Search Results (20)

This study aimed to produce activated carbon from desilicated rice husks using various carbonization and activation methods, including a tube furnace, muffle furnace, and artisanal pyrolysis. The resulting activated carbons were characterized for their adsorptive capacity through the determination of iodine number and methylene blue adsorption; these are key indicators of specific surface area and adsorbent quality. Advanced characterization techniques were employed, such as scanning electron microscopy (SEM), which revealed a highly porous and irregular surface structure, and energy dispersive X-ray spectroscopy (EDS), confirming the effective removal of impurities and optimization of the elemental composition. Atomic force microscopy (AFM) demonstrated favorable surface roughness for adsorption processes. Among the samples, CaDH162-CADH53 exhibited the highest performance, with an iodine number of 1094.8 mg/g and a yield of 93.5%, signifying a high adsorption capacity. The activation treatments with phosphoric acid and calcium carbonate significantly improved the porous structure, further enhancing the material’s adsorptive properties. In conclusion, the activated carbons produced in this study demonstrated optimal physicochemical properties for water purification and contaminant treatment applications. These findings highlight the potential of using agricultural waste, such as rice husk, as a sustainable and scalable alternative for industrial-scale activated carbon production. Full article

A new composite material with enhanced sorption-selective properties for uranium recovery from liquid media has been obtained. Sorbents were synthesized through a polycondensation reaction of a mixture of 4-amino-N’-hydroxy-1,2,5-oxadiazole-3-carboximidamide (hereinafter referred to as amidoxime) and SiO₂ in an environment of organic solvents (acetic acid, dioxane) and highly porous SiO₂. To establish optimal conditions for forming the polymer sorption-active part and the synthesis as a whole, a series of composite adsorbents were synthesized with varying amidoxime/matrix ratios (35/65, 50/50, 65/35). The samples were characterized with FT-IR, XRD, SEM, EDX, XRFES spectroscopy and TGA. Under static conditions of uranium sorption, the dependence of the efficiency of radionuclide recovery from mineralized solutions of various acidities on the ratio of the initial components was established. In the pH range from 4 to 8 (inclusive), the uranium removal efficiency exceeds 95%, while the values of the distribution coefficients (Kd) exceed 10⁴ cm³g⁻¹. It was demonstrated that an increase in the surface development of the sorbents enhances such kinetic parameters of uranium sorption as diffusion rate by 10–20 times compared to non-porous materials. The values of the maximum static capacity exceed 700 mg g⁻¹. The enhanced availability of adsorption centers, achieved through the use of a porous SiO₂ matrix, significantly improves the kinetic parameters of the adsorbents. A composite with optimal physicochemical and sorption properties (amidoxime/matrix ratio of 50/50) was examined under dynamic conditions of uranium sorption. It was found that the maximum dynamic sorption capacity of porous materials is four times greater compared to that of a non-porous adsorbent Se-init. The effective filter cycle exceeds 3200 column volumes—twice that of an adsorbent with a monolithic surface. These results indicate the promising potential of the developed materials for uranium sorption from liquid mineralized media under dynamic conditions across a wide pH range. Full article

The aim of this study was to evaluate the mobility of copper (Cu) and zinc (Zn) and their impact on the properties of bentonites and unfrozen water content. Limited research in this area necessitates further analysis to prevent the negative effects of metal interactions on bentonite effectiveness. Tests involved American (SWy-3, Stx-1b) and Slovak (BSvk) bentonite samples with Zn or Cu ion exchange. Sequential extraction was performed using the Community Bureau of Reference (BCR) method. Elemental content was analyzed via inductively coupled plasma optical emission spectrometry (ICP-OES). Unfrozen water content was measured using nuclear magnetic resonance (¹H-NMR) and differential scanning calorimetry (DSC). Results showed a significant influence of the main cation (Zn or Cu) on ion mobility, with toxic metal concentrations increasing mobility and decreasing residual fractions. Mobile Zn fractions increased with larger particle diameters, lower clay content, and shorter interplanar spacing, while the opposite was observed for Cu. Zn likely accumulated in larger clay pores, while Cu was immobilized in the bentonite complex. The stability of Zn or Cu ions increased with higher clay content or specific surface area. Residual Zn or Cu fractions were highest in uncontaminated bentonites with higher unfrozen water content, suggesting the potential formation of concentrated solutions in sub-zero temperatures, posing a threat to the clay–water environment, especially in cold regions. Full article

