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This study aims to investigate the physical and chemical characterization of six fly ash samples obtained from different municipal solid waste incinerators (MSWIs), namely grate furnaces, rotary kiln, and fluidized bed reactor, to determine their potential for CO2 and thermochemical energy storage (TCES). Representative samples were characterized via simultaneous thermal analysis (STA) in different atmospheres, i.e., N2, air, H2O, CO2, and H2O/CO2, to identify fly ash samples that can meet the minimum requirements, i.e., charging, discharging, and cycling stability, for its consideration as TCES and CO2-storage materials and to determine their energy contents. Furthermore, other techniques, such as inductively coupled plasma optical emission spectroscopy, X-ray fluorescence (XRF) spectrometry, X-ray diffraction (XRD), scanning electron microscopy, leachability tests, specific surface area measurement based on the Brunauer&ndash, Emmett&ndash, Teller method, and particle-size distribution measurement, were performed. XRF analysis showed that calcium oxide is one of the main components in fly ash, which is a potentially suitable component for TCES systems. XRD results revealed information regarding the crystal structure and phases of various elements, including that of Ca. The STA measurements showed that the samples can store thermal heat with energy contents of 50&ndash, 394 kJ/kg (charging step). For one fly ash sample obtained from a grate furnace, the release of the stored thermal heat under the selected experimental conditions (discharging step) was demonstrated. The cycling stability tests were conducted thrice, and they were successful for the selected sample. One fly ash sample could store CO2 with a storage capacity of 27 kg CO2/ton based on results obtained under the selected experimental conditions in STA. Samples from rotary kiln and fluidized bed were heated up to 1150 &deg, C in an N2 atmosphere, resulting in complete melting of samples in crucibles, however, other samples obtained from grate furnaces formed compacted powders after undergoing the same thermal treatment in STA. Samples from different grate furnaces showed similarities in their chemical and physical characterization. The leachability test according to the standard (EN 12457-4 (2002)) using water in a ratio of 10 L/S and showed that the leachate of heavy metals is below the maximum permissible values for nonhazardous materials (except for Pb), excluding the fly ash sample obtained using fluidized bed technology. The leachate contents of Cd and Mn in the fly ash samples obtained from the rotary kiln were higher than those in other samples. Characterization performed herein helped in determining the suitable fly ash samples that can be considered as potential CO2-storage and TCES materials.

In this work, we employed a step-by-step sol-gel process to controllably deposit ultra-thin layers of SiO2 on anatase nanoparticles in the range between 0 and 1 nm. The deposition was confirmed by TEM, EDX, and ATR-FTIR (e.g., Ti-O-Si band at 960 cm-1). Zeta potential measurements unravelled a continuous change in surface charge density with increasing silica shell thickness. The photocatalysts were evaluated towards adsorption and degradation of positively-charged and negatively-charged dyes (methylene blue, methyl orange) under UV illumination. The growth mechanism follows the Stranski&ndash, Krastanov model with three thickness regimes: (a) Flat islands (first step), (b) mono/bilayers (second/third step), and (c) regular thick films (fourth/fifth step). The results suggest different rate limiting processes for these regimes: (a) For the thinnest scenario, acidic triple-phase boundaries (TPBs) increase the activity for both dyes with their accessibility being the rate limiting step, (b) for continuous mono/bilayers, dye adsorption on the negatively-charged SiO2 shells becomes the rate liming step, which leads to a stark increase in activity for the positively-charged MB and a decrease for MO, (c) for thicker shells, the activity decreases for both dyes and is limited by the charge transport through the isolating shells.