Co-doped TiO2 Nanorod Research Articles

Cathodic shift of onset potential on TiO2 nanorod arrays with significantly enhanced visible light photoactivity via nitrogen/cobalt co-implantation* *Project supported by the National Natural Science Foundation of China (Grant No. 11875211), the Major Science and Technology Program of Changsha, China (Grant No. kq1902046), and the Fundamental Research Funds for the Central Universities, China.

Despite anionic doping has been widely implemented to increase the visible light activity of TiO2, it often gives rise to a dramatical anodic shift in current onset potential. Herein, we show an effective method to achieve the huge cathodic shift of TiO2 photoanode with significantly enhanced visible light photo-electrochemical activity by nitrogen/cobalt co-implantation. The nitrogen/cobalt co-doped TiO2 nanorod arrays (N/Co-TiO2) exhibit a cathodic shift of 350 mV in onset potential relative to only nitrogen-doped TiO2 (N-TiO2). Moreover, the visible-light (λ > 420 nm) photocurrent density of N/Co-TiO2 reaches 0.46 mA/cm2, far exceeding 0.07 mA/cm2 in N-TiO2 at 1.23 V versus reversible hydrogen electrode (RHE). Systematic characterization studies demonstrate that the enhanced photo-electrochemical performance can be attributed to the surface synergic sputtering of high-energy nitrogen/cobalt ions.

Photocatalytic degradation evaluation of N-Fe codoped aligned TiO2 nanorods based on the effect of annealing temperature

In this paper, a comparative study on the photocatalytic degradation of the Rhodamine B (RhB) dye as a model compound using N-Fe codoped TiO2 nanorods under UV and visible-light (λ ≥420 nm) irradiations has been performed. TiO2 photocatalysts were fabricated as aligned nanorod arrays by liquid-phase deposition process, annealed at different temperatures from 400 to 800 °C. The effects of annealing temperature on the phase structure, crystallinity, BET surface area, and resulting photocatalytic activity of N-Fe codoped TiO2 nanorods were also investigated. The degradation studies confirmed that the nanorods annealed at 600 °C composed of both anatase (79%) and rutile phases (21%) and offered the highest activity and stability among the series of nanorods, as it degraded 94.8% and 87.2% RhB in 120 min irradiation under UV and visible-light, respectively. Above 600 °C, the photocatalytic performance of nanorods decreased owning to a phase change, decreased surface area and bandgap, and growth of TiO2 crystallites induced by the annealing temperature. It is hoped that this work could provide precious information on the design of ID catalyst materials with more superior photodegradation properties especially under visible-light for the further industrial applications.

Inverted pyramid Er3+ and Yb3+ Co-doped TiO2 nanorod arrays based perovskite solar cell: Infrared response and improved current density

In this study, a Yb3+, Er3+ co-doped TiO2 inverted pyramid nanorod (NR) array and a compact TiO2 film are simultaneously fabricated as the mesoporous support layer and electron-blocking layer, respectively, by a one-pot hydrothermal method. The scanning electron microscopy results show that the incorporation of Er3+ and Yb3+ causes changes not only in the growth rate of the NRs, but also in the TiO2 NR morphology. The Er3+, Yb3+ co-doped TiO2 NRs exhibit an inverted pyramidal morphology, which is beneficial for perovskite permeation and light utilization. Notably, the Er3+, Yb3+ co-doping causes changes in the band gap of TiO2 and leads to 25% increase in the current density. The electrochemical impedance spectroscopy results show that the device based on the doped TiO2 NRs has a higher recombination resistance and a lower transfer resistance than those of the undoped device, and thereby, the doped device exhibits a lower electron recombination rate. In addition, the upconversion Er and Yb co-doped device exhibits 25% higher current density and 17% higher photon-to-electron conversion efficiency, as revealed by the J-V test results. Moreover, the optimized efficiency of the TiO2 NR array-based perovskite solar cell is determined to be 10.02%. Furthermore, the Er and Yb co-doped device exhibits a near-infrared response, an efficiency of 0.1% is achieved under infrared light (800–1100 nm) irradiation. This upconversion material can widen the photovoltaic responses of solar cells into the near-infrared region and improve the utilization of sunlight.

