Light Diffuse Reflectance Spectra Research Articles

Construction of Co-doped TiO2/rGO nanocomposites for high-performance photoreduction of CO2 with H2O: Comparison of theoretical binding energies and exploration of surface chemistry

We report the enhancement of the photocatalytic performance of CO2 reduction in H2O by introducing Co and reduced graphene (rGO) into TiO2 photocatalyst. The synthesized nanocomposites were characterized by a range of analyses including X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet–visible light diffuse reflectance spectra (UV–vis DRS), Fourier transform infra-red spectroscopy (FT-IR), thermogravimetry-differential scanning calorimetry (TGA-DSC), energy dispersive X-ray analysis (EDX), Brunauer-Emmett-Teller (BET) surface area and X-ray photoelectron spectroscopy (XPS). It was found that wrapping Co-doped TiO2 with rGO expanded the light absorption ability of Co-doped TiO2/rGO, thus, improving the photoreduction efficiency of CO2 and selectivity for methanol. The conversion yields of CO2 to methanol with TiO2, Co-doped TiO2 and Co-doped TiO2/rGO reached 32.3 μmol/gcat, 730 μmol/gcat and 936 μmol/gcat, respectively, after 7 h of irradiation. Theoretical studies via Density functional theory (DFT) revealed that doping TiO2 with Co ions facilitated the formation of adsorbed carbonate or CO2•- species, as CO2 adsorbs onto Co-doped TiO2 surface with binding energy (BE) of −18.12 kJ/mol. The research will deepen the understanding of mole ratio (Ti:Co) content on the nanocomposites performance and provide new ideas for designing efficient photocatalysts.

Microstructures and optical performances of nitrogen-vanadium co-doped TiO2 with enhanced purification efficiency to vehicle exhaust

Titanium dioxide (TiO2) is widely used to purify air pollutants in environmental engineering, but it is only activated by ultraviolet (UV) light. The metal or nonmetal single doping of TiO2 cannot observably improve the purification efficiency of TiO2 under visible light. To further increase the photocatalytic activity and purification efficiency of TiO2 on vehicle exhaust under visible light, nitrogen (N)-vanadium (V) co-doped TiO2 was first prepared. The influences of N–V co-doping on phase structures, morphology, microstructures, electronic structures, and photo-absorption performances were then observed and examined using X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–visible light diffuse reflectance spectra. Purification efficiency and reaction rates of N–V co-doped TiO2 on NOx, HC, CO and CO2 in vehicle exhaust were studied using a purification test system under UV and visible light irradiations, respectively. Results indicate that N and V are synchronously doped into the crystal structures of TiO2 to replace O and Ti, respectively. N and V show the synergistic co-doping effect to suppress the grain growth of TiO2 and improve the dispersity and specific surface area of TiO2. Also, the N–V co-doping introduces more lattice distortions and defects in the crystal lattices of TiO2. Further, N presents in the form of Ti–O–N and O–Ti–N bonds, and V exists in the form of V5+ and V4+. These form the impurity energy level in the band gap to narrow the energy band of TiO2. Additionally, the N–V co-doping broadens the photoabsorption threshold of TiO2 from 387 nm to 611 nm. These results show that N–V co-doping increases the photocatalytic activity of TiO2. Finally, the N–V co-doped TiO2 shows higher catalytic purification efficiency on NOx and HC under UV and visible light. The N–V co-doping obviously increases the purification efficiency of TiO2 on CO and CO2 when exposed to visible light, and their reversible reactions are not found. The N–V co-doping of TiO2 is a feasible approach to purify vehicle exhaust under visible light irradiations.

Microstructures, Optical Properties and Degradation Efficiency of Nitrogen-doped Titanium Dioxide to Automobile Exhaust

To understand the influence of nitrogen (N) dopant on phase structure, morphology, optical property, photocatalytic degradation of TiO2 to automobile exhaust (AE) under visible light irradiation, the N-doped TiO2 was first prepared, and then X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS) and photocatalytic degradation tests were conducted. Results indicated that only anatase phase was found in both pure TiO2 and N-doped TiO2, and the N doping improved the dispersity of TiO2. Also, the N doping increased the absorbance of TiO2 under UV and visible light, respectively. An obvious red shift was observed on UV-Vis DRS of pure and N-doped TiO2 samples, indicating that the spectral response range of TiO2 was expanded to visible light region, and the utilization efficiency of solar irradiance was increased. The prepared N-doped TiO2 nanoparticles with an N dopant content of 3.0% showed better optical properties. Finally, the N doping improved the photocatalytic activity of TiO2 to AE in the visible light region. Furthermore, the N-doped TiO2 presented lower degradation efficiency to CO than that to CO2 under visible light radiation. Thus, it is found that the degradation efficiency of TiO2 to AE can be increased by the N doping under visible light radiation.

