A series of Y2.94Al5−mGamO12:0.06Ce3+ (1≤m≤2.5) green phosphors were successfully synthesized by a solid-state reaction method. The microstructure, morphology, luminescence spectra and thermal stability of the phosphors were investigated. NaF flux can greatly promote the growth and crystallization of Y2.94Al5−mGamO12:0.06Ce3+ (1≤m≤2.5) phosphors. The luminescence properties of Y2.94Al5−mGamO12:0.06Ce3+ (1≤m≤2.5) green phosphors dramatically depend on the m value. When m≤1.5, the phosphor shows strong luminescence and excellent thermal stability. At 150 °C, the luminescence intensity of the m=1.0 and m=1.5 samples still maintains 90.3% and 88.8% of that measured at 25 °C, respectively. The experimental results demonstrate that Y2.94Al4GaO12:0.06Ce3+ and Y2.94Al3.5Ga1.5O12:0.06Ce3+ are promising green phosphors, which have great potential for use not only in high color rendering index white LEDs but also in high-power white LEDs.

A series of Ce3+-doped Y3Al3.5Ga1.5O12 green phosphors were successfully synthesized by a solid-state reaction method. The microstructure, morphology, luminescence spectra, luminescence quantum yield (QY) and thermal stability of the phosphor were investigated. The critical concentration of Ce3+ ions in Y3−mAl3.5Ga1.5O12:mCe3+ is m=0.06. The QY of Y2.94Al3.5Ga1.5O12:0.06Ce3+ phosphor is as high as 94% under excitation at 450 nm and its luminescence intensity at 150 °C still maintains 90% of that measured at 25 °C, which are just a little worse than those of commercial Lu3Al5O12:Ce3+ green phosphor but much better than those of commercial (Sr,Ba)2SiO4:Eu2+ green phosphor. A white LED lamp was fabricated by employing Y2.94Al3.5Ga1.5O12:0.06Ce3+ as a green phosphor and commercial (Ca,Sr)AlSiN3:Eu2+ as a red phosphor (628 nm), its Ra value, correlated color temperature (CCT), CIE1931 chromaticity coordinates and luminous efficiency is 84, 3081 K, (x=0.4369, y=0.4142) and 102 lm/W, respectively. The experimental results demonstrate that Y2.94Al3.5Ga1.5O12:0.06Ce3+ is a promising green phosphor not only can be used for high color rendering index white LEDs but also for high-power white LEDs.

Silica aerogel microspheres were synthesized by a two-step acid–base sol–gel reaction in water-in-oil emulsion systems, in which tetraethoxysilane was used as a precursor and ethanol as a solvent, and HCl and NH4OH as acid–base catalysts in two steps. The synthesis process and parameters of the emulsion process including viscosity, surfactant concentration and stirring rate have been investigated. In the emulsifying process, the viscosity of silica sol is vital to restrain the occurrence of flocculation phenomenon for forming monodisperse alcogel microspheres. The smooth silica aerogel microspheres can be formed from the silica sol with the viscosity of 107 mPa s. The resultant silica aerogel microspheres with similar surface areas above 650 m2/g, bulk densities in the range of 0.094–0.138 g/cm3, and mean diameters ranging from 40.3 to 126.1 μm can be formed by controlling these parameters of the emulsion process. The minimum of polydispersity and roundness of silica aerogel microspheres are 0.058 and 1.11, respectively. Furthermore, silica aerogel microspheres show a high capacity of uptaking bean oil, isopropanol, kerosene and n-hexane, highlighting the possibility to remove oils from water for oil spill cleanup.

