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Hydrogen generation through water electrolysis is an efficient technique for hydrogen production, but the expensive price and scarcity of noble metal electrocatalysts hinder its large-scale application. Herein, cobalt-anchored nitrogen-doped graphene aerogel electrocatalysts (Co-N-C) for oxygen evolution reaction (OER) are prepared by simple chemical reduction and vacuum freeze-drying. The Co (0.5 wt%)-N (1 wt%)-C aerogel electrocatalyst has an optimal overpotential (0.383 V at 10 mA/cm2), which is significantly superior to that of a series of M-N-C aerogel electrocatalysts prepared by a similar route (M = Mn, Fe, Ni, Pt, Au, etc.) and other Co-N-C electrocatalysts that have been reported. In addition, the Co-N-C aerogel electrocatalyst has a small Tafel slope (95 mV/dec), a large electrochemical surface area (9.52 cm2), and excellent stability. Notably, the overpotential of Co-N-C aerogel electrocatalyst at a current density of 20 mA/cm2 is even superior to that of the commercial RuO2. In addition, density functional theory (DFT) confirms that the metal activity trend is Co-N-C > Fe-N-C > Ni-N-C, which is consistent with the OER activity results. The resulting Co-N-C aerogels can be considered one of the most promising electrocatalysts for energy storage and energy saving due to their simple preparation route, abundant raw materials, and superior electrocatalytic performance. [ABSTRACT FROM AUTHOR]

Amine hybrid silica aerogel globule (AHSAG) for CO 2 capture including direct air capture (DAC) was firstly synthesized via wet casting assisted self-catalyzed sol-gel process. AHSAG has abundant interpenetrating macropores, which favors diffusion of CO 2 into internal amine sites and can enhance CO 2 adsorption kinetics and capacity. The optimal CO 2 adsorption capacity of AHSAG with dry 100% and 400 ppm CO 2 are 3.82 (30 °C) and 1.86 mmol/g (55 °C), respectively. Corresponding amine efficiencies are 0.478 and 0.233. The effect of temperature on CO 2 adsorption capacity is attributed to simultaneous enhancement of mass transfer kinetics and adsorption thermodynamics. The highest CO 2 adsorption rate of AHSAG is achieved at 70 and 55 °C with 100% and 400 ppm CO 2 , respectively. The trend of CO 2 adsorption rate with temperature is attributed to the synergistic effect of diffusion kinetics and desorption. Based on experimental CO 2 adsorption kinetics, adsorption mechanism in 400 ppm CO 2 was estimated with different diffusion models. Both film diffusion resistance and intraparticle diffusion resistance are involved in CO 2 capture of AHSAG from air under given condition to control the overall adsorption process. Three kinetics models were used to fit the experimental data of AHSAG for DAC, and the Avrami model showed the best fitting within the whole adsorption period. Comparing with its state-of-the-art counterparts, AHSAG offers significant advantages for practical DAC, such as high adsorption capacity and amine efficiency, fast adsorption kinetics, and excellent cyclic stability. [Display omitted] • A new amine hybrid silica aerogel globule (AHSAG) via a facile wet casting assisted sol-gel process. • Plentiful interpenetrating macropores of AHSAG can enhance CO 2 adsorption kinetics and capacity. • CO 2 adsorption performances of AHSAG were studied with dry 100% and 400 ppm CO 2. • CO 2 adsorption performances were analysed from capacity, amine efficiency, adsorption rate, and cyclic stability. • Adsorption mechanism was estimated with different diffusion models to determine the rate-limiting step in. [ABSTRACT FROM AUTHOR]

As special nanoporous materials with consecutive 3D network, aerogels have many unique properties, such as low density, high surface area, large pore volume and porosity, leading to their high performances and promising applications in aerospace, military, industrial production, green building, new energy and biological medicine, etc. Large porosity and penetrating nanopore of aerogels provide good gas diffusion capacity and enough space for the retention of adsorbates, high specific surface area of aerogels favours the gas-phase interaction. Therefore, aerogels are ideal mediums for the removal of indoor air pollutants, such as airborne particles, VOCs, formaldehyde and CO2. In this paper, recent advances on the removal of these indoor air pollutants u-sing aerogels were reviewed. [ABSTRACT FROM AUTHOR]

