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Paul A Kohl - One of the best experts on this subject based on the ideXlab platform.
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the influence of 2 2 dipyridyl on non formaldehyde electroless copper plating
Electrochimica Acta, 2004Co-Authors: Jun Li, Harley Hayden, Paul A KohlAbstract:Abstract High electroless copper deposition rates can be achieved using Hypophosphite as the reducing agent. However, the high deposition rate also results in dark deposits. In the Hypophosphite baths, nickel ions (0.0057 M with Ni 2+ /Cu 2+ mole ratio 0.14) were used to catalyze Hypophosphite oxidation. In this study, additives (e.g. 2,2′-dipyridyl) were investigated to improve the microstructure and properties of the copper deposits in the Hypophosphite (non-formaldehyde) baths. The influence of 2,2′-dipyridyl on the deposit composition, structure, properties, and the electrochemical reactions of Hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The electroless deposition rate decreased with the addition of 2,2′-dipyridyl to the plating solution and the color of the deposits changed from dark brown to a semi-bright with improved uniformity. The deposits also had smaller crystallite size and higher (1 1 1) plane orientation with the use of 2,2′-dipyridyl. The resistivity and nickel content of the deposit were not affected by 2,2′-dipyridyl additions to the bath. The electrochemical current–voltage results show that 2,2′-dipyridyl inhibits the catalytic oxidation of Hypophosphite at the active nickel site. This results in a more negative electroless deposition potential and lower deposition rate.
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the deposition characteristics of accelerated nonformaldehyde electroless copper plating
Journal of The Electrochemical Society, 2003Co-Authors: Jun Li, Paul A KohlAbstract:The deposition process of an electroless copper plating solution using sodium citrate as the main complexing agent and sodium Hypophosphite as the reducing agent has been investigated. The deposit composition, structure, and catalytic activity for the oxidation of Hypophosphite during the process have been investigated. Formamidine disulfide (fd) has been shown to accelerate the deposition rate of the electroless plating just as it does with electroless plating solutions using N-(2-hydroxyethyl)ethylenediaminetriacetic acid trisodium salt hydrate (HEDTAI as the complexing agent. For solutions with the Cu 2+ /Ni 2+ mole ratio of 42, the deposition rate decreased with time and terminated after 90 min plating because the surface catalytic activity of the deposit had decreased with thickness. A copper deposit with total thickness of 6.48-6.59 μm was obtained after 90 min plating. The decrease in the deposition rate with time was mitigated by decreasing the Cu 2+ /Ni 2+ mole ratio, holding the concentration of copper ions constant. An optimized electroless copper plating process with sustained deposition rate with time and high metal conductivity was developed. The bath was used in a fully additive high density wiring process.
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the influence of 2 2 dipyridyl on non formaldehyde electroless copper plating
Copper interconnects new contact metallurgies structures and low-k interlevel dielectrics, 2003Co-Authors: Jun Li, Harley Hayden, Paul A KohlAbstract:2,2'-dipyridyl was introduced to improve the microstructure and properties of the copper deposits from electroless copper plating using Hypophosphite as the reducing agent. The influences of 2,2'-dipyridyl on the deposit composition, structure, properties, and the electrochemical reactions of Hypophosphite oxidation and cupric ion reduction have been investigated. The results show that the electroless deposition rate decreased significantly with the addition of 2,2'-dipyridyl in the plating solution and the color of the deposits changed from dark brown to a semi-bright, pink-tint. The deposits became uniform and compact. The deposits had a decreased crystallite size and intensified (111) plane orientation with the addition of 2,2'-dipyridyl in the plating bath. However, the resistivity and nickel content in the deposit were not effected by 2,2'-dipyridyl. The electrochemical measurements prove that 2,2'-dipyridyl inhibited significantly the catalytic oxidation of Hypophosphite at the nickel active site on the deposit surface and increased the overpotential for cupric ion reduction, thus reducing the deposition rate and making the deposit become fine.
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the acceleration of nonformaldehyde electroless copper plating
Journal of The Electrochemical Society, 2002Co-Authors: Jun Li, Paul A KohlAbstract:Nonformaldehyde, low pH (compared to highly alkaline bath) electroless copper plating has been investigated. Thiourea and its derivatives have been shown to increase the deposition rate of electroless copper plating solutions using HEDTA [N-(2-hydroxyethyl)ethylenediaminetriacetic acid trisodium salt hydrate] as the complexing agent and sodium Hypophosphite as the reducing agent. A thiourea concentration of 1.0 ppm produced a fourfold increase in the deposition rate of copper from about 1 to 4 μm/h. The effect of thiourea on the electrochemical reactions, and the crystal structures and electrical properties of the copper deposits were examined. A small amount of thiourea, or its derivatives, in the electroless copper solution improves the catalytic activity of the copper surface for the oxidation of Hypophosphite, resulting in a higher electroless deposition rate. The thiourea also increases the growth colony size of the copper deposits and improves its conductivity. A reaction mechanism is proposed to describe the function of the thiourea and its derivatives on the process.
