Basic Properties of MgAl-Mixed Oxides in CO2 Adsorption at High Temperature.

The increase of consciousness towards global warming and the need to reduce greenhouse gas emissions lead to the necessity of finding alternative applications based on easy-to-use materials in order to control and reduce global CO2 emissions. Layered Double Hydroxides (LDHs) and LDH-derived materials are potentially good adsorbents for CO2, thanks to their low cost, easy synthesis, high sorption capacity, and surface basicity. They have been intensively studied in CO2 capture at high temperature, presenting variable sorption capacities for MgAl LDHs with the same composition, but prepared under different synthesis conditions. The ambient temperature coprecipitation synthesis method is an attractive one-step procedure to synthesize LDHs under mild conditions, with low energy consumption and short synthesis time. The present study is based on the synthesis and characterization of hydrotalcites by a mild-conditions coprecipitation process and the production of derived mixed oxides to be used as CO2 adsorbents. A critical comparison to similar materials is reported. Moreover, the effect of the surface basicity of the derived mixed oxides (measured by adsorption calorimetry) and the CO2 sorption capacity are discussed, showing a linear correlation between the amount of weak and very strong basic sites and the CO2 adsorption behavior.

Corn Cobs' Biochar as Green Host of Salt Hydrates for Enhancing the Water Sorption Kinetics in Thermochemical Heat Storage Systems.

Heat storage technologies are essential for increasing the use of solar energy in the household sector. Their development can be achieved by designing new storage materials; one way is to impregnate a porous matrix with hygroscopic salts. In this article, the possibility of using biochar-based composite sorbents to develop promising new heat storage materials for efficient thermal storage is explored. Biochar-based composites with defined salt loadings (5, 10, 15, and 20%) were produced by impregnating MgSO4 into a biochar matrix derived from corn cobs. The new materials demonstrated a high water sorption capacity of 0.24 g/g (20MgCC). After six successive charging-discharging cycles (dehydration/dehydration cycles), only a negligible variation of the heat released and the water uptake was measured, confirming the absence of deactivation of 20MgCC upon cycling. The new 20MgCC composite showed an energy storage density of 635 J/g (Tads = 30 °C and RH = 60%), higher than that of other composites containing a similar amount of hydrate salt. The macroporous nature of this biochar increases the available surface for salt deposition. During the hydration step, the water molecules effectively diffuse through a homogeneous layer of salt, as described by the intra-particle model applied in this work. The new efficient biochar-based composites open a low-carbon path for the production of sustainable thermal energy storage materials and applications.

Tomato waste biochar in the framework of circular economy.

Tomato pomace was slowly pyrolyzed at 350 and 550 °C (under an N2 flow of 50 L/h) at a rate of 6 °C/min and a residence time of 1:30 h to produce two biochars named B350 and B550, respectively. In addition, the two biochars were chemically activated with ΚΟΗ (at a ratio of 1:10 w/v) at 800 °C to produce two new materials named BA350 and BA550. The four biochars produced were characterized physically and chemically (pH, yield, calorific value). They were also analyzed by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (B.E.T), elemental analysis (EA), and thermogravimetric analysis (TGA). The results showed that as the pyrolysis temperature increased (350 to 550 °C), the specific surface area (SSA) increased. The latter was also significantly increased by the activation process. EA showed a variation in the mineral content of the produced biochars, resulting in a different content of the biochars after activation. The parameters studied showed that biochars from tomato waste could be used as an organic amendment to improve soil fertility in agricultural. In addition, because of their ability to absorb water, they could be used as a water reservoir in soils in arid areas.

Unveiling the Potential of Corn Cob Biochar: Analysis of Microstructure and Composition with Emphasis on Interaction with NO2.

In the context of sustainable solutions, this study examines the pyrolysis process applied to corn cobs, with the aim of producing biochar and assessing its effectiveness in combating air pollution. In particular, it examines the influence of different pyrolysis temperatures on biochar properties. The results reveal a temperature-dependent trend in biochar yield, which peaks at 400 °C, accompanied by changes in elemental composition indicating increased stability and extended shelf life. In addition, high pyrolysis temperatures, above 400 °C, produce biochars with enlarged surfaces and improved pore structures. Notably, the highest pyrolysis temperature explored in this study is 600 °C, which significantly influences the observed properties of biochars. This study also explores the potential of biochar as an NO2 adsorbent, as identified by chemical interactions revealed by X-ray photoelectron spectroscopy (XPS) analysis. This research presents a promising and sustainable approach to tackling air pollution using corn cob biochar, providing insight into optimized production methods and its potential application as an effective NO2 adsorbent to improve air quality.

