Heterojunction architecture of Nb2O5/g-C3N4 for enhancing photocatalytic activity to degrade organic pollutants and deactivate bacteria in water

Water pollution has become a serious problem owing to the development of society. Photocatalysis is a promising approach to remove various pollutants in water, such as organic pollutants and antibiotic resistance bacteria. Meanwhile, the design of heterojunction between two semiconductors is an effective path to improve photocatalytic properties due to its potential in improving separation and transfer of photoinduced carriers. In this study, Nb₂O₅/g-C₃N₄ (NO/CN) composite materials were prepared through a one-step heating method. Characterizations confirmed successful preparation of NO/CN heterojunction structure and better optical properties than pure g-C₃N₄ and Nb₂O₅. NO/CN composite materials showed excellent photocatalytic efficiency for Escherichia coli (E. coli) inactivation (95%) compared with the pure Nb₂O₅ (10%) and g-C₃N₄ (77%). Meanwhile, NO/CN exhibited better organic pollutants removal (RhB for 94%, methyl orange (MO) for 15% and methylene blue (MB) for 87%) under visible light, which is likely owing to the heterojunction structure between g-C₃N₄ and Nb₂O₅ that leads to the good separation of photogenerated electron-hole pair. Free radical scavenging and electron spin resonance (ESR) experiments demonstrated that superoxide radicals (^?O₂^?) and holes (h⁺) were the dominant radicals. Therefore, the NO/CN was proposed to be a promising material for effective disinfection and removal of organic contaminants in water treatment.     

Preparation of FeS/iron oxide composite and flax stem‐based porous carbon and its Cr(VI) removal ability

Using flax stem and ferrous sulfate, a composite porous carbon material was prepared by means of high‐temperature roasting and a one‐step process in a muffle furnace. The samples were characterized using X‐Ray diffraction (XRD) and Scanning electron microscopy (SEM), and the effects of ferrous sulfate concentration, carbonization temperature, and pH values of Cr(VI) aqueous solution on the removal performance of Cr(VI) were studied. XRD and SEM analysis showed that the prepared samples were amorphous porous carbon loaded with FeS/Fe₂O₃/Fe₃O₄. High FeSO₄ impregnation concentration, high carbonization temperature, and a low pH value of Cr(VI) aqueous solution were beneficial for Cr(VI) removal. When pH = 2, the amount of Cr(VI) removal was 99.93 mg/g by the sample obtained from 1 g flax powder impregnated in 4.5 mmol FeSO₄/40 mL H₂O solution and calcined for 2 hr at 800°C.     

Acid‐Stable Peroxoniobophosphate Clusters To Make Patterned Films

Two new peroxoniobophosphate clusters were isolated as tetramethylammonium (TMA) salts having the stoichiometries: TMA₅[HNb₄P₂O₁₄(O₂)₄]?9 H₂O and TMA₃[H₇Nb₆P₄O₂₄(O₂)₆]?7 H₂O. The former is stable over the pH range: 3<pH<12 and the latter is stable only below pH 3. These two molecules interconvert as a function of solution pH. The [H₇Nb₆P₄O₂₄(O₂)₆]^3? cluster can be used to fabricate patterned niobium phosphate films by electron‐beam lithography after solution deposition.     

Yolk–shell microspheres assembled from Preyssler‐type NaP5W30O11014− polyoxometalate and MIL‐101(Cr) metal–organic framework: A new inorganic–organic nanohybrid for fast and selective removal of cationic organic dyes from aqueous media