Jun Li - One of the best experts on this subject based on the ideXlab platform.
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the influence of 2 2 dipyridyl on non formaldehyde electroless copper plating
Electrochimica Acta, 2004Co-Authors: Jun Li, Harley Hayden, Paul A KohlAbstract:Abstract High electroless copper deposition rates can be achieved using Hypophosphite as the reducing agent. However, the high deposition rate also results in dark deposits. In the Hypophosphite baths, nickel ions (0.0057 M with Ni 2+ /Cu 2+ mole ratio 0.14) were used to catalyze Hypophosphite oxidation. In this study, additives (e.g. 2,2′-dipyridyl) were investigated to improve the microstructure and properties of the copper deposits in the Hypophosphite (non-formaldehyde) baths. The influence of 2,2′-dipyridyl on the deposit composition, structure, properties, and the electrochemical reactions of Hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The electroless deposition rate decreased with the addition of 2,2′-dipyridyl to the plating solution and the color of the deposits changed from dark brown to a semi-bright with improved uniformity. The deposits also had smaller crystallite size and higher (1 1 1) plane orientation with the use of 2,2′-dipyridyl. The resistivity and nickel content of the deposit were not affected by 2,2′-dipyridyl additions to the bath. The electrochemical current–voltage results show that 2,2′-dipyridyl inhibits the catalytic oxidation of Hypophosphite at the active nickel site. This results in a more negative electroless deposition potential and lower deposition rate.
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the deposition characteristics of accelerated nonformaldehyde electroless copper plating
Journal of The Electrochemical Society, 2003Co-Authors: Jun Li, Paul A KohlAbstract:The deposition process of an electroless copper plating solution using sodium citrate as the main complexing agent and sodium Hypophosphite as the reducing agent has been investigated. The deposit composition, structure, and catalytic activity for the oxidation of Hypophosphite during the process have been investigated. Formamidine disulfide (fd) has been shown to accelerate the deposition rate of the electroless plating just as it does with electroless plating solutions using N-(2-hydroxyethyl)ethylenediaminetriacetic acid trisodium salt hydrate (HEDTAI as the complexing agent. For solutions with the Cu 2+ /Ni 2+ mole ratio of 42, the deposition rate decreased with time and terminated after 90 min plating because the surface catalytic activity of the deposit had decreased with thickness. A copper deposit with total thickness of 6.48-6.59 μm was obtained after 90 min plating. The decrease in the deposition rate with time was mitigated by decreasing the Cu 2+ /Ni 2+ mole ratio, holding the concentration of copper ions constant. An optimized electroless copper plating process with sustained deposition rate with time and high metal conductivity was developed. The bath was used in a fully additive high density wiring process.
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the influence of 2 2 dipyridyl on non formaldehyde electroless copper plating
Copper interconnects new contact metallurgies structures and low-k interlevel dielectrics, 2003Co-Authors: Jun Li, Harley Hayden, Paul A KohlAbstract:2,2'-dipyridyl was introduced to improve the microstructure and properties of the copper deposits from electroless copper plating using Hypophosphite as the reducing agent. The influences of 2,2'-dipyridyl on the deposit composition, structure, properties, and the electrochemical reactions of Hypophosphite oxidation and cupric ion reduction have been investigated. The results show that the electroless deposition rate decreased significantly with the addition of 2,2'-dipyridyl in the plating solution and the color of the deposits changed from dark brown to a semi-bright, pink-tint. The deposits became uniform and compact. The deposits had a decreased crystallite size and intensified (111) plane orientation with the addition of 2,2'-dipyridyl in the plating bath. However, the resistivity and nickel content in the deposit were not effected by 2,2'-dipyridyl. The electrochemical measurements prove that 2,2'-dipyridyl inhibited significantly the catalytic oxidation of Hypophosphite at the nickel active site on the deposit surface and increased the overpotential for cupric ion reduction, thus reducing the deposition rate and making the deposit become fine.
