Ge Chen

Slightly hydrogenated TiO2 with enhanced photocatalytic performance

Hydrogenated TiO2 (H-TiO2) has triggered intense research interest in photocatalysis due to its substantially improved solar absorption and superior activity. However, the main factors that induce the enhanced photocatalytic performance of H-TiO2 are still under debate. In order to clarify this issue, the structural properties of H-TiO2, and their effects on photo-generated charges are comprehensively investigated in this study. H-TiO2 nanoparticles with different hydrogenation degrees are rapidly synthesized through H2 plasma treatment in several minutes; and their photocatalytic activities are evaluated by methylene blue (MB) degradation and CO2 reduction in aqueous and gaseous media, respectively. The slightly hydrogenated TiO2 (s-H-TiO2) nanoparticles with the original white color exhibit enhanced photoactivity compared with the pristine TiO2 (pristine-TiO2) nanoparticles especially for CO2 reduction; while the gray or black H-TiO2 nanoparticles with higher hydrogenation degrees (h-H-TiO2) display much worse catalytic performances. Further investigations reveal that the higher ratio of trapped holes (O− centers) and a lower recombination rate induced by the increase of surface defects might be the critical factors for the high activity of s-H-TiO2; in contrast, h-H-TiO2 nanoparticles possess high concentration of bulk defects, leading to a significantly decreased amount of O− centers and enhanced non-radiative recombination, which strongly inhibit their photoactivity. These results might provide new insights into the photoactivity of H-TiO2, and pave the way for further studies of other hydrogenated metal oxides for photocatalytic applications.

Synthesis of anatase TiO2 nanosheets with enhanced pseudocapacitive contribution for fast lithium storage.

Anatase TiO2 nanosheets (ATNs) are successfully prepared by a biomimetic layer-by-layer titania mineralization approach, and the electrochemical performance of the ATNs as negative electrode for lithium-ion batteries is investigated by the galvanostatic chronopotentiometry and cyclic voltammetry. A high initial discharge capacity (311 mA h g(-1)) and initial Coulombic efficiency (81.7%) were obtained for ATNs, and capacities of 252, 202, 186, 158, 136, and 119 mA h g(-1) were obtained at 0.2, 1, 5, 10, 20, and 30 C, respectively. Particularly, the ATNs can still maintains a capacity of 108 mA h g(-1) after 4000 cycles at 30 C (only a capacity loss of 10%), which indicated a superior rate capabilities and cyclability. The CVs analysis revealed that the ANTs have both diffusive lithium storage in the bulk and pseudocapacitive lithium storage at the surface (also called interfacial lithium storage), and the pseudocapacitive lithium storage dominates the total capacity when the scan rates are above 1 mV s(-1). The fast and stable lithium storage of ATNs might be attributed to the high pseudocapacitive lithium storage contribution in the material, and it was suggested the pseudocapacitive lithium storage could occurred at grain-grain interfaces as well as nanosheet surfaces.

Understanding the fast lithium storage performance of hydrogenated TiO2 nanoparticles

Anatase TiO2 is considered as one of the promising anode materials for lithium ion batteries (LIBs) because of its nontoxicity, safety, and excellent capacity retention. However, the poor rate capability of TiO2 electrodes, caused by the low electrical conductivity and lithium diffusion coefficient, strongly hinders its practical application in high power LIBs. Herein, we report on the fast lithium storage performance of hydrogenated anatase TiO2 nanoparticles (H-TiO2) prepared by a H2 plasma treatment. The scan-rate dependence of the cyclic voltammetry (CV) analysis reveals that the improved rate capability of H-TiO2 results from the enhanced contribution of pseudocapacitive lithium storage on the particle surface. Combined with the structural properties of H-TiO2, it is suggested that the disordered surface layers and Ti3+ species of H-TiO2 play an important role in the improvement of pseudocapacitive lithium storage. The results help to understand the fast lithium storage performance of H-TiO2 and might pave the way for further studies of other hydrogenated metal oxide electrodes for high power LIBs.