Novel inorganic–organic yolk–shell microspheres based on Preyssler‐type NaP₅W₃₀O₁₁₀^14? polyoxometalate and MIL‐101(Cr) metal–organic framework (P₅W₃₀/MIL‐101(Cr)) were synthesized by reaction of K_12.5Na_1.5[NaP₅W₃₀O₁₁₀], Cr(NO₃)₃·9H₂O and terephthalic acid under hydrothermal conditions at 200°C for 24 h. The as‐prepared yolk–shell microspheres were fully characterized using various techniques. All analyses confirmed the incorporation of the Preyssler‐type NaP₅W₃₀O₁₁₀^14? polyoxometalate into the three‐dimensional porous MIL‐101(Cr) metal–organic framework. The results revealed that P₅W₃₀/MIL‐101(Cr) demonstrated rapid adsorption of cationic methylene blue (MB) and rhodamine B (RhB) with ultrahigh efficiency and capacity, as well as achieving rapid and highly selective adsorption of MB from MB/MO (MO = methyl orange), MB/RhB and MB/RhB/MO mixtures. The P₅W₃₀/MIL‐101(Cr) adsorbent not only exhibited a high adsorption capacity of 212 mg g^?1, but also could quickly remove 100% of MB from a dye solution of 50 mg l^?1 within 8 min. The effects of some key parameters such as adsorbent dosage, initial dye concentration and initial pH on dye adsorption were investigated in detail. The equilibrium adsorption data were better fitted by the Langmuir isotherm. The adsorption kinetics was well modelled using a pseudo‐second‐order model. Also, the inorganic–organic hybrid yolk–shell microspheres could be easily separated from the reaction system and reused up to four times without any change in structure or adsorption ability. The stability and robustness of the adsorbent were confirmed using various techniques.     

Preparation and comparison of the photoelectronic properties of Sr2Nb2O7 and Ba0.5Sr0.5Nb2O6

The two alkaline earth niobates Sr₂Nb₂O₇ and Ba_0.5Sr_0.5Nb₂O₆ have been prepared, their electronic properties measured, and their photoresponses compared. The indirect band gap in Sr₂Nb₂O₇ is 3.86 eV compared with 3.38 eV for Ba_0.5Sr_0.5Nb₂O₆. Hence, photoanodes composed of Sr₂Nb₂O₇ respond to much less of the “white” light spectrum than those made from Ba_0.5Sr_0.5Nb₂O₆. Nevertheless, their electrical outputs at an anode potential of 0.8 eV with respect to SCE in 0.2 M sodium acetate under “white” xenon arc irradiation of 1.25 W/cm² are comparable.     

Photocatalytic Cr(VI) reduction over MIL-88A(Fe) on polyurethane sponge: From batch to continuous-flow operation

MIL-88A(Fe)@sponge (MS) was synthesized by a dip-coating method, which displayed efficient photocatalytic Cr(VI) reduction efficiency under both low power LED UV light and real solar light irradiation. It was observed that MS (0.2 g/L) could remove 100% Cr(VI) (10 mg/L) by adding 0.4 mmol/L tartaric acid (TA) without adjusting pH (pH 5.05) within 6.0 min and 3.0 min under UV light and real solar light irradiation, respectively. Besides, the photo-induced e⁻ and radicals (O₂^•− and CO₂^•−) were found to play the momentous roles in the MS/TA/UVL/Cr(VI) system by the scavenger experiments and electron spin resonance (ESR) tests. MS was also filled into a fixed-bed reactor to test the possibility of long-term Cr(VI) reduction operation in TA/UVL system. As expected, the results revealed that MS could still maintain 100% activity up to 60 h. These results demonstrated that MIL-88A(Fe) might be the potentially efficient catalyst for large-scale wastewater treatment in the near future.     

Superwetting and photocatalytic Ag2O/TiO2@CuC2O4 nanocomposite-coated mesh membranes for oil/water separation and soluble dye removal

A novel oily wastewater treatment strategy of simultaneously removing insoluble oily compounds and soluble organic pollutants is highly desirable. Herein, a hierarchical Ag₂O/TiO₂ heterojunction-loaded CuC₂O₄ nanosheet-decorated copper mesh (Ag₂O/TiO₂@CuC₂O₄ CM) was rationally designed by a combination of chemical etching and solvothermal deposition methods to implement the strategy. The Ag₂O/TiO₂@CuC₂O₄ CM with hierarchical nanostructures derived from hydrophilic CuC₂O₄ nanosheets and belt-like Ag₂O/TiO₂ heterojunction was proven to exhibit superior superhydrophilicity, underwater superoleophobicity, and photocatalytic ability, which greatly improved the antipollution ability of the substrate mesh. The as-fabricated mesh with a reasonable mesh number can efficiently separate oil/water mixtures with an ultra-high flux (～70 kL m^?2 h^?1) and surfactant-stabilized oil-in-water emulsions with an ultra-low residue oil content in filtrate (<60 mg L^?1). More importantly, the loaded heterojunction on the CM showed a high photodegradation efficiency of about 94.1% toward soluble methylene blue and self-cleaning ability to regenerate oil-contaminated mesh within 60 min under visible light irradiation by photo-Fenton-like reaction. Besides, the favorable salt resistance, acid and alkali resistance, and stability of the CM for long-term use were also observed. Thus, this study provides a new way for the treatment of complex oily wastewater.     