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the acceleration of nonformaldehyde electroless copper plating
Journal of The Electrochemical Society, 2002Co-Authors: Jun Li, Paul A KohlAbstract:Nonformaldehyde, low pH (compared to highly alkaline bath) electroless copper plating has been investigated. Thiourea and its derivatives have been shown to increase the deposition rate of electroless copper plating solutions using HEDTA [N-(2-hydroxyethyl)ethylenediaminetriacetic acid trisodium salt hydrate] as the complexing agent and sodium Hypophosphite as the reducing agent. A thiourea concentration of 1.0 ppm produced a fourfold increase in the deposition rate of copper from about 1 to 4 μm/h. The effect of thiourea on the electrochemical reactions, and the crystal structures and electrical properties of the copper deposits were examined. A small amount of thiourea, or its derivatives, in the electroless copper solution improves the catalytic activity of the copper surface for the oxidation of Hypophosphite, resulting in a higher electroless deposition rate. The thiourea also increases the growth colony size of the copper deposits and improves its conductivity. A reaction mechanism is proposed to describe the function of the thiourea and its derivatives on the process.
Shichao Tian - One of the best experts on this subject based on the ideXlab platform.
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ti4o7 g c3n4 visible light photocatalytic performance on Hypophosphite oxidation effect of annealing temperature
Frontiers in Chemistry, 2018Co-Authors: Wei Guan, Zhenghua Zhang, Gaoge Sun, Lei Yin, Shichao TianAbstract:The oxidation of Hypophosphite to phosphate is the key to recover the phosphorus resource from the Hypophosphite wastewater. In the present work, Ti4O7/g-C3N4 composites were synthesized at two different temperatures (100 and 160 °C) and their performance on photocatalytic oxidation of Hypophosphite under visible light irradiation and the corresponding mechanism were evaluated. A hydrolysis method using g-C3N4 and Ti4O7 was applied to synthesize the Ti4O7/g-C3N4 composites with their hybrid structure and morphology confirmed by XRD, SEM and XPS. The annealing temperature significantly affected the photocatalytic performance of Ti4O7/g-C3N4 that the 160-Ti4O7/g-C3N4 composite (fabricated at 160 °C) showed the highest oxidation efficiency of Hypophosphite of 81% and the highest photocatalytic oxidation rate of 0.467 h-1 comparing with the 100-Ti4O7/g-C3N4 composite (fabricated at 100 °C) and pure g-C3N4. The enhanced photocatalytic performance of 160-Ti4O7/g-C3N4 could be ascribed to the effective charge separation and enhanced photoabsorption efficiency. Additionally, electron spin resonance (ESR) results showed that hydroxyl radicals and superoxide anion radicals were mainly responsible to the oxidation of Hypophosphite with superoxide anion radicals accounting for a more significant contribution. Moreover, Ti4O7/g-C3N4 photocatalysts showed the remarkable stability in the repetitive experiments.
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An electrochemical method through hydroxyl radicals oxidation and deposition of ferric phosphate for Hypophosphite recovery.
Journal of Colloid and Interface Science, 2018Co-Authors: Wei Guan, Shichao Tian, Xu ZhaoAbstract:Abstract Phosphorus is an essential and irreplaceable element of the ecosystem. In this work, phosphorus has been recovered using an electro-Fenton process. The effects of current intensity, initial pH and H2O2 concentration on the recovery of Hypophosphite were investigated. When the current intensity, pH value, and H2O2 concentration were 0.2 A, 3.0 and 90 mM, respectively, Hypophosphite was completely oxidized to phosphate. Under such conditions, the phosphate was recovered through the generation of deposition. In order to determine the mechanism of Hypophosphite recovery, the morphology and microstructure of the deposition were analyzed using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, high resolution transmission electron microscopy, Fourier transform infrared and X-ray photoelectron spectra. The generation of hydroxyl radicals was confirmed using electron spin resonance technique. This method is a clean process for phosphorus recovery, and does not generate hazardous substances.