We report a facile approach to synthesize superhydrophobic and superoleophilic “sponge-like” aerogels through sol–gel reaction followed by supercritical drying, in which MTES and DMDES are used as co-precursors, EtOH as a solvent, CTAB as a surfactant, and HCl and NH3·H2O as catalysts. The MTES–DMDES-based aerogels formed at the optimal molar ratio of MTES: DMDES: EtOH: H2O: HCl: NH3·H2O: CTAB at 1.1: 0.9: 6: 12: 2 × 10−3: 2 × 10−3: 0.14 with a low density of 0.0897 g/cm3 show a compression ratio of 80 % under 36.85 kPa stress. They are superhydrophobic and superoleophilic with a water contact angle of 153.6° and an oil contact angle of 0°. We find that the MTES–DMDES-based aerogels show the high adsorption capacity for various kinds of organic liquids and the excellent recyclability in removing oil from water.

We report the synthesis of flexible, hydrophobic, and oleophilic silica aerogels through a two-step acid–base sol–gel reaction followed by supercritical drying, in which methyltriethoxysilane (MTES) is used as a precursor, ethanol (EtOH) as a solvent, and hydrochloric acid (HCl) and ammonia (NH3·H2O) as catalysts. At the optimal molar ratio of MTES:EtOH:H2O:HCl:NH3·H2O is 1:18:3.5:1.44 × 10−4:1.2, MTES-based silica aerogels show the minimum density of 0.046 g/cm3 and the maximum compression ratio of 80 % with 15.09 kPa stress. They are superhydrophobic with a water contact angle of 157° and thermally stable up to 350 °C. We also find that they show the excellent adsorption for ethanol with a ratio of 1400 %.

The polyyttriocarbosilane (PYCS) with various quantities of yttrium was obtained by reacting yttrium acetylacetonate (Y(AcAc)3) with polycarbosilane (PCS). The molecular weight, softening point, and Si–H bond content of the resulting PYCS are controlled by the Y(AcAc)3:PCS weight ratio, reaction temperature and reaction time. The main chain of the PYCS is made up of alternating carbon and silicon atoms with small amount of Si–O–Y presented in the main chain and Si–H groups at the side chain. The pyrolysis process of PYCS was investigated by TG and XRD. The results reveal that the polymer-to-ceramic transition of the PYCS occurs in three steps. The final ceramics obtained at 1,800 °C contain a large number of β-SiC crystallites and a small amount of α-SiC crystallites.

Silica aerogels were synthesized via sol–gel processing followed by a two-step surface modification using methyltrimethoxysilane (MTMS) and trimethylchlorosilane (TMCS)/ethanol (EtOH)/n-Hexane as modifying agents via ambient pressure drying. The bulk modification and surface modification of silica network from the alcogels were accomplished in this approach. The obtained silica aerogels exhibited three-dimensional nanoporous structure with the porosities, densities and specific surface areas in the ranges of 87.7–92.3%, 0.27–0.17 g cm−3, and 852–1005 m2 g−1, respectively. The presence of Si–CH3 functional groups on the surface of silica network resulted in hydrophobic property with the contact angle as high as 156°. The promotion of pore water displacement during the surface modification strengthened the backbone of silica aerogels leading to good thermal and hydrophobic stabilities. Possible mechanism of surface modification and solvent exchange by a two-step modification is suggested.Highlights► We explore a novel route to prepare hydrophobic and highly stable silica aerogels. ► A two-step surface modification via ambient pressure drying was adopted. ► Both the surface and bulk modifications of silica network can be accomplished through this method. ► We also discuss the possible mechanism of surface modification.

The SiC coatings were fabricated by the pyrolysis of polycarbosilane (PCS)/aluminum, in which PCS acts as precermaic precursor of SiC and aluminum (Al) powder acts as an active filler to both compensate the volume shrinkage of SiC coatings during pyrolysis and enhance the adhesion of SiC coatings with Fecralloy substrate. SiC coatings as thick as ~35 μm without cracking can be fabricated through our approach. Microstructural analysis revealed that the SiC coatings were composed of α-Al2O3 and β-SiC. Hardness and modulus of the SiC coatings as measured by nano-indentation were 12.2 ± 4.0 and 153.7 ± 47.0 GPa, respectively.

