Adsorption Capacity For Organic Compounds Research Articles

Application of machine learning in predicting the adsorption capacity of organic compounds onto biochar and resin

Detailed prediction of the adsorption amounts of organic pollutants in water is essential to the clean development and management of water resources. In this study, Kriging and polyparameter linear free energy relationship model are coupled to predict adsorption capacity of organic pollutants by biochar and resin. It's based on 1750 adsorption experimental data sets which contains 73 organic compounds on 50 biochars and 30 polymer resins. The Kriging-LFER model shows better accuracy and predictive performance for adsorption (R2 are 0.940 and 0.976) than the published NN-LFER model (R2 are 0.870 and 0.880). Local sensitivity analysis method is adopted to evaluate the influence of each variable on the adsorption coefficient of resin and find out that top sensitive parameters are V and log Ce, to guide parameter optimization. Data's uncertainty analysis is presented by Monte Carlo method. It predicts that the adsorption coefficient will range from 0.062 to 0.189 under the 95% confidence interval. The Kriging-LFER model provides great significance for understanding the importance of various parameters, reducing the number of experiments, adjusting the direction of experimental improvement, and evaluating the fate of organic pollutants in the environment.

TiO2 nanosheet/NiO nanorod/poly(dopamine) ternary hybrids towards efficient visible light photocatalysis

Herein, TiO2 nanosheet/NiO nanorod/poly(dopamine) (PDA) photocatalysts with PDA coated on surfaces of TiO2/NiO p-n heterojunctions have been developed. The PDA coating amount in TiO2/NiO/PDA hybrids has been tuned to revel the optimal constituent of hybrids for photocatalysis. The photocatalytic results reveal the improved photocatalytic activity of TiO2/NiO/PDA hybrids as compared with TiO2/NiO hybrids involved in methyl blue (MB) and phenol decomposition, as well as hydrogen generation under visible light irradiation. The optimized TiO2/NiO/PDA hybrids with the best photocatalytic activity has also been revealed. The introduction of PDA in TiO2/NiO hybrids plays an important role in enhancement of photocatalytic activity: 1) high adsorption capacity for organic compounds; 2) high separation properties of electron and hole, as well as high harvesting of the visible light; 3) a good hole conductor.

Synthesis of silver nanoparticles with remediative potential using discarded yerba mate: An eco-friendly approach

Silver nanoparticles (Ag-NPs) applications are strongly dependent on their stability against aggregation. In the present work, environmentally-friendly Ag-NPs were synthesized by a simple and efficient procedure, using discarded yerba mate extract (DYME) as a reducing and capping agent. The Ag-NPs thus obtained (DYME-Ag-NPs) were spectroscopically characterized by ultraviolet-visible (UV-Vis) spectrophotometry, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). These NPs were also evaluated for their adsorbent capacity through the adsorption isotherms using three organic substances, as well as for their antimicrobial properties on two bacterial strains. DYME-Ag-NPs were mostly spherical, monodispersed, with an average size of 24.07 ± 3.00 nm (DLS), and proved to be stable for 70 days without any noticeable aggregation or change in size under room temperature (20-25 °C). The adsorption efficiency for crystal violet, methylene blue, and safranin was calculated. The adsorption data derived from the isotherm analysis fitted a Langmuir isotherm model, revealing the presence of homogeneous adsorption sites, probably coming from the DYME. Using the diffusion method, we obtained a 99.99 % growth inhibition for Escherichia coli by using 10 μg/mL of Ag-NPs. However, no inhibition of Enterococcus faecalis growth was observed. We conclude that yerba mate waste may be used to obtain improved Ag-NPs highly stable and with a high surface area, which results in an enhanced adsorption capacity for organic compounds.

Adsorption Capacity of Organic Compounds Using Activated Carbons in Zinc Electrowinning

The influence of adsorbate (D2EPHA and kerosene) on the process of zinc electrowinning from sulfuric acid electrolytes was analyzed. The main objective was to critically compare three factors: (1) Three types of activated carbon (AC); (2) adsorption temperatures and contact time; and (3) zinc recovery efficiency. The results showed that organic components reduced the efficiency of zinc recovery. Moreover, wood-based ACs had a higher adsorption capacity than coal- and coconut-based ACs. To maintain a removal efficiency of 99% or more, wood-based ACs should constitute at least 60% of the adsorbate. The temperature of adsorption did not affect the removal efficiency. Additionally, the feeding rate of adsorbate in the solvent was inversely proportional to the removal efficiency. A feeding rate of the liquid pump of over 3 mL/min rapidly increased the delta pressure. For the same contact time, 99% of adsorbate removal occurred at 1 mL/min compared to approximately 97% at 0.5 mL/min. In the presence of 100 mg/L zinc, with increasing adsorbate from 0–5%, the recovery efficiency of zinc decreased from 100% to 0% and the energy consumption increased from 0.0017–0.003 kwh/kg zinc. Considering the energy consumption and zinc deposit mass, 0.1% of the adsorbate is recommended for zinc electrowinning.