Clays are a class of porous materials; their surfaces are naturally covered by moisture. Weak thermal treatment may be considered practical to remove the water molecules, changing the surface properties and making the micro- and/or mesoporosities accessible to interact with other molecules. Herein, a modulated thermogravimetric analysis (MTGA) study of the moisture behavior on the structures of five, both fibrous and laminar, clay minerals is reported. The effect of the thermal treatment at 150 °C, which provokes the release of weakly adsorbed water molecules, was also investigated. The activation energies for the removal of the adsorbed water (Ea) were calculated, and they were found to be higher, namely, from 160 to 190 kJ mol⁻¹, for fibrous clay minerals compared to lamellar structures, ranging in this latter case from 80 to 100 kJ mol⁻¹. The thermal treatment enhances the rehydration in Na-montmorillonite, stevensite, and sepiolite structures with a decrease in the energy required to remove it, while Ea increases significantly in palygorskite (from 164 to 273 kJ mol⁻¹). As a proof of concept, the MTGA results are statistically correlated, together with a full characterization of the physico-chemical properties of the five clay minerals, with the adsorption of two molecules, i.e., aflatoxin B1 (AFB1) and β-carotene. Herein, the amount of adsorbed molecules ranges from 12 to 97% for the former and from 22 to 35% for the latter, depending on the particular clay. The Ea was correlated with AFB1 adsorption with a Spearman score of −0.9. When the adsorbed water is forcibly removed, e.g., under vacuum conditions and high temperatures, the structure becomes the most important, decreasing the Spearman score between β-carotene and Ea to −0.6. Full article

Plastic waste disposal is a major environmental problem worldwide. One recycling method for polymeric materials is their conversion into carbon materials. Therefore, a process of obtaining activated carbons through the carbonization of waste CDs (as the selected carbon precursor) in an oxygen-free atmosphere, and then the physical activation of the obtained material with CO₂, was developed. Dyes such as methylene blue (MB) and malachite green (MG) are commonly applied in industry, which contaminate the water environment to a large extent and have a harmful effect on living organisms; therefore, adsorption studies were carried out for these cationic dyes. The effects of the activation time on the physicochemical properties of the activated materials and the adsorption capacity of the dyes were investigated. The obtained microporous adsorbents were characterized by studying the porous structure based on low-temperature nitrogen adsorption/desorption, scanning electron microscopy (SEM-EDS), elemental analysis (CHNS), Raman spectroscopy, X-ray powder diffraction (XRD), infrared spectroscopy (ATR FT-IR), thermal analysis (TG, DTG, DTA), Boehm’s titration method, and pH_pzc (the point of zero charge) determination. Moreover, adsorption studies (equilibrium and kinetics) were carried out. The maximum adsorption capacities (q_{m exp}) of MB and MG (349 mg g⁻¹ and 274 mg g⁻¹, respectively) were identified for the obtained material after 8 h of activation. The results show that the use of waste CDs as a carbon precursor facilitates the production of low-cost and effective adsorbents. Full article

Covalent Organic Frameworks (COFs) are a newly emerged class of porous materials consisting of organic building blocks linked by strong covalent bonds. The physical and chemical properties of COFs, i.e., modularity, porosity, well-developed specific surface area, crystallinity, and chemical-thermal stability, make them a good application material, especially in the aspects of adsorption and gas separation. The organic compositions of their building blocks also render them with biocompatible properties; therefore, they also have potential in biomedical applications. Depending on the symmetry of the building blocks, COF materials form two-dimensional (2D COF) or three-dimensional (3D COF) crystal structures. 3D COF structures have a higher specific surface area, they are much lighter due to their low density, and they have a larger volume than 2D COF crystals, but, unlike the latter, 3D COF crystals are less frequently obtained and studied. Selecting and obtaining suitable building blocks to form a stable 3D COF crystal structure is challenging and therefore of interest to the chemical community. Triptycene, due to its 3D structure, is a versatile building block for the synthesis of 3D COFs. Polymeric materials containing triptycene fragments show good thermal stability parameters and have a very well-developed surface area. They often tend to be characterized by more than one type of porosity and exhibit impressive gas adsorption properties. The introduction of a triptycene backbone into the structure of 3D COFs is a relatively new procedure, the results of which only began to be published in 2020. Triptycene-based 3D COFs show interesting physicochemical properties, i.e., high physical stability and high specific surface area. In addition, they have variable porosities with different pore diameters, capable of adsorbing both gases and large biological molecules. These promising parameters, guaranteed by the addition of a triptycene backbone to the 3D structure of COFs, may create new opportunities for the application of such materials in many industrial and biomedical areas. This review aims to draw attention to the symmetry of the building blocks used for COF synthesis. In particular, we discussed triptycene as a building block for the synthesis of 3D COFs and we present the latest results in this area. Full article

