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Recently, the ambient drying method for the preparation of xerogels has attracted great attention due to its low cost and high drying efficiency. However, the strong capillary forces existing during ambient drying cause severe shrinkage or even collapse of the aerogels (called xerogels). Although chemical crosslinking or displacement of water by organic solvents have been tried to solve the problem, extensive usage of chemicals and time-consuming displacement processes seem to be environmentally unfriendly and complex. Herein, we reported a green and efficient method for the preparation of a lignocellulosic xerogel. The xerogel was fabricated by alkali freezing of unbleached eucalyptus fibers followed by water washing and ambient drying. The alkali freezing promoted fiber swelling and enhanced the hydrogen bonds among the fibers, resulting in the gelation of lignocellulosic fibers. In particular, the residual lignin in the fibers reduced the capillary force during the drying process. The resulting lignocellulosic xerogel achieved a low shrinkage rate (27.50%), low density (0.039 g cm−3 ), high porosity (97.57%), and excellent mechanical strength (782.23 kPa) as well as environmental stability, and low thermal conductivity (44.76 mW m−1 K−1 ). Similarly structured xerogels could be generated using recycled NaOH solution. This technique was suitable for production using various kinds of plant fibers, which shows its great scalable production prospects. [ABSTRACT FROM AUTHOR]

[Display omitted] The electrochemical performance of pristine metal–organic xerogels as anodes in lithium-ion batteries is reported for the first time. We propose a novel synthesis approach for the in situ generation of highly dispersed, ultrafine cobalt sulfide nanoparticles on humic acid gels (CoSHA). The CoS nanoparticles in CoSHA have an average diameter of approximately 3 nm. CoSHA electrodes demonstrate enhanced lithium storage capacity, delivering a capacity of 662 mAh g−1 at 0.1 A g−1. They also show stable long-term cycling performance, with no capacity decay after 900 cycles at 1.0 A g−1. Furthermore, our experiments indicate that the improved lithium-ion adsorption results from the oxygen-containing functional groups in humic acid and the ultrafine CoS active sites. This study offers a practical methodology for synthesizing ultrafine metal sulfides and new insights into using pristine gel-based electrodes for energy storage and conversion. [ABSTRACT FROM AUTHOR]

Herein, the first report on gel-to-gel transformations via [2 + 2] photopolymerization in MOGs of metal halides and rigid dienes is presented. The MOGs and their xerogels show exceptional ability to undergo [2 + 2] polymerisation upon UV irradiation. Gel-to-gel transformations are very rare as the post-modification of gelators weakens the gel and transforms it to a sol. Such transformations change the molecular assemblies into gels with altered mechanical and chemical properties. These phenomena pave the way to synthesize new MOGs with improved rigidity that cannot be synthesized otherwise. [ABSTRACT FROM AUTHOR]

Enzyme immobilization can offer a range of significant advantages, including reusability, and increased selectivity, stability, and activity. In this work, a central composite design (CCD) of experiments and response surface methodology (RSM) were used to study, for the first time, the L‐asparaginase (ASNase) immobilization onto functionalized carbon xerogels (CXs). The best results were achieved using CXs obtained by hydrothermal oxidation with nitric acid and subsequent heat treatment in a nitrogen flow at 600 °C (CX−OX‐600). Under the optimal conditions (81 min of contact time, pH 6.2 and 0.36 g/L of ASNase), an immobilization yield (IY) of 100 % and relative recovered activity (RRA) of 103 % were achieved. The kinetic parameters obtained also indicate a 1.25‐fold increase in the affinity of ASNase towards the substrate after immobilization. Moreover, the immobilized enzyme retained 97 % of its initial activity after 6 consecutive reaction cycles. All these outcomes confirm the promising properties of functionalized CXs as support for ASNase, bringing new insights into the development of an efficient and stable immobilization platform for use in the pharmaceutical industry, food industry, and biosensors. [ABSTRACT FROM AUTHOR]

Platinum-group-metal free catalysts have been widely studied in the last decade as an alternative to Pt, employed in fuel cells. Several carbon precursors have been investigated as carbon matrix for iron-nitrogen-carbon (Fe–N–C) catalysts, characterized by a large amount of micropores, fundamental to create Fe-N x -C active sites. Nonetheless, it is also acknowledged that wider pores are needed to facilitate mass transfer of oxygen/water (reagent/product of fuel cells) towards/from the active sites. Organic xerogels are known as easily tunable materials, that allow doping with a variety of heteroatoms. The present manuscript presents an investigation on the use of organic xerogels combined with iron and nitrogen in a single-step to obtain Fe–N-CXG electro-catalysts for the oxygen reduction reaction (ORR) of proton exchange membrane fuel cells. Several features of both organic xerogels and catalysts on the ORR activity are assessed: the textural properties of the organic xerogel, the iron loading of the Fe–N–C catalysts and the effect of acid-leaching of the catalysts. The present study proves the feasibility of using organic xerogels as carbon precursor to obtain PGM-free catalysts in an easy manner and scalable single-step synthesis. Catalysts obtained from organic xerogels synthesized at mildly acid pHs (5.8 and 6), with a nominal iron loading of 2 wt%, and subjected to two sets of acid leaching/thermal treatments, present enhanced catalytic activity towards the ORR. • Organic carbon xerogels are investigated as carbon matrix for Fe–N–C catalysts. • One-step and template-free synthesis of Fe–N–C catalysts is proposed. • Balanced iron doping creates enough active sites without impacting porosity. • Acid/thermal treatments enhance catalysts improving chemical properties. • High mesopore volume organic xerogels (pH 5.8) yield highly active ORR catalysts. [ABSTRACT FROM AUTHOR]

Atomically dispersed Fe-N-C catalysts for the oxygen reduction reaction (ORR) have been synthesized with a template-free method using carbon xerogels (CXG) as a porous matrix. The porosity of the CXGs is easily tunable through slight variations in the synthesis procedure. In this work, CXGs are prepared by formaldehyde and resorcinol polymerization, modifying the pH during the process. Materials with a broad range of porous structures are obtained: from non-porous to micro-/meso-/macroporous materials. The porous properties of CXG have a direct effect on Fe-N-CXG activity against ORR in an acidic medium (0.5 M H2SO4). Macropores and wide mesopores are vital to favor the mass transport of reagents to the active sites available in the micropores, while narrower mesopores can generate additional tortuosity. The role of microporosity is investigated by comparing two Fe-N-C catalysts using the same CXG as the matrix but following a different Fe and N doping procedure. In one case, the carbonization of CXG occurs rapidly and simultaneously with Fe and N doping, whereas in the other case it proceeds slowly, under controlled conditions and before the doping process, resulting in the formation of more micropores and active sites and achieving higher activity in a three-electrode cell and a better durability during fuel cell measurements. This work proves the feasibility of the template-free method using CXG as a carbon matrix for Fe-N-C catalysts, with the novelty of the controlled porous properties of the carbon material and its effect on the catalytic activity of the Fe-N-C catalyst. Moreover, the results obtained highlight the importance of the carbon matrix's porous structure in influencing the activity of Fe-N-C catalysts against ORR. [ABSTRACT FROM AUTHOR]

