Ana S. Mestre

Waste-derived activated carbons for removal of ibuprofen from solution: Role of surface chemistry and pore structure

The removal of a widespread used drug (i.e., ibuprofen) from water was investigated using high valuable carbon adsorbents obtained from chemical and physical activation of a bioresource (cork) and a municipal waste (plastic). The waste-derived carbons outperformed the adsorption capacity of commercial carbonaceous adsorbents due to their adequate features for the removal of the targeted compound. Regarding the adsorption mechanism, the results obtained point out that ibuprofen retention is favored in activated carbons with basic surface properties. On the other hand, the textural features also play an important role; the presence of a transport pores network (i.e., mesopores) is crucial to ensure the accessibility to the inner porosity, and the microporosity must be large enough to accommodate the ibuprofen molecule. Specifically, adsorbents with a large fraction of ultramicropores (pore widths <0.7 nm) are not adequate to effectively remove ibuprofen.

Activated carbons from sisal waste by chemical activation with K2CO3: Kinetics of paracetamol and ibuprofen removal from aqueous solution

Sisal waste was used as precursor to prepare carbons by chemical activation. The influence of the K(2)CO(3) amount and activation temperature on the materials textural properties were studied through N(2) and CO(2) adsorption assays. As the severity of the treatment increases there is a development of supermicropores, and the micropore size distribution changes from mono to bimodal. A carbon with an apparent surface area of 1,038 m(2)g(-1) and pore volume of 0.49 cm(3)g(-1) was obtained. TPD results showed the incidence in acidic type groups although the pH(PZC) reveals an almost neutral character of the surface. Adsorption kinetic data of ibuprofen and paracetamol show that the processes obey to a pseudo-second order kinetic equation. Regarding the removal efficiency the prepared samples attained values comparable to a commercial carbon (>65%), revealing that chemical activation of sisal wastes with K(2)CO(3) allows obtaining samples suitable for pharmaceutical compounds removal from liquid phase.

Powdered activated carbons as effective phases for bar adsorptive micro-extraction (BAμE) to monitor levels of triazinic herbicides in environmental water matrices

Bar adsorptive micro-extraction using three powdered activated carbons (ACs) as adsorbent phases followed by liquid desorption and high performance liquid chromatography with diode array detection (BAμE(ACs)-LD/HPLC-DAD), was developed to monitor triazinic herbicides (atrazine, simazine and terbutylazine) in environmental water matrices. ACs used present apparent surface areas around 1000 m(2) g(-1) with an important mesoporous volume and distinct surface chemistry characteristics (pH(PZC) ranging from 6.5 to 10.4). The textural and surface chemistry properties of the ACs adsorbent phases were correlated with the analytical data for a better understanding of the overall enrichment process. Assays performed on 10 mL water samples spiked at the 10.0 μg L(-1) levels under optimized experimental conditions yielded recoveries around 100% for the three herbicides under study. The analytical performance showed good precision (RSD<15.0%), convenient detection limits (≈0.1 μg L(-1)) and suitable linearity (1.0-12.0 μg L(-1)) with good correlation coefficients (r(2)>0.9914). By using the standard addition method, the application of the present method on real water matrices, such as surface water and wastewater, allowed very good performances at the trace level. The proposed methodology proved to be a suitable sorptive extraction alternative for the analysis of priority pollutants with polar characteristics, showing to be easy to implement, reliable, sensitive and requiring a low sample volume to monitor triazinic compounds in water matrices.

Chars from gasification of coal and pine activated with K2CO3: Acetaminophen and caffeine adsorption from aqueous solutions

The high carbon contents and low toxicity levels of chars from coal and pine gasification provide an incentive to consider their use as precursors of porous carbons obtained by chemical activation with K2CO3. Given the chars characteristics, previous demineralization and thermal treatments were made, but no improvement on the solids properties was observed. The highest porosity development was obtained with the biomass derived char (Pi). This char sample produced porous materials with preparation yields near 50% along with high porosity development (ABET≈1500m(2)g(-1)). For calcinations at 800°C, the control of the experimental conditions allowed the preparation of samples with a micropore system formed almost exclusively by larger micropores. A mesopore network was developed only for samples calcined at 900°C. Kinetic and equilibrium acetaminophen and caffeine adsorption data, showed that the processes obey to a pseudo-second order kinetic equation and to the Langmuir model, respectively. The results of sample Pi/1:3/800/2 outperformed those of the commercial carbons. Acetaminophen adsorption process was ruled by the micropore size distribution of the carbons. The caffeine monolayer capacities suggest a very efficient packing of this molecule in samples presenting monomodal micropore size distribution. The surface chemistry seems to be the determinant factor that controls the affinity of caffeine towards the carbons.

