•The Fenton-like degradation of AO7 depends much on the exposed facets of CeO2.•H2O2 decomposition shows higher Ea with nanocubes than that with nanorods.•Exposed {110} facet of CeO2 improves the Fenton-like degradation of AO7.Recently, ceria-based Fenton-like reactions have been developing in wastewater treatment. Nevertheless, the effects of geometric (exposed facets) of the CeO2 on its Fenton-like reactivity have rarely been considered. In this work, shaped CeO2 nanocrystals with different exposed facets were synthesized and applied in the Fenton-like degradation of Orange II (AO7). Due to the relative low oxygen vacancy formation energy on {110} facet, H2O2 decomposition shows higher apparent activation energy with nanocubes ({100} facet) than that with nanorods ({110} and {100} facets). CeO2 nanorods calcined at 300 °C exhibits the maximal activity for the decomposition of H2O2, while that for the Fenton-like degradation of AO7 is achieved with CeO2 nanorods calcined at 500 °C. Calcination at higher temperature decreases the surface Ce(III) content of CeO2, thus lowers the H2O2 decomposition rate. On the contrary, the decrescent formation energy of oxygen vacancy, the decreased amount of surface hydroxyls, as well as reduced coordination status of surface Ce cations, play important roles in promoting the adsorption and Fenton-like degradation of AO7 for CeO2 nanorods calcined at 500 °C.Download high-res image (129KB)Download full-size image

•RuO2 serves as the electrocatalytic active component for RuO2-TiO2/Ti electrode.•The electrode exchanging strategy greatly improves the stability of electrode.•Epitaxial spread of RuO2 on TiO2 stabilizes the RuO2 in the electrocatalytic uses.•Oxidation and reduction of NO2− give NO3− (main product) and NH4+, respectively.RuO2-TiO2/Ti electrode was prepared for the electrocatalytic removal of nitrite in this work. The influences of calcination temperatures on crystal phase and morphology of RuO2-TiO2 composite were explored by XRD and TEM. The formation of RuO2 epitaxial layers on the surface of TiO2 by calcination at 400 °C reduces the impedance (EIS test) and improves the electrocatalytic activity for RuO2-TiO2. The CV test shows that the electrochemically surface active sites increase along with the increase of RuO2 content from 0 to 2.0 wt%. The nitrite removal rate of 2.0 wt% RuO2-TiO2/Ti electrode is found ca. 6.7 and 2.5 times faster than those of 0.02 wt% and 0.1 wt% RuO2-TiO2/Ti electrodes, respectively. Oxidation of the active sites on the RuO2 results in an obvious activity decrease for RuO2/Ti and RuO2-TiO2/Ti electrodes in just 3 reaction cycles (30 min/cycle). By exchanging the anode and cathode after every cycle, the catalytic activity of corresponding 2.0 wt% RuO2-TiO2/Ti electrode remains almost unchanged after 50 cycles. Although the electrocatalytic service life of RuO2/Ti electrode is also greatly improved, its electrocatalytic activity decreases much after 50 cycles. The relatively longer service life of 2.0 wt% RuO2-TiO2/Ti electrode should own to the intensified interaction between the epitaxially spread RuO2 and TiO2, which stabilizes the chemical states of RuO2. The main product for the electrocatalytic removal of nitrite is nitrate by indirect oxidation, while a small amount of ammonium is also produced at the cathode. The as-produced ammonium will be oxidized into nitrogen molecule, which is released from the aqueous solution afterwards and contributes the decrease of the total content of N in the solution.Download high-res image (119KB)Download full-size image

•TiO2 acts as an adhesion agent to fix the NiO grains on the Ti plate.•NiO acts as the active component for electrocatalytic use.•Heterojunction between NiO and TiO2 increases the Ni(III) and Ti(III) contents.•Ti/TNO-350-700 shows a superior electrocatalytic performance.Ti/TiO2/NiO (Ti/TNO) electrode used for electrocatalytic oxidation of nitrite was fabricated by a simple thermal decomposition method in this work. The influences of calcination temperature on crystal phase and morphology of Ti/TNO composite were explored by XRD and TEM. After being calcined at 700 °C, NiO grains are closely surrounded by TiO2 grains, in which TiO2 acts as an adhesion agent to fix the NiO grains on the Ti plate. The relative contents of Ni(III) and Ti(III) species were found increase due to the close heterojunction between NiO and TiO2, which reduces the impedance and improves the electrocatalytic activity of Ti/TNO. Ti/TNO-350-700 not only exhibits as high activity as those of Ti/TNO-350 and Ti/TNO-700 for electrocatalytic removal of nitrite contaminant, but also owns a superior electrocatalytic stability, which is more than 30 times and 2.5 times longer than those of Ti/TNO-350 and Ti/TNO-700, respectively.Download high-res image (308KB)Download full-size image

