Adsorption of 2,4-dichlorophenoxyacetic acid on activated carbons from macadamia nut shells.

This study reports on the application of activated carbons from macadamia nut shells as adsorbents for the removal of 2,4-dichlorophenoxyacetic acid, a commonly used pesticide, from water. Different activating agents (FeCl3, ZnCl2, KOH and H3PO4) were used to obtain adsorbents within a wide range of porous texture and surface properties. The characterization of the resulting activated carbons was performed by N2 adsorption-desorption, elemental analysis, TG and pHPZC. The adsorption experiments were conducted in batch at 25, 45 and 65 °C. The adsorption kinetics on activated carbons obtained with FeCl3 H3PO4 or KOH was well described by the pseudo-second order model, whereas for the resulting from ZnCl2 activation the experimental data fit better the pseudo-first order model. The equilibrium studies were performed with the KOH- and ZnCl2-activated carbons, the two showing higher surface area values. In both cases, high adsorption capacities were obtained (c.a. 600 mg g-1) and the experimental data were better described by the Langmuir and Toth models. The thermodynamic study allows concluding the spontaneous and endothermic character of the adsorption process, as well as an increase of randomness at the solid/liquid interface. Breakthrough curves were also obtained and fitted to the logistic model.

Degradation of diclofenac in water under LED irradiation using combined g-C3N4/NH2-MIL-125 photocatalysts.

This study reports the photocatalytic degradation of diclofenac by hybrid materials prepared by combination of graphitic carbon nitride (g-C3N4) and titanium-metal organic framework (NH2-MIL-125), in different mass proportions (MOF:C3N4 of 25:75, 50:50 and 75:25). The hybrid materials were fully characterized, and their properties compared to those of the individual components, whose presence was confirmed by XRD. The porous structure was the result of the highly microporous character of the MOF and the non-porous one of g-C3N4. The band gap values were very close to that of MOF component. Photoluminescence measurements suggested an increase on the recombination rate associated to the presence of g-C3N4. Photodegradation tests of diclofenac (10 mg·L-1) were performed under UV LED irradiation at 384 nm. The hybrid materials showed higher photocatalytic activity than the individual components, suggesting the occurrence of some synergistic effect. The photocatalyst with a MOF:g-C3N4 ratio of 50:50 yielded the highest conversion rate, allowing complete disappearance of diclofenac in 2 h. Experiments with scavengers showed that superoxide radicals and holes played a major role in the photocatalytic process photodegradation, being that of hydroxyl radicals less significant. From the identification of by-products species, a degradation pathway was proposed for the degradation of diclofenac under the experimental operating conditions.

Phenol adsorption on high microporous activated carbons prepared from oily sludge: equilibrium, kinetic and thermodynamic studies.

The purpose of this study was the preparation, characterization and application of high-performance activated carbons (ACs) derived from oily sludge through chemical activation by KOH. The produced ACs were characterized using iodine number, N2 adsorption-desorption, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The activated carbon prepared under optimum conditions showed a predominantly microporous structure with a BET surface area of 2263 m2 g-1, a total pore volume of 1.37 cm3 g-1 and a micro pore volume of 1.004 cm3 g-1. The kinetics and equilibrium adsorption data of phenol fitted well to the pseudo second order model (R2 = 0.99) and Freundlich isotherm (R2 = 0.99), respectively. The maximum adsorption capacity based on the Langmuir model (434 mg g-1) with a relatively fast adsorption rate (equilibrium time of 30 min) was achieved under an optimum pH value of 6.0. Thermodynamic parameters were negative and showed that adsorption of phenol onto the activated carbon was feasible, spontaneous and exothermic. Desorption of phenol from the adsorbent using 0.1 M NaOH was about 87.8% in the first adsorption/desorption cycle and did not decrease significantly after three cycles. Overall, the synthesized activated carbon from oily sludge could be a promising adsorbent for the removal of phenol from polluted water.

Zr-doped TiO2 supported on delaminated clay materials for solar photocatalytic treatment of emerging pollutants.

Solar light-active Zr-doped TiO2 nanoparticles were successfully immobilized on delaminated clay materials by a one-step sol-gel route. Fixing the amount of TiO2 at 65wt.%, this work studies the influence of Zr loading (up to 2%) on the photocatalytic activity of the resulting Zr-doped TiO2/clay materials. The structural characterization demonstrates that all samples were formed by a delaminated clay with nanostructured anatase assembled on its surface. The Zr dopant was successfully incorporated into the anatase lattice, resulting in a slight deformation of the anatase crystal and the reduction of the band gap. These materials exhibit high surface area with a disordered mesoporous structure formed by TiO2 particles (15-20nm) supported on a delaminated clay. They were tested in the solar photodegradation of antipyrine, usually used as an analgesic drug and selected as an example of emerging pollutant. High degradation rates have been obtained at low antipyrine concentrations and high solar irradiation intensities with the Zr-doped TiO2/clay catalyst, more effective than the undoped one. This work demonstrates the potential application of the synthesis method for preparing novel and efficient solar-light photocatalysts based on metal-doped anatase and a delaminated clay.