A Near Infrared Light Triggered Hydrogenated Black TiO2 for Cancer Photothermal Therapy

White TiO2 nanoparticles (NPs) have been widely used for cancer photodynamic therapy based on their ultraviolet light-triggered properties. To date, biomedical applications using white TiO2 NPs have been limited, since ultraviolet light is a well-known mutagen and shallow penetration. This work is the first report about hydrogenated black TiO2 (H-TiO2 ) NPs with near infrared absorption explored as photothermal agent for cancer photothermal therapy to circumvent the obstacle of ultraviolet light excitation. Here, it is shown that photothermal effect of H-TiO2 NPs can be attributed to their dramatically enhanced nonradiative recombination. After polyethylene glycol (PEG) coating, H-TiO2 -PEG NPs exhibit high photothermal conversion efficiency of 40.8%, and stable size distribution in serum solution. The toxicity and cancer therapy effect of H-TiO2 -PEG NPs are relative systemically evaluated in vitro and in vivo. The findings herein demonstrate that infrared-irradiated H-TiO2 -PEG NPs exhibit low toxicity, high efficiency as a photothermal agent for cancer therapy, and are promising for further biomedical applications.

Protein-Mediated Layer-by-Layer Synthesis of TiO2(B)/Anatase/Carbon Coating on Nickel Foam as Negative Electrode Material for Lithium-Ion Battery

Through an aqueous, protein-mediated layer-by-layer titania deposition process, we have fabricated a protamine/titania composite layer on nickel foam. The coating was composed of amorphous carbon and TiO2(B)/anatase nanoparticles and formed upon organic pyrolysis under a reducing atmosphere (5% H2-Ar mixture). X-ray diffraction analyses, Auger electron spectroscopy, and high-resolution transmission electron microscopy revealed that the obtained coatings contained fine monoclinic TiO2(B) and anatase nanocrystals, along with amorphous carbon. Moreover, the coating can be used as a binder-free negative electrode material for lithium-ion batteries and exhibits high reversible capacity and fast charge-discharge properties; a reversible capacity of 245 mAh g(-1) was obtained at a current density of 50 mA g(-1), and capacities of 167 and 143 mAh g(-1) were obtained at current densities of 1 and 2 A g(-1), respectively.

Biomimetic synthesis of titania with chitosan-mediated phase transformation at room temperature

We have demonstrated the glucan polymer-mediated syntheses of titania at room temperature, which is an energy-conserving and environmentally benign synthetic pathway. Wormhole-like particles (both rutile and anatase) with high surface areas and quasi-sphere-shaped particles (anatase) were obtained for chitosan, sodium alginate and cellulose, respectively. Particularly, we have observed the phase transformation from anatase to rutile in the chitosan-mediated titania process; the experimental results revealed a distinct dependence of the phase transformation on the protonation level of the amino groups in chitosan. The obtained results suggest that different charged groups of glucan polymers strongly impact on the size, shape and polymorph of the obtained titania particles, which might provide new insights into in vitro bio-enabled titania formation and pave the way for further studies of titania phase transformations.

Integrating the hierarchical structure with well-dispersed conductive agents to realize synergistically enhanced electrode performance

A newly designed TiO2 electrode with enhanced electrochemical performance is obtained by integrating the hierarchical structure with well dispersed graphene and nitrogen doped carbon through a bottom-up assembly approach. The obtained novel hierarchical structure is composed of loosely stacked TiO2 nanosheets, in which graphene was sandwiched and nitrogen doped carbon was uniformly dispersed. When used as the anode material for lithium-ion batteries, the material showed excellent rate capability and long cycle life; a high capacity of 151 mA h g−1 is achieved at a current rate of 5 C (1 C = 168 mA g−1) after 100 cycles for the integrated TiO2 electrode, and a capacity of 105 mA h g−1 is retained at a current rate of 25 C after 200 cycles, which is superior to either single hierarchical structures or just well dispersed conductive agents of the TiO2 electrode.