Based on photocatalysts, solar energy can be converted into the energy that human can directly utilize, so as to solve the problems such as the depletion of the Earth’s resources and the deterioration of living environments. The unique structure of g-C₃N₄ gives it good photocatalytic performance. Its development and utilization have been a research hotspot recently. Generally, g-C₃N₄ can be used in the degradation of pollutions, hydrolysis to generate hydrogen and oxygen, organic synthesis and oxygen reduction. However, in practical, its performance is not satisfactory. Researchers have tried many new methods to improve its photocatalysis, which include physical coupling modification, chemical bonding modification and microstructural modification. The review summarizes its photocatalysis and improving methods, briefly illustrates the catalysis mechanism, and presents detailed discussions and analysis on the existing problems as well as potential applications.

Nanocrystalline TiO₂ particles immobilized on opal by a hydrolysis precipitation method are used as a novel catalyst in photocatalysis. Effects of crystalline and size, BET specific surface area and porous properties on the photoactivity were investigated by characterizing samples obtained under various calcination temperatures and periods. Results reveal that there is still no evidence of rutile phase in XRD patterns when the calcination temperature increases to 800℃. This indicates that the opal support impedes the phase transformation. The photocatalytic reactivity of this nano-TiO₂/opal composite catalyst was evaluated by degrading Rhodamine B (RhB) under ultraviolet light. The sample calcined at 600℃ for 2 h exhibits the smaller crystalline size and larger specific surface area with a concomitant higher activity of 97.24% for RhB degradation by 4 h irradiation under 250 W Hg lamp.

Co-doped mesoporous TiO₂ photocatalysts were prepared by an ionic liquid 1-butyl-3-methylimida-zolium tetrafluoroborate ([C₄MIM]BF₄) modified Sol-Gel method. The effects of Co doping on the surface area, crystalline phase, chemical binding states and compositions, and absorbance of the Co-doped mesoporous TiO₂ photocatalysts were studied by N₂ adsorption-desorption measurements (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance absorption spectra (UV-Vis DRS). BET analysis showed that Co/TiO₂ photocatalyst was mesoporous structure with large surface area. XRD patterns indicated that the Co-doped mesoporous TiO₂ photocatalysts was anatase structure. XPS spectra indicated that the Co²⁺ replaced Ti⁴⁺ and entered into TiO₂ lattice, which reduced the band gap of TiO₂ and thereby extending the light response range to the visible region (UV-Vis spectra). Photocatalytic activity of the Co/TiO₂ mesoporous photocatalysts was evaluated by photodegradation of methylene blue (MB) under visible light (λ>420 nm). Co-doped TiO₂ exhibited obvious visible light activity for MB photodegradation, and 0.3%Co/TiO₂ exhibited the highest photocatalytic activity.

N-doped BiVO₄ photocatalysts (CS-BiVO₄-xN) were successfully prepared by Sol-Gel method taking the corn stem as template and C₆H₁₂N₄ as N source. The samples were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), Fourier infrared spectrum (FTIR), and UV-Vis absorption spectroscope (UV-Vis). The photocatalytic activity were investigated by degradation of methyl oran ge (MO) under visible-light irradiation. The results showed that N doping did not change the crystallinity of the BiVO₄. The doped N replaced some of O atoms in BiVO₄ and formed the -N-V-O band. The synergetic effect of impurity energy levels and oxygen vacancies led to narrower band-gap and red-shift of optical absorption band. Furthermore, the N doped BiVO₄ with honeycomb like structure and smaller crystal sizes was prepared by using corn stem as template, which is beneficial to higher initial MO absorption and better photocatalytic activity. The degradation rate of MO under visible light illumination for 50 min is 80.9% in presence of CS-BiVO₄-12N, which is much higher than those in presence of CS-BiVO₄ (25.56%) and BiVO₄-12N (28.34%).

Carbon nanofibers-supported palladium nanoparticle catalysts were prepared by electrospinning, chemical reduction and the subsequent high temperature carbonization methods. The experiments were carried out to investigate the influence of different reducing agents (sodium borohydride, hydrazine hydrate and hydrogen gas) on morphology of palladium nanoparticles and carbon nanofibers in detail. Catalysts were characterized by UV-Vis spectra, X-ray diffraction, fourier transform infrared spectrum, scanning electron microscope, field emission transmission electron microscope. Results show that the palladium nanoparticles are distributed uniformly on the carbon nanofibers with dimension of about 7 nm, and the catalyst is relatively flexible by using hydrogen gas as reducing agent. Then it was applied to the Heck coupling reaction to test catalytic properties and recyclability. Results indicate that the catalyst possesses excellent stability and recyclability.