Effect of Rh valence state and doping concentration on the structure and photocatalytic H2 evolution in (Nb,Rh) codoped TiO2 nanorods.

The simultaneous realization of visible light response and high photocatalytic activity remains a challenging task for TiO2 despite extensive research. Herein, (Nb,Rh) codoping is adopted to extend the absorption band of anatase TiO2 into the visible-light region. Meanwhile, the dependence of the electronic structure, visible-light absorption, and photocatalytic performance on the dopant ratio as well as doping concentration is studied. Open shell t2g5 Rh(iv) and closed shell t2g6 Rh(iii) coexist in Rh-doped TiO2, and the codoped Nb promotes a change in valence state from Rh(iv) to Rh(iii). Rh(iii) is the main active species in charge of the excellent photocatalytic performance, while Rh(iv) doping introduces electron/hole recombination centres. However, surprisingly, a trace of Rh(iv)-doping contributes to a decrease in electron transfer resistance and an increase in donor density, which help to improve photocatalytic performance. By virtue of the controlled content of Rh(iii) and Rh(iv), Ti1-2xNbxRhxO2 exhibits a high hydrogen evolution rate of ∼9000 μmol g-1 h-1 in methanol solution, along with a remarkable photocurrent density of ∼9 μA cm-2 under visible-light irradiation, which are about 170 and 30 times higher than those of pristine TiO2 nanorods, respectively.

Simultaneous and synergistic effect of heavy metal adsorption on the enhanced photocatalytic performance of a visible-light-driven RS-TONR/TNT composite

A hydrothermally synthesized rhodium/antimony co-doped TiO2 nanorod and titanate nanotube (RS-TONR/TNT) composite was prepared for removal of heavy metals and organic pollutants from water under visible light irradiation. The composite provides the dual function of simultaneous adsorption of heavy metal ions and enhanced degradation of dissolved organic compounds. Acid treatment transformed titanate nanotubes to irregular tubular structures distributed homogeneously over untransformed RS/TONRs. Synergistic removal and degradation was studied with various heavy metals, Orange (II) dye, and Bisphenol A. The adsorption capacity of the composite for heavy metal ions was Pb(II) > Cd(II) > Cu(II) > Zn(II). The adsorbed metals enhanced photocatalytic degradation of the organic pollutants, but Cu was most effective, with degradation exceeding 70% for the dye and 80% for Bisphenol A after 5 h of treatment. Photocatalytic activity was enhanced more by adsorption than photodeposition of Cu ions. A decrease in XRD rutile peak intensity with adsorbed metal indicates a change in crystallinity which may enhance photocatalytic activity. Thick and bulging nanostructures in FE-SEM images signify ion adsorption within titanate pores. BET analysis indicated titanate nanotubes with adsorbed metal are mesoporous but their tubular structure persists. XPS showed more active Cu 2p3/2 states under light, supporting an active role of Cu+ in photocatalytic ROS generation. Detection of ROS and Cu species using methanol, EDTA, pCBA, and benzoic acid probes provided strong evidence for degradation via a charge transfer mechanism. Findings demonstrate the potential of the RS-TONR/TNT composite for simultaneous removal of heavy metals and degradation of organic pollutants.

Synergistic effect of N-Ho on photocatalytic CO2 reduction for N/Ho co-doped TiO2 nanorods

The photoreduction of CO2 by using Ho and N co-doped TiO2 was explored. The doping elements can further improve the separation efficiency of photogenerated electron-hole pairs via refining grains, causing lattice distortion and adsorbing more hydroxyl radicals(·OH). We found that there exists product selectivity such that the photoreduction products of Ho/N-TiO2 mainly consist of CO and methanol, while the counterparts of pristine TiO2 are CO and methane. The possible mechanism of CO2 reduction is depicted involving the generation and combination of specific radicals. Thus, the amount of ·OH adsorbed on the surface of the catalyst makes a significant difference in the selectivity in the reduction products. Ho/N-TiO2 catalyst with the synergic effect of Ho and N showed the best photoreductive performance for CO2 with H2O to CO and CH4, and its formation rate of CH4 was 29 μmol/gcatal./hour.

