Decrease In Adsorption Capacity Research Articles

Uncovering the role of free lanthanum (La3+) ions and La oligomer on the surface of La (oxy)hydroxide particles for phosphate removal

La (oxy)hydroxide-based materials have been recognized as promising adsorbents for aqueous phosphate (P) removal. However, comprehending the adsorption behavior of P onto La (oxy)hydroxide particles remains challenging, given the heterogeneous low-crystalline surface encompassing La oligomers and free La3+ ions. In this study, a hydrogen (H) bond capping method was developed to construct La (oxy)hydroxide oligomers (LHOs) to simulate the low-crystalline La on the surface of La (oxy)hydroxide particles. The P uptake capacity was compared among free La3+ ions, LHOs, and La nanoparticle (La-NP) with maximum capacities of 1967.3 ± 30.8 mg/g, 461.1 ± 53.7 mg/g and 62.5 ± 6.0 mg/g, respectively. The FT-IR, Raman, in situ-XRD and XPS deconvolution analyses revealed that the removal of P by free La3+ ions mainly involve the process of chemical precipitation to form LaPO4·0.5H2O. Conversely, the elimination of P by LHOs is primarily attributed to inner-sphere complexation and hydroxyl exchange effect between LaOOH and P. Based on this study, the free La3+ ions and La oligomers on the surface of La (oxy)hydroxide particles play a primary role in P adsorption. These results also suggest that the successively decreased adsorption capacity of La (oxy)hydroxide-based adsorbents in the continuously adsorption/desorption cycles might be due to the irreversible inactivation and recrystallization of free La3+ ions and La oligomers on the surface.

Adsorption performance of 1,4-dioxane by MCM-22 and Beta zeolites and their bio-zeolite composite system in the presence of co-contaminants

Addressing the significant challenge of efficiently separating 1,4-dioxane from aquatic environments using traditional adsorbents is crucial. In this study, we evaluated the adsorption performance of MCM-22 and Beta zeolites. Both were identified as highly effective adsorbents. Equilibrium adsorption of 1,4-dioxane was achieved within 20 min for an initial concentration of 500 mg L-1 on both MCM-22 and Beta zeolites. At 288 K, the maximum adsorption capacities fitted by Langmuir isotherm were 79.66 mg g−1 for MCM-22 and 121.66 mg g−1 for Beta zeolite. Fixed-bed column studies demonstrated that the Yan model properly predicted the behavior of both zeolites under varying flow rates. Additionally, MCM-22 exhibited a wider pore size distribution compared to Beta zeolite, while Beta zeolite demonstrated a higher volume of ultra-micropores (<1 nm) than MCM-22. This highlights the importance of pore volume filling in facilitating excellent adsorption of 1,4-dioxane by both zeolites. Further analysis via FTIR and 1H NMR confirmed the significance of Brønsted acid sites in 1,4-dioxane adsorption. The adsorption performance of both zeolites remained unaffected by initial pH values ranging from 2 to 11, as well as variations in ionic strength or the presence of natural organic matter (NOM) for both zeolites. However, the co-existence of 1,1-dichloroethene (1,1-DCE) resulted in competitive adsorption with 1,4-dioxane, leading to a notable decrease in adsorption capacity of 1,4-dioxane. In contrast, the presence of metal ions Cu2+ and Ag+ did not compete for adsorption sites with 1,4-dioxane. Our study demonstrated the effectiveness of the bio-zeolite system in regenerating spent adsorbents, surpassing water and solvent regeneration methods in efficiency and recyclability. Although addressing the persistence of 1,1-DCE remains a challenge, bio-zeolites emerge as versatile tools for mitigating the bio-inhibition of heavy metals, such as Cu2+ and Ag+, while offering a sustainable solution for 1,4-dioxane bioremediation.