The present study reported the obtention of xerogels based on chitosan and citral and their use as materials for mercury ion recovery from aqueous solutions, this being a serious problem related to the environment. The systems were prepared by the acid condensation of chitosan with citral, followed by the lyophilization of the resulting hydrogels, in order to obtain highly porous solid materials. The structural, morphological and supramolecular characterization of the systems was performed using 1H-NMR and FTIR spectroscopy, scanning electron microscopy and wide-angle X-ray diffraction. The ability of the obtained materials to be used for the recovery of mercury from aqueous solutions revealed the high potential of the xerogels to be used in this sense, the analysis of the materials post mercury absorption experiments revealing that this ability is predominantly conferred by the imine linkages which act as coordinating moieties for mercury ions. [ABSTRACT FROM AUTHOR]

In this study, we report the synthesis of copper ion containing polyisocyanurate-urea xerogels (Cu-PIU) by reaction of organic monomers containing isocyanate functional groups catalyzed by copper chloride. Wet gels were dried under ambient temperature and pressure conditions to yield Cu-PIU xerogels which is a simple and economic process. The obtained xerogels were found to have bulk and skeletal densities of 1.2 and 1.4 g/cc respectively. The metal ions were found to catalyze the reaction of polyisocyanurate-urea by initiating the trimerization of isocyanate to isocyanurate; additionally, the water present in the hydrated metal salts was found to form urea linkages by reacting with the isocyanate functional groups. The copper containing polyisocyanurate-urea xerogels and coatings were found to exert excellent antibacterial properties on both 'Staphylococcus Aureus' (Gram positive) and 'Escherichia Coli' (Gram negative) bacteria through the zone of inhibition method. Moreover, the prepared polymer composites and metal-ion doped polymeric xerogels exhibited good bioadhesion and bio-compatibility towards MG63 cells which indicates the non-toxic nature of the materials and hence they can be used in the biomedical field. [ABSTRACT FROM AUTHOR]

This work is dedicated to the study of the effect of the synthesis conditions (drying and calcination) of sulfated zirconia on the final catalytic behavior of bifunctional composite catalysts prepared by the physical mixing of the sulfated zirconia (methanol dehydration catalyst) with Cu/ZnO/Al2O3 (CZA; methanol synthesis catalyst). The main objective was to optimize the CZA-ZrO2/SO42− composite catalyst for its use in the direct production of dimethyl ether (DME) from syngas. Sulfated zirconia aerogel (AZS) and xerogel (XZS) were prepared using the sol–gel method using different solvent evacuation conditions and calcination temperatures, while the Cu-ZnO(Al) catalyst was synthesized using the coprecipitation procedure. The effectivity of CZA-ZrO2/SO42− composite catalysts for the direct production of dimethyl ether (DME) from syngas was evaluated in a flow reactor at 250 °C and 30 bar total pressure. The characterization of the sulfated zirconia aerogels and xerogels using different techniques showed that the mesoporous aerogel (AZS0.5300) exhibited the best textural and acidic properties due to the gel drying under supercritical conditions and calcination at 300 °C. As a result, the composite catalyst CZA-AZS0.5300 exhibited seven times higher DME production than its xerogel-containing counterpart (364 vs. 52 μmolDME·min−1·gcat−1). This was attributed to its well-matched metal surface, mesoporous structure, optimal crystallite size and, most importantly, its higher acidity. [ABSTRACT FROM AUTHOR]

By using the method of coprecipitation of hydroxides in the ZrO2–CaO–MgO system, xerogels, powders, and ceramics based on them are obtained. The effect of low temperatures during the preparation of precursors on the phase composition and physicochemical properties of the materials is studied. It is shown that the use of precipitate's cryotreatment makes it possible to reduce the open porosity and water absorption of the ceramics. [ABSTRACT FROM AUTHOR]

Xerogels and powders of a solid solution based on zirconium dioxide are synthesized by the method of coprecipitation of hydroxides from aqueous solutions of salts of zirconium nitrate ZrO(NO3)2⋅2H2O, aluminum Al(NO3)3⋅9H2O, and cerium Ce(NO3)3⋅9H2O with an aqueous 1 M solution of ammonia NH4OH. A dense ceramic with low porosity and water absorption is obtained. The effect of the ultrasonic treatment of the precipitate and mechanical treatment of the xerogel on the physicochemical properties of the obtained materials is evaluated. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploitation of solid-state proton-conducting materials with high anhydrous proton conductivity from subzero temperature (<273 K) to moderate temperature (>353 K) is a great challenge. Here, Brönsted acid-dopped zirconium-organic xerogels (Zr/BTC-xerogels) are prepared for anhydrous proton conduction from subzero to moderate temperature. Abundant acid sites and strong H-bonding interactions make the CF 3 SO 3 H (TMSA)-introduced xerogel gain high proton conductivity from 9.0 × 10-4 S cm−1 (253 K) to 1.40 × 10-2 S cm−1 (363 K) under anhydrous conditions, which are in the leading level. This provides a new possibility to develop wide-operating-temperature conductors. [ABSTRACT FROM AUTHOR]

Xerogels (X-Gs) are porously open, functionalized, and high-performance materials constituted of cross-linked, dried, and ambient polymeric architectures exhibiting very high porosity, wide surface area, along with low-cost preparation strategies which can be garnered from differing organic and inorganic initiating entities for multifunctional uses. X-Gs are solidified gels fabricated by gradual drying at ambient temperature with shrinkage. X-Gs generally exhibit elevated porosity with broad surface area and very smaller pore sizes. The enchanting properties of this porous gels emanate from the remarkable flexibility of the sol–gel procedure, capable of synergizing with varying drying strategies resulting to aerogels (supercritically drying) or xerogels (ambient drying). Hybrid X-Gs are polymeric architectures, in either physical or covalent cross-linking with each other and/or with nanoparticulates or nanoarchitectures. X-G polymeric nanoarchitectures and X-G biopolymeric bionanoarchitectures can mimic native tissue behaviors, architectures, and microenvironment as a result of their hydrated as well as interconnected porosity. A vast range of nanoparticulates, including carbon derivatives, ceramic, polymeric, as well as metallic nanoparticulates, can be embedded within the X-G architecture to garner nanoarchitectures with customized functionalities. X-G polymeric or biopolymeric nanoarchitectures/nanocomposites can undergo engineering to exhibit superior physically, chemically, electrically, and biologically affiliated behaviors. Therefore, this paper presents state of the art, blue chip synthesis, preparation, characterization, and properties of X-G polymeric nanoarchitectures and X-G biopolymeric bionanoarchitectures and multifunctional applications. [ABSTRACT FROM AUTHOR]

The high cost and toxicity associated with the use of orthosilicates as silica precursors drive growing interest in an environmentally friendly and cost - efficient natural silica source. Rice husk (a biomass) and beach sand are both natural and non - toxic and the extraction of silica from each using sodium hydroxide makes the process green for the production of nanosilica gels (xerogel and aerogel) via the sol - gel route. The gels from the ash of rice husk and pulverized beach sand were dried by the use of a laboratory oven and supercritical extraction methods. The structures of the gels were studied through X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), X - ray fluorescence (XRF) spectroscopy and Fourier transform infrared (FTIR) spectroscopic analyses. XRF spectroscopy revealed silicon in its oxide form as the prominent element with low levels of trace elements concentrations. XRD results showed the crystalline nature of the prepared silica. TEM images confirmed the crystalline and nanometric structures of the streak - free xerogel and aerogel. SAED confirmed that the gels were polycrystalline with no streaks. SEM monographs showed varied globes of fine surfaces indicating the high level of purity of the gels. FTIR showed the absorption peaks of the silanol-OH bond and Si-O-Si vibration, confirming the gels as nanometric structures. The high yield, crystalline nature, purity and crystallographic features of the produced silica suggest rice husk ash and pulverized beach sand as alternative silica sources for the production of silica gels nanoparticles with potential applications in biomedical field, nanofiltration and as additive for improving the strength of materials. [ABSTRACT FROM AUTHOR]

