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•Addition of dopants to TiO2 led to an increase in surface area except for Mn/ TiO2.•Optical reflection edge shifted to visible light range with additives.•Cu/TiO2 exhibited the ...highest activity under visible light for both of the dyes.
The purpose of this work is to design and develop a series of stable and effective TiO2 photocatalysts prepared by a modified precipitation method. In order to improve the photo response of the TiO2 to the visible region, the effect of addition of six successive transition metal elements of fourth period, namely chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu) was studied. Two different types of dyes, methyl orange (MO, azo dye) and methylene blue (MB, thiazine dye group), were used to investigate the influence of structure of dyes on the photocatalytic degradation rates. The results showed that loading titania with 0.3wt.% of different transition metal elements was found to have significant influences on the crystallographic structure, physical properties and optical absorption properties of titania based catalysts, as well as catalytic activity during dye degradation reactions. The optical reflection edge was obviously shifted to the visible light range with the transition metal additives. The band gap energies of the doped TiO2 samples were considerably narrower than that of plain TiO2. The different activity levels of the catalysts for both dyes clearly show that the photocatalytic activity of samples strongly depended on the metal dopant used. Among all the catalysts, Cu/TiO2 sample exhibited the highest photocatalytic activity under visible light for both of the dyes owing to the low band gap energy and delayed electron-hole recombination.
Although the seminal work of Fujishima et al. dates back to 1971, TiO2 still remains the most diffused and studied semiconductor, employed in photo-oxidation processes for cleantech (i.e., polluted ...water and air treatment), in solar fuel production (mainly hydrogen production by water photo splitting), and in Carbon Capture and Utilization (CCU) processes by CO2 photoreduction.
The eleven articles, among them three reviews, in this book cover recent results and research trends of various aspects of titanium dioxide photocatalysis, with the chief aim of improving the final efficiency of TiO2-based materials. Strategies include doping, metal co-catalyst deposition, and the realization of composites with plasmonic materials, other semiconductors, and graphene. Photocatalysts with high efficiency and selectivity can be also obtained by controlling the precise crystal shape (and homogeneous size) and the organization in superstructures from ultrathin films to hierarchical nanostructures. Finally, the theoretical modeling of TiO2 nanoparticles is discussed and highlighted. The range of topics addressed in this book will stimulate the reader’s interest as well as provide a valuable source of information for researchers in academia and industry.
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•Ni/P25 TiO2 and Au/P25 TiO2 afford similar H2 production rates in alcohol-water mixtures.•Ni/P25 TiO2 outperforms Au/P25 TiO2 in methanol-water mixtures under UV excitation.•H2 ...production rates depend on the alcohol hole scavenger and alcohol concentration.•At 10 vol%, rates follow the order glycerol > ethylene glycol > methanol > ethanol.•At 40 vol%, rates follow the order methanol > ethylene glycol > glycerol > ethanol.
This study systematically compares the performance of 0.5 wt% Ni/P25 TiO2 and 2 wt% Au/P25 TiO2 photocatalysts for H2 production in alcohol-water mixtures under UV excitation. HRTEM, XANES and EXAFS confirmed the presence of 5–8 nm Ni0 and Au0 nanoparticles on the surface of the photocatalysts. H2 production tests were conducted in various alcohol-water systems (0–100 vol%), using methanol, ethanol, ethylene glycol and glycerol. The Ni/P25 TiO2 and Au/P25 TiO2 photocatalysts demonstrated remarkably similar performance for hydrogen production in all the alcohol-water systems tested. At low alcohol concentrations (15 vol% or less), H2 production rates followed the order glycerol > ethylene glycol > methanol > ethanol, whilst at higher alcohol concentrations methanol (optimum 40 vol%) and ethanol (optimum 80–90 vol%) afforded the highest rates. Rates depended on the polarity and oxidation potential of the alcohol. Further, anatase-rutile heterojunctions in P25 TiO2 were found to greatly enhance H2 production.
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•Doping effectively improves the photochromic properties of TiO2.•Nb doping has strongest effect on the total transmittance change.•Hf doping provides fast recovery of optical ...transmittance.
TiO2 quantum dot (QD) size nanoparticle colloids have shown tremendous photochromic response. Here we show that the of the photochromic response of TiO2 QDs can be further enhanced by doping. Our synthesis approach allows to reach high nominal doping level by substituting up to 20 % of Ti in TiO2 without phase segregation simultaneously keeping particles in ultra-small. We compare the effect of different dopants (Nb5+, Hf4+ and Ta5+) on photochromic properties of TiO2 QDs. We show all dopants in study enhance the response kinetics and total transmittance change. From all three dopants, Nb5+ provides strongest response and fastest coloration while Hf4+ doped TiO2 QDs exhibit fastest recovery when the UV light is off. The presented insight in photochromic properties of doped TiO2 QDs will allow to develop photochromic devices and materials with better performance.
Characterization and evaluation of hazardous spent V2O5-WO3/TiO2 catalysts are critical to determining their treatment or final disposal. This study employs a thermal approach to simulate the ...preparation of spent catalysts derived from commercial V2O5-WO3/TiO2 catalysts and investigate the structure-activity relationship of the carrier changes during the deactivation process. The results indicate that the catalyst carrier undergoes two processes: an increase in grain size and a transformation in crystal structure. Both structural and catalytic investigations demonstrate that the grain size for catalyst deactivation is 24.62 nm, and the formation of CaWO4 occurs before the crystalline transformation. The specific surface area is susceptible to an increase in grain size. The reactions of selective catalytic reduction involve the participation of both Brønsted acid and Lewis acid sites. The deactivation process of the carrier initially affects Brønsted acid sites, followed by a reduction in Lewis acid sites, resulting in a decline in NH3 adsorption capacity and oxidation. Correlation analysis reveals that changes in the physicochemical properties of the catalyst reduce the NO conversion, with the order being The grain size > Total acid amount > The surface area. It is recommended to recycle the spent catalyst if the carrier grain size is less than 25 nm. The findings of this investigation contribute to expanding the database for evaluating and understanding the physicochemical properties of spent catalysts for disposal.