Lanthanum-loaded geopolymer for phosphate removal from agricultural runoff

The removal of phosphate from agricultural runoff is of great importance to mitigate an overabundance of nutrients discharging into receiving water bodies, which are susceptible to eutrophication. In this study, a La-loaded geopolymer was produced by adding metakaolin within an alkaline medium, consisting of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The ratio of Na2SiO3:NaOH within the geopolymer slurry was manipulated to evaluate its effect on phosphate adsorption capacity. The 1.54 ratio yielded the highest adsorption capacity of 33.65 mg g−1. However, due to structural strength, safety, and economic considerations, the 2.0 ratio was used for the isotherm and kinetic adsorption testing. The La-loaded geopolymer exhibited higher phosphate removal in batch adsorption experiments at an acidic level (pH 4) and elevated temperature (40 °C). Moreover, ionic strength (3.5–20 mM) had a negligible impact on phosphate removal, indicating inner-sphere complexation as the main mechanism of adsorption. Additionally, bicarbonate and humic acid increased phosphate removal, whereas sulfate slightly decreased adsorption capacity. The La-loaded geopolymer was further evaluated using a synthetic agricultural solution, which yielded a Type III adsorption isotherm, demonstrating unrestricted multilayer phosphate adsorption. Results from this study verified the La-loaded geopolymer is a promising adsorbent for phosphate removal from agricultural runoff and underlined the importance of matrix effects on treatment performance.

Calcium-Based Metal-Organic Framework: Detection and Idiosyncratic Removal of Copper by Nano-Particle Deposition.

A novel calcium-based metal-organic framework (CaMOF@LSB) was designed and synthesized, exhibiting dual functionality for both selective detection and removal of Cu2+ ions from aqueous solutions. The framework's stability, including solvent and pH variations, was established with notable thermal resilience. Colorimetric Cu2+ detection (≥5 ppm) with a high capture capacity of 484.2 mg g-1 by CaMOF@LSB places this material among the few that ensure efficient colorimetric detection and high removal capabilities of Cu2+ ions. Batch adsorption experiments revealed pH-dependent behavior and competitive interactions. Langmuir and pseudo-second-order kinetics models aptly described adsorption isotherms and kinetics, respectively. Thermodynamic assessments confirmed spontaneous and endothermic adsorption. Mechanistically, nanoparticle deposition contributes to the Cu2+ uptake. CaMOF@LSB also exhibited one of the best removal behaviour of Cu2+ by means of oxide formation on the surface. Regeneration of CaMOF@LSB was achieved by simple sonication in 0.1 M aqueous NaOH solution. The recyclability was also tested up to 5 cycles, and it exhibited a small decrease in adsorption capacity observed across the cycles. This research presents a promising avenue for addressing heavy metal pollution using metal-organic frameworks, thereby offering potential applications in water purification and environmental pollution monitoring and remediation.

Optimizing fertilizer usage for source reduction of salt and fluoride ion runoff discharge from a soda saline-alkali paddy field

Planting rice is a beneficial strategy for improving soda saline-alkali soil, but it comes with the challenge of increased runoff discharge of salt and fluoride (F−) ions. The use of different nitrogen (N) fertilizers can impact this ion discharge, yet the specific characteristics of ion runoff under different N-fertilizer applications remain unclear. A field experiment was conducted in this study, applying five commonly used N-fertilizer types to monitor the ion runoff throughout an entire rice growing season. Salt ions and F− runoff discharge was significantly affected by N-fertilizer type, runoff event, and their interaction (p < 0.001). Regardless of N-fertilizer types, sodium (Na+) and bicarbonate (HCO3−) ions were consistently discharged from runoff in soda saline-alkali fields, constituting 20.55–25.06 % and 47.57–50.49 % of total ion discharges, respectively. Compared to no N-fertilizer (CK) and other N-fertilizer treatments, the organic-inorganic compound fertilizer (OCF) application significantly reduced Na+ and HCO3− runoff discharge, causing a decrease in the competitive adsorption capacity between HCO3− and F− (p < 0.05). The use of OCF and inorganic compound fertilizer (ICF) lowered pH in runoff water, resulting in reduced dissolution capacity of calcium fluoride in the soil and thereby decreasing total F− runoff discharge. In conclusion, OCF proves to be an effective N-fertilizer in mitigating salt ions and F− runoff discharge in soda saline-alkali paddy fields. Additionally, ICF demonstrates the ability to control F− runoff discharge.