Composite Magnetic Photocatalyst Bi₅O₇I/MnxZn1-xFe₂O₄: Hydrothermal-Roasting Preparation and Excellent Photocatalytic Activity.

A new composite magnetic photocatalyst, Bi5O7I/MnxZn1−xFe2O4, prepared by a hydrothermal-roasting method was studied. The photocatalytic properties of Bi5O7I/MnxZn1−xFe2O4 were evaluated by degradation of Rhodamine B (RhB) under simulated sunlight irradiation, and the structures and properties were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible light (UV-Vis) diffuse reflectance spectra (DRS), and a vibrating sample magnetometer (VSM). The results indicated that Bi5O7I/MnxZn1−xFe2O4 was an orthorhombic crystal, which was similar to that observed for Bi5O7I. Bi5O7I/MnxZn1−xFe2O4 consisted of irregularly shaped nanosheets that were 40–60 nm thick. The most probable pore size was 24.1 nm and the specific surface area was 7.07 m2/g. Bi5O7I/MnxZn1−xFe2O4 could absorb both ultraviolet and visible light, and the energy gap value was 3.22 eV. The saturation magnetization, coercivity and residual magnetization of Bi5O7I/MnxZn1−xFe2O4 were 3.9 emu/g, 126.6 Oe, and 0.7 emu/g respectively, which could help Bi5O7I/MnxZn1−xFe2O4 be separated and recycled from wastewater under the action of an external magnetic field. The recycling experiments revealed that the average recovery rate of the photocatalyst was 90.1%, and the photocatalytic activity was still more than 81.1% after five cycles.

Effective shuttling of photoexcitons on CdS/NiO core/shell photocatalysts for enhanced photocatalytic hydrogen production

Hierarchical structure of NiO immobilized on CdS photocatalyst (CdS/NiO) was synthesized for stable and efficient H2 production. The catalyst is designed to suppress the photo-corrosion behaviour without affecting catalytic activity of CdS structures having tamarind leaf-like morphology is protected by fabricating thin-layer of NiO. The exterior thin-layer transmits the light into CdS in-turn exciton moved to surface for reaction with adsorbed reactant species. Structural, morphological and optical properties were studied using X-ray diffraction (XRD), ultraviolet-visible light (UV–vis) diffuse reflectance spectra (DRS), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS). The results illustrates that synthesized catalyst composed of crystalline CdS/NiO hierarchical structure that absorbs light in the visible spectrum and improved charge carrier separation than CdS or NiO alone. The photocatalytic activity was examined for H2 generation under visible light irradiation using Xe-lamp as light source. In order to achieve enhanced H2 production rate amount of NiO loading was optimized and results were found in the following order CdS/NiO > CdS. Under optimal conditions the catalyst showed stable H2 evolution for 30 h of continuous irradiation. Under optimal conditions catalyst showed visible light to H2 conversion efficiency of 6.63%.

Application of visible light on copper-doped titanium dioxide catalyzing degradation of chlorophenols

Chlorophenols are extensively used in the anthroposphere, and their fates in the atmosphere, hydrosphere, biosphere and lithosphere and their degradations under natural light of great interests. The homogeneous photocatalytic degradation of 2-chlorophenol (2-CP) in titanium dioxide suspensions containing copper ions or/and sulfates has been well examined. In this study, TiO2 is directly doped with copper sulfate by a sol-gel method to promote its visible light activity (VLA) following a post-calcination step. The effects of three parameters of synthesis (calcination temperature, amounts of dopant and nitric acid) on 2-CP degradations were experimentally investigated using a three-factor, two-level factorial design in the first stage. Catalysts of the most significant synthetic parameters were further synthesized at five calcined temperatures and characterized in the second stage. 2-CP was completely removed using catalysts that were doped 0.21 mol.% CuSO4 with 0.1 vol.% nitric acid and then calcined at 300 °C for 6 h. Morphological variations with doping amount are observed from scanning electron micrographs. XRD patterns demonstrated a transformation from amorphous to the anatase phase, with replacement of Ti4+ by Cu2+ in the crystal structure of TiO2. UV–visible light diffuse reflectance spectra of the doped catalysts exhibited red-shifts, revealing their VLA. Surface areas, measured by the BET method, decreased as the calcination temperatures increased, and the pore sizes increased. Moreover, effect of three operational parameters, including: (del) initial concentration of 2-CP, initial pH and the photocatalyst dosage, under visible-light irradiation were investigated to simulate the scenarios of degradation in the natural and artificial conditions. Optimal operational parameters were obtained at a catalyst dosage of 3 g·dm−3, an initial 2-CP concentration of 20 ppm and a solution pH of 5.5. The pHzpc of the undoped and CuSO4-doped TiO2 were determined to be 3.5 and 3.84.