Cork-based activated carbons as supported adsorbent materials for trace level analysis of ibuprofen and clofibric acid in environmental and biological matrices

In this contribution, powdered activated carbons (ACs) from cork waste were supported for bar adsorptive micro-extraction (BAμE), as novel adsorbent phases for the analysis of polar compounds. By combining this approach with liquid desorption followed by high performance liquid chromatography with diode array detection (BAμE(AC)-LD/HPLC-DAD), good analytical performance was achieved using clofibric acid (CLOF) and ibuprofen (IBU) model compounds in environmental and biological matrices. Assays performed on 30 mL water samples spiked at the 25.0 μg L(-1) level yielded recoveries around 80% for CLOF and 95% for IBU, under optimized experimental conditions. The ACs textural and surface chemistry properties were correlated with the results obtained. The analytical performance showed good precision (<15%), suitable detection limits (0.24 and 0.78 μg L(-1) for CLOF and IBU, respectively) and good linear dynamic ranges (r(2)>0.9922) from 1.0 to 600.0 μg L(-1). By using the standard addition methodology, the application of the present approach to environmental water and urine matrices allowed remarkable performance at the trace level. The proposed methodology proved to be a viable alternative for acidic pharmaceuticals analysis, showing to be easy to implement, reliable, sensitive and requiring low sample volume to monitor these priority compounds in environmental and biological matrices.

Sustainable activated carbons prepared from a sucrose-derived hydrochar: remarkable adsorbents for pharmaceutical compounds

We present a two-step methodology for the preparation of highly activated carbons with tailored morphologies and micropore size distributions (MPSD) through the hydrothermal carbonization (HTC) of renewable biomass (i.e. sucrose) and further activation. Depending on the activation agent, activated carbons with spherical (K2CO3 or steam activation) or sponge-like morphologies (KOH activation) were obtained. The control of the activation variables allows tailoring the MPSD of the materials with K2CO3 activation at 700–800 °C originating porous materials with molecular sieve properties, and KOH activation giving porous carbon materials with wider MPSD. The highly developed porous structures of the activated carbons give them remarkable adsorption capacities for the removal of pharmaceutical compounds of distinct therapeutical classes (i.e. ibuprofen, paracetamol, clofibric acid, caffeine and iopamidol). Although the superactivated carbon obtained by the KOH activation at 800 °C has very high adsorption capacities for all the pharmaceutical compounds assayed, the material obtained by the K2CO3 activation at 800 °C has a similar adsorption capacity for all pharmaceuticals but iopamidol, the most voluminous compound. The distinct performance of the porous carbon materials for the removal of the pharmaceutical compounds is mainly related to their MPSD. The high performance of some of the synthetized carbons combined with the possibility of controlling the size of the particles in the HTC step allows not only their possible use as filter media but also coupling to other advanced water treatment technologies (e.g. membrane systems). Moreover, the abovementioned properties associated with the acidic surface chemistry of the developed activated carbons open new possibilities for the synthesis of functional carbon-based materials.

High performance microspherical activated carbons for methane storage and landfill gas or biogas upgrade

Microspherical activated carbons were successfully prepared via a novel synthetic route that involves hydrothermal carbonization of a renewable material, sucrose, and activation with K2CO3. The use of K2CO3 resulted in better yields (∼50%) and the retention of the spherical shape of the hydrochar, while with the less environmentally desirable and commonly used activating agent, KOH, the process occurs at the expense of the spherical morphology. The superior performance of the K2CO3 activated samples for methane storage and upgrade of landfill gas or biogas results from the combination of several key properties including high packing densities (∼0.9 g cm−3), high surface areas (up to 1400 m2 g−1) and micropore sizes suitable for methane storage and selective CO2–CH4 separation. In fact, the micropore size distributions assessed from CO2 adsorption data through a methodology not imposing a Gaussian distribution gave meaningful values to explain both the selectivity and storage capacity of samples. Sample activated with K2CO3 at 800 °C presenting micropore sizes ∼0.8 nm and high packing density has high volumetric methane uptake (90 (V/V) at 1000 kPa), close to the best activated carbons reported in the literature. Sample activated with K2CO3 at 700 °C has narrower micropores (∼0.5 nm) and presents a remarkable selectivity (4–7) in CO2–CH4 mixtures for the upgrade of methane based fuels, like natural gas, landfill gas, and biogas. Although a superactivated carbon (∼2400 m2 g−1) was obtained with KOH activation, the low packing density and wider micropores rendered it less effective for both methane storage and upgrade.