A mechanism study on the photocatalytic inactivation of Salmonella typhimurium bacteria by CuxO loaded rhodium–antimony co-doped TiO2 nanorods

This study presents the first report on the photocatalytic inactivation mechanism for a Salmonella typhimurium pathogen by visible-light active CuxO loaded rhodium-antimony co-doped TiO2 nanorods (CuxO/Rh-Sb-TiO2 NRs) under visible light irradiation (cutoff filter, λ ≥ 420 nm). Remarkably higher pathogenic inactivation of 4 log within 40 min by a CuxO supported Rh-Sb-TiO2 NR photocatalyst was observed. The visible light active photocatalyst mainly produced reduced Cu+ in the lattice of CuxO by charge separation. By this means, photo-generated electrons at the conduction band of Rh-Sb-TiO2 NRs play an important role in reducing Cu2+ to Cu+ through the photocatalytic reduction reaction (PRR), and at the valence band of Rh-Sb-TiO2 NRs, photo-generated holes generate OH˙ radicals through the photocatalytic oxidation reaction (POR). This Cu+ copper species is lethal to microbial pathogens. The inactivation mechanism for the Salmonella typhimurium pathogen was investigated by protein oxidation, HCHO production, and the API-ZYM system. To investigate the role of OH˙ radicals, t-BuOH and MeOH as hole scavengers were used in photocatalytic inactivation reactions. Our experimental results confirmed that the reduced Cu+ species play a major role in bacterial inactivation, while ROS have a major effect on the degradation of organic pollutants.

Fluorine and tin co-doping synergistically improves the photoelectrochemical water oxidation performance of TiO2 nanorod arrays by enhancing the ultraviolet light conversion efficiency.

Fluorine and tin co-doped rutile TiO2 nanorod arrays are grown on fluorine-doped tin oxide substrates by a hydrothermal process and are used as photoanodes to perform photoelectrochemical water oxidation. Fluorine and tin co-doping synergistically enhances the ultraviolet light conversion efficiency of the resulting TiO2, which enables its photocurrent density of photoelectrochemical water oxidation to be more than four times that of the undoped samples. Such improvement in photoelectrochemical performance is attributed to changes in the electronic structure of the rutile TiO2 due to fluorine and tin co-doping. It is found that introducing tin into the matrix of rutile TiO2 can improve the charge separation efficiency because of the enhanced migration of photogenerated electrons from the conduction band of TiO2 to that of SnO2 that occurs at local sites, while fluorine doping can greatly reduce the recombination of the photogenerated electron-hole pairs due to the presence of the Ti3+ state that is produced to compensate for the charge difference between F- ions and O2- ions. It is envisaged that the fluorine and tin co-doped TiO2 nanorod arrays described will provide valuable platforms for wide photocatalytic applications that are not merely limited to photoelectrochemical water oxidation.

Cadmium and ytterbium Co-doped TiO2 nanorod arrays perovskite solar cells: enhancement of open circuit voltage and short circuit current density

TiO2 nanorod arrays of crystalline Cd, Y-co-doped rutile were synthesized and successfully assembled in perovskite solar cells (PSCs) as the photoanode. In this work, CH3NH3PbI3−xClx was used as the light absorber and spiro-OMeTAD as hole transport material (HTM). The synthesized TiO2 nanorod arrays were investigated by field emission-scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD) and UV–Vis diffused reflectance. FE-SEM images indicate that the co-doped TiO2 nanorod arrays were slightly sparser and shorter in length than that of un-doped ones. XRD pattern demonstrates that the as-prepared TiO2 nanorod arrays were rutile phase. The UV–Vis spectrum proves that the co-doped samples possess higher light scattering intensity than the un-doped samples, which may contribute to improve the short current density of PSCs. And the band gap of the TiO2 nanorod shows a positive shift when doped with cadmium and ytterbium. Furthermore, a negative shift in the flat-band potential (Vfb) was also observed. Finally, the device based on co-doped TiO2 nanorod arrays has improved open circuit voltage (Voc) and short circuit current density (Jsc). A higher power conversion efficiency (η) of 9.06% was obtained for the co-doped device while 8.12% for the un-doped TiO2 nanorod arrays. This paper opens a door to multi-element co-doped 1-D nanostructured materials for the improving the open circuit voltage and short circuit current density of perovskite solar cells.