Low Metal Loading (Au, Ag, Pt, Pd) Photo-Catalysts Supported on TiO2 for Renewable Processes.

Photo-catalysts based on titanium dioxide, and modified with highly dispersed metallic nanoparticles of Au, Ag, Pd and Pt, either mono- or bi-metallic, have been analyzed by multiple characterization techniques, including XRD, XPS, SEM, EDX, UV-Vis and N2 adsorption/desorption. Mono-metallic photo-catalysts were prepared by wet impregnation, while bi-metallic photocatalysts were obtained via deposition-precipitation (DP). The relationship between the physico-chemical properties and the catalyst's behavior for various photo-synthetic processes, such as carbon dioxide photo-reduction to liquid products and glucose photo-reforming to hydrogen have been investigated. Among the tested materials, the catalysts containing platinum alone (i.e., 0.1 mol% Pt/TiO2) or bi-metallic gold-containing materials (e.g., 1 wt% (AuxAgy)/TiO2 and 1 wt% (AuxPtz)/TiO2) showed the highest activity, presenting the best results in terms of productivity and conversion for both applications. The textural, structural and morphological properties of the different samples being very similar, the main parameters to improve performance were function of the metal as electron sink, together with optoelectronic properties. The high activity in both applications was related to the low band gap, that allows harvesting more energy from a polychromatic light source with respect to the bare TiO2. Overall, high selectivity and productivity were achieved with respect to most literature data.

Effect of Metal Cocatalysts and Operating Conditions on the Product Distribution and the Productivity of the CO2 Photoreduction.

The CO2 photoreduction is a promising way to convert one of the most abundant greenhouse gases to valuable chemicals. The photoreduction in the liquid phase is limited by the low solubility of CO2 in water, but this point is overcome here by using an innovative photoreactor, which allows one to work up to pressures of 20 bar, improving the overall productivity. The photoreduction was performed in the presence of Na2SO3 and using in primis commercial titanium dioxide (P25) and a set of titania catalysts functionalized by surface deposition of either monometallic or bimetallic cocatalysts. The gaseous products were hydrogen and traces of CO, while, in the liquid phase, formic acid/formate, formaldehyde and methanol were quantitatively detected. The pH was observed to shift the products distribution. A neutral environment led mainly to hydrogen and methanol, while, at pH 14, formate was the most abundant compound. The trend for monometallic cocatalysts showed enhanced productivity when using noble metals (i.e., gold and platinum). In order to limit the cost of the catalytic material, bimetallic cocatalysts were explored, adding titania with Au+Ag or Au+Pt. This may open to the possibility of performing the reaction with a smaller amount of the most expensive metals. In the end, we have expressed some conclusions on the cost of the photocatalysts here employed, to support the overall feasibility assessment of the process.

Potential Valorization of Waste Tires as Activated Carbon-Based Adsorbent for Organic Contaminants Removal.

The present study investigates the potential of waste tires to produce a valuable adsorbent material for application in wastewater treatment. In the first stage, the pyrolysis of ground rubber tire was explored using non-isothermal and isothermal thermogravimetric analysis experiments. The effect of operating parameters, such as heating rate and pyrolysis temperature, on the pyrolysis product yields was considered. The slow pyrolysis of ground rubber tire was taken up in a large-scale fixed-bed reactor for enhanced char recovery. Four pyrolysis temperatures were selected by thermogravimetric data. The product yields were strongly influenced by the pyrolysis temperature; at higher temperatures, the formation of more gases and liquid was favored, while at lower pyrolysis temperatures, more char (solid fraction) was formed. The produced chars were characterized in terms of mineral composition, textural properties, proximate analysis, and structural properties to identify the relationships between the pyrolysis temperature and the char properties. In a second step, a series of activated chars were prepared, starting from the pyrolytic chars via chemical and/or physical activation methods. Then, the activated chars were characterized and tested as adsorbents for atrazine and ibuprofen. Adsorption experiments in aqueous media were carried out in a small-scale batch reactor system. Chemical activation seems appropriate to significantly reduce the inorganic compounds initially present in ground rubber tire and contribute to an important increase in the surface area and porosity of the chars. Adsorption experiments indicated that chemically activated chars exhibit high aqueous adsorption capacity for atrazine.

