Development of Novel Fe3O4/AC@SiO2@1,4-DAAQ Magnetic Nanoparticles with Outstanding VOC Removal Capacity: Characterization, Optimization, Reusability, Kinetics, and Equilibrium Studies

Enhanced benzene vapor adsorption through microwave-assisted fabrication of activated carbon from peanut shells using ZnCl2 as an activating agent

Herein, microwave-assisted activated carbon (MW-AC) was fabricated from peanut shells using a ZnCl2 activator and utilized for the first time to eliminate benzene vapor as a volatile organic compound (VOC). During the MW-AC production process, which involved two steps-microwave treatment and muffle furnace heating-we investigated the effects of various factors and achieved the highest iodine number of 1250 mg/g. This was achieved under optimal operating conditions, which included a 100% impregnation ratio, CO2 as the gas in the microwave environment, a microwave power set at 500 W, a microwave duration of 10 min, an activation temperature of 500 °C and an activation time of 45 min. The structural and morphological properties of the optimized MW-AC were assessed through SEM, FTIR, and BET analysis. The dynamic adsorption process of benzene on the optimized MW-AC adsorbent, which has a significant BET surface area of 1204.90 m2/g, was designed using the Box-Behnken approach within the response surface methodology. Under optimal experimental conditions, including a contact duration of 80 min, an inlet concentration of 18 ppm, and a temperature of 26 °C, the maximum adsorption capacity reached was 568.34 mg/g. The experimental data are better described by the pseudo-second-order kinetic model, while it is concluded that the equilibrium data are better described by the Langmuir isotherm model. MW-AC exhibited a reuse efficiency of 86.54% for benzene vapor after five consecutive recycling processes. The motivation of the study highlights the high adsorption capacity and superior reuse efficiency of MW-AC adsorbent with high BET surface area against benzene pollutant. According to our results, the developed MW-AC presents itself as a promising adsorbent candidate for the treatment of VOCs in various industrial applications.

Designing novel perlite-Fe3O4@SiO2@8-HQ-5-SA as a promising magnetic nanoadsorbent for competitive adsorption of multicomponent VOCs

Volatile organic compounds (VOCs), which emerge as multicomponent pollutants through many industrial processes, pose a serious threat to human health and the eco-environment due to their volatility, toxicity and dispersion. Hence, the study of competitive adsorption of multicomponent VOCs is of practical and scientific importance. Herein, the perlite-supported Fe3O4@SiO2@8-hydroxyquinoline-5-sulfonic acid (perlite-Fe3O4@SiO2@8-HQ-5-SA) was designed as a novel magnetic nanoadsorbent by a simple strategy and employed for the competitive adsorption of multicomponent toluene, ethylbenzene and xylene in the vapor-phase targeted as VOCs. The successfully prepared perlite-Fe3O4@SiO2@8-HQ-5-SA was characterized by means of SEM, EDX, FT-IR, VSM and BET analyses. Adsorption capacities of 558 mg/g, 680 mg/g and 716 mg/g were achieved for single component toluene, ethylbenzene and xylene, respectively. It was concluded that the adsorption capacities for both binary and ternary components were significantly decreased compared to single component adsorption. The competitive adsorption capacity order of the binary and ternary component VOCs was xylene > ethylbenzene > toluene due to their competitive dominance. The rate-limiting kinetic analysis indicated that the adsorption rates were determined by both the film diffusion and intraparticle diffusion. The analysis of the error metrics demonstrated that the three-parameter isotherm models better described the adsorption data compared to the two-parameter models. In particular, the Toth model provided the closest fit to the experimental equilibrium data. The thermodynamic analysis indicated the spontaneous nature and probability (ΔG° <0), exothermic (ΔH° <0), physical (ΔH° <20 kJ/mol) and a declination in the degree of randomness (ΔS° <0) of the adsorption processes. The reuse efficiency of perlite-Fe3O4@SiO2@8-HQ-5-SA for toluene, ethylbenzene and xylene decreased to only by 88.91%, 88.07% and 87.16% after five recycles. The perlite-Fe3O4@SiO2@8-HQ-5-SA has a significant adsorptive potential compared to other adsorbents reported in the literature, thus it could be recommended as a promising nanoadsorbent for VOCs in industrial processes.

Physicochemical Properties and Application of Silica-Doped Biochar Composites as Efficient Sorbents of Copper from Tap Water

This article concerns research on new sorption materials based on silica-doped activated carbon. A two-stage synthesis involved pyrolysis of plant material impregnated in a water glass solution, followed by hydrothermal activation of the pyrolysate in KOH solution. The resulting composite can be used as a sorbent in drinking water filters. The proposed method of synthesis enables the design of materials with a surface area of approximately 150 m²·g^-1, whose chemical composition and structure were confirmed by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG/DTA) and Fourier-transform infrared spectroscopy (FTIR). The sorption properties of the obtained materials were determined relative to copper ions using the batch experiment method. The optimal operating parameters of the obtained materials relative to copper ions are T = 313.15 K, pH = 5, S:L ratio = 4 g·dm^-3 and t = 120 min. The research shows that the sorption kinetics of copper ions can be described by a pseudo-second-order model. The plotted copper(II) sorption isotherm clearly indicates the Langmuir model. Under optimal conditions, the maximum sorption of copper ions was 37.74 mg·g^-1, which is a satisfactory result and confirms the possibility of using the obtained material in drinking water filters.