A synthesis of titanium-containing polycarbosilane (Ti-PCS) and transformation to SiO2/TiO2 hybrid ceramics are investigated. The Ti-PCS is prepared by blending polycarbosilane (PCS) and tetrabutyl titanate in xylene. The structural evolution and chemical composition change during the pyrolysis of the Ti-PCS are characterized by chemical analysis, TG-DTA, XRD, XPS and TEM. The results reveal that the polymer-to-ceramic transition of the Ti-PCS involves three steps. The final ceramics obtained at 1200 °C contain amorphous silica and rutile-TiO2 nanocrystallites of ~10 nm.

We developed a process for preparing SiO2/TiO2 fibers by means of precursor transformation method. After mixing PCS and titanium alkoxide, continuous SiO2/TiO2 fibers were fabricated by the thermal decomposition of titanium-modified PCS (PTC) precursor. The tensile strength and diameter of SiO2/TiO2 fibers are 2.0 GPa, 13 μm, respectively. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) measurements, the microstructure of the SiO2/TiO2 fibers is described as anatase–TiO2 nanocrystallites with the mean size of ~10 nm embedded in an amorphous silica continuous phase.

A hybrid polymer as the precursor for TiO2/SiO2 composite fibers was prepared by blending polycarbosilane (PCS) and tetrabutyl titanate, named as PCST, which contains unreacted organic tetrabutyl titanate compound. The PCST was characterized by FT-IR, TGA and NMR (1H, 13C and 29Si). The results showed that the PCST could be described as a part dispersion of Ti(OC4H9)4 groups in the PCS chain matrix. The TiO2/SiO2 composite fibers were manufactured by melt-spinning PCST, maturing and curing the resulting fibers in air, followed by a final pyrolysis at 1200 °C in air. Based on the XRD, EPMA, EDS, SEM and HRTEM measurements, the TiO2/SiO2 fibers were made up of anatase-TiO2 nanocrystallites with a mean size of ∼10 nm and in the amorphous silica phase.

The aluminum-containing polycarbosilane (Al-PCS) with various quantities of aluminum was obtained by adding aluminium acetylacetonate (Al(AcAc)3) as an aluminum source to polysilacarbosilane (PSCS). Subsequently, thermal decomposition and condensation at various conditions were carried out. The molecular weight \( \left( {\overline{\text{Mn}} } \right),\,\overline{\text{Mn}} \) distribution, yield and softening point of the resulting Al-PCS differ with the Al(AcAc)3:PSCS weight ratio, the thermolysis temperature and the reaction time. The larger the Al(AcAc)3:PSCS weight ratio, the higher the thermolysis temperature and the longer the reaction time, the greater the \( \overline{\text{Mn}} , \) yield and softening point of Al-PCS. In addition, the oxygen and aluminum contents of Al-PCS increase at higher Al(AcAc)3:PSCS weight ratios. As the mixing weight ratio of Al(AcAc)3:PSCS increased, additional oxygen was introduced into Al-PCS with the increased Al content. The structure of Al-PCS was characterized by the FT-IR. These results show that Al-PCS is very similar to polycarbosilane in structure.

A hybrid polymer as the precursor for TiO2/SiO2 composite fibers was prepared by blending polycarbosilane (PCS) and tetrabutyl titanate, named as PCST, which contains unreacted organic tetrabutyl titanate compound. The PCST was characterized by FT-IR, TGA and NMR (1H, 13C and 29Si). The results showed that the PCST could be described as a part dispersion of Ti(OC4H9)4 groups in the PCS chain matrix. The TiO2/SiO2 composite fibers were manufactured by melt-spinning PCST, maturing and curing the resulting fibers in air, followed by a final pyrolysis at 1200 °C in air. Based on the XRD, EPMA, EDS, SEM and HRTEM measurements, the TiO2/SiO2 fibers were made up of anatase-TiO2 nanocrystallites with a mean size of ∼10 nm and in the amorphous silica phase.