Jeriffa De Clercq

New ultrastable mesoporous adsorbent for the removal of mercury ions

To find a more stable adsorbent for the selective removal of mercury ions, a new mesoporous adsorbent is developed and compared with a number of carefully selected mesoporous silica adsorbents described in literature. This new adsorbent is based on a pure trans-ethene bridged periodic mesoporous organosilica (PMO) which is subsequently modified to obtain a suitable adsorbent. The outcome is a new thiol-containing ethene bridged PMO which combines the adsorption efficiency of the thiol group toward mercury ions with the stability of ethene bridged PMOs. During the adsorption process, this material not only maintains its mesoporous structure and ordering, it also completely preserves the amount of organic functionalities, allowing recycling and reuse of the adsorbent. Additionally, this PMO is able to reduce the Hg(2+) amount in aqueous solutions below 0.5 microg/L, and the adsorbent has a maximal adsorption capacity of 64 mg/g which means an apparent 1:1 ratio mercury(II) ion to thiol.

Removal of mercury from aqueous solutions by adsorption on a new ultra stable mesoporous adsorbent and on a commercial ion exchange resin

BackgroundThe performance of two adsorbents, i.e. a new ultra stable adsorbent SH-ePMO and a commercial ion exchange resin TP-214, for the removal of mercury from aqueous solutions was investigated. The operating variables studied were initial mercury concentration and contact time.ResultsThe adsorption isotherms showed favourable adsorption. The adsorption isotherms were analysed using Langmuir and Freundlich models. The Langmuir model yielded the best fit for the SH-ePMO, whereas the Freundlich model fitted best the adsorption on TP-214. The maximum adsorption capacities were 66 and 456 mg/g for SH-ePMO and TP-214, respectively. TP-214 is capable of purifying water to parts per trillion levels.The adsorption kinetics showed a fast adsorption for both adsorbents. The kinetics was analysed using Lagergrens pseudo-first-order and pseudo-second-order kinetic models. The pseudo-first-order kinetic model showed a good description of the experimental data of both adsorbents.ConclusionsThis study clearly shows the potential of the ultra stable SH-ePMO for removing mercury from aqueous solutions and confirms the performance of the ion exchanger resin TP-214.The performance of two adsorbents, i.e. a new ultra stable adsorbent SH-ePMO and a commercial ion exchange resin TP-214, for the removal of mercury from aqueous solutions was investigated. The operating variables studied were initial mercury concentration and contact time. The adsorption isotherms showed favourable adsorption. The adsorption isotherms were analysed using Langmuir and Freundlich models. The Langmuir model yielded the best fit for the SH-ePMO, whereas the Freundlich model fitted best the adsorption on TP-214. The maximum adsorption capacities were 66 and 456 mg/g for SH-ePMO and TP-214, respectively. TP-214 is capable of purifying water to parts per trillion levels. The adsorption kinetics showed a fast adsorption for both adsorbents. The kinetics was analysed using Lagergrens pseudo-first-order and pseudo-second-order kinetic models. The pseudo-first-order kinetic model showed a good description of the experimental data of both adsorbents. This study clearly shows the potential of the ultra stable SH-ePMO for removing mercury from aqueous solutions and confirms the performance of the ion exchanger resin TP-214.

Tuning the Pore Geometry of Ordered Mesoporous Carbons for Enhanced Adsorption of Bisphenol-A

Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with fine pores of 3 nm and less. The hard templated carbon (CMK-3) material had an even higher BET-surface of 1420 m2/g with an average pore size of 4 nm. The soft templated carbon (SMC) reached a BET-surface of 476 m2/g and a pore size of 7 nm. The maximum observed adsorption capacity (qmax) of CMK-3 was the highest with 474 mg/g, compared to 290 mg/g for PAC and 154 mg/g for SMC. The difference in adsorption capacities was attributed to the specific surface area and hydrophobicity of the adsorbent. The microporous PAC showed the slowest adsorption, while the ordered mesopores of SMC and CMK-3 enhanced the BPA diffusion into the adsorbent. This difference in adsorption kinetics is caused by the increase in pore diameter. However, CMK-3 with an open geometry consisting of interlinked nanorods allows for even faster intraparticle diffusion.

