Presence Of Borohydride Research Articles

New HCHO-scavenger for enhancing the HCHO-based adhesive in production environmentally friendly agro-based composites

Recently, green products are essential requirements. This work deals with synthesizing novel formaldehyde-scavenger based on black liquor to enhance the urea-formaldehyde (UF) adhesive for production of eco-friendly bio-composites. These HCHO-scavengers are synthesized from black liquor-based aerogel precursors. The assessment is carried out via estimating the HCHO adsorption capacities versus type of black liquor; as well as its beneficial effect on characterization of UF adhesive (Differential Scanning Calorimetry (DSC)-curing temperature; gel time and adhesive strength). The UF-scavenger system, which provides palm fiber-composite with properties (static bending, internal bond, and free-HCHO) compliance with the standard specifications is optimized. The data evidenced the effective role of black liquor (BL) from alkali pulping RS in presence of borohydride in resulting aerogel precursor of scavenger with higher HCHO-adsorption capacities (∼64 mg/g) than that produced from native aerogels (AG) in absence of BL. The kinetic adsorption is most applicable with the pseudo-second order equation. This observed behavior reflected on reducing the gel time and improved the bond strength of scavenger (Scv)-UF systems. It is interesting to note that all investigated BL-scavengers provide reduction in free HCHO of palm composites (from 30.7 mg/100g to 5–11 mg/g). These values are lower than that obtained from scavengers in absence of BLs (17.4 mg/100g). Based on the value of free-HCHO and mechanical properties, we recommend the scavenger resulted from black liquor of alkali pulping RS in presence of anthraquinone and borohydride (NaOH-AQ-BH) of screened RS as effective scavenger to provided eco-palm-wood composites with MOR, MOE, IB, free-HCHO and thickness swelling ∼ 27 MPa, 0.72 MPa, 7157 MPa, 7 % and 11 %, respectively. According to international standard specifications this type of palm-composite fulfills the grade H-3 and E1 according to environmental specification.

A Coordination Polymer Based on Nickel(II)–Cyamelurate: A Robust Catalyst with Highly Dispersed Nickel Sites for Nitrophenol Reduction under Ambient Conditions

Cyamelurate anions obtained from the hydrolysis of polymeric graphitic carbon nitride were used for the preparation of a water-stable and crystalline coordination polymer based on nickel(II)–cyamelurate. The polymer was prepared and applied as a catalyst for the reduction of 4-nitrophenol to 4-aminophenol in the presence of borohydride under ambient conditions. The catalyst was prepared by a simple and environmentally friendly method in an aqueous medium, and it was completely characterized by a variety of techniques, including FTIR, UV–Vis, XRD, TGA, TEM, and STEM. The obtained catalyst was able to catalyze the reaction of 4-nitrophenol to 4-aminophenol with a good kinetic constant. In addition, the catalyst proved to be significantly robust, maintaining a conversion rate greater than 80% after five minutes of reaction for eight consecutive catalytic cycles. In addition, the catalytic activity of the coordination polymer was much higher than that observed for a homogeneous catalyst based on aqueous Ni2+ ions, suggesting the importance of the structure of the coordination sphere formed by the cyamelurate anions. The results presented here can contribute to the application of other coordination polymers anchored with cyamelurate-like ligands and derivatives, as well as to new catalyst designs based on this coordination site formed by oxygen and nitrogen donor atoms.

Catalytic dechlorination of 1,2-DCA in nano Cu0-borohydride system: effects of Cu0/Cun+ ratio, surface poisoning, and regeneration of Cu0 sites

Aqueous-phase catalyzed reduction of organic contaminants via zerovalent copper nanoparticles (nCu0), coupled with borohydride (hydrogen donor), has shown promising results. So far, the research on nCu0 as a remedial treatment has focused mainly on contaminant removal efficiencies and degradation mechanisms. Our study has examined the effects of Cu0/Cun+ ratio, surface poisoning (presence of chloride, sulfides, humic acid (HA)), and regeneration of Cu0 sites on catalytic dechlorination of aqueous-phase 1,2-dichloroethane (1,2-DCA) via nCu0-borohydride. Scanning electron microscopy confirmed the nano size and quasi-spherical shape of nCu0 particles. X-ray diffraction confirmed the presence of Cu0 and Cu2O and x-ray photoelectron spectroscopy also provided the Cu0/Cun+ ratios. Reactivity experiments showed that nCu0 was incapable of utilizing H2 from borohydride left over during nCu0 synthesis and, hence, additional borohydride was essential for 1,2-DCA dechlorination. Washing the nCu0 particles improved their Cu0/Cun+ ratio (1.27) and 92% 1,2-DCA was removed in 7 h with kobs = 0.345 h−1 as compared to only 44% by unwashed nCu0 (0.158 h−1) with Cu0/Cun+ ratio of 0.59, in the presence of borohydride. The presence of chloride (1000–2000 mg L−1), sulfides (0.4–4 mg L−1), and HA (10–30 mg L−1) suppressed 1,2-DCA dechlorination; which was improved by additional borohydride probably via regeneration of Cu0 sites. Coating the particles decreased their catalytic dechlorination efficiency. 85–90% of the removed 1,2-DCA was recovered as chloride. Chloroethane and ethane were main dechlorination products indicating hydrogenolysis as the major pathway. Our results imply that synthesis parameters and groundwater solutes control nCu0 catalytic activity by altering its physico-chemical properties. Thus, these factors should be considered to develop an efficient remedial design for practical applications of nCu0-borohydride.

