Search Results (170)

Pollution of soil and groundwater by chemical fertilizers is an alarming environmental problem. Both bamboo powder and charcoal are known to adsorb nitrates. This study aimed to recommend an effective method by applying a mixture of chemical fertilizers and bamboo charcoal to soil to prevent NO₃ leaching through adsorption. Magnesium treatment and hydrogelation were investigated to increase the amount of NO₃ adsorption and improve handling properties, and subsequently, their behavior in soil was examined. The maximum adsorption of nitrate in bamboo charcoal powder (BC) with a particle size of 15 µm or less was 4.44 mg/g. When the BC was treated with magnesium chloride (Mg-BC), the maximum adsorption capacity was 99.09 mg/g. The Langmuir adsorption model fits well for both BC and Mg-BC. When Mg-BC was hydrogelized (Gel-Mg-BC), the Freundlich equation provided a better fit, with the maximum adsorption estimated at 25–30 mg/g. When the soil was mixed with Mg-BC hydrogel and treated with a nitric acid solution, the nitrate concentration in the leachate decreased by approximately 15–60% (depending on the feed concentration) compared to that in the leachate from the soil alone. Full article

This study intended to examine and assess the performance of raw and treated Eriobotrya Japonica seed waste for the adsorption-based removal of methylene blue dye from an aqueous solution. The effects of several factors, including pH, adsorbent dose, and initial concentration, on the elimination of this dye were examined. To optimize the removal process, a Box-Behnken design (BBD) based on response surface methodology (RSM) was employed to evaluate the influence of key variables, adsorbent dose, initial dye concentration, and pH, along with their interactions. The findings demonstrated that the statistical analysis reveals a high significance of the dye for raw and treated Eriobotrya Japonica seed waste, with extremely weak probability values (p < 0.0001). The optimal conditions achieved were the adsorbent dose = 21.21 mg, initial dye concentration = 7.54 mg/L, and pH = 10.92 for the raw waste and adsorbent dosage = 21.75 mg, initial dye concentration = 7.5 mg/L, and pH = 11.7 for the extracted waste. These conditions result in a dye removal efficiency of 99.48% and 99.88% for raw and treated Eriobotrya Japonica seed waste, respectively. The methylene blue adsorption kinetics on the adsorbent can be precisely represented by an effective pseudo-second-order equation. The Freundlich model showed a significantly better fit to the experimental results compared to the Langmuir model. Full article

Clay minerals are promising candidates for caffeine removal due to their environmental friendliness and natural abundance. In this study, a commercially available bentonite was modified by Na⁺ exchange and characterized using Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy, zeta potential measurements, and specific surface area analysis. Caffeine adsorption was rapid, reaching equilibrium within 15 min. Adsorption isotherms for caffeine and its metabolites (theobromine, paraxanthine, and theophylline) in pure water were analyzed at 25.0 ± 0.5 °C using Langmuir and Freundlich models, both individually and in mixtures. Only caffeine exhibited favorable adsorption behavior, fitting the Langmuir equation, which allowed for the determination of a maximum adsorption capacity of 20 ± 3 mg/g, regardless of metabolite presence. The removal exceeded 85% of the caffeine from a 5.0 mg/L solution. The adsorption affinity of the studied compounds toward Na⁺-exchanged bentonite followed the order: caffeine >>> theobromine > paraxanthine ~ theophylline. The modified bentonite was then tested for caffeine removal from beverages and synthetic urine, achieving removal efficiencies exceeding 87%. To our knowledge, this is the first study investigating the effect of major caffeine metabolites on adsorption rates across different sample matrices, such as artificial urine, cola soda, soluble coffee, energy drinks, green tea, and yerba mate. Full article

