Tailoring the textural properties of an activated carbon for enhancing its adsorption capacity towards diclofenac from aqueous solution

Synthesis, characterization, and application of pristine and clay-templated carbon xerogel microspheres for removing diclofenac and heavy metals from water solution

Organic xerogel microspheres (SX) were synthesized by inverse emulsion sol-gel polymerization and carbonized to obtain carbon xerogel spheres (SXCs). The catalyst was K₂CO₃ or Fe(C₂H₃O₂)₂, and the clay sodium sepiolite (SNa) or exfoliated vermiculite (V_exf) was added during the synthesis. Depending on the catalyst and clays, the SXCs were designated SXC-K, SXC-Fe, V_exf-K, V_exf-Fe, SNa-Fe, and SNa-K. At pH = 7 and T = 25 °C, the SXCs' adsorption capacities towards diclofenac (DCF) in water increased as follows: SXC-K < V_exf-Fe < SXC-Fe < SNa-Fe < SNa-K < V_exf-K and this order is associated with the SXCs' surface area and mesopore volume. The V_exf-K displayed the highest capacity for DCF due to its optimal textural and chemical properties, and the DCF maximum uptake was 560 mg/g at pH = 6 and T = 35 °C. The adsorption capacity towards Cd²⁺ and Pb²⁺ decreased as SX-K > SX-Fe > SXC-K > SXC-Fe, indicating that the non-carbonized materials (SX) presented higher adsorption capacity than the SXCs because the SXs had a higher acidic site content. Adding SNa or V_exf to SXs enhanced the adsorption capacity towards Cd(II), and SNa-SX-K presented an exceptionally high capacity of 182.7 mg/g. This synergistic effect revealed that the Cd²⁺ was adsorbed on the SX-K acidic sites and by cation exchange on the SNa.

Single adsorption of diclofenac and ronidazole from aqueous solution on commercial activated carbons: effect of chemical and textural properties

The importance of the textural and physicochemical characteristics upon the adsorption capacity of the commercial activated carbons (ACs) Coconut, Wood, Merck, Darco, and Norit towards ronidazole (RNZ) and diclofenac (DCF) from water solution was investigated thoroughly in this work. At pH = 7, Coconut AC and Wood AC presented the highest adsorption capacity towards RNZ (444 mg/g) and DCF (405 mg/g). The maximum mass of RNZ adsorbed onto Coconut AC was higher in this study than those outlined previously in other works. Besides, the maximum capacity of Wood AC for adsorbing DCF was comparable to those found for other ACs. The adsorption capacity of all the ACs was increased by surface area and was favored by incrementing the acidic site concentration. The π-π stacking interactions were the predominant adsorption mechanism for the RNZ and DCF adsorption on ACs, and the acidic sites favored the adsorption capacity by activating the π-π stacking. Electrostatic interactions did not influence the adsorption of RNZ on Coconut AC, but electrostatic repulsion decreased that of DCF on Wood AC. The adsorption of DCF on Wood AC was reversible but not that of RNZ on Coconut AC. Besides, the adsorption of RNZ and DCF on the Coconut and Wood ACs was endothermic in the range of 15-25 °C.

Tuning the pore structure of templated mesoporous poly(melamine-co-formaldehyde) particles toward diclofenac removal

The increasing demand and implementation of pharmaceutics poses severe risk to different aquatic species as detectable contaminant in almost every surface water worldwide. Diclofenac (DCF) as one of the most common used analgesics was investigated as contaminant to be removed by adsorption onto nanoporous poly(melamine-co-formaldehyde) (PMF) particles featuring a very high amount of nitrogen functionalities. To achieve a high specific surface area (up to 416 m²/g) and a tunable pore system by hard templating, four different SiO₂ nanoparticles were used as template. Differences in the pore formation and achieved pore structure were elucidated. For the first time, the adsorption of DCF onto PMF was tested. In batch adsorption experiments, impactful adsorption capacities as high as 76 μmol/g were achieved and complete removal at initial concentrations of 2 mg/L DCF. Differences in the connectivity and the micropore structure were decisive for uptake in low concentrations and the achieved adsorption capacity, respectively. As the presented PMF particles can be easily synthesized with the monomers formaldehyde and melamine combined with colloidal silica as sacrificial template and water as green solvent, this material presents a viable adsorbent for the removal of DCF at a larger scale. Our study further indicates a high potential for the removal of other pharmaceuticals.

Dynamic adsorption of diclofenac onto a magnetic nanocomposite in a continuous stirred-tank reactor

In this study, a waste-based magnetic activated carbon (MAC) was used for the first time in a continuous-flow stirred tank reactor (CSTR). The aim was to evaluate the dynamic removal of diclofenac (DCF) from water and wastewater. Firstly, the breakthrough curves corresponding to DCF adsorption from distilled water at different feed flow rates and doses of MAC were determined. After selecting the most favourable conditions, namely 0.18 h L^-1 flow rate and 400 mg L^-1 of MAC, the effect of different aqueous matrices was studied, with the breakthrough curves evidencing a performance decline in wastewater in comparison with distilled water. Finally, the exhausted MAC was magnetically recovered, regenerated by microwave-assisted heating and applied in two subsequent adsorption cycles. The regeneration studies pointed to a decrease of the specific surface area and an improvement of the magnetic retrievability of MAC. After the first regeneration step, just mild effects were observed in the dynamic adsorptive performance of MAC. However, after a second regeneration step, the performance declined ca. 50%. Overall, the results highlight the feasibility of producing waste-based magnetic composites that simultaneously combine high adsorption efficiency under dynamic operation in a CSTR, with easy retrievability and successful one-stage regeneration for further reutilization.

