CdS is a well-known and efficient photocatalyst for photocatalytic hydrogen production. However, CdS is prone to photocorrosion in the photocatalytic reaction, in which CdS itself is oxidized by the photogenerated holes. Most of the work reported, to date, has focused only on the structure of CdS.However, less attention was paid to the kinetic changes of CdS during the photocatalytic reaction, which, in our opinion, is a crucial step for its practical utilization. In this report, we have developed a facile in situ Raman analysis, aiming to clarify the microstructural changes of CdS during the photocatalytic reaction process. In this study, photocatalytic hydrogen production over CdS in an Ar or air atmosphere was studied using various techniques in addition to in situ Raman spectroscopy. With Raman spectroscopy, a significant increase in the surface lattice strain of CdS was only observed when it was exposed to air, while the electron-phonon interactions remained the same regardless of the atmosphere. A direct correlation between the interfacial crystal lattice and photocorrosion of the CdS photocatalyst during photocatalytic hydrogen production was found based on our in situ Raman investigation. Finding the photocorrosion of the CdS photocatalyst at its very early stage using our in situ Raman technique is expected to provide meaningful guidance for the design of active and stable chalcogenide photocatalysts, which, however, cannot be achieved using traditional characterization techniques.

A series of upconversion luminescent erbium-doped SrTiO(3) (ABO(3)-type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er(3+) ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high-energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO(6) octahedra promoted energy transfer from the high-energy excited states of Er(3+) with B-site occupancy to the host SrTiO(3) and thus enhanced the band-to-band transition of the host SrTiO(3). Consequently, the erbium-doped SrTiO(3) species with B-site occupancy showed higher photocatalytic activity than those with A-site occupancy for visible-light-driven H(2) or O(2) evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low-energy photons and maintaining redox ability for photocatalytic H(2) and O(2) evolution and that the site occupancy of doped elements in ABO(3)-type perovskite oxides greatly determines the photocatalytic activity.

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α-Fe2O3 nanoparticle has been widely used in water purification because of its effective adsorption performance. However, aggregation and difficulty in separation limit its practical application. Herein, we presented a polyacrylonitrile (PAN) nanofiber mat decorated with α-Fe2O3 as adsorbent for effective removal of Pb 2+ from contaminated water, which can solve the above problems easily. The α-Fe2O3/PAN nanofiber mats were prepared via electrospinning followed by a facile hydrothermal method and characterized by SEM, HRTEM, FTIR and XRD. We demonstrated the formation mechanism of α-Fe2O3 anchored on PAN nanofiber surface consists of the adsorption of iron ions on the surface of PAN, and then the α-Fe2O3 nucleation and growth. The pH value of FeCl3 solution has a great impact on the formation process of α-Fe2O3/PAN nanofiber mat, which lead to the variation of morphology and the quantity of the coating coverage. When the pH value was 2.4, polyhedral particles were coated on PAN nanofibers uniformly and the optimized α-Fe2O3/PAN nanofiber mat was obtained. Controlled experiments were carried out to quantify the adsorption capacities of different samples and adsorption kinetics. The isotherm data from our experiments fitted well to the Langmuir model and the adsorption process can be described using the pseudo-second-model. Finally, the adsorption mechanism for Pb 2+ was investigated and the results revealed that ion exchange between proton of surface hydroxyl groups and Pb 2+ was accounted for the adsorption. Fig. 6 The effect of contact time on Pb 2+ adsorption capacity with different initial concentration (a), SEM image of α-Fe2O3/PAN (S2.4) after adsorption (b), the fitting results using pseudo first order (c), and pseudo second order (d) kinetic model.

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