Unveiling the destabilization of sp3 and sp2 bonds in transition metal-modified borohydrides to improve reversible dehydrogenation and rehydrogenation

Borohydrides offer promise as potential carriers for hydrogen storage due to their high hydrogen concentration. However, the strong chemical bonding within borohydrides poses challenges for efficient hydrogen release during usage and restricts the re-hydrogenation process when attempting to regenerate the material. These high thermodynamic and kinetic barriers present obstacles in achieving reversible de-hydrogenation and re-hydrogenation of borohydrides, impeding their practical application in hydrogen storage systems. Employing density functional theory calculations, we conduct a comprehensive investigation into the influence of transition metals on both the BH4 cluster, a fundamental building block of borohydrides, and pure boron, which is formed as the end product following hydrogen release. Our research reveals correlations among the d-band center, work function, and surface energy of 3d and 4d transition metals. These correlations are directly linked to the weakening of bonding within the BH4 cluster when adsorbed on catalyst surfaces. On the other hand, we also explore how various intrinsic properties of transition metals influence the formation of boron vacancies and the hydrogen bonding process. By establishing a comprehensive correlation between the weakening of sp3 hybridization in the BH4 cluster and the sp2 hybridization in boron, we facilitate the identification and screening of optimal candidates capable of achieving reversible de-hydrogenation and re-hydrogenation in borohydrides.

The Effectiveness of Silver and Gold in Catalytic Homogenous and Heterogenous Borohydride Hydrolysis - a DFT Study

Energy demands, and environmental aspects raised the need to study hydrogen-carrying material such as borohydride for the practical usage of hydrogen as a cleaner and more efficient fuel. A proper understanding of the hydrogen generation mechanism is a key requirement for the designing of efficient catalysts as the non-catalytic hydrolysis of borohydride in non-acidic media is a slow process. The hydrolysis mechanism of borohydride varies considerably using homogeneous and heterogenous catalysts. A comparison of the hydrolysis mechanism of borohydride using gold and silver as homogenous and heterogeneous catalyst is given in this review. Unexpectedly, with gold catalyst, Au+ or Au(111), only two steps of hydrolysis occur and BH(OH)2 is produced, while with silver catalyst, Ag+ or Ag(111), the hydrolysis can proceed to completion.

CoP/Co heterojunction on porous g-C3N4 nanosheets as a highly efficient catalyst for hydrogen generation

Designing non-precious catalysts to synergistically achieve a facilitated exposure of abundant active sites is highly desired but remains a significant challenge. Herein, a hetero-structured catalyst CoP-Co supported on porous g-C3N4 nanosheets (CoP-Co/CN-I) was prepared by pyrolysis and P-inducing strategy. The optimal catalyst achieves a turnover frequency (TOF) of 26 min-1 at room temperature and the apparent activation energy (Ea) is 35.5 kJ·mol-1. The catalytic activity is ranked top among the non-precious metal phosphides or the other supports. Meanwhile, the catalytic activity has no significant decrease even after 5 cycles. The CoP/Co interfaces provide richly exposed active sites, optimize hydrogen/water absorption free energy via electronic coupling, and thus improve the catalytic activity. The experimental results reveal that the CoP/Co heterojunction improves the catalytic activity due to the construction of dual-active sites. This research facilitates the innovative construction of non-noble metal catalysts to meet industrial demand for heterogeneous catalysis.

Quantifying the Influence of Covalent Metal-Ligand Bonding on Differing Reactivity of Trivalent Uranium and Lanthanide Complexes

Qualitative differences in the reactivity of trivalent lanthanide and actinide complexes have long been attributed to differences in covalent metal-ligand bonding, but there are few examples where thermodynamic aspects of this relationship have been quantified, especially with U³⁺ and in the absence of competing variables. Here we report a series of dimeric phosphinodiboranate complexes with trivalent f-metals that show how shorter-than-expected U-B distances indicative of increased covalency give rise to measurable differences in solution deoligomerization reactivity when compared to isostructural complexes with similarly sized lanthanides. These results, which are in excellent agreement with supporting DFT and QTAIM calculations, afford rare experimental evidence concerning the measured effect of variations in metal-ligand covalency on the reactivity of trivalent uranium and lanthanide complexes.