Efficient adsorptive removal of 2,4-dichlorophenoxyacetic acid (2,4-D) using biomass derived magnetic activated carbon nanocomposite in synthetic and simulated agricultural runoff water

This study focused on evaluating the efficacy of a magnetic activated carbon material (CPAC@Fe3O4) derived from pods of copper pod tree in adsorbing the toxic herbicide, 2,4- (2,4-D) from aqueous solutions. The synthesized CPAC@Fe3O4 adsorbent, underwent various characterization techniques. FESEM images indicated a rough surface, incorporating iron oxide nanoparticles, while EDS analysis confirmed the presence of elements like Fe, O, and C. Notably, the CPAC@Fe3O4 exhibited high surface area (749.10 m2/g) and pore volume (0.5351 cm³/g), confirming its mesoporous nature. XRD investigations identified distinct signals associated with graphitic carbon and magnetite nanoparticles, while VSM analysis verified its magnetic properties with a high magnetic saturation value (2.72 emu/g). The adsorption process was exothermic, with a decrease in adsorption capacity at higher temperatures. Freundlich isotherm provided the best fit for the adsorption, and the pseudo-second-order equation effectively described the kinetics. Remarkably, the maximum adsorption capacity ranged from 246.43 to 261.03 mg/g, surpassing previously reported values. The ΔH° value (−8.67 kJ/mol) suggested a physisorption mechanism, and the negative ΔG° values established the spontaneous nature. Furthermore, the synthesized adsorbent demonstrated exceptional reusability, allowing for up to five cycles of adsorption-desorption operations. When applied to simulated agricultural runoff, CPAC@Fe3O4 showcased a significant adsorption capacity of 160.71 mg/g for 50 mg/L 2,4-D, using a 0.2 g/L dosage at pH 2. This study showcased the transformation of copper pod biomass into a valuable magnetic nanoadsorbent capable of efficiently eliminating the noxious 2,4-D pollutant from aqueous environments.

Synthesis of novel bentonite/pectin-grafted-poly(crotonic acid-co-acrylic acid) hydrogel nanocomposite for adsorptive removal of safranin O dye from aqueous solution

ABSTRACT This novel work is devoted to the synthesis of the bentonite/pectin-grafted-poly(crotonic acid-co-acrylic acid (AA-co-CA) hydrogel nanocomposite by free-radical copolymerisation method for exploring its potential towards safranin O dye removal. The prepared nanocomposite was characterised by different techniques revealing the presence of numerous functionalities, porous nature and greater swelling % at basic pH. The pHpzc of the nanocomposite was determined to be 4. Maximum of 97.09% of safranin O dye removal take place under optimised conditions, that is, 0.03 g of bentonite dose (bentonite to net hydrogel weight ratio (1.295%), with pH of 7, nanocomposite dose of 5 g/l for 120 min. The dye concentration was 500 mg/l at the temperature of 25°C. Effect of ionic strength confirmed the greatest decrease in adsorption capacity in the presence of divalent cations. The highest R2 and the lowest error margins of the Freundlich isotherm and pseudo-second-order kinetic models make these models well fitted to the experimental data. Further, the spontaneous and exothermic nature of the process was confirmed by the negative values of ΔG and ΔH, respectively. The enhanced adsorption of safranin O dye by the prepared nanocomposite was informed by several mechanisms, including electrostatic, pore filling and H-bonding. A comparison of the adsorption capacity of the prepared nanocomposite with various other adsorbents was also studied. Stability of the prepared adsorbent was revealed from its recovery upto five cycles in different desorption media. Finally, the treatment of the adsorbent with real textile wastewater showed its removal efficiency as 95.8% highlighting its promising nature for treating large industrial wastewater.

Powdered Cogon Grass (Imperata cylindrica) as a Biosorbent for the Removal of Iron (II)

Powdered Cogon Grass (Imperata cylindrica) as a Biosorbent for the Removal of Iron (II)

Investigation on sacrificial hydrolysis reaction of octadecyltrimethoxysilane for moisture resistance enhancement of metal–organic framework