Effect of protonation and deprotonation on surface charge density of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>

The protonation and deprotonation of the Nb₂O₅ surface has been followed in order to understand the reactions of surface of this catalyst. The simultaneous potentiometric and conductometric titrations had been carried by using 50 mL of water suspension of Nb₂O₅ 40 g L⁻¹. The oxide was entirely deprotonated when adding 0.4 mL NaOH 1 mol L⁻¹, and later titrated with 0.1 mol L⁻¹. The titration had supplied K ₁ and K ₂ and the obtained values were 3.24 × 10⁻³ and 4.17 × 10⁻⁸, respectively. The zero point charge was pH_pcz = 4.94. The thermodynamic studies were carried out by using 50 mL of a 40 g/L Nb₂O₅ aqueous suspension with the pH adjusted to pH_PZC value. The suspension was titrated with 0.5 mol/L of HNO₃ or NaOH for protonation or deprotonation studies, respectively, in an isoperibol calorimeter CSC ISC-4300. Thus, the obtained thermodynamic values of the protonation and deprotonation of Nb₂O₅ were Δ_dp G = −37.60 kJ/mol, Δ_dp H = −23.72 kJ/mol and Δ_dpS = 47 J/(mol K).     

Green synthesis of reduced graphene oxide/Fe3O4/Ag ternary nanohybrid and its application as magnetically recoverable catalyst in the reduction of 4‐nitrophenol

Materials having both magnetic and catalytic properties have shown great potential for practical applications. Here, a reduced graphene oxide/iron oxide/silver nanohybrid (rGO/Fe₃O₄/Ag NH) ternary material was prepared by green synthesis of Ag on pre‐synthesized rGO/Fe₃O₄. The as‐prepared rGO/Fe₃O₄/Ag NH was characterized using Fourier transform infrared spectroscopy, X‐ray diffractometry, Raman spectroscopy, vibrating sample magnetometry, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. rGO sheets were covered with Fe₃O₄ (8–16 nm) and Ag (18–40 nm) nanoparticles at high densities. The mass percentages were 13.47% (rGO), 62.52% (Fe₃O₄) and 24.01% (Ag). rGO/Fe₃O₄/Ag NH exhibited superparamagnetic behavior with high saturated magnetization (29 emu g⁻¹ at 12 kOe), and efficiently catalyzed the reduction of 4‐nitrophenol (4‐NP) with a rate constant of 0.37 min⁻¹, comparable to those of Ag‐based nanocatalysts. The half‐life of 4‐NP in the presence of rGO/Fe₃O₄/Ag NH was ca 1.86 min. rGO/Fe₃O₄/Ag NH could be magnetically collected and reused, and retained a high conversion efficiency of 94.4% after the fourth cycle. rGO/Fe₃O₄/Ag NH could potentially be used as a magnetically recoverable catalyst in the reduction of 4‐NP and environmental remediation.     

Tetradecacobalt(II)‐Containing 36‐Niobate [Co14(OH)16(H2O)8Nb36O106]20− and Its Photocatalytic H2 Evolution Activity

A gigantic Co₁₄‐containing 36‐niobate, Na₁₂K₈[Co₁₄(OH)₁₆(H₂O)₈Nb₃₆O₁₀₆] ? 71H₂O ( 1 ), has been prepared by the hydrothermal method and structurally characterized. Polyanion [Co₁₄(OH)₁₆(H₂O)₈Nb₃₆O₁₀₆]^20? ( 1 a ) comprises a central Co₇ core, surrounded by another seven isolated Co²⁺ ions and six Lindqvist‐type (Nb₆O₁₉) hexaniobate fragments. This is the first example of a high‐nuclear cobalt‐cluster‐containing polyoxoniobate. The photocatalytic H₂ evolution activity of Pt‐loaded 1 was observed in methanol solution under irradiation using a 300 W Xe lamp.     