Development of a Powdered Activated Carbon in Bar Adsorptive Micro-Extraction for the Analysis of Morphine and Codeine in Human Urine

In the present work, bar adsorptive microextraction using an activated carbon (AC) adsorbent phase followed by liquid desorption and high-performance liquid chromatography with diode array detection was developed to monitor morphine (MOR) and codeine (COD) in human urine. Under optimized experimental conditions, assays performed in aqueous media spiked at the 30.0 µg/L level yielded recoveries of 41.3 ± 1.3% for MOR and 38.4 ± 1.7% for COD, respectively. The textural and surface chemistry properties of the AC phase were also correlated with the analytical data for a better understanding of the overall enrichment process. The analytical performance showed good precision (relative standard deviation < 8.0%), suitable detection limits (0.90 and 0.06 µg/L for MOR and COD, respectively) and convenient linear dynamic ranges (r(2) > 0.991) from 10.0 to 330.0 µg/L. By using the standard addition methodology, the applications of this analytical approach to water and urine matrices allowed remarkable performance to monitor MOR and COD at the trace level. This new confirmatory method proved to be a suitable alternative to other sorptive micro-extraction methodologies in monitoring trace levels of opiate-related compounds, because it was easy to implement, reliable, sensitive and required a low sample volume.

Sucrose-derived activated carbons: electron transfer properties and application as oxygen reduction electrocatalysts

The development of carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) is one of the most attractive topics in fuel cell field. Herein, we report the application of two sustainable sucrose-based activated carbons (ACs), denominated SC800 and SH800, as ORR electrocatalysts. In alkaline medium the ACs showed similar onset potentials at Eonset ≈ −0.20 V vs. Ag/AgCl (0.76 V vs. ERHE), which are 0.06 V more negative than that observed for 20 wt% Pt/C used as a reference. Higher diffusion-limiting current densities (jL(−1.0 V, 1600 rpm) = −3.44 mA cm−2) were obtained for the SH800 electrocatalyst, in contrast to SC800 (jL(−1.0 V, 1600 rpm) = −3.04 mA cm−2). These differences can be related with their different textural properties. The SH800 electrocatalyst revealed a higher specific surface area (ABET ≈ 2500 m2 g−1), larger micropores (widths between 0.7 and 2 nm) and sponge-like morphology. Conversely, SC800 showed a spherical shape, ABET ≈ 1400 m2 g−1 and narrow micropores with pore width <0.7 nm. Both ACs were neither selective to 2- or 4-electron ORR processes, opposing Pt/C which showed selectivity towards direct O2 reduction to water. SH800 and SC800 showed very similar Tafel plots, but with SH800 showing in both low and high current density regions, the lowest slopes values 53/171 mV dec−1 vs. 68/217 mV dec−1. Furthermore, the ACs presented excellent tolerance to methanol, with the SH800 electrocatalyst also showing greater long-term electrochemical stability than the Pt/C electrocatalyst which are very important advantages. The ACs-based electrocatalysts also showed ORR catalytic activity in acidic media, which makes them promising candidates for applications with acidic electrolytes (e.g. proton exchange fuel cells). In this case, Eonset = 0.06 V vs. Ag/AgCl (0.41 V vs. ERHE) for SC800 and Eonset = −0.01 V vs. Ag/AgCl (0.34 V vs. ERHE) for SH800, and the diffusion-limiting current densities are very similar for both ACs (jL = −2.59/−2.76 mA cm−2 at −1.3 V vs. Ag/AgCl, at 1600 rpm). SH800 and SC800 Tafel plots also showed two different slopes, but with higher values in both low and high current density regions, when compared with those obtained in an alkaline medium; still SH800 continues to show the lowest slopes.

Biodiesel production waste as promising biomass precursor of reusable activated carbons for caffeine removal

Biodiesel production generates low particle size rapeseed waste (recovered from warehouse air filtration systems) that was herein explored as promising biomass precursor of chemically activated carbons. The influence of several experimental parameters on the porosity development was investigated. No benefit was observed when solution impregnation was made nor a significant dependence of the biomass : K2CO3 ratio was observed and, as expected, high porosity development was obtained only for treatments at 700 °C. Microporous materials with apparent surface area around 1000 m2 g−1 were obtained comparing favorably with literature data regarding activated carbons from rapeseed processing by-products. A selected lab-made sample and two commercial carbons were tested as adsorbents of caffeine from aqueous solution. Although commercial materials present a quicker adsorption rate, regarding adsorption capacity the lab-made sample reaches the same value attained by a benchmark material. The regeneration tests made over the rapeseed derived carbon through heat treatments at 600 °C for 1 hour under N2 flow proved that at least two exhaustion–regeneration cycles can be made since the material retains a caffeine adsorption capacity similar to that of the fresh carbon. Therefore, a waste management problem of biodiesel industry – rapeseed residue – can be transformed in a valuable material with promising properties for environmental remediation processes.