Imparting water resistance is important for structures which is vulnerable to moisture to maintain the performance. In this study, octadecyltrimethoxysilane (ODTMS), which forms a hydrophobic surface through polymerization on the surface of the material, was used to enhance the hydrophobicity of HKUST-1 (HHK-x). This self-assembled structure reacts as sacrificial barrier to continuously penetrating H2O molecules and this effect is evaluated with detection of O–H peak (3323 cm−1) in FT-IR spectra. The gas adsorption performance is conducted with CO2 gas and the adsorption amount was reduced by 20 % (from 5.77 to 4.62 mmol/g at 25 °C, 1 bar) compared with the pristine HKUST-1 following the trend of specific surface area. However, water adsorption amount was reduced by 50.2 %, which is 2.5 times higher than the decrease in CO2 adsorption capacity. In addition, when the N2 adsorption and cycle adsorption performances were compared after exposing the sample to air for five days, it was confirmed that HHK-40 maintained its microporous structure and stable performance. The manufactured materials exhibited higher durability in a cyclic vapor sorption test depending on the loading amount of ODTMS and exhibits different tendency depending on the rate of humidity. These results experimentally indicate that accessible self-assembly process of ODTMS on water-vulnerable materials to be sustainable and stable in humid air conditions.

ZIF-67 loaded thio-groups modified chitosan hydrogel for high efficient Hg(II) removal from water

In the past few years, there has been an increasing worry about the pollution of water caused by the presence of heavy metals. To address this environmental issue, a highly effective adsorbent called ZIF-67/CS-SH was developed. This adsorbent was prepared by grafting thioglycolic acid and loading a metal-organic framework called ZIF-67 onto chitosan, to remove Hg(II) from water. Confirmation of the ZIF-67/CS-SH was achieved by employing a range of techniques including FTIR, XRD, TGA, SEM, EDS, BET, and XPS. Due to the presence of abundant active sites (-SH, O/N-containing functional groups) and ZIF-67, ZIF-67/CS-SH exhibited a high adsorption capacity (949 mg/g at 298 K) and rapid adsorption kinetics (20 min for 91 % removal). The optimal pH for the adsorption process was found to be 5. The adsorption process followed a pseudo-second-order kinetics and Langmuir isotherm, with chemisorption being the main adsorption mechanism. The adsorption process was determined to be spontaneous and endothermic. Additionally, ZIF-67/CS-SH demonstrated selective adsorption in the presence of other metal cations at concentrations of 100 mg/L. Furthermore, ZIF-67/CS-SH exhibited excellent regenerative properties, with only a 10 % decrease in adsorption capacity after ten cycles. The key adsorption sites were identified as the –SH groups, O/N-containing functional groups, and ZIF-67 in ZIF-67/CS-SH through FTIR, EDS, and XPS analyses. Considering its outstanding performance in removing Hg(II), ZIF-67/CS-SH shows promise for application in industrial wastewater treatment.

Ultrastable superhydrophobic melamine sponge via a one-step aqueous solution-based approach for oil/water separation

In this study, an eco-friendly aqueous solution-dipping method was developed for the synthesis of an ultrastable superhydrophobic melamine sponge (MS). The MS exhibits not only a high oil adsorption capacity of 46.3–149.5 times of its own weight, but also a good reusability with a slight decrease in adsorption capacity after 20 absorption-desorption cycles. Moreover, the continuous separation of immiscible oils/organic solvents and water with vacuum assistance is also realized. Besides, the material also features with exceptional physicochemical stability and fire-retardant performance, enabling its potential applications in extreme environments (high temperature, strong wind and waves, strong acids and alkalis, UV radiation, etc.). The as-established synthesis pathway has its chance in simplifying the industrial fabrication processes of composited functional sponges.

Polymeric monolithic columns based on natural wood for rapid purification of targeted protein

With multiscale hierarchical structure, wood is suitable for a range of high-value applications, especially as a chromatographic matrix. Here, we have aimed to provide a weak anion-exchange polymeric monolithic column based on natural wood with high permeability and stability for effectively separating the targeted protein. The wood-polymeric monolithic column was synthesized by in situ polymerization of glycidyl methacrylate and ethylene glycol dimethacrylate in wood, and coupled with diethylaminoethyl hydrochloride. The wood-polymeric monolithic column can be integrated with fast-protein liquid chromatography for large-scale protein purification. According to the results, the wood-polymeric monolithic column showed high hydrophilicity, permeability and stability. Separation experiments verified that the wood-polymeric monolithic column could purify the targeted protein (spike protein of SARS-COV-2 and ovalbumin) from the mixed proteins by ion exchange, and the static adsorption capacity was 33.04 mg mL−1 and the dynamic adsorption capacity was 24.51 mg mL−1. In addition, the wood-polymerized monolithic column had good stability, and a negligible decrease in the dynamic adsorption capacity after 20 cycles. This wood-polymerized monolithic column can provide a novel, efficient, and green matrix for monolithic chromatographic columns.

