An effective generation of reactive oxygen species (ROS) is of interest from the perspective of environmental technology and industrial chemistry, and here piezocatalysis and photocatalysis using ...heterostructures based on iodide‐doped BiVO4/BaTiO3 with photodeposited Ag or Cu nanoparticles (BiVO4:I/BTO‐Ag or BiVO4:I/BTO‐Cu) is studied. The generation rates of •OH and •O2− radicals over BiVO4:I/BTO‐Ag during piezophotocatalysis are 371 and 292 µmol g−1 h−1, respectively, and significantly higher than those of sole piezocatalysis and photocatalysis. These rates are among the highest reported for the production of free radicals with the piezophototronic effect. Among the catalysts, BiVO4:I/BTO shows the highest reactivity for the production of H2O2 in piezocatalysis (with a concentration of 468 µm after 100 min of irradiation, and still constantly increasing). On BiVO4:I/BTO‐Ag and BiVO4:I/BTO‐Cu, it seems that redundant electrons and holes had reacted effectively with the generated H2O2 and in turn had reduced their activities; however, the amounts of H2O2 that are formed on BiVO4:I/BTO‐Ag or BiVO4:I/BTO‐Cu under piezophotocatalysis are superior to those of individual piezocatalysis and photocatalysis. A piezophototronic coupling via an ultrasound‐mediated and piezoelectric‐based polarization field and photoexcitation accounting for the enhanced photocatalytic activity of the iodine‐doped heterostructures with plasmonically sized Ag or Cu nanoparticles is suggested.
Iodide‐doped BiVO4/BaTiO3 heterostructures produce piezoelectric potentials with ultrasound irradiation and catalyze the formation of reactive oxygen species. A combination of the piezophototronic effect and plasmonic excitation of BiVO4/BaTiO3‐Ag/Cu induce well‐separated photogenerated charges and an effective use of natural light and vibration energy in various catalytic reactions.
A heterogenized alternative to the homogeneous precapture of CO2 with amines and subsequent hydrogenation to MeOH was developed using aminated silica and a Ru‐MACHOTM catalyst. Commercial mesoporous ...silica was modified with three different amino‐silane monomers and used as support for the Ru catalyst. These composites were studied by TEM and solid‐state NMR spectroscopy before and after the catalytic reaction. These catalytic reactions were conducted at 155 °C at a H2 and CO2 pressures of 75 and 2 bar, respectively, with the heterogeneous system (gas‐solid) being probed with gas‐phase infrared spectroscopy used to quantify the resulting products. High turnover number (TON) values were observed for the samples aminated with secondary amines.
Heterogeneous catalysts were prepared and tested in the hydrogenation of CO2 to methanol. These are based on the concept of precapture and transformation used in homogeneous systems.
Calcium carbonate is an abundant biomineral that is of great importance in industrial or geological contexts. In recent years, many studies of the precipitation of CaCO3 have shown that amorphous ...precursors and intermediates are widespread in the biomineralization processes and can also be exploited in bio-inspired materials chemistry. In this work, the thorough investigation of a urinary stone of a guinea pig suggests that amorphous calcium carbonate (ACC) can play a role in pathological mineralization. Importantly, certain analytical techniques that are often applied in the corresponding analyses are sensitive only to crystalline CaCO3 and can misleadingly exclude the relevance of calcium carbonate during the formation of urinary stones. Our analyses suggest that ACC is the major constituent of the particular stone studied, which possibly precipitated on struvite nuclei. Minor amounts of urea, other stable inorganics, and minor organic inclusions are observed as well.
Microporous activated carbon was prepared by depositing and pyrolyzing propylene within the microporous voids of SAPO-37 and subsequently removing the template by a treatment with HCl and NaOH. The ...carbon had a high surface area and large micropore and ultramicropore volumes. The yield, crystallinity, morphology, and adsorption properties compared well with those of a structurally related zeolite-Y-templated carbon. No HF was needed to remove the SAPO-37 template in contrast to the zeolite Y template, which could be of industrial importance.
Porous tablets of crystalline calcium carbonate were formed upon sintering of a precursor powder of amorphous calcium carbonate (ACC) under compressive stress (20 MPa) at relatively low temperatures ...(120-400 °C), induced by pulsed direct currents. Infrared spectroscopy ascertained the amorphous nature of the precursor powders. At temperatures of 120-350 °C and rates of temperature increase of 20-100 °C min-1, the nanoparticles of ACC transformed into crystallites of mainly aragonite, which is generally difficult to achieve using wet-chemicals under kinetic control. The amorphous precursor particles (∼10 nm) transformed into crystallites (∼30-50 nm) during sintering. Consistently, the specific surface areas of 140-160 m2 g-1 for the precursor particles were reduced to 10-20 m2 g-1 for the porous tablets. The porous network within the tablets consisted of fused aragonite and vaterite particles in a ratio of ∼80:20. The fraction of aragonite to vaterite was invariant to the temperature and rate of temperature change used. The particle size increased only to a small amount on an increased rate of temperature change. At temperatures above 400 °C, porous tablets of calcite formed. The later transformation was under thermodynamic control, and led to a minor reduction of the specific surface area. The size of the crystallites remained small and the transformation to calcite appeared to be a solid-state transformation. Porous, template- and binder-free tablets of calcium carbonate could find applications in for example, biology or water treatment.