By using an oxygen vacancy (Ov)-enriched TiO2 surface, herein we report a photo-induced activation process of Pt-deposited TiO2 (Pt/V-TiO2) for its photocatalytic application. The Ov-related photo-induced modulation of Pt nanoparticles is realized, with which the average size of Pt nanoparticles decreases from 2.65 to 1.82 nm and a more active Pt0 component is generated.

Pt–Ru alloy loaded TiO2 (RP-AH) photocatalyst with superior photocatalytic performances was prepared in this work. First, RuO2/TiO2/Pt ternary photocatalyst (RP) is calcined in air to epitaxially spread RuO2 nanoclusters on the surface of TiO2 (RP-A), which ensures the close contact of RuO2 with the Pt nanoparticles nearby. Then, RuO2 is reduced into metallic Ru to form Pt–Ru alloy via calcining in a H2 atmosphere. XRD, TEM, XPS, and CV are applied to verify the formation of Pt–Ru alloy nanoparticles, while the photocurrent and Mott–Schottky plots suggest that RP-AH is a p-type semiconductor. The RP-AH catalyst shows a superior photocatalytic activity to those of RP, RP-A, and RP-H (Ru/TiO2/Pt) in CO oxidation under UV irradiation. CO of a concentration of 1000 ppm was completely photocatalytically oxidized into CO2 with RP-AH in 120 min. Either Pt–Ru alloy or p-type semiconductor property of RP-AH plays an effective role in improving the photocatalytic performance of RP-AH. Academically, Pt–Ru alloy clusters favor the adsorption of CO and O2 as well as promote the separation of the photogenerated charges in RP-AH; meanwhile, the high hole mobility due to the p-type semiconductor property of RP-AH also benefits the reactivity of holes in oxidizing CO into CO2 with O–(a).

Coexisting oxidation and reduction cocatalysts play a significant role in the photocatalytic oxidation reaction. Here a surface modification method was used to synthesize the ternary photocatalyst RuO2/TiO2/Pt with RuO2 nanoclusters of ca. ∼2 nm size. Further, thermal treatment was adopted to transform RuO2 nanoclusters into an epitaxial layer on the surface of TiO2 to form ep-RuO2/TiO2/Pt. XRD, TEM, and XPS were used to verify the formation of the RuO2 epitaxial layers on both rutile and anatase TiO2. The interfacial atom arrangement match between the RuO2 and TiO2 is suggested as the possible physical basis for the transformation process of RuO2 from nanoparticles to epitaxial layers. The photocatalytic performance of RuO2/TiO2/Pt and ep-RuO2/TiO2/Pt was studied by photocatalytically oxidizing gaseous CO under the UV irradiation. The optimal RuO2 contents in the ep-RuO2/TiO2/Pt were 0.05, 0.1, and 0.02 wt % for P25, commercial anatase, and commercial rutile TiO2, respectively. In their optimal RuO2 contents, the photocatalytic activity of the ep-RuO2/TiO2/Pt for CO oxidation are ca. 2.6, 2.4, 1.7 times than that of their uncalcined ones and ca. 20, 15, 8 times that of their corresponding bare TiO2 for P25, anatase, and rutile, respectively. The formation of interfacial epitaxial RuO2 layers leads to more significant exposure of RuO2 (110) facets in the ep-RuO2/TiO2/Pt ternary photocatalyst, which plays an effective role in promoting photocatalytic CO oxidation.Keywords: CO oxidation; epitaxial heterojunction; RuO2; ternary photocatalysts; TiO2

Gradual oxidation of g-C3N4 was carried out using a mild hydrothermal method to obtain oxidized g-C3N4 (CNO). Besides occurring as N–O, oxygen also occurs in CNO as CO and C–O, all of which are of electron-withdrawing character and play a significant role in improving the photocatalytic performances of CNO materials. The photocurrent response of g-C3N4 treated for 12 hours, denoted as CNO-12, is ca. 10 times higher than that of raw g-C3N4, while the photocatalytic activity of CNO-12 is ca. 7 times higher than that of g-C3N4 in the degradation of Acid Orange 7.