Adsorption behavior and application properties of natural alcohol polyoxyethylene polyoxypropylene ether sulfate

In recent years, the Polyoxypropylene (PO) group has been introduced between the hydrophobic group and the polyoxyethylene (EO) group of traditional surfactants to enhance interfacial properties. However, literature on surfactants introducing PO chains between EO and hydrophilic groups remains scarce. In this study, three variants of natural alcohol polyoxyethylene polyoxypropylene ether sulfate (C1214E3PnS), each with different PO addition numbers, were synthesized from natural alcohol ether through sulfation and neutralization reactions. The adsorption behavior of C1214E3PnS with different PO addition numbers was investigated and compared to AES by measuring surface tension, dynamic surface tension, and contact angle. The results indicate that as the number of PO increases, both the critical micelle concentration and maximum adsorption capacity decrease. Additionally, pC20 and the number of PO groups introduced in the surfactant show a linear negative correlation, indicating a decline in surfactant efficiency. Due to an adsorption barrier, C1214E3PnS is governed by a mixed diffusion-kinetics adsorption mechanism. According to the application performance of C1214E3PnS, as the number of PO increases, wettability and foam stability have decline, while emulsifying performance is significantly enhanced. In conclusion, surfactants such as C1214E3PnS do not favor adsorption at the solid–liquid interface, but enhance the properties at the oil–water interface.

Enhanced Copper Ion Adsorption by Rice Husk and Sugarcane Bagasse-based Magnetic Nanoparticles Biocomposites

Rice husk and sugarcane bagasse are biomass waste by-products of agriculture activities. High cellulose content makes them a potential material to develop. Biomass utilization is more interesting to develop due to its high cellulose content and nature abundance. Cellulose from rice husk and sugarcane bagasse is utilized as fiber in producing magnetic biocomposites. The Biocomposites can adsorb Cu(II) ions in aqueous solutions. A one-step solvothermal reaction was used to synthesize biocomposites. The amine functionalization on biocomposites was also studied for adsorption performance. The magnetic particle was generated on the surface of fiber and verified by XRD as Fe3O4. Amine group on biocomposites is also found on 570 cm-1 and 1636 cm−1 peaks for Fe-O bonds and N-H bending, respectively. Batch isothermal adsorption employing magnetic biocomposites has optimal conditions for Cu(II) ions adsorption at pH 5 for 60 minutes, with an adsorption capacity of 118.26 mg/g. The reusability of biocomposites for the next run showed a good performance at 3rd repetitions with only a decrease in adsorption capacity of 8.81%. The rice husk and sugarcane bagasse-based magnetic nanoparticles biocomposites can adsorb Cu(II) ions and potential material to develop for wastewater treatment.

Preparation and ammonium adsorption behavior of interpenetrating polymer networks hydrogel of chitosan‐g‐poly(acrylic acid)/bentonite and chitosan‐glutaraldehyde

AbstractIn this article, new interpenetrating polymer network (IPN) hydrogel as an efficient adsorbent for ammonium was prepared by a two‐step process. First, semi‐IPN hydrogel of chitosan‐g‐poly(acrylic acid)/bentonite (CAB) and chitosan (CTS) was synthesized by grafting polymerization in the presence of exfoliated bentonite as both cross‐linking agent and nanoscale inorganic filler. Second, cross‐linking polymer network of chitosan‐glutaraldehyde (CGA) was formed by reaction of CTS with glutaraldehyde (GA). The obtained IPN hydrogel (CAB/CGA) was characterized by Fourier‐transform infrared spectroscopy, scanning electron microscopy and its swelling degree and PZC value were also measured. These results demonstrate that copolymerized graft reaction was occurred between CTS, AA and bentonite forming CAB, and CGA presented as a cross‐linker in CAB/CGA polymer network. CAB/CGA has a moderate swelling degree of 7.8. CAB/CGA exhibits high adsorption capacity and fast adsorption rate for ammonium. Adsorption process reaches equilibrium in 30 min and fits well to Langmuir adsorption model with a fairly high maximum adsorption capacity of 41.06 mg g−1. The material has a good regeneration ability. After five times of adsorption–desorption, there was almost no decrease in ammonium adsorption capacity. Moreover, the low swelling degree leads to an improvement in material strength and a reduction of equipment cost.