Ammonia and sulfide derived from the reduction of sulfate by the sulfate-reducing bacteria (SRB) are two of the most common inhibitors in anaerobic digestion. Zeolites and bentonites are characterized as porous materials able to adsorb both ammonia and sulfur compounds and seem to be promising candidates as additives in anaerobic digestion to counteract this co-inhibition. In this study, bentonite and zeolite 13X were subjected to alkali modification at different concentrations of NaOH to alter their physicochemical properties, and their effect on the alleviation of ammonia and sulfate co-inhibition in anaerobic digestion of cow manure was examined. The methane production in 13X treatments (13X without NaOH, 13X02-NaOH 0.2 M and 13X1-NaOH 1 M) was elevated by increasing the NaOH concentration in the modification step, resulting in a significance increase by 8.96%, 11.0% and 15.56% in 13X treatments compared to the treatment without additive. Bentonite treatments did not show the same behavior on the toxicity mitigation. The results appear to be influenced by the combined effect of 13X zeolites on the sulfur compounds adsorption and on the increase in pH and Na⁺ concentration in the batch reactors. Full article

Biochar is a carbonaceous and porous material with limited adsorption capacity, which increases by modifying its surface. Many of the biochars modified with magnetic nanoparticles reported previously were obtained in two steps: first, the biomass was pyrolyzed, and then the modification was performed. In this research, a biochar with Fe₃O₄ particles was obtained during the pyrolysis process. Corn cob residues were used to obtain the biochar (i.e., BCM) and the magnetic one (i.e., BCM_Fe). The BCM_Fe biochar was synthesized by a chemical coprecipitation technique prior to the pyrolysis process. The biochars obtained were characterized to determine their physicochemical, surface, and structural properties. The characterization revealed a porous surface with a 1013.52 m²/g area for BCM and 903.67 m²/g for BCM_Fe. The pores were uniformly distributed, as observed in SEM images. BCM_Fe showed Fe₃O₄ particles on the surface with a spherical shape and a uniform distribution. According to FTIR analysis, the functional groups formed on the surface were aliphatic and carbonyl functional groups. Ash content in the biochar was 4.0% in BCM and 8.0% in BCM_Fe; the difference corresponded to the presence of inorganic elements. The TGA showed that BCM lost 93.8 wt% while BCM_Fe was more thermally stable due to the inorganic species on the biochar surface, with a weight loss of 78.6%. Both biochars were tested as adsorbent materials for methylene blue. BCM and BCM_Fe obtained a maximum adsorption capacity (q_m) of 23.17 mg/g and 39.66 mg/g, respectively. The obtained biochars are promising materials for the efficient removal of organic pollutants. Full article

A set of Y-type zeolites with Si/Al atomic ratios between 7–45 were studied as catalysts in the aminocyclization reaction between acrolein and ammonia to produce pyridine and 3-picoline. The catalytic activity tests at 360 °C revealed that the acrolein conversion increased in the order Z45 < ZY34 < ZY7 < ZY17, in agreement with the increase of the total acidity per gram of catalyst. In all cases, pyridine bases and cracking products (acetaldehyde and formaldehyde) were detected in the outflow from the reactor. The total yield of pyridines was inversely proportional to the total acidity for the catalysts, which presented large surface areas and micro- and mesoporosity. The selectivity towards 3-picoline was favored when using catalysts with a Brønsted/Lewis acid sites ratio close to 1. The formation of pyridine occurred more selectively over Lewis acid sites than Brønsted acid sites. The deactivation tests showed that the time on stream of the catalysts depended on the textural properties of zeolites, i.e., large pore volume and large BET area, as evidenced by the deactivation rate constants and the characterization of the spent catalysts. The physicochemical properties of the catalysts were determined by XRD, UV-vis, and Raman spectroscopies, infrared spectroscopy with adsorbed pyridine, N₂ physisorption, and SEM-EDXS. After the reaction, the spent catalysts were characterized by XRD, Raman spectroscopy, TGA, and SEM-EDXS, indicating that the uniform deposition of polyaromatic species on the catalyst surface and within the porous system resulted in the loss of activity. Full article

