Study on Adsorption and Aggregation in the Mixed System of Polyacrylamide, Cu(II) Ions and Innovative Carbon-Silica Composite

Adsorption Capacity of Carbon-Silica Composites Towards Diclofenac in Poly(acrylic acid) Containing Systems: A Crucial Study on Common Wastewater Contaminants

Diclofenac is one of the most popular over-the-counter non-steroidal anti-inflammatory drug and poly(acrylic acid) is a frequently used as thickener, filler or stabilizer. For these reasons, they are common organic contaminants in raw wastewater. The purpose of the presented studies was to compare the adsorption capacity of three carbon-silica composites - metal-free C/SiO2, iron-enriched C/Fe/SiO2 and manganese-enriched C/Mn/SiO2 towards diclofenac. The studies were carried out in single, and mixed systems in the presence of poly(acrylic acid) polymer. Adsorption, desorption and kinetics of the adsorption process were investigated. The concentration of diclofenac in the supernatants was determined using high-performance liquid chromatography. The solids were also characterized with an ASAP apparatus using low-temperature nitrogen desorption adsorption isotherms at liquid nitrogen temperature. In addition, potentiometric titrations and electrophoretic mobility measurements, as well as stability tests of the studied suspensions were carried out. The most efficient composite among investigated ones proved to be C/Fe/SiO2 removing diclofenac at the level of 46.68 mg/g for its initial concentration of 90 ppm. The results obtained clearly demonstrated that the carbon-silica composites are effective in separation of drugs from aqueous solutions and can be successfully used in the future for the removal of organic pollutants from water environment.

Synthesis and characterization of iron oxide-commercial activated carbon nanocomposite for removal of hexavalent chromium (Cr6+) ions and Mordant Violet 40 (MV40) dye

Iron Oxide-commercial activated carbon nanocomposite (CAC-IO) was prepared from commercial activated carbon (CAC) by the co-precipitation method, and the resulting nanocomposite was used as an adsorbent to remove hexavalent chromium (Cr6+) ions and Mordant Violet 40 (MV40) dye from wastewater. The produced materials (CAC, CAC after oxidation, and CAC-IO) were comparatively characterized using FTIR, BET, SEM, EDX TEM, VSM, and XRD techniques. The adsorption mechanism of Cr6+ ions and MV40 dye on CAC-IO was examined using Langmuir and Freundlich isotherm models.. Different models were applied to know the adsorption mechanism and it was obtained that Pseudo-second order fits the experimental data better. This means that the adsorption of the adsorbate on the nanocomposite was chemisorption. The maximum removal percent of Cr6+ ions by CAC-IO nanocomposite was 98.6% determined as 2 g L-1 adsorbent concentration, 100 mg L-1 initial pollutant concentration, solution pH = 1.6, the contact time was 3 h and the temperature was room temperature. The maximum removal percentage of Mordant Violet 40 dye (C.I. 14,745) from its solutions by CAC-IO nanocomposite was 99.92% in 100 mg L-1 of initial dye concentrations, 1.0 g L-1 of adsorbent concentration, solution pH = 2.07, the contact time was 3 h. The MV40 dye adsorption on CAC-IO was the most fitted to the Freundlich isotherm model. The maximum adsorption capacity was calculated according to the Langmuir model as 833.3 mg g-1 at 2 g L-1 of adsorbent concentration and 400 mg L-1 of initial MV40 dye concentration. The Cr6+ ions adsorption on CAC-IO was more fitted to the Freundlich model with Qmax, equal to 312.50 mg g-1 at 1 g L-1 adsorbent concentration and 400 mg L-1 of Cr6+ ions initial concentrations.

