CO_(2)capture costs of chemical looping combustion of biomass:A comparison of natural and synthetic oxygen carrier

Chemical looping combustion has the potential to be an efficient and low-cost technology capable of contributing to the reduction of the atmospheric concentration of CO_(2) in order to reach the 1.5/2°C goal and mitigate climate change.In this process,a metal oxide is used as oxygen carrier in a dual fluidized bed to generate clean CO_(2) via combustion of biomass.Most commonly,natural ores or synthetic materials are used as oxygen carrier whereas both must meet special requirements for the conversion of solid fuels.Synthetic oxygen carriers are characterized by higher reactivity at the expense of higher costs versus the lower-cost natural ores.To determine the viability of both possibilities,a techno-economic comparison of a synthetic material based on manganese,iron,and copper to the natural ore ilmenite was conducted.The synthetic oxygen carrier was characterized and tested in a pilot plant,where high combustion efficiencies up to 98.4%and carbon capture rates up to 98.5%were reached.The techno-economic assessment resulted in CO_(2) capture costs of 75 and 40€/tCO_(2) for the synthetic and natural ore route respectively,whereas a sensitivity analysis showed the high impact of production costs and attrition rates of the synthetic material.The synthetic oxygen carrier could break even with the natural ore in case of lower production costs and attrition rates,which could be reached by adapting the production process and recycling material.By comparison to state-of-the-art technologies,it is demonstrated that both routes are viable and the capture cost of CO_(2) could be reduced by implementing the chemical looping combustion technology.

Chemical looping oxidative propane dehydrogenation controlled by oxygen bulk diffusion over FeVO_(4)oxygen carrier pellets

The oxygen distribution and evolution within the oxygen carrier exert significant influence on chemical looping processes.This paper describes the influence of oxygen bulk diffusion within FeVO4 oxygen carrier pellets on the chemical looping oxidative propane dehydrogenation(CL-ODH).During CL-ODH,the oxygen concentration at the pellet surface initially decreased and then maintained stable before the final decrease.At the stage with the stable surface oxygen concentration,the reaction showed a stable C3H6 formation rate and high C3H6 selectivity.Therefore,based on Fick’s second law,the oxygen distribution and evolution in the oxygen carrier at this stage were further analyzed.It was found that main reactions of selective oxidation and over-oxidation were controlled by the oxygen bulk diffusion.C3H8 conversion rate kept decreasing during this stage due to the decrease of the oxygen flux caused by the decline of oxygen gradient within the oxygen carrier,while C3H6 selectivity increased due to the decrease of overoxidation.In addition,reaction rates could increase with the propane partial pressure due to the increase of the oxygen gradient within the oxygen carrier until the bulk transfer reached its limit at higher propane partial pressure.This study provides fundamental insights for the diffusion-controlled chemical looping reactions.

Application of Fe_2O_3/Al_2O_3 Composite Particles as Oxygen Carrier of Chemical Looping Combustion

Chemical looping combustion （CLC） of carbonaceous compounds has been proposed, in the past decade, as an efficient method for CO2 capture without cost of extra energy penalties. The technique involves the use of a metal oxide as an oxygen carrier that transfers oxygen from combustion air to fuels. The combustion is carried out in a two-step process： in the fuel reactor, the fuel is oxidized by a metal oxide, and in the air reactor, the reduced metal is oxidized back to the original phase. The use of iron oxide as an oxygen carrier has been investigated in this article. Particles composed of 80 wt% Fe2O3, together with Al2O3 as binder, have been prepared by impregnation methods. X-ray diffraction （XRD） analysis reveals that Fe2O3 does not interact with the Al2O3 binder after multi-cycles. The reactivity of the oxygen carrier particles has been studied in twenty-cycle reduction-oxidation tests in a thermal gravimetrical analysis （TGA） reactor. The components in the outlet gas have been analyzed. It has been observed that about 85% of CH4 converted to CO2 and H2O during most of the reduction periods. The oxygen carrier has kept quite a high reactivity in the twenty-cycle reactions. In the first twenty reaction cycles, the reaction rates became slightly higher with the number of cyclic reactions increasing, which was confirmed by the scanning electron microscopy （SEM） test results. The SEM analysis revealed that the pore size inside the particle had been enlarged by the thermal stress during the reaction, which was favorable for diffusion of the gaseous reactants into the particles. The experimental results suggested that the Fe2O3/Al2O3 oxygen carrier was a promising candidate for a CLC system.