Hydrogen peroxide (H₂O₂), an accessible and eco-friendly oxidant, was employed for the template-free hydrothermal synthesis of mesoporous CeO₂ based on a cerium carbonate precursor (Ce₂(CO₃)₃•xH₂O). Its microstructure and physicochemical properties were characterized by XRD, TEM and N₂ sorption techniques. The formation of the CeO₂ phase with a porous structure was strongly dependent on the presence of H₂O₂, while the values of the BET surface area, pore diameter and pore volume of CeO₂ were generally related to the amount of H₂O₂ in the template-free hydrothermal synthesis. The BET surface area and pore volume of the mesoporous CeO₂ synthesized hydrothermally at 180 °C with 10 mL H₂O₂ were 112.8 m²/g and 0.1436 cm³/g, respectively. The adsorption process had basically finished within 30 min, and the maximum adsorption efficiency within 30 min was 99.8% for the mesoporous CeO₂ synthesized hydrothermally at 140 °C with 10 mL, when the initial AO7 concentration was 120 mg/L without pH preadjustment. The experimental data of AO7 adsorption were analyzed using the Langmuir and Freundlich isotherm modes. Moreover, the mesoporous CeO₂ synthesized at 140 °C with 10 mL H₂O₂ was regenerated in successive adsorption–desorption cycles eight times without significant loss in adsorption capacity, suggesting that the as-synthesized mesoporous CeO₂ in this work was suitable as an adsorbent for the efficient adsorption of AO7 dye from an aqueous solution. Full article

In the current study, cornstarch (CS) and eggshell powder (ESP) were combined using a casting technique to develop a biodegradable film that was further morphologically and physicochemically characterized using standard methods. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology of the ESP/CS film, and the surface of the film was found to have a smooth structure with no cracks, a spherical and porous irregular shape, and visible phase separation, which explains their large surface area. In addition, the energy dispersive X-ray (EDX) analysis indicated that the ESP particles were made of calcium carbonate and the ESP contained carbon in the graphite form. Fourier Transform Infrared Spectroscopy indicated the presence of carbonated minerals in the ESP/CS film which shows that ESP/CS film might serve as a promising adsorbent. Due to the inductive effect of the O–C–O bond on calcium carbonate in the eggshell, it was discovered that the ESP/CS film significantly improves physical properties, moisture content, swelling power, water solubility, and water absorption compared to the control CS film. The enhancement of the physicochemical properties of the ESP/CS film was principally due to the intra and intermolecular interactions between ESP and CS molecules. As a result, this film can potentially be used as a synergistic adsorbent for various target analytes. Full article

In this paper, we investigated the abilities of five sugar-based synthetic surfactants and biosurfactants from three different families (i.e., alkyl polyglycoside (APG), sophorolipid (SL), and rhamnolipid (RL)) to dissolve and mobilize non-aqueous phase liquid (NAPL) components, i.e., toluene and perchloroethylene (PCE), adsorbed on porous matrices. The objective of this study was to establish a benchmark for the selection of suitable surfactants for the flushing aquifer remediation technique. The study involved a physicochemical characterization of the surfactants to determine the critical micelle concentration (CMCs) and interfacial properties. Subsequently, a batch study, through the construction of adsorption isotherms, made it possible to evaluate the surfactants’ capacities in contaminant mobilization via the reduction of their adsorptions onto a reference adsorbent material, a pine wood biochar (PWB). The results indicate that a synthetic surfactant from the APG family with a long fatty acid chain and a di-rhamnolipid biosurfactant with a shorter hydrophobic group offered the highest efficiency values; they reduced water surface tension by up to 54.7% and 52%, respectively. These two surfactants had very low critical micelle concentrations (CMCs), 0.0071 wt% and 0.0173 wt%, respectively; this is critical from an economical point of view. The batch experiments showed that these two surfactants, at concentrations just five times their CMCs, were able to reduce the adsorption of toluene on PWB by up to 74% and 65%, and of PCE with APG and RL by up to 65% and 86%, respectively. In general, these results clearly suggest the possibility of using these two surfactants in surfactant-enhanced aquifer remediation technology. Full article