BaTiO3 aerogels with a photocatalytic property were synthesized from metal barium via nanoparticle assembly method combined with ethanol supercritical drying technology. The specific surface area of the BaTiO3 aerogel could reach up to 233.24 m2/g, and the average pore size and total pore volume were 26.1 nm and 3.50 cm3/g, respectively. The sample showed excellent adsorption capacity and photocatalytic performance for 10 mg/L methyl orange solution (pH = 3), and the degradation rate reached up to 92.59% in 2 h, which was superior to BaTiO3 nanopowder. Moreover, the photodegradation rate was still about 80% after five-cycle experiments. (a) Photograph of sample, (b) SEM image, (c) nitrogen adsorption/desorption isotherms with pore size distribution curve and (d) photocatalysis performance test of BaTiO3 aerogels Highlights: The bulk BaTiO3 aerogel is synthesized via nanoparticle assembly method without heat treatment. The specific surface area of the BaTiO3 aerogel can reach up to 233.24 m2/g. When the volume ratio of ethanol/water is 2:1, the BaTiO3 aerogel exhibits an outstanding photodegradation performance that 92.59% methyl orange (MO) can be removed in 2 h. [ABSTRACT FROM AUTHOR]

Ceramic aerogels are promising candidates for high-temperature thermal resistance and thermal insulation materials. However, their application can be restricted by their brittleness when exposed to harsh conditions. Herein, this study has developed a novel synthesis process based on a sol-gel method and carbothermal reduction-nitridation to produce a porous TiN composite aerogel from an organic/inorganic hybrid. The resulting TiN displays a polyhedral particle size of around 30–60 nm with nanoscale pores. In addition, the TiN aerogel demonstrates a high BET-specific surface area of 653.42 m2/g and a very low thermal conductivity of 0.046 W/(m·K). Furthermore, the TiN aerogel composite displays a good thermal difference with no shrinkage and cracks of the morphology during the butane blazing torch at 1300 °C for 10 min under air environment, demonstrating its excellent thermal insulation property and anti-oxidation characteristics. The gas-solid reaction mechanism of TiN aerogel based on the Gibbs free energy calculations is also proposed. [ABSTRACT FROM AUTHOR]

Aerogels, with ultra-low density and thermal conductivity, are key materials for the development of high-efficient thermal insulations. Yet, their low compressive strength, oxidation behavior, and poor thermal stability limit their further development. Herein, we have prepared a novel monolithic mullite aerogel using the RF/Al 2 O 3 -SiO 2 aerogel organic/inorganic hybrid as the precursor, followed by the CO 2 supercritical drying, and high-temperature mullitization. The resulting mullite aerogel displays typical "pearl-necklace" three-dimensional network, with the average pore size at around 10–20 nm, showing a large BET specific surface of 481 m2/g. The compressive strength of the mullite aerogel is as high as 15.5 MPa, much larger than those of the reported ceramic aerogels. The mullite aerogel exhibits excellent thermal insulation property, and the mass loss is only 2.5% after the butane torch evaluation with 1300 °C for 10 min under air, showing its rather excellent anti-oxidation performance, and the anti-oxidation mechanism is also proposed. • A novel monolithic mullite aerogel for high temperature thermal insulation is developed. • The aerogel shows large BET specific surface area with excellent thermal insulation property. • The aerogel displays much higher mechanical strength as compared with the reported aerogels. • The mechanism of superior anti-oxidation property for mullite aerogel is proposed in this work. [ABSTRACT FROM AUTHOR]

Photoreduction of CO 2 to valuable fuels provides a promising strategy for managing the global carbon balance using renewable solar energy, yet the design of active, cost-effective, highly selective, and stable CO 2 reduction photocatalysts remains a big challenge. Herein, we report a novel SiOC aerogel photocatalyst synthesized by a simple one-step sol-gel process, combined with the supercritical drying technique and heat treatment processes. The resulting SiOC aerogel exhibits a large BET specific area with typical hierarchical structures, which is responsible for the enhanced photocatalytic activity. In addition, the formation mechanism of the SiOC whisker aerogel is revealed in this study. The optimized SiOC aerogel exhibits CH 4 and CO evolution activity of 5.8 and 20.5 μmol/g under simulated sunlight irradiation, respectively, without any additional co-catalyst or sacrificial agent, which is 6.4 and 3.9 times higher than those of the pristine SiC aerogel. The density functional theory (DFT) calculation confirms that the resulting SiOC aerogel can effectively adsorb and activate CO 2 and H 2 O molecules on the catalyst surface. The Gibbs free energy diagram further verifies the superior performance of the resulting SiOC aerogel over the pristine SiC and SiO 2 cluster via the rate-determining step calculations. The high efficiency of CO 2 reduction can be attributed to the structural merits and the electronic structures modulation, which greatly achieves fast separation and transfer of charge carriers. The work paves an insight into the rational design of photocatalysts toward simultaneously facilitating carrier separation and CO 2 activation from aerogel-based porous materials. • A novel highly efficient SiOC aerogel for CO 2 photoreduction reaction (CRR) is developed. • The SiOC aerogel displays greatly enhanced CRR activity as compared with the reported works. • The formation mechanism of the SiC whisker within the SiOC aerogel is revealed. • The density functional theory calculations are carried out for revealing the CRR mechanism. [ABSTRACT FROM AUTHOR]