An interfacial lattice Ag+ doped on TiO2 (Ag+/TiO2) was prepared by eluting Ag0 clusters from a hydrothermally prepared Ag0/Ag+/TiO2 composite. An Ag+/TiO2@Ag0 composite photocatalyst was subsequently obtained via a secondary Ag0 clusters loading process to the Ag+/TiO2. The photocatalytic activity of Ag+/TiO2@Ag0 was greatly improved compared to Ag0/Ag+/TiO2 and Ag+/TiO2. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) testing verified that Ag+ ions occur as an interfacial lattice Ag+ species in the composites. The enhancement effect of the interfacial lattice Ag+ species is exhibited by the newly-formed Ag+/TiO2@Ag0 as the interfacial lattice Ag+ is fully exposed but not overlapped with the re-loaded Ag0 clusters. The interfacial lattice Ag+ ions and Ag0 clusters are both responsible for the photocatalytic performance improvement of the catalyst, in either the photocatalytic degradation of methyl orange or photocurrent measurement.

A high level (∼9 mM) of hydrogen peroxide is photocatalytically synthesized by using O2 as an oxidant and 2-ethyl-9,10-anthraquinone (EAQ) as an electron condenser. The photo-catalytic efficiency of the EAQ-assisted H2O2 production is ca. 10-fold higher than that of H2 generation with Pt/P25.

•Sulfated ceria shows enhanced activity in catalytic degradation of AO7 with H2O2.•Sulfated ceria exhibits stronger surface acidity compared with bare CeO2.•Sulfation of CeO2 activates the surface peroxide species for degradation of AO7.•A mechanism for the catalytic activity improvement of sulfated ceria is proposed.Organic pollutants can be effectively degraded by CeO2/H2O2 system, the catalytic activity of which is restricted by over-complexation of H2O2 with CeO2. In this study, nano ceria was pretreated simply in different ways. Degradation of AO7 was employed to evaluate the catalytic activity of the pretreated ceria samples in the presence of H2O2 in pre-adsorbed mode (AO7 pre-adsorbed on CeO2 before the addition of H2O2) and pre-mixed mode (CeO2 pre-mixed with H2O2 before the addition of AO7). Two sulfated ceria samples (H2SO4–CeO2 and Na2SO4–CeO2) exhibit enhanced catalytic performance in both modes compared with un-pretreated bare CeO2. XRD, BET, FTIR and potentiometric titration methods were used to characterize the pretreated ceria samples. The sulfated samples display stronger surface acidity due to the sulfate ions anchored on their surface. Raman and XPS measurements were carried out to analyze the samples after reacting with H2O2. A mechanism to explain the improved catalytic activity of sulfated CeO2 is proposed that the active surface peroxide species (Ce(III)O2H−), which are excessive due to the over-complexation of H2O2 with surface Ce3+ sites, can be decomposed into high-active hydroxyl radicals under surface acidic environment.

The Fenton-like degradation of nalidixic acid was studied in this work. The effects of Fe3+ concentration and initial H2O2 concentration were investigated. Increasing the initial H2O2 concentration enhances the degradation and mineralization efficiency for nalidixic acid, while Fe3+ shows an optimal concentration of 0.25 mM. A complete removal of nalidixic acid and a TOC removal of 28 % were achieved in 60 min under a reaction condition of [Fe3+] = 0.25 mM, [H2O2] = 10 mM, T = 35 °C, and pH = 3. LC–MS analysis technique was used to analyze the possible degradation intermediates. The degradation pathways of nalidixic acid were proposed according to the identified intermediates and the electron density distribution of nalidixic acid. The Fenton-like degradation reaction of nalidixic acid mainly begins with the electrophilic attack of hydroxyl radical towards the C3 position which results in the ring-opening reaction; meanwhile, hydroxyl radical attacking to the branched alkyl groups of nalidixic acid leads to the oxidation at the branched alkyl groups.

Me3SiI-promoted reaction of salicylic aldehydes with β-dicarbonyl compounds provided a facile way to construct 4H-benzopyrans in moderate to good yields. This tandem reaction proceeds with high efficiency through nucleophilic addition, silyl enol ether formation, substitution, reduction, and intramolecular nucleophilic cyclization.