With the aim of better directing the polycondensation of oligomers during the synthesis of amorphous aluminosilicate xerogels by the sol-gel process using Na2SiO3, we reinforced the sols with K+ counterion and studied its effect on the physicochemical and structural properties of the xerogels using XRD, FTIR, N2 physisorption, SEM, EDX, and TGA techniques as well as quantitative analysis of the acid sites by N-butylamine adsorption followed by potentiometric titration. Based on the results, the introduction of K+ generated xerogels with good porosity and conferred resistance to matrix cracking. The amorphous character of the xerogels did not change after adding K+. FTIR spectra showed that the composition of the xerogels was improved after the addition of K+. Cation exchange and sulfur removal were much more efficient in the presence of K+ which improved the acidity of the xerogels. The best percentages of Si and Al were observed at the Na+/K+ ratios of 4 and 1.The enhanced xerogel prepared with Na+/K+ ratio of 1 gave a biodiesel yield of 80.44% at the optimum parameters and was used for three reaction cycles without significant loss of biodiesel yield. [ABSTRACT FROM AUTHOR]

Carbon xerogels (CXs) are materials obtained via the pyrolysis of resins prepared via the sol–gel polycondensation of resorcinol and formaldehyde. These materials attract great attention as adsorbents, catalyst supports, and energy storage materials. One of the most interesting features of CXs is the possibility of fine-tuning their structures and textures by changing the synthesis conditions in the sol–gel stage. Thus, the first part of this review is devoted to the processes taking place in the polycondensation stage of organic precursors. The formation of hydroxymethyl derivatives of resorcinol and their polycondensation take place at this stage. Both of these processes are catalyzed by acids or bases. It is revealed that the sol–gel synthesis conditions, such as pH, the formaldehyde/resorcinol ratio, concentration, and the type of basic modifier, all affect the texture of the materials being prepared. The variation in these parameters allows one to obtain CXs with pore sizes ranging from 2–3 nm to 100–200 nm. The possibility of using other precursors for the preparation of organic aerogels is examined as well. For instance, if phenol is used instead of resorcinol, the capabilities of the sol–gel method become rather limited. At the same time, other phenolic compounds can be applied with great efficiency. The methods of gel drying and the pyrolysis conditions are also reviewed. Another important aspect analyzed within this review is the surface modification of CXs by introducing various functional groups and heteroatoms. It is shown that compounds containing nitrogen, sulfur, boron, or phosphorus can be introduced at the polycondensation stage to incorporate these elements into the gel structure. Thus, the highest surface amount of nitrogen (6–11 at%) was achieved in the case of the polycondensation of formaldehyde with melamine and hydroxyaniline. Finally, the methods of preparing metal-doped CXs are overviewed. Special attention is paid to the introduction of a metal precursor in the gelation step. The elements of the iron subgroup (Fe, Ni, Co) were found to catalyze carbon graphitization. Therefore, their introduction can be useful for enhancing the electrochemical properties of CXs. However, since the metal surface is often covered by carbon, such materials are poorly applicable to conventional catalytic processes. In summary, the applications of CXs and metal-doped CXs are briefly mentioned. Among the promising application areas, Li-ion batteries, supercapacitors, fuel cells, and adsorbents are of special interest. [ABSTRACT FROM AUTHOR]

Aerogels are highly porous and ultralight three-dimensional materials with great potential for various applications. To obtain highly porous and structurally stable aerogels, a carefully designed synthesis process is required. These materials offer flexibility in manipulating their properties, allowing the incorporation of modifying agents according to specific needs. In this study, compounds were synthesized using graphene oxide (GO) and nanocellulose fibers (NFC) through the hydrothermal reduction methodology. Two drying techniques were employed: lyophilization and oven evaporation, resulting in materials called cryogel and xerogel, respectively. Various parameters that can interfere with the properties of these nanomaterials were evaluated. The results indicated that the cryogel dried by lyophilization provided the best applicability due to its structural flexibility after compressions, whereas the xerogel obtained through the oven evaporation process resulted in a compound with high rigidity and disintegration. Structural characterizations demonstrated the successful development of the precursors and promising characteristics in the synthesized nanomaterials. With its flexibility, approximately 98% porosity, low shrinkage rate, light weight, and electrical conductivity, the developed cryogel showed high potential in various applications, such as pressure sensors, electromagnetic shielding, and other research and development fields. [ABSTRACT FROM AUTHOR]

Composites based on silicon dioxide xerogels, containing glycerin and nicotine, were prepared by means of tetraethoxysilane hydrolysis using the single-stage synthesis and two-stage sorption procedures. In the single-stage synthesis, glycerin sorption 3 : 1 by weight with respect to the sorbent was achieved. The kinetics of the release (desorption) of nicotine from an aerosol mixture with glycols has been studied. The synthesized sorbent is promising for use in aerosol generating systems, and also as carriers and means of delivery of biologically active compounds and medicines. [ABSTRACT FROM AUTHOR]

Inorganic gels are an important group of nanostructured materials whose applications are expanding day by day. This group of gels with a solid colloidal shape are three-dimensional hydrophilic networks with cross-linked bonds that consist of inorganic macromolecules. Inorganic gels are categorized into xerogels, aerogels and cryogels. This type of gels is of particular importance due to their increasingly important applications in medicine, energy, wastewater treatment, electrolytes, fuel, thermal insulation, etc. Due to the growing research and application importance of this type of gels, this article comprehensively deals with their various aspects. Within the scope of the present study, the classification of gels is first discussed, and then, synthesis methods, including sol–gel, thermal processes, non-aqueous sol–gel and precipitation, are scrutinized. The discussion continues with hybrid gels and ends with investigating the different uses of the gels. [ABSTRACT FROM AUTHOR]

We have analyzed the nature and role of functional groups on the self‐assembly modes and the physical properties of multicomponent gels with structurally similar individual components. The gelation properties of individual and mixed enantiomeric compounds of biphenyl bis‐(amides) of alanine (BPA) or phenylalanine (BPP) methyl ester were analyzed in various solvent/solvent mixtures. Multicomponent gels were formed by mixing the enantiomeric BPP compounds at a lower concentration, but a higher concentration was required for mixed alanine‐based BPA gels. The comparison of the mechanical strength of the individual and mixed BPP compounds indicated that the mixed BPP gels displayed enhanced mechanical strength (∼2‐fold increase) in p‐xylene, but a weaker gel was observed in DMSO/water. However, a reverse trend was observed for BPA gels, indicating the role of functional groups in the gel network formation. X‐ray diffraction analysis of the gelator and the xerogels in the solid state confirmed the formation of co‐assembled networks in mixed enantiomeric gels. The stability of the gels towards anions was evaluated by analyzing the anion induced stimuli‐responsive properties. These results indicate the effective modeling of the functional groups of the individual components could lead to multicomponent gels with tunable properties. [ABSTRACT FROM AUTHOR]