Removal of Diclofenac-Na from aqueous solution onto H3PO4 modified composite clay

Under batch experiment conditions, this work seeks to successfully remove Diclofenac-Na (DCF-Na) from an aqueous solution utilizing a composite sorbent made of Bentonite, Kaolinite clay, and Worm casting (BKW). This study investigated the structural modification of the H3PO4 Modified Clay by X-ray fluorescence and the effect of selected adsorption factors – DCF-Na concentration and modified BKW composite dosage. The concentration equilibrium data was used to study six isotherm models. Freundlich isotherm model better explained the adsorption of DCF-Na onto modified BKW composite with a correlation coefficient close to 1. Kinetics models were examined, and the Elovich model gave a better fit than other kinetic models studied. Mass diffusion mechanisms and thermodynamics studies were successfully carried out. The enthalpy change values evaluated were negative, which revealed the spontaneity of DCF-Na remediation onto modified BKW, and that DCF-Na adsorption is exothermic and occurred through a physisorption process.

Conversion of Argan Nutshells into Novel Porous Carbons in the Scope of Circular Economy: Adsorption Performance of Emerging Contaminants

The present work proposes an experimental strategy to prepare argan nutshell-derived porous carbons using potassium hydroxide (KOH). Several experimental parameters of the activation process were evaluated (temperature, impregnation ratio, and activation time), and an optimized carbon (ACK) was obtained. The surface properties of the ACK sample were determined, and the porous carbon was applied as an adsorbent of diclofenac (DCF) and paroxetine (PARX). A commercial carbon (CC) was used as a benchmark. The ACK porous carbon presented a higher surface area and micropore volume (1624 m2 g−1 and 0.40 cm3 g−1, respectively) than CC carbon (1030 m2 g−1 and 0.30 cm3 g−1, respectively), but the maximum adsorption capacities of DCF (214–217 mg g−1) and PARX (260–275 mg g−1) were comparable among the two carbons. Besides π-π interactions, H-bonds with the electronegative atoms of the adsorbate molecules and the electropositive H of the oxygen functional groups were appointed as the most probable mechanisms for adsorption onto ACK porous carbon. The electrostatic attraction was also considered, particularly for DCF with CC carbon. The pore size might have also been critical, since CC carbon presented more supermicropores (0.7–2 nm), which are usually more favorable toward the adsorption of pharmaceutical molecules. The reusability of the ACK carbon was tested up to four cycles of adsorption–desorption by using ultrasonic washing with water. The results indicated that no more than one cycle of use of ACK should be performed.

Toxicity and remediation of pharmaceuticals and pesticides using metal oxides and carbon nanomaterials

The worldwide development of agriculture and industry has resulted in contamination of water bodies by pharmaceuticals, pesticides and other xenobiotics. Even at trace levels of few micrograms per liter in waters, these contaminants induce public health and environmental issues, thus calling for efficient removal methods such as adsorption. Recent adsorption techniques for wastewater treatment involve metal oxide compounds, e.g. Fe2O3, ZnO, Al2O3 and ZnO-MgO, and carbon-based materials such as graphene oxide, activated carbon, carbon nanotubes, and carbon/graphene quantum dots. Here, the small size of metal oxides and the presence various functional groups has allowed higher adsorption efficiencies. Moreover, carbon-based adsorbents exhibit unique properties such as high surface area, high porosity, easy functionalization, low price, and high surface reactivity. Here we review the cytotoxic effects of pharmaceutical drugs and pesticides in terms of human risk and ecotoxicology. We also present remediation techniques involving adsorption on metal oxides and carbon-based materials.

Surface Properties of Halloysite-Carbon Nanocomposites and Their Application for Adsorption of Paracetamol

Analysis of surface properties of halloysite-carbon nanocomposites and non-modified halloysite was carried out with surface sensitive X-ray photoelectron spectroscopy (XPS) and inverse gas chromatography (IGC). The XPS spectra were measured in a wide range of the electron binding energy (survey spectra) and in the region of C 1s photoelectron peak (narrow scans). The IGC results show the changes of halloysite surface from basic for pure halloysite to acidic for carbon-halloysite nanocomposites. Halloysite-carbon nanocomposites were used as adsorbents of paracetamol from an aqueous solution. The adsorption mechanism was found to follow the pseudo-second-order and intra-particle diffusion models. The Langmuir multi-center adsorption model described well the obtained experimental data. The presence of carbon increased significantly the adsorption ability of halloysite-carbon nanocomposites for paracetamol in comparison to the non-modified halloysite.

Effective removal of carbamazepine and diclofenac by CuO/Cu2O/Cu-biochar composite with different adsorption mechanisms

In this study, the CuO/Cu₂O/Cu-biochar composite (CBC) was fabricated by calcining Cu²⁺-loaded cauliflower root at 500 °C. The CBC displayed the higher specific surface area and total pore volume than raw biochar, which attributed to Cu²⁺ acting as a pore-forming agent in the synthesis process. The adsorption experiments indicated that CBC could remove 88.96% diclofenac and 93.02% carbamazepine, which was nearly double higher than the raw biochar. The film diffusion mainly controlled the adsorption rate. Meanwhile, the common adsorption mechanisms for two pollutants were deemed to hydrogen-bonding interaction, π-π interaction and micropore filling effect, and copper oxide particles providing more adsorption sites. In addition, the adsorption of diclofenac involved electrostatic attraction. Lastly, the higher adsorption capacity of carbamazepine than diclofenac on CBC was mainly attributed to two mechanisms: Lewis acid-base interaction enhancing the adsorption of carbamazepine and size exclusion effect reducing the adsorption of diclofenac. Therefore, the study provided a possible method that Cu-contaminated biomass converted to CuO/Cu₂O/Cu-biochar, which could achieve win-win results.