A novel nanorod-like spinel aerogel is synthesized by the sol-gel method combined with the supercritical technique. The Mg 4 Al 2 (OH) 14 ·3H 2 O and boehmite is formed in the spinel precursor aerogel and Mg 4 Al 2 (OH) 14 ·3H 2 O transforms into MgO and spinel at 350 °C. Structural transition of boehmite to γ-Al 2 O 3 occurs at ca. 400 °C, which is favorable to the further solid reaction between MgO and γ-Al 2 O 3 forming spinel aerogel at 500 °C. This formation temperature is much lower than the conventional methods. The highly pure nanorod spinel with length of 150–200 nm and width of 5–10 nm is well crystallized after 800 °C. The nanocrystal maintains a large specific surface of 81.87 m 2 /g after calcining at 1200 °C. [ABSTRACT FROM AUTHOR]

The high-polymeric degree or molecular-weight of self-made polyethoxydisiloxane (PEDS) was successfully used to synthesize aerogels with several advantageous mechanical characteristics, compared with those based on conventional tetraethylorthosilicate (TEOS) aerogel preparation methods. The first advantage is their lower initial values of bulk modulus ( K 0 ), compared with those prepared via the two - step method; this is due to release of internal stress during the shrinkage of wet gel. Secondly, a collapse index n of −0.125 is obtained by the collapse law; this implies a new buckling destruction model. This is different from those prepared via the two - step method, and suggests that a hierarchical filament structure, formed by the connection of nano-particles, constitutes the solid skeleton of pores. In this paper, average aerogel pore sizes between 16.0 and 39.3 nm are analyzed by the combination of Mercury Intrusion Porosimetry (MIP) and Nitrogen Adsorption–Desorption (NAD). The microstructure and morphology of the aerogels are demonstrated by Transmission Electron Microscopy (TEM) and Field Emission Scan Electron Microscopy (FE-SEM). [ABSTRACT FROM AUTHOR]

Since the lotus effect was reported by Barthlott and Neinhuis in 1997, superhydrophobic and superoleophobic materials have received much attention due to special rough morphology and great potential applications in self-cleaning, anti-fouling, corrosion-resistance, and other fields. However, the conventional preparation process of superamphiphobic materials is complicated, including pre- and post-treatments which are used to achieve micro-nano hierarchical structures and low surface energy. In this study, we used methyltrimethoxysilane (MTMS) and 1,1,2,2- tetrahydroperfluorodecyltrimethoxysilane (FAS-17) as precursors and successfully prepared superamphiphobic FAS-17/MTMS composite aerogel via facile sol-gel method. Three-dimensional networks and long fluorocarbon chains formed micro-nano hierarchical structures. As-prepared aerogels had water contact angle (WCA) of 153.68°, oil contact angle (OCA) of 156.28°, water sliding angle (WSA) of 3.32° and oil sliding angle (OSA) of 4.57°, suggesting excellent superamphiphobic performance. Besides external superamphiphobicity, the cross section of sample also exhibited great liquid-repellency with WCA of 160.43° and OCA of 153.43°. Moreover, although cracked into powders with particle size of 0.1 mm, aerogel sample still retained its liquid-repellency with WCA of 122.85° and OCA of 128.01°, respectively. After thermal treatment under 200 ℃ for 2 h, the aerogel sample had WCA of 152.45° and OCA of 135.67°, showing excellent thermal stability. Taking advantage of low thermal conductivity and superamphiphobic properties, superamphiphobic aerogel has potential for fabricating self-cleaning and thermal insulating materials. [Display omitted] • In-situ fabrication of superamphiphobic aerogel by MTMS and fluoroalkysliane. • The unique three-dimensional networks yield superamphiphobic property. • Aerogel powders maintain liquid-repellency. • As-prepared aerogel has good thermal stability. [ABSTRACT FROM AUTHOR]