Cleaning wastewater containing low concentrations of phenolic compounds is a challenging task. In this work, agar–alginate beads impregnated with trihexyltetradecylphosphonium bromide ([P₆₆₆₁₄][Br]) ionic liquid adsorbent were synthesized as a potential adsorbent for such applications. FTIR, TGA, SEM, EDX and PZC studies were performed to characterize and understand the physicochemical properties of the adsorbent. The Fourier transformation infrared spectroscopy (FTIR) study showed that [P₆₆₆₁₄][Br] ionic liquid was effectively incorporated into the agar–alginate structure. TGA and SEM confirmed comparative enhanced thermal stability and porous surface, respectively. Chemical reaction rate-altering parameters, i.e., pH, contact time, initial phenol concentration and temperature, are optimized at highest phenol removal. It was found that the maximum phenol adsorption capacity and highest removal efficiency by the adsorbent occurred at pH 2, initial phenol concentration of 150 mg/L, beads dosage of 6 mg/mL and contact time of 2 h with values of 16.28 mg/g and 65.12%, respectively. The pseudo-second order model fitted the adsorption kinetics well, and the Freundlich isotherm model gave the experimental data the best fit. Analysis of thermodynamic data demonstrated that the adsorption process is fundamentally exothermic in nature, and low temperature favors spontaneity of the chemical reaction. Regeneration studies indicated that the adsorbent can at least be used for four cycles in such applications without any considerable loss in adsorption efficiency. Full article

In the present work, beta-calcium pyrophosphate (β-Ca₂P₂O₇) was investigated as a potential adsorbent for the removal of heavy metal ions from water. Single-phase β-Ca₂P₂O₇ powders were synthesized by a simple, scalable and cost-effective wet precipitation method followed by annealing at 800 °C, which was employed for the conversion of as-precipitated brushite (CaHPO₄∙2H₂O) to β-Ca₂P₂O₇. Physicochemical properties of the sorbent were characterized by means of X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA/DSC), scanning electron microscopy (SEM) and low temperature adsorption–desorption of nitrogen (BET method). The synthesized powders consisted of porous plate-like particles with micrometer dimensions. Specific surface area calculated by the BET method was found to be 7 m² g⁻¹. For the estimation of sorption properties, the aqueous model solutions containing different metal ions (Al³⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Sn²⁺, Sr²⁺ and Zn²⁺) were used. The adsorption test revealed that β-Ca₂P₂O₇ demonstrates the highest adsorption capacity for Pb²⁺ and Sn²⁺ ions, while the lowest capacity was observed towards Sr²⁺, Ni²⁺ and Co²⁺ ions. The optimal pH value for the removal of Pb²⁺ ions was determined to be 2, which is also related to the low solubility of β-Ca₂P₂O₇ at this pH. The adsorption capacity towards Pb²⁺ ions was calculated as high as 120 mg g⁻¹. Full article

As a potential adsorbent material, loose, porous livestock manure biochar provides a new approach to livestock manure resource utilization. In this study, coconut husks (CH) and livestock manure, i.e., cow dung (CD), pig manure (PM), and chicken manure (CM) were used as biomass precursors for preparation of biochar via high-temperature pyrolysis and CO₂ activation. Characterization technologies, such as scanning electron microscopy, Fourier transform infrared spectroscopy, adsorption–desorption isotherms, and pore size distributions, were used to study the microscopic morphologies and physicochemical properties of unactivated and activated biochar materials. The results showed that CD biochar provides better adsorption performance (up to 29.81 mg H₂S/g) than CM or PM biochar. After activation at 650° for 1 h, the best adsorption performance was 38.23 mg H₂S/g. For comparison, the CH biochar removal performance was 30.44 mg H₂S/g. Its best performance was 38.73 mg H₂S/g after 1 h of activation at 750 °C. Its best removal performance is equivalent to that of CH biochar activated at a temperature that is 100 °C higher. Further material characterization indicates that the H₂S removal performance of livestock-manure–derived biochar is not entirely dependent on the specific surface area, but is closely related to the pore size distribution. Full article