SEARCH · Engineering Papers

Results for “RECOMBINATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,657 records · Page 92

All sources NASA NTRS DOE OSTI

NASA NTRS1993

Performance assessment of low pressure nuclear thermal propulsion

An increase in Isp for nuclear thermal propulsion systems is desirable for reducing the propellant requirements and cost of future applications, such as the Mars Transfer Vehicle. Several previous design studies have suggested that the Isp could be increased substantially with hydrogen dissociation/recombination. Hydrogen molecules (H2), at high temperatures and low pressures, will dissociate to monatomic hydrogen (H). The reverse process (i.e., formation of H2 from H) is exothermic. The exothermic energy in a nozzle increases the kinetic energy and therefore, increases the Isp. The low pressure nuclear thermal propulsion system (LPNTP) system is expected to maximize the hydrogen dissociation/recombination and Isp by operating at high chamber temperatures and low chamber pressures. The process involves hydrogen flow through a high temperature, low pressure fission reactor, and out a nozzle. The high temperature (approximately 3000 K) of the hydrogen in the reactor is limited by the temperature limits of the reactor material. The minimum chamber pressure is about 1 atm because lower pressures decrease the engines thrust to weight ratio below acceptable limits. This study assumes that hydrogen leaves the reactor and enters the nozzle at the 3000 K equilibrium dissociation level. Hydrogen dissociation in the reactor does not affect LPNTP performance like dissociation in traditional chemical propulsion systems, because energy from the reactor resupplies energy lost due to hydrogen dissociation. Recombination takes place in the nozzle due primarily to a drop in temperature as the Mach number increases. However, as the Mach number increases beyond the nozzle throat, the static pressure and density of the flow decreases and minimizes the recombination. The ideal LPNTP Isp at 3000 K and 10 psia is 1160 seconds due to the added energy from fast recombination rates. The actual Isp depends on the finite kinetic reaction rates which affect the amount of monatomic hydrogen recombination before the flow exits the nozzle. A LPNTP system has other technical issues (e.g. flow instability and two-phase flow) besides hydrogen dissociation/recombination which affect the systems practicality. In this study, only the effects of hydrogen dissociation/recombination are examined.

Gerrish, Harrold P., Jr.↗

NASA NTRS1997

The Effect of Diffusional Transport and Surface Catalysis on the Aerothermodynamic Heating for Martian Atmospheric Entry

For the reentry heating of 70-degree blunt sphere-cones entering Mars at velocities in excess of 6 km/sec, a study was performed to determine the magnitude of both convective and catalytic heating on the cone forebody. Case studies of the peak heating conditions for the current NASA Mars Pathfinder entry probe, as well as the peak heating conditions of the proposed NASA Mars 2001 aerobraking orbiter mission were performed. Since the actual behavior of the chemical recombination of Mars atmosphere hypersonic shock layer species on heat shield materials is not known, and no experimental studies of any consequence have been done to determine surface reaction rates for the CO2 system, a parametric analysis of various reaction schemes and surface catalytic mechanistic models was performed. In many cases the actual Mars entry probe will have a heat shield composed of an ablative material which can either partially or completely preclude the existence of catalytic surface recombination phenomena. The extent of this blockage effect has not been examined at this time and is not considered in this effort. Instead only non-ablative computations are performed to separately evaluate the full extent of the surface catalysis and related diffusional phenomena. Parametric studies include peak heating point comparisons of non-catalytic, partially catalytic and fully catalytic total surface heat transfer for three difference surface recombination catalytic mechanisms (with and without simultaneous CO + O and O + O recombination) as well as with different species diffusion models. Diffusion model studies include constant Schmidt number (equal diffusivities) and the bifurcation, approximate multi-component diffusion model. Since the gas phase reaction kinetics for the Mars CO2 based atmosphere have also not been validated, the effect of two different (fast and slow) sets of gas kinetics on heat transfer is presented.