Sustainable metropolitan areas perspectives through assessment of the existing waste management strategies.

Human activities are considered among the main producers of any kind of pollution. This paper, through a Driver-Pressure-State-Impact-Response (DPSIR) model analyses, focuses on the evaluation and assessment of the existing practices, procedures, and results obtained in order to determine whether the municipal solid waste (MSW) management implemented in three major Greek municipalities in the greater urban area of Attica, namely the municipalities of Nea Smirni, Vyronas, and Piraeus, could be considered viable and sustainable. The evaluation indicated that MSW in Greek cities have reduced over the last years, also suggesting a steady downward trend, which could be considered consistent with that of the per capita incomes in Greece due to the extended economic austerity, while at the same time the recycling indicator seems to optimize. The results are very useful for policymakers and local authorities towards taking actions related to the targets set from the circular economy strategies as well as the targets set from United Nation Development Program and the European Green Deal Strategy.

Layered double hydroxides and LDH-derived materials in chosen environmental applications: a review.

With increasing global warming awareness, layered double hydroxides (LDHs), hydrotalcites, and their related materials are key components to reduce the environmental impact of human activities. Such materials can be synthesized quickly with high efficiency by using different synthesis processes. Moreover, their properties' tunability is appreciated in various industrial processes. Regarding physical and structural properties, such materials can be applied in environmental applications such as the adsorption of atmospheric and aqueous pollutants, hydrogen production, or the formation of 5-hydroxymethylfurfural (5-HMF). After the first part that was dedicated to the synthesis processes of hydrotalcites, the present review reports on specific environmental applications chosen as examples in various fields (green chemistry and depollution) that have gained increasing interest in the last decades, enlightening the links between structural properties, synthesis route, and application using lamellar materials.

Synthesis, Characterization and Catalytic Activity of Ternary Oxide Catalysts Using the Microwave-Assisted Solution Combustion Method.

Ni-Co-Al, Ni-Cu-Al and Co-Cu-Al ternary oxide catalysts, with a fixed 5 wt% transition metal loading, were prepared by the microwave-assisted solution combustion method and tested in CO oxidation. The bulk and surface properties of the catalysts were investigated, using XRD, N2 adsorption-desorption, SEM, XPS and TEM techniques. XRD, XPS and TEM results revealed that nickel and cobalt were present as spinels on the surface and in the bulk. Differently, copper was preferentially present in "bulk-like" CuO-segregated phases. No interaction between the couples of transition metal species was detected, and the introduction of Cu-containing precursors into the Ni-Al or Co-Al combustion systems was not effective in preventing the formation of NiAl2O4 and CoAl2O4 spinels in the Ni- or Co-containing catalysts. Copper-containing catalysts were the most active, indicating that copper oxides are the effective active species for improving the CO oxidation activity.

Free-standing cellulose film containing manganese dioxide nanoparticles and its use in discoloration of indigo carmine dye.

In this study, we report the production of a free-standing film of non-modified cellulose impregnated with 12 wt.% of MnO2 nanoparticles with less than 100 nm in size. The method here described can be applied to the immobilization of different types of nanoparticles. The film was prepared by dissolving microcrystalline cellulose in an ionic liquid followed by its regeneration by adding water to the former solution. Then, the wet film was impregnated with the nanoparticles by dipping it in a MnO2 dispersion. Electron microscopy images revealed manganese dioxide nanoparticles distributed not only at the film surface but also in its interior. The cellulose film impregnated with MnO2 nanoparticles was capable of efficiently discolouring an Indigo Carmine dye solution in 25 min upon ambient light. The film was easily removed from the dye solution and repeatedly reused for at least 10 times without losing its discolouring efficiency.

Binary Oxides Prepared by Microwave-Assisted Solution Combustion: Synthesis, Characterization and Catalytic Activity.