A series of brookite and anatase TiO2 hybrids with different ratios were synthesized by in situ hydrolysis of tetrabutyl titanate (TBOT) on the pre-prepared brookite nanoflowers. The composition and content of the mixture were examined by X-ray diffraction (XRD). The morphology and construction of the hybrids were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), while BET was used to measure the specific surface area of all the samples. Anatase nano-grains grow on the surface of brookite petals, which builds special heterojunction on their interface and thus benefits the separation of photogenerated electrons and holes under UV irradiation. The TiO2 hybrids appeared superior photocatalytic activity to the single phase toward the degradation of methyl orange (MO) and 2,4-dichlorophenol (2,4-DCP). The hybrid contains 40% anatase and 60% brookite exhibited the highest activity, the degradation rate constants of which are 2.27 and 1.80 times higher than that of the corresponding physically mixed sample for the degradation of MO and 2,4-DCP, respectively.Graphical abstractHighlights► Brookite/anatase hybrids with superior photocatalytic activity were prepared. ► Hybrids have an optimal brookite/anatase ratio of 6/4 for photocatalytic activity. ► Special heterojunction forms from the in situ nucleation of anatase on brookite. ► The heterojunction benefits the separation of photogenerated carriers in hybrids.

A feasible approach to synthesize pure brookite was achieved in an aqueous ammonia system via a hydrothermal process. By hydrothermal treatment of the titanate that directly hydrolyzed from tetrabutyl titanate (TBOT), a phase transition from titanate to TiO2 was observed with XRD. Anatase TiO2 was produced with an unobstructed closure of titanate layers. The phase transition process can be controlled by adding an electrolyte such as NaCl into the hydrothermal media. Na+ ions locally stop the direct closure of titanate layers at their adjacent position, which induce the formation of a brookite-like structure. The optimal hydrothermal reaction parameters for the crystal lattice formation of brookite in aqueous ammonia media were found to be 180 °C, 0.5 M NaCl and ≥72 h. The phase transition process of titanate precursor to TiO2 depends heavily on the electrolyte. Metal cations play a crucial role in conducting the transition procedure from layered titanate into brookite or anatase. Na+ is preferred to conduct the phase transition from titanate to brookite rather than K+ and Li+. Although anions do not determine the phase transition rule during the hydrothermal process, they are influential in the phase transition process, as they can promote the phase transition by interacting with the TiO6 octahedra.

Ultralong mesoporous TiO2-B nanowires were synthesized via a hybrid hydrothermal-ion exchanging-thermal treatment using tetrabutyl titanate (TBOT) as a raw material. The phase transformations and porous structures of TiO2-B nanowires were characterized and studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N2 adsorption–desorption measurement. Mesoporous TiO2-B nanowires showed a length of several micrometers and diameter of about 25 nm. The porous structures of obtained TiO2-B nanowires were demonstrated by BJH pore distribution measurement. The wirelike morphologies and porous structures of monodisperse nanowires calcined at 600 °C showed little change, which indicated that such nanowires possessed high thermal stability. The formation mechanism of TiO2-B nanowires with mesoporous structures were also discussed based on our experimental results.Graphical abstractResearch highlights► Synthesis of ultralong mesoporous TiO2-B nanowires from protonated dititanate. ► Porous structures of TiO2-B nanowires possessed high thermal stability. ► The formation of TiO2-B nanowires follows the oriented attachment mechanism.

Ce-intercalated layered titanate (CeTO) was synthesized through an ion-exchange process combined with thermal treatment. According to X-ray diffraction (XRD) analysis, the interlayer shrinkage, lattice cell contraction and lattice dislocation of CeTO occur during the ion-exchange process. The ion-exchange process lengthens the bond length of Ti–O in the a-axis direction, which results in a bathochromic shift of titanate in UV–vis spectrum. Calcination treatment intensifies the interlayer shrinkage and reduces the lattice dislocation via lattice rearrangement. The photocatalytic reactivity of CeTO is significantly improved with thermal treatment at 400 °C. EPR study shows that most of the intercalated cerium ions are oxidized to Ce4+ after intercalation, while thermal treatment changes little the chemical valence of cerium ion. It is suggested that lattice dislocation but not chemical valence of cerium ion plays an important role in determining the photocatalytic activity of CeTO. Further, the photocatalytic reactivity of CeTO is much higher than cerium doped sodium titanate prepared by solid-state reaction (SSR) method.Graphical abstract.Highlights► Ce-intercalated titanate was prepared with a hybrid method of ion-exchange and thermal treatment. ► Lengthening of Ti–O bond and the bathochromic shift of CeTO occurs. ► Lattice dislocation of CeTO reduces its photocatalytic reactivity. ► Thermal treatment improves the photocatalytic reactivity of CeTO by reducing the dislocation.