Polyoxometalate encapsulated in metal‐organic gel as an efficient catalyst for visible‐light‐driven dye degradation applications

Contamination of industrial sewage by organic dye pollutants is one of the most common challenges to the daily life. Decontamination can be achieved by adsorption and photodegradation of the pollutants. Herein, an effective visible light‐driven photocatalyst of polyoxometalate encapsulated in metal–organic gel was presented. The resulting composite was named PMA@ MOG‐Cr [PMA= H₃PMo₁₂O₄₀, MOG= metal‐organic gel]. Photodegradation of dye pollutants with PMA@ MOG‐Cr were tested. The introduction of Phosphomolybdic Acid significantly enhanced the light‐absorption properties of MOG‐Cr. The PMA@MOG‐Cr showed an excellent photodegradation efficiency of MB, RhB and MO as high as 99% and 97% in 60 min and 91% in 120 min of visible‐light irradiation with only 10 mg photocatalyst, which was the highest among the tested samples MOG‐Cr, PMA@ MOG‐Cr and Degussa P‐25. The mechanism of the photodegradation of dye pollutants with H₂O₂ over PMA@MOG‐Cr under the visible light was further illustrated. The introduction of PMA promotes effective separation of electron–hole pair by trapping and transferring photogenerated electron. Thus, the two components act in synergy to result in much improved adsorption of certain common organic dyes as well as enhanced oxidative degradation. This work provides a new approach to design MOG encapsulated Polyoxometalate for visible light‐induced photodegradation of organic contaminants for the environmental remediation.     

Mixed phase Fe2O3/Mn3O4 magnetic nanocomposite for enhanced adsorption of methyl orange dye: Neural network modeling and response surface methodology optimization

In this research, a novel magnetic mesoporous adsorbent with mixed phase of Fe₂O₃/Mn₃O₄ nanocomposite was prepared by a facile precipitating method and characterized extensively. The prepared nanocomposite was used as adsorbent for toxic methyl orange (MO) dye removal from aqua matrix considering its high surface area (178.27 m²/g) with high saturation magnetization (23.07 emu/g). Maximum dye adsorption occurs at solution pH 2.0 and the electrostatic attraction between anionic form of MO dye molecules and the positively charged nanocomposite surface is the main driving force behind this adsorption. Response surface methodology (RSM) was used for optimizing the process variables and maximum MO removal of 97.67% is obtained at optimum experimental condition with contact time, adsorbent dose and initial MO dye concentration of 45 min, 0.87 g/l and 116 mg/l, respectively. Artificial neural network (ANN) model with optimum topology of 3–5–1 was developed for predicting the MO removal (%), which has shown higher predictive ability than RSM model. Maximum adsorption capacity of this nanocomposite was found to be 322.58 mg/g from Langmuir isotherm model. Kinetic studies reveal the applicability of second‐order kinetic model with contribution of intra‐particle diffusion in this process.     

Centrosymmetric aliovalent KTP isomorphs KMIII0.5Nb0.5OPO4 (M = Cr and Fe)

Aliovalent KTP isomorphic compounds potassium chromium niobium oxide phosphate, KCr_0.5Nb_0.5OPO₄, and potassium iron niobium oxide phosphate, KFe_0.5Nb_0.5OPO₄, exhibit structures that differ from that of the non‐centrosymmetric KTiOPO₄. There are two crystallographically independent octa­hedral sites, M1 and M2, statistically occupied by Nb and Cr (or Fe) atoms. The M1O₆ and M2O₆ octa­hedra are connected alternately to form a chain with a cis–trans arrangement. The Nb atoms prefer the M2 sites arranged in a cis‐like configuration. Each PO₄ tetra­hedon has the P atom on a twofold axis. Site‐splitting at the K‐atom position is observed in both compounds. In the isomorphous structures, one Nb atom lies on an inversion centre and the other on a twofold axis. Similarly with the pairs of Fe/Cr sites, one is on an inversion centre and the other on a twofold axis.     