Reduction of 4-nitrophenol using copper loaded surfactant-modified chitosan beads: An approach towards sludge management

Chitosan hydrogel (CS) beads and surfactant-modified chitosan hydrogel (SMCS) beads are used for the removal of Cu(II) ions from aqueous solution. After removal of metal ions, the waste Cu(II) ion-adsorbed beads have been used as an efficient catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in aqueous NaBH4. This approach can be considered as a part of ‘zero waste management practice’. The first step of the present work deals with the preparation of CS hydrogel beads with their further modification using anionic surfactant e.g. sodium dodecyl sulfate (SDS) at a concentration greater than the critical micelle concentration (CMC). This step leads to the formation of SMCS beads. In the second step, the CS and SMCS beads are used to remove Cu(II) ions from aqueous solution. The Cu(II) ion-loaded CS beads are designated as Cu-CS beads, and the Cu(II) ion-loaded SMCS beads are named as Cu-SMCS. These beads can be recognized as waste (or spent) beads. The Cu(II) ion removal efficiency and the calculated Cu(II) loading of SMCS beads are very similar to that of normal CS beads. In the third step these waste Cu-CS and Cu-SMCS beads have been utilized as a catalyst to reduce 4-NP to 4-AP in presence of borohydride. The 4-NP reduction using Cu-CS and Cu-SMCS follows zero order kinetics at varying catalyst doses in the range of 0.2–0.6 g/L, and at varying 4-NP concentrations in the range of 4 × 10−5 – 1.2 × 10−4 M. However, at all the doses the induction time required to start the reduction is higher in case of Cu-CS than Cu-SMCS beads. It is interesting to observe that, at a catalyst dose of 0.2 g/L and under identical condition, the Cu-SMCS beads act as a much better catalyst compared to the Cu-CS, and the zero order rate constant obtained with Cu-SMCS as the catalyst is found to be ~ 30 times higher compared to that obtained using Cu-CS. This is due to the synergistic effect offered by the surfactant bilayer present on the surface of Cu-SMCS. The characterization of the Cu-SMCS beads has been done using XRD, SEM, EDAX, FTIR analyses. The turnover number (TON) and turnover frequency (TOF) of Cu-SMCS are compared with other reported catalysts, and they are found comparable. Thus waste Cu-SMCS beads have been proved to be an effective catalyst for 4-NP reduction.

Fabrication of palladium and platinum nanocatalysts stabilized by polyvinylpyrrolidone and their use in the hydrogenolysis of methyl orange

Following the thermal reductive method, the synthesis of nanoparticles stabilized by polyvinylpyrrolidone was performed using ethylene glycol as a reductant and solvent. The PVP-capped platinum and palladium were well-dispersed and stable for more than 3 months, and their average sizes were 2.53 ± 0.07 nm and 4.13 ± 0.14 nm. By means of inductively coupled plasma mass spectroscopy (ICP-MS) analysis, the amount of colloidal metal nanoparticles was found to be 6.38 wt% and 5.93 wt% for platinum and palladium, respectively. The PVP-capped Pt and Pd nanocatalysts were evaluated for the hydrogenolysis of azo dyes using methyl orange as a model compound in the presence of borohydride as a reductant. Substrates adsorption on the nanocatalysts surface constituted the rate-determining step of the catalytic reduction. The Langmuir–Hinshelwood approach was applied to interpret the interface interaction between nanocatalyst and substrates. The activation energy was 65.70 ± 4.49 kJ mol−1 and 89.27 ± 2.12 kJ mol−1 using Pt and Pd nanocatalysts, respectively.