Ship-in-a-bottle CMPO in MIL-101(Cr) for selective uranium recovery from aqueous streams through adsorption

Mesoporous MIL-101(Cr) is used as host for a ship-in-a-bottle type adsorbent for selective U(VI) recovery from aqueous environments. The acid-resistant cage-type MOF is built in-situ around N,N-Diisobutyl-2-(octylphenylphosphoryl)acetamide (CMPO), a sterically demanding ligand with high U(VI) affinity. This one-step procedure yields an adsorbent which is an ideal compromise between homogeneous and heterogeneous systems, where the ligand can act freely within the pores of MIL-101, without leaching, while the adsorbent is easy separable and reusable. The adsorbent was characterized by XRD, FTIR spectroscopy, nitrogen adsorption, XRF, ADF-STEM and EDX, to confirm and quantify the successful encapsulation of the CMPO in MIL-101, and the preservation of the host. Adsorption experiments with a central focus on U(VI) recovery were performed. Very high selectivity for U(VI) was observed, while competitive metal adsorption (rare earths, transition metals...) was almost negligible. The adsorption capacity was calculated at 5.32mg U/g (pH 3) and 27.99mg U/g (pH 4), by fitting equilibrium data to the Langmuir model. Adsorption kinetics correlated to the pseudo-second-order model, where more than 95% of maximum uptake is achieved within 375min. The adsorbed U(VI) is easily recovered by desorption in 0.1M HNO3. Three adsorption/desorption cycles were performed.

Tunable Large Pore Mesoporous Carbons for the Enhanced Adsorption of Humic Acid

Tunable large pore soft templated mesoporous carbons (SMC) were obtained via the organic self-assembly of resorcinol/formaldehyde with the triblock copolymer F127 and by investigating the effect of carbon precursor to surfactant (p/s) ratio and carbonization temperature on the material characteristics. The p/s ratio and carbonization temperature were varied respectively from 0.83 to 0.25 and from 400 to 1200 °C. The resulting SMCs had various average pore sizes, tunable from 7 up to 50 nm. At lower p/s ratios, the pore size increased, pore size distributions broadened, and pore volumes increased. An increase of hydrophobicity was observed at elevated carbonization temperatures. A 2D hexagonal ordered SMC with a narrow pore size distribution was obtained at a ratio of 0.83. Lower ratios (0.5 and 0.25) transformed into disordered porous carbons containing micropores, mesopores, and even macropores. The SMCs were tested for adsorption of a large organic molecule, humic acid (HA), from water. The material characteristics that significantly affected HA adsorption capacity were pore size and mass % (wt %) carbon. The novel SMCs showed an unprecedented high adsorption of HA in the entire molecular weight distribution range. SMCs with large mesopores resulted in higher maximum adsorption capacities and improved HA adsorption kinetics compared to activated carbon.

Carbamoylmethylphosphine Oxide-Functionalized MIL-101(Cr) as Highly Selective Uranium Adsorbent

The carbamoylmethylphosphine oxide (CMPO) functionalized MIL-101(Cr) was investigated as a potential uranium scavenger. This metal-organic framework-based adsorbent shows very high selectivity toward uranium, as well as thorium, in competition with various rare earth metals. Furthermore, it showed rapid adsorption kinetics, in both batch conditions and a dynamic (column) setup. The adsorbent is fully regenerable, using oxalate solution. Fast elution kinetics in the column setup were observed during the regeneration. In addition, reusability studies were performed under dynamic conditions. Five consecutive adsorption/desorption cycles were carried out, showing a consistent 100% recovery, at pH 4, using 0.1 M oxalate solution as an effective stripping agent. Additionally, the successive use over various adsorption/desorption cycles with constant performance proves the high stability of this adsorbent in an acidic, aqueous environment.

