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•A K impregnated, Ga substituted microwave aged hydrotalcite was prepared.•An astonishing CO2 sorption capacity of 2.09mol/kg was achieved at 573K.•Two different kinetic contributions ...were identified during CO2 uptakes.
Hydrotalcite-like materials were prepared by the co-precipitation method, characterized by PXRD, FTIR, physical adsorption of N2 at 77K and SEM/EDS, and after calcination they were tested for CO2 sorption at 573K under dry conditions. The simultaneous effect of aluminum partial substitution with gallium, microwave aging of the precipitated gel and modification with potassium on their sorption capacity was assessed. Sorption isotherms were well described by the Freundlich model for all samples. A remarkable sorption capacity of 2.09mol/kg at 3.10bar was obtained for the Ga-containing sample, aged under microwave irradiation and impregnated with 20wt% of potassium. The sorption kinetics was analyzed from uptake measurements and two distinct contributions (related to fast and slow uptakes), which are considered by the proposed model, were observed. Despite the slower sorption kinetics on the potassium-modified samples, they showed sorption capacities considerably higher than those reported in the literature for commercial hydrotalcites under similar conditions, even for prolonged exposition to CO2.
Organic−inorganic hybrid hydrotalcite-like compounds containing Zn2+ and Al3+ in the brucite-like layers (nominal Zn:Al molar ratios of 2:1, 3:1, and 4:1) and lactate (Lc) as counteranion were ...synthesized by coprecipitation using 0:1 and 3:1 lactic acid:Al molar ratios to prepare the starting solutions. Their physicochemical properties were studied by element chemical analysis, powder X-ray diffraction, infrared spectroscopy, and thermal analyses. Powder X-ray diffraction showed a pattern characteristic of a hydrotalcite-like structure. FT-IR spectroscopy confirmed the retention of the lactate anions in the interlayer without further contamination. Thermal analyses showed four stages of weight loss and five of heat change when recorded under oxidizing conditions. Dispersion of the dried samples in decarbonated water by ultrasound-assisted treatment at room temperature led to delamination of all wet fractions. Upon solvent evaporation, dried fractions restacked with a higher crystallinity and an increase in basal spacing.
Two series of layered double hydroxides (LDHs) with compositions Mg,Al–CO
3 and Mg,Cr–CO
3 were prepared by microwave and conventional hydrothermal treatment to study the role of microwave radiation ...on their physicochemical properties. Aging temperature was 125
°C in all cases. The samples were fully characterised by element chemical analysis, powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis,
27Al MAS NMR, FT-IR and UV–Vis diffuse reflectance spectroscopies, and specific surface area and porosity assessment by N
2 adsorption at −196
°C. In all cases, the only crystalline phase obtained was hydrotalcite which crystallinity is further enhanced by microwave hydrothermal treatment than by conventional hydrothermal treatment. The microwave-aged samples also have larger amounts of interlayer water and smaller particle size than those prepared by conventional hydrothermal ageing. The textural properties of the solids are strongly modified during the ageing treatment, and large specific surface areas values are observed at shorter times for those samples subjected to microwave radiation.
The effect of microwave–hydrothermal treatment (MWHT) on the properties of Mg,Al-layered double hydroxides with the hydrotalcite-like structure intercalated with carbonate and organic anions ...(terephthalate, adipate and dodecyl sulphate) and on their thermal decomposition products is studied. All solids have been characterised by element chemical analysis, powder X-ray diffraction, FT-IR spectroscopy, thermal analysis, transmission electron microscopy, specific surface area determination by N
2 adsorption at −
196
°C and particle size distribution. The MWHT yielded a larger improvement of the crystallinity for carbonate-containing samples than for the organic-intercalated ones; however, although the crystallinity is not greatly modified for the latter, the thermal properties and particle size distribution are significantly affected by the ageing treatment.
Potassium birnessites were prepared using two methods, sol-gel or oxidation. The solids were characterised by element chemical analysis, powder X-ray diffraction, FT-IR spectroscopy, thermal ...analyses, and nitrogen adsorption. The evolution of the properties as a function of the preparation method was discussed. The photocatalytic performance of these solids was preliminarily tested for the degradation of 4-nitrophenol. The degradation pathway and the nature of the by-products were investigated by mass spectrometry. The solids showed good catalytic behaviour, although their preparation must be improved, mainly concerning the calcination step involved in sol-gel synthesis, which led to the formation of Mn
2
O
3
that worsened the catalytic behaviour.
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A potassium impregnated magnesium–aluminum–gallium hydrotalcite, aged under microwave irradiation (K-HTCGa MW), was tested for CO2 capture during a long term breakthrough experimental ...campaign. Higher total pressures, CO2 concentrations in the feed and temperatures resulted in higher outstanding sorption capacities. The presence of H2O was considerably advantageous for increasing the CO2 capture. Finally, it was observed that higher total pressures, temperatures and H2O contents allowed higher bed usage efficiencies. EDS elemental distribution mapping showed that potassium and gallium were mobilized towards the sorbent surface under wet conditions, which could have contributed to the enhanced behavior of the sorbent under such conditions.