Carbon dioxide (CO₂) injection into geologic formations has gained global traction, including in South Africa, to mitigate anthropogenic emissions through carbon capture, utilisation, and storage technology. These technological and technical developments require a comprehensive and reliable study of CO₂ sorption equilibria under in situ unmineable coal reservoir conditions. This paper presents novel findings on the study of the equilibrium adsorption of CO₂ on two South African coals measured at four temperatures between 30 and 60 °C and pressures up to 9.0 MPa using the volumetric technique. Additionally, the sorption mechanism and thermodynamic nature of the process were studied by fitting the experimental data into Langmuir–Freundlich (Sips), Tóth, and Dubinin–Astakhov (DA) isotherm models, and the Clausius–Clapeyron equation. The findings indicate that the sorption process is highly exothermic, as presented by a negative temperature effect, with the maximum working capacity estimated to range between 3.46 and 4.16 mmol/g, which is also rank- and maceral composition-dependent, with high-rank vitrinite-rich coal yielding more sorption capacity than low-rank inertinite-rich coal. The experimental data fit well in Sips and Tóth models, confirming their applicability in describing the CO₂ sorption behaviour of the coals under the considered conditions. The isosteric heat of adsorption varied from 7.518 to 37.408 kJ/mol for adsorbate loading ranging from 0.4 to 3.6 mmol/g. Overall, the coals studied demonstrate well-developed sorption properties that characteristically make them viable candidates for CO₂ sequestration applications for environmental sustainability. Full article

This study developed a new way of designing choline chloride-modified MOF-based materials with advanced gas adsorption properties. To design better carbon capture materials, MIL-101 (Cr) was prepared using the hydrothermal method, and then was modified with different concentrations of choline chloride in a one-step method to enhance its CO₂ adsorption capacity. The characterization and experimental results indicated that the modified ChCl-MIL-101(Cr) significantly enhanced the adsorption capacity for CO₂. Specifically, the 0.075-ChCl-MIL-101(Cr) showed a 61.191% increase in adsorption capacity compared to that of the raw material. Moreover, the regenerated adsorption loss rate of the modified material was below 4%, proving the permanence of the material synthesis. Simulating isotherms using Langmuir and Freundlich equations revealed the non-uniformity of surface bonding. Full article

A series of ionic liquids consisting of anilinium cations with varying alkyl chains and metallic (Sb and Bi) halides as anions have been synthesized and thoroughly characterized by using multinuclear (¹H and ¹³C) NMR, FT-IR, Raman and XPS techniques. They have been exploited as adsorbents for the dye’s removal, such as malachite green, rhodamine B and Sudan II, from the aqueous solution. Various parameters like the effect of stirring rate, pH, reaction time, adsorbent amount and initial dye concentration have been optimized. Both antimony- and bismuth-based ionic liquids exhibit high adsorption efficiencies and have comparable performance for each dye. Kinetic data have been analyzed by applying kinetic models, and the best-fitted model was found to be pseudo-second order with an R² value greater than 0.98. Adsorption capacity has been determined by analyzing the sorption data using the Langmuir and Freundlich equations, and the Langmuir isotherm model has been found to be the best fitting. The maximum adsorption capacities (q_max) derived from the Langmuir isotherm for malachite green, Sudan II and rhodamine B by M-Sb ILs were 217.36, 162.10 and 62.94 mg·g⁻¹, whereas by M-Bi ILs, the adsorption capacities were slightly higher, at 230.18, 170.00 and 64.21 mg·g⁻¹, respectively. Kinetic studies indicated pseudo-second-order behavior (R² > 0.98), while thermodynamic analysis demonstrated an endothermic adsorption, and a spontaneous reaction was carried out by a physisorption process. These findings accentuate the potential of Sb- and Bi-based ionic liquids as efficient and reusable adsorbents for removing dyes from wastewater. Full article