Er and Mg co-doped TiO2 nanorod arrays and improvement of photovoltaic property in perovskite solar cell

Abstract Doping metal element on One-dimension (1-D) nanostructure to improve the photoelectric properties of metallic oxides has been widely studied. In this paper, Magnesium (Mg) and Erbium (Er) ions were co-doped onto TiO2 nanorod arrays (NRAs) via a facile hydrothermal method and applied in perovskite solar cells (PSCs). The synthesized Er/Mg co-doped TiO2 NRAs was investigated by field emission-scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), UV–vis diffused reflectance and electrochemical impedance spectroscopy (EIS). Er/Mg co-doped TiO2 changed the band gap, which increases the charge injection efficiency. The EIS exhibited that the Er/Mg co-doped device has a higher recombination resistance than un-doped device, which enhances the open circuit voltage (Voc) of the solar cells. Simultaneously, UV–Vis absorption reflectance spectra show that the co-doped TiO2 NRAs enhance the light capture ability via absorbing infrared light and increase the short-circuit current (Jsc). The power conversion efficiency (PCE) of Er/Mg co-doped PSC device increased from 8.26% to 9.67%, which was 17% higher than that of the un-doped device. This paper opens a door to single-element doping or multi-element co-doping 1-D nanostructured materials for the improving the utilization of solar energy and the photoelectric conversion performance of PSCs.

Active composite photocatalyst synthesized from inactive Rh & Sb doped TiO2 nanorods: Enhanced degradation of organic pollutants & antibacterial activity under visible light irradiation

In this study, rhodium-antimony co-doped TiO2 nanorods and titanate nanotube (RS-TONR/TNT) composite was hydrothermally synthesized from rhodium-antimony co-doped TiO2 nanorod (RS-TONR). Initially, RS-TONR and RS-TONR/TNT samples were photocatalytic inactive under visible light irradiation (λ≥420 nm). Catalytic performance of RS-TONR/TNT composite was improved by surface protonation and then post-calcination process. Calcination of protonated sample has transformed most titanate nanotubes of RS-TONR/TNT into anatase TiO2 nanoparticle (TNP) in the composite. This composite contains admixture of both rutile phase of TiO2 nanorods and TiO2 nanoparticle (48/RS-TONR/TNP-400). The photocatalytic activity of 48/RS-TONR/TNP-400 composite was increased for decomposition of organic compounds under visible light irradiation. In the composite structure rutile phase of TiO2 nanorods composed of rhodium-antimony co-doping is responsible for absorption of visible light irradiation and low band edge position of TNP facile the transport of conduction band charge carriers. At next step, 48/RS-TONR/TNP-400 sample was loaded with copper oxide as co-catalyst. The synergistic effect of calcination and co-catalyst was observed as Cu(3 wt%) 48/RS-TONR/TNP-400 sample showed the highest photocatalytic performance for degradation of organic pollutants. Also, Cu(3 wt%)-48/RS-TONR/TNP-400 photocatalyst was successfully applied for disinfection of both Gram-negative and Gram-positive bacterial pathogens such as E. coli, S. typhimurium and L. monocytogenes.

One-pot synthesis of sulfur and nitrogen codoped titanium dioxide nanorod arrays for superior photoelectrochemical water oxidation