Ag0-loaded brookite/anatase composite was prepared via an alkalescent hydrothermal process. The photocatalytic performance of as-prepared catalysts was evaluated in terms of the degradation of methyl orange (MO). The physical features of the catalysts were measured with XRD, BET and HRTEM techniques. The phase content of brookite and anatase in the TiO2 can be controlled by fixing the concentration of the electrolyte in the hydrothermal system. The as-formed Ag0 clusters have an average diameter of ca. 1.5 nm and intersperse throughout the surface of both anatase nanoparticles and brookite nanorods. Ag0 has an optimal loading dosage of 2.0 mol%, with which the photocatalytic degradation of MO are 4.82 and 2.28 times of that with Ag0-free composite and P25 TiO2, respectively. The synergistic effect of hetero-junction in brookite/anatase composite and the schottky barrier at the interface of Ag0 and TiO2 significantly improved the separation of the photogenerated electrons and holes under UV irradiation and thus resulted in a much enhanced photocatalytic reactivity towards the degradation of MO.Graphical abstractHighlights► Ag0-loaded brookite/anatase TiO2 with uniform Ag0 size distribution was prepared. ► 2.0% Ag0-loaded brookite/anatase TiO2 has the highest photocatalytic reactivity. ► Hetero-junction in brookite/anatase composite benefits the charge separation. ► Schottky barrier between Ag0 and TiO2 further improved the charge separation.

A systematic morphological phase diagram of titania/titanate was determined by the most important synthesis parameters of reaction temperature and NaCl concentration via a facile one-step alkalescent approach. X-Ray diffraction and Raman spectroscopy were used to generally assess the phase composition and crystallite size of different titania/titanate samples, which were also used to investigate the phase transition behavior in connection with the synthesis parameters. Scanning/transmission electron microscopy was employed to characterize the morphology, size, and lattice plane, and to further elucidate the morphological evolution of the resulting products. According to the Ostwald's step rule, a phase transition mechanism was proposed based on our current systematic experimental results, which reveals the phase transitions from layered hydrogen titanate to anatase or brookite under hydrothermal treatment. The brookite–anatase composite exhibited excellent photocatalytic activity in the photodegradation of methyl orange, phenol and salicylic acid solution under UV irradiation.

BiOCl exhibited high photocatalytic activities for the degradation of rhodamine B, methyl orange and phenol. Surface chloride ions were adverse to the BiOCl photocatalysis and dissociated from BiOCl via reaction with photogenerated holes and electrons under UV irradiation. Conduction band electrons of BiOCl directly reduced either chlorine radical or the azo-bond of MO during the photocatalytic process. Hydroxyl radical was the main oxidative species in the BiOCl photocatalysis, whose generation can be accelerated via enhancing the conduction band electron consumption by MO. After the photocatalytic reaction, the dissolved chloride ion would spontaneously recombine back to the BiOCl photocatalyst, hence qualifies BiOCl as a practical high-activity photocatalyst with long lifetime.

Carbon-deposited TiO2 (TiO2@C) was prepared with a one-pot hydrothermal process by using glucose as a carbon source. The physical properties of TiO2@C were studied by XRD, TG-DTA, HRTEM, and UV−vis diffuse reflectance spectra (DRS), while the chemical states of carbon were discussed via X-ray photoelectron spectroscopy (XPS). A graphite carbon layer was formed out of the TiO2 grain during the hydrothermal process via the dehydration of glucose, which consisted of not only Cn but also C—OH (and C—O—C) and C═O (and COO). TiO2@C has remarkable light absorption in the visible region. It was found that the photocatalytic activity of TiO2@C was greatly enhanced compared to noncarbon-TiO2 under visible irradiation. The photocatalyst with the highest photocatalytic activity for the degradation of Acid Orange 7 (AO7) was G15 TiO2@C, while that for the degradation of 2,4-dichlorophenol (2,4-DCP) was G5 TiO2@C. Two kinds of sensitization processes, carbon sensitization and dye sensitization, are responsible for the visible light-induced photocatalysis of TiO2@C. Carbon sensitization reached its optimal condition in G5, while dye sensitization occurred in its maximum efficiency in G15.