Henline, William D.↗

NASA NTRS2003

Molecular Carbon in the Galaxy: Laboratory and Observational Studies

In a collaboration with the Mats Larsson group from Stockholm, we carried out a new measurement of the rate of dissociative recombination of H(sup *, sub j), using a new pulsed supersonic beam source of rotationally cold H(sup *, sub j). This source was first designed and characterized in our lab by IR cavity ringdown spectroscopy, determining a rotationaYtranslationa1 temperature of 20-60K, depending on conditions. This new source was then taken to Stockholm for the recombination rate studies at the CRYRING storage ring. The recombination rate constant measured against temperature yields values consistent with the most recent calculations, whereas previous experimental measurements varied over a range of 10(exp 4) and were poor agreement with theory. This is a crucial achievement for understanding the ion chemistry of diffuse clouds. Moreover, this result in combination with recent observations implies a greatly enhanced (factor of 40) cosmic ray ionization rate in a diffuse cloud (zeta Persei) relative to previous studies. The implications of this are discussed in our recent Nature paper. An enhanced cosmic-ray flux towards zeta Persei inferred from a laboratory study of the H(sup *, sub j)-e(sup -) recombination rate.

Saykally, Richard James↗

NASA NTRS2002

Momentum and Heat Flux Measurements in the Exhaust of VASIMR Using Helium Propellant

Electromagnetic thrusters typically use electric and magnetic fields to accelerate and exhaust plasma through interactions with the charged particles in the plasma. The energy required to create the plasma, i.e. ionization energy, is potential energy between the electron and ion. This potential energy is typically lost since it is not recovered as the plasma is exhausted and is known as frozen flow loss. If the frozen flow energy is a small fraction of the total plasma energy, this frozen flow loss may be negligible. However, if the frozen flow energy is a major fraction of the total plasma energy, this loss can severely reduce the energy efficiency of the thruster. Recovery and utilization of this frozen flow energy can improve the energy efficiency of a thruster during low specific impulse operating regimes when the ionization energy is a large fraction of the total plasma energy. This paper quantifies the recovery of the frozen flow energy, i.e. recombination energy, via the process of surface recombination for helium. To accomplish this task the momentum flux and heat flux of the plasma flow were measured and compared to calculated values from electrostatic probe data. This information was used to deduce the contribution of recombination energy to the total heat flux on a flat plate as well as to characterize the plasma conditions. Helium propellant was investigated initially due to its high ionization potential and hence available recombination energy.

Chavers, D. Gregory↗

NASA NTRS2002

Tissue engineering skeletal muscle for orthopaedic applications

With current technology, tissue-engineered skeletal muscle analogues (bioartificial muscles) generate too little active force to be clinically useful in orthopaedic applications. They have been engineered genetically with numerous transgenes (growth hormone, insulinlike growth factor-1, erythropoietin, vascular endothelial growth factor), and have been shown to deliver these therapeutic proteins either locally or systemically for months in vivo. Bone morphogenetic proteins belonging to the transforming growth factor-beta superfamily are osteoinductive molecules that drive the differentiation pathway of mesenchymal cells toward the chondroblastic or osteoblastic lineage, and stimulate bone formation in vivo. To determine whether skeletal muscle cells endogenously expressing bone morphogenetic proteins might serve as a vehicle for systemic bone morphogenetic protein delivery in vivo, proliferating skeletal myoblasts (C2C12) were transduced with a replication defective retrovirus containing the gene for recombinant human bone morphogenetic protein-6 (C2BMP-6). The C2BMP-6 cells constitutively expressed recombinant human bone morphogenetic protein-6 and synthesized bioactive recombinant human bone morphogenetic protein-6, based on increased alkaline phosphatase activity in coincubated mesenchymal cells. C2BMP-6 cells did not secrete soluble, bioactive recombinant human bone morphogenetic protein-6, but retained the bioactivity in the cell layer. Therefore, genetically-engineered skeletal muscle cells might serve as a platform for long-term delivery of osteoinductive bone morphogenetic proteins locally.