One‐step synthesized magnetic MIL‐101(Cr) for effective extraction of triazine herbicides from rice prior to determination by liquid chromatography‐tandem mass spectrometry

The magnetic metal‐organic framework MIL‐101(Cr) material‐based solid‐phase extraction method coupled with high‐performance liquid chromatography and tandem mass spectrometry was applied to extract seven triazine herbicides in rices. Fe₃O₄/MIL‐101(Cr) was synthesized using reduction‐precipitation method, in which steps including pre‐synthesis and modification of Fe₃O₄ nanoparticles were by‐passed. Various parameters including extraction solvent type and volume, ultrasonic extraction time, amount of Fe₃O₄/MIL‐101(Cr) microspheres, adsorption time, desorption volume and time were investigated. Under optimal conditions, the proposed method had the limit of detection (S/N = 3) and the limit of quantification (S/N = 10) of 1.08–18.10 and 3.60–60.20 pg/g, respectively. Relative standard deviations calculated for all herbicides with concentrations of 2 and 20 ng/g were in the range of 0.5 to 13% (n = 3). In addition, at the two above‐mentioned concentrations, the method achieved relative recoveries percentages of 79.3 to 116.7% when applied to determine the triazine herbicides in real samples spiked. This rapid, green, non‐polluting, pre‐concentrated extraction method was successfully developed and applied to analyze herbicides in rice samples.     

Effect of inorganic oxide supports on the activity of chromium‐based catalysts in ethylene trimerization

Novel heterogeneous catalysts were prepared using immobilization of bis(2‐decylsulfanylethyl)amine–CrCl₃ (Cr‐SNS‐D) on various supports, namely commercial TiO₂, Al₂O₃ and magnetic Fe₃O₄@SiO₂ nanoparticles, to yield solid catalysts denoted as support@Cr‐SNS‐D. The structure of the catalysts was confirmed on the basis of spectroscopic analyses, N₂ adsorption–desorption and inductively coupled plasma (ICP) analysis. The surface areas of Al₂O₃@Cr‐SNS‐D, Fe₃O₄@SiO₂@Cr‐SNS‐D and TiO₂@Cr‐SNS‐D catalysts were determined to be 70, 23 and 41 m² g^?1, respectively. A decrease in surface area from that of the supports clearly establishes accurate immobilization of Cr‐SNS‐D catalyst on the surface of the parent carriers. The loading of Cr was determined to be 0.02, 0.16 and 0.11 mmol g^?1 for Cr‐SNS‐D supported on TiO₂, Al₂O₃ and Fe₃O₄@SiO₂, respectively, using ICP analysis. After preparation and full characterization of the catalysts, ethylene trimerization reaction was accomplished in 40 ml of dry toluene, at 80°C and 25 bar ethylene pressure and in the presence of methylaluminoxane (Al/Cr = 700) within 30 min. The supported chromium catalysts were found to be efficient and selective for the ethylene trimerization reaction. The highest activity (74 650 g_1‐hexene g_Cr^?1 h^?1), as well as no polyethylene formation during reaction processes, was observed when TiO₂ was used as the catalyst support.     

Vergleich der Elektronendichteverteilungen des Hydrido-Interstitialkomplexes HNb6I11 und des Interstitalhydrids HNb Ein Beitrag zur Cluster-bulk-Analogie

Comparison of Electron Density Distributions in the Hydrido-interstitial Complex HNb₆I₁₁ and in the Interstital Hydride HNb: A Contribution to Cluster-Bulk-Analogy The SW? Xα? SCF method has been used to compare changes of the electronic distributions in Nb₆I₁₁ and in Nb-metal caused by hydrogen at the octahedrally coordinated interstitial sites. Density maps of clusters Nb₆, Nb₆, Nb₆I₈³⁺, and HNb₆I₈³⁺ show: 1. The influence of the iodine ligands on the electronic distribution at the interstitial site is slight. 2. The spherically symmetric electron density of hydrogen at the interstitial sites is only deformed by the bonds to the neighbouring niobium atoms in both cases. Difference electron density maps illustrate that the interstitial hydrogen is weakly polarized in HNb₆I₁₁ as well as in HNb.     

Chromhexacyano‐Komplexe: Die Kristallstrukturen der Cyanoelpasolithe (NMe4)2ACr(CN)6 (A = K,Cs) und der kubischen Bariumverbindung Ba3[Cr(CN)6]2 · 20 H2O