The applications of silica aerogels are restricted due to their intrinsic fragile property. Polymerization of di-isocyanates can be templated onto the mesoporous surface of the –NH 2 group modified silica clusters, resulting in the conformal crosslinked coating on surface of silica clusters. Aminopropyltriethoxysilane (APTES), as the silica co-precursor and amine group modification agent, is involved containing tetramethyl orthosilicate (TMOS) silica precursor, while hexamethylene diisocyanate (HDI) is incorporated as the polymer crosslinking agent. The effects of different amounts of APTES on the physicochemical properties of the resulting crosslinked aerogels are investigated. The results show that the optimized APTES/TMOS volume ratio can be determined at 0.5:1. The resulting optimal crosslinked silica aerogel possesses large BET specific surface area of 150.9 m2/g, low thermal conductivity of 0.037 W/(m·K), and the Young's modulus is as large as 18 MPa under strain of 4.2%, much higher than that in the previously published works. The polymerization reaction mechanism forming the polyurethane chains has also been proposed. In addition, the interactions between silica clusters and polymer chains are studied by molecular mechanics and molecular dynamics. The interactions are mainly dependent on non-bonding energy, and the electrostatic energy has decisive impact on the combination of silica clusters and polymer chains. The density field of C, H, N, O, and Si elements overlaps with each other, indicating that the polymer crosslinked silica aerogel maintains typical three-dimensional porous structure. The N element enriches in the region between silica clusters, further verifying the formation –CONH–(CH 2) 6 –CONH- polyurethane chains, which is actually responsible for the much enhanced mechanical property. [ABSTRACT FROM AUTHOR]

Abstract: Resorcinol–formaldehyde/silica composite (RF/SiO2) gels were synthesized in one pot using a facile process. RF/SiO2 aerogels were obtained after supercritical carbon dioxide fluid drying. Monolithic mesoporous silicon carbide (SiC aerogels) was prepared from RF/SiO2 aerogels after carbothermal reduction and calcination. The as-prepared SiC products exhibited monolithic mesoporous morphology and possessed a BET specific surface area of 251m2/g and a pore volume of 0.965cm3/g. X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrated that the resulting SiC aerogels were composed of α-SiC nanocrystals. The bulk density and skeleton density of SiC products is 0.288g/cm3 and 3.12g/cm3, respectively. The porosity of SiC products is 90.8%. The SiC aerogels were stable up to temperatures near 650°C. [Copyright &y& Elsevier]

Schematic diagram of the preparation procedures of PEG/rGO-HT and PEG/rGO-MI samples. • Different techniques are carried out for preparing the PCM/aerogel composites. • The structures evolution and chemical interactions within PCM composites are revealed. • The PCM composite possesses excellent thermal stability and extremely large latent heat. Form-stable phase change material (PCM) composites is fabricated by vacuum-assisted melting infiltration (PEG/rGO-MI) technique, while the sample prepared by hydrothermal reduction method (PEG/rGO-HT) is also provided as control. PEG-6000 and reduced graphene oxide (rGO) are used as PCM and the porous supporting material, respectively. PEG molecules are fully filled in the connecting pore matrix of rGO aerogel with disordered arrangements for the PEG/rGO-HT sample, while distributed in the lamellar gaps of rGO nanoflakes with a regular orientation due to hydrogen bonding interactions for the PEG/rGO-MI sample. The C/O atomic ratios increase from 2.03% to 3.12% and 2.3%, respectively, for the PEG/rGO-HT and PEG/rGO-MI samples, indicating an increased sp2-hydridized C and simultaneously a decreased fraction of oxygen-containing functional groups. The Liquid leakages indicate that they both possess shape-stabilized property. The PCM mass percentage is 85.6% for the PEG/rGO-HT sample, while up to 96.6% for the PEG/rGO-MI sample. The melting latent heat of the PEG/rGO-HT sample is 139.4 J/g, whereas it is 205.2 J/g for the PEG/rGO-MI sample, much larger than that of most published works. The PEG/rGO-MI sample also exhibits excellent short-term thermal insulation property, which has promising application in complex environment for thermal energy management. [ABSTRACT FROM AUTHOR]

• PVDF aerogel was fabricated by phase inversion induced sol-gel process followed by supercritical drying. • PVDF aerogel possessed a water contact angle of 126° and a thermal conductivity of 0.03602 W/(m·K). • PVDF aerogel had good thermal stability up to 400 °C in aerial environment. A polyvinylidene fluoride (PVDF) aerogel was fabricated by a phase inversion induced sol-gel process along with supercritical drying. The PVDF aerogel exhibited a hierarchical structure consisting of agglomerates and micron-size voids. The agglomerates consisted of nanoparticles and nanopores. The PVDF aerogel showed a water contact angle of 126° and was thermally stable up to 400 °C in aerial environment. The thermal conductivity of the PVDF aerogel was as low as 0.03602 W/(m·K). The PVDF aerogel is promisingly applied in thermal insulation under humid conditions and water treatment. [ABSTRACT FROM AUTHOR]

