Yue-Hua Xu

Photocatalysis fundamentals and surface modification of TiO2 nanomaterials

Abstract As a green and sustainable technology, heterogeneous photocatalysis using semiconductors has received much attention during the past decades because of its potential to address energy and environmental problems. Among various semiconductors, TiO 2 has been regarded as the best and most widely investigated photocatalyst in the past 10 years. Based on the fundamentals of photocatalysis and surface chemistry of TiO 2 nanomaterials, we herein summarize and discuss the achievements in the different surface modification strategies employed to date such as surface doping and sensitization, construction of surface heterojunctions, loading of nano-sized co-catalysts, increase in the accessible surface areas, and usage of surface F effects and exposure of highly reactive facets. Especially, the interesting synergistic effects of these different surface modification strategies deserve more attention in the near future. Studying these important advances in photocatalysis fundamentals, and surface chemistry and modification may offer new opportunities for designing highly efficient TiO 2 -based and non-TiO 2 -based photocatalysts for solar fuel production, environmental remediation, organic photosynthesis, and other related fields such as solar cell device fabrication, thermal catalysis, and separation and purification.

Photocatalytic reduction of carbon dioxide to methanol by Cu2O/SiC nanocrystallite under visible light irradiation

Abstract The Cu2O/SiC photocatalyst was obtained from SiC nanoparticles (NPs) modified by Cu2O. Their photocatalytic activities for reducing CO2 to CH3OH under visible light irradiation have been investigated. The results indicated that besides a small quantity of 6H-SiC, SiC NPs mainly consisted of 3C-SiC. The band gaps of SiC and Cu2O were estimated to be about 1.95 and 2.23 eV from UV-Vis spectra, respectively. The Cu2O modification can enhance the photocatalytic performance of SiC NPs, and the largest yields of methanol on SiC, Cu2O and Cu2O/SiC photocatalysts under visible light irradiation were 153, 104 and 191 μmol/g, respectively.

Preparation, characterization and photocatalytic activity of manganese doped TiO2 immobilized on silica gel

A series of Mn-TiO(2)/SiO(2) (silica gel loaded with manganese doped TiO(2)) photocatalysts have been prepared by sol-gel method, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Photocatalytic activities were enhanced in photocatalytic degradation of methyl orange over Mn-TiO(2)/SiO(2). XPS analysis shows that a Ti-O-Si or Ti-O-Mn bond is formed on the surface of photocatalyst. Mn is doped as a mixture of Mn(2+) and Mn(3+) on the surface of 1.0mol% Mn-TiO(2)/SiO(2). Mn(3+) appears to trap electrons and prohibit the electron-hole recombination. The electrons trapped in Mn(3+) site are subsequently transferred to the adsorbed O(2). As a result, the combination of the electron-hole pair was reduced.

Earth-abundant NiS co-catalyst modified metal-free mpg-C3N4/CNT nanocomposites for highly efficient visible-light photocatalytic H2 evolution.

In the present work, the earth-abundant NiS co-catalyst modified mesoporous graphite-like C3N4 (mpg-C3N4)/CNT nanocomposites were prepared via a two-step strategy: the sol-gel method and the direct precipitation process. The mpg-C3N4/CNT/NiS composite photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy, photoluminescence spectroscopy (PL), photoelectrochemical (PEC) and electrochemical impedance spectra (EIS) experiments. The photocatalytic H2-production activity over the composite catalysts was also evaluated by using an aqueous solution containing triethanolamine under visible light (λ≥ 420 nm). The results showed that the loading of earth-abundant NiS co-catalysts onto metal-free mpg-C3N4/CNT nanocomposites can remarkably enhance their photocatalytic H2-production activity. The optimal loading amount of NiS on metal-free mpg-C3N4/CNT nanocomposites was about 1 wt%. The as-obtained mpg-C3N4/CNT/1% NiS ternary composite photocatalyst exhibits the best H2-evolution activity with the highest rate of about 521 μmol g(-1) h(-1) under visible light (λ≥ 420 nm), which is almost 148 times that of a pure mpg-C3N4/CNT sample. The enhanced photocatalytic activity can be mainly attributed to the synergistic effect of effectively promoted separation of photo-generated electron-hole pairs and enhanced H2-evolution kinetics. The co-loading of nanocarbon materials and earth-abundant co-catalysts onto metal-free mpg-C3N4 photocatalysts offers great potential for practical applications in photocatalytic H2 evolution under visible light illumination.