Characterization and applicability of the Naima–Tiaret–Algeria illite-montmorillonite clay for methylene blue dye removal: adsorption kinetic, isotherm and thermodynamic studies

ABSTRACT An illite-montmorillonite clay from Naima, IMN (Algeria) was treated via physical and chemical treatment (TIMN) and investigated for the removal of methylene blue. IMN and TIMN clays were characterized by XRD, XRF, SEM-EDS, DSC-TG, FTIR and DC electrical conductivity methods. To analyze the sorption behavior of MB on the clays, a mechanistic model for interpreting the sorption data was developed. IMN clay revealed high sorption capacity (1.925 × 10−2 kg kg−1) for MB in 60 min. The pseudo-second-order model had a very good agreement to describe the MB adsorption process. The adsorption capacities, qe,exp, of 4.327 × 10−2 and 4.914 × 10−2 kg kg−1 for IMN and TIMN, respectively, were obtained. The free energy from the D–R model from adsorbing MB using IMN and TIMN ranged from 1.581 to 0.745 × 10−3J mol−1, respectively, suggesting that the process is physisorption. Besides, the sorption process was more sensible to temperatures that increase was beyond 40 °C causing a decrease in adsorption capacity, indicating that the adsorption reaction of MB onto IMN was exothermic. The adsorption mechanism of I/M clay to remove MB was likely based on hydrogen bonding, electrostatic attraction, cation exchange and n–π interaction. These results proved that TIMN was a promising adsorbent for removing MB from simulated wastewater.

Synthesis of Na-Alginate templated Montmorillonite-Silica Composite as adsorbent for removal of Rhodamine B

AbstractIn this study, mesoporous Montmorillonite-Silica composites prepared by using different amount Alginate as sacrificial template, for removal of Rhodamine B is investigated. By alternating Alginate amount it is aimed to switch the porosity of adsorbents thus the adsorption capacities of adsorbents. Synthesized adsorbents had been characterized by using Scanning Electron Microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and N2-Ads/Des techniques. It is observed that beside the decrease in the micropore volume, the total pore volume of the adsorbents increased with the increasing of used Alginate amount. The total pore volumes of adsorbents synthesized with different Clay/Alginate ratio (10, 5, 1) were found as 0.116, 0.172, and 0.178 cm3/g, respectively. Batch adsorption studies showed that the maximum removal efficiencies were obtained at acidic conditions and the adsorbents had better fit with Freundlich isotherm. Qm values obtained from Langmuir isotherm were found as 24.47, 31.97 and 28.48 mg/g for synthesized adsorbents. Also, adsorption kinetic studies showed that for all adsorbents, experimental data had good fit to the pseudo-second order kinetics model. The model parameters were found as 5.9,6.3 and 6.5 (10–3 g/ (mg min). Thermodynamic parameters were also investigated in the study. Negative ∆Go values pointed out that the adsorption of RhB onto synthesized adsorbents was favorable process. Positive values of ∆Ho and ΔS indicated that the adsorption of RhB on adsorbents were endothermic and rising of randomness during the adsorption of RhB on the surface of the adsorbent. Adsorbents could be recovered at least five times without significant decrease in adsorption capacity.

Adsorption of CO2 and H2 on the polymer-based membrane from High-density Polyethylene (HDPE) Plastic