The xerogels based on the aqueous solutions of urea in potassium silicate liquid glass (PSLG) were produced by CO2 bubbling and investigated. The structure and chemical composition of the obtained materials were analyzed. Using the SEM, XRD, IR-FT, DSC, and low energy local EDS analysis, it was recognized that the dried gels (xerogels) contained three forms of urea: oval crystals of regular shape appeared onto the surface of xerogel particles; fibrous crystals were located in the silicate matrix; and molecules/ions were incorporated into the silicate matrix. It was shown that an increase in [(NH2)2CO] in the gel-forming system promoted increased contents in crystalline forms of urea as well as the diameter of the fiber-shaped urea crystals. A rate of the urea release in water from the granulated xerogels containing 5.8, 12.6, and 17.9 wt.% of urea was determined by the photometric method. It was determined that the obtained urea-containing xerogels were characterized with a slow release of urea, which continued up to 120 days, and could be used as controlled release fertilizers containing useful nutrients (N, K). [ABSTRACT FROM AUTHOR]

Two different silica conformations (xerogels and nanoparticles), both formed by the mediation of dendritic poly (ethylene imine), were tested at low pHs for problematic uranyl cation sorption. The effect of crucial factors, i.e., temperature, electrostatic forces, adsorbent composition, accessibility of the pollutant to the dendritic cavities, and MW of the organic matrix, was investigated to determine the optimum formulation for water purification under these conditions. This was attained with the aid of UV-visible and FTIR spectroscopy, dynamic light scattering (DLS), ζ-potential, liquid nitrogen (LN2) porosimetry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results highlighted that both adsorbents have extraordinary sorption capacities. Xerogels are cost-effective since they approximate the performance of nanoparticles with much less organic content. Both adsorbents could be used in the form of dispersions. The xerogels, though, are more practicable materials since they may penetrate the pores of a metal or ceramic solid substrate in the form of a precursor gel-forming solution, producing composite purification devices. [ABSTRACT FROM AUTHOR]

To evaluate possible structural changes and thermal stability of the polyurea unloaded and loaded with diclofenac sodium, polyurea networks based on polyetheramine containing polypropylene oxide (PPO) or polyethylene oxide (PEO) and hexamethylene diisocyanate trimer-HDI were synthesized. The formation of the network was controlled by sol-gel reactions, and the obtained materials were then characterized by different techniques (FTIR, XRD, TGA). Moreover, the amount of diclofenac released could be modulated as a function of time, studying the water absorption or swelling capacity, the cytotoxicity of the material and the amount of drug released. A choice was therefore made on the hydrophilicity of PEO- or PPO-based polyetheramine (with similar molecular weight), and the release profile was hereafter correlated with the water absorption by the PEO/PPO polyurea matrix. Links could finally be established between the release of diclofenac and the polyurea matrices properties, such as the nature of polymer (PEO/PPO) and the hydrophilicity (water uptake). Our objective here is to identify challenges and opportunities for the development of innovative functional biomaterials for health applications. [ABSTRACT FROM AUTHOR]

Dynamic covalent gels are synthesized from an aromatic trialdehyde and α,ω‐dinitroalkanes via the nitroaldol reaction in organic solvents. The gelation process can be fine‐tuned by changing the starting nitroalkanes, solvents, feed concentration, catalyst loading, or reaction temperature. The resulting organogels demonstrate good structural integrity and excellent self‐healing ability. Intact xerogels are produced upon drying, without damaging the network, and the solvent‐free network can recover its gel form in the presence of an organic solvent. Furthermore, the crosslinked dynameric gel depolymerize to small molecules in response to excess nitromethane. [ABSTRACT FROM AUTHOR]

As a promising material with porous structure and large surface area, metal organic xerogel (MOX) has got extensive attention in the field of CO 2 photocatalytic reduction. The skeleton structure and pore morphology of organic xerogel framework materials contribute to the diffusion and transfer of CO 2 molecules. In this work, we prepared a serial of bimetallic Co/Fe-MOX by one-step solvent method, which can provide sufficient adsorption sites for CO 2 molecules. Meanwhile, the presence of cobalt and iron in Co/Fe-MOX enhances greatly not only the absorption and utilization of light energy in a synergistic manner, but also the separation and transfer of carriers. During the photocatalytic reduction process, the metal center of Co acts as major active site for photocatalysis. Therefore, the rapid conversion of CO 2 to CO is promoted. The Co/Fe-MOX with a molar ratio of 1:3 exhibits a high CO yield (67 μmol g−1 h−1), about 8.4 times that of Fe-MOX with a single Fe center (8 μmol g−1 h−1), implying the metal center Co acts as the main active site. This work provides ideas for designing metal organic xerogel materials with polymetallic centers for efficient photoreduction of CO 2. [ABSTRACT FROM AUTHOR]

Carbon surface oxidation was investigated to assess the effects of porosity and particle size on its course. Carbon xerogels that differed in porosity (micro-, micro-meso-, and micro-meso-macroporous materials) and particle size (from fine powders to monolithic cubes) were prepared. The prepared materials were characterized in detail with nitrogen sorption, SEM, and HRTEM. The oxidation of carbon xerogels was studied by isothermal thermogravimetry (TG) in an oxidizing atmosphere (50% O 2 and 50% Ar). Isothermal TG experiments showed that the effects of particle size and porosity are interrelated and should be evaluated together as both significantly influence diffusion and heat transfer during carbon oxidation. On the basis of isothermal TG data, apparent kinetic parameters were determined assuming that carbon burn-off, the creation of oxygen surface groups, and the decomposition of created oxygen surface groups are reactions controlling the carbon surface oxidation. Detailed analysis of the obtained parameters proved that porosity and particle size do not affect the basic chemical reactions that occur on the carbon surface during oxidation. [Display omitted] [ABSTRACT FROM AUTHOR]

Composite hydrogels samples consisting of poly(methyl methacrylate/butyl acrylate/2-hydroxyethylmethacrylate) (poly-OH) and up to 60% reduced graphene oxide (rGO) containing rGO were synthesized. The method of coupled thermally induced self-assembly of graphene oxide (GO) platelets within a polymer matrix and in situ chemical reduction of GO was applied. The synthesized hydrogels were dried using the ambient pressure drying (APD) and freeze-drying (FD) methods. The effects of the weight fraction of rGO in the composites and the drying method on the textural, morphological, thermal, and rheological properties were examined for the dried samples. The obtained results indicate that APD leads to the formation of non-porous xerogels (X) of high bulk density (D), while FD results in the formation of highly porous aerogels (A) with low D. An increase in the weight fraction of rGO in the composite xerogels leads to an increase in D, specific surface area (SA), pore volume (Vp), average pore diameter (dp), and porosity (P). With an increase in the weight fraction of rGO in A-composites, the D values increase while the values of SP, Vp, dp, and P decrease. Thermo-degradation (TD) of both X and A composites takes place through three distinct steps: dehydration, decomposition of residual oxygen functional group, and polymer chain degradation. The thermal stabilities (TS) of the X-composites and X-rGO are higher than those of the A-composites and A-rGO. The values of the storage modulus (E') and the loss modulus (E") of the A-composites increase with the increase in their weight fraction of rGO. [ABSTRACT FROM AUTHOR]

