Structural Insight on Defect-Rich Tin Oxide for Smart Band Alignment Engineering and Tunable Visible-Light-Driven Hydrogen Evolution.

Herein, a series of defect-rich tin oxides, SnxOy, were synthesized with tunable Sn2+/Sn4+ composition ratio and defect chemistry, aiming to explore the impact of local structural modulation, non-stoichiometric chemistry, and defective center on the modulation of band gap values, band edge potential positions, and photocatalytic hydrogen evolution performance. The phase structure, morphology, surface component, and photoelectric properties were analyzed by multiple testing methods. The modulation of the Sn2+/Sn4+ molar ratio was analyzed by X-ray photoelectron spectroscopy and the spectra of Mossbauer and electron spin resonance, which indicated the existence of interstitial tin and oxygen vacancy, predicting a highly disordered local structure. In addition, the photocatalytic activity was evaluated by water splitting for hydrogen production under visible light. The optimal photocatalytic activity toward H2 production rate reached 58.6 µmol·g-1·h-1 under visible light illumination. However, the photocatalytic activity gradually decreased with an increase of synthetic temperature. Much higher Sn2+/Sn4+ molar ratio in the present defective tin oxide gave rise to more negative band edge potentials for hydrogen production. Meanwhile, the driving force was decreased with the diminished Sn2+. Large amounts of hydroxyl groups, Sn2+, and relatively negative potential of conduction band in non-stoichiometric SnxOy play critical roles in visible light harvesting and photocatalytic water splitting. Furthermore, the relationships among crystal structure, electronic properties, and photocatalytic activities were clarified by theoretical calculation. This work provides a novel strategy for the development of highly efficient photocatalytst by regulating the internal electronic structure and surface defects.

Towards Long-Term Photostability of Nickel Hydroxide/BiVO4 Photoanodes for Oxygen Evolution Catalysts via In†Situ Catalyst Tuning.

Increasing long-term photostability of BiVO4 photoelectrode is an important issue for solar water splitting. The NiOOH oxygen evolution catalyst (OEC) has fast water oxidation kinetics compared to the FeOOH OEC. However, it generally shows a lower photoresponse and poor stability because of the more substantial interface recombination at the NiOOH/BiVO4 junction. Herein, we utilize a plasma etching approach to reduce both interface/surface recombination at NiOOH/BiVO4 and NiOOH/electrolyte junctions. Further, adding Fe2+ into the borate buffer electrolyte alleviates the active but unstable character of etched-NiOOH/BiVO4 , leading to an outstanding oxygen evolution over 200 h. The improved charge transfer and photostability can be attributed to the active defects and a mixture of NiOOH/NiO/Ni in OEC induced by plasma etching. Metallic Ni acts as the ion source for the in situ generation of the NiFe OEC over long-term durability.

Structure and Optimum Luminescence for Nearly Block-Like LaOCl:Eu3+ Nanoparticles.

In this work, we report a simple method for the synthesis of block-like Eu3+ doping LaOCl nanophosphors with different doping content. It was found that the average grain diameter of Eu3+ doping LaOCl samples decreased with increasing Eu3+ doping concentration. The lattice volume shrinked due to different response for different axial under high pressure that led to lower lattice symmetry of LaOCl:Eu3+. The emission of LaOCI:Eu3+ increased with the increasing Eu3+ concentration due to the lower local symmetry, which also led to a gradual reduction in lifetime.

Enhanced luminescence of CaWO4:Eu3+ loaded in SBA-16.

CaWO4:Eu3+/SBA-16 composites with various molar ratios of Eu3+ to CaWO4(x) were successfully synthesized by impregnation and subsequent hydrothermal treatment. The physicochemical properties of the resultant composites were well characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR) and luminescence spectra. The results demonstrated that the resultant CaWO4:Eu3+/SBA-16 composites still had ordered mesostructure, i.e., the loading of CaWO4:Eu3+ has little impact on the uniform mesostructure of the host matrix SBA-16, but just reduced the specific surface area and pore volume of the host matrix. Furthermore, the CaWO4:Eu3+/SBA-16 composites with various x showed enhanced luminescent properties than the pure CaWO4:Eu3+ counterparts, and reached the highest luminescence intensity when x was 3%.