Comparison of LaFeO_3,La_(0.8)Sr_(0.2)FeO_3,and La_(0.8)Sr_(0.2)Fe_(0.9)CO_(0.1)O_3 perovskite oxides as oxygen carrier for partial oxidation of methane

Comparison of LaFeO3, La0.8Sr0.2FeO3, and La0.8Sr0.2Fe0.9CO0.1O3 perovskite oxides as oxygen carrier for partial oxidation of methane in the absence of gaseous oxygen was investigated by continuous flow reaction and sequential redox reaction, Methane was oxidized to syngas with high selectivity by oxygen species of perovskite oxides in the absence of gaseous oxygen. The sequential redox reaction revealed that the structural stability and continuous oxygen supply in redox reaction decreased over La0.8Sr0.2Fe0.9Co0. 1O3 oxide, while LaFeO3 and La0.8Sr0.2FeO3 exhibited excellent structural stability and continuous oxygen supply.

Chemical looping catalytic gasification of biomass over active LaNixFe1-xO_(3)perovskites as functional oxygen carriers

Oxygen carriers(OCs)with perovskite structure are attracting increasing interests due to their redox tunability by introducing various dopants in the structure.In this study,LaNixFe1-xO3(x=0,0.1,0.3,0.5,0.7,1.0)perovskite OCs have been prepared by a citric acid–nitrate sol–gel method,characterized by means of X-ray diffraction(XRD)analysis and tested for algae chemical looping gasification in a fixed bed reactor.The effects of perovskite types,OC/biomass mass ratio(O/B),gasification temperature and water injection rate on the gasification performance were investigated.Lower Ni-doped(0≤x≤0.5)perovskites crystalized in the rhombohedra system which was isostructural with LaNiO3,while those with composition 0.5≤x≤1 crystalized in the orthorhombic system.Despite the high reactivity for LaNiO_(3),LaNi_(0.5)Fe_(0.5)O_(3)(LN5F5)was found to be more stable at a high temperature and give almost as good results as LaNiO_(3)in the formation of syngas.The relatively higher syngas yield of 0.833 m^(3)·kg^(-1) biomass was obtained under the O/B of 0.4,water injection rate of 0.3 ml·min^(-1) and gasification temperature at 850C.Continuous high yield of syngas was achieved during the first 5 redox cycles,while a slight decrease in the reactivity for LN5F5 after 5 cycles was observed due to the adhesion of small grains occurring on the surface of OCs.However,an obvious improvement in the gasification performance was attained for LN5F5 compared to raw biomass direct gasification,indicating that LN5F5 is a promising functional OC for chemical looping catalytic gasification of biomass.

Efficient CO2 to CO conversion at moderate temperatures enabled by the cobalt and copper co-doped ferrite oxygen carrier

Chemical looping technology holds great potential on efficient CO2 splitting with much higher CO production and CO2 splitting rate than photocatalytic processes.Conventional oxygen carrier requires high temperature(typically 850–1000°C)to ensure sufficient redox activity,but the stable and high CO2 conversion is favored at a lower temperature,leading to the degrading on the reaction kinetics as well as the low CO production and CO2 splitting rate.In this paper,we prepared several ternary spinels and demonstrated their performance for chemical looping CO2 splitting at moderate temperatures.Using the promotion effect of Cu to cobalt ferrite reduction and reversible phase change of the reduced metals,Cu0.4 Co0.6 Fe2 O4 exhibits high CO2 splitting rate(144.6μmol g–1 min–1)and total CO production(9100μmol g–1)at 650°C.The high performance of this earth-abundant spinel material is also consistent in repeated redox cycles,enabling their potential in industrial use.