A binary and ternary system of highly bioactive nanoparticles of xerogel (88SiO 2 –12CaO (wt.%), solvXG88, 78SiO 2 –16CaO–6P 2 O 5 , solvXG78P6) and glass (69SiO 2 –25CaO–6P 2 O 5, solvBG69P6) were prepared following an unconventional solvothermal path of the synthesis. These nanosized (<50 nm), non-spherical in shape and mesoporous materials with different compositions greatly enhanced the formation process of hydroxyapatite (HA) in simulated physiological fluids compared to reference 45S5 glass, commonly used in orthopedics and dentistry. The deposition of a HA layer on the glasses was analyzed by various techniques, namely XRD, IR-ATR, 31P CP-MAS NMR, EDS analyses, SEM, and HR-TEM imaging. For both types of nanoparticles (glass and obtained at lower temperature xerogels) superior apatite-mineralization ability in time as short as 4 h in the physiological-like buffer was achieved thus, exceeded the bioactivity of the 45S5 glass. This unique bioactivity was complemented by biocompatibility with human dermal fibroblasts and MC3T3 mouse osteoblast precursors, verified in a wide range of concentrations, as well as hemocompatibility studies. The most promising candidate which can compete with clinically used Bioglass is solvXG78P6. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon xerogels co-doped with nitrogen (N) and phosphorus (P) or sulfur (S) were synthesized and employed as catalysts for the electrocatalytic reduction of p-nitrophenol (p-NP). The materials were prepared by first synthesizing N-doped carbon xerogels (NDCX) via the pyrolysis of organic gels, and then introducing P or S atoms to the NDCX by a vapor deposition method. The materials were characterized by various measurements including X-ray diffraction, N2 physisorption, Transmission electron microscopy, Fourier Infrared spectrometer, and X-ray photoelectron spectra, which showed that N atoms were successfully doped to the carbon xerogels, and the co-doping of P or S atoms affected the existing status of N atoms. Cyclic voltammetry (CV) scanning manifested that the N and P co-doped materials, i.e., P-NDCX-1.0, was the most suitable catalyst for the reaction, showing an overpotential of −0.569 V (vs. Ag/AgCl) and a peak slop of 695.90 μA/V. The material was also stable in the reaction and only a 14 mV shift in the reduction peak overpotential was observed after running for 100 cycles. [ABSTRACT FROM AUTHOR]

This work proposed new black-wattle tannin/kraft lignin H 3 PO 4 -activated carbon xerogels as sustainable and efficient adsorbents. The precursors were chosen based on their eco-friendly and cost-effective nature, aiming to achieve adsorbents with high adsorption capacities. Carbon xerogels were synthesized through polycondensation with formaldehyde and alkaline catalyst in a simple one-pot procedure. Activation was performed using H 3 PO 4 in a tubular furnace (500 °C), under a nitrogen atmosphere. Results show that the inclusion of the kraft lignin led to changes in the morphology of the materials, facilitating the development of their porous structure and increasing specific surface area and pore volume. The best adsorbent (XLT 50 %) was synthesized using a 1:1 tannin/kraft lignin mass ratio. This material presented an adsorption capacity of nearly 1150 mg g−1 of methylene blue (pH = 5 and T = 298 K), which was linked to its high specific surface area of 1348 m2 g−1. The adsorption process followed the pseudo-second-order kinetic model, whereas the adsorption isotherms were best fitted by the Sips model. The XLT 50 % presented good reusability properties, maintaining its adsorption capacity for 3 cycles. Finally, the XLT 50 % presented good adsorptive properties toward other pollutants (methyl orange, 4-chlorophenol, and hexavalent chromium), indicating its versatility for adsorption processes. [ABSTRACT FROM AUTHOR]

Summary: Shape transforming foods are an emerging area of interest that could be customised according to consumer needs with the desirable structure and reduced package space. The current work aims to investigate the shape transformation behaviour of a 2D xerogel developed from rice hydrogel at the concentration of 4% and 90 °C. This flat xerogel is coated with ethyl cellulose as constraint material in the form of linear equally spaced strips. Immersing the xerogels in hot water over a temperature of 70 °C, resulted in a 3D transformation of the discs in 12 s (Video S1). The transformation is achieved owing to xerogel's increased swelling power (0.27–0.78) due to the anisotropic nature. This is confirmed by the SEM images of top (smooth) and bottom (rough) xerogel. In order to characterise the process of shape transformation bending analysis was done wherein a significant difference in bending angle (35.86–63.10°), height (24.73–50.26 mm), curvature (0.57–2.38 μ mm−1) and end‐to‐end distance (118.23–15.11 mm) from 2 to 12 s. The formed 3D shape was similar to the commercial tubular (penne) pasta. This study opens up the utilisation of less concentrated rice xerogel in shape transformation for designing engineered food. [ABSTRACT FROM AUTHOR]

Natural fiber welding (NFW) typically uses an ionic liquid such as 1-ethyl-3-methylimidazolium acetate (EMImAc) to partially dissolve cellulose and weld strands of cotton thread into an amorphous network. Removal of EMImAc through successive solvent rinses and drying produces all-cellulose structures ranging from non-porous biocomposites to highly porous xerogels based on the identity of the solvent exchange. However, how and why certain solvent interactions actually deliver mesoporous fiber-welded biopolymer materials with controlled porosity is poorly understood. In this study, we demonstrate that the porosity of a welded cotton xerogel can be controlled by tuning the solvent exchange and drying steps. NFW cotton thread is rinsed of EMImAc by solvent exchange with one or a series of solvents of varying polarities. We determine that the polarity of the final solvent in the series can control the BET surface area of the dry product, with nonpolar solvents creating xerogels. This porosity can be further enhanced using lyophilization, a less disruptive evaporation technique, to deliver a maximum BET surface area of 232 m2 g–1 when cyclohexane is used as the final rinse solvent. [ABSTRACT FROM AUTHOR]

Organic xerogels based on lignin and tannins isolated from pine bark and wood were for the first time obtained by condensation with formaldehyde and furfuryl alcohol in the presence of hydrochloric acid. Sulfated pine ethanol lignin made it possible to obtain the first sulfur-containing (up to 1.3 wt %) lignin–(tannin)–formaldehyde and lignin–(tannin)–furfuryl xerogels. The gel density increased with the addition of tannins to lignin and ranged 0.13– 0.39 g/cm3. Xerogels synthesized by condensation with furfuryl alcohol were stronger than those obtained using formaldehyde. The presence of sulfur in xerogels was confirmed by elemental and chemical analyses and IR spectroscopy. Scanning electron microscopy showed that lignin–formaldehyde xerogels were formed from large polymer chains, which consisted of interconnected aggregates of micron-sized particles, and had large pores. A more compact, spatially crosslinked gel structure formed when tannins were added to the polycondensation system. The BET method showed that all xerogels had low porosity and that lignin–furfuryl samples had a larger average pore diameter (7.2–14.5 nm) as compared with lignin–formaldehyde samples (3.03–6.80 nm). [ABSTRACT FROM AUTHOR]