Microwave-assisted synthesis and luminescence properties of Cd(1-x)Eu(x)MoO4 red phosphor.

Cd(1-x)Eu(x)MoO4 nanoparticles were prepared by a microwave-assisted method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectra were used to characterize the structures, morphologies and the luminescent properties of as-prepared products. Emission and excitation spectra showed that the phosphor exhibits a dominant red emission at 612 nm with excitation wavelength of 330 nm at room temperature. The optimized concentration of Eu3+ is 5 mol.% for the highest emission intensity at 612 nm. The concentration quenching mechanism can be interpreted by the nearest-neighbor ions interaction of Eu3+ ions. It is found that Eu3+ concentration has great impact on the luminescent intensity which is attributed to the variation of the local symmetry. The red emission is visible to naked eyes, indicating that CdMoO4 may act as a promising host material for Eu3+ doped red phosphors.

Facile synthesis and enhanced near infrared luminescent properties of CaWO4:Ln3+/Na+ (Ln = Nd, Er, and Yb) core/shell microstructure.

In this work, we reported the fabrication and characterization of CaWO4:Ln3+/Na+ (Ln = Nd, Er, and Yb) core/shell microspheres via a facile hydrothermal method in the presence of citric acid and PVP. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectra, and photoluminescence. It's found that citric acid could modulate the nucleation and growth of CaWO4 nanocrystals and enable the co-incorporation of Na+ and Ln3+ (Ln = Nd, Er, and Yb) into CaWO4 lattice. Meanwhile, PVP controlled the assembly of CaWO4 nanocrystals into a core/shell spherical structure. All CaWO4:Ln3+/Na+ (Ln = Nd, Er, and Yb) core/shell microspheres exhibited intense near-IR luminescence. In comparison with CaWO4:Ln3+/Na+ nanocrystals, the self-assembled core/shell nanoarchitechtures showed highly enhanced IR luminescent properties due to the depressing of surface energy-loss.

An oxygen vacancy-modulated bifunctional S-NiMoO4 electrocatalyst for efficient alkaline overall water splitting.

S-doped nickel molybdate nanorods grown on nickel foam (S-NiMoO4/NF) were fabricated by a two-step hydrothermal method. The resultant S-NiMoO4/NF exhibited remarkable bifunctional electrocatalytic activity, with overpotentials of 235 mV for the hydrogen evolution reaction and 150 mV for the oxygen evolution reaction at a current density of 50 mA cm-2. Assembled into the two-electrode S-NiMoO4/NF electrolyzer in alkaline electrolytes for overall water splitting, it required only low cell voltages of 1.55 V and 1.63 V to drive 50 mA cm-2 and 100 mA cm-2, respectively. No significant performance degradation occurred during the water electrolysis process. The experimental results confirmed that S-doping induced the increase of the oxygen vacancies, accelerating the reaction kinetics and thus improving the electrocatalytic performance. Meanwhile, more active sites exposure on the surface of S-NiMoO4/NF enhanced the reactivity. This work may guide the development of efficient bifunctional catalysts in alkaline electrolysis through oxygen vacancy regulation.

Unexpected catalytic performance in silent tantalum oxide through nitridation and defect chemistry.

This work reports on the preparation of a noble-metal-free and highly active catalyst that proved to be an efficient and green reductant with renewable capacity. Nitridation of a silent Ta1.1O1.05 substrate led to the formation of a series of TaOxNy hollow nanocrystals that exhibited outstanding activity toward catalytic reduction of nitrobenzenes under ambient conditions. ESR and XPS results indicated that defective nitrogen species and oxygen vacancies at the surfaces of the TaOxNy nanocrystals may play synergetic roles in the reduction of nitrobenzenes. The underlying mechanism is completely different from those previously reported for metallic nanoparticles. This work may provide new possibilities for the development of novel defect-meditated catalytic systems and offer a strategy for tuning any catalysts from silent to highly reactive by carefully tailoring the chemical composition and surface defect chemistry.

Hydrothermal preparation of copper doped NaTaO3 nanoparticles and study on the photocatalytic mechanism.