Synergetic effect of polydopamine particles and in-situ fabricated gold nanoparticles on charge-dependent catalytic behaviors

The versatile catechol unit of polydopamine (PDA) endows this molecule with a broad ranging adhesive properties and reducibility. We prepared free-standing PDA particles by a simple self-polymerization and these particles served as both an effective reductant and scaffold for a hybrid catalyst. The raspberry-like nanocomposites featured a high density of AuNPs uniformly deposited on PDA particles (PDA@Au). This system was prepared in-situ with assistance from the active catechol and amine groups of the PDA particles. To quantify the effect of the PDA carriers, we studied the catalytic activity of the PDA and PDA@Au particles. The PDA particles showed a pronounced charge-dependent catalytic activity for reduction of cationic methylene blue, negatively-charged 4-nitrophenolate, and zwitterionic rhodamine B in the presence of borohydride, whereas PDA@AuNPs showed catalytic activity with a less pronounced charge-dependence of the catalytic efficiency of the AuNPs. The PDA particles served as a redox mediator and adsorbent accelerator in degradation of the dyes owing to its unique chemical structure.

Polyurethane/Keratin/AgNPs nanofibrous mats as catalyst support for 4-nitroaniline reduction

Silver nanoparticles loaded polyurethane/keratin nanofibrous mats (PU/Keratin/AgNPs) were fabricated via electrospinning, silver ion immobilization, followed by in situ reduction. The size and loading amount of AgNPs were regulated by varying the solution concentration of silver ions. The mats were characterized with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The PU/Keratin/AgNPs mats were exploited as catalyst support to reduce 4-nitroaniline (4-NA) in presence of borohydride, and their excellent catalytic activity showed the loading dependent feature. Moreover, these mats exhibited a stable catalytic activity up to 5 cycles.

DFT Study on Fe(IV)-Peroxo Formation and H Atom Transfer Triggered O2 Activation by NiFe Complex

The mechanism for dioxygen activation using the biomimetic model complex of [NiFe]-hydrogenase, [NiLFe(η5-C5Me5)]+ [L = N,N′-diethyl-3,7-diazanonane-1,9-dithiolato] was established using density functional theory (DFT) and artificial force-induced reaction (AFIR) methods. Our computational results suggest that O2 binds to the FeII center in an end-on fashion and forms a high-valent iron complex, NiFe–peroxo (NiIIFeIV(η2-O2)), which has been experimentally observed. The O–O bond cleavage occurs in the presence of borohydride (BH4–) through hydrogen atom transfer (HAT). Once the HAT occurs, the generated BH3 radical anion (BH3•–) binds to the terminal oxygen of NiFe–OOH, giving rise to BH3OH– and NiIIFeIV═O. The second HAT from BH4– to the oxygen of NiIIFeIV═O leads to BH3OH– and Fe-reduced NiIIFeII complex. Importantly, the dioxygen activation is triggered by HAT, not by proton transfer or hydride transfer. The O2 is activated by the Fe center, and the oxidation state of Fe varies during the process, while...

POSS nanocrosslinked poly (ethylene glycol) hydrogel as hybrid material support for silver nanocatalyst

Silver nanoparticles supported on polyhedral oligomeric silsesquioxane (OA‐POSS) nanocrosslinked poly (ethylene glycol)‐based hydrogels (PEG600‐POSS/Ag NPs) as novel nanohybrid catalysts were synthesized for the first time. The as‐prepared nanohybrid hydrogels were fully characterized by FT‐IR, SEM, EDX, XRD, TEM and TGA. PEG600‐POSS/Ag NPs exhibited excellent catalytic performance for the reduction of 4‐nitrophenol (4‐NP) to 4‐aminophenol (4‐AP) in water at room temperature in the presence of borohydride.

Facile Preparation and High Activity of TiO2 Nanotube Arrays toward Oxygen Reduction in Alkaline Media

Four TiO2 electrodes have been investigated for the oxygen reduction reaction (ORR) in 2 M NaOH. Anodic oxidation of Ti-foil was used as the final or the first step in the preparation of four electrodes based on TiO2: amorphous (Ti/AM-TiO2), two anatase forms (Ti/A400-TiO2 and Ti/A550-TiO2), and, finally, lithium-anatase form (Ti/A-Li0.25TiO2), all of them obtained as TiO2 nanotube arrays. The electrodes’ structure was examined by Raman spectroscopy. Cyclic voltammetry and chronoamperometry were employed for the study of kinetics of ORR. Ti/A-Li0.25TiO2 and Ti/A400-TiO2 electrodes showed the highest catalytic activity for ORR with the highest cathodic peak current density and the lowest Tafel slope values. Number of electrons exchanged during ORR at TiO2 electrodes was in the range from 2.3 to 2.8. Additionally, TiO2 electrodes showed good stability as well as acceptable selectivity in the presence of borohydride, methanol or ethanol as typical fuels for fuel cells. Thus this study introduces a simple, low-cost preparation route of TiO2-based electrodes with high efficiency for ORR for energy conversion and storage applications.