Chemical looping gasification of sewage sludge using copper slag modified by NiO as an oxygen carrier

Chemical looping gasification(CLG) provides a novel approach to dispose the sewage sludge.In order to improve the reactivity of the calcined copper slag,NiO modification is considered as one of the good solutions.The copper slag calcined at 1100℃ doped with 20 wt% NiO(Ni20-CS) was used as an oxygen carrier(OC) in sludge CLG in the work.The modification of NiO can evidently enhance the reactivity of copper slag to promote the sludge conversion,especially for sludge char conversion.The carbon conversion and valid gas yield(V_(g)) increase from 67.02% and 0.23 m^(3)·kg^(-1) using the original OC to 78.34% and 0.29 m^(3)·kg^(-1) using the Ni20-CS OC, respectively.The increase of equivalent coefficient(Ω) facilitates the sludge conversion and a suitable Ω value is determined at 0.47 to obtain the highest valid gas yield(0.29 m^(3)·kg^(-1)).A suitable steam content is assigned at 27.22% to obtain the maximum carbon conversion of 87.09%,where an acceptable LHV of 12.63 MJ·m^(-3) and Vg of 0.39 m^(3)·kg^(-1)are obtained.Although the reactivity of Ni20-CS OC gradually decreases with the increase in cycle numbers because of the generation of NiFe_(2) O_(4-δ) species,the deposition of sludge ash containing many metallic elements is beneficial to the sludge conversion.As a result,the carbon conversion shows a slight uptrend with the increase of cycle numbers in sludge CLG.It indicates that the Ni20-CS sample is a good OC for sludge CLG.

Thermodynamic Analysis and Synthesis Gas Generation by Chemical-Looping Gasification of Biomass with Nature Hematite as Oxygen Carriers

Thermodynamic parameters of chemical reactions in the system were carried out through thermodynamic analysis. According to the Gibbs free energy minimization principle of the system, equilibrium composition of the reactions of chemical-looping gasification (CLG) of biomass with natural hematite (Fe2O3) as oxygen carrier were analyzed using commercial software of HSC Chemistry 5.1. The feasibility of the CLG of biomass with hematite was experimental verified in a lab-scale bubbling fluidized bed reactor using argon as fluidizing gas. It was indicated the experimental results were consistent with the theoretical analysis. The presence of oxygen carrier gave a significant effect on the biomass conversion and improved the synthesis gas yield obviously. It was observed that the gas content of CO and H2 was over 70% in CLG of biomass. The reduced hematite particles mainly existed in form of FeO. It was showed that the reduction of natural hematite with biomass proceeds in a stepwise manner from Fe2O3 →Fe3O4→ FeO. Reduction product of natural hematite can be restored the lattice oxygen by oxidation with air.

Reaction characteristics investigation of CeO_(2)-enhanced CaSO_(4) oxygen carrier with lignite

Calcium sulfate(CaSO_(4))has been verified as a promising oxygen carrier(OC)in the chemical looping combustion(CLC)for its high oxygen capacity,abundant reserve and low cost,but its low reactivity and deleterious sulfur species emission from the side reactions of CaSO_(4) should be well considered for its wide application in CLC.In order to promote the reactivity of CaSO_(4) and increase its potential to inhibit the gaseous sulfur emission,a CeO_(2)-enhanced CaSO_(4) OC mixed OC of core–shell structure was prepared using the combined template synthesis method.Reaction characteristics of the prepared CaSO_(4)-CeO_(2) mixed OC with a typical lignite was first conducted and systematically investigated,and an improved reactivity of the prepared CaSO_(4)-CeO_(2) mixed OC was demonstrated than its single component CaSO_(4) or CeO_(2) due to the fast transfer and exchange of oxygen from the CaSO_(4) substrate to coal via the doped CeO_(2).Furthermore,the solid products formed from the mixed CaSO_(4)-CeO_(2) OC with the selected coal were collected and analyzed.Especially,evolution and redistribution of the sulfur species of different forms were focused.At the latter reaction stage of YN reaction with the CaSO_(4)-CeO_(2) mixed OC,the SO_(2) emitted from the side reactions of CaSO_(4) was greatly diminished and the doped CeO_(2) was proven effective to directionally fix the SO_(2) released to turn into different solid sulfur compounds,which were determined as Ce_(2)O_(2)S,Ce_(2)S_(3) and Ce_(2)(SO_(4))_(3)·5H_(2)O and formed through the different pathways.In addition,good regeneration of the reduced CaSO_(4)-CeO_(2) mixed OC could be reached in spite of the unavoidable interaction between the included minerals in coal and the reduced mixed OC.Overall,the combined template method-made CaSO_(4)-CeO_(2) mixed OC reported herein was not only endowed with enhanced reactivity for coal conversion,but also owned the potential to directionally fix the gaseous sulfur emission,which is quite applicable as OC for simultaneous decarbonatization and desulfurization in the real CLC process.