Effects of copper cations doping into wide band gap semiconductor photocatalysts of tantalate on morphology, visible light response, and photocatalytic performance were studied. A series of Cu-doped NaTaO3 catalysts were prepared by hydrothermal method. XRD and XPS results suggested that copper were successfully doped into the NaTaO3 nanocrystal in the Cu2+ state. TEM studies showed the formation of the cube shape nanoparticles of NaTaO3 as well as Cu-doped NaTaO3. UV-Vis diffuse reflectance spectra clearly indicated the red-shift in the series of copper doped NaTaO3 catalysts, resulting in a decrease in the band gap of NaTaO3. The trend of red shift was increased with an increase of copper doping concentration, whereas the photo-degradation methylene blue (MB) is not improved by the doping of copper ions. The simulation of energy band structure by density functional theory unfolded that the substitution of Ta5+ ions by Cu2+ ions results in forming an intermediate band (IB) upper the top of the valence band (VB), which is mainly attributed to the state of Cu 3d. The intermediate band is responsible for the red-shift caused by the doping of Cu ions. Meanwhile Cu species can become the recombination centers of photoinduced electrons and holes. Thus, the quickly recombination of e(-)h(+) pairs is one of the most significant factors which deteriorate the photoactivity of Cu-doped NaTaO3.

Intercalation of Well-Dispersed Fe2 O3 with SnO2 toward Durable Peroxymonosulfate Activation to Eliminate Antibiotics: Performance and Mechanism.

Sustainable Fe2 O3 /SnO2 with fine interfacial feature derived from FeSnO(OH)5 was prepared and employed for elimination contaminants. The synergistic effect between Fe2 O3 and SnO2 endowed a remarkable degradation performance for tetracycline degradation. Well dispersed SnO2 can function as fine protective layer to enhance the anchoring of iron ions. In addition, SnO2 with excellent conductivity can accelerate electron transfer on the surface of Fe2 O3 , further activation PMS. Approximately 89.3% of tetracycline (TC) was removed in Fe2 O3 /SnO2 /PMS system, which was higher than alone Fe2 O3 /PMS (73.2%) and SnO2 /PMS (39.7%) systems. The operating parameters were evaluated and studied. Electron paramagnetic resonance (EPR) and quenching tests manifested that 1 O2 was primary active specie, and ⋅OH, ⋅SO4 - and ⋅O2 - were participated in the degradation process. Besides, degradation pathways were proposed by identifying the intermediate products. This work is expected to offer a potential design for construction eco-friendly heterogeneous catalyst toward wastewater treatment.

Construction of novel photocatalysts for efficient hydrogen evolution: The key role of natural halloysite nanotubes.

Hydrogen (H2) evolution by photocatalytic water splitting is a potential strategy to solve worldwide energy shortage. Sulfide nanocatalysts showed great potential for H2 evolution, but suffered from low charge separation efficiency and easy agglomeration. In this work, ZnIn2S4 (ZIS) nanoflowers were anchored onto the surface of halloysite nanotubes (HNTs) modified by ethylenediaminetetraacetic acid (EDTA). Photocatalyst 3ZnIn2S4-HNTs/EDTA3 (3ZIS-HNTs/E3) displayed the optimum H2 evolution rate of 10.4 mmol·g-1·h-1, being 3.4 times as that of the original ZIS. Moreover, 3ZIS-HNTs/E3 presented satisfied property in the photocatalytic hydrogenation reaction of 4-nitrophenol to produce 4-aminophenol. HNTs as substrates not only hindered the growth and agglomeration of ZIS, but also induced more S vacancies in ZIS. The production of Schottky junctions between ZIS and Pt, the high utilization of light energy in tubular HNTs, and the trapping effect of EDTA for photogenerated h+ were all favorable for enhancing the catalytic property. The density functional theory (DFT) calculations showed that 3ZIS-HNTs/E3 with more S vacancies had the lowest adsorption energy and the most appropriate ΔGH* for H* to enhance the H2 evolution efficiency, which was consistent with the experimental catalytic results. This study contributes a novel thought for synthesizing composites on the basis of natural minerals for taking part in and enhancing the catalytic performance.

Toward the Long-Term Stability of Cobalt Benzoate Confined Highly Dispersed PtCo Alloy Supported on a Nitrogen-Doped Carbon Nanosheet/Fe3C Nanoparticle Hybrid as a Multifunctional Catalyst for Zinc-Air Batteries.