The challenging problem of chlorine “poisoning” SnO₂ for poorly recoverable detection of dichloromethane has been solved in this work. The materials synthesized by Ni or/and Mo doping SnO₂ were spread onto the micro-hotplates (<1 mm³) to fabricate the MEMS sensors with a low power consumption (<45 mW). The sensor based on Mo·Ni co-doped SnO₂ is evidenced to have the best sensing performance of significant response and recoverability to dichloromethane between 0.07 and 100 ppm at the optimized temperature of 310 °C, in comparison with other sensors in this work and the literature. It can be attributed to a synergetic effect of Mo·Ni co-doping into SnO₂ as being supported by characterization of geometrical and electronic structures. The sensing mechanism of dichloromethane on the material is investigated. In situ infrared spectroscopy (IR) peaks identify that the corresponding adsorbed species are too strong to desorb, although it has demonstrated a good recoverability of the material. A probable reason is the formation rates of the strongly adsorbed species are much slower than those of the weakly adsorbed species, which are difficult to form significant IR peaks but easy to desorb, thus enabling the material to recover. Theoretical analysis suggests that the response process is kinetically determined by molecular transport onto the surface due to the free convection from the concentration gradient during the redox reaction, and the output steady voltage thermodynamically follows the equation only formally identical to the Langmuir–Freundlich equation for physisorption but is newly derived from statistical mechanics. Full article

In this study, an effective composite material, manganese-modified magnetic dual-sludge biochar (Mn@MDSBC), was developed for the adsorption of ciprofloxacin hydrochloride (CIP). This composite was prepared by means of a simple one-pot method, which involved the pyrolysis of iron-based waterworks sludge (IBWS) and paper mill sludge (PMS) loaded with manganese (Mn) under controlled conditions in a nitrogen atmosphere. The synthesized Mn@MDSBC was subjected to a comprehensive suite of characterization approaches, which included N₂ adsorption–desorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Subsequently, static adsorption tests were conducted to investigate how different factors, including the initial solution pH, reaction time and temperature, CIP concentration, and ionic strength influence the adsorption of CIP by Mn@MDSBC. Mn@MDSBC had the maximum CIP adsorption capacity of 75.86 mg/g at pH 5, among the pH values ranging from 3 to 9. The pseudo-second order model provided the best description of the adsorption process, while the experimental data aligned more closely with the Langmuir equation than with the Freundlich model, indicating monolayer adsorption. The adsorption process was found to be non-spontaneous and exothermic according to thermodynamic analysis. The presence of Cl⁻ and SO₄²⁻ enhanced CIP adsorption, while PO₄³⁻ weakened it. After five cycles of reuse, Mn@MDSBC experienced a 17.17% loss in CIP adsorption capacity. The primary mechanisms for CIP removal by Mn@MDSBC were identified as physical and chemical adsorption, hydrogen bonding, and π-π stacking interactions. In summary, the study underscores the high efficiency of Mn@MDSBC as a composite material for CIP adsorption, highlighting its potential for application in wastewater treatment processes. Full article

Excess nitrate ions should be avoided in agriculture as they are absorbed by plants and ingested by humans, which can have serious effects on soil and groundwater. In this study, environmentally friendly bamboo flour and nano-sized oyster shells were used as adsorbents. The equilibrium time for nitrate adsorption was found to be short, less than five minutes, and the treatment temperature had little effect on adsorption. The adsorption capacity and adsorption mechanism were investigated using experiments and adsorption isotherms. Bamboo powder treated with magnesium chloride (Mg bamboo), crushed oyster shell (oyster shell), and hydrogel induced with sodium alginate (hydrogel) were used. The maximum adsorption of nitrate ions on the magnesium-treated bamboo flour was estimated to be 399 mg NO₃⁻/g by the Dubin–Radushakevich equation (correlation coefficient 0.84), with the Langmuir (correlation coefficient 0.91) and Freundlich (correlation coefficient 0.91) equations also fitting relatively well. The D-R equation (correlation coefficient 0.938) and Freundlich equation (correlation coefficient 0.943) also fitted oyster shells relatively well. The maximum adsorption was estimated at 354 mg NO₃⁻/g. In oyster shell treatments where phosphate and nitrate ions were present, it was observed that both substances were adsorbed simultaneously. For the hydrogels, only the D-R equation (correlation coefficient 0.944) and the Freundlich isotherm were applicable. The maximum adsorption was estimated at 156 mg/g. Full article