Hierarchical structured SAPO-5 molecular sieve was ionothermally synthesized by microwave irradiation using a mixture solution of succinic acid, choline chloride and tetraethyl ammonium bromide as solvent and template under ambient pressure. The effects of the molar ratios of P₂O₅/Al₂O₃ and HF/Al₂O₃, silicon source, and crystallization time on the structure of SAPO-5 molecular sieve were systematically investigated. The resulting SAPO-5 molecular sieve was characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), N₂ physical adsorption-desorption and ²⁹Si magic-angle spinning nuclear magnetic resonance (²⁹Si MAS-NMR) techniques, respectively. The results indicate that intra-crystalline and inter-crystalline mesopores coexist within the SAPO-5 molecular crystals, while ²⁹Si MAS-NMR test shows that the incorporation of Si in the sample follows the SM3 mechanism. In addition, SEM images exhibit that hierarchical structured SAPO-5 molecular sieve with hexagonal nanometer-disc morphology can be synthesized under specific synthetic conditions.

Magnetic carbon composite nanofibres, using the mixed homogeneous solution consist of polyacrylonitrile (PAN), ferric acetylacetonate (AAI) and dimetbylformamide (DMF) as raw material, were prepared by electrospinning-calcination technology. TEM analysis showed that the carbon nanofibre diameter of sample CF900 was about 130-210 nm, in which magnetic nanoparticles were uniformly distributed. The magnetic properties of carbon composite nanofibres under different carbonization temperature was also investigated. Results showed that saturation magnetization (M_s) and remanent magnetization (M_r) increased with the increase of the temperature. When carbonization temperature was 900 ℃, the sample was of good magnetic property with high saturation magnetization (M_s=27.55 A·m²/kg). Moreover, the specific surface area (S_BET) and total pore volume (V_total) were up to 354.0 m²/g and 0.315 mL/g, respectively.

Zircon whisker was synthesized at 700 ℃ via non-hydrolytic Sol-Gel method using anhydrous zirconium tetrachloride (ZrCl₄) as zirconium source, tetraethylorthosilicate (TEOS) as silicon source, lithium fluoride (LiF) as mineralizer, ethanol as solvent and carbon black as reducing agent. Thermogravimetric analysis and differential thermal analysis (TG-DTA), X-ray diffraction analysis (XRD) and transmission electron microscope (TEM) were employed to characterize the influences of adding ways and amount of carbon black on the synthesis and morphology of zircon whisker. The results show that the carbon black added in form of suspension is favorable to the one-dimension growth of zircon. When 6wt% carbon black is added, optimized zircon whiskers are achieved along the growth direction of [001], which diameter and aspect ratio are in the range of 30-90 nm and 6-15, respectively. Because of carbon black reacting with oxygen to form carbon dioxide and monoxide, the adding way and amount of carbon black efficiently regulate the oxygen partial pressure in the reaction system. Reducing oxygen partial pressure can form more SiF₄ gas, which is the basis of one-dimensional direction growth of zircon. However, excessively low oxygen partial pressure is against the ZrSiO₄ formation. Therefore, appropriate oxygen partial pressure can promote the growth of zircon whisker.

Single-phase Na₂Zr(PO₄)₂ powders were directly synthesized by hydrothermal method using ZrOCl₂•8H₂O and sodium polyphosphate as raw materials, water as solvent. The effects of hydrothermal conditions and calcination temperature on the microstructure of sodium zirconium phosphate powders were investigated systemically by SEM, XRD and TG-DSC, etc. It is found that, when the molar ratio of raw materials is 1:2 (n(ZrOCl₂•8H₂O): n(Na₅P₃O₁₀)) without adjusting pH value, slices being assembled coil-like Na₂Zr(PO₄)₂ powders with good dispersion and uniform size can be obtained after 14 h hydrothermal treatment at 140℃. Appropriate extension of time and increase of temperature are beneficial to the powder formation. The higher the temperature, the shorter time the desired powders form. After calcination, Na₂Zr(PO₄)₂ powders decompose and their morphology are destroyed. The growth mechanism of the sodium zirconium phosphate powders being prepared by hydrothermal method is explained by a basic growth unit model.

