A novel nanocomposite of carbon quantum dots (CQDs) and TiO₂ nanotubes was fabricated and its enhanced photocatalytic and photoelectrochemical properties were demonstrated. Carbon quantum dots were obtained by electrochemical-etching graphite electrodes and TiO₂ nanotubes arrays were prepared by anodization methods. Subsequently, CQDs were assembled on the surface of vertically aligned TiO₂ nanotube arrays (CQDs/TiO₂ nanotubes) and the as-prepared samples were characterized by field-emission scanning electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, photoelectrochemical and photocatalytic measurements. XPS measurement shows the presence of carbon species which come from CQDs. A red shift of light absorption edge and more absorption in the visible light region were observed for the resulting samples from the UV-vis diffuse reflectance spectra. An enhanced photocurrent and photopotential were demonstrated for the CQDs sensitized TiO₂ nanotubes under visible light irradiation and the photocurrent density was 2.7 times larger than that of pristine TiO₂ nanotubes. A solar cell was fabricated for further verifying the sensitization of CQDs over TiO₂ nanotubes. Moreover, the photocatalytic activity of CQDs/TiO₂ nanotubes towards the degradation of methylene blue was demonstrated and about 14% enhanced degradation efficiency was obtained with the presence of CQDs. This work developed a simple method to fabricate CQDs and demonstrated the introduction of CQDs to be a new approach for improving the utilization of visible light for TiO₂ nanotube arrays.

Doping with transition metal ions is widely employed to adjust the optical and photocatalytic properties of wide band semiconductors, however, quantitative information about the energetics and charge transfer dynamics of the impurity states is often difficult to obtain. Here we use surface photovoltage spectroscopy (SPS), optical spectroscopy, and irradiation experiments to study the effect of several dopants on the ability of SrTiO₃ nanocrystals to generate a photovoltage and to catalyse H₂ evolution from aqueous methanol. Phase pure SrTiO₃:TM nanocrystals with TM = Ni, Cu, Fe, Mn, Rh were synthesized by hydrothermal reaction of TiO₂, Sr(OH)₂, KOH, and transition metal chlorides and nitrates in water. SPS data was obtained on thin films of these nanocrystals on fluorine doped tin oxide substrates under vacuum atmosphere. All samples are n-type, which can be gauged from the negative photovoltage caused by the transfer of electrons into the FTO substrate. All dopants produce sub-bandgap states in the SrTiO₃ lattice, whose energetic positions can be determined from the photovoltage onset energy in SPS and from optical absorption spectra. The reversibility and size of the photovoltage provide information about the photohole dynamics and their ability to oxidize sacrificial electron donors at the nanocrystal surface. Overall, this work provides an explanation for the inability of Ni, Cu, Fe, Mn dopants to enhance visible light photocatalytic activity in SrTiO₃, and it establishes SPS as a useful tool to map the energetics and photochemistry of impurity states in metal oxide nanocrystals.

TiO₂/γ-graphyne nanocomposites were successfully synthesizedviaa simple hydrothermal method, and demonstrated as a promising photocatalyst for hydrogen evolution.

Flos Lonicerae Japonicae (FLJ) is a popular herb used for many centuries in Traditional Chinese Medicine as a treatment of fever and inflammation. Non-fumigated processing of FLJ has been the traditional approach used in post-harvest preparation of the commodity for commercial use. However, in recent years, natural drying processing of FLJ has been replaced by sulfur-fumigation for efficiency and pest control. Sulfur-fumigation can induce changes in the volatile compounds of the herb, altering its medicinal properties. A comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF/MS) method was established for the resolution and determination of volatile components in non-fumigated and sulfur-fumigated FLJ. In this paper, analysis of the volatile oils in non-fumigated and sulfur-fumigated (including lab-prepared sulfur- fumigated and industrial sulfur-fumigated) FLJ was performed using GC×GC-TOF/MS. Seventy-three representative volatile components were identified, including furans, alkalies, acids, aldehydes, ketones, alcohols, terpenes, esters, and others, as the main components of FLJ volatile oils. The proposed method was successfully applied for rapid and accurate quality evaluation of FLJ and its related medicinal materials and preparations.