In this work, the series of Dy3+-doped silicate xerogels were synthesized by sol-gel technique and further processed at 350 °C into SiO2-LaF3:Dy3+ nano-glass-ceramic materials. The X-ray diffraction (XRD) measurements, along with the thermal analysis, indicated that heat-treatment triggered the decomposition of La(TFA)3 inside amorphous sol-gel hosts, resulting in the formation of hexagonal LaF3 phase with average crystal size at about ~10 nm. Based on the photoluminescence results, it was proven that the intensities of blue (4F9/2 → 6H15/2), yellow (4F9/2 → 6H13/2), and red (4F9/2 → 6H11/2) emissions, as well as the calculated yellow-to-blue (Y/B) ratios, are dependent on the nature of fabricated materials, and from fixed La3+:Dy3+ molar ratios. For xerogels, the emission was gradually increased, and the τ(4F9/2) lifetimes were elongated to 42.7 ± 0.3 μs (La3+:Dy3+ = 0.82:0.18), however, for the sample with the lowest La3+:Dy3+ molar ratio (0.70:0.30), the concentration quenching was observed. For SiO2-LaF3:Dy3+ nano-glass-ceramics, the concentration quenching effect was more visible than for xerogels and started from the sample with the highest La3+:Dy3+ molar ratio (0.988:0.012), thus the τ(4F9/2) lifetimes became shorter from 1731.5 ± 5.7 up to 119.8 ± 0.4 μs. The optical results suggest, along with an interpretation of XRD data, that Dy3+ ions were partially entered inside LaF3 phase, resulting in the shortening of Dy3+-Dy3+ inter-ionic distances. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical-pore MOF xerogels with tunable mesopore size were synthesized. • The preparation of H-UiO-66-NH 2 xerogels possesses the record space–time yield. • The RR 195 uptake capacity of H-UiO-66-NH 2 -11.6 nm is 477.97 % of the UiO-66-NH 2. • H-UiO-66-NH 2 -11.6 nm can also efficiently capture other organic pollutants. Persistent organic pollutants in water are not only a potential threat to human health, but also cause damage to the ecological environment. Hence, the removal of large organic pollutants from wastewater is of great importance for environmental protection. Herein, hierarchical-pore UiO-66-NH 2 xerogels (H-UiO-66-NH 2 xerogels) with different mesopore size, H-UiO-66-NH 2 -11.6 nm and H-UiO-66-NH 2 -3.7 nm, were successfully synthesized by combining sol–gel-based method and acid modulator, featuring the characteristics of simple operation, rapid and scalable process, low cost, and the high space–time yield (STY). N 2 adsorption–desorption isotherms reveal that the obtained H-UiO-66-NH 2 xerogels possess high surface area, hierarchical-pore structures, large pore volume, and turntable mesopore size. Batch adsorption experiments demonstrate that H-UiO-66-NH 2 -11.6 nm has excellent adsorption performance for reactive red 195 (RR 195) dye removal. The maximum adsorption capacity of H-UiO-66-NH 2 -11.6 nm is 884.96 mg g−1, which is 4.7 times of the microporous UiO-66-NH 2 (185.15 mg g−1). Moreover, the removal efficiency of H-UiO-66-NH 2 -11.6 nm for RR 195 can exceed 99 %. The adsorption mechanism reveals that the excellent RR 195 capture stems from the large mesoporous structure and abundant adsorption sites provided by the Zr cluster and –NH 2 groups in H-UiO-66-NH 2 -11.6 nm. Besides, H-UiO-66-NH 2 -11.6 nm also exhibits a much larger adsorption capacity for some other organic pollutants, such as tetracycline, reactive black 5, and amoxicillin, demonstrating that the H-UiO-66-NH 2 xerogel has great potential for organic pollutant removal. [ABSTRACT FROM AUTHOR]

The review summarizes the author's results concerning the complex formation in the phase of modified xerogels synthesized by the sol–gel process for application as sensor materials. The results of studying the complex formation (pH ranges of reactions, light absorption maxima and compositions of complexes, and equilibrium constants) are presented and discussed for 87 systems of two types, that is, immobilized ligand (organic analytical reagent)–metal ion and immobilized metal ion–organic or inorganic compound. The approach proposed by the author to describe the complex formation in the modified xerogel phase is presented. The results of applications of modified xerogels as sensor materials are considered, including their use for determining metal ions; organic compounds; hydrogen peroxide; chloride, fluoride, and oxalate ions in food and hygienic products, pharmaceuticals, biological fluids, and environmental media. [ABSTRACT FROM AUTHOR]

In situ extraction is a method for separating plant secondary metabolites from in vitro systems of plant biomass cultures. The study aimed to investigate the MTMS-based xerogels morphology effect on the growth kinetics and deoxyshikonin productivity in xerogel-supported in vitro culture systems of Rindera graeca hairy root. Cultures were supplemented with three types of xerogel, i.e., mesoporous gel, microporous gel, and agglomerated precipitate, in the disintegrated or monolithic form. Structure, oil sorption capacity, and SEM analyses for xerogel-based additives were performed. Application of monolithic macroporous xerogel resulted in the highest biomass proliferation, i.e., 5.11-fold fresh biomass increase after four weeks of the screening culture. The highest deoxyshikonin production (i.e., 105.03 µg) was noted when hairy roots were maintained with particles of disintegrated mesoporous xerogel. The detailed kinetics investigations (6-week culture) revealed the highest growth of hairy root biomass and secondary metabolite production, equaling 9.46-fold fresh weight biomass and 204.08 µg deoxyshikonin, respectively. MTMS-based xerogels have been recognized as selective biocompatible scaffolds for boosting the proliferation of transgenic roots or for productivity enhancement of naphthoquinones without detrimental effects on biomass growth, and their successful applicability in in situ removal of secondary plant metabolites has been experimentally confirmed. [ABSTRACT FROM AUTHOR]

A simple and easily operated supercritical CO 2 dryer was designed and manufactured with the aim of producing high-surface-area mesoporous α-Fe 2 O 3 (hematite) and NiO aerogels. The gels were synthesized by a sol−gel method with the aid of propylene oxide (PO), as the gelation agent, and then dried and calcined at different conditions. The effects of drying and calcination conditions on the physicochemical properties of the final aerogels were investigated using X-ray diffraction (XRD), N 2 adsorption-desorption, Fourier-transformed infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FE-SEM) analyses. It was demonstrated that α-Fe 2 O 3 and NiO aerogels with high surface areas and mesoporosities could be successfully synthesized using the home-made supercritical CO 2 dryer. Supercritical drying of the gels resulted in α-Fe 2 O 3 (186 m2/g) and NiO (178 m2/g) aerogels with 186% and 34% higher surface areas, respectively, than xerogels obtained via simple drying at 80°C using a laboratory oven. In addition, the results showed that supercritical CO 2 drying could enhance preservation of the porous network of the oxide nanostructures at high calcination temperatures via suppression of sintering phenomenon. Calcination of α-Fe 2 O 3 and NiO aerogels at 600°C yielded 225% and 53% higher surface areas than the corresponding xerogel, confirming the significance of drying step in the sol − gel method. Asphaltene adsorption from a model oil with asphaltene concentration of 3000 ppm indicated that the aerogels possessed higher adsorption capacities for the bulky asphaltene molecules than xerogels calcined at the same temperature of 600°C, which was due to their enhanced textural properties. [ABSTRACT FROM AUTHOR]

