Papers by Author: Hao Du

Abstract: F-doped TiO2 has exhibited superior photocatalytic activity. However, its electronic structures and photocatalysis mechanism are still unclear. In the present work, the structural optimization and electronic structure of F-doped anatase TiO2 have been investigated by means of the first-principles pseudopotential total energy method. It has been demonstrated that F doping would modify the valence band at the lower energy direction in the F-doped TiO2. Calculation results confirm that doping of fluorine would not shift the absorption edge into the visible light region. Instead, we attributed its photocatalytic activity to the enhancement of the oxidative power of F-doped TiO2.

Abstract: TiO2 films were deposited by using mid-frequency twin magnetron reactive sputtering technique at ambient temperature on quartz and Si wafer. The films were annealed after deposition. The phase composition and surface morphology of the TiO2 films were characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy, while the optical properties and contact angle were measured using a UV-Vis spectrophotometer and a contact angle meter. It is indicated that anatase phase dominates below 900°C and a mixture of rutile and anatase exists in the film annealed at 1000°C. Furthermore, the hydrophilic property depends on phase composition and morphological change in TiO2 films.

Abstract: A WC-Co coating with self-lubricating property was deposited by detonation gun (D-gun) process, using a WC-Co powder doped with a MoS2-Ni powder, under a proper spray condition. It is proved that the MoS2 composition was kept in the resulting coating by SEM, XRD and EPMA. Evaluation on sliding wear property indicates that the MoS2 composition plays an important role in lowering both coefficient of friction and wear rate for the resulting coating, which is confirmed by observations on wear track. It suggests that the deposition of WC-Co coating with self-lubricating property by D-gun spray is feasible by controlling lubricant powder and spray conditions, which can exhibit higher sliding wear resistance.

Abstract: The sliding wear property of plasma sprayed TiO2 coatings with porosity of 4.2% and 5.4% mating against silicon nitride ball were comparatively investigated with a reciprocating tribometer under dry conditions. The results indicate that the wear resistance of the TiO2 coating with lower porosity is superior, which is attributed to its homogeneous microstructure and improved microhardness. The morphologies of the wear tracks of the two TiO2 coatings, as well as wear debris reveal the pore is the main location wear occur. The coefficients of friction of the two TiO2 coatings decrease with the increase of applied load, while the wear rates increase, which is attributed to the difference of the dependence of microhardness on load between the coating and the Si3N4 ball. No apparent dependence of wear resistance on sliding speed was found on these two coatings.

Abstract: Cold spray process offers an oxidation-free atmosphere. It is usually used for TiO2 coatings used in photocatalytic applications to purify a given medium. Cold sprayed coatings with spray dried powder and evaporated powder were compared. Investigation of properties using SEM, XRD, roughness test were performed. SEM and XRD data were found to be very similar, however, variations were found for the surface roughness. Nano-sized powders were used in this investigation, therefore the coatings achieved were very thin in comparison to those from conventional powders, also they showed high uniformity.benzene removal from air by means of photoelectrocatalytic reaction was achived.

Abstract: The influence of the two deposition parameters on microstructure, and microhardness of plasma sprayed TiO2 coatings were investigated. It was found that a higher spraying power and a shorter distance resulted in a lower porosity and a higher microhardness for the coatings. The anisotropy on the microstructure and microhardness of TiO2 coatings was also found. The denser microstructure is attributed to the higher degree of melting and higher velocity of the TiO2 powders during spraying. The improvement of microhardness is associated with the lower porosity. The difference of porosity and microhardness between surface and cross section resulted from their different microstructures.