The demand for intensive agriculture to boost food and crop production has increased. High nitrogen (N) fertilizer use is crucial for increasing agricultural productivity but often leads to significant nitrate losses, posing risks to surface and groundwater quality. This study examines the role of biochar as a soil amendment to enhance nutrient retention and mitigate nitrate leaching. By improving nitrogen efficiency, biochar offers a sustainable strategy to reduce the environmental impacts of intensive agriculture while maintaining soil fertility. An incubation study investigated four biochar feedstocks: spruce bark biochar at 550 °C (SB550), hardwood biochar (75% sugar maple) at 500 °C (HW500), sawdust (fir/spruce) biochar at 427 °C (FS427), and softwood biochar at 500 °C (SW500), to identify the most effective nitrate adsorbent. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) were employed to analyze biochar morphology and surface functional groups. Adsorption isotherms were modeled using the Langmuir and Freundlich equations. The results indicated that surface functional groups, such as aromatic C=C stretching and bending, aromatic C–H bending, and phenolic O–H bending, play crucial roles in enhancing electrostatic attraction and, consequently, the nitrate adsorption capacity of biochar. The equilibrium adsorption data from this study fit well with both the Langmuir and Freundlich isotherm models. Among the four biochar types tested, SB550 exhibited the highest nitrate adsorption capacity, with a maximum of 184 mg/g. The adsorption data showed excellent conformity to the Langmuir and Freundlich models, with correlation coefficients (R²) exceeding 0.987 for all biochar types. These findings highlight the high accuracy of these models in predicting nitrate adsorption capacities. Full article

As the mining depth increases, the effect of stress on the gas adsorption of coal gradually becomes significant. There are significant differences in the pore volume, specific surface area, and adsorption characteristics of coal before and after stress. In this study, the porosity variation characteristics of coal were studied using axial and confining pressure loading processes, and volumetric stress was introduced to characterize the pore variation law of coal under triaxial stress. By calculating the stress values at different burial depths, gas isothermal adsorption experiments were conducted on coal under different stress effects. The Langmuir equation, D-A equation, and Freundlich empirical formula were used to fit the adsorption experimental results. Combining experiments and models to predict the adsorbed and free gas content under stress, we described the gas adsorption law of coal under different stress effects. Full article

For many decades, natural and modified clay minerals have been used as adsorbents to clean up aquatic and soil ecosystems contaminated with organic and inorganic pollutants. In this study, organoclays based on bentonite and various amphoteric and nonionic surfactants were synthesized and tested as effective sorbents for lead ions. The maximum values of R were obtained when describing the sorption processes using the Langmuir model, which ranged from 0.97 to 0.99. The adsorption of lead ions by these organoclays was investigated using different sorption models including the Langmuir, Freundlich, and BET. It was found that, according to the values of limiting adsorption to the Langmuir equation, the synthesized organoclays formed an increasing series: organoclay with cocamide diethanolamine < bentonite < organoclay with lauramine oxide < organoclay with sodium cocoiminodipropionate < organoclay with disodium cocoamphodiacetate < organoclay with alkyl polyglucoside. The Gibbs energy for all of the analyzed samples was calculated and found to be negative, indicating the spontaneity of the cation adsorption process in the forward direction. The maximum value of the adsorption capacity of lead cations on organoclay-based bentonite with alkyl polyglucoside was 1.49 ± 0.05 mmol/g according to the Langmuir model, and 0.523 ± 0.003 mmol/g as determined by the BET model. In the process of modifying bentonite, there was an increase in negative values of the zeta potential for organoclays compared to the initial mineral, which clearly enhanced their electrostatic interactions with the positively charged lead ions. It was hypothesized, based on the physicochemical principles, that exchange adsorption is the main mechanism for lead absorption. Based on chemical approaches, organoclays based on amphoteric surfactants absorb lead mainly through the mechanisms of electrostatic attraction, ion exchange, and complexation as well as the formation of insoluble precipitates. Organoclays based on nonionic surfactants, on the other hand, absorb lead through mechanisms of complexation (including chelation) and the formation of insoluble chemical precipitates. The comparison of isotherms from different models allows us to find the most accurate match between the model and the experimental data, and to better understand the nature of the processes involved. Full article