•CO2 sorption isotherms of Ga-substituted hydrotalcites were determined at 573K.•Promotion with K led to increased sorption capacity towards CO2.•Isotherms are adequately fitted with a simple ...Freundlich equation.•Outstanding working capacity was obtained at 573K after sorption–desorption cycles.•The kinetic model proposed adequately fitted CO2 sorption/desorption uptakes.
Hydrotalcites (HTC) and gallium-substituted hydrotalcites (HTC-10Ga) were prepared by co-precipitation and modified by impregnation with alkali (K and Cs) and alkaline-earth (Sr) metals. The materials were tested and screened for CO2 sorption at 573K. The results indicate that the modification with potassium greatly enhanced the sorption capacity when compared with the original materials (both HTC and HTC-10Ga). An outstanding sorption capacity (2.01mmolcm−3 at 1.08bar) was obtained for the sample partially substituted with gallium and modified with potassium (HTC-10Ga–20K). Moreover, this material was also submitted to sorption–desorption cycles towards CO2 under low-pressure conditions (<0.0001–0.15bar) to assess its use in cyclic operation. An average working capacity of 0.97mmolcm−3 and 0.25mmolcm−3 was obtained after repeated cycles at 573K and 473K, respectively. The sorption kinetics was assessed through uptake measurements, showing two parallel resistances, which were well described by the proposed model.
Montmorillonite has been treated with Ti-based solutions, alone or doped with Cu2+, Fe3+ or Cr3+ cations, yielding new intercalated solids, which have been calcined at various temperatures to test ...the stability of the so-formed pillars. The solids calcined at 500°C were fully characterized by chemical analysis, X-ray diffraction, FT-IR spectroscopy, thermal analyses, nitrogen adsorption and acidity evaluation. The evolution of the specific surface area, porosity and acidic properties is discussed, analysing the effect of pillaring and doping procedures on these properties.
•Ti-PILC montmorillonites doped with Cu2+, Fe3+ or Cr3+ were prepared.•Doping elements, although in low content, strongly affected polymerization of Ti.•Doped solids were better ordered than undoped pillared montmorillonite.•Specific surface area and acidity were larger in the doped solids.
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•TiO2 was doped with B, F, N and P during sol–gel preparation.•Anatase phase was obtained in all cases upon calcination of the solids at 400°C.•The doped-TiO2 catalysts were used for ...degradation of emerging contaminants.•Doping with 5wt% B led to the most active catalyst.•The degradation trend was caffeine>diclofenac=ibuprofen>salicylic acid.
Photocatalysts composed of titanium dioxide modified with B, F, N and P have been synthesized, characterized and applied to the degradation of caffeine, diclofenac, ibuprofen and salicylic acid. The modified TiO2 samples were prepared by the sol–gel technique starting from titanium(IV) isopropoxide and using H3BO3, NH4F, N(C2H5OH)3 and H3PO4 as precursors of the modifiers, with the content varying between 0 and 5wt%. Structural characterization was based on nitrogen physisorption at −196°C, powder X-ray diffraction (PXRD), simultaneous thermogravimetric/differential thermal analysis (TG/DTA) and X-ray photoelectron spectroscopy (XPS). The structural properties of the modified TiO2 solids were significantly different depending on the nature and amount of modifiers and the calcination temperature. TiO2 in the anatase phase was obtained in all cases and was stable upon calcination at 400°C. The photocatalytic degradation of caffeine, diclofenac, ibuprofen and salicylic acid by modified TiO2 was investigated under ultraviolet irradiation at 25°C. The photocatalytic degradation behavior followed the order: caffeine>diclofenac=ibuprofen>salicylic acid. B-doped TiO2 was the most efficient catalyst in the degradation of these selected emerging contaminants.
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► Zn/Al hydrotalcites were used as precursors for the obtention of ZnO and ZnAl
2O
4. ► Zn
2+/Al
3+ ratio and calcination temperature were modulated to obtain photocatalyts. ► Pure ...spinel was obtained after a treatment in NaOH of the samples calcined at 800
°C. ► All the samples were active as photocatalysts for 2-propanol degradation. ► Photocatalytic activity increased with Zn amount and calcination temperature.
Layered double hydroxides (LDH) containing zinc and aluminium within the brucite-like layers and carbonate as the interlayer anion have been used as precursors for the preparation of mixed metal oxides by calcination. Zinc oxide and the ZnAl
2O
4 spinel were formed with different degree of crystallinity depending of two parameters, i.e., the Zn
2+/Al
3+ molar ratio and the calcination temperature (500–800
°C) of the LDH precursor. A pure spinel phase was obtained to remove ZnO upon a basic post-treatment in NaOH solution of the samples calcined at 800
°C. All the samples were tested for the photodegradation of 2-propanol in gas–solid regime. All the samples resulted active as heterogeneous photocatalysts. The photocatalytic activity increased by increasing the Zn
2+/Al
3+ molar ratio and the calcination temperature of the solids.
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