Unpredictable adsorption and visible light induced decolorization of nano rutile for the treatment of crystal violet

Photocatalysts containing different ratios of anatase and rutile are prepared via heat treatment of Degussa P-25 titania. X-ray diffraction (XRD), Bruuauer-Emmett-Teller (BET), ultraviolet–visible light diffuse reflectance spectra (DRS), Raman spectra (Raman), positron annihilation lifetime spectra (PAL) and temperature-programmed desorption (TPD) are applied to investigate the phase composition of the synthesized catalysts. Using crystal violet (CV) as the target pollutant, the unexpected visible light decolorization of rutile is observed. Despite the decreased specific surface area, the as-synthesized rutile samples exhibit much higher adsorption capability of CV than P-25 does, which in turn leads to improved photoreaction efficiency. Since the rutile samples can't absorb the visible light, the degradation under visible light irradiation is attributed to self-sensitization of CV on the surface of rutile.

Effects of vanadium doping on microstructures and optical properties of TiO2

To improve the photocatalytic activity of titanium dioxide (TiO2), the vanadium (V) was selected to modify TiO2. Pure and V-doped TiO2 samples were first synthesized, then effects of the V doping on microstructures and optical properties of TiO2 were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible light diffuse reflectance spectra (UV–vis DRS). Results indicated that the prepared TiO2 samples only contained anatase phase. The V dopant was uniformly dispersed in TiO2 lattices, not affecting the crystal phase structures of TiO2. The crystallite sizes of TiO2 were decreased first and then increased with the increase in V dopant content within the diameter range from 12 to 16nm. The V dopant inhibited the increase in TiO2 crystallite size. Also, the dispersity of TiO2 nanoparticles was improved with the increase in V dopant content. The V doping brought more defects in TiO2 lattices to capture charge carriers, and to decrease the recombination of electron–hole pairs. Additionally, the prepared TiO2 included such elements as Ti, V and oxygen (O). V consisted of two chemical states of V4+ and V5+, which were served as trapping centers of photo-generated electrons to promote the photocatalytic oxidation process. Ti existed in the form of Ti4+, and O presented in the form of such chemical bonds as Ti-O, Ti-OH and Ti-O-V in V-doped TiO2. Finally, the optical absorption edges of V-doped TiO2 show obvious red shift. The optimal V dopant content is 1.0% for pure TiO2 sample. The V dopant could introduce the doping energy level and narrow the band gap of TiO2, extending the absorption spectral range of TiO2. The V doping was an effective method to improve optical absorption properties of TiO2 in visible light region.

A General Synthesis Strategy for Highly Dispersed Amorphous MoO3 over Supported Catalysts

AbstractAmorphous MoO3 was evenly deposited on a Bi2SiO5/SiO2 support by a strategy of heterogenous coprecipitation using Ti as structural promoter. The structure and properties of MoO3‐Bi2SiO5/SiO2 have been characterized by a series of techniques, including N2 adsorption/desorption analysis, X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and ultraviolet‐visible light (UV‐vis) diffuse reflectance spectra (DRS).The addition of n‐butyl alcohol into synthesis medium resulted in the most dispersive amorphous MoO3, with an average particle size of 4 nm. Selective oxidation of propylene was chosen as a probe reaction to test the performance of catalysts. Kinetic study revealed that the method of heterogeneous coprecipitation enhanced catalytic performance via increasing the number of active sites, rather than changing the nature of it. This is well compatible with characterization results.