Chromium Hexacyano Complexes: The Crystal Structures of the Cyano Elpasolites (NMe₄)₂ACr(CN)₆ (A = K, Cs) and of the Cubic Barium Compound Ba₃[Cr(CN)₆]₂ · 20 H₂O The crystal structures of the cyano elpasolites (NMe₄)₂KCr(CN)₆ (a = 1527.3(1), b = 888.1(1), c = 1539.0(1) pm, β = 109.92(1)°; C2/c, Z = 4) and (NMe₄)₂CsCr(CN)₆ (a = 1278.9(1) pm; Fm3m, Z = 4), as well as of the cubic compound Ba₃[Cr(CN)₆]₂ · 20 H₂O (a = 1631.0(1) pm; Im3m, Z = 4) were determined by X‐ray methods with single crystals. Reasons for the enlarged distances within the [Cr(CN)₆]^3–‐octahedron of the K compound (Cr–C: 209.3 pm) compared to the observations within both cubic complexes (206.1 resp. 206.9 pm) are discussed in context with the tolerance factors of cyano elpasolites. As is the case there concerning the cyano bridges Cr–CN–A towards the alkali ions the novel structure type of the barium compound, too, exhibits nearly linear bridging towards Ba. It contributes, however, only four N ligands to the ninefold [BaN₄O₅] coordination; part of the aqua ligands show disorder (Ba–N: 287.5, Ba–O: 281/293 pm).     

Highly stable polyoxometalate‐resorcin[4]arene‐based inorganic‐organic complexes for catalytic oxidation desulfurization

Self‐assembly of a resorcin[4]arene‐based ligand (TMR4A) with metal salts and H₃PMo₁₂O₄₀·xH₂O offers two isostructural complexes, namely, [Ni₂Cl(TMR4A)₂(CH₃CN)₂]·[PMo₁₂O₄₀]·4CH₃CN ( 1 ) and [Co₂Cl(TMR4A)₂(CH₃CN)₂]·[PMo₁₂O₄₀]·4CH₃CN ( 2 ). In both 1 and 2 , one Cl^? anion bridges two metal cations, and each metal cation is further chelated by four 2‐mercaptopyridine N‐oxide groups of one TMR4A, producing a [M₂Cl(TMR4A)₂]³⁺ dimer (M = Ni or Co). The negative [PMo₁₂O₄₀]^3? as a counter‐anion balances the positive charge. Markedly, 1 and 2 exhibit high stability in aqueous solutions with different pH values and in organic solvents. Remarkably, the efficient heterogeneous catalytic capability for oxidative desulfurization was studied by suing 1 and 2 as recycled catalysts. Moreover, the electrochemical behaviors of the two compounds were discussed as well.     

Removal of Chromium Ions by Fe3O4‐containing Polypyrrole Matrix and Environmental Applications

In this work, the PPy/Fe₃O₄@TiO₂ composite was synthesized and characterized by X‐ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and magnetic measurements (using a vibrating sample magnetometer). The adsorption performance of PPy/Fe₃O₄@TiO₂ composite for Cr(VI) ions was evaluated by UV irradiation. The effects of pH, adsorbent dose, contact time, and the initial concentration on the adsorption performance of Cr(VI) onto PPy/Fe₃O₄@TiO₂ were investigated. The maximum adsorption capacity of Cr(VI) upon doped PPy/Fe₃O₄@TiO₂ is 85.30 mg/g at room temperature. The total adsorption process likely follows the Langmuir model and pseudo‐second‐order kinetics. Our study suggests that the PPy/Fe₃O₄@TiO₂ composite can be efficiently used for the adsorption of Cr(VI) ions.     

HPLC analysis of Cr, V and Mo using pre- in combination with on-column derivatisation by oxine, bipyridine and H2O2

Summary The HPLC behaviours of Cr(VI), Mo(VI) and V(V) peroxo complexes in a H₂O₂-8-hydroxyquinolinebipyridine system were studied by using pre-column in combination with on-column derivatisation. The chromatograms of Cr(VI), Mo(VI) and V(V) show them to be CrO^2– ₄, oxine-Mo peroxo and oxine-V-bipyridine peroxo complexes, respectively, and were used for the separation, identification and determination of Cr(VI), Mo(VI) and V(V) using acetonitrile-water as mobile phase. The calibration curves obtained for 20 l injections were linear for 1.4–7.0 mg/l Cr, 1.3–6.5 mg/l Mo and 0.7–3.4 mg/l V. The relative standard deviations were between 6 and 10%.

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HPLC-Analyse von Cr, V und Mo unter Verwendung von Vorsäulen- in Kombination mit Säulenderivatisierung durch Oxin, Bipyridin und H₂O₂