The reduction of CO2 is relevant for the production of compounds as part of the carbon capture and utilization research approaches. Thus, photocatalytic reduction of CO2 over a tailored BiOCl-based ...photocatalyst (BTEG) was tested under UV light (365 nm). BTEG was synthesized in the presence of triethylene glycol, which gave 4-nm crystallites, much smaller than the 30 nm crystallites of commercial BiOCl. Commercial BiOCl reduced CO2 mainly to methane with a minor fraction of ethanol, and was inactivated after 20 h. BTEG was a more active catalyst for CO2 photoreduction, producing approximately equal amounts of methane, methanol, and ethanol while consuming 0.38 µmol g−1 h−1 of CO2 before the experiment was stopped after 43 h, with the catalyst still active. The different products formed by the BTEG photocatalyst samples were tentatively ascribed to its greater content of {110} facets. Thus, in addition to band-gap tuning, the relative fractions of BiOCl facets had a key role in the effective photocatalytic reduction of CO2, and the BiOCl-based BTEG catalyst promoted the formation of important compounds as methanol and ethanol.
Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO2 over N2. Here, we showed that the exchangeable cations (e.g., Na+ or K+) on zeolite ZK-4 play ...an important role in the CO2 selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8–2.8 had very high CO2 selectivity when an intermediate number of the exchangeable cations were K+ (the rest being Na+). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO2 uptake capacity and very high CO2-over-N2 selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO2 selectivity with an intermediate number of K+ cations. The high CO2 selectivity was related to the K+ cation in the 8-rings of the α-cage, together with Na+ cations in the 6-ring, obstructing the diffusion of N2 throughout the zeolite. The positions of the K+ cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO2, as revealed by in situ X-ray diffraction. The CO2-over-N2 selectivity was somewhat reduced when the number of K+ cations approached 100%. This was possibly due to the shift in the K+ cation positions in the 8-ring when the number of Na+ was going toward 0%, allowing N2 diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO2 was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO2 could be relevant for applications in carbon capture and bio- and natural gas upgrading.
A series of porous polymers with ultramicropores and tunable mesopores were synthesized by condensation reaction (Schiff base) of triamine and trialdehyde monomers. They had specific surface areas ...and pore volumes of up to 694 m2/g and 0.67 cm3/g. The ultramicropores seemed to have been templated by the solvent (DMSO) primarily. The size of the mesopores depended strongly on the amine-to-aldehyde ratio used during synthesis. With a moderate aldehyde excess, the irregular mesopores of the porous polymers increased in size. The polymers' capacities to adsorb CO2 were large (0.93–1.58 mmol/g at 0.15 bar and 2.20–3.28 mmol/g at 1 bar; 0 °C) due to their large ultramicropore volumes, and the estimated CO2-over-N2 selectivities were also relatively high (31–90 for CO2/N2 mixtures with 15 v%/85 v% at 0 °C). The uptake of CO2 on the polymers was quite rapid, and it appears advantageous to have a combination of meso- and ultramicropores in this class of polymers for applications in carbon capture and storage.
Display omitted
•Polyimines with ultramicropores and mesopores were synthesized.•The porosities of porous polymers were tunable under off-stoichiometric synthetic conditions.•The porous polymers have high CO2 uptakes and high CO2-over-N2 selectivities.•The uptake of CO2 on the porous polymers was quite rapid.
Micrometer-sized particles of calcium carbonate were formed by adding NaHCO3 (aq) to a buffered aqueous solution of CaCl2 (aq) and polyelectrolytes. Particle morphology and crystal polymorphology ...were tuned by varying the stirring rate. Vigorous stirring led to the formation of micrometer-sized spherical particles of nanocrystalline vaterite; slow stirring formed rhombohedral nanostructured particles of calcite.
Organosilica foams are commonly formed by a multistep process involving hydrolysis and condensation of organosilanes followed by solvent exchange and e.g. supercritical CO 2 drying. Here, we propose ...a straightforward route to synthesize lightweight hybrid foams from aqueous dispersions of a surface-active aminosilane (AS) and TEMPO-oxidized cellulose nanofibrils (TCNFs). Air bubbles were introduced in the TCNF/AS dispersion by mechanical blending, and the foam was solidified by oven-drying. Evaporative drying at mild temperature (60 °C) resulted in dry foams with low densities (25–50 kg m −3 ), high porosities (96–99%) and macropores of 150–300 μm in diameter. The foaming and foam stabilization were successful for a pH range of 10.4–10.8 for foams containing 55–65 wt% of organosilica in the dry state. The protonation of AS increased the ionic strength of the dispersion and enhanced the interparticle interactions with TCNFs and, in turn, the foam viscosity and foam stability upon drying. The evaporation of water catalyzed the condensation of the AS to form low-molecular linear polymers, which resulted in an increased stiffness and strength of the foam lamella. The crosslinking of the AS polymeric network with the TCNF matrix allowed lightweight and homogeneous macroporous foams to be obtained with controlled densities and high amine content (amine content >4.5 mmol g −1 ) using an environmentally friendly technique.
PDF