Band gap manipulation of cerium doping TiO2 nanopowders by hydrothermal method

Cerium doped TiO2 nanopowders were prepared by hydrothermal method with cerium nitrate. The samples were characterized by high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), ultraviolet–visible light diffuse reflectance spectra. Results show that the crystal of cerium dioxide can be observed in the grains of TiO2. The morphology of TiO2 prepared by hydrothermal methods changed from nanosheets to nanopowders by cerium doping. Meanwhile cerium doping can significantly reinforce the absorption of visible light, and adjust the absorption cut-off wavelength, from 373 nm to 499 nm for the undoped and the 25% doped 499 nm samples respectively. With the increase in doping ratio of cerium, the band gaps also decreased from 3.32 to 2.48 eV. Based on our observations, it can be concluded that cerium oxide can improve the absorptivity of TiO2 and may have potential applications in the areas of solar cells and photocatalysis.

Enhanced photocatalytic activity of titania nanotube array films supported with highly dispersed Pt nanoparticles

Self-organized Pt–TiO2 nanotube array films were prepared on Ti sheets by anodizing in ethylene glycol solution containing a low concentration of NH4F and subsequent photoreduction process. Pt–TiO2 nanotube array films were characterized by means of X-ray diffraction, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and ultraviolet–visible light diffuse reflectance spectra. SEM images show the highly dispersed Pt nanoparticles were deposited on the surface of TiO2 nanotube array films. The effect of reduction treatment on the photocatalytic degradation activity of methyl orange for Pt–TiO2 nanotube array films was investigated. The photocatalytic results showed that an optimum calcination temperature of methyl orange photocatalytic degradation activity was at 473 K and the further increased temperature could be detrimental to the photocatalytic activity due to the decrease of surface Pt concentration.

A facile one-pot synthesis of gadolinium doped TiO2-based nanosheets with efficient visible light-driven photocatalytic performance

Gadolinium doped TiO2-based nanosheets (Gd-TNSs) with different Gd/Ti ratios are prepared by a facile one-pot hydrothermal method using gadolinium nitrate as the gadolinium precursor. The photocatalysts are characterized by high-resolution transmission electron microscopy (HRTEM), Raman spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible light diffuse reflectance spectra (DRS), fluorescence spectra (FL), and N2 adsorption–desorption measurement. The as-synthesized samples show clearly sheet-like structure, with the width of about 30–100 nm, length greater than 100 nm, and high specific surface area (200–300 m2/g). The patterns of XRD and Raman analyses indicate that doped gadolinium has obvious influence on the structure of samples. The band-gap energy (E g) of photocatalysts reduce from 3.17 to 3.02 eV with the content of gadolinium increasing from 0.1 to 1.5 at. %. The FL emission intensity initially decreases with the content of Gd increasing and then increases after minimizing at 0.5 %-Gd-TNSs, which reveals that appropriate amount of gadolinium doping can effectively inhibit the recombination of photo-generated electrons and holes. The adsorption capacity and photocatalytic activity are evaluated by Rhodamine B (RhB). The best photocatalytic performance is obtained when the doping ratio of gadolinium is 0.5 at. %. The visible reaction rate (K app) of 0.5 %-Gd-TNSs was 2.0-fold as compared to TNSs, and 4.7-fold as compared to P25. The possible mechanisms for enhanced visible-light photocatalytic activities are discussed in detail.

Effect of holmium doping on the structure and photocatalytic behavior of TiO2-based nanosheets

A series of holmium-doped TiO2-based nanosheet (Ho-TNS) photocatalysts with different Ho/Ti molar ratios were prepared via a simple hydrothermal method. The photocatalysts were characterized by field-emission scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction (XRD), Raman Spectroscopy, X-ray photoemission spectroscopy, nitrogen adsorption–desorption isotherm measurement, ultraviolet–visible light diffuse reflectance spectra (DRS), and fluorescence spectra (FL). The TEM images of Ho-TNS exhibit clearly sheet-like structures and existence of the (201) plane of H2Ti3O7. The increased (101) peak intensity in XRD spectrum and the enhanced Eg mode (141 cm−1) in Raman spectrum indicate that Ho doping has obvious influence on the formation and structure of Ho-TNS, which can be explained by the formation of Ho–O–Ti bonds. With the doping ratio (Ho/Ti molar ratio) increasing from 0 to 2.0 %, the absorption edge shifts to a longer wavelength, and the band-gap of photocatalysts reduces from 3.18 to 3.07 eV. The decline of FL intensity implies that the photocatalysts with higher Ho content have higher electron–hole separation efficiency. However, after Ho doping, the surface structure of specimens is significantly altered, which will lead to the specific surface areas and adsorption capacity decrease. Under the combined effect of the variables, the photocatalyst with a doping ratio of 1.0 % reaches the best photoactivity, which is 1.90-fold and 12.38-fold higher compared with undoped TNS and P25 under visible light, respectively. The high photoactivity of the prepared Ho-TNS indicates that it may be useful for dealing with wastewater.