High-density polyethylene (HDPE), a widely used polymer globally, notably found in plastic bags, presents an environmental concern due to its non-biodegradable nature. Transforming non-biodegradable HDPE waste into a valuable resource presents a formidable ecological challenge. This research aims to study CO2 and H2 gases toward HDPE-based membranes through the adsorption process with pressure and temperature variation. The highest CO2 and H2 adsorption capacities of 14.19 mmol.g−1 (62.43 %wt) and 18.04 mmol.g−1 (3.61 %wt) were obtained by pressure feeding 3 bar at 30°C. The adsorption capacity decrease as the temperature increase. At an adsorption temperature of 50°C, the adsorption capacity of CO2 and H2 decrease, respectively by 75.86 % and 69.81 %. The adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, and intraparticle diffusion models. The kinetic study shows that adsorption at 30°C follows the pseudo-second order. The adsorption at elevated temperatures reveals the intraparticle diffusion mechanism, indicating that the gas is adsorbed directly into the polymer matrix. Thermodynamic results include enthalpy of adsorption (ΔH), standard entropy of adsorption (ΔS), energy Gibbs (ΔG), and energy activation (Ea). ΔH CO2 and H2 are -22.339 and -23.654 kJ mol−1, respectively, which indicates that the process is exothermic and physisorption. The ΔS value shows that the irregularity and randomness of gas movement during the adsorption process, with the respective values for CO2 and H2 are -0.069 and -0.072 kJ mol−1K−1, respectively. ΔG for adsorption of CO2 and H2 with increasing temperature becomes less spontaneous, which results in decreased adsorption capacity. Ea of CO2 is greater than H2, so the adsorption capacity of CO2 is smaller than H2. The thermodynamic study shows that the adsorption process is preferable at lower temperatures.

Optimization of Cadmium Removal Using Tetraethylene Glycol-Modified Silica-Based Adsorbent via Response Surface Methodology

In solid-phase extraction for preconcentration, silica (Si) is the most commonly used as an adsorbent. However, the selectivity and effectiveness of silica gel adsorption on metal ions are low, so it needs to be modified to improve the adsorption capability. The modification was done using reflux and oven heating in the modification silica with 3-glycidoxypropyl trimethoxysilane (GPTMS) and tetraethylene glycol (TEG). A central composite design batch process determined the optimum conditions for cadmium adsorption. TEG-modified silica was successfully synthesized and characterized using FTIR spectroscopy, SEM, and elemental analyzers. Peaks of C-H and epoxy on FTIR spectra showed that Si- GPTMS was formed. The increase of %C and %H from the first to the second step indicated that Si-TEG was successfully synthesized. There was no significant difference in silica particle morphology on SEM before and after modification. The reflux method gave a higher yield compared to the heating method. The constant stirring by the magnetic bar and solvent cycle in the reflux method catalyzed the reaction. This study found that at pH 7, 30 mg of adsorbent weight at 35°C and 22 minutes of contact time were optimum Cd2+ adsorption conditions. As the weight of the adsorbent increases, the adsorption capacity decreases. Contact time and temperature have no significant effect on Cd adsorption by Si-TEG.

Calculation of hydrogen adsorption isotherms and Henry coefficients with mixed CO2 and CH4 gases on hydroxylated quartz surface: Implications to hydrogen geo-storage

Hydrogen is a clean fuel that is becoming increasingly popular in addressing future energy challenges, however, its viable storage requires an understanding of its interaction with underground rock minerals. For this purpose, this study focuses on developing adsorption isotherms and Henry coefficients for hydrogen in hydroxylated quartz surfaces, which are predominant in sandstone and shale rocks. In this study, a molecular-scale hydroxylated quartz structure with a pore space is generated and the Monte Carlo (MC) simulation is utilized to assess the adsorption isotherms and Henry coefficients. Initially, the CO2 adsorption with the hydroxylated quartz is matched with the published data to determine the accuracy of MC simulation and the mineral-fluid interaction. After that, the concentration of H2 within the pore is progressively increased and the competitive adsorption is calculated under various subsurface temperature and pressure conditions. Additionally, CH4 is introduced to understand the competitive adsorption dynamics between H2 and CH4. The findings indicate that increasing pressure results in increasing molecules of hydrogen that monotonically increase H2 adsorption. On the contrary, increasing temperature reduces the affinity of hydrogen with the quartz surface causing a decrease in adsorption capacity and Henry coefficients. Furthermore, a weak single hydrogen adsorption layer is developed at all pressure and temperature conditions, while most of the hydrogen remains as a free gas in the pore. In addition, the hydroxyl group controls most of the adsorption of hydrogen in the hydroxylated quartz. Furthermore, the addition of water film (approximately 1 wt%) reduces the hydrogen adsorption by around 3 %. The H2 adsorption values further experience a notable decrease with the introduction of CO2 and CH4, primarily due to the establishment of a strong adsorption layer caused by the high electrostatic attraction between these gases and the quartz mineral. The study offers crucial microscopic details regarding H2 adsorption alongside CO2 and CH4 gases within hydroxylated quartz pores. These insights support efficient hydrogen geo-storage and larger-scale simulation research.