mg g−1) and removal percentage (92 %) (at pH = 9.0, C0 = 50.0 mg L−1, adsorbent dosage = 0.5 g L−1, the temperature at 293 ± 1.00 K). Moreover, the Sips model showed the best adjustment for isothermal experimental data. This model suggests that the adsorption occurs at heterogeneous surfaces when the qs value increases with the increase in temperature (from 235.57 mg g−1 at 20 ºC to 463.34 mg g−1 at 50 ºC). The thermodynamic study confirms that AMT adsorption onto GO·Fe3O4 1:1 is a spontaneous and endothermic process (ΔH = 32.75 kJ mol−1). Elovich kinetic model presented the best adjustment for experimental data and showed that the adsorption rate (α) and surface coverage constant (β), decrease with the increase of the adsorbate dosage. Additionally, the ionic strength study reveals that a high concentration of NaCl (1.0 M) decreases the qe to 25.74 mg g−1. Lastly, after five consecutive adsorption/desorption cycles, the removal percentage of GO·Fe3O4 1:1 remained elevated (79 %). Overall, this paper reports the efficiency of GO·Fe3O4 1:1 on AMT removal, in addition to investigating the several variables involved in this adsorption.