Review↗

NASA NTRS2002

Bystander effects in radiation-induced genomic instability

Exposure of GM10115 hamster-human hybrid cells to X-rays can result in the induction of chromosomal instability in the progeny of surviving cells. This instability manifests as the dynamic production of novel sub-populations of cells with unique cytogenetic rearrangements involving the "marker" human chromosome. We have used the comet assay to investigate whether there was an elevated level of endogenous DNA breaks in chromosomally unstable clones that could provide a source for the chromosomal rearrangements and thus account for the persistent instability observed. Our results indicate no significant difference in comet tail measurement between non-irradiated and radiation-induced chromosomally unstable clones. Using two-color fluorescence in situ hybridization we also investigated whether recombinational events involving the interstitial telomere repeat-like sequences in GM10115 cells were involved at frequencies higher than random processes would otherwise predict. Nine of 11 clones demonstrated a significantly higher than expected involvement of these interstitial telomere repeat-like sequences at the recombination junction between the human and hamster chromosomes. Since elevated levels of endogenous breaks were not detected in unstable clones we propose that epigenetic or bystander effects (BSEs) lead to the activation of recombinational pathways that perpetuate the unstable phenotype. Specifically, we expand upon the hypothesis that radiation induces conditions and/or factors that stimulate the production of reactive oxygen species (ROS). These reactive intermediates then contribute to a chronic pro-oxidant environment that cycles over multiple generations, promoting chromosomal recombination and other phenotypes associated with genomic instability.

NASA Discipline Radiation Health↗

NASA NTRS2013

Method and Apparatus for Measuring Near-Angle Scattering of Mirror Coatings

Disclosed herein is a method of determining the near angle scattering of a sample reflective surface comprising the steps of: a) splitting a beam of light having a coherence length of greater than or equal to about 2 meters into a sample beam and a reference beam; b) frequency shifting both the sample beam and the reference beam to produce a fixed beat frequency between the sample beam and the reference beam; c) directing the sample beam through a focusing lens and onto the sample reflective surface, d) reflecting the sample beam from the sample reflective surface through a detection restriction disposed on a movable stage; e) recombining the sample beam with the reference beam to form a recombined beam, followed by f) directing the recombined beam to a detector and performing heterodyne analysis on the recombined beam to measure the near-angle scattering of the sample reflective surface, wherein the position of the detection restriction relative to the sample beam is varied to occlude at least a portion of the sample beam to measure the near-angle scattering of the sample reflective surface. An apparatus according to the above method is also disclosed.

Chipman, Russell A.↗

NASA NTRSDate not supplied

Thermoradiative Conversion for Space Power Systems

The thermoradiative cell is a new method for converting heat energy to electrical power, first detailed by Strandberg in 2015. The cell is structurally similar to a photovoltaic cell, in that it is a p-n junction semiconductor device, but thermodynamically operates in the reverse direction, converting the thermal dark current into electrical power by utilizing the recombination radiation from thermally-generated electron hole pairs to radiate waste heat to space. This technology may have application for space missions in converting thermal energy produced by a radioisotope source or from a nuclear reactor into power. The power and efficiency can be calculated as a function of bandgap in the detailed-balance case (the Shockley-Queisser limit), in which all of the thermal emissivity of the cell is due to the recombination of thermally generated electron-hole pairs, and all other recombination losses are ignored. The current produced is directly proportional to the recombination radiation, and thus the more thermally generated pairs, the higher the current. The voltage is proportional to the external bias. These two constraints allow optimization of the optimum bias point for maximum power, and allow calculation of the efficiency at maximum power point. Unlike photovoltaic cells, the maximum power operating point is not the same as the maximum efficiency point, and higher efficiency can be achieved at a higher (negative) bias in the ideal case. Incorporating non-ideal losses, however, shifts the maximum efficiency point toward lower bias. Since a thermoradiative cell operates by radiating directly to space, the current produced by a themoradiative cells will increase with the Stefan-Boltzman radiative efficiency; roughly the fourth power of the temperature. Thus, in contrast to a photovoltaic converter, the power produced is highest at high operating temperatures. Likewise, in contrast to conventional thermal conversion, high radiator temperature increases, rather than decreases the efficiency. Thus, the thermoradiative conversion may fill a mission niche in which small radiator size is required. The basic operation will be summarized, applications to space power discussed, and the requirements for further research outlined.

Photovoltaic Cell↗

DOE OSTI2014

Re-engineering bacteria for ethanol production

The invention provides recombinant bacteria, which comprise a full complement of heterologous ethanol production genes. Expression of the full complement of heterologous ethanol production genes causes the recombinant bacteria to produce ethanol as the primary fermentation product when grown in mineral salts medium, without the addition of complex nutrients. Methods for producing the recombinant bacteria and methods for producing ethanol using the recombinant bacteria are also disclosed.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2019

Methods for degrading or converting plant cell wall polysaccharides

The present invention relates to methods for converting plant cell wall polysaccharides into one or more products, comprising: treating the plant cell wall polysaccharides with an effective amount of a spent whole fermentation broth of a recombinant microorganism, wherein the recombinant microorganism expresses one or more heterologous genes encoding enzymes which degrade or convert the plant cell wall polysaccharides into the one or more products. The present invention also relates to methods for producing an organic substance, comprising: (a) saccharifying plant cell wall polysaccharides with an effective amount of a spent whole fermentation broth of a recombinant microorganism, wherein the recombinant microorganism expresses one or more heterologous genes encoding enzymes which degrade or convert the plant cell wall polysaccharides into saccharified material; (b) fermenting the saccharified material of step (a) with one or more fermenting microoganisms; and (c) recovering the organic substance from the fermentation.