Preparation of amphiphilic TiO2 Janus particles with highly enhanced photocatalytic activity

Stearic-acid-modified TiO2 (STA-TiO2) particles were prepared via the impregnation approach and used as a precursor for preparing TiO2 Janus particles. The morphology, structure, and properties of the TiO2 Janus particles were characterized using Fourier-transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, thermogravimetric analysis, fluorescence microscopy, high-resolution transmission electron microscopy, contact angle analysis, dynamic light scattering, biological microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy measurements. The results show that TiO2 Janus particles can be successfully prepared via toposelective surface modification. STA grafted on the surface of TiO2 enhances its hydrophobicity, promotes charge separation, and improves its adsorption capacity for organic compounds. The TiO2 Janus particles strongly adsorb on an oil-water interface to form a stable Pickering emulsion. The degradation rates of high-concentration kerosene and nitrobenzene wastewaters when the photocatalyst is pure TiO2, STA-TiO2, or TiO2 Janus particles are discussed and compared. The degradation rates were determined using an ultraviolet-visible spectrophotometer. It was found that the Pickering emulsion stabilized by the TiO2 Janus particles exhibited the best photocatalytic performance; these Janus particles show promising potential for catalytic application.

Adsorption and correlations of selected aromatic compounds on a KOH-activated carbon with large surface area

Knowledge of adsorption mechanism and behavior of organic compounds by KOH-activated carbons (KOH-ACs) from wastewater is crucial to its environmental application in wastewater treatment as adsorbent. A superior adsorbent, KOH-activated carbon (KOH-AC), with large surface area (3143m2/g), total pore volume of 2.03cm3/g, relatively low micropore fraction of 53.2%, and having adsorption capacities of organic compounds up to >1000mg/g, was prepared. It is an adsorbent significantly different with common ACs because the molecular sieving effect, widely observed for common ACs, is insignificant for KOH-AC. This difference could be attributed to the lower micropore fraction of KOH-AC than common ACs. A negative relationship of adsorption capacity of 25 aromatic compounds (including phenols, anilines, nitrobenzenes and polycyclic aromatic hydrocarbons) with chemical melting point was observed, suggesting that adsorption is dependent on the packing efficiency and stacking density of molecules on KOH-AC. A linear solvation energy relationships of adsorption affinity of 25 aromatic compounds with solute solvatochromic parameters was also observed, that can be used to quantify the contributions of π-π interaction, hydrogen-bonding interaction and hydrophobic effect to adsorption on KOH-AC. Combined with the reported results of adsorption of organic compounds on carbon nanotubes and biochars, it was also observed that external surface area of adsorbents is controlling the packing efficiency and stacking density of molecules on adsorbents and thus affecting adsorption capacity of organic compounds. Moreover, micropore surface area and the fraction of micropores are the adsorbent properties mainly affecting adsorption affinity of organic compounds. The observations and the developed correlations in this study would be helpful in the application of KOH-AC as superior adsorbent by enhancing the understanding of adsorption mechanisms of organic compounds on KOH-AC and by giving a method to predict the adsorption behaviors.

Effect of carbon precursors and pore expanding reagent on ordered mesoporous carbon for resorcinol removal

Ordered mesoporous carbons (OMCs) with well-controlled pore structures have recently attracted much attention because of their potential applications as adsorbents. The specific surface area and surface chemistry of OMCs have been considered as two of the most important factors that affect their adsorption capacity for organic compounds. The objectives of this study were to compare the adsorption capacities of OMCs for resorcinol removal by using different carbon precursors (acrylic acid, sucrose and glucose) and optimizing the pore structure by using boric acid as the pore expanding reagent via hard template method. Among the three carbon precursors, sucrose demonstrated the highest adsorption performance for resorcinol removal and hence, was selected as the carbon precursor to evaluate the effect of pore expanding reagent. The tailored pore sizes ranging from 4.7nm to 11.0nm were obtained by varying the ratio of boric acid to sucrose from 0 to 4. It was observed that OMC with boric acid to sucrose ratio of 2 yielded the highest adsorption capacity (64mg/g). OMC structure was characterized by small angle X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), surface area and porosimetry analyzer, Fourier Transfer Infrared spectroscopy (FT-IR), elemental analysis, Boehm titration and adsorption study. The results suggested that the effect of specific surface area of OMC on resorcinol removal was more significant than that of the surface chemical properties.

