Search

This study aimed at optimizing the one-step chemical activation and microwave pyrolysis of an agro-industrial waste to obtain a microporous activated carbon (AC) with superior textural and adsorptive properties by a fast, low-reagent and low-energy process. Spent brewery grains were used as precursor, and the antibiotics sulfamethoxazole (SMX), trimethoprim (TMP) and ciprofloxacin (CIP) were considered as target adsorbates. A fractional factorial design was applied to evaluate the effect of the main factors affecting the preparation of AC (activating agent, activating agent:precursor ratio, pyrolysis temperature and residence time) on relevant responses. Under optimized conditions (K2CO3 activation, pyrolysis at 800 °C during 20 min and a K2CO3:precursor ratio of 1:2), a microporous AC with specific surface area of 1405 m2 g-1 and large adsorption of target antibiotics (82-94%) was obtained and selected for further studies. Equilibrium times up to 60 min and maximum Langmuir adsorption capacities of 859 µmol g-1 (SMX), 790 µmol g-1 (TMP) and 621 µmol g-1 (CIP) were obtained. The excellent textural and adsorptive properties of the selected material were achieved with a very fast pyrolysis and low load of activating agent, highlighting the importance of optimization studies to decrease the environmental and economic impact of waste-based AC.

This work aimed at producing easily recoverable magnetic iron-oxide functionalized activated carbons (AC) through environmentally and energetically sustainable methods, evaluating their efficacy towards the removal of the pharmaceuticals diclofenac (DCF) and venlafaxine (VEN) from different aqueous matrices (ultrapure water and wastewater treatment plant effluents). Two AC were prepared by chemical activation of a biomassic industrial waste followed by either conventional (CP) or microwave (MW) pyrolysis. Then, magnetic iron oxide nanoparticles were loaded onto the produced AC. Differences related to the production procedure were not especially remarkable, since both the resulting magnetic composites (MAC-CP and MAC-MW) presented well-developed micropore structures with specific surface areas of 644 and 548 m2 g−1 and saturation magnetization of 32.9 and 22.5 emu g−1, respectively, which conferred them a high adsorptive performance and efficient magnetic recovery from solution. The kinetic data were well described by both pseudo-first and pseudo-second order models. As for the equilibrium data, Langmuir isotherm provided a good fitting, with maximum adsorption capacities ranging between 97 ± 2 and 215 ± 4 µmol g−1 for MAC-CP and between 80 ± 2 and 172 ± 3 µmol g−1 for MAC-MW. Additionally, in binary (DCF and VEN) solutions and wastewater, adsorption onto both MAC was somewhat inhibited due to competitive effects. MW-assisted regeneration of exhausted MAC was effective, as their adsorptive properties and chemical surface features (according to X-Ray photoelectron spectroscopy) remained unchanged. Overall, the produced waste-based magnetic carbon composites simultaneously combine high adsorptive efficiency, easy retrievability and successful regeneration/reutilization.

In view of a simple after-use separation, the potentiality of producing magnetic activated carbon (MAC) by intercalation of ferromagnetic metal oxide nanoparticles in the framework of a powder activated carbon (PAC) produced from primary paper sludge was explored in this work. The synthesis conditions to produce cost effective and efficient MACs for the adsorptive removal of pharmaceuticals (amoxicillin, carbamazepine, and diclofenac) from aqueous media were evaluated. For this purpose, a fractional factorial design (FFD) was applied to assess the effect of the most significant variables (Fe3+ to Fe2+ salts ratio, PAC to iron salts ratio, temperature, and pH), on the following responses concerning the resulting MACs: Specific surface area (SBET), saturation magnetization (Ms), and adsorption percentage of amoxicillin, carbamazepine, and diclofenac. The statistical analysis revealed that the PAC to iron salts mass ratio was the main factor affecting the considered responses. A quadratic linear regression model A = f(SBET, Ms) was adjusted to the FFD data, allowing to differentiate four of the eighteen MACs produced. These MACs were distinguished by being easily recovered from aqueous phase using a permanent magnet (Ms of 22–27 emu g−1), and their high SBET (741–795 m2 g−1) were responsible for individual adsorption percentages ranging between 61% and 84% using small MAC doses (35 mg L−1).

The main goal of this work was to produce an easily recoverable waste-based magnetic activated carbon (MAC) for an efficient removal of the antiepileptic pharmaceutical carbamazepine (CBZ) from wastewater. For this purpose, the synthesis procedure was optimized and a material (MAC4) providing immediate recuperation from solution, remarkable adsorptive performance and relevant properties (specific surface area of 551 m g and saturation magnetization of 39.84 emu g) was selected for further CBZ kinetic and equilibrium adsorption studies. MAC4 presented fast CBZ adsorption rates and short equilibrium times (< 30–45 min) in both ultrapure water and wastewater. Equilibrium studies showed that MAC4 attained maximum adsorption capacities (q) of 68 ± 4 mg g in ultrapure water and 60 ± 3 mg g in wastewater, suggesting no significant interference of the aqueous matrix in the adsorption process. Overall, this work provides evidence of potential application of a waste-based MAC in the tertiary treatment of wastewaters. [Figure not available: see fulltext.].