Three different alumina-based Ni, Cu, Co oxide catalysts with metal loading of 10 wt %, and labeled 10Ni⁻Al, 10Co⁻Al and 10Cu⁻Al, were prepared by microwave-assisted solution combustion. Their morphological, structural and surface properties were deeply investigated by complementary physico-chemical techniques. Finally, the three materials were tested in CO oxidation used as test reaction for comparing their catalytic performance. The 10Cu⁻Al catalyst was constituted of copper oxide phase, while the 10Ni⁻Al and 10Co⁻Al catalysts showed the presence of "spinels" phases on the surface. The well-crystallized copper oxide phase in the 10Cu⁻Al catalyst, obtained by microwave synthesis, allowed for obtaining very high catalytic activity. With a CO conversion of 100% at 225 °C, the copper containing catalyst showed a much higher activity than that usually measured for catalytic materials of similar composition, thus representing a promising alternative for oxidation processes.

Systems for stimuli-controlled release: Materials and applications.

The design and development of delivery controlled systems of molecules of interest has attracted great interest over the last years. pH variation, light irradiation, temperature increasing, variation of the redox potential and the application of a magnetic field are among the most widely used stimuli that can be used to induce the release of an active molecule in a medium. The dominance of pH and photo-controlled release is clearly highlighted by the numerous articles published in these fields as well as all the related applications. In the case of pH-controlled release, two main parameters govern the release: the solubility of the active molecule in the releasing medium and the stability of the carrier materials. In the photo-controlled release, the carrier needs to contain a photosensible functionality; this stimulus can be successfully applied in the medical field when red light, that is able to penetrate the human tissues, is used. A large panel of applications of controlled release can be identified in the pharmaceuticals, agriculture, cosmetics, chemistry and dyes industry fields. More recently, biological, enzymatic, and mechanical (ultrasounds, stretching, shear stress) stimuli have been developed for target applications, in particular for drugs and hormones release. Consequently, many types of materials (polymers, silica, oxides, MOF…) can be used as carrier in relation to their compatibility with the active molecule and the type of releasing medium. This review aims to gives a useful overview on the materials, applications and mechanisms implied in stimuli-controlled release.

Factors Influencing NO2 Adsorption/Reduction on Microporous Activated Carbon: Porosity vs. Surface Chemistry.

The textural properties and surface chemistry of different activated carbons, prepared by the chemical activation of olive stones, have been investigated in order to gain insight on the NO2 adsorption mechanism. The parent chemical activated carbon was prepared by the impregnation of olive stones in phosphoric acid followed by thermal carbonization. Then, the textural properties and surface chemistry were modified by chemical treatments including nitric acid, sodium hydroxide and/or a thermal treatment at 900 °C. The main properties of the parent and modified activated carbons were analyzed by N2-adsorption, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to enlighten the modifications issued from the chemical and thermal treatments. The NO2 adsorption capacities of the different activated carbons were measured in fixed bed experiments under 500 ppmv NO2 concentrations at room temperature. Temperature programmed desorption (TPD) was applied after adsorption tests in order to quantify the amount of the physisorbed and chemisorbed NO2. The obtained results showed that the development of microporosity, the presence of oxygen-free sites, and the presence of basic surface groups are key factors for the efficient adsorption of NO2.

A Comparative Study of Basic, Amphoteric, and Acidic Catalysts in the Oxidative Coupling of Methanol and Ethanol for Acrolein Production.

The impact of acid/base properties (determined by adsorption microcalorimetry) of various catalysts on the cross-aldolization of acetaldehyde and formaldehyde leading to acrolein was methodically studied in oxidizing conditions starting from a mixture of methanol and ethanol. The aldol condensation and further dehydration to acrolein were carried out on catalysts presenting various acid/base properties (MgO, Mg-Al oxides, Mg/SiO2 , NbP, and heteropolyanions on silica, HPA/SiO2 ). Thermodynamic calculations revealed that cross-aldolization is always favored compared with self-aldolization of acetaldehyde, which leads to crotonaldehyde formation. The presence of strong basic sites is shown to be necessary, but a too high amount drastically increases COx production. On strong acid sites, production of acrolein and carbon oxides (COx ) does not increase with temperature. The optimal catalyst for this process should be amphoteric with a balanced acid/base cooperation of medium strength sites and a small amount (<100 µmol g-1 ) of very strong basic sites (Qdiff >150 kJ mol-1 ).