在FTO导电玻璃上电化学沉积高效可见光光电化学分解水Cu 2 O/g-C 3 N 4 异质结膜

Abstract An immobilized Cu2O/g-C3N4 heterojunction film was successfully made on an FTO substrate by electrophoretic deposition of g-C3N4 on a Cu2O thin film. The photoelectrochemical (PEC) performance for water splitting by the Cu2O/g-C3N4 film was better than pure g-C3N4 and pure Cu2O film. Under –0.4 V external bias and visible light irradiation, the photocurrent density and PEC hydrogen evolution efficiency of the optimized Cu2O/g-C3N4 film was –1.38 mA/cm2 and 0.48 mL h−1 cm−2, respectively. The enhanced PEC performance of Cu2O/g-C3N4 was attributed to the synergistic effect of light coupling and a matching energy band structure between g-C3N4 and Cu2O as well as the external bias.

Nickel sulfide/graphitic carbon nitride/strontium titanate (NiS/g-C3N4/SrTiO3) composites with significantly enhanced photocatalytic hydrogen production activity

NiS/g-C3N4/SrTiO3 (NS/CN/STO) composites were prepared using a facile hydrothermal method. The synergistic effect of g-C3N4/SrTiO3 (CN/STO) heterojunction and NiS cocatalyst enhanced the photocatalytic hydrogen evolution activity of NS/CN/STO. A hydrogen production rate of 1722.7 μmol h-1 g-1 was obtained when the 2%NiS/20%g-C3N4/SrTiO3 (2NS/20CN/STO) was used for the photocatalytic hydrogen evolution in the presence of methanol used as a sacrificial agent under UV-vis light irradiation; the photocatalytic hydrogen production rate of 2NS/20CN/STO is 32.8, 8.9 and 4.2 times the value of that obtained with pure g-C3N4, SrTiO3 and 20%g-C3N4/SrTiO3 (20CN/STO), respectively. Moreover, in photoelectrochemical investigations when compared with 20CN/STO, SrTiO3 and g-C3N4, 2NS/20CN/STO exhibited significant photocurrent enhancement. The heterojunction and cocatalyst in NS/CN/STO improved the charge separation efficiency and the lifetime of the charge carriers, leading to the enhanced generation of electrons for photocatalytic hydrogen production.

Two-step hydrothermal synthesis of peanut-shaped molybdenum diselenide/bismuth vanadate (MoSe2/BiVO4) with enhanced visible-light photocatalytic activity for the degradation of glyphosate

The novel peanut-like shaped MoSe2/BiVO4 composites were fabricated via a facile two-step hydrothermal method and their photocatalytic activity was evaluated by the degradation of glyphosate under the visible light irradiation. The efficient transfer of photogenerated carriers and the charge separation were confirmed by photoluminescence spectra (PL), electrochemical impedance spectroscopy (EIS) and photocurrent. The coupling of MoSe2 and BiVO4 remarkably enhanced the photocatalytic activity. The 0.15MoSe2/BiVO4 composite showed the highest photocatalytic performance for the degradation of glyphosate among all the as-prepared photocatalysts and presented the high stability and good reusability in the photocatalytic reactions.

TiO2 supported on SiO2 photocatalysts prepared using ultrasonic-assisted sol-gel method

TiO2-SiO2 (TiO2 supported on SiO2) photocatalysts were prepared using an ultrasonic-assisted sol-gel method. These photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and photoluminescence spectra (PL). Their photocatalytic activities were investigated by the method of methyl orange oxidation. It was found that the photocatalytic activity of TiO2-SiO2 was optimal when the molar ratio of hexadecyl trimethyl ammonium bromide to titanium butoxide was 1:10. The average crystallite size of TiO2-SiO2 was smaller than that prepared by the stirring method. Furthermore, for pure anatase phase samples, it was shown that the lower the photoluminescence intensity, the higher the photocatalytic activity.