Prediction of the adsorption capacities for four typical organic pollutants on activated carbons in natural waters

A new model is developed to predict the competitive adsorption isotherms of atrazine, methyl tertiary butyl ether (MTBE), 2-methylisoborneol (2-MIB) and 2,4,6-trichlorophenol onto activated carbons (ACs) in natural water. Based on the Polanyi-Dubinin (PD) equation, with the limiting pore volume of adsorbent estimated from the pore size distribution data, and the Ideal adsorbed solution theory - equivalent background compound (IAST-EBC) model approximation, the model takes into account both the properties of ACs and the impact of natural organic matters in water. Only one set of isotherm in deionized water and one set in natural water are needed to obtain the parameters for the prediction of adsorption isotherms onto different ACs in natural water. The model was employed for the predictions of adsorption capacities for atrazine, MTBE, 2-MIB and 2,4,6-trichlorophenol onto 14 ACs in 22 synthetic and natural waters reported in 9 references, with errors between 14.9% and 44.5% SDEV only. The results suggest that in the proposed PD-IAST-EBC approach, prediction of adsorption capacity for organic compounds onto different ACs in the same natural water is feasible, if the ACs are thermally activated with known pore size information. The model may provide a simple approach for the prediction of adsorption of organic compounds in natural water, and thus greatly reduces the effort required for water utilities when change of AC is needed.

Sorption of Light Organic Compounds onto Silica Mesoporous and Modified Zeolites

The adsorption of acetone, 1-propanol and carbon dioxide was tested with mesoporous silica materials made from non ionic surfactants with a long hydrophilic chain. The synthesis carried out in strongly acidic medium use tetraethylorthosilicate and zeolites as silica sources. X-ray powder diffraction (XRD), nitrogen adsorption–desorption analysis and scanning electron microscopy (SEM) were applied to characterize the prepared samples. Acetone, 1-propanol and CO 2 adsorption at 298K was evaluated by a volumetric method, and the sorption results indicate a high adsorption capacity of organic compounds, depending essentially on the porous texture of the materials. An adsorption kinetic model was proposed to describe the adsorption of VOCs over template-free mesoporous siliceous materials. A good agreement with experimental data was found.

WO3–TiO2 based catalysts for the simulated solar radiation assisted photocatalytic ozonation of emerging contaminants in a municipal wastewater treatment plant effluent

This work is focused on the use of TiO2–WO3 photocatalysts for the removal of a mixture of emerging contaminants through photocatalytic ozonation using simulated solar light as radiation source. Own-made TiO2–WO3 catalysts with WO3 content around 4wt% were synthesized using P25 and titanate nanotubes as TiO2 starting materials. Photocatalysts were thoroughly characterized by means of ICP–OES, N2 adsorption–desorption isotherms, XRD, TEM, Raman, XPS and DR–UV–Vis spectroscopy. Photocatalytic ozonation using WO3 based titanate nanotubes composite gave place to complete removal of emerging contaminants (caffeine, metoprolol and ibuprofen in a Municipal Wastewater Treatment Plant effluent aqueous matrix) in less than 40min with TOC removal up to 64% after 2h. The highest catalytic activity of this material in the reaction under study compared to bare TiO2 is due to several effects such as higher activity under visible light radiation joined to an increase in adsorption capacity of organic compounds and catalytic ozonation ability caused by the presence of WO3.

Charcoal Application to Arable Soil: Effects on CO2 Emissions

Activated carbon and commercial household charcoal were added to soil in a 36-day incubation study at 20 °C measuring carbon dioxide evolution. The black carbon materials were found to decompose slowly, releasing between 1.4% and 0.8% of their carbon content per year, respectively. The main experiment tested whether the black carbon additions to soil (2% and 4% by mass) affected decomposition of selected substrates in soil, both respiration dynamics and total respiration. The results indicated that the black carbon materials tested had no effect on total respiration from added glucose. However, decomposition rates of amylose, xylan, casein, and ryegrass were reduced in soil with addition of activated carbon but were not significantly affected by household charcoal. A larger surface area of activated carbon than that of household charcoal, and thus a greater adsorption capacity for organic compounds and exo-enzymes required to break down water-insoluble substrates, may explain the results.