Syngas production from chemical looping reforming of ethanol over iron-based oxygen carriers: Theoretical analysis and experimental investigation

Chemical looping reforming(CLR)is a recent trend for syngas production,which has several merits compared to the conventional manner.One of the most important issues for CLR is to find low-cost material as oxygen carriers,so iron is a promising candidate.This paper contributes to testing the thermodynamic ability of iron-based oxygen carrier for chemical looping reforming of ethanol(CLRE).Iron thermodynamically investigated in temperature 100–1300℃and excess oxygen number(φ)0–4.It was found that the temperature andφhave an apparent effect on the gaseous composition produced from the process.Increases in temperature within the range of 100–1300℃enhanced syngas generated and reduced coke formation and CH4.Whereas,increasedφ,particularly at higher temperatures,had also enhanced syngas production as well as reduced coke formation.However,increasingφfor values beyond one had decreased syngas and not significantly reduced coke deposition.Moreover,an experimental investigation was carried out in a fixed bed reactor for more in-depth verification of iron ability as an oxygen carrier through using magnetite ore(mainly Fe3O4).It found that the effect of temperature on syngas production was consistent with that calculated thermodynamically,as syngas increased with raising the temperature through the CLRE.

Layered Mg-Al spinel supported Ce-Fe-Zr-O oxygen carriers for chemical looping reforming

A series of layered Mg-Al spinel supported Ce-Fe-Zr-O oxygen carriers were prepared for co-production of syngas and pure hydrogen via chemical looping steam reforming(CLSR).The presence of magnesium-aluminum layered double oxides(Mg Al-LDO)significantly increases the specific surface area of the mixed oxides,reduces the particle size of CeO2-based solid solution and promotes the dispersion of free Fe2O3.When reacting with methane,Mg Al-LDO supported oxygen carrier shows much lower temperature for methane oxidation than the pure CeFe-Zr-O sample,indicating enhanced low-temperature reactivity.Among different Ce-Fe-Zr-O(x)/Mg Al-LDO samples,the Ce-Fe-Zr-O(40 wt%)/Mg Al-LDO sample shows the best performance for the selective oxidation of methane to syngas and the H2 production by water splitting.After a long period of high temperature redox experiment,the Ce-Fe-Zr-O(40 wt%)/Mg Al-LDO oxygen carrier still shows high activity for syngas generation.The comparison on the morphology of the fresh and cycled oxygen carriers indicates that the Mg-Al spinel support still forms a stable skeleton structure with high dispersion of active components on the surface after the long-term cycling,which contributes to excellent redox stability of the Ce-Fe-Zr-O(40 wt%)/Mg Al-LDO oxygen carrier.

Experimental Study on Chemical Looping With Oxygen Uncoupling Using Copper Based Oxygen Carrier and Different Volatiles Contained Coal Chars

采用溶胶一凝胶法制备CuO／CuAl204氧载体，研究了该氧载体在N2气氛下的释氧性能，发现氧载体774℃时开始释氧，且随着温度的升高氧气含量不断升高。随后，在流化床反应器中研究了挥发分含量不同的6种煤焦的化学链氧解耦燃烧（chemicalloopingwithoxygenuncoupling，CLOU）特性，结果表明，挥发分含量的增加和温度的升高均会加速煤焦燃烧，煤焦中碳元素转化率达到95％所需要的时间随着挥发分含量及温度的升高不断减少，相应的碳的平均转化率也不断增加；然而，较高的挥发分含量和反应温度都会导致CO2捕集率的下降。对于挥发分含量低的高平煤焦和东欢坨煤焦，C02捕集率超过99％，而对于挥发分高的胜利褐煤焦，C02捕集率不足95％。

Cycle performance of Cu-based oxygen carrier based on a chemical-looping combustion process

The cycle life of oxygen carrier（OC） is crucial to the practical applications of chemical looping combustion（CLC）. Cycle performance of Cu/SiO2 prepared with a mechanical mixing method was evaluated based on a CLC process characterized with an added methane steam reforming step. The Cu/SiO2 exhibited high redox reactivity in the initial cycles, while the performance degraded with cycle number. Through characterization of the degraded Cu/SiO2, the performance degradation was mainly caused by the secondary particles＇ fragmentation and the fine particles＇ local agglomeration, which worsened the distribution and diffusion of the reactive gases in the packed bed. A regeneration method of the degraded OC based on re-granulation has been proposed, and its mechanism has been illustrated. With this method, the performance of the degraded OC through 420 redox cycles was recovered to a level close to the initial one.

