Cunyu Zhao

Photocatalytic conversion of CO2 and H2O to fuels by nanostructured Ce–TiO2/SBA-15 composites

Cerium-doped titanium oxide (Ce–TiO2) nanoparticles were prepared by a simple sol–gel method. Ce-doping decreased the crystal size of TiO2, increased the catalyst surface area, and inhibited the growth of rutile TiO2 crystals. Ce–TiO2 nanoparticles were also dispersed on SBA-15, mesoporous silica with one-dimensional pores, forming a Ce–TiO2/SBA-15 nanocomposite. The nanocomposite materials were well characterized and tested as photocatalysts to convert CO2 and H2O to value-added fuels, mainly CO and CH4, under UV-vis illumination. Compared with pristine TiO2, TiO2 doped by 1 or 3% Ce improved the production of CO by four times. The reason may be due to the facilitated charge transfer induced by the doped Ce ions, the higher surface area of the catalyst, as well as the stabilization of anatase phase. However, too high a Ce concentration reduced the catalytic activity, likely due to the formation of recombination centers. Compared with unsupported Ce–TiO2, Ce–TiO2 supported on SBA-15 remarkably enhanced the CO2 reduction rate. Ce–TiO2/SBA-15 with a Ti : Si ratio of 1 : 4 demonstrated 8-fold enhancement in CO production and 115-fold enhancement in CH4 production. By contrast, amorphous silica as the substrate was much inferior to SBA-15. The findings in this work reveal a promising nanostructured catalyst material for solar fuel production using CO2 and H2O as the feedstock.

CO2 photoreduction with H2O vapor by porous MgO–TiO2 microspheres: effects of surface MgO dispersion and CO2 adsorption–desorption dynamics

Photocatalytic reduction of CO2 with H2O vapor for CO production at a temperature of 150 °C was studied using porous MgO–TiO2 microspheres as the photocatalysts with the benefits of improved CO2 adsorption by incorporating MgO and enhanced products/intermediates desorption at a higher temperature. The MgO–TiO2 microspheres were fabricated by two methods: (1) a one-step spray pyrolysis method using TiO2 (P25) nanoparticles dispersed in Mg(NO3)2 solution as the precursors (Mg/Ti-SP), and (2) spray pyrolysis synthesis of pure TiO2 (P25) microspheres first and then wet-impregnation with MgO (Mg/Ti-WI). The two material synthesis methods led to different MgO dispersion on the TiO2 surface. For Mg/Ti-SP, the strong aggregation of MgO nanoparticles caused a rough surface of the MgO–TiO2 microsphere; while for Mg/Ti-WI, MgO was more uniformly deposited leading to a much smoother surface of the microsphere. The surface dispersion of MgO was found to significantly affect the performance of MgO–TiO2 in CO2 photoreduction. At the same MgO concentration, Mg/Ti-SP had more than two times higher activity than Mg/Ti-WI, and most importantly, little deactivation of the catalyst was observed on Mg/Ti-SP while Mg/Ti-WI started to deactivate after 1 to 2 h when the reactor was operating in a continuous flow mode. The ease of photo-induced electron transfer to the catalyst surface may have contributed to the superb activity of Mg/Ti-SP samples. The optimum MgO concentration was found to be 5% for both types of materials. Besides the dispersion of MgO, we also found that the CO2 adsorption–desorption dynamics strongly influenced the CO2 photoreduction. The results from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed two advantages of Mg/Ti-SP over Mg/Ti-WI: (1) more abundant bicarbonates (important intermediates for CO production) on the surface and (2) easier desorption/transformation of intermediates.

Giant magnetoresistance in non-magnetic phosphoric acid doped polyaniline silicon nanocomposites with higher magnetic field sensing sensitivity

Phosphoric acid doped conductive polyaniline (PANI) polymer nanocomposites (PNCs) reinforced with silicon nanopowders have been successfully synthesized using a facile surface initiated polymerization (SIP) method. The chemical structures of the nanocomposites are characterized using Fourier transform infrared (FT-IR) spectroscopy. The enhanced thermal stability of the silicon-PANI PNCs compared with pure PANI is obtained using thermogravimetric analysis (TGA). The obtained optical band gap of the PNCs using Ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) decreases with increasing silicon loading. The dielectric properties of the PNCs are strongly related to the silicon loading level. Temperature dependent resistivity analysis reveals a quasi 3-D variable range hopping (VRH) electrical conduction mechanism for the synthesized PNCs. Room temperature giant magnetoresistance (GMR) is observed in the synthesized non-magnetic nanocomposites and analyzed using the wave-function shrinkage model.

Synthesis of novel MgAl layered double oxide grafted TiO2 cuboids and their photocatalytic activity on CO2 reduction with water vapor

A series of magnesium/aluminum (MgAl) layered double oxide (LDO) grafted TiO2 cuboids (MgAl-LDO/TiO2) with various molar ratios of (Mg + Al) to Ti were synthesized by a combination of hydrothermal and coprecipitation methods, in which the growth of MgAl-LDO platelets was controlled. The MgAl-LDO/TiO2 composite materials were used for photocatalytic CO2 reduction with water vapor under UV light irradiation in a continuous-flow reactor. CO was found to be the main product from CO2. At near room temperature (e.g., 50 °C), MgAl-LDO/TiO2 did not significantly enhance CO2 reduction compared with pure TiO2 cuboids. At a moderately elevated reaction temperature (e.g., 150 °C), the MgAl-LDO/TiO2 sample with an optimum 10 wt.% MgAl-LDO loading demonstrated CO2 reduction activity five times higher than that of bare TiO2 cuboids. The photo-induced electrons on TiO2 may migrate to the MgAl-LDO/TiO2 interfacial sites to promote CO2 reduction. Findings in this work may lead to a new area of hybrid adsorbent/photocatalyst materials that are capable of sequential CO2 capture and photocatalytic conversion.