RESUMO
The current increase in the use of photovoltaic (PV) energy demands the search for solutions to recycle end-of-life modules. This study evaluated the use of a mechanical pre-treatment in the thermal recycling of c-Si crystalline PV modules, which were submitted to recycling routes to separate and concentrate the materials of interest. The first route was constituted by only thermal treatment, and the second route was constituted by a mechanical pre-treatment to remove the polymers from the backsheet, and subsequent thermal treatment. The exclusively thermal route was performed at 500°C, varying dwell times between 30 and 120 minutes in the furnace. In this route, the best results were obtained in 90 minutes, with a maximum degradation of 68% of the polymeric mass. In route 2, a micro-grinder rotary tool was used to remove the polymers from the backsheet and, subsequently, thermal treatment performed at 500°C, with dwell times in the furnace ranging between 5 and 30 minutes. The mechanical pre-treatment removed about 10.32 ± 0.92% of the mass of the laminate PV module. By this route, only 20 minutes of thermal treatment were needed for the total decomposition of the polymers, that is, a reduction of 78% in the oven time. With route 2, it was possible to obtain a concentrate with 30 times more silver than the PV laminate and 40 times more than a high-concentration ore. Furthermore, with route 2 it was possible to reduce the environmental impact of heat treatment and energy consumption.
Assuntos
Polímeros , Reciclagem , Reciclagem/métodos , Meio AmbienteRESUMO
Photocatalytic water treatment has significant potential to disinfect and degrade recalcitrant organic pollutants while minimizing the need to add chemicals, but current approaches have poor energy efficiency due, in part, to inefficient utilization of photo-generated reactive oxygen species (ROS). Organic coatings such as cyclodextrin (CD) can adsorb target contaminants and bring them close to the photocatalyst surface to enhance ROS utilization efficiency, but the coatings themselves are susceptible to ROS attack. Here, we report an ROS-resistant fluorinated CD polymer (CDP) that can both adsorb contaminants and resist degradation by ROS, yielding a more efficient material for "trap and zap" water treatment. We produced the CDP through condensation polymerization of ß-cyclodextrin and tetrafluoroterephthalonitrile, resulting in a cross-linked, covalently bound CD film that is much more stable than prior approaches involving physi-sorption. We optimized the coating thickness on TiO2 microspheres to improve the efficiency of contaminant degradation, and found that increasing the CDP content enhanced BPA adsorption but also occluded photocatalytic sites and hindered photocatalytic degradation. The optimum content of CDP was 5% by weight, and this optimal CDP-TiO2 composition had a BPA adsorption capacity of 36.9 ± 1.0 mg g-1 compared with 24.1 ± 1.1 mg g-1 for CD-coated TiO2 (CD-TiO2) and 21.9 ± 1.5 mg g-1 for bare TiO2. CDP-TiO2 exhibited minimal photoactivity loss after 1000 h of repeated use in DI water under UVA irradiation (365 nm, 3.83 × 10-6 E L-1s-1), and no release of organic carbon from the coating was detected. Photocatalytic treatment using CDP-TiO2 only showed a small decrease in BPA removal efficiency in secondary effluent after four 3-h cycles, from 80.2% to 71.7%. In contrast, CD-TiO2 and P25 removed only 29.8% and 6.2% of BPA after 4 cycles, respectively. Altogether, the CDP-TiO2 microspheres represent promising materials for potential use in photocatalytic water treatment.