This work reports a new type of platinum-based heterostructural electrode catalyst that highly dispersed PtCo alloy nanoparticles (NPs) confined in cobalt benzoate (Co-BA) nanowires are supported on a nitrogen-doped ultra-thin carbon nanosheet/Fe3C hybrid (PtCo@Co-BA-Fe3C/NC) to show high electrochemical activity and long-term stability. One-dimensional Co-BA nanowires could alleviate the shedding and agglomeration of PtCo alloy NPs during the reaction so as to achieve satisfactory long-term durability. Moreover, the synergistic effect at the interface optimizes the surface electronic structure and prominently accelerates the electrochemical kinetics. The oxygen reduction reaction half-wave potential is 0.923 V, and the oxygen evolution reaction under the condition of 10 mA•cm-2 is 1.48 V. Higher power density (263.12 mW•cm-2), narrowed voltage gap (0.49 V), and specific capacity (808.5 mAh•g-1) for PtCo@Co-BA-Fe3C/NC in Zn-air batteries are achieved with long-term cycling measurements over 776 h, which is obviously better than the Pt/C + RuO2 catalyst. The interfacial electronic interaction of PtCo@Co-BA-Fe3C/NC is investigated, which can accelerate electron transfer from Fe to Pt. Density functional theory calculations also indicate that the interfacial potential regulates the binding energies of the intermediates to achieve the best performance.

N, S codoped carbon matrix-encapsulated CoFe/Co0.2Fe0.8S heterostructure as a highly efficient and durable bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries.

The realization of durable and efficient oxygen evolution reactions (OER) at large current densities and low overpotentials is of significant importance but remains a great challenge. In this study, a CoFe/Co0.2Fe0.8S@NS-CNTs/CC (CF/CFS@NS-CNTs/CC) heterogeneous structure was fabricated by isolating CoFe/Co0.2Fe0.8S (CF/CFS) particles locked in nitrogen/sulfur codoped carbon nanotubes (NS-CNTs). Appreciable oxygen evolution reaction activity and durability was achieved with an ultralow overpotential of 110 mV at 10 mA•cm-2. The operation was stable for 300 h at a current density of 500 mA•cm-2. The structure was then assembled into a zinc-air battery (ZAB), which delivered a high power density of 194 mW•cm-2, a specific capacity of 837.3 mAh•gZn-1, and stable operation for 788 h without obvious voltage attenuation and altered morphology. The electronic interactions were studied by X-ray photoelectron spectroscopy (XPS), which revealed that both the bimetal components and the synergistic effect at the interface stimulated the transfer of Co and Fe sites to higher chemical valence states. Theoretical calculations indicated that the synergistic effect of the bimetal components, build-in interfacial potential, and surface chemical reconstruction adjusted the Fermi level to optimize the thermodynamic formation of O* to OOH*, thus enhancing the intrinsic activity.

Adsorbent biochar derived from corn stalk core for highly efficient removal of bisphenol A.

Environmental-friendly biochar (BC) with low cost was obtained by simple pyrolysis of corn stalk core, which was employed as an adsorbent for efficiently removing organic pollutants in water. The physicochemical properties of BCs were characterized by various techniques, including X-ray diffractometer (XRD), Fourier transforms infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometer (XPS), Raman, Thermogravimetric (TGA), N2 adsorption-desorption and zeta potential tests. The influence of pyrolysis temperature on the structure and adsorption efficiency of the adsorbent was emphasized. The graphitization degree and sp2 carbon content of BCs were enhanced by increasing the pyrolysis temperature, which was favorable for the enhancement of the adsorption efficiency. The adsorption results showed that corn stalk core calcined at 900 °C (BC-900) displayed exceptional adsorption efficiency toward bisphenol A (BPA) in wide pH (1-13) and temperature (0-90 °C) ranges. Moreover, adsorbent BC-900 could adsorb various pollutants from water, including antibiotics, organic dyes, and phenol (50 mg·L-1). The adsorption process of BPA over BC-900 matched well with the Langmuir isotherm and pseudo-second-order kinetic model. Mechanism investigation suggested that large specific surface area and pore filling acted the foremost role in the adsorption process. Adsorbent BC-900 has the potential application in wastewater treatment due to its simple preparation, low cost, and excellent adsorption efficiency.