Practical applications of silica aerogels have been restricted due to their hydrophilicity, fragility and high cost of supercritical drying technique. In this work, the successful synthesis of the super hydrophobic polymethylsilsesquioxane (PMSQ) based silica aerogel via the sol-gel technique and ambient pressure drying method is proposed. Dimethoxydimethylsilane (DMDMS) and methyltrimethoxysilane (MTMS) are used as the co-precursors. The MTMS/DMDMS volume ratio is determined at 3/1, and the water contact angle as large as 165°, confirming its super hydrophobicity. The CH 3 groups rendering the hydrophobicity gradually disappear after heat treatment at 400 °C. The aerogel is composed of the spherical and smooth secondary particles with diameters at around 3–4 μm, with the most probable pore diameter locating at around 20 μm. The aerogel exhibits excellent elastic property under compression cycling test. Moreover, it displays good adsorption properties over many kinds of organic solvents, as well as excellent cycling adsorption property. Schemicatic diagram of the formation for the superhydrophobic and flexible PMSQ based silica aerogel. Unlabelled Image • A novel PMSQ-based aerogel is prepared via ambient pressure drying technique. • The mechanism of hydrophobicity evolution and flexible aerogel formation is proposed. • The aerogel has a high contact angle of 165° and excellent flexibility under compression cycling test. [ABSTRACT FROM AUTHOR]

The development of low-cost and highly active oxygen evolution reaction (OER) electrocatalysts is of significant importance for the advancement of sustainable new clean energy and storage systems. Herein, reduced graphene oxide (rGO) anchored with spinel CoFe 2 O 4 (rGO/CoFe 2 O 4) is prepared by hydrothermal synthesis, combined with freeze-drying and heat treatment processes. The effects of different spinel types, the loading amount of CoFe 2 O 4 and heat treatment temperatures on the OER performance are investigated. The resulting possesses a typical mesoporous structure composed of CoFe 2 O 4 nanoparticles with 20–50 nm and the lamellar rGO, leading to a large BET specific surface area. The as-prepared rGO/CoFe 2 O 4 has an overpotential of 325 mV, a low Tafel slope (63.02 mV/dec) at a current density of 10 mA cm−2, and shows excellent stability with no significant current decay. Based on Density Functional Theory (DFT) calculations, the transition from *O to *OOH has the highest Gibbs free energy, which is the rate-determining step of the entire catalytic process. The Fe site on the (100) crystal plane of CoFe 2 O 4 is most likely the reactive site for the OER process, improving the OER activity by decreasing the binding strength between the catalytic surface and adsorbed *O intermediates. (a) Synthesis diagram of rGO/CoFe 2 O 4. (b) OER electrocatalytic performance. (c) Tafel slope. (d) Potential curve at a constant current density of 10 mA cm−2 for CFGA0.2-600 catalyst. [Display omitted] [ABSTRACT FROM AUTHOR]

C/silica (RF/SiO 2) aerogel (RFSA) was synthesized via a one-step sol-gel process and supercritical fluid drying. Then, monolithic silicon nitride (Si 3 N 4) aerogel (SNA) was prepared via carbothermal nitridation of the RFSA in flowing N 2. The effects of the RFSA density and carbothermal temperature on the formation of the SNA were investigated. The evolution of the physical properties, chemical structure, morphology, pore structure, and thermal performance of the SNA was examined. Si 3 N 4 nanocrystals were formed from the RFSA at a carbothermal temperature of 1500 °C. The as-prepared SNA had a low density (0.127 g/cm3), large specific surface area (445 m2/g) and low thermal conductivity (0.04909 W/(m·K)), which were far better than those of its state-of-art counterparts. Because of its good thermal stability, the SNA can be used as a thermal insulator and support at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract A novel Na 2 SO 4 @SiO 2 @Al 2 O 3 -SiO 2 phase change material doped aerogel composite (PDAC) using the sol-gel technique is prepared. This new kind of composite material is composed of a core-shell structured Na 2 SO 4 @SiO 2 phase change material (PCM) with high melting temperature and Al 2 O 3 -SiO 2 aerogel with high thermal resistance and low thermal conductivity. The effects of PCM amounts and heat treatment temperatures on the physicochemical properties of Na 2 SO 4 @SiO 2 @Al 2 O 3 -SiO 2 PDCA are investigated. X-ray diffraction (XRD) shows that when the mass percentage of Na 2 SO 4 @SiO 2 PCM powders increases to 36.7%, the peaks corresponding to Na 2 SO 4 can be well observed. The boehmite phase within Na 2 SO 4 @SiO 2 @Al 2 O 3 -SiO 2 PDAC can be transformed to γ-Al 2 O 3 via structural adjustment after heat treatment at 600 °C. The pore size distribution doesn't shift after 600 °C heat treatment, and the most probable pore diameter is at around 30 nm. Transmission Electron Microscopy (TEM) shows that the Na 2 SO 4 @SiO 2 PCM powders with diameters at around 500 nm can be effectively trapped and are homogeneously distributed within the aerogel matrix even after further heat treatment at 1000 °C, therefore, liquid leakage can be inhibited during melting process. The peak latent heat of Na 2 SO 4 @SiO 2 @Al 2 O 3 -SiO 2 PDCA can be as high as 153.84 J/g with the PCM mass percentage at 36.7%. The Brunauer-Emmett-Teller (BET) specific surface area increases from 419.3 m2/g to 630.6 m2/g due to structural adjustment, and then decreases to 277.7 m2/g caused by volume shrinkage. Thermal simulation results show that the total melting time can be 254.8 s, and development of the temperature distribution keeps well with that of the liquid fraction. The velocity distribution of the liquid PCM keeps at 0 due to the constraint of aerogel matrix. This Na 2 SO 4 @SiO 2 @Al 2 O 3 -SiO 2 PDAC can be a promising high temperature PCM in thermal energy storage applications. [ABSTRACT FROM AUTHOR]