09 BIOMASS FUELS↗

DOE OSTI2021

Microorganisms and methods for producing 2-pyrone-4,6-dicarboxylic acid and other compounds

Recombinant microorganisms configured for enhanced production of compounds such as 2-pyrone-4,6-dicarboxylic acid (PDC) and methods of using the recombinant microorganisms for the production of these compounds. The recombinant microorganisms include one or more modifications that reduce 2-pyrone-4,6-dicarboxylic acid (PDC) hydrolase activity, 4-carboxy-2-hydroxy-6-methoxy-6-oxohexa-2,4-dienoate (CHMOD) cis-trans isomerase activity, 4-carboxy-2-hydroxy-6-methoxy-6-oxohexa-2,4-dienoate (CHMOD) methyl esterase activity, and/or vanillate/3-O-methylgallate O-demethylase activity. The recombinant microorganisms can be used to generate PDC from media comprising plant-derived phenolics, such as syringyl phenolics, guaiacyl phenolics, and p-hydroxyphenyl phenolics. The plant-derived phenolics can be derived from pretreated lignin, including depolymerized lignin or other chemically altered lignin.

Noguera, Daniel R.↗

DOE OSTI2023

Loss Analysis and Performance Optimization Pathways of 729-mV VocSi Solar Cells with Poly-Si on Locally-Etched Dielectric Passivating Contacts

In this article, the performance analysis of a 22.5% efficient polysilicon on silicon oxide (poly-Si/SiOx) passivated contact solar cells with deliberately introduced pinholes using metal-assisted chemical etching (MACE) has been performed with the help of optical analysis using Sunsolve and electrical analysis using Quokka3. The power loss is maximum due to recombination and resistive losses in the bulk (~0.76 mW/cm2 ) followed by power loss due to rear contact recombination (~0.35 mW/cm2 ). Recombination at the front surface also contributes to 0.24 mW/cm2. The effect of improving the bulk lifetime and lowering the recombination current density at the rear side on Voc, FF and efficiency has been investigated.

MACE↗

NASA NTRS2003

Complex formation by the human Rad51B and Rad51C DNA repair proteins and their activities in vitro

The human Rad51 protein is essential for DNA repair by homologous recombination. In addition to Rad51 protein, five paralogs have been identified: Rad51B/Rad51L1, Rad51C/Rad51L2, Rad51D/Rad51L3, XRCC2, and XRCC3. To further characterize a subset of these proteins, recombinant Rad51, Rad51B-(His)(6), and Rad51C proteins were individually expressed employing the baculovirus system, and each was purified from Sf9 insect cells. Evidence from nickel-nitrilotriacetic acid pull-down experiments demonstrates a highly stable Rad51B.Rad51C heterodimer, which interacts weakly with Rad51. Rad51B and Rad51C proteins were found to bind single- and double-stranded DNA and to preferentially bind 3'-end-tailed double-stranded DNA. The ability to bind DNA was elevated with mixed Rad51 and Rad51C, as well as with mixed Rad51B and Rad51C, compared with that of the individual protein. In addition, both Rad51B and Rad51C exhibit DNA-stimulated ATPase activity. Rad51C displays an ATP-independent apparent DNA strand exchange activity, whereas Rad51B shows no such activity; this apparent strand exchange ability results actually from a duplex DNA destabilization capability of Rad51C. By analogy to the yeast Rad55 and Rad57, our results suggest that Rad51B and Rad51C function through interactions with the human Rad51 recombinase and play a crucial role in the homologous recombinational repair pathway.