Synthesis and characterization of co-doped TiO2 thin films on glass-ceramic

In this research, an attempt was made to improve TiO2 photo-catalyst properties, thus pure, N–Ce co-doped TiO2 thin films were prepared on glass-ceramic substrate using a sol–gel dip-coating technique. The samples were calcinated in air at 475°C, 550°C, and 650°C for 2h. The result of simultaneous thermal analysis (STA) and X-ray diffraction (XRD) showed that the presence of Ce in TiO2 could inhibit the phase transformation from anatase to rutile and enhance the thermal stability, and anatase was the dominant phase in N–Ce co-doped TiO2 samples. Also based on the results, the doping results in decreasing the size of TiO2 crystallite. The results of ultra violet-visible light diffuse reflectance spectra (UV–vis DRS) presented that cerium doping results in a shift in the absorption spectra of N–Ce co-doped TiO2 to the visible region. The photo-induced hydrophilicity and photo-catalytic activity of the films were evaluated by the water contact angle measurement and photo-catalytic degradation of aqueous methyl orange, respectively. It was found that N–Ce co-doped TiO2 thin films showed a higher photo-catalytic activity, and better photo-induced hydrophilicity than the pure TiO2 thin films. However, too much doping did not improve properties of N–Ce co-doped TiO2. The results of the experiments showed that doping with Ce content of Ce/Ti% equal to 3% and N content of urea/tetra n-butyl ortho titanate equal to 0.25 can improve N, Ce co-doped TiO2 properties.

Microcirculation assessment using an individualized model for diffuse reflectance spectroscopy and conventional laser Doppler flowmetry.

Microvascular assessment would benefit from co-registration of blood flow and hemoglobin oxygenation dynamics during stimulus response tests. We used a fiber-optic probe for simultaneous recording of white light diffuse reflectance (DRS; 475-850 nm) and laser Doppler flowmetry (LDF; 780 nm) spectra at two source-detector distances (0.4 and 1.2 mm). An inverse Monte Carlo algorithm, based on a multiparameter three-layer adaptive skin model, was used for analyzing DRS data. LDF spectra were conventionally processed for perfusion. The system was evaluated on volar forearm recordings of 33 healthy subjects during a 5-min systolic occlusion protocol. The calibration scheme and the optimal adaptive skin model fitted DRS spectra at both distances within 10%. During occlusion, perfusion decreased within 5 s while oxygenation decreased slowly (mean time constant 61 s; dissociation of oxygen from hemoglobin). After occlusion release, perfusion and oxygenation increased within 3 s (inflow of oxygenized blood). The increased perfusion was due to increased blood tissue fraction and speed. The supranormal hemoglobin oxygenation indicates a blood flow in excess of metabolic demands. In conclusion, by integrating DRS and LDF in a fiber-optic probe, a powerful tool for assessment of blood flow and oxygenation in the same microvascular bed has been presented.

Photocatalytic Reduction of CO2to Methane on Pt/TiO2Nanosheet Porous Film

Anatase TiO2nanosheet porous films were prepared by calcination of the orthorhombic titanic acid films at 400°C. They showed an excellent photocatalytic activity for CO2photoreduction to methane, which should be related to their special porous structure and large Brunauer-Emmett-Teller (BET) surface area. In order to further improve the photocatalytic activity, Pt nanoparticles were loaded uniformly with the average size of 3-4 nm on TiO2porous films by the photoreduction method. It was found that the loading of Pt expanded the light absorption ability of the porous film and improved the transformation efficiency of CO2to methane. The conversion yield of CO2to methane on Pt/TiO2film reached 20.51 ppm/h·cm2. The Pt/TiO2nanosheet porous film was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS). Moreover, the transient photocurrent-time curves showed that the Pt/TiO2nanosheet porous film exhibited higher photocurrent, indicating that the higher separation efficiency of the photogenerated charge carriers was achieved.