Alkali functionalized carbon nitride with internal van der Waals heterostructures: Directional charge flow to enhance photocatalytic hydrogen production.

Improving the charge separation and migration in graphitic carbon nitride (CN) is the critical issue to enhance its photocatalytic performance, but still remains very challenging. Herein, the alkali metals were introduced into the interlayer and intralayer of CN to tackle this challenge. The lithium sodium-modifying carbon nitride layer (LiNaCN2) and the adjacent CN layer formed a van der Waals heterostructures (VDWHs), while the potassium-intercalating served as interlayer charge transfer channels to induce the directional charge flow. Experiments and theoretical calculations indicated that such unique construction provided intrinsic driving force to obtain the electrons from LiNaCN2 to CN via directional potassium channels. In accordance with the theoretical prediction, a dramatically red-shift of the light absorption feature was achieved for interlayer potassium-intercalating and intralayer lithium sodium-modifying co-functionalized carbon nitride (LiNaCN-K-CN2) to show narrowed bandgap energy of 2.15 eV. This directional charge flow in CN resulted in the rapid transfer of charge carriers in both interlayer as well as intralayer of CN, which reduced the electronic localization as well as extended the π conjugative effect. Consequently, the LiNaCN-K-CN2 displayed stable and remarkable hydrogen production rate of about 2.46 mmol g-1 h-1 with apparent quantum yield (AQY) of about 13.68% at 435 nm, which was 22 folds higher than that of the pristine CN. This finding provides the feasible strategy to precisely tune the directions of charge transfer for high-performance CN-based photocatalysts.

Photoelectrocatalytic peroxymonosulfate activation over CoFe2O4-BiVO4 photoanode for environmental purification: Unveiling of multi-active sites, interfacial engineering and degradation pathways.

This work reported on the development of CoFe2O4-BiVO4 photoanode based photoelectrocatalytic system collaborating with peroxymonosulfate activation for organic contaminants removal. CoFe2O4 layer not only provided active sites for direct peroxymonosulfate activation but also accelerated charge separation process for the enhancement of photocurrent density and photoelectrocatalytic performance. Junction of CoFe2O4 layer on BiVO4 photoanode led to the improvement of photocurrent density to 4.43 mA/cm2 at 1.23 VRHE, which was approximately 4.06 times higher than that of pure BiVO4. Subsequently, the corresponding optimal degradation efficiency toward the tetracycline model contaminant achieved to be 89.1% with total organic carbon removal value of about 43.7% within 60 min. Moreover, the degradation rate constant of CoFe2O4-BiVO4 photoanode in photoelectrocatalytic system was 0.037 min-1, which was about 1.23, 2.64 and 3.70 times higher than the values in photocatalysis, electrocatalysis and PMS only based systems, respectively. In addition, radical scavenging experiments and electron spin resonance spectra indicated a synergy of radical and nonradical coupling process where •OH and 1O2 played vital roles during tetracycline degradation. Plausible photoelectrocatalytic mechanism and degradation pathway were proposed. This work provided an effective strategy to construct peroxymonosulfate assisted photoelectrocatalytic system toward green environmental applications.

Durable and eco-friendly peroxymonosulfate activation over cobalt/tin oxides-based heterostructures for antibiotics removal: Insight to mechanism, degradation pathway.

Potential leaching of Co ions could decrease the catalytic activity and cause secondary pollution of water, thereby threatening ecological safety and human health. In response, the in-situ generation of well-dispersed Co2SnO4 and SnO2 with fine interfacial feature was constructed for PMS activation toward efficient tetracycline degradation and lower cobalt ion leaching feature. The synergistic effect of Co2SnO4 and SnO2 endowed Co2SnO4-SnO2 an outstanding catalytic performance for tetracycline degradation in alkaline condition. Meanwhile, the catalysts can effectively degrade the quinolones, dyes and mixture pollutant solution. The excellent performance can attributed to the in-situ introduction of SnO2, which stabilizes the microstructure and provides an effective electronic pathway to enhance the activity of Co2SnO4 in the Co2SnO4-SnO2. In optimized condition, the tetracycline degradation efficiency was enhanced to 94.9% within 20 min and maintained the stability at least four cycles. The degradation rate constant of Co2SnO4-SnO2 was 0.149 min-1, which was about 1.93, 2.98, 11.5 times higher than of Co2SnO4, Co3O4 and SnO2, respectively. Notably, the leaching performance of Co2SnO4-SnO2 was greatly suppressed to be 7.45 ug/L, which was lower than that of Co2SnO4 (6.41 mg/L) and Co3O4 (1.12 mg/L). Radical quenching and EPR experiments showed that singlet oxygen (1O2), rather than hydroxyl active species and sulfate radicals, played a predominating role for PMS activation in the Co2SnO4-SnO2/PMS system. The intermediates and degradation routes for tetracycline degradation were characterized by liquid chromatograph-tandem mass spectrometry. This study expected to provide a novel strategy to construct heterostructural catalysts with lower cobalt ion leaching for the activation of PMS.