The limited supply of drinking water has aroused people’s curiosity in recent decades. Adsorption is a popular method for removing hazardous substances from wastewater, especially heavy metals, as it is cheap, highly efficient, and easy to use. In this work, a new sludge-based activated carbon adsorbent (thickened samples SBAC1 and un-thickened samples SBAC2) was developed to remove hazardous metals such as cadmium (Cd⁺²) and lead (Pb⁺²) from an aqueous solution. The chemical structure and surface morphology of the produced SBAC1 and SBAC2 were investigated using a range of analytical tools such as CHNS, BET, FT-IR, XRD, XRF, SEM, TEM, N₂ adsorption/desorption isothermal, and zeta potential. BET surface areas were examined and SBAC2 was found to have a larger BET surface area (498.386 m²/g) than SBAC1 (336.339 m²/g). While the average pore size was 10–100 nm for SBAC1 and 45–50 nm for SBAC2. SBAC1 and SBAC2 eliminated approximately 99.99% of Cd⁺² and Pb⁺² out the water under all conditions tested. The results of the adsorption of Cd⁺² and Pb⁺² were in good agreement with the pseudo-second-order equation (R² = 1.00). Under the experimental conditions, the Cd⁺² and Pb⁺² adsorption equilibrium data were effectively linked to the Langmuir and Freundlich equations for SBAC1 and SBAC2, respectively. The regeneration showed a high recyclability for the fabricated SBAC1 and SBAC2 during five consecutive reuse cycles. As a result, the produced SBAC1 and SBAC2 are attractive adsorbents for the elimination of heavy metals from various environmental and industrial wastewater samples. Full article

In the face of current challenges related to climate change, maintaining the appropriate quality of freshwater becomes crucial. This study examined the effectiveness of removing heavy metals (Cu(II) and Co(II)) using Chlorella vulgaris biosorbents (dietary supplements in the form of powder). This study determined the parameters of the biosorbent (point of zero charge (PZC) analysis using scanning electron microscopy with back-scattered electron (SEM-BSE) and Fourier transform infrared spectroscopy (FT-IR) analysis). Batch tests were also performed to determine the kinetic constants and adsorption equilibrium of Cu(II) and Co(II) ions. Based on the conducted research, it was found that a pseudo-second-order equation describes the kinetics of the biosorption process. Among the studied adsorption isotherms, the Langmuir and Freundlich models fit best. The results indicate that single-layer adsorption took place and Chlorella vulgaris is a microporous adsorbent. The maximum sorption capacity in the single-component system for Cu(II) and Co(II) was 30.3 mg·g⁻¹ and 9.0 mg·g⁻¹, respectively. In contrast, in the binary system, it was 20.8 mg·g⁻¹ and 19.6 mg·g⁻¹ (extended Langmuir model) and 23.5 mg·g⁻¹ and 19.6 mg·g⁻¹ (Jain-Snoeyinka model). Chlorella vulgaris is an effective biosorbent for removing heavy metals from freshwater. This technology offers an ecological and economical solution for improving water quality, making it a promising alternative to traditional purification methods. Full article

Defluoridation of water was evaluated using a copper–magnesium (Cu-Mg) coated sand (CMCS) as a sustainable adsorbent containing binary metal oxides. The CMCS sorbent coating contained mostly amorphous copper and magnesium oxides in the Cu-Mg coating on the crystalline sand surface. Pseudo-second-order kinetics was observed where most fluoride was removed rapidly within an hour. Favorable adsorption occurred according to the Langmuir and Freundlich adsorption equations, while physisorption occurred according to the Dubinin–Radushkevich (D-R) adsorption equation. The adsorption capacity of the CMCS sorbent based on sorbent surface was similar to various other adsorbents with larger adsorbent surface areas, likely due to the efficacy of the Cu-Mg coating despite the CMCS sorbent’s much smaller surface area. Fluoride was adsorbed effectively from pH 3 to pH 11 through adsorption of anionic fluoride onto the CMCS sorbent’s protonated surface with a pH_PZC of 10.5, indicative of electrostatic attraction as the main adsorption mechanism. The CMCS sorbent’s re-coating was conducive to successful recycling and reuse of the CMCS sorbent as a sustainable adsorbent for water defluoridation. Full article