Monitoring of rat brain ischemia degree with visible light diffuse reflectance spectra and its significance

Objective To observe role of the visible light diffuse reflectance spectra in monitoring the severity of brain ischemia in normal,ischemic and necrotic rat brain tissues so as to offer research basis for intraoperative real-time monitoring of brain reperfusion.Methods Thirty-six SD rats were randomly divided into noumal group and ischemia 1 hour,3 hours,6 hours,12 hours and 24 hours groups,with 6 rats per group.Models of middle cerebral artery occlusion were established using thread technique in ischemic groups.Visible light diffuse reflectance spectroscopy was detected by a spectrometer and mean diffuse reflectance spectroscopy ratio (R630/R545) was measured.Results Spectral reflectance of infarcted brain tissue was enhanced with the prolonged ischemic time while the trough of the spectra at 542 nm and 577 nm was shallowed.Moreover,small trough was appeared at 630 nm at 12 h and 24 h after ischemia.Diffuse reflectance spectroscopy ratio (R630/R545) showed statistical difference among all groups (P ＜ 0.05) with the exception between ischemic 12 hours and 24 hours groups.Conclusion Visible diffuse reflectance spectroscopy can timely monitor and discriminate the normal,ischemic and necrotic brain tissues and even the severity of brain ischemia and hence lay a research basis for intraoperative real-time monitoring of brain reperfusion. Key words: Infarction, middle cerebral artery; Brain ischemia; Rats; Diffuse reflectance spectra

Research on the effect of crystal structures on W-TiO2 nanotube array photoelectrodes by theoretical and experimental methods

W-doped/undoped TiO2 nanotube array (TNAs) photoelectrodes with different nanostructures were successfully fabricated using the anodization method. Their morphology and characteristics were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and ultra violet/visible light diffuse reflectance spectra (UV/vis/DRS). Their electronic structure and optical properties were studied by means of first-principle. Photocatalytic (PC) performance of W-TNAs photoelectrodes with different crystal structures was evaluated using the decomposition rates of Rhodamine B (Rh.B) under xenon light illumination. The results demonstrated that W substituting Ti broadened the width of conduction band (CB) and valence band (VB) of anatase and rutile TiO2, reduced the band gap of rutile TiO2 and even caused its red-shift. W incorporated into TNAs photoelectrodes extended light absorption threshold and enhanced its utilization of solar light and PC activity, particularly, the PC performance of W-TNAs photoelectrodes with mixed crystal and rutile crystal structure.

Study on enhanced photocatalytic performance of cerium doped TiO2-based nanosheets

Cerium doped TiO2-based nanosheets (Ce-TNSs) photocatalysts were prepared by a one-pot hydrothermal method using cerium nitrate as the cerium precursor. The photocatalysts were characterized by high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Raman spectra, ultraviolet–visible light diffuse reflectance spectra (DRS), X-ray photoemission spectroscopy (XPS) and fluorescence spectra (FL). The results show that Ce3+ and Ce4+ co-exist in Ce-TNS. The doping leads to changes in binding energies of Ti and O. The concentration of Ti3+ increases gradually when the cerium doping amount keep increasing. Appropriate amount of cerium doping can significantly inhibit the recombination of electron–hole pairs, which is proved by the decline in the intensity of the fluorescence spectra. Ce-TNS with doping ratio of 0.5% (molar ratio) possesses the highest photocatalytic activity when degrading Rhodamine B (RhB), which is 5 times and 1.6 times of that of P25 and the undoped TNS, respectively. It is suggested that cerium ions are efficient electron trappers to improve the separation efficiency of electrons and holes.

Synthesis and photocatalytic activity of nanocrystalline TiO2 co-doped with nitrogen and cobalt(II)

Nitrogen-modified cobalt-doped TiO2 materials were successfully prepared via a modified sol–gel method. The structure and properties of the catalysts were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM, ultraviolet–visible light diffuse reflectance spectra (UV–Vis DRS), N2 adsorption–desorption isotherms, and energy-dispersive X-ray spectroscopy. The XRD patterns of the pure and co-doped TiO2 samples indicate that the predominant phase was anatase. The average grain size obtained from TEM was approximately 10 nm. The Brunauer–Emmett–Teller analysis results indicate that the specific surface area was 77.7 m2 g−1. The UV–Vis DRS results for the co-doped sample reveal an absorption edge that had been red-shifted to 500 nm. The photocatalytic activities of the samples were evaluated through photodegradation of papermaking wastewater under UV and visible light irradiation. Compared with the cobalt-doped TiO2 sample and Degussa P25, the 3 mol% N-doped mesoporous N/Co-TiO2 photocatalyst exhibited the highest photocatalytic activity, which can be ascribed to the synergistic effect of the N and Co co-doping.