In this study, Ce x Zr 1−x O 2 solid-solution oxide (x = 0.7) was prepared using hydrothermal method , and the obtained Ce 0.7 Zr 0.3 O 2 nanoparticles were modified with wood–based carbon quantum dots (CQDs). Furthermore, we report a composite photocatalyst of vacuum heat-treated CQDs/Ce 0.7 Zr 0.3 O 2 for degrading methylene blue. The structural properties and photocatalytic activity of CQDs/Ce 0.7 Zr 0.3 O 2 were systematically studied after vacuum heat treatment. Herein, a part of the functional groups present on CQD surfaces changed through high–temperature heating during vacuum heat treatment. The dominant structures sp 2 hybrid carbon atoms and amorphous carbon were transformed to defect states of sp 3 hybrid oxygen atoms, thus increasing the surface oxygen vacancy concentration. The high activity and excellent stability of vacuum heat-treated CQDs/Ce 0.7 Zr 0.3 O 2 system can be attributed to increased surface oxygen vacancy concentration, modification of CQDs, and the protruding structure of Ce 0.7 Zr 0.3 O 2 , contributing to efficient charge transfer. This study provides potential systems of CQD-modified photocatalysts and also reveals the substantial effect of vacuum heat treatment on enhancing the photocatalytic properties of composites.
The tribological properties of metal-CuS/MoS2 composite coatings were improved by selecting the metal materials and optimizing the heat treatment process. The composite coatings were prepared by magnetron cosputtering of copper or aluminum metals, CuS, and MoS2. Then, the prepared Cu-CuS/MoS2 and Al-CuS/MoS2 were subjected to vacuum heat treatment at 220, 320, and 420 °C. The structure and tribological properties of the composite coatings were analyzed by scanning electron microscope, energy spectrum, x-ray diffraction, Raman spectrum, and multifunction friction tester. The results showed an island-like growth and a dense noncylindrical cross-sectional morphology of the metal-CuS/MoS2 composite coating. Metal- and CuS-doped MoS2 solid solution is a practical component in composite coatings. The wear scar of the composite coatings showed different color layers at different annealing temperatures due to composition deviation. After heat treatment at 320 °C, the friction coefficient of Cu-CuS/MoS2 coating was reduced to a minimum of 0.08. After heat treatment at 420 °C, the Al-CuS/MoS2 coating showed three different color layers of wear scar, and good tribological properties were obtained. The friction coefficient of the Al-CuS/MoS2 coating was as low as 0.06, and the adhesion of the Al-CuS/MoS2 coating was expressed in the HF1 level. The results show that the vacuum heat treatment can stimulate the action of CuS by forming a solid solution with MoS2, complementing the missing S atom during the sputtering deposition of MoS2 and improving the lubrication of the composite coating. In addition, although the action mechanisms are different, Cu and Al doping are all conducive to obtaining composite coatings with better tribological properties.
Peng Huang,Xinchun Chen,Wei Qi,Jisen Tian,Jianxun Xu,Kai Wang,Wenli Deng,Chenhui Zhang,Jianbin Luo
Hydrogenated diamond-like carbon (H-DLC) films are limited by their poor thermal stability, which significantly affects the tribological applications and needs improvement. Accordingly, nanodiamond (ND) and hexagonal boron nitride (h-BN) are used to address this issue. When the H-DLC surface is deposited using ND+h-BN mixture with mass ratio of 1:1 and a concentration of 0.1 mg mL −1 and vacuum-heated at 200 °C and 1 × 10 −5 Pa, a superlow friction coefficient of 0.0015 can be obtained, with a reduction of 98.33% as compared to pure H-DLC. Correspondingly, the wear rates of wear scar and wear track decreased by 81.95% and 24.83%, respectively. High vacuum thermal treatment can purify the adsorbed species on the surfaces of ND and h-BN, and produce newly-exposed dangling bonds. Simultaneously, new bonds of C-N are formed between ND and h-BN, and the nanoparticles adhere together to form a polymer-like structure under friction. Furthermore, the ND can support h-BN and reduce its agglomeration. Under the action of tribochemical reaction, the layer spacing of hexagonal boron nitride is increased to obtain a better shear slip. The combination of these factors resulted in ultra-low friction. This study paved the way for developing functional anti-friction additives for durable and high-performance lubrication.
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