CoFe₂O₄-graphene (CFO-GN) nanocomposites were synthesized by in situ co-precipitation method, involving homogeneous co-precipitation of Co²⁺ and Fe²⁺ on the surface of graphite oxides and in situ thermal reduction of graphite oxides simultaneously. The morphology, structure, composition and microwave absorption properties of the nanocomposites were characterized and analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray energy dispersive spectroscope (EDS), thermogravimetric analyzer (TGA), Fourier transform infrared spectroscope (FT-IR) and vector network analyzer (VNA). The results indicate that the CoFe₂O₄ nanoparticles are uniformly dispersed on the interlayer and surface of the graphene sheets, CoFe₂O₄-graphene nanocomposites possess dielectric loss and magnetic loss, and exhibit excellent microwave absorption properties. The reflection losses of the nanocomposites with 88.62wt% and 74.53wt% CoFe₂O₄ are up to -11.0 dB and -12.4 dB, respectively, the bandwidths of reflection loss below -8 dB are 2.0 GHz and 4.3 GHz, respectively. The nanocomposites with higher content of graphene exhibit higher dielectric loss and reflection loss, wider absorption band, and thus exhibit better microwave absorption properties.

Sm³⁺ doped (Bi_0.5Na_0.5)TiO₃ lead-free piezoelectric ceramics were fabricated by the conventional solid-state reaction method. Phase and crystallinity of the synthesized materials were investigated by X-ray diffraction (XRD). The influences of the Sm³⁺ dopant concentration, sintering temperature and charge compensation on photoluminescence properties were systematically investigated. The results showed that the (Bi_0.5Na_0.5)TiO₃ ceramics realized red-green emission by additives of Sm³⁺ ions, and the excitation bands were well adaptable to the emission band of commercial blue light-emitting diodes. The emission intensities were strongly dependent on the dopant concentration and sintering temperature with the optimal value at 0.015 mol and 1100℃ , respectively. The enhanced luminescence was observed for the Li⁺, Na⁺ and K⁺ doped compositions as compensators compared to the host matrix with only Sm³⁺ ions, indicating that host activator energy transfer of Sm³⁺ could be responsible for this enhancement. Among the compensators of Li⁺, Na⁺ and K⁺ ions, the K⁺ compensated (Bi_0.5Na_0.5)TiO₃-Sm³⁺ samples showed the remarkable improvement in photoluminescence properties. Hence, the Sm³⁺ doped (Bi_0.5Na_0.5)TiO₃ ceramics as a multifunctional material may have significantly technological promise for optical-electro integration devices.

Polycrystalline charges of CdSiP₂ (CSP) were synthesized by direct reaction method using P, Si, and Cd elements as the initial materials. Single crystals with the dimension of 8 mm in diameter and 40 mm in length were successfully grown by vertical Bridgman method. The dimension and the composition of the optical scatter particles in the CSP crystals were identified by SEM measurement. The results show that most of optical scattering particles are round-shaped with dimension of 2-8 μm. The EDS measurement result shows that the atomic percent of Si in the optical scattering particles is over 88%. The synthesis mechanism of CSP by single temperature zone method was studied by powder XRD. The results show that there is some unreacted silicon left when synthsized process is carried out below 1150℃. By optimizing the synthesis parameters and the Si inclusions were successfully restrained and the high optical quality CSP single crystal was obtained.

Bi₂O₃-SiO₂ glasses and glass ceramics were prepared by melting method. Infrared and VIS luminescence spectra, excitation spectra and fluorescence decay curves were measured. Near infrared (NIR) luminescence of Bi₂O₃-SiO₂ glasses and glass ceramics was observed under 808 nm Laser Diode pumping. When the content of Bi₂O₃ is low (30mol%, 40mol%, 50mol%), NIR luminescence peak at 1336 nm (or 1300 nm) with full width at half maximum (FWHM) about 200 nm is observed. With the increase of Bi₂O₃ content, another peak at about 1070 nm with narrow FWHM appears and becomes the main peak, while the FWHM of the NIR emission centered at 1336 nm (or 1300 nm) decreases to only tens of nanometer. Two emission bands have different excitation bands and lifetime. We propose NIR emissions located at 1070 nm and 1336 nm (or 1300 nm) originate from different bismuth centers. The infrared emission peaked at about 1336 nm (or 1300 nm) derives from low valence Bi ions.

Ti₃AlC₂ is a new type of nano-layered machinable ceramic with numerous salient properties. Therefore, recently it is considered to be a promising candidate for new generation reactors as the key structural material. In this work, the reaction product and material morphology between nano-layered Ti₃AlC₂ and hydrogen were investigated by XRD, SEM, EDS, XPS and Raman. The resulted gaseous products were calculated by Factsage sofeware. Under the condition of 700-1000℃, hydrogen atmosphere (low oxygen pressure), solid products are Al₂O₃, TiO₂ and C and gaseous product is CH₄. Hydrides are not detected in the current experiments. The SEM results indicate that the reacted samples keep intact and cracks are not formed on the surface, indicating the high temperature thermal stability of Ti₃AlC₂ in hydrogen. These results can be attributed to the formation of oxides on the surface of specimens.

