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- Start-up, adjustment and long-term performance of a two-stage bioremediation process, treating real acid mine drainage, coupled with biosynthesis of ZnS nanoparticles and ZnS/TiO2 nanocompositesPublication . Vitor, G.; Palma, T. C.; Vieira, Bernardete; Lourenço, J. P.; Barros, R. J.; Costa, Maria ClaraAcid mine drainage (AMD) generation is a widespread environmental problem in Europe, including Portugal. Previous experience has shown that a combined process consisting of an anaerobic sulphate-reducing bioreactor, following neutralization with calcite tailing, produces water complying with legal irrigation requirements from synthetic AMD. Aiming the treatment of real AMD a new bioreactor was inoculated with a SRB enrichment obtained from sludge from a local WWTP anaerobic lagoon. In the initial batch phase, sulphate supplementation was needed to achieve high sulphate-reducing bacteria counts before continuous feeding of AMD was started. The system quickly achieved good performance, proving it is easy to start-up. However, this time the neutralization step failed to keep bioreactor affluent pH higher than 5 for longer than three weeks. This was due to armouring of calcite by precipitates of various metals present in AMD. A new configuration, replacing a packed-bed column by a shallow contact basin, proved to be more robust, avoiding clogging, short-circuiting and providing long-term neutralization. The treated effluent, with excess of biologically generated sulphide, was successfully used to synthesize zinc sulphide nanoparticles, both in pure form and as a ZnS/TiO2 nanocomposite, thus proving the feasibility of coupling an AMD bioremediation system with the synthesis of metal sulphide nanoparticles and nanocomposites.
- Novel titanate nanotubes-cyanocobalamin materials: Synthesis and enhanced photocatalytic properties for pollutants removalPublication . Silva, T. A.; Diniz, J.; Paixio, L.; Vieira, Bernardete; Barrocas, B.; Nunes, C. D.; Monteiro, O. C.New hybrid nanomaterials, with improved photocatalytic performance in pollutants removal, were obtained through the modification of titanate nanotubes (TNT) with a cobalt porphyrin, the cyanocobalamin, also knowing as vitamin B12 (812). The nanocrystalline TNT were produced by hydrothermal treatment and after treated with cobalamin to produce B12-TNT materials. The characterization of the new hybrid material was performed by XRD, FTIR, TEM-EDS, DRS, XPS and ICP. The results show that the immobilization of the cobalt containing specie is dependent on the point of zero charge of the TNT and no modifications on the structure and morphology were observed. No significant changes in the optical band gap were observed after B12 incorporation, but an increasing in the visible light absorption, which arises from charge transfer and d-d transitions of the cobalt, was visualized. The samples photocatalytic performance was studied for the hydroxyl radical production and the highest catalytic ability was achieved by the B12-HTNT sample. The catalytic ability of these new hybrid nanomaterials for two model pollutants photodegradation, phenol and rhodamine B (RhB) was investigated. For both pollutants, the best results were achieved using B12-HTNT with a removal of 94% of a 10 ppm RhB and 87% of a 20 ppm phenol solution in 90 min of irradiation (150 mL, 0.2 g catalyst/L). (C) 2016 Elsevier Masson SAS. All rights reserved.
- Síntese de nanomateriais por via biológica e estudos de fotodegradação de poluentesPublication . Vieira, Bernardete dos Santos; Costa, Maria ClaraA poluição ambiental por poluentes orgânicos assim como por resíduos metálicos presentes em descargas de efluentes aumenta diariamente afetando o nosso dia-a-dia. Usando sulfureto gerado biologicamente por ação de bactérias sulfato redutoras (SRB), é possível precipitar metais sob a forma de sulfuretos metálicos e estes, se semicondutores, podem ser usados posteriormente como catalisadores na fotodegradação de poluentes orgânicos. Este trabalho teve dois objetivos claros: o primeiro foi sintetizar nanopartículas de sulfuretos metálicos e respetivos nanocompósitos de dióxido de titânio (TiO2), com recurso ao sulfureto gerado biologicamente; o segundo foi a fotodegradação de poluentes orgânicos, neste caso do antibiótico cloranfenicol presente nos efluentes da indústria farmacêutica, usando como catalisadores as nanopartículas e os nanocompósitos sintetizados previamente. Foram realizadas sínteses químicas e “biológicas”, por forma a comparar as partículas obtidas por ambas, de modo a determinar-se se as nanopartículas sintetizadas biologicamente apresentam as mesmas características do que as sintetizadas quimicamente. Foram sintetizadas com sucesso nanopartículas de sulfureto de cádmio (CdS) e de sulfureto de prata (Ag2S). Estas últimas encontram-se numa mistura heterogénea de tamanhos, que variam entre os 63 – 173nm. Não foi possível obter sulfureto de níquel (NiS) nem sulfureto de cobalto (CoS) em nenhuma das sínteses. Realizaram-se ensaios de fotodegradação do cloranfenicol em fotorreator e à luz solar. Em ambos os ensaios nenhum dos catalisadores sintetizados previamente, obteve melhores resultados do que o TiO2 comercial. As nanopartículas e nanocompósitos de CdS sofreram fotocorrosão. Os nanocompósitos de sulfureto de cobre (CuS) com TiO2 não se mostraram capazes de degradar o antibiótico.