The main objective of this study was to assess the photoactive properties of iron-doped silica xerogels under solar radiation. For this purpose, silica xerogels (XGS) synthesized by the sol-gel method were doped with Fe (III) by two routes: impregnation and polymerization. XGS samples were texturally and chemically characterized by N2 adsorption, XRD, FTIR, Raman, SEM-EDX, DRS, and PL, evidencing the suitability of using XGS substrates to host iron clusters on their surface with total compatibility. Chlorphenamine (CPM), ciprofloxacin (CIP), and ranitidine (RNT) were used as model compounds. The degradation of the molecules was made under simulated solar radiation testing the synthesis pad, load, material size, and reuse. It was found that XGS doped with Fe by the impregnation route (XGS-Fe-Im) were able to completely degrade CPM and RNT in 30 min and 10 min, respectively, whilst for CIP it achieved the removal of 60% after 1 h of solar radiation exposure, outperforming parent materials and solar radiation by itself. The study of the degradation mechanism elucidated a major influence from the action of HO• radicals. The present investigation offers a potential route of application of XGS Fe-doped materials for the removal of emerging concern contaminants under near real-world conditions. [ABSTRACT FROM AUTHOR]

Pectin hydrogel is a soft hydrocolloid with multifaceted utilities in the food sector. Substantial knowledge acquired on the gelation mechanisms and structure-function relationship of pectin has led to interesting functions of pectin hydrogel. Food applications of pectin hydrogels can be categorized under four headings: food ingredients/additives, food packaging, bioactive delivery and health management. The cross-linked and tangly three-dimensional structure of pectin gel renders it an ideal choice of wall material for the encapsulation of biomolecules and living cells; as a fat replacer and texturizer. Likewise, pectin hydrogel is an effective satiety inducer due to its ability to swell under the simulated gastric and intestinal conditions without losing its gel structure. Coating or composites of pectin hydrogel with proteins and other polysaccharides augment its functionality as an encapsulant, satiety-inducer and food packaging material. Low-methoxyl pectin gel is an appropriate food ink for 3D printing applications due to its viscoelastic properties, adaptable microstructure and texture properties. This review aims at explaining all the applications of pectin hydrogels, as mentioned above. A comprehensive discussion is presented on the approaches by which pectin hydrogel can be transformed as a resourceful material by controlling its dimensions, state, and rheology. The final sections of this article emphasize the recent research trends in this discipline, such as the development of smart hydrogels, injectable gels, aerogels, xerogels and oleogels from pectin. [ABSTRACT FROM AUTHOR]

Carbon xerogels were obtained by polycondensation of resorcinol and formaldehyde in a water medium. Their surface was oxidized by ammonium persulfate and then modified with amine groups. Four amines were used: methylamine, ethylamine, propylamine, and ethylenediamine, differing in carbon chain length and number of amine groups. The materials were characterized by low-temperature nitrogen sorption, elemental analysis, thermal analysis, X-ray diffraction, infrared spectroscopy, and determination of the surface oxygen group content with the use of the Boehm method. The final carbon adsorbents had surface areas ranging from 172–663 m2/g and acid–base nature. They were applied for adsorption of thymol blue from water solution. The sorption capacities of the studied adsorbents ranged from 83 to 140 mg/g. The presence of amine groups on the xerogel surface was found to increase its sorption capacity towards the dye studied. The dye adsorption process is endothermic and spontaneous, as indicated by the positive values of ΔH and the negative values of ΔG, respectively. The kinetics of adsorption of thymol blue was established to be described by the pseudo-second-order model. The equilibrium data were analyzed by the Langmuir and Freundlich models. The character of thymol blue adsorption is much better described by the Langmuir isotherm. [ABSTRACT FROM AUTHOR]

Cylindrical, cm‐sized monolithic Al2O3 xerogels with hierarchical meso‐/macropore system were prepared by sol‐gel synthesis. The influence of both solvent exchange and drying on monolith stability and the resulting pore system was studied following mass and volume of the monolith as well as by porosimetry and electron microscopy. Crack‐free drying of the monoliths requires a proper management of drying stress. This is achieved by adjusting the drying rate and solvent exchange procedure applied to the intermediate lyogels. Moreover, mainly through differences in capillary pressure, changing the pore fluid allows an adjustment of the mesopore width from 7.6 nm to 10.5 nm. Neither solvent exchange nor drying affect the macropores, the width of which stays at 1.5 μm. Finally, CO2 methanation over Ni‐impregnated Al2O3 monoliths reveals CO2 conversion and CH4 selectivity comparable to an industrial Ni/Al2O3 benchmark catalyst. [ABSTRACT FROM AUTHOR]

• Compares alumina aerogel vs xerogel Pd and Rh catalysts under identical conditions. • Catalyst performance tests representative of use in automotive three-way catalysts. • Aerogel and xerogel catalysts characterized via: TEM, XRD, BET and BJH analysis. The structural (low density, high porosity), thermal (low thermal conductivity, high temperature stability), and chemical (high degree of tailorability) properties of aerogels make them attractive in a range of applications, including catalysis. The automotive industry relies on three-way-catalysts (TWCs) for automotive pollution mitigation, and TWCs in turn depend heavily on the use of platinum group metals (PGMs). Reduction of the use of PGMs in TWCs would be advantageous. To investigate the effect of aerogel structure and processing on three-way catalytic performance we prepared alumina wet gels doped with ca. 15 nm rhodium and palladium nanoparticles and dried them (1) supercritically to form aerogels and (2) under ambient conditions to form xerogels. Nanoparticle concentration was adjusted to ensure that both forms of the catalyst (aerogel and xerogel) had the same volumetric concentration of PGM after calcination to 800°C. Powder x-ray diffraction and transmission electron microscopy (TEM) confirmed the presence of PGMs. TEM images showed PGM particle agglomeration on the order of 40 to 200 nm in both the aerogel and xerogel materials. Gas adsorption analysis indicated that the aerogels have a surface area of 460 m2/g with most pores in the 2- to 100-nm range, whereas the xerogel surface area was 170 m2/g with a narrow pore distribution around 10 nm. Catalytic performance tests under a range of simulated automotive operating conditions show that, in all cases, the aerogels outperformed the xerogels. The aerogel light-off temperatures (the temperature at which a 50 % conversion is achieved) were 45 to 120 °C lower for the conversion of HCs, 25 to 55 °C lower for the conversion of CO and 40 to 145 °C lower for the conversion of NO. This study provides direct evidence that aerogel processing of catalysts provides catalytic performance benefits separate from the underlying chemistry of the catalysts. TEM/EDX showing palladium nanoparticles in a Pd/Al 2 O 3 aerogel sample [Display omitted] [ABSTRACT FROM AUTHOR]