Pure brookite TiO2 nanoflowers consisting of single crystalline nanorods were synthesized for the first time using a facile one-step hydrothermal process.

TiO2-B nanowires were synthesized by an ion exchanging-thermal treatment. The unique morphology of pits and dislocations interspersed on TiO2-B nanowires were firstly characterized and studied by high-resolution transmission electron microscopy (HRTEM). Oriented attachment is suggested as an important growth mechanism in the evolvement of pits and dislocations on TiO2-B nanowires. Lattice shears and fractures were originally formed during the ion exchanging process of the sodium titanate nanowires, which resulted in the formation of primary crystalline units and vacancies in the layered hydrogen titanate nanowires. Then the (110) lattice planes of TiO2-B grown in [110] direction is faster than the other lattice planes, which caused the exhibition of long dislocations on TiO2-B nanowires. The enlargement of the vacancies, which was caused by the rearrangement of primary crystalline units, should be the reason of the formation of pits. Additionally, the transformation from TiO2-B to anatase could be also elucidated by oriented attachment mechanism.The unique morphology of pits and dislocations on TiO2-B nanowires shown in high-resolution transmission electron microscopy (HRTEM) and a proposed evolvement mechanism of pits and dislocations on TiO2-B nanowires.

Gradual oxidation of g-C3N4 was carried out using a mild hydrothermal method to obtain oxidized g-C3N4 (CNO). Besides occurring as N–O, oxygen also occurs in CNO as CO and C–O, all of which are of electron-withdrawing character and play a significant role in improving the photocatalytic performances of CNO materials. The photocurrent response of g-C3N4 treated for 12 hours, denoted as CNO-12, is ca. 10 times higher than that of raw g-C3N4, while the photocatalytic activity of CNO-12 is ca. 7 times higher than that of g-C3N4 in the degradation of Acid Orange 7.

An interfacial lattice Ag+ doped on TiO2 (Ag+/TiO2) was prepared by eluting Ag0 clusters from a hydrothermally prepared Ag0/Ag+/TiO2 composite. An Ag+/TiO2@Ag0 composite photocatalyst was subsequently obtained via a secondary Ag0 clusters loading process to the Ag+/TiO2. The photocatalytic activity of Ag+/TiO2@Ag0 was greatly improved compared to Ag0/Ag+/TiO2 and Ag+/TiO2. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) testing verified that Ag+ ions occur as an interfacial lattice Ag+ species in the composites. The enhancement effect of the interfacial lattice Ag+ species is exhibited by the newly-formed Ag+/TiO2@Ag0 as the interfacial lattice Ag+ is fully exposed but not overlapped with the re-loaded Ag0 clusters. The interfacial lattice Ag+ ions and Ag0 clusters are both responsible for the photocatalytic performance improvement of the catalyst, in either the photocatalytic degradation of methyl orange or photocurrent measurement.

Me3SiI-promoted reaction of salicylic aldehydes with β-dicarbonyl compounds provided a facile way to construct 4H-benzopyrans in moderate to good yields. This tandem reaction proceeds with high efficiency through nucleophilic addition, silyl enol ether formation, substitution, reduction, and intramolecular nucleophilic cyclization.

A systematic morphological phase diagram of titania/titanate was determined by the most important synthesis parameters of reaction temperature and NaCl concentration via a facile one-step alkalescent approach. X-Ray diffraction and Raman spectroscopy were used to generally assess the phase composition and crystallite size of different titania/titanate samples, which were also used to investigate the phase transition behavior in connection with the synthesis parameters. Scanning/transmission electron microscopy was employed to characterize the morphology, size, and lattice plane, and to further elucidate the morphological evolution of the resulting products. According to the Ostwald's step rule, a phase transition mechanism was proposed based on our current systematic experimental results, which reveals the phase transitions from layered hydrogen titanate to anatase or brookite under hydrothermal treatment. The brookite–anatase composite exhibited excellent photocatalytic activity in the photodegradation of methyl orange, phenol and salicylic acid solution under UV irradiation.

Pure brookite TiO2 nanoflowers consisting of single crystalline nanorods were synthesized for the first time using a facile one-step hydrothermal process.