Non-NASA Center↗

DOE OSTI2018

Surface Passivation and Carrier Collection in {110}, {100} and Circular Si Microwire Solar Cells

Surface recombination is a major bottleneck for realizing highly efficient micro/nanostructure solar cells. Parametric studies of the influence of Si microwire (SiMW) surface-facet orientation (rectangular with flat-facets, {110}, {100} and circular), with a fixed height of 10 µm, diameter (D = 1.5–9.5 µm), and sidewall spacing (S = 2.5–8.5 µm), and mesh-grid density (1–16 mm -2 ) on recombination and carrier collection in SiMW solar cells with radial p-n junctions are reported. An effective surface passivation layer composed of thin thermally grown silicon dioxide (SiO 2 ) and silicon nitride (SiN x ) layers is employed. For a fixed D of 1.5 µm, tight SiMW spacing results in improved short-circuit current density (J sc = 30.1 mA cm -2 ) and sparse arrays result in open-circuit voltages (V oc = 0.552 V) that are similar to those of control Si planar cells. For a fixed S, smaller D results in better light trapping at shorter wavelengths and higher J sc while larger D exhibits better light trapping at larger wavelengths and a higher V oc . With a mesh-grid electrode the power conversion efficiency increases to 15.3%. Finally, these results provide insights on the recombination mechanisms in SiMW solar cells and provide general design principles for optimizing their performance.

14 SOLAR ENERGY↗

DOE OSTI2019

Numerical analysis of HgCdTe dual-band infrared detector

In this paper we describe recent progress in the HgCdTe multilayer heterostructures grown by metaloorganic chemical vapour deposition on GaAs substrates for photodetectors operated above 200 K. We present example of design and characterization of the new classical N{sup +}–n–P{sup +}–p–N{sup +} back to back HgCdTe dual-band photodiode structure, that operates within the mid-wavelength infrared band in sequential mode. A numerical modelling was used for investigation of the device design on the current responsivity and dark currents. The program based on the solution of the system of the carrier transport equations including the whole spectrum of various generation and recombination mechanisms consisting of Shockley–Read–Hall, Auger and radiative generation-recombination terms. Additionally, tunneling effects such as band-to-band and trap-assisted tunnelling models are included in the continuity equations by incorporating them as additional generation–recombination processes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

One possible source of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth

Energy transfer mechanism for recombination of two sulfur atoms into a diatomic molecule, S 2 , is studied theoretically and computationally to determine whether the rate coefficient of this process can be significantly affected by isotopic substitutions, and whether the resultant isotope effect is expected to be mass-dependent or mass-independent. This is one of sulfur polymerization processes thought to be important in the anoxic atmosphere of the Archean Earth and, potentially, relevant to mass-independent fractionation of sulfur isotopes. A simplified theoretical approach is employed, in which all properties of S 2 molecule are characterized rather accurately, whereas the process of stabilization of metastable S 2 * by bath gas collisions is described approximately. Properties of individual scattering resonances in S 2 are studied in detail, and it is found that most important contributions to the recombination process come from ro-vibrational states formed near the top of centrifugal barrier, and that the number of such states is about 50 (in 32 S 32 S). Absolute value of recombination rate coefficient is computed to be 1.22 x 10 -33 cm 6 /s (for 32 S 32 S at room temperature and atmospheric pressure), close to experimental result. Two distinct isotope effects are identified. One is a classical mass-dependent effect due to translational partition function, which leads to a weak, smooth, and negative mass-dependence of rate coefficient (4% decrease when the mass is raised from 32 S 32 S to 34 S 34 S). Second effect, due to quantized resonances, is two orders of magnitude stronger, but is local. In practice, due to presence of multiple individual resonances, this phenomenon leads to irregular mass-independent variations of rate coefficients in the ranges ±5%. It is also demonstrated that in real molecules this irregular behavior is expected to be somewhat smoother, and the isotope effect is somewhat smaller, due to dependence of stabilization cross section on properties of individual resonances (not described by present model). So additional calculations of stabilization cross sections are needed in order to give quantitative prediction of this mass-independent isotope effect, and to determine its relevance to mass-independent fractionation of sulfur isotopes in the Archean rock record.