Magnetic Propulsion of Recyclable Catalytic Nanocleaners for Pollutant Degradation.

Electrochemically fabricated magnetic mesoporous CoNi@Pt nanorods are excellent nanomotors with controlled magnetic propulsion and excellent catalytic properties. The core-shell structure allows a double functionality: (i) controlled motion of the nanorods by applying rotating magnetic fields at different frequencies and field strengths and (ii) effective catalytic activity of the platinum shell for reactions involving sodium borohydride. The structure and magnetic properties of the CoNi core are not modified by the presence of the Pt shell. Nanorods were propelled via a tumbling-like dynamic by a rotating magnetic field. While in absence of NaBH4, nanorods move at constant speed showing a linear path; in the presence of NaBH4, they showed an intermittent trajectory. These catalytic nanorods can be used as nanocleaners with controlled directionality for pollutants degradation in the presence of borohydride. Their magnetic character allows control of the velocity and the direction throughout the contaminated solution by degrading the different pollutants in their path. The magnetic character of nanorods also allows their easy recycling.

Rapid Degradation of Methyl Orange by Ag Doped Zeolite X in the Presence of Borohydride

A series of Ag nanoparticles impregnated on zeolite X (Ag-ZX) containing various amounts of Ag (in wt%) were prepared via impregnation method. The pristine zeolite X and Ag-ZX catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption desorption analyses and atomic absorption spectroscopy (AAS). The prepared catalysts were employed for the decolourization of methyl orange (MO) in the presence of potassium borohydride (KBH4). Various parameters such as the amount of Ag impregnated, MO concentration, KBH4: MO mole ratios, pH and catalyst reusability were investigated. It was found that the best decolourization efficiency was obtained when 0.06g of Ag-ZX (6.7) catalyst was employed using a KBH4: MO mole ratio of 731: 1 at pH 5. The degradation process obeyed pseudo first-order kinetics.

Surfactant modification of chitosan hydrogel beads for Ni@NiO core-shell nanoparticles formation and its catalysis to 4-nitrophenol reduction

Chitosan (CS) in its hydrogel bead form is widely used to remove metal ions from aqueous medium. In the present work CS gel beads were modified with sodium dodecyl sulfate (SDS), an anionic surfactant, in a novel way, with formation of bilayer (admicelle) on to it. The concentration of SDS used for CS bead modification was 6000mg/L. These surfactant-modified chitosan beads were designated as POSTCS beads. In the next step, Ni(II) was loaded on the SDS bilayer present in the POSTCS beads through a process called ‘adsolubilization'. The loading of nickel was ∼4 times higher in POSTCS beads compared to that in normal CS beads. The property of surfactant to form admicelle helped in enhanced Ni(II) adsorption, and its stabilization. Further Ni@NiO core-shell type particles were formed on POSTCS beads by borohydride reduction. The particles were characterized by XRD, FTIR, SEM/EDX and TEM analysis. The as-prepared particles exhibited excellent catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of borohydride. The reduction was carried out with various catalyst doses, and it was found to follow first order rate. The turn over number (TON) and turn over frequency (TOF) of the catalyst at a dose of 2.0g/L and 1×10−4M 4-NP concentration were found to be 3.0115×1019 molecules/g and 5.019×1016 molecules/g/s, respectively.

Carbon Supported Nanocrystalline Manganese Oxide: Surpassing Platinum as Oxygen Reduction Catalyst in Direct Borohydride Fuel Cells

Manganese oxide (MnO2) nanodispersed on high surface area carbon was tested as cathode catalyst for direct borohydride fuel cells with an anion conducting membrane. In order to investigate the effects of borohydride crossover, ex-situ experiments toward oxygen reduction reaction were conducted employing rotating disk electrodes in presence of borohydride and thiourea. Although platinum showed superior catalytic properties at ideal conditions, manganese oxide outperformed platinum significantly in presence of borohydride. Direct borohydride fuel cell tests were conducted using Pt/C-based and MnO2/C-based. After one hour of operation at 0.40 V the platinum based membrane electrode assembly lost approx. 30% of its initial peak power density while the non-precious metal MEA showed constant performance. The peak power density of the single test cell with a Pt/C based anode, an anion exchange membrane and a MnO2/C based cathode was 38 mW cm−2.