Synthesis of Calcium Phosphate Controllable Coating Thickness on Oil-in-Water Nanoemulsion with Performance of Oxygen Release as Oxygen Carrier

Perfluorocarbon emulsion has been studied as an oxygen carrier, due to its high oxygen content. In clinical trials, it has shown stability in delivering oxygen to the target region. The purpose of the present study was to increase the stability of the emulsion by coating its surface with calcium phosphate. A layer-by-layer method was employed to coat the flexible emulsion surface. Considering the ionic affinity of calcium and phosphate to the lecithin emulsion surface, the first layer of coating was calcium and the second layer was comprised of phosphate ion. The coated emulsion demonstrated various oxygen release times depending on the thickness of the layers: from 0.04 sec. for a thickness of 8 nm to 0.17 sec. for a thickness 38 nm. Overall, the stability of the calcium phosphate coated emulsion was increased, while its original function as an oxygen carrier was maintained.

Performance of Ni-based, Fe-based and Co-based Oxygen Carriers in Chemical-Looping Hydrogen Generation

Ni-based, Fe-based and Co-based oxygen carriers with perovskite oxides used as the supports were prepared by citric acid complexation method. The oxygen carriers were characterized by thermal analysis, H2-temperature-programmed reduction and X-ray diffraction methods. Performance tests were evaluated through Chemical-Looping Hydrogen Generation in a fixed-bed reactor operating at atmospheric pressure. The characterization results showed that all samples were composed of metal oxides and perovskite oxides. Performance results indicated that CH4 conversion over the oxygen carriers decreased in the following order: NiO/LaNiO3 >Co2O3 /LaCoO3 >Fe2O3 /LaFeO3 . The ability of NiO/LaNiO3 and Fe2O3 / LaFeO3 to decompose water was stronger than that of Co2O3 /LaCoO3 as evidenced by our experiments. H2 amounting to 80 mL upon reacting on methane in every cycle could be completely oxidized by NiO/LaNiO 3 at 900 ℃ in the period from the third cycle to the eighth cycle.

Copper-based oxygen carriers supported with alumina/lime for the chemical looping conversion of gaseous fuels

Copper（Ⅱ） oxide in varying ratios was combined with either an alumina-based cement（Al300）, or CaO derived from limestone as support material in a mechanical pelletiser. This production method was used to investigate its influence on possible mechanical and chemical improvements for oxygen carriers in chemical looping processes. These materials were tested in a lab-scale fluidised bed with CO or CH;as a reducing gas at 950 °C. As expected, the oxygen carriers containing a greater ratio of support material exhibited an enhanced crushing strength. Oxygen carriers comprised of a 1:3 ratio of support material to active CuO exhibited increased crushing strength by a minimum of 280% compared to pure CuO pellets.All oxygen carriers exhibited a high CO conversion yield and were fully reducible from CuO to Cu. For the initial redox cycle, Al300-supported oxygen carriers showed the highest fuel and oxygen carrier conversion. The general trend observed was a decline in conversion with an increasing number of redox cycles.In the case of CaO-supported oxygen carriers, all but one of the oxygen carriers suffered agglomeration.The agglomeration was more severe in carriers with higher ratios of CuO. Oxygen carrier Cu25Al75（75 wt% aluminate cement and 25 wt% CuO）, which did not suffer from agglomeration, showed the highest attrition with a loss of approximately 8% of its initial mass over 25 redox cycles. The reducibility of the oxygen carriers was limited with CH;in comparison to CO. CH;conversion were 15%-25% and 50% for Cu25Ca75（25 wt% CuO and 75 wt% CaO） and Cu25Al75, respectively. Cu25Ca75 demonstrated improved conversion, whereas Cu25Al75 exhibited a trending decrease in conversion with increasing redox cycles.

