Titanium dioxide (TiO2) is one of the most attractive transition-metal oxides because of its superior physical and chemical properties, which has been widely applied in environmental clean-up (photocatalytic pollution removal), energy conversion (hydrogen production and solar cells), energy storage (lithium batteries and supercapacitors), security (sensors), panel display (transparent conducting films), biomedical devices, and so forth [1–18]. The performance of TiO2 in these applications highly depends on its structural, electronic, optical, and morphological as well as the surface properties (exposed facets). Great effort has been devoted to adjust these properties and apparent progress has been made on the synthesis of the 0-, 1-, 2-, and 3-dimensional nanostructured TiO2 materials. Nevertheless, further investigations are required on the development of new synthetic methods and the understanding of its relationship between the intrinsic properties and performance, to facilitate the commercialization of TiO2-based materials in advanced environmental and energy-related areas.
This issue includes original research articles and a review that cover the synthesis of TiO2-based nanomaterials and their environmental and energy-related applications. We summarize the published articles as below.
In “Influence of Anodic Oxidation Parameters of TiO2 Nanotube Arrays on Morphology and Photocatalytic Performance,” X. Zhao et al. present the influence of electrolyte, applied potential, and duration of oxidation process on nanomorphology and photocatalytic property of titanium dioxide nanotube arrays (TNTAs). Compared to the glycol electrolyte, the TNTAs grown by using the DMSO electrolyte exhibit much better photocatalytic activity, but their nanomorphology is much worse. Longer time and higher oxidation voltage benefit the growth of TNTAs.
TiO2-based catalysts for the selective catalytic reduction of NO are hotspots in environmental catalysis. X. Chen et al. in their paper entitled “Experimental Study on the Deactivating Effect of KNO3, KCl, and K2SO4 on Nanosized Ceria/Titania SCR Catalyst” investigated the deactivating effect of potassium compounds on nanosized CeO2/TiO2 selective catalytic reduction catalyst. This study would provide useful insights for the application and life management of CeO2/TiO2 in potassium-rich environments such as biofuel-fired boilers.
Development of supported titanium dioxide- (TiO2-) based nanomaterials would promote their performance. In “Preparation of Stellerite Loading Titanium Dioxide Photocatalyst and Its Catalytic Performance on Methyl Orange,” H. Chen et al. reported the photocatalytic decomposition of methyl orange (MO) over a stellerite modified-TiO2 photocatalyst. This work would provide a promising strategy to explore highly efficient photocatalyst and thus promote their further application in environmental fields.
Volatile organic compounds have been identified as indoor and outdoor pollutants and the treatment of them has been studied for decades. In “New Insights into Benzene Hydrocarbon Decomposition from Fuel Exhaust Using Self-support Ray Polarization Plasma with Nano-TiO2,” T. Zhu et al. developed a new strategy of using nano-TiO2 as the catalyst in the self-support ray polarization of nonthermal plasma. This strategy showed improved performance to remove benzene. Indeed, at electric field strength of 12 kV/cm, 99% of benzene was removed. Moreover, the final products are environmentally friendly with decreased residence of ozone. This study with advances in potential industrial application should be of interest to the community.
Carbon materials have been extensively investigated and have been well incorporated with TiO2 materials to improve the performance of their composites. In “Modified Sol-Gel Synthesis of Carbon Nanotubes Supported Titania Composites with Enhanced Visible Light Induced Photocatalytic Activity,” Q. Wang et al. report a multiwalled carbon nanotube enhanced TiO2 nanocomposites for photocatalytic degradations. The nanocomposites possess good absorption properties not only in the ultraviolet but also in the visible light region. Under irradiation of ultraviolet lamp, the prepared composites have the highest photodegradation efficiency of 83% within 4 hours towards the degradation of methyl orange (MO) aqueous solution. The results indicate that the carbon nanotubes supported TiO2 nanomaterials exhibit high photocatalytic activity and stability, showing great potentials in the treatment of wastewater.
In a paper entitled “Enhanced Adsorption and Removal of Ciprofloxacin on Regenerable Long TiO2 Nanotube/Graphene Hydrogel Adsorbents,” J. Ma et al. reported the investigation of regenerable long TiO2 nanotube/graphene oxide hydrogel adsorbent for antibiotic pollutants, which would attract the attention of environmental science, materials, and nanotechnology community to development a safe and sustainable society.
In “Preparation of TiO2/Activated Carbon Composites for Photocatalytic Degradation of RhB under UV Light Irradiation,” J. Cao et al. used a sol-gel method to prepare TiO2/activated carbon (AC) composites and they have found that the loading cycles of TiO2 precursor play an important role in controlling the morphological structure and photocatalytic activity of TiO2/AC composites. The porosity parameters of these composite photocatalysts such as specific surface area and total pore volume decrease whereas the loading amount of TiO2 increases. The TiO2/AC composite synthesized at two loading cycles exhibits the highest photocatalytic activity.
TiO2 is a kind of promising anode material because of its low cost, excellent structural stability, small volume expansion, and good safety performance due to its high discharge plateau potential (about 1.5–1.8 V versus lithium) that would not decompose the organic electrolyte, large exposed surface offering more lithium-insertion channels. However, the poor electronic conductivity and low lithium ion diffusivity of TiO2 result in poor cycling stability and lithium ion depletion at high current rates. A review entitled “Recent Progress of TiO2-Based Anodes for Li Ion Batteries” by Y. Liu and Y. Yang is specifically focused on the recent progress in enhancing the lithium ion batteries (LIBs) performance of TiO2 with various synthetic strategies and architectures control, such as designing hollow structure to form more open channels and active sites for Li ion transport, coating or combining TiO2 with metal to improve its electronic conductivity, or incorporating carbonaceous materials such as active carbon, CNTs, and graphene to enhance its capacity and cycling stability.
The guest editors hope that this special issue will inspire further research in the field of TiO2 nanomaterials and their applications in advanced environmental and energy-related areas.
Acknowledgments
The editors gratefully thank the authors for their contributions to this special issue and the reviewers for their constructive comments.
Xujie Lü
Baoyu Xia
Cunming Liu
Yefeng Yang
Hao Tang