In Situ Synthesis of Catalytic Active Au Nanoparticles onto Gibbsite-Polydopamine Core-Shell Nanoplates.

We report a facile method to synthesize anisotropic platelike gibbsite-polymer core-shell particles. Dopamine is self-polymerized on the surface of gibbsite nanoplates and forms a homogeneous layer on it. Transmission electron microscopy characterization of the resulting latexes demonstrates the formation of well-defined platelike core-shell particles. Reaction time and ultrasonification are found to be important factors to control the thickness of the polymer shell and avoid aggregation. Good control over the platelike morphology and 100% encapsulation efficiency have been achieved via this novel route. The resulting well-defined gibbsite-polydamine (G-PDA) core-shell nanoplates show excellent colloidal stability and can form opal-like columnar crystal with iridescent Bragg reflection after modest centrifugation. In addition, G-PDA core-shell nanoplates can serve both as reductant and stabilizer for the generation of Au nanoparticles (NPs) in situ. Au NPs with tunable size have been formed on the G-PDA particle surface, which show efficient catalytic activity for the reduction of 4-nitrophenol and Rhodamine B (RhB) in the presence of borohydride. Such nanocatalysts can be easily deposited on silicon substrate by spin-coating due to the large contact area of platelike G-PDA particles and the strong adhesive behavior of the PDA layer. The substrate-deposited nanocatalyst can be easily recycled which show excellent reusability for the reduction of RhB.

A Theoretical Study on Reduction of Acyl Radicals with Borohydride Anions

Abstract Ab initio and DFT calculations predict that the reduction of the acetyl radical with borohydride proceeds via hydride attack to afford the ketyl radical; the energy barrier for the hydride transfer was calculated to be 54.5 kJ mol−1 at the CCSD(T)/aug-cc-pVDZ//BHandHLYP/aug-cc-pVDZ level of theory. The DFT calculations also indicated that the hydroxymethylation of iodocyclohexane with CO in the presence of borohydride would proceed smoothly.

Catalytic Reduction of 4-Nitrophenol Using Gold Nanoparticles Supported on Carbon Nanotubes

This study involves the catalytic applications of multi-walled carbon nanotube-supported Au nanoparticles. Catalytic activity is demonstrated via the probe reaction of reducing 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) in the presence of borohydride under ambient temperature and pressure conditions. Multi-walled carbon nanotubes (MWCNTs) were coated with 12 nm Au nanoparticles to form the catalyst, and the reduction of 4-NP to 4-AP was successful using 1.00 mg of the Au nanoparticles supported on the MWCNTs. This efficient and eco-friendly highly reactive catalyst has potential for use in a wide variety of large-scale applications.

Manganese dioxide electrocatalysts for borohydride fuel cell cathodes?

Electrocatalysts of manganese dioxide (MnO2) supported on activated carbon (AC) were prepared by low-temperature (ltMnO2/AC) and high-temperature (htMnO2/AC) procedures. Structure, morphology and composition of the synthesised materials were investigated by X-ray diffraction analysis, transmission electron microscopy and thermogravimetric analysis. Activity of the two prepared electrocatalysts for the oxygen reduction reaction (ORR) was investigated in alkaline media and ORR kinetic parameters evaluated from rotating disc electrode measurements. It was found that the ORR proceeds as two-electron process at ltMnO2/AC-based electrode, while it proceeds as four-electron process at htMnO2/AC-based electrode. The two electrocatalysts were further investigated for application as cathode materials in direct borohydride fuel cells. For that purposes the ORR at MnO2/AC was investigated in the presence of borohydride in alkaline solution and in the temperature range from 25 to 65°C. It could be observed that the activity of ltMnO2/AC for the ORR is significantly suppressed in the borohydride-containing solution whereas htMnO2/AC still showed high activity for the ORR.

ChemInform Abstract: Free Radical Mediated Hydroxymethylation Using CO and HCHO

AbstractReview: 36 refs.

Free Radical-mediated Hydroxymethylation Using CO and HCHO

Tin-free radical hydroxymethylations of haloalkanes using CO and HCHO as a C1 unit proceed efficiently in the presence of borohydrides as radical mediators. In the approach using CO, the formation of aldehydes by radical carbonylation and their subsequent reduction by hydrides lead to alcohols. On the other hand, the use of formaldehyde is more straightforward, in which the key reaction is alkyl radical addition to formaldehyde to give alkoxy radical, which abstracts hydrogen from borohydride reagents. The cascade sequences were observed in the reaction of cholesteryl bromide with HCHO, which displays the diverse applications of HCHO in radical chemistry.