Low temperature in situ fabrication of NiFe2O4/tetragonal-BiVO4/Bi2MoO6 ternary heterostructure: A conjugated step-scheme multijunction photocatalyst with synergistic charge migration for antibiotic photodegradation and H2 generation

Rational design of novel conjugated step-scheme (S-scheme) multijunction heterostructure with synergistic charge channelization, superior light harvesting efficiency and strong redox ability is a pioneering approach to mimic natural photosynthesis process. Herein, a mild cetyltrimethyl ammoniumbromide (CTAB) assisted one pot reflux synthesis route is designed for in situ integration of metal organic framework (MOF)-derived NiFe2O4 with tetragonal-BiVO4 (t-BiVO4) and γ-Bi2MoO6 to prepare NiFe2O4/t-BiVO4/Bi2MoO6 (NFO/BVO/BMO) ternary composites. Morphologically, fine dispersion of NiFe2O4 (NFO) quantum dots over γ-Bi2MoO6 (BMO) and t-BiVO4 (BVO) nanoplates yielded three types of microscopic heterojunctions among BMO-BVO, BVO-NFO and BMO-NFO phases. The ternary composites displayed important physicochemical attributes including high surface area, strong optical absorption, superior charge mobility and higher excited state lifetime which accounted for its improved photocatalytic activity towards ciprofloxacin degradation (>99% in 90 min) and H2 evolution (1.11 mmolh-1g-1, photon conversion efficiency 18.5%). Kinetics study revealed 12-55 fold higher ciprofloxacin photodegradation activity and 31-41 times higher H2 evolution rate for the ternary composite in comparison to the pure semiconductors. A conjugated S-scheme charge transfer mechanism has been deduced from comprehensive band position analysis and radical trapping study to explain the enhanced photocatalytic activity. This work for the first time demonstrated the rational construction of conjugated S-scheme heterostructures with potential application in water remediation and green H2 production.

Enlarging the Ni-O Bond Polarizability in a Phosphorene-Hosted Metal-Organic Framework for Boosted Water Oxidation Electrocatalysis

The emerging lattice-oxygen oxidation mechanism (LOM) presents attractive opportunities for breaking the scaling relationship to boost oxygen evolution reaction (OER) with the direct OLattice-*O interaction. However, currently the LOM-triggering rationales are still debated, and a streamlined physicochemical paradigm is extremely desirable for the design of LOM-defined OER catalysts. Herein, a Ni metal-organic framework/black phosphorene (NiMOF/BP) heterostructure is theoretically profiled and constructed as a catalytic platform for the LOM-derived OER studies. It is found that the p-type BP host can enlarge the Ni-O bond polarizability of NiMOF through the Ni-O bond stretching and Ni valence declining synergically. Such an enlarged bond polarizability will in principle alleviate the lattice oxygen confinement to benefit the LOM pathway and OER performance. As a result, the optimized NiMOF/BP catalyst exhibits promising OER performance with a low overpotential of 260 mV at 10 mA cm-2 and long-term stability in 1 M KOH electrolyte. Both experiment and calculation results suggest the activated LOM pathway with a more balanced step barrier in the NiMOF/BP OER catalyst. This research puts forward Ni-O bond polarizability as the criterion to design LOM-scaled electrocatalysts for water oxidation.

Sulfur Vacancies-Engineered Ni3 S4-x Hollow Microspheres with Optimized Anionic Adsorption Energy for High-Performance Supercapacitor

Nickel sulfides with high theoretical capacitance have aroused tremendous attention for next-generation supercapacitors. Unfortunately, the structural durability of nickel sulfides is insufficient to support the long-term working situation. Herein, Ni₃ S_4-x hollow microspheres with sulfur vacancies (Ni₃ S_4-x HMs) are constructed by a liquid-phase anion exchange process using the Ni-MOF as the precursor. Both experimental investigation and theoretical analysis suggest that the deliberately introduced sulfur vacancies effectively improve the anionic adsorptive ability of nickel sulfides in the KOH electrolyte, significantly enhancing the reversible capacitance and structural durability (1884 F g^-1 at 2 A g^-1 , capacity retention of 97.9% after 10 000 cycles). In addition, an asymmetrical solid-state supercapacitor consisting of Ni₃ S_4-x HMs cathode and activated carbon anode shows infusive energy/power density (33.05 Wh kg^-1 /1.68 kW kg^-1 ) and remains 82.4% over 10 000 repeated charging/discharging processes in the KOH-PVA gel electrolyte. The strategies can be developed to enlighten the structural design of various metal sulfides materials adopted in electrochemical energy storage devices including alkali ion batteries, supercapacitors, and electrocatalysts.

Special Issue “Metal Nanoparticles as Catalysts for Green Applications”

This Special Issue of Processes on “Metal Nanoparticles as Catalysts for Green Applications” collects recent works of researchers on metal nanoparticles as catalysts for green applications [...]