Despite its abundant, nontoxicity and photochemical stability, titanium dioxide shows low solar water oxidation performance due to low photogenerated carrier transport and wide optical band gap, which results in substantially low photogenerated carrier density that impair the solar to hydrogen conversion efficiency. Herein, highly enhanced water oxidation performance of high-aspect-ratio TiO2 nanorods doped with dual heteroatoms, sulfur and nitrogen, for photoelectrochemical solar water oxidation is demonstrated. The codoped TiO2 NRs have shown enhanced optical absorption coefficient due to the induced impurities energy states near to the top of the valance band and result in a red shift in the optical absorption edges. Consequently, a 2.82 mAcm−2 photocurrent density at 1.23 V vs. RHE is obtained from the sulfur and nitrogen codoped TiO2 nanorods, and pristine TiO2 nanorods photoanode shows 0.7 mAcm−2. The applied bias photon-to-current conversion efficiency and external quantum efficiency of the codoped TiO2 nanorods are 1.49% and 97.0% at λ = 360 nm and 0.69% and 19.1% at λ = 370 nm for pristine TiO2 nanorods, respectively. Our study offers experimental and theoretical evidence for codoping of sulfur and nitrogen improve the optical and electrical properties of TiO2 for efficient photoelectrochemical solar water oxidation.

Enhanced Photocatalytic Degradation of Organic Pollutants and Inactivation of Listeria monocytogenes by Visible Light Active Rh–Sb Codoped TiO2 Nanorods

In this work, we prepared visible-light active and rhodium and antimony codoped rutile TiO2 nanorods (Rh–Sb:TiO2 NR) for the degradation of organic pollutants and inactivation of microbial pathogens. The Rh–Sb:TiO2 NR sample showed a shift in the absorption band in the visible light region (650 nm). Initially, photocatalytic activity of the Rh–Sb:TiO2 NR was hindered due to its poor surface properties. To improve the surface quality of the less active Rh–Sb:TiO2 NR photocatalyst, the effect of the acid treatment and CuxO impregnation on the Rh–Sb:TiO2 NR were evaluated (CuxO/A–Rh-Sb:TiO2 NR). The photocatalytic activity of the CuxO/A–Rh-Sb:TiO2 NR photocatalyst was remarkably higher than that of the as-prepared sample. The improved photocatalytic activity of less active Rh–Sb:TiO2 NR is due to the synergistic effect of acid treatment and finely dispersed CuxO nanoparticles which improve the charge transfer near the interface of the A–Rh-Sb:TiO2 NR photocatalyst toward CuxO nanoparticles. Deconvolution of ...

Efficient photocatalytic hydrogen production over Rh and Nb codoped TiO2 nanorods

It is important to tune the electronic structure of TiO2 to harvest solar light for efficient photocatalytic hydrogen production. As a widely used approach, doping enables TiO2 to respond to visible light, but generally does little to improve the photocatalytic performance because of the serious charge recombination. In this work, (Rh, Nb) codoped TiO2 nanorods (with Ti0.996Nb0.002Rh0.002O2 as an example) are found to be capable for both obvious absorption of visible light and efficient separation of photogenerated carriers. Consequently, this photocatalyst displays ultra-high activity for hydrogen production under the irradiation of either UV or visible light. The hydrogen evolution rate under simulated sunlight is as high as 7.85 mmol g−1 h−1 in methanol solution and 0.99 mmol g−1 h−1 in pure water, far higher than that for pristine TiO2 nanorods and Pt-loaded P25, respectively. This study demonstrates that Rh/Nb codoping is a promising strategy for enhancing the photocatalytic efficiency of TiO2.

1-D and 2-D morphology of metal cation co-doped (Zn, Mn) TiO2 and investigation of their photocatalytic activity

Abstract Morphology and electronic bandgap of titania (TiO2) are considered to be the primary factors for determining the photocatalytic efficiency, as they determine the number of active sites for the photocatalytic reactions. In the present study, two different morphologies of TiO2 (nanosphere and nanorod) with varying Zn and Mn co-doping were synthesized by solvothermal and hydrothermal methods to examine their photocatalytic efficiency by methylene blue degradation. The co-doped photocatalysts were characterized by XRD, XPS, SEM, TEM, Raman, FTIR and UV–vis DRS. Further, a comparison has been made with co-doped TiO2 nanospheres and TiO2 nanorods, where Zn, Mn co-doped TiO2 nanorods show higher photocatalytic activity compared to nanospheres. This higher photocatalytic activity of co-doped TiO2 is attributed to its polymorphic phases, as they act as heterojunctions for TiO2. Further, being 1-D nanostructure, the TiO2 nanorods exhibit the straight diffusion path for charge carriers, which reduces the recombination possibilities. The obtained results suggest that the photocatalysis efficiency of TiO2 can be significantly enhanced by tailoring the shape and co-doping concentration, which enforce a new concept for developing the new nanostructures of TiO2.