Adsorptive removal of dichlorophenoxyacetic acid (2,4-D) using novel nanoparticles based on cationic surfactant-coated titania nanoparticles

A novel nanomaterial based on cationic surfactant-coated TiO₂ nanoparticle (CCTN) was systematically fabricated in this work. Synthesized titania nanoparticles were thoroughly characterized by XRD, FT-IR, HR-TEM, TEM-EDX, SEM with EDX mapping, BET, and ζ potential measurements. The adsorption of cationic surfactant, cetyltrimethylammonium bromide (CTAB), on TiO₂ was studied under various pH and ionic strength conditions. Adsorption of CTAB on TiO₂ increased with ionic strength increment in the presence of hemimicelle monolayer structure, indicating that nonelectrostatic and electrostatic forces control CTAB uptake. CTAB adsorption isotherms on TiO₂ were according to a two-step model. Potential application in pesticide removal of 2,4-dichorophenoxy acetic acid (2,4-D) using CCTN was also studied. Optimum parameters for 2,4-D treatment through adsorption technique were pH 5, adsorption time of 120 min, and CCTN dosage of 10 mg·mL^-1. Very low 2,4-D removal efficiency using TiO₂ without CTAB coating was found to be approximately 28.5% whereas the removal efficiency was up to about 90% by using CCTN under optimum conditions, and the maximum adsorption capacity of 12.79 mg·g^-1 was found. Adsorption isotherms of 2,4-D on CCTN were more suitable with the Langmuir model than Freundlich. Adsorption mechanisms of 2,4-D on CCTN were mainly governed by Columbic attraction based on isotherms and surface charge changes.

Column optimization of adsorption and evaluation of bed parameters-based on removal of arsenite ion using rice husk

The objective of this study deals with column optimization of adsorption-based on removal of arsenite ion using rice husk. The parameters affecting the column adsorption study, i.e., influent-concentration, bed depth, and flow rate, were optimized. The range of parameters, i.e., influent-concentration (15-50 mg/L), flow rate (20, 35, 45, and 60 mL/min), and bed depth (15-60 mm), were studied experimentally. Kinetics models Bohart-Adams and Hutchins were studied to measure the amount adsorbed, depth of mass transfer zone, saturated concentration, and time observed at 10% & 90% breakthrough. The percentage amount adsorbed q_m enhanced with enhancement in bed depth but got reduced with influent ions concentration and volumetric flow rate. Established model Bohart-Adams and Hutchins equations were used for calculation of mass transfer zone which came out to be 51 mm. An adsorption capacity (q_m) of 4.5 mg/g for arsenite ions was achieved at optimum parameter values of 60 mm of bed depth, 20 mL/min volumetric flow rate, and 50 mg/L of influent ions concentration. The adsorption bed parameters were also evaluated using Hutchins and Michaels equations. The column study proved rice husk to be a potential adsorbent for the adsorption of arsenite.

Research Progress of a Composite Metal Oxide Catalyst for VOC Degradation

Volatile organic compounds (VOCs) are atmospheric pollutants that have been of concern for researchers in recent years because they are toxic, difficult to remove, and widely sourced and easily cause damage to the environment and human body. Most scholars use low-temperature plasma biological treatment, catalytic oxidation, adsorption, condensation, and recovery techniques to treat then effectively. Among them, catalytic oxidation technology has the advantages of a high catalytic efficiency, low energy consumption, high safety factor, high treatment efficiency, and less secondary pollution; it is currently widely used for VOC degradation technology. In this paper, the catalytic oxidation technology for the degradation of multiple types of VOCs as well as the development of a single metal oxide catalyst have been briefly introduced. We also focus on the research progress of composite metal oxide catalysts for the removal of VOCs by comparing and analyzing the metal component ratio, preparation method, and types of precursors and the catalysts' influence on the catalytic performance. In addition, the reason for catalyst deactivation and a correlation between the chemical state of the catalyst and the electron distribution are discussed. Development of a composite metal oxide catalyst for the catalytic oxidation of VOCs has been proposed.