Organic and inorganic acids are common catalysts to promote the hydrolysis of methyltrialkoxysilanes, but they are challenging to modulate the inherent CH 3 SiO 1.5 backbone of polymethylsilsesquioxane (PMSQ) xerogels. Here, an aluminum chloride aqueous solution is proposed for the first time as an acid catalyst to enhance the hydrolysis of methyltriethoxysilane (MTES). This approach allows the PMSQ xerogels to have a more flexible [-Al-O-] m -[Si O ] n backbone structure. The optimal concentration of aluminum chloride and surfactant cetyltrimethylammonium bromide in the MTES sol was 1.069 mmol/L and 0.885 mmol/L, respectively, endowing the as-synthesized PMSQ xerogel with a high compression strength of 0.450 MPa and maximum compression strain of 76.1%. Notably, the tiny incorporation of alumina phase (0.4 mol%) in the Si-O-Si backbone made the PMSQ xerogels hydrophobic up to 400 °C for 1 h in the air. The PMSQ xerogels possessed superior thermal insulation properties (32.0–38.0 mW/(m·K)) and could be processed into desired large-sized shapes. [Display omitted] • AlCl 3 aqueous solution was proposed as the acid catalyst for the hydrolysis of MTES precursors. • The pH stabilities of MTES precursors catalyzed by various acid catalysts were compared. • The AlCl 3 and surfactant CTAB concentrations in the MTES sols were optimized. • Properties of PMSQ aerogels synthesized in various acid catalysts were compared. • Emerging design aspects regarding aerogels with [-Al-O-] m -[Si-O] n backbone were proposed. [ABSTRACT FROM AUTHOR]

Recycling polluted water via different techniques has become one of the most feasible ways to solve the freshwater crisis. We describe a novel method to prepare reusable and efficient photothermal energy conversion materials for water purification. Using crosslinked xerogels as precursor, the porous and interconnected carboxymethylcellulose sodium-derived carbon aerogels (abbreviated as CCAs) with good hydrophilic performance and strong light absorption capability are firstly fabricated through pyrolysis. Photothermal measurement results show that CCA15 exhibit excellent solar steam generation rate of 2.31 kg m−2 h−1 with high light-to-vapor conversion efficiency of 95.9% under 1 sun illumination. In addition, the feasible application of CCA15 for efficient water purification under 1 sun irradiation using a homemade water treatment device has been demonstrated successfully. The as-prepared CCAs shown in here can be a continuable solution to mitigate the global freshwater crisis. [Display omitted] • CCA with high specific surface area and abundant pores is fabricated. • CCA exhibits good hydrophilic and photo-thermal performance. • CCA15 shows solar steam generation rate of 2.31 kg m−2 h−1 and efficiency of 95.9%. • CCA displays water purification capability for dye pollutants and heavy metal ions. [ABSTRACT FROM AUTHOR]

Carbon xerogel with different mean pore sizes (10, 50, 100, 500 nm) but analogous structure, chemical composition, surface area, and microporosity, which are produced by an energy-effective microwave-based process, and activated carbon xerogels (100 nm-pore size) with higher microporosity were investigated as anodes for sodium dual-ion batteries. The objective of this study was to optimize the material textural properties for this specific application to be further matched with a carbon xerogel-based cathode in a full battery configuration. To this end, the role of these properties was evaluated, specifically the pore size and the microporosity since the storage of the Na+ ions in these carbon xerogels was demostrated to occur mainly by a pseudocapacitive mechanism based on adsorption on surface, defects (i.e. microporosity) and pores. The balance between the pore size and the associated external surface area of the carbon xerogels was a determining factor for their anodic performance. In this context, a material pore size of ∼ 100 nm and an associated external surface area of ∼ 100 m2 g−1 was the optimum balance. For a given material pore size, the increase of the microporosity by physical activation improved the anode capacity as well as the cycling stability. However, the development of the microporosity in relation to the external surface area must be optimized to avoid an undesirable increase in the first cycle irreversible capacity. Overall, the physically activated carbon xerogel with a pore size of 100 nm, a micropore volume of 0.47 cm3 g−1 and an external surface of 123 m2 g−1 was the most suitable active anode material for sodium dual-ion batteries. This material provided a specific discharge capacity of ∼ 154 mAh g−1 after 300 discharge/charge cycles with excellent cycling stability and coulombic efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

• A catalytic ozonation process (COP) of pCBA using tailored Ti/γAl 2 O 3 catalysts was applied. • Morphology engineering tuning during synthesis enhanced COP: Xerogels > Ambigels > Aerogels. • Besides Ti4+ incorporation, high surface acidity was the key to an effective COP by Xerogels. • These robust mesoporous catalysts demonstrated excellent reusability and stability. • Hydroxyl radicals (HO•) and (less) O2•--mediated reactions drove pCBA degradation. Herein, we optimized the catalytic ozonation process (COP) by engineering the morphology of versatile mesoporous Ti-doped γAl 2 O 3 materials. Ti/γAl 2 O 3 catalysts were synthesized as xerogels, ambigels, and aerogels for p-chlorobenzoic acid (pCBA) degradation by catalytic ozonation. The roles of Lewis acids and basic sites in Ti/γAl 2 O 3 were investigated along with the synthesis parameters affecting the morphology, structure, and surface acidity. The incorporation of Ti4+ increased the surface acidity, resulting in an effective COP. Full characterization confirmed the uniform Ti distribution and well-defined acidic properties. The sole ozonation process was insufficient, while 0.5 g/L catalyst addition rapidly degraded 50 mg/L pCBA (xerogel: 30 min, ambigel/aerogel: 60 min) while showing excellent reusability and robustness under ions' presence. EPR analysis suggested that pCBA removal occurs via bulk HO• and less by O 3 and O 2 •--mediated reactions, without 1O 2 generation. Based on the above findings, we proposed an integrated pCBA degradation pathway, providing insights into enhancing the COP for organic pollutant degradation via novel, cheap, and sustainable mesoporous materials. [ABSTRACT FROM AUTHOR]

This work provides insight into the correlation between the luminescent response of a water-vapour optical fibre sensor and the textural properties of its lanthanide-doped silica coating. To this end, a library of 16 silica xerogels derived from combinations between 2 lanthanide dopants (EuIII, TbIII) and 8 antenna ligands was synthesised and characterised by photoluminescence spectroscopy and N 2 and CO 2 adsorption-desorption isotherms, among others. Based on the best luminescent response and most-suited porous texture, the material doped with TbIII and 2,2′-(4-(2-Ethoxyethoxy)pyridine-2,6-diyl)bis(4,5-dihydrooxazole) was selected to construct the probe. A film of this material was affixed to a commercial silica fibre by dip-coating and the resulting sensor was tested in a climatic chamber with relative humidity ranging from 20 to 90% to obtain normalised time-response and calibration curves at three temperatures. The response was linear up to certain water-vapour concentrations, beyond which abruptly changed to polynomial, acting against the sensor resolution. The adsorption mechanism was elucidated by comparing the isosteric enthalpies of adsorption calculated from the sensor calibration curves to those determined from the monolith water-vapour isotherms, revealing that capillary condensation in the membrane mesopores was the key phenomenon leading to the response deviating from linearity. • Luminescent silica xerogel as the chemical membrane for a fibre optic sensor. • Luminescent xerogel with remarkable Stokes Shift and photostability for sensing. • Relationship between silica coating textural parameters and sensor response. • Relationship between isosteric enthalpy of adsorption and sensor response. • Measurement mechanism explanation in a water vapour fibre optic sensor. [ABSTRACT FROM AUTHOR]