The CdS/TiO2NTs composite was prepared by a simple two-step chemical solution routes to directly transfer trititanate nanotubes to TiO2NTs and simultaneously coupled with CdS nanoparticles. The results of XRD, TEM, Diffuse reflectance UV–Visible absorption spectra revealed that the CdS nanoparticles were homogeneously embedded on the surface of TiO2NTs and the absorption spectrum of TiO2NTs was extended to visible region. The activity of hydrogen production by photocatalytic water decomposition for the CdS/TiO2NTs composite was examined under visible light irradiation (λN400 nm) and the quantity of H2 evolution was ca. 1708 μL/g for 6h.

The hydrogen production from photocatalytic water decomposition is one of the best approaches that convert solar energy to hydrogen energy. At present, the hydrogen production from photocatalytic water decomposition has a low efficiency. In order to determine a valuable hydrogen production process from photocatalytic water decomposition in the aspect of energy conversion, the concept of critical conversion efficiency of light energy is proposed in this paper. Critical conversion efficiency of light energy is defined as the conversion efficiency of light energy when the hydrogen energy output is equal to an equivalent energy input of the system. The criterion introduced is that only if the conversion efficiency of light energy is greater than the critical one, an energy profit can be achieved in a system. A hypothetical system with 20,000 tons annual hydrogen production by using Na2S/Na2SO3 as the sacrificial reagent is analyzed and calculated in this paper to determine the critical conversion efficiency of light energy by means of energy balance, cumulative exergy balance, and emergy balance, respectively. The results show that the critical conversion efficiency of light energy determined by emergy balance is the most reasonable, which gives the figure around 15%.

Aligned polypyrrole (PPy) micro/nanotubules were synthesized via a self-assembly method using FeCl3 as oxidant and Acid Red 1 (C.I. 18050, 5-(acetylamino)-4-hydroxy-3-(phenylazo)-2,7-naphthalenedisulfonic acid) as dopant. PPy has a typical length of 530 mm and a unique rectangular-sectioned morphology. Its general morphology could be manipulated by varying synthetic conditions including polymerization time, monomer concentration, oxidant species, and stirring. The synthesized PPy and reaction intermediates were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and solubility tests in methanol and water. Our observation and results suggest a plausible formation mechanism of rectangular-sectioned PPy micro/nanotubules. AR1eFe(II) complex formed from the complexation of Acid Red 1 and Fe2þ(reduced from Fe3þ), which precipitated in the aqueous solution, might have functioned as"template"during the polymerization of pyrrole monomers. The conductivity of PPy with different morphologies was also measured and compared.

A composite photocatalyst, Pd-TiO2-xNx-WO3, was synthesized by the template method and characterized by energy dispersive X-ray microanalysis (EDX), X-ray diffraction (XRD), UV-vis spectrometer, and scanning electron microscope (SEM). The results of EDX analysis reveals that the molecular formula of the composite photocatalyst can be expressed as Pd-TiO1.72N0.28-WO3. The UV–vis absorption spectrum indicates that the absorption edge of the catalyst red-shifts to around 600 nm. Under the irradiation with ultraviolet and visible light, the catalyst showed good performance for photocatalytic hydrogen production with a Na2S/Na2SO3 system as the sacrificial agent.

A novel composite photocatalyst, Pt-TiO2-xNx-WO3 was synthesized by the template method and characterized by X-ray diffraction (XRD), ultraviolet-visible light diffusion spectroscopy (UV-vis), and element analysis. XRD spectra indicated that the photocatalyst was in anatase form and the diagnostic peak for WO3 existed. Combined with the XRD spectra and the results of elemental analysis, the formula of the composite photocatalyst was determined to be Pt-TiO2-xNx-WO3. UV-vis spectra showed the absorption edge was red-shifted to around 750 nm. Under the irradiation of ultraviolet, and with Na2S/Na2SO3 as the sacrificial reagent, the composite photocatalyst showed higher hydrogen production activity than anatase TiO2, and under irradiation with visible light (λ>400nm) it showed higher hydrogen production activity than TiO2-xNx while the anatase TiO2 showed negligible activity. An explanation was put forward for the mechanism of the red-shift of the absorption edge and the hydrogen production activity improvement.