Mechanistic insights into ball milling enhanced montmorillonite modification with tetramethylammonium for adsorption of gaseous toluene

Montmorillonite is widely used for pollutants adsorption due to its porous structure and low price. However, the low specific surface area and small porosity limit its application in gas adsorption field. In this study, montmorillonite was organically modified using a facile dry ball milling method by tetramethylammonium bromide. The adsorption behaviour of toluene as a model VOC compound on organic montmorillonite was systematically investigated through adsorption breakthrough curves, adsorption kinetics and isotherms. After modification by ball milling, the specific surface area of ball milling with tetramethylammonium bromide for montmorillonite modification (BMTMt) was increased from 20.6 m²/g to 186.4 m²/g, and the microporosity proportion was up to 47%. Dynamic adsorption experiments showed that the best performance of BMTMt for toluene (55.9 mg/g) was 6 times higher than that of original montmorillonite (8.8 mg/g). Compared with the water bath preparation method, ball milling method promoted the intercalation of tetramethylammonium bromide into the layers of montmorillonite, resulting in a higher proportion of micropores. Density functional theory calculations indicated that the interaction between tetramethylammonium bromide and montmorillonite was mainly electrostatic forces, and the enhanced adsorption performance for toluene was mainly through microporous filling. BMTMt was proved to be a promising adsorbent for VOCs removal.

Adsorption/desorption characteristics of low-concentration semi-volatile organic compounds in vapor phase on activated carbon

The adsorption/desorption behaviors of semi-volatile organic compounds (SVOCs: 1,2,3,4-tetrachlorobenzene (TCB) and phenol) in vapor phase by activated carbon (AC) were investigated by the experiments and density functional theory calculation. Investigations showed that at 100-160 °C, the adsorption capacities of TCB and phenol on AC were in the range of 176.6-342.0 mg/g and 24.0-66.4 mg/g, respectively. Increasing the temperature inhibited the SVOCs adsorption. TCB tended to be adsorbed on AC surface by monolayer, whereas the phenol was multilayer adsorption. The stronger interaction between SVOCs and active sites resulted in a higher desorption temperature (TCB: 255-689 °C; phenol: 200-369 °C). The SVOCs adsorption on AC was fitted well by the pseudo-first-order kinetic model, their lower concentration and larger molecular structure influenced the AC external mass transfer and intraparticle diffusion. TCB and phenol were adsorbed on graphite layer by a parallel manner, their highest adsorption energies were -75.59 kJ/mol and -55.00 kJ/mol, respectively. Oxygen-containing groups altered the charge distribution of the atoms at the edge of the graphite layer, which improved the SVOCs adsorption through enhancement of electrostatic interactions and formation of hydrogen bonds. The carboxyl and lactone groups played a critical role in improving the TCB adsorption capacity, while the carboxyl was important for phenol adsorption.

Antibiotic Removal from the Aquatic Environment with Activated Carbon Produced from Pumpkin Seeds

Antibiotics are among the most critical environmental pollutant drug groups. Adsorption is one of the methods used to eliminate these pollutants. In this study, activated carbon was produced from pumpkin seed shells and subsequently modified with KOH. The adsorbent obtained through this procedure was used to remove ciprofloxacin from aqueous systems. Fourier Transform-Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), elemental, X-ray Photoelectron Spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and Zeta analyses were used to characterize the adsorbent. The surface area, in particular, was found to be a very remarkable value of 2730 m²/g. The conditions of the adsorption experiments were optimized based on interaction time, adsorbent amount, pH and temperature. Over 99% success was achieved in removal operations carried out under the most optimal conditions, with an absorption capacity of 884.9 mg·g⁻¹. In addition, the Langmuir isotherm was determined to be the most suitable model for the adsorption interaction.

Preparation and characterization of activated carbon from hydrochar by hydrothermal carbonization of chickpea stem: an application in methylene blue removal by RSM optimization

Herein, mesoporous activated carbon (AC) was prepared through potassium hydroxide (KOH) activation of hydrochar derived from the hydrothermal carbonization (HTC) of chickpea stem (CS), and successfully applied to remove methylene blue (MB) dye from aqueous solutions in a batch system. The HTC-CSAC was prepared depending on different impregnation ratios (hydrochar:KOH, 50-150%), impregnation times (12-48 h), activation temperatures (400-600°C) and activation times (30-60 min). To define HTC-CSAC, various analytical techniques such as iodine adsorption number (IAN), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) were used. In the removal process of MB by the best HTC-CSAC with a high IAN of 887 mg g^-1 obtained under conditions including impregnation ratio of 70%, activation time of 45 min, activation temperature of 600°C and impregnation time of 24 h, the effects of adsorption parameters such as pH factor (2-10), adsorbent dosage (50-100 mg), initial MB concentration (40-80 mg/L) and contact time (90-180 min) were studied. Besides, a detailed evaluation of the adsorption mechanism for the removal of MB by HTC-CSAC was performed. The Langmuir model indicated the best isotherm data correlation, with a maximum monolayer adsorption capacity (Q_max) of 96.15 mg g^-1. The adsorption isotherm findings demonstrated that the MB removal process is feasible, and that this process takes place through the physical interaction mechanism. Additionally, the HTC-CSAC adsorbent exhibited a high regeneration and reuse performance in MB removal. After five consecutive adsorption-desorption cycles, HTC-CSAC maintained the reuse efficiency of 77.86%. As a result, the prepared HTC-CSAC with a high BET surface area of 455 m² g^-1 and an average pore diameter of 105 Å could be recommended as a promising and reusable adsorbent in the treatment of synthetic dyes in wastewaters.