58 GEOSCIENCES↗

DOE OSTI2016

Green and facile synthesis of graphene nanosheets/K{sub 3}PW{sub 12}O{sub 40} nanocomposites with enhanced photocatalytic activities

Highlights: • A new graphene/K{sub 3}PW{sub 12}O{sub 40} (GPW) composite was synthesized via photoreduction method. • Graphene in the GPW could reduce the recombination of electron-hole pairs. • Graphene in the GPW could increase adsorptive property. • GPW hybrid shows an enhancement photocatalytic activity. - Abstract: K{sub 3}PW{sub 12}O{sub 40} is a promising polyoxometalate photocatalyst for the removal of organic pollutants from water. However, two main disadvantages of poor adsorptive performance and high recombination rate of photogenerated electron-hole pair hinder its practical applications. In this paper, a new graphene nanosheets/K{sub 3}PW{sub 12}O{sub 40} nanocomposite has been synthesized via a green photoreduction strategy, being low-cost and scalable production. Characterizations show that K{sub 3}PW{sub 12}O{sub 40} nanoparticles with 60 nm or so have been successfully deposited on the graphene nanosheets. As a kind of photocatalyst, the binary graphene nanosheets/K{sub 3}PW{sub 12}O{sub 40} nanocomposite displays improved photocatalytic activity compared to pure K{sub 3}PW{sub 12}O{sub 40}. This improvement is ascribed to the introduction of graphene nanosheets in the nanocomposite, which could increase adsorptive property and reduce the recombination of electron-hole pairs.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Effect of surface loading and bulk doping of La{sup 3+} on the thermal stability and photocatalytic activity of Bi{sub 2}O{sub 2}CO{sub 3}

Graphical abstract: The Bi{sub 2}O{sub 2}O{sub 3} modified La{sup 3+} was synthesized using two methods of co-precipitation (La-Bi{sub 2}O{sub 2}O{sub 3}) and wet impregnation (La/Bi{sub 2}O{sub 2}O{sub 3}). As compared with La-Bi{sub 2}O{sub 2}O{sub 3}, Bi{sub 2}O{sub 2}CO{sub 3} can be effectively stabilized by impregnation method, as La{sup 3+} is mainly dispersed onto the surface of Bi{sub 2}O{sub 2}O{sub 3}. In photocatalytic degradation of MO, it is found that the surface modification with La{sup 3+} can enhance the photocatalytic efficiency of Bi{sub 2}O{sub 2}O{sub 3}. The surface loading La{sup 3+} could act as an effective electron scavenger to trap the CB electrons of Bi{sub 2}O{sub 2}CO{sub 3} to reduce the recombination of electrons and holes in the surface. - Highlights: • The effect of La{sup 3+} on the thermal stability of Bi{sub 2}O{sub 2}CO{sub 3} is different for the impregnation method and coprecipitation method. • Bi2O2CO3 can be effectively stabilized by impregnation method, as La3+ is mainly dispersed onto the surface of Bi2O2O3. • Surface loading La3+ is benefit for the improvement in the photocatalytic activity of Bi2O2CO3. • Surface modification of La3+ greatly suppresses the charge recombination of photogenerated electron–hole pairs in Bi2O2CO3. - Abstract: The Bi{sub 2}O{sub 2}O{sub 3} modified La{sup 3+} was synthesized using two methods of co-precipitation (La-Bi{sub 2}O{sub 2}O{sub 3}) and wet impregnation (La/Bi{sub 2}O{sub 2}O{sub 3}). The effects of the above two modification methods on the stability of Bi{sub 2}O{sub 2}CO{sub 3} after calcination and the physicochemical properties of Bi{sub 2}O{sub 2}CO{sub 3} were investigated by XRD, SEM, BET, and XPS. As compared with La-Bi{sub 2}O{sub 2}O{sub 3}, it is observed that Bi{sub 2}O{sub 2}CO{sub 3} can be effectively stabilized by impregnation method, as La{sup 3+} is mainly dispersed onto the surface of Bi{sub 2}O{sub 2}O{sub 3}. The photocatalytic activities for the methyl orange degradation for the La/Bi{sub 2}O{sub 2}CO{sub 3} and the La-Bi{sub 2}O{sub 2}CO{sub 3} samples were tested, and the results showed that surface doping (impregnation method) is benefit for the improvement in the photocatalytic activity, as compared with bulk doping (coprecipitation method). PL characterization revealed the differences in the photocatalytic process for surface doping and bulk doping. The surface modification of La{sup 3+} greatly suppresses the charge recombination of photogenerated electron−hole pairs in Bi{sub 2}O{sub 2}CO{sub 3}, which would be beneficial to improve their photocatalytic activity.

36 MATERIALS SCIENCE↗