Herein, we have demonstrated a novel Ru-promoted NiFe oxyhydroxide anchored on N-doped carbon aerogel (RuNi 7 FeO x (OH) y @NCA) aerogel electrocatalyst via a facile sol-gel process, combined with a supercritical drying technique. The optimal RuNi 7 FeO x (OH) y @NCA shows a typical "pearl-like" aerogel nanostructure with a three-dimensional network, showing a large specific surface area of 227.7 m2·g−1. The achieved RuNi 7 FeO x (OH) y @NCA exhibits high OER activity with a low overpotential of 278.0 mV at 10 mA·cm−2 and a high TOF of 0.107 s−1. Moreover, the RuNi 7 FeO x (OH) y @NCA aerogel displays excellent hydrogen evolution reaction (HER) activity under alkaline conditions, with a small overpotential of 99.0 mV at a current density of 10 mA·cm−2, and a small Tafel slope of 61.1 mV·dec−1. DFT calculations show that the enhanced OER activity is attributed to the improved binding strength of *OOH intermediate on the catalyst surface, and the introduced Ru with larger electron density and weaker spin density leads to the improved HER activity. [Display omitted] • A highly efficient novel aerogel electrocatalyst for dual-functional OER/HER is firstly developed. • The aerogel displays much enhanced OER/HER activity as compared with the reported works. • The density functional theory calculations are carried out for revealing the OER/HER mechanism. [ABSTRACT FROM AUTHOR]

In this study, highly cross-linked and completely imidized polyimide aerogels containing carboxyl groups were successfully synthesized using a mild sol-gel method at room temperature from 3,5-diaminobenzoic (DABA) and biphenyl-3,3′,4,4′-tetracarboxylic (BPDA) and cross-linked with 1,3,5-triaminophenoxybenzene. The densities of the obtained polyimide aerogels are between 0.116 and 0.386 g/cm 3 , the specific surface areas range from 173 to 461 m 2 /g, and the porosities are as high as 97%. The CO 2 adsorption-desorption isotherms are reversible, and the CO 2 uptakes at 25 °C and 1 bar are as high as 21.10 cm 3 /g, which are comparable to those of previously reported microporous organic polymers. The high CO 2 adsorptions are attributed to the abundance of electron-rich heteroatoms in the polyimide networks and to the presence of carboxyl groups, a type of CO 2 -philic group. The facile preparation and high CO 2 adsorptive capacity indicate that polyimide aerogels may be ideal candidates for capturing CO 2 . [ABSTRACT FROM AUTHOR]