- Recovery of gold(0) nanoparticles from aqueous solutions using effluents from a bioremediation processPublication . Assunção, Ana; Vieira, Bernardete; Lourenço, J. P.; Costa, Maria ClaraThe use of biological processes with the aim of the recovery of gold from low-concentration solutions derived from leaching of secondary sources is gaining increasing importance owing to the scarcity of the primary resources and the economic and environmental advantages usually presented by these methods. Thus, the addition in batch and continuous processes of different solutions containing biogenic sulphide, which was generated by the activity of sulphate-reducing bacteria (SRB), to gold(III) solutions was investigated for that purpose. In the batch experiments, AuS nanoparticles with sizes of between 6 and 14 nm were obtained (corresponding to 100% removal of Au(III) from solution) if the biogenic sulphide was generated in a typical nutrient medium for SRB, whereas Au(0) nanoparticles with sizes of below 8 nm were obtained (corresponding to 62% removal of Au(III)) if effluent from a SRB bioremediation process for treating acid mine drainage (AMD) was used instead. These results stimulated the development of a continuous process of addition, in which two sulphide-rich effluents, which resulted from a SRB bioremediation process for treating two types of AMD (from a uranium mine and a polysulphide mine), were tested. In both cases, Au(0) nanoparticles with sizes of between 6 and 15 nm were mainly obtained, and the percentage removal of Au(III) from solution ranged from 76% to 100%. The processes described allow the simultaneous treatment of AMD and recovery of metallic gold nanoparticles, which are a product with a wide range of applications (e.g., in medicine, optical devices and catalysis) and high economic value. The synthesis process described in this work can be considered as novel, because it is the first time, to our knowledge, that the use of effluent from a SRB bioremediation process has been reported for the recovery of gold(III) as gold(0) nanoparticles.
- Photodegradation of chloramphenicol and paracetamol using PbS/TiO2 nanocomposites produced by green synthesisPublication . Palma, Tânia Cristina da Luz; Vieira, Bernardete; Nunes, J.; Lourenço, J. P.; Monteiro, O. C.; Costa, Maria ClaraThe present study describes the photocatalytic potential of the successfully synthesized nanocrystalline PbS/TiO2 nanocomposites in the photodegradation of chloramphenicol and paracetamol. PbS and PbS/TiO2 nanoparticles were synthesized using biological sulphide produced by sulphate-reducing bacteria in batch and in a coupled bioremediation system (upflow anaerobic packed-bed reactor) for acid mine drainage treatment, yielding near-complete metal precipitation (~ 100–99%, respectively). The PbS and PbS/TiO2 composites obtained using sulphide generated in batch have an average particle size ranging from 17 to 25 nm and 15 to 20 nm, respectively, while in bioreactor, both PbS and PbS/TiO2 particles have a similar size range from 20 to 50 nm. All the produced particles presented crystalline cubic structure. The specific surface area of TiO2 and PbS/TiO2 was estimated to be 46.559 m2/g and 38.005 m2/g, respectively. Chloramphenicol removal by photolysis was about 61% after 60 min of Hg irradiation and 36% under sunlight exposition. Chloramphenicol photodegradation using PbS/TiO2 as catalyst was successfully performed in a photoreactor (Hg medium pressure, 450 W) and under solar exposition with a high drug removal efficiency of 96% and 93% after 60 min and 240 min irradiation, respectively. Using TiO2 as a catalyst for photodegradation achieved 98% removal for both Hg and sunlight irradiation (UV index ranging 7–8) after 60 min and 240 min, respectively. Paracetamol removal by photolysis was about 18%. Drug’s photocatalytic degradation using PbS/TiO2 was successfully performed under sunlight exposition with a high removal efficiency of 93%, while in the presence of TiO2, the removal was complete, after 235 min irradiation.