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Ti4O7/g-C3N4 for Visible Light Photocatalytic Oxidation of Hypophosphite: Effect of Mass Ratio of Ti4O7/g-C3N4
'Frontiers Media SA', 2018Co-Authors: Wei Guan, Zhenghua Zhang, Shichao TianAbstract:Hypophosphite wastewater treatment is still a critical issue in metallurgical processes and the oxidation of Hypophosphite to phosphate followed by the precipitation of phosphate is an important strategy for Hypophosphite wastewater treatment. Herein, Ti4O7/g-C3N4 photocatalysts with various mass ratios (Ti4O7 (m): g-C3N4 (m) = 0.5, 0.2, 0.1, and 0.05) were synthesized by a hydrolysis method and the effect of the mass ratio of Ti4O7 (m): g-C3N4 (m) on Ti4O7/g-C3N4 visible light photocatalytic oxidation of Hypophosphite was evaluated. The as-prepared Ti4O7/g-C3N4 were characterized and confirmed by SEM, XPS, XRD and FTIR. Moreover, the specific surface area and the distribution of pore size of Ti4O7/g-C3N4 was also analyzed. Our results showed that Ti4O7/g-C3N4 exhibited remarkably improved photocatalytic performance on Hypophosphite oxidation compared with g-C3N4 and meanwhile 1:2-Ti4O7/g-C3N4 with a mass ratio of 0.5 showed the best photocatalytic performance with the highest oxidation rate constant (17.7-fold and 91.0-fold higher than that of pure g-C3N4 and Ti4O7, respectively). The enhanced performance of photocatalytic oxidation of Hypophosphite was ascribed to the heterojunction structure of Ti4O7/g-C3N4 with broader light absorption and significantly enhanced efficiency of the charge carrier (e−-h+) generation and separation. Additionally, the generated ·OH and ·O2- radicals contributed to the Hypophosphite oxidation during the photocatalytic system
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Ti4O7/g-C3N4 Visible Light Photocatalytic Performance on Hypophosphite Oxidation: Effect of Annealing Temperature
Frontiers Media S.A., 2018Co-Authors: Wei Guan, Zhenghua Zhang, Gaoge Sun, Lei Yin, Shichao TianAbstract:The oxidation of Hypophosphite to phosphate is the key to recover the phosphorus resource from the Hypophosphite wastewater. In the present work, Ti4O7/g-C3N4 composites were synthesized at two different temperatures (100 and 160°C) and their performance on photocatalytic oxidation of Hypophosphite under visible light irradiation and the corresponding mechanism were evaluated. A hydrolysis method using g-C3N4 and Ti4O7 was applied to synthesize the Ti4O7/g-C3N4 composites with their hybrid structure and morphology confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS). The annealing temperature significantly affected the photocatalytic performance of Ti4O7/g-C3N4 that the 160-Ti4O7/g-C3N4 composite (fabricated at 160°C) showed the highest oxidation efficiency of Hypophosphite of 81% and the highest photocatalytic oxidation rate of 0.467 h−1 comparing with the 100-Ti4O7/g-C3N4 composite (fabricated at 100°C) and pure g-C3N4. The enhanced photocatalytic performance of 160-Ti4O7/g-C3N4 could be ascribed to the effective charge separation and enhanced photoabsorption efficiency. Additionally, electron spin resonance (ESR) results showed that hydroxyl radicals and superoxide anion radicals were mainly responsible to the oxidation of Hypophosphite with superoxide anion radicals accounting for a more significant contribution. Moreover, Ti4O7/g-C3N4 photocatalysts showed the remarkable stability in the repetitive experiments
Wei Guan - One of the best experts on this subject based on the ideXlab platform.
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ti4o7 g c3n4 visible light photocatalytic performance on Hypophosphite oxidation effect of annealing temperature
Frontiers in Chemistry, 2018Co-Authors: Wei Guan, Zhenghua Zhang, Gaoge Sun, Lei Yin, Shichao TianAbstract:The oxidation of Hypophosphite to phosphate is the key to recover the phosphorus resource from the Hypophosphite wastewater. In the present work, Ti4O7/g-C3N4 composites were synthesized at two different temperatures (100 and 160 °C) and their performance on photocatalytic oxidation of Hypophosphite under visible light irradiation and the corresponding mechanism were evaluated. A hydrolysis method using g-C3N4 and Ti4O7 was applied to synthesize the Ti4O7/g-C3N4 composites with their hybrid structure and morphology confirmed by XRD, SEM and XPS. The annealing temperature significantly affected the photocatalytic performance of Ti4O7/g-C3N4 that the 160-Ti4O7/g-C3N4 composite (fabricated at 160 °C) showed the highest oxidation efficiency of Hypophosphite of 81% and the highest photocatalytic oxidation rate of 0.467 h-1 comparing with the 100-Ti4O7/g-C3N4 composite (fabricated at 100 °C) and pure g-C3N4. The enhanced photocatalytic performance of 160-Ti4O7/g-C3N4 could be ascribed to the effective charge separation and enhanced photoabsorption efficiency. Additionally, electron spin resonance (ESR) results showed that hydroxyl radicals and superoxide anion radicals were mainly responsible to the oxidation of Hypophosphite with superoxide anion radicals accounting for a more significant contribution. Moreover, Ti4O7/g-C3N4 photocatalysts showed the remarkable stability in the repetitive experiments.