SnO 2 is a charming contributor to sensors, while the intrinsic deficiencies, like facile conglomeration, hard stimulation, and poor stability, limit its potential prospects. The SnO 2 aerogel (SA) is proposed through an achievable fabrication, effectively solving the difficulties and exhibiting a satisfactory ability in ethanol detection. The SA450 behaves as the spearhead, which owns the narrowest bandgap of 3.2 eV and the largest double-layer capacitance of 559 μF/cm2, symbolizing the most prone electronic transitions and active sites. Besides, SEM, TEM, and AFM are served to obtain the nanoparticle size and the rough surface. The SA450 exhibits an outstanding sensing ability at 150 ℃, and the DFT calculation is taken as evidence. Interestingly, the SA0 without calcination can exhibit a satisfying SERS detection towards 4-MBA, which applies to explosive detection. Finally, the bandgap structure and response process are discussed. This work introduces a brand-new preparation of metal oxide semiconductors (MOSs), overcoming plenty of aporias in gas sensors and simultaneously producing the SERS response, which can lead to a fresh direction for sensing materials. • SA can exhibit SERS adsorption without heat treatment and show gas sensitivity after calcination. • The LOD of SA450 can reach 4.3 ppb at 150 ℃. • DFT calculation was introduced to certify the sensitivity and selectivity of SA450. [ABSTRACT FROM AUTHOR]

• A highly efficient Pd 3 Cu aerogel alloy for oxygen reduction reaction is firstly developed. • The aerogel alloy displays much enhanced ORR activity as compared with the noble metals. • The aerogel alloy also delivers excellent and multifunctional HER and EOR performance. • The density functional theory calculations are carried out for revealing the ORR mechanism. Pd has been considered as a potential substitution of the Pt-based electrocatalyst for oxygen reduction reaction (ORR) in the fields of fuel cells, however, the binding strength between the bare surface and the intermediates is much stronger than that on Pt, leading to its inferior ORR activity. Alloying noble metals with nonprecious metals provides a cost-effective strategy for electrocatalyst design. In this work, we have demonstrated a novel Pd 3 Cu aerogel electrocatalyst derived from a mild reduction agent via the self-assembly and freeze-drying technique. The resulting catalyst shows a typical three-dimensional and "pearl-like" aerogel structure. Combining the structural features and optimized chemical compositions, the Pd 3 Cu aerogel exhibits remarkable pH-independent performance over the commercial Pt/C electrocatalyst. Notably, the optimized Pd 3 Cu aerogel displays excellent ORR activity with a half-wave potential of 0.90 V vs RHE, with a limiting current density of 5.8 mA/cm2 under the alkaline conditions, which is among the best of the reported noble metal-based ORR electrocatalysts. In addition, the resulting Pd 3 Cu aerogel delivers excellent hydrogen evolution reaction (HER) and ethanol oxidation reaction (EOR) performance. Furthermore, the density functional theory (DFT) calculations reveal that the unique partially oxidized Pd 3 Cu aerogel has led to a shift‐down of the d-band center of the active sites, which energetically optimizes the binding strength of the adsorbed O intermediate during the ORR process, therefore accelerating the ORR activity. These findings provide a new pathway for the integrated engineering of geometric and electronic structures of metal alloys to improve their electrocatalytic property. [ABSTRACT FROM AUTHOR]

Given the sluggish kinetics limiting the oxygen evolution reaction (OER), developing efficient and robust OER catalysts is highly demanded in developing efficient energy conversion technologies. Herein, we have grown FeCo oxyhydroxides on the 3D graphene oxide (GO) framework (FeCo 2 O x (OH) y /GO) via a simple sol-gel process, combined with the supercritical drying technique. The resulting FeCo 2 O x (OH) y /GO aerogel-based electrocatalyst possesses high porosity and a large BET specific surface area with 223.52 m2/g, which exposes more active sites, as well as provides diffusion channels for the reaction products. The resulting electrocatalyst requires an overpotential of 305 mV at a current density of 10 mA cm−2, with a low Tafel slope (43.7 mV dec−1) and excellent stability, which indicates superior OER catalytic activity to that of the commercial RuO 2 /C under alkaline conditions. Based on density functional theory (DFT) calculations, the synergistic effect between the GO layer and FeCo oxyhydroxides layer has been revealed by the electronic structures calculations. The incorporation of GO results in a negative shift of the d -band center of the surface active sites, indicating a decrease in the binding strength between the catalyst surface and the intermediates, therefore accelerating the OER process. [Display omitted] • A novel 3D FeCo 2 O x (OH) y /GO aerogel is synthesized via the supercritical drying technique. • The resulting FeCo 2 O x (OH) y -2.4 %GO exhibits rather remarkable OER performance. • Electrons structures calculations are carried out for studying the OER mechanism. [ABSTRACT FROM AUTHOR]