Novel carbon-based composites enriched with Fe and Mn as effective and eco-friendly adsorbents of heavy metals in multicomponent solutions

With increasing demand for adsorbents highly effective in pollutant removal, carbon-based porous materials are becoming more and more popular. In this work, a new approach to the synthesis of such solids using an environmentally friendly, two-step preparation method is presented. A series of hybrid porous silica-containing carbon composites was synthesized, namely: metal free (C/SiO2), enriched with manganese (C/Mn/SiO2), as well as iron (C/Fe/SiO2). The effect of additives on the structure and morphology of the composites was evaluated using X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption and scanning electron microscope (SEM). The as-synthesized carbons were used as effective adsorbents for the simultaneous removal of heavy metals, including lead (Pb(II)) and zinc (Zn(II)) ions. In particular, it was determined that C/Mn/SiO2 sample demonstrated the highest adsorption capacity towards Pb(II) and Zn(II) ions. It was equal to 211.60 mg/g for Pb(II) and 74.95 mg/g for Zn(II). Zeta potential and surface charge density of the solids, with and without metals, were investigated to determine electrical double layer structure, whereas stability studies and aggregate size measurements were performed to estimate solid aggregation under selected conditions. It was established that solids with adsorbed metals formed suspensions with lower stability than those without ions. This, in turn, facilitates their separation from aqueous solutions.

Adsorption properties and mechanisms of methylene blue and tetracycline by nano-silica biochar composites activated by KOH

Dyestuff wastewater and pharmaceutical wastewater have become typical representatives of water pollution. In this study, a novel nano-silica-biochar composite (NSBC) was synthesized based on corn straw as raw material, by a combination of ball milling, pyrolysis and KOH activation. The modified biochar with rough surface had higher specific surface area (117.67-132.82 m²/g), developed pore structure (0.12-0.15 cm³/g) and abundant surface functional groups (-OH, -COOH, Si-O and aromatic CC were dominated). These provided abundant active sites for the adsorption of pollutants. The adsorption capacities of NSBC for Methylene Blue (MB) and Tetracycline (TC) were both higher than that of other similar products, the maximum adsorption capacity of Langmuir were 247.22 and 86.95 mg/g, respectively. After five adsorption-desorption cycle experiments, the adsorption capacities of NSBC for both were still excellent, reaching 99.30 and 19.87 mg/g, respectively. Due to the different structure and molecular size of MB and TC, the adsorption capacities of NSBC were significantly different, especially the influence of solution pH value. The adsorption mechanisms were comprehensively discussed by FTIR and XPS of the samples before and after adsorption, and combining experimental results of BET and simultaneously, which were manifested as monolayer chemisorption, specifically surface complexation, hydrogen bonding, n-π/π-π conjugation, electrostatic interaction and pore filling.

Management of hazardous fly-ash energy waste in the adsorptive removal of diclofenac by the use of synthetic zeolitic materials

Zeolite-carbon composites (Na-P1(C), Na-X(C)) and pure zeolites (Na-P1, Na-X) were synthesized from hazardous high-carbon fly ash waste (HC FA) via hydrothermal reaction with sodium hydroxide (NaOH). These solids were applied in the removal of diclofenac (DCF) from aqueous solution, with and without poly(acrylic acid) (PAA). The experiments included adsorption-desorption measurements, as well as electrokinetic and stability analyses. The obtained results showed that HC FA and Na-P1(C) had the greatest adsorption capacity towards DCF, i.e., 26.51 and 21.19 mg/g, respectively. PAA caused considerable decrease in the DCF adsorption due to the competition of both adsorbates of anionic character for active sites. For example, the adsorbed amount of DCF on Na-P1 without PAA was 14.11 mg/g, whereas the one measured with PAA was 5.08 mg/g. Most of prepared solids were effectively regenerated by the use of NaOH. Desorption degree reached even 73.65% in the single systems (with one adsorbate) and 97.24% in the mixed ones (with two adsorbates). Zeolitic materials formed suspensions of rather low stability, which underwent further deterioration in the organic molecules presence. All the results obtained in this study indicated that HC FA can be successfully managed in the removal of organic substances.