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An electrochemical method through hydroxyl radicals oxidation and deposition of ferric phosphate for Hypophosphite recovery.
Journal of Colloid and Interface Science, 2018Co-Authors: Wei Guan, Shichao Tian, Xu ZhaoAbstract:Abstract Phosphorus is an essential and irreplaceable element of the ecosystem. In this work, phosphorus has been recovered using an electro-Fenton process. The effects of current intensity, initial pH and H2O2 concentration on the recovery of Hypophosphite were investigated. When the current intensity, pH value, and H2O2 concentration were 0.2 A, 3.0 and 90 mM, respectively, Hypophosphite was completely oxidized to phosphate. Under such conditions, the phosphate was recovered through the generation of deposition. In order to determine the mechanism of Hypophosphite recovery, the morphology and microstructure of the deposition were analyzed using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, high resolution transmission electron microscopy, Fourier transform infrared and X-ray photoelectron spectra. The generation of hydroxyl radicals was confirmed using electron spin resonance technique. This method is a clean process for phosphorus recovery, and does not generate hazardous substances.
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Ti4O7/g-C3N4 for Visible Light Photocatalytic Oxidation of Hypophosphite: Effect of Mass Ratio of Ti4O7/g-C3N4
'Frontiers Media SA', 2018Co-Authors: Wei Guan, Zhenghua Zhang, Shichao TianAbstract:Hypophosphite wastewater treatment is still a critical issue in metallurgical processes and the oxidation of Hypophosphite to phosphate followed by the precipitation of phosphate is an important strategy for Hypophosphite wastewater treatment. Herein, Ti4O7/g-C3N4 photocatalysts with various mass ratios (Ti4O7 (m): g-C3N4 (m) = 0.5, 0.2, 0.1, and 0.05) were synthesized by a hydrolysis method and the effect of the mass ratio of Ti4O7 (m): g-C3N4 (m) on Ti4O7/g-C3N4 visible light photocatalytic oxidation of Hypophosphite was evaluated. The as-prepared Ti4O7/g-C3N4 were characterized and confirmed by SEM, XPS, XRD and FTIR. Moreover, the specific surface area and the distribution of pore size of Ti4O7/g-C3N4 was also analyzed. Our results showed that Ti4O7/g-C3N4 exhibited remarkably improved photocatalytic performance on Hypophosphite oxidation compared with g-C3N4 and meanwhile 1:2-Ti4O7/g-C3N4 with a mass ratio of 0.5 showed the best photocatalytic performance with the highest oxidation rate constant (17.7-fold and 91.0-fold higher than that of pure g-C3N4 and Ti4O7, respectively). The enhanced performance of photocatalytic oxidation of Hypophosphite was ascribed to the heterojunction structure of Ti4O7/g-C3N4 with broader light absorption and significantly enhanced efficiency of the charge carrier (e−-h+) generation and separation. Additionally, the generated ·OH and ·O2- radicals contributed to the Hypophosphite oxidation during the photocatalytic system
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Ti4O7/g-C3N4 Visible Light Photocatalytic Performance on Hypophosphite Oxidation: Effect of Annealing Temperature
Frontiers Media S.A., 2018Co-Authors: Wei Guan, Zhenghua Zhang, Gaoge Sun, Lei Yin, Shichao TianAbstract:The oxidation of Hypophosphite to phosphate is the key to recover the phosphorus resource from the Hypophosphite wastewater. In the present work, Ti4O7/g-C3N4 composites were synthesized at two different temperatures (100 and 160°C) and their performance on photocatalytic oxidation of Hypophosphite under visible light irradiation and the corresponding mechanism were evaluated. A hydrolysis method using g-C3N4 and Ti4O7 was applied to synthesize the Ti4O7/g-C3N4 composites with their hybrid structure and morphology confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS). The annealing temperature significantly affected the photocatalytic performance of Ti4O7/g-C3N4 that the 160-Ti4O7/g-C3N4 composite (fabricated at 160°C) showed the highest oxidation efficiency of Hypophosphite of 81% and the highest photocatalytic oxidation rate of 0.467 h−1 comparing with the 100-Ti4O7/g-C3N4 composite (fabricated at 100°C) and pure g-C3N4. The enhanced photocatalytic performance of 160-Ti4O7/g-C3N4 could be ascribed to the effective charge separation and enhanced photoabsorption efficiency. Additionally, electron spin resonance (ESR) results showed that hydroxyl radicals and superoxide anion radicals were mainly responsible to the oxidation of Hypophosphite with superoxide anion radicals accounting for a more significant contribution. Moreover, Ti4O7/g-C3N4 photocatalysts showed the remarkable stability in the repetitive experiments
William W Metcalf - One of the best experts on this subject based on the ideXlab platform.