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•The process of carrier transformations was studied from grain size and crystal.•The grain size is a signification indicator of the recovery of spent catalysts.•Regeneration of spent catalysts caused by grain size <25 nm is recommended.•The related relationship of carriers guiding the disposal of spent catalysts.
The commercial feasibility of biodiesel production highly depends on the effective utilization of byproduct glycerol through an environmentally friendly process like photocatalytic reforming. ...However, the process should be possible under visible light if solar energy is used. In this work, this process was studied over Pt, Au, Au–Cu, and Cu on reduced TiO2 (by NaBH4), which is more effective under visible light than pristine TiO2, for the first time in literature. Au, Au–Cu, and Cu were loaded by deposition precipitation with urea, while Pt was loaded by impregnation. Although the performance under UV–vis and white TiO2 is still higher, the visible light performance of Pt, Au–Cu, and Cu is much better over reduced TiO2 (91, 36, and 27 μmol/h. gcat respectively) than those over pristine TiO2 (9, 14 and 18 μmol/h. gcat respectively). This indicates that reduced TiO2 has the potential for the visible light reforming of glycerol.
•Photocatalytic glycerol reforming was studied on Pt, Au, Au–Cu, Cu/black TiO2.•TiO2 surface was chemically reduced using NaBH4.•Bandgap of TiO2 decreased and visible light absorption increased by reduction.•Visible light activity of Au based catalysts were higher.•Visible light activity on Pt, Au–Cu and Cu/black TiO2 was higher than regular TiO2.
•It is the first time to demonstrate visible light photodegradation of TC over black TiO2.•Black TiO2 exhibits much higher TC removal efficiency than white TiO2.•TC can be mineralized by black TiO2 ...under visible light irradiation, but not by white TiO2.•TC photodegradations by white TiO2 and black TiO2 have different mechanisms.
As an emerging semiconductor different from regular white TiO2, black TiO2 has attracted intensive attention on visible light driven photocatalysis for degrading dyes, but rarely for degradation of antibiotics. In this study, black anatase-TiO2 was demonstrated to be an effective catalyst for tetracycline (TC) visible light photodegradation. 66.2% removal efficiency of TC was achieved over black TiO2 under visible light illumination, while white TiO2 and N-doped TiO2 exhibited 43.4% and 59.6% removal efficiencies, respectively. Furthermore, only ⋅O2− radicals played an important role in TC photodegradation over white TiO2, whereas both ⋅O2− and h+ were responsible for the degradation over black TiO2 and N-doped TiO2. Different from white TiO2 for visible light photocatalytic TC degradation that follows photosensitization, the visible light photodegrataion over black TiO2 is due to photoexcitation.
Shifting the ultraviolet (UV) to visible-light-driven photocatalysis is realized by introducing extrinsic band gap via incorporation of additional components in the TiO2 structure.
•Morphological ...change and chemical modification by incorporation of additional components in the TiO2 structure.•Various strategies for enhancing TiO2 photocatalytic efficiency.•Further strategies on how to tackle the challenge of the photocatalytic activity across the entire visible range.
Titanium dioxide (TiO2) has been proved to be a leading semiconductor material to removal of environmental pollutants. However, it suffers from low photocatalytic efficiency under visible-light irradiation and narrow light response range because of its intrinsic large band gap. One of the most significant scientific and commercial progresses to date has been the development of visible light active TiO2 by incorporation of additional components in the TiO2 structure. In this review, a variety of strategies to improve the photocatalytic efficiency and shift the photocatalysis to visible light range are discussed. The materials are covered in the review including TiO2/SiO2, TiO2/carbon nanotube, TiO2-graphene/grapheme oxide, non-metal and/or metal doped TiO2. Emphasis is given to highlight current techniques and recent progress in enhancing photocatalytic efficiency of TiO2-based materials, which drives the rising of some key strategies involved in the ongoing challenges and potential new directions of TiO2 photocatalysts.
Titanium dioxide remains a benchmark photocatalyst with high stability, low cost, and less toxicity, but it is active only under UV light; thus, in practical applications using visible light, its ...catalytic reactions are stalled. To enhance its catalytic activity under visible light, non-metal/codoped TiO2 structures are being studied. These structures improve the photocatalytic activity of TiO2 in visible light by reducing its energy bandgap. This might be useful in wastewater treatment for the photocatalytic degradation of organic contaminants under visible and UV light irradiation. In this intensive review, we describe recent developments in TiO2 nanostructured materials for visible-light driven photocatalysis, such as (i) mechanistic studies on photo-induced charge separation to understand the photocatalytic activity and (ii) synthesis of non-metal doped/codoped TiO2 and TiO2 nanostructured hybrid photocatalysts. Furthermore, the effects of various parameters on their photocatalytic efficiency, photodegradation of various organic contaminants present in wastewater, and photocatalytic disinfection are delineated.
•Metals-doped, non-metals doped and co-doped TiO2 nanostructures are promising visible-light driven photocatalysts.•Doped TiO2 nanostructures showed excellent photocatalytic efficiency for different photocatalytic applications.•Various influencing parameters were investigated on photocatalytic efficiency.•Photocatalytic efficiency can be further enhanced with design of efficient synthesis methodologies.