To deposit alumina thin films on ammonium dinitramide (ADN) by atomic layer deposition (ALD), trimethylaluminum and water were used as the precursors. The surface morphology and chemical compositions of the ALD alumina coated ADN were characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). The hygroscopic property of the ALD alumina coated ADN was studied by a vapor adsorption analyzer (VSA). The possible mechanism of ALD alumina film growth on the surface of ADN was discussed. The characterization results indicate that the ALD alumina film completely covers the surface of ADN. The thickness of the alumina film can reach hundreds of nanometers. After 48 h of air exposure, the shapes and topologies of the alumina coated ADN particles are maintained. The hygroscopicity of the ADN samples coated by 200 and 400 cycles of ALD alumina are 40.99% and 40.75%, respectively. Although the ALD alumina coating completely covers the surface of ADN and successfully maintains the shapes and topologies of ADN particles in a wet environment, the hygroscopicity of the ALD alumina coated ADN is not improved.

U₂N_3+xO_y films were deposited on Si substrate by magnetic sputtering deposition method. The behaviors of U₂N_3+xO_y after exposure to CO atmosphere was analyzed by X-ray photoelectron spectroscopy (XPS) to explore its CO corrosion mechanism. Under ultra-high vacuum (UHV) condition, it is found that CO atmosphere is oxidative on the surface of U₂N_3+xO_y film. The dissociated carbon in forms of amorphous is segregated on the outmost surface rather than diffuses inside, and the diffusion of the dissociated oxygen resulted in oxidation of U₂N_3+xO_y, leading to the formation of uranium oxy-nitrides in higher valence state on the surface and an N-rich layer as an intermediacy in the subsurface. The diffusion of oxygen in the film is suppressed on the very surface by the product of uranium oxides or uranium oxy-nitrides in higher valence state due to the potential barrier. The distance of the N-rich layer to the outmost surface dominates the intensity variation of satellites at 386.7 eV and 397.5 eV, which is enlarged with the oxidation process. All abore chemical changes play a very important role for understanding the corrosion mechanism of U₂N_3+xO_y films.

Wool-like products were fabricated on the stainless-steel substrates by directly heating amorphous B powder at high temperature (1300℃) at 50 mL/min ammonia gas with different flow of oxygen gas (10, 15, 20, 40 mL/min). It was found that B powder could be oxidized by trace oxygen gas to form the intermediate B₂O₂ vapor, which can act as highly active boron source for the growth of BN nanotubes. When an appropriate amount of oxygen was introduced, the obtained nanotubes had an average diameter of about 80 nm and the lengths of several hundred micrometer. Both the diameter and the yield of BN nanotubes could be influenced dramatically by the flow rate of oxygen. With the increase of oxygen flow, the diameter of nanotubes was gradually increased, and the yield of nanotubes was improved obviously at first and then turned down. The formation mechanism of these nanotubes is governed by a vapor-liquid- solid (VLS) growth model.

Two compositions of the Y₂O₃-Al₂O₃ (YA) and Y₂O₃-MgO (YM) systems were chosen to investigate the effect of sintering additive composition on the mechanical and tribological properties of gas pressure sintered Si₃N₄/SiC ceramics. The relative density, flexural strength, fracture toughness, hardness, coefficient of friction and wear rate were verified to depend substantially on the sintering additive composition. Compared with YM, the Si₃N₄/SiC ceramics with YA exhibit superior sinterability and show preferable mechanical and tribological properties, especially for the Si₃N₄/SiC ceramics with 20wt% SiC addition. These properties can be primarily attributed to the higher relative density and the grain size with smaller aspect ratio.

Flower-like hierarchical TiO₂ microspheres assembled by nanosheets with exposed {001} facets were prepared through a cost-effective hydrothermal synthesis method, using cheap Ti(SO₄)₂ as the feedstock and hexafluorosilicic acid as the capping agent. These hierarchical microspheres were assembled by numerous and cross-linked nanosheets. The fine structure of hierarchical microspheres could be easily controlled by adjusting the concentration of hexafluorosilicic ions. The growth process of the microspheres was examined through XRD and SEM characterizations, and a possible formation mechanism was proposed. Compared with other solvothermal synthesis methods, this cost-effective hydrothermal synthesis route is attractive and can be potentially applied in the production of flower-like TiO₂ hierarchical microspheres in large scale. The as-prepared flower-like TiO₂ hierarchical microspheres exhibit good photocatalytic ability to degrade methyl orange dye.