C.I. Basic Red 46 Removal from Sewage by Carbon and Silica Based Composite: Equilibrium, Kinetic and Electrokinetic Studies

The worldwide production of colored products and intermediates is increasing year on year. The consequence of this is an increase in the number of liquid effluents containing toxic dyes entering the aquatic environment. Therefore, it is extremely important to dispose of them. One of the techniques for the elimination of environmentally harmful dyes is adsorption. The main purpose of this study was to explore the possibility of using a carbon and silica (C/SiO₂)-based composite for the removal of the azo dye C.I. Basic Red 46 (BR46). The adsorption capacity of C/SiO₂ was found to be temperature dependent and increased from 41.90 mg/g to 176.10 mg/g with a temperature rise from 293 K to 333 K in accordance with the endothermic process. The Langmuir isotherm model seems to be the better one for the description of experimental data rather than Freundlich or Dubinin–Radushkevich. The free energy (ΔG^o) confirmed the spontaneous nature of BR46 adsorption by C/SiO₂. Kinetic parameters revealed that BR46 uptake followed the pseudo-second-order equation; however, the external diffusion plays a significant role. Surfactants of cationic, anionic and non-ionic type influenced BR46 retention by C/SiO₂. The electrokinetic results (solid surface charge density and zeta potential) indicated that the adsorption of cationic dye and surfactant influences the structure of the electrical double layer formed at the solid–liquid interface.

Removal of Toxic Copper Ion from Aqueous Media by Adsorption on Fly Ash-Derived Zeolites: Kinetic and Equilibrium Studies

This study investigated the adsorption capacity of one material based on the treatment of fly ash with sodium hydroxide as a novel adsorbent for toxic Cu2+ ion removal from aqueous media. The adsorbent was obtained through direct activation of fly ash with 2M NaOH at 90 °C and 6 h of contact time. The adsorbent was characterized by recognized techniques for solid samples. The influence of adsorption parameters such as adsorbent dose, copper initial concentration and contact time was analyzed in order to establish the best adsorption conditions. The results revealed that the Langmuir model fitted with the copper adsorption data. The maximum copper adsorption capacity was 53.5 mg/g. The adsorption process followed the pseudo-second-order kinetic model. The results indicated that the mechanism of adsorption was chemisorption. The results also showed the copper ion removal efficiencies of the synthesized adsorbents. The proposed procedure is an innovative and economical method, which can be used for toxicity reduction by capitalizing on abundant solid waste and treatment wastewater.

Simultaneous adsorption of Cu(II) ions and poly(acrylic acid) on the hybrid carbon-mineral nanocomposites with metallic elements

In order to propose a novel, effective adsorbent of Cu(II) ions, hybrid carbon-mineral nanocomposites with metallic elements (Mn/Fe in the case of B-6, Mn - B-8) were examined. A combination of mechanochemical and pyrolytic methods was used to obtain these bimodal micro-mesopore systems. First, mechanochemical mixing of phenol-formaldehyde resin and inorganic compounds in a ball mill was carried out. Then, the pyrolysis of the mixture under inert atmosphere at 800 °C was performed. The obtained composites were characterized using nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, electron microscopes as well as X-ray diffraction, X-ray fluorescence and X-ray photoelectron spectroscopy. Adsorption, electrokinetic and aggregation studies were also performed, in the absence and presence of poly(acrylic acid) (PAA) - a macromolecular compound commonly used in industry and agriculture, which may be present in wastewater together with copper(II) ions. Under examined conditions (at pH 5 and 6), Cu(II) adsorbed amount was higher on the B-8 surface than on the B-6 one. At pH 6 for the initial Cu(II) concentration 100 ppm, 51.74% of the ions was adsorbed on B-8% and 46.68% - on B-6. Heavy metal adsorption contributes to stronger aggregation of nanocomposite particles. Thus, the presented bimodal solids, especially that containing Mn (called B-8), can be considered as adsorbents in heavy metal removal from aqueous solutions.