Enhanced Photovoltaic Performance of Perovskite Solar Cells Based on Er-Yb Co-doped TiO2 Nanorod Arrays

In the present study, Er and Yb co-doped TiO2 (Er-Yb:TiO2) nanorod arrays were grown with a hydrothermal method, and perovskite solar cells were fabricated using them as an electron transfer material. The photovoltaic performance of the solar cells based on Er-Yb:TiO2 was enhanced compared with that of solar cells based on un-doped TiO2. The power conversion efficiency of the solar cells on Er-Yb:TiO2 increased to 13.4%, which is 20.8% higher than that of the solar cells based on un-doped TiO2. The experimental results indicate that the larger open circuit voltage could be due to the larger conduction band difference between Er-Yb:TiO2 and perovskite material. The enlarged short circuit current could be attributed to the faster electron transfer, reduced recombination, and the upconversion of Er-Yb:TiO2 NRs.

C, N and S codoped rutile TiO2 nanorods for enhanced visible-light photocatalytic activity

A highly efficient visible-light-driven photocatalyst, carbon, nitrogen and sulfur codoped rutile TiO2 nanorods, was synthesized by our proposed two-step hydrothermal method. For comparison, carbon, nitrogen and sulfur codoped anatase TiO2 nanoparticles were also synthesized. The formation of rutile CNS-TiO2 nanorods and anatase CNS-TiO2 nanoparticles were confirmed by the results from X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy characterization. Photocatalytic tests showed that rutile CNS-TiO2 nanorods had much higher visible-light-driven photocatalytic activity in degrading Rhodamine B, as compared with anatase CNS-TiO2 nanoparticles. The superior photocatalytic performance of rutile CNS-TiO2 nanorods was likely attributed to the nanorod structure, which is favorable for the effective separation of photogenerated electrons and holes.

Phosphate modified N/Si co-doped rutile TiO2 nanorods for photoelectrochemical water oxidation

Surface modification of TiO2 film provides possibilities to improve photoelectrochemical (PEC) activity. In this study, we report on phosphate modified N/Si co-doped TiO2 nanorods films (Pi-N/Si-TiO2 NRs) for PEC water oxidation. Compared to the pristine TiO2 NRs, the Pi-N/Si-TiO2 NRs photoanode shows a 4.65-fold enhanced photocurrent density (1.44mAcm−2) under light illumination. This significant improvement can be attributed to the synergistic effect of phosphate modification and the N and Si co-dopants. In addition to the improvement of ultraviolet and visible light response by N and Si co-dopants, phosphate modification is mainly responsible for charge transfer at the interface of the photoanode/electrolyte.

Magnetic properties of Sm-doped rutile TiO2 nanorods

Sm-doped TiO2 nanorods are synthesized by a molten salt method. The expansion of lattice parameters of Sm-doped TiO2 samples verified by XRD and TEM characterizations suggests the successful incorporation of Sm ions into TiO2 matrix. M-H loops show weak room temperature ferromagnetism in Sm-doped samples. Sm and N co-doped TiO2 nanorods are also prepared to study the magnetic behaviour. The results indicate that the co-doping does not enhance the room temperature ferromagnetism but leading to a strong paramagnetic signal at 5 K.

Doping concentration dependence of microstructure and magnetic behaviours in Co-doped TiO2 nanorods.

Co-doped titanium dioxide (TiO2) nanorods with different doping concentrations were fabricated by a molten salt method. It is found that the morphology of TiO2 changes from nanorods to nanoparticles with increasing doping concentration. The mechanism for the structure and phase evolution is investigated in detail. Undoped TiO2 nanorods show strong ferromagnetism at room temperature, whereas incorporating of Co deteriorates the ferromagnetic ordering. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) results demonstrate that the ferromagnetism is associated with Ti vacancy.