Evaluation of oxygen uncoupling characteristics of oxygen carrier using micro-fluidized bed thermogravimetric analysis

Oxygen uncoupling characteristics of a natural manganese ore and a perovskitetype oxide CaMn_(0.5)Ti0_(37)5Fe_(0.125)O_(3)were studied by using a microfluidized bed thermogravimetric analysis(MFBTGA)technology which is based on a realtime mass measurement of fluidizing particles inside a bubbling bed reactor.The chemical stability,kinetics of the oxygen release and uptake reactions and fluidization property were investigated and the experimental data measured by MFBTGA were compared with the results in a regular TGA instrument(TGA Q500).The regular TGA Q500 results show the reactivity of both the manganese ore and perovskite oxide are stable for multi cycles,and the oxygen uncoupling capacity of the manganese ore is~1.2%(mass)which is~2 times higher than that of the perovskite oxide.However,the experimental results from the MFBTGA indicated that there is a serious agglomeration for the manganese ore.A very important finding is that the reaction rate of oxygen release and oxygen uptake of the perovskite oxide measured by the MFBTGA are~2 and~4 times faster than that of testedby the TGA Q500.We can conclude that MFBTGA is a very useful tool to measure the reactivity stability and kinetics of oxygen carriers in highthroughput analysis instead of the regular TGA.

New Insight into the Development of Oxygen Carrier Materials for Chemical Looping Systems

化学链燃烧(CLC)和化学链重整(CLR)是通过循环氧化还原反应,清洁高效地将烃类转化为动力、燃料和化学品的创新技术。金属氧化物材料在化学链氧化还原过程中起着至关重要的作用。在还原过程中,氧载体为烃类的转化和产物合成提供所需的氧离子量。在氧化步骤中,耗尽的金属氧化物氧载体从空气中补充分子氧,同时释放热量。近年来,用于各种化学链应用的氧载体材料已经取得了较大进展。在这些金属氧化物材料中,铁基氧载体由于其高携氧能力、显著的成本效益,以及化学链反应在实际应用方面的多功能性而具有吸引力。它们的反应性也可以通过结构设计和改性进一步得到增强。本文综述了氧载体材料的发展及其在这些材料上的烃类转化机制的最新进展。这些进展将有助于氧载体材料的开发,以实现更有效的化学链技术应用。

Insights into the intrinsic interaction between series of C1 molecules and surface of NiO oxygen carriers involved in chemical looping processes

Understanding and modulating the interaction between various reactive molecules and oxygen carriers are the key issue to achieve process intensification of chemical looping technology.C1 chemical molecules play an important role in many reactions involved with chemical looping processes.However,up to now,there is still a lack of systematic and in-depth understanding of the adsorption mechanism of C1 molecules on the surface of oxygen carriers(OCs).In this work,the intrinsic interaction between a series of C1 molecules composed of CH4,CO,CO2,CH3OH,HCHO and HCOOH and surface of Ni O OCs in the chemical looping process have been studied using density functional theory calculations.Various adsorption configurations of C1 molecules and also different adsorption sites of Ni O have been considered.The structural features of stable configuration of C1 molecules on the surface of NiO OCs have been obtained.Further,the interacted sites,types and strengths of C1 molecules on the surface of NiO have been directly pictured by the independent gradient model methods.Also,the nature of the interaction between C1 molecule and Ni O surface has been investigated with the aid of energy decomposition analysis from a quantitative view.

Introducing oxygen vacancies in TiO_(2) lattice through trivalent iron to enhance the photocatalytic removal of indoor NO

The synthesis of oxygen vacancies(OVs)-modified TiO_(2)under mild conditions is attractive.In this work,OVs were easily introduced in TiO_(2)lattice during the hydrothermal doping process of trivalent iron ions.Theoretical calculations based on a novel charge-compensation structure model were employed with experimental methods to reveal the intrinsic photocatalytic mechanism of Fe-doped TiO_(2)(Fe-TiO_(2)).The OVs formation energy in Fe-TiO_(2)(1.12 eV)was only 23.6%of that in TiO_(2)(4.74 eV),explaining why Fe^(3+)doping could introduce OVs in the TiO_(2)lattice.The calculation results also indicated that impurity states introduced by Fe^(3+)and OVs enhanced the light absorption activity of TiO_(2).Additionally,charge carrier transport was investigated through the carrier lifetime and relative mass.The carrier lifetime of Fe-TiO_(2)(4.00,4.10,and 3.34 ns for 1at%,2at%,and 3at%doping contents,respectively)was longer than that of undoped TiO_(2)(3.22 ns),indicating that Fe^(3+) and OVs could promote charge carrier separation,which can be attributed to the larger relative effective mass of electrons and holes.Herein,Fe-TiO_(2)has higher photocatalytic indoor NO removal activity compared with other photocatalysts because it has strong light absorption activity and high carrier separation efficiency.