RESUMEN
Layered double hydroxides (LDHs) play a fundamental role in the processes for the abatement of pollutants in water, with reference to heavy metal decontamination. The research on the topic is multiobjective target oriented, aiming at combining environmental remediation with the possibility of reusing a sorbent as many times as possible, turning it into a renewable resource. In this study, the antibacterial and catalytic properties of a ZnAl-SO4 LDH and its resulting product after being subjected to a Cr(VI) remediation process are compared. Both solid substrates have also been tested after undergoing a thermal annealing process. The sorbent (previously described and tested for remediation) has been investigated for its antibacterial activity in view of further surgery and drug delivery applications. Finally, its photocatalytic properties have been experimentally tested in the degradation of a model pollutant, i.e., Methyl Orange (MO), under solar-simulated light. Identifying the best recycling strategy for these materials requires an accurate knowledge of their physicochemical properties. The results show that both the antimicrobial activity and the photocatalytic performance may considerably improve after thermal annealing.
RESUMEN
Owing to their structure, layered double hydroxides (LDHs) and allophane are nowadays considered as promising materials for application in different fields. The goal of this work is to compare the efficacy of allophane and ZnAl-SO4 LDH to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater. Both compounds were synthesized via the co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered turbostratic (ZnAl-SO4 LDH) or amorphous (allophane) structure. The characterization of the obtained compounds was performed by means of powder x-ray diffraction (PXRD), thermal gravimetry analysis (TGA), field emission scanning electron microscopy analysis (FESEM), and Fourier-transform infrared spectroscopy (FT-IR). The sorbents were tested using wastewater produced by a real metalworking plant and containing ionic species such as Cu(II), Fe(III) and Cr(VI), whose concentration was measured by means of inductively coupled plasma-optical emission spectrometry (ICP-OES). This investigation represents an alternative procedure with respect to standard protocols based on customarily made and artificially lab-produced wastewaters. Both sorbents and their combination proved to be efficient in Cr(VI) removal, irrespective of the presence of cations like Cu(II) and Fe(III). A synergistic effect was detected for Cu(II) adsorption in a mixed allophane/LDH sorbent, leading to a Cu(II) removal rate of 89.5%.
RESUMEN
A synthetic Cu-Al-SO4 layered double hydroxide (LDH), analogue to the mineral woodwardite [Cu1-xAlx(SO4)x/2(OH)2·nH2O], with x < 0.5 and n ≤ 3x/2, was synthesised by adding a solution of Cu and Al sulphates to a solution with NaOH. The pH values were kept constant at 8.0 and 10.0 by a continuous addition of NaOH. The material obtained had poor crystallinity, turbostratic structure, and consisted of nanoscopic crystallites. The analyses performed in order to characterise the obtained materials (X-ray diffraction (XRD), thermogravimetry (TG), and Fourier Transform Infra-Red (FTIR) spectroscopy) showed that the Cu-Al-SO4 LDH is very similar to woodwardite, although it has a smaller layer spacing, presumably due to a lesser water content than in natural samples. The synthesis was performed by adding light rare earth elements (LREEs) (La, Ce, and Nd) and heavy rare earth elements (HREEs) (Gd and Y) in order to test the affinity of the Cu-Al-SO4 LDH to the incorporation of REEs. The concentration of rare earth elements (REEs) in the solid fraction was in the range of 3.5-8 wt %. The results showed a good affinity for HREE and Nd, especially for materials synthesised at pH 10.0, whereas the affinities for Ce and La were much lower or non-existent. The thermal decomposition of the REE-doped materials generates a mixture of Cu, Al, and REE oxides, making them interesting as precursors in REE oxide synthesis.
RESUMEN
Due to the wide range of applications in high-tech solutions, Rare Earth Elements (REEs) have become object of great interest. In the last years several studies regarding technologies for REE extraction from secondary resources have been carried out. In particular biotechnologies, which use tolerant and accumulator microorganisms to recover and recycle precious metals, are replacing traditional methods. This paper describes an original biometallurgical method to recover REEs from waste electrical and electronic equipment (WEEE) by using a strain of Penicillium expansum Link isolated from an ecotoxic metal contaminated site. The resulting product is a high concentrated solution of Lanthanum (up to 390ppm) and Terbium (up to 1520ppm) obtained from WEEE. Under this perspective, the proposed protocol can be considered a method of recycling exploiting biometallurgy. Finally, the process is the subject of the Italian patent application n. 102015000041404 submitted by the University of Genoa.