Effect of Ion Exchange Resin Functionality on Catalytic Activity and Leaching of Palladium Nanoparticles in Suzuki Cross-Coupling Reactions

Macroporous ion exchange resin supported palladium nanoparticle (Pd‐NP) catalysts are prepared by an intermatrix synthesis. For the first time, the effect of resin functionality (weak acid, strong acid, strong base) on the NP size, their catalytic activity, and leaching is investigated in the Suzuki cross‐coupling of iodobenzene and phenylboronic acid. Whereas the smallest NPs (1.34 nm) are found in the thiol Ambersep GT74 resin, the sulfonic acid Lewatit K2629 and quaternary amine Lewatit MP500 OH resins resulted in NPs of a similar size (2.42 and 2.59 nm, respectively). Despite their smaller size, the NPs on Ambersep GT74 exhibited the lowest conversion (21.6 %), which is attributed to a too strong coordination of the NPs by the thiol groups. The conversions obtained by using Lewatit K2629 (76.8 %) and Lewatit MP500 OH (94.2 %) were considerably higher, the excellent performance of the latter catalyst being ascribed to the promoting effect of the hydroxyl groups on the transmetallation and reductive elimination steps in Suzuki cross‐coupling. No Pd leaching was observed when using Ambersep GT74 as the support, compared with Pd leaching amounting to 1.1 % and 4.8 % when using Lewatit MP500 OH and Lewatit K2629, respectively. Such low values indicate that ion exchange resins are ideal supports to stabilize the NPs. Particularly, the combination of high conversion and limited leaching on Lewatit MP500 OH opens up new perspectives for catalyzing Suzuki cross‐coupling with a heterogeneous catalyst.

Thiol-ethylene bridged PMO: A high capacity regenerable mercury adsorbent via intrapore mercury thiolate crystal formation

Highly ordered thiol-ethylene bridged Periodic Mesoporous Organosilicas were synthesized directly from a homemade thiol-functionalized bis-silane precursor. These high surface area materials contain up to 4.3mmol/g sulfur functions in the walls and can adsorb up to 1183mg/g mercury ions. Raman spectroscopy reveals the existence of thiol and disulfide moieties. These groups have been evaluated by a combination of Raman spectroscopy, Ellmans reagent and elemental analysis. The adsorption of mercury ions was evidenced by different techniques, including Raman, XPS and porosimetry, which indicate that thiol groups are highly accessible to mercury. Scanning transmission electron microscopy combined with EDX showed an even homogenous distribution of the sulfur atoms throughout the structure, and have revealed for the first time that a fraction of the adsorbed mercury is forming thiolate nanocrystals in the pores. The adsorbent is highly selective for mercury and can be regenerated and reused multiple times, maintaining its structure and functionalities and showing only a marginal loss of adsorption capacity after several runs.

Removal of Arsenic (V) from Aqueous Solutions Using Chitosan–Red Scoria and Chitosan–Pumice Blends

In different regions across the globe, elevated arsenic contents in the groundwater constitute a major health problem. In this work, a biopolymer chitosan has been blended with volcanic rocks (red scoria and pumice) for arsenic (V) removal. The effect of three blending ratios of chitosan and volcanic rocks (1:2, 1:5 and 1:10) on arsenic removal has been studied. The optimal blending ratio was 1:5 (chitosan: volcanic rocks) with maximum adsorption capacity of 0.72 mg/g and 0.71 mg/g for chitosan: red scoria (Ch–Rs) and chitosan: pumice (Ch–Pu), respectively. The experimental adsorption data fitted well a Langmuir isotherm (R2 > 0.99) and followed pseudo-second-order kinetics. The high stability of the materials and their high arsenic (V) removal efficiency (~93%) in a wide pH range (4 to 10) are useful for real field applications. Moreover, the blends could be regenerated using 0.05 M NaOH and used for several cycles without losing their original arsenic removal efficiency. The results of the study demonstrate that chitosan-volcanic rock blends should be further explored as a potential sustainable solution for removal of arsenic (V) from water.