Influence of Surface Oxidation of Multiwalled Carbon Nanotubes on the Adsorption Affinity and Capacity of Polar and Nonpolar Organic Compounds in Aqueous Phase

Adsorption of organic contaminants on carbon nanotubes (CNTs) is a critical behavior in the environmental application of CNTs as sorbents and in the environmental risk assessment of both organic contaminants and CNTs. Oxidation of CNTs may introduce oxygen-containing groups on CNTs' surface and then alter the adsorption of organic contaminants. In this study, adsorption of polar and nonpolar organic compounds on four multiwalled carbon nanotubes (MWCNTs) containing varied amounts of surface oxygen-containing groups were investigated to examine the influence of CNTs' surface oxidation on adsorption. We observed that surface oxidation of MWCNTs reduced the surface area-normalized adsorption capacity of organic compounds significantly because of the competition of water molecules but did not alter the adsorption affinity. The interactions (i.e., hydrophobic effect, π-π bonds, and hydrogen bonds) and the interaction strength for adsorption of organic molecules on MWCNTs could not be altered by the surface oxidation of MWCNTs and thus were responsible for the unaltered adsorption affinity. In addition, the decrease of surface area-normalized adsorption capacity of the organic compound with more polarity and higher adsorption affinity by surface oxidation was less because of the heterogeneous nature of hydrophilic sites of MWCNTs' surface.

Effects of Powdered Activated Carbon Pore Size Distribution on the Competitive Adsorption of Aqueous Atrazine and Natural Organic Matter

The pore size distribution (PSD) of adsorbents has been found to be an important factor that affects adsorption capacity for organic compounds; consequently, it should influence competitive adsorption in multisolute systems. This research was conducted to show howthe PSD of activated carbon affects the competition between natural organic matter (NOM) and the trace organic contaminant atrazine, with a primary emphasis on quantifying the pore blocking mechanism of NOM competition. Isotherm tests were performed for both atrazine and NOM from a groundwater on five powdered activated carbons (PACs) with widely different PSDs. The capacity for NOM correlated best with the surface area of pores in the diameter range of 15-50 A, although some NOM also adsorbed in the smaller pores as evidenced by a reduction in capacity for atrazine when NOM was present. Kinetic tests for atrazine on PACs with various levels of preadsorbed NOM showed that the magnitude of the pore blockage effect by NOM was lower for PACs with higher surface area of pores with diameter in the range of 15-50 A. Therefore increasing pores in the size range where NOM adsorb can reduce the extent of the pore blockage competitive effect on the target compound atrazine. The effect of PSD was further studied with a flow-through PAC-membrane hybrid watertreatment system, in which experimental results successfully verified model simulations by the COMPSORB model.

<b>HYPERCROSSLINKED SORBENTS AND THEIR ADSORPTION PROPERTIES</b>

Hypercrosslinked sorbents which have excellent adsorption capacities for organic compounds were prepared by cross-linking the polypropylene grafted styrene-divinylbenzene fiber according to the Friedel-Crafts reaction. As crosslinking agents, we have used monochloromethylether and bis-chloromethylated derivatives of benzene or biphenyl. We have performed detailed investigations of the preparation and the optimal synthesis conditions of hypercrosslinked sorbents were obtained. Compared with the initial fiber, hypercrosslinked fibers were remarkable materials exhibiting high specific surface area and exceptional adsorption properties for organic compounds. The adsorption capacities on the hypercrosslinked sorbents were related with the size of cross-linking agents, which increased by about 8 to 10 fold. KEY WORDS: Hypercrosslinked sorbents, Fibers, Surfaces; Adsorption; Organic compounds Bull. Chem. Soc. Ethiop. 2007, 21(3), 397-403.

Liquid-Phase Adsorption of Organic Compounds by Granular Activated Carbon and Activated Carbon Fibers

Liquid-phase adsorption of organic compounds by granular activated carbon (GAC) and activated carbon fibers (ACFs) is investigated. Acetone, isopropyl alcohol (IPA), phenol, and tetrahydrofuran (THF) were employed as the model compounds for the present study. It is observed from the experimental results that adsorption of organic compounds by GAC and ACF is influenced by the BET (Brunauer-Emmett-Teller) surface area of adsorbent and the molecular weight, polarity, and solubility of the adsorbate. The adsorption characteristics of GAC and ACFs were found to differ rather significantly. In terms of the adsorption capacity of organic compounds, the time to reach equilibrium adsorption, and the time for complete desorption, ACFs have been observed to be considerably better than GAC. For the organic compounds tested here, the GAC adsorptions were shown to be represented well by the Langmuir isotherm while the ACF adsorption could be adequately described by the Langmuir or the Freundlich isotherm. Column adsorption tests indicated that the exhausted ACFs can be effectively regenerated by static in situ thermal desorption at 150 C, but the same regeneration conditions do not do as well for the exhausted GAC.