Carbon-Silica Composite as Adsorbent for Removal of Hazardous C.I. Basic Yellow 2 and C.I. Basic Blue 3 Dyes

Treatment of wastewaters containing hazardous substances such as dyes from the textile, paper, plastic and food industries is of great importance. Efficient technique for the removal of highly toxic organic dyes is adsorption. In this paper, adsorptive properties of the carbon-silica composite (C/SiO2) were evaluated for the cationic dyes C.I. Basic Blue 3 (BB3) and C.I. Basic Yellow 2 (BY2). The sorption capacities were determined as a function of temperature (924.6-1295.9 mg/g for BB3 and 716.3-733.2 mg/g for BY2 at 20-60 °C) using the batch method, and the Langmuir, Freundlich and Temkin isotherm models were applied for the equilibrium data evaluation using linear and non-linear regression. The rate of dye adsorption from the 100 mg/L solution was very fast, after 5 min. of phase contact time 98% of BB3 and 86% of BY2 was removed by C/SiO2. Presence of the anionic (SDS), cationic (CTAB) and non-ionic (Triton X-100) surfactants in the amount of 0.25 g/L caused decrease in BB3 and BY2 uptake. The electrokinetic studies, including determination of the solid surface charge density and zeta potential of the composite suspensions in single and mixed adsorbate systems, were also performed. It was shown that presence of adsorption layers changes the structure of the electrical double layer formed on the solid surface, based on the evidence of changes in ionic composition of both surface layer and the slipping plane area. The greatest differences between suspension with and without adsorbates was obtained in the mixed dye + SDS systems; the main reason for this is the formation of dye-surfactant complexes in the solution and their adsorption at the interface.

Carboxin and Diuron Adsorption Mechanism on Sunflower Husks Biochar and Goethite in the Single/Mixed Pesticide Solutions

The study focused on the adsorption mechanism of two selected pesticides: carboxin and diuron, on goethite and biochar, which were treated as potential compounds of mixed adsorbent. The authors also prepared a simple mixture of goethite and biochar and performed adsorption measurements on this material. The adsorbents were characterized by several methods, inter alia, nitrogen adsorption/desorption, Boehm titration, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The adsorption study included kinetics and equilibrium measurements, in the solution containing one or two pesticides simultaneously. The adsorption data were fitted to selected theoretical models (e.g., Langmuir, Freudlich, Redlich-Peterson, pseudo first-order and pseudo second-order equations). Based on the obtained results, it was stated that, among all tested adsorbents, biochar had the highest adsorption capacity relative to both carboxin and diuron. It equaled 0.64 and 0.52 mg/g, respectively. Experimental data were best fitted to the pseudo second-order and Redlich-Peterson models. In the mixed systems, the adsorption levels observed on biochar, goethite and their mixture were higher for diuron and lower for carboxin, compared to those noted in the single solutions. The presented results may enable the development of new mixed adsorbent for remediation of soils polluted with pesticides.

Preparation of RGO and Anionic Polyacrylamide Composites for Removal of Pb(II) in Aqueous Solution

Graphene oxide (GO) have been reported as adsorbent materials, because its surface contains a large number of oxygen-containing groups, which provide masses of active sites. Nevertheless, it is difficult to separate GO from aqueous solution by conventional means after the end of the adsorption process. Therefore, ethylene diamine-reduced graphene oxide/anionic polyacrylamide (E-RGO/APAM), with a large quantity of adsorption sites and strong flocculation was prepared in this study. The composite E-RGO/APAM was characterized by Fourier transform infrared (FTIR), laser Raman spectrometer (IR), scanning electron microscope (SEM). The obtained results indicated that amino groups were successfully introduced into GO. Particle size test showed that the particle size of E-RGO/APAM is up to three micrometers, which can be separated from the water by conventional means, such as filtration and centrifugation, to avoid secondary pollution. The efficiency of E-RGO/APAM for removing Pb(II) was tested. The results showed that the process of adsorption of Pb(II) by E-RGO/APAM can be fitted by pseudo second order kinetic equation, indicating that the adsorption rate of the adsorbent depends on the chemisorption process, and the theoretical maximum adsorption amount of E-RGO/APAM is 400.8 mg/g. Based on these results, it can be stated that E-RGO/APAM is effective in the removal of Pb(II) from aqueous solutions, and provides a new method for the removal of heavy metal ions from industrial wastewater.