Borohydride and metallic copper as a robust dehalogenation system: Selectivity assessment and system optimization

Hydrodechlorination (HDC) using noble-metal catalysts in the presence of H-donors is a promising tool for the treatment of water contaminated by halogenated organic compounds (HOCs). Cu is an attractive alternative catalyst to noble metals since it is cheaper than Pd, Rh, or Pt and more stable against deactivation. Cu with borohydride (BH₄^-) as reductant (copper-borohydride reduction system; CBRS) was applied here for the treatment of saturated aliphatic HOCs. The HDC ability of CBRS was evaluated based upon product selectivities during reduction of CCl₃-R compounds (R = H, F, Cl, Br, and CH₃). For CHCl₃, CH₂Cl₂, and CHCl₂-CH₃, the dechlorination reaction proceeds predominantly via α-elimination with initial product selectivities to CH₄ and C₂H₆ of 84-85 mol-% and 70-72 mol-%. For CCl₄, CBrCl₃, CFCl_3, and CCl₃-CH₃, stepwise hydrogenolysis dominates. CH₂Cl-R compounds are formed as recalcitrant intermediates with initial selectivities of 50-72 mol-%, whereas CH₄ and C₂H₆ are minor products with 16-35 mol-% and 30-35 mol-%. The effect of reaction conditions on product selectivities were investigated for CHCl₃ as target. Solution composition, variation of reducing agents (BH₄^-, H* from H₂) and increase of electron pressure (electric potential at Cu electrode and Fe⁰ as support) did not have marked influence on the selectivities (ratio of CH₄ : CH₂Cl₂). Product selectivities for reduction of CCl₃-R compounds were found to be substrate-specific rather than reductant-specific. Since the formation of halogenated by-products could not be avoided, transformation via a second reduction step was optimized by higher catalyst dose, addition of Ag, and vitamin B12 to the CBRS. Comparison between Pd and Cu based on costs, catalyst activities, selectivities, metal stability, and fate of halogenated by-products shows that the CBRS is a potent alternative to conventional HDC catalysts and can be recommended as 'agent of choice' for treatment of α-substituted haloalkanes in heavily contaminated waters.

Surface enhanced Raman scattering of bacteria using capped and uncapped silver nanoparticles

Surface enhanced Raman scattering (SERS) spectra of bacteria were obtained using citrate (capped) and borohydride (uncapped) generated silver nanoparticles (Ag NPs).The observed differences in SERS spectra are attributed to the manner in which these Ag NPs interact with bacteria. Capped Ag NPs are able to partition through the surface polysaccharides of the bacterial cell to bind to the inner and outer cell membranes, as well as the periplasmic space between them. The resultant spectra show contributions due to the components of the cell envelope and cellular secretions. Uncapped Ag NPs are unable to partition through the polysaccharide outer structures of the cells. Spectral features observed for these uncapped Ag NPs are secretions primarily due to the metabolites of purine degradation.

Preparation of nitrogen-doped Cu-biochar and its application into catalytic reduction of p-nitrophenol

Nitrogen-doped copper-biochar (N-Cu-biochar) was synthesized via pyrolysis of glucose in the presence of copper and melamine and used as a catalyst in the reduction of p-nitrophenol by NaBH₄. N-Cu-biochar was characterized by field emission scanning electron microscopy/energy-dispersive spectroscopy, Raman spectroscopy, X-ray Diffraction, and Brunauer-Emmett-Teller surface analyzer. The catalytic performance of N-Cu-biochar was evaluated under varying conditions of NaBH₄ concentration, biochar dosage, and initial p-nitrophenol concentration. N-Cu-biochar was composed of ~83% C, ~9% O, and ~8% Cu, with Cu/Cu₂O phases evenly dispersed on graphitic carbon aggregates possessing both macro- and meso-pores. N-Cu-biochar showed superior catalytic ability in mediating p-nitrophenol reduction as compared to Cu-biochar and N-doped biochar, achieving complete reduction of 0.35 mM p-nitrophenol within 30 min at a dose of 0.25 g L^-1. Reduction of p-nitrophenol catalyzed by N-Cu-biochar followed pseudo-first-order kinetics, and the reaction rate was dependent upon NaBH₄ concentration. The overall results indicate that biochar can be a suitable candidate as a support for catalyst synthesis, and N-doped Cu-biochar can be a promising catalyst for the reduction of p-nitrophenol.