Junction of ZnmIn2S3+m and bismuth vanadate as Z-scheme photocatalyst for enhanced hydrogen evolution activity: The role of interfacial interactions.

A series of ZnmIn2S3+m photocatalysts were synthesized to show tunable band gap energy with the variation of Zn/S atomic ratio. The junction of ZnmIn2S3+m and BiVO4 led to intimate interfacial contacts. Both experimental and theoretical results implied that electrons flowed from ZnmIn2S3+m to BiVO4 at the ZnmIn2S3+m/BiVO4 interface to form built-in electric field due to the variation of Fermi level, which promised Z scheme charge transfer feature for improving separation of charge carriers for enhanced photocatalytic performance. A higher degree of charge transfer process occurred for Zn2In2S5/BiVO4 heterostructure promised stronger built-in electric field, higher charge separation efficiency and improved photocatalytic activity in comparison to ZnIn2S4/BiVO4 and Zn3In2S6/BiVO4 heterojunctions. The optimal hydrogen production rate of Zn2In2S5/BiVO4 photocatalyst is 8.42 mmol•g-1•h-1 with apparent quantum yield of 22.32 % at 435 nm, which is about 2.2 and 1.5 times higher than that of ZnIn2S4/BiVO4 and Zn3In2S6/BiVO4, respectively.

Metastable monoclinic ZnMoO4: hydrothermal synthesis, optical properties and photocatalytic performance.

Metastable monoclinic ZnMoO4 was successfully synthesized via a hydrothermal route with variation of reaction temperatures and time at pH value of 5.7. Systematic sample characterizations were carried out, including X-ray powder diffraction, scanning electron microscopy, Fourier transformed infrared spectra, UV-visible diffuse reflectance spectra, and photoluminescence spectra. The results show that all as-prepared ZnMoO4 samples were demonstrated to crystallize in a pure-phase of monoclinic wolframite structure. All samples were formed in plate-like morphology. Six IR active vibrational bands were observed in the wave number range of 400-900 cm(-1). The band gap of as-prepared ZnMoO4 was estimated to be 2.86 eV by Tauc equation. Photoluminescence measurement indicates that as-prepared ZnMoO4 exhibits a broad blue-green emission under excitation wavelength of 280 nm at room temperature. Photocatalytic activity of as-prepared ZnMoO4 was examined by monitoring the degradation of methyl orange dye in an aqueous solution under UV radiation of 365 nm. The as-prepared ZnMoO4 obtained at 180 degrees C for 40 h showed the best photocatalytic activity with completing degradation of MO in irradiation time of 120 min. Consequently, monoclinic ZnMoO4 proved to be an efficient near visible light photocatalyst.

Preparation and photocatalytic performance of iodine-doped NaTaO3 nanoparticles.

Iodine-doped NaTaO3 nanoparticles were prepared by hydrothermal conditions and explored as the visible-light-driven photocatalysts for photodegradation of methylene blue in water. It is found that I-doped NaTaO3 showed photodegradation efficiency superior over the un-doped NaTaO3. UV-Vis diffuse reflectance spectra indicate that the absorption edges shifted towards longer wavelength with increasing the iodine concentration. The energy band structure and the transient behavior of the photogenerated charge carriers for both un-doped and doped NaTaO3 powders were investigated using density functional theory. The improved photocatalytic activity under visible light for I-doped NaTaO3 may be caused by both the broadening of valence band that inhibited the recombination of e-h+ pairs and the narrowing of energy band gap due to the much negative energy levels in the bottom of conduction bands.