Influence of Catalyst Acid/Base Properties in Acrolein Production by Oxidative Coupling of Ethanol and Methanol.

Oxidative coupling of methanol and ethanol represents a new route to produce acrolein. In this work, the overall reaction was decoupled in two steps, the oxidation and the aldolization, by using two consecutive reactors to investigate the role of the acid/base properties of silica-supported oxide catalysts. The oxidation of a mixture of methanol and ethanol to formaldehyde and acetaldehyde was performed over a FeMoOx catalyst, and then the product mixture was transferred without intermediate separation to a second reactor, in which the aldol condensation and dehydration to acrolein were performed over the supported oxides. The impact of the acid/base properties on the selectivity towards acrolein was investigated under oxidizing conditions for the first time. The acid/base properties of the catalysts were investigated by NH3 -, SO2 -, and methanol-adsorption microcalorimetry. A MgO/SiO2 catalyst was the most active in acrolein production owing to an appropriate ratio of basic to acidic sites.

Ammoniation-dehydration of fatty acids into nitriles: heterogeneous or homogeneous catalysis?

Fatty nitriles have lately become of interest in the framework of biofuels and for the valorization of the oil part of biomass to form fine chemicals or polymers. The production of long-chain fatty nitriles by the direct reaction of acids with NH3 has not been extensively studied, although several catalysts have been developed and published as patents. The characterization of this reaction with and without catalyst is, to the best of our knowledge, performed for the first time in this study. Several catalysts with various acid-base features were tested, and the best catalysts at 250 °C (Zn- and In-based catalysts) were further studied. Catalytically active forms and models are proposed for the Zn- and In-based catalysts, and the kinetic parameters for the amide to nitrile reaction are evaluated.

Design of amphoteric mixed oxides of zinc and Group 3 elements (Al, Ga, In): migration effects on basic features.

The design of new amphoteric catalysts is of great interest for several industrial processes, especially those covering dehydration and dehydrogenation phenomena. Adsorption microcalorimetry was used to monitor the design of mixed oxides of zinc with Group 3 elements (aluminium, gallium, indium) with amphoteric character and enhanced specific surface area. Acid-base features were found to evolve non-linearly with the relative amounts of metal, and the strengths of the created acidic or basic sites were measured by adsorption microcalorimetry. A panel of bifunctional catalysts of various acid-base (amounts, strengths) and redox character was obtained. Besides, special interest was given to In-Zn mixed oxides for their enhanced basicity: this series of catalysts displays important basic features of high strength (q(diff) (SO2 ads.) > 200 kJ mol(SO2)⁻¹ in substantial amounts (1 - 2 µmol m(catalyst)⁻²), whose impact on efficiency or selectivity in catalytic dehydration/dehydrogenation can be valuable.

Experimental and modelization approach in the study of acid-site energy distribution by base desorption. Part I: modified silica surfaces.

The acid properties of pure and modified silica surfaces were studied by 2-phenylethylamine (PEA) desorption in a thermogravimetric (TGA) apparatus, carrying out the experiments at different heating rates (5 < beta/(degrees C.min(-1)) < 30). The samples, containing about 13 wt % alumina, titania, and zirconia, were prepared by the sol-gel route from molecular precursors. The textural, structural, and surface properties of the materials were studied by complementary techniques (ICP, XRD, N(2) physisorption, SEM-EDS, and XPS). The chemical modification of the silica surface by enrichment with Al, Ti, or Zr, in amounts of about 90, 50, and 60% of that introduced in the preparation as determined by XPS, justified the increase of acidity of the modified silica surfaces compared with that of pure silica. The total number of strong acid sites was found to be in the order of SZ > SA > ST >> S. Two different kinetic approaches were applied to the thermogravimetric data to kinetically interpret the PEA desorption from the different types of acid sites. The classical differential Kissinger model was found to be inadequate in representing the very complex situation of the acid surfaces. A more complex model is proposed by simultaneously taking into account PEA desorption from the different acid sites by a set of parallel and independent desorption reactions following Arrhenius's kinetic law. The fraction of each type of acid site on each surface and the relevant activation parameters were optimized through a computational procedure. Very good fitting of the experimental-calculated desorption profiles corroborated the validity of the model. For each surface, the acid-site energy distribution is presented and discussed in relationship to the surface composition of the oxides.