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genetic diversity and horizontal transfer of genes involved in oxidation of reduced phosphorus compounds by alcaligenes faecalis wm2072
Applied and Environmental Microbiology, 2005Co-Authors: Marlena M Wilson, William W MetcalfAbstract:Enrichment was performed to isolate organisms that could utilize reduced phosphorus compounds as their sole phosphorus sources. One isolate that grew well with either Hypophosphite or phosphite was identified by 16S rRNA gene analysis as a strain of Alcaligenes faecalis. The genes required for oxidation of Hypophosphite and phosphite by this organism were identified by using transposon mutagenesis and include homologs of the ptxD and htxA genes of Pseudomonas stutzeri WM88, which encode an NAD-dependent phosphite dehydrogenase (PtxD) and 2-oxoglutarate-dependent Hypophosphite dioxygenase (HtxA). This organism also has the htxB, htxC, and htxD genes that comprise an ABC-type transporter, presumably for Hypophosphite and phosphite transport. The role of these genes in reduced phosphorus metabolism was confirmed by analyzing the growth of mutants in which these genes were deleted. Sequencing data showed that htxA, htxB, htxC, and htxD are virtually identical to their homologs in P. stutzeri at the DNA level, indicating that horizontal gene transfer occurred. However, A. faecalis ptxD is very different from its P. stutzeri homolog and represents a new ptxD lineage. Therefore, this gene has ancient evolutionary roots in bacteria. These data suggest that there is strong evolutionary selection for the ability of microorganisms to oxidize Hypophosphite and phosphite.
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molecular genetic analysis of phosphite and Hypophosphite oxidation by pseudomonas stutzeri wm88
Journal of Bacteriology, 1998Co-Authors: William W Metcalf, R S WolfeAbstract:The first molecular and genetic characterization of a biochemical pathway for oxidation of the reduced phosphorus (P) compounds phosphite and Hypophosphite is reported. The pathway was identified in Pseudomonas stutzeri WM88, which was chosen for detailed studies from a group of organisms isolated based on their ability to oxidize Hypophosphite (+1 valence) and phosphite (+3 valence) to phosphate (+5 valence). The genes required for oxidation of both compounds by P. stutzeri WM88 were cloned on a single ca. 30-kbp DNA fragment by screening for expression in Escherichia coli and Pseudomonas aeruginosa . Two lines of evidence suggest that Hypophosphite is oxidized to phosphate via a phosphite intermediate. First, plasmid subclones that conferred oxidation of phosphite, but not Hypophosphite, upon heterologous hosts were readily obtained. All plasmid subclones that failed to confer phosphite oxidation also failed to confer Hypophosphite oxidation. No subclones that conferred only Hypophosphite expression were obtained. Second, various deletion derivatives of the cloned genes were made in vitro and recombined onto the chromosome of P. stutzeri WM88. Two phenotypes were displayed by individual mutants. Mutants with the region encoding phosphite oxidation deleted (based upon the subcloning results) lost the ability to oxidize either phosphite or Hypophosphite. Mutants with the region encoding Hypophosphite oxidation deleted lost only the ability to oxidize Hypophosphite. The phenotypes displayed by these mutants also demonstrate that the cloned genes are responsible for the P oxidation phenotypes displayed by the original P. stutzeri WM88 isolate. The DNA sequences of the minimal regions implicated in oxidation of each compound were determined. The region required for oxidation of phosphite to phosphate putatively encodes a binding-protein-dependent phosphite transporter, an NAD + -dependent phosphite dehydrogenase, and a transcriptional activator of the lysR family. The region required for oxidation of Hypophosphite to phosphite putatively encodes a binding-protein-dependent Hypophosphite transporter and an α-ketoglutarate-dependent Hypophosphite dioxygenase. The finding of genes dedicated to oxidation of reduced P compounds provides further evidence that a redox cycle for P may be important in the metabolism of this essential, and often growth-limiting, nutrient.