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.

In order to reveal the heat transfer performance of nanofluids in solar collectors, the thermal conductivity and dynamic viscosity of five kinds of graphene oxide nanofluids, with a mass fraction of 0.002% to 0.01%, were studied in the temperature range of 25–50 °C. To ensure the dispersion and stability of the prepared nanofluids, UV–Vis absorption spectrum, zeta potential and particle size distribution were employed for nanofluid characterization. Agglomeration and sedimentation of the prepared nanofluids after standing for 20 days were observed, showing the good stability of the prepared graphene oxide–water nanofluid. The dynamic viscosity and thermal conductivity were measured. They show that with the increase in temperature, the dynamic viscosity of nanofluids decreases and the thermal conductivity increases. With the increase in mass concentration, the viscosity and thermal conductivity are improved. The highest thermal conductivity increase is obtained when the nanofluid concentration is 0.01% and the temperature is 50 °C. Finally, and most importantly, considering the inaccuracy of the existing experimental correlations to the predicted values of thermal conductivity, we propose our new mathematical model of correlation and carry out a series of tests to verify its reliability. The experimental correlations with temperature and concentration as independent variables show good agreement and accuracy with the experimental data.