A simplified diagram of photocatalytic Cr(VI) reduction mechanism of the ZZA-400 aerogel heterojunction. [Display omitted] • A novel magnetic 3-D ZnFe 2 O 4 /ZnO aerogel based heterojunction has been synthesized. • ZnFe 2 O 4 /ZnO shows much superior photoreduction property than those in the reported works. • DFT calculations are carried out for studying electronic structures of the resulting catalyst. • The photocatalytic mechanism of Cr(VI) degradation has been proposed in the work. A novel magnetic type Ⅱ ZnFe 2 O 4 /ZnO aerogel (ZZA) heterojunction photocatalyst is firstly developed for photocatalytic reduction of Cr(Ⅵ) to Cr (III). The optimal ZZA-400 shows typical "pearl-like" nanostructures, with particle diameters at around 20–30 nm. It possesses a large BET specific surface area of 127.5 m2/g and an appropriate bandgap of 1.9 eV. It exhibits an efficiency of 87.0 % for photocatalytic Cr(VI) reduction within 120 min under extremely high Cr(VI) concentration (100 mg/L), with the rate constant up to 7.08 × 10−3 min−1. Density functional theory (DFT) calculations show that the incorporation of ZnFe 2 O 4 (ZFO) introduces an impurity energy level in the gap region of ZnO (ZO), which contributes to the optical absorption in the visible light region. It is energetically favorable for the electrons' migration from ZnO to ZnFe 2 O 4 due to the lower Fermi energy level of ZnFe 2 O 4. However, the electrons migrate from ZnFe 2 O 4 to the conduction band of ZnO with the assistance of the built-in electric field under visible light illumination, therefore, the separation of electron-hole pairs can be greatly promoted. The combination of formed O 2 –, the electrons in the conduction band of ZnO, and the reductive CO 2 – radical together enhance the photocatalytic property of the aerogel heterojunction. [ABSTRACT FROM AUTHOR]

• Doping Ag as a catalyst to improve the internal electron mobility is proposed. • The Ag-SnO 2 /RGO aerogel exhibits the ability of capacitance for redox by C-V test. • The Ag-SnO 2 /RGO aerogel responses better at RT instead of heating conditions. • A non-liner relationship between gas concentration and response is observed. A new material of Ag-SnO 2 /rGO aerogel is fabricated by the sol-gel method and freeze-drying technique. The SnO 2 particles are tightly arranged on the rGO sheets to form a p-n heterojunction, and the rGO aerogel possesses abundant pore structures for effective adsorption. Besides, the Ag particles are dispersed on the surface as a catalyst to improve the internal electron mobility, further promoting the gas-sensing performance. To be noted, the Ag-SnO 2 /rGO aerogel can exhibit a response of 2.13 towards 50 ppm NO 2 at RT instead of heating conditions, and shows a cyclic capacitance property of redox. Moreover, the non-linear growth between gas concentration and response is observed, which proves the chemical adsorption that results in the high selectivity. [ABSTRACT FROM AUTHOR]

• Nanostructure TiO2-reduced graphene oxide composite aerogels (rGO-TA) were synthesized. • The rod-like TiO 2 with a width of 10–20 nm and length of 100–150 nm are decorated on the network structure of rGO aerogel. • In-situ rGO-TA composite exhibited highest visible light absorption. • Anchoring of oxygen vacancies and C-O-Ti bond contribute to the enhanced activity. • The highest carbon conversion of composite aerogel was 15.7 times than that of P25. ga1 In response to the worldwide over-standard carbon dioxide emission problem, this work synthesized a series of titanium dioxide/reduced graphene oxide composite aerogels (TiO 2 -rGO) for photoconversion of CO 2 by a one-step hydrothermal and freeze-drying method. The prepared composite aerogel presents a high specific surface area of 287.3 m2/g and pore volume of 0.72 cm3/g, contributing to remarkable absorption capability of reactants and fast intraparticle molecular transfer. In the three-dimensional structure of rGO aerogel, TiO 2 with nano-rod shape (10–20 nm × 100–150 nm) is uniformly interspersed. Through applying the composite catalytic aerogel for the photocatalysis reaction, CO 2 was efficiently converted to MeOH, CH 4 , and EtOH, etc. The total yield of carbon generated by G-25Ti (TiO 2 -rGO with 25 mmol Ti4+) was found 15.7 times higher than that of the pure P25. The corresponding characteristic analysis demonstrated that the photocatalytic performance of TiO 2 -rGO composite aerogel has been highly improved, originated from two folds: (1) the introduction of 3-D rGO to nano-rod shape TiO 2 promoted its light absorption efficiency, and more significantly (2) the specific chemical bonding sites and strong O˭C‒O‒Ti group between rGO and TiO 2 effectively mitigate the recombination of photogenerated electron–hole pairs. In this work, rod-like TiO 2 -rGO composite aerogels prepared by using TiCl 4 as precursor for the first time have been found a new application in CO 2 reduction using visible sunlight. [ABSTRACT FROM AUTHOR]